PELVIC REHABILITATION DEVICE VERSION II

Transcription

1 PELVIC REHABILITATION DEVICE VERSION II MIE Technical Design Report The Capstone Design Course Report Format Project #F05/F06 Mid-Term Report Design Advisor: Prof. Dinos Mavroidis Design Team Anthony Tanner, Ben Davies James Forte, Marshal Doughty, Matteo Batista Additional Authors Mark Guidi, Raymond Lo Andy Othman, Jeff Paquette, Stephen Proulx December 3, 2006 Department of Mechanical, Industrial and Manufacturing Engineering College of Engineering, Northeastern University Boston, MA i

2 TABLE OF CONTENTS LIST OF FIGURES AND TABLES... iv ABSTRACT... vi CHAPTER 1 INTRODUCTION MOTIVATION MISSION STATEMENT DELIVERABLES PROJECT SPONSOR... 2 CHAPTER 2 BACKGROUND GAIT COMPLICATION GAIT BIOMECHANISMS THE GAIT CYCLE GAIT CYCLE TIME FOOT PLACEMENT CADENCE AND SPEED OVERVIEW OF A GAIT CYCLE THE DETERMINANTS OF GAIT GAIT IN THE ELDERLY PATHOLOGICAL GAIT CURRENT & EMERGING TECHNOLOGY STATIC SYSTEMS DYNAMIC SYSTEMS ROBOTIC AMBULATION FORCE FIELD HARNESS CONTROL DEVICES SUMMARY CHAPTER 3 PAST DESIGN VERSION I OVERALL SYSTEM DESIGN FORCE FIELD SYSTEM POSITION ADJUSTOR SYSTEM WEIGHT SUPPORT SYSTEM PURPOSE OF REDESIGN FORCE FIELD SYSTEM POSITION ADJUSTOR SYSTEM CHAPTER 4 CHOSEN DESIGN VERSION II OVERALL SYSTEM DESIGN DYNAMIC WEIGHT SUPPORT SYSTEM CORONAL DISPLACEMENT SYSTEM COMPONENT SPECIFICATIONS DYNAMIC WEIGHT SUPPORT SYSTEM CORONAL DISPLACEMENT SYSTEM COMPONENT SELECTION DYNAMIC WEIGHT SUPPORT SYSTEM CORONAL DISPLACEMENT SYSTEM STRUCTURAL ANALYSIS FINITE ELEMENT ANALYSIS ANALYSIS RESULTS CONTROL SYSTEM CONTROL ALGORITHM HARDWARE SOFTWARE CHAPTER 5 FABRICATION AND ASSEMBLY ii

3 5.1 SYSTEM FABRICATION CHAPTER 6 FINANCIAL ANALYSIS... 2 CHAPTER 7 FUTURE WORK... 2 REFERENCES iii

4 LIST OF FIGURES AND TABLES Figures Figure 1: The AutoMove System... 4 Figure 2: Gait Cycle... 5 Figure 3: Gait Cycle Timing... 5 Figure 4: Foot Placement during Gait Cycle... 6 Figure 5: Joint Moments during Gait Cycle... 7 Figure 6: Joint Angles during Gait Cycle... 7 Figure 7: Joint Power Generation/Consumption during Gait Cycle... 7 Figure 8: Muscle Activity during Gait Cycle... 7 Figure 9: Terminal Stance... 9 Figure 10: Circumduction Figure 11: Hip Hiking Figure 12: Steppage Figure 13: Vaulting Figure 14: The LiteGait System Figure 15: The LiteGait System Patent Design Figure 16: The Biodex Unweighing System Figure 17: TR Space Trainer Figure 18: The Lokomat System Figure 19: Lokomat Leg Braces Figure 20: Lokomat in action Figure 21: Closed-loop force controlled body weight support system Figure 22: Bi-lateral body weight support system Figure 23: Robotic Gait Orthosis Figure 24: Orthopedic apparatus for walking and rehabilitation Figure 25: The MIT-Manus Figure 26: The MIT Anklebot Figure 27: Gait assistance harness apparatus Figure 28: Unweighing apparatus Figure 29: Body Support Harness Figure 30: Bledsoe Hip Brace Figure 31: Uncased IMU Figure 32: Load Cells Figure 33: Position Sensors Figure 34: Overall Version I System Figure 35: Force Field System Figure 36: Position Actuator Figure 37: Weight Support Figure 38: Version 2 Gait Trainer Figure 39: Weight Support Frame Figure 40: Misalignment Sub-System Figure 41: Coronal Displacement System Figure 42: THK Rail Loads Figure 43: Load Placement on Weight Support Frame Figure 44: Stress Distribution of Loaded Weight Support Frame Figure 45: Net Deflection of Loaded Weight Support Frame Figure 46 (a): Same Amplitude and Same Nominal Position Figure 46 (b): Same Amplitude and Different Nominal Position Figure 46 (c): Different Amplitude and Same Nominal Position Figure 46 (d): Different Amplitude and Different Nominal Position Figure 47: Basic Closed-Loop Control System Figure 48: Hardware Schematic iv

5 Figure 49: Chosen Copley Control Servotube Motor Figure 50: Labview Schematic Figure 51: Labview Interface Tables Table 1: Product Summary Table 2: Rail Analysis Results Table 3: Motor Specifications v

6 PELVIC REHABILITATION DEVICE VERSION II Design Team Anthony Tanner, Ben Davies James Forte, Marshal Doughty, Matteo Batista Design Advisor Prof. Dinos Mavroidis Sponsor Paolo Bonato Abstract This report details the development of a Version II S.A. Trainer. The S.A. Trainer is a rehabilitation device designed in conjunction with the Motion Analysis Lab of the Spaulding Rehabilitation Hospital. The device is designed to help patients with abnormal gait patterns regain natural pelvic obliquity with the use of newly developed corrective system. Force-field correction induces a patient to use their own muscular structure to correct abnormal gait. This will decrease rehabilitation time and improve brain to muscle communication. Patent and literature searches concerning existing rehabilitation devices have shown that no current device utilizes force fields around the pelvis to improve gait patterns. In the S.A. Trainer, lateral corrective forces will be applied to control the obliquity of a patient while allowing free motion for the natural translation and rotations of the pelvis. The envisioned end result is the delivery of a fully-functional prototype designed for human testing with a minimum safety factor of 2.5. The focus of this project will be on the creation of a truly rigid mechanical structure (for purposes of motion analysis) and the implementation of a closed-loop control algorithm. The control system will gather real-time data on a patient s gait, compare it to the gait profile derived from a healthy subject, and facilitate the necessary forces to normalize the two patterns. vi

7 1.1 MOTIVATION CHAPTER 1 INTRODUCTION Victims of many conditions, such as stroke, Parkinson s disease, and cerebral palsy are left debilitated and weak. Their ability to walk is affected, reducing their mobility. Patients often undergo therapy in an effort to regain some or all of their previous physical facilities. The therapy is generally administered by a physical therapist and/or a device designed for rehabilitative purposes. Although a patient may regain the ability to walk, this type of rehabilitation often leaves them with an abnormal walking pattern or gait. A previous design team spearheaded a first attempt at designing a device to help patients regain a normal gait. 1.2 MISSION STATEMENT Our goal is to continue the development of an existing device (S.A. Trainer) which rehabilitates pelvic obliquity in stroke and spinal chord injury patients using force fields. The needs originally identified by the Motion Analysis Lab at the Spaulding Rehabilitation Hospital were to provide constant weight support to an individual during ambulation, and to provide a force field to assist in the correction of abnormal gait patterns. There are two main objectives that our group will accomplish: improve mechanical systems, and design and implement a basic closed-loop control algorithm. Above all, our objective is to deliver a safe, fully functioning prototype, which improves a patient s gait pattern in the lateral pelvic direction. 1.3 DELIVERABLES The original design team was unable to take the device to the testing phase. This is because a control system has not yet been implemented. The development of a control system and the necessary algorithms will be the main design focus of our group. The control system must tell the actuator when to activate, how much force to apply, and what direction the force must be applied. It will do this by continuously sampling data from sensors such as load cells and position encoders. The collected data will then be run through the relevant control algorithms and processed by a control program which will then send the appropriate signal to the actuators. Although the previous team developed an excellent prototype, they were not able to develop a functioning model in the time available to them. Our group will focus on improving mechanical issues, including the replacement of current actuators, and the development of a control system. An overhead weight support frame will also be incorporated, allowing movement in any direction. 1

8 1.4 PROJECT SPONSOR Dr. Paolo Bonato is our main sponsor. Dr. Bonato, an electrical engineer, is the Director of the Motion Analysis Laboratory at Spaulding Rehabilitation Hospital and he is also an Assistant Professor at Harvard Medical School. Dr. Bonato received his master s degree from the Politecnico di Torino, Italy and his PhD from Universita di Roma La Sapienza, Italy. His research and interest revolves around rehabilitation engineering; biomechanics of movement and electromyography. Prior to Harvard, he was Research Assistant Professor at the NeuroMuscular Research Center of Boston University. Throughout his career, Paolo has written notable literature that has proven significant to the rehabilitation field. The Motion Analysis Laboratory s objective is to combine laboratory and field assessments to enhance mobility in individuals with mobility-limiting conditions. In the laboratory setting, a camera-based system is used to study human movement during specific motor tasks under well-defined conditions. In the home and the community settings, wearable technology is utilized to capture movement patterns during the performance of real-life motor tasks. These two types of assessments complement each other. In the laboratory setting, data can be gathered during highly-controlled experiments thus satisfying the need for accuracy and repeatability. This data is useful in developing models of joint biomechanics. On the other hand, experiments conducted in the laboratory setting can only mimic real-life conditions, but are unlikely to capture the great variety of situations observed in the home and community settings. Conversely, recordings performed in the field constitute direct observations of real-life tasks. However, the inability of controlling the conditions in which data are gathered makes it extremely challenging to perform a detailed analysis of biomechanical patterns. The team of clinicians and engineers in the M.A.L. focuses on developing techniques to overcome the challenges inherent in combining traditional, laboratory-based assessments with real-life observations performed via wearable technology in the home and community settings. Activities performed in the Motion Analysis Laboratory range from evaluating gait in children with cerebral palsy to supporting surgical and rehabilitation decisions, to building biomechanical models of joint biomechanics and designing novel prosthetic and orthotic devices. 2

9 2.1 GAIT COMPLICATIONS CHAPTER 2 - BACKGROUND Strokes are caused by reduced blood flow to the brain. This can occur through a blood clot or when an artery leading to the brain bursts. The loss of blood flow can cause nerve cells in the brain to die, leading to the impairment of bodily motor functions. Only about 10% of stroke victims regain the same levels of activity that they exhibited before the stroke. A loss of balance can occur following a stroke, ranging from a slight loss of balance to one which is severe and disabling. Another common human function affected by strokes is speech, caused by the weakening of a patient s muscles. This muscle impairment is what causes the patient to have difficulties ambulating. The leading characteristic is that patients tend to drop their foot mid-swing. [1] There are a variety of methods currently being used in practice and in research for helping patients regain lost functions. Physical therapists can help to restore motor control and strength in patients through exercise programs. These therapies attempt to stabilize and strengthen muscles. Sometimes braces that work like joints are used to help support muscles weakened as a result of the stroke. There are exercise programs designed to help with speech, cognitive thinking, and mobility among the other disabilities caused by a stroke. [1] Biofeedback is a process that can be used to help increase mobility and muscle function for a rehabilitation patient. Biofeedback uses sensors placed over target muscles that are important to motor control and functionality. When the patient activates the muscle during exercise, the sensor picks up the electrical activity generated by the muscle. This sensor information is then used to provide feedback to the patient. This feedback is passed along to the patient either through a visual or audio signal when they have activated the muscle. The idea is that if the patient is provided a signal each time they activate a certain muscle they will eventually learn the physical process through which this occurred and will be able to repeat this action in the future. [1] Electrical Stimulation is another form of therapy used to encourage the regeneration of muscle strength. It is often referred to as Functional Electrical Stimulation or FES. As with biofeedback, sensors are placed on target muscle groups and pertinent information is recorded. This information about muscle activity is then used to apply electrical currents to specific muscle and stimulate it into a spasm like action. Although commercial products such as the AutoMove System exist (Figure 1), FES is considered an experimental treatment by many researchers. [1] A study on gait retraining through electrical stimulation compared two groups of stroke patients during their rehabilitation. In this study one group received FES treatment while the control group received just 3

10 intensive gait retraining. Each patient received four weeks of treatment. At the end of the treatment period, both groups were given conventional gait retraining therapy. The results of this study showed that both groups made significant improvements in walking speed. It also showed that the group receiving FES as part of their treatment program regained a more significant amount of their original walking capabilities and even showed better symmetry in their walking patterns than the control group. The study concludes that FES improves the recovery of walking function of stroke patients more effectively than just gait retraining alone. [2] Figure 1 - The AutoMove System 4

11 2.2 GAIT BIOMECHANISMS One of our major goals is to provide constant support for patients in the pelvic area and supply a corrective force when their gait becomes abnormal. In order for us to solve this problem, we need to understand how the pelvis moves during a normal gait pattern. The difficulty in providing a standard gait pattern is that many factors contribute to one s gait. Age, sex, and even body geometry are all important factors when determining a normal gait. An elderly man s gait will show great differences when compared to that of a young, physically fit woman, even if each are within the normal limits of their sex and age. Nevertheless there are several key aspects and terms that can be applied to gait analysis as a whole, focusing more on similar patterns rather than absolute values THE GAIT CYCLE The gait cycle is defined as the time interval between two successive occurrences of one of the repetitive events of walking [20]. There are many cycles involved in the process of walking, but for convenience and clarity this report will use the instant at which one foot contacts the ground as a point of reference. Throughout this paper the term gait cycle will refer to the cycle shown below in figure 2. The gait cycle is broken down into two separate phases, during which each leg alternates between the role of support (stance phase) and movement (swing phase). These phases are further divided into seven stages, with four corresponding to the stance phase and three to the swing phase. The duration of an entire gait cycle is called the cycle time, again further divided into stance and swing time. Although Figure 2 shows the gait cycle of the right foot, it is important to understand that the left foot is undergoing the same cycle, but displaced in time by half a cycle. [20] Figure 2 - Gait Cycle 5

12 2.2.2 GAIT CYCLE TIME Figure 3 shows the relative time duration of each phase involved in one gait cycle. During normal walking speeds (< 2 m/s) 60% of the cycle subsists of the stance phase, with the swing phase making up the remaining 40%. The period of double support, during which both legs are in the stance phase, are each about 10% of the entire cycle. Outside of variance in age and sex, which will be discussed later in this section, stance and swing phase length will change proportionally with the speed of walking. As speed is increased the stance and double support phases will shorten, while the swing phase becomes larger. The transition from walking to running is marked by the disappearance of the double support phase, replaced by the flight phase. During the flight phase neither foot is on the ground. [20] [23] FOOT PLACEMENT Figure 3 - Gait Cycle Timing Foot placement is of special importance to a normal gait. Figure 4 displays the terminology commonly used to describe foot placement. Step lengths refer to the distance one foot places itself ahead of the other. Stride length is the distance covered by one foot during its consecutive placements. Although the stride length is always equal when comparing the right and left foot (provided the subject is walking in a straight line) it is possible for step lengths to be disproportionate. This is the most common trait of an abnormal or pathological gait, and will be further discussed in the pathological gait section [20]. The dashed line extending forward from each foot in figure 4 is the normal pattern of progression for each foot. The pathological gait pattern known as circumduction is the deviation from this normal progression, and will also be described in the pathological gait section. The walking base is the distance between each foot s line of progression. The toe out (or toe in, in abnormal gaits) is the angle made from the line of progression and the direction that the tip of the foot is pointing. 6

13 Figure 4 - Foot Placement during Gait Cycle CADENCE AND SPEED Cadence is the number of steps taken in a given period, usually measured as steps per minute. As there are two steps in every gait cycle, cadence can also be thought of a measure of half-cycles. Tables 1 and 2, shown in the appendix, show some of the normal ranges of cadence and cycle time for men and women. Cadence may be related to cycle time by the formula Cycle time (s) = 120/cadence (steps/min). (1) By using that relationship, the average speed of walking can be found by dividing stride length by cycle time. [20] OVERVIEW OF A GAIT CYCLE The following four figures (5-8) provide an overview for a typical gait cycle. Although gaits differ depending on many factors, many patterns remain the same and are important to understand. The specific measurements shown in the first three figures were take from a 22 year old female subject, walking with a stride length of 1.45 m, cycle time of 1.1s, and a walking speed of 1.32 m/s. Data was obtained using a Vicon television/computer system and Bertec force platform. [20] Although movement occurs in frontal, transverse, and sagittal planes, all measurements shown were take sagittal plane. The sagittal plane, or plane of progression in normal walking, is where the majority of movement takes place. The last figure in this section, figure 8, is a typical gait cycle, and is not based on any one subject. The data is represents was captured using electromyography. Figure 5 shows the sagittal angles measured over a single gait cycle. Figure 6 and 7 shows the corresponding joint moments and power generation/consumption, respectively. It is important to note that the measurements were scaled for body mass, but not for limb length. Lastly, figure 8 shows the muscle activity during a gait cycle, largely based on data by Perry [21], Iman [22], and Rose and Gamble [23]. During a single gait cycle, the hip flexes and extends once. Max flexion is achieved during the middle of 7

14 the swing phase and remains flexed until initial condition. The peak extension is reached before the end of the stance phase, after which the hip begins to flex again. Figure 5 Joint Moments during Gait Cycle Figure 6 Joint Angles during Gait Cycle Figure7 Joint Power Generation Figure 8 Muscle Activity during Gait Cycle THE DETERMINANTS OF GAIT In 1953 Saunders published The Major Determinatmants in Normal and Pathological Gait in Journal of Bone and Joint Surgery, detailing several optimizations performed by the body to minimize the excursions of the center of gravity. [20] These determinants are all important to affect a normal gait, but for the device s purposes it is most important to understand the first and second determinants, dealing with pelvic rotation and pelvic obliquity. 8

15 Figure 9 shows how pelvic rotation decreases the necessary displacement of the center of gravity. The hip moves forward, as well as rises and falls, whenever a motion occurs that results in hip moving from a flexed to extended position. The amount of forward progression by the hip, as well as the amount by which it rises and falls, depends on the total angle the hip joint moves from flexion to extension. The greater the stride length, the greater the necessary angles the hip goes through from flexion to extension. The first determinant of gait is the process by which the pelvis rotates about a vertical axis, bringing the hip joint forward during flexion and backward during extension. This allows for a lower necessary flexion and extension of the hip during a given stride length, and a portion of the length comes from the forward/backward motion of the hip. This results in a reduction of vertical movement of the hip.[20] The second determinant of gait, pelvic obliquity, is the way the pelvis tilts along the anteroposterior axis, alternately raises each side of the pelvis. If the pelvis were to remain level, the trunk and center of gravity would follow the rise and fall in the hip joints during pelvic rotation. Pelvic obliquity allows the hip of the stance-phase leg to be higher than the hip of the swing-phase. Since the height of the center of gravity is the average of both hip heights, pelvic obliquity reduces the total vertical displacement of the center of gravity. It is important to note that this optimization requires that the swing phase leg be sufficiently functionally shortened to allow it to clear the ground despite its lower hip height. [20] GAIT IN THE ELDERLY Because our device is mainly targeted toward the rehabilitation of stroke victims, it is important to understand the difference, if any, in the normal gait of the elderly. In a study by Murray, it was found that the gait of the elderly mimics that of younger adults, but a slowed-down pace. Age related changes begin to take place from the ages of years old. Generally speaking there is a decrease in swing time and cadence, and an increase in walking base. Murray suggested that the gait changes provided increased security in walking. Balance is more easily maintained by the increase in base size and lengthening of the support phase. The decrease in the swing phase also reduces the amount of time during which there is only a single limb support. Lastly, the decrease in stride length allows a reduction in the total range of hip flexion and extension. [20] The initial thought on pelvic or center of mass displacement was that it is different for everyone. Studying the normal gait pattern, it was discovered that every person s center of mass displacement is roughly the same. When a person walks, both of the legs are on the ground just like the picture of terminal stance (Figure 9) below. The picture shows that a right triangle has formed when a person walks. As they proceed through the swing phase of the cycle, they support their weight on only one leg. The difference in their pelvic location is approximately equal to the ratio between the side and hypotenuse of the triangle. Since this is a ratio, the vertical displacement ends up being about the same for everyone. The pelvis also moves 9

16 in three degrees of rotation and in the other two displacements. In the sagittal plane (looking from the side), the pelvis will give an anterior or posterior tilt of 4 degrees in the swinging phase. In the coronal plane (looking from the front), the pelvis will drop 7 degrees on the leg that was standing, and 7-degree rise on the leg that was swinging. In the transverse plane (looking down from the sky), the pelvis will rotate 10 degrees on each side when each of the legs is swinging. [3] Figure 9 Terminal Stance PATHOLOGICAL GAIT Although variability is present and expected in gait patterns, arising from numerous factors, some semblance of a normalized pattern should exist. Abnormal, or pathological, gaits deviate from this expected pattern. Pathological gait can result from numerous neurological conditions including cerebral palsy, Parkinsonism and stroke. This section will focus more intently on the symptom of pathological gait associated with functional leg length discrepancy, a common abnormality found in many neurological victims. A functional leg length discrepancy signifies that, though not actually different lengths, one or both legs are unable to appropriately adjust during the stance or swing phases of the gait cycle. As was mentioned before, for normal gait to occur the swing leg must be functionally shorter than that of the stance leg. If this is not the case, the swing leg will hit the ground, prematurely ending its swing phase. A leg is functionally shortened during the swing phase, by flexion at the hip and knee, and by dorsiflexion at the ankle. Alternatively, a leg is lengthened, during the stance phase, by extension at the knee and hip and plantar flexion at the ankle. Inability to functionally shorten or lengthen a leg will lead to gait abnormalities as a means of compensation. Four pathological gaits exist, all of which attempt to overcome a functional leg length discrepancy.[20] As all four involve abnormal movement of the pelvis, they are seen as some of the abnormal gaits correctable with use of the S.A. Trainer. 10

17 Premature ground contact by the swing leg can be avoided if swung in an outward motion, described as circumduction and shown in Figure 10. Circumduction is often used to advance the progression of the swinging leg in light of weak hip flexors, by improving the ability of abductor muscles to act in the stead of said flexors. This motion occurs while the hip joint of the swinging leg is extended. [20] Figure 10 - Circumduction Hip hiking is the abnormal gait modification by which, through contraction of the lateral abdominal wall and spinal muscles, the swing phase side of the pelvis is elevated. This phenomenon is a reversal of the second determinant of gait, and often involves an exaggeration of the first determinant to assist with the leg progression. In studies by New York University it was found that hip hiking is often used in slow walking to accommodate weak hamstrings, which lead to the swing leg prematurely extending near the end of the swing phase. Hip hiking is shown in Figure 11 [20] Figure 11 Hip Hiking A swing phase modification, steppage is an exaggerated knee and hip flexion, used to lift the swing leg higher than normal for ground clearance. This is often used to counteract a plantar flexed ankle, also known as drop foot. Drop foot is a common occurrence with stroke victims, and is a result of weak anterior muscles. Steppage is shown in Figure 12 [20] 11

18 Figure 12 - Steppage A stance phase modification, vaulting is another method by which clearance for the swing foot may be increased. A subject will rise up on the toes of the stance foot, resulting in an exaggerated vertical displacement of the center of gravity, as well as a significant increase in energy expended. [20] Vaulting is shown in figure 13 below. Figure 13 - Vaulting 12

19 2.3 CURRENT AND EMERGING PRODUCTS Since patients are often not capable of maintaining their equilibrium at the start of the rehabilitation process, body weight support systems are often employed to assist them. Studies show that patients who do gait retraining therapy while a percentage of their body weight is supported have regained better walking capabilities as compared to those patients that were bearing their full weight during treatment. Systems that provide body weight support can be classified into two categories: those that account for the displacement of center of mass (dynamic systems) and those that do not (static systems). There are currently products available in both categories. Products are also available that provide forced movement through the use of robotics. These devices shift the body in order to simulate proper movement patterns. These robotic devices can be actual robots in that they are position controlled systems which force movement, or force field-like devices that only guide movement and in some cases resist unwanted movement. The last group of products related to gait rehabilitation is harnesses which are or could be used in the body weight support systems STATIC SYSTEMS Several of the systems found which fall into the category of devices that provide robotic movement also utilize static lift mechanics. These devices will be described in a subsequent section, since the robotic movement is the primary feature of those devices. The current section will describe devices that only provide static weight support with no additional features. Figure 14 - The LiteGait System One static lift system currently commercially available is the LiteGait (Figure 14) manufactured by Mobility Research. This product is patented under patent number 5,569,129, entitled Device for patient gait training. The basic unit consists of a structure with a crane-like appearance and harness for the support of the patient. The unique design of the LiteGait units allows a single person to move a person up to about 350 pounds from a seated position such as in a wheelchair to an upright position. This is done 13

20 through a mechanically actuated telescoping lift. The device is engineered so it fits around most conventional treadmills for assistance in gait therapy, but is on wheels to accommodate use as a walker over flat ground. [4] The device aids gait therapy by allowing the individual monitoring the therapy to freely adjust limb placement, weight shift, walking symmetry, and gait timing. Proper upright posture is maintained throughout the entire procedure with the use of the LiteGait device, due to an upper body harness. This facilitates muscular development in the areas associated with maintaining this posture. [5] Figure 15 - The LiteGait System Patent Design The LiteGait (Figure 15), has its advantages and disadvantages. Its main advantage is that it is a very simple, very portable device that is easy to operate and is a low cost weight support solution. Its simplicity, however, introduces drawbacks. Because it is only a static support device, it does not provide weight support in a manner that is realistic to actual walking. In other words, it does not allow for displacement of the pelvis. The simplicity again poses a disadvantage this time in the nature of the training. During early sessions a therapist has to physically move the patient s lower body. This poses three problems. First, the therapist can t accurately create a normal walking pattern for the patient. The second problem is that this is tiresome to the therapists and sessions have a limited length. Machines don t get tired and can keep going as long as the patient can. [6] The third problem with manual treadmill gait retraining is the costs incurred. It costs more money for each therapist involved with helping the patient. Manual treadmill gait retraining is not commonly done since insurance companies are reluctant to cover the costs of multiple therapists. [6] Another drawback is the exclusion of a computerized recording system which tracks patient progress. [5], [4] DYNAMIC SYSTEMS 14

21 As described in the previous section, static systems do not allow the patients hips to move vertically, which therefore does not allow for a realistic walking pattern. Dynamic systems however account for the vertical displacement need and are designed to create a more accurate walking pattern. The devices listed below all have been designed with a dynamic system in place. Figure 16 - The Biodex Unweighing System The Biodex system enables a suspension system that accommodates the vertical displacement of the center of gravity that occurs during normal gait. The suspension of this device allows up to 4 of vertical displacement, which enables patients to move naturally through rehabilitation. At the same time, this device maintains a consistent level of weight support. Another critical aspect that this device successfully addresses is the pelvic rotation when walking. Two-point suspension systems have a tendency to restrict rotation on the horizontal plane. This device responds to pelvic rotation similar to the way a playground swing undulates back to neutral after being twisted. The single-point suspension of the device allows unrestricted pelvic rotation. Patients can train for weight-bearing ambulation without compromising proper gait kinematics. [7] This device also provides pelvic stabilization by utilizing retention cords that can be attached to special attachment rings on the sides of the support vest, secured to the frame, and adjusted for the desired degree of pelvic stabilization. The ability to allow rotation has other advantages. When training with a treadmill, single-point suspension permits functional pelvic rotation and versatility when walking, sidestepping, retrowalking and turning. With a Biodex Unweighing System (Figure 16), the patient can change direction without repositioning the entire patient support system. [7] The Biodex s prime advantage is obvious, the dynamic suspension system. There are a few other major advantages as well. It is relatively small and lightweight. This enables for it be to portable, which is 15

22 necessary for therapists to move it around. The ability to adjust heights for patients is also very important. This enables patients to use it with various equipment such as treadmills, walking devices and wheelchairs. The Biodex is not without its drawbacks. For instance it is not compatible with all treadmills. This is due to the fact that the crossbars don t provide much clearance, so larger treadmills would not be able to fit in between the supports. Similar to the static systems the therapists have to manually move the patient s lower body. The same problems persist, accuracy and abbreviation of session. Figure 17 - TR Space Trainer The TR Space Trainer (Figure 17), developed by TR Equipment, is a patented commercial product for gait retraining. The product is essentially a treadmill with an overhead structure for cables, a harness, and a computerized control system. All of the components are built into one system. The system is able to provide constant body weight support through a closed-loop feedback system, in which the applied weight support is constantly measured and adjusted through means of raising or lowering the support cables. This approach provides the patient with a constant amount of body weight support. This system does not completely satisfy our goals. The TR Space Trainer does not facilitate pelvic movement in the manner necessary for normal gait patterns. It is important that a system not be so rigid that it forces a patient s body to move in straight lines but rather allow for oblique movements which are necessary for normal movements of the pelvis. The system is not extremely portable due to the fact it is built as one complete unit. The harnessing system is not very adjustable and there is only one size harness available, which makes it difficult to train individuals of large or small body size. Also, it does nothing to guide patient into performing correct walking behaviors. In fact, it could be argued that the system encourages poor walking patterns by providing support during these behaviors, in effect encouraging and strengthening these poor walking behaviors. [8] 16

23 Figure 18 - The Lokomat System The Lokomat system (Figure 18) for gait therapy consists of the actual Lokomat, which is the robotic gait orthosis; the Lokobasis, which is the body weight support system; and two PCs. A Woodway treadmill is incorporated into the setup of the system. Hocoma is the parent company responsible for the design and the manufacturing. Hocoma is a medical engineering company developing innovative equipment for application in rehabilitation. The Lokomat is currently in the field at prestigious clinics worldwide.[9] The Lokomat is highly effective in gait therapy due to its design. The actual Lokomat system is attached to the patient in order to control the movement of the lower body. On each leg, braces are placed on the thighs and two locations along the lower portions of the leg (Figure 19), providing for four degrees of freedom. A force motor that creates the leg movement of the patient drives these braces. The idea of moving the patient legs is not new to gait therapy. Traditionally, this is accomplished by having two therapists physically pick up the patients legs and manually move them. By having this controlled by machines a few advantages occur. Without having the need for two additional therapists, a single trained professional can run a session. Additionally, the traditional method was very tiresome for therapists. Lokomat allows for a longer training session that in turn brings faster results. Moreover, even the most highly trained therapist can only be so accurate when moving the patient. Being in the braces ensures the patient s lower body is moving in a proper gait pattern. [9], [10] 17

24 Figure 19 - Lokomat Leg Braces The Lokomat has a much greater importance then the force motors that move the patient. This is because the braces and motors are equipped with position and force sensors. The therapist can pre-program a percentage of the patient s body weight it wants the Lokomat to support. Using the sensors the Lokomat can measure how much work the patient is actually doing then readjust the amount of force it is applying to make sure the patient is supporting the proper percentage of their weight. According to the brochure for the Lokomat: The Lokomat System utilizes high quality computer controlled motors (drives) which are integrated in the gait orthosis at each hip and knee joint. Force transducers at the joints accurately measure the interaction between the patient and the Lokomat. The drives are precisely synchronized with the speed of the treadmill. This sensitive system assures a precise match between the speed of the gait orthosis and the treadmill. [9] These sensors have another meaningful quality besides measuring force: they also measure the position of the patient s limbs. The sensors ensure the force motor is moving the patient in a manner in which it will allow for rehabilitation of a proper gait pattern. The brochure provided in Figure 20 below along with a statement on gait movement: [9],[10] 18

25 Figure 20 - Lokomat in Action Hip and knee joint angles are controlled in real time by software to achieve a physiologically meaningful gait pattern. Each of the four joints is constantly monitored by the Lokomat s software to ensure that they are precisely held to the predefined gait pattern. [9] Lokobasis is the system that support s the weight of the patient. The patient is fitted into a harness that attaches around their midsection and is elevated by four cables. The designers at Hocoma created the harness so it could accommodate patients of various sizes. This is accomplished by two distinct methods. The harness itself is adjustable allowing for the midsection size of the patient to vary. The second method requires that the cables are horizontally adjustable. This allows for the height of the patient to vary. [9] The sensors on the braces allow for the weight support to be measured exactly. It is then registered by the computers, which can automatically adjust how much weight is supported. These actions are referred to as a closed-loop system. By combing these two methods the patient can be correctly set into the system, allowing for Lokomat to create a proper gait pattern. [10] The Lokomat system is equipped with two PC s. The first PC is the control system for setting up and executing a session. According to Hocoma: A user interface allows the therapist to easily operate the Lokomat and adjust training parameters to suit the individual patient s needs at any point during a training session. The second PC serves as a graphical user interface (GUI). The GUI provides biofeedback of the session. Again according to Hocoma: [9] The Biofeedback System displays the patient s effort during therapy in realtime on an additional flat panel display. This enhances the patient s motivation to do as much as possible instead of allowing the Lokomat to do the work. The patient sees his own performance evaluated through direct feedback and can 19

26 then control correct functional movement. The visual Biofeedback can be adjusted to suit the patient s needs. The same Biofeedback data is displayed also on the Lokocontrol PC for the therapist s control and for gait analysis. [9] The Lokomat has some distinct advantages. Similar to the other dynamic systems, it allows for midsection displacement and height of the patient to be adjustable. Unlike the other dynamic systems the Lokomat utilizes its braces for robotic moment. This allows for kinematics and adjustable levels of assistance. In addition physical strain on the therapists is removed, allowing longer training sessions, for more rapid results. The computers and GUI provide monitoring of gait patterns in conjunction with visual feedback of the patient s performance. [9], [10] The disadvantages of the Lokomat are quite unique to the system described. They are not based on the performance of the system but the overall feasibility of it. Due to the complexity of the design the Lokomat is very costly. A single unit is currently priced around $250,000. Most institutions can t afford this and are unable of obtaining its services. The Lokomat system is very large: a unit requires a ceiling clearance of 280 cm, as well a perimeter of 550 x 350 cm. This large size makes it impossible for a single person to move, as compared to the previous units which are small and extremely portable.[9] Figure 21 Closed-Loop Weight Support System Figure 22 Bi-lateral Weight Support System There are several patent applications on inventions that relate to the Spaulding sponsored project that can be classified as dynamic support systems. One patent application in this category is named Closed-loop 20

27 force controlled body weight support system (Figure 21) and the other (Figure 22) is named Bi-lateral body weight support system. Both of these inventions provide a constant weight support to patients as they walk by attaching cabling to a body harness and varying the cable length as the center of mass of the patient s body varies. They do this under a closed loop system, which measures body weight support and adjusts the support system accordingly. Both systems utilize an overhead support structure for attaching the cable. The cable lengths can be varied using motors or pneumatic & hydraulic cylinders. Although these systems are much more advanced and useful than body weight support systems that provide static support, they do not account for the fact that the patients gait pattern may not be correct. By failing to incorporate into their systems features that force patients into proper gait patterns, patients may learn incorrect gait through rehabilitation training. Also, overhead supports limit portability and possible locations for use ROBOTIC AMBULATION Another category of inventions found can be classified as robotic systems, which force movement and walking. These systems all use powered leg braces to force legs to perform walking maneuvers. Some utilize static lift and harness systems to lift patients into machines and support weight as this forced walking takes place. There has been a lot of work in the medical field into researching powered braces that simulate and force limb movement, and commercially available products are starting to emerge (such as the Lokomat system previously described). Since braces provide the force for movement, training which utilizes these devices may not be as effective as training in which patients move their legs on their own. Our project aims to focus on the movement of the center of mass as the movement of this location affects all other movement. These systems focus on the movement of the limbs, so although relevant in the sense that they are related to ambulation, they do not address the exact issue of ambulation we are focusing on. It may be useful to incorporate some of the limb movement techniques and technology into a similar device for the pelvis, however. Figure 23 Robotic Gait Orthosis Device 21

28 The invention pictured above is a structure that provides for lifting a patient from a wheelchair or seating apparatus onto a treadmill, provides weight support, and robotically forces movement of the patient s leg. The invention (Figure 23) is entitled Robotic gait orthosis. When using the device, a patient is initially fitted with a special harness and is lifted from a wheelchair to a standing position. Weight is measured during this process. A database containing individual set-up and historical information will be displayed on the touch screen. The patient is then moved over the treadmill and lowered to a level that provides the desired weight support. The percent of supported body weight can be adjusted as required as muscle strength of the patient develops. The gait assist mechanisms are then attached to one or both legs of the patient. The first attachment cuff is connected to the first depending arm for attachment to a patient's leg just above the knee. A second attachment cuff is connected to the second depending arm for attachment to a patient's ankle. All component speeds are synchronized and controlled by operator input with treadmill speeds ranging from 0 to 2 mph. During a session, information such as blood pressure, heart rate, blood oxygen content, treadmill speed, session duration, etc. can be displayed and recorded for further analysis. [11] Similar to the Lokomat, the advantage of this device focuses on the gait pattern of the patient as well as the relief of the therapist. The braces allow for proper kinematics and longer training sessions, for more rapid results. The ability of the harness to lift the patient from the wheelchair is a unique advantage, again helping the therapist. Unlike the Lokomat the harness is static, which despite proper gait movement of the legs creates improper gait pattern for the hip and pelvis. Figure 24 Orthopedic Apparatus for Walking and Rehabilitation 22

29 The next device, Orthopedic apparatus for walking and rehabilitation, (Figure 24) is a mobile robotic legforcing device. Unlike other systems, this system does not incorporate a treadmill or any weight support. The central part of this device is the hard outer structure (shell) for the support of a patient's upper and lower body. Joints are located opposite the hip and knee. Actuators are connected to the jointed members and the movements are relative to each other and to the human gait. [12] A control unit is programmed to control the operation of the actuators. A remote control for operation of the control unit allows the patient to transmit commands to the unit in order to start or stop the lower limbs, as well as to adjust the step speed. The system utilizes virtual reality to entice patients to actively participate. An external work platform can be used to steady and support the person, and has grips having operating push buttons for the remote control unit. [12] This device has truly a unique advantage over the other systems. Patients are able to conduct exercise and training by themselves. They can rehabilitate on their own without the supervision of trained professionals. This however does pose unique drawbacks as well. The device does not support the patient s weight, as they are to hold themselves upright. This is not applicable to early stages of patient rehabilitation or patients with severe mobility conditions. It is more suited to patients who are capable of self-care FORCE FIELD & ROBOTIC REHABILITATION DEVICES One of the emerging techniques for regaining agility in stroke patients during rehabilitation is the use of force fields. Devices using force fields for rehabilitation are already being used and researched for the arms, hand and wrists, knees, and ankles. Until now, nothing had been done to implement force fields into a device that would assist the movements of the pelvis. Force field devices can be used two ways in the rehabilitation process. First, the device can be used to actually control the movements, if the patient is unable to move the particular part of the body being targeted by the device on their own. Second, the device can be used to assist or guide the patient in the desired movements. It can be said that the second method of assisting the movements is the better process for rehabilitation of the limbs. By assisting the movement and not just forcing it, the patient has the liberty of making mistakes and learning from them as the device provides resistance to guide the patient back into the proper range of motion for particular targeted area. A great deal of research is being done into the use of force fields for rehabilitation purposes at the Massachusetts Institute of Technology through the MIT-Manus program (Figure 25). 23

30 Figure 25 - Manus Programmers MIT-Manus project originally designed a robotic device to assist with movements of the lower arm. With the MIT-Manus a patient would place their arm in a brace that is attached to a robotic arm. The patient follows a video screen, which instructs the patient to perform an arm exercise such as connecting the dots or drawing the hands of a clock. The robotic arm monitors the patient s movement and provides assistance when necessary. It was found from clinical trials that stroke patients who used the MIT-Manus device, when compared to stroke patients who did not receive treatment with the device, improved the movement of the impaired arm more rapidly. It was also found through the clinical trials that patients who used the device found it comfortable and accepted it. Another device recently developed by the same group as the MIT-Manus is the Anklebot. The Anklebot (Figure 26) performs conceptually much the same way that the earlier MIT-Manus operates. Figure 26 - Anklebot The S.A. Trainer is the first device developed for the use of gait rehabilitation by means of force field generation upon the pelvis. However, in July 2005, a team at the University of California produced a robotic device called PAM (Pelvic Assist Manipulator). PAM implements a series of actuators and sensors 24

31 to allow for six degrees of freedom on the pelvis. It is a pneumatic robotic device designed to measure and manipulate naturalistic pelvic motion: We are developing a robotic device, PAM (Pelvic Assist Manipulator) that assists the pelvic motion during human gait training on a treadmill. PAM allows naturalistic motion of the pelvis actuated by six pneumatic cylinders, which, combined with a nonlinear force-tracking controller, provide backdrivability and large force output at a relatively low cost. [19] PAM is very similar to the S.A. Trainer but it relies more heavily on assisted robotic movement through pneumatics. The S.A. Trainer on the other hand works as a guide for its patients. The S.A. Trainer does not force proper movement; it nudges the user into proper obliquity so that actually gait correction is being done by the patient and in theory the patient eventually remembers the correct movement through muscle use. The advantages of the PAM system are the complete degrees of freedom among all planes and its advanced controls system. Human testing has been done and it was reported that subjects had difficulty synchronizing their movements with the gait pattern reproduced by PAM, even when the gait pattern was sampled from that particular subject. At the moment the multiple degrees of freedom are predictably complicating issues for the PAM team HARNESSES The final group of devices is not specific to gait rehabilitation systems, but is essential to weight support systems. In order to create optimal displacement of the pelvis, a well-designed harness is crucial. The harness is especially important as it responsible for securing and positioning the patient. Although most harnesses have the same main function, supporting the patient, their designs vary. Figure 27 Gait Assistance Harness Apparatus This particular invention, Gait assistance harness apparatus (Figure 27) consists of a gait belt that is 25

32 fastened about the waist of a patient and worn like suspenders. There are two additional restraining straps available to attach the patient securely and comfortably to a seating device such as a wheelchair. [12] This style is advantageous because the material used in the harness is semi rigid; this creates stability while securing the patient. However the harness s support ends at the belt, meaning the pelvis and center of mass (COM) are not secured. Figure 28 Unweighting Apparatus There are designs that support the pelvis and COM. Exercise harness for use with unweighting apparatus (Figure 28) is an example of such a design. The harness is connected to a system above it by shoulder straps. The harness contains a waist belt suspended by the shoulder straps. Left and right knee bands are also connected to the side and middle of the waist belt. [14] Unlike the previous design this harness utilizes support for the pelvis and midsection. The harness s belt and straps secure the midsection and legs, creating the support. However, this design is made of cloth; the material no longer creates stability. In combination of the first two design styles, a third style was found, Body Support Harness (Figure 29). This invention is essentially a semi-rigid full-body harness for overhead weight support. Similar to the first design style it is made of semi rigid material, creating stability. It also contains components that secure around the body s core and legs, as well as over the shoulder supports. [15] This similar to the second design style allows for the pelvis and COM to be secured. Since the material is made of semi rigid material the patient s core area can be stabilized as well. 26

33 Figure 29 Body Support Harness Figure 30 Bledsoe Hip Brace Also notable and similar to harnesses are hip braces (Figure 30). These devices attach to the midsection and legs of the patient, with each part connected by a rigid hinged rod. The hinge on this rod can be set to only allow a certain range of motion. This is useful in patients who may have just had hip surgery and should not swing their legs beyond a certain range. The adjustable range is usually large enough to allow full rotation. These braces are applicable to this design project because they are usually made of a rigid plastic shell. They exhibit excellent stability properties, and would transmit forcing loads rather well. The ability to limit range of swing is also an added feature that harnesses do not have CONTROL DEVICES The control devices that will be used on the S.A. Trainer will elevate it from a mechanical device of limited usefulness to a dynamic rehabilitation system that provides corrective force fields, active weight support, and biofeedback by continuously sampling data. The control devices will allow a therapist to see how the patient s current gait pattern looks and how that compares to a normal pattern. Once the therapist has this data, they will be in a better position to design an effective training program. The therapist should be able to increase or decrease the level of the force with the control interface in real-time, which in turn will minimize total rehabilitation time. A simple bench setup combined with a closed-loop algorithm (most likely LabView based) will be sufficient to control the system. The software and programming issues are a crucial element to this project and will be addressed after the new hardware is integrated into the system. The device will not need too many additional parts to do this. One important device is the Inertial Measurement Units (IMU). These devices will be used on the patient 27

34 as they walk on the S.A. Trainer without weight support and without obliquity assistance. The data collected from the IMUs will be used to output a graph of the patient s vertical hip displacement against time on an X-Y axis. This is possible because an IMU detects changes in the location and motion in all degrees of freedom. An IMU is essentially a small box (Figure 31) with 3 gyroscopes and 3 accelerometers. Both the gyroscopes and accelerometers are placed with their measuring axis orthogonal to each other so that accelerometers can detect inertial acceleration and the gyroscopes can detect rotation rates. Load cells (Figure 32) are transducers that have the capabilities to convert force acting upon it, into an analog electrical signal. Modern day load cells are tiny strain gauges that have been bonded to a load cell beam and integrated into a Wheatstone bridge configuration. These load cells will serve as an interface in between the patient and the actuator. This will allow one to see the forces being applied to hip in real time. It will serve both safety and general measuring purposes. Figure 31 Uncased IMU Figure 32 Load Cells The most important piece of hardware for the controls design will be the Linear Position Sensor (Figure 33). This device is used to make accurate readings of position from a specified zero point. The position sensor will be mounted on the actuator fixture where it can easily read the position of the actuator arm. With the position sensor the therapist will know where the actuator is at all times. This provides a clear readout of how much movement is being produced from the actuator thus yielding information on hip position. The linear sensor works through a process called magnetostriction. Any material that can change shape when it is enters in a magnetic field can be defined as a ferromagnetic material. This change in size or shape is due to the presence of magnetic moments in the material. Magnetic theories such as the Villari effect and the Wiedemann effect are used to define the capabilities of a given position sensor. Using these theories as models allows an internal timer of the position sensor to read distance traveled as it relates to time. The output of the position sensor can vary depending on the needs of the user; the SA Trainermj will most likely use a sensor where the output is DC voltage. 28

35 Figure 33 - Position Sensors SUMMARY After researching the products that are available commercially and applicable patents for this problem, we came to realize each has its own benefits and drawbacks. These findings are crucial and significant for our preliminary design solution. The results are shown in Table 1 below: 29

36 CHAPTER 3 PREVIOUS DESIGN VERSION I 3.1 OVERALL SYSTEM DESIGN Figure 34 shows the Pro/Engineer model of the Version I design. As shown in the figure, the design consists of three subassemblies: a force field system, a position adjustor system, and a weight support system. These will be described in detail in the subsequent sections. As is shown, the system is built upon a U shaped frame suspended over a treadmill. This frame is a commercial Biodex unweighing device that was donated to the sponsor. Figure 34 - Overall Version I System FORCE FIELD SYSTEM The force field system is the most important part of the S.A. Trainer. The force field system manipulates the movement of the pelvis in order to correct patient gait patterns. These actuators are not meant to force proper movement but to persuade the patient to move their pelvis in an appropriate manner by the patients own effort. There are currently several devices on the market that force proper movement but these devices can lead to improper gait. The system consists of two identical assemblies, pictured in Figure 35. The assembly is clamped to the Biodex frame via four bolts. Attached to this clamp are telescoping slides, supported by diagonal braces. 30

37 The telescoping slide supports a rail slider, which in turn supports the actuator and load cell assemblies. A ball and socket joint provides the connection to the pelvic brace, and allows the hip to rotate. The combination of telescoping and rail sliders allowed movement in the horizontal plane. This movement is normal during walking. The rail sliders are also long enough to provide the patient some freedom in varying their ambulation speed and thus moving forwards and backwards on the treadmill. Figure 35 - Force Field System POSITION ADJUSTOR SYSTEM The patient is harnessed into the frame and a portion of their weight is supported by an overhead support on the frame. The weight is partially supported to allow patients to practice walking early in their rehabilitation process without the burden of their entire weight. It has also been shown that patients regained greater walking capabilities when part of their weight was supported as opposed to patients who did not have any weight support. The overhead support utilizes rail sliders allowing varying patient location on the treadmill in the X-axis. This rail slider arrangement is the Position Adjuster System. A fixed attachment point would lead the cable to provide weight support at an acute angle if the patient were to vary their position relative to the normal starting location. This angular support creates unbalancing lateral forces which could upset the patient s gait. The position adjustor system, pictured in Figure 36, will prevent this from happening by moving the attachment point directly over the patient. It does this through the use of a position sensor and actuator. The position sensor would be mounted to the force field system and track the position of the rail slider. This would then be used to control the actuator, which would be moved to the patient s new position. 31

38 Figure 36 - Position Actuator WEIGHT SUPPORT SYSTEM The model of the weight support system is shown in Figure 37. The system consists of an actuator, a load cell, a winch, and a spring (not pictured in Figure 37). This system will provide weight support to a patient making them feel lighter and thus allow them to ambulate using less muscle strength. The system will provide dynamic weight support, meaning that weight support will be kept relatively constant as the patient s pelvis moves vertically throughout the gait cycle. This system will allow this to occur by the use of the spring and actuator combination. Weight support will initially be provided by tensioning the spring with the winch. The load cell will allow the user to set weight support to the desired level. As the patient ambulates, they will move vertically up and down as well as forwards and backwards on the treadmill. Although the spring can account for the small displacements of vertical movement, the forward backward movement causes a considerable stretch in the spring and cable. This increases or decreases weight support significantly. For this reason, the actuator is needed. The load cell will detect large increases or decreases in weight support and adjust the length of the cable accordingly in order to keep weight support within a user specified tolerance range. Neither the weight support system nor the position adjustor system were implemented in the Version I prototype. Figure 37 - Weight Support 32

39 3.2 PURPOSE OF REDESIGN The Version I S.A. Trainer was not designed with enough mechanical rigidity to sustain the capabilities of the Version II control system; thus a completely new design was necessary. A number of components were added to the Biodex frame to reach the Version II level. These components include: Dynamic Weight Support, Coronal Displacement System, and the Controls system. Finite element analysis was used throughout the design process to ensure a robust mechanical structure, allowing for a steady real-time control system FORCE FIELD SYSTEM The force field system of Version I was based on telescoping slides which were essentially furniture drawer slides. They were constructed of thin walled stamped sheet metal. They were very weak and not quantitatively load rated. By inspection it was hypothesized that large deflections under relatively light loading would occur. The slides posed a safety hazard in that they were under rated for the application. Also, the ease with which they deflect would create large errors in data collection when the control system was implemented. To test the hypothesis a laboratory procedure was conducted. The slide was clamped to a bench and fully extended. Weights were then incrementally added to the end of the slide. At 55 lbs a vertical deflection of the end of the slide was measured to be.75 in. This is not acceptable for the Version II control system. The deflection itself was greater than the measured displacement of the pelvis in some cases making the error in excess of 100% from that source alone. When 115 lbs was added to the end of the slide, a permanent deformation of the slide s carriage was observed. This confirmed the assertion that the underrating of the slides was, in fact, a safety hazard. The motors that were selected for Version 1 were found to be unsatisfactory for the needs of the system. They are not back drivable, which means the actuators force movement, rather than allow the patient to attempt proper gait on their own. This means they are not capable of providing the intended force field which is a fundamental aspect of the S.A. Trainer Position Adjuster System The Position Adjuster system was never implemented in the Version I prototype. The cable was simply attached to the patient, then traveled through a pulley over head who s position was fixed, then to the spring and winch. When a person is walking normally, they naturally vary their speed and position slightly. Although this setup accomplishes the goal of weight support, it exerts an undesirable force on the patient as he varies his position on the treadmill slightly, impeding rehabilitation, as described earlier. 33

40 The intended Position adjuster system of Version I was decided against for Version II. First, it only allows movement in the X-direction (Fore-Aft). In addition, the single degree of freedom that the system allows is actively driven. This requires the implementation of additional sensors, motors and controls. It is believed that the same effect can be accomplished in a well executed passive system while at the same time adding an additional degree of freedom. 34

41 CHAPTER 4 CHOSEN DESIGN VERSION II 4.1 Overall system design Version II features several improvements over Version I. The system as a whole is much more robust. The Version II system can be seen in Figure 38. This is important not only for safety reasons but the increased rigidity makes accurate collection of data from various sensors possible. Also, eliminating unnecessary displacements of the mechanical fixtures ensures that the mechanical inputs from the motor are actually affecting the patient as intended and their efforts are not wasted in deflecting the frame. A new dynamic weight support system will be implemented in the Version II design. Instead of supporting the patient s weight from one point a three degree of freedom system will be used. The patient can move in XYZ space while their weight is always supported directly overhead. This allows for natural gait to be achieved by eliminating a force that will pull the patient to a single point. Figure 38 - Version 2 Gait Trainer DYNAMIC WEIGHT SUPPORT SYSTEM The main structural component of the dynamic weight support system is a welded mild steel frame shown in Figure 39. The frame is comprised of 1018 steel, ½ in. square tubing with 1/8 in. wall thickness. The members are fashioned into a square and triangulation is used in connecting each side of the square with an X in its center. This adds considerable strength to the structure. 35

42 Figure 39 - Weight Support Frame The frame is connected to the Biodex frame by two large THK precision slides which allow motion in the Z-direction (vertically, up and down). These slides support all moments and allow only linear displacement of the weight support frame. On the underside of the frame, two THK slides are fixed to the forward and rear legs of the square portion of the frame. These slides allow motion in the Y-direction (side to side). They experience only a force normal to the slide s mounting surface. These slides are connected by an aluminum member which supports a final THK slide which allows movement in the X-direction (fore-aft). Like the Y-direction slides, it experiences only a normal force. The aluminum member housing the final slide presents a problem in connecting the two Y-direction slides. If the member were hard mounted to each slide, alignment of the slides would have to be nearly perfect for the slides to function smoothly without binding. Tolerances this tight (parallelism within.001 in/ft) are not reasonable in the construction of a welded fixture of this type. Furthermore, even the small deflections under loading inherent in any mechanical system could through off alignment enough to cause binding. FEA has shown that the frame can deflect as much as.032 inches under expected loading conditions. To solve this problem a misalignment sub-system is implemented which is shown in Figure

43 Figure 40 - Misalignment Sub-System The aluminum member is hard mounted to the rear slide only. The front slide is attached to a plate with a heim joint hanging from the center. Heim joints have a swivel joint which allows for a relatively high degree of misalignment. The free end of the aluminum member has a pin pressed into its center. The pin is free to slide through the heim while the joint allows misalignment in any direction as required by the nature of the design. This solves any binding issues in either the case of tolerancing or deflection. The entire frame is supported from its center by the chord which leads to the weight support spring and winch. This portion of the weight support system is unchanged from Version I. The patient is connected to the final THK slide via a cord and harness. The weight support frame moves up and down with the patient while allowing him to move freely front to back and side to side. This accomplishes partial weight support while allowing freedom of movement in the traverse plane as is encountered during normal gait CORONAL DISPLACMENT SYSTEM The Coronal Displacement System allows a force field to be applied to the pelvis of the patient. This system begins with a triangular steel structure shown in Figure 41. A plate is mated flat to the outside of the Biodex frame. A piece of 2 x 3 x 3/16 thick rectangular 1018 steel tubing is attached to the top of the plate and is situated perpendicular to the Biodex frame. A piece of 2 x 2 x 1/8 thick square tubing connects both the plate and the rectangular tubing forming the hypotenuse of the triangle. This arrangement of the members creates a strong structure by keeping the parts primarily in tension and compression and out of bending. 37

44 Figure 41 - Coronal Displacement System The fixture is mounted to the frame with bolts through the plate. There is an identical plate on the opposite side of the vertical member of the Biodex frame to which the triangular fixture is mounted. The Biodex frame is in the grip of the bolts and plates. There are heavy duty, telescoping slides attached to either side of the rectangular tubing. These allow movement in the Y-direction. The ends of these slides are coupled together by a rail to which a THK slide is affixed which allows motion in the X-direction. Linear motors are attached to these slides. The motors are actuated in the Z-direction and are responsible for the application of a force field. The corrections are applied in the coronal plane. The key aspect of each component in the Coronal Displacement System is rigidity. This provides safety for the patients and allows the system to function properly. Any deflection of the components degrades the system s effectiveness by creating error in measurements HANDLE ASSEMBLY Because motors are mounted very close to the patient s hips, it is not possible for him to swing his arms by his side. To account for this a specialized handle was implemented (Fig #). 38

45 Figure # While the patient holds the handle he is able to walk normally despite the location of the motors. The handle is adjustable both vertically and horizontally. A quick release cam system allows for easy adjustment up and down. Horizontal motion is accomplished by two lengths of box tubing on each side with one sliding through the other. The position can be fixed by a ball plunger which is attached to the inner tube which fits into incremental holes in the outer tube. The handle is mandrel bent to allow for a comfortable hand position. Each hand can be rotated up to 45 degrees off horizontal making positioning of the hands much more ergonomic. 39

46 4.2 COMPONENT SPECIFICATIONS Linear slides are used throughout the system to allow motion in designated planes. The specification of each of these slides is very important in preventing mechanical failure as well as ensuring accurate system controls. A person weighing 400 lbs was used as a worst case scenario. A factor of safety of 2.5 was chosen to be used for all calculations for slide selection DYNAMIC WEIGHT SUPPORT SYSTEM Each linear slide in the dynamic weight support system undergoes different loading conditions. Calculations were completed to identify all possible loads for worst case scenarios. Loads shown Figure 42 - THK Rail Loads Figure 42 were considered when completing rail analysis. The results of the rail analysis can be viewed in Table 2. The highlighted load is the determining factor when choosing the actual model. Slide lengths Table 2 - Rail Analysis Results Vertical (Z-axis) Frame Rails (2X) mm Required Rated Loads Model # : SHS 35C M a : knm M a : 1.36 knm M b : knm M b : 1.38 knm M c : N/A M c : 1.53 knm P T : N/A P T : 96.6 kn P R : N/A P R : 96.6 kn P L : N/A P L : 96.6 kn Sagittal Plane (X-axis) Rails (2X) mm 40

47 Required Rated Loads Model # : SHS 15C M a : N/A M a : knm M b : N/A M b : knm M c : N/A M c : knm P T : N/A P T : 24.2 kn P R : N/A P R : 24.2 kn P L : 2.224kN P L : 24.2 kn Coronal Plane (Y-axis) Rail mm Required Rated Loads Model # : SHS 15C M a : N/A M a : knm M b : N/A M b : knm M c : N/A M c : 0.16 knm P T : N/A P T : 24.2 kn P R : N/A P R : 24.2 kn P L : kn P L : 24.2 kn were not a concern when specifying rail systems. Rail length is independent of loading conditions and can be chosen to be any length during any point in the selection process CORONAL DISPLACMENT SYSTEM A telescoping slide is necessary in the coronal plane to allow the patient to translate side to side. Two slides are used on either side of the structure for a total of four telescoping slides. The pair of slides is used to add overall strength to the cantilevered structure as well as reduce the amount of torque that the coronal displacement system experiences. The necessary slide stroke is determined to be 15 inches. A load rating of 1000 lbs (400 lbs person, factor of safety of 2.5) was needed for a dynamic load rating. Each pair must be able to support the dynamic load rating in the case that the patient falls to one side. Each slide must have a dynamic load capacity of 500 lbs. The fore-aft slides were specified using the same process as mentioned in section

48 4.3 COMPONENT SELECTION THK offers a number of different major types of linear motion guide systems. The three basic types include: Caged Ball, Caged Roller, and Full-Ball Type. Use of a caged ball system eliminates friction between balls, and achieves low noise, acceptable running sound, long-term maintenance-free operation, and superbly high speed response DYNAMIC WEIGHT SUPPORT SYSTEM The SHS sub-type of the caged ball section was chosen to be able to be used in all directions. This is possible since each row of balls is arranged at a contact angle of 45. The vertical (Z-axis) frame rail bearings are SHS 35C with a rail length of 330mm. This rail length was matched to the motor stroke. The saggital plane (x-axis) rail bearings are SHS 15C with a rail length of 460 mm. This rail length was chosen to match the existing rail lengths on the coronal displacement system. The coronal plane (Y-axis) rail bearing is SHS 15C with a rail length of 370 mm. This rail length was chosen by determining the maximum y-axis translation of the patient without falling off of the treadmill CORONAL DISPLACMENT SYSTEM Telescopic slides with the desired stroke length were found available from McMaster. The dynamic load capacity of the slides far exceeds the specifications. Inherently, this means heavier slides but no weight constraints are present in the design. Part number 8379K13 from the McMaster catalog is the telescopic slides that are used. The existing THK bearings from Version I for the fore-aft motion are used on version II with the same overall stroke. 42

49 4.4 STRUCTURAL ANALYSIS In any design project it is crucial to begin structural analysis before any actual fabrication takes place. This allows the designer to see critical points within the current concept saving both time and money. In any kind of mechanical structure the best source of structural analysis is found in finite element analysis. If a computation model exist, advance computer programs such as Ansys, Algor, or Abaqus, can take the model and break it down into a specific number of elements defined by the user. As element size decreases, the net number of elements increases; as element size approaches zero the number of elements approaches infinity which would theoretically create a solid model. In other words, the more elements that are used, the better the computer model will be. This process of breaking down a model into smaller dependent elements is called meshing. It is an absolutely necessary process in finite element analysis and is often the restricting value in structural analysis. Fine meshes can contain thousands of elements so designers are limited by the power of the computer FINITE ELEMENT ANALYSIS For the stress and displacement examination of the Weight Support frame, Ansys 10.0 was used to do all of the finite element analysis. Ansys is a program that can do thermal, magnetic, and electrical analysis in addition to FEA. The first step in Ansys is to define an imported part as a structural figure and define its element type. Deciding on the proper element type can be difficult. A general element form to use for a solid 3-D structure is Solid, Brick 8 node. In Ansys this is defined as SOLID185 which was used with a Modulus of Elasticity of 30 x 10^6 pounds per square inch. SOLID185 is used for the 3-D modeling of solid structures that do not contain thin planes. It is defined by eight nodes having three degrees of freedom at each node: translations in the nodal x, y, and z directions. For the actual meshing of the part the Ansys MeshTool was used. In the MeshTool the smart size option was implemented with a size of ten. A size of ten is a good mesh for this part, it is composed of over 100,000 elements after meshing. The different elements that compose this part can be seen in Figure #. This large amount of elements makes for an accurate model resulting in precise FEA calculations. In Ansys characteristics of the system are defined before the linear system is solved. Areas of zero displacement and load types are defined by the user in the preprocessor functions. For the weight support, the square lateral plates which connect the weight support to the rails on the Biodex frame were defined as having zero displacement. These areas were limited in Ansys to have zero displacements in space along the x, y, and z coordinate axis. It was determined that the Version II S.A. Trainer would be designed with a factor of safety of 2.5. It was also assumed that a user of 400 pounds would be used to test the device at severe limits; therefore, the loads applied to the weight support frame were 1000 pounds (400 x 2.5). One 1000 pound force was applied as a point load at the center of the frame (wire which connects frame to spring) and one 1000 pound force was applied as a point load at a corner of the frame in the opposite 43

50 direction. Figure 43 shows how the loads and displacements are defined. This is an extreme exaggeration for two reasons: point loads were used to embellish the force because actual forces will be distributed pressure loads, and the frame will never encounter 1000 pound. This device is intended for human use so it is imperative to design for safety at every step. Figure # - Weight Support Element Count Figure # - Load Placement on Weight Support Frame 44

51 The Motor Bracket is the other part in the system which may encounter extreme loads (if failure were to occur) so it is important to model this piece in Ansys as well. The S.A. Trainer contains two motor brackets, one for each actuator. The bracket must be capable of supporting the motor plus half the weight of the patient within the guidelines of a factor of safety of 2.5. The motor brackets will be fabricated from 6061 Aluminum which has a Modulus of Elasticity of 10,000 KSI. An element type of Solid, Brick 8 node (SOLID 185) is also implemented on this part. A very fine mesh can work on the Motor Bracket, MeshTool size 3 is used, which corresponds to the creation of over 17,000 elements. The four tapped holes which connect the Motor Bracket to the S.A.Trainer have zero displacement in Ansys. A force of 500 pounds is applied even amongst the area of the four tapped holes which connect the Motor Bracket to the Linear Actuator. Figure # shows how the loads and displacements are defined and Figure # shows the element count for the Motor Bracket. Figure # - Motor Bracket Element Count Figure # - Load Placement on Motor Bracket 45

52 4.4.2 ANALYSIS RESULTS The Weight Support frame went through the computational analysis and successfully held up to the applied stresses. The first output checked was the Von Mises stresses in the x, y, and z directions. Figure 44 shows the Von Mises stress distribution for the weight support frame. The highest stress the frame ever encounters is characterized by a teal color. This color is defined by a stress that falls between pounds per square inch and pounds per square inch. The Weight Support frame will be fabricated with mild steel, specifically ½ inch box with a 1/8 inch wall thickness steel has a yield point of 50 KSI. The resulting stresses are well under the yielding point and with just this info it would be tempting to change the design to avoid over designing. However, the plot of the displacements shows how the part will distort under the applied forces and this magnitude of displacement illustrates that the part was not over designed. As stated earlier, displacement of the parts must be avoided at all cost to ensure a rigid body design for controls purposes. Figure # - Stress Distribution of Loaded Weight Support Frame Displacement of the Weight Support frame was an important analysis which truly exemplified that the frame had been designed correctly. The plot of the displacement can be seen in Figure #. The displacement in Ansys is magnified so the designer can visually make note of the changes. The Coronal plane of the frame has a length of 18 inches while the maximum displacement of the frame is approximately 30 thousandths of an inch. The maximum displacement occurs at the corner where the point 46

53 load was applied as expected. The maximum displacement is inches. A movement of 30 thousandths of an inch is a tolerable displacement but any higher would be unacceptable. Figure # - Net Deflection of Loaded Weight Support Frame The Motor Bracket went through the computational analysis and successfully held up to the applied stresses. The first output checked was the Von Mises stresses in the x, y, and z directions. Figure # shows the Von Mises stress distribution for the Motor Bracket. The highest stress the frame ever encounters is characterized by a red color. This color is defined by a stress that theoretically falls between 40,000 pounds per square inch and 83,496 pounds per square inch. This stress is pinpointed at two tangential moments on the radius of the (upper) tapped holes. The part does not actually reach these stress levels, the jump in stress is a result of Ansys trying to quantify loads that are applied as points when in reality they are disturbed evenly. The weight support frame will be fabricated with an Aluminum alloy, specifically /8 of an inch thick Aluminum has a yield point of 40 KSI. 47

54 Figure # - Stress Distribution of Loaded Motor Bracket Displacement of the Motor Bracket is an important analysis to make sure the bracket is rigid enough for use with a real-time control system that can accurately measure force and movement. The plot of the displacement can be seen in Figure #. The highest displacement naturally occurs at the furthest corner from the areas of zero displacement. The maximum displacement is defined by red shading and corresponds to inches. This is an acceptable unit of displacement based on the tolerances of the overall system and the motor specifications. Figure # - Net Deflection of Loaded Motor Bracket 48

55 4.5 CONTROL SYSTEM The objective of the control system is to provide a force field around the sinusoidal motion profile that represents ideal ambulatory motion. This force field will resist abnormal movements in the patients gait profile as they deviate from this ideal profile. This was done by determining an ideal motion profile that is specific in amplitude and frequency and synchronizing it to the patient s trajectory profile. This sinusoidal profile was then set as the nominal position of the actuator thereby creating a dynamic nominal position. With this profile as the base, a control system will create a linearly increasing resistive force on the patient as they deviate further from this dynamically changing nominal position. As mentioned above, accurate control of pelvic motion during gait training requires a model, or ideal motion profile, by which to compare the patient s motion profile. Even the gait profile of a healthy subject will not conform to a single sine wave due to changes in stride length, frequency and inconsistencies in stride kinematics. Therefore, a sinusoidal wave will be the theoretical template for all patients but will never be truly obtained. At the start of each therapy session the patients gait profile will be recorded in order to determine the specifics of there abnormality. This data will allow the therapist to prepare a proper training session and track the patient s performance. The collection of this data was done using the internal position encoders in the actuators. During this process the linear actuators do not apply a force field; however they will be in a back-drivable state which allowed the subject to ambulate with minimal interference. An abnormal gait pattern is difficult to define because it too does not follow a simple sinusoidal wave and can have different nominal positions from the left to right side. This presents an interesting challenge when developing one control system that can incrementally correct all possible abnormal gait patterns. These abnormalities will be discussed below to identify the demands on the control system. Ambulatory motion will be characterized by the motion of two points, one on either side of the pelvis (Right and Left). Ambulatory abnormalities, when represented as a function of time, can be compiled into four groups with right and left pelvic motion profiles having: 1.) Same Amplitude and Same Nominal Position Figure # (a) 2.) Same Amplitude and Different Nominal Position Figure # (b) 3.) Different Amplitude and Same Nominal Position Figure # (c) 4.) Different Amplitude and Different Nominal Position Figure # (d) 49

56 Abnormal wave forms in Figures 46 are approximated as sinusoidal waves to illustrate the combinations of amplitude and nominal position listed above. Left Right Position Time Figure # (a): Same Amplitude and Same Nominal Position Left Right Position Time Figure # (b): Same Amplitude and Different Nominal Position Left Right Position Time Figure # (c): Different Amplitude and Same Nominal Position 50

57 Left Right Position Time Figure # (d): Different Amplitude and Different Nominal Position It is important to note that the intent of this design is not to force the patient to conform to an ideal profile, but to assist the patient in incrementally achieving a similar gait. This will be done by nudging the patient with linear actuators until the desired motion profile is met. This process may take a number of sessions before it is completed. A closed-loop control system must be designed to drive these actuators in real time. This system will eliminate the need for a physical therapist to directly interact with the patient during gait training but will still require management by the therapist CONTROL ALGORITHM Development of a control system is necessary to bring the S.A. Trainer into the human testing phase. The block diagram illustrates what the basic control loop looks like (Figure 47). Based on the motion profiles discussed earlier, a control algorithm has been created and implemented in order to properly control the actuators. This algorithm will compare the position of the patient s pelvis to the optimal position. The two pelvic control actuators are at the heart of this system. They are represented in Figure 47 by the block labeled Actuator System. These actuators demand the most scrupulous control as the function and safety of the system depends on it. The input to the control algorithm is the ideal motion profile previously discussed. As the profile of the patient deviates from this profile due to abnormalities in thier gait, the first comparator quantifies this deviation. This deviation is in the form of position error until it is converted to force by a simple calculation labeled Force Field Factor resulting in a signal representing the desired force. This force is then compared to the actual force providing a second error in the form of force. This error is then sent to the PID controller which adds positive corrections. The signal is then sent to the actuators and a force is applied to either side of the patient s pelvis which results in an alteration of there original motion profile. Therefore if the patient deviates from the optimal motion profile a force will be applied apposing the direction of deviation. This force will act as a resistance, urging the patient to conform to normal ambulatory motion. It is in this way that abnormalities in the patient s gait can be 51

58 reduced or even eliminated. The therapist managing this process has the ability to alter the amount of resistance per unit of deviation through the software s user interface. Figure # - Basic closed-loop control system 52

59 4.5.2 HARDWARE In order to implement the controls previously discussed, numerous sensors, amplifiers, and an acquisition board must be used. Figure 48, is a schematic of all of the hardware that was used for the control of the force field. Figure # Hardware Schematic Two Servo Tube Actuators will be used to apply resistive force to either side of the patient s pelvis. The motors used are backdrivable, electro-magnetic linear actuators. These motors consist of a shaft that is comprised of stacked magnets. This shaft floats inside a stator cylinder wrapped with copper wire. When no current is passed to the motor, the motor is essentially in neutral requiring little force for the magnet stack to pass through the stator. 53

60 Should the actuators provide too much resistance to movement when they are not engaged they could alter a proper gait pattern. Because of this it was necessary to continuously drive the actuators even when gait is correct. It is for this reason that continuously back-drivable actuators were chosen for this application. Figure # - Chosen Copley Control servotube motors These motors (shown in figure 49) were chosen from Copley Controls to work with the desired mechanical specifications including stroke, maximum force, and overall dimensions. Specifications for the family of the linear electro-magnetic actuators that the chosen motor belongs to can be seen in Table #. Table #: Motor Specifications These actuators feature built in position sensors. It is these position sensors that will allow for the detection of the patient s motion profile during gait training. The power for driving these actuators will come from the Zenus digital amplifier. This amplifier directly interfaces with a canopen card in a personal computer. This computer acts as the user interface for the actuator/drive assembly. All software to run the servo system will be created in LabView. The amount of force that the actuators apply to the patient s pelvis is controlled using a closed loop system with a load cell as the feedback sensor. The low voltage signal created by these load cells will be amplified by two Honeywell in-line amplifiers (Model UV-10). The amplified signal is then converted to a digital code by a Analog to Digital PCI. 54

61 In order to assure accurate control of loading, calibration curves were created for the load cells with the input in units of force and an output in units of voltage. This was done by applying known loads to the load cells with an Instron Machine. This was repeated for compression as well as tension. These curves can be seen in figures # and #, below. Compression Calibration Curve Voltage Output (V) y = x R 2 = Compression Load (lbf) Figure #- Compressive Calibration Curve for Load Cell Voltage Output (V) Tensile Calibration Curve y = x R 2 = Tensile Load (lbf) Figure #- Tensile Calibration Curve for Load Cell 55

62 From these calibration curves it can be seen that the sensitivity of the load cell used was roughly V/lbf. This information allowed the conversion from voltage to load in order to produce an output in the user interface with the proper units. These curves also provided R 2 values indicating that the load cells used were performing in a linear manor. When looking at the motion profile, created by the position sensors, it is difficult to determine where crucial components of the gait profile occur. To determine where these physical events occur during the patient s motion profile, four FSRs will be used. One of these sensors will be placed under the heal of the patients foot and the other under the ball of the foot. These FSRs will produce a pulse of energy every time they are loaded above a certain threshold. By placing these sensors in the patient s footwear the resulting pulses can be amplified and read by software. It is then possible to indicate where the patient is in their motion profile at anytime during training. Each time the patient s heel hits the ground (heel strike) a pulse will be produced by the FSR. This is a beneficial tool because it allows the user as well as the control program to know where key phenomena occur in a signal gate cycle with respect to when the pulse occurs. The low amplitude pulse from the FSRs will be amplified using Op-amps. This amplified signal is them sent to the same 16 channel, analog to digital board that was used with the position sensors. A single potentiometer controls the threshold for all four of the FSRs. By changing the threshold one can change the force required to trigger the FSRs SOFTWARE To use the information provided by the sensors, a software package was created in LabView. This program is a key component of the control system because it contains the control algorithm that executes the control loop discussed earlier. The program also act as a user interface accepting inputs that control key parameters, such as the PID gain, and providing graphical representations of the patient s progress both during a single training session and through several sessions. Figure #, is a snapshot of the user interface. As seen, it contains graphical outputs for both current trajectory and target trajectory. It also provides graphical indication of location of the patients heal strike as indicated by the FSRs. There is also outputs for loading and controller output in graphical form. To the left of the graphical indicators is an indicator for the position of the shaft with respect to its nominal position. On the lower left of the interface are three numeric inputs controlling the gain of the PID controller. 56

63 Figure # Labview Interface 57

64 CHAPTER 5 FABRICATION AND ASSEMBLY 5.1 SYSTEM FABRICATION A goal during the design of Version II was ease of manufacturability. With this in mind, a conscious effort was made to eliminate the need for CNC machined parts and exotic materials. The structure consists of parts, assemblies and weldments fabricated of T Aluminum and 1018 mild steel. Designed parts for the S.A. Trainer Version II require machining work using both a manual mill and lathe. Steel and Aluminum are commonly machined materials with this equipment. Correct feeds and speeds are known for these machines and will be used throughout the machining process. Figure # - Milling on Bridgeport Both the dynamic weight support system and coronal displacement system call for welding of mild steel. The dynamic weight support frame is Tungsten Inert Gas (TIG) welded. This is done on the structure for strength and reliability of a non-tooled frame. TIG welding requires less filler wire and has less heat affected area than Mixed Inert Gas (MIG) welding. A 2-percent-thiorated tungsten electrode is used as well as ER80S-D2 filler wire. All joints were thoroughly prepared by wire brushing followed by cleaning with acetone. This eliminates the possibility of unwanted contamination during the welding process. A suggested pre-heat of 70 degrees Fahrenheit was followed during all TIG operations. Figure # - TIG Welding on Aluminum Surface 58

65 Bending Section Figure # - Mandrel Bending 59

66 CHAPTER 6 FINANCIAL ANALYSIS 6.1 PROJECT FINANCES The cost of the S.A. Trainer II is comprised of three separate subsections: controls, mechanical materials, and mechanical parts. The majority of the cost of the device was in the controls sections. The sponsor, Spaulding Rehabilitation Hospital, covered a large portion of the controls hardware as well as the linear bearings from THK. The remaining costs are paid for by the Northeastern University Capstone department. All of the components purchased for this device were found at Honeywell, Copley Controls, Turner Steel, McMaster, Motion Industries, and Carr-Lane. The costs for the Controls, Mechanical Materials, and Mechanical Parts are $3,919, $412.90, and $2, respectively, totaling $6, Table # - Financial Total The total purchased parts order of $6, encapsulates the entire cost of the device. Vocational labor including machining and welding was completed by design team members. The full Bill of Materials including machined parts can be seen in appendix (LETTER). 60

67 7.1 INITIAL HUMAN TESTING CHAPTER 7 TESTING Human testing was conducted on Version II of the S.A. Trainer after extensive analysis was completed to ensure safety of the patient. The purpose of this testing phase was to prove functionality from both a mechanical as well as controls perspective. Results from these tests indicate that Version II of the S.A. Trainer meets all of the criteria initially set forth. A healthy patient was placed in the Orthomerica Newport 4 Hip Brace. The right side of the brace was connected to the right actuator via the load cell connection assembly. The dynamic weight support system was not connected to the patient during this testing phase because it has little or no influence on a healthy patient s gait profile. Testing was divided into three subsections: passive, back-driven, and active. In the passive mode, the motion profile of the patient was captured and frictional forces from the motor and mechanical system were obtained. When back-driven, the frictional forces previously mentioned are virtually eliminated by tuning the PID controller in software. When the system is active, the force field is applied to the patient. This active system testing measures the effectiveness of the overall functionality of the system. The patient was asked to ambulate following two different trajectory profiles including normal gait and an abnormal gait profile mimicking hip-hiking. Figure # shows the patient ambulating normally to capture motion profile data. Figure # - Recording Patient Motion Profile 61

68 The mechanical and controls system can be seen in figure #. The patient has a clear view of the graphical user interface and control system. On observation that was made during this phase of testing was that the patient was able to achieve a motion profile closer to the ideal profile when they have the ability to visualize the profile by interaction with the Graphical User Interface (GUI) themselves. Figure # - Mechanical and Controls system in Sync This testing phase provided a significant amount of information about the functionality of the system. As mentioned in the controls section of this report the objective of the control system is to provide a force field to the patient s pelvis opposing abnormal motion with respect to a predetermined ideal motion profile. Figure #, below is a graphical representation of a healthy patient s profile with respect to the ideal profile. For this test we set the ideal profile to represent hip hiking in order to magnify the deviation of the subject s profile. By doing this relatively large forces were applied to the subject s pelvis. These forces are graphically represented in figure #. It should be noted that as the deviation between the ideal and actual motion profile increases so does the applied force. This shows that both the controls as well as the components of the control system are functioning appropriately. 62

69 Figure # - Motion Profile of Actual Gait versus Ideal Gait Figure # - Load Testing 63