Patent Publication Number: US-2006005592-A1

Title: Manipulation-resistant combination lock

Description:
TECHNICAL FIELD  
      The present invention relates to combination locks, and more particularly to a combination lock having a structure that resists manipulation.  
     BACKGROUND OF THE INVENTION  
      Combination lock structures, particularly those that are used in safes, must be designed to resist unauthorized manipulation. Knowledgeable locksmiths may pick combination locks by removing a dial, spindle and back cover plate of the lock and then using tools to manipulate the tumbler wheels in the lock or by slowly rotating the combination dial and observing the effects of the rotation (e.g., by feel, by listening to clicks in the lock, and/or by visual observation of a laser beam directed on the lock).  
      The combination dial is attached to a cam wheel having a roller that rides along an underside of a rocker arm. The rocker arm is made of metal and is attached to a lock housing via a screw. The cam wheel operates a plurality of tumbler wheels that each have a gate. If the gates are aligned with each other, a notch in the cam wheel allows a protrusion in a lever arm to drop downward into the notch and a bar attached to the lever arm to drop into the aligned gates, freeing a latch bolt to move into an unlocked position.  
      The cam wheel has a roller fastened to it. The roller rides against an underside of the rocker arm, which is coupled to the lever arm via a spring, to pull the second arm downward and move the protrusion toward the notch. As noted above, if the gates are also aligned with each other and the lever arm, the protrusion drops completely into the notch on the cam wheel, freeing the bolt. Ideally, the roller and rocker arm also hold the lever arm free of the cam wheel if the gates are not aligned; however, because cam wheels tend not to be perfectly round, the protrusion may ride on at least part of the circumference of the cam wheel, allowing a locksmith to detect the position of the cam wheel. The friction between the rocker arm and the roller, as well as the rigid attachment of the rocker arm on the housing, provides further information about the position of the cam wheel, making the lock easier to crack.  
      There is a desire for a combination lock that can resist manipulation without increasing the complexity of the lock structure.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to a combination lock having various features that make the lock manipulation-resistant. In one embodiment, the combination lock has a rocker arm with a curved underside section that contacts a roller on a cam that rotates when the lock dial is rotated. The smooth curve and an angled contact portion on the rocker arm causes the force applied to the rocker arm by the roller to be gradual rather than abrupt, obscuring the contact point between the rocker arm and the roller. A spring may support the rocker arm against the lock housing to allow both translational and rotational movement of the rocker arm. The rocker arm structure and the spring cause a fence on a lock lever to contact wheels in the lock in an unpredictable manner.  
      The lock may also include various spring-biased relocking devices. The springs in the relocking devices are biased away from the travel path of the bolt when the back cover is attached to the housing. In one embodiment, the relocking device is a torsional spring attached to the housing. The torsional spring is held against its biasing force by a tab that protrudes through the housing. In another embodiment, the relocking device is a linear spring having a contact portion on the first end and a second end that is lifted away from the travel path of the bolt when the contact portion is depressed by a projection on the back cover. The linear spring is disposed in a slot in the housing, making it inaccessible to locksmith tools. Regardless of the specific device configuration, removal or displacement of the back cover will release the relocking device, causing the spring biasing force in the device to move the device in the travel path of the bolt and prevent it from moving to an unlocked position.  
      In another embodiment, the inventive combination lock decreases the dial span of the lock by incorporating a toothed washer having a trapezoidal tooth and a corresponding trapezoidal notch on a tube that supports the wheels in the lock housing. The engagement between the tooth and the notch eliminates transfer of rotation from one wheel to another. The trapezoidal shapes eliminate air gaps between the tooth and the notch, tightening the dial span of the lock.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exploded view of a combination lock according to one embodiment of the invention;  
       FIGS. 2A through 2D  illustrate an operation of a rocker arm and roller in the lock of  FIG. 1  according to one embodiment of the invention;  
       FIG. 3  illustrates first and second relocking mechanisms according to one embodiment of the invention, with the first relocking mechanism in a released state;  
       FIGS. 4A and 4B  are section views illustrate the second relocking mechanism in a biased state and a released state, respectively;  
       FIGS. 5A and 5B  are sectional perspective views illustrating the first relocking mechanism in a biased state and a released state, respectively; and  
       FIG. 6  is a representative diagram of a toothed washer according to one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      The combination lock according to one embodiment of the invention incorporates several features that simplify the structure as well as improve the lock&#39;s resistance to manipulation. For context,  FIG. 1  illustrates the main components of a combination lock  100  according to one embodiment of the invention. Note that for clarity, not all of the figures will show every component in the lock  100 .  
      The lock  100  contains a housing  102  and a back cover  104  to contain the lock components. The lock  100  includes a rocker arm  106  that is resiliently supported against the housing by a spring  108 . The rocker arm  106  has a slot  110  that cooperates with a protrusion  112  on a lever  114  that drops downward when the lock is unlocked to release a bolt  116 . As the lever  114  pivots and as the rocker arm  106  moves, the protrusion  112  slides in the slot  110 . The cooperation between the protrusion  112  and the slot  110  eliminates the need for a separate spring to operably connect the rocker arm  106  to the lever  114 .  
      The lever  114  has a fence  118  that rides on top of a plurality of wheels  120  that are mounted on a tube  122  formed in the housing  102 . The wheels  120  are turned by rotating a numbered dial (not shown). Each wheel  120  also has a gate  140 . When the wheels  120  are turned such that the gates  140  all align with each other and with the fence  118  on the lever  114 , the fence  118  drops down into the gates  140 , releasing the bolt  116  and allowing the bolt  116  to move to an open position. One or more toothed washers  141  may be included to engage the tube  122  to hold non-rotating wheels  120  in place as one wheel  120  is rotating.  
      Rotation of the dial causes a cam  144  to rotate, thereby causing the wheels  120  to selectively rotate depending on the dial position and rotational direction. As shown in  FIGS. 2A through 2D , the cam  144  has a roller  146  attached to or integrally formed thereon that contacts the rocker arm  106  as the cam  144  rotates. The rocker arm  106  moves slightly when the roller  146  contacts a curved underside section  148  of the rocker arm  106 , lifting the lever  114  slightly away from the wheels  120  to provide a smooth feel and obscure the positions of the wheels  120  as they are rotated ( FIGS. 2A through 2C ). The underside of the rocker arm  106  is curved smoothly to obscure the contact point between the rocker arm  106  and the roller  146 .  
      Also, the spring  108  forces the rocker arm  106  upward when the roller  146  does not contact the rocker arm  106 , forcing the lever  114  upward away from the wheels  120 . Lifting the lever  114  prevents contact between the fence  118  and the wheels  120 , making it impossible to test the locations of the gates  140  by riding the fence  118  along the wheels  120  as the wheels  120  rotate or by rotating the dial to detect when then fence  118  contacts the wheels  120 . Instead, the fence  118  drops downward only once per revolution of the cam  144 , when the roller  146  contacts the rocker arm  106 . Moreover, when the fence  118  does drop downward, the lost motion provided by the spring  108  prevents the fence  118  from contacting the same points on the wheels  120  during each revolution and in both rotational directions, further obscuring the positions of the gates  140  at any given time.  
      More particularly, the curved underside section  148  has a slightly angled portion  149  at a end contact point at which the rocker arm  106  makes initial contact with the rocker arm  106  when the cam  144  is rotating clockwise. The roller  146  will contact the angled portion  149  of the rocker arm  106  at an angle, rather than straight on, causing the force applied to the rocker arm  106  by the roller  146  to be gradual rather than abrupt. This gradual contact between the rocker arm  106  and the roller  146 , caused by the angled portion  149  of the curved underside section  148 , introduces an error in the rocker arm movement by constantly changing the leverage force on the rocker arm  106  each time the roller  146  makes contact.  
      This error makes it more difficult to detect the wheel  120  position, and therefore the lock combination, via physical feedback at various lock dial positions.  
      In one embodiment, the rocker arm  106  is made out of plastic instead of metal. The natural lubricity of the plastic eliminates the need for a multi-part roller assembly and smoothes the movement of the roller  146  or any other similar structure against the rocker arm  106 . Further, the rocker arm  106  can be made flexible to further make the movement of lock components smoother and to provide additional range of motion.  
      As noted above with respect to  FIG. 1 , the rocker arm  106  is movably coupled to the housing  102  by a spring  108 . The housing  102  also has a pin  150  that is disposed in an oval-shaped opening  152  in the rocker arm  106 . This oval-shaped opening  152  offers an escapement structure to absorb any motion caused by rotation of the cam  144  and the resulting contact with the roller  146 . In one embodiment, the spring  108  and pin  150  allow the rocker arm  106  to translate as well as rotate as the roller  146  contacts the rocker arm  106 . This play in the rocker arm  106  caused by the spring  108 , either alone or combined with the curved underside portion  148 , ensures that the roller  146  gradually applies force to the rocker arm rather than abruptly moving the rocker arm  106  upon contact. The error in the rocker arm  106  movement caused by the spring  108  and the curved underside portion  148  makes it much harder to predict when the rocker arm  106  will actually start moving upon contact with the roller  146 , thereby reducing any physical feedback information that locksmiths can use to deduce the positions of the gates  140 .  
      This structure reduces the total number of lock components in the lock and provides a more secure operable connection between the rocker arm  106  and the lever  114 . Further, because the slot  110  provides a lower range of motion for the lever  114 , the protrusion  112  on the lever  114  reliably holds the lever  114  away from the wheels  120  to minimize or eliminate contact between the fence  118  and the wheels  120  until the fence  118  drops to test for aligned gates  140 , allowing the bolt  116  to move to an open position ( FIG. 2D ). This eliminates further potential physical feedback information from the locksmith regarding the positions of the gates  140 .  
      As shown in the Figures, the inventive combination lock may also include a torsional spring  200  disposed on a front surface of the housing  102 , near the top of the lock  100 . The torsional spring  200  acts as a relocking mechanism that is biased to block the lock bolt  116  from moving into an open position when the back cover  104  of the lock is removed or displaced from the housing  102 , releasing the torsional spring  200 .  
      More particularly, as shown in  FIG. 5A , the back cover  104  has a tab  202  that fits into a slot  204  in the housing  102 . The torsional spring  200  is disposed in a recessed portion  206  on the front of the lock housing near the slot  204  so that is inaccessible to locksmith tools. When the back cover  104  is attached to the housing  102 , the tab  202  projects into the slot  204  to hold the torsional spring  200  against its biasing force so that a leg portion  208  is held away from the travel path of the bolt  116 . As a result, the bolt  116  is allowed to move freely between the locked and unlocked positions if the gates  140  in the wheels  120  are properly aligned and the lever  114  drops down to release the bolt  116 . Thus, as long as the back cover  104  is properly attached to the housing  102 , the tab  202  in the back cover  104  will hold the torsional spring  200  away from the bolt path.  
      Referring to  FIGS. 3 and 5 B, if the back cover  104  is displaced or removed from the housing  102  (e.g., in an attempt to pick the lock), the tab  202  withdraws from the slot  204  in the housing, freeing the torsional spring. The biasing force of the spring  200  causes the leg portion  208  of the spring  200  to move into the travel path of the bolt  116 , blocking the bolt  116  from moving into the unlocked position even if the gates  140  are aligned with the fence  118  to ordinarily allow unlocking. Thus, any manipulation of the wheels  120  while the back cover  104  is displaced or removed will not allow the lock to be unlocked, even if the lever  114  has dropped down to free the bolt  116 . Further, replacing the back cover  104  onto the housing  102  still will not move the leg portion  208  of the spring  200  out of the bolt&#39;s path due to the biasing force of the spring  200 . In one embodiment, the biasing force of the spring  200  causes the leg portion  208  to drop below the slot  204 , making it impossible for the tab  202  to re-engage with the leg portion  208  once the back cover  104  has been displaced. By placing the spring  200  in a recessed portion  206  in the middle of the lock housing  102 , the relocking mechanism formed by the spring  200  is much more difficult to access and manipulate with tools.  
      As shown in  FIGS. 3, 4A  and  4 B, the combination lock may include another or an alternative relocking mechanism in the form of a substantially V-shaped linear spring  250  having first and second feet  252 ,  254  at the ends of the V. Note that the linear spring  250  may have other configurations as well as long as one end of the spring is lifted as the other end is depressed and if the biasing force of the spring is generally orthogonal to the bolt&#39;s travel direction. In the illustrated embodiment, the first foot  252  is anchored to the housing  102  and the second foot  254  is biased to fall in the travel path of the bolt  116 . The bolt  116  itself has a notch  256  that is aligned with the second foot  254  when the bolt  116  is in the locked position. In one embodiment, the linear spring  250  is disposed in a slot  258  in an interior portion of the housing  102 . The slot  258  is disposed generally perpendicular to the travel direction of the bolt  116 .  
      When the back cover  104  is properly attached to the housing  102 , a projection  260  on the back cover  104  presses against a contact portion  262  of the linear spring  250 . The contact portion  262  is at an end substantially opposite the end of the second foot  254  so that when the contact portion  262  moves downward, the second foot  254  lifts upward. The contact portion  262  and moves downward inside the slot  258  against the spring biasing force of the linear spring  250 . When the projection  260  presses downward against the contact portion  262 , the second foot  254  lifts out of the path of the bolt  116 . Thus, the bolt  116  is able to move between the locked and unlocked positions freely past the second foot  254 .  
      As shown in  FIG. 4B , if the back cover  104  is displaced or removed during an attempt to manipulate the lock  100 , the projection  260  on the back cover  104  will separate from the contact portion  262  and release the linear spring  250 . The biasing force of the linear spring  250  will cause the contact portion  262  of the linear spring  250  move upward, causing the second foot  254  to drop downward into the notch  256  formed in the bolt  116 . The engagement of the second foot  254  in the notch  256  immobilizes the bolt  116 , making it impossible to move the bolt  116  into the unlocked position.  
      The slot  258  makes the linear spring  250  virtually inaccessible from any angle except via the projection  260  on the back cover  104 . As a result, it is difficult to gain access to the spring  250  with locksmith tools. Moreover, the angle at which the biasing force needs to be applied to lift the second foot  254  is virtually impossible from any direction other than the direction applied by the projection  260 . Thus, the spring  250  cannot be biased to allow the bolt  116  to move via tools inserted from the front of the lock through the tube  122 .  
      A given lock may incorporate either the torsional spring  200  or the linear spring  250  as the relocking mechanism. For added security, the lock  100  may incorporate both types of springs  200 ,  250 . Because the springs  200 ,  250  are disposed in different locations, biased in different directions, engage with the bolt  116  at different locations, and operate independently of each other, incorporating both springs  200 ,  250  makes the lock  100  extremely difficult to manipulate with tools.  
      For convenience, it is desirable to allow the lock to open if the operator moves the lock dial slightly (e.g., one-half gradation) off from the intended mark. However, it is also desirable to prevent the lock from opening if the operator dials any part of the combination one full mark or more away from the intended mark, for security reasons. Creating a lock with tolerances that accomplish this can be difficult. Ideally, the tolerances are set to prevent any given wheel from moving when it is not intended to move. Any unintended movement increases the rotational “slop” in the lock, allowing combinations other than the intended combination to open the lock (i.e., “dial span”).  
      As noted above with respect to  FIG. 1 , toothed washers  141  may be disposed on the tube  122 . Currently known structures form a square tooth on the toothed washer that fits in a square notch (not shown) on the tube  122 . This configuration ensures that the toothed washer  141  will easily engage with the notch, but size tolerances between the tooth and the notch creates an air gap that creates rotational slop. Depending on the amount of slop present in the lock and the resulting increased dial span, the actual number of possible combinations that can open the lock due to the slop may increase to undesirable levels.  
       FIG. 6  shows a structure for the toothed washer  141  and the tube  122  to improve security in the lock in greater detail. In this structure, the toothed washer  141  has a trapezoidal tooth  300  that engages a corresponding trapezoidal notch  302  formed on the tube  122  in the lock housing  102  ( FIG. 1 ) to prevent transfer or rotation between wheels  120 . The trapezoidal tooth  300  and notch  302  ensure that the tooth  300  can easily and reliably fit within the notch  302  while eliminating the airspace that normally is present between a conventional washer tooth and notch.  
      In one embodiment, the toothed washer  141  is slightly out of round and is stretched slightly to fit the tube  122 , creating a loaded condition on the toothed washer  141 . This washer structure eliminates transfer of rotation from one wheel to another, which would ordinarily cause the rotation of an intended wheel to inadvertently rotate another wheel that should remain stationary.  
      By shaping the tooth  300  on the washer  141  and the notch  302  on the tube  122  as trapezoids, the tooth  300  can easily center itself and fit snugly into the notch  302  with virtually no airspace between the tooth  300  and the notch  302  This snug fit ensures that there is little or no unintended transfer of rotation from one wheel  120  to another as the cam  144  reverses direction while the combination is dialed into the lock. As a result, the inventive tooth and gate structure eliminates rotational slop, tightens the dial span and therefore increases the number of unique settings that the dial can have for a given combination.  
      All of the above features, either alone or in combination, improve the manipulation resistance of a combination lock and further enhance security.  
      It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.