A servo motor is an engine that controls the operation of mechanical components in a servo system; it is a type of auxiliary motor with indirect speed control. Servo motors enable highly accurate speed and position control, converting voltage signals into torque and speed to drive the controlled object. The rotor speed of a servo motor is controlled by the input signal and can respond quickly. In automatic control systems, it is used as an actuator and possesses characteristics such as a small electromechanical time constant, high linearity, and low starting voltage. It can convert received electrical signals into angular displacement or angular velocity output on the motor shaft.
DC servo motors and AC servo motors
Servo motors are divided into two main categories: DC and AC. Their main characteristic is that they do not rotate when the signal voltage is zero, and their speed decreases uniformly as the torque increases.
A DC servo motor includes a stator, a rotor core, a motor shaft, a servo motor winding commutator, a servo motor winding, a tachometer motor winding, and a tachometer motor commutator. The rotor core is constructed by stacking and fixing silicon steel laminations onto the motor shaft.
The structure of an AC servo motor can be mainly divided into two parts: the stator and the rotor. The stator structure is basically the same as that of a rotary transformer, with two-phase windings spaced 90 degrees apart electrically in the stator core. One set is the excitation winding, and the other is the control winding. An AC servo motor is a two-phase AC motor.
Comparison of the advantages and disadvantages of the two
DC servo motors are divided into brushed and brushless motors. Brushed motors are low-cost, simple in structure, have high starting torque, wide speed range, and are easy to control. They require maintenance, but maintenance is convenient (replacing carbon brushes). They generate electromagnetic interference and have environmental requirements. Therefore, they can be used in cost-sensitive general industrial and civilian applications. Brushless motors are small in size, light in weight, have high output power, fast response, high speed, low inertia, smooth rotation, and stable torque.
DC servo motors are easy to intelligentize, and their electronic commutation methods are flexible, allowing for either square wave or sine wave commutation. These motors are maintenance-free, eliminating carbon brush wear, and are highly efficient. They operate at low temperatures with low noise and minimal electromagnetic radiation, have a long lifespan, and can be used in various environments.
AC servo motors offer excellent speed control characteristics, providing smooth control across the entire speed range with virtually no oscillation. They boast high efficiency (over 90%), low heat generation, high-speed control, and high-precision position control (depending on encoder accuracy). Within their rated operating range, they can achieve constant torque, low inertia, low noise, no brush wear, and are maintenance-free (suitable for clean and explosive environments). AC servo motors are also brushless motors, available in synchronous and asynchronous versions. Currently, synchronous motors are generally used in motion control due to their wide power range, high power output, large inertia, low maximum speed, and uniform speed decrease with increasing power, making them suitable for low-speed, stable operation.
The disadvantages of AC servo motors are that they are more complex to control, the driver parameters need to be determined by adjusting the PID parameters on site, and more wiring is required to support their operation.
Comparison of their application areas
DC servo motors are used in actuator drives in various digital control systems and in power drives requiring precise control of constant speed or precise control of speed variation curves. Because DC servo motors possess the advantages of AC motors (simple structure, reliable operation, and easy maintenance) while also having the high efficiency, zero excitation loss, and good speed regulation performance of DC motors, their application is increasingly widespread in various sectors of the national economy, such as medical devices, instruments, chemicals, textiles, and household appliances.
AC servo drives are suitable for applications requiring high precision in position, speed, and torque control. Examples include machine tools, printing equipment, packaging equipment, textile equipment, laser processing equipment, robots, electronics, pharmaceuticals, financial equipment, and automated production lines. Because servos are primarily used for positioning and speed control, they are also known as motion control systems.
Summarize
Both DC and AC servo motors are types of servo motors, and their characteristics determine their different application areas. In practical applications, they complement and assist each other. The application areas of servo motors are numerous. Generally, any equipment requiring a power source and demanding precision will likely involve servo motors. Examples include CNC machine tools, printing equipment, packaging equipment, textile equipment, laser processing equipment, robots, and automated production lines—equipment with relatively high requirements for process precision, processing efficiency, and operational reliability. Even your computer contains servo motors.
