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The stages are carefully cleaned to UHV standards and baked out before delivery to the customer, and should therefore not be touched with bare hands. The stages should never be immersed in cleaning solvents because the special vacuum-compatible lubrication system may be disrupted. Also, the motors have internal areas that may trap cleaning solvents. Should a motor or stage become fingerprinted, use a clean room wipe moistened with a mixture of freon and alcohol. If the contamination is extensive, return the item to PRI for disassembly and cleaning.
The stages are constructed of a special aluminum alloy, and are machined and cleaned to minimize out gassing. The crossed roller ways and assemblies are made of 440C stainless steel, which is magnetic. They are lubricated with dry film lubricants. The lead screw is ground from stainless steel, and is coated with both dry and wet film lubricants which can be disturbed by improper cleaning. The lead screw will attract dirt and dust if improperly stored. It is therefore desirable to install the slide in vacuum promptly and to keep it there.
One of the most difficult things to achieve in vacuum is a tight, smooth, lead screw. In PRI stages we use a special nut which includes a set screw that is visible from the top of the slide. The set screw pushes down on a small Teflon slug which in turn pushes against one side of the nut, thereby eliminating backlash. However, if this screw is over-tightened the resulting friction may stall the motor. The set screw is adjusted at our laboratory, and no further adjustment should be required. Adjustment is tricky, and the user should consult us before changing the setting. There is also another small set screw that pushes against another small plug. This one presses against the side of the shaft that protrudes from the nut. Once again, this screw was adjusted at our lab and should not be disturbed.
Screws on one side of the slide adjust the pre load of the crossed roller way assemblies, and these screws should be left undisturbed. The disassembly of the gearbox from the main slide body could result in improper alignment between the lead screw and the axis of travel after reassembly.
The lead screws on the slides are not intended to be of superb accuracy. However, because the lead screws are ground to make them smooth, the accuracy is acceptable for most applications. Accuracy will vary as a function of the load and of the amount of power applied to the motor. Repeatability will vary with the same parameters. A variation in step size on the order of 20% will occur due to variations in friction with the lead screw, in torque produced by the motor, in load, and in the mesh of the gear teeth.
The slides have a pattern on both top and bottom that allows them to be compounded with other slides from our line. We recommend that slides be compounded at our labs. Please call for details if you wish to compound slides that were not originally compounded by us.
The motors can be run for several minutes without overheating as long as the motor operating voltage is kept between 16 and 24 Volts. Continuous operation of the slides must be performed with great care. Please consult our Application Note Using PRI In Vacuum Motors for details.