Abstract:
An apparatus for process management includes a unit that receives a planned number of a product to be produced on a production line operated by a tact system in a predetermined operating time. The unit calculates a plurality of delivery times included in the predetermined operating time, and the unit outputs instructions indicating that a part applied to the product is to be brought to the production line from the warehouse for use in a process of a plurality of processes which form the production line. Each of the plurality of delivery times indicates a planned time at which the part stored in the process runs out. The quantity of parts stored in each of the processes of the production line can be reduced because the parts are delivered at the time at which the previously stored parts run out.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present invention claims priority under 35 USC 119 based on Japanese patent application No. 2004-293283, filed on Oct. 6, 2004. The subject matter of these priority documents is incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a process management apparatus and a process management method. More specifically, the present invention relates to a process management apparatus and a process management method for calculating a schedule of a production line.  
         [0004]     2. Description of the Related Art  
         [0005]     To manufacture a product by an appointed day, process management for efficiently carrying parts that constitute the product is performed.  FIG. 6  shows a factory where the process management is performed. The factory, shown in  FIG. 6 , is adapted to assemble a plurality of parts into a motor vehicle, and includes a production line  101  and a warehouse  102 . The warehouse  102  is a facility for storing the parts. The parts are manufactured by customers  103  and carried to the warehouse  102  from the customers  103  by trucks  104 .  
         [0006]     The production line  101  includes a plurality of processes  106 - 1  to  106 -n (where n=2, 3, 4 . . . ). The production line  101  forms a tact system including a conveyor that carries semi-manufactured vehicles, and configured so that the conveyor is stopped for a certain length of time, and when the certain length of time passes, all the vehicles stopped in respective processes  106 -i (where i=1, 2, 3 . . . ) are carried to the next processes  106 -(i+1). That is, the processes  106 - 1  to  106 -n are equal in operating time pattern that indicates a plurality of time zones of a day in which each process operates.  
         [0007]     Each process  106 -i includes a line sidetrack space  107 -i. The line sidetrack space  107 -i stores the parts attached to a vehicle in the process  106 -i. The warehouse  102  also includes tractors  108 . Each tractor  108  carries parts  105  stored in the warehouse  102  from the warehouse  102  to the line sidetrack spaces  107 - 1  to  107 -n.  
         [0008]     The parts  105  should be carried from the warehouse  102  to the line sidetrack spaces  107 - 1  to  107 -n in a number that is a multiple of a lot size set by the customers  103 . According to conventional process management, a plurality of delivery time periods is appropriately set. Quantities of delivered parts to be delivered at the respective delivery time periods are then calculated. The quantity of parts to be delivered at each delivery time period is a multiple of the lot size, and is set to the quantity by which the parts are kept in the warehouse  102  until the next delivery time period.  
         [0009]      FIG. 7  shows the total stock for the case in which conventional process management is performed. In  FIG. 7 , the total stock is expressed by a value on the vertical axis of the curve  141 . It is desirable that the area of the line sidetrack space  17 -i is minimized, and that the maximum quantity of the total stock is also minimized.  
         [0010]     A stock interest, which means an interest burden caused by having the stock, is calculated according to the area of the region  142  surrounded by the curve  141  and the horizontal axis of the graph. As the area is increased, the stock interest is higher. It is desirable for the stock interest to be low.  
         [0011]     Japanese Laid Open Patent Publication No. H10-151533 (1998) discloses a part delivery time period calculating method capable of more accurately calculating a delivery time period at which parts are delivered for use on an assembly line. The part delivery time period calculation method is a method for calculating a part delivery time period in which parts are delivered for use on the assembly line having different tact time according to a vehicle type from a part working line. The method is characterized by accumulating tact time periods for the number of vehicles produced per day with a maximum tact time in tact time periods of different vehicles present on the assembly line assumed as a tact time of the assembly line to thereby calculate a flow time of a day, dividing an operating time of a day by this flow time to thereby calculate a correction value, multiplying the tact time of each vehicle by this correction value to provide a corrected tact time, accumulating the corrected tact time periods and adding the accumulated value to an opening time, and calculating a delivery time at which a specific part is delivered the assembly line.  
         [0012]     Japanese Laid Open Patent Publication No. H10-244445 (1998) discloses a part delivery indication method and a part delivery indication apparatus capable of automating an accurate, smooth, and appropriate delivery indication if it is necessary to issue a part preceding delivery indication. The part delivery indication method is a method for issuing a delivery indication for a specific part based on a production progress result at a specific position upstream of a utilization position at which the part is used. The position is determined according to a margin time required to deliver the part for the utilization position, characterized by including a preceding part calculation step of calculating a quantity of preceding parts according to a production status; and a correction step of correcting the specific position to be moved in a production line upstream direction by as much as the quantity of preceding parts.  
         [0013]     Japanese Laid Open Patent Publication No. 2000-339015 (2000) discloses a dynamic part delivery indication system for a vehicle body factory capable of preventing a shortage of stock in vehicle body production processes and a warehouse, appropriately keeping the parts in stock, and improving operation rate and thereby greatly improving productivity. This is accomplished by calculating various pieces of data necessary to deliver parts based on vehicle type information and a dynamic production plan for each process in cooperation with the system during vehicle body production, and by providing equipment and supply personnel with part delivery information that enables delivering parts necessary for the processes at necessary time and at real time. The dynamic part input delivery system for the vehicle body factory is characterized by including: a materials host that provides logistics basic information, information on parts in stock, and information on parts; a management server that manages the dynamic part delivery indication and stock in processes and a warehouse based on the part information supplied from the materials host; a management system that collects and manages information on the dynamic part delivery indication, an online correction indication for the stock in the processes and the warehouse, and information on a process-specific vehicle type, and that manages results, a present status of pressing, and a present status of the vehicle body warehouse; and an on-board radio terminal device that informs completion of delivery of the parts over radio, corrects the stock in the processes and the warehouse, and refers to a present status of the stock.  
       SUMMARY OF THE INVENTION  
       [0014]     An object of the present invention is to provide an apparatus and a method for process management capable of efficiently supplying parts from a warehouse to each production line.  
         [0015]     Another object of the present invention is to provide an apparatus and a method for process management capable of reducing a quantity of parts in stock for each process on a production line.  
         [0016]     A further object of the present invention is to provide an apparatus and a method for process management capable of reducing a stock interest of parts in stock for each process on a production line.  
         [0017]     In an aspect of the present invention, the apparatus for process management includes a number of production change registration unit that collects from an input unit a planned number of product to be produced on a production line operated by a tact system in a predetermined operating time. It also includes a delivery time calculation unit that calculates a plurality of delivery times included in the predetermined operating time, and a delivery instruction unit that outputs an instruction indicating that a part to be applied to the product is to be brought from a warehouse to a process that is included in a plurality of processes which form the production line. Each of the plurality of delivery times indicates a planned time that the part stored in the process will run out.  
         [0018]     In another aspect of the present invention, a quantity of the parts delivered during each of the plurality of delivery times is constant.  
         [0019]     In another aspect of the present invention, the apparatus for process management further includes a delivery quantity calculation unit that calculates a delivery quantity of the part delivered during each of the plurality of delivery times. A delivery quantity of the parts delivered to the process during a delivery time included in the plurality of delivery times is either a first quantity or a second quantity. The first quantity is calculated so that a first kind of part stored in the process runs out at a time that the part applied to the product in the process is changed from the first kind of part to a second kind of part. The second quantity is a constant value. The first quantity is smaller than the second quantity.  
         [0020]     In another aspect of the present invention, the apparatus for process management further includes a delivery quantity calculation unit calculating a delivery quantity of a part delivered at each of the plurality of delivery times. The plurality of delivery times are calculated so that a quantity of the part just runs out when applied to the product in the process carried out during a period between two adjacent delivery times of the plurality of delivery times. In other words, a delivery quantity of the part delivered the process at a first delivery time of the plurality of delivery times is calculated so that the part stored in the process has run out at a second delivery time, the second delivery time being adjacent to the first delivery time in the plurality of delivery times. The instruction includes a delivery quantity of the part delivered at each of the plurality of delivery times.  
         [0021]     In another aspect of the present invention, a method for process management includes the steps of: collecting a planned number of product to be produced on a production line in a predetermined operating time from an input unit, calculating a plurality of delivery times included in the predetermined operating time; and outputting an instruction indicating that a part applied to the product is to be brought in from a warehouse to a process in a plurality of processes which form the production line. Each of the plurality of delivery times indicates a planned time at which the part stored in the process is to run out.  
         [0022]     In another aspect of the present invention, a quantity of the part delivered during each of the plurality of delivery times is constant.  
         [0023]     In another aspect of the present invention, the method for process management further includes a step of calculating a delivery quantity of the parts delivered during each of the plurality of delivery times. A delivery quantity of the parts delivered to the process during a delivery time included in the plurality of delivery times is either a first quantity or a second quantity. The first quantity is calculated so that a first kind of part stored in the process is run out at a time that the part applied to the product in the process is changed from the first kind of part to a second kind of part. The second quantity is a constant value. The first quantity is smaller than the second quantity.  
         [0024]     In another aspect of the present invention, the method for process management further includes a step of calculating a delivery quantity of a part delivered at each of the plurality of delivery times. The plurality of delivery times are calculated so that a quantity of the part just runs out when applied to the product in the process carried out during a period between two adjacent delivery times of the plurality of delivery times. A delivery quantity of the part delivered the process at a first delivery time of the plurality of delivery times is calculated so that the part stored in the process has run out at a second delivery time next to the first delivery time in the plurality of delivery times. The instruction includes a delivery quantity of the part delivered at each of the plurality of delivery times.  
         [0025]     The apparatus and method for process management according to the present invention can reduce the quantity of parts in stock for each process on the production line. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  is a block diagram that depicts a factory to which a process management apparatus according to the present invention is applied;  
         [0027]      FIG. 2  is a block diagram that depicts the process management apparatus according to one embodiment of the present invention;  
         [0028]      FIG. 3  depicts an initial registration database;  
         [0029]      FIG. 4  is a flowchart that depicts an operation for calculating a method for carrying parts;  
         [0030]      FIG. 5  is a graph that depicts the total stock;  
         [0031]      FIG. 6  is a block diagram that depicts a conventional factory; and  
         [0032]      FIG. 7  is a graph that depicts the total stock when the factory is process-managed by a conventional method. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     Referring to the drawings, a process management apparatus according to an embodiment of the present invention will be described. As shown in  FIG. 1 , a factory to which the process management apparatus is applied is adapted to assemble a plurality of parts into a motor vehicle and includes a production line  1  and a warehouse  2 . The warehouse  2  is a facility for storing the parts. The parts are manufactured by customers  3  and carried from the customers  3  to the warehouse  2  by trucks  4 .  
         [0034]     The production line  1  includes a plurality of processes  6 - 1  to  6 -n (where n=2, 3, 4 . . . ). The production line  1  forms a tact system that includes a conveyor for carrying semi-manufactured vehicles, and the tact system is configured so that the conveyor is stopped for certain length of time, and when the certain length of time passes, all vehicles stopped in respective processes  6 -i are carried to next processes  6 -(i+1). Namely, the processes  6 - 1  to  6 -n are equal in an operating time pattern that indicates a plurality of time zones of a day in which each process operates.  
         [0035]     Each process  6 -i (i=1, 2, 3, . . . , n) includes a line sidetrack space  7 -i. The line sidetrack space  7 -i stores the parts to be attached to a vehicle in the process  6 -i. The warehouse  2  also includes tractors  8 . Each tractor  8  carries parts  5  stored in the warehouse  2  from the warehouse  2  to the line sidetrack spaces  7 - 1  to  7 -n.  
         [0036]      FIG. 2  shows a diagram which represents the process management apparatus according to this embodiment of the present invention. The process management apparatus  10  is an information processing device (namely, a computer) that includes an input unit  11  and an output unit  12  as well as a central processing unit (CPU) and a memory which are not shown in  FIG. 2 . The process management apparatus  10  is, for example, a workstation. The input unit  11 , which is operated by a user, outputs information generated in response to the user&#39;s operation to the process management apparatus  10 . The input unit  11  is, for example, a keyboard. The output unit  12 , which is disposed in the warehouse  2 , recognizably outputs information generated by the process management apparatus  10  to the user. The output unit  12 , exemplified by a visual display, displays the information output from the process management apparatus  10 . Alternatively, the output unit  12 , exemplified by a printer, prints out the information output from the process management apparatus  10  on a paper sheet.  
         [0037]     The process management apparatus  10  includes software including an initial registration database  21 , and an initial registration database updating unit  22 . The process management apparatus  10  also includes a number-of-produced-vehicles change registration unit  23 , a delivery time calculation unit  24 , a quantity-of-delivered-parts calculation unit  25  and a delivery instruction unit  26 .  
         [0038]     The initial registration database  21  records a table that indicates information on the parts  5  on a recording unit. The initial registration update unit  22  updates the table recorded by the initial registration database  21  based on information input to the input unit  11  by a user.  
         [0039]     The number-of-produced-vehicles change registration unit  23  collects an operating time pattern of the production line  1  of a target day from the input unit  11 , and collects the planned number of produced vehicles to be produced on the production line  1  on the target day. The delivery time calculation unit  24  calculates a plurality of delivery time periods for carrying the parts  5  from the warehouse  2  to the line sidetrack space  7 -i based on the operating time pattern collected by the number-of-produced-vehicles change registration unit  23  and the planned the number of produced vehicles. The quantity-of-delivered-parts calculation unit  25  calculates quantities of the parts  5  to be carried from the warehouse  2  to the line sidetrack space  7 -i at the respective delivery time periods calculated by the delivery time calculation unit  24 .  
         [0040]     The delivery instruction unit  26  generates a delivery instruction that indicates the delivery time periods calculated by the delivery time calculation unit  24  and the quantities of delivered parts calculated by the quantity-of-delivered-parts calculation unit  25 . The delivery instruction unit  26  outputs the generated delivery instruction to the output unit  12 .  
         [0041]      FIG. 3  shows the table recorded on the recording unit by the initial registration database  21 . In the table  30 , a process section  31  and the number of process preceding vehicles section  32  are associated with parts section  33 . The parts section  33  provides a location for storing information for identifying the type of parts  5  and indicates the identification numbers of the parts  5 . The process section  31  provides a location for storing information for identifying one process selected from the processes  6 - 1  to  6 -n and in which the parts identified by the parts section  33  is consumed.  
         [0042]     The number of process preceding vehicles section  32  indicates the number of vehicles arranged between the vehicles in the process identified by the process section  31  and the finished vehicles on the production line  1 .  
         [0043]     Further, in the table  30 , an applied vehicle type section  34 , the number of parts applied to a vehicle section  35 , a partial lots delivery section  36 , a lot size section  37 , the number of delivered lots section  38 , and a receive type section  39  are associated with the parts section  33 . The applied vehicle type section  34  identifies a type of the vehicle to which the parts identified by the parts section  33  are attached, and indicates the vehicle type thereof. The number of parts applied to a vehicle section  35  indicates the number of parts applied to one vehicle of the type identified by the applied vehicle type section  34  and identified by the parts section  33 .  
         [0044]     The partial lots delivery section  36  indicates the conditions that the parts identified by the parts section  33  are delivered the line sidetrack space  7 -i at one time, and shows either “partial lots delivery possible” and “partial lots delivery impossible”. The lot size section  37  is a value set by the customer  3  and indicates the quantity of the parts identified by the parts section  33  per lot. The number of delivered lots section  38  indicates the number of lots when the parts identified by the parts section  33  are delivered the line sidetrack space  7 -i at one time. Namely, the parts identified by the parts section  33  are delivered the quantity indicated by the lot size section  37  in units of the quantity that is a multiple of the number of lots indicated by the number of delivered lots section  38 .  
         [0045]     Namely, when the partial lots delivery section  36  shows “partial lots delivery impossible”, the parts  5  are carried from the warehouse  2  to the line sidetrack space  7 -i only in delivery units. If the partial lots delivery section  36  shows “partial lots delivery possible”, the parts  5  are carried from the warehouse  2  to the line sidetrack space  7 -i in delivery units or in factions smaller than the delivery unit.  
         [0046]     The receive type section  39  indicates an index for calculating a method for carrying the parts identified by the parts section  33 , and shows either “lot preceding” or “time preceding”.  
         [0047]     The delivery time calculation unit  24  calculates the tact time. The tact time is a quotient obtained by dividing the operating time of the production line  1  of the target day by the planned number of produced vehicles on the target day. Namely, the tact time indicates a time period for which one vehicle is produced on the production line  1 , i.e., a time period required until the conveyor carries the vehicle to the next process  6 -(i+1) after the vehicle is stopped in one process  6 -i. The delivery time calculation unit  24  calculates a speed at which the process identified by the process section  31  consumes the parts identified by the parts  31  based on the tact time.  
         [0048]     Referring to the initial registration database  21 , if the receive type section  39  shows “lot preceding”, the delivery time calculation unit  24  divides the operating time of the target day into a plurality of time periods for which the process consumes the parts in delivery units. Referring to the operating time pattern of the target day, the delivery time calculation unit  24  calculates a time of dividing the operating time of the target day into a plurality of time periods, and sets a time adjusted from the calculated time by as much as the number of vehicles indicated by the number of process preceding vehicles section  32  as the delivery time.  
         [0049]     Referring to the initial registration database  21 , if the receive type of the parts shows “time preceding”, the delivery time calculation unit  24  divides the operating time of the target day generally equally into a plurality of time periods so that the quantity of the parts consumed in the process is smaller than a predetermined quantity. Referring to the operating time pattern of the target day, the delivery time calculation unit  24  calculates a time of dividing the operating time of the target day into a plurality of time periods, and sets a time adjusted from the calculated time by as much as the number of vehicles indicated by the number of process preceding vehicles section  32  as the delivery time.  
         [0050]     Referring to the initial registration database  21 , if the receive type section  39  of the parts shows “time preceding”, the quantity-of-delivered-parts calculation unit  25  sets the quantity of parts just consumed by the next delivery time as the quantity of delivered parts at the delivery time based on the speed calculated by the delivery time calculation unit  24  at which speed the process identified by the process section  31  consumes the parts.  
         [0051]     Referring to the initial registration database  21 , if the receive type section  39  shows “lot preceding” and the partial lots delivery section  36  shows “partial lots delivery impossible”, the quantity-of-delivered-parts calculation unit  25  sets the quantity of parts in the quantity indicated by the lot size section  37  only in delivery units of the quantity, which is a multiple of the number of lots indicated by the number of delivered lots section  38 , as the quantity of the delivered parts.  
         [0052]     Referring to the initial registration database  21 , if the receive type section  39  shows “lot preceding”, the partial lots delivery section  36  shows “partial lots delivery possible”, and the type of vehicles produced on the production line  1  is not changed, the quantity-of-delivered-parts calculation unit  25  sets the quantity of parts only in delivery units of quantity as the quantity of the delivered parts.  
         [0053]     Referring to the initial registration database  21 , if the receive type section  39  shows “lot preceding” and the partial lots delivery section  36  shows “partial lots delivery possible”, the quantity-of-delivered-parts calculation unit  25  determines whether the process consumes the parts in delivery units by a changing time at which the type of produced vehicles is changed and at which the process consumes the other parts. If it is determined that the process consumes the parts in the delivery units, the quantity-of-delivered-parts calculation unit  25  sets the quantity of parts in delivery units as the quantity of delivered parts. If it is determined that the process does not consume the parts in the delivery units, the quantity-of-delivered-parts calculation unit  25  sets the quantity of parts calculated so that the parts are consumed just by the changing time, based on the speed calculated by the delivery time calculation unit  24 . If the time for which the other parts are consumed is within a predetermined time or if the time the other parts are consumed is only a day after the former time, the quantity-of-delivered-parts calculation unit  25  can set the quantity of parts in delivery units as the quantity of delivered parts.  
         [0054]     The process management method according to the embodiment of the present invention is executed by the process management apparatus  10 . The method includes an operation of updating the table  30  and an operation of calculating the method for carrying parts.  
         [0055]     In the operation of updating the table  30 , at first, the user inputs information to be updated in the table  30  to the process management apparatus  10  using the input unit  11 . Examples of the information to be updated include information on the delivery unit in which the parts are delivered, information as to whether the index for calculating the method for carrying parts is “lot preceding” or “time preceding”, and information as to whether the parts can be delivered fractions. The process management apparatus  10  updates the table  30  based on the input information.  
         [0056]      FIG. 4  is a flow diagram showing the operation of setting the method for carrying the parts by a calculation. In step S 1 , using the input unit  11 , the user inputs the operating time pattern of a target day on which the process management is performed on delivery of the parts to the process management apparatus  10 . Then, in step S 2 , using the input unit  11 , the user inputs the planned number of produced vehicles to be produced at the target day to the process management apparatus  10 . In step S 3 , the process management apparatus  10  divides the operating time of the production line  1  of the target day by the planned number of produced vehicles on the target day, thereby calculating the tact time, the tact time indicating the time for which one vehicle is produced on the production line. The process management apparatus  10  further calculates the speed at which the parts in the process  6 -i are applied to the vehicles based on the tact time.  
         [0057]     Referring to the initial registration database  21 , in step S 4 , if the receive type section  39  indicates “lot preceding” and the partial lots delivery section  36  indicates “partial lots delivery impossible”, the process management apparatus  10  divides the operating time of the target day into a plurality of time periods at which the process consumes the parts in delivery units. The process management apparatus  10  calculates the time by dividing the operating time of the target day into a plurality of time periods, and sets the hour adjusted from the operating time pattern of the target day by as much as the number of vehicles indicated by the number of process preceding vehicles section  32  as the delivery time. Referring to the initial registration database  21 , in the step S 5 , the process management apparatus  10  sets the quantity of parts in delivery units of the number, which is a multiple of the number of delivered lots of the lot size of the parts.  
         [0058]     Referring to the initial registration database  21 , in step S 4 , units if the receive type section  39  indicates “lot preceding” and the partial lots delivery section  36  indicates “partial lots delivery possible”, the process management apparatus  10  divides the operating time of the target day into a plurality of time periods at which the process consumes the parts in delivery units. The process management apparatus  10  calculates the hour by dividing the operating time of the target day into a plurality of time periods, and sets the time adjusted from the operating time pattern of the target day by as much as the number of vehicles indicated by the number of process preceding vehicles section  32  as the delivery time. The process management apparatus  10  determines whether the process consumes the parts in delivery units by the changing time at which the type of produced vehicles is changed and at which the process consumes the other parts. If it is determined that the process consumes the parts in the delivery units, at step S 5  the process management apparatus  10  sets the quantity of parts in delivery units as the quantity of delivered parts. If it is determined that the process does not consume the parts in the delivery units, at step S 5  the process management apparatus  10  sets the quantity of parts calculated so that the parts are consumed just by the changing time based on the speed calculated by the process management apparatus  10 . If the time for which the other parts are consumed is within a predetermined time or if the time the other parts are consumed is only a day after the former time, the process management apparatus  10  can set the quantity of parts in delivery units as the quantity of delivered parts.  
         [0059]     Referring to the initial registration database  21 , at step S 4 , if the receive type of the parts is “time preceding”, the process management apparatus  10  divides the operating time of the target day generally equally into a plurality of time periods so that the quantity of the parts consumed in the process is smaller than the predetermined quantity. The process management apparatus  10  calculates the time of dividing the operating time of the target day into a plurality of time periods, and sets the time adjusted from the operating time pattern of the target day by as much as the number of vehicles indicated by the number of process preceding vehicles section  32  as the delivery time. At step S 5 , the process management apparatus  10  sets the quantity of parts just consumed by the next delivery time as the quantity of parts at the delivery time based on the speed at which the process consumes the parts. Such calculations of the delivery time and the quantity of delivered parts are executed, whether the parts can be delivered fractions or not.  
         [0060]     In step S 6 , the process management apparatus  10  generates a list indicating the delivery time and the quantity of delivered parts calculated in the steps S 4  and S 5 , respectively, and outputs the generated list using the output unit  12 . An operator carries the parts  5  from the warehouse  2  to the line sidetrack spaces  7 - 1  to  7 -n while referring to the list.  
         [0061]      FIG. 5  shows the total stock of the parts in the line sidetrack space  7 -i when the process management is performed by the process management method according to the embodiments of the present invention. Specifically,  FIG. 5  shows the total stock of parts if the receive type of the parts is “lot preceding” and “partial lots delivery impossible” is shown in the partial lots delivery section  36 . Namely, a graph of  FIG. 5  includes a curve  41  and the total stock is expressed by the value on the vertical axis of the graph of the curve  41 . The total stock can be made always smaller than a predetermined quantity by setting the delivery unit to be smaller than the quantity in the delivery unit. As a result, it is unnecessary for the line sidetrack space  7 -i to keep the parts in stock larger in quantity than the predetermined quantity, thereby making it possible to design the line sidetrack space  7 -i to be smaller in size.  
         [0062]     The stock interest indicates an interest burden based on the total stock. The stock interest is calculated according to the area of the region  42  surrounded by the curve  41  and the horizontal axis of the graph. As the area increases, the stock interest is higher. The stock interest when the process management is performed as shown in the flow of  FIG. 4  is advantageously smaller than that when the total stock is changed as shown in  FIG. 7 .  
         [0063]     The total stock can be made always smaller than the quantity in the delivery unit by setting the delivery unit to be smaller than the predetermined quantity similarly to the graph of  FIG. 5  if the receive type of the parts is “lot preceding” and “partial lots delivery possible” is shown. If the type of produced vehicles is changed and the process is changed to consume the other parts, the smaller quantity of parts than the quantity in the delivery unit among the total stock are carried to the line sidetrack space  7 -i. As a result, it is unnecessary for the line sidetrack space  7 -i to keep the parts in stock larger in quantity than the quantity in the delivery unit, thereby making it possible to design the line sidetrack space  7 -i to be smaller in size. Besides, the stock interest at this time is advantageously lower than the stock interest when the total stock is changed as shown in  FIG. 7 .  
         [0064]     The total stock can be made always smaller than the predetermined quantity by dividing the operating time into a plurality of time periods so that the quantity of delivered parts is smaller than the predetermined quantity if the receive type of the parts is “time preceding”. As a result, it is unnecessary for the line sidetrack space  7 -i to keep the parts in stock larger in quantity than the quantity in the delivery unit, thereby making it possible to design the line sidetrack space  7 -i to be smaller in size. Besides, the stock interest at this time is advantageously lower than the stock interest when the total stock is changed as shown in  FIG. 7 .  
         [0065]     While a working example of the present invention has been described above, the present invention is not limited to the working example described above, but various design alterations may be carried out without departing from the present invention as set forth in the claims.