FR2647588A1 - KEYBOARD SWITCH FOR CONTROL PANEL OF AN ELECTRICAL APPLIANCE - Google Patents

Abstract

This keyboard comprises keys 1 protruding from respective housings 2 formed in the front wall 3 of the panel and molded in a silicone sheet 4, and each having one end 10 carrying a conductive zone located opposite two electrical pads, said key being mounted mobile according to a determined stroke d. According to the invention, the outer face 17 of the front wall 3 is covered with a membrane 18 made of semi-rigid plastic material such as "Bayfol" and has, facing each housing 2, a blister 19 having the shape of a spherical cap whose height h is equal to or slightly greater than the stroke d of the button. The invention applies in particular to keyboards intended for controlling microwave ovens for household use.

Description

Keyboard switchboard control panel of an electric appliance

  The invention relates to switchboard keypads for an electrical appliance comprising a plurality of keys projecting slightly from respective housings formed in the front wall of said panel and integrally molded in a sheet of resilient insulating material such as a each having an end carrying a conductive zone situated opposite two studs carried by a plate comprising a printed circuit, and a end forming a bearing zone, said key being mounted to move in a direction orthogonal to said plate and according to a determined race by means of a frustoconical skirt whose small base is connected to the central region of the key, and whose large base is attached to

the insulating sheet.

  The invention aims to improve not only the waterproofness of these keyboards, but also their electrical operation while providing the user a tactile sensation of correct actuation of the switch key, this being particularly interesting when the keyboard is intended to control the different functions of a microwave oven to

household use.

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  According to the invention, the outer face of the front wall of the board is covered with a membrane of semi-rigid plastic material and has, opposite each key slot, a blister having the shape of a spherical cap whose convexity is turned to the outside and whose height is equal to or slightly greater than the determined stroke of

the key.

  Thanks to this embodiment of the membrane, not only a sealed protection of the electrical parts of the control panel, but also a flexibility of actuation of the keys which is very attractive to the user and which allows, thanks to the blisters, get a type effect at

  sudden action at the electrical contact.

  According to another characteristic of the invention, the semi-rigid plastic material of the membrane is a copolymer of

polycarbonate and polyester.

  With this type of material, blisters are produced whose elastic characteristics remain reliable over time, and it is also possible to perform a direct screen printing on

  said blisters which has an indelible character.

  The features and advantages of the invention will emerge

  moreover from the following description, & title

  for example, with reference to the accompanying drawing in which: Figure 1 is a partial vertical sectional view on a large scale of a keyboard switch for control panel, illustrating more particularly a key forming

switch according to the invention.

  This keyboard switch for control panel is intended to equip an electrical appliance such as for example a microwave oven and comprises for this purpose a plurality of identical keys 1 which project slightly housing

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  respective 2 formed in the front wall 3 of the control panel, and which have been molded into a sheet 4 in

  elastic insulating material such as, for example, silicone.

  As shown in FIG. 1, each key 1 has an end 5 carrying a conducting zone 6 made of conductive material, for example a carbon-loaded silicone, located opposite two studs 7 carried by a wafer 8 comprising a printed circuit 9, and an end 10 forming a bearing zone, said key 1 being mounted movable in a direction orthogonal to said plate 8 and in a determined course a by means of a frustoconical skirt 11 whose small base 12 is connected to the central region of the key 1, and whose large base 13 is attached to the

insulating sheet 4.

  The assembly of the plate 8 and the sheet 4 to the front wall 3 is made by means of rivets 14 which are integral with said front wall 3 and pass through said sheet and said plate, and which are intended to grip the plate 8 and the sheet 4 between the end of ribs 15, also integral with the front wall 3, and

the heads 16 of the rivets 14.

  According to the invention, the external face 17 of the front wall 3

  is covered with a membrane 18 made of semi-plastic material

  rigid consisting of a copolymer of polycarbonate and polyester and known under the trade name "Bayfol" (registered trademark of the Company Bayer Ag), said membrane having opposite each housing 2 of key 1, a blister 19 in the form of a spherical cap whose convexity is turned towards the outside, and whose height h, taken on the vertical line AA passing through its summit region, is equal to or slightly greater than the race

determined a of the key 1.

  In the preferred embodiment, the ideal stroke is equal to 0.7 mm and the plastic material, referenced by BAYER

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  under the name BAYFOL K L 3-1010, has a thickness of about 175 g and receives on its outer surface and even on the blisters a silkscreen illustrating the various functions

keys 1.

  In addition, to allow the proper functioning of the blistering without permanent deformation, it has been found that the ratio of the height h of the cap to its basic polar circle p must be between 0.06 and 0.07. This ratio should be considered important because the "Bayfol" membrane has practically no extensibility and the stroke of the key must be relatively large to avoid accidental contact with slight pressure.

touch on this membrane.

  In order to guarantee the tightness of the control panel and the rigorous maintenance of the membrane on the front wall 3, while improving the flexibility of the blistering, this membrane is bonded to the outer face 17 of the front wall 3 by means of a glue layer 20 with a thickness of, for example, 250 μm, the gluing zone stopping around each blister 19 at a determined distance x from the corresponding base polar circle p. This distance x being substantially equal to or less than one eighth of the diameter of said basic polar circle p. In addition, to ensure linear guidance of the crown region of the cap during a tactile pressure along the axis AA, the housing 2 of each key has a flared edge outlet 21. To avoid permanent blistering, this edge flared 21 must have a slope a lower & 9 'and

  preferably equal to 8 '(eight degrees).

  On the other hand, to promote the initiation of blistering and the depression of the key 1, the support zone 10 of each key 1 has the shape of a dome so as to be in point contact with the concave region from the summit 19 'of the

spherical cap.

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  The operation of the switch keypad is as follows: when a tactile pressure is applied on the top 19 'of a blister 19, it causes at first a slight depression of the border 22 located opposite the unglued zone, then the depression of said vertex 19 'which bears punctually on the dome top 10 of the key 1 and which transmits in a virtually linear manner the tactile pressure to said key, and in a second step, the sudden blistering of the blister 19, until the concave face stumbles on the

flared edge 21 of the outlet 19.

  This sudden movement amplifies the tactile pressure and causes, in a manner known per se, the elastic deformation of the skirt 11 and the sudden depression of the key 1 thus achieving the sudden momentary closure of the contact by applying the conductive zone 6 on both pads 7 and

  thus avoiding the creation of an electric arc.

  When releasing the tactile pressure on the blister 19 and thanks to the flared edge 21 of the outlet 19 limited to 8 degrees, the blistering is not permanent and the blister returns to its initial convex shape thus releasing the key 1 which, under effect of the opposite deformation of the skirt 11 returns &

  its open position illustrated in Figure 1.

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Claims (7)

claims   1. Switchboard for a control panel of an electrical apparatus comprising a plurality of keys (1) slightly protruding from respective housings (2) formed in the front wall (3) of said board and integrally molded in a sheet (4) of elastic insulating material such as a silicone, and each having an end (5) carrying a conductive zone (6) located opposite two studs (7) carried by a plate (8) comprising a printed circuit (9), and an end (10) forming a bearing zone, said key (1) being mounted movable in a direction orthogonal to said plate (8) and in a determined stroke (d) by means of a frustoconical skirt (11) whose small base (12) is connected to the central region of the key, and whose large base (13) is attached to the insulating sheet (4), characterized in that the outer face (17) of the front wall (3) of the board is covered with a membrane (18) of semi-plastic material rigid and presents opposite each housing (2) of key (1) a blister (19) having the shape of a spherical cap whose convexity is turned outwards and whose height jh) is equal to or slightly greater than the determined stroke (d) of the key (1). Switchboard keyboard according to Claim 1, characterized in that the semi-rigid plastics material of the membrane (18) is a polycarbonate copolymer and polyester type "Bayfol".   3. Keyboard switch according to claim 1 or 2, characterized in that the ratio of the height of _] h) the cap (19) on its basic polar circle (R) is included between 0.06 and 0.07. 7 2647588   4. Keyboard switch according to any one of preceding claims,   characterized in that the bearing zone (10) of each key (1) has the shape of a dome so as to be in point contact with the concave region of the crown (19 ') of the cap spherical (19).   5. Keyboard switch according to any one of preceding claims,   characterized in that the membrane (18) is adhered to the outer face (17) of the front wall (3) of the board, the gluing area (20) stopping around each blister (19) at a distance determined (x) of the corresponding basic polar circle (r), this distance (x) being substantially equal to or less than one-eighth of the length of the diameter of the basic polar circle.   6. Keyboard. switch according to any of preceding claims,   characterized in that the housing (2) of each key (1)   has a flared edge outlet (21).   7. Keyboard switch according to claim 6, characterized in that the flared edge (21) has a slope (a) less than nine degrees and preferably equal to eight degrees.