JPH0783621B2 - Piezoelectric actuator control circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to controlling a lip opening of an extruder T die or an ink supply device of a printing machine when controlling a target mechanism using a plurality of piezoelectric actuators. The present invention relates to a piezoelectric actuator control circuit to be used.

[Prior Art] For example, when describing a plastic extruder, the initial adjustment of the lip opening of the T die of the extruder is performed by adjusting the fixed lip 12 and the flexible lip 13 of the T die 11 as shown in FIGS. 6 and 7. A lip 14 was formed between them, and the opening degree of the lip 14 was adjusted by the pressing force given by a plurality of bolts 15 in contact with the flexible lip 13. As described above, the adjustment of the lip gap is performed manually, but due to automation in recent years, it is changed from manual to automatic. The 8th drawing is an automated conventional example and is called a heat bolt system. In this example, the bolt 15 is an electric heater.
It is heated by 16 and the lip opening is adjusted by the extension of the bolt 15.

This heat bolt method has advantages such as a simple structure, low cost, and fine displacement adjustment.However, since the bolt 15 is heated by the electric heater 16, the response speed is as slow as several seconds to several tens seconds. It was In addition, this heat bolt is 20 or
Since about 100 rods are used and the lip itself is a continuous body, even if one bolt is properly controlled, it has a drawback that it affects the bolts on both sides and changes the lip opening.

On the other hand, a piezoelectric element that generates strain when a DC voltage is applied was an actuator that could only generate a minute displacement of about 1 μm, but in recent years, by stacking thin layers, it is possible to use a large actuator of 300 to 400 kg / cm ₂ . By load
Since a large displacement of about 0.1 mm is possible and a high response of about 1 ms is obtained, it has been developed as a high-precision actuator for small-quantity control. The condition of the piezoelectric element actuator is T
It is suitable for adjusting the opening of the die lip.
It is published as No. 10418.

When a piezoelectric actuator is used for the T-die, the piezoelectric actuators to be used have different strains due to the relationship of the lip opening, that is, the applied voltage is different, so that one piezoelectric actuator requires one power source. The power supply price described above is considerably high even in the open loop system, and the closed loop system having position feedback for preventing distortion change due to charge leakage is 4 to 5 times as expensive as the open loop system. Therefore, in the case of a T-die made of plastic extruded material or an ink supply device for a printing machine, which uses 20 to 100 piezoelectric actuators per unit, the piezoelectric actuator 1
If one power source is provided for each unit, the price will be as high as the price of the extruder or printing machine itself even if only one power source is provided. Although there is one that controls two or three piezoelectric actuators with one power source, the price of the power source is high in any case.

[Object of the Invention] The present invention eliminates such a drawback that the power supply cost is high, and an object of the present invention is to provide a low cost piezoelectric actuator by controlling all the piezoelectric actuators with about 1 to 3 power supplies. It is to provide a control circuit.

Here, the piezoelectric actuator will be described prior to the description of the embodiments. FIG. 4 shows an example of the basic circuit of the open-loop piezoelectric actuator. Although one piezoelectric actuator 21 is shown in the figure, a large number of piezoelectric actuators 21 are actually stacked. When a DC power source 22 is applied to this piezoelectric actuator 21, distortion (displacement) occurs and the distortion causes the actuator to function.

The material of the piezoelectric actuator 21 is a thin ceramic, which is usually an electrical insulator. A conductive material is applied as an electrode on both sides of this thin layer to form a kind of capacitor (capacitance C), which is supplied by applying a power supply voltage V. Distortion occurs due to the charge amount (Q = CV). However, when a constant voltage is applied to the piezoelectric actuator 21 by the open loop as described above, the strain starts to decrease in ten to several ten minutes due to the leakage of the element of the piezoelectric actuator 21 itself, and the predetermined strain amount should be maintained. Becomes impossible.

Therefore, as shown in Fig. 5 as a closed loop,
The piezoelectric actuator 21 is equipped with a position sensor 23, which is connected to the controller 24.
By applying a voltage to the piezoelectric actuator 21 via 24, the reduction of the strain amount is corrected. The position sensor includes strain gauge type, potentiometer type, differential transformer type, eddy current type, capacitance type and the like.

SUMMARY OF THE INVENTION A piezoelectric actuator control circuit according to the present invention includes a plurality of piezoelectric actuators, one or more physical quantity detectors including displacements of the piezoelectric actuators, a change amount detected by the physical quantity detectors, and the piezoelectric actuators. A control circuit for a piezoelectric actuator, comprising: a controller that outputs a related DC voltage based on a change amount; and a switching unit that performs switching for applying the output voltage of the controller to each of the plurality of piezoelectric actuators. It is characterized in that capacitors are connected in parallel to each of the piezoelectric actuators.

[Embodiment of the Invention] The present invention uses a common power source for a plurality of piezoelectric actuators in the system shown in FIG. 5, which is a closed loop system described above. The basic circuit uses the controller shown in FIG. 9 and a capacitor 31 is connected in parallel to the piezoelectric actuator 21 as shown in FIG. 2, and the piezoelectric actuator 21 has a DC power supply built-in controller 32 to a current limiting resistor 33. The voltage is applied through the switch 34.

By this connection, the piezoelectric actuator 21 is distorted and deformed, while the capacitor 31 is charged, and when the piezoelectric actuator 21 is deformed and the capacitor 31 is sufficiently charged, when the switch 34 is opened, the piezoelectric actuator 21 is not deformed. Due to the charge on the capacitor 31, it is held for a longer period of time compared to when it was not there. Since the piezoelectric actuator 21 also has a capacitor capacity C or is very small, if the switch 34 is opened without the capacitor 31, the piezoelectric actuator 21
21 A very small current flows through the high resistance inside and the amount of strain decreases in a very short time.

FIG. 3 is a cross-sectional view showing a state in which the piezoelectric actuator 21 is attached to the T die 11. The piezoelectric actuator 21 is attached on the flexible lip 13 and determines the preload that determines the initial opening of the lip 14, that is, the initial large displacement. It is pressed by the giving bolt 35. Although the condenser 31 (see FIG. 2) is not shown, this is because the condenser, the controller, etc. are vulnerable to heat and are therefore installed away from the high temperature place where the T-die is placed.

FIG. 1 shows an embodiment of the present invention. The voltage actuator 21 in FIG. 2 and the capacitor 31 connected in parallel thereto, and the physical quantity detection position sensor 23 such as the displacement amount of the piezoelectric actuator 21, the thickness of the extruded film, the ink density, etc. in correspondence with the piezoelectric actuator 21 (FIG. 5). The reference number) is enclosed by a square dotted line, and a number such as a piezoelectric actuator is denoted by 51. In FIG. 1, n piezoelectric actuators 51-1, 51-2, 51-3 ... 51-n are provided.
Then, the piezoelectric actuators 21 such as the plurality of piezoelectric actuators 51 and the position sensor 23 are taken out and connected to the respective elements of the changeover switches 52 and 53. The switch body 53A of the changeover switch 53 on the piezoelectric actuator 21 side is connected to the controller 54 via the current limiting resistor 33,
Switch body of the changeover switch 52 on the physical quantity detection sensor 23 side
52A is connected to the controller 54, and is compared with a set value inside the controller 54 via a physical quantity / voltage converter (not shown). Although not shown, the controller 54 is provided with a variable voltage DC power supply.
The changeover switch 52 and the like described above may be a scanner, and the switching element may be a mechanical switch or an analog switch, and the point is that the voltage of the controller 54 is correctly supplied to each piezoelectric actuator 21.

Next, the operation of the above-described embodiment will be described. First 3rd
Multiple lips 35 for each lip as shown
Set a gap interval that is considered appropriate for 14. When the operation is started in this state and the changeover switches 52 and 53 are connected to the piezoelectric actuator 51-3 as shown in FIG. 1, the controller 54 detects the physical quantity of the piezoelectric actuator 51-3. A signal from the sensor 23 enters and is compared here with a set value. When the incoming position signal is equal to the set value, both changeover switches 52 and 53 are immediately switched and connected to the piezoelectric actuator 51-4 (not shown).
When the incoming signal is smaller or larger than the set value, a voltage adapted to the difference is sent from the controller 54 to the piezoelectric actuator 21 such as the piezoelectric actuator 51-3 through the current limiting resistor 33.

The distortion amount of the piezoelectric actuator 21 changes according to the input voltage, and the change is fed back from the physical quantity detection sensor 23 to the controller 54. In this way, when the position signal of the physical quantity detection sensor 23 and the set value match and the electricity is stored in the capacitor 31 (see FIG. 2), the changeover switches 52 and 53 are connected to the piezoelectric actuator 51-4 (not shown). ) Is switched to. Similarly, the piezoelectric actuators 51 and the like are switched and controlled in the same manner.

In this embodiment, each of the piezoelectric actuators 51 and the like is provided with the physical quantity detection sensor 23. However, the physical quantity detection sensor 23 is made one and the changeover switch 52 is eliminated, and when the changeover switch 53 is changed, it is synchronized with this. Piezoelectric actuator 21 such as switched piezoelectric actuators 51
A physical quantity detecting sensor 23 may be guided to the vicinity of the above by a rail or the like (not shown) so as to be carried to a corresponding point of each piezoelectric actuator 21.

[Effects of the Invention] As described above, the piezoelectric actuator control circuit according to the present invention has conventionally been thought to require one power source for each piezoelectric actuator, but an inexpensive capacitor is connected in parallel to the piezoelectric actuator. As a result, a large number of piezoelectric actuators are driven by a small number of power sources, which enables a significant price reduction and space saving.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a principle diagram of the present invention, FIG. 3 is a sectional view when a piezoelectric actuator is attached to a T die, and FIG. 4 is an open loop of the piezoelectric actuator. FIG. 5, FIG. 5 and a basic view of a closed loop of a piezoelectric actuator, FIGS. 6 and 7 show a conventional example in which a lip adjustment is a bolt, and FIG. 6 is a perspective view.
FIG. 8 is a cross-sectional view, FIG. 8 is a cross-sectional view of a conventional example using a heat bolt for lip adjustment, and FIG. 9 is a block diagram of feedback control in a controller. 21 …… Piezoelectric actuator, 23 …… Physical quantity detection sensor,
31 …… Condenser, 33 …… Current limiting resistor, 51 …… Voltage actuator, 52,53 …… Changeover switch, 54 …… Controller.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-60-102778 (JP, A) JP-A-61-153025 (JP, A)

Claims (4)

[Claims] 1. A plurality of piezoelectric actuators, respective capacitors connected in parallel with each of the plurality of piezoelectric actuators, to which the same voltage is applied, and a driven body driven by each of the plurality of piezoelectric actuators. Each displacement sensor that detects a displacement amount, one controller that outputs a DC voltage applied to one piezoelectric actuator corresponding to a signal input from one of the displacement sensors, the controller, and the plurality of controllers. A piezoelectric actuator control circuit, comprising: switching means for sequentially connecting one of the piezoelectric actuators and a corresponding displacement sensor while switching the piezoelectric actuators. 2. The piezoelectric actuator control circuit according to claim 1, wherein the switching means is a mechanical scanner. 3. The scanner according to claim 1, wherein the switching means is a scanner including an analog switch.
2. A piezoelectric actuator control circuit according to item. 4. A current limiting resistor is provided in at least one of a positive line and a negative line of an output line for applying a voltage from a controller to a piezoelectric actuator. Piezoelectric actuator control circuit.