Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-02-06
2001-06-19
Gordon, Paul P. (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S108000, C702S182000
Reexamination Certificate
active
06249715
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method and apparatus for optimizing a work distribution, and in particular, to the optimization of work distribution along an assembly line or in a production process. This invention is applied, e.g., to assembling a wire harness, or a subassembly (hereinafter referred to as wire assembly) which forms a wire harness.
2. Discussion of Background and Other Information
Industrial products are generally manufactured using complex and multiple handling procedures. When large products, having a number of components, such as, for example, wire harnesses, are manufactured, more work space and additional workers may be involved.
A wire harness is an electrical network of, for example, a car, and may be considered to be equivalent to the nervous system of a human body. The wire harness has a plurality of branches derived from junction points on a main line (or sometimes from another branch line). Each wire that makes a connection from one branch to another branch has a crimped terminal that is inserted into an associated connector.
The assembly line for manufacturing a wire harness is based upon a preestablished standard time for manufacturing the product. However, when the number of operators (workers) or their positions at each station of the assembly line changes, the actual assembly time required to manufacture the wire harness changes from the preestablished standard time. This usually happens when new or less skilled workers are positioned at work stations that require a high degree of skill.
The process of assembling a wire harness may include a manufacturing process, an arranging process, a selecting process, and a gross-assembly process. For example, the wire harness manufacturing process begins by making one or more sub-assemblies (e.g., the manufacturing process). Each sub-assembly comprises some connectors and wires with crimped terminals on each extremity. The sub-assembly is then laid upon an assembly table (e.g., the arranging process), where a junction position is determined through the use of appropriate jigs (e.g., the selecting process) for additional wiring. When all the wiring is finished, the main line and the branch lines are bundled with, for example, vinyl tape, tubing, or other sheathing material (e.g., the gross-assembly process).
Most of these respective processes are performed by a flow production assembly line of approximately 10 to 20 workers. Some assembly processes may require significant manual assembly. In such manual assembly cases, the man-hours (assembling real man-hours) required to perform the work when a production variation occurs (or when one or more assembly workers are absent) greatly exceed a predetermined normal man-hours (preestablished standard man-hours) required to perform the work, resulting in delays and backlogs in the assembly process, and possibly affecting the quality of the completed product. Therefore, a conventional assembly line employs a manager who controls the work flow of the assembly line. The manager carries out the work distribution (work flow) based upon his experience and intuition by judging the length of experience and work capabilities of each worker in the assembly line.
The work distribution in the above-discussed assembly line frequently calls for the manager to consider the skill level of each worker, whether any workers are absent, the difficulty level of the work to be performed by the individual workers, and the difficulty in quantifying the same. As a result, it is often difficult to maximize the worker efficiency or to optimize the handling distribution.
In addition, when manufacturing comparatively large size products, such as, for example, a wire assembly, it becomes even more difficult to optimize the assembly procedure, due to the need to assemble or arrange components according to a work order determined in a preferential order on a drawing board (work bench) with a size of approximately 0.8 m by 4 m.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an optimizing procedure for the distribution of work that is capable of optimizing the work distribution in an assembly line, while eliminating possible errors made by the manager.
In order to solve the above-mentioned problem, the present invention provides an optimized work distribution for each worker. A difficulty level is set for each element work (task) and a skill level is set for each respective worker. A time variation factor is set based upon the ranked work difficulty and the skill level of the workers. A compensation value is provided in accordance with the worker to whom an operation time of each element work is distributed, based upon a time variation factor. An assigned operation time per worker is maintained in equilibrium among respective workers by distributing each element work in a preferential order, based on the compensated operation time.
It is understood that the phrase “element work”, as employed in the present application, is analogous with the terms “job”, “task” and “operation”, and each term may be interchangeably employed.
By the present invention, a difficulty level for each task (element work) for the flow production, and the skill level of the respective workers are ranked, from which a time variation factor is created. A work difficulty level for each task (element work) is determined by a questionnaire, based on, for example, an AHP (Analytical Hierarchy Process), while the skill level of each worker is determined based upon, for example, the worker's years of work experience plus a test that measures real times required to perform predetermined tasks.
An x-y matrix is formed based upon the determined difficulty levels versus the skill levels, with a time variation factor being assigned to each intersection point (e.g., a point where an x-axis intersects a y-axis) for carrying out each element work. The time variation is required because the range of time required for a worker to perform a task (e.g., the time required for a skilled and non-skilled worker to perform a predetermined task) increases in relation to the difficulty of the work to be performed. That is, a non-skilled worker may require, for example, 10 percent additional time to perform a simple task, as compared with a skilled worker, but, if a complex task is to be performed, the non-skilled worker may require, for example, 40 percent more time to complete the task as compared to the skilled worker.
Determining the time variation factor for the skill level of the workers and the level of difficulty of each element work permits an efficient distribution of element work among the various workers when one or more workers are absent. By assigning a time variation factor to each worker for each specific task, it is possible to calculate predicted operation times to develop an optimum work distribution. By assigning each element work to respective workers so that an assigned operation time per worker is kept in equilibrium with the predicted operation time between respective workers (based on a calculated predicted operation time), the operation time for respective workers can be made equal (or nearly equal) within a minimum operation time.
It is desired to maintain an assigned operation time per worker, among respective workers, in equilibrium, so that a balanced operation time among each worker will not exceed a predetermined allowance. In other words, in this portion of the process, the goal is to equalize the operation time for each worker, so that substantial uniformity in working time per worker is achieved. While 100 percent equalization is not required, 90 percent equalization is desired.
According to another embodiment of the present invention, a work distribution is optimized for a plurality of workers in handling a flow production consisting of multiple element works, the order of assembly being determined based upon a preferential order in accordance with the plurality of workers along a conveyor which transfers produc
Kurihara Kiyokazu
Yuri Hidetaka
Gordon Paul P.
Greenblum & Bernstein P.L.C.
Sumitomo Wiring Systems Ltd.
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