Hybrid injection molding machine

• US 6,299,427 B1
• Filed: 07/05/2000
• Issued: 10/09/2001
• Est. Priority Date: 02/27/1998
• Status: Expired due to Fees

• Current Assignee: Van Dorn Demag Corp. (Sumitomo Heavy Industries Limited)
• Original Assignee: Van Dorn Demag Corp. (Sumitomo Heavy Industries Limited)
• Inventors: Richards, Thomas H., Eterovich, George L., Bulgrin, Thomas C.
• Primary Examiner(s): HEITBRINK, TIMOTHY W
• Application Number:
  US09/610,068
• Time in Patent Office: 461 Days
• Field of Search: 425/135, 425/145, 425/149, 425/150, 425/169, 425/170, 425/171, 425/589, 425/592, 425/593, 425/451.5, 425/451.6, 264/40.3, 264/40.5, 264/40.7
• US Class Current: 425/145
• CPC Class Codes: B29C 2045/1792 Machine parts driven by an electric motor, e.g. electric servomotor
• CPC Class Codes: B29C 2945/76006 Pressure
• CPC Class Codes: B29C 2945/76113 linear movement
• CPC Class Codes: B29C 2945/7612 rotational movement
• CPC Class Codes: B29C 2945/7617 Sequence, e.g. the order in which operations are conducted
• CPC Class Codes: B29C 2945/76187 screw
• CPC Class Codes: B29C 2945/76214 drive means
• CPC Class Codes: B29C 2945/7623 clamping or closing drive means
• CPC Class Codes: B29C 2945/76307 hydraulic fluids
• CPC Class Codes: B29C 2945/76598 linear movement
• CPC Class Codes: B29C 2945/76605 rotational movement
• CPC Class Codes: B29C 2945/76648 Sequence, e.g. the order in which operations are conducted
• CPC Class Codes: B29C 2945/76692 drive means
• CPC Class Codes: B29C 2945/76709 clamping or closing drive means
• CPC Class Codes: B29C 2945/76943 compare with thresholds
• CPC Class Codes: B29C 45/76 Measuring, controlling or regulating measuring in general G01; controlling or regulating in general G05
• CPC Class Codes: B29C 45/82 Hydraulic or pneumatic circuits

Abstract

An energy efficient general purpose injection molding employs a hydraulic drive for injection and clamp machine functions and an electric drive for screw recovery. Both drives use AC “squirrel cage” induction motors under vector control. Speed command signals for the vector controls are generated by the machine'"'"'s controller utilizing state transition and predictive signal techniques to account for motor and motor/pump response latencies. Hydraulic drive efficiency is improved by varying motor speed/pump output to match cycle requirements to retain hydraulic drive advantages for mold clamp and injection functions while improving the electric drive performance for screw recovery.

Claims

1. An injection molding machine comprising:

an injection unit for injecting molding material into the mold cavity of a mold, said injection unit including a screw member rotatably and translatably carried in a tubular barrel, said barrel having an end in fluid communication with a mold cavity;

a clamp unit for supporting first and second sections of said mold selectively movable from a parted position in which said mold sections are opened to a molded position in which the mold sections are closed to define said mold cavity therebetween;

a first drive unit coupled to said injection unit for rotating said screw in said barrel;

said first drive unit including an AC induction motor, a mechanical coupling connecting said AC induction motor with said screw and a vector control drive for controlling the operation of said AC motor pursuant to a variable rotate command signal;

a second drive unit coupled to said injection unit for translating said screw in said barrel pursuant to a variable translate command signal;

a third drive unit operable to move said clamp between said parted and said molded positions and maintain said clamp in said molded position at a set force pursuant to a variable clamp command signal;

a machine controller for generating said command signals to cause said molding machine to perform a given molding cycle, said machine controller including motor speed sensors measuring the speed of said AC motor and the translating speed of said screw; and

,

said vector control drive for said AC motor including means for calculating maximum torque and flux current components passing through stator windings of said AC motor only from a speed signal comparing a motor speed signal with a set command speed signal.

2. An injection molding machine comprising:

an injection unit for injecting molding material into the mold cavity of a said injection unit including a screw member rotatably and translatably carried in a tubular barrel, said barrel having an end in fluid communication with a mold cavity;

a clamp unit for supporting first and second sections of said mold selectively movable from a parted position in which said mold sections are opened to a molded position in which the mold sections are closed to define said mold cavity therebetween;

a first drive unit coupled to said injection unit for rotating said screw in said barrel;

said first drive unit including an AC induction motor, a mechanical coupling connecting said AC induction motor with said screw and a vector control drive for controlling the operation of said AC motor pursuant to a variable rotate command signal;

a second drive unit coupled to said injection unit for translating said screw in said barrel pursuant to a variable translate command signal;

a third drive unit operable to move said clamp between said parted and said molded positions and maintain said clamp in said molded position at a set force pursuant to a variable clamp command signal;

a machine controller for generating said command signals to cause said molding machine to perform a given molding cycle, said machine controller including motor speed sensors measuring the speed of said AC motor and the translating speed of said screw;

said vector control drive for said AC motor including means for calculating maximum torque and flux current components passing through stator windings of said AC motor only from a speed signal comparing a motor speed signal with a set command speed signal; and

,

said machine includes sensors developing feedback signals indicative of a machine process state;

said machine controller includes state transition means for developing said variable control signals upon a sensed change in state of said feedback signals to sequence said machine through the phases of a given molding cycle and predictive signal means causing said command signals to be initiated in advance of the transition to a successive phase where at said command signals controlling said motors are changed in advance of the time said motor'"'"'s operation is to be changed in said molding cycle.

3. The machine of claim 2 wherein each state in said state transition means processes a first set of logic sequences and said predictive signal means for said AC motor processes a second set of logic sequences predictive of the latent response time of said drive units to attain an operating condition equal to that set by said command signal.

4. The machine of claim 3 wherein one of said sensors measures the rotational speed and position of said screw to generate rotational speed feedback control signals to said controller, said state transition means effective to adjust a rotate command signal by the difference between said feedback rotational speed and the command speed in said normal set of state equations and said predictive signal means for said AC motor utilizing said position control signals in said second set of logic sequences to cause a change in state for said first motor to occur in advance of said screw reaching a position whereat its speed is to be varied.

5. The machine of claim 4 wherein said vector control drive includes an inverter for receiving pulse width modulated trigger signals to drive said AC motor based on said calculated torque and flux components.