Re: Tuning EMC

John thank you for the reply.

I am using 320 gecko drives, and I was able to cure the "backlash"
problem by tuning the deadband.

my servo motors are just sitting on the bench right now. I want to
make darn sure they are tame before I mount them on the machine

I am still having problems with the MDI. I request a g91 x1. and the
motor only moves between .100 and .200" (no following error though)

I don't use steppermod because it couldn't handle the input output
resolution of 10,000 (250 cpr, 2:1 belt reduction, 5 tpi leadscrew)
(the computer is really sluggish even the mouse moved really slow)

I am running a 650 athlon with lots of memory. but my motors seem to
starve for input when I ask for more than 35 imp of max velocity.

final question
what could cause my motors to jump when I turn off the power supply?

thank you
Matthew

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> mjf462001 wrote:
>
> > I am now discovering the joys, and pitfalls of tuning a servo
system.
> > There are two problems I have not overcome.
> >
> > 1) using frequency mod, I step one axis away from zero in 0.100"
> > increments and then back again, but it doesn't return to zero.
there
> > seems to be some backlash<?> Each axis has a different amount of
> > error from 0.0009 to 0.005". If I keep stepping in the same
direction
> > it moves 0.100 like it should. could the encoder be loose?
>
> All servo systems have some amount of deadband. If the DC gain is
> very high, the static error should be quite small, no more than 1
or 2
> encoder counts. Freqmod adds a whole bunch of complications. as
> it simulates a servo system in software, and then you are driving a
servo
> system with the step pulses. Why don't you try stepmod?
>
> How are you measuring this? With a dial indicator? That will cause
> additional errors, as there is no such thing as no backlash. I'm
> assuming you are using a rotary encoder on the motor, but that
> you have no encoder feedback to the computer.
>
> Yes, encoders can show subtle error conditions, especially when
there
> is dirt on the wheel. You might try making small moves while
watching
> with a dial indicator, and see if they are of uniform size. I mean
moves
> of perhaps .001, .005 or .010", and make a bunch of them. If some
of
> the moves are not uniform, that could mean the encoder is missing
> some of the slots in the grating wheel. A loose encoder wheel or
> coupling would usually cause violent movement when making small
> moves. Any time the encoder is not following the motor, the system
> goes "open loop", at least momentarily, and the servo loop
accelerates
> the motor, wildly trying to make the encoder start moving again.
If this
> is happening, you should be able to easily see and hear it, unless
the
> slipping/looseness is in very small amounts.
>
> Ahh, you must be using Gecko drives, you should know that they
> have a somewhat odd way of interpreting the direction signal.
Basically,
> the Gecko wants the direction signal to only change in coincidence
> with the step pulse. If the particular step-pulse code you are
using
> doesn't do it this way, the Gecko drive may lose or gain one step
> (encoder) position every time it changes direction.
>
> > 2)in mdi I ask it to move .100" and the motors do not move nearly
as
> > much as a .100" step in manual mode. It seems I have overlooked a
> > variable somewhere.
>
> Oh, now this is REALLY odd. Make sure you have set either
incremental
> (G91) or absolute (G90) coordinates, as having the machine in the
> wrong setting will add much confusion. How much is the difference?
> If the acceleration is very high, you may have different velocities
causing
> the machine to stop on the near or far end of the mechanical and/or
> deadband backlash, depending on how abrupt the stop was, and from
> what speed.
>
> Jon