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AKM, KBM in a vacuum

There are three issues with motors in a vacuum and/or high altitude:

  1. Heat dissipation

    Most Kollmorgen frame motors (AKM, VLM, etc) rely on convection cooling.  We expect heat to be dissipated into the air over the full body of the motor and also through the motor flange (using the machine as a heatsink).  In the case of the KBM frameless motors, we rely on thermal conduction to transfer the heat, from the stator, to the machine frame.  The rotor also generates heat and will require heat transfer into the spindle.  In a vacuum, there is no convection cooling so the heat generated by the motor has to be (either) stored in some type of heat sink until the vessel can be returned to atmosphere pressure and the heat is dissipated into the air or the heat is removed from the vessel by some kind of heat transfer method. 

  2. Out gassing

    The AKM, KBM motor has polymers used in its construction.  Thermal epoxy used for potting of the stator winding.  Kevlar string used help bond the magnets to the rotor.  The magnets themselves are powder bonded by a glue.  When put into a vacuum, these materials will outgas.  The two issues are:

    1. One use of a vacuum is thin layer coating of an object.The “gas” from the motor can also be attracted to the target object and cause defects.

    2. Another issue is the gas preventing the ability to reach the level of vacuum needed.It’s like having a leak in the vessel.

  3. Creepage – Clearance (Arc to ground)

    Air is actually a pretty good insulator, so it is a factor that contributes to a motor’s ability to operate at high voltage with specific creepage/clearance distances. When a vacuum is pulled, the ambient air and its insulating properties are removed. In vacuum it is easier for arc-over to occur from a hot energized surface (i.e., a PCB trace or motor winding) to a grounded metal surface (i.e., core stack, housing enclosure or customer’s machine structure).  Reducing the operating voltage can sometimes solve this problem without motor design changes.