| Nowadays, as the problems of the ageing of population and the shortage ofhuman resources etc. have become more and more serious, it is an urgent need forthe robots to do part of jobs as a replacement of human beings. As one of the keysystems of the robot，the robotic arms’ dexterous operation capability and friendlyinteraction will have a great effect on the region of the application. Supported bythe theme of dexterous arm in the major project of the National High TechnologyResearch and Development Program “High performance unit and system ofhumanoid robot”, the light weighted robotic arm is investigated in this thesis, whichincludes the joint controller architecture, joint parameters identification and thecontrol methods etc. In addition, position control, impedance control and zero forcecontrol of light weight manipulator have been further studied in this thesis.Firstly, a set of6DOF manipulator system is designed based on thecharacteristic of light weight manipulator in the paper. Considering of the elasticcomponents, such as harmonic gearbox and torque sensor, are integrated in theanthropomorphic manipulator joint, it is reasonable to control it as an elastic jointwith the spring and damping structure. By the analysis of the controller of flexiblejoint, the nonlinear part and linear part of flexible joint control laws areimplemented in the Cartesian space controller based on the digital signal processor(DSP) and joint controller based on field programmable gate array (FPGA)respectively. The joint controller not only implements signal collection andprocessing of the sensors, but also realizes the motor vector control modular inVery High Speed Integrated Circuit Hardware Description Language (VHDL) every50s, which is a quarter of the joint controller, so that the motor can perfectly trackthe desired torque given by the flexible joint controller. With the information ofmotor current, joint torque and motor velocity etc. measured by the joint controller,we can identify the key parameters of flexible joint, which include the joint stiffness,damping, friction and so on, in different experiments. These parameters provideaccurate values in the following simulations and experiments to verify the flexiblejoint control method.In the theoretical study of the flexible joint control, firstly, the flexible joint system was simplified and descripted in a port controlled Hamiltonian system withdissipation (PCHD) with a certain physical meaning. Then, by analyzing theinterconnection matrix and damping matrix of PCHD system, and studying thetraditional passivity control method, an interconnection and damping assignmentpassivity based control (IDA PBC) method is put forward to implement thecompliance control of flexible joint robot. By modifying the interconnecting matrixand damping matrix, this method can reshape the energy and inject damping into theclosed loop system to make sure the system asymptotically stable at the desiredposition. Finally, the flexible joint model and controller are built in Simulink withthe SimMechanics toolbox, and the results verify the proposed method.As the friction has a great effect on the control performance, a friction observeris proposed based on IDA PBC method for friction compensation. The dynamicsfriction compensation not only improves the position and force tracking capacity,but also assures the stability of the manipulator system. Experiments are carried outon the joint of the6DOF manipulator to verify the compensation，and the resultsshow that position accuracy as well as torque vibration of the flexible joint systemare evidently improved in the position control. In addition, the force tracking abilityof impedance control is also improved by the friction compensation.Finally, integrated all the research findings into the manipulator system, thevalidity of the light weight manipulator system and control algorithm are verifiedby performing the position tracking control, impedance control and zero forcecontrol experiments in the Cartesian space. |
PDF Full Text Request