Face Book

Ladder diagram

10 posts in this topic

Hi

Can any member draw  the ladder diagram for this application:

1-O/P pulse high from the photocell sensor to enable rejection system

2-Bottle passes in front of another photocell and after certain time O/P is high"rejection arm"for a certain time.

3-If O/P pulse low from the photocell sensor: nothing to do

Thank you

Share this post


Link to post
Share on other sites

Homework?

1 person likes this

Share this post


Link to post
Share on other sites

Posted (edited)

yes

Can you help me?

bottle-cap-inspection.png

Edited by Face Book
Add attached file

Share this post


Link to post
Share on other sites

typical store info and use it later situation

1. you need a way to track information (FIFO or bit array plus another sensor to keep track of conveyor position)

2. every time you do a check, you need to

           a) index your tracker (a bit field or FIFO)

           b) check for cap present and 

           c) store result into your tracker (a bit field or FIFO)

3. use information in tracker (single entry) to trigger eject arm. 

 

tracking conveyor position can be done by encoder or sensor counting gear teeth etc.

implementation is yours...

 

1 person likes this

Share this post


Link to post
Share on other sites

Posted (edited)

Hi

1-I will install the rejection sensor and rejection arm followed to detection sensor to simplify the application.

2-rejection arm will be active for certain time after  the bottle detected by rejection sensor after certain time.

Can you draw  the ladder diagram for this application? 

bottle-cap-inspection.png

Edited by Face Book
Add attached file

Share this post


Link to post
Share on other sites

any concerns about thing called academic integrity?

here is an example that is 99% complete but there is an intentional bug (or feature) and language is from another PLC so you still have to do something....:-)

basic conveyor tracking.png

1 person likes this

Share this post


Link to post
Share on other sites

Posted (edited)

Hi

Thank you very much for your support.

1-Sorry,Iam not understood all the ladder diagram.

Can you explain it?

2-Where are the signals of sensor tracking position and rejection sensor  in the ladder diagram?

3-What do you mean by conveyor indexed signal?

Edited by Face Book

Share this post


Link to post
Share on other sites

1-Sorry,Iam not understood all the ladder diagram. Can you explain it?

i did ... in previous post. the whole point is that you should not focus on this ladder diagram and try to make your own. also syntax will be different. tip when programming, you need to understand what happens with information/data that you work. if you cannot explain it on paper, you don't understand it.


2-Where are the signals of sensor tracking position and rejection sensor in the ladder diagram?

did you read at all...? IN1 and IN2 are in the diagram. 

 

3-What do you mean by conveyor indexed signal?

since you don't do decision making and processing on the spot, information need to be stored for later use (reject station is some distance away from station where you check for cap). this means that stored data (in PLC memory) need to corelate with physical situation you are looking at (bottles on conveyor and their position and their status to be rejected).

so let's suppose we have bit field (i used an 16-bit integer which ws sufficient in this case).
i am showing TWO bit fields here, first one represents bottles on conveyor, second one only shows locations that need to be rejected.
in ladder example above, i only use the second one (that is all that we really need to know in this case).

suppose no bottles need rejecting, then data will look like:

0000000000000000 ' no bottles present (just used for illustration)
0000000000000000 ' no bottles need to be rejected yet (this is our tracker)
          ^    
          |
          |______' reject position

 

 

after while it may looks something like this (i choose to track bottles as if they were moving to the left - new bottles are inserted on the right side):

0000000110101111 ' 7 bottles present, there are some gaps in bottle stream
0000000000000000 ' no bottles need to be rejected yet
          ^    
          |
          |______' reject position

          

eventually we may encounter bottle that has no cap or it has wrong cap

0000011010111111 ' 9 bottles present, there are some gaps in bottle stream
0000000000000001 ' bottle detected that will need to be rejected 
          ^    
          |
          |______' reject position

 

but we need to wait until reject reaches certain position (this is why we must track conveyor)

0011010111111101 ' bottles keep shifting, there are some gaps in bottle stream
0000000000001000 ' bottle that will need to be rejected has traveled, information about reject is shifted in memory to keep track of the bottle position in the stream

Eventually bottle to be rejected WILL reach our reject station:

1101011111110111 ' bottles keep shifting, there are some gaps in bottle stream
0000000000100000 ' reject reached reject station - KICK IT OUT, NOW!
          ^    
          |
          |______' reject position

 

2 people like this

Share this post


Link to post
Share on other sites

you are welcome. depending on used PLC, instruction set will differ. specialized instructions are vendor specific so i tried making an example using only the most basic instructions. this should make porting to other platforms simple but it adds some restrictions of course (here it is size of word). nevertheless, idea is to learn concepts. once you can represent data in a form that corresponds to real world, you can use it any way you like.

good luck...

 

1 person likes this

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now