Patent GB-304690-A (GB)
Title: Improvements in electric clock systems
IPC: G04C13/04
Filed: 1929-01-14
Abstract: 304,690. Warren, H. E. Jan. 24, 1928, [Convention date]. Electric clocks; winding-apparatus, electric.- A master and secondary clocks are driven by synchronous motors connected to a source of alternating current, these motors constantly winding up the clock springs at the same rate at which the springs run down. When the source of current fails, switch connections are made by the master clock so that on the resumption of the supply the clocks are run at a higher rate until they resume their correct positions. This higher rate may be achieved (1) by the use of a special synchronous motor affecting the epicyclic gear transmission between the normal motor and the clock spring or (2) by the use of a frequency converter so that current of increased frequency is supplied to the normal motor for the appropriate length of time. The master clock comprises a standard marine movement 10 between plates 11 and 12 (carrying the dial) and having a spring 13 which is wound by gearing 14, 15, 27, 26, 25 from a stationary pinion 24.. The entire movement is mounted bodily on a gear wheel 19 so that the minute shaft 16 is co-axial with the centre of gear 19. Hence as gear 19 rotates relatively to the fixed base 22, the wheel 25 rolls round the stationary pinion 24 and the spring is wound up at the same rate at which it runs down. This gear 19 is rotated by the normal synchronous motor 28 through an epicyclic train in which a certain gear 34 is normally stationary. When the current fails a switch 17, 49 is operated so that on resumption of the supply a second motor 29 is actuated and this rotates the gear 34 whereby the epicyclic gearing is so modified in its action that the gear 19 is rotated ten times as fast as normal until the clock is again in correct position. When the latter occurs the switch 17, 49 again cuts out the motor 29. The pointer 17 is fixed to the minute hand shaft 16 and normally is rotated counter-clockwise by the gear 19 at the same rate as it is rotated clockwise by the spring 13, i.e. one revolution per hour. Hence normally, this pointer is stationary, holding a contact blade 49 against a terminal 51. When the current fails the gear 19 remains stationary and pointer 17 is moved clockwise by the spring 13 so that blade 49 is released and makes contact with a second terminal 50. This, brings the motor 29 into circuit. Fig. 4 shows a clock system in which the master clock with its motors 28, 29 works in conjunction with secondary clocks 42. Each secondary clock has normal and special motors (together wtih epicyclic gearing) equivalent to the motors 28, 29. 40 and 41 are A.C. supply lines, and 44, 48 are the common lines for the motors 28 and 29, respectively, of the secondary clocks. When the current fails a thermostatic device 53 (normally heated by a coil 55) cools and makes contact at 54, and the pointer 17 permits contacts 49, 50 to close. This closes the circuit of a coil 52 which thereby, upon resumption of current, closes a switch 46 to energize the motors 29. 61 is a resistance short-circuiting the contacts 49, 50 and 53, 54 once. the coil 52 is energized. When the clock is correct contacts 49, 51 close and de-energize these circuits. The thermal device 53 is employed to prevent frequent use of the motors 29 for slight variations in the supply frequency. In a modification, the epicyclic gearing and the motors 29 are omitted from the master and secondary clocks and when the contacts 49, 50 close a frequency converter is brought into circuit to supply the motors 28 with current of double the normal frequency. Means are provided whereby, if the current fails for exactly an hour (or any exact number of hours' up to twelve) the switch arm 17 is prevented from returning after one or more revolutions by the spring 13 to its normal position, in which position it would leave the clock one or more hours uncorrect. Specification 125,766 is referred to, for the construction of synchronous motor preferably used.