JP2004284215A - Device and method for temperature control of injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for temperature control of an injection molding machine which enables saving of power and which generates no noise and controls with high accuracy the temperature of a region to be heated. <P>SOLUTION: In this device, an inductance 112 is connected in series to a heater 111 and they constitute an H type bridge with four power transistors 113a, 113b, 113c and 113d. Turning on/off of the power transistors of this H type bridge is controlled by a control signal generated on the basis of a set temperature and a detected temperature and subjected to PWM modulation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a temperature control device for an injection molding machine.
[0002]
[Prior art]
FIG. 3 shows a configuration example of an electric injection molding machine as a conventional injection molding machine.
[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 provided in the heating cylinder 21. A screw 23 is provided in the heating cylinder 21 so as to be able to move forward and backward and rotate freely. The rear end of the screw 23 is rotatably supported by a support member 24. A weighing motor 25 such as a servomotor is attached to the support member 24 as a driving unit. The rotation of the weighing motor 25 is transmitted to the screw 23 via a timing belt 27 attached to an output shaft 26 of the weighing motor 25. You.
[0005]
The injection device 20 further includes a screw shaft 28 rotatably 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 an output shaft 30 of the injection motor 29 such as a servomotor. 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. Accordingly, when the injection motor 29 as a driving unit is driven to rotate the screw shaft 28 via the timing bell 31, the support member 24 can move forward and backward, and as a result, the screw 23 can move 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 a tie bar 55. Further, the mold clamping device 50 includes a toggle mechanism 57 having one end connected to the movable platen 52 and the other end connected to the toggle support 56. At the center of the toggle support 56, a ball screw shaft 59 is rotatably supported.
[0007]
A nut 61 formed on a crosshead 60 provided on the toggle mechanism 57 is screwed to the ball screw shaft 59. A pool 62 is provided at the rear end of the ball screw shaft 59, and a timing belt 65 is stretched between the output shaft 64 of the clamping motor 63 such as a servomotor and the pulley 62.
[0008]
Accordingly, when the mold clamping device 63 is driven in the mold clamping device 50, the rotation of the mold clamping motor 63 is transmitted to the ball screw shaft 59 as a drive transmission unit via the timing belt 65. Then, the rotational motion is converted into a linear motion by the ball screw shaft 59 and the nut 61, and the toggle mechanism 57 operates. When the toggle mechanism 57 operates, the movable platen 52 slides along the tie bar 55, and the mold is closed, clamped and opened.
[0009]
As described above, in the electric injection molding machine 10 shown in FIG. 3, the electric motors (motors) such as the measuring motor 25, the injection motor 29, and the mold clamping motor 63 are employed as the actuators. The operation is performed continuously.
[0010]
In the injection molding machine as described above, a plurality of heaters are used for melting the raw material resin and for maintaining the molten state of the resin. Specifically, as shown in FIG. 4, a plurality of (here, four) heaters 43 are attached to the heating cylinder 41 and the nozzle portion 42 of the injection molding machine. Each of the heaters 43 is feedback-controlled by a temperature control device (not shown) such that the temperature of a region to be heated (a region to be heated) becomes a desired temperature.
[0011]
A temperature control device used in a conventional injection molding machine includes a setter for setting a target temperature, a temperature sensor for detecting a temperature of a heated area, and a target temperature (also referred to as a set temperature) set from the setter. A controller that determines whether or not to energize the heater based on the difference (temperature deviation) from the temperature detected by the temperature sensor, and controls the energization to each heater by turning on / off under the control of the controller And a switching element such as a solid state relay.
[0012]
The control unit of the conventional temperature control device controls the PID (Proportional, PID) based on the difference between the set temperature from the setter and the detected temperature from the temperature sensor so that the temperature of the heated area is maintained at a predetermined temperature. An operation such as an integration and differential operation is performed to determine a time for energizing the heater (a ratio of the energizing time in a predetermined cycle (for example, one second)). Then, the control unit controls on / off of the switching element according to the determination.
[0013]
When the switching element is turned on / off, a current having a waveform as shown in FIG. 5 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 area. On the other hand, when the switching element is turned off, no current flows to the heater and no heat is generated, so that the temperature of the heated area is reduced by heat radiation.
[0014]
As described above, the conventional temperature control device controls the energization time to the heater so as to keep the temperatures of the heating cylinder and the nozzle portion constant.
[0015]
However, since the conventional temperature control device performs on / off control, it cannot follow the temperature change of the heated region during the on period or the off period. That is, in the conventional temperature control device, there is a period during which the heater cannot be controlled so as to suppress a large change in the temperature of the heated region.
[0016]
Further, since the conventional temperature control device uses a contactor or a solid-state relay having a low response speed as a switching element, it can be turned on / off in a shorter cycle so as to follow a temperature change in a heated area. Can not.
[0017]
From the above, it is difficult for the conventional temperature control device to accurately and consistently maintain the temperature of each heated region. That is, the conventional temperature control device has a problem that the temperature of the entire heating cylinder and the entire nozzle portion cannot be controlled uniformly and with high accuracy. Then, if a plurality of regions to be heated vary, the molten state of the resin in the heating cylinder is not stabilized, which affects the quality of the molded product.
[0018]
As a temperature control device that does not have the above-described problems, there is a temperature control device that includes a power amplifier in place of a switching element such as a contactor in order to control energization of a heater (for example, see 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
[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 controlled uniformly with high accuracy.
[0021]
Further, the temperature control device described in the above-mentioned publication has a problem that, when the power amplifier performs the switching operation by the PWM control, the current flowing through the heater becomes a rectangular wave, and the current amount (amplitude) cannot be controlled. is there. Another problem is that if the current flowing through the heater has a rectangular waveform, it becomes a source of noise.
[0022]
Therefore, an object of the present invention is to provide a temperature control device of an injection molding machine that can save power, does not generate noise, and can control the temperature of a heated area with high accuracy. .
[0023]
In addition, the electric injection molding machine has a power transistor for regenerative control that is not used, and the configuration is wasted.
[0024]
Therefore, an object of the present invention is to provide an inexpensive temperature control device for an injection molding machine by effectively using a power transistor for regeneration control that is not used.
[0025]
[Means for Solving the Problems]
According to the present invention, the temperature control of an injection molding machine that controls a heater for heating a heated area of the injection molding machine based on a difference between a target temperature set in a setting device and a temperature detected by a temperature sensor. In the device, an inductance connected in series with the heater, an H-bridge circuit for supplying an alternating current to a series connected body composed of the heater and the inductance, and a control signal generated based on a difference between the target temperature and the detected temperature And a PWM modulation unit that performs PWM modulation of the control signal to obtain a PWM-modulated control signal, and controls the H-bridge circuit using the PWM-modulated control signal. Thus, a temperature control device for an injection molding machine is obtained.
[0026]
The H-bridge circuit of this temperature control device includes four power transistors that form an H-type bridge together with the series-connected body.
[0027]
Also, according to the present invention, energization of the heater is controlled based on a difference between the target temperature set in the setter and the temperature detected by the temperature sensor, so that the injection molding machine heated by the heater is heated. In a temperature control method of an injection molding machine for controlling a temperature of a region, an inductance is connected in series to the heater in advance to form a series connection, and an H-type bridge circuit for supplying an alternating current to the series connection is connected. In addition, a control signal is generated based on a difference between the target temperature and the detected temperature, the control signal is PWM-modulated to generate a PWM-modulated control signal, and the PWM-modulated control signal is used. A temperature control method for an injection molding machine is provided, wherein the temperature of the heated area is controlled by controlling the H-bridge circuit.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a temperature control device for an injection molding machine of the present invention will be described in detail with reference to the drawings.
[0029]
FIG. 1 shows a temperature control device for an injection molding machine according to one embodiment of the present invention.
[0030]
The illustrated temperature control device includes four power transistors 113a, 113b, and 113c that form an H-type bridge in combination with an inductance 112 connected in series to a heater 111 and a series connection body composed of the heater 111 and the inductance 112. And 113d, a diode 114 connected between the collector and the emitter of each power transistor, and a base connected to two diagonally located power transistors 113b and 113c among the four power transistors 113a to 113d. A setting circuit 116 for setting a target temperature (set temperature) of a heated area to be heated by the heater 111; a temperature sensor 117 such as a thermocouple for detecting the temperature of the heated area; Set temperature from 116 and temperature sensor 117 A temperature control unit 118 for generating a control signal based on a difference between al of the detected temperature, and a PWM modulation unit 119 generates a control signal which is PWM modulated control signal to PWM modulation.
[0031]
The H-type bridge is connected to a DC power supply 123 including a diode bridge 121 for rectifying and smoothing the three-phase AC from the three-phase AC power supply 120 and an electrolytic capacitor 122. When the injection molding machine is electrically driven, it has a DC power supply for supplying a DC current to an inverter (not shown) for driving and controlling a servomotor (not shown). Can be used as a DC power supply for supplying the power.
[0032]
When the injection molding machine is electrically driven, a plurality of (normally four) power transistor modules including the inverter are provided, and a power transistor for a regenerative resistor is provided in each module. Of these power transistors for regenerative resistors, only one or two regenerative resistors are actually connected. Therefore, at least two power transistors for regenerative resistors are used in the electric injection molding machine without being used. . Therefore, among the four power transistors constituting the H-type bridge, an unused power transistor for a regenerative resistor is used as at least one of the power transistors 113a and 113b or 113c and 113d located on the upper or lower arm. be able to. Thereby, the temperature control device can be configured at low cost.
[0033]
Hereinafter, the operation of the temperature control device will be described.
[0034]
First, the target temperature of the heated area is set from the setting device 116. The setter 116 outputs a signal indicating the set target temperature (set temperature) to the subtractor 181 of the temperature controller 118.
[0035]
In addition to the signal indicating the set temperature from the setter 116, a signal indicating the detected temperature from the temperature sensor 117 is input to the subtractor 181 of the temperature control unit 118. The subtractor 181 calculates a difference between the set temperature and the detected temperature, that is, a deviation (temperature deviation) of the detected temperature from the set temperature, and outputs a signal indicating the obtained temperature deviation to the control calculation unit 182.
[0036]
The control calculation unit 182 determines the amount of current to be supplied to the heater 111 based on the signal indicating the temperature deviation supplied from the subtractor 181. Specifically, the control calculator 182 obtains the temperature deviation from the subtractor 181 and the time integral value and the time differential value thereof, and outputs a control signal for controlling the heater 111 so that the temperature deviation becomes zero. Generate (perform PID operation). Then, control operation section 182 outputs the generated control signal to PWM modulation section 119.
[0037]
The PWM modulator 119 PWM-modulates the control signal from the temperature controller 118, and outputs the PWM-modulated control signal to the H-bridge. The H-type bridge converts a DC current supplied from the DC power supply 123 into an AC current and supplies the AC current to the heater 112. For example, when the PWM-modulated control signal output from the PWM modulator 119 is as shown in FIG. 2, the current flowing through the heater 111 changes as shown by a broken line in FIG.
[0038]
As described above, in the temperature control device according to the present embodiment, the value of the current flowing through heater 111 can be controlled by PWM control. As a result, power saving can be realized, and temperature control with substantially no limit cycle can be performed. Further, since the current flowing through the heater 111 is close to a sine wave and there is no high frequency component, no noise is generated. Thus, the temperature control device according to the present embodiment can control the temperature of the heated region with high controllability and high accuracy. If the temperature control device is used, the temperature of the entire heating cylinder can be controlled with high precision, so that the state of the resin measured and melted by the heating cylinder is stabilized, and the quality of the molded product can be improved.
[0039]
In the above embodiment, the case where the number of the heaters 111 is one has been described. However, usually, a plurality of heaters are used for heating the heating cylinder and the nozzle portion of the injection molding machine. Is applicable to heaters.
[0040]
In the above embodiment, the feedback control is performed based only on the temperature detected from the temperature sensor 117. However, in order to further improve the control accuracy, a current detector that detects a current value flowing through the heater is provided. The temperature control unit may calculate the difference between the detection value from the current detector and the current value indicated by the previously generated control signal, and thereafter generate a control signal corrected so as to eliminate the difference. . With this configuration, stable temperature control that is not affected by the temperature of the heater can be performed.
[0041]
【The invention's effect】
According to the present invention, by connecting the inductor to the heater and controlling the current direction switching circuit that changes the direction of the current flowing through the heater with the PWM-modulated control signal, power saving is possible and high. The temperature of the heated area can be controlled with high accuracy.
[0042]
Further, according to the present invention, the temperature control device can be configured at low cost by using the transistor for regenerative resistance included in the putter transistor module used for servo motor control of the electric injection molding machine.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a temperature control device according to an embodiment of the present invention.
2 is a diagram showing a waveform of a PWM-modulated control signal generated by the temperature control device of FIG. 1 and a waveform of a current flowing through a heater at that time.
FIG. 3 is a view showing a schematic configuration of a conventional injection molding machine.
FIG. 4 is a diagram for explaining an arrangement of heaters used in the injection molding machine.
FIG. 5 is a diagram showing a waveform of a current flowing through a heater by on / off control by a conventional temperature control device.
[Explanation of symbols]
111 Heater 112 Inductance 113a, 113b, 113c, 113d Power transistor 114 Diode 115 NOT circuit 116 Setting unit 117 Temperature sensor 118 Temperature control unit 119 PWM modulation unit 120 Three-phase AC power supply 121 Diode bridge 122 Electrolytic capacitor 123 DC power supply 41 Heating cylinder 42 Nozzle part 43 heater

Claims (6)

In a temperature control device of an injection molding machine that controls a heater for heating a heated region of the injection molding machine based on a difference between a target temperature set in a setter and a detected temperature detected by a temperature sensor,
An inductance connected in series with the heater;
An H-type bridge circuit that supplies an alternating current to a series connection body including the heater and the inductance;
A temperature control unit that generates a control signal based on a difference between the target temperature and the detected temperature,
A PWM modulation unit that performs PWM modulation on the control signal to obtain a PWM-modulated control signal,
A temperature control device for an injection molding machine, wherein the H-type bridge circuit is controlled using the PWM-modulated control signal. 2. The temperature control device for an injection molding machine according to claim 1, wherein the H-type bridge circuit includes four power transistors forming an H-type bridge together with the series connection body. 3. When the injection molding machine is an electric injection molding machine, at least one of the four power transistors is a power transistor for driving a regenerative resistor included in a power transistor module included in the electric injection molding machine. The temperature control device for an injection molding machine according to claim 2, wherein When the injection molding machine is an electric injection molding machine, the H-type bridge circuit converts a DC current supplied from a DC power supply of a servo motor driving inverter to the AC current. A temperature control device for an injection molding machine according to claim 1, 2 or 3. A current detector that detects a current flowing through the heater, wherein the temperature controller corrects the control signal by comparing a current value detected by the current detector with a current value indicated by the control signal. 5. The temperature control device for an injection molding machine according to claim 1, wherein the temperature control is performed. Injection molding for controlling energization of a heater based on a difference between a target temperature set in a setter and a detected temperature detected by a temperature sensor to control a temperature of a heated region of an injection molding machine heated by the heater. In the temperature control method of the machine,
In advance, an inductor is connected in series to the heater to form a series connection, and an H-type bridge circuit that supplies an alternating current to the series connection is connected in advance.
Generate a control signal based on the difference between the target temperature and the detected temperature,
PWM modulating the control signal to generate a PWM modulated control signal,
A temperature control method for an injection molding machine, wherein the temperature of the heated area is controlled by controlling the H-type bridge circuit using the PWM-modulated control signal.

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