An omni‐directional, ultrasonic acoustical source for three‐dimensional position monitoring in air

Abstract

An acoustically based means of tracking the position of the end effector of a moving industrial robot arm has been proposed. The system consists of an omni‐directional acoustical source fixed to the robot arm, and several stationary sensors positioned throughout the robot's workspace. Based upon the time‐of‐flight of a 500‐kHz signal traveling from the source to each sensor, the position of the end effector can be determined. This scheme is potentially an effective, yet economical alternative to the more complex optical tracking systems currently in use. The acoustical source incorporates an exponentially tapered solid Webster's horn that is driven in resonance by a commercial piezoelectric transducer mounted on its wide end. A high‐amplitude vibration is produced at the narrow end of the horn, where the resulting sound field can be described by the piston equations. The pressure and omni‐directional characteristics of the acoustical field produced are enhanced beyond those that could be generated by a simple flat piezoelectric source alone. Results obtained with this source confirm the feasibility of using ultrasound in air as a means of accurately determining positions in three dimensions. [Work supported by General Motors Research Laboratories.]