Scheduling Problem

mishaelsmith

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Joined
Jul 18, 2014
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I have a job shop scheduling problem. I am pretty good with formulas and functions but what I am struggling with is understanding the problem and coming up with a method for solving it.

So pretend you are in a factory making all kinds of different widgets. To make a widget you have a number of different processes involved, and the variety and length of time of each process can be quite different widget to widget. Every widget project also has a due date.

What I am trying to do is create schedules for each process, so that we can say this process should work on this widget, followed by this widget and so on. What I am using is a backtrack scheduling method, that is, for each widget I am summing the time of all future processes of that widget and subtracting that from the widgets due date and this decides the order of what widget should be made first. So I am prioritising widgets in the process schedule by how much work is left to go and it's due date priority. Now that I have done this I want to calculate what the finish date of each widget would be in the process schedule and this is where I am running into problems.

Because each widget uses different processes from one widget to another it means that to calculate when a widget will be finished it's not just a matter of going down each process schedule and adding the length of time it takes to do the process on to the finish date of the above item in the schedule because the process needs to check whether the preceding process for the widget is complete or not. That is, you can't start work on a widget unless the work on the previous process is complete. But because the processes for each widget is so random I am getting all these circular reference issues in the formulas I am trying, or I am not getting enough data to work with to make a calculation.

I have attached a really simplified JPG which illustrates the problem. I sure hope I have explained this somewhat understandably! I am using Excel to try and solve the problem but maybe it needs some kind of genetic algorithm to solve it?! Your help would be amazing

schedule problem.JPG
 
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