Business operating management summary

Yuzhi Zhao

chapter14.pptx

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Operations Scheduling and Sequencing

COLLIER/EVANS

Operations + Supply Chain Management

LEARNING OUTCOMES, Part 1

Explain the concepts of scheduling and sequencing

Describe staff scheduling and appointment system decisions

Explain sequencing performance criteria and rules

OM6 | CH14

LEARNING OUTCOMES, Part 2

Describe how to solve single- and two-resource sequencing problems

Explain the need for monitoring schedules using Gantt charts

Describe how to use the Clarke–Wright method for vehicle routing and scheduling

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Scheduling and Sequencing

LO 14-1

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Scheduling

LO 14-2

Applies to all aspects of a value chain

Planning and releasing orders in a factory

Determining work shifts for employees

Making deliveries to customers

Software applications

Customized scheduling spreadsheets

Desktop and Web-based software packages

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Staff Scheduling, Part 1

LO 14-2

Attempts to match available personnel with the needs of the organization by:

Accurately forecasting demand and translating it into the quantity and timing of work to be done

Determining the staffing required to perform the work by time period

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Staff Scheduling, Part 2

LO 14-2

Determining the personnel available and the full- and part-time mix

Matching capacity to demand requirements, and developing a work schedule that maximizes service and minimizes costs

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Appointments

LO 14-2

Reservation of service time and capacity

Help maximize the use of time-dependent service capacity and reduce the risk of no-shows

Reduce the cost of providing services as the service providers are idle less each workday

Try to accommodate customers and forecast their behavior

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Designing Appointment Systems

LO 14-2

Includes:

Determining the appointment time interval

Determining the length of each workday and time off duty

Deciding how to handle overbooking

Developing customer appointment rules that maximize customer satisfaction

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Sequencing Performance Criteria

LO 14-3

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Process-Focused Performance Criteria Measures

LO 14-3

Flow time: Amount of time a job spent in the shop or factory

Fi = ∑pij + ∑wij = Ci − Ri

Where

Fi - Flow time of job i

∑pij - Sum of all processing times of job i at workstation or area j (run + setup times)

∑wij - Sum of all waiting times of job i at workstation or area j

Ci - Completion time of job i

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Process-Focused Performance Criteria

LO 14-3

Ri - Ready time for job i, where all materials, specifications, etc. are available

Makespan: Time needed to process a given set of jobs

M = C − S

Where

M - Makespan of a group of jobs

C - Completion time of last job in the group

S - Start time of first job in the group

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Due-Date Criteria Measures

LO 14-3

Lateness: Difference between the completion time and the due date

Tardiness: Amount of time by which the completion time exceeds the due date

Li = Ci − Di

Ti = Max(0, Li)

Where

Li - Lateness of job i

Ti - Tardiness of job i

Di - Due date of job i

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Sequencing Rules, Part 1

LO 14-3

For prioritizing jobs in the short term

Shortest processing time (SPT)

Tends to minimize average flow time and WIP inventory and maximize resource utilization

Earliest due date (EDD)

Minimizes the maximum of jobs past the due date

Does not perform well on average flow time, WIP inventory, or resource utilization

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Sequencing Rules, Part 2

LO 14-3

For prioritizing jobs that arrive intermittently

First come, first served (FCFS)

Used in service-delivery systems

Focuses only on the time of arrival for the customer or job

Fewest number of operations remaining (FNO)

Does not consider the length of time for each operation

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Sequencing Rules, Part 3

LO 14-3

Least work remaining (LWR)

Sum of all processing times for operations not yet performed

Least amount of work at the next process queue (LWNQ)

Amount of work awaiting the next process in a job’s sequence

Tries to keep downstream workstations and associated resources busy

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Single-Resource Sequencing Problem

LO 14-4

Processing a set of jobs on a single processor

Sequencing rules

SPT sequencing rule uses average flow time as a criterion to minimize the average time a job spends in a workstation

FCFS rule is used when processing times are relatively equal

EDD rule minimizes the maximum job tardiness and lateness

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Two-Resource Sequencing Problem, Part 1

LO 14-4

Exists for flow shop with only two resources or workstations

Solved by finding a minimum makespan schedule

Johnson’s algorithm

Step 1 - List the jobs and their processing times on Resources #1 and #2

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Two-Resource Sequencing Problem, Part 2

LO 14-4

Step 2 - Find the job with the shortest sequencing time

Step 3 - Process the job first if the time corresponds to Resource #1 and last if it corresponds to Resource #2

Step 4 - Repeat steps 2 and 3 using the next-shortest processing time

Work inward from both ends of the sequence until all jobs have been scheduled

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Schedule Monitoring and Control

LO 14-5

Necessary for rapidly changing scheduling environments in service and goods manufacturing industries

Gantt (bar) charts

Help monitor planned schedules

Display and track jobs that are behind, on, or ahead of schedule

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Exhibit 14.7

Gantt Chart Example for Monitoring Schedule Progress

LO 14-5

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Vehicle Routing and Scheduling Approaches

LO 14-6

Complete enumeration is carried out for all possible routes to find the best route plan and shortest total delivery time

Helps reduce operating costs and greenhouse gas emissions

Clarke–Wright Heuristic method

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Clarke–Wright Heuristic Method, Part 1

LO 14-6

Assumes that each customer is serviced individually from the depot

Seeks to combine customers into longer routes to reduce the total travel time and remain within capacity restrictions

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Clarke–Wright Heuristic Method, Part 2

LO 14-6

Step 1 - Compute the savings s(i,j) for all pairs of customers i and j

Step 2 - Find the pair of customers with the largest savings, and determine if there is sufficient capacity to link those customers together

New route is constructed if customers with the largest savings can be linked; if not, the next largest savings are tried

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Clarke–Wright Heuristic Method, Part 3

LO 14-6

Step 3 - Step 2 is applied as long as the next largest savings is positive

Procedure is stopped when all positive savings have been considered

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Exhibit 14.8

Combining Customers i and j on the Same Route

LO 14-6

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KEY TERMS

Scheduling

Sequencing

Flow time

Makespan

Lateness

Tardiness

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SUMMARY

Scheduling is defined as the assignment of start and completion times to particular jobs, people, or equipment

Sequencing helps determine the order in which jobs or tasks are processed

Gantt charts are tools for monitoring schedules

Clarke–Wright Heuristic Method helps solve scheduling problems in logistics

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4LTR Press

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