In the walking positioning system, there are two main types of stepping motor and servo motor. The stepping motor mainly includes 2-phase, 5-phase and micro-stepping. The servo motor mainly includes AC servo motor and DC servo motor. Classification of brush and brushless motors. So, how to choose stepper motor and servo motor?

A stepper motor is a discrete motion device that has an essential connection with modern digital control technology. Stepper motor is one of the most widely used digital control systems in China. With the emergence of the all-digital AC servo system, the AC servo motor in the digital control system has also been widely used.

In the motion control system, in order to adapt to the development trend of digital control, stepper motor or full digital AC servo motor is mostly used as the executive motor. Although the control methods (pulse train and direction signal) of the two are similar, their performance and applications are quite different. This article compares the performance of the two.

Currently, there are many controllers for stepper motors and servo motors, but most of them require programming. Nowadays, stepper motors and servo motors are widely used, and they are the preferred control motors for many equipment. Due to the need for programming, it is difficult to control the application of manufacturers without technical force, so they have to rely on foreign aid to solve them.

First, the control accuracy is different.

The step angle of the stepper motor is generally 3.6°, 1.8°, and the step angle of the five-phase hybrid stepper motor is generally 0.72°, 0.36°. There are also some high-performance stepper motors with relatively small step angles. For example, the stepping motor of a slow wire-feeding machine tool produced by Stone Company has a step angle of 0.09°; the three-phase hybrid stepping motor produced by Germany's Bagra Company, its step angle can be set by the DIP switch. It is set at 1.8 degrees, which is consistent with the step angle of the two-phase and five-phase hybrid stepping motors, 0.9°, 0.36°, 0.18°, 0.09°, 0.072°, 0.036°.

The rotary encoder at the rear end of the motor shaft ensures the control accuracy of the AC servo motor. As an example, Panasonic's all-digital AC servo motor, a motor with a standard 2500-line encoder, has a pulse equivalent of 360°/10000=0.036° because the motor uses quadruple frequency technology. For a motor with a 17-bit encoder, every time it receives 217=131072 revolutions of the pulse motor, that is, the pulse equivalent of the drive is 360°/131072=9.89 seconds. It is the equivalent pulse of stepper motor stepper motor 1/655 stepper motor.

Second, the low frequency characteristics are different.

The stepper motor is prone to low frequency vibration at low speed. The vibration frequency is related to the load condition and the performance of the actuator. Generally, the vibration frequency of the motor is considered to be half of the no-load take-off frequency. This working principle of the stepper motor determines its low frequency vibration phenomenon, which is detrimental to the normal operation of the machine. When the stepper motor runs at low speed, vibration reduction technology should generally be used to overcome low frequency vibration, such as adding vibration dampers to the motor, or using subdivision technology for the driver.

The AC and DC servo motors run smoothly without any vibration even at low speed. The AC servo system has a resonance suppression function, which can cover the lack of mechanical rigidity, and has a frequency analytic function (FFT) inside the system, which can detect the resonance point of the machine and facilitate system adjustment.

Third, the moment-frequency characteristics are different.

The output torque of the stepping motor decreases with the increase of the speed, and drops sharply when the speed is high, so the upper limit of its working speed is usually 300~600RPM. It is a constant torque output, that is, its rated speed (usually 2000RPM or 3000RPM), output rated torque, and constant power output beyond the rated speed.

Fourth, the overload capacity is different.

Stepper motors generally have no overload capacity. The AC inverter has a strong overload capacity. As an example, Panasonic AC servos are capable of high-speed overload and torque overload. Its maximum torque is three times the rated torque, which can overcome the inertia moment generated by inertial load at startup. Because there is no such overload capacity, in order to overcome this inertia moment, the stepping motor often needs to choose a motor with a larger torque, but the machine does not need such a large torque during normal operation, so there is a torque loss phenomenon .

Fifth, the operating performance is different.

The stepper motor controls open-loop control. If the starting frequency is too high or the load is too large, it is easy to lose step or stall. When the speed is too high, it is easy to cause the phenomenon of rushing and stopping. Therefore, in order to ensure its control accuracy, the starting frequency should be adjusted. The AC/DC servo drive system adopts closed-loop control. The driver directly collects the feedback signal of the motor encoder, and the internal position loop and speed loop are formed. Generally, there will be no stall or overshoot in the stepping motor, and the control performance is more reliable.

Sixth, the speed response characteristics are different.

It takes 200~400ms for the stepper motor to accelerate from static to working speed (usually several hundred revolutions per minute). Taking the Panasonic MSMA400W AC servo motor as an example, the system accelerates from static to rated speed of 3000RPM, which can be used in control occasions and can be quickly started when a fast start control occasion is required.

Seven, the price is different.

Because the manufacturing cost and technical content of the servo motor and its driving device are relatively high, the price is also much higher than that of the stepper motor, especially the price gap of the servo motor is larger at the beginning. Domestic servo motors have developed very rapidly this year, and there are many varieties and models to choose from, which are more cost-effective.

From this point of view, the choice of stepper motor and servo motor is a better method, because it has better performance than stepper motor, but it is also commonly used in some occasions with low requirements . Therefore, when designing a control system, a variety of factors should be considered comprehensively to select a suitable stepper motor.