inter arrival time for pulling sink

Hi,

I want to set up a kanban controlled production line. the last object should be sink that's pulling items from a upstream queue. The sink should represent a customer who pulls items in statistical distributed intervalls. It's pretty much like a source that feeds the production line with items arriving to the production line in statistical distributed inter arrival times. Only this times the items should depart from the production line in statistical distributed "inter departure times".

Unfortunatly I couldn't find a function in the sinks parameter page similar to the inter arrival time of the source. Does anyone know a solution?

Thanks for your help!

Congshi

Is this an extension to your CONWIP model is the other post?

If so, it sounds like you'd have another counter which is the number of unfulfilled orders. On the entry to the sink you'd only release them from the source if you have orders outstanding.

There are two events:
1) Order generated: If WIP<MaxWIP open source output (or release a queued item if using transport). Increment ORDERS
2) Order fulfilled: If ORDERS>0 open source input (or release a queued item if using transport)

You can generate the order arrival by sending a delayedmessage to the object, or to do it globally use a User Event.

Not exactly.

What I want is to build is a fully pull-controlled production line like this:

Source => JobQueue => Queue1 => Processor1 => Queue2 => Processor2 => Queue3 => Processor3 => Queue4 => Processor4 => Queue5 => Processor5 => Sink

Now the whole demand is pulled by the sink and not pushed by the source. On reset the queues are filled with a defined number of item (= number of kanbans). By the departure of an item from the last queue (Queue5) to the sink (in statistic distributed "inter departure times") the predecessor-processor (Processor5) gets a free kanban that opens his inputs port for one item to process. And this way the production pulled by the demand makes its way from the sink to the source.

There are some differences to CONWIP:
-First the cards doesn't represent the WIP but the inventory of one kanban-control-loop. This inventory can be the WIP of a processor (if it's processed right now) or finished goods in the queue after the processor.

-Second the control-loop doesn't go across the whole production line but only throught one processor and it's successional queue.

What I need now it a sink that simulated the stochastic behaviour of the customer. Therefor it should exacty got the function of the source in the source tab with inter arrival style, inter arrival time, etc., but just inversed: inter departure style, inter departure time, etc.

Thanks a lot!

Hello Conshi,

If I understand your problem correctly, you may can solve it like this:
Start with the input port of your processor5 closed and send a message on Reset to itself, with a delay of your statistical distribution to open the port and let an item in. Once the item enters the processor, send a message to close its input port again (delay = 0 ) and send the next message to open the port, with a delay according to your statistical distribution.
If your processor can contain more than 1 item (i.e. the interval of your statistical distribution is shorter than your process time) make sure your processor can contain more than one item.
I suggest to put the code on the processor, because I assume that there will always be items in the queue, but there might nog always be items in the processor.

Hope this might help you to solve your problem.

Esther

Thanks, it works. But it seems that the source always wants to release items by itself. Can I set the source so that it will just release items if a next processor is pulling items. Otherwise, if no succeding processor is pulling, it should not release (or "push") any items.

Thanks

Congshi

Congshi,

the Flow tab of each object that is able to receive items has a "Pull" logic predefined you can easily use for what you need to do. Of course there can only be pulled flowitems which are available somewhere upstream, but you can´t (by default) create flowitems when you need them anywhere in the model.

Let us know, if that worked for you

Good luck

Ralf

Thanks Ralf,

the hint of Esther helped me out. To simulate a stoachastic demand coming from the sink (sink = customer) I set send delayed message on the resettrigger and on the entrytrigger. The delay time corresponds to a statistic distribution. After recieving the message the output port of the last queue feeding the sink (=customer) should be opened. This should work like this:

At starts of the simulation run the resettrigger waits the delay time ("inter departure time", equals the inter arrival time of a push-controlled production line) to fire its first message (first customer demand). The output of the last queue will be opened. Immediatly after the sending of an item (delivery to customer) the last queue closes its output port again (on exittrigger + on messagetrigger). The second demand will be fired by the onentrytrigger of the sink after a delaytime (same delaytime as in the reserttrigger) after recieving the first delivery. The last queue opens its output port and closes it again after delivery, the sinks fires the next demand after recieving the delivery and another statistically distributed delay time, and so on...

I hope it can simulate a pulling sink as well as an ordinary pushing source. Perhaps you have some suggestions how to improve it.

Thanks!