IP Law Daily, PATENT—Fed. Cir.: Noninfringement ruling affirmed in ladder locking mechanism patent dispute, (Feb 6, 2026)

By Ravindra Kumar Singh, B.L.

The district court correctly construed the claim limitations, excluded flawed infringement opinions, and applied prosecution history estoppel to bar the doctrine of equivalents.

In a non-precedential disposition, the U.S. Court of Appeals for the Federal Circuit has affirmed a District of Minnesota judgment granting summary judgment of noninfringement in a patent dispute between competing ladder manufacturers, holding that the accused products did not literally infringe the asserted patent and that prosecution history estoppel barred reliance on the doctrine of equivalents. The appellate court also upheld the district court’s construction of the disputed claim term “cavity” and its exclusion of the patentee’s infringement expert, concluding that the expert’s opinions conflicted with the adopted claim construction and could not create a genuine issue of material fact (Little Giant Ladder Systems, LLC v. Tricam Industries, Inc., No. 24-2115 (Fed. Cir. Feb. 5, 2026)).

Background. The plaintiff/appellant, Little Giant Ladder Systems, LLC, designs, manufactures, and sells multi-position ladders and related access products. It competes directly in the consumer and professional ladder market with the defendant/appellee, Tricam Industries, Inc., which likewise manufactures and sells ladders and ladder accessories.

The dispute concerned U.S. Patent No. 10,767,416 (the ’416 patent), titled “Ladder Locking Mechanism.” The patent is directed to a multi-position ladder having two sets of rails that are slidably coupled and a locking mechanism designed to improve ease of use and safety. Claim 1, the sole independent claim, recites a locking mechanism including a bracket, a rotatable component, and an engagement pin.

Little Giant alleged that Tricam’s ladders, which incorporate a locking mechanism marketed as the “Speed Lock,” infringed the ’416 patent. Little Giant filed suit in the District of Minnesota, asserting literal infringement and infringement under the doctrine of equivalents. After claim construction, expert discovery, and cross-motions for summary judgment, the district court construed the claim term “cavity” to mean “a hollowed-out space (not passing all the way through)” and further construed the limitation to require that more than a majority of the bracket be placed inside that space. The court excluded Little Giant’s infringement expert for failing to apply that construction and granted Tricam summary judgment of noninfringement, finding no literal infringement and holding that prosecution history estoppel barred equivalents. Little Giant appealed.

Claim construction. The Federal Circuit reviewed claim construction de novo and affirmed the district court’s interpretation of “cavity.” The court emphasized that the construction adopted below reflected the parties’ “essentially agreed-upon” understanding during claim construction and was supported by the intrinsic record. Little Giant attempted on appeal to narrow or recharacterize the phrase “not passing all the way through,” arguing for a more particularized, directional interpretation. The Federal Circuit rejected that effort, holding that Little Giant had forfeited any challenge to the inclusion of that language because it had advocated the same wording in the court below. Citing TVIIM, LLC v. McAfee, Inc., 851 F.3d 1356 (Fed. Cir. 2017), the court reiterated that a party may not alter its claim construction position for the first time on appeal.

The court further declined to read additional concepts of “hidden or concealed” into the term. Relying on the Notice of Allowance and the patent’s figures, the Federal Circuit agreed that the claimed cavity was a space bounded such that, when assembled, it did not pass all the way through the component in any direction. The court held that the district court properly used the figures to explain the examiner’s understanding, rather than to import extraneous limitations.

Exclusion of expert testimony. Applying Eighth Circuit law, the Federal Circuit reviewed the exclusion of Little Giant’s infringement expert for abuse of discretion and affirmed. The expert opined that tunnel-like or taco-shaped spaces in Tricam’s Speed Lock handle satisfied the cavity limitation, even though those spaces passed all the way through the component. The district court excluded the testimony because it rested on a materially different claim construction. The Federal Circuit agreed, citing Treehouse Avatar LLC v. Valve Corp., 54 F.4th 709 (Fed. Cir. 2022), for the principle that expert testimony based on an incorrect claim construction cannot create a genuine dispute of material fact.

Literal infringement. The Federal Circuit also affirmed summary judgment of no literal infringement. Under the adopted construction, the cavity limitation required that more than a majority of the bracket be placed inside a hollowed-out space that did not pass all the way through. Although Tricam’s Speed Lock contained several small hollowed-out spaces that met the “not passing all the way through” requirement, it was undisputed that only about 20% of the bracket was disposed of within those spaces. Little Giant’s infringement theory relied on treating a larger “wing space” that extended all the way through the handle as the claimed cavity. The court held that this theory failed as a matter of law because it contradicted the claim construction and relied solely on the excluded expert opinion.

Doctrine of equivalents and estoppel. Finally, the Federal Circuit upheld the district court’s application of prosecution history estoppel. During prosecution, the applicant amended the claim language from a bracket concealed between components to one “disposed within a cavity” to overcome prior art. The court held that this narrowing amendment created a presumption of estoppel under Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002), surrendering claim scope covering designs where the bracket was concealed without being in a true cavity. The court further held that Little Giant failed to establish the tangential relation exception recognized in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 344 F.3d 1359 (Fed. Cir. 2003), because the distinction between concealment and disposition within a cavity was central to the amendment made to avoid the prior art.

Finding no error in the claim construction, evidentiary rulings, or infringement analysis, the Federal Circuit affirmed the judgment in full.

The case is No. 24-2115.

Judge: Chen, R.

Attorneys: Mark A. Miller (Dorsey & Whitney LLP) for Little Giant Ladder Systems, LLC. Eric Hugh Chadwick (Dewitt LLP) for Tricam Industries, Inc.

Companies: Little Giant Ladder Systems, LLC; Tricam Industries, Inc.

Cases: Patent FedCirNews GCNNews