Patent GB-632685-A (GB)
Title: Improvement in secondary time-keeping apparatus
IPC: G04C11/00
Filed: 1947-03-21
Abstract: 632,685. Electric c clocks. INTERNATIONAL BUSINESS MACHINES CORPORATION. March 21, 1947, No. 7788. Convention date, April 25, 1946. [Class 139] A secondary clock comprises a time member normally rotated at a definite rate by a synchronous motor, a no r m a lly stationary clock advancing-member arranged adjacent the time member and rotatable about the same axis as the time member, and a one way coupling between the clockadvancing member and the time member by means of which when the clock - advancing member is rotated it rotates said time member to a predetermined position, such rotation of the clock-advancing member taking place when a time signal from a master clock is received by the secondary clock. A self start i n g synchronous motor 18, Fig. 2, driven from the mains drives through gearing a seconds driving gear 22 which is mounted by a friction clutch 26 on a shaft 23 carrying the seconds hand 12. A pinion 27 on the shaft 23 drives through a gear wheel 31 and a pinion 35 a gear wheel 36 mounted on a sleeve 24 which carries the minutes hand 13. Projecting from the front face of the gear wheel 36, Fig. 5, is a stud 37 and fixed to the rear face of the gear 36 is a spring finger 38 having a cam face 41. The hour hand 14 is carried by a sleeve 25 which is rotated through the reduction gear train 42-45. Rotatably mounted on the shaft 23 behind the gear wheel 36 is a disc 46, Fig. 9, forming the clockadvancing member. The disc is normally held stationary by the engagement of a spring pressed stop pawl 49 with a pawl 52 pivoted on the disc 46. In this position of the disc 46 a notch 58 therein is engaged by a spring urged detent lever 55 fixed on a shaft 59. A stud 67 projects from the front face of the disc 46 into the path of the spring finger 38 which normally flexes past said stud 67. A trigger mechanism 82, Fig. 10, comprising an electromagnet 83, an armature 84, a trip pawl 86 and the stop pawl 49 the depending latch plate 89 of which co-acts with a notch 90 of the trip pawl 86 is arranged so that at the fifty ninth minute past every hour the pawl 49 is rocked counter clockwise to free the pawl 52 which is then moved by a spring 68, Fig. 9, so that its forward hooked end 69 engages the teeth of an adjacent ratchet wheel 70 rotatable with the gear wheel 22. The disc 46 is then rotated one revolution in one minute at the end of which revolution the pawl 49 re-engages the pawl 52 the end 69 of which moves out of engagement with the ratchet wheel 70. Two control arms 74, 75, Fig. 7, fixed to the shaft 59 are urged by springs 77, 80 into supporting engagement with the pawls 72, 73. The arrangement is such that at the start of the revolution of the disc 46 a tooth 57 of the detent 55 rides out of the notch 58 thereby rocking the shaft 59 counter-clockwise whereupon the two stop pawls come into their operative position in the path of movement of an arm 29 on the shaft 23 and the stud 37 on the wheel 36 respectively. Before the end of the revolution of the disc 46, if the clock is anything up to fifty-nine minutes slow, the stud 67 engages the cam face 41 of the spring finger 38 and so for the rest of the revolution the wheel 36 is rotated with the disc 46. The pawl 72 abuts the arm 29 to stop the seconds hand 12 at zero and the pawl 73 abuts the stud 37 to stop the minutes hand 13 at zero. At the end of the revolution of the disc 46 the pawl 55 again engages the notch 58 and by rocking the shaft 59 clockwise returns the pawls 72, 73 to their inoperative position. The above action of the disc 46 would also correct the seconds and minutes hand for a gain of anything less than a minute. Specification 594,070 is referred to.