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Author Topic: Gaining steps...maybe? with Servo Drive  (Read 12516 times)

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Offline Hood

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Re: Gaining steps...maybe? with Servo Drive
« Reply #20 on: July 28, 2011, 10:23:35 AM »
Not sure wht the line drivers consist of in this case but normally when you talk about line drivers it  turns the single ended encoder signal into differential signals. In other words instead of just A and B pulse you will have A+ A- B+ B-. This makes the signal much more immune to noise and is the reason I do it for my Step/Dir signals (encoders are already differential). However did you get receivers as well as if the line drivers are like I say then you will need to convert back to single ended signals at the Geckos, as I dont think the Geckos can accept differential signals.
Hood
Re: Gaining steps...maybe? with Servo Drive
« Reply #21 on: July 28, 2011, 11:19:20 AM »
http://usdigital.com/products/PC4-H5#purchasing

Here is the link to the line Driver. Guess I will have to follow up on that. I am pretty sure the new G320X's can handle differential signalling, But I am using the old 320's on this machine.

Offline Hood

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Re: Gaining steps...maybe? with Servo Drive
« Reply #22 on: July 28, 2011, 11:24:55 AM »
Yes its a differential line driver so it will put out differential signals.
Hood
Re: Gaining steps...maybe? with Servo Drive
« Reply #23 on: July 28, 2011, 01:17:02 PM »
Just talked to a guy who uses these line drivers and he is claiming he uses them with the older Gecko 320's to eliminate noise without any extra hardware. So I guess the proof will be in the pudding when they arrive.

CB

Offline Hood

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Re: Gaining steps...maybe? with Servo Drive
« Reply #24 on: July 28, 2011, 02:24:24 PM »
Not really sure how they would without using a receiver just before the Gecko but you never know.
So what is he doing with the extra A and B signals? Just leaving them unconnected at the drive or line driver end?
Hood
Re: Gaining steps...maybe? with Servo Drive
« Reply #25 on: July 28, 2011, 02:38:58 PM »
As best as I understand from what Tommy at IHCNC is telling me. You can buy them with a ten pin out or a 5 pin out. The five pin out basically snaps right over the existing encoder pins (it has five pins) and then you plug the original  5 wire connector for the cable into it. so you basically have the same connections at the driver end as you originally had. He says he does it on all his machines.
    If you look on the Gecko site, They want you to "Solder a 1uF 25V capacitor between the +5V and GND pins on the encoder body" to use this style of encoder in the first place. This basically performs that task as well as acting as a line driver. It may be that is the only real function in this installation, but if it helps quiet things down and fixes my issue I am game to try it since his machines work and mine currently does not.
    I am afraid I am not savvy enough with electronics at the moment, so I feel a bit over my head here trying to fix this. I talked to Steve over at PMDX for a while too, He had a lot of good info for me and things I could try as well. Like putting an EMI filter on my VFD and Grounding the negative lead on my power supply to prevent a ground loop from occurring. going to tinker with all of that to see if any of it does some good.


Offline Hood

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Re: Gaining steps...maybe? with Servo Drive
« Reply #26 on: July 28, 2011, 03:00:43 PM »
Ah ok I see now, instead of soldering a cap on he is putting a  line driver on just to use the cap that is incorporated in the line driver board. Seems a rather expensive way to get a capacitor but if it works then great :)
Hood

Offline stirling

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Re: Gaining steps...maybe? with Servo Drive
« Reply #27 on: July 28, 2011, 04:38:04 PM »
Ok well I tried it that way too. No movement either. Is this to rule out noise on the step signal?
That was the idea but apparantly it hasn't yielded anything useful, so sorry - I'm stumped.

Ian
Re: Gaining steps...maybe? with Servo Drive
« Reply #28 on: August 03, 2011, 01:04:44 PM »
I am scratching my head on this one so I thought I would consult the Hive Mind. I am having an issue where my Z axis on my Mill is gaining steps. If I move the z head down 1" I get exact motion. If I move the z axis up, I get between 1.008" and 1.015" of movement (not lost steps, but gained steps). I do not think it is slop in the system because the error is cumulative and based on the feed rate. the slower I move the Z the greater the error. If I do a test program that moves the head +1" then -1" and runs the cycle 50 times. at 40 IPM I get a total accumulated error of about .015" if I run the same program at 5 IPM I get a total accumulated error of .05"-.075" or more!!

I am using Gecko Servo Drives and the servo's are from Industrial Hobbies. I am using Bob Campbell s break out board as well.

If anyone has any test suggestions I am open.
So far I have tried
- re tuning the servo drive with no effect.
- check the ball screw and bearing to make sure it was not moving in and out.
- Backlash on my Ball nut is approximately .003" (its a heavy mill head so preloaded nuts dont really work so good)
- adjusted the motor acceleration way down to be sure I wasnt loosing steps that way.

I have had this machine for 5 years and it generally has run well, this is a new development I cant seem to sort. anyone got any ideas.

Chris



friend,
I had same issue while using a stepper driver but it turned out to be a bad direction pin on my parallel port.
Re: Gaining steps...maybe? with Servo Drive
« Reply #29 on: August 03, 2011, 01:23:19 PM »
Well, Thank you everyone for the help. Looks like I got it sorted. A new encoder and a line driver seems to have done the trick, not sure if it was noise or just a damged encoder, but I am back up and running.

CB