Electric drive with hydraulic assist in an injection moulding machine

摘要

An electrical drive system for an injection moulding machine has a hydraulic back-up system used esp. during forward movement of the screw (2) during the injection stage and/or the holding pressure phase. An electric motor (9) produces initial axial forward movement via a transmission arrangement (5, 6, 7) and is assisted in subsequent phases by a piston (11) in a cylinder (12) supplied with pressure from a hydraulic accumulator (15). Pressure from the accumulator (15) is released when a defined controlled variable is reached which corresponds to a specific loading on the electric motor (9) and the pressure rise in the cylinder (13) is proportional to the load bearing capacity of the motor (9). Pref. the hydraulic cylinder (12) is connected to the accumulator (15) via a controllable hydraulic valve (14). Measurement of the controllable variable is made at the electric motor (9), e.g. by measuring the motor torque or current used. The return signal for controlling the hydraulic pressure circuit may be initiated either by the actual injection speed or the actual melt pressure during the holding pressure phase falling below set limits. The pressure signal is produced either by melt pressure measuring eqpt. or by measuring the force at the connection between the screw (2) and the linear drive member (5). The hydraulic accumulator (15) is charged by a pump (16) driven by the electric motor (9), a switching system (8) alternately linking the motor (9) with the pump (16) or the transmission system (5, 6, 7).