WO2022152371A1

WO2022152371A1 - Haptic button assembly and a keypad containing such button assembly

Info

Publication number: WO2022152371A1
Application number: PCT/EP2021/050550
Authority: WO
Inventors: Marek WOŹNIAK; Leszek KWIECIEŃ
Original assignee: Merit Automotive Electronics Systems S.L.U.
Priority date: 2021-01-13
Filing date: 2021-01-13
Publication date: 2022-07-21
Also published as: EP4278436A1

Abstract

The invention relates to a haptic button assembly, comprising a housing, at least one button held in the housing and apt to be moved in the activation direction, at least one elastomeric dome shaped member disposed beneath the button having an activating surface, wherein the elastomeric dome shaped member normally maintains an extended equilibrium position and buckles, while the button is pressed contributing to the tactile response of the button, and an electric switch corresponding to said button and cooperating with said activating surface.

Description

The present invention relates to a to a haptic button assembly, in particular for use in an automotive vehicle, comprising a housing, at least one button held in the housing and apt to be moved in the activation direction along an activation axis, at least one elastomeric dome shaped member disposed beneath the button having a chamber and an activating surface disposed within the chamber, wherein the elastomeric dome shaped member normally maintains an extended equilibrium position and buckles, while the button is pressed contributing to the tactile response of the button by providing at least one local maximum of the force with regard to the button stroke, and an electric switch corresponding to said button and cooperating with said activating surface. The present invention also relates to a keypad comprising a number of such button assemblies.

Background of the invention

Button assemblies of this kind are commonly used in consumer devices to provide a distinct tactile response of the button. The activating surface is covered with a conductive layer and maintained at certain non-zero-distance over a printed circuit board (PCB) held in the housing. When user presses the button against the elastomeric dome equilibrium position this conductive layer electrically connects separated conductive tracks of the PCB. When user releases the button, strain energy stored in the elastomeric dome shaped member during its deformation is released forcing it to return to its equilibrium, inactive position along with the button.

It is desirable to achieve an appropriate relation between the force experienced by user touching the button and the position of the activating projection. This relation defines the haptic response of the button assembly.

Unfortunately such contact button assemblies have a number of disadvantages. Wear and oxidation of the conductive layer and tracks limit the number of cycles of the assembly even if expensive materials (e.g. gold) are used. They feature a limited angular activation (usually within a range of ±5 degrees with regard to the axis normal to the PCB), a negative phenomenon known as “debouncing” (multiple signal generation at the switching limit transient state). Small debris, water droplets, etc. can get between the contact layers and render the assembly inoperable and the conductive layer and tracks are susceptible to burn out.

Capacitive switches operating on the basis of measuring changes in electrical capacitance between two capacitive regions are devoid of the aforementioned drawbacks. Yet their haptic response is limited.

Patent publication US6914785B1 discloses a circuit component having an elastically deformable first structure, a second structure, and a support structure coupling the first and second structures, wherein the support structure acts a fulcrum about which the first structure can be variably deformed in response to a variable force, to provide either a variable capacitor or a variable tank circuit having a variable capacitor and an inductor. In one particular embodiment, the circuit component includes a zipper actuator for elastically deforming the first structure.

Patent publication US2013299331 discloses a dome switch that includes a capacitive sensor. A dome switch can include a dome operative to deform to provide tactile feedback to a user. To provide an electrical instruction to the device, the region underneath the dome can define a free space separating conductive regions forming a capacitor. For example, a tip of the dome, a button placed between the dome and a circuit board, or a user's finger can form a first conductor of a capacitor, and a support structure for the dome can include a terminal forming a second conductor completing the capacitor. When the dome deflects, the distance between the conductors can change and provide a measurable capacitance variation, which the device can detect.

A button assembly comprising stacked metal and elastomeric domes is disclosed in patent publication US9012795. The stacking of the elastomeric metal domes takes advantage of the abrupt force drop in the metal dome buckling and applies it to the elastomeric dome force, making it possible to design a low-travel key while still maintaining or improving the tactile feeling of the key switch.

It has been the object of the present invention to provide a compact, cost efficient and simple to manufacture button assembly of the kind mentioned in the outset featuring tunable and versatile haptic characteristic and an extended service life. Another object of the present invention has been to provide a keypad comprising a number of such button assemblies.

Summary of the invention

The invention provides a button assembly of the kind mentioned in the outset which is characterised in that said electric switch is defined by at least one first capacitive region formed on a first member and separated along the axis from at least one second capacitive region formed on a second member disposed beneath the activating surface of the dome shaped member, wherein said second member is capable of being deflected or displaced under the pressure of the activating surface when the button is being pressed, wherein displacement of said second member further contributes to the tactile response of the button, and the change of the capacitance between said capacitive regions indicates the state of the button.

Therefore the elastomeric dome shaped member is devoid of its mechanical, electrical contact activation function and is responsible solely for the haptic response of the button assembly. This also reduces the cost of the assembly as the relatively expensive conductive layers are no longer necessary. The assembly is resistant to contamination by liquids or solids, burn outs and debouncing phenomenon, what extends its service life. The elimination of short circuiting positively affects the design of other electrical components of the assembly. The tactile response felt by user pressing the button can be shaped and fine-tuned to a large extent by modification of materials, number and geometry of the elastomeric dome shaped member, as well as materials, geometry of said second displaceable or deflectable member. The assembly is particularly advantageous to implement a short stroke tactile response providing versatile digital tuning options for adjusting the point of the button activation.

Preferably said second member has a form of a metal plate.

Preferably said second member is deflectable or biased by a spring.

This enables to compensate any mechanical imperfections and free-play of the components of the assembly. Preferably said elastomeric dome shaped member has an activating projection terminated with said activating surface.

In such a case said second member can be preloaded by said activating projection in an extended equilibrium position of the elastomeric dome shaped member.

Preferably said activating surface is curved and preferably spherical.

This improves activation in direction slanted with regard to the activation axis, as the second member will displace substantially in the same way irrespectively on the angle of activation.

Preferably said elastomeric dome shaped member is formed in an elastomeric sheet, wherein said at least one first capacitive region and said at least one second capacitive region are located on the opposite sides of said elastomeric sheet.

Thanks to that the elastomeric sheet serves as a dielectric layer of the capacitive switch.

Preferably said first member is provided with an opening surrounding the dome shaped member.

This reduces the height of the button assembly as the first member is located within the working space of the elastomeric dome shaped member.

Preferably said first member has a form of a printed circuit board.

This also compensates any intolerances and free-play of the components of the assembly, as the second member presses the elastomeric sheet towards the PCB.

Preferably said elastomeric dome shaped member is provided with a light guide.

Thus additional elements, such as LEDs, can be disposed beneath the elastomeric dome shaped members to illuminate the buttons.

The invention also provides a keypad comprising a number of button assemblies defined above. Brief description of drawings

The invention shall be described and explained below in preferred embodiments and in connection with the attached drawings in which:

Fig. 1 is a schematic axonometric and exploded view of an embodiment of the button assembly (Fig. 1a as seen from the top, Fig. 1b as seen from the bottom);

Fig. 2 is a schematic cross-sectional view of the button assembly shown in Fig. 1 (Fig. 2a in an inactive, standby state, Fig. 2b upon activation);

Fig. 3 is a schematic cross-sectional view of another embodiment of the elastomeric dome shaped member;

Fig. 4 is a schematic cross-sectional view of subsequent embodiment of the elastomeric dome shaped member;

Fig. 5 is a schematic cross-sectional view of yet another embodiment of the elastomeric dome shaped member;

Fig. 6 is a schematic cross-sectional view of another embodiment of the button assembly upon activation;

Fig. 7 is a schematic axonometric view of an elastomeric sheet and a metal plate of the button assembly shown in Fig. 1 and 2 (Fig. 7a in an inactive, standby state, Fig. 7b upon activation);

Fig. 8 is a schematic axonometric view of a metal plate of the button assembly shown in Fig. 1 ;

Fig. 9 is a schematic axonometric view of another embodiment of a metal plate illustrating additional light sources to illuminate the buttons;

Fig. 10 is a force vs. displacement characteristic of a typical elastomeric dome shaped member; and

Fig. 11 outlines force vs. displacement characteristics of two embodiments of the haptic button assemblies of the present invention.

Detailed description of preferred embodiments

In the following description numerical references of elements performing the same functions remain the same in the drawings, wherein suffixes (a, b, ...) were added, where appropriate, to distinguish distinct components having analogous construction or functionality. An embodiment of a button assembly 1a shown in Figs. 1 , 2, 7 and 8 comprises a plastic housing 2 comprising a cover 21 and a bottom 23 fixed to a housing body 22. Two buttons 3a and 3b are held in the housing 2 apt to be moved axially in the activation direction along an activation axis A.

Each button 3 cooperates with an elastomeric dome shaped member 51 disposed beneath the button 3. The geometry of the member 51 ensures that it normally maintains an expanded state due to elastic forces and thus maintains an inactive state of the button 3. Each dome shaped member 51 defines a chamber 52 and has an activating surface 53 disposed within the chamber 52. In this embodiment two pairs of the elastomeric dome shaped members 51a and 51b corresponding respectively to the buttons 3a and 3b are shaped in a single elastomeric sheet 5.

Furthermore each elastomeric dome shaped member 51 cooperates with an electric capacitive switch defined by a first capacitive region 41 formed on a first, immovable member 4 and separated along the axis A from a second capacitive region 61 formed on a second member 6 disposed beneath the activating surface 53 of the dome shaped member 51 and capable of being displaced under the pressure of the activating surface 53 as a result of a user pressing the button 3. Thus, in this embodiment the elastomeric sheet 5 works additionally as a dielectric separator between the capacitive regions 41 and 61 and its thickness influences the referential capacitance of the electric capacitive switch 41 , 61 .

In this embodiment the first, still member 4 has a form of a printed circuit board (PCB) fixed between the housing bottom 23 and the housing body 22 and provided with openings 42 surrounding the dome shaped members 51. The first capacitive regions 41a and 41b have a form of a circular conductive rings printed around the openings 42a and 42b on the PCB 4 surface adjoining the elastomeric sheet 5.

Furthermore in this embodiment the second member 6 has a form of a metal plate 6 held in the housing bottom 23. The second capacitive regions 61a and 61b are the areas of the plate 6 located beneath the activating surfaces 53a and 53b and capable of deflection while pressed. In this embodiment the metal plate 6 (and thus also the second capacitive regions 61a and 61b) is common for all two buttons 3a and 3b. The metal plate is made of spring stainless steel and has a thickness of about 0.2 mm. It is also provided with four connecting surfaces 64 that are soldered to the corresponding connecting surfaces 43 of the PCB. The metal plate 6 further comprises three pairs of shaped projections 62 supporting it within the housing bottom 23 and remains deflectable between each pair of projections 62 and each pair of connecting surfaces 64.

The housing bottom 23 on the other hand comprises four three-element sets of supporting protrusions 24, each set corresponding to one dome shaped member 51. Each protrusion 24 passes through an opening 63 in the metal plate and supports the PCB 4. To this end the elastomeric sheet 5 and is provided with bridges 54 defining gaps 55 around the dome shaped members 51 . The metal plate 6 presses the elastomeric sheet 5 to the PCB 4 compensating any mechanical imperfections within the assembly 1 .

Fig. 2 illustrates the functionality of the button assembly 1.a As shown in Fig. 2a in the button inactive state the distance between the capacitive regions 41 and 61 is small and defined by the thickness of the elastomeric sheet 5. As shown in Fig. 2b, upon pressing the button 3b, the activating surface 53 of the collapsed dome shaped member 51b forces the metal plate 6 to deflect, thus increasing the distance between the capacitive regions 41 and 61 which results in a measurable decrease of the capacitance C = ErA/(4TTd), of the capacitive switch 41 , 61 , where s_r is the relative permittivity of the elastomeric sheet 5, A is a substantially constant area of the capacitive regions 41 and 61 and d is the distance between them. After the force acting on the button is released, the elastomeric dome shaped member 51 b returns to its equilibrium position illustrated in Fig. 2a decreasing the distance between the capacitive regions 41 and 61 to minimum.

The button assembly 1a is a digital system and for its operation requires an electronic control unit (not shown) that can be conveniently installed at the PCB 4 and connected with the first capacitive regions 41a, 41b and the metal plate 6a defining the second capacitive regions 61a, 61b to measure the capacitance and provide appropriate output to further systems (not shown) controlled by the button assembly 1a. Skilled technician shall appreciate that this output can be Boolean (button_off/button_on), as well as continuous, indicating the stroke of the buttons 3a, 3b even if not entirely pressed. Various embodiments of the dome shaped members 51c, 51 d and 51 e are shown in Figs. 3-5. The member 51c shown in Fig. 3 has a relatively short activating projection 56 and thus relatively long idle stroke S₄. In yet another embodiment (not shown) the dome shaped member could have no activating projection 56 at all. The member 51 d shown in Fig. 4 has an activating projection 56 extending below the metal layer 5 and thus normally preloading it at the stroke S₅. The member 51 e has an activating projection 56 terminated with a spherical activating surface 53 which improves angular activation in direction slanted with regard to the activation axis A. Furthermore the activating projection 56 of the member 51 e is provided with a light guide 57 that can be used to illuminate the buttons by light sources disposed beneath the second capacitive region 61 (cf. Fig. 9).

Fig. 6 illustrates another embodiment of the button assembly 1 b in which a first capacitive region 41 is disposed beneath a second capacitive region 61 and formed on the top surface of the PCB 4 held within the housing 2. The second capacitive region 61 is formed on a plastic, displaceable second member 6 biased by a spring 9 positioned on a dielectric member 7 separating the PCB 4 and the second member 6. In this embodiment the capacitance C between the capacitive regions 41 and 61 increases with the button 3c stroke.

Another embodiment of a metal plate 6b is shown in Fig. 9. The metal plate 6b is flat and each second capacitive region 61a, 61b is provided with linear cutouts 65 extending radially from its centre, where the force can be applied by the activating surface 53, so that the regions between the adjoining cutouts 65 can freely deflect. Furthermore the cutouts 65 allow light transmission through the plate 6b, so that additional light sources 8 (such as LEDs) can be used to illuminate the buttons. To this end the elastomeric dome shaped members 51 should be transparent or provided with light guides 57, as in the embodiment 51 e shown in Fig. 5.

The skilled technician will appreciate that the number of possible shapes of the metal plates that can be used to define the second capacitive regions 61 is unlimited. The reaction haptic force generated by the plate can be controlled and tuned inter alia by the shape and thickness of the plate and characteristics of the plate material. Fig. 10 schematically illustrates a graph of reaction force of an exemplary elastomeric dome shaped member, of a geometry corresponding to the dome shaped member 51c shown in Fig. 3, when used in a contact switch known from the state of art, as a function of its stroke (displacement along the activation axis). As shown the elastomeric dome provides a buildup of the force from zero to a local maximum Fi at certain stroke Si. Further increase of the stroke decreases the reaction force, as the collapsed dome buckles inwardly, up to the stroke S2, where the activating surface 53 contacts with the conductive tracks of the PCB. This is a local minimum F2 of the force from which it rapidly increases along with the stroke to reach a stable electrical connection at the stroke S₃. This difference between S2 and S3 is responsible for debouncing phenomenon (multiple signal generation at the switching limit transient state). The skilled technician will appreciate that the graph shown in Fig. 10 is exemplary, and that the actual forces and strokes will depend on the material and the geometry of a dome shaped member.

Fig. 11 outlines the tactile feel that would be experienced by a user pressing the button of the present invention and provided with the dome shaped member 51 b (ST, S₂’, FT, F₂’) shown in Fig. 3 and the dome shaped member 51c (ST’, S2”, FT’, F₂”) shown in Fig. 4. As shown the haptic properties of the button assembly according to the invention is achieved from amplifying nonlinear haptic properties of the dome shaped member 51b, 51c with substantially linear haptic of the metal plate.

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. button assembly

2. housing

21. cover

22. body

23. bottom - IQ -

24. supporting protrusion button first member (PCB)

41. first capacitive region

42. opening

43. contact surface elastomeric sheet

51. dome shaped member

52. chamber

53. activating surface

54. bridge

55. gap

56. activating projection

57. light guide second, deflectable or displaceable member (metal plate)

61. second capacitive region

62. supporting projection

63. opening

64. connecting surface

65. cutout dielectric separator light source spring

Claims

1. A haptic button assembly (1), in particular for use in an automotive vehicle, comprising a housing (2), at least one button (3) held in the housing (2) and apt to be moved in the activation direction along an activation axis (A), at least one elastomeric dome shaped member (51) disposed beneath the button (3) having a chamber (52) and an activating surface (53) disposed within the chamber (52), wherein the elastomeric dome shaped member (51) normally maintains an extended equilibrium position and buckles, while the button (3) is pressed contributing to the tactile response of the button (3) by providing at least one local maximum of the force with regard to the button (3) stroke, and an electric switch corresponding to said button (3) and cooperating with said activating surface (53), characterised in that said electric switch is defined by at least one first capacitive region (41) formed on a first member (4) and separated along the axis (A) from at least one second capacitive region (61) formed on a second member (6) disposed beneath the activating surface (53) of the dome shaped member (51), wherein said second member (6) is capable of being deflected or displaced under the pressure of the activating surface (53) when the button (3) is being pressed, wherein displacement of said second member (6) further contributes to the tactile response of the button (3), and the change of the capacitance between said capacitive regions (41 , 61) indicates the state of the button (3).

2. The button assembly according to any one of the preceding Claims, characterized in that said second member (6) has a form of a metal plate.

3. The button assembly according to Claim 1 or 2, characterized in that said second member (6) is deflectable or biased by a spring (9).

4. The buton assembly according to any one of the preceding Claims, characterized in that said elastomeric dome shaped member (51) has an activating projection (56) terminated with said activating surface (53).

5. The button assembly according to Claim 4, characterized in that, said second member (6) is preloaded by said activating projection (56) in an extended equilibrium position of the elastomeric dome shaped member (51).

6. The buton assembly according to any one of the preceding Claims, characterized in that said activating surface (53) is curved and preferably spherical.

7. The buton assembly according to any one of the preceding Claims, characterized in that said elastomeric dome shaped member (51) is formed in an elastomeric sheet (5), wherein said at least one first capacitive region (41) and said at least one second capacitive region (61 ) are located on the opposite sides of said elastomeric sheet (5).

8. The buton assembly according to any one of the preceding Claims, characterized in that said first member (4) is provided with an opening (42) surrounding the dome shaped member (51).

9. The button assembly according to any one of the preceding Claims, characterized in that said first member (4) has a form of a printed circuit board.

10. The button assembly according to any one of the preceding Claims, characterized in that, said elastomeric dome shaped member (51) is provided with a light guide (57).

11. A keypad comprising a number of button assemblies (1) defined in any one of Claims 1 to 10.