1. The servo system (servo mechanism) is an automatic control system that enables the output controlled quantities such as position, orientation, and state of an object to follow any changes in the input target (or given value). Servo mainly relies on pulses for positioning, and it can be understood in this way: when a servo motor receives one pulse, it will rotate by an angle corresponding to that pulse, thereby achieving displacement. Because the servo motor itself has the function of generating pulses, when the motor rotates by one angle, it will emit a corresponding number of pulses, thus forming a correspondence or called a closed loop. In this way, the system will know how many pulses were sent to the servo motor and how many pulses were returned, allowing for very precise control of the motor’s rotation, enabling precise positioning, reaching 0.001mm. DC servo motors are divided into brushed and brushless motors. Brushed motors have low cost, simple structure, large starting torque, wide speed regulation range, easy control, and require maintenance, but the maintenance is inconvenient (changing carbon brushes), generating electromagnetic interference, and having environmental requirements. Therefore, they can be used in ordinary industrial and civilian scenarios with sensitive costs.
Brushless motors are small in size, light in weight, have high output, fast response, high speed, small inertia, smooth rotation, and stable torque. The control is complex, and it is easy to achieve intelligence. Its electronic commutation method is flexible, allowing for square wave commutation or sine wave commutation. The motor is maintenance-free, has high efficiency, low operating temperature, very little electromagnetic radiation, long lifespan, and can be used in various environments.
2. AC servo motors are also brushless motors, divided into synchronous and asynchronous motors. In motion control, synchronous motors are generally used. They have a wide power range and can achieve large power. High inertia, the highest rotational speed is low, and it decreases rapidly with power increase. Therefore, they are suitable for applications with low-speed and smooth operation.
3. The rotor inside the servo motor is a permanent magnet. The driver controls the U/V/W three-phase electricity to form an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the motor’s built-in encoder provides feedback signals to the driver. The driver compares the feedback value with the target value and adjusts the rotation angle of the rotor. The accuracy of the servo motor depends on the accuracy of the encoder (the number of lines).
The differences in function between AC servo motors and brushless DC servo motors: AC servo motors are better because they are sinusoidal wave controlled, with smaller torque pulsation. DC servo is trapezoidal wave. However, DC servo is simpler and cheaper.