594,070. Synchronous clocks. IN T E RNATIONAL BUSINESS MACHINES CORPORATION. Oct. 18, 1943, No, 17119. Convention date, Jan. 1. [Class 139] The hands of a secondary clock are operated by motion work driven by a synchronous motor and controlled by a master clock, so that during the last minute of each hour the minute hand is driven at a greatly accelerated rate until it completes the hour of movement, is then stopped, and is released at the end of the hour for movement at normal rate. The adjustment is initiated and stopped by the master clock sending out a single electrical impulse, lasting for one minute, or two separate impulses with one minute interval, each impulse lasting for two seconds. In Fig. 3, shaft 20 carrying the second hand 24 is driven by a wheel 21 engaging a pinion on the motor shaft and drives a planet cam 34 fixed to a collar 22 on the shaft and carrying a planet gear 35 engaging sun wheels 38, 39 with 60 and 59 teeth respectively. Sun wheel 31 is fixed to a sleeve 25 carrying the minute hand 27. Sun wheel 39 is fixed to a sleeve 40 carrying a disc 42 held stationary for 59 minutes of each hour. The planet wheel 35 is rotatably mounted on a sleeve 36 and is held in frictional contact with a wheel 55 held to the sleeve by a spring 57 and friction disc 58. Wheel 55 gears with a wheel 56 on a sleeve 60 secured to a disc 61 which is free when disc 42 is held stationary and vice versa. During the last minute of each hour disc 42 is released and disc 68 is held stationary to control the rotation of the planet wheel 35 on its own axis. Both discs 42 and 61 have toothed edges adapted for engagement with projections on the arms 45, 64, Fig. 6, of a rocking lever operated alternately in opposite directions at the beginning and end of the synchronising minute of each hour by a solenoid 74 through levers 71, 50 and a pin 66 on the latter engaging a third arm 67 on the rocking lever. The minute hand is stopped on completing an hour's movement by a projection 83 on a spring-loaded lever 84 engaging a notch in the rim of a disc 80 fixed to the minute sleeve. At the end of the synchronising minute, the lever 84 is moved to disengagement position by the pin 66. The lever 84 has a parallel integral arm with a pin 88 engaging a slot in a spring-loaded arm 90 with a projection. 94 for engaging the planet arm to arrest the seconds hand. In a modification, wheels 55, 56 and disc 61, are omitted and the planet wheel 35 is held in continuous frictional engagement with the planet arm by a spring and friction disc. When the sun wheel 39 is released the planet wheel is held against rotation on its own axis and the second and minute hand move together to the positions at which they are arrested. The secondary clocks 15, Fig. 7, are supplied with A.C. current from a secondary winding 100 and the solenoids 74 are energised by current supplied from secondary winding 110 through a rectifier 115 when switch 95 is closed by the master clock during the last minute of each hour. During this minute switch 96 is opened. This switch is bridged by a condenser 112. The motors are protected aganist D.C. current by condensers 106. A modification employs a single secondary winding and a single switch which is closed during the last minute of each hour to supply D.C. current to the motors. In Fig. 6, the levers 71, 50 are interconnected by a pin on the former engaging a slot in an extension 68 on the latter. In a modification, Fig. 13, the lever 50 includes an arm 175 with a slot engaged by a pin 177 carried by a lever 178, Fig. 16, with a follower pin 180 adapted to co-operate with a cam 183 integral with a ratchet wheel 186 engaged by a pawl 87 pivoted to the lever 71. The supply and control circuit is such that the solenoid is energised to operate the ratchet wheel during the last two seconds of the 59th and 60th minute of each hour. The cam has half the number of teeth of the ratchet wheel so that the rocking lever 45, 64 operates as in the previous constructions. A pawl 192 prevents the ratchet wheel from rotating clockwise.