Servo Driven 4th Axis for CNC Mill

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awemawson:
Thanks Pete.

Not much done today as I was planting hedges - a 100 metres of 'em :(

However I've bored and reamed the pulleys and test mounted the drive enclosure on the back of the SEM servo motor, and fitted the encoder thus proving that the allowance for belt tension is ok. But is also shows me I need to bore a hole to let me fix the encoder pulley's grub screw. I'll tap it and seal it with a larger grub screw when the settings are finalised.

Andrew

Pete W.:
Hi there, Andrew,

I'm confused! :scratch: :scratch: :scratch: :scratch: :scratch: :scratch:

You seem to have mounted the larger pulley at the smaller end of the casing. Is that because it's just a trial assembly? Or have I missed something?

awemawson:
Pete,

Yes you ARE confused! :lol:

The housing has it's two circular ends the size that they are to accommodate the existing mounting holes for the SEM servo motor (larger end) and the Heidenhain encoder (smaller end). However the encoder needs to be slowed down to give 100 counts per motor rev, and not the 125 that one revolution of the encoder gives. Hence the encoder has a 50 tooth pulley, and the servo motor has a 40 tooth one.

Thus one 'table revolution' gives x90 (worm wheel ratio) x4 (gear train ratio) x100 (encoder pulses per motor rev)

so 90 x 4 x 100 = 36,000 which is the count the TNC355 controller needs to give the required accuracy of 100 turns counts per degree

Andrew

Andrew

philf:

--- Quote from: awemawson on January 21, 2014, 05:00:07 PM ---
Thus one 'table revolution' gives x90 (worm wheel ratio) x4 (gear train ratio) x100 (encoder pulses per motor rev)

so 90 x 4 x 100 = 36,000 which is the count the TNC355 controller needs to give the required accuracy of 100 turns per degree

--- End quote ---

Andrew,

Shouldn't "100 turns per degree" be "100 pulses (or counts) per degree"?

Phil.

awemawson:
Phil yes it was a typo,

The TNC355 requires either 18,000 or 36,000 encoder 'counts' per 360 degree 4th axis revolution (set by parameter) - I've settled on 36,000 as it makes the gearing easier. So there are 100 encoder counts per degree.

To turn the table by one degree takes one revolution of the servo motor.

:coffee: I keep re-working those figures but I >think< that's right :scratch:

Andrew

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