Re: rotary encoder versus glass scales

Well thankyou Eric
That made perfect sense..I'll look for a new encoder.
Steven
.--- In CAD_CAM_EDM_DRO@yahoogroups.com, "pondindustrial"
<pondindustrial@y...> wrote:

> Steven,
>
> > machine today I found that the X-axis motor's rotary encoder had
> been
> > disconnected and somebody had installed a glass scale on backside
> of
> > the bed for that axis.Reckon I should try to find a new rotary
> > encoder or is the linear scale gonna be alright?
>
> I suggest that the glass scale, in most cases, will not work

properly

> with modern day servo drives. The most important reason is that
> encoder feedback should be on the 'drive' (motor) side of the
> mechanism to be controlled and not the 'driven' (in your case the x-
> axis). In simple terms, servo motors are controlled by switching

the

> polarity at high frequencies back and forth between the two motor
> leads and hence, bounce the motor shaft between the two adjacent
> encoder signals in order to maintain position. If the encoder were
> mounted on the `driven' side of the table, this bounce would be
> proportional to the backlash in your drive screws etc. and would
> result in the motor becoming unstable, just my thoughts.
>
> Eric
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "alphawolf45"

<haushahn@c...>

> wrote:
> > I am in the process up gathering info and parts to upgrade an old
> > Hurco Bedmill to PC controls.I have ripped all the old

electronics

> > off the machine cept motors and limit switchs ..I have new servo
> > drivers in hand and just gotta get a coat of frsh paint on the
> > machine and will be ready to wire something up....Cleaning on the
> > machine today I found that the X-axis motor's rotary encoder had
> been
> > disconnected and somebody had installed a glass scale on backside
> of
> > the bed for that axis.Reckon I should try to find a new rotary
> > encoder or is the linear scale gonna be alright? I been reading
> about
> > rotary optical encoders but havent a clue at the electrical
> > differences between them and the linear scales..I want to keep
> this
> > simple where I can and save the sweat for the worthy
> > problems..Hehhehehheh
> > Then another question if somebody wants to take a stab at it

is

> > why did the old controller make use of a tach signal from the
> > servomotor and these PC run conversions dont use that signal?--Or
> > maybe they do and I havent got to that part of the reading
> > materials..This is my winter project and I got a lot to learn

yet.I

> > figure this isnt the last time I'll ask questions here.
> > Thanks
> > Steven