Depressurization method in plasticization and metering process for a motor-driven injection molding machine

• US 6,340,439 B1
• Filed: 06/17/1999
• Issued: 01/22/2002
• Est. Priority Date: 06/17/1998
• Status: Expired due to Term

• Current Assignee: Sumitomo Heavy Industries Limited
• Original Assignee: Sumitomo Heavy Industries Limited
• Inventors: Hiraoka, Kazuo
• Primary Examiner(s): HEITBRINK, JILL LYNNE
• Application Number:
  US09/334,670
• Time in Patent Office: 950 Days
• Field of Search: 264/40.1, 264/40.4, 264/40.5, 264/4.07, 264/328.17, 264/349, 366/78, 425/582, 425/583, 425/587, 425/586, 425/145, 425/147
• US Class Current: 264/40.1
• CPC Class Codes: B29C 2045/5032 using means for detecting injection or back pressures
• CPC Class Codes: B29C 2045/5096 decompression of the moulding material by retraction or opposite rotation of the screw
• CPC Class Codes: B29C 2945/76006 Pressure
• CPC Class Codes: B29C 2945/76083 Position
• CPC Class Codes: B29C 2945/76187 screw
• CPC Class Codes: B29C 2945/7619 barrel
• CPC Class Codes: B29C 2945/76498 Pressure
• CPC Class Codes: B29C 2945/76525 Electric current or voltage
• CPC Class Codes: B29C 2945/76568 Position
• CPC Class Codes: B29C 2945/76605 rotational movement
• CPC Class Codes: B29C 2945/76665 screw
• CPC Class Codes: B29C 2945/76668 barrel
• CPC Class Codes: B29C 2945/76688 nozzle
• CPC Class Codes: B29C 2945/76846 Metering
• CPC Class Codes: B29C 45/47 using screws B29C45/54 takes precedence
• CPC Class Codes: B29C 45/5008 Drive means therefor
• CPC Class Codes: B29C 45/76 Measuring, controlling or regulating measuring in general G01; controlling or regulating in general G05

Abstract

A motor-driven injection molding machine comprises an injection device which includes a heating cylinder for heating resin powder therein to melt the resin powder into molten resin and a screw disposed in the heading cylinder for feeding the molten resin in the heating cylinder forward to meter the molten resin. A controller positions, in response to a position detected signal detected by a position detector, the screw at a metering position using an injection servomotor on and immediately after completion of the plasticization and metering process. In addition, the controller rotates, in response to a pressure detected signal detected by a load cell, the screw in the opposite direction using a screw-rotation servomotor on and immediately after the completion of said plasticization and metering process to carry out depressurization of the molten resin in the heating cylinder that is metered ahead of the screw.

Claims

1. A method for operating an injection molding machine, comprising:

(a) disposing a resin powder in a heating cylinder to melt the resin powder, creating a molten resin;

(b) rotating a screw disposed in the heating cylinder in a first direction to feed the molten resin to a nozzle end of the heating cylinder and adjusting the position of the screw along the longitudinal axis of the screw to achieve a first desired pressure of the molten resin at the nozzle end of the heating cylinder; and

(c) rotating the screw in the heating cylinder in a direction opposite the first direction to achieve a second desired pressure of the molten resin at the nozzle end of the heating cylinder; and

said first desired pressure is greater than said second desired pressure.

2. The method of claim 1, further comprising:

(d) during step (c), controlling the position of the screw along the longitudinal axis of the screw to achieve a desired position.

3. The method of claim 1, wherein

step (c) includes controlling the rotation of the screw in the direction opposite the first direction by comparing the second desired pressure of the molten resin at the nozzle end of the heating cylinder with an actual pressure of the molten resin at the nozzle end of the heating cylinder.

4. A controller for an injection molding machine, the injection molding machine including a heating cylinder to melt a resin powder to create a molten resin, a screw disposed in the heating cylinder to feed the molten resin to a nozzle end of the heating cylinder, a first motor operable to rotate the screw and a second motor operable to move the screw in a longitudinal axis of the screw, the controller comprising:

a first subtractor, having a desired pressure value representing a desired pressure of the molten resin at the nozzle end of the heating cylinder as an input, an actual pressure value representing an actual pressure of the molten resin at the nozzle end of the heating cylinder as an input, and having an output of a difference between the desired pressure and the actual pressure; and

a switch connected to said output of said first subtractor, connecting said output of said first subtractor to control the second motor during a period when the molten resin is metered to the nozzle end of the heating cylinder, and connecting said output of said first subtractor to control the first motor after the period when the molten resin is metered to the nozzle end of the heating cylinder.

5. The controller of claim 4, further comprising:

a command setting section outputting said desired pressure value, wherein the command setting section lowers the desired pressure value after the period when the molten resin is metered to the nozzle end of the heating cylinder so that the first subtractor has an output to said first motor which causes the screw to rotate in a direction opposite to the direction the screw rotates during the period when the molten resin is metered to the nozzle end of the heating cylinder;

a command setting section having an output of a desired screw speed rotation command, an output of the desired pressure of the molten resin at the nozzle end of the cylinder, and an output of a desired longitudinal position of the screw; and

a second subtractor, having an input of said desired longitudinal position of the screw, an input of the actual longitudinal position of the screw and an output of a difference between the desired longitudinal position and the actual longitudinal position, wherein

said switch includes first and second switches, during an initial metering period, said first switch connects said output of the desired screw speed rotation to control the first motor and said second switch connects said output of said first subtractor to control the second motor, after the initial metering period, said first switch connects said output of the first subtractor to control the first motor and said second switch connects said output of said second subtractor to control the second motor.

6. A motor-driven injection molding machine comprising:

a heating cylinder for heating resin powder therein to melt the resin powder into molten resin,

a screw disposed in said heating cylinder for feeding the molten resin in said heating cylinder forward to meter the molten resin to creating back pressure in the molten resin,

a screw-rotation servomotor operatively coupled to said screw for rotating said screw,

an injection servomotor operatively coupled to said screw for driving said screw along an axial direction to inject the molten resin metered in said heating cylinder forward,

a first motor driver driving said screw-rotation,

a second motor driver driving said injection,

a load cell for detecting the back pressure of the molten resin in said heating cylinder to produce a pressure detected signal,

a position detector for detecting a position of said screw to produce a position detected signal, and

a controller controlling, in response to the pressure detected signal and the position detected signal, driving of said screw-rotation servomotor and of said injection servomotor through first and second motor drivers by supplying said first and said second motor drivers with first and second actuating commands, respectively, said controller including

rotating means, connected to said load cell, for rotating said screw in a first direction during a plasticization and metering process and then, in response to the pressure detected signal, said screw in the opposite direction by supplying a first actuating command to said first motor driver on and immediately after completion of the plasticization and metering process, thereby depressurizing the molten resin in said heating cylinder that is metered ahead of said screw; and

positioning means, connected to said position detector, for positioning, in response to the position detected signal, said screw at a metering position by supplying the second actuating command to said second motor driver on and immediately after the completion of the plasticization and metering process.

7. The injection molding machine of claim 6, wherein said rotating means comprises:

pressure setting means for producing a pressure command indicative of a depressurization target value on and immediately after the completion of the plasticization and metering process;

a subtracter, connected to said pressure setting means and said load cell, for subtracting the pressure detected value indicated by the pressure detected signal from the depressurization target value indicated by the pressure command to produce a subtraction result signal indicative of a pressure difference between the depressurization target value and the pressure detected value;

a compensator, connected to said subtracter, for compensating the subtraction result signal to produce a compensated signal; and

supplying means, connected to said compensator and said first motor driver, for supplying said first motor driver with the compensated signal as the first actuating command on and immediately after the completion of the plasticization and metering process.

8. The injection molding machine of claim 6, wherein said rotating means comprises:

pressure setting means for producing a pressure command indicative of a depressurization target value on and immediately after the completion of the plasticization and metering process;

a subtracter, connected to said pressure setting means and said load cell, for subtracting the pressure detected value indicated by the pressure detected signal from the depressurization target value indicated by the pressure command to produce a subtraction result signal indicative of a pressure difference between the depressurization target value and the pressure detected value;

a compensator, connected to said subtracter, for compensating the subtraction result signal to produce a compensated signal;

a limiter, connected to said compensator, for limiting the compensated signal; and

supplying means, connected to said limiter and said first motor driver, for supplying said first motor driver with the limited signal as the first actuating command on and immediately after the completion of the plasticization and metering process.

9. The injection molding machine of claim 6, wherein said rotating means comprises:

pressure setting means for producing a pressure command indicative of a depressurization target value on and immediately after the completion of the plasticization and metering process;

a comparator having a noninverting input terminal supplied with the pressure command signal and an inverting input terminal supplied with the pressure detected signal, said comparator comparing the pressure detected value indicated by the pressure detected signal with the depressurization target value indicated by the pressure command to produce a comparison result signal indicative of a comparison result between the depressurization target value and the pressure detected value; and

supplying means, connected to said comparator and said first motor driver, for supplying said first motor driver with the comparison result signal as the first actuating command on and immediately after the completion of the plasticization and metering process.

10. The injection molding machine of claim 6, wherein said positioning means comprises:

position setting means for producing a position command indicative of a screw position command value on and immediately after the completion of the plasticization and metering process;

a subtracter, connected to said position setting means and said position detector, for subtracting the screw position detected value indicated by the position detected signal from the screw position command value indicated by the position command to produce a subtraction result signal indicative of a position difference between the screw position command value and the screw position detected value;

a compensator, connected to said subtracter, for compensating the subtraction result signal to produce a compensated signal; and

supplying means, connected to said compensator and said second motor driver, for supplying said second motor driver with the compensated signal as the second actuating command on and immediately after the completion of the plasticization and metering process.

11. A motor-driven injection molding machine comprising:

a heating cylinder for heating resin powder therein to melt the resin powder into molten resin,

a screw disposed in said heating cylinder for feeding the molten resin in said heating cylinder forward to meter the molten resin to creating back pressure in the molten resin,

a screw-rotation servomotor operatively coupled to said screw for rotating said screw,

an injection servomotor operatively coupled to said screw for driving said screw along an axial direction to inject the molten resin metered in said heating cylinder forward,

a first motor driver driving said screw-rotation,

a second motor driver driving said injection,

a load cell for detecting the back pressure of the molten resin in said heating cylinder to produce a pressure detected signal,

a position detector for detecting a position of said screw to produce a position detected signal, and

a controller controlling, in response to the pressure detected signal and the position detected signal, driving of said screw-rotation servomotor and of said injection servomotor through first and second motor drivers by supplying said first and said second motor drivers with first and second actuating commands, respectively, said controller including

a command setting section for producing a screw rotation speed command indicative of a screw rotation speed command value, a pressure command indicative of a pressure command value, and a screw position command indicative of a screw position command value;

a first subtracter, connected to said command setting section and said load cell, for subtracting the pressure detected value indicated by the pressure detected signal from the pressure command value indicated by the pressure command to produce a first subtraction result signal indicative of a pressure difference between the pressure command value and the pressure detected value;

a first compensator, connected to said first subtracter, for compensating the first subtraction result signal to produce a first compensated signal;

a second subtracter, connected to said command setting means and said position detector, for subtracting the screw position detected value indicated by the position detected signal from the screw position command value indicated by the position command to produce a second subtraction result signal indicative of a position difference between the screw position command value and the screw position detected value;

a second compensator, connected to said second subtracter, for compensating the second subtraction result signal to produce a second compensated signal;

a first switch, connected to said command setting means, said first compensator, and said first motor driver, for selecting, as a first selected signal, one of the screw rotation speed command and the first compensated signal, said first switch supplying said first motor driver with the first selected signal as the first actuating command; and

a second switch, connected to said first and said second compensators and said second motor driver, for selecting, as a second selected signal, one of the first and the second compensated signals, said second switch supplying said second motor driver with the second selected signal as the second actuating command.

12. The injection molding machine of claim 11, wherein said command setting section produces the pressure command indicative of a depressurization target value on and immediately after completion of a plasticization and metering process,

said first switch producing the screw rotation command as the first selected signal during the plasticization and metering process, said first switch producing the first compensated signal as the first selected signal on and immediately after the completion of the plasticization and metering process,

said second switch producing the first compensated signal as the second selected signal during the plasticization and metering process, said second switch producing the second compensated signal as the second selected signal on and immediately after the completion of the plasticization and metering process.

13. The injection molding machine of claim 11, further comprising:

a limiter interposed between said first compensator and said second switch, for limiting the first compensated signal.

14. The injection molding machine of claim 11, further comprising:

a compensator, interposed between said subtracter and said second switch, for compensating the second subtraction result signal.