Re: [CAD_CAM_EDM_DRO] Re: Encoders on stepper motors.

Tony Jeffree wrote:

> At 22:30 25/03/2001 +0000, you wrote:
> > The ecoders catches missed steps caused by: Bad feed rates,
> >dull tools and line noise. Set you machine and program up to drill a
> >hole in each corner of your table. Use a scrap piece of plastic. Use a
> >tiny drill. Run the machine for two hours drilling the same holes
> >over and over. Use your fastest traveling speed between holes. All
> >four holes should look round when it is done. A broken bit says it
> >all. I used to have a line noise problem before I moved my controller
> >to a computer supply. Running a Shop Vac or electric drill on the same
> >line as the machine can also cause problems. I run my Dremel on a line
> >cord plugged into a different socket on a different line.
>
> Surely if you have line noise problems, using encoders won't necessarily
> fix the problem - its just as likely that the encoder signal will be
> affected, giving a false reading of the actual position.

If you have EMI problems, these really need to be fixed, and encoders
are only a band-aid if you can be sure the encoders are not affected
by the noise.

But, there are a host of other problems in stepper systems, such as
resonance, stall, emergency stops and crashes, where the encoder will
continue to read true position, even when the motor is no longer in
the position it was commanded to be in. Also, you could use it as
a DRO when the stepper drives were not turned on. In some
installations, people find it very convenient to do some operations
manually, and then switch the CNC on for other tasks.

Jon