Patent Publication Number: US-8994314-B2

Title: Injection molding machine

Description:
FIELD 
     The present invention is related to an injection molding machine which includes a motor, a driver circuit that drives the motor; and a rectifying part that supplies electric power to the driver circuit. 
     BACKGROUND 
     Japanese Laid-open Patent Publication No. 2006-54947 discloses a converter which performs regeneration to a power supply when a voltage across a DC link exceeds a predetermined upper limit voltage. 
     However, according to Japanese Laid-open Patent Publication No. 2006-54947, powering electric power and regenerative electric power are generated via the same A/C converter circuit, and thus the regenerative electric power generated at the time of decelerating the motor can not regenerated effectively. 
     SUMMARY 
     An injection molding machine according to an embodiment includes a motor, a driver circuit that drives the motor; and a rectifying part that supplies electric power to the driver circuit. A regenerative line for regenerative electric power of the motor is connected to the rectifying part in parallel. A converting part and a harmonics component reducing part are provided in the regenerative line. The converting part converts direct electric power between the driver circuit and the rectifying part into alternating electric power which is input to the harmonics component reducing part. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram for illustrating a configuration of an injection molding machine according an embodiment of the present invention. 
         FIG. 2  is a diagram for schematically illustrating an example of a motor driving power supply circuit including a converter of the injection molding machine. 
         FIG. 3  is a diagram for illustrating an example of a circuit configuration of the converter. 
         FIG. 4  is a diagram for illustrating a first configuration example of a harmonics component reducing part. 
         FIG. 5  is a diagram for illustrating a second configuration example of a harmonics component reducing part. 
         FIG. 6  is a functional block diagram of a controller  26 . 
         FIG. 7  is a flowchart for illustrating a method of controlling the converter according to the present embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, embodiments for carrying out the present invention will be described in detail by referring to the accompanying drawings.  FIG. 1  is a diagram for illustrating a configuration of an injection molding machine  1  according an embodiment of the present invention. 
     The injection molding machine  1 , which is a motor-operated injection molding machine in the illustrated example, includes a servo motor for injection  11 . The rotation of the servo motor for injection  11  is transmitted to a ball screw  12 . A nut  13 , which is moved in the forward and backward directions by the rotation of the ball screw  12 , is fixed to a pressure plate  14 . The pressure plate  14  is configured to be movable along guide bars  15  and  16  which are fixed to a base frame (not illustrated). The motion of the pressure plate  14  in forward and backward directions is transmitted to a screw  20  via a bearing  17 , a load cell  18  and an injection shaft  19 . The screw  20  is disposed in a heating cylinder  21  in such a manner that it can rotate in the heating cylinder  21  and can move in an axial direction. A hopper  22  for supplying a resin is provided in a rear portion in the heating cylinder  21 . The rotational motion of a servo motor for screw rotation  24  is transmitted to the injection shaft  19  via coupling members  23  such as a belt, a pulley, etc. In other words, the screw  20  is rotated when the injection shaft  19  is driven to rotate by the servo motor for screw rotation  24 . 
     In a plasticizing/metering process, the screw  20  is rotated and moved backward in the heating cylinder  21 , thereby molten resin is stored in a front portion of the screw  20 , that is to say, on the side of a nozzle  21 - 1  of the heating cylinder  21 . In an injecting process, molds (dies) are filled with the molten resin stored in the front portion of the screw  20 , and molding is performed by applying pressure. At that time, a force pressing the resin is detected by the load cell  18  as a reaction force. In other words, a resin pressure in the front portion of the screw  20  is detected. The signal representing the detected pressure is amplified by a load cell amplifier  25  and input to a controller  26  (a control apparatus) functioning as controlling means. Further, in a holding process, the pressure of the resin filling in the molds is held at a predetermined pressure. 
     A position detector  27  for detecting an amount of movement of the screw  20  is attached to the pressure plate  14 . The detection signal of the position detector  27  is amplified by an amplifier  28  and input to the controller  26 . This detection signal may be used to detect a movement speed of the screw  20 . 
     The servo motor  11  and  24  are provided with encoders  31  and  32  for detecting a number of revolutions, respectively. The numbers of revolutions detected by the encoders  31  and  32  are input to the controller  26 . 
     A servo motor  42  is provided for opening and closing the molds, and a servo motor  44  is provided for extruding (ejecting) a molded article. The servo motor  42  drives a toggle link (not illustrated), for example, to implement the mold opening/closing. Further, the servo motor  44  moves an ejector rod (not illustrated) via a ball screw mechanism, for example, to implement the ejection of the molded article. The servo motor  42  and  44  are provided with encoders  43  and  45  for detecting a number of revolutions, respectively. The number of revolutions detected by the encoders  43  and  45  are input to the controller  26 . 
     The controller  26  is comprised mainly of a microprocessor that includes a CPU, a ROM in which control programs are stored, a RAM in which calculation results are stored, a timer, a counter, an input interface, an output interface, etc., for example. 
     The controller  26  transmits current (torque) instructions to motor driver circuits according to the respective processes in an injection molding process. The motor driver circuits drive the servo motors  11 ,  24 ,  42  and  44  used in the respective processes according to the instructions. For example, the controller  26  controls the number of revolutions of the servo motor  24  with the motor driver circuit  52  to implement the plasticizing/metering process. Further, the controller  26  controls the number of revolutions of the servo motor  11  with the motor driver circuit  51  to implement the injecting process and the holding process. Further, the controller  26  controls the number of revolutions of the servo motor  42  with the motor driver circuit  53  to implement the mold opening process and the mold closing process. Further, the controller  26  controls the number of revolutions of the servo motor  44  with the motor driver circuit  54  to implement the molded article ejecting process. 
     A user interface  35  includes an input setting part with which injection molding conditions can be set for the respective processes, such as a mold opening/closing process, an injecting process, etc. Further, the user interface  35  includes an input part with which a user inputs various instructions and an output part (a display part, for example) configured to output various items of information. 
     Typically, a cycle of the injection molding process in the injection molding machine  1  includes a mold closing process for closing the molds; a mold clamping process for clamping the molds; a nozzle contacting process for abutting a nozzle  21 - 1  onto a sprue (not illustrated) of the molds; an injecting process for moving the screw  20  in the heating cylinder  21  to inject the molten resin stored in the front portion of the screw  20  into a mold cavity (not illustrated); a holding process for maintaining the dwell pressure afterward for a while so as to prevent emergence of air bubbles and sink marks; a plasticizing/metering process and a cooling process for melting the resin and storing the molten resin in the front portion of the heating cylinder  21  by rotating the screw  20  so as to prepare for the next cycle, utilizing the time until the molten resin filling in the mold cavity is cooled to set; a mold opening process for opening the molds; and a molded article ejecting process for pushing the molded article out with ejector pins (not illustrated) provided in the mold. 
       FIG. 2  is a diagram for schematically illustrating an example of a motor driving power supply circuit including a converter  100  of the injection molding machine  1 . In  FIG. 2 , the servo motor for injection  11  and a motor driver circuit  51  for driving the servo motor for injection  11  are illustrated as an example. Other servo motors  24 ,  42  and  44  and the motor driver circuits  52 ,  53  and  54  may be the same. According to an alternative embodiment, the converter  100  may be connected to servo motors and motor driver circuits for driving the servo motors in parallel. 
     The converter  100  is connected to a power supply  200 . The power supply  200  may be an AC power supply. Further, the converter  100  is connected to the servo motor  11  via a DC link  300  and the motor driver circuit  51 . The converter  100  converts the electric power from the power supply  200  to supply the converted electric power to the servo motor  11  via the DC link  300  and the motor driver circuit  51 . The motor driver circuit  51  may be an inverter for converting the output (direct electric power) of the converter  100  to a three-phase alternating electric power, for example, and the inverter may include a three-phase bridge circuit having six power transistors, for example. The DC link  300  includes a capacitor (a capacitor), a bus bar, a cable, or the like. 
     A voltage detecting part  190  is provided such that it detects a voltage across the DC link  300  which is provided between the output side of a rectifier  102  (see  FIG. 3 ) and the input side of the motor driver circuit  51 . A direct voltage detected by the voltage detecting part  190  is supplied to the controller  26  (see  FIGS. 3 and 6 ). 
       FIG. 3  is a diagram for illustrating an example of a circuit configuration of the converter  100 . In the example illustrated in  FIG. 3 , the converter  100  includes terminals R, S and T which are connected to the AC power supply and terminals P and N which are connected to the DC link  300 . The converter  100  includes the rectifier (powering circuit part)  102  which is formed of a three-phase diode bridge including six diodes, and a bridge circuit (regenerating circuit part)  104  which is formed of a three-phase inverter including six transistors. It is noted that in  FIG. 3  a flow of the electric power at the time of a powering mode and a flow of the electric power at the time of a regenerating mode are indicated by arrows. 
     The rectifier  102  performs a conversion operation (powering operation) from the alternating electric power to the direct electric power in the DC link  300  with diode rectification. The bridge circuit  104  performs a PWM (Pulse Width Modulation) control according to a driving signal output from a PWM generator  71  to implement a conversion operation (power supply regenerating operation) from the direct electric power in the DC link  300  to the alternating electric power in the alternating power supply. The bridge circuit  104  controls magnitude of the alternating electric power (alternating electric current) between the alternating power supply and the bridge circuit  104  and magnitude of the direct electric power (direct electric current) of the DC link  300  during the power supply regenerating operation. 
     As illustrated in  FIG. 3 , the converter  100  includes a regenerative line  82  connected to a powering line  81  in parallel. The powering line  81  is between the alternating power supply and the motor driver circuit and has the rectifier  102  provided therein. The regenerative line  82  is connected to the input and the output of the rectifier  102  in parallel. One end of the regenerative line  82  is connected to an alternating current line part of the powering line  81  on the input side of the rectifier  102 , and another end of the regenerative line  82  is connected to a direct current line part of the powering line  81  on the output side of the rectifier  102 . The regenerative line  82  has the bridge circuit  104  and a harmonics component reducing part  63  inserted in series therein. 
     The bridge circuit  104  is a converting part which converts the direct electric power between the output side of the rectifier  102  and the input side of the motor driver circuit  51  (see  FIG. 2 ) into the alternating electric power. The alternating electric power output by the power conversion operation of the bridge circuit  104  is input to the harmonics component reducing part  63 . The harmonics component reducing part  63  may function as a low-pass filter. 
     The harmonics component reducing part  63  includes plural inductors inserted to the respective phases of R, S and T in series and capacitors (capacitors) connected between the inductors, for example. The harmonics component reducing part  63  may have a Y-connection configuration in which plural capacitors whose ends are connected to the respective phases are commonly connected at a neutral point, as illustrated in  FIG. 4 . The harmonics component reducing part  63  may have a delta connection configuration in which the capacitors are connected between the respective phases, as illustrated in  FIG. 5 . Further, the harmonics component reducing part  63  may be configured such that only the inductors are inserted to the respective phases in series. 
     Further, the injection molding machine  1  includes, as a controlling part of the converter  100 , the controller  26 , the PWM generator  71  which generates a PWM driving signal, and a phase detecting part  72  which detects a phase of the alternating voltage in a line connecting between the output side of the harmonics component reducing part  63 , the alternating power supply and the input side of the rectifier  102 . The controller  26  performs the PWM control of the bridge circuit  104  with the PWM generator  71  to regenerate the electric power of the servo motor  11  which is input to the bridge circuit  104  via the motor driver circuit  51 . 
     The controller  26  controls the regenerating operation of the bridge circuit  104  with the PWM driving signal generated by the PMW generator  71  such that the alternating current output from the bridge circuit  104  is shaped to have a shape of a sine wave. The PWM control has advantage over the non-PWM control in that it can reduce the harmonics current, which is generated by the switching operations of the transistors of the bridge circuit  104  and passes to the alternating power supply, and improve the power-factor at the time of regenerating. 
     The controller  26  controls the regenerating operation by the power converting operation of the bridge circuit  104  with the PMW generator  71 , based on a direct voltage value Vdc detected by the voltage detecting part  190  (see FIG.  2 ), an alternating current value Iacf detected by a current detecting part  61  between the alternating output side of the bridge circuit  104  and the alternating input side of the harmonics component reducing part  63 , and an alternating voltage value Vacf detected by a voltage detecting part  62 , such that the alternating current output from the bridge circuit  104  has a sine wave shape with a target frequency. A phase detecting part  72  is capable of detecting the phase of the alternating voltage based on the alternating voltage value Vacf detected by the voltage detecting part  62 . 
     For example, the controller  26  generates an instruction value Ir of the alternating current by performing processes, such as a process of multiplying a voltage error output Verr, which is generated according to an error between an instruction value Vr of the direct voltage and the direct voltage value Vdc supplied from the voltage detecting part  190 , by the alternating voltage value Vacf supplied from the phase detecting part  72 . Then, the controller  26  supplies an current error output Ierr, which is generated according to an error between the instruction value Ir and the alternating current value Iacf supplied from the current detecting part  61 , to the PMW generator  71 . The PMW generator  71  compares the current error output Ierr with a predetermined carrier such as a triangle wave to generate the PWM driving signal for driving the gates of the transistors of the bridge circuit  104  to implement the regenerating operation. 
       FIG. 6  is a functional block diagram of the controller  26  which functions as a control apparatus of the converter  100 . It is noted that the control apparatus of the converter  100  may be implemented by a control apparatus other than the controller  26 . 
     The controller  26  includes a converter controlling part  261  and a regeneration determining part  263 . The controller  26  includes one or more calculation processing apparatuses and a storage device for storing software (programs) and data, etc., such as a RAM and a ROM. The respective functional parts  261  and  263  of the controller  26  are functional parts for performing various processes for input data, using the calculation processing apparatus mainly, and are implemented by a hardware resource, a software resource or a combination thereof. The functions of the respective functional parts  261  and  263  are described with reference to  FIG. 7 . 
       FIG. 7  is a flowchart for illustrating an example of a method of controlling the converter  100  according to the present embodiment. The control process illustrated in  FIG. 7  is executed by the controller  26  in connection with the regeneration of the servo motor  11  (at the time of decelerating the injection speed in the case of the servo motor  11 ). 
     In step  10 , the regeneration determining part  263  acquires a voltage Vdc across the capacitor of the DC link  300  with the voltage detecting part  190  to determine the regenerating status of the motor. 
     In step  12 , the regeneration determining part  263  determines whether the voltage Vdc of the DC link  300  is greater than a predetermined threshold voltage Vth. The regeneration determining part  263  determines that the motor is not in the decelerated status, that is to say, the motor does not generate the regenerative electric power if the voltage Vdc is not greater than the predetermined threshold voltage Vth. If it is determined by the regeneration determining part  263  that the voltage Vdc is not greater than a threshold voltage Vth (i.e., it is determined that the motor does not generate the regenerative electric power), the converter controlling part  261  controls the transistors of the bridge circuit  104  such that all the transistors are tuned off, thereby not performing the regenerating operation of the bridge circuit  104 . On the other hand, if the voltage Vdc is greater than the predetermined threshold voltage Vth, the regeneration determining part  263  determines that the motor is in the decelerated status, that is to say, the motor generates the regenerative electric power. 
     In step  14 , the converter controlling part  261  starts the regenerating operation, if the voltage Vdc is not greater than the threshold voltage Vth based on the determination result of the regeneration determining part  263 . In step  16 , the converter controlling part  261  performs the switching operations of the transistors of the bridge circuit  104  with the PWM control such that the alternating current output from the bridge circuit  104  has a shape of a sine wave (step  16 ). 
     In steps  16 ,  18  and  20 , the converter controlling part  261  stops the regenerating operation of the bridge circuit  104  by tuning off all the transistors of bridge circuit  104 , if it is determined by the regeneration determining part  263  that a regeneration stop criterion is met. For example, the regeneration determining part  263  determines that the regeneration stop criterion is met, if the direct voltage value detected by the voltage detecting part  190  is smaller than a predetermined voltage value which is smaller than the threshold voltage Vth and a peak value of the alternating current detected by the current detecting part  61  is smaller than a predetermined current value. 
     In this way, according to the embodiment, since the regenerative line  82  is provided in parallel to the powering line  81 , the regenerative electric power can be effectively recovered, thereby reducing the energy consumption. Further, since the bridge circuit  104  and the harmonics component reducing part  63  have only the regenerative current passing therethrough (i.e., the powering current does not pass through the bridge circuit  104  and the harmonics component reducing part  63 ), a rating can be decreased in comparison with a case where a powering line and a regenerative line is common. For example, it is possible to select the switching elements such as the transistors, the inductors, etc., according not to the powering electric power but instead to regenerative electric power. Further, the regeneration by the PWM control using the PMW generator  71  increases the power factor. 
     The present invention is disclosed with reference to the preferred embodiments. However, it should be understood that the present invention is not limited to the above-described embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
     For example, according to the present embodiment, a voltage or a current as a dimension of a physical quantity is used for control; however, substantially the same control can be performed by equivalently using other dimensions of a physical quantity such as energy. 
     The present application is based on Japanese Priority Application No. 2011-163695, filed on Jul. 26, 2011, the entire contents of which are hereby incorporated by reference.