JPH0568195B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric motor driven by electromechanical energy conversion using piezoelectric or electrostrictive effects.

Conventionally, the most common method for converting this type of electrical energy into mechanical energy for rotational driving is the application of electromagnetic force, and it is well known that various motors have been put into practical use. however,
This uses electromagnetic force as its power source, and utilizes the magnetic force that acts between the magnetic fields generated by the current flowing through the windings, and between the magnetic field generated by the current and the magnetic field of the permanent magnet. This is essentially accompanied by Joule heat generated, hysteresis loss during magnetization of the field, or eddy current loss. Furthermore, due to its structure and principle, it tends to generate electrical and magnetic noise, and therefore its applications are limited.

By the way, in recent years, motors based on a new principle using ultrasonic vibrators as a driving source have been considered.
Compared to the structure using electromagnetic force, this has extremely advantageous advantages in that it has less energy loss in principle, is lighter in weight, and does not generate noise.

However, it requires a dedicated drive power source for the motor with a frequency of several tens of kHz and a different phase, and this power supply device has become a roadblock to downsizing the entire device.

In view of these points, the present invention is configured to rotate a rotating body using electrostrictive and piezoelectric effects, and is configured to use a three-phase power source when driving the electrostrictive and piezoelectric elements. The main objective is to propose this type of motor with low energy loss and low noise.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing an example of a laminated piezo-electrostrictive displacement element serving as a rotational drive source. Reference numeral 1 indicates a rectangular plate made of piezoelectric ceramics or electrostrictive ceramics, and a plurality of rectangular plates 1 made of piezoelectric ceramics or electrostrictive ceramics are laminated, and electrodes 2 are placed between each plate 1, 1, 1...
and connection 3. It is preferable to use lead zirconate titanate porcelain for piezoelectric ceramics, and Pb for electrostrictive ceramics.
(Mg _{1/2 Nb 1/2} ) _{O 3} based porcelain is preferably used.

In this case, if piezoelectric ceramics are used, by applying a voltage V between the terminals 3a and 3b, each piezoelectric ceramic plate connected in parallel will elongate in the thickness direction. This growth
dl is expressed by the following formula.

dl=t・_d33V /t= _d33V ...(1) (however, _d33 : piezoelectric constant of the material) In this way, the elongation of each piezoelectric ceramic plate 1 mechanically connected in series is added. Therefore, when the number of laminated layers is n, the overall elongation Δl is given by Δl=nd ₃₃ V (2).

Note that when the laminated displacement element is constructed of piezoelectric ceramics, it is necessary to use a direct current bias voltage in order to prevent deterioration of polarization usually caused by reverse voltage.

Furthermore, when electrostrictive ceramics are used, as shown in Fig. 2, by applying an alternating current voltage V between terminals 3a and 3b, each electrostrictive ceramic plate connected in parallel will elongate in the thickness direction. It turns out. This elongation dl is expressed by the following formula.

dl = t・P ₃ (V/t) ² = P ₃ V ² /t (where P ₃ is the electrostrictive constant of the material, t is the thickness of the material) Therefore, the overall elongation Δl is the sum of the individual parts. Therefore, Δl=ndl=nP ₃ ·V ² /t. Incidentally, FIG. 3 shows a change curve of the strain So depending on the applied voltage shown in FIG. 2.

When an electrostrictive element is used, it does not have residual polarization, so it stretches in proportion to the square of the applied electric field, and there is no deterioration in performance even with AC drive.
Since the electric field shows elongation even in the opposite direction, as shown in Fig. 4, the length of the strain So changes at a period of 1/2 with respect to the AC electric field Ei.

When using an electrostrictive element, it expands and contracts when an alternating current voltage is applied between its terminals, but if the voltage value exceeds a certain percentage compared to the coercive electric field value of the material. , by applying a voltage in the opposite direction to the polarization during a half-cycle of AC, the polarization decreases rapidly and performance deteriorates. Therefore, normally, a constant DC bias voltage is always applied in the forward direction, and a reverse voltage is not applied to the piezoelectric ceramic.

FIG. 5 shows a schematic diagram of the motor of the present invention.
Numerals 11, 12, and 13 indicate laminated displacement elements, three of which are arranged radially at an interval of 120°, one of which is connected to the fixed shaft 1.
It is fixed at 4. The other end is attached to the inner peripheral surface of the ring body 15 via the elastic body 6.
However, the number of laminated displacement elements can be a multiple of three. Reference numeral 16 indicates a cylindrical rotating body that is in contact with the ring body 15 and transmits rotational force.

FIG. 6 is a diagram showing another embodiment of the motor of the present invention. In this example, the outer ends of three piezoelectric or electrostrictive ceramics 11, 12, 13 are fixed, and the rotating ring 17 is held at the inner end. Reference numeral 18 indicates a cylindrical rotating body that contacts the ring body 17 and transmits rotational force. Therefore, it is clear that the same effect as the example in FIG. 5 can be obtained in this example as well.

Next, with reference to FIG. 7, the temporal change in expansion and contraction of the piezoelectric/electrostrictive ceramic laminated displacement element in response to an applied alternating current electric field, that is, the principle of operation will be described.

First, due to a constant pressure applied to the three sets of elastic bodies sandwiched between the laminated displacement element and the ring body, they are compressed in advance by a value of Δξ, and if this spring constant is K, then KΔξ This means that the ring is supported from three directions by the force of .

Next, as shown in Figure 8, to explain the case where each displacement element is driven by Y-connecting three terminals of different phases of a three-phase AC power supply, the extension of the displacement element is dli, and the direction of the expansion/contraction axis is When the displacement of the ring body is Δli, the force with which the element presses the ring body in the axial direction is given by the following equation.

Fi=K(Δξ+dli−Δli) (where i=1, 2, 3,..., Δξ>｜dli｜,
Δli) Next, considering the coordinates where the expansion and contraction axis of the displacement element is the Y axis and the direction perpendicular to it is the X axis, for displacement elements 11, 12, and 13, V ₁ =V ₀ sinωt V ₂ = A sine curve such as V ₀ sin (ωt-2/3π) V ₃ =V ₀ sin (ωt-4/3π) is obtained. Note that the direction of each expansion and contraction toward the central axis is defined as the positive direction.

The center of the toroid is, when no voltage is applied,
The coordinates are at the center point (0, 0), but in the state of motion they are at any point (x, y), and in this state the directions of the three forces F ₁ , F ₂ , F ₃ remain unchanged. , as shown in FIG. 9, the absolute values of each force are equal.

That is, |F→ ₁ |=|F→ ₂ |=|F→ ₃ |.

The amount of movement of the center point is determined by the directions of the three forces Δl ₁ , Δl ₂ ,
It can be decomposed into Δl ₃ , and each vector quantity is determined from the displacement amount of the displacement element and the balance of the three forces. That is, the three forces |F→ ₁ |, |F→ ₂ |, |F→ ₃
｜
is |F→ ₁ |=F ₁ =K[Δξ+nd ₃₃ V ₀ sinωt−(−y)] |F→ ₂ |=F ₂ =K[Δξ+nd ₃₃ V ₀ sin(ωt−2/3π)
−(√3/2x+y/2)] |F→ ₃ |=F ₃ =K[Δξ+nd ₃₃ V ₀ sin(ωt−4/3π)
−(√3/2x+y/2)] |F→ ₁ |=|F→ ₂ |, nd ₃₃ V ₀ (3/2sinωt+√3/2cosωt)=−√3/2x−
3/2y…(6) |F→ ₁ |=|F→|, nd ₃₃ V ₀ (3/2sinωt−√3/2cosωt)=√3/2x−3
/2y...(7) From (6) and (7), x=-nd ₃₃ V ₀ cosωt y=-nd ₃₃ V ₀ sinωt x ² = (nd ₃₃ V ₀ ) ² cos ² ωt y ² = (nd ₃₃ V ₀ ) ² sin ² ωt ∴x ² +y ² = (nd ₃₃ V ₀ ) ² cos ² ωt + (nd ₃₃ V ₀ ) ² sinωt = (nd ₃₃ V ₀ ) ² (cos ² ωt＋sin ² ωt) ∴x ² +y ² = (nd ₃₃ V ₀ ) ² …(9) In other words, the center point of the ring body will draw a circular orbit with radius nd ₃₃ V ₀ . Also, the rotation speed at this time is equal to the power supply frequency, and in the case of 50Hz, 50 turns/
seconds.

Therefore, as shown in Fig. 7, the central axis inscribed in the ring body is rubbed around the ring body in the direction of rotation as the center point of the ring body rotates.
This will generate rotational torque. Incidentally, FIG. 8 shows the phase of the power supply for each state.

Next, a case will be described in which the laminated displacement element is constructed of electrostrictive ceramics. The three forces supporting the ring from three directions |F→ ₁ |, |F→ ₂ |, |F→| are |F→ ₁ |K[Δξ+nP ₃ /tV ₀ ² sin ₂ ωt−(−y)] |F→ ₂ |=K[Δξ+nP ₃ /tV ₀ ² sin ² (ωt−2/3π
)−(√3/2x+y/2)] |F→|=K]Δξ+nP ₃ /tV ₀ sin ² (ωt−4/3π)
−(−√3/2x+y/2)] From F ₁ = F ₂ , nP ₃ V ₀ ² /t(−3cos2ωt+√3sin2ωt)=2√3x−6
y…(11) Due to F ₁ = F ₃ , nP ₃ V ₀ ² /t(−3cos2ωt−√3sin2ωt)=−2√3x
−6y…(12) From (11) and (12), x=nP ₃ V ₀ ² /2tsin2ωt y=nP ₃ V ₀ ² /2tcos2ωt x ² +y ² =nP ₃ V ₀ ² /2t(sin ² 2ωt＋cos ² 2ωt) x ² +y ² = (nP ₃ V ₀ ² /2t) In other words, the center point of the ring will draw a circular orbit with a radius of nP ₃ V ₀ ² /2t. Further, the rotational speed at this time is twice the power supply frequency. In any case, as shown in FIGS. 5 and 6, the driving force can be obtained from the inscribed ring body in the same way as in the case of a structure made of piezoelectric ceramics. However, in the case of electrostrictive ceramics, the disadvantage of deterioration of polarization due to reverse voltage does not occur in principle, and therefore it can be driven without a bias voltage.

As described above, according to the present invention, at least three laminated displacement elements each having a plurality of laminated piezoelectric ceramic or electrostrictive ceramic plates are arranged so that their axial directions form an angle of 120 degrees, and one end of the laminated displacement element is The ring body is supported by being tightly attached to the inner circumference of the ring body via an elastic body and the other end is fixed, or one end of the laminated displacement element is fixed and the other end is attached to the outer circumference of the ring body via an elastic body. A rotating body is provided that is in close contact with the surface and transmits rotational force in contact with the ring body, and the laminated displacement element is configured to be driven by a three-phase AC power source, which is more effective than the conventional method of generating a magnetic field. Therefore, it is possible to provide a motor of this type that has less joule heat, hysteresis loss, eddy current loss, and magnetic noise. Furthermore, there is no need to provide a dedicated power supply which is required when an ultrasonic transducer is used as a drive source, and the overall effect is that it is small, lightweight, and can easily utilize a commercial power source.

Therefore, the present invention can be applied to a wide range of fields, and is extremely suitable for application to, for example, drive motors for precision machines, optical measuring instruments, and laser-applied equipment.

[Brief explanation of the drawing]

Figure 1 is a schematic perspective view showing an example of a laminated displacement element, Figure 2 is a waveform diagram of applied voltage, Figure 3 is a diagram of changes in strain when piezoelectric ceramics are used, and Figure 4 is a diagram of changes in strain when piezoelectric ceramics are used.
The figure is a change in strain when electrostrictive ceramics are used, Figures 5 and 6 are schematic sectional views showing one embodiment and another embodiment of the present invention, and Figures 7 and 8.
9 and 9 are operation diagrams for explaining the operation of the present invention, respectively. 11, 12, 13... Laminated displacement element, 14... Fixed shaft, 15, 17... Annular body, 16... Cylindrical rotating body, 18
...Cylindrical rotating body.

Claims (1)

[Claims] 1. At least three laminated displacement elements each made of a plurality of laminated piezoelectric ceramic plates are arranged so that their axial directions form an angle of 120°, and one end of the laminated displacement element is attached to the inner periphery of an annular body. The ring body is supported by being in close contact with the ring body through the body and the other end is fixed, or the ring body is supported by fixing one end of the laminated displacement element and having the other end in close contact with the outer peripheral surface of the ring body through an elastic body. 1. A piezoelectric motor, comprising: a rotating body that is in contact with a body and transmits rotational force; and the laminated displacement element is driven by a three-phase AC power source. 2 At least three laminated displacement elements each made of a plurality of laminated electrostrictive ceramic plates are arranged so that their axial directions form an angle of 120°, and one end of the laminated displacement element is tightly attached to the inner periphery of the ring body via an elastic body. and the other end is fixed to support the ring body, or one end of the laminated displacement element is fixed and the other end is tightly attached to the outer peripheral surface of the ring body via an elastic body, and rotates in contact with the ring body. 1. An electrostrictive motor, comprising a rotating body for transmitting force, and configured to drive the laminated displacement element with a three-phase AC power source.