An ultrasonic measuring system of 3-D position and orientation of a robot has been proposed in the previous report.The system is based on distance measurement between ultrasonic transmitters attached to a robot arm and receivers placed around the work space of the robot.This paper describes a new method of 3-D position measurement which employs one redundant receiver and estimates the sound velocity in the measured space in real time and with high accuracy.The error distribution was simulated by using Monte Carlo method and it was proved theoretically that the accuracy achieved by this method is better than that achieved by the conventional method which uses three receivers.A3-D measuring system of which receivers are able to rotate and face up to the transmitter precisely was developed and the accuracy of it was estimated experimentally by using an NC machine too1.The average of errors of X, Y, Z-coordinates was about±0.2mm respectively in the X × Y × Z space of 300 ×400 ×400mm.The causes of the measuring error were also discussed.
