PTAB

IPR2015-01108

Mitsubishi Cable Industries Ltd v. GoTo DenShi Co Ltd

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1. Case Identification

2. Patent Overview

  • Title: Wire for Coil
  • Brief Description: The ’888 patent discloses a wire for use in coils, such as speaker voice coils, having a square cross-section with chamfers at its four corners. The purported invention lies in specific geometric relationships: the wire’s cross-sectional area must be at least 1.15 times that of a reference circle (claims 1, 2, 5, 6), or its perimeter must be at least 1.09 times the circumference of that same reference circle (claims 3, 4, 7, 8). The reference circle is defined as having a diameter equal to the length of one side of the wire's square shape.

3. Grounds for Unpatentability

Ground 1: Anticipation of Claims 1-8 under 35 U.S.C. §102 by Sugita

  • Prior Art Relied Upon: Sugita (JP Publ. No. 2003-245711).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that Sugita, which discloses a die for drawing square-shaped wire with arc-shaped corners for use in coils, inherently anticipates every limitation of claims 1-8. Although Sugita does not explicitly state the claimed area or perimeter ratios, it provides specific dimensions for an exemplary resulting wire: a side length of 0.35 mm and corner radii of 0.03 mm. Petitioner performed standard geometric calculations on these disclosed dimensions, demonstrating that the resulting wire necessarily possesses a cross-sectional area ratio of 1.265 (exceeding the claimed threshold of 1.15) and a perimeter ratio of 1.226 (exceeding the claimed threshold of 1.09). Sugita also discloses wire dimensions of 0.35 mm, satisfying the "1 mm or less" limitation of dependent claims 5-8.

Ground 2: Anticipation of Claims 1-8 under 35 U.S.C. §102 by Harada

  • Prior Art Relied Upon: Harada (JP Appl. 2002-260461).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner contended that Harada, which was not considered during prosecution, anticipates all challenged claims. Harada describes a square wire with arc-shaped corners for coil winding and teaches improving its "space factor" to between 96% and 99%. Petitioner argued that this "space factor"—the ratio of the wire's area to that of a perfect circumscribing square—is a mathematically fixed property that inherently discloses the claimed ratios. Calculations showed that a wire with a 99% space factor necessarily has a cross-sectional area ratio of 1.26 and a perimeter ratio of 1.21, both exceeding the claimed thresholds. Since this relationship is inherent to the disclosed space factor, Harada anticipates the limitations of all claims regardless of the wire's specific dimensions.

Ground 3: Obviousness of Claims 1-8 under 35 U.S.C. §103 over Sugita in view of MWSWire

  • Prior Art Relied Upon: Sugita (JP Publ. No. 2003-245711) and MWSWire (MWS Wire Industries Web Pages, archived 1999).

  • Core Argument for this Ground:

    • Prior Art Mapping: Petitioner argued that even if Sugita does not inherently disclose all claim limitations, the claims are obvious when Sugita is combined with MWSWire. Sugita taught the core concept: a die for producing square wire with rounded corners to achieve high space efficiency in coils. MWSWire, a well-known industry resource, provided standardized tables of commercially available "Microsquare Magnet Wire," explicitly listing various side dimensions and corresponding corner radii for different American Wire Gauge (AWG) sizes.
    • Motivation to Combine: A Person of Ordinary Skill in the Art (POSITA) implementing the wire-drawing die taught by Sugita would be motivated to consult a standard industry reference like MWSWire to select known, proven, and commercially relevant dimensions for the wire. Both references shared the common goal of creating compact, efficient coils that deliver "more power in less space."
    • Expectation of Success: Using standard, tabulated wire dimensions from MWSWire to produce a wire with the die taught by Sugita would have been a predictable and straightforward design choice with a high expectation of success. Many of the standard wire sizes listed in MWSWire, such as AWG 21, met the dimensional and ratio limitations of the challenged claims.

  • Additional Grounds: Petitioner asserted additional obviousness challenges, including combining Sugita or Harada with the Math Pocket Reference to provide the basic geometric formulas to calculate the claimed ratios, and combining Harada with Nakagawa (Japanese Utility Model Publ. No. H01-176315) to explicitly teach applying a specific radius to Harada’s corner portions.

4. Key Claim Construction Positions

  • "length of one side of said square": Petitioner argued this term should be construed as "the length of the side of the smallest circumscribing square surrounding the square wire with chamfers." This construction is based on figures and examples in the ’888 patent and is critical for applying the dimensions disclosed in the prior art to the claimed ratios.
  • "chamfer": Petitioner proposed this term means "any corner break, including linear or arc-shaped, on the corner of an otherwise square wire." This broad construction is supported by the specification and encompasses the rounded or arc-shaped corners described in the primary prior art references.

5. Relief Requested

  • Petitioner requests institution of an inter partes review and cancellation of claims 1-8 of the ’888 patent as unpatentable.