Abstract: A safety apparatus which can set an appropriate rated load curve which can be grasped readily by an operator and takes a difference between horizontal extension amounts of outrigger jacks into consideration and can facilitate calculation of a load factor. Entire circumference load calculating means calculates a first rated load regarding a forward and backward direction and calculates a second rated load based on extended conditions of the front and rear outrigger jacks, and then calculates inflection angles of a rated load curve based on the rated loads and the extended conditions of the outrigger jacks, whereafter it sets, from the inflection angles, a final rated load curve which continues over the entire circumference. Further, load factor calculating means calculates a load factor making use of the rated load calculated by the entire circumference load calculating means, and a safety operation is performed in accordance with the load factor.

Abstract: A safety device for a crane which can make a safety operation precisely taking a relationship between a swinging condition of a boom and a limit working region into consideration. In the device, a working radius and a swinging angle of the boom and projection amounts of projectable support members of the crane are detected, and a limit working region of the boom is set in accordance with a weight of a suspended cargo and the projection amounts. A remaining angle over which the boom can be swung until the set limit working region is exceeded is calculated, and also a braking angular acceleration at which swinging movement of the boom is braked and stopped without leaving a shake of the suspended cargo is calculated. Further, a swinging angle of the boom required to brake and stop the swinging movement of the boom at the braking angular acceleration is calculated, and the thus calculated required angle and the remaining angle are compared with each other.

Abstract: A slewing control device for a hydraulic slewing crane adapted to supply a discharge oil from a hydraulic pump through a slewing control valve to a slewing motor and control a rotational direction and a rotational speed of the slewing motor. The slewing control device includes a brake pressure control valve for variably controlling a discharge pressure of the slewing motor, an acceleration pressure control valve for variably controlling a suction pressure of the slewing motor, and a controller for outputting to both pressure control valves a pressure control signal to be determined according to an operational condition of the crane upon braking of a slewing body and controlling both the discharge pressure and the suction pressure of the slewing motor to control a pressure differential therebetween. Accordingly, even when a braking torque is small, the slewing body can be smoothly braked to be stopped at a target position accurately with no oscillation of a suspended load remaining.

Abstract: A method of controlling the slewing of a revolving superstructure of a hydraulic backhoe includes setting a swing mode selector valve in a driving position to supply fluid discharged from a pump through a supply-and-discharge line to a hydraulic motor to drive the hydraulic motor for a driving operation, setting one of a pair of relief valves provided between the swing mode selector valve and the hydraulic motor, associated with the supply side of the hydraulic motor for a set relief pressure higher than the set relief pressure of a main relief valve for limiting the pressure in supply-and-discharge lines to the set relief pressure of the main relief valve while the hydraulic motor is operating in a driving mode, and setting the other relief valve associated with the discharge side of the hydraulic motor for a set relief pressure lower than the set relief pressure of the main relief valve to limit the pressure in the supply-and-discharge line associated with the discharge side of the hydraulic motor to the se

Abstract: A slewing control device for a crane for supplying a discharge oil from a pump through a direction selecting valve to a slewing motor and for controlling a rotational direction of the slewing motor. The device includes a selector provided in a main circuit between the pump and the direction selecting valve for selecting either an unload condition of the pump where a hydraulic oil in the main circuit is communicated with a tank or an on-load condition of the pump where the communication from the main circuit to the tank is blocked. A controller outputs a select signal to the selector to select the unload condition in response to detecting a dangerous operating condition. The controller also outputs a pressure control signal to an electromagnetic proportional pressure control valve provided between the direction selecting valve and a discharge port of the slewing motor to control oil pressure on a discharge side of the slewing motor when slewing needs to be stopped.