U.S. patent application number 11/961902 was filed with the patent office on 2008-05-01 for optical illumination system and method.
This patent application is currently assigned to LOGITECH EUROPE S.A.. Invention is credited to Pascal Eichenberger, Francis Pilloud, Olivier Theytaz.
Application Number | 20080100936 11/961902 |
Document ID | / |
Family ID | 38430506 |
Filed Date | 2008-05-01 |
United States Patent
Application |
20080100936 |
Kind Code |
A1 |
Theytaz; Olivier ; et
al. |
May 1, 2008 |
Optical Illumination System and Method
Abstract
A system, method, and method of manufacturing directed to an
optical device with an efficient optical illumination. The optical
illumination can be provided by tilting a light source and using a
refractive lens to direct the light onto a surface. Alternatively,
the optical illumination can be provided using total internal
reflection with a conical light pipe and a curvatured entrance and
exit surface.
Inventors: |
Theytaz; Olivier; (Savigny,
CH) ; Pilloud; Francis; (Clarens, CH) ;
Eichenberger; Pascal; (Lausanne, CH) |
Correspondence
Address: |
FENWICK & WEST LLP
SILICON VALLEY CENTER
801 CALIFORNIA STREET
MOUNTAIN VIEW
CA
94041
US
|
Assignee: |
LOGITECH EUROPE S.A.,
Moulin du Choc D
Romanel-sur-Morges
CH
1122
|
Family ID: |
38430506 |
Appl. No.: |
11/961902 |
Filed: |
December 20, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10033427 |
Dec 27, 2001 |
7333083 |
|
|
11961902 |
Dec 20, 2007 |
|
|
|
60290268 |
May 10, 2001 |
|
|
|
Current U.S.
Class: |
359/838 |
Current CPC
Class: |
G06F 3/03543 20130101;
G06F 3/0317 20130101 |
Class at
Publication: |
359/838 |
International
Class: |
G02B 5/08 20060101
G02B005/08 |
Claims
1. An illumination system in an optical pointing device comprising:
an entrance surface positioned to gather light from a light source
positioned at a first angle relative to a target surface; a light
pipe truncated along a first truncation plane, the light pipe
coupled to the entrance surface for directing the light gathered
from the entrance surface by reflecting at the first truncation
plane meeting a total internal reflection condition for the light;
and a curvatured exit surface coupled to the light pipe, the
curvatured exit surface directing the light onto the target surface
at a second angle relative to the target surface, the second angle
different than the first angle.
2. The system of claim 1, wherein a portion of the light pipe is
frustro-conical shaped.
3. The system of claim 2, wherein the light pipe has a larger
entrance cross-section than an exit cross-section.
4. The system of claim 1, wherein the truncated plane is covered
with a metal coating.
5. The system of claim 1, further comprising a second truncated
plane for further directing the light toward the exit surface at a
third angle relative to the target surface, the third angle
different than the second angle.
6. The system of claim 5, wherein the second truncated plane is
covered with a metal coating.
7. The system of claim 1, wherein the light source is a light
emitting diode.
8. The system of claim 1, wherein the light pipe is made from an
optical plastic.
9. The system of claim 1, wherein the truncated light pipe is made
from glass.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 10/033,427 entitled "An Optical Illumination
System and Method," filed Dec. 27, 2001, which claims priority from
provisional U.S. Patent Application Ser. No. 60/290,268, for "An
Optical Illumination System and Method," filed May 10, 2001, the
disclosure of which are incorporated herein by reference in their
entirety.
BACKGROUND
[0002] A. Technical Field
[0003] The present invention relates generally to optical
technology, and more particularly, to optical technology in an
input device.
[0004] B. Background
[0005] Optical technology is used in many contexts, including in
optical input devices. There are many different types of input
devices, including a mouse, a trackball, and a joystick. There are
significant advantages to using optical input devices over
mechanical and opto-mechanical input devices. For example,
mechanical or opto-mechanical input devices have mechanical
components that are more susceptible to breakdown or wear out.
Optical devices having only solid state components are less
susceptible to such breakdown or wear out. However, one
disadvantage of some optical input devices is increased power
consumption, caused in part by an inefficient illumination source
or system. Illumination requires a precise angle of illumination
and a sufficient optical power to create a pattern on a surface
(e.g., a table surface) that can then be captured by a photosensor.
The pattern is the surface pattern itself illuminated by the beam
or the light and shadow of the surface microstructure that is
generated by the illumination beam impinging at the appropriate
angle. In conventional illumination systems, in order to achieve
the desired illumination at the desired angle and the desired
optical power, large power consumption is required due to an
inefficient illumination system. This power consumption shortens
battery life in wireless, optical pointing device systems.
[0006] As an example of an optical displacement system, consider an
optical mouse. The optical mouse includes a conventional
illumination system. Conventional illumination systems consist of a
light emitting diode (LED) and a double prism system. The double
prism system consists of an entrance surface, a double prism, and
three exiting facets approximating a cylindrical concave exit
surface. The entrance surface is a piano-convex lens shape linked
to the double prism body that collects the LED light and collimates
it. The double prism conducts the light beam to a target area on
the table surface with the required incidence angle. The
cylindrical concave exit surface attempts to spread the light
evenly on the target area. An imaging lens creates an image of the
lighted area on an optical sensor. The double prism system serves
as a light conductor between the LED and the table surface (e.g. a
table top or mousepad). Conventional illumination systems require
that a total internal reflection (TIR) condition on be met. A TIR
condition is met when an incidence angle of a light ray, for
example, inside a plastic media interfaced with air, is larger than
a critical angle resulting in total internal reflection at the
transparent material surface and no rays are refracted outside the
transparent material. However, rays that do not encounter the
entrance surface or rays that do not satisfy the IR condition
within the double prism path are lost. In conventional illumination
systems, the LED is mounted on a printed circuit board (PCB) in a
horizontal configuration on the component side of the PCB. In this
conventional configuration, the LED can be easily soldered to the
PCB simultaneously with the other electronic components. Thus, to
direct the light to the target surface, the double prism is
required to achieve both the vertical distance and the required
incidence angle.
[0007] Conventional illumination systems, using a double prism
system, have a long light path, multiple direction changes, and no
way to recover diverging rays, thus, increasing loss and reducing
efficiency. Furthermore, as the light source, which includes an LED
die and LED optics, size is not a single point, it is not possible
to accurately focus all rays coming from the LED. There is a
significant amount of loss across this conventional system.
Examples of four types of loss are: TIR loss, reflection/refraction
loss, transmission loss, and coupling efficiency loss. Coupling
efficiency loss is caused by the fact that not all light from the
LED can get into the double prism because the alignment of the LED
with the entrance surface of the prism cannot be perfect and the
surface of the entrance lens of the prism is not large enough to
collect all the viewing angle emitted by the LED. Each of many
intermediate parts contribute to this misalignment, for example, an
LED package, an LED support, the PCB, and a mouse case. Due to the
above mentioned limitations, the intensity, the uniformity, and the
position of the illumination spot are degraded.
[0008] Therefore, there is a need for improving the illumination of
an optical input device while improving the image signal power on a
photosensor. Accordingly, it is also desirable to provide an
optical input device with an efficient illumination source that
helps reduce power consumption and increase battery life and
illuminate the target area uniformly.
SUMMARY OF THE INVENTION
[0009] The present invention provides an efficient illumination
system. The illumination system can be used in optical input
devices, for example, an optical mouse. The present invention
includes an optical system that has a conical light pipe with a
curvatured (e.g. toroidal) entrance or exit surface (or "window")
in one embodiment and a refractive illumination lens in another
embodiment. For ease of discussion the term "or" as used herein
means both inclusive or and exclusive or, i.e., and/or.
[0010] In one embodiment, a refractive lens is used with a tilted
light source. The light source can be a light emitting diode (LED)
in the visible or near infrared spectrums. The light source can
emit light at any one or multiple wavelengths. In alternative
embodiments, refractive surfaces of the refractive lens can be
replaced with a Fresnel surface or a diffractive optical element
(DOE) surface. For ease of discussion, the present invention will
be discussed with regard to a lens system that may comprise any one
of the above optical surfaces or any combination of the above
optical surfaces. It is understood that a refractive lens shall be
used to refer to a lens that is either a refractive lens, a Fresnel
surface, a diffractive optical element (DOE), or any combination of
these lens types.
[0011] The light source can be angled relative to the printed
circuit board. In one embodiment, there is an opening in the
printed circuit board for the light source to protrude through. In
another embodiment, the light source is mounted on a separate PCB.
The lens system directs the light emitted from the light source to
a target area on a surface, e.g., a tabletop or other surface.
Typically, the PCB is parallel to the table surface. The table
surface can be planar or curvatured, for example, in the case of an
optical trackball the surface is a curvatured surface. In one
embodiment, the light source is configured to be approximately
parallel to the printed circuit board. In this embodiment, a
conical light pipe with a curvatured entrance surface or exit
surface can be formed to direct the light emitted from the light
source to the target area on the table surface. It is understood
that a curvatured surface shall be used to refer to a surface with
a toroidal shape, a spherical shape, an aspherical shape, a
cylindrical shape, or a spline shape. The illuminated target area
size is linked to the table surface seen by the sensor through any
imaging lens plus safety margins for tolerances.
[0012] There are many benefits and advantages of the present
invention. One advantage is that less LED current is required for a
higher optical power on the table surface due to an illumination
yield gain. This helps to prolong battery life for a wireless
product. Another advantage is removing a need for a high efficiency
LED to compensate for an inefficient lighting system. This helps
reduce costs because a less efficient light source may be used.
Another advantage is reducing mechanical dimensions for the system
thereby increasing design flexibility and reducing cost. For
example, there is a significant reduction in the size of the
optical portion of an illumination system. The reduction in size
permits a smaller lens part to be used, which uses less optical
material in manufacturing, less injection time and a smaller mold,
and therefore, reduces the cost. Another advantage is that the
illumination area position robustness with respect to the target
area is increased. Another advantage could be an increase in depth
of field because a smaller aperture can be used with the imaging
lens. An increase in depth of field allows for greater mechanical
tolerances. Another advantage is a reduction in exposition time,
the sensor being illuminated with the required amount of energy in
a shorter amount of time. The time reduction factor is equivalent
to the illumination yield gain.
[0013] In one embodiment of the present invention, a refractive
illumination lens is used. It is noted that this embodiment of the
present invention provides an overall lighting system that is
refractive only, meaning that TIR, which causes additional losses,
is not used. In this embodiment, the optical system length is
reduced significantly by using a tilted LED that is interfaced with
a refractive lens instead of a double prism or a light pipe. In
this embodiment, the LED can be tilted and moved closer to the
target area. In one embodiment, the LED is tilted such that it is
not parallel to the PCB, for example placing the LED at a 20 degree
to 30 degree angle to the PCB. The LED can be positioned such that
it protrudes down through the PCB. In cone embodiment, the
refractive lens has a curvatured entrance surface and a curvatured
exit surface.
[0014] In one embodiment of the present invention, losses in the
system are reduced by the illumination light pipe, thus making it
more efficient. The losses are reduced by the light pipe with a
conical shape that reduces the region or surfaces where rays are
not under the TIR condition. In one embodiment, instead of using a
double prism, a conical (or cylindrical) light pipe is used. The
conical light pipe has a larger entrance surface than exit surface.
The large entrance surface combined with the light pipe function
allows larger position errors for the LED. In one embodiment, a
curvatured (e.g. toroidal) entrance surface or exit surface is
used. The toroidal shape means that the entrance surface or exit
surface has at least two different radii) f curvature orthogonal to
each other, in a vertical and a horizontal plane. One embodiment
has a curvatured surface at each end of the conical light pipe
portion. The conical section can be truncated by a first reflective
surface. This truncation is advantageous because it allows the LED
to be positioned horizontally or obtains the required angle of
incidence beam on the target surface. In another embodiment, a
second reflective surface also acts to further direct the light
toward the surface. The second truncation allows other positions of
the LED and further increases design flexibility. In one
embodiment, the reflective surfaces combined with the light pipe
direct most of the light out the exit surface, forming a
twice-truncated cone. In one embodiment the reflective surfaces can
be coated with a metallic covering to guarantee reflection of rays
not satisfying the TIR condition. In an alternate embodiment, the
first reflective surface and the second reflective surface can be
removed when the LED is positioned at a predetermined angle.
[0015] In one embodiment, an illumination efficiency gain of at
least two is realized over a conventional illumination system by
using, for example, a conical light pipe truncated by two
reflective planes. This gain means two times less current in the
LED or half as much power needed for the same illumination. For
embodiments with the tilted LED, the efficiency of the illumination
system may increase to a factor of at least three. The length
reduction of the complete lens system can be about 10 millimeters
(mm).
[0016] As described above, the benefits of the present invention
include an improved battery life, for example for an optical
cordless mouse, due to reduced power consumption and component
efficiency gains. An efficient or powerful light source is not
required with the present invention due to increased efficiency in
the illumination system. One embodiment of the present invention
reduces the length of the optical system, which enables greater
industrial design flexibility. Using the present invention allows
for the possibility of gaining depth of field by reducing the
imaging lens aperture because there is more energy on the surface.
The present invention provides a much more robust system to the
misalignment between the light source and the illumination lens by
providing enough energy on the surface. The present invention
allows a reduction of the exposure time of the sensor if the
conventional (high efficiency) light source and the driving current
are kept the same. The present invention aims at illuminating the
surface with a spot that is more uniform.
[0017] As can be seen from the above description, the present
invention may be applied to many different domains, and is not
limited to any one application. Many techniques of the present
invention may be applied to illumination in a number of optical
displacement detection systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIGS. 1A and 1B are an illustration of a side view of one
embodiment of the present invention that includes a refractive
illumination lens with a plane, cylindrical, spherical, aspherical,
or toroidal entrance surface or exit surface.
[0019] FIG. 2 is an illustration of a second side view of one
embodiment of the present invention that includes the refractive
illumination lens, LED, target area, imaging lens, and sensor
only.
[0020] FIGS. 3A, 3B, and 3C are an illustration of the construction
method of a conical light pipe that includes zero, one, and two
truncating planes.
[0021] FIG. 4 is an illustration of a side view of one embodiment
of the present invention that includes a conical light pipe with a
single truncation plane.
[0022] FIG. 5 is an illustration of a side view of one embodiment
of the present invention that includes a conical light pipe with
two truncating planes and a curvatured entrance surface or exit
surface.
[0023] FIG. 6 is an illustration of a top view of one embodiment of
the present invention that includes a conical light pipe with two
truncating planes and a curvatured entrance surface or exit
surface.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The following description of the present invention is
presented in the context of an optical illumination for optical
displacement detection system for use in, for example, a computer
input device. In some embodiments, the principles disclosed may be
implemented for use in an optical mouse or an optical trackball.
One skilled in the art will recognize that the present invention
may be implemented in many other domains and environments, both
within the context of optical illumination for optical displacement
detection, and in other contexts. Different embodiments of the
present invention are now described with reference to the figures
where like reference numbers indicate identical or functionally
similar elements. Also in the figures, the left most digit of each
reference number corresponds to the figure in which the reference
number is first used.
[0025] Accordingly, the following description, while intended to be
illustrative of a particular implementation, is not intended to
limit the scope of the present invention or its applicability to
other domains and environments. Rather, the scope of the present
invention is limited and defined solely by the claims.
[0026] Now referring to FIG. 1A, there is shown a side view of one
embodiment of an optical lens system of the present invention that
includes a refractive illumination lens. It is understood that the
refractive illumination system (e.g., with a flat, cylindrical,
spherical, aspherical, or toroidal entrance or exit surface, or
window) is also referred to as a lens 135. FIG. 1A shows a light
source 100, the lens 135 having an entrance surface 110 and an exit
surface 115, a printed circuit board 105, a target area (or a
concentration spot) 120 on a surface and an imaging lens 125. In
one embodiment, the light source 100 may protrude through an
opening in the printed circuit board ("PCB") 105. Light emitted
from the light source 100 enters the lens 135 through the entrance
surface 110. The light exiting the exit surface 115 of the lens 135
forms a light beam 130 and is directed to a surface at the target
area 120. The target area 120 is in line with imaging lens 125. The
surface can be any surface, for example, a tabletop or surface, a
mouse pad, a paper, or any other surface. For each discussion the
application will refer to a table surface as a generic
representation of all surfaces, including a ball surface for a
trackball.
[0027] In an alternative embodiment, the light source 100 does not
protrude through the PCB 105. In that embodiment, there is an
opening in the PCB 105 for the light emitted from the light source
100 to go through the PCB 105. In one embodiment, the lens 135
protrudes through the PCB 105.
[0028] The entrance surface 110 of the lens 135 is curvatured. In
one embodiment, the entrance surface 110 can be aspherical in shape
to collect as much light as possible. In another embodiment, the
entrance surface 110 of the illumination lens 135 can be matched
with a shape of the LED tip so that a continuous media without
changes of refractive index will result. The exit surface 115 bends
the light such that it has the desired angle and focuses the light
to produce an illumination spot on the target area that is as
uniform as possible on the surface. In one embodiment, the exit
surface or the entrance surface can be ground to diffuse the light
making it more uniform on the target area 120. The LED die has a
contact point in the center causing a hole in the illumination and
a ground entrance 110 or exit surface 115 can avoid imaging the die
on the surface in some embodiments.
[0029] The entrance surface 110 is closest to the light source 100.
The entrance surface 110 can be symmetrical about the optical axis
of the LED or it can be shifted by design. The entrance surface 110
can be used to collect the light. The exit surface 115 is also a
curvatured surface and can be configured to shape the light beam to
compensate for elongation resulting from the oblique angle of the
beam. Since the beam hits the target area at an angle, the
corresponding dimension will be increased, resulting in a light
spot with a width and a height that are approximately the same.
[0030] The entrance surface 110 of the lens 135 may be, for
example, a spherical surface a cylindrical surface, a toroidal
surface, or an aspherical surface and may be refractive, Fresnel,
or DOE. Similarly, the exit surface 115 of the lens 135 also may
be, for example, spherical, cylindrical, toroidal, or aspherical
and may be refractive, Fresnel or DOE. The entrance surface 110 and
the exit surface 115 each refract light. By adjusting the shape of
both or either the entrance surface 110 or the exit surface 115,
the light beam emerging from the lens 135 can be shaped or tilted
as needed. As an example, if one surface is cylindrical, it will
affect one dimension of the light beam from the light source 100.
If the one surface is spherical, it will affect both dimensions of
the light beam from the light source 100 the same way. If one
surface is toroidal, it will affect two dimensions of the light
beam from the light source 100, but in a different way. The
entrance and exit surfaces 110 and 115 can be parallel (in the
sense of two plano-convex lenses linked together by their flat
surfaces) or angled (a prism of wedge being added between the two
flat surfaces). In the aligned configuration, the entrance and the
exit beams axis will be the same. In the angled configuration, the
beam axis will be folded.
[0031] In one embodiment of the present invention, a refractive
lens 135 is used. In one embodiment, the entrance surface 110 is an
aspherical shape and the exit surface 115 is a cylindrical shape.
The aspherical entrance surface gathers and focuses the light. The
cylindrical exit surface spreads the light evenly on the target
area 120.
[0032] In one embodiment, the light source 100 of the present
invention can be a light emitting diode (LED) emitting at
approximately 630 nm. In another embodiment, the light source 100
can be any other light source at any wavelength in the visible
spectrum or near the infrared spectrum. The light source can emit
light at any one or multiple wavelengths. The lens 135 can be made
of many materials including any optical polymer or glass. Some
examples of materials that can be used for the lens 135 are
polycarbonate, polystyrene, acrylic, polymethylmethacrylate, or
another optical plastic. In all embodiments, any material can be
used such that the desired result of gathering and focusing light
can be achieved.
[0033] A benefit of embodiments of the present invention using the
lens 135 is that they do not require the use of total internal
reflection. By not using total internal reflection to direct the
light to the table surface, the system is more robust because there
are fewer critical surfaces, which result in fewer errors or
misalignments. Further, an optical path for light can be
significantly shorter than in lens systems that use total internal
reflection, which also allows for potentially fewer chances of
encountering flaws. The present invention prevents compounding
light transmission errors that may exist when a precise angle
between the light source 100 and the entrance surface 110 of the
lens 135 is not properly set.
[0034] Typically, a lens is close to the light source and
symmetrical with an axis of symmetry of the light source. In an
implementation that relies on total internal reflection, the lens
is sensitive to small variations in alignment between the light
source and the lens. However, some embodiments of the present
invention do not rely on total internal reflection, including the
embodiment shown in FIG. 1, and therefore, are not as sensitive to
misalignment between the light source and the lens.
[0035] Now referring to FIG. 1B, there is shown another embodiment
of a side view of the present invention. FIG. 1B shows another
light source 140, a printed circuit board 105, a wedge-shaped
refractive lens 145, a target area 120, and an imaging lens 125.
The embodiment shown uses a light source 140 with a narrow viewing
angle. For example, the viewing angle can be 15 degrees or less.
Typically, the LED viewing angle is approximately 30 degrees.
[0036] In this embodiment, since the light source has a narrow beam
it is not necessary to concentrate the beam and planar entrance or
exit surfaces can be used. The wedge-shaped lens 145 functions to
fold the light beam so that it reaches the target area at the
desired angle. When the light source 140 with a narrow viewing
angle is used, the entrance surface 110' may be flat. The lens 135
(shown in FIG. 1A) can be replaced with wedge-shaped lens 145. The
wedge-shaped lens 145 bends a light beam axis so that it hits a
target area 120 at a required angle. The target area is in line
with an imaging lens 125. With a highly directive light source, an
entrance surface 110' of the wedge-shaped lens 145 is simplified,
although a cylindrical or toroidal exit surface 115' may be used to
shape the light beam into a thin, but wide, shape. The angle 150
pointing away from the PCB 105 can be any angle necessary to
achieve the desired deviation angle and avoids the TIR condition.
For example, the angle 150 can be between 5 degrees and 35 degrees.
For an LED with a typical viewing angle of 30 degrees, the wedge
135 can have an entrance or an exit surface that is curvatured, a
combination of FIGS. 1A and 1B. Either the entrance surface 110' or
exit surface 115' can be partially or totally ground.
[0037] Now referring to FIG. 2, there is shown a side view of one
embodiment of the present invention, including the lens 135 with
entrance surface 110 and exit surface 115. FIG. 2 shows the light
source 100, the lens 135, including the entrance surface 110 and
the exit surface 115, the target area 120, the imaging lens 125,
and a sensor die surface 205. In one embodiment, the light source
100 shown is an LED. In one embodiment, the LED is at an angle
relative to an upper surface of the PCB (not shown). Similarly to
FIG. 1, light emitted from the LED, enters lens 135. In one
embodiment, the entrance surface 110 gathers and refracts the light
emitted from the LED 100. In one embodiment, the exit surface 115
refracts the light gathered by entrance surface 110 and spreads the
light. The light is focused onto the table surface where the target
area 120 is located. The imaging lens forms an image of the table
surface where the target area 120 is located. The pattern on the
table surface or the pattern of the microstructure of the surface
is imaged by the imaging lens 125 on the sensor surface 205.
[0038] Now referring to FIG. 3A, there is shown a side view of a
conical light pipe. FIG. 3A shows a light source 100 and a conical
light pipe 312. The conical light pipe has an entrance surface 355
or exit surface 310. The entrance surface 355 or exit surface 310
can be a curvatured surface. The conical light pipe is larger at
the entrance than the exit. The conical light pipe 312 shown is not
truncated at all.
[0039] Now referring to FIG. 3B, there is shown a side view of the
conical light pipe shown in FIG. 3A with a single truncation plane.
FIG. 3B shows the light source 100, the entrance surface 355, an
outline of conical light pipe 312, first truncation plane 315, and
a second conical light pipe section 322. The first truncation plane
is such that the TIR condition is satisfied. In one embodiment, if
the TIR condition is not met for most of the contributing rays, the
truncation plane can be covered with a metallic surface. For
example, the incidence cone axis is between approximately 32
degrees and 90 degrees. The first truncation plane 315 is such that
the rays inside the cone 312 are folded, respecting the TIR
condition. When the rays encounter truncation plane 315, they are
reflected and continue in the conic section 322 until exit surface
317. Conic section 322 is the mirrored image of conic section 312
that is removed by the truncation.
[0040] Now referring to FIG. 3C, there is shown aside view of the
single truncated conical light pipe shown in FIG. 3B with a second
truncation plane added. FIG. 3C shows the light source 100, the
entrance surface 355, an outline of the once truncated conical
light pipe 322, the first truncation plane 315, a second truncation
place 320, and a third conical light pipe section 380. The
resulting twice truncated conical light pipe is shown with hatch
marks. The second truncation plane can be at an angle such that the
TIR condition is satisfied, forming cone 380. In one embodiment,
the second truncation plane could also be covered with a metallic
coating.
[0041] In one embodiment of the present invention, no truncation
plane is used, as discussed above in reference to FIGS. 1 and 2. In
another embodiment, one truncation plane is used, as discussed
below in reference to FIG. 4. In a third embodiment, two truncation
planes are used, as discussed below in reference to FIGS. 5 and 6.
In the embodiments using zero, one, or two truncation planes a
conical light pipe can be used. In the embodiments using zero, one
or two truncation planes a cylindrical light pipe can be used
instead of the conical light pipe.
[0042] In one embodiment, the second truncation plane could be
angled such that conic section 360 points to the left instead of
the to the right. The light pipe shown in FIG. 3C forms a "Z"
shape. However, the light pipe could also be formed to for a "C" or
a "U" shape. In these embodiments, the axis of the different
conical sections are all in the same plane. Other embodiments are
also possible.
[0043] Now referring to FIG. 4, there is shown a side view of one
embodiment of the present invention including a once truncated
conical light pipe. It is understood that in any of the Figs. or
description of a conical light pipe, a cylindrical light pipe could
be implemented in place of the conical light pipe. FIG. 4 shows a
light source 100, an entrance surface 455, a truncation plane 415,
an outline of a conical light pipe 412, a once truncated cone 422,
and an exit surface 460. In this embodiment, the light source 100
is at an angle approximately vertical, such that the first
truncation plane can reflect the light to a target area on a table
surface.
[0044] Now referring to FIG. 5, there is shown a side view of one
embodiment of the present invention including a twice-truncated
conical light pipe with a curvatured entrance and exit surface. The
conical light pipe can be a circular cone or another shape cone,
for example, a rectangular cone. The light pipe may comprise
multiple sections. In one embodiment, the sections are not the same
shape. For example, one section can be a circular cone shape and
another section can be a rectangular cone shape. FIG. 5 shows a
horizontal light source 100, a PCB 510, a curvatured entrance
surface 555, a sensor 125, reflective surfaces 515 and 520, a
curvatured exit surface 560, a target area (or a concentration
point) 550 on a table surface 545, and an imaging lens 120. In the
embodiment shown in FIG. 5, the light source 100 is used to emit
light. In one embodiment, the light source 100 is an LED. The light
source 100 can be parallel to the PCB 510. The light emitted from
the light source forms a beam 525. The light beam 535 can be
directed towards the target area 550 on a highly oblique angle
using the reflective surfaces 515 and 520. The light diffused from
the imaged area 550 is captured by the imaging lens 120 to form an
image of the target area on the sensor 125.
[0045] In one embodiment, the light source 100 of the present
invention can be a light emitting diode (LED) emitting at
approximately 630 nm. In another embodiment, the light source 100
can be any other light source at any wavelength in the visible
spectrum or near the infrared spectrum. The lens shown in FIGS. 4-6
can be made of many materials including any optical polymer or
glass. Some examples of materials that can be used for the lens are
polycarbonate, polystyrene, acrylic, polymethylmethacrylate, or
another optical plastic. In all embodiments, any material can be
used such that the desired result of a light pipe satisfying the
TIR condition is met.
[0046] In the embodiment shown, the light is gathered by the
entrance surface 555. The surfaces and truncation planes between
the light source 100 and the exit surface 560 forms a conical light
pipe with the curvatured entrance surface 555 and exit surface 560.
The exit surface 560 can be toroidal, meaning the exit surface 560
may have two different radii of curvature in a vertical plane than
in a horizontal plane. The truncation planes 515 and 520 can form a
truncated cone. The light beam diameter at the entrance surface 555
is larger than the light beam diameter at the exit surface 560.
[0047] Now referring to FIG. 6, the conical light pipe with a
curvatured entrance surface 555 and exit surface 560 is shown from
a top view. Similarly to FIG. 5, a light source 100 is used to
illuminate a surface 545 such as a table surface. The light is
focused on the target area 550 on the surface 545. Again, similar
to FIG. 5, the reflecting surfaces 515 and 520 form the
twice-truncated conic light pipe. In one embodiment, the exit
surface 560 can be a toroidal exit surface.
[0048] From the above description, it will be apparent that the
invention disclosed herein provides a novel and advantageous system
and method for illumination in an optical device. The foregoing
discussion discloses and describes merely exemplary methods and
embodiments of the present invention. As will be understood by
those familiar with the art, the invention may be embodied in other
specific forms without departing from the spirit or essential
characteristics thereof. For example, the invention may be applied
to other domains and environments, and may be employed in
connection with additional applications where optical displacement
or movement detection is desirable. Accordingly, the disclosure of
the present invention is intended to be illustrative, but not
limiting, of the scope of the invention, which is set forth in the
following claims.
* * * * *