Functional analysis of cell production system as just-in-time manufacturing.

Takakuwa, S. ; Ichikawa, H. ; Miwa, K. 等

Abstract: The characteristics of the cell production system are described from the standpoint of management and technology. Then, the procedure is proposed to decide the set of operation elements to be assigned to the designated workers in the assembly line. Performance measures of the system are analyzed to compare with those of the traditional conveyor system, by using simulation. It is found that the cell production system with RFID/traceability is much more efficient than the traditional conveyor systems.

Key words: Cell production system, Just-in-time manufacturing, Traceability, Simulation.

1. INTRODUCTION

The cell production system is one of major means to realize the philosophy of just-in-time (JIT) manufacturing to produce or retrieve required amounts of necessary items at the right time, as well as the Kanban system and Mizusumashi system (Monden, 1983). The cell production system is mainly applied to the assembly lines of manufacturers in Japan.

In addition, bar codes have been traditionally utilized to identify the exact parts to assemble a lot of different kinds of finished products. Recently, radio frequency identification (RFID) transponders and reader systems have been introduced and widely applied to the manufacturing and logistics fields. In this study, the cell production system together with RFID/traceability is examined especially from the standpoint of the efficiency.

2. CELL PRODUCTION SYSTEM

Just-in-time manufacturing is defined in many ways, and the most popular is the elimination of all waste and continuous improvement of productivity. Systems such as the Kanban system, the Mizusumashi system and the cell production system have been introduced to realize the actual goal of just-in-time manufacturing (Takakuwa &Nomura, 2003).

A cell production system has been widely introduced to realize just-in-time manufacturing especially in assembly lines since 1990s in Japan. The system comprises one or a series of multiple workers performing direct operations in an assembly line, and workers called Mizusumashi operators usually provide the associated parts to the assembly line. A cellular manufacturing or a manufacturing cell, on the other hand, is an application of GT (Group Technology) where a portion of a firm's manufacturing system has been converted to cells. Hence, a cell production system is different from a cellular manufacturing system.

A cell production system studied in this study is shown in Fig. 1, and the associated schematic layout is shown in Fig.2. In this system, three workers perform the operation elements to assemble notebook computers in a manufacturer. The average operation elements have been assigned to each worker. However, they cooperate with each other in performing their operations. In other words, when a worker takes time to perform the assigned operations, his/her adjacent workers help and perform some operation elements of the delayed worker.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

3. TRACEABILITY AS A MANAGEMENT TOOL

Bar codes have been widely utilized to identify the exact parts to assemble a lot of kinds of finished products for the past decades. As a traceability tool, radio frequency identification (RFID) transponders and reader systems recently have been introduced and widely applied to the manufacturing and logistics fields. 2D bar codes are commonly utilized in RFID, the associated amount of data increase up to one hundred times compared with those of 1D bar codes. Furthermore, by utilizing RFID with 2D bar codes, time to read bar codes in order to make up products on the assembly lines can be drastically reduced.

4. OPERATION ASSIGNMENT OF CELL PRODUCTION

In the assembly line of a notebook computer, there are assembling, testing before and after aging the body of the machine, and packaging operations. In the testing operations, there are waiting times or idle times needed to await to proceed to the next operation element. Selected waiting times are shown together with operation elements and the associated times in Table 1. A worker could perform operations on multiple pieces of products at the same time in his/her working position not to waste time. Assignments of operation elements and space for the storage of products should be determined for each worker before introducing the assembly line, and the system is developed to obtain the optimal assignments of a cell production system.

Fig. 3 shows the dialog of the screen in the proposed procedure to input the numbers of operation elements before and after the aging operation. By performing the procedure, the eligible assignments of operation elements can be obtained. The Gantt charts are shown for both the conveyor line and the cell production system in Fig. 4.

5. COMPARISON AMONG THE SYSTEMS

Simulation experiments are performed to evaluate the magnitude of improvement in the volume of production especially by introducing the RFID/traceability tool and the cell production system. The simulation models in this study were created using Arena (Kelton, Sadowski, and Sturrock 2004). The resultant results are summarized together with the contents from the associated website in Table 2 (pcweb, 2002). From the table, it is found that introducing PFID/traceability increases efficiency of production almost twice, and that introducing the cell production system increases efficiency almost twice again.

6. CONCLUSIONS

The cell production system is studied as just-in-time manufacturing. Then, how to determine the optimal assignments of operation elements for each worker is proposed. It is found that the cell production system with PFID/traceability is quite efficient for the assembly lines as just-in-time manufacturing.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

7. ACKNOWLEDGMENTS

The authors wish to thank NEC Custom Technica, Ltd. for their valuable suggestions.

8. REFERENCES

Kelton, W. D.; Sadowski, R. P. & Sturrock. D. T. (2004). Simulation with Arena. 3rd ed., McGraw-Hill, ISBN 0-07-285694-7, New York.

Monden, Y. (1983). Toyota Production System, Industrial Engineering and Management Press, ISBN 0-89806-034-6, Atlanta.

Takakuwa, S. and Nomura, J. (2003). Optimization analysis of Mizusumashi system as just-in-time manufacturing, Annals of DAAAM for 2005 & Proceedings, Katalinic, B. (Ed.), pp. 461-462, ISSN 1726-9679.

http://pcweb.mycom.co.jp. Report on NEC Custom Technica. 2002. (in Japanese)

Table 1. Operation elements

Element Operation Waiting
 No. Description time(sec.) time(sec.)

Operation : Testing (before aging)
 2-1 plug in 2.3 -
 2-2 insert test material; turn on 3.4 -
 2-3 plug in printer loop and RTC 3.4 -
 PC-connecter
 2-4 initialization 16.5 20
 2-5 write data from FD to HDD 1.6 85
 2-6 write PMI Information 7.4 -
 : : : :

Table 2. Comparison on productivity

 No. of Length Expected
 operators of lines volume (pcs./day
Adopted system (persons) (m.) & person)

1D bar code 11 17 8 (estimated)

PFID (2D bar code) 11 17 19.7
Conveyor line

PFID (2D bar code) 3 4 37.5
Cell production