# Industrial Robot Positioning Performance Measured on Inclined and Parallel Planes by Double Ballbar
## 6 Conclusions  
Renishaw Ballbar QC20-W is a tool designed and used specifically for troubleshooting CNC machine tools with a Cartesian kinematic system. When used in connection with industrial robots, it is necessary to proceed from the fact that, unlike CNC machine tools, the circular motion required for measurement is created by the simultaneous motion of several or all of the robot joints. Differences in the kinematics of CNC machine tools and industrial robots renders Ballbar software incapable of identifying and evaluating errors of industrial robots. Therefore it is necessary to approach measurements and evaluation differently. In the case of standard measurement of industrial robots, when the measuring plane is parallel to the robot base, not all robot joints move. The same applies to the so-called volumetric analysis, in which the circle in the XY plane is supplemented by two more circular arcs in the mutually perpendicular planes ZX and ZY. The purpose of the experiments of the present paper was to verify the hypothesis of the motion of all the robot joints when the desired circular path is placed on an inclined plane. The impetus for this work was the measurements previously done with the Renishaw Ballbar at the Department of Automation and Production Systems. The individual experiments described in the paper can be divided into two parts, preceded by setting the conditions for and preparing the experiment. The key step was the choice of the orientation of the measuring plane in the workspace of the selected Fanuc LR Mate 200 iC robot. Based on the recommendations of the ISO 9283 standard, which deals, among other things, with the conditions for measuring the operating characteristics of industrial robots, an inclined plane at an angle of \(-45^{\circ}\) (rotation around the Y-axis) was chosen in the robot's WCS. The starting points for determining other conditions have already been mentioned in experiments conducted in the past. In the first part of the experiments, a positional analysis was performed with a simulation model of the LR Mate 200 iC robot in the environment of the Creo Parametric software 5.0.4.0. The result is the confirmation of the hypothesis that when placing a circle on the selected inclined plane, all its joints, including the J4 joint, would participate in the circular movement of the TCP robot. Commonly, when the measuring plane is parallel to the robot base, the J4 joint is static throughout the movement. The results of the positional analysis were subsequently used to evaluate the results of measurements. The practical measurements with the Renishaw Ballbar QC20-W are described in the second part of this paper. The analysis of the measurement results was performed using polar graphs and circularity values, which represent one of the possible outputs of the Ballbar 20 software. Two series of measurements were done. In the first series, a circle with a radius of 100 mm was placed on an inclined plane, under the before-mentioned angle. The second series represented measurements in a plane parallel to the robot base. In addition to the measurement conditions, the common feature of all measurements was also the identical position of the center of the circle in the robot's workspace. Only the orientation of the measuring plane has changed. The result is the finding that in the selected position and orientation of the measuring plane, the change in the shape of the polar graph was locally caused mainly by a change in the configuration of the robot arm, which is related to the motion of the J4 and J5 joints. At the same time, the similarity of the results was observed when comparing the two series of measurements, which can be attributed to the just mentioned unchanged position of the center of the circular path. The measurement on an inclined plane provides mainly a better view of industrial robot properties. The standard measurement of industrial robot properties that utilize the Renishaw Ballbar system is conducted on the plane parallel to its base plane.