EP0233926B1 - Key module for contact foil keyboards - Google Patents

Abstract

PCT No. PCT/EP86/00453 Sec. 371 Date Mar. 9, 1987 Sec. 102(e) Date Mar. 9, 1987 PCT Filed Jul. 31, 1986 PCT Pub. No. WO87/01236 PCT Pub. Date Feb. 26, 1987.A key module for a membrane switch keyboard has a flat spring running diagonally to the key housing on the bottom side which, with the aid of a plunger, is bent for the operation of membrane contacts. The flat spring with one free end is inserted into a slot which is open toward the top and permits an adjustment of the flat spring by pressure loading on the free end or on the bottom side against the lower section of the flat spring, which is adjacent to the bent free end. The free end of the flat spring is rigidly retained in a slot at the key housing. For the adjustment of the operating force a compression spring is arranged inside the plunger and is supported against a cross-piece running over the flat spring.

Description

The invention relates to a key module for membrane keyboards with a leaf spring clamped in the key housing on one side according to the preamble of claim 1 and a method for setting the switching point.

From GB-A-2141 874 a key module for membrane keyboards is known, in which a right-angled leaf spring extends on one side on the underside of the key housing, the bent end of which is inserted in a recess in the key housing from below. In the button housing, a button plunger can be moved, which acts on the free end of the leaf spring and bends it downwards, whereby an upper switching film of a film switch panel is bent by a space in a spacer film against a lower switching film and the contact points on the switching film come into contact. The key tappet is guided in a cylindrical housing attachment which, based on the center point of the mounting surface of the key module, lies opposite the recess which recesses the clamped end of the leaf spring. A key cap can be attached to the plunger from above. Since the leaf spring does not have sufficient rigidity to ensure the desired characteristic curve with a given actuation force, a helical compression spring is additionally arranged between the key cap and the key body in the practical embodiment, the spring running around the shoulder receiving the key tappet. In this arrangement, it is considered disadvantageous that the key module can only function in the fully assembled state with the key cap and thus no verification of the course of the characteristic curve and the position of the switching point is possible during manufacture.

A key module is known from EP-A-1 87 396, which does not need this additional spring which determines the desired actuating force, but this key module requires a space requirement that extends over two module grids.

Since in GB-A-2141 874 the key cap is simply pushed onto the plunger and, on the other hand, the distance between the underside of this key cap and the key body determines the clamping length of the additional helical compression spring, it is difficult for all key modules because of the relatively large plug-in tolerances that result. the z. B. to be housed in a keyboard to ensure a constant initial operating force in a very narrow tolerance range. It is therefore desirable to provide a tappet stroke limitation with which the initial actuating force of the additional compression spring can be precisely determined and its value can be checked during the assembly of the key module.

For an optimally designed keyboard, it is not only desirable that the individual key modules can be actuated with an almost exactly the same initial force, but also that the switching point, i. H. the switching time is set as precisely and defined as possible. With the type of clamping of the leaf spring in the key module according to GB-A-2 141 874, large spreading ranges are inevitable for the switching point, since the positioning of the leaf spring is very difficult to readjust. Furthermore, not only the positioning of the leaf spring, but also to a certain extent the stiffness of the upper switching film is a determining factor for the scattering of the switching point. This results in the desire for a possibility not only to be able to set the switching point when mounting the key module, but also for particularly high-quality keyboards, as are particularly desirable for typing systems, a possibility for readjusting the switching point after mounting the key module on a membrane switch panel to have.

The invention is therefore based on the object of providing a key module for a membrane keyboard in which the switching point can be set as precisely as possible, both with regard to the switching time and the actuating force required at the switching time.

This object is achieved for the key module according to the features of claim 1 and for the method for setting the switching point by the measures of claim 9.

Further embodiments of the invention are the subject of dependent claims. The measures of the invention are advantageously suitable for creating a key module with which membrane keyboards can be created, to which the highest demands are placed on the same initial actuation force of all built-in key modules and a precisely set switching time as well as constant actuation force at the switching time. Due to the self-locking clamping of the clamped end of the leaf spring, which protrudes upwards from the recess and is exposed downwards with a section adjoining the clamped end through the membrane switch panel, the leaf spring can be precisely adjusted with regard to the switching point by means of the finest adjustment strokes with a plunger hammer. On the other hand, since the web extending over the switching spring in the key housing enables the helical compression spring determining the actuating force to be clamped very precisely between the key plunger inside and the key housing, the actuating force is very uniform across the individual key modules, since the helical compression springs used are very high constancy with regard to the spring constant can be produced. In addition, since the key tappet is provided with resilient hooks which engage under locking stops in the key housing and limit the stroke of the key tappet upwards, the initial actuation force can thus be determined Specify very precisely the possibility that the key tappet and the key housing can be manufactured with the highest dimensional accuracy and the smallest tolerances. This possibility of specifying a very defined and constant initial actuation force for the individual key modules also results in an actuation force that is very constant within narrow limits at the time of switching when this is adjusted. On the basis of these advantages resulting from the measures of the invention, it is possible to use the key modules according to the invention to create membrane keyboards which are particularly well suited for high-quality writing systems for highly qualified typists, and for which the switching times are set as finely as possible with high writing performance and high writing speed and constant actuation power is particularly important for achieving high writing performance.

The advantages of the invention result from the following description of an exemplary embodiment in conjunction with the drawings.

• Fig. 1 ein explosionsartig auseinandergezogenes Tastenmodul gemäß der Erfindung;
• Fig. 2 eine Draufsicht auf das Tastenmodul ;
• Fig. 3 einen Schnitt längs der Linie 111-111 der Fig. 2 ;
• Fig. 4 einen Schnitt längs der Linie IV-IV der Fig. 2 ;
• Fig. 5 einen Schnitt längs der Linie V-V der Fig. 2 mit Einrichtungen zum Justieren der Blattfeder in dem Tastenmodul mit in Ruhelage befindlichem Tastenstößel ;
• Fig. 6 einen dem Schnitt gemäß Fig. 5 entsprechenden Schnitt durch das Tastenmodul in Arbeitsposition ;
• Fig. 7 einen dem Schnitt gemäß Fig. 5 entsprechenden Teilschnitt durch eine andere Auführungsform der selbsthemmenden Befestigung der Blattfeder.

Show it :

• Figure 1 shows an exploded button module according to the invention.
• 2 shows a plan view of the key module;
• Fig. 3 is a section along the line 111-111 of Fig. 2;
• Fig. 4 is a section along the line IV-IV of Fig. 2;
• 5 shows a section along the line VV of FIG. 2 with devices for adjusting the leaf spring in the key module with the key tappet in the rest position;
• 6 shows a section corresponding to the section according to FIG. 5 through the key module in the working position;
• 7 shows a partial section corresponding to the section according to FIG. 5 through another embodiment of the self-locking fastening of the leaf spring.

The exploded view of the key module shown in FIG. 1 consists of a key housing 11, a key tappet 12, a leaf spring 14 and a helical compression spring 15. The key housing 11 and the key tappet 12 are injection molded with very high dimensional accuracy. The button housing 11 consists of a base plate 20, which is essentially flat on the underside, from which a hollow cylindrical extension 21 with a substantially square cross section extends upwards in a central position. In the interior of the hollow cylindrical extension 21, starting approximately from the plane of the base plate 20 and running in the direction of a diagonal of the base plate, a web 22 is provided, the central region of which, as can be seen in FIG. 3, is pulled up and a plug pin 23 for placement the helical compression spring 15 carries in the four corners of the hollow cylindrical extension 21 there are guide grooves 26 for the key tappet 12 in the inner region. Furthermore, locking projections 27 are provided on two mutually opposite inner walls, the function of which will be explained in more detail below.

The leaf spring 14 runs on the underside of the base plate along a diagonal that runs perpendicular to the web 22 and along the section line V-V according to FIG. 2. On the base plate 20, a leaf spring fastening 28 is provided in a corner region penetrated by the above-mentioned section line, which is designed in the form of an upwardly projecting projection and has a recess 29 into which, according to FIGS. 4 to 7, the upwardly angled end 30 of the Leaf spring 14 can be used from below. This recess is explained in more detail below.

The leaf spring 14 is formed in one piece and has a section 31 which lies in the central region and which connects with its one side to the end 30 which extends at a right angle and with its other side to a spring arm 32 which, with respect to the plane of the section 31, is angled is oriented upwards. A tappet contact surface 33 is formed at the free end of the spring arm 32.

As can be seen from FIGS. 3, 5 and 6, the spring arm 32 runs under the web 22, the folded edge 34 coming to lie over the contact area.

The key plunger 12 which can be inserted into the hollow cylindrical extension 21 from above has an essentially box-shaped structure which is open at the bottom and from the top surface 40 of which a fastening projection 41 for a key cap (not shown) extends upwards. Guide ribs 42 are formed along the corner areas, which fit into the guide grooves 26 in the key housing 11. A sleeve-shaped projection 43 is provided under the fastening projection 41 on the inside of the key tappet, and the helical compression spring 15 can be inserted into its inner bore, as can be seen in FIG. 3. The guide rib 42 'coming over the tappet contact surface 33 and guided in the guide groove 26' is convex on the underside so that the actuation force for bending the leaf spring is introduced with the least possible friction on the tappet contact surface 33 due to the inevitable transverse displacement.

Notches 44 are provided in two wall surfaces of the key tappet 12 opposite the locking projections 27 in the key housing 11 in order to obtain spring tongues 45 which protrude with a hook 46 over the lateral surface of the box-shaped key tappet. In the inserted state of the key tappet, these hooks 46 engage under the locking projections 27 on the key housing and limit the stroke of the key tappet upwards, so that a defined distance results between the plug pin 23 on the web 22 and the sleeve-shaped extension 43 due to narrow dimensional tolerances, one very precisely defined initial actuation force for the key module is ensured on account of the helical compression spring 15 which is also manufactured with very narrow tolerances. Appropriate recesses 48 over the resilient hook 46, both in the key housing and in the key tappet, can the resilient hooks 46 are pressed together with a simple tool if the key tappet is to be removed from the key housing upwards.

Compared to the helical compression spring arranged on the outside in the known prior art, the helical compression spring 15 arranged in the interior of the key module has the advantage that, after the key tappet 12 and the leaf spring 14 have been installed, the leaf spring can be adjusted and preselected without the key cap being used for this purpose. as in the aforementioned prior art, must be put on, which usually takes place only at the end of the assembly of the keyboard. It cannot be prevented that so-called “outliers” are occasionally installed in a keyboard and have to be replaced again after a disproportionate amount of time if high demands are placed on the keyboard.

4 to 6 show the assembly of the right-angled end 30 of the leaf spring 14 in the leaf spring fastening 28. As can be seen from FIG. 4, the side edges of the end 30, which is bent upward at right angles, are provided with teeth 36 which, after being inserted into the recess 29, engage in the side walls of the recess. The top view according to FIG. 2 shows that the free end 30 is clamped in the recess 29 in a slightly curved manner, in that the lateral grooves 37 receiving the side edges of the leaf spring run in a plane which lies behind the front edge of a rib 38 which is substantially above the entire length of the recess 29 runs in the plane of the diagonal of the key housing from top to bottom. This rib 38 is only in the lower region, where the end 30 merges into the section 31, not on the leaf spring.

The distance of the rib 38 from the opposite wall of the recess 29 is preferably greater than the thickness of the leaf spring, so that for inserting the leaf spring it can be bent more with the help of a tool, so that the lateral edges or teeth 36 without significant Allow system to move along side grooves 37 when inserting.

5 and 6 also show that a recess 40 is provided in the bottom surface of the base plate 20 which is deeper than the thickness of the portion 31 of the leaf spring 14. This recess 40 creates sufficient space for adjusting the leaf spring.

The leaf spring of the fully assembled key module is adjusted either after the module has been installed on the membrane switch panel 50 or after the key module has been placed on a corresponding adjustment gauge, which can be provided, for example, in the case of automatic installation within the automatic assembly machine. Both the film switch panel 50 and the adjustment gauge are provided below the section 31 of the leaf spring 14 with an opening 52 through which a plunger hammer 62 can grip. A corresponding plunger hammer 63 is arranged above the free end 30 protruding from the leaf spring fastening 28. The two plunger hammers can press the leaf spring either suddenly or continuously and move it up or down in the recess to adjust the switching time. This adjustment can take place automatically by the plunger hammers 62 and 63 being acted upon by a control circuit which, depending on the measurement of the switching time carried out during the adjustment, initiates more or fewer adjustment strokes from above or below when the key module is actuated.

For the control of the tappet hammers, circuits known per se can be used, with which the switching time and its deviation from the desired value are determined and the tappet hammers are controlled accordingly.

The adjustment of the leaf spring can also be done with the aid of the upper plunger hammer 63 alone, for example by inserting the leaf spring into the recess 29 so that it assumes the highest possible position. With the aid of the plunger hammer, the leaf spring is then slowly moved downwards into the position in which the desired value of the switching point is reached by several carefully metered blows. In this position, the leaf spring is held securely by the teeth 36, since the teeth engage in the lateral wall of the grooves 37 under the pretension of the curved leaf spring.

5 and 6 show a button module mounted on a membrane switch panel, FIG. 5 showing the leaf spring in the rest position and FIG. 6 the leaf spring in the contact position. The film switch panel consists of an upper switching film 52, a lower switching film 53 and a spacer 54 arranged in between. The spacer 54 is provided with cutouts in the contact area, so that the upper switching film 52 can be bent downward through the cutout in the spacer 54 until it comes into contact with the lower switching film 53. The upper switching film 52 is bent by the action of the folded edge 34, as can be seen in FIG. 6. With this construction, the initial operating force must first be applied in order to move the key plunger 12 downward against the force of the helical compression spring 15 and the leaf spring 14. The assembly of the leaf spring along a diagonal of the key module results in a relatively long spring arm, so that reliable contact is already ensured with a relatively low actuating force. Due to the relatively long spring arm, a flat characteristic curve can be achieved for the actuating force, which means that the switching time is passed through in a flat rise and can be adjusted very precisely with the aid of the adjusting device. The desired operating forces for membrane keypads between see about 50 to 60 grams can be developed with the key module according to the invention with a sufficiently large key stroke for secure typing, with a caster with a slight, jump-free increase in force after contact by the final deformation of the helical compression spring 15 and the leaf spring 14 no problems. Since the bending of the upper switching film 52 is also represented in the functional sequence of the contact making, as is the actuation of an additional spring connected in series, there is a series connection of three spring constants for the key actuation, which inevitably leads to a larger spreading range with regard to the switching instant. For this reason, it may be desirable to subject the key modules that have already been selected for installation in the keyboard to a final adjustment after installation in order to eliminate the influence of the switching film on the scatter and to set a uniform switching time for all keyboard modules within the range of narrow tolerances. For this purpose, the opening 52 already mentioned is provided in the membrane switch panel adjacent to the contact area, so that after the keyboard has been installed, each individual key module can be finely adjusted in the manner described above with the plunger hammers 62 and 63.

7 shows a further embodiment of a self-locking bracing of the leaf spring 14 'in the leaf spring fastening 28. This leaf spring attachment is constructed in the same manner as in the embodiment described above, but the right-angled end 30 'of the leaf spring is provided with a punched-out tab 39 which is bent out in the plane of the diagonal from the end 30' of the leaf spring and is sharp Edge abuts against the wall of the recess 29 opposite the rib 38. This tab 39 jams in the recess, in particular when it is pressurized from above under the action of the plunger hammer 63 shown in FIG. The bent-out tab 39 can be provided in addition to the side teeth 36 or as the sole measure for self-locking clawing of the leaf spring in the recess 29. Finally, although not shown in the drawing, two tabs pushed out from the right-angled end in opposite directions can also be used, which cling to each other in the wall of the recess and additionally deform when adjusted under pressure and thus with increased force tense.

Claims (9)

1. Key module for key-actuated membrane switch panels forming part of a keyboard comprising key housing (11), a flat spring (14; 14'), which is stretched in the key housing (11) unilaterally, the stretched end (30 ; 30') of which is bent perpen- diculady and inserted into a slot (29) situated in the key housing (11), and on the free end (33) of which a plunger (12), which is guided in the key housing (11), deflects the flat spring downward, whereby the flat spring comes to rest on an upper membrane (52) of a membrane switch array (50) and moves the upper membrane through the free space which is formed by a spacer (54), by means of which contact points located opposite each other are closed when the plunger (12) is actived, characterized in :

- that the slot (29) on the key housing (11) is open toward the top,

- that the unilaterally stretched end (30 ; 30') of the flat spring (14, 14') is extended upward the mounting area and projects out of the slot (29),

- that the self-locking end (30 ; 30') of the flat spring (14; 14') is secured in the slot (29) and is adjustable in different holding positions,

- that in the key housing (11) a cross-piece (22) runs diagonally over the flat spring (14 ; 14'),

- that the plunger (12) on its bottom side is provided with a housing-shaped shoulder (43) to receive one end of a compression spring (15), which with the other end rests on the cross-piece (22),

- and that on the plunger (12) flexible hooks (46) are arranged, which during the assembling of the plunger (12) into the key housing (11), grasp in a detachable manner under locking shoulders (2⁷) which terminate the lifting of the plunger (12) toward the top and thereby determine the initial key actuating force.

2. Key module in accordance with claim 1, characterized in that the end (30 ; 30') of the flat spring (14; 14') along the side edge is provided with formed teeth (36), which, because of the gripping force, clutch in the wall of the slot (29).

3. Key module in accordance with claim 1, characterized in that the end (30') of the flat spring (14') comprises one or several tongues, which span against the wall of the slot (29).

4. Key module in accordance with one of claims 1 to 3, characterized in that a recess (40), which is arranged in the bottom surface of the key housing for receiving a section (31) bordering the end (30 ; 30') of the flat spring (14 ; 14'), is deeper than the thickness of the flat spring.

5. Key module in accordance with claims 1 to 4, characterized in that in the membrane switch array (50) under the area of the recess (40), a passing through opening (52) is provided through which section (31) of the flat spring (14; 141 bordering the end (30 ; 30') is exposed.

6. Key module in accordance with claim 1, characterized in that the flat spring (14 ; 14') is arranged alongside a diagonal of the key housing (11) running vertically to the cross-piece (22).

7. Key module in accordance with claims 1 and 6, characterized in :

- that the plunger (12) is formed as a somewhat cube-shaped hollow body, which opens toward the bottom,

- that the longitudinal edges of the plunger are provided with guide ribs (42), which run vertically downward, and interlocking with corresponding guide grooves (26) designed on the key housing,

- and that two opposite surfaces of the key housing integrally comprise in spring-type tongues, which carry hooks (46) on the lower end thereof.

8. Key module in accordance with claim 7, characterized in that the lower end of one of the guide ribs (42') is enlarged spherically and is formed as a tripping cam (49) for the flat spring (14 ; 14').

9. Method for setting the switch-over times of a flat spring for a key module in accordance with claims 1 to 8, characterized in :

- that the flat spring is set from the bottom into the slot (29) of the key module in such a manner that the inserted free end (30) of the flat spring projects out of the slot at the top side,

- that the free end projecting upward from the mounting area or the section (31) of the flat spring, which is located over the passing through opening (52), after fastening at one or several key modules on the membrane switch array, provided under the flat spring, or after fastening of one or several key modules on a corresponding adjusting pattern, is intermittently or continuously pressure loaded with a ramming tool (62 ; 63),

- and that the switch-over time is measured simultaneously by the operation of the key module and, corresponding to the deviations of the desired switch-over time, the operation of the ramming tool is controlled.

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