GB2436135A

GB2436135A - Touch sensitive cursor control

Info

Publication number: GB2436135A
Application number: GB0616340A
Authority: GB
Inventors: David Peter Gilbert
Original assignee: PRETORIAN TECHNOLOGIES Ltd
Current assignee: PRETORIAN TECHNOLOGIES Ltd
Priority date: 2006-03-09
Filing date: 2006-08-17
Publication date: 2007-09-19
Anticipated expiration: 2026-08-17
Also published as: GB2436135B; GB0604742D0; GB0616340D0

Abstract

Apparatus for controlling movement of a cursor on a display screen comprises a touch sensitive device interacting with electronic circuitry arranged to move the cursor in a direction determined by the angular position at which the device is touched and for a distance determined by the length of time for which the device is touched, or the cursor is controlled by an algorithm whereby the speed increases over time during each touch event, and whereby the speed at the start of each touch event increases in proportion to the time interval since the previous touch event. The touch sensitive device can be an annular ring or other loop shape of capacitive segment elements (15, fig 2) surrounding a 'select' button (13) and an inner region (12) which is not touch sensitive. Look up tables may be used to convert Polar coordinates to Cartesian, and a user may choose an acceleration curve (fig 4c). In an embodiment the touch elements are a keypad of a mobile phone or music player, and alphabetic characters may also be produced. Thus both cursor repositioning and fine control are possible.

Description

USER IN PUT DEVICE FOR ELECTRONIC EQUIPMENT

Field of the Invention

This invention relates to apparatus for controlling the movement of a cur-sor on a display screen, to user input device for electronic equipment, and to electronic equipment incorporating such a device.

Background to the Invention

Cursor controlling devices (often referred to as pointing devices) such as mice, trackballs, joysticks and touch pads are ubiquitous in modern computer systems and, although different types of pointing device function in different ways, all require multiple degrees of freedom to correctly control a cursor.

For example, the direction in which a mouse body is moved imparts the direction in which the cursor moves, the speed at which the mouse body is moved imparts cursor speed information and duration of mouse body travel im-parts cursor movement duration. That is to say, there are three independent degrees of freedom. In this instance, cursor movement exactly mirrors physical mouse movement which at first sight may be viewed as highly ergonomic.

However, when a mouse is used by operators with limited motor or cog-nitive skills or with poor hand-eye coordination, the conventional mouse may present serious operational difficulties. Those with motor skills difficulties and poor hand-eye coordination may experience problems moving the mouse body in such a way as to control all three degrees of freedom. Those with cognitive skills difficulties may have difficulties understanding how to control all three de-grees of freedom simultaneously.

A further widely used type of pointing device is a joystick. Similarly, this has three degrees of freedom, viz: directional information which imparts the di-rection of cursor movement, displacement from central position which imparts the speed of cursor movement and duration of displacement from central posi-tion which imparts duration of cursor movement.

It is an object of this invention to reduce the number of degrees of free-dom in a cursor control device to just two, thereby greatly simplifying cursor control. This has immediate application to computer users with the aforemen- tioned difficulties but is equally suitable for users who do not have such difficul-ties.

US-A-4 736 191 discloses a touch pad in the form of a ring of touch sen-sitive elements, the position of the user's finger on the pad being translated into X-Y co-ordinates, movement of the cursor being determined from the change in these co-ordinates.

Other touch-pad arrangements are disclosed in US-A-4 862 215, US-A-5 327 161, US-A-5 508 719 and US-A-5 856 822.

Summary of the Invention

According to one aspect of the invention, apparatus for controlling the movement of a cursor on a display screen comprises a touch sensitive device which is a ring formed of a plurality of touch sensitive segment elements, said touch sensitive segment elements interacting with electronic circuitry arranged to move the cursor in a direction determined by the angular position at which the device is touched and for a distance determined by the length of time for which the device is touched.

Preferably the ring is an annular ring surrounding an inner region which is not touch sensitive.

It will be appreciated that, while the touch sensitive surface is conven-iently arranged as a circle, other configurations are possible, such as ovals, or other non-circular loops, squares, rectangles, triangles, or indeed any polygonal structure, and the references herein to "ring" encompass all such shapes.

Brief Description of the Drawings

In the drawings, which illustrate exemplary embodiments of the invention: Figure 1 shows the general scheme of an embodiment of this invention; Figure 2 is a diagram of the touch sensitive sensor element in more de-tail; Figure 3 is a block diagram of the device; Figure 4a is a graph illustrating a simple speed transfer function; Figure 4b is a graph illustrating a speed transfer function with constant starting speed; Figure 4c is a graph illustrating user selectable speed transfer function; Figure 5 is a block diagram of the speed demand process; Figure 6 is a graph illustrating typical speed demand output for a multi-plicity of consecutive touch events using the speed transfer function of Figure 4a; Figure 7 is a block diagram of the speed demand process according to an alternative embodiment of the invention; and Figure 8 is a graph illustrating the speed demand output for a multiplicity of consecutive touch events using the speed demand process of Figure 7.

Detailed Description of the Illustrated Embodiments to Referring first to Figure 1, an annular ring 11 is constructed in such a way as to be sensitive to the touch of a finger, and associated electronics which are able to determine the angle at which the annular ring is touched, relative to a known datum, control the movement of a cursor on a display screen.

Information from the annular ring 11 is processed by the associated elec-tronics and relevant data passed to a host computer, whereupon movement of the cursor takes place at the said angle for such period as the annular ring re-mains touched. Cursor movement ceases when the finger is removed from said annular ring.

The speed at which the cursor moves may be determined by the associ-ated electronics in a number of ways according to factors of personal prefer-ence, ergonomics, productivity and the like. For example, it may simply move at a constant speed, or have some form of ballistic acceleration such that the speed of the cursor increases with the duration for which the ring remains touched. Alternatively there may be provided a separate speed selection button, allowing the cursor speed to be selected according to user preferences.

Those studied in the art will appreciate that the degree of freedom which imparts duration of cursor movement is implicit-that is to say, the user simply removes the finger when the cursor arrives at the desired position. This requires little by way of cognitive skill and can almost be disregarded as a degree of freedom.

This being the case, the salient degree of freedom is simply the direction of movement. Furthermore, once the user has decided upon the desired angle of movement, she/he is simply required to touch the annular ring for the appro-priate period of time at the desired angular position. No further movement or application of force is necessary to keep the cursor moving and the user is re-quired only to remove his/her finger at the appropriate time.

In a preferred embodiment, the presence and position of the operator's finger is sensed by monitoring changes in the capacitance to electrical earth around the annular ring. It follows that any electrically semi-conducting material may be used in place of a finger, provided the circuit with electrical earth is in-tact.

Thus a hand-held stylus made of metal or an electrically semi-conducting material could be used to make contact with the annular sensing ring to good effect. Alternatively, operators who have no use of their limbs may use a head-mounted stylus of similar materials or may even use their tongues directly on the annular ring. This arrangement is particularly advantageous since it requires very little movement of the head to effect full control of the cursor. It will be ap-preciated that various other arrangements are possible depending on the user's particular disabilities.

The annular ring 11 of touch sensitive segment elements generally sur-rounds an inner region 1 2 which is not touch sensitive. Figure 1 shows the pro- vision of an optional select' button 13 in the centre of the annular ring, sur- rounded by the insensitive inner region 12. The button 13 may be either simi- larly touch sensitive or of the traditional mechanical type. When applied to cur-sor control this button may be typically deployed in the same way as the Left Click' button of a mouse.

The touch sensitive sensor element is shown in more detail in Figure 2. A number of segment-shaped elements 15 are defined in the copper layer of a standard printed circuit board, each linked to the next via a resistor 16. The pre-cise number of elements is unimportant, provided the width of each element is approximately that of the user's finger. The resultant electric field developed around the contact area is sufficiently large to operate through the thickness of the printed circuit board substrate.

The touch sensor of Figure 2 acts as a means for collecting information relating to the angle of contact of a user's finger around its annular contact area.

The contact area is typically five to ten centimetres in diameter with an insensi-tive void' in its centre of typically two centimetres diameter. These dimensions are merely indicative of a preferred embodiment and in practice may be almost any size, dependent on human factors. The contact area is preferably made visible on the outer face of the equipment as a whole in such a way that the user may readily make contact with its surface using a finger, pen or similar probe.

The contact area may be a polycarbonate or similar decal such that the touch sensor elements themselves are not visible to the user, in order to create a more aesthetically pleasing product. The electric field developed around the contact area is sufficiently large to operate through several millimetres of insu-lating material such as the outer box moulding and polycarbonate decal as well as the thickness of the printed circuit board substrate.

Figure 3 is a block diagram showing in more detail the associated elec-tronics' of Figure 1. The system comprises the following salient blocks: * Touch Sensor, as described above, to collect angular contact infor-mation from user input.

* Capacitive Sensor integrated circuit to convert user input to digital representation of angle of contact.

* Two similar processes to convert angular information into respective x and y ordinate values.

* A Speed Algorithm process to create speed demand information.

* Two identical multiplication processes to scale the x and y ordinate values according to speed demand information.

* Computer Interface Process to present scaled x and y ordinate val-ues to computer according to the required industry standard interface protocols.

The Capacitive Sensor IC provides electrical excitation of the sensor elements. Several techniques can be employed to effect touch detection includ-ing phase shift measurement; capacitive bridge techniques and charge transfer techniques. Commercial integrated circuits are available employing these tech-niques.

A particularly advantageous embodiment may be effected using a Quan-tum Research QT51O integrated circuit which uses the charge transfer tech-nique. This measures the amount of charge transferred from a pre-charged ref-erence capacitor to the variable capacitance formed by the user touching the conductive sensor elements through the aforementioned dielectric materials.

The output from the 0510 device is essentially a digital word represent-ing the angular position of contact and a further single bit flag' which indicates io when the sensor is currently touched.

Whilst these two pieces of information may be considered empirical, in fact they do not lend themselves readily to interpretation when applying them to cursor control devices. This is because industry standard interface protocols be-tween a cursor controlling device and a computer universally require that the information is presented in terms of Cartesian (x and y) axis information. Con-versely, the QT51 0 device represents the data in Polar form (0).

Hence to process the numerical data from the QT51O device it is neces-sary to perform Polar to Cartesian conversion using standard trigonometrical techniques. Two similar processes are used to perform this conversion: one for x and one for y. The following formulae show how these conversions are carried out: x=Acos0 (1) y = A sin 0 (2) where A is an arbitrary scaling factor and in a preferred embodiment may be taken as 128 to scale number system into a convenient signed 8-bit value.

With reference to the block diagram shown in Figure 3, equation 1 is car- ried out by one Polar to Cartesian block, and equation 2 by the other. The resul-tant output is two signed variables representing the x and y ordinate values of the angle at which the sensor is touched.

These processes may be conveniently implemented using two look-up tables in a microprocessor device where the offset in each table is the angular information from the QT51 0 and the resultant entry in the look-up table repre-sents the x or y value.

Whilst these processes effectively convert the number system into one that is readily usable by a modern computer, there is only directional information contained in the number system, with no speed information. Therefore, it is not possible to effect cursor movement with this information alone. For this to be possible, it is necessary to superimpose' speed information onto the existing io number system.

It should be understood that there is no speed information whatsoever contained in the user input and consequently for the system to function cor-rectly, speed information must be determined by the system itself. This may be readily achieved by inference of the duration for which the user contacts the touch sensor.

For example, in a simple algorithm, the speed may simply increase in a fashion proportional to the duration of contact, up to a maximum, as repre-sented by the graph of Figure 4a. Under this algorithm, the cursor accelerates steadily from rest in the direction indicated by the angle at which the user touches the sensor until an upper speed is achieved, stopping only when the user removes his finger from the sensor.

It should be appreciated that the simple algorithm explained above may be modified for improved ergonomics and that many different algorithms may be arrived at.

A simple modification, for example, would be to move the cursor initially at a low constant speed, as shown in Figure 4b, allowing the user to accurately position the cursor over an icon or other feature.

A further development may be to implement a speed selector switch on the unit so that the user may choose the acceleration curve which he finds most acceptable-see Figure 4c.

The 01510 device conveniently produces a TOUCH' signal which indi-cates when the sensor is currently touched by the user. This may be used di-rectly as an input to the Speed Algorithm process and in one embodiment starts a timer whose output directly represents the position on the horizontal axes of the transfer curves shown in Figure 4.

The Speed Demand may thus be created using the above timer and a further look-up table in the system microprocessor. Figure 5 shows the Speed Algorithm process in more detail. The TOUCH signal is used to control the counter which increments in value at a known constant rate but sticks' at its maximum value rather than returning to zero. This is used as an offset into the look-up table, the output of which is a direct representation of the Speed De- mand as an unsigned byte value. Whenever the TOUCH signal becomes inac-tive, the timer is cleared to zero and remains so until TOUCH again becomes active, whereupon the incrementing process begins again from zero. Figure 6 shows a typical cursor speed sequence relative to the TOUCH signal, assuming the transfer curve depicted in Figure 4a.

Once an instantaneous speed value has been created by the Speed Al-gorithm process, this must be combined with the instantaneous directional in-formation to create a unified set of data which may be presented to the host computer.

In practice this is achieved by multiplying the speed value independently by both the x and y directional values, as shown in Figure 3. It is important to note that the x and y values are signed since both may have positive and nega-tive values, therefore a signed multiplication is required.

Once again, it is convenient to implement this multiplication in firmware in the system microprocessor. This has the further advantage that only one in-stance of the multiplication process is required as a subroutine which is invoked twice-once for the x value and once for y.

Once the scaled x and y components have been created, containing both directional and speed information, they may be processed for presentation to the host computer in the way normally associated with a mouse or similar cur-sor controlling device.

In practice this involves organising the x and y data into packets to be sent isochronously to the computer, usually together with button information.

Persons studied in the art will appreciate that the data presentation protocols are well understood and generally take the form of the de facto PSI2 or USB standards.

The various speed transfer functions of Figures 4 to 6 all show that the cursor moves slowly when the sensor is first touched. This can lead to user frustration since it takes time for the speed to increase to the required level if the cursor needs to be moved a large distance on the screen. By analysis of various cursor operations it can be shown that when users begin a new cursor movement after a long period of non-movement, it is generally necessary to io move a large distance. This is because the user is generally beginning a new operation, perhaps to click on a new icon or pop down a new menu item. It is on these occasions that a very slow starting speed becomes frustrating.

Conversely, a high starting speed may be equally frustrating if the user is attempting to accurately hone the cursor position. This would inevitably lead to repeated over-shoot. Similar analysis of cursor operations shows that small, ac-curate movements such as this usually follow soon after a period of faster movement. That is to say, the users require that the cursor moves quickly to the vicinity of the intended position and then honing follows on very soon after this using slow cursor movements.

The invention can in an alternative embodiment, shown in Figures 7 and 8, provide a more complex speed algorithm to further increase system ergo-nomics. This algorithm gives higher starting speeds after periods of non-use whilst still allowing low speeds immediately following a period of use. In this al- gorithm the speed of the cursor is a function not only of the duration of the cur-rent touch event, but also of the duration of the preceding period for which the sensor is not touched.

In terms of practical implementation, this function is carried out by main-taining a counter within the device firmware. During touch events, the counter is incremented successively at a constant rate up to maximum. The contents of the counter are used to reference a look-up table from which a Speed Demand word is derived. At the end of a touch event (i.e. as the user removes the f in-ger), the counter is cleared and cursor movement is arrested. These aspects are identical to the embodiment described above with reference to Figures 4a, 5 and 6. In the embodiment of Figures 7 and 8, however, the counter then con-tinues to increment from zero during a stationary period rather than being held at zero. Incrementing continues, as long as the sensor is untouched, up to a pre-determined threshold value.

Thus a period of virtual acceleration' takes place whilst the sensor is un-touched. Although no actual cursor movement takes place, the speed increases internally such that when the next touch event occurs, the speed of the cursor begins from a finite value which depends on the period for which the sensor io was untouched. The upper threshold value effectively caps' the starting speed to a pre-determined value so that the cursor does not move excessively fast to begin with. Once the cursor begins moving again, normal acceleration due to the touch event takes place, allowing the speed to increase up to absolute maximum if its duration allows.

It is not necessary for the incremental rate during a touch event to be the same as the incremental rate during the stationary period between touch events. For example, it may be advantageous for the rate of increase in poten-tial cursor speed during stationary periods to be slower than the rate of increase in speed during touch events during touch events.

Furthermore the pre-determined threshold value which controls the maximum starting speed of the cursor after a long period of no movement need not be the same as the maximum speed of the cursor during a touch event and it is often preferred that this pre-determined threshold value is lower than the absolute maximum value.

In operational terms, if the user begins a new cursor movement operation after a long period of no movement, the cursor begins moving at the pre- determined maximum rate and continues to accelerate until the absolute maxi- mum rate is achieved. This allows the cursor to be moved relatively long dis-tances quickly and ergonomically. When the cursor gets close to the target', be it an icon, drop-down menu or similar, the user will typically remove the finger momentarily from the sensor pad and then re-apply the finger. In doing so the internal counter is cleared and because the stationary period was very short, the resulting cursor speed is low, allowing the user to home in on the required position.

The arrangements for controlling the cursor speed in this alternative em-bodiment can with advantage be applied to other types of pointing device. For example, a mouse would benefit from these techniques as would a trackball.

The invention thus includes according to this aspect apparatus for con-trolling the movement of a cursor on a display screen, wherein the cursor is moved in response to an operator touching a device, characterised in that the speed of movement of the cursor is controlled by an algorithm whereby the speed increases over time during each touch event, and whereby the speed at the start of each touch event increases in proportion to the time interval since the previous touch event.

Figure 7 shows a flow diagram which implements the algorithm of the al-ternative embodiment of the invention. Figure 8 shows a typical cursor speed sequence relative to the TOUCH signal according to this alternative embodi-ment. Figure 8 depicts the two incremental rates as different, that is the rate at which the cursor speed increases over time during each touch event is greater than the rate at which the cursor speed at the start of each touch event in-creases in proportion to the time interval since the previous touch event.

Clearly, many different algorithms can be conceived which would be en-compassed within the generality of the foregoing. For example, the unit may take more events into consideration than the previous stationary period and the current touch event, It may instead maintain an historic look-up table of events which would enable it to better predict the likely duration of cursor movement and therefore the required speeds. If such a table were stored in a non-volatile area of memory, the algorithm could be developed to be adaptive to a particular user's typical operations.

When a mouse is used for cursor control in known systems, it generally has one or more buttons to instigate various functions corresponding to the icon covered by the cursor on a monitor screen. The apparatus of the invention can include equivalent buttons; these are preferably arranged to be touch sensitive using techniques such as a capacitive sensor IC as described in the foregoing.

Advantageously, one or more of these buttons may be placed in the insensitive inner region of the annulus, as described above with reference to Figure 1.

A further development of the cursor control device of the invention allows the touch sensitive surface to be contextually redeployed as a keypad. Such an arrangement is particularly advantageous in mobile equipment where there are significant space constraints such as mobile telephones, music players and the like.

To achieve this, the annular touch sensitive surface can be segmented' into a defined number of segments, each of which constitutes one discrete key in the keypad arrangement. The keys are not constrained to be equal in size, so for example, an Enter' key could be made larger than the others on the basis that it is used most regularly. Similarly, the key configuration does not need to be fixed-the quantity and dimensions of each button may be changed accord-ing to the context. For example, there may be occasions where a telephone keypad (O9,*,#) may be required, whereas on other occasions two buttons (yes, no) may be adequate.

Such segmentation is carried out electronically according to the method-ology described below, and is also be carried out visually so that that the user is made aware of the location of each button. In a fixed keypad configuration this may simply be achieved by placing a printed overlay onto the touch sensitive surface. With a contextually changing number of keys, the visual indication must also be changeable, implying that the touch sensitive surface must be overlaid onto a changing electronic display of some kind.

Electronic segmentation of the touch sensitive surface may be readily achieved mathematically using the system microprocessor. The typical output from the Charge Transfer Capacitive Sensor shown is a binary number repre-senting the angle at which the sensor is currently touched. Let us suppose that the output is in tact an 8-bit number, i.e. an output of 0 means 00 and 255 means 3590 (since 3600 and 0 are coincident).

That is to say, each bit of output represents 359/255 = 1.410.

If we were required to segment the surface into 12 equally sized keys for a telephone keypad arrangement we would require each to subtend an angle of 30 . The number of bits associated with each key is therefore 30/1.41 21.

Hence membership sets can be created as follows Key Binary Values 0 0-20 1 21-41 2 42-62 3 63-83 -4 84-104 105-125 6 126-146 7 147-167 8 168-198 9 198-219 * 220-237 (narrow) # 238-255 (narrow) For example, if the touch sensor chip returns a binary value 151, this In an alternative configuration requiring a simple Yes/No response, the io membership sets would be as follows....

Key Binary Values Yes 0-127 No 128-255 It is also possible to define dead spaces where no valid keystroke is re- turned. This may be advantageous in preventing inadvertent keystrokes by pro-viding a gap between adjacent keys. In the above Yes/No example we might want to limit the size of each key to 1200 rather than 1800, giving a possible membership set as follows....

Key Binary Values Yes 0-85 None 86-1 27 No 128-213 None 214-255 Clearly any number of membership sets may be devised and stored within the microprocessor and invoked according to the context of the current operations.

An important advantage of this aspect of the invention is the facility to switch contextually between pointing device functionality and keypad functional- ity, thus allowing a single input device to be used for cursor control and key-stroke duties. This has clear advantages in terms of ergonomics and space constraints.

It is important that the user knows whether the user input device of the invention is in cursor control or keypad mode, and if it is the latter, the position and function of each key.

If the key layout is fixed it may simply be adequate to overlay a decal onto the annular touch sensitive area, although it is not then immediatelyap-parent whether the unit is currently acting as a cursor controller or keypad.

As an alternative, the plastic surface of the touch sensitive area can be manufactured of a translucent plastic material and backlit by a series of light emitting diodes (LEDs). The user input device can then be arranged so that when in cursor control mode, the backlights are off and the touch sensitive sur-face appears plain. When the unit is switched to keypad mode the backlights are turned on, illuminating each individual key with an image representing the function of that key.

Alternatively the touch sensitive surface can be overlaid onto a liquid crystal display (LCD). In this case the touch sensitive surface is fabricated in a transparent material, preferably an optically clear material such as indium tin oxide (ITO). This allows a full graphical representation to be displayed of the position and function of each button which is readily changed with the button functions themselves. This can create a very powerful graphical user interface.

One important application area for the new user input device of the in-vention is in mobile telephones. It is becoming increasingly clear that mobile telephones will employ complex operating systems in the future more akin to those we are familiar with on personal computers. It will be an advantage in such systems to use a cursor.

For example, it is likely that the telephone display will have a virtual desk-top with a series of icons for telephone, music play, texting and so on. The user will select the required application program by positioning the cursor over an icon and clicking. Up to this point the operating system regards the user input device of the invention as a pointing device, giving cursor control.

As the telephone application is launched, for example, the operating sys- tem will know that a dialled number is now required and will regard the user in- put device as a telephone keypad. Once the number has been entered, the op-erating system may ask whether it should dial the number, and regard the user input device as a Yes/No keypad.

Once the call is completed the operating system will finally switch the user input device back to cursor control.

Given the decreasing size of modern mobile equipment, it is unlikely to be practical to segment the annular ring into 26 segments required to implement an alphabetic keyboard. Nevertheless it would be advantageous to provide this facility. Of course the usual technique of using button 1 as A,B,C; button 2 as D,E,F etc may be used. However the input device of the invention can have a continuously variable output, and this makes other techniques possible.

In one technique a monitor screen displays an initial character corre-sponding to the position at which the input device is touched and subsequently displays characters in sequence as the user rotates the point of contact with the input device. Such a technique has been successfully demonstrated incorporat-ing a small display capable of displaying a single letter. This initially displays the letter M' and if the user rotates the point of contact with the input device around its annular surface the displayed letter increments through the alphabet either towards Z' for clockwise rotation or towards A' for anticlockwise rotation.

Once the required letter has been arrived at the user may select it by pressing an Enter' button, for example a button at the void centre of the annular ring, or perhaps by tapping once on the input device.

Alternatively, a slightly modified technique could be employed where the initial letter is based upon the approximate position at which the sensitive sur-face is first touched and then movement either side of this allows the user to set the letter accurately.

For example, each button in a 26 button keypad would subtend an angle of 13.8 . If the user were to touch the surface at an angle of 69 this would give the fourth letter of the alphabet, D'. Due to the inaccuracy with which this task may be carried out, it may be that the user actually required the letter E', in which case he simply moves his finger clockwise slightly to give the next letter and then enters it.

Claims

CLAIMS

1. Apparatus for controlling the movement of a cursor on a display screen, comprising a touch sensitive device which is a ring formed of a plurality of touch sensitive segment elements, said touch sensitive segment elements interacting with electronic circuitry arranged to move the cursor in a direction determined by the angular position at which the device is touched and for a dis-tance determined by the length of time for which the device is touched.

2. Apparatus according to Claim 1, wherein each touch sensitive segment element is linked to the next via a resistor.

io 3. Apparatus according to Claim 1 or 2, wherein the ring is an annu-lar ring surrounding an inner region which is not touch sensitive.

4. Apparatus according to Claim 3, further comprising a central but-ton surrounded by the insensitive inner region, said button effecting a function indicated by the position of the cursor on the screen.

5. Apparatus according to any preceding claim, wherein the touch sensitive elements monitor changes in the capacitance to electrical earth around the annular ring when a sensitive element is touched.

6. Apparatus according to Claim 5, wherein the touch sensitive ele-ments are associated with a capacitive sensor integrated circuit effecting touch detection by phase shift measurement, a capacitive bridge technique or a charge transfer technique.

7. Apparatus according to Claim 6, wherein the integrated circuit measures the amount of charge transferred from a pre-charged reference ca-pacitor to the variable capacitance formed by the user touching a sensor ele-ment.

8. Apparatus according to Claim 6 or Claim 7, wherein the direction of movement of the cursor is controlled by said integrated circuit and the speed of movement of the cursor is controlled by an algorithm for which the user input is a signal indicating whether or not a sensitive element is being touched.

9. Apparatus according to Claim 8, wherein the speed of the cursor increases during each touch event.

10. Apparatus according to Claim 8 or Claim 9, wherein the speed of the cursor at the start of each touch event increases in proportion to the time interval since the previous touch event.

11. Apparatus according to any preceding claim, wherein the touch sensitive ring is overlaid on a changing electronic display.

12. Apparatus according to Claim 11, wherein the surlace of the touch sensitive area is manufactured of a translucent plastic material and backlit by a series of light emitting diodes.

13. Apparatus according to Claim 11, wherein the touch sensitive sur-face is fabricated in a transparent material and is overlaid on a liquid crystal display.

14. Apparatus according to any preceding claim, including the touch sensitive device as a keypad and to control the movement of a cursor on a dis-play screen, and also comprising electronic circuitry interacting with the user input device to change the function of the user input device from keypad to cur-sor control and vice versa.

1 5. Apparatus according to Claim 14 having a touch sensitive ring as defined in Claim 12, wherein the backlights are off when the device is in cursor control mode so that the touch sensitive surface appears plain, whilst when the unit is switched to keypad mode the light emitting diodes are turned on, illumi-nating each individual key with an image representing the function of that key.

16. Apparatus for controlling the movement of a cursor on a display screen, wherein the cursor is moved in response to an operator touching a de-vice, characterised in that the speed of movement of the cursor is controlled by an algorithm whereby the speed increases over time during each touch event, and whereby the speed at the start of each touch event increases in proportion to the time interval since the previous touch event.

17. Apparatus according to Claim 16 comprising a counter within the firmware of the touch sensitive device, which counter increments during touch events up to a maximum value and also increments during the time interval be- tween touch events up to a predetermined threshold value, said algorithm con-trolling the speed of the cursor in proportion to the incremented value recorded by the counter.

18. Apparatus according to Claim 17, wherein said predetermined threshold value is less than said maximum value.

19. Apparatus according to any of Claims 16 to 18 wherein the rate at which the cursor speed increases over time during each touch event is greater than the rate at which the cursor speed at the start of each touch event in-creases in proportion to the time interval since the previous touch event.