Transcript
Wearable elbow exoskeleton actuated with Shape Memory Alloy in antagonist movement D. Copaci, D. Blanco, L. Moreno Abstract— This paper presents a wearable rehabilitation exoskeleton for the elbow joint with two degrees of freedom (DOF), flexion-extension and pronation-supination, actuated with Shape Memory Alloy (SMA) based actuators. Due to the actuation system, the proposed exoskeleton presents a light weight, noiseless operation and everything in a simple design structure. It is a segment exoskeleton for evaluation and treatment for the elbow joint, based in a low cost components which give the possibility that it can be acquired by specialized hospitals and even patients themselves.
I. INTRODUCTION The upper limbs play an important role in daily living and the movement disorders significantly reduce the quality of life. Fortunately, one part of this movement functionality can be restored with the physical rehabilitation therapies. Among to the most promising technologies it is considered that the robotic therapies with exoskeletons are very beneficial for patients rehabilitation requiring a repetitive treatment for reeducation of lost movements. Robotic rehabilitation devices offer a more effective and stable rehabilitation process compared to the traditional rehabilitation sessions effectuated by therapists and reducing the cost of hospitalization [1]. In the last years, some systems have been developed for rehabilitation of the elbow joint, although almost of all use DC or AC motors and some of them hydraulic or pneumatic actuators. Between the rehabilitation devices for the elbow joint in flexion-extension, can be find stationary systems (for example [2], MEDARM [3]) and portable and wearable orthosis (for example [4]). With independent movement of pronation-supination of forearm and more related with our proposal can be find RUPERT [5]. A broad review can be found at [6]. The majority of this devices present a considerably weight, which in the case of portable devices is supported by the patient. A large part of this weight is related with the weight of actuator. This paper presents a wearable rehabilitation exoskeleton for the elbow joint with 2DOF actuated with SMA based actuator actuated in antagonist movement. Using this type of actuation we propose a solution for issues like the total weight of the device, the noise operation and the financial costs. The structure of this paper was divided in: the first part of the paper presents an introduction to the actual problem, the second part presents the methodology, the third part presents the control strategy and preliminary results and the last part presents a brief conclusions of this paper. D. Copaci, A. Flores, D. Blanco, L. Moreno are with the Carlos III University, Madrid, Spain (corresponding author to provide e-mail:
[email protected]).
Fig. 1. SMA actuated exoskeleton with two DOF for flexion-extension and pronation-supination and the control hardware (the white box)
II. METHODOLOGY This section presents the structure design of the rehabilitation exoskeleton and the actuators used in this device. A. Structure design The design of the rehabilitation exoskeleton was based on a biomechanical simulation presented in [7]. It has been proposed for certain types of patients: weight 70Kg, height 1,7m, range of movement for the right elbow joint 0 and 150 degrees with a maximum frequency of movement 0,25Hz. In addition the patient maight have an additional weight in the hand up to 0,2Kg. In function of these requirements, to complete the rehabilitation task in the elbow articulation successfully, the exoskeleton may exert a torque of 3,5Nm in flexion-extension and approximately 1Nm for pronationsupination. The design of the exoskeleton can be seen in the Fig. 1. This is made of simple parts that give the possibility to easy assembly and set them in function of the patient. The exoskeleton presents four attachment points with the human body, two of them with the arm, one with the forearm and the last one with the hand. The attachment points are adjustable in function of the patient. In the elbow joint articulation, the exoskeleton presents one DOF and in the hand point attachment, the exoskeleton presents another DOF which gives the possibility of pronation-supination of the forearm. For the safety of the patient, the exoskeleton movement is mechanically limited between 0 and 150 degrees. For the comfort all intern part in contact with the patient was
Fig. 2. Antagonist control scheme with two parallel four-term bilinear PID controllers
Fig. 3. The reference patron angular position of the exoskeleton and the response of this actuated in antagonist movement
covered with a very soft hypoallergenic material. In the sensor integration part the structure incorporates one absolute encoder and two temperature sensors . Comparing to the current solution, the proposed rehabilitation device presents advantages such as reducing drastically the weight of exoskeleton - the whole structure with the actuators weights less than 1Kg and noiseless. B. SMA based actuator In function of the necessary torque in the elbow joint (3.5Nm) and the structure design of the exoskeleton, a first solution was presented in [7] consisting in four wires of Shape Memory Alloy (SMA) inserted in four Bowden cable for the flexion movement and for extension using the force of a torsion spring placed in the elbow exoskeleton joint. For the reasons of heating, energy consumption and dimensions of the actuator, this was re-designed: four SMA wires in one Bowden cable. This configuration has a lower power consumption, quick response and a more compact design. In addition, in extension movement of the elbow joint was introduced a actuator with two wires of SMA, giving the possibility to execute movements more larger and more faster, obligating the antagonist wire to recuperate quickly the initial position (extension). III. C ONTROL STRATEGY AND FIRST RESULTS A simple four-term bilinear PID controller was used successful in a past work presented in [7]. In this work an antagonist control based in two parallel four-term bilinear PID controllers was used (Fig. 2). The reference of each controller (flexion and extension) was generated in function of the different parameters such as the reference of desired angle of the elbow joint, the temperature of the wires and the actual position of the actuators. In Fig. 3, may be seen the angular position reference of the exoskeleton and its response who is capable of following the reference pattern without any problems. The antagonist montage forces the recuperation of the actuators compensating the thermal inertia of the antagonist. The control signals corresponding to the Fig. 3, can be seen in Fig. 4. The two controls are activated in function of the generated reference. IV. C ONCLUSIONS This is the first wearable elbow exoskeleton actuated with SMA based actuators in antagonist movement which permit to reduce drastically the weight of the exoskeleton (less than
Fig. 4. Control signal of antagonist control corresponding to reference signal of Fig 2
1kg) and achieve a noiseless operation characteristic which increase the comfort of the system. The exoskeleton was built as a low-cost rehabilitation device, which can be made with a 3D printer, with a low-cost electronics and actuators, which can be configured depending on the patient. V. ACKNOWLEDGMENT The research leading to these results has received funding from the RoboHealth (DPI2013-47944-C4-3-R) Spanish research project. R EFERENCES [1] G. Kwakkel, B. Kollen, and H. Krebs, ”Effects of robot-assisted therapy on upper limb recovery after stroke: A systematic review”, Neurorehabilitation and Neural Repair, vol. 22, pp.111-121, 2007. [2] J.A. Cozens, ”Robotic assistance of an active upper limb exercise in neurologically impaired patients”. Rehabil Eng, IEEE Trans 1999, 7(2):254256. [3] S. J. Ball, I. E. Brown and S. H. Scott, ”MEDARM: a rehabilitation robot with 5DOF at the shoulder complex,” 2007 IEEE/ASME international conference on advanced intelligent mechatronics, Zurich, 2007, pp. 1-6. doi: 10.1109/AIM.2007.4412446 [4] N. Vitiello, T. Lenzi, S. Roccella, S. M. M. De Rossi, E. Cattin, F. Giovacchini, F. Vecchi, M. C. Carrozza, ”NEUROExos: A Powered Elbow Exoskeleton for Physical Rehabilitation” IEEE Transactions on Robotics, vol. 29, Feb. 2013, pp. 220235. [5] S. Balasubramanian, R. Wei, M. Perez, B. Shepard, E. Koeneman, J. Koeneman J. He, ”RUPERT: An Exoskeleton Robot for Assisting Rehabilitation of Arm Functions ”, 2008 Virtual Rehabilitation, Aug. 2008, pp.163-167. [6] P. Maciejasz et al , ”A survey on robotic devices for upper limb rehabilitation” Journal of NeuroEngineering and Rehabilitation, 2014, DOI: 10.1186/1743-0003-11-3. [7] D. Copaci, A. Flores, F. Rueda, I. Alguacil, D. Blanco, L. Moreno, ”Wearable elbow exoskeleton actuated with Sape Memory Alloy”, International Conference on NeuroRehabilitation (ICNR2016) - accepted.
