6b scheduling

Operations Management Scheduling

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INDEX


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Sr No. Topics Covered Page No.

1 Scheduling Types of scheduling. How scheduling fits in operations mgmt.

1-2

2 Scheduling customer demand.

3

3 Scheduling employees demand.

4

4 Objectives of operations scheduling.

5

5 Inputs of scheduling.

6-7

6 Purpose of scheduling.

8

7 Scheduling method.

9

8 Scheduling activities.

10

9 Job dispatching.

11

10 Performance measures.

12

11 Gantt charts.

13-14

12

14

Johnson’s rule. Scheduling by type of operation.

15

16-18

15 Scheduling jobs for multiple work stations.

19

16 Scheduling jobs for one work station 20-21 17 Bibliography 22


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Scheduling

Types of Scheduling:

Scheduling: Scheduling is allocation of resources over time to accomplish specific

tasks. It involves developing and assigning specific dates for the start and

completion of the necessary task or operations in a production shop floor. The

output plans indicated in master production schedules must be implemented on

a shop floor on a day to day basis.

Demand scheduling: Demand scheduling is a type of scheduling whereby customers are

assigned to a definite time for order fulfillment. Customers are assigned to a

definite time for order fulfillment. It provides the capability to receive and

manage customer requirements as a time phased schedule of demand rather

then a series of separate sales order. This helps enterprise to track the activities

of the customers and thereby increase its own efficiency.

Workforce scheduling:

A type of scheduling that determines when employees work. It is the process

of balancing work to be completed with the resources available to compute the

work. It is very important to know the expected work load and resources to be


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allocated accordingly. The amount of work may vary from day to day or minute

to minute.

Operations scheduling:

A type of scheduling in which jobs is assigned to workstations or employees

are assigned to jobs for specified time periods. Operations scheduling pertains

to both establishing the time and resources with an organizations requirement.

Operations scheduling relates to the use of equipment and facilities, the

scheduling of human activities and materials

How Scheduling fits the Operations Management Philosophy?

Operations As a Competitive Weapon

Operations Strategy Project Management

Process Strategy Process Analysis

Process Performance and Quality Constraint Management

Process Layout Lean Systems

Supply Chain Strategy Location

Inventory Management Forecasting

Sales and Operations Planning Resource Planning

Scheduling


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Scheduling Customer Demand

Three methods are commonly used to schedule customer demand: (1) Appointments:

Assign specific times for service to customers. A customer is asked to

come at a specific time.

E.G..: A medical clinic typically determines the employees work schedule

and then uses an appointment system to control the arrivals of patients in

accordance with the availability of employees.

(2) Reservations :

Reservations are used when the customer actually occupies or uses

facilities associated with the service. It is basically scheduling the time and date

in advanced for customers convenient.

E.G: Reservation done for airlines so that a customer can fly on the

scheduled time rather then last minute chaos or reservations of room scheduled

in a hotel in advance to avoid last minute search.

(3) Backlogs:

• The customer is given a due date for the fulfillment a product order, or


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• Allow a backlog to develop as customers arrive at the system. Customers

may never know exactly when their orders will be fulfilled

Scheduling Employees

� Rotating schedule:

Rotating schedule is a schedule that rotates employees through a series

of workdays or hours.

E.G: on a shop floor workers who work on machines a kept to work on rotation

basis so that they don’t get stressed out. People working in textile miles or any

other industry general work on shift basis.

� Fixed schedule:

Fixed schedule is the one that calls for each employee to work the same

days and hours each week.

E.G: in a office employees usually work on a fixed hours basis i.e. they usually

work on 8 to 8 time basis.

� Constraints:

The technical constraints imposed on the workforce schedule are the

resources provided by the staffing plan and the requirements placed on the

operating system.


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Other constraints, including legal and behavioral considerations, also can

be imposed.

Objectives of Operations Scheduling

Following are the objectives of scheduling:

� Ensure maximum utilization of resources, plant at a minimum cost.

� Ensure that the requirement of manpower is optimum and is evenly

distributed; there should not be any peaks and valleys.

� Possess up to date information regarding availability of raw material,

expected delivery dates, materials rejection, shortages, purchase orders

cancelled, etc.

� Possess up to date data on each machine regarding its breakdown,

availability of spares, average frequency breakdowns, servicing, etc.

� Possess complete information on performance standards and their revisions

method improvement changes in material, machines etc.


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� Obtain quick feedback from shops regarding delays and interruptions which

may hold up production activity.

� Minimizes the average flow time through systems.

� Reduce setup costs.

� Minimize WIP inventory.

Inputs of Scheduling

a) Performance Standard:

Performance standard is the first & foremost requirement of good

scheduling. Performance standard enables the scheduler to determine the

machine capacity in order to assign required machine hours for the various

operations. Good scheduling is always possible if the time study or

industrial engineering dept exist in the plant. The approx time estimate can

be prepared by breaking the task into elements & then estimating time for

each manual & machine element.

b) Unit of Measurement:

Unit of measurement refers to the unit in which loading &

scheduling is to be extended. This unit of measurement is usually different

for different industries. Industries such as sugar, cement, fertilizers, steel

general use weight (kg/tons) as unit of measurement while in textile mills, it

is in length (meters). The most common unit of measurement in engineering

firms is “man-hour” & “machine-hours”.


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c) Unit of loading & Scheduling:

This refers to the duration for which loading & scheduling

should be done. The unit of loading & scheduling start & finish time

depends on the company’s scheduling needs & operating cycle. This implies

that scheduling should be done on daily basis if the company makes

promises in day & it should be done on daily or weekly basis if promises are

made in weeks.

d) Extent rush orders:

Provision of rush orders is another important consideration in

scheduling. No machine should be scheduled for its cent percent effective

capacity because if rush order comes in, scheduling has to be changed to

allow rush order to be put through the shops. Such rush orders, if received

frequently are bound to put company’s scheduling out of gears. The

disturbance of rush orders can be avoided by not scheduling the machine for

100% effective capacity.

e) Overlapping of Operations:

Overlapping of operations is yet another useful consideration

in scheduling. Overlapping of operations refers to running of a job

simultaneously on more than one machine & it occurs in jobs which involves

two or more operation. It helps to reduce manufacturing time & hence the

delivery period of customers.


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WHY SCHEDULING?

Every order whether it is from customer or from the assembly benches

must be completed on or before the contracted date. To ensure that the

delivery date is met, each component entering the assembly should be made

available on time. Determines start and completion data of each operations

Scheduling is the process of fitting a shop order into committed time

available for machine or group of machines required for the manufacture of

time and within the total time which is no greater than the promised delivery

period.

PURPOSE OF SCHEDULING

Scheduling of operations is essential for all firms as it helps them

maximize customer satisfaction and minimize service delays. Proper

scheduling enables firms allocate their production capacity to meet their

customer requirements on time. If a firm schedules too much capacity, the

facilities may remain idle, resulting in wastage of resources. Likewise,

scheduling low capacity may result in incomplete jobs at the specified time

resulting in poor service to customers. So firms should develop their

schedules in such a way that the optimum amount of resources is allocated



to meet customer requirements. For all these reasons, organizations use

scheduling in their day-to-day activities.

In spite of its short-term nature, firms consider scheduling as an

important activity that provides them a competitive advantage. For example,

firms that provide courier services emphasize package pickup and delivery

sequencing, and the scheduling of truck and aircraft movements. This is

because on-time delivery is very important to these firms and it gives them a

competitive advantage over others in the same line of business.

SCHEDULING METHODS

Forward scheduling

Forward scheduling is a scheduling method in which actual

production activities start when a job order is received. In this method, the

operations manager schedules each operation forward in time starting from

the date of production. Using forward scheduling, the operations manager

determines the start and finish times for jobs to be done by assigning them to

the earliest available time slots at the work center. As the jobs start at the

earliest possible time, they are completed before they are required at

subsequent work centres.Therefore; the work-in-process inventory level is

high in the forward scheduling method.

Forward scheduling is used in fabrication operations where the products

are so customized that customers specify the product specifications.

Backward Scheduling

The backward scheduling method schedules orders according to their due

dates. The operations manager obtains the due dates for the job orders and

develops the schedule backwards, thereby determining the latest point when



the production activity can be started in order to complete the order on time.

In this scheduling, the start and finish times of the jobs are assigned

according to the latest available time slot. For example, the Annual General

Meeting of a firm is scheduled to be held on 30th December. So the

operations manager can schedule the required operations backward in such

a way that they will be completed by the due date. This scheduling can also

be done in service organizations when the demand for services can be

anticipated earlier.

Scheduling Activities

� Operations schedules are short-term plans designed to implement the

master production schedule. � Operations scheduling focuses on how best to use existing capacity.

� Often, several jobs must be processed at one or more workstations.

Typically, a variety of tasks can be performed at each workstation.

� Job shop: A firm that specializes in low- to medium-volume production and

utilizes job or batch processes. � Flow shop: A firm that specializes in medium- to high-volume production

and utilizes line or continuous processes.

Job Shop Dispatching � Dispatching:

A method of generating schedules in job shops whereby the decision

about which job to process next is made using simple priority rules

whenever the workstation becomes available for further processing.

� Priority sequencing rules:



The rules that specify the job processing sequence when several jobs

are waiting in line at a workstation.

� Critical ratio (CR):

It is a ratio that is calculated by dividing the time remaining until a job’s

due date by the total shop time remaining for the job.

CR = (Due date – Today’s date)/Total shop time remaining

� Total Shop Time = Setup, processing, move, and expected waiting times of

all remaining operations, including the operation being scheduled.

Job Shop Dispatching

� Earliest due date (EDD):

A priority sequencing rule that specifies that the job with the earliest due

date is the next job to be processed.

� First-come, first-served (FCFS):

A priority sequencing rule that specifies that the job arriving at the

workstation first has the highest priority.

� Shortest processing time (SPT):

A priority sequencing rule that specifies that the job requiring the

shortest processing time is the next job to be processed.

� Slack per remaining operations (S/RO):

A priority sequencing rule that determines priority by dividing the slack by

the number of operations that remain, including the one being scheduled.



Performance Measures Following are the performance measures used in scheduling:

� Job flow time:

The amount of time a job spends in the service or manufacturing system. Also

referred to as throughput time or time spent in the system, including service.

� Make span:

The total amount of time required to complete a group of jobs.

� Past due (Tardiness):

The amount of time by which a job missed its due date or the percentage

of total jobs processed over some period of time that missed their due dates.

� Work-in-process (WIP) inventory:

Work in progress is any job that is waiting in line, moving from one

operation to the next, being delayed, being processed, or residing in a semi-

finished state.

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� Total inventory:

Total inventory is the sum of scheduled receipts and on-hand inventories.

� Utilization:

Utilization is the percentage of work time that is productively spent by an

employee or machine.

Gantt Charts

� Gantt chart:

Gantt Charts are simple bar charts that can be used to schedule any type of

operation

� The chart takes two basic forms: (1) the job or activity progress chart, and

(2) the workstation chart.

� The Gantt progress chart graphically displays the current status of each job

or activity relative to its scheduled completion date.

� The Gantt workstation chart shows the load on the workstations and the

nonproductive time.

Gantt Progress Chart:

Gantt Progress Chart for an Auto Parts Company

Start activity

Finish activity

Nonproductive time

Start activityStart activity

Finish activityFinish activity

Nonproductive timeNonproductive time

Scheduled activity timeActual progress

Scheduled activity timeScheduled activity timeActual progressActual progress

Current date



Gantt Workstation Chart Gantt Workstation Chart for Hospital Operating Rooms



Johnson’s Rule

� Johnson’s rule:

A procedure that minimizes makes span when scheduling a group of

jobs on two workstations.



� Step 1.

Find the shortest processing time among the jobs not yet scheduled.

If two or more jobs are tied, choose one job arbitrarily.

� Step 2.

If the shortest processing time is on workstation 1, schedule the

corresponding job as early as possible. If the shortest processing time is

on workstation 2, schedule the corresponding job as late as possible.

� Step 3.

Eliminate the last job scheduled from further consideration. Repeat

steps 1 and 2 until all jobs have been scheduled.

Johnson’s Rule at the Morris Machine Co.

Scheduling By Type of Operations

The scheduling of operations is different for different types of

operations. For instance the scheduling for manufacturing operations is

different from the scheduling of services operations. This is mainly because

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of product complexity, and greater material requirement involved in the

manufacturing process. Hence the operations manager has to take great

efforts to co-ordinate between vendors and workers.

In services operation services are delivered as when demanded. For

example a manager of the hospital has to ensure that adequate health care

facilities are provided to meet the patient’s requirement and demands.

Job Operation

Job operations refer to the manufacturing of products or services on

the basis of orders. They are scheduled as per requirements of customers.

These operations involve the production of products and services in low

volume. There is considerable variation in the materials used. Gantt charts,

job sequencing methods and critical ratio are some methods used.

Repetitive Operations

Repetitive operations are also called as continuous operation; normally

involve mass production of a product or services. Therefore there is little

variation in the production process, in this operation the labor is trained

and the equipment is designed for a narrow range of application. It

minimizes idle time and maximizes the flow of inventory. Therefore the

scheduling for these activities focuses on synchronization between customers

demand and production activities. JIT and queuing analysis are used.

Labor Intensive Operations

Manager may find it advantageous to consider the opinions of employees

while scheduling their work times, as the work involved in this operation is

routine. Some personnel related scheduling approaches are outlined below.



Flextime:

In this approach the employees are given the option of choosing their work

timings, provided that specified no. of hours is completed in a week.

Flex tour:

In this approach, employees are given some freedom in choosing their start

time, but they must work each day for eight hours.

Staggered times:

Here employees are given a option to select their work timing from a list of

shifts.

Compressed workweek:

In this approach employees have an option of working ten hours a day for

four days a week.

And

Part time

Service Operation

The scheduling of services operation is different from manufacturing

operations for two reasons



1) Services cannot be stored to meet demands of the customers at peak

hours, for example unused train seats cannot be stored for future use.

2) Variation in demand is relatively high in services operation. For

example deadlines to file income tax returns create a peak in demand

at the financial year.

Firms normally meet the peak demand by engaging part time workers.

Therefore different managers use different methods to deal with constraints.

For example an airline service provider my reduce the travel fare in the off

– season to create more demand.

Scheduling Jobs for Multiple Workstations



� Priority sequencing rules can be used to schedule more than one

operation. Each operation is treated independently.

� Identifying the best priority rule to use at a particular operation in a

process is a complex problem because the output from one process becomes

the input for another.

� Computer simulation models are effective tools to determine which

priority rules work best in a given situation.

� When a workstation becomes idle, the priority rule is applied to the jobs

waiting for that operation, and the job with the highest priority is selected.

� When that operation is finished, the job is moved to the next operation in

its routing, where it waits until it again has the highest priority.

Scheduling Jobs for One Workstation Scheduling Jobs for One

Workstation



� Single-dimension rules:

A set of rules such as FCFS, EDD, and SPT, that bases the priority

of a job on a single aspect of the job, such as arrival time at the workstation,

the due date, or the processing time.

� Priority rules, such as CR and S/RO, incorporate information about the

remaining workstations at which the job must be processed. We call these

rules multiple-dimension rules.

� Multiple-dimension rules:

It is a set of rules that apply to more than one aspect of a job.

Labor-limited Environments � The limiting resource thus far has been the number of machines or

workstations available. A more typical constraint is the amount of labor

available.

� Labor-limited environment :

It is an environment in which the resource constraint is the amount of

labor available, not the number of machines or workstations.

1. Assign personnel to the workstation with the job that has been in the

system longest.

2. Assign personnel to the workstation with the most jobs waiting for

processing.



3. Assign personnel to the workstation with the largest standard work

content.

4. Assign personnel to the workstation with the job that has the earliest due

date.

Linking Operations Scheduling to the Supply Chain

� Advanced planning and scheduling (APS) systems: Systems that seek to

optimize resources across the supply chain and align daily operations with

strategic goals. Four characteristics of these systems are:

1. Demand Planning. This capability enables companies in a supply chain to

share demand forecasts.

2. Supply Network Planning. Optimization models based on linear

programming can be used to make long-term decisions.

3. Available-to-Promise. Firms can use this capability to promise delivery to

customers by checking the availability of components and materials at its

suppliers.

4. Manufacturing Scheduling. This module attempts to determine an optimal

grouping and sequencing of manufacturing orders based on detailed

product attributes, production line capacities, and material flows.

Bibliography



Reference Book: Production Management : by L.C. Jhamb. Operations Managament : by Buffa. Websites search: www.yahoo.co.in www.google.com

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