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?Self-Organizing Chasing-Overtaking Production Lines to Maximize Worker Capabilities
9th IFAC Conference on Manufacturing Modelling, Management and 9th IFAC IFAC Conference Conference on on Manufacturing Manufacturing Modelling, Modelling, Management Management and and 9th Control Control Control 9th Conference on Modelling, Management and online at www.sciencedirect.com 9th IFAC IFAC Conference on Manufacturing Manufacturing Modelling, Management and Berlin, Germany, August 28-30, 2019 Available Berlin, Germany, Germany, August August 28-30, 28-30, 2019 2019 Berlin, Control Control Berlin, Berlin, Germany, Germany, August August 28-30, 28-30, 2019 2019
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Self–Organizing Self–Organizing Chasing–Overtaking Chasing–Overtaking Production Production Lines Lines to to Maximize Maximize Worker Worker Self–Organizing Chasing–Overtaking Production Lines to Maximize Worker Capabilities Capabilities ShiLong Liao*, XiaoQing Xie*, Capabilities Qin Chen**, JingJing Li*, ZongGuang Wang* ShiLong Liao*, XiaoQing Xie*, Qin Chen**, JingJing Li*, ZongGuang Wang* *Lanzhou University of Technology ShiLong Liao, （ ） ShiLong XiaoQing Xie*, ， Qin Chen**, Li*, ZongGuang Wang* *LanzhouLiao*, University of Technology Technology ， ShiLong Liao,JingJing （e-mail:[email protected] e-mail:[email protected] ） *Lanzhou University of ， ShiLong Liao, （ e-mail:[email protected] ） **Harbin Institute of Technology, Qin Chen, （ e-mail: [email protected] ） *Lanzhou University of Technology ， ShiLong Liao, （ e-mail:[email protected] ） *Lanzhou University ofof Technology ，ShiLong Liao, e-mail:[email protected] **Harbin Institute of Technology, Qin Chen, Chen, （（ e-mail: [email protected] ） ） ） **Harbin Institute Technology, Qin （ e-mail: [email protected] **Harbin Institute of Technology, Qin Chen, （ e-mail: [email protected] ） **Harbin brigade Institute of Technology, Qin Chen,is （ e-mail: [email protected] ） Abstract: Abstract: The The bucket bucket brigade production production line line (BBPL) (BBPL) is aa self-organizing self-organizing and and self-balancing self-balancing line line with with
Abstract: The bucket brigade production line (BBPL) is a self-organizing and self-balancing line with high and The path of from of sharing high flexibility flexibility and productivity. productivity. The evolutionary evolutionary pathis ofaaBBPL BBPL from the the perspective perspective of work workline sharing Abstract: The bucket brigade line self-organizing and with high flexibility and productivity. The evolutionary path BBPL from the perspective of work sharing Abstract: The bucket brigade production production line (BBPL) (BBPL) isof self-organizing and self-balancing self-balancing line with and that of the new self-organized chasing-overtaking production line (COPL) from the perspective of and that of the the and newproductivity. self-organized chasing-overtaking production line (COPL) (COPL) from the the perspective of high flexibility The evolutionary path of BBPL from the perspective of work sharing and that of new self-organized chasing-overtaking production line from perspective of high flexibility and productivity. The evolutionary path of BBPL from the perspective of work sharing undertaking all production tasks were determined. Because the production capacity of the BBPL is undertaking all production tasks were determined. Because the production capacity of the BBPL is and of self-organized chasing-overtaking production line (COPL) from the undertaking all new production tasks were determined. Because the production capacity of perspective the BBPL of is and that that by of the the new self-organized chasing-overtaking production linecapacity (COPL) fromonly the perspective of affected the differences in the worker efficiency, the production can be maximized affected by the differences in the worker efficiency, the production capacity can only be maximized undertaking all production tasks were determined. Because the production capacity of the BBPL is affected by the in the were worker efficiency,Because the production capacitycapacity can onlyofbethemaximized undertaking all differences production tasks determined. the production BBPL is when the worker efficiency is sorted from high to low. Similar to BBPL,COPL also needs to consider when theby worker efficiency is isin sorted from high high to low. low. Similar Similar to the the BBPL,COPL BBPL,COPL also needs to consider affected the differences the worker efficiency, the production capacity can only be maximized when the worker efficiency sorted from to to the also needs to consider affected by the differences in the worker efficiency, the production capacity can only be maximized the worker sequence. Our simulation and statistical analysis verified that the worker sequence does not the worker sequence. Our simulation simulation and high statistical analysis verified that the the worker worker sequence does not when the worker efficiency is to Similar to the also needs to consider the worker sequence. Our and statistical analysis verified that not when the worker efficiency is sorted sortedoffrom from high toInlow. low. Similar toability the BBPL,COPL BBPL,COPL alsosequence needscan to does consider affect on the production capacity a COPL. COPL, the of every employee be fully affect on the production capacity of a COPL. In COPL, the ability of every employee can be fully the worker sequence. Our simulation and statistical analysis verified that the worker sequence does not affect on the production capacity of a COPL. In COPL, the ability of every employee can be fully the worker sequence. Our simulation and statistical analysis verified that the worker sequence does not Copyright © IFAC utilized. utilized. Copyright © 2019 2019capacity IFAC of affect the utilized. © 2019 IFAC affect on onCopyright the production production capacity of aa COPL. COPL. In In COPL, COPL, the the ability ability of of every every employee employee can can be be fully fully Keywords:work-sharing system; chasing-overtaking production line; worker sequence;balance utilized. Copyright © 2019 IFAC © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. utilized. Copyright © 2019 IFAC Keywords:work-sharing system; system; chasing-overtaking chasing-overtaking production production line; line; worker worker sequence;balance sequence;balance ratio; ratio; Keywords:work-sharing ratio; worker efficiency worker efficiency Keywords:work-sharing system; worker efficiency Keywords:work-sharing system; chasing-overtaking chasing-overtaking production production line; line; worker worker sequence;balance sequence;balance ratio; ratio; worker worker efficiency efficiency 1. The 1. INTRODUCTION INTRODUCTION 1. INTRODUCTION The worker-distributed worker-distributed rules rules in in aaa work-sharing work-sharing production production The worker-distributed rules in work-sharing production 1. INTRODUCTION system based on work movement is introduced in detail 1. INTRODUCTION The worker-distributed rules in a work-sharing production Reducing the idle time of limited resources is key to The worker-distributed rules in ais production system based on on work work movement movement is work-sharing introduced in in detail detail later later Reducing the the idle idle time time of of limited limited resources resources is is key key to to system based introduced later Reducing in this paper. In 2016, Chen and Liao proposed a U-shaped system based on work movement is introduced in detail later improving the production efficiency of a manufacturing Reducing the idle time of limited resources is key to system based on work movement is introduced in detail later in this this paper. paper. In In 2016, 2016, Chen Chen and and Liao Liao proposed proposed aa U-shaped U-shaped Reducing time ofefficiency limited resources is key to improving the the idle production efficiency of aa manufacturing manufacturing in improving the production of production line using a "chasing-overtaking"(CO) rule. in In 2016, and system. aa serial production layout, workers improving production efficiency aa manufacturing in this this paper. paper. In using 2016, aaChen Chen and Liao Liao proposed proposed aa U-shaped U-shaped production line using "chasing-overtaking"(CO) rule. To To improving the production efficiency ofwhen manufacturing system. In In the serial production layout,of when workers are are production line "chasing-overtaking"(CO) rule. To system. In a serial production layout, when workers are maintain the configuration of U-shaped production line, the production line using a "chasing-overtaking"(CO) rule. To considered as limited resources, work sharing is an effective system. In a serial production layout, when workers are production line using a "chasing-overtaking"(CO) rule. To maintain the configuration of U-shaped production line, the system. In as a limited serial production layout, whenis are considered as limited resources, work work sharing is workers an effective effective maintain the configuration of U-shaped production line, the considered resources, sharing an "CO" rule was set to achieve higher efficiency and overtake maintain configuration of U-shaped production line, means idle time. not considered as resources, work sharing maintain the configuration of higher U-shaped production line, the the "CO" rulethe was set to to achieve achieve higher efficiency and overtake overtake considered as limited limited resources, workcross-training sharing is is an an effective effective means of of reducing reducing idle time. Worker Worker cross-training not only only "CO" rule was set efficiency and means of reducing idle time. Worker cross-training not only low-efficiency workers at an overtaking station, avoid "CO" to higher efficiency and enables to master aa variety skills,but makes means reducing time. Worker not only "CO" rule rule was was set set to achieve achieve higher efficiencystation, and overtake overtake low-efficiency workers at an an overtaking station, avoid means ofworkers reducing idle time. Workerof cross-training not only enablesof workers to idle master variety ofcross-training skills,but also also makes low-efficiency workers at overtaking avoid enables workers to master a variety of skills,but also makes blocking by low-efficiency workers,and bring the low-efficiency workers at an overtaking station, avoid them for the of aa variety of equipment. enables workers aa variety skills,but makes low-efficiency at an overtaking blocking by workers low-efficiency workers,andstation, bring avoid the enables workers to to master variety of skills,but also makes them responsible responsible formaster the operation operation ofof variety of also equipment. blocking by low-efficiency workers,and bring the them responsible for the operation of a variety of equipment. high-efficiency workers into the U-shaped staff-movement blocking by low-efficiency workers,and bring the On the one hand, multi-functional workers can increase the them responsible the aa variety equipment. blocking by workers low-efficiency workers,and bring the high-efficiency workers into the the U-shaped U-shaped staff-movement them responsible for the operation operation of of variety ofincrease equipment. On the the one hand, hand,for multi-functional workers canof increase the high-efficiency into staff-movement On one multi-functional workers can the production line.Thus, the traditional U-shaped production high-efficiency workers into the U-shaped staff-movement flexibility of a production system and more simply address On multi-functional workers increase the high-efficiency workersthe the U-shaped staff-movement production line.Thus, theinto traditional U-shaped production On the the one oneof hand, multi-functional workers can increase the flexibility ofhand, production system and and morecan simply address production line.Thus, traditional U-shaped production flexibility aa production system more simply address efficiency was further improved. production line.Thus, the traditional U-shaped production uncertainties in the production process. On the other hand, flexibility ain system and simply address productionwas line.Thus, the traditional U-shaped production efficiency was further improved. improved. flexibility of of in a production production system and more more simply address uncertainties the production production process. On the the other hand, efficiency further uncertainties the process. On other hand, First, for a variety of work sharing efficiency was further improved. the movement of workers between the machines and uncertainties in process. On other efficiency further improved. First, for aawas variety of work work sharing systems, systems, in in Section Section II II we we uncertainties in the the production process. the On the the other hand, hand, the movement of production workers between between the machines and First, for variety of sharing systems, in Section II we the movement of workers machines and discuss, the evolutionary relationship among various work First, for a variety of work sharing systems, in Section II we equipment via working sharing enables the production line the movement of workers between the machines and First, for a variety of work sharing systems, in Section II we discuss, the the evolutionary evolutionary relationship relationship among among various various work work the movement of workers machines line and equipment via working working sharingbetween enables the the production production line discuss, equipment via sharing enables the sharing production lines . In section III , we discuss the discuss, the to achieve balance improves the utilization rate of equipment via sharing enables production discuss, production the evolutionary evolutionary relationship among various work sharing production lines ..relationship In section section among III ,, we wevarious discusswork the equipment via working working sharing enables the production line to achieve task task balance and and improves thethe utilization rateline of sharing lines In III discuss the to achieve task balance and improves the utilization rate of impact of worker heterogeneity on COPL productivity in sharing production lines . In section III , we discuss the workers. It eliminates the calculation process of production to achieve task balance and improves the utilization rate of sharing production lines . In section III , we discuss impact of worker heterogeneity on COPL productivity in to achieveIt balancethe and improves process the utilization rate of workers. It task eliminates the calculation process of production production impact of worker heterogeneity on COPL productivity the in workers. eliminates calculation of new organizations via simulation. In Section IV ， we impact of on productivity in balance assembly line,which shows good compatibility workers. eliminates calculation process production impactorganizations of worker worker heterogeneity heterogeneity on COPL COPL productivity in new organizations via simulation. simulation. In Section Section IV ， ， we we workers.in Itan eliminates the calculation process of production balance inIt an assemblythe line,which shows goodof compatibility new via In IV balance in an assembly line,which shows good compatibility consider the effect of worker sequence on the production new via simulation. In Section IV with the difference in worker For balance an line,which shows compatibility new organizations organizations viaworker simulation. In on Section IV ， ， we we consider the effect effect of of worker sequence on the production production balance in an assembly assembly line,which shows good goodefficiency. compatibility with thein difference in the the worker processing processing efficiency. For consider the sequence the with the difference in the worker processing efficiency. For capacity of a self-organizing COPL using a simulation consider the effect of worker sequence on the production example, the rule brigade with in the efficiency. For consider the of worker sequence on the capacity of aaeffect self-organizing COPL using using simulation with the the difference difference in brigade”(BB) the worker worker processing processing efficiency. For example, the “bucket “bucket brigade”(BB) rule in in aaa bucket bucket brigade capacity of self-organizing COPL aa production simulation example, the “bucket brigade”(BB) rule in bucket brigade method. capacity of a self-organizing COPL using a simulation production line (BBPL) represents a core element in example, “bucket brigade”(BB) rule aa bucket brigade capacity of a self-organizing COPL using a simulation method. example, the theline “bucket brigade”(BB) ruleaain incore bucket brigade production line (BBPL) represents core element in method. production (BBPL) represents element in method. achieving a self-balancing production line and is a method production represents aa core element in method.22 EVOLUTION productionaa line line (BBPL) (BBPL) production represents line core element in achieving self-balancing production line and is is method EVOLUTION OF OF THE THE WORK-SHARING WORK-SHARING achieving self-balancing and aa method 2 EVOLUTION OF THE WORK-SHARING PRORDUCTION LINE that can be used to distribute the tasks of workers. However, achieving a self-balancing production line and is a method PRORDUCTION LINE 2 EVOLUTION OF THE WORK-SHARING achieving a self-balancing production line and is a method PRORDUCTION LINE that can be used to distribute the tasks of workers. However, 2 EVOLUTION OF THE WORK-SHARING that can be used to distribute the tasks of workers. However, PRORDUCTION LINE the rules of a BBPL are based on the rules of the Toyota PRORDUCTION LINE that can to the tasks workers. However, Following in that rules can be beof used to distribute distribute the on tasks ofrules workers. However, the rules ofused BBPL are based based on theof rules of the the Toyota Following the the rules rules of of worker worker distribution distribution in BBPL, BBPL, we we the aa BBPL are the of Toyota Following the rules of worker distribution in BBPL, we Sewn Product System (TSS). Therefore, this study first the rules of a BBPL are based on the rules of the Toyota further evolved the said process. Then, a new work-sharing Following the rules of worker distribution in BBPL, we the rules of a BBPL are based on the rules of the Toyota Sewn Product System (TSS). Therefore, this study first Following the rules of worker distribution in BBPL, we further evolved evolved the the said said process. process. Then, Then, aa new new work-sharing work-sharing Sewn Product System (TSS). Therefore, this study first further reviews the existing organizational rules of a work-sharing Sewn Product System (TSS). Therefore, this study first system was formed. We presented a detailed review of the further the process. aa new work-sharing Sewn Product System (TSS). Therefore, study first reviews the existing existing organizational rules of of this work-sharing further evolved evolved the said said process. Then, Then, newreview work-sharing system was formed. formed. We presented presented detailed review of the the reviews the organizational rules aa work-sharing system was We aa detailed of system,which mainly includes the following. reviews the existing organizational rules of a work-sharing system reviews the existing rules of a work-sharing system,which mainly organizational includes the the following. following. system was was formed. formed. We We presented presented aa detailed detailed review review of of the the system,which mainly includes system,which mainly includes the following. system,which mainly includes the following. 2405-8963 © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
Copyright © 2019 IFAC 2812 Copyright © © 2019 2019 IFAC IFAC 2812 Copyright 2812 Peer review under responsibility of International Federation of Automatic Control. Copyright © 2019 IFAC 2812 10.1016/j.ifacol.2019.11.624 Copyright © 2019 IFAC 2812
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worker
returning
2753
worker-distribution rules in a work-sharing system. Figure 1
another
from
the
upstream.
A
shows that this study divides the work-sharing system into
pre-designated worker zone is defined to limit the movement
two types according to the number of tasks the workers
of workers, and each worker has a fixed production zone. If
undertake after the system is stabilized,namely,undertaking
a machine is operating, a worker may choose to wait or
part and undertaking all of the production tasks. The left side
return to start a new processing round. According to Black
in Figure 1 shows the first one,i.e., undertaking part of the
et.al (1993), multi-functional workers can quickly realize
production line tasks, wheres the right side shows the second
production rebalance. Zavadlav et.al (1996) noted that
one,i.e.,undertaking all the production line tasks.
TSSPL is partially self-organizing .However, it may not be able to achieve self-balancing.
2.1 Work-sharing production line that undertakes part of the
BBPL, is also known as a process-split production line.
production tasks
Eisenstein and Bartholdi (1996) were inspired by the
The worker-distribution rules for undertaking part of the
phenomenon of self-organization in a TSS production
production tasks include four types (A1-A4), namely, the
line(shown as A4 in Figure 1) in Japan. The “BB” rule was
cherry-picking production line (CPPL), the diversity-skill
introduced into the study of production line balance, and the
chain production line (DSCPL), TSSPL, and BBPL
self-organization theory was applied to production line
respectively. In the business practice of enterprises, a
balance for the first time. The rules can be summarized as
bottleneck process in serial production lines has been found
“forward rule”and “backward rule”. If the workers are sorted
resulting from the differences in the abilities of workers,
along the production line from fast to slow, the production
which led to loss in the production capacity of
line spontaneously reaches an equilibrium state. Sriram et.al
not only in
the bottleneck but also in the whole production line.
(2014) noted that workers do not have a fixed work area in a
CPPL is also known as a CP strategy. Figure 1 shows that
U-type BB line.However,at low variability, workers can
Hopp et. al. (2004) introduced the rules for A1. In a serial
always perform a repetitive work cycle when sorted from
production line with multiple workstations, each worker
slow to fast. Simultaneously, the processing by workers
understands the skills needed in the bottleneck workstation
also periodic and relatively fixed in a certain zone. However,
to ensure full-load operation. When the M3 workstation
in the case of high variability,
is
these zones are not
needs help, workers can effectively help the bottleneck
guarantee to naturally occur. Bartholdi and Eisenstein (1998
workstation.Thus, the system production capacity can be
, 1999 , 2005) and Lim and Yang (2009) demonstrated that
improved. However, the assignment rule of CP is not
the production system can achieve self-organization and a
sufficient to realize a self-balance.
self-balance
DSCPL is also known as a skill chain. According to Jordan
rules.Bartholdi et al. (2006) and Hopp et al. (2004) applied
et.al (2004), in a serial production line with multiple
the BB rule to a tree assembly line. Using the work-sharing
workstations, each workstation is assigned a special
principle in BBPL, high efficiency and synchronization were
worker,as shown by A2 in Figure 1.Balance in the
achieved. Bartholdi and Eisenstein (2012) also extended the
production line cannot be achieved. Each worker masters
BB rules to bus scheduling to prevent congestion. In
two or more skills need in adjacent stations, and provides
addition, Manzini et al. (2015) and Hong et al. (2016)
assistance to adjacent downstream workers. Then, a skill
applied the BB model to the picking system of logistics
chain is formed. DSC provides the possibility for the
distribution and warehousing.
introduction of TSSs. TSSPL is formed when the number of
From the aforementioned rules, we can see that from the CP
equipment
to the DSC rules, the skills acquired by workers are one or
is greater than that of workers.
state
when
workers
follow
the
BB
as
two additional skills attached to fixed work positions. When
A3 in Figure 1. Bischak et.al (1996) emphasized the rule of
the number of equipment is greater than that of workers, the
TSSPL.A worker moves down along the production line
TSS rules dynamically balance the work tasks via walking
with one item (or a small batch) and operates each machine
behavior. The BB rule follows the TSS rule and
in a designated zone until this machine is taken over by
simultaneously introduces the pre-emption rule, finally
TSS, also known as a "bump-back "module, is shown
realizing self-balance in the production line. Although 2813
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BBPL assumes part of the production line, everyone is
The fully skilled worker production line that undertakes all
required to process all the necessary skills to achieve system
production tasks is in contrast to that of undertaking part of
stability. The production line under the BB rules further
the tasks. Figure 1 show its four forms(B1–B4), namely,
evolves to form a new type of self-organizing and
Stalls, PRPL, XPPL and COPL.
self-balancing production system, which is called cellular
The Stalls production line originated from a single-person
bucket brigade（CBB）, such as the combination shown in
barbecue-booth model in Japan. B1 in Figure 1 shows that
Figures A4 and B3 , which adopts the BB rule in the U-line.
workers are required to master all the processes of
Lim (2011) and Lim and Wu (2014) minimized the waste in
organizing the products. No equipment and large fixtures are
workers
CBB.
required. When large equipment and fixtures are needed, the
Accordingly, the efficiency improved and the production
Stalls production line is limited by the floor space.Thus,
line achieved self-organization and self-balance. Zhou et al.
PRPL was developed.
(2017) demonstrated that the CBB self-organization
PRPL, known as a picking strategy, is a touring U-shaped
characteristics are different under different constraints.
production line operated by individual workers (Hopp et al.,
Pratama et al. (2018) revealed that because of blocking or
2004). Workers master all the skills and independently
pausing at discrete workstations, the throughput of the
complete all processing steps for one workpiece. No
movement
without
production
using
discrete workstations can also be reduced by blocking. In
collaboration and no work sharing is performed among
addition, a method to overcome the blocking condition has
workers . The working-hour utilization rate is 100%, but the
been proposed, which combined the BB rules with worker
equipment utilization rate is much lower. To improve the
collaboration to enable up to two workers to collaborate on
utilization of equipment, XPPL was developed.
the same task. However, Lim (2017) showed that whereas
XPPL, also known as an expediting policy, is a touring
CBB reduces workers waste dueing movement without
U-shaped line that operates in teams (Van Oyen, 2001). It
production, in practice, each hand-off can be complex and
dynamically adjusts the production capacity by increasing or
time consuming. Hand over a workpiece during a process is
decreasing the number of workers. It has high flexibility.
not realistic or presents a certain risk .Furthermore, the
However, because of the differences in worker efficiency
effect of hand-off times on the performance needs further
and technical level, workers are blocked in the production
study. To reduce loss due to waiting time and movement in
line. The subsequently developed COPL solves this
hand-off of a workpiece without production, workers can
problem.
perform multiple processes in succession, which is a 2.3 Self-organizing Chasing-Overtaking production line
significant improvement. However,completing an entire process
in
production
M3
A1
lines
would
be
best.
M1
M3
M2
A
M4
B M5
B1 W1
W2 W3
The stalls Cherry- picking
A2
B2
W5
M10
Pick and Run)
M9
W4
M8
M7
M6
Diversity-skilled Chain
B3
Fig. 2 Chasing-Overtaking production line
worker2
worker3
A3
worker1
COPL is shown in Figure 2. Liao et al. (2012) explained the from the first process and carry the workpiece to a
B4
downstream station according to the process until the end of
Overtaking -station
M2
A4
production rules of CO lines. Multi-functional workers start
Expedite Policy
Toyota Sewn-products System
processing. Each worker is responsible for the entire process Bucket Brigade
TimeLine
Chasing-overtaking
TimeLine
of carrying the workpiece except when an overtaking
Fig 1 Work-sharing production line
phenomenon occurs. When no overtaking occurs, the
2.2 Work-sharing production line that undertakes all
overtaking station (M4) degenerates into an ordinary
production tasks 2814
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2755
workstation, and the workers finish processing their
expressed by the balance ratio. As expressed in Equation (1),
workpiece in the overtaking station and
leave with their
four levels, namely, 70%, 80%, 90%, and 100%, are used in
own workpiece. When overtaking happens, two situations
the simulation test. The balance ratio reflects the dispersion
occur. For a more detailed introduction to the COPL rule,
of the processing time of the workstation after the process
please refer to Chen and Liao (2015).Chen and Liao et al.
balance. The smaller the balance ratio is, the more dispersed
(2016) deduced the productivity calculation formulas of two
is the process time, which is expressed as follows:
workers
balance ratio = total processing time / (number of
with
effectiveness of
different
efficiency
and
verified
the
workstations * bottleneck process time).
COPL. They concluded that under the
same conditions, COPL is better than BBPL in these
5. The worker efficiency coefficients are found to be 1,1.1,
respects. Nakade (2015, 2017) thoroughly studied the
and 1.2.
production
capacity
of
a
worker-touring
Actual processing time of workers = standard working
U-shaped
production line and provided a calculation formula.
hours ×worker efficiency coefficient.
However, its operating rules in the U-shaped line were
6. Experimental design
limited to the worker sequence. The production efficiency of
1) By using worker sequence as an independent variable,
COPL is significantly better than that of the touring
three levels are obtained: Level 1—the worker with the
U-shaped production line. The specific research results can
highest efficiency is ranked as the first, and the least
be found in Chen and Liao's papers.
efficient worker is ranked as the last. Level 2—the least efficient worker is ranked as the first, and the worker with
3. EFFICIENCY DIFFERENCE IN WORKER SEQUENCE AND PRODUCTION CAPACITY
the highest efficiency is ranked as the last. Level 3—all
According to Eisenstein and Bartholdi (1996),the production
workers in the process have the same efficiency. To ensure
capacity of BBPL can only be maximized when the worker
fairness in efficiency, the sum of the efficiency coefficients
efficiency is sorted from high to low. Similar to
BBPL,
is equal in all three levels. For example, two workers with
COPL also has this feature. Because of the complexity of the
efficiency coefficients 1 and 1.2 are compared with two
COPL operation, establishing an accurate mathematical
workers with efficiency coefficients of 1.1. Three workers
model is difficult. In the present study, the simulation
with efficiency coefficients of 1 + 1.1 + 1.2 = 3.3 are
method was used to simulate the COPL processing.
compared with three workers with efficiency coefficients of 1.1 + 1.1 + 1.1 = 3.3.
3.1.Establishment of a Simulation Model
2)
The
production-line
balance
ratio
contains
four
1. In the simulation environment, we can dynamically
levels ,namely,70%, 80%, 90%, and 100%. Exponential,
observe the system process using the Siemens Plant
uniform, and normal distributions occur at each level. Three
Simulation10® discrete-event simulation platform. This
sets of random data are collected under each distribution,
platform truly reflects an actual production situation. We
i.e., 3×3=9 sets are collected at each level.
then develop a COPL simulation model.
3) The production capacity is used as a dependent variable to verify whether the worker sequence affects the production
2. By considering published works and comprehensiveness
capacity.
of the data, the processing time is subjected to three
4) The total number of experiments is as follows: 3 (worker
distributions as follows: exponential, normal, and uniform
sequence) × 4 (balance ratio) × 3 (distribution) × 3 (standard
distributions.
deviation) × 2 (number of people) = 216 experiments. 3. We consider 25 product processes as an example. The
5) The simulation duration is 10 days with no break time i.e,.
total standard working time is 250 min. We generate 25
10 days × 24 h × 60 min = 14,400 min.
random data using the Minitab 16® random-number 3.2 Simulation data collection
generator, which is used as the processing time of the 25 processes.
The simulation results are organized as follows, 216
4. The simulation platform contains 10 workstations, which
experimental data are listed in a table. The data listed in
balance the 25 processes. The balance effect can be 2815
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Table 1 are the production capacity of the workers in two work sequences and four balance ratios in two- or
100%
three-person COPL. EX denotes an exponential distribution,
154
154
154
171
171
171
154
154
154
154
154
154
171
171
171
154
154
154
154
154
154
171
171
171
154
154
154
No denotes a normal distribution, and Un denotes a uniform distribution. Under the normal distribution, the mean is 10
3.3 Simulation results and Statistical analysis
and the standard deviations are one, three,and five. The The simulation data were analyzed using SPSS 21®
uniform distribution has an upper limit of 10 and a lower
software.The experimental results are as follows:
limit of zero. The exponential-distribution scale is 10 and the
1) According to the statistical results of SPSS21®, the
threshold is zero. The cardinality is zero. Each of the
worker
aforementioned distributions considers three sets of data for
showed
no
statistically
significant
difference in productivity between the two- and three-person
the simulation. With a balance ratio of 70%, the two-person
production lines regardless of
process has a worker sequence from high to low,The
how the workers
were
sorted,i.e., from faster to slower or from slower to faster.
standard deviations of the normal distribution are one, three,
Statistically, the P values were equal to 0.976 and less than
and five, and the corresponding capacity values are
0.05, respectively.From the simulation platform, we found
104,103,and 103.
that in the CO line, the overtaking stations reduced the
Table 1. Two-person COPL worker sequence and capacity
blocking time by changing the positions of
worker sequence 2
sequence
level 1
level 3
the high- and
low-efficiency workers at the overtaking station .In the BB
level 2
peop
Exp
No
Un
Ex
No
Un
Ex
No
Un
line, when the low-efficiency workers were first process ,
le
103
104 r
103
114
11
11
103
10
103
they blocked the high-efficiency worker processing. In other
70%
104
103
102
114
11 4
11 3
104
10 4
102
words, BBPL could achieve maximum production capacity
103
103
103
114
11 4
11 2
103
10 3
103
only when the high-efficiency workers were located
103
104
103
114
11 4
11 4
103
10 3
103
downstream and the low-efficiency workers were located
103
103
103
114
11 4
11 4
103
10 4
103
upstream. However, for COPL, the worker sequence had no
104
103
104
114
11 4
11 4
104
10 3
104
significant effect on
103
104
104
112
11 4
11 4
103
10 3
104
2) According to the statistical results of SPSS 21®, by
105
104
104
115
11 4
11 4
105
10 4
104
comparing the equally efficient workers with different
105
103
104
116
11 4
11 4
105
10 4
104
efficiency
104
104
104
114
11 2
11 4
104
10 3
104
the production capacity of the equally efficient workers was
104
104
104
114
11 4
11 4
104
10 4
104
higher than that of the different efficiency workers although
114
11 4
11 4
104
10 4
104
the sum of the worker efficiency was equal. Statistically, the
4
4
80%
90%
100%
104
104
104
4
was that when the equally efficient workers were moving
worker sequence level 1
in the two- and three-person production lines ,
P values were equal to 0.891 and less than 0.05. The reason
Table 2. Three-person COPL worker sequence and capacity
3
the production capacity.
level 3
and processing in the COPL, a parallel movement happened
level 2
peopl
Ex
Nor
Un
Ex
No
Un
Ex
No
Un
among workers, and a CO phenomenon occurred during the
e
p 155
155
154
171
171
169
155
155
153
initial stage of the system. The workers with different
70%
156
154
153
171
170
169
155
154
153
efficiency shifted in the workstation, although they were
154
155
154
171
171
170
154
154
154
constantly overtaking the station in the COPL. Before
154
155
155
170
171
171
153
154
154
reaching the overtaking station, the high-efficiency workers
155
154
153
171
171
170
155
154
153
156
154
155
171
170
171
155
154
155
154
155
155
168
171
171
153
155
155
156
155
154
172
171
171
156
155
155
157
152
156
173
168
171
157
152
155
80%
90%
continued processing at low efficiency. Consequently, the system production capacity was reduced. 4.CONCLUSION In BBPL, because the workers cannot overtake one another, the worker sequence needs to be distributed first according to the working efficiency. Only when the workers are sorted 2816
2019 IFAC MIM Berlin, Germany, August 28-30, 2019
ShiLong Liao et al. / IFAC PapersOnLine 52-13 (2019) 2752–2757
2757
according to their work efficiency from high to low can the
‘chasing-overtaking’ production line. International
production
Journal of Production Research,54(12),3677-3690.
capacity
be
maximized.
Otherwise,
the
low-efficiency workers would block the high-efficiency
Hong,S., Johnson, A. L., and Other, B.A.(2016). Order
workers. However, the COPL production capacity is not
batching in a bucket brigade order picking system
affected by the worker efficiency and worker sequence.
considering picker blocking. Flexible Services and
Furthermore, the existence of an overtaking station ensures
Manufacturing Journal, 28(3),425-441. Hopp，W.J., Tekin, E., and Other, M.P.(2004）. Benefits of
that the ability of a high-efficiency worker is periodically released. In summary, COPL is more inclusive than BBPL
skill
in terms of worker distribution.
cross-trained workers. Management Science, 50(1),
in
serial
production
lines
with
83-98.
Acknowledgements The author would like to thank the Editor-in-Chief of the International Journal of Production Research，Professor Alexandre Dolgui, who encourage the author to publish this paper. The author would aslo like to thank Professor Bartholdi and Eisenstein, who pioneered the subject area of a self-organizing production line. This research was supported by a grant from the National Natural Science Foundation of China [Grant Number 71761026].
Jordan W C , Inman R R , Blumenfeld D E(2004) . Chained cross-training of workers for robust performance. IIE Transactions, 36(10): 953-967 Lim, Y. F., and Yang, K. K.(2009). Maximizing throughput of
bucket
brigades
on
discrete
work
stations.
Production and Operations Management,18(1),48-59. Lim ， Y.F.(2011). Cellular bucket brigades. Operations research,59(6),1539-1545. Lim, Y.F., and Wu, Y.（2014）. Cellular Bucket Brigades on
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2817
ScienceDirect
IFAC PapersOnLine 52-13 (2019) 2752–2757
Self–Organizing Self–Organizing Chasing–Overtaking Chasing–Overtaking Production Production Lines Lines to to Maximize Maximize Worker Worker Self–Organizing Chasing–Overtaking Production Lines to Maximize Worker Capabilities Capabilities ShiLong Liao*, XiaoQing Xie*, Capabilities Qin Chen**, JingJing Li*, ZongGuang Wang* ShiLong Liao*, XiaoQing Xie*, Qin Chen**, JingJing Li*, ZongGuang Wang* *Lanzhou University of Technology ShiLong Liao, （ ） ShiLong XiaoQing Xie*, ， Qin Chen**, Li*, ZongGuang Wang* *LanzhouLiao*, University of Technology Technology ， ShiLong Liao,JingJing （e-mail:[email protected] e-mail:[email protected] ） *Lanzhou University of ， ShiLong Liao, （ e-mail:[email protected] ） **Harbin Institute of Technology, Qin Chen, （ e-mail: [email protected] ） *Lanzhou University of Technology ， ShiLong Liao, （ e-mail:[email protected] ） *Lanzhou University ofof Technology ，ShiLong Liao, e-mail:[email protected] **Harbin Institute of Technology, Qin Chen, Chen, （（ e-mail: [email protected] ） ） ） **Harbin Institute Technology, Qin （ e-mail: [email protected] **Harbin Institute of Technology, Qin Chen, （ e-mail: [email protected] ） **Harbin brigade Institute of Technology, Qin Chen,is （ e-mail: [email protected] ） Abstract: Abstract: The The bucket bucket brigade production production line line (BBPL) (BBPL) is aa self-organizing self-organizing and and self-balancing self-balancing line line with with
Abstract: The bucket brigade production line (BBPL) is a self-organizing and self-balancing line with high and The path of from of sharing high flexibility flexibility and productivity. productivity. The evolutionary evolutionary pathis ofaaBBPL BBPL from the the perspective perspective of work workline sharing Abstract: The bucket brigade line self-organizing and with high flexibility and productivity. The evolutionary path BBPL from the perspective of work sharing Abstract: The bucket brigade production production line (BBPL) (BBPL) isof self-organizing and self-balancing self-balancing line with and that of the new self-organized chasing-overtaking production line (COPL) from the perspective of and that of the the and newproductivity. self-organized chasing-overtaking production line (COPL) (COPL) from the the perspective of high flexibility The evolutionary path of BBPL from the perspective of work sharing and that of new self-organized chasing-overtaking production line from perspective of high flexibility and productivity. The evolutionary path of BBPL from the perspective of work sharing undertaking all production tasks were determined. Because the production capacity of the BBPL is undertaking all production tasks were determined. Because the production capacity of the BBPL is and of self-organized chasing-overtaking production line (COPL) from the undertaking all new production tasks were determined. Because the production capacity of perspective the BBPL of is and that that by of the the new self-organized chasing-overtaking production linecapacity (COPL) fromonly the perspective of affected the differences in the worker efficiency, the production can be maximized affected by the differences in the worker efficiency, the production capacity can only be maximized undertaking all production tasks were determined. Because the production capacity of the BBPL is affected by the in the were worker efficiency,Because the production capacitycapacity can onlyofbethemaximized undertaking all differences production tasks determined. the production BBPL is when the worker efficiency is sorted from high to low. Similar to BBPL,COPL also needs to consider when theby worker efficiency is isin sorted from high high to low. low. Similar Similar to the the BBPL,COPL BBPL,COPL also needs to consider affected the differences the worker efficiency, the production capacity can only be maximized when the worker efficiency sorted from to to the also needs to consider affected by the differences in the worker efficiency, the production capacity can only be maximized the worker sequence. Our simulation and statistical analysis verified that the worker sequence does not the worker sequence. Our simulation simulation and high statistical analysis verified that the the worker worker sequence does not when the worker efficiency is to Similar to the also needs to consider the worker sequence. Our and statistical analysis verified that not when the worker efficiency is sorted sortedoffrom from high toInlow. low. Similar toability the BBPL,COPL BBPL,COPL alsosequence needscan to does consider affect on the production capacity a COPL. COPL, the of every employee be fully affect on the production capacity of a COPL. In COPL, the ability of every employee can be fully the worker sequence. Our simulation and statistical analysis verified that the worker sequence does not affect on the production capacity of a COPL. In COPL, the ability of every employee can be fully the worker sequence. Our simulation and statistical analysis verified that the worker sequence does not Copyright © IFAC utilized. utilized. Copyright © 2019 2019capacity IFAC of affect the utilized. © 2019 IFAC affect on onCopyright the production production capacity of aa COPL. COPL. In In COPL, COPL, the the ability ability of of every every employee employee can can be be fully fully Keywords:work-sharing system; chasing-overtaking production line; worker sequence;balance utilized. Copyright © 2019 IFAC © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. utilized. Copyright © 2019 IFAC Keywords:work-sharing system; system; chasing-overtaking chasing-overtaking production production line; line; worker worker sequence;balance sequence;balance ratio; ratio; Keywords:work-sharing ratio; worker efficiency worker efficiency Keywords:work-sharing system; worker efficiency Keywords:work-sharing system; chasing-overtaking chasing-overtaking production production line; line; worker worker sequence;balance sequence;balance ratio; ratio; worker worker efficiency efficiency 1. The 1. INTRODUCTION INTRODUCTION 1. INTRODUCTION The worker-distributed worker-distributed rules rules in in aaa work-sharing work-sharing production production The worker-distributed rules in work-sharing production 1. INTRODUCTION system based on work movement is introduced in detail 1. INTRODUCTION The worker-distributed rules in a work-sharing production Reducing the idle time of limited resources is key to The worker-distributed rules in ais production system based on on work work movement movement is work-sharing introduced in in detail detail later later Reducing the the idle idle time time of of limited limited resources resources is is key key to to system based introduced later Reducing in this paper. In 2016, Chen and Liao proposed a U-shaped system based on work movement is introduced in detail later improving the production efficiency of a manufacturing Reducing the idle time of limited resources is key to system based on work movement is introduced in detail later in this this paper. paper. In In 2016, 2016, Chen Chen and and Liao Liao proposed proposed aa U-shaped U-shaped Reducing time ofefficiency limited resources is key to improving the the idle production efficiency of aa manufacturing manufacturing in improving the production of production line using a "chasing-overtaking"(CO) rule. in In 2016, and system. aa serial production layout, workers improving production efficiency aa manufacturing in this this paper. paper. In using 2016, aaChen Chen and Liao Liao proposed proposed aa U-shaped U-shaped production line using "chasing-overtaking"(CO) rule. To To improving the production efficiency ofwhen manufacturing system. In In the serial production layout,of when workers are are production line "chasing-overtaking"(CO) rule. To system. In a serial production layout, when workers are maintain the configuration of U-shaped production line, the production line using a "chasing-overtaking"(CO) rule. To considered as limited resources, work sharing is an effective system. In a serial production layout, when workers are production line using a "chasing-overtaking"(CO) rule. To maintain the configuration of U-shaped production line, the system. In as a limited serial production layout, whenis are considered as limited resources, work work sharing is workers an effective effective maintain the configuration of U-shaped production line, the considered resources, sharing an "CO" rule was set to achieve higher efficiency and overtake maintain configuration of U-shaped production line, means idle time. not considered as resources, work sharing maintain the configuration of higher U-shaped production line, the the "CO" rulethe was set to to achieve achieve higher efficiency and overtake overtake considered as limited limited resources, workcross-training sharing is is an an effective effective means of of reducing reducing idle time. Worker Worker cross-training not only only "CO" rule was set efficiency and means of reducing idle time. Worker cross-training not only low-efficiency workers at an overtaking station, avoid "CO" to higher efficiency and enables to master aa variety skills,but makes means reducing time. Worker not only "CO" rule rule was was set set to achieve achieve higher efficiencystation, and overtake overtake low-efficiency workers at an an overtaking station, avoid means ofworkers reducing idle time. Workerof cross-training not only enablesof workers to idle master variety ofcross-training skills,but also also makes low-efficiency workers at overtaking avoid enables workers to master a variety of skills,but also makes blocking by low-efficiency workers,and bring the low-efficiency workers at an overtaking station, avoid them for the of aa variety of equipment. enables workers aa variety skills,but makes low-efficiency at an overtaking blocking by workers low-efficiency workers,andstation, bring avoid the enables workers to to master variety of skills,but also makes them responsible responsible formaster the operation operation ofof variety of also equipment. blocking by low-efficiency workers,and bring the them responsible for the operation of a variety of equipment. high-efficiency workers into the U-shaped staff-movement blocking by low-efficiency workers,and bring the On the one hand, multi-functional workers can increase the them responsible the aa variety equipment. blocking by workers low-efficiency workers,and bring the high-efficiency workers into the the U-shaped U-shaped staff-movement them responsible for the operation operation of of variety ofincrease equipment. On the the one hand, hand,for multi-functional workers canof increase the high-efficiency into staff-movement On one multi-functional workers can the production line.Thus, the traditional U-shaped production high-efficiency workers into the U-shaped staff-movement flexibility of a production system and more simply address On multi-functional workers increase the high-efficiency workersthe the U-shaped staff-movement production line.Thus, theinto traditional U-shaped production On the the one oneof hand, multi-functional workers can increase the flexibility ofhand, production system and and morecan simply address production line.Thus, traditional U-shaped production flexibility aa production system more simply address efficiency was further improved. production line.Thus, the traditional U-shaped production uncertainties in the production process. On the other hand, flexibility ain system and simply address productionwas line.Thus, the traditional U-shaped production efficiency was further improved. improved. flexibility of of in a production production system and more more simply address uncertainties the production production process. On the the other hand, efficiency further uncertainties the process. On other hand, First, for a variety of work sharing efficiency was further improved. the movement of workers between the machines and uncertainties in process. On other efficiency further improved. First, for aawas variety of work work sharing systems, systems, in in Section Section II II we we uncertainties in the the production process. the On the the other hand, hand, the movement of production workers between between the machines and First, for variety of sharing systems, in Section II we the movement of workers machines and discuss, the evolutionary relationship among various work First, for a variety of work sharing systems, in Section II we equipment via working sharing enables the production line the movement of workers between the machines and First, for a variety of work sharing systems, in Section II we discuss, the the evolutionary evolutionary relationship relationship among among various various work work the movement of workers machines line and equipment via working working sharingbetween enables the the production production line discuss, equipment via sharing enables the sharing production lines . In section III , we discuss the discuss, the to achieve balance improves the utilization rate of equipment via sharing enables production discuss, production the evolutionary evolutionary relationship among various work sharing production lines ..relationship In section section among III ,, we wevarious discusswork the equipment via working working sharing enables the production line to achieve task task balance and and improves thethe utilization rateline of sharing lines In III discuss the to achieve task balance and improves the utilization rate of impact of worker heterogeneity on COPL productivity in sharing production lines . In section III , we discuss the workers. It eliminates the calculation process of production to achieve task balance and improves the utilization rate of sharing production lines . In section III , we discuss impact of worker heterogeneity on COPL productivity in to achieveIt balancethe and improves process the utilization rate of workers. It task eliminates the calculation process of production production impact of worker heterogeneity on COPL productivity the in workers. eliminates calculation of new organizations via simulation. In Section IV ， we impact of on productivity in balance assembly line,which shows good compatibility workers. eliminates calculation process production impactorganizations of worker worker heterogeneity heterogeneity on COPL COPL productivity in new organizations via simulation. simulation. In Section Section IV ， ， we we workers.in Itan eliminates the calculation process of production balance inIt an assemblythe line,which shows goodof compatibility new via In IV balance in an assembly line,which shows good compatibility consider the effect of worker sequence on the production new via simulation. In Section IV with the difference in worker For balance an line,which shows compatibility new organizations organizations viaworker simulation. In on Section IV ， ， we we consider the effect effect of of worker sequence on the production production balance in an assembly assembly line,which shows good goodefficiency. compatibility with thein difference in the the worker processing processing efficiency. For consider the sequence the with the difference in the worker processing efficiency. For capacity of a self-organizing COPL using a simulation consider the effect of worker sequence on the production example, the rule brigade with in the efficiency. For consider the of worker sequence on the capacity of aaeffect self-organizing COPL using using simulation with the the difference difference in brigade”(BB) the worker worker processing processing efficiency. For example, the “bucket “bucket brigade”(BB) rule in in aaa bucket bucket brigade capacity of self-organizing COPL aa production simulation example, the “bucket brigade”(BB) rule in bucket brigade method. capacity of a self-organizing COPL using a simulation production line (BBPL) represents a core element in example, “bucket brigade”(BB) rule aa bucket brigade capacity of a self-organizing COPL using a simulation method. example, the theline “bucket brigade”(BB) ruleaain incore bucket brigade production line (BBPL) represents core element in method. production (BBPL) represents element in method. achieving a self-balancing production line and is a method production represents aa core element in method.22 EVOLUTION productionaa line line (BBPL) (BBPL) production represents line core element in achieving self-balancing production line and is is method EVOLUTION OF OF THE THE WORK-SHARING WORK-SHARING achieving self-balancing and aa method 2 EVOLUTION OF THE WORK-SHARING PRORDUCTION LINE that can be used to distribute the tasks of workers. However, achieving a self-balancing production line and is a method PRORDUCTION LINE 2 EVOLUTION OF THE WORK-SHARING achieving a self-balancing production line and is a method PRORDUCTION LINE that can be used to distribute the tasks of workers. However, 2 EVOLUTION OF THE WORK-SHARING that can be used to distribute the tasks of workers. However, PRORDUCTION LINE the rules of a BBPL are based on the rules of the Toyota PRORDUCTION LINE that can to the tasks workers. However, Following in that rules can be beof used to distribute distribute the on tasks ofrules workers. However, the rules ofused BBPL are based based on theof rules of the the Toyota Following the the rules rules of of worker worker distribution distribution in BBPL, BBPL, we we the aa BBPL are the of Toyota Following the rules of worker distribution in BBPL, we Sewn Product System (TSS). Therefore, this study first the rules of a BBPL are based on the rules of the Toyota further evolved the said process. Then, a new work-sharing Following the rules of worker distribution in BBPL, we the rules of a BBPL are based on the rules of the Toyota Sewn Product System (TSS). Therefore, this study first Following the rules of worker distribution in BBPL, we further evolved evolved the the said said process. process. Then, Then, aa new new work-sharing work-sharing Sewn Product System (TSS). Therefore, this study first further reviews the existing organizational rules of a work-sharing Sewn Product System (TSS). Therefore, this study first system was formed. We presented a detailed review of the further the process. aa new work-sharing Sewn Product System (TSS). Therefore, study first reviews the existing existing organizational rules of of this work-sharing further evolved evolved the said said process. Then, Then, newreview work-sharing system was formed. formed. We presented presented detailed review of the the reviews the organizational rules aa work-sharing system was We aa detailed of system,which mainly includes the following. reviews the existing organizational rules of a work-sharing system reviews the existing rules of a work-sharing system,which mainly organizational includes the the following. following. system was was formed. formed. We We presented presented aa detailed detailed review review of of the the system,which mainly includes system,which mainly includes the following. system,which mainly includes the following. 2405-8963 © 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.
Copyright © 2019 IFAC 2812 Copyright © © 2019 2019 IFAC IFAC 2812 Copyright 2812 Peer review under responsibility of International Federation of Automatic Control. Copyright © 2019 IFAC 2812 10.1016/j.ifacol.2019.11.624 Copyright © 2019 IFAC 2812
2019 IFAC MIM Berlin, Germany, August 28-30, 2019
ShiLong Liao et al. / IFAC PapersOnLine 52-13 (2019) 2752–2757
worker
returning
2753
worker-distribution rules in a work-sharing system. Figure 1
another
from
the
upstream.
A
shows that this study divides the work-sharing system into
pre-designated worker zone is defined to limit the movement
two types according to the number of tasks the workers
of workers, and each worker has a fixed production zone. If
undertake after the system is stabilized,namely,undertaking
a machine is operating, a worker may choose to wait or
part and undertaking all of the production tasks. The left side
return to start a new processing round. According to Black
in Figure 1 shows the first one,i.e., undertaking part of the
et.al (1993), multi-functional workers can quickly realize
production line tasks, wheres the right side shows the second
production rebalance. Zavadlav et.al (1996) noted that
one,i.e.,undertaking all the production line tasks.
TSSPL is partially self-organizing .However, it may not be able to achieve self-balancing.
2.1 Work-sharing production line that undertakes part of the
BBPL, is also known as a process-split production line.
production tasks
Eisenstein and Bartholdi (1996) were inspired by the
The worker-distribution rules for undertaking part of the
phenomenon of self-organization in a TSS production
production tasks include four types (A1-A4), namely, the
line(shown as A4 in Figure 1) in Japan. The “BB” rule was
cherry-picking production line (CPPL), the diversity-skill
introduced into the study of production line balance, and the
chain production line (DSCPL), TSSPL, and BBPL
self-organization theory was applied to production line
respectively. In the business practice of enterprises, a
balance for the first time. The rules can be summarized as
bottleneck process in serial production lines has been found
“forward rule”and “backward rule”. If the workers are sorted
resulting from the differences in the abilities of workers,
along the production line from fast to slow, the production
which led to loss in the production capacity of
line spontaneously reaches an equilibrium state. Sriram et.al
not only in
the bottleneck but also in the whole production line.
(2014) noted that workers do not have a fixed work area in a
CPPL is also known as a CP strategy. Figure 1 shows that
U-type BB line.However,at low variability, workers can
Hopp et. al. (2004) introduced the rules for A1. In a serial
always perform a repetitive work cycle when sorted from
production line with multiple workstations, each worker
slow to fast. Simultaneously, the processing by workers
understands the skills needed in the bottleneck workstation
also periodic and relatively fixed in a certain zone. However,
to ensure full-load operation. When the M3 workstation
in the case of high variability,
is
these zones are not
needs help, workers can effectively help the bottleneck
guarantee to naturally occur. Bartholdi and Eisenstein (1998
workstation.Thus, the system production capacity can be
, 1999 , 2005) and Lim and Yang (2009) demonstrated that
improved. However, the assignment rule of CP is not
the production system can achieve self-organization and a
sufficient to realize a self-balance.
self-balance
DSCPL is also known as a skill chain. According to Jordan
rules.Bartholdi et al. (2006) and Hopp et al. (2004) applied
et.al (2004), in a serial production line with multiple
the BB rule to a tree assembly line. Using the work-sharing
workstations, each workstation is assigned a special
principle in BBPL, high efficiency and synchronization were
worker,as shown by A2 in Figure 1.Balance in the
achieved. Bartholdi and Eisenstein (2012) also extended the
production line cannot be achieved. Each worker masters
BB rules to bus scheduling to prevent congestion. In
two or more skills need in adjacent stations, and provides
addition, Manzini et al. (2015) and Hong et al. (2016)
assistance to adjacent downstream workers. Then, a skill
applied the BB model to the picking system of logistics
chain is formed. DSC provides the possibility for the
distribution and warehousing.
introduction of TSSs. TSSPL is formed when the number of
From the aforementioned rules, we can see that from the CP
equipment
to the DSC rules, the skills acquired by workers are one or
is greater than that of workers.
state
when
workers
follow
the
BB
as
two additional skills attached to fixed work positions. When
A3 in Figure 1. Bischak et.al (1996) emphasized the rule of
the number of equipment is greater than that of workers, the
TSSPL.A worker moves down along the production line
TSS rules dynamically balance the work tasks via walking
with one item (or a small batch) and operates each machine
behavior. The BB rule follows the TSS rule and
in a designated zone until this machine is taken over by
simultaneously introduces the pre-emption rule, finally
TSS, also known as a "bump-back "module, is shown
realizing self-balance in the production line. Although 2813
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BBPL assumes part of the production line, everyone is
The fully skilled worker production line that undertakes all
required to process all the necessary skills to achieve system
production tasks is in contrast to that of undertaking part of
stability. The production line under the BB rules further
the tasks. Figure 1 show its four forms(B1–B4), namely,
evolves to form a new type of self-organizing and
Stalls, PRPL, XPPL and COPL.
self-balancing production system, which is called cellular
The Stalls production line originated from a single-person
bucket brigade（CBB）, such as the combination shown in
barbecue-booth model in Japan. B1 in Figure 1 shows that
Figures A4 and B3 , which adopts the BB rule in the U-line.
workers are required to master all the processes of
Lim (2011) and Lim and Wu (2014) minimized the waste in
organizing the products. No equipment and large fixtures are
workers
CBB.
required. When large equipment and fixtures are needed, the
Accordingly, the efficiency improved and the production
Stalls production line is limited by the floor space.Thus,
line achieved self-organization and self-balance. Zhou et al.
PRPL was developed.
(2017) demonstrated that the CBB self-organization
PRPL, known as a picking strategy, is a touring U-shaped
characteristics are different under different constraints.
production line operated by individual workers (Hopp et al.,
Pratama et al. (2018) revealed that because of blocking or
2004). Workers master all the skills and independently
pausing at discrete workstations, the throughput of the
complete all processing steps for one workpiece. No
movement
without
production
using
discrete workstations can also be reduced by blocking. In
collaboration and no work sharing is performed among
addition, a method to overcome the blocking condition has
workers . The working-hour utilization rate is 100%, but the
been proposed, which combined the BB rules with worker
equipment utilization rate is much lower. To improve the
collaboration to enable up to two workers to collaborate on
utilization of equipment, XPPL was developed.
the same task. However, Lim (2017) showed that whereas
XPPL, also known as an expediting policy, is a touring
CBB reduces workers waste dueing movement without
U-shaped line that operates in teams (Van Oyen, 2001). It
production, in practice, each hand-off can be complex and
dynamically adjusts the production capacity by increasing or
time consuming. Hand over a workpiece during a process is
decreasing the number of workers. It has high flexibility.
not realistic or presents a certain risk .Furthermore, the
However, because of the differences in worker efficiency
effect of hand-off times on the performance needs further
and technical level, workers are blocked in the production
study. To reduce loss due to waiting time and movement in
line. The subsequently developed COPL solves this
hand-off of a workpiece without production, workers can
problem.
perform multiple processes in succession, which is a 2.3 Self-organizing Chasing-Overtaking production line
significant improvement. However,completing an entire process
in
production
M3
A1
lines
would
be
best.
M1
M3
M2
A
M4
B M5
B1 W1
W2 W3
The stalls Cherry- picking
A2
B2
W5
M10
Pick and Run)
M9
W4
M8
M7
M6
Diversity-skilled Chain
B3
Fig. 2 Chasing-Overtaking production line
worker2
worker3
A3
worker1
COPL is shown in Figure 2. Liao et al. (2012) explained the from the first process and carry the workpiece to a
B4
downstream station according to the process until the end of
Overtaking -station
M2
A4
production rules of CO lines. Multi-functional workers start
Expedite Policy
Toyota Sewn-products System
processing. Each worker is responsible for the entire process Bucket Brigade
TimeLine
Chasing-overtaking
TimeLine
of carrying the workpiece except when an overtaking
Fig 1 Work-sharing production line
phenomenon occurs. When no overtaking occurs, the
2.2 Work-sharing production line that undertakes all
overtaking station (M4) degenerates into an ordinary
production tasks 2814
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2755
workstation, and the workers finish processing their
expressed by the balance ratio. As expressed in Equation (1),
workpiece in the overtaking station and
leave with their
four levels, namely, 70%, 80%, 90%, and 100%, are used in
own workpiece. When overtaking happens, two situations
the simulation test. The balance ratio reflects the dispersion
occur. For a more detailed introduction to the COPL rule,
of the processing time of the workstation after the process
please refer to Chen and Liao (2015).Chen and Liao et al.
balance. The smaller the balance ratio is, the more dispersed
(2016) deduced the productivity calculation formulas of two
is the process time, which is expressed as follows:
workers
balance ratio = total processing time / (number of
with
effectiveness of
different
efficiency
and
verified
the
workstations * bottleneck process time).
COPL. They concluded that under the
same conditions, COPL is better than BBPL in these
5. The worker efficiency coefficients are found to be 1,1.1,
respects. Nakade (2015, 2017) thoroughly studied the
and 1.2.
production
capacity
of
a
worker-touring
Actual processing time of workers = standard working
U-shaped
production line and provided a calculation formula.
hours ×worker efficiency coefficient.
However, its operating rules in the U-shaped line were
6. Experimental design
limited to the worker sequence. The production efficiency of
1) By using worker sequence as an independent variable,
COPL is significantly better than that of the touring
three levels are obtained: Level 1—the worker with the
U-shaped production line. The specific research results can
highest efficiency is ranked as the first, and the least
be found in Chen and Liao's papers.
efficient worker is ranked as the last. Level 2—the least efficient worker is ranked as the first, and the worker with
3. EFFICIENCY DIFFERENCE IN WORKER SEQUENCE AND PRODUCTION CAPACITY
the highest efficiency is ranked as the last. Level 3—all
According to Eisenstein and Bartholdi (1996),the production
workers in the process have the same efficiency. To ensure
capacity of BBPL can only be maximized when the worker
fairness in efficiency, the sum of the efficiency coefficients
efficiency is sorted from high to low. Similar to
BBPL,
is equal in all three levels. For example, two workers with
COPL also has this feature. Because of the complexity of the
efficiency coefficients 1 and 1.2 are compared with two
COPL operation, establishing an accurate mathematical
workers with efficiency coefficients of 1.1. Three workers
model is difficult. In the present study, the simulation
with efficiency coefficients of 1 + 1.1 + 1.2 = 3.3 are
method was used to simulate the COPL processing.
compared with three workers with efficiency coefficients of 1.1 + 1.1 + 1.1 = 3.3.
3.1.Establishment of a Simulation Model
2)
The
production-line
balance
ratio
contains
four
1. In the simulation environment, we can dynamically
levels ,namely,70%, 80%, 90%, and 100%. Exponential,
observe the system process using the Siemens Plant
uniform, and normal distributions occur at each level. Three
Simulation10® discrete-event simulation platform. This
sets of random data are collected under each distribution,
platform truly reflects an actual production situation. We
i.e., 3×3=9 sets are collected at each level.
then develop a COPL simulation model.
3) The production capacity is used as a dependent variable to verify whether the worker sequence affects the production
2. By considering published works and comprehensiveness
capacity.
of the data, the processing time is subjected to three
4) The total number of experiments is as follows: 3 (worker
distributions as follows: exponential, normal, and uniform
sequence) × 4 (balance ratio) × 3 (distribution) × 3 (standard
distributions.
deviation) × 2 (number of people) = 216 experiments. 3. We consider 25 product processes as an example. The
5) The simulation duration is 10 days with no break time i.e,.
total standard working time is 250 min. We generate 25
10 days × 24 h × 60 min = 14,400 min.
random data using the Minitab 16® random-number 3.2 Simulation data collection
generator, which is used as the processing time of the 25 processes.
The simulation results are organized as follows, 216
4. The simulation platform contains 10 workstations, which
experimental data are listed in a table. The data listed in
balance the 25 processes. The balance effect can be 2815
2019 IFAC MIM 2756 Berlin, Germany, August 28-30, 2019
ShiLong Liao et al. / IFAC PapersOnLine 52-13 (2019) 2752–2757
Table 1 are the production capacity of the workers in two work sequences and four balance ratios in two- or
100%
three-person COPL. EX denotes an exponential distribution,
154
154
154
171
171
171
154
154
154
154
154
154
171
171
171
154
154
154
154
154
154
171
171
171
154
154
154
No denotes a normal distribution, and Un denotes a uniform distribution. Under the normal distribution, the mean is 10
3.3 Simulation results and Statistical analysis
and the standard deviations are one, three,and five. The The simulation data were analyzed using SPSS 21®
uniform distribution has an upper limit of 10 and a lower
software.The experimental results are as follows:
limit of zero. The exponential-distribution scale is 10 and the
1) According to the statistical results of SPSS21®, the
threshold is zero. The cardinality is zero. Each of the
worker
aforementioned distributions considers three sets of data for
showed
no
statistically
significant
difference in productivity between the two- and three-person
the simulation. With a balance ratio of 70%, the two-person
production lines regardless of
process has a worker sequence from high to low,The
how the workers
were
sorted,i.e., from faster to slower or from slower to faster.
standard deviations of the normal distribution are one, three,
Statistically, the P values were equal to 0.976 and less than
and five, and the corresponding capacity values are
0.05, respectively.From the simulation platform, we found
104,103,and 103.
that in the CO line, the overtaking stations reduced the
Table 1. Two-person COPL worker sequence and capacity
blocking time by changing the positions of
worker sequence 2
sequence
level 1
level 3
the high- and
low-efficiency workers at the overtaking station .In the BB
level 2
peop
Exp
No
Un
Ex
No
Un
Ex
No
Un
line, when the low-efficiency workers were first process ,
le
103
104 r
103
114
11
11
103
10
103
they blocked the high-efficiency worker processing. In other
70%
104
103
102
114
11 4
11 3
104
10 4
102
words, BBPL could achieve maximum production capacity
103
103
103
114
11 4
11 2
103
10 3
103
only when the high-efficiency workers were located
103
104
103
114
11 4
11 4
103
10 3
103
downstream and the low-efficiency workers were located
103
103
103
114
11 4
11 4
103
10 4
103
upstream. However, for COPL, the worker sequence had no
104
103
104
114
11 4
11 4
104
10 3
104
significant effect on
103
104
104
112
11 4
11 4
103
10 3
104
2) According to the statistical results of SPSS 21®, by
105
104
104
115
11 4
11 4
105
10 4
104
comparing the equally efficient workers with different
105
103
104
116
11 4
11 4
105
10 4
104
efficiency
104
104
104
114
11 2
11 4
104
10 3
104
the production capacity of the equally efficient workers was
104
104
104
114
11 4
11 4
104
10 4
104
higher than that of the different efficiency workers although
114
11 4
11 4
104
10 4
104
the sum of the worker efficiency was equal. Statistically, the
4
4
80%
90%
100%
104
104
104
4
was that when the equally efficient workers were moving
worker sequence level 1
in the two- and three-person production lines ,
P values were equal to 0.891 and less than 0.05. The reason
Table 2. Three-person COPL worker sequence and capacity
3
the production capacity.
level 3
and processing in the COPL, a parallel movement happened
level 2
peopl
Ex
Nor
Un
Ex
No
Un
Ex
No
Un
among workers, and a CO phenomenon occurred during the
e
p 155
155
154
171
171
169
155
155
153
initial stage of the system. The workers with different
70%
156
154
153
171
170
169
155
154
153
efficiency shifted in the workstation, although they were
154
155
154
171
171
170
154
154
154
constantly overtaking the station in the COPL. Before
154
155
155
170
171
171
153
154
154
reaching the overtaking station, the high-efficiency workers
155
154
153
171
171
170
155
154
153
156
154
155
171
170
171
155
154
155
154
155
155
168
171
171
153
155
155
156
155
154
172
171
171
156
155
155
157
152
156
173
168
171
157
152
155
80%
90%
continued processing at low efficiency. Consequently, the system production capacity was reduced. 4.CONCLUSION In BBPL, because the workers cannot overtake one another, the worker sequence needs to be distributed first according to the working efficiency. Only when the workers are sorted 2816
2019 IFAC MIM Berlin, Germany, August 28-30, 2019
ShiLong Liao et al. / IFAC PapersOnLine 52-13 (2019) 2752–2757
2757
according to their work efficiency from high to low can the
‘chasing-overtaking’ production line. International
production
Journal of Production Research,54(12),3677-3690.
capacity
be
maximized.
Otherwise,
the
low-efficiency workers would block the high-efficiency
Hong,S., Johnson, A. L., and Other, B.A.(2016). Order
workers. However, the COPL production capacity is not
batching in a bucket brigade order picking system
affected by the worker efficiency and worker sequence.
considering picker blocking. Flexible Services and
Furthermore, the existence of an overtaking station ensures
Manufacturing Journal, 28(3),425-441. Hopp，W.J., Tekin, E., and Other, M.P.(2004）. Benefits of
that the ability of a high-efficiency worker is periodically released. In summary, COPL is more inclusive than BBPL
skill
in terms of worker distribution.
cross-trained workers. Management Science, 50(1),
in
serial
production
lines
with
83-98.
Acknowledgements The author would like to thank the Editor-in-Chief of the International Journal of Production Research，Professor Alexandre Dolgui, who encourage the author to publish this paper. The author would aslo like to thank Professor Bartholdi and Eisenstein, who pioneered the subject area of a self-organizing production line. This research was supported by a grant from the National Natural Science Foundation of China [Grant Number 71761026].
Jordan W C , Inman R R , Blumenfeld D E(2004) . Chained cross-training of workers for robust performance. IIE Transactions, 36(10): 953-967 Lim, Y. F., and Yang, K. K.(2009). Maximizing throughput of
bucket
brigades
on
discrete
work
stations.
Production and Operations Management,18(1),48-59. Lim ， Y.F.(2011). Cellular bucket brigades. Operations research,59(6),1539-1545. Lim, Y.F., and Wu, Y.（2014）. Cellular Bucket Brigades on
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