Improved robot trajectory from acoustic range servo control

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Abstract
A technique is described for improving the accuracy of the path followed by a robot arm in precision tracking of an object surface contour. Acoustic pulse echo data from a sensor mounted on an end effector was processed to compute distance to an object surface several inches from the sensor. Real-time path modification was then based on this computed distance. An eddy current proximity sensor positioned approximately 30 mils from the surface was used to monitor the acoustic sensor and robot performance. Both sensors produced identical results in tracking variations in distance from the surface with the robot in open loop mode for a linear path over a precision ground surface for which the robot was taught the two endpoints of the trajectory. Variation from the linear path was as large as 10 mils. With the acoustic range sensor providing input for a control algorithm to maintain a fixed offset as the robot traversed the surface, path deviation was reduced to +/- 3 mils using single measurements in the real-time mode. This is attributable to the inherent noise level of the sensor system. Averaging 10 measurements reduced the standard deviation in position measurement and control to +/- 1.2 mils.

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