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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND TO THE INVENTION  
         [0001]    It has been a desirable feature of locks that they be able to be rekeyed without changing the lock. Another desirable feature is a lock that has a master key and subordinate keys which do not need a new lock mechanism when one of the keys needs to be replaced.  
           [0002]    U.S. Pat. No. 4,741,188 discloses a pin tumbler lock in which keys can be replaced without changing the locks. This lock can also have a master key and subordinate keys. One difficulty with pin tumbler locks is the cost of manufacture because of the skilled machining and complex assembly required.  
           [0003]    U.S. Pat. No. 4,898,011 disclosed an alternative lock to the pin tumbler which also avoided the need to change the lock. Instead of the key aligning pins to enable rotation of a cylinder the key aligned pins with slots so that elongate members could pass through to allow actuation of a latch. Each key had an associated biscuit which set one set of pins in position and the matching key aligned slots in a second set of pins with the slots of the first set. Master keying was possible by using more than one slot per pin.  
           [0004]    Patent specification WO98/40589 discloses a programmable cylinder lock capable of having one or more levels of master key and able to be rekeyed. The cost of making such a lock and the capital cost of the machinery required to make it is very high.  
           [0005]    Locks with deadbolts can be dangerous where they are deadlocked from both sides of the door. It is also desirable in a multi key environment to restrict the ability to deadbolt a door to a master key. A similar benefit is desired with night latches so that only one key holder can double lock the latch. Thus there is a need to provide a lock which enables some functions to be carried out by a different key.  
           [0006]    U.S. Pat. No. 4,506,530 discloses a lock with a servant key that can throw the bolt to a first position and open it and a master key that can throw the bolt to a deadlock position. This is achieved by the presence of a dogging slide that restricts the servant key rotation but is displaced by the master key.  
           [0007]    U.S. Pat. No. 4,704,884 discloses a pin tumbler cylinder lock with a rotary plug a control plug and a stationary plug. A first key can rotate the rotary plug counterclockwise 90°, the second key rotates the control and rotary plug clockwise 90°. the master key rotates the rotary plug the control plug and the master plug 360° in either direction. Thus 3 different functions can be actuated by 3 different keys. By simply inserting the appropriate key rotation in a given direction is possible to achieve a desired function. This arrangement is expensive to manufacture in terms of production tooling and machining costs.  
           [0008]    It is an object of this invention to provide an inexpensive lock that provides a mechanism to enable different keys to carry out the different functions on the same lock  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0009]    To this end the present invention provides a lock and key set in which the lock includes a cylinder rotatable in a barrel which barrel is rotatable to actuate the latch and the cylinder incorporates a laterally biased bar which incorporates slots or projections adapted to engage with corresponding slots or projections on the keys so that the bar can be aligned in one of up to three positions in which its ends are within the diameter of the cylinder or one of each end of the bar projects beyond the cylinder to engage with the barrel.  
           [0010]    This means that the functions available can be distributed amongst 3 different keys each of which will place the lateral bar into a different position corresponding to a different function. If only two different keys are required then the lateral bar can be dimensioned so that there are only two positions namely co-terminal with the cylinder circumference or extending from one side only.  
           [0011]    When the lateral bar is co-terminal with the cylinder diameter the cylinder can be removed from the barrel and this enables the cylinder to be adjusted or replaced. This invention is especially applicable to the lock arrangement wherein the lock is of the type in which a latch means is able to be actuated if elongated members are able to pass through associated slots in latch elements, wherein the latch elements are positioned by a key.  
           [0012]    This type of lock is described in U.S. Pat No. 4,898,011 and enables master keying at more than one level to be achieved. The content of U.S. Pat. No. 4,898,011 is incorporated herein by reference.  
           [0013]    When the end of the lateral bar extends beyond one end of the cylinder, rotation of the cylinder may actuate the latch. This is a function which would be common to all key holders.  
           [0014]    When the end of the lateral bar extends in the opposite direction, rotation of the cylinder by the appropriate key may actuate another lock function such as throwing a deadbolt or a night latch which is a function reserved for a master key. Thus the lateral bar can be moved into one of up to three positions. Each of the two positions in which an end of the lateral bar extends beyond the cylinder circumference enables two possible functions to be carried depending on the direction of rotation of the key in the cylinder. Thus it is conceivable that their may be 5 functions that are possible to be carried out from the 3 different positions possible for the lateral bar. This would be easily achieved where the cylinder is used in an electric actuated lock.  
           [0015]    This arrangement may be used with a cylinder in a pin tumbler lock. Preferably it is used in a lock of the type in which a latch means is able to be actuated if elongated members are able to pass through associated slots in latch elements there being two sets of latch elements such that, when the slots in each set of elements are aligned, the actuating members can pass through, wherein one set of latch elements are positioned by a setter which effectively programs the lock and the other set are positioned by a key that corresponds to the shape of the setter to align the slots of corresponding elements in each set. This is a lock of the kind described in U.S. Pat. No. 4,898,011. When the cylinder is removed the biscuit or programmable setter can be replaced, which means that the key that can be used to remove the cylinder is the code changing key.  
           [0016]    In another aspect of this invention there is provided a lock and key in which the lock has a keyway and the base of the keyway is formed by a plate having an upstanding longitudinally extending rib that lies parallel to the base of the key wherein the base of the key and the longitudinally extending rib have complementary mating longitudinally extending protrusions and recesses and the base plate is removeable from the lock. This provides a replaceable component of the lock that can be changed as part of a rekeying exercise. This provides a new range of combinations in addition to those provided by the arrangement of latch elements. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    A preferred embodiment of the invention using the coding system disclosed in U.S. Pat. No. 4,898,011 will be described with reference to the drawings in which  
         [0018]    [0018]FIG. 1 is an exploded view of the cylinder and barrel arrangement for a night latch in accordance with one embodiment of this invention;  
         [0019]    [0019]FIG. 2 is a schematic illustration of the keys and lateral bar configurations useful in this invention;  
         [0020]    [0020]FIG. 3 is an exploded view of a deadbolt lock in accordance with another embodiment of this invention;  
         [0021]    [0021]FIG. 4 is a set of views of the key plate;  
         [0022]    [0022]FIG. 5 is a set of views of the inner end plate to the key cylinder;  
         [0023]    [0023]FIG. 6 is a pair of views of the cylinder body;  
         [0024]    [0024]FIG. 7 is a view of the pawl which rotates within the cylinder body;  
         [0025]    [0025]FIG. 8 is a set of views of the guide for the T pins;  
         [0026]    [0026]FIG. 9 is a set of views of the side plate at the end of the T pin guide arrangement;  
         [0027]    [0027]FIG. 10 is a set of views of the pin location plate;  
         [0028]    [0028]FIG. 11 is a pair of views of the T pins;  
         [0029]    [0029]FIG. 12 is a view of one of the pins in the two sets of coding pins;  
         [0030]    [0030]FIG. 13 is view of the spring top plate which covers the two sets of pins;  
         [0031]    [0031]FIG. 14 illustrates another embodiment of the lock mechanism. 
     
    
       [0032]    The latching mechanisms of the two locks in FIGS. 1 and 3 are conventional and based on commercially available lock mechanisms so that the cylinder and its components can be used to replace an existing cylinder.  
         [0033]    The key code cylinder is defined by the end plates  40  and  50  held together by the spring top plate  130  and the bottom plate  135  all of which fit within the barrel  60  which in turn fits within the body  10  of FIG. 1 or the cone  156  shown in FIG. 3. The bottom plate  135  not only functions to secure the end faces  40  and  50  but also acts as the floor of the key way for the setter and the key. The barrel  60  is fixed and the spring  65  on its circumference functions as part of the latch mechanism as described below. The key code cylinder contains the coding section defined by the pawl  70  and the pin location side plate  90 . The pawl incorporates a wedge protrusion  71  on its outer face which protrudes through the window  62  of barrel  60  when the cylinder is in its neutral position. The coding section is made up of two rows  32  and  33  of latch pins  120  which are separated by a separation plate  34  and held between the pin location plates  90  and  100 . The plate  100  incorporates elongate slots  102  for the T bars  110  to pass through. The pins  120  as seen in FIG. 12 each have a coding slot  122  for the passage of the T bars  110  which are held within the grooves  85  of the T bar slide or guide  80  and pass through the elongate slots  102  of the pin location plate  100 . The T bar slide  80  [FIG. 8] incorporates springs  84  fitting within the grooves  82  in the side arms  81  of the T bar slide  80 . These springs  84  abut against the ends of the screws  132  that also serve to fasten the top plate  130  to the code cylinder ends  40  and  50 . The springs  84  urge the slide  80  away from the pin location plate  90 . The T bar slide incorporates grooves  85  to guide the T bars  110 . The T bars  110  [FIG. 11] are notched at their ends with a v slot  111  to make it difficult to probe and pick the lock. If in picking the lock the pins are biased upwardly the notched ends formed by the V slot  111  will engage one of the grooves  128  which lie immediately above and below the coding slots  122  as shown in FIG. 12. This will cause the lock to stick and frustrate attempts to pick the lock.  
         [0034]    The pins  120  [FIG. 12] are biassed downwardly by springs  123  which each fit into the cylindrical spring chamber  124  of each pin and abut the spring top plate  130 . It is within the ambit of this invention to use a single leaf spring to bias the pins  120 . As shown the coding slots  122  are formed in a wall of each pin which abuts the next pin to form an enclosed groove for passage of the t bars. This reduces the width of each pin and the length of each row of pins. However it is within the ambit of this invention to include one or more wider pins to accommodate a fully enclosed hole.  
         [0035]    Rotation of the end plates  40  and  50  by the key  28  [FIG. 2] in the key hole  41  allows the inclined surface wedged protrusion  71  of the pawl  70  [FIG. 7] to be engaged by the cylindrical wall of the fixed barrel  60  and push the T bars  110  toward the pin location plate  90 . If the slots  122  in the rows  32  and  33  of the pins  120  are aligned, the T bars can travel though to abut the plate  90  and thus allow the coding cylinder to rotate. Rotation of the end plate  50 , which functions as a drive member, causes actuation of the latching mechanism via the tongue  150  engaging the slot  153  in the latch actuator  152  [FIG. 1].  
         [0036]    The key way for the key  28  corresponds with pin row  32  and that of the code programming setter [not shown] with pin row  33 . The key and setter will have matching slots to lift each pin in the rows  32  and  33  to matching incremental positions in the manner described in U.S. Pat. No. 4,898,011. When the key is fully inserted it allows rotation of the coding cylinder. The setter is inserted via the setter slot  52  in the end plate  50  and can only be accessed by removal of the coding cylinder. The setter may be inserted via a slot provided in the front plate  41  but for added security it is preferred to provide access via the end plate  50  which can only be accessed by removing the coding cylinder The bottom plate  135  which defines the keyway for key  28  and the setter has an upstanding rib  136  which lies between the key and the setter. This rib  136  may incorporate longitudinal ribs or grooves that engage with complementary ribs or grooves in the key  28  and setter and act as a further means of ensuring that the key and setter are correct. A different broach design with a different arrangement of longitudinal ribs and grooves on the upstanding rib  136  means that all new setters and keys will have to have a complementary broach arrangement. This provides a new range of combinations in addition to those provided by the arrangement of pins and can be used for different models of locks. Optionally, the bottom plate may be removeable, to provide a replaceable component of the lock, that can be changed as part of a rekeying exercise.  
         [0037]    The functions which can be performed by the key  28  will depend on its interaction with the function slide  20  as shown in FIG. 2. The slide  20  incorporates a groove  22  which houses the spring  21 . The spring  21  is biased by the flange  73  of pawl  70  [FIG. 7] which seats within the end of groove  22 . The slots  25 ,  26  and  27  cut into the slide  20  seat into the corresponding slots on the keys  28 A,  28 B and  28 C as shown in FIG. 2. Once the key  28  is inserted the slide  20  is positioned relative to the end face  40  so that its ends lie within the circumference of end face  40  or one of its ends  23 , 24  extends beyond the periphery of end face  40 . Key  28  A with slot  25  positions the slide  20  so that the flange  23  protrudes beyond the circumference of the coding cylinder to engage with the stops on the latching mechanism. When no key is inserted the spring  21  biasses the slide  20  so that its flange  23  protrudes in the same position preventing removal of the cylinder. For the night latch of FIG. 1 or the deadlock of FIG. 3 the key  28 A enables the latch to be opened or closed in its latching position. With reference to FIG. 1 the key  28 A can only rotate the cylinder clockwise because of the engagement of the end 23  with the flange  66  of the spring  65  fitted to the barrel  60 . Key  28 A is the common key used to gain entry.  
         [0038]    Key  28 B with slot  26  positions the slide so that its ends  23  and  24  are co-terminal with the circumference of the coding cylinder. This enables this key to be used to remove the cylinder primarily to change the setter.  
         [0039]    Key  28 C which incorporates slot  27  positions the slide  20  so that flange  24  protrudes beyond the circumference of the coding cylinder. This flange  24  engages the stop of the latching mechanism that prevents actuation of the latch knob of the night latch [FIG. 1] or throws the dead bolt to its fully extended position [FIG. 3]. This means that the throwing of the dead bolt can be reserved for one key .  
         [0040]    In FIG. 15 an alternative mechanism is disclosed with a smaller number of parts.  
         [0041]    The key  201  is inserted into the key way  205  of the lock body  210  while the setter  202  is inserted into a keyway on the opposite face of the body  210  to keyway  205 .  
         [0042]    Compared to the embodiment shown in FIG. 1 the differences are: The top plate  230  is shaped to better contain the springs  223  and pin rows  232  and  233   
         [0043]    The T bar guide  280  is equivalent to the pawl  70  and T bar slide  80  of FIG. 1. the T bar guide  280  carries the T bars  310  and with plate  300  guides the movement of the T bars  310 .the top plate is secured in position with the longitudinal pin  240 . In other respects the embodiment of FIG. 15 functions similarly to the other embodiments.  
         [0044]    Other variations may be made without departing from the core teachings of this invention. For example with reference to FIGS. 1 and 3 the top plate  130 , the separation plate  34  and the bottom plate  135  may be formed as one piece to fit within a hollow body section.  
         [0045]    From the above it can be seen that the present invention provides a keying arrangement which enables different keys to actuate different functions within the lock. The setter enables the lock to be rekeyed without having to change the code cylinder. A lock can be rekeyed by a new set of keys which would consist of a setter for the code cylinder, a cylinder removal key, a master key and as many common keys as is needed. Each of the keys will have the same code as the setter but differ in respect of the grooves which interact with the function slide  20 . Because the number of moving parts in the lock as described above is much less than in a conventional pin tumbler lock it is easier to assemble. It is also possible to make most of the components by moulding which is less expensive than the machining required in pin tumbler locks.

Summary:
A lock and key set in which the lock includes a cylinder rotatable in a barrel which barrel is rotatable to actuate the latch wherein the cylinder incorporates a laterally spring biased bar which includes slots or projections adapted to engage with corresponding slots or projections on the keys so that the bar can be aligned in one of three positions in which its ends are within the diameter of the cylinder or one of each end of the bar projects beyond the cylinder to engage with the barrel. This is applicable to pin tumbler locks and locks of the type in which a latch means is actued by movement of actuating members through associated slots in latch elements there being two sets of latch elements such that when the slots in each set of elements are aligned, the actuating members can pass through. One set of latch elements are positioned by a setting key and the other set are positioned by a corresponding access key.