PTAB Erred In Determining “Mechanical Control Assembly” Was Not A Means-Plus-Function Limitation

  • September 1, 2019
MTD Products Inc. v. Andrei Iancu, No. 17-2292

In MTD Products, the Federal Circuit overturned the final written decision of the Patent Trial and Appeal Board in inter partes review finding the challenged claims of a patent to be obvious, because the Board erred in construing the claim term “Mechanical Control Assembly” to not be a means-plus-function limitation.

MTD Products was the owner of a patent directed to a steering mechanism for zero turn radius (ZTR) lawn mowers. The Toro Company challenged MTD’s patent in an IPR, and the Board issued a final written decision finding that the claim term “mechanical control assembly” was not a means-plus-function limitation. Under the Board’s broader construction of the term, the patent was found to be obvious over the prior art. The Board’s decision was supported by the fact that the specification did not mention mechanical control assemblies, and therefore there would have been no corresponding structure in the specification to support means-plus-function claiming.

A means-plus-function limitation permits an element in a claimed combination to be expressed as a means or a step for performing a specified function without the recital of a particular structure, material, or acts in support thereof. Once it is determined that a term is a means-plus-function limitation, it must be construed to cover the corresponding structure, material, or acts described in the specification and its equivalents.

MTD Products appealed, arguing that “mechanical control assembly” was a means-plus-function limitation and that the asserted prior art did not disclose the term’s corresponding structure.

While the patent specification did not explicitly recite a “mechanical control assembly,” it did describe a preferred embodiment that included a “ZTR control assembly.” The specification further identified components and configurations of the ZTR control assembly, such as its inputs, outputs, and linkages. Although the Federal Circuit agreed with the Board that the specification plays a role in assessing whether particular claim language invokes means-plus-function claim requirements, it did not agree that the instant patent specification rendered the nonce term “mechanical control assembly” sufficiently structural to a person of ordinary skill in the art.

Key takeaway: Means-plus-function limitations are narrowly construed to the supporting disclosure in the specification, and they prevent an undesired narrowing of claim scope for such terms. The specification must be written broadly enough to capture many possible configurations and functions.


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