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Topic: CNC Shield with +/-10V per axis servo control signal? (Read 174 times) previous topic - next topic

centaurys

I have a CNC machine with 3 brushed DC motors (32lb/in with encoders) and line voltage powered drives. The drives require a +/-10V signal. I would like to suggest a shield with a PID loop to control these motors. I purchased the machine without a controller. Does anything already exist or can this be done? I do not have the programming skills to tackle the job. I would like to use the whole setup with GRBL.

ballscrewbob

I would suggest you give a lot more detail for the motors and the encoders.

Type numbers and better specifications etc. are a good start.

Are they straight would or spiral wound ? (spiral is a better constant torque but more expensive)
Is the minus voltage just reverse or some other form of signal ?
The encoder type would be critical to know otherwise position would be a nightmare ?
It sounds like some form of HAPTIC motor or low voltage AC drive ?


It may not be the answer you were looking for but its the one I am giving based on either experience, educated guess, google or the fact that you gave nothing to go with in the first place so I used my wonky crystal ball.


centaurys

Thanks to the above for your inputs. What I have is some good iron with motors and drives but no controller. As stated the drives require a +/-10V control signal - quite common a while back and plenty are still around. The motors have integral tachometers the outputs of which go directly to the respective axis drives. The motors are also fitted with 500 line incremental encoders with quadrature outputs (A & B) plus a separate single pulse per rev output for homing. Again, this was a common arrangement for the period. What I would like to see is a 3 axis shield, or whatever makes sense, which can receive the encoder outputs and compare these to the commanded position of each axis and then output a control signal in the range of +/-10V with a PID algorithm. Being as most of the Arduino systems use a 5V supply, the actual output for each axis could lie between, say, +1V and +4V with +2V being the 'zero' point. With subsequent analog circuitry this can be scaled to effect a +/-10 signal. To state what may be obvious, the drives provide no motor motion with a zero volt input. In the 0 t0 +10V range the motors move progressively faster in one direction and for the 0 to -10V range the reverse. To summarize, it would be nice to have a 3 axis system using GRBL to generate axis position commands inputted into a PID control which reads encoder feedback signals from the axis motors and outputs a +/-10V signal to the motor drives.

ballscrewbob

I am sure your project is DO-ABLE but you might hit a few problems with GRBL itself.
It lends more to an increment from zero for most outputs and a set of defined pulses.

Really does sound like a more expensive solution would be where you need to head.
Not saying it cannot be done but I think the pitfalls would be the biggest stumbling block

Only controllers I could find were quite expensive so you would probably have to build your own custom units.
And again its down to cost vs adaptability.

We asked for some motor specs and I think they might help narrow down your needs.
Just saying what they are as you did still leaves some questions unanswered.

BTW you are allowed to use line spacing around here ;)

It may not be the answer you were looking for but its the one I am giving based on either experience, educated guess, google or the fact that you gave nothing to go with in the first place so I used my wonky crystal ball.


centaurys

Thanks justone! Great thread - I will follow it up as it is just what I am needing.

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