LED array PCB with adhesive rod lens

The inventive lens is formed from an optical adhesive is used to collect light from a 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. The inventive lens collects light that is emitted by the LEDs at extreme angles and directs the light to the scan location.

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 1/4 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.

DETAILED DESCRIPTION OF THE INVENTION
 FIG. 1 depicts an isometric view of the inventive lens 11 attached to a
 printed circuit (PC) board 12 that includes a plurality of light emitting
 diodes (LEDs) 13 formed in an array 14. Note that the lens 11 does not
 require any specific lens mount, as the lens is directly attached to the
 board 12. The board includes connections 15 to power the PC board 12. The
 lens 11 is formed by pumping an optical adhesive through a needle directly
 onto the board 12. The amount of adhesive dispensed determines the size of
 the lens. The surface tension and viscosity characteristics of the
 adhesive, as well as the effects of gravity, determine the shape of the
 lens 11. These characteristics and the effects of gravity co-act to form
 the crown or cylindrical shape of the lens 11. Specifically, gravity and
 viscosity cause the adhesive to spread out and form the base of the lens
 11 and cover the LEDs 13. Surface tension maintains the curvature or
 radius of the adhesive on the upper surface during dispensing. After
 dispensing, lens must be cured, either via heat or ultraviolet (UV) light,
 to prevent slumping or loss of curvature. Note that curing may not
 immediately occur after dispensing, depending on the viscosity of the
 adhesive, it might take some time for the lens shape to form, thus curing
 takes place after the shape has been formed. Thus, the lens is either
 passed beneath a UV light or processed through an oven. The overall
 operation is relatively short, perhaps approximately 10 seconds to
 dispense, and approximately 30 seconds for UV cure or 30-120 minutes for
 heat cure. Note that this process will not yield a perfect lens, as the
 radius will not accurately controlled or duplicated over the length of the
 lens. However, the inventive lens 11 does provide reasonable light
 collection results, and it is also very quick and inexpensive. Note that
 lens 11 also encapsulates and protects the LEDs 13. Further note that the
 board may be inverted during or subsequent to the dispensing of the
 adhesive. The inversion would cause gravity to assist in maintaining
 curvature of the adhesive.
 As shown in FIG. 2, lens 11 collects light, including light 21 that is
 emitted from diode 13 at a large solid angle 21. This light is then
 delivered to the target area, and is used for illumination of scan target
 31, as shown in FIG. 3. The inventive lens and PC board 32 is mounted at
 approximately 45 degrees with respect to and approximately 0.16 inches (or
 about 4mm) from the scan target surface 31. The light reflected from the
 surface 31 is captured by lens system 33 and focused onto detector 34.
 Note that lens 32 does not have to be capable of image quality light
 delivery, i.e. lens 32 may by a non-imaging lens, as lens 32 is intended
 to provide more light to surface 31.
 The adhesive materials contemplated for use as lens 11 include UV15-7TK1A,
 UV15X-5, and Sil 410, which are UV cured materials produced by Master
 Bond, as well as PT1002A/B, which is a heat cured material produced by
 Pacific Polytech, Inc. Of these materials, UV15 has been shown to perform
 the best. However, other materials may be used, such as epoxy, urethane,
 or acrylic, so long as the material has sufficient optical properties to
 transmit and refract light, at the correct wavelength in the visible range
 of the spectrum, and sufficient adhesive properties to adhere to the PC
 board 12. Note that the lens 11 is depicted and described in connection
 with LEDs, however lens 11 can be used with other elements for other
 systems, particularly where ever a integral lens with less than perfect
 optical characteristics can be used.
 An alternative lens 11 may be formed using a lens form or mold that has the
 desired shape. For example, to form the lens shown in FIG. 1, a
 cylindrical lens form can be applied to the adhesive material. The form
 may be pressed onto the PC board 12 or the board 12 may be moved through
 the form. The form would be coated with a non-stick material such as
 Teflon to prevent the adhesive from sticking to the form. The form would
 ensure that the lens 11 has an optically correct curvature. The form could
 be incorporated with the curing system, such that the proper shape is
 maintained during curing. Note that this system would require more tooling
 and expense than the simpler system described above, but would produce
 lenses with accurate and uniform shapes, whereby the lenses would be image
 capable.
 FIG. 4A depicts lens 41 with a plurality of spherical lenses. Note that
 this lens arrangement will result in more light, it will by extremely
 non-uniform. The spherical lenses are formed via a lens mold that is
 pressed onto the adhesive on board 12. The shape and size of the spherical
 lenses would be selected to concentrate light onto the target area. Note
 that aspherical lenses may be used to collect more of the off-axis light
 emitted from the led. Further note that other lens shapes may be used,
 including cylindrical lense 42 as shown in FIG. 4B. Still further note
 that a non-lens shape may be pressed onto the adhesive, so long as the
 light modifier formed collects and bends light. For example, a grating may
 be formed in the adhesive, which may then collect and focus the light onto
 the target area.
 Another alternative lens 11 may be formed when the LEDs are formed. Note
 that each individual LED 13 comprises a wire frame with semiconductor
 material that is encased in an epoxy cube. Instead of encasing the LED in
 a cube, the LED wire frame would be encased in a lens. Thus, each
 individual LED wire frame would be placed into a mold that has a lens
 shape and cured. This would yield LEDS with individual, integral lenses
 43, as shown in FIG. 4C. Note that a plurality of LED wire frames could be
 placed into a larger lens mold to form a single lens array, e.g. as shown
 in FIG. 1.
 Although the present invention and its advantages have been described in
 detail, it should be understood that various changes, substitutions and
 alterations can be made herein without departing from the spirit and scope
 of the invention as defined by the appended claims.