Garage Door LL

Hello, im a 1st timer entry level plc student,I have a project where I am trying to edit my LL. Ive bn given a gagrage door problem, here are details...1 momentary push/start button, push it door begins to rise and will do so until upper limit sw is reached. W/ door up, pushing button again will start it in the down direction & cont until down limit switch is reached. If button is pushed while door is closing it will reverse and continue up. If button is pushed while going up, motor will stop. Pressing it again will cause motor to start in down direction. Also have safety reverse system light beam (closed toggle switch), will remain closed if beam is unbroken. If beam is broken door will not begin to close, but if broken while door is closing, the door will reverse.
I can use only coils, contacts, and OSR (one shot rising), latch and unlatch commands and branches

my labels pushbutton 0 (B3:1/0) -- activates door
momentary push button (I:1/2)
OSR (B3:0/0)
Switch 6 (I:2/1) -- upper limit Switch 11 (I:2/2) -- bottom limit
Light 0 (O:3/1) -- motor up
Light 7 (O:3/2) -- motor down
Beam (I:2/3)
Im missing something when drawing out my logic & my program obviously does not run right.
Can anyone politely help me cross this hurdle? This is my 1st time dealing with PLC and Ladder Logic.

Your description of the problem has enough "what-ifs" to justify using what is commonly called a "state engine" for the design of the logic.

The garage door has a definite number of states, and then there are different transitions among those states. List the states first:

0-idle, position unknown (this will be where the flow chart starts)
1-idle fully open
2-idle fully closed
3-opening
4-closing

Did I miss any?

Next, get a blank piece of paper, and make a flowchart with these states in blocks (rectangles or ovals). Then draw lines with arrows which represent the transitions between each state, and label the transitions. For example, to get from state "0-idle, position unknown" to state "1-idle fully open", the fully open limit switch would be all that is needed. Another example, to get from "3-closing" to "4-opening", you press the button or open the safety photocell.

Once you have your program/flow chart on paper, going from there to ladder logic is pretty straight forward. The method I use looks like what is in this thread (post #5):

http://www.plctalk.net/qanda/showthread.php?t=52654&highlight=state+engine

Being a school project, make sure there are no restrictions on the types of instructions you can use. Also, there are other methods for coding a state engine without using word or latch instructions. I'll see if I can find a link for that later.

Paul

Okie, thank you, yes this helps. However the wash is even more complex than what I am dealing with. Finally got clarification that we could use multiple branches per rung, and wow, made a world of difference in trying to make this 1 button control all operation work. Thanks for taking time out to help with question. I definately have my garage door up (latch) and stop (unlatch) rungs complete, now I have to move to down, which is close to the same but just couple more functions. Thanks again