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IndustryArena Forum > CNC Electronics > Servo Motors / Drives > Encoder/servo selection for a Robotool centroid retrofit
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  1. #25
    Community Moderator Al_The_Man's Avatar
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    I could never understand that decision by Gecko to go the single ended route, when it would be so easy to add a RS485 receiver on the drive.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  2. #26
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    What is lost by not connecting the /A and /B signals? I was doing a little research and could not figure out if it was related to filtering out noise or its positional accuracy.

    Also since the centroid Acorn board is actually connected to the drive and not the encoder, does it matter if the encoder is running in TTL if the drive is still outputting the step/dir signals? I'm also trying to figure out if the encoder requirements are actually for the spindle encoder (which is connected to the board through a DB9 port) and not the servo drives.

    If losing the /A and /B signals is a significant loss though, I will scratch the Gecko as an option and look elsewhere.

  3. #27

    Re: Encoder/servo selection for a Robotool centroid retrofit

    The full differential quadrature signal from the encoder is more or less noise immune, at least much more so than single ended. The way the encoder is read by the device is a function of how the device (drive in this case) is designed. In reading the specs, it looks like the Gecko does read both the rising and falling square wave signal from the encoder channel, so you would get 4 pulses per encoder line. Two for A channel and two for B channel, which are 90° out of phase with each other.

    In the interest of clarity, the Acorn outputs a step & direction signal to the drive. The drive then tries to keep up with what the Acorn is telling it to do to position the machine correctly, it does actually work.

    Any encoder requirement in the Acorn manual should be related to the spindle. The Acorn has no idea what the drive is doing with the exception of any error signal between the drive and the Acorn.
    Jim Dawson
    Sandy, Oregon, USA

  4. #28
    Community Moderator Al_The_Man's Avatar
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    What I have done in the past where I had no choice and had inputs that were single ended with a long run in a noisy environment was to use one of the RS485 IC's 26LS32 for receiving and 26LS31 for transmitter, if needed.
    As Jim said using the 4 edges of a A & B multiplies the resolution x4, some controllers also allow options, natural count, or plus x2 (2 edges) or plus x4 (four edges).
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  5. #29
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Ok so my take away is that the Gecko would be ok except in a very "noisy" environment?

    Would it be worth looking at something like CNCdrive DG4S 08020 drive? Reading over its manual it does seem to have the capability to read the full differential quadrature signal through an RJ45 connector. Any opinions on that drive? I have never heard of the brand before.

    https://cnc4pc.com/dg4s-08020-dc-servo-drive.html

    Also thanks for the help, you guys have been amazing. Was really just planning on trying to put together a semi plug and play system (DMM) but this stuff is cool.

  6. #30

    Re: Encoder/servo selection for a Robotool centroid retrofit

    I have only heard about them, but know nothing personally. A cursory look indicates it is worth taking the time to study it a bit.
    Jim Dawson
    Sandy, Oregon, USA

  7. #31
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    So I pulled the cap off the top of one of the servos and found something kinda interesting about the encoders on this machine. Looks like they are Broadcom HEDS-5500 A06. Resolution is a little low at 500 CPR. That means I don't have to worry about tacks though I assume.

    HEDS-5500#A06 - BROADCOM LIMITED - Incremental Rotary Encoder, Optical, 2 Channel, 3000rpm, 500 Cycles, 1/4" Shaft Diameter | Newark element14

    I emailed Marcus Freimanis about the CUI encoders and he said they are actually what they use to test the drives, so definitely a good fit. He also said that the G320X can support a line count up to 5000, though it becomes increasingly difficult to tune them above 2500 due to the gain settings on the drive.

  8. #32
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    The MassMind non-contact encoders would work nicely in that setup. 4000cpr, TTL AB, and easy to mount since they just use a little magnet.
    ENC2b: AS5047P High Resolution Magnetic Encoder. massmind
    James hosts the single best wiki page about steppers for CNC hobbyists on the net:
    http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)

  9. #33
    Community Moderator Al_The_Man's Avatar
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by WesM View Post

    I emailed Marcus Freimanis about the CUI encoders and he said they are actually what they use to test the drives, so definitely a good fit.
    It is not that they don't work, just not ideal in a noisy environment, IOW more susceptible to interference on a long cable run.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  10. #34
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    Quote Originally Posted by James Newton View Post
    The MassMind non-contact encoders would work nicely in that setup. 4000cpr, TTL AB, and easy to mount since they just use a little magnet.
    ENC2b: AS5047P High Resolution Magnetic Encoder. massmind
    Those are cool little encoders, I will have to look into them for future projects. At this point I have a few AMT113Q-V encoders coming in I plan on testing out. They should be drop in (hole spacing) replacements for the encoders I have right now

    Quote Originally Posted by Al_The_Man View Post
    It is not that they don't work, just not ideal in a noisy environment, IOW more susceptible to interference on a long cable run.
    Al.
    Thats what I assumed. Now what constitutes an environment that is too noisy would be an interesting discussion. Also what components would cause a levels of noise that would interfere with the encoders?

  11. #35
    Community Moderator Al_The_Man's Avatar
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    An extreme example is a large plasma gantry where the torch and power cables share the same cable chain to the gantry..
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  12. #36
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    Re: Encoder/servo selection for a Robotool centroid retrofit

    So i'm trying to figure out how I want to power the servos on this retrofit. The machine currently seems to use a transformer (Western Magnetics NX-189) and then rectifier. The from the manual the Robo power requirements are 10 amp 3ph 220v and 15 amp 120 volt. Would it be safe to assume that they are putting the 120v into the transformer?

    So my thought is, get rid of the motor starter/coil system, reuse or replace the fuses and use the transformer with rectifier/filters to power my servo system. The Acorn will have a separate 5v power source (which comes with the Acorn). Does that seem doable?

    As a side, it seems like they are using two transformers in the robo system? The first one has numbers on it, which i assume is the voltage output, the second one has no markings. The label shows the smaller transformer as a Western Magnetics WX-190, 012-0306 REV J. I cant find any info on the company though, must less the transformer.

    With these kinds of systems/retrofits is it worth trying to use the old power supply/transformer system? Or would you guys just buy a new PSU?

    I just noticed I didn't get pics/specs of some of the other rectifiers, will have to try and see what those are when I get the machine on Monday.
    Attached Thumbnails Attached Thumbnails DSC_0337.jpg   DSC_0338.jpg   IMG_20140421_165439168.jpg   IMG_20140421_165513667.jpg  

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