The servo drive is used to drive the servo motor, the servo motor may be a stepper motor, an AC induction motor may be, mainly in order to achieve fast, precise positioning, like the kind of stop and go, with high precision in many applications .

Is to drive the inverter frequency alternating current adapted to adjust the motor speed to drive the motor, the inverter and now some of the servo control can be achieved, i.e. can drive servo motors, servo drives and drive but is not the same of!

Both definitions

Inverter (Variable-frequency Drive, VFD) and inverter technology is the application of microelectronic technology, controlling the AC motor by changing the frequency of the motor operating mode power supply control apparatus. The main inverter rectifier (AC to DC), a filter, an inverter (DC-AC), a braking unit, a driving unit, the detection unit composed of a micro processing unit or the like. By breaking the IGBT inverter to adjust the output power voltage and frequency to its desired power supply voltage according to actual needs of the motor, so as to achieve the purpose of energy saving, the governor, in addition, there are many drive protection , Such as over current, over voltage, overload protection and so on. With the continuous improvement of industrial automation, the inverter has also been very widely used.

Servo system (servomechanism), also known as servo system, is used to accurately follow or reproduce a process feedback control system. Automatic control system for a servo system so that any change in position of the object, orientation, state, etc. can be output to follow the input target amount charged (or a given value). Its main task is to control commands as required, amplifies power, and control conversion processing such that the torque, speed and position control of the output drive means is flexible. In many cases, the servo system specifically refers to (output system) is a control amount of mechanical displacement or displacement velocity, acceleration feedback control system, which effect the displacement of the output a mechanical displacement (or angle) to accurately track the input ( Or corner), its structural composition and other forms of feedback control system there is no principle difference. Initially servo system for national defense, control of artillery, ships, aircraft autopilot, missile launchers and so on, then gradually extended to many sectors of the national economy, such as automatic machine wireless tracking control.

The working principle of both

N speed governor main principle is subject to the inverter induction motor, the frequency F of the asynchronous motor, motor slip s, the motor number of poles p of these four factors pairs. N speed proportional to the frequency f, the frequency f can be changed as long as the change speed of the motor, when the frequency f varies in the range of 0-50Hz, the motor speed adjustment range is very wide. Frequency control is to change the frequency of motor power to achieve speed regulation. Mainly AC – DC – AC mode, first frequency AC power into DC power through a rectifier, and then converting the DC power into AC power frequency, supply voltage to the motor can be controlled. Inverter circuit generally by the rectifier, the middle of the DC link, inverter and control of four parts. Three-phase bridge rectifier is not controlled rectifier, IGBT inverter part of a three-phase bridge inverter, and the output of the PWM waveform, intermediate DC link to filter, buffer, and DC energy storage reactive power.

Servo system works is simply on the basis of speed and position signals AC DC motor open-loop control by a rotary encoder, a resolver, etc. is fed back to the driver to do a closed loop negative feedback control of the PID regulator. Coupled with the current loop inside the driver, through the three loop adjustment, the output of the motor are much increased accuracy and setpoint follow time response characteristics. Servo system is a dynamic follow-up system to reach the homeostasis is also a dynamic balance.

The two have in common:

AC servo technology itself is the draw and the application of frequency conversion technology, implemented on the basis of the DC motor servo control on the way to imitate the DC motor control through the frequency of the PWM mode, which means that there must be frequency AC servo motor of this link: frequency is the frequency of the alternating current into direct current rectified prior 50,60HZ, then adjust the adjustable frequency inverter is similar to the waveform of various types of transistors can be controlled by the gate electrode (IGBT, IGCT, etc.) by a PWM carrier frequency and cosine ripple level, since the frequency is adjustable, the adjustable speed AC motor on the (n = 60f / p, n speed, f the frequency, P number of pole pairs).

The difference between the two is:

1. Overload capacity is different. Servo drives generally have 3-fold overload, load inertia may be used to overcome the inertia moment of starting torque, and generally allows the inverter overload 1.5 times.

2 control accuracy. Servo system control accuracy is much higher than the frequency, usually servo motor control accuracy is guaranteed by the rotary encoder of the motor shaft rear. Some servo system control accuracy even up to 1: 1000.

3 different applications. Frequency control and servo control are two areas of control. The former belongs to the field of transmission control, which belongs to the field of motion control. One is to meet the general requirements of industrial applications, the performance of the less demanding applications, the pursuit of low-cost. The other is the pursuit of high precision, high performance, high response.

4 different acceleration and deceleration performance. Under no-load condition, the servomotor can be processed from standstill to 2000r / min without exceeding 20ms. The motor acceleration time depends on the motor shaft inertia and load. The higher the usual inertia, the longer the acceleration time.

Servo and inverter market competition

Due to the difference in performance and function of frequency converter and servo, the applications are not the same. The main competition is concentrated in:

Technical competition. In the same area, the purchaser chooses the servo system if the technical requirements of the machine are high and complex. Otherwise it will choose inverter products. Such as some CNC machine tools, electronic equipment and other high-tech machinery will be the preferred servo products.

price competition. Most buyers will be concerned about the cost, often ignore the technology preferred low-cost inverter. As we all know, the price of servo system is almost frequency converter products several times.

Despite the current application of the servo system has not been popular, especially domestic servo system, where the application of servo compared to foreign products less and less. However, with the acceleration of industrialization, people will gradually realize the advantages of the servo system, and the servo system will also be approved by the buyers. Similarly, domestic servo technology will not be stalled, whether based on profit return or historical mission to revitalize the country, I believe there will be more and more manufacturers will be put into research and development servo system. Will usher in the heyday of China’s “servo industry.”

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