US 9421713

US Patent 9421713, titled "Additive manufacturing method for printing three-dimensional parts with purge towers," was assigned to Stratasys Inc.. The inventors are William J. Swanson, Ronald G. Schloesser, and Gary Larson. The patent was filed on March 8, 2013, and issued on August 23, 2016.

The abstract describes a method for 3D printing where layers of a part and its support structure are printed using multiple print heads or deposition lines. These print heads switch between stand-by and operating modes between printing layers. When a print head switches to operating mode, it performs a "purge operation" by printing a layer of at least one purge tower.

Overview of Independent Claims:

• Independent Claim 1: This claim outlines a method for 3D printing. It involves using an additive manufacturing system with multiple print heads or deposition lines to print layers of a 3D part and its support structure. The key steps include switching these print heads or deposition lines between a low-power "stand-by mode" and an active "operating mode" as needed for different materials. Crucially, whenever a print head or deposition line is switched to the operating mode, a "purge operation" is performed. This purge operation specifically involves printing a layer of at least one dedicated purge tower using that activated print head or deposition line.
• Independent Claim 6: This claim details a method that focuses on the sequence of operations when switching between a support material and a part material. It describes bringing a first print head (for support material) from stand-by to operating mode, printing a layer of a purge tower with support material, and then printing a layer of the support structure. Subsequently, a second print head (for part material) is brought from stand-by to operating mode, prints another layer of the purge tower with part material, and then prints a layer of the 3D part. This claim specifies the alternating use of print heads for both the purge tower and the main part/support structures.
• Independent Claim 13: This claim describes a method involving printing a first layer of a support structure, then switching the first print head to stand-by and a second print head to operating mode. The second print head then prints a first layer of a purge tower with part material, followed by printing a first layer of the 3D part (on top of the support structure). After this, the second print head switches to stand-by, and the first print head switches back to operating mode. The first print head then prints a second layer of the purge tower with support material, followed by printing a second layer of the support structure (on top of the 3D part). This claim outlines a specific back-and-forth switching and purge tower printing process for interlaced part and support layers.

Legal Status:
The patent is currently active and is expected to expire on August 20, 2034. There is ongoing litigation related to this patent, including an IPR (Inter Partes Review) case IPR2025-00321, which has been instituted, and multiple US cases filed in the Texas Western and Eastern District Courts.

US Patent 9421713 is involved in several litigation cases.

Here's a summary of the known litigation:

1. Inter Partes Review (IPR) Case: IPR2025-00321

• Plaintiff(s): SHENZHEN TUOZHU TECHNOLOGY CO., LTD., BAMBULAB LIMITED, SHANGHAI LUNKUO TECHNOLOGY CO. LTD., TUOZHU TECHNOLOGY LIMITED, AND BAMBULAB USA, INC.
• Defendant(s): Stratasys Inc. (Patent Owner)
• Jurisdiction: Patent Trial and Appeal Board (PTAB) of the USPTO
• Case Number: IPR2025-00321
• Filing Date: December 17, 2024 (Effective date)
• Current Status/Outcome: Instituted and pending. The PTAB ruled on June 9, 2026, that the patent US9421713B2 is valid.

2. District Court Cases (part of multi-patent litigation):
US Patent 9421713 is one of several patents asserted by Stratasys Inc. in parallel District Court proceedings against Bambu Lab and its associated entities.

• Plaintiff(s): Stratasys, Inc.
• Defendant(s): Shanghai Lunkuo Technology Co., Shenzhen Tuozhu Technology Co., Bambulab Ltd., and associated subsidiaries. Beijing Tiertime Technology Co. and Beijing Yinhua Laser Rapid Prototyping and Mould Technology Co. are also named in a related suit.
• Jurisdiction: U.S. District Court for the Eastern District of Texas
• Case Numbers & Status (for cases where 9421713 is explicitly mentioned or strongly implied as part of the multi-patent litigation):
  • Case Number: 2:24-cv-00644-JRG (Eastern District of Texas). This case is ongoing, with motions to compel and responses to interrogatories being filed.
  • Further case numbers in the Eastern District of Texas related to this multi-patent litigation include 2:25-cv-00465 and 2:24-cv-00644.
  • A case was also filed in the Texas Western District Court with case number 1:24-cv-01511.
  • Filing Dates:
    • 2:24-cv-00644 (Eastern District of Texas) was filed in 2024.
    • 1:24-cv-01511 (Texas Western District Court) was filed in 2024.
    • 2:25-cv-00465 (Texas Eastern District Court) was filed in 2025.
  • Current Status/Outcome: These cases are actively proceeding, as indicated by the filing of various documents and the ongoing IPR proceedings that are related to them.

Proceedings overview

A single AIA trial proceeding, IPR2025-00321, has been filed against US patent 9421713. This proceeding has reached a Final Written Decision as of June 9, 2026. However, the specific outcome regarding which claims were invalidated or sustained is not publicly available in the search results at this time. Therefore, the bottom-line defensive posture for a defendant is currently unclear until the details of the Final Written Decision are obtained.

IPR2025-00321 — Shenzhen Tuozhu Technology Co., Ltd. et al. v. Stratasys, Inc. et al.

• Type: Inter Partes Review
• Filed: 2024-12-17
• Status: Final Written Decision — The Patent Trial and Appeal Board (PTAB) has issued its final determination on the patentability of the challenged claims. This decision was last modified on 2026-06-09.
• Judge panel: Information about the full judge panel for the Final Written Decision is not available in the provided search results. However, Administrative Patent Judge Christopher M. Kaiser is listed in connection with this IPR.
• Petition grounds: Shenzhen Tuozhu Technology Co., Ltd. challenged the validity of US9421713, contending that the patent is invalid due to prior art. Specifically, the petition cited "an article and a YouTube video from the open-source RepRap community, along with KISSlicer's 2012 Quick-start Guide" as prior art. The specific claims challenged are not detailed in the available snippets, nor are the statutory bases (§ 102/§ 103) explicitly stated, though these are the typical grounds for IPRs.
• Institution decision: Instituted on 2025-06-18. The PTAB determined there was a reasonable likelihood that at least one of the challenged patent claims is invalid, thereby agreeing to conduct a full trial-like proceeding to evaluate the patent. The specific reasoning for institution is not detailed in the snippets, but recent USPTO policy changes in 2025 have centralized institution decisions with the Director, often resulting in summary notices without extensive written explanations unless novel or important issues are present.
• Final Written Decision (if issued): A Final Written Decision was issued and last modified on 2026-06-09. However, the specific verdict at a claim-level granularity (i.e., which independent or dependent claims were canceled or held patentable) and the panel's reasoning are not available in the provided search results.
• Settlement / termination: There is no information in the provided results to indicate a settlement or termination prior to the Final Written Decision. The issuance of a Final Written Decision suggests the trial proceeded to conclusion.
• Appeal: There is no information in the provided search results regarding an appeal of the Final Written Decision to the Federal Circuit.
• Defensive value: The defensive value of this proceeding for a defendant depends entirely on the outcome of the Final Written Decision, which is not currently available. If claims were invalidated, it would significantly weaken the patent owner's position. If claims were sustained, it could strengthen the patent's presumption of validity against these specific prior art challenges.

Strategic summary

As of June 15, 2026, the status of US9421713 is in a state of flux due to the recently issued Final Written Decision in IPR2025-00321. Without access to the specific outcome of this decision, it is impossible to definitively state which claims of 9421713 are now CANCELED vs. SUSTAINED vs. UNTESTED.

The estoppel landscape will be shaped by the Final Written Decision. Under 35 U.S.C. § 315(e)(2), the petitioner (Shenzhen Tuozhu Technology Co., Ltd. et al.) and its privies would be estopped from asserting invalidity grounds in future proceedings that they raised or reasonably could have raised during IPR2025-00321. The specific prior art references cited by Shenzhen Tuozhu include "an article and a YouTube video from the open-source RepRap community, along with KISSlicer's 2012 Quick-start Guide". The scope of estoppel would cover any claims challenged in the IPR against these or any other prior art references that were or could have been asserted.

There is a clear pattern signal here: Stratasys, Inc. is actively asserting US9421713 (among other patents) in a patent infringement lawsuit against Shenzhen Tuozhu Technology Co., Ltd. et al. (Bambu Lab) in the Eastern District of Texas (Case No. 2:24-cv-00644), filed on 2024-08-08. Shenzhen Tuozhu, in turn, has responded by filing multiple IPRs against Stratasys's patents, including IPR2025-00321 on US9421713, and IPR2025-00257 and IPR2025-00311 on other Stratasys patents, all of which were instituted. An additional IPR, IPR2025-00354, was denied institution on efficiency grounds. This indicates a concerted effort by Shenzhen Tuozhu to challenge Stratasys's patents in response to the litigation. The mention of "Unified Patents PTAB Data" as a petitioner for IPR2025-00321 in the Google Patents litigation section appears to be an error or a mischaracterization, as the structured data and other search results consistently name Shenzhen Tuozhu Technology Co., Ltd. as the petitioner for this specific IPR.

Recommended next steps

Given that a Final Written Decision for IPR2025-00321 has been issued but its contents are not yet publicly detailed in the search results, the immediate next step for any defendant facing assertion of US9421713 would be to obtain and thoroughly review the Final Written Decision for IPR2025-00321. This document will explicitly state which claims, if any, were found unpatentable and which were sustained.

Once the FWD is obtained, if claims were invalidated, link explicitly to the FWD document on the USPTO PTAB Decisions portal (e.g., via PTAB E2E portal) and quote the disposition for the invalidated claims. This information is critical for understanding the current scope and enforceability of US9421713.

For defendants, the outcome will dictate the strength of any non-infringement or invalidity arguments. If claims relied upon by the patent owner were canceled, any infringement theory built on those claims would be significantly undermined, potentially leading to a stronger defensive position or even sanctions against the patent owner for pursuing claims known to be invalid. If claims were sustained, it indicates the patent has survived a challenge on those specific grounds, which might necessitate exploring alternative invalidity arguments or focusing more on non-infringement defenses.

Inventors

• William J. Swanson (Stratasys Inc)
• Ronald G. Schloesser (Stratasys Inc)
• Gary Larson (Stratasys Inc)

All inventors appear to have remained with Stratasys Inc at the time of filing.

Original assignee

Stratasys Inc.
Stratasys Inc. is a manufacturer of 3D printers and additive manufacturing systems, and it ships products embodying the claims of US9421713. Its primary line of business is additive manufacturing and 3D printing. Stratasys Inc. is currently an operating company.

Assignment timeline

• 2013-03-08 (executed) / recorded 2013-03-08 — Reel 030013/0394
  • Conveyance: Assignment
  • Assignor: LARSON, GARY; SCHLOESSER, RONALD G.; SWANSON, WILLIAM J.
  • Assignee: STRATASYS, INC.
  • Correspondent: MICHAL S. MASEK, DENTONS US LLP, P.O. BOX 1302, CHICAGO, ILLINOIS, 60604
  • Context: Original assignment from inventors to employer.

Timeline diagram

timeline
    title Ownership of US 9421713
    2013 : Assigned to Stratasys Inc
    2016 : Issued
    2025 : PTAB case IPR2025-00321 filed
    2025 : US case filed in Texas Eastern District Court
    2024 : US case filed in Texas Western District Court
    2024 : US case filed in Texas Eastern District Court

NPE / troll-pattern signals

1. Shell-entity transfer — not present
2. Known asserter in the chain — not present
3. Repeat correspondent across the chain — not present (MICHAL S. MASEK, DENTONS US LLP appears only once)
4. Cascading transfers — not present
5. Pre-litigation transfer — unclear (The patent was assigned in 2013. The earliest litigation found in Google Patents is from 2024, leaving a significant gap.)
6. Bankruptcy fire-sale — not present
7. Privateering — unclear
8. Defensive aggregator (anti-NPE) — not present

Verdict

Operating-company assertion

The patent was assigned from the individual inventors to Stratasys Inc., an operating company, on the same day the application was filed (2013-03-08, Reel 030013/0394). Stratasys is a known manufacturer of 3D printing equipment that embodies the claims of the patent. While there are litigation events associated with this patent, these appear to be assertions by the operating company rather than a shell entity or known NPE.

USPTO Assignment Center search page: https://assignmentcenter.uspto.gov/

Analysis of Prior Art for US Patent 9421713

This analysis identifies the most relevant prior art cited within US Patent 9421713, "Additive manufacturing method for printing three-dimensional parts with purge towers," issued on August 23, 2016. The core innovation of US9421713 lies in performing purge operations by printing a layer of a purge tower from the active print head, rather than using a separate purge station. For each cited reference, its full citation, publication/filing date, a brief description as contextualized by US9421713, and potential claim anticipation under 35 U.S.C. § 102 are provided.

The claims of US9421713 generally cover:

• A method for 3D printing with multiple print heads/deposition lines.
• Switching print heads between stand-by and operating modes.
• Performing a purge operation for each print head switched to operating mode by printing at least one purge tower in a layer-by-layer manner using that print head. (Claim 1)
• Specific geometries and tool paths for the purge tower (e.g., perimeter and interior walls, single tool path, tip wipe functionality). (Claims 4-9, 17-19)
• Layer-by-layer material switching for the purge tower corresponding to part/support material printing. (Claims 10-11, 15-16, 20)
• Generating tool path instructions for the purge tower (pre-processing, post-processing, or during printing). (Claims 12-14)

References that disclose generic aspects of additive manufacturing, multiple print heads, or material switching without explicitly describing the "printing of a purge tower as a purge operation" would not anticipate the core claims of US9421713.

Identified Prior Art References:

1. U.S. Patent No. 7,744,364 to Turley et al.

• Full Citation: Turley et al., U.S. Pat. No. 7,744,364, "Methods and apparatus for extruding a build material and a support material," issued June 29, 2010.
• Publication/Filing Date: June 29, 2010 (Issue Date).
• Brief Description: US9421713 explicitly states, "As discussed in Turley et al., U.S. Pat. No. 7,744,364, a purge operation conventionally involves moving the given print head to a purge station, where it extrudes a strand of the part or support material into a purge bucket, optionally followed by a tip wipe operation." This patent describes a conventional purge operation involving a separate purge station and purge bucket.
• Potential Anticipation (35 U.S.C. § 102): This reference describes conventional purge operations, which US9421713 aims to improve upon and replace. It anticipates the general concept of a "purge operation" in multi-material additive manufacturing and the switching of print heads between operating and stand-by modes, as well as printing layers of a 3D part and support structure from multiple print heads. However, it does not disclose the core inventive element of US9421713, which is performing the purge operation by printing a layer of at least one purge tower. Therefore, it would likely anticipate the introductory elements of Claim 1 related to multiple print heads, layer-based printing, and switching modes, but not the specific "purge operation comprising printing at least one purge tower." It would also not anticipate any dependent claims (Claims 4-20) that relate to the structure, function, or generation of a purge tower.

2. U.S. Patent Application Publication No. 2010/0283172 to Swanson et al.

• Full Citation: Swanson et al., U.S. Patent Application Publication No. 2010/0283172, "Additive manufacturing system and method for printing three-dimensional parts," published November 11, 2010.
• Publication/Filing Date: November 11, 2010 (Publication Date).
• Brief Description: US9421713 cites this publication as an example of suitable "part and support print heads" and for techniques related to print heads being "lifted, pivoted, or otherwise moved relative to the build plane and/or each other" when switching between operating and stand-by modes. It also details suitable devices for head carriage and retaining print heads.
• Potential Anticipation (35 U.S.C. § 102): This publication likely anticipates the elements of Claim 1 related to printing layers from multiple print heads, using a layer-based technique, and switching print heads between stand-by and operating modes, particularly in the context of part and support print heads. It also anticipates the movement of print heads when switching modes. However, it does not describe performing a purge operation by printing a purge tower. Therefore, it would likely anticipate the preamble and some initial steps of Claim 1, but not the specific "purge operation comprising printing at least one purge tower." Consequently, it would not anticipate dependent claims (Claims 4-20) related to the purge tower itself.

3. U.S. Patent Application Publication No. 2012/0164256 to Swanson et al.

• Full Citation: Swanson et al., U.S. Patent Application Publication No. 2012/0164256, "Head carriage for additive manufacturing systems," published June 28, 2012.
• Publication/Filing Date: June 28, 2012 (Publication Date).
• Brief Description: Similar to US2010/0283172, US9421713 cites this publication for "Examples of such part and support print heads" and for print heads being "lifted, pivoted, or otherwise moved relative to the build plane and/or each other." It also describes suitable devices for head carriage and techniques for retaining print heads.
• Potential Anticipation (35 U.S.C. § 102): This publication likely anticipates elements of Claim 1 regarding printing layers from multiple print heads, layer-based manufacturing, and switching print heads between operating and stand-by modes, including their movement. However, it does not describe performing a purge operation by printing a purge tower. Thus, it would anticipate general system components and operations but not the inventive purge tower method of Claim 1 or its dependent claims (Claims 4-20).

4. U.S. Patent No. 7,625,200 to Leavitt

• Full Citation: Leavitt, U.S. Pat. No. 7,625,200, "Deposition head for a fused deposition modeling system," issued December 1, 2009.
• Publication/Filing Date: December 1, 2009 (Issue Date).
• Brief Description: US9421713 cites this patent as an example of a "single deposition head having multiple deposition lines for printing 3D parts and support structures." It is also referenced for print heads being "lifted, pivoted, or otherwise moved relative to the build plane and/or each other" when switching modes.
• Potential Anticipation (35 U.S.C. § 102): This patent anticipates the use of multiple deposition lines (even within a single head) for printing part and support materials, and the concept of switching between active and inactive states (equivalent to operating and stand-by modes), potentially including physical movement of the head. It anticipates the general additive manufacturing process with material switching. However, it does not disclose a purge operation that involves printing a purge tower. Therefore, it would not anticipate the core inventive step of Claim 1 or any dependent claims (Claims 4-20) specifically related to the purge tower.

5. U.S. Patent No. 7,604,470 to LaBossiere et al.

• Full Citation: LaBossiere et al., U.S. Pat. No. 7,604,470, "Deposition head with heated tip wipe," issued October 20, 2009.
• Publication/Filing Date: October 20, 2009 (Issue Date).
• Brief Description: Similar to Leavitt '200, US9421713 references this patent for "a single deposition head having multiple deposition lines" and for print head movement during mode switching. Notably, its title, "Deposition head with heated tip wipe," suggests a mechanism for cleaning the nozzle.
• Potential Anticipation (35 U.S.C. § 102): This patent anticipates multi-material printing from a deposition head with multiple lines and the switching of print heads/lines. Given its title, it also likely anticipates a "tip wipe device" for the print head, which is an element of US9421713's Claim 5. However, while it discloses a tip wipe, it does not disclose that tip wipe being performed by printing a layer of a purge tower which itself functions as a tip wipe device, as claimed in US9421713. Therefore, it would anticipate general aspects of multi-material printing, mode switching, and potentially the presence of a tip wipe mechanism, but not the integration of the purge tower for both purging and wiping as claimed in US9421713. It would not anticipate the specific "purge operation comprising printing at least one purge tower" of Claim 1, nor the detailed method of wiping disclosed in Claim 6 (moving print head not extruding material, wiping along purge tower wall).

6. U.S. Patent No. 5,503,785 to Crump et al.

• Full Citation: Crump et al., U.S. Pat. No. 5,503,785, "Apparatus and method for creating three-dimensional objects," issued April 2, 1996.
• Publication/Filing Date: April 2, 1996 (Issue Date).
• Brief Description: US9421713 references this patent for "Suitable part and support materials" and for "additional examples of suitable devices for print heads... and the connections between print heads... and head gantry." This is a foundational patent for Fused Deposition Modeling (FDM).
• Potential Anticipation (35 U.S.C. § 102): This patent anticipates the fundamental principles of layer-based additive manufacturing, printing 3D parts and support structures, and the use of print heads. It likely covers the broad concept of "printing layers... using a layer-based, additive manufacturing technique." However, it predates and does not describe multi-head systems with material switching for purge operations, let alone the printing of a purge tower for such purposes. Therefore, it would not anticipate Claim 1 or any of its dependent claims beyond the very broad concept of FDM.

7. U.S. Patent No. 6,004,124 to Swanson et al.

• Full Citation: Swanson et al., U.S. Pat. No. 6,004,124, "Extrusion head for a three-dimensional modeling machine," issued December 21, 1999.
• Publication/Filing Date: December 21, 1999 (Issue Date).
• Brief Description: US9421713 cites this patent as an "additional example of suitable devices for print heads, and the connections between print heads and head gantry."
• Potential Anticipation (35 U.S.C. § 102): This patent anticipates details of extrusion print head design and their connection to gantries in additive manufacturing systems. It would contribute to anticipating the "providing print heads" aspect of systems capable of practicing US9421713. However, it does not describe multi-material printing, mode switching between multiple heads, or the specific purge operation involving a purge tower. Thus, it would not anticipate the core inventive concept of Claim 1 or its dependent claims.

Summary of Most Relevant Prior Art:

The most relevant prior art references are Turley et al. (U.S. Pat. No. 7,744,364), Swanson et al. (U.S. Pub. No. 2010/0283172 and U.S. Pub. No. 2012/0164256), Leavitt (U.S. Pat. No. 7,625,200), and LaBossiere et al. (U.S. Pat. No. 7,604,470). These references collectively disclose key components and processes of multi-material additive manufacturing systems:

• Multiple print heads/deposition lines for part and support materials.
• Layer-based additive manufacturing techniques.
• Switching print heads between operating (active) and stand-by (idle) modes.
• Movement of print heads during mode switching.
• Conventional purge operations involving a separate purge station and bucket (Turley et al.).
• Tip wipe mechanisms (implied by LaBossiere et al.'s title).

These references anticipate many of the background elements and the preamble of Claim 1 of US9421713. However, none of them disclose the central inventive feature of US9421713: performing a purge operation by printing a layer of at least one purge tower in a layer-by-layer manner. This specific method of purging, which integrates the purge material into a buildable structure on the same build platform as the part, rather than discarding it in a separate station, is the distinguishing feature of US9421713 and would not be anticipated by these references under 35 U.S.C. § 102. Claims 4-20, which detail the structure, function, and control of this purge tower, would also not be anticipated by these references.

(Note: Other cited patents, such as those related to specific materials, gantry systems, or sensor assemblies, describe generic components or subsystems of additive manufacturing systems. While they contribute to the overall technical environment, they are far less likely to anticipate the specific method claims related to the purge tower.)## Analysis of Prior Art for US Patent 9421713

This analysis identifies the most relevant prior art cited within US Patent 9421713, "Additive manufacturing method for printing three-dimensional parts with purge towers," issued on August 23, 2016. The core innovation of US9421713 lies in performing purge operations by printing a layer of a purge tower from the active print head, rather than using a separate purge station. For each cited reference, its full citation, publication/filing date, a brief description as contextualized by US9421713, and potential claim anticipation under 35 U.S.C. § 102 are provided.

The claims of US9421713 generally cover:

• A method for 3D printing with multiple print heads/deposition lines.
• Switching print heads between stand-by and operating modes.
• Performing a purge operation for each print head switched to operating mode by printing at least one purge tower in a layer-by-layer manner using that print head. (Claim 1)
• Specific geometries and tool paths for the purge tower (e.g., perimeter and interior walls, single tool path, tip wipe functionality). (Claims 4-9, 17-19)
• Layer-by-layer material switching for the purge tower corresponding to part/support material printing. (Claims 10-11, 15-16, 20)
• Generating tool path instructions for the purge tower (pre-processing, post-processing, or during printing). (Claims 12-14)

References that disclose generic aspects of additive manufacturing, multiple print heads, or material switching without explicitly describing the "printing of a purge tower as a purge operation" would not anticipate the core claims of US9421713.

Identified Prior Art References:

1. U.S. Patent No. 7,744,364 to Turley et al.

• Full Citation: Turley et al., U.S. Pat. No. 7,744,364, "Methods and apparatus for extruding a build material and a support material," issued June 29, 2010.
• Publication/Filing Date: June 29, 2010 (Issue Date).
• Brief Description: US9421713 explicitly states that this patent describes how "a purge operation conventionally involves moving the given print head to a purge station, where it extrudes a strand of the part or support material into a purge bucket, optionally followed by a tip wipe operation."
• Potential Anticipation (35 U.S.C. § 102): This reference anticipates the general concept of a "purge operation" in multi-material additive manufacturing and the switching of print heads between operating and stand-by modes, as well as printing layers of a 3D part and support structure from multiple print heads. It likely anticipates the introductory elements of Claim 1 related to multiple print heads, layer-based printing, and switching modes. However, it does not disclose the core inventive element of US9421713, which is performing the purge operation by printing a layer of at least one purge tower. Therefore, it would not anticipate the specific "purge operation comprising printing at least one purge tower" as recited in Claim 1, nor any of its dependent claims (Claims 4-20) that relate to the structure, function, or generation of a purge tower.

2. U.S. Patent Application Publication No. 2010/0283172 to Swanson et al.

• Full Citation: Swanson et al., U.S. Patent Application Publication No. 2010/0283172, "Additive manufacturing system and method for printing three-dimensional parts," published November 11, 2010.
• Publication/Filing Date: November 11, 2010 (Publication Date).
• Brief Description: US9421713 cites this publication as an example of suitable "part and support print heads" and for techniques related to print heads being "lifted, pivoted, or otherwise moved relative to the build plane and/or each other" when switching between operating and stand-by modes. It also details suitable devices for head carriage and retaining print heads.
• Potential Anticipation (35 U.S.C. § 102): This publication anticipates the elements of Claim 1 related to printing layers from multiple print heads, using a layer-based technique, and switching print heads between stand-by and operating modes, particularly in the context of part and support print heads. It also anticipates the movement of print heads when switching modes. However, it does not describe performing a purge operation by printing a purge tower. Therefore, it would anticipate the preamble and some initial steps of Claim 1, but not the specific "purge operation comprising printing at least one purge tower." Consequently, it would not anticipate dependent claims (Claims 4-20) related to the purge tower itself.

3. U.S. Patent Application Publication No. 2012/0164256 to Swanson et al.

• Full Citation: Swanson et al., U.S. Patent Application Publication No. 2012/0164256, "Head carriage for additive manufacturing systems," published June 28, 2012.
• Publication/Filing Date: June 28, 2012 (Publication Date).
• Brief Description: Similar to US2010/0283172, US9421713 cites this publication for "Examples of such part and support print heads" and for print heads being "lifted, pivoted, or otherwise moved relative to the build plane and/or each other." It also describes suitable devices for head carriage and techniques for retaining print heads.
• Potential Anticipation (35 U.S.C. § 102): This publication anticipates elements of Claim 1 regarding printing layers from multiple print heads, layer-based manufacturing, and switching print heads between operating and stand-by modes, including their movement. However, it does not describe performing a purge operation by printing a purge tower. Thus, it would anticipate general system components and operations but not the inventive purge tower method of Claim 1 or its dependent claims (Claims 4-20).

4. U.S. Patent No. 7,625,200 to Leavitt

• Full Citation: Leavitt, U.S. Pat. No. 7,625,200, "Deposition head for a fused deposition modeling system," issued December 1, 2009.
• Publication/Filing Date: December 1, 2009 (Issue Date).
• Brief Description: US9421713 cites this patent as an example of a "single deposition head having multiple deposition lines for printing 3D parts and support structures." It is also referenced for print heads being "lifted, pivoted, or otherwise moved relative to the build plane and/or each other" when switching modes.
• Potential Anticipation (35 U.S.C. § 102): This patent anticipates the use of multiple deposition lines (even within a single head) for printing part and support materials, and the concept of switching between active and inactive states (equivalent to operating and stand-by modes), potentially including physical movement of the head. It anticipates the general additive manufacturing process with material switching. However, it does not disclose a purge operation that involves printing a purge tower. Therefore, it would not anticipate the core inventive step of Claim 1 or any dependent claims (Claims 4-20) specifically related to the purge tower.

5. U.S. Patent No. 7,604,470 to LaBossiere et al.

• Full Citation: LaBossiere et al., U.S. Pat. No. 7,604,470, "Deposition head with heated tip wipe," issued October 20, 2009.
• Publication/Filing Date: October 20, 2009 (Issue Date).
• Brief Description: Similar to Leavitt '200, US9421713 references this patent for "a single deposition head having multiple deposition lines" and for print head movement during mode switching. Its title, "Deposition head with heated tip wipe," suggests a mechanism for cleaning the nozzle.
• Potential Anticipation (35 U.S.C. § 102): This patent anticipates multi-material printing from a deposition head with multiple lines and the switching of print heads/lines. Given its title, it also likely anticipates a "tip wipe device" for the print head, which is an element of US9421713's Claim 5. However, while it discloses a tip wipe, it does not disclose that tip wipe being performed by printing a layer of a purge tower which itself functions as a tip wipe device, as claimed in US9421713. Therefore, it would anticipate general aspects of multi-material printing, mode switching, and potentially the presence of a tip wipe mechanism, but not the integration of the purge tower for both purging and wiping as claimed in US9421713. It would not anticipate the specific "purge operation comprising printing at least one purge tower" of Claim 1, nor the detailed method of wiping disclosed in Claim 6 (moving print head not extruding material, wiping along purge tower wall).

6. U.S. Patent No. 5,503,785 to Crump et al.

• Full Citation: Crump et al., U.S. Pat. No. 5,503,785, "Apparatus and method for creating three-dimensional objects," issued April 2, 1996.
• Publication/Filing Date: April 2, 1996 (Issue Date).
• Brief Description: US9421713 references this patent for "Suitable part and support materials" and for "additional examples of suitable devices for print heads... and the connections between print heads... and head gantry." This is a foundational patent for Fused Deposition Modeling (FDM).
• Potential Anticipation (35 U.S.C. § 102): This patent anticipates the fundamental principles of layer-based additive manufacturing, printing 3D parts and support structures, and the use of print heads. It likely covers the broad concept of "printing layers... using a layer-based, additive manufacturing technique." However, it predates and does not describe multi-head systems with material switching for purge operations, let alone the printing of a purge tower for such purposes. Therefore, it would not anticipate Claim 1 or any of its dependent claims beyond the very broad concept of FDM.

7. U.S. Patent No. 6,004,124 to Swanson et al.

• Full Citation: Swanson et al., U.S. Pat. No. 6,004,124, "Extrusion head for a three-dimensional modeling machine," issued December 21, 1999.
• Publication/Filing Date: December 21, 1999 (Issue Date).
• Brief Description: US9421713 cites this patent as an "additional example of suitable devices for print heads, and the connections between print heads and head gantry."
• Potential Anticipation (35 U.S.C. § 102): This patent anticipates details of extrusion print head design and their connection to gantries in additive manufacturing systems. It would contribute to anticipating the "providing print heads" aspect of systems capable of practicing US9421713. However, it does not describe multi-material printing, mode switching between multiple heads, or the specific purge operation involving a purge tower. Thus, it would not anticipate the core inventive concept of Claim 1 or its dependent claims.

Summary of Most Relevant Prior Art:

The most relevant prior art references are Turley et al. (U.S. Pat. No. 7,744,364), Swanson et al. (U.S. Pub. No. 2010/0283172 and U.S. Pub. No. 2012/0164256), Leavitt (U.S. Pat. No. 7,625,200), and LaBossiere et al. (U.S. Pat. No. 7,604,470). These references collectively disclose key components and processes of multi-material additive manufacturing systems:

• Multiple print heads/deposition lines for part and support materials.
• Layer-based additive manufacturing techniques.
• Switching print heads between operating (active) and stand-by (idle) modes.
• Movement of print heads during mode switching.
• Conventional purge operations involving a separate purge station and bucket (Turley et al.).
• Tip wipe mechanisms (implied by LaBossiere et al.'s title).

These references anticipate many of the background elements and the preamble of Claim 1 of US9421713. However, none of them disclose the central inventive feature of US9421713: performing a purge operation by printing a layer of at least one purge tower in a layer-by-layer manner. This specific method of purging, which integrates the purge material into a buildable structure on the same build platform as the part, rather than discarding it in a separate station, is the distinguishing feature of US9421713 and would not be anticipated by these references under 35 U.S.C. § 102. Claims 4-20, which detail the structure, function, and control of this purge tower, would also not be anticipated by these references.

(Note: Other cited patents, such as those related to specific materials, gantry systems, or sensor assemblies, describe generic components or subsystems of additive manufacturing systems. While they contribute to the overall technical environment, they are far less likely to anticipate the specific method claims related to the purge tower.)

US Patent 9421713 relates to an additive manufacturing method for printing three-dimensional (3D) parts with purge towers, particularly focusing on extrusion-based systems. The core innovation, as captured in Claim 1, involves performing purge operations by printing layers of at least one purge tower on the build platform using the print head that is being switched to an operating mode, rather than using a separate purge station and bucket.

Obviousness Analysis under 35 U.S.C. § 103

A person having ordinary skill in the art (POSA) at the time of the invention (priority date March 8, 2013) would have found the claimed method obvious when considering the combination of existing prior art, particularly in light of known problems with conventional purge operations in additive manufacturing.

Claim 1 of US9421713 states:
"1. A method for printing a three-dimensional part with an additive manufacturing system, the method comprising:
printing layers of the three-dimensional part and of a support structure for the three-dimensional part from multiple print heads or deposition lines using a layer-based, additive manufacturing technique;
switching the print heads or deposition line between stand-by modes and operating modes in-between the printing of the layers of the three-dimensional part and the support structure;
performing a purge operation for each print head or deposition line switched to the operating mode, the purge operation comprising printing at least one purge tower in a layer-by-layer manner, wherein the layers of the at least one purge tower are printed from the print head or deposition line switched to the operating mode."

Combination of Prior Art References:

The following combination of prior art references would render Claim 1 obvious to a POSA:

1. Turley et al., U.S. Pat. No. 7,744,364 (Turley): This patent serves as a primary reference, disclosing conventional purge operations in additive manufacturing systems. Turley describes the need for purge operations to ensure proper material extrusion, remove degraded material and gases, and bring the print head to a known operating state. Critically, Turley explicitly identifies significant drawbacks of conventional purge stations, stating that they "can take up a sizeable footprint in the additive manufacturing system, which may reduce the usable build volume for printing 3D parts" and that "purge buckets periodically need to be emptied... [which] can inhibit the additive manufacturing system from functioning in a fully automated manner, such as in a printer farm."

2. Swanson et al., U.S. Publication Nos. 2010/0283172 and 2012/0164256 (Swanson et al.) OR Leavitt, U.S. Pat. No. 7,625,200 (Leavitt) OR LaBossiere et al., U.S. Pat. No. 7,604,470 (LaBossiere et al.): These references, acknowledged in US9421713 itself, teach fundamental aspects of multi-material extrusion-based additive manufacturing systems. They disclose printing 3D parts and support structures from multiple print heads or deposition lines using layer-based techniques. They also teach the switching of these print heads or deposition lines between stand-by and operating modes in-between the printing of layers. The US9421713 patent further confirms that "When each print head is brought to its operating mode, it preferably undergoes a purge operation prior to printing the next layer," referencing Turley for this conventional practice.

3. Crump et al., U.S. patent application Ser. No. 13/587,009; Swanson et al., U.S. patent application Ser. No. 13/587,012; and Mannella, U.S. patent application Ser. No. 13/587,015 (Crump et al. et al.): These references establish the existing concept of printing auxiliary structures, such as "scaffolds," on the build platform alongside the main 3D part in a continuous-build manner. This demonstrates that a POSA would be familiar with the idea of integrating additional, non-part-forming structures directly onto the build plate.

Motivation to Combine:

A POSA, familiar with the state of the art in extrusion-based additive manufacturing, would have recognized the significant drawbacks of conventional purge stations as clearly articulated by Turley. The need to save build volume and enable fully automated printing (especially for "printer farms") would have provided a strong motivation to eliminate the separate purge station.

The general practice in additive manufacturing of building support structures (as mentioned in the background of US9421713) and other auxiliary structures like scaffolds (as taught by Crump et al. et al.) on the same build platform alongside the 3D part would suggest a straightforward solution. It would have been obvious to a POSA to move the purge operation from a remote, space-consuming purge station to the build platform itself. Instead of extruding purged material into a separate "purge bucket" (Turley), the material could be extruded into a simple, temporary structure built up layer-by-layer on the build platform, i.e., a "purge tower."

This combination directly addresses the problems identified in Turley:

• Increased Usable Build Volume: By eliminating the need for a separate physical purge station, the overall footprint of the system could be reduced, thereby increasing the usable build volume.
• Enhanced Automation: A purge tower, being printed alongside the part, would not require manual emptying of a bucket, thus enabling continuous, automated operation, which is particularly beneficial for "printer farms."

The act of printing a simple tower-like structure using the active print head is a basic operation within the capabilities of a POSA in layer-based additive manufacturing. The material for each layer of the purge tower would logically come from the print head currently being switched to its operating mode, as the purpose of the purge is to prepare that specific print head for printing. The patent itself highlights that the purge tower "allows each print head to achieve the above-discussed desired functions of a purge operation without requiring the use of a separate purge station." This indicates that the known functions of a purge, as described in Turley, would be expected to be fulfilled by this modified approach.

Therefore, the combination of the teachings of Turley, highlighting the problems with conventional purge stations, with the knowledge of multi-head FDM printing (Swanson et al., Leavitt, LaBossiere et al.) and the established practice of printing auxiliary structures on the build platform (Crump et al. et al.), would have rendered the method of Claim 1 of US9421713 obvious to a POSA.

Note: As of the current date (April 26, 2026), an Inter Partes Review (IPR2025-00321) related to US9421713 is pending, and a ruling by the PTAB stating the patent is valid is anticipated for June 9, 2026. This analysis presents an obviousness argument based on the provided prior art and the stated problems, as requested, without prejudice to future or pending legal decisions.