Obviousness

Obviousness Analysis under 35 U.S.C. § 103 for US Patent 11338511

This analysis identifies combinations of prior art references that would render the independent claims of US Patent 11338511 obvious to a person having ordinary skill in the art (PHOSITA) as of the priority date of July 30, 2018.

Background Problem and Motivation for Combination

US Patent 11338511 addresses the challenge in additive manufacturing (specifically photoreactive 3D printing systems, PRPS) of scaling up build areas using digital light processing (DLP) without sacrificing resolution and energy density. The patent notes that conventional DLP systems suffer from increased pixel size and reduced projected energy density as layer size increases, leading to decreased resolution, part accuracy, and longer exposure times. The solution proposed is a multi-projector system projecting a composite image, coupled with a suite of digital filters for image correction and alignment.

A PHOSITA in additive manufacturing, seeking to overcome the inherent trade-offs between build area size, resolution, and print speed in single-projector DLP systems, would be motivated to leverage known techniques from both the additive manufacturing field and the broader multi-projector display industry. The goal would be to produce larger, high-resolution parts with consistent quality.

Prior Art Combinations and Obviousness Arguments

Combination 1: Zhou and Chen (2010) + General Multi-Projector Display Correction Techniques

This combination addresses Independent Claims 1 (Method) and 11 (System).

• Reference 1: Chi Zhou and Yong Chen, "Additive Manufacturing Based on Multiple Calibrated Projectors and Its Mask Image Planning" (2010)
  • Disclosure: This paper presents a novel additive manufacturing process that uses multiple Digital Micromirror Devices (DMDs), i.e., multiple projectors, to significantly improve the accuracy and resolution of built components. It describes using multiple DMDs to project images, thereby forming a composite image for additive manufacturing. Crucially, it discusses an "optimized pixel blending method" and the need to "compensate the calibrated light intensity in a projection image that is usually non-uniform and non-linear."
• Reference 2: General Multi-Projector Display Technologies (e.g., Userful Blog (2018), Lumen and Forge, GeoBox)
  • Disclosure: These references, well prior to 2018, describe multi-projector display systems that create large, seamless images by combining multiple overlapping projected images (sub-images) arranged in an array. They explicitly teach techniques such as:
    • Edge blending: To compensate for double brightness in overlapping regions and create seamless transitions.
    • Warp correction (or image warping): To adjust and align projected images precisely, compensating for geometric distortions, even on non-planar surfaces.
    • Gamma correction: For adjusting grayscale transitions and ensuring brightness uniformity.
    • Irradiance/Brightness compensation: To address non-uniformities in projected light.

Obviousness Argument for Claims 1 and 11:

A PHOSITA, aiming to scale DLP additive manufacturing to larger areas with high resolution, would find motivation in Zhou and Chen's explicit teaching of using multiple calibrated projectors for AM to improve accuracy and resolution, along with their mention of "optimized pixel blending" and compensating for "non-uniform and non-linear" light intensity.

The challenges of combining multiple projectors to form a single, coherent image are well-known in the art, especially for large displays. Faced with the requirement for precise and uniform energy delivery in resin-based additive manufacturing, a PHOSITA would look to the analogous field of multi-projector display technology for solutions to these known problems.

1. Plurality of Image Projectors, Composite Image, Sub-images in an Array, Overlap: Zhou and Chen directly teach the use of "multiple DMDs" (projectors) for additive manufacturing to project images that form a composite build area. The "optimized pixel blending method" implies overlapping regions between these projected images to create a seamless whole, analogous to how multiple projectors form a composite image with overlapping sub-images in general displays.
2. Adjusting Properties and Aligning Positions using Filters:
   • Irradiance Mask: Zhou and Chen specifically identify the need to "compensate the calibrated light intensity in a projection image that is usually non-uniform and non-linear" in an AM context. A PHOSITA would readily understand that applying an "irradiance mask that normalizes irradiance" from general multi-projector display technology is a direct and obvious way to achieve this necessary compensation for uniform resin curing.
   • Gamma Adjustment Mask: While general display systems use "gamma correction" for brightness and color consistency, a PHOSITA in AM would recognize the inherent non-linear response of photoreactive resins to light intensity. Adapting this known gamma correction technique to specifically "adjust sub-image energy based on a reactivity of the resin" would be an obvious design choice to ensure consistent cure depth and material properties across varying light intensities and different resin formulations. The patent itself highlights that "different resins have different reactivity ranges" and gamma correction can "map the irradiance range to the particular resin reactivity range." This is a known problem in photopolymerization that existing display technology principles could be adapted to solve.
   • Warp Correction Filter: The patent acknowledges that mechanical assembly and mounting geometry can lead to skewed projected sub-images in PRPSs. In the field of multi-projector displays, warp correction is a standard technique to provide "geometric correction" and precisely align images, even on non-planar surfaces. A PHOSITA would be motivated to apply this known filter to correct the geometric distortions of individual sub-images in an AM system to achieve the high dimensional accuracy required for 3D printed objects.
   • Edge Blending Bar: Zhou and Chen's "optimized pixel blending method" in AM directly points to the need for seamless transitions between adjacent projected sub-images. This problem is directly solved in general multi-projector displays through "edge blending," where brightness is adjusted in overlapping regions. A PHOSITA would apply an "edge blending bar" to the overlapping sub-images in an AM system to ensure uniform energy delivery and prevent artifacts (e.g., over-cured or under-cured regions, or visible seams) in the final printed part where sub-images meet.

Therefore, the combination of Zhou and Chen (2010) with well-established multi-projector display correction techniques (irradiance normalization, gamma correction, warp correction, and edge blending) would have rendered the methods of Claim 1 and the systems of Claim 11 obvious to a PHOSITA.

Combination 2: Combination 1 + MPS's Motorized Step-Stitching (Pre-2018)

This combination addresses Independent Claim 15 (Method with Moving Projectors).

• Reference 1: Combination 1 (Zhou and Chen (2010) + General Multi-Projector Display Correction Techniques) (as described above).
• Reference 2: "Multipath Projection Stereolithography for Three-Dimensional Printing Microfluidic Devices" (MPS)
  • Disclosure: MPS, which was available prior to the priority date, discusses "motorized step-stitching method that involves dividing the CAD file into a series of steps, moving either a motorized stage or the digital light engine by a defined distance before irradiation of pixelated images" in the context of DLP-VPP (Vat Photopolymerization) for AM. It also mentions "concurrent light projection and stage movement." This explicitly discloses moving the projection system relative to the build area in additive manufacturing.

Obviousness Argument for Claim 15:

Even with a fixed array of multiple projectors, there are practical limits to the size of the build area. A PHOSITA, seeking to further expand the printable area beyond what a static multi-projector array can cover (without sacrificing resolution through increased magnification), would find motivation in existing AM techniques for scaling. MPS explicitly teaches using a "motorized step-stitching method" where the "digital light engine" (which encompasses the projector) is moved to cover a larger area in an additive manufacturing process.

Therefore, it would have been obvious for a PHOSITA to combine the multi-projector system with its associated digital correction filters (irradiance mask, gamma adjustment mask, warp correction filter, and edge blending bar) from Combination 1, with the known technique of "moving the array of image projectors relative to a build area" as taught by MPS. This combination allows for a practically unlimited build area at high resolution, addressing the scalability challenge that the patent seeks to solve. The motivation is to achieve even larger-scale additive manufacturing without compromising the established benefits of multi-projector resolution and image correction.