Note: Descriptions are shown in the official language in which they were submitted.
37~.
This application is a divisional of copending application Serial
No. 257 526 filed July 22, 1976 in the name of The Magnavox Company.
The invention relates to a light transmitter capable of being used in
a television remote control system, and to a lens forming part of the transmit-
ter.
Remote control systems for operating a television receiver are well
known in the art. The operator initiates a command from a hand held trans-
mitter. The transmitted command is usually a burst of ultrasonic energy or
light energy which is directed toward the television receiver. The television
receiver is equipped with a receiver for capturing the transmitted ultrasonic
or light energy. This receiver provides an electrical signal which is de-
coded into a command which additional circuitry executes.
In one type of system for remotely controlling a television, a single
ultrasonic frequency corresponds to each remotely controlled function or com-
mand. The receiver detects the presence of this signal and executes the com-
mand. Ultrasonic transmitters are efficienl: and the signal path loss is low.
The ultrasonic signals are strongly reflected by many room surfaces. Thus,
ultrasonic systems are not particularly sbnsitive to transmitter orientation
with respect to the receiver. Ultrasonic noise is present, however, in most
home environments. Thè use of home appliances which emit ultrasonic energy
may initiate a false command in a system where a single frequency is used
to initiate a command. A single frequency command system also makes impractical
a larger number of function conmands. Digital coding techniques in ultrasonic
systems are not practical because of the reflections and propagation time of
` acoustic energy in an air medium.
Light activated remote control systems overcome some of the dis-
advantages of ultrasonic systems but have distinct disadvantages of their own,
e.g., line of sight propagation and substantial path loss. Because light
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energy has a lower propagation time than ultrasonic energy, and a wider use-
able bandwidth, more functions may be defined and controlled than in ultra-
sonic systems. A pulse coding scheme also increases the noise immunity over
a system which detects only the presence of a single frequency. Light energy
however is subjectto a much greater path loss than ultrasonic energy.
Additionally, transducers which convert electrical signals into light energy
are not as efficient as their ultrasonic counterparts. To overcome the losses
sustained by the light remote control link, it has been necessary to intro-
duce more directivity into the remote control link than is found in the ultra-
sonic system. The operator must ta~e care in aiming the transmitting sourcetoward the light receiver. Since television styling restrictions limit the
size of the light receiver aperture, the receiver gain is further limited
thus making aiming of the transmitter at the receiver more critical. The
present invention reduces the directivity requirement of previous light
activated remoted control systems without compromising the system reliability.
According to the present invention, there is provided a transmitter
for transmitting light comprising a lens formed of optical material having a
front light transmitting surface, said front surface being cylindrical about
an axis, said axis being located rearwardly of said front surface, side sur-
faces, a top surface, and a bottom surface, and further comprising a lightemitting diode located within said optical material.
~` In a preferred embodiment the front surface is part cylindrical
about an axis of curvature, the sub surfaces are planar and converge toward
a line located rearwardly of the front surface and the top and bottom sur-
faces are planar and converge toward a line located rearwardly of the front
surace.
A light emitting diode (IED) is used to convert electrical energy
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into light energy. Since the dispersion pattern of commercially available
LEDs are usually too narrow or too broad for use in light activated remote
control systems, a modified cylindrical lens is used to shape $he dispersion
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pattern of an LED. The resulting dispersion pattern is broad in the horizontal
plane to overcome operator difficulty in horizontally aiming the transmitter
towards the receiver. Since in the past it has been determined that horizontal
aiming is more difficult to achieve than vertical aiming, the energy content
in the horizontal plane is increased at the expense of the vertical plane thus
improving the performance of the light transmitter.
The dispersion pattern for the lens is controlled by altering the angle
of the sidewalls. Further tr~lsmitter efficiency is achieved by directly bond-
ing the LED to the lens thus removing losses which occur when an air surface
10 exists between two optical mediums. The transmitter will work well with a
number of rece`ivers. One such receiver is described in a copending application
serial no. 257 522 filed on the same date as the present application in the
name of Eugene P. Mierzwinski and entitled Remote Control Light Receiver.
The invention together with that of pending application Serial No.
257 526, will now be described in greater detail with reference to the accom-
paning drawings, in which:
Figure 1 is a perspective view of a light transmitter incorporating
the invention.
Figure 2 is a diagrammatic view of a light emitting diode used to
convert electrical signals into light energy in the transmitter of Figure 1.
Figure 3 is a horizontal sectional view, taken on line 3-3 of
Figure 1, o the light transmitter illustrating the horizontal light dispersion
of the transmitter.
Figure 4 is a vertical sectional view, taken on line 4-4 of Figure
1, of the light transmitter illustrating the vertical light dispersion of the
transmitter.
Referring to Figure 1, the transmitter comprises a lens 11 for shap-
ing the radiation pat~ern of a light emitting diode ~LED) 12. The lens 11 has
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a convex part cylindrical surface 13 having an axis of curvature 139 which
forms the object side of the lens 11. The cylindrical lens front 13 produces
a line focus as shown. Positioning the LED between the focus and cylinder sur-
face 13 changes the light dispersion. Further control of the dispersion
angle of the lens is achieved by converging the surfaces 1~, 15 subtending the
cylindrical arc. These surfaces 14, 15 are coated with a reflective material
24. Light incident to the surface is reflected out the fron~ lens surface 13.
~ithout the reflective coating~ light incident to these surfaces 14, 15 at
an angle greater than the critical angle would pass through the surfaces and
not reach the remote control reciever. The angle these surfaces 14, 15 make
with each other aid in determining the vertical dispersion angle of the trans-
mitter. The walls 16, 17 subtending the length of the cylindrical face 13
also converge towards a line to the rear o~ the front surface 13. They are
similarly coated with a reflective material and shape the horizontal disper-
sion pattern. The lens material is *Plexiglas having an index of refraction
of 1.36 at a wavelength o 940 nm. Other ~laterials will suggest themselves
to those skilled in the art.
The LED 12 is located in a hole in the rear surface 18 of the lens
11. The preferred location for the LED 12 was experimentally determined to
be in front of the lens ~ocus. The LED 12 is bonded to the lens 11 with a
clear epoxy having an index of refraction substantially the same as the index
of refraction of lens 11. This reduces losses which would otherwise occur with
an air interface between the LED 12 and the lens 11. Referring to Figure
2, the overall olltline of the LED is shown. The lead wires 19 supply electri-
cal current to the junction of the diode. The diode is encapsulated in a
lens cap 20. When the lens cap 20 is bonded to the lens 11 a continuous
optical medium is formed. As noted above, this structure minimizes losses
that would occur with air between different optical surfaces.
* Trade mark
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379~
Figure 3 illustrates the transmitter operation in the horizontal plane.
Llght originating from the LED 12 which is incident to the side walls 16J 17
is reflected out the front of the lens. The transmitter angle of dispersion
is controlled by the angle between surfaces 14, 15 and the location of the LED.
Positioning the LED forward of the focus minimizes the effect of the LED
position on the dispersion angle.
Figure 4 illustrates the operation of the lens in the vertical
plane. The surface 16, 17 control the transmitter horizontal dispersion
angle in a method similar to that of surfaces 14, 15 of Figure 3. By re-
- 10 ducing the angle between surfaces 14~ 15 the vertical dispersion angle is
reduced. Since the transmitter vertical location with respect to the re-
ceiver location is restricted, it is desirable to restrict the vertical
dispersion in favor of distributing more energy in the horizontal dispersion
angle. Those skilled in the art will recogrlize tother energy dispersion pat-
terns which this invention may be readily modified to produce.
The following specifications are given by way of example only of one
embodiment of a light transmitter. Specifics for other applications will be
obvious to those skilled in the art.
~ Cylinder radius 7/16"
Cylinder width 5/8"
Overall length 5/8"
Rear surface LxW 1/4" x 1/4"
LED type *GE 55C
Lens material *Plexiglas
LED distance to front surface 1/2"
* Trade marks
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