Briefly describe the six performance differences between servo motor and stepping motor

by:V&T Technologies     2019-11-09
Caption: stepping motor, as an open-loop control system, is essential to modern digital control technology. Stepping motors are widely used in digital control systems in China at present. With the emergence of all-digital AC servo systems, AC servo motors are increasingly used in digital control systems. In order to adapt to the development trend of digital control, stepping motors or all-digital AC servo motors are mostly used as executive Motors in motion control systems. Although the two are similar in control mode (Pulse string and direction signal) However, there are great differences in performance and application. This paper compares the performance of the two. First, the control accuracy is different, the step angle of the two-phase Hybrid Stepping Motor is generally 1. 8 °, 0. 9 °, the step angle of the five-phase Hybrid Stepping Motor is generally 0. 72 °, 0. 36 °. There are also some high-performance stepping motors with smaller step angle after subdivision. Such as Sanyo company (Sanyo denki) The step angle of the two-phase Hybrid Stepping Motor produced can be set to 1 through the dialing switch. 8 °, 0. 9 °, 0. 72 °, 0. 36 °, 0. 18 °, 0. 09 °, 0. 072 °, 0. 036 °, compatible with the step angle of the two-phase and five-phase hybrid stepping motor. The control accuracy of the AC servo motor is guaranteed by the rotary encoder at the back end of the motor shaft. Taking Sanyo all-digital AC servo motor as an example, for a motor with a standard 2000-wire encoder, the pulse equivalent is 360/8000 = 0 because the driver adopts quadruple frequency technology inside. 045 °. For a motor with a 17-bit encoder, the driver rotates for every 131072 pulse Motors received, I . e. its pulse equivalent is 360/131072 = 0. 0027466, the step angle is 1. The pulse equivalent of an 8 stepping motor is 1/655. Second, the low frequency characteristics are different, the stepping motor is prone to low frequency vibration at low speed. The vibration frequency is related to the load condition and driver performance. It is generally considered that the vibration frequency is half of the motor's no-load take-off frequency. This low-frequency vibration phenomenon determined by the working principle of the stepping motor 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 low frequency vibration phenomenon, such as adding a damper to the motor or using subdivision technology on the driver. The AC servo motor runs very smoothly and does not vibrate even at low speed. The AC servo system has resonance suppression function, which can cover the mechanical rigidity shortage, and has Frequency analysis function inside the system (FFT) , Can detect the mechanical resonance point, easy to adjust the system. Third, the moment frequency characteristics are different, the output torque of the stepping motor decreases with the increase of the rotation speed, and decreases sharply at higher rotation speed, so its zui high working speed is generally 300 ~ 600 RPM. AC servo motor is constant force moment output, I . e. at its rated speed ( Usually 2000RPM or 3000 RPM) Within, the rated torque can be output, and the constant power output is above the rated speed. Four, different overload capacity, stepping motor generally does not have overload capacity. AC servo motor has strong overload capability. Taking Shanyang AC servo system as an example, it has the capability of speed overload and torque overload. Its zui large torque is two to three times the rated torque and can be used to overcome the inertial torque of the inertial load at the start-up moment. Because stepping motors do not have this kind of overload capacity, in order to overcome this kind of inertia torque during selection, it is often necessary to select motors with larger torque, however, the machine does not need such a large torque during normal operation, resulting in torque waste. 5. The operation performance is different. The control of the stepping motor is open-loop control. If the starting frequency is too high or the load is too large, it is easy to lose or block, when the speed is too high, it is easy to overflush. Therefore, in order to ensure its control accuracy, the problem of rising and slowing should be handled. The AC servo drive system is closed-loop control. The driver can directly sample the feedback signal of the motor encoder, and the position ring and speed ring are formed inside. Generally, there is no phenomenon of stepping or overshoot of the stepping motor, control performance is more reliable. Six, the speed response performance is different, stepping motor from static acceleration to working speed (Usually a few hundred turns per minute)Need 200 ~ 400 milliseconds. AC servo system has good acceleration performance. Taking 400 w ac servo motor as an example, it takes only a few milliseconds to accelerate from rest to its rated speed of 3000 RPM, which can be used in control occasions requiring fast start-stop.
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