Slingshot Printing LLC v. Canon U.S.A., Inc. — Federal Circuit Affirms PTAB Invalidity of Inkjet Temperature-Sensor Patents

Background

Slingshot Printing LLC held two patents covering temperature-monitoring technology used in inkjet printer chips: U.S. Patent No. 7,484,823 (the ‘823 patent) and U.S. Patent No. 7,594,708 (the ‘708 patent). Both patents describe placing temperature-sensing elements (“thermal sense resistors”) in thermal regions between heater arrays on a printer chip, allowing each region’s temperature to be monitored and regulated independently for more precise print-quality control.

Canon U.S.A. and Canon Inc. petitioned the Patent Trial and Appeal Board (PTAB) for inter partes review (IPR) of both patents, arguing that the claims were obvious over a combination of two prior art patents: Benjamin (U.S. Patent No. 7,384,113), which taught a multi-region inkjet temperature monitoring architecture, and Giere673 (U.S. Patent No. 6,612,673), which disclosed thermal sense resistors placed equidistantly between heater arrays. The Board agreed, finding all challenged claims unpatentable for obviousness. Slingshot appealed to the Federal Circuit.

The Court’s Holding

The Federal Circuit affirmed the PTAB’s invalidity findings across the board.

No improper hindsight. Slingshot argued the Board improperly relied on the ‘823 patent itself to reconstruct the invention—a classic hindsight-bias objection. The Federal Circuit found the Board had used the patent’s background section only to identify admissions about what was already known in the art at the time of the invention, which is a proper use of a patent’s own disclosure. Attacking the prior art references individually, as Slingshot attempted, was also insufficient when the invalidity finding rested on their combination.

Yabe does not teach away. Slingshot also contended that a third reference, Yabe (U.S. Patent No. 6,527,367), taught away from placing temperature sensors in the central portion of each region. The Federal Circuit rejected this argument, noting that Yabe merely states that one particular design makes a central sensor unnecessary—not that central placement is disadvantageous or should be avoided. That is not the level of discouragement required to establish teaching away.

Motivation to combine was supported by the record. Slingshot argued there was no reason a skilled engineer would add Giere673’s per-region thermal sense resistors to Benjamin’s architecture given the cost of additional sensors. The Board found that the improved per-region temperature accuracy—and thus better print quality—outweighed any cost concerns. The Federal Circuit found substantial evidence supported that finding. The Board also relied on credible expert testimony establishing that Giere673’s sensor leg placement, equidistant from the heater arrays, satisfied the patents’ “substantially centrally disposed” claim limitation.

Key Takeaways

• A patent’s own background section may be used in IPR proceedings to establish what was known in the art—courts treat such statements as admissions about prior-art knowledge at the time of invention.
• Prior art “teaches away” only if it affirmatively discourages a particular approach; merely suggesting that approach is optional is not enough to foreclose an obviousness finding.
• The Federal Circuit continues to give substantial deference to PTAB factual findings on motivation to combine, affirming when the Board weighs benefits (print quality improvement) against costs (additional sensors) and finds the balance favors combination.
• Nonprecedential, but confirms that thermal-management patent claims in the printing technology space remain difficult to defend against well-constructed IPR petitions pairing complementary prior art references.

Why It Matters

For patent holders in the printing and imaging technology space, this decision is a reminder that PTAB inter partes review remains an effective and widely-used tool for challengers. Canon successfully cleared two patents covering core thermal-sensing functionality using a combination of relatively old references, and the Federal Circuit’s deferential review of the PTAB’s factual findings gave Slingshot little room to mount a successful appeal.

More broadly, the case reinforces the standard obviousness-combination analysis: courts will not require a challenger to show that each prior art reference is a perfect standalone substitute for the claimed invention. Showing that a skilled engineer would have been motivated to combine features from two references—even if neither alone teaches the full claim—is sufficient. Companies seeking to enforce printer or peripheral-device patents should be prepared to defend against creative prior art combinations reaching back to fundamental thermal-management concepts.