Development of an onsite calibration device for robot manipulators

Abstract

A novel in-contact three-dimensional (3D) measuring device, called MultiCal, is proposed as a convenient, low-cost (less than US$5000), and robust facility for onsite kinematic calibration and online measurement of robot manipulator accuracy. The device has μm-level accuracy and can be easily embedded in robot cells. During the calibration procedure, the robot manipulator first moves automatically to multiple end-effector orientations with its tool center point (TCP) constrained on a fixed point by a 3D displacement measuring device (single point constraint), and the corresponding joint angles are recorded. Then, the measuring device is precisely mounted at different positions using a well-designed fixture, and the above measurement process is repeated to implement a multi-point constraint. The relative mounting positions are accurately measured and used as prior information to improve calibration accuracy and robustness. The results of theoretical analysis indicate that MultiCal reduces calibration accuracy by 10% to 20% in contrast to traditional non-contact 3D or six-dimensional (6D) measuring devices (such as laser trackers) when subject to the same level of artificial measurement noise. The results of a calibration experiment conducted on a Staubli TX90 robot show that MultiCal has only 7% to 14% lower calibration accuracy compared to a measuring arm with a laser scanner, and 21% to 30% lower time efficiency compared to a 6D binocular vision measuring system, yielding maximum and mean absolute position errors of 0.831 mm and 0.339 mm, respectively.

Keywords

Calibration device / Kinematic calibration / Onsite calibration / Absolute accuracy

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