Programmable lock having incidental change control

A programmable cylinder lock for operating a bolt or a latch, that can be reconfigured to operate with a user key selected from a set of keys, without disassembling the lock or replacing the tumblers, including:

• a. a set of keys comprising a plurality of user keys;
• b. a housing having a cylindrical bore with an inner surface and a plurality of driver chambers intersecting the inner surface;
• c. a plurality of drivers, each driver being movable within one of the plurality of driver chambers, and having a means for urged each driver toward the inner surface;
• d. a plug having a cylindrical periphery and rotatably mounted within the bore so as to form a shear surface at the interface with the inner surface, the plug being rotatable from a key insertion position to an operating position, and to a programming position, the plug having:
• i) a keyway configured to receive a key selected from the set of keys,
• ii) a plurality of tumbler chambers intersecting the plug periphery and the keyway, each tumbler chamber being aligned with a corresponding one of the plurality of driver chambers when the plug is at the key insertion position to form a pin chamber, and
• iii) at least one retainer cavity disposed within the plug, spaced apart from a corresponding one of the plurality of tumbler chambers, and being alignable with the corresponding driver chamber when the plug is at the programming position;
• e. a plurality of tumblers, each tumbler being movable within a corresponding one of the plurality of tumbler chambers;
• f. at least one lock configuration change ball, movable within the lock between at least a second position within the at least one retainer cavity, and a first position within the corresponding driver chamber;
• and
• g. a cavity carriage movably positioned within the plug, and forming a portion of the periphery of the plug, within which the at least one retainer cavity is formed, the cavity carriage movable relative to the plug between a first aligned position wherein the at least one retainer cavity is aligned with the corresponding driver chamber when the plug is in the programming position, and the change ball can be moved between the at least one retainer cavity and the corresponding driver chamber, and a second non-aligned position wherein the at least one retainer cavity is not aligned with the corresponding driver chamber, and the change ball cannot be moved between the at least one retainer cavity and the corresponding driver chamber when the plug is in the programming position.