Chain and sprockets are non-linear.
At 09:34 AM 10/29/02 -0500, you wrote:
This may be a stupid question, but why not to use a normal bicycle
chain\sprocket combination for driving an encoder?
Is it a backlash issue?
Alex
----- Original Message -----
From: jcc3inc <jccinc@...>
To: <CAD_CAM_EDM_DRO@...>
Sent: Tuesday, October 29, 2002 9:44 AM
Subject: [CAD_CAM_EDM_DRO] Re: DRO encoders- Rotary or Linear?
--- In CAD_CAM_EDM_DRO@y..., "Roger Linscheid" <r.linscheid@a...>
wrote:
Hi, I am ready to begin adding a DRO to my G4003 lathe. What is
the
current thought on the best method to accomplish my goal?
IIRC, when I was looking into this before, the linear strips from
U.S. Digital were only available in 250 CPI and this was not
considered high enough to provide the necessary resolution. Using
rotary encoders meant the possibility of losing counts if the drive
cable slipped or stretched.
Now U.S. Digital has linear strips in 300 and 360 CPI. Will these
provide a resolution of 0.0005 or better?
Roger:
Since you seem interested in accuracy, why not use rack and pinion
for rotary encoder drive. A 1/10 inch circular pitch rack with a 20
tooth pinion requires a 500 count encoder to read .001". Precision
rack is available from PIC Instruments, Berg, and Allied Devices.
They can also provide you the pinions. Less expensive rack is
available elsewhere.
Linear encoders eliminate backlash and encoder mounting errors and
are probably the better of the two approaches. A 250 line scale will
give you (with 4x multiplication) a .001" resolution. A 360 line
scale yields 1440 steps per inch or .6944 mils per step.
Good luck,
Jack C.
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