Design And Implementation Of Servo System For Mechanical Arm Gravity Compensation Device

With the development of human space technology, the ground simulation test for micro-gravity environment becomes more and more important. For the moment,methods for micro gravity simulation include flotation, buoyancy method, drop tower and suspension method etc, the suspension method is mainly through the wire pulling force to balance its own gravity, in this system only 5/6 of the mechanical arm’s gravity will be compensated. Because of its simple structure,easy implementation and 3D simulation, the suspension method is widely concerned.This subject design and implement a servo system for mechanical arm gravity compensation device. Mechanical arm gravity compensation device is used to compensate 5/6 of the mechanical arm’s gravity and provide a Mechanical environment of microgravity on moon for its ground test. In the process of mechanical arm movement,servo system makes the gravity compensation device following the mechanical arm’s movement. The gravity compensation device is implemented by suspension method, suspension point’s position tracking error is the key factors that affect the ground test, larger following error will cause horizontal disturbance torque to mechanical arm and destroy the mechanical environment for ground test. In this topic, a tracking servo method based on visual servo is proposed, designed and implemented a microgravity ground test system which can reduce the following errors effectively and reduce the lateral disturbance torque caused by gravity compensation device to mechanical arm.In this paper, the hardware structure of the ground simulation test device for lunar mechanical arm is firstly introduced; Secondly, this paper introduces the structure of servo system based on position servo and the reliability of the system;Finally, introduces all parts’ designing and implementation of the servo system.The requirement of following error’s accuracy in the process of suspension micro gravity simulation is very high, so the image as the key feedback information of the whole system, its quality directly affects the accuracy of the system. In order to satisfy the imaging condition of high precision, wide and large depth of field and high frequency, this system designs a vision measuring system based on multi-sensor fusion of laser range finder and dual camera.How to select the appropriate image features and ensure the detection of the target and accurate positioning is the key to the process of image processing. Thissystem designs a laser light source as the target and presents a method of target recognition and detection based on the target.In the traditional following system, the following target’s movement is always before the servo of actuator, so the actuator always lags behind the moving target and it is hard to decrease the following error. In order to solve this problem,this paper proposes a method of using Calman filter to estimate the motion of mechanical arm,improved the dynamic performance of servo system, this method reduces the servo errors effectively.In the aspect of control for the actuator,in order to simplify the design of the controller, the controller is divided into visual controller and actuator controller.The actuator controller adepts the personal computer and PMAC(Programmable Multi-Axis Controller)motion control card realizes the PID control. The digital PID controller is simple and reliable the PMAC motion control card can simultaneously on multiple motor control and provide good software open. The two combined perfectly realize the precise control of the actuator.After experimental verification, the performance indicators of the mechanical arm gravity compensation device’s following system developed in this subject meet the requirements of the ground experiments.