Scheduling

Chapter 15: Scheduling

Overview

This chapter compares scheduling for low and high volume operations.  The various methods of sequencing work are presented, demonstrated and compared.  The performance measures for schedules are presented and discussed.  The scheduling of bottlenecks is explained.  The theory of constraints (TOC) approach to scheduling the bottleneck is explained.  This approach is known as drum-buffer-rope (DBR).  Workforce scheduling issues are explained.

Answers to Discussion Questions in Textbook

Compare and contrast high-volume and low-volume scheduling operations.

Scheduling in a high-volume environment, which includes assembly lines and continuous flow processes, is determined by the line design and its balance.  Scheduling in low-volume operations, which include batch and project processes, involves the use of priorities rules, such as SPT and EDD.

Describe a high-volume service operation and describe how scheduling should be done.

A high-volume environment uses a line flow approach to production, such as an assembly line or continuous flow process.  The schedule is decided when the line is designed so that it will give us the desired output.

Describe a low-volume service operation and describe how scheduling should be done.

Low-volume operations focus on scheduling each machine since they are arranged in departments, such as the batch or project process.  Scheduling involves the use of priority rules, such as SPT and EDD.

Visit a local service operation and describe their scheduling procedures.

Let’s look at the way Kinko’s Copy Center schedules the customer orders.  They are using intermittent operations.  So they should use priority rules for scheduling each copier and machine in the facility.  It appears that they use FCFS as a rule for processing work for customers who wait for their order.  They probably use the EDD rule for orders where the customer is not waiting. 

Visit a local manufacturing operation and describe their scheduling procedures.

This answer depends on the area in which the university is located.

Describe infinite loading.

We can use infinite loading to schedule all the work proposed in the MPS to see if there is enough capacity to do the work.  Infinite loading determines the capacity needed at each work center to meet the proposed schedule.

Explain how the output from infinite loading is used.

The output from infinite loading is used to change the MPS to make it feasible in terms of capacity.

Explain how finite loading is done.

Finite loading schedules work according to the available capacity.  It plans production in each work center so that the capacity needed at that work center for the production schedule is sufficient. 

Explain the benefits of finite loading.

The benefits of finite loading are the creation of a feasible production schedule, in terms of capacity, more quickly than infinite loading.

Describe forward scheduling.

Forward scheduling starts work on the job in production when it is arrives.  It helps us determine the earliest possible completion time of the job. 

Describe backward scheduling.

Backward scheduling starts by scheduling the last processing step of a job and works backward through the production process in order to ensure on-time completion.

Visit a local service or manufacturing organization and learn how they measure schedule effectiveness.

Many service organizations measure schedule effectiveness based on tardiness.  Let’s consider a restaurant that does not take reservations.  They probably are more concerned that the actual waiting time does not exceed the estimated waiting time given to the customer.    Or they could measure lateness to have an idea of how accurate the estimates in terms of not being too high or too low.

Describe the principles of OPT.

OPT is a technique for scheduling production that focuses on effectively dealing with the bottleneck.  The bottleneck should be kept busy, while non-bottlenecks should support the bottleneck, not be kept busy for the sake of efficiencies.  Here are the principles of OPT:

Balance the process with demand.
Use non-bottlenecks only as needed to support the constraint.
Understand that using the resource to produce do not necessarily mean that it is contributing to the bottom line.
An hour lost at the bottleneck is an hour lost forever.  Since the bottleneck determines the capacity of the entire plant, we need to use its capacity effectively.
Bottlenecks determine throughput and system inventory.
The transfer batch does not have to equal the process batch.  If we are processing in batches of 10 units, we do not necessarily have to wait until all 10 units are done on a process before moving them to the next process.

Describe the theory of constraints.

The theory of constraints uses a five-step process for dealing with the constraint, which can be a policy or physical resource that limits us from improving our performance.  Here are the steps:

Identify the constraint(s).
Exploit the constraints(s) by finding ways to deal with them directly in order to improve performance.
Subordinate to the exploitation by making sure that all other areas or resources provide support.
Elevate the constraint(s) by focusing on dealing with the constraint in order to gain more improvements.
Repeat these steps if the constraint has moved.

Describe different methods that might be useful for scheduling service operations.

We can schedule service operations by taking appointments, reservations, posting schedules and delayed services and backlogs.  Doctors schedule appointments.  Airlines take reservations.  Movie theaters post schedules.  Restaurants use delayed services and backlogs when they use waiting lists.