Patent Publication Number: US-6904778-B2

Title: Mechanical combination lock

Description:
FIELD OF THE INVENTION 
   The invention relates to combination locks and, in particular, to combination locks that resist surreptitious compromise by radiographic imaging or automatic dialers and that accommodate combination changes while retaining the resistance against surreptitious compromise. 
   BACKGROUND OF THE INVENTION 
   Combination locks are used to secure lockable, high-security enclosures, such as vaults, safes, and cabinets, that afford controlled access to stored items. Mechanical combination locks rely on the rotation of an external dial to manipulate various mechanical elements housed inside a lock casing to register gates in rotatable tumbler wheels or gate wheels with at least one fence carried by a movable fence bar. When the tumbler wheel gates and fences are registered by the entry of a proper combination, the dial may be used to retract a lock bar or dead bolt so that the enclosure can be opened and accessed. 
   Mechanical combination locks are susceptible to illicit or surreptitious attack by operation of an automatic dialer. The automatic dialer, which is coupled with the lock&#39;s dial, systematically dials different combinations of the mechanical combination lock. If a particular combination fails, the automatic dialer proceeds to dial other successive combinations in an attempt to unlock the lock. For example, for a three-tumbler combination lock, the automatic dialer parks one gate wheel at a specific combination number, dials all possible pairs of combination numbers for the other two gate wheels and attempts to retract the dead bolt at each dialed pair, increments the combination number of the first gate wheel, and repeats this process until the proper combination is discovered. Given sufficient time to perform the trial-and-error manipulation, the automatic dialer is particularly effective in compromising the access control afforded by a mechanical combination lock. 
   Conventional combination scrambler mechanisms have been developed for use in mechanical combination locks that rotate one of the gate wheels as an automatic dialer attempts to systematically dial all possible combinations and to retract the lock bolt at each dialed combination. The rotation of the gate wheel prevents the automatic dialer from parking the gate wheel at a fixed angular location and relying upon that angular location as a reference point. However, conventional combination scrambler mechanisms increment the angular orientation of the gate wheel by an equal angular increment each time that an attempt is made to retract the lock bolt. Because the angular increment is constant and predictable, sophisticated automatic dialers can compensate for changes in the parked angular position of the gate wheel imparted by the combination scrambler by a simple correction factor consisting of the number of attempts multiplied by the constant angular increment. 
   Mechanical combination locks are also susceptible to surreptitious attack by radiographic imaging methods. Penetrating radiation, such as x-rays and neutrons, can be used to image the internal elements, such as the tumbler wheels and tumbler wheel gates, inside the lock case otherwise hidden from view. As a result, the angular locations of the internal elements, such as the gates, of conventional mechanical combination locks may be observed by radiographic imaging. 
   The tumbler wheels of mechanical combination locks may be designed to resist radiological detection by, for example, disguising one true gate among multiple false gates each having a similar construction to the true gate. However, conventional false gates are incapable of providing adequate protection or add significantly to the cost of manufacture. In addition, other internal elements, such as fixed-position features on a tumbler wheel or a combination change mechanism, of the mechanical combination lock have a fixed angular position relative to one or more of the gates. The internal elements may be used as fixed reference points or features for determining the angular location of the true gate despite the presence of multiple false gates. As a result, the presence of false gates alone frequently cannot defeat the use of radiographic imaging for determining the angular locations of lock internal elements, such as tumbler wheel gates. 
   Accordingly, there is a need for combination locks having an increased level of security, while at the same time overcoming many of the shortcomings of conventional mechanical combination locks. 
   SUMMARY OF THE INVENTION 
   The present invention provides apparatus and methods that increase the level of security afforded by a mechanical combination lock. A combination lock in accordance with the principles of the present invention is provided with a rotatable first gate wheel having a first gate, a rotatable second gate wheel having a second gate, at least one fence capable of being engaged with the first and the second gates, and a combination entry device capable of rotating the first and the second gate wheels for varying an angular alignment between a corresponding one of the first and second gates and the one fence. When a proper combination is entered, the first and second gates are aligned angularly with the fence. If one of a plurality of improper combinations is entered, at least one of the first and the second gates is non-aligned angularly with the fence. The combination lock includes a lock bolt actuatable between a locked position and an unlocked position and a lock-bolt drive mechanism capable of actuating the lock bolt from the locked position to the unlocked position, after the proper combination is entered, and capable of attempting to actuate the lock bolt from the locked position to the unlocked position, after one of the plurality of improper combinations is entered. The combination lock further includes a combination scrambler configured to rotate the first gate wheel by first and second different angles if the lock-bolt drive mechanism attempts to move the lock bolt from the locked position to the unlocked position after entry of successive improper combinations. 
   The combination scrambler of the invention increases the resistance of the combination lock to unauthorized opening by an attempt to sequentially enter all possible lock combinations, for example, by operation of an automatic dialer. Specifically, the combination scrambler prevents at least one of the gate wheels from being parked with a predictable angular orientation while the other gate wheels are dialed to enter serial combinations and an attempt is made at each dialed combination to open the combination lock. To that end, the combination scrambler moves the associated gate wheel by unequal angular increments as possible combinations are successively or consecutively dialed on the other gate wheels and an attempt is made to open the lock at each successive or consecutive combination. As a result, the automatic dialer cannot rely on predictability in the angular location of the scrambled gate wheel or gate wheels acted upon by the combination scrambler and cannot otherwise sense the operation of the combination scrambler. In other words, the automatic dialer loses track of the angular position of the scrambled gate wheel as the other gate wheels are serially rotated and, thereafter, cannot systematically increment the angular position of the scrambled gate wheel. The operation of the combination scrambler significantly lengthens the time required for an automatic dialer to compromise the combination lock. 
   In accordance with one aspect of the invention, a combination lock comprises a fence, a combination entry device, a drive hub operatively coupled with the combination entry device, a rotatable gate wheel assembly having a gate wheel with a gate configured to be engageable with the fence, a lock bolt movable between locked and unlocked positions, and a lock-bolt drive mechanism configured for moving the lock bolt from the locked position to the unlocked condition when the gate is aligned angularly with the fence by operation of the combination entry device. The gate wheel assembly includes a first outer wheel and a second outer wheel in which the gate wheel is positioned between the first and the second outer wheels. The gate wheel assembly is rotatable in response to operation of the combination entry device for changing the relative angular alignment between the gate and the fence. The first and the second outer wheels have a coupled condition in which the gate wheel assembly is coupled for rotation with the drive hub, and an uncoupled condition in which the gate wheel assembly is uncoupled from, and rotatable independently of, the drive hub. The combination lock further includes a combination change key or mechanism operative for selectively manipulating the first and the second outer wheels to provide the coupled and uncoupled conditions. 
   The combination change mechanism of the invention may be constructed such that it lacks any feature, such as an opening or a rivet, that would be visible in a radiographic image of the combination lock. As a result, no feature of the combination change mechanism bears a predictable relationship relative to the gate of the combination lock in the radiographic image. Similarly, the gate wheels are free of features that would be visible and recognizable in a radiographic image of the combination lock. 
   In accordance with another aspect of the invention, a combination lock comprises a fence and a rotatable gate wheel operatively coupled with the combination entry device. The gate wheel includes an outer rim, an axis of rotation, a first projection extending radially outward from the outer rim, and a plurality of second projections extending radially outward from the outer rim. The first and the second projections are circumferentially arranged with a spaced relationship about the outer rim. The first projection has a different shape than the second projections, in which the first projection has a triangular or irregular cross-sectional profile in a radial direction relative to an axial centerline of the gate wheel. The first projection and an adjacent one of the second projections define a first recess shaped to permit engagement by the fence. A plurality of second recesses are defined between adjacent pairs of second projections. 
   The combination lock further includes a combination entry device capable of rotating the gate wheel about the axis of rotation for changing the relative angular alignment between the first recess and the fence, a lock bolt movable between locked and unlocked positions, and a lock-bolt drive mechanism configured for moving the lock bolt from the locked position to the unlocked condition when the first recess is aligned with the fence. 
   According to the principles of this aspect of the invention, the true gate has an appearance in a radiographic image that is substantially indistinguishable from the multiple false gates of the mechanical combination lock. According to the principles of the invention, the projections defining the false and true gates provide imaged features that cannot be distinguished from one another. As a result, radiographic imaging cannot be relied upon for determining the angular location of the true gate on the gate wheel. 
   These and other advantages, objectives and features of the invention will become more readily apparent to those of ordinary skill upon review of the following detailed description of an illustrative embodiment of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a combination lock constructed according to the principles of the invention. 
       FIG. 2  is a perspective view of the interior of the lock case of the combination lock of  FIG. 1  in which one of the tumbler wheel assemblies is exploded. 
       FIG. 2A  is an exploded perspective view of one of the tumbler wheel assemblies of FIG.  2 . 
       FIG. 3  is an exploded rear perspective view of the combination lock of  FIG. 1  in which the rear cover is removed. 
       FIG. 4  is a partial cross-section view taken generally along line  4 — 4  of FIG.  3 . 
       FIG. 4A  is an enlarged perspective view partially broken away of FIG.  4 . 
       FIGS. 5A  is a rear elevation view with the rear cover removed taken generally along line  5 A— 5 A in FIG.  1 . 
       FIGS. 5B-5F  are rear elevation views similar to  FIG. 5A  showing the operation of a combination scrambler according to the principles of the invention. 
       FIG. 6  is a partial cross-section view taken along line  6 — 6  of  FIG. 5A  in which the combination lock is in the unlocked condition. 
       FIG. 7  is a partial cross-section view similar to  FIG. 6 , in which the combination dial and spindle have been pushed inwardly into the lock case to verify the accuracy of a dialed combination. 
       FIGS. 8A-8C  are cross-sectional views of a portion of the combination lock of the invention illustrating operation of a combination change key for changing the lock combination. 
       FIG. 9  is a cross-sectional view taken generally along line  9 — 9  in FIG.  8 A. 
       FIG. 10  is a cross-sectional view taken generally along line  10 — 10  in FIG.  8 C. 
       FIG. 11  is a diagrammatic perspective view in which the change key is being actuated to move a gate wheel of one of the tumbler wheel assemblies. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference to  FIG. 1 , a combination lock  10  of the invention is mounted on a supporting door  12  of a safe, vault, cabinet or other high security enclosure. The combination lock  10  includes a substantially rectangular lock case  14  configured to be mounted using conventional fasteners against an inner surface of door  12 . A detachable rear closure or cover  15  closes the rear of the lock case  14  and operates for supporting various components of the combination lock  10 . 
   Secured to an outer surface of the supporting door  12  is a combination entry device in the form of a dial  16  having an outer periphery shrouded by a shield  18  and a knob  20  used to manually manipulate the dial  16 . Arranged with equal angular intervals about the outer periphery of the dial  16  is a plurality of, for example, one hundred markings. The periphery of shield  18  conceals the markings from view other than markings located within a circumferential sight opening  22 . An indicator  24  of shield  18  overhangs a small portion of the outer periphery of the dial  16  and includes a stationary index mark for indicating the current marking value as dial  16  is rotated. 
   Dial  16  is coupled with a spindle  28  extending rearwardly through the thickness of the supporting door  12  and into the lock case  14 . The spindle  28  is journalled for free rotation within a tubular tumbler post  30 , as best visible in  FIGS. 6 and 7 , projecting inwardly from a front wall  32  of the lock case  14 . The spindle  28  is also supported by the tumbler post  30  for axial movement relative to the tumbler post  30  over a limited linear displacement distance. The dial  16  and spindle  28  are biased outwardly from the lock case  14  by a biasing element (not shown). 
   With reference to  FIGS. 2 and 5A , a lock bolt  34  projects outwardly through an opening provided in a side edge of lock case  14 . The lock bolt  34  is movable or actuatable in a suitable guideway provided in the lock case  14  between a locked position (FIG.  5 A), in which an exposed length of the lock bolt  34  is extended from the lock case  14 , and an unlocked position (FIG.  5 F), in which the lock bolt  34  is retracted to be positioned substantially within lock case  14 . A pair of pivotal locking pawls  36   a ,  36   b  are configured for engaging respective stop surfaces  40   a ,  40   b , when the lock bolt  34  is in the locked position, so as to resist an inwardly-directed tampering force applied to the protruding free end of the lock bolt  34 . The locking pawls  36   a ,  36   b  are pivoted by a sliding release mechanism  38  to disengage the stop surfaces  40   a ,  40   b  when a correct combination is dialed to free the lock bolt  34  for retraction into lock case  14 . 
   Manual manipulation of the dial  16  operates a lock-bolt drive mechanism capable of moving the lock bolt  34  between its locked position and unlocked positions if a proper combination is entered. The lock-bolt drive mechanism includes spindle  28 , a drive cam  46  and a bolt lever  42 . One end of the bolt lever  42  is pivotally attached to the lock bolt  34 . An opposite end of the bolt lever  42  includes a lever nose  43  that is selectively engageable with a notch  44  in a drive cam  46  by lowering when a proper combination is entered. Entry of a proper combination angularly aligns the notch  44  with the lever nose  43 . The bolt lever  42  is raised from the drive cam  46  so that, unless a proper combination is entered, the lever nose  43  is normally disengaged or otherwise uncoupled from the notch  44  in the drive cam  46 . A biasing element or spring  51  biases the bolt lever  42  in a direction for moving the lever nose  43  toward the notch  44 . 
   The drive cam  46  and spindle  28  are coupled together for concurrent rotation by a pair of spline keys  47 , as best visible in  FIG. 5A , inserted into corresponding registered pairs of splines in the spindle  28  and spline ways in the drive cam  46 . Rotation of the spindle  28  and drive cam  46 , with the lever nose  43  and notch  44  coupled, operates to retract the lock bolt  34  from its locked position to its unlocked position only if a proper or correct combination is entered. Following entry of an improper or incorrect combination, the lever nose  43  and notch  44  are not aligned and cannot be coupled when the bolt lever  42  is lowered, so that rotation of the spindle  28  and drive cam  46  is futile and results in an unsuccessful attempt to retract the lock bolt  34  from its locked position to its unlocked position. 
   With reference to  FIGS. 2 ,  2 A,  3  and  4 , housed within the lock case  14  is a wheel pack consisting of a front tumbler wheel assembly  48 , a middle tumbler wheel assembly  50 , and a rear tumbler wheel assembly  52  that are each rotatably journalled about the outer circumference of the tumbler post  30 . The three tumbler wheel assemblies  48 ,  50  and  52  have a coaxial, juxtaposed spaced relationship and are independently rotatable about an axis of rotation  53  when the dial  16  is manipulated to enter a combination. Each number of the proper three-number combination is associated with a corresponding one of the three tumbler wheel assemblies  48 ,  50  and  52 . 
   Projecting away from the drive cam  46  is a pair of drive pins or fly stops (not shown) that cooperate with a fly  54  to supply a lost motion connection with a drive hub  56  mechanically coupled with the rear tumbler wheel assembly  52 . The fly  54  includes projections that engage corresponding ones of the fly stops on the drive cam  46 . A similar lost motion connection is provided by respective flies, such as fly  54 , between the drive hub  56  of each of the other tumbler wheel assemblies  48 ,  50  to provide driven rotation as the drive cam  46  is rotated by revolution of spindle  28 . The lost motion connections permit each of the tumbler wheel assemblies  48 ,  50 ,  52  to be individually picked up for rotation as a combination is entered using dial  16  and to be individually parked at a specific angular orientation so that another of the tumbler wheel assemblies  48 ,  50 ,  52  may be rotated without changing the angular orientation of the parked ones of the tumbler wheel assemblies  48 ,  50 ,  52 . 
   Located between the front tumbler wheel assembly  48  and the front wall  32  of lock case  14  is a drive cam  41  having a number of serrations or teeth  41   a . A travel arm  45  is movable for causing a number of serrations or teeth  49  on one end of travel arm  45  to become engaged with the teeth  41   a  of the drive cam  41  when the dial  16  is manipulated to return the lock bolt  34  from the unlocked position to the locked position. An opposite end of the travel arm  45  is pivotally coupled with the sliding release mechanism  38 . Movement of the travel arm  45  moves the sliding release mechanism  38 , when teeth  49  are engaged with teeth  41   a  and the drive cam  41  is revolved by manipulation of dial  16  and rotation of spindle  28 , to cause the lock bolt  34  to extend from the unlocked position to the locked position. 
   The travel arm  45  and drive cam  41  constitute components of the lock-bolt drive mechanism. The drive cam  46 , which operates to retract lock bolt  34  from the locked position to the unlocked position, does not operate to extend the lock bolt  34  from the unlocked position to the locked position. Instead, the travel arm  45  and drive cam  41  cooperate to transfer motion from the spindle  28  to the lock bolt  34  for extending the lock bolt  34 . The cooperation of the drive cam  41  and travel arm  45  require manipulation of the dial  16 , such as by reentering the proper lock combination, to move each of the tumbler wheels  48 ,  50 ,  52  out of position relative to the fences  90 ,  91 ,  92 , while the lock bolt  34  is retracted, before the lock bolt  34  is extendible by operation of the drive cam  41  and travel arm  45  to relock combination lock  10 . A similar mechanism for extending a lock bolt from an unlocked position to a locked position is described in U.S. Pat. No. 5,343,723, the disclosure of which is incorporated by reference herein in its entirety. 
   Because the tumbler wheel assemblies  48 ,  50  and  52  are constructed in a substantially identical manner, the following discussion of rear tumbler wheel assembly  52  is equally applicable to tumbler wheel assemblies  48  and  50 . It is contemplated by the invention that, although three individual wheel assemblies  48 ,  50 ,  52  are shown in this embodiment of the invention, two or more individual wheel assemblies may cooperate to form a wheel pack for use with combination lock  10 . 
   With specific reference to  FIGS. 2 and 2A , rear tumbler wheel assembly  52  includes a pair of generally annular outer wheels  58 ,  60 , a pair of generally annular gate wheels  62 ,  64  positioned between the outer wheels  58 ,  60 , and a generally annular coupling or middle wheel  66  positioned between the gate wheels  62 ,  64 . The rear tumbler wheel assembly  52  is staked or pin riveted together by deforming or upsetting the free end of each of a plurality of tabs or pins  57  ( FIG. 2A ) projecting from outer wheel  58  that protrude through individual arcuate slots  68  provided in outer wheel  60  so as to capture a corresponding one of a plurality of fastening elements  70 . The arcuate slots  68  permit the outer wheels  58 ,  60  to be relatively rotatable, as described herein, while maintaining their staked or pin riveted mutual attachment for securing the various components of the rear tumbler wheel assembly  52  together. The two gate wheels  62 ,  64  and middle wheel  66  are united as an assembly and rotate collectively as an assembly about axis  53 . 
   An inner peripheral rim of the middle wheel  66  includes a plurality of teeth  72  and an outer peripheral rim of drive hub  56  includes a plurality of teeth  74  that are spaced radially from teeth  72 . Drive hub  56  is disposed inside the inner diameter of middle wheel  66  and operates to transfer rotation from the spindle  28  and drive cam  46  to the rear tumbler wheel assembly  52 , as described herein. A central opening of the drive hub  56  is rotatably coupled with the tumbler post  30 . Arranged with equal angular spacings about the outer peripheral rim of outer wheel  58  is a plurality of triangular teeth  76  and, similarly, arranged with equal angular spacings about the outer peripheral rim of outer wheel  60  is a plurality of triangular teeth  78 . Triangular teeth  76  and  78  permit the scrambler mechanism  96  and combination change key  140 , each described herein, to interact with or otherwise operate upon the outer wheels  58 ,  60 . 
   With reference to  FIGS. 2A ,  4  and  4 A, disposed with uniform angular spacing about the rim of gate wheel  62  is a plurality of projections  80   a  having a radially-measured cross-sectional profile and a single projection  82   a  having a different radially-measured cross-sectional profile. Similarly, a plurality of projections  80   b  having a radially-measured cross-sectional profile and a single projection  82   b  having a different radially-measured cross-sectional profile are disposed with uniform angular spacing about the rim of gate wheel  64 . Each of the projections  80   a,b  and  82   a,b  extend radially outward from the rim from the corresponding one of the gate wheels  62 ,  64 . Projections  80   a,b  may have a generally trapezoidal cross-sectional profile viewed in a radial direction relative to common axis  53  (FIGS.  2  and  3 ), which is aligned with the centers of gate wheels  62 ,  64 . Generally, projections  82   a,b  have a non-trapezoidal cross-sectional profile viewed radially relative to axis  53 . In a preferred embodiment, projections  82   a,b  have a generally triangular cross-sectional profile that includes a corresponding inclined surface  84   a,b , which may be flat or planar. The cross-sectional profile of projections  82   a,b  may be right triangular in which a respective hypotenuse of each right triangle defines a corresponding one of the inclined surfaces  84   a,b . The inclined surfaces  84   a,b  may extend, as shown, across the dimension of the projections  82   a,b  that is generally parallel to axis  53  or may only partially extend thereacross. In one specific embodiment of the invention, the inclined surfaces  84   a,b  are each angled at about 36°. Gate wheels  62 ,  64  are angularly aligned about axis  53  relative to one another so that the inclined surfaces  84   a,b  lie substantially in a common plane and, typically, inclined surfaces  84   a,b  are coplanar to within about ±0.25°. 
   The gaps or recesses  81   a  between adjacent pairs of projections  80   a  and the recesses  81   b  between adjacent pairs of projections  80   b  define corresponding sets of false gates on the corresponding one of gate wheels  62 ,  64 . Typically, the number of false gates on each of the gate wheels  62 ,  64  is at least ninety-nine. The gap or recess  83   a  between projection  82   a  and the one of projections  80   a  adjacent to inclined surface  84   a  defines a portion of a true gate on gate wheel  62 . Similarly, the gap or recess  83   b  between projection  82   b  and the one of projections  80   b  adjacent to inclined surface  84   b  defines another portion of a true gate on gate wheel  64 . The false and true gates each correspond in angular position with a corresponding marking provided on the outer periphery of dial  16 . The marking on dial  16  corresponding to the true gate provides one number in the proper combination for combination lock  10 . 
   With reference to  FIGS. 3 ,  4 ,  6  and  7 , pivotally coupled with the lock case  14  is a fence bar  86  having a plurality of, for example, three fences  90 ,  91 ,  92  each associated with a corresponding one of the tumbler wheel assemblies  48 ,  50 ,  52 . Extending from the fence bar  86  toward the rear cover  15  is a flange  88  that is coupled with a corresponding flange  42   a  of the lever arm  42  so that the movements of the fence bar  86  and lever arm  42  are correlated as the dial  16  is manipulated to enter a combination and to attempt to unlock the combination lock  10 . Each of the fences  90 ,  91 ,  92 , for example, fence  90  consists of a pair of axially-spaced prongs  94  overhanging the outer periphery and the gates, defined by recesses  81   a,b  and  83   a,b , of the respective gate wheels  62 ,  64  of front tumbler wheel assembly  48 . Similarly, fence  91  has prongs  94  that overhang the gates, defined by recesses  81   a,b  and  83   a,b , of middle tumbler wheel assembly  50  and fence  92  has prongs  94  that overhand the gates, defined by recesses  81   a,b  and  83   a,b , of rear tumbler wheel assembly  52 . Each prong  94  is angled to permit the fences  90 ,  91 ,  92  to engage the recesses  83   a,b  on each of the gate wheels  62 ,  64 . The pair of prongs  94  associated with each of the fences  90 ,  91 ,  92  have flat surfaces that are coplanar and that are angled to permit engagement with the respective recesses  83   a,b  but prohibit engagement with recesses  81   a,b . The middle wheel  66  defines an alignment guide that steers the lowering of fence  82  for bringing the fences  90 ,  91 ,  92  into properly alignment with the recesses  83   a,b.    
   The fence bar  86  will lower so that each of the prongs  94  fits into a corresponding one of the recesses  83   a,b  when a proper combination is entered to interrelate or register the angular orientation of the recesses  83   a,b  with the respective prongs  94  on fences  90 ,  91 ,  92 , the drive cam  46  is oriented in angular position with the notch  44  confronting the lever nose  43 , and the bolt lever  42  is capable of being lowered for engaging the lever nose  43  with the notch  44 . It is contemplated by the invention that each of the fences  90 ,  91 ,  92  may include a single prong  94  and that each tumbler wheel assembly  48 ,  50 ,  52  may include only a single one of the two gate wheels  62 ,  64  having a single true gate and multiple false gates. It is also contemplated by the invention that the fences  90 ,  91 ,  92  of fence bar  86  may be constructed as a single fence, which may or may not include multiple prongs  94 , that is engagable with the recesses  83   a,b  on the gate wheels  62 ,  64 . 
   The tumbler wheel assemblies  48 ,  50 ,  52  are configured to prevent surreptitious attack by radiographic imaging methods. To that end, the features of each of the tumbler wheel assemblies  48 ,  50 ,  52 , including but not limited to projections  80   a,b ,  82   a,b  and recesses  81   a,b ,  83   a,b , possess a rotational symmetry about axis  53  so that no single feature can be imaged in relation to the position of the true gates defined by recesses  83   a,b . In addition, the tumbler wheel assemblies  48 ,  50 ,  52  lack change key openings because of the construction of the combination change key  140 , described herein. Moreover, the true gates  82  on each of the tumbler wheel assemblies  48 ,  50 ,  52  are substantially indistinguishable or imperceptible from the recesses  81   a,b  defining false gates in a radiographic image. Moreover, the constructive overlapping in the radiographic image of the recesses  81   a,b ,  83   a,b  of a plurality of tumbler wheel assemblies  48 ,  50 ,  52  further obscures the angular location of the true gates defined by recesses  83   a,b  about the outer periphery of gate wheels  62 ,  64 . 
   With reference to  FIGS. 3 ,  4 ,  5 A and  5 B and in accordance with the principles of the invention, the combination lock  10  further includes a combination scrambler or scrambler mechanism, indicated generally by reference numeral  96 , which is configured to prevent surreptitious attack by operation of an automatic dialer. Specifically, the scrambler mechanism  96  rotates, for example, front tumbler wheel assembly  48  if an incorrect combination is entered and the dial  16  is pressed inwardly to attempt to retract the lock bolt  34 . The scrambler mechanism  96  includes a scrambler assembly  98  mounted to the lock case  14 , an actuator  100  operatively coupled with the scrambler assembly  98  by a drive pawl  102 , and a spaced-apart pair of projections  104 ,  106  projecting from the rear cover  15 . The actuator  100  includes an annular disk  108  having a central opening aligned concentrically with, and rotatable about, an arbor  110  of the drive cam  46 . The actuator  100  is also movable in an axial direction when the dial  16  and the spindle  28  are displaced axially relative to the tumbler post  30  by the application of an inwardly-directed force to knob  20 . 
   Extending circumferentially about the annular disk  108  of the actuator  100  and spaced radially inward from its outer peripheral edge is a pair of cam surfaces or inclined ramps  112 ,  114 . The inclined ramps  112 ,  114  are an angularly spaced approximately 180° apart and are located at equal radii from the center of the annular disk  108 , although the invention is not so limited. The inclined ramps  112 ,  114  are radially positioned for contacting the projections  104 ,  106 , respectively, on the rear cover  15  when the actuator  100  is moved axially, as shown best by directional arrow  115  in FIG.  7 . In this manner, the inclined ramps  112 ,  114  and the projections  104 ,  106  cooperate for transforming translation of the spindle  28  into rotation of the actuator  100 . Each inclined ramp  112 ,  114  is declined inwardly away from a generally-planar surface of the annular disk  108  facing the rear cover  15 . The length of each inclined ramp  112 ,  114  and the travel distance of the projections  104 ,  106  thereon are chosen to provide sufficient movement of the drive pawl  102  for actuating the scrambler assembly  98 , as described herein. 
   The actuator  100  includes a lobe or cam surface  101  coupled with the flange  88  of the fence bar  86 . As the actuator  100  is rotated by an inwardly-directed force displacing the dial  16  and the spindle  28  axially relative to the tumbler post  30 , a portion of flange  88  is guided along the cam surface  101 . When an improper combination is dialed using dial  16 , the cam surface  101  has one portion that suspends fence bar  86  so that the fences  90 ,  91 ,  92  have a non-contacting relationship with the corresponding one of the tumbler wheel assemblies  48 ,  50 ,  53  and permits the fences  90 ,  91 ,  92  to drop toward the tumbler wheel assemblies  48 ,  50 ,  52  when the dial  16  is pressed inwardly to test the dialed combination. The cam surface  101  has another portion of lesser radius that permits the lever nose  43  of bolt lever  42  to drop into the notch  44  in the drive cam  46  when a proper combination is entered. 
   One end of the drive pawl  102  is pivotally coupled to an arm  116  projected outwardly from a peripheral rim of the annular disk  108 . Arm  116  provides the mechanical drive link between the scrambler assembly  98  and actuator  100 . Projecting outwardly from an opposite free end of the drive pawl  102  is a pinion-engagement spur or nib  118  configured for engaging the scrambler assembly  98  when the actuator  100  is rotated. A spring-engaging flange  120  is provided near the midpoint of the drive pawl  102  and provides an attachment point for a biasing element  123 , such as an extension spring. 
   The scrambler assembly  98  includes a lever  122  pivotally coupled with the lock case  14  and a wheel-scrambling element  124  rotatably coupled with the lever  122 . Lever  122  includes a spring-engaging flange  125  that is resiliently coupled to the spring-engaging flange  120  by biasing element  123 . The biasing element  123  applies a biasing force that urges the wheel-scrambling element  124  to normally have a non-contacting relationship with the outer wheels  58 ,  60  of front tumbler wheel assembly  48 . The wheel-scrambling element  124  includes a pinion  126  and a pinion  128  of greater diameter than pinion  126 . The pinions  126 ,  128  are rotatably attached or affixed by a stud or pin  129  with the lever  122 . Adjacent side faces of the pinions  126 ,  128  are joined together so that the pinions  126 ,  128  rotate collectively about pin  129 . It is contemplated that the pinions  126 ,  128  may comprise either a single-piece, unitary structure or joined individual components. A plurality of teeth  130  encircling pinion  128  are configured for meshing with the teeth  78  of outer wheel  60  to provide a positive driving engagement. Pinion  126  has a plurality of spaced teeth  132  configured to permit selective mechanical coupling with the nib  118  on the drive pawl  102 . 
   The center of pinion  126  is offset from an axis of rotation  131  defined by the pin  129 . The center of pinion  128  is aligned with the axis of rotation  131  so that teeth  130  mesh with teeth  78  of outer wheel  60  regardless of the angular orientation of pinion  128 . As the pinions  126 ,  128  collectively rotate, the rotation of pinion  126  is eccentric about the axis of rotation  131 . As a result of the eccentricity, successive incremental angular rotations imparted by pinion  128  to outer wheel  60  from successive or consecutive attempts to open the combination lock  10 , after entry of corresponding improper combinations, are not predictable among the successive attempts. 
   In operation and with reference to  FIGS. 4 ,  5 A-E,  6  and  7 , the pinion  128  of the wheel-scrambling element  124  is initially spaced from front tumbler wheel assembly  48 , as shown in  FIGS. 5A and 6 , due to the biasing force applied by biasing element  123 . A combination is dialed using dial  16  and the dial  16  and spindle  28  are collectively pushed axially into the lock case  14  to verify whether or not the dialed combination is correct. As shown in  FIGS. 5B ,  5 C, and  7 , the inward movement of the dial  16  displaces the spindle  28  and the actuator  100  axially toward the rear cover  15 , which causes each of the projections  104 ,  106  to engage a corresponding one of the inclined ramps  112 ,  114 . Continued axial movement of the spindle  28  toward the rear cover  15  slidingly moves the projections  104 ,  106  along the ramps  112 ,  114  which causes the actuator  100  to rotate in the direction of directional arrow  134  (FIG.  5 B). As the actuator  100  rotates, the lever  122  pivots toward the front tumbler wheel assembly  48  generally in the direction of directional arrow  135  ( FIG. 5C ) so that the teeth  130  on pinion  128  mesh with the teeth  78  on outer wheel  60  and the drive pawl  102  pivots so as to engage nib  118  with one of the teeth  132  of pinion  126 . 
   Entry of an improper combination results in the lever nose  43  not being engaged with notch  44  as at least one of the fences  90 ,  91 ,  92  is not angularly aligned with the corresponding recesses  83   a,b  and, as a result, contacts a radially outermost portion of the projections  80   a,b . After the combination has been verified, the dial  16  is released and the spindle  28  is biased to translate outwardly, which causes rotation of the actuator  100  in the sense of directional arrow  136 , as shown in FIG.  5 D. As the projections  104 ,  106  slidingly move along the inclined ramps  112 ,  114 , the drive pawl  102  moves generally in the direction of directional arrow  137 , while the nib  118  is engaged with one tooth  132  of pinion  126 , which causes the pinions  126 ,  128  to collectively rotate in the sense of directional arrow  138 . The collective rotation of pinions  126 ,  128  with the teeth  130  of pinion  128  meshed with the teeth  78  of outer wheel  60  precipitates rotation of the front tumbler wheel assembly  48 , including the gate wheels  62 ,  64 , in the sense of directional arrow  139 . Thus, each time an improper combination is entered and the combination is checked, the scrambler mechanism  96  causes the front tumbler wheel assembly  48  to rotate through an angle. The scrambler mechanism  96  returns to the position shown in  FIG. 5A  with the nib  118  disengaged from pinion  126  and the pinion  128  spaced apart from the front tumbler wheel assembly  48  in anticipation of the entry of another combination. If another improper combination is entered and checked, the scrambler mechanism  96  will rotate front tumbler wheel assembly  48  through an angle in the direction of directional arrow  139  that differs from the angle of the previous unsuccessful attempt to unlock the combination lock  10 . 
   According to the principles of the invention, the scrambler mechanism  96  defeats or, at the least, delays surreptitious attack from an automatic dialer operating in a systematic manner to unlock the combination lock  10 . Specifically, the scrambler mechanism  96  rotates front tumbler wheel assembly  48  if successive or consecutive improper combinations are entered and the dial  16  is pressed inwardly after each improper combination is enter to attempt to retract the lock bolt  34 . The rotation of front tumbler wheel assembly  48  causes the automatic dialer to lose its reference point, after each improper combination is entered, so that a succession of entered improper combinations is not systematic. Moreover, the eccentricity of the rotation of pinion  126  about the axis of rotation  131  operates to vary the angle or angular arc through which the front tumbler wheel assembly  48  rotates, among successive failed attempts to unlock combination lock  10 . As a result, the automatic dialer cannot rely on a predictable angular position of the front tumbler wheel assembly  48  because of the unpredictable variation in its angular orientation imparted by the scrambler mechanism  96 . Therefore, the combination lock  10  is less likely to be compromised by the action of the automatic dialer. 
   If a proper combination is entered, the recesses  83   a,b  of each tumbler wheel assembly  48 ,  50 ,  52  are aligned angularly with the corresponding one of the fences  90 ,  91 ,  92 . The fence bar  86  pivots toward the tumbler wheel assemblies  48 ,  50 ,  52  and the prongs  94  of each of the fences  90 ,  91 ,  92  enter recesses  83   a,b  on the corresponding gate wheels  62 ,  64 . As a result of the increased travel distance available to the fence bar  86 , the bolt lever  42  lowers by the action of spring  51  so that the lever nose  43  engages the notch  44  in the drive cam  46 , which is oriented by the entry of a proper combination in angular position with the notch  44  confronting the lever nose  43 , as shown in FIG.  5 E. When the dial  16  and spindle  28  are pushed inwardly into the lock case  14  to verify whether or not the dialed combination is correct, the drive cam  46  is rotated and, due to the engagement between the lever nose  43  and notch  44 , the bolt lever  42  moves in a direction for retracting the lock bolt  34 . The actuator  100  moves toward the rear cover  15  and the projections  104 ,  106  engage the ramps  112 ,  114 , respectively. The locking pawls  36   a,b  are pivoted by release mechanism  38  to a non-contacting relationship with the stop surfaces  40   a,b  so that the lock bolt  34  can be retracted for unlocking the combination lock  10 . 
   Continued rotation of the drive cam  46  causes the lock bolt  34  to retract into the lock case  14 , which disengages the lock bolt  34  from a strike (not shown), or the like, associated with a frame surrounding door  12 , as shown in  FIG. 5F , so that the supporting door  12  may be opened. The teeth  130  of pinion  128  are meshed with the teeth  78  of the outer wheel  60  and the nib  118  is engaged with one tooth  132  of pinion  128 . However, as the projections  104 ,  106  slidingly move along the inclined ramps  112 ,  114 , the pinions  126 ,  128  cannot collectively rotate as the fence  92  is engaged with the recesses  83   a,b  of front tumbler wheel assembly  48 . As a result, the scrambler assembly  98  is not effective for altering the angular orientation of the front tumbler wheel assembly  48 . The scrambler mechanism  96  returns to the position shown in  FIG. 5A  with the nib  118  disengaged from pinion  128  and pinion  126  spaced apart from the front tumbler wheel assembly  48  in anticipation of the entry of another combination. The dial  16  is turned to extend the lock bolt  34  by operation fo travel arm  45  and drive cam  41  out of the lock case  14  to reestablish the locked position (FIG.  5 A). 
   With reference to  FIGS. 2A ,  3 , and  8 A- 11  and according to the principles of the invention, the combination lock  10  is equipped with a combination change mechanism or key  140  that is operative for decoupling the tumbler wheel assemblies  48 ,  50 ,  52  from rotating with the spindle  28  and drive cam  46  so that the lock combination may be changed. To that end, the outer wheels  58 ,  60  of each of the tumbler wheel assemblies  48 ,  50 , and  52  incorporate a releasable mechanical linkage or coupling that provides a selective drive coupling between the drive cam  46  and the outer wheels  58 ,  60  and, therefore, a selective drive coupling between the spindle  28  and the gate wheels  62 ,  64 . Specifically, the outer wheel  58  of, for example, rear tumbler wheel assembly  52  includes a plurality of, for example, four arcuate inner spring arms  142  and a corresponding plurality of four arcuate outer spring arms  144 . Pairs of the inner and outer spring arms  142 ,  144  are releasably spread apart or separated from each another, in a coupled state, by a corresponding one of a plurality of spreading elements, such as arcuate wedges  146 , provided on outer wheel  60  on tumbler wheel assembly  52 . The arcuate wedges  146  are positioned on the side of outer wheel  60  facing outer wheel  58 . It is appreciated that the outer wheels  58 ,  60  of the other two tumbler wheel assemblies  48 ,  50  also have inner and outer spring arms  142 ,  144  and wedges  146 , respectively, identical to those of rear tumbler wheel assembly  52  and that the following discussion is equally applicable to tumbler wheel assemblies  48 ,  50 . 
   The inner spring arms  142  extend circumferentially about the outer wheel  58  and the outer spring arms  144  likewise extend circumferentially about the outer wheel  58  at a greater circumference of larger radius. Pairs of the inner and outer springs arms  142 ,  144  are angularly positioned so that one of the outer springs arms  144  is spaced radially outwardly from a corresponding one of the inner spring arms  142 . Each inner spring arm  142  has a plurality of spaced apart teeth  147  facing radially inward toward the center of the outer wheel  58 . Similarly, each of the outer spring arms  144  has a plurality of spaced apart teeth  148  facing radially outward away from the center of the outer wheel  58 . 
   The inner and outer spring arms  142 ,  144  have a cantilevered attachment at one end to the outer wheel  58 . The free end of each inner spring arm  142  includes an inclined surface  150  and, similarly, the free end of each outer spring arm  144  includes an inclined surface  152  that confronts the inclined surface  150 . One end of each wedge  146  includes a tapered head  154  that is oriented circumferentially in a direction that confronts the respective free ends of a corresponding pair of the inner and outer spring arms  142 ,  144 . The tapered head  154  and the inclined surfaces  150 ,  152  cooperate to guide the wedge  146  between the corresponding pair of inner and outer spring arms  142 ,  144  when at least one of the outer wheels  58 ,  60  is rotated for mechanically engaging the outer wheels  58 ,  60  to provide the coupled state. 
   When the outer wheels  58 ,  60  are in the coupled condition, each of the wedges  146  is positioned between a corresponding pair of inner and outer spring arms  142 ,  144 . Specifically, the wedges  146  operate to separate the inner and outer spring arms  142 ,  144  to provide a drive coupling between the drive hub  56  and the assembly consisting of the middle wheel  66  and gate wheels  62 ,  64 . More specifically, in the coupled condition (FIGS.  8 A and  9 ), the teeth  147  of the inner spring arms  142  are meshed with the teeth  74  of the drive hub  56  and the teeth  148  of the outer spring arms  144  are meshed with the teeth  72  on the inner peripheral rim of the middle wheel  66 . When the outer wheels  58 ,  60  are in an uncoupled condition (FIGS.  8 C and  10 ), the rear tumbler wheel assembly  52  is uncoupled from its drive hub  56  so that rotation of the spindle  28  by dial  16  does not induce rotation of rear tumbler wheel assembly  52 . In the uncoupled condition, the rear tumbler wheel assembly  52  is freely rotatable relative to its drive hub  56 . It is appreciated that the combination change key  140  is operative for coupling and uncoupling the front and middle tumbler wheel assemblies  48 ,  50  from their respective drive hubs  56  in a manner similar to that described for front tumbler wheel assembly  52  so that each number of the lock combination can be changed. 
   With reference to  FIGS. 8A-D ,  9 ,  10  and  11 , the uncoupled state between the tumbler wheel assemblies  48 ,  50 ,  52  and the associated drive hub  56  is provided by rotating outer wheel  58  relative to outer wheel  60  for each of the tumbler wheel assemblies  48 ,  50 ,  52  so that the wedges  146  are disengaged from the inner and outer spring arms  142 ,  144 . To that end, the combination change key  140  includes a change lever  160 , a gear drive shaft  162  extending through the change lever  160 , a plurality of, for example, three rotatable spur gears  164 ,  166 ,  168  coupled with the gear drive shaft  162 , a corresponding plurality of toothed sections  170 ,  172 ,  174  provided on the change lever  160 , a change key drive  176 , and a change key cam  178  with which the change key drive  176  is engaged. The change key drive  176  and the change key cam  178  cooperate to provide the pivoting action of the change lever  160  when the change key drive  176  is rotated about its rotation axis. 
   The combination change key  140  is normally spring-biased so that the spur gears  164 ,  166 ,  168  and toothed sections  170 ,  172 ,  174  have a non-contacting relationship with the corresponding outer wheels  58 ,  60 . It is appreciated that the number of spur gears and toothed sections will correlate with the number of tumbler wheel assemblies. The spur gears  164 ,  166 ,  168  are identical and have teeth configured for engaging the teeth  78  of outer wheel  60  of a corresponding one of the tumbler wheel assemblies  48 ,  50 ,  52 . Similarly, the toothed sections  170 ,  172 ,  174  are identical and have teeth configured for engaging the teeth  76  of the other outer wheel  58  of a corresponding one of the tumbler wheel assemblies  48 ,  50 ,  52 . 
   The head of the change key drive  176  includes a drive recess  177  capable of being engaged by a complementary portion of a driving tool or implement (not shown), which is used to apply a pivoting force via the change key drive  176  that moves the combination change key  140  into engagement with outer wheels  58 ,  60  of each of the tumbler wheel assemblies  48 ,  50 ,  52  (FIG.  8 A). Similarly, the head of gear drive shaft  162  also includes a drive recess  163  capable of being engaged by a complementary portion of another driving tool  180  for rotating the spur gears  154 ,  156 ,  158  relative to the housing in one rotational direction for uncoupling the wedges  146  from the inner and outer spring arms  142 ,  144  and in an opposite rotational direction for inserting the wedges  146  between the inner and outer spring arms  142 ,  144 . 
   The combination change key  140  lacks any identifying feature or features, such as openings or rivets, that would be visible in a radiographic image of the combination lock  10 . As a result, no feature of the combination change key  140  bears a predictable relationship relative to the gate(s) of the combination lock  10  in a radiographic image. It is apparent that the spring arms  142 ,  144  and wedges  146  of each tumbler wheel assembly  48 ,  50 ,  52  have rotational symmetry about axis  53 . 
   In use and with reference to  FIGS. 8A-D , a proper combination is entered so that the fence bar  86  pivots toward the tumbler wheels assemblies  48 ,  50 ,  52  and the fences  90 ,  91 ,  92  enter the corresponding recesses  83   a,b  defining true gates. A pivoting force is applied to the change key drive  176  in a direction  182  that pivots the combination change key  140  from a home position into engagement with outer wheels  58 ,  60  of each of the tumbler wheel assemblies  48 ,  50 ,  52 , as shown in FIG.  8 A. The pivoting action is provided by the cooperation between change key drive  176  and change key cam  178 . The teeth of spur gear  164  are meshed with the teeth  78  of the outer wheel  60  of the front tumbler wheel assembly  48  and the teeth of the toothed section  170  are meshed with the teeth  76  of the other outer wheel  58  of front tumbler wheel assembly  48 . Similarly, the teeth of spur gears  166 ,  168  and the teeth  78  of the outer wheel  60  of the corresponding one of the tumbler wheel assemblies  50 ,  52  are meshed and the teeth of the toothed sections  172 ,  174  and the teeth  76  of the other outer wheel  58  of the corresponding one of the tumbler wheel assemblies  50 ,  52  are meshed. 
   As shown in  FIG. 8B , the gear drive shaft  162  is rotated in one direction to simultaneously turn the three spur gears  164 ,  166 ,  168  so that the outer wheels  60  are rotated relative to the other outer wheels  58 , which are held stationary by the engagement with the corresponding one of toothed sections  170 ,  172 ,  174 , for removing the wedges  146  from between the inner and outer spring arms  142 ,  144 . The angular orientation of the gate wheels  62 ,  64  remains stationary as the outer wheels  60  are rotated due to the engagement between the fences  90 ,  91 ,  92  and the corresponding recesses  83   a,b . When the wedges  146  are removed from between the inner and outer spring arms  142 ,  144 , the dial  16 , the spindle  28 , the drive cam  46 , the flies  54 ,  55 , and the drive hubs  56  may be rotated to select a new set of angular positions of the dial  16  to establish a new lock combination. 
   After the new combination is set, the gear drive shaft  162  is rotated in an opposite direction to simultaneously rotate the three spur gears  164 ,  166 ,  168  so that the outer wheels  60  are rotated relative to outer wheels  58 , which are held stationary in angular position by the engagement with the toothed sections  170 ,  172 ,  174 , for driving the wedges  146  between the inner and outer spring arms  142 ,  144 , as shown in  FIGS. 8A and 8C . The angular position of the gate wheels  62 ,  64  remains stationary as the outer wheels  60  are rotated due to the engagement between the fences  90 ,  91 ,  92  and the corresponding recesses  83   a,b . When the wedges  146  are engaged with the inner and outer spring arms  142 ,  144 , the outer wheels  58 ,  60  are returned to the coupled condition and the combination lock  10  is again functional. The pivoting force is released from the change key drive  176  so that the combination change key  140  pivots out of engagement with outer wheels  58 ,  60  and returns to the home position. 
   While the present invention has been illustrated by a description of preferred embodiments and while the embodiments have been described in considerable detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages, modifications and adaptations of this invention will become apparent to those skilled in the art upon reviewing this disclosure. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method as shown and described. The invention itself should only be defined by the appended claims, wherein I claim: