JPH01234142A - Production planning method for mixed production lines - Google Patents

Abstract

PURPOSE:To enhance the levelling of production planning by deciding a flow pattern of basic combinational codes by a supply cycle fixed by an arrangement line and repeating the pattern during a unit period to equalize unrealization in the whole program all over. CONSTITUTION:In response to a start signal from an operator console 20, a cycle table creating process is started. A facility constraint condition table including the position number of a supply cycle, a table of designated restrict conditions for combinational codes and restrict conditions for restrict codes, the priority of which s decided, equalizing condition table levelling codes, the priority of which is decided, are input, and the order deciding process is conducted with a product production planning table 22 where combinational codes corresponding to necessary products are stored to create a cycle table 24. Secondly, creation of an order table is started a designated time before the production start time, the contents of the cycle table 24 are read out from the number of total production planning number per day to decide the order for deciding free positions in each cycle table. Thus, uniformalized production with high levelling can be done.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a production planning method for a mixed production line, in particular a method for assembling or processing parts supplied from each production table during one round of the flow line. The present invention relates to a production planning method for a mixed production line that imposes predetermined constraints and leveling on the supply order of each part when products with different desired specifications are mixedly produced in an assembly line.

[Conventional technology] Mixed production lines have been put into practical use in recent years in order to apply mass production systems to a wide variety of products.In such mixed production lines, each product is individually produced, unlike traditional lot production. They form products of different types or with different specifications.

This type of mixed production line includes various products such as automobiles, their component engines, and home appliances.

In particular, automobiles or engines have a large number of assembled parts, and it is necessary to assemble various miscellaneous parts for each vehicle.
Parts must be supplied correctly in accordance with the desired product plan, and it is extremely important to appropriately determine the order in which the parts are assembled.

That is, if such parts supply is not performed correctly, parts shortages, excess inventory, etc. occur, leading to problems such as lowering the efficiency of the production line and parts production factory.

In particular, on mixed production lines, the time required to assemble or process dissimilar parts varies greatly, and for this reason, combined parts that require long assembly processing times and combined parts that require short assembly processing times are supplied to the line alternately or mixed at a constant ratio as much as possible. It is preferable that

These assembly conditions are known as constraint conditions. For example, when handling electronically controlled fuel injection systems (EFI) and regular carburetors on an engine assembly line, the former requires a significantly longer assembly time. An assembly line in which such EFIs continue is not desirable, and a condition is required that prohibits EFIs from continuing, and this is called a constraint condition.

On the other hand, from the viewpoint of the parts manufacturing department, it is preferable to manufacture a wide variety of parts as uniformly as possible, and from a product assembly line, it is also desirable to have a combination arrangement that allows a variety of parts to be assembled at equal frequencies.

Such a request from the parts manufacturing department is known as a leveling condition, and it is desirable that the combination permutation of parts supplied to each table be a combination order that satisfies the leveling condition.

FIG. 13 shows an example of a mixed production line, in which a rotary 10 forms a flow line, and a large number of production tables A, B, C,
The parts are sequentially supplied to the parts, and when the flow line completes one cycle, the assembly or processing of the product with the specifications determined by each supplied part is completed. Therefore, by supplying parts to each production table in a predetermined order, it becomes possible to mix products having arbitrary specifications and mass-produce them in an assembly line.

In the normal case, it is preferred that the groups of parts supplied to each table are of the same type, for example, in an automobile assembly line, typical carburetor or EFI parts are supplied to the same table.

The low table 10 normally has a certain number of cheaples in its N area, and for example, a 10-tally is formed from 100 tables. According to such a rotary, if one supply cycle corresponds to the flow line l cycle, for example, 100 parts are supplied as one cycle, and the supply order of parts is repeated in the sequential loading cycle, 100 types of products with different specifications can be produced. can be produced repeatedly.

FIG. 14 shows a model of a production process when multiple types of automobiles are produced on a mixed production line according to the present invention.

As is clear from FIG. 14, for example, if we look at what kind of parts or assemblies the car AMt is assembled with, we can see that there is a possibility that the engine EC-EGN will be installed in the car AMl tomorrow, and that each of these engines It is understood that a plurality of parts a to n are used for each EC. Therefore, in a production process that combines many types of parts, there is a problem in that when producing many car models with different specifications on a single flow line, the parts must be supplied appropriately. .

As is well known, the assembly or processing of each of the above-mentioned parts a''-'n or the engine assembly EC-EGN is rarely performed from the beginning to the completion of the final product on one production line, and the production department is specialized. In most cases, the division of labor is aimed at.This division of labor in the production department inevitably necessitates the transportation of parts or engines between each production factory - temporary storage warehouses, etc. It is well known that the transportation and storage of external parts and the like impede the smooth distribution of external parts along the production line, and that some kind of management, ie, production control, is required.

Normally, parts to be supplied to a production line are supplied to the production line from multiple production plants or storages, and this supply must be done in accordance with the movement of the flow line, with just the right amount and shortage. Demand and supply efficiency on the production side do not necessarily match, and the order or arrangement of parts supplied to each production table in the flow line is an extremely important issue for both the assembly and production departments.

From the viewpoint of production and storage, it is preferable to equalize the frequency of parts required in the mixed production line, thereby improving storage efficiency and production equipment efficiency. This means that, for example, for a production plan that intensively consumes specific parts over a -week period, the parts production equipment will be large and a large space will be required to store it. It is clear from certain things.

Leveling the requirements for parts in such a mixed production line is extremely important for increasing overall production efficiency.

On the other hand, as is clear from FIG. 13, the flow line or rotary 10 moves at a constant speed, and it is preferable that the assembly or processing time at each production table be equalized. However, in a mixed production line, such leveling is virtually impossible, and as mentioned above, due to the difference in the working process between a normal carburetor and an EFI, it is impossible to completely level the parts.

Therefore, as described above, at least in order to achieve overall leveling, it is necessary to supply parts by mixing parts with different levels of work difficulty as uniformly as possible. In practice, this condition is achieved by not continuously supplying parts that require difficult work, ie by satisfying the constraints mentioned above.

As is well known, in the production of automobiles, the monthly production plan, weekly production plan, and per-zero production plan are corrected with the previous work-in-process results, etc. to formulate the product production plan for the day, and the parts supply program is planned based on this. be done. For example, if a flow line is planned to produce 1,500 cars per day, and this flow line has 100 tables, the desired product production will be performed by moving the flow line 15 times per day. , this 1.500
Parts are supplied that match the different types of specifications assigned to the machine.

In FIG. 13, the products to be finally produced are shown as a combination of "a1* bt + Ct + ..." or a combination of "C2, b2.C2, ...", etc., and each number 71. indicates a part symbol.

Therefore, based on the product production plan, the combination of parts or the combination of these parts units (hereinafter referred to as combination codes) is first determined, and by determining the arrangement and order of these combination codes, products with different specifications can be created. The production order is determined. Then, it will be understood that if the parts to be supplied to each table are instructed in the order in which they are arranged based on the part code or unit code, the desired product can be produced in one cycle of the rotary 10.

[Problems to be Solved by the Invention] However, according to the conventional planning method, necessary conditions are included for a predetermined production period, for example, the entire daily production plan. It is not possible to satisfy both the leveling condition and the constraint condition, and in reality, the arrangement of combination codes that determine the production order and their order are determined only by the leveling condition.

That is, the leveling condition requires that the frequencies of occurrence of necessary parts be as uniform as possible;
The constraint is a matter of the time required at each production table during product assembly or processing, and it is known that both of these do not necessarily hold true and are often contradictory conditions.

Therefore, as long as it is not possible to obtain a combination that satisfies such contradictory conditions or the order in which they are arranged, conventionally only one of them is selected, and in fact, only the leveling condition as described above is given priority. was.

Therefore, if mixed production is performed only under such leveling conditions, there is a problem that the production order will be thrown out of order when the planned number of units per day fluctuates significantly during mixed production of products that have a large number of shared parts.

Furthermore, as a result of prioritizing leveling conditions, constraints are often not satisfied, and in particular, the inconvenience of not satisfying such constraints, that is, the continuation of difficult work, is concentrated in the final part of the production process. There was a problem with this.

Furthermore, the leveling conditions are determined at a certain period, for example, a daily production cycle, and are set independently of one cycle of the flow line, so the parts supply cycle varies for each table, and each There is a problem in that, for example, 1,500 sorting orders must be set for each table, and a great deal of effort is required to calculate or store them.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to eliminate work stagnation on the flow line while leveling the parts supplied to each table in a mixed production line, and to further improve production. An object of the present invention is to provide an improved production planning method that allows planning to be carried out simply and in a short time.

, [Means for Solving the Problems] In order to achieve the above object, the present invention sequentially supplies parts with specifications appropriately selected from similar parts in a predetermined order to a plurality of production tables arranged along a flow line. In order to mix and produce products with different predetermined specifications in assembly lines by assembling parts that are assembled or processed at each production table after going around the flow line, parts are supplied to each table. In a production planning method for a mixed production line that determines the arrangement of combination codes and the order of combination codes, the supply ratio for each code in the supply cycle corresponding to one cycle of the flow line is determined from the required number based on the product production plan. The seats constituting this supply cycle are allocated to each combination code at the supply ratio described above, and the resulting fractions are combined as unreserved seats, and the arrangement of the combination codes and combination code group in each supply cycle is calculated. The arrangement order of the seats is determined based on constraint conditions and leveling conditions during production, and then the combination code of unreserved seats is determined through a plurality of supply cycles.

[Operation] According to the present invention, the ratio of parts or units within the same type is determined based on a given product production plan. For example, for a carburetor supply table, three types of supply ratios, EFI, normal, and other, are determined from, for example, a daily production plan.

The characteristic feature of the present invention is that this supply ratio is determined as the supply ratio during the supply cycle corresponding to one cycle of the flow line (a fraction of the total number of nails per day or a fraction of 10/61 or less nails). It is.

The supply cycle in FIG. 13 is defined to have 100 seats, that is, 100 seats that match the number of 0% feeding tables in the flow line. Conventionally, this supply cycle has not been used in production planning at all, but in the present invention, a basic supply ratio is actively determined for each supply cycle.

Therefore, since the planning plan of the present invention sets the supply cycle as one standard, the arrangement and order of the combination codes in the supply cycle may be changed several times depending on how many times the per-mouth production is this supply cycle. By simply copying, for example, it is possible to determine the arrangement and order of all the daily combination codes.

When each seat constituting the supply cycle is allocated at the supply ratio, the ratio obtained from the basic product production plan is a fraction H, but the second feature of the present invention is to assign this fraction to a specific code. The idea is to leave the seat open as an unreserved seat rather than giving it as a seat.

Therefore, it is understood that each supply cycle will be allocated according to a fair proportion and will include free seats as a part thereof.

Next, the allocation of each seat divided into integers thus determined is determined based on the constraint conditions and leveling conditions at the time of production.

In the present invention, the constraint condition has the highest priority, and the leveling condition is then determined based on that priority.

Therefore, although it is not possible to completely satisfy both conditions, it is understood that the constraint conditions and the leveling conditions are distributed in a substantially uniform manner within the supply cycle.

Then, after the allocation of seats within the supply cycle is completed, in the present invention, the constraint condition and the leveling condition are set for the predetermined n seats for each supply cycle with respect to the total mouthfeel. Part or unit No. 1 is given by the same procedure as above.

Therefore, by going through such a procedure, according to the production planning plan of the present invention, the combination unit 1 that satisfies the uniform constraint conditions and leveling conditions within the supply cycle.
The arrangement and order of the numbers are determined, and it is also possible to uniformly allocate a certain period, for example, the order of mouthfeel, taking into account the total amount passed through the supply cycle several times.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a system configuration diagram for executing the production planning method according to the present invention, and FIG. 2 shows a procedure for determining the arrangement and order of combination codes according to the present invention.

The method of the present invention is roughly divided into two steps, the first step is a step of creating a cycle table that determines the arrangement and order of combination codes in the supply cycle, and the second step is a step of creating the cycle table. This is a procedure for further preparing a mouthfeel order table for a predetermined period of time. The actual supply of parts to the flow line will be carried out according to the above-mentioned order table.

Here, an example of the combination code assigned to each product with different specifications will be explained based on FIG. 3.

The combination code in FIG. 3 consists of 10 digits, and each digit symbol consists of a number or an alphabet, and a unique code is assigned to each product with the desired specifications.
For example, the engine type, displacement, EFI and normal carburetor, engine bore diameter, and other characteristics are shown.

Therefore, by supplying parts corresponding to these respective codes to the production table, it is possible to produce a product having desired specifications, such as an automobile or an engine, by going around the flow line.

The operation of the system configuration diagram of FIG. 1 will be explained below with reference to the flowchart of FIG. 2.

First, in order to create a cycle table, a cycle table creation process is started by a start signal from the operator console 20. Step 101 in FIG. 2 is a pretreatment step,
This includes reading the equipment constraint condition table, constraint condition table, and leveling condition table.

In the present invention, the equipment constraints include the number of seats in the supply cycle, and for example, when a flow line with 100 table seats is used, it means that a cycle table is created within the supply cycle 100.

An example of the constraint condition table is shown in FIG. 4, and it is understood that predetermined constraint conditions are defined for the 1st, 3rd, 6th, and 8th digits of the combination code.

Then, each digit is assigned a priority order, i.e. 8.1
．． The priority order is determined in the subsequent cycle table creation process so that the constraint conditions are satisfied in the order of 3.6 digits.

The constraint code in FIG. 4 is, for example, rEJ in the first digit.
This means that a part numbered rEJ or rTJ must not be supplied consecutively after a part No. 71. Similarly, in the first digit, there is a constraint that following the ITJ code part, the rTJ or "E" code part cannot also be supplied.

Further, FIG. 5 shows an example of a leveling condition table, and like FIG. 4, this condition is also imposed only on the 1st, 3rd, 6th, and 8th digits, and the priority order thereof is also determined in advance.

The meaning of the leveling code in FIG. 5 is that, for example, in the first digit, rEJ and rTJ are required to be distributed as evenly as possible within the cycle.

Pre-processing] When Step 1 101 is completed, the combination code is determined in Step 1-102, and a product production schedule table containing the planned daily production quantity of each product type, which is stored in advance in the auxiliary storage of the computer. The contents of 22 are input, and the combination codes corresponding to these necessary products are stored.

Therefore, in determining the combination unit code in step 102, the combination code shown in FIG. 3 described above is determined for each product.

FIG. 6 shows the unit symbols read from the production planning table 22 and their planned numbers.

FIG. 6 shows that when the daily planned numbers of t and so vehicles are classified according to their required specifications, they are classified into approximately 50 types of specifications.

Next, in step 103, a ratio that satisfies the constraint condition and leveling condition is determined from the planned number of vehicles and combination code read in this way.

In the present invention, this ratio is determined as the supply ratio for each combination code that satisfies each constraint and leveling condition during the supply cycle corresponding to one cycle of the flow line.

That is, in the embodiment, the supply cycle consists of 100 seats, and the occurrence frequency ratio of combination codes requiring constraint and leveling conditions among these 100 seats is calculated.

FIG. 7 shows the process during which this ratio is determined, and the planned number of units shown in FIG. 6 is further summarized in terms of the digits necessary for restraint and leveling.

In other words, for digits that do not require constraint and leveling conditions, for example, the 7.9th and 1G digits, an @ mark is added to indicate an optional symbol ffJ, and as a result, the number of units is summarized for each condition. It is understood that this is taking place.

8A to 8E show a method for determining the supply ratio within a supply cycle from the aggregate values shown in FIG. 7.

FIG. 8A shows the ratio calculated for the 8th digit of priority 1. What is important here is that in the present invention, when calculating the supply ratio for each unit code in the supply cycle, this supply cycle is configured. Each seat is allocated according to the supply ratio, and the resulting fractions are combined into unreserved seats. According to Figure 88, "?" indicating unreserved seats is -
I have been given a seat.

FIG. 8B shows how to calculate the ratio of the first digit whose priority is 2, and in this case as well, fractional seats are reserved as in the case of the 8 digits.

Thereafter, the ratio is calculated in order of priority from the 3rd digit in Figure 8C to the 6th digit in Figure 8D, and the supply ratio in the final supply cycle is shown as an integer value in Figure 8E. Given.

Once the supply ratio shown in Figure 8 is determined as described above, each combination code within the supply cycle is then distributed at the ratio based on the constraint and leveling conditions. Prior to this, grouping of constraints is performed in step 104. As mentioned above, as is clear from the constraint conditions in Figure 4, the code for each digit is divided into a constraint group and a non-constraint group, and the ratio of the pgE diagram is divided into the constraint group and the non-constraint group under the leveling condition. The respective ratios when separated into groups are shown in FIG.

As is clear from FIG. 9, the symbol "?" is treated as a constraint symbol.

Next, in step $'j105, the order determination process is finally performed based on the constraints and leveling conditions, and the cycle table 2
4 is determined.

FIG. 10 shows a preferred example of determining the order of step 105.

A feature of the present invention is that the supply cycle is created in a fixed cycle, for example, by determining the arrangement order of the basic combination codes for 100 seats in the example, which is determined by the supply cycle, regardless of the total number of production per day. Therefore, by repeating this cycle table, it is possible to always satisfy the uniform constraint or leveling condition no matter how much the total production quantity increases. and,
When creating a cycle table, it is possible to achieve such orderly distribution by leaving the remaining fractions in the actual supply cycle open as unreserved seats.

As will be described later, the specific content of the unreserved seats is determined by determining whether each unreserved seat is uniformly constrained or level when the entire order is determined in the next step after cycle 5 is determined. decentralization that satisfies these conditions.

In FIG. 10, several initial rounds of order determination are shown,
Digits to which constraints and leveling conditions are imposed are arranged from the top in descending order of priority, and the possible codes for these are, for example, "0", "1", "2", and "7" for the 8th digit. , “?
” is displayed. In this code, constraint conditions are surrounded by solid lines, while non-constraint conditions are surrounded by broken lines.

Once the order is determined [1], the ratios shown in FIG. 8E described above are used as they are, and first a group that satisfies the constraint condition is selected, and from this group, a unique code that satisfies the leveling condition is obtained for each digit. And in FIG. 10, ? is selected? Criteria No. 1 are selected in descending order of ratio, and are indicated with a star in the figure.

Therefore, the combination code adopted on the 1st day is rrJ L+
2E E? 0? ? It becomes J.

Next, the ordering after the second day is performed as follows.

That is, after the second day, the one with the largest ratio is selected after satisfying the constraint condition and the leveling condition, and the ratio at this time is
After one day has been selected, the selection is made based on the following calculation formula.

For the code previously adopted for each digit, when the ratio of 1 times 11 is Pl and the ratio of 0 times 1] is Pn, pH''''p0. +pl-100. Therefore, for two days, the ratio is 53 + 53 - 100 - since the ratio of 1 is 53.
6 is applied.

On the other hand, regarding codes that were not adopted last time, Pn″″
It is given by Pn-1+Pl, and for example, the code "1" in the 8th digit has a ratio of 8 for the first day, and a ratio of 16 for the second day.

When all the digits are calculated as described above, and the one with the highest ratio is selected by combining the above conditions, the symbol marked with ☆ will be selected.

As described above, the respective combination codes of 3 times [114 times [-1] are determined in sequence.

FIG. 11 shows the cycle table determined in this way.

As is clear from the figure, unreserved seats "?" are arranged in the 6th and 92nd races, and by dispersing the unreserved seats within the supply cycle in this way, the allocation is divisible within the supply cycle. , that is, it becomes possible to complete allocation without fractions.

Next, a procedure for creating an actual sequence table from the cycle table obtained as described above will be explained.

In practice, the creation of the sequence table is activated by the system timer 26, for example, at a predetermined time before the daily production start time, and first, in step 201, the contents of the cycle table 24 are read for the total planned daily production number.

In the example, the number of machines per day is 1,532, and the cycle table is prepared for each 100 machines, so this is copied for 15.32 cycles.

Therefore, even if the number of produced units is enormous by copying this cycle table, there is no need to sequence the total number of produced units, which is 1.532 units in this embodiment, for each unit as in the conventional method. According to this method, there is an advantage that the order setting can be extremely simplified.

Step 202 shows the actual ordering, which is:
It is used to determine unreserved seats in each cycle table, and as is clear from the above explanation, fractional unreserved seats are mixed in when creating the cycle table, and it is step 202 to correctly determine this throughout the entire program. It is an order determination.

This order determination is performed in the same manner as step 105 when determining the cycle table described above, and the free seats can be sequentially ordered while taking into consideration the constraint conditions, leveling conditions, and ratios.

The number required for ordering at this time, that is, the number of unreserved seats, is extremely small compared to the total number of seats, and there is an advantage that the unreserved seats can be determined in a very short time.

FIG. 12 shows an example of the order table in which the order is determined in this way, and in the above-mentioned FIG. 11, 6 1! ,! l The 3rd and 6th digits of L”l are correct.

It is understood that a predetermined combination code is given by Ii.

According to the present invention, by performing the two-step procedure of creating and ordering the cycle table as described above, it is possible to determine the overall arrangement and order of the combination codes extremely easily.

In addition, a limiter is installed that subtracts the adopted number from the planned number of combination symbols each time a symbol is adopted in the corresponding order, and removes that symbol from the processing target when the remaining number becomes 0. It is possible to reliably eliminate discrepancies with the number of processing machines.

Although the above description has been made mainly with respect to automobiles or engines, the present invention can of course be widely applied to the assembly or processing of any other equipment.

Effects of the Invention As explained above, according to the present invention, the basic combination code flow pattern is determined by the supply cycle determined by the line, and this is repeated for a 111th period, for example, for the number of units produced per day. In order to further equalize the failures in the program as a whole, specific parts,
For example, there is an advantage that it is possible to formulate an extremely uniform production plan with a high degree of leveling without the risk of inconvenient restrictions or concentration of products that cannot be leveled after production.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram showing a preferred embodiment of the planning method according to the present invention, FIG. 2 is an explanatory diagram showing an example of a flowchart when operating the system shown in FIG. FIG. 4 is an explanatory diagram showing an example of constraint conditions when the present invention is used in the assembly of an automobile. FIG. 5 is an explanatory diagram showing an example of the constraint conditions when the present invention is used in an automobile assembly method. Figure 6 is an explanatory diagram showing the relationship between the unit code and the daily planned number of vehicles based on the production plan for automobiles, and Figure 7 is an explanatory diagram showing an example of the leveling conditions for the number of vehicles in Figure 6. Figure 8 is an explanatory diagram showing the number of cars grouped by matching digits, Figure 8 is an explanatory diagram showing the ratio calculation when calculating the ratio while considering the number of seats as unrestricted seats, Figure 9 is the number of vehicles grouped by matching digits, An explanatory diagram summarizing the ratios of other digits, Fig. 10 is an explanatory diagram showing the ordering action of obtaining a cycle table using the ordering method of the present invention, and Fig. 11 is an explanatory diagram showing an example of the cycle table. 12 is an explanatory diagram showing an example of a sequence table, FIG. 13 is an explanatory diagram showing a flow line diagram, and FIG. 14 is an explanatory diagram showing a combination of an automobile, an engine, and parts. Applicant: Toyota 11 Motors Co., Ltd. Agent Patent Attorney: Kenji Yoshida [8-57] Rei O O System Hiroho Diagram Figure 1, Orientation Flow Intervention Diagram 2, How Much Yield 1 2 3 4 5 6 7 8 9 10
Box No., □ l E-P5 1 A-Taiise Code Tei-Example 3rd figure ↑Coming condition 4th figure Figure 8A (Village 5) Figure 88 9m-416 18 fingers 1 digit N3 Wei 6 digits' 48 technique 1 1 13 5 Mao 6 kan Gai t/R4+
b+ - 0155%T/2% 1/11% 2734%1/8
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2L/20? /I? /2?
/3? /7 Negative node Ak for 8E figure 1M12 figure cause DOco o roller j line diagram 'a13 figure

Claims (1)

[Claims] Parts with specifications appropriately selected from similar parts are sequentially supplied in a predetermined order to a plurality of production tables arranged along a flow line, and assembled at each production table after going around the flow line. Mixing that determines the arrangement of combination codes that determines the parts to be supplied to each table and the order of combination codes in order to mix and produce products with different predetermined specifications in assembly lines by a collection of attached or processed parts. In the production planning method for a production line, the supply ratio for each code in the supply cycle corresponding to one cycle of the flow line is calculated from the required quantity based on the product production plan, and each seat making up this supply cycle is calculated for each combination code. are allocated according to the above-mentioned supply ratio, and the resulting fractions are collectively set as free seats, and the arrangement of combination codes and the order of combination codes within each supply cycle are determined based on the constraints and leveling conditions at the time of production. and then determining a combination code of free seats through a plurality of supply cycles.