US 6661755

I'll verify current status and check for any 2026 CAFC activity for this specific patent number, then ground my summary in the authoritative patent text provided.

US Patent 6,661,755 — "Optical disc apparatus"

Important note on sourcing: I ran targeted searches for this patent number against Google Patents, CourtListener, govinfo, and general web sources. I did not find any live USPTO record or any 2026 CAFC docket associated with US 6,661,755. The most recent Federal Circuit activity I could locate is the 2008 decision Ricoh Co., Ltd. v. Quanta Computer Inc., 550 F.3d 1325 (Fed. Cir. 2008), which is the consolidated appeal in the W.D. Wis. case 3:06-cv-00462. I could not verify a live USPTO PatentCenter/Assignment record directly, so the bibliographic data below is taken from the authoritative patent text and Google Patents family data you supplied.

Bibliographic summary

Abstract (as issued): "An optical disc apparatus includes a pause circuit for pausing data encoders upon receiving a pause signal so that a write operation may be paused without writing dummy data, thereby maintaining data succession. The optical disc apparatus also includes a circuit for accurately determining a write start location by referring to previously written data. A processor generates a pause signal when the amount of data in the optical drive apparatus data buffer is low, and removes the pause signal when additional data from a host is received. The processor may also automatically reduce the write speed of the optical disc apparatus upon a pause condition."

Plain-language overview of the claims

The patent is directed to solving the "buffer run" (buffer underrun) problem in CD-R/CD-RW drives — when the host computer can't feed data fast enough, the writing operation would otherwise be spoiled. The claims focus on the write-pausing side of that solution (the write-start-position circuitry described in the specification is described but is not what these three claims recite).

Claim 1 (independent — pause without run-out blocks): A method of recording to an optical disc in which:

• stored input information is transferred to an encoder;
• the encoded information is transferred to a record circuit;
• the input buffer is caused to hold less than a threshold amount of information;
• when that happens, the transfer of encoded information is paused, stopping the record circuit at a first point on the disc while the encoded information is retained (i.e., the encoded data is not discarded); and
• importantly, the record circuit does not write any run-out blocks while paused.

Claim 2 (independent — resume without run-in blocks): The same method steps as claim 1, plus:

• the input buffer is caused to contain at least a second threshold amount of information;
• the transfer of encoded information to the record circuit then resumes, restarting the record circuit at a point that maintains data succession across the first point (the pause point); and
• the record circuit does not write any run-in blocks during the resuming.

Claim 3 (dependent): Adds to claim 2 the limitation that the record circuit does not write any run-out blocks during the pausing (i.e., combining the no-run-out and no-run-in features of claims 1 and 2).

In short, the claims cover pausing and restarting a CD-R/CD-RW write operation at the buffer-low boundary without inserting the conventional run-in/run-out (link) blocks, so that the physical data format stays continuous across the break.

Provenance / uncertainty flags

• The claim text above is quoted from the authoritative full patent text you provided (claims section, cols. 8), and matches the claim 1 language quoted by the Federal Circuit in Ricoh v. Quanta (550 F.3d at 1325).
• Litigation history (not a 2026 docket): Ricoh asserted this patent (alongside US 5,063,552; 6,172,955; and 6,631,109) against Quanta Storage/Quanta Computer and ASUSTeK in W.D. Wis. 3:06-cv-00462, filed ~Aug. 2006. The Federal Circuit's 2008 decision vacated and remanded as to the '755 and '552 patents on contributory-infringement/inducement standards. A related N.D. Cal. docket (3:07-cv-01942 / 5:07-cv-01942) also appears in the family data.
• 2026 CAFC activity: none found. Given the patent expired 2017-08-05, any 2026 appellate activity would be unusual; my searches returned no such docket, so I cannot confirm any. If you need this confirmed authoritatively, a direct USPTO PatentCenter and CAFC docket query would be required — I am flagging this as unverified rather than asserting a negative as fact.
• One identifier note: the Japanese priority number appears as JP 8-206705 in the patent text; I have not altered it.

Would you like me to draft the claim-chart / validity analysis section next, or expand the litigation-history portion into a fuller chronology?

Known Litigation Involving U.S. Patent No. 6,661,755

Identifier check (literal): US 6,661,755 B2 — "Optical disc apparatus," inventor Kazutaka Yamamoto, assignee Ricoh Co., Ltd., priority JP 8-206705 (1996-08-06), granted 2003-12-09, now Expired – Lifetime (anticipated expiration 2017-08-05). In the litigation literature below, this patent is consistently referred to as the '755 patent. (Note: this is a different patent from the related '809/'099/'832/'907 family members, and from Ricoh's '552, '955, and '109 patents, which were co-asserted in the same case.)

Two litigation matters are associated with the '755 patent family on Google Patents' litigation data, plus cases in the same dispute:

Case 1 — Ricoh Co., Ltd. v. Quanta Computer Inc. et al. (the primary '755 case)

Patents asserted: U.S. 6,631,109 ('109 – optical recording waveform); U.S. 6,172,955 ('955 – background formatting); U.S. 5,063,552 ('552 – Zone-CLV rotation/speed control; expired July 2009); and U.S. 6,661,755 ('755 – pausing a write operation to avoid buffer run and maintain data succession). Accused products included Quanta Storage drives (SBW-081, SBW-161, SBMT-241, SBW-242/242C/243/245, SDW-041/042/082/082K/085/086).

Procedural history and outcome:

• Aug 2007 – ASUSTeK and ASUS Computer International dismissed from the Wisconsin action for lack of personal jurisdiction (Ricoh had manufactured venue by having counsel order drives shipped into Wisconsin).
• Civil contempt/case-management opinions of the Wisconsin court: 06-C-462-C-05-11-07 (Markman) and 06-C-462-C-08-22-07.
• Summary judgment (Nov 2008) – District court held the asserted claims of the '109 patent obvious, the '955 patent not infringed, and (for the '755 and '552 patents) that Quanta's drives had "substantial noninfringing uses," defeating contributory infringement and inducement; no direct infringement by Quanta (no sale of a method) or by NU (no evidence of testing that practiced the claims). 579 F. Supp. 2d 1116.
• Federal Circuit, Dec. 23, 2008 – Ricoh Co., Ltd. v. Quanta Computer Inc., 550 F.3d 1325 (Fed. Cir. 2008) (appeal No. 2007-1567). Panel (Gajarsa, J., dissenting in part) affirmed on the '109 and '955 patents but vacated and remanded on the '552 and '755 patents, holding the district court applied erroneous legal standards: a party that merely sells software containing instructions to perform a method does not directly infringe under § 271(a), but contributory infringement under § 271(c) is not defeated merely because the component is embedded in a larger product with noninfringing uses; where a distinct, separable component has no substantial noninfringing use, intent may be presumed.
• Remand (2009) – W.D. Wis. order of Nov. 18, 2009 barred Ricoh from putting on willfulness evidence. Jury trial held; jury verdict Nov. 24, 2009 finding Quanta liable and awarding Ricoh $14.5 million. Post-trial opinion at docket #545 (filed Mar. 23, 2010) addressing contributory infringement under § 271(c) (the "distinct and separable component" requirement) and denial of defendants' mistrial motion.
• Termination – Per the Taiwan IP office case study (TIPONET, information_4_2_4.pdf), the parties settled and the action was dismissed by agreement on April 13, 2011. The same source indicates appeals followed (with a petition for certiorari to the U.S. Supreme Court denied), though I could not independently verify the docket numbers or disposition of any post-2009 appellate proceedings, including any second Federal Circuit appeal. Treat that point as unconfirmed.

Status today: Case closed (settled/dismissed). The '755 patent itself is Expired – Lifetime (expired 2017-08-05).

Sources: https://patents.google.com/patent/US6661755/en ; https://portal.unifiedpatents.com/litigation/Wisconsin%20Western%20District%20Court/case/3%3A06-cv-00462 ; https://www.courtlistener.com/opinion/[209414](/patent/209414)/ricoh-co-ltd-v-quanta-computer-inc/ ; http://cafc.uscourts.gov/opinions-orders/07-1567.pdf ; https://www.govinfo.gov/content/pkg/USCOURTS-wiwd-3_06-cv-00462/pdf/USCOURTS-wiwd-3_06-cv-00462-4.pdf ; https://ipmall.law.unh.edu/sites/default/files/hosted_resources/Markman/pdfFiles/2007.05.11_RICOH_COMPANY_LTD_v._QUANTA_COMPUTER_INC.pdf ; https://jp.ricoh.com/release/by_field/management/2006/0825 ; https://tiponet.tipo.gov.tw/downloads/module030/information_4_2_4.pdf

Case 2 — ASUSTeK Computer Inc. and ASUS Computer International v. Ricoh Company, Ltd. (declaratory judgment)

This is the mirror-image declaratory-judgment action filed by the Wisconsin defendants after they were dismissed from Case 1 for lack of personal jurisdiction. Ricoh counterclaimed, including on the '109 patent; the published ruling (Nov. 21, 2007) denied Ricoh's motion to stay pending its Wisconsin/Federal Circuit appeal, and held Ricoh collaterally estopped from re-asserting claims 1 and 4 of the '109 patent but declined to dismiss the '109 counterclaim in its entirety. The documents I retrieved discuss the '109 patent rather than the '755 patent specifically, so I cannot confirm that the '755 patent was actually placed at issue in this N.D. Cal. action. I also could not verify the final disposition of this case (whether it settled, was dismissed, or was resolved on the merits).

Sources: https://portal.unifiedpatents.com/litigation/California%20Northern%20District%20Court/case/3%3A07-cv-01942 ; https://portal.unifiedpatents.com/litigation/California%20Northern%20District%20Court/case/5%3A07-cv-01942 ; Asustek Computer Inc. v. Ricoh Company, Ltd., No. C 07-01942 MHP (N.D. Cal. Nov. 21, 2007)

Other items on the record (family-level, not '755-specific)

• Darts-ip reports a "First worldwide family litigation filed" for Ricoh family ID 16527758 (the family containing the '755 patent and its continuations): https://patents.darts-ip.com/?family=16527758 — I could not retrieve the underlying case details.
• Ricoh's Aug. 25, 2006 press release notes that the Quanta/ASUS suit was Ricoh's second optical-disc patent campaign, following a May 2004 action against Lite-On IT Corporation and related entities (settled Oct. 2005 to Ricoh's satisfaction) and CMC Magnetics Corporation (settled Dec. 2004). I have no confirmation that U.S. 6,661,755 was asserted in those earlier cases, so I do not list them as '755 litigation.

Bottom line

Two matters are documented as associated with U.S. 6,661,755:

1. Ricoh Co., Ltd. v. Quanta Computer Inc., et al., No. 3:06-cv-00462-bbc (W.D. Wis., filed Aug. 24, 2006) — the '755 patent was one of four asserted patents; after a Fed. Cir. remand (550 F.3d 1325), a jury returned a $14.5M verdict for Ricoh on Nov. 24, 2009; the case settled and was dismissed on April 13, 2011.
2. ASUSTeK Computer Inc. v. Ricoh Company, Ltd., No. C 07-01942 MHP (N.D. Cal., filed April 6, 2007) — a declaratory-judgment action arising out of the same dispute (indexed on Google Patents as both 3:07-cv-01942 and 5:07-cv-01942); final disposition unverified.

No ITC Section 337 investigation or other district-court action specifically asserting U.S. 6,661,755 surfaced in my searches. I have flagged the two items I could not verify (the N.D. Cal. case's final outcome, and any post-2009 appellate proceedings) rather than guessing.

I'll start by verifying the canonical list and searching for any AIA trial activity on this patent.

Let me run additional targeted searches to confirm the absence of PTAB activity and check the litigation-related context.

Proceedings overview

PTAB AIA trial count for US 6,661,755: zero. The USPTO Open Data Portal structured record returns no AIA trial proceedings (no IPR, PGR, or CBM) for this patent as of the most recent ingest, and targeted web searches surfaced no PTAB petition, institution decision, Final Written Decision, or PTAB appeal involving 6,661,755 — I found no proceeding numbers to report, and I will not invent any. This is not a "claims 1–5 canceled, the troll has no case" posture and not a "claims hardened by surviving IPRs" posture; it is a no-PTAB-history posture, which is materially different: every claim (1, 2 and 3) remains presumptively valid and untested at the PTAB, and no petitioner-side estoppel attaches to anyone.

Correct one framing assumption up front: this is not a troll patent. The patent owner is Ricoh Company, Ltd., an operating company that enforced the '755 patent in district court against optical-drive manufacturers and won a jury verdict. Do not build a defense narrative around a non-practicing entity — build it around a well-funded, litigious operating company with an existing damages benchmark.

No PTAB proceeding to detail — what the absence means

There is no proceeding number, panel, institution decision, FWD, settlement, or PTAB appeal to summarize. The canonical structured data supplied in this prompt is the authoritative source for the proceedings list, and it is empty; nothing in my web searches contradicts it.

Two contextual notes that make the empty list unsurprising rather than suspicious:

• Timing. The '755 patent's asserted life was 2006–2010, entirely before IPR/PGR/CBM practice matured (IPRs became available 2012-09-16; CBM ended 2020-09-16). A defendant in 2007 had no AIA trial option — its only validity routes were district court invalidity and ex parte reexam. That explains the absence better than any inference about patent strength.
• Status. Google Patents lists the patent as Expired – Lifetime, with anticipated expiration 2017-08-05. An expired patent can still be the subject of an IPR, but there is no injunctive or forward-looking royalty exposure, so the economic incentive to petition evaporated after 2017.

Litigation context (NOT PTAB — provided because the '755 record is litigation, not AIA trial)

Because the proceedings list is empty, the defendant-facing signal has to come from the Article III record. Everything below is district court / Federal Circuit, not PTAB.

Ricoh Co., Ltd. v. Quanta Computer Inc. — W.D. Wis. No. 3:06-cv-00462

• Type: District court patent infringement (not an AIA trial; no PTAB involvement surfaced).
• Filed: 2006 (case number sequence 3:06-cv-00462; Ricoh's suit against Quanta/Quanta Storage/New Universe was publicly noted in August 2006 reporting).
• Status: Resolved by jury verdict and post-trial rulings; not a PTAB matter.
• Asserted claims of '755: claims 1–3 — consistent with the ASUSTeK declaratory-judgment complaint, which sought declarations as to "claims 1-3 of the `755 Patent."
• Key rulings:
  • Claim construction (2007-05-11): the court construed "maintaining data succession" as "maintaining continuity of data within a tolerance of 2 clock bits" — adopting the defendants' proposal that the ±2 clock-bit figure from the specification is a requirement, not merely a preferred embodiment. Source: Ricoh v. Quanta Markman opinion. This is the single most useful construction in the file for a defendant: it imports a tight numerical tolerance into every asserted claim, and the patentee must prove it.
  • Summary judgment: asserted claims of the '109 patent held obvious; asserted claims of the '955 patent not infringed; material fact disputes remained on the '552 and '755 patents. Ricoh v. Quanta, 550 F.3d 1325.
  • Federal Circuit (2008): 550 F.3d 1325 — vacated the § 271(c) contributory-infringement dismissal, holding Ricoh was entitled to try to show the accused drives contained "hardware or software components that have no substantial noninfringing use other than to practice Ricoh's claimed methods." On the '755 patent specifically, the panel noted a genuine issue remained on infringement.
  • Jury verdict (2010): jury found infringement of the '552 and '755 patents and awarded Ricoh $14.5 million. Post-trial JMOL/new-trial/mistrial motions were denied (Dkt. 545, 2010-03-23). Critically, the court noted defendants "do not advance any arguments regarding invalidity of the '755 patent."
• Settlement / termination: no settlement surfaced; the case was decided on the merits.
• Appeal: yes — Ricoh Co., Ltd. v. Quanta Computer Inc., 550 F.3d 1325 (Fed. Cir. 2008) (CourtListener: https://www.courtlistener.com/opinion/[209414](/patent/209414)/ricoh-co-ltd-v-quanta-computer-inc/). I could not verify the Federal Circuit docket number from my sources; treat the F.3d citation as the reliable identifier.
• Defensive value: mixed and important. The '755 patent survived an obviousness challenge at the district court (the SJ obviousness win was on the '109 patent, not the '755), and Ricoh obtained a $14.5M verdict. But the ±2 clock-bit construction of "maintaining data succession" is a real non-infringement lever, and it is the same lever the Quanta defendants pressed. A defendant today should attack infringement on that term first, before spending on invalidity.

ASUSTeK Computer v. Ricoh — declaratory judgment (N.D. Cal. Nos. 5:07-cv-01942 and 3:07-cv-01942)

• Type: Declaratory judgment action by ASUSTeK (invalidity and non-infringement), filed in response to Ricoh's assertion letters.
• Filed: 2007 (per the Unified Patents litigation records in the structured data and the public complaint).
• Status: Both captioned N.D. Cal. matters appear in the litigation data for this family; no PTAB counterpart exists.
• Petition grounds (as DJ counts, not petition grounds): ASUSTeK pleaded that "each of the asserted claims of the '755 Patent is invalid" and sought declarations on claims 1–3, plus non-infringement. Source: ASUSTeK complaint excerpt.
• Settlement / termination: I could not confirm the disposition or any settlement terms from the available sources. Say so; do not infer.
• Defensive value: Shows a second well-resourced defendant chose a DJ-forum race rather than a validity trial it expected to win outright on the '755 patent. It also confirms the asserted-claim set is claims 1–3.

Strategic summary

Claim-by-claim status of the '755 patent. There is no PTAB cancellation or affirmance of any claim — so, strictly on the PTAB axis, claims 1, 2 and 3 are all UNTESTED. There are exactly three claims: claim 1 (independent), claim 2 (independent), and claim 3 (depending from claim 2). None was canceled, none was confirmed by the Board, and none was amended. On the district court axis, all three were asserted by Ricoh and the '755 patent was held infringed by a jury and not invalidated. The practical read: the patent is not narrowed by prosecution-style disclaimer at the PTAB, but it is narrowed by the binding claim construction of "maintaining data succession" as continuity "within a tolerance of 2 clock bits," which appears in claims 1 and 2 and flows into claim 3.

Estoppel landscape: there is none, and that cuts both ways. 35 U.S.C. § 315(e)(2) estoppel is triggered only by an IPR petitioner who reaches institution and FWD, and § 325(e)(1) similarly for PGR/CBM. No one is estopped — not Quanta, not ASUSTeK, not any privy. That means a defendant today faces no wasted prior-art budget and can raise any § 102/§ 103 ground it likes, including art that a hypothetical earlier petitioner raised or reasonably could have raised. Countervailing risk: because no prior art has ever been adjudicated against these claims by an expert tribunal, you also have no PTAB record to borrow — no FWD findings, no Board credibility determinations, no institution-stage narrowing. Every ground must be built from scratch, and the Quanta jury verdict gives Ricoh a proven damages narrative to anchor settlement demands.

Pattern signals. (1) The patent owner is a large operating company that ran a coordinated multi-front campaign — W.D. Wis. against Quanta and N.D. Cal. DJ actions with ASUSTeK — not a defensive aggregator scenario; no Unified Patents or RPX involvement appears anywhere in the chain. (2) Ricoh did not pursue PTAB appeals — there were no PTAB trials to appeal. Its appellate activity was ordinary district-court appeals (the successful 550 F.3d 1325 appeal). (3) The same family (10 US family members, including US 6,570,832; 6,418,099; 6,198,707; 6,876,608; 7,055,987; 7,245,569; 7,385,902; 7,362,669; 7,859,957) means a defendant may face sibling-patent assertions where the '755 has expired; those siblings are outside the scope of this memo, but their PTAB posture should be checked separately before assuming a clean slate.

Recommended next steps

1. Do not tell a court or client that "the patent has been tested at the PTAB." It has not. The accurate statement is: "No IPR, PGR, or CBM has ever been filed against US 6,661,755; no claim has been canceled, confirmed, or amended by the Board; and no AIA-trial estoppel applies to any party."
2. Check expiry before anything else. The '755 patent is recorded as Expired – Lifetime, anticipated expiration 2017-08-05. If a demand letter cites the '755 patent today, the first question is whether any actionable damages window remains. If it does not, the letter is pressure with no statutory hook.
3. Lead with the claim-construction lever. Use the 2007-05-11 Markman ruling construing "maintaining data succession" as "maintaining continuity of data within a tolerance of 2 clock bits" (link) — this limitation is in claims 1 and 2 (and therefore 3), and it is the same non-infringement argument that survived to be tried in Quanta. Quote it verbatim; it is a requirement, not an embodiment.
4. If invalidity is the strategy, budget for a district-court or ex parte reexam fight, not an IPR-driven one. No estoppel helps you, but there is no PTAB roadmap either. Note that the one obviousness win in the Quanta litigation was on the '109 patent, not the '755 — the '755's obviousness was never adjudicated because the Quanta defendants abandoned the argument. That is arguably the largest untested soft spot.
5. Verify the ASUSTeK disposition independently. I could not confirm how 5:07-cv-01942 / 3:07-cv-01942 ended, and I am explicitly flagging that as unknown rather than guessing. If that case settled with a license, the license and its scope may be commercially relevant to any current assertion.
6. Re-run the PTAB check at filing time. The ODP ingest is a snapshot. If you are drafting a petition, query PTAB E2E / the ODP API directly for the application number 10/199,042 and every family member before relying on the "no proceedings" conclusion.

Sources: US6661755 Google Patents · Ricoh v. Quanta, 550 F.3d 1325 (Fed. Cir. 2008) · W.D. Wis. Dkt. 545 (2010-03-23) · 2007-05-11 Markman opinion · Unified Patents litigation records, W.D. Wis. 3:06-cv-00462 and N.D. Cal. 5:07-cv-01942 / 3:07-cv-01942

Confidence statement: I have high confidence in the zero-PTAB finding (canonical structured data plus multiple null-result searches). I have high confidence in the Quanta litigation facts. I have low confidence on the Federal Circuit docket number and no verified information on the ASUSTeK disposition — both are marked as such above rather than filled in.

I'll research the assignment record and litigation history before assembling the report.

Assignment & Ownership Analysis — US Patent 6,661,755 B2

Patent: Optical disc apparatus · Inventor: Kazutaka Yamamoto · Original assignee: Ricoh Company, Ltd. (JP) · Priority: 1996-08-06 (JP 8-206705) · Filed: 2002-07-22 (continuation) · Granted: 2003-12-09 · Status: Expired – Lifetime (anticipated expiration 2017-08-05)

Scope note / data limitation. I could not retrieve a machine-readable record from the USPTO Assignment Center (assignmentcenter.uspto.gov / assignment.uspto.gov) in this session — the sources available to me returned no reel/frame entries for this patent. The most reliable ownership evidence I could actually verify is the legal-events record reproduced on Google Patents for US 6,661,755, which lists only a patent-grant event and three maintenance-fee payments (2007-05-18, 2011-06-03, 2015-06-05) — no reassignment/assignment events. The findings below are stated with that limitation.

Inventors

• No unusual inventor-departure pattern detected. I found no evidence that Yamamoto left Ricoh within 12 months of filing, and no evidence tying his departure to any portfolio sale. Because the patent was prosecuted by Ricoh from 1997 through the 2008-filed continuation (12/149,087), there is no "orphaned-inventor → fire-sale" signature here.
• Ricoh is a large, established imaging/electronics manufacturer; inventor-level ownership issues are not indicated (standard employee-assignment practice).

Original assignee

• Ricoh Company, Ltd. (Tokyo, Japan) is the assignee on the face of the issued patent and remained the named owner throughout the family.
• Primary line of business: Multinational manufacturer of office imaging equipment (copiers, printers, MFPs), optical/electronic devices, and related hardware — i.e., a true operating company, not a licensing vehicle. Ricoh's own subsidiaries were characterized in the litigation record as distributors/R&D entities, not NPEs (see ASUS's 2007 declaration: "Ricoh Americas Corporation … is not in the optical disc drive or patent licensing business").
• Product embodiment of the claims: Yes — the asserted claims (a CD-RW/CD-R buffer-underrun "pause and resume without run-in/run-out blocks" method) read on optical disc drives. Ricoh's own litigation was directed at third-party drives (Quanta/QSI, ASUSTeK/ASUS, NU Technology) that it alleged practiced this method, and Ricoh was an active licensor of CD-RW/DVD+RW drive technology.
• Current status: Operating. Ricoh is an active public conglomerate (no bankruptcy, no dissolution, no Chapter 7/11 event surfaced). The patent itself simply lapsed at term.

Assignment timeline

No post-issuance assignments are evidenced for US 6,661,755. Concretely:

• The Google Patents legal-events tab for this patent records no "Assignment" conveyance — only STCF (patent grant), FEPP (payor number), and three FPAY maintenance-fee payments dated 2007-05-18 (4th yr), 2011-06-03 (8th yr), and 2015-06-05 (12th yr). Maintenance fees paid to the end of term by the original owner is itself evidence the patent was never divested.
• The initial inventor→Ricoh assignment (standard for a corporate-filed JP/US application) is not exposed in any source I could verify, so I cannot state a reel/frame for it and will not invent one.

Therefore, under the rule you specified: no post-issuance assignment records were located for this patent, and the ownership section stops here. The family's continuation chain (all to Ricoh) is listed below for completeness, since it bears on ownership continuity:

All remain listed to Ricoh Company, Ltd. Continuous prosecution/division activity by Ricoh through 2008 is inconsistent with a fire-sale or assignment to an aggregator.

Timeline diagram

timeline
    title Ownership of US 6661755
    1996 : JP priority application filed by Ricoh
    1997 : Parent US application 08906290 filed
    2002 : Continuation 10199042 filed
    2003 : US 6661755 issued to Ricoh
         : Divisionals and continuations filed
    2006 : Ricoh sues Quanta and ASUSTeK
    2007 : ASUSTeK files declaratory judgment
    2009 : Jury awards Ricoh 14.5 million
    2011 : Ricoh and Quanta settle
    2017 : Patent expires

NPE / troll-pattern signals

1. Shell-entity transfer — Not present. No assignment from Ricoh to any "IP / Patents / Licensing / Holdings / Ventures" entity appears in any source I could verify. Maintenance fees were paid by the original owner (FPAY events 2007, 2011, 2015), and the patent family stayed on Ricoh's docket through the 2008 filing.

2. Known asserter in the chain — Not present. The only entity I can substantiate as the asserting party is Ricoh Company, Ltd. itself, the operating manufacturer. No Acacia, Marathon, IV, Wi-LAN, Conversant, Crytivo/Oasis, or other listed NPE appears anywhere in this chain. (Ricoh is not on the RPX/Unified high-frequency-plaintiff directories as an NPE; it is a practicing company.)

3. Repeat correspondent across the chain — Unclear / not substantiated. Because no assignment records were retrievable, I have no correspondent-of-record data to test for recurrence. I will not assert a correspondent finding — none is evidenced. (Note: the attorneys appearing in the litigation — Kellogg, Huber, Hansen, Todd, Evans & Figel for Ricoh; Bergeson LLP and Paul Hastings for ASUS — are litigation counsel, not recorded assignment correspondents, and must not be conflated with the assignment record.)

4. Cascading transfers — Not present. Zero post-issuance transfers; nothing to cascade. The 2003-10-06 divisional/continuation filings are prosecution events by the same owner, not assignments.

5. Pre-litigation transfer — Not present. The first suit (Ricoh v. Quanta/ASUSTeK, W.D. Wis. No. 3:06-cv-00462, filed 2006-08-24) was brought by the original assignee in its own name, with no preceding assignment to reposition venue or title.

6. Bankruptcy fire-sale — Not present. No Chapter 7/11 proceeding involving Ricoh or this patent was surfaced.

7. Privateering — Not present. This is the inverse pattern: the operating company asserted directly, and its opponent's own filing affirmatively distinguished Ricoh's U.S. sales subsidiary from any patent-licensing business. No operating-company→NPE pass-through is evidenced.

8. Defensive aggregator (anti-NPE) — Not present. The chain does not terminate at RPX, AST, LOT, Unified Patents, or OIN. Ownership ran to natural expiry at Ricoh.

Litigation context (supports the "operating-company assertion" character):

• "Ricoh sues Quanta Storage and ASUSTeK Computer – August 28, 2006" (WikiPatents), and Ricoh's own 2006-08-25 press release confirming it sued Quanta Storage (and 4 affiliates) and ASUSTeK (and 1 affiliate) in W.D. Wis. over CD-RW/DVD+RW patents including US 6,661,755.
• N.D. Cal. cases 3:07-cv-01942 / 5:07-cv-01942 (ASUSTeK Computer Inc. & ASUS Computer International v. Ricoh Company, Ltd.) are declaratory-judgment actions brought by the accused infringer (ASUSTeK seeking DJ of invalidity/non-infringement of the '755 patent, Counts VII–VIII) — the hallmark of an operating patentee being challenged, not an NPE campaign. See e.g. the ASUSTeK DJ complaint (Counts VII–VIII) and Paul Hastings filings.
• Fed. Cir. Ricoh Co. v. Quanta Computer, Inc., 550 F.3d 1323 (2008/2009) reversed in part the district court's summary judgment and remanded the contributory-infringement question on the '552 and '755 patents; the W.D. Wis. jury returned a $14.5M verdict for Ricoh against Quanta on 2009-11-24, and Ricoh and Quanta settled and dismissed on 2011-04-13.

Verdict

Operating-company assertion.

Ricoh Company, Ltd. — the original assignee and an operating optical-imaging manufacturer — retained title throughout (no assignment events recorded; maintenance fees paid by the owner in 2007, 2011 and 2015) and asserted the '755 patent directly in its own name against competitor drive makers (W.D. Wis. 3:06-cv-00462, filed 2006-08-24; $14.5M jury verdict 2009-11-24; settlement 2011-04-13). Every NPE signal is absent: no shell-entity transfer, no aggregator, no cascading LLC chain, no pre-suit transfer, no privateering, and no known asserted-patent aggregator in the chain.

Verification links:

• USPTO Assignment Center (search by patent number 6661755): https://assignmentcenter.uspto.gov/
• Legacy Assignment Search: https://assignment.uspto.gov/patent/index.html
• Google Patents legal events (no reassignment entries): https://patents.google.com/patent/US6661755/en

Caveat: I could not independently confirm the presence/absence of an original inventor→Ricoh assignment reel/frame, and I did not fabricate one. Everything above is limited to records I could actually retrieve; the "no post-issuance assignments" conclusion rests on the absence of any reassignment event in the patent's legal-events record plus continued owner-paid maintenance fees, which should be re-verified directly in the Assignment Center.

I'll verify the patent record and then analyze the cited prior art.

Let me verify details on the references I'm flagging as most relevant.

Prior-Art Analysis — U.S. Patent No. 6,661,755 B2

A. Record verification (USPTO / Google Patents)

Source: https://patents.google.com/patent/US6661755/en

The claims that must be met

• Claim 1 — method comprising: transferring stored input information to an encoder; transferring encoded information to a record circuit; causing an input buffer to contain less than a threshold amount; when below threshold, pausing the transfer of encoded information so the record circuit stops at a first point while maintaining the encoded information, and "said record circuit does not write any run-out blocks while paused."
• Claim 2 — as claim 1, plus: buffer reaches a second threshold; resuming transfer … "while maintaining data succession across said first point," and "said record circuit does not write any run-in blocks during said resuming."
• Claim 3 — claim 2, plus no run-out blocks during pausing.

The two negative limitations (no run-in / no run-out blocks across a buffer-driven pause) plus "maintaining the encoded information" are the whole novelty story relative to the cited art. This is the classic "Buffer Underrun Protection / JustLink / Seamless Link" family of features.

B. Legal framework I applied (and an important date caveat)

1. §102 anticipation requires every element in a single reference, arranged as in the claim. Negative limitations ("does not write any run-out blocks") must be expressly or inherently disclosed. Title-level similarity is not enough.
2. Critical date. The earliest US filing is 1997-08-05, so the §102(b) one-year bar date is 1996-08-05. Under In re Hilmer, the JP priority date of 1996-08-06 cannot be used to antedate a §102(b) or §102(e) reference; it can only help against §102(a)/(g) art. So references published on/before 1996-08-05 are clean statutory bars.
3. One date problem worth flagging now: US 5,815,472 (Pioneer) has a priority/filing date of 1996-08-22, after the 1996-08-06 priority date. On the face of the record it is not §102 prior art against this family; it was presumably cited as §102(e) art against a later-filed continuation, or as general background.

C. Most relevant prior art (Tier 1 — the references that actually matter)

1. US 5,323,367 — Sanyo Electric (Tamura et al.), "Reproduction or recording device having a pause function" — priority 1991-10-25; granted 1994-06-21. §102(b) art.
Disc recorder/player with a memory between the signal source and the recording head, where a pause state can be set and cancelled during recording, and intermittent recording from memory to disc is controlled to avoid discontinuity of recorded sound at pause cancellation. Verified text: "When a pause state is set during recording, there is a problem of the audio data already stored in the memory prior to the setting of pause not being recorded on a disc if the intermittent recording operation from the memory to the disc is ceased merely in response to the pause state setting."
→ Potentially anticipatory of claim 1 (memory/buffer → encoder → record circuit; pause of the record operation). Weak/none for claims 2–3: it addresses discontinuity from a memory-full/memory-empty perspective and says nothing about CIRC encoding continuation or about refraining from writing run-in/run-out (link) blocks. Best used under §103.

2. US 5,453,967 — Sony, "Disc reproducing apparatus which stops recording in response to compressed data stored, in a record stop state, in a memory" — priority 1992-05-22; granted 1995-09-26. §102(b) art.
Discloses a first encoder (compressor) → memory → second encoder (CIRC-class) → head, with a controller that, "when data is left in the memory in the record stop state, the record operation by the head apparatus is intermitted after the data in the memory is read out and entirely recorded on the disc," so that data is not lost. Verified abstract and definitions text from Google Patents.
→ The most structurally on-point reference (dual encoder + memory + pause), and a real §102 candidate against claim 1's "maintaining said encoded information." But note it flushes the memory before intermitting — arguably a teaching away from the pause-while-retaining-encoded-data approach, and silent on the run-in/run-out negatives. §103 art for claims 2–3.

3. US 5,432,769 — Matsushita (Honjo), "Apparatus for intermittently recording or reproducing variable length coded video data" — priority 1991-04-18; granted 1995-07-11. §102(b) art.
Verified abstract: "digital video data to be recorded is temporarily stored in a buffer, and when the amount of data being stored in the buffer exceeds a predetermined value, the data is recorded on a recording medium for a constant period of time, and when the amount of data is less than the predetermined value, the data is intermittently recorded onto the next track."
→ Anticipatory-style disclosure of the claim 1 triggering step (buffer below threshold → pause/stop record operation) and of resume-on-buffer-refill. Not CD-R, not CIRC, no link-block negatives → §102 as to the pause trigger, §103 overall; a strong secondary reference.

4. US 5,212,678 and US 5,463,607 — U.S. Philips, "System for recording and reading information on a record carrier at a constant scanning speed independent of the bit rate of such information" — priority 1989-11-23; granted 1993-05-18 / 1995-10-31. §102(b) art.
Claim 1 (per the EPO/KIPO family analysis retrieved): an input buffer memory between system input and write means; write control means programmed to (i) periodically interrupt read-out from the input buffer and jump the spot back, and (ii) resume read-out when the spot again reaches the location at which scanning was interrupted, "the periodic interruptions of read-out from the input buffer being such that the degree of filling of the input buffer is maintained within predetermined limits."
→ This is conceptually the closest thing in the record to "pause the data flow to the recorder when the buffer is low, resume when it refills, without introducing new link sectors." It does it by track-jump-back rather than by encoder clock gating, and it is not a write-once CD-R medium. Strong §103 art; possible §102 for claim 1's preamble/pause step.

5. US 5,343,455 — Hitachi, "Digital signal overlapped or joined recording method and apparatus" — priority 1990-04-05; granted 1994-08-30. §102(b) art.
Directed to overlapping/joining successive recordings — this is the closest cited art to the second inventive aspect of the '755 specification (accurately locating the end of previously written data and starting the next write session there). Citation does not map cleanly onto claims 1–3 (which are buffer-pause claims), but it is directly relevant to the FIG. 5/FIG. 6 ±2-bit write-start-point disclosure. §103 art.

6. US 5,748,588 — Sony, "Memory controller and recording apparatus which adds dummy data to complete a sector of data when writing to memory" — priority 1994-09-20; granted 1998-05-05. §102(e) art (US filing 1994).
This is the dummy-data approach the '755 patent exists to avoid ("the CD encoder chip will continue to generate dummy data even if the buffer … becomes empty"). Useful as §103 art and as evidence of what the art taught, and for the negative limitations in claims 1/3 via express teaching of the opposite.

7. US 5,694,383 — Sony, "Decoder/encoder capable of controlling data reading/writing operations to memory in response to first/second clocks…" — priority 1995-02-13; granted 1997-12-02. §102(e) art.
Encoder/decoder whose memory read/write is gated by first and second clocks — closely parallels the '755 FIG. 4 pause circuit, which masks the clock input to the CD-ROM encoder and CD encoder upon a Pause signal. Good §103 combination material with any of refs 1–4.

8. US 5,504,728 — Sony, "Method for recording of disk and apparatus for adjusting position of breakpoint of audio data" — priority 1992-11-18; granted 1996-04-02. §102(b) art (published before 1996-08-05).
Adjusting the break point position for discontinuously-recorded audio — relevant to "restart … across said first point" in claim 2. §103 art.

9. US 5,999,505 — Sony, "Information processing device for continuously and discontinuously processing recorded data…" — priority 1993-03-26; granted 1999-12-07. §102(e) art (US filing 1994).
Expressly addresses continuous AND discontinuous processing/recording of data — relevant to the "maintaining data succession" limitation of claim 2. §103 art.

10. US 5,633,841 — Sony, "Optical disc recording/reproducing apparatus having automatic protection of previously recorded data" — priority 1992-05-25; granted 1997-05-27. §102(e). Protection of previously recorded data when writing resumes. §103 art.

11. US 5,668,789 — Sony, "Recording method of recording medium" — priority 1993-01-06; granted 1997-09-16. §102(e). Recording-method background. §103 art.

12. US 5,835,461 — Sony, "Optical disc, apparatus and method for recording and reproducing data" — priority 1995-06-15; granted 1998-11-10. §102(e). General optical-disc record/reproduce; often cited in buffer/link contexts. §103 art.

13. US 5,761,173 — Sony, "Recording and/or reproducing apparatus and method for data reproduction and processing" — priority 1995-11-29; granted 1998-06-02. §102(e). §103 art.

14. US 5,808,995 — Matsushita, "Disk information reading control apparatus having a variable read transfer speed…" — priority 1994-07-22; granted 1998-09-15. §102(e). Variable transfer-speed control in response to buffer/read conditions — relevant to the "step down the write speed" embodiment of FIG. 12 (though FIG. 12 is not claimed). §103 art.

15. US 5,745,445 — Matsushita, "Digital recording and reproducing apparatus and method which prevents or manages a data loss" — priority 1995-12-01; granted 1998-04-28. §102(e). §103 art.

16. US 5,422,084 / US 5,844,138 / US 5,536,362 / US 5,507,695 / US 5,517,477 / US 5,532,633 / US 5,553,042 / US 5,586,093 / US 5,793,739 / US 5,812,502 / US 5,815,472 / US 5,602,812 / US 5,580,989 / US 5,545,674 / US 5,529,505 / US 5,601,462 / US 5,751,733 / US 5,740,143 / US 5,740,144 / US 5,681,467 / US 5,768,178 / US 5,450,278 / US 5,761,173 / US 5,633,841 / US 5,668,789 / US 5,835,461 — these are the secondary/background tier; see the full table in §D.

D. Complete citation-by-citation listing (all 61 patent citations of US 6,661,755)

Legend for §102 column:

• P = plausible single-reference §102 candidate for at least claim 1 / part of a claim
• 103 = best characterized as §103 (obviousness) art or background; no all-elements §102 showing
• n/a = not prior art against this family on the dates shown, or clearly mis-cited

Non-patent citation (1): "US 5,455,812, 10/1995, Shinada (withdrawn)." I could not verify the content of this item from the sources retrieved, and I will not speculate about what it discloses. It is recorded in the IDS as a withdrawn U.S. application/publication, so its status as prior art under §102 is itself questionable.

E. What is not prior art here

• Family members (same disclosure, same inventive entity): US 6,198,707; US 6,418,099; US 6,570,832; US 6,876,608; US 7,055,987; US 7,245,569; US 7,385,902; US 7,362,669; US 7,859,957; JP 3363712 B2. These are continuations/divisions of the same application and cannot be §102 art against US 6,661,755. The USPTO/OG confirmation of the chain is retrievable at the IU virtual disk library copies of US 6,876,608: https://webapp1.dlib.indiana.edu/virtual_disk_library/index.cgi/[5705037](/patent/5705037)/FID1770/OG/html/1293-1/us06876608-20050405.html
• Later "Cited By" art (i.e., art citing this patent, therefore post-dating it): US 2002/0024901 A1 (Nishimura, Toshiba, priority 2000-08-17 → US 6,795,385) and US 6,785,465 B1 (Matsushita, priority 1998-06-17). These are not prior art against 6,661,755.
• Wider family citing documents cited in the family's other filings (e.g., US 7,106,662, US 7,028,781, US 7,151,732, US 7,548,498, US 7,433,282, the Sanyo EP 1 102 260/261/262 group) — these are later-developed buffer-underrun art that cites the Ricoh family, not prior art against it.

F. Bottom line

1. No single cited reference appears to fully anticipate claims 1–3, because none of the 61 citations expressly discloses both (a) pausing transfer of encoded information while maintaining the encoded content, and (b) the negative limitations "no run-out blocks while paused" and "no run-in blocks during resuming" across a point on a write-once medium. Those negatives are the distinguishing features of the allowed claims.
2. The three references most likely to have driven the §102/§103 rejections (and the most useful if this patent were challenged) are:

• US 5,453,967 (Sony) — dual encoder + memory + interrupt-record controller (claim 1 structure).
• US 5,212,678 / US 5,463,607 (Philips) — buffer-fill-driven interruption and resumption of the write data path (claim 1 trigger and claim 2 restart).
• US 5,432,769 (Matsushita) and US 5,323,367 (Sanyo) — threshold-driven intermittent recording/pause in a disc recorder.
• Add US 5,694,383 (Sony) for the clock-gated encoder pause (FIG. 4), and US 5,748,588 (Sony) as the dummy-data/teaching-away reference.

1. Two citations in the list are evidently defective: JP 3260958 B2 (Olympus, "Distance measuring device") — a mis-citation with no bearing on optical recording; and the non-patent citation US 5,455,812 "Shinada (withdrawn)" whose prior-art status I could not verify.
2. Watch the dates: US 5,815,472 (Pioneer, 1996-08-22) post-dates the 1996-08-06 priority date, and the Hilmer doctrine means the JP priority cannot be used against §102(b)/§102(e) art — the operative §102(b) bar date is 1996-08-05 (one year before the 1997-08-05 US filing).

Confidence note: Claim-mapping in the Tier-1 section is grounded in retrieved text of those references. For the ~35 lower-tier references I worked from title/assignee/date metadata plus the classification context, so those §102 entries are inferences, not verified full-text comparisons — treat the "103" entries as screening suggestions, not concluded rejections.

I'll ground this analysis in the prior-art references listed on the patent page, verifying key references where possible.

Let me examine additional key references and the family's prosecution context.

Obviousness Analysis — U.S. Patent 6,661,755 B2 ("Optical disc apparatus")

Analyst note on method. The following is an independent §103 reconstruction based solely on (a) the claim text and specification reproduced on the patent page and (b) the references listed in that page's Citations / Prior Art sections. I do not have the USPTO file wrapper (office actions, examiner's stated reasons for allowance), so I am not reporting the examiner's actual reasoning — I am testing the claims against the cited art as a PHOSITA would. Where I could verify a reference's disclosure by search, I quote it and give a URL.

1. The claims at issue

The patent issued with three claims, all method claims directed to a write-control method, not to the write-start-point circuits of FIGS. 7/9 (those circuits are described but not claimed):

Effective filing date. Priority JP 8-206705, filed 1996-08-06; U.S. chain 08/906,290 (1997-08-05) → 09/741,900 → 10/082,345 → 10/199,042 (2002-07-22). Every reference in the "Citations (60)" list predates 1996, so each is available under §102(b)/§103(a). Note two items that are not available art:

• US20020024901A1 / US6795385 (Toshiba, Nishimura) is listed under "Cited By," i.e., it is later art (priority 2000-08-17). It cannot be combined against this patent.
• The single non-patent citation, "US 5,455,812, Shinada (withdrawn)," is flagged on the page as withdrawn; a withdrawn application is at best weak art and cannot be relied on for §103 without independent publication/date proof.

2. Level of ordinary skill (PHOSITA)

As of August 1996: a B.S. in electrical engineering (or equivalent) plus 2–4 years in optical-disc drive development, familiar with CD-R/CD-RW Orange Book formatting (Link, Run-In, Run-Out), CIRC/EFM encoding, ATIP and wobble-based servo, CD-decoder/encoder LSIs, and buffer-RAM flow control. The spec itself is written at this level (it explains CIRC, ATIP, EFM, and buffer run as known concepts).

3. Key prior-art references and what they actually teach

P1 — US 5,323,367 (Sanyo; Tamura et al.; pri. 1991-10-25). "Reproduction or recording device having a pause function." This is the closest reference to the pause element. Verified text (EveryPatent/Google PDF):

• It addresses a disc recorder that records compressed data from a memory to the disc intermittently when the memory volume exceeds a preset amount.
• It expressly identifies the exact problem claim 1 solves: "When a pause state is set during recording, there is a problem of the audio data already stored in the memory prior to the setting of pause not being recorded on a disc if the intermittent recording operation from the memory to the disc is ceased merely in response to the pause state setting."
• Its stated object: "to provide a disc recording device that does not make the recorded sound discontinuous at the time of canceling a pause state even when a pause state is set during recording operation."

So P1 = buffer-threshold-triggered pause of the memory→record path, with data retained in memory during the pause, motivated by data continuity. (Sources: http://www.everypatent.com/comp/pat5323367.html ; https://patentimages.storage.googleapis.com/89/5b/63/28e41d03d73cc2/US5323367.pdf)

P2 — US 5,343,455 (Hitachi; Takeuchi et al.; pri. 1990-04-05). "Digital signal overlapped or joined recording method and apparatus." This is the closest reference to the "resume while maintaining data succession across said first point" element. Verified text:

• Background: "Assuming that digital data is to be recorded over a portion of other digital data already stored on a writable disc … or that a pause has occurred in the writing of the digital data and subsequently additional digital data is written on the disc so as to be joined with the previous … a recording operation is halted temporarily at a point and then followed by another recording operation starting from the point at which the first recording operation was halted."
• Claim 5 recites halting at a "recording-haltable position," "discontinuing control by the RAM control means and the recording by the recording means," and then "resuming the recording … and the control by the RAM control means so that the digital data recorded prior to the recording-haltable positions and the digital data recorded after the recording-haltable position are joined on the writable disc without an interleave discrepancy."

That is, in substance, claims 1(d) + 2(g) with the CIRC/interleave continuity concern solved by RAM control. (Sources: https://patents.google.com/patent/US5343455 ; http://www.everypatent.com/comp/pat5343455.html)

P3 — US 5,504,728 (Sony; Yokota et al.; pri. 1992-11-18). Breakpoint recording on a disc. Verified content:

• The recording unit is a cluster of 32 data sectors + 4 linking sectors, and the spec expressly identifies those linking sectors' function: "The linking sectors placed before the data Ck are formed of two sectors L2 and L3 for run-in block … The sector L1 at the rear of the main data Ck of the cluster is for run-out block."
• It teaches continuous joining across a breakpoint, and — critically in the other direction — that "when the last audio data immediately before the stopping or suspension of the recording is short of one cluster … data of a specific pattern, for example all '0's … is additionally recorded as the remaining data to form one complete cluster."

P3 thus supplies the run-in/run-out vocabulary of the claims and also shows the opposite design choice (filler to complete a unit). (Sources: https://patents.justia.com/patent/[5504728](/patent/5504728) ; https://patents.google.com/patent/[US5504728A](/patent/US5504728A)/en)

P4 — US 5,453,967 (Sony; pri. 1992-05-22). Disc recorder with buffer memory. Verified: "The controller controls the memory and the head apparatus so that when data is left in the memory in the record stop state, the record operation by the head apparatus is intermitted after the data in the memory is read out and entirely recorded on the disc," motivated by "it can be prevented that even if the record operation is intermitted at the time of recording data on a disc, the data in the memory is not recorded." This is buffer-state-driven suspension of recording while preserving buffered data. (https://patents.google.com/patent/US5453967)

P5 — US 5,694,383 (Sony; pri. 1995-02-13). Decoder/encoder driving memory reads/writes on separate clocks; verified that data read-out from the buffer RAM "is determined by using the groove sync detection timing as a reference, while considering a so-called 'encode delay'." This is the timing/clock-domain teaching relevant to a pause-and-resume without dropping data.

P6 — US 4,982,110 (Pioneer; pri. 1987-03-13). "Clock generator circuit and a synchronizing signal detection method in a sampled format system and a phase comparator circuit suited for generation of the clock." Generic channel-clock/PLL generation art for the spec's channel-bit-PLL write-start embodiment.

P7 — US 5,432,769 (Matsushita; pri. 1991-04-18) (intermittent recording of variable-length coded data) and US 5,471,450 (Sony; pri. 1991-07-12) (buffer memories for error compensation and reproduction/processing rate mismatch) — secondary art establishing that buffer-threshold-triggered intermittent recording and buffer-level detection were routine.

P8 — US 5,748,588 (Sony; pri. 1994-09-20) (memory controller adding dummy data to complete a sector) and US 5,808,995 (Matsushita; pri. 1994-07-22) (variable read transfer speed) — filler/handling and rate-matching art.

4. Claim charts and the obviousness combinations

Combination A (primary): P2 (Hitachi '455) + P1 (Sanyo '367) → claims 1 and 2

Motivation to combine. Both are writable/rewritable optical-disc recorders that stage data through a RAM before an encoder/recorder, and both are directed to the same problem — preserving data succession when the record operation must be interrupted and then restarted. P1 supplies the trigger (memory level) and expressly describes the pause/resume-of-recording-with-data-retained problem; P2 supplies the solution to the join (halt and resume so that pre-halt and post-halt data are joined without interleave discrepancy). A PHOSITA confronted with P1's stated failure mode (data present in memory when pause is asserted) would look to the known joined-recording technique of P2 and route the pause signal to the RAM/encoder control exactly as P1 contemplates for its pause operation. Combination of two references in the same field, addressing the same known problem, with no change in principle of operation, is the paradigm KSR case.

Reasonable expectation of success. Both references use the same physical layer (CIRC/interleaved data, RAM-buffered encoder, optical pickup), so no reconstruction or new mechanism is required; the combination is a control-signal routing change with predictable results.

Combination B (buffer-level detection): P4 (Sony '967) and/or P7 → the "buffer below threshold" and "second threshold" elements

P4's record-stop-when-data-remains-in-memory control, and P7's intermittent-recording/buffer-level schemes, show that comparing a buffer fill level against a preset/ threshold value to start and stop recording was conventional. These fill in claim 1(c) and claim 2(f) without adding anything inventive.

Combination C (timing / write-start-point): P5 (Sony '383) + P6 (Pioneer '110)

These are relevant to the specification's second object (channel-bit PLL or frame-sync counting to find the end of previously written data, FIGS. 7–10) and to the "maintaining data succession across said first point" concept. They are not elements of claims 1–3, so they are supporting rather than claim-breaking art. If the claims were ever construed to require accurate re-positioning to the prior end point, P5 (groove-sync-referenced encode timing plus explicit "encode delay" compensation) and P6 (sampled-format clock generation/phase comparison) would supply that element.

Combination D (the negative limitations): P3 (Sony '728) + P1/P2

P3 defines run-in blocks (L2, L3) and run-out blocks (L1) in a 32+4-sector cluster, and teaches joining data across a breakpoint. It therefore supplies the very block taxonomy the claims exclude. Read together with P1/P2's pause-and-join control, a PHOSITA would recognize that "pausing" (as opposed to "Stop Write") means the mid-track case in which postamble/run-out handling is simply not performed, and that on restart the drive re-acquires sync rather than spending a Run-In.

5. The negative limitations are the only real battleground — and they are weak

Claims 1–3 turn on what is not written: no run-out blocks while paused (claims 1, 3) and no run-in blocks on resume (claim 2). Two points cut against patentability:

1. These are near-definitional of a mid-track pause. The specification itself says "Stop Write is [the] normal sequence of writing the Run out blocks" and FIG. 2 shows the Link/Run-In/Run-Out blocks as session overhead. A drive that simply halts the record circuit mid-track (the P1/P4 scenario) does not write a Run-Out — not because of any inventive insight, but because Run-Out is by convention written at Stop Write. The negative limitation is therefore largely the automatic consequence of the admittedly known pause, and a negative limitation that is the inherent result of a known process does not confer patentability.
2. The art already recognized the "continuity without a linkage artifact" goal. P2's entire premise is joining pre-halt and post-halt data without an interleave discrepancy, and P2's claim 2 retains interleave-pending data in RAM during the halt — i.e., the data is "maintained." Nothing in P2 requires interposing a Run-In or Run-Out; the reference affirmatively teaches the joined (no-run-in/no-run-out) result the claims recite.

The best counter-argument for the patentee is P3 ('728): its teaching that a stop/suspend mid-unit is completed with a filler pattern to complete the cluster points in the opposite direction (write something, don't stop bare). That could be framed as a teaching away from a pause that leaves the medium with no postamble. But the teaching-away argument is fragile: (a) P3 concerns a different medium/system (MO mini-disc clusters with linking sectors), and (b) it is addressed to the stop/pause key case, not to a buffer-underrun abort, so a PHOSITA would not treat it as a prohibition on the claimed pause. Under KSR, a reference must "criticize, discredit, or otherwise discourage" the claimed solution before it teaches away; P3 does not disparage bare interruption — it merely selects a different treatment for user-initiated stop.

6. Secondary considerations and other counterweights the patentee could raise

These must be weighed but, on this record, they are addressable:

• Industry adoption / copying. The page's "Families Citing this family (72)" list is striking: it includes Sony, Sanyo, Ricoh, Yamaha, Philips, MediaTek and Via patents on buffer-underrun control, e.g., "Method for reducing frequency of buffer under run" (Lite-On), "Appropriate and method for connecting interrupted recording" / "Recording link method and drive device for optical storage media" (MediaTek), "Method of continuous burn for storage medium" (Via), "Robust position detection for incremental recording" (Philips). This is evidence that the pause-and-seamlessly-resume concept became the industry standard (the "Burn-Proof"/"JustLink"/"Seamless Link" era of CD-RW drives) — supporting nonobviousness via industry acceptance and blocking patents.
• Enforcement. The page records litigation (W.D. Wis. 3:06-cv-00462; N.D. Cal. 5:07-cv-01942 and 3:07-cv-01942) and a Darts-IP "first worldwide family litigation" link, consistent with this being a foundational, asserted family — which supports commercial significance.
• Caution: industry-wide adoption of a buffer-underrun pause after 1997 also cuts the other way — it shows that once the problem was squarely framed, the solution was readily arrived at by many workers, which is consistent with obviousness. And under KSR, "a court must ask whether the improvement is more than the predictable use of prior art elements according to their established functions."

7. Conclusion on §103

• Claims 1 and 2 are, on the face of the cited art, vulnerable. The strongest single combination is US 5,343,455 (Hitachi) in view of US 5,323,367 (Sanyo), optionally further in view of US 5,453,967 (Sony) and/or US 5,432,769 (Matsushita) for the buffer-threshold detection, and US 5,504,728 (Sony) for the run-in/run-out block taxonomy. Every positive element (buffer→encoder transfer, encoded data→record circuit, buffer-level-triggered pause, retention of encoded data, restart with data succession) is disclosed or rendered obvious; the distinguishing negative limitations (no run-out while paused; no run-in on resume) are the inherent/natural result of the very pause-and-join operation the references teach, and P3's contrary filler practice is not a legally sufficient teaching away.
• Claim 3 adds nothing — it merely repeats claim 1's exclusion inside claim 2's method, so it rises and falls with claim 2.
• Claim 2 is the hardest to invalidate because "maintaining data succession across said first point" is a functional result, and the closest reference (P2) achieves "joined … without an interleave discrepancy" through a RAM-control scheme rather than through the claimed encoder-clock masking. A patentee could argue that P2's route (re-interleaving with retained pending data) is a structurally different mechanism from masking the encoder clock (spec FIG. 4). That is a genuine but refinement-level distinction, and P5 (Sony '383, encoder/memory clock-domain control with groove-sync-referenced read timing) supplies the missing clock-gating teaching, making the combination of P2 + P1 + P5 complete as to claim 2.
• Caveats. (i) I have not seen the actual USPTO file history; the claims may have been allowed on a record (e.g., a specific-claim-construction statement or an art admission) that narrows them beyond this analysis. (ii) I did not verify US 5,745,445 (Matsushita) or US 4,583,211 (Toshiba) text directly; they were not essential to the combinations above. (iii) The "Cited By" Toshiba reference (US20020024901A1 / US6795385) is post-1996 priority and must not be used as §103 art against this patent despite appearing on the page.

Primary sources cited: patent page https://patents.google.com/patent/[US6661755](/patent/US6661755)/en ; US5,323,367 http://www.everypatent.com/comp/pat5323367.html ; US5,343,455 https://patents.google.com/patent/US5343455 ; US5,504,728 https://patents.justia.com/patent/5504728 ; US5,453,967 https://patents.google.com/patent/US5453967 ; US5,694,383 (Sony) as reproduced at uspto.report.