EP0001031B1 - Push button switch with snap action - Google Patents

Description

Technical field of the invention

The present invention relates to electrical key switches and, more particularly, to key switches of the type in which, during an operation of changing the electrical conduction state of the switch, energy is first accumulated in a compression spring, then released in order to produce an abrupt tilting movement of a control element ensuring said change of state.

State of the prior art

Many switches of the prior art use a contact control element which switches suddenly. Some of them use a column compression spring, associated with said control element, in order to cause the latter to tilt. However, as will be seen below, these switches generally require a large number of mechanical elements to ensure the desired movement of the contact control element. These elements are generally pushers or return elements to cause the control element to tip over to its closed contact position or to return it to its rest or open contact position.

For example, US-A-2,810,031 discloses a push button switch in which a coil spring is used to cause tilting of a pivotally mounted control member. However, an additional member must be added between the push button and the rocking element to orient the stroke in the appropriate direction, when the actuation begins and to apply a restoring force in a rest position, release of the push button. . In addition, another additional member is used to orient the torque in the appropriate direction, in order to tilt the control element in the desired manner. This last additional member can be a source of instability and a possible cause of breakdowns.

US-A-3,863,040 presents a compression column spring subjected to buckling in order to come into contact with contact elements located on either side thereof. Publication FR-A-2 138658 presents a device of the same type, but in neither of these two patents, the column compression spring switch subjected to buckling is used to produce the switching of a contact control element . In fact, the spring itself constitutes the contact element.

A switch of the abruptly tilting control element type is presented in US Pat. No. 3,491,218, but an additional member is disposed between the push button and the tilting element, so that the latter switches in the appropriate direction.

According to the foregoing switches of the compression spring type and with a control element for abruptly rocking contacts, of the prior art, use additional mechanisms to orient the initial tilting of said control element. These additional mechanisms increase the cost of manufacturing the switches and are a source of possible breakdowns due to wear or blockage issues that can affect them. The assembly of these devices is also quite complicated.

Statement of the invention

In order to eliminate the drawbacks presented by switches of the prior art, the object of the present invention is to provide an electrical switch of the type with a control element suddenly tilting, using only a column compression spring and more precisely, the reaction torque of such a spring, subjected to a force which causes it to buckle, to tilt the control element to which it is coupled and to restore the latter to its initial position when said force is eliminated.

The column compression spring used in the switch according to the invention is of the type described in the publication FR-A-2 138 658 mentioned above. This spring has characteristics well known to those skilled in the art (such as length, diameter, size of the wire, material, etc.) which allows it to flame suddenly when a predetermined compression force is applied to it. A first end of the spring is coupled to a push button or button and the second to a control element, pivotally mounted so as to be able to switch between a first position and a second position, positions in which said control element cooperates with electrical elements in order ensure separate states of electrical conduction.

This spring is mounted between said button and said control element in a precompression state and its second end is located, relative to the pivot point of the control element, in a location such that the precompression of the spring maintains the the control element in its first position. Means are also provided which ensure that the buckling of the spring always occurs in the same direction when a force is applied to the key. When, as a result of pressing the key, said predetermined compression force is reached, the spring suddenly flares up by applying a torque to the control element which causes it to tilt towards its second position. The control element is automatically returned to its first position when the key is released, since the spring then exerts on the control element a torque in the opposite direction to that which caused it to switch to its second position.

Description of the drawing figures

• Figure 1A is a longitudinal sectional view of a preferred embodiment of the electrical switch according to the present invention.
• Figure 1B shows the switch of Figure 1A when the switch button is partially depressed.
• Figure 1 C shows the switch of Figures 1 A and 1 B when the key is pressed to the point where the sudden buckling of the compression spring occurs.
• Figure 1 D shows the switch of Figures 1 A to 1 C when the key is pressed further after the sudden buckling of the spring has already occurred.
• Figure 2 is a graph of the force applied to the key as a function of its stroke, in the switch of the present invention as shown in Figures 1 A to 1 D.

Description of the preferred embodiment Reference will now be made to FIG. 1A of the drawings which represents the rest position of a preferred embodiment of the electrical switch according to the invention. In this preferred embodiment, the switch comprises a button or push button 1 secured to a rod or barrel 2 which is mounted to slide in a housing 3. The barrel 2 is provided with a pin 4 which moves in a groove 5 of the housing 3. The purpose of this pin 4 is to limit the upward stroke of the key 5 while coming into abutment on the end 6 of the groove 5.

The stroke of the key 1 down is limited by a shoulder 7, inside the key 1, which abuts against the top 8 of the housing 3. The distance DO, indicated in FIG. 1A, represents the total stroke possible from the button. In the preferred embodiment of the invention, the button 1, its barrel 2 and the housing 3 are made of injection molded plastic.

The housing 3 is mounted above a substrate 9, made of an electrically non-conductive material and having individual electrical contacts 10A, 10B, 10C. The contacts 10B and 10C are placed respectively to the left and to the right of the central contact 10A.

The coupling between the central contact 10A and one or the other of the lateral contacts 10B and 10C is ensured by means of a control element 11 having a general flattened V shape and which is mounted between the housing 3 and the substrate 9 to switch, between a first and a second position, around an axis 12 perpendicular to the plane of the sheet.

As it appears in the figures, the pivot axis 12 is constituted simply, in the preferred embodiment of the invention, by the line of contact between the base of the flattened V-shaped element and the substrate 9.

This design of the control element 11 reduces the manufacturing cost of the device and simplifies its assembly. Those skilled in the art will however understand that other configurations of the control element 11 can be made, the only condition to be observed being that this element must switch between two distinct positions relative to the substrate 9 and its contacts.

In its first position or rest position (represented in FIG. 1A) the control element 11 ensures the coupling between the contacts 10A and 10B, while in its second position (represented in FIG. 1C) it ensures the coupling between contacts 10A and 10C.

In the preferred embodiment of the invention, the control element 11 is made of electrically conductive plastic material, injection molded, and the contacts 10A, 10B, 10C constitute the plates of a capacitive switching system and are therefore covered by a thin layer of dielectric material to create a capacitive action when the control element 11 is brought in the vicinity of one or other of the sets of plates 10A, 1 OB, or 10A , 10C.

The connections which must be made on the contacts 10A, 10B, 10C in order to use the electrical characteristics ensured by either of the positions of the control element 11 with respect to the contacts, are not shown since they are obvious to those skilled in the art.

As it appears in the figures, the control element 11 comprises a pin 13 which is offset to the left, in the figures, relative to the pivot axis 12 of the element 11. The bottom 15 of the barrel of the key has another mounting stud 16 whose base is inclined relative to the axis of the barrel of the key so as to point to the right in the drawings. The base of this pin 16 is surrounded by a shallow circular groove (not referenced) in which is freely housed the first turn of the first end of a helical compression spring 17, the second end of which is fitted on the pin 13 .

It will be noted, as illustrated in the figures of the drawings, that the position of the pin 13 is such that, the spring being fitted on the latter, the right side of the turn which rests on the element 11, is located at the plumb with the pivot axis 12.

The compression spring 17 is of the sudden buckling type described in the publication FR-A-2 138 658 mentioned above. Those skilled in the art will understand, however, that other configurations of snap springs (such as blades, wires, or spring bars) can be used for the same purpose.

The sudden-buckling spring 17 is mounted between the control element 11 and the bottom of the test barrel 2 in a state of slight precompression which, thanks to the offset of the pin 13 relative to the pivot axis 12, ensures the maintenance of the control element 11 in its first position as shown in FIG. 1A, until, (as will be seen in more detail below) the key 1 has moved, under the action of a force F directed downwards, over a predetermined distance D2 (see FIG. 1C) which corresponds to the sudden buckling of the spring and the tilting of the element 11 towards its second position illustrated in FIG. 1C.

The inclination, mentioned above, of the seat of the spring 17, on the bottom of the test barrel, makes it possible to create a slight initial buckling of the spring directed towards the right side of FIG. 1 A which ensures that the sudden buckling which will occur when the key is pressed, will always occur on this same side.

The operation of the switch according to the invention will now be described with reference to Figures 1B, 1C, 1D and 2 of the drawings.

FIG. 1B represents the mechanism of FIG. 1A when a force F is applied to the key 1 in order to depress it relative to its high position represented in FIG. 1A. This force F caused a slight depression D1 of the key and the compression of the helical compression spring 17. This compression accentuates the initial buckling of the spring and generates reaction torques at each end of the spring. The torque exerted on the control element 11 is directed counterclockwise and its moment is approximately equal to the force F multiplied by the distance between the pivot point 12 and the central axis of the spring. This torque holds the element 11 firmly against the contacts 10A and 10B.

The torque exerted on the upper end of the spring is directed clockwise and its moment is approximately equal to the half-product of force F by the diameter of the spring. This couple maintains the first turn of the spring pressed against the test barrel.

As the key is pressed, the bending of the spring increases, and the moments of the reaction torques mentioned above decrease. When the value of these moments reaches zero, the control element 11 switches.

FIG. 1C represents the mechanism of FIGS. 1A and 1B when the key 1 has been pressed over a distance D2, greater than the distance D1 mentioned above, and has reached the point where the sudden buckling of the spring 17 occurs. It will be noted that, during this sudden buckling, the end of the spring 17 which is coupled to the pin 16 of the barrel 2 partially emerges from the groove, in which it is housed, pivoting freely in the counterclockwise direction.

As will be understood by those skilled in the art and as indicated in the publication FR-A-2 138 658 cited above, this action takes place in an abrupt manner. The sudden buckling of the spring applies a moment of rotation clockwise to the control element 11 and causes the latter to tilt clockwise around its pivot axis 12, so that a capacitive coupling appears between the contacts 10A and 10C via the right part of the control element 11. The contacts 10A and 10B are then no longer coupled as they were before the tilting.

The sudden buckling of the spring results in a tactile sensation experienced by the user, due to the sudden decrease in the reaction force exerted by the key on the user's finger. In addition, the sudden tilting of the control element 11 produces an audible click.

FIG. 1 D represents the mechanism when the key 1 has been pressed even more and has traveled a distance D3 greater than the distance D2. This FIG. 1 D represents the state of the mechanism a little before the contact between the surfaces 7 and 8 occurs which will end the movement of the button downwards.

When the pressure on the key is released, the spring 17 relaxes and returns to the position it had in FIG. 1A, causing the control element to tilt backwards, to its first position or initial position.

Going to Figure 2, there is a graphical representation of the force exerted on the key as a function of the stroke thereof. This force is the force F required to press key 1 and the values of this force F are indicated in grams-force on the ordinate axis. The values for the stroke of the key are indicated in millimeters on the abscissa axis. It will be noted that the strokes DO, D1, D2 and D3 of the key which have been discussed above have been indicated on the abscissa, with reference to FIGS.

The upper part of the curve shown in FIG. 2 corresponds to the pressing of the key and the lower part corresponds to the return of this same key to its high position.

It will be observed that, when the stroke of the key, when the latter is pressed, reaches the value D2, the force exerted on the key decreases suddenly and causes the tactile sensation which has been mentioned above. For the sake of simplification, the corresponding state of the mechanism has been designated by "closing" in FIG. 2. Those skilled in the art will understand that the intention here was to designate the tilting of the control element towards the position where it "closes" the contacts 10A and 10C. The same observation applies to the indication "opening" carried on the part of the curve illustrating the return of the key to its high position.

The abscissa shift between the "closing" point of the contacts, when the key is pressed, and the "opening" point of these same contacts when the key is returned or released, reflects the phenomenon of physical hysteresis which exists in the structure of the switch according to the invention, hysteresis which is important for the stability of the mechanism.

Although the version of the capacitive type described above is that preferred for the switch according to the invention, the latter could just as easily be designed in a version with purely ohmic contacts. To do this, it would suffice to leave the electrical contacts 10A, 10B and 10C bare, so that they can be directly touched by the control element 11. It goes without saying, also, that the electrical contacts 10A, 10B and 10C could be replaced by other types of means producing electrical signals such as inductive, piezoelectric elements, light interruption detectors, etc.

Claims (5)

1. An electric switch of the type that includes a housing (3) in which a key (1, 2) is slidably mounted, said housing containing a control member (11) for controlling the electrical conduction state of the switch, said control member being mounted to rock back and forth, in accordance with the position of the key, between two distinct positions in which it cooperates with electrical contacts (10A, 10B, 10C) to establish two distinct electrical conduction states of the switch, the key motions being imparted to the control member through a catastrophically buckling compression spring (17) mounted between the key and the control member under precompression, said switch being characterized in that it comprises:

means for determining the direction in which catastrophic buckling of the spring occurs, said means being located within the housing and engaging said spring to cause an initial buckling thereof in a predetermined direction corresponding to that of the desired catastrophic buckling.

first mounting means (16) integral with the key for coupling an end of the spring to said key,

second mounting means (13) integral with said control member for directly coupling the control member to the other end of the spring, said second mounting means being positioned in such a way, relative to the rocking axis (12) of the control member, that the precompression state of the spring will maintain the control member in one of said positions until, upon the key being pressed down a predetermined distance from a rest position, catastrophic buckling of said spring occurs and causes the control member to rock to its other position.

2. An electrical switch according to claim 1, characterized in that said spring (17) is a helical compression spring.

3. An electrical switch according to claim 2, characterized in that said means for determining the direction in which buckling of the spring occurs is comprised of a mounting surface for that end of the spring which is associated with the key, said surface being angled relative to the direction in which the key slides and including a groove for loosely receiving the proximal turn of the spring, said groove forming part of the first mounting means.

4. An electrical switch according to claim 2 or 3, characterized in that said second mounting means is comprised of a projection (13) over which the associated end of the spring fits.

5. An electrical switch according to claim 4, characterized in that a side of the end of the spring (17) that fits over said projection is aligned with said rocking axis of the control member.

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