Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
2001-04-17
2004-11-16
Lao, Lun-Yi (Department: 2673)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S178000, C345S179000, C178S018010, C178S018060, C178S018050, C178S018070
Reexamination Certificate
active
06819316
ABSTRACT:
TECHNICAL FIELD
This invention relates to touch sensors and, in particular, to capacitive touch sensors and to a method of manufacturing capacitive touch sensors.
BACKGROUND OF THE INVENTION
Touch sensors are widely used to provide a user-friendly interface to a computer system. The sensor usually is affixed over the computer system's monitor to enable the user to directly interact with the system through the monitor by means of finger-touch or a stylus.
Touch sensors fall into two broad categories, namely, digital touch sensors and analog touch sensors. The touch surface of a digital touch sensor is segregated into a plurality of discrete segments. Each of these segments produces a discrete signal when touched. Sensing resolution is limited, therefore, to identifying the particular segment contacted by a finger or stylus. The signal from an analog touch sensor, on the other hand, is not discrete. Sensing resolution is limited only by the overall sensitivity of the sensor and its controlling electronics.
Both analog and digital touch sensors employ a variety of techniques to determine the point at which a finger or stylus contacts the touch surface. These techniques include resistive sensing, capacitive sensing, acoustic sensing and optical sensing. The vast majority of touch sensors, however, use either resistive sensing or capacitive sensing techniques.
A resistive touch sensor employs a flexible membrane positioned over a substrate. The opposing surfaces of the membrane and substrate are coated with a transparent conductive film. Insulating dot spacers are interposed between the membrane and the substrate. When the flexible membrane is pressed by a user, the conductive film of the membrane contacts the conductive film of the substrate. This contact causes current to flow between the membrane and substrate. A controller identifies the point of contact by comparing the current flowing from various electrodes or busbars printed on the conductive surfaces.
A capacitive touch sensor employs no moving parts. In a capacitive touch sensor, a resistive coating is deposited directly upon a solid, insulating substrate. This substrate usually is made of glass. Electrodes positioned at the corners of the substrate establish an electrical field on the coating. A controller connected to these electrodes monitors the amount of current flowing through each of these electrodes. A user's finger, or a conductive stylus, touching, or coming within close proximity to, the resistive coating causes capacitive coupling between the finger or stylus and the coating. This coupling causes a small amount of current to flow through the coating and each of the electrodes. Capacitive coupling through the user's body and ground complete the current path back to the controller. The controller calculates the Cartesian coordinates, i.e., the X and Y coordinates, of the point of touching from the amount of current flowing through each of these electrodes.
Capacitive touch sensors also can function to detect the proximity of an object to the touch sensor. In this case, physical contact with the touch sensor is not required. Capacitive coupling occurs between the object and the sensor through the space separating the object from the sensor.
Since resistive sensors require moving parts, they are more complex and often more costly to manufacture than capacitive touch sensors. The optics of resistive touch sensors also are degraded by the sensor's multiplicity of separated layers having different refractive indices. Touch sensors located in bright environments require a low reflection touch screen to maintain display contrast. This problem is particularly acute for resistive touch sensors. Although an excessively bright display can overcome this problem, such a display requires additional electrical power and adds to the display's cost. This solution, therefore, is not desirable for a device operating on batteries.
Although analog capacitive touch sensors are less complex and provide better optics, the solid, rigid substrate used on these devices diminish their suitability for mobile computerized systems, such as laptop computers, handheld computers, cellular telephones and the like. The weight of such sensors, and their capacity for breaking, also are important factors militating against their use in such systems. Mobile devices also experience far more mechanical flexing than stationary devices. A rigid, brittle and heavy component incorporated into such a device is incompatible with light, flexible components and could cause such flexible components to fail. Similar considerations apply to displays mounted in vehicles and large displays mounted on walls. Brittle, rigid substrates also increase the thickness of a display in products for which a low profile provides a commercial advantage.
Touch sensors based on glass substrates also require a specially fitted frame for mounting the sensor over a monitor or display. Such frames further add to the weight, cost and complexity of the device. A flat, solid substrate also does not conform well to displays or monitors with uneven or curved surfaces, and bending rigid substrates requires expensive processing. Glass based touch sensors, moreover, must be manufactured from individual substrates of cut glass. Such manufacture is costly and time consuming. All of these deficiencies diminish the desirability of existing capacitive touch sensors in some applications.
SUMMARY OF THE INVENTION
The present invention overcomes many of the deficiencies of capacitive touch sensors. The present invention provides an inexpensive, light weight, flexible, transparent capacitive touch sensor and an efficient, low cost method of manufacturing such a touch sensor. Notwithstanding the low cost, light weight and flexibility of a touch sensor in accordance with the present invention, the touch sensor has an unexpectedly high durability enabling it to perform satisfactorily in numerous environments and with a wide variety of devices. The present invention also provides a thin, transparent, flexible layer of protective material to protect the active touch area of a flexible, transparent touch sensor. This protective material substantially enhances the touch sensor's performance and durability.
In one aspect, the present invention provides a flexible, capacitive touch sensor. This touch sensor comprises a thin, flexible, transparent substrate having a first side and a second side. A first layer of resistive material is applied to the first side of the substrate. This first layer is thin, transparent, electrically continuous, flexible and covers on the substrate's first side a surface coincident with an active touch area. The first layer is adapted to receive an electrical potential across the first layer within the active touch area and to transmit an electrical signal indicative of the X and Y position of a point at which an object contacts the active touch area.
The flexible, capacitive touch sensor preferably includes a plurality of thin, flexible electrodes in electrical communication with the first layer. These electrodes are positioned along the periphery of the active touch area and are adapted to apply the electrical potential. The flexible, capacitive touch sensor also preferably includes a plurality of thin, flexible, electrical leads in electrical contact with the electrodes for transmitting electrical signals to and from the electrodes. A plurality of thin, flexible, conductive areas also preferably are included on the touch sensor. The conductive areas are in electrical communication with the first layer and are positioned along the periphery of the active touch area. The conductive areas form a pattern which is adapted to linearize, within the active touch area, the electrical potential throughout the first layer applied by the electrodes.
The flexible, capacitive touch sensor preferably also comprises a second layer of protective material. Depending upon the configuration of the touch sensor, i.e., which side of the substrate corresponds to the t
Chernefsky Anthony F.
Geaghan Bernard
Schulz Stephen C.
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