Input data Regarding

Hello...

I need your help ...

I have been given a problem where a single type of product is manufactured. That is it goes through different machines following a set of operations. There are about 27 machines in the plant.There is an idle time between the transition phase of the product from machine 1 to 2 and so on.The data for this idle time has been collected..This does not follow any distribution (random)Also the setup time, processing time and unloading time is known to us(which is on an average constant for each job)... Before the first machine, small inventory is there wherein daily 200 products are brought in.At the end of the day, same number is given as the output(finished product).. It is continuous production..
For this scenario, simulation is to be done...
I am not understanding, what kind of input shall I give for source? Number is 200 but the second job can leave the inventory only after the first job is over on first machine and similarly the second job can leave the first machine only after the first job is over on second machine..

What kind of input data would you think be suitable for this case, both for source and processor?

Kindly give your suggestions...

I think you may need to create an arrival schedule and use it in the the source. If you do not have a specific release time for each product and the only requirement is continously feed the first machine after the job on the first machine is finished. You may use only one row in the arrival schedule and put 200 for the Quantity column.

For the constraints you mentioned, you may put a series of processors between the source and the sink. For transfer times, you may use conveyors to transfer the product and set the speed of conveyors according to the delay.

I have attached a screen-shot to illustrate the suggested model.

shivrash,

I think the easiest way would be just to open/close the output ports of the source and the processors on exit (by sending a delayedmessage to same object). So, when the source exits, close its output ports. When it exits the 1st processor, close that processors output port (all with delayed messages) and open the output port of the source. Just do that all the way along the line.

Some points to remember about the way the source works, the arrival schedule, and the times between processors:

First, there is no guarantee that a source will act like a queue and hold flowitems for you. I know that in some cases it does do this but in some it does not so it is best if we just assume that it doesn't. Therefore, you will want to have a queue immediately after your soure with a max content greater than 200.

Second, if you set up your source as Alan has suggested you will get 200 flowitems all at time zero and will never get another batch of them. If you want to be able to run more than one days worth of product through your model you will want to add a second arrival to your arrival schedule that will occur X time units later and have a quantity of zero. X time units being the number of time units in a day or shift and a quantity of zero because we don't want anything to actually arrive. You will then want to check the Repeat Schedule/Sequence check box, this will cause your source to produce 200 units every X seconds starting at time zero.

Third, you have not specified exactly what the transition time between parts is composed of. Is it the time for the operator of the machine to transport the item to the next machine in which case the machine can't start on the next part until the operator gets back. Is there a queue for parts to wait for the next machine to become available? If not then one machine that finishes early will be blocked if the next machine has not finished yet. As you can see there are many ways to simulate the delay between machines and the best way will be determined by the real world situation. If the parts are merely sitting in a queue waiting for the next machine to be available then use a queue (just like real life) and let the simulation tell you what the delay between the machines is. If it isn't a queue and the delay is something else then the best way to solve the problem may be to use expert fit to get a distribution for your data and then use a processor to simulate the delay. I would caution against using conveyors unless you plan on leaving the speed constant throughout the entire simulation. Changing speeds on a conveyor during a simulation is bad mojo and will more than likely give you problems (lots of them).

Good Luck,
Brandon

Thanks Alan, Jeff & Brandon

I would like to mention here that, there are conveyors in between each and every machine(a total of 27 machines).. The total time(including loading, machining & unloading time) is almost constant for each job on a given single machine.. For ex: the first machine is a Milling machine & the total time taken for 1st, 2nd & 3rd job is 5:14min, 5:17min & 5:07min respectively; similarly second machine is a Drilling machine and the total time for 1st, 2nd & 3rd job is 5:01min, 5:01min & 5:01min.. It is a continuous production process hence on any given day, as soon as the job leaves first machine, it may not get the second machine empty hence has to wait(idle time). In between the machines, we have conveyors..

Kindly put in your valuable suggestions over this problem...