Problem with sending items in a job shop model

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Steven Chen asked Nov 1, '21 Steven Chen edited Nov 2, '21

Problem with sending items in a job shop model

Dear Everyone,

As you can see in the attached model file, an operator sends four items on the first queue to 4 different machines in various steps. With all processes done, each item is transferred to the second queue. Where items are processed in every step is in accordance with the pull requirement created in every machine.

However, a wrong logic appeared in my job shop model when I simulated item processing and transportation. The operator transports unfinished items to the second queue while they should continue being processed. For example, the problem occurs at ninety seconds of the runtime. The type-2 item in green should be in process, rather than being sent to the second queue. That item requires two more stations to be fully in completion. But it turns out that the operation does not follow the logic created in the Use Transport function in every processor.

A few months ago, I built this type of model in a previously-released version of FlexSim(21.0.3), but such a similar issue did not show up at that time. Whether or not the current processing logic has changed is my uncertainty. Otherwise, it seems to be a bug.

Has anyone ever encountered the same problem so far?

Thank you for your time and check

Job Shop Simulation Model.fsm

Software Version:

FlexSim 21.2.3

item job shop tranport

job-shop-simulation-model.fsm (34.5 KiB)

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CSN commented · Nov 01, 2021 at 08:18 AM

Hi,

it seems that you want to realize the steps of flexible mixed flow processing. I have made simple modifications on your model. I don’t know if it meets your needs.

job-shop-simulation-modelv21.2.4.fsm

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job-shop-simulation-modelv2124.fsm (38.0 KiB)

Steven Chen CSN commented · Nov 02, 2021 at 01:38 AM

Dear CSN,

Thank you for your kind response and modifications. In your model, the By Expression method is adopted to send finished items to the second queue, and the new "On Process Finish" function has made an adjustment to the processing time per machine. These changes are helpful for me because they solve the problem that I am facing.

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Answer 1 · 2021-11-01T09:13:27Z

Felix Möhlmann answered Nov 1, '21 Steven Chen edited Nov 2, '21

The "Pull" option isn't active on the second queue, so the first one sees it as a valid destination and sends items there if no processor is available for them. When I activated it, it was already configured correctly (pulling items where station = 0). Maybe you deactivated it by accident or it got deactivated when you copied the queue from a different model?

CSN's solution of using the "Send to Port" option on the first queue and adjusting the "router" table also works. They also changed the "On Entry" triggers of the processors to "On Process Finish". Otherwise the wrong process time is used, because the label would be increment before the time is evaluated. Alternatively, you could simply add a "-1" to the column field of the process time option.

job-shop-simulation-model_1.fsm

job-shop-simulation-model-1.fsm (35.9 KiB)

· 1

Steven Chen commented · Nov 02, 2021 at 01:57 AM

Hello Felix,

Thank you for your feedback and suggestions. As you mentioned, the "Pull Requirement" option should have been activated to pull finished items with the station label being 0. Items are sent to their right places after the modification is made. The item-sending solution presented by CSN has resulted in the same correction.

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