US 5731575

I'll search for authoritative information on this patent, including any recent litigation.

Let me check specifically for any litigation or Federal Circuit activity.

Let me run a couple of targeted checks for recent (2025–2026) litigation activity.

US 5,731,575 — Record Check and Summary

Scope note on the "CAFC 2026 docket" request: I ran targeted searches for litigation and Federal Circuit activity tied to this patent number and to the Zingher/duress‑ATM patent family. I found no evidence of any 2026 (or any-year) CAFC docket, appeal, or co‑pending district court case involving US 5,731,575. I cannot treat that as proof of absence — CAFC docket databases (CM/ECF, PACER) are not fully indexed by the web search available to me, and appeal records are often not surfaced by general search. Treat "no litigation found" as not located, not as affirmatively none. Two traps I explicitly did not fall into:

• An OSTI record carrying "OSTI ID: 5731575" resolves to US 4,576,134 (Honda Giken Kogyo, fuel supply control) — a pure numeric ID collision, not this patent. (osti.gov)
• A Federal Circuit declaration document (gov.uscourts.cafc.21085) mentions "duress access" and "alert access," but it concerns U.S. 9,269,208 / Mathiassen / McKeith — a different patent and different parties, not 5,731,575.

Per the operating rule, I have not auto-corrected any identifier: this is patent number 5,731,575, application 08/844,626.

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Bibliographic Data (from the authoritative patent text)

Source: Google Patents US5731575A

Corroborating third‑party listing (Radaris inventor index) confirms: "#5731575 Mar 24, 1998 — Apr 21, 1997 — Joseph P. Zingher (Peru, IL) · Abraham R. Zingher (Zion, IL) — 8/844626." (radaris.com)

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Abstract (verbatim)

"A system and method for the discrete identification of a duress transaction at an ATM banking machine. The system and method allows the customer to alert the police that a crime is taking place without alerting the criminal that an alarm has been given by the entry of an access number equating to a non-prestored personal distress or emergency number in place of the stored PIN number. When an access number is entered to begin a transaction, the system compares the entered access number with the prestored PIN number. If the entered access number is the same as the PIN number, the transaction proceeds as normal. If not, an algorithmic function is applied to either the entered access number or the PIN number. These two number are then again compared and if after application of the algorithmic function they are the same, then the duress signal is triggered. Thus, the non-prestored personal distress number is successfully entered when the access number entered to begin the transaction equates to the PIN number after the algorithmic function is applied to either the entered access number or the PIN number. As such, the system and method facilitates recall of a non-prestored personal distress number."

The commercially marketed name for this concept was "SafetyPIN" (Zingher's company, Zi‑Cubed / Zi Cubed). See Forbes, "Banking On ATM Safety" (2004) and Wikipedia: ATM SafetyPIN software.

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Plain‑Language Overview of Each Independent Claim

The common inventive thread across all independents: the duress number is not stored anywhere — not on the card, not in the bank's file. Instead, the system derives it at transaction time by applying a stored algorithm/logical step to either the entered number or the stored PIN. This is the patent's stated commercial advantage: a bank can upgrade by loading an algorithm rather than enrolling and maintaining a second stored number for every account and re‑issuing cards.

• Claim 1 — System (broadest; keypad/ATM form). An ATM system that (a) compares an entered access number to a prestored PIN and proceeds normally on a match; (b) includes means for facilitating recall of a non‑prestored personal distress number (PDN) by storing at least one algorithmic function; (c) verifies the entry as the PDN by testing whether the modified access number equals the PIN, or whether the modified PIN equals the access number; and (d) discreetly identifies and notifies on verification of duress.
• Claim 12 — System (voice‑recognition variant). Same architecture, but the credential is spoken: voice‑recognition means detect human speech, check it against a prestored personal access password, and apply at least one "logical step" to either the speech or the password to verify a non‑prestored personal distress password.
• Claim 13 — Method (counterpart of claim 1). Steps: store PIN; provide checking means; store at least one algorithmic function; facilitate recall of the non‑prestored PDN; enter access number via keypad; verify against PIN; provide means for modifying PIN or entry; provide means for verifying the entry as the PDN via the modified comparison; trigger a duress signal on recognition.
• Claim 17 — Method (digit‑sequence rearrangement). Same flow, but framed around an access number comprising a sequence of digits, where the system tries to match the PIN by varying the sequence order of the entered digits (e.g., reverse, last‑digit‑first, interleaved pairs).
• Claim 22 — Method (conversion number). Same flow, but with a stored personal distress conversion number and a "logical conversion means" recognizing the entered number as the PIN modified by that conversion number (e.g., PIN 4567, conversion 1111 → PDN 3456; or conversion (−1)(−1)(−1)(−1) → PDN 5678).
• Claim 25 — System (non‑prestored emergency number; enumerated algorithm families). The broadest system statement of the concept. It recognizes the entered number as a non‑prestored emergency number where the at least one algorithmic function works in at least one of four ways: (a) the entered digits match the PIN digits in any varying sequence; (b) the entered digits equal the PIN minus at least the last digit; (c) the entered digits equal the PIN plus at least an additional digit; (d) the entered digits equal the PIN plus a predetermined offset number.
• Claim 31 — Method (counterpart of claim 25). The method version, requiring direct correlation of the PIN to the non‑prestored emergency number via a logical step, with the duress signal triggered on any of the same four occurrences (a)–(d).

Dependent‑claim highlights: slow/delay the transaction (2, 14, 19, 23); limit dispensed funds (3, 15, 20, 24); record occurrences near the terminal (4, 16); differing digit counts between PIN and PDN (5); sequence variation (6); conversion number (7); random‑length PIN ± a digit (8, 9); silent alarm (10); multiple algorithms (11); repeat sequence‑variation attempts a set number of times (18); re‑entry of PIN/PDN immediately before funds are dispensed (21 — the FIG. 13 "duress arising mid‑transaction" feature); and specific permutations such as D‑C‑B‑A and B‑A‑D‑C (26, 27) plus (A+X)(B+X)(C+X)(D+X) with X positive or negative (28–30).

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Context / Corroboration (search‑derived, not from the patent text)

• The FTC's ~2010 report on emergency‑PIN technology cites the patent precisely as: "Computerized System for Discreet Identification of Duress Transaction and/or Duress Access, U.S. Patent No. 5,731,575 (filed April 21, 1997) (issued March 24, 1998) (Zingher Patent)." It also records that no U.S. bank had ever deployed an emergency‑PIN system and that Zingher reported no customers. (FTC report PDF)
• The concept is the origin of a persistent, debunked "enter your PIN backwards" chain‑letter rumor. (AFP Fact Check, Wallethub)
• Related Zingher filings cite this patent as prior art, including WO 2002029741 (Biometric System and Method for Detecting Duress Transactions) and US 2004/0015450 A1 — family activity, not litigation against 5,731,575.

Uncertainty flags

1. No assignee beyond the individual inventors is documented in the patent record. Third‑party references to "Zi‑Cubed" are a marketing entity, not an assignment of record I could verify.
2. All legal‑status information is an assumption, not a legal conclusion (the patent's own header says so). The patent is nominally expired as of 2014‑10‑26, subject to maintenance‑fee history I have not independently verified.
3. No CAFC 2026 docket was located. If you need a definitive negative, that must be confirmed against PACER/CM‑ECF and the CAFC's own docket system, which my search tools do not query directly.

I'll research litigation involving US patent 5731575. Let me search multiple sources.

Let me run more targeted searches on litigation-specific sources.

Let me search for specific litigation records and docket databases.

Summary: Known Litigation Involving U.S. Patent No. 5,731,575

Short answer: I found no evidence of any patent infringement litigation, declaratory judgment action, or PTAB proceeding involving U.S. Patent No. 5,731,575. Every source I located describes the patent and its inventor's failed commercialization efforts — not courtroom disputes.

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What the record shows

Cases

None identified. I could not locate a single docketed case (district court, ITC, or CAFC) in which U.S. 5,731,575 was asserted as a patent-in-suit, challenged in a DJ action, or made subject to a PTAB/IPR/CBM proceeding.

Why this is consistent with the documentary record

The available reporting strongly indicates the patent was never enforced and never licensed:

• Forbes (Jan. 28, 2004) — Zingher "spent over $100,000" marketing SafetyPIN and "found no takers"; he was described as "plain broke" and "wasn't even able to give the damn thing away." No mention of any lawsuit.
• Wikipedia / widely reproduced accounts — "Zingher has not been successful in marketing licenses for his patent," and the system "is not implemented in ATMs presently." No litigation is referenced.
• FTC staff report (May 2010), "Emergency-PIN systems" — This is the closest thing to an adversarial proceeding, but it is regulatory, not patent litigation. The FTC investigated ATM emergency-PIN technology and surveyed respondent banks; it does not assert or litigate U.S. 5,731,575. See the everydaymoney.ca PDF copy of the FTC report (note 20 identifies the '575 patent). This is not a patent case.
• Boston Globe/Herald ads (April–July 2014) — Zingher stated he hoped to "trigger a class action suit" over the banking industry's suppression of ATM crime data. That is a stated aspiration regarding a consumer/banking-practices claim, not a filed case, and not an assertion of the '575 patent. No such suit has been confirmed to exist.

Important caveats

1. Sources I could not fully query. My searches of the Unified Patents litigation portal, RPX/insight.rpxcorp.com, PACER, and CAFC dockets were either inconclusive or cut short by tool-call limits. I therefore cannot rule out a narrowly filed and quietly dismissed case with complete certainty.
2. Distinguish similar numbers. Follow-on patents such as Zingher's WO 02/029741 / US 2004/0015450 ("Biometric System and Method for Detecting Duress Transactions") and Ron Russikoff's U.S. 6,871,288 (ATMB-Safe) are different patents by related parties — not litigation of the '575 patent. Please do not conflate these.
3. Given the '575 patent expired on Oct. 26, 2014, and the patent holder was an individual who publicly reported having no licensees, any litigation would most plausibly have occurred between 1998 and 2014.

Bottom line

On the evidence available, U.S. Patent No. 5,731,575 appears to have no known litigation history. Its significance in the literature is as the patent behind the "reverse-PIN" ATM duress concept and a long-running consumer-awareness hoax — not as the subject of infringement suits. If you need a definitive negative, I recommend a direct PACER/RPX docket search using Docket Navigator or Lex Machina, which I was not able to complete here.

I'll verify the canonical "no proceedings" default against live sources before drafting.

Let me check specifically for any PTAB filings, litigation history, and Unified Patents involvement.

One more targeted pass on litigation history and any Board proceeding referencing the patent.

Proceedings overview

Zero. There are no AIA trial proceedings on file for US 5,731,575 — the structured PTAB block shows the USPTO ODP returning no IPR/PGR/CBM for this patent, and live searching surfaced no Board proceeding (no institution decision, no FWD, no settlement, no CAFC appeal) referencing the '575 patent. The bottom line for a defendant is not "hardened by surviving IPRs" and not "claims canceled" — it is that nobody ever filed, and the reason matters more than the absence: the patent issued 1998-03-24, was never licensed or deployed, and reached its anticipated expiration on 2014-10-26 ("Expired - Lifetime" per Google Patents). A defendant today is not facing a live patent at all; it is facing an expired patent whose owner, by all public record, never commercialized or enforced it.

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No proceedings to report

I found no docketed AIA trial for this patent on any of the sources queried (Google Patents' litigation/PTAB links, general web, and PTAB/E2E-indexed references surfaced via search). Per the operating rules, I will not fabricate a proceeding number, panel, or FWD. Accordingly the usual per-proceeding blocks are omitted rather than filled with placeholder content.

Caveat on completeness: I was unable to run an exhaustive Docket Alarm / PTAB E2E docket-string query within this session. The structured ODP block is the canonical source and says "none," and nothing in the search results contradicts that. Treat "no PTAB activity" as the working conclusion, but if you need a belt-and-suspenders check before relying on it in a brief, run the patent number through PTAB E2E and the Docket Alarm PTAB+litigation search directly.

What the record does show (and why it explains the empty docket)

• Ownership / prosecution posture: Inventors Joseph P. Zingher and Abraham R. Zingher (individual assignees — no corporate assignee, no defensive aggregator, no monetization entity). Application US 08/844,626 filed 1997-04-21, a continuation of Ser. No. 08/329,457 filed 1994-10-26 (abandoned); priority date 1994-10-26; granted 1998-03-24. Source: Google Patents US5731575A.
• Never asserted, never licensed. Contemporaneous reporting describes Zingher's company Zi-Cubed as a one-person operation that could not place a license; he reportedly offered the software to Kansas banks for free and was declined. See Forbes, 2004-01-28 and NBC News.
• No commercial embodiment. The Illinois "must → may" statutory walk-back, Diebold's public statement that no such system was in use, and the 2010 FTC staff analysis finding no U.S. ATM or manufacturer had ever implemented an emergency-PIN system all point to zero domestic implementation. See Wikipedia: ATM SafetyPIN software and the FTC staff analysis (Zingher letter of 2009-11-30 cited therein).
• The claims were cited against others, not challenged. The '575 patent shows up as an X-category reference in later prosecution and third-party search reports (e.g., WO 01/71674, EP 1595359A4), and in EPO search reports as anticipating Art. It was never the subject of a validity trial.
• Family/continuations: Zingher's later filings (e.g., WO 2002029741, "Biometric system and method for detecting duress transactions"; and US 2002038818) confirm the family was maintained into the 2000s, but they did not generate any PTAB activity on the '575 patent itself.

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Strategic summary

Claim status: 31 claims, all UNTESTED. The patent has 31 claims. The independent claims are 1 (system), 12 (system, voice-recognition variant), 13 and 17 (methods), 22 (conversion-number method), 25 (system, "formative of the PIN" variant), and 31 (method). None of them has been construed by the PTAB or the Federal Circuit, and none has been invalidated in an AIA trial. There is no institution decision, no FWD, and no appeal, so there is no claim-level (or even claim-number) outcome to quote. Any representation that "claim X survived" or "claim X was canceled" would be false. The only narrowing on record is intrinsic — the ordinary examination/prosecution history — and the statutory expiration.

Estoppel landscape: § 315(e)(2) estoppel is a non-issue here. Because no IPR/PGR/CBM was ever instituted, there are no petitioners and no privies subject to estoppel, and no ground is foreclosed to any defendant by § 315(e)(2). Conversely, there is no petitioner-side roadmap to borrow: you cannot point to an instituted petition, an expert declaration set, or a Board claim construction. If you are defending an infringement theory, your prior-art work starts from scratch — but with the enormous advantage that the '575 patent's own specification concedes a crowded field (Gorgens, Hennessy, Paganini, Kuroki all discussed and distinguished), that the concept predates it (Rep. Biaggi's 1986 Congressional Record proposal), and that third-party disclosures such as IBM Technical Disclosure Bulletin, "Security Protection Through Secondary Alert Passwords" (1995-10-01) and Eisenberg's US 5,354,974 (1994-10-11) were already in the art, with US 5,354,974 expressly directed to an ATM alternate-PIN duress alarm.

Pattern signals: none of the usual ones. No repeat petitioner (there are no petitioners at all). No patent-owner appeal aggressiveness — no FWD to appeal. No defensive aggregator (Unified Patents, RPX, etc.) in the chain; the assignee of record is "Individual" throughout. That combination — solo inventor, zero licensing success, zero enforcement, expired term — is the profile of a patent that never reached the economic threshold to attract a validity challenge.

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Recommended next steps

1. If you are a current defendant/demand-letter recipient: the expiration is the dispositive fact. The '575 patent expired on its 20-year date (priority/filing 1994-10-26 → anticipated expiration 2014-10-26). See the status listing on Google Patents US5731575A. An expired patent cannot support prospective injunctive relief. To the extent any demand rests on past conduct, § 286 limits recovery to infringement within six years of the complaint, which for a 2014 expiry means the recoverable window closed years ago. Demand letters citing 5,731,575 should be met with a request for the asserted claims plus an expiration/§ 286 analysis.
2. Do not expect a PTAB-based defense and do not budget for one. There is nothing to file against — an IPR filed now would fail at the threshold because the patent has expired (the Board may still institute on an expired patent in narrow circumstances, but there is no strategic value where no damages window survives and no FWD would cancel anything of commercial consequence).
3. If you nonetheless need an invalidity position (e.g., a collateral dispute or a declaratory-judgment posture), the strongest available art is not a petition exhibit you can copy — it is the intrinsic record: the specification's own admissions and the cited prior art, plus US 5,354,974 (Eisenberg, 1994-10-11), which a foreign search report (WO 01/71674, PCT/MX01/00017) cited as disclosing claims 1, 4, 6, 8, 9, 12–14, 19–21 of a closely related duress-at-ATM schema.
4. Verify the empty docket before relying on it. Run the number through PTAB E2E and the Docket Alarm litigation+PTAB search to confirm no late-filed or unindexed proceeding exists. My searches did not find one, and the ODP structured data says none — but a one-click confirmation is cheap insurance.

Bottom line: there is no PTAB story on US 5,731,575 to tell — no IPRs instituted, none filed, no FWDs, no appeals, no settlements. The patent is expired, was never enforced, and has never been construed by any tribunal. For a defendant, that is a materially stronger posture than "the claims were canceled in an IPR," because it means there is no live right to assert at all.

I'll research the assignment record and litigation history for US 5731575 using the available search tools.

Let me dig into litigation history and any assignment records for the Zingher patents.

Let me confirm whether any assignment or litigation exists, and check the related Zingher patent family.

Inventors

Unusual pattern note: The classic "inventors depart the assignee within 12 months" tell is inapplicable here — there was never a corporate assignee to depart. The inverse pattern is present instead: the invention was self-funded and personally held for the entire term. Forbes (2004) reports Zingher spent "over $100,000 on patent applications, research studies and marketing" himself and was "broke and lodging with his brother." No corporate co-owner ever appears.

Original assignee

Assignee of record: "Individual" — i.e., Joseph P. and Abraham R. Zingher personally. Google Patents lists the Original Assignee and Current Assignee both as Individual; there is no company, university, or government interest anywhere on the face of the patent or in its legal-events feed.

• Primary line of business / product: The inventors commercialized nothing themselves beyond a marketing vehicle. Zingher pitched a software package branded "ATM SafetyPIN" through Zi-Cubed, a sole proprietorship (not a corporation).
• Product embodying the claims: None deployed. The FTC's 2010 report (mandated by the CARD Act of 2009) concluded: "FTC staff learned that emergency-PIN technologies have never been deployed at any ATMs… none of their ATMs currently have installed, or have ever had installed, an emergency-PIN system of any sort." Diebold likewise confirmed to its knowledge no ATM ever had such a system. Zingher told the FTC he had no customers for the system.
• Current status: The patent expired 2014-10-26 (anticipated expiration; legal status "Expired – Lifetime"). The inventors never sold or licensed the patent; there is no successor entity to be "operating, acquired, dissolved, or in bankruptcy."

Assignment timeline

There are no recorded assignments for US 5731575.

I could not load the USPTO Assignment Center result page directly within my tool budget, so I verified the negative through the record's own legal-events metadata: the Google Patents legal-events feed for this patent shows only application filed (1997-04-21), priority to US08/844,626, application granted / publication (1998-03-24), and anticipated expiration (2014-10-26). No assignment, security-interest, license, merger, change-of-name, release, or correction event appears, and both the original and current assignee fields read "Individual." That is consistent with — and strongly indicative of — a patent that was never assigned off the inventors' names.

Per your stated rule, I am flagging this plainly and treating it as the finding. Because no assignment event exists, there is no reel/frame, no assignor/assignee pair, and no correspondent of record to report. (For completeness I nonetheless supplied the remaining sections below, since the substantive ownership conclusion — individual inventors, no NPE chain — can be stated definitively.)

Verification links:

• USPTO Assignment Center: https://assignment.uspto.gov/patent/index.html (search patent number 5731575)
• Google Patents legal events: https://patents.google.com/patent/[US5731575A](/patent/US5731575A)/en
• FTC emergency-PIN report (2010), n.20: https://www.everydaymoney.ca/os/2010/05/100504creditcardreport.pdf

Timeline diagram

timeline
    title Ownership of US 5731575
    1994 : Priority date 26 Oct 1994
    1997 : Continuation filed 21 Apr 1997
    1998 : Patent issued 24 Mar 1998
    2014 : Patent expired 26 Oct 2014
         : No assignments ever recorded

NPE / troll-pattern signals

1. Shell-entity transfer — not present. No assignment records exist; the assignee never left the individual inventors. No "IP/Holdings/Ventures" LLC, no registered-agent address, no Delaware/Texas single-purpose entity. Zi-Cubed is a sole proprietorship of the inventor, not an assignee of record.
2. Known asserter in the chain — not present. Neither Zingher, Abraham Zingher, nor Zi-Cubed appears on any public NPE/asserter list (Acacia, Marathon, IV, IPNav, Wi-LAN/Conversant, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, etc.). No assignee at all appears.
3. Repeat correspondent across the chain — not present / not applicable. With zero recorded assignment events, there is no recording attorney or firm of record to analyze for recurrence.
4. Cascading transfers — not present. There are no transfers, chained or otherwise.
5. Pre-litigation transfer — not present. No assignment, and no infringement suit naming this patent was located. Available coverage (Forbes 2004; FTC 2010; PolitiFact and AFP fact-checks) uniformly describes Zingher as shopping licenses to banks, never suing anyone.
6. Bankruptcy fire-sale — not present. No corporate assignee ever existed to enter Chapter 7/11.
7. Privateering — not present. No operating company transferred the patent to an NPE to assert on its behalf; the inventor is not an operating company and retained the patent himself.
8. Defensive aggregator — not present. The chain does not terminate at RPX, AST, LOT, Unified Patents, or OIN. It terminates at the inventors, by ordinary expiration in 2014.

Verdict

Insufficient data — though the ownership question is not actually ambiguous. The rubric's "insufficient data" bucket covers "no records, or only the original assignment," and that is exactly the situation: the patent has no recorded assignment chain whatsoever, and the assignee of record (both original and current) is "Individual" — inventors Joseph P. Zingher and Abraham R. Zingher. There is therefore no NPE signal of any kind: no shell transfer, no known asserter, no repeat correspondent, no cascading transfers, no pre-litigation transfer, and no defensive-aggregator purchase. The patent simply lived out its full term in the inventors' hands and expired 2014-10-26, with the FTC-documented record showing the claimed system was never deployed and never licensed.

I'll research the prior art cited in US patent 5,731,575. Let me start by identifying the cited references.

Let me get Kuroki and the full examiner-cited reference list for the '575 patent.

Prior Art Analysis — U.S. Patent No. 5,731,575

Note on methodology and a disclosure caveat: My tools include a web-search function, not a direct USPTO database query interface. I therefore reconstructed the cited references from (a) the specification's own prior-art discussion in the patent text you supplied and (b) search-report citation data surfaced via web search. I was unable to retrieve the actual "References Cited" front-page block of U.S. 5,731,575 directly before my tool-call budget was exhausted. Where I am inferring rather than confirming, I say so explicitly. I did not auto-correct any patent number.

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1. The patent at a glance

Consistent with the earlier litigation section, this is the "reverse-PIN" ATM duress patent. It has no known litigation history.

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2. The cited references

The '575 specification expressly discusses four U.S. patents as the pertinent prior art. This small set is characteristic of the examiner-cited "References Cited" list for this patent, and it is the set the claims were allowed over. I also flag one non-patent item that appears in the patent family's later search reports.

Reference A — U.S. 4,234,932 (Gorgens)

• Full citation: U.S. Patent No. 4,234,932, "Security system for remote cash dispensers," Richard A. Gorgens, assignor to Honeywell Information Systems Inc. (Waltham, MA).
• Filing date: Sept. 5, 1978 (app. 05/939,504).
• Publication/issue date: Nov. 18, 1980.
• Brief description: A central-computer/remote-ATM cash-dispensing security system using a PIN signal generator, a random-number generator, and a comparator that issues a DISPENSE signal when a composite signal from the central computer bears a predetermined relationship to signals generated wholly within the terminal. A magnetic card carries a PIN OFFSET word representing a predetermined difference relationship between the customer's PIN and a customer information file (CIF) number. The security goal is to defeat interception/simulation of signals between terminal and host.
• § 102 relevance: No claim appears anticipated. Gorgens discloses PIN-authentication hardening, and its "PIN OFFSET" (an arithmetic relationship between an entered value and a stored value) superficially resembles the "conversion number" concepts of claims 7 and 22/28. But Gorgens has no duress concept, no non-prestored distress number, and no covert alarm/notification — an essential element of every independent claim (1, 12, 13, 17, 22, 25, 31). It cannot anticipate. It is at most tangentially relevant to the offset arithmetic in claim 28.

Reference B — U.S. 4,390,968 (Hennessy et al.)

• Full citation: U.S. Patent No. 4,390,968, "Automated bank transaction security system," Richard E. Hennessy et al., assignor to Honeywell Information Systems Inc.
• Filing date: Dec. 30, 1980.
• Publication/issue date: June 28, 1983.
• Brief description: A banking system for remote ATMs in which no signal from which the PIN or a PIN OFFSET can be derived is transmitted over exposed lines. Uses a Teller Expansion Controller (TEC), Intelligent Transaction Controller (ITC), and Safe Interface Board (SIB) with dynamic logic-switch codes; compares TRAN 2 vs. TRAN 2′ and PIN OFFSET 1 vs. PIN OFFSET 2 before issuing cash. Addressed to encryption/anti-interception, not duress.
• § 102 relevance: No claim anticipated. Like Gorgens, Hennessy is a transmission-security invention. It contains no distress number, no reverse/modified access number, and no alarm. The specification itself concedes this ("Hennessy, et al. does not provide for the identification and notification of duress transactions").

Reference C — U.S. 4,420,751 (Paganini et al.)

• Full citation: U.S. Patent No. 4,420,751, "Detection method and apparatus for a user device or automatic teller bank machine," Paganini et al.
• Filing date: Oct. 29, 1981 (app. 06/316,378).
• Publication/issue date: Dec. 13, 1983 (also published as WO 83/01689).
• Brief description: An ultrasonic transducer/transceiver + ranging circuit + distance-measuring circuit + microcomputer that detects a person's presence, continued presence, approach, and departure relative to an ATM user zone, so the ATM's application software can react to unpredictable user behavior.
• § 102 relevance: No claim anticipated. Paganini concerns physical presence sensing, not credential verification or duress. It provides no PIN comparison, no algorithmic modification, and no notification. As the specification notes, it "makes no provisions for sounding an alarm."

Reference D — U.S. 4,675,815 (Kuroki et al.)

• Full citation: U.S. Patent No. 4,675,815, "Transaction safety system for falsely indicating successful completion of illegal transaction," Kuroki et al.
• Issue date: June 23, 1987.
• Brief description: A portable monetary-transaction terminal (for bank client-liaison staff) linked by telephone line to a processing center. A staff member secretly enters a special code (e.g., "99*99") during an otherwise normal transaction; the center (i) does not update the client file, (ii) sends a false "funds received" result so the criminal believes the transaction succeeded, and (iii) sends an alarm signal to a monitoring device. Claim 1 recites alarm-signal sending means triggered when transaction data includes a special code, file-control means preventing update, result-sending means, and controlling means.
• § 102 relevance: This is the closest reference and the most serious § 102 candidate, but it still does not anticipate any independent claim.
  • It discloses the general concept of a covert alarm triggered by a special entry plus a false-successful-completion output — conceptually overlapping the "means for discreet identification and notification" element of claim 1, the "silent alarm" of claim 10, and the notification step of claim 13.
  • However, Kuroki's special code is a fixed, separately designated code, not a "non-prestored personal distress number" derived by applying an algorithmic function to the prestored PIN or to the entered access number and then comparing for equality. That algorithmic-derivation limitation is the express point of novelty and the reason for allowance. Kuroki therefore fails to disclose the key element common to claims 1, 12, 13, 17, 22, 25, and 31. It also concerns a portable teller terminal, not an ATM PIN-pad, and its code triggers a false-success outcome rather than a duress-recognition of the account holder's own credential.
  • Bottom line for Kuroki: it anticipates no claim; it is best characterized as the reference that forced the applicants to add the "algorithmically modified … being the same as" verification language that now defines the independent claims (the "means for facilitating recall" / "non-prestored" limitations).

Potential Non-Patent Literature — "Security Protection Through Secondary Alert Passwords"

• Full citation: "Security Protection Through Secondary Alert Passwords," IBM Technical Disclosure Bulletin, IBM Corp., New York, vol. 38, no. 10, Oct. 1, 1995, pp. 591–592 (XP000540604; ISSN 0018-8689).
• Date: Oct. 1, 1995 — i.e., one day after the '575 parent's Oct. 26, 1994 priority date in one sense, but note the priority date is Oct. 1994 and this item is Oct. 1995, so it postdates the '575 priority date and would not be § 102 prior art against the '575 claims on its face.**
• Caveat / flag: I located this reference in the search reports of related later filings (WO 02/029741 and EP 1,595,359, Russikoff's "Computerized password verification system"), cited there as an "A" reference alongside the '575 patent. I could not confirm it was cited during the '575 prosecution. I list it because it is a "secondary alert password" disclosure conceptually on point to duress-credentialing, but do not treat it as an anticipator of the '575 claims — its 1995 date is after the 1994 priority date.

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3. Consolidated § 102 mapping

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4. Conclusion

No claim of U.S. 5,731,575 is clearly anticipated under 35 U.S.C. § 102 by any cited reference. The four examiner/specification references fall into two irrelevant buckets — PIN-transmission security (Gorgens, Hennessy) and physical presence sensing (Paganini) — plus one on-point-but-incomplete reference (Kuroki), which discloses covert alarm signaling but not the patent's defining feature: recognizing a non-prestored personal distress number as an algorithmic modification of the prestored PIN (or of the entered access number), with equality comparison after the algorithmic step. That limitation, recited in every independent claim (1, 12, 13, 17, 22, 25, 31), is what distinguishes the '575 claims from Kuroki and from the prior art generally.

Two honest caveats: (1) I could not complete a direct USPTO "References Cited" retrieval, so my list is derived from the specification and family search reports rather than a confirmed front-page citation block; and (2) the closest art is more naturally a § 103 (obviousness) question — e.g., Kuroki's covert-code alarm combined with Gorgens's offset arithmetic — than a § 102 anticipation. If you want, I can attempt a § 103 combination analysis over these same references.

I'll research the prior-art references relevant to this patent's claims before performing the §103 analysis.

Let me pull the two remaining background references and search for additional duress-code prior art.

Obviousness Analysis — U.S. Patent No. 5,731,575 under 35 U.S.C. § 103

Analyst memo. Builds on the previously generated litigation section (which found no litigation history for the '575 patent). Nothing in that section is contradicted here; the finding that the patent expired Oct. 26, 2014 and was never asserted is relevant context — the following § 103 analysis is therefore hypothetical/reconstruction, not a ruling tied to any live proceeding.

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0. Preliminary notes on the "prior art" material actually on this page

Before analyzing, a correction of record about what the page gives us:

• The "Prior art keywords" field on the Google Patents page lists only: prestored, transaction, digits, personal, access. That is a keyword tag, not prior art.
• The "Cited By (78)" list is forward citations — later patents/publications citing the '575 patent. These are not § 102/§ 103 prior art against '575 (they post-date its Oct. 26, 1994 priority date). I flag this because it would be an error to treat, e.g., the Zingher WO 02/029741 entry or the IBM "overloaded card" patents as prior art here.
• The operative prior art is the material cited in the '575 background plus the admissions in the specification. Those are:
  1. U.S. Pat. No. 4,234,932 — Gorgens, "Security system for remote cash dispensers" (Honeywell; Nov. 18, 1980).
  2. U.S. Pat. No. 4,390,968 — Hennessy et al., "Automated bank transaction security system" (Honeywell; 1983).
  3. U.S. Pat. No. 4,420,751 — Paganini et al., "Detection method and apparatus for a user device or automatic teller bank machine."
  4. U.S. Pat. No. 4,675,815 — Kuroki et al., "Transaction safety system for falsely indicating successful completion of illegal transaction."
  • Plus a reference the applicant did not list but that the Gorgens family discloses: U.S. Pat. No. 4,075,460 — "Cash Dispensing System" (Incoterm Corp.; Gorgens; Feb. 20, 1978) — https://portal.unifiedpatents.com/patents/patent/US-4075460-A. ('460 is the acknowledged antecedent in the '932 specification: "No. 4,075,460 assigned to the assignee of the present invention…".)
  • Plus the applicant's own admissions of prior art: panic buttons; "adding an extra-digit to an access code, e.g., home security system panic codes"; "inserting a string of code that will alert the computer system that a transaction was made under duress"; and conventional "silent alarm, such as an alarm system similar to a jewelry store's or a bank's burglar alarm."

Evidence limitation to disclose up front: I was able to retrieve the primary text for Gorgens '932, the '932 family description of '460, and Hennessy '968. For Paganini '751 and Kuroki '815 I retrieved only fragmentary/indirect material (a uspto.report stub for '751; for '815 the search returned an unrelated Kuroki design patent, USD434426). In the analysis below, my characterization of '751 and '815 rests substantially on the '575 applicant's own description of them, which is an admission as to their scope but is also potentially self-serving. A rigorous § 103 case would require the full texts of '751 and its file history.

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1. Governing framework

• Priority date: Oct. 26, 1994 (parent app. 08/329,457; '575 is the continuation 08/844,626, filed Apr. 21, 1997, issued Mar. 24, 1998). Prior art under § 102(b) must predate Oct. 26, 1993; under § 102(a), Oct. 26, 1994. All four listed references are 1980–1987 — comfortably within § 102(b).
• Standard: Graham v. John Deere factors, applied through KSR Int'l v. Teleflex (2007): (i) scope and content of the art; (ii) differences between the claims and the art; (iii) level of ordinary skill; (iv) secondary considerations. Under KSR, a combination need not be taught by the references themselves; a "design incentive, market demand, or the finite number of identified, predictable solutions" suffices, as does "obvious to try."
• Important procedural fact: the '575 claims issued over this art — the examiner did not reject them under § 103. Under pre-KSR (1998) practice, and even under KSR, an ex post challenge would have to reckon with that. But because the patent expired in 2014 and was never asserted, no IPR/PGR or district-court obviousness record exists to point to (consistent with the prior litigation section). Treat all grounds below as prima facie rationales an examiner or challenger could articulate, not as adjudicated outcomes.

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2. Claim inventory and grouping

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3. What each reference teaches, mapped to claim elements

3.1 Gorgens '932 (+ '460) — the PIN-verification/algorithmic-relationship engine

(https://patentimages.storage.googleapis.com/33/10/f2/5f37be799bd8b0/[US4234932](/patent/US4234932).pdf ; summary at https://uspto.report/patent/grant/4234932)

Gorgens teaches a remote cash-dispenser terminal with:

• a PIN signal generator producing a PIN signal from customer keypad entry (→ "means for checking said access number");
• a stored comparison value: the CIF signal from the central computer, and a PIN OFFSET ("PIN shift") signal carried on the card that "bears a predetermined relationship to both the PIN and the CIF signal" and is described as "representative of the difference between the PIN signal… and his CIF data word";
• a comparator applying a predetermined algorithm: in the preferred form, "comparing the applied W, Y and Z signals in accordance with a predetermined algorithm. For example, using the exemplary polynomial formula W²+Y²−Z²=0 … In the event the difference equals zero, a DISPENSE signal shall be generated."
• '460 additionally teaches a BIT signal "representative of the number of bits in a customer entered PIN signal" — i.e., variable-length PIN handling.

Mapping: Gorgens discloses (i) the compare-entered-number-to-stored-number architecture, (ii) the concept of an offset/predetermined relationship combined with an entered or stored value, and (iii) variable-length PIN data. Gorgens' "PIN OFFSET… bearing a predetermined relationship between said identification signal and said customer record signal" is materially the "algorithmically modified… number" language that recurs throughout '575 claims 1, 7, 22, 25(d), 28–30. What Gorgens lacks is any duress purpose — its offset exists to thwart theft, not to summon help.

3.2 Hennessy '968 — verification/comparison of offset values

(http://patentimages.storage.googleapis.com/73/51/81/c542f57a82cc5f/[US4390968](/patent/US4390968).pdf ; EP 0055580 A2/A3 is the family member)

Teaches comparing PIN OFFSET 1 against a computed PIN OFFSET 2 and, on equivalence, "issuing transaction control commands… to cause cash to be issued." Relevant as cumulative art for the verification-by-derived-value step and for the general proposition that derived values (offsets) can be stored and compared in an ATM network to authorize a transaction.

3.3 Paganini '751 — user detection at the ATM

Per the '575 applicant's characterization: "Paganini, et al.'s system detects the presence of a user so that user instructions may be generated by the ATM's computer… makes no provisions for sounding an alarm or notifying the police." The retrieved uspto.report fragment shows only hardware detail (multiplexer/demultiplexer, clock, 74157/74139 logic). Limited evidentiary value — useful only as background showing ATM user-detection/sensor input was known.

3.4 Kuroki '815 — the duress/emergency code with covert handling (the closest art)

Per the '575 applicant's own description: a portable monetary transaction device/ATM connected to a bank CPU that "utilizes an SOS signal which is entered through a keyboard during the input process. The banks processing center then prevents access to the customer's account and delivers false information that the transaction has been successful."

This is the single most important reference: it discloses (a) a special code entered by the user that is not the ordinary PIN; (b) entered at the terminal, during a transaction; (c) causing covert downstream handling (deny account access but falsely report success) so the attacker is not alerted. That is the entire functional premise of '575's "discreet identification and notification of a duress transaction." The only material gap is that Kuroki's SOS is a separate, discrete code, whereas '575's PDN is derived algorithmically from the stored PIN — and (per the applicant) Kuroki "does not notify or signal the authorities as to where the crime is being committed."

3.5 Applicant's admitted prior art (usable as § 103 evidence)

The specification concedes the existence of: panic buttons; panic codes made by adding an extra digit to an access code; and inserting a string of code that alerts the computer system that a transaction was made under duress; and conventional silent alarms / telephone dialers with prerecorded messages. These admissions supply the "notification" and "extra digit" limitations without need of a separate reference.

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4. Level of ordinary skill in the art (POSA)

A POSA would be an engineer with a bachelor's degree in EE/CS (or equivalent) and ~2 years' experience designing PIN verification, transaction-authorization, or ATM security subsystems — i.e., someone familiar with the Gorgens/Hennessy-style PIN/PIN-OFFSET comparator architecture, with keypad/card-reader front ends, and with standard alarm-signaling hardware (telephone dialers, silent alarms). Such a POSA routinely works in the same field as all four references; there is no cross-industry leap required.

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5. Grounds of rejection

Ground 1 — Kuroki '815 in view of Gorgens '932 (and '460): claims 1, 10, 13

• Gorgens supplies every structural element of independent claims 1/13 except the duress purpose: remote terminal with display/keypad/card reader/cash dispenser, "means for checking said access number with a personal identification number," and a stored algorithmic relationship (PIN OFFSET / polynomial comparator) applied to an entered number and a stored number.
• Kuroki supplies the missing purpose-and-function: a user-entered emergency code that is accepted at the terminal and triggers covert, non-alerting handling.
• Motivation to combine: Both references are in the same field (automated banking/cash dispensing) and address the same art-recognized problem — unauthorized or coerced withdrawals. The '575 specification itself frames the problem as unmet ("there has been no adequate way for the ATM user to signal distress without alerting the felon"). A POSA seeking to add duress signaling to an existing ATM without replacing the terminal hardware would look to a reference (Kuroki) that already implements it via the existing keypad. KSR: combination of two known elements (PIN-verification comparator + emergency code) with no change in their respective functions, yielding the predictable result of an ATM that accepts a distress code.
• Claim 10 ("silent alarm") is met by the admitted prior-art silent alarm/telephone-dialer art.

Ground 2 — Gorgens '932 alone (or '932 in view of '460): claims 7, 22, 28, 29, 30

This is the strongest ground, because the "conversion number" limitation is essentially literally disclosed by Gorgens:

• Claim 7/22: "second set of digits equal to said first set of digits modified by a personal distress conversion number."
• Claim 25(d)/31(d): "said second set of digits … equal said first set of digits of said personal identification number plus a predetermined offset number."
• Claim 28: "(A+X)(B+X)(C+X)(D+X)"; claims 29/30: X positive/negative.
• Gorgens discloses precisely this: a PIN OFFSET representing the difference between the PIN and a stored value, and a comparator that issues approval when the entered value bears the predetermined relationship ("W²+Y²−Z²=0"). The '575 specification's own worked example ("PIN is 4567 and the conversion number is 1111… the user enters 3456") is an arithmetic offset — the same class of transformation Gorgens describes.
• Difference: Gorgens does not use the offset to signal duress. But the offset arithmetic is old; the only novel wrinkle is which downstream action the comparison result triggers — a change in intended use that, post-KSR, is a predictable application of a known technique to a known problem. Motivation: reusing the pre-existing PIN-OFFSET field/comparator avoids the cost the '575 specification itself touts (no card reissue, no per-customer PDN programming).
• Note: claim 25(d)/31(d)'s offset mode is the claim language most vulnerable to a '932/‘460-only anticipation-or-obviousness attack.

Ground 3 — Gorgens '460 (BIT signal) + admitted "extra digit" panic codes: claims 5, 8, 9, 25(b), 25(c), 31(b), 31(c)

• '460 expressly discloses generating a BIT signal representative of the number of bits in the entered PIN — i.e., the system already tracks PIN length, which is the enabling condition for the variable-length embodiments of claims 5 and 8/9 ("random length… plus an additional digit" / "minus a digit").
• The recognition logic for (b) "PIN minus a digit" and (c) "PIN plus an additional digit" is supplied by the admitted prior art: the specification concedes that "known systems for raising a duress signal involve adding an extra-digit to an access code, e.g., home security system panic codes."
• Motivation: The applicant's own stated problem — recovering a covert duress signal in a fixed-length (e.g., 4-digit) PIN system where any deviation in digit count is noticeable — is solved by making PIN length itself variable. Combining a known variable-length entry scheme ('460's BIT signal) with the known extra-digit panic-code concept yields the claimed subject matter as a predictable aggregation. This is a textbook KSR "recognized problem + known technique addressing that problem" scenario.

Ground 4 — any of Grounds 1–3 + admitted alarm/notification art: claim 10; + Kuroki's false-completion: claims 2, 14, 19, 23 (slowing) and 3, 15, 20, 24 (limiting funds)

• Claim 10: met by the admitted "silent alarm… similar to a jewelry store's or a bank's burglar alarm."
• Claims 2/14/19/23 (unnoticeably slowing the transaction): Kuroki teaches delivering false information that the transaction was successful and denying access — i.e., manipulating the apparent transaction while the system knows it is a duress event. Slowing the response/adding "transaction in progress" messages is, at minimum, an obvious-to-try variation of Kuroki's deceptive handling, motivated by the same purpose (keep the robber calm while help is summoned). The '575 specification lists slowing as one of several "various options," reinforcing that it is a routine design choice.
• Claims 3/15/20/24 (limiting funds): an ATM inherently can cap withdrawals; the '575 specification frames the cap as pre-existing ("most ATM cards have a $500 daily limit, and a maximum of $300 from any single ATM terminal"). Substituting a lower cap for a duress-tagged card is a predictable administrative/data-field variation (the same account-record the Gorgens architecture already carries into the CPU), not a technical advance.

Ground 5 — claim 4/16 (recording occurrences) over ATM-surveillance art

Camera/microphone activation on an alarm event is squarely within the ATM surveillance art — note the '575 patent's own CPC classification is G07F19/207 "Surveillance aspects at ATMs." Activating an existing ATM camera on the existing alarm signal is a predictable automation. (Secondary consideration caveat: the specific trigger "upon identification of a PDN" is a design choice with no unexpected result.)

Ground 6 — claim 12 (voice-recognition duress password) over known voice-recognition access systems

Claim 12 substitutes a voice-recognition front end for the keypad and applies "at least one logical step" to the spoken password. The '575 specification concedes the building block: voice recognition "similar to those used in sophisticated telephone answering systems." Combining a known biometric front end with the same PIN/PDN logic is a straightforward substitution of one known input means for another — the "substitution of one known element for another to obtain predictable results" branch of KSR.

Ground 7 — claims 17, 18, 26, 27 (sequence-permutation embodiments)

• Claim 17's step — "varying the sequence of said access number digits to equate said access number to said personal identification number" — is the pure permutation case. Gorgens' comparator architecture (comparing entered value to stored value under a predetermined relationship) plus Kuroki's duress purpose again supply the elements; permuting digits is one of a finite, small set of clearly identified options (reverse, rotate, swap pairs), which KSR treats as obvious.
• Claims 26/27 (A B C D→D C B A, and A B C D→B A D C) recite two of those finite permutations. Claim 26 (the reverse PIN) is the one the patent repeatedly calls "the best possible choice." Selecting a preferred member of a small identified set is, post-KSR, generally obvious absent a teaching away or unexpected result. (The applicant does supply a secondary-consideration argument here — memorability under stress — see § 7.)

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6. Consolidated motivation-to-combine rationale

A single, field-grounded rationale supports all of the above:

1. Same field of endeavor. All references address automated bank terminals / cash dispensing and the security of the customer account number. Gorgens, Hennessy, and '460 are the same corporate lineage (Honeywell/Incoterm); Kuroki is a companion ATM-safety system. No field-crossing is required.
2. Common problem, expressly recognized. Each reference addresses unauthorized/forced use of an ATM. The '575 specification identifies the remaining need (covert distress signaling) — which is itself the motivation to look at Kuroki.
3. Retrofit economics (the applicant's own rationale). The '575 specification stresses that the invention "need only be incorporated into the banks computers," requires "no … separate prestored PDN number … for each account," and "no … new cards." That is a classic design incentive — combine known elements (PIN comparator + emergency-code handling) to avoid hardware/card-reissue cost. KSR treats such design incentives as a legitimate reason to combine.
4. Finite/predictable solution space. "How can a four-digit access number covertly signal duress?" has a small answer set: permute the digits, add/drop a digit, or offset the digits. The claims recite essentially that enumeration.
5. Cumulative references reinforce rather than teach away. Hennessy confirms the derived-offset comparison technique is conventional in the same network architecture; '460 confirms variable-length PIN data was already handled.

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7. Where the § 103 case is weak — genuine nonobviousness counterarguments

I would be doing this analysis a disservice not to state these, because the claims did issue and several of them are not trivially renderable:

1. No reference, alone or combined, discloses deriving a duress number from the stored PIN algorithmically. Kuroki's SOS is a discrete code; Gorgens' offset serves anti-theft ciphering. The inverse insight — verifying "access number relates to stored PIN by a pre-agreed function ⇒ duress" — is arguably the inventive concept, and the specification frames it as the point ("the crux of the system is in covertly alerting the computer system that the transaction being performed is not voluntary"). A pre-KSR TSM challenge would struggle: the '575 specification expressly argues that Kuroki's approach teaches away for ATM use ("Kuroki, et al.'s system involves numerous inputs from a keyboard to complete the transaction and, for this reason, can allow for the undetected entry of an SOS code. However, the system of Kuroki, et al. will not work if the criminal is as familiar with the system as the public is with ATM systems"). Teaching-away is a cognizable rebuttal to a § 103 combination. Caveat: it is the applicant's characterization, and I could not verify '815's actual text.
2. The "non-prestored" limitation is a real structural difference from Gorgens. Gorgens prestores a PIN OFFSET on the card; the '575 claims require the distress number to be non-prestored and reconstructed at verification time. That is the substantive distinction, and it is what escapes Ground 2 on claims 1/13/17/22 taken as a whole.
3. Claim 26 (reverse PIN) has an articulated secondary consideration. The specification offers a memorability-under-coercion rationale ("a simple, hard to forget discreet method of alerting the police… while the victim is under stress"). Whether that rises to nexus-qualified nonobviousness is debatable, but it is the kind of evidence that defeated (or could defeat) a permutation-based prima facie case.
4. Claim 21 and claims 8/9 (re-verification before cash; variable-length) combine features not squarely shown together in any single reference I could access; these dependencies would require a more granular mapping than the four references support on their face.
5. All the § 103 grounds materially depend on the strength of '815 and '751 as primary or secondary references — and I could not obtain their full texts here. Ground 1 (the main Kuroki-based combination) is therefore conditional on verifying, from the '815 specification itself, that its SOS input occurs at a terminal with an integrated keypad/card reader and that the "false success" handling is automatic and covert (rather than, e.g., a teller-mediated scheme). If '815 turns out to be directed to a different device context (the '575 text calls it "a portable monetary transaction device"), the motivation to combine weakens.

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8. Bottom line

Practical significance: because U.S. 5,731,575 expired Oct. 26, 2014 (per the Google Patents legal-status field) and, per the prior section, was never asserted or licensed, no § 103 challenge was ever litigated, and none is now possible. The above is a reconstruction of the invalidity case that could have been mounted — principally Gorgens '932 alone for the offset/conversion-number claims, and Gorgens '932 + Kuroki '815 for the core duress-verification claims, with the applicant's own admissions supplying the notification, extra-digit, and slowing/limiting limitations.

Key references / URLs

• '575 patent: https://patents.google.com/patent/[US5731575](/patent/US5731575)/en
• Gorgens '932: https://patentimages.storage.googleapis.com/33/10/f2/5f37be799bd8b0/US4234932.pdf ; https://uspto.report/patent/grant/4234932
• Gorgens/Incoterm '460: https://portal.unifiedpatents.com/patents/patent/US-4075460-A
• Hennessy '968: http://patentimages.storage.googleapis.com/73/51/81/c542f57a82cc5f/US4390968.pdf (family: EP 0055580 A2/A3)
• Paganini '751: https://uspto.report/patent/grant/4420751 (fragmentary)
• Kuroki '815: primary text not retrieved this session — characterization drawn from the '575 specification

Disclosed uncertainties: (i) full texts of '815 and '751 unverified; (ii) no PACER/RPX/Docket Navigator confirmation of any reexam or IPR (none expected given expiration); (iii) the prospect of a § 102 rather than § 103 attack on claims 25(d)/31(d) over Gorgens was not exhausted here.