# Synching speed and position using VFD's



## HARRY304E (Sep 15, 2010)

mrt19 said:


> 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.



Bump! Welcome to ET...:thumbup:


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## KennyW (Aug 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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## JRaef (Mar 23, 2009)

KennyW said:


> 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.
> 
> ...


I agree with everything except the first line, only because you already KNOW that you have zero support on the existing product, and now you are going to try to stretch the functionality. In my experience, that generally ends up being a colossal waste of time and you end up going with plan B anyway. 

KennyW's plan B suggestion would actually be my plan A. The machine designer may have originally used that specialized controller because at the time this was made, high speed comms from PLC to VFD was non-existent. But with modern technology, that is no longer the case. Siemens, since that's what you have, can now use Profinet (Siemens version of Ethernet) to have the PLC talk straight to the VFDs, and it is now considered "deterministic", which means you can predict the exact rate of data transfer so as to reliably accomplish high speed timing functions as you are describing here. In fact that may explain why you cant find info on the other company, Siemens may have essentially put them out of business if that's all they did. 

If your CPU is too old you may have to upgrade it to get Profinet, but I think that you may be ultimately ahead of the game to do so. Get hold of your local Siemens office, they should be able to quickly assess whether or not that will work and may even help you to implement it, or find you an integrator who can.

My plan B would be to find another similar "line shafting" controller with established local (North American) support. Two names off the top of my head are Bardac (New England area) and Brock Solutions (Ontario Canada area). Both offer synchronizing hardware systems for drives similar to what you described. Brock, who also has offices in the US, is also a large system integrator and could take it on turn key for you. Bardac may be able to also, I just have never asked.

PS:
As a bit of followup, I looked on both sites and Brock apparently got out of the hardware side of it, likely for the same reason, it's no longer necessary. Looks as though Bardac changed theirs too, it's now essentially a PLC that uses Ethernet, which is what you could do with what you already have.


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## KennyW (Aug 31, 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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## JRaef (Mar 23, 2009)

KennyW said:


> 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.


Yeah those drive synchronizers used to be a good fix for multi drive coordinated systems like web presses and rolling mills, and there used to be several more people doing it. But when I started seeing "line shafting" functions turning up in VFD programming, I remember thinking that this was likey going to hurt those niche companies. I guess it happened faster than I thought.


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## Jlarson (Jun 28, 2009)

I haven't seen a synchron in a long time. I think we have one machine that still has one but it's on its last legs.

The PLC route would get my vote too.


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## xsryman (Dec 4, 2012)

if the VFD has analog outputs built in to it, as most do these days, you may even not need to go through a network.


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## lefleuron (May 22, 2010)

xsryman said:


> if the VFD has analog outputs built in to it, as most do these days, you may even not need to go through a network.


 Your thinking about making B the master, then having A+C follow using scaling to determine their speed reference from B.

Could maybe even throw in 10 turn pot of some low resistance to do a final hand tune based off speed from a handwheel?

Good idea.


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## KennyW (Aug 31, 2013)

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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## lefleuron (May 22, 2010)

KennyW said:


> 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.
> 
> ...


 Agreed.

But it sounds like he has some type of disappeared older system he cant find anything about. At least the analog (be it 4-20mA or even 0-10 volts) will get it going, and with some tuning would be fine as a "line locked" system.

I know a few years ago a company sent us some info on a controller that basically did a lot of conversions and scaling, but it also did like 15 different communications protocols, and could convert them all. Like Hart to Mod-bus and what-not. We looked at it, but did not buy it. I seem to remember it was almost the same cost to upgrade as it was to band-aid.

Something "Smart ???????????", maybe someone else here has them. 

It was designed for exactly this type of situation, where you need to integrate some old equipment with new equipment because the old is no longer supported and there are no parts anywhere.


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## Gravy (Feb 19, 2009)

Funny to read that this is still a challenge.

When I was in the custom packaging and printing world a million years ago, we struggled with a lot of problems on this. 

I also worked in the steel mill industry for a number of years. 

A mill setting where your product is fed in one end, processed, and packaged at the other end is much simpler than a continual setting like a web to web printing press.

In the early 90's me and a few guys tried to develop what was basically a printing press with out the print. Think web fed lamination, perforating, and die cutting stations with a conveyor outfeed.

Boy did we struggle on start up! 

Thanks for the memories.


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