Need help for conveyor system control

[appleplc07]

Dear All,

Basically there are 8 conveyors as shown. Each conveyor will be controlled by a Siemens Micromaster 420 Drive. And each conveyors has a proximity switch/sensor to sense the container.

The objective is to move the container from one area to another.
The PLC used is the S7-300, 315-2 DP.

Anybody can guide me on how to do the above? Basically i am from the process control background and this is the 1st project involving a conveying system which is more to factory automation/motion control. I am unsure on how to move the container i.e. how to start/stop the conveyors.


The system looks simple but i think it is more complicated than that, as i have to address the following issue :
1) The conveyor must only move/activate when there is a container on top and the conveyor in front is empty.

2) Need to track the location of the container on the conveyor belt.

3) There may be containers queuing or stopping in front i.e. maybe on conveyors 4 and 5. Therefore the system must be intelligent to move and stop the incoming containers on conveyor 3; and to move only when conveyors in front are empty.


I would appreciate if anybody out there can just guide me on the correct path to implement this project.

Thanks.

apple
[email protected]

 

[Rube]

Basic conveyor movement like you are describing: Using conveyor 5 as an example, when it is empty and the sensor detects no container, move conveyor 4 until both sensors 5 and 4 are blocked (you must be able to control the movement of conveyor 5 from a downstream sensor). Accordingly, when 4 is empty, move 3 until the sensors on 4 and 3 are blocked.

Hope this helps.

 

[Doug-P]

Ignoring for the moment things which will affect every section, such as SYSTEM ON, E-STOP ACTIVATED, and MOTOR RUNNING, the essentials for a typical section (4) are:

IF
permissive from section 5 (downstream) TRUE AND load present at section 4

OR

IF

section 4 empty and section 3 occupied

THEN

run section 4

--

First, make the system move product correctly and reliably without the tracking feature. Only when this is done add the tracking logic. You'll probably want timers on the sensors to do things like insure that a load has completely exited a given section before shutting that section off and verify that a sensor has been blocked enough time before moving the data forward.

I'm assuming there is a certain minimum space maintained between each container and that the sections are longer than a container. That is, the containers will not touch each other while they're moving toward the output. Is this true?

I see that Rube has replied while I was composing. I will leave my post intact on the theory that seeing it explained slightly differently may help.

p.s. Nice graphic. Goes a long way toward the explanation.

 

[Rube]

I should mention that by the drawing (which I agree with Doug about) the container appears to be almost as long as the "zone" between sensors. If there are shorter containers on the conveyor, you will need to use timers to prevent two or more containers from entering one zone. Any upstream conveyor can be allowed to run until it and the downstream zone are full.

 

[jrwb4gbm]

Here are a few hints on the tracking. Put an encoder, or, a prox to monitor a toothed sprocket on each belt. This will allow you to determine where on the belt that the container is. Start the count when the container activates the entry prox for the beginning of the count and the next prox to reset the count for that container.
Ther is more to it than this but this is a start.

Sid

 

[OkiePC]

Another thing that may help, Our conveyors use a photo beam at each exit and entry point. With both sensors, you have the option to index each conveyor only when its entry eye is blocked and its exit eye is not. This allows the conveyor to act as storage when downstream conditions prohibit it from running continuously. It also helps with detecting jam-ups at the transitions between belts.

 

[appleplc07]

Thanks all for the information.

Doug, you are right to assume that there is space between the containers and the conveyors are longer than the containers as shown in my latest drawing here. The containers will not touch each other.
Our design only caters for 1 proximity sensor on each conveyor exit point.

Based on the given hints and the latest dwg :

Conveyor 1:
IF conveyor 1 occupied AND conveyor 2 empty THEN Start conveyor 1

IF conveyor 1 Running AND sensor detects empty (delay timer will be implemented to stop the conveyor 1 after proximity sensor detects container has exited) THEN Stop conveyor 1

Conveyor 2:
IF conveyor 2 occupied AND conveyor 3 empty
OR
IF conveyor 1 occupied AND conveyor 2 empty THEN Start conveyor 2

IF conveyor 2 Running AND sensor detects empty(ditto) THEN Stop conveyor 2
OR
IF conveyor 2 Running AND conveyor 3 occupied AND sensor detects container THEN Stop conveyor 2

Conveyor 3:
IF conveyor 3 occupied AND conveyor 4 empty
OR
IF conveyor 2 occupied AND conveyor 3 empty THEN Start conveyor 3

IF conveyor 3 Running AND sensor detects empty(ditto) THEN Stop conveyor 3
OR
IF conveyor 3 Running AND conveyor 4 occupied AND sensor detects container THEN Stop conveyor 3

Conveyor 4:
IF conveyor 4 occupied AND conveyor 5 empty
OR
IF conveyor 3 occupied AND conveyor 4 empty THEN Start conveyor 4


IF conveyor 4 Running AND sensor detects empty(ditto) THEN Stop conveyor 4
OR
IF conveyor 4 Running AND conveyor 5 occupied AND sensor detects container THEN Stop conveyor 4

Conveyor 5:
IF conveyor 4 occupied AND conveyor 5 empty THEN Start conveyor 5
IF conveyor 5 Running AND sensor detects container THEN Stop conveyor 5

I will use this code to start off with and actually this project is more complicated than that as I will have to change the direction of the containers left or right and move them up and down a lifter. In fact, there are about 300 conveyors in total to control and massive amount of sequences.


Thanks for the help,