WO2004088694A1

WO2004088694A1 - A cover for a push button switch

Info

Publication number: WO2004088694A1
Application number: PCT/DK2004/000229
Authority: WO
Inventors: Steffen Haslund Schmidt
Original assignee: Danfoss Drives A/S
Priority date: 2003-04-03
Filing date: 2004-04-01
Publication date: 2004-10-14
Also published as: DE112004000492B4; WO2004088694B1; DE112004000492T5

Abstract

A cover and a method of making a cover for a push button switch. A frame and a key for switching the push button switch are moulded directly onto a flexible layer forming an outer surface of the cover. The flexible layer shields the key and the associated push button switch from dust and water and the frame shields against rough handling. Since the frame is joined to an inner surface of the flexible layer, it also supports the flexible layer when the layer is deformed during switching of the switch. When the frame, the key and the flexible layer is moulded together, tightness of the cover can be maintained even if one of the parts is perforated, e.g. the outer flexible layer is scratched during rough handing of the covered switch.

Description

A COVER FOR A PUSH BUTTON SWITCH

Introduction

The present invention relates to a cover, a housing and a method of making a cover for shielding a push button switch or a number of switches arranged e.g. in a keypad. In particular, the invention relates to a cover allowing operation of an associated switch through the cover and which exhibits resistance against rough handling as well as penetration of dust and water, and which thus protects the switch and associated electronic components shielded by the cover.

Background of the invention

In a conventional keypad, dome switches or similar keys are brought into contact with switching contact points, e.g. arranged in a printed circuit board. Since the functioning of the switch is highly dependent on a direct contact between dry and clean contact points, it is in general desired to protect switches and associated electronic components from rough, wet and dusty environments. At the same time, it is often desired to provide direct access to switching operations without preceding removal of covers etc.

Covers which shield keypads and allow operation of keys through the cover exist. The known covers are typically made from a flexible foil material arranged in a frame to cover one or more switches arranged below the frame. When a covered switch is operated, the foil material is pressed into contact with a switching key and further down until contact is made between the contact points. As long as the foil is new and flexible, it may provide an acceptable shielding of associated switches against the environment. During use it may, however, happen that the foil is ruptured, e.g. due to rough handling of the switch and over time most flexible foils becomes less flexible or even brittle, in particular when subjected to sunlight or moist. Accordingly, the operation of the associated switches becomes more difficult and the risk of rupturing the foil increases. Often, a symbol visualising a function associated with a specific switch is printed either directly onto a key for switching that switch, or onto a foil covering that key, e.g. below the foil or onto the top of the foil, i.e. facing either the switching key or the operator. Unfortunately, such prints tend to be rubbed of either by the repeated contact between the foil and the switching key or by the repeated contact between the finger of an operator and the foil.

In US 6,423,171 a keypad for a portable telephone and the manufacturing method thereof is disclosed. According to this method, characters are printed on a transparent, planar film which is subsequently formed into a shape comprising a plurality of depressions by a pressing process. The depressions are filled with liquid silicone rubber and the silicone rubber is subsequently formed into a keypad in a metal mould. In order to avoid difficulty of operation due to the hardness of the film, slits 10 are formed around each key on the film, c.f. US 6,423,171 col. 3, lines 11-15 and Figs. 2C, 2D. Due to the slits, the switching contacts are only protected from the environment via the relatively thin single layer of a silicone material. US 6,423,171 discloses a front housing 22 protecting the front of the film. However, due to the arrangement of the front housing in front of the keys in a key pushing direction, the thin layer of a silicone material remains unsupported in the direction of the push button pushing. As a consequence thereof, repeated use of the keypad may over time lead to fractures in the silicone material, thus jeopardizing the functioning of the switch.

In the Japanese publication, JP 11126536 A2, a cover member for a push button is disclosed wherein switching contacts 11 , 22 are brought into contact by a movable projected part 42 formed by a silicone rubber composition by compressive moulding. In JP 11126536 A2, the switches are protected merely by the projected part 42, i.e. by one single component made from a silicone material, and any rupture in this frequently depressed and thus deformed component, will cause access from the ambient environment to the contacts. Moreover, the movably projected part in JP 11126536 is unsupported in the direction of the pushing whereby the pushing of a single button will cause a deflection of the entire part 42 with a resulting higher risk of wear and a reduced protection of the switch.

German utility model application No. 296 13 811 U1 discloses a cover for a push button switch comprising an elastic foil, which covers an outer housing with a recess, in which there is arranged a key element for transmitting a switching force to a switching element arranged inside an inner housing. The outer housing is joined to an inner surface of the flexible foil. The key element forms an integrated part of the inner housing, the key element and the inner housing thus being manufactured as one separate part. One disadvantage of the cover of DE 296 13 811 U1 is that the switching element is only protected from contamination, such as dust or water, by the elastic foil. As the foil deforms at every single depression of the key element, it is subject to substantial wear, which may cause fractures, which in turn comprise protection of the switching element and other electronic equipment associated with the switch. Protection is also compromised, if the foil does not adhere properly to the outer surface of the outer housing, even if no fractures exist in the foil itself.

Description of the invention

It is an object of the present invention to provide a cover and a housing which provide enhanced protection of a switch and other electronic components. It is a further object to provide a manufacturing method for the cover. Accordingly, the present invention, in a first aspect, relates to a cover for a push button switch, said cover comprising:

- a flexible layer with an inner surface and an opposite outer surface, the outer surface forming an outer surface of the cover,

- a supporting frame having a recess allowing the flexible layer in a switch activation area to be deformed into the frame, the supporting frame being joined to the inner surface of the flexible layer, and - a key element arranged at least partly in the recess for transferring, to an associated switch, a key switching force applied to the outer surface of the flexible layer in the switch activation area, characterized in that the key element is joined tightly to the inner surface of the flexible layer and to the supporting frame to form one single component. The joining of the key element tightly to the inner surface of the flexible layer and to the supporting frame to form one single component result in a particular water and dust proof cover. At the same time, since the supporting frame is joined to an inner surface of the flexible layer, a cover structure is formed wherein the flexible layer is supported by a frame in a switch pushing direction. Due to the support of the flexible layer in this direction, excessive deformation of the flexible layer is avoided, and accordingly, an enhanced lifetime of the cover and protection of the associated switch can be expected.

In the following description, the outer surface of the cover or of parts of the cover describes a surface facing outwardly towards the user of the covered switch, whereas the inner surface of the cover or of parts of the cover describes a surface facing inwardly towards the switch and other electronics being shielded by the cover.

The flexible layer could be made from a sheet of a foil material, e.g. a flexible plastic material with a thickness in the range of 0,1-0,5 mm such as in the size of 0,25 mm. The supporting frame could be made from a relatively hard plastic material, e.g. from Bakelite or from a similar hardening plastic material or from a hard thermoplastic material or even from a metal alloy, e.g. aluminium or steel. Moreover, the supporting frame could be made from a composite material, e.g. glass- or carbon fibre reinforced polyester or epoxy. The recess could be formed e.g. as a through hole in the frame. The recess is arranged under the switch activation area of the flexible layer and it is therefore possible to depress the flexible material in this area. Pressing against the flexible layer in the switch activation area, causes the flexible layer to deform into the recess or through hole of the frame. It is therefore possible to depress a key element arranged under the flexible layer in the switch activation area and thus to activate an associated switch.

The key element could be arranged in the recess or through hole of the frame and preferably in direct contact with the inner surface of the flexible layer. The key element could in fact have any shape as long as it allows deformation caused by depression of the flexible layer to be transferred to an associated switch. The key element could be made from a hard or a resilient material. If the key element is made from a hard material, it must be allowed to slide in the recess or through hole of the frame. A pressure applied to the switch activating area is transferred by deformation of the flexible layer to the key element whereby the key element shifts downwardly and activates the switch. If, on the other hand, the key element is resilient, e.g. made from a relatively soft rubber or silicone material, it could be fixated, e.g. adhesively, to the frame, e.g. to the edges of the recess or through hole of the frame. If the switch activation area is depressed, the flexible layer deforms into the recess or through hole of the frame. This will cause the key element, which is arranged in the recess or through hole of the frame, to deform in an inward direction and thus to activate an associated switch. In other words, the activation of the switch occurs due to a deformation of resilient material of the key element and the element itself remains in fixed contact with the frame. If depression of the switch activation area causes a major deflection of the entire cover, repeated use may damage the cover over time. Accordingly, the frame may advantageously be made from a material which is relatively inflexible compared with the flexibility of the key element and preferably, the frame is made from a hard material such as Bakelite or steel etc.

The key element is advantageously fixed, e.g. adhesively, to the inner surface of the flexible layer under the switch activation area thereof. In this way, repeated sliding and rubbing between the inner surface of the flexible layer and the key element occurring when the switch activation area is depressed, is avoided. The joining of the key element to the inner surface of the flexible layer and to the frame, respectively, can be performed in a combined moulding and assembling process wherein the key element is moulded directly into the recess or through hole of the frame and onto the inner surface of the flexible layer. When the key element is joined tightly to the frame, the cover can remain water and/or dust proof even if the flexible layer is damaged. In order further to improve the tightness of the cover, the cover and the flexible layer may be joined completely tight to each other. Again, this joining may efficiently be achieved by moulding the frame directly onto the flexible layer. In summing up the production process, the cover could be made by arranging a flexible layer, e.g. a sheet of a foil material in a cavity of a tool for injection moulding. In a first injection, the frame is formed directly onto the inner surface of the sheet. Subsequently, in a second injection, e.g. in another cavity of the same injection moulding tool, the key element is moulded inside the recess or through hole of the frame and directly onto the inner surface of the sheet.

In order further to improve the water and/or the dust tightness of the cover, the key element could be comprised in an inner resilient layer joined to an inner surface of the supporting frame. As an example, the key element could be formed as a bulge on a resilient mat, e.g. made from rubber or silicone and adhered or moulded directly to the inner surface of the frame. Preferably, the mat is made in a dimension so that it covers the entire inner surface of the supporting frame. Naturally, the mat with the integrated key element could be formed in one and the same injection in a tool for injection moulding.

In order to allow a light source arranged below the cover to shine through selected areas of the cover, the flexible layer and/or the supporting frame could be made from an at least substantially transparent material, e.g. a coloured and yet transparent material. If the key element is comprised in a mat which covers substantially the entire inner surface of the frame, it may also be an advantage to provide the key element and mat in a transparent material. However, in some applications it is rather desired to be able to control precisely where light is allowed to shine through the cover, and in that case, a non- transparent inner mat and key element may be used to mask off areas which on the outer surface should remain without any light shining through.

The cover could be provided with various decorations, e.g. characters and/or symbols which are indicative for certain functions related to a switch. If the frame, and/or the flexible layer and/or the mat and key element is provided in a transparent material, the decoration may comprise a layer of a non-transparent ink covering substantially the entire inner surface of one of either the flexible layer, the frame and/or the mat. The best result is achieved by applying the ink as close as possible to the outer surface of the cover, i.e. to the flexible layer. However, in order to avoid the ink in being washed or rubbed off over time, the ink may advantageously be applied to the inner surface of the flexible layer before the frame and key element is joined therewith. In areas wherein it is desired to have light shining through the cover, e.g. in an area around or in the switch activation area, the flexible layer, the frame and/or the mat could be masked off prior to the application of the ink to leave this area free from the ink. Alternatively, applied ink can be removed subsequently, e.g. by use of a laser technique wherein the paint is burned off in a specific pattern. The ink, i.e. the decoration may also be at least substantially transparent, e.g. coloured in a specific colour, thus allowing light to shine through the cover and to form a decoration via a colour pattern.

In order to allow a user more easily to find the switch activation area, the flexible layer may be made with an embossed mark forming an elevation of a part of the outer surface, e.g. in an area around the switch activation area, or the entire switch activation area can be marked as an elevated or depressed area. Moreover, such an embossed mark may support a more precise arrangement of the flexible layer in the cavity of a tool for injection moulding. In the cavity of the tool, a depressed mark corresponding to the embossed mark in the flexible layer is made. When the flexible layer is arranged in the cavity of the tool, the embossed mark is arranged in the depressed mark of the tool. It is therefore ensured, that the flexible layer is arranged with the switch activation area exactly at the spot where the recess or through hole of the frame is formed, i.e. at the spot where a core or similar arrangement of the tool prevents the frame from being formed onto. Accordingly, it may be an advantage to emboss the mark into a sheet of a foil material prior to the moulding of the frame and/or the key element thereon.

In order to support the assembling of the cover onto a casing for housing the switch and other electronic components, the supporting frame may be formed to define a peripheral rim portion in the shape of a flange. In that case, the mat formed by a resilient rubber material may advantageously extend through openings in the flange to form a seal extending along an outer surface of the flange.

According to one embodiment of the invention, the flexible layer and/or the frame, and/or the resilient layer comprise(s) a conductive material forming a shield against electrical noise. The conductive material could consist of fibres of metal suspended in the plastic material used for the moulding of e.g. the frame or mat and key element.

According to a second aspect, the present invention relates to a housing for a push button switch, said housing comprising a cover according to the description above, and a casing. Any of the first aspects described for the cover applies also for the housing and, in particular, the housing may comprise light emitting means arranged to illuminate an inner surface of the cover.

According to a third aspect, the present invention relates to a method of making a cover for a push button switch, said method comprising the steps of:

arranging a sheet of a foil material in a cavity of a tool of an injection moulding machine, - in a first injection, moulding a supporting frame onto a first side of the sheet, leaving a switch activation area of the sheet free,

- in a second injection, moulding a key element onto the switch activation area of the sheet.

Any of the first aspects described for the cover applies for the method of making a cover, in particular, the key element could be moulded in a material which, after curing, becomes relatively hard compared to the material of the supporting frame, and in particular, it is an advantage to perform the first and second injection successively within a very short time-period, e.g. within 10- 100 seconds, such as within 50 seconds. Thereby, it is possible to mould the supporting frame and the key element, optionally with a mat covering substantially the entire inner surface of the frame, into one single component without any well defined transition between the two parts and therefore with a superior tightness against dust and water. Moreover, it is an advantage to print an image onto the first side of the sheet, the image being visible from an opposite second side of the sheet, i.e. the sheet is at least partly transparent.

The above description of the first, second and third aspects of the invention is based on a cover for a single switch. However, the invention is not limited to a cover for a single switch and all aspect may be applied for a cover for a plurality of switches, e.g. for a keyboard or a keypad or the cover may be applied in general for any control panel, e.g. of an industrial machine application.

Detailed description of the invention

In the following, a preferred embodiment of the invention will be described in further details with reference to the drawing in which:

Fig. 1 shows a cross sectional view of cover according to the present invention and an associated switch, Fig. 2 shows a cross sectional view with indication on the application of ink to form decoration of the cover, and

Fig. 3 shows a perspective view of the cover and switch.

Fig. 1 shows a cross-sectional view of the switch in which a flexible layer 1 is joined to a frame 2. A key element 5 is arranged in the opening 4 of the frame. The key element is preferably made from a flexible material which allows the element to be pushed into contact with the associated switch 6, 7, when the switch activation area 8 of the flexible layer is depressed. The switch activation area is elevated in respect of the outer surface 10 of the flexible layer. The elevation supports the user in finding the depressable point on the outer surface of the cover. Moreover, the elevation or similar embossed mark facilitates easy orientation of the cover during the manufacturing thereof. Manufacturing will be described in further details later. In the chamfered transistion between the surface 10 and the elevated area 8, the switch activation area can be clearly highlighted, e.g. by the application of a colour mark along this edge, e.g. a phosphorescent or florescent mark or by illuminating the edge by light from a light source arranged below the cover, e.g. circumferentially around the switch. The flexible layer 1 and the frame 2 may preferably be made in a substantially transparent material allowing light to pass through the cover at least on pre-specified spots thereof. The flexible layer can preferably be made from a foil of a plastic material such as PVC, PU, PE or more specifically, such as Bayfoil CR6-2 from Bayer, e.g. in the thickness of 0,25 mm. The Frame could be made from a relatively hard plastic material, e.g. Bakelite or from Polycarbonat Makrolon 6555. This material can be moulded at approximately 210 °C. The key element may as visualized in Fig. 1 , fill out the opening 4 of the frame and extend along the lower surface thereof. In that way, the key element forms an inner liner which further improves the isolation of the switch from the environment. The key element could be made of a rubber material, e.g. a soft rubber material, e.g. TPE TC5 MCA kreiburg Shore 60 A, e.g. in a black colour. This material can be moulded at approximately 120 °C. The Polycarbonat Makrolon 6555 and the materials are characteristic in that they support a particular good bonding of the key element material (TPE TC5 MCA Kreiburg Shore 60) to the frame material (Polycarbonat Makrolon 6555) during a moulding process wherein the key element is moulded directly and shortly after the frame. In this process, the injection of 120°C TPE TC5 MCA Kriburg Shore 60 onto the solidified Polycarbonat Makrolon 6555 results and a partly re-melting of the edge of the frame and a mixture of the melt of the two materials solidifies an a transition zone with a superior tightness and bonding between the two components.

Fig. 2 shows the same cover and switch as shown in Fig. 1 but with indications on how decorations and similar light shielding application can be made. Lighting means 21 , 22 has been arranged in a position below the cover. The lighting means projects light toward the underneath of the cover. The frame and the flexible layer are made from transparent materials allowing light from the lighting means to pass through. However, before the assembling operation wherein the flexible layer, the frame and the key element is assembled into one unit, the lower surface of the flexible layer and/or the upper surface of the frame is decorated with a non-transparent colour, e.g. Proll norphan colour and optionally with a Prδll IMD lacquer or in general with any paint which effectively shields the light from radiating through the cover. The colour may simultaneously be used for decorating the cover and/or for forming signs, characters or similar instructive insignia for the user of the device for which the cover is intended. During the decoration process, the flexible layer has been masked off along the chamfered edges 18, 20. Accordingly, light is allowed to pass through these edges. The key element 13 is made from a non-transparent material. However, since holes, slits or similar arrangements, 17,19 have been provided, light is allowed to pass from underneath the cover towards the upper surface thereof, whereas, in the embodiment shown, lower exterior portions 11 and 12 are opaque. Likewise, upper exterior portions 15 and 16 as well as central portion 14 are opaque. The light is helpful in finding the switch activation area, in particular when the device to which the cover is attached, is used in dark areas. As an alternative to the illustrated cover, the key element could be made of a transparent material allowing light to shine through all areas where no decoration has been painted onto the flexible layer. However, the disadvantage of this solution is, that the slightest perforation caused by errors in the decoration process can result in light shining through the cover at unintended locations thereof. The light may be produced by LEDs or by regular Edison-type lamps.

Fig. 3 shows a perspective view of the cover and switch. This view shows an outer peripheral flange 27 formed by the frame 24. The flange may be used for connecting the cover to a casing for forming a housing for the switch 26 and for other electronic components. The key element 25 extends along the inner surface of the frame to form an inner liner for improving the tightness of the cover. The key element and a portion of the outer surface of the frame 24 are covered the flexible layer 23. In order to further improve the tightness of the housing formed by the cover and a casing (not shown), the key element 25 extends through openings in the flange and forms a seal 28 outside the flange. The seal is brought in contact with a corresponding flange of the casing during the assembling process and thus ensures improved tightness and resistance toward water and dust. Chamfered edge portions 29, 30, 31 of the flexible layer 23 may be opaque or transparent in order to allow light possibly emitted by light emitting means arranged inside the housing to escape through the flexible layer.

The cover could be made as follows:

A sheet of a foil material, e.g. a transparent Bayer Bayfoil CR6-2 is decorated, e.g. by printing on an inner surface with a colour and with IMD lacquer. Subsequently, the sheet is embossed or stamped in a cold stamping or pressing process. In this process, an embossed mark is formed on the outer surface of the sheet. The mark could e.g. be indicative for a user to easily find the switch activation area of the cover. Subsequently, the sheet is arranged in a first cavity of a tool for an injection moulding machine. The tool is closed and a core is arranged onto the inner surface of the sheet at the switch activation area. The core prevents moulding of the frame onto this area of the inner surface of the sheet. In a first injection, a first material is injected to form a frame directly onto the inner surface of the sheet. After curing, the sheet and frame is moved from the first cavity of the tool to a second cavity, e.g. of the same tool. In a second injection, a second material is injected to form a key element directly onto the inner surface of the sheet at the area where the core was placed during the first injection. Optionally the second injection moulds a resilient mat which may cover the entire inner surface of the frame and which comprises the key element.

Claims

1. A cover for a push button switch, said cover comprising:

- a flexible layer with an inner surface and an opposite outer surface, the outer surface forming an outer surface of the cover, - a supporting frame having a recess allowing the flexible layer in a switch activation area to be deformed into the frame, the supporting frame being joined to the inner surface of the flexible layer, and - a key element arranged at least partly in the recess for transferring, to an associated switch, a key switching force applied to the outer surface of the flexible layer in the switch activation area, characterized in that the key element is joined tightly to the inner surface of the flexible layer and to the supporting frame to form one single component.

2. A cover according to claim 1 , wherein the key element is more resilient than the supporting frame.

3. A cover according to claim 1 or 2, wherein the flexible layer, the supporting frame and the key element are joined in a moulding process to form one single component.

4. A cover according to any of the preceding claims, wherein the key element is comprised in an inner resilient layer joined to an inner surface of the supporting frame.

5. A cover according to claim 4, wherein the resilient layer covers substantially the entire inner surface of the supporting frame.

6. A cover according to any of the preceding claims, wherein the flexible layer is formed from a foil material onto which the supporting frame and the key element is moulded.

7. A cover according to any of the preceding claims, wherein the supporting frame is made from an at least substantially transparent material.

8. A cover according to any of the preceding claims, wherein the flexible layer is made from an at least substantially transparent material.

9. A cover according to claim 9, wherein the flexible layer comprises a surface decoration on the inner surface thereof.

10. A cover according to claim 9, wherein the decoration is at least substantially non-transparent.

11. A cover according to claim 9 or 10, wherein the supporting frame and/or the key element are/is adhesively bonded to the surface decoration.

12. A cover according to claim 4, wherein the resilient layer is made from an at least substantially non-transparent material.

13. A cover according to claim 12, wherein the resilient layer is penetrated to allow light to pass through selected areas of the non-transparent material.

14. A cover according to any of the preceding claims, wherein the flexible layer comprises an embossed mark forming an elevation of a part of the outer surface.

15. A cover according to any of the preceding claims, wherein the supporting frame forms a peripheral rim portion forming a flange for attaching the cover to a corresponding push button switch casing.

16. A cover according to any of claims 4-15, wherein the resilient layer extends through openings in the flange and forms a seal along an outer edge thereof.

17. A cover according to any of the preceding claims, wherein the flexible layer and/or the frame, and/or the resilient layer comprises a conductive material so as to isolate electronic components shielded by the cover from electrical noise.

18. A housing for a push button switch, said housing comprising a cover according to any of the preceding claims, and a casing.

19. A housing according to claim 18, further comprising light emitting means arranged to illuminate an inner surface of the cover.

20. A method of making a cover for a push button switch, said method comprising the steps of:

- arranging a sheet of a foil material in a cavity of a tool of an injection moulding machine, - in a first injection, injecting a first material for moulding a supporting frame onto a first side of the sheet, leaving a switch activation area of the sheet free, - in a second injection, injecting a second material moulding a key element onto the switch activation area of the sheet.

21. A method according to claim 20, wherein the key element is moulded in a material which, after curing, becomes relatively hard compared to the material of the supporting frame.

22. A method according to claim 20 or 21 , wherein the second injection is performed within a period of 10-100 seconds after the first injection and wherein the second material is capable of adhering to the first material by the formation of a composition comprising a melt of the first and of the second material.

23. A method according to claim 22, wherein the first material is selected with a higher melting point than the second material.

24. A method according to any of claims 20-23, wherein an image is printed onto the first side of the sheet, the image being visible from an opposite second side of the sheet.