RE: [CAD_CAM_EDM_DRO] Linear vs. Rotary Enc.

I have used linear encoders on a tiny xyz table, but
I can't really show pictures as it belongs to a client.

I used the U S Digital glass strips. They are pretty expensive.
My impression is that there would be some sliding wear possible
on these...They run with teflon sliding bearings on the glass.
Obvoiusly great care must be taken in mounting these. One end
must be allowed to float to allow for different expansion rates.

There is no real difference in the operation of optical linear
or rotary other than that wear factor. Many rotaries use a hollow
wheel with no bearing other than whatever it is attached to.

Of course the linears used on machine DROs have much too poor
resolution for servo control usually.

I have not used laser encoders (other than a $$$$$ interferometer).

Les

Leslie M.Watts
L M Watts Furniture
Tiger Georgia

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-----Original Message-----
From: cnc002@... [mailto:cnc002@...]
Sent: Wednesday, August 11, 2004 10:19 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Linear vs. Rotary Enc.




In a message dated 8/10/2004 8:32:32 PM Eastern Daylight Time,
bussema@... writes:

Howdy. I have a few questions about encoders. . . the main one being: Is it
possible to use linear and rotary encoders interchangeably? If both give
the
same quadrature feedback. . . is there even a difference besides the
obvious
mechanical differences (and price)? For that matter, I guess I could ask the
same of laser linear encoders. Has anyone tried to use linears on a small
machine tool? I would sure like to see some pictures, because it seems like
mounting them might be a little tricky.

Thanks,

John

[Non-text portions of this message have been removed]



In my industry, woodworking machinery, both are used. The linear needs a
machined surface that is long enough to allow full travel over the encoder
strip and that can make mounting it a bit more of a problem. As far as
cost
goes, that would depend upon the quality and resolution you would need, the
same
would go for a rotary encoder as well.

Mounting rotary encoders might be a little easier as you can just mount
them
on a shaft, such as the lead screw or even use a small timing belt and
pulley to drive them. Not as much room needed.

I have heard pros and cons regarding both. The biggest con regarding
linear
is that you MUST protect the strip from being damaged and that can be a
real
trick. Rotory encoders are fairly easy to protect with just a cover over
them.

Well, hope this helps some.

Randy Abernathy
4626 Old Stilesboro Road NW
Acworth, GA 30101-4066
Phone / Fax: 770-974-5295
Cell: 678-772-4113
E-mail: Cnc002@...

I furnish technical support, repair, and other related services for your
industrial woodworking machinery. My background as Senior Service Engineer
for
the SCMI Group for nearly fifteen years with factory training, combines with
my extensive background in electronics, mechanics, pneumatics, electrical
and
CNC machinery to offer you needed support for your machinery.


[Non-text portions of this message have been removed]



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