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Limiting velocity during torque mode on SureServo

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  • Limiting velocity during torque mode on SureServo

    I have set-up an application that requires the servo to home to a hard stop. This is done by putting the drive into torque mode and monitoring when the motor reaches zero velocity. This has been very reliable and gives me a good zero position to reference moves against. The issue is, the torque setting has to be high enough to get the application moving and this tends to be a bit fast on the velocity. I read in the manual P1-02 can be used to limit the velocity in torque mode. This is what I need but I do not have enough digital inputs for the VCS0 and VCS1 selection.
    I see also in the servo manual that I can apply an analog voltage to the Vref input. What is not clear to me is how to wire this? I am thinking of using an analog output module, P2-04DA. How would I wire this module? Connect the analog V+to the Vref and the COM to GND on the servo drive? Am I understanding how this velocity limit works during torque mode?


  • #2
    I have only used the servos for velocity / positioning with serial communication / DI inputs, but it looks like it should work in the manner you are describing.
    It would be easy to test with a pot first and then add in the plc analog out after.
    The direction the unit is homed also may play a part. The reference can be -10vdc to +10vdc.

    P2-04DA Analog Output Module
    +24vdc to terminals 1, 9, 18
    0vdc to terminals 5, 10, 14
    Terminal 2 (V1+) to Servo terminal V-REF
    Terminal 5 (Com) to Servo terminal GND

    Servo wiring pg 2-27

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    • #3
      Many drives allow you to accomplish the same thing with a velocity move towards your hard stop and watching the position error. Doesn't the drive support any homing methods automatically?

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      • #4
        Originally posted by Adisharr View Post
        Many drives allow you to accomplish the same thing with a velocity move towards your hard stop and watching the position error. Doesn't the drive support any homing methods automatically?
        They do, but they use sensors that go to a DI for the home sensor so some applications may need to do something else to achieve the home they want. Hopefully the new servo series is released soon with the much more modern drive features.

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        • #5
          Is there a new servo series in the works?

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          • #6
            When I've homed to a hard stop, I did the reverse - jog in velocity mode with a torque limit and watch for position error. Doing that might address this issue for you.

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            • #7
              Originally posted by RogerR View Post
              Is there a new servo series in the works?
              There was talk that a new servo series would be released with EtherNetIP support sometime late last year along with the GS drives that had that support. Havent seen them yet, but the OEM does have new servo drive series available with a bunch of Ethernet stuff so it shouldnt be *too* long before Automation gets their branded versions with EtherNetIP built in, and hopefully keeps the more advanced movement features.

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              • #8
                Thanks everyone for your replies. I am going to try the analog output card today or tomorrow.

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                • #9
                  That's good news on the new line of servos. I have several projects coming up that faster communication, more DI, and/or the ability to stop short in positioning mode would be beneficial.

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                  • #10
                    The analog output card works great and was easy to set-up and use. Agree with RogerR that a newer servo with faster communication, more DI, and more homing options would be great. Adding the analog card was really easy, but now the system is another $200. If the servo had more DI or another homing option this could be done without additional hardware. I know I could use a potentiometer, but I wanted to give the user the ability to adjust the homing velocity from the HMI.
                    I designed this system to be fairly universal. I can run 1 to 4 servos using the same program. I simply deselect certain lines if there is less than 4 servos. I limit the total number of servos to four. Primarily because we have no application that uses more than four. But I also noted that as I add more servos the communication transaction time starts to slow down for each individual servo. I have the MODBUS rate at maximum and have not had any communication problems, but I also want timely feedback to the PLC. All the control is in the servo drive, but the PLC uses the MODBUS DI/DO parameters to identify end of move and initiate next move. Any lag time is not noticed in the application as moves typically take 1 to 2 seconds and the next move is not required for several seconds. The physical DI is e-stop and DO is servo enable (I also interlock the motor power through the e-stop and PLC logic). What would be nice is expanded MODBUS DI/DO and use these for velocity and torque selection. These can use 2 inputs each (4 total) and this leaves you little availability for other functions (like position select requiring three inputs).

                    Thanks everyone for your input.

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