Comparison of Stepping and Servo Performance2016-10-28
Stepper motor as an open-loop control system, and modern digital control technology is essentially linked. In the current domestic digital control system, the stepper motor is widely used. With the emergence of all-digital AC servo system, AC servo motor is also increasingly used in digital control systems. In order to adapt to the development trend of digital control, most of the motion control system using stepper motor or all-digital AC servo motor as the implementation of the motor. Although the two are similar in the control mode (pulse train and direction signal), but in the use of performance and applications there is a big difference. Are on the use of performance for the two comparison.
First, the control accuracy is different
Two-phase hybrid stepping motor step angle is generally 1.8 °, 0.9 °, five-phase hybrid stepping motor step angle is generally 0.72 °, 0.36 °. There are also some high-performance stepper motors that are subdivided by a smaller step angle. Such as the SANYO DENKI production of two-phase hybrid stepping motor can be set by the DIP switch angle is 1.8 °, 0.9 °, 0.72 °, 0.36 °, 0.18 °, 0.09 °, 0.072 °, 0.036 ° , Compatible with two-phase and five-phase hybrid stepping motor step angle. AC servo motor control accuracy by the motor shaft back-end rotary encoder to ensure. To Sanyo all-digital AC servo motor, for the standard 2000-line encoder with the motor, the drive as a result of the internal quadruple frequency technology, the pulse equivalent of 360 ° / 8000 = 0.045 °. For a motor with a 17-bit encoder, the drive receives one pulse of 131072 pulses per revolution, ie, a pulse equivalent of 360 ° / 131072 = 0.0027466 °, which is a pulse equivalent of a stepping motor with a step angle of 1.8 ° 1/655.
Second, low-frequency characteristics of different Stepping motor at low speed prone to low frequency vibration phenomenon. Vibration frequency and load conditions and drive performance, generally considered that the vibration frequency of the motor no-load take-off frequency of half. This stepper motor by the working principle of the low-frequency vibration of the phenomenon of the normal operation of the machine is very detrimental. When the stepper motor at low speed, the general should be used to overcome the damping technology to reduce the phenomenon of low-frequency vibration, such as in the motor damper, or the use of subdivision technology on the drive. AC servo motor running very smooth, even at low speed will not appear when the vibration phenomenon. AC servo system has a resonance suppression function, can cover the mechanical rigidity, and the system has a frequency analysis function (FFT), can detect the mechanical resonance point, easy to adjust the system.
Third, the frequency characteristics of different The output torque of the stepper motor decreases with the increase of speed, and it will drop sharply at high speed, so its maximum working speed is generally 300 ~ 600RPM. AC servo motor for the constant torque output, that is, its rated speed (usually 2000RPM or 3000RPM) within the rated torque can be output in the rated speed above the constant power output.
Fourth, overload capacity is different Stepper motors generally do not have overload capability. AC servo motor has a strong overload capacity. Taking Sanyo AC servo system as an example, it has speed overload and torque overload capacity. The maximum torque of two to three times the rated torque can be used to overcome the moment of inertia inertia moment load. Stepper motor because there is no such overload capacity, in order to overcome this inertia in the selection of torque, often need to select a larger torque of the motor, and the machine during normal work without the need for such a large torque, there has been torque Waste of the phenomenon.
5, running performance is different Stepping motor control for the open-loop control, start the frequency is too high or too large load prone to lose step or stall phenomenon, stop when the speed is too high prone to overshoot phenomenon, so in order to ensure its control accuracy, should be handled well Rise, slow down problem. AC servo drive system for closed-loop control, the drive can be directly on the motor encoder feedback signal sampling, the internal composition of the position loop and speed loop, stepper motor is generally not lost step or overshoot phenomenon, the control performance is more reliable.
Sixth, the speed response performance is different Stepping motor acceleration from standstill to the working speed (usually hundreds of revolutions per minute) need 200 to 400 milliseconds. AC servo system to accelerate the performance of the better, to Sanyo 400W AC servo motor, for example, from the static acceleration to its rated speed 3000RPM only a few milliseconds, can be used for fast start-stop control of the occasion.
In summary, the AC servo system in many performance is better than stepper motor. But in some less demanding occasions, often with a stepper motor to do the implementation of the motor. Therefore, in the control system design process to take into account the control requirements, cost and other factors, the selection of appropriate control motor.
Selection calculation method
First, the speed and encoder resolution confirmation. Second, the motor shaft load torque conversion and acceleration and deceleration torque calculation. Third, calculate the load inertia, inertia matching, Yaskawa servo motor, for example, some products inertia matching up to 50 times, but the actual smaller the better, so the accuracy and good response speed. Fourth, the calculation and selection of regenerative resistance, for the servo, generally more than 2kw, to external configuration. 5, cable selection, twisted-pair shielded cable encoder for Yaskawa servo and other Japanese products absolute encoder is 6-core, incremental is 4-core.
