Synch two DC drives together.

I am working on an old plastic extruder and I need to synch two chilled rollers of different diameters together. On roller is ~20" and the other is ~9.5". I will be using two AB Powerflex DC drives to control the motors. I am thinking about using a CompactLogix PLC to synch and scale them. Anyone have any ideas of how to do this, or a better way.

Thanks,
Gary

how close do you need

In the PLC you could take setpoint for drive 1 (9.5" drum) and multiply by 2.105263157894737 (ratio of drums) and that would be the setpoint for drive 2. This would work only if loads are constant and linear .

Thanks so much for replying. The drums are chilled and smooth out the melted plastic into a sheet, so they have to be matched very closely.
That should work just fine, thanks again.
gary

If the surface of the drums are to move at the same distance per time period
then the 9.5" drum needs to run more than two times faster than the 20" drum
with a set ratio of 40 : 19

If it is a simple control that you can send the same analog signal to both drives,
you then only need to set the max speed limit of each drive at the 40 : 19 ratio
without the need for a PLC interface to get your speeds wanted.

If tight control of speeds are required you may need to use encoders to do the exact synch for your drives at exact matching speed and drum rotations

It all depends on whether a slight plastic slipage is able to be tolerated
as each drum rotates and jockeys for position and rotation,
as I have never had to deal with plastics manufacture
it is something for you to determine and decide
of your needs

This really should be done with electronic gearing(position)if there is any kind of pattern matching to be done(front to back of sheet). If not, then velocity gearing will work. Analog typically isn't very accurate.

Highland Controls said:

This really should be done with electronic gearing(position)if there is any kind of pattern matching to be done(front to back of sheet). If not, then velocity gearing will work. Analog typically isn't very accurate.

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Amen!!