GB555463A - Improvements in or relating to crane limit switches - Google Patents

Abstract

555,463. Snap-action switches. IGRANIC ELECTRIC CO., Ltd. Sept. 18, 1942, No. 13204. Convention date, Sept. 20, 1941. [Classes 38 (iii) and 38 (v) ] A crane limit switch, operated by part of the hoisting cable, comprises a horizontal shaft 3 bearing pivoted, spring-pressed contact arms 17 on brackets 14, co-operating contacts 5 mounted on insulating bearers 6 supported on insulating blocks 7, and an operating lever, having at one end a weight provided with adjustable loops through which the hoisting cables run and a counter-weight at the other. This lever is secured to a casting 30, Fig. 3, which runs on ball bearings in the casing and on an extension 33 of the shaft 3, and rocks the shaft 3 through a snap-action mechanism comprising a compressed spring 41 closely fitting on a guide 36 secured in arm 35 of casting 30, and sliding in arm 38 of a bell crank pivoted at 39 in the casting. The other end of the crank 38a bears a roller 42 running on a cam 43 secured to the shaft 3. With the contacts and lever in running position, as shown, an undue lift of the crane, the weight is raised, a counter weight moves the lever and casting 30 anti-clockwise, whereon the roller runs up the cam 43 and, on reaching the peak swings the cam, and hence shaft 3 over in a clockwise direction to cause the right hand contacts 5, 18 to engage. Springs 45 and 48 cushion the movement of the lever and shaft respectively. At the limit of the lift, power is cut-off and the motor armature and series field are connected in a short circuit braking loop.