Burden of Proof and 1st Requirement for Doctrine of Equivalets
(Conclusion) A patentee and an alleged infringer owe the burden of proof for the requirements (1) to (3) and (4) and (5) respectively for the doctrine of equivalents, and the essential part of a patented invention in the requirement (1) means a unique technical idea not seen in prior arts to be found based on the claims and specification, the comparison with prior arts, and the degree of contribution.
A patentee owes the burden of proof for the requirements (1) to (3) for the doctrine of equivalents, since the requirements (1) to (3) are required for the subject product, etc., to be considered as substantially identical with the patented invention beyond literal construction, while an alleged infringer owes the burden of proof for the requirements (4) and (5), since the requirements (4) and (5) are required to eliminate the application of the doctrine of equivalents even to such subject product, etc.
The essential part of a patented invention in the requirement (1) (the different part is not the essential part of the patented invention) means a unique technical idea not seen in prior arts to be found first by understanding the problem to be solved, means for solving the problem, and its effects based on the claims and specification, and then by determining a unique technical idea not seen in prior arts based on the comparison with prior arts, and the degree of contribution. Depending on the degree of contribution, the application of the requirements (1) may be broader or narrower. In addition, in determining the application of the requirements (1), it is not appropriate first to divide the elements in the claim into essential parts and non-essential parts, and then to consider that the requirements (1) cannot be fulfilled for such essential elements, but it is necessary first to determine whether the subject product, etc. commonly has the essential part of the patented invention, and then to consider whether the different part is within such essential part.
<Writer: Kei IIDA (Attorney-at-law and Patent Attorney)>
https://www.ip.courts.go.jp/app/files/hanrei_en/003/002003.pdf