Inexpensive Ways to Measure the Performance Characteristics of a Linear Motion Device - Zaber Technologies - #9

impossible to distinguish the Z error from the component of roll error that would also be measured.

The setup for measuring the roll error is shown in Photo 5. The linear slide and granite surface plate are kept in the same positions as for pitch measurement, but the dial gauge setup is turned so that the points of contact lie along the Y axis. One can see that small motions in X and Y will have no effect on the dial readings. Nor will small changes in pitch or yaw angle. Therefore this is a good setup for measuring Z error and roll error provided there is a way to distinguish between the two. The dial gauges are set up such that the points of contact are 2.5" apart and the contact point of the rightmost probe is 2.5" from the center of the stage. It may not be immediately obvious, but a little geometry will show that the Z position is given by doubling the rightmost reading and subtracting the leftmost reading. The roll angle is given by the difference between the two readings divided by the distance between the probes (2.5" in this case). The variation in Z position and roll angle over the full range oftravel gives the Z error and roll error respectively. Z error is more commonly referred to as vertical run-out. There are simpler methods of measuring the Z error if that is your only interest, but ifyou are measuring position errors in all degrees offreedom, measuring Z error and roll error with the same setup is convenient.