Chapter 4 Scheduling Management New

JABATAN KEJURUTERAAN MEKANIKAL

POLITEKNIK SULTAN HAJI AHMAD SHAH

JJ619 - INDUSTRIAL MANAGEMENT

Upon completion of this course, students should be able to :•1. Apply the basic concept of industrial management system in industry.•2. Identify the suitable concept industrial management system in related industry by group.

SUMMARY•This topics elaborates on scheduling management, scheduling in high-volume system, scheduling in low-volume system.

o Identify scheduling management.oDetermine scheduling in high-volume

system.oUnderstand scheduling in low-volume

system.o Loading such as Gantt Chart, input /

output control and assignment method.

• Prescribing of when and where each operation necessary to manufacture the product is to be performed.

Under the operations function (both manufacturing and services), scheduling relates to use of equipment and facilities, the scheduling of human activities and receipt of material.

Activities: job, task, delivery, transportation, machining, milling, grinding, painting, sanding, chemical bath, ..

Resources: machines, operators, power, etc.

• To minimize processing time.• To reduce cost• To minimize completion time.• To minimize over time.• To minimize lateness.• To minimize customer waiting time.• To keep inventory levels low.• Effectively utilize personnel and

equipment.

• Scheduling is to establish the timing of the use of equipment, facilities, and human activities in an organization.

• The objective is to achieve trade offs among conflicting goals, which include efficient utilization of staff, equipment, and facilities, and minimization of customer waiting time, inventories, and process times.

• Scheduling normally starts with the Master Schedule. A master schedule resembles central office which passes information about all the orders in hand.

2 general approach scheduling:-o Forward scheduling

• scheduling ahead from a point in time.• useful to answer the question “How long will it take to complete this job?”

o Backward scheduling• scheduling backward from a future due date• useful to answer the questions:

• “Can we complete this job in time?”• “When is the latest we can start this job and still complete it by the due date?”

Scheduling of operations depends on the type of operations : Manufacturing Operations

• High-volume• Intermediate-volume • Low-volume

Service Operations

ADVANTAGES• 1. It is simple and easy to understand,• 2. It can be kept running (i.e., current)• 3. It involves less cost to make it any maintain,• 4. It can be maintained by non-technical staff, and• 5. A certain percentage of total weekly capacity can be allocated for such orders.

DISADVANTAGES• 1. It provides only overall picture, and• 2. It does not give detailed information.

Scheduling is difficult :• Modeling: real-world domains are hard to model.• Complexity: large/options, combination, explosion.• Criteria/Objectives: vague, ambiguous, difficult to

quantify, multiple objectives, conflicting objectives.• Uncertainty: unexpected events, new orders,

cancellations, changing costs/priorities, failures.• Domain-Specific Dependencies: unique heuristics

and rules of thumb - makes it hard to transfer results from one domain to another.

Levels of Scheduling (Morten) :• Long Range Planning

o Plant expansion, layout, design.• Middle Range Planning

o Production smoothing, logistics.• Short Range Planning

o Requirements, shop bidding, due date setting.• Scheduling

o Shop routing, line balancing, batch sizing.• Reactive Scheduling

o Hot jobs, down machines, late material.

Intervals• Job schedules are defined using the Intervals Daily, Weekly, Monthly, and

Yearly. Intervals are used to defined which days a job will run, what type of backup (full, incremental, differential, or copy) will be done, and how many sets of media are dedicated to the interval. The size of an interval refers to the amount of time between runs of that interval. o Daily — run on sequential weekdays. o Weekly — run once per week on the day specified by the user, for

example, Friday.o Monthly — run once per month on a day specified by the user such as

the first day, the last day, the first Monday, and others. You can also specify how many months should elapse between monthlies. Setting the monthly interval to every 3 months will create a backup every quarter.

o Yearly — run once per year on a specified day of the year. By increasing the interval you can also schedule a job to run once every so many years.

The following factors affect production scheduling and areconsidered before establishing the scheduling plan :• External factors :

o Customer's demand.o Customer's delivery dates.o Stock of goods already lying with the dealers and retailers.

• Internal factors :o Stock of finished goods with the firm.o Time interval to process finished goods from raw material.o Availability of equipment and machinery.o Availability of materials.o Additional manufacturing facilities if required.o Feasibility of economic production runs.

• High-volume systems are characterized by standardized equipment and activities that provide identical or highly similar operations on customers or products as they pass through the system. All items follow virtually the same sequence of operations.

• The goal is to get a high utilization of labor and equipment. Because of the highly repetitive nature of these systems, many of the loading and sequence decisions are determined during the design of the system.

• High-volume systems are often referred to as flow systems; scheduling in these systems is referred to as flow-shop scheduling.

• Major aspects of system design include line balancing and flow system design. o Line balancing concerns allocating the required tasks to

workstations so that they satisfy technical (sequencing) constraints and are balanced with respect to equal work times among stations. It results in the maximum utilization of equipment and personnel as well as the highest possible rate of output.

o Flow system design considers the potential discontent of workers in connection with the specialization of job tasks in these systems; high work rates are often achieved by dividing the work into a series of relatively simple tasks assigned to different workers.

Several approaches that can be used to meet the demand for varying volumes and product mixes in high-volumes and repetitive manufacturing operations are: • i. To have separate production facilities for each product and

to vary the production rate in response to the demand pattern. But this would require a high investment in various facilities that would seldom be fully utilized.

• ii. To run one large facility on a product for a while and then change to another product for a while. In this case, the rescheduling and coordinating problems could be significant.

• iii. To stabilize the product-mix and the production rate for an extended period so that, many of the advantages of just-in-time production can be achieved.

• Process and product design. Cost and manufacturability are important, as is achieving a smooth flow through the system.

• Preventive maintenance. Keeping equipment in good operating order can minimize breakdowns that would disrupt the flow of work.

• Rapid repair when breakdowns occur. This can require specialists as well as stocks of critical spare parts.

• Optimal product mixes. Techniques such as linear programming can be used to determine optimal blends of inputs to achieve desired outputs at minimal costs.

• Minimization of quality problems. Quality problems can be extremely disruptive, requiring shutdowns while problems are resolved. Moreover, when output fails to meet quality standards, not only is there the loss of output but also a waste of the labour, material, time, and other resources that went into it.

• Reliability and timing of supplies. Shortage of supplies is an obvious source of disruption and must be avoided. On the other hand, is the solution is to stockpile supplies, that can lead to high carrying costs. Shortening supply lead times, developing reliable supply schedules, and carefully projecting needs are all useful.

• Job Shopso products are made to order.o orders differ considerably in their processing

requirements.

• Job-shop schedulingo Scheduling for low-volume systems with many

variations in requirements.

• Loading - assignment of jobs to process centers.

• Sequencing - determining the order in which jobs will be processed.

• In low-volume systems, products are made to order, and orders usually differ considerably in terms of processing requirements, materials needed, processing time, and processing sequence and setups. Because of these circumstances, job-shop scheduling is usually fairly complex. This is compounded by the impossibility of establishing firm schedules priori to receiving the actual job orders.

• Job-shop processing gives rise to two basic issues for schedulers: • loading, how to distribute the workload among work

centers, and• sequencing, what job processing sequence to use.

• 1. Loading• Gantt chart (used as a visual aid for loading and

scheduling) – Load chart and Schedule chart.• Input / Output control.• Assignment method.

• 2. Sequencing• Priority rules – FCFS, SPT, EDD, CR, S/O and

Rush.• Sequencing jobs through two work center –

Johnson’s Rule.• Sequencing jobs when setup time are sequence-

dependent.

Definition :o Assigning specific jobs to each work centres for the planning period.

Type of Loading :• 1. Infinite loading. Jobs are assigned to work centres without regard to

the capacity of the work centres.• 2. Finite loading Jobs are assigned to work centres with regard to the

capacity of the work centres and job processing times.• 3. Vertical loading: Loading jobs at a work centres, job by job, usually

according to some priority criterion, using infinite loading i.e. Jobs are assigned to work centres without regard to the capacity of the work centres.

• 4. Horizontal loading: Loading each job on all work centres it will require, then the next job on all work centres, according to some priority, using finite loading i.e. Jobs are assigned to work centres with regard to the capacity of the work centre and job processing times.

• Gantt Charto Simple graphical display technique – suitable for

less complex situations,o Chart used as visual aid for loading and

scheduling purposes.o Can be used in a number of different ways.

• This does not provide any rules for choosing but simply presents a graphical technique for displaying results (and schedule) and for evaluating results makespan (completion time), idle time, waiting time, machine utilization, etc.)

• Progress charts:

o Illustrates the planned schedule compared to actual performanceo Brackets show when activity is scheduled: start to finish. Design

and pilot run both finished late and feedback has not started yet.

• There are a number of different types of Gantt charts. Two of the most commonly used are the load chart and the schedule chart.

• Load Chart• A load chart depicts the loading and idle times for a group of machines

or a list of departments. The chart shows when certain jobs are scheduled to start and finish, and where to expect idle time.

• Schedule Chart

• There are two general approaches to scheduling: forward scheduling and backward scheduling. Forward scheduling means scheduling ahead from a point in time, "How long will it take to complete this job?" ; backward scheduling means scheduling backward from a due date, " When is the latest job can be started and still be completed by the due date?“

• Input / output (I/O) control refers to monitoring the work flow and queue length at work centres.

• The purpose is to manage work flow so that queues and waiting times are kept under control. Example :

• The assignment method is used to determine what resources are assigned to which department, machine or centre of operation in the production process.

• This method is used to allocate the proper number of employees to a machine or task, and the number of jobs that a given machine or factory can produce.

• Any quantitative or qualitative methodology by which one determines how to assign capital, employees, and almost anything else as efficiently as possible.

• For example, an assignment method may help a company determine how many employees it puts on a task or how much a major project should cost.

• The following table contains information on the cost to run three jobs on four available machines. Using the assignment method, determine an assignment plant that will minimize costs.

• Row operation

• Column operation

• Assign the machine

• Select the smallest not covered by lines. • Subtract it from all the other number which are not covered by line. • Add the number at the intersection of horizontal and vertical.

• Assign the machine

• The optimal assignment is :

• Total cost of assignment = RM 27

• Definition:-o Specifies the order in which jobs should be

done at each center.o Priority sequencing is a systematic procedure

for assigning priorities to waiting jobs thereby determining the sequence in which the jobs will be performed.

• Example :o Suppose that ten patients are assigned to a

medical clinic for treatment.

• 1. Set up cost.• 2. In process inventory.• 3. Idle times.• 4. Average time to complete jobs.• 5. Average number of jobs waiting in the queue.• 6. Average time the jobs are late.

• FCFS (first come, first served)o Given top priority to the waiting job that arrived earliest in the

production system.• SPT

o job with shortest processing time is processed first.• EDD (Earliest due date )

o job having earliest due date is processed first.• CR (critical ratio)

o job having smallest critical ratio (time remaining until due date/ processing time remaining) is processed next.

• S/O (slack per operation)o job processed according to average slack time = (time until due date

– remaining time to process)/(number of remaining operations).• Rush

o emergency or preferred customers go first.

The priority rules can be classified as either local or global. • Local rules take into account information pertaining only to a

single workstation; global rules take into account information pertaining to multiple workstations. FCFS, SPT, and EDD are local rules;

• CR and S/O are global rules. Rush can be either local or global. Global rules require more effort than local rules.

• A major complication in global sequencing is that not all jobs require the same processing or even the same order of processing. As a result, the set of jobs is different for different workstations. Local rules are particularly useful for bottleneck operations, but they are not limited to those situations.

• Average completion time = Total flow time No. of jobs

• Average number of jobs in the system = Total flow time . Total process time (completion)

• Average job lateness = Total job lateness No. of jobs

• Critical ratio (CR) of less than one means that the job is already late.

• The critical value of one indicates that the job is on schedule and greater than one indicates that the job has some slack available to it.

• The critical ratio is computed as :• Critical ratio (CR) = Time remaining for due date of the job Time needed to complete the job = Time remaining

Work remaining = Tr Tn• The lower is the critical ratio and higher is its priority.

• The processing times for five jobs and their due dates a given for a single machine scheduling below :-

• Using FCFS, SPT, EDD, and CR. Determine :› i) The sequence of jobs› ii) Total completion time› iii) Average completion time› iv) Average number of jobs› v) Average delay (lateness)

The sequence of jobs= A-B-C-D-E

Total completion time= 38 days

Average completion time= 116 5= 23.2 days

Average number of jobs= 116 38= 3.05 jobs

Average delay= 17 5= 3.4 days

The sequence of jobs= D-A-B-C-E




Average delay= 18

5= 3.6 days

The sequence of jobs= C-E-B-A-D





• Using the critical ratio, we find :

• At day 11 (D completed), the critical ratios are :

• At day 20 (D and A completed), the critical ratios are :

• At day 27 (D, A and B completed), the critical ratios are :

The sequence of jobs= D-A-B-C-E





• SPT often performs very well, especially when trying to speed jobs through system (minimize flow time) and minimize WIP inventories FCFS often chosen when managers are interested in completing the project early.

• Use S/O (slack per operation) rule to schedule the following jobs. Note that processing time includes the time remaining for the current and subsequent operations. In addition, you will need to know the number of operations remaining, including the current one.

Job Remaining

processing time (PT) Due Date

(DD) Remaining. number of

operation (OP)

A 4 14 3

B 16 32 6

C 8 8 5

D 20 34 2

E 10 30 4

F 18 30 2

• Determine the difference between the due date and the processing time for each operation. Divide the amount by the number of remaining operations, and rank them from low to high. This yields the sequence of jobs:

• The indicated sequence is C-B-A-E-F-D.• Using the S/O rule, the designated job sequence

may change after any given operation, so it is important to re-evaluate the sequence after each operation.

• Note that any of the previously mentioned priority rules could be used on a station-by-station basis for this situation; the only difference is that the S/O approach incorporates downstream information in arriving at a job sequence.

• “In operations research Johnson's Rule is a method of scheduling a number of jobs on two successive work centers. The primary objective of Johnson's Rule is to find an optimal sequence of jobs to reduce makespan (the total amount of time it takes to complete all jobs). It also reduces the number of idle time between the two work centers”.

• Is a need for determining an optimum order of performing a number of jobs by number of facilities according to some pre-assigned order so as to optimize the output in terms of cost, time and profit.

Assumptions :

• 1) No machine can process more than one job at a time.• 2) Processing times are independent of processing of jobs.• 3) Each job once started on one machine is continued till completion on it.• 4) Time involved in moving a job from one machine to another is negligibly small.

Johnson's Rule is as follows :• List the jobs and their times at each work center.• Select the job with the shortest time. If the job is for the

first work center, then schedule the job first. If that job is for the second work center then schedule the job last. Break ties arbitrarily.

• Eliminate the job selected from further consideration.• Repeat steps 2 and 3, working towards the center of the

job schedule until all jobs have been scheduled. “In case there is significant idle time at the second work

center (from waiting for the job to be finished at the first work center), then job splitting may be used.”

n jobs and 2 machine problem :• There are only two (2) machines A and B.• Each job is processed in the order A and B.

Procedure :• Step 1 : Select the smallest processing time from the given list of

processing times A1, A2,…An and B1, B2,…Bn.• Step 2 : If the minimum processing time is Ar, do the rth job first in the

sequence. If the minimum processing time is Bs, do the sth job last in the sequence.

• Step 3 : after doing this step, (n-1) jobs are left to be sequenced. Repeat step 1 and step 2 till all the jobs are ordered.

• Step 4 : Find the total processing time as per the sequence determined and also determine idle time associated with machines.

n jobs and 2 machine problem :

Elapsed time :•To compute the elapsed time, •The starting time on machine M1 is assumed as 0.00.•The machine M2 starts processing job 2 only when it comes out of machine M1 after completion. So it is idle for 1 hour in the start till job comes to it from machine M1.

• Five jobs are to be processed on two machines M1 and M2 in the order M1M2. Processing time (hours) are given below :

• Determine the sequence that minimizes total elapsed time. Find out the total elapsed time and idle time (if any) on M2.

• 1) Determine the sequence : • (i) The minimum processing time is 1 for job 2, machine M1.

• So, job 2 should be processed first in the sequence.

• (ii) Once the job 2 is over, it is excluded from the list. The reduced list of processing times for remaining jobs are :

• Now, the minimum processing time is 2 for job 1, machine M2. Process job 1 last in the sequence.

• (iii) The processing times for remaining jobs are :

• The minimum processing time is 3 for job 4 machine M1. So, process job 4 next in the sequence.

• (iv) The processing times for remaining two jobs are :

• The minimum processing time is 4 for job 5 machine M2. So, process job 5 last in the sequence.

• (v) The optimal sequence is :

• 2) Total elapsed time :

• The minimum total elapsed time is 30 hours to process all the 5 jobs through two machines M1 and M2.

• Sketch the time bar chart : Machine 0 1 4 13 23 28 M1

M2 1 7 15 22 23 27 28

30 1 1 1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Time (hrs)

• 3) The idle time on machine M2 :

The idle time = 1 + 1 + 1 = 3 hours.

• The simplest way to determine which sequence will result in the lowest total setup time is to list each possible sequence and determine its total setup time.

• As the number of jobs increases, a manager would use a computer to generate the list and identify the best alternative(s).

Resulting following job setup time (hrs) is

Setup time (hrs) A B C

If the proceding

job is

A 3 - 6 2

B 2 1 - 4

C 2 5 3 -

Solution: B-A-C.

Sequence Setup Time Total

A-B-C 3+6+4= 13

A-C-B 3+2+3= 8

B-A-C 2+1+2= 5

B-C-A 2+4+5= 11

C-A-B 2+5+6= 13

C-B-A 2+3+1= 6

Chapter 4 Scheduling Management New

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