OPMT 303 CH. 16
Effective scheduling can yield:
- Cost savings - Increases in productivity
Why can scheduling be difficult?
- Except for small job sets, there is no method for identifying an optimal schedule - Scheduling is not an exact science - It is an ongoing task for a manager - Variability in: ○ Setup times ○ Processing times ○ Interruptions ○ Changes in the set of jobs
What are the key factors that determine the success of a high volume system?
- Process and product design - Preventive maintenance - Rapid repair when breakdowns occur - Optimal product mixes - Minimization of quality problems - Reliability and timing of supplies
What are priority rules and what are they used for?
- Simple heuristics used to select the order in which jobs will be processed - The rules generally assume that job setup cost and job time are independent of processing sequence
Johnson's Rule:
- Technique for minimizing makespan for a group of jobs to be processed on two machines or at two work centers - Minimizes total idle time
What are the six priority rules?
1. FCFS - first come, first served 2. SPT - shortest processing time 3. EDD - earliest due date 4. CR - critical ratio 5. S/O - slack per operation 6. Rush - emergency
What are the four measures of effectiveness for priority rules?
1. Job time must be known and constant for each job at the work center 2. Job times must be independent of sequence 3. Jobs must follow same two-step sequence 4. All jobs must be completed at the first work center before moving to second work center
List three things a manager can do to achieve good scheduling results:
1. Set realistic due dates 2. Focus on bottleneck operations 3. Consider lot splitting of large jobs
Suppose there are six jobs to be done, and six processing resources available to do these jobs. How many possible assignments (i.e., job-resource matchups) are there?
720
What is scheduling?
Establishing the timing of the use of equipment, facilities and human activities in an organization
Local priority rules:
Focus on information pertaining to a single workstation when establishing a job sequence.
What is a flow system?
High-volume system in which all jobs follow the same sequence
Which one of these involves managing work flow and queues at work centers?
I/O control
Global priority rules:
Incorporate information from multiple workstations when establishing a job sequence.
A supermarket that dedicates some checkout lines for customers with very small quantities of items is using a form of the __________ rule.
SPT
Which rule minimizes work-in-process inventory?
SPT
What is makespan?
The total time needed to complete a group of jobs from the beginning of the first job to the completion of the last job
Which approach is not used for job shop sequencing?
assignment method
Which one of these is an optimizing technique?
assignment method
The drum-buffer-rope technique is associated with
bottleneck operations.
Which approach takes into account job processing times and work center capacities?
finite loading
Job X arrived at a particular work center at noon. Job X required two hours of processing at that work center, but had to wait one hour to be processed. Job X's __________ was therefore three hours.
flow time
Typically, scheduling decisions are made:
just prior to the conversion of inputs into outputs.
Assigning specific jobs to specific processing resources is known as:
loading.
Suppose we have a specific collection of jobs, all of which are currently available for processing. Each of these jobs will follow the same route: first step A, then step B. Using Johnson's rule will, if other considerations are met, minimize the __________ for these jobs.
makespan
The total time required for some specific collection of jobs to be completely processed is called the:
makespan.
Which of the following is typically assumed by priority rules?
setup times that are independent of processing order
A possible disadvantage of the SPT priority rule is that it:
tends to make jobs with long processing times wait.
