Speed control problem


I have a problem where I need to control the speed of a conveyor so that rubber strips are neither too tight nor too loose. This speed changes with every batch and temperature fluctuation. The conveyor is controlled by a powerflex 70 drive with speed regulation controlled via a trimpot by the operator. I have considered a dancer but it would be best if there was no contact with the product. Anyone have a suggestion?

Thanks, Bill

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Sounds like you want the drive to run in constant torque mode or something related to it. In order to control tension, you have to be able to measure tension, in some fashion and a control input. A dancer is only one way to do this. Think about all the other forces in your system that are directly related to the tension to be controlled (e.g. forces on bearing mounts). Perhaps a load cell could be mounted somewhere that would perform the tension measuring function. Then you need to add a PID controller to the drive to compare the measurement to a setpoint, and produce appropriate adjustments to the drive control input. When that is all interconnected, you tune the 3 factors in the controller (proportional, integral and derivative) to achieve stabile control.

Reply to
John Popelish
1) Need to determine if you really need to control SPEED or TORQUE instead. Not sure from what you wrote. 2) Need feedback to determine the Speed or Torque. Encoder or Torque sensor input to powerflex 70 drive. 3) Need a simple summing junction or maybe a PI or PID control, which your powerflex 70 drive w/ regulation should be configurable to do.
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Have you considered displacement as an indirect tension measurement. How much sag occurs? use laser or ultrasonic distance measurement w/

4-20mA for a lo>Hi,
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This drive may NOT have feedback inputs, others in series do, but could add circuitry at the speed control pot or different drive controller, like 700.

Also see below link:

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My suggestion is to mount the whole assembly on a slider restrained by a load cell. the cell will give a direct reading of force, i.e. tension. Even toque alone does not give tension.


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Walter Driedger

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