On Fri, 5 Feb 2010, richard harris wrote:
Date: Fri, 5 Feb 2010 18:17:39 -0800 (PST)
From: richard harris <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
<[email protected]>
To: "Enhanced Machine Controller (EMC)" <[email protected]>
Subject: [Emc-users] Directional motion loss
Hey,
I am running emc 3.2.0 off the BDI with Jon Elson's pwm servo boards. The
machine is a knee mill, of similar size and mass to a hurco.
This machine gets little use as its bigger brother does all the heavy lifting
so the problem i describe below might have existed for some time and not been
noticed based upon part configuration and tolerance.
I notice during the last few days, while machining a thin wall box that one sidewall was
thicker than the other. At first i assumed that i had a chip in the vise when i loaded
the part, however the next part had a similar condition. I re-zeroed the machine and
noted that it showed i was .010" off. Ran the next part and it was fine, the second
part showed some issues, and the third clearly had a problem. Part is taking 17 minutes,
and the properties pull down shows 400" of motion.
I checked the machine for a loose belt, loose ball screw to thrust washer, and
loose ball nut, all of these looked fine.
I continued to run the code, cutting air and double checking the machine position to
the zero point on the vise. I am loosing .002-.005" to the in the minus x
direction.
I have checked for backlash within the working envelope with a dial indicator
and have not found anything that would alarm me.
Any ideas on what would causing a loss of position in one direction only it is
repeatably losing in the minus direction only. Mechanical, electrical,
anything at this point.
As always thanks.
Richard
Like Jon Elson said, check the encoders. ISTR a situation where a hair in the
encoders got pulled into the sensor area in one direction of rotation and
pushed away in the other direction, so it only lost counts in one direction!
Peter Wallace
Mesa Electronics
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