[BillTodd]

but it would be nice if it could correct itself.

I see. Can mach3 do that, if it has encoder/count inputs?

What sort of input does Mach3 need?

[Marzan]

I see. Can mach3 do that, if it has encoder/count inputs?

What sort of input does Mach3 need?

I`m not really sure.I was thinking along the lines of another pic or such countin pulses and comparing the result with an encoder (sort of like a virtual closed loop system) and if it misses steps using one of the inputs to signal a positioning error

Marz

[Robin Hewitt]

I'm brewing up much the same but with a home made computer board reading scales and stepping motors.

The step timer interrupt compares "where I am" with "where I want to be" and steps accordingly.

The "where I am" can change at any moment should a report be received from any of the 3 scale interrupts. (I read them with hardware because any lag will only serve to confuse it).

At the end of an x,y,z stepping sequence it works out the error on all 3 axes. Should any be outside tolerance it doesn't update the "where I want to be" to a new position. This means I get remedial steps to put it back on course.

Questions are, wil it do more remedial steps than moving steps, and, how tight can I put the tolerance

I only have to mount the scales and I can find out

[BillTodd]

I'm brewing up much the same but with a home made computer board reading scales and stepping motors.

The step timer interrupt compares "where I am" with "where I want to be" and steps accordingly.

The "where I am" can change at any moment should a report be received from any of the 3 scale interrupts. (I read them with hardware because any lag will only serve to confuse it).

At the end of an x,y,z stepping sequence it works out the error on all 3 axes. Should any be outside tolerance it doesn't update the "where I want to be" to a new position. This means I get remedial steps to put it back on course.

Questions are, wil it do more remedial steps than moving steps, and, how tight can I put the tolerance

I only have to mount the scales and I can find out

Interesting idea Although,the missed steps may not be able to be corrected until the cause has been removed.

i.e. if it drops steps because of excess speed v load, will there be time to correct them before the next motion without increasing the frequency of the pulses thus exacerbating the speed v load problem?

(Well worth trying though )

[Robin Hewitt]

The fast traverse is a completely separate interrupt handler, precise placement only happens at speeds where the motors can handle an instantaneous reversal.

There is more work to do. When it encounters back lash it will tend to trail by the tolerance and I will need extra remedial steps. OTOH I'm not going to try to fix anything until it has had a chance to tell me what needs fixing.

I'm writing the code and everything runs in SRAM. I can recompile and upload all new in a matter of seconds. I am in control

[Marzan]

Hi Robin. What a brilliant idea. When you get it right you will have solved one of the major issues with using steppers. i would be interested in the outcome.I had another thought that if i had the knowhow would be worth pursuing. What if you had a PIC counting pulses sent my Mach 3 and then the PIC moved the stepper motor using the encoder to go to the correct position? Its probably complicated, and you would get some lag,but i would gladly put up with lag for accuracy.

[BillTodd]

What if you had a PIC counting pulses sent my Mach 3 and then the PIC moved the stepper motor using the encoder to go to the correct position?

Hmmm , That wouldn't be too difficult.

I use a PIC (16F84 and an L6219) to drive the Z motor on my engraver, it'll happily keep up with the step inputs from the controller using interrupts. It even has has a couple of unused timer/counters that could be used to track an encoder. Might be worth a look

[I still wonder, if you're going to add all this complexity you might be better of using proper servo-motors]

[aadityadengle]

tried the circuit with verniers too
but no data