(19)
(11) EP 0 600 648 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
04.01.1995 Bulletin 1995/01

(43) Date of publication A2:
08.06.1994 Bulletin 1994/23

(21) Application number: 93309242.1

(22) Date of filing: 19.11.1993
(51) International Patent Classification (IPC)5: B41J 2/05
(84) Designated Contracting States:
DE FR GB IT

(30) Priority: 30.11.1992 US 983009

(71) Applicant: Hewlett-Packard Company
Palo Alto, California 94304 (US)

(72) Inventors:
  • Canfield, Brian
    San Diego, California 92109 (US)
  • Holstun, Clayton
    Escondido, California 92026 (US)
  • Yeung, King-Wah W.
    Cupertino, California 95014 (US)

(74) Representative: Colgan, Stephen James et al
CARPMAELS & RANSFORD 43 Bloomsbury Square
London WC1A 2RA
London WC1A 2RA (GB)


(56) References cited: : 
   
       


    (54) Method and apparatus for the control of thermal ink jet printers


    (57) The volume of drops ejected from thermal ink jet printheads varies with the temperature of the printhead (20). The variation in drop volume degrades print quality by causing variations in the darkness in black and white text, the contrast of gray scale images, and variations in the chroma, hue, and lightness of color images. The present invention reduces the range of drop volume variation by reducing the range of printhead (20) temperature variation during the print cycle by keeping the printhead temperature above a reference temperature. When the printhead temperature falls below the reference temperature during a print cycle the printhead is heated with nonprinting pulses.






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