motor control for conveyor

[backendcode]

Is this a classroom assignment or a real world application?

The answers you give for an assignment have to accomplish the requirement of the instruction/curriculum. The answers you give for a real world application need to be more robust and think through all of the what-ifs.

What if my logic starts moving a product and then a sensor fails. Do I run the conveyors forever or for a time limit?

What if the door stops at the instant it first makes the switch and the laborer would suffer much less back strain if it traveled another X seconds before stopping?

What if debris accumulates on the conveyor and makes one or more of the sensors flicker?

Those are just the most obvious what-ifs, real world practice is likely to reveal others.

OkiePC, This is real world application and I do understand the points you mentioned in your reply but I am trying to make baby steps and getting hand on experience on basic logic, there are alot in the project like e-stop, start line, stop line, motor overload indicator, prox sensor fault indicator. but I don't want to through everything on table and expect people to reply my every single problem. you know what i mean.

I am just figuring out the basic logic and go from there and will try to do myself and come back here with my problem and get advice from people like you!

Thank you again for your time.

 

[James Mcquade]

What is the conveyor speed?

where is the prox sensor located on the conveyor?
with a 10 ft conveyor and 3" gap between sections you will have 3 1/2ft of space with no idea of what is on the system.

I was unable to make out your logic, but I have some questions for you to think about.

how will you track the part if you loose power?
someone hits an e-stop?
what happens when the operator is removing a door, are you going to run another part into the part he is unloading?
what happened if a prox switch fails?

lots to take in I know, but if you can ask what if, you need an answer.
take it one piece at a time and think things out.

I don't think 4 prox sensors will get the job done.

james

 

[Ronnie Sullivan]

You are right to think of it in baby steps. Think of it even lower
Think of only the first conveyor in the line.
No other conveyors exist for now.

it's job is to transport the product from a start proxy to the end of conveyor proxy.
A simple job - I see a product, I start the conveyor, I see the end of conveyor proxy, I stop the conveyor.
This logic should bring in an internal memory coil to run the output

We then add a timer to this logic in case the product does not get to the end of the conveyor in time - or it was a false trigger (someone put their hand in front of the proxy etc)
The 'what ifs' pile up at this time and those can be gone into later

Now we have the product at the end of conveyor proxy
A new logic sequence:
Take the product to the next end of conveyor
Before this happens - check nothing is at the next proxy and also check the second conveyor is not running (it might have a product mid-way going to that proxy)
When these conditions are met run both conveyors but conveyor 1 only until it has left the first end of conveyor proxy
do this again with internal flags - 1 running the first conveyor output and the other running the second.
Now you will have 2 flags in parallel for the first conveyor and if the route is clear one will take over from the other with conveyor 1 and it wont actually stop.
If the route is not clear it will stay at that proxy until it is


A start for you

 

[nerdbotbot]

Just expanding what @JamesMcquade has said.

Location and number of the sensors is important.

If it is one sensor per conveyor, the sensor, depending on its location, will indicate whether a part (hollow rod) has entered or exited the system.

Also, the hollow rod is 6.6 feet and its travel length is 10 feet (conveyor length). Therefore, it will be unaccounted for a travel of 3.3 feet. The rod will be present on a conveyor, but the sensor will be OFF.

At least 5 sensors will be needed. An 'Entry' sensor on the first three conveyors. They can also be used as 'Exit' sensor for the previous conveyor. 'Entry' and 'Exit' sensor for the last conveyor.

Let's us know how the project turns out.

 

[ScottTheEngineer]

Yep. Using .TT bit the conveyor motor will turn on for 5 seconds and shut off. Like the others have said though there are many other factors. Breaking it down into smaller parts is a great idea. One conveyor section at a time.
I'd also use a memory address for the timer. ACC value. That way if you need to adjust the time you can change the value in an address instead of editing the rung every time you need to make a small adjustment. Doing things based on time is never the best way. Sometimes you have to but eventually the motors get slower or speed changes as the conveyor wears.
I'd be concerned about the mechanics of the Conveyor setup too. You never want your product to rub on anything. It will damage the conveyor and the product. Many places use lift tables. A part or pallet rolls onto a conveyor, the lift table lowers onto the next section of conveyor which then turns on to move the product down the line.

 

[backendcode]

Thank you so much for the feedback! I really appreciate everyone's input! I am going to focus on just one conveyor and make a program according to that and later I can expand and consider other factors. I will also prepare an AutoCAD drawing so I can share with you the graphical representation of project and position of my proximity sensors as well.

I have all day to work on this program to figure out the logic.

Thanks again!

I will give an update soon!

Best,
Backendcode

 

[backendcode]

UPDATE!

I attached the graphic representation of conveyor system. here is the link below
https://ibb.co/mVTQ45
Reference from the link, the worker will put the part on the conveyor and make sure it hit the proximity sensor. Now part is on the conveyor and proximity sensor 1 become active from 0 to 1 but the motor will not start until there is no part on proximity sensor 2, once cindition become true ( part on prox 1 and no part on prox 2) motor will turn ON and I latched the motor to keep it ON.

Now part will reach at proximity sensor 2 and condition become false on rung 1 and it will turn OFF the motor.

I attached the PLC program as well. here is the link
https://ibb.co/f1fzWk

What do you guys think, will this logic work?

thanks again!

Best,

 

[Mad_Poet]

Ummmmm.
I'm looking at the code, and it looks to me like the first product on the first conveyor will start the first conveyor, and relay conveyor(o)motor contacts are going to latch in and I do not see where or what will cause the relay to drop back out.

(Or does the PLC scan turn the relay off once every scan cycle then re-check the prox to see if it still needs to be on?)

Rung 0 turns conveyor(0)motor on . . . and rung 1 turns conveyor(0)motor back off?
I really do not like this logic.

Poet.

 

[backendcode]

Ummmmm.
I'm looking at the code, and it looks to me like the first product on the first conveyor will start the first conveyor, and relay conveyor(o)motor contacts are going to latch in and I do not see where or what will cause the relay to drop back out.

(Or does the PLC scan turn the relay off once every scan cycle then re-check the prox to see if it still needs to be on?)

Rung 0 turns conveyor(0)motor on . . . and rung 1 turns conveyor(0)motor back off?
I really do not like this logic.

Poet.

Hey Mad_poet,

I am very new to PLC and it might be the reason you are not liking my logic but I can try my best to explain what will stop the motor.

To turn on the motor, condition is Part at prox 1(conveyor1) & Nothing on Prox 2(conveyor2), turn on the motor and scan next branch which will latch the motor to keep it on even though part moving from conveyor 1 to conveyor 2 ( means now there is no part at proxy 1 and 2)

Once part will reach at the prox 2, it will shut down the motor of the first conveyor. (prox2 will work like stop button) i guess

What you think?

Thanks

 

[nerdbotbot]

Here is how I have understood the problem, correct me if I'm wrong:

If a part is present on a conveyor, the preceding conveyor should be OFF.
For example: If a part is travelling on Conveyor 2, Conveyor 1 should be OFF. When the part exits Conveyor 2, Conveyor 1 should turn ON.

 

[backendcode]

Here is how I have understood the problem, correct me if I'm wrong:

If a part is present on a conveyor, the preceding conveyor should be OFF.
For example: If a part is travelling on Conveyor 2, Conveyor 1 should be OFF. When the part exits Conveyor 2, Conveyor 1 should turn ON.

let me rephrase it again! damnn i am so bad in explaining but I am going to try my best to explain you.

when part is available on conveyor 1, no part at conveyor 2 = Motor 1 turn ON to start conveyor 1.
When same part reach at conveyor 2, it should turn OFF the motor 1 to stop the conveyor 1
Now I have part on conveyor 2 and no part on conveyor 1 and let's say operator put the another part on conveyor 1, it shouldn't be ON because there is already part at conveyor 2, if someone will manually move the part from conveyor 2, then part from conveyor 1 should move to conveyor 2.(same logic repeat)

I hope it helps you to understand now!

Thanks again for your time!

 

[nerdbotbot]

Okay. Then you have to write a program that will generate an output, say X1, when a part is present on Conveyor 2. This output, as NC contact, can be used to keep Conveyor 1 OFF. When the part is moved from Conveyor 2, the output (X1) will become LOW, its NC contact will be HIGH and Conveyor 1 will turn back ON.

Update:

Program in POST#22

 

[nerdbotbot]

Update:

Program in POST#22 will turn OFF Conveyor 1, only momentarily, when the Part is in front of Proximity Sensor 2. (The program works if the Part has to be moved from beginning to end of Conveyor 1.) As the Part moves down Conveyor 2, Proximity Sensor 2 will turn OFF, if the next Part is placed on Conveyor 1, it will turn back ON.

To keep Conveyor 1 OFF, when a Part is present on Conveyor 2, the signal from Proximity Sensor 2 should be latched. Later, this latch should be broken either manually or by Proximity Sensor 3.

 

[backendcode]

Update:

Program in POST#22 will turn OFF Conveyor 1, only momentarily, when the Part is in front of Proximity Sensor 2. (The program works if the Part has to be moved from beginning to end of Conveyor 1.) As the Part moves down Conveyor 2, Proximity Sensor 2 will turn OFF, if the next Part is placed on Conveyor 1, it will turn back ON.

To keep Conveyor 1 OFF, when a Part is present on Conveyor 2, the signal from Proximity Sensor 2 should be latched. Later, this latch should be broken either manually or by Proximity Sensor 3.

Ok, Thanks nerdbotbot,

Can you please check your PM, I am going to message you and discuss something if you have time!

 

[Mad_Poet]

BackEndCode> Once part will reach at the prox 2, it will shut down the motor of the first conveyor. (prox2 will work like stop button) i guess

Dear Sir,
I took a look at the code you posted after the one I was looking at. I see the Prox 2 sensor is now in series with the conveyor motor coil - much better. (Before the latching contact was paralleled with the Prox 2 sensor.)

Poet.