US3729964A

US3729964A - Lock

Info

Publication number: US3729964A
Application number: US00155162A
Authority: US
Inventors: Ming Hsu S Shiao
Original assignee: Proof Lock International Inc
Current assignee: Proof Lock International Inc
Priority date: 1971-06-21
Filing date: 1971-06-21
Publication date: 1973-05-01
Anticipated expiration: 1990-05-01
Also published as: CH536920A; SU442609A3

Abstract

A lock capable of being operated by a limited access key and an unlimited access key so as to control the number of persons having lock opening capability. The lock is setable to a trapping phase whereby a key normally operable to open the lock will be rendered inoperable and attempted use of the key will result in the key being trapped in the lock.

Description

O United States Patent 11 1 1 1 3,729,964 Hsu 5] May 1, 1973 LOCK [56] References Cited [75] Inventor: Sam Shiao-Ming Hsu, New York, UNITED STATES PATENTS N.Y. 3,656,328 4/1972 Hughes ..70/276 1,092,474 4/1914 Carroll ..70/284 g Proof Lock International, New 3,408,841 11/1968 Hsu ..70/390 York, NY.

Primary ExaminerRobert L. Wolfe 22 d. 2 7 I Flle June 1 l9 1 Attorney-Alex Friedman et al. [21] Appl.No.: 155,162

[57] ABSTRACT 52 US. Cl. ..70/338, 70/358, 70/382, A lock capable of being Operated y a limited access 70/389 key and an unlimited access key so as to control the [51] Int. Cl ..E05b 27/00, E05b 35/08 number of Persons having 00k Opening capability. [58] Field of Search ..70/3 89, 358, 390, 12 i E 133: 2 i fz gi f i g ffgS ig r a y e 70/382 340-343 419-421 inoperable and attempted use of the key will result in the key being trapped in the lock.

19 Claims, 26 Drawing Figures a l x I 0 Z 1 a l 5 //4 #5 Patented May 1, 1973 9 Sheets-Sheet 1 INVEN'IOR. SAM SHIAO-MING HSU ATTORNEYS l I I I I "I :I l I HII Patented May 1, 1973' 3,729,964

9 Sheets-Sheet 4 INVENTOR. SAM SHIAO-MING HSU ATTORNEYS Patentd May 1, 1973 3,129,964

9 Sheets-Sheet 5 FIG. 9

w, FIG. 1/ w I INVENTOR, A A SAM SHlAO-MING HSU Patented May 1, 1973 3,729,964

9 Sheets-Sh eet a ENTOR.

ATTORNEYS SAM Q-MING HSU Patented May 1, 1973 3,729,964

9 Sheets-Sheet-9 FIG. /9 //5 50 FIG-23 INVENTOR. SAM SHlAO-MING HSU ATTORNEYS LOCK BACKGROUND OF THE INVENTION This invention relates generally to an improved lock whose operation can be controlled so as to render the lock inoperable even to persons to whom keys have been issued. While locks have been available which prevent unauthorized entry by outside persons, a major problem exists in that companies and individuals find it necessary to issue keys to employees or others so that such persons can gain access to a locked area to perform certain functions. Once a key is issued, it has been possible to duplicate such keys and use the duplicates at anytime until the lock is changed. Additionally, persons in possession of a. key may use the key at unauthorized times, for example at night or on holidays.

With existing locks having extensive master key systems, it is possible for an individual having knowledge of locks to determine the master key by examination of the tumblers of a few of the locks in the master system. Also, present master systems do not have changeability capability to expand or contract the scope of the master system without replacement of the system of tumblers.

The instant invention is concerned with a substantially improved lock system with greatly increased versatility in all areas of security.

SUMMARY OF THE INVENTION Generally speaking, this invention relates generally to a lock designed to prevent entry by persons who attempt to use their own keys or stolen or duplicated keys at an unauthorized time. The lock of the instant invention also includes means for preventing forced methods of entry such as picking. Additionally, existing master key lock systems are vulnerable to the loss of a master key. Master key systems are typically used during construction of a building to reduce costs but the buildings are susceptible to theft and pilferage by construction and other personnel who have obtained or duplicated master keys. For example, many apartment houses have a high incidence of theft through the use of master keys during the first months of occupancy until the tenants install a second look of their own.

Also, existing locks provide minimal deterrence to burglars in that the burglars take little risk when attempting to defeat known locks. However, the probability of failure of access and the probable identification of the would be thief can provide a great degree of deterrence.

Accordingly, it is an object of this invention to provide an improved lock having greater safety charac* teristics.

Another object of the invention is to provide an improved lock having a master system incorporating means for shifting or modifyig the master system without changing parts in the lock.

A further object of the invention is to provide a lock capable of preventing unauthorized use of master keys while permitting authorized use of such keys.

Still another object of the invention is to provide a lock which allows for identification of an individual who attempts to use his key for unauthorized purposes.

Still other objectsand advantages of the invention will in part be obvious and will in part be apparent from the specification and drawings.

In a preferred embodiment of the lock of the instant invention, a standard size lock cylinder housing cooperates with a rotatable dial which is externally accessible. Three types of keys are provided: a limited access key, a control key and a permanent access key. The limited access key can open the look under certain prescribed circumstances. The control key is used to control the circumstances and thus to set the mechanism to permit or prevent opening of the lock by use of the limited access key. The permanent access key acts independently for operation of the lock at all times.

The lock has a trapping phase and a non-trapping phase which operate on the limitedaccess key. The phases are set by use of the control key. When the lock is in the trapping mode, the lock can be operated by a limited access key only by rotating the dial to a preset number or position (opening number). In the trapping mode, a limited access key will not open the lock if the dial is not set to the opening number but attempted opening will result in trapping of the limited access key thereby preventing its removal. When a key is trapped in the lock, the control key can be utilized to return the lock to the non-trapping mode to thereby release the trapped limited access key.

If the lock is in the non-trapping mode, the limited access key can be utilized regardless of the position of the dial. Even with the lock in trapping mode, authorized individuals with limited access keys can successfully operate the lock by first setting the dial to the opening number.

Each of the numerated keys has its own keyway and operates on a different combination of tumblers. Even if the lock is set to the trapping mode, the permanent access key is capable of overriding the key trapping mechanism and can successfully operate the lock at all times, regardless of the position of the dial.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference is had to the following descriptiontaken in connection with the accompanying drawings, in which:

FIG. 1 is an exploded, elevational view ofa lock constructed in accordance with a preferred embodiment of the instant invention;

FIG. 2 is a front elevational view of the lock of FIG. 1 in assembled condition and with a limited access key inserted in its keyway;

FIG. 2A is a partial sectional view taken along line 2A--2A ofFlG. 2;

FIG. 3 is a broken away view of the lock of FIG. 2 mounted in a door;

FIG. 4 is a perspective view of a. permanent access y;

FIG. 5 is a perspective view of a limited access key;

FIG. 6 is a perspective view ofa control key;

FIG. 7 is a partial front elevational view of a lock showing a limited access key in a trapped position;

FIG. 8 is a view similar to FIG. 7 with a control key in position for releasing the trapped limited access key;

FIGS. 9 through 1 1 are partial plan views of the stem portions of typical limited access keys showing examples of identification of trapped keys;

FIG. 12 is a partial sectional view showing a control key in position for insertion;

FIG. 13 is a view similar to FIG. 12 but showing the control key in inserted position and rotated to the nontrapping mode;

FIG. 14 is a cross sectional, elevational view of the lock with multiple tumblers for coding of a limited access key and for master keying of limited access keys;

FIG. 15 is a sectional view taken along line 15-15 of FIG. 2;

FIG. 16 is a partial sectional view taken 16-16 ofFIG.15;

FIG. 17 is a partial elevational view of the trapping mechanism;

FIG. 18 is a sectional view taken along line 18-18 of FIG. 17;

FIG. 19 is a partial elevational view showing the trapping and selection mechanism in non-trapping mode;

FIG. 20 is a view similar to FIG. 19 with the trapping mechanism in trapping mode;

FIG. 21 is a view similar to FIG. 20 with a limited access key inserted and partially turned and with the selection mechanism in proper position for opening;

FIG. 22 is a view similar to FIG. 21 but showing the selection mechanism set for the trapping of a limited access key with the key trapped;

FIG. 23 is a partial view of the trapping mechanism;

FIG. 24 is a view similar to FIG. 23 showing the mechanism in the first stage of trapping; and

FIG. 25 is a view similar to FIG. 24 with the trapping mechanism in the final stage of trapping.

along line DESCRIPTION OF THE PREFERRED EMBODIMENTS The lock of the instant invention operates with a limited access key which, in the usual manner, operates a number of vertical tumblers. However, the key has a circular cross section to mate with the circular cross section of the keyway. This configuration renders it extremely difficult to pick the lock since there is no bearing surface against which a torsion spring may bear in attempted picking of the lock. In order to provide a motion transmitting surface between the key and the lock, the end of the key is generally chisel-shaped for driving cooperation with a mating recess.

To control the operation of the tumblers, the shaft of the key is provided with a plurality of dimples or bores which control the heights of the various tumblers.

As an additional safety and identifying factor, the limited access key is weakened between the handle and the shaft or stem so that the handle will break off if a trapped key is forced. Once the trapped key is released by a control key, the shaft can be readily withdrawn from the lock and the individual to whom the key was assigned may thereby be identified by suitable coding on the key stem.

A control key is provided with a plurality of prongs and a flange for insertion into the front of the lock. The. 7

control key fits around a limited access key and acts on,

the trapping mechanism through a series of tumblers to release the trapping mechanism and permit a trapped limited access key to be withdrawn.

A permanent access key operates all tumblers. A control portion prevents key trapping and thus allows use of the permanent access key regardless of the trapping phase of the lock.

The lock may include a dial which, when set to an opening number, allows a limited access key to open the lock even with the lock in trapping mode. The opening number can be reset at will by the owner.

A limited access key which has become trapped can be identified by variations in the dimples or bores in the trapped shaft. These can be recorded and compared.

Also, the vertical tumblers may be split to double the number of possible shear lines so that different bore depths may be used to operate the lock. The variation in bore depths can be recorded and coded as identifying features of the keys. Alternatively, the stems can be stamped with identifying indicia which can be recorded when the keys are distributed.

With the foregoing general description of the preferred embodiment in mind, a detailed description of the mechanism will now ensue.

Referring now to FIGS. 1, 2, and 2A, cylinder housing is provided with a bore 51 in which is mounted a permanent access disc 53 and a primary key plug 52. Bore 51 communicates with an enlarged bore 51A in which is mounted a trapping plug 54 and a beveled washer 55. Externally of housing 50 is a lock actuating cam 56 which is connected to primary key plug 52 through screws 57 passing through trapping plug 54 and beveled washer 55.

Slidably mounted in housing 50 and extending into primary key plug 52 are a plurality of tumblers 58 acted on by a plurality of drivers 59, springs 60 and plugs 61. A plate 61A is mounted in housing 50 to retain plugs 61.

Bore 51 extends through the front face of housing 50 and includes cylindrical bore portions 518 and 51C. Mounted within bore portion 51C is a control cam 79, a false pick disc and a tumbler retainer disc 81. Spaced circumferentially about the central axis of bore 51 are a plurality of drivers 62 operated on by springs 63 to outwardly bias a series of

tumblers

83, 84, and 86. Tumbler retaining disc 81 carries a connecting pin 82 which extends into false pick disc 80. The length of drivers 62 is such that they do not interfere with the rotation of primary key plug 52 so long as drivers 62 are not depressed. A limited access key is indicated at 64 and extends through primary key plug 52 and into cooperating engagement with trapping plug 54 whereby rotation of the trapping plug 54 through key 64 rotates the lock actuating cam 56. When limited access key 64 is inserted, it acts on tumblers 58 as best seen in FIG. 2A to permit rotation of primary key plug 52. With drivers 62 in the non-depressed condition, rotation of primary key plug 52 is not prohibited by horizontal tumblers 83 through 86.

Referring additionally to FIG. 15, a passage 67 extends through cylinder housing 50 and has slidably received therein a trapping pin 66, said pin being biased rearwardly by means of a spring 68 held in position by a front plate 68A fitted on to cylinder housing 50. A trapping disc 69 is secured to one end of trapping pin 66 by means of a screw 71 and trapping disc 69 is provided with a depending trapping finger 70. Trapping finger 70 extends into the path of rotation of trapping plug 54. Trapping plug 54 is provided with a central retaining shoulder 73, a recessed surface 72 and a deeper recessed surface 74 on each side of retaining shoulder 73. The side walls between retaining shoulder 73 and recessed surfaces 72 are indicated at 75. When the lock is in the trapping mode, trapping finger 70 rests against retaining shoulder 73 (FIG. 23). When a limited access key is inserted and the primary key plug 52 is rotated in either direction, trapping plug 54 is also rotated whereupon trapping finger 70, under the biasing of spring 68 moves into contact with recessed surface 72 (FIG. 24) and retaining shoulder 75 prevents return rotation of the limited access key. On continued rotation, trapping finger 70 drops into deeper recessed surface 74 (FIG. 25) and is held therein by means of walls 76. In such position, the limited access key may not be rotated in either direction. Also, with tumblers 58 in a rotated position bearing against the inside surface of the cylinder housing, the tumblers may not be deflected to permit withdrawal of limited access key 64 and thus the lock may not be operated and the key is trapped preventing removal thereof.

FIG. 7 shows a limited access key in trapped position. To effect a release of the trapped key, a control key 77 (FIG. 6) must be used. Control key 77 includes a spaced flanged 90 and prongs 87 for operation of tumblers 83 86 through front plate 68A. A passage 89 in front plate 68A has a configuration adapted to mate with spaced flanged 90 and front plate 68A is undercut at 91 to permit spaced flange 90 to bear on the front plate as best seen in FIG. 13.

As best seen in FIG. 17, trapping pin 66 includes a depending control finger 78 positioned in the path of rotation of control cam 79. Control cam 79 includes cam surfaces 93 and 94 for controlling the axial position of trapping pin 66. When limited access key 64 is trapped as shown in FIG. 7, control key 77 is fitted about the shaft of the limited access key and moved into the position shown in FIG. 8 with prongs 87 depressing tumblers 86 whereby to effect rotation of control cam 79. Rotation of control key 77 in the direction indicated by the arrowing FIG. 8 causes control finger 78 to ride on cam surface 93 to move trapping pin 66 to the right to the phantom line position shown in FIG. 17 to thereby move trapping finger 70 out of trapping relationship with trapping plug 54. After the trapping pin has been moved to the right by cooperation between control finger 78 and cam surface 93 (FIG. 18), control finger 78 retains trapping pin 66 in a non-trapping mode by cooperation with retaining flange 95.

Conversely, if it is desired to set the lock to the trapping mode, control key 77 is rotated in a counter clockwise direction as viewed in FIG. 8 whereby the under surface of cam surface 94 drives trapping pin 66 to the left as viewed in FIG. 17 under the biasing of spring 68 to the full line position thereby placing trapping finger 70 in a position to latch with trapping plug 54 as hereinabove described. Note that tumbler retaining disc 81 is pinned to rotate with false pick disc 80 through connecting pin 82 and the provision of

tumblers

85 and 86 with a parting line will permit rotation of false pick disc 80 when an attempt is made to pick the control phase of the lock whereby picking will be prevented as control cam 79 will not be rotated. Note also that the apertures through tumbler retaining disc 81 are smaller in diameter than the tumblers to prevent outward movement of the tumblers. The foregoing is best seen in FIG. 2A.

Referring to FIG. 16, a ball 96 rides in a bore 96A under the biasing of a spring 98 held in position by a screw 98A. Ball 96 enters an annular recess 97 in trapping pin 66 so as to retain the trapping pin in the righthand position as viewed in FIG. 7 when the trapping pin has been biased to the non-trapping position by cam surface 93 to prevent movement of the trapping pin to the trapping position while control cam 79 is rotated to bring retaining flange to the neutral position opposite control finger 781.

Referring again to FIGS. 2 and 2A, seven sets of

horizontal tumblers

83, 84, 85 and 86 are provided with access thereto being through apertures in tumbler retainer disc 81. As seen in FIG. 6, control key 77 is provided with five prongs 87 for engagement with five of the aforesaid tumbler sets. The split line between

tumblers

84 and 85 is indicated at 101 and the plane of rotation between control cam 79 and housing 50 is indicated at 101A. With control key 77 in operative position, the five tumbler sets operated by prongs 87 bring split lines 101 into the plane 101A with respect to the five tumbler sets operated by prongs 87. By rotation of control key 77, control cam 79 can thus be rotated for setting trapping pin 66 to a trapping or a non-trapping position, depending on the direction of rotation. These positions cannot be externally distinguished and thus one with a limited access key will be unable to determine in advance whether or not his key will be trapped. The deterrent value of this is apparent. Also, if a limited access key 64 has been trapped in the position shown in FIG. 8, control key 77 can be placed around limited access key 64 by utilizing slot 99 where after control key 77 can be rotated in the clockwise direction as indicated by the arrow in FIG. 8 to thereby move trapping pin 66 to the non-trapping position whereby limited access key 64 is released and may be rotated to the normal position and removed.

As aforenoted, seven sets of tumblers 83 86 are provided but the control key 77 operates only five tumbler sets. The remaining two tumbler sets are acted on by the permanent access key 102 (FIG. 4) to be hereafter described. However, it should be noted that the two tumbler sets not acted on by control key 77 are normally positioned with a split line in plane 101A so that the two tumbler sets need not be operated for rotation of control cam 79 by control key 77.

The permanent access key 102 is provided with a plurality of dimples 105 which are identical to the dimples 105 in limited access key 64 with the stems 104 being likewise identical. The permanent access key 102 is provided with a plurality of prongs 103, the prongs in the embodiment disclosed being seven in number. The permanent access key 102 is capable of opening the lock regardless of whether trapping pin 66 is in the trapping or non-trapping phase. When the permanent access key 102 is inserted, the prongs 103 act on the seven sets of tumblers 83 86 in the following manner. Permanent access disc 53 defines a split plane 106 between itself and cylinder housing 50. A split plane 107 is also defined between false pick disc 80 and control cam 79. When tumblers 83 86 are depressed by prongs 103, all seven sets of tumblers 83 86 are brought into register with

split planes

106 and 107 whereby tumbler retainer disc 81, false pick disc 80, permanent access disc 53, primary key plug 52 and trapping plug 54 may be rotated. During use of a limited access key 64, permanent access disc 53 remains stationary.

Referring to FIGS. 1, 2A and 15, permanent access disc 53 is provided with a slot 108 positioned opposite a blocking arm 109 on trapping plug 66. When trapping is to be effectuated, trapping plug 66 must move fully toward the rear so that trapping finger 70 may enter recessed

surfaces

72 and 74. However, when using the permanent access key 102, the rotation of permanent access disc 53 moves slot 108 out of alignment with blocking arm 109 whereby trapping plug 66 is prevented from full rearward movement and thus trapping finger 70 cannot enter recessed

surfaces

72 and 74 to effect a trapping by trapping plug 54. For this reason, the permanent access key 102 will always operate the lock, regardless of whether or not the lock is in a trapping mode.

It should be noted that the rotation of trapping plug 54 and through it the lock actuating cam 56 are accomplished by means of a recess 123 in trapping plug 54 and a chisel point 124 on the end of stems 104 of the limited and permanent access keys.

An additional feature of the disclosed embodiment is its capability of permitting one with a limited access key to operate the lock even when the lock is in trapping mode. This is accomplished by means ofa dial 110 rotatably mounted on cylinder housing 50 and externally accessible from the front of the look outside a door 125 as indicated in FIG. 3. A plurality of numerals 126 and corresponding marks 127 are engraved on the face of dial 110. An indicator mark 1 18 for visual alignment of the indicia (numerals 126) is provided on a washer 117 which mounts over cylinder housing 50 and bears against door 125.

Referring to FIG. 2, dial 110 is provided with a plurality of slots 111 on the inner circumferential surface thereof. The slots are equal in number to the numerals 126 inscribed on the face of the dial. A selectivity ring 112 (FIGS. 1 and 2A) and a retaining washer 113 are mounted over cylinder housing 50 within dial 110. Selectivity ring 112 is provided with two projections 114 adapted to interfit with dial slots 111 in a releasable manner. Selectivity ring 112 carries a plurality of spring arms 115 which bear against washer 113 and releasably bias projections 114 into dial slots 1 1 1.

A blocking arm 116 extends outwardly from selectivity ring 112 and rotates with the selectivity ring within washer 113. The blocking arm is adapted to prevent the trapping of a limited access key when the lock is in trapping mode if the dial has been set to the proper number. Referring to FIGS. 19 through 23, a selection arm 119 carried by trapping pin 66 is shown in various operative positions. In FIG. 19, selection arm 119 is shown with trapping pin 66 in the non-trapping mode. In FIG. 20, selection arm 119 is shown with the lock in the trapping mode and blocking arm 1 16 in the desired selected position to prevent trapping of the limited access key. FIG. 21 shows selection arm 119 moved up against blocking arm 116 as will occur when a limited access key is inserted in the lock and rotated. At such point, trapping finger 70 will no longer be blocked by retaining shoulder 73 (FIG. 23) and trapping pin 66 will move slightly toward the rear of the lock. However, movement of the trapping pin to the trapping position will be prevented by engagement between selection am 119 and blocking arm 116 as shown in FIG. 21. However, had dial not been rotated to the correct number to bring blocking arm 116 to the correct position, a non-blocking position such as that shown in FIG. 22 will result and thus selection arm 119 will move with trapping pin 66 to the rear to effectuate a trapping of the limited access key as hereinabove described.

With selection arm 119 in the path of movement of blocking arm 116 as dial 110 is rotated, means are also provided for changing the number which will allow a limited access key to open the lock even when the lock is in trapping mode. It can be seen from FIG. 22 that further rotation of selectivity ring 112 is prevented in one direction by selection arm 119. However, dial 110 can be manually rotated with relative movement being permitted by the releasable engagement between projections 1 14 and slots 1 1 1. In FIG. 22, the displacement of blocking arm 116 from the blocking position as represented by FIG. 21 constitutes the equivalent of a displacement of one slot 111 or a displacement between two adjacent numerals 126. Thus, for example, with the numerals oriented as shown in FIG. 3, the rotation of the dial to numeral 24 when the trapping pin is in the trapping position as represented by FIG. 22 would mean that opening number 23 has been selected as a new opening number. Thus, to change the correct opening number, it is only necessary to insert a limited access key with the lock in trapping mode and with the dial on any nonopening number, turn the key to have it trapped and then rotate dial 110 so that a new opening number is set. The control key 77 is used to release the limited access key.

The sixth tumbler set (FIG. 2A) includes a driver 59 and a plug 129 having a cone shaped tip 130, with a spring 131 acting between driver 59 and plug 129. The cone shaped tip 130 projects into the area of dial slots 111 and thus provides a releasable detent or indexing ratchet for dial 1 10.

If desired, the foregoing dial feature which allows opening with a limited access key when the lock is in trapping mode, can be omitted.

If one with a limited access key attempts to use the key at an unauthorized time when the lock is in trapping mode, the key will be trapped and cannot be removed. Limited access key 64 (FIG. 5) is preferably provided with a section of reduced dimension 128 so that if an attempt is made to forcibly remove the limited access key the key will break through the section of reduced dimension 128 thereby preventing further attempts at removal while assuring that a sufficient length of stem 104 projects beyond the face of the lock to permit ready removal by one utilizing a control key 77. To identify the owner of the trapped key, suitable indicia may be engraved on stem 104 and the indicia may be recorded in a book identifying the individual to whom the key was issued.

It is also possible to code the limited access key in such a way that the configuration of the key carries the coding and cannot be duplicated without duplicating the coding.

Referring first to FIG. 14, an embodiment is shown wherein each tumbler 58 has been replaced by two tumblers 58A and 58B resulting in the provision of two split lines 122A and 1228 which means that, as respects each tumbler, there are two positions at which the tumbler will permit rotation of the primary key plug 52.

Referring to FIGS. 9 through 11, three different stems 104 are shown, each with different sets of dimples 105. While a visual comparison of dimples 105 shows different sizes and depths of dimples, each of the stems 104 is capable of opening the same lock in view of the multiple split lines shown in the embodiment of FIG. 14. If, for example, there are six tumbler sets with two split lines in each set the number of key configurations that would open the lock would be 2. Thus, for example, with 64 different key configurations, limited access keys can be issued to 64 employees and the configurations recorded. If a limited access key is trapped, the identity of the key holder can be readily ascertained. Also, if the key holder has a duplicate made, the coding will automatically become part of the duplicate.

It should be noted that tumbler sets can be master keyed by providing master key split lines. For example,

the limited access key can be master keyed but capable of opening only those locks set to a preselected opening number when such locks are in a trapping mode. The splits indicated between tumblers 58A and 58B in FIG. 14 can be used as part of a master key system for limited access keys. Also, the setting numerals 126 can be used as part of a changeable master key system using limited access keys with or without splits as shown in FIG. 14.

It will thus be seen that the objects set forth above, 1

and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter oflanguage, might be said to fall therebetween.

What is claimed is:

1. A lock comprising a housing, key plug means movably mounted in said housing, first tumbler means carried by said housing and key plug means for controlling movement of said key plug means, a first key for insertion in said key plug means for moving same, trapping means cooperating with saidkey plug means for slectively arresting movement of said key plug means at a partially moved position, control means cooperating with said trapping means for setting said trapping means to a first non-arresting position and to a second arresting position, said key plug means preventing withdrawal of said first key when said key plug means is arrested in said partially moved position, and a second key for operating said control means.

2. A lock as claimed in claim 1 and including second tumbler means cooperating between said control means and said key plug means for actuation by said second key.

3. A lock as claimed in claim 2 wherein said key plug means includes override means acted on by said second tumbler means for preventing operation of said trapping means, and further including a third key for operating said first and second tumbler means regardless of the position of said trapping means.

4. A lock as claimed in claim 2 and further including selection means carried by said housing for preventing operation of said trapping means regardless of the position of said trapping means.

5. A lock as claimed in claim 3 wherein said key plug means includes a trapping plug .having recessed surfaces and said trapping means includes a trapping pin having a trapping finger thereon adapted for engagement with said recessed surfaces.

6. A lock as claimed in claim 5 wherein said control means includes a control cam, said trapping pin having a control finger thereon in operative engagement with said control cam.

7. A lock as claimed in claim 6 wherein said trapping pin includes a blocking arm in operative engagement with said override means.

8. A lock as claimed in claim 2 wherein said first key includes first tumbler operating means for operating said first tumbler means and said second key includes second tumbler operating means for operating said second tumbler means.

9. A lock as claimed in claim 8 wherein said first key includes a stem and said second key includes a stem receiving slot whereby to permit utilization of said second tumbler operating means when withdrawal of said first key is prevented by said key plug means.

10. A lock as claimed in claim 7 and including a third key having first tumbler operating means for operating said first tumbler means and second tumbler operating means for operating said second tumbler means.

11. A lock as claimed in claim 1 wherein said first key has a substantially cylindrical stem and a plurality of radially directed dimples for operating said first tumbler means.

12. A lock as claimed in claim 2 wherein said second key includes a plurality of parallel prongs for operating said second tumbler means.

13. A lock as claimed in claim It) wherein said third key has a substantially cylindrical stem and a plurality of radially directed dimples for operating said first tumbler means and a plurality of parallel prongs having axes parallel to the longitudinal axis of said cylindrical stem for operating said second tumbler means.

14. A lock as claimed in claim 2 wherein said key plug is generally cylindrical and has a longitudinal axis, said first tumbler means extending generally perpendicular to said longitudinal axis and said second tumbler means extending generally parallel to said longitudinal axis.

15. A lock as claimed in claim 14 wherein said second tumbler means are:circumferentially spaced with respect to the longitudinal axis of said key plug.

16. A lock as claimed in claim 11 wherein said dimples are coded whereby to identify the individual to whom a first key has been issued.

17. A lock comprising a housing, key plug means movably mounted in said housing, first tumbler means carried by said housing and key plug means for controlling movement of said key plug means, a first key for insertion in said key plug means for moving same, lock opening preventing means cooperating with said key plug means for preventing operation of said lock to an unlocked position, control means cooperating with said lock opening preventing means for setting said lock opening preventing means to a first position permitting operation of said lock to an unlocked position and to a second position preventing operation of said lock to an unlocked position, a second key for operating said control means, and means carried by said first key for identification of said first key at least when operation of said lock to an unlocked position is prevented.

18. A lock as claimed in claim 17 and further including selection means carried by said housing for preventing operation of said lock opening preventing means regardless of the position of said lock opening preventing means.

19. A lock as claimed in claim 17 wherein a plurality of first keys are provided, each of said first keys carrying a different identification means as compared with others of said first keys whereby to identify the individual to whom a first key has been issued.

Claims

1. A lock comprising a housing, key plug means movably mounted in said housing, first tumbler means carried by said housing and key plug means for controlling movement of said key plug means, a first key for insertion in said key plug means for moving same, trapping means cooperating with said key plug means for slectively arresting movement of said key plug means at a partially moved position, control means cooperating with said trapping means for setting said trapping means to a first nonarresting position and to a second arresting position, said key plug means preventing withdrawal of said first key when said key plug means is arrested in said partially moved position, and a second key for operating said control means.

5. A lock as claimed in claim 3 wherein said key plug means includes a trapping plug having recessed surfaces and said trapping means includes a trapping pin having a trapping finger thereon adapted for engagement with said recessed surfaces.

13. A lock as claimed in claim 10 wherein said third key has a substantially cylindrical stem and a plurality of radially directed dimples for operating said first tumbler means and a plurality of parallel prongs having axes parallel to the longitudinal axis of said cylindrical stem for operating said second tumbler means.

15. A lock as claimed in claim 14 wherein said second tumbler means are circumferentially spaced with respect to the longitudinal axis of said key plug.