Safety device for a top boom pivotally mounted on a crane boom

Claim 1

In combination with a crane having a main boom and a top boom pivotally connected to said main boom, a safety device which includes: a. a first control system arranged on said top boom and comprising: b. a means for measuring the actual angle formed by said top boom with a horizontal plane; c. a means for measuring the actual load suspended on said top boom; d. a means for supplying the rated values of the load permissible to be suspended on said top boom, this means being tuned by said means for measuring the actual angle; e. a comparing device comparing the values received from said means for measuring the actual load suspended on said top boom with the values received from said means for supplying the rated values of the load permissible to be suspended on said top boom; f. a second control system arranged on a part of said crane other than said top boom and comprising: g. a source of constant current; h. a decoder electrically connected to said source of constant current for receiving energy therefrom and being operable to emit pulses for generating operative-warning signals; i. an angle indicator electrically connected to said source of constant current for receiving energy therefrom and indicating the antual angle formed by said top boom with a horizontal plane; k. a first conductor interconnecting said first and said second control systems: l. said first conductor on the one hand being connected to a second conductor within said first control system which second conductor is connected to the mass of said top boom and said main boom through a potentiometer tuned by said means for measuring the actual angle and through a resistor arranged in series with said potentiometer; m. a first branch conductor branching off from said second conductor and being connected to said mass and including a first switch means which normally is open, but under the influence of said comparing device is closed to short-circuit said potentiometer and said resistor when the value received by said comparing device from said means for measuring the actual load suspended on said top boom reaches the value received by said comparing device from said means for supplying the rated values of the load permissible to be suspended on said top boom; n. a second branch conductor branching off from said second conductor and being connected to said mass and including a second switch means which normally is open, but under the influence of said means for measuring the actual angle is closed to short-circuit said potentiometer and said resistor when the top boom has lowered to the horizontal plane; o. said first conductor on the other hand being connected to a third conductor within the second control system and through said third conductor and through said constant current source to said mass.