Patent GB-723870-A (GB)
Title: Improvements in and relating to protective devices for electric motors
Inventor: MILES JOSEPH WILLIAM
IPC: H02K11/00
Filed: 1952-02-29
Abstract: 723,870. Controllers. I.B.M. UNITED KING- DOM, Ltd., [formerly INTERNATIONAL TIME RECORDING CO., Ltd.]. Feb. 29, 1952 [March 14, 1951], No. 6135/51. Class 38 (3) [Also in Group XIX]. A protective device for an electric motor controlled by a switch associated with a periodically translated operating member and with one or more control elements each operable to close the switch comprises switch-opening means and interlock means operable upon movement of one or more of the control elements to switch-closing position to establish a driving connection between the periodically translated operating member and the switch opening means, the latter being operable to open the motor circuit after a predetermined number of movements have been transmitted through the driving connection while the one or more control elements remain in switch-closing position. The invention is shown applied to a workmen's time-recorder wherein a master clock causes energization of a solenoid periodically to operate trip mechanism for starting an electric motor used to drive a type wheel unit for time printing on an inserted card and wherein the motor is also used in the printing operation. For a few seconds every minute the solenoid is energized and pivots a lever 3 which moves an arm 5 to the right. Fig 1, so that a latch point 9 thereof enters a slot in a latch member 7 and is urged upwards by a spring 8 to engage the upper edge of the slot. Upon de-energization of the solenoid the spring 8 draws the arm 5 leftwards and rocks the member 7 about its pivot 10 against a spring 11 to permit a spring-biased pawl 12 to drop into engagement with a ratchet wheel 13 which is fixed on a shaft 17 rotated by the electric motor 1 whose circuit has just been closed by the member 7 bearing on a spring blade 15 of a pair 15, 16 which carry contacts 15a, 16a. The pawl 12 is pivoted on a disc cam 14, mounted loosely on the shaft 17 but now driven therewith through the pawl 12 and ratchet 13. A cam follower 18 rides out of a recess 21 in the cam 14 and maintains the contacts 15a, 16a closed during one revolution of the cam 14 with which turns an eccentric cam 22 which causes a follower 24 to operate a lever 29 carrying a knock-off stud 31 which bears down on the arm 5 and unlatches it from the member 7 which returns to the initial position. At the end of one revolution of the shaft 17 the follower 18 rides into the recess 21 and allows the contacts to open and the motor to coast to a stop. Other latches may be arranged co-laterally with the latch member 7 and cam follower 18 to control the motor 1 for various purposes and any one of these parts bearing on the contact blade 15 may fail to return so that the motor is not switched off and should it continue for more than a predetermined number of minutes, a lever 48 is urged by a spring 52 to cause its toe 51 to move the contact blade 15 away from the blade 15. Normally the lever 48 is inhibited by its knee 47 bearing against a curved abutment face 46 of a bell-crank 44 and extension 50 of the latter's arm 43 while the bell-crank 44 is held by a crank 42 of a multi-limbed lever 39 having another limb 41 in the path of all latch members 7 and followers 18 and a limb 38 with a slot for engagement with a trip rod 35 pivoted on the arm 5 and urged apart therefrom by a spring 36. While any member is holding the contacts closed it bears on the limb 41 and rocks the crank 42 free from the bell-crank 44 so that its arm 53 lies in the path of the trip rod 35 and if this is happening when a minute-impulse causes the rod 35 to move, with the arm 5, to the right the first step 55 of the rod 35 will engage the arm 53 and rock the bell-crank so that the knee 47 moves part way round the abutment face 46 and if the condition persists for another minute at the next reciprocation of the rod 35 its next step 56 engages the arm 53 and rocks the face 46 free from the knee 47 so that the toe 51 opens the contacts and the motor stops. The number of steps on the rod 35 can be increased if a longer delay is required.