Patent Publication Number: US-5829579-A

Title: Key switch assembly for a computer keyboard

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a key switch assembly for a computer keyboard, more particularly to a key switch assembly which can be easily assembled in an automated manner and which has a more stable structure as compared with the conventional ones. 
     2. Description of the Related Art 
     Referring to FIGS. 1 and 2, a conventional key switch assembly for a computer keyboard is shown to include a base plate 1, a key cap 2, and a scissors-type key cap support 5 which comprises first and second support levers 3, 4, and which is connected between the base plate 1 and the key cap 2. The base plate 1 is formed with an opening 1f to permit extension of a biasing member (not shown) therethrough for biasing the key cap 2 upwardly, a pair of aligned first slot retainers 1a on one side of the opening 1f, a pair of stop plates 1b formed respectively at the first slot retainers 1a, and a pair of first pivot retainers 1d at the other side of the opening 1f. The key cap 2 has a bottom side formed with a pair of second slot retainers 2a and a pair of second pivot retainers 2c opposite to the slot retainers 2a. The first support lever 3 is formed as a generally U-shaped frame and has an upper portion formed with a transverse first pivot shaft 3b which is retained pivotally in the second pivot retainers 2c, a lower portion formed with a pair of outwardly projecting first slide shafts 3a which are retained slidably and respectively in the first slot retainers 1a and which are limited by the stop plates 1b of the base plate 1, and an intermediate portion with an inner edge formed with a pair of opposed recesses 3c which open inwardly and upwardly. The first support lever 3 further has a triangular tab 3d which projects inwardly from the first pivot shaft 3b. The second support lever 4 has an upper portion formed with a transverse second slide shaft 4b which is retained slidably in the second slot retainers 2a of the key cap 2, a lower portion formed with a pair of outwardly projecting second pivot shafts 4a which are retained pivotally and respectively in the first pivot retainers 1d of the base plate 1, and an intermediate portion formed with an opposite pair of outward projections 4c which extend respectively into the opposed recesses 3c of the first support lever 3 for coupling pivotally the first and second support levers 3, 4. The second support lever 4 further has an indented portion 4d for receiving the triangular tab 3d of the first support lever 3. 
     Since the first and second support levers 3 and 4 are coupled to one another via the engagements between the outward projections 4c and the recesses 3c and between the tab 3d and the indented portion 4d, the first and second support levers 3, 4 are not firmly coupled to one another and tend to disengage from one another when the first and second support levers 3, 4 move pivotally relative to one another during operation of the key cap 2. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to provide a key switch assembly which has a relatively firm and stable structure and which can be easily assembled in an automated manner with the use of a machine. 
     Accordingly, the key switch assembly of the present invention includes a base board, a membrane circuit provided on the base board, an upright biasing member supported on the membrane circuit, a base plate, a scissors-type key cap support and a key cap. The membrane circuit has an electrical contact. The base plate is disposed on the membrane circuit and is formed with an opening to permit extension of the biasing member therethrough. The opening has opposite first and second sides. The base plate is further formed with a first slot retainer unit adjacent to the first side of the opening, and a first pivot retainer unit adjacent to the second side of the opening. The key cap support includes first and second support levers with upper and lower portions and intermediate portions that are coupled rotatably about a pivot axis. The lower portion of the first support lever is retained pivotally in the first pivot retainer unit of the base plate. The lower portion of the second support lever is retained slidably in the first slot retainer unit of the base plate. The key cap has a bottom side formed with a second slot retainer unit for retaining slidably the upper portion of the first support lever, and a second pivot retainer unit for retaining pivotally the upper portion of the second support lever. The key cap is biased upwardly by the biasing member and is depressible to compress the biasing member and enable the membrane circuit to produce an electrical signal. The first support lever has a generally U-shaped frame section with upper and lower sides and opposite outer edges. The intermediate portion of the first support lever is formed with an aligned pair of cylindrical outward pins disposed respectively on the outer edges of the first support lever. The second support lever is formed as a generally U-shaped frame which includes parallel rods that flank the outer edges of the first support lever, and a transverse rod that interconnects the parallel rods at the upper portion of the second support lever. Each of the parallel rods has upper and lower sides and an inner edge. The intermediate portion of the second support lever is formed with an aligned pair of pin bores disposed respectively on the inner edges of the parallel rods. Each of the pin bores is formed with an entrance that opens to the lower side of the respective one of the parallel rods. The outward pins on the first support lever extend fittingly and rotatably into a respective one of the pin bores via the entrance so as to couple rotatably the intermediate portions of the first and second support levers. The intermediate portion of the second support lever is further formed with an engaging tab which is disposed on the inner edge of one of the parallel rods adjacent to the pin bore and which extends between the upper and lower sides of said one of the parallel rods. The intermediate portion of the first support lever is further formed with an engaging notch which is disposed on one of the outer edges of the first support lever adjacent to the outward pin and which extends from the upper side to the lower side of the first support lever. The engaging notch receives the engaging tab therein and has a predetermined width sufficient to limit pivoting movement of the engaging tab therein between a first position, where the key cap is in a non-depressed state, and a second position, where the key cap is in a fully depressed state. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment with reference to the accompanying drawings, of which: 
     FIG. 1 is an exploded perspective view of a conventional key switch; 
     FIG. 2 is a perspective view of the conventional key switch of FIG. 1; 
     FIG. 3 is an exploded perspective view of a key switch assembly according to a preferred embodiment of the present invention; 
     FIG. 4 is a side view of a first support lever of a key cap support of the key switch assembly of the preferred embodiment; 
     FIG. 5 is a vertical sectional view of the key switch assembly of the preferred embodiment when a key cap thereof is in a non-depressed state; 
     FIG. 6 is a vertical sectional view of the key switch assembly of the preferred embodiment when the key cap is slightly depressed; and 
     FIG. 7 is a vertical sectional view of the key switch assembly of the preferred embodiment when the key cap is in a fully-depressed state. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 3, the key switch assembly of the preferred embodiment of the present invention is shown to include a base board 10, a membrane circuit 20, an upright biasing member 40, a base plate 30, a scissors-type key cap support 50, and a key cap 60. 
     The membrane circuit 20 is provided on the base board 10 and has an electrical contact 21. 
     The biasing member 40, preferably a rubber cone, is supported on the membrane circuit 20. 
     The base plate 30 is disposed on the membrane circuit 20 and is formed with an opening 33 to permit extension of the biasing member 40 therethrough. The base plate 30 has a hollow rectangular key confining frame portion 34, a first hole defining portion 35 which extends inwardly from the frame portion 34 and which has a terminating edge 351, and a second hole defining portion 36 which extends inwardly from the frame portion 34 and which has a terminating edge 361. The terminating edges 351, 361 of the first and second hole defining portions 35, 36 are on opposite first and second sides of the opening 33. 
     As shown, the first hole defining portion 35 has a top surface that is indented with respect to a top surface of the frame portion 34. The base plate 30 further has a pair of opposite flange units 32 which extend inwardly from the frame portion 34 toward a respective one of two opposite longitudinal edges of the first hole defining portion 35 so as to form two L-shaped slots 323 within the frame portion 34 at the two opposite longitudinal edges of the first hole defining portion 35. The L-shaped slots 323 constitute a first slot retainer unit. The flange units 32 have bottom surfaces which cooperate with the membrane circuit 20 to form slide recesses 324 therebetween (see FIG. 5). Each of the flange units 32 has an inclined top surface 322 which inclines downwardly in a direction toward the L-shaped slots 323. 
     The second hole defining portion 36 is formed with opposite cantilevers 311 which extend away from a respective one of two opposite longitudinal edges thereof, and opposite barb projections 312 formed on the opposite longitudinal edges of the second hole defining portion 36. The barb projections 312 are aligned respectively and spacedly with the cantilevers 311 so as to define first pivot retainers 313 between aligned ones of the cantilevers 311 and the barb projections 312. The barb projections 312 and the cantilevers 311 constitute a first pivot retainer unit 31. The aligned ones of the cantilevers 311 and the barb projections 312 have top edges that form a converging entrance 313a (see FIG. 5) therebetween. As best shown in FIG. 5, each of the cantilevers 311 forms a clearance 315 with the frame portion 34 to enhance resiliency of the cantilevers 311. 
     The key cap 60 has a bottom side formed with an aligned pair of second slot retainers 62 which constitute a second slot retainer unit, and an aligned pair of second pivot retainers 61 which are opposite to the second slot retainers 62 and which constitute a second pivot retainer unit. The key cap 60 is biased upwardly by the biasing member 40 that extends through the opening 33 of the base plate 30, and is depressible to compress the biasing member 40 and enable the biasing member 40 to contact the electrical contact 21, thereby enabling the membrane circuit 20 to produce an electrical signal. 
     The scissors-type key cap support 50 includes a first support lever 51 and a second support lever 52. The first support lever 51 is formed as a generally rectangular frame with upper and lower sides and opposite outer edges. The first support lever 51 has an upper portion (see FIG. 5) formed with an opposite pair of inward slide projections 512 which extend into the second slot retainers 62 of the key cap 60 and which are retained slidably therein. The first support lever 51 further has a lower portion formed with a pair of opposite outward pivot shafts 511 forced into the first pivot retainers 313 formed between aligned ones of the cantilevers 311 and the barb projections 312 via the converging entrance 313a for pivotal retention in the first pivot retainer unit 31 of the base plate 30. The first support lever 51 further has an intermediate portion formed with an aligned pair of cylindrical outward pins 513 which are disposed respectively on two outer edges of the first support lever 51, and a pair of engaging notches 514 that are disposed respectively on the outer edges of the first support lever 51 adjacent to the outward pins 513. Referring to FIG. 4, each of the engaging notches 514 extends from an upper side to a lower side of the first support lever 51 and is confined by opposite angled first and second walls. The angled first wall has a first upper wall section 514a and a first lower wall section 514b. The angled second wall has a second upper wall section 514c parallel to the first lower wall section 514b, and a second lower wall section 514d parallel to the first upper wall section 514a. As shown, the engaging notch 514 has a constricted intermediate section and opposite diverging end sections, each of which opens to a respective one of the upper and lower sides of the first support lever 51 and has a predetermined maximum width. 
     Referring again to FIG. 3, the second support lever 52 is formed as a generally U-shaped frame which includes parallel rods 526 that flank the outer edges of the first support lever 51, and a transverse rod 521 which interconnects the parallel rods 526 at an upper portion of the second support lever 52. The transverse rod 521 is retained pivotally in the second pivot retainers 61 of the key cap 60. The second support lever 52 is formed with opposite outward slide shafts 522 which project outwardly and respectively from the parallel rods 526 at a lower portion of the second support lever 52. Each of the outward slide shafts 522 tapers in a direction away from a respective one of the parallel rods 526 to form an inclined bottom face 523 that complements the inclined top surface 322 on a respective one of the flange units 32 so as to facilitate insertion of the slide shafts 522 resiliently into the L-shaped slots 323. The outward slide shafts 522 abut against the bottom surfaces of the flange units 32 for slidable retention in the slide recesses 324 (see FIG. 5). The lower portion of the second support lever 52 is further formed with opposite inward slide shafts 527 which project inwardly from inner edges of the parallel rods 526 and which abut slidably against the indented top surface of the first hole defining portion 35. 
     The second support lever 52 further has an intermediate portion formed with an aligned pair of pin bores 524 disposed respectively on the inner edges of the parallel rods 526. Each of the pin bores 524 is formed with an entrance 524a which diverges in a direction away from the pin bore 524. Each of the cylindrical outward pins 513 on the first support lever 51 extends fittingly and rotatably into a respective one of the pin bores 524 via the entrance 524a to serve as a pivot axis and to couple rotatably and firmly the intermediate portions of the first and second support levers 51, 52. The intermediate portion of the second support lever 52 is further formed with a pair of generally rectangular engaging tabs 525 which are formed on the inner edges of the parallel rods 526 adjacent to the pin bores 524 and which extend between upper and lower sides of the parallel rods 526. Each of the engaging tabs 525 is received in a respective one of the engaging notches 514 of the first support lever 51, and has a thickness generally equal to the width of the constricted intermediate section of the engaging notch 514. 
     Referring to FIGS. 5 and 7, each of the engaging tabs 525 has opposite first and second side surfaces 525a, 525b which are parallel to each other. The maximum predetermined width of the diverging end sections of the engaging notches 514 is sufficient to limit pivoting movement of the engaging tabs 525 between a first position where the key cap 60 is in a non-depressed state, as shown in FIG. 5, and a second position where the key cap 60 is in a fully-depressed state, as shown in FIG. 7. In the first position, referring to FIG. 5, the first side surfaces 525a of the engaging tabs 525 abut against the first lower wall sections 514b while the second side surfaces 525b of the engaging tabs 525 abut against the second upper wall sections 514c. In the second position, referring to FIG. 7, the first side surfaces 525a abut against the first upper wall sections 514a while the second side surfaces 525b abut against the second lower wall sections 514d. 
     In mass production, assembly of the key switch assembly of the present embodiment may be completed in an automated manner with the use of a machine. The pivot shafts 511 of the first support lever 51 are forced resiliently into the first pivot retainers 313 in the base plate 30. Since the slide shafts 522 of the second support lever 52 have inclined bottom surfaces 523 that complement the inclined top faces 322 of the flange units 32, and since the parallel rods 526 impart inward resiliency to the slide shafts 522, the slide shafts 522 can be easily pressed downward for insertion into the L-shaped slots 323 of the base plate 30. Subsequently, the intermediate portion of the second support lever 52 is pushed toward the intermediate portion of the first support lever 51 so as to press-fit the cylindrical outward pins 513 of the first support lever 51 in the pin bores 524 of the second support lever 52 via the entrances 524a. In this situation, the engaging tabs 525 of the second support lever 52 are simultaneously received in the engaging notches 514 of the first support lever 51. The key cap 60 is then assembled to the key cap support 50 and the base plate 30 by press-fitting the transverse rod 521 of the second support lever 52 into the second pivot retainers 61 in the key cap 60 and by extending the inward slide projections 512 of the first support lever 51 into the second slot retainers 62. 
     After assembly, the key cap 60 is normally biased upwardly by the biasing member 40 when the key cap 60 is in a non-depressed state, as shown in FIG. 5. At this time, since the first side surfaces 525a of the engaging tabs 525 abut against the first lower wall sections 514b of the notches 514 while the second side surfaces 525b abut against the second upper wall sections 514c of the notches 514, an enhanced positioning effect in the first position can be provided to the first and second support levers 51, 52. 
     Referring to FIG. 6, when the key cap 60 is depressed, the inward slide projections 512 of the first support lever 51 and the outward slide shafts 522 of the second support lever 52 are moved slidably and respectively in the second slot retainers 62 and the L-shaped slots 323, in the longitudinal direction of the base plate 30 and the key cap 60, thereby causing pivoting movement of the first and second support levers 51, 52 relative to each other. In this situation, the engaging tabs 525 are restricted by the constricted intermediate sections of the engaging notches 514. None of the first and second side surfaces 525a, 525b abut against the wall sections 514a, 514b, 514c, 514d at this time. 
     As shown in FIG. 7, when the key cap 60 is continuously depressed to reach a fully-depressed state, the first side surfaces 525a abut against the first upper wall sections 514a while the second side surfaces 525b abut against the second lower wall sections 514d, thereby positioning the engaging tabs 525 in the second position. 
     Accordingly, the key switch assembly of the present invention permits convenient assembling thereof in an automated manner. In addition, the first and second support levers 51, 52 of the key cap support 50 are more firmly and stably coupled to each other via the coupling between the cylindrical outward pins 513 formed in the first support levers 51 and the pin bores 524 formed in the second support levers 52. Moreover, an enhanced positioning effect can be provided to the key cap support 50 by means of the engagement between the engaging tabs 525 and the engaging notches 514 when the key cap 60 is in a non-depressed state or in a fully-depressed state. 
     With this invention thus explained, it is apparent that numerous modifications and variations can be made without departing from the scope and spirit of this invention. It is therefore intended that this invention be limited only as indicated in the appended claims.