Patent Document

CROSS REFERENCE TO RELATED APPLICATION 
     The present application is related to and claims priority of U.S. provisional patent application Ser. No. 61/894,324, filed on Oct. 22, 2013, which is hereby incorporated by reference in its entirety for all purposes as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to electromechanical polymer (EMP) actuators. In particular, the present invention is related to applications of EMP actuators to keyboards or keypads of electronic devices, such as desktop and notebook computers. 
     2. Discussion of the Related Art 
     In some conventional keyboards, each key is seated on a snap dome that acts as a force resistor. The snap dome returns the key to the upright position after a depression by a user. However, conventional snap domes are incapable of lying flat in a stable state. The need to be ready for keyboard operation requires the snap domes to always return to their upright positions. 
     SUMMARY 
     According to one embodiment of the present invention, a retractable snap dome in a keyboard, in addition to serving as a force resistor for a key in a conventional manner, includes an additional collapsed state in which the key can be retracted by an electromechanical polymer (EMP) actuator to a persistent down position. In one embodiment, the EMP actuator is a bimorph EMP actuator that can be actuated to bring the key from the down position to the up position, ready for conventional keyboard operation, and vice versa. Such operations allow the keyboard to have a desirable decreased thickness relative to conventional keyboards. Thus, a keyboard of the present invention finds application in ultra-slim electronic devices. When provided in a notebook computer in which the keyboard is folded against a video or graphic display, the keys of the keyboard may be placed in the retracted down position, thereby preventing the keys from pressing against the video or graphical display with a force that may damage the display. 
     The present invention is better understood upon consideration of the detailed description below in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1( a )  shows a side view of retractable snap dome  100 , according one embodiment of the present invention. 
         FIG. 1( b )  shows a first perspective view of retractable snap dome  100 , from a first direction that is roughly 45 degrees out of the page from the side view of  FIG. 1( a ) . 
         FIG. 1( c )  shows a second perspective view of retractable snap dome  100 , from a second direction that is roughly 45 degrees into the page from the side view of  FIG. 1( a ) . 
         FIG. 2( a )  illustrates three stages of retractable snap dome  100  in a conventional operation. 
         FIG. 2( b )  illustrates the same three stages of retractable snap dome  100  of  FIG. 2( a )  in the conventional operation, as seen from the first direction. 
         FIG. 2( c )  illustrates the same three stages of retractable snap dome  100  of  FIG. 2( a )  in the conventional operation, as seen from the second direction. 
         FIG. 3  shows a force profile of retractable snap dome  100  during the conventional operation. 
         FIG. 4( a )  illustrates three stages of retractable snap dome  100 —from upright to collapsed—under powered, activated and powered and activated and unpowered states, in accordance with one embodiment of the present invention. 
         FIG. 4( b )  illustrates the same three stages of retractable snap dome  100  of  FIG. 4( a )  under the powered, the activated and powered and the activated and unpowered states, as seen from the first direction. 
         FIG. 4( c )  illustrates the same three stages of retractable snap dome  100  of  FIG. 4( a )  under the powered, the activated and powered and the activated and unpowered states, as seen from the second direction. 
         FIG. 5( a )  illustrates three stages of retractable snap dome  100 —from collapsed to upright—under powered, activated and powered and activated and unpowered states of EMP actuator  105 , in accordance with one embodiment of the present invention. 
         FIG. 5( b )  illustrates the same three stages of retractable snap dome  100  of  FIG. 5( a )  under the powered, the activated and powered and the activated and unpowered states, as seen from the first direction. 
         FIG. 5( c )  illustrates the same three stages of retractable snap dome  100  of  FIG. 5( a )  under the powered, the activated and powered and the activated and unpowered states, as seen from the second direction. 
     
    
    
     In the figures and the detailed description below, like reference numerals denote like features. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1( a )  shows a side view of retractable snap dome  100 , according one embodiment of the present invention.  FIG. 1( b )  shows a first perspective view of retractable snap dome  100 , from a first direction that is roughly 45 degrees out of the page from the side view of  FIG. 1( a ) .  FIG. 1( c )  shows a second perspective view of retractable snap dome  100 , from a second direction that is roughly 45 degrees into the page from the side view of  FIG. 1( a ) . As shown in each of  FIGS. 1( a ), 1( b ) and 1( c ) , retractable snap dome  100  include sections  101 - 1 ,  101 - 2 ,  101 - 3 ,  101 - 4  and  101 - 5 , which are joined by folding ridges  102 - 1 ,  102 - 2 ,  102 - 3 , and  102 - 4 . These folding ridges are hinge points that facilitate and define the upright and collapsed positions of retractable snap dome  100 . The upright position of retractable snap dome  100  is maintained by both the elasticity of segments  101 - 1  to  101 - 5  and shape-retention characteristics of folding ridges  102 - 1  to  102 - 4 . 
     Sections  101 - 1  and  101 - 5  are also joined by hinge bars  103 - 1 ,  103 - 2  and  103 - 3  which form a bi-stable hinge between sections  101 - 1  and  101 - 5  of retractable snap dome  100 . The bi-stable hinge has a first bi-stable state and a second bi-stable state, as described in further details below. As shown in  FIG. 1( b ) , the bi-stable hinge connects between sections  101 - 1  and  101 - 5  at curved boundaries  104 - 1  and  104 - 2 . Alternatively, section  101 - 1  and  101 - 5  may also be joined by an elastic ribbon to provide the same bi-stable states, as described in further details below. Embedded in section  101 - 5  is EMP actuator  105  adjacent to curve boundary  104 - 2  of section  101 - 4 . In one embodiment, EMP actuator  105  may be provided by a bimorph EMP actuator which can be selectively actuated to provide a mechanical response (e.g., bending) in either one of two directions. A bimorph EMP actuator has two active regions, such that electrical stimulation in the first active region provides bending in one direction, and electrical stimulation in the second region provides bending in a second or opposite direction. 
     An electromechanical polymer (EMP) actuator typically includes one or more EMP layers formed out of a relaxor ferroelectric fluoropolymer and electrodes bonded thereto. When an external electric field is imposed across an EMP layer, the EMP layer becomes charged. The EMP layer thus behaves electrically as a capacitor. The electric field also provides an electromechanical response in the form of elongation in the transverse directions relative to the imposed electric field. The electromechanical property of the EMP layer is used to create the EMP actuator. EMP actuators are described, for example, in copending U.S. patent application (“Copending Application”), Ser. No. 13/683,963, entitled “Localized Multimodal Electromechanical Polymer Tranducers,” filed on Nov. 21, 2012, naming B. Zellers et al. as inventors. The Copending Application is hereby incorporated by reference herein. 
       FIGS. 2( a ), 2( b ) and 2( c )  each illustrate three stages of retractable snap dome  100  in a conventional (i.e., key depression) operation.  FIG. 3  shows a force profile of retractable snap dome  100  during the conventional operation.  FIG. 2( a )  shows, in the left portion, a first stage in which retractable snap dome  100  is in its up position supporting a key (not shown) ready to receive the downward force of a key depression. Retractable snap dome  100  is designed to collapse and rise with little force. A downward force on segments  101 - 3  and  101 - 4  pushes segments  101 - 2  and  101 - 5  in opposite outward directions. The downward force is represented in  FIG. 3  by curve segment  301 . 
     In the middle portion,  FIG. 2( a )  shows a second stage in which sections  101 - 3  and  101 - 4  of retractable dome  100  are depressed to horizontal positions. In this stage, sections  101 - 2  and  101 - 3  are designed to be angled to the left of vertical and to be substantially vertical, respectively, so as to predispose retractable dome  100  to collapse to the left. Initially, the depression increases the load on section  101 - 2 , with corresponding increased resistance, as represented by curve segment  302  of  FIG. 3 . Upon further depression, retractable snap dome  100  buckles to the left. The buckling action is represented by curve segment  303  of  FIG. 3 . The buckling brings retractable snap dome  100  to its collapsed position. The force profile in this configuration is represented by curve segment  304  in  FIG. 3 . 
     In the right portion,  FIG. 2( a )  shows a collapsed position of retractable snap dome  100  upon further depression. 
       FIG. 2( b )  illustrates the same three stages of retractable snap dome  100  of  FIG. 2( a )  in the conventional operation, as seen from the first direction.  FIG. 2( c )  illustrates the same three stages of retractable snap dome  100  of  FIG. 2( a )  in the conventional operation, as seen from the second direction. 
     According to one embodiment of the present invention, EMP actuator  105  may be actuated to bring retractable snap dome  100  to a collapsed position that may persist indefinitely, even after electrical stimulation is withdrawn.  FIG. 4( a )  illustrates three stages of retractable snap dome  100 —from upright to collapsed—under powered, activated and powered and activated and unpowered states of EMP actuator  105 , in accordance with one embodiment of the present invention. In the left portion,  FIG. 4( a )  shows retractable snap dome  100  when activation of EMP actuator  105  is initiated by application of a voltage across one or more EMP layers in EMP actuator  105 . Initially, retractable snap dome  100  is in its upright position, bi-stable hinge is in a first bi-stable state, and EMP actuator  105  is unpowered. As shown in the left portion of  FIG. 4( a ) , activation causes EMP actuator  105  to provide an electromechanical response (e.g., bending) that acts on curved boundary  104 - 1  and pushes section  101 - 5  towards the right, and eventually causes the bi-stable hinge to the second bi-stable state. 
     As mentioned above, hinge bars  103 - 1 ,  103 - 2  and  103 - 3  form the bi-stable hinge. (The bi-stable hinge can also be formed by an elastic ribbon, as also mentioned above). The two bi-stable states are lower energy configurations than the unstable intermediate state in which curved boundaries  104 - 1  and  104 - 2  have the greatest distance from each other at hinge bars  103 - 1  and  103 - 3 . This configuration compresses hinge bar  103 - 2  and puts hinge bars  101 - 1  and  101 - 3  in greatest tension. The unstable state may resolve into either one of the bi-stable states, in which hinge bars  103 - 1  and  103 - 3  are relatively unstrained. As further electrical stimulation is applied to EMP actuator  105 , retractable snap dome  100  flattens to the right, the tension in each of hinge bars  101 - 1  and  101 - 3  increases towards the unstable state. When the bi-stable hinge reaches the unstable state, further bending of EMP actuator  105  pushes the bi-stable hinge to rapidly snap into the second bi-stable state. At this point, retractable snap dome  100  has buckled and collapsed to the right, as shown in the middle portion of  FIG. 4( a ) . 
     As mentioned above, EMP actuator  105  remains charged even when power is withdrawn. Even when disconnected from power, EMP actuator  105  maintains its mechanical state at the time of power disconnection. Therefore, if power is disconnected after the bi-stable hinge settles in the second bi-stable state, EMP actuator  105  locks retractable snap dome  100  in the collapsed state, as shown in the right portion of  FIG. 4( a ) . 
       FIG. 4( b )  illustrates the same three stages of retractable snap dome  100  of  FIG. 4( a )  under the powered, the activated and powered and the activated and unpowered states of EMP actuator  105 , as seen from the first direction.  FIG. 4( b )  illustrates the same three stages of retractable snap dome  100  of  FIG. 4( a )  under the powered, the activated and powered and the activated and unpowered states of EMP actuator  105 , as seen from the second direction. 
     To return retractable snap dome  100  to the upright position, EMP actuator  105  may be provided the electrical stimulation in reverse from that illustrated by  FIGS. 4( a ), 4( b ) and 4( c ) .  FIG. 5( a )  illustrates three stages of retractable snap dome  100 —from collapsed to upright—under powered, activated and powered and activated and unpowered states of EMP actuator  105 , in accordance with one embodiment of the present invention. In the left portion of  FIG. 5( a ) , retractable snap dome  100  is shown initially in the locked-down collapsed state shown in the right portion of  FIG. 4( a ) . In the embodiment in which EMP actuator  105  is implemented by a bimorph EMP actuator, EMP actuator  105  is activated to bend in the opposite direction to drive the bi-stable hinge from the second bi-stable state to the first bi-stable state, which is shown in the middle portion of  FIG. 5( a ) . After retractable snap dome  100  is returned to the upright position, as shown in the right portion of  FIG. 5( a ) , electrical stimulation of EMP actuator  105  may be withdrawn. Retractable snap dome  100  is thus locked-down to the upright position to be ready to perform conventional operation. 
       FIG. 5( b )  illustrates the same three stages of retractable snap dome  100  of  FIG. 5( a )  under the powered, the activated and powered and the activated and unpowered states, as seen from the first direction.  FIG. 5( b )  illustrates the same three stages of retractable snap dome  100  of  FIG. 5( a )  under the powered, the activated and powered and the activated and unpowered states, as seen from the second direction. 
     In one embodiment, EMP actuator  105  produces a force in the ˜10 g range to facilitate retractable snap dome  100  to rise to the upright state or to fall to the collapsed state through the action of the bi-stable hinge. (Movement in the bi-stable hinge is realized by a weak pull/push horizontal force). In comparison, from the locked-down upright position of retractable snap dome  100 , a downward force in the range of ˜50-200 g is required to collapse retractable snap dome  100  in conventional operation. 
     A retractable snap dome of the present invention consumes power only for collapsing the structure for storage or returning the structure back to its upright position. In a keyboard application, for example, the EMP actuator is not involved in the conventional typing operation, and thus the advantages are achieved with little power consumption. 
     The above detailed description is provided to illustrate specific embodiments of the present invention and is not intended to be limiting. Numerous variations and variations within the scope of the present invention is possible. The present invention is set forth in the accompanying claims.

Technology Category: 5