Re: [CAD_CAM_EDM_DRO] PC based CNC system architecture/Black Box

I wont be offended if you tell me this wont work:-
Supposing you control a voltage controlled oscilator as if it was a servo,
Count the output pulses as if they were encoder pulses so you can start
and finish a move at a controlled accelerate/decelerate and have nice even
pulses for your stepper drives. I think the VCO would be followed with a
flip flop or divider to give a nice square wave out. The limit to step
speed would be only how fast you can count output.
The software would have to switch on one paralell port pin to raise VCO
frequecy and another pin to lower so an input (serial port ?) counts
oscilator output . so the program commands a move, the Vco starts from 0
accelerating at a rate set by a resistor and capacitor untill the pulses
comming back exceed or equal the desired rate, the port pin is swithed off.
remembering the software is counting pulses, when it reaches a point maybe
derived from the acceleration time it switches on the decelerate pin slowing
smoothly to around about the right position (havent thought this out quite
right yet) but the pulse count knows where we realy are. Can a PC manage to
keep a good count while deriving a speed figure and dead reckoning positon,
also may be re calculating while decelerating? I shold mention In am
thinking of a high resistance and capacitor on the VCO input which controls
the maximum rise and fall time to suit stepper hardware.
If it works It would be very cheap apart from programmers time......
I suppose you will say that phase jitter on the VCO would spoil the nice
step pulses but I think it could work ok.
This idea is cheap and old technology so I could afford it and understand
it!

Chris Paine
Sussex
UK