On Fri, 10 Apr 2020, Leonardo Marsaglia wrote:
Date: Fri, 10 Apr 2020 20:32:23 -0300
From: Leonardo Marsaglia <ldmarsag...@gmail.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] Home use index problem (In step + dir mode)
I'm playing with the homing at slow speeds so I can hit the home switch
always half a turn away from the index pulse more or less.
One thing is happening is the following:
If I let the mark (keyway in this case) of the motor at 3 o'clock and then
I turn off LinuxCNC, whenever I home the axis again (with the switch and
index and home position and offset both in 0) the axis goes to this same
position after the home sequence stops. Does that make sense?
I was hoping that with both the home offset and home position in 0 the
motor would stop near the index pulse with some overshoot may be. But
always there and not in the last position when the machine turned off. By
the way I'm not using the POSITION_FILE option and I also tried to use
VOLATILE_HOME with the same results.
Sorry for all the questions but this is the first machine I'm using with a
proper homing sequence.
As I tried to explain, you cannot really do homing to index without using the
encoder as feedback, because only the encoder hardware has the suported ability
to zero the position at the edge of index.
You can use homing with index if you use the drives encoder output
for feedback, but this is a bit more work and more difficult
to tune
Do you think is a good practice to use them as feedback? Because I'll
be coupling the servos to the ballscrews with a timing belt, so this might
not be that accurate as having the encoders mounted directly on the
ballscrews. In that case anyway I would be using the servos with analog
voltage for velocity command because I can't use them in speed mode with
the speed reference being pulsed.
This can also be done with step/dir, though tuning may be difficult
if there is substantial lag between step --> motion
Also there's the difference in diameter of the pulleys, but that can be
scaled so it would be no problem.
By the way, I finally succeeded in using the home switch + index. I think
it was me trying to imitate the sequence in a wrong way pushing the switch.
I'll try a little more to be sure.
El vie., 10 abr. 2020 a las 19:23, Peter C. Wallace (<p...@mesanet.com>)
escribi??:
On Fri, 10 Apr 2020, Leonardo Marsaglia wrote:
> Date: Fri, 10 Apr 2020 19:01:51 -0300
> From: Leonardo Marsaglia <ldmarsag...@gmail.com>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: "Enhanced Machine Controller (EMC)" <
emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] Home use index problem (In step + dir mode)
>
>>> Do you have a home switch and is it working?
> If you want to home to index only you must set HOME_SEARCH_VELOCITY to 0
>
>
>The home switch is working perfectly. I'm pushing it by hand because I'm
>only testing in the desk but it works. If I only use home switch for
homing
>it works perfectly. The problem starts when I try to use the index pulse.
>
If you have homing setup for home switch + index, motions index-enable
output
should be set high when the home switch is tripped
>If I set HOME_SEARCH_VELOCITY to 0 and try to home using index only, the
>joint.0.index-enable pin turns to TRUE and when the motor trips the index
>pulse it stops but I get the following error message and the homing
aborts.
>Always in the same position of the motor, so the index is detected.
The following error is expected unfortunately since motion expects the
position
to have been zeroed on index detection, but the stepgen position is not
affected
by the encoder index
>>Do the servos have a emulated encopder output (you mentioned a Z
signal, is
>> that from the drive?)
>
>
>Yes the drive has the encoder output pins for the A, /A, B, /B, Z and /Z
>signals. I'm only using the Z and /Z signals because I thought I could
home
>with index independently of the feedback I was using.
No, index handling is intimately entangled with the position feedback.
This is because index detection effectively zeros the position feedback
at the instant of index detection so its is precise regardless of the
detection
speed. As I mentioned, there is firmware to support index detection with
the
stepgen hardware, but it is not currently supported by the hostmot2 driver
Also as you might expect, the stepgen index input pin is not an encoder
input
rather, its part of the stepgen.
You can use homing with index if you use the drives encoder output
for feedback, but this is a bit more work and more difficult
to tune
Peter Wallace
Mesa Electronics
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Peter Wallace
Mesa Electronics
(\__/)
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(")_(") signature to help him gain world domination.
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