A servo motor refers to an engine that controls the operation of mechanical components in a servo system, and is an indirect transmission device that supplements the motor. Servo motors can control speed and position accuracy very accurately, and can convert voltage signals into torque and speed to drive control objects. The rotor speed of a servo motor is controlled by input signals and can react quickly. In automatic control systems, it is used as an actuator and has characteristics such as small electromechanical time constant, high linearity, and starting voltage. It can convert the received electrical signal into angular displacement or angular velocity output on the motor shaft. It is divided into two categories: DC and AC servo motors. Its main feature is that when the signal voltage is zero, there is no self rotation phenomenon, and the speed decreases uniformly with the increase of torque.

Characteristics of DC brushless servo motor

Small moment of inertia, low starting voltage, and low no-load current; Abandoning the contact reversing system greatly increases the motor speed, with a maximum speed of up to 100000 rpm; Brushless servo motors can control speed, position, torque, etc. without the need for encoders during servo control; There is no wear of the electric brush. In addition to high speed, it also has the characteristics of long service life, low noise, and no electromagnetic interference.

Characteristics of DC brushed servo motor

1. Small size, fast action and response, large overload capacity, wide speed range

2. High low-speed torque, small fluctuation, smooth operation

3. Low noise, high efficiency

4. Backend encoder feedback (optional) forms advantages such as DC servo

5. Large voltage range and adjustable frequency

Advantages of servo motors

Firstly, let's take a look at the advantages of servo motors compared to other motors such as stepper motors

1. Accuracy: Closed loop control of position, speed, and torque has been achieved; Overcoming the problem of stepping motor out of step;

2. Speed: Good high-speed performance, generally rated speed can reach 2000-3000 revolutions per minute;

3. Adaptability: Strong overload resistance, able to withstand loads up to three times the rated torque, especially suitable for situations with instantaneous load fluctuations and fast starting requirements;

4. Stability: Running smoothly at low speeds, there will be no stepping phenomenon similar to that of a stepper motor during low-speed operation. Suitable for occasions with high-speed response requirements;

5. Timeliness: The dynamic response time of motor acceleration and deceleration is short, usually within a few tens of milliseconds;

6. Comfort: significantly reduced heat and noise.

Simply put, it means that the ordinary motor we usually see will continue to rotate for a while due to its own inertia after power failure, and then stop. And servo motors and stepper motors stop at will and leave at will, with extremely fast response times. But there is a phenomenon of stepping out of step in the stepper motor.

There are too many application fields for servo motors. As long as there is a power source and precision requirements, servo motors are generally involved. Equipment with relatively high requirements for process accuracy, processing efficiency, and work reliability, such as machine tools, printing equipment, packaging equipment, textile equipment, laser processing equipment, robots, and automated production lines.

Servo motors are divided into two categories: DC and AC, with DC motors further divided into brushed and brushless types; AC motors can be divided into two categories: asynchronous and synchronous.

Brushed motors have low cost, simple structure, large starting torque, wide speed range, easy control, and require maintenance. However, maintenance is inconvenient (such as replacing carbon brushes) and generates electromagnetic interference, which has environmental requirements. Therefore, it can be used in cost sensitive general industrial and civilian applications.

Brushless motors have small size, light weight, high output, fast response, high speed, low inertia, smooth rotation, and stable torque. The control is complex and easy to achieve intelligence. Its electronic commutation method is flexible and can be square wave commutation or sine wave commutation. The motor is maintenance free, highly efficient, operates at low temperatures, emits minimal electromagnetic radiation, has a long lifespan, and can be used in various environments.

AC servo motors are also brushless motors, divided into synchronous and asynchronous motors. Currently, synchronous motors are generally used in motion control, which have a large power range and can achieve high power. High inertia, low maximum rotational speed, and rapidly decreases with increasing power. Therefore, it is suitable for applications that operate smoothly at low speeds.

Servo motor: It is an engine that controls the operation of mechanical components in a servo system and is an indirect variable speed device that supplements the motor. A servo motor is an electro-mechanical converter that can rotate continuously. As a servo motor for hydraulic valve controllers, it belongs to the category of low-power micro motors, with permanent magnet DC servo motors and parallel excited DC servo motors being the most commonly used.

The function of servo motor: Servo motor can control speed and position accuracy very accurately.

Classification of servo motors: DC servo motors and AC servo motors.

The output speed of a DC servo motor is proportional to the input voltage and can achieve forward and reverse speed control. It has the advantages of large starting torque, wide speed range, good linearity of mechanical and adjustment characteristics, and convenient control. However, the wear and spark generation of the reversing brush can affect its service life. In recent years, brushless DC servo motors have emerged to avoid brush friction and commutation interference, resulting in high sensitivity, small dead zone, low noise, long lifespan, and minimal interference with surrounding electronic devices.

The transfer function of the output speed/input voltage of a DC servo motor can be approximated as a first-order delayed link, and its electromechanical time constant is generally between tens of milliseconds and tens of milliseconds. However, the time constant of some low inertia DC servo motors (such as hollow cup rotor type, printed winding type, slotless type) is only a few milliseconds to twenty milliseconds.

The rated speed of low-power DC servo motors is above 3000r/min, and even greater than 10000r/min. Therefore, as a controller for hydraulic valves, a high-speed ratio reducer is required. And DC torque servo motors (i.e. low-speed DC servo motors) can work at low speeds of tens of revolutions per minute, even under long-term stall conditions, so they can directly drive the controlled components without deceleration

DC servo motors are divided into brushed and brushless motors.

Brushed motors have low cost, simple structure, large starting torque, wide speed range, easy control, and require maintenance. However, they are easy to maintain (such as replacing carbon brushes), generate electromagnetic interference, and have environmental requirements. Therefore, it can be used in cost sensitive general industrial and civilian applications.

Brushless motors have small size, light weight, high output, fast response, high speed, low inertia, smooth rotation, and stable torque. The control is complex and easy to achieve intelligence. Its electronic commutation method is flexible and can be square wave commutation or sine wave commutation. The motor is maintenance free, highly efficient, operates at low temperatures, emits minimal electromagnetic radiation, has a long lifespan, and can be used in various environments.

AC servo motors are also brushless motors, divided into synchronous and asynchronous motors. Currently, synchronous motors are generally used in motion control, which have a large power range and can achieve high power. High inertia, low maximum rotational speed, and rapidly decreases with increasing power. Therefore, it is suitable for applications that operate smoothly at low speeds.

Working principle of communication servo motor

The rotor inside the servo motor is a permanent magnet, and the U/V/W three-phase electricity controlled by the driver forms an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the encoder provided by the motor feeds back the signal to the driver, and the driver compares the feedback value with the target value to adjust the angle of rotor rotation. The accuracy of servo motors depends on the accuracy (number of lines) of the encoder.

What are the functional differences between AC servo motors and brushless DC servo motors?

Communication servo is better because it is a sine wave control with less torque ripple. DC servo is a trapezoidal wave. But DC servo is relatively simple and cheap.

Permanent magnet AC servo motor

Since the 1980s, with the development of integrated circuits, power electronics technology, and AC variable speed drive technology, permanent magnet AC servo drive technology has made outstanding progress. Famous electrical manufacturers in various countries have successively launched their own AC servo motor and servo drive series products and continuously improved and updated them. The communication servo system has become the main development direction of contemporary high-performance servo systems, which poses a crisis of phasing out the original DC servo. After the 1990s, the commercialized AC servo systems in various countries around the world were driven by sine wave motors with fully digital control. The development of communication servo drive devices in the field of transmission is advancing rapidly. The main advantages of permanent magnet AC servo motors compared to DC servo motors are:

(1) Without electric brushes and commutators, it works reliably and requires low maintenance and upkeep.

(2) The heat dissipation of stator winding is relatively convenient.

(3) Small inertia makes it easy to improve the speed of the system.

(4) Suitable for high-speed and high torque working conditions.

(5) Under the same power, it has a smaller volume and weight.

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