JP4188729B2 - Injection molding machine and temperature control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a temperature control device that performs temperature control of a heating cylinder, a nozzle portion, and the like of an injection molding machine, and more particularly, to a temperature control device of an electric injection molding machine that includes a plurality of power transistor modules for driving a motor.
[0002]
[Prior art]
As a conventional injection molding machine, one configuration example of an electric injection molding machine is shown in FIG.
[0003]
The illustrated electric injection molding machine 10 includes an injection device 20, a mold clamping device 50, and the like.
[0004]
The injection device 20 includes a heating cylinder 21, and a hopper 22 is disposed in the heating cylinder 21. In addition, a screw 23 is disposed in the heating cylinder 21 so as to be able to advance and retract and rotate. The rear end of the screw 23 is rotatably supported by the support member 24. A measuring motor 25 such as a servo motor is attached to the support member 24 as a drive unit. The rotation of the measuring motor 25 is transmitted to the screw 23 via a timing belt 27 attached to the output shaft 26 of the measuring motor 25. The
[0005]
The injection device 20 further includes a screw shaft 28 that is rotatable in parallel with the screw 23. The rear end of the screw shaft 28 is connected to the injection motor 29 via a timing belt 31 attached to the output shaft 30 of the injection motor 29 such as a servo motor. Accordingly, the screw shaft 28 is rotated by the injection motor 29. The front end of the screw shaft 28 is screwed with a nut 32 fixed to the support member 24. Therefore, when the injection motor 29 as a drive unit is driven and the screw shaft 28 is rotated via the timing bell 31, the support member 24 can be moved forward and backward, and as a result, the screw 23 can be moved forward and backward.
[0006]
The mold clamping device 50 includes a movable platen 52 to which a movable mold 51 is attached, and a fixed platen 54 to which a fixed mold 53 is attached. The movable platen 52 and the fixed platen 54 are connected by a tie bar 55. The movable platen 52 is slidable along the tie bar 55. The mold clamping device 50 also includes a toggle mechanism 57 having one end connected to the movable platen 52 and the other end connected to the toggle support 56. A ball screw shaft 59 is rotatably supported at the center of the toggle support 56.
[0007]
A nut 61 formed on a cross head 60 provided in the toggle mechanism 57 is screwed onto the ball screw shaft 59. A pool 62 is disposed at the rear end of the ball screw shaft 59, and a timing belt 65 is stretched between the output shaft 64 of the mold clamping motor 63 such as a servo motor and the pulley 62.
[0008]
Therefore, in the mold clamping device 50, when the mold clamping motor 63 that is the drive unit is driven, the rotation of the mold clamping motor 63 is transmitted to the ball screw shaft 59 that is the drive transmission unit via the timing belt 65. Then, the rotary motion is converted into a linear motion by the ball screw shaft 59 and the nut 61, and the toggle mechanism 57 is activated. When the toggle mechanism 57 is operated, the movable platen 52 slides along the tie bar 55, and mold closing, mold clamping, and mold opening are performed.
[0009]
As described above, in the electric injection molding machine 10 of FIG. 4, electric motors (motors) such as the metering motor 25, the injection motor 29, and the mold clamping motor 63 are used as actuators. The operation is performed continuously.
[0010]
In the injection molding machine as described above, a plurality of heaters are used in order to melt the raw material resin and maintain the molten state of the resin. Specifically, as shown in FIG. 5, a plurality of (here, four) heaters 503 are attached to the heating cylinder 501 and the nozzle portion 502 of the injection molding machine. These heaters 503 are feedback-controlled by respective temperature control devices (not shown) so that the temperature of the area to be heated (heated area) becomes a desired temperature.
[0011]
A temperature control device used in a conventional injection molding machine includes a setter that sets a target temperature, a temperature sensor that detects the temperature of a heated region, and a target temperature (also referred to as a set temperature) set from the setter. A control unit that determines whether or not to energize each heater based on a difference (temperature deviation) from the temperature detected by the temperature sensor, and an energization to each heater that is turned on / off by the control of the control unit. Switching elements such as contactors or solid state relays to be controlled.
[0012]
The control unit of the conventional temperature control device is configured so that the PID (Proportional, An operation such as an integration and differential operation is performed to determine the time for energizing the heater (the ratio of the energization time in a predetermined cycle (for example, 1 second)). And a control part controls ON / OFF of a switching element according to the determination.
[0013]
When the switching element is turned on / off, a current having a waveform as shown in FIG. 6 flows through the heater (in the case of AC driving). When the switching element is turned on, a current flows through the heater to generate heat, thereby increasing the temperature of the heated region. On the other hand, when the switching element is turned off, no current flows through the heater and no heat is generated, so that the temperature of the heated region decreases due to heat dissipation.
[0014]
As described above, the conventional temperature control device controls the energization time to the heater so as to keep the temperature of the heating cylinder and the nozzle part constant.
[0015]
However, since the conventional temperature control apparatus performs the on / off control, it cannot follow the temperature change of the heated region during the on period or the off period. That is, the conventional temperature control device has a period (limit cycle) in which the heater cannot be controlled so as to suppress even if the temperature of the heated region changes greatly.
[0016]
Further, since the conventional temperature control device uses a contactor or a solid state relay with a slow response speed as a switching element, it can be turned on / off at a shorter cycle so as to follow the temperature change of the heated region. Can not.
[0017]
From the above, it is difficult for the conventional temperature control device to keep the temperature of each heated region constant with high accuracy. That is, the conventional temperature control device has a problem that the heating cylinder and the entire nozzle portion cannot be temperature-controlled uniformly and with high accuracy. And if a variation arises in a several to-be-heated area | region, the molten state of resin in a heating cylinder will not be stabilized, but will affect the quality of a molded product.
[0018]
As a temperature control device that does not have the above-mentioned problems, there is one that includes a power amplifier in place of a switching element such as a contactor in order to control energization to a heater (see, for example, Patent Document 1). In this temperature control device, the current flowing through the heater is controlled by controlling the power amplifier. In this temperature control device, the power amplifier is PWM-controlled in order to realize power saving.
[0019]
[Patent Document 1]
JP-A-8-72115 [0020]
[Problems to be solved by the invention]
As described above, the temperature control device of the conventional injection molding machine has a problem that the temperature of the entire heating cylinder cannot be uniformly controlled with high accuracy.
[0021]
Further, in the temperature control device described in the above publication, when the power amplifier performs a switching operation by PWM control, the current flowing through the heater becomes a rectangular wave and there is no delay in the response of the current. There is a problem that (amplitude) cannot be controlled. In addition, when the current flowing through the heater becomes a rectangular wave, there is a problem that it becomes a noise generation source.
[0022]
Accordingly, an object of the present invention is to provide an injection molding machine including a temperature control device that can control the temperature of a heated region with high accuracy without generating noise.
[0023]
Further, the electric injection molding machine has a power transistor for regenerative control that is not used, and the configuration is wasted.
[0024]
Accordingly, an object of the present invention is to provide an injection molding machine including an inexpensive temperature control device that effectively uses a power transistor for regeneration control that is not used.
[0025]
[Means for Solving the Problems]
According to the present invention, there is provided a injection molding machine for supplying / interrupting the current to the heater for heating the heated region using power transistors, in an injection molding machine having a power transistor module for multiple motors driving, Among the power transistors for regenerative braking included in the plurality of power transistor modules for driving the motor as the power transistors, regenerative braking power transistors that are not used for regenerative braking are used and connected in series to the heater. An injection molding machine characterized by having inductance is obtained.
[0026]
Specifically, the injection molding machine includes a setter for setting a target temperature for the heated area, a temperature sensor for detecting the temperature of the heated area, the target temperature, and the detected temperature. A temperature control unit that generates a control signal based on a difference between the control signal and a modulation unit that PWM-modulates the control signal and outputs a PWM-modulated control signal, and performs on / off control of the power transistor. It is characterized in that it is performed by a PWM modulated control signal.
[0028]
According to the present invention, in the temperature control method of the injection molding machine for maintaining the temperature of the heated area of the injection molding machine at a predetermined temperature, the temperature of the heated area is detected by a temperature sensor, and the temperature sensor On / off control of a power transistor that controls energization to a heater based on the detected temperature detected, and energization to the heater is performed via an inductance connected in series to the heater. A temperature control method for the molding machine is obtained.
[0029]
More specifically, in the temperature control method, a control signal is generated based on a difference between a target temperature set in advance on a setting device and the detected temperature, and the control signal is PWM-modulated and PWM-modulated control is performed. A signal is obtained and on / off control of the power transistor is performed using the PWM-modulated control signal.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, with reference to drawings, the temperature control apparatus used for the injection molding machine of this invention is demonstrated in detail. The configuration other than the temperature control device is the same as the conventional one.
[0031]
FIG. 1 shows a temperature control apparatus according to an embodiment of the present invention. This temperature control apparatus is used in an electric injection molding machine, and FIG. 1 shows a servo motor of the electric injection molding machine and a drive circuit for driving the servo motor.
[0032]
The drive circuit of the electric injection molding machine shows a diode bridge 120 that rectifies three-phase alternating current from the three-phase alternating current power supply 110, an electrolytic capacitor 130 that smoothes the output thereof, and a plurality (usually four or more, only two are shown here). A plurality of power transistor modules 150 respectively corresponding to the servo motors 140).
[0033]
Each power transistor module 150 includes an inverter circuit 151 including a plurality of power transistors, and a regenerative resistor transistor 152 formed of a single power transistor. In other words, the inverter circuit 151 including a plurality of power transistors and the regenerative resistance transistor 152 including a single power transistor constitute a set of power transistor modules 150. In general, a set of power transistors has seven transistors. The breakdown is six motor control transistors constituting the inverter circuit 151 for controlling the motor, and one regenerative resistance transistor 152 for controlling the regenerative energy.
[0034]
In an injection molding machine, usually, an injection motor for moving the screw back and forth, a metering motor for rotating the screw to melt the resin, a mold clamping motor for opening and closing the mold, and molding in the mold An eject motor for projecting the molded product is provided, and each motor is provided with a plurality of sets of power transistor modules 150 corresponding thereto. In general, since the motor with the largest capacity is an injection motor, the regenerative current generated by the metering motor or mold clamping motor is stored in the electrolytic capacitor 130 and then passed through the regenerative resistor transistor 152 for the injection motor. Radiated by the regenerative resistor. Therefore, among all the regenerative resistance transistors 152, the regenerative resistor 160 is actually connected, and the regenerative resistance transistor used for the regenerative braking of the servo motor 140 is normally connected to a motor having a large capacity. The regenerative resistor transistor 152 in the two sets of power transistor modules is used. For this reason, there are usually two to three regenerative resistor transistors 152 that are not used at all in the injection molding machine. The temperature control device according to the present embodiment uses the regenerative resistance transistor 152 that is not used at all to supply / cut off the current to the heater 170. As a result, there is no need to prepare a power transistor dedicated to energization control of the heater 170, so that the temperature control device can be configured at low cost.
[0035]
The temperature controller shown in the figure is a setting device 210 for setting a target temperature for a heated region (not shown) of a heating cylinder in which the heater 170 performs resin melting and heat retention, that is, a heating cylinder, a nozzle portion, and the like. A temperature sensor 220 such as a thermocouple that detects the temperature of the heated region; a temperature control unit 230 that generates a control signal based on the set temperature set in the setting device 210 and the detected temperature from the temperature sensor 220; A PWM modulation unit 240 that PWM modulates a control signal from the temperature control unit 230, an unused regenerative resistance transistor 250 included in the power transistor module 150, and an inductor 260 connected in series to the heater 170. is doing. A diode 270 is connected in parallel to the series connection body of the heater 170 and the inductor 260.
[0036]
The operation of this temperature control device will be described below.
[0037]
First, the target temperature of the heated area is set from the setting device 210. The setter 210 outputs a signal indicating the set target temperature (set temperature) to the subtracter 231 of the temperature control unit 230.
[0038]
In addition to the signal indicating the set temperature from the setting device 210, a signal indicating the detected temperature from the temperature sensor 220 is input to the subtractor 231 of the temperature control unit 230. The subtracter 231 obtains a difference between the set temperature and the detected temperature, that is, a deviation from the set temperature (temperature deviation), and outputs a signal indicating the obtained temperature deviation to the control calculation unit 232.
[0039]
The control calculation unit 232 determines whether to energize the heater 170 based on the signal indicating the temperature deviation supplied from the subtractor 231. Specifically, the control arithmetic unit 232 obtains the time integral value and the time differential value for the temperature deviation from the subtractor 231, and controls the heater 170 so that the temperature deviation becomes zero. A signal is generated (PID calculation is performed). Then, the control calculation unit 232 outputs the generated control signal to the PWM modulation unit 240.
[0040]
The PWM modulation unit 240 performs PWM modulation on the control signal from the temperature control unit 230 and controls on / off (switching duty) of the regenerative resistance transistor 250. The signal waveform output from the PWM modulator 240 is as shown in FIG. 2 (a) or 2 (b). That is, the PWM modulator 240 has a signal having a waveform as shown by a solid line in FIG. 2A when the temperature deviation is small, and a solid line as shown in FIG. 2B when the temperature deviation is large. Outputs a signal with a waveform.
[0041]
The regenerative resistor transistor 250 is turned on / off according to the PWM signal from the PWM modulator 240 to supply / cut off the current to the heater 170. At this time, due to the action of the inductor 260 connected in series to the heater 170 (because an electric time constant occurs due to the presence of the inductor 260), the current that actually flows through the heater 170 is shown in FIGS. 3 (a) and 3 (b). It becomes a waveform like this. That is, the current flowing through the heater 170 changes slowly, does not contain harmonic components, and is difficult to generate noise. Further, the amplitude (the maximum value of the current) changes according to the temperature deviation.
[0042]
From the above, the temperature control device according to the present embodiment is inexpensive, has good control, and can control the temperature of the heated region with high accuracy. As a result, the temperature of the entire heating cylinder can be controlled with high accuracy, so that the state of the resin that is measured and melted by the heating cylinder is stabilized and the quality of the molded product is improved.
[0043]
In the above embodiment, the case where the number of the heaters 170 is one has been described. Usually, a plurality of heaters are used for heating the heating cylinder and the nozzle portion of the injection molding machine. It is applicable to other heaters. Further, when the number of heaters is larger than the number of unused regenerative resistance transistors, a number of heater-dedicated power transistors equal to the difference may be prepared. Therefore, the number of heater-dedicated power transistors can be reduced, and the device cost can be reduced.
[0044]
In the above embodiment, feedback control is performed based on the detected temperature from the temperature sensor 220. However, in order to further improve the control accuracy, the current value flowing through the heater is detected, and the heater temperature is detected together with the detected temperature. You may make it utilize for control.
[0045]
【The invention's effect】
According to the present invention, in the temperature control device that controls the energization of the heater using the power transistor, the temperature of the object to be heated can be controlled with high accuracy by connecting the inductor to the heater.
[0046]
Further, according to the present invention, in the temperature control device that controls the energization of the heater using the power transistor, the regenerative resistance transistor included in the pattern transistor module used for servo motor control of the electric injection molding machine is used. As a result, the temperature control device can be configured at low cost.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a temperature control device according to an embodiment of the present invention.
FIGS. 2A and 2B are diagrams illustrating waveforms of PWM-modulated control signals generated by the temperature control apparatus of FIG. 1, wherein FIG. 2A is a control signal when the temperature deviation is small, and FIG. 2B is a control signal when the temperature deviation is large; The waveform is shown.
FIGS. 3A and 3B are diagrams showing waveforms of a current flowing through a heater, where FIG. 3A shows a state when the temperature deviation is small, and FIG. 3B shows a state when the temperature deviation is large.
FIG. 4 is a schematic view showing a configuration example of a conventional injection molding machine.
FIG. 5 is a diagram for explaining the arrangement of heaters used in an injection molding machine.
FIG. 6 is a diagram showing a waveform of a current flowing through a heater when a conventional temperature control device is used.
[Explanation of symbols]
110 Three-phase AC Power Supply 120 Diode Bridge 130 Electrolytic Capacitor 140 Servo Motor 150 Power Transistor Module 151 Inverter Circuit 152 Regenerative Resistor Transistor 160 Regenerative Resistor 170 Heater 210 Setter 220 Temperature Sensor 230 Temperature Controller 240 PWM Modulator 250 Regenerative Resistor Transistor 260 Inductor 270 Diode 501 Heating cylinder 502 Nozzle part 503 Heater

Claims (5)

The supply / cutoff of the current to the heater for heating the heated region a injection molding machine performed using power transistors, in an injection molding machine having a power transistor module for multiple motors driving,
Among the regenerative braking power transistors included in each of the plurality of motor driving power transistor modules as the power transistor, a regenerative braking power transistor that is not used for regenerative braking is used,
An injection molding machine having an inductance connected in series to the heater.   A setting device for setting a target temperature for the heated region, a temperature sensor for detecting the temperature of the heated region, and a control signal is generated based on a difference between the target temperature and the detected temperature A temperature control unit; and a modulation unit that PWM-modulates the control signal and outputs a PWM-modulated control signal, and performs on / off control of the power transistor by the PWM-modulated control signal. The injection molding machine according to claim 1. In the temperature control method of the injection molding machine for keeping the temperature of the heated area of the injection molding machine at a predetermined temperature,
Detecting the temperature of the heated area with a temperature sensor;
On / off control of a power transistor that controls energization to the heater based on the detected temperature detected by the temperature sensor,
A temperature control method for an injection molding machine, wherein the heater is energized through an inductance connected in series to the heater. A control signal is generated based on a difference between the target temperature set in advance in the setting device and the detected temperature, the control signal is PWM-modulated to obtain a PWM-modulated control signal, and the PWM-modulated control signal is The temperature control method for an injection molding machine according to claim 3 , wherein the power transistor is used for on / off control. As the power transistor, among the regenerative braking power transistors included in each of the plurality of motor driving power transistor modules provided in the injection molding machine, a regenerative braking power transistor that is not used for regenerative braking is used. The temperature control method for an injection molding machine according to claim 3 or 4, wherein:

Images