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Interpretation of the Functional Features Recited in a Patent Claim



Patent claims rely solely on text. However, it is indeed difficult to define the scope of a patent right by describing an inventive concept or feature by text alone. It is not uncommon for a patent claim to involve not only structure, ingredients and/or movement, but also function.  Appropriate interpretation of the scope of features defined by functional description has been a matter of longstanding controversy.
 
The currently effective Patent Examination Guidelines (issued in 2013) do not deny the legitimacy of such claims employing functional description; the Guidelines only stress that a claim employing solely functional description without any other technical feature will fail to meet the requirements for clarity/definiteness. The current Guidelines only provide two kinds of functional feature: "object defined by function" and "means-plus-function." Said "object defined by function" is exemplified by claim language such as "storage device" and "output circuit" (please refer to IP Court judgment No. 103-Civil-Patent-Suit 48) which has been commonly used or recognized by persons in the art for a long time and is easily understood. Interpretation of the claim language "object defined by function" should include all objects/means which can perform such function. Said "means-plus-function" has to meet the following two requirements: (1) the claim language is in the form of "means for..." and (2) the claim language does not cover all necessary structures, materials and/or movements for performing the claimed function. In addition, interpretation of means-plus-function language has to include the structures, materials and/or movements for performing the function as its limitations and the equivalent scope thereof.
 
However, if a functional description in a claim is not apparently drafted in the form of "object defined by function" or "means-plus-function," how should it be interpreted? 
 
The Amended Points of Patent Infringement Assessment, which are undergoing public discussion prior to final drafting by the patent office, provide a third type of functional feature: "functional clause." For example, in the claim description "a changing direction device...comprising...whereby...to quickly change the operation direction," the language "whereby...to quickly change the operation direction" is a functional clause, not "object defined by function" or "means-plus-function."
 
However, is a "functional clause" to be considered a limitation of the claim scope? The Amended Points of Patent Infringement Assessment provide the following two different opinions:
  • Opinion 1: If the functional clause is only to describe the result that the technical feature is intended to achieve, it should not be considered a limitation of the claim scope.
  • Opinion 2:  Since the functional clause is part of the claimed features, it apparently relates to the limitations of the claim scope.
 
IP Court Judgment No. 99-Civil-Patent-Suit-58 adopts Opinion 2 because it indicates: "a functional clause relates to the limitations of claim scope; according to the All-Elements Rule, it has to be taken into consideration when the claim is compared with prior art and the accused product."
 
Though the Amended Points of Patent Infringement Assessment provide definition of a functional clause, it remains unclear whether a claimed feature drafted as a functional clause would be considered means-plus-function language if it does not contain all necessary structures, materials and/or movements for performing the claimed function. Interpretation of functional features/descriptions will merit scrutiny of future practice of the court and patent office.

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