ON A MECHATRONIC SYSTEM TO DETERMINE DYNAMIC PARAMETERS OF THE HUMAN LIMB DURING LOCOMOTION USED FOR ARTIFICIAL MUSCLES AND IMPLANT DESIGN

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1 6th International DAAAM Baltic Conference INDUSTRIAL ENGINEERING April 2008, Tallinn, Estonia ON A MECHATRONIC SYSTEM TO DETERMINE DYNAMIC PARAMETERS OF THE HUMAN LIMB DURING LOCOMOTION USED FOR ARTIFICIAL MUSCLES AND IMPLANT DESIGN Roşca, I.C. & Radu, C. Abstract: The design of a medical implant or an artificial muscle assumes previously some complex kinematic and dynamic studies of the interested anatomical system. In this way, in the firs part of our study, in the proposed paper On the design of the analytical ankle foot model used to determine dynamic parameters during locomotion, we have analysed from analytically point of view the ankle foot system during human locomotion and we have determined the dynamic and kinematic parameters, which are used to design artificial muscles and medical implants. Thus, this paper treats some experimental aspects concerning the conception of a mechatronic system used to determine the dynamic and kinematic parameters: ground reaction forces, linear accelerations respectively the angles between anatomical segments. Key words: force plate, video camera, artificial muscles, medical implants, mechatronic system. 1. THE METHODOLOGY OF THE EXPERIMENTAL INSTALATION 1.1 Experimental objectives The design of artificial muscles and medical implants assumes previously some complex kinematic and dynamic studies of the interested anatomical system. The biomechanical analytical modelling of the ankle foot anatomical system is based on inverse dynamic method, which was presented in the previous paper work: On the design of the analytical ankle foot model used to determine dynamic parameters during locomotion. Using this technique, we have written the analytical equilibrium dynamic equation of human foot during locomotion. Solving these equations, we have obtained some unknowns, such us dynamic and kinematic parameters. In this case, ground reaction forces and foot s linear acceleration and velocity represent the dynamic parameters. For kinematic parameters, the unknowns are: the angle between foot and ground and the angle between centre line which passes through ankle joint and shank. Also, for a complete biomechanical analyse we have decided to determine the trajectories of lower limb s joints during normal walking. Afterwards, these data can be used to determine the ankle joint reaction forces that will help to design artificial muscles and medical implants. 1.2 Measuring methods Biped human locomotion is a phenomenon that progresses in real time, so it s necessary to chose a right method to be concluding in this way [ 1 ]. Since we try to qualitative analyse some continuously and successive positions of lower limb s joints during normal walking, it s necessary a high precision visual analyse. Once, human eye can perceptible for a distinct number of 24 different frames per second (for 24 frames per second the images will be in continuously movement), it s necessary that the tracking to be made to a high speed frequency that is comparable with locomotion speed and then to bring it close to the normal observation frequency of human eye [ 2 ].

2 Considering these, we have chosen a video method, called high speed video method, which consist in continuously video recording of the human subjects during normal locomotion ( km/h) on the force plate, followed afterwards by image discrete quantity which succeed in 1/125 frames per second. The discrete frames can be edited using image edit software, finally to obtain the successive positions of the markers, which are positioned in the lower limb s joints (hip, knee and ankle joints), hell and the second metatarsal s pick [ 2 ][ 3 ]. Beside that, it s necessary to obtain dynamic parameters (ground reaction forces, foot linear acceleration) and kinematic parameters (the angles between foot and ground and the angle between centre line which passes through ankle joint and shank). To do that, we have coshed a very precise method that uses following devices: a Kistler force plate with it s associate software BioWare, a digital goniometer and two accelerometers with their associated software AcqKnowledge [ 1 ][ 2 ]. All these methods have been used for a complex analyse, from the biomechanical point of view, the human locomotion in normal conditions. In this way, we have determinated the dynamic and kinematic parameters for all lower limb s segments, such as: tight, shank and foot segment. For our necessity we have extracted only the parameters that we needed for the present study (foot s dynamic and kinematic parameters) and we have used them to design artificial muscles and medical implants. 2. THE PROCESS DESIGN OF THE MECHATRONIC SYSTEM To determine the ankle joint reaction forces is necessary to know the dynamic and kinematic parameters. From this point of view, it s necessary to design an experimental installation that can help as to determine these unknowns. This experimental installation, which is presented in figure 1, is compound from: a Kistler force plate, a signal amplifier (Kistler type), two acquisition cards (PC CARD type), two accelerometers TSD109C, a digital goniometer TSD130A, a high speed video camera (Trouble Shooter) with three light sources, five markers and a central acquisition system (Dell laptop) [ 2 ]. a) b) Fig. 1. a) The mechatronic experimental installation used to determine the dynamic and kinematic parameters of human foot during locomotion: a) schematic view; b) picture of the experimental installation [ 2 ] 2.1 Kistler force plate Kistler force plate is a device that enables measurement of the total vector force (F m ) manifested in a various locomotor activities during contact between the subject s body (typically the foot) and the

3 surface (floor) in which the device is embedded (see figure 2) [ 1 ]. This device can be used dynamic conditions, to study human locomotion and in static conditions, to study the human body stability, by measuring the centre of mass displacement. Kistler plate is equipped with four piezoelectric sensors, positioned on each plate s corner (see figure 2). These sensors transform a mechanical action (the human foot force which acts on the plate) in an electrical signal, without any external energy source. Each of these sensors contain three annular discs, piezoelectric sensible to compression forces (F y ) and shearing forces (F x, F z ) [ 1 ][ 5 ]. mounting supports can do eventual corrections. To eliminate the step effect between plate s contact area and ground area, has been used two wood platforms of 760 x 360 x 35 mm in size, placed on both sides of the force plate. The contact between wood platforms and force plate is made by a tampon material (expanded polystyrene) to enable truly non-invasive vibration introduced by the human subject during walking (see figure 3). Fig. 2. Kistler force plate used to measure ground reaction forces in static and dynamic conditions The force plate s accuracy to measure forces on the horizontal and vertical directions is 1% and a sensibility up to 0.005Pa, in a work domain of kpa on vertical direction and kpa on horizontal direction [ 5 ]. The instrument s contact area is a rectangular plane usually 600 x 400 mm in size embedded on a firm, substantial base. The main condition that the plate s surface has to accomplish is plan parallelism condition. The platform s surface was obtained by auto level coating cement covered by linoleum carpeting to enable truly non-invasive measurements. Planparallelism deviation of the surface s platform assumes a maximum values of Δp = ± ( ) mm [ 1 ]. The Kistler force plate s ground level of verified using a level device, and adjusting the plate s Fig. 3. The assembly formed by the Kistler force plate, two wood platforms and the tampon material Under the external force induced by the subject, the piezoelectric sensors deform themselves transforming the mechanical action into the electrical signal. This signal, initial in milivolts, is received and amplified by the signal amplifier [ 1 ]. The amplifier has the roll to transform the output data of the pressure sensors into the tension standard signals (tension between ± 1V and ± 10 V with low impedance), to effectuate the compensation of the sensors characteristics and to limit the frequency to the exact domain [ 5 ]. For the conversion of the analogue/digital signals we used two acquisition boards, respectively PC CARD DAS 16/16 and PC CARD D24/CTR3 [ 5 ]. 2.2 TSD109C accelerometers The TSD109C accelerometers are highly electrical transducers, which measure simultaneously linear accelerations up to ± 5g, in the Ox, Oy and Oz axes (figure 4) [ 4 ].

4 For this experiment we have used two accelerometers, one for the foot s segment and other one for the shank, to measure the segment s linear acceleration only for two axes, Ox respectively Oy, that because our working plane is sagittal plane (xoy plane). Before starting the experimental tests, both accelerometers have been calibrated for each measuring axis. By calibrating these accelerometers, we have determinated normal voltage, for each measuring axis, for a gravitational acceleration of 1g [ 4 ]. measure bending strain along or around a particular axis, transforming angular position into a proportional electrical signal. The bending strain is proportional to the sum of the total angular shift along the axis. Because the bending force is extremely small, the output signal is uniquely a proportional function of the angular shift [ 4 ]. Fig. 6. TSD130A goniometer Fig. 4. TSD109 accelerometer First accelerometer is placed on the foot s posterior side, in mass s centre of foot, respectively 56.06% of total foot s length, from distal point (metatarsal extremities). The second accelerometer is placed on the shank s lateral side, in mass s centre of shank, respectively 50.85% of total shank s length, from ankle s centre of rotation (see figure 5) [ 2 ]. Before starting the experimental tests, we have calibrated the goniometer. In the first phase, the calibration has been done for foot s initial angular position (human subject is in a orthostatic position), which in this case is 0. In the second step, the calibration has been done for the foot s final position of 30 (maximum extension of foot during human locomotion). One part of the goniometer (extensible part) is placed on the foot, closed to the heel and the other part (fixed part) is placed on the shank s segment, as shown in figure 7. For this experiment the goniometer is used to measure the angle between centre s line that passes through ankle joint and shank, in sagittal plane (xoy), during human locomotion. Fig. 5. The placement of accelerometers on the foot and shank segment 2.3 TSD130A goniometer The TSD130A goniometer is an electrical transducer, designed for the measurement of limb angular movement (figure 6). This device incorporates gauge elements that Fig. 7 The placement of goniometer on the anatomical interest area

5 2.4 TroubleShooter high-speed camera High-speed video camera is a device that allow user to analyse video processes in a very short time. This video camera records an image clip with a higher speed then eye can do and afterward plays it back in a very short time, allowing users to observe, to measure and to analyse the events [ 1 ][ 3 ]. TroubleShooter video camera (see figure 8) is produced by Fastec Images Company, and has a maximum video resolution of 640 x 480 pixels and a record speed of 25 to 500 frames/second in normal conditions. limb s joints trajectories and the angle between foot and ground, during human locomotion [ 2 ]. 2.5 Light markers In this experiment, the light markers are used in combination with a high-speed camera, to determine kinematic parameters of lower limb s joints. There are five markers, which are placed on the hip, knee and ankle joint, on the heel and the second metatarsal s pick (see figure 9) [ 1 ][ 2 ][ 3 ]. Fig. 8. TroubleShooter high-speed video camera and light source Video camera was embedded on a tripod, perpendicularly on the human subject s movement direction, on an optimal distance of 3.5 m. This distance permits a good visualisation of the human subject from chest s level down and implicit correct visualization of all markers mounted on the lower limb [ 2 ]. Minimum illumination for a recording rate of 25 frames/second and a maximum resolution of 640 x 480 pixels is 10 lux. The higher number of frames the higher illumination needed. For our experiment we have used a normal optical objective with a focal distance of 12 mm and a recording rate of 125 frames/second with a maximum resolution of 640 x 480 pixels. Because of that, we have used three light sources (halogen light) with a total illumination of lux [ 2 ]. Using this video camera and an image software editor (Adobe After Effects), it helps as to determine the lower Fig. 9. The placement of light markers on the hip, knee and ankle joint, on the heel and second metatarsal They have a spherical shape, with a 30 mm diameter and they were painted with a special paint, which is highly sensible to the halogen light. Also, the lower limbs of the human subject are dressed up in black-moulded pants that because the marker s colour is in highly contrast to the pant s colour [ 2 ]. For concluding results, the markers have to be placed exactly on the interest areas, more precisely the marker s centre has to coincide to the joint s centre off rotation, and heel and second metatarsal s markers have to be on the same axis. In advance, to determine the right position of each marker, we have made repetitive palpations of the anatomic areas. Anyway, the marker s placement is relative, that because it s impossible to determine the right position of the joint s centre of rotation and on the other hand because of the relative sliding between moulded pants and skin tegument [ 2 ].

6 3. CONCLUSIONS In the figure 10 are represented graphically some of the results obtained using the experimental system, which we designed. Ground reaction forces, foot s acceleration and velocity are obtained using BioWare and AcqKnowledge software and for light marker s trajectories and segment s angles we have used Adobe After Effects. 4. REFERENCES a) b) 1. Medved, V. Measurement of Human Locomotion, Congress Library.USA, Radu, C. Contribution to the prosthetic element by Rapid Prototyping - PhD thesis. Transylvania University, Brasov, Vaughan, C., L., Davis, B.,L., O Connor, J.C. Dynamics of human gait. Kiboho Publishers, Cape Town, BIOPAC System Inc. MP system hardware guide, 5. Kistler Group. Multicomponent force plate type 9286AA - data sheet ADDITIONAL DATA ABOUT AUTHORS c) d) Fig. 10 Some of the results obtained using the experimental system: a) ground reaction forces; b) foot acceleration; c) foot velocity; d) light marker s trajectories and segment s kinematic angles 1) Author names: Rosca, I.C., Professor and Radu, C., Lecturer. 2) Title of manuscript: On a mechatronic system to determine dynamic parameters of the human limb during locomotion used for artificial muscles and implant design. 3) Full address: Rosca, I.C., Professor of Mechanical Engineering Faculty, Fine Mechanics and Mechatronic Department, Transylvania University from Braşov; 29, Eroilor Avenue, Braşov, , Romania; tel: ; roscaileana@ yahoo.com; Radu, C., Lecturer of Mechanical Engineering Faculty, Fine Mechanics and Mechatronic Department, Transylvania University from Braşov; Barbu Lautaru, No. 13, Bl. 26, Sc. C. Ap. 15, Braşov, Romania; tel: ; ciprian1_radu@yahoo.com; 4) Corresponding author: Rosca, I.C., 29 Eroilor Avenue, Braşov, , Romania; tel: ; roscaileana@ yahoo.com.