The traditional AC servo motor characteristics soft, and its output characteristic is not a single value servo motor; stepper motor is generally open-loop control and can not accurately locate the motor itself, there are speed resonance region, pwm speed control system for position tracking performance is poor , frequency control is relatively simple but the accuracy is sometimes not enough, DC motor servo system for its excellent performance has been widely applied to the position servo system, but it also has disadvantages, such as structural complexity, low speed when the dead zone in contradiction, and Commutation brush will bring noise and maintenance issues.
Currently, the new permanent magnet AC servo motor developed rapidly, especially from the square wave to sine wave control controlled development, the system performance is better, it is wide speed range, especially in low-speed and superior performance.
For frequently used in radar systems DC Servo drive motor power amplifier section, antenna, light weight, slow speed, drive power is small, typically tens of watts, you can directly control the motor with a DC power supply. When the drive power requirement kW or kW or more in the past, the choice driven program, that amplify DC motor armature current is an important part of the design of the servo system. Currently used in high-power DC power supply has more: transistor amplifier, power amplifier and motor thyristor amplifier and so on. For kilowatt transistor amplifier using less. SCR technology in the last century, 60 to the early 70s rapid development and wide application, but then to various reasons, such as reliability, many products abandoned thyristor control. The current integrated drive modules are generally manufactured for the transistor or thyristor. Motor amplifier is conventional DC servo motor amplifier device, because of its control is simple, durable, current new models are still used on the radar products. Here mainly to zoom motor, for example, and AC servo motor to compare their advantages and disadvantages.
Often referred to zoom motor amplifier, is generally used AC asynchronous induction motor drag tandem two DC generators, in order to achieve DC control. Two control windings, each of the input impedance of a few thousand Ohms, if the input impedance in series with about 10 kilohms, the servo motors are generally symmetrical balance of the complementary input, when the system input is not zero when breaking the equilibrium, the zoom motor has output signal. When the input current of more than a dozen to tens of milliamperes above its output DC voltage up to 100v and a few to tens of Ann Ann current, directly connected to the DC servo motor armature winding. Its main drawback is the volume weight, non-linearity, in particular, is not very good in the vicinity of zero, which requires high system requires careful handling.
The AC servo motors are equipped with a special drive, which in size and weight is far less than the same power zoom motor, it relies on the internal transistor or thyristor switch circuit, according to the servo motor photoelectric encoder or Hall devices judgment position of the rotor at the time, determines how the drive motor a, b, c three respective output state, so its efficiency and smoothness are good. So do not control the zoom motor requires specialized amplifier circuit. These motors are permanent magnet generally, the drive generated by a, b, c-phase current control motor rotation changes, so called AC servo motor; drive the input of the control signal may be a pulse train, a DC voltage can be signal (typically ± 10v), so there will be referred to as the DC brushless motor.
The two motors made simple experiment comparison: as long as the system was originally a DC error signal is directly connected to AC servo drive analog control input with AC servo motor and its drive to replace the original differential amplifier, amplifier and DC motors servo motor, and the control section and the same angular element etc., a simple comparison of the output characteristics of the two solutions.