PLC programming Exam Question

I'm taking a course in mechatronics and Im very new to PLC programming. The problem statement is this

A conveyor belt moves Large and Small boxes down an assembly line. At the end of the assembly line their is a swinging arm that is operated by a motor. The swinging arm moves Large boxes down one conveyor belt and Small boxes down another conveyor belt. Their is a optical sensor that detemines if the box is large or small. Their are also two other sensors that determines if the boxes have cleared down the each assembly line (small conveyor line large conveyor line. Develop The ladder logic for the problem. Your ladder logic must consist of a Power button with indicator light, and emergency stop button with indicator light, and all 3 sensors and motor.

If anybody could help me start this it would be greatly appreciated

First you should write it down the way it functions. You can even do pseudo code straight.

Example of pseudo:

If part at conveyor end and part is big then...

Then when you have that done, its really lot easier to transfer it to ladder program.

Then again, you need to show your work first. It is not custom in this forum to do homework for students. Help you get when you show effort yourself.

Also what brand of plc and model?

osk5000 said:

I'm taking a course in mechatronics and Im very new to PLC programming. The problem statement is this

A conveyor belt moves Large and Small boxes down an assembly line. At the end of the assembly line their is a swinging arm that is operated by a motor. The swinging arm moves Large boxes down one conveyor belt and Small boxes down another conveyor belt. Their is a optical sensor that detemines if the box is large or small. Their are also two other sensors that determines if the boxes have cleared down the each assembly line (small conveyor line large conveyor line. Develop The ladder logic for the problem. Your ladder logic must consist of a Power button with indicator light, and emergency stop button with indicator light, and all 3 sensors and motor.

If anybody could help me start this it would be greatly appreciated

Click to expand...

If I remember correctly there's an old postdealing withyour system.Do a search on here and you may get lucky.
OR:
Think of the power button as a start button for a motor circuit.
use the E-stop button first. if it is on (nc)then when you press the Start (power button)energize the output (Coil) that will run the system.
IF the output is on, the indicator light is on.
Use a separate output to run the Indicator light.
You will also need a "Holding" contact or "Memory" contact.
As soon as you press the start button and the output (coil)turns on, use the holding contact to keep the output ON.
The only case that the output will turn Off is if the E-Stop button is pressed (the NC I mentioned becomes NO and you'll lose power to the rung and drop the output for the motor (since the indicator light is on when the motor runs the indicator light output will turn off as well).
When the E-stop button is open assign an output to it that will turn the E-Stop indicator on.
If the E-Stop button closes again (NC) then the output for its indicator light will drop out thus you clear the e-Stop condition and as soon as you press start the system will run again.
Use a timer to detect short/long boxes and decide how to use the diverter accordingly.
Short time accumulated on the timer means short length box.
Longer time accumulate on the timer= Long Lenght box.
The sensor will initiate the timer as soon as one box breaks the beam.
The sensor is cleared after the box goes through.
Capture the ccumulated time to a working register and use it to determine which box made it through.The start button is wired NO.
The E-stop button is wired NC.

Hope this is a starting point.

Need a starting point? GO TO CLASS, READ THE BOOK, DO THE ASSIGNMENTS

If this is an exam question, it will not be for something you have not yet learned.

What, no "stop" button? Oh, that's right, just use the E-stop to stop it...



-Eric

What, no "stop" button? Oh, that's right, just use the E-stop to stop it

ROFLMAO after 12 years in the industry I've found this is more nromal than using the stop button after a few years of trying to get ppl to use the stop button I gave up so now I try to make it so that its a greater effort to reset the emergency stop condition. After a while of having to go through the extra effort to get the system working again they usually start using the stop button

For someone like mr.osk5000, i see myself i his shoes. Well, thanks to those who still answered.

mordred said:

What, no "stop" button? Oh, that's right, just use the E-stop to stop it

ROFLMAO after 12 years in the industry I've found this is more nromal than using the stop button after a few years of trying to get ppl to use the stop button I gave up so now I try to make it so that its a greater effort to reset the emergency stop condition. After a while of having to go through the extra effort to get the system working again they usually start using the stop button

Click to expand...

To help out here, the e-stop sounds a very loud alarm and the stop just stops the conveyors. After a while (and a couple of horn replacments), they started using the stop button so they would have to hear the horn for 15 seconds.

mordred said:

What, no "stop" button? Oh, that's right, just use the E-stop to stop it

ROFLMAO after 12 years in the industry I've found this is more nromal than using the stop button after a few years of trying to get ppl to use the stop button I gave up so now I try to make it so that its a greater effort to reset the emergency stop condition. After a while of having to go through the extra effort to get the system working again they usually start using the stop button

Click to expand...

I am glad to see that this use E stop and not the STOP switch problem is international and not restricted to just the USA.

Dan Bentler

sheryl86_ann said:

For someone like mr.osk5000, i see myself i his shoes. Well, thanks to those who still answered.

Click to expand...

Sheryl and Osk5000
Having been a student I remember the difficulty with new assignments and trying to figure out what to do. Learning is the pits when you dont know what to do because you are in the process of learning it.

I think some of the reluctance here is that there is no evidence of even trying. Here is what I would recommend students do when asking for help.

1. Give us a block diagram of how or what you think the system should do. Hand drawn is just fine
2. Then a block diagram of each component ie stop switch to the next switch etc etc.
3. IF you get that far a list of switches (start stop etc etc) and their function.
4. Later on when you decide which PLC you need to do the job you take list in #3 and type in the PLC number descriptions and how you have that switch / input / output configured.

Dan Bentler

essentially what Lietmotif is saying is the student has to show he/she is making an effort if its a specific question on a small aspect of the program thats one thing thats usually accepted. Students that show their work or an effort usually get good responses. I for one have gone out on a limb to help the ones that do. Almost to the point of giving them the answer instead of a direction