Re: [CAD_CAM_EDM_DRO] Re: tach output

David Micklethwaite wrote:

> "Jon Elson" <elson@...> wrote:
>
> >
> > Well, I have a strong preference for real servos. The difference with the
> > Gecko drives is that the CPU has no position feedback. It sends step
> > pulses to the Gecko, and hopes it got there.
>
> Is it possible to use a linear encoder of some sort to provide the feedback
> to the Gecko driver in place of a rotary encoder on the servo motor shaft? I
> realise that this would still not provide position feedback to the CPU but
> it might provide some compensation for backlash in the lead screw.

Well, sort of. the problem is the Gecko will sit there and bang back and forth

across whatever backlash continuously, all the time that the geckos are
enabled. This will be not only nerve-wracking, but will wreck the screw
and nut quickly. It may also overheat the gecko or the servo motor.
If the backlash is more than .001", I think you would find the system
unusable. The gecko would accelerate across the backlash in open
loop runaway, as it is, indeed open loop, because the motor is moving, but
no feedback of that is coming back from the encoder (and there's no
separate tach). Then it hist the other side of the nut and bumps the
encoder hard, overshooting the one encoder count it was trying to
adjust. Then it starts accelerating rapidly the other way.

Clearly, not an example of stability.

Jon