Melt pressure observer for electric injection molding machine

A method for controlling longitudinal translation of an injection ram in an injection molding machine during injection by ram pressure, said ram moved by an electric motor the method comprising:

• obtaining a first input value indicative of one of a velocity and a position and an acceleration associated with said electric motor;
• obtaining a second input value indicative of one of a current and a torque associated with said electric motor;
• determining sensed melt pressure from said first and second input valves correlated to a present position of said ram;
• and,
• generating a command signal to said motor as a result of the difference between said sensed melt pressure and a set pressure at said present position.

An injection molding machine, comprising:

• an injection unit with a motor drive powering an electric motor to provide longitudinal translation of an injection ram for pressurizing a melt for injection into a mold cavity during a molding cycle;
• a processor having stored in memory a model routine and a melt pressure observer routine;
• said model having at least one state equation indicative of translation forces of said injection ram;
• and,
• said melt pressure observer receiving a first input value representative of one of motor velocity and motor position from said injection molding machine and a second input value representative of one of motor current and motor torque from said injection molding machine, and providing a current melt pressure value according to said first and second input values using said model.

A computerized control system for controlling by programmed routines stored in memory an injection ram in an injection molding machine using an electric motor, said control system comprising:

• a model simulating behavioral characteristics of said injection molding machine and having at least one state equation representative of ram translational force;
• a melt pressure observer operatively associated with said injection molding machine and solving said at least one state equation to provide a current melt pressure value according to first and second input values using said model, wherein said first input value is indicative of one of a velocity and a position associated with said electric motor, and wherein said second input value is indicative of one of a current and a torque associated with said electric motor;
• and,
• a control law providing a control signal to a motor drive associated with said electric motor using said current machine state so as to achieve a desired translation of said injection ram in a controlled fashion without sensing pressure.

A system for sensorless estimation of a melt pressure in an injection molding machine having an injection unit providing longitudinal translation of an injection ram to pressurize a melt for injection into a mold cavity, said system comprising:

• at least one state equation representative of behavior of an injection molding machine;
• an observer component operatively associated with said injection molding machine to solve said at least one state equation to provide a current melt pressure value without sensing pressure;
• and,
• said observer component is operative to solve said at least one state equation according to first and second input values from said injection molding machine, wherein said first input value is indicative of one of a velocity and a position associated with an electric motor adapted to provide longitudinal translation of said injection ram, and wherein said second input value is indicative of one of a current and a torque associated with said electric motor.

In an injection molding machine having an electrically driven in-line reciprocating screw, a controller for controlling said position of said screw as a function of a pressure of a melt in said mold, an improvement comprising:

• a first sensor for sensing a first variable in said molding machine indicative of position, velocity and/or acceleration;
• a second sensor for sensing a second variable in said molding machine indicative of current and/or torque of the electric motor causing translational movement of said screw;
• and,
• said controller having a programmed routine for determining said pressure of said melt at any current time in a molding cycle given only said first and second variables, and wherein said first and second sensors do not comprise a pressure transducer measuring melt pressure or a force transducer measuring axial force on said screw whereby pressure on the screw is measured without any sensor directly measuring same.

A computer-readable medium having computer-executable instructions for controlling longitudinal translation of an injection ram in an injection molding machine using an electric motor to cause said longitudinal translation and comprising computer-executable instructions for:

• obtaining a first input value indicative of one of a velocity and a position associated with said electric motor;
• obtaining a second input value indicative of one of a current and a torque associated with said electric motor;
• and,
• solving at least one state equation representative of forces imposed on a melt by said ram to provide a current melt pressure value according to said first and second input values without sensing pressure.