Abstract:
Existing small and medium-sized solenoid-operated locking containers are vulnerable to undesired impact-induced opening. An impact-resistant solenoid-operated locking container is disclosed. The container is protected against impact by the use of two solenoids oriented 180 degrees opposite each other. The solenoids are further protected against binding in a retracted position by T-shaped end caps, affixed to their retractable plungers, engaging notches cut into a movable plate. A silent, or nearly silent, impact-resistant solenoid, for use in an impact-protected locking container, is also disclosed, having the motion of its retractable plunger slowed and quieted by a viscous fluid such as damping grease.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    None 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND 
       [0003]    1. Field 
         [0004]    The application relates to container locks, and specifically to solenoid-operated container locks which are resistant to unauthorized opening by kinetic impact. 
         [0005]    2. Prior Art 
         [0006]    U.S. Pat. No. 5,249,831 is an electric lock, having the bolt directly moved by a solenoid, with a counterweight to protect it against impact opening. 
         [0007]    U.S. Pat. No. 7,424,814 B2 is a complex dead bolt lock with an inertial device to protect it against impact opening. 
         [0008]    U.S. Pat. App. No. 20020011085 is an electric lock equipped with an anti-shock belcrank. 
         [0009]    U.S. Pat. App. No. 20100132418 is an electric lock with a lever and counterweight anti-shock mechanism. 
         [0010]    There is some prior art, cited above, regarding impact-resistant lock design for electrically operated locking containers. However, none of this prior art is applicable to the most common, inexpensive, and vulnerable electrically operated locking container design: the solenoid-operated locking container with an opening knob. The present device is a simple and inexpensive protection device that can be added to these existing locking container designs to make them highly impact resistant. 
       SUMMARY 
       [0011]    The vast majority of small and medium-sized electronic locking containers, including firearm safes, use an electromagnetic solenoid and opening knob to release the bolt carriage. This design is simple and inexpensive, does not require high manufacturing tolerances, and easily accommodates a key bypass lock. Small containers with more secure motor-driven mechanisms are less common, and are far more expensive than solenoid-operated containers. 
         [0012]    Unfortunately, small and medium-sized solenoid-operated containers are highly vulnerable to unauthorized impact opening, by simply dropping the container a few centimeters and turning the opening knob. At least one fatality has allegedly resulted from a child gaining access to a firearm in this way. There is an urgent need for an improvement to this solenoid-operated design to make it impact resistant. 
         [0013]    In a solenoid-operated locking container, the solenoid&#39;s retractable plunger normally blocks the sliding motion of a movable plate and attached bolt carriage when someone attempts to turn the opening knob. When the user authenticates, for example by using a code or fingerprint, the electronic controller energizes the solenoid. The plunger retracts, generally less than one centimeter, and the bolt carriage is free to move when the user turns the opening knob. When the solenoid&#39;s power is removed, the spring extends the retractable plunger once more. 
         [0014]    If the container is “bumped”, or accelerated downward and then abruptly stopped, inertia causes the retractable plunger to continue to move downward. If the opening knob is turned at this moment, the container will open. Due to the combination of the heavy retractable plunger, low return spring constant, and short plunger travel, only a small impact is required to momentarily retract the plunger enough to open the lock. The vulnerable interval is only a fraction of a second, so careful timing is required to use this method, hereafter called the timing vulnerability. 
         [0015]    If the opening knob is first turned so that the movable plate lightly contacts the retractable plunger, and the container is then dropped, in many cases the plunger will descend and bind in the refracted position against the movable plate. When this happens, the container can be opened by turning the opening knob further. No skill or timing is required to use this method, hereafter called the binding vulnerability, and children have allegedly performed it accidentally while playing with safes. 
         [0016]    One method of preventing the binding vulnerability is to add a T-shaped cap to the end of the retractable plunger, and to cut a corresponding notch into the movable plate. If the plate is moved to contact the plunger, the cap engages the notch to prevent the downward motion of the plunger. 
         [0017]    One method of preventing the timing vulnerability is to place a second solenoid above the plate with its retractable plunger facing downward, 180 degrees opposite the first solenoid&#39;s retractable plunger. Because the plungers move in opposite directions, an impact which displaces one solenoid&#39;s plunger will not affect the other solenoid. 
         [0018]    Another method of reducing the motion of an electromagnetic solenoid&#39;s retractable plunger when the solenoid is decelerated is to coat the plunger with a velocity-dependent viscous fluid, such as damping grease. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    A more complete understanding of the present device can be obtained by considering the detailed description in conjunction with the accompanying drawings, in which: 
           [0020]      FIG. 1  illustrates the mechanical and electrical components located on the inside panel of the door of an exemplary embodiment of a prior art solenoid-operated locking container, which is not impact protected. 
           [0021]      FIG. 2  illustrates the mechanical and electrical components located on the inside panel of the door of an exemplary embodiment of a solenoid-operated locking container, which is impact protected by two opposing electromagnetic solenoids with T-shaped retractable plungers, and corresponding notches cut into its movable plate. 
           [0022]      FIG. 3  illustrates the mechanical and electrical components of an exemplary embodiment of an electromagnetic solenoid, the motion of which is slowed by a velocity-dependent viscous fluid, such as damping grease, to prevent impact opening. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  illustrates the mechanical and electrical components of an exemplary embodiment  101  of a prior art solenoid-operated safe, which is not protected against impact, as seen from the inside of the safe door  102 , with its covers removed. 
         [0024]    Hinge pins  103  and hinges  104  attach the door to the safe. Locking bolts  105  are affixed to a bolt carriage  127 , and pass through holes in a fixed plate  128  attached to the safe body, so that when the door is closed and locking bolts  105  are extended, the door cannot be opened until locking bolts  105  are retracted. 
         [0025]    Bolt carriage  127  is affixed at a right angle to movable plate  116 . Pin  114  is affixed to the safe door  102  and passes through notch  117  in movable plate  116 . Washer  115 , affixed to pin  114 , holds movable plate  116  parallel to the safe door  102  while leaving it free to slide back and forth, thus moving locking bolts  105 . 
         [0026]    Shaft  119  extends through a hole in safe door  102  and attaches to the opening knob on the front of the safe, enabling the user to move movable plate  116  from outside the safe. Wheel  118  is affixed to shaft  119 . Notch  120  is cut into movable plate  116 , and pin  121  is affixed to wheel  118 . Therefore, turning wheel  118  counter-clockwise (facing  FIG. 1 ) causes movable plate  116  to move leftward, retracting locking bolts  105 , while pin  121  moves upward in notch  120 . Turning wheel  118  clockwise causes movable plate  116  to move rightward while pin  121  moves downward in notch  120 , extending locking bolts  105 . 
         [0027]    Tab  129  is part of movable plate  116 , and extends downward. Electromagnetic solenoid  122  is affixed to safe door  102 . Solenoid  122  has a retractable plunger  124 , a return spring  125 , and a plate  126 . Plate  126  is affixed to retractable plunger  124 . Cable  123  connects solenoid  122  to circuit board  109 . With locking bolts  105  extended, when a user turns the opening knob and thus wheel  118 , in an attempt to retract locking bolts  105 , tab  129  is blocked by retractable plunger  124 , preventing movable plate  116  from moving, and so preventing locking bolts  105  from retracting. 
         [0028]    When the unlocking criteria are met, circuit board  109  energizes solenoid  122 , causing retractable plunger  124  to move downward, compressing spring  125 . Tab  129  is no longer blocked, and the user can turn the opening knob to retract locking bolts  105 . When the current to solenoid  122  is turned off, tab  129  holds down plunger  124  until the opening knob is turned to extend locking bolts  105 . Spring  125  then lifts plunger  124 , thus blocking tab  129  again and locking the safe. 
         [0029]    Bypass lock  112  passes through safe door  102  from the front and is affixed to safe door  102 . Bypass lock cam  113  is affixed to the cylinder of bypass lock  112 . When the user inserts the correct key and rotates the lock cylinder, bypass lock cam  113  rotates clockwise and presses against plate  126 , depressing retractable plunger  124  and permitting the safe to be opened. 
         [0030]    Battery holder  106  contains four AA-type alkaline cells  107  in a series circuit. Cable  108  connects battery holder  106  to circuit board  109 . Ribbon cable  111  passes through slot  110  cut into door  102 , and connects circuit board  109  to the keypad on the front of the door. 
         [0031]    This embodiment is commonly used as described. However, it is flawed in that, if the entire safe assembly is accelerated downward and then abruptly stopped, retractable plunger  124 &#39;s inertia causes it to continue moving downward. There are two distinct vulnerabilities created by this. 
         [0032]    In the timing vulnerability, tab  129  is not in contact with retractable plunger  124  when the safe is impacted. Wheel  118  must be manually turned using the opening knob during the fraction of a second while plunger  124  is below the bottom of tab  129 . In practice, this is not difficult to accomplish, and after a few attempts, many people can open the safe using the timing vulnerability. All safes of the design shown in  FIG. 1  are vulnerable to the timing vulnerability. 
         [0033]    In the binding vulnerability, turning the opening knob moves tab  129  into light contact with retractable plunger  124 , causing plunger  124  to tilt slightly leftward inside solenoid  122 . If the safe is now impacted, plunger  124  will descend below tab  129  and return to its vertical orientation while compressing spring  125 . Spring  125  then causes plunger  124  to rebound. Plunger  124  contacts the bottom of tab  129  and stops. The safe can then be opened by further turning the opening knob. Not all solenoid-operated safes are vulnerable to the binding vulnerability, but no skill or timing is required to exploit this flaw. Children have allegedly opened safes accidentally while playing with them. 
         [0034]      FIG. 2  illustrates an exemplary embodiment of a solenoid-operated locking container  201 , which is protected against both the binding and timing vulnerabilities. Electromagnetic solenoid  203  has been modified, in that retractable plunger  204  has a T-shaped end cap  205 . A corresponding notch  206  has been cut into movable plate  211 . If movable plate  211  is moved into contact with plunger  204 , T-shaped end cap  205  engages notch  206  and prevents plunger  204  from descending when the safe is impacted. This protects against the binding vulnerability. 
         [0035]    Electromagnetic solenoid  208  is identical to solenoid  203  and is placed at a 180-degree angle to solenoid  203 . Cables  214  and  215  connect solenoids  203  and  208  to circuit board  213 . Both solenoids are energized simultaneously by circuit board  213  when the safe is electrically unlocked. Bypass lock cam  212  has two lobes, so when it is turned clockwise, the left side of bypass lock cam  212  presses against plate  210 , and the right side of bypass lock cam  212  presses against plate  207 , depressing both retractable plungers  204  and  209 , and permitting movable plate  211  to pass. 
         [0036]    If the safe is accelerated downward and then abruptly stopped, plunger  204  will move downward, while plunger  209  will continue to block movable plate  211 &#39;s motion. If the safe is accelerated upward and then abruptly stopped, plunger  209  will move upward while plunger  204  will continue to block movable plate  211 &#39;s motion. Since solenoids  203  and  208  are placed opposite each other, no impact will retract both plungers  204  and  209  simultaneously. This protects against the timing vulnerability. 
         [0037]      FIG. 3  shows the mechanical and electrical components of an exemplary embodiment  301  of an electromagnetic solenoid which is internally protected against impact. Solenoid  301  has a retractable plunger  302 . Plate  303  is affixed to plunger  302 , and compresses spring  304  when the solenoid coil  305  is energized via cable  308 . 
         [0038]    Solenoid  301 &#39;s retractable plunger  302  is removed and coated with a viscous fluid  306 , such as Nye Lubricants Fluorocarbon Gel #868 Damping Grease. When plunger  302  is replaced in solenoid  301 , some of fluid  306  will transfer to inner wall  307  of the solenoid body, forming a bead between inner wall  307  and retractable plunger  302 . 
         [0039]    It is also possible to apply viscous fluid  306  directly to inner wall  307 , or to both inner wall  307  and retractable plunger  302 . Coating plunger  302  is the easiest method. 
         [0040]    Viscous fluids such as damping grease are available in a range of viscosity grades, and the appropriate grade must be chosen based on the spring constant of spring  304 . A stronger spring  304 , combined with higher viscosity fluid  306 , provides greater impact resistance, but requires more electrical power to retract plunger  302 . 
         [0041]    When solenoid coil  305  is energized, viscous fluid  306  provides velocity-dependent dynamic friction between inner wall  307  and retractable plunger  302 , slowing the downward motion of plunger  302  without stopping it. Similarly, when solenoid coil  305  is turned off, viscous fluid  306  slows the upward motion of plunger  302 . 
         [0042]    If fluid-damped solenoid  301  is accelerated rapidly upward, viscous fluid  306  produces a high degree of velocity-dependent dynamic friction, preventing retractable plunger  302  from fully retracting. In this way, solenoid  301 &#39;s vulnerability to impact opening is reduced, compared to a solenoid without fluid damping. Solenoid  301  can be used alone, or in an upper and lower solenoid pair for maximum impact protection. 
         [0043]    Fluid-damped solenoid  301  has the further advantage of being silent or nearly silent in operation. A solenoid-operated locking mechanism is often used in firearm storage containers intended to be opened while an intruder is present in the house. The click of an undamped solenoid could alert the intruder to the user&#39;s location, while a silent operating mechanism would provide a tactical advantage for the user. 
       CONCLUSION 
       [0044]    The foregoing Detailed Description has disclosed, to those skilled in the field of mechanical engineering, how to construct a solenoid-operated locking container which is protected against impact-induced opening, and which can be unlocked by either electric current or a backup key. The opposed solenoids with T-shaped end cap and notch embodiment, and the viscous fluid embodiment, can be used together or separately. 
         [0045]    For the foregoing reasons, the Detailed Description is to be regarded as being in all respects exemplary and not restrictive, and the breadth of the device and method disclosed herein is to be determined not from the Detailed Description, but rather from the claims, as interpreted with the full breadth permitted by the patent laws.