RE: [CAD_CAM_EDM_DRO] DRO Encoders

>-----Original Message-----
>From: Larry Edington [mailto:larrye@...]
>Sent: Friday, April 07, 2000 1:25 PM
>To: CAD_CAM_EDM_DRO@egroups.com
>Subject: [CAD_CAM_EDM_DRO] DRO Encoders
>
>
>I've been following the discussion of linear encoders for a DRO. And have a
>couple of questions again.....

>(1). Why not use rotary encoders? They are very available and cheap. If my
>math memory is correct Diameter * Pi = Circumfrence of a circle. So, a .318
>diameter wheel gives a linear distance of .9990264786... per rotation.

Using

>a 1000 count per rev encoder results in a resolution of .0009990264.....

If

>that's not good enough, use a 2000 counts per rev. That's only another $7

or

>so from US Digital. It's not that difficult to mount the rotary encoder on
>the non moving base of each axis's slide.

It is not as easy as you think. If you add up all the time it takes
research, manufacturer and install the brackets for the encoders it's about
the same cost as linear scales. Then you have the issues of inaccuracy due
to the measuring device being so far away for the work area, repeatability
due to backlash in the machine, the screws might be english pitch while the
encoders are metric so the count per revolution are not correct and other
matters.

>(2) If #1 is not acceptable, why not use some of the el cheapo digital
>calipers that have serial port output? Then feed the serial output to a PIC
>and let the PIC display the 3 axis values on an LCD.

A set of calipers that are 20" x 9" are still expensive and not a as
accurate as a standard dro system.
That PIC better have some linear correction factor for each axis so you can
compensate for machine error and lost motion compensation to correct for the
backlash in the screw (for rotary use).

>Larry Edington
>larrye@...

Tim Barnard
Fagor Automation

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