Shift Register?

Dear experts,

In my plant I’ve 44 manually operated machines. These machines may run all at the same time, but may not be started at the same time. When several machines are switched on one by one, the first machine starts directly. The other machines are waiting (e.g. 5 minutes). After these 5 minutes the second machine starts. All other machines are still waiting. After 5 minutes the third machine starts and so on.

So if all 44 machines are switched on, every 5 minutes one machine starts in order “who comes first, goes first”. (see attached situation 1)

I want to create some sort of “waiting queue” for the machines. That means that if one machine leaves the queue (by switching the machine off) all machines, which are behind, will move one step forward to fill up the gap. (see attached situation 2)

I’m thinking of using an Array [0…43] of bits starting at DB1.DBX0.0.

The first machine in the waiting queue is getting address 0.0, the second machine 0.1, the third machine 0.2 etc.

My question:

How do I program this?

Do I need a shift register?

If somebody can give me an example (LAD, STL or SCL) it will be very helpful

I'm using TIA V13 with a S7-300 system.

Thanks in advance,

Alex

Dear Alex Mol,


you are pretty much asking for a complete solution to your problem, but this is something I will not offer you. Instead I will give you some pointers on how you can solve your problem and give yousome sample SCL codewhich showshow you can create a queue. Note that this code it quickly made and can contain bugs.

Let's assume we havean input for each machine,the inputindicates wether or not a machine is powered on, each input is linked to a machinenumber (1 to 5). Once a machine get's powered on it gets a place in the queue (machinenumber gets assigned in the queue), when the power switches off it gets removed from the queue (machinenumber gets set to zero '0').

The queue is ordered continiously, if a zero is detected in the queue the machinennumbers move a spot and overwrite the zero. This way we create a queue which hold the machinenumbers and is chronologicly ordered.

This is the code:
[code]
FUNCTION_BLOCK "FB_MachineQueue"
{ S7_Optimized_Access := 'FALSE' }
VERSION : 0.1
VAR
"di_PowerMachine" { S7_HMI_Accessible := 'False'; S7_HMI_Visible := 'False' } : array[1..5] of Bool;
"Queue" : array[1..5] of Int;
"Index" : Int;
"Disable" : array[1..5] of Bool;
END_VAR

VAR_TEMP
"I" : Int;
"J" : Int;
END_VAR

BEGIN
// LINK INPUTS WITH INSTANCE DB
#di_PowerMachine[1] :=%I0.0;
#di_PowerMachine[2] := %I0.1;
#di_PowerMachine[3] := %I0.2;
#di_PowerMachine[4] := %I0.3;
#di_PowerMachine[5] := %I0.4;

// ORDER QUEUE ARRAY
// CHECK FOR 0, IF 0 IS FOUND THEN SHIFT ALL FOLLWOING INTEGERS ONE SPOT SO THE 0 GETS OVERWRITTEN
FOR #I := 1 TO 4 DO
IF #Queue[#I] = 0 THEN
FOR #J := #I+1 TO 5 DO
#Queue[#J-1] := #Queue[#J];
#Queue[#J] := 0;
END_FOR;
END_IF;
END_FOR;


// SEARCH FOR ZERO AND ADAPT INDEX ACCORDINGLY, FIRST ZERO FOUND MEANS FIRST EMPTY SPOT
FOR #I := 1 TO 5 DO
IF #Queue[#I] = 0 THEN
#Index := #I;
EXIT;
END_IF;
END_FOR;

// ADD A POWERED ON MACHINE TO THE QUEUE AND ADAPT INDEX ACCORDINGLY
// MAKE SURE EVERY POWERED ON MACHINE CAN ONLY BE ONCE IN THE QUEUE
FOR #I := 1 TO 5 DO
IF #di_PowerMachine[#I] = true AND #Disable[#I] = false THEN
#Disable[#I] := true; // once in the queue the machine can not be added again (exept when it's powered down first)
#Queue[#Index] := #I; // Place machine in queue
#Index := #Index + 1; // increase index
END_IF;

// ONCE A MACHINE GETS POWERED OFF, MAKE SURE IT CAN BE RE-QUEUED
IF #di_PowerMachine[#I] = false THEN
#Disable[#I] := false;
FOR #J := 1 TO 5 DO
IF #Queue[#J] = #I THEN // ONCE A MACHINE GETS POWERED OFF THEN REMOVE IT FROM QUEUE
#Queue[#J] := 0;
END_IF;
END_FOR;
END_IF;
END_FOR;

END_FUNCTION_BLOCK

[/code]

Now I've only shown how you could create a queue, it can be programmed better and cleaner, but it's up to you to improve the code and implement the queue in your final program.

For the next step you couldbuild in a timer which removes apowered on machine from the queue after 5 minutes, and use the first machinenumber in the queue to decide which machine has to be powered on.

I hope this helps you.


Kind regards,
Jens

In my old program I gave all the machines an ID. Each machine was looking to the last given ID and it’s ID became “last given ID + 1”. If a machine had ID#1 it could go. When the timer was done all ID’s decreased -1. This worked fine, but not for the “gap in the queue” situation because I’d no solution for that. It was a very rare situation, but this lack of programming knowledge was annoying me. The program must be working 100% and not 99%.

Thank you once again.

Best regards,

Alex

Alex Mol

Hello Jens,

Thank you so much for helping me out. With the code you provided I’ve a very good starting point, especially how to fill the gaps in the queue.

In my old program I gave all the machines an ID. Each machine was looking to the last given ID and it’s ID became “last given ID + 1”. If a machine had ID#1 it could go. When the timer was done all ID’s decreased -1. This worked fine, but not for the “gap in the queue” situation because I’d no solution for that. It was a very rare situation, but this lack of programming knowledge was annoying me. The program must be working 100% and not 99%.

Thank you once again.

Best regards,

Alex

Alex Mol

Hello Jens,

Sorry for my late response. Holidays...

I will do my very best to provide you the project when it's done. For now I'm making my very first steps into SCL. Wow! What a nice language!!! The queues are finished, but that was only a small part of the program.

Best regards,

Alex