motor snynchroniczation

Gentlemen, I have 3 motors with gearboxes on all three of them.
All 3 motors have diffrent RPM at 60 Hz at the output shaft, and all need to sync up with one speed pot.

Al three motors would be driven by a seperate VFD(Ab PF 4)

An existing SLC 5/05 can be used to write logic and a 8 chanell 4-20 mA output card for the speed signal from PLC to VFD.

Any Idea how to get this going??? I bet I have to know the Rpm of each motor at 60 HZ. Please help me out with writing logic for this set up.

its possible the AB drives each have a analog reference parameter. This works like amultiplier for your external potentiometer. You can tach the shaft of each but I wold think taching the application speed is more to what you would need. You can do this without calculations simply raise or lower the analog reference parameter to suit your needs.

Mordred any Idea on how this could be interpred into logic and a coresponding 4-20 signal would each of the motors at same speed?

looks like on the PF 4 you will need to use A112 and A113 4-20 analog lo and 4-20 analog hi to set your scale for the external potentiometer.

Into logic? Are you including a PLC? as you can do this without a PLC. In both cases the process is the same you set your analog input scaling to suit your application

choise one of them to be the master speed and use this speed feedback (Read from VFD) as a setpoint for the others and close the loop by ajusting other sp according to each of their real speed feedback from vfd.....

Depend on the flexibility of your mecanic, if you are synchronising a paper maching i wouldn't got this way but using close loop in the vfd woth encoder feedback or servo-motors but if your stuff can handlle a little speed difference your fine with the first option....

A n existing plc is in the panel and costumer would like to use it if possible.
Jeff thats what i was thinking to use. The motor with the highest rpm at 60hz would be lets say a lead motor , than i would pick up the 4-20 output signal from the drive and referance the signal to the other 2 motors.
This just a set of conveyors carring some metal material so i do not need to be precise.

in logic would i just use a SCP instruction ??? to achive this?

would i than have to know the maximum RMP at 60 Hz of each motor as well as the minimum rpm of each motor?

yes it definetely depends on application. Jeff's suggestion is a good one however there is one consideration "If the master should quit you will not be able to control the other two. In the other method of wiring you can parallel the potentiometer to each drive ( keep in mind each drive analog input has a 250 Ohms resister. Then set the analog lo and analog hi on each drive. Potential hazard on this method is more connection failure possibilities from the external reference MA. In Jeff's example a parer machine would require more finite control than can be accurately provided with a potentiometer

OK so you do have a PLC lol yes SCP can handle your output frequency.
You will from the external potoentiometer scale that to a corresponding desired output frequency. Each drive will then use the same output frequency from the analog output card. However each drive will have its own scale according to its motor slip compensation etc. Using the parameters I mentioned will handle that. essentailly send the analog signal from the PLC through one channel have that as an input to each drive or you can send the same value from 3 channels of the analog output card one to each drive. The drive itself will handle the differences between each motor setup. So on the PLC you are merely scaling the input frequency from the Potentiometer with the output frequency (Analaog output card). Then each drive will scale that once again for its own unique variations such as different sprockets RPM slip compensation etc.

Adam303 said:

would i than have to know the maximum RMP at 60 Hz of each motor as well as the minimum rpm of each motor?

Click to expand...

Minimum RPM would be 0 at 0 hertz.
at 60 hertz it will be you motor name plate data. The max RPM wil be limited by your max frequency and max current depending on the amount of torque you have. (Also I recommend never go beyond 80 hertz it tends to be too hard on the staters. Gear ratio to stay lower than 80 hertz if possible.)
So for example we know that if the motor name plate data states its a 1750 RPM motor the input shaft will turn at 1750 RPM at 60 hertz. You can apply this linear relation to the SCP.
Here is a drive book you will find handy.
http://literature.rockwellautomation.com/idc/groups/literature/documents/at/drive-at001_-en-p.pdf

in there it discusses how to calculate your speed relations and torque as well as slip comp etc.

Thanks mordred. The key factor in this project is that all three motors have gearboxes, with diffrent gear ratios thus difrrent rpm will be at the output shaft of the gear box.
I do have some more info about the motors anf gear boxes.
Al three motors are 1750 RPM at 60 hz
from what I was told the output rpm at the gaer box at motors 60 hz 1750 rpm are as followes:
M1 45 rpm
M2 78 rpm
M3 66 rpm
Again this iformation was given to me by someone that stood at the gear box output shaft with a stop watch running all three motors at 60hz 1750 rpm.

this can be handled through those parameters I mentioned or you can set three different scale of ranges with three different channels. Lol please don't use the stop watch method get the gear ratios from the gear bioxes and apply this formula. I tried to work out those RPM ranges to the gear ratio and end up with unequal values

mordred can you explain to me or give an exemple how i would use the scp to scale an output signal to each drive (4-20) insted of using the drive parameter. not that I'm saying the method you described above will not work i JUST CANT FIGURE OUT HOW TO USE THE SCP IN THIS SET UP.
Thank YOu again