Optical: systems and elements – Lens – Including a nonspherical surface
Reexamination Certificate
1999-04-12
2001-02-13
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Including a nonspherical surface
C257S100000
Reexamination Certificate
active
06188527
ABSTRACT:
BACKGROUND
In scanners and copiers, the light used to illuminate the target area is typically provided by light emitting diodes (LEDs). As shown in
FIG. 5
, the light emitted from a LED
50
is spread over a large area. The light is emitted at a broad angle, with the half power point
52
,
53
being 80 degrees from the vertical axis
51
.
Thus, most of the light produced by a LED is wasted. Consequently, scanning systems typically employ a collection lens to collect and focus the light onto the target area. As shown in
FIG. 6
, an LED
61
includes collection lens
63
to collect and focus the light onto target area
31
. Note that LED
61
typically comprises a plurality of LEDs arranged in a single column array, and that lens
63
is a cylindrical lens. In
FIG. 6
, lens
33
is the SELFOC lens array from NSG. The lens
63
, is typically an extruded or injection molded plastic lens, e.g. polycarbonate or acrylic. The light reflected from the surface
31
is captured by lens system
33
and focused onto detector
34
.
FIG. 7
depicts an alternative LED arrangement
71
that uses reflecting optics
72
to reflect the light onto the target area in place of the refracting lens
63
of FIG.
6
. The light reflected from the surface
31
is captured by lens system
33
and focused onto detector
34
.
The arrangements of
FIGS. 6 and 7
are expensive in terms of manufacturing, as each requires additional tooling to attach the lens or reflector to the LED board. Moreover, the lens and reflectors are additional parts which increase cost. Furthermore, note that the lens
63
requires lens mount
62
to attach the lens
63
to the LED
61
. This lens mount adds a space requirement to the scan system, and in smaller systems such as a hand-held scanner space is expensive. Also the arrangement of
FIG. 7
is also costly in terms of space. For this arrangement to be effective, the trough formed by the reflector
72
must be deep, and thus reflector
72
protrudes from the LED board. Thus, the LED board
81
arrangement shown in
FIG. 8
is typically used. Note that there is no light collection optics, instead a bare LED is used to illuminate the target area
31
. The light reflected from the surface
31
is captured by lens system
33
and focused onto detector
34
. Thus, most of the light produced by LED board
81
is wasted, specifically only about 0.1% of the light is used and about 99.9% of the light is wasted.
Therefore, there is a need in the art for a LED light collection system that is efficient and compact.
SUMMARY OF THE INVENTION
These and other objects, features and technical advantages are achieved by a system and method that uses optical adhesive to form a collection lens.
The optical adhesive is dispensed to cover the LED array. As the adhesive is dispensed, it is formed into the shape of a lens. The adhesive is then cured, and a lens is formed that covers the LED array. A lens shape is formed by the act of dispensing. The combination of gravity, viscosity characteristics of the adhesive, and surface tension characteristics of the adhesive co-act to form the lens shape. Alternatively, a lens form or mold can be used to provide better and more uniform lens shape to the adhesive.
As an example, assume that the LED array is located on a small PC board that is approximately 5 inches long by ¼ inch wide. The LED array is comprised of
18
LEDs evenly spaced in one column on the PC board. The optical adhesive is then dispensed over the LEDs as a long rope of adhesive. Gravity, viscosity, and surface tension cause the adhesive to settle around the LEDs and retain a curved shape. Thus, the adhesive forms an approximately cylindrical lens over the LEDs. The adhesive is then either cured with heat or UV light. Note that the lens formed in this manner is not an accurate lens, as the lens will have irregularities in the lens shape, Moreover, and the shape will not be uniform over the length of the lens, when compared with a standard cylindrical lens. However, the inventive lens does not require the additional manufacturing costs of the prior art lens, nor does the inventive lens require the space of the prior art lens, as the inventive lens is integral with the LED array. Moreover, the inventive lens collects light that is emitted by the LEDs at extreme angles and directs the light to the scan location, and thus provides more light than the prior art arrangement of not using a lens.
Therefore, it is a technical advantage of the present invention to use optical adhesive to form a LED light collection lens.
It is another technical advantage of the present invention to collect light that would be wasted and direct the light to the scan target area. Moreover, the light is diffused by the inventive lens and is more uniformly distributed to the target area. Note that this depends on the composition of the adhesive. Additives in the adhesive would make the light more diffuse. The adhesive would have a “milky” appearance. If the light is more diffuse the system will be slightly less efficient. Thus, there is a trade off between light uniformity and total light output, which depends on the dynamic range of the detector to calibrate out the non-uniformity,.
It is a further technical advantage of the present invention that the lens is integral with the LEDs, and thus does not require attachment to the LED board.
It is a still further technical advantage of the present invention that the invention is inexpensive as the adhesive has a low cost, and additional tooling and/or elements are not required to secure the lens to the array.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
REFERENCES:
patent: H445 (1988-03-01), Bock et al.
patent: 3805347 (1974-04-01), Collins et al.
patent: 4774434 (1988-09-01), Bennion
patent: 4843036 (1989-06-01), Schmidt et al.
patent: 6054222 (2000-04-01), Takami et al.
Epps Georgia
Hewlett--Packard Company
Schwartz Jordan M.
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