EP0001031A1 - Push button switch with snap action - Google Patents

Abstract

Electric key switch in which the changes in electrical conduction states occur suddenly when the key is operated. The switch comprises a button (1) coupled only by means of a snap compression spring (17) to a control element (11) mounted to switch according to the position of the button between two positions in which it cooperates respectively with the contacts (10A and 10B or 10A and 10C). The spring (17) is mounted between the key (1) and the element (11) in a precompression state which ensures that the element (11) is maintained in one of its positions as long as the key is not not pressed. The seat (16) of the spring on the key is inclined to determine a single direction of buckling of the spring when the key is pressed. Switch usable for opening and / or closing one or more electrical circuits.

Description

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 tilting element to tip over. control to its contact closed position or recall it to its rest or contact open position.

For example, the U.S. patent No. 2 810 031 presents a push button switch in which a coil spring is used to cause the pivoting of a pivotally mounted control element. However, an additional member must be added between the push button and the rocking element to orient the stroke in the appropriate direction, when initiating the action and to apply a restoring force when the push button is released. 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.

U.S. Patent No. 3,863,040 discloses a columnar compression spring subjected to buckling in order to come into contact with contact elements located on either side thereof. French patent No. 72 14732 filed in France by the plaintiff on April 18, 1972 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 tilting of a contact control element. In fact, the spring itself constitutes the contact element.

A switch of the abruptly tilting control member type is disclosed in US Patent No. 3,491,218 but an additional member is disposed between the push button and the tilting member to that the latter rocks 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 aforementioned French patent No. 72 14732. This spring has characteristics well known to those skilled in the art (such as length, diameter, size of the wire, material, etc.) which allow it to flare 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 to ensure distinct 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 compressive force is reached, the spring suddenly flares up by applying a torque to the control element which causes it to tip over to 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 1C shows the switch of Figures 1A and 1B when the key is pressed up to the point where the compression spring suddenly buckles.

Figure 1D shows the switch of Figures 1A to 1C 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 1A to 1D.

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 electric 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 stud 4 which moves in a groove 5 of the housing 3. The function of this stud 4 is to limit the upward stroke of the key 5 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 D0, 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, in material not electrically conductive 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 generally flat 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 the 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 the other of the sets of plates 10A, 10B, 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 stud 13 which is offset to the left, in the figures, with respect 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 stud 16 is surrounded by a shallow circular groove (not referenced) in which the first turn of the first end of a helical compression spring 17 is freely housed, the second end of which is fitted on the stud 13 .

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

The compression spring 17 is of the type with sudden buckling described in the aforementioned French patent No. 72 14732. 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 snap-action 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 stud 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. 1A 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 key 1 in order to depress it relative to its high position shown in FIG. 1A. This force F caused a slight depression Dl 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 takes place. that, during this sudden buckling, the end of the spring 17 which is coupled to the stud 16 of the barrel 2 partially leaves the groove, in which it is housed, pivoting freely counter-clockwise.

As will be understood by those skilled in the art and as indicated in the aforementioned French patent No. 72,14732, 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. 1D represents the mechanism when the key 1 has been pressed even further and has traveled a distance D3 greater than the distance D2. This FIG. 1D 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 resumes 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 necessary 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 D0, Dl, D2 and D3 of the key mentioned above have been indicated on the abscissa, with reference to FIGS. 1A to 1D.

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 offset 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 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.

Although the essential characteristics of the invention applied to a preferred embodiment of the invention have been described in the foregoing and represented in the drawings, it is obvious that a person skilled in the art can provide all of them. modifications of form or detail which he judges useful, without departing from the scope of said invention.

Claims (5)

1. Electric switch of the type comprising a box in which a button is mounted for sliding, said box containing an element for controlling the state of electrical conduction of the switch, mounted in said box for switching, as a function of the position of the button , between two distinct positions in which it cooperates with electrical elements to determine two distinct electrical conduction states of the switch, the movements of the key being transmitted to the control element by means of a compression spring with sharp buckling mounted between the key and the control element in a precompression state, said switch being characterized in that it further comprises: means for determining the direction of buckling of the spring, located inside the casing and in contact with said spring, in order to impart to the latter a slight initial buckling in a predetermined direction which corresponds to the direction of sudden buckling desired, a first mounting means, integral with the key, making it possible to couple one of the ends of the spring to said key, a second mounting means, integral with said control element, making it possible to couple the latter directly to the other end of the spring, said second mounting means being located, with respect to the tilting axis of the control element, a location such that the state of precompression of the spring maintains the control element in one of said positions, until, when a key is pressed, over a predetermined distance, said spring flares suddenly and tilt the control element to the other of its positions. 2. Electric switch according to claim 1 characterized in that said spring is a helical compression spring. 3. Electrical switch according to claim 2, characterized in that said means for determining the direction of buckling of the spring consists of a seat surface, of the end of the spring associated with the key, having a predetermined inclination relative to the direction in which the key slides, said inclined seat surface comprising a shallow groove in which the extreme turn of the spring is freely housed, said groove constituting said first mounting means. 4. Electric switch according to claim 2 or 3 characterized in that said second mounting means is constituted by a stud on which is fitted the associated end of the spring. 5. An electrical switch according to claim 4 characterized in that one side of the end of the spring fitted on said stud is perpendicular to said tilting axis of the control element.

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