Control methods of servo control motors commonly used in robot servo systems

Theoretically, the error, clearance and lost momentum of the entire drive and transmission link can be eliminated. It has high position control accuracy. Since the friction characteristics, rigidity and clearance of many mechanical transmission links in the position loop are nonlinear, it is easy to cause system instability, making the design, installation and debugging of the closed-loop system quite difficult. The system is mainly used for boring and milling machines, super-precision lathes, super-precision grinders and larger CNC machine tools with high precision requirements.

Robotic Servo System

Normally, what we call a robot servo system refers to a precision servo system used for multi-axis motion control. A multi-axis motion control system is composed of a high-order motion controller and a low-order servo driver. The motion controller is responsible for decoding motion control commands, the relative motion between each position control axis, acceleration and deceleration contour control, etc. Its main function is to reduce the path error of the overall system motion control; the servo driver is responsible for the position control of the servo motor, and its main function is to reduce the following error of the servo axis. The robot's servo system consists of three major parts: a servo motor, a servo driver, and a command mechanism. The servo motor is an actuator that realizes motion. The servo driver is the power supply of the servo motor. The command mechanism sends pulses or gives speed to cooperate with the normal operation of the servo driver.

The robot has higher requirements for servo motors than the other two parts. First, the servo motor is required to have fast response. The time from the motor receiving the command signal to the completion of the working state required by the command should be short. The shorter the time to respond to the command signal, the higher the sensitivity of the electric servo system and the better the fast response performance. Generally, the size of the electromechanical time constant of the servo motor is used to illustrate the fast response performance of the servo motor. Secondly, the starting torque-to-inertia ratio of the servo motor should be large. In the case of driving the load, the robot's servo motor is required to have a large starting torque and a small moment of inertia. Finally, the servo motor must have the continuity and linearity of the control characteristics. With the change of the control signal, the motor speed can change continuously, and sometimes the speed must be proportional or approximately proportional to the control signal. Of course, in order to match the robot's body shape, the servo motor must be small in size, small in mass, and short in axial size. It must also withstand harsh operating conditions, can perform very frequent forward and reverse and acceleration and deceleration operations, and can withstand several times overload in a short time. A servo drive is an actuator that can utilize the torque and force generated by various motors to directly or indirectly drive the robot body to obtain various movements of the robot. It has the advantages of high torque-to-moment-inertia ratio, no brushes, and no commutation sparks, and is widely used in robots.

Well-known foreign servo motor/system manufacturer

Lenze (Germany) Lenze is a world-renowned manufacturer of electromechanical transmission products. Its main products include DC speed control devices, AC inverters, AC servos, various motors, small transmission transpositions, reduction gearboxes, transmissions, brakes, clutches, etc. The company's current product, MCM synchronous servo motor, is mainly aimed at the robot market. It has a compact structure, a good load-to-motor inertia ratio, a smooth shell, and is simple and easy to use. It is suitable for packaging, handling and other application scenarios.

Bosch Rexroth (Germany)

Bosch Rexroth, a wholly-owned subsidiary of the German Bosch Group, is a leading supplier in the global industrial technology market and has an outstanding reputation in the field of transmission and control. The company has a wide range of products, mainly focusing on high-quality electronic control, hydraulic, pneumatic, mechatronic components and systems.

Lust (Germany) Lust is a subsidiary of Körber Group, a manufacturer and trader that focuses on providing general-purpose, programmable and multi-axis motion control servo drive products and related solutions to the robot/machine tool manufacturing industry. The standard product spectrum is wide, covering general-purpose, programmable and multi-axis motion control types, which are widely used in various industrial machinery and machine tools.

Beckhoff (Germany) Beckhoff uses new PC-based automation technology as its development concept. The industrial PCs, fieldbus modules, drive products and TwinCAT automation software it produces form a complete and mutually compatible control system, which can provide open automation systems and complete solutions for various industrial control fields.

Siemens (Germany) Siemens is one of the world's largest electrical and electronics companies. It has been prosperous for 150 years. The company's business is mainly concentrated in six major areas: information and communication, automation and control, power, transportation, medical systems and lighting. Siemens' servo motors are rich in variety and compact in structure, which can achieve excellent dynamic characteristics and operating efficiency, with full performance levels and various installation specifications. The characteristics of European servos are high overload capacity, good dynamic response, strong drive openness, and bus interfaces, including fieldbus, industrial Ethernet and even wireless network technology. But they are expensive and have large volume and weight. (Although most of the current high-speed servo buses are open standards, the technology is controlled by large international companies. In particular, based on industrial Ethernet technology, such as EtherCAT, Profinet, EtherNet/IP, SERCOS III, etc., it has played a pivotal role in improving the high performance of industrial robot dedicated AC servo systems. EtherCAT launched by German company Beckhoff has developed rapidly in recent years and has become the preferred network standard for most high-performance drive systems. Foreign servo manufacturers such as Yaskawa and Lenze have used EtherCAT bus as the bus standard for the next generation of products.)

Panasonic (Japan) Panasonic is a large multinational company, with products covering home appliances, digital audio-visual electronics, office products, aviation and many other fields. Panasonic Electric, a subsidiary of Panasonic, mainly provides electrical and mechanical services. The small AC servo motors and drivers launched by the company are very popular in the market. Among them, the large inertia series is suitable for CNC machine tools, and the medium inertia series is suitable for robots (maximum speed of 3000r/min, torque of 0.016~0.16Nm).

Yaskawa (Japan) Yaskawa Electric is a world-class transmission product manufacturer and the first company in Japan to make servo motors. Its products are known for their stability, speed and high cost performance. It is the world's largest servo brand with the most sales and the most industries. From general industrial machinery to semiconductor and electronic component manufacturing equipment, Yaskawa can provide the most suitable servo and controller products for various purposes.

Mitsubishi (Japan) Mitsubishi is not an independent company, but a group of many independent companies. The company is involved in mining, shipbuilding, banking, insurance, warehousing, trade, paper, steel, glass, electrical equipment, aircraft, oil and real estate and many other fields. It is an industrial giant in Japan. Mitsubishi Electric has been committed to improving product performance. The FA product lineup covers programmable controllers (PLCs), human-machine interfaces (HMIs), AC servo systems, inverters, industrial robots and low-voltage power distribution products that dominate in Asia.

Sanyo (Japan) Sanyo is an electrical company under Panasonic of Japan, targeting the mid-range market. The brand was discontinued on April 1, 2012. Sanyo's Denki AC servo drive system is one of the earliest servo systems to enter China. It is well-known for its excellent performance, high speed, precision, flexibility, long service life and high cost performance. It can realize the switching of different control modes, full closed-loop control, output detection function, automatic filtering function, and real-time self-tuning function. It is widely used in metallurgical blast furnace printing machinery, packaging machinery, textile machinery, plastic machinery, medical equipment, automated production lines and other fields. Japanese servo motors are relatively low in price, small in size and light in weight. But the disadvantages are also obvious, that is, the dynamic response ability is relatively weak and the openness is poor.

ELMO (Israel) Elmo Motion Control is a company specializing in the development of compact, high-power servo motors. For 25 years, it has been committed to designing servo drives for various harsh industrial environments, while providing advanced network motion controllers and complete motion control solutions. The company claims to build the best servo motors in the world.

SERVOTRONIX (Midea) Servotronix (Gaochuang) focuses on the business of motion control and is also a company specializing in the development of high-performance servo drive series and motion control solutions. The company has been acquired by Midea and will become the main supplier of servo motors for Kuka robots in the future.

AMC (USA) AMC (ADVANCED Motion Controls) is a company that provides reliable and high-performance motion control systems. Founded in 1987, it has remained small for decades, with only more than 300 employees, 40% of whom are engineers. The company's goal is to become the best servo company, so it only produces products in the servo drive field. Relying on superb manufacturing level and advanced R&D capabilities, the company's customer retention rate has reached 91% in the past seven years.