Servo adjust with encoder feedback

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09 Oct 2019 19:26 #147589 by chris@cnc
Hi,
I'm trying to connect the feedback from the encoder to a 7i76e. Was not easy but now it works more or less. The problem now is after arrived servo the final position he reverses. I'm programming X200. -> Servo drives with 2m / min to about 200.5 and then slowly back to 200mm. Depends also on the speed and over 4m / min is alarm Joint following error. He is right, too.
The scaling fits and with or without encoder the position is correct at the end. When I turn on PID and I it gets a bit better until the servo begins to vibrate. If I increase the gain of the servo, it is better just not good. Is there something else with which I can adjust on servo and control?
Does anyone have an example configuration of a servo with encoder feedback or had similar problems?
Thanks Christian

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09 Oct 2019 19:40 #147591 by tommylight
That is due to tuning, overshooting it's position.
Have a read through this:
forum.linuxcnc.org/10-advanced-configura...ning-detailed-how-to

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11 Oct 2019 17:54 - 11 Oct 2019 17:57 #147718 by chris@cnc
Hi,
thanks for the guide but it was more than one problem. I found a parameter in the amplifier: Max encoder scale output. I have set it now equal to the input signal and then started to test with P0. Sometimes luck is with the stupid ones. It runs without vibration noise and overshoot.:)

Can one still tell me what the max frequency is for the encoder output signal? At the moment I have a resolution of 5μm and measure almost 40Hz at 12m / min rapid feed. The signal is differential A, B. I've read something from 40 Hz but do not know where ...

And last question. My dream would be a homing with Z-phase and parameter shift. This would make it easier to adjust the gantry drive. Otherwise I have to push the reference cam and that is not so accurate.
Does anyone have an example hal and ini section?
Thanks Christian
Last edit: 11 Oct 2019 17:57 by chris@cnc.

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12 Oct 2019 13:28 #147736 by Hakan
You are using the spindle encoder on the 7i76e aka high speed encoder? That one handles 10 MHz.
Don't know about the MPG-encoder interface if that's what you are using.

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12 Oct 2019 19:56 #147754 by chris@cnc
I use the input TB3 pin 7-14 on the 7i76e and tried it on the 7i85s on TB3 1-8. Works well, I am still in the test run. Only drive from X0 -> X200 in rapid traverse and with F1000 m / min back and measure how well the position holds. After about 10-15 minutes, everything is still in tolerance. At 40HZ nothing is lost from the encoder feedback. It would be nice to know what the card can do. I want to prevent a bad surprise later in the gantry operation. Any idea for homing. I have found in the HAL pin joint.0.motor.offset. Unfortunately nothing in the manual. Has one already played around with it?

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12 Oct 2019 21:36 #147758 by tommylight
Where do you keep getting that "40HZ" ???
If you sneeze near an encoder, chances are it will count faster than that.
Do you mean 40kHz ? That is 40000Hz. That is still very low for what the encoder input on the 7i76E ( spindle encoder ) can handle, but if you are using MPG encoder feedback, that is to much.
Can you please share more info on what you are using and how it is wired/connected ?

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13 Oct 2019 13:17 - 13 Oct 2019 13:19 #147816 by chris@cnc
Hello Tommy,
Of course you are right there are no 40HZ in any case. It 40KHZ
My scaling is: One pulse is 5μ and one motor turn = 5mm. If I turn the servo, the control changes in 5μ steps.
Connection are as follows:
Step + Dir from 7i76e to Amplifier (Delta ASD-B2) =>
Power from the amplifier to the servo (Delta ECMA C20604) =>
Feedback (incremental) from the servo encoder to the amplifier =>
and in the end: feedback from the amplifier to the input encoder on tb3 7i785s. The signal is a difference signal with A, B and Z phase
I have measured once with the hal scope but unfortunately I can read anything on it. First image is at 500mm / min feed and the second with 1m / min. Maybe you can explain that.
Then I took my scope and simply measured between A and / A. Are 24V with a period of 49,6μs at 12m / min rapid feed. 3rd picture. On the top right you can see delta t = 49,6μs
Calculated I have now 1 / 0,00005s = 20000HZ * 2 (A and B phase) = 40KHZ. My mistake I forgot the K
I hope that my idea is not so bad ...
An idea what and how to start with the Z phase?
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Last edit: 13 Oct 2019 13:19 by chris@cnc.

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13 Oct 2019 13:40 #147818 by PCW
24V is _way_ too large a signal for a 7I76E or 7I85S encoder input
Both cards expect 5V signals

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13 Oct 2019 14:44 #147819 by chris@cnc
Ohhh
This is snippet from the manual. And that's exactly how the cables are. Where does the power come from?
+5V and GND are not connect.


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13 Oct 2019 14:58 #147820 by PCW
OK those _should be_ 5V signals
no power is needed

(the OCZ signal is not used)

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