DE8911792U1 - Membrane switch - Google Patents

Description

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Membrane key i

The innovation relates to an elastic membrane button according to the generic term of claim 1.

Membrane switches of this type are preferred for splash-proof and

dust-proof or dust-tight membrane keyboards of control panels, such as machine controls, telephone handsets, etc. The well-known membrane buttons have a cap-shaped button head with a cavity for accommodating a light, whereby the cavity is surrounded by a wide cap edge that is completely covered all around with an electrically conductive layer. The button head lies over pairs of conductors that are usually arranged in a meandering pattern on a circuit board and that are electrically bridged by the conductive layer when the button head is pressed. Surface-mountable, miniaturized, cubic components with connecting electrodes, so-called SMD light-emitting diodes (SMD "surface mounted device"), are usually used as lights.

Jh8369H, 21 Aug 89

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The SMD LED is soldered on the component side of the circuit board.

It has been shown that devices equipped with the well-known membrane buttons tend to malfunction. The innovation is based on the knowledge that this malfunction is caused by improper operation of the button head: If the button head is not pressed vertically downwards with the finger, but at an angle to the side, i.e. if it is kneaded, the conductive layer not only bridges the conductor pairs, but also the two connections of the SMD lamp, which leads to incorrect information or even destruction of the circuit.

This is where the innovation aims to remedy the situation. The innovation, as described in the protection claims, solves the problem of creating a membrane button that avoids incorrect information even when the button head is operated incorrectly.

Patent claims 2 to 6 describe preferred embodiments of the membrane switch according to the innovation.
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In the following, examples of the membrane switch according to the innovation are explained in more detail using the drawings. They show:

Fig. 1 a cross-section through a membrane switch,
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Fig. 2. a plan view of a membrane keyboard obliquely from above,

Fig. 3 shows a section through a membrane switch along the line III - III in Figure 1,

Fig. 4 a view of a mat with twelve probe heads from below, and
Fig. 5 shows a cross-section through a variant of a membrane switch.

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The elastic membrane keyboard 3 shown in Figure 2 has twelve self-resetting, elastic membrane keys 1, one of which is in the

Jh8369H, 21 Aug 89

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Cross section shown in Figure 1. Each tester head 6 of a membrane key 1 is printed with characters or symbols, is dimensionally stable and is connected in one piece via a bendable spring ring 7 to a mat 9 from which all the key heads 6 protrude. The key head 6, the ring 7 and the mat 9 consist of an elastic plastic film. The key head 5 has an almost flat key surface that is adapted to an average human fingertip. |

The button head 5 is cap-shaped with the cap opening facing the material

tsniinterssite formed. The cavity formed in the T5et°rkopf ß 11 ^

is used to hold a 16 mm thick printed circuit board

so-called surface-mountable (SMD = surface mounted device] '{

Light-emitting diode 12, which is soldered to its two opposite electrodes 13a and 13b on the connection surfaces 14a and 14b of two electrical conductors 18a and 18b located on the circuit board 16. Surface mountable components (SMD) allow a miniaturization of the circuit arrangement compared to conventional electronic components with feet.

The cap opening is surrounded by a wide cap rim 19 as an

printing surface. The edge 19 carries, as shown in Figure 4 and Figure 3 (un- f

broken horizontal hatching, as not visible in the section), 2»?ei opposing crescent-shaped electrically conductive sub-areas (segments) 21a and 21b, produced by printing with a conductive mixture of amorphous carbon with silicone rubber (IeI-tender HTV silicone rubber), which are separated from each other by an electrically insulating sub-area 22a and. 22b. The conductive sub-areas 21a and 21b lie at a distance a shown in Figure 1 above each 2.#ei approximately semicircular, on the surface of the conductor plate. -

te 15 lying conductors 23a and 23b and 24a and 24b. As shown in Figure 3 _-

As shown, the conductor 23b is connected below the partial area 21b to the |

Conductor 23a is connected below the sub-area 2la and goes into a &phgr; Conductor 25, which leads to an evaluation electronics (not shown) |

j is connected. The conductor 24a below the section 21a is marked with §

Conductor 24b is connected below the section 21b and goes into the conductor *

ter 27, which also leads to the evaluation electronics. The conductors 23a ;\

and 23b, as well as 24a and 24b are below the sub-areas 21a and 21b |

iJh8369B, 21 Aug. 89 I

designed as gold-plated contact surfaces and otherwise, like the entire circuit including the conductors 18a, 18b, 26 and 27 except for the soldering points and their immediate surroundings, coated with a solder resist, which is shown in Figure 3 with a solid or interrupted, crossed hatching depending on visibility.

If the button head 6 is pressed down by the distance a with the finger, the sections 21a and 21b are pressed against the spring force of the elastic ring 7 onto the conductors 23a and 24a and 23b and 24b, whereby both are electrically connected. A current flowing through the conductors 25 and 27 connected to the conductors 23a and 23b or 24a and 24b or a potential change generated by the bridging is evaluated by the evaluation electronics. As a result, the LED 12 flashes, is illuminated or switched off.

The underside of the hat 9 shown in Figure 4 has several grooves 36 approximately half a millimeter deep, which connect the individual cavities 11 of the button heads 5 to one another. The grooves 36 ensure that when the volume of the cavity 11 is reduced by pressing down a button head 5, the compressed air flows from the cavity 11 in question into the neighboring ones. When the pressed button head 5 is released, the air from neighboring cavities 11 flows into the cavity 11 of the button head 5 in question, thereby preventing the partial areas 21a and 21b from sticking to the conductors 23a, 23b, 24a and 24b.

The two sections 21a and 21b were designed in a crescent shape so that even when the button head 5 is pressed at an angle or from the side, the conductors 23a and 24a or 23b and 24b are perfectly bridged.

In contrast to the known single, circumferential conductive ring, the two crescent-shaped sections 21a and 21b ensure that the sections 21a and 21b only short-circuit the conductors 23a and 24b or 23b and 24b, but never connect one of the conductors 23a, 23b, 24a, or 24b to the electrodes 13a or 13b of the light-emitting diode 12.

JB8369H, 21 Aug 89

When the crescent-shaped sections 21a and 21b are pressed with the conductive coating, the layer material runs slightly over the edge to the cavity 11 by fractions of a millimeter. Instead of forming the edge 19 as a flat pressure surface, in a variant of a membrane button 30 shown in Figure 6 it is provided with a circumferential shoulder 32 adjoining the lower edge of the cavity 11. This shoulder 32 ensures that the sections 34a and 34b, which are produced analogously to the sections 21a and 21b, are always kept far enough away from the soldering points between the electrodes 13a and 13b of the LED 12 and the connection surfaces 14a and 14b that no electrical contact occurs even when the membrane button 30 is pressed with great effort or at an angle. For this purpose, a heel would be sufficient, which is only attached in the immediate vicinity of the printed area; however, for manufacturing reasons, the circumferential heel 32 shown in Figure 6 was chosen.

Instead of accommodating only one light-emitting diode 12 in a single cavity 11 in the membrane switch 1, several cavities, which are preferably separated by partitions, can also be provided with one light-emitting diode each or with several light-emitting diodes of different colors.

In addition to using several membrane buttons 1 in a membrane button structure 3, only a single membrane button 1 or 30 can be used in an operating panel.

Fh8369H, 21 Aug 89

Claims (6)

_ I. —&igr; 1. Self-resetting elastic membrane button (1; 30), with flatly arranged electrical conductors (23a, 23b, 24a, 24b) and a hollow button head (5) made of elastic foil material, which has a pressure surface (19) to be pressed against the conductors (23a. 23b. 24a, 24b) for electrical bridging, characterized in that only one or more partial areas (21a. 21b; 34a, 34b) of the pressure surface (19) are electrically conductive and the remaining partial area or areas (22a, 22b) are electrically insulating. 2. Foil button (1: 30) according to claim 1, characterized in that the conductive partial area or areas (21a, 21b; 34a, 34b) consists or consist of electrically conductive material printed onto the pressure surface (19) of the elastic foil material, preferably of an electrically conductive mixture of amorphous carbon with silicone rubber. 3. Membrane switch (1; 30) according to claim 1 or 2, in which the electrical conductors (23a, 23b, 24a, 24b) are arranged on a circuit board (16) together with a lamp (12) covered by the switch head (6), characterized in that the conductive partial areas (21a, 21b; 34a, 34b) are arranged opposite the electrodes (13a, 13b) of the lamp (12) and its Soldering points (13a/14a, 13b/14b) on the circuit board (16) are offset are arranged so that even if the button head (6) is pressed incorrectly, only the electrically insulating portions of the pressing surface (19) can come into contact with the electrodes (13a, 13b) and soldering points (14a, 14b) of the lamp (12). 30 4. Polientaster (1; 30) according to one of claims 1 to 3, characterized
characterized in that the pressure surface (19) is annular and the electrically conductive portions are two opposite, mutually
segments separated by the insulating portions (22a, 22b) (21a, 21b; 34a, 34b). JM369H, 21 Aug 89 • t t
t · · · - a: 5. Membrane key (30) according to one of claims 1 to 4, characterized in that at least the electrically conductive partial areas (34a. 34b) of the pressure surface are separated from the cavity (11) of the key head by a recessed shoulder (32). 6. Fsiieiitastats? (S) salt ■■isefcr-erea Foil tester (1) according to one of claims 1 to 5, characterized in that the foil button {*> is formed in one piece from foil material. Jh8369H, 21 Aug 69 (•11 · *