CAFC Affirms PTAB Decision Invalidating Flow Meter Patent Claims

“Although Kamstrup contended that there were functional differences in polymer structures cast in a single mold as opposed to multiple molds, the appellate court found that this simply pointed to restrictions inherent to the manufacturing process.”


Flow meter housing, Fig. 1A (from CAFC opinion)

On August 12, the U.S. Court of Appeals for the Federal Circuit (CAFC) issued a precedential decision in Kamstrup A/S v. Axioma Metering UAB affirming a final written decision by the Patent Trial and Appeal Board (PTAB) that invalidated all challenged claims as obvious or anticipated. In so holding, the Federal Circuit found that the PTAB properly construed a product-by-process claim element as not entitled to patentable weight and dismissed Kamstrup’s arguments that the asserted prior art was not analogous to the patented invention.

‘Cast In One Piece’ Product-By-Process Claim Element Not Relevant to Patentability

The patent-at-issue in this case is U.S. Patent No. 8806957, Ultrasonic Flow Meter Housing Formed By a Monolithic Polymer Structure. Issued to Kamstrup in August 2014, the ‘957 patent claims an ultrasonic flow meter having a monolithic polymer structure being cast in one piece, a flow tube with a straight flow section arranged for fluid passage, as well as a cavity sharing a wall with the flow tube and housing an ultrasonic transducer and a measurement circuit connected to the ultrasonic transducer for measuring the fluid’s flow rate. The invention was developed to overcome issues with prior art ultrasonic flow meters measuring gas or water consumption, which required a number of molding steps to produce the assembly.

Kamstrup, a Danish developer of smart metering solutions, filed a lawsuit asserting the ‘957 patent against rival Lithuanian firm Axioma Metering in June 2019, leading Axioma to petition for inter partes review (IPR) proceedings that September to challenge the validity of all 15 claims of the ‘957 patent. During the IPR, the PTAB construed “cast in one piece” as a product-by-process claim element and determined that the element was not entitled to any weight during the patentability analysis as Kamstrup had not presented any evidence that the claim element exhibited any structural or functional differences from the prior art. In construing “cavity separated from the flow tube,” the PTAB also rejected Kampstrup’s arguments that the cavity cannot surround the flow tube.

Under these claim constructions, the PTAB determined that several claims of the ‘957 patent were invalid as anticipated by European Patent No. 1482284, Flow Sensor (“Ueki”), which claims a flow sensor for detecting the flow quantity of a fluid. The PTAB’s previous claim constructions frustrated Kamstrup’s arguments that Ueki did not disclose those particular claim elements. In finding the remainder of the claims of the ‘957 patent invalid for obviousness, the PTAB combined the primary Ueki reference with U.S. Patent No. 6248077, System for Sensing a Characteristic of Fluid Flowing To or From a Body (“Elson”), and/or U.S. Patent No. 4476877, Fluid Temperature Sensor (“Barker”). In finding that skilled artisans would have a motivation to combine Ueki with Elson or Barker, the PTAB credited Axioma’s expert who testified that it was common to measure fluid temperature while also measuring flow.

No Functional or Structural Differences in Polymer Housing for Flow Meter

On appeal, the Federal Circuit noted that product-by-process claim elements allow patentees to claim an invention that resists definition other than by the process by which the product is made but is otherwise patentable. Citing to its 1985 decision in Amgen v. F Hoffman-La Roche, the Federal Circuit acknowledged that if the resulting product had structural and functional differences from the product created by the prior art, then those differences are relevant evidence of no anticipation. Looking to Amgen as an example, the Federal Circuit in that case credited the district court for properly considering differences in a chemical compound purified from mammalian cells, including a higher molecular weight and different charge, as making that compound distinct from a similar compound purified from urine.

In the present case, the “cast in one piece” claim limitation was a product-by-process claim element on its face as it discusses the structure being cast in a particular way. Kamstrup argued that the ‘957 patent’s specification disclosed that the flow meter can be fabricated in fewer steps than prior art meters, but the Federal Circuit found that this only further supported the product-by-process claim limitation finding. Although Kamstrup contended that there were functional differences in polymer structures cast in a single mold as opposed to multiple molds, the appellate court found that this simply pointed to restrictions inherent to the manufacturing process and that the use of a single mold was detached from the claim language, which focused on the structure being cast in one piece instead of one mold.

Kamstrup similarly lost out on its challenge to the district court’s construction of the claim term “cavity separated from the flow tube.” The Federal Circuit noted that nothing in the ‘957 patent’s claim language prohibited the cavity from surrounding the flow tube, leading the court to conclude that Kamstrup’s proposed construction improperly read in a limitation from non-limiting embodiments. Because the “cast in one piece” product-by-process claim limitation was not relevant to patentability, it did not provide a limitation requiring that the flow tube and the housing be manufactured at the same time, the Federal Circuit concluded. Further, the Federal Circuit rejected Kamstrup’s argument that the “measurement tube element” of claim 6 could only be an ultrasonic measurement element, as the claim language did not include such a limitation and the patent’s specification disclosed the use of temperature sensors in the flow meter.

Failed Claim Construction Arguments Doom Kamstrup’s Appeal on Patentability

Addressing Kamstrup’s appeal to the PTAB’s patentability determination, the Federal Circuit first struck down the patent owner’s argument that Elson and Barker, which are both directed to medical devices for thermodilution, are not analogous art to the ‘957 patent. The Federal Circuit found that Elson, which discloses a system for sensing fluid flowing characteristics with the use of a sensor probe, and Barker, which discloses a fluid temperature sensor having a through lumen for conducting fluid, were at least in the same field of endeavor as the ‘957 patent’s flow meter including different types of sensors.

In affirming the PTAB’s findings of anticipation and obviousness, the Federal Circuit held that “Kamstrup’s remaining challenges to the Board’s patentability determinations rise and fall with Kamstrup’s proposed claim constructions,” which were all dismissed by the appellate court. The court did not consider whether the PTAB correctly identified the prior art references or properly found a motivation to combine as Kamstrup did not raise either challenge on appeal.


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