What Is an Electrostatic Motor?

Is an energy conversion device using static electricity as an energy source. It has the advantages of simple structure and high no-load speed. With MEMS ( The development of micro-electromechanical systems ( MEMS ) has attracted more and more attention as a key component of MEMS . At present, electrostatic motors have been applied in some situations where power output is basically not required.

With the in-depth development of MEMS (Micro Electro Me-chanical System, slightly referred to as MEMS, meaning micro-electro-mechanical system), the development of electrostatic motors as key components in MEMS has attracted more and more attention. An electrostatic motor is an energy conversion device that uses static electricity as an energy source. It has the advantages of simple structure and high no-load speed, but also has the disadvantages of low power and difficult starting. At present, developed countries are racing to develop electrostatic motors and have made some progress. In view of the importance of MEMS in promoting the development of the national economy and military technology, China's National Defense Science and Technology Commission has included MEMS in the "Ninth Five-Year" national defense pre-research project. At present, in the field of aerospace satellites and medical equipment, attempts have been made to replace traditional electromagnetic motors with electrostatic motors.

There are two operating principles of electrostatic motors: one is to use the principle of dielectric relaxation, and the other is to use the principle of variable capacitance.

1. Electrostatic motors using the principle of dielectric relaxation are generally referred to as electrostatic induction motors or asynchronous dielectric induction motors. The specific principle is as follows: If a dielectric rotor is placed in a rotating electric field, charges will be induced on the surface of the rotor. Due to dielectric relaxation, these charges lag behind the rotating electric field. The deviation between these induced charges and the rotating electric field The displacement produces a torque acting on the rotor. If the rotor is composed of multiple media, different dielectric relaxation processes are superimposed and function at different frequencies. Because the angular velocity of the rotor is smaller than the angular velocity of the rotating electric field when the motor is running, this type of motor is called "asynchronous". The torque and efficiency of the motor depend on the ratio of the angular velocity of the rotor to the angular velocity of the rotating electric field. Figure 1 shows a schematic diagram of the structure of an asynchronous dielectric induction electrostatic motor.

At present, the research on variable capacitance electrostatic motors is most widespread in various countries. The variable capacitance electrostatic motors are divided into linear and rotary types.

The linear motor has a simple structure and is easy to adopt a variety of manufacturing methods and materials.

The electrostatic motor has a long history of development:

In 1742, that is, more than 100 years before the birth of electromagnetic motors, Andrew Gordan invented the electric bell and electro-elastic car using the principle of same-phase charge repulsion and different-phase charge phase attraction. This can be seen as the earliest example of using electrostatic drive .

In 1889, Karl Zipernowsky invented the capacitive electrostatic motor.

In 1893, Arno used the dielectric relaxation characteristics of insulating materials to manufacture a 3800V, 50Hz voltage-driven asynchronous induction electrostatic motor.

In 1969, B.Boilée developed several variable-capacitance electrostatic motors, one of which was machined with a gap of 0.1mm between stator and rotor, with 100 electrodes, the working voltage dropped to 200V, and the output power was 600W. The results of this research have drawn attention to electrostatic motors.

For an electromagnetic motor, its structure is relatively complicated. When the size is small, the magnetic field density is limited by the surface resistance of the conductor and the temperature rise caused by the heating of the coil. The performance of magnetic materials and the leakage flux will further reduce the energy Density, so the electromagnetic motor does not have the advantages of the traditional size when miniaturized. But for electrostatic motors, it has the following advantages:

First, structurally speaking, the electrostatic motor has a simple structure. The strength of the electric field generated on the electrode surface has nothing to do with the thickness of the electrode. The cross-sectional area of the electrode and wiring can be made very small.

Second, the electric field strength of an electrostatic motor is limited only by the properties of the insulating material. Reducing the size does not affect the electric field strength. The force generated is proportional to the surface area. Generally, the smaller the size of the insulating material, the stronger the performance. According to Paschen's law, the smaller the gap, the sharper the electric field strength generated by air sparks. For example, a silicon oxide film has an insulation strength of several hundred kV / mm.

Therefore, the electric field energy density of a miniaturized electrostatic motor can be compared with the magnetic field energy density of an electromagnetic motor.

Third, compared with electromagnetic motors, electrostatic motors have higher energy conversion efficiency.

Based on these characteristics of electrostatic motors,

At present, electrostatic motors have been applied in some places where power output is basically not required, such as optical and magnetic fields. The electrostatic motor using surface micromachining researched by the Toyota Central Research Institute in Japan was used to drive a micromechanical optical chopper, and a corresponding tensile force of 0.4 N was generated by applying a 100V voltage between the motor electrodes, thereby shifting the grid 2. 5m. With the continuous development of micro-electro-mechanical systems ( MEMS ) and the in-depth study of basic theories in the micro-field, as the power of micro-mechanics, electrostatic motors will exert their advantages and have broad application prospects in various delicate and complex micro-environments. . For example, in the medical field, electrostatic motors can be used in ultra-small machines that integrate electron transmitters, automatic recorders and computers. Such machines can enter the human stomach, blood vessels; in the aerospace field, electrostatic motors can be used in video Elephant equipment enters satellites and aerospace aircraft to check for faulty machines; in the military field, ultra-electrostatic motors can be used as power components of miniature aerial robots, which are equipped with infrared sensors and can complete prescribed reconnaissance tasks.

At present, the research and development of electrostatic motors are still in the exploration stage, and further research can be carried out in the following aspects:

(1) As the size of an electrostatic motor becomes smaller and smaller, the problem of friction becomes the biggest factor that restricts the life and performance of an electrostatic motor (currently, the life of an electrostatic motor is generally calculated in hours), and the friction force also directly affects Efficiency of electrostatic motors. For ultra-miniature electrostatic motors, the friction force is mainly due to the interaction of the surface and is no longer the load pressure. Traditional macroscopic friction theory and research methods are no longer applicable. It is necessary to study the micro-friction theory to obtain the boundary conditions without friction and wear under the conditions of small mass and light pressure.

(2) At present, the driving torque of an electrostatic motor is still relatively small, which limits its application range. In order to realize the long-distance heavy load movement of the electrostatic motor, new manufacturing materials and new structures are needed. At the same time, the transmission mechanism between the electrostatic motor and the driven object must be studied.

(3) Because the size of the electrostatic motor is relatively small, especially because its structure is mostly flat (radial diameter is greater than the axial length), it is necessary to analyze the three-dimensional field of the electrostatic motor. Generally, the finite element method (FEM) is used. ) Or boundary element method (BEM). Through the calculation of the three-dimensional electrostatic field, an analytical model (also called lumped parameter model) is established, which combines the optimization of the voltage excitation method and the optimization of the external dimensions to realize the automation of electrostatic motor design.