Patent Application
20080266272
This invention relates to touch sensors and, in particular, to a luminous touch sensor.
In a personal electronic device, such as a hand-held computer or a laptop computer, a touch sensor is often used as an input device. The touch sensor is a separate device or is built into the personal electronic device. A touch sensor uses a capacitive element or piezo-resistive element to indicate a point of contact between a user's finger and the surface of the touch sensor. The location is calculated by a microcontroller in the touch sensor or in the personal electronic device. The location, or a series of locations, is then used for control or as data entry.
In the prior art, U.S. Pat. No. 6,433,846 (Omar et al.) discloses the combination of a liquid crystal display overlying a touch sensor, wherein both are back lit by a gas discharge lamp and a light guide. U.S. Pat. No. 6,822,640 (Derocher) discloses a touch sensor back lit by an electroluminescent (EL) lamp. U.S. Pat. No. 6,842,170 (Akins et al.) discloses a liquid crystal display back lit by an EL lamp, both overlying a touch sensor. Anything overlying a touch sensor interferes with its operation. Liquid crystal displays are relatively thick and do not bend well over a short radius. Most EL lamps are relatively stiff, although urethane based lamps can be relatively flexible. A back lit piezoresistive touch sensor is currently an impossibility because known piezoresistive materials are opaque. Thus, a back lit touch sensor must be capacitive, which can be made transparent.
An EL lamp is used for back lighting because, as known in the art, the light produced by an EL lamp is very uniform across a large area. As also known in the art, an EL lamp can produce noise and requires high voltage to operate, as do gas discharge lamps. Back lit structures of the prior art are stacked elements, which are necessarily relatively thick. Not only adding to the thickness, an EL lamp is also the rear most portion of a structure, which means that the light from the lamp must pass through whatever is placed on top of the lamp. So-called transparent electrodes, e.g. for a liquid crystal display, are transparent in the sense of not substantially scattering light but they do absorb light. A transparent electrode typically absorbs twenty percent of the light passing through the electrode.
In view of the foregoing, it is therefore an object of the invention to provide a luminous touch sensor; that is, a touch sensor that emits light.
Another object of the invention is to provide a luminous touch sensor that is back lit.
A further object of the invention is to provide a luminous touch sensor that emits light from a surface that is between a user and the touch sensitive element.
Another object of the invention is to provide a luminous touch sensor that is thinner than back lit touch sensors of the prior art.
A further object of the invention is to provide a personal electronic device having a luminous touch sensor.
Another object of the invention is to provide a luminous touch sensor that does not produce noise.
A further object of the invention is to provide a luminous touch sensor that does not require high voltage or alternating current.
Another object of the invention is to provide a luminous touch sensor that is less expensive to manufacture than back lit touch sensors of the prior art.
The foregoing objects are achieved by this invention in which a luminous touch sensor includes a touch sensor having a major surface, a light guide overlying at least a portion of the major surface, and at least one light emitting diode optically coupled to the light guide. The light emitting diode is preferably an edge emitter and the plastic sheet is preferably relatively thin.
A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:
Except for reference numerals,
In
In operation, power is supplied to LED 27, which preferentially emits light in a direction indicated by arrow 28, into light guide 21. The light spreads through light guide 21 by transmission and by total internal reflection from the major surfaces of the light guide. Some light is scattered toward a user, e.g., by roughening an area of the upper surface of the light guide to cause refraction rather than total internal reflection.
In
As illustrated in
In
The invention thus provides a luminous touch sensor. The luminous touch sensor is thinner than back lit touch sensors of the prior art and is suitable for any type of personal electronic device. A luminous touch sensor constructed in accordance with the invention does not require high voltage or alternating current and does not emit noise. The light guide can be behind or in front of the touch sensing element, enabling the invention to be used with a wider variety of touch sensors than in the prior art. Because of the fewer elements involved, a touch sensor constructed in accordance with the invention is simpler and less expensive to make.
Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, the LED can have any desired color or, if plural LEDs are used, any combination of colors. Protective layer 29 can be transparent, translucent, tinted or include graphics, in any combination.
