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# Centrifugue standard planetary gear and DIRECT DRIVE gearbox differences????!!!

## Centrifugue standard planetary gear and DIRECT DRIVE gearbox differences????!!!

(OP)
Hello!

I'm automation technician and here they want to put to dcs a sludge centrifugue equipment. This thing is a bowl and a screw in the middle, and it has pulley to the bowl in one side and in the other side a planetary "direct drive" gearbox.
we have many planetary gearboxes but this I have is called "direct drive gearbox" I would like to know if there is some difference in terms of speed references between each others.

the centrifugue should control with speed difference. In standard planetary centrifugues here we control like this:

Bowl Speed = Main motor reference x Kpulley
Speed Difference = (Bowl Speed - Screw Motor speed)*Planetary Gear Ratio

But I have seen this "Direct Drive planetary gearbox" speed references and looks like the aren't the same...

Do you have any hint???

kind regards,
martin

### RE: Centrifugue standard planetary gear and DIRECT DRIVE gearbox differences????!!!

A sketch or schematic would be helpful. Is the purpose of the planetary gearbox simply to provide the correct direction of rotation between the bowl and screw?

### RE: Centrifugue standard planetary gear and DIRECT DRIVE gearbox differences????!!!

(OP)
hello tbuelna, it is alfa laval "direct drive", It says "planetary drive 2-stage direct drive".
in "standard" planetary drives we control torque by changing speed difference. But this speed difference is relative to bowl speed. So I calculate the speed difference.
But what I've seen is that apparently the screw motor drive has a setpoint of "Screw Speed = Motor speed reference * Gear Ratio" (not depending on bowl speed) that I find strange because in "standard" drives you have to calculate screw motor speed reference as a function of bowl speed.

(OP)

### RE: Centrifugue standard planetary gear and DIRECT DRIVE gearbox differences????!!!

It appears that there are two different configurations of this machine. One uses a planetary gearbox connecting the drum and screw conveyor driving them at a fixed speed ratio. The other uses an electric VFD between the drum and screw conveyor permitting a variable speed ratio.

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