Patent Publication Number: US-6706985-B2

Title: Key switch

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application takes priority from Korean Application No. 10-2002-0026724 filed May 15,2002. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a key switch for use in an input device such as a keyboard of a PC (Personal Computer), and more particularly to a key switch which is intended to realize a compact and slim keyboard and to enable a high keystroke rate and a resilient clicking sensation to a user via its simple configuration, thereby affording reliable key-input performance. The present invention also relates to a key switch, which is simplified in its construction so as to be produced by a simple manufacturing process. 
     2. Description of the Prior Art 
     These days, keyboard keys have been thinned and flattened to comply with needs for compact keyboards, and a high keystroke rate and a reliable and clear clicking sensation are required to enhance ease and reliability of a key-input operation. There are proposed various key switches for use in such keyboards. 
     For example, Japanese Patent Laid-Open No. 9-190735 discloses a key switch, described hereinafter. 
     In the key switch disclosed in the above Japanese Patent Laid-Open, a guide assembly for guiding an up-and-down motion of a keyboard key is comprised of first and second linking members. The first and second linking members are provided at lower facing ends thereof with teeth engaging with each other, and are connected at upper ends thereof to the top of key, to be slid along a lower surface thereof. Accordingly, when the key is pushed downward, the upper ends of the first and second linking members move far away from each other while sliding along the lower surface of the key. By this movement, the teeth of the first and second linking members are rotated while being engaged with each other. As the key is depressed, a resilient rubber actuator provided between the key and a base housing is pressed by the key, and the lowering actuator comes into contact to a contact of a membrane switch, thereby causing the key-input operation to be recognized. Upon release of the pushing force acting on the key, the pressed actuator is restored to its normal position while pushing the key upward, thereby allowing the key to be restored to its normal position. 
     The above-described key switch is advantageous in that the first and second linking members do not intersect in a “X” form, thereby affording simplification of the link guide assembly. 
     However, since the conventional key switch, as disclosed in the Japanese Patent Laid-Open, is equipped with a rubber actuator, the key switch inevitably becomes large. 
     Furthermore, since the key switch requires an additional rubber actuator, which is produced separately from the linking members, its manufacturing process is complicated. 
     In addition, since the key switch employs an actuator, which is configured to be simply pressed and to provide only a linear repulsion to the key, an acceptable clicking sensation cannot be achieved. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a key switch in which linking members of a linkage assembly are provided at connecting portions thereof with a connecting groove and protrusion, which serve as rotating shaft to simplify a structure of the linkage assembly, and in which the linkage assembly and means for restoring a keyboard key are integrally formed to achieve an acceptable clicking sensation and a compact key switch. 
     In order to accomplish the above object, the present invention provides a key switch comprising a keyboard key which is pressed down by a user&#39;s finger, a linkage assembly comprised of a first linking member with an arm connected to an outer end thereof, a second linking member with an arm connected to an outer end thereof, and a downwardly convex bow-shaped elastic object connected between the arms of the first and second linking members, which is lowered by pressure of the key to cause a key-input operation to be recognized and is raised together with the key by release of the pressure on the key, one of the first and second linking members including a coupling recess at its inner end and a hinge protrusion at its side surface, and the other of the first and second linking members including a coupling protrusion at its inner end and a hinge protrusion at its side surface, the coupling recess and protrusion being engaged with each other to constitute a linkage rotating shaft, a frame including hinge hooks engaged with the hinge protrusions of the first and second linking members, and an FPC (Flexible Printed Circuit) placed on the frame, which enables a key-input operation to be recognized via contact with the linkage assembly, wherein, as the key is pressed down, the arms of the first and second linking members are rotated downward around the linkage rotating shaft while the linkage rotating shaft is raised, and the elastic object is gradually flattened and then bent into an upwardly convex bow shape, thereby providing a clicking sensation to a user and a restoring force to the linkage assembly. 
     The keyboard key may be provided at its lower surface with ribs, each of which include an elongated linkage guide hole and a support cut, and each of the first and second linking members may be provided at its outer end with a key-positioning protrusion and a support knob, each key-positioning protrusion being slid along a link guide hole when the key is depressed, the support knob continuously supporting the key from the time when the key is positioned at its uppermost level. 
     The elastic object may be provided at its lower surface with a contact protrusion to reliably push a contact portion of the flexible printed circuit. 
     The key switch may further include a linkage bar disposed under the key to support the key and to evenly distribute pushing force acting on the key, wherein a rotating axis of the linkage bar is positioned to have an angle of 90° with respect to a rotating axis of the linkage assembly, so that the linkage bar does not interfere with the linkage assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view of a key switch according to the present invention; 
     FIG. 2 is a partial side view showing a coupling structure between a rib of a key and a linking member; 
     FIG. 3 is a cross-sectional view of a leaf spring with contact protrusions, according to the present invention; 
     FIGS. 4A to  4 C are side views and schematic views of the key switch according to the present invention, in which FIG. 4A shows the key switch in its initial position, FIG. 4B shows the key switch in a lowering state, and FIG. 4C shows the key switch in its fully depressed state; 
     FIG. 5 are schematic views of arms of first and second linking members, and a rotating protrusion of the key switch according to the present invention, in which FIG. 5A shows an initial normal state thereof, FIG. 5B shows a lowering state thereof, and FIG. 5C shows a lowermost state thereof; 
     FIG. 6 is a graph showing a relation between pushing force acting on the key and a keystroke; and 
     FIG. 7 is a side view of a multiple key to which a key switch and a linking bar according to the present invention are applied. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention will be described in further detail by way of example with reference to the accompanying drawings. 
     FIG. 1 is an exploded perspective view of a key switch according to the present invention, FIG. 2 is a fragmentary side view showing a coupling portion between a key  10  and a linking member  20 , and FIG. 3 is a side cross-sectional view showing contact protrusions  23   s  of a leaf spring  23  serving to restore the key to its normal position. 
     As shown in FIG. 1, the key switch of the present invention comprises a key  10 , a linkage assembly  20 , a FPC (flexible printed circuit)  30  and a frame  40 , which are positioned in order, from top to bottom, in the drawing. 
     The keyboard key  10  is mounted on an upper surface of a keyboard, and is printed on its upper surface with numeric characters (0, 1, 2, 3, - - - ), alphabet characters (a, b, c, - - - , @, #, - - - ) or functional indications (Esc, Ctrl, Alt, Home, PgUp, - - - ). The key  10  is depressed by a user&#39;s finger to send a key signal to a PC, and then resiliently raised to its normal position by elasticity of the linkage assembly  20 . The key  10  is generally formed into an approximately cubic shape, and is made of a hard plastic material. 
     The linkage assembly  20  serves to guide an up-and-down motion of the key  10 , and is adapted to be opened at its outer ends  24  while being flattened at its leaf springs  23  by pressure of the key  10 , thereby providing a clicking sensation to a user. 
     The FPC  30  is comprised of a matrix circuit, which is adapted to recognize a character printed on the associated key  10  when its contact point comes into contact with a lower contact point of the linkage assembly  20  by a lowering motion of the key  10 . 
     The frame  40  includes a coupling mechanism for coupling the linkage assembly  20  thereto, and supports the linkage assembly  20  and thus the key  10 . 
     The above-mentioned coupling mechanism and components of the linkage assembly  20  will now be described. 
     The key  10  is provided at its lower surface with four ribs  11  so as to allow the key  10  to be coupled to the linkage assembly  20 . The ribs  11  are formed into a rectangular shape, and provided at four corners of the lower surface of the key  10 , respectively. Each of the ribs  11  is formed with a linkage guide hole  12  and a linkage support cut  13 . The linkage guide hole  12  is elongated into an arc shape, and receives a key-positioning protrusion  27  therein, so as to convert a lowering movement of the key  10  into a horizontal movement. The linkage support cut  13  is formed into an arc shape, and is in contact with a support knob  28  of the linkage assembly  20  so that a lowering movement of the key  10  causes both ends of the linkage assembly  20  to be moved outwardly. That is, when the key  10  is lowered, the support knob  28  of the linkage assembly  20  is moved to an outer and upper surface of the linkage support cut  13  while sliding along the surface of the linkage support cut  13 . 
     The linkage assembly  20  will now be described. 
     The linkage assembly  20  comprises a pair of first linking members  21  with an arm  24  connected between outer ends thereof, a pair of second linking members  22  with an arm  24  connected between outer ends thereof, and a leaf spring  23  connected between the arms of the first and second linking members  21  and  22 , all of which are integrally formed. 
     Each of the first linking members  21  is provided at its inner end with a coupling recess  25 , and each of the second linking members  22  is provided at its inner end with a rotating protrusion  26 , both of which are engaged with each other to form a linkage rotating shaft  26 T. When the key  10  is lowered, the first linking members  21  are rotated counterclockwise about the linkage rotating shaft  26 T while the second linking members  22  are rotated clockwise around the linkage rotating shaft  26 T. Each of the first and second linking members  21  and  22  is provided between its outer end and the linkage rotating shaft  26 T with a hinge protrusion  29 , which is rotatably retained in a hinge hook  41  of the frame  40 . Accordingly, when the key  10  is lowered, the inner ends of the first and second linking members  21  and  22  are moved upward about hinge protrusions  29  thereof. 
     The hinge protrusions  29  of the first and second linking members  21  and  22  are symmetrically engaged in the hinge hook  41 , so that the hinge protrusions  29  are horizontally slid in the hinge hooks  41  when the arms  24  of the first and second linking members  21  and  22  are rotated outwardly about the linkage rotating shaft  26 T. At this point, the key-positioning protrusions  27  and the support knobs  28  are equally rotated outwardly about the rotating axis while being lowered, and the ribs  11  engaged with the key-positioning protrusions  27  and the support knobs  28  are uniformly lowered, thereby allowing the key  10  to be constantly maintained in the horizontal position. 
     Each of the first and second linking members  21  and  22  is provided with a stopper  20   s  at the side opposite to the side having the hinge protrusion  29 , so as to prevent the linkage assembly  20  from being lowered under the frame  40  in cooperation with the hinge protrusions  29 . 
     The arms  24  are provided at opposite ends thereof with the key-positioning protrusions  27  and the support knobs  28 , respectively. Each of the key-positioning protrusions  27  has a circular section, and is received in the corresponding link guide hole  12 . When the key  10  is depressed by a user&#39;s finger, the key-positioning protrusions  27  are moved outward and upward in the link guide holes  12 . Each of the support knobs  28  has a bow-shaped section, and serves to transmit a lowering force of the key  10  to the linkage assembly  20 . The support knobs  28  are always in contact with the linkage support cuts  13 . Therefore, when the key  10  is lowered, the lowering force of the key  10  is transmitted to the support knobs  28 , and the support knobs  28  are moved outward while sliding along arched surfaces of the linkage support cuts  13 . When the support knobs  28  are rotated downward around the linkage rotating shafts  26 T, the key-positioning protrusions  27  are rotated along bow-shaped trajectories about the support knobs  28 . At this point, since the key-positioning protrusions  27  of the first and second linking members  21  and  22  are symmetrically moved, a center line of the linkage assembly  20  always coincides with a center line of the key  10 . Since the key-positioning knobs  28  are positioned at opposite sides of the key  10  and rotated about the linkage rotating shaft  26 T, it is possible to obtain high keystroke even though the linking members are rotated within a relatively small rotation angle. Since the linkage support cuts  13  are supported on the support knobs  28  from its initial operation, a high keystroke can be achieved. 
     The leaf spring  23  is connected between center portions of the arms  24  of the first and second linking members  21  and  22 . The leaf spring  23  is bent into an arcuate form to upwardly bias the arms  24  of the linkage assembly  20 . 
     The frame  40  is provided with the hinge hooks  41  to be engaged with the hinge protrusions  29  of the linkage assembly  20  so as to prevent the linkage assembly  20  from being separated from the frame  40 . Furthermore, the frame  40  is formed with receptive holes to receive the linking members  21  and  22  therein. Accordingly, when the arms  24  of the linking members  21  and  22  are lowered by the key  10  being downwardly depressed, the linking members  21  and  22  of the linkage assembly  20  are completely received in the reception holes of the frame  40 , thereby enabling an overall height of the resulting key switch to be reduced. 
     An up-and-down movement of the key switch according to the present invention will now be described with reference to FIGS. 4A to  4 C. 
     FIG. 4A shows the key  10 , which is positioned at its uppermost level by resiliency of the leaf spring  23  because the key  10  is not subjected to a pushing force. In this case, the key-positioning protrusions  27  are positioned at inner and lower ends of the link guide holes  12 . 
     When a pushing force is applied to the key  10 , the support knobs  28  engaging with the linkage support cuts  13  are rotated downward. At this point, biasing force of the leaf spring  23  and resiliency of the linkage assembly  20  are further intensified. When the opposite connecting points (PS 1  and PS 2 ) of the leaf spring  23  and the rotating axis point (PS) are aligned on a straight line, as shown in FIG. 4B, a lifting force of the linkage assembly  20  (a lifting force of the key) is abruptly decreased, thereby providing a clicking sensation to a user. Subsequently, the key  10  comes into contact with the frame  40 , thereby preventing a further lowering movement of the key  10 , as shown in FIG.  4 C. At this point, contact protrusions  23   s  of the leaf spring  23  (see FIG. 3) push the FPC  30 , thereby causing a key-input signal to be recognized. At the same time, since the leaf spring  23  is bent into a reverse shape of its normal shape, the lifting force acting on the linkage assembly  20  is further increased. 
     Upon releasing the pushing force from the key  10 , the key  10  and the linkage assembly  20  are restored to their initial normal positions, as shown in FIG.  4 A. 
     A principle of providing a clicking sensation and a restoring force by the key switch according to the present invention will now be described with reference to FIGS. 5 to  7 . 
     FIG. 5 shows the arm  24  (PS 1 ) of the first linking member  21 , the arm  24  (PS 2 ) of the second linking member  22 , and the rotating protrusion  26  (PS), which are positioned at an initial normal state thereof (FIG.  5 A), at a lowering state thereof (FIG.  5 B), and at a lowermost state thereof (FIG.  5 C). 
     In the initial state (FIG.  5 A), a point (PS 1 ) designating the arm  24  of the first linking member  21  and a point (PS 2 ) designating the arm  24  of the second linking member  22  are positioned above a point (PS) designating the rotating protrusion  26 , thereby defining an inverted triangle. As the linking members  21  and  22  are rotated downward, a length of a line defined between the point (PS 1 ) and the point (PS 2 ) is varied while a line defined between the point (PS 1 ) and the point (PS) and a line defined between the point (PS 2 ) and the point (PS) are maintained at a constant length. The variation of the length of the line (PS 1 -PS 2 ) results from deformation of the arched leaf spring into a linear state and bending deformation of portions of the arms  24  to which the leaf spring is connected. 
     In FIG. 5A, showing an initial state of the key switch according to the present invention, there is present a force (F 1 ) resulting from resiliency due to initial deformations of the leaf spring  23  and the portions of the arms  24  (a resisting force against the deformations). 
     The extent of F 1  is proportional to a length of a line (PS 1 -PS 2 ), which is varied as the first and second linking members  21  and  22  are rotated downward. Accordingly, F 1  is rapidly varied (increased) in an initial lowering stage of the key  10  and then gradually decreased. When the first and second linking members  21  and  22  are rotated to a state shown in FIG. 5B, that is, when the points (PS 1 , PS 2  and PS) are aligned on a straight line, a variation of a length of the line (PS 1 -PS 2 ) becomes zero, and an extent of F 1  is constant. As the key  10  is further lowered, the line (PS 1 -PS 2 ) is decreased, thereby reducing an extent of F 1 . 
     More specifically, as the key  10  is gradually lowered from its normal state, F 1  tendancy to restore the arms  24  toward the point (PS) designating the rotating protrusion  26  is generated. F 1  may be decomposed into a component F 2 , which tends to rotate the points (PS 1  and PS 2 ) upward. That is, F 2  may be expressed by the following Equation: F 2 =F 1  sin θ2, wherein F 2  may be further decomposed into a reaction force F 3 . F 3  may be expressed by the following Equation: F 3 =F 2  cos θ2. 
     Since force that is felt by a user is F 3  when the key  10  is pushed downward, F 3  is varied according to F 2 , which is varied by variation of F 1  and a position of the linking members  21  and  22 . In an initial stage, F 1  is rapidly increased thereby rapidly increasing F 3  by a rapid variation of a length of a line (PS 1 -PS 2 ). 
     As a variation rate of a length of line (PS 1 -PS 2 ) is decreased, an increasing rate of F 1  is also decresed. As the linking members  21  and  22  are rotated downward, an angle θ1 is highly increased while an angle θ 2 is rapidly decreased, thereby rapidly decreasing F 3  and thus F 3 . In a state shown in FIG. 5B, in which θ2 becomes zero so that the points (PS 1 , PS 2  and PS) are aligned in a straight line, an reaction force F 3  decomposed from F 1 , which is caused by a variation of a length of the leaf spring  23  and deformation of the portions of the arms  24 , is zero. Consequently, since only a reaction force caused by a lifting force by deformation of the leaf spring remains, a variation rate of F 3  is abruptly increased, thereby providing a clicking sensation to a user. 
     When the key  10  is further lowered from a position shown in FIG. 5B, F 3  serves as a negative force to pull the key  10  down, as can be seen in FIG.  5 C. 
     At this time, if there is not an additional positive force to raising the key  10 , the key  10  cannot be restored to its normal position. 
     When the key  10  is lowered to its lowermost level as shown in FIG. 5C, the contact protrusions  23   s  provided at a lower surface of the leaf spring  23  come into contact with the FPC contact portion, thereby causing a rapid deformation of the leaf spring  23 . Accordingly, the deformation of the leaf spring  23  enables the key  10  to be restored to its normal position. 
     FIG. 6 is a graph showing a relation between pushing force acting on the key  10  and a keystroke. 
     A key switch applied to a so-called ‘multiple key, such as a ‘Space bar,’ a ‘Shift’ key or an ‘Enter’ key, which are larger than usual keys, will now be described with reference to FIG.  7 . 
     To enable the linkage assembly  20  to support a whole lower surface of a multiple key, the linkage assembly  20  must be enlarged according to the area of the multiple key. In this case, the linkage assembly  20  is positioned under the key to support a part of the key, and an additional linking bar is provided under the remaining portion of the key to support the remaining portion. 
     As shown in FIG. 7, the linking bar  60  is made of a steel wire to have a rectangular shape with an opening lower side. The linking bar  60  supports a portion that is not supported by the linkage assembly  50 , and serves to evenly distribute pushing force acting on the key  10  over the entire area of the key  10 . 
     In this embodiment, the linkage assembly  50  includes a first linking member  51  and a second linking member  52 , which are configured to be asymmetrical in length. If the linking members used in a multiple key are symmetrically configured, an angle defined between both the linking members is increased. Due to the increased angle, a variation rate of a length between contact points of the leaf spring  23  is decreased when the key  10  is depressed, thereby decreasing its service life and resistibility to various dimensional changes. 
     Contrary to the symmetrical configuration, when the linking members are asymmetrically configured, the angle defined between both the linking members can be maintained as little as possible, and thus a variation rate of a length between opposite ends of the leaf spring is increased, thereby improving its service life. 
     In this embodiment, since a rotating axis between inner ends of the linking members is positioned to have an angle of about 90° with respect to a rotating axis of the linking bar  60 , the linking bar  60  does not interfere with the linkage assembly  50 . 
     Where the linking bar and the linkage assembly are positioned to interfere with each other, a size of the linkage assembly must be reduced. Therefore, a pushing property of a key may be deteriorated when the key is locally pressed. To overcome this problem, this embodiment prevents the linking bar and the linkage assembly from interfering with each other, thereby enabling the linkage assembly to be considerably enlarged. 
     Furthermore, an arrangement of the linkage assembly  50  and the linking bar  60  may be embodied in various manners. That is, one linking bar  60  and one linkage assembly  50  may be provided to be replaced with each other, or two linking bars  60  and one linkage assembly  50  disposed between the two linking bars  60  may be provided. 
     As described above, the present invention provides a key switch which can be easily produced at a low production cost by simplifying a structure of its linkage assembly and by connecting first linking members and second linking members via a simplified coupling means, comprised of a coupling recess and a coupling protrusion engaging with each other. 
     Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.