Safety device for hydraulic working machine

A safety device for hydraulic working machine, comprising:

• a hydraulic source;
• at least first, second, and third hydraulic actuators that are driven by pressure oil from the hydraulic source;
• first, second, and third control valves that control flow of pressure oil from the hydraulic source to the first, second, and third hydraulic actuators, respectively;
• first, second, and third electric lever devices that output first, second and third electrical operation signals, which are drive instructions for the first, second, and third hydraulic actuators respectively, in correspondence to lever operation;
• first and second electromagnetic proportional valves through which control pressures for controlling the first control valve are output;
• third and fourth electromagnetic proportional valves through which control pressures for controlling the second control valve are output;
• fifth and sixth electromagnetic proportional valves through which control pressures for controlling the third control valve are output;
• a pressure calculating unit that calculates first and second control pressures in correspondence to a first operation signal that is output from the first electric lever device, third and fourth control pressures in correspondence to a second operation signal that is output from the second electric lever device, and fifth and sixth control pressures in correspondence to a third operation signal that is output from the third electric lever device;
• a control unit that controls the first to sixth electromagnetic proportional valves so that control pressures to be output from the first to sixth electromagnetic proportional valves respectively become the first to sixth control pressures that have been calculated by the pressure calculating unit;
• a first high-pressure selection circuit that selects a maximum control pressure from among control pressures that have been output from the first to fourth electromagnetic proportional valves;
• a second high-pressure selection circuit that selects a higher pressure between control pressures that have been output from the fifth and sixth electromagnetic proportional valves;
• a first pressure detector that detects the control pressure selected by the first high-pressure selection circuit;
• a second pressure detector that detects the control pressure selected by the second high-pressure selection circuit;
• an abnormality determination unit that determines an abnormality in the first to fourth electromagnetic proportional valves based upon the control pressure detected by the first pressure detector and the first to fourth control pressures calculated by the pressure calculating unit, and determines an abnormality in the fifth and sixth electromagnetic proportional valves based upon the control pressure detected by the second pressure detector and the fifth and sixth control pressures calculated by the pressure calculating unit;
• and
• an inhibiting device that prohibits the first to fourth electromagnetic proportional valves from controlling the first and second control valves when the abnormality determination unit determines that an abnormality has occurred in the first to fourth electromagnetic proportional valves, and prohibits the fifth and sixth electromagnetic proportional valves from controlling the third control valve when the abnormality determination unit determines that an abnormality has occurred in the fifth and sixth electromagnetic proportional valves, wherein:
• said control unit determines whether the first operation signal output from the first electric lever device, the second operation signal output from the second electric lever device, and the third operation signal output from the third electric lever device are abnormal, and
• when said control unit determines that the first operation signal output from the first electric lever device, the second operation signal output from the second electric lever device or the third operation signal output from the third electric lever device is abnormal, the pressure calculating unit calculates the first and second control pressures, the third and fourth control pressures or the fifth and sixth control pressures to be smaller than the first and second control pressures, the third and fourth control pressures or the fifth and sixth control pressures calculated when the first operation signal, the second operation signal or the third operation signal is normal.