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Holding hands

When To Use Parts Sensing

Part Sensing is used as a Poke-Yoke ("fail-safing" or "mistake-proofing") design to ensure one or all of the following:

  1. The correct part is loaded into the fixture.  When a fixture is designed for more than one part, Part Sensing can be used to determine which part has been loaded.  Typically a unique feature of the part will be checked to determine which part is in the fixture and a signal is sent back to the controller to indicate what machine cycle is to be initiated.
  2. The part is seated/located correctly.  Air pressure or an electrical switch can be used to determine if the part is contacting the datums.  A signal is sent back to the machine tool controls confirming that the part is loaded properly.

The most common and inexpensive way of part sensing is with air pressure.  By routing compressed air (about 5-20 psi) to the datum locators, a properly located part will create back pressure by sealing off small air ports.  A pressure switch will signal the increase in pressure and confirm that the part is seated properly.  The machine tool cycle is allowed to initiate and the part is machined.  If the increase in pressure is not acknowledged, the machine cycle is disabled until the part is seated properly.  This assures that no part can be machined unless it is properly located in your fixture, reducing scrap, protecting cutting tools and increasing productivity.

Some limitations to this system are:

  1. Four or less sensing ports are preferred for each pressure switch.
  2. An air passage to the fixture is required for each pressure switch.
  3. Logic should be programmed into the controller to eliminate false readings.  The switch should cycle on and off between each cycle so that ports plugged by debris are not interpreted as the part being properly located when it is not.
  4. Routine maintenance is required to keep the air passages clean and to verify the system is operating as intended.

Please contact DMTworkholding for more information on justification and interface options.  DMTworkholding can provide this and other value added options to provide you a complete workholding system.