JPH0359680B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling a pulse motor (stepping motor)-driven flow control valve for controlling the injection speed of a die-casting machine. This makes it possible to use the entire range of low injection speeds, including the rising portion from 1 to a predetermined low injection speed.

[Prior Art] A pulse motor (stepping motor) is an electric motor that rotates by a fixed angle in response to one input pulse.The rotation angle is determined by the number of input pulses, and the angular velocity is determined by the pulse frequency. There are many different types in terms of structure and drive method. For simplicity, a three-phase pulse motor will be described here as an example.

FIG. 2 is a structural diagram of a three-phase pulse motor, which is composed of three blocks with a coil 3 at its center. The teeth of the stator 1 are in the shape of an internal gear, and the number of teeth per phase is equal to the number of teeth of the rotor 2, and the teeth of the three sets are 1/3
They are stacked one on top of the other in a staggered manner. 4 is a yoke, 5 is a flange, 6 is a bearing, and 7 is a shaft.

3a and 3b show the shape of the rotor 2. FIG.

Figure 4 is a diagram of the operating principle of a three-phase pulse motor. When the coil 3 is excited by the coil wound in three phases, the rotor 2 stabilizes at the position shown in the figure, and then turns off. By switching the excitation to , it moves by θ1 and stabilizes at the matching position.

When the excitation is turned off and the is energized, it comes to rest at the position of the partner. In this way, the pulse motor repeatedly starts, accelerates, and stops due to the excitation of the coil 3 for each input pulse, and forms rotational motion in a series of transient states.

[Problems to be solved by the invention] As mentioned above, even though a pulse motor appears to be rotating continuously, microscopically, each pulse consists of steps such as starting, accelerating, and stopping. Because the driver is stepping on the motor, damped vibrations occur when the motor stops momentarily. This damped vibration takes a value specific to the system consisting of the pulse motor and the driven part driven by the pulse motor. When this frequency and the frequency of the pulse input as a command to the pulse motor (hereinafter referred to as command pulse) almost match, the next command will be input in synchronization with the damped vibration that appears at each step, and convergence will occur. Instead of moving toward the desired state, it instead falls into an excited and resonant state. As a result, in response to a command pulse near that frequency, the pulse motor significantly reduces its torque or does not operate at all, which is a major cause of the so-called step-out phenomenon.

On the other hand, when performing low-speed injection in a die-casting machine, the size of the low-speed injection speed and the degree of increase in speed from speed 0 to a predetermined low-speed injection speed are determined based on the shape of the product to be injected and other factors. It is necessary to select the optimum injection speed and optimum speed increase degree by making various changes according to the injection conditions. For this purpose, it is necessary to change the opening degree of the flow rate control valve as appropriate, and even if the injection speed is changed, it is necessary to always be able to use the entire range of the low injection speed.

In that case, when ramping up to low-speed injection using a pulse motor-driven flow control valve for controlling injection speed, the pulse motor is If the command frequency to drive the pulse is reached, a step-out phenomenon may occur. When the valve opening F of the flow rate control valve changes from 0 to a predetermined low injection speed V ₁ , for example, as shown in FIG. The degree of increase in the valve opening when the valve opening increases up to F ₁ is such that a portion b that increases faster and a portion c that increases slower than the ideal linear valve opening increase degree a alternate. Become. In this case, not only is it necessary to perform extra control or operation to increase the valve opening degree, but also the increase in the valve opening degree is not performed smoothly.

In other words, in a die casting machine, when the plunger tip of the injection device pushes the molten metal forward, the speed of the plunger tip does not increase linearly, but rather increases relatively quickly and increases relatively slowly. As the molten metal increases in size in a zigzag pattern, it vibrates the molten metal and causes it to ripple.

If this happens, not only will the temperature of the molten metal drop and the flow of the molten metal into the mold cavity during injection will become poor, but the surface of the molten metal will ripple and the air in the injection sleeve will be drawn into the molten metal, causing air to flow into the injected product. This causes so-called cavities, which reduce the strength and density of the injection product.

In addition, when increasing the injection speed from 0 to low injection speed V ₁ , that is, when increasing the valve opening from 0 to F ₁
The degree of increase in _the valve opening, _a , when increasing the opening to
It is always desirable to increase linearly.

For these reasons, the technique disclosed in Japanese Patent Application Laid-Open No. 58-107094 is not preferable for use in controlling a pulse motor-driven flow control valve for controlling the injection speed of a die-casting machine.

Note that a part of JP-A-58-107094 discloses that an inertial load is provided to shift the natural frequency of the machine, but this is because the inertial load is always placed on the output shaft of the pulse motor. It seems to be fixed and an inertial load is constantly applied. Therefore, not only does the torque of the pulse motor decrease and its capacity decrease, but also, as in the injection control of a die-casting machine, it is necessary to change the startup state to a low injection speed, etc., as appropriate depending on the injection product. The disadvantage is that it cannot be used in some places.

[Means for Solving the Problems] In the present invention, in order to solve the above-mentioned problems in injection speed control of a die-casting machine, a pulse motor-driven flow control valve for controlling the injection speed of a die-casting machine is provided. Using a device that can connect or disconnect a moment of inertia change member such as a flywheel to the motor output shaft via a clutch, the injection speed is increased to a predetermined low injection speed by selecting a predetermined rate of increase in speed. When raising, the command frequency for driving the pulse motor comes close to the natural frequency of the thread made up of the pulse motor of the pulse motor-driven flow control valve for controlling the injection speed and the driven part driven by the pulse motor. In some cases, the moment of inertia of the pulse motor output shaft is changed by connecting the pulse motor output shaft and the moment of inertia changing member via a clutch, and the command frequency for driving the pulse motor comes near the natural vibration. If not, the clutch is disengaged, allowing use of the entire range of low injection speeds.

[Operation] The natural frequency ω ₀ of a system consisting of a pulse motor and a driven part driven by the pulse motor is generally expressed as follows, where T is the drive torque of the pulse motor and J is the moment of inertia of the system. Since we have the relationship, if the moment of inertia changes,
The state of the damped vibration during the step changes, and as a result, resonance with the frequency of the command pulse can be prevented.

Here, whenever we change the moment of inertia,
Since there is an inherent moment of inertia of rotating parts such as the rotor of a pulse motor and driven parts driven by the pulse motor, there are limited means to reduce it even relatively. Most of the time, it changes. Therefore, from the perspective of pulse motor torque, an increase in the moment of inertia leads to a decrease in performance, but
In the present invention, in view of the method of applying the pulse motor and the above-mentioned resonance situation, it has been determined that this torque reduction does not become a serious drawback. That is, (1) a pulse motor is generally a power constant type in which torque decreases as the rotation speed (command pulse factor) increases. (See Figure 5) (2) Since it has high responsiveness, it is mostly used for high-speed positioning and feeding. (3) The frequency that causes the resonance phenomenon is relatively low and is within the self-starting frequency, that is, the limit frequency at which the pulse motor can be started immediately at that frequency. (See Figure 6) Figure 5 shows that within the self-starting frequency shown in Figure 6,
This is the relationship between the command pulse frequency and torque when the command pulse frequency of the pulse motor that has started is gradually increased.For reasons (1) and (2) above, the holding torque (pulse motor stopped state, In most cases, the frequency fc range from 1/2 to 1/3 of T0 (torque when frequency = ₀ ) is used. This means that the load torque of the driven part driven by the pulse motor is less than (1/2 to 1/3) T ₀ , and the rest is due to the driven part and rotating parts such as the rotor of the pulse motor. This is the torque that can be used as the acceleration torque necessary to rotate and move according to the required acceleration characteristics. (See Figure 1) As shown in Figure 1, even if you try to drive a pulse motor with a command pulse with a frequency near the system's natural frequency ω ₀ , the resonance phenomenon described above will occur and the motor will step out. However, as shown in FIG. 6, the resonant frequency is almost always a low frequency within the self-starting frequency. Here, if acceleration is performed at a constant rate up to the final frequency fc, the torque TA required for the acceleration is constant and is within the range obtained by subtracting the load torque TL from the drive torque Tc of the pulse motor at fc. Therefore, the portion obtained by subtracting T _A + T _L from the driving torque Tc at a frequency lower than fc is all surplus torque, and becomes the surplus power of the pulse motor that does not contribute to actual driving.
This surplus power increases as the frequency decreases (as shown in (1) above, the pulse motor is a constant power type),
Near the resonance frequency number ω ₀ , the driving torque is approximately equal to the holding torque T ₀ , so it can be said that there is sufficient surplus.

Therefore, even if the moment of inertia of the pulse motor output shaft is increased near this resonance frequency ω ₀ ,
There are no problems with the drive. For example, even if it is increased by an amount equal to the total moment of inertia of the current pulse motor and its drive unit (even if it is doubled), the effect on the drive torque will be approximately the same as the acceleration torque _TA . According to equation (a), the resonant frequency decreases to ω ₁ , (≒1/√2ω ₀ ) as shown by the broken line in Figure 1, and as a result, the resonance frequency near the ω ₀ frequency The torque increases, and the occurrence of step-out can be prevented.

When using the above to control the rising state to a low injection speed using a pulse motor-driven flow control valve for controlling the injection speed of a die-casting machine,
If the command frequency for driving the pulse motor comes close to the natural frequency of the system consisting of the pulse motor of the pulse motor-driven flow control valve for injection speed control and the driven part driven by the pulse motor, the pulse motor The moment of inertia of the pulse motor output shaft is changed by connecting the output shaft and the moment of inertia changing member via a clutch, and when the command frequency for driving the pulse motor does not come near the natural frequency, the clutch This enables the use of the entire range of low injection speeds.

[Example] Next, the present invention will be explained in more detail with reference to an example shown in the drawings.

FIG. 7 shows an example in which a pulse motor 13 is used to drive a spool 12 of a flow control valve 11 that controls the speed of an injection cylinder 10, etc. of a die-casting machine. is converted into a force in the direction of stroke movement. Pressure of hydraulic pressure source 15 and spool 1
The force due to the pressure receiving area 2 corresponds to the load torque of the pulse motor 13 necessary to hold the spool 12 in a predetermined position via the ball screw 14,
The torque required to open the spool 12 at a predetermined speed appears as the acceleration torque of the pulse motor 13. The position detector 16 detects the position of the injection cylinder 10, and upon receiving this position signal 21, the command pulse generator 17 activates the pulse motor 1 in order to move the spool 12 at a predetermined speed to a predetermined opening degree.
A command pulse 19 is output to drive 3. A drive unit 18 has a function of converting the command pulse 19 into a signal 22 having a voltage and phase current that can ultimately drive the pulse motor 13.

Now, with respect to the position signal 21 of the injection cylinder 10, the opening degree of the spool 12, that is, the opening of the injection cylinder 1
The moving speed of the piston at 0 is as shown in Figure 8,
Assume that the command pulse generator 17 is programmed.

At position S ₂ , opening degree V ₁ → V ₂ , at position S ₃ , opening degree V ₂ → V ₃
In order to change to S, it is necessary to make a large opening difference in a short time, so the command pulse ₁₉ cannot be achieved unless the self-starting frequency starts driving and reaches a high frequency. Since a low frequency is sufficient for opening up to the degree V ₁ , the command pulse 19 may have a constant frequency as long as the required frequency is within the self-starting frequency.

In such a case, the frequency is the resonant frequency ω ₀
As is clear from the previous explanation, if it is nearby,
It induces loss of synchronicity. Therefore, the resonant frequency ω ₀
When a nearby frequency is programmed into the command pulse generator 17, the inertia switching signal 20 is output to the clutch 23 immediately before the command pulse near the resonance frequency ω ₀ is issued, and the output shaft of the pulse motor 13 and the milling wheel 24 are output. , increasing the moment of inertia of the system and lowering the resonant frequency ω ₀ . In this embodiment, a flywheel is used as a means for increasing the moment of inertia of the pulse motor output shaft, but the same result can be obtained by using a braking force such as an electromagnetic brake.

In addition, FIG. 9 shows another embodiment, in which the pulse motor 1
A DC motor 25 is attached to the output shaft of 3 with a coupling 26.
The moment of inertia is controlled by the voltage applied to the DC motor 25.

Upon receiving the inertia switching signal 20, the amplifier 27 applies a predetermined voltage value 28, and the DC motor 25 is switched to the pulse motor 1.
By applying rotation in the opposite direction to 3, it is possible to obtain an arbitrary braking state, that is, to arbitrarily increase the moment of inertia.

Moreover, if the present embodiment is used, the DC motor 2
It may be rotated in the same direction as the 5-pulse motor 13. Then, when viewed from the pulse motor 13 side, the moment of inertia of the system remains unchanged.
Since the torque increases, according to equation (a), the frequency ω ₀ increases and deviates from the frequency range of the command pulse, thereby preventing resonance. Furthermore, since there is no (increased) torque loss, there is no problem with driving at all.

[Effect] In the present invention, as described in the claims, it is possible to drive the pulse motor near the resonance frequency, and, for example, the rising slope of the opening of the flow rate regulating valve at low speed can be set arbitrarily. It became like I could take it. Conventionally, the rising slope was limited due to resonance problems, and when this was applied to control the injection cylinder of a die-casting machine, air was drawn into the molten metal, turbulence of the molten metal occurred, and the molded product was damaged. However, by implementing the present invention,
These things will almost disappear.

That is, the present invention is a method of controlling a pulse motor-driven flow control valve for controlling the injection speed of a die-casting machine, and in which the injection speed is increased to a predetermined low injection speed by selecting a predetermined speed increase degree. In this case, a moment of inertia changing member such as a flywheel can be connected or disconnected to the pulse motor output shaft via a clutch,
If the command frequency for driving the pulse motor comes close to the natural frequency of the system consisting of the pulse motor of the pulse motor-driven flow control valve for injection speed control and the driven part driven by the pulse motor, the pulse motor By connecting the output shaft and the moment of inertia changing member via a clutch, the moment of inertia of the pulse motor output shaft is changed. If the clutch is not available, the clutch is kept in the disengaged state, making it possible to use the entire range of low injection speeds.

Therefore, in the present invention, even if the speed rise state is variously changed as shown by a, a ₁ , a ₂ in FIG. It can be started up smoothly.

As a result, during low-speed injection, vibrations and ripples in the molten metal can be suppressed as much as possible, preventing a drop in molten metal temperature and maintaining good running conditions at all times, and preventing air from entering the molten metal. By minimizing the formation of cavities within the product, it is possible to reliably and easily obtain injection products with good mechanical properties that have high strength, high density, and almost no blistering when heat-treated or welded later. be able to.

The present invention is particularly useful when it is necessary to appropriately change the low injection speed or the rise state to the low injection speed in injection of a die-casting machine.

[Brief explanation of drawings]

Figure 1 is for explaining the principle of the present invention, and is a diagram showing the relationship between frequency and torque. Figure 2 is a front view (the upper half is a vertical cross-sectional view) of a commonly used three-phase pulse motor. Figure 3a is a front view of the rotor;
Figure 3b is a right side view of Figure 3a, Figure 4 is a diagram of the operating principle of a three-phase pulse motor, Figure 5 is a diagram showing the relationship between command pulse frequency and torque, and Figure 6 is a self-starting frequency. Fig. 7 is a diagram illustrating an embodiment of the device for carrying out the present invention, Fig. 8 is a diagram showing the relationship between the position of the injection cylinder during operation and the opening degree of the flow rate control valve. FIG. 9 is a diagram showing another embodiment of the apparatus implementing the present invention, and FIG. 10 is a diagram showing a conventional method for increasing the valve opening of a pulse motor-driven flow control valve for injection speed control. FIG. 3 is a diagram for explaining the differences in the present invention. 10...Injection cylinder, 11...Flow control valve,
12...Spool, 13...Pulse motor, 14
... Ball screw, 15 ... Hydraulic supply source, 16 ...
Position detector, 17... Command pulse generator, 18...
...Drive unit, 19...Command pulse, 20
...Inertia switching signal, 23...Clutch, 24...
Flywheel, 25...DC motor, 26...
cutlet ring.

Claims (1)

[Claims] 1. A pulse motor output shaft of a pulse motor-driven flow control valve for injection speed control of a die-casting machine,
When increasing the injection speed to a predetermined low injection speed by selecting a predetermined speed increase rate and starting up, using a device that can connect or disconnect a moment of inertia changing member such as a flywheel via a clutch, When the command frequency for driving the pulse motor comes close to the natural frequency of the system consisting of the pulse motor of the pulse motor-driven flow control valve for controlling the injection speed and the driven part driven by the pulse motor, the pulse By connecting the motor output shaft and the moment of inertia changing member via a clutch, the moment of inertia of the pulse motor output shaft is changed, and when the command frequency for driving the pulse motor does not come near the natural frequency, A control method for a pulse motor-driven flow control valve for controlling injection speed of a tie casting machine, characterized in that a clutch is kept disengaged to enable use of the entire range of low injection speeds.