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torque control is not working for my system using analog feedback

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In the test bed, we are testing a brushless DC motor and a load motor generates torque to the test motor. The test motor is running with torque control scheme. They were connected together and I measured the torque signal to feedback the signal and control it. However, I just realized it only control when the torque was static. If I commanded a certain torque value (in this case, counts command), it kept generating that value. However, it did not generate the same torque in different position. I heard NI motion controller could develop torque values by mapping the torque signal with encoder signal. If it's true, the torque generation based on analog feedback, also, needs constraint by rotor position, right? W
hen I turned on the load machine with constant speed (50 RPM), the torque from the test motor did not provide the constant torque that I commanded. It generated the fluctuated torque values. This means the max torque was generated at one point and decreasing by rotating the shaft and increasing the torque. Keep going in this way. Could you please tell me if this is the correct response when we are using analog torque feedback?

Thank you.
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Message 1 of 6
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Try the following:

1.-Set your test motor to encoder feedback instead of analog feedback.
2.-Load a velocity move on the axis for the test motor.
3.-Set the following error limit on you axis to 0 (disable following error).
4.-Use the load torque limit function to limit the amount of torque the 73xx PID loop will generate,this value is in volts, so you will need to do a correlation between the voltage output from the controller and the torque reported by your torque cell.
5.- Start the load motor.
6.-Engage the cluch.
7.-Start the velocity move on the test motor, you will see the torque ramp up to the torque limit.
8.-Call the load torque limit function on the fly to vary the torque setpoint to where you want it.
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Message 2 of 6
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Thank you,
The torque control works great in the motor test system. I have one more question. I have a set of data file to load torque in the test motor. In order to provide the number of data to "Load Torque Limit.flx" from text file, I was using "Read file.vi" and it also worked in one cycle. However, after end of the file data, I want to repeat this motion until I hit "Stop". Then, how can I modify my program?
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Do you need to read the file each time through the while loop? It should be the same data still in there, so you can read the file before entering the loop and just pass the data into the loop.

Hope this helps-
Julie S
Applications Engineer
National Instruments
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My problem is different with your answer.
I have already generated a bunch of data which was saved in text file. These data only represent some curve which could develop a torque profile in the motor. However, the curve had only one cycle and I want to repeat the motion as many as I want. Therefore, once the controller read the file and pass the data to the loop, this data should be repeat until I hit stop. I used to get zeros after I read all of the numbers in the file. Thank you.
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Message 5 of 6
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I solved this problem.
Thank you.
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