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Four Quadrant Drives: Torque Mode with Hybrid Drives

In our last posting we discussed an application where we used our “Hybrid” drive in the “Torque Mode” to apply tension to a web.And we asked how does the “Hybrid” drive know what speed to operate at when the web velocity changes? It’s looking at its own rotor encoder information. If the encoder begins to move, then the control generates an appropriate number of steps at the appropriate frequency to keep pace with the web and keep the stator one full step ahead of the rotor.

Did you catch my mistake in the last posting? I had written that the rotor was ahead of the stator’s position in the third paragraph. What does transposing the words “rotor and stator” imply in that sentence? Take a minute and think about it before you keep reading.

If the rotor is ahead of the stator, that would mean that the motor is being overhauled by the web. In other words the web is pulling the rotor causing it to lead as opposed to the rotor pulling the web and causing the rotor to lag
If you caught that error, good for you. You’re paying attention.

Now where were we? There are no additional tachometers or encoders monitoring the web speed, and that relates to a nice cost savings as well as a reduced component count and increased reliability.

Let’s embellish our “Hybrid” drive even more by adding an input and an output that can change the mode of operation. Let’s say if the input is off then the “Hybrid” drive is in an operating mode that allows the “Hybrid” drive to act just like a standard stepper drive.

If the input is on the “Hybrid” drive is in the torque mode. The output is off and latches on when the motor stalls. This embellishment allows us to automatically thread the web and then apply the appropriate torque/tension on the web once it’s fully threaded and the web is taut.

We set the current level to an appropriate amount so that it can pull the web through its threading mechanism at a comfortable set speed. When the web is fully threaded and the tension is high enough the stepper will stall. This stall condition is a good thing. The Stall flag output turns on and signals the input that the web is fully threaded and taut. The output changes the sate of the input and we switch over to the torque mode to continue to maintain the web tension. Pretty slick, huh?

What other applications can you think of that we could use this for?

How about tightening a bottle cap?

The “Hybrid” drive is set for the torque mode and the torque that is produced tightens the bottle cap to the proper torque rating.
Let’s assume that the cap should be tight within three full revolutions.

If the “Hybrid” drive makes three revolutions and stops then everything is fine. The cap is properly installed and tightened to the proper value. The system goes onto the next bottle.
If the “Hybrid” drive turns less than three revolutions then the cap is cross threaded and an output flags the system to divert the problem.

If the “Hybrid” drive spins the motor more than three revolutions then either the cap wasn’t present or the bottle wasn’t there. Again an output signals the system that an error has occurred.

Folks, we have one very versatile “Hybrid” control.
More next time.

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