An automated method to calibrate industrial robot joint offset using virtual line-based single-point constraint approach

Abstract

This paper describes an industrial robot joint offset calibration method called the virtual line-based single-point constraint approach. Previous methods such as using CMM, laser trackers or cameras are limited by the cost or the resolution. The proposed method relies mainly upon a laser pointer attached on the end-effector and single position-sensitive detector (PSD) arbitrarily located on the workcell. The automated calibration procedure (about three minutes) involves aiming the laser lines loaded by the robot towards the center of the PSD surface from various robot positions and orientations. The intersections of each pair of laser lines eventually should converge to the same point after compensating the joint offsets. An optimization model and algorithm have been formulated to identify the robot offset. For the highly precise feedback, a segmented PSD with a position resolution of better than 0.1 µm is employed. The mean accuracy of robot localization is up to 0.02 mm , and the mean error of the parameter identification is less than 0.08 degrees. Both simulations and experiments implemented on an ABB industrial robot verify the feasibility of the proposed method and demonstrated the effectiveness of the developed calibration system. The goal of fast, automated, low-cost, and high precision offset calibration are achieved.

Development and sensitivity analysis of a portable calibration system for joint offset of industrial robot

“…A model of the IRB1600 robot according to DH conventions is built [9]. Consider the joint offset, let i δ denote the offset value of the ith joint, in the DH convention each homogeneous transformation is represented as,…”

“…Thus, the total number of calibration parameters to be identified is 8 (4 joint offsets + 4 laser line parameters). The calibration method represented in [9] relies mainly upon a laser pointer attached on the end-effector of a robot and single PSD. The calibration procedure is aiming a laser beam from the laser pointer at the same point from various positions and orientations by using hybrid visual/PSD servoing [11], as shown in Fig.…”

“…To fit this requirement of joint offset calibration, a new parameter calibration approach called virtual lines-based single-point constraint (VLBSPC) is proposed and a calibration device based on PSD and laser was implemented in our paper [9]. Unlike previous calibration methods, this approach does not need any physical contact and the developed device is affordable.…”

Industrial Robot Calibration Using a Virtual Linear Constraint

“…Liu et al [17] described a virtual line-based singlepoint constraint approach. This approach relies mainly upon a laser pointer attached on the endeffector and single PSD arbitrarily located on the work cell.…”

A reflected laser line approach for industrial robot calibration

“…Liu et al have proposed a line-based method to calibrate the robot's external parameters [7] and also an approach to calibrate the robot's joint offset [8]. Both methods were developed in our lab.…”