Conveyor Speed

Iangwf

Member
Join Date
Sep 2010
Location
Castlemaine
Posts
15
Hi
Background information
I am currently in the process of putting together some logic / ideas for a machine modification at my place of work. (1756-L73S Controller)

The machine has a conveyor (main) running through the middle at about (1) revolution every 10 minuets,
throughout the day this conveyor may speed may change.
There is also another conveyor (pusher) that pushes product onto the main conveyor, this is currently operating and pushing every 30 seconds or so.
Both conveyors are controller by VSDs and are programmed into the original PLC code and currently running fine.

Challenge
I need to make the speed of the pusher conveyor follow the speed of the main conveyor as this varies throughout the day.

Code
I was thinking using a prox on an intermediate gearbox shaft to count pulses of about 50 per rotation of this shaft. (1000mm belt travel = about 600 pulses)

I was considering counting pulses for 20 seconds then storing the value in some type of memory location, then repeating the count for another 20 seconds and storing this vale. I am not sure what type of memory / function to use.

Then I could compare the (2) vales and come up with a deviation if the main conveyor speed changes.
This deviation value could then be used to modify the speed of the pusher conveyor if the main conveyor speed changes.

Does this seem like a reasonable approach or have I got it all wrong.

This is a very basic concept and does not need to be precise, as it is not super important to make this extremely accurate.

Please try to dumb down your solution as I am extremely green at PLC programming. (as you can probably tell)
Thanks
Iangwf
 
"Both conveyors are controller by VSDs and are programmed into the original PLC code and currently running fine."

How are try controlled now? If it is an analog signal from the PLC to VSD's for speed control, then you should be able to use the main conveyor commanded speed to calculate the pusher conveyor speed set point.
 
If their belt conveyors you'd need to have your sensor on the non-driven shaft. Either use an encoder or make some sort of toothed wheel with a proximity to pick up pulses.
 
Last edited:
Keep it simple. Use the actual speed of the one conveyor as the set point of the other. You will need some simple maths if there are gearboxes at different ratios, but if not then it should be a quick 5 minute job in the code.

As you have VSD's, you don't need external forces to tell you the speeds, the info will be there already.
 
Yes janner 10 is right! Just take the Real value of Main conveyor. Calculate the ratio of Main conveyor & other conveyor Gearbox. Suppose Main conveyor Gearbox ratio is 200 and other conveyor Gearbox I/P to O/P ratio is 100. you just need to create a analog output (for same speed) of
Main conveyor RPM*100/200
NOTE- If drive motor max RPM is same, then only this logic will work.
 
If I had to guess, I'd say that there was an amber beverage with several X's on it on these conveyors? ;)

First things first - if the main conveyor is on a VSD and is having it's speed changed, you should be able to use whatever method is changing the main conveyor speed to also change the pusher speed proportionally. What are the roadblocks you see with doing that - are they on separate PLC's? I'd be pursuing that option over any others first.

If there really is a reason we can't do that, a prox counting pulses is definitely a viable way of doing it if you don't need fine-grained accuracy, although as Peter mentioned, you might want to investigate putting it on a non-driven shaft to account for belt slippage (although there could also be belt slippage on that non-driven shaft too, so...). At the end of the day, where you mount the sensor is not going to make a huge difference if high accuracy is not required.

A couple of options come to mind, and it depends on how frequent your pulses are going to be.

If we're talking multiple pulses per second, then yes, I'd count how many pulses you receive in a fixed time period, calculate the speed from that, and then rinse and repeat. I'd probably shorten the time window down to 3-5 seconds, but again, that depends on how frequent your pulses are. And of course, you'll need to make sure the pulses aren't so fast that you end up need a high speed counter card.

If we're talking pulses that are a couple of seconds or more apart, then I'd approach it slightly differently. I'd measure the time in between each pulse, and use that to calculate the instantaneous speed based on those pulses. You can store the last 5-10 intervals in an array and use a moving average to give yourself a more stable and true figure - might sound complicated if you're new to programming, but there's not much to it and if you end up going that way, there are plenty of examples on the forum on how to do it.

But as I said, my first move would be to just find and use the main conveyor's speed reference directly, rather than reinvent the wheel trying to calculate it using sensors and timers.

Oh, and welcome to the forum!
 

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