Real-time optical measurement of robot structural deflections

This paper presents a sensor system, called DIOMEDES (Laser DIode Optical System for MEasuring Structural DEflectionsS), used to measure in real-time the spatial structural deflections of the flexible links of a robot. The deflections are measured at the tip of each link. This measurement is crucial because the deflections affect the position and orientation of the robot end-effector. The system consists of three semiconductor laser diodes and three position sensitive detectors (PSD's), one mounted in the focal plane of a lens. The laser diodes are mounted at one end of the link, and the PSD's at the other end. The PSD is of a planar type and measures the position co-ordinates of the laser spot on the sensor surface. The deflections are calculated in real-time from the co-ordinates measured by the PSD's. Equations are derived for the calculation. The calibration of the sensor system is discussed to derive the system parameters necessary for the calculation of the deflections. Finally, an experimental set-up is presented to demonstrate the feasibility of the sensor system to determine in real-time the spatial structural deflections of a flexible link. © 1991