JPH04347616A - Molding machine - Google Patents

Abstract

PURPOSE:To obtain a product having high quality stably by directly controlling pressure at the time of an injection process, and to simplify setting operation at the time of molding. CONSTITUTION:A screw is moved forward and retreated by driving the screw by an electric servomotor 12. Pressure applied to the screw is detected by a load cell 15. A speed command signal corresponding to the difference of detected pressure and a pressure set value set through a pressure command-value setting means 42 is arithmetically operated by an arithmetic section 43 on an injection process. The speed command signal is output to a motor control section 14, and the servomotor 12 is controlled. Accordingly, the servomotor 12 is used, and a closed loop for controlling pressure is formed in simple constitution, thus improving response, then accurately controlling pressure. Products having constant quality are acquired without depending upon the conditions of a mold by controlling pressure. A small number of pressure command values may be set even in previous setting work.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding machine, and more particularly to resin injection control.

0002

[Prior Art] Generally, in an injection molding machine or a transfer molding machine for producing plastic products using a resin such as a thermoplastic resin or a thermosetting resin, a nozzle that is connected to a mold is provided at the tip. A screw (or plunger) driven by a hydraulic or electric drive source is installed in the heating cylinder so that it can move forward and backward, and by moving this screw forward,
The resin in the heating cylinder is pressed to fill the cavity in the mold. Conventionally, a hydraulic cylinder device was mainly used as the drive source to move the screw forward and backward, and during the injection process, the hydraulic cylinder device was controlled according to the pressure from the screw or the resin in the mold. . However, hydraulic cylinder devices have poor responsiveness and cannot properly control pressure, so speed control has come to be used. Furthermore, recently, electric servo motors have come to be used as a drive source for advancing and retracting the screw, but even with this servo motor, speed control has conventionally been performed during the injection process.

[0003]Here, an injection molding machine using an electric servo motor will be explained with reference to FIG. In the figure, 1 is a mold, and a cavity 1a is formed in this mold 1. A heating cylinder 2 is a resin reservoir, and a nozzle 3 provided at the tip of the cylinder 2 is connected to the mold 1. Further, the cylinder 2 is provided with a hopper 4 for charging resin material thereinto. A screw 5 is slidably fitted into the cylinder 2. This screw 5 is connected to the output shaft of a motor 7 via a gear train 6, and is rotationally driven by this motor 7. In addition, the screw 5
is rotatably connected to a slider 9 via a thrust bearing 8, and a ball screw 10 is threaded through the slider 9. This ball screw 10 is connected to the output shaft of an electric servo motor 12 via a gear train 11. With this configuration,
When the output shaft of the servo motor 12 rotates, this rotation is transmitted to the ball screw 10 via the gear train 11, and as the ball screw 10 rotates, the screw 5 moves forward or backward together with the slider 9. A control unit 13 consisting of a computer or the like is connected to the servo motor 12 via a motor control unit 14 for controlling the servo motor 12. Further, a load transducer such as a load cell 15 for detecting the pressure applied to the screw 5 by the resin in the mold 1 and the cylinder 2 is incorporated in the thrust bearing 8 portion, and the load cell 15 is equipped with section 13 is connected via a load cell amplifier 16. During molding, the resin material supplied from the hopper 4 into the cylinder 2 is first heated and kneaded by the screw 5, which is rotated by the drive of the motor 7, to be plasticized. At this time, the resin is sent to the front side in the cylinder 2 by the rotating screw 5, and the screw 5 is retracted to perform metering (metering step). Next, the screw 5 is moved into the mold 1 by the drive of the motor 12.
The molten resin in the cylinder 2 is pressed and injected and filled into the cavity 1a of the mold 1 (injection step). Next, the forward pressurized state of the screw 5 is maintained, and a pressure holding process is performed. Furthermore, after the resin in the cavity 1a is sufficiently cooled and solidified, the mold is opened and the product is taken out.

Next, the control system 21 of the servo motor 12 during the injection and pressure holding steps will be explained with reference to FIG. In the figure, 22 is the CPU of the computer, 15 is the load cell, and 16 is the load cell amplifier. Further, 23 is a digital control unit of the computer, and this digital control unit 23 is
It consists of a pulse shaping/direction determining means 24, a deviation counter 25, and a D/A converter 26. Furthermore, 14 is the motor control section (motor control means), and this motor control section 14 is composed of a subtracter 27 and a servo amplifier 28. Reference numeral 29 denotes a modular servo motor, in which a tachometer generator 30 and a pulse generator 31 are assembled to the servo motor 12. The load cell 15 detects the pressure applied from the resin in the cylinder 2 or the mold 1 via the screw 5, and outputs the detected value to the CPU 22 via the load cell amplifier 16. The pulse shaping/direction determining means 24 receives a command pulse signal and a command code signal from the CPU 22, and also receives a position feedback signal from the pulse generator 31. This position feedback signal corresponds to the position of the screw 5 in the forward and backward directions. The deviation counter 25 calculates the deviation between the command pulse signal and the position feedback signal, and outputs a speed command signal corresponding to the deviation to the motor control section 14. This motor control unit 14 inputs a speed feedback signal from the tachogenerator 30, and according to this speed feedback signal and the speed command signal,
The servo motor 12 is controlled according to the speed deviation calculated by the subtractor 27. During the injection process, the CPU is operated based on a program pre-installed in the computer and various setting values set by the operator.
The servo motor 12 is controlled in accordance with a command pulse signal and a command code signal outputted from the servo motor 22 to the digital control section 23 . At this time, the digital control unit 2
3 to the motor control section 14 changes appropriately. As a result, the servo motor 12 is controlled so that the screw 5 is positioned appropriately. Further, when the screw 5 advances to a predetermined position, or when the pressure detected by the load cell 15 increases to a predetermined value, the injection process is switched to the pressure holding process. In the pressure holding step, pressure control is performed. That is, for example, the servo motor 12 is controlled via the digital control section 23 and the motor control section 14 so that the pressure detected by the load cell 15 is maintained at a predetermined value for a predetermined time.

However, when controlling the speed during the injection process in this way, it is susceptible to many disturbances such as the characteristics of the resin, the temperature of the mold 1, and the mold structure. This makes it difficult to consistently obtain high-quality products. In order to stably obtain high-quality products depending on various conditions such as the characteristics of the resin, the state of the mold 1 at the time of molding, and the mold structure, the speed of the servo motor 12 and the speed of the screw 5 must be adjusted. Regarding the relationship with the position, etc., the settings that the operator must make are many and complicated, and the setting work during molding becomes troublesome. For example, in order to obtain a high-quality product, it is necessary to fill the cavity 1a of the mold 1 slowly in areas where the resin does not flow easily, and quickly in areas where it flows easily. If speed control is performed during the injection process as in the above, it becomes difficult to set the speed switching position. Furthermore, setting work for switching from the injection process to the pressure holding process is also difficult.

[0006]

[Problems to be Solved by the Invention] As mentioned above, conventional molding machines that control the hydraulic cylinder device that drives the advancing screw during the injection process according to the pressure from the resin have the problem of poor responsiveness. there were. In addition, in conventional molding machines in which the screw 5 is driven by a servo motor 12, the speed is controlled during the injection process, which is affected by various disturbances, making it difficult to consistently obtain high-quality products, and making it difficult to work during molding. However, there is a problem in that the setting work that must be performed by a person becomes cumbersome. The present invention solves the above-mentioned problems and provides a molding machine that can stably produce the same high-quality product without being affected by various disturbances, and that allows the operator to easily perform setting operations during molding. The purpose is to

[0007]

[Means for Solving the Problems] In order to achieve the above object, the molding machine of the present invention includes a resin reservoir, and a molding machine that can move forward and backward to press the resin in the resin reservoir and fill it into a cavity in a mold. a pressing member, an electric servo motor for driving the pressing member, a motor control means for controlling the electric servo motor according to an input speed command signal, and A pressure detection means for detecting pressure, a pressure command value setting means, and a pressure command value that is set in advance by the pressure command value setting means and the pressure detected by the pressure detection means during an injection process for filling a cavity with resin. and calculation means for calculating a speed command signal according to the difference and outputting the speed command signal to the motor control means.

[0008]

[Operation] According to the above structure, during the injection process, the pressing member moves forward by driving the electric servo motor, presses the resin in the resin reservoir, and fills the cavity in the mold. At this time, the pressure detection means detects the pressure from the resin in the resin reservoir or the mold, and the calculation means uses the pressure detected by the pressure detection means and the pressure set in advance through the pressure command value setting means. A speed command signal corresponding to the difference from the pressure command value is calculated and outputted to the motor control means, and the motor control means controls the electric servo motor according to the input speed command signal. Since the pressing member is driven by the electric servo motor in this manner, responsiveness that can correspond to pressure control can be obtained. Since pressure is the most influential factor on the product, by directly controlling the pressure as described above during the injection process, it is possible to control various conditions such as the characteristics of the resin, the state of the mold at the time of molding, and the mold structure. It is possible to respond flexibly automatically, and the same high-quality products can be stably obtained, and the setting work that the operator has to perform during molding is reduced to setting only a small number of pressure command values, which simplifies the process.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the accompanying drawings. 1 and 2 show one embodiment of the present invention, and the mechanical configuration of the injection molding machine is as shown in FIG. 2 and is the same as a conventional electric injection molding machine, so a description thereof will be omitted. In addition, FIG. 1 shows a heating cylinder 2 which is a resin reservoir.
The control system 41 of the electric servo motor 12 that drives the screw 5, which is a pressing member that can move forward and backward to press the resin inside and fill the cavity 1a in the mold 1, is shown in FIG. Portions corresponding to those in the conventional example are given the same reference numerals. The control system 41 includes a CPU 22 of a computer, a load cell 15 and a load cell amplifier 16, which are pressure detection means for detecting the pressure applied to the screw 5 from the resin in the cylinder 2 or the mold 1.
A digital control section 23 consisting of a pulse shaping/direction determining means 24, a deviation counter 25, and a D/A converter 26;
In addition to the motor control unit 14 which is a motor control means and the modular servo motor 29 in which a tachogenerator 30 and a pulse generator 31 are assembled to the electric servo motor 12, a pressure command value for the pressure from the resin is set. Pressure command value setting means 4
2, and a calculation section 43 which is a calculation means. In the conventional example, the speed command signal from the digital control section 23 is directly input to the motor control section 14, whereas in this embodiment, the speed command signal from the digital control section 23 is once input to the calculation section 43. is input. In addition, this calculation section 43 also includes a load cell amplifier 1 from the load cell 15.
A pressure feedback signal is inputted via 6, and a pressure command value set via pressure command value setting means 42 is inputted. In the initial stage of the injection process for filling the resin into the cavity 1a, the calculation unit 43 outputs the speed command signal from the digital control unit 23 as it is to the motor control unit 14, and after the injection process, it outputs the speed command signal as it is to the motor control unit 14. A speed command signal is calculated according to the difference between the pressure and the pressure command value, and this speed command signal is sent to the motor control section 14.
This is what is output to. In addition, this motor control section 14
is for controlling the servo motor 12 according to the input speed command signal.

Next, the operation of the above structure will be explained. The operator sets the pressure command value in advance via the pressure command value setting means 42 before molding. By the way, if other conditions such as the volume of the cavity 1a are the same, the desirable relationship between the resin temperature and the resin pressure is uniquely determined. A desirable relationship is one that prevents the occurrence of sink marks and overfilling. Therefore, the pressure command value can be determined based on this pressure. During the injection process, the screw 5 is driven by the servo motor 12 to advance toward the mold 1, and the molten resin in the cylinder 2 is pressed and injected and filled into the cavity 1a of the mold 1. At the beginning of this injection process, the digital control section 23 and the calculation section 43
A position control loop is formed by the motor control section 14, servo motor 12, and pulse generator 31,
The servo motor 12 is controlled according to a speed command signal outputted from the digital control section 23 to the motor control section 14 via the calculation section 43. The reason why the servo motor 12 is controlled by the position control loop at the beginning of the injection process is to start up the servo motor 12. Then, in the injection process, when the pressure feedback value output from the load cell 15 to the calculation unit 43 via the load cell amplifier 16 reaches the pressure command value,
The position control loop is separated, and a closed loop for pressure control is formed by the motor control section 14, calculation section 43, servo motor 12, and load cell 15. That is, in the injection process, after the pressure from the resin in the cylinder 2 or the mold 1 increases to a certain extent, the calculation unit 43 issues a speed command according to the difference between the pressure feedback value from the load cell amplifier 16 and the pressure command value. The signal is calculated and outputted to the motor control section 14. Specifically, control is performed such that when the pressure decreases, the speed of the servo motor 12 increases. In this way, pressure control is performed so that the pressure from the resin in the cylinder 2 or the mold 1 is maintained at the pressure command value. Furthermore, the injection process is transferred to the pressure holding process without any special switching, but in the pressure holding process, the servo motor 12 is controlled depending on, for example, time and pressure. In addition, the servo motor 12
While driving, the speed control loop consisting of the motor controller 14, servo motor 12, and tacho generator 30 is always in operation.

As described above, in the embodiment described above, since the screw 5 is driven by the electric servo motor 12, responsiveness that can correspond to pressure control can be obtained. Moreover, compared to the conventional example shown in FIG. 3, there are fewer devices involved in the closed loop for pressure control consisting of the motor control section 14, calculation section 43, servo motor 12, and load cell 15, so higher responsiveness can be achieved. This makes it possible to achieve more accurate pressure control. By directly controlling the pressure that has the greatest effect on the product, we can improve the properties of the resin.
The control system 41 can automatically and flexibly respond to various conditions such as the state of the mold or the mold structure at the time of molding, and the same high quality product can be stably obtained without being influenced by external disturbances. Moreover, according to the pressure control described above, control can be automatically and easily carried out such that resin is slowly filled in areas where the resin does not easily flow in the cavity 1a of the mold 1, and quickly filled in areas where it is easy to flow. Furthermore, the setting work that the operator has to perform during molding is reduced to setting only a small number of pressure command values, which simplifies the process. Settings for switching from the injection process to the holding pressure process are also not required, making it simple.

Note that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made. For example, in the embodiment described above, an injection molding machine was taken as an example, but the present invention can also be applied to a transfer molding machine for thermosetting resin. Further, the position control loop for starting up the servo motor 12 can be omitted, and the servo motor 12 may be controlled by a closed loop for pressure control from the start of the injection process.

[0013]

Effects of the Invention The present invention provides a resin reservoir, a pressing member that can move forward and backward to press the resin in the resin reservoir to fill a cavity in a mold, and an electric servo that drives this pressing member. A motor, a motor control means for controlling the electric servo motor according to an input speed command signal, a pressure detection means for detecting pressure from the resin in the resin reservoir or the mold, and a pressure command value setting means. The speed command is calculated by calculating a speed command signal corresponding to the difference between the pressure detected by the pressure detection means during the injection process of filling the resin into the cavity and the pressure command value preset by the pressure command value setting means. Since it is equipped with calculation means that outputs signals to the motor control means, it is possible to realize accurate pressure control, and it is automatically flexible to various conditions such as the characteristics of the resin, the state of the mold at the time of molding, and the mold structure. The same high-quality product can be stably obtained without being affected by various disturbances, and the setting work that must be performed by the operator during molding is simplified.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a schematic diagram showing the mechanical configuration of an injection molding machine.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

1 Mold 1a Cavity 2 Heating cylinder (resin reservoir) 5 Screw (pressing member) 12 Electric servo motor 15 Load cell (pressure detection means) 27 Motor control section (motor control means) 42
Pressure command value setting means 43 calculation section (calculation means)

Claims (1)

[Claims] 1. A resin reservoir, a pressing member that can move forward and backward to press the resin in the resin reservoir to fill a cavity in a mold, an electric servo motor that drives the pressing member, and a motor control means for controlling an electric servo motor according to an input speed command signal;
a pressure detection means for detecting the pressure from the resin in the resin reservoir or the mold; a pressure command value setting means; and a pressure and pressure command value detected by the pressure detection means during an injection process for filling a cavity with resin. 1. A molding machine comprising: calculation means for calculating a speed command signal according to a difference from a pressure command value preset by a setting means and outputting the speed command signal to the motor control means.