Varying results while using multiple operations in same processor

[Anonymous]

Hi All,

I am trying to simulate a simple manufacturing process: Source -> Process -> Product. In the process I have 3 different operations with varying processing times.

The output from Source is fixed and infinite and the outing route is "Round-Ribbon". "Ignore when unavailable" box is unchecked.

My target quantity is 100.

The problem is that every time I run the simulation, I get different time periods in which 100 quantities would be manufactured. I find it strange as my output routing is the same and so I expect same time period for 100 products.

Some of the time periods for 100 parts are:

3D:21:40:20

3D:22:30:20

3D:23:10:20

3D:22:20:20

The difference in the time periods increases with increasing number of operations in the same process.

Can somebody pls explain me why this happens?

Thank you in advance

Regards

Naishal Thakker

[XuesongBai]

Hi there,

That should be affected by the distrubution that is set in the simulation setting.

So I think the different running time  for every time sound like making sense in the real environment.

Thanks,

-Xuesong

[Anonymous]

Hi,

Thank you for your time and reply.

But I have no variability in any source/processes/end product.

Is the variation in result by default or can I do something to have the same result every time?

Thank you in advance

Regards

Naishal Thakker

[liqinomickey · Accepted solution]

Hi Naishal,

This difference actually caused by the Random engine behind the simulation.

Before we get to this random engine, I would like to point out some issues of the simulation model: Not everything is fixed.

1. First, what this model want to simulate? We want to simulate a machine that has 3 operations, and each operation runs in a fixed order, 1à2à3.
2. The round robin Output Routing setting in Source 1 is reasonable. But it ALONE cannot guaranty your simulation is fixed. It can only guaranty the output of source1 is in this order.
3. Let’s take a look at the first 2 minute 1 second of this simulation. The Source1 output 1 item to each connection. When the clock comes to 3:01, the Source output 1 item to connection 1. By the time Processor finished Operation1, all 3 Operations has input ready. Then the Random Engine will start to pick 1 operation next.
4. So, originally we would like 1,2,3 to run in this order, which means 170 minutes to have a round. But the output rate of Source 1 is set to be 60 per hour. So it is better to set this value as 3 item per 170 minutes. Or to be more specific. It should be set as a pattern. This will guaranty your simulation runs as expected.
5. 

Now let’s get back to the Random Engine. This engine starts when our Processor faces a “either way works” situation. For instance, in the Bullet 3, after processor finished first operation 1, it will choose an operation to start next. All 3 operations are ready to start (raw material waiting), so random engine will pick, which resulted in your total simulation time difference.

To shut down the random engine, we have an environment variable value to control:

Variable	Value	(Effect)
PA_ENGINE_RANDOM_MODEL	0	Engine shut down
PA_ENGINE_RANDOM_MODEL	1	Engine enabled

I hope this answers your questions.

Thank you,

Mickey Li

[email protected]