GB2515286A

GB2515286A - Pressure-sensitive interface

Info

Publication number: GB2515286A
Application number: GB1310763.6A
Authority: GB
Inventors: Roland Lamb; Ning Xu
Original assignee: ROLI Ltd
Current assignee: ROLI Ltd
Priority date: 2013-06-17
Filing date: 2013-06-17
Publication date: 2014-12-24
Anticipated expiration: 2033-06-17
Also published as: GB201310763D0; GB2515286B

Abstract

Apparatus for providing variable electrical characteristics responsive to a pressure applied to the apparatus is disclosed along with a corresponding method of manufacture. The apparatus is for use as a user interface for an electronic device such as a musical instrument. It comprises a first electrode 100, a second electrode 140, and an electrically conductive pressure sensitive layer 120 (such as a piezoresistive film) arranged between the first and second electrodes and arranged for being electrically connected to both the first and second electrodes, wherein the pressure sensitive layer has an electrical resistance that varies according to a level of pressure applied to the electrically conductive pressure sensitive layer. The apparatus further comprises at least one electrically insulating spacer layer 110, 130 arranged between the pressure sensitive layer and one of the first and second electrodes, preventing electrical current flowing from the one or more of the first and second electrodes and the pressure sensitive layer when no pressure is applied to the apparatus. Also disclosed is a flexible electronic interface device for operating a computer and a corresponding method of manufacture.

Description

Intellectual Property Office Applicalion Nc,. (lB 1310763.6 RTM Dale:25 Noverriher 2013 The following terms are registered trade marks and should he rcad as such wherever they occur in this document: 3M Caplink Inlelleclual Property Office is an operaling name of the Pateni Office www.ipo.gov.uk Pressure-sensitive Interface

Field of Invention

An interface for an electronic device is disclosed herein. More specifically, but not exclusively, a pressure-sensitive interface is disclosed. Means for manufacturing components of the pressure-sensitive interface are also considered.

Background to the Invention

Since the advent of electronic devices there has been extensive research and development in the creation and advancement of electronic musical instruments. Some electronic musical instruments are specifically arranged to emulate their acoustic equivalents, while others are designed to enable musicians to create new and exciting sounds.

Most musical instruments provide various means for controlling characteristics of pitch and volume. Many acoustic musical instruments allow musicians to vary these properties as a note is played, and to influence the timbre of sounds, which may be affected by characteristics of the way in which the instrument is played. For example, characteristics can be imparted on the sounds made by an acoustic musical instrument by a musician playing the instrument adding effects such as vibrato. This control of the sound made by an instrument provides musicians with their own musical personality. There has always been a desire to impart such personality to the sounds produced by electronic instruments.

Electronic musical instruments generally comprise a processor arranged to create one or more sounds responsive to inputs from a user on an interface. It is particularly easy to process electronically originated sounds in order to vary many different characteristics of the sounds.

However, a problem for engineers producing electronic musical instruments is the development of a user interface that gives the user control over such characteristics of the sound at their fingertips, as is possible with most acoustic musical instruments. Hence, the development of the interface for electronic musical instruments is of particular importance for providing musicians with increased and improved natural control of the instrument.

Over the years many electronic musical instruments have been developed with different electronic user interfaces. In particular, there has always been a desire to create more user-friendly and accurate electronic musical instrument interfaces. Of those that have focused on developing interfaces that enable users to have a wider range of controls over the sound, some have also provided users with a greater level of tactile control. Those electronic musical interfaces providing greater tactile control often include interfaces that are sensitive to the pressure, position, and direction of travel of a body that interacts with its surface in order to provide the user with the maximum amount of control of the computer via the interface.

For example, keyboards have existed for many years that are printed onto ribbon controllers, enabling instinctive and continuous control of pitch. Such controllers take the form of a resistive track that makes contact with a conductive plate at the point where a user touches it, to provide a gated control voltage that pertains to horizontal finger position. However, the ribbon technology may detect only one finger press, lirriiting the application to monophonic music, and it is entirely insensitive to finger pressure. Devices that use capacitive sensor technology may allow polyphony, but are likewise insensitive to pressure. Therefore, musical dynamics cannot be played instinctively by modulating the force applied to the keyboard.

One example of a unique electronic musical instrument interface that provides both pressure and multiple position sensitivity is the Haken Continuum (US Patent Application No. US200310015087 Al). In this device, finger position and pressure is sensed using an array of rigid bars mounted on springs underneath a compliant tactile surface, the displacement of each bar being sensed continually at both ends by position sensors. This provides a continuous controller with limited multi-touch capabilities in one spatial dimension, as the device cannot discern two distinct presses upon the same rod. As this solution comprises several moving parts, it is also complex to assemble, test, and service.

Another attempt to provide a pressure-and position-sensitive music controller is the Eigenharp (International Patent Application No. W02010/010338) in which individual buttons are sensed in such a way that lateral force in each direction, as well as perpendicular force, can be determined. This provides the opportunity for natural expression to be applied to any number of notes being played. However, this instrument forces the performer to trade versatility against controllability. If the lateral force in one dimension is assigned to bend pitch, for example, setting the bend range more than a few semitones will cause the instrument to fall out of tune should the player strike a key at a non-perpendicular angle without applying a corrective counter-pull.

Whilst the Eigenharp allows intuitive expression, it cannot be controlled by a skilled musician without considerable retraining.

In summary, existing technologies fail to provide sufficient natural musical control to a user in a way that does not compromise ease of use. Furthermore, these and other solutions require expensive and complex components and manufacturing methods, which makes the interfaces commercially undesirable.

Summary of Invention

In accordance with an aspect of the invention there is provided apparatus for providing variable electrical characteristics responsive to a pressure applied to the apparatus. The apparatus is for use as a user interface for an electronic device. Furthermore, the apparatus comprises a first electrode, a second electrode, an electrically conductive pressure sensitive layer arranged between the first and second electrodes and arranged for being electrically connected to both the first and second electrodes, wherein the pressure sensitive layer is electrically conductive and has an electrical resistance that varies according to a level of pressure applied to the electrically conductive pressure sensitive layer, and an electrically insulating spacer layer arranged between the pressure sensitive layer and one of the first and second electrodes, wherein the electrically insulating spacer layer prevents electrical current flowing from the one or more of the first and second electrodes and the pressure sensitive layer when no pressure is applied to the apparatus.

The first and second electrodes may be formed on respective first and second electrode layers.

The spacer layer may be arranged to connect one of the first and second electrode layers to the pressure sensitive layer. The spacer layer may have an adhesive film on each side for connecting to the one of the first and second electrode layers and the pressure sensitive layer.

Furthermore, the spacer layer may be arranged to adhere to one or more portions of the one or more first and second electrode layers where the first and second electrodes are not formed.

The spacer layer may include a cut-out at a position where the one of the first and second electrodes is formed on the respective electrode layer.

The electrically conductive pressure sensitive layer may be a piezoresistive film. The spacer layer may have a thickness of approximately 100 microns. The apparatus may further comprise a further electrically insulating spacer layer arranged between the other of first and second electrodes and the pressure sensitive layer.

According to another aspect of the invention there is provided a method of manufacturing an apparatus for providing variable electrical characteristics responsive to a pressure applied to the apparatus. The apparatus is for use as a user interface for an electronic device. The method comprises providing a first electrode, providing a second electrode, providing an electrically conductive pressure sensitive layer arranged between the first and second electrodes and arranged for being electrically connected to both the first and second electrodes, wherein the pressure sensitive layer is electrically conductive and has an electrical resistance that varies according to a level of pressure applied to the electrically conductive pressure sensitive layer, and providing an electrically insulating spacer layer arranged between the pressure sensitive layer and one of the first and second electrodes, wherein the electrically insulating spacer layer prevents electrical current flowing from the one or more of the first and second electrodes and the pressure sensitive layer when no pressure is applied to the apparatus.

The spacer layer may have an adhesive film on each side. The method may further comprise using the spacer layer to connect the one of the first and second electrodes to the pressure sensitive layer.

The method of manufacturing an apparatus for providing variable electrical characteristics responsive to a pressure applied to the apparatus may comprise any further aspects disclosed herein.

According to yet another aspect of the invention there is provided an electronic interface device for operating a computer. The interface comprises a pressure sensitive device having one or more engaging features, and a flexible interface arranged to at least partially encapsulate the pressure sensitive device and engage with the one or more engaging features of the pressure sensitive device.

The flexible interface device may be formed of multiple moulded parts which are joined together to at least partially encapsulate the pressure sensitive device. The multiple moulded parts of the flexible interface may comprise engaging features arranged to complement the engaging features of the pressure sensitive device. The flexible interface may be formed by being introduced, when in a liquid state, into a mould in which the pressure sensitive device is located so as to at least partially encapsulate the pressure sensitive device and engage with the one or more engaging features. The flexible interface may be formed from silicone. The pressure sensitive device may be formed from a number of layers and each of the layers comprises one or more complementary engaging features. The one or more engaging features may be one or more of a hole, a recess, a protrusion, a groove, and a ridge. When the one or more engaging features comprises at least one hole, the flexible interface may be formed of a material arranged to allow light to pass through, and the electronic interface device may further comprise a light source arranged to emit light through the at least one hole and the flexible interface.

According to a further aspect of the invention there is provided a method of manufacturing an electronic interface for operating a computer. The method comprises providing a pressure sensitive device having one or more engaging features, and providing a flexible interface arranged to at least partially encapsulate the pressure sensitive device and engage with one or more engaging features associated with the pressure sensitive device.

The flexible interface may be formed of multiple moulded parts. The method may further comprise at least partially encapsulating the pressure sensitive device by joining the multiple moulded parts of the flexible interface together around the pressure sensitive device. The method may further comprise moulding the multiple parts of the flexible interface. The multiple moulded parts of the flexible interface may comprise engaging features arranged to complement the engaging features of the pressure sensitive device.

The method may further comprise placing the pressure sensitive device within a mould.

Furthermore, the step of providing the flexible layer may comprise introducing a liquid substance into the mould to at least partially encapsulate the pressure sensitive device and allowing the liquid substance to solidify to form the flexible interface that is engaged with the one or more engaging features. The method may further comprise forming the one or more engaging features in the pressure sensitive device. The pressure sensitive device may be formed from a number of layers. Each layer may comprise one or more complementary engaging features.

The forming the one or more engaging features may further comprise punching holes in one or more of the number of layers of the pressure sensitive device. When the one or more engaging features comprises at least one hole, the flexible interface may be formed of a material arranged to allow light to pass through. Furthermore, the method may further comprise providing a light source arranged to emit light through the at least one hole and the flexible interface.

According to an aspect of the invention there is provided a method of manufacturing an electronic interface for operating a computer. The method comprises placing a pressure sensitive device having one or more engaging features within a mould, pouring or otherwise introducing a liquid substance into the mould to at least partially encapsulate the pressure sensitive device, and allowing the liquid substance to solidify to form a flexible interface that is engaged with the one or more engaging features.

Also disclosed herein is a method for manufacturing one or more electrodes for use in a pressure-sensitive sensor arrangement. The method comprises providing a flexible substrate.

The method also comprises printing a pattern onto the flexible substrate, the pattern indicative of positions for forming one or more electrodes on the flexible substrate. Furthermore, the method comprises forming the one or more electrodes on the pattern. The pattern may be printed using a catalytic ink, and the electrodes formed by electroless plating of metal onto the ink. Alternatively the pattern may be printed using an electrically conductive ink.

An apparatus for use in a pressure-sensitive sensor arrangement is also disclosed. The apparatus comprises a flexible substrate, a pattern printed on the flexible substrate, the pattern indicative of positions for forming one or more electrodes, and one or more electrodes formed on the pattern. The ink may be catalytic. The one or more electrodes may be formed by means of electroless plating. Alternatively the pattern may be formed of electrically conductive ink.

Embodiments of the invention provide a printing process for making flexible conductive membranes. An advantage of the printing process is that it enables for large sensors to be made, under which circumstances conventional techniques cannot scale economically.

Certain embodiments of the invention provide pressure sensors with an increased active pressure range. This may be achieved by incorporating one or more spacing layers between active components of the pressure sensor. More specifically, when the pressure sensor comprises a set of electrodes with a piezoresistive layer placed therebetween, the spacing layers may be interposed between each electrode and a surface of the piezoresistive layer.

Use of spacer layers or masks improves the dynamic range and recovery time of a signal obtained during sensor activation. As a consequence, an amount of latent power consumption is saved that would otherwise be incurred by current passing through the piezoresistive layer as it is scanned. In addition, the impact of sensor calibration on the range of the output data is reduced by diminishing quiescent sensor activation, which otherwise occurs when no pressure is applied owing to the finite resistance between the electrodes. Thus, the masks directly increase the range of data that can pertain to a meaningful finger touch or movement. The spacing masks may also adhere the sensor arrangement together, preventing the layers from mutually slipping during handling and installation.

Mechanical improvements of utilising spacer masks are mathematically equivalent to certain digital signal processing techniques that might be applied instead. It would therefore be possible to render such improvements in the digital domain rather than using a spacing mask, but this would compromise the resolution of the digital output. Moreover, the equalisation required in such additional processing would require raising the level of high-frequency noise in order to improve response time. The advantage of a mechanical solution over an algorithmic one is that such compromises can either be mitigated or avoided entirely.

Embodiments of the invention extend a tactile surface to enclose and permeate sensor assemblies, such that the two components become electromechanically combined. More specifically, the sensor assemblies may include one or more engaging elements such as holes, grooves, recesses or protrusions and the tactile surface may be moulded to the sensor assembly such that it engages with the engaging elements. This arrangement enhances the stability and dynamic range of output data, improves resilience of such sensors to mechanical and environmental wear, and reduces the impact of a pressure calibration process upon output data. The engaging elements may also provide reference points for registration of components of the interface with respect to one another.

Embodiments of the invention provide an interface allowing a user to interact with a processor.

The interface may take the form of a piezoresistive pressure sensitive array. The interface has some specific advantageous improvements. The suitability of the sensor to the application of a touchable surface is enhanced. Greater control is afforded over its electrical and mechanical properties. Furthermore, sensitivity to vibration and environmental factors is reduced.

According to some embodiments, an electrode array is formed by a printing process. The printed pattern may be Cartesian coordinate based. Alternatively, a sensor membrane may be produced that reads natively in polar coordinates. In such arrangements a plurality of electrodes may be provided and arranged such that their electrode tracks cross at right angles.

Also disclosed is a method for manufacturing electrodes comprising use of ink-jet printing and electroless plating to build flexible electrode membranes. Such techniques scale economically enabling electrode arrays over a metre long to be fabricated.

Advantageously, a sensor arrangement is disclosed that is comparatively simple and inexpensive to manufacture. Competing methods for fabricating resistive pressure transducers require either more exotic materials, electroplating or otherwise depositing a force-sensitive superstrate onto electrical conductors.

Brief Description of the Drawings

Exemplary embodiments of the invention shall now be described with reference to the drawings in which: Figure 1 provides a schematic overview of a musical instrument system with a simplified exploded view of the musical instrument interface; Figure 2 is an exploded view of the component parts of the interface of Figure 1; Figure 3 is a plan view of the first electrode array shown in Figure 2; Figure 4 is a plan view of the second electrode array shown in Figure 2; Figure 5 is an isometric view of the interface in which it can be seen how the connectors of the respective electrode arrays protrude through the silicone; Figures 6 is a plan view of a first electrode array of an alternative interface utilising a native polar coordinate system; and Figure 7 is a plan view of a second electrode array used with the first electrode array of Figure 6 in the alternative interface.

Throughout the description and the drawings, like reference numerals refer to like parts.

Specific Description

Figure 1 is a schematic exploded view of the components of a musical instrument system. The system comprises an interface 10 that includes a flexible layer 11 of a soft resilient material having a three-dimensionally shaped input surface ha similar in form to that of a standard piano or keyboard interface. In this example, the flexible layer 11 is made from silicone rubber, but it will be appreciated that any suitable flexible material could be used. The flexible layer 11 serves the purpose of protecting the sensor array from degradation and wear, while providing comfort and tactile feedback to the user. Furthermore, the flexible layer is arranged to be sufficiently compliant to translate downward pressure to a sensor arrangement 12 positioned underneath the flexible layer 11, and is hard-wearing enough to withstand regular use within the intended environment.

The sensor arrangement 12, which forms part of the interface 10 and is positioned underneath the flexible layer 11, and is arranged to sense pressure applied to the flexible layer 11. The sensor arrangement 12 is supported on a rigid surface 13. The sensor arrangement 12 comprises a plurality of sensors arranged in an array. Each of the sensors of the sensor arrangement 12 is pressure sensitive and can produce an output in accordance with the pressure exerted on it.

Sensor arrangement 12 is scanned by circuitry 160, providing an output to a microprocessor system 14. The microprocessor system 14 includes algorithms that respond to certain combinations of signals from the sensors of the sensor arrangement 12 to determine positional information of the applied pressure(s). For example, the configuration enables a region of greatest pressure to be determined, and hence the position of activation. In particular, the circuitry 160 includes scanning electronics, driven by appropriate software, that ascertains a raw pressure map from the sensor arrangement, and converts this into a more succinct representation, for example by movement tracking of the user's interactions, which is then relayed to a data processor. Movements are usually recorded with either two or three degrees of freedom comprising one or two positional axes and the pressure component over time at a scanning rate in the order of several hundred times per second. Complexity is added to the processing software by the fact that any number of activations, such as multiple finger movements, may be happening simultaneously.

Once the microprocessor 14 has received the signals indicative of applied pressure and position it then produces an output that is arranged to drive a component, which is a loud speaker 15 in this example. Hence, pressure applied to the interface 10 results in sounds being produced by the loudspeaker 15.

Figure 2 provides an exploded view of all of the component parts of the interface 10 of Figure 1.

It will be appreciated that only a right-most segment of the interface is depicted in Figure 2 and in practice the interface is significantly wider. The flexible layer 11 and the rigid surface 13 are substantially the same as those shown in Figure 1. However, it can be seen that the structure of the sensor arrangement 12 is shown in more detail in Figure2than in Figure 1. This arrangement shall therefore now be discussed in more detail.

The sensor arrangement 12 comprises first and second electrode arrays 100, 140 with a piezoresistive film 120 sandwiched therebetween. First and second sensor masks 110, 130 are provided between the piezoresistive film 120 and each of the first and second electrode arrays 100, 140 respectively. A silicone layer 150 is positioned underneath the second electrode array 140, between the second electrode array 140 and the rigid surface 13. The sensor arrangement 12 works such that when pressure is applied to the interface 10 the resistance of the piezoresistive film 120 changes, and therefore the resistance between electrodes of the electrode arrays 100, 140 changes accordingly. The signals produced by the electrodes 100, due to variation in resistance due to the applied pressure are the signals used by the processor 14 to produce sounds accordingly.

Each of the components of the interface 10 shall now be described in detail with reference to their structure, functionality and fabrication.

The piezoresistive film 120 is a polymer sheet with a concentration of carbon particles distributed throughout so as to produce a conductive film. The piezoresistive film 120 is fabricated in such a way that the resistance of the sheet decreases significantly and controllably when it is compressed. Carbon black-impregnated polymer films are available from a number of manufacturers, for example 3M (as VeloStat) and Caplink (as Linqstat). These and similar films are widely exploited as flexible packaging material to form antistatic enclosures for sensitive electronics. In this example, 200 micron VeloStat is used for the piezoresistive film 120.

While in the arrangement shown in Figure 2 the piezoresistive film 120 has constant properties throughout its surface, in alternative arrangements the piezoresistive film may be segmented into cells to reduce electrical crosstalk between electrodes.

The first electrode array 100 has a plurality of parallel electrically conductive electrodes lOla -lOb formed on a substrate. The electrodes 101 are elongate in form being substantially longer than they are wide. Furthermore the electrodes 101 of the first electrode array 100 are arranged to extend from a front to a back of the interface and are arranged in parallel across the width of the interface.

The second electrode array 140 also has a plurality of conductive electrodes 141a -141] formed on a substrate, which are elongate strips of metal arranged in parallel. The electrodes 141 of the second electrode array 140 each run across the width of the interface, perpendicularly to the electrodes 101 of the first electrode array 100.

Together the first and second electrode arrays 100, 140 form a matrix of sensors. The position of pressure applied to the interface 12 at any position on the interface can therefore be deduced by passing current in turn through each of the electrodes 141 a-i of the second electrode array and sensing electrical signals resulting in the first electrode array 100.

Figures 3 and 4 are plan views of the first and second electrode arrays 100, 140 respectively.

In particular, both Figures 3 and 4 depict detail from the top-right hand corner of the respective electrode arrays of a large-format sensor arrangement.

It can be seen from Figures 2, 3 and 4 that both the first and second electrode arrays 100, 140 comprise a plurality of holes 102, 142 which are provided for the flexible layer 11 to connect with the lower silicone layer 150 through sensor arrangement 12 during fabrication, as will be discussed in more detail when the fabrication of the flexible layer 11 is discussed.

The electrode arrays 100, 140 are made of flexible material. The first electrode array 100, which is positioned between the flexible layer 11 and the piezoresistive film 120 needs to be flexible to ensure that pressure applied to the flexible layer 11 is transferred to the piezoresistive film 120 to modulate the electric current. However, the second electrode array 140 need not be flexible. However, fabricating both electrode arrays 100, 140 from the same material helps to reduce manufacturing costs because both electrode arrays can be fabricated using the same materials and using the same processes.

The electrode arrays 100, 140 comprise a flexible plastic film. An catalytic ink is then printed onto one surface of the flexible plastic film to form the shape of the conductive tracks or electrodes 101, 141. The flexible plastic film with catalytic ink tracks is then electroless-plated in metal, for example copper, which adheres only to the position of the catalytic ink.

Consequently, the electrodes 101, 141 are formed on one surface of the flexible plastic film. The thickness of the plated metal is preferably 20 microns or less, such that the electrodes remain flexible. Since the electrodes are formed on one surface of the flexible plastic film, it will be appreciated that in use the electrode arrays 100, 140 are orientated so that the plated side of the electrode arrays 100, 140 faces the piezoresistive film 120 enabling electrical conduction between the electrodes and through the piezoresistive film 120.

The resulting sensor electrodes are completely flexible, and have a very low electrical resistance over the conductive area. The technique scales economically to sensor membranes of arbitrary shape and length, and is therefore convenient for large-format sensors.

The sensor masks 110, 130 act as adhesive spacing layers which adhere the electrode arrays 100, 140 to a respective side of the piezoresistive film 120. Formed within the adhesive spacing layer are cut-outs that in use are positioned in line with respective electrodes 101, 141 and thereby allow for the electrode arrays 100, 140 to touch the piezoresistive film 120.

As mentioned above, the first functionality of the sensor masks 110, 130 is to act as an adhesive components to hold the electrode arrays 100, 140 to a respective side of the piezoresistive film 120. As such, the sensor masks 110, 130 are made from a double sided adhesive film. More specifically, each mask is made of double-sided adhesive tape of 5 millimetre width and 100 micron thickness that is arranged in a single layer between, and parallel to, the electrodes. In particular, it will be appreciated that the sensor masks 110, 130 are formed from a number of strips of double sided tape arranged together to form the adhesive layer. It will be appreciated that any flexible material with adhesive properties on both sides could be utilised. In alternative arrangements, a non-adhesive mask is used and a separate adhesive is used to adhere the component parts of the sensor arrangement 12. While the first and second masks 110, 130 are formed to complement the electrode arrays 100, 140 with which they are respectively arranged to connect, it will be appreciated that the masks 110, 130 could be identical in form in order to reduce manufacturing costs. However, the masks must provide some space for the electrodes to electrically connect to the piezoresistive film.

A second functionality of the sensor masks 110, 130 is to incorporate a switching functionality into the sensor arrangement 12. Hence, the sensor arrangement is effectively a hybrid switch and pressure sensor. In operation, when no pressure is applied to the interface the first sensor mask 110 provides a spacing between the first electrode array 100 and the piezoresistive film such that there is no electrical contact between the first electrode array 100 and the piezoresistive film. The second sensor mask 130 likewise separates the second electrode array from the piezoresistive film. Consequently, the resistance of the sensor arrangement 12 when no pressure is being applied is infinite. This is advantageous in that no electrical current is passing through the sensor array, and power is therefore not dissipated, when no pressure is being applied. When pressure is applied to the interface 10, such that the surface of the flexible layer 11 is deflected, the sensor masks 110, 130 are compressed and the electrode arrays 100, are flexed such that the electrode arrays 100, 140 touch the piezoresistive film 120 allowing electrical current to flow between the electrodes.

By adjusting the height of the spacing layers the feel and response of the sensor arrangement can be varied.

It will be appreciated that to provide the switching functionality only one spacer mask is required such that one of the electrode arrays is not connected to the piezoresistive film when no pressure is applied. If only one spacer mask is used, one electrode array would be connected to the piezoresistive film via separate adhesive. However, using spacer masks to connect both electrode arrays to the piezoresistive film helps to simplify the manufacturing process.

A further functionality of the masks 110, 130 is to add a mechanical stiffness and increase restorative force to the sensor arrangement 12.

Like the electrode arrays 100, 140, the masks 110, 130 include a plurality of engaging features.

As with the electrode arrays 100, 140, the masks 110, 130 these engaging features take the form of holes. In practice, the sensor arrangement is formed and then punched with holes all the way through. The sensor arrangement 12 is punched with 3mm holes at every point where the two spacing masks cross, allowing holes to be made without the metal coating of the electrodes being exposed to the environment, and without disrupting the alignment between perforations when the sensor assembly is flexed. It will be appreciated that the engaging features may be of any size, shape or regularity.

Silicone layer 150 is shown underneath the second electrode array 140. In practice, the silicone layer 150 and flexible layer 11 are both formed from the same material in one moulding process so that the components of the sensor arrangement are encased in silicone as can be seen from Figure 5. In particular, the tactile interactive surface of the flexible layer is formed in a mould or casting tool by pouring or otherwise introducing the silicone into the mould. Then, the components of the sensor arrangement 12 are placed on the silicone formed within the mould.

Further silicone is then formed around the sensor arrangement 12 so that the sensor arrangement 12 is encased in the silicone. As can be seen in Figure 5, connecting portions of the respective electrode arrays still protrude through the silicone for connection to the processor 14. Hence, the tactile surface is formed around the sensor on all sides except one. In alternative arrangements, the silicone may completely encase the sensor arrangement and the output of the sensor arrangement may be transmitted to the processor wirelessly, for example by means of an RF or optical signal. In other alternative arrangements, the silicone is moulded using compression or heat-setting techniques.

The flexible layer 11 is formed of sufficient depth and hardness to spread the force of a point actuation across the sensor such that, should it occur perpendicularly over part of the spacing mask, it will nevertheless flex the surrounding sensor membrane sufficiently to register an impact.

As has been discussed, both the electrode arrays 100, 140 and masks 110, 130 comprise engaging features, preferably in the forni of holes. When pouring the silicone onto the sensor arrangement 12 the silicone therefore passes through the holes. When the silicone sets it is therefore formed within the holes. This helps to register the position of the sensor arrangement 12 with respect to the flexible layer 11 such that perpendicular finger pressure applied to a particular place will always map to a certain pattern of sensor actuation. In addition, this connection secures all of the component parts of the interface together. Furthermore, casting the sensor arrangement into the silicone renders the sensor arrangement less sensitive to false activation through vibration.

The silicone is made from a translucent material that allows for light to pass through. The holes in the sensor arrangement also allow for light to pass through so that the top flexible layer can be backlit.

It will be appreciated that in alternative arrangements the engaging features may be holes, slots, grooves, ridges or protrusions. In fact, any feature that the silicone can form around or within in order to provide the aforementioned positioning and securing would be suitable.

In alternative arrangements the silicone is formed of multiple parts. For example, the silicone arranged to be placed on top of the sensor arrangement 12 may be formed in one moulding process, while the silicone on which the sensor arrangement sits is formed in one or more separate processes. These materials and processes are chosen such that the parts thus made combine securely during manufacture. For example, the upper sensor material may comprise a preformed compression-moulded elastomer combined with a layer of poured silicone, and the lower sensor material may comprise a second poured layer of liquid silicone that is fused while curing onto a plastic base.

The sensor arrangement 12 is connected to the processor 14 via a connection unit 160. The connection unit 160 comprises a connection part for connecting to the electrodes 141 of the second electrode array 140 at a connection point of the second electrode array 140, wherein the electrodes 142 at one end of the array turn at right angles and run to a small area 143 for connection to the scanning and interface circuitry connection unit 160. The connection unit also comprises a plurality of connectors 162a -162g (not all can be seen in Figure 2), for connecting to each of the electrodes of the first electrode array 100. A cable (not shown in Figure 2) connects the circuitry connection unit 160 to the processor 14.

Figures 6 and 7 are plan views of first and second electrode arrays 200, 240 of an alternative sensor arrangement. The sensor arrangement of Figures 6 and 7 is a native polar coordinate sensor. In other words, the sensor arrangement is configured to be circular in form and sense movements throughout the circular array of sensors. First electrode array 200 comprises a plurality of concentric semi-circular electrodes 201a -201d. The electrodes each extend into an electrode connection portion 202 at one end of the semi-circular form. The first electrode array is formed of two identical parts, which together form a full circle, even though only one half is shown in Figure 6. The second electrode array comprises a plurality of electrodes 241a -2411 that extend from a central region out towards a peripheral region, the electrodes being evenly spread circumferentially. An electrode connection portion 242 is provided at one side of the periphery of the second electrode array, with each electrode having a connection portion extending around the periphery of the electrode array from the respective electrode 241 to the connection portion 242.

While the above-example relates specifically to an electronic musical instrument it will be appreciated that many of the features disclosed above may be utilised in other applications. A related application would be the manipulation of graphical data, such that a digital image may be painted, retouched, or distorted using the sensor. In particular, the interface disclosed above has many other advantageous applications. For example, its sensitivity to position and pressure, controllable degree of friction against the user's finger during movement, and immediate tactile feedback ideally suits the sensor to precise control of servo motors and articulated robotic tools. From this, application can be found for improving control of electromechanical systems in automotive, aerospace, industrial, and surgical fields. Numerous other applications will be evident to the skilled person on the basis of the discussions herein.

Claims

Claims: 1. Apparatus for providing variable electrical characteristics responsive to a pressure applied to the apparatus, the apparatus for use as a user interface for an electronic device, the apparatus complising: a first electrode; a second electrode; an electrically conductive pressure sensitive layer arranged between the first and second electiodes and arranged for being electrically connected to both the first and second electrodes, wherein the pressure sensitive layer is electrically conductive and has an electrical resistance that varies according to a level of piessure applied to the electrically conductive pressure sensitive layer; and an electiically insulating spacei layer alianged between the pressuie sensitive layel and one of the first and second electrodes, wherein the electrically insulating spacer layer prevents electrical current flowing from the one or more of the first and second electrodes and the piessure sensitive layel when no piessure is applied to the appalatus.
2. The apparatus according to claim 1, wherein the first and second electrodes are formed on respective first and second electrode layers and the spacer layel is airanged to connect one of the first and second electrode layers to the pressure sensitive layer.
3. The apparatus according to claim 2, wherein the spacer layer has an adhesive filni on each side for connecting to the one of the first and second electrode layers and the pressure sensitive layel.
4. The apparatus according to claim 2 oi claim 3, wherein the spacer layer is arianged to adhere to one or niore portions of the one or more first and second electrode layers where the first and second electrodes are not formed.
5. The apparatus according to claim 4, wherein the spacer layer includes a cut-out at a position where the one of the first and second electrodes is formed on the respective electrode layer.
6. The apparatus according to any preceding claim, wherein the electrically conductive pressure sensitive layer is a piezoresistive film.
7. The apparatus according to any preceding claim, wherein the spacer layer has a thickness of approximately 100 microns.
8. The apparatus according to any preceding claim, further comprising a further electrically insulating spacer layer arranged between the other of first and second electrodes and the pressure sensitive layer.
9. A method of manufacturing an apparatus for providing variable electrical characteristics responsive to a pressure applied to the apparatus, the apparatus for use as a user interface for an electronic device, the method comprising: providing a first electrode; providing a second electrode; providing an electrically conductive pressure sensitive layer arranged between the first and second electrodes and arranged for being electrically connected to both the first and second electrodes, wherein the pressure sensitive layer is electrically conductive and has an electrical resistance that varies according to a level of pressure applied to the electrically conductive pressure sensitive layer; and providing an electrically insulating spacer layer arranged between the pressure sensitive layer and one of the first and second electrodes, wherein the electrically insulating spacer layer prevents electrical current flowing from the one or more of the first and second electrodes and the pressure sensitive layer when no pressure is applied to the apparatus.
10. The method according to claim 9, wherein the spacer layer has an adhesive film on each side and the method further comprises using the spacer layer to connect the one of the first and second electrodes to the pressure sensitive layer.
11. An electronic interface device for operating a computer, the interface comprising: a pressure sensitive device having one or more engaging features; and a flexible interface arranged to at least partially encapsulate the pressure sensitive device and engage with the one or more engaging features of the pressure sensitive device.
12. The electronic interface device according to claim 11, wherein the flexible interface device is formed of multiple moulded parts which are joined together to at least partially encapsulate the pressure sensitive device.
13. The electronic interface device according to claim 12, wherein the multiple moulded parts of the flexible interface comprise engaging features arranged to complement the engaging features of the pressure sensitive device.
14. The electronic interface device according to claim 11, wherein the flexible interface is formed by being introduced, when in a liquid state, into a mould in which the pressure sensitive device is located so as to at least partially encapsulate the pressure sensitive device and engage with the one or more engaging features.
15. The electronic interface device according to any one of claims 11 to 14, wherein the flexible interface is formed from silicone.
16. The electronic interface device according to any one of claims 11 to 15, wherein the pressure sensitive device is formed from a number of layers and each of the layers comprises one or more complementary engaging features.
17. The electronic interface device according to any one of claims 11 to 16, wherein the one or more engaging features is one or more of a hole, a recess, a protrusion, a groove, and a ridge.
18. The electronic interface device according to claim 17, wherein when the one or more engaging features comprises at least one hole, the flexible interface is formed of a material arranged to allow light to pass through, and the electronic interface device further comprises a light source arranged to emit light through the at least one hole and the flexible interface.
19. A method of manufacturing an electronic interface for operating a computer, the method comprising: providing a pressure sensitive device having one or more engaging features; and providing a flexible interface arranged to at least partially encapsulate the pressure sensitive device and engage with one or more engaging features associated with the pressure sensitive device.
20. The method according to claim 19, wherein the flexible interface is formed of multiple moulded parts and the method further comprises at least partially encapsulating the pressure sensitive device by joining the multiple moulded parts of the flexible interface together around the pressure sensitive device.
21. The method according to claim 20, wherein the method further comprises moulding the multiple parts of the flexible interface.
22. The method according to claim 20 or claim 21, wherein the multiple moulded parts of the flexible interface comprise engaging features arranged to complement the engaging features of the pressure sensitive device.
23. The method according to claim 19, wherein the method further comprises placing the pressure sensitive device within a mould; wherein the step of providing the flexible layer comprises introducing a liquid substance into the mould to at least partially encapsulate the pressure sensitive device and allowing the liquid substance to solidify to form the flexible interface that is engaged with the one or more engaging features.
24. The method according to any one of claims 19 to 23, further comprising forming the one or more engaging features in the pressure sensitive device.
25. The method according to any one of claims 19 to 24, wherein the pressure sensitive device is formed from a number of layers and each layer comprises one or more complementary engaging features.
26. The method according to claim 25, wherein the forming the one or more engaging features further comprises punching holes in one or more of the number of layers of the pressure sensitive device.
27. The method according to claim 26, wherein when the one or more engaging features comprises at least one hole, the flexible interface is formed of a material arranged to allow light to pass through, and the method further comprises providing a light source arranged to emit light through the at least one hole and the flexible interface.