Ultrasonic Sensor Triangulation for Accurate 3D Relative Positioning of Humanoid Robot Feet

A simple measurement system with a set of six ultrasonic piezoelectric transducers is presented for direct 3D positioning of humanoid robot limbs. A configuration with three emitters and three receivers leads to millimetric estimation of the distances. Millimetric resolution achievement over 70 cm range is aimed with high angular tolerance in order to mount the sensor on a humanoid robot. Sampling frequency up to 60 Hz is obtained. The sensor is then used to estimate relative positions and orientations in the space of each foot of the robot with regard to the pelvis. The principle and experimental performances of the sensor are presented in the first part with uncertainty estimations and discussions. In the second phase, the sensor has been setup on the ROBIAN humanoid robot to illustrate an application case and test the performances.