RE: EMC

Karl,

I don't think I am explaining real well, let me try to cover some of the
background that may help.

You seem to get the idea that a stepper motor has a number of windings
(phases?) and they need to be energized in a particular sequence to make the
motor rotate. One way to achieve this is to have the program in the computer
output the actual signals that are required by each winding on the motor and
then use a simple electronic box to amplify the signals to each winding.
That is pretty much what you are describing below, except that you would be
pretty limited in the speed you could achieve if you are using a relay as
your switching mechanism.

The other way and this is what is most common currently, is to output 2
signals per motor from the computer. One signal is referred to as the Step
and this one sends a pulse for each step that the motor is required to move.
The other signal is called the Direction and it is high for rotation in one
direction and low for rotation in the other. When using this system the
controller electronics have to not only switch the high voltage the motors
require, but also interpret the step pulses into the sequence the windings
must be energized in taking into account the state of the direction signal
and the stepping mode (single step, half step, micro step, etc.) that the
controller is configured to run. This is the type of controller that EMC
requires.

Regarding your idea of using relays to switch the high voltage to the
stepper motors. To give you an idea of the frequency that is required to
drive a machine as a reasonable speed, here is an example from my setup. I
am using 200 step / revolution motors and running in a half step mode. I
have a 2:1 belt drive hooked to 5 turn/inch ball screws. So, it takes 400
half steps to turn the motor 1 turn and that then turns the lead screw 1/2
turn which moves the table .100 inch. This gives us 4000 steps (switching of
the windings) to move 1 inch. If you want 10 inches/minute (not a
particularly fast speed) you have to switch the voltage to the windings
40,000 times per minute or 666.666666 times per second. I would guess this
is a little beyond most relays. The normal setup is dedicated ICs that
provide the interpretation of the signal and the logic to drive the motor
windings running through an H-bridge circuit to provide the switching.

Again, fire away with any questions.


Tim
[Denver, CO]

> -----Original Message-----
> From: Karl Klemm [mailto:kklemm@...]
> Sent: Sunday, November 21, 1999 6:55 PM
> To: Tim Goldstein
> Cc: CAD_CAM_EDM_DRO@onelist. com
> Subject: RE: [CAD_CAM_EDM_DRO] EMC
>
>
> From: Karl Klemm <kklemm@...>
>
>
> > When used for steppers EMC outputs TTL signals for step and direction on
> > each of the 3 axis's. To interface it with stepper motors you
> need what is
> > generally referred to as a controller. It is an electrical unit
> that turns
> > each step pulse from EMC into the correct series of high voltage and
> > amperage pulses the motor requires to move the specified direction and
> > number of steps. If you are looking for a controller I would highly
> > recommend the kit units that Dan at Camtronics
>
> So what you're saying is that I could run the outputs from the parallel
> port to some relays that will turn on and off a high voltage source to the
> steppers? The reason I ask this is because I heard somewhere that the
> outputs from the parallel port had to be four different motor phases, or
> was I supposed to read that the phases for the four motors?
>
>
> Thanks,
> Karl
>
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