Research On Vibration Measurement And Control Of Flexible Arm Structure Based On Stereo Vision System

Due to the characteristic of being light and flexible,flexible structure is widely used in various engineering fields including Space Engineering.And flexible arm structure like flexible manipulator is an important application.Such structure has low stiffness,small damping and dense vibration modal.These factors could lead to long time persistent vibration of flexible structure while motivated by external disturbance.This will interfere the normal function of system Therefore it is necessary to test and analyze the vibration characteristics of the structure,and put forward corresponding control strategy to suppress the vibration.This paper proceeds the study of vibration problem for flexible arm structure from these three aspects—structural dynamic modeling,stereo vision vibration detection,and active vibration control algorithm.Firstly,for the problem of modeling of the experimental structure,this paper analyzes the dynamic characteristics of flexible arm structure via Hamilton principle according to the theory of modal truncation.After that dynamic model of the structure is derived to achieve its vibration mode,so that the foundation for designing vibration control algorithm is established.Secondly,based on 3D reconstruction mechanism of stereo vision,this paper studies the calibration of vision system,and then designs binocular vision detecting system and laser vision detecting system.For binocular vision,a 3D reconstruction model with four constraints is proposed based on Zhang's calibration method,and it is compared with parallax method.For laser vision,a new method to calibrate laser plane is proposed based on the collinear condition of three plane.After that vision detecting systems for measuring vibration displacement of flexible arm are built up using these two sets of stereo vision systems.According to different types of vibration,respective image processing scheme and vibration detection scheme are designed.At last vibration information of flexible arm is achieved through signal processing.Thirdly,considering the existence of nonlinear factors in flexible arm structure,ant colony PD control algorithm and nonlinear PD control algorithm are designed respectively based on ordinary PD control.For ant colony PD control,this paper abstracts the parameters into a directed graph path,and abstracts the optimization of parameters into the process of finding the optimal path on the directed graph.For nonlinear PD control,this paper puts forward two measuring indices of vibration state,and they are used as reference standard for parameter optimization in control process.Synthesizing the theoretical analysis and research above,this paper builds up three vibration experimental platforms of flexible arm structure respectively using two sets of stereo vision system.Then vibration detection scheme and control strategy are programmed based on MFC frame,and vibration measurement and control problem of structure are researched by experiment.The experimental results show that the proposed calibration method can achieve the model of visual system effectively,and vibration of flexible arm can be measured accurately.Compared with normal PD control,the proposed two control algorithm can suppress the vibration of flexible arm faster and more efficient,especially small amplitude vibration.Thus the feasibility of system calibration method and vibration measurement method are verified.And the superiority of designed algorithm in vibration control is proved too.