Application of Acoustics to Control Kinematic and Dynamic Behavior in Robots

Abstract

A 215 kHz acoustic pulse-echo ranging system was integrated with a robotic arm and real-time controller system to enhance the precision of the manipulator trajectory relative to an object surface. Total ranging capability was two feet. The noise limit of the system is attributed primarily to thermally induced fluctuations in the air velocity and the inherent stability of the sensor electronic design. This limits distance measurment accuracy to +/- 3 mils in data taken at 10 Hz rates. Signal averaging ten readings improves the precision to +/- 1.2 mils. This determines the limit of accuracy of position control using the acoustically measured range for position control of the robot arm. Open loop (non-servoed) position accuracy was normally +/- 6 mils for trajectories over one foot.. Thus kinematic accuracy was improved by a factor of 2 to 5 times. down to the noise limit of the sensor. Dynamically changing force loading on the robot arm causes deflection of the links and error in the true portion. A 1.5 kg mass produces an 18 mil sag vertically of the robot arm end point. Using the acoustic sensor for servo control, vertical position error was reduced to +/-3 mils. The performance of the acoustic sensor was verified on a test surface accurate to +I- 0.1 mil over two feet with an eddy current sensor accurate to +/- 0.1 mil.