Patent Application
20140266250
The present invention relates to capacitive sensors. More particularly, the present invention relates to capacitive touch and object sensors.
Capacitive sensors are usually connected directly to a system's measurement electronics module by a wire, conductive trace, or other ways, depending on the construction of the system. There are many applications where this is not convenient. Systems that use interchangeable sensor modules are one example. Detecting touch on an object that simply can't be electrically connected to the system is another example. In other cases, the connections for capacitive sensors are difficult to route in a single layer, but multi-layer sensor assemblies that include connections between layers are much more expensive to produce than assemblies that use multiple, unconnected layers.
What is needed is a way to connect capacitive sensors to electronics without a direct electrical connection.
Sensor extensions are a way of connecting capacitive sensors to a system using capacitive coupling rather than a conductive connection. Sensor extensions enable many unique applications. For example, a sensing system can be designed to support interchangeable sensor modules without exposed metal contacts. In another application, multi-layer sensor assemblies can be implemented without requiring connections between layers (“vias”), simplifying routing and allowing the area of touch sensors to be expanded. In yet another application, product packaging can include sensors that are extensions of the product's sensors. In-store display solutions can use the technique to make products on display touch-sensitive.
The present invention will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which:
The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the detailed description, serve to explain the principles and implementations of the invention.
Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference materials and characters are used to designate identical, corresponding, or similar components in different figures. The figures associated with this disclosure typically are not drawn with dimensional accuracy to scale, i.e., such drawings have been drafted with a focus on clarity of viewing and understanding rather than dimensional accuracy.
In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application and business related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.
Use of directional terms such as “upper,” “lower,” “above,” “below”, “in front of,” “behind,” etc. are intended to describe the positions and/or orientations of various components of the invention relative to one another as shown in the various Figures and are not intended to impose limitations on any position and/or orientation of any embodiment of the invention relative to any reference point external to the reference.
Those skilled in the art will recognize that numerous modifications and changes may be made to the exemplary embodiment(s) without departing from the scope of the claimed invention. It will, of course, be understood that modifications of the invention, in its various aspects, will be apparent to those skilled in the art, some being apparent only after study, others being matters of routine mechanical, chemical and electronic design. No single feature, function or property of the exemplary embodiment(s) is essential. Other embodiments are possible, their specific designs depending upon the particular application. As such, the scope of the invention should not be limited by the particular embodiments herein described but should be defined only by the appended claims and equivalents thereof.
A sensor extension is a capacitive sensor that is connected to the system's measurement electronics module through one or more capacitive links.
The sensor extension 104 comprises a secondary extension pad 112, a sensor pad 114 and a secondary conductive trace 116 there between. A capacitive link is formed by the primary extension pad 108 of the primary sensor 102 in close proximity to the secondary extension pad 112 of the sensor extension 104.
An insulating layer 118 or layers separates the extension pads 108, 112 so that there is no conductive contact between sensor extension 104 and the measurement electronics module 106. In some embodiments, the insulating layer 118 is a dielectric film. In other embodiments, the insulating layer 118 is an air gap.
In some embodiments, the extension pads 108, 112 partially or completely overlap each other, but on different planes and separated by the insulating layer 118. In other embodiments the extension pads 108, 112 are coplanar as is the separating insulating layer 118.
The measurement electronics module 106 is configured for measuring capacitance on the primary conductive trace 110 or stated differently, for measuring capacitance between the primary conductive trace 110 and a system ground. This is done by one of several well-known methods, most of which involve charging the primary conductive trace 110 to voltage, then connecting to system ground and timing the rate of discharge.
Components conductively connected to the primary conductive trace 110, such as the primary extension pad 108, will change the capacitance on the primary conductive trace 110 as measured by the measurement electronics module 106. Stated differently, the measurement electronics module 106 is configured for measuring capacitance of the primary sensor 102. Components capacitively coupled to the primary sensor 102, such as the sensor extension 104, will change the capacitance on the primary conductive trace 110 measured by the measurement electronics module 106.
In some embodiments, the sensor extension 104 does not have a separate sensor pad 114 and secondary conductive trace 116, just the secondary extension pad 112. The secondary extension pad 112 functions both as the secondary extension pad 112 and as the sensor pad 114. Stated differently, in such embodiments, the secondary extension pad 112 is also the sensor pad 114.
The typical configuration for a capacitive sensor is a conductive pad or pads connected to a measurement system by a conductive trace or wire. The sensor pad(s) is usually covered by an electrical insulator and does not make direct contact with the objects or people it is designed to detect.
In sensor extension applications, the direct trace or wire connection is broken into 2 or more segments with capacitively coupled connections between the segments. In effect, the sensor is connected to the measurement system through one or more capacitors.
The capacitive links reduce the sensitivity of the sensors, but this can usually be overcome. How much the sensitivity will be affected can be determined by calculation. For a basic self-capacitance sensor, the system measures a sensor's capacitance to ground and detects an event as a change in this value. The sensor has a base level capacitance CB due to coupling between the sensor and system ground. A touch to the sensor or the presence of an object on the sensor increases this capacitance by the amount of a touch capacitance CT. The total capacitance of the sensor is then CB+CT, and the increase is the full value of CT.
The total capacitance of the extended sensor 101 (extended sensor total capacitance CTot) when the sensor extension is touched or when a conductive object is adjacent is
Analyzing these formulas leads to two important facts. First, the larger the value of sensor extension capacitance CX, the less impact it has on the sensitivity of the sensor (change in total sensor capacitance CTot when touch capacitance CT is changed). Second, the change in capacitance due to the addition of touch capacitance CT is dependent on sensor extension base capacitance CBX in the sensor extension case. The smaller sensor extension base capacitance CBX is, the smaller the sensitivity of the total sensor capacitance CTot. Maximizing sensor extension capacitance CX and minimizing sensor extension base capacitance CBX achieves the largest sensor sensitivity.
The sensor extension capacitance CX can be increased by making the extension pads 108, 112 larger, by reducing their separation, and by insulating the pads with a higher dielectric constant material. Sensor extension base capacitance CBX can be reduced by placing the sensor extension 104 away from any grounded metal such as a shield, by mounting the sensor extension 104 on a low-dielectric material such as foam, and by separating the sensor extension 104 from other sensor extensions as much as possible.
Extended sensors work well as touch sensors. The reduced sensitivity of extended sensors has less impact on touch detection than on object or proximity detection applications.
In systems where the extended portion of the extended sensor is on a removable module (see applications below for examples), the extension pad on the base unit can itself be used as a touch sensor as well when no module is present.
Because the sensor extension is isolated from the system electronics, it is also not necessary that the extension's touch pad be electrically insulated. Directly touching the exposed conductive material of the extension will result in higher sensitivity, possibly at the expense of the durability of the extension.
It is feasible to use a set of extended sensors to perform object detection just as normal sensors can be used, including the use of multi-sensor object identity systems. This capability can be used, for example, to allow a multi-level play set to include sensors in the upper levels of the set without requiring a conductive connection back to the system's electronics.
A set of extended sensors is used—one for the measurement signal and one for a ground. In contrast, a touch sensor only uses a single extended sensor for measurement, omitting the extended sensor for the ground. Since the human body has a significantly large capacitance, a touch sensor can rely on a general system ground for a return path.
The sensor extension pads can also be object detection sensors in their own right, so that an object can be placed directly on the extension pads for identity or on the extended identity pads when an additional piece of the system is present. For example, a playset with interchangeable buildings could allow a toy car to be detected either on the roof of a parking garage add-on building or on the base playset when no building is present.
The sensor extension concept can be used in a variety of quite different applications. Several examples are given below.
Sensor extensions allow systems that work with objects such as trading cards and figures to include sensors within the objects. In such a system, the base unit includes sensor extension pads that line up with pads in the objects. The pads in the objects are then connected to sensor pads. All sensors and extension pads are fully insulated from the user, and the objects do not require any electronics.
When an object is placed on or in the base, the object's sensors become active and can be used by the base. The sensor extensions in the object are low-cost allowing the objects to each have a unique sensor configuration.
One application of the sensor extension system 100 is an interactive trading card game.
There are several options for implementing the capacitive sensing system. The easiest to implement would be a set of buttons 138 around the periphery of the electronic card holder 132, outside of the card holder frame 136. Each card would include labels 140 for the buttons 138. The buttons 138 may be capacitive touch sensors or they may be mechanical switch buttons. Such a solution would work well, but it would increase the size of the holder and limit the design options for the cards.
What is needed is a simple, low-cost system that allows customized touch locations on each card. It is possible to build the touch sensors into the cards. Using low-cost conductive carbon ink or hot-stamped foil, the touch locations and their connecting traces can be embedded into the cards. Unfortunately, the cards and the holder would ordinarily need to include exposed contacts to make the connection between the sensors in the card and the holder's electronics, as illustrated in
Replacing the electrical contacts 180, 182 with sensor extensions allows the card 174 and electronic card holder 172 to be connected capacitively instead, as illustrated in
The sensor extension concept can be used to build multi-layer sensor assemblies that don't require conductive connections between the layers. This allows, for example, large touch areas to be placed on a separate layer from that used for routing and capacitively coupled to extension pads on the routing layer. The touch areas may be constructed on the opposite side of the substrate that includes the routing layer, or the touch areas may be on a separate assembly, such as incorporated into a printed label on top of the sensor assembly.
This technique can make routing easier by reducing the size of sensor pads that signals must be routed around. Sensor extension coupling is dependent on area, so if narrow connecting traces are used, it is possible to route the connecting traces for other sensors under a sensor's extended touch area.
In
In the embodiment of
Another application is a sensor matrix. A sensor matrix has row touch sensors and column touch sensors arranged in a grid. A user triggers one or more row sensors and one or more column sensors when touching the matrix, allowing the x-y touch position to be determined. A sensor matrix can be constructed with multiple layers because the row and column sensors cross. Sensor extensions allow this routing to be accomplished with no conductive connections between the layers.
Sensor extension pads can be placed directly on a PCB. This allows the capacitive sensing electronics to be connected to a sensor assembly using low-cost methods such as pressure-sensitive adhesive. This can save space, especially height, in space-sensitive applications.
Sensor extensions that couple to sensors in a product can be incorporated into the product's packaging. This enables in-store try-me and other features without requiring either additional electronics in the packaging or elaborate packaging that allows access to the product.
Sensor extensions can be used to produce an in-store product display that uses the product itself as a sensor extension. For example, a display could include an array of sensor extension pads designed for plastic bottles of cleaning product to sit on. The plastic bottle acts as the insulating layer. The conductive cleaner itself forms the extension pad and touch pad and is covered by the plastic bottle.
The display would include electronics that react when a shopper touches one of the bottles. This could include flashing lights, playing sounds, or dispensing a coupon, among other actions. In effect, the entire portion of the container that is in contact with the product becomes a touch sensor.
The present application claims priority to co-pending U.S. Provisional Application No. 61/799,162 filed on 15 Mar. 2013, incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61799162 | Mar 2013 | US |
