WO1988007753A1

WO1988007753A1 - Press switch, in particular as key for a keyboard

Info

Publication number: WO1988007753A1
Application number: PCT/EP1988/000223
Authority: WO
Inventors: Rolf K. MÜLLER
Original assignee: Mueller Rolf K
Priority date: 1987-03-21
Filing date: 1988-03-18
Publication date: 1988-10-06
Also published as: DE3709305A1

Abstract

A press switch has an actuator (4) which counteracts the force of a spring (7) and actuates a switch (8, 13) when depressed. The spring (7) is designed as a two-legged spiral spring with a longer lower leg (8) and a shorter upper leg (9) at an angle thereto such that its lower leg is loaded when the actuator (4) is depressed until the switch (8, 13) is actuated and its upper leg (9) is loaded when the actuator (4) is fully depressed. The lower leg (8) is a component of the switch (8, 13), e.g. of a proximity switch. The spring (7) has an imprint not shown in the drawing such that after compression of the lower leg (8) of the leaf spring (7), a peak occurs in the otherwise steeply sloping characteristic curve of the upper leg (9), beyond which the circuit is shown to have been closed.

Description

'Pressure switch, especially as a keyboard key'

The invention relates to a pressure switch, in particular as a key on a keyboard, which has a plunger which presses in against the force of a spring and actuates a switching element, the leaf spring being constructed in two parts such that one part of it when the plunger is pressed in until the switching element is actuated and its other part is stressed when the plunger is pressed in further, in particular in the form of a double-leg spiral spring with a lower leg, which forms a part, preferably a longer lower leg, and an upper leg which is angled and forms the other part, preferably shorter, is held at the end of the lower leg and abuts the plunger at the end of the upper leg.

Such a pressure switch, known from US Pat. No. 4,090,229, is simple in construction and assembly, but is nevertheless user-friendly. The specified design of the leaf spring saves having to push the plunger as far as it will go when operating the pressure switch and then involuntarily apply an increased force again to ensure that the stop has been reached. If the finger only feels the first stronger resistance, one can be sure that the circuit has long been completed. The design specified in particular has the form in the known pressure switch that the upper leg of the leaf spring branches off from the lower leg, namely as a stamped tongue. The upper leg is stiffer than the lower one, ie it has a steeper spring characteristic than the lower one. When the plunger is pressed in, the steeper rise in the spring characteristic is perceived and confirms the completed switching. The finger can still "bounce" further.

The invention has for its object to produce a clearly noticeable indication for the completion of the circuit independent of a steeper spring characteristic of the other part of the leaf spring mentioned.

According to the invention, a pressure switch of the type mentioned at the beginning fulfills this purpose, in which the leaf spring has a tip in the spring characteristic such that the drop in spring force at the tip shows the completion of the circuit.

The suddenly lower counterforce of the spring after overcoming the tip becomes clear and is perceived as a relief, the "bouncing" is easier.

According to one embodiment of the invention, the essential spring travel of the two parts of the leaf spring mentioned are separated from one another by the tip in the spring characteristic. Then the ad comes after the delivery is complete.

According to another embodiment of the invention, the display comes beforehand: the peak in the spring characteristic lies in the spring travel of the one part of the leaf spring just before the switching position, but in such a way that the switching position is still safely reached due to the drop in spring force.

The tip can be produced in the spring characteristic by means of a transverse curvature, preferably in the form of an embossing, in the leaf spring, as was known from the children's toy "cracked frog" is.

In addition, the desired spring characteristic can be shaped by changing the width of the leaf spring. With this measure, practically any desired spring characteristic can be achieved and also bending of the spring at the desired point.

The spring can be held, for example, by a plug-in surround of the end of the lower leg or by an angled, preferably two-armed, support.

The switching element can be actuated directly by the plunger, but also by means of the lower leg of the spring mentioned. This can also be a moving part of the switching element, particularly in conjunction with a capacitive switch, which is a portion of the lower leg of the spring in length and width without further ado can be adapted as a capacity-changing, moving component of the switch. However, a contact switch in which the lower leg of the spring forms the contact bridge, directly or with a special contact piece attached to it, would also be quite conceivable.

The drawings show schematically various pressure switches and associated leaf springs.

1 shows a section through a switch,

Fig. 2 shows a section through another switch, Fig. 3 shows a Fig. 1 and 2 corresponding section through a, but different, spring,

4 shows a top view of the spring according to FIG. 3,

5 shows a section through another spring in the initial state,

Fig. 6 shows a section along line VI-VI in Fig. 5,

Fig. 7 shows a Fig. 5 corresponding section through the spring immediately after the switching process and Fig. 8 shows the spring in a Fig. 4 and 5 corresponding section later after the switching process.

A circuit board 1 carries a housing 2 with a guide 3, in which a plunger 4 is slidably held. The plunger forms a structural unit with a cap 16. The cap 16 covers the housing 2 and has a depression 17 for the fingertip pressing the switch.

In a pocket 5 formed on the housing 2, a leaf spring 7 is inserted with an upstand 6. It is divided into a lower leg 8 and an upper leg 9, which is angled from it and extends backwards about half as long. The upper leg 9 lies with a bulge 14 in a groove c. the like 15 of the ram.

In this arrangement, the leaf spring 7 presses the plunger 4 upwards, where it is held by abutment on the housing 2.

If the plunger is pressed in, the lower leg 8 of the leaf spring primarily bends downward, mainly with bending near its upstand 6, where the force has the largest lever arm.

Finally, if the leg 8 lies on the surface of the circuit board, it works together with fixed switch parts 13 arranged on the circuit board as a capacitive switch.

Further pushing in of the plunger 4 is then taken up by bending in the upper leg 9. The characteristic of this suspension can be designed arbitrarily through the shape of the leg. Furthermore, an indentation that does not appear in the schematic representation in the leaf spring is to be thought of in such a way that after the lower leg 8 of the leaf spring 7 is pressed down, a peak occurs in the characteristic instead of a steeply increasing spring characteristic of the upper leg 9, the overcoming of which occurs when the circuit is completed clearly shows. Corresponding parts in FIG. 2 have the same reference numbers as in FIG. 1.

Fig. 2 shows as a modification that the leaf spring 7 also forms an electrical line connection: At its ends, lines 18 and 19 connect. The line 18 forms a connection to the circuit board. The line 19 leads into the plunger, for example to an LCD display.

The mechanical mounting of the leaf spring 7 is not shown in Fig. 2.

3 to 8 in FIG. 1 corresponding parts are provided with the same reference numerals.

The leaf spring according to FIGS. 3 and 4 is held in place by the plug-in version of the upstand 6 in the pocket 5 by a support which consists of two arms 2 lying flat on the board. The bending of the upper leg 9 with respect to the lower leg 8 is not bent as in FIGS. 1 and 2, but curved.

The leaf spring 7 with its legs 8 and 9 and the arms 22 are recognizably made in one piece as a stamped part. When the leg 8 is pressed down, the bending takes place largely in the region of the connection of the leg 8 to the arms 22. The arms 22 bend slightly upwards there. In the extension of the incisions 23 between the leg 8 and the arms 22, the spring plate may twist somewhat and, in this respect, may also be a torsion spring. The same applies as for FIG. 1 for the further giving of the upper leg 9.

5 to 8, the leaf spring 7 is shown with a flat embossing 25. The indentation 25 extends in the upper leg 9 of the leaf spring 7 approximately from the bend 26 separating the upper leg 9 from the lower leg 8 to just about the longitudinal center of the upper leg 9 Leaf spring 7 by an end 28 fastened in the pocket 27 of the circuit board 1, to which the lower leg adjoins with a curvature 29.

If the push button is depressed, the lower leg 8 of the leaf spring 7 is primarily depressed, since the force with the longest lever arm acts on it. The upper leg 9 is bent down only slightly above the indentation 2, as in FIG. 7, perhaps somewhat exaggerated there. A bend at the lower end of the leg 9 hardly takes place because of the stiffening present here through the embossing 25, although here the lever arm has the greatest length; the bend 26 itself is comparatively stiff.

Only after further depression after placing the leg 8, which causes the switching process, the force at the lower end of the leg 9 is so great that the indentation 25 springs back into the spring plane, so that the stiffening is eliminated and bending is possible. This takes place in a narrow area approximately along the transverse line 30 designated in FIG. 8 at the end of the impression 25, where it ends with a curve or the like and becomes flatter. It is the effect of the "click frog. At the moment of this jump, the spring force suddenly drops so that the previous bending of the leg 9 above the embossing 25 decreases; the leg 29 bends down as a whole with less force, see FIG. 8. This A sudden drop in the counterforce associated with a peak in the spring characteristic is clearly perceived and confirms the completed switching.

Instead of the transverse curvature restricted to the embossing, a transverse curvature could also extend over the entire width of the spring. The transverse curvature could also extend further down on the leaf spring; the transverse line 30 would even be conceivable below the bend 26.

It goes without saying that all of these are quantitatively coordinated got to .

Instead of the drawn and described impression 25, an impression or other transverse curvature at and / or near the curvature 29 in the leg 8 would be possible such that the force required to overcome the tip then leads in any case to the complete depression of the leg 8 , d the leg 8 so to speak "cracked". For this embodiment, it may be expedient to stiffen the upper leg 9, for example by means of an elongated embossed bead

As I said, the drawings are only schematic.

There are various possibilities for the connections between the housing and the circuit board 1, not shown. Many other variations are also conceivable. The plug-in connection through the upstand 6 and the pocket 5 could be directed to another frame or to a base part egg instead of to a housing. Instead of the capacitive switch, inductive and contact switches can also be used. However, the easy-to-design and easy-to-assemble two-part spring with the tip in the characteristic curve always gives confirmation of the fullness of the circuit.

Claims

Claims:

1. Pressure switch, in particular as a key on a keyboard, which has a plunger (4) to be pressed in against the force of a leaf spring (7), a switching element (8, 13), the leaf spring (7) being formed in two parts in such a way that it a part (8) when pushing in the plunger (4) until actuation of the switching element (8, 13) and its other part (9) when the plunger (4) is pushed in further, especially as a double-legged spiral spring with one, the one mentioned Part-forming, preferably longer, lower leg (8) and an angled from this, forming the other part, preferably shorter, upper leg (9) is formed, is held at the end of the lower leg (8) and at the end of the upper leg (9) on the plunger (4), characterized in that the leaf spring (7) has a tip in the spring characteristic such that the drop in spring force at the tip recognizes the completion of the circuit eats.

2. Pressure switch according to claim 1, characterized in that the essential spring travel of said two parts (8; 9) of the leaf spring (7) are separated from each other by the tip in the spring characteristic.

3. Pressure switch according to claim 1, characterized in that the tip in the spring characteristic in the spring travel of the called / ^ ils of the leaf spring just before the switching position is such that the switch position due to the spring force drop is still safely reached.

4. Pressure switch according to one of claims 1 to 3, characterized in that the tip in the spring characteristic by means of a Quer¬ arch (25), preferably in the form of an impression (25), i of the leaf spring (7) is generated.

5. Pressure switch according to claims 2 and 4, characterized in that the transverse curvature (25) in the lower region of said other part (9) of the leaf spring (7) is arranged.

6. Pressure switch according to claims 3 and 4, characterized in that the transverse curvature is arranged in the lower region of said part of the leaf spring.