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Author: Yung-Chieh Hung (2007-03-13); recommendation: Yeh-Liang Hsu (2007-03-13).
Note: This article is Chapter 4 of Yung-Chieh Hung’s PhD thesis “Development of an Innovative Patent-based Design Methodology.”

Chapter 4. Design matrix representation of patents

The patent-based design process developed in this research can be divided into four major stages as shown in Figure 4-1. This chapter discusses how the related patents obtained from patent analysis are symbolized using the concept derived from axiomatic design (stage 1 and 2). The example of a portable magnetic impact tool (U.S. Patent 6,918,449) is used again to illustrate the detailed steps of implementation and required considerations of the patent-based design process.

Figure 4-1. Conceptual flowchart of the patent-based design process

4.1       Patent analysis

There are 3 major tasks in the patent analysis process:

(1)   Patent search and screen

The first step of patent analysis is to search related patents. Keywords for searching patents can be obtained by considering the names of products, brands, characteristics of products and technologies, names of related competitive companies or patent holders, and patent classification numbers. Searched results often have many unrelated patents. Therefore, the designers have to read the specifications or drawings to screen for related patents.

(2)   Develop the abstract lists of patents

The next step is reading and analyzing each concerned patent to develop the abstract lists of patents. The designers construe a patented invention and record the disclosed techniques and functions in the abstract list to establish the patent database. The designers should not only understand and confirm the subject matter that is to be resolved in this step, but also point out which techniques are used to obtain the objectives of the investigated patents, and the roles and contributions of each technique. Table 4-1 shows the abstract list of U.S. Patent 6,918,449.

Table 4-1. The abstract list of U.S. Patent 6,918,449


Magnetic impact tool

Patent No.

U.S. 6,918,449

Date of field


Date of issued



Matsushita Electric Works, Ltd.


Shinagawa; Sou, Nakayama; Satoshi, Sekino; Fumiaki




magnetic, impact, rotate



173/117; 173/176; 173/213;



B25B 21/02; H02K 7/14; H02K 7/10; H02K 49/10; H02K 49/00 

Date of analysis


Background of the invention

Figure (a) shows the major components of a portable power tool driven by an electric motor. The rotational motion of the motor is transmitted to a chuck that holds a tool output shaft by means of a hammer. The motor is generally small due to restrictions imposed on the overall size and weight of the portable power tools. Limited power of the small motor might not be enough to drive the intended load. A hammer type of mechanism is used to generate high output torque from a small drive.

Figure (a). Components of a portable power tool

As shown in Figure (b), the hammer stores the rotational energy of the motor over a large angle of rotation, for example, a half turn. Then the hammer hits the chuck to create an impact torque over a small angle (for example 10 degrees) of rotation of the chuck. In this type of portable power tool, loud noise is generated when the hammer hits the chucks.

Figure (b). Top plan view of a hammer type impact generator

Functions of the patent

l          Tighten/ loosen screw

l          Generate impact torque

l          Change magnetic flux

Results of the patent

The present applicants have previously proposed a magnetic impact tool with which screws are tightened by using magnetic coupling to deliver a strike without any contact, and obtaining a tightening rotational impact force without a collision sound.

Means for solution, composition and important figures

l          During the screw-tightening work, when the load torque is initially low, the magnetic hammer (2) and magnetic anvil (1) begin to rotate together without any impact action. When the load torque exceeds the magnetic attraction torque, the magnetic hammer and magnetic anvil are not synchronized anymore. Impact action can be generated, and screw tightening and loosening work can be carried out even if a low-torque motor is used.

l          This tool comprises a magnetic bypass device (24) for distributing magnetic flux between the magnetic anvil and the magnetic hammer, and a changing device (28) for changing the distribution of magnetic flux by the magnetic bypass device (24).

l          The torque generated between the magnetic hammer and magnetic anvil can be changed by the changing device to vary the distribution ratio of the magnetic flux from the magnetic hammer to the magnetic anvil.

Figure (c). U.S. Patent 6,918,449

Independent claims

l          A motor for generating rotational force.

l          A drive shaft rotatably driven by the motor.

l          A magnetic hammer rotatably moved in a coupled state with the drive shaft.

l          A magnetic anvil which faces the magnetic hammer and to which the rotational force is transmitted by magnetic coupling, with one of the opposing surfaces of the magnetic hammer and magnetic anvil having a magnetic pole, and the other having a magnetic pole or magnetic body.

l          An output shaft rotated by the magnetic anvil.

l          A magnetic bypass device that bypasses the magnetic flux between the magnetic anvil and the magnetic hammer, and changes the state of magnetic coupling there between.

l          A changing device that changes the bypass quantity of the magnetic flux with the magnetic bypass device, with the torque transmitted from the magnetic hammer to the magnetic anvil being changed in accordance with the change in bypass quantity of the magnetic flux varied by the changing device.

(3)   Develop technology/function matrix

Lastly, the technology/function matrix is constructed to classify each concerned patent. The technology/function matrix is used to investigate which techniques can produce the specific functions. The column of the matrix represents the functions while the row lists the disclosed techniques. The technologies and functions are obtained from the patent abstract lists of each concerned patent. Table 4-2 shows an example of technology/function matrix of U.S. Patent 6,918,449.

Table 4-2. Technology/function matrix



Tighten/ loosen screw

Generate impact torque

Change magnetic flux



Magnetic hammer


Magnetic anvil


Drive shaft


Output shaft



Magnetic bypass device



Changing device



4.2       Axiomatic design

In this research, each concerned patent in the technology/function matrix is then symbolized by a “design matrix”, which is inspired by the “axiomatic design” methodology proposed by Suh [2001].

Axiomatic design is a system design methodology using matrix method to analyze the transformation of customer needs into functional requirements, design parameters, and process variables. The axiomatic design approach consists of two axioms. Axiom 1, which is called the independence axiom, deals with the relationship between functional requirements (FRs) and design parameters (DPs). Axiom 2, which is called the information axiom, deals with the complexity of the design. In this research, Axiom 1 is used for representing each patent that to be designed around. A brief introduction to Axiom 1 is described below.

Let there be m components represented by a set of independent FRs where FR is the vector of functional requirements. DPs in the physical domain are characterized by vector DP with n components. The design process is choosing the right set of DPs to satisfy the given FRs. The design matrix representing the relationship between FRs and DPs vectors is expressed as



Equation (4.1) is a design equation for the design of a product, where is a “design matrix” that characterizes the product design. The components in the design matrix are either “0” or “1”. A cell takes a “0” if varying the design parameter has no effect on the corresponding functional requirement and a “1” if it does.

In general, Equation (4.1) may be written in terms of its elements as,


where n is the number of DPs.

4.3       Design matrix representation

In the “technology/function” matrix in Table 4-2, the “technologies” resembles the design parameters (DPs), and the “function” resembles the functional requirements (FRs) in Equation (4.3). In this case,

        FR1 = Tighten/ loosen screw

        FR2 = Generate impact torque

        FR3 = Change magnetic flux

The corresponding DPs are as follows:

        DP1 = Motor

        DP2 = Drive shaft

        DP3 = Magnetic hammer

        DP4 = Magnetic anvil

        DP5 = Output shaft

        DP6 = Magnetic bypass device

        DP7 = Changing device

The technology/function matrix in Table 4-2 can be expressed as


where  is the transformation matrix which transfers the DRs into FRs. For example, in Equation (4.4)


The first equation above means that “Transforming components motor, drive shaft, magnetic hammer, magnetic anvil, and output shaft achieves function of tightening/ loosening screw.” Similarly, the second equation above means that “Transforming components motor, drive shaft, magnetic hammer, and magnetic anvil achieves the function of generating impact torque”; the third equation above means that “Transforming components magnetic bypass device and changing device achieves the function of changing magnetic flux.”

In summary, a patent can be represented by the following equation:




where [FR] is a column vector of the “functions” of the patent, and [DP] is a column vector of the “technologies (components)” of the patent. Both [FR] and [DP] are extracted directly from the technology/function table of the patent. Matrix A is a design matrix that characterizes the patent. The components in matrix A are 0s and 1s representing the relation between functions and technologies. Finally row vector T is a transformation matrix which transforms the technologies into function.


Suh, N. P., “Axiomatic Design: Advances and Applications,” New York: Oxford University Press, 2001.