11-09-2007, 06:32 AM
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| | | Join Date: Sep 2005 Location: USA Age: 60
Posts: 755
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I can answer two of your questions. For the motor and controller specifications, you'll have to find the Fanuc documentation. They did publish a "DC Spindle Descriptions" manual for each model, which should have the specs you need.
Fanuc DC spindle controllers use a variable field voltage. There are circuits on the controller board to weaken the field as the motor speed increases. You'll probably notice that the field voltage will be pretty constant until the motor reaches a certain speed (say, 1000 or 1500 rpm), then it begins to ramp down as the speed increases.
The 12 SCRs are because these are 3-phase FULL WAVE amplifiers, just like the Fanuc servo drives. 6 are facing "forward" to control the motor current running in one direction, the other 6 are facing "backward" to control the motor current in reverse. You will probably notice another 2 smaller SCRs and a pair of diodes that are used as a single phase rectifier to control the field current.
The controller board has two feedback circuits, one for current feedback, and the other for a speed (velocity) feedback. The current feedback comes from a coil that's wound around one of the DC armature outputs, which generates a small current proportional to the armature current. The tach provides the speed feedback, and is mounted on the end of the motor shaft. The tach MUST be kept in good order for proper speed control. The tiny brushes last a long time, but you do have to occasionally clean the tach commutator. I like to rotate the motor slowly and use a pencil eraser for this.  |
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