A servo motor refers to an electric motor used within a servo system to control the operation of mechanical components; it functions as an auxiliary motor and an indirect speed-regulating device. Servo motors offer precise control over speed and position accuracy, converting voltage signals into torque and rotational speed to drive the controlled object. The rotor speed of a servo motor is governed by input signals, to which it responds rapidly. In automatic control systems, servo motors serve as actuating elements; they are characterized by a small electromechanical time constant and high linearity, enabling them to convert received electrical signals into angular displacement or angular velocity outputs at the motor shaft. Servo motors are widely utilized in fields such as robotics, industrial automation, lithium-ion battery manufacturing equipment, photovoltaic equipment, high-end CNC machine tools, and small-scale CNC machinery. DC servo motors, specifically, find application in equipment such as EDM machines, robotic manipulators, and precision machinery.
Servo motors are broadly categorized into two main types: DC and AC. Permanent magnet AC servo motors represent a significant evolutionary step in this field, with brushless servo motors and their associated drives standing as exemplary products within this category. Their primary characteristics include the absence of self-rotation (drifting) when the control signal voltage is zero, and a rotational speed that decreases uniformly as the applied torque increases. By 2025, China is projected to achieve a higher rate of localization for core components-such as servo motors-and is expected to emerge as a net exporter of these technologies. Furthermore, products such as "smart electric rotary cylinders" utilize servo motors as their direct power source; in this context, the servo motor acts as the core driving unit, capable of replacing the hydraulic clamping systems traditionally found in CNC machine tools. Servo motors have also been identified as one of the critical components within the emerging field of embodied AI.
A servo system (or servo mechanism) is an automatic control system designed to ensure that controlled output variables-such as an object's position, orientation, or state-accurately track and follow any arbitrary changes in the input target (or setpoint). Servo systems primarily rely on pulses for positioning. Fundamentally, the concept is as follows: when a servo motor receives a single pulse, it rotates through an angular displacement corresponding to that pulse, thereby achieving linear or rotational movement. Since the servo motor itself possesses the capability to generate pulses, it emits a corresponding number of pulses for every increment of rotation. This creates a reciprocal exchange-known as a "closed loop"-between the pulses received by the motor and those it generates. Consequently, the system is able to track precisely how many pulses were transmitted to the servo motor versus how many were received back. This enables highly precise control over the motor's rotation, facilitating positioning accuracy down to 0.001 mm. DC servo motors are broadly categorized into brushed and brushless types. Brushed motors are characterized by low cost, simple construction, high starting torque, a wide speed control range, and ease of control; however, they require maintenance-specifically, the inconvenient task of replacing carbon brushes-and are prone to generating electromagnetic interference, necessitating specific environmental conditions for operation. Consequently, they are well-suited for cost-sensitive general industrial and consumer applications.
Brushless motors, conversely, feature a compact size, light weight, high power output, rapid response, high rotational speed, low inertia, smooth rotation, and stable torque. While their control mechanisms are more complex, they readily facilitate intelligent control integration; furthermore, their electronic commutation methods are flexible, allowing for either square-wave or sine-wave commutation. These motors are maintenance-free, highly efficient, operate at lower temperatures, emit minimal electromagnetic radiation, and boast a long service life, making them suitable for use in a wide variety of environments.
AC servo motors are also a type of brushless motor, classified into synchronous and asynchronous categories. In motion control applications, synchronous motors are generally preferred due to their extensive power range, which allows for the realization of very high power outputs. They typically exhibit high inertia and a relatively low maximum rotational speed-a limit that decreases rapidly as the motor's power rating increases. Consequently, they are ideally suited for applications requiring smooth, low-speed operation.
3. The rotor within a servo motor consists of permanent magnets. The three-phase U/V/W currents controlled by the motor driver generate an electromagnetic field, causing the rotor to rotate under the influence of this field. Simultaneously, the encoder integrated into the motor feeds back signals to the driver; the driver then compares these feedback values against the target values to adjust the rotor's rotational angle. Ultimately, the positioning accuracy of a servo motor is determined by the precision of its encoder (specifically, its line count). In terms of functionality, AC servo motors differ from brushless DC servo motors in that the AC servo offers superior performance; this is because it utilizes sinusoidal control, resulting in minimal torque ripple. DC servo motors, conversely, employ trapezoidal waveforms. However, DC servo systems are simpler in design and more cost-effective.
