Active Control And Experiment Study Of Flexible Manipulator

With the development of science and technology, lightweight and flexible components have been widely used in mechanism. Meanwhile, the requirements on operating speed and precision of mechanism become higher and higher. Research in this area comes to the so-called flexible multibody dynamic system or rigid-flexible coupling dynamic system which features large-scale movement of rigid body and small elastic vibration of flexible components. The flexible manipulator is a typical application in this area. Since the flexible multibody dynamic system has lots of applications in high tech engineering areas such as aerospace, aviation and robot, it is of importance, both theoretically and practically, to study its dynamic modeling and active control method.With both direct piezoelectric effect and reverse piezoelectric effect, piezoelectric material can make both a sensor and an actuator, which explains its wide application in active vibration control systems. Piezoelectric actuator can make part of a component by means of either adhering or embedding, which is useful for vibration control of flexible components with large-scale movement.Based on the dynamic theory of flexible multibody system and the advanced technique of active vibration control, the dynamic analysis and control of a piezoelectric flexible manipulator are studied extensively in this dissertation. This research was funded by the National Natural Science Foundation of China (Grant No. 10472065), the Key Project of Ministry of Education of China (Grant No. 107043) and the"Shu Guang Project"of Shanghai (Grant No. 04SG16). Some achievements are acquired in both theory and application and the main research and achievements are as follows:(1) The dynamic modeling theories and vibration control of flexible manipulators are comprehensively reviewed. The research extent and contents of this dissertation are put forward.(2) Frequency characteristics of the flexible manipulator system are studied, which include the following factors: (i) arbitrary setting positions of attached mass; (ii) weight of attached mass; (iii) the ratio of joint radius with respect to the length of manipulator; (iv) joint radius; (v) moment of inertia of manipulator joint; (vi) damping. Simulation results indicate that (a) when the system is in a certain large-scale motion (i.e., non-inertial case), response frequency of the flexible arm decreases as the attached mass moves from the fixed end to the free end on the arm. It's also noticed that damping has little effect on response frequency of the arm and it only affects its dynamical equilibrium position. (b) When the system is in an uncertain large-scale movement (i.e., rigid-flexible coupling case) and the attached mass is located at far end of the flexible arm, it may result in enlarging of amplitude and decreasing of response frequency. As the attached mass moves from the fixed end to the midpoint of the arm, response frequency fluctuates instead of showing any obvious degressive trend, whereas it decreases significantly as the attached mass continues moving to the free end of the arm. Damping affects where the arm is going to stop and also affects its amplitude as well, but it has little effect on response frequency of the arm. The response frequency is subject to the change of the hub'radius when the radius is within a small range; however the radius change has little effect when the radius exceeds a certain value.(3) This dissertation discusses the influence of inertia and stiffness of piezoelectric materials on vibration characteristics of the flexible manipulator and it also provides the corresponding piezoelectric modeling. Simulation results show that: (i) when the length of piezoelectric material is very short, its effect on system dynamics is little and could be ignored; (ii) when the length of piezoelectric material is shorter than half length of the manipulator arm, piezoelectric stiffness has biggish effect on system dynamics, whereas piezoelectric inertia has less effect compared to piezoelectric stiffness. Furthermore, when the length of piezoelectric material is longer than half of the manipulator arm, piezoelectric inertia has considerable effect on system dynamics while the effect of piezoelectric stiffness is less herein.(4) Active position control of the flexible manipulator is studied in this dissertation, in which linearization control strategy and nonlinear control strategy are considered respectively. Simulation results indicate that, with linearization control strategy, the flexible arm can reach an expected position with suppressed vibration; however the time taken to position is longer than expected. While nonlinear control strategy works well with precise positioning, suppression of vibration and time control.(5) DSP control board is used in the experiment on position control of the flexible manipulator. The test apparatus mainly consists of a high performance AC servo motor, a flexible beam and a DSP board. With angular motion driven by the servo motor and vibration suppressed by a piezoelectric actuator, the flexible beam achieves precise positioning and controllable vibration. Theoretical results are verified by the experiment.The topic of dynamic modeling and control of the piezoelectric flexible manipulator is challenging both in mechanics and in control engineering, where many aspects need further study and more efforts. At conclusion, a summary of work done in this dissertation is given and some problems of interest are also brought forward for future research.