Student projects on pneumatically driven musclelike

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1 Student projects on pneumatically driven musclelike actuators József Sárosi Attila Gergely Fabian Tölgyi Abstract Pneumatic artificial muscles (PAMs) or pneumatic muscle actuators (PMAs) have been commonly used in robotics and rehabilitation/prosthetic appliances for the disabled. This is because of their favourable properties such as high strength, good power/weight ratio, good power/volume ratio, low price, little maintenance needed, great compliance, compactness, flexibility, inherent safety and usage in rough environments. PMAs are contractile and extensional devices operated by pressurized gas, usually air. Similarly to human muscles PMAs are usually coupled antagonistically to generate bidirectional motion. This article describes two PMA actuated applications produced by our students. It primarily focuses on the design and construction of devices. Keywords pneumatic muscle actuators, Fluidic Muscles, hand therapy device, leg prototype, Autodesk Inventor I. INTRODUCTION Smart equipment and systems for mechatronic applications can be found in [1], [2], [3], [4], [5] and operational reliability of mechatronic equipment based on PMA is well described in [6] and [7]. The first investigations in PMA were done by a Russian researcher Garasiev in 1930 [8], [9]. Due to lacks in technology, the production was limited. In 1950, Joseph L. McKibben was the first who designed an artificial muscle for practical use in medicine. McKibben is often mentioned as the pioneer in PMA. In 1980, engineers in Bridgestone Co. in Japan produced the so called Rubbertuator PMA which was installed in the Soft Arm Robots [10], [11]. Recently, the most often applied are the Shadow Air Muscle (SAM) produced by the Shadow Robot Co. and the Fluidic Muscle developed by Festo Co. As PMAs are one-way acting, two are needed to generate bidirectional motion: as one of them moves the load, the other one will act as a brake to stop the load at its desired position. To move the load in the opposite direction the muscles change function. This opposite connection of the muscles to the load is generally referred to as an antagonistic set-up: the driving muscle is called the flexor or agonist, while the brake muscle is referred to as the extensor or antagonist. The antagonistic coupling can be used for either linear or rotational motion [12]. Different investigations of PMAs in antagonistic connection are well described in [13], [14], [15] and [16]. In the paper [17] another model for two direction motion is shown. It is a spring returned pneumatic artificial muscle which model contains a spring for bidirectional motion. Basically PMAs can be divided into three groups [8], [12]: braided muscles, netted muscles and embedded muscles. Braided muscles contain an elastic tube made of latex and silicone rubber, for example, and a surrounding helical shaped layer made from nylon, fiberglass or aramid along the muscle. If the muscle is pressed, the elastic tube acts radially on the layer and moves the load which is allocated on the muscle. Two types of braided muscle are usually applied: one, where both the tube and layer ends are fixed (e.g. McKibben type) and second, only the ends of layer are clamped. The maximum pressure is limited with the stiffness of the tube. If the pressure is too high, the tube gets out of the layer and the muscle bursts. The maximal contraction is approximately 25%. The difference between netted muscles (e.g. Shadow Air Muscle) and braided muscles is in the density of fastening threads in the membrane: it is higher for the braided muscles. In embedded muscles (e.g. Festo Fluidic Muscle) the loaded threads are settled into the elastic tube. This paper is organized in four sections. After Introduction, Section II illustrates a hand therapy device actuated by PMAs. In Section III, a leg prototype driven by pneumatic muscles is shown. Finally, conclusion and future work are summarized in Section IV. II. PNEUMATIC MUSCLE ACTUATED HAND THERAPY DEVICE Physical therapy is the primary means of rehabilitation and recovery for people having suffered a stroke. The design aims were to develop a simple device for improvement of hand function in stroke survivors. This project was carried out on the basis of [18]. The therapy device driven by two different PMAs (MAS (with inner diameter of 10 mm and initial length of 100 mm) and DMSP (with inner diameter of 10 mm and initial length of 250 mm)) produced by Festo Company (Fig. 1). The first one will move the wrist and the second one will move the fingers. 153

functions of these muscles are demonstrated in Fig. 2 [19].

thick) because of their light weight and workability.

It should be fixed in two places (at the upper phalanges and at the lower phalanges)

fixing the pneumatic muscles with two straps on the upper side of the forearm which

fixing the pulley with one strap on the top of the wrist (Fig. 6), 3.

Permissible force F [N] as a function of the contraction h [%] The therapeutic

2 Fig. 1. MAS (above), DMSP (below) Force-contraction (relative displacement) functions of these muscles are demonstrated in Fig. 2 [19]. The structure was made of aluminium (Al-Mg, 2 mm thick) and plastic (PVC, 3 mm thick) because of their light weight and workability. The hand has to be put into the device. It should be fixed in two places (at the upper phalanges and at the lower phalanges) with the next steps: 1. fixing the pneumatic muscles with two straps on the upper side of the forearm which depends on the patient's arm length (Fig. 5), 2. fixing the pulley with one strap on the top of the wrist (Fig. 6), 3. fixing the finger-mounted part with two straps (Fig. 7). Fig. 2. Permissible force F [N] as a function of the contraction h [%] The therapeutic device was designed in Autodesk Inventor. The virtual model of the finger holding tool and the completed tool that moves the fingers by a PMA can be seen in Fig. 3 and Fig. 4. Fig. 5. First step in fixing Fig. 6. Second step in fixing Fig. 3. Virtual model of the finger holding tool Fig. 7. Third step in fixing The whole hand therapy device is illustrated in Fig. 8. Fig. 4. The finger holding tool 154

Fig. 8. The wearable device for hand rehabilitation The therapeutic device is responsible for lifting and stretching the fingers and moving the wrist.

During this test a pressure of 6 bar was applied.

PNEUMATIC MUSCLE ACTUATED LEG PROTOTYPE The object of this project was the design and realization of a rudimentary humanoid leg prototype actuated by pneumatic muscles.

The frame of the leg was projected to be made out of Tecamid 4.6, however the first prototype's frame was made entirely out of wood.

3 Fig. 8. The wearable device for hand rehabilitation The therapeutic device is responsible for lifting and stretching the fingers and moving the wrist. The appropriate pressure which moves the hand to the desired range depends on the patient's condition. It is important to note that the test was carried out on a healthy man. During this test a pressure of 6 bar was applied. The finger and wrist movements have met our expectation, but the planned range of motion could not be reached because of the short contraction of the muscle. III. PNEUMATIC MUSCLE ACTUATED LEG PROTOTYPE The object of this project was the design and realization of a rudimentary humanoid leg prototype actuated by pneumatic muscles. Paper [20] illustrates how to model a human knee joint. The designing of the skeleton was integrally done in Autodesk Inventor. The 3D model of the prototype is shown in Fig. 9. The frame of the leg was projected to be made out of Tecamid 4.6, however the first prototype's frame was made entirely out of wood. The prototype's purpose was to make the movement visible and to measure certain parameters such as angle of rotation at certain values of pressure. The frame has two degrees of freedom: one found in the knee joint and one found in the ankle joint. Both of these joints permit movement in the sagittal plane. In both cases the axis of rotation was created by using an 8 mm steel bolt. Fig. 10 shows both the passive and active elements that make the movement of the knee possible. The section highlighted with 1 shows the Fluidic Muscle's anchoring point on the calf. The section highlighted with 3 shows the passive mechanism that allows the knee to return to its initial position. This movement was achieved by using two 0.07 mm thick spring steel plates. These steel plates were fixed to the tibia and move freely within the casing highlighted with number 2. The casing has a special entrance created out of a block of solid bronze. In the area highlighted with number 4, the 0.8 mm bolt is highlighted as the axis of rotation. Fig. 10. The knee joint of the leg Another important design feature of the knee that can only be seen once the muscle starts contracting is an extended bump. This bump creates a surface on which the spring steel plates can move. As the muscle starts contracting and thus the angle or rotation increases, so does the distance between the spring steel plates and the rotational axis thus creating a lever arm. By increasing the lever arm it increases the torque generated, which in turn makes the return process easier and more effective. Fig. 11 exemplifies this process. Fig. 9. 3D model of the leg The angle of rotation is given by contraction of the Fluidic Muscles. Two DMSP Nmuscles (with inner diameter of 20 mm and initial length of 200 mm) were used. These have a maximum contraction of 25% which means 50 mm compared to the initial length. Fig. 11. The knee joint during contraction of the calf muscle 155

The ankle of the prototype also contains both active and passive elements. The Fluidic Muscle is the active element and the spring is the passive element (Fig. 12).

Therefore the mounting mechanism needed to be created in such a way as to partially mitigate or to completely eliminate this type of stress.

12 is a different mounting mechanism compared to that of the other mountings. In this case it is not a fixed point but has an axis of rotation given by the bolt.

The foot does not have any active actuating mechanism it is instead comprised entirely of passive ones. All three of the toes have spring steel plates similar to those used in the knee joint.

The complete prototype When the Fluidic Muscle was placed under a maximum pressure of 500 kpa it produced a maximum angle of rotation of 47 (Table 1). TABLE I.

4 The ankle of the prototype also contains both active and passive elements. The Fluidic Muscle is the active element and the spring is the passive element (Fig. 12). One challenge that needed to be overcome was the fact that these muscles have very little tolerance for axial deformation. Therefore the mounting mechanism needed to be created in such a way as to partially mitigate or to completely eliminate this type of stress. The complete elimination of this stress was achieved by designing the mountings to be axles (Fig. 15). Fig. 16 shows the complete prototype. Fig. 12. Tibia and foot The highlighted area in Fig. 12 is a different mounting mechanism compared to that of the other mountings. In this case it is not a fixed point but has an axis of rotation given by the bolt. Essentially this permits the muscle to transfer its movement to the ankle. Fig. 13 and Fig. 14 show the prototype of the foot. The foot does not have any active actuating mechanism it is instead comprised entirely of passive ones. All three of the toes have spring steel plates similar to those used in the knee joint. The connection between the toes and the foot is provided by three hinges, one for each toe. Fig. 15. Fluidic Muscle's mountings Fig. 16. The complete prototype When the Fluidic Muscle was placed under a maximum pressure of 500 kpa it produced a maximum angle of rotation of 47 (Table 1). TABLE I. ANGLE OF ROTATION CAUSED FLUIDIC MUSCLE PRESSURE LOAD Pressure [kpa] Angle of rotation [ ] Fig. 13. Side view of the foot IV CONCLUSION AND FUTURE WORK Generally, rehabilitation devices and prosthetic arms and legs are built with electric motors, but the movements are far from natural. This paper reported on the pre-study of a therapy device and a leg prototype actuated by biologically inspired pneumatic muscle actuators. As a future work, the first tests with patients will be performed. Different sensors will be tested and control method will be developed. Fig. 14. Frontal view of the foot 156

5 REFERENCES [1] S. Csikós, Robot Remote Control Over the Internet, 28th International Conference Science in Practice, Subotica, Serbia, 3-4 June, 2010, pp [2] L. Gogolák, I. Fürstner and Sz. Pletl, Wireless Sensor Network Based Localization in Industrial Environments, Review of Faculty of Engineering, Analecta Technica Szegedinensia, vol. 1, no. 1, 2014, pp [3] L. Gogolak, S. Pletl and D. Kukolj, Neural Network-based Indoor Localization in WSN Environments, Acta Polytechnica Hungarica, vol. 10, no. 6, 2013, pp [4] K. Lamár and P. Zalotay, Microcontroller Implementation of Lookup Table-based Control Functions with Special Emphasis on Sequential Control According to IEC , International Journal of Electrical Engineering Education, 2015, pp. 1-20, in press [5] I. Fuerstner, and L. Gogolak, Presentation of the developed mechatronic devices for exhibition purposes, International Journal of Electrical and Computer Engineering Systems, vol. 6, no. 1, 2015, pp [6] L. Straka, Operational Reliability of Mechatronic Equipment Based on Pneumatic Artificial Muscle, Applied Mechanics and Materials, vol. 460, 2013, pp [7] L. Straka and S. Fabian, Modelling of Selected Reliability Indicators of Prototype PAM Equipment, Applied Mechanics and Materials, vol. 460, 2013, pp [8] F. Daerden, Conception and Realization of Pleated Artificial Muscles and Their Use as Compliant Actuation Elements, PhD Dissertation, Vrije Universiteit Brussel, Faculteit Toegepaste Wetenschappen Vakgroep Werktuigkunde, 1999, pp [9] R. Ramasamy, M. R. Juhari, M. R. Mamat, S. Yaacob, N. F. Mohd Nasir and M. Sugisaka, An Application of Finite Element Modeling to Pneumatic Artificial Muscle, American Journal of Applied Sciences, vol. 2, no. 11, 2005, pp [10] N. Tsagarakis and D. G. Caldwell, Improved Modelling and Assessment of Pneumatic Muscle Actuators, IEEE International Conference on Robotics and Automation, San Francisco, CA, USA, April, 2000, pp [11] B. Tondu, S. Ippolito, J. Guiochet and A. Daidie, A Sevendegrees-of-freedom Robot-arm Driven by Pneumatic Artificial Muscles for Humanoid Robots, The International Journal of Robotics Research, vol. 24, no. 4, 2005, pp [12] F. Daerden and D. Lefeber, Pneumatic Artificial Muscles: Actuator for Robotics and Automation, European Journal of Mechanical and Enviromental Engineering, vol. 47, no. 1, 2002, pp [13] B. Tondu and P. Lopez, Modeling and Control of McKibben Artificial Muscle Robot Actuators, IEEE Control Systems Magazine, vol. 20, no. 2, 2000, pp [14] M. Balara, The Upgrade Methods of the Pneumatic Actuator Operation Ability, Applied Mechanics and Materials, vol. 308, 2013, pp [15] M. Tothova and J. Pitel, Operating Characteristics of Antagonistic Actuator with Pneumatic Artificial Muscles, Applied Mechanics and Materials, vol. 616, 2014, pp [16] J. Pitel and M. Tothova, Design of Hybrid Adaptive Control of Antagonistic Pneumatic Muscle Actuator, 34th IASTED International Conference Modelling, Identification and Control (MIC 2015), Innsbruck, Austria, February, 2015, pp [17] J. Sárosi, S. Csikós, I. Asztalos, J. Gyeviki and A. Véha, Accurate Positioning of Spring Returned Pneumatic Artificial Muscle Using Sliding-mode Control, 1st Regional Conference - Mechatronics in Practice and Education (MECH-CONF 2011), Subotica, Serbia, 8-10 December, 2011, pp [18] E. J.Koeneman, R. S. Schultz., S. L. Wolf, D. E. Herring and J. B. Koeneman, A Pneumatic Muscle Hand Therapy Device, 26th Annual International Conference of the IEEE EMBS, San Francisco, CA, USA, 1-5 September, 2004, pp [19] Festo, Fluidic Muscle DMSP, with Press-fitted Connections, Fluidic Muscle MAS, with Screwed Connections, 2005, 39 p. [20] I. Bíró and G. Fekete, Approximate Method for Determining the Axis of Finite Rotation of Human Knee Joint, Acta Polytechnica Hungarica, vol. 11, no. 9, 2014, pp

12 th National Congress on Theoretical and Applied Mechanics September 2013, Saints Constantine and Helena, Varna, Bulgaria

12 th National Congress on Theoretical and Applied Mechanics 23-26 September 2013, Saints Constantine and Helena, Varna, Bulgaria DESIGN OF UPPER LIMB EXOSKELETON ACTUATED WITH PNEUMATIC ARTIFICIAL MUSCLES