7i76 +/-10V spindle output

Hello,I'm currently working on upgrading my Bridgeport Interact 4 Series 2 machine, which has a Contraves Serie 200 unit at the back. Next on my to-do list is implementing the spindle drive. I want to stick with the original motor to save both time and money eventhough .Here's the catch: the controller requires -10V to +10V signals for left and right turning. This means I won't be able to do rigid tapping. I don't have an encoder on the spindle however I'd like to be able to in the future. After some thought, I was considering using an op-amp to solve this problem.The Contraves controller can supply +15V, 0V, and -15V signals. While researching on a forum, I learned that some people use a simple setup with +10V and -10V signals and a relay to switch them.I'm seeking advice on which method is better and why. I'd also appreciate it if someone could check my proposed wiring for correctness.Many thanks,

Andries Tuinhof

The OP amp solution is probably better as it would be more smooth through reversals
but it probably needs voltage regulators for the +- 5V rather that a resistive  divider because
of the variable current draw of the 7I76 spindle interface vs output.

Also it depends on the enable working as the analog out will go full negative at startup
and when communication is stopped.

 

I must agree that the OP-amp is a much smoother solution.

However, I do not understand why the spindle interface has a variable current draw. From what I was able to see, it also contains an op-amp.

The 7I76 uses a H11 Opto to isolate the PWM.
This is a transistor output device with a fairly stiff pullup
resistor (for speed) which means the supply current will
vary several mA with PWM duty cycle.

A 5V and -5V regulator are needed or perhaps just run
The 7I76 spindle interface on +15 and use a slightly different
OP-AMP setup with the proper offset and gain to get +-10V

I have implemented a pcb with  + - 5v regulators and a opamp. I also have the linuxcnc hal file working. One thing that i didn't realize beforehand is the finetunning. The mesa card works from 0 to 100%. In this instance 50% is supposed to be 0% spindle speed. This with the different brand votlage regulators (-5v and +5v) created an equal voltage span. One side is like 9.8v and the other 10.1. This causes the spindle to be off by 300-400rpm in my instances.

For now it just works but i'll will improve the pcb and then fine tune it.
I was thinking maybe an pcb designs with two opamps and using the direction pin the select which output will go the driver might be better.