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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 (conventional housed servo motors, such as 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 heat sink).  In the case of frameless motors (such as KBM, TBM, etc.) 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 through the spindle.  In a vacuum, there is no convection cooling.  So the heat generated by the motor must be stored in some type of heat sink until the vessel can be returned to atmospheric pressure and the heat is dissipated into the air, or the heat must be removed from the vessel by some kind of direct heat transfer method. 

  2. Out gassing

    Most servo motors have polymers used in their construction.  Thermal epoxy used for potting of the stator winding.  Kevlar string used to 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 application making use of a vacuum is for thin layer coating of an object.  The “gas” from the motor can also be attracted to the target object, causing defects.

    2. The "gas" can prevent 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 a 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.