Two conveyor merges controled with PLC

alexbeatle · Sep 8, 2015

Good day,

I have a main line and two merging conveyors at 45*.
_____\_______\_______

Does anyone have an example for "priority merging"?
Priority merging - if there're more than one bag sitting on both merge lines, a main line will create a gap for both to merge.

The difficulty I am having is that everything merges from the 1st merge line and only after its done, everything starts to merge from the second. I need them to merge one by one.

Thank you.

ASF · Sep 8, 2015

Start by thinking about where you have/need sensors. A PLC is only as good as the information you give it.

alexbeatle · Sep 8, 2015

I am looking for an algorithm.
I can successfully space out the mainline inflow for the merge bags, but if there're bags sitting on both lines I cannot merge one and then the other - one by one. They all merge from one line and then all from the other

I am looking in the direction of the shift resisters ... parallel to serial conversion.

ASF · Sep 8, 2015

I follow you now. You want some sort of gap tracking and reserving code.

It can be done, but for my money, I'd be buying a half dozen cheap PE sensors, and forgetting the shift register. Put a sensor at the end of each merge conveyor, and on the main conveyor before each merge. If you have bags at each merge point just use a simple toggle to identify which merge's turn it is to feed on; if only one merge point has a bag it can feed on into the next available gap.

Doing it programatically would save you buying a few sensors, but it depends how much your programming time is worth to you (or whoever's paying the bill).

Doug-P · Sep 8, 2015

ASF said:
Start by thinking about where you have/need sensors. A PLC is only as good as the information you give it.

What he said.

A simple way to keep one line from hogging the resource (open places on the main line) is to implement a round robin scheme. This means each line gets a chance at releasing while other lines are inhibited from releasing. Be it two lines or ten, the concept is the same. Each feeder line will need a sensor to detect product at the release point and a controlled release to output product for a: a given, limited time, or b; a defined number of products during its 'turn' and some sort of control will need to be imposed on the main line to create gaps for product to go into or, failing this, at least to detect gaps. Depending on your system, the main line could even be treated as just another release line and be incorporated into the round robin.

The round robin can be realized as a state machine or sequencer, although it can also be done with just timers and 'glue' logic.

cwal61 · Sep 8, 2015

Not sure how you know you have parts to merge unless you have some sort of detection. That being said if you have PE's at the intersection then this is what I have used in the past.

The way I handled that type of merge is with Photo-eye blocked timers. Which ever blocked timer is greater then let that part go. A simple compare of timer ACC will decide who goes first. Once the part leaves then that timer resets to zero and the other blocked timer is greater. This will alternate your releases.

alexbeatle · Sep 9, 2015

Doug-P said:
What he said.

A simple way to keep one line from hogging the resource (open places on the main line) is to implement a round robin scheme. This means each line gets a chance at releasing while other lines are inhibited from releasing. Be it two lines or ten, the concept is the same. Each feeder line will need a sensor to detect product at the release point and a controlled release to output product for a: a given, limited time, or b; a defined number of products during its 'turn' and some sort of control will need to be imposed on the main line to create gaps for product to go into or, failing this, at least to detect gaps. Depending on your system, the main line could even be treated as just another release line and be incorporated into the round robin.

The round robin can be realized as a state machine or sequencer, although it can also be done with just timers and 'glue' logic.

Interesting idea. Thank you

cwal61 said:
Not sure how you know you have parts to merge unless you have some sort of detection. That being said if you have PE's at the intersection then this is what I have used in the past.

The way I handled that type of merge is with Photo-eye blocked timers. Which ever blocked timer is greater then let that part go. A simple compare of timer ACC will decide who goes first. Once the part leaves then that timer resets to zero and the other blocked timer is greater. This will alternate your releases.

Thank you. Ended up doing somewhat this.

I now have two timers which accumulate whenever a box is sitting on the merge line. Once .DN is on I create a gap in mainline based on size of the box. If there're two .DNs I release upstream merge, then block it with a memory bit which is reset by the downstream merge.

Two conveyor merges controled with PLC

alexbeatle

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