1460075 Safety lock K YOSHIZAWA 14 Jan 1974 1749/74 Heading E2A A lock for operation with a forked key includes a first mating engagement member actuable by a first leg of the key upon an initial rotation of the key and a second mating engagement member connected to first member in such a way as to be put into an operative condition by the engagement of the first member with the first leg of the key. Further rotation of the key causes its second leg to engage the, now operative, second engagement member to release a locking slide and effect unlocking. In the preferred embodiment, the first mating engagement member 44 comprises a number of semi-circular platelike elements provided with slots and mounted upon a shaft 154. All but one of the elements is rotatable about the shaft the other being fixed to it and the elements are normally spring biased to a position in which the slots are misaligned. The shaft 154 also carries a gear 186 which mates with a gear 194 forming part of a second mating engagement member 188 mounted on a shaft 196. The member 188 also includes a central annular element 192 having a window 200, the gear and element being freely rotatable about the shaft 196, and a part 190 fixed to the shaft which is provided with a projection 202. Part 190 is biased in a clockwise direction by one end of a pusher 218 which is slidable in a holder 232 fixed to the locking piece 32, the other end of the pusher being engaged by a biasing spring 236. The locking piece is itself biased towards the right to a locking position by a spring 248 and is provided with a locking element 34 engageable with a spring loaded latch 28, 30, a central element 230, and a rear element 238. In the locked position the undersurface of the rear element 238 engages an upwardly spring biased detent 250. The gear 194 is provided with a notch 204 engageable by the hooked end 212 of a first pivoted member 210 biased downwardly by a spring 206. A bifurcated pivoted lever 178, engageable with the first pivoted member, is biased downwardly by a spring 182 into engagement with a second pivoted member 174 having a hooked end 176. In operation, starting from the locked position shown in Fig. 4, in which position the slots of the elements of member 44 are misaligned, the hooked end of the member 210 is seated in the notch 204, and the projection 202 on the shaft 196 is shielded by the element 192, the key is inserted with its first engagement elements 356 in the groove 40 of the shaft 38 and its second engagement elements 358 in the groove 42. Upon initial rotation of the key in a clockwise direction the second engagement elements 356 engage and raise lever 178, moving it away from the member 174, which becomes free to rise, and raising the member 210 so that its hooked end is withdrawn from the notch 204, thus freeing the gear 194, the gear 186, and the shaft 154 for rotation. At the same time, the first engagement elements engage the elements of the member 44 to pivot them to bring their slots into alignment and to cause rotation of the shaft 154, this in turn rotating, through the gears 186 and 194, the element 192 to a position in which the projection 202 of the shaft 196 is no longer shielded. The element is held in this position by the spring 194 whose hooked end 176 moves upwardly into the aligned slots of the parts of the member 44. (See position of Figure 5c). Upon further rotation of the key the second engagement elements pass through the window 200 to engage the projection 202, and the first engagement elements move free of the member 44. Engagement of the second engagement elements with the projection 202 causes the shaft 196 and thus the part 190 to rotate in an anti-clockwise direction. This rotation of part 190 moves the pusher 218, against its bias, to the left to engage the control element 230 of the locking piece and move it to the left to an unlocking position. Movement to the unlocking position moves the rear element 238 of the locking piece clear of the detent 250 which rises behind the element to hold the locking piece in the unlocking position (See Figure 5e). Upon yet further rotation of the key (through a full 180‹ see Fig. 5f), the second engagement elements move clear of the projection 202 to allow the pusher to move back to its original position thus biasing the part 190 back to its original position. The second engagement elements also move clear of the lever 178 thus letting it move downwardly under the action of spring 182. This in turn lowers the end of member 174 out of the aligned slots of the elements of member 44 and allows them to return under the influence of their spring biasing to their initial non-aligned positions. This rotates shaft 154 and, thus through gear 186, rotates gear 194 to move the notch 204 back to its initial position to receive the end of member 210 and the element 192 back to its initial projection shielding position. The key can then be withdrawn to leave the lock open. To lock the lock the key is inserted into the shaft in the same position as at the start of the unlocking operation and is twisted anti-clockwise. This causes a projection 384 forming part of the second engagement element 358 to engage a hook on the detent 250 to move it downwardly away from the element 238 of the locking piece and allowing the locking piece to move to the right under its biasing spring to the backing position; The key is then twisted clockwise to its original position for withdrawal this allowing the detent to regain its initial position under the element 238. To effect unlocking without the use of a key, pins 264, 266, provided on the locking piece, and detent, are engageable by parts 268, 270 on a rotatable shaft 272, rotation of the shaft moving the detent downwardly into an unlocking position. To prevent the unauthorized unlocking by false key a slidable spring retainer 300, Fig. 11a, has a recess 316 in which engages the leaf spring 174, the retainer, upon rotation of the key being moved by the part 180 of the lever 178 to release the spring; the detent 250 projects through the case of the lock to function as a lock bolt.