Automatic pressure control apparatus for counterbalancer

In a press machine having a movable portion including a crank for translating rotary motion into linear motion, a connecting rod connected to the crank, a slide connected to the connecting rod, and an upper die detachably mounted on the slide;

• an automatic pressure control apparatus for a counterbalancer, comprising:
• cylinder means mounted on a frame of said press machine, said cylinder means having a piston with a piston rod slidably mounted therein, and a rod-side chamber defined therein, said piston rod being connected to said slide;
• a pressurized fluid source;
• tank means for containing pressurized fluid connected at one end thereof with said pressurized fluid source, the other end thereof being connected to the rod-side chamber of said cylinder means;
• pressurized fluid supply and ventilation control means disposed between said pressurized fluid source and said tank means for controlling the supply and ventilation of the pressurized fluid into and from the rod-side chamber of said cylinder means, said pressurized fluid supply and ventilation control means having pilot operated main regulator valve means for regulating the pressurized fluid flowing therethrough;
• a plurality of pilot regulator valve means connected with said main regulator valve means for controlling the same;
• detector means movable into and out of physical contact with the movable portion of the press machine for directly measuring the amount of displacement of a reference point given on the movable portion of the press machine in a preselected posture of the press in response to the interchange of the upper dies with varying weights;
• and means for selectively operating said pilot regulator valve means in response to a detected signal detected by said detector means whereby the fluid pressure in the rod-side chamber of said cylinder means can be automatically controlled in response to the amount of displacement of the reference point.