very slow to position a servo motor with 8i20
- clematites93
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23 Dec 2015 21:43 #67275
by clematites93
very slow to position a servo motor with 8i20 was created by clematites93
Hi all,
Quick reminder I have a 7i43 + 7i52 + 8i20 and a used servo motor, as I stated in my last post I haven't the technical information of the motor.
After several tests I managed to get the following details about it:
With this setup I'm trying to pilot a table, I'm doing small moves of 5mm.
For the very first move after homing the machine and every first move after changing the direction, I'm seeing the following behavior, the machine reach 4.9mm at the specified speed, and then very slowly moves to final position, the resulting error is quite acceptable (3/100) but really the speed is not.
But also for any subsequent move it seems that the machine is able to reach the final position at the specified speed with good precision (2/100).
I don't think that the problem is due to the mechanical backslash, because this exact same table when used with a step motor deliver a good precision (2/100 sur 100mm with a backslash of +/- 1/100).
I tried to change the values of the P, I and D and also the bldc.0.encoderoffset without success.
I'd like to remind that I got from Mesa a custom firmware due to my control chain.
Any clue on how to fix this ?
Quick reminder I have a 7i43 + 7i52 + 8i20 and a used servo motor, as I stated in my last post I haven't the technical information of the motor.
After several tests I managed to get the following details about it:
- 6 poles
- encoder 2500 x 4
With this setup I'm trying to pilot a table, I'm doing small moves of 5mm.
For the very first move after homing the machine and every first move after changing the direction, I'm seeing the following behavior, the machine reach 4.9mm at the specified speed, and then very slowly moves to final position, the resulting error is quite acceptable (3/100) but really the speed is not.
But also for any subsequent move it seems that the machine is able to reach the final position at the specified speed with good precision (2/100).
I don't think that the problem is due to the mechanical backslash, because this exact same table when used with a step motor deliver a good precision (2/100 sur 100mm with a backslash of +/- 1/100).
I tried to change the values of the P, I and D and also the bldc.0.encoderoffset without success.
I'd like to remind that I got from Mesa a custom firmware due to my control chain.
Any clue on how to fix this ?
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30 Dec 2015 12:13 #67506
by andypugh
I am surprised by the poles -6 / scale 1000 but it is actually the same, in effect, as poles 6 / scale -1000
I wonder if what you are seeing is the system running at reduced current until it sees the first encoder index?
Can you look at (halscope, halmeter) bldc.0.in-type to see if the increase in speed is due to the bldc component switching from homing mode to sinusoidal mode?
I am a bit confused by your two HAL files, there is a lot commented out in one, but then also a lot duplicated. How is your bldc.0.init pin driven?
Replied by andypugh on topic very slow to position a servo motor with 8i20
Any clue on how to fix this ?
I am surprised by the poles -6 / scale 1000 but it is actually the same, in effect, as poles 6 / scale -1000
I wonder if what you are seeing is the system running at reduced current until it sees the first encoder index?
Can you look at (halscope, halmeter) bldc.0.in-type to see if the increase in speed is due to the bldc component switching from homing mode to sinusoidal mode?
I am a bit confused by your two HAL files, there is a lot commented out in one, but then also a lot duplicated. How is your bldc.0.init pin driven?
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- clematites93
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03 Jan 2016 11:04 #67745
by clematites93
Replied by clematites93 on topic very slow to position a servo motor with 8i20
The two configuration files are the same, the first one is the one that I use.
But there is a lot of comments related to my journey with linuxcnc and servo motors. So I ran grep -vE '^#' | sed '/^$/d' to remove all the comments and empty lines.
Regarding the bldc.0.init, here is the related line in the HAL file:
net after-estop-touch iocontrol.0.user-enable-out => bldc.0.init # demarrage du composant HAL BLDC / start of bldc
But there is a lot of comments related to my journey with linuxcnc and servo motors. So I ran grep -vE '^#' | sed '/^$/d' to remove all the comments and empty lines.
Regarding the bldc.0.init, here is the related line in the HAL file:
net after-estop-touch iocontrol.0.user-enable-out => bldc.0.init # demarrage du composant HAL BLDC / start of bldc
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03 Jan 2016 11:14 #67746
by andypugh
Replied by andypugh on topic very slow to position a servo motor with 8i20
Does bldc.0.in-type shoe different values in the slow and normal modes?
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03 Jan 2016 21:09 #67776
by clematites93
Replied by clematites93 on topic very slow to position a servo motor with 8i20
Hello Andy,
So I have the following values for bldc.0.in-type:
* before homing 12
* after homing 2
The motor is unknown, I'm supplying 160V but it could be still underpowered.
I'm attaching the screenshot of halscope
So I have the following values for bldc.0.in-type:
* before homing 12
* after homing 2
The motor is unknown, I'm supplying 160V but it could be still underpowered.
I'm attaching the screenshot of halscope
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03 Jan 2016 22:16 #67784
by andypugh
Replied by andypugh on topic very slow to position a servo motor with 8i20
So, the slow-move and the fast-move variants are both with the in-type at 2?
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05 Jan 2016 22:06 #67939
by clematites93
Replied by clematites93 on topic very slow to position a servo motor with 8i20
Hello,
Yes I checked that the value stays at 2 in both situations.
Yes I checked that the value stays at 2 in both situations.
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05 Jan 2016 22:09 #67940
by andypugh
Replied by andypugh on topic very slow to position a servo motor with 8i20
If it isn't a change in state of the bldc component and the PID parameters are not being changed then I have no ideas left.
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05 Jan 2016 22:17 #67941
by clematites93
Replied by clematites93 on topic very slow to position a servo motor with 8i20
I'm starting to wonder if this couldn't be related to wrong PID values ?
I tried one more time to tweak P and I without any improvements.
I tried one more time to tweak P and I without any improvements.
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06 Jan 2016 10:41 #67958
by andypugh
Not if it is sometimes fast and sometimes slow.
You need to figure out what is different when it is fast to when it is slow. There must be something.
Replied by andypugh on topic very slow to position a servo motor with 8i20
I'm starting to wonder if this couldn't be related to wrong PID values ?.
Not if it is sometimes fast and sometimes slow.
You need to figure out what is different when it is fast to when it is slow. There must be something.
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