Re: A crazy idea / maybe great for PWM

Hi,
Why not just add octal latch's, one for direction, and one for steps,
that's alternately enabled( steered ) by one( or more) of the exta
parallel port bits. This expansion could also include intput latches.
Maybe a single global fault line, which when responded to polls the
input latch for the source. Basic CPU I/O type expansion, but using
the parallel port. Overhead addressing writes will lower pules rates
a bit. Just an idea. ;-)

Mariss's idea will work fine if the pulse timing can be be guarenteed.

-Lee

--- In CAD_CAM_EDM_DRO@y..., Doug Fortune <pentam@c...> wrote:
> mariss92705 wrote:
> >
> > Hi,
> >
> > Parallel port output CNC programs are limited to 3 or 4 axies
because
> > of the limited number of port bits. Each axis requires a STEP and
> > DIRECTION bit pair. What if it could be done with a single bit per
> > axis where STEP and DIRECTION were combined on the same line?
>
> Last Jan 1, 2002 I annouced the SiMAD (Simultaneous Multi-Axis
Direction)
> algorithm which allows you to control N axes with N+1 bits
> (ie control 6 Step & Direction axes with 7 bits):
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/message/36258
>
> I didn't explain it very well, but in a nutshell, you'd apply
> only one direction bit to all the axes simultaneously, and step
> the axes you wanted. Of course you can't step two axes
simultaneously
> in opposite directions, but in practice stepping them a microsecond
> apart should be fine.
>
> However I was told that supporting Geckos using this scheme is
> impossible, due to the timing delay's required by the Gecko
hardware.
>
> What is your opinion Mariss? If solvable, the gains are great!
>
> --------------------------------------------------------------
>
>
> PWM:
>
> A number of us have been discussing something similar, although
> it is vectored more towards PWM.
>
> It is a simple scheme, but part of the problem is that the
> motor driver has to know about the scheme. That is no problem
> for you Mariss, as the manufacturer!
>
>
> ____________|------|______|-------|_|-----|_|---------------------
>
> signal low equal=freewheeling |--pwm CW-| signal high=brake
> emit braking
> behavior
> (logic or power)
>
>
> Comments:
> - the signal is comprised of the (times) of the last two
> transitions (ie time of the previous and 2nd previous signal).
> If they are valid as a pair, the motor controller emits an
> output based on the PWM duty cycle.
>
> - signal is low for a long time, or high for a long time
> (maybe the PC is frozen, or a cable has become undone)
> emit braking behavior (maybe bring a braking output bit high
> on the motor controller). The brake being on, for example
> prevents the vertical Z axis from falling under gravity when
> you expect it to hold its position.
>
> Hopefully, the length of time that constitutes 'a long time'
> can be controlled by a trim potentiometer.
>
> - PWM duty cycle approx 50% emits a freewheeling behavior
> (brake is off, but no power applied to motor.... this allows
> the motor to coast to a stop if it is already moving....)
>
> The possible deviation from 50% either side constitutes your
> deadband, which hopefully can be controlled by a trim
potentiometer.
>
> - A PWM that is mostly 'logic high' would be ClockWise, and a PWM
> that is mostly 'logic low' would be CounterClockWise.
>
> The really neat thing about PWM control is that the width of the
> PWM <high and low grouping> can be narrow for a rapidly changing
> velocity, but can be wide (and thus less intensive on resources)
> for a constant velocity.
>
> Doug Fortune
> http://www.cncKITS.com
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