Piezoelectric motors. Encyclopedia of radio electronics and electrical engineering

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A piezoelectric motor (PD) is an electric motor in which the mechanical movement of the driven body (rotor or armature) is carried out due to the piezoelectric effect.

The first thing that attracts them is the absence of induction windings, usually made of copper or aluminum wire and a special type-setting core. The working element in them is piezoelectric ceramics.

It would seem that it is enough to excite the piezoelectric element with an alternating electrical voltage and, using known mechanical means, convert the oscillations of the piezoelectric element into the rotational movement of the working body. But, although this principle is simple, it is difficult to implement it for the frequencies and amplitudes of piezoelectric oscillations that are encountered in practice.

In one of the variants of PD, it is proposed to bend the piezoelectric element simultaneously in three planes using a three-phase electric field so that its end, moving forward, describes a circular trajectory (Fig. 1).

At the movable end there was a pin 1, which frictionally interacted with the rotor 2, causing it to rotate. This principle has not been applied in practice.

Step-by-step PDs have received greater practical application. In these engines (Fig. 2), a tuning fork or a cantilevered piezoelectric element transmits an oscillatory motion to the rod 2, which moves the rotor 3 by one tooth.

When the rod moves in the opposite direction, the pawl 4 fixes the position of the rotor 3. A simpler version of this PD is an engine (Fig. 3, a), consisting of a piezoelectric element 1, made in the form of a rectangular plate, which is pressed at one end by an external force against the surface of the rotor 2 When the piezoelectric element is electrically excited, this end, like an oar blade, moves along a closed path, periodically giving an impulse to the rotor. Its design is shown in more detail in Fig. 3b. A piezoelectric element 1 and bearings 2 are installed on the basis of stator 3. Rotor 4 is usually made of hard materials (steel, ceramics). The clamp element 7 can be made in the form of a flat steel spring, the end of which, through the elastic gasket 8, presses on the end of the piezoelectric element 2. To change the clamping force, an adjusting screw 9 is installed.

The rotation speed of the rotor in this system is determined by the maximum allowable displacement amplitude of the piezoelectric element or its overheating. When overheated above the Curie point, the piezoelectric properties are lost. For most industrial materials, the Curie temperature exceeds 250°C, so the maximum displacement amplitude is limited by the tensile strength of the material. For material TBK-3, the maximum permissible linear velocity Vl is 1,5 m/s. Taking into account the double strength margin, we will take Vl = 0,75 m/s. The rotation frequency of the PD rotor is n = 60Vl/πD (min-1). For D = 0,5 cm, n = 3000 min-1, for D = 5 cm, respectively, n = 300 min-1. Thus, by changing only the diameter of the PD rotor, it is possible to cover a wide range of frequencies of rotation of the PD shaft. Reducing the supply voltage makes it possible to reduce the rotational speed to 30 min-1 while maintaining a sufficiently high power on the shaft per unit mass.

An important characteristic of PD, which makes it possible to compare them with other electric motors, is the coefficient of performance (COP). Estimation of this parameter for PD is very difficult, since the efficiency depends on the PD design, pressure force and angle, contact angle, rotor material and wear-resistant gasket, and operating frequency.

For the above-described PD with an end-mounted piezoelectric element, the dependence of the efficiency on the moment on the shaft M (Fig. 4, a), on the clamping force was studied. (Fig. 4b) and on the excitation frequency f (Fig. 4c). The maximum efficiency depends on the material of the piezoelectric element, for example, for PKR-10 a record efficiency of 85% was obtained. Currently, there are more than 50 fundamentally different PD designs.

One of the most important advantages of PD is the ability to obtain very small movements of the rotor. For example, some PD samples with a rotation frequency of 0,2-6 rpm, when a single pulse is applied, give an angular displacement of the rotor 1/3000000 of the circumference, i.e. 0,4 arc seconds. In addition, PDs can be controlled directly from a computer. Due to the fact that the dimensions and weight of PDs are 3-5 times smaller than those of conventional electric motors, they can be used in video cameras, magnetic and laser disk drives, and in scientific research.

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