Six Differences Between Stepper Drive and Servo Drive of CNC Cutting Machine

The selection of the drive motor in the drive system of the CNC cutting machine is mainly the configuration of the stepping motor and the configuration of the servo motor. Stepper motors are discrete motion devices that have an essential connection to modern digital control technology. In the current domestic digital control system, stepper motors are widely used. Servo motors, with the advent of all-digital AC servo systems, are increasingly being used in digital control systems.

In China, from the perspective of product applications, the use of CNC cutting machine motors, whether stepper motors or servo motors have a certain market. Today, we make a comparison of the differences between stepper motors and servo motors:

First, the control accuracy is different

The step angle of the two-phase hybrid stepping motor is generally 3.6° and 1.8°. The step angle of the five-phase hybrid stepping motor is generally 0.72° and 0.36°. There are also some high performance stepper motors with smaller step angles.

AC servo motor control accuracy is guaranteed by a rotary encoder at the rear end of the motor shaft.

Second, different low-frequency characteristics

Stepper motors are prone to low frequency vibration at low speeds. The vibration frequency is related to load conditions and driver performance. It is generally believed that the vibration frequency is half of the motor's no-load take-off frequency. This kind of low frequency vibration, which is determined by the working principle of the stepper motor, is very unfavorable to the normal operation of the machine. When the stepper motor operates at a low speed, damping techniques are generally used to overcome the low-frequency vibration phenomena, such as adding a damper to the motor, or using a subdivision technique on the driver.

The AC servo motor operates very smoothly and does not vibrate even at low speeds. The AC servo system has a resonance suppression function that can cover the lack of mechanical rigidity, and the system has a frequency resolution function (FFT), which can detect the mechanical resonance point and facilitate system adjustment.

Third, different characteristics of the moment frequency

The output torque of the stepper motor of the CNC cutting machine decreases as the rotation speed increases, and sharply decreases at higher rotation speeds, so the maximum working rotation speed is generally 300 to 600 RPM.

AC servo motor is a constant torque output, that is, it can output rated torque within its rated speed (generally 2000RPM or 3000RPM), and it is a constant power output above the rated speed.

Fourth, different overload capacity

CNC cutting machine stepper motors generally do not have overload capability.

AC servo motor has strong overload capability.

Fifth, different performance

The control of the stepper motor of the CNC cutting machine is open-loop control. The phenomenon of lost or blocked rotation may occur when the starting frequency is too high or the load is too large. Overshoot occurs when the rotation speed is too high, so to ensure the control accuracy, Should deal with the issue of rising or falling speed.

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

Sixth, different speed response performance

Stepping motors for CNC cutting machines require 200 to 400 milliseconds to accelerate from standstill to operating speed (typically several hundred revolutions per minute).

Acceleration performance of the AC servo system is better. Take the Panasonic MSMA 400W AC servo motor as an example. Acceleration from standstill to its rated speed of 3000 RPM takes only a few milliseconds. It can be used in control applications requiring fast start-stop.

In summary, the AC servo system is superior to the stepper motor in many aspects of performance, and is suitable for demanding applications. However, stepper motors are often used to perform the motor in some less demanding applications. Therefore, we must consider various factors such as control requirements and costs in the selection process of the control system, and select appropriate control motors.

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