could this possibly be a rigidity or mounting movement issue? Have
you tried to move it back and forth a number of times to see if error is
add up or stay bounded?
Craig
On 11/4/2018 3:17 PM, John Dammeyer wrote:
This discussion of servo gear heads brings up an interesting question for
me.
I've been working on a system that has a CANopen controller Step/Servo with
integrated encoder. The motor turns a lead screw (10 TPI) which moves a
scissor jack type mechanism. We have an extra external encoder mounted on
the screw to be able to determine where the screw is on power up since it
could be anywhere. The step/servo is configured to have 200 steps per rev
which still works out to 0.0005" of linear movement. More than accurate
enough.
What we're finding is that occasionally, a CAN message with a Move to
Position command of 2549 steps moves one or two less steps than it should.
To position 2547. The status CANopen message does not report move complete.
Our software times out waiting for that move complete message after 15
seconds. The actual move up to that position is only 4 seconds. So the
step/servo has over 10 seconds to move 1.8 to 3.6 degrees (2 steps) to reach
the end of move position.
I've been told to ignore this and when the external encoder is close enough
go on with the rest of the motion profile. In other words, ignore that the
motor isn't reaching the target position.
If I allowed my Electronic Lead Screw to not always reach the end position I
think I'd have users
complaining.
The process isn't severely compromised by that two step shortfall. So we
can go on by ignoring motion complete. But this has all the appearance of
something that will fail worse later on if not addressed.
Am I being too fussy?
Thanks
John
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