EP2342728B1 - Keypad with long key travel and improved touch feeling - Google Patents

Description

The invention relates to a keyboard comprising at least one push switch and a key for operating the switch. It relates to taking into account geometric dispersions of the keyboard, lengthening the stroke of the key and improving the tactile sensation when pressing the key to operate the switch. The invention finds particular, but not exclusive, utility in a dashboard of an aircraft.

When it is intended for a dashboard of an aircraft, but also for other areas, a keypad must meet a number of constraints, in particular dimensional constraints. A first constraint is the tolerance on the key override. The difference in height between the upper surface of the key and the fixed surface of the keyboard is called the key overhang. This tolerance is generally low, of the order of two to three tenths of a millimeter. A second constraint relates to the stroke of the key. This race must generally be between seven and ten tenths of a millimeter depending on the application. A third constraint relates to the effort to be applied to a key in order to actuate the switch. The effort is for example five or six newtons with a tolerance around a newton. A fourth constraint may also relate to the switch maneuverability, that is to say the tactile sensation provided at the touch of a key. This sensation is notably related to the resistance opposed by the key when it is stressed and the resistance break observed when the switch goes from the open state to the closed state. This feeling is important to ensure reliable feedback to the operator operating the key.

Dimensional constraints can be all the more difficult to satisfy as the fixed part of the keyboard is often made by an assembly of parts. An assembly is necessary for example when the keyboard is backlit. The keyboard then comprises at least one front face, a printed circuit forming a support and a diffuser interposed between the front face and the printed circuit. The keyboard may further include sealing elements between the fixed part and the movable part, that is to say the key or keys. The assembly of the different parts of the keyboard causes a geometric dispersion generally of the same order of magnitude as the stroke of the key and the tolerance on exceeding the key. For a keyboard intended for an aircraft dashboard, the geometric dispersion is usually between six and ten tenths of a millimeter depending on the tolerances of the parts and the care taken in mounting the keyboard.

An example of a keyboard with a long stroke of keys is described in JP-A-1264125 . In addition, the push switches have insufficient travel to achieve the minimum stroke required for the key. In this case, the stroke of a dome switch is rarely more than three tenths of a millimeter. Even for a switch incorporating elastomers, the stroke is generally less than seven tenths of a millimeter. Therefore, it is generally not possible to make a rigid connection between the key and the moving part of the switch.

Several solutions have been considered by the applicant to ensure both the tolerance of exceeding the key and the minimum stroke of the key. The figure 1 illustrates a first embodiment of a keyboard in a sectional view of a portion of the keyboard in a plane passing through a key. The keyboard comprises a printed circuit 10 forming a support, a front face 11 fixedly secured to the printed circuit 10 by means of a plate 12 and a push-button switch 13 mounted on the printed circuit board 10. The pushbutton switch 13 is for example a switch of the type called "dome" or "blistering", that is to say where the switching is effected by deflection of a conductive elastic blister dome against two conductors to connect. This type of switch is known in the Anglo-Saxon literature as the "dome switch". The front face 11 and the plate 12 comprise an opening 14 allowing a key 15 to translate along an axis X and to operate the switch 13. According to this first embodiment, the tolerance of greater than 16 key 15 is guaranteed by a plating of the key 15 against the front face 11. This plating can be achieved by a spring 17 prestressed between the key 15 and the assembly consisting of the printed circuit 10, the front face 11 and the plate 12. In particular, the spring 17 can rely on a internal flange 18 made on the plate 12. The stroke of the key 15 may be limited on the opposite side to the switch 13 by the support of a shoulder 20 made on the key 15 against the bottom of a countersink 19 made on the front face 11. The minimum stroke of the key can in turn be guaranteed by the existence of a clearance 21 between the lower end 151 of the key 15 and the switch 13.

This first exemplary embodiment makes it possible to absorb large dispersions in the assembly and to greatly lengthen the stroke of the key 15. However, it has several drawbacks. The figure 2 represents in the form of a graph the evolution of a force applied to the key 15 as a function of a stroke of this key 15 for the first exemplary embodiment. For the following description, we consider that the key 15 moves along the X axis, the origin O of the race being determined by the rest position, that is to say when the key is not stressed and that it is pressed against the bottom of the countersink 19. It is also considered that the force is applied to the key 15 along the X axis towards the switch 13. The evolution of the force as a function of the stroke is represented by a curve 24. A first portion 241 of this curve 24 is represented by a positive slope line. This portion 241 corresponds to the biasing of the spring 17 alone, the slope of the straight line corresponding to the stiffness of the spring 17. Beyond a race point C ₁ , the lower end 151 of the key 15 comes into contact with the moving part of the switch 13. The stiffness of the switch 13 is then added to the stiffness of the spring 17. On the graph, the accumulation of the stiffness of the spring 17 and the switch 13 results in a second part 242 of curve 24 represented by a line of steeper slope and therefore by a discontinuity of the variation of the force for the stroke point C ₁ . This discontinuity is a disadvantage insofar as it results in a hard point reminiscent of an operator operating the key 15 that the switch 13 has arrived at the end of the race and has therefore made an electrical contact. A third portion 243 of the curve 24 may be represented by a convex curve portion. This part 243 corresponds to the beginning of the deflection of the switch 13 and includes the point of maximum effort F _{max that} can be applied to the key 15 before the switch 13 establishes an electrical contact. This maximum effort F _max occurs for a race point C ₂ . A fourth portion 244 of the curve 24 may be represented by a portion of concave curve, the force falling abruptly after the crossing of the travel point C ₂ . This portion 244 corresponds to the further deflection of the switch 13. It comprises the minimum stress point F _{min that} can be applied to the key 15 to keep the switch 13 closed. This minimum effort F _min corresponds to a race point C ₃ . Beyond the travel point C ₃ , the key 15 can still be pressed a short distance until complete compression of the spring 17 for a stroke point C ₄ corresponding to the mechanical stroke C _m of the key 15. The key 15 is then at the end of the race. The exemplary embodiment as illustrated in figure 1 therefore has the disadvantage of introducing a discontinuity of effort in the stroke of the key 15.

The figure 3 illustrates a second example envisaged by the applicant for the realization of a keyboard in a sectional view similar to the figure 1 . According to this second exemplary embodiment, the tolerance of greater than 16 of key 15 is also guaranteed by a plating of the key 15 against the front face 11. On the other hand, the plating is carried out by a deformable element, called plunger 31, prestressed between the lower end 151 of the key 15 and the switch 13. The plunger 31 consists for example of a cylinder of revolution.

Plus ce rapport R est important, autrement dit plus la pente moyenne de la courbe 24 entre les courses C₂ et C₃ est importante en valeur absolue, meilleure est la sensation tactile. En effet, un opérateur actionnant la touche 15 ressent plus fortement la transition de l'interrupteur 13 lorsque l'effort qu'il applique sur la touche 15 chute brutalement pour un léger déplacement de cette touche 15. Sur la figure 4, le fait que la sensation tactile d'un plongeur à forte raideur soit meilleure que celle d'un plongeur à faible raideur est clairement visible. En effet, pour une même différence d'effort ΔF, la différence de course ΔC₁ entre les points de course C₂ et C₃₁ est supérieure à la différence de course ΔC₂ entre les points de course C₂ et C₃₂. Ce phénomène est lié à une restitution plus rapide de l'énergie emmagasinée dans un plongeur 31 à forte raideur que dans un plongeur 31 à faible raideur. Par ailleurs, lors d'appuis décentrés sur la touche 15, c'est-à-dire lors d'appuis selon un axe faisant un angle avec l'axe X ou selon un axe parallèle à l'axe X mais sur un bord de la touche 15, l'interrupteur 13 risque de ne pas être actionné avec un plongeur 31 à faible raideur. En effet, le plongeur 31 risque de se déformer en flexion et d'emmagasiner l'énergie sans pouvoir la restituer suivant l'axe X pour activer l'interrupteur 13. En conclusion, pour ce deuxième exemple de réalisation, un compromis doit être trouvé sur la raideur du plongeur 31 pour, d'une part, avoir une capacité suffisante d'allongement et d'absorption des dispersions et, d'autre part, garantir l'activation de l'interrupteur 13 lors d'appuis décentrés sur la touche 15. En pratique, ce deuxième exemple de réalisation est surtout adapté à un faible allongement de la course de l'interrupteur 13 et nécessite une adaptation de la longueur de chaque plongeur 31 aux dispersions géométriques du clavier au niveau de chaque touche 15. Le réglage individuel des longueurs de plongeurs 31 est évidemment coûteux et rend cette réalisation inappropriée à une production en série de claviers.The figure 4 represents in the form of a graph similar to the figure 2 , the evolution of the force applied to the key 15 as a function of its stroke for the second embodiment. A first curve 41 represents the evolution of the force for a plunger 31 with low stiffness and a second curve 42 represents the evolution of the effort for a plunger 31 with greater stiffness. In this example, the race points C ₂ and C ₄ defined above are considered identical for the two curves 41 and 42. The running point C ₃ is marked C ₃₁ for the curve 41 and C ₃₂ for the curve 42. second embodiment eliminates the clearance 21 between the lower end 151 of the key 15 and the switch 13. As a result, there is no break in stiffness when actuating the key 15 between the origin O and the race point C ₂ . In addition, this second embodiment allows to a certain extent to lengthen the race of the key 15 and absorb the geometric dispersions of the assembly. The lengthening of the stroke of the key 15 and the absorption capacity of the dispersions are favored by a low stiffness of the plunger 31, which then easily deforms between the key 15 and the switch 13. However, a plunger 31 with a low stiffness has a less good tactile sensation. The tactile sensation associated with the transition of the switch 13 from the open position to the closed position can be represented by the ratio R between the force difference ΔF between the minimum forces F _min and maximum F _max and the travel difference ΔC between race points C ₂ and C ₃ . The ratio R can be defined by the following relation: $$\mathrm{R}=\frac{\mathrm{Fmax}-\mathrm{fmin}}{{\mathrm{VS}}_{\mathrm{3}}-{\mathrm{VS}}_{\mathrm{2}}}=\frac{\mathrm{.DELTA.F}}{\mathrm{.DELTA.C}}$$

The higher this ratio R is important, in other words the greater the average slope of the curve 24 between the races C ₂ and C ₃ is important in absolute value, the better is the tactile sensation. Indeed, an operator actuating the key 15 feels more strongly the transition of the switch 13 when the force it applies to the key 15 drops abruptly for a slight movement of the key 15. On the figure 4 the fact that the tactile sensation of a high-stiffness diver is better than that of a low-stiffness diver is clearly visible. Indeed, for the same force difference ΔF, the travel difference ΔC ₁ between the race points C ₂ and C ₃₁ is greater than the travel difference ΔC ₂ between the travel points C ₂ and C ₃₂ . This phenomenon is related to a faster return of the energy stored in a plunger 31 with high stiffness than in a plunger 31 low stiffness. Furthermore, when the eccentric supports on the key 15, that is to say when pressing along an axis making an angle with the X axis or along an axis parallel to the X axis but on an edge of the key 15, the switch 13 may not be operated with a plunger 31 low stiffness. Indeed, the plunger 31 may deform in flexion and store energy without being able to restore it along the X axis to activate the switch 13. In conclusion, for this second embodiment, a compromise must be found on the stiffness of the plunger 31 to, on the one hand, have a sufficient capacity for elongation and absorption of the dispersions and, on the other hand, to guarantee the activation of the switch 13 when pressing off-center on the key 15. In practice, this second example of embodiment is especially adapted to a weak lengthening the travel of the switch 13 and requires an adaptation of the length of each plunger 31 to the geometric dispersions of the keyboard at each key 15. The individual adjustment of the lengths of plungers 31 is obviously expensive and makes this implementation inappropriate to a mass production of keyboards.

An object of the invention is in particular to overcome the aforementioned drawbacks by providing a simple keyboard whose keys 15 have a long stroke and a good tactile sensation. For this purpose, the subject of the invention is a keyboard comprising a push-button switch, a button for operating the push-button switch along a translation axis and a plunger interposed between the button and the switch. According to the invention, a stiffness of the plunger along the translation axis increases continuously with an increase in the compression of the plunger.

The invention has the particular advantage that it allows to combine the advantages of a keyboard with a low stiffness plunger with those of a keyboard with a high stiffness plunger for low production cost.

• la figure 1, déjà décrite, un premier exemple de réalisation d'un clavier dans une vue en coupe selon un plan passant par une touche du clavier,
• la figure 2, déjà décrite, l'évolution d'un effort appliqué sur la touche du clavier de la figure 1 en fonction d'une course de cette touche,
• la figure 3, déjà décrite, un deuxième exemple de réalisation d'un clavier dans une vue analogue à celle de la figure 1,
• la figure 4, déjà décrite, l'évolution de l'effort appliqué sur une touche du clavier de la figure 3 en fonction de sa course,
• la figure 5, un exemple de réalisation d'un clavier selon l'invention dans une vue analogue à celle des figures 1 et 3,
• la figure 6, l'évolution de l'effort appliqué sur une touche du clavier de la figure 5 en fonction de sa course pour une première forme de réalisation d'un clavier selon l'invention,
• la figure 7, l'évolution de l'effort appliqué sur une touche du clavier de la figure 5 en fonction de sa course pour une deuxième forme de réalisation d'un clavier selon l'invention,
• les figures 8A, 8B et 8C, des exemples de configuration d'un clavier selon la deuxième forme de réalisation,
• la figure 9, l'évolution de l'effort appliqué sur une touche d'un clavier de la figure 8A, 8B ou 8C en fonction de sa course.

The invention will be better understood and other advantages will appear on reading the detailed description of embodiments given by way of example, a description given with regard to the appended drawings which represent:

• the figure 1 , already described, a first embodiment of a keyboard in a sectional view along a plane passing through a key of the keyboard,
• the figure 2 , already described, the evolution of an effort applied to the key of the keyboard of the figure 1 according to a stroke of this key,
• the figure 3 , already described, a second embodiment of a keyboard in a view similar to that of the figure 1 ,
• the figure 4 , already described, the evolution of the effort applied on a key of the keyboard of the figure 3 according to his race,
• the figure 5 , an embodiment of a keyboard according to the invention in a view similar to that of figures 1 and 3 ,
• the figure 6 , the evolution of the effort applied on a key of the keyboard of the figure 5 according to its stroke for a first embodiment of a keyboard according to the invention,
• the figure 7 , the evolution of the effort applied on a key of the keyboard of the figure 5 according to its stroke for a second embodiment of a keyboard according to the invention,
• the Figures 8A, 8B and 8C , examples of configuration of a keyboard according to the second embodiment,
• the figure 9 , the evolution of the effort applied on a key of a keyboard of the FIG 8A, 8B or 8C according to his race.

The figure 5 represents an exemplary embodiment of a keyboard according to the invention in a sectional view similar to figures 1 and 3 . The keyboard according to the invention is similar to the second embodiment, the main difference relating to the plunger 31. According to the invention, the stiffness of the plunger 31 along the X axis increases continuously when pressing the front button 15 the actuation of the switch 13. In other words, the stiffness of the plunger 31 increases with an increase in its compression for a stroke of the key 15 preceding the actuation of the switch 13.

According to a first embodiment, the stiffness of the plunger 31 increases continuously until reaching a given compression point, the stiffness remaining constant beyond this point of compression. This particular embodiment makes it possible to obtain a better tactile sensation. The plunger 31 is for example made of a single piece of homogeneous material. The plunger 31 can thus be produced by molding in a very economical manner. The material is advantageously an elastomer such as silicone. To enable both a good tactile sensation and a large deformation capacity of the plunger 31 to be obtained, and thus to increase the travel of the switch 13 and to absorb the geometric dispersions of the keyboard, the hardness of the The elastomer may be between 60 and 80 Shore A. It is for example 70 Shore A. The present description relates to a keyboard with a single key 15. Of course, the keyboard may comprise several keys 15 and, in particular, a plunger 31 as described above for each key 15 of the keyboard.

The figure 6 represents, in the form of a graph similar to the graphs of figures 2 and 4 , the evolution of the effort applied on a key 15 of the keyboard of the figure 5 according to the stroke of this key 15 for the first embodiment of the invention. The evolution of the force is represented by a curve 61. On this curve 61, it is possible to see that the plunger 31 is prestressed between the lower end 151 of the key 15 and the switch 13, the ordinate to the origin F ₀ of the curve 61 being greater than zero. It is also possible to see that, on a first portion 611 of the curve 61, the stiffness of the key 15, represented by the slope of the curve 61, increases progressively without discontinuity. On a second portion 612 of the curve 61, the reaction of the switch 13 becomes preponderant over that of the plunger 31, the deflection of the switch 13 being initiated. This portion 612 of the curve 61 comprises the point of maximum effort F _{max that} can be applied to the key 15 before the switch 13 establishes an electrical contact. This maximum effort F _max occurs at the race point C ₂ . On a third portion 613 of the curve 61, the force drops sharply with the continued deflection of the switch 13 to reach the minimum effort F _min at the stroke point C ₃ . The force can then increase until it reaches the mechanical stop of the key 15 at the travel point C ₄ . The difference in stroke ΔC between the race points C ₂ and C ₃ is of the same order of magnitude as the difference in stroke ΔC ₂ observed for a plunger 31 with high stiffness. This phenomenon is explained by the fact that, just before the deflection of the switch 13, the plunger 31 is strongly compressed and is thus characterized by a high stiffness. Therefore, the ratio R is important and the key 15 has a good tactile sensation.

According to a second embodiment, the plunger 31 has two distinct constant stiffnesses. In this case, it has a low stiffness k ₁ at the beginning of compression and stiffness stronger k ₂ at the end of compression. The low stiffness k ₁ allows, by its high deformation capacity, to absorb the geometric dispersions and lengthen the stroke of the key, and the high stiffness k ₂ provides a good tactile sensation.

A plunger 31 whose stiffness increases with its compression can in particular be achieved by a suitable form of the plunger 31. According to the invention, the plunger 31 comprises a recess 63, as shown in FIG. figure 5 . This recess 63 defines an upper portion 31a of the plunger 31 and a lower portion 31b of the plunger 31, the upper portion 31a corresponding to the portion of the plunger 31 comprising the recess. The plunger 31 and / or the recess 63 may be of revolution along the axis X. According to a particular embodiment, represented in FIG. figure 5 the plunger 31 and / or the recess 63 are cylindrical.

According to a particularly advantageous embodiment, the recess 63 is used to fix the plunger 31 to the key 15. The key 15 then comprises a lug 152 whose shape is complementary to that of an upper portion 63a of the recess 63. The plunger 31 is fitted on the lug 152 and is held there by elastic deformation. The relative heights of the lug 152 and the recess 63 along the X axis are determined so as to leave a gap 63b between the lug 152 and the bottom of the recess 63. The height of this empty space 63b is for example between five and fifteen tenths of a millimeter for a total height of the plunger 31 for example between three and four millimeters. The height of the void space 63b is determined by a calculation of the average geometric dispersion of the keyboard assembly and the knowledge of the key stroke required. It is the presence of the empty space 63 which makes it possible to modify the stiffness of the plunger 31 with its compression.

The figure 7 represents, in the form of a graph similar to the graphs of figures 2 , 4 and 6 , the evolution of the effort applied on a key of the keyboard of the figure 5 according to its stroke for the second embodiment of the invention. The evolution of the force is represented by a curve 71. At the origin of the stroke of the key 15, the upper part 31a of the plunger 31 bears the major part of the deformation of the plunger 31. This upper part 31a indeed has an initial stiffness k ₁ less than a stiffness k ₂ of the lower part 31 b. Beyond a certain race point C ₁ , corresponding to the height of the empty space 63b, the pin 152 between in contact with the bottom of the recess 63. The additional deformation of the plunger 31 is then substantially supported by the lower portion 31b which has the constant stiffness k ₂ . On the figure 7 this phenomenon results in a first segment 711 of slope k ₁ between the origin and the travel point C ₁ and a second segment 712 of slope k ₂ between the travel point C ₁ and the travel point C ₂ for which occurs the maximum force before the switch 13 establishes an electrical contact. On the figure 7 , the transition between the stiffness k ₁ and the stiffness k ₂ is brutal. However, it is possible to obtain a smoother transition.

The Figures 8A, 8B and 8C illustrate exemplary key and plunger configurations according to the second embodiment and wherein the transition between the two stiffnesses k ₁ and k ₂ is smoothed. According to a first configuration example, represented on the figure 8A , the lug 152 of the key 15 has a convex shape coming into contact with the bottom of the recess 63. In this figure, the bottom of the recess 63 is flat. According to a second configuration example, represented on the Figure 8B it is the bottom of the recess 63 of the plunger 31 which has a convex shape, the part of the lug 152 coming into contact with the bottom of the recess 63 having a flat shape. According to a third configuration example, represented on the Figure 8C both the lug 152 and the bottom of the recess 63 have a convex shape. On the Figures 8A, 8B, 8C it has been considered that the smoothing of the transition between the two stiffnesses k ₁ and k ₂ is ensured by a curved shape. Of course, any form ensuring a gradual increase in the contact surface between the key 15 and the bottom of the recess 63 may be made within the scope of the invention.

The figure 9 represents, in the form of a graph similar to the graphs of figures 2 , 4 , 6 and 7 , the evolution of the force applied on a key of the keyboard according to its course according to the examples of configuration of the Figures 8A, 8B, 8C . The evolution of the force is represented by a curve 91. With respect to the curve 71, the curve 91 is essentially distinguished in that it comprises a portion of curve 92 connecting the first segment 711 of slope k ₁ to the second segment 712 of slope k ₂ in the vicinity of the race point C ₁ .

The plunger 31 according to the invention can be elastically deformed substantially in its upper part 31a. It thus allows a long stroke of touch and a great capacity of absorption of the dispersions of the keyboard. In this case, it is not necessary to adapt the length of the various plungers 31 to the geometric dispersions of the keyboard at each key 15. The plungers 31 may have standard dimensions. The plunger 31 also has a high stiffness in its lower portion 31b. It offers a good tactile sensation.

Claims (12)

1. A keypad comprising a push button switch (13), a key (15) for moving said push button switch (13) along a translation axis (X) and a plunger (31) interposed between said key (15) and said switch (13), wherein a stiffness of said plunger (31) along said translation axis (X) increases with a travel of said key (15) before the activation of said switch (13), with said plunger (31) comprising a recess (63), characterised in that a portion of said plunger (31) that comprises said recess (63) which defines an upper part (31a) of said plunger that has a first stiffness (k₁) and a remaining portion of said plunger (31) which defines a lower part (31b) of said plunger that has a second stiffness (k₂) at the source of the travel of said key (15), said second stiffness (k₂) being higher than said first stiffness (k₁), with said plunger (31) being substantially deformed at said upper part (31a) of said plunger and beyond a point of travel (C₁) at which said key (15) makes contact with the bottom of said recess (63), with said plunger (31) being substantially deformed at said lower part (31b) of said plunger (31), the stiffness of said plunger (31) thus increasing from the first to the second stiffness.
2. The keypad according to claim 1, characterised in that said first and second stiffnesses (k₁, k₂) are substantially constant.
3. The keypad according to claim 2, characterised in that it comprises means for providing a progressive transition between said first stiffness (k₁) and said second stiffness (k₂) along the travel of said key (15).
4. The keypad according to any one of the preceding claims, characterised in that said plunger (31) is produced from a single piece of homogenous material.
5. The keypad according to any one of the preceding claims, characterised in that said plunger (31) is made of an elastomer material.
6. The keypad according to any one of the preceding claims, characterised in that said plunger (31) is cylindrical.
7. The keypad according to any one of the preceding claims, characterised in that said recess (63) is cylindrical.
8. The keypad according to any one of the preceding claims, characterised in that said key (15) comprises a lug (152), the shape of which is complementary to that of an upper part (63a) of said recess (63), said lug (152) being inserted into said upper part (63a) of said recess (63).
9. The keypad according to claim 8 in combination with claim 3, characterised in that said lug (152) or the bottom of said recess (63) has a shape that provides a progressive increase of a contact surface between said key (15) and the bottom of said recess (63), with said lug (152) or the bottom of said recess (63) forming the means for providing a progressive transition between said first stiffness (k₁) and said second stiffness (k₂) along the travel of said key (15).
10. The keypad according to any one of the preceding claims, characterised in that it comprises a front face (11) integral with said switch (13) and comprising an opening (14) that is traversed by said key (15) and means (19, 20) for limiting a travel of said key (15) on the opposite side of said switch (13), said plunger (31) being pre-stressed between said key (15) and said switch (13).
11. The keypad according to claim 10, characterised in that said means (19, 20) for limiting the travel of said key (15) comprise:

    - a shoulder (20) on said key (15); and

    - a counterbore (19) realised on said front face (11).
12. The keypad according to any one of the preceding claims, characterised in that a hardness of the material of said plunger (31) is between 60 and 80 Shore A.

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