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Closed loop end piece control of a servo controlled manipulator

University of British Columbia

This thesis discusses the possibility of attaining closed loop end piece control of a servo controlled manipulator by externally modifying the independent control loop set point of each robot link. This procedure leaves the existing servo control loops intact and thus has the benefit of acquiring the advantages of an advanced control strategy while retaining the inherent reliability and stability of the existing control loops. Algorithms are proposed for compensating for known disturbance torques, eliminating end piece position errors, and applying specified forces to the surroundings with the end piece. These algorithms are demonstrated for the three degree of freedom case using a simulation package ROBSIM.FOR which simulates the response of a servo controlled manipulator to set point inputs. To compensate for known disturbance torques the torques generated by the robot control system are assumed to be directly proportional to the changes in set points. These approximate relations are used to estimate the adjustment in set points necessary to generate the required additional joint torques. Simulation results show that this method is effective in compensating for gravity disturbance torques. The Jacobian relates changes in position of the end piece to changes in joint angles. Using the Jacobian combined with a weighting factor to prevent overshoot an algorithm is developed which drives end piece position errors to zero. The transpose of the Jacobian is used to relate forces exerted on the surroundings by the end piece to generated joint torques. The required torques are created by adjusting the set points. Simulation results indicate that this method can be used to exert specified forces. Force control is more difficult to achieve than position control because the robot interacts physically with its surroundings. The ability of the robot to exert forces depends strongly on the robot's configuration. All work in this thesis can be generated using the single program ROBSIM.FOR.

Text

2010-05-26

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http://hdl.handle.net/2429/25054

Mechanical Engineering

University of British Columbia

Graduate