2012 International Conference on Biomedical Engineering (ICoBE),27-28 February 2012,Penang
Design and Development of Inexpensive Pneumatically-Powered Assisted Knee-Ankle-Foot Orthosis for Gait Rehabilitation-Preliminary Finding ChunMan TENG, ZhenYang WONG, WeyYew TEH, Yu Zheng CHONG Faculty of Engineering and Science Universiti of Tunku Abdul Rahman Kuala Lumpur, Malaysia.
[email protected],
[email protected] Abstract—Locomotion training has proven to be a highly effective approach to assist patients in recovering their normal walking patterns. A pneumatically-actuated orthosis will improve gait rehabilitation significantly by providing a stable, accurate and precise lower extremities motion. This paper presents the design and development of a knee ankle foot orthosis (KAFO) powered by pneumatic artificial muscles. The KAFO is intended as a proof-of-concept rehabilitation device for the assessment of the conceptual design and testing of the power control system. McKibben Pneumatic Artificial Muscles is selected as the pneumatic actuator and the frame were made of aluminum. The general approach of this project is to develop an inexpensive rehabilitation robotic prototype consisting of a powered exoskeleton for the lower extremities. Keywords- gait rehabilitation; pneumatic artificial muscle; knee-ankle-foot orthosis
I.
INTRODUCTION
Orthotics is normally used in reducing the effect of physical disabilities. Advancements in technology have given rise to rapid development in orthotics. For example, KAFO are commonly prescribed in many neurological diseases such as cerebrovascular accident, cerebral palsy patients with leg muscle weakness or spinal cord injury, in order to provide knee support, enable limited degree of mobility and reduce risk of falling [1].
artificial muscle (MPAM). MPAM is well-known for their exceptionally high power and force to weight/volume ratios. Additionally, MPAM is inherently compliant that generate soft contact, thus guarantee a safe man-machine interaction [9], compared to rehabilitation system that is driven by electrical motors, where joints are driven with less flexibility, lack of smoothness and the resistance of active movement of the joints is not yielding. These features have benefited the development of powered-orthosis application or robotic exoskeleton where not only in term of safety interaction but also lightweight actuation design properties [9,10]. Several research groups across the world have developed lower extremities rehabilitation robotics and are briefly presented in three categories: stationary, mobile and standalone (exoskeleton-based) devices [19]. Table I describes the types of lower extremities rehabilitation robotics based on stationary, mobile and standalone devices. The power-assisted pneumaticbased KAFO that proposed in this paper falls under mobile rehabilitation robotics. TABLE I.
Rehabilitation Robotics Stationary 1.
The locomotion training has proven to be a highly effective approach to assist patients recovering their normal walking patterns [2,3,4]. The gait rehabilitation of an automation actuated orthosis is significantly improved the locomotion training by providing a stable, accurate and precise lower extremities motion [5,6]. For a social perspective, the development of the automation actuated orthosis relieves the therapist from heavy burden. Pneumatic muscle actuator (PMA) has been increasing used in rehabilitation system and primarily focuses on hand and arm rehabilitation [7,8]. The operation of PMA is very similar to the actual human muscle, which is very effective to be implemented in humanoid robot design. In this project, we propose a wearable power assisted pneumatic-based orthotic for lower extremities. The power-assisted KAFO is actuated by pneumatic muscle actuator, or so-called McKibben pneumatic
978-1-4577-1991-2/12/$26.00 ©2011 IEEE
TYPES OF LOWER EXTREMITIES REHABILITATION ROBOTICS
Mobile
Standalone
Types Lokomat [6]
2.
PAM/ POGO [11,19]
3.
LOPES [12,19]
4.
GaitTrainer and HapticWalker [13,19]
1.
KineAssist [14,19]
2.
WalkTrainer [19]
1.
BLEEX [15]
Description Developed by Hocoma AG is a treadmill-based gait trainer with BWS system. Consist of two pneumatic driven robots to assist gait retraining. Uses series elastic actuation where motors fixed to the treadmill frame transmit the mechanical power. Replace treadmill by two motorized footplates. Endeffector machines allow different foot trajectories. An overground gait training device. No leg orthosis with a custom designed harness. An omnidirectional mobile base allowing sidestepping. Locomotion training device. A harness-based BWS system and mobile based controlled by two motors. These exoskeletons assist and
28
2. 3. 4.
HAL-5 [16] RoboKnee [17] ReWalk [18,19]
strengthen human performance. The movements are detected by sensors. BLEEX and HAL-5 can manage an extra payload besides their own weight.
This paper is organized as follows. In section II, the design applications and the design characteristic of power assisted pneumatic-based KAFO are outlined. In Section III, explains the configuration of actuator system and mechanical design concept of power assisted pneumatic-based KAFO. In Section IV, provides the preliminary result of McKibben artificial muscle and the prototype overall consideration made from the mechanical design: material selection, adaptability of the orthosis to the user, fittings of the prototype to the leg and foot support. In section V, discusses the future development stage of this project. II.
•
Ankle joint is limited to -25° to 45° to match the properties of an ankle for safety purpose.
•
Torque requirements are determined by large peak extension moment of force occurring at early stance, where up to 50Nm for an average male subject at a normal walking cadence [20].
•
The device must able to be strapped to the user at sitting position but the automation assistance sit-tostand motion has not been considered.
•
The design must include a safety precaution of joint flexion-extension motion especially to prevent knee from hyperextension.
•
Excessive generated torque has to be avoided from being transferred to the user.
•
The adjustability of the orthosis would be easily fitted properly to the user.
III.
MECHANICAL DESIGN CONCEPT AND DIMENSIONING
DESIGN SPECIFICATION
The early stage of the project involves the design and development of the power assisted KAFO actuated by MPAMs. The main design characteristics identified for a powerassisted lower extremities orthosis are outlined as the following: •
Knee joint torque must be sufficient to achieve physiological walking gait patterns [20].
•
The device should be easily adaptable to the anatomy of the user to provide comfortable wear.
•
The device should not limit the patient’s leg muscles from functioning to avoid muscle atrophy.
•
The foot, shank and thigh link length must be adjustable to allow variation according to anatomy length of user.
•
The device should be able to support the body weight and morphologies of user.
•
The safety angle of the device for knee and ankle joint should be sufficient to prevent hyperextension of the knee and ankle.
•
Ideally, the device should be lightweight, compact, ergonomic and ensure a safe human-machine interaction [20].
A. Actuator Configuration Prior to the actual dimensioning of the actuation mechanism, a suitable actuator configuration is important to be selected. The MPAM is a single-acting force actuator as shown in Fig. 1. In order to obtain a bidirectional rotative actuator system, two single-acting actuators are required to configure in an antagonistic configuration. Fig.2 depicts the mechanical design of a bidirectional rotative actuator powered by MPAMs in an antagonistic configuration. Both the MPAMs are connected by a hinge joint with its axis in O. Ai and Bi are rotors to allow the freedom of rotation during muscle contraction and relaxation in order to have a smooth knee joint movement. Xi represents the length of the MPAM. The relationship between inclination angle of each joint and MPAMs’ displacement can be express in a formula using trigonometry method. For example, to find the relationship between the knee joint and the MPAM that functions to create flexion at knee joint, each parameter is defined as shown in Fig. 3 and Fig. 4. By using trigonometry method the relationship between inclination angle of knee joint, and the respective MPAM’s length, x can be written as (1)
As the power assisted pneumatic-based KAFO is intended as a proof-of-concept prototype rather than an end-user product, the applications and the complexity of the system can be compromised. Although in that case, the dimension of the prototype and actuation system has to be in accordance to the kinematic and dynamic requirements [20]. The important requirements of the power assisted pneumatic-based KAFO are outlined as follows: •
Figure 1. McKibben pneumatic artificial muscle at pressurised condition.
A knee joint of 90° flexion is sufficient in normal walking gait patterns.
29
antagonistic configuration is used. In antagonist configuration, two MPAM is used for each joint. The actuator force can be transferred through fixed levers connected along the axis of the MPAM. The footplate allows the rotation of the metatarsalphalangeal joint during toe off to preserve a normal walking pattern. Furthermore, the footplate is added to carry the orthosis weight and prevent it from sliding down the user’s leg. The length of the lower leg sidebar relative to the footplate is made adjustable to fit the height of the user. The braces for upper and lower leg are designed that does not fully cover the leg muscles to provide spaces for muscle to function and hence avoid muscle atrophy.
Figure 2. An antagonistic configuration of McKibben Pneumatic Artificial Muscle.
Figure 3. The knee joint of the power-assisted KAFO design.
Besides the footplate is modular, the fittings are also modular where they are piece of fiberglass cast with foam inlay and Velcro straps chosen for both at the thigh and shank. These meet the requirement of an easy and adaptable fit. The orientation and position of each shell are designed to be adjustable in the sagittal plane by mean of slider and lock mechanism. At the early stage, the distance and the inclination of the shells with respect to the frame are set with bolt and nut. Although it is a simple attachment element but the adjustability should be sufficient to align the orthosis, and achieve the requirement of comfortable fit according to the anatomy of user. For safety reasons, mechanical limiters will be integrated at the two hollow sidebars to prevent hyperextension of the knee and flexion angle exceeding 90°, whereas the range of rotation of ankle joint is limited at -25° to 45°. The upper leg hollow sidebar is designed to be quarter circle at the knee joint instead of semi circle to limit the knee joint of 90° flexion only and prevent hyperextension.
Figure 4. Mathematical model of the frame of power assisted KAFO.
B. Mechanical Design Concept Based on the design requirement in the previous section, a first prototype has been designed by using SolidWorks. Fig. 5 and Fig. 6 show the proof-of-concept power assisted KAFO. The prototype consists of unilateral frame divided into upper and lower leg sidebars that are interconnected by a hinge at the knee joint. MPAMs are attached to the unilateral frame where it functions exactly like human muscle to pull the sidebars in order to generate a series of joint motion. A footplate is designed to be modular for the ease of user to wear before assemble to the sidebar. The MPAMs are attached to the unilateral frame of the lower leg sidebar by means of a hinge at the ankle. MPAM is a single-acting force actuator, which only perform contraction. Hence, to obtain a bidirectional actuator,
Figure 5. Drawing of power-assisted KAFO.
30
Figure 8. Hysteresis value and loading charecteristic for a 30cm long MPAM.
Figure 6. SolidWorks drawing of knee joint (left) and ankle joint (right).
IV.
RESULTS AND DISCUSSION
A. McKibben Pneumatic Artificial Muscle The inner tube of the MPAM is made of latex glove and the muscle end capping is fabricated by CNC turning machine. The size and contour of the end capping will determine the size of the MPAM consequently contributed to a variable of forces the MPAM could exert upon pressurization. The suitable material to fabricate the muscle end capping is aluminum because of its lightweight characteristic. Fig. 8 depicts the MPAM maximum forces exerted under pressure condition of 1 bar, 2 bar and 2 bar with parallel muscle connection. The force is increasing with the increment of tension but decreasing after 6kg of tension. Based on the observation, the exerted force could not overcome the tension after 6kg. Fig. 9 depicts the hysteresis and the loading characteristic of a 30cm long McKibben muscle. Pressure of 1 bar to 3 bar is applied to the MPAM to determine the contraction ratio. Result has shown the maximum contraction ratio of 22.33 at 3 bar.
B. Knee-Ankle-Foot Orthosis Aluminum material is used to construct the prototype including the muscle end capping. The reason the aluminum is selected is its lightweight characteristic and these meet the design requirement whereas the orthosis should be lightweight. Fig. 10 depicts the first prototype of the power-assisted KAFO, powered by McKibben Pneumatic Artificial Muscle. The subject selected is 1.75m in height, 0.45m long of upper leg and 0.48m of lower leg. The prototype is constructed to be modular to ease and fit the user in various height of 1.65m to 1.75m. For the fittings, the fiberglass cast is fabricated directly from the thigh and shank of a subject. The size of the fiberglass cast fit to the user is adjustable by the Velcro strap and the foam inlay guarantee the comfortable wear of the prototype. A foot support is attached to the prototype in order to support the weight of the prototype and prevent shifting. The total weight of the prototype at current stage is 2.7kg. Fig. 11 depicts the prototype able to perform sitting position. The comfortable of user and the ease of physician are important to preserve a good rehabilitation environment. Therefore, the prototype has to be easily fit to the user rather than the user fit to the prototype. However, sit-to-stand automation system of the prototype has not been considered but can be achieved with the assist of a walker without wheel.
Figure 7. Relationship of force and tension for a 30cm long MPAM. Figure 9. Prototype of power-assisted KAFO.
31
[5]
[6]
[7]
[8]
Figure 10. Sitting position of KAFO prototype.
V.
CONCLUSION AND FUTURE WORKS
In this paper, we proposed a prototype of power-assisted KAFO using McKibben pneumatic artificial muscle. The MPAM is constructed and tested in several conditions. On the other hand, the power assisted KAFO can be easily fitted to the user comfortably has achieved the main design specification. Furthermore, the frame and the fittings of the power assisted KAFO are modular to fit the height of the user within the range of 1.65m to 1.75m. Finally, a normal walking gait can be performed by the user while wearing the prototype without actuation from MPAMs. The next stage of the prototype will be the development of the control system and software programming. Accelerometer and potentiometer will be used as sensor to detect the joint angle and the coordination of the prototype. A microswitch will be used to detect the floor contact of the foot support. Furthermore, the cosmetic of the prototype and sit-to-stand automation system will be the next development of this project. A locking mechanism or clamping mechanism will replaces the bolt and nut mechanism to reduce the complexity and increase the safety of the user. The Velcro straps will be replaced by a belt mechanism to increase the comfortably wear of user. REFERENCES [1]
[2]
[3]
[4]
J.C. Moreno, F. Brunetti, E. Rocon, J. L. Pons, “Immediate effects of a controllable knee ankle foot orthosis for functional compensation of gait in patients with proximal leg weakness,” Med Bio Comput, 46: 43-53, 2008. M. Wirz, G. Colombo, V. Dietz, “Long term effects of locomotor training in spinal humans,” J Neurol Neurosurg Psychiatry, 71:93-96, 2001. A. Wernig, S. Muller, “Laufband locomotion with body support improved walking in persons with severe spinal cord injuries,” Paraplegia, vol.30, no.4, pp.229-238, 1992. V.R. Edgerton, R. D. de Leon, S. J. Harkema, J. A. Hodgson, N. London, D. J. Reinkensmeyer, R. R. Roy, R. J. Talmadge, N. J.
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18] [19]
[20]
[21]
Tillakaratne, W. Timoszyk, A. Tobin, “Restraining the injured of spinal cord,” J Physiol (Lond) 533: 15-22, 2001. H. Krebs, M. Aisen, N. Hogan, “Increasing productivity and quality of care: robot-aided neuro-habilitation,” Journal of Rehabilitation Research and Development, vol. 37, no. 6, pp. 639-652, 2000. G. Colombo, M. Wirz, V. Dietz, “Driven gait orthosis for improvement of locomotor training in paraplegic patients,” Spinal Cord, vol. 39, pp. 252-5., 2001. X. Li, H. Xia, and T. Guan, “Development of Legs Rehabilitation Exercise System Driven by Pneumatic Muscle Actuator,” 2008 2nd International Conference on Bioinformatics and Biomedical Engineering, pp. 1309-1311, May. 2008. J. a Blaya and H. Herr, “Adaptive control of a variable-impedance ankle-foot orthosis to assist drop-foot gait.,” IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society, vol. 12, no. 1, pp. 24-31, Mar. 2004. T.-J. Yeh, M.-J. Wu, T.-J. Lu, F.-K. Wu, C.-R. Huang, “Control of McKibben pneumatic muscles for a power-assist, lower-limb orthosis,” Mechatronics, vol. 20, no. 6, pp. 686-697, Sep. 2010. K. C. Wickramatunge, T. Leephakpreeda, “Study on mechanical behaviors of pneumatic artificial muscle,” International Journal of Engineering Science, vol. 48, no. 2, pp. 188-198, Feb. 2010. D. J. Reinkensmeyer, D. Aoyagi, et al., “Tools for understanding and optimizing robotic gait training”, J. Rehabil. Res. Dev. vol. 43, no. 5, pp. 657-670, 2006. J. F. Veneman, R. Kruidhof, E. E. G. Hekman, R. Ekkelenkamp, and E. H. F. V. Asseldonk, “Design and Evaluation of the LOPES Exoskeleton Robot for Interactive Gait Rehabilitation,” Rehabilitation, vol. 15, no. 3, pp. 379-386, 2007. H. Schmidt, C. Werner, R. Bernhardt, S. Hesse, J. Krüger, “Gait rehabilitation machines based on programmable footplates”, J. Neuroeng. Rehabil., vol. 4, no. 2, 2007 M. Peshkin, D. A. Brown, J. J. Santos-Munné, A. Makhlin, E. Lewis, J. E. Colgate, J. Patton, D. Schwandt, “KineAssist: A robotic overground gait and balance training device”, in Proc. IEEE Int. Conf. Rehabil. Robot. (ICORR), pp. 241-246, 2005. A. B. Zoss, H. Kazerooni, A. Chu, “Biomechanical design of the Berkeley Lower Extremity Exoskeleton (BLEEX)“, IEEE/ASME Trans. Mechatronics, vol. 11, no. 2, pp. 128-138, 2006. H. Kawamoto, S. Lee, S. Kanbe, Y. Sankai, “Power assist method for HAL-3 using EMG-based feedback controller”, In Proc. IEEE Int. Conf. Syst., Man, Cybern. pp. 1648-1653, 2003 J. E. Pratt, B. T. Krupp, C. J. Morse, and S. H. Collins, “The RoboKnee: An exoskeleton for enhancing strength and endurance during walking,” in Proc. IEEE Int. Conf. Robot. Autom., New Orleans, pp. 2430–2435, 2004. A. Goffer, “Gait-locomotor apparatus”, U.S. Patent US7153242, 2006. Y. Allemand, Y. Stauffer, R. Clavel, R. Brodard, and A. Background, “Design of a new lower extremity orthosis for overground gait training with the WalkTrainer,” Rehabilitation, pp. 550-555, 2009. P. Beyl, J. Naudet, R. Van Ham, and D. Lefeber, “Mechanical Design of an Active Knee Orthosis for Gait Rehabilitation,” 2007 IEEE 10th International Conference on Rehabilitation Robotics, no. c, pp. 100-105, Jun. 2007. T. Noritsugu, D. Sasaki, and M. Kameda, “Wearable Power Assist Device for Standing Up Motion Using Pneumatic Rubber Artificial Muscles,” Journal of Robotics and Mechatronics, 2007.
32
