Repairing MINI-1(PM500-1L) stage (25mm travel, 50mm/sec speed, 0.025micron precision)

Sergei P. Skorobogatov
sps32 (at)

Manufacturer: Kensington Laboratories (Newport Corporation), USA

Date of production: Unknown

General information:<wo=Motion%20Control

This is another motorised stage that came second-hand and in a poor working condition. This time it was a Kensington ultra-precision compact linear stage which has outstanding positioning accuracy and performance. Unfortunately, even moving the stage manually was problematic. The movement was very stiff and unpleasant noise was produced during the move. The stage did not respond to the controller commands and sometime produced unpleasant noise. I decided to investigate the problem and, if possible, repair the stage.

First, the encoder compartment was opened. Simple observation revealed some damage caused to the glass encoder. There were a few scratches on it, probably caused by dropping the stage on a floor.

Further disassembling revealed that the positining nut was tighten too high on the leadscrew. As a result some shaving appeared at the end of the leadscrew. The damage to the glass encoder can now be observed clearly and very likely they are not fatal as they appeared to be below the limit detection area. The problem was fixed by slightly displacing the encoder plate so it will not touch the interference plate.

The positioning nut was disassembled and untightened to reduce the tension, then assembled back.

The motor was still not operational. To remove and test it, the handle was opened and unscrewed first. This allowed to open the belt compartment and remove the belt.

Then the motor was untighten and pulled out. The gearwheel was unscrewed and the tachometer pulled out of the shaft. Testing the motor with a power supply shown that it is irrecoverably damaged. A new motor and tachometer were ordered. Once the assembly arrived, the shaft of the motor was filed to the same shape as it was in the original motor. Finally I assembled the stage back and test it. Everything worked perfectly.

Sergei Skorobogatov <Sergei.Skorobogatov (at)> <Sergei.Skorobogatov (at)>
created 08-11-2004 -- last modified 17-11-2004 --