Elevators - need help

Hi,
I have to program an plc for an elevator and I am stucked in a problem. For exemple: whem car go down from 5 to 1 floor and get a comand to stop to 3 (where pasenger come in ) and then comand to go to 4, how can I made the plc do not forget the 1 floor comand and not to go to 4 ? In other words to keep the comand in mind till it is executed with its priority ?
Thanks, Dorin


p.s. my english is not very good but I think you understood me, if not I'll explain again

You may want to hit the search button at the top of the forum page, and dig through a lot of the threads about elevators..... With that said, here's some links to a couple of different discussions.
elevators....
more elevators

Hello my friend. Have you ever used a FIFO instruction. It is First in First out. Each time someone executes a "Car Call" cmd. From any entry point. That Call is loaded into the FiFo. Set up individual sub-routines for y-axis travel. Next you want to always "Load" your Starting position as no elevator ever has a "Return to home" routine unless you are recalibrating the encoder. Using a FiFO allows you to Store each Floors "Encoder Value" and "Mov" it into the "GOTO" framework while still reserving all other comands. The only clean way to execute an elevator program is to complete each "Call" Sub-routine before initializing a new on. Inside each "GOTO" sub insert an interupt bit for "New Stop" cmd.(to pick-up new passangers)Once they are on the car, and even if they are wanting to "GO DOWN" if you have loaded passangers going up, they have first priority. When a "New Stop" cmd. is introduced, load the FIFO. After the "GOTO" sub is complete, exicute the next "New Call" by Mov. with the encoder position value being loaded into the "GOTO" #F file.

I hope this points you in the right direction and remember, ALLWAYS REMEMBER TO CLOSE THE DOORS BEFORE MOVING.

This should give you the general idea where to start with it....

Mike I am not sure if this has been discussed before.
Does the run of the mill Elevator actually use a PLC, or do they usually have embedded electronics?

Private Mesage from Dorin

"?
Thanks for ladder , but , can you give me the meanings of the abreviatiovs for the contacts ?"

CA = Call Above or UP

CB = Call Below or Down

*CL = latched car call

*UL or *DL = Latched Hall Call

*PI = Current Floor Poisition.

"A ladder diagram is good for any type of PLC, what ever is the production company of it ? (AB, Siemens, Moeller, ...)"

I have no idea as to what type of PLC your using. But the Ladder I provided should give you a basic understanding on how to set direction preference, for any plc. That was my only intention.

gbradley said:

Mike I am not sure if this has been discussed before.
Does the run of the mill Elevator actually use a PLC, or do they usually have embedded electronics?

Click to expand...

Yes. However many manufactures use custom built propritary equipment, which is programmable, but only for them. That's because the REAL money in this busniess is in providing service. So they sell a controller on the cheap, and charge big $$$$ for repairs. I'd say the current market share right now is about 50/50. But as the customers are getting smarter/wiser to the long term costs, many are specing PLCs, sometimes by brand name.

Comment..I don't know why, but I've never seen an AB on an elevator.