Injection molding machines having a brushless DC drive system

• US 4,988,273 A
• Filed: 06/23/1989
• Issued: 01/29/1991
• Est. Priority Date: 06/23/1989
• Status: Expired due to Term

• Current Assignee: Milacron LLC (Milacron Holdings Corp.)
• Original Assignee: Cincinnati Machines Incorporated (Fives SA)
• Inventors: Sparer, Ronald M., Faig, Harold J.
• Primary Examiner(s): Heitbrink, Timothy
• Application Number:
  US07/370,669
• Time in Patent Office: 585 Days
• Field of Search: 425/145, 425/149, 425/150, 425/169, 425/170, 425/171, 425/135, 425/589, 264/40.5, 264/40.7, 264/40.3, 318/138, 318/254
• 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 45/5008 Drive means therefor
• CPC Class Codes: B29C 45/66 mechanical
• CPC Class Codes: B29C 45/70 Means for plasticising or homogenising the moulding material or forcing it into the mould, combined with mould opening, closing or clamping devices
• CPC Class Codes: B29C 45/77 of velocity or pressure of moulding material
• CPC Class Codes: H02P 2209/07 Trapezoidal waveform
• CPC Class Codes: H02P 6/04 Arrangements for controlling or regulating the speed or torque of more than one motor H02P6/10 takes precedence
• CPC Class Codes: H02P 6/10 Arrangements for controlling torque ripple, e.g. providing reduced torque ripple

Abstract

An injection molding machine utilizing brushless DC motors in its servomechanism drive systems. Brushless DC motors provide a cost effective high power drive system which has the simplicity of control of brush-type DC motors. By utilizing higher resolution encoders and controlling pressure with the servomotor velocity control loop, motor cogging and zero velocity oscillatiions are minimized.

Claims

1. An injection molding machine for producing a molded part by injecting a molten material into mold elements having a mold cavity defining the molded part, the machine comprising:

(a) clamp means for supporting the mold elements;

(b) injection means for injecting the molten material into the mold cavity, said injection means including a screw member rotatably and translatably carried in a tubular barrel, said tubular barrel having an end in communication with the mold cavity;

(c) first drive means mechanically coupled to the clamp means for imparting relative motion between the mold elements;

(d) second drive means mechanically coupled to the injection means for rotating the screw member;

(e) third drive means mechanically coupled to the injection means for translating the screw member within the tubular barrel;

(f) wherein at least one of the first drive means, the second drive means and third drive means further includes

(i) a brushless DC motor producing an electromotive force having an approximately trapezoidal waveform, said motor comprising a rotor having permanent magnets and stator windings surrounding said rotor, detecting means for detecting angular positions of the rotor, and

(ii) motor controller means for controlling the brushless DC motor, said motor controller means connected to the brushless DC motor and responsive to a motor command signal, said motor controller means including

(1) supplying means for supplying positive and negative DC signals,

(2) switching circuit means for applying the positive and negative DC signals to the stator windings, said switching circuit means connected between the stator windings and the supplying means, and

(3) control circuit means connected to the switching circuit means and the detecting means for activating the switching circuit means to selectively apply the positive and negative DC signals in a predetermined phase relationship to the stator windings to produce a commutation effect thereby creating a torque on the rotor to produce rotor rotation; and

(g) machine control means connected to the motor controller means for producing the motor command signal.

2. The apparatus of claim 1 wherein at least another of the first drive means, the second drive means and the third drive means comprises:

(a) a brushless DC motor producing an electromotive force having an approximately trapezoidal waveform, said motor comprising a rotor having permanent magnets and stator windings surrounding said rotor, detecting means for detecting angular positions of the rotor; and

(b) motor controller means connected to the brushless DC motor for controlling the motor, said motor controller means including

(i) supplying means for supplying positive and negative DC signals,

(ii) switching circuit means for applying the positive and negative DC signals to the stator windings, said switching circuit means connected between the stator windings and the supplying means, and

(iii) control circuit means connected to the switching circuit means and the detecting means for activating the switching circuit means to selectively apply the positive and negative DC signals in a predetermined phase relationship to the stator windings to produce a commutation effect thereby creating a torque on the rotor to produce rotor rotation.

3. The apparatus of claim 1 wherein each of the first drive means, the second drive means and the third drive means comprises:

(a) a brushless DC motor producing an electromotive force having an approximately trapezoidal waveform, said motor comprising a rotor having permanent magnets and stator windings surrounding said rotor, detecting means for detecting angular positions of the rotor; and

(b) motor controller means connected to the brushless DC motor for controlling the motor, said motor controller means including

(i) supplying means for supplying positive and negative DC signals,

(ii) switching circuit means for supplying the positive and negative DC signals to the stator windings, said switching circuit means connected between the stator windings and the supplying means, and

(iii) control circuit means connected to the switching circuit means and the detecting means for activating the switching circuit means to selectively apply the positive and negative DC signals in a predetermined phase relationship to the stator windings to produce a commutation effect thereby creating torque on the rotor to produce rotor rotation.

4. The apparatus of claim 1 wherein the commutation effect creating a torque on the rotor produces periodic torque variations thereby causing deviations in a process variable in response to the torque variations, and wherein the machine control means further comprises means for controlling the process variable by modifying the motor command signal in response to the deviations in the process variable caused by the torque variations.

5. The apparatus of claim 1 wherein the commutation effect creating a torque on the rotor produces periodic torque variations thereby causing deviations in a process variable in response to the torque variations and wherein the machine control means further comprises:

(a) means for producing a process feedback signal representing the process variable changing in response to the torque variations;

(b) means for providing a set point signal representing a predetermined value of the process variable; and

(c) means responsive to the process feedback signal and the set point signal for modifying the motor command signal in response to changes in the process variable from the predetermined value thereby reducing the deviations in the process variable caused by the torque variations.

6. An injection molding machine for producing a molded part by injecting a molten material into a mold cavity defining the molded part, the machine comprising:

(a) injection means for injecting the molten material into the mold cavity, said injection means including a screw member rotatably and translatably carried in a tubular barrel, said tubular barrel having an end in communication with the mold cavity;

(b) first drive means mechanically coupled to the injection means for translating the screw member within the tubular barrel, said first drive means including

(i) a brushless DC motor producing an electromotive force having an approximately trapezoidal waveform, said motor comprising a rotor having permanent magnets and stator windings surrounding the rotor, detecting means for detecting angular positions of the rotor, and

(ii) motor controller means for controlling the brushless DC motor, said motor controller means connected to the brushless DC motor and responsive to a velocity command signal, said motor contoller means including

(1) supplying means for supplying positive and negative DC signals,

(2) switching circuit means for applying the positive and negative DC signals to the stator windings, said switching circuit means connected between the stator windings and the supplying means, and

(3) control circuit means connected to the switching circuit means and the detecting means for activating the switching circuit means to selectively apply the positive and negative DC signals in a predetermined phase relationship to the stator windings to produce a commutation effect thereby creating a torque on the rotor with torque pulsations,

(c) means for producing a process feedback signal representing a nonvelocity variable changing in response to the torque pulsations; and

(d) machine control means connected to the motor controller means and the means for producing the process feedback signal for controlling the machine, said machine control means including

(i) means for producing the velocity command signal representing a predetermined motor velocity,

(ii) means for providing a set point signal representing a predetermined value of the nonvelocity variable,

(iii) means responsive to the set point signal and the process feedback signal for generating an error signal representing the difference between the set point signal and the process feedback signal, and

(iv) means responsive to the error signal for modifying the velocity command signal as a function of the error signal thereby reducing changes in the nonvelocity variable caused by the torque pulsations.

7. The apparatus of claim 6 wherein the means for producing a process feedback signal further comprises means for producing a pressure feedback signal representing pressure exerted against the screw member by the molten material.

8. An injection molding machine for producing a molded part by injecting a molten material into a two-part mold having a cavity defining the molded part, the machine comprising:

(a) injection means for injecting the molten material into the mold cavity, said injection means including a screw member rotatably and translatably carried in a tubular barrel, said tubular barrel having an end in communication with the mold cavity;

(b) first drive means mechanically coupled to the injection means for rotating the screw member to provide a quantity of molten material at one end of the screw member;

(c) second drive means mechanically couple to the injection means for translating the screw member within the tubular barrel, said second drive means including

(i) a brushless DC motor producing an electromotive force having an approximately trapezoidal waveform, said motor comprising a rotor having permanent magnets and stator windings surrounding said rotor, detecting means for detecting angular positions of the rotor, and

(ii) motor controller means for controlling the brushless DC motor, said motor controller means connected to the brushless DC motor and responsive to a velocity command signal, said motor controller means including

(1) supplying means for supplying positive and negative DC signals,

(2) switching circuit means for applying the positive and negative DC signals to the stator windings, said switching circuit means connected between the stator windings and the supplying means, and

(3) control circuit means connected to the switching circuit means and the detecting means for activating the switching circuit means to selectively apply the positive and negative DC signals in a predetermined phase relationship to the stator windings to produce a commutation effect thereby creating a torque on the rotor with torque pulsations,

(d) means connected to the injection means for producing a pressure feedback signal representing a pressure exerted against the screw member by the molten material, said pressure feedback signal changing in response to the torque pulsations; and

p`(e) machine control means connected to the first and second drive means and the means for producing the pressure feedback signal for controlling the machine, said machine control means including

(i) means for commanding the first drive means to rotate the screw member to provide a quantity of molten material at one end of the screw member,

(ii) means for producing the velocity command signal for commanding the motor controller means to maintain the motor and screw member at a zero translational velocity,

(iii) means for providing a pressure limit signal representing a desired pressure force between the screw member and the quantity of molter material,

(iv) comparing means responsive to the pressure limit signal and the pressure feedback signal for comparing said signals, and

(v) means responsive to the comparing means for modifying the velocity command signal thereby reducing changes in the pressure feedback signal caused by the torque pulsations.

9. An injection molding machine for producing a molded part by injecting a molten material into mold elements having a mold cavity defining the mold part, the machine comprising:

(a) clamp means for supporting the mold elements;

(b) injection means for injecting the molter material into the mold cavity, said injection means including a screw member rotatably and translatably carried in a tubular barrel, said tubular barrel having an end in communication with the mold cavity;

(c) first drive means mechanically coupled to the clamp means for imparting relative motion between the mold elements;

(d) second drive means mechanically coupled to the injection means for rotating the screw member;

(e) third drive means mechanically coupled to the injection means for translating the screw member within the tubular barrel;

(f) wherein at least one of the first drive means, the second drive means and the third drive means further includes

(i) a brushless DC motor producing an electromotive force having an approximately trapezoidal waveform and further producing a maximum torque at a predetermined velocity, said motor comprising a rotor having a plurality of permanent magnets and stator windings surrounding said rotor, each of said magnets producing a corresponding magnetic vector, detecting means for detecting angular positions of the rotor, and

(ii) motor controller means for controlling the brushless DC motor, said motor controller means connected to the brushless DC motor and responsive to a velocity command signal representing a velocity exceeding the predetermined velocity, said motor controller means including

(1) supplying means for supplying positive and negative DC signals,

(2) switching circuit means for applying the positive and negative DC signals to the stator windings, said switching circuit means connected between the stator windings and the supplying means,

(3) control circuit means connected to the switching circuit means and the detecting means for activating the switching circuit means to selectively apply the positive and negative DC signals to the stator windings in a predetermined phase relationship with the magnetic vectors of the rotor to produce a commutation effect thereby creating a torque on the rotor to provide the maximum torque at the predetermined velocity, and

(4) phase angle advance means for changing the phase relationship between the positive and negative DC signals and the magnetic vectors of the rotor to increase the motor velocity beyond the predetermined velocity in response to the motor achieving the predetermined velocity; and

(d) machine control means connected to the motor controller means for producing the velocity command signal representing a velocity exceeding the predetermined velocity.