Abstract:
A locking mechanism with an electronic solenoid opening and a mechanical reset is disclosed. The locking mechanism comprises a solenoid which requires low power levels to activate and has a short activation period, resulting in reduced energy requirements and extended battery life. After being placed in the unlocked position, the locking mechanism remains unlocked until a mechanical reset is activated by a person turning a handle of the mechanism.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable.  
       BACKGROUND  
       [0003]     The embodiments of the present invention are directed toward methods and apparatus for providing a secure and reliable locking mechanism with an electronic solenoid unlock and a mechanical reset. The embodiments of the present invention can be utilized in locks that are commonly found in doors and that retract a latch bolt or striker via rotation of a door handle or knob.  
         [0004]     When a conventional door lock is placed in the locked position, rotation of the door handle or knob is prevented due to a steel member that creates a shear condition between the door and a rotating member that is connected to the outer door handle. This shear condition can be disabled by a conventional tumbler type lock located in the inner door handle or knob. Although tumbler type locks are simple and relatively inexpensive, these locks are vulnerable in many aspects. For example, tumbler locks can be mechanically manipulated (or “picked”) by a person who does not have a key. In addition, unauthorized duplicate keys can also create safety concerns. With conventional tumbler locks, unauthorized access can often be obtained by using a large wrench or lever to break off the external handle. This provides access to the door latching mechanism, which can then be retracted manually. Furthermore, conventional locks typically require that a hole of approximately two inches or larger be drilled in the door to install the lock. This weakens the door in the area of the lock and creates further safety concerns.  
         [0005]     Although known electronic locks address some of these concerns, they also have undesirable features. For example, certain prior art electronic locks activate a solenoid (or motor) for a specific period of time, usually a few seconds, in order to unlock the door. In such devices, the mechanism is only unlocked during the time interval in which the solenoid or motor is activated. The user must therefore activate the solenoid, typically by using an electronic key or by entering a code on a keypad, and then open the door during the time period in which the solenoid is activated. Opening the door within a relatively short time window can be quite bothersome if the user has items that he or she is trying to carry after opening the door, or if the user must open the door repeatedly.  
         [0006]     Conventional electronic locks such as those described above utilize a solenoid (or motor) that converts electrical energy to mechanical energy needed to move the mechanism from a locked to an unlocked position. The electrical energy is typically provided from a permanent alternating current source (i.e. “hard-wiring” the locking mechanism) or from a direct current battery. Hard-wiring the lock can lead to significant increases in installation costs and render the lock inoperable in the event of a power failure. While a battery has lower installation costs, it must be replaced when it is no longer capable of providing sufficient electrical energy to activate the solenoid. Since the available space within a door lock is very limited, a small battery must be used and therefore a limited amount of electrical energy is available.  
         [0007]     The energy produced by a battery is the product of the current produced, the voltage measured across the battery terminals, and the length of time that the current is produced. A conventional battery has a finite life, typically measured in ampere-hours, defined as the amount of time a battery will be able to produce a specified current at a specified voltage. In an electronic locking mechanism, each time the solenoid is activated, a certain amount of energy will be drawn from the battery, thereby reducing remaining battery life. In order to maximize battery life, it is therefore desirable to minimize the amount of energy that is drawn from the battery during the solenoid activation. This can be accomplished by reducing either the length of time the solenoid is activated or reducing the electrical power (i.e., the current multiplied by the voltage) drawn from the battery during the period of activation.  
         [0008]     Reducing the electrical power consumed from the battery can be accomplished by reducing the mechanical power produced by the solenoid. However, the mechanical power produced by the solenoid must be sufficient to unlock or lock the mechanism. In certain prior art designs, sufficient mechanical power must be provided to account for factors which increase the power needed to unlock the mechanism. These factors include misalignment of the door and door frame, door warpage, or increased friction between components.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0009]     Embodiments of the present invention relate to methods and apparatus comprising a locking mechanism with an electronic solenoid opening and a mechanical reset. Certain embodiments of the present invention comprise a solenoid that requires low power levels to activate and a solenoid activation period that is relatively short. This results in reduced energy consumption and extends the life of a battery used to power the mechanism. Some embodiments of the present invention also comprise a reset or re-locking mechanism utilizing a pin and collar with an inclined surface, or cam, which is activated by a person turning a handle of the locking mechanism. Therefore the reset mechanism does not rely on the solenoid to reset, and it is less susceptible to malfunction that might arise due to increased friction caused by wear or misalignment. In addition, certain embodiments of the present invention may comprise a security plate and other components that provide increased reliability and security. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is an exploded view of a locking mechanism;  
         [0011]      FIG. 2  is a side view of a partial assembly the locking mechanism of  FIG. 1 ;  
         [0012]      FIG. 3  is a side view of the locking mechanism of  FIG. 1  in a locked position;  
         [0013]      FIG. 4  is a side view of the locking mechanism of  FIG. 1  in an intermediate position;  
         [0014]      FIG. 5  is a side view of a locking mechanism of  FIG. 1  in an unlocked position;  
         [0015]      FIG. 6  is an end view of a locking mechanism of  FIG. 1 ;  
         [0016]      FIG. 7  is a top view of an alternative embodiment of a locking mechanism; and  
         [0017]      FIG. 8  is an end view of the embodiment of  FIG. 7 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     Referring initially to  FIGS. 1-5 , a locking mechanism  100  is shown relative to a door  15 . As shown in the exploded view of  FIG. 1 , locking mechanism  100  comprises an inner shaft assembly  110 , a door assembly  120  and an outer shaft assembly  130 . The components of inner shaft assembly  110  will be described initially, followed by the components of the other assemblies. Inner shaft assembly  110  comprises an inner shaft  10  with an inner handle  12  and an inner collar  30 , both disposed on inner shaft  10 . Inner shaft  10  further comprises a radial slot  64 , an axial slot  17 , and an engagement portion  11 . Further disposed on inner collar  30  are a release member  33  with a magnet  34  and a release biasing member  50 . Inner collar  30  further comprises a guide pin  54 , a notch  39 , and a first cam or inclined surface  35 .  
         [0019]     Door assembly  120  comprises an inner protective cover  16 , a security plate  55 , and an outer protective cover  18 . A solenoid  70 , with a latching member  60  and a solenoid biasing member  62 , is connected to security plate  55  via a fastener  77 . A stationary collar  40  is disposed on security plate  55 , in addition to an anti-rotation member  57  via a fastener  78 . Stationary collar  40  comprises a second cam or inclined surface  45 . A plurality of standoffs  72  are connected to security plate  55  via a plurality of fasteners  76 . Door assembly  120  further comprises a striker  52 , a striker cover  71 , a primary biasing member  74 , a secondary biasing member  75 , and a biasing member guard  73 . In certain embodiments, solenoid  70  is a 6 volt solenoid with 30 ohm resistance wiring and solenoid biasing member is an arc-shaped metallic component approximately 0.004″ thick.  
         [0020]     Outer assembly  130  comprises an outer shaft  20  with a proximal portion  25  and a distal portion  23 . A pin  63  is disposed on proximal portion  25  and an outer handle  22  is disposed on distal portion  23 . A shoulder  24  is disposed between proximal portion  25  and distal portion  23 .  
         [0021]     It is understood that the same embodiment depicted in  FIG. 1  is also depicted in  FIGS. 2-5 . For purposes of clarity, not all of the components shown in the exploded view of  FIG. 1  are shown in  FIGS. 2-5 . In addition, some of the components in the assembled views of  FIGS. 2-5  are not labeled for purposes of clarity.  
         [0022]     As shown in the partial assembly of  FIG. 2 , striker  52  and standoffs  72  are disposed between striker cover  71  and security plate  55 . Inner shaft  10  extends through inner collar  30 , stationary collar  40 , security plate  55  and into striker  52 . Outer shaft  20  extends through outer protective cover  18 , biasing member guard  73 , striker cover  71 , striker  52  and into inner shaft  10 . Solenoid  70  is positioned so that latching member  60  can engage release member  33  on collar  30 . Biasing member guard  73  is disposed on outer shaft  20  and held in place by a retaining ring  79 . Primary biasing member  74  (shown in  FIG. 1 ) is not shown in  FIG. 2  for clarity, but is normally disposed between striker  52  and biasing member guard  73 . Secondary biasing member  75  (also not shown in  FIG. 2  for clarity) is disposed between a shoulder  24  on outer shaft  20  and the end of inner shaft  10  that is extended into striker  52 . In this manner, secondary biasing member  75  biases outer shaft  20  away from inner shaft  10 , and primary biasing member  74  biases outer shaft  20  towards outer handle  22 . As discussed in greater detail below, pin  63  on outer shaft  20  extends through radial slot  64  of inner shaft  10 ; therefore, primary biasing member  74  will also bias inner shaft  10  towards outer handle  22 .  
         [0023]     A general overview of locking mechanism  100  will be provided initially, followed by a more detailed description of the operation of locking mechanism  100 .  FIG. 3  depicts locking mechanism  100  in the “locked” position. In this position, outer handle  22  (placed on the side of door  15  that is to be secured) can not be used to open door  15 .  FIG. 4  depicts locking mechanism  100  in an intermediate position when solenoid  70  is being activated (i.e., an electric current is being supplied to solenoid  70 ).  FIG. 5  depicts locking mechanism  100  in the “unlocked” position after solenoid  70  has been de-activated. In the position shown in  FIG. 5 , rotation of outer handle  22  can be used to open door  15 . Locking mechanism  100  can only be used to open door  15  if inner shaft  10  is rotated, thereby allowing engagement portion  11  of inner shaft  10  to engage striker  52 . The means for retracting a striker via the rotation of a shaft in a locking mechanism is well known in the art, and includes gear mechanisms such as a rack and pinion or equivalent means. In the positions shown in  FIGS. 3-5 , inner shaft  10  comprises a square cross section and inner handle  12  comprises a corresponding shaped recess into which inner shaft  10  extends. Therefore, rotation of inner handle  12  will cause inner shaft  10  to rotate and cause engagement portion  11  to retract striker  52 , allowing a person to open door  15 . Other embodiments may comprise different means for mounting handle  12  on inner shaft  10 .  
         [0024]     A significant difference between  FIGS. 3 and 5  is the position of inner collar  30 . In  FIG. 3 , inner collar  30  is separated from pin  63 , so that rotation of outer handle  22  and outer shaft  20  will cause pin  63  to rotate within the gap between inner collar  30  and stationary collar  40 . In  FIG. 5 , inner collar  30  is engaged with pin  63 , so that rotation of outer handle  22  and outer shaft  20  will cause pin  63  to rotate inner collar  30 . Guide pin  54  is connected to inner collar  30  and disposed within axial slot  17  of inner shaft  10 ; therefore, rotation of inner collar  30  will cause inner shaft  10  to also rotate.  
         [0025]     In the embodiment of  FIGS. 1-5 , outer shaft  20  comprises distal portion  23  with a square cross section that fits into a corresponding square recess in outer handle  22  so that rotation of outer handle  22  will cause outer shaft  20  to rotate as well. In the embodiment shown, inner shaft  10  also comprises a square cross section that fits into a square recess of inner handle  12  so that rotation of inner handle  12  will cause inner shaft  10  to rotate in both the locked an unlocked positions so that a person can always exit in case of fire or other emergency. In the embodiment of  FIGS. 1-5 , outer shaft  20  also comprises proximal portion  25  which is disposed within inner shaft  10 . Although proximal portion  25  is a round bar in the embodiment shown, proximal portion  25  may comprise other shapes in other embodiments. In the embodiment of  FIGS. 1-5 , inner shaft  10  is comprised of square tubing being about 0.310 inches square on the outside and about 0.230 inches square on the inside. As shown in  FIGS. 1-5 , inner shaft  10  extends from inner handle  12 , through inner collar  30 , stationary collar  40 , and security plate  55 . In the embodiment shown, distal portion  23  of outer shaft  20  is about 0.300 inches square and proximal portion  25  is approximately about 0.220 inches in diameter. With the above-described dimensions, outer shaft  20  may be rotated within, and independent from, inner shaft  10  when locking mechanism  100  is placed in the locked position.  
         [0026]     In the embodiment shown, pin  63  is disposed upon or connected to outer shaft  20  in an orientation generally perpendicular to the primary axis of outer shaft  20 . Pin  63  can be connected to shaft  20  in various manners, but in the embodiment shown pin  63  is a hardened pin pressed into a hole drilled in outer shaft  20 . In the assembly of the embodiment shown, outer shaft  20  is inserted into inner shaft  10  before pin  63  is connected to outer shaft  20 . Outer shaft  20  is positioned so that the hole in which pin  63  is going to be inserted is aligned with radial slot  64  of inner shaft  10 . When the hole for pin  63  is aligned with radial slot  64 , pin  63  can then be connected to shaft  20 . Pin  63  is long enough that it extends through radial slot  64  and beyond the outer surface of inner shaft  10 . After locking mechanism  100  is assembled, pin  63  is aligned with radial slot  64 . This allows outer shaft  20  to be rotated the full ninety degrees right or left rotational movement allowed by handle  22 , without rotating inner shaft  10  when locking mechanism  100  is in the locked position shown in  FIG. 3 , as described in more detail below.  
         [0027]     In the locked position shown in  FIG. 3 , latching member  60  of solenoid  70  is engaged with magnet  34 , so that latching member  60  is resting on top of and held in place by the magnetic attraction of magnet  34 . In certain embodiments, latching member  60  is made of a ferromagnetic metal so that it is attracted to magnet  34 . In addition, solenoid biasing member  62  biases latching member  60  towards magnet  34  so that the end of latching member  60  engages a lip  67  of release member  33 . Release member  33  is disposed upon inner collar  30  and secured with a pair of retaining rings  59  (shown in  FIG. 2 ). Release member  33  comprises an inner bore that is slightly larger than the outer diameter of inner collar  30  so that inner collar  30  may rotate independently of release member  33 . In the embodiment shown, guide pin  54  is pressed into inner collar  30  and fits into axial slot  17  (not shown in  FIGS. 3-5  for purposes of clarity) in inner shaft  10 . Axial slot  17  in inner shaft  10  allows inner collar  30  to move a limited axial distance relative to inner shaft  10 . In the locked position shown in  FIG. 3 , the engagement of latching member  60  with lip  67  and magnet  34  prevents release biasing member  50  from further biasing release member  33  and inner collar  30  towards stationary collar  40 .  
         [0028]      FIG. 4  shows locking mechanism  100  in an intermediate position while solenoid  70  is activated. The activation of solenoid  70  causes latching member  60  to be drawn up towards solenoid  70  and away from magnet  34 . In certain embodiments, solenoid  70  is activated for a brief period of time (approximately 50 to 200 milliseconds), which reduces the amount of electrical energy needed to unlock locking mechanism  100 . In certain embodiments, the electrical energy needed to activate solenoid  70  is provided by a lithium battery (not shown). As shown in the embodiment of  FIG. 6 , solenoid  70  can be activated when an electronic key reader  80  detects a code from an electronic key (also not shown) that is programmed to allow locking mechanism  100  to be unlocked. Other embodiments can comprise a small electric motor to perform the release action of latching member  60 .  
         [0029]     As shown in  FIG. 4 , when solenoid  70  is activated, latching member  60  is drawn towards solenoid  70  so that latching member  60  is no longer engaged with magnet  34  or lip  67  of release member  33 . Minimizing the thickness of solenoid biasing member  62  (to 0.004 inches in certain embodiments) also reduces the amount of force that solenoid biasing member  62  exerts on latching member  60 . This consequently reduces the amount of force that solenoid  70  must exert on latching member  62  to retract it to the position shown in  FIG. 4  that is needed to unlatch latching member  60  from lip  67  and magnet  34 . During the time latching member  60  is not engaged with magnet  34  or lip  67 , release biasing member  50  moves release member  33  and inner collar  30  towards stationary collar  40  and pin  63 . As shown in  FIG. 5 , when solenoid  70  is no longer activated, solenoid biasing member  62  and magnet  34  cause latching member  60  to move away from solenoid  70 . However, because release member  33  has now moved towards pin  63 , latching member  60  can no longer engage magnet  34  and lip  67  of release member  33 . Instead, latching member  60  rests on top of lip  67 . This allows pin  63  to engage notch  39  of inner collar  30 .  
         [0030]     In the position shown in  FIG. 5 , rotation of outer handle  22  (and outer shaft  20 ) will cause inner collar  30  to rotate because pin  63  is engaged with notch  39  of inner collar  30 . Mounted on collar  30  is pin  54 , which extends into slot  17  of inner shaft  10  to allow limited axial movement of collar  30  relative to inner shaft  10 . While axial slot  17  is longer than the diameter of pin  54 , it is only slightly wider than the diameter of pin  54 . Therefore, the radial movement of inner collar  30  relative to inner shaft  10  is extremely limited and as inner collar  30  is rotated, inner shaft  10  will also be rotated. The cross section of inner collar  30  also comprises a circular exterior shape, which allows inner collar  30  to rotate relative to release member  33 , which comprises a circular inner bore. Anti-rotation member  57  prevents release member  33  from rotating as inner collar  30  is rotated. Because release member  33  does not rotate, magnet  34  remains at the top of release member  33  and near latching member  60 .  
         [0031]     As shown in  FIG. 5 , if outer handle  22  is rotated counterclockwise (so that pin  63  moves down in the embodiment of  FIG. 5 ), there will be no axial movement between stationary collar  40  and inner collar  30 . If moved in this direction, pin  63  will follow the portion of stationary collar  40  that is substantially parallel with plate  55 . However, if outer handle  22  is rotated clockwise (so that pin  63  moves up as shown in  FIG. 5 ), pin  63  will travel along second inclined surface  45  of stationary collar  40 . This will cause pin  63  to move axially away from outer handle  22  and cause primary biasing member  74  to compress. As pin  63  moves axially, it will impart an axial force on notch  39  of inner collar  30  sufficient to overcome the force imparted on inner collar  30  by release biasing member  50 . This will cause inner collar  30  to move axially away from outer handle  22  and towards inner handle  12 . Retaining rings  59  restrict release member  33  from moving axially relative to inner collar  30 . Therefore, release member  33  will also move towards inner handle  12  when pin  63  pushes inner collar  30  in an axial direction as pin  63  is rotated clockwise.  
         [0032]     In the embodiment shown in  FIGS. 3-5 , pin  63  has a round cross section in the portion that is engaged with outer shaft  20 . However, in the portion of pin  63  that engages inner collar  30 , pin  63  has been modified so that approximately half of its cross section has been removed. This allows a more positive engagement between pin  63  and notch  39  and also reduces the axial distance that inner collar  30  and release member  33  must travel in order to fully engage notch  39 .  
         [0033]     When release member  33  travels a sufficient axial distance (approximately 0.060 of an inch in certain embodiments), latching member  60 , which is biased toward magnet  34  by solenoid biasing member  62 , will engage magnet  34  and lip  67 . This will restrict release biasing member  50  from axially displacing inner collar  30  and release member  33  towards outer handle  22 . Therefore, pin  63  will not be able to engage notch  39  of inner collar  30  after handle  22  has returned to its central or neutral home position, and repeated rotation of outer handle  22  will not cause inner shaft  10  or engagement portion  11  to rotate. Consequently, locking mechanism  100  will be in a “locked” position such that rotation of outside handle  22  will not cause engagement portion  11  to rotate and engage striker  52 , and therefore will not allow a person to open door  15  more than once per each key usage.  
         [0034]     Similarly, if inner handle  12  is rotated in a counterclockwise position when the embodiment of  FIGS. 1-5  is in the unlocked position (so that notch  39  moves in an upward direction as shown in  FIG. 5 ), inner collar  30  will rotate pin  63  relative to stationary collar  40 . Pin  63  will thereby engage second inclined surface  45  and cause inner collar  30  to move axially towards inner handle  12 . Again, release member  33  is restricted from moving axially relative to inner collar  30 . Therefore, as inner collar  30  moves, release member  33  will also move axially. When release member  33  moves a sufficient axial distance, latching member  60  will engage magnet  34  and lip  67  and restrict release biasing member  50  from moving release member  33  and inner collar  30  towards pin  63  after handle  12  is returned to its neutral position. As previously described, rotation of inner handle  12  will cause inner shaft  10  to rotate and retract striker  52 , irrespective of whether locking mechanism  100  is in the locked or unlocked position.  
         [0035]     To summarize the embodiment shown in  FIGS. 1-5 , if inner handle  12  is rotated counterclockwise or outer handle  22  is rotated clockwise when locking mechanism  100  is in the unlocked position, then locking mechanism  100  will be reset to the locked position. If inner handle  12  is rotated clockwise or outer handle  22  is rotated counterclockwise when locking mechanism is in the unlocked position, then locking mechanism  100  will remain in the unlocked position. The direction of rotation used to reset locking mechanism  100  is for the embodiment of  FIGS. 1-5 ; other embodiments of the present invention may use different directions of rotation to reset locking mechanism  100  or may be designed to lock when either handle is rotated in either direction. Furthermore, the number of degrees or angular measure that inner handle  12  or outer handle  22  must be rotated to reset locking mechanism  100  will depend on the dimensions of various components, such as pin  63 , stationary collar  40  and inner collar  30 .  
         [0036]     In addition to the embodiment of  FIGS. 1-5 , a second embodiment of locking mechanism  100  is shown in  FIG. 7 , which represents a top view of a partial assembly of locking mechanism  100 . This embodiment comprises additional components that increase the security of locking mechanism  100  and make it more difficult for locking mechanism  100  to be manually manipulated. For sake of clarity, certain redundant components from the embodiment shown in  FIGS. 1-5  are not shown in  FIG. 7 .  
         [0037]     As shown in  FIG. 7 , a proximal end  25  of outer shaft  20  is disposed within inner shaft  10 . Similar to the embodiment shown in  FIGS. 1-6 , pin  63  also extends through a radial slot  64  in inner shaft  10 . A stationary collar  40  with an inclined or angled surface  45  is also disposed on a security plate  55 . The embodiment shown in  FIG. 7  operates in the same general manner to lock and unlock locking mechanism  100  as that described for the embodiment in  FIGS. 1-6 . However, the embodiment of  FIG. 7  also comprises axial stop  87  disposed on security plate  55  and radial stop  88  disposed on stationary collar  40 . These components provide additional security and make it more difficult for an individual to mechanically manipulate locking mechanism  100 .  
         [0038]     For example, without axial stop  87 , it could be possible for a person to remove outer handle  22  and push outer shaft  20  in an axial direction towards first security plate  55 . Pin  63  could thereby engage notch  39  of inner collar  30  (not shown in  FIG. 7 ), allowing inner shaft  10  to be rotated and door  15  to be opened. However, axial stop  87  makes it more difficult to mechanically manipulate locking mechanism  100 . In the embodiment shown in  FIG. 7 , if handle  22  is removed and shaft  20  is pushed in an axial direction towards security plate  55 , pin  63  will engage will engage axial stop  87  and prevent pin  63  from engaging notch  39 . Therefore, the axial manipulation of outer shaft  20  could not be used to mechanically unlock locking mechanism  100  and open door  15 .  
         [0039]     The embodiment in  FIG. 7  further comprises radial stop  88 , which also provides additional security for locking mechanism  100 . In normal operation, outer handle  22  comprises internal tabs (not shown) which prevent handle  22  from being rotated more than 90 degrees. However, if outer handle  22  is removed and radial stop  88  was not present, outer shaft  20  could be rotated more than 90 degrees. This would allow pin  63  to engage the ends of radial slot  64  in inner shaft  10 . With pin  63  engaging an end of radial slot  64 , further rotation of outer shaft  20  would cause inner shaft  10  to rotate. This would also allow a person to mechanically unlock locking mechanism  100  and open door  15 .  
         [0040]     However, the addition of radial stop  88  prevents this manipulation of locking mechanism  100 , as described in more detail below.  FIG. 8  is a view of section A-A from  FIG. 7  and depicts an end view of outer shaft  20  in a neutral or centered rotational position. As shown in  FIG. 8 , if outer shaft  20  is rotated approximately 90 degrees in either direction, pin  63  would engage radial stop  88  before it engages radial slot  64 . Specifically, if outer shaft  20  is rotated approximately 90 degrees clockwise in the view of  FIG. 8 , pin  63  will engage end  89  of radial stop  88  before pin  63  engages end  65  of radial slot  64 . Similarly, if outer shaft  20  is rotated approximately 90 degrees counter-clockwise, pin  63  will engage end  91  of radial stop  88  before it engages end  66  of radial slot  64 . Therefore, outer shaft  20  cannot be rotated more than 90 degrees even if outer handle  22  is removed. As a result, locking mechanism  100  cannot be mechanically manipulated to allow pin  63  to engage either end  65  or end  66  of radial slot  64 . Therefore, locking mechanism  100  cannot be operated in this manner to unlock and open door  15 .  
         [0041]     As described above, locking mechanism  100  comprises many safety, reliability, and convenience benefits. For example, solenoid  70  only requires a brief pulse activation (50-200 milliseconds in certain embodiments) to unlock locking mechanism  100 , which remains unlocked after the solenoid activation period has ended. By remaining unlocked after solenoid  70  is activated, the solenoid activation period can be shortened because a user does not have to open door  15  during the solenoid activation period. The brief pulse needed to activate solenoid  70  in embodiments of the present invention thereby minimizes the amount of electrical energy that is consumed when locking mechanism  100  is unlocked. In addition, the design of solenoid biasing member  62  minimizes the mechanical forces that must be overcome to unlock locking mechanism  100 . This also minimizes the amount of electrical energy that is used when unlocking locking mechanism  100 .  
         [0042]     In addition to reducing energy requirements, embodiments of the present invention allow a user to unlock the locking mechanism without having to open the door immediately. This feature is particularly useful when the user has items such as luggage that he or she wishes to carry after unlocking the door.  
         [0043]     The embodiments described above also provide the convenience of allowing a user to open the door and either reset the locking mechanism to the locked position or have it remain unlocked, depending on which way the user turns the handle. This feature allows a user to electronically unlatch the mechanism and open the door repeatedly without having to unlock it each time; however, when the user wishes to lock the door after exiting, he or she may reset the locking mechanism simply by turning a handle in a certain direction.  
         [0044]     Embodiments of the present invention also comprise features that allow for safe and reliable operation. For example, the use of magnet  34  and latching member  60 , which is made of ferromagnetic material in certain embodiments, helps to ensure there is a positive engagement between latching member  60  and lip  67 . In addition, solenoid biasing member  62  also biases latching member  60  towards magnet  34  to ensure positive engagement. Solenoid biasing member  62  and magnet  34  greatly reduce the likelihood that the components can be unlatched through the application of an external impact force. The placement of solenoid  70 , latching member  60 , and release member  33  also minimize the effects of door warpage or misalignment on the operation of locking mechanism  100 . The movement of release member  33  is in an axial direction along inner shaft  10 , and is therefore not dependent on the alignment between door  15  and a corresponding door frame (not shown). In certain prior art devices, misalignment or warpage of a door will negatively effect the operation of the locking mechanism.  
         [0045]     Other safety features of locking mechanism  100  include security plate  55 , striker cover  71 , and inner and outer protective covers  16  and  18 , which reduce the likelihood that an intruder would be able to mechanically unlock the locking mechanism by forcibly removing outer handle  22 . In certain prior art devices, removal of an external handle can expose components that can be mechanically manipulated to unlock the locking mechanism. In certain embodiments described above, inner and outer protective covers  16  and  18 , security plate  55 , and striker cover  71  are made of steel or other suitably strong materials to reduce the likelihood that these components could be breached. In certain embodiments of the present invention using an electronic key, safety is also improved due to the vast number of codes available to program the key that is used to activate the solenoid. The number of key codes available greatly reduces the likelihood of an unauthorized duplicate code being used to unlock the locking mechanism.  
         [0046]     Some embodiments of the present invention also provide safety benefits because the locking mechanism does not rely on a solenoid or motor to return to the locked position. A user can manually re-lock the mechanism by simply turning a handle in a certain direction. Thus, the re-locking mechanism is not limited to the power supplied by the solenoid or motor, and therefore is not as susceptible to increased frictional forces within the locking mechanism.  
         [0047]     Certain embodiments of the present invention also include the benefit of providing additional structural support to a door. For example, when a locking mechanism such as the embodiment shown in  FIG. 2  is installed in a door, inner protective cover  16 , outer protective cover  18 , security plate  55 , and striker cover  71  all provide additional stiffening and structural support to the door. These features reduce the likelihood that an intruder could gain access to a location by forcibly pushing or pulling on the door or the door handle.  
         [0048]     While various preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments herein are exemplary only, and are not limiting. Many variations and modifications of the apparatus and methods disclosed herein are possible and within the scope of the invention. For example, embodiments described herein comprise shafts of square and round cross sections; other embodiments may comprise shafts of with cross sections of different shapes. In addition, embodiments described herein utilize an electronic key to unlock the locking mechanism; other embodiments may comprise a keypad to enter an authorization code or other means for activating an electric solenoid. Furthermore, embodiments described herein comprise a solenoid with a flapper style latch; other embodiments may comprise a solenoid with a different configuration, such as a solenoid with a pin or rod that extends and retracts. Additionally, other embodiments may combine some of the components described herein. For example, other embodiments may combine the second collar and security plate into a single component. Terms used herein are intended to be interpreted broadly. For example, use of the term “connect” (and variations thereof) to describe the relationship between components is not intended to require a direct connection between the components. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.