On-Line Precision Calibration of Mobile Manipulators Based on the Multi-Level Measurement Strategy

Autonomous industrial mobile manipulator (AIMM), which is composed of a mobile platform and a robot arm of six degrees of freedom (DoFs), can move autonomously and perform dexterous tasks independently in the industrial environment. A novel on-line calibration system for AIMM in real manufacturing workshop is proposed in this paper. Compared to calibration scenarios of fixed-base robot, we focus on the large-space autonomous calibration for AIMM. To cope with the issue of high precision calibration in large space, we propose a multi-level guided-based measurement strategy, which includes the low-cost vision positioning and guidance system, and the high-precision distributed base station (BS) measurement system. The corresponding experiment proves that the total uncertainty of measurement system is less than 0.1 mm. Based on the measured data of end-effector installed at the end of robot arm, the AIMM can perform on-line calibration tasks anywhere automatically without taking into account the expensive devices for the high-precision location of mobile platform and the downtime for the robotic off-line calibration. The mean positioning error of AIMM after calibration reduces 93% based on the calibration experiment.