ISSN 1068798X, Russian Engineering Research, 2013, Vol. 33, No. 1, pp. 32–35. © Allerton Press, Inc., 2013. Original Russian Text © A.I. Sergeev, A.N. Goncharov, 2012, published in STIN, 2012, No. 6, pp. 2–5.

Simulating the Operation of Production Systems A. I. Sergeev and A. N. Goncharov Orenburg State Technical University, Orenburg DOI: 10.3103/S1068798X13010073

Automated machinetool systems offer the oppor tunity for competitive production. According to State Standard GOST 26228–90, these are known as flexi ble production cells and systems. Automated opera tion of flexible production systems for 140 h per week permits the manufacture of components of the required quality at minimum cost, within the timeline specified by the customer. That represents the produc tion pattern of the twentyfirst century. The creation of Russian flexible production sys tems that match global standards demands the devel opment of scientific principles for their design and operation. Simulation offers the only means of verify ing the quality of designs for new flexible production systems or proposals for converting existing equip ment to flexible production systems. Such complex systems are often regarded as stochastic. Globally, flexible production systems are designed on the basis of simulation—that is, stochastic representation (in terms of order fluxes, random events, etc.) by means of GPSS, Arena, or other software. However, this approach fails to take into account that the opera tional cycle of the flexible production systems is rigidly determined and may be expressed as a cyclic chart (a set of successive operating cycles of the individual components, modules, and the system as a whole), illustrating the sequence and duration of operation of the individual elements. Consider the algorithm for the simulation of flexi ble production systems on the basis of the automated formulation of cyclic charts [1]. This approach may also be applied to traditional production.

An automatic system (robot car) transports the blanks. The stage of machining is taken into account in transferring the blanks from one machine tool to another: as the number of stages already completed increases, the priority of the blank rises. The sequenc ing of the blanks is determined in accordance with the machining required. The blank is sent to the loading position as needed. We need to develop algorithms capable of repro ducing the required cyclic charts, calculating the dis charge times of the parts, and monitoring the opera tional efficiency of the department. INPUT AND OUTPUT DATA FOR THE PRODUCTION MODEL We now determine the parameters used in develop ing the model of the production system. In Fig. 2a, we show the input and output data for the production model. Then the file format with the initial data may be organized as in Fig. 2b. In the upper part of the file, the information regarding the basic equipment is pre sented; the subsequent data corresponds to the trans port system. On the basis of the data regarding the machine tools, the number of groups of information is determined. Then the information regarding the pro duction program is presented: in particular, the prior ities of the groups of equipment, which determine the machining pathway; and the difficulty of each machining operation. In the lower part of the file, the order in which the blanks are sent for machining is presented. Since the firstnamed blanks (Fig. 2b) are

FORMULATION OF THE PROBLEM Consider a production department consisting of the main technological equipment, which may be assigned to different technological groups (Fig. 1). This department produces a specific range of parts. The manufacturing route for this part calls for process ing on several machine tools. Some of the operations are performed in a strictly determined sequence, while others are performed in an arbitrary sequence. Before machining, the blank is sent to the loading position. It is returned to that position after machin ing. At each machine tool, there is a store that holds the blank before and after machining.

3

2 1

6

5

Fig. 1. Production department: (1) loading position; (2) milling center; (3) lathe complex; (4) store; (5) device for switching the blanks in the working zone; (6) automatic transportation system (robot car).

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4

SIMULATING THE OPERATION OF PRODUCTION SYSTEMS (a) Number of machine tools Equipment group

Loading cycle, s Coordinate, m Range of parts Number of transport vehicles, pcs Vehicle speed, m/s Cycle of blank replacement in vehicle, s Machining sequence

Start Input queue Output queue

Model of flexible production system

Positions in store

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Input times, min Output times, min Actual time, min Effectiveness, % Number of blanks processed, pcs No

Expected completion time, min Actual completion time, min

No

Operating cycle, min

mig := Var_Time

Record the model time

obslug := 999 pozl := 999

Specification of limiting values of variables

i, 1...Stanki Begin cycle 1

Selection cycle for machine tools

j, 1...PN Begin cycle 2

Selection cycle for stores

Zapret (i, j) = 0 Yes (1)

Yes mig := MomentPN[i, j]

Mean productivity, min–1 Load factor, %

poz := j (b) Type Information Setup 10 Machine tools 2 3 2 1 1 3 2 1 1 4 4 4 4 4 4 4 4 4 50 50 50 50 50 50 50 50 50 10 15 20 25 30 35 40 45 5 2 Robot car 60 3 Group of machine tools 3 2 1 3 Group of parts 1 2 0 7.0 12.0 0.0 1 1 1 4.0 7.0 5.0 1 1 1 0.0 7.0 12.0 4 Input queue 2 1 3 1 25 25 25 25

File

obslug := i 1 4 50 50

DU := kodPN[i, j]

End cycle 2 End cycle 1 No

obslug :> PN Yes j, 1...RazmSZ Begin cycle 3

No

(2) Yes

sent for machining twice (in the first and last batches), the size of the batches in each group is 25 pieces.

zagwka := i DU := NomT [zagwka]

FORMALIZATION OF SYSTEM OPERATION Before simulation, we determine the sequence in which the parts are machined. To this end, we create the POSLED_ZAP procedure, which converts the specification for the shift into an input queue. In this procedure, an embedded cycle for selecting the blanks in the input batch is organized within the cycle for selection of the input batches. After determining the input sequence, the blank for the next transport operation is selected by the WYBOR_DO procedure (Fig. 3). Before the blank is placed in the corresponding store, it is necessary to Vol. 33

Record the number of the store from which the blank Record the number of the machine tool from which the blank is removed Record the code of the blank removed from the machine tool

1

Fig. 2. Input and output data of the production model (a) and file format with initial data (b).

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Is the removal of the blank forbidden? (0, no; 1, yes) (1) (KodPN[i, j] > 0) and (Priznak[i, j] = 0 and MomentPN[i, j] <= mig) Has the blank been machined? Record the time of introduction in store

No. 1

obslug := 0

If no machined blank is present, insert new blank Selection cycle for blanks (2) (posled[i] > 0) and (Zapret_1[i] < 1) Once the input queue has been processed, is there a prohibition on the selection? Record the number of the blank from the input queue Record the code of the blank selected for machining Set the number of the machine tool employed to zero

End cycle 3 End

Fig. 3. The procedure WYBOR_DO. 2013

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SERGEEV, GONCHAROV Start max := 0 gruppa := 0

Set the variables to zero Selection cycle for he equipment group

i, 1...Grupp Begin cycle 1 No Put[DU, j] >max Yes max := Put[DU, j]

Selection condition for maximum priority of operation

Gruppa := j

Retain the equipment group required for machining

Record the required maximum priority

End cycle 1 No

If all the equipment groups are in use, then exit

max := 0 Yes pribyt := 0

Set the number of the machine tool for blank intake to zero

Exit; 1 pribyt := 999

Select the limiting number of the machine tool for blank intake

i, 1...Stanki Begin cycle 2

Select machine tools

2 No Gruppa_Stan[ i] = Gruppa Yes x := 0 j, 1...PN Begin cycle 3 No

KodPN[i, j] = 0 Yes

Select the equipment group in accordance with thcurrent stage of the machining process Indicator that free equipment is available Selection cycle for store Is there a free store position? Record the number of the machine tool

pribyt := i

Record the number of the position in the store Indicator that free equipment is available

poz := j x := x + 1 End cycle 3 Yes x>0 1 No

If the required machine tool has been selected, then exit the procedure

End cycle 2 Zapret_1 [DU] : = 1 1

If there is no free machine tool, then prohibit the selection of the incoming blank

End

Fig. 4. The procedure WYBOR_RM.

check whether the store contains a blank that has already been machined and, if so, to first remove that blank, which is then replaced by the incoming blank. If there is no equipment available for the machining of the incoming blank, it is returned to the machining queue. Machining of the incoming blank requires analysis of the state of the equipment and selection of the worksite, by means of the WYBOR_RM procedure (Fig. 4). The procedure begins with the selection cycle for the equipment group, in which the group of machine tools with the next highest priority is selected for the incoming blank. The machining route is selected by a procedure in which the priority for the equipment is established. For example, suppose that there are three machine tools in different technological groups: Machine tool

1

2

3

Technological group

2

3

1

The machining route is then as follows: machine tool 2, then 3, then 1. In that case, the priorities for forming the machining route are as follows Technological group

1

2

3

Priority

2

1

3

Since a zero value is established in the set of prior ities for the specific blank after each operation in any piece of equipment, the blank is regarded as com pletely machined when the set of priorities consists entirely of zeroes. In that case, the blank is sent to the final store. If the blank has not completed the produc tion cycle, the equipment that it must still traverse is determined. Then a free machine tool within that technological group is identified, and the blank is sent there. When all the equipment of the required group is occupied, the machining of the blank is prohibited until a suitable machine tool is free. After determining the destination, the next step is to determine the transport system that will be used. In the WYBOR_TS procedure, the availability of the transport systems is analyzed. If several transport options are available, the delivery time for each is analyzed. The quickest option is selected. In simulation of the depart ment’s operation, by analogy with the procedures just described, we also use procedures for calculation of the robot car’s downtime (PROS_TT); for output of the blank (WYGRUZKA); for part replacement in the working zone of the machine tool (SMENADU); and for determination of the changes after transportation (PEREKODIR). Then, by means of the WYWOD procedure, the intermediate states of the system are entered in a file

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SIMULATING THE OPERATION OF PRODUCTION SYSTEMS

that may be used to construct the cyclic chart and to cal culate the efficiency of the flexible production system. CONCLUSIONS We have developed algorithms for the simulation of a flexible production system. Those algorithms form the basis of Raspisanie software, with the output data shown in Fig. 2 [2]. The use of cyclic charts in simula tion allows us to take account of the operation of pro duction departments with different levels of automa tion, different sets of production equipment, different maintenance systems, different transport systems, and different storage systems. Accordingly, in simulation, we may take account of the losses due to mismatch of the technological equipment and the maintenance systems.

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ACKNOWLEDGMENTS Support was provided within the framework of the Russian Ministry of Education and Science’s program for developing the scientific potential of universities between 2009 and 2011 (project 9282). REFERENCES 1. Serdyuk, A.I. and Sergeev, A.I., Cyclic Charts in For mulating Computer Models of Flexible Production Systems, Avtomat. Sovrem. Tekhnol., 2005, no. 11, pp. 17–23. 2. Kornipaeva, A.A., Kornipaev, M.A., Sergeev, A.I., and Rakhmatullin, R.R., Formulating Production Schedules on the Basis of Cyclic Charts, Vestn. Komp. Inform. Tekhnol., 2011, no. 1, pp. 20–25.

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