Patent GB-601665-A (GB)
Abstract: 601,665. Control of motors. IVOR POWER SPECIALTY CO., Ltd., and WEBB, E. F. D. July 7, 1944, Nos. 13055/44 and 14996/45. [Class 38 (iii)] A mechanically driven timing or limit switch mechanism comprises a cam-operated magnet actuating the armature or float of mercury displacement switch or switches by means of which a controlled device driving the mechanism is caused to rotate a predetermined number of revolutions and an additional switch and cam driven by the spindle of the aforesaid cam to be operated at a given position of the mechanism. The invention is applicable to the operation of soot blowers and in sequence. In Fig. 5 the rotary mechanism of a soot-blower drives a cam-shaft 9 and cam 10 through worm-gearing 3-4 and a gear train 6-7-8- which can be readily changed to alter the gear ratio. After a certain number of revolutions, the cam 10 opens switch 14 to stop the soot-blower motor. Another cam on the shaft can close a switch 57 to start-up the next blower in sequence. For a retractable blower, switch 14 controls rotation in one direction and switch 54 actuated by cam 52 controls reverse rotation ; in such case switch 57 is actuated by the form of cam 52a (shown in Fig. 5b) carrying plate 55 loosely pivoted at 56. Anti-clockwise rotation of cam 52a will close switch 57 but during clockwise rotation the roller 59 will push plate 55 sufficiently into recess 58 to allow switch 57 to remain open. The connections for an automatically reversible motor 43 supplied from mains 38 are shown in Fig. 4, wherein the equivalents of cams 10 and 52 and switches 14 and 54 are shown diagrammatically. Push switch 39 closes the circuit of operating coil 41 of forward contactor 42. The resulting forward motion of motor 43 with cams 52 and 10 closes switches 54 and 14, the latter maintaining the supply to coil 41 after switch 39 opens. After the desired movement, cam 10 opens switch 14, which opens contactor 42 to stop motor 43 and also re-closes interlock contact 44. As switch 54 is still closed, this closes the circuit of relay 47 which, after a time delay, closes the circuit of coil 48 of the reverse contactor 50. The motor 43 then runs backward until the starting position is reached and switch 54 re-opens ; the re-closure of switch 14 during return movement is ineffective because interlock contacts 51 or contactor 50 keep open the circuit of coil 41. To cause the movements in the two directions to be unequal cam 10 can be driven only in the forward direction and cam 52 only in the reverse direction at a different speed, each through a free wheel. Rotation of a cam in the wrong direction, due to a free wheel sticking, is prevented by an abrupt edge on the cut-away part of the cam (see Fig. 6d) which engages the switch arm. During forward movement, with the free-wheel for the reverse cam 52 slipping, the reverse switch 54 will be open ; just before the motor stops, an arm 77 on pinion 78 driven through gearing by the reverse cam engages peg 79 and so drives cam 52 a sufficient distance to close the reverse switch 54. To give increased accuracy of positioning, each cam is replaced by a high speed and a slow speed cam, geared together ; the switch opens only when the cut-away portions of the two cams are both in the same circumferential position. The connections for controlling a number of soot-blowers, operable automatically in sequence, either singly or in pairs and such that any may be put out of service at will, is illustrated. The Specification sets forth the application of the invention to valves and states that it may be applied to water lances for boilers and to automatic lifts and hoists. Specification 542,242, [Group XXVIII], is referred to.