DCT
4:19-cv-08044
Zircon Corp v. Stanley Black Decker Inc
I. Executive Summary and Procedural Information
- Parties & Counsel:
- Plaintiff: Zircon Corporation (California)
- Defendant: Stanley Black & Decker, Inc. (Delaware)
- Plaintiff’s Counsel: Palo Alto Legal Group, P.C.
- Case Identification: 4:19-cv-08044, N.D. Cal., 03/04/2020
- Venue Allegations: Plaintiff alleges venue is proper in the Northern District of California because Defendant maintains regular and established places of business in the district, including offices and a technology incubator, transacts significant business, and committed acts of infringement there.
- Core Dispute: Plaintiff alleges that Defendant’s DeWalt and Craftsman-branded stud finders infringe four patents related to auto-recalibration, dual-capacitor sensing, ergonomic design, and projected visual displays.
- Technical Context: The lawsuit concerns electronic handheld stud finders, a common tool used in construction and home improvement to locate structural members like studs behind wall surfaces.
- Key Procedural History: The complaint alleges a history of litigation between Zircon and both Stanley and Black & Decker prior to their 2010 merger, as well as failed acquisition discussions. This history is noted to support allegations of knowledge and willfulness. The complaint also limits its request for remedies for the ’241 patent to infringement occurring on or before June 22, 2019, corresponding to the patent's expiration date.
Case Timeline
| Date | Event |
|---|---|
| 1999-06-22 | ’241 Patent Priority Date |
| 2001-07-10 | ’241 Patent Issue Date |
| 2004-04-29 | ’662 Patent Priority Date |
| 2004-05-14 | ’703 Patent Priority Date |
| 2006-01-24 | ’662 Patent Issue Date |
| 2006-12-12 | ’703 Patent Issue Date |
| 2007-12-14 | ’771 Patent Priority Date |
| 2008-12-12 | ’771 Patent Filing Date |
| 2009-01-01 | Start of Prior Litigation Period Mentioned in Complaint |
| 2010-03-01 | Stanley merges with Black & Decker (approx.) |
| 2011-12-31 | End of Prior Litigation Period Mentioned in Complaint |
| 2013-12-10 | ’771 Patent Issue Date |
| 2019-06-22 | ’241 Patent Expiration / Last date of infringement alleged |
| 2020-03-04 | Complaint Filing Date |
II. Technology and Patent(s)-in-Suit Analysis
U.S. Patent No. 6,989,662 - "Sensor Auto-Recalibration," Issued January 24, 2006
The Invention Explained
- Problem Addressed: Capacitive stud finders must first be calibrated on a "blank" section of wall to establish a baseline capacitance. If a user inadvertently calibrates the device over a stud, the resulting "erroneous calibration value" is too high, preventing the device from detecting that stud or others as it is moved across the wall (Compl. ¶28; ’662 Patent, col. 1:50-59). The patent illustrates this problem with a prior art figure showing an erroneous calibration value (150) set at a peak capacitance, masking the stud's presence (Compl. ¶29, FIG. 1C).
- The Patented Solution: The invention provides a method and device that automatically corrects an erroneous calibration. The device continuously monitors capacitance readings and, if it detects a new reading that is significantly lower than the stored calibration value, it determines that the initial calibration was likely performed over a stud and automatically updates the calibration value to the new, lower reading without user intervention (Compl. ¶30-31; ’662 Patent, col. 4:15-32). This process can repeat until a proper baseline is established (Compl. ¶30, FIG. 2).
- Technical Importance: This auto-recalibration feature purports to solve a common user-error problem, improving the reliability and ease of use of capacitive sensors by making them more forgiving of improper initial placement (Compl. ¶24, ¶30; ’662 Patent, col. 1:63-66).
Key Claims at a Glance
- The complaint asserts claims 1-20, which include independent method and apparatus claims (Compl. ¶112).
- Independent method claim 1 includes the essential elements of:
- Holding a stud sensing device at a first location and sensing a first density to set an initial calibration value.
- Moving the device to a second location and sensing a second density.
- Determining if the device was calibrated over or near a stud (e.g., by comparing the first and second densities).
- Recalibrating the device if it was determined to be calibrated over or near a stud.
- The complaint also asserts apparatus claims covering a device with memories, a sensor, a comparator, and an updater to perform this auto-recalibration (Compl. ¶116).
U.S. Patent No. 7,148,703 - "Auto-Deep Scan For Capacitive Sensing," Issued December 12, 2006
The Invention Explained
- Problem Addressed: Standard stud sensors struggle to accurately locate studs behind thick or deep wall surfaces (e.g., >1.5 inches). Increasing sensor sensitivity to find deeper studs can cause a "ballooning" effect, where the perceived width of the stud is distorted, making it difficult to find its true center and edges. This effect can be asymmetric if other objects like pipes or wires are nearby (Compl. ¶34-36; ’703 Patent, col. 1:62-2:12).
- The Patented Solution: The invention uses a sensor with two separate, side-by-side capacitive plates. By measuring the capacitance at each plate independently and then generating a ratio of the two values, the device can more accurately determine the lateral location of a stud's features. Furthermore, by comparing one or both of the capacitance values to a threshold, the device can also determine the depth of the stud (Compl. ¶37, ¶40-41; ’703 Patent, col. 11:2-17). The patent illustrates this with capacitance curves showing how two plates (301, 302) produce distinct signals (310A, 320A) that can be analyzed relative to each other (Compl. ¶38-39, FIG. 1A, FIG. 2C).
- Technical Importance: This dual-plate, ratiometric approach allows the sensor to distinguish between changes in capacitance caused by the stud's edge versus its center, and to infer the stud's depth, thereby improving accuracy for objects behind thicker surfaces (Compl. ¶34; ’703 Patent, col. 2:26-30).
Key Claims at a Glance
- The complaint asserts claims 1-14, which include independent apparatus claims (Compl. ¶137).
- Independent apparatus claim 1 includes the essential elements of:
- A first plate and a second plate for forming two separate capacitors with the structure behind a surface.
- A first and a second measurement circuit coupled to the respective plates.
- A comparison circuit that generates a ratio of the first and second capacitance values to determine the lateral location of a feature.
- The comparison circuit also compares a capacitance value to a threshold to determine the depth of the feature.
- The complaint reserves the right to assert other claims (Compl. ¶138).
Multi-Patent Capsule: U.S. Patent No. 8,604,771 - "Hand Tool Having A Pivot Grip For Sensing A Measurement Behind A Target Surface," Issued December 10, 2013
- Technology Synopsis: The patent addresses the ergonomic problem of using stud sensors on varied surfaces like walls, ceilings, and floors (Compl. ¶44; ’771 Patent, col. 1:35-38). The solution is a hand tool with a grip having a pair of opposing three-dimensional concave finger holds, which creates a natural pivot axis for the user's thumb and finger, allowing for more comfortable rotation and use of the tool at different orientations (Compl. ¶45, ¶48; ’771 Patent, col. 1:45-50).
- Asserted Claims: Claims 1-24 are asserted (Compl. ¶160).
- Accused Features: The "concave gripping means" of the Stanley Stud Sensor 150 and 200 are alleged to provide the claimed axis of rotation (Compl. ¶99).
Multi-Patent Capsule: U.S. Patent No. 6,259,241 - "Projected Display For Portable Sensor Indicating The Location Of A Detected Hidden Object Behind Surface," Issued July 10, 2001
- Technology Synopsis: The patent addresses the difficulty of seeing a stud finder's built-in display when working in unusual positions or near obstructions (Compl. ¶51; ’241 Patent, col. 1:60-2:9). The invention solves this by having the device project a visible pattern, such as a line of light, directly onto the wall surface to indicate the location of the detected object's edge or center (Compl. ¶52-53; ’241 Patent, col. 2:11-27).
- Asserted Claims: Claims 1-26 and 31-51 are asserted (Compl. ¶185).
- Accused Features: The Stanley IntelliSensor, IntelliLaser, and Craftsman Hi-Vis stud sensor products are alleged to infringe by projecting a visible pattern (e.g., a laser line) onto the surface to indicate a detected object's location (Compl. ¶104, ¶109, ¶188).
III. The Accused Instrumentality
- Product Identification: The complaint names multiple stud finder models sold under the DeWalt, Craftsman, and Stanley brands, including the DeWalt DW0100 and DW0150; Craftsman CMHT77620, CMHT77621, CMHT77623, and Hi-Vis Stud Sensor CMHT77633/CMHT77636; and Stanley Stud Sensor 150/200 and IntelliSensor/IntelliLaser lines (collectively, the "Infringing Products") (Compl. ¶55).
- Functionality and Market Context:
- The accused products are handheld electronic devices that use capacitive sensing to locate objects like wood and metal studs or live AC wires behind drywall (Compl. ¶63).
- Key accused functionalities, based on product marketing and images, include "constant auto-calibration," "Center-find technology," concave ergonomic grips, and the projection of laser lines to mark stud locations (Compl. ¶58, ¶61, ¶99, ¶104, ¶108).
- The complaint alleges that these products are sold through major hardware retailers like Home Depot and Lowes and constitute a significant part of Defendant's $9.8 billion tools and storage business, directly competing with and diverting market share from Plaintiff (Compl. ¶14-15).
IV. Analysis of Infringement Allegations
’662 Patent Infringement Allegations (re: Auto-Recalibration)
The complaint alleges that the "constantly calibrating" or "Auto Calibration" feature of the accused products performs the patented method of auto-recalibration (Compl. ¶58, ¶66, ¶74). An image in the complaint depicts a test where an accused device is first placed "On Stud" (CAL #3), then moved to a position "Between Studs" (CAL #2), illustrating the recalibration process (Compl. ¶59, p. 19).
| Claim Element (from Independent Claim 1) | Alleged Infringing Functionality | Complaint Citation | Patent Citation |
|---|---|---|---|
| holding the stud sensing device at a first location on the surface; | The user holds the device against the wall to begin operation. | ¶60, ¶68 | col. 10:51-52 |
| placing the stud sensing device in an calibration mode; sensing a first density at the first location | The user places the device on the wall, which initiates calibration. The device's "constant auto-calibration" feature senses an initial density/capacitance (Compl. ¶58, ¶66). | ¶60, ¶68 | col. 10:53-56 |
| setting a calibration value based on the first sensed density; | The device sets an internal calibration value based on this first reading. | ¶60, ¶68 | col. 10:57-58 |
| moving the stud sensing device to a second location on the surface; sensing a second density | The user slides the device along the wall to a new position, where it senses a new density/capacitance value. | ¶60, ¶68 | col. 10:59-61 |
| determining if the stud sensing device was calibrated over or near a stud; | The device internally compares the new, lower density reading to the initial, higher calibration value, thereby determining it was likely calibrated over a stud. | ¶60, ¶68 | col. 10:63-65 |
| and the stud sensing device recalibrating itself if it determined that the stud sensing device was calibrated over or near the stud. | The device automatically updates its calibration value to the new, lower density reading, thereby "recalibrating itself" (Compl. ¶59, ¶67). | ¶60, ¶68 | col. 10:66-11:2 |
- Identified Points of Contention:
- Technical Question: What evidence demonstrates that the accused "constant auto-calibration" performs the specific sequence of steps required by the claims (e.g., determining an over-a-stud condition and then recalibrating), as opposed to a more generic continuous averaging or updating process?
- Scope Question: Does the marketing term "constant auto-calibration" describe the specific two-location comparison and conditional update process recited in the claims, or does it describe a different technical process that the patentee may have disclaimed or not covered?
’703 Patent Infringement Allegations (re: Dual-Capacitor Sensing)
The complaint alleges that the accused products' "Center-find technology" and ability to detect studs through deeper surfaces are achieved using a dual-plate sensor structure that infringes the ’703 patent (Compl. ¶61, ¶69). A teardown photograph is provided showing the alleged infringing two-plate structure inside a DeWalt DW0100 device (Compl. ¶62, p. 21).
| Claim Element (from Independent Claim 1) | Alleged Infringing Functionality | Complaint Citation | Patent Citation |
|---|---|---|---|
| a sensor for finding a feature of a structure behind a surface comprising: a first plate... and a second plate... | The accused devices contain a two-sensor plate structure, as shown in teardown images, with a first plate/capacitor and a second plate/capacitor (Compl. ¶62, ¶70, p. 21, p. 24). | ¶64, ¶72 | col. 16:51-56 |
| a first measurement circuit coupled to the first plate... a second measurement circuit coupled to the second plate... | The devices use electronic signals to locate studs, which implies circuitry to measure the capacitance from each of the two plates (Compl. ¶63, ¶71). | ¶64, ¶72 | col. 16:56-61 |
| a comparison circuit... generating a ratio of the first and second capacitance values to determine a lateral location of the feature... | The "Center-find technology" is alleged to work by comparing the signals from the two plates (i.e., generating a ratio) to determine the center of a stud, which is a lateral location (Compl. ¶61). | ¶64, ¶72 | col. 16:62-17:2 |
| and comparing one of the first or second capacitance values to a first threshold to determine a depth of the feature... | The devices are marketed as detecting studs at specific depths (e.g., 3/4 in. or 1.5 in.), which the complaint alleges is accomplished by comparing capacitance values to an internal threshold to determine if a feature is deep (Compl. ¶61, ¶69, p. 20, p. 24). | ¶64, ¶72 | col. 17:2-5 |
- Identified Points of Contention:
- Technical Question: Does the accused "Center-find technology" actually operate by "generating a ratio" of capacitance values as required by the claim, or does it use a different algorithm (e.g., finding a peak, or comparing differences) to locate the center?
- Evidentiary Question: Beyond marketing materials stating a depth rating, what evidence does the complaint provide that the accused devices perform the claimed step of comparing a capacitance value to a "threshold to determine a depth"?
V. Key Claim Terms for Construction
For the ’662 Patent:
- The Term: "recalibrating"
- Context and Importance: This term is the core of the invention. The infringement case may turn on whether Defendant's "constant auto-calibration" (Compl. ¶58) is the same as the patent's specific, event-triggered "recalibrating" process. Practitioners may focus on this term to distinguish between a continuous, unconditional update and the discrete, conditional process of identifying an error and then correcting it, as claimed.
- Intrinsic Evidence for Interpretation:
- Evidence for a Broader Interpretation: The patent summary states the invention relates to sensors that "detect and correct a miscalibration" and "automatically recalibrates itself," which could be argued to encompass any automatic correction mechanism (Compl. Ex. A, Abstract; ’662 Patent, col. 1:5-8).
- Evidence for a Narrower Interpretation: The detailed description and flow chart (FIG. 2) describe a specific sequence: taking a second measurement, "determining if a correction is needed," and then updating the value if needed (Compl. ¶31, FIG. 2; ’662 Patent, col. 4:24-32). This suggests "recalibrating" is not just any update, but a conditional update performed in response to detecting an error.
For the ’703 Patent:
- The Term: "generating a ratio"
- Context and Importance: This term defines the specific mathematical operation allegedly used to achieve superior lateral positioning. Infringement depends on whether the accused devices actually perform this calculation. The defense may argue their "Center-find technology" uses a different, non-infringing comparison method.
- Intrinsic Evidence for Interpretation:
- Evidence for a Broader Interpretation: The term "ratio" could be argued to broadly cover any comparison of the two capacitance values that yields a relative measure, not just a strict division. The summary describes the invention as using "an amplitude and a ratio of capacitance measurements," suggesting these might be distinct concepts (Compl. Ex. B, Abstract).
- Evidence for a Narrower Interpretation: The specification explicitly states the "comparison circuit generating a ratio of the first and second capacitance values" and provides a formulaic example: "ratio is calculated by dividing the smaller first plate's change in capacitance value by the second plate's change" (Compl. Ex. B; ’703 Patent, col. 9:20-30). This suggests a specific mathematical division is required.
VI. Other Allegations
- Indirect Infringement: The complaint alleges induced infringement for all four patents, stating Defendant instructs customers on how to use the infringing features through product manuals, advertising, and websites (e.g., Compl. ¶125, ¶155-156). It is also alleged that the accused products are especially adapted for use in an infringing manner and are not staple articles of commerce, supporting contributory infringement (e.g., Compl. ¶131-133).
- Willful Infringement: Willfulness is alleged for all patents based on Defendant's alleged long-standing awareness of Zircon's patent portfolio. The complaint cites prior patent litigation between the parties (from 2009-2011) and past acquisition discussions as evidence of pre-suit knowledge (Compl. ¶119-120, ¶149-150). The complaint further alleges that despite this knowledge, Defendant made no effort to design around the patents and continued to sell infringing products, constituting blatant and reckless disregard (Compl. ¶121, ¶151).
VII. Analyst’s Conclusion: Key Questions for the Case
- A central issue will be one of technical implementation: Does the accused "constant auto-calibration" feature of Defendant's products operate by executing the specific, conditional error-detection and update sequence required by the ’662 patent's claims, or does it employ a functionally different, non-infringing continuous update algorithm?
- A key evidentiary question will be one of algorithmic proof: Can Plaintiff demonstrate that the accused "Center-find technology" literally performs the "generating a ratio" calculation recited in the ’703 patent's claims, or will the dispute center on whether a different comparison method used by the Defendant is technically and legally equivalent?
- The willfulness claim will likely depend on the impact of prior interactions: To what extent does the alleged prior litigation and the failed acquisition talks from nearly a decade ago establish that Defendant had the requisite knowledge and intent regarding these specific patents and accused features, particularly for patents that issued after the litigation concluded?