However, from the practical point of view, the DC servo motor introduces a mechanical reversing device. The cost is high, the fault is many, the maintenance is difficult, and the spark generated by the carbon brush often affects the production and generates electromagnetic interference to other equipment. At the same time, the commutation capability of the mechanical commutator limits the capacity and speed of the motor. The armature of the motor is on the rotor, making the motor inefficient and poorly dissipated. In order to improve the commutation ability and reduce the leakage inductance of the armature, the rotor becomes short and thick, which affects the dynamic performance of the system. Previous page next page [Automatic Switch, Free Your Hands]: Cabinet light has two working modes, Motion & Light Sensor Mode, Always On and Off Mode. In G mode, this counter light automatically turns on when it senses human motion within 10 feet in a dark environment, and automatically turns off after 20 seconds of inactivity. You can use these lights as normal light or safe light. Solar Motion Light,Best Outdoor Motion Sensor Lights,Indoor Motion Sensor Light,Outdoor Sensor Lights Ningbo Wason Lighting Technology Co.,Ltd , https://www.wasonlight.com
(3) The AC servo system is for the defect of the DC motor. If it is treated as “inside and outâ€, the electric drive winding is mounted on the stator and the rotor is a permanent magnet part, and the magnetic pole position is measured by the encoder on the rotor shaft. The permanent magnet brushless motor is formed, and the AC servo system has good servo characteristics with the practical application of the vector control method. Its wide technical range, high speed accuracy, fast dynamic response and four-quadrant operation make its dynamic and static characteristics comparable to DC servo systems. At the same time, the weak magnetic high-speed control can be realized, the speed range of the system is widened, and the requirements of high-performance servo drive are adapted.
At present, the permanent magnet synchronous AC servo system is mainly used in the machine feed servo. There are three types: analog form, digital form and software form. The analog servo has a single purpose and only receives analog signals. The position control is usually implemented by the host computer. Digital servo can realize multi-purpose of one machine, such as speed, torque and position control. It can receive analog commands and pulse commands, and various parameters are set digitally with good stability. Has a rich self-diagnosis, alarm function. Software servo is a microprocessor-based all-digital servo system. It implements the monitoring program of servo motors of various control modes and different specifications and powers in software. When used, the user can set the code and related data to automatically enter the working state. With a digital interface, when changing the working mode and replacing the motor specifications, you only need to reset the code, so it is also called universal servo.
AC servo has occupied the dominant position of machine tool feed servo, and has been continuously improved with the development of new technology, which is embodied in three aspects. First, the power electronic devices in the system power drive device continue to develop toward high frequency, intelligent power modules are popularized and applied; second, based on the maturity of microprocessor embedded platform technology, it will promote the application of advanced control algorithms; It is the promotion of networked manufacturing mode and the maturity of fieldbus technology, which will enable network-based servo control.
(4) Linear servo system The linear servo system adopts a direct drive method (Direct Drive). Compared with the traditional rotary transmission method, the biggest feature is to cancel all mechanical intermediate transmission links between the motor and the workbench. The length of the machine feed chain is reduced to zero. This "zero-drive" mode brings performance indicators that cannot be achieved by the rotary drive method. For example, the acceleration can reach more than 3g, which is 10 to 20 times that of the conventional drive device, and the feed speed is 4 to 5 times that of the conventional one. From the working principle of the motor, the linear motor has various methods such as DC, AC, stepping, permanent magnet, electromagnetic, synchronous and asynchronous; and in terms of structure, there are moving coil, moving iron, flat and Cylindrical type. At present, there are mainly two types of high-precision high-frequency ring-stroke linear motors and high-thrust long-stroke high-precision linear motors applied to CNC machine tools.
Linear servo is an ideal driving mode for high-speed and high-precision CNC machine tools. It is highly valued by machine tool manufacturers and its technology is developing rapidly. At the 2001 European Machine Tool Show, dozens of companies exhibited high-speed machine tools driven by linear motors, with a rapid traverse speed of 100-120 m/min and an acceleration of 1.5-2 g, especially the German DMG company and the Japanese MAZAK company. Sex. In 2000, DMG's 28 models were driven by linear motors, with an annual output of more than 1,500 units, accounting for about one-third of the total output. MAZAK will also introduce a supersonic machining center based on linear servo system. The cutting speed is 8 Mach, the maximum spindle speed is 80000r/min, the rapid traverse speed is 500m/min, and the acceleration is 6g. All of these marks the second generation of high-speed machine tools represented by linear motor drives, which will replace the first-generation high-speed machine tools represented by high-speed ball screw drives, and gradually take the lead in use.
Fourth, the status quo and prospect of the spindle servo system
The spindle servo provides the cutting power required to machine all types of workpieces. Therefore, only the spindle speed regulation and forward and reverse functions are required. However, when the machine tool is required to have functions such as thread machining, quasi-stop and constant line speed machining, the corresponding position control requirements are also proposed for the spindle. Therefore, it is required to have a large output power, a constant torque segment and a constant power segment, and a quasi-stop control. The spindle is linked with the feed. Like the feed servo, the spindle servo has experienced a transmission from a common three-phase asynchronous motor to a DC spindle drive. With the advancement of microprocessor technology and high-power transistor technology, it has now entered the era of AC spindle servo systems.
(1) AC asynchronous servo system AC asynchronous servo generates a sinusoidal current with variable amplitude and frequency in the stator winding of the three-phase asynchronous motor, and the rotating magnetic field generated by the sinusoidal current interacts with the induced current generated by the rotor of the motor to generate Electromagnetic torque to achieve motor rotation. The amplitude of the sinusoidal current can be decomposed into a vector sum of the given or adjustable excitation current and the equivalent rotor torque current; the frequency of the sinusoidal current can be decomposed into the sum of the rotor speed and the slip to achieve vectorization control.
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Research on servo system in CNC machine tools (2)