Patent Application
20060005592
The present invention relates to combination locks, and more particularly to a combination lock having a structure that resists manipulation.
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.
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.
The combination lock according to one embodiment of the invention incorporates several features that simplify the structure as well as improve the lock's resistance to manipulation. For context,
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
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
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 (
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
Referring to
As shown in
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
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
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.
