JPS62151315A - Controller of fluid pressure actuator - Google Patents

Abstract

PURPOSE:To enable the titled controller to perform changeover to pressure control from speed control smoothly without generating overshoot or undershoot, by applying speed controlling information and pressure setting information of a speed control system selectively to an input part of pressure setting information of an operational processing part in a pressure control system through a changeover device. CONSTITUTION:In such a case wherein a changeover device has been changed over to a speed control side, control information Cv of a speed is applied to an input part 4a of an operational processing part 4 of pressure and speed control is performed by a closed loop of a speed control system Xv. On the other hand, a minor lop of a pressure control system Xp is constituted within the speed control system Xv and the control information Cv of the speed is applied to the pressure control system Xp as a function of pressure. In consequence of the above, control having the speed control function for its main purpose is performed by the speed control system Xv, through which it follows that the speed is controlled by pressure control. When the speed control is being performed by the speed control system Xv in this manner, the pressure control system Xp of the minor loop is operated at a time similarly to that at the time of the pressure control.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to fluid pressure actuators such as injection molding machines and hydraulic presses that selectively and continuously control speed elements and pressure elements using a feedback control system. Regarding a control device.

BACKGROUND OF THE INVENTION Generally, fluid pressure actuators, such as screw drive actuators in typical in-line screw injection molding machines, are process-controlled by an attached control device. Particularly focusing on the actuator injection process, there are two steps: an injection filling process in which molten molding material is injected into the mold cavity, and a compression process in which a certain pressure is applied to compress the molten resin after filling the material into the mold. There is a pressure holding step whose purpose is to compensate for the shrinkage of the compressed molten resin due to cooling and to prevent backflow of the resin in the product portion. Of these, the injection filling process is controlled by a speed control system, and the compression process and pressure holding process are each controlled by a pressure control system, and transitions between these processes are performed continuously.

By the way, in order to achieve smooth control, improve reproducibility, and eliminate speed and pressure fluctuations caused by external influences such as viscosity changes due to fluid temperature fluctuations, recent injection molding machine control devices have been There is a trend to adopt a closed loop control system (feedback control system) using a servo valve from the oven loop control system that has been the mainstay (see, for example, Japanese Patent Publication No. 55-7374 (US Pat. No. 3,767,339), etc.).

Since it is not possible to control both the speed element and the pressure element at the same time in this rose-loop control method, the speed control system and pressure control system are usually provided independently.
These prefectures are selectively controlled by switching between them using a predetermined switching means. Specifically, a circuit that generates the required control information by comparing and calculating preset setting information and detection information detected based on the operation of the fluid pressure actuator using a processing unit is installed in the speed system and pressure system, respectively. Correspondingly, they are provided separately, and the speed or pressure control information obtained therefrom is selectively applied to the servo valve side via a changeover switch. In this case, each piece of control information is applied to the changeover switch via a characteristic compensation circuit section including a phase lag compensation circuit, a phase lead compensation circuit, a gain one cycle adjustment circuit, and the like. The control systems on the selected side each form a closed loop of feedback control type.

(Problems to be Solved by the Invention) However, the conventional control device described above has the following problems.

First, the speed control system and pressure control system are provided independently, and control is performed by switching between these prefectures for each target control element. For example, when the speed control system is selected, the system is performing closed-loop feedback control, but the other pressure control system is in an oven loop state even though it is provided with detection information from the actuator based on speed control. Therefore, when switching from the speed control system to the pressure control system, the oven loop state shifts to a closed loop state, and this transition cannot be performed smoothly, resulting in unstable control such as pressure undershoot or overshoot. . To explain the cause of this in more detail, as described above, the characteristic compensation circuit section includes a lead compensation circuit and a lag compensation circuit, each circuit comprising a differential element and an integral element using a CR circuit. Therefore, when the speed control system is selected, pressure detection information (feedback signal) based on pressure fluctuations during speed control is also given to the pressure control system, thereby charging or discharging the capacitor of the CR circuit. As a result, when switching from the speed control process to the pressure control process, charging and discharging occur due to the offset between the charge that the capacitor had stored immediately before and the charge that was originally required at the time of switching.
During this charging and discharging time, pressure undershoot or open neatness occurs (see FIG. 4 (N)). Note that this phenomenon has a direct negative effect on molding quality, for example, 7
This causes defects such as 0-marks and overfilling.

Secondly, increasing the gain of the control system is generally an effective means to correct the steady-state deviation of the control system due to disturbances, but simply increasing the gain will cause oscillations such as hunting, and the control system will worsens the stability of Therefore, in order to change this, it is only necessary to provide an appropriate phase lead compensation circuit or phase lag compensation circuit in the loop of the control system. Since the compensation circuit is configured, a response delay occurs when switching the control system, which is also a factor that further increases the overshoot and undershoot. For this reason, conventionally, the gain has not been adjusted too much, and compensation has been performed to such an extent that overshoot and the like do not become a problem during the switching. Therefore, it is not possible to sufficiently eliminate the influence of disturbances, and it is also not possible to perform an optimal design for characteristic compensation suitable for each prefecture, resulting in a feedback control system with poor followability in each control region. This went against the original purpose of the feedback control system for injection molding machines that require high speed and high response.

(Means for Solving the Problems) The present invention provides a new device that solves the problems of the conventional control device described above, and can be achieved by the following fluid pressure actuator control device. .

That is, the control device for a fluid pressure actuator according to the present invention (
1) is the setting information (Sp), (
A speed control system (Xv) and a pressure control system (Xp) that obtain control information by comparing and calculating detection information (F p ) and (Pv) regarding the operation of the fluid pressure actuator (2) with Sv) by an arithmetic processing unit. and which selectively applies each control information to the servo valve (3) to feedback control the velocity element and pressure element of the fluid pressure actuator (2), wherein the calculation processing in the pressure control system (Xp) The setting information input section (4a) of section (4) is
) control information (Cv) of the speed control system (Xv)
and pressure setting information (Sp) are selectively provided.

(for production) Next, the operation of the present invention will be explained.

In the fluid pressure actuator control device (1) according to the present invention, when the switching means (5) is first switched to the speed control side, the speed control information (Cv) is transferred to the pressure calculation processing section (4).
) input; given to l<(4a). Therefore, a closed loop of the speed control system (Xv) is constructed through this arithmetic processing IT≦(4), and speed control is performed by this loop.

On the other hand, this speed control system (Xv) includes a pressure control system (Xp
) is configured, and the above speed control information (C
v) is the arithmetic processing unit (4) in the pressure control system (Xp).
) is given as setting information. In other words, since pressure fluctuation and speed have a functional relationship, speed control information (Cv) during speed control is given to the pressure control system (Xp) as a function of pressure, and as a result, the speed control system (Xv) controls the speed. Control is performed with the main purpose of and,
This means that the speed is controlled by pressure control, and when viewed from the speed control side, the pressure is controlled as a minor feedback loop.

Next, when the changeover switch (5) is switched to the pressure control side, pressure setting information (Sp) is given to the manual power ff (4a) of the arithmetic processing section (4). This allows a single pressure control system (
A closed loop of Xp) is constructed, and control with the main purpose of pressure control is performed by this loop.

By the way, when speed control is being performed by the speed control system (Xv) as described above, the pressure control system (Xp) of the minor lube is also operating at the same time in the same manner as during pressure control. In other words, even during speed control, speed control is performed in terms of pressure using the minor lube of the pressure control system (Xp). Therefore, even if the speed control step r is switched to the pressure control step, only the magnitude of the setting information of the pressure control system changes.

Moreover, the pressure control system (Xp) has optimal responsiveness, and no overshoot or undershoot occurs during switching.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail based on the drawings.

Fig. 1 is a basic block diagram of the control device according to the present invention, Fig. 2 is a block diagram of the control device according to the present invention applied to an in-line screw injection molding machine, and Fig. 3 is a basic block diagram of the control device according to the present invention. Figure 4 is an electric circuit diagram illustrating a specific circuit in the dotted chain line frame Δ. Figure 4 is a time chart of the signals in the inner part of Figure 3 when the injection molding machine is controlled. First, please refer to Figure 1. The basic block configuration of the control device (1) will now be explained.

Reference numeral (2) denotes a fluid pressure actuator, which has at least a speed element and a pressure element as control objects. The speed element and the pressure element are each controlled by fluid pressure, such as oil pressure, and the fluid pressure is further controlled by a servo valve (3).

On the other hand, (4) is an arithmetic processing section of the pressure control system (Xp) which has at least a human-powered comparison and arithmetic processing function for two pieces of information. A power amplifier (7) is connected to the output section (4b) of the arithmetic processing section (4) via a characteristic compensation circuit section (6) including a phase lead compensation circuit, a phase lag compensation circuit, a gain adjustment circuit, etc. The output side of this power amplifier (7) is connected to the servo valve (3). In addition, the niI calculation processing unit (
One contact (for example, a fixed contact) of a two-circuit changeover switch (8) is connected to the setting information input section (4a) in step 4). This switching switch (8) has the function of connecting one circuit and disconnecting the other circuit by switching. Furthermore, the output side of a pressure sensor (9) for detecting the magnitude of actual pressure attached to the fluid pressure actuator (2) is connected to the detected information input section (4c) in the arithmetic processing section (4).

In addition, the other contact (for example, a movable contact) in the changeover switch (8) has a pressure setting part (10) on one circuit side.
and the output side of the characteristic compensation circuit section (11) of the speed control system (Xv) is connected to the other circuit side. This characteristic compensation circuit section (11) includes a phase lead compensation circuit, a phase lag compensation circuit, a gain adjustment circuit, etc., like the characteristic compensation circuit section (6). The input side of the characteristic compensation circuit section (11) is connected to the output section side of an arithmetic processing section (I2) having at least a function of comparing and processing two pieces of input information. In addition, a speed setting section (
13), and the output side of a speed sensor (14) attached to the fluid pressure actuator (2) that detects the magnitude of the actual speed is connected to the detection information input section.

Next, the operation of the control device (1) shown in FIG. 1 will be explained. First, assume that speed control is performed by switching the changeover switch (8) as shown in the figure. In this case, the arithmetic processing unit (4
) is connected to the input section (4a) of the characteristic compensation circuit section (11). Preset speed setting information (Sv) is provided from the speed setting ff1 (13) to one input section of the arithmetic processing section (12), and speed detection information (Pv) is also provided from the speed sensor (14). It is applied to the other input section of the processing section (12). The processing section (12) performs a comparison calculation process on the two pieces of information (Sv) and (Fv) given, and outputs speed control information (Cv) by determining the deviation between the two.

The speed control information (Cv) is input to the input section (4) of the calculation processing section (4) via the characteristic compensation circuit section (11) and the changeover switch (8).
4a) is given. In addition, pressure detection information (Fp) is sent from the pressure sensor (9) to the other input section (4) of the same processing section (4).
4c), and the processing unit (4) performs a comparison calculation process on the two given pieces of information (Cv) and (Fp), calculates the deviation, and outputs control information (Cvo). Due to the minor loop of the pressure control system (Xp), this control information (CvO) becomes information that further includes speed corrections based on pressure fluctuations in addition to the speed control information (Cv) described above. The control information (Cvo) is given to the servo valve (3) via the characteristic compensation circuit section (6) and the power amplifier (7), and by driving and controlling the servo valve (3), the fluid pressure actuator (2 ) speed element as speed setting information (Sv
) to match.

Next, assume that pressure control is performed by switching the changeover switch (8). In this case, the input section (
A pressure setting section (10) is connected to 4a).

During pressure control, the human power of the calculation processing section (4) is 131T (4a
) is given preset pressure setting information (Sp) from the pressure setting part (lO), and the other input part (4c) is given pressure detection information (Fp) from the pressure sensor (9) as described above. be done. The processing section (4) performs a comparison calculation process on the two pieces of information (Sp) and (Fp) given, determines the deviation, and outputs pressure control information (Cp). The control information (Cp) is transmitted to the characteristic compensation circuit section (6) and the power amplifier (7).
) to the servo valve (3), and feedback controls the pressure element of the fluid pressure actuator (2) to match the pressure setting information (Sp).

Next, with reference to FIGS. 2 and 3, a case will be described in which the present control device is applied to an in-line screw set injection molding machine.

First, in order to facilitate understanding of this embodiment, the configuration of the injection molding machine will be explained. The injection molding machine designated by the symbol (20) has a screw cylinder (2
2), the rear end of this cylinder (22) is integrated with the injection cylinder (24), and the screw (21) is connected to the piston (25) provided inside the injection cylinder (24).
) join the rear ends together. The injection cylinder (24) has a front oil chamber (24a) and a rear oil chamber (2) before and after the piston (25).
4b), and each oil chamber is connected to a hydraulic power source (hydraulic pump) (26) and a return tank (27) via a servo valve (3). Therefore, by selectively applying hydraulic pressure to each oil chamber and controlling its magnitude, the screw (21) moves back and forth or stops at a predetermined speed and pressure. Also, the piston (2
The rear end of 5) is connected to an oil motor (29) via a splined shaft (28), and the screw (2I) is rotated by the rotation of the oil motor (29). In addition, (30) shows the hopper provided in the screw cylinder (22), and (31) shows the injection nozzle.

Next, the control device (40) according to the present invention that controls such an injection molding machine (20) will be specifically explained.

Ma'4', injection cylinder (24) of the injection molding machine (20)
A pressure sensor (9) facing the rear oil chamber (24b) is disposed.

For example, a strain sensor that is displaced by the action of pressure can be used as the pressure sensor (9). Additionally, a detection lever (32) is provided that moves following the displacement of the rod of the piston (25), and this detection lever (32) acts on the speed sensor (14) to detect the speed of the screw (21). do. As the speed sensor (14), for example, a position sensor using a potentiometer can be used, and the speed is determined by differentiating the output.

On the other hand, the main body side of the control device (40), as shown in FIG. 2, has basically the same basic configuration as shown in FIG. 1. Therefore, the same parts as in FIG. 1 are given the same reference numerals to clarify the structure.

First, (10) is the pressure setting section, which sets the thickness of the pressure in terms of the voltage level. The set pressure setting signal (Sp
s) is amplified by an amplifier (41), and is amplified by a controller (42).
) is 0N()FF controlled.
3) through the calculation process jπ≦(4) input; i<(4
a). On the other hand, a pressure detection signal (Fps) with a voltage level proportional to the pressure is obtained from the pressure sensor (9),
This signal (Fps) is supplied to the arithmetic processing section (4) via the phase lead compensation circuit (6a).

The arithmetic processing section (4) calculates the deviation between the two manually input signals and outputs a control signal based on this deviation.

The control signal is then supplied to the servo valve (3) through the phase lag compensation circuit (6b) and the gain adjustment circuit (6c), and further through the power amplifier (7).

On the other hand, the speed setting section (13) sets the magnitude of the speed using a voltage level. The set speed setting signal (Svs) is amplified by the amplifier (44) and supplied to the arithmetic processing J (12). On the other hand, a speed detection signal (Fvs) with a voltage level proportional to the speed is obtained from the speed sensor (14), and this signal (
Fvs) is supplied to the arithmetic processing unit (12) via the phase lead compensation circuit (lla).

In the arithmetic processing unit (12), both signals (Svs) and (Fvs)
A speed control signal (Cvs
) is output. This speed control signal (Cvs) is then sent to the arithmetic processing unit (4) via an analog switch (45) that is ON-OFF controlled by the controller (42).
is supplied to the input section (4a) of.

In the second configuration, the pressure setting section (10) and the speed setting section (13) can be arbitrarily set 17 by manual operation, for example, and the set values can be changed in one or more stages over time. Note that each setting section (10) and (step 3) may be of a type that is automatically corrected depending on conditions or the like. Further, when the controller (42) turns on the analog switch (45) during speed control, it turns off the analog switch (43), and on the other hand, when controlling the pressure, it turns on the analog switch (43) and turns off (45). The timing of this switching is determined, for example, by detecting an increase in pressure with the completion of filling into the mold cavity with a pressure sensor (9), and switching when the value reaches a set value set to -f. In this case, a decrease in the speed of the screw (21) upon completion of filling may be detected, or the resin pressure within the mold or cylinder (22) may be detected.

The circuit shown in the dot-dashed line frame A in FIG. 2 is illustrated in more detail in FIG. In Figure 3, parts that are the same as those in Figure 2 are marked with the same symbol to clarify their structure.

In Figure 3, (50), (51), (52), (5
3) is an operational amplifier, (old) to (1-12) are resistors, (C
I) to (C4) indicate capacitors. Also, (6a),
(lla) is the phase lead compensation circuit described above using the CR circuit, (6b) and (1, Ib) are the same <i due to the CR circuit;
This is the phase lag htf compensation circuit described above. Although FIG. 3 shows an example of a circuit that processes analog signals, the circuit may be replaced with a microcomputer or the like that converts signals from other sensors from analog to digital and performs each process using software.

Next, the operation of the system shown in FIGS. 2 and 3 will be explained.

First, during speed control, the analog switch (45)
is turned on, the output deviation control signal (Cvs) is supplied from the RIS calculation processing unit (12) to the servo valve (3) via the minor lube of the pressure control system, and the speed is controlled by controlling AI + pressure (flow rate). Feedback control is performed to maintain the target speed. At the same time, pressure fluctuations caused by disturbances are detected, and speed changes due to pressure fluctuations are corrected using a minor loop in the pressure control system.

On the other hand, during pressure control, the analog switch (43)
is turned on, the pressure control signal (Cps) output from the arithmetic processing unit (4) is supplied to the servo valve (3), which performs feedback control to maintain the pressure at the target pressure by controlling the pressure (flow rate). conduct.

Note that FIG. 4 is a time chart of signals in each part of the control device shown in FIGS. 2 and 3.

In particular, in FIG. 4, the horizontal axis indicates the time axis corresponding to the speed control process and the pressure control process of the injection molding machine, and point M is the switching point between each process. Further, the symbols given to the signals in FIG. 4 and the symbols given to the lines of the circuit in FIG. 3 are made to match.

As is clear from FIG. 4, when transitioning from the conventional speed control process to the pressure control process, an open neat or undershoot as shown by (N) occurred at the M point.
With the control device according to the present invention, these overshoots and the like do not occur at all, and quick switching can be performed.

Although the embodiments have been described in detail above, the present invention is not limited to these embodiments.

For example, any other sensor having the same function can be used as the pressure sensor or speed sensor. Furthermore, the illustrated specific circuit configuration is arbitrary, and the illustrated amplifier, adjustment circuit, and compensation circuit may be omitted, or other auxiliary circuits may be added.

Furthermore, although an in-line screw set injection molding machine is illustrated, the present invention can be widely used in plunger type injection molding machines, hydraulic presses, and the like. Other changes may be made in the detailed structure, etc., without departing from the spirit of the present invention.

(Effects of the Invention) As described above, the control device for a fluid pressure actuator according to the present invention has a speed control system and a pressure control system that obtain control information by comparing setting information and detection information from the fluid pressure actuator using the arithmetic processing section. and which selectively applies each control information to the servovalve to feedback control the speed element and pressure element of the fluid pressure actuator, wherein the input part of the pressure setting information of the arithmetic processing part in the pressure control system is switched. Since the speed control information and pressure setting information of the speed control system are selectively provided through the means, the following significant effects are obtained.

- Since minor loop control of the pressure control system is performed during speed control, switching from speed control to pressure control can be performed extremely smoothly and stably without causing open neat or undershoot.

■ The minor lube in the pressure control system allows the system to operate stably, with high precision, and with high response, which dramatically increases the degree of freedom in designing characteristics compensation, etc., and as a result, it is possible to create the most suitable compensation for each prefecture. It can be carried out.

■ Therefore, when applied to an injection molding machine, it will enable high-precision control of the injection molding machine, improve reproducibility, improve stability, and be more resistant to external disturbances, resulting in precision molding. can be easily carried out, and the molding quality can be improved. Therefore, although such an effect is obtained, there is no disadvantage in terms of cost.

[Brief explanation of drawings]

Fig. 1 2 Basic block configuration diagram of the control device according to the present invention, Fig. 2: Block configuration diagram when the control device according to the present invention is applied to an in-line screw set injection molding machine, Fig. 3: Fig. 2 An electric circuit diagram illustrating a specific circuit of the 81-line frame A section, FIG. 4: A time chart diagram of signals at the convex portion in FIG. 3 when the injection molding machine is controlled. In the drawings, (1), (40): Control device (2)/Fluid pressure actuator (3): Servo valve (4): Arithmetic processing unit (4a): Human power II< (5): Switching means (Sp) , (Sv): Setting information (Fp), (Fv): Detection information (Cp), (Cv); Control information patent applicant Nissei Jushi Kogyo Co., Ltd. Representative Patent Attorney 1) Shigeru Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] A speed control system and a pressure control system that obtain control information by comparing and calculating setting information and detection information from a fluid pressure actuator using an arithmetic processing unit, and selectively impart each control information to the servo valve. In a control device for a fluid pressure actuator that performs feedback control of a speed element and a pressure element of a fluid pressure actuator, a control device for controlling the speed control system is inputted to an input section of setting information of an arithmetic processing section in the pressure control system via a switching means. A control device for a fluid pressure actuator, characterized in that information or pressure setting information is selectively provided.