JPH0137862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for electronically recording using a xerographic machine, and more particularly, to an apparatus for electronically recording using a xerographic machine, in particular a fairly long array of light emitting diodes (LEDs) with high light density and a set of adjacent light emitting diodes (LEDs). The present invention relates to an assembly of monoliths containing a light emitting diode providing a center. The term monolith used here is synonymous with chip.

Light emitting diodes have numerous applications, among them the provision of light in the printing industry. for example,
LEDs are used with xerographic copiers, photographic film, etc. to record images of electronically transmitted messages. The use of LEDs for this purpose has drawbacks. first,
In such printing applications, a high density of light is required to obtain good contrast and high resolution, but the light output of individual LEDs is not high.
Therefore, a large number of LEDs must be arranged in a small area to provide the necessary high density of light.
This has proven difficult to achieve due to the size limitations imposed by the crystal structure involved. More specifically, a significant drawback to the use of LEDs is the limited length of the monoliths from which the LEDs are constructed. This is because LEDs are formed by monoliths in the form of single crystals. The methods required to form single crystal materials impose limitations on the size of the monolith produced. Current manufacturing methods can produce single crystal boules that are 3 inches in diameter, which limits the length of the monolith to approximately 3 inches long. The crystal boules most commonly used commercially for LED manufacturing are only slightly larger than 1 inch in diameter, which precludes their lengths from increasing further. A number of methods have been used in an attempt to overcome these drawbacks, but to date none have proven fully satisfactory.

Another problem with using LEDs in the printing industry is their fragile nature, especially when
This is the fragility of the electrical connection to the LED.
To ensure that the amount of light emitted to the receiving surface is large, the LED is placed as close to that surface as possible. This increased the possibility of damaging the LED due to its movement relative to the light receiving surface.

A summary of the invention will be described. has a high density of light
It has been found that LED assemblies can be obtained by forming LEDs in rows within a monolith such that the individual LEDs of one row are laterally staggered with respect to the LEDs of the other row. Furthermore, the monolith from which the assembly is constructed has ends cut at a predetermined angle and assembled together, so that the unit forms the required length and one set of adjacent units on each center. are combined as follows. Additionally, an optical cover is provided over the exposed surface of the LED;
It transmits light from the LED to the receiving surface in a cylindrical manner, protecting the LED from damage due to inadvertent contact with the receiving surface. A gel with a fairly high refractive index is filled between the LED and the optical cover to suppress the effect of the divergence angle of the light emitted from the LED.

The present invention will be described in detail below with reference to the drawings.

A monolith assembly having a number of LEDs thereon is shown generally at 10 in FIGS. 1 and 2. In FIGS. Assembly 10 is spaced apart from a surface 12, such as a photoconductive belt or drum of zinc oxide, selenium, cadmium sulfide, or the like. Assembly 10 includes a substrate 14 of a dielectric material, such as aluminum oxide (Al ₂ O ₃ ), having a conductive material 15 provided on a portion of its surface. A number of n-type monoliths 16 are bonded to an adhesive 17 such as silver epoxy.
It is attached to the conductive material 15 by. The monolith 16 is made of a material such as gallium arsenide and has a number of doped locations that together with the monolith form a P-type region 18 defining a light emitting diode (LED). This doping is
The P-shaped regions 18 of LEDs are completed along two rows, each row abutting the longitudinal ends of the monolith 16. As shown in FIG. 1, the LED portions 18 of one row are
They are staggered (staggered) laterally. Although the LED sections are shown as circular, non-circular, e.g. oval, sections can be formed as needed when non-rectangular resolution is required. In the present invention, there are eight monoliths 16, one inch long, with 32 LED sections placed on each monolith. This monolith 16 is joined together at its ends to form the required assembly length. For example, if an 8-inch assembly is required, 64 monoliths may be assembled end-to-end in tandem to provide 2048 LED sections 18.

A metal coating 20 is deposited on the monolith 16 at the location of each LED portion 18, with an opening formed in each metal coating 20 to allow exposure of the LED. Leads 22 provide an electrical connection between conductive material 15 and metal coating 20 to provide power to each LED. lead 22
is soldered or epoxied to the conductive material 15 and metal coating 20. optical cover 2
4 is located on the length of monolith 16 intermediate the monolith and photoconductive surface 12. optical cover 2
4 has a relief portion 25 located above where the lead 22 is connected to the metal coating 20 and extending the length of the cover. Optical cover 24 is made of glass or methylmethacrylate. A gel 28 having a refractive index greater than 1 is filled between the LED 18 and the optical cover 24. Preferably,
This gel is polydimethyl siloxane with a refractive index of 1.465.

Assembly 10 is comprised of a plurality of monoliths 16, each monolith being diagonally cut at both ends 26 thereof. The oblique end 26 is the monolith 1
4, preferably at an angle of about 60 degrees.

The advantage of the configuration shown in FIG.
By staggering the LEDs 18 with respect to adjacent rows of LEDs, a high light density can be obtained. That is, the two rows of LEDs 18 extend vertically with the LEDs in one row being staggered laterally with respect to the LEDs in the other row. This staggered arrangement appears to give surface 12 one continuous beam of light. This staggered array of LEDs is held at the end 26 of the monolith 16 to provide a continuous center set. That is, the crystal boule has a cylindrical shape after being drawn. This is then cut into a number of thin wafers in the shape of thin flat disks. Portion 18 is then doped to create a P-type junction and metal coating 20
is deposited around the LED as shown in FIG. This flat disk is then sawed into 3000 monoliths, typically with 1 inch cuts. Due to the diagonal cuts, none of the sections 18 are damaged and the monolith 16 is assembled to give one continuous assembly with a uniform distribution of LEDs along its entire length. Although only two rows of LEDs 18 are shown, many rows can be constructed. Another way to obtain diagonal cuts is to cut the monolith by laser scoring. By driving the laser with a step motor controlled by a microprocessor, steps can be formed that are aligned with steps on adjacent monoliths. This monolith is then assembled as described above.

An advantage of using an optical cover 24 on the surface of the LED 18 is that a column of light is delivered to the surface 12. Light sources such as LEDs tend to form a diverging cone of light as a result of the light passing through the air. It has been found that the use of optical cover 24 and gel 28 having a refractive index greater than that of air increases the light focusing properties and reduces the aforementioned light losses. Furthermore, the optical cover 24 provides some protection for the LED, which is quite fragile, especially the bond connections to the leads 22. this is,
This is particularly important since the LED must be placed close to the light receiving surface 12 to increase resolution.

FIG. 3 shows a portion of the circuitry used to selectively control the inputs to the LEDs 18. 1 set of anode rails or busbars 3
0 is shown with individual leads or tapes 22 providing connections between busbars 30 and LEDs 18. There is one busbar 30 for each LED in one monolith.
A set of cathode rails or busbars 32 is also provided. Each busbar 32 is connected in parallel to all LEDs 18 of a given monolith 16a.
Although suitable controls may be used to selectively enable LED portions 18, such controls do not form part of the present invention and are therefore not described herein.

[Brief explanation of drawings]

FIG. 1 shows portions of a pair of adjacent monoliths incorporating features of the present invention; FIG. 2 is a partial cross-sectional view of an LED assembly facing a light-receiving surface incorporating features of the present invention; FIG. 2 is a diagram illustrating a portion of the circuitry involved in enabling the LED of the assembly of FIG. 1; FIG. 10: Assembly, 12: Surface, 14: Substrate,
15: conductive material, 16: monolith, 17: adhesive, 18: P-type region, 20: metal coating,
22: Lead, 24: Optical cover, 25: Relief portion, 26: End portion, 28: Gel, 30: Bus bar, 32: Bus bar.

Claims (1)

[Scope of Claims] 1 comprising a plurality of monoliths arranged substantially vertically and means for connecting the plurality of monoliths in tandem,
each of said monoliths having longitudinally opposed ends forming an angle other than 90° with the longitudinal sides of said monolith, said plurality of monoliths being disposed longitudinally thereon; comprising two rows of LED portions laterally facing each other, and having electrical connection means for selectively energizing said LED portions, the LED portions of one row being connected to the LED portions of the other row. In contrast, the arrays formed by the laterally staggered and end LEDs of each vertical row are arranged approximately parallel to the ends of the monolith, thereby making them integral. The assembled monolith has a set of uniformly distributed LEDs close to the center
A light emitting diode assembly having a plurality of light emitting diodes forming a part. 2. The light emitting diode assembly according to claim 1, wherein the angle is about 60 degrees.