kenny powers

Anyone with Powerflex electronic gearing experience?

10 posts in this topic

I'm about to tackle a project that involves synchronizing two  turntable's rotation together. I will be using two PF755 drives, one with a dual encoder board and the other with a single encoder board. Each table will have a motor with encoder directly mounted to shaft. The master drive will have the dual board and utilize encoder feedback from both table's motors. The slave will only use it's own encoder.  

I've found an example somewhat similar on Rockwell's technotes that outlines the parameters I will need to make this happen. There are differences with gearbox ratios on the motors, which the techconnect note also details how to handle. So, the remaining questions I have are:

I assume tuning the drive(s) will be necessary. Will a static tune suffice?

Also, the technote states the drives will fault if start/stop procedure is not properly followed. The slave drive must be issued the start command before the master, and when stopping the master must stop first. For this application, occasionally the slave table will not be needed. Will running the master alone be a problem?

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Autotune on the PF755 works as follows:

  • ROTATE - For my money this is the best tune. It rotates the motor, but the motor must not be coupled to anything.
  • INERTIA - Rotates the motor while it's coupled to a load, such as an integral gearbox or pump that can't be uncoupled.
  • STATIC - If for any reason the motor can not be rotated at all, but can be energized, Static does the job.

So, Static=Good, Inertial=Better, Rotate=Best. 

I don't know enough about your process to advise on the best way to get around the sometimes-master/sometimes-standalone drive situation. One possible solution could be to write code to change the drive to standalone, IF the affected parameters can be data-linked. 

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Static and rotate tunes populate the same parameters. Inertia tune is something completely separate and only comes to play in FV modes. The main difference of static vs rotate is the measuring of flux current. Static uses a lookup table whereas rotate measures it. You may need rotate tune for some motor types like pm for the offset tests for the encoder. You can run the master independently from slave but just know that they will become in un synchronized. Sounds like for your tables that won’t matter though. If it does, you’ll just have to rehome the master to re synch to slave

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Thanks for the info guys. From what I've read at Rockwell after posting here, as long as the drive's firmware is newer (it will be), the problems that occurred when running the master alone have been taken care of. I tried getting someone at Rockwell to confirm this won't be a problem but I suppose this application is too specific for anyone to know for sure.

Also, the drives WILL be using Induction FV mode, so this means inertia tune is needed? I will go read on what this entails.

9 hours ago, VFD Guy said:

Static and rotate tunes populate the same parameters. Inertia tune is something completely separate and only comes to play in FV modes. The main difference of static vs rotate is the measuring of flux current. Static uses a lookup table whereas rotate measures it. You may need rotate tune for some motor types like pm for the offset tests for the encoder. You can run the master independently from slave but just know that they will become in un synchronized. Sounds like for your tables that won’t matter though. If it does, you’ll just have to rehome the master to re synch to slave

 

Edited by kenny powers

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Rotate and Inertia tunes provide better results than Static, regardless of operating mode.

https://literature.rockwellautomation.com/idc/groups/literature/documents/at/drives-at004_-en-p.pdf

Page 36:  Auto Tune The Auto Tune test is used to identify the correct motor flux and stator electrical properties, including:

  • IR volt drop, which is voltage drop over resistance.
  • Ixo volt drop, which is voltage drop over inductance.
  • Flux current (estimated in Static Tune and measured during Rotate Tune test).
  • Slip RPM, which is calculated from motor nameplate data. If an encoder is used, the Slip RPM becomes a measured value using the encoder.

Page 37:   Static Tune This test is used when the motor is connected to a high friction load and cannot easily be uncoupled from the motor, or when the load cannot be rotated due to mechanical constraints or a limited range of movement. The Static Tune test does not generate any motor movement. The Static Tune test results may not be as accurate as the Rotate Tune test.

Rotate Tune This test is used when the motor is not coupled to the load, or the load is low friction. Rotate Tune is used to better identify motor flux and stator electrical properties, which are used to automatically tune the torque/current loop. The Rotate Tune test causes motor rotation at different speeds while it is executing.

Inertia Auto Tune Test This test measures the total system inertia ( Jt). When using Load Observer, this test is executed with the load disconnected from the motor so that only motor inertia is measured. Otherwise, this test is executed with the load connected to the motor so that motor + load inertia is measured. During the test, the drive/motor is accelerated using the entered ‘Autotune Torque’ value. The time required to accelerate the motor and load from zero speed to rated speed is measured. The value of Total Inertia ( Jt) is determined from this measurement and the value of Par 9 [Total Inertia] is updated to reflect this measurement. The Par 9 [Total Inertia] value is used for a number of internally calculated parameters for the Speed Regulator. These relationships are described in Chapter 3.

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I agree that rotate is better than static for FV and SV modes. Static tune populates motor characteristic parameters like IR voltage drop which isn't used in V/Hz modes. So Rotate and Static only apply to SV and FV modes. Econ mode is technically part of SV. So the mode matters here. Inertia tune populates total inertia which is only used by Flux vector modes. If you read the description for parameter 76 which is populated during the inertia tune, it even states this. If you read the description for load observer parameters, it also states that it's only used in Flux vector modes, so the mode does matter.

Here is right from the manual: Inertia Tune (4) – A temporary command that initiates an inertia test of the motor/load
combination. The motor will ramp up and down while the drive measures the amount of
inertia. This option only applies to FV modes selected in P35 [Motor Ctrl Mode]. Final
test results should be obtained with load coupled to the motor.

Anyway, getting to Kenny's question, I'm not sure what issues you're referring to in firmware with gearing. Do you have a technote that talks about this issue? If you are using FV mode, it is best to get an inertia tune completed. If this is not, the default of total inertia in parameter 76 will be default of 2.0 which will then affect your speed bandwidth in parameter 636. I've had projects where an inertia tune was simply not feasible so I either left 76 at default and adjusted 636 manually or played with the inertia until I got something acceptable. You can also adjust the kp and ki of the speed loop manually if 636 = 0.

Hope this helps you.

Edited by VFD Guy
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Yes, the technote that contains much of the info I'm using is from QA58907. I think I have a pretty good grasp on it all now, including the tuning requirements, thanks! I'm trying to minimize the amount of unforeseen setup issues ahead of time as this will be a retrofit on a currently in-production line (currently using SEW MD60s).

1 hour ago, VFD Guy said:

Anyway, getting to Kenny's question, I'm not sure what issues you're referring to in firmware with gearing. Do you have a technote that talks about this issue?

The issue I'm concerned with comes from the above mentioned technote:  Related Anomalies:
In firmware version 6.002 and earlier, if the leader drive is run  without the follower drive, when the follower drive is finally run it will try to advance to the position the leader drive moved to while the follower was stopped.  If both leader and follower are run simultaneously the follower will overspeed  by the threshold set up in  Port 10 Parameter 1766 [PReg Vel Limit Pos] or Port 10 Parameter 1768 [PReg Vel Limit Neg] depending on the direction.  To avoid this anomaly, cycle power to the follower drive if the leader was run while the follower was stopped. This anomaly has been corrected in firmware 6.003 and later.

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That technote applies to 755T drives not 755 drives. Are you using a T drive?

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30 minutes ago, VFD Guy said:

That technote applies to 755T drives not 755 drives. Are you using a T drive?

I did notice this, but didn't see anything in that application example that seemed to specifically require the T, am I wrong? 

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Use QA13283 instead. The technote you provided states that the content of that technote only applies to T drives

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