Skip to content

Archaic Legal Glossary & Citations

“Letters Patent”14th–20th Century
19th-C Meaning:

Open public letters from a monarch or government (literae patentes) granting monopoly rights.

Modern Engineering Decoded:Issued USPTO utility or design patent publication.
Historical note: Contrasted with 'letters close' (private sealed royal correspondence).
“In testimony whereof”19th Century
19th-C Meaning:

Formal concluding legal formula affirming under oath the execution of the instrument.

Modern Engineering Decoded:Inventor and witness digital/physical signatures.
Historical note: Required two witness attestations in 19th-century USPTO filing procedure.
“Aeroplane”Early 20th Century (Wright era)
19th-C Meaning:

A flat or cambered lifting aerofoil surface supported dynamically by air pressure.

Modern Engineering Decoded:Wing / Airfoil lifting surface (later evolved to mean the entire motorized aircraft).
Historical note: The Wrights used 'aeroplane' to denote the individual fabric-covered wings.
“Undulating Current”19th Century (Bell era)
19th-C Meaning:

An electric current whose magnitude varies continuously and periodically without interruption.

Modern Engineering Decoded:Continuous analog AC or audio-frequency electrical waveform.
Historical note: Bell's central legal weapon against telegraph companies who relied on pulsed DC make-and-break circuits.
“Subdivision of the Electric Light”1870s–1880s (Edison era)
19th-C Meaning:

The problem of operating numerous small domestic lamps off a single electrical generator.

Modern Engineering Decoded:Parallel circuit wiring of high-resistance incandescent electrical loads.
Historical note: Pundits claimed it was physically impossible until Edison increased filament resistance to 100 ohms.
“Optically Anisotropic Solution”1960s (Kwolek era)
19th-C Meaning:

A liquid solution that exhibits direction-dependent refractive indices due to molecular alignment.

Modern Engineering Decoded:Liquid crystalline nematic phase polymer dope.
Historical note: Technicians initially tried to throw out Kwolek's cloudy solution thinking it was contaminated.
“Unitary Body of Semiconductor Material”1950s–1960s (Noyce era)
19th-C Meaning:

A single continuous crystal structure of silicon or germanium.

Modern Engineering Decoded:Monolithic single-crystal silicon die / integrated circuit wafer.
Historical note: Differentiated Noyce's monolithic planar circuit from Jack Kilby's hybrid flying-wire prototype.
“Peculiar and Novel Construction”19th Century
19th-C Meaning:

A distinctive, patentable structural arrangement not found in prior art.

Modern Engineering Decoded:Novel and non-obvious mechanical embodiment under 35 U.S.C. § 103.
Historical note: Standard 19th-century legal terminology establishing novelty.

Museum Broadside & Archival Print Edition

Authentic archival layout formatted for framing, study, and high-resolution printing

Paper:
Theme:
The United States Patent & Trademark Archive

Historical Specification & Engineering Broadside

Curated, Verified & Restored by Classic Patents (classic-patents.com)
APPARATUS FOR PRODUCTION OF THREE-DIMENSIONAL OBJECTS BY STEREOLITHOGRAPHYProgrammed Surface Curing and Layer-by-Layer Formation of a Three-Dimensional Object
US 4,575,330Class: 425/174.4
Inventor(s):Charles W. Hull
Origin / Location:Arcadia, California
Grant & Filing:Filed August 8, 1984 · Granted March 11, 1986

I. Historical Context & Grant Summary

Charles W. Hull's 1986 grant describes a system that forms a three-dimensional object by creating and integrating successive cross-sectional laminae at the surface of a curable fluid medium. Its preferred embodiment uses a computer-programmed ultraviolet spot and an elevator platform; the claims also reach other prescribed forms of stimulation and object-support arrangements.

II. Core Mechanism & Scientific Principles

Hull identifies the practical problem as the slow, tooling-heavy loop between a plastic-part design, its prototype, and production. The grant's move is not a particular modern printer: it is to make a cross-section at a selected fluid surface, join it to the prior cross-section, and repeat. The preferred working apparatus uses a programmed ultraviolet spot and an elevator platform. The grant says a computer can prepare and deliver the commands; it also claims other forms of stimulation, including particle bombardment and chemical application. Modern SLA machines often use different optics and mechanics, so those later implementations must not be read back into the 1986 preferred embodiment.

Physical Operation:In the printed Figure 3 embodiment, container 21 holds UV-curable liquid 22 and defines working surface 23. Computer 28 controls the position of ultraviolet spot 27 from source 26 and moves elevator platform 29. The source draws one solid pattern at the surface; the platform moves the growing object away so fresh liquid occupies that surface; the next pattern adheres to the prior solid layer. Hull's working source is a 350-watt mercury short-arc lamp coupled to a 1 mm ultraviolet-transmitting fiber-optic bundle, shutter, lens tube, and H-P digital plotter. The patent says that a UV laser might ultimately be a better source—it does not describe a laser or galvanometer scanner as its working embodiment.
Governing Formulation:
Optical attenuation in a curable fluid (modern engineering interpretation):E(z) = E_0 e^{-z/D_p}
Dose and motion at the working surface (modern engineering interpretation):H = \int_0^t I(t)\,dt
Layer continuity by adhesion:z_{n+1} = z_n + \Delta z

III. The Granted Legal Monopoly (Key Claims)

Claim 1 (Independent)Layer-by-layer cross-sectional lamina drawing at a 2D interface

A foundational system for producing a 3D object from a curable fluid medium by drawing successive cross-sectional laminae at a 2D interface and translating the growing object away from the interface in stepwise fashion to build up the object.

Claim 2 (Independent)Liquid photopolymer container with designated surface

A stereolithography system with a vat holding curable liquid, a reaction source applying synergistic stimulation in a prescribed pattern to only a thin surface layer, and an elevator translating the object to expose fresh liquid for subsequent layers.

Claim 3 (Dependent)Impinging radiation energy source

The system of claim 2 wherein the reaction means is a source of impinging radiation.

IV. Mechanical Organ Breakdown

Programmed Ultraviolet Spot SourceTerm: “reaction means for selectively applying synergistic stimulation in a prescribed pattern” → programmed ultraviolet exposure head

The printed working source is a mercury short-arc lamp, fiber-optic bundle, shutter, lens tube, and plotter that moves a focused ultraviolet spot.

Submerged Elevator Build PlatformTerm: “translational means for moving said object as it is formed away from said designated surface” → z-axis build platform

A platform supports the forming object and is moved away from the working surface between laminae.

Photopolymer Resin Vat & ChemistryTerm: “fluid medium capable of altering its physical state in response to synergistic stimulation” → UV-curable photopolymer resin vat

The curable fluid must form a thin cohesive layer, adhere to adjacent layers, and remain practical to handle and clean.

Bottom-Up Immiscible Fluid InterfaceTerm: “container wherein exposure is through the bottom and a second non-reactive medium” → inverted bottom-up vat photopolymerization with non-stick release interface

An alternative arrangement forms the object at the interface above a heavier ultraviolet-transparent, non-miscible liquid.

CLASSIC PATENTS DIGITAL ARCHIVE • PERMANENT EXHIBIT ID: us-4575330-hull-stereolithography
classic-patents.com/patents/us-4575330-hull-stereolithography
Original USPTO PDF
Classic Patents/US 4,575,330
Computing & Digital (1970–Present)Additive Manufacturing & 3D Printing

Chuck Hull 3D Printing / Stereolithography (SLA)

US 4,575,330

Programmed Surface Curing and Layer-by-Layer Formation of a Three-Dimensional Object

Inventor(s)Charles W. Hull
Grant DateMarch 11, 1986
Filing DateAugust 8, 1984
LocationArcadia, California
Charles W. Hull's 1986 grant describes a system that forms a three-dimensional object by creating and integrating successive cross-sectional laminae at the surface of a curable fluid medium. Its preferred embodiment uses a computer-programmed ultraviolet spot and an elevator platform; the claims also reach other prescribed forms of stimulation and object-support arrangements.
USPTO PDF
Audio Engineering Breakdown~2 min listen

Listen to the narrated mechanical breakdown and civilizational context

Engineering Analysis & Physical Principles

How It Works: Step-by-Step Mechanical & Physical Breakdown

Hull identifies the practical problem as the slow, tooling-heavy loop between a plastic-part design, its prototype, and production. The grant's move is not a particular modern printer: it is to make a cross-section at a selected fluid surface, join it to the prior cross-section, and repeat. The preferred working apparatus uses a programmed ultraviolet spot and an elevator platform. The grant says a computer can prepare and deliver the commands; it also claims other forms of stimulation, including particle bombardment and chemical application. Modern SLA machines often use different optics and mechanics, so those later implementations must not be read back into the 1986 preferred embodiment.
The Core Breakthrough Mechanism

In the printed Figure 3 embodiment, container 21 holds UV-curable liquid 22 and defines working surface 23. Computer 28 controls the position of ultraviolet spot 27 from source 26 and moves elevator platform 29. The source draws one solid pattern at the surface; the platform moves the growing object away so fresh liquid occupies that surface; the next pattern adheres to the prior solid layer. Hull's working source is a 350-watt mercury short-arc lamp coupled to a 1 mm ultraviolet-transmitting fiber-optic bundle, shutter, lens tube, and H-P digital plotter. The patent says that a UV laser might ultimately be a better source—it does not describe a laser or galvanometer scanner as its working embodiment.

Interactive Real-Time Physical Simulation

Drag to rotate · Pinch to zoom · Shared controls update the displayed model
INITIALIZING THREE.JS WEBGL SIMULATION...
Source-Bounded Surface-Lamina Formation & Elevator Topology.
Host-Model Telemetry/Computed Readout
Source-Bounded Surface-Lamina Formation & Elevator Topology
Effective Electronic Shutter
Normalized
opensource-state[1]
Spot 27 Position
Normalized
(0.00, 0.00)normalized plotter travel[1]
Platform 29 Position
Normalized
next-layer working positionq=0.00 normalized[1]
Preferred Lamp Rating
Source
350W electrical[1]
Preferred Surface UV
Source
about 1W/cm² long-wave UV[1]
Quantitative Cure / Motion
Source Refusal
refusedmissing resin and motion cards[1]
Discrete Shutter / Sequence State
Δstate / Δreader control (host sensitivity)
1 discrete display state
Electronic Shutter Request1 0 closed / 1 open
Plotter Spot X0 normalized
Plotter Spot Z0 normalized
Platform Recoating Excursion0 normalized
Illustrative Integrated Laminae7 display layers

Detailed Component Architecture

1Programmed Ultraviolet Spot Source
The printed working source is a mercury short-arc lamp, fiber-optic bundle, shutter, lens tube, and plotter that moves a focused ultraviolet spot.

Hull specifies a 350 W mercury short-arc lamp focused into a 1 mm ultraviolet-transmitting fiber-optic bundle. A water-cooled bundle end, electronically controlled shutter blade, and quartz lens tube produce a spot somewhat less than 1 mm in diameter, with about 1W/cm21 \mathrm{W/cm^2} long-wave UV intensity. An H-P Model 9872 digital plotter moves the lens tube; an H-P 3497A unit controls the shutter. The source is intentionally programmed on and off while the spot moves across working surface 23.

19th-C. Term: reaction means for selectively applying synergistic stimulation in a prescribed patternModern: programmed ultraviolet exposure head
2Submerged Elevator Build Platform
A platform supports the forming object and is moved away from the working surface between laminae.

After a layer forms, Hull moves the object beyond the next-layer level to let liquid flow into the momentary void, then returns it to the correct level for the next layer. The printed requirements are programmed, sufficiently precise motion and enough force to carry the forming object; manual fine adjustment is useful during setup and removal. The Figure 3 platform is attached to an analog plotter driven by the H-P 3497A unit. The grant does not specify a ball screw, perforated plate, recoater blade, or a numerical layer thickness.

19th-C. Term: translational means for moving said object as it is formed away from said designated surfaceModern: z-axis build platform
3Photopolymer Resin Vat & Chemistry
The curable fluid must form a thin cohesive layer, adhere to adjacent layers, and remain practical to handle and clean.

Hull lists six properties: curing fast enough for practical formation time; adhesion between layers; low enough viscosity to flow after elevator movement; UV absorption for a reasonably thin film; liquid-state solubility with solid-state insolubility in a cleaning solvent; and low toxicity/irritation. The working-material example is Potting Compound 363, a modified acrylate made by Locktite Corporation. The grant does not print penetration-depth, threshold-dose, wavelength, or millisecond-cure values.

19th-C. Term: fluid medium capable of altering its physical state in response to synergistic stimulationModern: UV-curable photopolymer resin vat
4Bottom-Up Immiscible Fluid Interface
An alternative arrangement forms the object at the interface above a heavier ultraviolet-transparent, non-miscible liquid.

In Figure 4, curable liquid 22 floats on heavier UV-transparent liquid 32 that is non-miscible and non-wetting with it. Hull gives ethylene glycol and heavy water as examples. The source focuses at their interface through a quartz (or similar) window 33 at the container bottom, and object 30 is pulled up from liquid 22. The thin upper layer directly limits layer thickness. Figure 5 is a different alternative: a collimated broad UV source and apertured mask form constant-shape cross-sections until a new mask is substituted.

19th-C. Term: container wherein exposure is through the bottom and a second non-reactive mediumModern: inverted bottom-up vat photopolymerization with non-stick release interface
Engineering Principles & Equations

Governing Equations & Engineering Principles

Authored explanation paired with its stated mathematical relation

Claim 2: Fixed Working Surface, Supported Translation, and Successive Laminae

Source-Bounded Apparatus SequenceClaim 2
Mathematical Governing Law
Terms:
Plain English DecoderHover or tap any highlighted phrase
At the , an open delivers spot 27 to . During the displayed recoating excursion, the shutter is held closed and object 30 remains on its support.
qrecoatq_{\mathrm{recoat}}
Normalized Platform-29 Excursion
Reader-controlled display coordinate between the next-layer position and an illustrative recoating over-travel
normalized display coordinate

The grant says platform 29 moves beyond the next layer and then returns to the correct level, but prints no stroke, layer thickness, speed, load, or timing value.

Physical Principle & Engineering Insight

This relation is a source-bounded sequencing predicate, not a cure-depth law. The patent prints a preferred lamp, fiber, shutter, spot, and approximate surface irradiance, but no absorption coefficient, critical exposure, scan dwell, reaction kinetics, layer thickness, or motion card from which a Beer–Lambert photopolymer solve could be evaluated.

Historical Context: The essential move is surface-by-surface construction on a translated support. The card keeps that claimed relationship visible without substituting later laser-SLA process parameters for Hull's grant.

Optical attenuation in a curable fluid (modern engineering interpretation)Authored Principle 1
Stated relationE(z)=E0e−z/DpE(z) = E_0 e^{-z/D_p}
This is a modern explanatory model, not an equation printed in the grant. It says radiant exposure E decreases with depth z in an absorbing fluid, with D_p as a material penetration scale. Hull's source-level observation is narrower: the liquid should absorb UV so the cured film is reasonably thin. The record does not assert a particular D_p, threshold, or layer-overcure margin.
Dose and motion at the working surface (modern engineering interpretation)Authored Principle 2
Stated relationH=∫0tI(t) dtH = \int_0^t I(t)\,dt
Here H is radiant exposure and I is irradiance over time. Hull's preferred system must make a spot small and intense enough for practical detail, then move it in a programmed pattern. The integral describes why shutter timing, source intensity, spot size, and motion all affect the cured pattern; it does not imply the unprinted laser-beam profile or numerical scanning performance formerly shown here.
Layer continuity by adhesionAuthored Principle 3
Stated relationzn+1=zn+Δzz_{n+1} = z_n + \Delta z
The discrete layer index n emphasizes the patent's essential sequence: form one lamina, move the object, and form an adjacent lamina that adheres to the prior one. The grant requires the fluid to be adhesive, but it does not state a gel-conversion fraction, an interlayer-strength integral, or a particular numerical step size.

Interactive Schematic Sheet (1)

Flowchart of step 10, generating individual solid laminae that represent object cross-sections, followed by step 11, combining successive adjacent laminae to form the three-dimensional object.

1.00x
US 4,575,330 · 1STEREOLITHOGRAPHY APPARATUS (FIG. 1 / FIG. 3)22 RESIN SURFACE29 PLATFORM30 CURED PART26 LASER27 SPOT
Tap any numbered pin2 Curated Callouts
Callout Pin Inspector

Select Any Numbered Pin

Click pins on the schematic or select from the list below to inspect historical specifications.

Why It Still Matters

The durable idea is the explicit engineering chain from a computer-defined cross-section, to a patterned change at a material surface, to a joined stack of layers. That chain is recognizable across later additive-manufacturing families, even when their energy source, feedstock, motion system, and post-processing differ. The distinction matters: this grant describes a curable fluid and surface formation; it should not be treated as a literal specification for every later 3D-printing process.

Legal Claims Decoder (47 Numbered Claims)

Compare dense legalistic claims directly with decoded plain-English functional specifications.
Claim #1Independent Master Claim
1/47
Verbatim Historical Legal Text
“1. A system for producing a three-dimensional object from a fluid medium capable of solidification when subjected to prescribed synergistic stimulation, said system comprising: means for drawing upon and forming successive cross-sectional laminae of said object at a two-dimensional interface; and means for moving said cross-sections as they are formed and building up said object in step wise fashion, whereby a three-dimensional object is extracted from a substantially two-dimensional surface.”
Plain English Engineering Translation
A foundational system for producing a 3D object from a curable fluid medium by drawing successive cross-sectional laminae at a 2D interface and translating the growing object away from the interface in stepwise fashion to build up the object.
Key Protected Innovations:
Layer-by-layer cross-sectional lamina drawing at a 2D interfaceStepwise translation of growing part away from interfaceExtracting 3D solid object from 2D fluid surface
Historical Legal Impact:
The broadest independent apparatus claim protecting the fundamental additive manufacturing architecture: slicing a 3D object into 2D layers and building it up stepwise from a fluid surface.

The Historical Bottleneck

In the early 1980s, product design cycles were severely constrained by the physical delay of building test prototypes. Translating a 2D engineering drawing or 3D CAD model into a physical plastic part required weeks or months of manual pattern making, skilled wood/metal machining, or expensive injection mold tooling (20,000–20,000–100,000 per mold). Designers could not afford to iterate rapidly, resulting in compromised designs and costly manufacturing retooling when prototype flaws were discovered late in development.

Why Prior Art Failed

  • •Subtractive CNC machining: limited to cutting external toolpaths; impossible to machine complex enclosed internal cavities, conformal channels, or undercut features in a single operation.
  • •Manual pattern-making: highly labor-intensive, requiring master mold makers and taking 6 to 16 weeks per design revision.
  • •Swainson dual-beam intersection (US 4,041,476): attempted two-photon polymer curing deep inside a resin block; suffered from extreme laser power instability, thermal blooming, and uncontrolled bulk gelation.
  • •Magat radiation grafting (US 2,708,617): demonstrated radiation-induced polymerization in bulk fluids, but lacked spatial scanning control, layer slicing, and geometric build platforms.
The Breakthrough Insight
“Chuck Hull realized that fabricating complex 3D solid parts does not require complex 3D tooling or unstable intersecting lasers in 3D space. Instead, any 3D object can be decomposed into an ordered stack of 2D laminar slices. By projecting a moving ultraviolet beam onto the 2D surface meniscus of a liquid photopolymer vat, polymerizing a thin slice, and indexing a submerged elevator downward by the slice thickness, each layer self-adheres to the previous layer. This elegant reduction from 3D space to sequential 2D surface printing established the foundational architecture of the modern 3D printing industry.”

Patent Wars & Legal Litigations

Vs. Dr. Hideo Kodama / Nagoya Municipal Industrial Research InstituteInfringement Challenge
Rival Claim & Defense:
In 1981, Dr. Hideo Kodama in Japan published the first technical paper describing a layer-by-layer photopolymer curing device and filed a Japanese patent application.
Litigation Conflict:
Due to institutional budget constraints, Dr. Kodama failed to file a full patent examination request within the statutory one-year deadline, causing his Japanese application to lapse and enter the public domain without issuing a patent.
Final Resolution & Judicial Outcome:
Hull independently conceived stereolithography in 1983 while working at UVP, Inc., built a working prototype (curing a small tea cup), and filed US Patent 638,905 on August 8, 1984.
Vs. EOS GmbH (Electro Optical Systems, Germany)Infringement Challenge
Rival Claim & Defense:
EOS developed laser stereolithography systems (STEREOS) in Europe, triggering transatlantic patent infringement litigation with 3D Systems.
Litigation Conflict:
3D Systems sued EOS in US and European courts for infringing Hull's stereolithography patent portfolio.
Final Resolution & Judicial Outcome:
In 1997, 3D Systems and EOS settled through a comprehensive cross-licensing agreement: EOS focused primarily on Selective Laser Sintering (SLS) and Direct Metal Laser Sintering (DMLS), while 3D Systems maintained leadership in SLA stereolithography.
After the Grant
Chuck Hull co-founded 3D Systems in Valencia, California in 1986, serving as Chief Technology Officer and Executive Vice President. In 2014, Hull was inducted into the National Inventors Hall of Fame and received the European Inventor Award. 3D Systems grew into a multibillion-dollar global manufacturer of production 3D printers, software, and materials.
Civilizational Impact
Chuck Hull's patent launched the global additive manufacturing revolution ($30+ billion market in 2026). It made rapid prototyping ubiquitous across aerospace (Boeing, SpaceX), automotive (Ford, Ferrari), medical (patient-specific surgical guides, Invisalign dental aligners, prosthetic limbs), consumer electronics (Apple, Sony), and industrial design. Hull's STL file format (.stl) remains the universal digital standard for 3D model exchange across all additive manufacturing software worldwide.
Historical Fact
The very first object Chuck Hull ever 3D-printed in his lab on March 9, 1983, was a small, blue eye-wash cup. That original printed plastic cup is now preserved in the collection of the Smithsonian National Museum of American History.
Further Context
  • Hull coined the term 'stereolithography' from the Greek 'stereo' (solid) and 'lithography' (writing on stone).
  • The original prototype apparatus used a high-voltage UV lamp mounted on a modified flatbed drafting pen plotter whose pen carriage was replaced with a focused optical lens tube.