Week 15A - Scheduling (Chapter 15)

Week 15A - Scheduling (Chapter 15) Terminology, lead time, priority rules, theory of constraints (discussed in Capacity), volume considerations SJSU Bus. 140 - David Bentley

Volume considerations • High volume (repetitive, continuous flow) • Flow-shop scheduling (rate based) • Intermediate volume (job/repetitive) • Mixed model scheduling • Low volume (job) • Operation scheduling (forward/backward/ midpoint) • Synchronized scheduling SJSU Bus. 140 - David Bentley

Low Volume Scheduling Job Shops SJSU Bus. 140 - David Bentley

Elements of Lead Time • Queue – job waiting to be worked on (jobs with higher priority are ahead) • Setup – Making the machine or workplace ready to work on a job • Run – performing the required action to complete an operation on a job • Wait – awaiting a move to the next operation / work center or the stockroom • Move (transit) – time moving to next operation / work center or stockroom SJSU Bus. 140 - David Bentley

Lead time elements Queue Setup Run Wait Move |----------------|--------|------------|------|-----| SJSU Bus. 140 - David Bentley

Scheduling Terminology • Operation – a discrete step or task, one of a number required to make an item • Workstation – a specific machine oremployee work space • Workcenter – a machine grouping or work grouping used for scheduling and costing • Routing – a sequenced list of operations, with associated work centers • Job – an order to produce a specific quantity of an item with a specific start and/or due date SJSU Bus. 140 - David Bentley

Sequence of operations Q S R W M |-----|----|------|---|---| Q S R W M Seq 010 |-----|----|-------|---|---| Seq 020 SJSU Bus. 140 - David Bentley

Loading and Scheduling • Loading – assigning jobs to work centers • Infinite vs. finite loading and scheduling • Infinite – ignored capacity constraints • Finite – considers capacity constraints • Forward vs. backward scheduling (+midpoint) • Forward – start with start date, determine due date • Backward – start with due date, determine start date • Midpoint – from current date, determine revised due date SJSU Bus. 140 - David Bentley

Sequencing and Dispatching • Sequencing – determining the sequence of processing jobs at a work center • Priorityrules – rules used in sequencing (see later overhead) • Dispatchlist – authorized sequence list • Input-OutputAnalysis – monitoring the flow of work into and out of work centers to assure a steady flow and to identify problem areas SJSU Bus. 140 - David Bentley

Sequencing & Priority Rules • FCFS – first come, first served • SPT – shortest processing time • EDD – earliestdue date • CR – critical ratio • (time remaining / processing time) • Time remaining = (due date – “now” date) • S/O – slack per remaining operation • ESD – earliest start date • Other – favorite customer, “hot” job, etc. SJSU Bus. 140 - David Bentley

Charts • Gantt – visual (bar chart) representation of schedule and actual performance • Load – Gantt chart showing load and idle time for a machine or work center by time period • Schedule – Gantt chart showing the progress of jobs by time period SJSU Bus. 140 - David Bentley

PerformanceMeasures • Job Flow Time • Time at a workstation, work center, or plant • Includes Q,S,R,W,M • Average Flow Time (group of jobs) • Sum of flow times for n jobs / n • Job Lateness • Expected due date – original due date • Makespan (group of jobs) • From start of first job to end of last job • Average number of jobs (group of jobs) • Total flow time / Makespan SJSU Bus. 140 - David Bentley

Other Related Activities - 1 • Dispatching • Expediting • Queue compression • Lot splitting • Job overlapping • “Stop what you’re doing and work on this!” BAD!! • Synchronized scheduling • Timing of production meshed with use rate • Example: bakery oven SJSU Bus. 140 - David Bentley

Other Related Activities - 2 • Input-OutputAnalysis • Monitoring the flow of work into and out of work centers to assure a steady flow and to identify problem areas • Reports the following: • Input for the period • Output for the period • Queue change SJSU Bus. 140 - David Bentley

High Volume Scheduling Repetitive and Continuous Flow SJSU Bus. 140 - David Bentley

Rate Based Scheduling • Schedule by quantity per • Month, • Week, • Day, • Shift • Limited number of items • Seek to achieve flow SJSU Bus. 140 - David Bentley

Intermediate Volume Scheduling Bridge Between Job Shop and Repetitive Operations SJSU Bus. 140 - David Bentley

Mixed Model Scheduling • Interspersing different models • Alternative to producing longer runs of each model • Look for: • Lowest ratio and • Most repetitive mix • Bicycle example SJSU Bus. 140 - David Bentley

Service Operations • Appointment book (e.g., dentist) • Reservations (e.g., airlines) • Scheduling multiple resources • Managing capacity SJSU Bus. 140 - David Bentley

Week 15A - Scheduling (Chapter 15)