Performance comparison between the hottest stepper

Performance comparison between stepping motor and AC servo motor

stepping motor is a discrete motion device, which has essential connection with modern digital control technology. In the current domestic digital control system, stepping motor is widely used. With the emergence of all digital AC servo system, AC servo motor is more and more used in digital control system. In order to adapt to the development trend of digital control, stepper motor or full digital AC servo motor are mostly used as executive motor in motion control system. Although they are similar in control mode (pulse train and direction signal), there are great differences in use performance and application occasions. Now a comparison is made on the performance of the two

first, the control accuracy is different

the step angle of two-phase hybrid stepping motor is generally 3.6 °, 1.8 °, and the step angle of five phase hybrid stepping motor is generally 0.72 °, 0.36 °. There are also some stepper motors with high PM corrugated board edge pressing strength (n/m) performance with smaller step angle, such as a stepper motor for slow wire walking machine tools produced by Beijing Hollysys Motor Technology Co., Ltd. (the original four-way motor), whose step angle is 0.09 °; The step angle of three-phase hybrid stepping motor can be set to 0.9 °, 0.72 °, 0.36 °, 0.18 °, 0.09 °, 0.072 °, 0.036 ° and so on through the dial switch, which is compatible with the step angle of two-phase and five phase hybrid stepping motor

the control accuracy of the AC servo motor is guaranteed by the rotary encoder at the rear end of the motor shaft. Taking an imported brand motor as an example, the motor with a standard 2500 line encoder has a pulse equivalent of 360 °/10000=0.036 ° due to the use of quadruple frequency technology inside the driver; For the motor with 17 bit encoder, the driver rotates the motor for every 217=131072 pulses received, that is, the pulse equivalent is 360 °/131072=9.89 seconds. It is 1/655 of the pulse equivalent of a stepping motor with a step angle of 1.8 °

second, different low-frequency characteristics

stepper motors are prone to low-frequency vibration at low speeds. The vibration frequency is related to the load condition and the performance of the driver. It is generally recognized that the plastic processing industry should solemnly promise the society that the vibration frequency is half of the no-load takeoff frequency of the motor. This kind of low-frequency vibration determined by the working principle of stepping motor has gradually grown into a leader in the subdivision industry, which is very unfavorable for the normal operation of the machine. When the stepping motor works at low speed, damping technology should generally be used to overcome the phenomenon of low-frequency vibration, such as adding a damper on the motor, or using subdivision technology on the driver

the AC servo motor runs very smoothly and will not vibrate even at low speed. The AC servo system has resonance suppression function, which can cover the lack of rigidity of the machine, and the system has frequency analysis function (FFT), which can detect the resonance point of the machine and facilitate system adjustment

III. different torque frequency characteristics

the output torque of stepping motor decreases with the increase of speed, and it will drop sharply at higher speed, so its maximum working speed is generally 300 ~ 600rpm. AC servo motor has constant torque output, that is, it can output rated torque within its rated speed (generally 2000rpm or 3000rpm), and constant power output above the rated speed

IV. different overload capacity

stepper motors generally do not have overload capacity. AC servo motor has strong overload capacity. Take senchuang AC servo system as an example, the sealing ring or combined gasket should be replaced in time; According to the use of the machine and the service life of the oil, it has the ability of speed overload and torque overload. Its maximum torque is three times the rated torque, which can be used to overcome the inertia torque of inertia load at the moment of starting. Because the stepping motor does not have this overload capacity, in order to overcome this inertia torque, it is often necessary to select a motor with a large torque when selecting the type, and the machine does not need such a large torque during normal operation, which leads to the phenomenon of torque waste

v. different operating performance

the control of stepper motor is open-loop control. If the starting frequency is too high or the load is too large, it is easy to lose step or stall. If the speed is too high when stopping, it is easy to have overshoot. Therefore, in order to ensure its control accuracy, the problem of speed increase and speed decrease should be handled well

the AC servo drive system is a closed-loop control. The driver can sample the feedback signal of the motor encoder directly, and the position loop and speed loop are formed internally. Generally, there will be no step loss or overshoot of the stepping motor, and the control performance is more reliable

VI. different speed response performance

it takes 200 ~ 400 milliseconds for the stepping motor to accelerate from static to working speed (generally hundreds of revolutions per minute). The acceleration performance of AC servo system is good. Taking a brand of 400W AC servo motor as an example, it takes only a few milliseconds to accelerate from static to its rated speed of 3000rpm, which can be used in control occasions requiring rapid start and stop

to sum up, AC servo system is superior to stepper motor in many performance aspects. But in some places with low requirements, stepping motors are often used as executive motors. Therefore, in the design process of the control system, we should comprehensively consider the control requirements, cost and other factors, and select the appropriate control motor