Position control of a robot end-effector based on synthetic aperture wireless localization

The implementation of lightweight robot concepts requires novel measurement and control strategies to deal with the flexibility of the robot arm. To the authors' best knowledge this paper introduces for the first time an innovative closed-loop concept to measure and control the absolute position of the tool center point (TCP) based on a synthetic aperture wireless localization approach. A radio-frequency identification (RFID)-like backscatter transponder is attached to the TCP, and several radar base stations measure the respective roundtrip time-of-flight and phase of the backscattered transponder signals. Inverse radar apertures are synthesized based on a small movement of the TCP. The small TCP trajectory is tracked with simple relative sensors. A holographic synthetic aperture reconstruction algorithm then determines the absolute TCP position - i.e., the trajectory coordinates in the world coordinate system. This absolute positional information is used to observe the control system and identify model errors, which are minimized in a closed-loop procedure. This iteratively improves both the system model and control quality as well as the precision of the synthetic aperture wireless localization. System simulations and first test results prove that the novel concept is suited to measure and control the position of an end-effector with mm-precision, even if the initial system model is partly erroneous.