| While Pick&Place robots are widely used in industries, parallel robots with itsspecial structure, usually have features as high stiffness, high speed and highacceleration thus they are especially appropriate for packaging industries. But theexisting control of robots basically uses kinematics to control robots without takinginto consideration the change of load. The program of a robot is likely to be writtenand debugged for a specific condition during installation and then the robot willalways run that same program.The Delta parallel robot is chosen as the subject of this paper to find whatproblems will happen if the load of robot has a wide range of change while thecontrol method computed torque control remains unchanged. The main problem isthat the tracking error of motion will become larger and affect the performance.Adaptive control, with the feature that it updates some parameters in a controlsystem, is chosen to update the load of robot and solve this problem.First of all, the kinematic model and dynamic model of the Delta robot is set upwith reference to some other articles and the models are prepared for furthersimulations or experiments.Then, theory about computed torque control (CTC) is given and simulation ofthe CTC for Delta robot within Simulink is conducted with some data forcomparison as result. After simulation, experiments of CTC for the Delta robotshows that when load of the robot changes with the program unchanged, the trackingerror of motion will increase as load rises. When there is a2kg load, the peak valueof tracking error become4times as big as when there isn’t any load.Finally, theory about adaptive control is discussed and adaptive controlequations for the Delta robot is given. Simulation results show that the trackingerror becomes smaller compared with CTC, meaning adaptive control has a betterperformance. After simulation, experiments are conducted and after thorough studyof adaptive control, it is concluded as suitable for the load change problem. |
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