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Магистр ДонНТУ Васютинский Андрей Васильевич

Vasutinskyy Andrey

Department: Electrotechnical

Chaire: Electrical Drive and Automatization of Production Facilities

Subject of master's thesis: Research of microprocessor- based positioning servo-drive

Research manager: Tolochko Olga

Technical consultant: Rozkarayka Pavel

Introduction

Progress in the field of electronics and materials which are used in the electrical engineer have changed a situation in technics of a drive. By this moment in servotechnics engines of a direct current with constant magnets were used as a whole.

The main lack of engines of an alternating current of comparison with engines of a direct current is limitation of an opportunity of regulation of speed. Last achievements in the field of electronics, it is especial in microcontrollers, allow to compensate this lack by use of modern control facilities.

Presently there is a displacement of accents in приводных systems from engines of a direct current to engines of an alternating current. The tendency of transition to synchronous engines of an alternating current especially obviously in servos. They were almost always carried out with use of electric drives of a direct current.

New constant magnets which are produced from alloys neodymium-iron-boron and samarium-cobalt due to the power intensity, can considerably improve characteristics of the engine. Thus are simultaneously reduced weight - dimensional parameters of electric machines. In a result dynamic characteristics of an occasion improve and his dimensions are reduced.

Definition of the servo-driver

In modern drive technics in the majority cases it is demanded much to:

1) Errors of positioning;

2) Errors of stabilization of speed;

3) A wide range of regulation;

4) Stabilization of the moment of a revolution;

5) Reloading ability;

6) To high dynamics

Requirements to dynamics, i.e. behaviour in time, productivity of the machine will consist of processes of processing which are accelerated, to increase in operation cycles and connected with it. High accuracy very much frequently defines opportunities of use of systems of the electric drive in new technologies. To these requirements should answer modern high dynamics systems of an occasion.

The servo-driver is a system of a drive which provides dynamic, precision processes in a wide range of regulation of speed and provides their good repeatability.

The mathematical description of a servomotor

Let's enter orthogonal system of coordinates d, q which rotates with any speed concerning motionless. One axis it is determined as valid (d), and another - as imaginary (q). Communication between systems of coordinates will be defined by the certain corner. Communication between mobile (d, q) and motionless (alfa, beta) systems of coordinates looks like:

At transition to mobile coordinates the equation of electric balance will be transformed to a kind:

where:

Displaying vectors of electromagnetic variables of a condition on axes d and q, we receive the scalar description of the machine. Thus the axis d is united with an axis of a stream of a rotor:

On last system of coordinates we make model of a servomotor in mobile system of coordinates which is represented on fig. 1.

Fig. 1 - Mathematical model of a servomotor

Advantages of the servo-driver:
1. Smoothness and accuracy of movings are accessible even on low speeds. Resolution can get out the user depending on a decided problem.
2. Noiselessness of work.
3. Reliability and non-failure operation. I.e. an opportunity to use it in responsible devices.
4. Ease of installation of a design.

Lacks of the servo-driver: :
1. High cost.
2. Complexity of adjustment{option} which sometimes makes application of the servo-driver unreasonable.

That is, servo-drivers on the basis of the synchronous electric motor (servomotor), now, are the most expedient for applying there where the drive with high accuracy and the big maximal speed is required. The engine of such drive has the built - in gauge of position of a shaft. The signal from the gauge moves on a servoamplifier. It essentially raises accuracy and dynamics of the servo-driver. For creation one or many coordinate systems of positioning are used the special controller of positioning.

Векторное управление

Fig. 2 - Vector management

Synchronous servomotors are three-phase synchronous electric motors with excitation from constant magnets and the gauge of position of a rotor. Distinctive feature of synchronous servomotors - high target capacity at any speed in a combination to the small sizes. Their basic advantage is very low moment of inertia of a rotor concerning the twisting moment. It allows to realize very high speed. Time of dispersal for nominal frequency of rotation for tens milliseconds and a reverser since full speed is achievable within the limits of one revolution of a shaft of the engine.

Servomotors can differ with the form, the sizes and a design - from big low-velocity direct driving rotary engines with the big twisting moment up to compact devices with a low-inertia rotor. It provides optimum dispersal and braking, engines without case, the linear engines creating the big traction force at huge accelerationі and speeds.


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