JB2020 (Customer) asked a question.

June 28, 2023 at 8:54 PM
Matching Speed with 2 drives...

I have a rotary moulder that produces pet food. There is a die roll that is driven by a 7.5 hp motor. Below this die roll is a press roll that is hydraulically pressed up against the die roll. A conveyor belt is driven by running between these rolls. The conveyor belt also runs around several other rollers. One of these rollers is considered a Belt Assist roller and is driven by a 2 hp motor. Some products require the belt assist to run and others don't.

 

On the products that require the belt assist roller to run...I would like to match the speed of the die roll. There will have to be offsets or some kind of math calculation to calculate the frequency at which it needs to run, because the die roll is approximately 12-14" in diameter and the belt assist roller is only 2-3" in diameter.

 

With all that said, here is my question....

 

Is an encoder the way to go with reading the speed of the die roll and then translating that to a frequency value for the belt assist roller? I'm not sure I like this idea because the die roll would have to start running before the belt assist roller.

 

Or can this be done within the GS20 drives by reading speed and/or frequency of the die roll and and sending the correct frequency to the belt assist roller? I'm thinking this will allow both motors to start simultaneously.

 

 

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  • z28z34man (Customer)

    I will over simplify this a bit but when the line is running i have the master drive running in speed control and the slave drive in torque control. I tell the slave to run with we will say 50% torque. I also calculate the theoretical speed I expect the slave motor to be running at based of the speed the master is running and do not let the slave run more than a certain amount over or under that calculated speed. I do that incase the rolls get glazed over and have no grip so it doesn't start slipping and running away.

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  • Cap (Customer)

    How far off on the speed can the Belt/Moulder be?.. If it must be exact, then Encoders are required.. If close it good enough, then two VFD running Open Loop, with Approximate Math to get things right will likely work..

     

    Cap

    • JB2020 (Customer)

      It doesn't need to be exact! I just need it to be close enough that they don't fight each other.

      • Istilldontknow (Customer)

        Cap is right, you can get it really close by just doing the math. one drive probably has more power than the other so that one will "win" the tug of war but it once you get the math right it should be close enough that you don't even notice.

  • PouchesInc (Customer)

    Could you use the analog output of the first drive and send that in to the 2nd drive as its speed reference? Once you program in the offsets for the analog curve everything should work

    • JB2020 (Customer)

      This might work...I've never had to do this before, hence the reason I'm asking. If the moulder is shut off and the frequency value is changed on the die roll, I want the belt assist to be set immediately, so when the machine does start it is going the correct speed. I also need it to work on the fly while the machine is running.

       

      I may have to do this via the PLC program because I'd like this to happen either way...If the frequency is change on the die roll then the belt assist follows, and vice versa, if the frequency is changed on the belt assist then the die roll follows.

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  • Cap (Customer)

    You say you have a PLC involved.. what aspect of the Moulder and Belt drive does the plc control?..

     

    I'd consider having the Moulder Drive ( ASSUMING its on a VFD ) Call the speed of the Belt.. Depending on the complication of the PLC Controls, the PLC might not send a speed control out to the Moulder Head if it's stopped.. In That case you might have to crack into the PLC Logic and output TWO Speeds ( Another analog Output? ).. or if you can have the PLC Output the requested speed of the Moulder and the Belt, even though the Moulder is not running, but the Belt is.. In the Belt Drive VFD, you can scale the Speed Output to match the Moulder Head..

     

    Many Options..

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    • JB2020 (Customer)

      First off, I apologize for the late reply.

       

      I will have a Productivity2000 running this machine. I will be using the GS Drive Read/Write instructions in the Productivity Suite software and communication with the GS20 drives via Ethernet cables to the drive ethernet option cards.

       

      I would like to be able to press a button on the HMI that says "Use Belt Assist". Or press it to turn it off. This would require some sort of electric clutch obviously, but I'm still wondering about the speeds.

       

      Is there a parameter within those instructions that the PLC can use to read and calculate the frequency of the second drive? The 0x2103 Output Frequency of the Drive Parameter maybe?

       

      Maybe I can use that and then create an Offset Integer to calculate the RunFrequency of the Belt Assist roller.

       

      Any thoughts or ideas are welcome...

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  • z28z34man (Customer)

    instead of speed control have you thought about torque control with a clamp for maximum speed difference vs calculated.

     

    We do this for some of our Squeegee rolls on web processing equipment. We do this because are squeegees are not all the same diameter new vs resurfaced.

    • JB2020 (Customer)

      Please elaborate on this in greater detail...

       

      Do you read the torque on Drive A and if the torque goes above a setpoint then Drive B starts to add torque??

       

      Or are you just reading torque on Drive A and then translating that to Drive B so it can match it??

       

      Would like some more details, please.........

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      • z28z34man (Customer)

        I will over simplify this a bit but when the line is running i have the master drive running in speed control and the slave drive in torque control. I tell the slave to run with we will say 50% torque. I also calculate the theoretical speed I expect the slave motor to be running at based of the speed the master is running and do not let the slave run more than a certain amount over or under that calculated speed. I do that incase the rolls get glazed over and have no grip so it doesn't start slipping and running away.

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