Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Patent
1995-08-02
1999-02-23
Le, N.
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
347237, B41J 247, B41J 2435, B41J 245
Patent
active
058749845
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optical character generator for an electrographic printer having a plurality of monolithic circuits which are arranged on a carrier, each monolithic circuit comprising LEDs which are integrated therein and can be driven individually, and a drive circuit which is assigned to the character generator.
2. Description of the Related Art
Such an optical character generator is disclosed in European Patent Document EP-A2-0 180 479.
LED array character generators such as those which are also described, for example, in European Patent Document EP-B1-0 403 476 are used in non-mechanical printers for point-by-point discharging of electrostatic charged photoconductors. The latent electrostatic image produced in this way is inked in with the aid of a developer station and is transfer-printed onto the recording medium in a transfer-printing station. LED array character generators, which are supplied with drive signals via a drive circuit and a BUS circuit, are used to produce the charge image. Both the drive circuit and the BUS circuit are normally designed as separate integrated circuits. The ICs are constructed on the basis of monocrystalline silicon and contain a large number of transistors for analog/digital conversion (a switch function) and for amplification of currents (a driver function), which are required for the supply of the LED arrays.
As a rule, the LED arrays comprise 8, 16, 32, 64 or 128 light-emitting diodes which are arranged in series in a row (also termed the x-direction) and are integrated in one or more rows on individual monolithic circuits. A plurality of monolithic circuits which are joined to one another form the character generator. The structuring of the diodes is carried out on the basis of gallium arsenide. Each diode contains a connection pad via whose connection a current is passed and the diode is thus energized to illuminate. The light energy for exposure of the photoconductor is controlled via the magnitude of the current and via the time over which the diode is energized. Each individual LED is to this end connected to in each case one amplifier output of an IC. For this purpose, each IC is positioned very close to the LED arrays, so that a connection pad of an amplifier output of the IC is opposite each connection pad of an LED array. The pads are now connected to one another with the aid of automatic bonding machines. Since each character generator requires up to 11,000 diodes, and thus a correspondingly high number of bonded joints, depending on the length and the diode separation, separation into an LED chip and an IC and the connection technology which would have to be used for this purpose are not only very time-consuming but, furthermore, are also highly susceptible to defects. For example, a 300 dpi character generator has a distance of 85 .mu.m between centers of the light-emitting diodes. The width of a connection pad can therefore be no greater than 60 .mu.m if a safety margin of 25 .mu.m is intended to remain between each pad. The positioning accuracy of each automatic bonding machine must therefore be so great over the length of the entire character generator of, for example, 300,000 .mu.m to 500,000 .mu.m that the first connection pad at the start of the bonding process and the last connection pad after 3000 to 6000 stepping movements as well lie in a reliable bonding area of approximately .+-.25 .mu.m.
Various options are used in order to reduce the difficulties which occur during bonding. The connection pads are arranged offset in the y-direction so that they can be designed to be broader and the tolerance band for the bonding can thus be enlarged. However, this necessitates a greater area requirement in the chip surface and thus increases the price of the chips.
Another option, which is described in German Patent Document DE-C2-37 04 984, comprises the LED arrays being driven from both sides with ICs. Although this results in the opportunity to double the connection pad width, it increas
REFERENCES:
patent: 4956684 (1990-09-01), Urata
H. Tanabe et al., "High-Accuracy Die-Bonding Technology for LED Array", 8091 IEEE Transactions on Components, Hybrids and Manufacturing technology, Bd. CHMT-8 (1985 Dec.), No. 4, New York, USA, pp. 500-504.
Japanese Abstract, vol. 14, No. 282, (E-0942), JP2089379, Mar. 29, 1990.
Japanese Abstract, vol. 13, No. 287 (M-844) (3635), JP,A,0180560, Mar. 27, 1989.
Japanese Abstract, vol. 11, No. 41 (E-478 (2488), JP,A,61207086, Sep. 13, 1986.
Scholz Christian
Wiedemer Manfred
Le N.
Nguyen Thinh
Oce Printing Systems GmbH
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