WO2008035041A2

WO2008035041A2 - Exchangeable input means for electronic device

Info

Publication number: WO2008035041A2
Application number: PCT/GB2007/003460
Authority: WO
Inventors: Andrew Peter Matthews; David Alun James
Original assignee: Sensopad Limited
Priority date: 2006-09-18
Filing date: 2007-09-13
Publication date: 2008-03-27
Also published as: WO2008035041A3

Abstract

An overlay, e.g. a detachable input device, is provided for an electronic device such as a cellular telephone, PDA, laptop, slate etc that includes a sensor, preferably an inductive sensor, and electronics that operate in response to input from the sensor. The overlay comprises an identification device, e.g. an RFID tag, and an intermediate coupler that is preferably electrically passive, and especially a passive resonant circuit formed from an inductor and a capacitor. The intermediate coupler is associated with a manually operable input device such as a key, button, slider, or knob that can be manually operated by a user, so that operation of the input device will change a property of the coupling device such, as its resonant frequency or position on the sensor, which change is sensed by the sensor in order to actuate a function of the device. The overlay enables a user to customise his device for various applications such as communication, games, music or audio visual, and since the overlay has no active components, it can be made for very low cost. A peripheral docking station may also communicate with the device inductively, and charge its batteries.

Description

OVERLAY FOR ELECTRONIC DEVICE

This invention relates to electronic equipment, especially portable electronic equipment such as cellular telephones, personal digital assistants

(PDAs) , laptop computers, tablet computers, ultra mobile personal computers (UMPCs) and the like.

Mobile audio, video, computing and telephony devices are already pervasive platforms for communicating visual, audible and digital data. Common to all these devices is a desire to create ever smaller products with user-friendly human-machine interfaces, and to provide multiple peripheral devices designed to add functionality to such products. However, frequently their small physical size limits their user- friendliness as manufacturers strive to provide multifunctional interfaces for all the possible functions of the device. These interfaces also tend toward standardization since costs of manufacture are predicated by production volumes, with the result that manufacturers therefore attempt to limit product variants . The result of this is that many users are frustrated by the limited user interface options, and their desires are at variance with those of the manufacturers who are aiming to reduce manufacturing costs by further standardization. While the production of peripheral devices can add significant profitability, the limited size further predicates very small user interfaces and small, delicate and costly connectors that often become a weak point in the design of the devices .

According to one aspect, the present invention provides an overlay for an electronics device that includes a sensor and electronics that operate in response to input from the sensor, the overlay comprising an identification arrangement for enabling which of a number of overlays has been positioned on the device, a manually operable input device, and an intermediate coupler, the intermediate coupler being associated with the input device so that operation of the input device by a user will change a property of the intermediate coupler, which change will, in operation, be sensed by the sensor to actuate a function of the device. The overlay according to the invention has the advantage that it may be used to enable the user to customise the electronic device to perform only a limited range of tasks at any one time. At other times, if the user wishes to require the device to perform a different range of tasks, it is possible for the user simply to place a different overlay on the device. Since the overlay is passive, it does not need to physically connect to the device, and it does not incorporate any complex electronic components in order to communicate with the device, and so may be manufactured at very low cost, and being detachable enables the device to be configured to act as a platform for telephony, touch or pen data input, media and gaming interaction as desired by the user at any time. Because the overlay may incorporate only limited range of the possible functions of the device, it is possible for the size of any input device such as keys or the like to be made sufficiently large to enable ease of use by the user, or, if a large number of input devices are employed as with a keyboard, the overlay may be made significantly larger than the sensor or even the electronic device.

In the broadest aspect of the invention, it is possible for the intermediate coupler to be an electrically active coupler, i.e. one that requires its own power source for example to transmit signals to any aerial of the sensor of the electronic device. However it is preferred for the intermediate coupler to be electrically passive, that is to say, that electrical current may flow in the coupler but the intermediate coupler has no separate power source. For example, where the device includes a transmit aerial as part of its sensing arrangement, the intermediate coupler takes any power from fields generated by the aerial (s). Electrically passive couplers have the advantage not only that no batteries or other power sources will be needed, but they may be formed as much smaller items than active devices.

Many users will want simple user interfaces with a minimal number of buttons for purely telephony applications. Expressly, users with limited mobility or sight find complex interfaces difficult to use and the invention allows a standard telephone to be customised precisely for their needs, limiting the number of control elements to those desired. Other more technical users may require fast-keys and extensive menu functions to extract higher functionality from their products. Business users desire QWERTY keyboard functionality, while others require pen input function to record written commands. MP3 and MPEG file compression as well as GPRS and 3G telecommunications have also enabled users to download audio visual files to such portable devices and many users now demand AV functionality from them. MP3 players now frequently incorporate scroll wheels to help navigate lists of audio and video files, and this may be enabled by the present invention. Digital games also require distinct user interface controls, and using the overlays according to the invention dedicated user interfaces can be attached to devices such as cellular telephones .

At present, implementing these different user interfaces would necessitate multiple telephone, PDA, gaming devices or mobile computer variants which would increase production costs and time to market, and inevitably users are forced to use compromised interfaces designed to accommodate a variety of tastes.

According to the present invention, the need for expensive tooling and production variants is eliminated by designing a fixed base product (the electronic device) capable of sensing a variety of motions or actions applied to a removable user interface overlay. A variety of simple or complex overlays could be made available to the user to provide a user-configurable interface to meet their specific needs. The manufactured cost of these overlays could be reduced considerably in high volumes, enabling significant numbers of variants to be produced at low cost and providing the consumer with a cost effective ability to customise his own device.

There are a number of mechanisms for providing the desired variable functionality, but it is desired to allow such functionality to be achieved with the minimum of electrical and physical connection between the overlay and the base device.

Where electrical contact is made between the overlay and the base electronic device, this may lead to complex mechanical requirements, mechanical wear and potential electrical contact problems, in addition to all the common complications associated with resistive touch sensing technology. It is desired, at least according to preferred aspects of the . invention, that physical contact between the detachable overlay and the base device be limited to the mechanism for retaining the overlay, and all control signals are therefore preferably sent between the overlay and the base device in a non-contact manner. This approach minimises the cost of the mechanical overlay and can be incorporated in a host device without the requirement for a touch sensitive surface (although it is possible for such a touch sensitive surface to be employed in the broadest aspect of the invention) .

Preferably the intermediate coupler does not physically contact the sensor of the electronic device, thereby obviating the need for any electrical connectors , and requiring only a mechanical attachment between the device and the overlay. In the broadest aspect of the invention, any of a number of sensing technologies may be employed in order for the sensor of the device to sense the position of the intermediate coupler. For example a capacitive sensor such as one described in US patent No. 5,730,165 or US patent No. 6,288,707 may be used, in which case the intermediate coupler may be a grounded object such as a metallic body or even a user's finger. Such sensors, however, have the disadvantage that they cannot resolve position to a fine degree, and also being subject to background noise/interference. Alternatively, magnetic sensors such as Hall effect sensors, can also be used as the non-contact position sensor, in which case the intermediate coupler would be a magnet. In other cases it may be possible to employ an optical sensor, for example using a photo-diode or a PSD, in which case the intermediate coupler would be an optical reflector. However, devices using such sensors need to be sealed from contamination which tends to increase the mechanical complexity and cost.

Preferably, the device includes an inductive sensor, in which case the intermediate coupler may be a resonant circuit, a metal foil or a ferromagnetic body. Inductive sensors are in common use, and they offer advantages over other types of sensor, particularly the fact that they offer a robust, non-contact sensing means that is generally more immune to the ingress of dirt over the lifetime of the device. These sensors are typically used as position or proximity sensors and they typically require a simple low-cost coupler or target that is interrogated by processing electronics. Inductive sensing arrangements have significant advantages over capacitive sensors including the ability to employ multiple targets (intermediate couplers) their sensing range, flexibility of design, ruggedness, accuracy, resolution, lifetime and lack of drift of the sensed position. Existing inductive joystick products use linear variable differential transformers (LVDTs ) and the mechanical arrangement for the joystick is built around the linear movement of two orthogonal LVDTs. Other inductive sensing technologies are now available that offer the potential to replace the high cost LVDTs and significantly to reduce the complexity and cost of the mechanical arrangements .

One form of inductive sensor that may be employed in the arrangement according to the present invention is a simultaneous transmit-receive device described in British patent application No. 2,374,424, the disclosure of which is incorporated herein by reference. In this form of arrangement a signal generator generates an excitation signal in the transmit aerial, and a sensed signal is induced in the receive aerial. The excitation signal comprises a periodic carrier signal that is modulated by a periodic modulation signal at a lower frequency, and the signal that is induced in the receive aerial is indicative of the position of the intermediate coupler (often referred to as the target) with respect to the transmit or receive aerial . The transmit aerial may be formed by a pair of loops, one being in the general form of a sine while the other is in the general form of a cosine and positioned with respect to each other in spatial quadrature, although other forms of coils are possible. The intermediate coupler may have any of a number of forms. For example, it may be in the form of a passive resonant coupler based on an LC circuit that may be formed in a simple manner by connecting the ends of a coil by means of a capacitor, so that it will resonate at a particular frequency, and the signal received by the receive aerial from the intermediate coupler will have a phase that differs from that of the signal transmitted by the transmit aerial, the phase difference indicating the position of the coupler. Alternatively, the intermediate coupler may comprise an element formed from a material that will perturb the magnetic field generated by the transmit aerial, for example it may be formed from a material having a high relative magnetic permeability such as a ferromagnetic material, although low-cost couplers can be made simply from a conductive material in which case the sensor responds to eddy currents that flow in the material. Although as described in GB-A-2 , 374 , 424, the sine and cosine windings each have only a single loop, this is a simplification, and in practice each sine and cosine loop will have a number of windings connected in series, either nested one inside the other so that different lobes of the sine and cosine loops take on the form of a spiral, or each sine and cosine loop may have a number of windings that are slightly offset with respect to one another. The use of a large number of windings to form each lobe of the sine and cosine loops is often necessary or desirable in order to increase the magnetic field generated by the windings, and so increase the magnetic field gradients across the aerial .

Another form of inductive sensor is described in US patent No. 5,815,091 to Scientific Generics, the disclosure of which is incorporated herein by reference, in which the transmit aerial is in the form of a single loop, and the receive aerial comprises a pair of loops, one in the general form of a sine and the other in the general form of a cosine. Similarly with the form of inductive position sensor described above, the loops of the transmit and receive aerials may be formed from a number of windings in order to increase magnetic coupling between the aerials.

Yet another form of inductive sensor that may be employed in the arrangement according to the invention is disclosed in US patent No. 4,878,553 to Wacom Co. Ltd, the disclosure of which is incorporated herein by reference. In this arrangement, the position of a resonant circuit is detected from signals sent by a generating circuit and transmit coils via the intermediary resonant circuit to a receive aerial. The transmit and receive aerials are in the form of an array of loops, that are located at defined positions along the pad, and the coordinate values of the position of the resonant circuit is determined from the amplitude or phase of the signal received in different loops of the receive aerial. The intermediate coupler may, as with the prior art devices disclosed above, be a passive resonant circuit, for example formed from an LC circuit. This has the advantage that, depending on the quality value (Q value) of the resonant circuit, the resonant circuit may amplify the signal at its resonant frequency as it is sent from the transmit aerial to the receive aerial. However, this is not necessary in all cases, and it is often possible to employ a non- resonant coupling device, for example one formed from a conductive or magnetic material. Thus, the intermediate coupler may comprise a sheet of conductive material such as a metal, and the signal in the transmit aerial may be coupled from the transmit aerial to the receive aerial by means of eddy currents formed in the intermediate coupler. Alternatively, the conductive material can be replaced by a permeable material, in which case the inductive EM field is modified by the material now drawing in the magnetic flux rather than repulsing it as is the case for conductive materials. In another embodiment a magnet can be used as the coupler. Such forms of intermediate coupler have the disadvantage that only a single coupler can be identified by the transmit and sense coils in the electronic device, so that if more than one coupler is present, all the couplers, or rather all but one of the couplers, should be a passive resonant circuit having its own characteristic resonant frequency.

Push-button functionality can be achieved by altering the resonant frequency of the coupler, either by modifying the inductor (e.g. by stretching the coil or changing its shape) , by bringing the coil close to a magnetic spoiler such as a ferrous or conductive material), or by adding or removing a capacitance. Alternatively, push-button functionality may be achieved by connecting the capacitance to the inductor or disconnecting it therefrom in order to create or destroy the resonant circuit. In yet other systems, the push-button functionality may be achieved by causing the sensor to measure the signal strength since the closer the intermediate coupler approaches the transmit or receive aerial, the greater the signal amplitude. Although this is a cruder system, it may be sufficient in a number of cases. Since there is normally no physical or wired electrical contact between the user interface overlay and the sensing circuits contained in the host device, a mechanism is preferably provided to identify which user interface overlay is positioned on the device, and also, as referred to below, which alternative peripheral device (station) , docking station or charging location is employed. This may be provided by a mechanical keying profile, a radio frequency identification (RFID) device, an intermediate coupler whose position and/or frequency of coupling (e.g. resonant frequency in the case of a passive resonant circuit) identifies the overlay, or a barcode.

Once the device recognises that a new overlay has been positioned on the device, the device has to modify its responses to the sensor outputs accordingly. This will typically involve activating different user interface interpretation functions in software on the device. These software functions could be pre-loaded onto the device or can be downloaded as required. One way to re-program the device for example, to recognise a different user interface overlay might be to incorporate an RFID device in the overlay, such identity being associated with a software subroutine capable of operating the interface. Alternatively, the user could be asked to download a limited size application program (applet) via the internet or through their telephony service provider. This download would transform the product from the old user interface controls to the new. In the broadest aspect of the invention, any of a number of different mechanisms may be employed in the overlay in order to enable the device to sense manipulation of the input device. For example, manipulation of the input device may change the position of the intermediate coupler in a direction toward or away from the sensor. Such a system could be employed where the overlay includes a number of buttons or keys that are depressed to actuate a function. In other forms of overlay, the input device may be a slider, and manipulation thereof may change the position of the intermediate coupler in at least one direction along which the sensor extends. Such a device could be employed, for example, for changing volume, picture brightness etc. smoothly over a range of values. In other arrangements, the input device may be in the form of a wheel which may be rotated, and rotation of the wheel will move the intermediate coupler in a circular path over the sensor or will change the orientation thereof. Such input devices may be employed in overlays used for games or as a volume control .

In yet other overlays, the input devices may be formed so that operation thereof will create or remove resonance of the passive resonant circuit or change some characteristic of the resonance, for example the resonant frequency, amplitude, phase, Q factor etc. The intermediate coupler may, for example, be formed as a coil terminated by a capacitor, and include a switch which creates the resonant circuit only when closed, or which may cause a further capacitor to be connected or disconnected in order to change the resonant frequency of the passive resonant circuit. For example, depression of a key may close the switch and create the resonant circuit so that the resonant frequency is sensed by the sensor. The overlay may include a plurality of input devices of the same or different type, in which case each input device may be associated with one or more intermediate couplers which may have a characteristic resonant frequency. In other forms of overlay, groups of input devices may be associated with separate intermediate couplers. For instance, if the overlay is in the form of a keypad or keyboard, e.g. a "QWERTY" keyboard, in which keys are arranged in a two dimensional arrangement of rows and columns, different intermediate couplers may be associated with different rows and columns. If the intermediate couplers have different resonant frequencies, it is possible for the sensor to determine which key has been pressed from the two couplers associated with each key.

Advantageously, the intermediate couplers extend from positions corresponding to the input devices, for example the keys in the case of a keyboard, to a smaller area corresponding to that of the sensor of the electronic circuit, or part of the sensor, that enables the couplers to be sensed.

According to the invention, a number of detachable overlays incorporating variable functions such as normal keypads, joysticks, sliders, scroll-wheels , trackballs, chess games, board games and other functions can be read by the electronics during one part of the measurement cycle and subsequently in the next part of the measurement cycle the electronics could be reconfigured to look for alternative user interface overlays or to sense touch or to communicate with external peripherals such as audio speaker amplifier and speakers, data cradles for stationary computers, docking stations and battery chargers.

According to another aspect, the invention provides a system which comprises an electronic device that includes a sensor and electronics that operate in response to input from the sensor, and an overlay according to the invention positioned on the device so that operation of the input device by a user will be sensed by the device.

It is possible for the overlay to extend over the entire surface of the device, or indeed for it to be larger than the dimensions of the device as may be the case with a keyboard. In other cases it may be desirable for the overlay to extend over part only of the device. For example, the device may include a screen, at least part of which is not obscured by the overlay so that the user can view the unobscured part during use. The device may, for example, include a touch screen, and/or the device may include an inductive sensor (e.g. in the region of the screen) to allow actuation by means of a stylus. Such forms of stylus typically are formed from a high permeability material that forms part of a passive LC circuit. The properties of the circuit, for example its resonant frequency, may change if desired when pressed against the screen. Thus, the device may be able to detect both finger touch and stylus generated data input, either in addition to or instead of the user interface overlays. It is possible according to the invention to combine the use of inductive and capacitive or other switching and sensing technologies within the same host device and even within the same control circuits.

In particular, inductive pen technology can allow the position of the pen to be detected while not in contact with the screen or sensor, so that additional functionality can be provided while the stylus is hovering. Furthermore, current resistive technologies demand multi-layer construction technique, which reduce screen brightness and contrast ratio, diminishing the user enjoyment and battery lifetime. Resistive and capacitive sensors are also known to drift, while inductive technology does not. By combining capacitive sensing, which can be embodied using only a single layer structure on a substrate material, with inductive sensing located beneath a screen, screen brightness and contrast ratio can be maximised while minimising battery consumption.

A mobile device user whose equipment incorporates this feature could re-program the device instantaneously at any time either to sense alternative user interfaces or indeed other data input devices , such as touch, user interface overlays or pen input. Once these circuits are incorporated within the mobile device, additional peripheral interfaces could be attached to the device and operated using circuits or components associated with the sensing circuits either contained in the peripheral device (described later) or the mobile device itself in order to enhance the functionality.

In addition to the user interface overlay according to the invention, the invention also provides a peripheral station that can communicate with the electronic device using non-contact inductive sensing to allow one-way or two-way communications. Such a peripheral station may be in the form of a docking station that can transmit and receive data such as wireless payment data, music, video, text (SMS) messages and other forms of digital data over short distances. These signals can either be used to control the electronic device's handset functions or to allow gaming activities at production costs hitherto unavailable to mobile devices, or to allow secure data transfer largely undetectable by wireless evesdroppers . In the case of devices that employ inductive sensors, such a system has the advantage that the ability of device to communicate with the peripheral station essentially comes at no extra cost since the electronics and the aerial used for the sensor can readily be used for wireless communications .

By way of example, an inductive sensor, or more simply the electronics capable of driving such an inductive sensor can be incorporated in a mobile device that will allow the device to detect the identity of a removable object and its position. Such a scheme would allow a low cost peripheral, such as a chess board, to be connected to the mobile device, and the electronics ideally, but not necessarily, contained in the mobile device could identify each chess piece by a variety of inductive techniques. By using the electronics already embodied in the mobile device, the cost of manufacture of the peripherals can be significantly reduced and alternative manufacturing approaches can. be taken for production and ease of use and portability. By way of example, (in this instance) , printed or embroidered circuits can be used to create a one or more dimensional sensing region that is flexible and light and could even be incorporated in articles of clothing. The portable host device incorporating the sense electronics could then communicate directly with the flexible or rigid circuits embedded in the peripheral, even if the embedded circuits were surrounded by fabric, plastics, glass or other materials.

These circuits may be combined with other inductive circuits to allow a variety of short-range communication techniques to be combined into a reduced number of circuits and components that would otherwise be the case if these alternative technologies were separately embodied in the host device or its peripherals. By way of example, it is possible to combine onto one or more structures the coils necessary for reconfigurable user interface sensing, pen input sensing, external peripheral sensing and uni- or bidirectional communications as well as possibly combining electrical circuits to drive these technologies with those required for resistive or capacitive touch sensing solutions. The uni- or bidirectional communications may be achieved by means of a number of near field communications protocols, for example A inductive communication, RFIDs, Bluetooth Zigbee (trademarks) (IEEE 802.15.4), WiBree and other short-range communication formats, as well as specific computer programming applications (e.g. Applets) that can be communicated to the mobile or fixed device by any of the commonly used digital data transfer mechanisms (email, text messaging, web download, pod- casting etc) . Implementation of these circuits, and in particular short-range inductive communications technology will have the added benefit of removing costly and delicate connectors from the mobile host devices and facilitating easy docking with stations without the need for precise location. These circuits may also be combined with other inductive circuits to allow inductive charging or powering of the device. Various forms of overlay and arrangements in accordance with the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a block diagram showing the basic elements of a position sensor employed in the arrangement according to GB 2,374,424 which may be employed in the present invention;

Figure 2A to 2C are schematic views of transmit and receive windings that may be used in the transmit and receive aerials of an inductive position sensor employed in the electronic device used in the arrangement according to the invention,-

Figure 3 is a more detailed block diagram explaining the operation of the position^' sensor shown in figure 1;

Figure 4 is a schematic plan view of the tracks of ■ a two-dimensional inductive position sensor that may be employed in the electronic device;

Figure 5 is a perspective view of an electronic device without an overlay thereon and showing the area of the inductive sensor;

Figures 6A and 6B are perspective views of the device of figure 5 showing one overlay being positioned thereon; Figures 7 to 9 show other forms of overlay for the electronic device;

Figure 10 shows an overlay positioned on the device in the form of a keypad;

Figure 11 is an enlarged schematic view of part of the overlay and device of figure 10 showing connections for the keys ;

Figures 12 to 14 are schematic diagrams showing further forms of overlay; and

Figure 15 is a view of the electronic device and overlay located in a peripheral station.

Referring to the accompanying drawings , the principle of operation of an inductive position sensor that may be employed in an electronic device such as a cellular telephone, PDA, laptop or the like is shown in figures 1 to 3.

In order to detect the position of an intermediate coupler in one direction, a control unit includes a quadrature ^' signal generator 31 which generates an in-phase signal I(t) and a quadrature signal Q(t) at respective different outputs. The in- phase signal I(t) is generated by amplitude modulating an oscillating carrier signal having a carrier frequency f_0/ which in this embodiment is 2MHz, using a first modulation signal which oscillates at a modulation frequency f_α, which in this embodiment is 3.9kHz. The in-phase signal I(t) is therefore of the form:

Similarly, the quadrature signal Q(t) is generated by amplitude modulating the oscillating carrier signal having carrier frequency f₀ using a second modulation signal which oscillates at the modulation frequency Jf₁, with the second modulation signal being π/2 radians (90°) out of phase with the first modulation signal. The quadrature signal Q(t) is therefore of the form:

Q(t) = AcoslπfjcoslTfJ _{( 2 )}

The in-phase signal I(t) is applied to a sine coil 37 and the quadrature signal Q(t) is applied to the cosine coil 39. The sine coil 37 is formed in a pattern which causes current flowing through the sine coil 37 to produce a first magnetic field B₁ whose field strength component resolved perpendicular to the PCB forming the sensor pad 20 varies sinusoidally along the measurement direction in accordance with the function:

B₁ = £sin(²^

(3) where L is the period of the sine coil in the x direction.

Similarly, the cosine coil 39 is formed in a pattern which causes current flowing through the cosine coil 39 to produce a second magnetic field B₂ whose field strength component resolved perpendicular to the sensor pad 20 also varies sinusoidally along the measurement direction, but with a phase difference of π/2 radians (90°) from the phase of the first magnetic field B₁, giving:

B₂ = Bcos(²^)

(4)

In this way, the total magnetic field B_τ generated at any position along the measurement direction will be formed by a first component from the first magnetic field B₁ and a second component from the second magnetic field B₂, with the magnitudes of the first and second components resolved perpendicular to the sensor pad 20 varying along the measurement direction.

By applying the in-phase signal I(t) and the quadrature signal Q(t) to the sine coil 37 and the cosine coil 39 respectively, the generated total magnetic field component B_τ resolved perpendicular to the sensor pad 20 oscillates at the carrier frequency f₀ in accordance with an amplitude envelope function which varies at the modulation frequency f_lr with the phase of the amplitude envelope function varying along the measurement direction. Thus:

(5) In effect, the phase of the amplitude envelope function rotates along the measurement direction.

A sensor element 40 whose position along the measurement direction is to be sensed may include a passive resonant circuit having a resonant frequency substantially equal to the carrier frequency f₀. The total magnetic field component B_τ therefore induces an electric signal in the resonant circuit which oscillates at the carrier frequency f₀ and has an amplitude which is modulated at the modulation frequency f₁ with a phase which is dependent upon the position of the sensor element 40 along the measurement direction. The electric signal induced in the resonant circuit in turn generates a magnetic field which induces a sensed electric signal S(t) in the sense coil 41, with the sensed electric signal S(t) oscillating at the carrier frequency f₀. The amplitude of the sensed signal S(t) is also modulated at the modulation frequency f_x with a phase which is dependent upon the position of the sensor element 40 along the measurement direction. The sensed signal S(t) is input to a phase detector 43 which demodulates the sensed signal S(t), to remove the component at the carrier frequency f₀, and detects the phase of the remaining amplitude envelope function relative to the excitation waveform. The phase detector 43 then outputs a phase signal P(t) representative of the detected phase to a position calculator 45, which converts the detected phase into a corresponding position value and outputs a drive signal to the display 45, for example provided by the screen 4 of the device, to display the corresponding position value . By using a carrier frequency f₀ which is greater than the modulation frequency f_lr the inductive coupling is performed at frequencies away from low- frequency noise sources such as the electric mains at 50/60 Hz, while the signal processing can still be performed at a relatively low frequency which is better suited to digital processing. Further, increasing the carrier frequency f₀ facilitates making the sensor element 40 small, which is a significant advantage in many applications. Increasing the carrier frequency f₀ also produces higher signal strengths .

As shown in Figure 2A, the sine coil 37 is formed by a conductive track which generally extends around the periphery of the PCB forming the inductive position detector apart from a cross-over point halfway along the PCB in the measurement direction, at which the conductive track on each widthwise edge of the PCB crosses to the corresponding opposing widthwise edge of the PCB. In this way, effectively a first current loop 21a and a second current loop 21b are formed. When a signal is applied to the sine coil 37, current flows around the first current loop 21a and the second current loop 21b in opposite directions, and therefore the current flowing around the first current loop 21a generates a magnetic field which has an opposite polarity to the magnetic field generated by current flowing around the second current loop 21b. This results in the sinusoidal variation of the field strength of the component of the first magnetic field B₁ resolved perpendicular to the PCB given by equation 3 above.

In particular, the lay-out of the sine coil 37 is such that the field strength of the component of the first magnetic field B₁ resolved perpendicular to the PCB which is generated by current flowing through the sine coil 37 varies along the measurement direction from approximately zero at the point where x equals 0 , to a maximum value at x equals L/4 (the position A as shown in Figure 3A) , then back to zero at x equals L/2 (the position C as shown in Figure 3A) , then to a maximum value (having opposite polarity to the maximum value at position A) at x equals 3L/4, and then back to zero at x equals L. Thus the sine coil 37 generates a magnetic field component perpendicular to the PCB which, varies according to one period of the sine function.

As shown in Figure 2B, the cosine coil 39 is formed by a conductive track which generally extends around the periphery of the PCB apart from two cross- over points, located one-quarter and three-quarters of the way along the PCB in the measurement direction respectively. In this way, three loops 39a, 39b and 39c are formed of which the outer loops 39a and 39c are half the size of the inner loop 39b. When a signal is applied to the cosine coil 39, current flows in one direction around the outer loops 39a and 39c and in the opposite direction around the inner loop 23b. The magnetic field generated by the current flowing around the inner loop 39b has an opposite polarity to the magnetic field generated by the current flowing around the outer loops 39a and 39c. This results in the sinusoidal variation of the field strength of the component of the second magnetic field B₂ resolved perpendicular to the PCB given by equation 4 above .

In particular, the lay-out of the cosine coil 39 is such that the field strength of the component of the second magnetic field B₂ resolved perpendicular to the PCB which is generated by current flowing through the cosine coil 39 varies along the measurement direction from a maximum value at x equals 0, to zero at x equals L/4 (the position A as shown in Figure 6B) , then back to a maximum value (having opposite polarity to the maximum value at x equals 0) at x equals L/2 (the position C as shown in Figure 6B) , and then back to zero at x equals 3L/4, and then back to a maximum value (having the same polarity as the maximum value at x equals 0) at x equals L. Thus, the cosine coil 7 generates a magnetic field component perpendicular to the PCB 5 which varies according to one period of the cosine function as given by equation 4 above .

As shown in Figure 2C, the sense coil 41 is formed by a conductive track which generally extends around the periphery of the PCB forming a single loop.

The layout of the sine coil 37 is such that the electric current induced in the sense coil 41 by current flowing around the first current loop 37a is substantially cancelled out by the electric current induced in the sense coil 41 by current flowing around the second current loop 37b. Similarly, for the cosine coil 39 the current induced in the sense coil 41 by the outer loops 39a, 39c is cancelled out by the current induced in the sense coil 11 by the inner loop 39b.

As shown in Figure 3, the processing circuitry used to generate the in-phase signal I(t) and the quadrature signal Q(t) consists of a microprocessor 31, digital components 61, analogue driving circuitry 81 and analogue signal processing components 91.

The microprocessor 31 includes a first square wave oscillator 33 which generates a square wave signal at twice the carrier frequency f₀ (i.e. at 4 MHz) . This square wave signal is output from the microprocessor 31 to a quadrature divider unit 63 which divides the square wave signal by two and forms an in-phase digital carrier signal +1 at the carrier frequency, an anti-phase digital carrier signal -I at the carrier frequency and a quadrature digital carrier signal +Q, also at the carrier frequency. As described hereafter, the quadrature digital carrier signal +Q is modulated to form the drive signals applied to the sine coil 37 and the cosine coil 39, while the in-phase and anti-phase digital carrier signals +1 are used to perform synchronous detection in order to demodulate the sensed signal S(t) .

The microprocessor 31 also includes a second square wave oscillator 35 which outputs a modulation synchronisation signal MOD_SYNC at the modulation frequency U₁ to provide a reference timing. The modulation synchronisation signal MOD_SYNC is input to a Pulse Width Modulation (PWM) type pattern generator 47 which generates digital data streams at 2MHz representative of the modulation signals at the modulation frequency f_lf i.e. 3.9 kHz. In particular, the PWM type pattern generator 47 generates two modulation signals which are in phase quadrature with one another, namely a cosine signal COS and either a plus sine or a minus sine signal +SIN in dependence upon whether the in-phase signal I(t) or the antiphase signal T(t) is to be generated.

The cosine signal COS is output by the microprocessor 31 and applied to a first digital mixer

65, in this embodiment a NOR gate, which mixes the cosine signal with the quadrature digital carrier signal, +Q, to generate a digital representation of the quadrature signal Q(t) . The sine signal ±SIN is output by the microprocessor and applied to a second digital mixer 67, in this embodiment a NOR gate, together with the quadrature digital carrier signal +Q to generate a digital representation of either the in- phase signal I(t) or the anti-phase signal I(t) . The digital signals output from the first and second digital mixers 65, 67 are input to first and second coil driver circuits 83, 85 respectively and the amplified signals output by the coil drivers 83, 85 are then applied to the cosine coil 39 and sine coil 37 respectively. The digital generation of the drive signals applied to the sine coil 37 and the cosine coil 39 introduces high frequency harmonic noise. However, the coil drivers 65, 67 remove some of this high frequency harmonic noise, as does the frequency response characteristics of the cosine and sine coils 37, 39. Furthermore, the resonant circuit within the sensor element 1 will not respond to signals which are greatly above the resonant frequency^' and therefore the resonant circuit will also filter out a portion of the unwanted high frequency harmonic noise.

As discussed above, the signals applied to the sine coil 37 and the cosine coil 39 induce an electric signal in the resonant circuit of the sensor element 40 which in turn induces the sensed signal S(t) in the sense coil 41. The sensed signal S(t) is passed through the analogue signal processing components 91. In particular, the sensed signal S(t) is initially passed through a high pass filter amplifier 93 which both amplifies the received signal, and removes low frequency noise {e.g. from a 50 Hertz mains electricity supply device) and any DC offset. The amplified signal output from the high pass filter 93 is then input to a crossover analogue switch 95 which performs synchronous detection at the carrier frequency of 2 MHz, using the in-phase and anti-phase square wave carrier signals +1 generated by the quadrature divider 21. The in-phase and anti-phase digital carrier signals which are 90 degrees out of phase to the quadrature digital carrier signal +Q used to generate the drive signals applied to the sine coil 37 and the cosine coil 39, which are used for the synchronous detection, because, as discussed above, the resonant circuit of the sensor element 1 introduces a substantially 90 degrees phase shift to the carrier signal.

The signal output from the crossover analogue switch 95 substantially corresponds to a fully rectified version of the signal input to the crossover analogue switch 95 (i.e. with the negative voltage troughs in the signal folded over the zero voltage line to form voltage peaks lying between the original voltage peaks) . This rectified signal is then passed through a low pass filter amplifier 97 which essentially produces a time-averaged or smoothed signal having a DC component and a component at the modulation frequency f₁. The DC component appears as a result of the rectification performed by the synchronous detection process . The signal output from the low pass filter amplifier 97 is then input to a band-pass filter amplifier 99, centred at the modulation frequency f_x, which removes the DC component. The signal output from the bandpass filter amplifier 99 is input to a comparator 101 which converts the input signal to a square wave signal whose timing is compared with the timing of the modulation synchronisation signal MOD_SYNC to determine the position of the sensor element 40. In this way, it is possible to detect the position of a sensor element formed from a resonant circuit in one direction. If a pair of sine and cosine coils are used so that one sine and cosine coil extend in one direction, and another sine and cosine coil extend in an orthogonal direction, it is possible to determine the position of the resonant circuit in the two orthogonal directions . Figure 4 shows an example of a transmit aerial that may be used in an electronic device having a two-dimensional sensor. The aerial comprises one sine coil 37x that extends over the horizontal dimension of the sensor pad 20 and a cosine coil 39x that also extends over the horizontal dimension of the pad and is superposed on the sine coil. In addition, a sine coil 37y and a cosine coil 39y are also present in order to monitor the vertical position of the sensor element. A single sense coil 41 that extends around the periphery of the sine and cosine coils may be present, or alternatively, separate sense coils 41 may be employed for measurement in each of the horizontal and vertical directions .

Also, although the arrangement has been described with reference to the use of a sine and cosine transmit coil and detection of the phase of the received signal in the receive coil by means of the phase detector 43, other forms of arrangement may be used. For example, a single transmit coil may be employed together with a receive aerial having balanced sine and cosine receive coils. In such a system, the phase difference in the receive coils may be detected, or the relative amplitude of the received signal in the two receive coils may be determined. Other forms of coil may alternatively be employed. Figure 5 shows a typical electronic device 1 in which an inductive sensor may be employed. This device has a general housing including a screen 2 and an area 3 in which a two-dimensional inductive sensor of the type described above is located. The screen 2 may be a conventional liquid crystal screen which may include a capacitive touch screen functionality so that options displayed on the screen may be selected by pointing a finger or stylus to the screen, or alternatively it may include an inductive sensor, which may be the same as that associated with area 3 or different, so that options displayed on the screen may be selected by means of a stylus that forms an intermediate coupler between transmit coils and sense coils arranged around the screen, for example as described in international patent application No. PCTGB2007/001680.

As shown in figure 5, the electronic device has no user input means. These may be provided by locating an overlay 4 (sometimes called a "skin") on the device over the inductive sensor area 3 by sliding it on as shown in figure 6A until the overlay clicks in place as shown in figure 6B. This overlay is in the form of a flexible inductive sensor 4a as described in U.S. Patent application No. 2006/0232269 that is formed in a circle so that the device can detect the angular position of pressure thereon about its centre by the user, for example in order to select different pieces of music that are stored in memory in the electronic device. The music can be selected by manually pressing against the sensor 4a and rotating the user's digit until the correct item has been found, and then the sensor can be pressed again in order to play the music. A rotatable knob 4b may be provided for example to adjust the volume of the music played. The software to perform these functions is conventional, and may be provided in the electronic device or may be purchased or downloaded when the overlay 4 is purchased. As can be seen, the functionality of the device has been reduced to that of selecting music by virtue of the overlay that has been selected. If it is desired to use the device for a different purpose, then it is simple to install a different overlay.

Figures 7 to 9 show a number of alternative overlays that may be provided for the electronic device. Apart from the music overlay, an audio-visual overlay 6 is shown. This overlay has buttons 7 to select different film clips etc. and buttons 8 to play, stop, pause, rewind and fast forward the film. In addition, a slider 9 can vary the volume of the playback. Each of the user input devices (the buttons 7, 8 and the slider 9) will be associated with an intermediate coupler, one of which may be in the form of a ferromagnetic material, and the remaining ones in the form of passive resonant circuits, although preferably all the intermediate couplers will be passive resonant circuits. Each of the intermediate couplers (in the case of passive resonant circuits) will have a resonant frequency that is different from that of the other intermediate couplers so that the electronics of the device can distinguish which input is being manipulated by the user. The inputs 7 and 8 are all in the form of buttons, and so it is possible for the device to detect movement (depression of the buttons) by detecting the change in signal strength as the intermediate coupler moves nearer to the sensor. However, this is not necessarily particularly sensitive, and it is usually preferred for depression of the button to be determined by a change in the resonant frequency of the intermediate coupler, for example by including a mechanical switch in the buttons that will create the resonant circuit by- closing or destroy it by opening, or by switching in additional capacitances in order to change the resonant frequency. Manipulation of the slider 9 to alter the volume of playback will alter the position of the intermediate coupler in the plane of the sensor, and this may be detected and processed by appropriate software. Other forms of overlay 4 are also shown in figure

9, one of which is a standard numeric keypad 10 for use with a cellular telephone, including numbers 0 to 9, off and on, and other symbols. Another overlay shown in figure 7 may be in the form of a games overlay that includes a wheel interface for steering a vehicle and buttons for altering its speed. Of course, many other forms of overlay may be produced depending on the particular application. Each of the overlays will be provided with its own identification device (not shown) , for example an RFID device or barcode, or a static intermediate coupler for receiving a signal transmitted by the transmit aerial of the device and sending its signal to the receive aerial, in which the particular overlay is identified by the position of the identification coupler with respect to the sensor of the device and/or the resonant frequency of the coupler.

With the types of overlay shown in figures 6 to 9, the overlays are generally of the same size as the sensor of the electronic device. Figure 10 shows an overlay in the form of a full-size QWERTY keyboard 13 that can be attached to the device 1 to enable the user to type, and to read the data input on the screen 2. Figure 11 is an enlarged schematic view of part of the keyboard 13 and device 1 of figure 10 showing how it functions. In this keyboard, a number of passive resonant circuits 15, 16, 17 and 18 are provided, only four of which are shown for the sake of clarity. Each resonant circuit is formed from a coil 20 or 21, normally having a number of turns (although only a single turn is shown) forming an inductance and optionally formed around a high permeability material 20a or 21a. The ends of the coils are closed by a capacitor 22 or 23, and the resonant circuit contains a number of switches 24, each of which is located at a key 14 and will be closed if the key is depressed. Each resonant circuit is associated with a single row or a single column of keys 14 of the keyboard, and the number of switches 24 in the passive resonant circuit corresponds to the number of rows or columns associated with that resonant circuit. Each resonant circuit has a different resonant frequency, or at least resonant circuits associated with columns have a different resonant frequency from resonant circuits associated with rows, so that they can be identified by the device 1. In this manner, depression of a single key 14 of the keyboard will close a switch 24 in two of the resonant circuits 15, 16, 17 and 18 , thereby completing those resonant circuits and allowing identification of the key 14 that has been depressed.

It is possible for keys to be associated with more than two resonant circuits if desired in order to reduce the number of different resonant frequencies required. For example, an array of approximately 120 keys would require 24 different resonant frequencies if the resonant circuits were arranged in a two- dimensional array of 7 rows x 17 columns (119 circuits) or 22 different resonant frequencies if they were arranged in a two-dimensional array of 10 rows x 12 columns (120 circuits) . If, however, each key were associated with three resonant circuits, 125 keys could be arranged in a 5 x 5 x 5 array, requiring only 15 different resonant frequencies. Also, in some circumstances, it is possible to combine the position of the resonant circuit with different resonant frequencies to identify a key.

Many other designs of overlay are of course possible. Figure 12 shows an overlay which is suitable for the special needs market such as the elderly where large clear buttons are needed, or for children where parental control is required by allowing the parent to limit the function of the telephone. Figure 13 shows another form of overlay which includes a rotary dial or a joystick/thumb-pad to allow a menu-driven input via the telephone's screen. Figure 14 shows an overlay which includes a fold-out membrane that can be used to program an address book into the telephone. In this instance the user writes the name onto the space available. The user only needs to press the appropriate button/zone on the fold-out membrane to dial that particular number. The idea can be extended not just for an address book, but also for web pages or games where pressing particular buttons/zones activates that particular function.

In addition to the cooperation of the overlays or skins with the electronic device, the invention may include a system in which the electronic device and optionally the overlay may be associated with a peripheral station or device in order to support various operations. A peripheral station 26 is shown in figure 15 together with an electronic device and overlay. The peripheral station, which may be powered, for example by mains electricity, may include an induction coil 28 that can cooperate with a corresponding coil in the electronic device 1, in order to charge the battery (ies) of the device. The coil in the electronic device that is used to charge the battery may either be a separate coil or one of the coils used for sensing the intermediate coupler or otherwise located in the position of the screen. Similarly, the coil present in the peripheral station that is used to charge the device battery may also be used to communicate with the electronic device. As shown in the figure, in which the electronic device is provided with a music overlay, the coil in the peripheral station may be used for communication with the electronic device, in order to receive the music that is being played, to amplify it, and to play it back through speakers at higher volume than is possible with the electronic device on its own. Different forms of peripheral station are also possible. For example, if the electronic device has an audiovisual overlay, and is playing back a film clip, it is possible for the film clip to be played back using the peripheral station, provided it has a screen, and/or a projector. In this way, the electronic device may be employed as a portable device, and yet may be combined with a powered station in order to provide a more powerful rendition of the clip. The advantages can be used with other overlays. For example, with a mobile telephone overlay, a peripheral station may be employed as a speaker telephone, or if the overlay is a games overlay, the peripheral station may be employed to enhance the sound or visual output of the game.

In addition to communicating with the electronic device either uni- or bi-directionally, preferably in a secure manner, the peripheral station may communicate with other objects or devices, and especially by a wired connection e.g. when the peripheral station is used for a financial transaction. One form of short distance communication is that employing the so-called Bluetooth protocols

(IEEE 802.15.1) which is a short range electromagnetic communications technology. Due to its relatively long-range communications ability, security of data transfer has always been of significant concern to implementers and designers alike. If the inductive circuits required for any of the above functionality are incorporated in the electronic device, then components of these circuits can be adapted or combined with the inductive coils and electronics necessary to communicate wirelessly and securely over short distances (less than one metre) with an external peripheral station by near field communication (NFC) in order, for example, to allow money payments to be made. Components of this inductive sensing technology can thus be used to replace or augment the capabilities of Bluetooth, WiBree or any other short range communications technology.

Further modifications of the invention may include joysticks, media navigation etc but in formats that are reconfigurable dependent on the overlay used. They may be larger than the electronic device for example for use by persons with limited sight or movement, child-friendly, suitable for in-car use, for use in hazardous environments, under water, usable in the kitchen, or elsewhere. They may be specific to gaming or audio visual processes. The detachable overlays may be used as platforms to convert motion of objects or fingers into specific instructions for an interactive computer game whether being played on-line or on the host device or for controlling the sounds and visions associated with, audio or audio-visual filed. They may be of two basic types: (a) high performance, function specific input devices such as keypads, keyboards, single or multiple joysticks, trackballs or virtual reality hand-motion/gripping devices, or (b) game-boards in which intermediate couplers are embedded in gaming pieces and their identity, location and motion is translated into game- specific messages to generate a game function.

Claims

Claims :

1. An overlay for an electronics device that includes a sensor and electronics that operate in response to input from the sensor, the overlay comprising an identification arrangement for enabling which of a number of overlays has been positioned on the device, a manually operable input device, and an intermediate coupler, the intermediate coupler being associated with the input device so that operation of the input device by a user will change a property of the intermediate coupler, which change will, in operation, be sensed by the sensor to actuate a function of the device.

2. An overlay as claimed in claim 1, wherein the intermediate coupler is electrically passive.

3. An overlay as claimed in claim 1, wherein the sensor is a capacitive sensor, and the intermediate coupler comprises an electrically conductive element whose position will be sensed by the sensor in operation.

4. An overlay as claimed in claim 1 , wherein the sensor is a Hall effect device, and the intermediate coupler comprises a magnet.

5. An overlay as claimed in claim 1 , wherein the sensor is an optical sensor, and the intermediate coupler comprises an optical reflector.

6. An overlay as claimed in claim 1 , wherein the sensor is a magneto-resistive sensor, and the intermediate coupler comprises a magnet.

7. An overlay as claimed in claim 1 , wherein the sensor is an inductive sensor, and the intermediate coupler comprises a passive resonant circuit, a ferromagnetic element or an electrically conductive element .

8. An overlay as claimed in claim 7 , wherein the intermediate coupler comprises a passive resonant circuit .

9. An overlay as claimed in any one of claims 1 to 8 , wherein manipulation of the input device by a user will change the position of the intermediate coupler.

10. An overlay as claimed in claim 9, wherein manipulation of the input device will change the position of the intermediate coupler in a direction toward, or away from, the sensor.

11. An overlay as claimed in claim 9, wherein manipulation of the input device by a user will change the position of the intermediate coupler in at least one direction along which the sensor extends .

12. An overlay as claimed in claim 9, wherein the input device is in the form of a slider.

13. An overlay as claimed in claim 9, wherein manipulation of the input device will cause the intermediate coupler to move in a circular path or will change the orientation thereof .

14. An overlay as claimed in claim 9, wherein manipulation of the input device will cause the intermediate coupler to tilt.

15. An overlay as claimed in claim 9, wherein the input device is in the form of a joystick or trackball.

16. An overlay as claimed in any one of claims 1 to 15, wherein the intermediate coupler does not contact the sensor

17. An overlay as claimed in claim 8 , wherein operation of the input device will create or remove resonance of the resonant circuit.

18. An overlay as claimed in claim 8, wherein operation of the input device will change a characteristic of the resonant circuit.

19. An overlay as claimed in claim 18, wherein the characteristic of the resonant circuit is its resonant frequency, its quality (Q) value, the amplitude of the sensed signal or the phase of the sensed signal.

20. An overlay as claimed in any one of claims 1 to 19, which includes a plurality of input devices.

21. An overlay as claimed in claim 20, wherein the or at least some of the input devices are in the form of keys .

22. An overlay as claimed in claim 20 or claim 21, which includes a plurality of intermediate couplers in the form of passive resonant circuits, and each input device is associated with at least one intermediate coupler .

23. An overlay as claimed in any one of claims 20 to

22, which includes a two-dimensional array of input devices, and groups of input devices are associated with separate intermediate couplers .

24. An overlay as claimed in any one of claims 19 to

23, wherein each input device is mechanically connected to a switch for creating or removing resonance of at least one intermediate coupler associated therewith or for altering its resonant frequency.

25. An overlay as claimed in any one of claims 19 to

24, which, includes a plurality of intermediate couplers in the form of passive resonant circuits having different resonant frequencies.

26. An overlay as claimed in any one of claims 19 to 25 wherein the input devices are in the form of keys forming a keypad, and the intermediate couplers extend in the plane of the keypad from^' positions corresponding to the keys to a smaller area that enables the intermediate couplers to be sensed by the sensor of the electronics device.

27. An overlay as claimed in any one of claims 1 to 26, wherein the identification arrangement is in the form of a mechanical keying profile, a radio frequency identification (RFID) device, at least one intermediate coupler whose position or frequency of coupling identifies the overlay, or a barcode.

28. An electronics arrangement, which comprises an electronic device that includes a sensor and electronics that operate in response to input from the sensor, and an overlay as claimed in any one of claims 1 to 27 positioned on the device so that operation of the input device by a user will be sensed by the device.

29. An arrangement as claimed in claim 28, wherein the electronics device includes a screen, at least part of which is not obscured by the overlay.

30. An arrangement as claimed in claim 28 or claim 29, wherein the sensor is an inductive sensor which comprises a transmit aerial for transmitting a signal, and a receive aerial in which a received signal that originates from the signal transmitted by the transmit aerial and sent from the transmit aerial to the receive aerial via the intermediate coupler is induced.

31. An arrangement as claimed in claim 30, wherein the sensor is a two-dimensional sensor and has a transmit aerial and/or a receive aerial arranged in each of two orthogonal directions.

32 An arrangement as claimed in any one of claims 28 to 31, wherein the electronics device is a cellular telephone, a personal digital assistant (PDA) , a laptop computer or a tablet computer.

33. An arrangement as claimed in claim 29, wherein the device includes an inductive sensor associated with the screen to allow actuation by means of a stylus.

34. An arrangement^' as claimed in claim 29, which includes a touch screen.

35. A system which comprises an arrangement as claimed in any one of claims 28 to 34, and a peripheral station that can communicate with the device in a single direction or in two directions by means of an inductive sensor .

36. A system as claimed in claim 35, wherein the device and the station are operative to communicate by near field communication.

37. A system as claimed in claim 35 or claim 36, wherein the station is operative to charge any battery of the arrangement inductively.