WO2011138200A1

WO2011138200A1 - Input device

Info

Publication number: WO2011138200A1
Application number: PCT/EP2011/056638
Authority: WO
Inventors: Alain Noll; Andreas Steier
Original assignee: Iee International Electronics & Engineering S.A.
Priority date: 2010-05-06
Filing date: 2011-04-27
Publication date: 2011-11-10

Abstract

An input device (310) for human-appliance interaction comprises a pressure sensor in form of a membrane switch (312) including a first carrier film (314), a second carrier film (316) and a spacer (318) with at least one gap defining a sensor cell (320). The input device further comprises a base member (322), on which the pressure sensor is applied with its second carrier film, and a cover member (324) exposed for user interaction and arranged on the first carrier film to transmit a force applied thereon to the first carrier film. The cover member is spaced from the first carrier film by at least one force-transmitting element centered on the sensor cell in such a way that the force applied on the cover member is transmitted to the first carrier film via the force-transmitting element and causes the first carrier film to bend into the sensor cell.

Description

INPUT DEVICE

Technical Field

[0001 ] This invention relates to input devices and more particularly to data input devices including a film-based pressure sensor for human-appliance interaction. Such devices are sometimes referred to as man-machine interfaces, user interfaces, or human-computer interfaces, depending on the application.

Background Art

[0002] Input devices are commonly used in conjunction with electronic appliances to feed the latter with various kinds of inputs, including e.g. control data influencing directly or indirectly the behavior of the appliance, input that is processed by the appliance and/or input that is simply stored.

[0003] It is known to construct input devices based upon film-type pressure sensors, whose resistance varies with pressure. The resistance may vary in discrete steps (e.g. between an insulating state and a conducting state) or gradually. Such a film-type pressure sensor comprises two carrier films, which are arranged at a certain distance from one another by means of a spacer. The spacer is provided with at least one opening that defines an active zone of the sensor, in which the two carrier films face one another. Inside this active zone, at least two electrodes are arranged on the carrier films, in such a way that electrical contact is established between the electrodes when the two carrier films are pressed together under the action of a compressive force acting on the sensor in the active zone. The pressure acting on the sensor is detected and/or determined as a function of the resistance between the electrodes.

[0004] Depending on the application of such a pressure sensor, a layer of semiconducting material may be disposed between the electrodes, so that the sensor shows a gradual pressure sensitive behavior, that is to say its resistance varies gradually or even continuously as a function of the force applied. The layer of semiconducting material may comprise a material whose internal electrical resistance varies as a function of compression or of deformation of the layer or a material whose surface structure confers to the layer a surface resistance that is reduced following an increase in the number of points of contact with a conducting surface of an electrode, against which the layer of semiconducting material is pressed under the action of the compressive force. [0005] A different kind of input devices is based upon capacitive sensing. Such input devices typically comprise one or more antenna electrodes that are driven by an oscillator and that emit electric fields into the sensitive volume. A person or an object intruding into the sensitive volume causes a change of the electric field of the antenna, which is detected by detection electronics. Capacitive input devices sometimes have difficulties to correctly sense user interaction, e.g. if the user has moist fingers or wears gloves. The use of capacitive input devices also raises the question of electromagnetic compatibility.

[0006] The present invention addresses improvements of input devices based upon film-type pressure sensors.

[0007] Fig. 1 shows an input device 10 comprising a film-type pressure sensor in form of a membrane switch 12. The membrane switch 12 includes a first carrier film 14, a second carrier film 16 and a spacer 18 arranged between the first and second carrier films 14, 16, the spacer having therein at least one gap 20 defining a sensor cell. The sensor cell has an electrode arrangement therein, which comprises at least a first and a second electrode (not shown) disposed on the first and second carrier film, respectively, in such a way that, when the first carrier film is caused to bend into the sensor cell towards the second carrier film, the first and second electrodes are pressed together and an electric contact is established between the electrodes. The membrane switch is sandwiched between a base plate 22, on which the membrane switch is supported, and a cover plate 24, which provides an outer surface for user interaction. To actuate the membrane switch, the user has to press on the cover plate, which is arranged to transmit the force to the first carrier film and thus to cause the first carrier film to bend until the electrodes are in contact. The base plate exerts the reaction force on the membrane switch. [0008] In many applications, the input device is required to have a stiff (rigid) cover plate, e.g. to protect the underlying pressure sensor, or for haptic or aesthetic reasons. For a given cover material, the activation force (i.e. the activation threshold, which is the minimum force the user has to apply to the input device to achieve the desired input action) is determined by the thickness d of the spacer (i.e. the height of the sensor cell) and by the sensor cell diameter D. In order to keep the activation force within reasonable limits, the stiffer the cover plate, the more the diameter D of the sensor cell has to be increased and/or the more the thickness d of the spacer has to be reduced. A reduced spacer thickness and an increased sensor cell diameter will lead to a decrease of the activation force. There is, however, a limitation in the freedom of adjusting these two parameters for designing a low activation force system. The limit is reached when the membrane switch becomes mechanically unstable or too sensitive.

[0009] Fig. 2 illustrates a classical way of achieving a low-activation force input device. To reduce the activation force, the diameter of the sensor cell has been considerably increased with respect to the example shown in Fig. 1 . In order to mechanically stabilize the input device, adhesive layers 26, 28 have been added to fix the carrier films 14 and 16 to the cover plate 24 and the base plate 22, respectively.

[0010] The addition of adhesive layers, however, renders the fabrication of the input device considerably more complicated. For example, great care has to be taken to avoid any air bubbles in the adhesive layers. Another reason why one usually wants to avoid adhesives is that it is difficult to find materials that have compatible thermal expansion coefficients in the desired temperature range. For automotive applications (in cars, buses, trucks etc.), the required temperature range is from - 40°C to more than 100°C. [001 1 ] A first aspect of the invention addresses the problem of bringing increased sensitivity and stable operation together.

[0012] A second aspect of the invention is concerned with the problem of production tolerances of (e.g. injection-molded) support frames for input devices. Summary of the Invention

[0013] According to the first aspect of the invention, it is proposed an input device for human-appliance interaction (e.g. in an automotive environment), which comprises a pressure sensor (e.g. a membrane switch), including a first carrier film, a second carrier film and a spacer arranged between the first and second carrier films. The spacer has therein at least one gap (opening or recess) defining a sensor cell, within which the pressure sensor comprises at least a first and a second electrode arranged on the first and second carrier film, respectively, in such a way that, when the first carrier film is caused to bend into the sensor cell towards the second carrier film, the first and second electrodes are pressed together and an electric contact is established between at least the first and second electrodes. The input device further comprises a (preferably rigid) base member, on which the pressure sensor is applied with its second carrier film, and a cover member exposed for user interaction and arranged on the first carrier film to transmit a force that may be applied thereon through the user interaction to the first carrier film. The cover member is spaced from the first carrier film by at least one force-transmitting element substantially centered on the sensor cell in such a way that the force that may be applied on the cover member is transmitted to the first carrier film via the force-transmitting element and causes the first carrier film to bend into the sensor cell towards the second carrier film.

[0014] The cover member is preferably a relatively stiff plate (e.g. made of plastic material, such as polycarbonate (PC), PMMA, or the like, or glass or metal).

[0015] The at least one force-transmitting distance element is preferably substantially incompressible. Those skilled will appreciate that in case the pressure sensor of the input device comprises more than one sensor cell, there is preferably a force-transmitting element for each of the sensor cells. The at least one force- transmitting element advantageously has a diameter which is substantially smaller than the diameter of the sensor cell. The height of the each force-transmitting element preferably amounts to at least the height of the sensor cells (i.e. the spacer thickness). The at least one force-transmitting distance element may be achieved as a printed elevation (e.g. using 3D-printing techniques). The at least one force- transmitting distance element may be made of dielectric material. It could, for instance be made of the same material as the carrier films (e.g. PET, PC, PEN; PI, or the like).

[0016] Those skilled will appreciate that in the input device according to the first aspect of the invention, the force-transmitting element (an possibly other spacer elements between the cover member and the first carrier film) are mutually spaced to an extent which allows the cover member to bend with a large bending radius when pressed by the user. The force-transmitting elements then press on the first carrier film, which bends with a much smaller bending radius.

[0017] The base member is advantageously made of PC, but it could also be made of glass, metal or any other rigid, substantially incompressible material. The cover member and the base plate are preferably made of the same material. In this case, the base plate is typically chosen with a greater thickness than the cover member, which has to be sufficiently flexible to be deflected by the user exerting a typical force on the input device (e.g. about 2 N).

[0018] According to the first aspect of the invention, it is proposed an input device for human-appliance interaction (e.g. in an automotive environment), comprising a pressure sensor, including a first carrier film, a second carrier film and a spacer arranged between the first and second carrier films. The spacer has therein at least one gap defining a sensor cell, within which the pressure sensor comprises at least a first and a second electrode arranged on the first and second carrier film, respectively, in such a way that, when the first carrier film is caused to bend into the sensor cell towards the second carrier film, the first and second electrodes are pressed together and an electric contact is established between at least the first and second electrodes. The input device further comprises a base member, on which the pressure sensor is applied with its second carrier film, and a cover member exposed for user interaction and arranged on the first carrier film to transmit a force that may be applied thereon through the user interaction to the first carrier film. The base member comprises a first plate and a second plate, which sandwich a compressible layer, e.g. comprising polyurethane foam or another elastic material, such as silicone, elastomeric material, rubber, or the like. The compressible layer could also comprise a plurality of springs.

[0019] Input devices may be mounted in a housing or frame. Usually, these housings or frames have much higher production tolerances than the pressure sensors employed in the input device, which makes it difficult to assemble the housing or frame and the input device. Reducing the production tolerances may be difficult (and thus costly) or impossible in certain cases due to the production process chosen (e.g. plastic injection molding). Those skilled in the art will appreciate that, in an input device in accordance with the second aspect of the invention, the base member may be compressed due to the presence therein of the compressible layer. As a result, the thickness of the base member and thus of the overall input device may be easily adjusted to the height of the mounting slot in the frame or housing by compression. The resilience of the compressible layer also contributes to secure hold the input device in the frame or housing.

[0020] The cover member is preferably a relatively stiff but nevertheless flexible plate (e.g. made of plastic material, such as polycarbonate, PMMA, or the like, or glass or metal).

[0021 ] The first and second plates are preferably rigid and substantially incompressible. Suitable materials are, e.g. PC, PMMA, glass, metal or the like. The cover member and the first and second plates are preferably made of the same material. In this case, the first and second plates are typically chosen with a greater thickness than the cover member, which must be sufficiently flexible to be deflected by the user exerting a typical force on the input device.

[0022] It is possible to combine the first and the second aspects of the invention in one input device.

Brief Description of the Drawings

[0023] Further details and advantages of the present invention will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawings, wherein: Fig. 1 is a schematic cross-sectional view of an input device according to the prior art;

Fig. 2 is a schematic cross-sectional view of a prior art input device with increased sensitivity; Fig. 3 is a schematic cross-sectional view of an input device according to an embodiment of the first aspect of the invention; and

Fig. 4 is a schematic cross-sectional view of an input device according to an embodiment of the second aspect of the invention;

Fig. 5 is a schematic cross-sectional view of a variant of the input device of Fig. 3.

[0024] It should be noted that the drawings are not to scale: for clarity reasons, the thickness of the various layers is exaggerated with respect to the diameter of a sensor cell.

Description of Preferred Embodiments

[0025] Fig. 3 shows an example of an input device 310 according to the first aspect of the invention. The input device 310 comprises a pressure sensor in the form of a membrane switch 312. The membrane switch 312 includes a first carrier film 314, a second carrier film 316 and a spacer 318 sandwiched between the first and second carrier films 314, 316. The membrane switch 312 comprises a plurality of sensor cells 320 (only one of which is shown) defined by respective openings in the spacer 318. In each sensor cell 320, the membrane switch comprises a first electrode 330a arranged on the first carrier film as well as a second and a third electrode 330b, 330c arranged on the second carrier film 316, in facing relationship with the first electrode. When a force exerted on the first carrier film 314 causes it to bend into the sensor cell 320 towards the second carrier film 316, the first and second electrodes as well as the first and third electrodes are pressed together and an electric contact is established between the second and third electrodes, via the first electrode. This kind of electrode configuration is sometimes referred to as "shunt-mode" configuration, because the first electrode shunts the insulating or highly resistive gap between the second and third electrodes when the first carrier film is pressed. [0026] The membrane switch 312 is sandwiched between a rigid base plate 322 (e.g. made of transparent or translucent material to allow backlighting of the input device), on which the membrane switch 312 is supported, and a thin, incompressible but flexible cover plate 324, which provides the outer surface for user interaction. To actuate the membrane switch 312, the user has to press on the cover plate 324, which is arranged to transmit the force to the first carrier film 314 and thus to cause the first carrier film 314 to bend until the electrodes 330a, 330b and 330c are in contact. The base plate 322 exerts the reaction force on the membrane switch 312.

[0027] The cover plate 324 is spaced from the first carrier film 314 by force- transmitting elements 332 (only one of which is shown) and a spacer frame 334. Each force-transmitting element 332 is centered on one of the sensor cells. Any force the user applies to the input device to achieve a switching is transmitted from the cover plate 324 to the first carrier film 314 via one of the force-transmitting elements 332 and causes the first carrier film 314 to bend into the sensor cell 320 towards the second carrier film 316.

[0028] The force-transmitting elements 332 are preferably made of substrate materials (i.e. of the same materials as the carrier films) or dielectric prints. The force-transmitting elements 332 are chosen substantially incompressible, which means that for pressures typically exerted thereon, they will not be significantly compressed. The distance between the force-transmitting elements 332 and the spacer frame is chosen such that the area, in which the cover plate may bend under the action of a force is much larger than the area of the sensor cell 320 underneath. The system sensitivity is adjustable by varying the distances between the force- transmitting elements 332 (and the spacer frame 334): the greater the diameter Δ of the "cover cell", the lesser the activation force of the input device 310, because the cover plate 324 may thus bend over a larger area.

[0029] Those skilled in the art will appreciate that the parameters of the membrane switch 312 (height and diameter of the sensor cell 320) may be kept within ranges allowing mechanically stability and reliable operation. [0030] A variant of the input device of Fig. 3 is shown in Fig. 5. For simplicity, the same reference numbers as in Fig. 3 are used in Fig. 5. The only difference with respect to the input device of Fig. 3 is that the height H of the force-transmitting element 332 is greater than the height h of the spacer frame 334 (H > h). This induces a preload on the first carrier film 314, since the cover plate 324 is substantially stiffer than the first carrier film 314. The first carrier film 314 is thus slightly bent into the sensor cell 320 but there is still a distance between the electrodes on the first and the second carrier film, respectively, so that the user still needs to press on the cover plate to actuate the membrane switch. One may vary the height H of the force-transmitting element 332 to adjust the activation force (and thus the sensitivity) of the input device 310. [0031 ] Fig. 4 shows an example of an input device 410 according to the second aspect of the invention. The input device 410 comprises a pressure sensor in the form of a membrane switch 412. The membrane switch 412 includes a first carrier film 414, a second carrier film 416 and a spacer 418 sandwiched between the first and second carrier films 414, 416. The membrane switch 412 comprises a plurality of sensor cells 420 (only one of which is shown) defined by respective openings in the spacer 418. In each sensor cell 420, the membrane switch comprises a first electrode 430a arranged on the first carrier film and a second electrode 430b arranged on the second carrier film 416, in facing relationship with the first electrode. When a force exerted on the first carrier film 414 causes it to bend into the sensor cell 420 towards the second carrier film 416, the first and second electrodes are pressed together and an electric contact is established there between. This kind of electrode configuration is sometimes referred to as "through-mode" configuration.

[0032] It may be worthwhile noting that the input device of Fig. 4 could alternatively have an electrode arrangement in "shunt-mode" configuration. Similarly, the input device of Fig. 3 could alternatively have an electrode arrangement in "through-mode" configuration.

[0033] The membrane switch 412 is sandwiched between a base 422 on which the membrane switch 412 is supported, and a thin, incompressible but flexible cover plate 424, which provides the outer surface for user interaction. To actuate the membrane switch 412, the user has to press on the cover plate 424, which is arranged to transmit the force to the first carrier film 414 and thus to cause the first carrier film 414 to bend until the electrodes 430a and 430b are in contact. The base 422 exerts the reaction force on the membrane switch 412.

[0034] The base 422 comprises a first rigid plate 422a and a second rigid plate 422c, between which a compressible layer 422b (e.g. a layer of elastic material such as rubber, silicone or the like; or a foam layer; or a layer of springs) is sandwiched.

[0035] The input device 410 further comprises a mounting frame 436, which securely holds the membrane switch 412, the base 422 and the cover plate.

[0036] The height of a membrane switch sensor cell is typically of the order of 100 μιτι, which implies that the cover plate only needs a displacement of the same amount to activate the membrane switch. The production tolerances for fabrication of plastic injection-molded parts are typically greater, which bears the risk that when the membrane switch and an injection-molded frame are assembled, the parts do not fit. This, in turn may lead to intolerable spread of the activation forces of the individual input devices thus produced. Mass production is thus rendered difficult. [0037] This problem is overcome with the input device as shown in Fig. 4. When the membrane switch 412, the cover plate 424 and the base 422 are clamped in the mounting frame 436, the compressible layer induces a permanent load into the assembly, which secures the membrane switch 412, the cover plate 424 and the base 422 in the frame. The first and second rigid plates are stiff enough not to bend significantly under the preload over the whole (application-dependent) temperature range within which the input device is required to operate. This way, it is ensured that the preload does not induce a deformation of the membrane switch 412 and/or the cover plate.

[0038] The compressible layer is configured to induce a preload amounting to several times the activation force in order to ensure that the activation force will not be influenced by the temperature behaviour of the compressible material or the other materials of the assembly.

[0039] The base 422 is preferably made of transparent or translucent materials to allow backlighting of the input device 410. [0040] While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims

1 . An input device (410) for human-appliance interaction, comprising

a pressure sensor (412), including a first carrier film (414), a second carrier film (416) and a spacer (418) arranged between said first and second carrier films, said spacer having therein at least one gap defining a sensor cell (420), said pressure sensor comprising at least a first and a second electrode (430A, 430B) arranged in said sensor cell on said first and second carrier film, respectively, in such a way that, when said first carrier film is caused to bend into said sensor cell towards said second carrier film, said first and second electrodes are pressed together and an electric contact is established between at least said first and second electrodes;

said input device further comprising a base member (422), on which said pressure sensor is applied with its second carrier film, and a cover member (424) exposed for user interaction and arranged on said first carrier film to transmit a force that may be applied thereon through said user interaction to said first carrier film;

characterized in that said base member (422) comprises a first plate (422a) and a second plate (422c), said first and second plates sandwiching a compressible layer (422b).

2. The input device as claimed in claim 1 , wherein said compressible layer comprises foam material, such as e.g. polyurethane foam.

3. The input device as claimed in claim 1 , wherein said compressible layer comprises elastic material, such as e.g. silicone, elastomeric material, rubber, or the like.

4. The input device as claimed in claim 1 , wherein said compressible layer comprises a plurality of springs.

5. The input device as claimed in any one of claims 1 to 4, comprising a frame (436) or housing wherein said pressure sensor (410), said base member (422) and said cover member (424) are held.

6. An input device (319) for human-appliance interaction, comprising a pressure sensor (312), including a first carrier film (314), a second carrier film (316) and a spacer (318) arranged between said first and second carrier films, said spacer having therein at least one gap defining a sensor cell (320), said pressure sensor comprising at least a first and a second electrode (330a, 330b, 330c) arranged in said sensor cell on said first and second carrier film, respectively, in such a way that, when said first carrier film is caused to bend into said sensor cell towards said second carrier film, said first and second electrodes are pressed together and an electric contact is established between at least said first and second electrodes;

said input device further comprising a base member (322), on which said pressure sensor is applied with its second carrier film, and a cover member (324) exposed for user interaction and arranged on said first carrier film to transmit a force that may be applied thereon through said user interaction to said first carrier film;

characterized in that said cover member (324) is spaced from said first carrier film (314) by at least one force-transmitting element (332) and one or more further spacer elements (334), said at least one force-transmitting element and said one or more further spacer elements being mutually spaced to an extent which allows said cover member to bend towards said first carrier member when said cover member is pressed by a user, said force-transmitting element being substantially centered on said sensor cell in such a way that said force that may be applied on said cover member is transmitted to said first carrier film via said force-transmitting element and causes said first carrier film to bend into said sensor cell towards said second carrier film.

7. The input device as claimed in claim 6, wherein said at least one force- transmitting element is substantially incompressible.

8. The input device as claimed in claim 6 or 7, wherein said at least one force- transmitting element has a diameter which is substantially smaller than the diameter of said sensor cell.

9. The input device as claimed in any one of claims 6 to 8, wherein said at least one force-transmitting element comprises a printed elevation.

10. The input device as claimed in any one of claims 6 to 9, wherein said at least one force-transmitting element is made of dielectric material.

1 1 . The input device as claimed in any one of claims 6 to 10, wherein the height (H) of said at least one force-transmitting element is greater than the height (h) of said one or more further spacer elements.