Computer Aided Drafting, Design and Manufacturing Volume 26, Number 2, June 2016, Page 53 CADDM The design of exoskeleton lower limbs rehabilitation robot Zhao Xiayun 1, Wang Zhengxing 2, Liu Zhengyu 1,3, Zhang Li 1,3 1. School of Machinery and Automobile Engineering, HFUT, Hefei 230009, China; 2. Zhejiang Henglin Chair Industry Co. Ltd. Anji 313300, China; 3. Engineering Research Center of Safety-critical Industry Measure and Control Technology of Ministry of Education, Hefei 230009, China. Abstract: To achieve human lower limbs rehabilitation training,the exoskeleton lower limbs rehabilitation robot is designed. Through respective motor driving, the retarding mechanism and telescopic adjusting mechanism, the function of human walking is accomplished. After the design of the mechanical structure, the finite element analysis is carried out on the important parts and the control system is achieved by Single Chip Microcomputer. Key words: SCM; lower limbs rehabilitation robot; finite element analysis 1 Introduction As the improvement of human living conditions, population structure has gradually entered the population ageing stage in China and the people with limb dysfunction have increased. Patients, who cannot get a full recovery by surgery or medication, need to take the rehabilitation robot as a part of their treatment. Although there are many researches on lower limbs rehabilitation robot in China, the structure of device is complex, low automation and can t satisfy the needs of the patients [1-2]. Therefore, this paper presents an exoskeleton lower limbs rehabilitation robot, which accords with human curve of gait and has flexible adjustment. It has important practical significance for a large part of the sick and the elderly s life and health. rehabilitation facility is divided into three parts. First of all, the servo motor, which is fixed at the waist, drives hip joint movement for the thigh part, through the reduction gear and waist hip joint actuator. Secondly, linear actuator drives the movement of crus and two degrees of freedom movement of the ankle. Thirdly, both thigh and crus support components include adjusting the length of the telescopic mechanism to meet the requirements of different height of the crowd. In addition, the exoskeleton lower limbs rehabilitation facility also includes some torque transducer and angle transducer to monitor the training process of each joint movement situation, achieving the monitoring and feedback function. The schematic diagram is shown in Fig.1. 2 Design of mechanism 2.1 Overall design scheme The exoskeleton lower limbs rehabilitation mechanism is mainly composed of hip joint actuator, thigh support components, knee joint actuator, crus support components, ankle joint actuator and the sole support parts. There are eight degrees of freedom in the whole structure, and four degrees of freedom in each leg, which can achieve flexible body movements and meet the demand of rehabilitation exercise [3]. The movement of exoskeleton lower limbs Fig. 1 Overall mechanism. Project item: Supported by Science and Technology Department of Anhui Province Regional Innovation Projects and Qiushi Plan (JZ2015QSJH0245) Corresponding author: Zhang Li, Female, Master, Professor, E-mail: 77zhangli@hfut.edu.cn.
54 Computer Aided Drafting, Design and Manufacturing (CADDM), Vol.26, No.2, Jun. 2016 2.2 Hip transmission mechanism Hip transmission mechanism is mainly composed of a set of universal joints and transmission shafts. Transmission shafts are connected by a spline, which can be adjusted within a certain distance and cooperate with the damping device at the waist to against lateral impact load. Also, two universal joints ensure the instantaneous angular velocity of the input shaft and output shaft. A set of universal joints and transmission shafts will eventually transfer power of servo motor to the hip gear to complete the rotation of the hip and lift the thigh part. Hip transmission mechanism schematic diagram is shown in Fig.2. 2.4 The ankle joint mechanism According to the movement rule of human feet, ankle joint structure should be designed into two degrees of freedom which can realize the forward and backward, turn right or left. Ankle joint actuator schematic diagram is shown in Fig.4. Fig. 4 Ankle joint actuator. Fig. 2 Hip transmission mechanism. 2.3 The leg telescopic adjusting mechanism A main supporting part of the lower limbs rehabilitation facility is the leg supporting. In order to meet the needs of different height of the crowd, the scalable adjusting organization is designed respectively in the thigh and crus support parts. As shown in Fig.3, thigh support part can form a slider mechanism and the fastening screw have the effect of locking. Crus support components are the same as thighs. Part of thigh and calf are hinged with linear actuator respectively, forming the leg drive mechanism. The using of individual motor makes the speed and position of crus more accurate. The analysis and calculate of the spatial degrees of freedom: W=P λ 3 K Tip: W represents the spatial degrees of freedom. P represents the total number of degrees of freedom of motion pair for space organization. λ represents excess number of degrees of freedom. K represents the number of closed loop. Let P=12, λ=1, K=3, get W=12 1 3 3=2. Therefor, ankle joint actuator needs two linear actuators to achieve the movement. The movement of two degrees of freedom can be achieved by controlling the pace of the two linear actuators. 3 The design of the control scheme Fig. 3 Leg telescopic adjusting mechanism. 3.1 The overall implementation plan This scheme is mainly based on single-chip microcomputer controller. And it is divided into the upper machine control system and lower machine control system [4-5]. The upper machine control system is composed of communication module, controller module and data sampling module. The main functions include collecting and analyzing sensor data, comparing with standard curve of human gait and communicating with PC by serial port. Lower machine control system is composed by communication module, D/A conversion module, processor, power converter module, drive and control module [6]. The main functions include
Zhao Xiayun et al., The design of exoskeleton lower limbs rehabilitation robot 55 processing the data transmission from the upper machine, amplifying the signal, accomplishing the motor control by driving control circuit of motor control and realizing the control of the sensor by D/A conversion circuit. Sensor signals are collected by the data sampling module which provide feedback, as shown in Fig.5. process return to the start of the main program, as shown in Fig.6. Fig. 6 The gait control flow diagram. 4 Stress and strain analysis Fig. 5 The overall control diagram. 3.2 The gait control process In the gait control process, the current position of mechanism should be determined firstly, and then enter the main program [7]. Detecting of initial state is detected by the speed sensor, displacement sensor and pressure sensor, before the movement of mechanism. Before entering the main program, the rest of the subsystems are idle and then accept the control instruction. Instructions need to handle, storage and send. Until accepting the signal of interrupt, the To verify the strength of the lower limbs rehabilitation facility designed in this paper, using the Simulation Xpress, which is one of the functions in the SolidWorks, making a finite element analysis for the support parts. The results of the analysis are used to improve the parts that yield strength is lower than the stress [8-9]. Exoskeleton type lower limbs rehabilitation facility is mainly composed of the support pedestal of hip joint and support pedestal of knee joint to under load. These key parts directly affect the stability and safety of the whole structure. Therefore, it is necessary to conduct stress analysis and displacement analysis by the finite element analysis method. The results of the analysis are shown in Fig.7 and Fig.8.
56 Computer Aided Drafting, Design and Manufacturing (CADDM), Vol.26, No.2, Jun. 2016 (a) (b) Fig. 7 Stress and strain of support pedestal of hip. (a) Strain of support pedestal of hip; (b) Stress of support pedestal of hip. (a) (b) Fig. 8 Stress and strain of support pedestal of knee. (a) Strain of support pedestal of knee; (b) Stress of support pedestal of knee. Through the analysis of the components of the stress diagram and displacement diagram, the maximum stress of the support pedestal of hip joint is located in the part of hinge joint with value of 30.4 MPa. The maximum stress of the support pedestal of knee joint is located in the connection part with value of 155 MPa. The maximum yield strength of the material selected 45 steel under normal temperature is no less than 355 MPa. As a result, the agency has high security and meet the design requirements. 5 Conclusion This paper describes the design of an exoskeleton lower limbs rehabilitation robot, which satisfies the crowd of lower limbs dysfunction or the need to lower limbs rehabilitation training in the elderly. This paper also applies single-chip microcomputer control technology combined with human gait curve data through real-time analysis of sensors. At the same time, SolidWorks simulation software accomplish finite element analysis of key components. References [1] Li X M, Wang Z X, Zhang S, et al. The Design of multi-function nursing wheelchair [J]. Computer Aided Drafting, Design and Manufacturing (CADDM), 2013, 23(1): 68-70. [2] Yuan K. Status and trends of intelligent wheelchair [J]. China Medical Devices Information, 2009, 15(1): 6. [3] Zheng Y F, Liu Z Y, Wu Z, et al. Design of lower limbs Powered Exoskeleton [J]. Computer Aided Drafting, Design and Manufacturing (CADDM), 2015, 25(4): 48-51. [4] Xie H S. The wearable lower limbs rehabilitation exoskeleton kinematic analysis and simulation [D]. Changchun: Changchun University of Science and Technology, 2014. [5] Rao L J, Xie L, Zhu X B. Research and design on lower
Zhao Xiayun et al., The design of exoskeleton lower limbs rehabilitation robot 57 exoskeleton rehabilitation robot [J]. Machine Design and Research, 2012, 28(3): 24-26. [6] Wang X F, Li X, Wang J H, et al. Data-driven model-free adaptive sliding mode control for the multi degree-of-freedom robotic exoskeleton [J]. Information Sciences, 2016, 327(C): 246-257. [7] Zhao C, Wang Z X, Jiang S H, et al. The Design of Wheelchair Lifting Mechanism and Control System [J]. Computer Aided Drafting, Design and Manufacturing (CADDM), 2014, 24(2): 43-47. [8] Qin H C, Zhao C, Wu B, et al. Nursing bed used in the smart home environment [J]. Computer Aided Drafting, Design and Manufacturing(CADDM), 2013, 23(1): 58-61. [9] Jiang S H, Fan J, Zhang C, et al. Digital design of multi-functional rehabilitation robot [J]. Computer Aided Drafting, Design and Manufacturing (CADDM), 2015, 25(3): 56-59. Zhao Xiayun received his B.Eng. degree in Mechanical from Datong University, China, in 2014. He is currently a graduate in the Department of Mechanical Engineering at Hefei University of Technology. His research interests include 3D design and analysis electrical control. Wang Zhengxing was born in 1975, and graduated in Zhejiang University of Science and Technology 2001 and is a senior engineer of ZheJiang Henglin Chair Industry Co. Ltd. He present main research interest is mechatronics. Liu Zhengyu was born in 1979,Ph.D candidate in School of Computer and Information at Hefei University of Technology and associate professor in School Machinery and Automobile Engineering. His present research direction is control safety. Zhang Li received her B.Eng. And M.Eng. degrees in Mechanical from Hefei University of Technology, China, in 1982 and 1997, respectively. She is currently a professor of School of Machinery and Automobile Engineering, Hefei University of Technology. Her research interests include electromechanical integration technology, computer aided design and manufacturing.