kamenges
Member
We have been using PowerFlex 70 drives around here for some time for various web handling applications. Last month we came across an issue in an application that we seem to have traced back to an issue with PowerFlex 70 drives.
The application is a two-roll extrusion casting stand. the two rolls are independently driven through AC motors by PowerFlex 70 drives. This is something we have done before without any real issues. However, the material being cast in this application is much more sensitive than we initially believed. One of our engineers began seeing scuffing on the formed product and traced it back to casting roll speed variations. More specifically it is a speed variation between the two casting rolls and the variation seems to match up with motor rotation.
We initially thought it was a mechanical issue since it timed so well to motor revolutions. But we went through the drivetrain and didn't find anything. Our guy finally tracked it back to motor speed variations.
This is where it gets interesting. Our guy couldn't get the speed variations to go away. So we set up a test back here with just a motor and drive. We saw the same issues. It is effectively a speed pulsation that is timed to motor rotation. We get two speed pulses per motor rotation (this is a 4-pole motor). The magnitude of the pulsation seems to decrease as the motor speed increases. At speeds below about 30 RPM you can physically see the shaft pulse. The pulse frequency is tied to shaft speed.
We have tried the drive in sensorless vector and FOC. the pattern is still visible in sensorless vector but isn't as pronounced. We have tried multiple motors with the same PF70. Same result. We have tried multiple PF70 drives on each motor. Same result. We have tried other manufacturers' drives on these motors. These other drives run the motors we have without issue.
We have Rockwell hunting this down but so far all they are having us do is change gains and various other parameters. Nothing really helps. Also, I just found out today that we seem to be having this issue at another installation that is going on right now.
I guess the motivation for this post is twofold. First, I am trying to see if anyone else is seeing this kind of thing. I am looking for some ammunition to shoot at Rockwell. Secondly, I would suggest being a little careful with the PF70 at this point. I wouldn't be too concerned with general pump, fan or conveyor type applications. But anything requiring steady torque output, especially at low speeds, might be a challenge.
Keith
The application is a two-roll extrusion casting stand. the two rolls are independently driven through AC motors by PowerFlex 70 drives. This is something we have done before without any real issues. However, the material being cast in this application is much more sensitive than we initially believed. One of our engineers began seeing scuffing on the formed product and traced it back to casting roll speed variations. More specifically it is a speed variation between the two casting rolls and the variation seems to match up with motor rotation.
We initially thought it was a mechanical issue since it timed so well to motor revolutions. But we went through the drivetrain and didn't find anything. Our guy finally tracked it back to motor speed variations.
This is where it gets interesting. Our guy couldn't get the speed variations to go away. So we set up a test back here with just a motor and drive. We saw the same issues. It is effectively a speed pulsation that is timed to motor rotation. We get two speed pulses per motor rotation (this is a 4-pole motor). The magnitude of the pulsation seems to decrease as the motor speed increases. At speeds below about 30 RPM you can physically see the shaft pulse. The pulse frequency is tied to shaft speed.
We have tried the drive in sensorless vector and FOC. the pattern is still visible in sensorless vector but isn't as pronounced. We have tried multiple motors with the same PF70. Same result. We have tried multiple PF70 drives on each motor. Same result. We have tried other manufacturers' drives on these motors. These other drives run the motors we have without issue.
We have Rockwell hunting this down but so far all they are having us do is change gains and various other parameters. Nothing really helps. Also, I just found out today that we seem to be having this issue at another installation that is going on right now.
I guess the motivation for this post is twofold. First, I am trying to see if anyone else is seeing this kind of thing. I am looking for some ammunition to shoot at Rockwell. Secondly, I would suggest being a little careful with the PF70 at this point. I wouldn't be too concerned with general pump, fan or conveyor type applications. But anything requiring steady torque output, especially at low speeds, might be a challenge.
Keith