Abstract:
An apparatus is described to reduce a play occurring in a micro-mechanical gear arrangement, the apparatus having a moveable hub coupled to a gear of the micro-mechanical gear arrangement, the moveable hub configured to permit a movement of the gear that reduces the play. A push rod is coupled to the moveable hub and at least one buckling beam is tethered to the push rod so that a force is exerted upon the push rod to cause the movement of the gear, the force being transferable to the gear via the moveable hub.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an arrangement, method, and system to reduce or prevent the “play” movement occurring in micro-mechanically produced gears.  
         BACKGROUND INFORMATION  
         [0002]    Micro-mechanical gears may be produced by a lithographic batch process. This process may be used to fabricate an arbitrary amount of gears and gear trains in a single step. However, due to limitations of the process, there may be a certain minimum gap between the teeth of the gears, that may result in a free-movement or “play” of the gears. For example, when a gear train is manufactured, the gears may include one or more “sacrificial” fabrication layers between the gears that remain after assembly. If the sacrificial layer(s) between the gears are subsequently removed, a gap may be created between the gears. Although this gap may be small (such as, for example, one micron), it may nonetheless permit “free” rotation of the gears. Such “free” rotation may limit the overall precision of the gear train and hence may be undesirable.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention provides an arrangement, method, and system to reduce or prevent the “play” movement occurring in micro-mechanically produced gears.  
           [0004]    The exemplary embodiments and/or exemplary method of the present invention is directed to an apparatus to reduce a play occurring in a micro-mechanical gear arrangement, the apparatus including a moveable hub coupled to a gear of the micro-mechanical gear arrangement, the moveable hub configured to permit a movement of the gear to reduce the play, the apparatus further including a push rod coupled to the moveable hub and at least one buckling beam tethered to the push rod and arranged to exert a force upon the push rod to cause the movement of the gear, the force being transferable to the gear via the moveable hub.  
           [0005]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus in which the micro-mechanical gear arrangement includes a gear train.  
           [0006]    Still another exemplary embodiment and/or exemplary method is directed to the apparatus further including a micro-mechanical mirror coupled to the gear train.  
           [0007]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus further including a micro-mechanical pump coupled to the gear train.  
           [0008]    Still another exemplary embodiment and/or exemplary method is directed to the apparatus further including a biological manipulator coupled to the gear train.  
           [0009]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus in which a width of the moveable hub is at least 200 μm.  
           [0010]    Still another exemplary embodiment and/or exemplary method is directed to the apparatus in which a width of the moveable hub is about 250 μm.  
           [0011]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus in which a length of the at least one buckling beam is at least 50 μm.  
           [0012]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus in which a width of the moveable hub is about 250 μm and a length of the at least one buckling beam is at least 50 μm.  
           [0013]    Still another exemplary embodiment and/or exemplary method is directed to the apparatus in which a buckling of the at least one buckling beam results from a compressive stress of a fabricated micro-mechanical device layer.  
           [0014]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus in which the at least one buckling beam has an initial slightly bended shape.  
           [0015]    Still another exemplary embodiment and/or exemplary method is directed to the apparatus in which the at least one buckling beam has an initial slightly bended shape of about 1%.  
           [0016]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus in which the at least one buckling beam includes two buckling beams arranged to suspend the push rod.  
           [0017]    Still another exemplary embodiment and/or exemplary method is directed to a fabrication of a buckling beam in which a fixed-fixed beam is subjected to a compressive stress of a fabricated micro-mechanical device layer.  
           [0018]    Yet another exemplary embodiment and/or exemplary method is directed to the fabrication of the buckling beam in which an initial slightly bended shape is provided to the fixed-fixed beam.  
           [0019]    Still another exemplary embodiment and/or exemplary method is directed to reducing a play occurring in micro-mechanical gear arrangement in which a moveable hub is coupled to a gear of the micro-mechanical gear arrangement, the moveable hub is operable to permit a movement of the gear to reduce the play, a push rod is coupled to the moveable hub, and at least one buckling beam is attached to the push rod so that a force is exerted on the push rod that causes the movement of the gear to reduce the play.  
           [0020]    Yet another exemplary embodiment and/or exemplary method is directed to coupling a moveable rack with the micro-mechanical gear arrangement.  
           [0021]    Still another exemplary embodiment and/or exemplary method is directed to an apparatus to reduce a play occurring in a micro-mechanically produced gear train, the apparatus including a moveable rack and at least one buckling beam tethered to the moveable rack and arranged to exert a force upon the moveable rack to cause a movement of the rack to reduce the play.  
           [0022]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus in which a width of the moveable rack is about 120 μm.  
           [0023]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus in which a width of the moveable rack is about 120 μm and the at least one buckling beam includes two buckling beams tethered to opposite ends of the moveable rack.  
           [0024]    Still another exemplary embodiment and/or exemplary method is directed to the apparatus in which the at least one buckling beam includes two buckling beams tethered to opposite ends of the moveable rack.  
           [0025]    Yet another exemplary embodiment and/or exemplary method is directed to the apparatus including a micro-mechanical comb drive to supply an electro-static force upon the moveable rack.  
           [0026]    Still another exemplary embodiment and/or exemplary method is directed to a micro-mechanical gear apparatus having a reduced play, the micro-mechanical gear apparatus including a gear, a moveable hub coupled to the gear and configured to permit a movement of the gear to result in the reduced play, a push rod coupled to the moveable hub, and at least one buckling beam tethered to the push rod and arranged to exert a force upon the push rod to cause the movement of the gear, the force being transferable to the gear via the moveable hub. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIG. 1 a  shows a micro-mechanical geartrain with play.  
         [0028]    [0028]FIG. 1 b  shows a side view of the micro-mechanical geartrain of FIG. 1 a  along axis A-A.  
         [0029]    [0029]FIG. 1 c  shows the micro-mechanical gear train of FIG. 1 a  with a micro-mechanical arrangement to reduce or eliminate the play.  
         [0030]    [0030]FIG. 1 d  shows a side view of the micro-mechanical gear train and arrangement of FIG. 1 c  along axis B-B.  
         [0031]    [0031]FIG. 1 e  shows the micro-mechanical gear train of FIG. 1 a  with a push rod/buckling beam arrangement to reduce or eliminate the play.  
         [0032]    [0032]FIG. 2 a  shows a deflection of a fixed-fixed beam due to a compressive stress of a fabricated MEMS device layer.  
         [0033]    [0033]FIG. 2 b  shows a deflection of a single-fixed beam within a fabricated MEMS device layer.  
         [0034]    [0034]FIG. 3 a  shows a push rod/buckling beam arrangement to reduce or eliminate play between a gear and a rack of a micro-mechanical gear/rod combination arrangement.  
         [0035]    [0035]FIG. 3 b  shows a rack-suspended/buckling beam arrangement to reduce or eliminate the play between gear and a moveable rack of a micro-mechanical gear/rod combination arrangement. 
     
    
     DETAILED DESCRIPTION  
       [0036]    [0036]FIG. 1 a  shows a micro-mechanical geartrain  100  with a play “P” and FIG. 1 b  shows a side view of the micro-mechanical geartrain  100  along axis A-A. The micro-mechanical gear train  100  includes micro-mechanical gears  101 ,  102 , and  103  upon a substrate  110  in an initial position of engagement after their fabrication and release. In particular, the micro-mechanical gear  101  is engaged with the gear  102 , which is also engaged with the gear  103 .  
         [0037]    Due to the manufacturing process, for example, the play P may occur between the gear  101  and the gear  102  and/or between the gear  102  and the gear  103 . In particular, the manufacturing process may require a “sacrificial” layer of approximately 1 μm, for example, to be applied and then removed, thereby leaving a gap between the gears. The play P, if left unreconciled or uncorrected, may result in several problems. For example, if the gear  101  is a driving gear, it may need to turn several degrees to compensate for the play P before the gear  103  may start to turn. Thus, if the gear  101  initiates a movement or a change in direction of rotation, the gear  103  may respond sluggishly, which may be undesirable. For example, if a micro-mirror is attached to the gear  103 , a precise reflection angle may not be achievable.  
         [0038]    [0038]FIG. 1 c  shows the micro-mechanical gear train  100  of FIG. 1 a  with a micro-mechanical arrangement  104  to reduce or eliminate the play P occurring between the gear  101  and the gear  102  and/or between the gear  102  and the gear  103 . FIG. 1 d  shows a side view of the micro-mechanical arrangement  104  along axis B-B. The micro-mechanical arrangement  104  includes a push rod  105 , a moveable hub  102 H, a micro-mechanical beam  106 , and a micro-mechanical beam  107 . In particular, the push rod  105  is coupled to the moveable hub  102 H and tethered by the two micro-mechanical beams  106 ,  107 . The moveable hub  102 H is further coupled to the gear  102 .  
         [0039]    To reduce the play P occurring between the gear  101  and the gear  102 , the micro-mechanical arrangement  104  presses the gear  102  against the other two gears  101  and  103 . More specifically, a force F (generated, for example, by an electrostatic drive) is applied to the push rod  105  that transfers the force F to the moveable hub  102 H, which moves the gear  102  closer to the gears  101  and  103 , thereby reducing or preventing play P from occurring between the gear  102  and the gear  101  and/or between the gear  102  and the gear  103 .  
         [0040]    The micro-mechanical arrangement  104  may be realized, for example, in a MEMS process with 2 moveable structural layers. According to one exemplary embodiment, if the diameter of the gear  102  is 100 μm, then the width of hub  102 H should be at least 200 μm to ensure a proper functioning. A width of 250 μm, for example, may be sufficient. Furthermore, the micro-mechanical beams  106  and  107  should extend at least 50 μm, for example, to achieve enough compressive stress. However, such a micro-mechanical actuator arrangement  104  may require additional space and electronics to accommodate the actuator.  
         [0041]    [0041]FIG. 1 e  shows the micro-mechanical gear train  100  of FIG. 1 a  with a push rod/buckling beam arrangement  112  to reduce or eliminate the play “P” between the gear  101  and the gear  102  and/or between the gear  102  and the gear  103 . The push rod/buckling beam arrangement  112  includes a push rod  111 , the moveable hub  102 H, and two buckling beams  109  and  110 . In particular, the push rod  111  is coupled to the moveable hub  102 H and tethered by the two buckling beams  109 ,  110 . The moveable hub  102   h  is further coupled to the gear  102 .  
         [0042]    The buckling action of the buckling beams  109 ,  110  exerts a force on the push rod  111  that is transferred to the moveable hub  102 H, which causes the gear  102  to be pressed against the gear  101  and the gear  103 . This eliminates or at least reduces the play P between the gear  102  and the gear  101  and/or between the gear  102  and the gear  103 . The push rod/buckling beam arrangement  112  of FIG. 1 e  may require less space and less energy as compared with the micro-mechanical actuator arrangement  104  of FIG. 1 c.    
         [0043]    The buckling action of the buckling beams  109 ,  110  results from compressive stresses within the MEMS fabricated device layer. The layers used to fabricate MEMS devices may possess small, but appreciable, intrinsic stress. In case of a compressive stress, the released layer or “thin film” may expand. Consequently, a fixed-fixed-beam within this layer may start to buckle.  
         [0044]    [0044]FIG. 2 a  shows a deflection D 1  of a fixed-fixed beam  201  due to a compressive stress of a fabricated MEMS device layer. FIG. 2 b  shows a deflection D 2  of a single-fixed beam  202  within the same fabricated device layer. As shown in FIGS. 2 a  and  2   b,  the deflection D 1  of the fixed-fixed beam  201  is greater than the deflection D 2  of the single-fixed beam  202  whose free end may expand unaffected by the compressive stress. The greater deflection D 1  may be used to exert an internal force upon moveable structures within the micro-mechanical device. The internal force may act upon, for example, a micro-mechanical gear within a micro-mechanical geartrain (such as, for example, the gear  102  of the geartrain  100  shown in FIGS. 1 a - 1   e ) thereby eliminating or at least reducing the play occurring between the gears which may have been created, for example, during fabrication of the MEMS device.  
         [0045]    [0045]FIG. 2 c  shows an alternative view of a fixed-fixed beam  203 . To define the direction of the deflection D 3 , the fixed-fixed beam  203  receives an initial slightly bended shape S 1 . The initial slightly bended shape S 1  may be configurable to as little as 1%, for example. Hence, arranging one or more fixed-fixed beams having an initial slightly bended shape within a micro-mechanical device may provide a predetermined directional movement of attached structures, as demonstrated by the push rod/buckling arrangement  112  of FIG. 1 e.    
         [0046]    In addition to micro-mechanical gears and gear trains, the push rod/buckling beam arrangement  112  may be applied to micro-mechanical gear rod combinations as well.  
         [0047]    [0047]FIG. 3 a  shows a push rod/buckling beam arrangement  312  to reduce or eliminate the play P between a gear  302  and a rack  301  of a micro-mechanical gear/rod combination arrangement  300 . The push rod/buckling beam arrangement  312  includes a push rod  311 , a moveable hub  302 H, and two buckling beams  309  and  310 . In particular, the push rod  311  is coupled to the moveable hub  302 H and tethered by the buckling beams  309 ,  310 . The moveable hub  302 H is further coupled to the gear  302 .  
         [0048]    The buckling action of the buckling beams  309 ,  310  exerts a force on the push rod  311  that is transferred to the moveable hub  302 H, which causes gear  302  to be pressed against gear  301  thereby eliminating or at least reducing the play P occurring between the gear  302  and the rack  301 . The push rod/buckling beam arrangement  312  may require less space and less energy than other micro-mechanical arrangements. According to one exemplary embodiment, the rack  301  may be approximately 120 μm in width, for example, to accommodate gears on the order of 100 μm in diameter.  
         [0049]    As an alternative to FIG. 3 a,  FIG. 3 b  shows a rack-suspended/buckling beam arrangement  313  to reduce or eliminate the play P between the gear  302  and a moveable rack  301  of a micro-mechanical gear/rod combination arrangement  300 . The rack-suspended/buckling beam arrangement  313  includes two buckling beams  314 ,  315  attached to two ends  301   a,    301   b  of the moveable rack  301 . In particular, the buckling beam  314  is attached to an end  301   a  and the buckling beam  315  is attached to another end  301   b.  According to another exemplary embodiment, the moveable rack  301  may be connected to another structure, such as, for example, a micro-mechanical comb driven by an electro-static force.  
         [0050]    The arrangements described herein may be applied to many driving mechanisms for many kind of MEMS applications, such as, for example, micro-mechanical mirrors, pumps, biological manipulators, etc.