Production planning device and program

Abstract

To create a production plan so as to minimize the total time required for production in multiple lines, considering the time for changing setups.SOLUTION: A production planning device is formed of multiple steps, and each step plans the production plan of a production line formed of multiple lines. The production planning device calculates total required time required for work in each line in each step, using a mixed integer planning system, and calculates a lot distribution method to minimize the maximum value (load time) of the total required time in each line. In this case, the production planning device calculates the load time, considering the setup changing time required for the setup changing work to occur when models to be worked are different. Input sequence of the lots distributed to each line is determined to reduce the number of times of setup changing work.SELECTED DRAWING: Figure 14B

Description

[Technical Field]

[0001] The present invention relates to a production planning device and program, and in particular to the creation of a production plan when a changeover operation occurs in a production line using a post-replenishment production method that has multiple processes, each including multiple lines that process multiple types of items in parallel, and item storage areas located between the processes.

[0002] In a production line where items to be worked on, such as work in progress and semi-finished products (hereinafter collectively referred to as "work in progress"), are sent through a series of processes in order to complete a product, it is desirable to minimize the amount of inventory held up between processes in order to keep the increase in product costs resulting from the operation of the production line low. However, if inventory is reduced too much, there is a risk that work in progress will not be able to be supplied to subsequent processes just in time.

[0003] The "post-replenishment production method" is a production method that aims to prevent inventory buildup while ensuring a continuous supply to downstream processes. The process of post-replenishment production is as follows:

[0004] That is, the subsequent process takes in only the amount of work-in-progress when it needs it from the inventory storage area set up at the end of the previous process. When taking in work-in-progress, the kanban attached to the work-in-progress (hereafter referred to as "work-in-progress kanban") is removed and placed in the kanban post. As the subsequent process continues production, multiple work-in-progress kanbans accumulate in the kanban post. These multiple work-in-progress kanbans are sent to the beginning of the previous process at regular intervals. In this way, in the previous process, the work-in-progress kanbans taken from the subsequent process become production instructions for replenishing the work-in-progress. In other words, the production plan for issuing production instructions to the previous process is drawn up based on the multiple work-in-progress kanbans sent from the subsequent process. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-92726 [Non-patent literature]

[0006] [Non-Patent Document 1] Nobuo Watanabe, "Description of Models and Computational Procedures in Mathematical Programming Software," Information Science Research, No. 33-57, (2017) Summary of the Invention [Problem to be solved by the invention]

[0007] If the upstream process has one production line and can only produce a few different product types, it is easy to create a production plan, because the production plan for the upstream process can be created by creating a single production line to produce the number of work-in-progress items of each type obtained from the multiple in-process kanbans sent from the downstream process.

[0008] However, if there are multiple production lines in the upstream process, it is necessary to allocate the number of each type of work-in-progress item obtained from the multiple in-process kanbans to each production line. This makes it difficult to create a production plan. If there were no constraints, allocation might not be difficult, but considering production efficiency, it is desirable to shorten the total time required for production as much as possible. Furthermore, when producing multiple types of products, work may be required to change jigs used for processing the products according to the type, so it is desirable to shorten the total time required for production by taking into account the time required for changing these jigs (hereinafter referred to as "changeover time").

[0009] An object of the present invention is to create a production plan that minimizes the total time required for production on multiple lines, taking into account the time required for setup changes. [Means for solving the problem]

[0010] The production planning device of the present invention is a production line that uses a post-replenishment production method and includes a plurality of processes, each including a plurality of lines that process a plurality of types of articles in parallel, and an article storage area, arranged between the processes, on which articles that have been processed in the immediately preceding process and will be processed in the immediately succeeding process are placed, and the production planning device creates a production plan for the production line in which setup work occurs when the types of articles processed on each line are different, characterized in that the production planning device has a planning means that creates a production plan by allocating the multiple types of articles to one of the lines so that the load time in each process is minimized when the total required time calculated for each process and line using mixed integer programming is the maximum of the total required times for each line included in the process, including the time required to process the articles and the setup time required for the setup work that occurs, as the load time in the process.

[0011] The planning means is also characterized in that it determines the processing order of the allocated items so as to reduce the number of occurrences of the setup changeover work.

[0012] Furthermore, the planning means is characterized in that, when repeatedly executing the creation of a production plan using the post-replenishment production method, the planning means creates a production plan so that the type of item to be processed first is the same as the type of item that was last processed in the creation of the immediately preceding production plan.

[0013] The planning means is characterized in that it prepares a production plan so that setup changeovers do not occur simultaneously in each line included in each process.

[0014] The program of the present invention causes a computer to function as planning means for creating a production plan for a production line that uses a post-replenishment production method and that includes a plurality of processes, each including a plurality of lines that process a plurality of types of articles in parallel, and an article storage area, located between the processes, on which articles that have been processed in the immediately preceding process and will be processed in the immediately succeeding process are placed, in which setup work occurs when the types of articles processed on each line are different.The program causes a computer to function as planning means for creating a production plan for a production line that uses a post-replenishment production method and that in which setup work occurs [Effects of the Invention]

[0015] According to the present invention, it is possible to formulate a production plan that minimizes the total time required for production on a plurality of lines, taking into consideration the time required for setup changeover. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a block diagram showing an embodiment of a production planning device according to the present invention; [Figure 2] FIG. 1 is a diagram showing a typical configuration example of a production line according to an embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing Table 1 for explaining the arrows shown in FIG. 2. [Figure 4] FIG. 2 is a conceptual diagram showing the equipment configuration of each line included in each process in the present embodiment. [Figure 5] FIG. 2 is a conceptual diagram showing the line configuration of each process included in the production line in the present embodiment. [Figure 6A] FIG. 2 is a diagram showing Table 2-1 showing cycle times for each piece of equipment handled in this embodiment. [Figure 6B]FIG. 6B is a diagram showing Table 2-2, which follows FIG. 6A and shows the cycle time for each piece of equipment. [Figure 7] 10 is a flowchart showing the flow of a production planning process in the present embodiment. [Figure 8] 10 is a flowchart showing an nth process planning process in the present embodiment. [Figure 9] FIG. 10 is a conceptual diagram showing the results of lot allocation in the present embodiment using a Gantt chart. [Figure 10] FIG. 3 is a diagram showing Table 3 showing parameters related to the production line in the present embodiment. [Figure 11] FIG. 4 is a diagram showing Table 4 showing parameters relating to product numbers in the present embodiment. [Figure 12] FIG. 5 is a diagram showing Table 5 showing parameters related to lots in the present embodiment. [Figure 13] FIG. 6 is a diagram showing Table 6 showing parameters used when determining allocation of lots to production lines in this embodiment. [Figure 14A] FIG. 10 is a conceptual diagram showing, using a Gantt chart, the allocation of lots before the lot allocation process according to the present embodiment is performed. [Figure 14B] FIG. 10 is a conceptual diagram showing, using a Gantt chart, the allocation of lots after the lot allocation process according to the present embodiment has been performed. [Figure 15] FIG. 7 is a diagram showing Table 7 showing an example of setting trial condition 1 in the present embodiment. [Figure 16] FIG. 7 is a diagram showing Table 7 showing an example of setting trial condition 2 in this embodiment. [Figure 17A] 10 is a graph showing a production plan created by production planning device 10 in the present embodiment operating in accordance with trial condition 1 and changes in inventory quantity in the inter-process buffer. FIG. [Figure 17B] FIG. 17B is a graph following FIG. 17A. [Figure 18A]10 is a graph showing the transition of the production plan created by the production planning device 10 in the present embodiment operating in accordance with trial condition 2 and the inventory quantity in the inter-process buffer. FIG. [Figure 18B] FIG. 18B is a graph following FIG. 18A. [Figure 19] FIG. 2 is a diagram showing details of line #3 of the first process in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0018] 1. Configuration of the production planning system 1 is a block diagram showing an embodiment of a production planning device according to the present invention. The hardware of the production planning device 10 in this embodiment can be realized by one or more computers such as a server computer or a personal computer. The hardware of the production planning device 10 can be realized by a conventional general-purpose device configuration. That is, the production planning device 10 is configured by connecting a CPU, ROM, RAM, a hard disk drive as storage means, a network interface as communication means, and a user interface including input means such as a mouse and keyboard and display means such as a display to an internal bus.

[0019] The production planning device 10 in this embodiment has an information input / output unit 11, an inventory management unit 12, and a planning unit 13. Components that are not used in the description of this embodiment are omitted from the drawing.

[0020] The information input / output unit 11 acquires information necessary for planning and inventory management, such as information managed by the production management system and information specified by the user, via the network, or information entered on the screen by a manager, etc. The information input / output unit 11 also provides the processing results of the production planning device 10, i.e., the planned production plan, etc., to the production management system or a computer used by the manager via the network, or by outputting it on the screen. The inventory management unit 12 manages the number of items placed in the inter-process buffer, or so-called inventory, when planning a production plan. The planning unit 13, which constitutes the main part of this embodiment, creates a production plan by referring to the information input by the information input / output unit 11 and the inventory quantity managed by the inventory management unit 12.

[0021] Each of the components 11 to 13 in the production planning device 10 is realized by the cooperative operation of a computer that constitutes the production planning device 10 and a program that runs on a CPU installed in the computer.

[0022] Furthermore, the programs used in the present embodiment can be provided not only by communication means, but also by being stored in a computer-readable recording medium such as a CD-ROM or USB memory. The programs provided from the communication means or recording medium are installed in a computer, and various processes are realized by the computer's CPU sequentially executing the programs.

[0023] 2.Production line configuration 2.1 Production Line Overview Next, a production line to which the production planning device 10 of this embodiment is suited will be described.

[0024] FIG. 2 is a diagram showing a typical example of the configuration of a production line in this embodiment. In this embodiment, a production line consisting of three processes, a first process, a second process, and a third process, will be described as an example. The process configuration shown in FIG. 2 is one example, and the number of processes does not need to be limited to this. In the production line shown in FIG. 2, the first process is shown as the first process and the third process as the last process, but other processes may be provided before the first process or after the third process.

[0025] Between each process, an inter-process buffer is installed to store intermediate inventory. Specifically, inter-process buffer 1 is installed between the first and second processes, and inter-process buffer 2 is installed between the second and third processes. Inter-process buffer 1 is a work-in-process storage area where work-in-process items processed in the immediately preceding first process are placed. The second process immediately following the first process retrieves the required number of work-in-process items from inter-process buffer 1 when needed and processes the work-in-process items. In this embodiment, work-in-process items are used as an example of the items to be processed in each process. In the third process, the work-in-process items are processed to complete the items as products. Furthermore, processing of work-in-process items includes various processes for finishing them into products. In this embodiment, "processing" and "processing" are used synonymously. Inter-process buffer 2 is a work-in-process storage area where work-in-process items processed in the immediately preceding second process are placed. The third process immediately following inter-process buffer 2 retrieves the required number of work-in-process items from inter-process buffer 2 when needed.

[0026] The production planning system 10 in this embodiment creates a production plan suitable for a production line using a replenishment production method. Here, the "replenishment production method" in this embodiment refers to a method in which a process immediately preceding a process replenishes the amount of work-in-progress received by a process. Here, if the "process" that received the work-in-progress is referred to as the "subsequent process" and the "immediately preceding process" as the "previous process," then, for example, if the subsequent process is the second process, the previous process is the first process. Taking this example, the second process retrieves only the necessary amount of work-in-progress from the inter-process buffer 1 when needed. When retrieving the work-in-progress, the second process removes the kanban (hereinafter referred to as the "in-progress kanban") associated with the work-in-progress and places it in the kanban post. As the second process continues production, multiple in-progress kanbans accumulate in the kanban post. These in-progress kanbans are sent to the beginning of the first process at regular intervals and serve as production instructions for the first process to replenish the work-in-progress received by the second process. In other words, the production plan for the first process is made based on the multiple in-process kanbans that arrive from the kanban post. Incidentally, as will be explained in more detail later, if the upstream process has a single production line and can produce only a few different product types, it is relatively easy to make a production plan. However, if the upstream process consists of multiple lines, it becomes relatively difficult to make a production plan because production instructions based on the multiple in-process kanbans must be assigned to one of the lines. Note that, since production instructions are given to each line according to the made-up production plan, in this embodiment, the terms "production plan" and "production instructions" are used interchangeably.

[0027] 2.2 Flow of Work-in-Process and In-Process Kanban In Figure 2, in addition to the configuration of the production line, the movement of work-in-progress items and in-process kanbans is also shown with arrows. Figure 3 shows Table 1, which explains the arrows shown in Figure 2. In Figures 2 and 3, black arrows indicate the movement of work-in-progress items, and gray arrows indicate the movement of in-process kanbans. Figures 2 and 3 show six types of arrows, each with an identifying number (No.). The flow of work-in-progress items and in-process kanbans will be explained below, and in the following explanation, these numbers will be used to identify the arrows.

[0028] In the third process, the work-in-progress items to be processed are retrieved from the inter-process buffer 2 (No. 1) and processed (No. 2). At this time, the technician who retrieved the work-in-progress items removes the in-progress kanbans attached to the work-in-progress items and places them in the kanban post (No. 3). After repeating steps 1 through 3 for a predetermined time, the in-progress kanbans accumulated in the kanban post are moved manually or mechanically to the beginning of the second process (No. 4). Based on the transferred in-progress kanbans, a production plan is then created (No. 5) that serves as the production instructions for the second process. In this embodiment, the "production instructions" determine the lines to which all work-in-progress items listed on the in-progress kanbans are assigned and the order in which they are to be loaded onto those lines. The technician in the second process retrieves the work-in-progress items from the inter-process buffer 1 (No. 1) and begins processing them (No. 2) in accordance with the production instructions. At this time, the in-process kanban moves to the second process together with the work-in-progress (No. 6).

[0029] As described above, the work-in-progress moves through a plurality of processes while being processed, while the in-process kanban circulates within each process and serves as a production instruction for that process.

[0030] 2.3 Process configuration Fig. 4 is a conceptual diagram showing the equipment configuration of each line included in each process in this embodiment. Each line is provided with one or more pieces of equipment that perform some kind of processing, such as machining, on work-in-progress items of a given product number, and the work-in-progress items are subjected to the desired processing on that line. In this embodiment, each line included in each process is realized with the same equipment configuration. The lines will be described later.

[0031] As shown in FIG. 4(a), each line included in the first process in this embodiment is configured to process work-in-progress products in sequence using seven pieces of equipment 1-1 to 1-7. Also, as shown in FIG. 4(b), each line included in the second process in this embodiment is configured to process work-in-progress products in sequence using nine pieces of equipment 2-1 to 2-9. While the second and third processes are configured with multiple stages of equipment, each line included in the third process in this embodiment is configured with only one piece of equipment 3-1, as shown in FIG. 4(c). Note that each piece of equipment is assigned an equipment number, "mn," as described above (m is the process number, and n is the sequence number within the process). Therefore, each piece of equipment is identified by a combination of a line number and an equipment number.

[0032] The number of pieces of equipment and the connection relationships of the pieces of equipment provided on each line are merely examples, and are not limited to the number of pieces of equipment and the connection relationships that are only serial as shown in FIG.

[0033] Fig. 5 is a conceptual diagram showing the line configuration of each process included in a production line in this embodiment. In this embodiment, a mixed production line is targeted, in which there are multiple lines like the one shown in Fig. 4, and each process can flexibly select a line for each product number. Fig. 5 shows a conceptual diagram of multiple lines. Note that each line is a production line that produces work-in-progress, but to avoid confusion with the overall production line that is the target of production planning shown in Fig. 2, the production line included in each process will be simply referred to as a "line."

[0034] As shown in Figure 5, the first, second, and third processes in this embodiment are each comprised of an equal number of lines, 10 in total. Such a production line is generally called a "flexible flow shop." Hereinafter, each line in the first, second, and third processes will be numbered and referred to as "line #." In the diagram, each line will be represented as "#n" (n is the line number).

[0035] As shown in Figure 5, work-in-progress items processed on each line in the first process are temporarily collected in inter-process buffer 1 and then moved to the second process. In this case, work-in-progress items processed on any line in the first process can be processed on any line in the second process. Furthermore, work-in-progress items processed on each line in the second process are temporarily collected in inter-process buffer 2 and then moved to the third process. In this case, work-in-progress items processed on any line in the second process can be processed on any line in the third process. As in Figure 2, arrows indicating the movement of work-in-progress items and in-process kanbans are also shown in Figure 5. The movement itself is the same as in Figure 2, so a detailed explanation is omitted here. The purpose of this embodiment is to create a production plan including production instructions for each of the 10 lines in each process based on multiple in-process kanbans moved to the beginning of the previous process.

[0036] 3. Example of Production Planning 3.1 Cycle time for each part number and each piece of equipment In this embodiment, a production plan is created to produce 100 product part numbers using the production lines identified in Figures 2, 4, and 5. Also, 24 units of each part number are to be produced, for a total of 2,400 units. The specified number of work-in-progress units in one lot is 12 units. One lot contains work-in-progress units of the same part number. Figures 6A and 6B show Tables 2-1 and 2-2, respectively, which show the cycle times for each part number and piece of equipment. These cycle times were set by simulating actual production conditions. Table 2-1 shows the cycle times for part numbers w001 to w050, and Table 2-2 shows the cycle times for part numbers w051 to w100 following Table 2-1. Equipment is indicated using the equipment numbers shown in Figure 4. There are five product types, each containing 20 part numbers. In this embodiment, the product types are referred to as "Product 1" to "Product 5." When the type of work-in-progress being processed on each line is changed, a changeover operation (hereinafter referred to as "changeover") is required to change to a jig used for processing the new type. In this embodiment, the time required for the changeover operation accompanying a change in type (hereinafter referred to as "changeover time") is set to 57 seconds. This is the same value as the maximum cycle time in Tables 2-1 and 2-2 (the corresponding part is shaded gray). The cycle times for multiple lines in each process are the same as those in Tables 2-1 and 2-2. In other words, the cycle times for each part number on each line within the same process (lines #1 to #10 in the first process, lines #11 to #20 in the second process, and lines #21 to #30 in the third process) are the same.

[0037] 3.2 Production planning process flow In this embodiment, the task of collecting multiple in-process kanbans from the kanban post and moving them to the head of the previous process is performed every two hours. In other words, the maximum value of the so-called lead time is set to two hours. Also, the time it takes for an in-process kanban to move from the kanban post to the head of the previous process is set to zero seconds.

[0038] An outline of the flow of the production planning process in this embodiment will be explained below using the flowchart shown in Fig. 7. In the production planning process in this embodiment, a production plan is created for the preceding process to replenish work-in-progress that has been taken over from the inter-process buffer by the following process over the next two hours.

[0039] First, the information input / output unit 11 collects information required prior to formulating a production plan (step 110). The information to be collected includes the cycle time for each piece of equipment and each part number shown in FIGS. 6A and 6B, the number of lots for each piece of equipment produced in the third process, the initial number of lots in the inter-process buffers 1 and 2 (hereinafter referred to as "initial inventory"), and the operating status of each of the 10 lines in the first, second, and third processes. The information is collected from an information storage location or management system, such as a production management system that manages production on the production lines according to the formulated production plan. Alternatively, the information may be input by a user such as a manager.

[0040] Next, the planning unit 13 creates a production plan for each process, and in this embodiment, the production plans are created in order from the later process to the earlier process. To do this, the final Nth process is substituted for variable n (step 120). In this embodiment, N=3 as shown in FIG. 2. In this embodiment, the explanation will be given with reference to the drawings, and for convenience of explanation, the explanation will be given assuming N=3.

[0041] First, in the case of the third process (Y in step 130), the planning unit 13 creates a plan that minimizes the load time for line 10 of the third process (step 150). Since there is no inter-process buffer 3, there is no need to calculate inventory quantities. In this embodiment, the "load time" refers to the maximum total time required for processing each line in each process. In other words, the maximum time required for processing each of the 10 lines is the load time for that process. Since the shorter the load time (i.e., the smaller the maximum value), the higher the production efficiency. Therefore, in this embodiment, the aim is to create a production plan that maximizes production efficiency in each process. Details of the planning process will be described later, but in this embodiment, the planning calculations are performed using mixed integer programming. For the third process, for which a production plan is first created, a two-hour production plan is created with a start time of zero seconds. The third process retrieves work-in-progress required for processing from the inter-process buffer 2. When a work-in-progress item is taken from the inter-process buffer 2, the in-process kanban attached to the work-in-progress item is removed and placed in a designated kanban post.

[0042] Since there is no inter-process buffer 3 (Y in step 160), step 170 is not executed. Next, the target of planning shifts to the second process (N in step 180, 190).

[0043] In the case of the second process (N in step 130), the inventory management unit 12 calculates the inventory quantity of each product number stored in the inter-process buffer 2 (step 140). The inventory quantity of each product number can be calculated by subtracting the number of work-in-progress items taken in the third process for each product number from the initial inventory of that product number in the inter-process buffer 2 obtained in step 110.

[0044] Next, the planning unit 13 creates a plan that minimizes the load time for line 10 of the second process, just as in the case of the third process (step 150). Details of the production planning process will be described later. However, the start time of the third process is set to zero seconds, while the start time of the second process is set to two hours later. Specifically, a production plan for two hours, from two hours to four hours after zero seconds, is created. Furthermore, the second process retrieves work-in-progress required for processing from the inter-process buffer 1. When retrieving the work-in-progress from the inter-process buffer 1, the work kanban attached to the work-in-progress is removed and placed in the designated kanban post.

[0045] Next, the inventory management unit 12 updates the inventory status of the inter-process buffer 2 (N, 170 in step 160). That is, the inventory management unit 12 adds, for each product number, the number of work-in-progress items to be replenished in the second process based on the production plan drawn up in step 150 to the inventory quantity of each product number placed in the inter-process buffer 2 calculated in step 140.

[0046] Next, the target of planning shifts to the first process (N, 190 in step 180), and in the case of the first process (N in step 130), the inventory management unit 12 calculates the inventory quantity of each product number placed in the inter-process buffer 1 (step 140). The inventory quantity of each product number can be calculated by subtracting the number of work-in-process items taken in the second process for each product number from the initial inventory of that product number in the inter-process buffer 1 obtained in step 110.

[0047] Next, the planning unit 13 creates a plan for the first process, line 10, that minimizes the load time, as in the third and second processes (step 150). Details of the production planning process will be described later. However, the start time of the third process is set to zero seconds, the start time of the second process is set to two hours later, and the start time of the first process is set to four hours later. Specifically, a production plan for two hours, from four hours after zero seconds to six hours after, is created. Furthermore, in the first process, raw materials required for processing are supplied as needed.

[0048] Next, the inventory management unit 12 updates the inventory status of the inter-process buffer 1 (N, 170 in step 160). That is, the inventory management unit 12 adds, for each product number, the number of work-in-progress items to be replenished in the first process based on the production plan drawn up in step 150 to the inventory quantity of each product number placed in the inter-process buffer 1 calculated in step 140. Here, n=1 (Y in step 180), so the process ends.

[0049] The series of processes described above allows for the creation of two-hour production plans for each of the first, second, and third processes. However, each preceding process will be scheduled with a two-hour delay from its succeeding process. Therefore, in this embodiment, it is desirable to create a production plan by repeating the production plan creation process shown in FIG. 7 multiple times.

[0050] 3.3 Overview of the nth process planning process Fig. 8 is a flowchart showing the nth process planning process in this embodiment, which corresponds to step 150 in the flowchart shown in Fig. 7. The nth process planning process is composed of three steps: allocating lots to each line (step 151), determining the input sequence for each line (step 152), and refining the processing time (step 153).

[0051] The allocation of lots to each line (step 151), which corresponds to the first stage, allocates the lot to 10 lines in each process. As mentioned above, the lot contains 12 work-in-progress units of the same part number. In this process, the total required time is calculated for each line based on the "bottleneck cycle time," which is the maximum cycle time for each lot on the line. At this time, a method for allocating lots that minimizes the maximum value of the total required time for each line (the above-mentioned "load time") is calculated for each process.

[0052] The determination of the introduction order for each line (step 152), which corresponds to the second stage, determines the introduction order for the lots allocated to each line based on the processing results of the first stage. This process is effective when the production planning process shown in Fig. 7 is repeated multiple times. If each repetition is expressed as a "round," such as the first round, the second round, etc., in this embodiment, the process is limited to determining the type of lot to be introduced first in each round on each line.

[0053] The third stage, refining the processing time (step 153), involves determining the detailed processing time for each piece of equipment on each line, taking into account the processing results from the second stage, i.e., the order in which lots are input. Specifically, the processing time for each piece of work-in-progress on multiple pieces of equipment that make up the line is determined by calculation based on a Gantt chart. Calculations based on a Gantt chart can be performed using existing technology. For example, the calculations described in "Foundations of System Theory Using Max Algebra" by Ushio Toshimitsu, Lectures of the Research Institute for Mathematical Sciences, Vol. 1020 (1997), pp. 165-179, are used.

[0054] 3.4 Allocating lots to each line (Step 151) This process is implemented by improving the knapsack problem. As described above, the planning unit 13 calculates how to allocate lots so as to minimize the maximum value of the total required time (the above-mentioned "load time") for each of the 10 lines included in one process.

[0055] FIG. 9 is a conceptual diagram using a Gantt chart to illustrate the results of lot allocation in this embodiment. FIG. 9 illustrates the results of lot allocation in the first process, and excerpts a portion of this allocation result included in the first process, specifically the total required times for lines #1 to #3. For ease of explanation, lines #4 to #10 will not be considered. Focusing on the total required times for lines #1 to #3 shown in the figure, line #1 has the largest total required time, so the total required time for line #1 is the load time for the first process. As shown in FIG. 9 , in this embodiment, the load time is calculated including the setup time required when switching between different lot types. This process does not take into account the order in which different lot types are introduced. For example, it is determined that three units of type 1, two units of type 2, and two units of type 1 are to be allocated to line #1, but the order in which types 1, 2, and 3 are introduced is not determined.

[0056] As described above, in this embodiment, the mixed integer programming method is used to perform calculations for formulating a production plan. In this embodiment, this calculation is formulated. The calculation formula will be explained below.

[0057] First, in accordance with mathematical notation, each parameter is described as a set. Figures 10, 11, and 12 show Tables 3, 4, and 5, respectively, which summarize parameters related to production lines, part numbers, and lots. To provide a concrete image of each set, examples of the corresponding sets are shown on the right side of Tables 3, 4, and 5. Furthermore, R and N represent a real number and a non-negative integer, respectively. Figure 13 also shows Table 6, which shows the parameters used when determining the allocation of lots to production lines. Specific examples will be omitted for Table 6.

[0058] From Tables 2 to 5, the load time LT of the i-th production line in process q i is expressed by equation (1).

number

[0059] The first term of equation (1) indicates the load time excluding the setup change time on the i-th line. However, max(N ji ) indicates the maximum cycle time (bottleneck cycle time) on the i-th line of lot j. The second term indicates the sum of the setup changeover times on the i-th line. In this embodiment, as shown in equation (1), the load time LT of each line i is calculated taking into account the setup changeover time. i Calculate.

[0060] σ in the second term of Eq. (1) ir is calculated using the following equations (2) to (4).

number

[0061] Here, M∈R is a sufficiently large number, for example, 100 or 200. Equations (3) and (4) use a technique for generating indicator variables called the big-M method.

[0062] Next, the objective function of this algorithm is shown in equation (5). Equation (5) shows that the maximum value of the load time of all lines expressed by equation (1) is minimized.

number

[0063] In this embodiment, the lot allocation method is as shown in equation (5), that is, x iy The arrangement of 0s and 1s in is determined (see Table 6). Next, the constraints for finding equation (1) are shown in equation (6). Equation (6) indicates that each lot is allocated to one line.

number

[0064] 3.5 Determining the input order for each line (step 152) In the above "3.4 Allocating Lots to Each Line (Step 151)", the order in which lots are introduced into each line is not taken into consideration. For example, in Fig. 9, the lots are arranged for convenience, but the arrangement of the lots shown in Fig. 9, i.e., the order in which lots are introduced, is not necessarily an efficient production plan. In this process, the order in which lots are introduced is determined based on the processing result in step 151.

[0065] FIG. 14A is a conceptual diagram using a Gantt chart to show lot allocation before this process is performed. Similar to FIG. 9, FIG. 14A shows an example of allocation for the first and second rounds in the first process when a production plan is created using the post-replenishment production method multiple times. Similarly to FIG. 9, FIG. 14A also shows a specific example of allocation only to lines #1 to #3. Note that in this embodiment, lots to be input are divided into groups by type (hereinafter referred to as "lot groups"), and their order is determined. Line #1 in FIG. 14A shows that lots have been divided into three groups A, B, and C, each consisting of type 1, 2, and 3, respectively.

[0066] In the allocation for the second and subsequent rounds, the first lot to be introduced may be introduced without considering the type of the last lot introduced in the previous round (i.e., the first round). For example, lots may be introduced in each round in ascending order of product type number. In this case, as shown in FIG. 14A, the type of the lot introduced last in the first round will be different from the type of the lot introduced first in the second round, increasing the possibility of a changeover occurring at the start of the second round. Furthermore, because changeovers will occur simultaneously on each line at the start of the second round, a situation may arise in which a single technician performing the changeovers will not be able to keep up with the production plan. In other words, to comply with the production plan, multiple technicians, for example, the same number of technicians as the number of lines, will be required.

[0067] FIG. 14B is a conceptual diagram using a Gantt chart to illustrate the allocation of lots after this process is performed. Similar to FIG. 14A, FIG. 14B illustrates an example of allocation for the first and second rounds in the first process. However, in FIG. 14B, this process is applied to allocation from the second round onward, and the lot to be introduced and processed first in the second round is determined taking into account the type of the lot that was introduced last and processed in the immediately preceding round (i.e., the first round). Specifically, if the same type of lot as the type of the lot introduced last in the immediately preceding round (i.e., the first round) is allocated to two types, the planning unit 13 determines the order in which lot groups of the same type are introduced in the second round so that lot groups of the same type are processed consecutively. This makes it possible to create a production plan that does not require a changeover at the start of the second round, as illustrated in FIG. 14B. In other words, it is possible to reduce the number of changeovers by one. Figure 14B shows the change in the order of lot groups only on line #1, but changing the order of lot groups as in this example does not increase the load time of the line. Rather, by changing the order in which the lots are input, it is possible to avoid the need for a changeover at the start of the second cycle, and further reduce the number of changeovers. In other words, the total time required on the line can be shortened.

[0068] 14B, the introduction order of the lot groups is determined so that no changeover occurs at the start of the second cycle on any of the lines, but a changeover may occur at the start of the second cycle on at most one line. Even in this case, one skilled worker can handle it. In this way, the planning unit 13 may determine the introduction order of the lots using the number of skilled workers as a constraint.

[0069] Incidentally, in this embodiment, the explanation has been given focusing on the start of the second or subsequent cycles, but there is also the possibility that setup changeovers may occur simultaneously on multiple lines during one cycle of one process. In this case, the planning unit 13 may make adjustments to prevent setup changeovers from occurring simultaneously on each line by, for example, swapping the order of lot groups as at the start of the cycle. In this embodiment, the explanation has been given focusing on the first process, but it is desirable to formulate a production plan that minimizes simultaneous setup changeovers in all processes constituting the production line.

[0070] 3.6 Processing Time Detailing (Step 153) In this process, the processing time is calculated for each lot allocated to each line in the first stage, for each work-in-progress item that makes up the lot, and for each piece of equipment that makes up the line. The planning unit 13 can calculate each processing time by accumulating the processing time, for example, by referring to Tables 2-1 and 2-2. Then, the planning unit 13 can calculate the total required time for each line and the load time for each process by referring to the number of lots to be input for each part number and the number of setup changes determined in the second stage.

[0071] 4. Trial Example A specific example will be given to explain what kind of production plan is created by the operation of the production planning device 10 in this embodiment. Here, the explanation will be divided into a case where a trial is performed when all lines #1 to #30 in all processes are operating normally and a case where this is not the case.

[0072] Table 7, showing an example of setting Trial Condition 1, is shown in Figure 15, and Table 7, showing an example of setting Trial Condition 2, is shown in Figure 16. The trial conditions to be set are "lines operating normally," "number of lots to be produced in the third process," "initial inventory in inter-process buffer 1," and "initial inventory in inter-process buffer 2." As in the example of setting "lines operating normally," Trial Condition 1 is a trial condition when all lines #1 to #30 are operating normally. Trial Condition 2 is an example of a case where two lines, line #1 of the first process and line #11 of the second process, are stopped. Conditions other than the operating lines are the same for both Trial Conditions 1 and 2. That is, the number of lots to be produced in the third process, i.e., the production line exemplified in this embodiment, produces two lots per cycle time. As mentioned above, one lot contains 12 work-in-process units of the same part number. The initial inventory in inter-process buffers 1 and 2 is four lots for each of part numbers w100 to w300, i.e., 48 units. In trials based on trial conditions 1 and 2, the production planning process described in 3.2 above is repeated three times to create a six-hour production plan for each process.

[0073] 4.1 When all lines are operating normally 17A and 17B are graphs showing the transition of the production plan created by the production planning device 10 operating in accordance with trial condition 1 shown in Fig. 15 and the inventory quantities in the inter-process buffers 1 and 2. When Fig. 17A and Fig. 17B are described without distinction, they will be collectively referred to as "Fig. 17." The same applies to Fig. 18, which will be described later.

[0074] In Figure 17, the horizontal axis represents time. The graphs with "First Process," "Second Process," and "Third Process" on the vertical axis represent Gantt charts for each line of the corresponding process. Note that some lines are omitted for convenience. In the Gantt chart, the work-in-progress items to be processed are shown in different patterns for each product type. Although not shown in Figure 17, changeover time is indicated in black. Each of lines #1-#10 and #11-#20 in the first and second processes consists of multiple pieces of equipment, 1-1-1-7 and 2-1-2-10, respectively. However, Figure 17 shows all the equipment together by line. This point will be discussed later. The graphs with "Inter-Process Buffer 1" and "Inter-Process Buffer 2" on the vertical axis represent the number of lots stored as inventory in each buffer. Note that the inventory transitions shown in Figures 17 and 18 are merely conceptual and may not represent accurate actual values.

[0075] As mentioned above, the production planning process shown in Figure 7 is performed three times for each process. In Figure 17, the time ranges for each cycle are indicated by double-headed arrows at the top of the Gantt chart, along with the notation "1st cycle," "2nd cycle," and "3rd cycle." As is clear from Figure 17, the calculations for the first cycle are shifted by two hours: from 0 seconds to 2 hours for the third process, from 2 hours to 4 hours for the second process, and from 4 hours to 6 hours for the first process. In other words, the production plan for the preceding process is formulated based on the production results of the succeeding process. Furthermore, as is clear from the processing procedure shown in Figure 7, the inventory changes in inter-process buffers 1 and 2 are also calculated appropriately in conjunction with these calculations.

[0076] In the calculation of each cycle for each process, a plan for 10 lines is created to minimize load time. However, according to the above trial condition 1, it took about 3 minutes to create a 2-hour plan for each process. Under trial condition 1, five varieties are produced on 10 lines each in the first and second processes, so production can be simply divided into two lines for each variety. Therefore, it is possible to create a production plan that does not require setup time, as shown in the example in Figure 17. For the sake of convenience, an example is shown in which a setup change occurs in the third process. However, as a result of performing the above "3.5 Determining the input sequence for each line (step 152)," a production plan is created so that setup change does not occur simultaneously on multiple lines, even at the beginning of the second cycle and thereafter, and even during each cycle.

[0077] 4.2 If any line is not operating normally 18 is a graph showing the transition of the production plan created by the production planning system 10 operating in accordance with trial condition 2 shown in FIG. 16 and the inventory quantities in the inter-process buffers 1 and 2. The way to read the graph is the same as in FIG. 17, so the explanation will be omitted.

[0078] In Figure 18, as indicated by dashed lines 31 and 32, line #1 of the first process and line #11 of the second process are not producing any products because it is assumed that the production lines will be stopped. Under trial condition 1, all 10 lines are in operation, so by allocating one product type to two lines, it is possible to create a production plan that does not require setup time, as shown in the example in Figure 17. In contrast, under trial condition 2, it is necessary to produce five products on nine lines that are both in operation for the first and second processes, so simple lot allocation like in trial condition 1 is not possible, and setup changes will be required.

[0079] In the Gantt charts corresponding to the first and second processes, each line is illustrated as a parallelogram rather than a rectangle. This will be explained using the Gantt chart 33 for line #3 of the first process as an example.

[0080] Figure 19 shows details of line #3 in the first process. As mentioned above, each line #1 to #10 in the first process is composed of equipment 1-1 to 1-7. Equipment 1-2 processes the work-in-progress items flowing from equipment 1-1. Equipment 1-3 processes the work-in-progress items flowing from equipment 1-2. In other words, the subsequent equipment starts processing one cycle time later than the previous equipment. Figure 19 shows this time lag of one cycle time, but if the production status of the seven equipment 1-1 to 1-7 were illustrated as a single line, it would form a parallelogram, as shown in Figures 17 and 18. Note that the third process is composed of only one equipment 3-1, so a rectangle would suffice. Strictly speaking, the height in the direction perpendicular to the time axis of the Gantt chart may vary depending on the number of equipment included in each process. However, for convenience, Figures 17 and 18 show them at the same height.

[0081] Returning to Figure 18, under trial condition 2, both the first and second processes require nine lines to operate. In particular, the second process is unable to replenish the work-in-progress items taken over by the third process within two hours. As a result, while the production lines are operating, the inventory in inter-process buffer 2 gradually decreases compared to trial condition 1.

[0082] 5. Summary In this embodiment, when creating a production plan for a production line that uses a replenishment production method, the production instructions for each process that makes up the production line, specifically the allocation of lots to each line, are formulated using a technique called mixed integer programming. In particular, this embodiment is designed to minimize the load time at each process while taking into account replacement time. Furthermore, it is designed to determine the order in which lots, i.e., work-in-progress items, are input so that the number of setup changes required is minimized.

[0083] In this embodiment, it is assumed that the production line is made up of multiple processes, and each process is made up of multiple lines, and specific numerical values ​​have been given for the explanation. However, the number of processes, lines, and equipment used in the above embodiment are merely examples, and are not limited to these.

[0084] Furthermore, in this embodiment, work in progress has been described as an example of an item that flows through a production line, but the item does not have to be work in progress; it may be, for example, a semi-finished product or a finished product, as long as it is an item that is subject to processing or other treatment. [Explanation of symbols]

[0085] 10 production planning device, 11 information input / output section, 12 inventory control section, 13 planning section.

Claims

1. A production line employing a post-replenishment production method, the production line comprising a plurality of processes each including a plurality of lines that process a plurality of types of articles in parallel, and article storage areas disposed between the processes for storing articles that have been processed in the immediately preceding process and will be processed in the immediately succeeding process, wherein a changeover operation is required when different types of articles are processed on each line, is provided, a planning means for creating a production plan by allocating the plurality of types of articles to any of the lines so as to minimize the load time in each of the processes, when the total required time is calculated for each of the processes and lines using mixed integer programming, and the maximum value of the total required times for each line included in the process, including the time required to process the articles and the setup time required for the setup work that occurs, is calculated as the load time in the process.

2. 2. The production planning device according to claim 1, wherein the planning means determines the processing order of the allocated items so as to reduce the number of occurrences of the setup changeover work.

3. 3. The production planning device according to claim 2, wherein, when repeatedly executing production planning using a post-replenishment production method, the planning means plans the production plan so that the type of item to be processed first is the same as the type of item processed last in the immediately preceding production plan.

4. 3. The production planning device according to claim 1, wherein the planning means creates a production plan so that setup changeovers do not occur simultaneously in each line included in each process.

5. A production line employing a post-replenishment production method, which includes a plurality of processes each including a plurality of lines that process a plurality of types of articles in parallel, and article storage areas disposed between the processes, on which articles that have been processed in the immediately preceding process and will be processed in the immediately succeeding process are placed, wherein a computer that creates a production plan for the production line in which changeover work occurs when different types of articles are processed on each line, A program for functioning as planning means for formulating a production plan by allocating the multiple types of items to one of the lines so that the load time in each of the processes is minimized, when the total required time is calculated for each of the processes and lines using mixed integer programming, and the maximum value of the total required time for each line included in the process, including the time required to process the items and the setup time required for the setup work that occurs, is calculated as the load time in the process.

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