The word 'servo' originates from the Greek meaning of 'slave'. A "servo motor" can be understood as a motor that absolutely follows the command of a control signal: before the control signal is sent, the rotor remains stationary; When the control signal is issued, the rotor immediately rotates; When the control signal disappears, the rotor can immediately stop rotating. A servo motor is a micro motor used as an executing element in an automatic control device, whose function is to convert electrical signals into angular displacement or angular velocity of the shaft.
The servo motor used in robots requires fast bus communication speed between the controller and the servo; High precision of servo; Additionally, there are processing requirements for basic materials. Especially for robot end effectors (grippers), motors with minimal volume and mass should be used, especially when fast response is required. Servo motors must have high reliability and stability, can withstand harsh operating conditions, can perform very frequent forward and reverse movements, acceleration and deceleration, and can withstand overload in a short period of time.
Special requirements for robot servo
Servo motors are divided into two categories: AC servo and DC servo
The basic structure of AC servo motors is similar to that of AC induction motors (asynchronous motors). There are two excitation windings Wf and control winding WcoWf with displacement of 90 ° in phase space on the stator, which are connected to constant AC voltage. The purpose of controlling motor operation is achieved by using the AC voltage or phase change applied to Wc. AC servo motors have the characteristics of stable operation, good controllability, fast response, high sensitivity, and strict nonlinearity indicators for mechanical and regulatory characteristics (less than 10% to 15% and less than 15% to 25%, respectively).
The basic structure of a DC servo motor is similar to that of a general DC motor. Motor speed n=E/K1j=(Ua IaRa)/K1j, where E is the armature back electromotive force, K is a constant, j is the magnetic flux per pole, Ua, Ia are the armature voltage and current, Ra is the armature resistance, change Ua or change φ， The speed of a DC servo motor can be controlled, but the method of controlling the armature voltage is generally used. In a permanent magnet DC servo motor, the excitation winding is replaced by a permanent magnet, and the magnetic flux φ Constant. DC servo motors have good linear regulation characteristics and fast time response.
The importance of servo motors
The control systems and automation products of industrial robots mainly involve servo motors, reducers, controllers, and sensors. The servo motor is the power system of industrial robots, usually installed at the "joints" of the robot, and is the "heart" of robot motion.
At present, the joint drive of robots cannot be separated from servo systems. The more joints, the higher the flexibility and accuracy of the robot, and the more servo motors need to be used. Robots have high requirements for servo systems, which must meet the requirements of fast response, high starting torque, large dynamic torque inertia ratio, wide speed range, small size, light weight, acceleration and deceleration operation, and high reliability and stability. At present, industrial robots mostly use AC servo systems.
Market distribution of servo motors
Currently, in the Chinese industrial machinery market, mainstream suppliers include Panasonic, Yaskawa, Mitsubishi from Japan, as well as Renz and Bosch Rexroth from Europe and the United States. From the perspective of market share, foreign servo companies currently have a market share of 75% in China. Among them, Japanese brands account for 50%; European and American brands account for 25%. Domestic brands only occupy about 20% of the market share.
At present, China's mid to low-end servo systems have been able to achieve large-scale production, but high-end servo systems have not yet formed commercialization and mass production capabilities. The demand for precision servo motor control systems in China mainly relies on imports. The development of the robot industry is booming. With the promotion of support policies for the robot industry and the continuous improvement of domestic servo technology, the pace of import substitution of servo systems in China will accelerate.