THE COMPLIANCE OF END EFFECTOR FORCE SENSORS FOR ROBOT MANIPULATOR CONTROL (WRIST, DYNAMICS, STIFFNESS)
Abstract
This dissertation analyzes the effect of wrist force sensor mechanical stiffness on robot manipulator control. Typically, wrist force sensors for robotic systems have been designed and fabricated viewing the transducer as an isolated element, with mechanically stiff structures instrumented with strain gages being the most common configuration. Research has indicated, however, that force control system implementation with such stiff sensors is complicated by the resulting low system damping. Thus, this thesis analyzes the overall manipulator-wrist sensor system to determine the optimal sensor parameters for control. A theoretical analysis of the manipulator system based on physical modeling was performed. The dynamic equations of motion in Cartesian coordinates for the general six link manipulator, assuming finite drive train stiffnesses at each joint, were derived. Next, the general form of the manipulator-sensor dynamics were established in a transfer function matrix formulation. From this analysis, the Cartesian stiffness of the overall robotic system was established. It was also shown that the actuator dynamics and drive train stiffness determine the dynamic response of the constrained manipulator system. Also, a control system to compensate for sensor deflections in free space due to gravity loads was developed so complaint sensors could be utilized. The theoretical analysis was verified as five different single degree-of-freedom force sensors, connected to one joint of a Puma 600 industrial robot, were experimentally evaluated. The force controlled joint was tested for both barrier impact recovery and surface tracking. In addition, the active sensor deflection compensator was evaluated for changes in load masses. The results indicate that the mechanical stiffness of a wrist sensor greatly influences the dynamic performance of both endpoint position and force controlled manipulators. The use of a compliant end effector force sensor enables larger control gains to be utilized for force control, resulting in better system performance. And by actively compensating for the sensor deflections in free space, the use of a compliant sensor does not degrade the static positioning capabilities of the robot manipulator.
Degree
Ph.D.
Subject Area
Mechanical engineering
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