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03-04-2016 #1
If we assume a machine with all limit switches on one input and a separate input for each home switch and wire it up with any old decent Normally Closed micro-switch at end of travel we get home positions but with accuracy and repeatability which is often dismissed by owners of pro systems and rarely proves good enough to pick up halfway through a finishing operation.
But what if we add a cam somewhere on each stepper shaft or ball-screw which operates a second switch wired in parallel to the end of travel switch for that axis?
The cam switch will operate once per turn but the home circuit will only open with both switches open, tune the cam switch to open/close a fraction of a turn after the linearly actuated switch is open and the accuracy and repeatability should be significantly better than is achievable with just linear switching.
Sound feasible?
- Nick
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03-04-2016 #2
you mean like using the index pulse on an encoder that is fitted to the motor, and making the homing more accurate? this is a standard feature, but will need an encoder.
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03-04-2016 #3
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03-04-2016 #4
Should work. Would increase the homing accuracy by the ratio of the perimeter of the cam 'sweep' to the ballscrew pitch length. But wouldn't like to have the microswitches continually opening and closing during normal jogging and machining. Swap to contact-less prox sensors (still cheap) reading off the 'cam' instead.
Could put it on the back of the stepper?
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03-04-2016 #5
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03-04-2016 #6
It's been done.
Have a read of this thread - http://www.machsupport.com/forum/ind...c,18323.0.html
Just had a quick scan, and look at the exchanges between me and Dickeybird starting around page 3. He implemented it on his lathe.Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
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