Patent Publication Number: US-2002011085-A1

Title: Anti-shock mechanism for an electronic lock

Description:
BACKGROUND  
       [0001] 1. Field of the Invention  
       [0002] This invention relates to the field of electronic locks and specifically to an antishock mechanism that prevents unauthorized lock break-ins occurring when an external force is applied to the lock displacing a solenoid plunger within the lock.  
       [0003] 2. Description of the Related Art  
       [0004] Items of extremely sensitive nature or very high importance must be stored securely in a safe or other containment device, with access restricted to select individuals given a predetermined combination, code, or key access necessary to enable authorized entry. It is essential to ensure that unauthorized entry by persons employing safecracking techniques including use of a translating actuator is prevented.  
       [0005] Electronic locks including combination and key entry locks are commonly used to secure safes and other containment devices. Numerous locking mechanisms are known which employ various combinations of electrical, mechanical and magnetic elements both to ensure against unauthorized entry and to effect cooperative movements among the elements for authorized locking and unlocking operations.  
       [0006] Electric/electronic locks often contain a solenoid that is used to place the mechanical portions of the lock in a position where the operator may open the lock. Such solenoids often contain a plunger that pushes a lever or sliding bar. Some safes and security containers are built such that an external force or impact can be applied to the safe or security containers and as a result to the lock. Thus, this force or impact may cause the solenoid plunger to place the mechanical portions of the lock in a condition to open. Therefore, allowing unauthorized access to the secured items.  
       SUMMARY OF THE INVENTION  
       [0007] The present invention solves the problem discussed above and is a mechanism designed to limit displacement of the solenoid plunger when an external force acts on the lock case of an electronic lock. An external force, such as that created by a translating actuator, applied in a direction parallel to the direction of solenoid plunger movement in a lock may cause the solenoid plunger in the lock to displace allowing the lock to be opened without authorization. The addition of a properly sized anti-shock mechanism limits displacement of the solenoid plunger due to an external force or impact and allows movement of the solenoid plunger when the solenoid plunger movement is due to an authorized access.  
       [0008] Under normal operating conditions when the lock is locked, the bolt is in the filly extended position and the solenoid is not actuated. Upon authorization, the solenoid actuates causing the mechanical components to be placed in a condition whereby the operator may open the lock. An anti-shock belcrank limits the solenoid plunger&#39;s travel and prevents the solenoid plunger from actuating the mechanical portions of the lock upon application of an external force upon the lock casing in a direction parallel to solenoid plunger movement. When the lock is subjected to a force or impact, the anti-shock belcrank moves or rotates to a position that will limit the plunger&#39;s movement and prevent the mechanical components of the lock from being placed in positions that would permit the lock to be opened. The anti-shock belcrank interacts with the solenoid plunger according to known principles of conservation of momentum. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009] The accompanying drawings incorporated in and forming part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention in the drawings:  
     [0010]FIG. 1 is a rear view of the bolt mechanism of an electronic lock with the lock case removed for clarity showing the mechanical components of the lock.  
     [0011]FIG. 2 is a rear view of the bolt mechanism of FIG. 1, showing the mechanical components not fully reset and subject to unauthorized opening after receiving a shock or impact.  
     [0012]FIG. 3 is a rear view of the bolt mechanism of FIG. 2, showing the position of the anti-shock mechanism after the lock case has been subjected to a shock parallel to the axis of bolt movement. 
    
    
     [0013] Reference will be now be made in detail to the present preferred embodiment to the invention, examples of which are illustrated in the accompanying drawings.  
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0014]FIG. 1 illustrates the back of one electronic lock  10  that uses a solenoid (not shown) to place the mechanical components in a condition whereby the lock  10  may be opened. The mechanical components are typically located within a lock case  20  that supports a bolt  22  that extends outside of the lock case  20  into a locked position and retracts within the lock case  20  when the lock is opened. The lock  10  may be opened upon entry of the correct combination, followed by energizing the solenoid. Rotation of an external knob (not shown) may be required for some locks.  
     [0015] Once the correct combination is entered, a solenoid (not shown) having a plunger (not shown) is actuated. The solenoid, in the lock case  20  shown, is mounted within the lock case  20  in area  24  with the solenoid plunger moving horizontally upon actuation and may be reset by a return spring  26  or other return system after the solenoid is de-energized.  
     [0016] When the solenoid is actuated, the plunger may contact and then move a knockoff belcrank  28 . In the embodiment shown, the knockoff belcrank  28  rotates about pivot  44  when acted upon by the solenoid plunger. Upon rotation, the knockoff belcrank  28  may push latch belcrank  30  away from notch  34  in slider  32 . The latch belcrank  30  may also rotate around pivot  44 . The slider  32  and lever  36 , which is connected by a pin to slider  32 , will move in the downward direction when lever  36  is positioned over the cutout in cam  38  under the urging of spring  40 .  
     [0017] When the lever  36  moves into the cutout in cam  38 , counterclockwise rotation of the cam  38  engages the cam  38  to lever  36  and enables the operator to withdraw bolt  22  that is connected to lever  36  with continued counterclockwise rotation.  
     [0018] For those embodiments of slider  32  that have a notch  34 , FIG. 2 illustrates the need for an anti-shock device of the present invention. With reference now to FIG. 2 showing the slider  32  and lever  36  raised slightly so that the latch belcrank  30  is almost free from notch  34  of slider  32  and resting on knob  42  of slider  32 . In this position, the application of an external horizontal force parallel to the direction of bolt retraction may cause the solenoid plunger to push the knockoff belcrank  28  and latch belcrank  30  beyond the control notch  34  on slider  32 . Because there is a slight vertical interference between the notch  34  and the latch belcrank  30 , the belcranks  28  and  30  will not return to their normal home position after the impact or application of the external force. Thus, the slide  32  is free from control of the latch belcrank  30  and slide  32  together with lever  36  can freely move. Further rotation of the cam wheel  38  will then allow opening lock  10  without actuating the solenoid unless there is an anti-shock mechanism  60  to inhibit movement of the solenoid plunger when an external force or shock is applied.  
     [0019] Thus, the need for a lock containing an anti-shock belcrank  60 . The embodiment shown has a tip  62  and a center of mass  64  above its pivot point  66 . An anti-shock belcrank  60  with the center of mass  64  located above the pivot point  66  rotates with the application of an external impact force to the lock case  20 . This same force or impact could cause rotation of the latch belcrank  30  and knockoff belcrank  28 . As shown in FIG. 3, the anti-shock belcrank  60  limits the movement of the solenoid plunger and belcranks  28  and  30  by limiting/preventing rotation or movement of either the knockoff belcrank  28  or latch belcrank  30 . Through proper design of anti-shock belcrank  60 , the displacement of the solenoid plunger may be made arbitrarily small.  
     [0020] The anti-shock belcrank  60  does not influence the movement of the solenoid or solenoid plunger under normal operating conditions of the lock  10  so that the lock  10  may freely open upon entry of the proper predetermined code which actuates the solenoid. Upon actuation, the solenoid plunger of the lock displaces a distance, approximately 0.080 inches with a variance of approximately 0.005 inches in the embodiment shown. For this reason, the anti-shock belcrank  60 , for the lock  10  shown is positioned to allow the an initial clearance equal to or larger than that required for normal lock operation between the contacting surfaces of the knockoff belcrank  28  and the anti-shock belcrank  60 , a minimum of 0.085 inches is used in the embodiment shown.  
     [0021] The anti-shock belcrank  60  must stop the movement of the solenoid plunger, latch belcrank  30  and knockoff belcrank  28  before the latch belcrank  30  moves beyond the control of notch  34 . This occurs, in the lock  10  shown, when the latch belcrank  30  moves approximately 0.03 inches. To maintain the latch belcrank  30  within control of the notch  34  and allow the solenoid to freely move upon actuation, the tip  62  of the anti-shock belcrank  60 , in the lock  10  shown, must move approximately 0.055 inches. Thus, the tip  60  of the anti-shock belcrank  60  travels slightly less than twice the distance traveled by the solenoid plunger during impact.  
     [0022] Using known principles of displacement versus time and momentum transfer requirements, the following parameters are established for the anti-shock belcrank  60 .  
     [0023] Upon application of an external force, the solenoid plunger, knockoff belcrank  28  and latch belcrank  30  typically move according to the equation:  
       X= ( V/wn )sin  wn t+F   0   /K (cos  wn t− 1),  
     [0024] wherein X is the horizontal displacement of the solenoid plunger, the latch belcrank  30  and the knockoff belcrank  28 ;  
     [0025] V is the velocity of the lock case  20  at impact, if dropped, or experienced if subject to an external force or strike;  
     [0026] wn is the natural frequency of the solenoid plunger, the latch belcrank  30 , the knockoff belcrank  28  and return spring system;  
     [0027] t is time to travel distance X;  
     [0028] F 0  is the equivalent initial force of the return spring  26  (the spring force translated to the center of the solenoid contact area); and  
     [0029] K is the equivalent spring rate ratio of the return spring  26  (the spring rate translated to the center of the solenoid contact area).  
     [0030] Upon application of an external force, the anti-shock belcrank typically moves according to the equation:  
       X   sa   =V/wn   sa (sin  wn   sa   t )+ F   osa   /K   sa (cos  wn   sa   t− 1),  
     [0031] wherein X sa  is the displacement of the anti-shock belcrank center of mass  64 ;  
     [0032] V is the velocity of the lock case  20  at impact, if dropped, or experienced if subject to an external force or strike;  
     [0033] wn sa  is the natural frequency of the anti-shock belcrank return spring system;  
     [0034] t is time to travel distance X sa ;  
     [0035] F osa  is the equivalent initial force of the anti-shock belcrank  60  return spring (the initial force of the anti-shock belcrank return spring translated to the anti-shock belcrank center of mass  64 ); and  
     [0036] K sa  is the equivalent spring rate of the anti-shock belcrank return spring (the spring rate of the anti-shock belcrank return spring referenced translated to the anti-shock belcrank center of mass).  
     [0037] The solenoid plunger and anti-shock belcrank make contact upon application of an external force by the conservation of momentum equations:  
       V   1 =[( M   1   −M   2 )/( M   1   +M   2 ) U   1 +[(2 M   2 )/( M   1   +M   2 )] U   2    
       V   2 =[(2 M   1 )/( M   1   +M   2 )] U   1 +[( M   2   −M   1 )( M   1   +M   2 )] U   2    
     [0038] wherein V 1  is the velocity of the solenoid plunger after impact with the anti-shock belcrank  60 ;  
     [0039] V 2  is the velocity of the anti-shock belcrank center of mass  64  after impact with the solenoid plunger;  
     [0040] U 1  is the velocity of the solenoid plunger before impact with the anti-shock belcrank  60 ;  
     [0041] U 2  is the velocity of the anti-shock belcrank center of mass  64  before impact with the solenoid plunger;  
     [0042] M 1  is the mass of the solenoid plunger and the effective mass of both the latch belcrank  30  and the knockoff belcrank  28  referenced to the point on the belcranks where the center of the solenoid plunger contacts the knockoff belcrank  28 ; and  
     [0043] M 2  is the effective mass ratio of the anti-shock belcrank  60  referenced to the anti-shock belcrank center of mass  64  radius.  
     [0044] When anti-shock belcrank  60  is properly designed, the velocity V 1  will be less than or equal to zero, indicating that the solenoid plunger has stopped or is moving back towards its home position. After the anti-shock belcrank  60  stops rotating, an anti-shock return spring  68  may return the anti-shock belcrank to its home or pre-impact position. The use of an anti-shock return spring  68 , while optional, permits the lock  10  to be mounted in any orientation.  
     [0045] In summary, numerous benefits have been described which result from employing the concepts of the invention. The foregoing description of a preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to a precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described in order to best illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.