JP2003216217A - Method and system for production planning - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production planning method and a production planning system for easily performing effective inventory management while taking production constraints into consideration. <P>SOLUTION: These production planning method and production planning system have the following (1) to (4) means: a means for setting a standard lot size in each brand name (1); a means for setting standard inventory quantity in each brand name and calculating the total of quantity demanded in a replenishment period of each inventory base (2); a means for extracting lots until the total of standard lot sizes of brand names constituting extracted lots reaches a produciable amount in a production plan object period in the order of a lot with a smaller margin calculated in the following expression when a combination of a brand name and an integer n≥0 is defined as a lot: a margin = (inventory quantity and account + n × standard lot size)/standard inventory quantity (3), and a means for deciding a production schedule while the brand names constituting the lots extracted by the extracting means are defined as a production candidate brand name and the number of lots extracted in each production candidate brand name as the number of lots requested for production (4). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a production planning method and a production planning system for a plurality of brands of products in a factory and a factory having one or more transit points as an inventory base in the process of product delivery from production to customers. Therefore, the present invention relates to a production planning method and a production planning system capable of easily performing effective inventory management while considering production constraints. INDUSTRIAL APPLICABILITY The production planning method and production planning system of the present invention are particularly suitable for a manufacturing industry that produces a large number of brands in a continuous production process such as polymer products such as synthetic resins and synthetic rubbers.

[0002]

2. Description of the Related Art For example, in the manufacturing business of polymer products such as synthetic resin and synthetic rubber, product orders are accepted every day, but the quantity of each order is from several tens of kg to several tens of tons. It varies, and the delivery time varies from 1 day to 1 month, but on the other hand, there is a strong demand for compliance with the delivery date, and the product is almost out of stock. Products are often shipped not only near the factory but also over a long distance, but there are orders with short delivery times. In order to meet such demands for shipping or to improve transportation efficiency by transporting them in bulk, we set up inventory bases (hereinafter referred to as “relay points”) at locations away from the factory, and to some extent from the factory to the relay points. When the order is received, it is shipped from the stock in the relay place (or factory) near the shipping destination.

On the other hand, the manufacturing plant has the following features. There are multiple plants (hereinafter referred to as production series) in the factory, and each production series is a continuous production plant. In one production series, usually 20 or more brands are continuously switched to produce. When switching between brands, there is a loss such as the occurrence of nonstandard products during the switching, so the number of times of switching is reduced, and the production quantity per brand is usually 100 t or more. In addition, there are various production constraints. For example, there are times when the brands can be switched and times when the brands cannot be switched, and there are brands in which one brand is in production while another brand cannot be produced in another series. Therefore, it is not possible to produce any brand at any time. Therefore, keep the products produced collectively as inventory,
When an order is received, it is shipped from stock.

Further, when the plant is stopped or the production is started, a large loss occurs, so that there is a demand to reduce the number of times of stop and start as much as possible. On the other hand, the production load, that is, the production amount per unit time can be adjusted within a certain range. Therefore, the adjustment of the production amount with respect to the fluctuation of the demand is made by the adjustment of the production load. In other words, the operating rate of the factory depends not only on the operating time but also on the production load.

[0005] Here, the product inventory management, that is, the management of maintaining an appropriate inventory amount while preventing out-of-stock, is performed by using an appropriate production plan.

[0006] Production planning is to extract the brands to be produced during the production planning period from a large number of brands that are handled,
It is to plan the production schedule of the extracted brands, that is, the production sequence and production quantity. When formulating a production plan, it is necessary to formulate a feasible plan in consideration of the above various constraints on production.

[0007] Conventionally, in a manufacturing industry that produces a large number of brands in a continuous production process, such as polymer products such as synthetic resins and synthetic rubbers, generally, the demand is forecast for a certain period in the future, and after that period elapses. A production planning method is adopted in which a brand that is expected to be out of stock is selected for production (hereinafter referred to as "prior art 1"). For example, the demand forecast for the next month is performed at the end of each month, and the brand is selected so that the brand expected to be out of stock by the end of the next month will be produced during the next month. At this time, when demand forecasting is performed on the whole, including those shipped via transit points, or demand is forecast for those shipped directly from the factory (hereinafter referred to as "direct shipping"), and the In some cases, the aggregated demanded quantity is added to form the overall demand forecast. The production order and production quantity are planned so that they can be executed most efficiently in consideration of various production constraints and losses caused by brand changes. In addition, the production quantity of each issue is determined so that the total production quantity balances with the production capacity. At that time, as a measure to balance while avoiding production constraints, there are cases where even a brand that is not expected to be sold out by the end of the next month is incorporated into a production brand.

The first problem with the above-mentioned prior art 1 is that the accuracy of demand forecasting is not necessarily high. As a result, unnecessary brands were produced, leading to an increase in inventory, or necessary brands were not produced and were out of stock. In addition, the movement of demand in the target period of the demand forecast is unknown, and the order in which each brand should be produced cannot be determined. Therefore, the production order is determined arbitrarily, but in the latter half of the production, the brands that produced in time are produced in the first half, which leads to an increase in inventory, and the production of the stock that runs out in the first half is in the latter half, causing out of stock. I went there If the target period of the demand forecast is shortened, such a problem will be alleviated, but if the target period is shortened, a large number of man-hours will be required only for the demand forecast, which is not realistic. In addition, there is no change in the order of production.

As the second problem in the prior art 1,
It is difficult to determine the production quantity so that the planned production quantity and production capacity are balanced. While this work needs to consider all of the demand forecasts, inventory levels, and constraints on production, including the selection of stocks that are not expected to be out of stock makes the work extremely complicated because the selection range is extremely wide. There is no method and it is decided arbitrarily. At this time, it is difficult to find a plan that maintains an appropriate inventory amount, but it is relatively easy to find a plan that avoids production constraints, so focus on production convenience rather than inventory management. It will be a plan left.

As the third problem in the prior art 1,
There is a point that abundant experience and knowledge are required for demand forecasting and production planning, and it takes a lot of time and effort to train personnel.

As described above, according to the conventional technique 1, it is difficult to effectively manage the inventory, though the complicated work is required.

On the other hand, the ordering point method has been known as a simple and effective stock management method from the past, and is widely used particularly in the retail business, wholesale business, etc. (hereinafter referred to as "prior art 2"). . The ordering point method is a method in which an ordering point is set for each brand, the stock amount is regularly checked, and a certain amount of stock is replenished when the stock amount falls below the ordering point.

In the prior art 2, effective inventory management can be easily realized, but when it is applied to the manufacturing industry, the following problems occur. That is, since the shipping volume fluctuates, there may be cases where there is no stock that is below the ordering point, but if production is stopped at that time, the operating rate will drop.
In addition, a large number of brands will be placed below the ordering point, and it will be impossible to produce all the brands. That is, it is difficult for Prior Art 2 to draw up a production plan that takes into account the constraints on production.

[0014]

SUMMARY OF THE INVENTION The present invention has solved the above-mentioned problems of the prior art. That is, the problem to be solved by the present invention is to provide a production planning method and production planning system for a plurality of brands of products in a factory and a factory having one or more transit points as an inventory base in the process of product delivery from production to customers. In addition, it is to provide a production planning method and a production planning system capable of easily performing effective inventory management while considering production constraints.

[0015]

[Means for Solving the Problems] That is, the first invention of the present invention is to provide a plurality of brands in a factory and a factory having one or more transit points as an inventory base in a product delivery process from production to a customer. A production planning method for a product, which has the following means (1) to (4). (1) A means for setting the standard lot size for each brand (2) A means for calculating the standard stock amount for each brand, and a means for calculating the sum of the demand amount in the replenishment period for each stock site (3) When a combination with an integer n of 0 or more is taken as a lot, the cumulative total of the standard lot sizes of the brands that make up the extracted lot can be produced during the production planning period in order from the lot with the smaller margin calculated by the following formula. Means for extracting lots up to a certain amount or more = (stock amount + n × reference lot size) / reference inventory amount (4) The production candidates are made up of the brands constituting the lot extracted by the extraction means, and production candidates Means for deciding the production schedule by using the number of lots extracted for each brand as the production required lot number. Further, the second invention of the present invention is the above (1) to (4).
The present invention relates to a production planning system that executes the above means on a computer.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a production planning method for a plurality of brands of products in a factory and a factory having one or more transit points as an inventory base in the process of product delivery from production to customers. It targets production plans for polymer products such as resins and synthetic rubber. Here, the production plan is to extract the brand to be produced during the production planning target period from a large number of brands that are handled, and determine the production schedule of the extracted brand, that is, the production order and the production quantity. . Normally, as a precondition, a production plan is drafted after setting a production plan target period and a production load.

The length of the production planning target period can be set arbitrarily, but if it is shortened, there is a high possibility that an executable plan that satisfies the production constraint conditions cannot be obtained.
On the other hand, if the length is increased, the inventory increases or the possibility of out of stock increases. If these are taken into consideration, for example, an inventory simulation can be performed based on the actual orders received, and a feasible plan can be set without fail or with the shortest period of time with an acceptable probability. As a result, for example, when the period is one week, the production plan for the period from the day after the planning day to one week later is drafted once a week. It is also possible to take a so-called rolling method in which a plan is provisionally made one week later and the plan after the plan drafting date is re-planned during the production planning of the next week.

The production load can be set in various ways according to the management policy and the demand situation. For example, in the case of a management policy that gives priority to maintaining the operating rate of the factory, the production load may be set so as to achieve the target operating rate. In the case of a policy of producing according to demand, it can be set based on the stock level. When setting based on inventory level,
In order to stably obtain a viable production plan that satisfies the production constraints, it is preferable to set the production load based on the number of lots whose inventory amount is equal to or less than the reference inventory amount when the production plan is created. For example, each time a production plan is made, if the number of lots that have fallen below the standard inventory quantity falls below the preset target, the production load is reduced, and conversely, if it exceeds the target, the production load is reduced. You can use a method such as raising. Such a method is particularly preferable when the production capacity is larger than the demand.

The production planning method of the present invention has (1) means for setting a reference lot size for each brand. The standard lot size is the quantity that becomes the unit of production for each brand,
As a general rule, the quantity produced at one time is an integral multiple of the standard lot size. In setting the value, the production quantity may be directly specified, or may be specified by a combination of the production load and the production time, and can be arbitrarily set according to the constraint condition of each factory. For example, when there is a time zone in which the brand cannot be switched in the same time zone every day, the production time can be set to 24 hours regardless of the brand and the production load can be set by designing each time. Further, for example, in a factory where the operation of product silos is a dominant constraint, the capacity of product silos can be used as the standard lot size. When there are a plurality of production series capable of producing a certain brand, the reference lot size of the brand can be set to a different value for each production series.

The production planning method of the present invention comprises (2) means for calculating the standard stock quantity for each brand, and means for calculating the sum of the demand quantity in the replenishment period for each stock location. The standard inventory amount is a numerical value (inventory amount) that serves as a standard for selecting a production brand according to the inventory amount. The standard inventory amount is calculated as follows. That is, the demand amount in the replenishment period is calculated for each stock site, the next sum is calculated, and the calculated sum is used as the standard stock amount. Here, the replenishment period is
It is the number of days from the production planning date to the date when it can be shipped from each inventory base, and the number of days varies depending on the inventory base. The factory replenishment period is the maximum production lead time, that is, the number of days until the brand produced at the end of the above-mentioned production planning period becomes ready for shipment. The replenishment period of the relay station is the maximum production lead time plus the number of days until the transportation is arranged and the transportation to the relay station is completed. The demand amount during the replenishment period can be calculated by any method.For example, the average value or maximum value of the past order results, a time series analysis method such as autoregressive integrated moving average (ARIMA), or a neural network is used. For example, a predicted value of shipping amount can be used. As an example, FIG. 2 schematically shows a method of calculating the demand amount in the replenishment period based on the maximum value of the actual orders. The sum of the demand amount calculated for each stock location for each issue is the standard stock amount. In the present invention, it is possible to continue to use the standard inventory amount once set, but from the viewpoint of inventory management accurately responding to changes in demand trends, each time a production plan is created, the order received so far It is preferable to calculate the standard stock amount based on the above and reset.
FIG. 1 schematically shows the concept of the standard inventory quantity, the standard lot size, and the like.

The production planning method of the present invention is (3) brand and 0
When the combination with the above integer n is taken as a lot, the lots are processed in order from a lot with a small margin until the cumulative total of the standard lot sizes of the brands forming the extracted lot reaches or exceeds the productionable amount in the production planning target period. Has a means for extracting.

A lot is a combination of a brand and an integer n. For example, if there are brands A, B, C, A
0, A1, A2, B0, B1, B2, C0, C1, C2
Etc. are called lots. The brand composing the lots A0, A1 and A2 is A. The margin is defined as follows for each lot. That is, margin = (stock amount + n × standard lot size) / standard inventory amount. Here, the inventory amount is the sum of the actual on-hand inventory amount at all inventory bases, but if there is a part that is planned to be produced before the production planning period even if it is not recorded in the on-hand inventory, the inventory amount Add to. n is 0, 1, 2, ... Therefore, a plurality of margins are calculated for one brand. In the example of FIG. 3, since the standard inventory amount, standard lot size, and inventory amount of the brand A are 50t, 200t, and 25t, respectively, the margin of the lot A0 is 25/50 = 0.50.
5, the margin of lot A1 is (25 + 200) / 50 =
It can be calculated as 4.5. When there are a plurality of production series capable of producing a certain brand, one production series is tentatively assigned and calculated by, for example, selecting the reference lot size of the production series having the highest productivity. However, depending on the result of lot extraction or scheduling described later,
You can change the allocation and recalculate.

Lots are extracted in order from a lot with a small margin calculated as described above until the cumulative total of the reference lot sizes of the brands forming the extracted lot reaches or exceeds the producible amount in the production planning target period. Have means. An example of a procedure for extracting a lot will be described below with reference to FIG. 4 based on the numerical example of FIG. In this example, AD
There are four brands, and the amount that can be produced during the production planning period is 600t. First, for all brands A to D,
The margin when n = 0 is calculated. If the lots are arranged in order from the smallest margin, A0, D0, B0, C0
In this order, the cumulative total of the standard lot sizes is 600 tons or more, which is the producible amount at B0. Therefore, A0, D0, B0
Is temporarily extracted. Here, with respect to the brands A, B, and D constituting the extracted three lots, the margin is calculated with n = 1. If the lots whose margins have been calculated so far are arranged in order from the smallest margin, A0, D0, D
Since the order is 1, ... Where n = 1
The margin is calculated for the brand D from which the lot is extracted with n = 2. Up to this point, if the lots are arranged in ascending order, the order is A0, D0, D1, ...
This is the same as the calculation up to n = 1. So A0,
The extraction is completed assuming that three lots D0 and D1 have been extracted.

In the case where the number of brands handled is larger than the number of brands that can be produced in the production planning target period, and the standard stock quantity of each brand is smaller than the standard lot size, the production brand extraction procedure described above is used. In the above, there is no problem even if the calculation is terminated when n = 0. By doing so, the amount of calculation can be reduced, and a production plan can be drafted in a short time.

Here, when the reference lot size is set by the load and the production time, it is sufficient to extract the lots until the cumulative production time exceeds the length of the planning period. Further, when there are a plurality of production series capable of producing a certain brand, the above-described lot extraction procedure is executed in the production series assigned when the margin is calculated. In this case, it is preferable that the maximum values of the margins of the extracted lots do not differ greatly depending on the production series. Therefore, select a stock that can be assigned to another production series with a large maximum margin value from the production series with a small maximum margin value, change the allocation, and then repeat the procedure from the calculation of the margin value. Therefore, it is desirable to reduce the difference.

The number of lots to be extracted may be any number as long as it is equal to or larger than the quantity that can be produced in the production planning period, but in order to efficiently execute the scheduling described later, the quantity that can be produced is It is preferable to extract 20 to 50% more than the above. If the number of lots to be extracted is small, a feasible schedule may not be obtained. On the contrary, if the number is large, there is a problem that scheduling takes time.

In the production planning method of the present invention, (4) the brands constituting the lot extracted by the extraction means are production candidate brands, and the number of lots extracted for each production candidate brand is the production required lot number. It has a means for determining the production schedule.

The production schedule is for determining in which production series and in what order the extracted lots will be produced. The production schedule must be executable in consideration of production constraints, but it is desirable to create a lot with a small margin so that it is produced as soon as possible. The production schedule creation method is arbitrary, but known methods such as a method based on a scheduling rule called AI or expert system, an enumerative method represented by a branch and bound method, a trial and error method such as a genetic algorithm, etc. Can be used.

In principle, the production quantity per lot is set to the standard lot size, but in order to avoid production constraint conditions, the minimum quantity should be adjusted before and after the standard lot size until the constraint can be avoided. May be. If it is not possible to produce all of the brands extracted by the above extraction means within the production planning target period, scheduling is performed beyond the production planning target period, and the range exceeding the production planning target period is set. The schedule can be reviewed at the next production planning. Alternatively, it is possible to change the production series assigned at the time of calculating the margin to another production series, and start over from the calculation of the margin. Also, if there is a production series that does not meet the production capacity, add a lot to be extracted in the lot extraction procedure to the production series, and then perform scheduling again, or use the margin calculation procedure After changing the allocation, lot extraction and scheduling may be executed again.

The production planning method of the present invention can be implemented by a production planning system using a computer. That is, the production planning system of the present invention is a production planning system that executes the above means (1) to (4) by a computer.

FIG. 5 shows an example of the configuration of a computer-based production planning system based on the method of the present invention. The production planning system includes a database located on a central host computer, a processing unit consisting of a stock calculation unit, a standard inventory amount calculation unit, and a production planning unit, and is arranged in each department. It is composed of input / output terminals connected by an area network (LAN). The database is composed of data tables as shown in FIG. 6, and the respective tables are linked and linked with each other as shown by solid lines.

The shipping management table is a table that stores order data and shipping record data. In each field of the order number, order date, planned shipping date, brand name, shipping destination, shipping source, and shipping quantity, order data input from the input / output terminal of the sales department is stored each time an order is received. The shipping source is a relay place or a factory that ships the order. After the shipment corresponding to the order is actually done,
When the shipping result report is input from the input / output terminal of the logistics department, the shipped flag is turned on, the shipping processing program of the inventory calculation unit is executed, and the inventory amount in the inventory table is updated.

The production management table is a table that stores production plan data and production performance data. In each of the fields of production number, planned production date, brand name, and planned production quantity, production planning data prepared by the production planning department is stored. When the production result report is input from the input / output terminal of the production department after the production corresponding to the production plan is performed, the reported data is stored in the fields of the production result date and the production result quantity, and the inventory The production processing program of the calculation unit is executed, and the inventory amount in the inventory table is updated.

The inventory table stores inventory locations on the day of processing,
It is a table in which inventory information for each brand is stored. The inventory location represents the name of the transit location or factory. The data of the inventory table is updated by the program of the inventory calculation unit.

The brand data table is data of a standard lot size and a standard stock quantity for each brand. The value input from the input / output terminal of the production department is stored in the standard lot size. The reference inventory amount stores the calculation result when the reference inventory amount calculation process of the reference inventory amount calculation unit is executed.

The production plan condition table is a table in which the conditions that are the premise of production planning are set. The data input from the input / output terminal of the production department is stored in each field. The production planning target period is the number of days that represents the length of the production planning target period, and normally is not changed once set. The production load is changed depending on the situation and is set as a relative value with the maximum capacity of the plant being 100%. The replenishment condition table is a table that stores the number of days of the replenishment period for each inventory base.

The production brand extraction table is a work table used when the program of the production planning unit, which will be described later, is executed.

The processing device is composed of an inventory calculation unit, a standard inventory amount calculation unit, and a production plan planning unit. The inventory calculation section has two types of programs, shipping processing and production processing.
The data in the inventory table is updated. The shipping process is a program that is executed when a shipping performance report is input, and the shipped quantity is subtracted from the inventory amount. The production process is a program that is executed when a production performance report is input, and the produced quantity is added to the inventory amount.

The standard stock amount calculation unit executes the standard stock amount calculation processing program by the method shown in FIG. 2 once a day, and the standard stock amount in the brand data table is updated.
The processing procedure is as follows. (1) Read the replenishment period from the replenishment condition table. (2) From the shipping management table, records in which the planned shipping date is three months or more before the processing date are extracted and read. (3) Based on the read data, the shipping quantity is totaled by inventory base, brand, and scheduled shipping date. (4) The total value is totaled for each section of the replenishment period for each inventory base. (5) The maximum value of the aggregated values is calculated for each inventory base. (6) Furthermore, find the sum of each issue,
Update the standard stock amount in the brand data table.

In the production planning section, the production brand extraction process and the production schedule creation process are continuously executed in response to a command from the input / output terminal of the production department.

The method of extracting the production brand is the method shown in FIGS. 3 and 4, and the procedure is as follows. (1)
The production planning target period and production load are read from the production planning condition table, the standard lot size and standard inventory amount are read from the brand data table, and the inventory amount is read from the inventory table. (2) Add the brand name data of all records in the brand data table to a new record in the production brand extraction table. (3) Substitute 0 into a work variable (hereinafter referred to as i). (4) Write the value of i in the lot of the added record. (5) In each added record, the margin is calculated with n = i and written in the field of the margin. (6) All records are sorted in ascending order of margin. (7) The reference lot size (production required time) is integrated in order from the first record, and the integrated value up to that record is written in the production required time.
(8) When the required production time exceeds the production planning target period, the records below the next record are deleted. (9) Of the remaining records, the brand name data of the record whose lot value is i is added to the new record. (10)
If there is no record to be added, the processing is terminated, and if there is one, 1 is added to the value of the work variable i and (4) the following procedure is repeated.

When the production brand extraction process is completed, the schedule creation process is subsequently executed. The schedule creation process is performed for a lot in the production brand extraction table according to a known algorithm, and the result is written in the production management table.

[0043]

Since the production planning method of the present invention is used to extract the brand that produces the ratio of the stock amount to the standard stock amount, effective stock management can be performed. In addition, since the calculation method is standardized, you can easily formulate a production plan without complicated work that requires abundant experience,
Inventory management is easy. Furthermore, the constraint conditions on production are taken into consideration by means of extracting the producible brands. As described above, according to the present invention, there are provided a production planning method and a production planning system for a plurality of brands of products in a factory and a factory having one or more transit points as an inventory base in the process of product delivery from a production to a customer. Thus, it was possible to provide a production planning method and a production planning system capable of easily performing effective inventory management while considering production constraints.

[Brief description of drawings]

FIG. 1 is a diagram schematically illustrating the concept of a standard inventory amount, a standard lot size, a margin of inventory, and a longest production lead time in the production planning method of the present invention.

FIG. 2 is a diagram schematically illustrating an example of a method of calculating the demand amount in the replenishment period for each inventory base in the production planning method of the present invention.

FIG. 3 is a diagram illustrating a numerical example of calculating a margin for each lot in the production planning method of the present invention.

FIG. 4 is a diagram illustrating an example of a procedure for extracting a lot that is a production candidate in the production planning method of the present invention according to the numerical example of FIG. 3.

FIG. 5 is a diagram showing a configuration example of a computer-based production planning system based on the production planning method of the present invention.

FIG. 6 is a diagram illustrating details of a database in the production planning system of FIG.

Claims (3)

[Claims] 1. A production planning method for a plurality of brands of products in a factory and a factory having one or more transit points as an inventory base in the process of product delivery from production to a customer, which comprises the following (1) to (4): ) A production planning method having means. (1) A means for setting the standard lot size for each brand (2) A means for calculating the standard stock amount for each brand, and a means for calculating the sum of the demand amount in the replenishment period for each stock site (3) When a combination with an integer n of 0 or more is taken as a lot, the cumulative total of the standard lot sizes of the brands that make up the extracted lot can be produced during the production planning period in order from the lot with the smaller margin calculated by the following formula. Means for extracting lots up to a certain amount or more = (stock amount + n × reference lot size) / reference inventory amount (4) The candidates constituting the lots extracted by the extracting means are production candidates and production candidates A means for determining the production schedule, using the number of lots extracted for each brand as the production required lot number. 2. The production planning method according to claim 1, wherein in the means for extracting production brands, the integer n is limited to n = 0 when the margin is calculated. 3. A production planning system for executing the means according to claim 1 or 2 by a computer.