Re: [CAD_CAM_EDM_DRO] Basic PWM - Step-Dir Questions

Matt,

In regards to the step and direction signals. The direction signal is a set level not a pulse. If you have access to one of our breakout boards you would see that the Dir led would come on and stay on as long as the stepper motor is going in one direction. When it reverses, the Dir led would go out.

Your question bipolar motor requires energizing and de-energizing the correct windings in the motor in the correct sequence. The answer is all of that is done in the electronics in the driver. Mach2 just puts out pulses.

> windings in the motor

Bob Campbell
Bob Campbell Designs
www.Campbelldesigns.com
Mach 2/3 breakout boards
Relay boards
Spindle Speed boards
Stepper motors
Plasma Torch Height control

----- Original Message -----
From: "skerbitz" <skerbitz@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, September 11, 2005 8:38 PM
Subject: [CAD_CAM_EDM_DRO] Basic PWM - Step-Dir Questions


> Can somebody explain some basic things for me ? I've searched on the
> internet and got a lot of conflicting info. What I am interested in is
> a basic explanation of PWM (pulse width modulation) and step &
> direction signals.
>
> Let's assume I have a basic type CNC system with signals coming from
> software on my PC to a controller/driver card and then on to the motor
> windings. So the pinouts from the parallel port will send pulses thru
> various pins on the port ... a (+ or -) 5V pulse on one pin eventually
> runs thru the controller board causing one of the stepper motors to
> move one single step (assume no microstepping here). A (+ or -) 5V
> pulse on another pin eventually runs thru the controller/driver board
> to change the direction of on one of the stepper motors.
>
> So let's say that in the software I have on my PC, I want to turn a
> single stepper motor 1 entire revolution clockwise, then reverse
> direction and turn 1 entire revolution counter clockwise. Assuming 200
> steps per revolution, does the PC first send a single pulse indicating
> direction on the dir pin, then 200 pulses on the step pin, then a
> pulse on the dir pin to reverse direction, then 200 more pulses to
> step the motor around 1 revolution ?
>
> If so, any idea what is the amount of time for a pulse in a standard
> system ? Do the pulses have to be a particular time width and
> duration, or is there something that controls this ?
>
> Now another question ... based on my reading, to move, say a standard
> bipolar motor requires energizing and de-energizing the correct
> windings in the motor in the correct sequence. For the sake of
> argument, lets say it takes 4 of these different mini-steps to
> energize/de-energize the motor to move one single stepper motor full
> step. Are these mini-pulses sent by the PC thru the parallel port ? So
> now the pulse train looks like 4 mini-pulses for dir, 800 mini-pulses
> for stepping, then repeat ? Or are these mini-pulses handled by the
> controller/driver board ??
>
> And finally ... I understand the purpose of PWM (to control the amount
> of current in the motor windings by rapidly measuring and adjusting
> the average current in the motor windings) but how does this relate to
> step/dir signals ? How does the low voltage step-dir signal from the
> PC get translated into a high voltage signal to the motor ? Is this
> done thru the big power transistors like MOSFETs etc. ? If so, how
> does the PWM fit into all this ?
>
> Thanks in advance for any light you can shed on this.
>
> Matt
>
>
>
>
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