# US 4,392,754 A · Magnetic dot matrix printing method and apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,392,754 A - Document ID: US4392754A - Status: Granted - Kind: A - Application number: 06/347,716 - Filed: 1982-02-10 - Granted: 1983-07-12 - Earliest claimed: 1982-02-10 - Assignees: Extel Corporation - Inventors: Robert Adler - Web page: https://patentgrep.com/patent/US4392754A ## CPC - B41J 2/43: for magnetic printing - B41J: TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS ## Abstract A method and apparatus for character-by-character magnetic printing on plain paper, using a dot matrix format; a sheet of paper is positioned on the surface of a thin, elongated strip platen of permanent magnet material and a magnetic printhead comprising a columnar array of electromagnets scans the platen. Selective energization of the electromagnets, during each scan, magnetizes dot-size portions of the platen in dot matrix patterns defining magnetic images of the characters in a line of text; limited quantities of toner are applied to the paper generally concurrently with formation of the magnetic images to develop those images as visible characters, which are subsequently fixed on the paper surface. ## Claims ### Claim 1 A method of magnetic dot matrix printing, for printing a character text, character-by-character, on a sheet of non-magnetic paper, comprising the following steps in sequence: A. positioning a sheet of non-magnetic paper on a platen of erasable permanent magnet material with the platen aligned with a portion of the paper comprising a location for a line of text; B. moving a magnetic recording head, comprising a plurality of electromagnets having magnetizing poles corresponding to a group of character matrix dots, along a print path transversing the text line location, in closely spaced relation to one platen surface; C. magnetizing dot-size portions of the platen in accordance with predetermined patterns constituting magnetic images of the characters for a line of text by selectively energizing the electromagnets for limited intervals during step B; D. developing visible images of the data characters on the paper by applying limited quantities of a magnetic toner to the exposed surface of the paper overlying the platen generally concurrently with formation of the magnetic images in step C; and E. fixing the visible toner images on the paper. ### Claim 2 (depends on 1) The method of character-by-character magnetic dot matrix printing, according to claim 1, comprising the following additional steps: F. erasing the magnetic images from the platen; G. advancing the paper across the platen to bring a new portion of the paper into alignment with the platen; and H. repeating steps A through E to print a subsequent line of text. ### Claim 3 (depends on 1, 2) The method of character-by-character magnetic dot matrix printing, according to claim 1 or claim 2, in which step D is carried out by moving a toner dispenser along the path of the recording head in synchronism with the recording head and in an alignment relative to the recording head such that development of the visible images occurs generally concurrently with formation of the magnetic images in step C. ### Claim 4 (depends on 3) The method of character-by-character magnetic dot matrix printing, according to claim 3, in which the toner dispenser is moved along the path a short distance behind the recording head so that development of the visible images occurs immediately after the formation of the magnetic images in step C. ### Claim 5 (depends on 3) The method of character-by-character magnetic dot matrix printing, according to claim 3, in which the toner dispenser and recording head are located on opposite sides of the platen and the toner dispenser is aligned directly opposite the recording head so that development of the visible images occurs essentially simultaneously with the formation of the magnetic images in step C. ### Claim 6 (depends on 2) The method of character-by-character magnetic dot matrix printing, according to claim 2, in which the recording head magnetizes the platen from the side of the platen opposite the paper. ### Claim 7 (depends on 6) The method of character-by-character magnetic dot matrix printing, according to claim 6, in which the recording head electromagnets magnetize the platen in a parallel mode, with each dot-size magnet formed in the platen comprising spaced north and south poles on the surface of the platen contacted by the paper. ### Claim 8 (depends on 6) The method of character-by-character magnetic dot matrix printing, according to claim 6, in which the recording head electromagnets magnetize the platen in a perpendicular mode, with each dot-size magnet formed in the platen comprising a pole of given polarity on the surface of the platen contacted by the paper and a pole of opposite polarity on the opposite surface of the platen. ### Claim 9 (depends on 8) The method of character-by-character magnetic dot matrix printing, according to claim 8, in which development of the visible images in step D is carried out essentially simultaneously with formation of the magnetic images in step C. ### Claim 10 (depends on 2) The method of character-by-character magnetic dot matrix printing, according to claim 2, in which step E is carried out by moving two opposed pressure rollers across the paper, along the recording head path, pressing the platen and paper together between the rollers and thereby pressure-fixing the visible toner images on the paper. ### Claim 11 (depends on 10) The method of character-by-character magnetic dot matrix printing, according to claim 10, in which the recording head magnetizes the platen from the side of the platen opposite the paper. ### Claim 12 (depends on 11) The method of character-by-character magnetic dot matrix printing, according to claim 11, in which the recording head electromagnets magnetize the platen in a parallel mode, with each dot-size magnet formed in the platen comprising spaced north and south poles on the surface of the platen contacted by the paper. ### Claim 13 (depends on 11) The method of character-by-character magnetic dot matrix printing, according to claim 11, in which the recording head electromagnets magnetize the platen in a perpendicular mode, with each dot-size magnet formed in the platen comprising a pole of given polarity on the surface of the platen contacted by the paper and a pole of opposite polarity on the opposite surface of the platen. ### Claim 14 (depends on 13) The method of character-by-character magnetic dot matrix printing, according to claim 13, in which development of the visible images in step D is carried out essentially simultaneously with formation of the magnetic images in step C. ### Claim 15 (depends on 2) The method of character-by-character magnetic dot matrix printing, according to claim 2, in which step E is carried out by moving a heating device across the paper, along the recording head path, heating the visible toner images to fix them on the paper. ### Claim 16 (depends on 15) The method of character-by-character magnetic dot matrix printing, according to claim 15, in which the recording head magnetizes the platen from the side of the platen opposite the paper. ### Claim 17 (depends on 16) The method of character-by-character magnetic dot matrix printing, according to claim 16, in which the recording head electromagnets magnetize the platen in a parallel mode, with each dot-size magnet formed in the platen comprising spaced north and south poles on the surface of the platen contacted by the paper. ### Claim 18 (depends on 16) The method of character-by-character magnetic dot matrix printing, according to claim 16, in which the recording head electromagnets magnetize the platen in a perpendicular mode, with each dot-size magnet formed in the platen comprising a pole of given polarity on the surface of the platen contacted by the paper and a pole of opposite polarity on the opposite surface of the platen. ### Claim 19 (depends on 18) The method of character-by-character magnetic dot matrix printing, according to claim 18, in which development of the visible images in step D is carried out essentially simultaneously with formation of the magnetic images in step C. ### Claim 20 (depends on 15) The method of character-by-character magnetic dot matrix printing, according to claim 15, in which two heating devices are provided, and in which successive lines of text are printed with the recording head moving in opposite directions along its print path. ### Claim 21 (depends on 2) The method of character-by-character magnetic dot matrix printing, according to claim 2, in which the recording head magnetizes the platen through the paper. ### Claim 22 (depends on 21) The method of character-by-character magnetic dot matrix printing, according to claim 21, in which the recording head electromagnets magnetize the platen in a perpendicular mode, with each dot-size magnet formed in the platen comprising a pole of given polarity on the surface of the platen contacted by the paper and a pole of opposite polarity on the opposite surface of the platen. ### Claim 23 (depends on 22) The method of character-by-character magnetic dot matrix printing, according to claim 22, in which step E is carried out by moving a heating device across the paper, along the recording head path, heating the visible toner images to fix them on the paper. ### Claim 24 (depends on 2) The method of character-by-character magnetic dot matrix printing, according to claim 2, in which step B is always carried out with the recording head moving in a given direction along its print path, and in which the recording head is moved back in the opposite direction along that path during step F. ### Claim 25 (depends on 2) The method of character-by-character magnetic dot matrix printing, according to claim 2, in which successive lines of text are printed with the recording head moving in opposite directions along its print path. ### Claim 26 A magnetic dot matrix printer for printing a data character text, character-by-character, on a sheet of non-magnetic paper, comprising: an elongated strip platen of erasable permanent magnet material; means for positioning a sheet of non-magnetic paper on one surface of the platen with the platen extending across the paper in alignment with a portion of the paper comprising a location for a line of text; carriage means reciprocally movable along a print path adjacent the platen, from one end of the text-line location to the other and back again; magnetic recording head means, mounted on the carriage means and comprising a plurality of electromagnets having magnetizing poles corresponding to a group of character matrix dots disposed in closely spaced proximity to one platen surface, for magnetizing dot-size portions of the platen in accordance with predetermined patterns constituting magnetic images of the characters for a line of text by selective energization of the electromagnets during movement of the carriage; magnetic toner dispensing means, mounted on the carriage means, for applying limited quantities of a magnetic toner to the exposed surface of the paper overlying the platen generally concurrently with formation of the aforesaid magnetic images to develop visible images on the paper; fixing means for fixing the visible toner images on the paper to complete printing of a line of text; and magnetic erasing means, mounted on the carriage means, for erasing the magnetic images from the platen in preparation for printing a further line of text. ### Claim 27 (depends on 26) A magnetic dot matrix character-by-character printer, according to claim 26, in which the carriage means comprises a first carriage positioned adjacent the side of the platen opposite the paper and a second carriage positioned adjacent the paper bearing side of the platen and movable conjointly with the first carriage, the recording head means and the erasing means being mounted on the first carriage and the toner dispensing means being mounted on the second carriage. ### Claim 28 (depends on 26, 27) A magnetic dot matrix character-by-character printer, according to claim 26 or claim 27, in which the toner dispensing means comprises a rotary magnetic brush, extending transversely of the print path, for dispensing magnetic toner by magnetic attraction to the magnetic images. ### Claim 29 (depends on 26, 27) A magnetic dot matrix character-by-character printer, according to claim 26, or claim 27, in which: each electromagnet comprises two magnetic cores aligned in closely spaced relation to each other immediately adjacent the side of the platen opposite the paper, and an electrical conductor extending through the space between the cores: and the platen comprises a thin strip of permanent magnet material having high remanence and moderate coercive force; each electromagnet, when energized, magnetizing a dot size area on the paper bearing surface of the platen in a parallel mode affording spaced north and south poles on that surface of the platen. ### Claim 30 (depends on 29) A magnetic dot matrix character-by-character printer, according to claim 29, in which magnetic recording and visible image development occur during movement of the carriages in a recording direction along the print path, and image fixing and magnetic erasing occur during return movement of the carriages in the opposite direction along the print path, and in which: the toner dispensing means is spaced by a short distance from the recording head, along the print path, trailing behind the recording head during movement of the carriages in the recording direction. ### Claim 31 (depends on 29) A magnetic dot matrix character-by-character printer, according to claim 29, for use with a pressure fixable magnetic toner, in which the fixing means comprises: a first fixing roller mounted on the carriage means on one side of the platen; and a second fixing roller mounted on the carriage means on the opposite side of the platen, directly opposite the first fixing roller; the two fixing rollers pressing the paper and the platen together during movement of the carriage means along the print path to pressure fix the visible images on the paper. ### Claim 32 (depends on 29) A magnetic dot matrix character-by-character printer, according to claim 29, for use with a heat fixable magnetic toner, in which the fixing means comprises heater means for heating the visible toner images. ### Claim 33 (depends on 32) A magnetic dot matrix character-by-character printer, according to claim 32, in which the heater means comprises a radiant heater, mounted on the carriage means, for fixing the visible toner images while still positioned on the platen. ### Claim 34 (depends on 26, 27) A magnetic dot matrix character-by-character printer, according to claim 26 or claim 27, in which: each electromagnet comprises a magnetic core having a single dot-size magnetizing pole immediately adjacent the side of the platen opposite the paper, and a coil mounted on the core; and the platen comprises a thin strip of permanent magnet material having high coercive force and low permeability; each electromagnet, when energized, magnetizing a dot size portion of the platen in a perpendicular mode affording a single pole of given polarity facing the paper. ### Claim 35 (depends on 34) A magnetic dot matrix character-by-character printer, according to claim 34, in which the recording head and the toner dispensing means are on opposite sides of the platen and the toner dispensing means is in direct alignment with the recording head so that development of the visible images occurs essentially simultaneously with formation of the magnetic images. ### Claim 36 (depends on 34) A magnetic dot matrix character-by-character printer, according to claim 34, in which the magnetic image dots are all of one polarity at the paper bearing surface of the platen, and the erasing means comprises a permanent magnet that magnetizes the entire platen uniformly so that the paper bearing surface of the platen is of the opposite polarity. ### Claim 37 (depends on 36) A magnetic dot matrix character-by-character printer, according to claim 36, in which the recording head and the toner dispensing means are on opposite sides of the platen and the toner dispensing means is in direct alignment with the recording head so that development of the visible images occurs essentially simultaneously with formation of the magnetic images. ### Claim 38 (depends on 34) A magnetic dot matrix character-by-character printer, according to claim 34, for use with a pressure fixable magnetic toner, in which the fixing means comprises: a first fixing roller mounted on the carriage means on one side of the platen; and a second fixing roller mounted on the carriage means on the opposite side of the platen, directly opposite the first fixing roller; the two fixing rollers pressing the paper and the platen together during movement of the carriage means along the print path to pressure fix the visible images on the paper. ### Claim 39 (depends on 34) A magnetic dot matrix character-by-character printer, according to claim 34, for use with a heat fixable magnetic toner, in which the fixing means comprises heater means for heating the visible toner images. ### Claim 40 (depends on 39) A magnetic dot matrix character-by-character printer, according to claim 39, in which the heater means comprises a radiant heater, mounted on the carriage means, for fixing the visible toner images while still positioned on the platen. ### Claim 41 (depends on 26, 27) A magnetic dot matrix character-by-character printer, according to claim 26 or claim 27, for use with a pressure fixable magnetic toner, in which the fixing means comprises: a first fixing roller mounted on the carriage means on one side of the platen; and a second fixing roller mounted on the carriage means on the opposite side of the platen, directly opposite the first fixing roller; the two fixing rollers pressing the paper and the platen together during movement of the carriage means along the print path to pressure fix the visible images on the paper. ### Claim 42 (depends on 26, 27) A magnetic dot matrix character-by-character printer, according to claim 26 or claim 27, for use with a heat fixable magnetic toner, in which the fixing means comprises heater means for heating the visible toner images. ### Claim 43 (depends on 42) A magnetic dot matrix character-by-character printer, according to claim 42, in which the heater means comprises a radiant heater, mounted on the carriage means, for fixing the visible toner images while still positioned on the platen. ### Claim 44 (depends on 43) An electromagnetic dot matrix character-by-character printer, according to claim 43, in which the fixing means comprises two radiant heaters mounted on opposite sides of the toner dispensing means, to enable printing during movement of the carriage means in opposite directions along the print path. ### Claim 45 (depends on 27) A magnetic dot matrix character-by-character printer, according to claim 27 in which: each electromagnet comprises a magnetic core having a single dot-size magnetizing pole immediately adjacent the side of the platen opposite the paper, and a coil mounted on the core; the platen comprises a thin strip of permanent magnet material having high coercive force and low permeability; each electromagnet, when energized, magnetizing a dot size portion of the platen in a perpendicular mode affording a single pole of given polarity facing the paper; and the toner dispensing means is in direct alignment with the recording head so that development of the visible images occurs essentially simultaneously with formation of the magnetic images and enabling printing during movement of the carriages in opposite directions along the print path. ### Claim 46 (depends on 45) A magnetic dot matrix character-by-character printer, according to claim 45, for use with a heat fixable magnetic toner, in which the fixing means comprises two radiant heaters mounted on opposite ends of the second carriage in spaced relation to the toner dispensing means. ### Claim 47 (depends on 26) A magnetic dot matrix character-by-character printer, according to claim 26, in which the carriage means comprises a single carriage positioned adjacent the paper bearing side of the platen, and in which the recording head means, the toner dispensing means, and the erasing means are all mounted on that carriage. ### Claim 48 (depends on 47) A magnetic dot matrix character-by-character printer, according to claim 47, in which: each electromagnet comprises a magnetic core having a single dot-size magnetizing pole immediately adjacent the paper bearing side of the platen, and a coil mounted on the core; the platen comprises a thin strip of permanent magnet material having high coercive force and low permeability; each electromagnet, when energized, magnetizing a dot size portion of the platen in a perpendicular mode affording a single pole of given polarity facing the paper; and the fixing means comprises a raadiant heating device mounted on the carriage in spaced relation to the toner dispensing means.