What is a servo motor?
A servo motor is a motor that controls the operation of mechanical components in a servo system. It is an auxiliary motor with indirect speed control.
Servo motors enable highly accurate speed and position control. They convert 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, they are used as actuators and have characteristics such as a small electromechanical time constant, high linearity, and low starting voltage. They can convert received electrical signals into angular displacement or angular velocity output on the motor shaft. 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.
Servo Motor Working Principle
Servo motors primarily rely on pulses for positioning. Essentially, a servo motor receives one pulse and rotates by the angle corresponding to that pulse, thus achieving displacement.
Because servo motors themselves have the function of emitting pulses, they emit a corresponding number of pulses for each angle they rotate. This creates a feedback loop, or closed loop, between the pulses sent to and received by the servo motor. In this way, the system knows how many pulses were sent to and received by the servo motor, allowing for very precise control of the motor's rotation and achieving accurate positioning down to 0.001mm.
The application of servo motors in industrial robots is booming. The robot industry is experiencing explosive growth, with numerous machine tool manufacturers, servo motor manufacturers, and other qualified companies turning to the robot market. Why are machine tool manufacturers and servo motor manufacturers so actively transforming and developing robots?
Industrial robots have four main components: the robot body, servo motor, reducer, and controller. Stepper motors are used to drive the robot's joints, requiring maximum power-to-weight ratio and torque-to-inertia ratio, high starting torque, low inertia, and a wide and smooth speed range. For the robot industry to grow, breakthroughs in servo motors and integrated control are necessary.
The general structure of an industrial robot's electric servo system consists of three closed-loop controls: current loop, speed loop, and position loop. Generally, for AC servo drives, multiple functions such as position control, speed control, and torque control can be achieved by manually setting their internal parameters.
The continuous advancement of industrial automation keeps the demand for automation software and hardware high. Currently, AC and DC servo motors with high starting torque, high torque, and low inertia are widely used in industrial robots. Other motors, such as AC servo motors and stepper motors, are also used in industrial robots depending on their application requirements.
Especially for robot end effectors (grippers), motors with the smallest possible size and weight should be used. When rapid response is required, servo motors must possess high reliability and significant short-term overload capacity. Specific usage requirements include: speed; high starting torque-to-inertia ratio; continuous and linear control characteristics, with the motor speed continuously changing with the control signal, sometimes proportional or approximately proportional to the control signal; wide speed range; small size, light weight, and short axial dimension; ability to withstand harsh operating conditions, frequent forward and reverse rotation and acceleration/deceleration, and short-term overload resistance. Future Trends in the Servo Motor Industry
Modern AC servo systems, after transitioning from analog to digital, have ubiquitous internal digital control loops, such as commutation, current, speed, and position control. Their implementation primarily relies on new power semiconductor devices, such as high-performance DSPs with FPGAs, and even dedicated servo modules are not uncommon. Furthermore, new power devices or modules are updated every 2-2.5 years, and new software algorithms are constantly evolving. Combined with changes in market demand, the following are some of the latest development trends in servo motor systems:
**High Efficiency**
While high efficiency has always been an important development topic for servo systems, it still needs further improvement. This mainly includes increasing the efficiency of the motor itself: for example, improving the performance of permanent magnet materials and better magnet mounting structure design; it also includes increasing the efficiency of the drive system: including optimization of inverter drive circuits, optimization of acceleration and deceleration motion, regenerative braking and energy feedback, and better cooling methods.
**Direct Drive**
Direct drive includes turntable servo drives using disc motors and linear servo drives using linear motors. By eliminating the transmission errors of intermediate mechanical transmission devices (such as gearboxes), it achieves high speed and high positioning accuracy. The ease with which linear motors can be reshaped allows for the miniaturization and weight reduction of various devices using linear mechanisms.
High Speed, High Precision, and High Performance: Employing higher-precision encoders, higher sampling accuracy and data bit depth, faster DSPs, high-performance rotary and linear motors without cogging effects, and utilizing various modern control strategies such as adaptive and artificial intelligence, the fundamental performance indicators (control speed and control accuracy) of servo systems are continuously improved.
Integration and Integration: Vertical integration of motors, feedback, control, drives, and communication has become a development direction for current low-power servo systems. Sometimes we call motors that integrate drives and communication intelligent motors, and sometimes we call drives that integrate motion control and communication intelligent servo drives. The integration of motors, drives, and controls allows for a tighter integration of these three aspects from design and manufacturing to operation and maintenance. However, this approach faces greater technical challenges and challenges in meeting engineers' usage habits, making it difficult to become mainstream and representing a small, distinctive segment within the overall servo market.
**General Purpose:** General-purpose drives are equipped with numerous parameters and rich menu functions, allowing users to easily configure them into five operating modes without changing the hardware: V/F control, sensorless open-loop vector control, closed-loop flux vector control, permanent magnet brushless AC servo motor control, and regenerative unit control. Suitable for various applications, they can drive different types of motors, such as asynchronous motors, permanent magnet synchronous motors, brushless DC motors, and stepper motors. They can also adapt to different sensor types, even those without position sensors. A semi-closed-loop control system can be constructed using the motor's built-in feedback, or a high-precision fully closed-loop control system can be formed by connecting to external position, speed, or torque sensors via an interface.
**Intelligent Features:** Modern AC servo drives possess parameter memory, fault self-diagnosis, and analysis functions. Most imported drives feature load inertia measurement and automatic gain adjustment. Some can automatically identify motor parameters and automatically determine encoder zero position, while others can automatically suppress vibration. Integrating electronic gears, electronic cams, synchronous tracking, interpolation motion, and other control functions with the drive provides a better experience for servo users.
