GB731593A - Short-time electric switch - Google Patents

Abstract

731,593. Switching systems. LICENTIA PATENT-VERWALTUNGS GES. May 4, 1951. [May 4, 1950], No. 10587/51. Class 38 (4). [Also in Group XXXVII] A time controlled switching system for spot-welding machines comprises cam-operated contact springs 15, a synchronous motor 1, 2, a clutch 3 between the motor shaft and cam-shaft 7 and a clutchoperating coil 29, which is momentarily energized when the welding electrodes engage the work, to actuate members 30, 28, 26 for effecting engagement of the clutch. Engagement occurs at a definite point in the A.C. cycle. The upper contact spring 15 is normally held clear (by a catch 13) of the lower contact spring which is supported by a " switch off " lever 17 riding on a cam 8. On energizing the coil 29 a catch 27 on clutch actuating member 26 is released from one of a series of peripheral recesses in control drum 25 on a shaft 19 which, together with shaft 7 commences to rotate synchronously with the supply voltage. A timing arm 10 which is angularly adjustable on the shaft 7 engages a striker 14 as the shaft rotates and releases catch 13, thereby allowing the two contacts 15 to engage and initiate flow of welding current. The contacts open to terminate the weld when a cut-away portion of cam 8 reaches the lever 17. The shafts 7, 19 continue to rotate until the catch 27, which has meanwhile been riding on the rim of drum 25, falls into the next recess and allows the clutch actuating member 26 to return to its inoperative position and so release the clutch. Prior to de-clutching, a cam 24 on shaft 19 has operated a re-setting lever 16 which raises the upper contact spring 15 on to the latch 13. To allow for timing periods in excess of those corresponding to a single revolution of the shaft 7, the shaft 19 is capable of longitudinal move. ment and is provided with cams 20, 21 adapted to prevent dropping of the " switch-off " lever during one or two revolutions of the shaft 7. Further cams 22, 23 are arranged to prevent operation of the re-setting lever until after shaft 7 has made one or two revolutions. Drum 25, similarly, has two further series of notches which do not become effective until the shaft 7 has completed one or two revolutions.