Method for detecting abnormality in hydraulic system of molding machine and apparatus therefor

A method for detecting an abnormality of a hydraulic system in a molding machine which comprises a hydraulic cylinder for reciprocating a movable member of the molding machine, a valve for controlling a hydraulic fluid which is supplied into the hydraulic cylinder, and a pair of pressure sensors which are provided on the hydraulic cylinder, for detecting the pressures in a pair of pressure chambers of the hydraulic cylinder;

• comprising the steps of:
• comparing the pressures in said pair of pressure chambers on the basis of detecting signals from said pair of pressure sensors when said movable member is inoperative;
• and
• outputting an abnormality signal when the pressures in said pair of pressure chambers are substantially out of balance.

An apparatus for detecting an abnormality of a hydraulic system in a molding machine comprising:

• said hydraulic system which comprises a hydraulic cylinder for reciprocating a movable member of the molding machine, a valve for controlling a hydraulic fluid which is supplied into said hydraulic cylinder, and a pair of pressure sensors provided on said hydraulic cylinder, for detecting the pressures in a pair of pressure chambers of said hydraulic cylinder;
• a controlling member for controlling the operation of said valve;
• and
• a pressure monitoring member for outputting an abnormality signal when the pressures in the pair of pressure chambers are out of balance or when at least one of the pressures in the pair of pressure chambers is out of a preset range of pressure, by comparing the pressures in the pair of pressure chambers or by judging whether each of the pressures in the pair of pressure chambers is in the preset range of pressure, on the basis of detecting signals from the pair of pressure sensors.

An apparatus for detecting an abnormality of a hydraulic system in a molding machine, said hydraulic system comprising a hydraulic cylinder for reciprocating a movable member of the molding machine, a valve for controlling a hydraulic fluid which is supplied into said hydraulic cylinder, and a pair of pressure sensors provided on said hydraulic cylinder, for detecting the pressures in a pair of pressure chambers of said hydraulic cylinder;

• comprising:
• a controlling means for controlling the operation of said valve;
• and
• a monitoring means for outputting an abnormality signal when the pressures in the pair of pressure chambers are out of balance or when at least one of the pressures in the pair of pressure chambers is out of a preset range of pressure.