A comparative evaluation of three industrial robots using three reference measuring techniques

Abstract

Purpose – The purpose of this paper is to present a technique for assessing and comparing the static and dynamic performance of three different models of small six-axis industrial robots using a Renishaw XL80 laser interferometer system, a FARO ION laser tracker and a Renishaw QC20-W telescoping ballbar. Design/methodology/approach – Specific test methods are proposed in this work, and each robot has been measured in a similar area of its working envelope. The laser interferometer measurement instrument is used to assess the static positioning performance along three linear and orthogonal paths. The laser tracker is used to assess the contouring performance at different tool center point (TCP) speeds along a triangular tool path, whereas the telescoping ballbar is used to assess the dynamic positioning performance for circular paths at different TCP speeds and trajectory radii. Findings – It is found that the tested robots behave differently, and that the static accuracy of these non-calibrated robots varies between 0.5 and 2.3 mm. On the other hand, results show that these three robots can provide acceptable corner tracking at low TCP speeds. However, a significant overshoot at the corner is observed at high TCP speed for all the robots tested. It was also found that the smallest increment of Cartesian displacement (Cartesian resolution) that can be taken by the tested robots is approximately 50 μm. Practical implications – The technique used in this paper allows extremely accurate diagnosis of the robot performance, which makes it possible for the robot user to determine whether the robot is in good or bad condition. It can also help the decision-maker to select the most suitable industrial robot to achieve the desired task with minimum cost and specific application ability. Originality/value – This paper proposed a new method based on the performance verification approach for solving the robot selection problem for flexible manufacturing systems. Furthermore, despite their importance, bidirectional repeatability and Cartesian resolution are never specified by the manufacturers of industrial robots nor are they described in the ISO 9283:1998 guide, and they are rarely the object of performance assessments. In this work, specific tests are performed to check and quantify the bidirectional repeatability and the Cartesian resolution of each robot.

Uncertainty measurement with the kinematic telescopic bar during industrial robot inaccuracy tests

“…Although the use of the QC20-W Ballbar system for CNC machine tools is very wide [1,4,[8][9][10], in robots it is applied on a much lower scale [2,[11][12][13][14]. Some authors [11,12] compare the accuracy of selected industrial robots with the use of a ball-shaped, telescopic kinematic bar. ABB IRB 1600 industrial robots were used in various tests (YZ and XZ) for variable radius values (100, 150 and 300 mm) and feed rates ranging from 20 to 700 mm/s.…”

“…The measurement was taken at the selected point with defined coordinates (0, 65, 149 mm) in the robot base coordinate system. Based on the results, the authors [11,12] determined the relationship between the programmed flow rate of the effector effect and the recorded deviations but did not determine measurement uncertainty. It is therefore possible to conclude that these results are not precise and are only subjective.…”

Industrial Robot Repeatability Testing With High Speed Camera Phantom V2511

“…A standardised testing method for industrial robots is defined in ISO 9283:1998 [22]. The major problem in robot testing and diagnostics consists in the lack of proper testing and measurement equipment [7][8][9][13][14][15][16][17][18][19]. This is by no means a problem in CNC multi-axis machine tools, where a wide range of diagnostic systems suitable for different applications are easily accessible [5][6][7][8][9].…”

“…This is by no means a problem in CNC multi-axis machine tools, where a wide range of diagnostic systems suitable for different applications are easily accessible [5][6][7][8][9]. This is confirmed by studies described in a relatively small number of existing research papers devoted to robot testing [2,[7][8][9][13][14][15][16][17]. One of the most common testing methods applied in robotics is measurement with laser trackers.…”

“…Similarly, in the case of ballbar instrumentation, the measurement can be taken only in a defined plane. In addition, the range of positioning errors in circular path tests (usually 1 mm) frequently proves insufficient in large industrial robots testing applications [16,17]. An interesting solution for robot error assessment is proposed in [14,15], where a custom made instrument consisting of several ballbar extension bars enables error detection in a multi-dimensional plane.…”