Use 0-10V + dir on 7i77 instead of +-10V out

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27 Dec 2015 23:25 #67384 by perra_e
I have 3 Lichuan AC Servo that I was told that they should work with +-10V. They kind of do but not in a correct way.
The +-10V sets the speed so the speed for +5V = speed for -5V, but in the same direction!
The direction is set by a separate pin.
On top of that the servo vibrates a lot when feed with negative voltage, but it runs smoot on positive voltage.

One solution is to build an interface with some opamps that derives the direction and rectifies the output voltage so it's Always positive.

One other solution that I suppose is possible is to do this in a hal-file or something.
There are a couple of statements in the machine hal-file that indicates it is possible.
net x-output => pid.x.output
net x-output => hm2_7180.0.7i77.0.1.analogout0

I'm completely new to Linuxcnc so any help where to start looking would be appreciated.

The actual Servo but an other seller.

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28 Dec 2015 15:59 #67400 by PCW
Its entirely possible to do this is HAL (using the absolute component),
but its not likely to work very well as the direction signal will not be synchronized
perfectly with the analog output (VFDs often use 0 to 10V + direction but its not a good way to drive servos)

Are you sure there is not some setup option to get true +-10V operation from the drive?

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28 Dec 2015 16:44 #67401 by perra_e
For the moment I'm afraid that it doesn't work with +-10V. I certanly hope I have missed somthing!

Ok, then it sounds like the best solution is to build an extra interface that generats a direction signal and converts the speed signal to 0-10V if it is not possible to make the servo work as a "standard servo"!

I will contact the seller of the servo and hear what they say about this.

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28 Dec 2015 21:03 #67411 by Iron-Man

I have 3 Lichuan AC Servo that I was told that they should work with +-10V. They kind of do but not in a correct way.
The +-10V sets the speed so the speed for +5V = speed for -5V, but in the same direction!
The direction is set by a separate pin.
On top of that the servo vibrates a lot when feed with negative voltage, but it runs smoot on positive voltage.

One solution is to build an interface with some opamps that derives the direction and rectifies the output voltage so it's Always positive.

One other solution that I suppose is possible is to do this in a hal-file or something.
There are a couple of statements in the machine hal-file that indicates it is possible.
net x-output => pid.x.output
net x-output => hm2_7180.0.7i77.0.1.analogout0

I'm completely new to Linuxcnc so any help where to start looking would be appreciated.

The actual Servo but an other seller.


There are several things that you will need to do. First post the model number of the servo drive.
Second, you will need to set the correct parameters in the servo itself. Most new servos allow programing to set the correct interface, i.e. +-10V, step-dir, etc. Third, the PID, max speed, input type( position, +-10V, +-5V etc) will need to be set.
When these are set, you will need to tune the Linux loop.

Post images and model number.

Hope this helps

Iron-Man

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29 Dec 2015 09:41 #67441 by perra_e
We got the answer from the seller now and it is confirmed that it works like I have decribed and that I have not missad any parameter.
Dear Bengt,

I consult the manufacturer and was told that the AI3 analog input connector (PIN 18, PIN19) cannot control with ±10V,just can control with 0-10V analog voltage signal.

And if you want change the motor direction, use the external DI4 to switch, which you could see the setting parameter according the manual, and i checked the manual and update it, please see now whether it could be helpful to you. And if you found anything which is fault, you also could let us know, I will check for you with Lichuan manufacturerer.

Helen

I have never heard about anything like this before and me and my friend that bought the drives feels scewed :angry:

If I shall use this drive an external interface that fix the signals feels like the only option.
This is a picture of how the drive is connected. It certanly looks like you should be able to use +-10V, but the fact that there is an input pin that can set direction talks for itself I think


Attachments:

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29 Dec 2015 10:03 #67442 by tecno
Yes I feel screwed :evil:

Been nagging since day 1 when I started with my inquiry that ±10VDC is what we want and seller agreed to this!
Manual clearly states that AI3 is bipolar so that was clear to me that all specs should be OK.

Awaiting answer from seller.

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29 Dec 2015 10:24 #67443 by tecno
Here is the reply
as for the ±10VDC, in the beginining, I really confirmed and it is no problem, and we also have specially statement on requirements to the manufacturer but we also don't know why they miss when producing, and I will check with them tomorrow and then tell us your further news.:)

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30 Dec 2015 13:45 - 30 Dec 2015 14:03 #67515 by andypugh
There is no need to build any extra circuitry, you can (as PCW said) do it all in HAL.

You need to use the HAL abs component

This will take the +/- 10V signal as input and output 0-10V on the abs.0.out pin and direction on abs.0.is-negative
Last edit: 30 Dec 2015 14:03 by andypugh.

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30 Dec 2015 13:59 #67517 by tecno
So, is there any timing issues going via HAL?

If the speed/torque isn't continuous through zero or there is a delay switching direction then that is likely to cause poor servo performance or instability.

Cheers
Bengt

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30 Dec 2015 14:04 #67519 by andypugh

So, is there any timing issues going via HAL?


No, I don't think so, the direction output will update at the same
time as the voltage output (and, possibly importantly, only when the
voltage output is very small).
External hardware would only be able to change state when the voltage
switched polarity, so would be working on the same sort of timing.
The following user(s) said Thank You: tecno

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