Electric actuator to produce a predetermined force

A heat seal station for heat sealing a plastic film comprising:

• a platen;
• a heat seal die;
• an electric actuator having a first end coupled to the platen and an opposing second end coupled to the heat seal die;
• a linkage system that couples the first end of the actuator to the second end such that moving the linkage system toward an over-center position causes the heat seal die to move toward the platen;
• an electric motor coupled to the linkage system, the electric motor capable of moving the linkage system toward the over-center position;
• a force transducer coupled to the actuator, the force transducer capable of producing a force signal responsive to a force produced by the actuator;
• a control system coupled to the electric motor and the force transducer, the control system capable of providing a control signal to the electric motor to move the linkage system to a position, the position having been determined by the control system in response to the force signal in a previous movement of the linkage system.

A method for producing a heat seal in a plastic film comprising:

• providing a first signal to move an electric motor to a end position and thereby move a linkage system toward an over-center position, the linkage system being coupled to a platen and a heat seal die such that moving the linkage system toward the over-center position causes the heat seal die to move toward the platen;
• and
• receiving a second signal from a force transducer coupled to the actuator when the electric motor is at the end position, the second signal responsive to a force produced by the actuator;
• wherein the end position is controlled to produce a desired force responsive to the second signal in a previous movement of the linkage system.

A method for producing a heat seal in a plastic film comprising:

• moving a heat seal die toward a platen a plurality of times by providing a first signal to move an electric motor to an end position and thereby move a linkage system toward an over-center position, the linkage system being coupled to the platen and the heat seal die such that moving the linkage system toward the over-center position causes the heat seal die to move toward the platen, and
• receiving a second signal from a force transducer coupled to the actuator when the electric motor is at the end position, the second signal responsive to a force produced by the actuator;
• storing a plurality of force values, each force value corresponding to the force produced by the actuator for one of the plurality of movements of the heat seal die;
• computing a representative force value from the stored plurality of force values;
• and
• computing a corrected end position responsive to a difference between the representative force value and a desired force value.