Absolute linear scales
21 Sep 2016 19:00 #80732
by terkaa
Replied by terkaa on topic Absolute linear scales
I have this position line in NC program
G54
G00 Y-35
It results in DRO reading -34.976mm and DTG shows 0.000 If I modify NC program:
G54
G00 Y-35.024
It results in DRO reading -35.000mm and DTG shows 0.000
I believe position shown in DRO is correct so problem is with commanded position.
Tero
G54
G00 Y-35
It results in DRO reading -34.976mm and DTG shows 0.000 If I modify NC program:
G54
G00 Y-35.024
It results in DRO reading -35.000mm and DTG shows 0.000
I believe position shown in DRO is correct so problem is with commanded position.
Tero
Please Log in or Create an account to join the conversation.
21 Sep 2016 19:02 #80733
by andypugh
Replied by andypugh on topic Absolute linear scales
The GUIs can be set to show absolute or commanded position.
Also, have a look in Halshow (or with Halmeter) and see what the PID command, feedback, error and output are. (If I am right to think that this is a servo system)
Also, have a look in Halshow (or with Halmeter) and see what the PID command, feedback, error and output are. (If I am right to think that this is a servo system)
Please Log in or Create an account to join the conversation.
22 Sep 2016 08:13 - 22 Sep 2016 08:46 #80765
by terkaa
Do these help? It seems that my error is in pid.y.error... Approaching direction does not have an affect. Do I understand correctly that control sees this -0.0239 postion error and tries to move Y by outputting -0.00952 volts to Servo Amp but it does not move with that voltage? Should I check if I have some setting in servo amp so that voltages below 0.01 are ignored? Or can this be solved by tuning PID?
Tero
Replied by terkaa on topic Absolute linear scales
![File Attachment:](http://i170.photobucket.com/albums/u243/terokaarlela/Kuvakaappaus%20-%2022.09.2016%20-%2011.03.06_zpsm9gccqqk.png)
![File Attachment:](http://i170.photobucket.com/albums/u243/terokaarlela/Kuvakaappaus%20-%2022.09.2016%20-%2011.02.27_zpshd4az0jh.png)
![File Attachment:](http://i170.photobucket.com/albums/u243/terokaarlela/Kuvakaappaus%20-%2022.09.2016%20-%2011.30.02_zpslxldfkbg.png)
Do these help? It seems that my error is in pid.y.error... Approaching direction does not have an affect. Do I understand correctly that control sees this -0.0239 postion error and tries to move Y by outputting -0.00952 volts to Servo Amp but it does not move with that voltage? Should I check if I have some setting in servo amp so that voltages below 0.01 are ignored? Or can this be solved by tuning PID?
Tero
Last edit: 22 Sep 2016 08:46 by terkaa.
Please Log in or Create an account to join the conversation.
22 Sep 2016 13:51 #80768
by PCW
Replied by PCW on topic Absolute linear scales
Is .4 the highest P term you can use? (raising P would decrease the error in inverse proportion to the P value)
You could zero the 7I77 output/drive input offset by setting the PID bias to -0.00952V but down at this level, the 7I77s output and drives input drift will make this setting somewhat unstable
adding some I term will help also
You could zero the 7I77 output/drive input offset by setting the PID bias to -0.00952V but down at this level, the 7I77s output and drives input drift will make this setting somewhat unstable
adding some I term will help also
The following user(s) said Thank You: terkaa
Please Log in or Create an account to join the conversation.
22 Sep 2016 15:56 #80776
by terkaa
Replied by terkaa on topic Absolute linear scales
0.5 started keeping noise. But I can try ie 0.45. I will also try adding a bit I to see what it does.
Tero
Tero
Please Log in or Create an account to join the conversation.
22 Sep 2016 16:00 - 24 Sep 2016 15:16 #80777
by PCW
Replied by PCW on topic Absolute linear scales
I think the I value has to be fairly large before it makes much difference
(a small value will take a long time to respond)
(a small value will take a long time to respond)
Last edit: 24 Sep 2016 15:16 by PCW.
Please Log in or Create an account to join the conversation.
22 Sep 2016 20:44 #80813
by andypugh
Yes, exactly. With only a P-Gain term you can never actually get to the set point, it is a real-life example of Zeno's paradox Or maybe not exactly.
For some small error the output of a P-only controller will be too small to move the system. So you will always settle at that small error from the setpoint. (though it would normally be symmetrical for a horizontal axis)
That is why you need some I-term to integrate the small error over time until it becomes a big enough voltage to move that final little bit.
Add some Igain and you should see the error disappear Start with about P/10 and increase from there. Too much IGain will eventually give slow oscillations.
Replied by andypugh on topic Absolute linear scales
[Do these help? It seems that my error is in pid.y.error... Approaching direction does not have an affect. Do I understand correctly that control sees this -0.0239 postion error and tries to move Y by outputting -0.00952 volts to Servo Amp but it does not move with that voltage?
Yes, exactly. With only a P-Gain term you can never actually get to the set point, it is a real-life example of Zeno's paradox Or maybe not exactly.
For some small error the output of a P-only controller will be too small to move the system. So you will always settle at that small error from the setpoint. (though it would normally be symmetrical for a horizontal axis)
That is why you need some I-term to integrate the small error over time until it becomes a big enough voltage to move that final little bit.
Add some Igain and you should see the error disappear Start with about P/10 and increase from there. Too much IGain will eventually give slow oscillations.
The following user(s) said Thank You: terkaa
Please Log in or Create an account to join the conversation.
22 Sep 2016 21:02 #80814
by terkaa
Replied by terkaa on topic Absolute linear scales
Ok, I tuning it is then. Btw this is HMC so Y in this case is vertical axis with hydraulic counterbalance.
Tero
Tero
Please Log in or Create an account to join the conversation.
23 Sep 2016 06:44 #80821
by terkaa
Replied by terkaa on topic Absolute linear scales
Ok I was able to increase P to 0.48 and also adding 0.06 to I And now positioning accuracy is within +-0.0002 mm and that is good enough for me.
Tero
Tero
Please Log in or Create an account to join the conversation.
03 Nov 2016 18:19 #82386
by terkaa
Replied by terkaa on topic Absolute linear scales
Today we noticed control cutting corners a lot with G00 moves. We have following G-code:
(current pos X-725. Y-100.)
G00 Y 65.
G00 X 725.
G00 Y -100.
In the first end about 40mm before reaching Y65. X starts to move towards 725. In the other end about 40mm before reaching X725. Y starts to move towards -100. Any ideas why? Attached is drawing of path. Black is what it should be and red is actual:
Tero
(current pos X-725. Y-100.)
G00 Y 65.
G00 X 725.
G00 Y -100.
In the first end about 40mm before reaching Y65. X starts to move towards 725. In the other end about 40mm before reaching X725. Y starts to move towards -100. Any ideas why? Attached is drawing of path. Black is what it should be and red is actual:
Tero
Please Log in or Create an account to join the conversation.
Time to create page: 0.115 seconds