Hartech

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

5 posts in this topic

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.

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https://industrial.omron.us/en/media/CP1L_E_OperationManual_en_201203_tcm849-112735.pdf
http://www.edata.omron.com.au/eData/PLCs/CP1/W471-E1-06.pdf

According to the manual  7-1 High-speed Counters -  The PRV(881) and PRV2 instructions can be used to measure the input pulse frequency (one input only).

I would use the raw values from counter 0 and 1. Read the values, compare and reset at an update frequency that will work in your application.

Regards,
Garry
 

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Though I am not familiar with Altivar drives I am sure there must be drive parameters that allow synchronizing the movement between two drives without having to do this via external from CP1L PLC's. In this arrangement typically one drive outputs an analog output to the follower drive and they both follow one another with no requirement for any PLC intervention. At the very least this would require encoder feedback signals within each drive to successfully implement. You could utilize torque or feedback position based upon requirements. With this arrangement response time is completely independent upon PLC cycle time and should be adequate for your application.

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15 hours ago, gclshortt said:

https://industrial.omron.us/en/media/CP1L_E_OperationManual_en_201203_tcm849-112735.pdf
http://www.edata.omron.com.au/eData/PLCs/CP1/W471-E1-06.pdf

According to the manual  7-1 High-speed Counters -  The PRV(881) and PRV2 instructions can be used to measure the input pulse frequency (one input only).

I would use the raw values from counter 0 and 1. Read the values, compare and reset at an update frequency that will work in your application.

Regards,
Garry
 

Thank you for the information - I will look at implementing this.

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13 hours ago, BITS N BYTES said:

Though I am not familiar with Altivar drives I am sure there must be drive parameters that allow synchronizing the movement between two drives without having to do this via external from CP1L PLC's. In this arrangement typically one drive outputs an analog output to the follower drive and they both follow one another with no requirement for any PLC intervention. At the very least this would require encoder feedback signals within each drive to successfully implement. You could utilize torque or feedback position based upon requirements. With this arrangement response time is completely independent upon PLC cycle time and should be adequate for your application.

Thanks for the tips - yes this is an option - I will look at the options of linking the analogue inputs and outputs of the drives - and possibly use the built-in PID of one drive to act as a master/slave to the other drive - so the slave will 'follow' the analogue actual speed reference output from the master drive - only if this is possible? - need to dig deeper to see if the analogue output is a true speed reference of the motor - i.e it's not a true closed-loop feedback control like an encoder.

The  Altivar™ 312 drives used in this project don't allow for the connection of a rotary encoder for feedback- only the larger more advanced drives have this option.

 

Thanks

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