Ch 16: Scheduling
johnson's rule conditions
- Job time must be known and constant -Job times must be independent of sequence - Jobs must follow same two-step sequence - Job priorities cannot be used -All units must be completed at the first work center before moving to second
Which of the following statements are correct about Johnson's rule?
-Johnson's rule minimizes total idle time for both machines or work centers -The job with the shortest time for Machine 1 is the first in the sequence.
intermediate volume systems
-Outputs fall between the standardized type of output of high-volume systems and the make-to-order output of job shops -Output rates are insufficient to warrant continuous production Rather, it is more economical to produce intermittently -Work centers periodically shift from one product to another
Which of the following statements about scheduling are correct?
-Scheduling decisions are the final step in the transformation process. -Scheduling is constrained by prior decisions such as capacity & aggregate planning.
Select all the actions that managers can take to minimize scheduling difficulties.
-Set realistic due dates whenever possible. -Focus on process bottlenecks and schedule around it if unable to eliminate it.
Select all of the constraints on workforce scheduling flexibility.
-Union rules -Legal issues -Behavioral issues -Technical issues
When appointment systems are used, what circumstances lead to problems in scheduling services?
-When customers arrive late -When customers do not show up
Which of these is a true statement? (Choose all that apply)
-a system can have more than one bottleneck -a factory's bottleneck can change depending on what products are being made
Select all of the industries which frequently use reservation systems to manage demand and capacity.
-hotels, resorts -car rentals -restaurants
all of the reasons why scheduling can be difficult for operations managers.
-interruptions in the work flow (machine break downs, quality issues, etc.) -Variability in setup times and processing times
Which of the following will minimize scheduling difficulties?
-set realistic due dates -focus on bottleneck operations -Split large jobs into smaller batches
johnson's rule sequence
1. list jobs and their times at each work center 2. select job with shortest time; if shortest job is at work center 1, schedule first. if shorts job is at 2nd work center, schedule last. 3. eliminate the job from further consideration 4. repeat steps 2 and 3, working toward the center of the sequence
important theory of constraints metrics
1. throughput: rate at which the system generates money though sales 2. inventory: represents money tied up in goods and materials used in process 3. operating expense
Load chart
A Gantt chart that shows the loading and idle times for a group of machines or list of departments
load chart
A Gantt chart that shows the loading and idle times for a group of machines or list of departments
Schedule chart
A Gantt chart that shows the orders or jobs in progress and whether they are on schedule.
schedule chart
A Gantt chart that shows the orders or jobs in progress and whether they are on schedule.
What does "drum-buffer-rope" mean in the theory of constraints.
A scheduling practice to keep inventory ahead of the bottleneck to minimize idle time at the constraint
Which of the following is the best definition of a workstation in the context of job loading and scheduling at a work center.
An area where one or a few workers and/or machines perform similar work
Which of the following is an example of cyclical scheduling?
Assigning a worker at a restaurant the same days off each week
backward scheduling
Backwards from some due date "When no's the latest this job can be started and still be completed on time"
Which priority rule calculates a ratio of time remaining until due date over processing time remaining for each job to determine sequencing?
CR- Critical ratio
To improve customer satisfaction at busy service times, capacity can be adjusted by what activity?
Cross-training workers to assist on bottleneck operations
Sequencing
Determine the order in which jobs at a work center will be processed
The two basic issues for schedulers in low-volume systems are what?
Distribution among work centers and sequencing
drum-buffer-rope
Drum = the schedule Buffer = potentially constraining resources outside of the bottleneck Rope = represents synchronizing the sequence of operations to ensure effective use of the bottleneck operations
Which sequencing rule is designed specifically to minimize job tardiness?
EDD
EDD Rule
Earliest due date; adresses due date and minimizes lateness; main limitation is it does not take processing time into account whic can result in jobs waiting a long time adding to congestions
cyclical scheduling
Employees are assigned to work shifts or time slots, and have days off, on a repeating basis
What is the best definition of scheduling from among the options given?
Establishing the timing of the use of equipment, facilities, and human activities in an organization.
Priority rules
FCFS, SPT, EDD, CR, S/O, rush
Which priority rule is used most often for service systems in which customers are directly involved?
FCFS- First come, first served
True or False Line balancing is a major factor in the design and scheduling of low-volume systems because of batch processing.
False
FCFS Rule
First Come First Serve; least effective of the rules, long jobs will tend to delay other jobs, idle time for downstream workstations increases, most dominant rule because of fairness and inability to obtain realistc estimates of process time for individual jobs, advantage of simplicity
Scheduling Approaches
Forward and backward
Which chart is used as a visual aid for both loading and scheduling in low-volume systems?
Gantt Chart
Challenges in scheduling services that do not occur in manufacturing?
Inability to store services and random customer requests for service
Which type of loading can lead to overloads in some time periods and underloads in others?
Infinite loading
What is the term used for managing work flow and queues at work centers?
Input/output (I/O) control
Low-Volume Systems
Job shop scheduling Loading
Scheduling in low-volume systems is known by what term?
Job-shop scheduling
Finite loading
Jobs are assigned to work centers taking into account the work center capacity and job processing times
finite loading
Jobs are assigned to work centers taking into account the work center capacity and job processing times
Infinite loading
Jobs are assigned to work centers without regard to the capacity of the work center.
A scheduling rule used for sequencing jobs through two work centers such that makespan is minimized is
Johnson's Rule
The assignment of jobs to processing centers in low-volume systems is know by what term?
Loading
In MRP, under lot-for-lot ordering, planned-order receipts are:
Open orders
high volume success factors
Process and product design Preventive maintenance Rapid repair when breakdowns occur Optimal product mixes Minimization of quality problems Reliability and timing of supplies
In assigning jobs to work centers in a low-volume system what three aspects are minimized?
Processing costs, idle time, job completion time
In theory of constraints scheduling, the synchronization of the sequence of operations is referred to as the
Rope
Under which priority rule are long jobs most likely to wait for processing?
SPT
What priority rule can result in lower in-process inventories?
SPT; shortest job first
What type of Gantt chart shows the orders or jobs in progress and whether they are on time?
Schedule chart
Determining the order in which jobs at and within a work center will be processed is known as what?
Sequencing
priority rule
Simple heuristics used to select the order in which jobs will be processed.
Lot-for-lot ordering in MRP eliminates the holding costs for parts that are carried over to other periods.
TRUE Lot-for-lot ordering minimizes holding costs.
Priority Rules: Assumptions
The set of jobs is known; no new orders arrive after processing begins and no jobs are canceled Setup time is independent of processing time Setup time is deterministic Processing times are deterministic There will be no interruptions in processing such as machine breakdowns or accidents
What is the primary purpose of reservation systems in scheduling services?
To estimate customer demand and provide a better service experience
What is the primary purpose of appointment systems in scheduling services?
To minimize customer waiting time
True or False Loading is the determination of which work centers should perform which jobs.
True
True or False The SPT priority rule always results in the lowest average completion time.
True
True or false The output of a factory can be no higher than the output of the slowest machine, the constraint of the system.
True
True or false scheduling decision are the final step in the transformation process before actual output occurs
True
True or false The inventory records contain information on the status of each item
True
Which of the following is required for cyclical scheduling?
Workers must have a standard schedule
assignment model
a linear programming model for optimal assignment of tasks and resources
Loading
assignment of jobs to process centers
Scheduling backward from a due date
backward scheduling
alternative schedling approach for intermediate volume sustems
base prodiction on a master schedule developed from customer orders and forecasted demand
The theory of constraints focuses on
bottleneck operation that limit system output
scheduling workforce involves
capactiy management -cyclical scheduling
effective shcedluing yields
cost savings increases in productivity
Service scheduling involves
customers (demand mgmt) workforce (capacity mgmt) equipment
scheduling customers involves
demand management: -appointment systems -reservations systems
flow system difficulties
entirely dedicated to a single profuct or service; change requires slightly different inputs, parts, materials processing requirements
scheduling
establishing the timing of the use o specific resources of that organization
True or false: Without input/output control, capacity may exceed demand, causing an overload at a work center.
false; An overload would be caused when demand exceeded capacity at a work center.
true or false job shop does not have a complex scheudling environment
false; complex, impossible to establish firm schedules until actual job orders are recieved
_______________ loading projects the actual job starting and finishing times at each work center by taking into account the capacities of the work center and the processing time of the jobs.
finite
which is not an assumption of priority rules?
finite loading is assumed
What does priority rule acronym FCFS stand for?
first come first serve
Scheduling in high-volume systems is known by what term?
flow-shop scheduling
What are the two general approaches to scheduling?
forward and backward
flow systems
high volume system in which all jobs follow the same sequence scheduling goal is to achieve SMOOTH RATE OF FLOW of goods or customers through the system in order to get utilization of labor and equipment
The first step in the Theory of Constraints is to:
identify the constraint
Loading Approaches
infinite loading and finite loading.
Which word below most accurately describes the processing involved in intermediate-volume systems.
intermittent
low-volume systmes
job shop scheduling: make to order products, requirements for processing, materials, processing time, sequence and setups
infinite loading
jobs are assigned to workstations without regard to the capactiy of the work center
What is the sequencing technique that minimizes the total time for a group of jobs to be processed on two machines or work centers called?
johnsons rule
Compared to a job shop, the batch sizes in intermediate-volume systems are ___________.
large
purpose of input/output (I/O) control
manage work flow so that queues and waiting times are kept under control.
Theory of constaints
production planning approach that emphasizes balancing flow throughout a system, and pursues a perpetual five-step improvement process centered around the systems most restrictive constraint.
Input/output (I/O) control
refers to monitoring the work flow and queue lengths at work centers
3 basic issues o intermediate volume systems
run size of jobs timing of jobs sequence in which jobs will be producred
forward scheduling
scheduling ahead from a point in time "how long will it take to complete this job?"
Backward Scheduling
scheduling backward from a due date; used when "when is the latest this job can be started and still be completed on time"
important considerations of intermediate volume systems
setup cost usage is not always as smooth as assumed in the economic lot size model
SPT Rule
shortest processing time; always results in lowest average flow time which results in lower in-process inventories; can result in better customer service levels, tends to be less congestions in work area, minimizes downstream idle time. doesnt incorporate due dates. major disadvantage is it tends to make long jobs wait,
What is the goal of a high-volume system?
smooth rate of flow of goods or customers through the system in order to get a High utilization of labor and equipment
constraints of scheduling
system capacity product and/or service design equipment selection worker selection and training aggregate planning and master scheduling
EXAMPLE 1 answer
tardiness= flow time-due date time makespan= total time of job time
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, conditions must be satisfied
process batch
the economical quantity to produce upon the activation of a given operation
transfer batch
the quantity to be transported from one operation to another, assumed to be smaller than the first operation's process batch
The purpose of Gantt charts is to organize and visually display the actual or intended use of resources in a ______.
time framework
makespan
total time needed to complete a group of jobs from the beginning of the first job to the completion of the last job
How do operations managers in the service sector mitigate the random variability in customer requests for service?
use appointment and reservation systems
gantt chart
used as a visual aid for loading and scheduling purposes; orgniaze and visually display the actual or intended use of resources in a time framework
Scheduling techniques assume a process can be modeled, but in reality, there can be ______ in setup times and processing times.
variability
