Machine does not home out

The sequence of homing out is the following. Machine goes some what at a rapid pace to the Reference switch, slows down, looks for a marker pulse and learns its home position. Then it might again move in either direction to go to Grid shift position. Then it will pull out a number from parameter and give itself a coordinate position.

 1)      Make sure the machine jogs or moves controllably (Not running away) in jog mode.

2)       Make sure the switch for home comes on and the input bit comes on, before it is supposed to home out.

3)      Carefully try actuating the home switch at the center after the homing process and see if the axis slows down and try to home out. This indicates whether the switch is OK. If it does not slow down then the switch is faulty

4)      If it slows down and still not homing out, this is either in the feedback device (Either a Resolver or encoder or Scale), cable or the board following the unit is faulty. Refer to positional feedback device sections.

5) In most OEMs you can adjust lower the reference speed in parameters to see if it homes out.  In Fanuc control some OEMs uses a timer. You can increase the timing and see if it homes out. In these cases the speed at which it homes out is crucial.

6) Homing is by means of a Pulse which comes on once a revolution. It comes on for a real short time. It can be recognized only with a scope. Heidenhain sells a diagnostic unit which can be put INLINE to test it too. It is not unusual for the feedback device to work normally and still not home out.

7) Watch out in old controls for the standstill following error. If the following error is high in an axis it may not home out either.

Author: Ven Swaminathan. Email - Ven@cnconestop.com

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