| 摘要 |
PROBLEM TO BE SOLVED: To provide a safety gear capable of detecting the abnormal operation of a lifting device in accordance with the abnormality of a proportional solenoid valve, regardless of booming operation, and then stopping its operation. SOLUTION: When an operation signal is input from a boom operating device 10, a control unit 30 outputs a corresponding command signal to the proportional solenoid valve 40 to operate a hydraulic actuator 60 which actuates the lifting device. The control unit 30 has a moving condition predicting circuit 31 for processing and predicting the moving condition of a working bench to move from the command signal and a moving condition detecting circuit 32 for processing and finding the actual moving condition of the working bench from the status of the positional change of the working bench detected by a boom position detector 20. The control unit 30 compares the predicted moving condition with the actual moving condition and discriminates abnormality if these are different, and then restricts the operation of each proportional solenoid valve 40 and actuates a shutoff valve 50 in each oil pressure circuit to shut off an oil passage.
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