Synchronize two motors with a Omron CP1L-EM and Omron Rotary Encoders

Hartech

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Jan 2016
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Rotorua
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Hello,

I need to Synchronize two 4kW motors connected to their own individual AltiVar VSDs.

To put it simply the two motors are pulling cables on a pulley and when loaded the motor's slip and the speed varies.

I have an Omron CP1L-EM PLC and 2x Omron Rotary Encoders ( E6C2-CWZ5B encoders - 360 PPR) - connected to each motor,



What is the best way to read the pulses from the two rotary encoders then convert to RPM?

1) Using PRV or PRV2(883) instruction, - this would be the best option as it would convert the value to RPM - however, can I use this instruction on both Counter 0 & Counter 1?

2) Or read the raw value from

Counter 0: A270 (connected to motor one's encoder)

Counter 1: A272 (connected to motor two's encoder)

Convert the pulses to RPM - then compare and adjust?

3) Or using CTBL. - is this a useful instruction for this application?



Once I get the RPM speed from each motor - I can then do a compare instruction - see if there is a mismatch and if so send a scaled analogue output to the VSDs to correct the speed if required. (10-50Hz)

What would be your recommendations? any help would be most helpful.

Thank you.
 
A few things there are various way to do this but a few things first
Is this a lift or rolling load application
Are you using 2 motors and drive to lift or pull a common load ( Load Shearing)
Or are both motors lifting or moving independent loads but must travel at the same speed.
Dose the speed command to the drive have to come from the PLC
Meaning the movement speed changes because of some changed in the PLC ( not speed matching)
Either way I would take the synchronization out of the PLC. Just use the PLC to give both drives run direction and if necessary commanded speed.

Load Shearing
Use a master slave torque follower configuration .
The PLC sets the speed of the master drive the slave drive is setup to follow the torque of the master
( Not the Speed ) the speed of the slave should be set about 10% faster than the master.
An encoder is not necessary for either drive unless the speed has to be matched to something else.

If the loads are independent of each other but must run at the same speed.

Then use 2 good flux vector drives set up to the exact same speed and acc / dec.
They don’t need to be synchronized with an outside device if the drives are setup identical the speed run at identical speeds.
You say the encoders are 360 PPR that will be a little low I would recommend at least 1024 PPR. The more counts you have the better the control will work.

One other thing , with both configurations make sure you interlock the 2 drives so that if one faults out the other is stopped. Otherwise you run the risk of dropping the load

I have done both types many times and both work well but you need to select their use carefully
 

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