PMAC motion control cards..........help!!! 4

[paulsuthie]

MOTION CONTROL CARD QUESTION.i am working on a machine that is controlled by multiple vsd's. Resolvers on the servo motors feedback to these vsd's that then in turn send signals to multiple pmac motion control cards via ad convertors. The motion control cards then appear to be connected to the encoder inputs back on the vsd's. Do the vsd's act on this signal from the motion ctrl cards to adjust their speed? ie. is the drive simply being used to recieve the resolver feedback signal and send it to the motion cards for analysis? i.e. is the resolver signal not actually being used by the drive? Is the "real" feedback signal that the drive is acting on coming from the pmacs and not from the resolvers?

 

[Skogsgurra]

Most likely as you assume. The PMAC cards are add-ons that give ordinary drives motion control qualities.

Curt Wilson of Delta Tau is a regular in here and he will probably give you a very thorough answer once sun dawns on the West coast.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

paulsuthie; The PMACs are what's controlling the VSDs. However the drives are likely doing control themselves also. They are doing stuff like profiling the speed ramps, maintaining the V/f ratios, providing the modulation frequency and limiting various parameters. So not all that comes out of the VSDs is directly caused by the PMACs. If you were to change out a VSD you would want to make sure the new one was set up the same way or your system would likely not perform correctly.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[sreid]

The usual PMAC servo cofiguration is PID control with a current command signal to the servo amplifier (this could be a servo amplifier for a PMDC motor or a Vector Drive VSD). Without add on interface boards, a PMAC accepts incremental A quad B encoder signals for position feedback. Resolvers are common feedback devices for both PMDC or induction motors driven by a vector drive. In both cases, the servo drive needs position information to comutate the motor (or compute the Vector Control). Often the drive converts the resolver position into A quad B encoder signals for use by the position controller.

 

[cswilson]

Hello everyone! I'm back from a long weekend of being a soccer dad. Thanks for covering for me while I was away!

paulsuthie: Almost surely, these are real servo drives, and not what most people would call VSDs. The drives will be accepting "instantaneous" commands and reacting to them; the PMAC will be doing all of the "profiling".

PMAC is a position controller; its trajectory generator will be computing the desired position profiles based on a stored program. It will accept position feedback -- what looks like synthesized AB quadrature signals from the drive in this case -- and compare the measured position to the instantaneous commanded position from the trajectory generator at a rate greater than 1 kHz. From the error between these, PMAC will close a position loop, and probably a velocity loop as well, with the velocity estimated from the position data, and output a command specifying what current magnitude is needed to try to drive the error to zero -- usually encoded as a +/-10V.

(Sometimes the servo drive will close the velocity loop itself. In this case, it is usually termed a "velocity-mode" drive. Some drives have a software switch that permits the drive to be put into either "velocity mode" or "torque mode" (accepting current-magnitude commands). If the drive is in velocity mode, the controller closes only the position loop; the drive computes the current-magnitude command by closing a velocity loop.)

From the current-magnitude (torque) command and the rotor angle value derived from the resolver through the drive's resolver-to-digital computer, the drive computes how much current is needed in each phase to get that torque. Then, using internal phase-current sensors, it computes how much voltage each phase needs to get that current. (We live in a world of voltage sources, so ultimately we modulate the available voltage to get the current we want.)

So the drive uses the resolver feedback to get the rotor angle for its own phase commutation algorithms. It may also use it to estimate the velocity if it is closing the velocity loop. Because the controller needs feedback to close its loops, all of these drives generate a synthesized quadrature signal that mimics the signal of an incremental encoder. This signal is sent from the drive to the controller.

I hope this covers your questions.

Curt Wilson
Delta Tau Data Systems

 

[paulsuthie]

wow...........u fullas know your stuff.I am only just moving into working with robotics so some of the some stuff is pretty heavy going but I appreciate all posts.....
Just to sum up.......this machine polishes several different profiles of steel sink inserts. Would I be right in assuming that the operator chooses the polishing sink profile that he wants to use then downloads this programme from the PC onto the PMACS. The servo drives do the speed control only as this is pretty much a constant while leaving the PMACS to take care of all position control.

 

[Skogsgurra]

That seems to be a concise and correct description. Considering time of post; where are you in this world?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[paulsuthie]

Thank you Mr Gunnar. I am sitting at my pc at 9.50pm in a little city called Christchurch in beautiful New Zealand.

 

[Skogsgurra]

Hey!

That's where I will be going (sometime) to see my friend Mark Empson! You know him? He is in drives and soft-starters. He is also a regular in here. Handle MarkE.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[paulsuthie]

mmm....Mark Empson? The only Mark I know that would be into drives etc would be the Mark who works for "Electrade."