Re: CNC: Spindle speed control

Hello All;

I have spent the last 2 months learning about the PIC Micro and have
90% completed the development and debugging of a PIC-Based PWM to DC
Controller designed around MACH1.

The 5hz output from MACH1 is just too slow to allow it to provide a
stable control voltage, so the only way to do it is to capture the
PWM signal and control the output via software routines.

The Micro runs at 4mhz and samples the 5mhz pulse from MACH1. As it
is running much faster than MACH1's PWM Pulse, It can do a LOT of
stuff in between ulses. Firstly, it has watchdog (charge pump)
safety compatible with MACH, it also has programmable speed ramp
up / ramp down (for large spindles).

This ramp also works if communication is broken between the parallel
port and the speed controller, so if the PC crashes, hangs or
someone accidentally disconnects the parallel port cable, the
controller will not immediatly shut of all control to the motor, but
will ramp down at the programmed ramp rate.

During direction change(M4>M3, M3>M4) , it will automatically ramp
down the motor to zero, change direction (energize a relay) and then
ramp up to speed in opposite direction again.

It has a rsolution of 1000 steps, so if your max spindle speed is
3000 RPM, it can control to 3 RPM, the accuracy is about 99.4% and
it outputs a DC Control voltage from 0 to 5v.

It has programmable minimum speed, maximum speed, resolution & ramp
speed. It has outputs to LEDs and / or relays for M3, M4, Motor On,
Ramp Up/ Down, Max Speed and 0-5v control voltage. The resolution
allows small fluctuations in the input PWM not to effect the output
control voltage, it is defaulted to 5 RPM so if any change is less
than 5 RPM, then the output voltage will not vary.

I have monitored the control voltage output over many hours, it is
stable within a couple of millivolts!

It can also be hooked up to a Serial LCD Display to show the status,
but other than in debugging, I'm not sure if its necessary !

It does this using 3 inputs, PWM, Charge Pump & Direction and If you
can think of any other features, I would welcome any suggestions.

Cheers

PeterC