Ultrasound-based robot position estimation

A novel 3-D ultrasound position sensor provides low-cost, high-precision measurements of the Cartesian position of a robot wrist within a the robot's workspace. These measurements can, for instance, be used in a taskspace feedback loop to reduce the kinematic error. The basic idea is to mount ultrasound senders on the manipulator wrist and compute the 3-D Cartesian position of these sensors using 1-D range measurements between the senders and an array of ultrasound receivers at fixed, known locations. The main obstacle to precise range measurements is the presence of air turbulences and convection currents. This gives rise to noise which is spatially and temporally correlated. A stochastic model of this noise is presented and backed by experiments. It is proposed that the changing 3-D Cartesian position of the moving wrist is tracked by the sensor using a modified extended Kalman filter which incorporates the stochastic noise model and information derived from a static reference sender.