Conveyor Speed Control

[MikeLB56]

Hi all,

I have an application where i need to sync up conveyors on an aerosol can line starting at the packaging portion of the line.

I have VFDs on the line but not at every motor. For instance, from the beginning, i start with 3 VFDs. i then get to 3 motors that the customer has asked not to automate. these run into, though and out of the labeling station. once onto the next station, the tipper (where they put on the little tip where the spay comes out)I have a VFD and into the next station the capper. after that i have 2 VFDs but again, the customer has asked to leave those operator controlled. once through there i have 6 VFDs through to the case packer and to the entrance of the case sealer where my control ends:
nc= no control
---[3vfds]---[3motors nc Labeler]---[TipperVFD]---[CapperVFD]---[staw&tape 2VFDs nc]---[6VFDs for Case Packer & Accum Table]-----[Box Sealer nc]----

At each station (labeler, tipper, capper, straw & tape, case packer, box sealer) there are photo eyes at each infeed and discharge. these act as start stop signals for the existing motor circuits.

the customer wants to increase their throughput as right now, the operators set the VFDs at "whatever speed the feel like" as my customer put it.

first, can i help the customer increase their throughput if i have motors in the middle of the line i cannot control or he would rather me not control?

second, how would i get feedback from the line as to how fast i should be running the VFDs? can i use the existing photoeyes some how in the program?

I will most likely being using analog signals into a CompactLogix but i am really looking for some concept help right now, not necessarily hardware.

any insight on this would be AWESOME!!!!!!!!!! THANKS!!!

i hope my little picture helped up there if still totally lost i can scan something in!

 

[mordred]

http://literature.rockwellautomation.com/idc/groups/literature/documents/at/drive-at001_-en-p.pdf

contained in the above book is the formulas to calculate your Torque RPM and feet per minute.

The non VFD conveyers will need to be changed through sprockets.
This could lead to problems if the operator decides to set the speed of the VFD conveyers too fast or too slow.
Each conveyer should be 10% faster than the previous conveyer.
One method to measure speed of each conveyer is to count the sprocket teeth. Using a proximity switch. One revolution will equal the number of teeth on said sprocket. Yuo can probably measure how many feet per minute is by measuring the change in one complete revolution.

 

[Eric Nelson]

I think the first thing to determine is the maximum speed for each of the processes. For instance, if you kept the infeed to the labeler filled with parts, how fast can you run? How about the capper? How about the fixed speed conveyor? With that information in hand, you will know which part is the SLOWEST process. That will be the fastest you can ever run, no matter what. In other words, there's no benefit to speeding up the capper, if the labeler will never be able to keep up.



-Eric

 

[MikeLB56]

Thats kind of what i was thinking. If i have a limitation somewhere won't that be the fastest my throughput can be. Thanks guys this gives me a GREAT starting point! I will let you know my progress!!

 

[bikerdude]

Mike,
I have learned over the years that conveyor speeds that are self regulating require the least amount of tweaking later on when the managers decide to speed up or upgrade various machinery. If there are proximitys along the different conveyors, use them to regulate the motor speed.

Usually each section (motor) will have 2 prox., one at the start & one at the end. If there is a "Gap" seen by the proxs, then speed up the motor that feeds containers into that "Zone". If the "Gap"has been "closed" for a time, then slow the motor back down some. This strategy allows the containers to "Keep up" with the machine that they supply with out "Crowding" or "Forcing".

Of course there must be limits (upper & lower) as to what is an acceptable speed. For instance, the motor will probably need to stay below 90 Hz & above 30Hz. If a motor has been "Idiling" @ 30hz for a time, stop the motor since we are wasting energy. Speeds will have to be limited to a reasonable rate that will prevent tipping or smashing of containers.

This is the overall strategy I use to maximize conveyor speed controls. Might help your situation or then maybe not.

BD

 

[MikeLB56]

There are Photo eyes at each infeed and discharge of each station. would these be the prox's you are speaking about? so logically, how would i say that in statement? (I am a beginner programmer so i try and put into words my logic before figuring out the ladder logic!:]) for example: If the outfeed can prox doesnt see a can for x seconds, then speed up conveyor going through the station?

Mike

 

[bikerdude]

Mike,
I don't think a photo-eye is going to perform as needed on this application. The eye looks across the entire line & gives a signal if there are any containers at all on the line, right?

A proximity switch is usually mounted on the conveyor side rail peeking in between the upper & lower side rails. This sensor configuration only sends out a signal if the containers are sufficiently packed into the conveyor so that they are rubbing along the rails. I'll see if I can round up a picture or drawing.

Logic:
If (X sensor is clear) & (Y sensor is clear) for (X time) then do something (speed up).
How much to speed up is a good question. You can determine that by trial & error or do the math. I usually just use the prox clear timer done bit in a rung with another self resetting timer. when both timers are done, I add about 5% to whatever speed is current. So.. whenever the time period of the self resetting timer is set to elapses, some speed is added. Clear as mud, right?


BD

 

[bikerdude]

Mike,
I'm thinking about control method for a mass conveyor system. Is yours several cans wide or single file?

 

[MikeLB56]

single. however there is an accumulation table at the beginning and before the case packer