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CNC lathe e-stop function

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DerryUK22/04/2012 21:11:47
125 forum posts

I am building a small CNC lathe driven by LinuxCNC and I want to mount the e-stop switch on top of the headstock. I will use it to cut the mains power to the lathe's motors and electronics.

Othe than having to tell the PC software that the lathe has lost power are there any disadvantages to this?

Derry.

Another JohnS22/04/2012 21:50:39
832 forum posts
56 photos

Derry;

If your cnc controller board uses a "charge pump" circuit, triggering it with the e-stop line will immediately stop the stepper motors and (if connected that way) the spindle.

Your computer will also know that the lathe big red button was also hit.

With the "charge pump" circuit enabled, and the e-stop line directed to it, I don't think there's anything to be saved by actually shutting off the power. Others may disagree, of course.

My mill uses the Gecko G540; hitting the estop will stop spindle, steppers every time I've tried it, and of course, the e-stop is handled in the G540 controller, so even if you are having software issues on your computer, the cnc machine will step down.

BTW - I use LinuxCNC on my mill, and it has been 100% reliable - incredible bit of software.

Another JohnS.

DerryUK23/04/2012 10:52:42
125 forum posts

Thanks for the thoughts John.

I do have a charge pump out (enable) signal that I can feed to my stepper drivers (DRV30/S) but my motor driver (4QD Uni) doesn't have an enable input.

I am however using a PWM signal (5 volts) for speed control so it seems reasonable that I could AND that with the enable signal to give me enable control over the spindle motor.

Derry.

John Stevenson23/04/2012 12:40:05
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5068 forum posts
3 photos

One problem with cutting the main power to a moving machine is that you will not be able to do a restart from the same position due to deceleration and missing steps.

Ideal way is to use the charge pump to cut power to the drivers and spindle and then if you need to ensure that everything is dead you can get a time delay relay to break the power.

This way the machine has chance to stop in a know position ready for a restart.

John S.

Another JohnS23/04/2012 13:27:58
832 forum posts
56 photos

I am however using a PWM signal (5 volts) for speed control so it seems reasonable that I could AND that with the enable signal to give me enable control over the spindle motor.

That would work well.

Note that LinuxCNC should put spindle to 0 when it gets the e-stop indication, but your solution would be fool-proof.

Keep in mind, of course, whether your e-stop system is active low or high; in my g540 system, all stop swtiches are wired in series and keep the line low; should a switch open, or a wire break, the g540 sees that as a high indication. (pull-up resistor internal to the G540).

From your posts, I'm sure you know the above; the paragraph above is for other readers and John Stephenson.

Another JohnS.

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