US 5924651

I'll verify the patent details and check for any 2026 litigation activity before summarizing.

US Patent 5,924,651 — Summary

Verification note: I confirmed this record against Google Patents and Unified Patents. I found no CAFC 2026 docket activity, no district court litigation, and no PTAB proceeding involving patent 5,924,651. My searches did not surface any 2026 Federal Circuit docket entry for this number. I cannot rule out activity that isn't indexed by those sources, but nothing appeared. Treating "no 2026 litigation found" as the result, not as proof of none.

Bibliographic data

Note on conflicting metadata: Unified Patents lists the priority date as 1997-03-25, the application date as 1998-03-16, and the grant date as 1999-07-19 — one day earlier on each. The patent text and Google Patents (consistent with each other) give 1997-03-26 / 1998-03-17 / 1999-07-20. I have used the patent-text values; the one-day discrepancies are likely a time-zone artifact in the secondary database and are flagged rather than silently resolved.

Relationship to US 5,727,758: This patent is a continuation-in-part of Ser. No. 08/827,346, filed 1997-03-26, which issued as US 5,727,758 with the same title. The two share the same specified title but are separate documents; do not conflate them.

Abstract (verbatim)

A train warning system and method for warning personnel in proximity to railroad tracks of an approaching train includes a train sensor operable with the railroad tracks for detecting passage of a train over the railroad tracks at a given location. The train sensor generates a train sensor signal upon detecting passage of a train over the railroad tracks at the given location. A transmitter is operable with the train sensor for transmitting a warning signal upon receipt of the train sensor signal. A portable radio frequency (RF) receiver is carried by at least one of the personnel in proximity to the railroad tracks remote from the railroad tracks at the given location for receiving the warning signal transmitted by the transmitter. The portable RF receiver generates an alarm signal to notify the at least one of the personnel of the approaching train upon receipt of the warning signal.

Independent claims in plain language

The patent has two independent claims (claim 1, system; claim 15, method) and 20 claims total. Claims 2–14 depend from claim 1; claims 16–20 depend from claim 15.

Claim 1 — the system. Four elements must all be present:

1. A train sensor operating with the railroad tracks that detects a train passing over the tracks at a particular location and emits a sensor signal when it does.
2. A transmitter that is disposed on the train and that operates with that track-side sensor, transmitting a warning signal when it receives the sensor signal.
3. A portable RF receiver carried by at least one worker who is near the tracks but away from the location where the train was sensed.
4. The receiver generates an alarm on receiving the warning signal, telling the worker a train is approaching.

Element 2 is the notable one and the point where this patent departs from its own specification's first embodiment: the claim requires the transmitter to be on the train, yet to be triggered by a track-mounted sensor. The specification's FIG. 1 embodiment instead describes a train-resident transmitter that transmits continuously during train operation with no track sensor at all; the track-sensor-plus-transmitter arrangement is the FIG. 5 second embodiment (75/95, sensor 96, transmitter 98). The claims blend these: an on-board transmitter that is nonetheless gated by a wayside train sensor.

Claim 15 — the method. The same four steps as claim 1, expressed as acts: detect train passage at a given location with a train sensor → generate a sensor signal → transmit a warning signal from a transmitter on the train, operable with the sensor, upon receiving the sensor signal → receive that signal at a portable RF receiver carried by a worker located away from the sensed location → generate an alarm notifying the worker of the approaching train.

Dependent-claim coverage (for context)

• Track mounting / sensing modality (2–3): sensor mounted to the rails; pressure sensing.
• Wireless RF path (4): transmitter sends over a wireless RF link.
• Control base relay (5–8): a control base with a transceiver receives the warning signal and re-transmits it over a wireless RF path to the pager; the transmitter/control-base link may be wireless (7), through the rails (6), or (per the specification) through a buried loop; the control base may itself sound an alarm (8).
• Alarm modalities (9–11): visual, audio, or vibrative — the "tactile and audible" of the title.
• Status/heartbeat monitoring (12–14, 20): periodic status signals so the receiver can validate that both transmitter and receiver are functioning; an alarm is raised when the heartbeat is missed; claim 14 extends this through a control base relay.
• Method counterparts (16–19): wireless RF path; visual, audio, and vibrative alarms.

Background and cited art (as stated in the patent)

The stated problem is that human lookouts/flagpersons become distracted and cannot reliably reach machine operators in cabs. The patent expressly discusses US 5,415,369 (railroad in-cab signaling — characterized as not addressing wayside personnel warning), Japanese Patent 4-126664 (track supervisor relays an RF train-passage signal to worker alarm receivers), and Japanese Kokai No. 52-35504 (track detector triggers an audible platform alarm for passengers) — the last criticized as insufficiently direct and not quiet enough for residential areas. Twenty-four references are cited on the face, including US 5,554,982 (Hughes, wireless train proximity alert), US 2,762,913, US 3,167,282, DE 2,405,408, and US 5,727,758 (the parent).

Caveats

• No authoritative litigation record located. My searches returned no CAFC 2026 docket, no infringement suit, and no PTAB filing for 5,924,651. This is a negative search result, not a guarantee.
• Claim/specification mismatch on the transmitter location (on-train vs. continuously transmitting train unit) is a genuine feature of the document, not a transcription error. Anyone reading claim 1 should note it requires both an on-train transmitter and a track-operable sensor.
• The face of the patent shows a typographical repetition, "a a train sensor signal," in claim 1; I have preserved the substance rather than reproducing the typo.

I'll research litigation involving US patent 5924651 on litigation-tracking sources.

Let me dig deeper into litigation-specific databases and case lists.

Let me search litigation-tracking databases directly for this patent.

Litigation Search — US Patent 5,924,651

Patent identified (interpreted literally): US 5,924,651 — "Tactile and Audible Warning System for Railroad Workers" — App. No. 09/042,886, filed 1998‑03‑17, granted 1999‑07‑20, priority 1997‑03‑26 (CIP of Ser. No. 08/827,346, now US 5,727,758). Inventors George Gregory Penza and George Robert Penza. Original assignee: Individual; current assignee Harsco Technologies LLC (assignment recorded 2016‑05‑02, effective 2016‑04‑28). Legal status: Expired – Lifetime, anticipated expiration 2017‑03‑26.

Known litigation

I found no litigation involving US 5,924,651.

Sources consulted and what they showed

• Unified Patents Portal (portal.unifiedpatents.com/patents/patent/US-5924651-A) — returns only the patent's bibliographic/portfolio record (grant data, assignee, expiration, "Referenced By (66)"). It surfaces no litigation entry for this patent.
• Google Patents family record for US5924651A — lists 24 cited references and 37/68 citing documents (a mix of examiner and third‑party citations, e.g., US 6,113,037 to Eva Signal Corp., US 6,232,887 to Carson, US 10,179,595 to Metrom Rail, Harsco's own later work‑block/rail‑warning patents), plus the 2016 Harsco assignment. Citations and continuations are not litigation and none of these records is an infringement suit over the '651 patent.
• CourtListener / Docket Alarm / PACER‑oriented searches for "5924651" and "5,924,651" — no district court or Federal Circuit docket returned for this patent number. Hits for the numeric string were for unrelated patents (e.g., US 5,825,651 in Versata v. Ford) and, on the international side, for JP 5924651 B2, a Japanese patent on a flag‑waving method (星野 昌史) — a different patent that I excluded per your instruction not to return similar numbers.
• Harsco Technologies / Penza enforcement searches — no reported enforcement action naming the '651 patent surfaced.

Important caveats

1. Absence of evidence is not conclusive proof of absence. Several litigation databases (RPX Insight, Lex Machina, Darts‑IP, PlainSite, and full PACER) were not fully accessible within this search session, and PACER coverage for older cases can be incomplete. I cannot rule out that a short‑lived or sealed case exists that does not appear in the indexed sources I could reach.
2. Timing context. The patent expired 2017‑03‑26, and the 2016 assignment to Harsco Technologies LLC (a company that does have a later rail‑worker safety portfolio, e.g., US 9,902,411 and US 10,179,596) is an ownership transfer, not a lawsuit. The '651 patent's commercially relevant enforcement window overlaps with Harsco's later, differently‑claimed rail warning patents — if any suit exists, it most plausibly concerns those later patents rather than the '651 patent itself, but I found none naming the '651 patent.
3. I did not auto‑correct or substitute any patent number; every result above is tied literally to 5,924,651 / 09/042,886.

Bottom line: Based on the sources I could access, no litigation is known involving US 5,924,651. If you need a definitive negative, a direct PACER/RPX Lex Machina query on the patent number and on Harsco Technologies LLC as patent owner is the recommended next step.

I'll verify the structured data against live sources before writing this up.

Proceedings overview

Zero AIA trial proceedings are on file for US 5,924,651 — the USPTO Open Data Portal returns no IPR, PGR, or CBM for this patent, and my independent searches of PTAB/CAFC sources surfaced nothing that contradicts that (0 active / 0 claims invalidated / 0 claims sustained / 0 settled / 0 institution denials). The bottom-line defensive posture is unusual and, in practice, more favorable to a defendant than any IPR outcome would be: the patent expired on 2017‑03‑26 (Google Patents "Anticipated expiration" entry; 20 years from the 1997‑03‑26 priority date, with the 12‑year maintenance fee paid 2010‑12‑22 and status "Expired ‑ Lifetime"), and it has never been tested at the Board. Before you spend any money on invalidity contentions, confirm what you are actually being asked to defend: a demand letter in 2026 citing US 5,924,651 is citing an expired patent whose entire enforceable term ended nine years ago, so the realistic exposure is a historical‑damages theory capped by the 35 U.S.C. § 286 six‑year lookback (i.e., no pre‑2017 conduct is recoverable, and no post‑2017 conduct infringes).

No proceeding sections follow, because there are no proceedings to describe. Rather than pad this section with invented case numbers — the constraint in this task is explicit — I am recording below what the absence does and does not mean, plus the one adjacent PTAB matter I did find so you can see it is not this patent.

No proceedings — evidentiary basis and scope of the null result

• Structured source (canonical): USPTO ODP "PTAB proceedings on file" block for US 5,924,651 returns none. That is the authoritative list per your instruction and I treat it as the default.
• Independent confirmation attempts (2026‑09‑29): searches for IPR/PGR/CBM petitions naming 5,924,651, and for the assignee "Harsco" plus the patent number, returned no PTAB trial. No Notice of Appeal to the Federal Circuit, no FWD, no institution decision.
• Caveat on completeness: PTAB E2E and my searches are not a substitute for a docket pull; pre‑2012 inter partes reexamination and ex parte reexamination would also not appear in an AIA‑trial list. I found no evidence of reexamination either, but I am flagging that as not searched to exhaustion rather than as a verified negative.
• Adjacent matter found (NOT this patent): IPR2026-00134, Westinghouse Air Brake Technologies Corporation, involving RE47,835 — 5,924,651 appears there only inside an examiner search string (... or US-5924651-.did) as prior art cited during prosecution, alongside US 5,727,758 (its own parent), US 6,145,792, US 6,113,037, US 9,902,411, and others. Docket reference: https://www.docketalarm.com/cases/PTAB/IPR2026-00134/. This is not a challenge to 5,924,651 and I am not reporting it as one.

Strategic summary

Claim status: all 20 claims are UNTESTED at the PTAB; none are canceled; none are sustained. Because there is no FWD, there is no claim‑level disposition to report — claims 1 and 15 are the independents (claim 1 system, claim 15 method; claims 2‑14 depend from claim 1, claims 16‑20 from claim 15), and every one of them carries its original, unamended, as‑granted scope. Note for your invalidity work that claim 1 was the limitation added in the CIP over parent US 5,727,758: it requires "a transmitter disposed on the train and operable with the train sensor," i.e., it couples the on‑board transmitter to a wayside/on‑track train sensor that generates the trigger signal. That combination — plus the status‑signal self‑check claims (12‑14, 20) and the track/loop‑coupled transmitter claims (6, 7) — is where the differentiation lives, and it is where a § 102/§ 103 attack in district court would focus. The parent's own art is relevant: 5,727,758 is listed as a cited reference against this patent's family and appears throughout the rail‑safety art landscape.

Estoppel landscape: there is none to navigate, and that is a net positive for a defendant. Section 315(e)(2) estoppel attaches only to a petitioner that obtained an FWD or that settled after institution; with no petition ever filed, no party is estopped, and no prior‑art ground is foreclosed. You are free to run the full art field in a § 282 defense — including US 2,762,913 (Jepson), US 3,167,282 (Hursh), SU 374214, FR 2,233,667, DE 2,405,408 (Philips, "Portable railway warning system … automatic detectors for trains and central reception and alarm station"), JPS 52‑35504, JPH 4‑126664, DE 4,219,067 (Wetzler, body‑sound signals in rails), US 5,465,366, US 5,554,982, US 5,737,591, and US 5,415,369 — all of which were cited by the examiner and are therefore fair game. Inverse point: just as no petitioner is estopped, you are not protected by anyone else's win, because nobody won.

Pattern signals — the real story here is the timeline, not the Board. First, the patent is a continuation‑in‑part of US 5,727,758 (filed 1997‑03‑26, granted 1998‑03‑17, same inventors, same title), so treat the two as a family when assessing exposure and any pre‑AIA conduct. Second, the original assignee was "Individual" and the patent was assigned to Harsco Technologies LLC effective 2016‑04‑28 (recorded 2016‑05‑02, Reel/Frame 038438/0034) — one year before expiration, which is a licensing/portfolio‑consolidation move, not the profile of a patent primed for an assertion campaign. Third, no defensive aggregator (Unified Patents, RPX, etc.) ever challenged it; Unified's portal hosts a page for US‑5924651‑A but shows no challenge. Fourth, the patent's forward citation list (37 third‑party cites; 68 including family members) shows the technology was absorbed into mainstream rail‑worker‑protection systems by Harsco itself (US 9,902,411; US 10,179,596; US 10,913,472; US 11,866,078 — the "Rail warning system and method" line) and by Miller Felpax, Metrom Rail, and STC — i.e., successors iterated around this disclosure rather than attacking it. And fifth: a PGR was never legally available (effective filing date 1997 is far before the 2013‑03‑16 AIA cutoff), and CBM review sunset on 2020‑09‑16 and would in any event likely have failed the "technological invention" exclusion for a railway‑safety apparatus — so IPR was always the only AIA vehicle, and it was never used.

Recommended next steps

1. Establish what is actually being asserted, and against what conduct. The patent expired 2017‑03‑26; Google Patents records status "Expired ‑ Lifetime" with the anticipated expiration at 2017‑03‑26 and the final recorded maintenance‑fee payment at the 12‑year mark on 2010‑12‑22. There is no injunction available and no ongoing infringement. Verify entitlement in the Office's own records via the patent's Google Patents page (https://patents.google.com/patent/US5924651/en, Legal Events and "Status" fields) and the USPTO Assignment record referenced above.
2. Run the § 286 math before anything else. With a 2026 assertion, the six‑year damages window reaches back only to 2020 — three years after expiration. If the demand letter cites claims 1‑20 of 5,924,651 for present‑day products, the response is straightforward: the asserted term is over and the recovery window is empty or nearly so.
3. If you nonetheless need an invalidity record, use district court, not the Board. A district‑court § 282 defense preserves the full art field with no § 315(b) one‑year clock, no estoppel, and no discretionary‑denial risk under § 314(a). If you are forced to consider an IPR: be aware the Board does institute on expired patents, but you would be spending a full trial budget to cancel claims that cannot be infringed going forward — typically poor economics. No institution‑decision deadline, oral‑hearing date, or statutory one‑year FWD date exists to track here, because no trial has ever been instituted.
4. Do not over‑read the null result, but do read it. The absence of any IPR is itself a signal: well‑asserted patents eventually attract petitions, and this one drew none across a 20‑year term, including several years in which it sat in Harsco's portfolio. That pattern is consistent with a patent that was never a serious assertion vehicle. Confirm no parallel reexamination exists before you commit to that conclusion in a brief.
5. Sibling check. If the assertion or the portfolio discussion involves US 5,727,758 (the parent, same title, same inventors), run the same PTAB/reexam check on it — I found no AIA trial there either, but its earlier (1998) grant date places it outside PGR eligibility on the same reasoning.

Confidence statement. High confidence in the zero‑proceeding finding, based on the canonical ODP block plus repeated web searches returning nothing. Lower confidence on two points I could not close out: (a) whether any pre‑AIA inter partes or ex parte reexamination was ever filed (not exhausted), and (b) the full litigation history of the patent (I did not verify docket‑by‑docket). Neither changes the headline. I have not named a single APJ, petitioner, FWD, claim outcome, or appeal docket number, because none exists for this patent — anything to the contrary would be fabrication.

Reference links

• Patent: https://patents.google.com/patent/US5924651/en
• Parent/CIP: https://patents.google.com/patent/US5727758A/en
• PTAB E2E (search proceedings by patent): https://ptacts.uspto.gov/ptacts/
• PTAB Decisions (FWDs and institution decisions): https://www.uspto.gov/ptab/decisions
• CAFC opinions / dockets: https://www.courtlistener.com/?type=o&court=cafc
• Adjacent (not this patent): https://www.docketalarm.com/cases/PTAB/IPR2026-00134/

I'll start by verifying the assignment record and gathering context on the parties.

Let me investigate the assignment correspondent, sibling patents, and any litigation involving this patent.

Assignment & Ownership Analysis — US 5924651

Patent: US 5924651 B1 — "Tactile and audible warning system for railroad workers"
App. No.: 09/042,886 · Filed: 1998-03-17 · Issued: 1999-07-20 · Priority: 1997-03-26 (CIP of Ser. No. 08/827,346, now US 5,727,758)
Legal status: Expired — Lifetime (anticipated expiration 2017-03-26)

Source note / data caveat: The Assignment Center search UI at https://assignmentcenter.uspto.gov/ (mirror: https://assignment.uspto.gov/patent/index.html) could not be queried live in this session, and the one recorded assignment is reproduced only through the Google Patents legal-events table for this patent. The correspondent of record could not be recovered — Google Patents does not surface it for reel 038438/0034. It should be pulled directly from the Assignment Center abstract before this analysis is relied on for correspondent-based NPE linkage. Everything below that is not marked unavailable is grounded in the fetched patent text and the legal-events record.

Inventors

Pattern notes:

• There was no corporate original assignee — the patent issued to the inventors as individuals. Therefore the classic "inventors depart the assignee within 12 months" fire-sale precursor cannot be assessed; there was no assignee to depart from.
• The two inventors appear to be a family pair (shared surname, "Gregory" vs "Robert" middle names), consistent with a small independent-inventor team, but the record does not state a relationship. Do not infer this is a finding.
• The inventor group filed at least three related railroad-warning cases in rapid succession — US 5,727,758 (filed 1997-03-26), US 5,924,651 (filed 1998-03-17), and US 6,145,792, "Railroad worker warning system for train conductors" (filed 1998-04-29) — all originally individual-owned. This is a small independent portfolio, not a corporate R&D pipeline.
• Discrepancy to verify: the recorded 2016 assignment names only George Gregory Penza as assignor. Either George Robert Penza had already conveyed his interest, was never a record owner, or his interest was recorded separately. The Assignment Center abstract for reel 038438/0034 should be checked against any second Penza reel.

Original assignee

• Entity on the issued patent: Individual — i.e., the two named inventors personally. (Google Patents "Original Assignee: Individual"; Unified Patents portal confirms "Original Assignee: Individual.") No operating company was the original owner.
• Product / line of business: N/A for the original assignee (private individuals). The record does not show the inventors commercializing under a corporate entity, and I found no verified evidence of a Penza-controlled operating company. Anything to the contrary would be speculation.
• Current status: The original individual ownership ended with the 2016 assignment; the individuals are not the current owners.

Current assignee (for context): Harsco Technologies LLC, Fairmont, Minnesota (415 North Main Street, Fairmont, MN 56031 per a 2021 Belgian patent-register entry). This is an operating railway-equipment/safety company, not a licensing vehicle: it ships rail safety hardware and holds a parallel rail-warning patent family, e.g. US 10,179,596 / US 10,913,472 "Rail warning system and method" and WO 2017/015110 A1 (filed 2015-07-17). Harsco Technologies is a subsidiary of the publicly traded Harsco Corporation (NYSE: HSC), which renamed itself Enviri Corporation in 2023. I could not verify the current corporate placement of the Harsco rail/technologies entity (divestiture status is commonly reported but I have no filing to cite), so treat the "current parent" line as needing SEC cross-check.

Assignment timeline

Only one post-issuance assignment is recorded. Google Patents' legal event table for US 5924651 shows no assignee of record other than the inventors until 2016.

• 2016-04-28 (executed/effective) / recorded 2016-05-02 — Reel 038438/0034
  • Conveyance: Assignment ("ASSIGNMENT OF ASSIGNORS INTEREST")
  • Assignor: George Gregory Penza
  • Assignee: Harsco Technologies LLC (Minnesota)
  • Correspondent: ⚠️ Not available in the sources accessible here. Cannot flag recurrence — only one link exists in this chain anyway, so the "repeat correspondent" signal is structurally unobservable from this patent alone. (A recurrence finding would have to come from matching this reel's correspondent against Harsco's other 2016 recordings.)
  • Context: Late-life portfolio acquisition by an operating railway-equipment manufacturer — executed ~11 months before the patent's 2017-03-26 expiry. Consistent with a defensive/portfolio buy tied to Harsco's own rail-warning product development (Harsco filed its own rail-warning application in July 2015, ~9 months before this purchase), not a shell-entity or asserter transfer.

Pre-2016 events of note (not assignments): Patent grant 1999-07-19; maintenance fees paid 2002-12-10 (yr 4), 2006-10-26 (yr 8), 2010-12-22 (yr 12). Full 12-year fee chain was paid while the inventors held the patent — the classic signal of an owner who expected to keep (or monetize) the asset, and who had not abandoned it.

Timeline diagram

timeline
    title Ownership of US 5924651
    1997 : Filed by inventors as individuals
    1999 : Patent issued to individual inventors
    2016 : Assigned to Harsco Technologies LLC
    2017 : Patent expires

NPE / troll-pattern signals

1. Shell-entity transfer — not present. Chain runs individuals → Harsco Technologies LLC, an operating manufacturer with a physical plant address (415 N Main St, Fairmont MN 56031) and an active product line in the very field of the claims. No "IP / Holdings / Ventures" shell, no registered-agent-only address. Reel 038438/0034.

2. Known asserter in the chain — not present. Neither the inventors nor Harsco Technologies LLC appears on the asserter lists referenced (Acacia, Marathon, IV, IPNav, Wi-LAN/Mosaid, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, Spangenberg entities, or any Unified Patents / RPX high-frequency-plaintiff list surfaced). Harsco is a public operating company.

3. Repeat correspondent across the chain — unclear / unobservable. The chain has exactly one recorded link, so recurrence cannot be established. The correspondent for reel 038438/0034 is not recoverable from the sources used; retrieve it from Assignment Center and then test it against Harsco's other 2016 recordings (the Penza sibling patents plus the Harsco rail-warning family). No positive or negative call is possible on current evidence — this is a gap, not a finding.

4. Cascading transfers — not present. One assignment only; no chained LLCs, no transfers inside 24 months, no shared assignee addresses.

5. Pre-litigation transfer — not present. I found no infringement litigation naming US 5924651. The only assignment predates expiry by ~11 months and is not followed by any suit in the record. (Not a clean "not present" — an absence of found suits; treat as unclear-leaning-not-present pending a Docket Navigator / PACER check.)

6. Bankruptcy fire-sale — not present. No Chapter 7/11 of the assignor (individuals) or the buyer; no court-supervised patent sale. The 2016 transfer is an ordinary negotiated assignment, not a §363 sale.

7. Privateering — not present. No evidence the operating company transferred the patent out to an NPE to assert on its behalf; the patent stayed inside the operating company and expired there.

8. Defensive aggregator (anti-NPE) — not present. The chain does not terminate at RPX, AST, LOT, Unified Patents, or OIN. It terminates at an operating manufacturer (Harsco Technologies LLC), which is a non-NPE endpoint but not a defensive aggregator.

Verdict

Insufficient data

The recorded ownership chain is a single, fully documented individual-to-operating-company transfer: George Gregory Penza → Harsco Technologies LLC, executed 2016-04-28 and recorded 2016-05-02 at reel 038438/0034, with no further assignments before the 2017-03-26 expiry. None of the eight NPE signals is present — the assignee is a physical-location operating manufacturer that ships rail-safety hardware, so this is plainly not an NPE chain — but the alternative non-NPE buckets in the taxonomy do not fit cleanly either: "operating-company assertion" requires evidence of enforcement against competitors (none found), and "defensive / non-asserting" is defined by termination at a defensive aggregator (not the case). The verdict is therefore a data limitation on the taxonomy, not a data gap in the chain: US 5924651 is a benign, non-asserted patent that ended its life inside an operating railroad-equipment company.

Verification links:

• USPTO Assignment Center (search patent 5924651): https://assignmentcenter.uspto.gov/
• Google Patents legal events (reel 038438/0034 entry): https://patents.google.com/patent/US5924651/en

Recommended follow-ups before relying on this file: (1) pull the reel 038438/0034 abstract to capture the correspondent of record; (2) confirm whether a separate reel covers George Robert Penza's co-inventor interest; (3) run Docket Navigator / PACER for any assertion of US 5924651, US 5,727,758, or US 6,145,792; (4) cross-check Harsco Corporation SEC 10-K/8-K filings around Q2 2016 for the acquisition and the current placement of Harsco Technologies LLC.

I'll verify the patent record and the cited references against live sources before building the analysis.

Record confirmed. Now let me pull details on the substantively important cited references.

A. Record identification (USPTO/Google Patents record, verified)

No similar-number results were substituted. One data discrepancy to flag rather than auto-correct: Google Patents renders the dates as 1997-03-26 / 1998-03-17 / 1999-07-20, while the Unified Patents portal renders 1997-03-25 / 1998-03-16 / 1999-07-19. Per your operating rule, I use the Google Patents values (the authoritative text supplied), but the discrepancy is a timezone-conversion artifact and does not affect any §102 date comparison below.

B. Claim architecture (relevant to the prior-art analysis)

Claims 1–14 are system claims and 15–20 method claims. The two independents:

• Claim 1: (a) a train sensor operable with the railroad tracks detecting passage of a train at a given location and generating a sensor signal; (b) a transmitter disposed on the train and operable with the sensor to transmit a warning signal on receipt of the sensor signal; (c) a portable RF receiver carried by personnel remote from the given location that generates an alarm.
• Claim 15: the mirror-image method.

Two structural observations that drive the whole §102 analysis, and that I state explicitly because the claims do not say what the specification's two embodiments disclose:

1. Claims 1/15 literally require a trackside train sensor and a train-mounted transmitter slaved to that sensor. FIG. 1–2 system 10 discloses a train-mounted transmitter 20 with no track sensor; FIG. 5 system 90 discloses a track sensor 96 with a trackside RF transmitter 98. Neither embodiment discloses the claimed combination. The "disposed on the train" language therefore narrows claim 1 substantially and explains why the examiner did not reject it outright.
2. The speed-responsive power control and "predetermined time" features (FIGS. 3–4, controller 64/speed sensor 66) are described but not claimed in US 5,924,651. They were claimed in the parent US 5,727,758. The CIP therefore traded the speed-control claims for the track-sensor limitation — a fact that matters when weighing US 5,554,982 (§C, ref. 20).

C. The 24 cited references — citation, dates, description, and §102 posture

All 24 are examiner-cited (asterisked) in the "Citations" list. None of the 24 discloses every element of claim 1 or claim 15 as literally written, because no single reference combines a track-mounted passage sensor with a train-borne transmitter slaved to that sensor. The table gives the closest claims and whether the reference is true §102 anticipation material or §103/element-level material.

D. Bottom line — the §102 picture

1. No single cited reference anticipates claim 1 or claim 15 as literally written. The two independent claims require the conjunction of a track-mounted passage sensor and a train-borne transmitter slaved to that sensor. References 4, 5, 11, 12, 15, 16 supply the sensor side; references 18, 20, 22, 24 supply the train-borne-transmitter side. That split is precisely why the claim survived prosecution.
2. The strongest §102 attack is JP H04-126664 A (ref. 11), which the applicants themselves conceded in the Background describes "a track supervisor [who] receives an RF train passage signal and then subsequently transmits an RF alarm signal to an alarm receiver carried by each worker," with per-station address checking. Add ref. 20 (US 5,554,982, train-mounted transmitter + remote receiver + visual/audible alarm) or ref. 22 (US 5,620,155, train-borne encoded RF to remote receivers) and you have a complete §103 case against claims 1/15 — and §102 anticipation of dependent claims 4, 9, 10, 12, 16, 17, 18, 20.
3. Claim 5's control-base relay is the most vulnerable dependent claim: DE 2,405,408 (ref. 5) discloses train detectors with a central reception/alarm station, and US 5,554,982 (ref. 20) and US 5,620,155 (ref. 22) both disclose an intervening transceiver relaying to a remote receiver.
4. Claim 6's rail-coupled signalling is squarely met by DE 4,219,067 (ref. 15), which teaches continuous signals transmitted in the rails to warn track-area personnel — a factually direct hit on "the transmitter is coupled to the railroad tracks and transmits the warning signal along the railroad tracks."
5. Claims 9–11 and 17–19 (visual/audio/vibratory alarms) are the weakest claims in the patent: US 5,572,201 (ref. 21), US 5,554,982 (ref. 20), WO 1994/021504 (ref. 17) and US 5,461,366 (ref. 19) collectively render these modalities routine.
6. Ref. 23 (US 5,727,758) is the parent, not prior art for the commonly disclosed subject matter. Its proper role is as a §120 benefit reference (and, if relied upon at all, only against the FIG. 5 track-sensor matter added in the CIP).

E. Confidence and caveats

• High confidence in the patent identification, dates, claim text, and the 24-reference citation set — all taken from the authoritative full text you supplied and corroborated by the Google Patents, Justia and Unified Patents records.
• Medium confidence in the brief descriptions for the non-English references (refs. 3, 7, 9, 10, 12, 13, 16, 17): for these I am working from the examiner-cited titles plus the patent's own Background characterizations, not from full-text translations. I could not retrieve full text for DE 4,219,067 (ref. 15) or JP H06-1239 (ref. 13) before exhausting the search budget; their descriptions rest on the citation titles.
• JP H04-126664 A (ref. 11) — I could not retrieve the reference's own text; my description relies on the applicants' Background statement about it, which is a party admission but not the reference itself. This matters because ref. 11 is my top §102 candidate, and its actual scope (e.g., whether it is a wired or wireless link, and whether an alarm is genuinely generated for workers) should be verified against the Japanese original before any rejection is built on it.
• The §102/§103 labels above are my legal characterization of each reference's technical reach, not a statement of what the examiner actually applied. The prosecution history is not in the supplied record, so I cannot confirm which references were used for which rejection.

I'll ground this analysis by pulling the actual disclosures of the key cited references before mapping them to the claims.

Now let me verify the remaining key references that map to specific claim limitations.

Obviousness Analysis — U.S. Patent No. 5,924,651

Patent: U.S. 5,924,651 A, "Tactile and audible warning system for railroad workers" (Penza & Penza)
App. No. 09/042,886 · filed 1998‑03‑17 · granted 1999‑07‑20 · CIP of Ser. No. 08/827,346 (U.S. 5,727,758, filed 1997‑03‑26)
Source of record: https://patents.google.com/patent/[US5924651](/patent/US5924651)/en

1. Legal framework and scope

The application has an effective priority of 1997‑03‑26 (CIP parent) and a filing date of 1998‑03‑17, so pre‑AIA 35 U.S.C. § 103(a) governs, with § 103(c) available for commonly‑owned/same‑inventor art. The operative test is Graham v. John Deere, 383 U.S. 1 (1966), as refined by KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007). Because the examiner allowed the case over 24 cited references, the analysis must explain why the specific combination — not the individual references — would have been obvious.

1.1 Claim 1 architecture, and its central ambiguity

Claim 1 requires five things:

Elements (a) and (b) are internally strained. In FIG. 1/FIG. 2 the transmitter 20 is on the train but there is no train sensor at all (continuous transmission). In FIG. 5 the train sensor 96 and transmitter 98 are both wayside. The claim is therefore a hybrid that is arguably not described in either disclosed embodiment — a § 112(a) concern noted further in § 6 below, which also affects the § 103 date window.

This yields two POSITA readings, and the claim is obvious under both:

• Reading A ("virtual wayside": the sensor is on the train). The specification expressly contemplates this: "Train sensor 96 may also be a part of a global positioning system operable with train 92 to determine the position of the train and when the train passes over given location 100" (spec., FIG. 5 discussion). So the "train sensor" = an on‑board position sensor detecting passage over a given location.
• Reading B (wayside sensor, train‑mounted transmitter). A wayside detector signals the train, and the train's transmitter broadcasts the warning.

2. Prior-art qualification (pre‑AIA §§ 102(b)/102(e))

3. Ground 1 — Claim 1

Ground 1A (Reading A — on‑board position sensor): US 5,554,982 + DE 2405408

The only missing element is a personnel‑carried receiver (5,554,982's is vehicle‑based); DE 2405408 supplies exactly that ("portable central station … in wireless contact"), and JPH 04‑126664 supplies a receiver "carried by each worker" (as the patent itself admits). Motivation: 5,554,982's own express statement that the purpose is to warn a party whose attention is diverted — the same problem the '651 addresses for machinery operators in cabs (spec., FIG. 1 discussion of cab 21).

Ground 1B (Reading B — wayside sensor, train‑mounted transmitter): JPH 04‑126664 + US 5,554,982 (or US 2,762,913 / US 5,620,155)

This is the strongest ground because the patentee's own Background admits the substance of JPH 04‑126664:

"A track supervisor receives an RF train passage signal and then subsequently transmits an RF alarm signal to an alarm receiver carried by each worker. The alarm receiver checks the alarm signal to determine whether the alarm signal has been sent to its own station." (US 5,924,651, Background Art)

That admission discloses elements (a), (c), (d) and most of (b), with the transmitter at the wayside rather than on the train. The remaining difference — moving the RF transmitter onto the train — is squarely met by US 5,554,982 (train‑mounted transceiver 24 with GPS), US 2,762,913 (train‑mounted transmitters for proximity warning), and US 5,620,155 (locomotive‑mounted transmitter with GPS and encoded signals). US 5,620,155 additionally discloses the wayside→train communication link needed to make a trackside sensor "operable with" a train‑mounted transmitter (crossing transceiver → locomotive receiver 30), removing any enablement/architecture gap.

4. Ground 2 — Dependent claims

5. Motivation to combine (KSR rationales, grounded in the record)

1. Same field, same problem, same solution class. Every reference above is in B61L23/06‑type art (warning workers or motorists of an approaching train), and DE 2405408, JPH 04‑126664, SU 374214 and FR 2233667 each state the objective of eliminating the human lookout — the exact deficiency the '651 identifies in its Background.
2. Simple substitution of one known element for another, predictable result. Substituting a train‑mounted RF transmitter for a wayside RF transmitter (or vice versa) changes only where the antenna sits. US 5,554,982 treats these as interchangeable alternatives in a single specification ("a transceiver, positioned on the train itself or at the side of the track," FIG. 1 vs. FIG. 5), which is powerful evidence that the substitution was within the ordinary skill level.
3. Known technique improves similar devices in the same way. A train‑mounted transmitter inherits the locomotive's higher power, elevated antenna and available electrical supply, improving range and reliability relative to a battery‑powered wayside transmitter (DE 2405408 expressly uses only a "relatively weak transmitter"). Notably, US 5,554,982 discloses a train‑transmitted general warning to all receivers in range when the wayside unit fails — the precise architecture of claim 1.
4. Finite, predictable design space / "obvious to try." Once a POSITA had a wayside detector (a) and a portable receiver (c), the location of the transmitter (b) reduced to two known options — at the detector or on the train — with no unexpected results either way.
5. Design incentives inherent in the problem. Locomotive power, obstruction of wayside RF paths, tunnels and curves are all recited in the record (spec. FIG. 1–2 discussion of obstructions; US 2,762,913 on rails guiding radiation around curves). These supply the "market forces"/"design incentive" prong of KSR.
6. The patentee's own disclosure bridges the two embodiments. The '651 describes a first embodiment (train‑mounted continuous transmitter, FIGS. 1–2) and a second embodiment (wayside sensor + wayside transmitter, FIG. 5), and further describes wayside→train coupling alternatives. Combining them is not an unbounded leap; the inventor's own specification treats the two halves as compatible modules.

6. Anticipated rebuttals, and limits of this analysis

Obviousness could be resisted as follows, with responses:

• "US 5,554,982 teaches away from a train‑mounted warning transmitter." The reference does say "transmitting a warning signal from the WAVS is preferable to transmitting it from the train." Response: that passage concerns the warning‑zone boundary signal to motor vehicles (precision of the zone and deactivation), not warnings to personnel, and the same reference affirmatively discloses train‑mounted transmission as its primary and fallback mode. KSR requires that a reference "criticize, disfavor, or otherwise discourage" the claimed arrangement; a stated preference among two disclosed alternatives does not.
• "The references are non‑analogous (grade crossings / motorists, not track workers)." Response: DE 2405408, JPH 04‑126664, SU 374214, FR 2233667, JPS 52‑35504, DE 4219067 and US 5,620,155 are all directed to track‑worker or trackside‑personnel warning; the field is identical.
• "No bodily incorporation." Response: KSR rejects the rigid TSM/bodily‑incorporation test; what matters is whether the claimed subject matter as a whole would have been obvious.
• "Secondary considerations." None appear of record — no evidence of unexpected results, licensing, or industry praise in the materials supplied. The '651 expired for full term on 2017‑03‑26 (fee payments at years 4, 8 and 12), and no reissue or disclaimer is noted.

Explicit uncertainties / items I could not verify:

• I verified full text for US 5,554,982, US 2,762,913, US 5,620,155, DE 2405408 and JPH 04‑126664 (the last only through the '651 specification's own admission and citation lists). I did not verify full text for US 5,465,366, US 5,572,201, US 5,735,491, US 2,762,913's Japanese counterparts (JPH 04‑39159, JPH 04‑163273, JPH 06‑1239, JPH 06‑183346), JPS 63‑315369, WO 92/04699, WO 94/21504, US 3,167,282 or SU 374214. Their mapping above rests on their titles/abstracts as listed in the '651 citation record and should be confirmed against full text before reliance.
• US 5,727,758 is not usable as § 103 prior art here. It is the CIP parent, lists the same inventor, and was filed on the same day as the '651 priority date (1997‑03‑26) and published the same day as the '651 filing (1998‑03‑17). It is disqualified as § 102(e)/§ 103(c) art by common inventorship, and is not § 102(a)/(b) art. Any rejection that leans on the '758 as a secondary reference for the train‑mounted transmitter should be replaced with US 2,762,913 or US 5,554,982.
• Priority/§ 112 interaction. Because claim 1's "transmitter disposed on the train" + "train sensor operable with the railroad tracks" combination appears in neither disclosed embodiment, a challenger could argue claim 1 is entitled only to the 1998‑03‑17 CIP filing date. That does not change the § 103 outcome (all listed references still qualify), but it does remove any argument that the parent's disclosure supplies a priority shield.
• Note also the literal claim text: claim 1 recites "generates a a train sensor signal" (duplicated article) and claim 20 is captioned "The training warning method of claim 15." Per the operating rules these identifiers/typographical artifacts are reproduced as‑is and not auto‑corrected.

7. Bottom line

Claim 1 would have been obvious under § 103(a) over:
(i) JPH 04‑126664 + US 5,554,982 (or JPH 04‑126664 + US 2,762,913), with DE 2405408 or US 5,554,982 supplying the personnel‑carried portable receiver and alarm; or, under the "virtual wayside" reading,
(ii) US 5,554,982 + DE 2405408 (optionally + US 5,620,155 for the wayside→train trigger link).

Claims 2–4, 7–11 fall with DE 2405408, US 5,554,982, US 2,762,913, US 5,415,369 and JPH 04‑126664. Claims 5 and 8 are met by DE 2405408's receiving/relaying central station. Claim 6 is met by DE 4219067 and US 5,265,831 (rail‑conducted signaling), with US 2,762,913 supplying the motivation. Claims 12–14 are met by US 2,762,913's periodic transmitter/receiver self‑test with fault lamp, combined with US 5,620,155's wayside status reporting and DE 2405408's relay station. Claims 15–20 stand or fall with their system counterparts.

The overall § 103 case is strong, and it is reinforced by the patentee's own Background admissions regarding JPH 04‑126664 and JPS 52‑35504 — the only distinctions the specification draws are that a warning to workers should be "more direct" and "quieter" than a station platform broadcast, which are functional/ergonomic preferences rather than technical advances over the cited art.