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COBACABANA (CONTROL OF

BALANCE BY CARD BASED

NAVIGATION): A CARD-BASED

SYSTEM FOR JOB SHOP CONTROL

Seminar Report

By

Lijo John

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CONTENTS

1. INTRODUCTION

2.PARADIGM SHIFT

3.WLC PARADIGM

4.WLC CONCEPTS

5.WLC FEATURES FOR JOB SHOP

6.CONCEPTUAL BACKGROUNDS

7. THE COBOCABANA SYSTEM

8. EXAMPLE

9.CONCLUSION

10. REFERENCE

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ABSTRACT

Since late 1940s Kanban, a card based control system was in use, but kanban is

still being used for the repetitive manufacturing. Thus in case of a make to order

job shop manufacturing this card based system fails. Thus a need for a new card

based system was realized for the job shops. The Cobacabana ( control of

balance by card based navigation) system is being proposed here by the

author. This system is based on the concept of work load control (WLC). Due to

recent developments in the understanding of the concepts of the work load

control it has become possible to convert the work load into a robust card

system. Here the card system is being divided into two. First is the release cards

which form a loop catering to release functions of the job to shop floor. Second

is the acceptance cards that forms the basis of accepting a order by the sales

department. Finally the implementation issues are also discussed in general

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1. INTRODUCTION

Small- and medium-sized enterprises (SMEs) in the make-to-order (MTO) sector

are of great interest, as they are a relevant part of the industrial infrastructure.

These companies have to react on turbulent environments: they have to cope

with changes in product mix and volume, production rate changes, a high

number of rush orders, and lot of internal uncertainty. As a consequence,

production planning and control (PPC) in MTO companies is rather complex and

often based on insecure data. Since a good functioning of the PPC concept is

crucial for the economic success of the enterprise, the selection of a fitting PPC

concept is an important decision process.

Industrial practice shows that hardly any job shop is able to use the planning and

control modules provided in its ERP-package. Many solutions provided in ERP-

packages focus on Gantt chart or Leitstand scheduling, which is generally

doomed to fail in job shops because of the high data maintenance

requirements and because of their high sensitivity to uncertainty, resulting in

unstable schedules. Other ERP- packages only provide material-oriented

planning solutions such as MRP, while capacity planning and control is critical in

most job shops. To prevent from turning back to legacy systems, these

companies often opt for a planning and control system which can be

implemented with limited software support. This creates an obvious need for

card-based systems in job shops.

The popularity of card-based control systems has been rising since the

introduction of Kanban as a material control system for repetitive manufacturing

environments. During the last decennium new card-based systems such as

POLCA (Suri, 1998) have been developed, which can be implemented in

capacity-oriented control situations. The Generic POLCA system (Fernandes and

do Carmo-Silva, 2006) can be seen as an important step to make POLCA

principles suitable for the specific situations of job shops. It links POLCA card loops

with capacity allocations at the order release decision. Still, the basic idea of

POLCA to use card loops for each possible combination of successive work

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centers will reduce its practical applicability in shops with high routing mix

variability. In a computerized system, POLCA principles have been adapted for

use in a job shop. But, as also concluded by Stevenson et al. (2005), none of the

currently available card-based systems will meet the dynamic requirements of

job shop manufacturing.

2. WLC PARADIGM

The WLC concept is based on principles of input/output control. Input control

relates to both accepting orders and releasing them to the shop floor. WLC

conceptualizes the job shop as a queuing system. In front of each work station,

an arriving job finds a queue of jobs waiting to be processed. The principle of

WLC concepts is to control the length of these queues. The main instrument for

this purpose is the release decision. The release decision allows a job to enter the

queue of its first work station in the shop. Once released, a job remains on the

floor until all its operations have been completed. The progress of jobs on the

shop floor is controlled by priority dispatching at each work

station.

WLC concepts do not release jobs to the shop floor if they are expected to

cause queue lengths to exceed certain workload norms. It results in a pool of

jobs waiting for release. As illustrated by Fig. 1 we refer to waiting time in the pool

as the pool time and to the interval between release and completion of a job as

the shop floor flow time. The shop floor flow time of a job can be subdivided into

station flow times. The pool is a new object of control. Unrestricted acceptance

of jobs at the entry could cause excessive pool times.

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Fig. 1. Lead time components.

A hierarchical control concept emerges [Kingsman et al, 1989], with three levels

which respectively relate to job entry, job release and priority dispatching (Fig. 2).

At each level, we distinguish two means of control, input control and output

control. Input control regulates the allowance of jobs to the next stage,

respectively accepting jobs for entry into the pool, releasing jobs to the shop

floor, and dispatching jobs for processing (thus allowing a job to enter the queue

of its next operation). On the output side, capacity management contributes to

the control of workload through regulation of the outward flow, by means of

respectively medium-term, short-term and daily capacity adjustments.

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Fig. 2. The hierarchical WLC concept.

The job entry level is very important, if one can influence the incoming orders. In

that case, order acceptance and due date assignment/acceptance can

support the release decision, providing it with a 'releasable' set of jobs, thus

keeping pool times small. In fact, the job pool between entry and release acts as

the visualized imbalance between job supply and production capacities. The

role of priority dispatching in WLC is a very modest one, because the choice

among jobs is limited due to short queues. Generally, WLC concepts favor

dispatching priorities such as first come- first-served (FCFS) which stabilize

operation flow times or due date oriented priorities which correct progress

differences among jobs. These kinds of priorities facilitate a good timing of job

release. However, the major strength of WLC concepts is withholding jobs from

the shop floor, reducing average queue lengths. Besides a reduction of work-in-

process, withholding jobs from shop floor has numerous additional advantages

as it enables management to delay final production decisions [Irastorza et al,

1974]. It reduces waste due to cancelled orders, facilitates later ordering of raw

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materials, takes away the need of expediting of rush orders, etc. Fluctuations in

the incoming order stream should be absorbed by the pool. Altogether, it should

create a stable stationary situation on the shop floor. Only restricting queue

lengths is generally not sufficient. If average queue lengths decrease but

variances do not, the idle time at work stations will increase. This situation is not

allowable for the common job shop, where many work stations can be

temporary bottlenecks. The loads of potential bottlenecks should be kept close

to a norm level instead of below a norm level. The release function which aims at

short queue lengths and a reduced variability of queue lengths is called load-

balancing.

In summary, WLC concepts try to create a situation on the shop floor of short and

stable queues. A pool of unreleased jobs, buffers the shop floor against external

dynamics, the incoming non-stationary job stream. The queuing of jobs on the

shop floor is turned into a stationary process. Release performs a key-role in

reaching this stationary situation. It is the most elaborated function within WLC

concepts.

3. WLC CONCEPTS

In the preceding section we have seen that release should control the queue

lengths in front of each work station. The queues must be short and stable, the

load-balancing function. On the other hand, each job should be released timely

with respect to its planned due date and expected flow time, the timing

function.

Leaving out capacity decisions at the release level, two components of the

release decision are distinguished: a sequencing decision and a selection

decision. The sequencing decision can be described as the setting of priorities for

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jobs to be released, 'selection' decides whether a job will be released or not at

some specific moment. Most WLC concepts focus the sequencing decision on

timely release and create due date based sequences. Taking into account this

sequence, release selects a set of orders that keep the workload of work stations

at certain norms. These workload norms are the main instrument of workload

control.

Three WLC concepts have been discussed in detail here.

3.1.Bechte's WLC concept

The release procedure proposed by Bechte [1988] builds on three parameters: a

release period,a time limit and a load limit. The decision to release jobs is taken

periodically, at the beginning of each release period. All jobs in the pool are

sequenced in order of their planned release date. The planned release date is

determined by backward scheduling from the job due date: norm station flow

times for all work stations in the routing of the job are subtracted from its duedate. All jobs within the time limit from their planned release date are candidates

for release. In the established sequence, jobs are released, until the workload

norm of a work station, the load limit, is exceeded for the first time. All other

candidates visiting this station have to wait in the job pool until the next moment

of release. The selection process goes on for the remaining candidates.

The workload considered in the concept of Bechte is the queue length at a work

station (in units of processing time). The workload is controlled by the load limit.

The load limit LLs of a work station s consists of two components: the planned

output during the release period and the planned queue length at the end of

the release period. The actual output Os, during the release period and the

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actual queue length QEs at the end of the release period satisfy the balance

equation:

QEs + Os = QBs + Is

with

QBs: the queue length at the beginning of the release period,

Is : the input to the queue from jobs arriving during the release period.

The release decision at the beginning of the release period must bring Q Es + Os at

the norm level LLs. The above balance equation is used. QB

s is known at themoment of release, the queue input Is is influenced by the jobs on the floor

upstream of s and by the release of new jobs.

3.2.Bertrand's WLC concept

Bertrand developed a WLC concept for the diffusion department of asemiconductor plant [1981]. Bertrand does not discuss the release sequence, but

elaborates the workload norms extensively. The release decision is taken

periodically and the release of jobs is allowed if the workload of each work

station remains below its norm value.

The workload definition of Bertrand covers the processing time of all jobs on the

shop floor which still have to be processed at the work station concerned. The

corresponding workload norm consist of two components: the planned work

station output during the release period and the planned quantity of work

upstream or in the queue at the end of the release period. An extended

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balance equation can be used to determine the actual workload of a work

station s at the end of the release period:

( UEs + QEs ) + Os = ( UBs + QBs ) + Rs

with UEs as the processing time (on s) of jobs upstream at the end of the release

period, UBs as the processing time of jobs upstream at the beginning of the

release period, Rs as the processing time of jobs released at the beginning of the

release period. At the moment of release the right-hand side of this equation is

completely known. The processing times of all jobs which are newly released are

the input to the workload. Thus, the release of new jobs directly influences the

workload. The release decision can be made without a sophisticated estimation

procedure.

3.3.Tatsiopoulos WLC concept

Tatsiopoulos [1993] developed a WLC concept for a small subcontracting

component manufacturer. The common push release takes place periodically,

intermediate push release can be forced by rush orders or orders with retardedmaterial availability, and an intermediate pull release can be triggered from the

floor when a foreman sees his station threatened by unplanned idleness. The

periodic release decision considers the orders in the sequence of their planned

latest release date. The calculation of the planned release dates is rough

compared with Bechte. For each job the same norm shop floor flow time is

subtracted from the job due date. The release of jobs is allowed unless a

workload norm is exceeded, which applies to the intermediate pull releases as

well. Additionally, a minimum workload is suggested. This definition covers all

work on the shop floor, even work completed at the work station concerned. For

each work station a norm is set for the accumulated processing times of jobs

upstream, job in the queue, and jobs downstream. The corresponding actual

workload satisfies the following balance equation

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( UEs + QEs + DEs) + Cs = ( UBs + QBs + DBs) + Rs

with DEs as the processing time (on s) of jobs downstream at the end of the

period, DBs as the processing time of jobs downstream at the beginning of the

period, Cs as the processing time of jobs which leave the shop during the release

period. All other variables as defined before. Again all right-hand-side

components are known at the moment of release. The WLC concept does not

clarify whether the shop output Cs from jobs fully completed during the release

period is included in the workload norm. Notice that the workload definition

further simplifies keeping up with the actual workload as it avoids the need for

data regarding the completion of single operations. The completion of the jobcan be reported when it leaves the shop floor.

4. WLC FEATURES FOR JOB SHOP

Most classical variants of the WLC concept take the release decision periodically

according to the following procedures. Orders in the pool are considered for

release in the sequence of their planned release dates. The order being

considered is added to the release selection as long as its release will not cause

any workload norm to be exceeded. Otherwise the order will have to wait in the

pool until the next release opportunity. An order with a later planned release

date maybe selected when it does fit in the norms. After this procedure is

completed, selected orders are sent to the capacity groups performing the first

operation and remain on the shop floor until all operations have been finished.

The five most distinguishing elements of the WLC approach to shop floor control

are the control point at release, the use of aggregate measures, resource

buffering, shop floor buffering, and central load buffering.

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5.1 Control point at release

The main control point of the WLC concept is the release decision. This decision

precedes the first shop floor operation of the orders. At this point fitting the orders

into workload norms should create predictable operation lead times.

Downstream on the shop floor, simple priority rules at capacity group s are

sufficient (Bechte, 1994). Examples of priority rules are first-come-first served,

which guarantees the smallest variation of operation lead times, or due-date-

oriented rules to correct for individual progress disturbances among orders. No

sophisticated methods are used for controlling the downstream operations of theorders. Although some of the orders arriving at a capacity group may come

directly from the pool, a significant amount may come indirectly via other

capacity group s which perform the upstream operations of the order ( Fig. 3).

Fig. 3. Control point at release.

5.2Aggregate measures

The decision to allow an order for release depends on the shop floor situation,

which is reflected in workloads. Workloads are calculated as an aggregate of

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essentially designed for situations where queues are inevitable, coping with

variations in order arrival and processing times

Fig. 5. Resource buffering.

5.4Shop floor buffering

Even though resources are buffered by queues, these queues are kept small. As

far as possible the waiting time is placed before the first operation in the form of

pool waiting time. Thus, the main buffer is placed before the shop floor (Fig. 6).

The pool should absorb all kinds of fluctuations in the arriving order flow in order

to keep the resource buffers small and stable. Pool waiting times of orders may

vary according to their urgency, which is reflected in the slack to planned

release dates, and whether they fit well into the shop floor situation, which is

reflected in the workloads.

Fig. 6. Shop floor buffering.

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5.5 Central load balancing

The main decisions of WLC are made centrally. The release decision compares

the urgency of orders and balances loads among capacity group s. This requiresa global view of the shop. As mentioned before, local decisions at individual

capacity group s can be based on simple priority dispatching rules not requiring

global information.

The central balancing of loads by fitting the orders from the pool into workload

norms (Fig. 7) will keep the resource buffers stable, despite variations in the

arriving order flow.

Fig. 7. Central load balancing

6.CONCEPTUAL BACKGROUNDS

The philosophy underlying WLC is based on creating predictable and short

throughput times for each critical workstation. Particularly, predictable and short

through- put times are lacking in most job shops because of all types of variability

that characterize this environment. Nevertheless, predictable throughput times

are important for a good timing of order releases, for quoting realistic delivery

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times and for a good timing of capacity adjustments. Short shop floor throughput

times increase the flexibility to deal with possible customer order changes,

changes which are not uncommon in most job shops. Besides, short throughput

times encompass the direct advantages of a transparent shop floor with low WIP.

A predictable short throughput time at a workstation is enabled by keeping its

direct load at a constant level, the direct load being measured as the sum of the

processing times of orders waiting or already being processed at the workstation.

Before being released orders will wait in a centrally controlled order pool. The

pool buffer can absorb both fluctuations in capacity requirements and capacity

availability. It is obvious that constant direct loads can only be realized by

releasing an appropriate set of orders to the shop floor. This function of order

release has been indicated as its load-balancing function (Land and Gaalman,1996). It should be recognized that order release is the last moment one can

effectively contribute to a constant direct load. The effectiveness of load-

balancing dispatching rules (e.g. Work-In-Next-Queue) after release is limited.

The direct load LDst of workstation s at time t being the sum of processing time so

fall orders waiting or being processed can be specified by equation .In the

calculations below orders will be addressed as jobs.

with pjs is the processing time of job j at station s; J the set of all existing jobs; tQjs

the time of arrival of job j at station s; tCjs the time of completion of job j at station

s. The indicator function I(t) is defined as I(t) = 1 at the specified interval, I(t) = 0

otherwise.

Notice that the release of a job will not directly affect the direct load of a

workstation, unless the station performs the first operation in the routing of the

job. Therefore a group of classical release methods focuses on controlling

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aggregate loads. Aggregate loads additionally incorporate all work which is still

upstream of the workstation being considered. The aggregate load LAst of station

s at time t can be specified by

with tjR time of release of job j (all other variables as defined before).

The control of aggregate loads does not necessarily leads to control of direct

loads in case of a fluctuating routing mix (Land ,2004). Moreover, the average

direct load LDst resulting from the set of jobs in the aggregate load of a

workstation will be at the level calculated as

Therefore ,the adjusted aggregate load norms as presented by Oosterman et

al.(2000) can be used for keeping the average direct loads as calculated by

equation at a constant level. Not the full processing times pjs of a job being

released are considered to be its contribution to the calculated loads but the

processing times multiplied with the fraction (tCjs- tQjs)/(tCjs- tRj). This fraction is the

ratio between the throughput time of the workstation considered and the up-to-

station throughput time. This up- to-station through put time consists of the

summed throughput times of all stations in the routing of the job upstream of the

station considered plus the station itself. When throughput times are well

controlled , the station throughput times can be estimated by their planned

values(TD

s), which results in a workload calculated for workstation s.

with Ujs: the set of stations in the routing of j up to and including station s.

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In the simple case of equal planned values for all workstations the estimated

ratio will simply be equal to 1/njs with njs being the routing position of station s. In

that case each job being released will in crease the workload with pjs/njs for

each station s in its routing. After the respective operation at a station is

completed, the workload will decrease accordingly.

The above equations have been developed in WLC research to facilitate the

specification of a constant norm level independent of routing mix changes. The

norm level forestation can be specified as its planned direct load level and

according to Littles result (specified in terms of processing time units, see Land,

2004) the planned direct load should be proportional to the planned station

throughput time. But even when the planned throughput times to be realized are

the same, each station may still require a different workload level, since

capacities may differ among stations. Therefore, further standardization can be

realized by depreciating the direct load contributions by the maximum output

O*Ds of station s during the planned station throughput time (T *Ds ). The maximum

output is a fraction of the stations capacity as100%utilizationcannotberealized. It

is measured in processing time. After transforming this into a percentage, the

workload calculation results in the following:

Thus, when each job contributes an amount Cjs as specified to the calculated

workload, this can further simplify norm setting. The norm for the workload LDst

can simply be set at 100% for each station and planned station throughput times

T*Ds are the main parameters to be specified.

Analogously to traditional WLC approaches, there lease method may allow

release of a job j as long as its load contribution Cjs will

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notcausethe100%normofanystation in its routing to be exceeded. A job is

included in the workload of each station in its routing from the moment it is

released to the shop floor until completion of the operation at a station. The load

contribution Cjs can be interpreted as the percentage of the planned average

station throughput time T*Ds which is filled by releasing this job.

The sequence of considering jobs for release is classically based on their planned

latest release dates t*Rj which can be derived from the due date j and the

planned station throughput times T*D .

with sj is the set of stations in the routing of job j.

By creating constant norm levels, the above definitions and calculations can be

used for translating workload requirements into numbers of cards. This forms the

starting point for development of the card-based system for job shop control.

7. THE COBOCABANA SYSTEM

The system will be briefly addressed as the Cobacabana system. The

Cobacabana system has been organized around the order acceptance and

order release decisions, being key decisions in job shop control.

7.1Order release and shop floor control

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The Cobacabana system uses card loops between the planner performing there

leases and all critical workstations. Fig. 8shows these loops for an example order

having the routing sawing-turning-drilling- finishing . In the figure each operation

has a different texture. In practice each operation has its own color.

Fig. 8. Cobacabana release card loops ,between release and workstations.

The release cards authorize the planner to release new orders. To release an

order the planner has to attach the right amount of cards for each work station

in the order routing to the order guidance form. The cards relating to a certain

work station return to the planner after completion of the operations performed

by the considered station. The system balances the work load for all critical

workstations by allowing a fixed number of cards summing to 100% per station on

the shop floor.

The task of the planner is supported by a display for collecting and distributing

the cards. The simple display, as shown in Fig. 9, gives a quick overview of the

situation on the shop floor. In Fig. 9each card represents 5 percent. Empty card

positions indicate the percentage of the planned station throughput time

already filled by released orders. The available cards on the display show the

possibilities for new releases. An even distribution of released cards a cross

stations indicates a workload which is well-balanced across stations. Similarly,

momentary bottle necks can be easily identified, which is mandatory for focused

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decision making in a job shop. E.g. the lathes required for turning seem to be the

restrictive resource for new releases in the situation depicted in Fig. 9.

Fig 9:Display of available release cards, indicating the actual shop floor situation

7.2. Order acceptance and due date promising

The release system can be extended for support of the order acceptance and

due date promising function. A minimal delivery time djmin for an order can be

determined by adding an estimated waiting time T*Pj in the order pool before

release to the sum of planned throughput times T*Ds for stations in the routing of

the order

Since the Cobacabana system keeps station throughput times at a constant

level, the waiting time T*Pj before release is the only variable component of the

delivery time. It can be estimated from the requirements of orders already

waiting for release. The station with the largest amount of work in the pool

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determines the waiting time before release. Thus, estimating this waiting time can

be supported by a card loop between the planner performing release and the

sales department accepting the orders. The card loop for the acceptance cards

is depicted in Fig. 10.

Until it is being released, each accepted order requires a number of

acceptance cards Ajs per workstation s as

Fig 10 Cobacabana acceptance card loops, between order acceptance and release

Notice that the denominator O*Ds /T*Ds specifies the maximum output (in

processing time units) per day. Thus each card represents a fraction of a working

day.

The acceptance cards are withdrawn from an acceptance display as depicted

in Fig. 11. In Fig. 11each card represents one-fifth of a day. A number of cards

amounting to 3 working days have been withdrawn from this display for turning.

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This means that a minimal pool waiting time of 3 days is to be expected for

orders requiring a turning operation, since orders already waiting for release will

require 3 days of turning work. To determine a realistic delivery time the

estimated pool waiting times can be

used and some slack should be added.

7.3. Use of the system

The Cobacabana system, in a job shop in real time would work like as

summarized below. The steps are given in the order it has to be followed in the

job shop

1. New order is being placed.

2. Sales department estimates realistic the delivery dates.

3. Process planner determines the routing and processing time of the order

received.

4. Latest release date is calculated.

5. Numbers of acceptance cards are determined.

6. Percentage requirement of release planning is determined and being

translated into number of cards.

7. Required numbers of release cards are removed from the display and are

being attached to the order guiding forms. If enough cards are not

available then the non-priority jobs are being released depending on the

availability of the cards.

8. After releasing the job the acceptance cards are removed from the order

guiding form and are placed back on the acceptance display.

9. Release planner sorts them into order of latest release dates.

10.Releases the order by removing the required number of cards from the

display.

11.On the floor the order are served as FCFS.

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The role of the cards in the Cobacabana system can be summarized as follows.

The constant number of cards moving between the release function and the

workstation will keep the station throughput time within their planned levels,

allowing for a good timing of order releases and for predictable throughputtimes when promising delivery dates. The procedure of selecting orders for

release will ensure that also the relative urgency of orders is considered .The use

of acceptance cardswithdrawn from the acceptance displayenables a

good estimate of the waiting time before release, which is the main variable

component to be estimated for quoting a realistic delivery date.

8. EXAMPLE

Consider a job arriving at the job shop which requires the following operation in

the sequence-

OPERATION

TIME

(mins)

SAWING 20

TURNING 30

POLISHING 40

DRILLING 15

FINISHING 25

Calculations for the implementation of Cobacabana system can be summerised

as below

1. Minimum delivery time

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Assuming this is the first order, therefore no waiting time (T*Pj = 0)

djmin = 20 + 30 + 40 + 15 + 25

= 130 min

2. Latest release date

Assuming due date to be 150 min

t*Rj = 150 130

= 20 min

3. Acceptance cards

Assuming O*Ds (maximum output) turning operation is 100 min(assuming no

machine failure)

Then O*Ds / T*Ds = 100/20

= 5 uts/hr

Therefore Ajs (turning) = 20/5

= 4 cards

4. Contribution to workload

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C js = 20%

Calculation for other operations are being summarized in the table below

Table.1 calculations for the number of cards

OPERATION

TIME

(mins) Ods

Ods/Tds

(uts/hr) Ajs Cjs

SAWING 20 100 5 4 20%

TURNING 30 180 6 5 4%

POLISHING 40 160 4 10 10%

DRILLING 15 45 3 5 11%

FINISHING 25 125 5 5 5%

9.CONCLUSION

A new card based system has been designed by using the workload control as

the controlling factor. Due to the recent advances in understanding the

concept of workload control, it is possible to convert the workload into cards.

These cards can be effectively managed, controlled and navigated to obtain

the balance in the system. Cobacabana is essentially a link between the sales

department and the operations department of the industry. It has enabled the

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sales department to quote realistic delivery dates with the help of the

acceptance cards and operations planner to release new orders with the help

of the release cards.

Cobacabana tries to achieve the control in the system by controlling the

throughput times, since the throughput time control is the factor which allows

good timing of the order release and promising realistic delivery dates. The

restricted number of cards in the system restricts the workload from increasing

indefinitely. The card based system gives the planner a very accurate idea of the

shop floor by just looking at the display. This helps the planner to identify the

bottleneck station immediately and take necessary actions. This information can

be crucial in other strategic and planning activities. This system lets the cards to

go around in a loop between the acceptance and release of the order,

therefore, by observing the number of cards in the loop will give an idea aboutthe length of the waiting time in the queue before the release. Simple priority

dispatching rule is being used to process the jobs, once they are in the shop

floor. Thus without using a computerized system we can effectively manage the

complexities arising in the job shop. The developed Cobacabana system

enables this control of balance by card based navigation.

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10. REFERENCE

Land,M.J,2009,Cobacabana(control of balance by card-based navigation):

A card based system for job shop control, International Journal of Production

Economics, 117,97-103

Suri, R.,1998.Quick Response Manufacturing: A Company wide Approach to

Reducing Lead Times. Productivity Press ,Portland , OR.

Fernandes, N.O.,doCarmo-Silva,S.,2006.GenericPOLCAA production and

materials flow control mechanism for quick response manufacturing.

International Journal of Production Economics104, 7484.

Stevenson,M.,Hendry,L.C.,Kingsman,B.G.,2005. A review of new and

established production planning and control (PPC)methods and their

applicability to make to order (MTO) companies. International Journal of

Production Research ,43,869898.

Land,M.J.,Gaalman,G.J.C.,1996.Workload control concepts in job shops: A

critical assessment .International Journal of Production Economics 4647,535

548

Kingsman , B.G, Tatsiopolous, I.P and Henry, L.C, 1989, A structural

methodology for managing lead times for make to order companies,

European Journal of Production Research, 40, 196-209.

Irastorza, J.C and Deane, R.H, 1974, Loading and balancing methodology for

job shop control, AIIE Transactions, 6, 302-307.

Bechet ,W, 1988, Theory and practice of load oriented manufacturing

control, International Journal of Production Research, 26, 375-395.

Bertrand, J.W.M and Wortmann, J.C, 1981, Production control and

information sytems for component manufacturing shops, Dissertation, Elsevier,

Amsterdam, The Netherlands

Tatsiopolous , I.P, 1993, Simplified production management software for small

manufacturing firm, Production Planning and Control, , 17-26.

8/8/2019 CobaCabana

30/30

Henrich,P.,Land,M.J.,Gaalman,G.J.C.,2004a.Exploring applicability of the

workload control concept. International Journal of Production Economics

,90,187198.

Bechte, W., 1994. Load-oriented manufacturing control just-in time

production for job shops. Production Planning and Control ,5, 292307 .

Henrich,P.,Land,M.J.,Gaalman,G.J.C.,vanderZee,D.J.,2004b.Reducing

feedback requirements of workload control. International Journal of

Production Research , 42,52355252.

Oosterman,B.,Land,M.J.,Gaalman,G.J.C.,2000.The influence of shop

characteristics on workload control International Journal of Production

Economics68,107119