Title of Invention

METHOD OF CALCULATING THE WORKPIECE LOADING TIMES FOR PRODUCT ASSEMBLY LINE

Abstract The present invention relates to a method of calculating the times to load workpieces in lots having different tact times onto a product assembly line, comprising the steps of: regarding a longest one of the tact times of the lots of workpieces that are present on the product assembly line as a tact time for the product assembly line; totaling tact times for the number of products to be manufactured per day by the product assembly line, thereby determining a flow time on the product assembly line per day; dividing a running time of the product assembly line per day by said flow time, thereby determining a corrective value; multiplying the tact times of the lots of workpieces by said corrective value, thereby determining corrected tact times; and adding said corrected tact times to each other and then to an assembly line start time at which said product assembly line starts to operate, thereby determining loading times at which to load the workpieces onto the product assembly line.
Full Text



tact time of the lot A, i.e., 24*0 seconds, has elapsed from
the assembly line start time, the first workpiece Ax
(completed product) of the lot A is unloaded from the prod-
i uct assembly line (line-off).
At the assembly line end time, a first workpiece A' i of the lot A' for the next day has already been delivered to the final step of the product assembly line, and a 140th workpiece A' 140 of the lot A' has already been delivered to the first step of the product assembly line (line-on).
The tact time of the product assembly line itself is set to a longest one of the tact times of different lots that are placed together on the product1 assembly linte. For example, as shown in FIG. 3 of the accompanying drawings, if the lots B, C, D are cdexistent on the product assembly line, then a 21st workpiece D21 of the lot D is delivered to the first step of the product assembly line a time interval of 27 seconds after a 20th workpiece D20 of the lot D has been delivered to the first step of the product assembly line. The time interval of 27 seconds is equal to the tact time of the lot B which is longest among the tact times of
the lots B, C, D, I
i
The above equation to determine the time Jc employs the tact times of different lots regardless of the fact that the tact time of the product assembly line itself is set to a longest one of the tact times of different lots that are placed together on the product assembly line. Therefore, the planned times at which to load first work-pieces of different lots onto the product assembly line have turned out to be considerably different from actual times at which those first workpieces are loaded onto the product assembly line.
Another problem is that the time at which the final workpiece is loaded onto the product assembly line deviates greatly from the assembly line end time.
It is therefore an object of the present invention to provide a method of accurately calculating the times to load workpieces onto a product assembly line.

According to the present invention, there is provided a method of calculating the times to load workpieces in lots having different tact times onto a product assembly line, comprising the steps of regarding a longest one of the tact times of the lots of workpieces that are present on the product assembly line as a tact time for the product assembly line, totaling tact times for the number of products to be manufactured per day by the product assembly line, thereby determining a,flow time on the product assembly line per day, dividing a running time of the product assembly line per day by the flow time, thereby determining a corrective value, multiplying the tact times of thp lots of work-pieces by the corrective value, thereby determining corrected tact times, and adding the corrected tact times to each other and then to an assembly line start time at which the product assembly line starts to operate, thereby determining loading times at which to load the lots of workpieces onto the product assembly line *
The method may further comprise the step of, prior to regarding the longest one of the tact times as the tact time for the product assembly line, determining work-pieces to placed on the product assembly line from the assembly line start time to an assembly line end time at which
i the product assembly line ceases to operate.
The method may further comprise the step oif, sub-sequent to the step of adding the corrected tact times to each other and then to the assembly line start time, regarding the loading times for the first workpieces of the respective lots as loading times at which to load the respective lots onto the product assembly line.
The above and further objects, details and ad
vantages of the present invention will become apparent from
the following detailed description of preferred embodiments
thereof, when read in conjunction with the accompanying
drawings, ;
FIG. 1 shows tables of production plans of a product assembly line for one day and a next day;

FIG. 2 is a diagram of the product assembly line
with in-process products thereon when it'starts to operate
j and when it ends its operation, with respect to a conventional process of calculating the time to load a workpiece onto the product assembly line;
FIG. 3 is a diagram of the product assembly line with different lots placed as in-process lots thereon;
FIG. 4 is a block diagram of a system for carrying out a method of calculating the time to load a workpiece onto a product assembly line according to the present invention;
FIG. 5 is a flowchart of an operation sequence of the system 'shown in FIG. 4 to carry out the method according to the present invention; and
FIG. 6 is a diagram of the product assembly line with in-process products thereon when it starts to operate and when it ends its operation, with respect to the method according to the present invention.
As shown in FIG. 4, a system for carrying out a
method of calculating the time to load a workpiece onto a
product assembly line according to the presentiinvention
generally comprises a factory host computer 1 for generating
production plans for a,factory as a whole and instructing a
product assembly line to carry out the production plans, a
processor 2 for calculating the times to load workpieces
onto the product assembly line (also referred,to as
"workpiece loading! time") based on instructions from the
i factory host computer 1, a display unit 3 and a printer 4
for outputting calculated results from the processor 2, and
a keyboard 5 for entering data or the like into the proces-
i scr 2 ,
The processor 2 has a production plan receiver 6
for receiving production plans of the product assembly line
from the factory host computer 1, a production plan file 7
for storing production plans received by the production plan
receiver 6, a assembly line running time file 8 for managing
a running time of the product assembly line, a workpiece

loading time calculator 9 for calculating the! times to load workpieces onto the product assembly line based on the production plans stored in the production plan file 7 and the running time managed by the assembly line running time file 8, and a workpiece loading time file 10 for storing the workpiece loading times calculated by the workpiece loading time calculator 9.
The production plan file 7 also- stores plans for unloading products from the product assembly line, the num-bers of in-process products on the product assembly line, and the tact times of different lots on the product assembly line.
The method of calculating the time to load a workpiece onto a product assembly line according to the present invention will be described below with reference to FIG, 5 which illustrates an operation sequence of the system shown in FIG. 4*
In a step SI, workpieces to be placed on the product assembly line from an assembly line start time to an assembly line end time are determined on the basis of the plans for unloading products from the product assembly line and the numbers of in-process products on the product assembly line which are stored in the production plan file 7, and also the running time managed by the assembly line running time file 8.
As shown in FJG. 6, a workpiece W¾ is unloaded as a completed product from the product assembly line a given tact time after the assembly line start time, and a work-piece Wm is loaded onto the product assembly line immediately prior to the assembly line end time. Therefore, the number of workpieces placed on the product assembly line from the assembly line start time to the assembly line end time is "m", If the number k of in-process workpieces on the product assembly line is "140" and the number P of products com-pleted per day is "1070", then the workpiece Wm is the 1210th (the sum of P = 1070 and k = 140) workpiece as counted from

the workpiece Wx. Thus, the parameters m, k, P are related to each other as follows: P - m - k.
In a step S2, if it is assumed that the work-pieces Wj ~* Wm have respective basic tact times Tx ~ Tm, then
i
a theoretical tact time 1" n (line-on interval) of an nth workpiece Wn that is loaded onto the product assembly'line is set to a longest one of the tact times of workpieces W„_^_^ ** Wn that are present on the product assembly line* The theoretical tact time T'n is determined according to the following equation:
In a step S3, theoretical tact times T'n of work-pieces Wn that are loaded onto the product assembly line within the running time thereof (for the number P of 1070 products) are totaled into a flow time S on the product assembly line per day. Specifically, the flow time S per day can be determined according to the following equation which adds the theoretical tact times T'n for the number P (P = m -k) of products per day:
±ii d £›ct;p oi, a i^u4.ic^Livt; vcu_ue Ot for correcting the theoretical tact times is determined from the flow time S and a running time H that is stored in the assembly line running time file 8, in order that the workpiece Wm will necessarily be loaded into the first step on the product assembly line at the assembly line end time., The corrective value a is calculated by the following equation which divides the running time H by the flow time S:
a = H/S
In a step S5, corrected tact times tx ~ tm of the workpieces V!i ~ Wm are determined* Specifically, a corrected tact time tn of the nth workpiece Wn is calculated by the following equation which multiplies the theoretical tact time T' by the corrective value (X:
tn = T'n x a = T'n x H/s
1

In a step S6, loading times J1 - Jn at which to load the workpieces WA - Wm onto the product assembly line are determined on the basis of the corrected tact times tx -tm of the workpieces Wa - Wm in view of the running time. Specifically, a loading time Jn for the nth workpiece Wn is calculated by the following equation with respect to the assembly line start time:

In a step S7, of the loading timfes Ji ~ Jm for the respective workpieces W2 ~ Wm, the loading times for the first workpieces of respective lots are regarded as loading times at which to load the respective lots onto the product assembly line- The operation sequence of the system shown in FIG. 4 for carrying out the method of calculating the time to load a workpiece. onto the product assembly line according to the present invention is now completed.
If the production plans are given as shown in
i FIG, 1 and workpieces are placed on the-product assembly
line at the assembly line start time and the assembly line end time as shown in FIG. 2, then since the number of products of the lot A is "300", a loading time JB at which to load the lot B onto the product assembly line is calculated as follows:

= assembly line start time + (160 x 24.0) Because the number of products of the lot A is "300" and the number of products of the lot B is "100", a loading time Jc at which to load the lot C onto the product assembly line is calculated as follows:
= assembly line start time + (20 X 24.0 + 240 X 27.0)

Similarly, a loading time Jx at which to load the lot I onto the product assembly line is calculated as follows :
According to the present invention, as described above, inasmuch as times at which to load workpieces onto the product assembly line can more accurately be calculated, it is possible to establish more accurate plans to fabricate workpieces to be delivered to the product assembly line.
Although there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that the invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description *








time, regarding the loading times for the first workpieces of the respective lots as loading times at which to load the respective lots onto the product assembly line*
4, A method of calculating the times to load workpieces substantially as herein described with reference to the
accompanying drawings,
i i


Documents:

2625-mas-1997-abstract.pdf

2625-mas-1997-claims filed.pdf

2625-mas-1997-claims granted.pdf

2625-mas-1997-correspondnece-others.pdf

2625-mas-1997-correspondnece-po.pdf

2625-mas-1997-description(complete)filed.pdf

2625-mas-1997-description(complete)granted.pdf

2625-mas-1997-drawings.pdf

2625-mas-1997-form 1.pdf

2625-mas-1997-form 26.pdf

2625-mas-1997-form 3.pdf

2625-mas-1997-form 4.pdf

2625-mas-1997-form 5.pdf


Patent Number 212505
Indian Patent Application Number 2625/MAS/1997
PG Journal Number 07/2008
Publication Date 15-Feb-2008
Grant Date 03-Dec-2007
Date of Filing 18-Nov-1997
Name of Patentee HONDA GIKEN KOGYO KABUSHIKI KAISHA
Applicant Address 1-1, MINAMI-AOYAMA 2-CHOME, MINATO-KU, TOKYO,
Inventors:
# Inventor's Name Inventor's Address
1 HITOMI OGATA C/O HONDA GIKEN KOGYO KABUSHIKI KAISHA, KUMAMOTO SEISAKUSHO HIRAKAWA, OOZU-MACHI, GUN, KUMAMOTO,
2 KOICHIRO CHAEN C/O HONDA GIKEN KOGYO KABUSHIKI KAISHA,KUMAMOTO SEISAKUSHO HIRAKAWA, OOZU-MACHI, KIKUCHI-GUN, KUMAMOTO,
PCT International Classification Number B 62D 65/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 8-309393 1996-11-20 Japan