Study On CPM Rehabilitation Device Of Intelligent Ankle Joint

Medical research and clinical experience have shown that Continuous Passive Motion can efficiently accelerate the restoration of joint injury and cartilage’s regeneration and repair. At present, the rehabilitation of injured ankle joint mainly depends on manual therapy, which not only has such disadvantages as time-consuming and one’s strength-consuming, but also has difficulty to record rehabilitation data and to make systemic scientific training. So it is very meaningful to do research on intelligent ankle CPM rehabilitation apparatus.Based on the in-depth analysis to human foot, the paper presents the design of CPM rehabilitation experimental device which can simulates plantar flexion, dorsiflexion, varus and valgus movements according to the physiological structure and motion characteristics of the human foot. Moreover, its swing angle, rotation speed and output torque can be set freely and measured in real-time, which ensures the real values not to exceed the set values, so that prevent the injured ankle from being damaged again.According to the requirement of rehabilitation device for driving system and the characteristics of common drivers, permanent magnet DC motor is chosen as driving motor which can meet the device’s requirements such as operating steadily, hard mechanical characteristics, controlling simply, saving energy, and so on. Planetary gear reducer is used to achieve huge reduction ratio between DC motor and actuator, and makes the device small in size.PWM speed governing technology has been used to regulate the speed of DC motor, and the incremental photoelectric rotary encoder are used to feedback the signal of motor’s revolution speed and to achieve the closed-loop speed control of DC motor. In order to improve the starting characteristics and running stability of DC motor, the traditional PID algorithm is improved by use of adding trapezoidal method and differential ahead algorithm into controlling system, which improves the stability and accuracy of DC motor’s PID speed governing.The paper presents a new method to measure DC motor’s output torque by measuring the armature current. Firstly, the relation curve between motor’s load and armature current at different control voltage level is obtained by experiments. Then, when the motor is working, the motor’s output torque can be calculated according to above-mentioned relation curves as soon as the armature current under a control voltage has been measured by use of shunt principle. Thus, a CPM rehabilitation device without torque sensor can be designed, which not only reduces the device’s size but also its costs.Finally, a CPM experimental device are built on the basis of LabVIEW, computer, NI ELVISⅢ+ experimental platform, DC motor, motor controller, shunt, shaft-position encoder, and the PID controlling experiment for DC motor has been done on the device. The experimental results show that it is feasible to measure the output torque of the DC motor by measuring armature current.