US20080018611A1

US20080018611A1 - Input Device

Info

Publication number: US20080018611A1
Application number: US11/679,535
Authority: US
Inventors: Bogdan Serban; Philippe Boyer; Aloyse Schoos
Original assignee: IEE International Electronics and Engineering SA
Current assignee: IEE International Electronics and Engineering SA
Priority date: 2006-07-18
Filing date: 2007-02-27
Publication date: 2008-01-24
Also published as: EP2041641B1; WO2008009687A2; EP2041641B8; US8063886B2; WO2008009687A3; US20080018608A1; EP2041641A2

Abstract

An input device comprises a capacitive proximity and pressure sensor, which includes a first carrier layer, a second carrier layer and a spacer arranged between the first and second carrier layers, the first carrier layer having a first capacitor electrode applied thereon, the second carrier layer having a second capacitor electrode applied thereon, the first and second capacitor electrodes being arranged opposite one another with respect to the spacer in such a way that, in response to a compressive force acting on the pressure sensor, the first and second capacitor electrodes are brought closer together. The input device further comprises a control circuit configured so as to operate in at least two modes of operation, including a first and a second mode of operation. The control circuit determines, while in the first mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and ground and, while in the second mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and the second capacitor electrode.

Description

TECHNICAL FIELD

This invention relates to input devices and more particularly to data input devices including a film-based pressure sensor for human-appliance interaction.

BACKGROUND ART

Input devices are commonly used in conjunction with electronic appliances to feed the latter with various kinds of inputs, including e.g. control data influencing directly or indirectly the behavior of the appliance, input that is processed by the appliance and/or input that is simply stored.
It is known to construct input devices based upon film-type pressure sensors, whose resistance varies with pressure. Such film-type pressure sensor comprises two carrier films, which are arranged at a certain distance from one another by means of a spacer. The spacer is provided with at least one opening that defines an active zone of the sensor, in which the two carrier films face one another. Inside this active zone, at least two electrodes are arranged on the carrier films, in such a way that electrical contact is established between the electrodes when the two carrier films are pressed together under the action of a compressive force acting on the sensor in the active zone. The pressure acting on the sensor is detected and/or determined as a function of the resistance between the electrodes.
Depending on the application of such a pressure sensor, a layer of semiconducting material may be disposed between the electrodes, so that the sensor shows a gradual pressure sensitive behavior, that is to say its resistance varies gradually or even continuously as a function of the force applied. The layer of semiconducting material may comprise a material whose internal electrical resistance varies as a function of compression or of deformation of the layer or a material whose surface structure confers to the layer a surface resistance that is reduced following an increase in the number of points of contact with a conducting surface of an electrode, against which the layer of semiconducting material is pressed under the action of the compressive force.
WO 2004/049364 relates to a data input device comprising several keys arranged in at least two rows. A unidirectional position detector of film-type construction is associated with each row of keys. Each unidirectional position sensor enables the detection of the actuated key along the direction of the unidirectional position detector. The unidirectional position sensors are interconnected in such a way that a control circuit can detect in which row a key has been actuated.
A different kind of sensors is based upon capacitive sensing. U.S. Pat. No. 3,896,425 discloses an electrical proximity detector that senses the changes in the contents of a defined sensitive volume. The detector comprises an antenna that is driven by an oscillator and that emits an electric field into the sensitive volume. A person or an object intruding into the sensitive volume causes a change of the electric field of the antenna, which is detected by the detector. To shape the electric field of the antenna the detector comprises a first shield, driven by the oscillator with a signal of same amplitude and phase as the signal of the antenna, and a second, grounded shield.
Other sensors based on electric field or “capacitive” sensing have been proposed by J. Smith et al. in “Electric Field Sensing for Graphical Interfaces”, IEEE Computer Graphics and Applications, Issue May/June 1998, 54-60, as a human-computer interface. The interfaces are based upon an array of electrodes to detect the gestures of a user.
The above-mentioned documents are herewith included herein by reference.

SUMMARY OF THE INVENTION

The invention provides an improved input device.
According to a first aspect of the invention, an input device comprises a capacitive proximity and pressure sensor, which includes a first carrier layer, a second carrier layer and a spacer arranged between the first and second carrier layers, the first carrier layer having a first capacitor electrode applied thereon, the second carrier layer having a second capacitor electrode applied thereon, the first and second capacitor electrodes being arranged opposite one another with respect to the spacer in such a way that, in response to a compressive force acting on the pressure sensor, the first and second capacitor electrodes are brought closer together. The input device further comprises a control circuit configured so as to operate in at least two modes of operation, including a first and a second mode of operation. The control circuit determines, while in the first mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and ground and, while in the second mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and the second capacitor electrode. Those skilled will appreciate that the capacitance between the first capacitor electrode and ground is itself indicative of the proximity of a part of a user's body (e.g. their finger) to the first capacitor electrode. The first mode of operation therefore is considered as a “proximity-sensing” mode. On the other hand, the capacitance between the first and the second capacitor electrode is indicative of the distance between these electrodes. Since a given distance corresponds to a certain amount of pressure or magnitude of force, the second mode of operation is considered as a “pressure-sensing” (or “force-sensing”) mode.
According to a second aspect of the invention, the input device comprises a capacitive proximity and pressure sensor, which includes a first carrier layer, a second carrier layer and a spacer arranged between the first and second carrier layers. The first carrier layer has a plurality of first capacitor electrodes applied thereon and the second carrier layer has a plurality of second capacitor electrodes applied thereon, each one of the plurality of first capacitor electrodes being arranged opposite a respective one of the plurality of second capacitor electrodes with respect to the spacer in such a way that, in response to a compressive force acting on the pressure sensor, respectively opposite ones of the first and second capacitor electrodes are brought closer together. The input device according to the second aspect further comprises a control circuit configured so as to operate in at least two modes of operation, including a first and a second mode of operation. The control circuit determines, while in the first (proximity-sensing) mode of operation, a quantity indicative of a capacitance between individual ones (single ones or groups) of the plurality of first capacitor electrodes and ground and, while in the second (pressure-sensing) mode of operation, a quantity indicative of a capacitance between individual ones of the plurality of first capacitor electrodes and the respectively opposite ones of the plurality of second capacitor electrodes.
According to a third aspect of the invention, the input device comprises a capacitive proximity and pressure sensor, which includes a first carrier layer, a second carrier layer and a spacer arranged between the first and second carrier layers. The first carrier layer has a plurality of first elongated capacitor electrodes applied thereon and the second carrier layer has a plurality of second elongated capacitor electrodes applied thereon, the plurality of first capacitor electrodes being arranged opposite the plurality of second capacitor electrodes with respect to the spacer. According to the present aspect, the first elongated capacitor electrodes extend transversally to the second elongated capacitor electrodes in such a way that, in response to a compressive force acting locally on the pressure sensor, opposite ones of the first and second capacitor electrodes are brought closer together at the location where the compressive force acts on the pressure sensor. The input device also comprises a control circuit, which determines, while in a first mode of operation, a quantity indicative of capacitance between individual ones of the plurality of first capacitor electrodes and ground and, while in a second mode of operation, a quantity indicative of a capacitance between individual ones of the plurality of first capacitor electrodes and individual ones of the plurality of second capacitor electrodes.
According to a fourth aspect of the invention, the input device comprises a capacitive proximity and pressure sensor, which includes a first carrier layer, a second carrier layer and a spacer arranged between the first and second carrier layers for keeping the first and second carrier layers apart from one another. The first carrier layer has a plurality of first capacitor electrodes applied thereon, the second carrier layer has a second capacitor electrode applied thereon, the plurality of first capacitor electrodes being arranged opposite the second capacitor electrode with respect to the spacer in such a way that, in response to a compressive force acting locally on the pressure sensor, individual ones of the first capacitor electrodes are brought closer to the second capacitor electrode at the location where the compressive force acts on the pressure sensor. The input device according to the fourth aspect comprises a control circuit, which determines, while in a first mode of operation, a quantity indicative of capacitance between individual ones of the first capacitor electrodes and ground and, while in a second mode of operation, a quantity indicative of a capacitance between the second capacitor electrode and individual ones of the first capacitor electrodes.
For the purposes of the present, the terms “first mode of operation” and “second mode of operation” are primarily used for distinguishing the modes of operation; these terms therefore should not be understood as indicating an order of the modes of operation in time. The control circuit may operate in the first mode of operation before and/or after operating in the second mode of operation. The control circuit may cyclically switch between the modes of operation, e.g. several times per second. Preferably, however, the control circuit remains in the proximity-sensing mode (first mode) until the proximity of a body having an electric-field-changing property is detected. Alternatively, the control circuit could remain in the pressure-sensing mode (second mode) until a force or pressure exceeding a predefined threshold has been detected.
For the purposes of the present, a “quantity indicative of a capacitance” can be any physical quantity that is linked to the capacitance by the laws of physics, such as, for instance, amplitude and/or phase of a current, amplitude and/or phase of a voltage, charge, impedance, etc.
According to a preferred embodiment of the input devices as recited hereinabove, the spacer is electrically insulating and compressible. According to this embodiment, opposite ones of the first and second capacitor electrodes are brought closer together when the spacer is compressed in response to a compressive force acting on the pressure sensor.
According to another preferred embodiment of the input device as recited hereinabove, the spacer has one or more openings therein, with respect to which the first capacitor electrode or electrodes are arranged opposite the second capacitor electrode or electrodes. The first capacitive electrode(s) and/or the second capacitor electrode(s) have an insulating layer or insulating pattern arranged thereon in such a way as to prevent a short circuit between the first capacitive electrode(s) and the second capacitor electrode(s). The insulating layer or pattern could be separate from the spacer or part of it (in the latter case the opening would rather be considered as a recess than as a through-hole). The spacer may be compressible or incompressible. In the latter case, the first and second capacitor electrodes are brought closer together when one or both of the carrier layers bend into the opening(s) of the spacer under the action of the compressive force.
If the spacer has a plurality of openings therein, if the first carrier layer has a plurality of first capacitor electrodes applied thereon and if the second carrier layer has a plurality of second capacitor electrodes applied thereon, each one of the plurality of first capacitor electrodes is preferably arranged opposite a respective one of the plurality of second capacitor electrodes with respect to a respective one of the plurality of openings. In this case, when a compressive force acts on the pressure sensor, respectively opposite ones of the first and second capacitor electrodes are brought closer together.
Those skilled will appreciate that various options exist for determining a quantity indicative of capacitance between the first capacitor electrode(s) and ground. For instance, the control circuit could determine, while in the first mode of operation,

(a) an amount of electric charge accumulated on (individual ones of) the first capacitor electrode(s) in response to applying a defined voltage to this (these) first capacitor electrode(s); or
(b) an amplitude and/or a phase of a loading current flowing in (individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to this (these) first capacitor electrode(s); or
(c) an in-phase component and/or a 90°-phase-offset component of a loading current flowing in (individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to this (these) first capacitor electrode(s); or
(d) a charge time and/or a discharge time of (individual ones of) the first capacitor electrode(s).

Similarly, various options exist for determining a quantity indicative of capacitance between (individual ones of) the first capacitor electrode(s) and (individual ones of) the second capacitor electrode(s). For instance, the control circuit could determine, while in the second mode of operation,

(a) an amount of electric charge accumulated on (individual ones of) the first capacitor electrode(s) and/or (on individual ones of) the second capacitor electrode(s) in response to an applying a defined voltage to the respectively opposite capacitor electrode(s);
(b) an amount of electric charge accumulated on (individual ones of) the first capacitor electrode(s) and/or (on individual ones of) the second capacitor electrode(s) in response to an applying a defined voltage to this (these) capacitor electrode(s);
(c) an amplitude and/or a phase of a loading current flowing (in individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to this (these) first capacitor electrode(s);
(d) an amplitude and/or a phase of a loading current flowing (in individual ones of) the second capacitor electrode(s) in response to applying an oscillating voltage to this (these) second capacitor electrode(s);
(e) an amplitude and/or a phase of a loading current flowing (in individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to the respectively opposite one(s) (of the) second capacitor electrode(s);
(f) an amplitude and/or a phase of a loading current flowing (in individual ones of) the second capacitor electrode(s) in response to applying an oscillating voltage to the respectively opposite one(s) (of the) first capacitor electrode(s);
(g) an in-phase component and/or a 90°-phase-offset component of a loading current flowing (in individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to this (these) first capacitor electrode(s);
(h) an in-phase component and/or a 90°-phase-offset component of a loading current flowing (in individual ones of) the second capacitor electrode(s) in response to applying an oscillating voltage to this (these) second capacitor electrode(s);
(i) an in-phase component and/or a 90°-phase-offset component of a coupling current flowing (in individual ones of) the first capacitor electrode(s) in response to applying an oscillating voltage to the respectively opposite one(s) (of the) second capacitor electrode(s);
(j) an in-phase component and/or a 90°-phase-offset component of a coupling current flowing (in individual ones of) the second capacitor electrode(s) in response to applying an oscillating voltage to the respectively opposite one(s) (of the) first capacitor electrode(s);
(k) a charge and/or a discharge time of the first and/or the second capacitor electrode.

While in the first mode of operation, the control circuit preferably applies a first voltage to the first electrode(s) and a second voltage to the second electrode(s), the first and second voltages having same amplitude and phase. As will be appreciated, this substantially cancels the electric field between the first and second capacitor electrodes so that the first capacitor electrode(s) becomes (become) substantially insensitive in direction of the second capacitor electrode(s).
According to a preferred embodiment of the input device, the first carrier layer, the spacer and the second carrier layer are laminated together.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the present invention will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawings, wherein:

FIG. 1 is a schematic cross sectional view of capacitive pressure and proximity sensor according to a first embodiment;

FIG. 2 is a schematic cross sectional view of an input device according to a second embodiment;

FIG. 3 is an illustration of different examples of electrically insulating patterns;

FIGS. 4 a and 4 b are cross sectional views of a touchpad having keypad functionality;

FIGS. 5 a and 5 b are cross sectional views of an alternative touchpad having keypad functionality;

FIGS. 6 a and 6 b are cross sectional views of yet another example of a touchpad having keypad functionality;

FIGS. 7 a-7 c are illustrations of a touchpad with keypad functionality, in which the keys are arranged along a straight line;

FIGS. 8 a-8 e are illustrations of an input device implemented as a linear slider;

FIGS. 9 a-9 d are illustrations of an input device implemented as a circular slider;

FIGS. 10 a-10 d are illustrations of variants of an alternative embodiment of a touchpad;

FIGS. 11 a-11 b are cross-sectional schematic views of yet another example of an input device.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a data input device 10, comprising a capacitive proximity and pressure sensor 12 of film-type construction. The capacitive proximity and pressure sensor 12 comprises first and second carrier layers in the form of the first and second carrier films 16, 18, made of substantially flexible, electrically insulating material, such as e.g. PET, PEN, PI or the like. A spacer 20 is sandwiched between the first and second carrier films 16, 18 so as to keep them apart from one another. The spacer 20 is also be made of a substantially flexible, electrically insulating material, e.g. a double-sided adhesive. The spacer 20 is provided with an opening 14 therein, which delimits an active zone of the pressure sensor 10. In the active zone 14, the first carrier foil 16 carries a first capacitor electrode 22 on the side directed towards the second carrier film 18, while the second carrier foil 18 carries a second capacitor electrode 24 on the side directed towards the first carrier film 16. The first and second capacitor electrodes 22, 24 are formed from conductive material (e.g. silver ink) applied directly on the first and second carrier films 16, 18, respectively. The second capacitor electrode has formed thereon a layer 26 of electrically insulating material (dielectric, e.g. PET, PEN, PI, etc.).
The right-hand side of FIG. 1 shows a control circuit 28 connected to the first and second capacitor electrodes 22, 24 by leads 30, 32. The control circuit 28 comprises a microprocessor, an application-specific integrated circuit (ASIC) or a programmable chip, configured so as to operate in at least a first and a second mode of operation. The control circuit determines, while in the first mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and ground and, while in the second mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and the second capacitor electrode.
The first mode of operation is associated to sensing the proximity of an object to be sensed, e.g. of a user's finger 34. In the first mode of operation the control circuit keeps the first and second electrodes essentially at the same electric potential so that the electric field substantially cancels between the first and second electrodes. The second electrode 24 thus acts as a driven shield for the first electrode 22 and the sensitivity of the latter is directed away from the second electrode 24. If an oscillating voltage is applied to the first capacitor electrode an oscillating electric field to ground is built up. The object to be sensed modifies the capacitance between the first capacitor electrode and ground, which is sensed by the control circuit 28. It should be noted that in the first mode of operation detecting the proximity of the object to be does not require the object touching or being in contact with the proximity and pressure sensor 12.
The second mode of operation is associated with sensing pressure exerted on the sensor by some kind of actuator, such as e.g. the user's finger or stylus. In the second mode of operation, the control circuit essentially determines the capacitance of the capacitor formed by the first and the second capacitor electrodes 22, 24. It is well known that the capacitance of a capacitor depends upon the distance between its electrodes. In the illustrated case, the distance between the first and second capacitor electrodes decreases with increasing pressure exerted upon the pressure sensor by the user. As a consequence, the capacitance between the capacitor electrodes increases, which is detected by the control circuit 28.
FIG. 2 shows a variant of the proximity and pressure sensor of FIG. 1. The construction is the same, except that the first capacitor electrode 22, like the second capacitor electrode 24, has formed thereon a layer 26 of electrically insulating material. Those skilled will appreciate that patterning one of the electrically insulating layers 26 allows tailoring the response of the proximity and pressure sensor in the second mode of operation. As long as the electrically insulating layers are spaced from one another (i.e. for low pressures exerted by the user) the pattern has no significant influence on sensor response. However, as the pressure increases the electrically insulating layers come into contact and a contact surface forms. A patterned insulating layer results in that the minimum distance between the first and second electrodes is varying on the contact surface. Accordingly, the capacitance increase is different from the case where the insulating layers are uniform. Examples of patterned insulating layers are shown in FIG. 3.
In FIGS. 4 a-4 b, elements similar to elements of FIG. 1 have been attributed the same reference numeral as the corresponding element of FIGS. 1 and 2, preceded by a prefix according to the number of the drawing.
FIGS. 4 a and 4 b show a cross section of a touchpad 412 having keypad functionality. The touchpad 412 comprises a laminated structure of a first carrier film 416, a second carrier film 418 and a spacer 420, sandwiched between the first and second carrier films so as to keep them spaced apart. The spacer 420 has a matrix-like arrangement of openings 414 therein, which define keys of the touchpad 412. To each key is associated a pair of a first capacitor electrode 422 and a second capacitor electrode 424 arranged on the first and second carrier films 416, 418, respectively. Each first capacitor electrode 422 is arranged opposite its second-capacitor-electrode counterpart 424, with respect to the associated opening 414 of the spacer 420. The touchpad 412 further comprises a control circuit (not shown, for the sake of clarity of the drawings), which determines, in a first mode of operation, a quantity indicative of capacitance between individual ones of the first capacitor electrodes 422 and ground and, in a second mode of operation, a quantity indicative of a capacitance between individual ones of the first capacitor electrodes 422 and the associated ones of the second capacitor electrodes 424.
In FIG. 4 a, a user's finger 434 lightly touches the first carrier film 416. The force exerted is not sufficient to cause significant bending of the first carrier film 416 in the region of a key. The position of the user's finger 434 is detected by determining, for each one of the first capacitor electrodes 422, the quantity indicative of capacitive coupling between this electrode 422 and ground. The position may e.g. be computed as the centroid of the positions of the first capacitor electrodes 422, weighed with the corresponding quantity indicative of capacitance. The first mode of operation is suitable, for instance, when the user controls a cursor (e.g. on the display of an appliance) with the touchpad 412.
In FIG. 4 b, the user presses down the first carrier film 416, so that it bends into an opening 414 of the spacer 420 and the distance between the corresponding first and second capacitor electrodes 422, 424 decreases. This causes the capacitance between these capacitor electrodes to go up, which can be detected in the second mode of operation of the touchpad 412. The second mode of operation is, therefore, associated to actuation of a key of the touchpad 412, e.g. by a user's finger 434 or a stylus.
In operation, the first and second modes of operation are carried out in alternance, i.e. the touchpad 412 is switched, more or less periodically, from the first mode of operation to the second mode and inversely. It should be noted that, in the second mode of operation, the touchpad does not need to determine the quantity indicative of capacitance for each key. Indeed, it is considered advantageous if the latter is determined only with respect to that key or those keys in the neighborhood of which the position of the user's finger 434 has been detected when the touchpad 412 operated in the first mode of operation.
FIGS. 5 a and 5 b show a cross section of an alternative touchpad 512 having keypad functionality. The touchpad 512 comprises a first carrier film 516, a second carrier film 518 and a spacer 521, sandwiched between the first and second carrier films 516, 518 so as to keep them spaced apart. The spacer 521 is made of an electrically insulating, compressible foam material, e.g. polyurethane foam or the like. The first and second carried films 516, 518 have capacitor electrodes 522, 524 applied on the surfaces that face the spacer 521. Each first capacitor electrode 522 is arranged on the first carrier film opposite a second capacitor electrode 524 on the second carrier film, with respect to the spacer 521. Each pair of opposite first and second capacitor electrodes defines a key of the touchpad 512. The latter further comprises a control circuit (not shown), which determines, in a first mode of operation, a quantity indicative of capacitance between individual ones of the first capacitor electrodes 522 and ground and, in a second mode of operation, a quantity indicative of a capacitance between individual ones of the first capacitor electrodes 522 and the associated ones of the second capacitor electrodes 524.
In FIG. 5 a, a user's finger 534 lightly touches the first carrier film 516. The force exerted is not sufficient to cause significant bending of the first carrier film 516 in the region of a key. The position of the user's finger 534 is detected by determining, for each one of the first capacitor electrodes 522, the quantity indicative of capacitive coupling between this electrode 522 and ground. As in the previous example, the position may e.g. be computed as the centroid of the positions of the first capacitor electrodes 522, weighed with the corresponding quantity indicative of capacitance. The first mode of operation is suitable, for instance, when the user controls a cursor (e.g. on the display of an appliance) with the touchpad 512.
In FIG. 5 b, the user presses on the first carrier film 516, so that the underlying spacer 521 is compressed, whereby the distance between a pair of first and second capacitor electrodes 522, 524 decreases. This causes the capacitance between these capacitor electrodes to go up, which can be detected in the second mode of operation of the touchpad 512. The second mode of operation is, therefore, associated to actuation of a key of the touchpad 512, e.g. by a user's finger 534 or a stylus.
Operation of the touchpad 512 is similar to the previous example: the first and second modes of operation are carried out in alternance, i.e. the touchpad 512 is switched, more or less periodically, from the first mode of operation to the second mode and inversely. In the second mode of operation, it is considered advantageous if the quantity indicative of capacitance between a first and a second capacitor electrode 522, 524 is determined only with respect to that key or those keys in the neighborhood of which the position of the user's finger 534 has been detected when the touchpad 512 operated in the first mode of operation.
FIGS. 6 a and 6 b illustrate that it is also possible to combine the embodiments of the preceding examples within a single touchpad. The touchpad 612 comprises a first carrier film 616, a second carrier film 618 and a first spacer 620, sandwiched between the first and second carrier films 616, 618 so as to keep them spaced apart. The spacer 620 has a matrix-like arrangement of openings 614 therein, which define keys of the touchpad 612. To each key is associated a pair of a first capacitor electrode 622 and a second capacitor electrode 624 arranged on the first and second carrier films 616, 618, respectively. Each first capacitor electrode 622 is arranged opposite its second-capacitor-electrode counterpart 624, with respect to the associated opening 614 of the spacer 620. Some of the openings (middle keys in FIGS. 6 a and 6 b) in spacer 620 are filled with electrically insulating, compressible foam material 621, e.g. polyurethane foam or the like. The spacer 620 is made, in this example, from a flexible material, which has substantially lower compressibility than the foam material 621. The haptic properties of keys with foam material 621 differ from those without the foam material. Similarly, their capacitance as a function of pressure behaves differently. Nevertheless, operation of touchpad 621 is analogous to operation of touchpads 412 and 512.
FIGS. 7 a-7 c show a touchpad 712 with keypad functionality, in which the keys are arranged along a straight line (a curve would also be feasible). FIG. 7 a shows the layout of the keys, FIGS. 7 b and 7 c show cross-sectional views of the touchpad 712. The touchpad 712 comprises a laminated structure of a first carrier film 716, a second carrier film 718 and a spacer 720, sandwiched between the first and second carrier films so as to keep them spaced apart. The spacer 720 has openings 714 therein, which are arranged along a line and which define the keys of the touchpad 712. To each key is associated a first capacitor electrode 722 arranged on the first carrier film 716. A common second capacitor electrode 724 extends over all the keys of the touchpad 712. The touchpad 712 further comprises a control circuit (not shown), which determines, in a first mode of operation, a quantity indicative of capacitance between individual ones of the first capacitor electrodes 722 and ground and, in a second mode of operation, a quantity indicative of a capacitance between individual ones of the first capacitor electrodes 722 and the common second capacitor electrode 724.
In FIG. 7 b, a user's finger 734 lightly touches the first carrier film 716. The force exerted is not sufficient to cause significant bending of the first carrier film 716 in the region of a key. The position of the user's finger 734 is detected by determining, for each one of the first capacitor electrodes 722, the quantity indicative of capacitive coupling between this electrode 722 and ground. The position may e.g. be computed as the centroid of the positions of the first capacitor electrodes 722, weighed with the corresponding quantity indicative of capacitance. The first mode of operation is suitable, for instance, when the user controls a cursor (e.g. on the display of an appliance) with the touchpad 712.
In FIG. 7 c, the user presses down the first carrier film 716, so that it bends into an opening 714 of the spacer 720 and the distance between the corresponding first electrode 722 and the second capacitor electrode 724 decreases. This causes the capacitance between these capacitor electrodes to go up, which can be detected in the second mode of operation of the touchpad 712. The second mode of operation is, therefore, associated to actuation of a key of the touchpad 712, e.g. by a user's finger 734 or a stylus.
In operation, the first and second modes of operation are carried out in alternance, i.e. the touchpad 712 is switched, more or less periodically, from the first mode of operation to the second mode and inversely. It should be noted that, in the second mode of operation, the touchpad does not need to determine the quantity indicative of capacitance for each key. Indeed, it is considered advantageous if the latter is determined only with respect to that key or those keys in the neighborhood of which the position of the user's finger 734 has been detected when the touchpad 712 operated in the first mode of operation.
FIGS. 8 a-8 c show possible layouts of a slider 812, FIGS. 8 d and 8 e show cross-sectional views thereof. The slider 812 comprises a laminated structure of a first carrier film 816, a second carrier film 818 and a spacer 820, sandwiched between the first and second carrier films so as to keep them spaced apart. The spacer 820 has an opening 814 therein, which extends, in this case, along a straight line (a curvilinear course is possible, see FIGS. 9 a-9 d). The opening 814 defines the active zone of the slider 812. The first carrier film 816 has first capacitor electrodes arranged thereon in the active zone, the second carrier film has a common second capacitor electrode 824 applied thereon in the active zone. The first capacitor electrodes 822 are arranged in facing relationship to the second capacitor electrode 824. The second capacitor electrode has a thin dielectric layer 826 arranged thereon, which prevents short-circuits between the first capacitor electrodes 822 and the second capacitor electrode 824, if they are brought closer to one another by a compressive force acting on the slider 812.
In FIG. 8 d, a user's finger 834 lightly touches the first carrier film 816. The force exerted is not sufficient to cause significant bending of the first carrier film 816 in the region of the active zone. In FIG. 8 e, however, the user presses down the first carrier film 816, so that it locally bends into the opening 814 of the spacer 820 and the distance between the first electrodes 822 and the second capacitor electrode 824 decreases at the point where the force is applied.
In the sliders of FIGS. 8 a and 8 b, the first capacitor electrodes 822 are separately connected to a control circuit (not shown). Accordingly, these sliders are able to detect the position of the user's finger 834 (in the first and the second mode of operation). In the first mode of operation, the control circuit determines, for each one of the first capacitor electrodes 822, the quantity indicative of capacitive coupling between this electrode 822 and ground. The said position may e.g. be computed as the centroid of the positions of the first capacitor electrodes 822, weighed with the corresponding quantity indicative of capacitance. In the second mode of operation, a quantity indicative of a capacitance between single ones of the first capacitor electrodes 822 and the common second capacitor electrode 824 can be detected. As can be seen, operation of the slider 812 as shown in FIGS. 8 a and 8 b is similar to operation of the keypad 712.
In the slider of FIG. 8 c, the first capacitor electrodes are not separately connected to the control circuit. Instead, there are three groups of first capacitor electrodes 822. The first capacitor electrodes 822 of each group are conductively interconnected. Along the active zone, a first capacitor electrode of the first group is followed by one of the second group, which is, in turn, followed by one of the third group, after which the succession starts again with a first capacitor electrode of the first group. A slider as shown in FIG. 8 c is not capable of detecting (absolute) position of the user's finger 834 or stylus. Nevertheless, such slider can detect movement of the user's finger 834 or stylus (in both modes of operation). In the first mode of operation, when the user's finger 834 moves from the left to the right, the succession of the groups of first capacitor electrodes that have increased capacitive coupling to ground is 2-3-1 (and cyclically continued). When the user's finger 834 moves from the right to the left, the succession of the groups of first capacitor electrodes that have increased capacitive coupling to ground is 3-2-1 (and cyclically continued). In the second mode of operation, the direction of movement can be determined from the succession of the groups of first capacitor electrodes that have increased capacitive coupling to the second capacitor electrode. Of course, in the second mode of operation, the amount of force exerted upon the slider can also be detected. For instance, if the quantity indicative of capacitance exceeds a predetermined threshold, some switching action may be triggered.
Given the reduced number of external connectors, the slider of FIG. 8 c is particularly interesting if the absolute position needs not to be known, e.g. for navigating though list-based menus (scrolling through a list of items displayed and selecting an item to enter a sub-menu or start a certain function). The action of selecting an item from the list can e.g. take place when the user presses on the slider with a force that causes the quantity indicative of capacitance between the first and second capacitor electrodes to exceed the predetermined threshold.
FIGS. 9 a-9 d show circular sliders 912. The sliders of FIGS. 9 a and 9 b are configured for detecting position (sliders with keypad functionality); those of FIGS. 9 c and 9 d are analogous to the linear slider of FIG. 8 c.
FIGS. 10 a-10 c show schematic top views, FIG. 10 d a schematic cross-sectional view of variants of an alternative embodiment of a touchpad 1012. The touchpad 1012 has a plurality of first elongated capacitor electrodes 1022 applied on the first carrier film 1016 and a plurality of second elongated capacitor electrodes 1024 applied on the second carrier films 1018. The first capacitor electrodes 1022 are arranged opposite the second capacitor electrodes with respect to an opening 1014 in spacer 1020, which is sandwiched between the carrier films 1016, 1018. The first capacitor electrodes 1022 extend crosswise to the second capacitor electrodes 1024. In the shown embodiment, the angle between any one of the first capacitor electrodes and any one of the second capacitor electrodes is 90°; it should, however, be noted that this angle could also be different from 90°, e.g. between 30° and 90°. The second capacitor electrodes 1024 are covered with a thin dielectric layer, which prevent a short-circuit when the first and second capacitor electrodes 1022, 1024 are brought closer together at the location where a compressive force acts on the touchpad 1012. The touchpad 1012 is connected to control circuit (not shown), which determines, while in the first mode of operation, a quantity indicative of capacitance between individual ones of the first capacitor electrodes 1022 and ground and, while in the second mode of operation, a quantity indicative of a capacitance between individual ones of the first capacitor electrodes 1022 and individual ones of the second capacitor electrodes 1024.
In the touchpads of FIGS. 10 a and 10 b, the capacitor electrodes 1022 and 1024 are separately connected to a control circuit (not shown). Accordingly, these touchpads are able to detect the position of the user's finger 1034 (with respect to one dimension in the first mode of operation and with respect to two dimensions in the second mode of operation). In the first mode of operation, the control circuit determines, for each one of the first capacitor electrodes 1022, the quantity indicative of capacitive coupling between this electrode 1022 and ground. The position may e.g. be computed as the centroid of the positions of the first capacitor electrodes 1022, weighed with the corresponding quantity indicative of capacitance. It should be noted that in first mode of operation, the position of the user's finger 1034 is detected in the direction perpendicular to the direction along which the first capacitor electrodes extend. In the second mode of operation, the control circuit determines, for each one of the first capacitor electrodes 1022, the quantity indicative of capacitance between this electrode 1022 and each one of the second capacitor electrodes 1024. The position of the user's finger (the point of application of the force) is obtained from those first and second electrodes, which show maximum capacitive coupling.
In FIG. 10 c, the first and the second capacitor electrodes 1022 and 1024 are not separately connected to the control circuit. Instead, there are three groups of first capacitor electrodes 1022 and three groups of second capacitor electrodes 1024. The capacitor electrodes of each group are conductively interconnected. Along the direction perpendicular to the first capacitor electrodes, a first capacitor electrode of the first group is followed by one of the second group, which is, in turn, followed by one of the third group, after which the succession starts again with a first capacitor electrode of the first group. The second capacitor electrodes are arranged analogously. A touchpad as shown in FIG. 10 c is not capable of detecting (absolute) position of the user's finger 1034 or stylus. Nevertheless, such touchpad can detect movement of the user's finger 1034 or stylus. In the first mode of operation, when the user's finger 1034 moves perpendicular to the first capacitor electrodes, the succession of the groups of first capacitor electrodes which have increased capacitive coupling to ground is 2-3-1 (and cyclically continued) or 3-2-1 (and cyclically continued), depending on the direction of the movement. In the second mode of operation, the direction of the movement perpendicular to the first capacitor electrodes can be determined from the succession of the groups of first capacitor electrodes which have increased capacitive coupling to the second capacitor electrodes. Likewise, the direction of the movement perpendicular to the second capacitor electrodes can be determined from the succession of the groups of second capacitor electrodes which have increased capacitive coupling to the first capacitor electrodes. Of course, in the second mode of operation, the amount of force exerted upon the touchpad can also be detected. For instance, if the quantity indicative of capacitance exceeds a predetermined threshold, some switching action may be triggered.
FIGS. 11 a and 11 b show yet another alternative embodiment of an input device including a proximity and pressure sensor 1112. The capacitive proximity and pressure sensor 1112 comprises a first carrier layer in the form of a substantially rigid cover 1116 and a second carrier layer in the form of a substrate 1118. The rigid cover 1116 includes a plurality of component layers, such as a protective hard plastic 1116 a, a double-sided adhesive 1116 b and a flexible thermoplastic film 1116 c. A pivot 1123 is sandwiched between the first and second carrier layers 1116, 1118. The capacitive proximity and pressure sensor 1112 comprises electrode pairs diametrically opposed with respect to the pivot 1123. Each electrode pair comprises a first capacitor electrode 1122 arranged on the first carrier layer 1116 (on the side directed towards the second carrier layer 1118) and a second capacitor electrode 1124 on the second carrier layer 1118 (on the side directed towards the first carrier layer 1116). The first and second capacitor electrodes 1122, 1124 are formed from conductive material (e.g. silver ink) applied directly on the first and second carrier layers, respectively. A spacer 1121 made of electrically insulating foam material is arranged between the first and second capacitor electrodes of a pair.
The first and second capacitor electrodes 1122, 1124 are connected to a control circuit (not shown). The control circuit determines, while in the first mode of operation, a quantity indicative of a capacitance between the first capacitor electrodes and ground and, while in the second mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and the second capacitor electrode of each pair.
The first mode of operation is associated to sensing the proximity of an object to be sensed, e.g. of a user's finger 1134. In the first mode of operation the control circuit keeps the first and second electrodes essentially at the same electric potential so that the electric field substantially cancels between the first and second electrodes. The second electrodes 1124 thus act as driven shields for the respective first electrodes 1122 and the sensitivity of the latter is directed away from the respective second electrode 1124. If an oscillating voltage is applied to the first capacitor electrode, an oscillating electric field to ground is built up. The object to be sensed modifies the capacitance between the first capacitor electrode and ground, which is sensed by the control circuit 1128.
The second mode of operation is associated with sensing pressure exerted on the sensor by some kind of actuator, such as e.g. the user's finger 1134 or stylus. In the second mode of operation, the control circuit essentially determines the capacitance of the capacitor formed by the first and the second capacitor electrodes 1122, 1124. In the embodiment of FIGS. 11 a and 11 b, pressure exerted on the proximity and pressure sensor 1112 by the user causes the first carrier layer to tilt, whereby the first and second capacitor electrodes of a first pair get closer together (right-hand side in FIG. 11 b) and those of a second pair are moved away from one another (left-hand side in FIG. 11 b). When the user stops pressing on the sensor, the foam spacers 1121 bring the first carrier layer back into the neutral position.

Claims

1. An input device comprising

a capacitive proximity and pressure sensor, including a first carrier layer, a second carrier layer and a spacer arranged between said first and second carrier layers, said first carrier layer having a first capacitor electrode applied thereon, said second carrier layer having a second capacitor electrode applied thereon, said first and second capacitor electrodes being arranged opposite one another with respect to said spacer in such a way that, in response to a compressive force acting on the pressure sensor, the first and second capacitor electrodes are brought closer together;

and a control circuit configured so as to operate in at least a first and a second mode of operation, said control circuit determining,

while in said first mode of operation, a quantity indicative of a capacitance between said first capacitor electrode and ground;

and, while in said second mode of operation, a quantity indicative of a capacitance between said first capacitor electrode and said second capacitor electrode.

2. The input device as claimed in claim 1, wherein said spacer has an opening therein, said first and second capacitor electrodes being arranged opposite one another with respect to said opening of the spacer, wherein said first and/or said second capacitor electrode has an insulating layer or insulating pattern arranged thereon in such a way as to prevent a short circuit between said first and second capacitor electrodes when said first and second capacitor electrodes are brought closer together.

3. The input device as claimed in claim 1, wherein said spacer is electrically insulating and compressible, and wherein said first and second capacitor electrodes are brought closer together when said spacer is compressed in response to a compressive force acting on the pressure sensor.

4. The input device as claimed in claim 1, wherein said control circuit determines, while in said first mode of operation, an amount of electric charge accumulated on said first capacitor electrode in response to applying a defined voltage to said first capacitor electrode.

5. The input device as claimed in claim 1, wherein said control circuit determines, while in said first mode of operation, an amplitude and/or a phase of a loading current flowing in said first capacitor electrode in response to applying an oscillating voltage to said first capacitor electrode.

6. The input device as claimed in claim 1, wherein said control circuit determines, while in said first mode of operation, an in-phase component and/or a 90°-phase-offset component of a loading current flowing in said first capacitor electrode in response to applying an oscillating voltage to said first capacitor electrode.

7. The input device as claimed in claim 1, wherein said control circuit determines, while in said first mode of operation, a charge time and/or a discharge time of said first capacitor electrode.

8. The input device as claimed in claim 1, wherein said control circuit, while in said first mode of operation, applies a first voltage to said first electrode and a second voltage to said second electrode, said first and second voltages having same amplitude and phase.

9. The input device as claimed in claim 1, wherein said control circuit determines, while in said second mode of operation, an amount of electric charge accumulated on one of said first and second capacitor electrodes in response to an applying a defined voltage to the other of said first and second capacitor electrodes.

10. The input device as claimed in claim 1, wherein said control circuit determines, while in said second mode of operation, an amount of electric charge accumulated on one of said first and second capacitor electrodes in response to an applying a defined voltage to said one of said first and second capacitor electrodes.

11. The input device as claimed in claim 1, wherein said control circuit determines, while in said second mode of operation, an amplitude and/or a phase of a coupling current flowing in one of said first and second capacitor electrodes in response to applying an oscillating voltage to the other of said first and second capacitor electrodes.

12. The input device as claimed in claim 1, wherein said control circuit determines, while in said second mode of operation, an amplitude and/or a phase of a loading current flowing in one of said first and second capacitor electrodes in response to applying an oscillating voltage to said one of said first and second capacitor electrodes.

13. The input device as claimed in claim 1, wherein said control circuit determines, while in said second mode of operation, an in-phase component and/or a 90°-phase-offset component of a coupling current flowing in one of said first and second capacitor electrodes in response to applying an oscillating voltage to the other of said first and second capacitor electrodes.

14. The input device as claimed in claim 1, wherein said control circuit determines, while in said second mode of operation, an in-phase component and/or a 90°-phase-offset component of a loading current flowing in one of said first and second capacitor electrodes in response to applying an oscillating voltage to said one of said first and second capacitor electrodes.

15. The input device as claimed in claim 1, wherein said control circuit determines, while in said second mode of operation, a charge and/or a discharge time of said first and/or said second capacitor electrode.

16. The input device as claimed in claim 1, wherein said first carrier layer, said spacer and said second carrier layer are laminated together.

17. The input device as claimed in claim 1, wherein said first carrier layer has a plurality of first capacitor electrodes applied thereon, said second carrier layer having a plurality of second capacitor electrodes applied thereon, each one of said plurality of first capacitor electrodes being arranged opposite a respective one of said plurality of second capacitor electrodes with respect to said spacer in such a way that, in response to a compressive force acting on the pressure sensor, respectively opposite ones of said first and second capacitor electrodes are brought closer together;

and wherein said control circuit determines

while in said first mode of operation, a quantity indicative of a capacitance between individual ones of said plurality of first capacitor electrodes and ground;

and, while in said second mode of operation, a quantity indicative of a capacitance between individual ones of said plurality of first capacitor electrodes and the respectively opposite ones of said plurality of second capacitor electrodes.

18. The input device as claimed in claim 1, wherein said first carrier layer has a plurality of first elongated capacitor electrodes applied thereon, wherein said second carrier layer has a plurality of second elongated capacitor electrodes applied thereon, said plurality of first capacitor electrodes being arranged opposite said plurality of second capacitor electrodes with respect to said spacer, said first elongated capacitor electrodes extending transversally to said second elongated capacitor electrodes in such a way that, in response to a compressive force acting locally on the pressure sensor, opposite ones of said first and second capacitor electrodes are brought closer together at the location where said compressive force acts on the pressure sensor;

and wherein said control circuit determines,

while in said first mode of operation, a quantity indicative of capacitance between individual ones of said plurality of first capacitor electrodes and ground;

and, while in said second mode of operation, a quantity indicative of a capacitance between individual ones of said plurality of first capacitor electrodes and individual ones of said plurality of second capacitor electrodes.

19. The input device as claimed in claim 1, wherein said spacer has a plurality of openings therein, wherein said first carrier layer has a plurality of first capacitor electrodes applied thereon, wherein said second carrier layer has a plurality of second capacitor electrodes applied thereon, each one of said plurality of first capacitor electrodes being arranged opposite a respective one of said plurality of second capacitor electrodes with respect to a respective one of said plurality of openings in such a way that, in response to a compressive force acting on the pressure sensor, respectively opposite ones of said first and second capacitor electrodes are brought closer together;

and wherein said control circuit determines,

20. An input device comprising

a capacitive proximity and pressure sensor, including a first carrier layer, a second carrier layer and a spacer arranged between said first and second carrier layers for keeping the first and second carrier layers apart from one another, said first carrier layer having a plurality of first capacitor electrodes applied thereon, said second carrier layer having a second capacitor electrode applied thereon, said plurality of first capacitor electrodes being arranged opposite said second capacitor electrode with respect to said spacer in such a way that, in response to a compressive force acting locally on the pressure sensor, individual ones of said first capacitor electrodes are brought closer to said second capacitor electrode at the location where said compressive force acts on the pressure sensor;

while in said first mode of operation, a quantity indicative of capacitance between individual ones of said first capacitor electrodes and ground;

and, while in said second mode of operation, a quantity indicative of a capacitance between said second capacitor electrode and individual ones of said first capacitor electrodes.

21. The input device as claimed in claim 20, wherein, wherein said spacer has an opening therein, said plurality of first capacitor electrodes being arranged opposite said second capacitor electrode with respect to said opening of the spacer, wherein capacitive electrodes of said plurality of first capacitive electrodes and/or said second capacitor electrode have an insulating layer or insulating pattern arranged thereon in such a way as to prevent a short circuit between capacitive electrodes of said plurality of first capacitive electrodes and said second capacitor electrode.

22. The input device as claimed in claim 20, wherein said spacer is electrically insulating and compressible, and wherein individual ones of said first capacitor electrodes are brought closer to said second capacitor electrode when said spacer is compressed in response to a compressive force acting on the pressure sensor.

23. The input device as claimed in claim 20, wherein said first carrier layer, said spacer and said second carrier layer are laminated together.