JPH0962941A - Safety stock amount calculation method - Google Patents

Abstract

(57) [Summary] [Purpose] Providing a safety stock calculation method that can place an order based on a reasonably calculated safety stock and optimize the inventory level even when supply and demand are unstable. [Structure] On the demand side, the actual difference of demand is calculated for each supply cycle period, the trend of the actual difference of demand and actual trend and the trend pattern are analyzed in time series, and the demand is met according to the analyzed trend. Calculate the safety factor. On the supply side, the actual and actual difference in supply is calculated in units of the supply cycle period, and the trend pattern of the actual and actual difference in supply and the trend pattern are analyzed in time series, and the safety factor corresponding to supply is calculated according to the analyzed transitional trend. To do. An appropriate safety stock amount is calculated based on the calculated demand forecast and demand safety coefficient and the supply schedule and supply 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,
In particular, it relates to a method for automatically calculating the safety stock amount in inventory management on the premise of periodic non-quantitative ordering.

[0002]

2. Description of the Related Art Conventionally, "practice of inventory management" has been used as an inventory management method when the expected value of demand is stable and the tendency of the difference between the expected value of demand and the actual demand amount is constant.
As described in (Yutaka Nakata, Nikkei Bunko, Chapter 7, P105 to P124), there is known a method of calculating a standard deviation from past actual demand data and calculating a safety stock amount according to a service policy.

The specific calculation method is as follows.

(1) The average demand amount is calculated from the actual demand amount within a certain range.

(2) The standard deviation is calculated from the actual demand amount and the average demand amount.

(3) A safety factor is determined according to the policy of the service rate (1-the allowable out-of-stock rate).

(4) The safety stock amount is obtained from the safety coefficient, standard deviation and lead time.

However, safety stock amount = safety factor x standard deviation x lead time

[0009]

Since the above-mentioned conventional technique is premised on that the supply and demand are stable, the expected value of demand changes with time, or the expected value of demand and the actual demand amount are When the tendency of the difference between the difference in value or the difference between the planned supply value and the actual supply amount changes with time, the safety stock amount cannot be logically derived and is often left to the experience and intuition of the person in charge. As a result, shortages and excess inventory have occurred, which has had a serious impact on companies, such as lower service quality and higher costs.

Therefore, even in such a case, the present invention has been made so that a reasonably appropriate safety stock amount can be calculated, and an object of the present invention is to stabilize the demand / supply, that is, the demand. Even if the expected value of changes with time, or the tendency of the difference between the expected value of demand and the actual demand, or the difference between the planned value of supply and the actual supply changes with time, it is calculated rationally. It is to provide an inventory management method that can place an order based on safety stock and optimize the inventory level.

[0011]

In order to solve the above-mentioned problems, the present invention assumes that the expected value of demand and the planned value of supply always change, and the difference between the expected value of demand and the actual demand amount or By grasping the change in the tendency of occurrence of the difference between the planned supply amount and the actual supply amount, and analyzing the trend pattern and trend pattern, the safety stock amount will be optimized from the next time.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, terms and basic information used in this embodiment will be defined.

The safety stock coefficient review cycle refers to the interval between reviews, such as how many months the safety stock coefficient is reviewed. A supply cycle refers to a supply-to-supply interval such as how many days a stock point is supplied.

The actual difference refers to a difference between a budget (plan) such as an expected value of a demand or a planned value of supply and an actual result, and an increase / decrease in the actual amount with respect to a numerical value of 100% of the budget is grasped as a rate (%). Furthermore, the difference between the trend formula obtained from the regression analysis of the actual / real difference and the actual value of each actual / real difference is called the actual / real deviation amount, and it is to be understood as a rate (%).

FIG. 1 is a diagram showing a basic system configuration. In FIG. 1, the safety stock amount calculation device 120 is
An apparatus for automatically calculating the safety stock amount according to the method of the present invention. The storage device 110 is a storage device such as a magnetic disk, and exchanges information with the inventory management system 100 that performs core business processing via the storage device. Basically, the storage content of the storage device 110 is limited to the information and the calculation result necessary for calculating the safety stock amount. Input device 140
Is for accepting inputs from the outside, such as complementing the information necessary for calculating the safety stock amount and outputting the calculation results.
A keyboard or mouse can be used. The output device 130 outputs a calculation status and a calculation result on a screen or a form, and a CRT display or a printer device is used. In FIG. 1, the inventory management system 100 for inventory management and the safety stock amount calculation device 120 for calculating the safety stock amount are realized by different devices.
Since both of these can be realized as software by a program, they may be executed by the same computer.

FIG. 2 is a diagram showing the relationship between the functional blocks of the safety stock amount calculation device and the stored information. The outline of each functional block is explained below together with the basic operation sequence.

In FIG. 2, first, regarding demand, the demand / actual difference calculation block 210 calculates the demand / actual difference in units of supply cycle periods, and the demand / actual difference transition trend analysis block 211 determines whether there is a trend in the demand / actual difference. And trend patterns are analyzed in time series. Then, the demand safety coefficient calculation block 212 calculates the safety coefficient corresponding to the demand along the analyzed trend. Similarly, regarding supply, the supply / actual difference calculation block 240 calculates supply / actual difference in units of supply cycle periods, and the supply / actual difference transition trend analysis block 241 determines presence / absence of trend of supply / actual difference and trend pattern. Analyze in series. Then, the safety factor corresponding to the supply is calculated in the supply safety factor calculation block 242 according to the analyzed trend. The final safety stock amount calculation block 250 calculates an appropriate safety stock amount based on the demand forecast, the demand safety coefficient, and the supply schedule and the supply safety coefficient.

The stock management specification information DB 200 holds basic information on stock management required for this method. As shown in the registration image in FIG. 3, the concrete contents of the DB include the safety stock factor review, the supply cycle, and the period information of the transition trend analysis regarding the actual difference between the demand and the supply. The specific contents of the following DB will be explained in the processing contents supplement of each functional block,
Here, only the outline of each DB will be described.

In relation to demand, the demand forecast record DB 220 is
The expected value of demand and the calculation result of the actual demand amount and the demand forecast actual difference for it are held in a time series. The demand / actual difference transition tendency DB 221 holds the analysis result of the transition tendency. The demand safety coefficient DB 222 holds the calculation result of the safety coefficient corresponding to the demand. And the demand forecast DB 223
Holds the expected value of demand from now on in time series. Each supply-related DB has the same data structure as the series of demand-related DBs, except that demand is replaced by supply. The safety stock amount DB 260 holds safety stock amount information as a final calculation result in time series.

The processing flow of the demand / actual difference calculation block will be described below with reference to FIG. The demand / actual difference calculation block is a part for calculating the demand / actual difference in units of supply cycle periods. In step 310, "supply cycle" information is obtained from the inventory management specification information DB in the storage device. In step 320, the demand forecast result information for the “supply start date + supply cycle period”, that is, the expected value of demand and the actual demand amount are obtained from the demand forecast result DB in the storage device. In step 330, the demand forecast actual difference is calculated. The following formula is applied as the calculation formula in that case.

Demand forecast actual difference = (actual demand amount-expected demand value) ÷ expected demand value × 100 In step 340, the calculation result of the demand forecast actual difference is registered in the demand forecast actual result DB.

As shown in the registration image of the demand forecast actual result DB in FIG. 5, for example, when the actual demand amount is 80 with respect to the demand expected value 100 of 7/1, the demand forecast actual difference is -20%.

Next, the processing flow of the demand forecast actual difference transition trend analysis block will be described with reference to FIG. The demand / actual difference transition trend analysis block is a part for analyzing the presence / absence of the trend of the demand / actual difference and the trend pattern in time series.

In step 410, the "target period for demand / actual difference transition trend analysis" is obtained from the inventory management specification information DB in the storage device. At step 420, the demand forecast actual difference information for the “target period of the demand forecast actual difference transition tendency analysis” is obtained from the demand forecast actual result DB in the storage device. Step 430
Then, using a straight line, a quadratic parabola, an exponential function, a logarithmic function, etc. as a tendency formula, a regression analysis of the actual demand / demand difference is performed. In step 440, the information statistic for each tendency formula is calculated, and in step 450, the tendency formula that minimizes the information statistic and best captures the transition tendency of the demand / actual difference is selected, and its coefficient of determination (multiphase relation) is selected. Number) is calculated. In step 460,
Judgment of transition tendency is made by Pearson's correlation coefficient test table. If the trend is recognized, step 470.
Add "trend" to the transition tendency recognition parameter.
If no tendency is recognized, it is considered that there is no correlation, and in step 480, “Random” is added to the transition tendency recognition parameter. In step 490, the transition tendency recognition parameter and the selected tendency formula are registered in the demand forecast actual difference transition tendency DB in the storage device as the analysis result regarding the transition tendency of the demand forecast actual difference.

Here, the contents registered in the demand / actual difference transition tendency DB are: -Trend tendency recognition parameter: "There is a transition tendency" -Tendency formula: y = 0.24t + 32.6. Therefore, the linear equation is selected as the tendency equation.

Next, the processing flow of the demand safety coefficient calculation block will be described with reference to FIG. The demand safety coefficient calculation block is a portion for calculating a safety coefficient corresponding to demand along the analyzed trend.

In step 510, the "safety stock factor review cycle" information and the "supply cycle" information are obtained from the stock management specification DB in the storage device. Step 52
At 0, the “target period of demand forecast actual difference transition trend analysis” information is obtained from the inventory management specification DB. In step 530, the analysis result regarding the transition tendency of the demand / actual difference is acquired from the demand / actual difference transition tendency DB in the storage device. In particular,
Transition trend recognition parameter and tendency formula. Step 5
At 40, the transition tendency of the demand forecast actual difference is determined. Rand
If it is other than om, it is assumed that there is a tendency, and in step 550, the safety stock coefficient review cycle and the supply cycle are compared. Subsequent calculation modes are switched according to the comparison result. If the safety stock coefficient review cycle is equal to the supply cycle, the next demand forecast actual difference forecast value is calculated according to the trend formula in step 560, and if the safety stock coefficient review cycle is longer than the supply cycle, step 5
At 70, the demand / actual difference prediction value is calculated for each supply cycle period until the next safety inventory coefficient review timing according to the tendency formula. If the safety inventory coefficient review cycle is shorter than the supply cycle, it is not considered and is not considered here. Next, at step 571, the maximum prediction value within the prediction target period is set as the next demand prediction actual difference prediction value. Further, in step 573 subsequent to step 560 and step 571, the deviation width of the demand forecast is actually corrected by residual analysis or the like. In addition, when there is no transition tendency in the demand / actual difference (Random), in step 580, the one with the largest demand / actual difference within the target period of the trend trend analysis is extracted from the demand forecast result DB, and the next demand forecast / actual difference is extracted. The difference is predicted. In this case, the shake width of the demand forecast is not corrected. In step 590, the prediction result of the next demand forecast difference is registered in the demand safety coefficient DB in the storage device as a safety coefficient for demand.

Here, the contents registered in the demand safety coefficient DB are, for example: next demand forecast actual difference predicted value: 43.3%, shake correction: 5.1%, demand safety coefficient: 48.4% Yes, the calculated value is stored here.

8 to 10 are views for conceptually explaining the prediction of the next demand forecast actual difference based on the trend tendency of the demand forecast actual difference, which is an important point of the present invention. It is possible to minimize the probability of out-of-stock occurrence by assuming a case where the actual demand amount exceeds the expected value of demand based on past results. Therefore, in the present invention, among the forecast values along the trend of the demand-actual difference, the maximum value within the forecast period (the maximum value in the past actual results within the predetermined period when no trend is seen) is the next safety value. It indicates that it will be used to calculate the safety stock amount until the inventory coefficient is reviewed.

Above, a supplementary explanation regarding the actual difference on the demand side has been given from FIG. 3 to FIG.

A supplementary explanation will be given below concerning the difference between the forecast and the actual on the supply side, but the basic idea is the same in FIGS. 7 to 10 only by replacing the demand with the supply. However, in FIG. 9 and FIG. 10, among the predicted values along the trend of the supply-actual difference, the smallest value within the prediction period (if the trend is not seen, the minimum value in the past actual results within the predetermined period). ) Is used to calculate the safety stock amount until the next revision of the safety stock coefficient. This is because the present invention uses the actual difference on the demand side as a positive (plus) variable factor and the actual difference on the supply side as a negative (minus) variable factor to offset them to obtain the final safety stock. are doing.

Next, the processing flow of the supply / actual difference calculation block will be described with reference to FIG. The supply / actual difference calculation block is a part that calculates the supply / actual difference of supply in units of supply cycle periods. In step 710, the “supply cycle” information is obtained from the inventory management specification information DB in the storage device. In step 720, the supply forecast record DB in the storage device
From this, supply forecast performance information for the "supply start date + supply cycle period", that is, the planned supply value and the actual supply amount are obtained. In step 730, the supply / actual difference is calculated. The following formula is applied as the calculation formula in that case.

Supply / actual difference = (actual supply amount-scheduled value of supply) / planned value of supply x 100 In step 740, the calculation result of the supply / actual difference is registered in the supply forecast result DB.

FIG. 12 designates the contents registered in the supply forecast actual result DB. For example, when the actual supply amount is 120 with respect to the expected supply value 100 of 7/1, the supply forecast actual difference is 20%.
Becomes

Next, the processing flow of the supply / actual difference transition tendency analysis block will be described with reference to FIG. The supply / actual difference transition tendency analysis block is a part for analyzing the presence / absence of the tendency of supply / actual difference and the tendency pattern in time series.

At step 810, the "target period for supply / actual difference transition trend analysis" is obtained from the inventory management specification information DB in the storage device. In step 820, the supply forecast / actual difference information for the “target period of the supply forecast / actual difference transition tendency analysis” is acquired from the supply forecast / actual result DB in the storage device. Step 830
Then, using a straight line, a quadratic parabola, an exponential function, a logarithmic function, etc. as a tendency formula, a regression analysis of the actual supply / demand difference is performed. In step 850, a tendency formula that has the smallest information statistic and best captures the transition tendency of the supply / actual difference is selected, and its coefficient of determination (multiple correlation coefficient) is calculated. At step 860, the transition tendency is judged by a Pearson's correlation coefficient test table or the like. If the tendency is recognized, “propensity” is added to the transition tendency recognition parameter in step 870. If no tendency is recognized, it is considered that there is no correlation, and step 880
In step 1, "Random" is added to the transition tendency recognition parameter. At step 890, the transition tendency recognition parameter and the selected tendency formula are registered in the supply forecast / actual difference transition tendency DB in the storage device as the analysis result regarding the transition tendency of the supply / actual difference.

Here, the contents registered in the supply / actual difference transition tendency DB are, for example, the following: Level officially approved parameter: "There is a transition tendency" -Trend equation: y = -0.31t + 17.6 Therefore, the linear equation is selected as the tendency equation.

Next, the processing flow of the supply safety coefficient calculation block will be described with reference to FIG. The supply safety coefficient calculation block is a portion for calculating a safety coefficient corresponding to supply in accordance with the analyzed transition tendency.

At step 910, the "safety stock factor review cycle" information and the "supply cycle" information are obtained from the stock management specification DB in the storage device. Also, step 92
At 0, the “target period for supply / actual difference transition trend analysis” information is obtained from the inventory management specification DB. In step 930, the analysis result regarding the transition tendency of the supply / actual difference is acquired from the supply / actual difference transition tendency DB in the storage device. In particular,
Transition trend recognition parameter and tendency formula. Step 9
At 40, the transition tendency of the supply and demand difference is determined. Rand
If it is other than om, it is assumed that there is a tendency, and in step 550, the safety stock coefficient review cycle and the supply cycle are compared. Subsequent calculation modes are switched according to the comparison result. If the safety stock coefficient review cycle and the supply cycle are equal, the next supply forecast / actual difference predicted value is calculated according to the trend formula in step 960, and if the safety stock coefficient review cycle is longer than the supply cycle, step 9
At 70, the predicted supply / actual difference value is calculated for each supply cycle period until the next safety inventory coefficient review timing according to the tendency formula. If the safety inventory coefficient review cycle is shorter than the supply cycle, it is not considered and is not considered here. Next, at step 971, the maximum predicted value within the prediction target period is set as the next predicted supply / actual difference. Further, in step 973 subsequent to step 960 and step 971, the deviation amount of the supply forecast is corrected by residual analysis or the like. In addition, when the transition tendency is not recognized in the supply / actual difference (Random), in step 980, the one with the largest supply / actual difference is extracted from the supply forecast / actual result DB within the target period of the trend analysis, and the next supply / estimation difference is extracted. The difference is predicted. In this case, the fluctuation amount of the supply forecast is not corrected. At step 990, the prediction result of the next supply forecast difference is registered in the supply safety coefficient DB in the storage device as a safety coefficient for supply.

The contents registered in the supply safety coefficient DB are, for example, the following predicted value of supply / actual difference: -27.3%, shake width correction: -4.2%, supply safety coefficient: -31.5%. is there.

FIGS. 15 to 17 are diagrams conceptually illustrating the prediction of the next supply forecast actual difference based on the transition tendency of the supply forecast actual difference. It is possible to minimize the probability of out-of-stock occurrence by assuming a case where the actual supply amount is below the expected value of supply based on past results. Therefore, in the present invention, among the predicted values along the transition tendency of the supply-actual difference, the maximum value within the prediction period (when there is no transition tendency, the maximum value in the past actual results within the predetermined period) is set as the next safety value. It indicates that it will be used to calculate the safety stock amount until the inventory coefficient is reviewed.

Finally, the processing flow of the safety stock amount calculation block will be described with reference to FIG. The safety stock amount calculation block is a part for calculating an appropriate safety stock amount based on the demand safety coefficient, the supply safety coefficient, the demand forecast and the supply schedule.

In step 1110, "demand safety coefficient" information is obtained from the demand safety coefficient DB in the storage device, and "supply safety coefficient" information is obtained from the supply safety factor DB in the storage device. In step 1120, the “supply cycle” information is acquired from the physical distribution management specification information DB in the storage device. In step 1130, the demand forecast information for “supply start date + supply cycle period” is obtained from the demand forecast record DB in the storage device. In step 1140, the supply forecast record DB in the storage device
Get supply schedule information for "supply start date + supply cycle period". Then, in step 1150, the safety stock amount is calculated. The following formula is applied as the calculation formula in that case.

Safety stock amount = Expected demand value × Demand safety coefficient ÷ 100-Planned supply value × Supply safety coefficient ÷
100 In step 1160, the calculation result of the safety stock amount is registered in the safety stock amount DB in the storage device.

19 (1) to 19 (3) show the demand forecast D.
It shows the registered contents of B, the supply schedule DB, and the safety stock amount DB. The supply start date is 8/2 and the supply cycle is 3 days.
Degree, the expected value of demand in the first supply cycle 350 (80
If the demand safety factor is 40% against + 120 + 130), the demand-corresponding safety stock is 140. Similarly, if the supply safety coefficient is -10% with respect to the planned supply value 250 (250 + 0 + 0) in the first supply cycle, the supply-corresponding safety stock is -25, and the safety stock quantity is considered to be 165 in the first supply cycle.

Safety stock DB which is the result of these calculations
Shall permit the reference from the inventory management system and reflect it in the planning / management of the inventory plan. If necessary, the calculation result of the safety stock amount (including the calculation status during calculation)
Enables screen confirmation or form output through the output device.

[Brief description of drawings]

[Figure 1] Basic system configuration diagram

FIG. 2 is a diagram showing the relationship between the functional blocks of the safety stock amount calculation device and stored information.

FIG. 3 is a diagram showing registered contents of an inventory management specification information DB.

FIG. 4 is a processing flow of a demand forecast actual difference calculation block.

FIG. 5 is a diagram showing registered contents of the demand forecast result DB.

[Fig. 6] Process flow of demand forecast actual difference transition trend analysis block

[Figure 7] Demand safety coefficient calculation process flow

[Fig. 8] Prediction of the next demand forecast actual difference based on the trend of the demand forecast actual difference (Part 1)

[Fig. 9] Prediction of the next demand-actual difference based on the trend of the demand-actual difference (Part 2)

[Fig. 10] Prediction of next demand forecast actual difference based on the trend trend of demand forecast actual difference (Part 3)

FIG. 11 is a processing flow of a supply / actual difference calculation block.

FIG. 12 is a diagram showing registered contents of a supply forecast result DB.

FIG. 13: Process flow of supply / actual difference transition trend analysis block

FIG. 14: Processing flow of supply safety coefficient calculation

FIG. 15: Prediction of next supply / actual difference based on the trend of supply / actual difference (Part 1)

FIG. 16: Prediction of next supply / actual difference based on the trend of supply / actual difference (part 2)

FIG. 17: Prediction of next supply / actual difference based on the trend of supply / actual difference (Part 3)

FIG. 18: Process flow of safety stock amount calculation block

FIG. 19 (1) is a registration content of the demand forecast DB,
(2) shows the registration contents of the supply schedule DB, and (3) shows the registration contents of the safety stock amount DB.

[Explanation of symbols]

 100 inventory management system 110 storage device 120 safety stock amount calculation device 130 output device 140 input device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiji Tadokoro 2-2 Kagahara, Tsuzuki-ku, Yokohama-shi, Kanagawa Hitachi Business Systems Development Center

Claims (1)

[Claims] 1. A demand / actual difference of demand is calculated for each supply cycle period, and the presence / absence of a trend of demand / actual difference and a trend pattern are analyzed in a time series, and a safety factor corresponding to demand is analyzed along the analyzed trend. Calculate the supply / difference of supply for each supply cycle period, analyze the trend of supply / difference of supply and the trend pattern in time series, and calculate the safety factor corresponding to the supply along the analyzed trend. A method for calculating a safety stock amount, which comprises calculating a safety stock amount based on the expected demand and supply schedule, and the calculated demand safety coefficient and supply safety coefficient.