Analysis of the Application Characteristics of Servo Motors in Numerical Control Systems
AC servo motors fall within the category of brushless motors and can be classified into synchronous and asynchronous types. In the field of motion control, synchronous servo motors are more common due to their wide power coverage range, which can meet the demands of high-power scenarios. Under high-load conditions, synchronous servo motors have the characteristic of stable low-speed operation, and as power increases, the decline in rotational speed is gentle, making them particularly suitable for applications that require high stability at low speeds.
Their core advantages lie in: high precision, wide speed regulation range, the ability to output large torque at low speeds, fast response, and no overshoot, providing reliable power support for precise control.
What unique advantages does a servo motor have over other electric motors?
Take the AC servo motor as an example. It far exceeds the stepper motor in many performance indicators. Although stepper motors are still widely used as actuating motors in specific special scenarios or those with low precision requirements, and are extremely common in domestic digital control systems, with the rise of all-digital AC servo systems, the application of AC servo motors in digital control systems has become increasingly widespread. Although both use pulse trains and direction signals in control methods, there are significant differences in their performance and applicable scenarios. So, in what specific aspects do AC servo motors and stepper motors differ?
There are significant differences in performance between AC servo motors and stepper motors, mainly reflected in the following four aspects:
I. Control accuracy
The control accuracy of the AC servo motor is guaranteed by the rotary encoder at the shaft end. Taking the 2500-line AC servo motor of Lishan Electromechanical as an example, after being processed by quadruple frequency technology, it can reach 10,000 lines, with a control accuracy of 0.036° (360°/ 10,000). However, the precision of stepper motors is relatively low. The step angles of two-phase stepper motors are usually 3.6° and 1.8°, while those of five-phase hybrid stepper motors are 0.72° and 0.36°.
Ii. Low-frequency characteristics
Stepper motors are prone to low-frequency vibration at low speeds, which affects the smooth operation of the equipment. This is caused by their inherent characteristics. The AC servo motor can maintain smooth operation at low speeds and is equipped with resonance suppression function, which can accurately detect the resonance frequency of the system and actively suppress vibration.
Iii. Torque-frequency Characteristics
The output torque of a stepping motor shows a nonlinear decreasing trend with the increase of rotational speed. At high rotational speed, the torque drops sharply, and the maximum operating speed is usually only 300 to 600RPM. The AC servo motor has the characteristic of constant torque output. It continuously outputs the rated torque within the rated speed (such as 2000RPM or 3000RPM), and enters the constant power output mode after exceeding the rated speed.
Iv. Overload Capacity
Stepper motors generally do not have overload capacity, while AC servo motors can withstand short-term overload and adapt to complex load conditions.
As can be seen from the above, AC servo motors are significantly superior to stepper motors in multiple performance indicators. However, in scenarios with lower precision requirements or cost sensitivity, stepper motors still become the preferred choice for actuating motors due to their economy. Therefore, in the design process of the control system, multiple dimensions such as control accuracy requirements and cost budget need to be comprehensively considered, and suitable control motors should be reasonably selected to achieve the optimal balance between performance and cost.
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