Synching speed and position using VFD's

4172 Views 11 Replies 8 Participants Last post by Gravy, Nov 15, 2013

mrt19

Discussion Starter · Oct 30, 2013

I have a production line that contains 3 separate pieces of equipment, let’s call them A, B, and C. Parts are transferred from A to B and then from B to C. Each is driven by its own separate motor controlled by their own Siemens VFD motor drive. A and B are synched speed and position using a 3rd device called a Synchron Controller made by a German company Mall+Herlan model Gleichlaufregler GLR 2.1. This works good for speed and position for A to B where B is the master and A is the slave. Its takes an analog speed input from B drive, outputs an analog speed to A drive, uses 2 input pulses one each from A and one from B, 1 pulse equals 1 cycle. Drive B is set up to run at a constant speed while drive for A uses the analog output from the synchron controller to adjust the speed. It uses the inputs to position them in time.
I need to do this for B to C. Currently, B and C are not synched up but I need to synch them for better production and to reduce scrap. Has anyone ever heard of the Synchron Controller mentioned above, I don’t have any info nor can I find anything on the internet about it? Does anyone know of something I can use that does the same thing? Having a hard time finding anything that does not use encoders.
The line runs 84 pieces per minute so it’s not that fast. Is there a better easy way to do this? The entire line is controlled by a Siemens S7-400 plc but it does not have analog output module. Just think adding a 3rd controller between B and C would be least expensive and easiest.
Any help or advice on the subject would be greatly appreciated.

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KennyW

· #3 · Oct 31, 2013

If the synchron works well for you I don't see much reason to reinvent the wheel.

That said if you were to control the speed of the drives via Profibus or whatever network you like, you could certainly use the plant PLC to sync the drives by bringing the sync pulses into the PLC. You would control the speed via the network insteasd of an analog output.

Whatever you do though if it were my plant I would make them all the same. There's nothing worse than a plant where every single part is a unique snowflake.

A standardized plant with consistent control methods is a reliable plant that maintenance stands a chance of keeping running. Just my opinion.

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KennyW

· #5 · Nov 1, 2013

I didn't connect the dots that the synchron is now a relic.

In that case, using the PLC+Network controlled drives would generally be the cleanest solution.

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KennyW

· #10 · Nov 12, 2013 (Edited)

My understanding is that the requirement is for closed-loop position synchronization. In other words, a position pulse (or several) from each belt is fed to the controller, which then determines if the slave belt is leading or lagging the master belt. It then calculates what temporary speed change is needed, and for how long, in order to to re-sync the belts.

The sync would be continuously monitored and small sync corrections, while uncommon, would nonetheless be made on the fly (no process interruption). If product is running and the sync falls outside a pre-determined setpoint, the system alarms/faults, or a gate closes and product is held back until the belts are resynchronized, etc etc.

What sucks about analogs for this is that as was said- they need to be scaled.
16mA to one drive could result in 1790rpm on one motor and 1795rpm on the other.

With network control, you literally command the drives to operate the motor at 1792rpm and the drives obey.

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