Programmable hydraulic power controls for injection molding machines

Claim 1

In the hydraulic drive system of an injection molding machine, which includes a hydraulic power unit with a variable delivery hydraulic pump driven by an electric motor and controlled by a pump control member, so as to supply variably pressurized hydraulic fluid at variable flow speeds from a fluid reservoir through a main supply line to such units as the die closing unit and the injection unit, in said hydraulic drive system, hydraulic power controls comprising in combination: a proportional-response flow control valve which is controlled by means of a proportional-force electromagnet and arranged in the main supply line of the variable delivery pump so as to control the flow rate at which pressurized fluid is supplied through said line, in response to an electronic control signal imposed on said electromagnet; a branch connection in the main supply line downstream of said flow control valve; a hydraulic feedback line leading from the branch connection to the control member of the variable delivey pump, thereby forming a feedback loop for the adjustment of the pump setting in compensation for fluid leakage and friction losses, the feedback line including in it an adjustable control diaphragm; a branch line connected to the feedback line at a point between its control diaphragm and the pump control member and leading from there to the fluid reservoir; a proportional-response pressure control valve which is controlled by means of a proportional-force electromagnet and arranged in said branch line so as to directly communicate with the pump control member, via the branch line and the hydraulic feedback line, thereby setting the pressure at which fluid is supplied by the pump, in response to an electronic control signal imposed on said electromagnet; and electronic feedback means for monitoring and eliminating in each of the two proportional-response control valves any deviations of the actual valve position settings from the nominal valve settings corresponding to the electronic control signals which are fed to the respective proportional-force electromagnets.