I. Servo Motor
Servo motors can control speed and position with extremely high accuracy. 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 and high linearity. 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 servo motors. 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 motors are divided into DC servo motors and AC servo motors. Both DC and AC servo motors have their own application areas, but DC servo motors have a wider range of applications, including:
1. Industrial Automation: DC servo motors are commonly used in industrial automation, such as conveyor belts, robotic arms, and automated assembly systems on production lines. They offer high precision and controllability, making them suitable for applications requiring rapid response and high-precision positioning.
2. Machine tools and CNC machinery: DC servo motors are widely used in CNC machine tools, milling machines, drilling machines, laser cutting machines and other equipment to provide precise position control and speed adjustment.
3. Robotics Technology: DC servo motors play a key role in industrial robots, collaborative robots, and service robots, and are used for various precision tasks such as picking and placing, welding, and spraying.
4. Medical Equipment: DC servo motors are used in medical equipment, such as CT scanners, surgical robots, and medical instruments, to ensure high-precision motion and control.
5. Aerospace: DC servo motors are also widely used in the aerospace field, such as navigation systems, aircraft control systems, and satellite equipment.
6. Laboratory equipment: DC servo motors are commonly used in various equipment in scientific laboratories, such as microscopes, lab benches, sample rotators, etc., to achieve precise control and movement.
II. Working Principle of Servo Motor
1. A servo system is an automatic control system that enables the output controlled variables, such as position, orientation, and state, of an object to follow any changes in the input target (or given value). Servo systems primarily rely on pulses for positioning. Essentially, a servo motor receives one pulse and rotates by the corresponding angle, thus achieving displacement. Because the servo motor itself has the function of generating pulses, it generates a corresponding number of pulses for each angle of rotation. This creates a feedback loop, or closed loop, between the pulses received and the output. In this way, the system knows how many pulses were sent to the servo motor and how many were received, allowing for very precise control of the motor's rotation and achieving precise positioning down to 0.001mm. 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. However, they require maintenance, which is inconvenient (replacing carbon brushes), generates electromagnetic interference, and has environmental requirements. Therefore, they are suitable for cost-sensitive general industrial and civilian applications.
Brushless motors are small in size, lightweight, powerful, fast-responding, high-speed, low-inertia, smooth-rotating, and stable in torque. While their control is complex, they are easily made intelligent. Their electronic commutation is flexible, allowing for either square wave or sine wave commutation. The motors are maintenance-free, highly efficient, operate at low temperatures, have minimal electromagnetic radiation, and a long lifespan, making them suitable for various environments.
2. AC servo motors are also brushless motors, and they are divided into synchronous and asynchronous motors. Synchronous motors are generally used in motion control because they have a wide power range and can achieve very high power. They have high inertia, a low maximum rotational speed, and their speed decreases rapidly as power increases. Therefore, they are suitable for low-speed, stable operation applications.
3. The rotor inside the servo motor is a permanent magnet. The U/V/W three-phase electricity controlled by the driver forms an electromagnetic field, and the rotor rotates under the influence of this magnetic field. At the same time, the motor's built-in encoder feeds back signals to the driver. The driver compares the feedback value with the target value and adjusts the rotor's rotation angle accordingly. The accuracy of the servo motor depends on the accuracy (line count) of the encoder.
The functional differences between AC servo motors and brushless DC servo motors: AC servo motors are generally better because they use sinusoidal wave control, resulting in less torque ripple. DC servo motors use trapezoidal wave control. However, DC servo motors are simpler and cheaper.
