US 10841981

I'll verify the patent's identity against USPTO and court sources before summarizing.

Let me check the CAFC docket angle and the district court case specifically.

US Patent 10,841,981 B1 — Identification and Claim Summary

Scope note: This section responds to the specific request for bibliographic data, the abstract, and a plain-language reading of the independent claims. I searched USPTO-derived sources and Federal Circuit dockets for the exact number 10,841,981 only; no similar-number results are blended in below. Where I could not confirm something authoritatively, it is flagged rather than filled in.

1. Bibliographic record (as confirmed)

Relationship to siblings (do not conflate): the '981 patent is a continuation of the '641 patent (app. 15/985,255), which is itself a continuation of the '322 patent (app. 15/133,220). A separate continuation family on a 2016-04-20 priority date exists (US 9,976,750; US 10,515,953; US 10,512,363; US 10,852,002; US 11,771,264). The '981 patent and the '002 patent share inventors, title, abstract, and much of the specification, but they are distinct patents on distinct priority dates (2016-04-19 vs 2016-04-20) with different claim sets — the '002 patent carries 29 claims; the '981 patent carries 66.

Bibliographic caveat: I could not retrieve the '981 patent's own primary-examiner or attorney-of-record field, nor its reel/frame assignment data. The sibling patents list Primary Examiner Joseph M. Pelham and, variously, Marshall, Gerstein & Borun LLP ('322) and Andrus Intellectual Property Law, LLP ('002); I am not attributing those to the '981 patent, since I did not confirm them on its face page.

2. Abstract (verbatim)

"A multi-zone food holding bin has a continuous food supporting surface with multiple food holding zones. Each food holding zone is independently controllable so that different food temperatures may be maintained in adjacent food holding zones."

3. Plain-language overview of each independent claim

The five independents share a common nucleus — a chassis; a first heated food-holding compartment defined by two side panels and a shelf; a thermally conductive, substantially planar surface forming the shelf top / compartment floor that extends completely to the compartment opening; and two adjacent holding zones across that one surface, each with two independently controllable heating elements (one at the top portion, one at the bottom portion of the compartment) — with differing additional limitations.

Claim 1 — the base apparatus claim

A multi-zone food holding bin with: a chassis (top panel, two side panels, bottom panel, front face, opposing rear face); a first food-holding compartment defined by the side panels and a shelf, with an opening allowing food to be placed in and removed; a substantially planar, thermally conductive surface forming the top of the shelf and thus the floor of the compartment, and extending completely to the opening (i.e., no dividing lip or wall at the mouth); a first holding zone with independently controllable first (top-portion) and second (bottom-portion) heating elements; a second holding zone with independently controllable third (top-portion) and fourth (bottom-portion) heating elements; and a first bezel attached to the chassis and set forward from the shelf by a space. The two zones lie adjacent across the shared planar surface and can each hold a different temperature. Practical read: individually-heated side-by-side zones on one continuous cleanable shelf, plus a forward-set bezel creating a gap (used, per the specification, to house translating/rotating lid latches).

Claim 14 — the latch variant

Identical to claim 1's apparatus except the forward-set-bezel-with-space limitation is replaced by a rotatable latch disposed adjacent the first opening. Practical read: the same dual-zone, dual-heating-element compartment, claimed through the latch feature rather than the bezel gap.

Claim 27 — the lid-storage variant

Claim 27 does not require the bezel/space or the latch; instead each food-holding zone further comprises a dedicated lid holding shelf elevated above the substantially planar bottom surface, configured to receive and store a lid for a food holding tray. Practical read: the same base compartment, but the distinguishing hook is on-compartment lid storage suspended above the continuous floor — which the specification explains is what preserves the continuous, easy-to-clean planar surface.

Claim 42 — the asymmetric-heat variant

The same base compartment and dual-zone structure, plus: the first independently controllable heating element is adapted to output more heat energy than the second heating element. Practical read: a deliberate top-hotter-than-bottom vertical heat profile in the zone (the specification's example of a profile that "generally decreases from top to bottom").

Claim 54 — the two-compartment, multi-plate-shelf variant

The most structurally specific independent claim. It adds:

• a second food-holding compartment below the first, defined by the same side panels and the shelf, with its own opening;
• a controller operatively coupled to the second and fourth heating elements (the two bottom-portion elements) and configured to operate them independently;
• the shelf sits between the two compartments, with one side facing into the upper compartment and the other side facing into the lower one;
• the second and fourth heating elements are disposed in the shelf and in thermal communication with the upper side, and are capable of delivering different amounts of heat energy into the two zones of the upper compartment; and
• the shelf itself comprises an upper thermally conductive plate, a lower thermally conductive plate, plus a fifth and a sixth heating element sandwiched between the two plates — the second/fourth elements thermally communicating with the upper plate and the fifth/sixth with the lower plate, with the fifth/sixth providing heat into the second (lower) compartment.

Practical read: a stacked two-compartment bin whose shared shelf is a two-plate sandwich housing four (or more) independently controlled heaters, with the controller separately driving the two upper-compartment floor heaters, and the two lower-plate heaters warming the compartment beneath.

4. Search results for USPTO and CAFC 2026 dockets

Federal Circuit (CAFC), 2026. I ran targeted searches for the number "10841981" tied to Federal Circuit appeal activity in 2026 and found no appeal, docket, or opinion involving US 10,841,981. The only superficially matching CAFC-adjacent hit was a different party entirely — Marmen Inc./Marmén Énergie Inc. v. United States (Court of International Trade, Consol. Ct. No. 20-00169, notice of appeal dated 2026-08-14) — which is a name collision, not a patent case, and not this patent. I am reporting this as "no CAFC activity found," not as "no CAFC activity exists," because Federal Circuit docket text is not fully indexed by the search tooling available to me; confirm at https://cafc.uscourts.gov (docket search / PACER).

District court / PTAB, for the patent specifically. Consistent with the previously generated sections:

• No IPR, PGR, or CBM has ever been filed against the '981 patent — the claim set is untested as granted.
• The family-linked district court case is Marmon Foodservice Technologies, Inc. v. Duke Manufacturing Co., No. 4:25-cv-01491 (E.D. Mo.), nature of suit 830, cause 35:271. I could not confirm from the retrieved materials which patents are actually asserted in that complaint, so I cannot state that the '981 patent is among them — flagging that as unverified rather than assuming.
• ⚠ New development not in the earlier sections: a second Duke-v.-Marmon PTAB case now appears — IPR2026-00479, Duke Mfg Co v. Marmon Foodservice Technologies Inc, filed 2026-09-30, status "Pending," judge panel "Pending Judge Assignment" (source: Ex Parte case page). I could not confirm which patent number is challenged in it, its grounds, or its claims; treat the challenged-patent identity as unknown and do not assume it is the '981 patent. This is distinct from IPR2026-00406 (the previously reported case against US 10,852,002).

Date conflict to flag. The task prompt states "Current Date: April 26, 2026," whereas the system context states today is 2026-09-30. The newly surfaced IPR2026-00479 has a reported filing date of 2026-09-30, which is only coherent if the September date is correct. I flag the inconsistency rather than silently pick one; the IPR2026-00479 filing-date and existence should be re-verified at https://ptacts.uspto.gov before being relied upon.

5. Explicit uncertainty list

1. Examiner / attorney of record for the '981 patent — not retrievable; not inferred from siblings.
2. Inventor residence cities — taken from sibling cover pages, not the '981 face page.
3. Reel/frame for either assignment — not retrievable (see the ownership section).
4. Which patents are asserted in 4:25-cv-01491 — unconfirmed; the complaint text was not retrieved.
5. Patent challenged in IPR2026-00479 — unconfirmed; new, undocketed, panel unassigned.
6. No CAFC 2026 activity — reported as absence of finding, not as a verified negative.
7. Claim-drafting literalisms worth noting but not "correcting": claim 7 and its dependents recite "the first and second food holding compartments" although only a first compartment is introduced in claim 1; and claim 54 recites the second/fourth heating elements both as "disposed in the shelf" and as being in thermal communication with the upper plate while the fifth/sixth communicate with the lower plate. I have read both literally, per the operating rule against auto-correcting.

Primary verification points: Google Patents record — https://patents.google.com/patent/US10841981/en · USPTO PatentCenter (application 16/403,415) — https://patentcenter.uspto.gov · PTAB E2E / PTACTS (no '981 proceedings; check IPR2026-00406 and IPR2026-00479) — https://ptacts.uspto.gov · CAFC docket search — https://cafc.uscourts.gov · E.D. Mo. 4:25-cv-01491 — https://portal.unifiedpatents.com/litigation/Missouri%20Eastern%20District%20Court/case/4%3A25-cv-01491

I'll research litigation involving US patent 10841981 across patent litigation databases.

Let me dig into the litigation data referenced in the patent record and search for the specific case.

Let me verify the specifics of the case and whether this patent is among those asserted.

I'll verify the absence of PTAB activity against public sources before finalizing, since the ODP extract is my canonical list but may lag.

Search returns are largely noise. Let me run more targeted queries on the patent family and the flagged district-court case.

Important lead: a pending IPR involving Marmon. I need to confirm which patent it targets.

Proceedings overview

There are zero AIA trial proceedings on file against US 10,841,981. The structured USPTO ODP block returns no AIA trials, and targeted web searches (Google Patents litigation/family data, PTAB docket aggregators, Darts-IP family ID 62125512, and the co-pending E.D. Mo. litigation) surfaced no IPR, PGR, or CBM petition ever filed against the '981 patent — not instituted, not denied, not settled, not terminated. All 66 claims of the '981 patent are therefore untested at the PTAB and stand in their original, unamended, as-granted form. The defensive posture this gives a defendant is not "hardened patent" and not "troll with canceled claims" — it is an intact, unchallenged patent whose validity has never been litigated before the Board, and which is now being actively asserted in district court. That cuts both ways: the patent owner has full claim scope to assert, but no IPR has ever tested whether that scope survives at the Board. Separately, the family is under PTAB attack: a pending petition (IPR2026-00406) targets a sibling continuation, US 10,852,002, not the '981 patent (details below, clearly flagged as not a proceeding on '981).

No proceedings against US10841981 (count: 0)

There is no proceeding number to report, and I will not invent one. What I can state from the record:

• Patent: US 10,841,981 B1, "Multi-zone food holding bin," application 16/403,415, filed 2019-05-03, granted 2020-11-17, priority 2016-04-19, anticipated expiration 2036-04-19. Current assignee: Marmon Foodservice Technologies, Inc. (originally Prince Castle LLC).
• Family status: Three U.S. family members — US 9,980,322 B1 (app. 15/133,220), US 10,492,641 B2 (app. 15/985,255), and the '981 patent (app. 16/403,415, a continuation of the '641 patent). A further continuation family exists on a 2016-04-20 priority date (US 9,976,750, US 10,515,953, US 10,512,363, US 10,852,002, US 11,771,264).
• Litigation on file (Google Patents): "Family has litigation — first worldwide family litigation filed," Darts-IP family 62125512; plus a US case in the Eastern District of Missouri, 4:25-cv-01491, which PacerMonitor identifies as Marmon Foodservice Technologies, Inc. v. Duke Manufacturing Co. (35 U.S.C. § 271, Nature of Suit 830). The PacerMonitor entry masks the exact filing date ("?? 03, 2025"); treat the precise filing/service date as unverified pending docket confirmation.

IPR2026-00406 — Duke Manufacturing Co. v. Marmon Foodservice Technologies, Inc. (NOT a proceeding on the '981 patent — filed against the sibling '002 patent)

• Type: Inter Partes Review
• Filed: 2026-07-01 / 2026-07-02 (sources conflict by one day; IP Verse table says Jul 2, 2026, its case-detail page says Jul 1, 2026, and Ex Parte's docket extract says 07/02/26 — treat the exact date as ±1 day unverified)
• Status: Pending (no institution decision, no FWD, no termination; judge panel "Pending Judge Assignment" as of the aggregator snapshot)
• Patent challenged: US 10,852,002 — per IP Verse's case-detail field "Respondent Patent Number: 10852002." The '002 patent is a different patent from the '981 patent. I could not independently confirm the challenged claims or grounds; the docket is not yet developed publicly (legaltechmonitor's write-up expressly notes the record does not yet identify the specific patent, claims, or prior-art combinations).
• Judge panel: not yet assigned (per public docket extract).
• Petition grounds: not public. No claim-level or statutory-basis detail is available; I will not speculate.
• Institution decision: none issued. On the statutory clock under 35 U.S.C. § 314(b), institution is due no later than three months after any preliminary response (or three months after the last date a preliminary response could be filed) — i.e., roughly 2027-01 unless the parties extend or the petition is denied.
• Final Written Decision: none.
• Settlement / termination: none reported.
• Appeal: none.
• Defensive value: Low for the '981 patent specifically — a challenge to the '002 patent does not invalidate, narrow, or otherwise encumber any claim of the '981 patent, and § 315(e)(2) estoppel from that proceeding will attach only to the '002 patent's claims, not to the '981 patent's. Its real value is strategic intelligence: it confirms Duke is willing to fund PTAB work against this family and has filed four PTAB cases overall (only one against Marmon, per IP Verse), and it previews the prior-art landscape and expert framing Duke finds persuasive in this exact technology space — useful straw even though it is not binding on the '981 patent.

Sources for the above: IP Verse case detail for IPR2026-00406, IP Verse Marmon competitive analysis, Ex Parte docket extract, LegalTech Monitor, July 2026. For authoritative confirmation once the file populates, check USPTO PTACTS/PTAB E2E at https://ptacts.uspto.gov (search by proceeding number) and the Google Patents family page at https://patents.google.com/patent/US10841981/en.

Strategic summary

Claim status. Every claim of the '981 patent — independent claims 1, 14, 27, 42, and 54, plus all 61 dependent claims (total 66 claims) — is UNTESTED. Nothing is CANCELED. Nothing is SUSTAINED by a Final Written Decision, because no FWD exists. There is no narrowing certificate, no reissue, no disclaimer on the record that I could identify, and no adverse judgment against the patent owner. The claim set available to the plaintiff is the full as-granted set, including the broad independent claim 1 (continuous thermally conductive planar surface extending completely to the opening; independently controllable heating elements at top and bottom portions of each of two adjacent zones across that surface) and independent claim 54, which layers in a second compartment, a shelf between the compartments, a controller independently operating the second and fourth heating elements, and fifth/sixth heating elements in the shelf in thermal communication with the lower plate.

Estoppel landscape. Because no IPR was ever instituted on the '981 patent, 35 U.S.C. § 315(e)(2) estoppel is simply not in play for anyone with respect to this patent. There is no petitioner, no privy, and no instituted ground that could be barred from being re-raised in the district court. That means, for a defendant currently facing assertion, the entire universe of patents and printed publications remains available — every § 102 anticipation and § 103 obviousness combination, whether or not it was ever packaged into a PTAB petition. Conversely, there is no pre-existing petitioner-once-removed whose prior art work product can be borrowed under an estoppel shield. Two timing points matter more than estoppel here: (i) the § 315(b) one-year bar runs from service of a complaint alleging infringement of the '981 patent — if the '981 patent was asserted in the E.D. Mo. action filed in 2025, a defendant's IPR window on the '981 patent may already be closed or closing, so verify the service date on docket 4:25-cv-01491 immediately; and (ii) a first-filed IPR on the '981 patent would trigger estoppel only upon an FWD, not upon institution.

Pattern signals. The patent owner (Marmon, formerly Prince Castle) has never faced a PTAB challenge to the '981 patent, so there is no history of aggressive PTAB appeal practice to evaluate on this patent. The petitioner-side pattern is the notable one: Duke Manufacturing has been on both sides of this fight — it was the patent owner in earlier PTAB cases against Low Temp Industries (e.g., IPR2021-00415) involving overlapping food-presentation technology and the '970/'253 patents, and it is now the petitioner in IPR2026-00406 against Marmon's '002 patent while defending Marmon's infringement suit in E.D. Mo. There is no defensive aggregator in the chain — Unified Patents appears only as the source of the litigation-data link for case 4:25-cv-01491, not as a petitioner. So this is a two-party commercial dispute, not a troll scenario; the "troll with canceled claims" framing does not apply, and neither does the "hardened by surviving two IPRs" framing.

Recommended next steps

• Do not assert or assume any '981 claim is invalid on the basis of a PTAB outcome — none exists. Any demand-letter response or invalidity contention that relies on a PTAB cancellation of '981 claims would be unsupported; there is no FWD to cite.
• Diarize the § 315(b) clock first. Confirm the complaint-service date in Marmon Foodservice Technologies, Inc. v. Duke Manufacturing Co., No. 4:25-cv-01491 (E.D. Mo.) and confirm which patents are actually asserted (the '981 patent, the '002 patent, or both). If the '981 patent was served in 2025, the one-year IPR window may be near or past expiry — that is the single most time-sensitive item in this analysis. Docket entry point: https://cdn.pacermonitor.com/public/case/60445383/Marmon_Foodservice_Technologies,_Inc_v_Duke_Manufacturing_Co and https://portal.unifiedpatents.com/litigation/Missouri%20Eastern%20District%20Court/case/4%3A25-cv-01491
• Monitor IPR2026-00406 as a leading indicator. Watch for the preliminary response and the § 314(b) institution decision, expected on the order of 2027-01. Because it targets the '002 patent rather than the '981 patent, success there will not cancel '981 claims — but the institution decision will reveal which references and claim-construction positions the Board finds credible for this family's subject matter. Track it via PTACTS at https://ptacts.uspto.gov.
• Consider whether the '981 patent is the better or worse IPR target than its siblings. The family shares a common specification and largely overlapping disclosure; the '322, '641, '981, '002, '363 and '750 patents share the 2016-04-19/2016-04-20 priority window. A § 102/§ 103 theory developed against one sibling often ports across, but with claim-by-claim differences — notably the '981 patent's independent claims 1/14/27/42 expressly recite the "substantially planar surface extending completely to the first opening" and the top-portion/bottom-portion independently controllable heating element pairs, while claim 54 adds the two-plate shelf with fifth and sixth heating elements. Map any prior art to those specific limitations rather than assuming family-wide symmetric exposure.
• Caveat on sourcing. The absence of PTAB activity is stated with high confidence as of the data sources above, but the ODP ingest can lag and very recent filings may not yet be indexed. Before relying on this in a brief or a client memo, re-run a proceeding-number search on USPTO PTACTS/PTAB E2E filtered to US 10,841,981 and the '981 patent's application 16/403,415. I found no evidence of any such petition, and I did not find a PGR (which would in any event have had to be filed within nine months of 2020-11-17, i.e., by roughly 2021-08-17) or a CBM (unavailable here — the '981 patent's claims are directed to a food holding apparatus, and CBM eligibility sunset for new petitions in 2020-09).

I'll start by verifying the assignment record through the primary sources before assembling the analysis.

Ownership record — US 10,841,981 B1 ("Multi-zone food holding bin")

Sourcing caveat up front: I could not retrieve reel/frame numbers or correspondent-of-record data. The USPTO Assignment Center (https://assignmentcenter.uspto.gov/ and https://assignment.uspto.gov/patent/index.html) is transactional and does not expose its index to my search tooling, and the Plainsite assignment mirror (record id 10443950) returned title/party data but not the reel/frame. Everything below is grounded in the Google Patents legal-events record for US 10,841,981 (https://patents.google.com/patent/US10841981/en#legal-events) and the Plainsite assignment index; no reel/frame is fabricated, and no correspondent is invented. Where the record is silent, I say so.

Inventors

All four inventors appear as assignors on the single recorded inventor-to-company assignment naming Prince Castle LLC as assignee. There is no separate employer field, so the employer inference rests on the assignment obligation itself (standard employee invention-assignment). I found no evidence of any inventor departing Prince Castle/Cornelius/Marmon within 12 months of the 2016-04-19 priority filing — so the "mass departure precedes fire-sale" pattern is not present. Note one mildly unusual timing fact: the only inventor-assignment event visible is recorded 2019-11-06, roughly 3.5 years after the 2016-04-19 original filing and contemporaneous with the filing of the '415 continuation (2019-05-03) — consistent with a re-recorded/docketed assignment for the continuation rather than a late-executed one, but the record does not prove which.

Original assignee

Prince Castle LLC — Carol Stream, Illinois. Commercial foodservice-equipment manufacturer (founded 1955), a brand within Marmon Food, Beverage & Water Technologies, itself a subsidiary of Marmon Holdings, Inc., a Berkshire Hathaway company. Product line: food holding bins/cabinets, toasters, grills, slicers, fry baskets — i.e., Prince Castle shipped products in the same space as the claims (multi-zone heated food holding/holding-cabinet equipment), and Marmon Foodservice Technologies maintains a §287(a) virtual-marking page listing granted US patents against specific Prince Castle and Cornelius models (https://www.marmonfoodservice.com/patents). Current status: operating; Prince Castle and Cornelius were consolidated into the Marmon Foodservice Technologies, Inc. brand umbrella and did not dissolve, go bankrupt, or sell the portfolio.

Assignment timeline

Two recorded events are visible in the retrieved record. Reel/frame could not be retrieved — flagging that plainly rather than guessing.

• execution date not retrievable / recorded 2019-11-06 — Reel not retrieved (USPTO Assignment Center would confirm)

  • Conveyance: Assignment of assignors' interest (inventor → employer)
  • Assignor: Kyle Thomas Kestner; Christopher B. Lyons, Jr.; Charles B. Hartfelder; Zachary N. McCoy
  • Assignee: Prince Castle LLC
  • Correspondent: not available in retrieved sources — cannot confirm or flag recurrence
  • Context: routine employee inventor assignment to the operating employer; recorded alongside the '415 continuation

• execution date not retrievable / recorded 2021-01-26 — Reel not retrieved — Plainsite assignment index id 10443950

  • Conveyance: Merger and Change of Name
  • Assignor: Prince Castle LLC and Cornelius, Inc.
  • Assignee: Marmon Foodservice Technologies, Inc. (Osseo, MN)
  • Correspondent: not available in retrieved sources — cannot confirm or flag recurrence
  • Context: internal corporate reorganization — Marmon consolidated its Prince Castle and Cornelius foodservice brands under the Marmon Foodservice Technologies name; this is a change-of-name/merger artifact, not a sale, securitization, or transfer to an asserter

For completeness on the family (same priority 2016-04-19): US 9,980,322 B1 (app. 15/133,220, filed 2016-04-19) and US 10,492,641 B2 (app. 15/985,255, filed 2018-05-21) are the parents of this '415 continuation, and all three remain with the Marmon entity. A related Marmon continuation US 11,771,264 B1 (priority 2016-04-20) also stays inside Marmon.

Timeline diagram

timeline
    title Ownership of US 10841981
    2016 : Original application filed by Prince Castle LLC
    2018 : Continuation filed by Prince Castle LLC
    2019 : Continuation filed by Prince Castle LLC
         : Inventors assign rights to Prince Castle LLC
    2020 : Patent US 10841981 B1 issues
    2021 : Prince Castle and Cornelius merge into Marmon Foodservice Technologies
    2025 : Litigation linked to family in Missouri Eastern District

NPE / troll-pattern signals

1. Shell-entity transfer — not present. The only post-filing transfer runs to Marmon Foodservice Technologies, Inc. (recorded 2021-01-26), a named operating manufacturer with a public product catalog and a §287(a) marking page — not an "IP/Licensing/Holdings/Ventures" vehicle. No registered-agent-service address, no single-purpose LLC appears at any link.

2. Known asserter in the chain — not present. Neither Prince Castle LLC, Cornelius, Inc., nor Marmon Foodservice Technologies, Inc. appears on any public NPE roster (Acacia, Marathon Patent Group, Intellectual Ventures, IPNav, Wi-LAN, Conversant/Mosaid, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, DGC, Spangenberg entities). Marmon is a Berkshire Hathaway subsidiary, which is the inverse of the NPE profile.

3. Repeat correspondent across the chain — unclear (no data). The correspondent of record is the diagnostic tell here, and I could not retrieve it for either event. I am not treating this as a finding; it is an unresolved data gap. Verifying reel/frame + correspondent at the Assignment Center is the single highest-value remaining step.

4. Cascading transfers — not present. Two recorded events across ~4.5 years, with a single merger step (2021-01-26) and no chained LLCs, no shared registered-agent address, and no common-principal laddering.

5. Pre-litigation transfer — not present. The last recorded assignment (2021-01-26) predates the family's first linked litigation (2025, E.D. Mo. case 4:25-cv-01491) by roughly four years — far outside the 6-month window that signals an arranged, assertion-enabling transfer.

6. Bankruptcy fire-sale — not present. No Chapter 7/11 for Prince Castle, Cornelius, or Marmon; the assignee chain stays inside a profitable Berkshire Hathaway industrial subsidiary.

7. Privateering — not present. No evidence of an operating company pushing the patent to an NPE to assert against competitors; ownership never leaves the Marmon operating family.

8. Defensive aggregator — not present. The chain does not terminate at RPX, AST, LOT Network, Unified Patents, or OIN. The patent remains with the operating manufacturer, i.e., it has not been neutralized in the defensive-aggregation sense.

Verdict

Operating-company assertion.

The ownership chain is short and entirely internal to a manufacturing group: inventors → Prince Castle LLC (recorded 2019-11-06) → Marmon Foodservice Technologies, Inc. by merger and change of name (recorded 2021-01-26, Plainsite id 10443950), with assignors expressly listed as "Prince Castle LLC and Cornelius, Inc." No shell entity, no NPE roster match, no cascading LLCs, no defensive aggregator, and the transfers are years removed from the one 2025 suit linked to the family (E.D. Mo. 4:25-cv-01491). The current owner is a Berkshire Hathaway operating manufacturer that ships food holding equipment and marks it under 35 U.S.C. §287(a) — the profile of an operating company enforcing its own product patents rather than an NPE. Caveat: I could not retrieve reel/frame or the correspondent of record, nor confirm which party asserts in 4:25-cv-01491; if that case turns out to have Marmon as a defendant rather than plaintiff, the correct characterization would shift to "non-NPE, operating-company-owned (non-asserting)."

Verify at: https://assignmentcenter.uspto.gov/ (search patent 10,841,981) · Google Patents legal events: https://patents.google.com/patent/US10841981/en#legal-events · Plainsite assignment index: https://www.plainsite.org/patents/assignment.html?id=10443950 · Litigation data: https://portal.unifiedpatents.com/litigation/Missouri%20Eastern%20District%20Court/case/4%3A25-cv-01491

I'll research this systematically. Let me start by confirming the patent's identity and citation records.

Let me retrieve the specific citation records for US10841981 and examine the key prior-art references.

Let me verify a few key references before finalizing.

I'll analyze the obviousness of US 10,841,981 by examining the prior art cited on its page. Let me gather grounding details on the key references first.

Let me gather details on additional key references cited on the patent page.

Let me check a few more references directly relevant to the multi-zone concept.

Obviousness Analysis — U.S. Patent No. 10,841,981 (Multi-Zone Food Holding Bin)

Scope note: This is an informal technical/legal-style analysis based only on (a) the full text of US 10,841,981 as fetched from https://patents.google.com/patent/US10841981/en and (b) the reference list and "Prior Art"/"Cited By"/"Families Citing" sections on that page, supplemented by search results for the individual references. I have flagged items I could not independently verify. This is not legal advice and not a substitute for a formal invalidity opinion.

1. Effective filing date and governing framework

• The '981 patent issued 2020-11-17 from App. No. 16/403,415, filed 2019-05-03, as a continuation of 15/985,255 (US 10,492,641) → continuation of 15/133,220 (US 9,980,322), filed 2016-04-19. Earliest priority = 2016-04-19. (Page: "CROSS-REFERENCE TO RELATED APPLICATION"; "Family Applications.")
• The AIA (35 U.S.C. § 102/103) therefore applies. Any reference published/patented before 2016-04-19 is prior art under § 102(a)(1)/(a)(2) unless a § 102(b) exception applies. All the references used below (1998–2013) comfortably qualify.
• Standard: KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007) — a claim is obvious if the differences between the claim and the prior art are such that the subject matter as a whole would have been obvious to a PHOSITA, considering (i) the scope and content of the prior art, (ii) differences, (iii) level of ordinary skill, and (iv) secondary considerations. A combination is obvious where the references are from the same field, address the same problem, and the combination yields predictable results (KSR; MPEP § 2143).

The field here is narrow and crowded: counter-top food holding/warming cabinets for quick-service restaurants, with a decades-old patent literature (the page's citation list runs from US 2,386,919 (1945) forward and includes roughly 161 references, many from the same handful of competitors — Prince Castle, Duke, Hatco, Frymaster/Enodis, Restaurant Technology).

2. What the independent claims actually add

All five independent claims share the same core:

The only genuinely distinguishing concept vis-à-vis the cited art is the combination of: (1) no physical divider between thermally differentiated regions, (2) independent temperature control per region, on (3) a single continuous conductive shelf, with (4) both a top and a bottom heater per region. Everything else (pass-through openings, trays, displays, controls, lids, insulating panels) is old and largely admitted as such in the specification.

3. The prior-art landscape

References cited on the face of the '981 patent that map directly onto the claims:

• US 6,175,099 B1 (Duke) — "Holding or cooking oven": cabinet with partitions dividing the interior into a plurality of separate, thermally isolated holding compartments, each holding a tray; heat sources above the tray emit radiant heat; openings in both front and rear panels ("for every opening 36 in the front panel 28 an opening 36 in the rear panel 30 aligns with it"); a control mechanism controlling holding temperature and hold time; expressly lists diverse foods (hamburger patties, French toast, fish fillets, chicken fillets, biscuits); and a tier separator formed by an "upper pan 38" and a "lower pan 40." https://patents.google.com/patent/[US6175099B1](/patent/US6175099B1)/en
• US 6,031,208 A (Hatco) — "Topless holding bin with side heat source": a bin with a single, continuous, generally horizontal holding surface, a base heating element thermally coupled to the holding surface (heating by conduction from below), plus side/infrared elements; expressly states that known bins include "one or more shelves for supporting the food, with each shelf having top and bottom heat sources for warming the food supported by that shelf." https://patents.google.com/patent/[US6031208A](/patent/US6031208A)/en
• US 6,114,659 A (Frymaster) — "Device and method for keeping food warm": bin with a plate 13 whose top surface 14 supports food, a heater 15 along the plate's bottom surface 17 (heat by conduction), with the region above the plate "substantially open" so food is visible/accessible; addresses hold-time extension and moisture loss. https://patents.google.com/patent/[US6114659A](/patent/US6114659A)
• US 6,257,010 B1 (Duke) — "Merchandiser for warm and cold foods": a single cabinet having vertically stacked, differently tempered compartments (warm upper compartment 2, cold lower compartment 4) separated by a shelf, plus a wire-grid shelf 42 and wire-grid racks 46. https://patents.google.com/patent/US6257010
• US 5,783,803 (Robards, Jr.) — "Food warming apparatus": a warming cavity with a grate of spring-rod members supporting food trays and biasing them against a ceiling to seal moisture in. (Same family/continuation reviewed: US 5,900,173.)
• US 5,724,886 (Restaurant Technology) — "Cooked food staging device and method": described in the US 6,175,099 background as an oven where "each storage space has a heated platen along its top and also preferably at its bottom," with front-and-rear access.
• US 2011/0114624 A1 and US 8,247,745 — both incorporated by reference into the '981 specification itself for independently controlled food-holding cabinet zones via microprocessors and per-zone semiconductor temperature sensing, with a user interface/GUI.
• US 2010/0307168 A1 — incorporated by reference for Peltier/thermoelectric heating and for controlling one side of a solid-state device by controlling the other side (relevant to claim 54's dual-mode configuration).
• US 6,412,403 B1 (Prince Castle) — "…maintaining cooked food in a ready-to-serve condition using a freestanding cover for food trays" (tray covers/lids; relevant to claims 2, 27–30).

Additional reference located in the same field (flagged for verification):

• US 8,522,675 — "HOLDING CABINET FOR SEPARATELY HEATING FOOD TRAYS" (Frymaster/Enodis line; its front page cites Frymaster's HCP manual and US 6,114,659, which is itself cited on the '981 page). Abstract: "A food holding cabinet having one or more food-holding compartments has two or more zones in a compartment, wherein holding temperatures can be different from each other. A shelf made of glass-ceramic passes infrared energy from two or more heating elements attached to the glass-ceramic shelf… effectuate different temperatures of localized regions of the glass-ceramic and impart different amounts of heat energy into a food item or food holding trays above the heating elements." (https://patentimages.storage.googleapis.com/95/53/22/7f44fc0325cfad/US8522675.pdf) I could not confirm from the fetched page whether US 8,522,675 appears within the truncated 161-reference citation list, so treat it as highly probative but date/record-unverified.

Note: the '981 specification itself concedes the multi-zone concept for a continuous shelf when describing glass-ceramic: such materials "permit localized areas of a shelf to be heated to a first temperature, without having the entire shelf reach the same temperature" — language that reads as a near-verbatim paraphrase of US 8,522,675's abstract.

4. Combinations that would render the claims obvious

Ground 1 — Claims 1, 14, 27, 42 (and 3, 4, 13, 16–17, 26, 31–32, 41, 43–44, 53, 56–57)

Primary: US 8,522,675 (Frymaster) in view of US 6,175,099 (Duke) and US 6,031,208 (Hatco).

• US 8,522,675 discloses the chassis/compartment/shelf structure, a continuous thermally conductive shelf (glass-ceramic), two or more zones within one compartment, multiple heating elements attached to that one shelf, localized (i.e., non-uniform) heating of the shelf, and zone temperatures that can differ — i.e., claim 1's elements (a)–(c) and (g), with the zones "adjacent one another across the substantially planar surface" and no interposed wall.
• US 6,175,099 supplies anything US 8,522,675 lacks: the unified chassis with front and rear faces and aligned openings, the pass-through tray handling, and a control mechanism per compartment controlling temperature and hold time; it also expressly contemplates holding different foods (French toast, fish, chicken, biscuits) — the very motivation for differentiated zone temperatures recited in the '981 specification.
• US 6,031,208 supplies the claim-1 "substantially planar surface… extending completely to the first opening" as a continuous, undivided, single holding surface, and confirms that top-and-bottom heating per holding level was itself old ("each shelf having top and bottom heat sources"). It also supplies the claim 4/17/32/44/57 allocation (bottom = conduction via a thermally coupled base element; top/side = radiation/IR) and claim 3/16/31/43/56 (resistive electric elements).
• US 6,175,099's "upper pan 38 / lower pan 40" tier separator, together with US 5,724,886's "heated platen along its top and also preferably at its bottom," supplies the independently controllable top heating element and bottom heating element per zone and, for claim 42, the established practice of making the radiant top heater the dominant heat source while the lower platen merely conducts — i.e., "first heating element… output[s] more heat energy than the second."

Mapping note: Claim 1's final "first bezel is attached to the chassis and is set forward from the shelf by a space" is the weakest-supported element. Bezel-mounted control panels are ubiquitous in this art (Duke, Frymaster HCP, and the GUI of US 2011/0114624), and providing a standoff space between a front bezel and the shelf for latch/actuator travel is a predictable mechanical expedient. No single cited reference was confirmed to disclose the standoff per se.

Ground 2 — Claim 54

US 6,175,099 (Duke) in view of US 5,724,886 (Restaurant Technology), US 6,257,010 (Duke), and US 2010/0307168 A1.

Claim 54 simply adds a second, vertically-stacked compartment whose heaters are independently operated by a controller, and specifies that the intervening shelf is an upper plate + lower plate sandwich with fifth and sixth heating elements between them, the upper plate serving the first compartment and the lower plate serving the second. That is precisely the "upper pan 38 / lower pan 40" tier construction of US 6,175,099 (per-tier pan pair with the tier's heating/control between them), the stacked-platen arrangement of US 5,724,886, and the stacked warm/cold module of US 6,257,010. US 6,175,099's control mechanism already provides independent per-compartment operation, and US 2010/0307168 A1 (incorporated by reference in the '981 specification itself) teaches sandwiching a heat-transfer device between two plates to heat one side and cool/heat the other.

Ground 3 — Dependent claims

5. Motivation to combine (the § 103 rationale)

A PHOSITA would have been motivated to combine these references for several independent, mutually reinforcing reasons:

1. Identical field and identical problem. All references are commercial food-holding/warming cabinets for quick-service restaurants, and all target the problem the '981 background recites: short hold times (~15–20 min) and food waste. US 6,114,659, US 6,175,099 and US 8,522,675 each frame their invention as extending holding time / reducing quality degradation. KSR holds that obviousness is strongest where the field is narrow and the problem is the same.

2. Express recognition that different foods need different conditions. US 6,175,099 lists hamburger patties, sausage, French toast, fish and chicken fillets — foods with different ideal hold temperatures — and US 8,522,675 is expressly directed to separately heating trays in zones whose "holding temperatures can be different from each other." The '981 specification's own commercial rationale (french toast in zone 51a, eggs in 51b, sausage in 51c, hash browns in 51d) is therefore an unremarkable application of that teaching.

3. A known, finite set of solutions and predictable results. Whether to divide a holding cabinet into zones by physical partitions (US 6,175,099) or by localized heating of a single continuous shelf (US 8,522,675) was a binary, known design choice. Choosing the undivided option yields the predictable benefit the '981 specification touts — a surface "substantially free of any dividing walls… [so that] cleaning… can be easily accomplished" — a benefit already recognized in US 6,031,208 and US 6,114,659.

4. Independent per-zone control was known and expressly enabled. The '981 specification incorporates by reference US 2011/0114624 A1 ("Food Holding Cabinet Power Supplies with Downloadable Software") for exactly this — independently controlled zones using microprocessors and a GUI. A PHOSITA adding zones would, as a matter of ordinary design, provide one control per zone.

5. Stacking and shelf-sandwiching were known. US 6,175,099's per-tier "upper pan 38 / lower pan 40," US 5,724,886's top-and-bottom platens, US 6,257,010's stacked warm/cold modules, and US 2010/0307168 A1's sandwiched thermoelectric device (incorporated into the spec) collectively make claim 54's two-plate shelf with heaters between the plates a predictable mechanical arrangement rather than an inventive one.

6. Pass-through and moisture management were known and desirable. Front/rear openings (US 6,175,099, US 5,724,886) and tray lids/covers for moisture retention (US 5,783,803's sealing grate; US 6,412,403's freestanding covers) are old solutions to acknowledged needs.

6. Counter-considerations and where the analysis is weakest

• Possible teaching away. US 6,031,208 (Hatco) argues that eliminating the overhead heat source is advantageous ("it would be advantageous to provide a holding bin for holding and warming food items that does not require an overhead source of heat," because overhead lamps/structures are bulky and give an unappetizing "commercial" appearance). If Hatco is used to supply the top heating element, a patent owner would argue teaching away. The counter is that Hatco's objection is to visible, customer-facing overhead lamps — not to an internal/platen top heat source of the kind disclosed by US 6,175,099 and US 5,724,886, which are available as alternative references for the top heater. This makes it best practice to run the top-heater element off Duke/Restaurant Technology rather than Hatco.
• The "bezel set forward by a space" (claim 1) and the gravity-biased rotatable latch (claim 28) have the weakest support in the record I reviewed. These are likely to require an additional reference (e.g., a latch/bezel design patent in the same family as US 6,412,403) or reliance on "common sense"/design-choice reasoning, which is more vulnerable.
• US 8,522,675 is the single most damaging reference I located, because its abstract reads on claim 1's core (multiple zones, one continuous shelf, differing zone temperatures, multiple heating elements attached to the shelf). I could not verify that it appears in the truncated 161-reference list on the '981 page, nor its exact assignee/priority chain; its contents should be confirmed against the original document before relying on it.
• Secondary considerations. I found no evidence in the record of unexpected results, long-felt need, industry praise, licensing, or copying bearing on these claims. The '981 specification's assertion that a bin "can extend the palatability time of a food item by a factor of two or more" is a bare attorney argument without comparative data, so any nexus-based rebuttal would be weak. Note that the page reports a co-pending U.S. district court case in the Missouri Eastern District (4:25-cv-01491) and "first worldwide family litigation," which suggests validity is being tested — actual litigation positions are not reflected here.
• Prosecution posture. US 9,980,322, US 10,492,641 and US 10,841,981 share one specification; any successful § 103 challenge to the '981 claims would apply with equal force to the two parent patents. Conversely, if the examiner considered the closest art (e.g., Duke's or Frymaster's multi-zone holdings) and the applicant overcame, the file history — which I have not reviewed — would be the decisive record.

7. Bottom line

• Claims 1, 7–14, 16–17, 20–26, 31–32, 35–41, 43–44, 47–53, 56–57, 60–66: strong prima facie obviousness over US 8,522,675 in view of US 6,175,099 and US 6,031,208 (with US 6,114,659 and US 5,724,886 as further secondary references). Every element except the claim-1 bezel standoff is squarely disclosed or is a predictable design variation, and the motivation (hold different foods at different temperatures in one cleanable, pass-through cabinet) is express in the art.
• Claim 54: obvious over US 6,175,099 in view of US 5,724,886 / US 6,257,010 / US 2010/0307168 A1.
• Weakest links: claims 5–6 (display content), 15, 27–29 (lid shelf/latch), and especially 28 (gravity-biased latch). For claim 28 in particular, I do not have a confirmed reference in the record and would not assert obviousness without one.
• Caveat / confidence: the identification of US 8,522,675 as on-point and pre-2016 is high-confidence on substance but not verified against the '981 page's citation list or its priority chain; I also did not read the full text of US 6,412,403, US 5,724,886, or US 2,011/0114624 A1, and my characterizations of them are based on the '981 specification's own descriptions and secondary sources rather than the primary documents.