GB955957A - Improvements in or relating to control systems for hydraulic and pneumatic presses - Google Patents

Abstract

955,957. Measuring electrically. NORMALAIR Ltd. May 6, 1960 [May 15, 1959], No. 16688/59. Heading G1N. In a system for the control of a press, the flow of fluid to and from the operating cylinder is controlled in accordance with the setting of the operator's control, the position of the press ram, and the load on the ram. Four embodiments of the control circuit are shown. In the embodiment of Fig. 1 the flow of fluid to the press operating cylinder A may be controlled by valve B or this valve may be rendered inoperative and the flow controlled via valve L, which is an electromagnetically operated valve and may be of the type disclosed in Specification 928, 802, by the amplified output signal of the bridge circuit formed by resistors G, E, and F; G being positioned by the spring loaded piston arrangement H in accordance with the pressure applied to the press ram, whilst also being manually adjustable in order to set the desired thrust, F being responsive to the press ram position, and E being manually adjustable in accordance with the desired press ram position. In two similar embodiments the ram pressure sensing circuit is a separate bridge circuit the output signal of which is mixed with the ram position signal, either in the amplifier, Fig. 2 (not shown), or, after amplification, in the electromagnetic valve, Fig. 3 (not shown). In the fourth embodiment, Fig. 5, the electromagnetic valve is operated by the ram position signal only, the ram pressure signal being used to control a pressure reducing valve, Q, in the hydraulic feed line to valve L and the ram cylinder.