Abstract:
A rotary mechanical latch for positive latching and unlatching of a rotary device with a latchable rotating assembly having a latching gear that can be driven to latched and unlatched states by a drive mechanism such as an electric motor. A cam arm affixed to the latching gear interfaces with leading and trailing latch cams affixed to a flange within the drive mechanism. The interaction of the cam arm with leading and trailing latch cams prevents rotation of the rotating assembly by external forces such as those due to vibration or tampering.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/139,044 filed on Dec. 19, 2008, the entirety of which is herein incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The United States Government has certain rights in this invention pursuant to Department of Energy Contract No. DE-AC04-94AL85000 with Sandia Corporation. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to apparatus and methods for a rotary mechanical latching mechanism to provide positive latching of a rotary device. The invention further relates to rotary latching mechanisms for enclosures that are operable by electrical drive means and are resistant to false unlatchings in a vibrational environment. 
     BACKGROUND OF THE INVENTION 
     Rotary latching mechanisms are used to provide controlled access to enclosures with examples ranging from electronics enclosures, vehicle compartments, control rooms etc. Typically a rotary mechanical latch finds application in locking mechanisms for securing the access panels, doors, lids and hatches to an interior volume of a controlled space. In one exemplary non-limiting application, the knob of a door acts as a driving device for applying torque to a rotating shaft that is coupled to a bolt mechanism for withdrawing the bolt from a corresponding strike plate located on the frame of the door. In this and other applications of rotary latching mechanisms, there is a need to prevent rotation of actuating shaft by unauthorized users and a further need to provide the drive input from a remote location (e.g. by electrical drive apparatus). Additionally there is a need for rotary latching mechanisms that provide positive latching of the actuating shaft in an unpowered state (e.g. passive latching) and are resistant to false unlatching of the actuating shaft due to vibrations in the environment of the latch. The present invention meets these needs by providing a positive rotary latching mechanism that is unlatchable by application of a drive torque to lock and unlock a cam arm attached to a rotary actuation shaft, where the cam arm is latched and unlatched by the cooperative positioning of leading and trailing cams incorporated into the drive mechanism. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form part of the specification, illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings provided herein are not drawn to scale. 
         FIG. 1  is a perspective illustration of an embodiment of a rotary mechanical latch according to the present invention. 
         FIG. 2  is a schematic detail view of the embodiment of a rotary mechanical latch of  FIG. 1 , in a latched state. 
         FIG. 3  is a schematic plan view illustration of the embodiment of  FIG. 1 , in a latched state. 
         FIG. 4  is a schematic plan view illustration of the embodiment of  FIG. 1 , in the process of beginning to unlatch. 
         FIG. 5  is a schematic plan view illustration of the embodiment of  FIG. 1 , in the process of unlatching where the teeth of the pinion gear are beginning to engage the toothed portion of the latching gear. 
         FIG. 6  is a schematic plan view illustration of the embodiment of  FIG. 1 , in an unlatched state. 
         FIG. 7  is a schematic plan view illustration of the embodiment of  FIG. 1 , in the process of beginning to relatch. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a perspective illustration of an exemplary embodiment of a rotary mechanical latch according to the present invention. Rotary mechanical latch  100  can comprise a drive assembly  110  and a rotating latchable assembly  140 . Drive assembly  110  has an axis of rotation  112  that is parallel to and spaced from the rotational axis  142  of the latchable assembly  140 . Drive assembly  110  further comprises means for providing a rotational torque such as an electric motor  114  to a pinion gear  116  having a flange  118  supporting leading latch cam  120 , trailing latch cam  122  and (optionally) balancing cam  124 . In this exemplary embodiment the drive means  114  comprises an electric motor, but could as well comprise a manual drive device such as a knob, wheel or lever, or other motorized drive means such as a solenoid or motor (electrically, pneumatically or hydraulically operated). The latchable assembly  140  comprises an output shaft  144  that can be coupled for example, to insert and withdraw a bolt (not shown) from a strike plate (not shown) in an exemplary non-limiting application such as a door latch. As described below, rotary mechanical latches (e.g.  100 ) according to the present invention operate to secure the output shaft  144  in a latched (e.g. locked) non-rotatable state and allow shaft  144  to achieve an unlatched (e.g. unlocked) rotatable state only after proper application of a drive torque to the pinion gear  116 , by use of drive means  114 . 
     The latchable assembly  140  comprises a latching gear  146 , cam arm  148  and a spring catchment  150  that can (as shown in this example) be implemented as a notch on the perimeter of spool  152 . The spring catchment  150  can be arranged to capture the free end of a flexural member  158  that as described below, can be configured to apply a latching torque (e.g. via the restoring force of a deformed elastic member) to the latching assembly  140  under certain conditions. The cam arm  148 , latching gear  146  and catchment spool  152  fixedly share the axis of rotation  142  and can be assembled onto the output shaft  144  as separate components or can exist as integrally formed or machined components as an application warrants. Latching gear  146  comprises an untoothed portion  156  and a toothed portion  154 , the teeth of which are engaged by the teeth of pinion gear  116  during latching and unlatching operations of the rotary latch  100 . 
     In  FIG. 1 , rotary mechanical latch  100  is illustrated in the latched state, where rotation of output shaft  144  is prevented by the cooperative action of leading cam  120  and trailing cam  122  which “lock” the cam arm  148  in the latched state. In the latched state, the gear teeth of the toothed portion  154  of the latching gear  146  are not engaged with the gear teeth of the pinion gear  116 . Latching/locking of the rotary mechanical latch is established by the positional relationship (e.g. interlocking) of the cam arm  148  with the leading  120  and trailing  122  latching cams. As described below, there is no need for power (e.g. manual, electrical etc.) to be applied to the drive means  114  to maintain the output shaft  144  in a latched state and prevent its rotation. Latching of the output shaft  144  is accomplished by rotary mechanical latches  100  of the present invention, by purely passive means. 
     In an exemplary application, the drive assembly  110  and the latchable assembly  140  can be supported in a common frame or housing, that further can provide an anchor point  160  for the flexible member  158 . The free end of the flexible member  158  can slideably engage the recess portion of the spool  152  and can be captured by the spring catchment  150  (e.g. notch or tang) at certain points (described below) during the operation of the rotary mechanical latch  100  to store energy within the flexible member  158  used to produce a latching torque applied to the latching gear  146 . 
       FIG. 2  is a schematic detail view of the embodiment of a rotary mechanical latch of  FIG. 1 , in a latched state.  FIG. 2  serves to illustrate the passive nature by which cam arm  148  (and therefore output shaft  144 ) is secured in a latched state. The terms clockwise and counterclockwise are used herein to illustrate the operation of the invention, and do not serve to limit or restrict the application of the invention to any particular rotational direction or orientation. In the exemplary embodiment illustrated in  FIG. 2 , the cam arm  148  is prevented from rotating in a counterclockwise manner from the latched state to an unlatched state by the leading latch cam  120 . If an attempt is made to rotate the cam arm  148  counterclockwise (e.g. to unlatch) by other than through the use of drive means  114  a curved contacting surface  182  of cam arm  148  is pressed against the corresponding contacting surface  184  of leading latch cam  120 , producing by the nature of their curvatures, a counterclockwise “restoring” torque being applied to flange  118 , acting to force engagement of the leading cam  120  with the cam arm  148 . If an increasing torque is applied to attempt to rotate the cam arm  148  in a counterclockwise direction, a greater contact pressure between surfaces  182  and  184  results, therefore creating an increasing counterclockwise torque applied to the flange  118  and further increasing the engagement of the leading cam  120  with the cam arm  148 . An attempt to rotate the cam arm  148  in a clockwise direction by other than through the use of drive means  114  is prevented in a manner similar to above. In a fully latched state, rotation of the cam arm  148  is physically blocked by the presence of trailing latch cam  122 . Where the cam arm  148  is slightly unlatched, by the nature of their curvatures, as the contacting surface  188  of the cam arm  148  is pressed against corresponding contacting surface  186  of the trailing latch cam  122 , a clockwise torque is applied to flange  118 , acting to force engagement of the trailing cam  122  with the cam arm  148 . 
     Therefore power is not required to maintain (e.g. latch, lock) the cam arm  148  in the latched state as the curved nature of contacting surfaces  184 ,  182 ,  188  and  186  are such as to generate torques (i.e. “restoring” torques) on the flange  118  acting to force engagement of the cam arm  148  with latch cams  120  and  122  in response to any attempt to rotate the cam arm into an unlatched state. In the present exemplary embodiment, it has been found that a useful geometry can be realized with a teardrop leading cam  120 , an oblong trailing cam  122  and a cam arm  148  each having contact surfaces ( 182 ,  184 ,  186  and  188 ) formed to create the opposing torques acting on the flange  118 , by the nature of their curvature. It is to be noted that other geometries could be utilized as well without affecting the practice of the present invention (e.g. an elliptical trailing cam in place of the oblong shaped trailing cam). Optional balancing cam  124  has been found useful in applications where the rotary mechanical latch  100  may be subjected to vibrational environments, either due to normal operational conditions or in attempts to defeat the latching device. By balancing the mass distribution of the latching cams  120  and  122  over the flange  118  with a suitable sized balancing cam  124 , motion of a drive assembly  110  in response to those vibrations can be minimized. In this embodiment, balancing cam  124  is illustrated as a cylindrical mass attached to the flange  118 , but any shaped mass as convenient to an application could be used as well. 
     The following series of figures serve to explain the operation of the embodiment of a rotary mechanical latch as presented in  FIG. 1 . Components below the plane of the illustration, such as spool  152 , spring catchment  150  and pinion gear  116  are shown in dashed outline for clarity. 
       FIG. 3  is a schematic plan view illustration of the embodiment of  FIG. 1 , in a latched state. Rotation of latching gear  146  and therefore output shaft  144  (not shown) is prevented as cam arm  146  is captured (e.g. locked) between the leading latch cam  120  and trailing latch cam  122 . The latch cams  120  and  122  are shaped such that rotation of the latching gear  146  in either direction produces a torque that rotates the flange  118  in a direction to force further engagement of latch cams  120  and  122  with the cam arm  148 . Flexible spring element  158  applies clockwise torque to latching gear  148 , further resisting counterclockwise rotation of the latching gear. Balancing cam  124  does not engage the cam arm  148  but serves to balance the pinion gear  116 , flange  118  and latch cams  120  and  122 , so that the drive assembly  110  cannot be easily rotated by mechanical vibrations. 
       FIG. 4  is a schematic plan view illustration of the embodiment of  FIG. 1 , in the process of beginning to unlatch. Drive means  114  (not shown) have been utilized to apply a clockwise torque to pinion gear  116 , rotating flange  118  approximately 45 degrees to a point where the leading latch cam  120  no longer interferes with the cam arm  148 . The interior edge of the trailing latch cam  122  is driving the latching gear  146  via contact with the cam arm  148 , and latching gear  146  is now free to continue rotation in a counter clockwise direction. The spring element  158  continues to provide a clockwise torque to the latchable assembly  140  at this point, which the drive means must overcome. In the exemplary embodiment, the drive means  114  (an electric motor) continues to drive (e.g. rotate clockwise) the pinion  116  somewhat beyond this point. 
       FIG. 5  is a schematic plan view illustration of the embodiment of  FIG. 1 , in the process of unlatching where the teeth of the pinion gear are beginning to engage the toothed portion of the latching gear. In  FIG. 5  the drive means  114  has rotated the pinion gear  116  and flange  118  to a point where the outer extent of the trailing cam  122  is pushing the cam arm  148 , causing continued counterclockwise rotation of latching gear  146 . The teeth of pinion gear  116  are about to engage the first tooth  170  on the toothed portion  154  of the latching gear  146 . Gear tooth  170  is illustrated as being shortened which has been found to facilitate engagement with the pinion gear  116 . In this embodiment, the outline of the contacting surfaces of the cam arm  148  and trailing latch cam  122  are such that the rotation ratio (e.g. here 4:1) of the pinion gear  116  and the latching gear  146  is the same as if their gear teeth were engaged. Further counterclockwise rotation of the latching gear  146  is now driven by engagement of the pinion gear  116  with the toothed portion  154  of the latching gear. Engagement of the gear teeth maintain the proper phase relationship between the latching gear  146  and the pinion gear  116  to insure the latching cams  120  and  122  will properly engage with the cam arm  148  upon latching. The spring flexural member  158  is near its overthrown position, i.e. where it will escape the spring catchment  150 . 
       FIG. 6  is a schematic plan view illustration of the embodiment of  FIG. 1 , in an unlatched state.  FIG. 6  shows the cam arm  148  completely disengaged from the latching cams  120  and  122 . The latching gear  146  is free to rotate (i.e. through less than 360 degrees) within the limits defined at either end where the cam arm  146  would encounter a latching cam ( 120 ,  122 ). At this point, the end of flexural member  158  has escaped the spring catchment  150  and is no longer applying a torque to the latching gear  146 . Drive means  114  no longer needs to be powered and can be allowed to freely rotate, allowing latching gear  146  to rotate freely as well (i.e. latching gear is “unlocked”). The unlatched state therefore does not consist of a singular position of the latching gear  146 , but rather comprises all rotational orientations of the latching gear  146  from the point at which the teeth of the pinion gear  116  begin to engage the first tooth  170  of the latching gear  146  continuing around to the orientation where further rotation would cause the cam arm  148  to collide with a cam. 
       FIG. 7  is a schematic plan view illustration of the embodiment of  FIG. 1 , in the process of beginning to relatch.  FIG. 7  illustrates the beginning of a latching sequence. The latching gear  146  has been rotated clockwise by the drive means  114  to the point where the end of flexural member  158  is captured by spring catchment  150 , and the force of continued rotation of latching gear  146  causes the flexural member  158  to begin to buckle. The drive means  114  applies a torque to the latching gear  146  to rotate the latching gear up to the overthrow point of the flexural element  158 . After the overthrow, the flexural element  158  provides the torque needed to latch the rotary latch  100 , as shown in  FIG. 5 . The flexural element  158  is providing torque to the latching gear  146  driving the pinion gear  116  counterclockwise. At this point, the latching gear  146  and pinion gear  116  teeth are just beginning to disengage and continued rotation of the pinion gear  116  is driven by the contact between the cam arm  148  and the trailing latch cam  122 . The torque provided by the flexural member  158  continues to drive the latching gear  146  and pinion gear  116  through the position shown in  FIG. 4  and into the fully latched position as shown in  FIG. 3 . 
     The exemplary embodiment of a rotary latch is described in the preceding text as allowing a rotation of the cam arm  148  in an unlatched state through less than 360 degrees. The invention could as well be applied to rotary latches wherein the cam arm  148  was allowed to rotate through a greater rotational angle (i.e. greater than 360 degrees) for example, by providing a rotary ramp element that would move the pinion gear  118  (e.g. or the cam arm itself) out of engagement with the cam arm  148  thereby allowing a greater degree of rotation. 
     In one exemplary application of the embodiment described above, a rotary mechanical latch has been built and operated with a DC motor drive means ( 114 ), and found to cosume 40 millijoules to unlatch. This example serves to illustrate suitability of rotary mechanical latches according to the present invention, to low power applications. 
     The above described exemplary embodiments present several variants of the invention but do not limit the scope of the invention. Those skilled in the art will appreciate that the present invention can be implemented in other equivalent ways. The actual scope of the invention is intended to be defined in the following claims.