# Industrial Robot Positioning Performance Measured on Inclined and Parallel Planes by Double Ballbar
## 5 Measurement with Renishaw Ballbar QC20-W
### Results Summary  
As part of measurements with the Renishaw Ballbar QC20-W, the possibility of measuring a circular path placed on an inclined plane has been confirmed as viable. The conducted experiments consisted of two series of measurements. The first of them was done with the circle radius of 100 mm, placed on an inclined plane at an angle P = \(-45^{\circ}\) concerning the robot's WCS. Two possible arm configurations--NOFLIP and FLIP, exist for the selected position and orientation of the measuring plane. The results of the measurements and their representation in polar graphs show a significant difference in the shape of the circular path between the two configurations. This difference has also been confirmed by the average circularity values in both measurements. Based on the motion analysis of the individual robot joints in connection with polar graphs, the motion of the J4, J5, and J6 joints was identified as a possible source of these errors. Subsequent measurements ruled out the effect of the J6 joint. The mentioned measurement was based on the modification of the robot program so that in two measurements in the FLIP configuration, the motion was different only in joints J4 and J5. The motion of the other joints during the measurement was identical.  
The second series of measurements took place with the same radius of the circle \(-100\) mm, but in a plane parallel to the base of the robot or parallel to the workbench. These measurements aimed to further examine the influence of the J4 and J5 joints on the measurement results. With the selected orientation of the measuring plane, the position of the joint J4 is static during the entire travel along the circular path. Depending on the selected configuration, the respective values are \(0^{\circ}\), \(-180^{\circ}\), or \(180^{\circ}\). By analyzing the range of motion of individual robot joints and the polar graphs obtained from the measurement, the greatest influence on the deformation of the circular path can be attributed to the selected configuration of the robot arm and especially the motion of the J5 joint.  
Although both series of measurements took place in two different orientations of the measuring XY plane, the center of the circular path was the same for both orientations. Partial similarity when comparing the polar graphs obtained in the measurement on an inclined plane and the FLIP configuration, with the polar graph in the second series of NOFLIP measurements and configurations, relates to this fact. This similarity is also indicated by the value of circularity, which takes on values of \(409.8\) mm, or \(389.3\) mm at an inclined plane, and a value of \(385.2\) mm when measured in a plane parallel to the robot base. At the same time, when comparing the ranges of motion of the J5 joint, it is possible to rule out their mutual similarity of motion in the above-mentioned configurations and orientations of the circular path. Based on this, it can be argued that the change in the shape of the polar graph is influenced not only by the J5 joint but also by the motion of the joint J4. When measuring was done in a plane parallel to the robot base, the mentioned influence of the J4 joint was corrected, as the J4 joint acquired only static values.