Dear Forum,

I have a problem ever since I use my milling machine controlled by Mach3 with steppers (Tormach PCNC). Every now and then the machine "forgets" its position, usually the Z position, but sometimes the X and Y, too. After this of course the part is destroyed and Mach doesn't give any indication that anything happened. I guess because it is an open loop system and it is how it suppose to behave.
I've checked everything over the years from cables, software, optimizing computer, checking post processor, etc. This issue still comes up often enough so I cannot leave the machine alone, which is not too convenient.

I want to fit encoders to the stepper motor shafts and compare the values to the DRO values in Mach3. When there is a big enough error the machine would just stop. Of course this comparison needs to happen outside Mach3, because otherwise the whole veryfying wouldn't make sense.

It seems easy enough to get the signals from the encoders, etc, but how to get the current position out of Mach3?

If anyone would have an answer I'd appreciate it so I wouldn't need to learn the whole Mach programming interface.

Best Regards
Attila

I guess because it is an open loop system and it is how it suppose to behave.

Not true if you have your motor tuning done correctly. Lower the velocity and accel so that you won't skip when machining.

RICH

While I agree that you should solve the problem rather than finding a workaround, something like this may be of interest to you.
http://www.rogersmachine.net/encoderinterface.html
Imo, it shouldn't be needed, and is a "fix" for a machine that doesn't work properly.

Hi Rich and Gerry,

Thank you for your answers.

Rich: On not having the proper tuning on the steppers I can only say that they are the factory Tormach settings and they are apparently conservative. These "loosing position" issues happen mostly under no load and particularly when there is a tool change in the G-code. But it exhibits something similar under two different CAM programs.
I thought about upgrading to either a servo system or Tormach multiphase steppers, but the latter would still be open loop.

Gerry: I am aware of that board, probably I should ditch the existing hardware and go for it. I thought my idea would be simpler to implement.

Unfortunately you didn't know how to get the DRO values out, but I appreciate your help.

Thanks
Attila