JP2631790B2 - Piezoelectric actuator and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure and a driving method of a piezoelectric actuator, and more particularly to a digital driving type piezoelectric actuator in which nonlinearity of a conventional piezoelectric actuator is improved and a driving method thereof.

[0002]

2. Description of the Related Art A piezoelectric ceramic actuator has the advantages of being smaller in size, generating less heat, and having a faster response speed than an electromagnetic actuator. In particular, a multilayer ceramic piezoelectric actuator in which a piezoelectric ceramic plate and an electrode are laminated has been proposed for use at a voltage level that is easy to handle, and is becoming one of the basic elements in mechatronics.

However, the voltage-displacement characteristic of the piezoelectric ceramic material is non-linear, and when the piezoelectric ceramic material is driven with a variable voltage, the same amount of displacement cannot be determined by ascending and descending. Therefore, when this actuator is used as a micro-displacement element, it is essential to use a servo mechanism together, which impairs operability and hinders the spread of piezoelectric actuators.

In general, in a device in which the effects of individual elements are simply integrated and output as the entire device, the elements can be coded and operated as a D / A converter. Therefore, also in the multilayer ceramic piezoelectric actuator, digital driving can be performed by weighting and encoding the number of piezoelectric ceramic plates to be driven. In such a method, the hysteresis and nonlinearity peculiar to the piezoelectric ceramic are improved, so that the piezoelectric ceramic can be applied as a displacement control device without a servo mechanism, and there is an advantage that a digital circuit recently used in various fields can be used.

[0005] A multilayer ceramic piezoelectric actuator having a 3-bit or 4-bit configuration has already been proposed, including Japanese Patent Application Laid-Open No. Sho 62-73787, and the basic characteristics of the operation have been confirmed.

[0006]

With respect to the number of bits of a digital drive type multilayer ceramic piezoelectric actuator,
By increasing the number of stacked layers, at least in principle, any number of bits can be increased. However, the number of laminated ceramic piezoelectric actuators is limited by the manufacturing technology, and the current technology is limited to about 6 bits, and it is difficult to obtain a high-bit piezoelectric actuator that can be used practically. is there.

The present invention is to solve such a problem and to provide a piezoelectric actuator capable of increasing the number of bits and a driving method thereof.

[0008]

According to the present invention, the number of bits of a piezoelectric ceramic plate to be laminated is encoded into several bits by the number of driving the piezoelectric ceramic plates, and these units are weighted by a power supply voltage using a plurality of units and driven. It is intended to solve the problem.

That is, in a piezoelectric actuator in which a plurality of piezoelectric elements which are displaced in accordance with an applied voltage are connected in series as a plurality of actuator units having different displacement amounts in the same displacement direction, a plurality of piezoelectric elements having different minimum displacement amounts are provided. Two or more actuator units, and the displacement amount of a portion of one of the actuator units that generates the smallest displacement amount is determined by the smallest displacement amount of the next largest displacement unit. The displacement amount of the generated portion is 1/2 ⁿ , and each actuator unit generates the minimum displacement amount, and 2 ¹ , 2 ² ... 2 ⁿ (n is a positive integer) times that Is characterized by being constituted by a portion that generates the amount of displacement.

Also, a plurality of actuator units having different minimum displacement amounts are formed by connecting a plurality of piezoelectric elements which are displaced in accordance with an applied voltage as a plurality of actuator units having different displacement amounts in series in the same displacement direction. In the method of driving two or more sets of piezoelectric actuators, each actuator unit generates a minimum displacement amount, and 2 ¹ , 2 ² ... 2 ⁿ (n is a positive integer) times A predetermined voltage is applied through a drive circuit that selectively turns on and off a portion that generates a displacement amount, and a voltage that is applied to a portion of one of the actuator units that generates a minimum displacement amount. In contrast, the voltage applied to the portion of the actuator unit having the next largest displacement amount that generates the smallest displacement amount is 1/2 ⁿ
It is characterized in that it is set so that

[0011]

For example, a multilayer ceramic actuator in which individual driving elements, which are the minimum units, are coded in 4 bits is used.
By displacing the set in the same direction and changing the displacement amount according to the power supply voltage, a digital piezoelectric actuator equivalent to 8 bits in hexadecimal class can be obtained.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing a laminated structure and wiring of a piezoelectric actuator according to the present invention. This piezoelectric actuator is composed of two units 10 and 11, each of which has a structure of a 4-bit digital actuator coded by the number of layers. That is, each of the units 11 and 12 has two, four, eight
Every 16 sheets are electrically connected in parallel, and a total of 30 piezoelectric ceramic plates are used.

The number of driving units is controlled by the switching circuits 12 and 13 in each unit, and a predetermined voltage is applied to a predetermined number of piezoelectric ceramic plates. A voltage is applied to the lower bit unit 11 so that the displacement per sheet is 1/16 that of the upper bit unit 10.

FIG. 2 is a perspective view showing an assembly structure of an example of the piezoelectric actuator according to the present invention. Sixty PZT-based piezoelectric ceramic plates 16 each having a side of 22 mm and a thickness of 0.2 mm, which are polarized in the thickness direction, were laminated with a phosphor bronze plate 17 having a thickness of 0.1 mm therebetween. The two units were insulated by an alumina porcelain plate of the same size as the piezoelectric ceramic plate 16. These are fixed by a pair of steel base plates 18 provided with a guide rod for keeping the displacement direction always in the stacking direction (thickness direction).
Fastened by bolts.

When the voltage applied to the upper unit 10 is 180 V, the voltage applied to the lower unit 11 is considerably larger than 1/16 due to the non-linearity of the characteristics of the piezoelectric ceramic, and 16 V is required. . The switching of these two DC power supplies may be a commonly used switching circuit. In this example, the DC power supply was connected to a personal computer through an interface, and switching was controlled by software.

FIG. 3 shows the result of measuring the displacement amount of the above-mentioned piezoelectric actuator with a minute displacement meter. Figure 3 for comparison
FIG. 3A shows an example in which the amount of displacement is controlled by a conventional analog-type applied voltage, and FIG. 3B shows an example according to the present invention. The reciprocating motion was measured over 255 seconds.

While a remarkable hysteresis phenomenon appears in FIG. 3A, the piezoelectric actuator according to the present invention has almost no hysteresis and very good linearity as shown in FIG. 3B. Met. Although only the outward route is shown in the figure, the return route also overlaps the outward route. In addition, since quantization is performed to 256 levels of 8 bits, a stepwise change due to quantization as in the related art is almost indistinguishable.

Since the input signal of the digital piezoelectric actuator device is a digital signal, control by a computer is extremely easy. As shown in FIG. 4, a sine wave can be written by a piezoelectric actuator according to the present invention by a simple program.

In the above example, a 4-bit 2-unit configuration is shown. However, a 4-bit 3-unit or 6-bit 2-unit configuration can realize a high-bit piezoelectric actuator by combining two or more units, such as 12 bits. it can. Further, the present invention can be applied not only to piezoelectric ceramics but also to a case where an actuator is made of an electrostrictive material or an antiferroelectric material.

[0021]

According to the present invention, a digital piezoelectric actuator having a higher bit number can be obtained, and a piezoelectric actuator which can be linearly controlled in displacement without being affected by hysteresis can be realized.

Further, by increasing the number of bits, a low-cost piezoelectric actuator capable of arbitrarily controlling the amount of displacement by digital driving can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention.

FIG. 2 is a perspective view showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a characteristic of a displacement amount.

FIG. 4 is an explanatory diagram showing another characteristic of a displacement amount.

[Explanation of symbols]

 10, 11: Unit 12, 13: Switching circuit

Claims (4)

(57) [Claims] 1. A piezoelectric actuator comprising a plurality of piezoelectric elements displaced in accordance with an applied voltage and connected in series as a plurality of actuator units having different displacement amounts in the same displacement direction, wherein a plurality of piezoelectric elements having different minimum displacement amounts are provided. Of two or more actuator units, of which
The minimum displacement of one actuator unit of
Next to the displacement of the generated part, the magnitude of the displacement
Generates the minimum displacement of the actuator unit
The displacement of each part is 1/2 ^n.
The eta unit generates the minimum displacement and
¹ , 2 ² ... 2 ⁿ (n is a positive integer) times displacement
A piezoelectric actuator characterized by comprising: 2. A plurality of piezoelectric elements displaced according to an applied voltage.
Actuators with multiple actuator units with different displacements.
Pressure formed by connecting in series with uniform displacement directions as a knit
In electric actuators, multiple
Two sets of actuator unitsOne of us
Generates the minimum displacement of one actuator unit
Of the other actuator unit
The displacement amount of the part that generates the minimum displacement amount is 1 /
2 ⁿ And each actuator unit has a minimum
The part that generates the amount of displacement and part 2 ¹ , 2 ^Two ... 2
ⁿ (N is a positive integer)Composed
A piezoelectric actuator characterized in that: 3. A plurality of actuator units having different minimum displacement amounts, which are formed by connecting a plurality of piezoelectric elements displaced in accordance with an applied voltage in series as a plurality of actuator units having different displacement amounts in the same displacement direction. In the method of driving two or more sets of piezoelectric actuators, each actuator unit generates a minimum displacement
2 ¹ , 2 ² ... 2 ⁿ (n is a positive integer)
Selectively turn on and off the part that generates the number of displacements
A predetermined voltage is applied through a driving circuit that operates,
Minimum change in one of the actuator units
The voltage applied to the part generating the potential
Of the actuator units with large displacement
Voltage applied to the portion for generating displacement amount I and 1/2 ⁿ
A driving method for a piezoelectric actuator, characterized in that the driving method is set as follows. 4. A plurality of actuator units having different minimum displacement amounts, which are formed by connecting a plurality of piezoelectric elements displaced according to an applied voltage in series as a plurality of actuator units having different displacement amounts in the same displacement direction. In the method of driving two sets of piezoelectric actuators, each actuator unit generates a minimum displacement.
Part and its 2 ¹ , 2 ² ... 2 ⁿ (n is a positive integer) times
Selectively turn on and off the part that generates the amount of displacement
A predetermined voltage is applied through the drive circuit, and among them,
The minimum displacement of one of the actuator units
The voltage applied to the part where the
Mark the part of the eta unit that generates the minimum displacement
The driving method of a piezoelectric actuator voltage pressurization is characterized in that it is set to be 1/2 ^n.