Optical: systems and elements – Lens – With multipart element
Reexamination Certificate
2001-11-08
2004-01-13
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With multipart element
C359S797000, C359S811000, C359S546000
Reexamination Certificate
active
06678097
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A COMPUTER PROGRAM APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to Fresnel reflectors, and more particularly to monolithic non-planar Fresnel reflector arrays, and mold patterns and mold structures for manufacturing the arrays which eliminate or substantially reduce negative draft during molding.
2. Description of the Background Art
Reflectors are often utilized within various detector and illumination assemblies to focus incident radiation onto a detector (sensor), or to direct radiation emitted from an illumination source toward specific directions. For example, a Fresnel reflector is capable of focusing radiation from a dispersed target zone onto a focal zone, and for directing radiation emanating from an illumination source located near the focal zone to a dispersed target zone. The focal zone comprises a volume that is at, or generally near, the focal point of the reflector. Fresnel reflectors are often utilized to reduce the size and cost of a reflector within a given application. Each Fresnel reflector comprises a series of joined reflector segments configured as rings that may be of a similar shape and/or angle to the sections within an equivalent curved reflector, such as spherical, aspheric, parabolic, or hyperbolic. The rings in a simple Fresnel reflector, however, are placed concentrically on a single plane with steps leading from one ring to the next. Fresnel reflectors may be employed for either focusing radiation, or dispersing radiation, such as radiation found within the visible, infrared, or ultraviolet spectrums.
Motion sensors utilized in alarm systems make extended use of these Fresnel reflectors for focusing radiation, such as at visible, near-infrared, and infrared wavelengths toward a suitable detector. Typically, the surface of the reflector is configured with a mirrored surface that reflects the optical wavelengths toward the detector. In some systems, a non-planar array of Fresnel reflector segments is utilized to collect radiation from a detection area which covers a wide angular spread. The individual Fresnel segments within the non-planar array are aligned adjacent one another at angles to form a generally curved shape. Often complex reflectors are created utilizing multiple tiers of these non-planar arrays, whereas the combination of tiers are typically configured with a single focal zone.
Illumination systems, such as those utilized in the law enforcement/rescue industry and illumination systems utilized in the commercial lighting industry make extended use of Fresnel reflectors for dispersing light which emanates from an illumination source, such as an incandescent lamp, a fluorescent lamp, arc lamp, strobe, an LED (visible or infra-red), ultra-violet lamp, infrared lamp, and similar illumination sources and combinations thereof. Use of Fresnel reflectors for directing illumination is not limited to single illumination sources, as multiple illumination sources may be combined, such as LEDs generating different colors, and placed sufficiently close to the focal point of the reflector system to benefit from being directed by the reflector. Light beacons can utilize Fresnel reflectors in a number of ways. For example, reflectors being utilized for general illumination purposes can be constructed with fixed reflectors to distribute light from an illumination source. For example, the mirrored Fresnel reflector can be utilized to create a regular pattern of bright spots such as radial patterns of bright bars and star effects, and so forth. Rotating emergency beacons can be designed, for instance using a halogen light around which a mirrored Fresnel reflector assembly is rotated.
A conventional single-tier non-planar Fresnel array is shown in
FIG. 1
having segments which direct radiation to, or from, a focal point. The figure illustrates radiation being received from a radiation source in the target zone and reflected from the reflector toward a pyro-electric detector. It will be appreciated that Fresnel arrays for the visible portion of the electromagnetic spectrum are typically manufactured from injection molded plastic to which a mirrored surface is applied, and that each Fresnel segment generally comprises an on-axis center section of a Fresnel reflector.
FIG. 1
depicts a conventional, single-tier, non-planar Fresnel reflector array
10
comprising the following series of joined Fresnel segments: first segment
12
, second segment
14
, third segment
16
, fourth segment
18
, and fifth segment
20
. Each of the Fresnel segments within the array has an optical axis centered within the center ring of the Fresnel reflector. Light paths
22
,
24
,
26
,
28
,
30
, are shown extending between the center of each segment
12
,
14
,
16
,
18
,
20
, respectively, to a detector
32
(shown in phantom) having a focal point FP. The dashed line of the light paths represents the center of the light which reflects from reflector
10
. Detector
32
is preferably positioned within the focal zone of the Fresnel reflector which is sufficiently near focal point FP to provide the desired pattern of reflection. In the figure, Fresnel segments
12
,
14
,
16
,
18
, and
20
, are generally arranged so that the focal point of each Fresnel segment is aligned with focal point FP of detector
32
. Radiation is exemplified as being received from a central portion
34
of a target zone
36
, which may be referred to as a detection area, or detection zone, within an alarm system. It will be appreciated that the light path from the target zones to reflector
10
is shown overlapping the light path from reflector
10
to detector
32
. It should also be appreciated that descriptions reciting the focusing of radiation onto a sensor or detector at the target zone or focal point, are generally applicable in the reverse direction for directing illumination away from an illumination source at the target zone, or focal point, and distributing the illumination according to the reflection pattern of the Fresnel lens. An angular offset, perpendicular to the plane of the illustrations, allows the radiation to pass underneath the detector for receipt by the segments of the non-planar Fresnel reflector array and subsequent reflection onto the detector. The non-planar Fresnel array is shown configured to receive radiation for a given arc of the target zone, wherein the inner three segments receive radiation from a first angular spread
34
, such as forty five degrees (45°), and the exterior two segments extend the angle to a second angular spread
36
, such as ninety degrees (90°). It will be appreciated that an alarm system utilizing the illustrated non-planar Fresnel reflector may have greater sensitivity to radiation being received from the first angular spread
34
, due to increased levels of radiation being coupled from the reflector to the detector. Furthermore, the Fresnel segments extending from center segment
16
are retained at progressively increasing angles in relation to center segment
16
in order to retain focus on focal point FP of detector
32
. A first tilt angle
38
is illustrated as 22.50 degrees, and a second tilt angle
40
is shown at an angle of 45.00 degrees. Joints
42
,
44
,
46
,
48
, between the Fresnel segments provide retention of the segments at the desired angle, although the segments may be mounted to a backing assembly to retain proximal retention of the adjacent segments. The Fresnel reflector tier of the figure is molded as five separate reflectors which are then joined to one another, or otherwise retained proximal to one another. It should be appreciated that a single mold incorporating the five segments of Fresnel array
10
as a monolithic structure would be subject to inclusive draft within the mold, irrespective of the chosen mold release pull direction. Given a particular pull direction
50
, a monolithic molded structure of non-planar Fresnel array
10
would contain inclusi
Collins Darryl J.
O'Banion John P.
Sugarman Scott J.
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