Need logic ideas for project

[Guest richie086]

hey i have a lab in my controll systems class where we have to go out and look at a control process in the real world. I went out with a few classmates to FedEx and saw how the whole system operated and decided to just do a small chunk of the system.. here's the basic layout 1 scanner (scans barcodes on boxes so it knows where all the boxes are and where they are going) conveyor belt 1 photoeye 1 override switch (if a package gets stuck and the photoeye connection is broken for more than 4s a technician has to come out and move the package that got stuck and hit the over-ride so the system starts again) 1 light to let the tech know where the stuck package is (goes off once over-ride switch is hit) the trainers we use are allen bradley 5/01 and 5/02 series. i know the photoeye will be represented by a NC switch, but im not so sure how to represent a scanner (mabye just a counter?) , conveyor belt, and were to place the override.. the books we have for labs and theory are really really really bad and have commands that arent even available on the allen bradley trainers we use :( a good chunk of the theory and labs dont relate to the trainers at all :( That's why im kind of lost when it comes to putting all of this together. the books actually show 2-3 outputs in series on a single rung.. from what my teacher was saying thats not possible (at least on the trainers were using its not) any help is appriciated.. but pls dont map everything out for me, i'd like to try doing some of it (whatever i can with the limited resources) myself :) thanks

[Guest Robert]

Sounds like your on the right track. The bar code scanner would provide a string of ASCII data more that likely and you could simulate that by just plugging in numbers to an array and then shifting them as the package moves through different points. You could simulate the convey "in motion" with a light or small motor connected to an output. As for the override you said it all. Use the photo eye to control a TON timer with with a preset of 4s it will reset itself each time the eye goes off but if the done bit goes on then use it to unlatch the conveyor run logic and turn on the fault light. The reset would be just a switch that enables your error handling code to start the system up agian.I hope this has helped and not confused you.

[Guest Guest]

hey thanks for the reply! nothing u said was confusing, it helps a little.. the main thing im having trouble with is how to put the actual ladder logic into the trainer (like where to place things).. any help in this area would be great :) richie

[RDay 0]

If you asking how to layout the components that make up the logic of the rung such as the XIO, XIC, OTE, and ect. Power flow (logic flow) is typically from the left rail to the right rail. So inputs or internal bits are on the left, outputs on the right.    I:0/1   I:0/2       O:0/1 |---| |-----| |----------()-----| |                      |   O:0/2   | |                      |-----()-----| |                                      | IE: If input 1 AND input 2 are both on, then turn on output 1 AND output 2.  I:0/1              O:0/1     |---| |---------------()---| |  I:0/2   |                  | |---| |----|                  | IE: If input 1 is on OR input 2 is on, then turn on output 1. If you have multiple outputs being controlled by a rung they should always be placed in parallel never in series. Now if you are asking how the programs control logic sequence should be laid out. Think of what you are trying to do and start at the beginning. 1. Start the conveyor. Latching logic that controls the conveyor. 2. Box tracking. The shift logic for your array. 3. Photo eye control. The timer control logic. 4. Fault handling. The logic that checks for the timers done bit, unlatches the conveyor, and turns on the fault light. You can post the code that you have so far for critiquing.

[Guest richie086]

hey yeah i know how ladder logic works, my question was more like where do i place the different parts of the ladder logic within the program.. heres the ideas i have so far   I:1/0 |--||----------------------|counter up|-en------|                                                     -dn------|  I:1/1 |-|\|----------------------|timer on 4s|---------|                                                       the first input, I:1/0 is i guess representing the scanner, where i'd just press input 0 on the plc to represent a box going past the scanner.. i am guessing the scanner works indipendently of the plc system (using software to then make a logical descision on where the box needs to go) so i may be wrong about how to represent the scanner. I:1/1 is the photoeye, which would be a NC connection and after 4s if the package hasnt cleared the photoeye then the whole system stops and someone has to come out and press a NO button (a light comes on after the 4s has passed to show where the stoppage has been) to restart it.. i need to know where to place the restart NO switch.. do i branch it off of the timer or is it on another rung? thanks for all the help! can anyone reccomend some good links or books that i can checkout because like i said, my book i got from school really really sucks :) Edited 6 Aug 2003 by richie086

[Chris Elston 78]

Did you look at this book? http://www.mrplc.com/dl/index.php?action=v...try&entryid=101