The purpose of this work is to demonstrate that it is feasible to calibrate a small serial robot using a new low-cost three-dimensional measuring device and an automated procedure. The new measuring instrument consists of three wireless digital indicators. These indicators are fixed on an aluminum support, orthonormal to each other. Each indicator has a measuring accuracy within 3 μm. The measuring instrument uses a zeroing device which allows for the definition of the tool center point (TCP) with high accuracy and high repeatability using the principle of kinematic couplings.
The calibration method developed for this new instrument is applied to a small six-axis robot, ABB’s IRB 120. The robot is modeled using Denavit-Hartenberg parameters by including all the geometrical parameters and the compliance of the joints. An additional parameter defines the geometrical relation which exists between the parallel axes of the robot to correct the problem of proportionality of the model.
Using position and orientation constraints, a pool of 360 robot configurations are generated in simulation. Then, the measurements are collected by constraining the new device to three 0.5-in precision balls located in the workspace of the robot at the TCP positions corresponding to the generated configurations. The set of configurations selected for identification of the parameters are chosen based on an observability analysis. The parameters of the model are identified using linear regression with the least squares method.
The performance of the calibration is validated using a laser tracker on a set of 506 robot configurations randomly generated in the complete workspace of the robot. The average, the standard deviation and the maximum absolute errors are reduced from 2.628 mm, 1.087 mm and 6.282 mm to 0.207 mm, 0.087 mm and 0.481 mm, respectively, after calibration. Finally, a brief comparison of the performances of several existing calibration methods using different measuring instruments is presented. It shows that the performance of this new calibration method is similar, although slightly lower, to the performance offered by the most common robot calibration method which is based on the use of a laser tracker, a much more expensive measuring device.
| Date | 18 Aug 2016 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Ilian Bonev (Supervisor) |
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Gaudreault, M. (Author),
Bonev (Supervisor),
18 Aug 2016Student thesis: Master's thesis › Master in Engineering: Engineering