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Application Note

Using PRI Motorized Stages at Cryogenic Temperatures

Revised 27 Jan 2000


Some precautions and adjustments to the stages are necessary at cryogenic temperatures. The differential expansion coefficients differ for the aluminum of the slide body and the tool steel of the rails. Calculation shows that as the slide assembly cools down the aluminum shrinks more then the tool steel and therefore the ways become significantly "over-preloaded" and may tighten up to the point to which they will not move. There is about .005" of differential shrinkage when going from room temperature to liquid nitrogen temperature.

Adjusting the Preload:

To use a slide at liquid nitrogen temperature first remove all the preload at room temperature, and then remove about an additional .005". The keepers that contain the crossed rollers will now be free to slide back and forth in the crossed roller ways. Therefore be careful not to jar the slide or otherwise move the roller keepers. The roller assemblies should be centered with respect to the way assemblies when the slide is centered in its range of travel.

Caution: relieving the preload can cause problems if the slide is mounted vertically because the rollers will fall to the bottom of their travel. When the slide is cooled and tightens up the roller keeper assembly will not be able to move in one direction.

Other Considerations at Cryo Temperatures:

A less common problem arises from differential expansion in the bearings that support the lead screw. The lead screw assembly is preloaded by the use of springs and therefore should be satisfactory at liquid nitrogen temperatures.

There will also be a slight change in the center distance between the axis of the lead screw and the axis of the motor that could, under certain circumstances, cause the gear mesh to bind. When you order a stage for cryogenic application we select one that has a generous tolerance for center to center distance.

Customer Feedback:

Some customers have reported best results with our stages at cryogenic temperatures if the cooling process is done in several phases, with a brief exercise of the slide in between phases. The exercise period is reported to minimize the possibility that the slide will bind up when the final temperature is reached.

Customers who have followed the suggestions above have used our stages at liquid nitrogen temperatures without problems. Other customers have used the motors and stages sucessfully at near liquid helium temperatures, but we cannot guarantee reliable operation at this level.

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