The present invention relates to a capacitive switch assembly comprising a housing, an activation button slidable along an activation axis, and a variable capacitor defining a capacitive switch having an off position and at least one on position.

Electric capacitive switches of this kind are used in keypads and other control systems. Due to the non-contact operation, they are less susceptible to mechanical wear and oxidation than contact switches.

Publication US6914785 discloses a circuit component comprising a top structure made from an elastically deformable material having a top and bottom surface, wherein the top structure has lever regions and a central region comprising a part having a first conductive layer; a bottom structure having a top and bottom surface and comprising a part having a second conductive layer; an insulator layer disposed between the first and the second conductive layers and preventing the conductive layers from coming into physical contact with each other; and support structures coupling the top and bottom structures which act as a fulcrums over which the top structure can be elastically deformed in response to a force applied in a neighbourhood of the lever regions. As a result said part having the first conductive layer displaces with respect to the bottom structure leading to a measurable change of capacitance between the conductive layers. A similar solution is disclosed in publication US7025324.

The object of the invention was to provide a non-contact capacitive switch assembly with a reliable, simple and cost-effective design, enabling a predefined haptic response.

The invention provides the switch assembly, as outlined in the outset which is characterised in that said variable capacitor comprises a resilient activation member with a closed cross-section supported on at least two support points and on an activation point, wherein said support points are located on the opposite sides of the activation axis and on one side of the longest, perpendicular to the activation axis, chord of said cross-section, define a support section located at least partially inside said cross-section, and are defined by at least one support member, while said activation point is located substantially on the activation axis; a first conductive layer located on the activation member; and a second conductive layer located in said off position at a non-zero distance from the first conductive layer; wherein the approach of said activation point to said support points along the activation axis causes bilateral centripetal compression of the activation member along the activation axis and centrifugal stretching of the activation member in a direction substantially perpendicular to the activation axis and displacement of said first conductive layer relative to the second conductive layer of the variable capacitor.

The resilient activation member with a closed cross-section enables a haptic response that is realized only by this member and can be easily predefined, for example by changing its dimensions and wall thickness. The change of the capacitance of the variable capacitor as a function of the travel of the activation button can also be easily predefined by changing the distance between the support points, as well as the arrangement of the capacitor conductive layer at a specific deformation of the resilient activation member.

Preferably said resilient activation member with a closed cross-section is supported on at least two external support points and said activation point located on the other side of the longest, perpendicular to the activation axis, chord of said cross-section.

Alternatively preferably said resilient activation member with a closed cross-section is supported on at least two internal support points and said activation point located on the same, with respect to said internal support points, side of the longest, perpendicular to the activation axis, chord of said cross-section.

Preferably said activation button is a part of said resilient activation member and includes said activation point.

Preferably said activation button is adjacent to said activation point.

Alternatively preferably said activation button is adjacent to said support points.

Preferably said resilient activation member has a cylindrical elliptic, oval or spherical cross-section.

Alternatively preferably said resilient activation member comprises at least two members, preferably connected with joints. Preferably said activation member has a hollow interior.

Preferably said resilient activation member is made of metal and constitutes said first conductive layer of said variable capacitor.

Alternatively preferably said first conductive layer of said variable capacitor is fixed to said resilient activation member.

The invention has been presented below in exemplary embodiments and in reference to the drawings, in which:

Fig. 1 shows a schematic axonometric view of a first embodiment of a capacitive switch assembly according to the invention;

Fig. 2 is a cross-sectional view of the first embodiment of the switch assembly in the off position;

Fig. 3 is a schematic enlarged detail of Fig. 2 showing the switch assembly according to the first embodiment in the off position (Fig. 3a) and in the on position (Fig. 3b); Fig. 4 is a schematic cross-sectional view illustrating the operating principle of the switch assembly according to the second embodiment;

Fig. 5 is a schematic cross-sectional view illustrating the operating principle of the switch assembly according to the third embodiment;

Fig. 6 is a schematic cross sectional view illustrating the operating principle of the switch assembly according to the fourth embodiment; and

Fig. 7 is a top view of the switch assembly according to the fifth embodiment.

Numerical references to the elements having the same functionally remain the same throughout the figures, with additional suffixes (a, b, ...), where appropriate, to distinguish elements with the same functionality but different structure.

The first embodiment of a switch assembly 1, according to the present invention, shown in Fig. 1-3, comprises a housing 2 and an activation button 3 disposed slidably within the housing 2 along an activation axis A. The button 3 cooperates with a variable capacitor 4 defining a capacitive switch having an off (inactive) position and at least one on (active) position.

Variable capacitor 4 comprises a resilient activation member 41 having a cylindrical cross-section S supported on two external support points P1 and P2 located on the opposite sides of the activation axis A and at a bottom side of the longest chord C of the cross-section S, which chord C is perpendicular to the activation axis A. Support points P1 and P2 define a support section B having a constant length, which is located inside the cross-section S. In this embodiment support points P1 and P2 are disposed at the external side of the activation member 41 and are defined by two elongated, conductive support members 42 fixed to a base member 43 in a form of a printed circuit board fixed within the housing 2 on a support plate 21. In this embodiment the activation member 41 defines a first conductive layer 44 of the variable capacitor 4. A second conductive layer 45 is disposed on the base member

43 underneath the first conductive layer 44. The second conductive layer 45 and the first conductive layer 44 (via conductive support members 42) are electrically connected with an activating circuit 5, schematically illustrated in Fig. 3b, that detects the capacitance of the variable capacitor 4, which is dependent on the distance between the conductive layers 44, 45.

Fig. 3a shows the variable capacitor 4 of the switch assembly 1 in the off (inactive) position. The resilient activation member 41 is undeformed, holding the off position of the switch 4, and the layers 44, 45 are spaced at a distance L1 apart. The longitudinal inner activation pin 31 of the activation button 3 defines an activation point P3 located between the support points P1 and P2, and generally on the activation axis A and on the upper side of the longest, perpendicular to the activation axis A, chord C of the section S, that is at the other, with regard to the position of the external support points P1 and P2, side of the chord C.

As illustrated by arrows in Fig. 3b, after a user centrally presses the activation button 3 along the activation axis A, the activation pin 31 presses against the activation member 41 causing it to deform and centrifugally stretch in a direction substantially perpendicular to the activation axis A. As a result, the cross-section of the activation member 41 takes the shape of an ellipse and the distance L2 between the first layer

44 and the second layer 45 becomes greater than the distance L1 in the off position. Thus, the capacitance of the capacitor 4 is smaller than its capacitance in the off position indicated by the broken line and shown in Fig. 3a. A specific change in the capacitance of the capacitor 4, for example a decrease in the capacitance below a certain threshold, may be interpreted as the on (active) position. Obviously the capacitance of the capacitor 4 varies continuously, depending on the deformation of the activation member 41, leading to a continuous change in the distance between the layer 44, 45, which can be used, for example, to detect the preliminary activation of a button 3, etc.

In the off position, in which the activation member 41 is undeformed, on the sides of the longest, perpendicular to the activation axis A, chord C of the S cross-section of this element 41, voids are provided enabling the walls of the element 41 to move during its deformation to the on position.

Fig. 4 shows a second embodiment of the switch assembly in which the variable capacitor 4a comprises a resilient activation member 41a made of plastic and comprising two longitudinal resilient activation members 411 and 412 with a curved cross-section whose curvatures are opposite to each other and which are connected to each other by joints 413. In this embodiment, the cross-section S of the activation member 41 is supported on four support points P 1 , P4 and P2, P5 arranged in pairs on opposite sides of the activation axis A. Points P1 and P2 are defined by two bottom support members 421a attached to the bottom base member 431, while points P4 and P5 are defined by two top support members 422a attached to the top base member 432. The first layer 44a of the capacitor 4a is glued to the bottom activation member 412, and the second layer 45a is glued to the bottom base member 431.

In this embodiment the activation button 3a is a part of the activation member 41 , and more specifically of the top activation member 411, and the area of the activation button 3a includes the activation point P3.

As in the first embodiment, centripetal pressure on the top activation member 411 adjacent to the activation point P3 of the cross-section S leads to its deformation which is transmitted through the joints 413 to the bottom activation member 412, which in turn leads to the separation of the first layer 44a and the second layer 45a from the off position defined by the distance L1 to the on position defined by the distance L2. In the off position, the top activation member 411 is spaced from the top support members 422a. Fig. 5 shows a third embodiment of a capacitive switch assembly. In this embodiment the variable capacitor 4b has a metal resilient cylindrical activation member 41b whose cross-section S is supported on an activation point P3 defined by the electrically conductive bottom support member 421b and two support points P1 and P2 defined by two top support members 422b connected to the activation button 3. The first layer 44b of the capacitor 4b is defined by the activation member 41b itself and is electrically connected to the bottom support member 421b, while the second layer 45b is glued to the shaped plastic base member 43b. In this embodiment, the deformation of the activation member 41b due to pressing the button 3 brings the first layer 44b closer from the off position, indicated by the dashed line and defined by the distance L1 , to the on position defined by the distance L2.

Fig. 6 shows a fourth embodiment of a capacitive switch assembly having a variable capacitor 4c, a cylindrical metal activation member 41c of which is slid over a metal support member 42c defining the inner support points P1 and P2 on opposite sides of the activation axis A and the support section B inside the cross-section S of the activation member 41c. With the internal support of the activation member 41c, the activation point P3 is on the same side of the longest, perpendicular to the activation axis A, chord C of the section S, as the internal support points P1 and P2.

Fig. 7 shows a fourth embodiment of a capacitive switch assembly. In this embodiment, a variable capacitor 4d has a spherical shaped, metal, resilient activation member 41 d, with a closed cross-section S, seated on a cylindrical support member 42d defining a set of support points P1 and P2, as well as a set of support sections B. As illustrated by arrows, centrifugal pressure on the activation member 41 d at the activation point P3 along the activation axis A, which is perpendicular to the drawing plane, leads to its centrifugal extension in the plane of the drawing in directions perpendicular to the activation axis A. In this embodiment, the entire spherical activation member 41 d defines the first layer 44d of the variable capacitor 4d and second layer 45d is defined by an annular, metal element base member 43d. In the off position of the switch assembly the activation member 41 d remains at a distance L1 from the base member 43d, while the deformation of the activation member 41 d lowers this distance L1 to L2. The above embodiments of the present invention are therefore merely exemplary. The figures are not necessarily to scale and some features may be exaggerated or minimized. These and other factors however should not be considered as limiting the spirit of the invention, the intended scope of protection of which is indicated in appended claims.

List of reference numerals

1. switch assembly

2. housing

21. support plate

3. button

31 activation pin

4. variable capacitor (capacitive switch) (4a, 4b, 4c, 4d)

41. activation member (41 a, 41 b, 41 d)

A. activation axis

S. cross-section P1. first support point P2. second support point P3. activation point

P4. third support point P5. fourth support point

B. support section

C. longest, perpendicular to the activation axis (A), chord of the cross- section (S)

411. top activation member

412. bottom activation member

413. joint

42. support member (42b, 42c, 42d)

421. bottom support member (421a, 421 b)

422. top support member (422a, 422b)

43. base member (43b, 43d)

431. bottom base member

432. top base member

44. first conductive layer (44b, 44d)

45 second conductive layer (45b, 45d)

5. activating circuit