Closed loop steppers?

[pfarber]

I like the price point of stepper equipment, but am concerned about accuracy.

Has there been any thought put into a closed loop stepper system? Something simple like an encoder that would tell the controller that the X,Y,Z step was actually done (by getting a single pulse back from the encoder on the leadscrew or somewhere). If the controller does not get its pulse in Xus, then don't ACK the last command back to software.

CAM software would put out a code, and wait for an interrupt or logic change on a pin to ACK that cmd and then issue the next.

Would this be overly complex to implement? Has it been done? Anyone come up with anything simple? Or is a general use stepper setup no real danger of getting out of position 'sync' with where the software thinks it is?

I can only think that backlash errors would ALWAYS put the cutting tool in a different postitin than the software thinks its at.

[ger21]

You can get a sytem that will pause your machine if it gets out of position, using Mach3 for the control software at www.rogersmachine.net It won't correct position during a program, but will stop it to prevent errors.

You can get a closed loop stepper system from MaxNC, but you're locked in to using their software.
http://www.maxnc.com/page14.html

[Episs]

Check this link http://www.mesanet.com/ they have 4I34M FPGA based Anything I/O card - with motor control firmware for stepper,servo motors it is very intresting product and price is low 161$
Also can check this link http://www.ni.com/motion/ I just found it by myself but price is high 799$ for stepper motor controller 7330 series