Abstract:
A capacitive sensor comprises patterned electrodes and printed wires of conductive material integrated with sensing circuits on flexible circuit substrates. The flexible circuit substrates are fingered or otherwise elongated to distribute sensing points to the limbs in a toy doll or animal, or squares on a board game. Such sensing points can detect the presence of a finger even though actual contact is not made by measuring the proportions and changes in stray capacitance attaching to the various electrodes. Touch sensors are therefore possible even when the capacitor sensor&#39;s sensing points are covered by a doll&#39;s plastic skin or a plush animal&#39;s fur. Including an interlayer of open cell foam under the flexible circuit substrate further implements a pressure sensor because applied pressures will deform the geometries of the capacitor electrodes and dielectrics enough to produce a measurable change in capacitance.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to electronic sensors, and in particular to pressure and touch sensors implemented directly on flexible substrates and based on measurements of capacitance variances. 
         [0003]    2. Description of the Prior Art 
         [0004]    Toys can be far more interesting to play with if they are able to interact with children and adults. One key to enabling interaction is to equip a toy with sensors that can detect when and how the toy is being touched. A touch on the toys hand, if a doll, can be interpreted differently than pressure applied to the foot. A touch on the head of a toy dog could be sensed and interpreted as a pat, and an appropriate response of the toy dog would be to wag its tail. 
         [0005]    Such pressure sensors need not be the precision instruments nor highly calibrated as commonly used in process control and scientific instrumentation. Very often, a touch having a pressure sense of a few ounces or more is enough to trigger and on-off output for a toy sensor. Temperature may also be interesting, as in having a toy comment verbally if the room environment is above, at, or below room temperature. 
         [0006]    Mass produced products like toys are highly sensitive to component costs. So a practical touch sensor for a toy would need to be very inexpensive to manufacture. 
       SUMMARY OF THE INVENTION 
       [0007]    Briefly, a capacitive sensor embodiment of the present invention comprises patterned electrodes and printed wires of conductive material integrated with sensing circuits on flexible circuit substrates. The flexible circuit substrates are fingered or otherwise elongated to distribute sensing points to the limbs in a toy doll or animal, or squares on a board game. Such sensing points can detect the presence of a finger even though actual contact is not made by measuring the proportions and changes in stray capacitance attaching to the various electrodes. Touch sensors are therefore possible even when the capacitor sensor&#39;s sensing points are covered by a doll&#39;s plastic skin or a plush animal&#39;s fur. Including an interlayer of open cell foam under the flexible circuit substrate further implements a pressure sensor because applied pressures will deform the geometries of the capacitor electrodes and dielectrics enough to produce a measurable change in capacitance. 
         [0008]    These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments that are illustrated in the various drawing figures. 
     
    
     
       IN THE DRAWINGS 
         [0009]      FIG. 1  is a functional block diagram and schematic of a toy automation device embodiment of the present invention; 
           [0010]      FIGS. 2A and 2B  are a perspective diagram and a schematic diagram of a capacitive proximity sensor embodiment of the present invention showing how the relative position of a finger presents different stray capacitances; 
           [0011]      FIG. 3  is a perspective and schematic diagram of a board game embodiment of the present invention showing how the relative position of a game piece on the board can present different stray capacitances; 
           [0012]      FIGS. 4A and 4B  are cross sectional views of a capacitive pressure sensor embodiment of the present invention which has a soft flexible dielectric substrate with top and bottom conductor layers, and  FIG. 4A  shows the capacitive pressure sensor before pressure is applied from above, and  FIG. 4B  represents how the top and bottom conductor layers are pressed closer together when pressure is being applied; 
           [0013]      FIGS. 5A and 5B  are cross sectional views of a capacitive pressure sensor array embodiment of the present invention which has a soft flexible dielectric middle layer, with top and bottom conductor layers on single-sided flexible circuit substrates, and  FIG. 5A  shows the capacitive pressure sensor array before any pressure is applied, and  FIG. 5B  represents how the capacitive pressure sensors nearer the center are pressed closer together more than at the edges when a point pressure is applied at the center from above; 
           [0014]      FIG. 6  is a perspective view diagram of an L-C pressure sensor embodiment of the present invention built with both inductors and capacitors on a foam substrate that will compress and flex under pressure; 
           [0015]      FIGS. 7A and 7B  are schematics of how a circuit on the sensor of  FIG. 6  could be wired to operate, and how a pressure being applied would deform the tuned L-C components enough to cause a change in resonant frequency; 
           [0016]      FIG. 8  is a plan view diagram of a flex circuit that was used in a prototype of toy doll embodiment of the present invention; and 
           [0017]      FIG. 9  is a perspective exploded assembly view diagram of a flex circuit and sensor electronics assembly mounted in a back torso of a toy doll, in an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]      FIG. 1  represents a toy automation device embodiment of the present invention, and is referred to herein by the general reference numeral  100 . Device  100  has a flexible circuit substrate  102  patterned to fit within a toy, in this case a hand  104  of the toy. A plastic skin covering  106  covers the toy&#39;s hand  104  and completely encloses device  100  within. In animal toys, skin  106  would consist of simulated animal fur or fish scales that are non-conductive to electricity. 
         [0019]    Device  100  further includes capacitive proximity sensors  110 - 114  in the thumb, index, middle, ring, and little fingers, and another capacitive proximity sensor  116  in the palm. These are all mounted directly on, or fashioned from, printed, patterned circuits on the flexible circuit substrate  102 . The capacitive proximity sensors are all connected by printed wires to a sensor controller  118 , also disposed directly on the flexible circuit substrate  102 . A connection  120  provides for communication and control signals, e.g., to other devices in the toy. 
         [0020]    Two conductors separated by a dielectric material can be used to form a capacitor. The capacitance of that capacitor is a function of the dielectric constant of the dielectric layer, the areas of the conductors separated, and the separation distance. If any of these change, the capacitance changes accordingly. A mechanical arrangement in which pressure compresses the separation distance of the dielectric layer will cause an increase in capacitance proportional to the pressure. 
         [0021]    In  FIG. 1 , capacitive proximity sensor  111  is shown that is sensitive to the near proximity and contact of a finger  130 . As finger  130  approaches capacitive proximity sensor  111 , a capacitive coupling develops, and controller  118  converts the change in capacitance to a digital value. In the simplest case, such value would be a one-bit binary, for touch/no-touch. In a more complex embodiment, the value could be a multi-bit binary and a measure of the distance to finger  130 . Skin covering  106  is intervening, and so will prevent actual contact. 
         [0022]    A flex substrate capacitor can be used that comprises a top, patterned layer, a flexible substrate, and a bottom plate. A capacitance is formed when the dielectric layer of flexible substrate separates the two conductor plates of patterned layer and bottom plate. If the area of the conductors, the thickness of the dielectric material separating the conductor, or the distance between the two conductors changes, the effective capacitance changes. The effective capacitance also increases significantly if stray capacitances, like a finger of a child or an adult couple-in, in parallel, or another conductor with an effectively large area contacts the top, patterned layer. 
         [0023]    The material of flexible substrate  102  can be polyimide, polyester, a flame retardant fiberglass and resin type-FR4, or other industry standard flexible printed circuit board (PCB) substrate material. 
         [0024]    A toy with device  100  can receive user input by touch and react according to the way it is touched, where on the toy it is touched, and when in a sequence of events it is touched. The toy can be programmed to respond in ways that depend on the nature of the touch sensed. The response can consist of a physical movement of the toy, speech or sound from the toy, light output from the toy from various LED&#39;s located on the toy, or a combination of responses. 
         [0025]    The flexible substrate, sensors and other electronics like that shown in  FIG. 1  require very little space. It can therefore be easily embedded into different parts of even preexisting toys. Choosing the patterns and materials used for the conductive materials on the flexible substrate allows for a great range of structures and topographies, each with a corresponding set of sensitivities and characteristics. 
         [0026]    In general, it is preferable to keep wiring runs between capacitor pads and their sensing circuits as short as possible. This helps avoid the problems associated with trying to detect small changes of capacitance in the relatively large capacitance created by the wiring runs, and problems with other stray capacitances. 
         [0027]      FIGS. 2A and 2B  represent a capacitive proximity sensor  200  that would be useful in device  100  to detect the presence and relative position and movement of a finger  201 . A bottom plate  202  and three top patterned electrodes  204 ,  206 , and  208 , are etched from copper on a flexible dielectric substrate  210  (not shown in  FIG. 2A ). A conventional way to do this would be to start with industry standard double-sided flexible printed circuits of polyimide or Mylar. 
         [0028]    A sensor controller  220  (not shown in  FIG. 2A ) measures the capacitances (C 1 , C 2 , C 3 ) of the three top patterned electrodes  204 ,  206 , and  208 , and any stray capacitances, with respect to bottom plate  202 . As finger  201  approaches, stray capacitances C s1 , C s2 , C s3 , grow in significance and will vary amongst themselves dependant on which is the closest and which is the farthest from the finger or other approaching object  201 . There is informational value in determining the position and velocity of finger  201  beyond just knowing it is present. So, sensor controller  220  makes relative measurements of C s1 , C s2 , C s3 , over time, to estimate the presence, position, and velocity of finger  201 . An output  222  connects to other sensors, controllers, and actuators that enable a toy to produce an appropriate response to the presence, position, and velocity of finger  201 . Such responses include speech, listening, limb movement, eye opening, sneezing, memorizing, etc. 
         [0029]    A board game  300  represented in  FIG. 3  is similar in its instrumentation to capacitive proximity sensor  200 . Here, a metallic game piece  301  is moved by the players along the surface of a board made of cardboard or plastic. Embedded within the game board are several electrodes  302 - 305  of copper etched or otherwise patterned on the topside of a flexible circuit substrate. A bottom electrode, or ground plane  310  is similarly fabricated on the bottom side of the flexible circuit substrate. A sensor controller, such as  220  in  FIG. 2B , could be used to determine the movement, position, and identity of game piece  301  on the game board. Such would be useful for board games like MONOPOLY, CHUTES and LADDERS, 1862 CIVIL WAR, and puzzles, etc. A computer in wireless communication with the board game  300  could track player wins, losses, advances, and points scores. Game play could also be distributed in real-time around the world amongst several players. 
         [0030]      FIGS. 4A and 4B  represent a capacitive pressure sensor  400  based on a soft interlayer material and flexible substrate for use in toys, dolls, plush animals, puzzles, board games, etc. Capacitive pressure sensor  400  is constructed by separating two surface layers  402  and  404  of sheet copper or other conducting material with a flex substrate  406  of a porous dielectric material. For example, flexible open-cell foam and sponge material could be used. By pressing or squeezing the flex substrate, the distance between the conductive layers on the opposite surfaces decreases. Thus significantly increasing the capacitance of the capacitor formed. The increase can be proportional to the pressure applied up to the compression limit of the materials. A change in the distance between the two conducting layers causes a measureable change in the capacitance, and thus can be roughly interpreted as pressure with an accuracy sufficient for the needs of a toy or game play. 
         [0031]    In another embodiment illustrated in  FIGS. 5A and 5B , a capacitive pressure sensor array  500  comprises an open-cell foam dielectric layer  502  sandwiched between a top single-sided flex circuit  504  and a bottom single-sided flex circuit  506 . The top single-sided flex circuit  504  can comprise several electrodes  511 - 516  that each form respective capacitors  521 - 526 . The bottom single-sided flex circuit  506  is a conductive layer ground-plane  530  for all the capacitors, and can be more rigid and not as flexible as the top layers.  FIG. 5B  demonstrates what happens when a point of pressure is applied from above near the center of the surface field of electrodes  511 - 516 . Capacitors  523  and  524  will increase in capacitance relative to capacitors  521  and  526  near the edges. The increase will be proportional to the applied pressure. 
         [0032]    In an alternative embodiment that would reduce sensitivities to the proximity of a finger to a pressure sensor, as in  FIGS. 2A and 2B , electrodes  511 - 516  could be buried inside the dielectric  502  between ground-planes  530  on opposite sides. That way, only pressure would have an effect on the capacitances of capacitors  521 - 526 . 
         [0033]    Determining the magnitude of bending and the location of the pressure points is possible with a device that measures the capacitances of each capacitor  521 - 526 , e.g., sensor controller  220  in  FIG. 2 . Devices that can measure capacitances in the picoFarad, nanoFarad and microFarad ranges are conventional, and therefore need not be disclosed in detail here. The copper pattern of each of the several electrodes  511 - 516  can be tailored to match the application and particular conditions of use. 
         [0034]    A flexible pressure sensor can be covered with cloth, fabrics, furs, plastic sheet, or other soft materials that can be either used in a toy at the surfaces or inside. When a flexible pressure sensor is embedded at a particular location in a toy, a change in pressure can be detected and interpreted according to its position from a measured change in capacitance. A pressure sensor with a flexible substrate can be embedded and extended into various parts of a toy with fingered elongations, as hinted at in  FIG. 1 . The pressure sensor output can be used as a trigger in a control system in another part of the toy or a nearby console. 
         [0035]    Thick interlayers can reduce the sensitivity of a capacitor-only pressure sensor. In such cases, inductors can be included in the patterned top layer of the flexible circuit substrates to use inductance and capacitor changes in combination to sense pressures. 
         [0036]      FIG. 6  shows a combination inductor-capacitor (L-C) pressure sensor embodiment of the present invention, and is referred to herein by the general reference numeral  600 . Although L-C pressure sensor  600  is shown on a flat rectangular piece of foam substrate  602 , when used in a toy it will probably be advantageous to shape the device with elongations that suit the particular spaces available and points needing instrumenting. 
         [0037]    The foam substrate  602  has a conductive backing  604  and a top sheet  606  on which are disposed capacitor electrodes  610 ,  612 ,  614 , and  616 , and inductors  620 ,  622 , and  624 . An integrated circuit (IC)  630  is collocated with the capacitors and inductors formed to keep wiring runs short and manufacturing costs low. 
         [0038]      FIGS. 7A and 7B  suggest a partial circuit  700  that could be used for the L-C pressure sensor  600  of  FIG. 6 . One inductor  702  and one capacitor  704  are connected in a parallel L-C tank circuit that will resonate at a tune frequency of f 1  with the assistance of an oscillator-amplifier (OSC)  706 . IC  630  of  FIG. 6  could include several OSC  706  devices. 
         [0039]    If the foam substrate  602  on which the inductors and capacitors are carried is subjected to a pressure from above,  FIG. 7B  represents that inductor  702  and capacitor  704  will be physically deformed or squashed. Such deformation will change the inductance and capacitance, and thus the resonant L-C will shift to f 2 . The change in frequency output will be proportional to the pressure applied, and that can be used to trigger a response from a toy or game. 
         [0040]      FIG. 8  represents a flex circuit  800  that was used in a prototype of toy doll embodiment of the present invention. Flex circuit  800  included right and left arm capacitive sensor circuits  804  and  805 . These were elongations from circuit panel  806  which also provided for a power on/off switch (not shown). Right and left leg capacitive sensor circuits  808  and  809  were constructed as elongations of a main circuit panel  810 . This attached to an audio circuit panel  812  having connections for a speaker and microphone. A panel  814  provided for mounting support and attachment inside the toy doll. A stiffer was included on the back, and a protective encapsulating coating was applied over the whole. 
         [0041]      FIG. 9  shows how a flex circuit and sensor electronics assembly  900  can be mounted in the back torso  902  of a toy doll. A capacitive sensor and supporting touch sensor integrated circuit devices for the arms and legs are provided on elongation pads  904 - 907 . These, in turn are fitted near arm and leg sockets  908 - 911 . A battery box  912  provides operating power to flex circuit and sensor electronics assembly  900 . An on/off switch (not shown) in switch pocket  914  connects to power switch pads  916 . A microphone and speaker (not shown) can be connected to pads provided on a circuit panel  918 . A main circuit panel  920  fits to the back of battery box  912 , and provides for accelerometers, temperature sensors, touch sensor integrated circuit devices, and a microcontroller unit (MCU). 
         [0042]    Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that the disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the “true” spirit and scope of the invention.