US 6523935

I'll verify the patent data and check for any 2026 litigation activity.

Let me check for any PTAB/IPR proceedings referencing this patent.

US Patent 6,523,935 — Analyst Summary

Note on scope: I searched for this patent number specifically and filtered out look‑alikes. Results surfaced several other patents that are frequently confused with it — e.g., U.S. 10,775,935 ('935 touch‑sensing, FlatFrog v. Promethean), U.S. 7,944,935 (Philips, In re 移远通信), and the "935‑Accused Products" in the FlatFrog case. None of those are U.S. 6,523,935, and I excluded them. Nothing in my searches ties this patent (6,523,935) to any litigation or Federal Circuit appeal.

Bibliographic data

Primary source: https://patents.google.com/patent/US6523935/en

Minor anomaly (flagging, not correcting): the assignment records show a 2001‑04‑09 assignment from the five named inventors, plus a separate 2002‑02‑05 assignment from an individual named Simon Dodd, who does not appear in the inventor list. I cannot explain this from the documents I have.

Abstract (as issued)

A narrow ink jet printhead having four columnar arrays of ink drop generators configured for monochrome single‑pass printing at a print resolution having a media axis dot spacing that is less than the columnar nozzle spacing of the ink drop generators. The ink jet printhead more particularly includes high resistance heater resistors and efficient FET drive circuits that are configured to compensate for variation in parasitic resistance presented by power traces.

Plain‑language overview of the independent claims

Claim 1 — the "narrow four‑column, single‑pass" claim

A thermal ink jet printhead built on a substrate containing multiple thin‑film layers, in which:

• Four side‑by‑side columnar arrays of drop generators run along a longitudinal extent;
• Each column has at least 100 drop generators, spaced by a pitch P;
• Columns 1 and 2 are within 630 µm of each other, and columns 3 and 4 are within 630 µm of each other (the tight pairing that makes the die "narrow");
• All four columns eject drops of the same color, with a drop volume sized so the head can print single‑pass monochrome at a resolution of 1/(4P) dpi along the media/print axis; and
• Four corresponding columnar arrays of FET drive circuits are formed in the same substrate, one adjacent each drop‑generator column, to fire them.

In plain terms: a compact, four‑row black‑ink head where each row is offset from its neighbors so that one pass of the carriage produces four times the row‑pitch resolution, with the switching transistors integrated right next to their nozzles.

Claim 23 — the "energy‑balancing" claim

Repeats the four‑column/≥100‑per‑column/630 µm/same‑color/single‑pass 1/(4P) dpi structure of claim 1, and adds three further requirements:

• Each drop generator has a heater resistor of at least 100 ohms (a "high‑resistance" resistor, letting the drive FETs be smaller);
• Power traces connect the drop generators and the FET drive circuits; and
• The FET drive circuits are configured to compensate for variation in the parasitic resistance presented by those power traces — i.e., the transistors are locally tuned so that every nozzle receives substantially the same firing energy despite differing trace lengths.

Dependent claim themes (selected)

• 2–3, 24–25: two ink‑feed slots with two columns straddling each slot (dual‑edge slot feeding); the two inboard columns are ≤800 µm apart.
• 4, 26: P in the range 1/300 inch to 1/600 inch.
• 5–6, 27–28: drop volume 12–19 pL (pigment) or 3–7 pL (dye).
• 7, 23: heater resistance ≥100 ohms.
• 8, 29: ground busses overlapping the FET active regions.
• 9–13, 30–34: efficient FETs — Ron < (250,000 Ω·µm²)/A, gate oxide ≤800 Å, gate length <4 µm, Ron ≤14 or ≤16 ohms.
• 14–18, 35–38: FET on‑resistance tuned to offset power‑trace parasitics, including via the length of continuously non‑contacted drain‑region segments.
• 19–20, 39–40: FET array region width ≤180 µm (or ≤250 µm).
• 21–22, 41–42: die aspect ratio LS/WS > 3.7, with WS ≈ 2900 µm.

Caveat on the claim language (literal reading)

Claim 1 and claim 23 recite the single‑pass resolution as "1/(4P) dpi." Read literally with P as a length (e.g., 1/300 inch), this does not arithmetically match the specification's description, which states the dot spacing is one‑quarter of the nozzle pitch P (equivalent to 4/P dpi — 1200 dpi at P = 1/300 inch, and "1/2400 dpi" as printed in the spec at P = 1/600 inch). I am reporting the claim text exactly as issued rather than correcting it; the apparent tension between the claim wording and the spec is worth noting for any validity or claim‑construction analysis.

Litigation / docket findings

• Federal Circuit (2026): I found no CAFC docket, appeal, or argued case involving US 6,523,935. The June 2026 CAFC scheduled‑cases listing contains no caption traceable to this patent (https://www.cafc.uscourts.gov/home/oral-argument/scheduled-cases/).
• District court / PTAB: No complaint, infringement contention, or IPR petition naming 6,523,935 appeared in my searches. The PTAB (P‑TACTS) hits that surfaced were petitions in unrelated matters (FlatFrog v. Promethean over U.S. 10,775,935; a document upload that merely reproduced the Torgerson et al. specification as an exhibit). I could not verify which proceeding, if any, attached this patent as an exhibit.
• This is consistent with the record: the patent expired 2021‑01‑30, so no active enforcement is expected.

Uncertainty / confidence

• High confidence on title, inventors, assignees, filing/issue dates, claim count, abstract, and claim content — these come from the full authoritative patent text.
• High confidence that the patent is expired and shows no 2026 CAFC activity based on the searches performed.
• Low confidence / unverified on: the reason for the Simon Dodd assignment; and whether any PTAB filing used this patent as an exhibit — I do not have direct access to PACER, the CAFC docket system, or PTAB APIs, only web search results, so a negative litigation finding is not a guarantee of no litigation.

Sources: https://patents.google.com/patent/US6523935/en · https://patents.justia.com/patent/6523935 · https://patents.google.com/patent/WO2002060696A1/en · https://www.cafc.uscourts.gov/home/oral-argument/scheduled-cases/

I'll search for litigation involving US patent 6523935.

Let me search more specific litigation databases.

Litigation Search Results: U.S. Patent No. 6,523,935

Finding: No litigation involving U.S. Patent No. 6,523,935 was identified in the sources searched.

What I searched

I ran targeted searches against general web indexes, court-document aggregators (CourtListener/RECAP, Docket Alarm), PTAB/PTACTS records, and Unified Patents–related litigation materials — including queries structured around the exact number forms "6523935," "6,523,935," paired with terms such as "infringement," "lawsuit," "case," "docket," and the patent owner (Hewlett-Packard). I did not find any district court complaint, ITC investigation, or Federal Circuit appeal identifying the '935 patent as an asserted patent.

Important caveats

• This is a negative search result, not a certification. I cannot confirm the absence of litigation with certainty. The public litigation portals (Unified Patents portal, RPX Insight, Docket Alarm, PACER) are not exhaustively full-text searchable by patent number through open search, and PACER is a paywalled, court-by-court system. A definitive negative requires a paid docket search (e.g., Lex Machina, Darts-IP, RPX, or an Orbit/LexisNexis patent-litigation module), which I could not execute here.
• I want to be explicit that my inability to find cases may reflect search limitations rather than a true absence of litigation.

What the record does show about this patent

Based strictly on the authoritative patent text supplied:

• Patent: U.S. 6,523,935 B2, "Narrow ink jet printhead"
• Application: US 09/773,182, filed 2001-01-30; granted 2003-02-25; priority date 2001-01-30
• Assignee/owner: Hewlett-Packard Company, later assigned to Hewlett-Packard Development Company, L.P. (assignment recorded 2005-01-11)
• Status: Expired – Lifetime; anticipated expiration 2021-01-30
• Family: A continuation (US 10/278,085) issued as US 6,722,759 B2 ("Ink jet printhead"); extensive international family (EP 1309455, JP 4472254, CN 1240543, etc.)
• Post-grant activity noted in the record: A certificate of correction (2004-01-27) and maintenance-fee payments (4th, 8th, 12th years). No inter partes review, reexamination, or district court proceeding appears in the supplied record.

Conclusion

Based on the sources available to me, I found no known litigation involving U.S. Patent 6,523,935. The patent appears in the record as an expired Hewlett-Packard printing-technology patent with no litigation history reflected in the documents I retrieved. Because this conclusion rests on a negative search, I recommend verification through a comprehensive commercial patent-litigation database before relying on it for any legal purpose.

AIA Trial Proceedings — US Patent 6,523,935 ("Narrow ink jet printhead")

Source of record: the structured "PTAB proceedings on file" block supplied with this task (USPTO Open Data Portal ingest), plus independent web verification performed 2026-09-30. Patent bibliographic data cross-checked against the Google Patents record at https://patents.google.com/patent/[US6523935](/patent/US6523935)/en.

Proceedings overview

Total AIA trial proceedings on file: 0. Breakdown: 0 active, 0 claims invalidated, 0 claims sustained, 0 settled, 0 institution denials — the structured ODP block returns no IPR, PGR, or CBM for US 6,523,935 as of the most recent ingest, and targeted web searches (patent number + "IPR", "PTAB", "inter partes review", and petitioner-side queries) surfaced no older or unindexed proceeding either. The bottom-line defensive posture is therefore not "the patent has survived two IPRs and is hardened," and it is also not "claims 1–5 have been canceled." It is a third, more mundane thing: the patent is expired (anticpated expiration 2021-01-30; status "Expired - Lifetime"), so the demand letter — not the PTAB — is the thing to attack. Any assertion of this patent today is limited at most to pre-expiration past damages for the six-year lookback window, and the absence of PTAB activity means there is no institution decision, FWD, or estoppel record to lean on.

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Per-proceeding detail

No proceedings to report. There is no IPR, PGR, or CBM number to populate the ### {PROCEEDING_NUMBER} — {Petitioner} v. {Patent Owner} template with, and I will not invent one. For completeness, the specific fields a defendant would want are all "not applicable":

• Type / Filed / Status / Panel / Grounds / Institution / FWD / Settlement / Appeal — N/A; no petition was ever filed, so none of these events exist.
• Defensive value — none is derived from PTAB activity, because there is none. The defensive value here comes from the patent's term and from the prior art cited on its face (see Strategic summary).

Search and verification trail (what I checked, and what it does and does not prove)

• Structured source: ODP returns zero AIA trials. Treated as canonical per instructions.
• Web search, 2026-09-30: queries pairing "6523935" / "6,523,935" with IPR/PGR/CBM, PTAB, and petitioner terms returned only unrelated matters (e.g., IPR2024-00015 on U.S. 10,775,935 — a different patent whose number merely contains "935"; the frequent "652" hits are the unrelated patents U.S. 8,050,652 and U.S. 10,217,523). No hit tied to US 6,523,935.
• Flag / limitation: the structured block covers AIA trials only. It would not capture a pre-AIA ex parte reexamination or inter partes reexamination under former 35 U.S.C. § 311. I found no reexamination certificate for this patent and none is listed among its published documents, but I could not positively exclude a reexam from the sources available at this step. If that matters to a case, pull the full file wrapper via Patent Public Search / Global Dossier (https://patents.google.com/patent/US6523935/en links to the USPTO Global Dossier).
• One administrative event is on the record and is unrelated to validity: a Certificate of Correction issued 2004-01-27 (Legal Events, code "CC"). The face of the patent shows at least one obvious typographical defect that such a certificate could address (the specification states a 1/600-inch pitch gives "a single pass print resolution of {fraction (1/2400)} dpi"). I am not asserting what the certificate corrected — that must be read from the printed certificate, not inferred.

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Strategic summary

Claim status: all 42 claims UNTESTED at the PTAB; none canceled, none adjudicated. Claims 1–22 (the first independent claim 1 plus dependents), claims 23–42 (independent claim 23 plus dependents) — every claim stands exactly as issued, subject only to whatever the 2004-01-27 Certificate of Correction made. There is no narrowing claim amendment, no disclaimer, and no adverse judgment under 37 C.F.R. § 42.73(b) anywhere in this patent's history. On paper that looks like an unblemished patent; in practice it means the strongest defensive asset is not a PTAB record but the calendar.

Term and exposure. The patent's own record gives a priority/filing date of 2001-01-30, a grant date of 2003-02-25, and an anticipated expiration of 2021-01-30, with maintenance fees paid at the 4-, 8-, and 12-year windows (last FPAY 2014-07-28), i.e., it ran its full 20-year term and is now Expired - Lifetime. Consequences: (1) post-2021-01-30 making/using/selling cannot infringe; (2) a damages case is confined to the § 286 six-year lookback from the complaint and cut off at expiration — a shrinking and soon-empty window; (3) the doctrine of laches is unavailable post-SCA Hygiene but estoppel-type delay arguments and § 287 notice limits remain live. The continuation in the same family, US 6,722,759 B2 ("Ink jet printhead," app. 10/278,085, filed 2002-10-22, claiming the 2001-01-30 priority) is likewise expired, so a demand letter that swaps in the '759 patent buys the patent owner no additional term.

Estoppel landscape. With zero IPRs, § 315(e)(2) estoppel is empty: no petitioner is barred from raising anything in district court or before the PTAB, and no institution decision has locked in any claim construction under the Phillips standard now applied at the PTAB. Conversely, nothing has been finally decided against the patent either — every invalidity theory remains open to a first-challenger, including § 102/§ 103 over the art already of record and over the eleven references cited on the face of the patent (see below) and, if a pre-AIA reexam is ever ordered, whatever the examiner adopts.

Prior-art springboard (from the patent's own citation list, not a PTAB record). The granted patent cites, among others: U.S. 5,757,400 (Spectra, "High resolution matrix ink jet arrangement," 1998-05-26); U.S. 5,984,455 (Lexmark, "Ink jet printing apparatus having primary and secondary nozzles," 1999-11-16); U.S. 6,264,297 B1 (Canon, "Liquid jet recording using a multi-part drive signal sequentially applied to plural blocks of thermal elements," 2001-07-24); U.S. 6,309,053 B1 (HP, "Ink jet printhead having a ground bus that overlaps transistor active regions," 2001-10-30 — note this is the ground-bus-overlap concept recited in claims 8/29 and described at length in the specification); EP 1,145,854 A2 and EP 1,145,856 A1 (both HP, 2001-10-17); and WO 02/014073 A1 (HP, "Ink jet printhead having four staggered rows of nozzles"). The specification also incorporates by reference U.S. 4,719,477, U.S. 5,317,346, and U.S. 5,469,199. Those are the obvious anchors for any § 102/§ 103 attack, especially on the "four columnar arrays / ≤630 µm spacing / 1/(4P) dpi single-pass" combination of independent claims 1 and 23 — but note these references were before the examiner, so a § 325(d) discretionary-denial argument is well teed up against any petitioner that re-packages them.

Pattern signals. None. No repeat petitioner, no serial-petition pattern, no defensive aggregator (searched for Unified Patents-type involvement; nothing on this patent), and no CAFC appeal traceable to this patent. This is consistent with the patent's profile: it is a Hewlett-Packard printing-hardware patent (assignee now Hewlett-Packard Development Company, L.P.), in a technology space where HP historically enforced in district court and at the ITC rather than litigating its own patents at the PTAB, and it expired without ever attracting a challenger.

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Recommended next steps

1. If you have a demand letter citing US 6,523,935, lead with the expiration date, not with invalidity. The record you should quote is the front-page/legal-events record: filed 2001-01-30, granted 2003-02-25, anticipated expiration 2021-01-30, status Expired - Lifetime (https://patents.google.com/patent/US6523935/en). Ask the sender to identify the specific pre-2021-01-30 acts and the § 286 damages window, and to address § 287 marking/notice.
2. Do not budget for an IPR on this patent as a term-extension play. PTAB trials take ~12–18 months to FWD, and the patent is already dead; an IPR would only affect past damages and would trigger § 315(e)(2) estoppel against you on all grounds you raised or reasonably could have raised. If past damages are material, an IPR or a district-court invalidity case is the lever — but see item 4.
3. Before relying on "no PTAB activity," confirm the reexamination gap. Since the ODP block covers AIA trials only, run the file wrapper through Patent Public Search and Global Dossier for any ex parte or pre-AIA inter partes reexamination and read the 2004-01-27 Certificate of Correction directly. I could not rule those out from the available sources; I can only say no reexam certificate appears in the published-document set for this patent.
4. If you do challenge validity, expect a § 325(d) fight and prepare to go outside the cited art. Every meaningful reference on the face of the '935 patent was considered by the examiner, and the claims are narrow apparatus claims with numeric spacing/volume limits (≤630 µm; ≤800 µm; P between 1/300 and 1/600 inch; 3–7 pL or 12–19 pL drop volumes; ≥100 Ω heaters; Ron ≤ 14–16 Ω). That footnote structure makes claim-by-claim anticipation arguments feasible but gives the patent owner an easy "already considered" story — so lead with art that is genuinely new, and map it to specific limits in claim 1 or 23 rather than to the general architecture.
5. Check the family and the litigation history of the siblings before assuming this patent is the only exposure. The record identifies continuation US 6,722,759 B2 (also expired) and a set of closely related HP printhead patents surfaced as similar documents (US 6,478,404 B2; US 6,412,917 B1; US 6,422,676 B1; US 6,398,347 B1; US 6,309,053 B1). If the demand letter bundles patents, run the same expiration check on each — several share the same 2000–2001 priority window and are therefore also at or near end of term.

Caveat on sourcing. I found no PTAB Final Written Decision, institution decision, termination, or Federal Circuit opinion to link for this patent, because none exists to my knowledge and none appeared in the structured data or in web search. If a proceeding exists that neither the ODP ingest nor public web sources surfaced, I have not seen it — treat any proceeding number you encounter elsewhere as unverified until it is confirmed on PTAB E2E (https://ptacts.uspto.gov) or CourtListener (https://www.courtlistener.com/?q=%226523935%22).

I'll verify the assignment record and check for any assertion/NPE activity before writing this up.

Let me check whether the '935 patent itself was ever asserted, and look for any post-2005 assignments.

Ownership & Assignment Reconstruction — US 6,523,935 B2

Patent: US 6,523,935 B2 — "Narrow ink jet printhead"
App. No.: 09/773,182 · Filed: 2001-01-30 · Issued: 2003-02-25
Source used: Google Patents legal-events table for US6523935B2 (mirrors the data Google ingests from USPTO assignment records). I could not query assignmentcenter.uspto.gov directly (it is a JavaScript application that my search tooling cannot render), so reel/frame and assignor/assignee data below come from the authoritative patent record supplied, while correspondent-of-record fields are marked as unverified rather than guessed. Verify all entries at https://assignmentcenter.uspto.gov/ (search by patent number) or https://assignment.uspto.gov/patent/index.html.

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Inventors

Pattern notes:

• All five inventors executed the assignment on 2001-03-27 through 2001-03-30 — i.e., contemporaneously with filing (2001-01-30) and within HP's standard corporate practice. No inventor retained any rights. There is no evidence of inventors departing the original assignee, which is the usual precursor to an inventor-owned portfolio fire-sale. Signal not present.
• Anomaly worth flagging: a sixth assignment is recorded on this patent's record — assignor SIMON DODD, effective 2002-01-23, recorded 2002-02-05, reel 012368/0814, to Hewlett-Packard Company. Simon Dodd is not a named inventor on US 6,523,935. A non-inventor assignor on a patent's own assignment record usually means the executed document covered a family of related HP applications (note the continuation US 10/278,085 → US 6,722,759 B2, filed 2002-10-22) and was recorded against multiple properties. This is a clerical/portfolio-scope artifact, not an ownership transfer to a third party, but it should be confirmed against the reel 012368/0814 instrument itself.

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Original assignee

Hewlett-Packard Company (Palo Alto / Fort Collins, CO records address), as named on the face of the issued patent and reflected in the assignment recorded at reel 011702/0797.

• Primary line of business: computing and imaging/printing hardware; at filing, HP's inkjet business was its highest-volume consumer franchise. The patent's own Figures 3 and 11 describe a drop-on-demand thermal inkjet printhead used in an HP-style carriage-mounted pen.
• Product embodying the claims: The claims (1–42) cover a four-column, dual-slot-feed monochrome printhead achieving 1/(4P) dpi single-pass resolution (e.g., 1200 dpi at a 1/300″ nozzle pitch), with high-resistance heater resistors and on-resistance-compensated FET drive circuits. This is a production printhead architecture, not a paper design — HP shipped the corresponding thermal inkjet cartridge/printhead families in the 2001–2005 timeframe. (Corroborating context: HP's sibling printhead patents — the '053, '347, '817, '279, '598, '917 patents — were asserted by Hewlett-Packard Company and Hewlett-Packard Development Company, L.P. in ITC Inv. No. 337-TA-723 (instituted 2010-06-25) against MicroJet/APM/PTC, where HP was found to have a domestic industry. See 76 FR 51055 and USITC Pub. 4373.)
• Current status: Operating company, never dissolved. HP's printing business was separated in 2015 into HP Inc.; the patent's record owner is Hewlett-Packard Development Company, L.P. (Houston, TX), HP's long-standing IP-holding subsidiary. The patent expired 2021-01-30 on its 20-year term (Google Patents legal status: "Expired – Lifetime").

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Assignment timeline

Only three assignment-type instruments are recorded, all internal to HP. Each is given below.

• Signed 2001-03-27 – 2001-03-30 (executed) / recorded 2001-04-09 — Reel 011702/0797

  • Conveyance: Assignment (Assignment of Interest)
  • Assignor: Torgerson, Joseph M.; Browning, Robert N. K.; MacKenzie, Mark H.; Miller, Michael D.; Bakkom, Angela White (signing dates 2001-03-27 to 2001-03-30)
  • Assignee: Hewlett-Packard Company
  • Correspondent: Not exposed by the source used — HP's practice at this time was to self-record through its in-house IP Administration / Legal Department (Fort Collins, CO), but I cannot confirm the named correspondent without the Assignment Center record. No recurrence finding can be made.
  • Context: Original inventor-to-employer corporate assignment; standard for a large operating-company filing.

• Effective 2002-01-23 / recorded 2002-02-05 — Reel 012368/0814

  • Conveyance: Assignment
  • Assignor: Dodd, Simon (not a named inventor on this patent)
  • Assignee: Hewlett-Packard Company
  • Correspondent: Not exposed by the source used.
  • Context: Related-matter/portfolio-scope instrument recorded against this patent; not a sale of the '935 assets to any third party.

• Effective 2005-01-11 / recorded 2005-01-11 — Reel 015583/0106

  • Conveyance: Assignment
  • Assignor: Hewlett-Packard Company
  • Assignee: Hewlett-Packard Development Company, L.P. (Houston, TX)
  • Correspondent: Not exposed by the source used. Note that this is HP's bulk intra-group IP transfer of the era; parallel HP→HP Dev Co recordings in the same period used a Fort Collins, CO IP Administration correspondence address, but that pattern is documented on other HP patents, not confirmed on '935.
  • Context: Internal corporate reorganization — transfer into HP's wholly owned IP-holding subsidiary. Not a third-party sale, not a securitization.

• 2004-01-27 — Certificate of Correction (type: Correction; no separate reel/frame shown in the legal-events table). This alters the printed claims/text but does not transfer ownership.

• 2003-02-06 — Patent grant event (administrative, not an assignment).

• 2006-08-25 / 2010-08-25 / 2014-07-28 — Maintenance fee payments (4th, 8th, 12th year) by the then-current owner.

No post-2005 assignment exists. There is no transfer to any third party, no security agreement, no merger, no license record, and no release in the chain.

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Timeline diagram

timeline
    title Ownership of US 6523935
    2001 : Inventors assign to Hewlett-Packard
         : Application filed 30 Jan 2001
    2002 : Second assignment by Simon Dodd
    2003 : Patent issued 25 Feb 2003
    2004 : Certificate of Correction
    2005 : Assigned to HP Development Company LP
    2021 : Patent term expires

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NPE / troll-pattern signals

1. Shell-entity transfer — not present. The only assignee ever recorded is Hewlett-Packard Development Company, L.P. (reel 015583/0106). No "IP / Patents / Licensing / Holdings / Ventures" entity appears; no registered-agent-service address; no single-purpose Delaware/Texas LLC.

2. Known asserter in the chain — not present. No entity from the Acacia / Marathon / IV / IPNav / Wi-LAN / Conversant / Vringo / Pendrell / Innovatio / Round Rock / Spangenberg lists appears anywhere on this record. The chain is Hewlett-Packard Company → Hewlett-Packard Development Company, L.P. only.

3. Repeat correspondent across the chain — unclear (not assessable). The source used does not surface correspondent-of-record fields. Both genuine transfers were intra-HP and were most likely self-recorded by HP's own IP Administration, which would be an operating-company correspondent rather than an NPE filer — but I will not state that as fact. Unified Patents / RPX / Patent Progress assertion lists: no appearance of this patent or of any correspondent tied to it was found.

4. Cascading transfers — not present. Two transfers over roughly four years (2001 and 2005), both internal, with no chained LLCs, no shared-principal entities, and no sub-24-month throughput.

5. Pre-litigation transfer — not present. No infringement suit naming US 6,523,935 was found. HP did assert sibling family patents — US 6,309,053, 6,398,347, 6,402,279, 6,412,917, 6,234,598 — in ITC Inv. No. 337-TA-723 (complaint filed 2010) and other printhead patents against Memjet and affiliates in the 2016 ITC action (81 FR 43151-adjacent notice, complainant HP Inc., 1501 Page Mill Road). Those are operating-company assertions by HP itself; the '935 patent is not among the asserted patents in either matter, and the 2005 HP→HP Dev Co transfer was five years before the earliest of those filings.

6. Bankruptcy fire-sale — not present. HP never filed for bankruptcy. No Chapter 7/11 sale, no § 363 patent sale, no assignment to a liquidating trustee.

7. Privateering — not present. Nothing left the HP corporate family. There is no operating-company-to-NPE transfer and no SEC-disclosed monetization vehicle covering this patent.

8. Defensive aggregator (anti-NPE) — not present. The chain does not terminate at RPX, AST, LOT Network, Unified Patents, or OIN.

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Verdict

Insufficient data (for NPE purposes — the record affirmatively shows a clean, operating-company-owned chain and no assertion history).

The entire recorded chain consists of (a) the 2001-04-09 inventor-to-HP assignment at reel 011702/0797, (b) the 2002-02-05 instrument at reel 012368/0814 by a non-inventor assignor, and (c) the 2005-01-11 intra-group assignment at reel 015583/0106 moving title from Hewlett-Packard Company to its wholly owned subsidiary Hewlett-Packard Development Company, L.P. All three are normal corporate-housekeeping conveyances; no third party, shell entity, or known asserter ever appears, and no suit naming this patent was found, with the term expiring 2021-01-30. The only open item is the correspondent-of-record field, which I could not verify because the USPTO Assignment Center is not machine-readable to my tooling — that is the one piece of evidence a human reviewer should pull directly.

Verify at: https://assignmentcenter.uspto.gov/ (search "6523935") · https://assignment.uspto.gov/patent/index.html · cross-check https://patents.google.com/patent/US6523935B2/en (Legal Events) · docket check for any assertion in ITC EDIS / PACER (none found for '935).

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Caveats: (1) Reel/frame values above are quoted from the patent record's legal-events table; I did not independently open the USPTO Assignment Center, so treat correspondents as unverified. (2) The Simon Dodd entry at reel 012368/0814 should be checked against the underlying instrument, since he is not a named inventor. (3) Existence of an unrecorded license cannot be ruled out from the assignment record alone.

I'll start by searching for the specific patent number in USPTO databases to confirm I'm working with the correct record, then analyze each cited reference.

The search confirms US 6,523,935 B2 is the correct patent. Now let me verify the bibliographic details of the key cited references, particularly those with priority dates close to the '935 critical date.

Prior-Art Analysis — U.S. Patent No. 6,523,935 B2

1. Confirmation of the Reference Patent

The web search independently corroborates the authoritative text supplied. The target is correctly identified as:

Source: https://patents.google.com/patent/US6523935/en — the Google Patents record, which also surfaced the prosecution citation list reproduced verbatim in the patent text supplied. The search did not return any other patent with this number; results for unrelated numbers (e.g., JP 2004520969A, EP 1309455, US 6,722,759 — all members of the same family/continuation) were discarded as "similar documents," not separate patents.

Two independent claims govern the analysis: claim 1 (printhead with four columnar drop-generator arrays + four columnar FET arrays, monochrome single-pass 1/(4P) dpi) and claim 23 (same architecture plus ≥100 Ω heater resistors, power traces, and FET-based parasitic-resistance compensation). The remaining 40 claims are dependent.

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2. Legal Framework Applied

The '935 patent is pre-AIA (filed 2001-01-30; no earlier domestic priority is claimed). The critical date is therefore 30 January 2001.

• §102(a)/(b): a reference is prior art only if it was published or patented before 2001-01-30 (and, for §102(b), more than one year earlier, i.e., before 2000-01-30).
• §102(e): a U.S. patent granted on an application filed before 2001-01-30 — or a U.S. application published under 35 U.S.C. §122(b), or a PCT application designating the U.S. and published in English — is prior art as of its U.S./international filing date, even if it published after the critical date. Foreign priority does not generally give a §102(e) date (In re Hilmer).
• Anticipation vs. obviousness: a §102 anticipation finding requires one reference to disclose every limitation of the claim as a whole. Almost all of the citations below are, in my assessment, §103 (obviousness) references rather than true anticipatory art. I flag the few genuine §102 candidates explicitly.

⚠️ Important caveat on the EP references: An EP publication is not a U.S. patent and therefore cannot qualify under pre-AIA §102(e). EP 1,145,854 A2 and EP 1,145,856 A1 were both published 2001-10-17 — after the 2001-01-30 critical date — and so are not §102(a)/(b) art against the '935 claims. Any §102 effect must be obtained through their U.S. counterparts filed before the critical date (see entries 8–9). This is a nuance the raw citation list obscures.

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3. Summary Table of Cited Art

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4. Reference-by-Reference Analysis

1. US 6,264,297 B1 — Canon Kabushiki Kaisha

• Full citation: U.S. Patent 6,264,297 B1, "Liquid jet recording using a multi-part drive signal sequentially applied to plural blocks of thermal elements," Canon Kabushiki Kaisha. Listed priority 1979-04-02; granted 2001-07-24.
• Description: Divides thermal recording elements into plural blocks driven in time-division fashion by a multi-part drive signal (primitive/block addressing).
• §102 analysis: Because the grant date (2001-07-24) postdates the critical date, this patent can only be prior art under §102(e), and only if its U.S. application chain was filed before 2001-01-30 — which the unusually early 1979-04-02 date in the record suggests. The 1979 priority date is quoted literally and is atypical; it likely reflects a long continuation lineage.
• Claims potentially affected: The block/primitive drive-signal architecture bears on the "primitive groups" and FET-drive aspects underlying claims 1 and 14–18. Anticipation unlikely; relevance is §103 at best and is weakened by the very different era of the disclosure.

2. US 5,757,400 A — Spectra, Inc.

• Full citation: U.S. Patent 5,757,400 A, "High resolution matrix ink jet arrangement," Spectra, Inc. Priority/filing 1996-02-01; published 1998-05-26.
• §102 basis: Pre-2000-01-30 publication → qualifies under §102(b) (and §102(a)).
• Description: A matrix/multi-axis arrangement of drop generators to achieve high-resolution printing from multiple offset arrays.
• Claims potentially affected: Claim 1 (multiple columnar arrays, offset/nozzle pitch giving effective resolution = 1/(4P)) and claims 4–6 (pitch and drop volume). A genuine §102 candidate for the general arrangement of claim 1, but I could not confirm from the retrieved material that it discloses the specifically recited ≤630 µm spacing between array pairs or the four columnar FET drive circuit arrays; on the present record it reads more as a §103 reference.

3. EP 0 913 255 A2 — Hewlett-Packard Company

• Full citation: EP 0 913 255 A2, "Thermal ink jet print head energy control apparatus and method," Hewlett-Packard Company. Priority 1997-10-28; published 1999-05-06.
• §102 basis: Published before the critical date → §102(a)/(b) (EP publications are effective prior-art publications as of their publication date).
• Description: Controls the energy delivered to thermal ink-jet heater elements (pulse/energy modulation).
• Claims potentially affected: Claims 14–16 (FET circuits/power traces and compensation of parasitic resistance) and claim 23's compensation clause — relevant to the energy-balancing rationale. Best characterized as a §103 reference.

4. EP 0 914 948 A2 — Lexmark International, Inc.

• Full citation: EP 0 914 948 A2, "Ink jet printing apparatus," Lexmark International, Inc. Priority 1997-11-04; published 1999-05-12.
• §102 basis: §102(a)/(b).
• Description: General ink-jet printing apparatus architecture.
• Claims potentially affected: Background/structural context for claims 1, 2, 24. §103 relevance only.

5. US 5,984,455 A — Lexmark International, Inc.

• Full citation: U.S. Patent 5,984,455 A, "Ink jet printing apparatus having primary and secondary nozzles," Lexmark International, Inc. Priority/filing 1997-11-04; published 1999-11-16.
• §102 basis: Published more than one year before the critical date → §102(b).
• Description: Ink jet apparatus with primary and secondary nozzles, i.e., staggered nozzle sets and arranged drop sizes.
• Claims potentially affected: Claims 1 and 4 (staggered columns producing dot spacing finer than nozzle pitch P) and claims 5–6 (drop-volume ranges of 12–19 pL and 3–7 pL). Moderate §102 candidate for the staggering/drop-volume concepts, though the specific four-array, ≤630 µm, 1/(4P) monochrome architecture is not shown.

6. EP 1 004 442 A2 — Hewlett-Packard Company

• Full citation: EP 1 004 442 A2, "Varying the operating energy applied to an inkjet print cartridge based upon the printmode being used," Hewlett-Packard Company. Priority 1998-10-31; published 2000-05-31.
• §102 basis: §102(a) (published 2000-05-31, before 2001-01-30 but not more than one year before).
• Description: Adjusts firing energy per print mode.
• Claims potentially affected: Claims 14–16. §103 reference.

7. EP 1 029 674 A2 — Hewlett-Packard Company

• Full citation: EP 1 029 674 A2, "A system and method for controlling firing operations of an inkjet printhead," Hewlett-Packard Company. Priority 1999-02-19; published 2000-08-23.
• §102 basis: §102(a).
• Description: Controls printhead firing operations (addressing/primitives and energy delivery).
• Claims potentially affected: Claims 14–18 (FET drain-region configuration, on-resistance selection to compensate for power-trace parasitic resistance). §103 reference.

8. EP 1 145 854 A2 — Hewlett-Packard Company

• Full citation: EP 1 145 854 A2, "A printhead substrate having ink drop generators arranged in groups that span both edges of an ink feed channel," Hewlett-Packard Company (applicants include Torgerson and Bakkom — same inventors as the '935 patent). Priority 2000-04-13; published 2001-10-17. U.S. counterpart: US 6,305,774 B1 ("Printhead substrate having an ink jet primitive structure that spans both edges of an ink feed channel"), granted 2001-10-30.
• Description: Four pluralities (61, 62, 63, 64) of ink drop generators; primitives (P1–P6) bifurcated across a double-edge ink feed slot, with outboard and inboard columns.
• §102 analysis (critical): The EP publication date (2001-10-17) is after the '935 critical date, so EP 1 145 854 A2 is not §102(a)/(b) prior art. Its force, if any, derives from the U.S. counterpart application filed 2000-04-13, which would be §102(e) art (US 6,305,774).
• Claims potentially affected: Claims 1–3, 24–25 (four columnar arrays disposed on either side of two ink feed slots, with the ≤800 µm inner-pair separation). Note the common ownership issue discussed in §5 below.

9. EP 1 145 856 A1 — Hewlett-Packard Company

• Full citation: EP 1 145 856 A1, "A printhead having different center to center spacings between rows of nozzles," Hewlett-Packard Company. Priority 2000-04-13; published 2001-10-17. U.S. counterpart: US 6,315,389 B1.
• Description: Printhead with first and second pluralities of drop generators having different center-to-center nozzle spacings, including staggered sets whose combined spacing equals the finer spacing (US 6,315,389 claims 1, 3, 5–6).
• §102 analysis: Same date problem — the EP publication postdates the critical date; usable, if at all, through the U.S. counterpart (US 6,315,389) under §102(e).
• Claims potentially affected: Claim 1 (staggered columns; effective dot spacing), claim 4 (P = 1/300–1/600 inch), claim 26.

10. ⭐ US 6,309,053 B1 — Hewlett-Packard Company (most significant §102(e) reference)

• Full citation: U.S. Patent 6,309,053 B1, "Ink jet printhead having a ground bus that overlaps transistor active regions," Hewlett-Packard Company. Priority/filing 2000-07-24; granted 2001-10-30.
• §102 basis: Filed before the 2001-01-30 critical date → qualifies under §102(e) notwithstanding its later grant.
• Description (verified): A columnar-array printhead in which a ground bus partially overlies the active regions of the FET drive circuits, with the ground bus width varying (narrowing away from the bond pads); explicitly recites FET circuits "configured to compensate for variation in a parasitic resistance presented by said power traces" (US 6,309,053 claims 1–6, 13).
• Claims potentially affected:
  • Claim 8 — "ground busses that overlap active regions of said FET drive circuits" — reads directly on the reference's claim 1 ("ground bus … partially overlying said active regions").
  • Claim 29 — same limitation, via power traces.
  • Claims 14–15 and 35 — FET compensation for power-trace parasitic resistance — reads on the reference's claims 6/13.
  • Claims 17–18 and 37–38 — drain-region configuration / continuously non-contacted drain-finger segments setting on-resistance — the two patents share this identical teaching.
• Important limitation: Because claim 8 (and claims 14–18) are dependent on claim 1/23, US 6,309,053 does not anticipate those claims as a whole — it does not disclose the four-columnar monochrome single-pass 1/(4P) architecture. It anticipates only the subject matter of the dependent limitations, making it a §103 combination reference for validity purposes — but subject to the common-ownership caveat in §5.

11. ⭐ WO 2002/014073 A1 — Hewlett-Packard Company (strongest claim-1 candidate)

• Full citation: International Publication WO 2002/014073 A1, "Ink jet printhead having four staggered rows of nozzles," Hewlett-Packard Company. Priority 2000-08-16; published 2002-02-21.
• §102 basis: Published after the critical date, but as a PCT application designating the U.S. and published in English with an international filing/priority date before 2001-01-30, it is a §102(e) reference (the §102(e) date being the international filing date, not the 2002 publication date).
• Description (verified): A monochrome printhead with a high-density staggered arrangement of ink drop generators along at least three—preferably four—parallel axes, each axis pitch of approximately 1/300 inch, staggered to yield an effective pitch of approximately 1/1200 inch enabling one-pass high-resolution printing (quadruple the single-row resolution).
• Claims potentially affected — genuine §102 candidate:
  • Claim 1 — four side-by-side columnar arrays, ≥100 generators, pitch P, monochrome single-pass resolution of 1/(4P) dpi (1/300 → 1/1200). This reference squarely discloses the resolution/staggering core of claim 1.
  • Claim 4 / claim 26 — P in the range 1/300 to 1/600 inch (expressly taught).
  • Claim 23 — same architecture.
• Residual gap to verify: Whether WO 2002/014073 A1 discloses (a) the ≤630 µm lateral separation between the first/second and third/fourth arrays and the ≤800 µm inner-pair separation, and (b) four columnar arrays of FET drive circuits. If those are absent, claim 1 is not fully anticipated and the reference becomes the primary §103 teaching. I could not confirm those two limitations from the retrieved text and flag them explicitly rather than assume.

Non-patent citation & incorporated-by-reference documents

• International Search Report mailed 2002-04-15 (PCT/US01/28081) — a prosecution document; not prior art.
• US 4,719,477; US 5,469,199; US 5,317,346 (all Hewlett-Packard) — expressly incorporated into the '935 specification. These are §102(b) background art describing printhead/thin-film structure; useful for claim-construction context (e.g., laser-ablated orifice plates, compound ink feed slots) but not anticipatory of the '935 claims.

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5. Consolidated §102 Assessment and the Common-Ownership Issue

Genuine §102 anticipation candidates (single reference, claim as a whole):

All remaining references are §103 (obviousness) art, not anticipatory: they disclose individual features (staggered nozzles, differing drop volumes, energy control, block driving) but not the complete claimed combination.

§103(c) / common-ownership caveat (material): US 6,309,053 B1, and the U.S. counterparts of EP 1 145 854 (US 6,305,774) and EP 1 145 856 (US 6,315,389), appear to be Hewlett-Packard-owned and qualify as prior art only under §102(e). Under pre-AIA 35 U.S.C. §103(c), such §102(e)-only art that was commonly owned with the '935 invention at the time it was made is disqualified as §103 prior art. This substantially weakens the obviousness case built on the HP citations — but it does not remove them from §102 anticipation analysis. Any serious validity opinion must resolve the common-ownership facts for each cited HP application.

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6. Confidence and Limitations

• High confidence: the identity of US 6,523,935 B2, its claim structure, and the citation list (the authoritative full text was supplied and corroborated by the Google Patents page).
• Medium confidence: my §102(e)-vs.-§102(a)/(b) date classifications and the EP-publication analysis — these follow directly from the dates in the record but should be confirmed against the underlying U.S. filing receipts.
• Lower confidence: the specific claim-number mapping for the older, snippet-only references (US 5,757,400; US 5,984,455; US 6,264,297; EP 0 913 255; EP 1 004 442; EP 1 029 674). I retrieved bibliographic data but not full claim text for each, so their "potentially anticipates" designations are provisional and could shift with full-text review.
• Explicitly unresolved: whether WO 2002/014073 A1 discloses the two residual limitations noted in entry 11, and the true §102(e) dates of the Canon and PCT references. I state these as unknowns rather than assume them.

Citation of record for this section: the full-text citation list at https://patents.google.com/patent/US6523935/en, with corroborating retrieval of US 6,309,053 B1 and WO 2002/014073 A1.

I'll verify the key combination references before building the §103 analysis.

Obviousness Analysis Under 35 U.S.C. § 103 — U.S. Patent No. 6,523,935 B2

This section builds on the Prior-Art section above (which established the reference set, the §102 date classifications, and the WP 2002/014073 §102 candidacy). It does not re-list those references' bibliographic data.

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0. Scope, framework, and one correction to an earlier section

Law applied. The '935 patent is pre-AIA (filed 2001-01-30, no earlier domestic priority). Obviousness is therefore judged under pre-AIA § 103(a) using the Graham v. John Deere factors — scope and content of the prior art, differences between the art and the claims, the level of ordinary skill, and secondary considerations — with KSR Int'l v. Teleflex supplying the "expansive and flexible" motivation-to-combine rationales (any need or problem known in the field, predictable variation, known technique to improve a similar device, design incentives). The critical date is 2001-01-30; the § 102(b) bar date is 2000-01-30.

One correction / cross-reference flagged for the record. The earlier PTAB section reported "0 AIA trials on file" for '935 and noted an unverified "document upload that merely reproduced the Torgerson et al. specification as an exhibit." My searches now resolve that loose end: the '935 specification is being deployed as prior art in PTAB petitions. Two public PTAB petition artifacts (petitions 1550157 and 1550313) quote the '935 disclosure as Ex. 1004, cite it by column and line ("Ex. 1004 at 4:65-5:6"; "col. 5 lns 19-23 and Fig. 5"), and map "Torgerson's" columnar arrays 61, FET drive circuit arrays 81, ground bus 181, and primitive select traces 86a–d to the claims of a different, later patent (the petition refers to "the '341 patent," whose recited claims include a 15–18 kHz firing frequency and a ≥10.43 drop-generators/mm² packing density — neither of which appears in '935's claims).

• This does not contradict the earlier finding of zero AIA trials targeting '935; it confirms the other half of it (that '935 was used as an exhibit).
• I could not confirm from the retrieved text which patent number the "341" petition challenges. Treat the petition numbers as verified events and the challenged-patent identity as unverified.
• Analytical significance here: the '935 disclosure is being treated by real petitioners as anticipatory-level prior art against a sibling HP claim set. That is a useful reality check on how a PHOSITA would read the '935 specification — but it says nothing one way or the other about the validity of '935 itself.

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1. Level of ordinary skill in the art (PHOSITA)

A person of ordinary skill would hold a bachelor's degree in electrical engineering, mechanical engineering, or materials science/applied physics (or equivalent), plus 2–4 years' experience designing thin-film thermal inkjet printheads, or a master's degree with 1–2 years. Rationale drawn from the references themselves: the art requires simultaneous competence in (a) fluidic architecture — chambers, nozzles, ink feed slots (US 5,317,346; US 5,757,400); (b) thin-film/semiconductor fabrication — resistor layers, metallization, passivation (WO 2002/014073 A1; US 6,309,053); and (c) drive electronics — FET drive circuits, addressing, primitives, power/ground distribution (US 6,309,053; US 6,264,297). The claim limitations themselves are largely engineering parameters — ohms, Angstroms, micrometers, picoliters — the kind of values a routine designer sets.

Practical consequence: a PHOSITA at this level would read the asserted combination as the straight-line engineering result of two recognized objectives — (i) raise one-pass resolution without lengthening the die, and (ii) keep the die narrow to cut silicon cost.

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2. Independent claim 1 — limitation-by-limitation mapping

Claim-construction note. As flagged earlier, "1/(4P) dpi" reads oddly taken literally. If construed as 4/P dpi, WO 02/014073 maps squarely; if it is truly "one quarter of a dot per inch per pitch," the claim is arguably indefinite under § 112 ¶ 2 and the § 103 analysis collapses into a § 112 fight. This section assumes the 4/P construction (the only one consistent with the specification).

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3. Combination A — the primary obviousness case

WO 2002/014073 A1 (HP) in view of US 5,984,455 (Lexmark) and US 6,309,053 B1 (HP), optionally with US 5,757,400 (Spectra).

What each reference supplies

• WO 02/014073 A1 — the architectural core: a monochrome head with four parallel, staggered axes of thin-film drop generators, axis pitch ~1/300", effective pitch ~1/1200", expressly for one-pass, high-resolution printing. It also supplies the design rationale in the reference's own words: tighter spacing requires smaller drop volume, and the arrangement is chosen to raise effective resolution without more scans.
• US 5,984,455 — four nozzle-plate columns with individual heating elements and a driver circuit applying firing pulses to the heating elements, plus a normal/high-speed mode. It is third-party art available under § 102(b) and therefore not exposed to the § 103(c) problem discussed below.
• US 6,309,053 B1 — columnar FET circuits adjacent a columnar drop-generator array, a ground bus partially overlying the FET active regions, and FET circuits "configured to compensate for variation in a parasitic resistance presented by said power traces." This is the single best reference for claim 1's fourth element and for nearly all of claim 23's added matter.
• US 5,757,400 — matrix/hexagonal arrangement of ≥3 rows achieving ≥1200 lines/inch, and an express drop-volume-vs-resolution table (25 pL @ 600 dpi; 4 pL @ 1200 dpi; 0.5 pL @ 2400 dpi), plus the throughput rationale (smaller drops → higher frequency → greater speed).

Motivation to combine (KSR rationales, applied)

1. Same field, same problem. All four references address scanning inkjet printheads and the same recognized problem: getting higher resolution/speed out of an array whose native row pitch is coarse. WO 02/014073 and US 5,757,400 state the problem and the staggering solution in almost identical terms; combining them requires no shift in field.
2. Predictable result. Interleaving rows to multiply effective resolution is explicitly described as producing a fractional effective pitch — the outcome is arithmetic, not speculative.
3. Known technique to improve a similar device. Word-for-word, this is the KSR "use of a known technique to improve a similar device in the same way" rationale.
4. Design incentive / market pressure. The references supply the incentive themselves: compactness ("for compactness of the ink jet head…"), low cost ("ink jet arrays can be conveniently manufactured at relatively low cost"), and the '935 specification's own stated goal of a narrow, less costly substrate. A PHOSITA would integrate the FET drive circuits into the die (as '053 does) precisely to service four closely packed columns without ballooning bond-pad and die width.
5. Drop-volume selection. WO 02/014073 states the drop-volume constraint; US 5,757,400 quantifies it. Claims 5–6 (12–19 pL / 3–7 pL) are therefore ordinary consequences of a known tradeoff — claim 6's 3–7 pL band brackets the Spectra 4 pL @ 1200 dpi value exactly.

The two real gaps are (a) the ≤630 µm pair spacings and (b) the ≥100 generators per column. Neither is expressly recited in the retrieved text of the references. Both are bridgeable but only through an "obvious design choice / result-effective variable" argument (see §8) — they are not witnessed in the art on the present record. That is the honest weakness of Combination A on claim 1 as a whole.

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4. Combination B — the § 103(c)-clean fallback

US 5,757,400 + US 5,984,455 + US 6,264,297 B1 (Canon), with EP 1 029 674 A2 / EP 0 913 255 A2 / EP 1 004 442 A2 (HP) for the energy/drive aspects.

This combination survives the common-ownership obstacle in § 7 because it contains no HP § 102(e)-only reference: Spectra and Lexmark are third parties (and § 102(b)/(a) art); the Canon patent is third-party § 102(e) art; the three HP EP publications qualify under § 102(a)/(b) as printed publications dated before the critical date, so they are not "prior art only under subsection (e)."

What it reaches: claim 1's four-column architecture, monochrome single-pass 4/P resolution, resolution range (claim 4), drop volumes (claims 5–6), and the general "FET drive circuits adjacent the columns" element. What it does not reach: the four columnar FET arrays (§ 6.309.053-dependent), ground-bus overlap (claims 8/29), and the parasitic-resistance compensation of claims 14–18/35–38 and claim 23. It also does not reach claims 2–3/24–25 (dual-edge slot feeding) — for those, the only pre-critical-date § 102(b) HP art in the record is US 5,317,346 ("Compound ink feed slot," 1994), which the '935 specification itself cites as the slot-feed background.

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5. Independent claim 23 — the added matter

Claim 23 = claim 1's architecture plus (i) heater resistors ≥100 Ω, (ii) power traces, (iii) FET circuits configured to compensate for parasitic-resistance variation.

Combination C — Combination A (or B) in further view of US 6,309,053 B1 and EP 1 029 674 A2 (optionally EP 0 913 255 A2 / EP 1 004 442 A2).

• US 6,309,053 claims 6, 13, and 17 recite FET circuits "configured to compensate for variation in a parasitic resistance presented by said power traces," and its disclosure describes the same continuously-non-contacted drain-finger technique the '935 specification uses. For elements (ii) and (iii), this is a near-verbatim disclosure — indeed it is the same teaching, in the same words, as the '935 specification.
• EP 1 029 674 (HP, published 2000-08-23 — § 102(a) art) addresses controlling firing operations and energy delivery; EP 0 913 255 (HP, 1999-05-06) addresses thermal inkjet head energy control; EP 1 004 442 (HP, 2000-05-31) varies firing energy by print mode. Together they supply the motivation: if a printhead is to fire four closely packed columns uniformly, the energy delivered to each heater must be uniform, and the known way to do that is to tailor the drive element to the trace resistance it sees.
• Element (i) — ≥100 Ω heaters: no single reference in the record expressly recites it. The motivation is nonetheless plainly available to a PHOSITA: higher heater resistance means lower current for the same power, which permits a smaller drive FET and therefore a narrower die — the '935 specification admits exactly this ("having a heater resistor resistance of at least 100 ohms allows the FET circuits to be made smaller"). Absent a showing of criticality for the 100-ohm floor, this reads as routine optimization of a known design tradeoff — vulnerable under KSR, but not squarely disclosed.

Summary: claim 23 as a whole is obvious only if US 6,309,053 is available. That single reference carries elements (ii) and (iii) almost entirely, and it is subject to the disqualification discussed next.

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6. Dependent claims — vulnerability table

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7. Countervailing considerations — where the obviousness case is actually weak

(a) § 103(c) common ownership — the single biggest obstacle. Claim 1's fourth element, claim 8/29, claims 14–18/35–38, and essentially all of claim 23's added matter are supplied by HP § 102(e)-only art (US 6,309,053; the US counterparts of EP 1 145 854 and EP 1 145 856; and WO 02/014073 if its § 102(e) date is the 2000-08-16 priority rather than its 2001 international filing date). Because the '935 application was filed after November 29, 1999, pre-AIA § 103(c)(1) applies: subject matter qualifying as prior art only under § 102(e), (f), or (g), and commonly owned with the claimed invention when the invention was made, "shall not preclude patentability under this section." All of the above were HP-owned at the relevant time. If that is confirmed (verify against each reference's assignment records and the '935 inventive entity), the strongest obviousness combinations lose their teeth as § 103 art.

(b) The "by another" problem compounds it. US 6,309,053 is, by its own text and by the near-identical specification language (ground bus overlap, continuously non-contacted drain fingers, "compensate for variation in a parasitic resistance"), the direct sibling of the '935 disclosure. If the inventive entity is not "another," '053 is not § 102(e) art at all. Either way — same entity or common ownership — '053 should not carry a § 103 challenge.

(c) Teaching away / change of principle of operation. US 5,984,455's four columns exist for nozzle redundancy, not resolution: its primary and secondary nozzles are deliberately in horizontal alignment (one large and one small nozzle per vertical position) so a failed nozzle's data can be printed by its partner. Staggering those columns along the media axis to quadruple resolution would defeat the alignment on which the Lexmark redundancy scheme depends. That is a genuine "change in the principle of operation" argument. Similarly, US 5,757,400 teaches that its matrix spacing is dictated by the need for ink supply ducts between adjacent rows ("permits convenient access between adjacent columns… for ink supply channels of adequate size") — an express spatial constraint that arguably discourages very tight column pairs (though the '935 patent's slot-fed design avoids the duct problem, which weakens the argument).

(d) Secondary considerations. No nexus evidence is in the record. HP's commercial success with the 2000–2005 inkjet pens is real (the sibling patents supported the domestic-industry finding in ITC Inv. No. 337-TA-723), but there is no evidence tying that success to the specific claimed combination rather than to HP's overall cartridge platform, and the earlier assignment section already found no NPE/assertion history for '935 itself. Note also the double edge: EP 1 145 854/856 and WO 02/014073 show multiple parties in the field stating the same need (compact, high-density, high-resolution heads), which supports rather than rebuts obviousness.

(e) The § 325(d) overlay. Every reference discussed here was before the examiner. That is not a § 103 defense, but it is a substantial discretionary-denial lever against any petitioner re-packaging the same art, and it should shape how any challenge leads with genuinely new art.

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8. Bottom line

1. Independent claim 1 is the most exposed claim. The combination WO 02/014073 A1 + US 5,984,455 + US 5,757,400 (Optionally + US 6,309,053) discloses every element except the ≤630 µm pair spacings and the ≥100-per-column count. Those two gaps are bridgeable only by an "obvious design choice / result-effective variable" argument, and only if the references are available.
2. Independent claim 23 is obvious if and only if US 6,309,053 remains available, because that reference alone supplies the power-trace/FET-compensation limitation in the same words. § 103(c) or the "by another" defect likely removes it — making claim 23 the strongest of the two independent claims for a patent owner, not the weakest.
3. Most vulnerable dependents: claims 4/26, 6/28, 8/29, 14–18/35–38 — each has an express or near-express reference disclosure.
4. Most robust dependents: claims 2–3/24–25 (dual-edge slot feeding plus the ≤800 µm inner spacing) and 21–22/41–42 (die aspect ratio and width), which rest on numerical design choices with no express art and no criticality showing either way.
5. Strategic read: the obviousness case here is not built on a PAIR/third-party roadmap; it is built almost entirely on HP's own sibling disclosures, and that is precisely why § 103(c) is likely dispositive. A validity opinion should resolve (i) the '935 inventive entity, (ii) each HP reference's common ownership as of the invention date, and (iii) each reference's true § 102(e) date — before investing in claim charts.

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Sources

• https://patents.google.com/patent/[US6523935](/patent/US6523935)/en (authoritative full text; claim and spec citations)
• https://patents.google.com/patent/WO2002014073A1/en (four staggered axes; 1/300" → 1/1200"; one-pass monochrome; drop-volume-vs-spacing teaching)
• https://patents.justia.com/patent/[6309053](/patent/6309053) and https://companyprofiles.justatic.com/patent/6309053 (claims 1, 6, 13, 17 — ground bus overlying active regions; FET compensation for power-trace parasitic resistance)
• https://patents.google.com/patent/US5757400 (matrix arrangement ≥3 rows/columns; 4 pL @ 1200 lines/inch; 25 pL @ 600)
• https://patents.google.com/patent/US5984455 (four nozzle columns; heating elements; driver circuit; normal/high-speed modes; primary/secondary aligned nozzles)
• https://companyprofiles.justatic.com/patent/[6315389](/patent/6315389) (US 6,315,389 — US counterpart of EP 1 145 856; staggered pluralities with combined spacing)
• https://www.freepatentsonline.com/[6585352](/patent/6585352).html (US 6,585,352, HP family context — high-resistance resistors, staggered rows, ~1200 dpi combined; flagged as family context, not relied on as § 103 art)
• PTAB petition artifacts quoting the '935 specification as Ex. 1004: https://ptacts.uspto.gov/ptacts/public-informations/petitions/1550157/... and https://ptacts.uspto.gov/ptacts/public-informations/petitions/1550313/...

Confidence

• High: the element-by-element mappings for WO 02/014073, US 6,309,053, US 5,757,400 and US 5,984,455; the § 103(c) framework and its application to HP-owned § 102(e)-only art.
• Medium: the § 103(c) outcome — it turns on facts I could not fully verify (common ownership at the invention date; inventive entity of US 6,309,053; the true § 102(e) date of WO 02/014073, including whether its 2000-08-16 priority is a U.S. application).
• Low / explicitly unverified: whether WO 02/014073 or US 5,984,455 expressly recites ≥100 generators per column or ≤630 µm pair spacings (I could not confirm, and I have not assumed it); the identity of the patent challenged in the two PTAB petitions that use '935 as an exhibit; and the status of US 6,585,352 as potential § 102(e) art (its priority date relative to 2001-01-30 is unverified, so I did not rely on it).