Re: Step/dir control for DC motor

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "justjuha"
<juha.keisala@n...> wrote:

> I was looking for Z axis slider for my plasma project and I found a
> height control from the old flame cutter.
> This would be fine if the DC motor can be used as it is
>
> Can the DC motor used instead of stepper/servo in such application

or

> do I have to replace the motor?
> Any ideas (circuits) how to control the DC motor from PC (step/dir)?
>
> This application should not have any kind of feedback from the
> encoder since the arc voltage is measured by a certain circuit
> (thanks to Tom) and the conroller drives the motor based on the arc
> voltage. Of course the speed of the motor should be proportional
> somehow to the steps but because the voltage is measured live, the
> direction of the motor will be changed if the movement has been too
> long ans so on.
>
> Nominal voltage for the motor is probably something between 48 and
> 110 V (24 V was too little)
> The motor is magnetized electrically (so it is not a permanent

magnet

> motor).
>
> Cheers,
> Juha

Dear Sir:
With normal torch height controllers, you do not need encoders since
the arc voltage feedback is a linear system. Therefore a DC motor
will work OK; however one needs a DC servoamp to run the slider up
and down, and a lower voltage motor with a permanent magnet motor
would be a better choice if you could manage it! We made torch
height controllers with PM DC motors running off 24V DC. There were,
however, some systems using up-down relays to run the motors. These
work within some limits (bang-bang servos), but are not as smooth as
the servoamp-DC motor combinations.
Regards,
Jack C.