Example schedule for a complex jobshop
Fig 3. Example schedule for a complex jobshop
Example schedule for a complex jobshop
Figure 3 is a Gantt chart showing an example of a complex schedule, which is in fact the output from a program designed to optimise schedules. This shows there are 20 jobs (numbered 0 to 19) scheduled for 4 machines (numbered 0 to 4). For clarity each job is represented in a different colour. Each job has a set number of operations required for completion. The placement of the job operations on the available machinery is plotted on the Gantt chart against a time base. The total time taken for the jobshop is the makespan.
Extra facilities built into this scheduler can be seen in the figure. The grey areas in the schedule are designated maintenance times for a particular machine. The cross-hatched areas before each job operation are the designated set-up times for a particular operation on that machine. For example the set-up time for a drilling operation will most probably differ from that for a milling machine.
What is not visible from this chart is that operations may be carried out on some alternate machines with a probable drop in time efficiency.
The above figure shows just one schedule for a jobshop. A typical Genetic Algorithm program designed to optimise such jobshops will employ many more (in the order of 400 or more).
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