| 摘要 |
646,401. Electromagnetic switches. GUARDIAN ELECTRIC MANUFACTURING CO. Feb. 18, 1948, No. 4753. Convention date, Dec. 22, 1938. [Class 38(v)] In a selector switch successive impulses at a rairly rapid rate to an electromagnet 40 cause the step-by-step rotation of a primary ratchet wheel 18 with its attached contact arm followed by the step-by-step rotation of a secondary ratchet wheel 26 with its attached contact arm. If the rate is not fast enough, the primary ratchet wheel is returned to the starting position 'before the next impulse arrives. The ratchet wheel 18 is loosely mounted on a shaft 11 to which the ratchet wheel 26 is fixed. Springs tend to bring both wheels to a starting position in which portions of the wheels bear against a stop 34, but such movement may be prevented by check pawls 56, 57 which are pivoted at 55 and tend, under spring bias, to engage ratchet wheels 18, 26 respectively. The toothed portion 18a of the wheel 18 is of greater radius than the toothed portion of the wheel 26. The pawl that operates both ratchet wheels consists of a U-shaped member or bail 50, the centre portion of the U engaging the wheels and the ends being pivoted to a member 48 fixed to the armature 43. Thus when the armature is reciprocated the bail first engages and drives the wheel 18 till a tooth 18b is reached, after which the wheel 18 stays still and further reciprocations drive the wheel 26. Prior to this, however, the engagement of the pawl 50 with the tooth 18b causes the pawl to engage and lift the cam-shaped end of the check pawls 57 causing the ratchet wheel 26 to return to its starting position. Should the impulses to the electromagnet not follow at sufficiently close intervals, the check pawl 56 for the primary ratchet wheel 18 is lifted by a spring-biassed toothed segment 59 engaging a part 56d. In normal operation, however, the segment 59 is moved upwards away from the part 56d by the member 48 on the armature engaging the tail 76 of the lever 74 pivoted at 72 whenever the armature is attracted. At each release of the armature, the segment 59 tends to return but this return movement is delaped by an escapement mechanism 68, 70. |
