{
  "patent_number": "US 4490728",
  "country": "US",
  "title": "How Thermal Inkjet Printers Use Two-Step Heating to Shoot Ink",
  "original_title": "Thermal ink jet printer",
  "summary": "Hewlett-Packard's 1982 patent on a two-stage electrical pulse method that preheats ink before vaporizing it, allowing thermal inkjet printers to reliably eject precise droplets without clogging.",
  "what_it_does": "The patent describes a method for ejecting ink droplets from a tiny nozzle using a heating resistor. Instead of hitting the resistor with a single blast of electricity, the system sends two distinct pulses. First, an electrical precursor current pulse preheats the ink to just below its boiling point without creating bubbles. This precursor pulse decreases over time proportional to the square root of the inverse of time. Second, a rapid nucleation pulse spikes the temperature to near the ink's superheat limit, instantly vaporizing a tiny layer of ink. This explosive bubble expansion acts like a piston, forcing a single, clean droplet of liquid ink out of the nozzle.",
  "what_it_does_not_cover": [
    "Does not cover inkjet printers that use piezoelectric elements to mechanically squeeze ink out of the nozzle.",
    "Does not cover thermal inkjet systems that use a single, uniform electrical pulse rather than a two-part precursor and nucleation sequence.",
    "Does not cover preheating methods where the precursor pulse current does not vary substantially as the square root of the inverse of time.",
    "Does not cover systems where the vaporized ink itself is allowed to escape through the nozzle orifice."
  ],
  "filed": "1982-09-07",
  "granted": "1984-12-25",
  "expires": "2002-09-07",
  "status": "expired",
  "holder": "Hewlett Packard Co",
  "holder_url": "https://patentbrief.org/company/hewlett-packard-co",
  "inventors": [
    {
      "name": "John L. Vaught",
      "url": "https://patentbrief.org/inventor/john-l-vaught"
    },
    {
      "name": "Frank L. Cloutier",
      "url": "https://patentbrief.org/inventor/frank-l-cloutier"
    },
    {
      "name": "David K. Donald",
      "url": "https://patentbrief.org/inventor/david-k-donald"
    },
    {
      "name": "John D. Meyer",
      "url": "https://patentbrief.org/inventor/john-d-meyer"
    },
    {
      "name": "Christopher A. Tacklind",
      "url": "https://patentbrief.org/inventor/christopher-a-tacklind"
    },
    {
      "name": "Howard H. Taub",
      "url": "https://patentbrief.org/inventor/howard-h-taub"
    }
  ],
  "times_cited": 329,
  "tags": [
    "consumer_electronics",
    "mechanical"
  ],
  "abstract": "A thermal ink jet printer is disclosed in which ink droplets are ejected from an orifice by the explosive formation of a vapor bubble within the ink supply due to the application of a two part electrical pulse to a resistor within the ink supply. The electrical pulse comprises a precurser pulse and a nucleation pulse; the precurser pulse preheats the ink in the vicinity of the resistor to a temperature below the boiling temperature of the ink so as to preheat the ink while avoiding vapor bubble nucleation within the ink supply and the subsequently occuring nucleation pulse very quickly heats the resistor to near the superheat limit of the ink.",
  "url": "https://patentbrief.org/patent/us/4490728/thermal-inkjet-printing",
  "markdown_url": "https://patentbrief.org/patent/us/4490728/thermal-inkjet-printing/md",
  "google_patents_url": "https://patents.google.com/patent/US4490728",
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}