Method for implementing capacitive sensing in the presence of conductive decorative materials

A control panel is disclosed. The control panel includes an electrically conductive substrate having a front surface. A first dielectric layer is disposed on the front surface of the substrate. A first electrode layer is disposed on a front surface of the first dielectric layer, wherein the first dielectric layer electrically isolates the first electrode layer from the substrate. The first electrode layer is in electrical communication with a switch circuit adapted to detect a change in a capacitance of the first electrode layer. A substantially transparent film can be provided to cover the electrode. The front surface of the substrate is a decorative surface substantially visible through the first dielectric layer, the first electrode layer, and the film.

FIELD OF THE INVENTION

The invention relates to a capacitive sensing switch. More particularly, the invention is directed to a capacitive sensing switch for a control panel including an electrically conductive decorative material.

BACKGROUND OF THE INVENTION

Automotive display control panel technology is moving from traditional non-interactive displays and mechanical switches to touch-sensitive screens and electronic sensing switches. One type of sensing switch is commonly referred to as a capacitive sensing switch. The capacitive sensing switch typically includes an electrode adapted to create an electric field adjacent thereto which generally defines a sensing zone. The electrode is coupled to a rear surface of a non-electrically conductive or a low-electrically conductivity panel, wherein the electrode is in electrical communication with sensing circuitry. When a conductive or a charged object such as a finger of a person, for example, is placed within the sensing zone on a front surface of the panel, the finger interacts with the electrical field and changes the capacitance of the electrode. The changed capacitance is detected by the sensing circuitry, indicating the occurrence of a switching event.

Electrically conductive panels are known to spread the electrical field from the electrode which reduces the sensitivity of the capacitive sensing switch within the desired sensing zone. Further, spreading the electric field extends the overall area of the sensing zone of the capacitive sensing switch which can result in undesirable switching performance. This is also present with the use of electrically conductive decorative finishes disposed on a surface of a control panel.

It is often desired to use the capacitive sensing switch with electrically conductive panels or panels having electrically conductive decorative finishes thereon. For example, electrically conductive decorative finishes are often employed with control panels to provide a desired aesthetic appearance to a passenger compartment for an automobile. When such electrically conductive decorative finishes have been used, the spreading of the electrical field of the electrode has been reduced by electrically isolating the portion of the panel within the sensing zone from the remainder of the panel and grounding the remainder of the panel. However, electrically isolating the portion of the panel within the sensing zone can cause unwanted performance characteristics in the capacitive sensing switch and produce an unwanted aesthetic appearance on the front surface of, the panel.

It would be desirable to produce a capacitive sensing switch for a control panel having a decorative surface formed from an electrically conductive material, wherein the electrically conductive material adjacent a sensing zone of the capacitive sensing switch is not electrically isolated from the remaining portions of the electrically conductive material and the electrically conductive material does not substantially spread an electrical field of the capacitive sensing switch to a point that a performance of the capacitive sensing switch is functionally compromised.

SUMMARY OF THE INVENTION

Compatible and attuned with the present invention, a capacitive sensing switch for a control panel, the control panel having a decorative surface formed from an electrically conductive material, wherein the electrically conductive material adjacent a sensing zone of the capacitive sensing switch is not electrically isolated from the remaining portions of the electrically conductive material and the electrically conductive material does not substantially spread an electrical field of the capacitive sensing switch to a point that a performance of the capacitive sensing switch is functionally compromised, has surprisingly been discovered.

In one embodiment, a control panel comprises an electrically conductive substrate having a front surface, wherein the substrate is electrically grounded; a first dielectric layer disposed on the front surface of the substrate; and a first electrode layer disposed on a front surface of the first dielectric layer and electrically isolated from the substrate, wherein the first electrode layer is in electrical communication with a switch circuit adapted to detect a change in a capacitance of the first electrode layer.

In another embodiment, a control panel comprises an electrically conductive substrate having a front surface, wherein the substrate is electrically grounded; a substantially transparent first dielectric layer disposed on the front surface of the substrate; a substantially transparent first electrode layer disposed on a front surface of the first dielectric layer and electrically isolated from the substrate, the first electrode layer in electrical communication with a switch circuit adapted to detect a change in a capacitance of the first electrode layer; and a substantially transparent film covering the first electrode layer.

The invention also provides methods for forming a control panel. One method comprises the steps of providing an electrically conductive substrate having a front surface, wherein the substrate is electrically grounded; disposing a substantially transparent first dielectric layer on the front surface of the substrate; disposing a substantially transparent electrode layer on a front surface of the first dielectric layer, the first electrode layer electrically isolated from the substrate and in electrical communication with a switch circuit adapted to detect a change in a capacitance of the first electrode layer; and covering the first electrode layer with a substantially transparent film.

FIG. 1illustrates a control panel10including an electrically conductive substrate12, a dielectric layer18, an electrode layer22, and a protective film24. It should be understood that the control panel10can be adapted for use within a vehicle such as an automobile, for example, wherein the control panel10is disposed within or integral with a console, a dash board, a trim panel, and other surfaces in an interior of the vehicle in a plurality of configurations.

The conductive substrate12includes a front surface14and a back surface16. The conductive substrate12can be produced from a metallic sheet, an electrically conductive composite material having a desired electrical conductivity, or any other material having suitable electrical conductivity. The conductive substrate12is electrically grounded. It should be understood that rather than electrically grounding the conductive substrate12, a reference signal can be provided to the conductive substrate12. It should be further understood that the front surface14of the conductive substrate12is visible to a user and provides a desired aesthetic appearance to the control panel10. Additionally, the front surface14of the conductive substrate12can include decorative designs and indicia such as letters, words, and numbers formed thereon, for example, wherein the decorative designs and indicia are visible to the user. The back surface16of the conductive substrate12can be provided with one or more attachment members (not show) such as bosses, tabs, clips, and the like, for example, to facilitate mounting the conductive substrate12to a support. Further, the back surface16of the conductive substrate12can be provided with one or more structural members (not shown) such as reinforcing ribs and the like, for example, to provide a desired rigidity or other physical property to the conductive panel12.

The electrode layer22is in electrical communication with a switch circuit30as is known in the art to form a capacitive sensing switch. The switch circuit30provides electrical energy to the electrode22to create an electric field adjacent thereto. Further, the switch circuit30is adapted to detect changes in a capacitance of the electrode layer22, wherein the changed capacitance indicates the occurrence of a switching event. It should be understood that the electrode layer22and the switch circuit30can be adapted to provide a plurality of capacitive sensing switches providing switching for selected devices such as HVAC systems, sound systems, and other accessories typically provided in vehicles, for example.

The dielectric layer18is interposed between the conductive substrate12and the electrode layer22, wherein the dielectric layer18is disposed on the front surface14of the conductive substrate12and the electrode layer22is disposed on a front surface20of the dielectric layer18. The dielectric layer18electrically isolates the electrode layer22from the conductive substrate12. The protective film24may be disposed on a front surface23the electrode layer22to provide protection from the surrounding environment, militate against physical wear of the electrode layer22, and provide desired tactile and visual attributes to a front surface26of the control panel10, for example.

The dielectric layer18, the electrode layer22, and the protective film24are substantially visually imperceptible to the user to maintain the visibility of the front surface14of the conductive substrate12. The dielectric layer18can be produced from a single layer and a multi-layer polymer film, for example. It should be understood that the dielectric layer18can be formed from any substantially transparent or translucent material now known or later developed providing effective electrical isolation of the electrode layer22from the conductive substrate12. The electrode layer22can be produced from a substantially transparent or translucent material such as indium tin oxide, for example, or from electrical traces small in size to be substantially imperceptible to the user. The protective film24can be produced from a substantially transparent material such as PET (polyester), PC (polycarbonate), PEN (Polyethylene), PES (Polyethersulfone), an acrylic, a plastic resin, and any other material now know or later developed having suitable physical, electrical, and chemical properties.

The electrode layer22includes electrical traces (not shown) to provide electrical communication between the electrode layer22and the switch circuit30. Interconnections between the electrical traces and the switch circuit30are also provided. The electrical traces and the interconnections are substantially imperceptible to the user by employing substantially transparent or translucent materials, by producing electrical traces and interconnections that are small in size, or by concealing the electrical traces and the interconnections behind panel trim pieces and the like, for example. It should be understood that the electrical traces and the interconnections are also electrically isolated from the conductive substrate12.

In use, the control panel10is formed by disposing the dielectric layer18on the front surface14of the conductive substrate12. The electrode layer22is disposed on the front surface20of the dielectric layer18. The protective film24may be disposed on the front surface23of the electrode layer22to provide a protective covering thereto. It should be understood that the control panel10can be formed in a variety of shapes such as a substantially flat panel and a curvilinear panel, for example. The switch circuit30is typically located remotely from the electrode layer22, wherein additional electrical traces, electrical conductors, and interconnections provide electrical communication between the electrode layer22and the switch circuit30.

The control panel10is typically mounted to a support structure. The front surface14of the conductive substrate12is positioned to be visible to and readily accessible by the user. For example, when the control panel10is a part of a dash board of an automobile, the dash board is mounted to appropriate support members in the interior of the automobile employing the attachment members formed in the back surface16of the conductive substrate12and/or other attachment members such as threaded fasteners, for example. The conductive substrate12is electrically grounded and the electrode layer22is placed in electrical communication with the switch circuit30. Once installed, the control panel10provides a capacitive sensing function to the user. Specifically, the switch circuit30provides electrical energy to the electrode layer22causing the electrical field to be created adjacent thereto and forming the sensing zone adjacent the front surface26of the control panel10. A finger positioned in proximity to the sensing zone interacts with the electrical field of the electrode layer22and changes the capacitance value of the electrical field of the electrode layer22, wherein the changed capacitance is detected by the switch circuit30as a switching event. It should be understood that the electrode layer22can be adapted to provide a plurality of sensing zones adjacent the front surface26of the control panel10. Since the electrode layer22is electrically isolated from the conductive substrate12and the electric field does not extend through the conductive substrate12to form the sensing zone, the electrical field is not spread out by the conductive substrate12. Accordingly, the sensing zone is maintained in a desired location and a performance of the capacitive sensing switch is maximized. Further, since the dielectric layer18, the electrode layer22, and the protective film24are substantially imperceptible to the user, the front side14of the conductive substrate12, together with any decorative designs and indicia formed thereon, remains visible to the user. The control panel10provides for the use of a decorative electrically conductive material as a decorative visible surface, wherein the performance of the capacitive sensing switch is maximized and options for producing a desired aesthetic appearance are maximized.

FIG. 2illustrates a control panel50according to an alternative embodiment of the present invention similar to the control panel10ofFIG. 1, except as described below. Structure repeated from the description ofFIG. 1includes the same reference numeral with a prime (′) symbol. As shown, the conductive panel50includes a substrate12′, a first dielectric layer18′, a first electrode layer22′, a second dielectric layer52, a second electrode layer54, and a protective film24′. The second dielectric layer52is interposed between the first electrode layer18′ and the second electrode layer52, wherein the second dielectric layer52is disposed on a front surface23′ of the first electrode layer22′ and the second electrode layer54is disposed on a front surface53of the second dielectric layer52. The second dielectric layer52electrically isolates the first electrode layer22′ from the second electrode layer54. It should be understood that the control panel50can include more than two electrode layers, wherein a dielectric layer is interposed between successive electrode layers. The protective film24′ may be disposed on a front surface56of the second electrode layer54to provide protection from the surrounding environment, militate against physical wear of the second electrode layer54, and provide desired tactile and visual attributes to a front surface26′ of the control panel10, for example.

The electrode layers22′,54are in electrical communication with a switch circuit30′. The switch circuit30provides electrical energy to the electrode layers22′,54causing an electrical field to be created adjacent thereto and forming the sensing zone adjacent the front surface26′ of the control panel50. A finger positioned in proximity to the sensing zone interacts with the electrical field from the electrode layers22′,54and changes the capacitance value of the electrical field of the electrode layers22′,54, wherein the changed capacitance is detected by the switch circuit30′ as a switching event. Using the first electrode layer22′ together with the second electrode layer54provides a desired array of capacitance switches for the control panel50, wherein a mutual capacitance of the electrode layers22′,54can be detected by the switch circuit30′. Further, the use of two or more electrode layers provides for improved electrode packaging density. The remaining structure and function of the embodiment illustrated inFIG. 2is substantially equivalent to the function and structure of the embodiment illustrated inFIG. 1previously described herein.

FIG. 3illustrates a cross sectional view of a control panel100according to an alternative embodiment of the present invention similar to the control panel10ofFIG. 1, except as described below. Structure repeated from the description ofFIG. 1includes the same reference numeral with a prime (′) symbol. As shown, the control panel100includes a substrate12′, a dielectric layer18′, an electrode layer22′, and a protective film24′. The substrate12′ includes a base layer102and an electrically conductive layer104. The base layer102can be formed from an electrically conductive material or an electrically non-conductive or a substantially electrically non-conductive material. The electrically conductive layer104is disposed on the substrate102. The electrically conductive layer104can be produced from a metallic sheet, a decorative electrically conductive film, an electrically conductive composite material having a desired electrical conductivity, an electrically conductive paint, an electrically conductive ink, a vacuum metalized finish, or any other material having suitable electrical conductivity. The electrically conductive layer104is interposed between the base layer102and the dielectric layer18′ and is electrically grounded. The electrically conductive layer104includes the front surface14′ of the substrate12′ and provides a desired aesthetic appearance to the control panel100. It should be understood that the control panel100can include two or more electrode layers, wherein a dielectric layer is interposed between successive electrode layers. The remaining structure and function of the embodiment illustrated inFIG. 3is substantially equivalent to the function and structure of the embodiment illustrated inFIG. 1previously described herein.

From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, make various changes and modifications to the invention to adapt it to various usages and conditions.