Ch15 operations scheduling

gantt chart

scheduling low-volume operations with no fixed routing → visualizes a time schedule

work loading : infinite loading

ignores capacity retsraints

uses a schedule as input

identifies bottlenecks in the schedule

work loading: finite loading

considers capacity constraints

uses a prioritized list of jobs as input

input-output control

capacity control technique to monitor the workflow in a work center

work scheduling : foreward scheduling

start processing a job when it is received regardless of its due date

work scheduling : backward scheduling

begin by scheduling the last activity such that the job is finished on its due date

operation or job sequencing =

short term planning of jobs based on available capacity and priorities → determines the sequence of jobs, start and end times, expected queues

job sequencing : priority rules

decide on the relative priority (sequence) when multiple jobs are waiting at a work center

local priority rules consider only the jobs waiting at the work center

gloval priority rules : also consider workload in remaining work centers

job sequencing : local priority rules

consider only the jobs waiting at the work center

job sequencing : global priority rules

also consider workload in remaining work centers

common priority rules : First come first served

the job that arrived first in the work center

common priority rules : last come first served

the job that arrived last in the work center

common priority rules : earliest due date

the job with the earliest due date, minimizes job tardiness

common priority rules : shortest processing time

the job with the smallest processing time → minimizes mean hob lateness, mean job flow time and numer of jobs in the system

common priority rules : longest processing time

the job with the longest processing time

common priority rules : critical ratio

the job with the smallest ratio of time remaining until due date to its processing time remaining

common priority rules : slack per remaining operation

the job with the smallest ratio slack per remaining operation

measure scheduling effectiveness : job flow time

completion time - time job was first available → measures total time that a job spends in the shop before it is ready (responsiveness)

measure scheduling effectiveness : makespan

completion time of the last job - starting time of the first job → measures the total time to finish a batch of jobs (efficiency)

measure scheduling effectiveness : average number of jobs in the system

sum of individual job flow times / makespan → relates to the size of the queues, work in process inventory ext

measure scheduling effectiveness : job lateness

completion time - due date

measures wheter a job is completed early, on time or too late

→ potentially hides large differences between very early and very late jobs

measure scheduling effectiveness : job tardiness

max(0, completion time- due date)

→ measures how many days after the deadline a job is completed (due date performance)

→ assumes that there is no benefit in finishing a job early

job sequencing : johnson’s rule

sequencing jobs through two subsequent work centers

• all jobs go through two successive operations, but have different durations

• objective : minimize makespan

optimized production technology OPT (by eli goldratt)

bottleneck activities determine the throughput of the system

• bottleneck resources must be used to their full capacity

• non-bottleneck resources must be scheduled to suppot bottleneck resources

scheduling in services : managing demand

appointments or reservations

posted schedules

delayed services (backlogs)

scheduling in services : scheduling employees

• staffing for peak demand,

• floating employees or employees on call

• temporary seasonal, or part time employees