Servo circuit with failure detection mechanism

A servo circuit with a failure detection mechanism comprising:

• a servo circuit including an adder in which a target signal is inputted, a servo valve provided in a hydraulic circuit, an actuator which is connected through said hydraulic circuit with a source of oil pressure and is operated by said hydraulic circuit which is changed over by said servo valve, and a detector which detects the operation of said actuator and transmits a feedback signal to said adder, the adder transmitting a control signal to said servo valve on basis of said target signal and said feedback signal;
• a monitor circuit arranged in parallel relationship with said servo circuit and including a monitor adder in which said target signal is inputted, and a substitute circuit having a transfer function of a predetermined value which is the compound of the transfer functions of said servo valve, actuator and detector of said servo circuit, the monitor adder generating a monitor control signal on the basis of said target signal and a monitor feedback signal from said substitute circuit;
• and
• a failure detection circuit in which said control signal of said servo circuit and said monitor control signal of said monitor circuit are inputted and which detects a failure of said servo circuit on the basis of said control signal and said monitor control signal;
• wherein
• said hydraulic circuit is provided with pressure detecting means for detecting a pressure thereof;
• and
• said monitor circuit includes a correction circuit in which a pressure signal from said pressure detecting means is inputted and which corrects a loop gain of said monitor circuit in correspondence with a value of said pressure signal.