Velocity and Position control

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30 Jul 2010 21:08 #3527 by mdurna
Dear All,

I have a linear axis control problem. In my machine, there are three linear axis and servo motors are directly coupled to the each axis.
The servo motor drivers have quadrature encoder outputs connected to EMC via a PCI add-on board.
The servo motor driver has three modes of control: position, velocity and torque control. Position is controlled via standart PULSE and DIR signals, and velocity and torque modes make use of +/-10V analogue inputs. The servo drives manual tells that, at one time user can use one of modes: position, velocity, torque, Position OR Velocity, etc.. In Position or Velocity mode, the driver is set via a disrete input MODE which selects between Position or velocity at a given time.

For a good machining quality, I would like to implement velocity control. Since I am new to the business, I am not sure which mode of control to use: Is it OK to run the machine in
1. only Position mode,
2. only Velocity mode or,
3. dynamically select between those modes while machining?

Int the Integrators Manual of EMC, it says that one can implement position and velocity loops using HAL blocks.

Does anyone have such an experience?

Best regards,
Mehmet

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30 Jul 2010 22:27 #3529 by BigJohnT
I use velocity mode for my servos on my lathe. AFAIK velocity mode is the easiest to tune the PID loop. I would not switch back and forth....

John

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31 Jul 2010 12:19 #3532 by mdurna
Do I understand correct: it is enough to connect the +/-10V VREF signal from control board of EMC to servo driver and feed quadrature encoder signals back to the EMC IO board and set the servo drive to velocity only mode? The PULSE and DIR signals are irrelevant then?

For five axis application, which MESA board configuration do you recommend for EMC? I think not all of them are ready for EMC.

Best regards,
Mehmet

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31 Jul 2010 12:34 - 01 Aug 2010 12:55 #3533 by BigJohnT
Yes that is all that is needed between EMC and the servo drive. The servo drive itself should have some form of feedback from the motor usually a tacko generator to know that the motor is spinning at the proper speed.

As for which mesa card(s) to use it just depends on what your total requirements are for I/O etc. I used a 5i20 with a 7i33TA and a couple of 7i37TA's for my setup. Some have used two 5i20's or a 5i22 (I think) to get enough I/O. I think there is one card that can drive up to 6 servos but I don't know which one it is. You might look on here to try and find that thread. I do know that the driver for that card is new and or experimental... do check it out before you buy something that is not listed in the manual.

John
Last edit: 01 Aug 2010 12:55 by BigJohnT.

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31 Jul 2010 13:51 #3534 by mdurna
Cheers BigJohn.

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