EP3547303B1 - Key with enhanced expressive possibilities - Google Patents

Description

TECHNICAL FIELD

The present invention relates to keys, in particular keys that open up more expressive possibilities for electronic musical instruments.

BACKGROUND AND PRIOR ART

Keys can be found in various areas of technology, such as in computers, automobiles, musical instruments and many more, and are in particular an essential part of keyboard instruments such as the piano or keyboard. But modern electronic musical instruments also use keys that can be arranged, for example, in a matrix with rows and columns (that is, 8 x 8, 8 x 4, etc.). Analogous to the piano, the touch response of the key (ie the speed at which the key is depressed) and thus the pressure that physically acts on the key can be electronically recorded and evaluated by sensors. This information from velocity and pressure usually serves as the basis for deriving the volume of the sound struck with the key. Electronic musical instruments or music controllers provided with such technology offer only a limited possibility of formulating or influencing the sound apart from the volume.

Since electronic musical instruments have existed, however, one would also like to emulate or simulate other analog instruments (e.g. string instruments, wind instruments). Therefore, there is a desire to measure and then reproduce the expressive options available to a musician on analog instruments (such as vibrato, timbre, tremolo, tone and volume variations, etc.) in electronic musical instruments. In order to meet this wish, many electronic key-based musical instruments or controllers have additional options for influencing or controlling the sound. These include, among other things, the possibility mentioned above to measure the key press or evaluate after the release, but also additional devices such as the sustain pedal, pitch bend wheel or modulation wheel. Such additional elements not only have to be actuated separately from the key to be played, but also only allow the creation of the same effect for all keys - the sounds generated with the keys cannot be individually modulated in this way and a simultaneous playing of several keys with each different expression effects (polyphonic) is not possible.

Electronic musical instruments or software-based musical instruments offer a wealth of expressive sounds with their sound library. However, in order to be able to control or play these sounds in a multidimensional manner, that is, depending on the position of, for example, a finger operating a key, a sensor system for the instrument keys or pads is required, which electronically on the one hand multidimensionally in the XY direction the finger position and on the other hand, in the Z direction, it can measure the force that the finger exerts on the button or pad. Another important piece of information is the detection of movements in the XY direction across key / pad boundaries. Against the background of a Cartesian coordinate system, "Z-direction" means the direction in which the - vertical - downward movement of the key takes place during In "X-" and "Y-direction" the orthogonal - horizontal - plane is spanned, in which, for example, the key surface lies.

The sensors known to date for exerting the force exerted on the key in the Z direction are generally FSR sensors ("Force Sensing Resistor"), as used, for example, in the US 6,909,354 B2 from Interlink Electronics, Inc. are disclosed. An FSR is a contact sensor that creates an electrical resistance between two electrodes in the event of contact. However, sensors of this type have certain disadvantages, such as a high response pressure point (“entry threshold”), a behavior which is difficult to reproduce in the area around this response pressure point and increased effort (ie several FSR sensor levels) in order to simultaneously use the Z- Dimension also capture the X and Y dimensions.

Another disadvantage of previous buttons - especially those that are provided with sensors - is for technical reasons that the lighting is not available or is only available to a very limited extent. The reason for this is that buttons with sensors, if they are to be illuminated on their surface, must be transparent or have openings in order to transmit light through them, which in turn leads to major problems in the design of the button. However, lighting is desirable in many cases for use in modern electronic musical instruments. The lighting can e.g. a note or key being played or the key status is displayed or other visual signaling is enabled.

So there is still a need for a button or a touchpad, whereby not only the force (or pressure) exerted thereon in the Z direction, but also the position in the X-Y direction, e.g. of a user's finger operating the button is detected. There is also a need for a button that is sufficiently illuminated.

JP 2007 052280 A , US 5 187 315 A and EP 2 073 194 A1 disclose other keys for musical instruments.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a key for electronic musical instruments which detects and processes both the force (or pressure) exerted thereon in the Z direction and the position in the X-Y direction, e.g. of a user's finger operating the button. (As mentioned at the beginning, "Z-direction" means the direction in which the - vertical - downward movement of the key takes place, while in "X-" and "Y-direction" the orthogonal - horizontal - plane is spanned, in which, for example, the key surface lies.)

This has been achieved according to the invention with a key according to claim 1, comprising a key unit suspended in a fixed frame vertically movably in the Z direction, having a key body which has an upper actuating surface and at least one shaft which extends vertically downward from the key body; an XY sensor unit arranged vertically below the key body and spaced apart by an air gap and firmly connected to the frame, for detecting XY positions on the actuating surface, the XY sensor unit having at least one opening for the at least one shaft through which through which the shaft can move vertically; at least one transmission element which is elastically suspended vertically below the at least one shaft and which is moved vertically downward when the at least one shaft moves downward; and a Z-sensor unit arranged vertically spaced below the at least one transmission element and firmly connected to the frame with at least one detection element for detecting the vertical downward movement of the at least one transmission element.

It is also an object of the present invention to provide such a key with improved lighting.

This has been achieved according to the invention with a key according to claim 17, wherein the shaft further extends horizontally outwards into an extension at its upper end below the key body, the shaft and extension being made of a translucent material, so that together they form a light guide which continues is firmly connected to the key body; a light source arranged vertically below the shaft, the light of which emerges vertically upwards and enters the shaft from below; and a first optical device arranged in the vertical upper region of the light guide above the shaft for deflecting the light that has entered the shaft from the light source in a horizontal direction into the surface of the extension.

Other advantageous features of the key according to the invention are disclosed in the further subclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1

shows a cross-sectional view of the button according to the invention in a preferred embodiment.

Fig. 2

shows a cross-sectional view of the button after Fig. 1 with additional lighting.

3A-F

show different views of the light guide of the button Fig. 2 .

Fig. 4

shows a cross section through the light guide 3A-F and schematically the light path in it.

Fig. 5

shows a cross-sectional view of the frame with several buttons arranged side by side.

Fig. 6

shows an exploded view of several buttons arranged in a grid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As mentioned at the beginning, conventional keys for electronic musical instruments include the disadvantage that, if necessary, additional means of expression available via sound libraries are neither polyphonic, i.e. depending on the key different (polyphonic), still multidimensionally controlled, i.e. depending on the position e.g. of a user's finger operating the button can be played.

1. (i) einer vertikal beweglich aufgehängten Tasten-Einheit 2,
2. (ii) einer unbeweglichen X-Y-Sensor-Einheit 5,
3. (iii) einer Einheit mit einem vertikal beweglichen Übertragungselement 7 und
4. (iv) einer unbeweglichen Z-Sensor-Einheit 8.

The present invention overcomes these problems. The key construction according to the invention generally consists of four main units Figure 1 can be seen from

1. (i) a vertically movably suspended key unit 2,
2. (ii) an immobile XY sensor unit 5,
3. (iii) a unit with a vertically movable transmission element 7 and
4. (iv) an immobile Z-sensor unit 8.

How Fig. 1 the key comprises a key unit 2 suspended vertically in the Z direction in a fixed frame 1 with a key body 2a which has an upper actuating surface 2b and at least one central shaft 3 which extends vertically downward from the key body 2a. The key body 2a can be made of a material that comprises silicone. For example, only one central shaft can be provided in the horizontal center of the key or several at different locations, such as four in the respective corner area of the key, if it is rectangular. Vertically below the key body 2a there is an XY sensor unit 5 which is fixedly connected to the frame 1 and has at least one opening 6 through which the at least one shaft 3 of the key unit 2 extends for movement in the Z direction. If a central shaft 3 is provided in the key unit 2, there is also a central opening 6 in the XY sensor unit 5; are eg four shafts 3 are provided in the key unit 2, there are also four openings 6 in the XY sensor unit 5, one for each shaft 3. The XY sensor unit 5 is vertical from the air gap 4 The underside of the key body 2a is spaced apart and is used to detect XY positions on the actuating surface 2b of the key unit 2, so that, for example, the XY position of a user's finger on the actuating surface 2b can be recorded. At least one elastically suspended transmission element 7 is located vertically below the at least one shaft 3 of the key unit 2 and is likewise moved vertically downward when the shaft 3 moves downward. If a central shaft 3 is provided in the key unit 2, there is also a transmission element 7 below it; if, for example, four shafts 3 are provided in the key unit 2, four transmission elements 7 can also be provided - one for each shaft 3 - but only one transmission element 7 can be provided for all four shafts 3. Beneath the at least one transmission element 7 there is a Z sensor unit 8 which is fixedly connected to the frame 1 and has at least one detection element 9 which detects the vertical downward movement of the at least one transmission element 7. In contrast to the opening (s) 6 in the XY sensor unit 5, the horizontal arrangement of the at least one transmission element 7 and the at least one detection element 9 is not at the location of the shaft 3 or the shafts 3 and the horizontal thereof Position tied. That is, regardless of the number of shafts 3 and their horizontal position, (i) only one transmission element 7 and also only one detection element 9 can be provided or (ii) only one transmission element 7, but one detection element 9 per shaft 3, or (iii) conversely, only one detection element 9, but one transmission element 7 per shaft, or (iv) both a transmission element 7 and a detection element 9 per shaft 3. The key according to the invention thus comprises two sensors arranged one below the other - a sensor for detecting a vertical movement of the key in Z direction and a sensor for detecting an XY position on the Actuating surface of the button - and can therefore be described as multidimensional in the sense described above.

The transmission element 7 can optionally be embedded in an elastic, electrically insulating substrate 10, at least partially enclosed by it or applied to it. Optionally, an air gap 11 can be provided in the substrate 10, vertically spaced below the transmission element 7. In this way, an almost barrier-free downward movement of the transmission element 7 is possible, which in turn requires a significantly lower effort to release the button, which reduces its response pressure. Optionally, the substrate 10 for reinforcement in the area of the air gap 11 can furthermore have at least one semicircular or conical spring-elastic projection 12 which projects vertically into the air gap 11. This at least one projection 12 serves as a resilient return aid. The substrate 10 can consist of silicone.

Again, the Z sensor unit 8 can optionally include a substrate 13, the detection element 9 being located vertically on top of the substrate 13 and / or being at least partially embedded in the substrate 13. The effectiveness of the detection element 9 can be increased by partial embedding: If the detection element 9 is e.g. a coil in connection with an LC resonator (see further below), this can be extended to several layers in the substrate 13 of the unit 8 - but the inductance increases with the length of the coil, which in turn increases the sensitivity of the sensor ( the properties of the LC resonator also change, since the coil is part of it).

Again, the key body 2a can optionally be suspended from the frame 1 via a movement bead 16 surrounding it. This movement bead is formed in one piece with the key body 2a and consists of one Material rejuvenation on the horizontally surrounding edge of the key body 2a. In this way, an almost barrier-free downward movement of the key body 2 a is possible, as a result of which the key can be triggered with less force, which — as already discussed in connection with the air gap 11 — reduces the response pressure of the key.

Again, optionally, the X-Y sensor unit 5 on its upper side or the key body 2a on its underside can have at least one semicircular or conical projection 17 horizontally outside the at least one shaft 3, which protrudes into the air gap 4. This at least one projection 17 serves - as already discussed in connection with the air gap 11 - as a resilient restoring aid.

Again, at least one pressure equalization line 18a can optionally be provided between the air gaps 4 and 11 and the air gap 11 can also be vented to the environment by at least one pressure equalization line 18b extending through the Z sensor unit 8. This ensures sufficient pressure equalization in the air gaps 4 and 11.

Again, the X-Y sensor unit 5 and the Z sensor unit 8 can optionally be fixedly spaced apart from one another by at least one spacer 19 provided vertically therebetween. This not only improves the strength of the overall key arrangement, but also increases its overall rigidity.

The sensor units 5 and 8, which are used in the button described above, can be configured differently electronically. In a preferred embodiment, the Z sensor unit 8 comprises an inductive sensor. As is known, an inductive sensor comprises an oscillating circuit with an LC resonator (L stands for the inductance of the coil present therein and C stands for the capacitance of the capacitor also present therein) and measures its frequency (the LC resonator frequency) with the aid of a reference oscillator (reference frequency), whereby in addition to the inductance, the impedance Z and the quality Q of the LC resonator can also be determined. The coil emits a magnetic field that causes eddy currents in an electrically conductive material that is moved relative to it, which changes the amplitude and frequency of the resonant circuit. In the present case, the detection element 9 is an induction coil and the transmission element 7 comprises a metallic material. If a force or pressure is now exerted on the key, for example with a finger, the shaft 3 moves downwards, which in turn reduces the distance between the metal transmission element 7, which is also moved downwards, and the induction coil 9 and leads to the above effects .

In the preferred embodiment, the XY sensor unit 5 in turn comprises a capacitive position sensor. A capacitive XY position sensor is known to comprise a grid of RX and TX electrodes, the RX electrodes being electrically connected to one another in columns and the TX electrodes each being connected in rows - but without an electrical connection between the RX and TX -Electrodes exists - and the capacitance between the electrodes is measured in a very rapid repetition. The capacity depends on the permittivity of the material that is in the immediate vicinity of the electrodes. If you come close to this arrangement with a finger, for example, which has a much stronger permittivity due to its water content than the ambient air, the capacitance between the electrodes is changed, whereby the two-dimensional XY position of the finger on or above the grid is determined can be - if a finger is drawn over the grid, the change in capacitance also moves between the electrodes. In the present case, the XY sensor unit 5 comprises the RX and TX electrodes 14a and 14b, the key body 2a not being metallic.

The XY sensor unit 5 can optionally comprise a covering layer 15, which covers the electrodes 14a, 14b and has the following purpose: In the case of a capacitive sensor, the field strength between the capacitively acting objects and the electrodes decreases quadratically with their distance from one another - which means that the field strength can be extremely large at a very short distance and, in the case of capacitive-acting objects in the electrical field that are subject to movement tolerance, can lead to disproportionate sensor signals with a small distance from the electrodes, with which it is no longer possible to achieve sensibly processable results. These very short distances between the sensor electrodes and the capacitive-acting objects subject to movement tolerance are enlarged by the overlay layer 15 and the dynamic range is therefore optimized and the sensor signal usable in this way is conditioned.

With such a key e.g. for musical instruments - instead of just one-dimensional in the Z direction - by recording the X-Y positions e.g. a finger on the key for each key individually provide additional sound expressions such as Vibrato, timbre, tremolo, tone and volume variations, etc.

In another embodiment, the Z sensor unit 8 can comprise a capacitive pressure sensor instead of an inductive one, wherein (i) the transmission element 7 is a capacitive electrode at least partially embedded in an elastic electrically conductive substrate 10 ', (ii) the detection element 9 is a is an electrically insulated embedded electrode with respect to the transmission element 7 and the substrate 10 'and (iii) there is an electrical connection between the transmission element 7 and the unit 8 via the conductive substrate 10', so that the transmission element 7 and the detection element 9 form a plate capacitor, the Signals on the unit 8 are available for further processing. With such a capacitive pressure sensor The change in capacitance is therefore evaluated as a sensor effect due to the change in the distance between the electrode of the transmission element 7 and the electrode of the detection element 9. The substrate 10 'can consist of silicone, which is mixed with a homogeneous mixture of electrically conductive fillers.

In yet another embodiment, the Z-sensor unit 8 can comprise a magnetic sensor, wherein (i) the transmission element 7 is a magnet at least partially embedded in an elastic electrically insulating substrate 10, the north pole of which points vertically upwards or downwards, and ( ii) the detection element 9 is a HALL sensor. If current flows through the HALL sensor, which is located in the perpendicular magnetic field of the transmission element 7, the HALL sensor supplies an electrical voltage that is proportional to the product of the magnetic flux density and the applied current - this voltage changes with that of the Triggering of the button changing the distance between the magnet and the HALL sensor.

The embodiments of the button according to the invention described above can be illuminated according to a further aspect of the present invention. To do this, the button includes how the Fig. 2 it can also be seen an extension 20 which extends horizontally outwards from the upper end of the shaft 3 below the key body 2a and which can be formed in one piece with the shaft. Shaft 3 and extension 20 are made of a translucent material and together form a light guide which is firmly connected to the key body 2a by a suitable method, such as, for example, by reshaping, gluing, casting, etc. Vertically below the shaft 3 of the key unit 2 is one Light source 21, which can be, for example, an LED, is arranged, the light of which emerges vertically upwards and enters shaft 3 from below. In the vertically upper region of the light guide above the shaft 3, a first optical device 22 is arranged to horizontally deflect the light that has entered the shaft 3 from the light source 21 Redirect direction in the surface of the extension 20. This first optical device 22 can be, for example, a free-form conical lens, which consists of a funnel-like depression in the light guide. This is a type of conical lens, which is developed in such a way that the light entering the shaft 3 vertically from below is deflected horizontally on the one hand by bringing a large part of the light into total reflection at the interface of the lens 22 and on the other hand a part of light also shines directly up through the lens. Fig. 2 and 3D show in cross section such a lens 22 in the form of a funnel-like depression, which has no tip in its lower region, but is rounded, and the outer surface of which is curved.

Optionally, the key illuminated in this way can further comprise a second optical device 23 arranged in the vertically lower region of the shaft 3, by means of which the light entering the shaft 3 from the light source 21 is focused in the direction of the first optical device 22 (collimation). This second optical device 23 can e.g. a free-form converging lens for coupling the light, which consists in a suitable surface shaping of the lower end of the shaft 3. In particular, the surface shaping can be done with convex and concave sections - e.g. wave-like - be designed such that it deflects a large part of the light onto the outer surface of the free-form conical lens 22.

Optionally, the illuminated button can further comprise at least one light scattering element 24 arranged on the underside of the extension 20. This light scattering element 24 serves to deflect light which radiates downwards in the light guide in such a way that the light is reflected upwards and can e.g. Surface structures on the underside of the extension 20 - e.g. in the form of spherical caps - include.

3A-F show different views of the light guide consisting of shaft 3 and extension 20, the one with the first and second optical Devices 22 and 23 and the light scattering element 24 is provided. Fig. 4 shows a cross section through this light guide with the light path.

Optionally, the first optical device 22 can furthermore be filled with the material from which the key body 2a is made, in order to correct brightness concentrations in the center of the actuating surface 2b. The material can be silicone.

Furthermore, the key body 2a can optionally be made of silicone and the first optical device 22 can be filled with silicone. Furthermore, the material from which the key body 2a is made can be pigmented with titanium dioxide or aluminum oxide. Likewise, the shaft 3 and the extension 20, which together form the light guide, can be pigmented with titanium dioxide or aluminum oxide. This pigmentation results in light scattering.

With a button illuminated in this way, e.g. display a note or key being played as well as the key status or other visual signaling.

It should be noted that the frame 1 can be an integral part of a device housing or a device cover or front plate in which the button according to the invention is installed. Fig. 5 shows a cross-sectional view of the frame 1 with several adjacent buttons, as described above. The frame 1 has screwing domes 25 which extend from the frame 1 via the XY sensor unit 5 and the substrate 10 with the transmission element 7 to the Z sensor unit and serve to screw these firmly together. Furthermore, the frame 1 has spacing projections 26 which space the frame from the XY sensor unit 5.

Fig. 6 shows an exploded view of several keys according to the invention arranged in a grid.

Claims (27)

1. A button for musical instruments, comprising

   - a button unit (2) which is suspended movably vertically in Z direction in a fixed frame (1) and which has a button body (2a) with an upper actuating surface (2b) and at least one shaft (3) extending vertically downwardly from the button body;

   - a X-Y sensor unit (5) which is arranged vertically below the button body (2a) and spaced therefrom by an air gap (4) and which is fixed to the frame (1) for detecting X-Y positions on the actuating surface (2b), wherein the X-Y sensor unit (5) has at least one opening (6) for the at least one shaft (3) such that the shaft (3) can vertically move therethrough;

   - at least one transfer element (7) which is elastically suspended vertically below the at least one shaft (3) and which is moved vertically downwardly upon downward movement of the at least one shaft (3); and

   - a Z sensor unit (8) which is arranged vertically below the at least one transfer element (7) and spaced therefrom and which is fixed to the frame (1), wherein the Z sensor unit has at least one detection element (9) for detecting the vertical downward movement of the at least one transfer element (7).
2. Button according to claim 1, wherein the Z sensor unit (8) comprises an inductive sensor, the detection element (9) is an induction coil and the transfer element (7) comprises a metallic material.
3. Button according to claim 1 or 2, wherein the transfer element (7) is embedded in an elastic electrically insulating substrate (10) and at least partly surrounded by the substrate or applied thereto.
4. Button according to claim 3, wherein an air gap (11) is provided in the substrate (10) vertically below the transfer element (7) and spaced therefrom.
5. Button according to claim 4, wherein the substrate (10) is provided with at least one semicircular or conical resilient protrusion (12) in the area of the air gap (11) protruding into the air gap (11).
6. Button according to one of claims 3 to 5, wherein the substrate (10) consists of silicone.
7. Button according to one of claims 1 to 6, wherein the Z sensor unit (8) comprises a substrate (13) and the detection element (9) is located vertically on top of the substrate (13) and/or at least partly embedded into the substrate (13).
8. Button according to one of claims 1 to 7, wherein the X-Y sensor unit (5) comprises a capacitive sensor with RX and TX electrodes (14a, 14b) and the button body (2a) is non-metallic.
9. Button according to claim 8, wherein the X-Y sensor unit (5) comprises a cover layer (15) covering the electrodes (14a, 14b).
10. Button according to one of claims 1 to 9, wherein the button body (2a) is suspended on the frame (1) by a movement crimp (16) surrounding the button body.
11. Button according to one of claims 1 to 10, wherein a semicircular or conical resilient protrusion (17) protruding into the air gap (4) is provided on the top side of the X-Y sensor unit (5) or on the bottom side of the button body horizontally outside the shaft (3).
12. Button according to claim 4 or 5, wherein a pressure equalization line (18a) is provided between the air gaps (4, 11) and wherein the air gap (11) is further vented to the environment by at least one pressure equalization line (18b) extending through the Z sensor unit (8).
13. Button according to one of claims 1 to 12, wherein the X-Y sensor unit (5) and the Z sensor unit (8) are fixedly spaced from each other by a spacer (19) provided vertically therebetween.
14. Button according to claim 1, wherein the Z sensor unit (8) comprises a capacitive sensor, wherein

    - the transfer element (7) is a capacitive electrode embedded at least partially in an elastic electrically conductive substrate (10');

    - the detection element (9) is an electrode embedded electrically insulated against the transfer element (7) and the substrate (10'): and

    - an electrical connection between the transfer element (7) and the unit (8) is provided by the conductive substrate (10').
15. Button according to claim 14, wherein the substrate (10') consists of silicone comprising a homogenous mixture of electrically conductive fillers.
16. Button according to claim 1, wherein the Z sensor unit (8) comprises a magnetic sensor, wherein

    - the transfer element (7) is a magnet embedded at least partially in an elastic electrically insulating substrate (10), wherein the north pole of the magnet points vertically upwardly or downwardly; and

    - the detection element (9) is a HALL sensor.
17. Button according to one of claims 1 to 16, wherein further

    - the shaft (3) extends at its upper end below the button body (2a) horizontally into an extension (20), wherein the shaft (3) and the extension (20) consist of a translucent material such that they commonly form a light guide which is fixedly connected to the button body (2a);

    - a light source (21) is provided vertically below the shaft (3), wherein the light of the light source leaves vertically upwardly and enters the shaft (3) from below;

    - a first optical device (22) for deflecting the light that has entered the shaft (3) from the light source (21) in a horizontal direction into the plane of the extension (20) is arranged in the vertical upper area of the light guide above the shaft (3).
18. Button according to claim 17, wherein the first optical device (22) is a free form conical lens.
19. Button according to claim 17 or 18, further comprising a second optical device (23) for collimating the light that has entered the shaft (3) from the light source (21) in the direction of the first optical device (22) is arranged in the vertical lower area of the shaft (3).
20. Button according to one of claims 17 - 19, wherein the second optical device (23) is the free form collecting lens for coupling the light.
21. Button according to claims 18 and 20, wherein the free form collecting lens (23) is designed in such a way that the major part of the light is deflected to the surface area of the fee form conical lens (22).
22. Button according to one of claims 17 to 21, further comprising at least one light scattering element (24) deflecting light radiating downwardly from the light guide in such way that it is deflected upwardly is arranged at the bottom side of the extension (20).
23. Button according to claim 22, wherein the light scattering element (24) comprises a surface structure on the bottom side of the extension (20).
24. Button according to one of claims 17 - 23, wherein the first optical device (22) is filled with the material that the button body (2a) consists of to correct brightness concentrations in the middle of the actuating surface (2b).
25. Button according to claim 24, wherein the button body (2a) consists of silicone and the first optical device (22) is filed with silicone.
26. Button according to one of claims 17 to 25, wherein the material that the button body (2a) consists of is pigmented with titanium dioxide or aluminum oxide.
27. Button according to one of claims 17 to 26, wherein the shaft (3) and the extension (20) forming the light guide are pigmented with titanium dioxide or aluminum oxide.

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