EP0100936B1 - Push button switch - Google Patents

Abstract

A low profile switch key has a base which slidingly supports a pushbutton. The pushbutton is slidingly engaged with a plunger body by a lost motion connection. The plunger body carries cams which control the flexing of contactors to make and break conductive connections with adjacent stationary contacts. A coil spring biases the pushbutton upwardly to its rest position. The sliding lost motion between the pushbutton and plunger body allows the pushbutton to slide by itself over an initial pretravel interval when it is pressed. At the end of the pretravel interval, the pushbutton strikes the plunger body and carries the body downward to complete the key stroke. The plunger body resists sliding movement and therefore provides a perceptible pressure point which indicates actuation of the switch. The stationary contacts and associated overlying cams are interlocked when the pushbutton is depressed to provide a relatively low switch profile with respect to the length of the key stroke.

Description

The invention relates to a key switch with at least one contact piece fixed in a base and a U-shaped contactor whose contact-side end can be resiliently pivoted from one switching position into another switching position by means of at least one key cam of a key tappet supported on a return spring.

Such key switches are well known in a versatile design and in use. For modern input keyboards of electronic systems and in particular for typing keyboards of computer-controlled typing systems, key switches in such a flat design are required that the keyboard has a maximum height of about 30 mm in the third row of keys according to a currently required standard. Key switches, which are suitable for the construction of such a keyboard, should on the one hand be extremely stable with a very long service life and fully automatic mountability and on the other hand have a tactile pressure point immediately before the contact is closed in the interest of a safe switching function. It is necessary that with a usual key stroke of about 4 mm a difference between the switch point and the switch back point, i. H. a hysteresis behavior is guaranteed and that the switch can be mass-produced very inexpensively.

This object is achieved in that the key tappet is divided into a tappet part and a differential path part, that the differential path part is pushed onto catches arranged on the tappet part and can be freely moved between an upper and lower end position, that the differential path part is displaced by a mechanical at the initial displacement of the tappet part Movement inhibition initially maintains its rest position until the differential path part assumes the upper end position relative to the plunger part and that the plunger part moves together with the differential path part after the initial displacement, the at least one button cam located on the differential path part actuating the contactor.

In a key switch constructed according to the measures of the invention, the differential path part is held in the rest position by the catches on the tappet part in the uppermost position. If the plunger section is pressed down when the button switch is pressed, it can initially move freely within the differential travel section until it stops on the top of the differential travel section and takes the differential travel section down with it. Since the at least one key cam rests under pressure on the contactor and the differential path part experiences mechanical movement inhibition, the differential path part remains in its uppermost position until the plunger part takes it down due to a mechanical stop. Only by moving the differential path part can the contactor move along the switch slope of the key cam to actuate the switch. When the button is released, the tappet part is returned by a spiral compression spring, with its catches reaching under the differential travel part and returning it to the rest position with upward.

An advantageous embodiment of the invention provides that the catches on the tappet part are designed as hook-shaped tabs, each with a projecting stop shoulder, and that the tabs run in a guide groove in the differential travel part, the stop shoulders engaging under a stop edge on the differential travel part. The provision of guide grooves for the hook-shaped tabs ensures that the differential path part can only move in the actuation direction of the key, so that transverse moments or eccentric moments cannot trigger premature entrainment of the differential path part, which would impair the desired switching function.

The differential path part is provided with a central bore through which a guide pin engaging in a guide sleeve in the base and two hook-shaped tabs lying on both sides of the guide pin extend, the respective stop shoulder of which engages under the edge of the differential path part in the region of the guide grooves. This configuration ensures that both the plunger part and the differential travel part are guided centrally within the key switch.

The mechanical movement inhibition for the differential path part is brought about by the button cams which are in pre-tension on the contactor in the rest position. This force with which the contact spring rests on the key cam thus requires an increased actuation force shortly before the switching point, which creates a pressure point feeling. In the event that a further mechanical movement inhibition is desirable, the invention provides that the differential path part is provided with at least one plastic spring, which rests on the inside of the cover of the key switch.

A further embodiment also provides that a spiral compression spring that biases the key switch into the rest position engages over the guide sleeve in the base and between the hook-shaped tabs over the guide pin on the plunger part. This ensures that the return force of the spiral compression spring can only act on the differential travel part via the tappet part.

In the event that it is desirable to further reduce the overall height of the key switch with a constant stroke, the invention provides that a cutout is made on the underside of the key cam, which engages in a corresponding recess on the contact piece when the key tappet is pressed .

A further safeguard against rotational movements due to off-center forces is ensured by the base opposite sides is provided with two lateral guide ribs, between which a guide projection encompassing the plastic spring engages. These lateral guide ribs can be designed to extend into the cover over the upper edge of the base, which also simplifies the assembly of the switch and, in particular, automatic assembly.

For better guidance of the tappet part, it is provided that it is provided with a cover plate which is guided in a corresponding cutout in the cover. Since this cover plate lies on the surface of the differential path part over a large area when the key switch is actuated, it is ensured that the differential path part cannot tilt when it is moved downward.

• Fig. 1 eine auseinandergezogene und teilweise geschnittene Darstellung eines Tastenschalters gemäß der Erfindung;
• Fig. 2 einen schematisierten schnitt durch den Tastenschalter gemäß Fig. 1 in seiner Ruhelage;
• Fig. 3 A, B, C schematisierte Teilschnittdarstellungen, aus welchen die Lage des Differenzwegteils für unterschiedliche Positionen des Stößelteils hervorgeht;
• Fig. 4 A, B Teilschnittdarstellungen, welche den Tastenschalter in Ruhelage und in Schaltlage zeigen;
• Fig. 5 ein Kraft-Wegdiagramm.

The invention with its advantages and features is explained in more detail with reference to an exemplary embodiment which refers to the drawing. Show it

• Figure 1 is an exploded and partially sectioned illustration of a key switch according to the invention.
• FIG. 2 shows a schematic section through the key switch according to FIG. 1 in its rest position;
• 3 A, B, C are schematic partial sectional representations from which the position of the differential travel part for different positions of the plunger part is evident;
• Fig. 4 A, B partial sectional views showing the key switch in the rest position and in the switch position;
• Fig. 5 is a force-displacement diagram.

The key switch shown in FIG. 1 consists of a base 10, which is closed with a cover 11. Inside the key switch, a key plunger is slidably attached, which consists of a plunger part 12 and a differential path part 13. The ram part 12, as will be explained in more detail below, snapped into the differential travel part 13. On the underside of the plunger part 12, a guide pin 14 is attached, which engages in a guide sleeve 15, which is formed in the central region of the base 10 upwards. This guide sleeve 15 also serves as a holding pin for a spiral compression spring 16 which is pushed outside over the guide sleeve and rests with its upper end on the underside of a cover plate 17 of the tappet part 12. With the help of the guide sleeve 15, on the one hand, the tappet part 12 is guided during the actuation of the button, the spiral compression spring being secured against lateral displacement at the same time.

At least one contactor 20 and one contact piece 21 are inserted into the base. The contactor 20 consists of a U-shaped contact spring material and carries at the end of one leg a solder tail 22 which is inserted through a corresponding opening in the base of the base 11. The leg carrying the soldering lug runs parallel to the inner wall of the base 10. The free contact end 23 of the other leg of the U-shaped bent contact 20 lies inside the base 10, opposite the contact piece 21 which is also inserted into the base and of which a soldering lug 24 protrudes downwards from the base. The contactor 20 is biased such that the crossbar contacts 25 attached to the contact piece and at the contact end rest on one another when the contactor is not lifted by the action of the key tappet.

As can be seen from the illustration, the contactor can be partially separated by a slot 26, wherein the slot at the contact-side end can be continuous, as indicated by dashed lines, in order to obtain a double contact. In this case, crossbar contacts are attached to both free contact ends, which work together with corresponding elements on the contact piece. Such a double contact has the advantage that the contact switch is less susceptible to contamination.

The U-shaped contactor protrudes with its base into a corresponding recess 27 in the cover 11. The U-shaped contact 20, which is open at the bottom, can thus be in a certain range with respect to the length of the legs without having to change the position of the contact plane can be varied, it being possible to achieve a relatively large spring length with reduced spring stiffness if the contactors project fully into the recess 27.

The contactor 20 is folded twice at the contact end, whereby a sliding edge is obtained which slides along the feeler cam 30 of the differential path part 13. The sliding edge merges on both sides of the contact end into a sliding vane 31, which is the actual part of the contactor which bears against the probe cam and runs along it.

The differential path part 13 consists of a frame with a central bore 35 which is expanded in the direction of the two narrow sides of the frame by a guide groove 36. On the two long sides of the differential path part 13, the key cams 30 are attached at a distance which corresponds to the distance between the sliding tabs 31 on the contactor 20. In the idle state of the key switch, the key cams rest with a vertically extending section 37 on the sliding edge of the sliding lugs 31, the crossbar contacts being lifted off. When the two-part tappet is depressed, the sliding edge of the associated sliding vane moves first along the vertical section 37 and then along one inwardly extending bevel 38, whereby the contact rail contacts 25 can come into contact with each other. The pressing force with which the contactor 20 rests on the section 37 brings about a pressure point feeling due to the increased actuating force during the initial displacement of the differential path part 13.

As can be seen in the drawing, the contact piece is inserted into the base 10 such that it is held on one side in the wall of the base. So that the contact end of the contactor 20 can be attached as deeply as possible, on the one hand the contact piece 21 is provided with a recess 40 and on the other hand the associated key cam 30 is provided with a cutout 41.

When the key tappet is depressed, the cutout 40 and the cutout 41 engage in one another, so that the differential path part 13 of the key tappet can be moved downward until it rests on the inner bottom surface of the base. This makes it possible to make the key switch very low while maintaining a relatively long key stroke.

On the tappet part 12 of the key tappet hook-shaped tabs 45 are attached which extend downward from the cover plate 17 and which are provided at the lower end with an outwardly projecting stop shoulder 46. These hook-shaped tabs are located on both sides of the guide pin 14, specifically outside the spiral compression spring 16 which grips over the guide pin. The size and position of these hook-shaped tabs 45 correspond to the guide grooves 36 in the differential path part 13, the stop shoulders engaging under a stop edge on the differential path part when the Ram part is inserted in the differential path part. The hook-shaped tabs 45 are sufficiently elastic so that they can be compressed when inserting the tappet part 12 into the differential path part 13 until they engage with their stop shoulder under the edge of the differential path part designed as a stop edge. In the locked state, the differential path part 13 is easily displaceable on the hook-shaped tabs 45 between an upper and a lower end position.

The assignment of the tappet part 12 and the differential travel part 13 in a closed key switch is shown in FIG. 2. The plunger part 12 is shifted into its upper end position with the aid of the spiral compression spring 16 and rests with the stop shoulders 46 of the hook-shaped tab 45 on a stop edge located on the underside of the differential travel part.

The differential path part 13 is also, as is apparent from FIG. 1, provided on its opposite narrow end faces with a guide projection 47. In the area of this guide projection 47, a plastic spring 48 is formed which, as can be seen from FIG. 2, rests on the inner surface of the base 10 in a sliding manner. With the help of this plastic spring 48, a mechanical movement inhibition for the differential path part can be created, which acts in addition to the key cams which are in pre-tensioned condition at the contactor.

Due to the key cams 30 attached to the differential path part 13 on both sides, the key switch according to the construction according to FIG. 1 offers the possibility of providing two mutually independent contact sets, as is shown in FIG. 1 by the contact set used and the explosively drawn out contact set. The functionality of the key switch is not affected in any way if it is only provided with a single key set. Since the guide path 47 between lateral ribs 50 in the base 10 of the differential path part is additionally protected both against twisting and against tilting. By extending the guide ribs 50 beyond the upper edge of the base 10, the assembly is considerably simplified, in particular in the case of an automatic assembly, since no additional positioning aids are required for inserting the tappet part snapped into the differential path part.

The operation of the key switch is explained with reference to FIGS. 3A to 3C taking into account the details from FIG. 1. The rest position and the switching position can also be seen in FIGS. 4A and 4B.

In the idle state, the key switch is biased by the spiral compression spring 16 in its uppermost position indicated in FIGS. 3A and 4A.

The stop shoulder 46 bears against the stop edge at the lower edge of the differential path part 13 and moves the differential path part up to the stop on the cover 11. In this position, the sliding edges of the contactor 20 rest on the vertically extending sections 37 of the key cams 30. The contacts are tensioned and the crossbar contacts are opened. When the key is pressed, the key plunger 12 initially moves downward against the force of the spiral compression spring 16, but the differential travel part 13 is still held in its rest position by the mechanical movement inhibition due to the sections 37 abutting the contactor, as can be seen from FIG. 3B . The mechanical movement inhibition is supported by the plastic springs 48 if such are provided on the differential path part. When the position shown in FIG. 3B is reached, the plunger part 12 comes to a stop on the surface of the differential travel part and moves it downward against the movement inhibition, the sliding edge on the contactor sliding upwards via the switching slope 38 and releasing the contact. Due to the mechanical movement inhibition, the entrainment of the differential travel part 13 can be determined as an increase in the key press, which achieves the function of a pressure point. When the key is released, the key tappet 12 moves upwards by the pressure of the spiral compression spring 16 and comes with the stop shoulder 46 against the stop edge on the underside of the differential path part 13 and takes the differential path part 13 upwards into the position shown in FIG. 3A. The difference path is essentially determined by the distance of the stop shoulder 46 from the stop edge on the underside of the difference path part. Although a uniform differential path should occur due to the structural conditions, it can be assumed that due to the dynamic influences, a different differential path is set depending on the actuation speed. In any case, however, a sufficiently large differential path can be achieved in order to obtain a switching path difference between the switching point and the switching point and thus a switching hysteresis.

A force-displacement diagram is shown in FIG. When the tappet part 12 is pressed, the compression spring 16 is tensioned, the actuating force initially increasing linearly. From the moment the differential travel part 13 is taken along, the actuating force rises steeply until the frictional force between the contactor 20 and the sensing cam 30 is overcome. While the sliding flag 31 is sliding along section 37, the actuating force continues to increase linearly until the sliding flag merges into the bevel 38.

Then there is a drop in the operating force to the switching point, i. H. the lifting of the contact rail contacts 25. The rest of the switching stroke runs with an actuating force that is further linearly dependent on the compression spring 16. When the button switch is released, the actuation force decreases linearly up to the switch-back point. This switch-back point is offset from the switching point by the differential travel, which results from the interaction of the plunger part with the differential travel section. This creates a switching hysteresis. The running of the sliding vane 31 on the switch slope 38 results in a rapid reduction in the actuating force, as the negative increase in the curve associated with the downshift path in FIG. 5 shows.

If a projection of low height, not shown in the drawing, is attached to the transition from section 37 into the bevel 38, the perceptibility of the pressure point can be increased. This elevation can be carried out in such a way that the vertically extending section 37 is changed into a section which rises slightly obliquely towards the front, the highest height being in the transition of this section into the switching slope.

Claims (11)

1. t. Push button switch with at least one fixed contact member (21) in a socket (10) and a contactor (20) bent into a in-shape whose contact end may be resiliently pivoted from one switch position into another switch position by means of at least one switch cam (30) of a switch slide (12, 13) supported on a compression coil spring (16), characterised in that, the switch slide is divided into a slide member (12) and a differential path member (13), the differential path member (13) is pushed on to stops (45, 46) arranged on the slide member (12) and is freely slidable between an upper and a lower end position, on initial sliding of the slide member (12) the differential path member (13) initially maintains its rest position by virtue of a mechanical restraint to movement until the slide member engages the differential path member, and after the initial sliding the slide member continues to slide together with the differential path member, whereby the at least one switch cam (30) situated on the differential path member actuates the contactor (20).
2. 2. Push button switch as claimed in claim 1, characterised in that, the stops on the slide member are constructed as hookshaped plates (45) with a respective projecting abutment shoulder (46), and the plates extend in a guide groove (36) in the differential path member (13), whereby the abutment shoulders (46) engage under an abutment edge on the differential path member (13).
3. 3. Push button switch as claimed in claim 1 or 2, characterised in that, the differential path member (13) is provided with a central bore (35) through which extend a guide peg (14), which engages in a spring sleeve (15) in the socket (10), and the two hook-shaped plates (45), which lie on both sides of the guide peg, and the abutment shoulders (46) engage under the edge of the differential path member (13) in the vicinity of the guide grooves (36).
4. 4. Push button switch as claimed in one of claims 1 to 3, characterised in that, the mechanical restraint to movement is effected by the switch cam (30) which in the rest position is biased against the contactor (20).
5. 5. Push button switch as claimed in claim 4, characterised in that, the differential path member (13) is provided with at least one plastics tongue (48) which engages the inner side of the lid (11) of the push button switch.
6. 6. Push button switch as claimed in one of claims 1 to 5, characterised in that, the socket (10) is provided on opposing sides with two lateral guide ribs (50) in each case, between which a guide projection (47) extending around the plastics tongue (48) engages.
7. 7. Push button switch as claimed in claim 6, characterised in that, the lateral guide ribs (50) extend beyond the edge of the socket into the lid (11) of the push button switch.
8. 8. Push button switch as claimed in one of claims 1 to 7, characterised in that, the compression coil spring (16) biasing the push button switch into the rest position engages the slide member over the guide sleeve (15) in the socket and between the hook-shaped plates (45) over the guide peg (14).
9. 9. Push button switch as claimed in one of claims 1 to 8, characterised in that, provided on the underside of the switch cam is a cutout (41) which engages in a corresponding recess (40) on the contact member (21) when the switch slide (12) is pushed.
10. 10. Push button switch as claimed in one of claims 1 to 9, characterised in that, the slide member (12) is provided with a cover plate (17) which is guided in a corresponding cut-out in the lid (11).

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