GB2409277A

GB2409277A - Finger mounted inductive digitiser input device with activation switch

Info

Publication number: GB2409277A
Application number: GB0329149A
Authority: GB
Inventors: Stephen Frank William Simmonds
Original assignee: Research Machines PLC
Current assignee: Research Machines PLC
Priority date: 2003-12-16
Filing date: 2003-12-16
Publication date: 2005-06-22
Anticipated expiration: 2023-12-16
Also published as: WO2005059734A3; GB2409277B; WO2005059734A2; GB0329149D0

Abstract

A passive input device 2 for use with a digitiser screen comprises a switch 10 and an inductive circuit which is only completed when the switch 10 is activated by pressing the device against the surface of the screen. The input device may be worn on a finger 6 (e.g. thimble 4) and the resonant circuit activated by the depression of a fingertip switch 10. A second switch (figures 4-7) may be provided to change the resonant frequency of the input device to increase functionality (e.g. menu selection). The device may also be provided in the form of a glove, pen or stylus. The device may be used with an on-screen keyboard and allows for rapid typing using two or more fingers by using one device on each finger as only the device in contact with the screen is activated.

Description

INPUT DEVICE FOR MULTIPLE USE WITH A

DIGITISING TABLET

This invention relates to an input device for multiple use with a digitising tablet, and in particular to an input device which can be worn on the finger of a user to facilitate typing on the screen of a digitising tablet.

A digitiser tablet, or graphic tablet, is a known input device comprising a screen on which graphical information, typically indicating available choices or options is displayed. A user can interact with the device usually by pointing at, or touching, the screen using a specialized pointing device such as a dedicated stylus or pen. Selection of an option presented graphically on the screen, can then be achieved by pointing at the region of the screen at which the option is displayed. Alternatively, graphics may be added to the screen by selecting a "draw" option and moving the pointer across the region of the screen where the graphics are to appear. In this way, lines, shapes, colours and text can be added to the screen.

An advantage of a user having a dedicated stylus or pen is that additional functionality can be built in to enhance the interaction of the stylus or pen with the digitiser screen. A digitiser tablet designed for use with a dedicated digitiser stylus is disclosed in US patent 4,878, 553.

The digitiser stylus described has a tuning or LC circuit, including a coil and a capacitor, designed to resonate with an electric field produced by the digitiser.

Underneath the digitiser screen on which the graphical information is presented, is a first and second plurality of loop-coils arranged in a side-by-side fashion respectively along the x and y directions of the screen. Each of the loop-coils is arranged so that, once activated by a clock pulse, it alternatively transmits and receives electromagnetic radiation. The clock pulses are supplied to respective ones of the loopcoils in turn, so that only one loop-coil is activated at a time. During the first half of a loop's activation, an alternating signal is applied to the loop causing it to produce an electric field which pervades into the space beyond the screen. If the digitiser stylus is in the vicinity, usually 3cm, of the electric field created by the activated loop, the tuning circuit of the input pen will be excited and will start to oscillate and a voltage will appear on the capacitor.

In the second half of the activation of the loop-coil, the coil is connected to a receiving circuit such that the electric wave from the loop-coil is quickly dissipated.

This dissipation is quicker than the associated attenuation of the oscillation induced in the LC circuit of the stylus.

As a result when the coil is put into the receiving mode, the loop-coil is set oscillating by the decaying electric

field emitted by the LC circuit of the stylus. A

measurement made of the voltage induced in the loop-coil indicates how close the stylus was to the loop-coil when it entered the receiving mode. By activating each of the loop- coils in turn, and comparing the detected voltage induced in the loop- coil by the decaying electric field of the stylus, the position of the pen above the screen can be accurately detected.

The stylus tuning circuit also has an additional capacitor which responds when the stylus is touched to the screen by changing the resonant frequency of the tuning circuit. The electrical oscillations from the stylus, at the default resonant frequency of the stylus tuning circuit (that is when the additional capacitor is not engaged) are continuously tracked by the digitiser screen such that a cursor on the screen can be made to follow the movements of the stylus. When the stylus is touched to the screen however, the variable capacitor is engaged, and the resulting change in the frequency of the electric field is detected by the digitiser as indicating a selection operation.

Personal computing devices which rely on this input method, such as personal digital assistants (PDAs), are well known. More recently, laptop sized personal computers, known as Tablet PCs have also been developed. These are provided with an on-screen keyboard function whereby a user can input text by selecting successive characters from a graphical keyboard.

While such devices do not require a traditional keyboard, and can therefore be more compact, typing on the graphical keyboard can be problematic. Typically, since only a single stylus is provided with the digitiser to operate the graphical keyboard, typing can only be achieved one key at a time, making typing slow. Furthermore, even if a second stylus is provided, the loop-coils of the digitiser detection circuit behind the screen can only track and detect one stylus at a time. This is because if two styli are provided, the electromagnetic wave provided by the decaying oscillation in the LC circuit from both styli compete, and only the strongest signal is tracked. As a result, typing quickly with two styli can be impossible, as the strongest signal does not always come from the stylus indicating the next letter that the user wishes to type. If two styli are used, one must usually be withdrawn from the surface of the digitiser by about 3cm before the other stylus can be used.

We have therefore appreciated that there is a need for an improved input device that can be used with such tablet PCs.

The invention is defined by the independent claims to which reference should now be made. Advantageous features are set forth in the dependent claims.

An input device 2, of the passive type, is provided that allows for multiple use with digitisers such as those used in Tablet PCS. The device mechanism comprises a switch and an inductive circuit, which is only completed when the switch is activated. This allows for more than one device to be used in proximity to the surface of the digitiser. The device is intended to be worn on the finger of a user, and in a preferred embodiment, the device is implemented as a thimble. The device is ideally suited therefore for use with an on-screen keyboard, and allows for rapid typing using two or more fingers, by using one device on each finger.

A preferred embodiment of the invention will now be described in more detail, by way of example, and with reference to the drawings in which: Figure 1 is an elevation view of the first preferred embodiment of the invention; Figure 2 is a cross-sectional view of inductor circuitry in the embodiment shown in figure 1; Figure 3 is a simplified circuit diagram of the inductor circuit; Figure 4 is an elevation view of the invention in a second preferred embodiment; Figure 5 is a cross-sectional view of inductor circuitry in the embodiment shown in figure 4; Figures 6 and 7 are alternative embodiments of an inductive circuit for use in the embodiment of Figure 4.

Figure 1 shows an input device, according to the first embodiment of the invention, for use with a digitiser tablet of the type described above. The input device is of the passive circuit type, which means that it has a tuning or resonant circuit for reciprocating an electric field emitted by the digitizer. As a result, the input device does not need its own power source, although one could be provided for additional functions.

The device 2 comprises a receptacle 4 in which a finger 6 of the user can be securely received. Preferably the receptacle 4 is a non-slip, soft, plastic or rubber casing, much like a thimble. Mounted on the receptacle 4 is a circuit housing 8, containing a resonant circuit for receiving the electric field of the digitiser detection loop-coil. At the end of the circuit housing 8 is a switch 10, preferably a microswitch. Preferably, the switch should be of a non- slip and relatively soft material, such that it does not skid on the screen or damage the screen in use.

The housing 8 is supported in position on the receptacle 4 by a support section 12 located between the end of the receptacle at the tip of the finger and the end of the circuit housing on which the microswitch is provided.

The construction and operation of the passive circuit contained in the housing 8 will now be described in more detail with reference to Figures 2 and 3. Figure 2 shows a cross-section through the circuit housing 8. The circuit comprises a coiled wire 20, wound around a soft iron core 22 to produce an inductor 24. It will be appreciated that the soft iron core may be included in the device or omitted depending on the desired electrical characteristics. The microswitch 10 is electrically connected between one of the two terminals of the inductor wire 22, and a terminal of the capacitor 26. The opposite terminal of the capacitor 26 is electrically connected to the second terminal of the inductor 24, to form a circuit that can be broken or completed by opening or closing of the microswitch. The microswitch 10 comprises a housing 11 and an actuator or activator 28, which when depressed, closes the switch and completes the LO circuit.

In use, the microswitch 10 is arranged to be open unless pressure is applied to the activator 28 to close it.

In the open state, the circuit comprising the inductor 24 and the inductor 26 is not complete, and the passive circuit does not therefore oscillate in response to the electric field received from the loop-coils behind the screen of the digitiser tablet. As a result, the digitiser tablet is not able to detect the presence of the input device in the vicinity of the screen.

However, when a user pushes the input device 2 against the screen, at the location of the graphical representation of a key for example, the microswitch activator 28 is pushed into the microswitch body lo, closing the resonant circuit, and allowing it to oscillate at a resonant frequency determined by the inductance of inductor 24 and the capacitance of capacitor 26. The values of the capacitor and inductor are chosen so that the resonant frequency of the closed resonant circuit corresponds to the selection frequency of the digitiser tablet. This allows the touching of the input device on the graphical representation of the keyboard to simulate a key press.

The inductor 24 is positioned within the housing 8 such that it points towards the end of the device. This ensures that when the circuit is completed, the digitizer responds in the way expected if a conventional stylus were to be used for example.

The activator of the microswitch is biased to its open position, so that once the user moves the input device away from the screen, the circuit is broken and the passive circuit is prevented from oscillating with the electric field emitted by the screen loop-coil. In this way, the input device 4 is configured to present a signal to the screen detection circuit only when it is in contact with the screen, when the microswitch portion 20 is closed. This is in contrast to known stlyi, which continuously present a signal to so that a cursor can track the movement of the stylus across the digitiser screen.

This aspect of the preferred input device means that a user can wear one of the devices shown in Figure l on each finger, allowing him to type freely onto the digitizer screen, in the same way as if he were using a conventional keyboard. Furthermore, while the user is wearing the input device described, he is also free to use a stylus, allowing him to swap quickly and easily between input methods.

Although the device shown in Figure l has a receptacle 4 shaped like a thimble, any receptacle which allows the passive circuit housing 8 to be securely mounted on the user's finger could also be used. For example, the circuit housing 8 might be mounted on a ring or loop around the finger, or a number of input devices might be provided in a glove to be worn on one or more fingers of the hand, or indeed on the whole hand. Alternative embodiments might dispense with the receptacle 4 altogether. For example, the circuit housing could be detachably secured to the finger or finger tip of a user by a suitable adhesive. Depending on the level of miniaturization of the circuit housing 8 and microswitch lO, the input device could be provided on a chip secured to the finger tip of the user.

The preferred input device described above needs to be able to operate only in close proximity to the digitiser screen. As a result, it may be readily miniaturized for applications where it is mounted on a fingertip, or on fingertip of a glove or thimble. An inductor and switch only a few mm long mounted in this way, would give better directional accuracy between the device and the screen.

In one embodiment, several miniature inductors could be mounted in a group as separate tuned circuits, with activation depending on a single common microswitch. The microswitch could for example be implemented as an etched metal plate, which when depressed closes each of the circuits underneath. This kind of arrangement would allow the electric field to be strengthen and would allow for further miniaturization.

A second embodiment of the device will now be described with reference to Figures 4 and 5.

Figures 4 and 5 show an input device for wearing on a finger, similar to that shown in Figures 1 and 2. However, the input device shown in the second embodiment comprises a second microswitch 30 mounted higher on the circuit housing 8 than the microswitch 10 at its tip. The second microswitch has an actuator 32 which when closed engages a second capacitor 34 in the resonant circuit, as can be understood from Figures 6 and 7. When engaged, the second capacitor causes a change in the resonant frequency of the resonant circuit which can be detected by the digitiser tablet. As a result, additional functionality can be provided to the input device shown in Figure 1.

The second microswitch can be operated easily by the thumb when the input device is located on the index finger.

The thumb can be squeezed against the circuit housing 8 to activate the second microswitch in much the same way that a person might grip a pencil. A useful configuration of multiple input devices therefore would comprise an input device according to the second embodiment for wearing on the index finger, and one or more input devices according to the first embodiment worn on the other fingers. Of course, it is possible that the input device of the second embodiment could also be worn on more than one finger, including or excluding the index finger, as desired.

Preferably, the effect of activating the second microswitch is to change the frequency to one used by the digitiser tablet to indicate a 'second selection' or 'menu' function, much like the effect of the second mouse button.

This allows the input device to be used for typing as well as more sophisticated menu interaction. The circuit diagram for this arrangement is shown in Figure 6.

The second microswitch 30 may also, for example, switch the second capacitor into the circuit, such that the circuit is completed and the effect of the first microswitch lo is overridden. This arrangement is shown in Figure 7.

This could be used to allow the digitiser to track the input device's movement across the screen in the same way as for conventional styli. This would temporarily deactivate the typing facility of the input device, but would allow the input device to control a cursor for, say, a drawing function that has been selected from application software.

By making the switch 30 sensitive to pressure and by providing a variable capacitor in place of the capacitor 34, the thickness of a line drawn by a drawing tool could be varied according to the pressure exerted on the switch as it is pressed against the screen.

In a further embodiment the first microswitch lo is preferably mounted on a pressure sensitive capacitor. Thus the switch has an ON-OFF activation function as well as a pressure sensitive function. Preferably, activation of the second switch, disables or overrides the first microswitch lo, so that the device acts in the same way as known styli to control a cursor. Menu functions of the stylus could then be accessed by providing a third switch, or alternatively by depressing the pressure sensitive switch for about a second, as is known in the art.

In this respect therefore, the functionality provided by the second microswitch would allow the input device of Figures 4 and 5 to share similar functionality known styli, and be used in place of styli.

Although it is clearly preferred to mount the passive circuitry on the user's fingers so that normal typing is possible, the passive circuit arrangement described with reference to the first and second embodiments, could also be employed in a conventional pen or stylus design. Two such stylus devices could then be used together, allowing an improvement in typing speed, though not to the same extent as with multiple use of the devices shown in Figures 1 or 4.

Claims

Claims 1. An input device, of the passive circuit type, for use with a

digitiser tablet having a screen on which selectable graphical information can be displayed, the device comprising: a housing having a resonant circuit for reciprocating electric field oscillations from the digitiser tablet such that the resonant circuit can be detected by the digitiser tablet, and such that a selection can be made from the displayed graphical information; and a switch which in an open position breaks the resonant circuit, and which in a closed position completes the resonant circuit; the switch being biased to the open position; wherein the switch is mounted on the housing such that when a user presses the device against the screen the switch is closed.
2. An input device according to claim 1 comprising a second switch mounted on the housing, the second switch being arranged to change the resonant frequency of the resonant circuit.
3. An input device according to claim 1 comprising a second switch mounted on the housing, the second switch being arranged to override the first switch, and thereby complete the resonant circuit.
4. An input device according to claim 1 or 2 wherein the first or the second switch is pressure sensitive, and wherein pressure applied to the first or second switch changes the frequency of the resonant circuit accordingly.
5. An input device according to any of claims 2 to 4, wherein the input device is capable of being worn on the finger of a user, and the second switch is located on the housing for actuation by the thumb.
6. An input device according to any preceding claim, wherein the input device is capable of being worn on the finger of a user.
7. An input device according to claim 6, wherein the housing is mounted on a thimble for receiving a user's finger.
8. An input device according to claim 6, wherein the housing is mounted on a ring or loop for receiving a user's finger.
9. An input device according to claim 6, wherein the housing is provided with adhesive such that it can be releasably attached to the finger of a user.
10. A glove comprising one or more of the input devices according to any of claims 1 to 4.
11. An input device according to any preceding claim wherein the graphical information displayed on the screen presents a keyboard to the user, and the input device is adapted such that a user can type on the keyboard using two or more input devices.
12. An input device according to any preceding claim wherein the resonant circuit is tuned to oscillate at a default frequency for indicating to the digitiser tablet that a selection is being made.
13. A stylus comprising the input device of any of claims 1 to 4.
14. An input device according substantially as described herein and with reference to the drawings.