LOCKS

Abstract: A lock has a keypad which operates members that can be disposed to allow movement to the locking device. The keys of the keypad are formed from elastomeric material and mounted at a matrix on elastomeric arms. The lock includes pins that can prevent the locking member moving and a device which re-sets the keys after they have been depressed. The lock also includes a casing formed in tow parts, one carrying the keys and the other carrying the members and the locking device. The handle of the lock includes a clutch device which prevents the mechanism being strained when the handle is turned with the lock locked. One key can be a prime key that must be depressed before the other keys are depressed to release a device that normally prevents unlocking movement of the other members. The lock includes a rotatable member for connection to a handle which meshes with the second rotatable member which is either held against rotation or released for rotation to lock or unlock the rotatable member. The lock includes a mounting plate and a handle loaded by a spring into a first position. A device is provided to hold the handle in a second position against the action of the spring angularly spaced from the first position. The lock includes a latch bolt with a retractable bolt and a snap fit casing.

Description: LOCKS The invention relates to locks including keypad locks, back plates for locks, latch bolts and associated components. According to a first aspect of the invention, there is provided a keypad lock comprising a locking device movable between a locking position and an unlocking position and a plurality of keys, each key being connected to a respective member that moves on depression of the associated key, each member having a first disposition in which said movement moves the member from a position in which the member prevents the locking device from moving from the locking position to a position in which the member allows movement of the locking device to the unlocking position and a second disposition in which the member does not interfere with movement of the locking device between the locking position and the unlocking position. According to a second aspect of the invention, there is provided a keypad operated lock comprising a locking device movable between a locking position and an unlocking position, a plurality of pins each engaging the locking device and a corresponding plurality of control members, each control member being associated with a respective pin and a respective key, each control member having a first disposition in which depression of the associated key moves the control member from a position in which the control member prevents movement of the associated pin and in turn prevents movement of the locking device from the locking position to the unlocking position to a position in which movement to the unlocking position is permitted, and a second disposition in which the control member and the associated pin do not affect the movement of the locking device either when the associated key is depressed or undepressed. According to a third aspect of the invention, there is provided a keypad lock comprising a locking device slidable between a locking position and an unlocking position and a plurality of locking members engaging said locking device, each locking device being associated with a key, the locking members being selectable either to lock the locking device in the locking position when the associated key is undepressed and to permit said sliding movement to said unlocking position when the associated key is depressed or not to affect the movement of the locking device. According to a fourth aspect of the invention, there is provided a keypad lock comprising a plurality of keys each associated with a respective member, selected of said members permitting unlocking of said lock on depression of the associated key, one of said selected members, on depression of the associated key, releasing a device that normally prevents unlocking movement of the remaining selected members. According to a fifth aspect of the invention, there is provided a keypad operated lock comprising a locking device movable between a locking position and an unlocking position and a plurality of members each associated with a respective key, depression of selected keys permitting the locking device to move to said unlocking position, means being provided for releasing said depressed selected keys. According to a sixth aspect of the invention, there is provided a keypad operated lock comprising a locking device movable between a locking position and an unlocking position and a plurality of members each associated with a respective key, depression of selected keys permitting the locking device to move to said unlocking position, the keys being carried by a first casing part and the members being carried by a second casing part, the two casing parts being separable. Preferably, the first casing part is accommodated within the second casing part. In this case, the two casing parts may be interconnected by the inter-engagement of respective latching parts on the first and second casings and a screw connection. According to a seventh aspect of the invention, there is provided a lock comprising a rotatable member for connection to a handle, said member meshing with a second rotatable member, a locking device being provided which, in a locking position, prevents rotation of said second member and, in an unlocking position, permits rotation of said second member. According to an eighth aspect of the invention, there is provided a lock comprising a handle connected to and rotatable with a mounting member, the mounting member being either permitted to rotate or prevented from rotating under the control of a locking device, a clutch mechanism being provided between the handle and the mounting member that allows relative rotation therebetween when the mounting member is prevented from rotation. According to a ninth aspect of the invention, there is provided a handle assembly comprising a mounting plate and a handle carried by the mounting plate for rotation relative thereto between first and second positions, the handle being urged by a spring towards said first position, the mounting plate carrying a mechanism which, when operative, holds the handle in said second position against the action of the spring. According to a tenth aspect of the invention, there is provided a latch bolt comprising a casing holding a bolt movable between retracted and extended positions, a rotatable member being provided and there being means between the rotatable member and the bolts as to the rotation of the member which causes said movement of the bolt. The latch bolt may include two casing parts that are a snap fit together. The latch bolt may include a device for preventing the bolt being retracted by a force applied to the bolt. According to an eleventh aspect of the invention, there is provided a keypad comprising a matrix and a plurality of keys, each key being connected to the matrix by a pair of flexible arms to mount the key for movement relative to the matrix. It will be appreciated that the features of any of the aspects of the invention referred to above may be combined with any other of the aspects of the invention. Figure 1 is an exploded view of a lock showing a back plate assembly, a chassis assembly and an outer case assembly. Figure 2 is a perspective view of the chassis assembly showing a chassis base plate and a chassis block, Figure 3 is a side elevation of the chassis block, Figure 4 is a plan view from above of the chassis block, Figure 5 is a plan view from beneath of the chassis block, Figure 6 is an end elevation of the chassis block, Figure 7 is a section on the line VII -VII of Figure 5, Figure 8 is a side elevation of a right-handed tumbler of the lock of Figure 1, Figure 9 is a side elevation of the tumbler of Figure 8 from a position rotated by 90° clockwise from the position of the view of Figure 8, Figure 10 is a side elevation of the tumbler of Figure 8 from a position rotated by 90° anti-clockwise from the position of the view of Figure 8, Figure 11 is a section on the line XI -XI of Figure 8, Figure 12 is a plan view of a tumbler holding spring for co¬ operation with the tumbler shown in Figures 8 to 11, Figure 13 is a side elevation of the spring of Figure 12, Figure 14 is an assembled perspective view of a barring plate assembly showing a chassis, barring pins and a barring plate, Figure 15 is an exploded view of the assembly of Figure 14, Figure 16 is a plan view of one side of the chassis of the assembly of Figures 14 and 15, Figure 17 is a plan view of the other side of the chassis of Figure 16, Figure 18 is a side elevation of the chassis of Figures 16 and 17, Figure 19 is a section on the line XIX-XIX of Figure 16, Figure 20 is a plan view of the barring plate of the barring plate assembly of Figure 14, Figure 21 is a side elevation of the barring plate of Figure 20, Figure 22 is an exploded view of the chassis block, the tumblers, a cancel arm, a quadrant gear, a pinion gear, a prime restraint arm and associated springs, Figure 23 is a plan view from above, a side elevation and a plan view from beneath of the pinion gear of Figure 22, Figure 24 is a plan view and a side elevation of the quadrant gear of Figure 22, Figure 25 is a side elevation of the prime restraint arm of Figure 22, Figure 26 is a plan view of the prime restraint arm of Figure 25, Figure 27 is a plan view of a priming plate for mounting in the chassis block of Figures 2 to 7, Figure 28 is a side elevation of the priming plate of Figure 27, Figure 29 is an end elevation of the priming plate of Figures 27 and 28, Figure 30 is a plan view of the chassis assembly with certain parts removed/cutaway to show the priming plate of Figures 27 to 29 in a rest position, Figure 31 is a side elevation of the chassis assembly with the parts shown in Figure 30 and showing the priming plate in the rest position, Figure 32 is a plan view of the chassis base plate of the chassis assembly of Figure 2, Figure 33 is a section on the line XXXIII-XXXIII of Figure 32, Figure 34 is a side elevation and a plan view of a part of the base plate of Figures 32 and 33 and of fingers of the priming plate of Figures 27 to 29 showing their relative dispositions in a rest position of the priming plate, Figure 35 is a side elevation and a plan view of the parts shown in Figure 34 in a latched position of the priming plate, Figure 36 is a side elevation and a plan view of the parts shown in Figure 35 in an unlatching movement of the parts, Figure 37 is a plan view of an autocancel device for mounting in the chassis assembly of Figures 1 and 2, Figure 38 is a section on the line XXXVIII -XXXVIII of Figure 37, Figure 39 is a section on the line XXXIX-XXXIX of Figure 37, Figure 40 is a side elevation of a cancel arm for mounting in the chassis assembly of Figures 1 and 2, Figure 41 is a plan view of the cancel arm of Figure 40, Figure 42 is a view of a part of the surface of the chassis block of Figures 3 to 7 showing markings around a hole of the chassis block, Figure 43 is a schematic exploded view of the outer case assembly of Figure 1 showing an outer case, a keypad matrix, a keypad sealing moulding and a lock handle assembly, Figure 44 is a plan view of the outer case of Figure 42 showing the exterior of the case, Figure 45 is a plan view of the outer case of Figures 43 and 44 showing the interior of the case, Figure 46 is a section on the line XLVI-XLVI of Figure 44, Figure 47 is an underneath plan view of the keypad matrix of Figure 43, Figure 48 is a plan view of an upper surface of the keypad matrix of Figure 47, Figure 49 is a section on the line XLIX-XLIX of Figure 48, Figure 50 is a plan view of a lock handle of the lock handle assembly of Figure 43, Figure 51 is a section on the line LI -LI of Figure 50, Figure 52 is an elevation of a handle insert of the lock handle assembly of Figure 43, Figure 53 is a plan view of the handle insert of Figure 52, Figure 54 is an elevation of a clutch spring ring of the lock handle assembly of Figure 43, Figure 55 is a further elevation of the clutch spring ring of Figure 54 from a position 90° rotated from the position of the view of Figure 54, Figure 56 shows a section on the line LVI-LVI of Figure 54 and a section on the line LVII-LVII of Figure 54, Figure 57 is a plan view, with certain parts omitted for clarity, of the chassis block assembly showing the barring plate of Figure 14 in a rest position, Figure 58 is a side elevation of the parts shown in Figure 57, Figure 59 is a plan view, with certain parts omitted for clarity, of the chassis block assembly showing the barring plate of Figure 14 in an open position, Figure 60 is a side elevation of the parts shown in Figure 59, Figure 61 is a similar view to Figure 30 but with the priming plate in a latched or primed position, Figure 62 is a side elevation of the parts shown in Figure 61, Figure 63 is a similar view to Figure 30 but with the priming plate in a re-set position, Figure 64 is a side elevation of the parts shown in Figure 63, Figure 65 is a cross-section through a portion of the chassis assembly and outer case assembly of Figure 1 with the chassis base plate of Figure 32 removed and showing the cancel arm of Figures 40 and 41 in an inoperative position, Figure 66 is a similar view to Figure 65 but showing the cancel arm in an operative position, Figure 67 is a plan view of one side of a rear outer case of the back plate assembly of Figure 1, Figure 68 is a plan view of the other side of the rear outer case of Figure 67, Figure 69 is a section on the line LXIX-LXIX of Figure 68, Figure 70 is a side elevation of an interior handle of the back plate assembly of Figure 1 with the handle carrying a 5 handle drive insert, Figure 71 is a plan view from beneath of the interior handle and handle drive insert of Figure 70, 0 Figure 72 is a plan view of a hold back button of the back plate assembly of Figure 1, Figure 73 is a side elevation of the hold back button of Figure 72, ■ 5 Figure 74 is a side elevation of the handle drive insert of Figure 70, Figure 75 is a plan view of the handle drive insert of Figure 0 70, Figure 76 is a plan view of a snib plate of the back plate assembly of Figure 1, Figure 77 is a section of the line LXXVII-LXXVII of Figure 76, Figure 78 is a plan view of a base plate of the back plate assembly of Figure 1, Figure 79 is a plan view of a rear cam of the back plate assembly of Figure 1, Figure 80 is a side elevation of the rear cam of Figure 79, Figure 81 is a plan view of the back plate assembly of Figure 1 with certain parts transparent to show the internal parts of the back plate assembly in a rest position, Figure 82 is a cross section of the back plate assembly as shown in Figure 81 along the line LXXXII-LXXXII of Figure 81, Figure 83 is a plan view of a latch bolt with certain parts cut-away and/or made transparent to show the internal parts of the latch bolt, Figure 84 is a side elevation of the latch bolt in the condition shown in Figure 83, Figure 85 is a vertical cross-section through the latch bolt of Figures 83 and 84, Figure 86 is a side elevation of a latch body case of the latch bolt of Figures 83 to 85, Figure 87 is a plan view from above of the latch body case of Figure 86, Figure 88 is a section on the line LXXXVIII-LXXXVIII of Figure 87, Figure 89 is a side elevation of a latch body top of the latch bolt of Figures 83 to 85, Figure 90 is a vertical cross-section through the latch body top of Figure 89, Figure 91 is an end elevation of the latch body top of Figures 89 and 90, Figure 92 is a side elevation of a cam drive plate of the latch bolt of Figures 83 to 85, Figure 93 is a section on the line XCIII-XCIII of Figure 92, Figure 94 is a plan view of an anti -thrust drive plate of the latch bolt of Figures 83 to 85, Figure 95 is an end elevation of the anti -thrust drive plate of Figure 94 , Figure 96 is a plan view of an anti -thrust lever of the latch bolt of Figures 83 to 85, Figure 97 is a section on the line XCVII-XCVII of Figure 96, Figure 98 is an end elevation of the anti -thrust lever of Figures 96 and 97, Figure 99 is a plan view of a latch bolt lath of the latch bolt of Figures 83 to 85, Figure 100 is a side elevation of the latch bolt lath of Figures 98 and 99, Figure 101 is a side elevation of a latch body head of the latch bolt of Figures 83 to 85 and incorporating the latch bolt lath of Figures 99 and 100, Figure 102 is an elevation of one end of the latch body head assembly of Figure 101, and Figure 103 is a section through a head mount of the latch body head assembly of Figures 101 and 102, Figure 104 is a vertical cross-section through the latch bolt of Figures 83 to 103 with a bolt of the latch in an extended position, Figure 105 is a similar view to Figure 104 but showing the bolt in a partially retracted position as a result of rotation of a cam of the latch bolt, Figure 106 is a similar view to Figure 105 but with the bolt fully retracted by rotation of the cam, Figure 107 shows a similar view to Figure 104 but with the bolt in a position adopted when the bolt engages a striker plate, an anti -thrust pin of the latch bolt being retracted. j Referring first to Figure 1, the lock comprises a back plate assembly 10, a chassis assembly 11, and an outer case assembly 12. The lock is designed to be fitted to a door 13 and the mode of fitting will be described in more detail below. 10 The principal component of the lock is the chassis assembly 11 and this will now be described in more detail. 1. The Chassis Assembly (a) The Chassis Block 15 Referring to Figure 2, the chassis assembly 11 comprises a base plate 14 and a chassis block 15. The base plate 14 will be described in more detail below but the chassis block 15 will now be described with reference to Figures 3 to 7. The chassis block has a front plate indicated generally at 16 20 surrounded by upstanding opposed elongate side walls 17 interconnected by first and second end walls 18,19. The first end wall 18 is arcuate and the second end wall 19 is also arcuate but with a greater radius than the first end wall 18. The front plate is, as best seen in Figure 3, stepped between the first end wall 18 and the second end wall 19 so that, starting from the first end wall 18, the front plate 16 is formed with a first planar portion 20 followed by a first arcuate upstanding step 21. This leads to a second planar portion 22 followed by a second upstanding arcuate step 23 having a reverse curvature to the first step 21. This leads to a third planar portion 24 followed by a third arcuate step 25 having a similar curvature to the second arcuate step 23. There then follows a fourth planar portion 26 which extends for the majority of the length of the front plate 16 and ends in a fourth step 27 which is a downward step and has the same curvature as the second and third steps. There is then, finally, a fifth planar portion 28 leading to the second end wall 19. The first planar portion 20 is provided with a fixing hole 29. The second planar portion is provided with a hole for receiving a lock handle (not shown in these figures but described below) . The third planar portion is provided with a mounting aperture 30 for a purpose to be described below. The fourth inner portion 26 is provided with two parallel rows of holes 31. There are six holes 31 in each row and the rows are spaced apart and extend generally parallel to the centre line of the chassis block 15. The holes 31 are to receive tumblers in a manner to be described below. The fifth planar surface 28 is provided with a central rectangular aperture 32 and is also provided, at its edge with the second end wall 19, with a pair of slots 33 that extend along the fifth planar portion 28 generally parallel to the length of the front plate 16 and then extend down the second end wall 19 as seen in Figure 6. The interior of the chassis block 15 is best seen in Figures 5 and 7. Referring to those figures, it will be seen that the fixing hole 29 is surrounded by an arcuate wall 34. There is also an arcuate wall 35 surrounding the mounting aperture 30 and a deeper wall 36 surrounding the hole 37 in the third planar portion 24. Each hole 31 in the fourth planar portion 26 is, within the chassis block 15, surrounded by a guide wall 38. Adjacent each hole 31, the guide wall 38 is generally circular and is formed with a slot 39 at a point diametrically opposite the associated side wall 17. Remote from each hole 31, the guide wall has an extension 40 which is semi-circular in cross-section and faces away from the associated wall 17. Between the two rows of guide walls 38, the underside of the fourth planar portion 26 is provided with a central channel 41 along which extends a pair of parallel ribs 42. An angled rib 43 extends from each guide wall 38 to the central channel subtending an angle of about 45° with the length of the front plate 16. A boss 44 is provided at the fourth step 27, with its axis normal to, and intersecting with, the centre line of the front plate 16. Again, the function of this will be described in more detail below. Two pairs of parallel ribs 45 extend along the undersurface of the fifth planar portion 28 with one rib 45 of each pair being intersected by an associated one of the slots 33. In addition, each rib has a mounting hole 45a (see Figure 7) towards its junction with the fifth planar portion 28. The purpose of these mounting holes 45a will be described below. (b) The Tumblers Each hole 31 in the fourth planar portion 26 receives a tumbler. There are two kinds of tumblers; left-handed tumblers 46 and right-handed tumblers 47. The right and left- handed tumblers 46, 47 have many features in common and so a right handed tumbler only will be described and common parts will be given the same reference numerals and will not be described in detail. Referring to Figures 8 to 11, each right-handed tumbler 47 comprises a head 48 formed with a cross-slot 49 and connected to a body 50 by a neck 51. As seen in Figure 11, the neck is provided with three equi-angularly spaced depressions 52 for a purpose to be described below. The body 50 is also generally circular in cross-section and is provided with six holes 53,54,55,56,57,58. The holes 53-58 are arranged in pairs with the holes of each pair 53,54; 55,56; 57,58; being axially aligned and the pairs being equi-angularly spaced around the body 50. The hole 53 closest to the head 48 in the first pair of holes 53,54 is a blind hole of no significant depth. The second hole 54 of this pair has a significant axial depth. The hole 55 closest to the head 48 of the second pair of holes has significant depth whereas the other hole 56 of that pair is a blind hole. The hole 57 of the third pair of holes closest to the head 48 has significant depth whereas the other hole 58 of that pair is a blind hole. The function of these holes will be described in detail below. A locating pin 59 projects from the base of the body 50 and, between the second and third pairs of holes 55,56; 57,58, the body 50 is provided with a skirt 60 having arcuate side walls 61 and a square end 62 which, as seen in Figures 9 and 10, projects slightly below the end of the pin 59. The description above is, as mentioned, of a right-handed tumbler 47. A left-handed tumbler 48 is similar to the right- handed tumbler but it has its features laterally reversed about a plane including the axis 63 of the tumbler and intersecting the centre line of the skirt 60. Each tumbler 46,47 is associated with a tumbler holding spring 64 shown in Figures 12 and 13. Each tumbler holding spring 64 is formed from a material such as steel and comprises a generally C-shaped clip 65 provided with enlarged ends 66 and having an outwardly projecting limb 67 intermediate the ends 66 and connected to an arm 68 extending at right angles to the plane of the clip 65 and the limb 67, as seen in Figure 13. At its end remote from the clip 65, the arm 68 is inclined over the clip 65 and terminates in a generally Z-shaped retaining head 69. Each tumbler 46,47 carries a respective holding spring 64 with the C-shaped clip 65 engaging around the neck 51 between the head 48 and the body 50. The ends 66 are arranged to engage in respective depressions 52. This means that the tumbler 46,47 has three possible angular dispositions relative to the associated holding spring 64 when the ends 66 are engaged in depressions 52, with the dispositions being angularly spaced by 120° . Six right-hand tumblers are inserted into the upper (as viewed in Figure 5) row of holes 31 of the chassis block 15. Six left-handed tumblers 47 are inserted in the lower (as viewed in Figure 5) row of holes 31 in the chassis block 15. Each tumbler 46,47 has its head 48 projecting through an associated hole 31 so that the head 48 projects above the fourth planar portion 26 with the cross-slot 49 exposed. The guide walls 38 embrace the body 50 of each tumbler 46,47 and the arm 68 of the associated holding spring 64 fits into the slot 39 to prevent rotation of the holding spring 64 relative to the chassis block 15. Referring next to Figure 42, the outer surface of the chassis block 15 is provided with markings around each hole 31. As seen in that Figure, there are three markings 174,175 and 176 which are shown as circular depressions but could take any suitable form. One marking 174 carries the indication NONCODE, one marking 175 carries the indication CODE and the other marking 176 carries the indication PRIME. The markings are equi-angularly spaced around the associated hole 31. As also seen in Figure 42, the head 48 of each tumbler 46,47 is provided with a marking 177. The relationship between the head marking 177 and the holes 53-58 in the tumblers 46,47 will be explained below. Each hole 31 has the same markings around it with the markings to one side of the centre line having positions that are laterally reversed as compared to the positions of the marking to the other side of the centre line. (c) The Barring Plate Assembly The chassis block 15 also contains a barring plate assembly shown schematically in Figures 14 and 15. The barring plate assembly comprises a chassis 70 shown in more detail in Figures 16 to 19. Referring to those figures, the chassis 70 is a generally rectangular block of plastics material having parallel elongate sides interconnected by parallel ends. Each side includes six cut-outs of generally circular cross-section with respective axes normal to the general plane of the chassis. Each cut-out 71 is provided at the centre of the arc defining its cross-section with a slot 72 of generally rectangular cross-section. The two sets of cut-outs are connected by a central web 73 (see Figure 19) . As also seen in Figure 19, the gap between the inner ends of each cut-out 71 defines, with the web, a channel 74 extending along the length of the chassis to one side of the web 73. On the other side, the chassis is provided with twelve guideways 75; one for each cut-out 71. Each guideway 75 is generally U-shaped and extends at an angle of 45° relative to a centre line 76 of the chassis 70. Each guideway 75 has a smaller diameter portion 77 at its intersection with the associated cut-out 71 and this is followed by a larger diameter portion 78 opening into the centre of the chassis 70. At one end of the chassis 70, on the side of the chassis 70 opposite the guideway 75, the chassis is provided with a pair of projecting U-shaped mounting blocks one of which is shown at 79 in Figure 18. The purpose of these will be described below. This surface is also provided, as seen in Figure 19, with a pair of parallel elongate ribs 80. The barring plate assembly also includes a barring plate 81. This is shown in more detail in Figures 20 and 21. As seen in those Figures, the barring plate 81 is generally T-shaped with a cross head 82 and a limb 83. The cross-head has, on its face remote from the limb 83, and in the centre of the cross head 82, an arcuate notch 84. The limb 83 has generally parallel side walls 85. Each side wall 85 is provided with six equi-distantly spaced recesses 86 which open on to one face of the limb 83 but are closed to the other face of the limb. The open face 134 of the limb 83 is provided a square section projection 135 extending normal to the face between the second and third recesses 86, from the cross-head 82. This surface 134 also carries a projecting stop 136 between the projection 135 and the cross-head 82 and on the centre line 137 of the barring plate 87. The barring plate 81 sits in the channel 74 in the chassis 70 and is thus guided by the channel 74 for sliding movement relative to the chassis 70 along the centre line of the chassis 70. The cross head 82 of the barring plate 81 projects from the end of the chassis 70 carrying the mounting blocks 79. As seen in Figures 14 and 15, each guideway 75 holds a barring pin 87 which has an elongate rod 88 and an enlarged head 89. The head of each barring pin 87 is towards the centre line 76 of the chassis 70 and, in the position of the barring plate 81 shown in Figure 14, engages in a respective one of the recesses 86 in the barring plate 81. A spring 90 surrounds each rod 88 and acts between a step 91 between the smaller diameter portion 77 and the larger diameter portion 78 of each guideway 75 and the head 89 of the associated barring pin to urge the associated barring pin 87 into engagement with the associated barring plate recess 86. When in this position, the head of the rod 88 of each pin 87 projects through the smaller diameter portion 77 of the associated guideway 75 and projects into the associated cut¬ out 71. This barring plate assembly is inserted into the chassis block 15 with the barring plate 81 lying in the channel 41 on the rib 42. The cross head 82 lies in the space between the ends of the rows of holes 31 and the hole 30 in the third planar portion 24. The cut-outs 71 embrace the bodies 50 of respective tumblers 46,47 with the arm 68 of each holding spring 64 extending into an associated slot 72. As a result of this, each rod 88 bears against an associated tumbler 46,47. The pins 59 and skirts of the tumblers 46,47, as well as the Z-shaped retaining heads 69 of the holding springs 64 project beyond the ends of the associated cut-outs. Referring next to Figure 22, the chassis block 15 also carries a pinion gear 92 which meshes with a quadrant gear 93. The chassis 70 carries a prime restraint arm 94 and the end of the chassis block 15 at the fifth planar portion carries a cancel arm 95. These parts will now be described in more detail with reference to Figures 23 to 29. (d) The, Pinion Gear Referring first to Figure 23, the pinion gear 92 comprises a toothed body 96 surrounded by an annular radially extending flange 97 that extends outwardly of the toothed body 96 to one side of the flange 97. A square section block 98 extends from the other side of the flange 97 and a generally circular cross-section boss 99 extends from the side of the toothed body 96 opposite the flange 97. The centre of the pinion gear 92 is provided with a hollow passage 100 that, as seen in Figure 23, is provided with a pair of diametrically opposed inwardly directing projections 101. The pinion gear 92 sits in the hole 37 in the chassis block 15 with the block 98 projecting through the hole 37. (e) The Quadrant Gear The quadrant gear 93, as seen in Figure 24, has a generally semi -circular toothed segment 102 with mounting axles 103 projecting from respective opposite sides of the segment 102 coaxial with the axis of the segment 102. In addition, one side of the segment 102 carries a pair of actuating pins 104 equi -distantly spaced on respective opposite sides of the pivot axis 105 of the segment 102 and lying on a diameter of the segment passing through the ends of the teeth. The quadrant gear 93 has one axle 103 projecting through the mounting aperture 30 in the third planar portion 24 of the chassis block 15. This mounts the quadrant gear 93 for rotation about its axis and, in this position, the teeth on the segment 102 mesh with the teeth on the body 96 of the pinion gear 92 so that rotation of the pinion gear 92 in one sense results in corresponding rotation of the quadrant gear 93 in an opposite sense. In this position, the notch 84 in the barring plate 81 engages the other mounting pin 103 and the cross head 82 of the barring plate 81 bears against the actuating pins 104. A pair of springs (shown in Figure 59 below) act between the end of the chassis 70 and the cross head 82 of the barring plate 81 to urge the barring plate 81 into this position. The barring plate 81 can thus be moved against the springs and relative to the chassis 70 away from the quadrant gear 93 and the pinion gear 92. (f) The Prime Restraint Arm The prime restraint arm 94 comprises, as seen in Figures 25 and 26, a plate 109 (Figure 26) with a central rectangular hole 110. The plate 109 is carried on a generally rectangular mounting block 111 lying in a plane generally normal to the plane of the plate 109 and connected along one end of the plate 109. A mounting axle 112 extends along an edge of the mounting block 111 and projects from either side of the mounting block 111, as seen in Figure 26. The axle 112 is mounted in the circular apertures of the mounting blocks 79 on the chassis 70 so that the plate 109 projects away from the quadrant gear 93. The prime restraint arm 94 is thus mounted for pivotal movement about an axis normal to the centre line of the chassis block 15 and the chassis 70. The function of this will be described below. (g) The Priminσ Plate The chassis block 15 also contains a priming plate 113 which may be formed of a plastics material and is shown in more detail in Figures 27, 28 and 29. The priming plate 113 is of generally elongate rectangular shape . The priming plate 113 comprises a pair of parallel side walls 114 interconnected by transverse webs 115. The outer surface of each side wall 114 carries six keepers 116 and six release mechanisms 117 with the keepers 116 and release mechanisms 117 being successively spaced along each side wall 114; the keepers 116 being equi- distantly apart and the release mechanisms 117 being equi- distantly apart. Each keeper 116 comprises, as seen in Figure 29, a short lateral projection with a chamfered upper surface 118 leading to an outer edge 119. Each release mechanism 117 comprises a laterally projecting arm 120 carrying at its outer end a block 121 having a ramp surface 122 lying in a plane parallel to the centre line 123 of the priming plate 113. At one end, the side walls 114 are connected to a generally U- shaped end member 124 with the limbs of the U generally parallel to the side walls 114 but spaced outwardly of the side walls 114. The ends of the U-shaped member 124 remote from the side wall 114 are interconnected by an end wall 125 which, as seen in Figure 28, projects outwardly of the plane of one side of the priming plate 113. The outer surface of the limbs of the U-shaped member 124 carry respective projections 126. One intermediate web 115 carries a pair of resilient fingers 127 extending generally parallel to the centre line 123 and on respective opposite sides of the centre line 123. Each finger has, at its free end, a hook 128, best seen in Figure 28. In addition, each finger 127 carries, intermediate its ends, a downwardly projecting peg 129, as also seen in Figure 28. The function of these will be described below. The priming plate 113 also carries a stop 130 which, as seen in Figures 28 and 29, projects from one side of the priming plate 113 at an end of the priming plate 113 opposite to the U-shaped end member 124 and to the same side as the projecting end wall 125. The stop 130 has an end surface 131 and an upper surface with a reverse downward chamfer 132. A slot 133 is formed between the side walls 114 at a position generally intermediate the ends of the priming plate 113. The priming plate 113 is mounted in the chassis block 15 with the chassis 70 in the following way. The priming plate 113 lies between the ribs 80 in the chassis 70. The U-shaped end member 124 embraces the boss 44 at the junction of the fourth and fifth planar portions 26,28, passing to either side of this boss 44. In this position, the end wall 125 is adjacent the second end wall 19 of the chassis block 15. The end wall 125 and the stop 130 project towards the chassis 70 and the barring plate 81. Further, the projection 135 on the barring plate 81 extends through the slot 133 in the priming plate 113 to allow relative movement between the priming plate 113 and the barring plate 81. The stop 130 is spaced from the stop 136 on the barring plate 81 in the direction of the length of the barring plate 81. Referring next to Figures 30 and 31, it will be seen that in the rest position of the priming plate 113 shown in those Figures, the arm 68 of each holding spring 64 is aligned with a gap between a keeper 116 on the priming plate and the back of an adjacent release mechanism 117. In addition, as seen in Figure 31, each tumbler 46,47 is, when the associated head 48 extends by its maximum amount from the associated hole 31, has the square lower edge 62 of the skirt 60 just clear of the priming plate 113. (h) The Base Plate Other parts of the priming plate 113 co-operate with the base plate 14 of the chassis assembly 11. This will now be described with reference to Figures 32 and 33. Referring to those Figures, the base plate 14 is formed of a suitable material such as glass fibre reinforced nylon and has elongate side edges 138 interconnected by convex end edges 139. The peripheral shape of the base plate 14 is the broadly the same as the peripheral shape of the chassis block 15; the base plate 14 being designed to close the chassis block 15. The base plate 14 has along its centre line, starting from one end edge 139, firstly a fixing hole 140 which, when the base plate 14 closes the chassis block 15, is in register with the fixing hole 29 in the chassis block 15. Next, there is a mounting aperture 141 which registers with the hole 37 in the chassis block 15 and receives the boss 99 on the pinion gear 92 to mount the pinion gear 92 for rotation. Next, there is a further aperture 142 which receives an axle 103 of the quadrant gear 93 to mount the quadrant gear 93 for rotation. In addition, there is a second fixing hole 143 towards the other end edge 139 of the base plate 14. This registers with the boss 44 on the chassis block 15. The base plate 14 also includes two rows of circular depressions 144. There are six depressions 144 in each row and the two rows are parallel equidistantly spaced on opposite sides of the centre line 145 of the base plate 14. As seen in Figure 31, an end of a coil spring 146 is received in each depression 44 with the other end of each coil spring 146 engaging a respective pin 59 on a tumbler 46,47. Each coil spring 146 thus acts to urge the associated tumbler 46,47 into a position in which the head 48 of the tumbler 46,47 projects a maximum distance from the associated hole 31 in the chassis block 15. The base plate 14 also includes an abutment wall 147 extending in a direction generally normal to the centre line 145 and lying in a plane generally normal to the plane of the base plate 16. The abutment wall 147 is located between the mounting aperture 142 and the start of the two rows of depressions 144. When the base plate 14 is connected to the chassis block 15, the priming plate 113 slidably engages the base plate 14 between the rows of depressions 144. The base plate 14 includes features which co-operate with the fingers and hooks 127,128 of the priming plate and are shown in Figures 34 to 36. Referring first to Figure 34, the base plate 14 is provided with a catch 148 formed with a reverse rebate 149 and aligned with the fingers 127. Extending along respective side edges of the catch 148 are two cam surfaces, one of which is shown at 150 in Figures 34 to 36. Each cam surface comprises a first wall extending generally parallel to the centre line 145 and a second wall extending generally parallel to the centre line 145. The second wall 151 is closer to the centre line than the first wall 150 and the two ~ walls are interconnected by a ramp 152 which is located just in front of the catch 148. In the rest position of the priming plate 113 shown in Figure 34, the hooks 128 on the fingers 127 abut the catch 148 but do not engage it. As the priming plate 113 is moved relative to the base plate 14 (in a motion to be described in more detail below) , the hooks 128 on the fingers 127 ride up over the catch 148 and engage behind the rebate 149 (see Figure 35) , the fingers 127 flexing to accommodate this movement. Further movement of the priming plate 113 in the same direction causes the pegs 129 on the fingers 127 to ride up the ramps 152 and engage on the first wall 150. As seen in Figure 36, this causes the fingers to be bent laterally so that the hooks 128 are no longer aligned with the catch. This allows the priming plate 113 to be moved back to the rest position shown in Figure 34. The final mechanism within the chassis block 15 is a cancel mechanism which will now be described with reference to Figures 37 to 41. (i) The Autocancel Mechanism The autocancel device is indicated generally at 153 and may be formed from a plastics material and comprises a pair of side- by-side plates 155. Each plate has a rear edge 156 leading to a side edge 157 normal to the rear edge 156. This is followed by an angled front edge 158 that subtends an angle of about 45° with the line of the side edge 157. This front edge leads to an L-shaped rebate having two surfaces 160,161 at right angles to one another. The portion between the end of the second rebate surface 161 and the rear edge 156 is provided with a U-shaped cutout 162. The two plates are separated by a spacer bar 163 connected between the respective lower ends of the second rebate surfaces 161. The outer surfaces 164 of the plates 155 carry respective L- shaped projections 165. Each L-shaped projection 165 has a first planar portion 166 lying in a plane parallel to the plane of the rear edges 156 of the plates 155 and a second planar portion 167 lying in a plane normal to the plane of the rear edges 156 of the plates 155. The first planar portion 166 is adjacent the second rebate surface 161 and the second planar portion 167 intersects the rear edge 156 about a third of the way along the edge from the side edge 157. The autocancel 154 engages the projections 126 on the U-shaped end member 124 of the priming plate 113. Each projection is received in a respective U-shaped cut-out 162 with the inner surfaces of the plates 155 of the autocancel device embracing the limbs of the U-shaped member 124. The sloping front edges 158 of the autocancel device 153 are aligned with the respective one of the slots 33 in the chassis block 15. A spring (not shown) holds the autocancel device 153 into a position where the nose formed by the sloping front edge 158 and the rebate 159 projects a maximum amount from the slots 33. (v) The Cancel Arm A cancel arm 154 is formed by a plate 168 having parallel side edges 169 and parallel chamfered front and rear edges 170,171. A pair of arms 172 project from one face of the plate with each arm being adjacent a respective side edge 169 of the plate 168 and the arms lying in respective planes normal to the plane of the plate 168. The free end of each arm 172 carries the circular cross section boss 173. The cancel arm 154 is mounted as follows. Each boss 173 of the cancel arm 154 is received in a respective mounting hole 45a in a respective one of the ribs 45 on the interior of the chassis block 15. The plate 168 lies in a plane normal to the plane of the priming plate 113 and transverse to the centre line 123 of the priming plate 113. One edge of the plate 168 engages behind the end wall 125 of the priming plate 113. Thus the plate 168 is mounted for pivotal movement about the bosses 173. 2. The Outer Cover Assembly The next part to be described is the outer cover assembly 12. This is shown schematically in Figure 43 from which it will be seen that it comprises an outer case 178, a keypad matrix 179, a keypad sealing moulding 180 and a lock handle assembly indicated generally at 181. These parts will now be described in more detail. (a) The Outer Case The outer case 178 is shown in Figures 44 to 46. The outer case 178 comprises a face plate 182 having straight but slightly diverging side edges 183 interconnected by convexly arcuate end edges 184,185. These edges are surrounded by respective side walls 186 and first and second end walls 187,188 extending generally normal to the face plate 182 to form a cavity (which is for receipt of the chassis block 15 as described in detail below) . The outer surface of the face plate 182 is formed with a first planar portion 189 provided with a circular boss 190 having with a central aperture 191. This portion 189 is connected by an arcuate curved upward step 192 to a second portion 193 which is curved in planes normal to a centre line 194 of the outer case 173. This portion 193 is formed with two rows of holes 195. Each row contains six holes and the two rows are equidistantly spaced on opposite sides of the centre line 194 (see Figure 44) . Each hole 195 is generally triangular with a first edge 196 generally parallel to the centre line 194 (see Figure 44) and curved edges 197 meeting at an apex which is connected by a channel 198 to an adjacent side edge 183 of the outer case 178. This second portion 198 terminates at the other end edge 185 but is provided, adjacent that edge, with a triangular recess 199 (see Figures 44 and 46) provided with a central hole 200. The under surface of the face plate 182 and the interior of the outer case 178 have the following features. First, there is a threaded boss 201 projecting from beneath the first planar portion 189 adjacent the first end wall 184. Next, each hole 195 is surrounded by a peripheral sealing surface 202. Four fixing points 203 are provided on the undersurface of the second portion 193 along the centre line 194. Four further fixing points 204 are provided at the junction of the undersurface of the second portion 193 and each side wall 186. Two additional fixing points 205 are provided at the junction of the end wall 188 and the face plate 182. The function of these fixing points 203,204,205 will be described below. (b) The Keypad Matrix The keypad matrix is shown in Figures 47, 48 and 49. Referring to these Figures, the keypad matrix 179 is formed from a moulded plastics material. It comprises a frame formed by side members 206 and first and second end members 207,208. A central member 209 extends from the first end member 207 along the centre line 210 of the keypad matrix 179 and terminates at a cross member 211 spaced from, but adjacent, the second end member 208. These members support twelve keys 212. The keys 212 are arranged in two parallel rows with six keys in each row. The keys 212 of each row are in lateral register. One row of keys 212 is arranged between the central member 209 and one side member 206 and the other row of keys 212 is arranged between the central member 209 and the other side member 206. Each key 212 is generally hollow and triangular in cross section with a straight end wall 213 adjacent the central member 209 and convexly curved walls 214 meeting at an apex. As seen in Figure 49, the keys 212 project to one side of the keypad matrix 179. Each key 212 is mounted on a square sub frame 215 which is connected by a first limb 216 to the central member 209 and by a second limb 217 to the associated side member 206. The sub frame 215 and the associated key 212 are thus cantilevered from the side member 206 and the central member 209 to provide the key 212 with a resilient mounting. A push button 218 of circular cross-section is mounted on an arcuate bar 219 extending between the side members 206 and arranged between the cross member 211 and the second end member 208. This mounts the push button 218 for resilient movement in a direction normal to the plane of the keypad matrix 179. Each key 212 carries a respective different numeral from 1 to 12 to allow the keys 212 to each be identified by a respective numeral . (c) The Sealing Moulding The sealing moulding 180 is shown in Figure 43. It comprises a pad of elastomeric material of generally the same shape as the outer case 178 and provided with a hole 220 towards one end. The sealing moulding 180 also includes two rows of circular thinner portions 221. These are arranged, as seen in Figure 43, to register with the keys 212. The undersurface of the other end carries a central depending rectangular cross - section projection (which is not shown in Figure 43, but which will be described below with reference to Figure 65) . (d) The Lock Handle Assembly The lock handle assembly 181 of Figure 43 is shown in more detail in Figures 50 to 56. Referring to those Figures, the lock handle assembly 181 comprises a lock handle 222 having a generally circular base 223 surmounted by an elongate shaped handle 224. As seen in Figure 50, the handle is wedge shaped in plan and, as seen in Figure 51, the handle 224 is also wedge-shaped in section narrowing to a point 225 at one end. The interior of the handle 224 is provided with supporting walls 226 and a central socket 227. The socket receives a handle insert 228 shown in Figures 52 and 53. Referring to those Figures, the insert 228 has a body 229 of generally circular cross section provided with an axially extending rib 230 (see Figure 53) along its outer surface. As compared to the diameter of the body 229, the depth of the rib 230 is comparatively small. The body 229 is connected at one end to an annular portion 231 of smaller diameter than the diameter of the body 229. This is in turn connected to a spigot -232. 5 The lock handle assembly also includes a clutch spring ring 233 shown in Figures 54 to 56. Referring to those Figures, the clutch spring ring 233 is formed from a suitable material such as carbon steel and comprises an upper portion 234 having a C-shaped cross-section (see Figure 56) and a lower portion 10 235 having a generally U-shaped cross-section. The two portions are interconnected by a neck 236 extending between the base of the U-shape of the lower portion 235 and the centre of the C-shape upper portion 234 (see Figures 54 and 55) . ■ 5 The final part of the lock handle assembly is a lock handle circlip 237 shown in Figure 43. This is formed by a domed annular disc with a central hole provided with gripping splines 238. 0 The way these parts fit together and the way they fit to the chassis block will now be described with reference to Figure 43. 3. Assembling the Outer Cover Assembly The keypad matrix 179 fits inside the outer case 178 with the keys 212 extending through the holes 195 in the outer case 178. Bosses (not shown) on the keypad matrix 179 fit into holes in the case 178. The keypad matrix 179 is provided with screw holes that register with the fixing points 203,204,205 and the keypad matrix 179 is fixed to the outer case 178 by screws extending through these holes and into the fixing points 203,204,205. This holds the keypad matrix 179 with the keys 212 projecting through the holes 179 with each key 212 being able to be depressed against its resilient mounting into the outer case 178. It will be appreciated that the screws may be omitted and the parts arranged to snap-fit together. The outer case 178 is closed by the sealing moulding 180 which engages with the side walls 186 and the first and second end walls 185. In this position each thinner portion 221 is aligned with a key 212. In addition, the push button 218 projects through the hole 200 and can also be depressed into the inner case 178 against its resilient mounting. The lock handle 222 is connected to the handle insert 228 by the spigot 232 being pushed into the socket 227 of the lock handle 222. The depending end of this insert is then passed through the aperture 191 in the outer case 178 with the under 5 surface of the lock handle 222 being spaced from the surface of the outer case 178 by a washer 239. The lock handle circlip 237 is then pushed on to the lock handle insert 228 until the splines engage the spigot. This mounts the lock handle 222 for rotation relative to the outer case 178. 0 The handle insert 228 is then connected to the clutch spring ring 233 with the C-shaped upper portion 234 being pushed over the body 229 to engage around the body 229. The relative orientation of the parts is arranged so that when the point ■ 5 225 of the lock handle is along the centre line 194 of the outer case 178 the rib 230 is between the ends of the C-shaped portion 234 of the clutch spring ring 233. The U-shaped portion 235 then projects from the end of the handle insert 228 for a purpose to be described below. 0 4. Fitting the Outer Cover Assembly to the Chassis Block This assembly is then fitted to the chassis block 15. The outer case 178 is sized so that it can accommodate the chassis block 15. In this position, a rib on the exterior of the second end wall 188 of the outer case 178 engages in a groove on the interior of the base plate 14. The outer case 178 can then be rotated to bring these two parts into engagement to hold the outer case 178 on to the base plate 14 covering the chassis block 15. In this disposition, the U-shaped lower portion 235 of the clutch spring ring fits over the block 98 of the pinion gear 92 to engage the lock handle 222 with the pinion gear 92. The other end of the outer case 178 is secured with a screw in a manner to be described below. In this position also, the lower end of each key 222 engages an upper end of each tumbler 46,47 via a thinner portion 221 of the sealing moulding 180. Further, the inner portion of the end wall 188 engages the front edges 158 of the autocancel device 153 and depresses the autocancel device 153. The effect of this will be described below. Further, the projection of the undersurface of the sealing moulding 180 extends through the rectangular aperture 32 in the chassis block 15. Within the chassis block, the projection engages an edge of the plate 168 of the cancel arm 154 opposite the edge engaging the priming plate 113. These parts form the operative part of the lock and their operation will now be described. 5. The Operation of the Chassis Assembly In brief, the lock operates by making certain of the tumblers 46,47 operative and thus designating the keys 212 that need to be depressed before the lock handle 222 can be rotated. Any number of tumblers 46,47 can be made operative but the greatest security is obtained by making four to six tumblers 46,47 operative. One tumbler 46,47 is designated as a "prime" tumbler the corresponding key 212 must be depressed first in the sequence. The priming plate 113 resets the tumblers 46,47 after the lock handle 222 has been operated and also when the outer case 178 is removed. These functions will now be described in more detail. (a) Setting the Tumblers The tumblers 46,47 are set by removing the outer case 178. This is done by lifting the lower end of the outer case 178 to disengage it from the base plate 14 by loosening a retaining bolt from the back plate and then lifting the rib 240 out of the co-operating groove on the base plate 14. The U-shaped lower portion 235 of the clutch spring ring 233 lifts off the block 98 of the pinion gear 92. This exposes the heads 48 of the tumblers 46,47 and allows them to be rotated by the insertion of a screw driver in the associated cross slots 49. In order to understand how the tumblers operate, it is necessary to know the relationship between the head marking 177 on the head 48 of each tumbler 46,47 and the holes 53-58 on the tumblers 46,47. When the head marking 177 is adjacent the "code" marking 175, as seen in Figure 42, the holes 55,56 on the tumblers 46,47 are positioned adjacent the ends of the associated barring pins 87 with the end of the associated barring pin received in the lower blind hole 56. In this orientation, the tumblers 46,47 are disposed in relation to the priming plate as shown in Figure 30. As shown in this Figure, the priming plate 113 is in its rest position so that the end wall 125 is spaced a maximum distance from the second end wall 19 of the chassis block 15. The Z-shaped retaining head 69 of each tumbler holding spring 64 are located between a keeper 116 and, as viewed in plan, in the L formed by an adjacent arm 120 and ramp surface 122. This is seen clearly in Figure 30. The skirt 60 on each tumbler 46,47 is, in this position, so orientated that it lies away from the path of travel of the priming plate 113. If a tumbler 46,47 is rotated so that the head marking 177 is adjacent the "prime" marking 176, the tumbler 46,47 is rotated by 120°. Since the associated holding spring 64 cannot rotate, the spring retains the same position but the holes 55,56 are moved out of alignment with the associated barring pin 87 and the holes 57,58 are moved into alignment with the associated barring pin 87 with the blind hole 58 aligned with the end of the barring pin 87. The skirt 60 overlies the associated ramp surface 122. In the rest position of the priming plate 113, the fingers 127 are spaced from the catch 149 as seen in Figure 34. The third position of each tumbler 46,47 is with the head marking 177 at the "non-code" marking 174. This position is spaced by 120° from the "prime" position and it brings the final pair of holes 53,54 into an alignment with the associated barring pin 87 with the open hole 54 aligned with the barring pin 87. In this disposition, the skirt 60 of the tumbler 46,47 is rotated to a position out of the path of the priming plate 113. The tumblers 46,47 are held in these positions by engagement of the C-shaped clips 66 in respective pairs of the depressions 52 in the neck 51 of the associated tumbler 46,47. The code is set by rotating one of the tumblers 46,47 to the "prime" marking 176 and a number of the other tumblers 46,47 to "code" markings 175. The greatest security is achieved by having five tumblers 46,47 at the "code" marking 175 in addition to one tumbler at the "prime" marking 176. However, as many tumblers 46,47 as required may be set in this way. The outer case 178 is then placed back over the chassis block 15 and engaged with the base plate 14. (b) The locking action The locking action is achieved by the barring plate 81. The cross head 82 of the barring plate 81 bears against the actuating pins 104 on the quadrant gear 93 to prevent the quadrant gear from rotating. Since this meshes with the pinion gear 92 that is connected to the lock handle 222, the lock handle 222 is prevented from rotating. The barring plate 81 cannot be slide along the channel 41 in the chassis block 15 because the heads 89 of the barring pins 87 engage in the recesses 86 in the barring plate 81 and because the barring pins 87 associated with the "prime" tumbler 46,47 and the "code" tumblers 46,47 are aligned with blind holes 56,58 and so cannot retract against the action of their associated springs 90. The barring pins 87 associated with "non-code" tumblers 46,47 can retract but the number of non-retractable barring pins 87 is quite sufficient to hold the barring plate 81 in this locking position. In this position, the projection 135 on the barring plate 81 is received in the slot 133 in the priming plate, towards a lower end of the slot 133. The function of this will be described below. The barring plate 81 is urged into engagement with the quadrant gear 93 by the springs 402 acting between the cross head 82 and the chassis block 15. The prime restraint arm 94 is in a position in which the plate 109 is aligned with the projection 135 on the barring plate 81 as seen in Figure 8. (c) Unlocking the lock (i) The "prime" tumbler The first key 212 to be operated when unlocking the lock is the key 212 associated with the "prime" tumbler 46,47. When this key 212 is depressed, the associated tumbler 46,47 is depressed via the thinner portion 221 of the sealing moulding 180 against the force of the associated spring 146. Since the skirt 60 of this tumbler 46,47 is aligned with the associated ramp surface 122, this downward depression of the tumbler 46,47 forces the square end 62 of the skirt 60 into engagement with this ramp surface 122. The effect of this is to move the priming plate 113 upwardly away from the lock handle 222 towards the second end wall 19. This position is shown in Figure 61. In this position, the retaining head 69 of the holding spring 64 of the remaining tumblers 46,47 are aligned with the keepers 116 on the priming plate 113. The retaining head 69 on the holding spring 64 of the "prime" tumbler 46,47 engages behind the associated keeper 116 to hold this tumbler 46,47 depressed. The associated key 212 returns, on release, to its extended position under the action of its own resilient mounting. (ii) The "code" tumblers The keys 212 associated with the "code" tumblers 46,47 are then depressed in any order (although they will usually be depressed in the order in which the code number is remembered) . The effect of this is to push the associated tumblers 46,47 against their associated springs 146 until the associated retaining heads 69 latch behind the associated keepers 116. This holds the tumblers 46,47 depressed (with the associated keys 212 returning after release) . The effect of this is to move the blind holes 56 out of alignment with the associated barring pins 87 and bring the open holes 55 into alignment with these barring pins 87. As the "prime" tumbler 46,47 is depressed, the fingers 127 on the priming plate 113 latch over the catch 148 and engage behind the rebate 149 as described above with reference to Figure 35. This prevents the priming plate 113 returning to the rest position under the action of the associated spring. (iii) The "non-code" tumblers If a non-code tumbler 46,47 is depressed by depression of the associated key 212 it will latch behind an associated keeper 116 in the same way as the other tumblers 46,47. The effect 5 of this will be to move the open hole 54 out of alignment with the associated barring pin 87 and move the blind hole 53 into alignment with the associated barring pin 87. The effect of this will be described below. 0 (d) Turning the Lock Hand! P If, with the "prime" tumbler depressed and the "code" tumblers 46,47 depressed, the lock handle 222 is rotated by 90° (in either sense) , the quadrant gear 93 is rotated. As seen in Figure 59, the effect of this is to cause one of the actuating *5 pins 104 to push against the cross-head 82 and slide the barring plate 81 along the chassis block 15 against the action of the associated springs 402. Since all the barring pins 87 are now aligned with open holes 0 54,55,57 in the tumblers 46,47, the barring pins 87 can retract against their associated springs as they are forced out of the recesses 86 by the movement of the barring plate 81. If, however, one or more "non-code" keys 212 have been depressed, this movement will not be possible. This is because, as described above, the depression of a "non-code" tumbler 46,47 brings a blind hole 53 into alignment with the associated barring pin 87. Thus, as the actuating pin 104 endeavours to push up the barring plate 81, this is resisted by one or more barring pins 87 engaging in its blind hole 53. The effect of this movement of the barring plate 81 is to cause the projection 135 to engage the end of the slot 133 on the priming plate and move the priming plate 113 upwardly away from the handle 222. The effect of this is to move the keepers 116 out of alignment with the Z-shaped retaining head 69 on the holding spring 64. This will not, of course, permit the associated tumblers 46,47 to move, because they are held in position by engagement of the barring pins 87 in the holes 54,56. Another effect of this is to move the fingers 127 on the priming plate 113 to the position shown in Figure 36 where the fingers 127 are bent laterally out of engagement with the catch 148. This is done by the projection 135 hitting the end of the slot 133 and picking up the priming plate 113 for movement with the barring plate 81. The position of the barring plate is shown in Figure 63. (e) Release of the T.nr-k Handle When the lock handle 222 is released and returned to the centre position aligned along the centre line 194 of the face plate 182, the quadrant gear 93 is rotated back to the position at which the actuating pins 104 lie on a line normal to the centre line 194. This allows the barring plate 81 to move downwardly under the action of the springs 402 back into engagement with the actuating pins 104. Although the priming plate 113 is no longer held by engagement with the projection 135, it does not immediately return to the rest position under the action of the spring. This is because of the action of the prime restraint arm 94. As seen in Figure 60, when the barring plate 81 slides upwardly to release the lock handle 222, the projection 135 on the barring plate 84 disengages from the plate 109 of the prime restraint arm and allows it to drop into the path of the stop 130 on the priming plate 113. The effect of this is that, as movement of the barring plate 81 commences, the plate 109 engages with the stop 130 to prevent return movement of the priming plate 113. This is maintained until the projection 135 on the barring plate 81 engages the plate 109 and pivots the prime restraint arm about the pivot blocks 108 to move it out of engagement with the stop 130. When this occurs, the priming plate 113 returns to the rest position under the action of the spring .. with the fingers 127 passing the catch 148 as shown in Figure 36. The purpose of this is to allow the tumblers 46,47 to move upwardly under the action of their associated springs 146 without the retaining head 69 on the holding spring 64 engaging the keepers 116 on the priming plate 113. As the notches 86 on the barring plate 81 re-align themselves with the barring pins 87, the heads 89 on the barring pins 87 re-enter the notches and withdraw from the holes 54,56 in the tumblers 46,47. This allows these tumblers 46,47 to move upwardly under the action of their associated coil springs 146. In this way, the mechanism is returned to the rest position as shown in Figures 30,31,57 and 58. (f ) Automatic Resetting of the Tumbl rs The chassis assembly 11 and outer case assembly 12 contain two mechanisms for automatically resetting the tumblers 46,47. Thus, if any tumbler 46,47 has been accidentally depressed and latched to the priming plate 113, it can be released. The first mechanism utilizes the autocancel 153 of Figures 37 to 39. As described above, when the outer case assembly 12 is removed from the chassis assembly 11, the plates 155 of the autocancel 153 are urged to project from the slots 33 in the second end wall 19 of the chassis block 15. However, when the outer cover assembly 12 is latched to the chassis assembly 11, the second end wall 188 of the outer case 178 depresses these plates 155 and the rest of the autocancel 153 against the action of a spring (not shown) until the plates 155 are forced back into the slots 33. The effect of this is to move the autocancel 153 relative to the priming plate 113 with the cut¬ out sliding relative to the projections 126 on the U-shaped end member 124 of the priming plate 113. When so positioned, the priming plate 113 can move from the rest position to the re-set position, as described above, without movement of the projections 126 being inhibited by engagement with the autocancel 154. However, as soon as the outer case assembly 12 is removed from the chassis assembly 11, the autocancel device 153 is moved by the spring to extend the plates 155 from the slots 33. The effect of this is to cause the ends of the U-shaped cut-out 162 to engage the projections 126 to drag the priming plate 113 to the re-set position described above. This has the effect of releasing any Z-shaped retaining head 69 that is engaged with a keeper 116 on the priming plate 113 so releasing any tumbler 46,47 that is depressed and allowing that tumbler 46,47 to return to a raised position. This moves the projecting arm of the priming plate 113 out of the path of the skirt projecting from the prime tumbler 46,47. A second cancel device is operated using the push button 218 on the outer case assembly 12 when the outer case assembly 12 is engaged with the chassis assembly 11. The operative and inoperative positions of the push button 218 and the cancel arm 154 are shown in Figures 65 and 66 respectively. As will be seen from Figure 65, when the priming plate 113 is in the operative position where the retaining head 69 of the holding spring 64 of the tumblers 46,47 are aligned with the keepers 116 on the priming plate. When in this position, one edge of the plate 168 engages behind the end wall 125 of the priming plate 113. The opposite edge of the cancel arm plate 168 engages the rectangular cross-section projection 304 on the sealing moulding 180. This is in turn engaged by the push button 218. If the push button 218 is depressed, this in turn depresses the projection 304. This causes the cancel arm plate 168 to rotate about the bosses 173 causing the lower edge of the plate 168 to move rearwardly. The effect of this is to push the priming plate 113 to the release position where the end wall 125 is adjacent the second end wall 19 of the chassis block 15. This position is shown in Figure 66. When the push button 218 is released, the priming plate 113 is free to move back to the rest position once the "prime" key 212 and the associated tumbler 46,47 have been depressed. When this motion occurs, the cancel arm 154 return to the position shown in Figure 65. Thus, if the "prime" key 212 has been depressed but the wrong "code" keys 212 have been depressed, depressing the push button will release all the depressed tumblers 46,47 and allow the code to be re-entered starting with the "prime" key 212. (g) Thp Lock Han le Clutch Mechan sm The lock handle 222 has a clutch mechanism formed by the co¬ operation of the C-shaped upper part 234 with the handle insert 228. If sufficient rotational force is applied to the lock handle 222 with the barring plate 81 locked, the lock handle 222 and the handle insert 228 will rotate relative to the clutch spring ring 233 with the rib 230 splaying out the C-shaped upper portion 234 and passing around the inner surface of that portion 234. After a full 360° rotation, the rib 230 will once again be between the ends of the arms of the C-shaped upper portion 234. As a result of this, it is not possible to overload the mechanism by trying to turn the lock handle 222 when the barring plate 81 is locked against movement. 6. The Pack Plate Assembly The chassis assembly 11 and the outer case assembly 12 are mounted on a door frame as shown in Figure 1 utilizing the back plate assembly 10. This assembly is shown in more detail in Figures 67 to 78. It is formed principally by a rear outer case 241 which co-operates with a base plate 282 and mounts an interior handle 243. The remaining components are within the rear outer case 241. These parts will now be described in more detail. (a) The Rear Outer Case This is shown in Figures 67 to 69. It comprises a face plate 244 having side edges 245 which are parallel towards one end of the face plate 244 and then increase their spacing to wider portions at the other end of the face plate 244. These side edges 245 are interconnected by convexly curved first and second end edges 246,247. A side wall, one of which is shown at 248 in Figure 69, extends along each side edge with the side walls 248 being interconnected by a first end wall 249 extending along the first end edge 246 and a second end wall 250 extending along the second end edge 247. The face plate 244 and the interior of the outer rear case 241 are formed with the following features, starting from the first end wall 249. First, there is a fixing hole 251 with its axis coaxial with a centre line 252 of the rear outer case 241. As seen in Figure 69, a hollow tube 253 continues this fixing hole 251 and terminates in a plane spaced outwardly from the plane of the free edges of the side walls 248 (see Figure 69) . Next, there is a mounting hole 254 of greater diameter than the fixing hole 251 with its axis on the centre line 252. As seen in Figure 69, on the interior of the face plate 244, this mounting hole 254 is surrounded by an annular rib 255. Next there is a transverse web 286 on the back of the base plate 242 that carries a pair of guide plates 257 spaced by equal distances on opposite sides of the centre line 252 and lying in respective planes parallel to the centre line 252. This is followed by a further transverse web 258 which is succeeded by an aperture 259. As seen in Figures 65, 67 and 69, two further guide plates 260 are mounted on respective opposite sides of the aperture 259 and lie in respective planes normal to the centre line 252 with the plates 260 being disposed about the centre line 252. There are then third and fourth transverse webs 261,262 intersected by two parallel longitudinal webs 263 equidistantly spaced from the centre line 252 (see Figure 67) . An intermediate web 264 extends between the longitudinal webs 263 beyond the fourth transverse web 262 and carries a pair of stop plates 265 (best seen in Figures 67 and 69) . These plates lie in respective planes parallel to the centre line 252 and are equidistantly spaced on opposite sides of the centre line 252. Finally, there is a second fixing hole 266 similarly formed as the first fixing hole 251 with an associated tube 267 projecting beyond the free edges of the side walls 248 (see Figure 69) . (b) The Interior Handle The interior handle 243 is shown in Figures 70 and 71 in combination with a handle drive insert 263 shown in Figures 74 and 75. These parts will be described together. The interior handle 243 is formed from a plastics material and comprises a disc- like base 269 which carries a grippable portion 270. As seen in Figures 70 and 71, this grippable portion is wedge-shaped in both plan and elevation providing it with a point 271 at one end. The portion has, towards the other end, generally oval depressions 272 to increase grip. The under surface of the base 269 is provided with an annular socket 273 which receives a shaft 274 of the handle drive insert 263. As seen in Figure 74, this shaft 274 is knurled to ensure a tight attachment between these parts. The attachment may, of course, be formed in any convenient alternative way. The shaft is connected to a drive block 275. This block 275 has an interior recess 276 generally coaxial with the axis of the shaft 274. The inner walls of the recess are formed with a pair of diametrically opposed triangular projections 277. The exterior of the drive block 275 is formed with a radially extending nib 278. As seen in Figure 75, this lies in a plane normal to the diameter between the interior projections 277 of the recess 276. This portion also has a pair of diametrically opposed flats 275a. (c) The Hold Back Button The hold back button is shown in Figures 72 and 73. It comprises a plate 279 which is generally rectangular in shape (see Figure 72) and has two opposed edges provided with respective rectangular notches 280. A button 281 extends from one face of the plate in a direction normal to the plane of the plate. (d) The Snib Plate The snib plate 282 is shown in Figures 76 and 77. The plate 282 is generally rectangular in plan view (see Figure 76) with two parallel side walls 283 interconnected by two parallel end walls 284 defining between them a generally rectangular central opening 285. One end wall 284 is provided with a flat tongue 286 projecting from the outer surface of the end wall 284 and lying in a plane which is generally the same as the plane of the plate 282. Each side wall 283 carries, on its inner surface, four projections 287 equidistantly spaced along the associated side wall 283 and, as seen in Figure 76, adjacent an edge of the associated side wall 283. The projections 287 of one side wall 283 are in register with the projections 287 of the other side wall. (e) The Base Plate The base plate 242 is shown in Figure 78. It is made of mild steel and has converging side edges 288 interconnected by convexly curved end edges 289. The plate 242 is provided, along its centre line 290, with a fixing hole 291, an aperture 292 and a second fixing hole 293. (f) Rear cam A rear cam 294 comprises a plate 295 with parallel side edges 296 and convexly curved end edges 297. One end edge 297 is provided with an upwardly projecting peg 298 (see Figure 80) . A shaped aperture 299 is provided in the centre of the plate 295 (see Figure 79) and this aperture has parallel side edges 300 interconnected at one end by a straight end edge 301. The other end is interconnected by two curved edges 302 which meet at a central notch 303. The back plate assembly 10 fits together in the following way. 7. Assembling the Back Plate Assembly The back plate assembly is shown in Figures 81 and 82. Referring to those Figures, the interior handle 243 is mounted on the rear outer case 241 by insertion of the handle drive insert 263 through the mounting hole 254 on the rear outer case 241. This mounts the interior handle 243 for rotation on the outer rear case 241 with the annular rib 255 engaging the drive block 275. The rear cam 294 is located with the drive block 275 projecting into the shaped aperture 299 in the rear cam 294 and with the rear cam 294 lying in a plane generally parallel to the centre line 252 of the rear outer case 241. The flats 275a on the drive block are shaped to be a close fit between the side edges 300 of the shaped aperture 299 of the rear cam 294. A clip (not shown) holds the end of the drive block to hold this assembly together and so mount the interior handle 243 on the rear outer case 241. A torsion spring 406 has one end engaging the peg 298 on the rear cam 294 and the other end engaging the rear outer case 241. This results in the rear cam 294 rotating with the interior handle 243 and also provides a self -centring function that ensures that the interior handle 243 is urged towards the inoperative position shown in Figures 81 and 82. The snib plate 282 is mounted between the guide plates 257 on the back of the rear outer case 241 and between the parallel webs 263. These constrain the snib plate 282 to reciprocal sliding movement in a direction parallel to the centre line of the rear outer case 241. Upward movement is limited by the stop plates 265. The snib plate 282 is arranged with the flat tongue 286 adjacent the interior handle 243 and the opposite end wall 284 provides a stop for a spring 407 which acts between the wall 284 and the outer rear case 241 to urge the snib plate 282 downwardly towards the interior handle 243. The button 281 of the hold back button projects through the aperture 259 and sits with the plate 279 sitting on the guide plates 260 of the outer rear case 261. A spring 408 acts between the hold-back button and the back plate assembly 10 to urge the button 281 through the aperture 251 in the position shown in Figures 81 and 82. The base plate 242 closes the outer rear case 241 and provides an abutment for the spring 408 associated with the hold back button. 8. Operating the Back Plate Assembly The purpose of the back plate assembly 10 is to mount the interior handle 243 and also allow the interior handle 243 to be held in an open position rotated by 90° from the position shown in Figures 81 and 82. As will be described below, in this position an associated latch is held in a retracted position so preventing a door to which the lock is fitted relatching. This is achieved in the following way. In the position of the back plate 10 shown in Figures 81 and 82, the spring 407 urges the tongue 286 on the snib plate 282 into engagement with a curved end edge 297 of the rear cam. The notches 280 on the hold-back button engage with respective opposed projections 287 on the snib plate 282. The snib plate 282 is thus prevented from reciprocating movement relative to the outer rear case 241. If the outer handle 243 is rotated with the push back button in this position, the rear cam 294 simply rotates with the interior handle 243 and the snib plate 282 remains stationary. If, however, the hold-back button is depressed and the interior handle 243 rotated through 90°, the snib plate 282 will be released for movement under the action of the associated spring 407 and the tongue 286 will move downwardly. Once this movement has commenced, the hold-back button can be released. When the interior handle 243 has rotated by 90°, the tongue 286 will engage one of the side edges 296 of the rear cam 294. Also in this position, the notches 280 on the hold back button will be in register with the next pair of projections 287 on the snib plate 282. Accordingly, the spring 408 on the hold-back button will urge the button 281 back out of the outer rear case 241 and the notches 280 will engage with these projections 287 to hold the snib plate 282 against movement. This will prevent reverse rotation of the interior handle 243 under the action of the torsion spring 406. The interior handle 243 is released from this position by pressing the hold-back button 281 which disengages the notches 280 from the associated projections 287. The rotational force on the rear cam 294 provided by the torsion spring 406 is sufficient to overcome the force of the snib plate spring 407 and the snib plate 282 is thus forced back up the outer rear case 241 until the notches 280 in the hold-back button 281 come back into register with the next pair of projections 287. When this happens, the hold back button spring 408 urges the hold back button out of the outer rear case 241 to re-engage the notches 280 with the projections 287. The assembly thus returns to the posit.ion shown in Figures 81 and 82. If the interior handle 243 is turned by less than 90° with the hold-back button 281 depressed, the tongue 286 on the snib plate 282 will not be square with either of the side edges 296 of the rear cam 294. In addition, the notches 280 on the hold-back button 281 will not be aligned with another set of projections 287 on the snib plate 282. Accordingly, the interior handle 243 will not be held in this position but will simply return to the position shown in Figures 78 and 79 with the snib plate 282 being pushed back to the position shown in those Figures where the notches 280 on the hold back button re-engage with the initial projections 287. 8. Tnsf.all i ng the Lock The back plate assembly 10, the chassis assembly 11 and the outer case assembly 12 are mounted on a door 13 in the following way, referring to Figure 1. The back plate assembly, chassis assembly and outer case assembly are dimensioned so that when the parts are in register, the first fixing hole 251 in the rear outer case 241 is aligned with the first fixing hole 291 in the base plate 242 which is in turn aligned with the first fixing hole 140 in the base plate 14, the first fixing hole 29 in the chassis block 15 and the boss 201 in the outer case 178. The drive block 275 of the interior handle 243 is aligned with the hollow passage 100 in the centre of the pinion gear 92. The second fixing hole 266 in the rear outer case 241 is aligned with a second fixing hole 293 in the base plate 242. This is in turn aligned with the second fixing hole 143 of the base plate 14 and the boss 44 of the chassis block 15. This boss 44 is threaded. The door 13 is drilled with three holes so that, when the back plate assembly 10 and the chassis assembly 11 are offered up to the door 13, fixing screws 305 can be passed through the back plate assembly 10, through the door 13 to engage in threaded boss 44 on the chassis block 15 and the threaded boss 201 in the outer case 178. This holds these parts securely on the door 13 with the base plates 14,242 pressed against the door surface. Prior to this fixing, a spindle (not shown) has one end inserted into the handle drive insert 263 of the interior handle 243 and the other end inserted into the passage 100 in the pinion gear. This allows rotation of the interior handle 243 to be transmitted to a latch bolt (not shown in Figure 1 but described below) which lies in a hole in a side edge surface 307 of the door 13 and intersects the hole in the door through which the spindle passes. Rotation of this interior handle 243 does not rotate the pinion gear 93 due to the provision of lost motion between this handle 243 and the gear 93. The latch bolt may be of any known type in which rotation of the spindle is converted into locking and unlocking movement of a bolt to either project the bolt from the door 304 to engage a keeper (not shown) in an associated frame or to retract the bolt and thereby release the door 304. One form of latch bolt assembly will now be described with reference to Figures 83 to 107. 9. The atch Bolt The latch bolt comprises a casing formed by a latch body case 308 together with a latch body top 309. The case contains a cam drive plate 310, an anti-thrust drive plate 311, and anti- thrust lever 312, a cam 313, an anti -thrust pin 314 and a latch body head assembly 315. These parts and their interrelationship will now be described in more detail. (a) The Latch Body Case Referring first to Figures 83 to 88, the latch body case 308 has an elongate body 316 which, at one end, is of circular cross section. This end carries a face plate 317 which lies in a plane normal to the centre line 318 of the body 316 and is provided with fixing holes 319 on diametrically opposite sides of the centre line 318. This circular cross-section portion leads to a portion 320 of semi-circular cross-section which in turn leads to an end section 321 of arcuate cross-section with the arc subtending an angle of less than 180° relative to the centre line 318. The semi-circular portion 320 is formed with a slot 322 circumferentially positioned midway between the edges of the semi-circular portion 320. A U-section buttress 323 extends diametrically across the latch body case 308 from a position axially aligned with the slot 322 to a free end axially aligned with the circular section portion of the casing (see Figure 86) . The buttress 323 has a centre section 324 lying in a plane generally normal to the centre line 318 and parallel side sections 325 lying in respective planes generally parallel to the centre line and extending in a direction away from the slot 322. The lower part of the centre section 324 carries a block 326 that projects over the slot 322 (see Figure 88) . The side sections 325 embrace a second slot 327 which is circumferentially wider than the first slot 322 and a catch 328 projects over this second slot 327 (see Figure 88) . The end section 321 is formed with a circular hole 329 surrounded by an annular wall 330. The end section 321 is closed by an end wall 331 provided with a semi-circular groove 332 (see Figures 87 and 88) having its axis normal to the centre line 318 and lying in a plane including the slots 322 and 327. (b) The Latch Body TOD The latch top body 309 shown in Figures 89 to 91 is designed to be a snap fit on to the latch body case 308 to form a complete casing. The latch body top 309 comprises a body indicated generally at 333 having a semi-circular portion 334 and an arcuate portion 335 that subtends an angle of less than 180° to the centre line 336 of the latch body top 309. The semi-circular portion 334 caries a pair of parallel axially extending ribs 337 (see Figure 91) lying in respective planes parallel to the centre line 336 and normal to the plane including the edges of the semi-circular portion 334. This portion also carries a peg 338 arranged at a circumferential position between the edges of the semi¬ circular portion 334 and lying in a plane including the centre line 336. The arcuate portion 335 carries a spring finger 339 projecting from a point on the arcuate portion 334 aligned with the peg 338 and having at its free end a catch portion 340. This arcuate portion 335 also has a U-shaped rib 341 embracing the lower part of the finger 339 and a hole 342 whose centre is axially aligned with the peg 338 and the finger 339 and is surrounded by an annular wall 343. The end of the arcuate portion 335 is closed by an end wall 344 provided with a semi¬ circular groove 345. (c) The Cam Drive Plate The cam drive plate 310 is shown in Figures 92 and 93. Referring to those Figures, the cam drive plate 310 is formed of any suitable material such as mild steel and comprises two elongate members 346 connected by a transverse end piece 347. Each elongate member 316 has a straight inner edge 348 and an outer edge 349 provided with an inwardly directed step 350 so that the member is wider at its end remote from the end piece 347. As seen in Figure 93, the narrower portion is provided with a crank 351 so that the free ends of the members 346 lie in a plane which is parallel to but spaced from the plane of the remainder of the members 346. The free end of each member is bent downwardly (see Figure 93) to form an end stop 352. The end piece 347 is, as seen in Figure 93, L-shaped in cross- section with a downwardly projecting limb 353 extending to the same side of the plate 310 as the end stops 352. (d) The Anti-Thrust Drive Plate The anti-thrust drive plate 311 is shown in Figures 94 and 95. The plate 311 is generally flat with a rectangular central cut-out 354 (see Figure 94). A mounting 355 projects from one face of the plate 311 at one end of the plate 311 and lies in a plane generally normal to the plane of the plate 311. As seen in Figure 95, the free end of the mounting is provided with a part-circular recess 356 which subtends an angle of more than 180° . The other end of the anti-thrust drive plate 311 is provided with a rectangular slot 357 to form the end of the plate 311 with a pair of parallel projections 358. The end of each projection is provided with an inward chamfer 359. As seen in Figure 95, the recess 356 on the mounting 355 has an axis that is parallel to a centre line 360 of the anti-thrust drive plate 311 and the projections 358 are spaced equi -distantly on either side of this centre line 360. (e) The Anti -Thrust Lever The anti-thrust lever 312 is shown in Figures 96 to 98. The lever 312 is formed from a suitable material such as mild steel and is formed as a plate having parallel side edges 361 formed with an inward chamfer 362 at each end of each side edge 361 (see Figure 96) . One end of the plate is formed with a square section slot 363 and a downwardly and rearwardly projecting tongue 364 (see Figure 97) . The other end of the plate is also provided with a slot so that there are provided a second pair of projections 365 which are longer than the first mentioned projections 358 at the other end of the plate. As seen in Figure 97, these projections 365 are angled away from the plane of the plate to one side of the plate and then curved through about 90° to extend across the plane of the plate to the other side of the plate (see Figure 97) . The transverse edge 366 between the second projections 365 is provided with a lug 367 which projects along the centre line 368 of the anti-thrust lever 311 and has a rounded end (see Figure 96) . A bar 369 extends between the second projections 365 intermediate the edge 366 and the ends of the projections 365. The bar is generally U- shaped in cross-section normal to the centre line 368 with a central portion angled relative to the plane of the rest of the plate at an angle slightly less than the angle of inclination of the first portions of the second projections 365. The side edges of this central portion 370 are connected to respective second projections by inclined portions 371 (see Figures 97 and 98) that form the limbs of the U-shaped cross- section. ( f ) The Cam The cam 313 is seen in Figures 83 to 85. It comprises a tubular body 372 whose interior is formed with two equi- angularly spaced inwardly directed triangular section projections 373 (see Figure 83) . The exterior surface of the body 372 carries a flange projecting radially outwardly from the body 372 and extending about 90° around the body 372 (see Figure 83) . As also seen in that Figure, the flange 374 is provided with chamfers 375 at its outer edges. The flange 374 has, at each end of its curved outer edge, a notch 401 provided in a radially extending portion leading from the outer edge to the body 372. (g) The Anti -Thrust Pin The anti-thrust pin 314 is also shown in these Figures. It comprises a sold cylindrical body 376 connected at one end by a neck 377 to a solid annular head 378 from which projects a pin 379 having a chamfer 380 at its free end. The anti -thrust pin may be formed from stainless steel . (h) The Latch Body Head Assembly The latch body head assembly 315 will now be described with reference to Figures 99 to 103. The assembly includes a latch bolt lath 381 formed by a generally rectangular plate of a suitable material such as mild steel with a flat central portion 382 and side edges bent along lines 383 parallel to but spaced from the centre line 384 of the lath 381 so that the side edges 385 are angled relative to the plane of the central portion 382. A central portion 382 is provided at one end with a hole 386 and at the other end with a rectangular slot 387. The end of this slot 387 carries a stop plate 389 which lies in a plane normal to the plane of the central portion 382 and extends to a side of the lath 381 opposite to the side to which the side edges 385 project. Each side edge 385 is provided with a semi-circular first notch 390 adjacent the slot 387 and an elongate second notch 391 between the first notch 390 and the end of the lath 381 formed with the hole 386. The lath 381 is encast in a latch body head 392 which forms the remainder of the latch body head assembly 315. This assembly is shown in Figures 101 to 103. As seen in those Figures and in Figures 83 to 85, the latch body head 392 has a head 393 which is part-circular in cross-section and a decreasing radius along its length (see Figure 101) . The edges of the curved surface are connected by a flat surface 394 formed with a part-circular groove 395 extending in a direction parallel to the centre line 396 of the latch body head 392. The head 393 is formed, as its maximum radius end, with a back wall 397 from which projects a head mount indicated generally at 398. As seen in Figure 103, this mount 398 has a central web 399 with a guide member 400 of segmental cross-section extending along each side edge of the web 399. The latch body head 392 is formed by a process such as moulding and the lath 381 is inserted into the latch body head 392 during such moulding. As seen in Figures 101, 102 and 103, the end of the lath 381 including the hole 386 is located within the head 393 with the material of the head 393 extending through the hole 386 to lock the parts together. The central portion 382 of the lath lies within the web 399 with the side edges 385 extending into respective guides 400 (see Figure 103) . The notches 390,391 help anchor the lath 381 in these parts. The stop plate 389 projects from the web 399 towards an end of the web 399 remote from the head 393, as seen in Figure 103. Referring to Figures 83 to 85 and 104 to 107, the parts described above with reference to those Figures fit together as follows. The assembled lock is shown in Figure 104. 10. Assembling the Latch Bolt Referring to Figure 104, the body 376 of the anti -thrust pin 314 sits in the groove 395 in the head 393 of the latch body head 392 with the neck 377, the head 378 and the pin 379 projecting over the web 399 (see Figure 104) . These parts fit into the circular cross-section of the portion of the body 316 of the latch body case 308 so that the latch body head assembly 392 is mounted for sliding movement along this portion. The guides 400 engage the interior of this portion of the latch body case to guide the assembly in this movement. A coil spring 404 extends between the back wall 397 and the buttress 323 with the block on the buttress 323 fitting into the end of the coil spring to locate the coil spring. The coil spring acts to urge the body head assembly out of the latch bolt casing. The anti-thrust drive plate 311 sits above the flat portion of the head 397 and the recess 356 in the mounting 355 on the anti-thrust drive plate 311 embraces the neck 377 of the anti- thrust pin 314. The stop plate 389 of the lath 381 lies within the cut-out 354 in the anti-thrust drive plate 311 with the upper end of the stop plate 389 level with the upper surface of the anti-thrust drive plate 311 and adjacent a transverse end edge of the recess 356. The cam drive plate 310 overlies the anti-thrust drive plate 311 with the limb 353 on the end piece 347 engaging the stop plate 389 on the lath 381 (see Figure 85) . The elongate members 346 of the cam drive plate 310 pass to either side of the wall 323 to embrace notches 401 at the circumferential ends of the flange 374 on the cam 313. The anti-thrust lever 312 has the curved portion of the second projections 365 resting on the anti-thrust drive plate 311. The first projections 398 embrace the wall 323 on the latch body case 308 with the tongue 364 resting against the centre section 324 of the buttress 323 (see Figure 87) . A coil spring 405 extends between the anti-thrust pin 314 and the anti-thrust lever 312 with one end of the spring receiving the pin 379 on the anti-thrust pin 324 and the other end of the spring receiving the lug 367 on the anti-thrust lever 312. The spring operates to urge these two parts apart. The latch body case 308 is closed by the latch body top 309. The semi -circular portion 344 of the latch body top 309 fits over the semi-circular portion 320 of the latch body case and the arcuate portion 335 of the latch body top 305 extends over the arcuate end section 321 of the latch body case 308 to provide a pair of diametrically opposed slots between these parts. As seen in Figure 83, these slots accommodate the edge of the flange 374 of the cam 313. The end wall 331 of the latch body case 308 co-operates with the end wall 344 of the latch body top 309 so that their respective grooves 332,345 are in register to form a continuous groove (see Figure 83) . The latch body case 308 and the latch body case 309 are held together by engagement of the catch 340 on the finger 339 with the catch 328 on the latch body case 308. This can be released by flexing the lever through the second slot 327. In this position, the ends of the body 372 of the cam 313 are received in respective annular walls 330,343 surrounding the holes 329,342 in the latch body case 308 and the latch body top 309 respectively. The hole through the body 372 is thus aligned with these holes 329,342. This mounts the "cam 313 for rotation about the axes of these holes 329,342. The latch bolt operates in the following way. 11. Operation of the Latch Ro.t (a) Fitting The latch bolt is fitted to a door as described above with reference to Figure 1. The latch bolt is received in a hole drilled in the edge of the door and extending normal to the edge. The face plate 317 is recessed into the edge surface of the door and screws pass through the fixing hole 319 to fix the latch bolt to the door. The spindle 306 extends through the body 372 so that rotation of either the lock handle 222 or the interior handle 243 causes rotation of the cam 313. (b) Movement of the Bolt Hf»ad The latch body head 393 can be moved in two ways. Either it can be moved by operation of the lock handle or the interior handle or it can be moved by engagement with a striker plate (not shown) on the associated door frame. The first to be described is movement of the latch body head 393 by rotation of the lock handle 222 or the interior handle 243. Such rotation is transmitted to the latch body head assembly 315 by the cam drive plate 310. As the cam 313 is rotated, a force is applied to one of the elongate members 346 to pull it away from the face plate 317. This force is transmitted via the limb 353 to the lath 381 which thus causes the latch bolt head assembly 315 to be withdrawn from the extended position shown in Figures 83 to 85 to an unlatched position (not shown) in which the latch body head assembly 315 lies significantly within the latch body case 308. During this movement, the anti-thrust drive plate 311 moves with the latch body head assembly 315 and the anti -thrust lever 312 rides up over the end piece of the cam drive plate 310. This is shown in Figure 105. The final position is shown in Figure 106. The bolt head assembly 315 is fully retracted and the spring 405 pushes the anti-thrust lever 312 downwardly to rest on the central web 399 of the head mount 398. Release of the lock handle 222 or the interior handle 243 allows the latch body head 315 to extend from the latch body case 308 under the action of the spring . The latch body head assembly 315 moves in the following way on engagement with the striker plate. This is the way in which the latch head assembly 315 will move as the door is closed {since, in general, it is not usual to close a door by turning the handle) . As the latch body head assembly 315 engages the striker plate (not shown) the latch body head assembly 315 is forced into the casing against the action of the spring 404. The cam drive plate 310 will remain stationary because there is no movement of the cam 313. The anti-thrust pin 314 will be pushed back into the casing with the head 393 and, as a result of its attachment to the cam drive plate 310, this will also move within the casing towards the cam 313. The effect of this is that the curved portions of the anti- thrust lever 312 will disengage from the cam drive plate 310 and drop so that the bar 369 between the projections 365 on the anti-thrust lever 312 engages behind the stop plate 389 on the lath 381 on the latch body head assembly 315. The spring 405 acting between the anti-thrust pin 314 and the anti-thrust lever 312 provides a force that urges the anti -thrust lever 312 into this position. Once the door is fully closed, the latch body head assembly 315 springs out of the casing and into a keeper in the striker plate (not shown) . The anti-thrust pin 314 will not, however, move because the striker plate (not shown) is dimensioned so that the anti-thrust pin 314 is not aligned with the keeper in the striker plate when the door is closed into the frame, but remains in engagement with the striker plate and thus retracted into the casing. This position is shown in Figure 107. (c) Operation of the Anti -Thrust Device If an attempt is made to force back the latch body head assembly 315 from the position shown in Figure 107, by applying an inward force to the assembly, such movement will be prevented by engagement between the stop plate 389 on the assembly 315 and the bar 369 on the anti-thrust lever 312. The force applied to the lever 312 will be resisted by the buttress 323. In this way, unauthorized forcing of the latch is resisted. The door can still be opened using the lock handle 222 or the interior handle 243 (when freed for rotation) , since such rotation will cause the cam 313 to move the cam drive plate 310 and this will in turn cause the end piece 347 of the cam drive plate 310 to lift the anti-thrust lever 312 and so allow movement of the latch body head assembly 315 into the casing. It will be appreciated that the lock described above with reference to Figures 83 to 107 is compact in both length and diameter. The anti-thrust system provides significant security against forced entry. It will be appreciated that there are a large number of alterations that can be made to the lock and latch bolt described above with reference to the drawings. Although twelve tumblers, 46,47 and associated keys 212 are shown; there could be more or less tumblers and keys . The priming plate 113 could be used with mechanisms other than the tumblers 46,47 and the tumblers 46,47 could be used without the priming device 113. The use of a barring plate 81 is only one example of the way in which the locking action may be achieved. It could be achieved by many other mechanisms in which a member is either held against movement or released for movement. The barring pins 87 are shown extending at an angle to the centre line of the lock; they could be otherwise disposed. The formation of the keys 212 on the keypad matrix 179 need not be as described above. Any form of moulded key 212 with suitable return springing could be used.. The keys 212 need not be shaped as described above; they could be of any shape, for example, they could be circular in cross- section. The use of the autocancel 153 is optional; the tumblers 46,47 could be reset in some other way on removal of the outer case assembly 12. The lock handle 222 and the interior handle 243 need not be shaped as shown in the drawings; they could have any required shape. The clutch mechanism between the lock handle 222 and the pinion gear 92 need not be as described above; any suitable clutch mechanism could be used. The "prime" tumbler 46,47 need not move the priming plate 113 as described above,- it could move it in any convenient way. In addition, the use of a "prime" tumbler 46,47 is optional. The priming plate 113 can always be in a position where the Z- shaped retaining heads 69 engage the keepers 116 with the priming plate 113 being moved between this position and the release position. In this case, the coded numbers can be entered in any order. The various parts can be made from any suitable material or materials . It will be appreciated that many of the parts described above may be replaced by mechanical equivalents. For example, although Figures 24 and 30 show a pair of fingers 127, these may be replaced by a single finger. Although the latch body case 308 and the latch body top 309 are described above as being engaged by a catch 340 with the catch 328 on the latch body case, there may be one or more additionail latches. The projection 135 on the barring plate 81 may be replaced by two projections .

Claims: CLAIMS 1. A keypad operated lock comprising a locking device movable between a locking position and an unlocking position, and a plurality of keys, each key being capable of being depressed and being operatively associated with a control member, each control member having a first disposition in which depression of the associated key moves the control member to a position in which the control member allows movement of the locking device from said locking position to said unlocking position and each control member having a second disposition in which depression of the associated key moves the control member to a position in which the control member prevents movement of the locking device from said locking position to said unlocking position. 2. A lock according to claim 1 wherein each control member, whether in the first disposition or the second disposition, and when the associated key is undepressed, prevents movement of the locking device from said locking position to said unlocking position. 3. A lock according to claim 1 or claim 2 wherein each control member is rotatable about an axis between said first disposition and said second disposition, each member moving along said axis on depression of the associated key. 4. A lock according to claim 3 wherein the axes of rotation of said control members are parallel and the locking device includes a locking member slidable in a plane normal to said axes between said locking and said unlocking positions. 5. A lock according to claim 4 wherein a detent assembly is arranged between the control members and the locking member, each control member being associated with a respective detent of the detent assembly, each detent being movable between an operative position in which the detent engages the locking member to prevent sliding movement thereof from the locking position and an inoperative position in which the detent is disengaged from the locking member to permit sliding movement thereof from the locking position. 6. A lock according to claim 5 wherein the locking member is spring biased towards said unlocking position, each detent in the operative position thereof, engaging the locking member in a position to prevent said movement, each control member controlling the movement of the associated detent so that when the control members in the first disposition thereof are depressed, the detents are all free to be moved to the inoperative position by the locking member against the spring bias of the detents. 7. A lock according to claim 6 wherein, when the control members in the first disposition are undepressed and when the control members in the second disposition are depressed the associated detents are prevented from retracting to the inoperative positions thereof. 8. A lock according to claim 7 wherein each detent comprises a pin that is spring biassed into the operative position. 9. A lock according to claim 8 wherein each control member includes a hole for receiving the associated pin when the control member is in said first disposition and depressed so that the pin is movable from said operative position to said inoperative position by the locking member when all the control members in said first disposition are depressed. 1 0. A lock according to claim 8 or claim 9 wherein each control member includes a hole for receiving a pin when the control member is undepressed and in said second disposition so that when all the control members in said first disposition are depressed, the locking member moves from the locking position to the unlocking position. 11. A lock according to claim 9 or claim 10 wherein each locking member includes a cylindrical surface co-axial with the axis of the control member, the or each hole extending radially into said surface, each pin abutting said surface when the associated control member is preventing movement of the pin from the operative to the inoperative; position. 12. A lock according to any one of claims 1 to 11 wherein each control member, when depressed by the associated key is held in said depressed position, each key being released from said depressed position on return movement from said locking position to said unlocking position, to return under a spring bias to an undepressed position. 13. A lock according to claim 12 wherein each key is spring biased into a projecting position, from which the key can be depressed, the key, once depressed, returning to said projecting position while leaving the associated control member held in said depressed position. 14. A lock according to claim 13 or claim 14 wherein a retaining member is provided which, when in a latching position, engages said depressed controlled members to hold said control members in said depressed position, movement of the locking member from said locking position to said unlocking position, moving said retaining member from said latching position to a rest position to release said control members for return to the undepressed position thereof. 15. A lock according to claim 14 wherein each control member has a third disposition, the control member in said third disposition that is first depressed, moving said retaining member from the rest position to the latching position . 16. A lock according to claim 15 wherein each control member includes a cam surface which, where the control member is in said third disposition and is the first depressed control member, engages a cam surface on said retaining member to move said retaining member from said rest position to said latching position. 17. A lock according to claim 15 or claim 16 wherein each control member, when depressed in said third disposition, allows movement of the locking device from the locking position. 18. A lock according to claim 17 when dependent on claim 9 wherein each control member includes a hole for receiving the associated pin when the control member is in the third disposition and depressed so that the pin is movable from said operative position to said inoperative position by the locking member when all the control members in said first disposition are also depressed. 19. A lock according to any one of claims 14 to 18 wherein each control member includes a latch member which engages the retaining member when the control member is depressed and when the retaining member is in said latching position, movement of the retaining member to the rest position releasing said latches . 20 A lock according to any one of claims 14 to 19 wherein a restraint device is provided for delaying the movement of the retaining member after return of the locking member from the unlocking position to the locking position to permit the detents to return to the operative position before the control members are released from said depressed position. 21. A lock according to any one of claims 1 to 20 and including a device operable to release control members that are depressed. 22. A lock according to claim 21 wherein said device is a manually operable device. 23. A lock according to claim 21 or claim 22 wherein said lock includes a back plate and a casing forming a housing accommodating said control members and said locking member, the keys projecting from said casing, the casing being separable from said back plate and said separation operating said device for releasing depressed control members . 24. A lock according to any one of claims 21 to 23 when dependent on claim 13 wherein operation of the release device moves the retaining member to said rest position, if the retaining member is in the latching position, to release any latch control members. 25. A lock according to any one of claims 1 to 24 and including a rotatable member for connection to a handle so that rotation of the handle rotates the member, the locking member in said locking position, engaging said rotatable member to prevent rotation thereof. 26. A lock according to claim 25 wherein the locking member comprises an elongate barring plate slidable between said locking and said unlocked positions, the barring plate including a head which, in the locking position of the barring plate, engages the rotatable member to prevent rotation thereof . 27. A lock according to claim 26 wherein the barring plate is generally T-shaped with a cross -head of the T- shape engageable with the rotatable member and a limb of the T-shape guided for said sliding movement. 28. A lock according to claim 27 wherein the rotatable member comprises a gear wheel rotatable about an axis, the gear wheel having opposed faces lying in respective planes generally normal to the axis, one of said faces carrying a pair of projecting diametrically opposed pins, the cross-head engaging said pins when the barring plate is in the locking position. 29. A lock according to any one of claims 25 to 28 and including a rotatable handle for connection to a bolt, rotation of the handle about an axis extending and retracting the bolt, the handle being connected to a pinion gear co-axial with the handle axis, said gear wheel engaging said rotatable member so that rotation of the handle tends to rotate said rotatable member. 30. A lock according to claim 29 when dependent on claim 28 wherein said pinion gear and said gear wheel are in meshing engagement and are rotatable about spaced parallel axes . 31. A lock according to claim 29 or claim 30 and including a clutch mechanism between the handle and the pinion gear such that the application to the handle of a twisting force above a predetermined level when the handle is locked by the locking member, results in the handle rotating relative to the pinion gear. 32. A lock according to claim 31 where;in said clutch comprises a spring member mounted between the handle and the pinion gear, the spring member gripping one of said handle and said pinion gear with a force sufficient to prevent relative rotation therebetween when the twisting force on the handle is below said predetermined level, a twisting force above said predetermined level breaking the grip with the spring member and allowing rotation of the handle relative to the pinion gear. 33. A lock according to claim 32 wherein the handle has an insert projecting from the handle and co-axial with the axis of the handle, the spring member including a U-shaped portion which normally grips the insert across a portion of lesser width with a portion of greater width lying at right angles to said portion of lesser width, the application to the handle of a twisting force greater than said predetermined force twisting the insert relative to the U-shaped spring portion so that the greater width portion of the insert spreads the limbs o f the U-shaped portion of the spring member to permit relative rotation therebetween. 34 . A lock according to any one of claims 1 to 33 wherein the keys are formed integrally with a key plate, the key plate providing spring means for each key tending to urge the associated key into an undepressed position. 35. A lock according to claim 34 wherein the key plate is formed from a plurality of sub-frames, each sub-frame surrounding an associated key and each key being connected to the associated sub-frame by at least one limb providing said spring means . 36. A lock according to claim 35 wherein each key is connected to the associated sub-frame by two limbs connected between the sub- frame and the key at spaced positions around the key. 37. A lock assembly according to any one of claims 34 to 36 when dependent on claim 21 or claim 22 wherein said manually operable device includes a push button, said push button being mounted in a sub- frame in the key plate by at least one limb providing a spring force urging the push button to an inoperative position, movement of the push button from said inoperative position against said spring force operating said device. 38. A lock assembly according to any one of claims 34 to 37 wherein said key plate is moulded from a plastics material. 39. A lock according to any one of claims 1 to 38 and further comprising a back plate assembly including a rotatable handle spring biased to an inoperative position, means being provided for holding the handle in a position rotated away from said inoperative position. 40. A lock according to claim 39 wherein said means include a plate normally held in a first position in which the plate permits the handle to rotate freely, the plate being releasable for movement to a second position, when the handle is rotated away from said inoperative position, in which the plate is locked to hold the handle in said rotated position, the plate being releasable from the locked position. 41. A lock according to claim 40 wherein the handle has a cam surface associated therewith, release of the plate engaging the plate with the cam surface, and rotation of the handle away from said inoperative position causing movement of the plate to said second position. 42. A lock according to claim 41 wherein said plate is urged against said cam surface by a spring to engage said plate with said cam surface. 43. A lock according to any one of claims 40 to 42 and comprising a push button which engages the plate to hold the plate in said first position, the push button being depressible to permit the plate for movement to said second position. 44. A lock according to claim 43 wherein the push button engages the plate in the second position of the plate, to lock the plate in said second position, the push button being depressible when so engaged to release the plate from the locked position. 45. A lock according to claim 43 or claim 44 wherein the plate includes an elongate slot, the push button engaging in said slot to hold the plate. 46. A lock according to any one of claims 1 to 45 wherein the locking device comprises a latch bolt including a body containing a cam rotatable by rotation of an associated handle, and a bolt assembly having a bolt head urged to extend from the body and retractable into the body either by rotation of the cam or by a retracting force applied to the head of the bolt. 47. A lock according to claim 46 and comprising an anti- thrust pin which is extendible and retractable independently of the bolt head, the anti-thrust pin, when retracted with the bolt head extended, allowing an anti-thrust device to move to a position in which the device resists retraction of the bolt by a retracting force applied to the bolt. 48. A lock according to claim 47 wherein the anti -thrust pin is associated with a plate that prevents the anti -thrust device moving to said retraction-resisting position when the bolt head and the anti-thrust pin move together, said retraction of the anti -thrust pin with the bolt extended, moving said plate to a position in which the plate permits the anti-thrust device to move to said retraction-resisting position. 49. A lock according to claim 47 or claim 48 wherein rotation of said cam to retract said bolt head, when the anti- thrust pin is retracted, moves said anti-thrust device from the retraction resisting position, so allowing retraction of the bolt. 50. A lock according to any one of claims 47 to 49 wherein the anti-thrust device comprises a lever urged by a spring towards said retraction-resisting position. 51. A lock according to claim 50 wherein the bolt head includes a rearward extension, the lever overlying the extension and locating behind a stop associated with the extension in said retraction resisting position. 52. A keypad lock comprising a locking device slidable between a locking position and an unlocking position and a plurality of locking members engaging said locking device, each locking device being associated with a key, the locking members being selectable either to lock the locking device in the locking position when the associated key is undepressed and to permit said sliding movement to said unlocking position when the associated key is depressed or not to affect the movement of the locking device . 53. A keypad lock according to claim 52 wherein each locking member is selectable by rotation relative to the associated key. 54. A keypad lock according to claim 52 or claim 53 wherein each locking member is associated with a pin that engages the locking device, movement of the locking device from the locking position tending to move said pins, said movement being prevented by those locking members selected to lock the locking device when the associated key is undepressed. 55. A keypad lock comprising a plurality of keys each associated with a respective member, selected of said members moving to a position permitting unlocking of said lock on depression of the associated key, one of said selected members, on depression of the associated key, releasing a device that normally prevents the remaining selected members being positioned to permit unlocking of said lock. 56. A keypad lock according to claim 55 wherein said device has a first position in which the device is disengaged from said selected members and a second position in which the selected members, when the associated keys are depressed, engage the device to position the selected members to permit unlocking of said lock, said device being moved from said first position to said second position by said one of said selected members on depression of the associated key. 57. A keypad lock according to claim 56 wherein each selected member is movable linearly on depression of the associated key, said movement engaging said selected members with said device when said device is in said second position. 58. A keypad lock according to claim 56 or claim 57 wherein the non-selected members also engage said device when the device is in said second position and the associated keys are depressed, said non-selected members not affecting the unlocking of the lock when so positioned. 59. A keypad lock according to any one of claims 56 to 58 wherein said device comprises a plate slidable between said first and second positions. 60. A keypad operated lock comprising a locking device movable between a locking position and an unlocking position and a plurality of members each associated with a respective key, depression of selected keys moving the associated members to a position in which the members are held to permit the locking device to move to said unlocking position, means being provided for releasing said depressed selected members. 61. A keypad lock according to claim 60 wherein said releasing means comprise a plate movable between a first position in which the plate engages the selected members that have been moved to a position in which the selected members permit the locking device to move to the unlocking position and a second position in which said engaged selected members are released for return movement . 62. A keypad lock according to claim 61 wherein the releasing means include means for moving said plate from said first position to said second position. 63. A keypad lock according to claim 62 wherein said moving means comprise a manually operable button. 64. A keypad lock according to claim 62 wherein the members are within a casing, the keys being carried on a mounting normally connected to the casing but separable therefrom, said separation operating said moving means to move the plate from said first position to said second position.

Inventors: BESSEY PETER JOHN HARVEY, JACKSON DAREN JOHN, MIDDLETON STEPHEN PATRICK, NAYLOR MARK ANTHONY, BESSEY, PETER, JOHN, HARVEY, JACKSON, DAREN, JOHN, MIDDLETON, STEPHEN, PATRICK, NAYLOR, MARK, ANTHONY
Applicants: BESSEY PETER JOHN HARVEY, JACKSON DAREN JOHN, MIDDLETON STEPHEN PATRICK, NAYLOR MARK ANTHONY, REYNOLDS UK LTD, BESSEY, PETER, JOHN, HARVEY, JACKSON, DAREN, JOHN, MIDDLETON, STEPHEN, PATRICK, NAYLOR, MARK, ANTHONY, REYNOLDS (UK) LIMITED
Application year: 1997
Main classification: E05B37
IPC codes: E05B37