Servo drive system can faithfully follow the control commands and actions, such as CNC machine tools and industrial machines were, servo drive technology has an important impact on product performance, and even play a key role. Thus a need to further understand the servo drive system in which the status and role.
2.1 AC Servo System
Electrical servo technology most widely used, mainly due to easy to control, flexible, easy access to drive energy, no pollution, pollution, maintenance is relatively easy. Especially with the electronic technology and computer software technology, it is the electrical servo technology provides a broad prospect.
Back in the 1970s, small inertia servo DC motor has a practical use. To the late 1970s began to develop AC servo system, and gradually practical, AC servo motor more widely, and there are DC servo system to replace the trend to become the mainstream of electrical servo system.
In the AC servo system can be divided into synchronous and asynchronous type AC servo system two.
AC servo systems - → asynchronous type - → two-phase asynchronous machine;
→ three-phase induction machine (motor torque).
→ reluctance synchronous (switched);
→ Hysteresis (reactive);
→permanent magnet.
Permanent magnet rotor of the permanent magnet synchronous servo motor as rising, prices falling, induction motor control off than a simple, easy to implement high-performance reasons, so the permanent magnet AC synchronous motor servo system more widely used.
At present, the AC synchronous servo drive system, the general application of AC permanent magnet synchronous servo motor, there are two. A class known as brushless DC motor, which requires the square wave current direct meditation stator windings. See parameter change literature; If a class is called three-phase permanent magnet synchronous motor, which requires the input of the stator windings are still three-phase sine wave power. See parameter change literature ⑵. The former referred to as BLDCM motor, which is referred to as PM · SM motors.
CNC machine tools, for example 2.2 to see AC permanent magnet synchronous motor servo system
System consists of computer numerical control (CNC), the servo drive (SD), permanent magnet synchronous servo motor (SM) and position (speed) sensor (S) and so on.
CNC machining programs used to store spare parts, various interpolation operations and real-time control software, to each axis servo drive system sends various control commands.
SD and SM CNC control command received after the fast ramp velocity and precise position control.
S represents the position and speed sensor (or detector)
AC servo system is currently used position and speed sensors are optical and electromagnetic two. For example, optical encoder, magnetic encoder, resolver (BR) and Multi-turn absolute encoder. Behind the two, can be used for a variety of detection applications, the system can detect the rotor position and speed, but also the rotor position and speed detection system, but also to detect the rotor magnetic pole position. 它 It is durable, not afraid to shock, high temperature, but there are shortcomings of the signal processing circuit complexity.
Brushless DC motor (BL, DCM) in the rotor magnetic pole position detection methods, generally do not contact, commonly used electromagnetic, photoelectric and indirect detection methods.
(1) Electromagnetic: a. differential transformer; b. proximity switch type;
(2) Magnetic-type: the Hall element and analog integrated circuits quickly;
(3) Optical: a. simple photoelectric (phototransistor);
b. absolute optical encoder disk;
c. incremental optical encoder disk.
(4) indirect: the use of the armature winding EMF (voltage) indirect detection of the rotor magnetic pole position. It is used for precision is not critical.
CNC machine tools for precision machining, so the servo system has a high dynamic and static accuracy requirements, and has a broad range of speed and positioning accuracy of industrial robots and servo system structure is similar, but waiting in the wings serving as an industrial motor SM robot arm and waist, leg drive actuator, requiring small size, light weight, and can produce large torque. Also, because the movement of industrial robots of different posture, the servo motor shaft inertia and torque will change dramatically, therefore, have higher adaptability requirements.
2.3 AC permanent magnet synchronous motor AC servo system
AC permanent magnet synchronous motor servo system consists of permanent magnet synchronous AC servo motors SM1 speed and position sensors BR, PWM power inverter UI and functionality of the speed controller with PI current controller ASR and ACR components.
AC servo system works as follows: speed command and speed feedback signals of the speed controller ASR input more, ASR output for the current command signal by multiplying the multiplier in order to get AC current.AC current command value compared with the current feedback signal, the difference between the current controller into the ACR.
PWM or SPWM (sinusoidal pulse width modulated) waveform generation circuit and power inverters, VVVF three-phase AC output permanent magnet synchronous motor SM to the stator windings, and to the input AC current in the armature winding to maintain a good sine sex. (SM rotor equipped with special shape of the permanent magnet, resulting in a constant magnetic field, thereby increasing the efficiency of SM).