JP2002012308A - Inventory management method - Google Patents

Abstract

(57) [Summary] [Problem] To provide a method for calculating a coefficient of a safety stock amount that satisfies a target service rate even when a characteristic of a past demand fluctuation does not follow a normal distribution in an inventory management method. To provide. SOLUTION: A safety coefficient calculation module 4 calculates a safety stock coefficient from a predicted amount, an actual amount, and a trial safety coefficient over a calculation target period by referring to a product information DB11 and a demand forecast / actual DB15. The theoretical service rate is calculated from the predicted amount, the actual amount, and the calculated safety stock coefficient over a period of time, and the target safety rate is changed by changing the safety coefficient to be tried until the calculated service rate substantially reaches the target service rate. Determine the coefficient. The evaluation criterion calculation module 5 calculates an evaluation criterion that is used as a reference when creating an order proposal based on the safety coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inventory management method, and more particularly to a method for determining a coefficient of a safety stock amount for achieving a required service rate (target service rate), and based on the safety coefficient. The present invention relates to a method of calculating an evaluation criterion that is used as a reference when determining an order quantity when ordering a product.

[0002]

2. Description of the Related Art As a method of determining a safety stock amount from a service rate and a demand amount record, there is a method described in, for example, "Total Logistics" (Takao Enkawa, Industrial Research Council). According to this method, the safety stock amount can be determined based on the standard deviation, which is an index of the range of fluctuation of the service rate and the actual demand amount, and the lead time from order placement to arrival. In this method, the safety stock coefficient that satisfies the required service rate is set under the premise that the characteristic of the fluctuation of the demand follows a normal distribution.

[0003]

According to the above prior art, it is assumed that the characteristic of the fluctuation of the demand in a certain past calculation target period follows a normal distribution. However, actual demand may not follow a normal distribution, in which case,
The actual service rate will be different from the target service rate.

It is an object of the present invention to provide a method for calculating a safety stock coefficient that satisfies a target service rate even when characteristics of past fluctuations in demand do not follow a normal distribution.

It is another object of the present invention to provide a method for calculating an evaluation criterion that is used when determining an order proposal.

[0006]

SUMMARY OF THE INVENTION The present invention is a method for calculating a safety factor of an inventory amount from a predicted amount of past demand and an actual amount using an electronic computer. The safety stock coefficient is calculated from the quantity, the actual quantity, and the safety coefficient to be tested, and the theoretical service rate is calculated from the predicted quantity, the actual quantity, and the calculated safety stock coefficient over the calculation target period, and the calculated service is calculated. Features a stock management method that calculates the service rate by changing the safety factor to be tried until the rate is almost the target service rate, and determines the safety factor when the service rate is almost the target service rate as the target safety factor And

If there is no predicted amount of demand, a theoretical service rate is calculated from the actual amount and the safety factor to be tried over the calculation target period, and the calculated service rate becomes almost equal to the target service rate. The service rate is calculated by changing the trial safety coefficient, and the safety coefficient when the service rate substantially reaches the target service rate is determined as the target safety coefficient.

Further, the present invention calculates a safety stock coefficient based on the determined target safety coefficient, and calculates a theoretical stock month as an evaluation reference from the calculated safety stock coefficient, the predicted amount and the actual amount. It is characterized by an inventory management method.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of an electronic computer for calculating a safety coefficient, an evaluation criterion, and an order draft according to the present embodiment. C
A memory (main storage device) for the PU 20 via a bus 35
1. External storage device 10, display device 25, and input device 3.
0 is connected. The storage device 10 stores a product information DB (database) 11 and a demand forecast / actual DB 15. The product information DB 11 stores safety stock parameters for each product,
Stores coefficients and order quantities related to safety stock. The demand forecast / actual DB 15 stores a demand forecast amount and an actual demand amount for each product. The memory 1 stores a control program 2, a safety coefficient calculation module 4, an evaluation criterion calculation module 5, an order proposal calculation module 6, and a work area 3. The safety coefficient calculation module 4 is a program executed by the CPU 20, and determines a safety coefficient and calculates a safety stock coefficient accordingly. The evaluation criterion calculation module 5 includes a CPU
This program is executed by 20 and calculates theoretical evaluation criteria (service rate, number of months in stock, and amount of stock). The ordering plan calculation module 6 is a program executed by the CPU 20, and calculates an ordering plan. The work area 3 is a work area that is accessed by the safety coefficient calculation module 4, the evaluation criterion calculation module 5, and the order proposal calculation module 6, and stores an intermediate result of the processing. The control program 2 includes the storage device 10 and the display device 2
5, a program that intervenes between the input device 30 and the safety coefficient calculation module 4, the evaluation criterion calculation module 5, and the order proposal calculation module 6, and controls these devices. The display device 25 is a device for displaying a target service rate, a theoretical evaluation criterion and an order proposal, and the input device 30 is for inputting a target service rate and the like, a safety coefficient calculation module 4, an evaluation criterion calculation module 5, and an order proposal calculation. A keyboard for inputting data and instructions into module 6;
It is a device such as a mouse.

The safety coefficient calculation module 4, the evaluation criterion calculation module 5, and the order proposal calculation module 6 are stored on a computer-readable storage medium, read into the memory 1 via a drive device such as the storage device 10, and executed. It is possible to

FIG. 2 is a diagram showing a data structure of the product information DB 11. As shown in FIG. The product information DB 11 is provided with a table for each product. Here, a table for a product with a product code 50 of 100 is shown. The unit price 52 indicates the unit price of the product. The safety coefficient calculation timing 54 indicates the timing at which the safety coefficient is calculated. For example, if the safety coefficient calculation timing 54 is 1, the timing for calculating the safety coefficient on the first day of each month is reached. The calculation target period 56 indicates a period during which calculation is performed when calculating the safety coefficient. For example, if the calculation target period 56 is 6, a safety coefficient is calculated for demand forecast actual data for the past 6 months. The ordering method 58 indicates an ordering method used when creating an ordering plan. The order cycle 60 indicates an interval at which an order is placed in the case of the regular order method. The delivery turn 62 indicates a period from order placement to delivery. For example, an order cycle 60 takes 5 days and a delivery order 62
Is 2 days, the quantity to be ordered is 5 days + 2 days (order cycle + delivery number), which is the quantity required for 7 days. The order reference date 64 indicates a date on which an order is placed. For example, if the order reference date 64 is one day and the order cycle is five days, the first, sixth, eleventh,... The target service rate 66 indicates a required service rate. The safety coefficient 68 is a coefficient to be multiplied by a numerical value indicating a demand characteristic of the part in order to keep the safety stock amount at a predetermined service rate. Here, an initial value for calculating the safety coefficient by the following processing is set. The safety stock coefficient 70 is a numerical value calculated from the relationship between the safety coefficient 68 and the error ratio between the predicted amount of demand and the actual amount (prediction error rate). The order quantity 72 is an order quantity determined as a result of the order quantity calculation.

FIG. 3 is a diagram showing a data structure of the demand forecast DB 15. The demand forecast DB 15 is provided with a table for each product and for each order cycle. Here, a table for an order date of 6th for a product with a product code of 100 is shown. The demand forecast amount and the actual amount are shown for each date. The delivery turn is a period (lead time) from when an order is placed until the product is delivered. The planning target period corresponding to the order date of 6th is from 6th to 12th. The future order table naturally stores only the estimated amount.

FIG. 4 is a PAD showing a schematic procedure of the processing of the safety coefficient calculating module 4 and the evaluation criterion calculating module 5.
FIG. When the processing time by the timer controlled by the control program 2 has come, or when there is a user's instruction via the input device 30, the safety coefficient calculation module 4 is started (Step 100). The safety coefficient calculation module 4 acquires the basic data used for calculating the safety coefficient, the predicted amount and the actual amount of demand from the product information DB 11 and the demand forecast / actual DB 15 for the target product, and stores them in the work area 3. (Step 102). Next, the safety coefficient calculation module 4 calculates a safety coefficient and a safety stock coefficient from the predicted amount and the actual amount of demand on the work area 3 by a method described later, and stores them in the work area 3 (step 104). Next, the evaluation criterion calculation module 5 calculates a theoretical evaluation criterion from the set safety stock coefficient on the work area 3 by a method described later, outputs it on the display device 25, and stores it in the work area 3 (step 106).

FIG. 5 is a PAD diagram showing a detailed procedure of the process of calculating the safety coefficient in step 104. In the processing of calculating the safety coefficient, steps 112 to 118 are repeated by increasing or decreasing the safety coefficient until a safety coefficient satisfying the target service rate is found with the safety coefficient 68 on the work area 3 as an initial value (step 110). That is, the safety stock coefficient is calculated from the safety coefficient to be tried, and the theoretical service rate is calculated based on the safety stock coefficient. If the calculated theoretical service rate is lower than the target service rate, the safety coefficient is increased by a predetermined increase and the next trial is performed.If the calculated service rate is higher than the target service rate, the safety coefficient is reduced by a predetermined decrease and the next trial is performed. To try. When the theoretical service rate has almost reached the target service rate in this way, step 1
The process of 10 is ended. The processing of the following steps 112 to 118 is processing in the case where the demand forecast is performed over the calculation target period 56. The processing when the demand forecast is not performed will be described later.

In step 112, the safety stock coefficient in the calculation target period 56 is calculated (step 112). The safety stock coefficient is obtained by calculating the prediction error rate from the predicted amount of demand and the actual amount, and is calculated by the formula of the average value of the prediction error rate + the safety coefficient × the standard deviation of the prediction error rate. The forecast error rate in the planning target period is obtained by dividing the quantity obtained by subtracting the total demand forecast quantity from the total demand actual quantity in this period, by the total demand forecast quantity. Therefore, the average value of the prediction error rates is a numerical value obtained by averaging the prediction error rates of the respective planning target periods over the calculation target period. The standard deviation of the prediction error rate is a standard deviation of the prediction error rate of each planning target period over the calculation target period. For example, when the safety coefficient to be tried is 1.65, the average value of the prediction error rate is 2, and the standard deviation of the prediction error rate is 3, the safety stock coefficient is 6.95.

Next, the processing of step 116 is repeated for each order cycle for each planning period over the calculation period (step 114). In step 116, a theoretical service rate is calculated for the order cycle (step 116). The theoretical service rate of the ordering cycle is obtained by the following equation (1).

[0018]

(Equation 1)

The ordering cycle in steps 114 and 116 is a case where the ordering method is a regular ordering method. For other ordering schemes, it is a specific period to be evaluated instead of the ordering cycle.

Next, the theoretical service rate in each order cycle or a specific period is averaged over the calculation target period to calculate the theoretical service rate in the calculation target period (step 1).
18).

FIG. 6 is a PAD showing a detailed procedure of the process of calculating the evaluation criterion in step 106. The evaluation criterion calculation process is performed in step 1 every month over the calculation target period.
Steps 22 to 126 are repeated (step 120).

In step 122, the theoretical service rate for the month is calculated (step 122). The calculation method uses Equation 1 as in Step 116. Here, the safety stock coefficient is calculated by the formula of the average value of the prediction error rate + the safety coefficient × the standard deviation of the prediction error rate, as in the case of step 112. Is calculated. In addition, the safety factor is
This is the safety factor determined in step 4.

Next, the theoretical number of months in stock for the month is calculated (step 124). The theoretical number of months in stock for each month is obtained by the following equation (2). Here, the safety stock coefficient is a numerical value calculated in step 122.

[0024]

(Equation 2)

Next, the theoretical inventory amount for the month is calculated (step 126). The theoretical inventory amount of each month can be calculated by the theoretical number of inventory months calculated in step 124 × the average monthly actual amount of the calculation target period × the product unit price.

Next, the theoretical service rate, the theoretical number of months in stock, and the monthly average value of the theoretical inventory amount for each month calculated in steps 122 to 126 are calculated (step 128).

It should be noted that the order cycle in the equation 2 in step 124 is the case where the order method is the regular order method.
For other ordering schemes, it is a specific period to be evaluated instead of the ordering cycle.

FIG. 7 is a PAD diagram showing a procedure of processing of the ordering plan calculation module 6 in the case of the regular ordering method. When the processing time of the timer controlled by the control program 2 has come, or when there is a user's instruction via the input device 30, the order proposal calculation module 6 is activated (step 140). Next, the ordering plan calculation module 6 executes the product information DB 11 and the demand forecast DB 1 for the target product.
5, the basic data used for calculating the order proposal and the expected and actual demand are acquired and stored in the work area 3 (step 142). Next, the order quantity at the time of this order is calculated as an order proposal based on the ordering method 58 (step 144). As a formula for calculating the order quantity, in the case of the regular order method, for example, the sum of the demand forecast quantity in the planning target period × (1 + safety stock coefficient) −
It is calculated by the formula (current stock amount + order remaining).

Next, the calculated order proposal is displayed on the display device 25, and a correction input by the user is accepted (step 146). Next, a theoretical service rate when the order proposal is corrected is calculated (step 148). This theoretical service rate is obtained by the following equation (3).

[0030]

(Equation 3)

Here, it is assumed that the theoretical service rate in the prediction target period for the calculation order proposal is equal to the average service rate in the calculation target period obtained in step 128. The planning target period is a planning target period starting from the order date when this order is placed. The prediction target period is a period to be predicted including the plan target period, and is, for example, a period from the order date to the last day of the month.

Next, the theoretical number of months in stock during the forecast period when the order proposal is corrected is calculated (step 150). The theoretical number of months in stock is obtained by the following equation (4).

[0033]

(Equation 4)

Here, it is assumed that the theoretical number of months in stock in the prediction target period for the ordering plan in the calculation is equal to the average number of months in stock in the calculation target period obtained in step 128. Equation 4
The middle working days / order cycle is the number of orders per month.

Next, a theoretical stock price in the forecast target period when the order proposal is corrected is calculated (step 152). This stock amount can be calculated by multiplying the number of months in stock calculated in step 150 × the average monthly actual amount in the calculation target period × the product price.

FIG. 8 is a diagram showing an example of the evaluation criterion calculation result displayed on the display device 25. The service rate, stock months and stock value for the target service rate are calculated in Step 1
It is a numerical value calculated in 28. The theoretical values of the monthly evaluation criteria are calculated in steps 122 to 1 for each month in the calculation target period.
It is a numerical value calculated in 26. The evaluation criterion serves as reference data for correcting the calculation order proposal. The actual value is a numerical value calculated for comparison with the theoretical value, but the details of the processing such as the calculation method are omitted.

FIG. 9 shows the calculated order plan, the corrected and input order plan, the evaluation criteria for the calculated order plan, and the evaluation criteria for the corrected order plan displayed on the display device 25.

If the demand prediction is not performed, the process of step 112 is not performed when calculating the safety coefficient.
In step 114, the process is repeated for each planning target period. In step 116, the theoretical service rate is calculated by the following equation (5).

[0039]

(Equation 5)

Here, the standard deviation of the actual amount of demand in the calculation target period is the standard deviation of the total of the actual amounts for each planning target period.

In step 118, the theoretical service rate for each planning target period is averaged over the calculation target period,
Calculate the theoretical service rate for the calculation target period.

When calculating the evaluation criterion when the demand forecast is not performed, in step 122, the theoretical service rate for the month is calculated by the following equation (6).

[0043]

(Equation 6)

Next, in step 124, the following formula 7 is used to calculate the theoretical number of months in stock.

[0045]

(Equation 7)

In step 126, the theoretical inventory amount is calculated by the theoretical number of months in stock × the average monthly actual amount in the calculation target period × the unit price of goods in the same manner as described above.

In the case of modifying the ordering plan, when applying an ordering method such as placing an order at any time when the ordering point is cut, it is not necessary to modify the theoretical service rate in step 148, and the Apply the theoretical service rate for the proposed order. In step 150, the theoretical number of months in stock is calculated by the following equation (8).

[0048]

(Equation 8)

In step 152, the above-mentioned step 126
Is calculated by the following equation.

[0050]

As described above, according to the present invention, it is possible to calculate the coefficient of the amount of safety stock required to provide the target service rate, and to calculate the coefficient by using the determined safety coefficient. The order quantity can be adjusted while referring to an evaluation criterion such as a service rate predicted when the order proposal is corrected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a computer according to an embodiment.

FIG. 2 is a diagram illustrating a data configuration of a product information DB 11 according to the embodiment.

FIG. 3 is a diagram illustrating a data configuration of a demand forecast DB 15 according to the embodiment;

FIG. 4 is a PAD diagram showing a schematic procedure of processing of a safety coefficient calculation module 4 and an evaluation criterion calculation module 5 of the embodiment.

FIG. 5 is a PAD diagram illustrating a flow of processing for calculating a safety coefficient according to the embodiment.

FIG. 6 is a PAD showing a flow of processing of an evaluation criterion calculation module 5 of the embodiment.

FIG. 7 is a PAD diagram showing a schematic procedure of a process of an order proposal calculating module 6 of the embodiment.

FIG. 8 is a diagram showing a display example of an evaluation criterion calculation result.

FIG. 9 is a diagram showing an example of an order proposal correction screen.

[Explanation of symbols]

4: Safety coefficient calculation module, 5: Evaluation criterion calculation module, 6: Order proposal calculation module, 11: Product information D
B, 15: Demand forecast DB

Continued on the front page (72) Inventor Takao Sato 890 Kashimada, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Within the Business Solution Development Headquarters, Hitachi, Ltd. F-term in Hitachi Tohoku Software Co., Ltd. (reference) 3F022 MM07 MM28 MM32 PP04 5B049 CC27 EE31

Claims (5)

[Claims] 1. A method of calculating a safety factor of an inventory amount from a predicted amount of past demand and an actual amount using an electronic computer, the method comprising calculating the predicted amount, the actual amount, and the trial amount over a calculation target period. A safety stock coefficient is calculated from the safety coefficient to be calculated, and a theoretical service rate is calculated from the predicted amount, the actual amount, and the safety stock coefficient over the calculation target period, and the calculated service rate is substantially equal to the target service. The service factor is calculated by changing the safety factor to be tried until the service ratio is reached, and the safety factor when the service rate substantially reaches the target service rate is determined as a target safety factor. Management method. 2. The method according to claim 1, further comprising calculating a safety stock coefficient based on the target safety coefficient, and calculating a theoretical stock month from the calculated safety stock coefficient, the predicted amount and the actual amount. The inventory management method according to claim 1. 3. The method according to claim 1, further comprising: calculating a safety stock coefficient based on the target safety coefficient; and calculating an order quantity from the calculated safety stock coefficient, a future demand forecast quantity, a current stock quantity, and a remaining order quantity. The inventory management method according to claim 1, wherein 4. The inventory management method according to claim 3, wherein the correction of the order quantity is received via input means. 5. A method of calculating a safety factor of an inventory amount from a predicted amount of past demand and an actual amount by using an electronic computer, wherein the safety factor is calculated based on the actual amount and a safety factor to be tried over a calculation target period. The service rate was calculated, and the service rate was calculated by changing the safety factor to be tried until the calculated service rate was substantially equal to the target service rate, and the service rate was substantially equal to the target service rate. An inventory management method characterized in that a safety factor at the time is determined as a target safety factor.