The device in order to limit the lifting capacity of the machines for public works, in particular, the lifting machines

摘要

1,171,637. Safety devices for jib cranes. BIALSKIE ZAKLADY URZADZEN TECHNICZNYCH. 17 Nov., 1966 [18 Nov., 1965], No. 51618/66. Heading B8B. A sheave arrangement for limiting load moments of a jib crane comprises an outer ring 1 with a groove for a rope or chain 6. The outer ring 1 is rotatably mounted on an inner ring 2 pivotally mounted on a sheave pin 5 in a jib 8 through intermediate resilient members 4 and a shackle 3. The rotary axis of the outer ring 1 is offset from the pivotal axis of the inner ring 2. A cam 10 is rigidly mounted on the pin 5, Fig. 2 (not shown), and co-operates with a spring-loaded cam follower on an arm 11 pivotally mounted on the inner ring 2 and arranged to co-operate with a micro-switch 9 which, when actuated, either stops the crane machinery or sounds an alarm. At any particular luffing angle of the jib 8 the forces acting on the sheave cause the axes of the outer and inner rings 1, 2 to lie on the reaction R, this causes an appropriate part of the cam 10 to come under the cam follower so that the microswitch 9 is operated when the load detected by the deflection of the rssilient members 4 is the maximum for that particular luffing angle. Instead of being fixed to the jib 8 the cam 10 may be pendulously mounted on the pin 5 and remain upright under gravity, the cam profile being modified appropriately.