The main role as everyone knows is to produce drive torque motor as power source of various mechanical, electrical and mechanical operation, is an important part of CNC cutting machine, but the motor is widely used on the market is mainly divided into 2 kinds, one is the stepper motor, the other one is the AC servo motor, the detailed comparison about two kinds of motor performance differences.
Step motor is a kind of discrete motion device, which has an essential connection with modern digital control technology. In the current domestic digital control system, the application of step motor is very wide. With the advent of all digital AC servo systems, AC servo motors are more and more used in digital control systems. In order to adapt to the development trend of digital control, the stepper motor or all digital AC servo motor are mostly used in the motion control system as the executive motor. Although the two are similar in the control mode (pulse string and direction signal), there are great differences in performance and application. This is a comparison of the performance of the two.
First, the control precision is different
The step angle of the two phase hybrid stepping motor is generally 3.6 degrees and 1.8 degrees, and the step angle of the five phase hybrid stepping motor is generally 0.72 and 0.36 degrees. There are also some high performance step motors with smaller step angles. As a Stone Company for the production of the WEDM machine of the stepper motor, the step angle is 0.09 degrees; Germany bergerlahr company (BERGER LAHR) three-phase hybrid step motor production by the step angle dial switch is set to 1.8 degrees, 0.9 degrees, 0.72 degrees, 0.36 degrees, 0.18 degrees, 0.09 DEG and 0.072 DEG, 0.036 DEG, compatible with the step angle two-phase and five phase hybrid stepping motor.
The control precision of the AC servo motor is guaranteed by the rotary encoder of the rear end of the motor shaft. Taking Panasonic full digital AC servo motor as an example, for a motor with standard 2500 wire encoder, the pulse equivalent is 360 degrees /10000=0.036 degrees due to the use of four frequency doubling technology in the driver. For a motor with 17 bit encoders, the driver receives one cycle of each 217=131072 pulse motor, that is, its pulse equivalent is 360 /131072=9.89 seconds. It is the 1/655 of the pulse equivalent of the step motor with a step angle of 1.8 degrees.
Two. The characteristics of low frequency are different
The low frequency vibration of the stepper motor is easy to appear at low speed. The frequency of vibration is related to the performance of the load and the performance of the driver. It is generally considered that the frequency of the vibration is half of the frequency of the motor's no-load take-off. The low frequency vibration, which is determined by the working principle of the stepping motor, is very bad for the normal operation of the machine. When stepping motor works at low speed, damping technology should be adopted to overcome low frequency vibration phenomena, for example, adding dampers on motors or subdividing technology on drives.
The AC servo motor operates very smoothly, even at low speed, there will be no vibration phenomenon. The AC servo system has the function of resonance suppression, which can cover the rigidity of machinery, and the frequency resolution function (FFT) inside the system. It can detect the resonance point of the machine and facilitate the system adjustment.
Three. Different moment frequency characteristics
The output torque of the stepper motor decreases with the speed increase, and it will drop sharply at a high speed, so the maximum working speed is usually 300 ~ 600RPM. AC servo motor for constant torque output, that is, at its rated speed (usually 2000RPM or 3000RPM), it can output the rated torque, and the constant power output is above the rated speed.
Four. Different overload ability
The stepper motor generally does not have the ability to overload. AC servo motor has strong overload ability. Taking the AC servo system of Panasonic as an example, it has speed overload and torque overload capability. The maximum torque is three times the rated torque, which can be used to overcome the inertia moment of the inertia load at the start of the start. Stepper motor because no such overload capacity, in order to overcome this kind of inertia torque when selecting type, often need to choose a larger torque motor, while the machine does not need such a large torque during normal operation, then there is a phenomenon of torque waste.
Five. The operating performance is different
The stepper motor control is open-loop control, with too high starting frequency or too high load. It is easy to lose step or block up. If the speed is too high, it will overshoot. So to ensure its control accuracy, we should deal with the problem of rise and fall. The AC servo drive system is closed loop control. The driver can directly sample the feedback signal of the motor encoder, and form a position loop and speed loop internally. Generally, there will be no stepping or overshoot of the stepping motor, and the control performance is more reliable.
Six. The performance of the speed response is different
It takes 200~400 milliseconds for the stepping motor to speed up from rest to working speed (usually hundreds of minutes per minute). The AC servo system has better acceleration performance. Taking the Panasonic MSMA 400W AC servo motor as an example, from static acceleration to its rated speed 3000RPM, it only needs a few milliseconds, and it can be used for the control occasion requiring fast start stop.
To sum up, the AC servo system is superior to the stepper motor in many aspects of performance. But in some cases that are not high, the stepping motor is often used to perform the motor. So, Shanghai Aibo remind consumers in the purchase process control requirements to be taken into account, cost factors, their selection for motor control.
