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  • BRX to servo positioning

    Is there an example of the best way to have a BRX send move commands to a sureservo.
    I would basically like to be able to read and write positions, get confirmation of "In position"

    Thanks


  • #2
    Could be done a couple of ways. BRX has high speed outputs built in for 3 axis. YOu can use those with the built in move commands with the servo in PT mode. This works ok, but the move commands sometimes have trouble and do not send the proper amount of pulses that the instruction was set to. It is reliable in some applications, but not others. So it depends on your specific use case whether this is a good fit or not. You can use servo DO's to send move complete signals to get confirmation from the servo drive back to the BRX to double check move finishes.

    Or you can use PR mode stuff and have the BRX use discrete outputs to tell the servo to go to pre programmed positions. I believe you can also use this and RS485 communication to set new position parameters so you can set many "pre set" positions.

    Or many servos can use network communication and command streaming to send position and velocity data. Not sure what specific servos you are using though.
    Last edited by MikeN; 07-11-2018, 08:55 AM.

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    • #3
      Originally posted by MikeN View Post
      Could be done a couple of ways. BRX has high speed outputs built in for 3 axis. YOu can use those with the built in move commands with the servo in PT mode. This works ok, but the move commands sometimes have trouble and do not send the proper amount of steps that the instruction was set to. It is reliable in some applications, but not others. So it depends on your specific use case whether this is a good fit or not. You can use servo DO's to send move complete signals to get confirmation from the servo drive back to the BRX to double check move finishes.

      Or you can use PR mode stuff and have the BRX use discrete outputs to tell the servo to go to pre programmed positions. I believe you can also use this and RS485 communication to set new position parameters so you can set many "pre set" positions.

      Or many servos can use network communication and command streaming to send position and velocity data. Not sure what specific servos you are using though.
      We aren't aware of this. If you can provide any details on how to duplicate this, it would be a big help.

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      • #4
        Originally posted by BobO View Post

        We aren't aware of this. If you can provide any details on how to duplicate this, it would be a big help.
        From what I remember it was something about the acceleration or deceleration getting too agressive would cause the "Axis move to position using trapezoid" to send more pulses than the instruction was set to. For instance we were making the servo go 1 revolution each time the instruction turned on so we set it to move to a position of "relative +10,000", but depending on the accel, decel, and velocity used it would send anywhere between 10000 to 10250 pulses instead of the 10k it was supposed to. I think the faster the machine was running the more pulses it would overshoot, so it wasnt a problem that was seen in initial testing but something that came up when the whole project was almost done and we had to go through a bunch of troubleshooting to figure it out.
        Last edited by MikeN; 07-11-2018, 09:20 AM.

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        • #5
          Originally posted by MikeN View Post

          From what I remember it was something about the acceleration or deceleration getting too agressive would cause the "Axis move to position using trapezoid" to send more pulses than the instruction was set to. For instance we were making the servo go 1 revolution each time the instruction turned on so we set it to move to a position of "relative +10,000", but depending on the accel, decel, and velocity used it would send anywhere between 10000 to 10250 pulses instead of the 10k it was supposed to. I think the faster the machine was running the more pulses it would overshoot, so it wasnt a problem that was seen in initial testing but something that came up when the whole project was almost done and we had to go through a bunch of troubleshooting to figure it out.
          This sounds vaguely familiar, and more importantly, I think it was fixed. When were you having issues?

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          • #6
            I've tested quite a bit and I can't break it with max accel. There may well have been as issue in the past.

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            • #7
              Originally posted by BobO View Post

              This sounds vaguely familiar, and more importantly, I think it was fixed. When were you having issues?
              I think it was something like 5-6 months ago that I encountered the problem using a BRX. THough I have no idea what firmware version it was on. I dont know if it was the latest, or a year old. So it could have been a problem in older firmware that was fixed.

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