RE: [CAD_CAM_EDM_DRO] Encoder question

It seems that a Z index could be derived by digital logic.

If you know the quadrature pulse count for a complete revolution, just
implement a inc/dec counter that counts that many pulses(minus 1) and
resets, using the Carry to generate the index. If Z needs to be
quadrature, the count sequence can have upper two MSB's grey-coded to
approximate 90deg phase transitions.

This would provide a 'relative' home location from power-on of the
encoder.

Btw, this would support the odd-ball encoders that may have weird
pulse/rev values (coupled optical/mech mouse encoders for example).

Can CNC control programs accumulate and apply fractional errors from
oddball encoders that are mounted on lathe spindles (for threading
applications) ?


-----Original Message-----
From: cnc002@... [mailto:cnc002@...]
Sent: Tuesday, April 05, 2005 7:38 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Encoder question


In a message dated 4/5/2005 1:48:48 AM Eastern Standard Time,
elson@... writes:
Yes, exactly. It is a pulse that goes true over a very short angle of
movement,
and is often referenced to a particular transition of the quadrature
signal, as well.
It is usually once per rev on shaft encoders. Some linear scales have
the Z
repeat every so often, or arrange it so that its relation to the
quadrature signal
allows the DRO to figure out which specific repeat of the Z it just
passed over.
That's how the absolute DRO's work.

Jon
Exactly, however some rotory incremental encoders have 2 Z pulses per
revolution. In many applications, the OEM puts either a limit switch or
proximity
sensor near the end of the reference travel on each axis and when the
controller
sees this limit switch/sensor, it starts looking for the Z pulse and
stops
when it sees that pulse. This allows for any change in the trip point
of the
limit switch/sensor over time. As you indicated, in some cases they use
the
relationship to the quadrature pulses for this.

My two cents worth, again,

Randy Abernathy
4626 Old Stilesboro Road
Acworth, GA 30101
Ph / Fax: 770-974-5295
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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