Identifiability and improvement of adjoint error approach for serial robot calibration

In this paper, we first analyze the identifiability of POE based Adjoint error approach. By carefully examining the linear dependence between calibration Jacobian columns, it is proved that joint offsets and Adjoint errors cannot be identified simultaneously, and the maximum dimension of identifiable parameters is 4r + 2t + 6. Some more scenarios are considered to augment the Adjoint error approach. To satisfy the constraints on joint relations, constrained method and projection method are proposed. Moreover, we present the identifiability of reduction ratios and joint pitches. Simulations of a 6 Degree-of-Freedom robot and a SCARA robot are given to illustrate and compare our methods. It shows that the constrained method can handle such situations effectively and yields better results.

I. Introduction

The advancement of technology makes more and more robots serving for factory automation, especially in computer/communication/consumer electronics (3C) industry with higher demands on precision, efficiency and adaptation. Offline programming is often used to quickly develop the robot-based automation system, and vision is now a regular tool for complex parts localization. Accuracy of the robot is of vital importance if a high precision of 0.03mm is expected in off-line programmed or visual guided motion. Kinematic calibration is an effective way to improve robot accuracy.