Siemens motor repair and replacement encoder malfunction in chemical plant - can be fixed on the same day

Siemens motor repair and replacement encoder malfunction in chemical plant - can be fixed on the same day,performance comparison

Performance comparison between servo motor and stepper motor

As an open-loop control system, stepper motors have essential characteristics with modern digital control technology. In domestic digital control systems, stepper motors are widely used. With the emergence of fully digital AC servo systems, AC servo motors are increasingly being used in digital control systems. In order to adapt to the development trend of digital control, stepper motors or fully digital AC servo motors are mostly used as executive motors in motion control systems. Although the two have similar control methods (pulse train and directional signal), there are significant differences in their performance and application scenarios. Now let's compare the performance of the two.

Siemens motor repair and replacement encoder malfunction in chemical plant - can be fixed on the same day,1、 Different control precision

The step angle of a two-phase hybrid stepper motor is generally 1.8°0.9The step angle of a five phase hybrid stepper motor is generally0.72 °0.36Some high-performance stepper motors also have smaller step angles after subdivision. Like Sanyo Company（SANYO DENKI）The step angle of the two-phase hybrid stepper motor produced can be set to1.8°0.9°0.72°0.36°0.18°0.09°0.072°0.036°, compatible with the step angle of two-phase and five phase hybrid stepper motors.

The control accuracy of the AC servo motor is ensured by the rotary encoder at the rear end of the motor shaft. Taking Sanyo's fully digital AC servo motor as an example, for standard2000For the motor of the line encoder, due to the use of quadruple frequency technology inside the driver, its pulse equivalent is360°/8000=0.045°. For the belt17For the motor of the bit encoder, the driver receives each131072A pulse motor rotates once, which means its pulse equivalent is360°/131072=0.0027466° is the step angle1.8The pulse equivalent of a stepper motor in degrees1/655.

2、 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 believed that the vibration frequency is half of the no-load take-off frequency of the motor. The low-frequency vibration phenomenon determined by the working principle of the stepper motor is very detrimental to the normal operation of the machine. When a stepper motor operates at low speeds, damping techniques should generally be used to overcome low-frequency vibration phenomena, such as adding dampers to the motor or using subdivision techniques on the driver.

The AC servo motor runs very smoothly, and there is no vibration even at low speeds. The communication servo system has resonance function, which can cover the insufficient rigidity of machinery, and the system has frequency analysis function internally（FFT）It can detect the mechanical resonance point and facilitate system adjustment.

3、 Different moment frequency characteristics

The output torque of a stepper motor decreases as the speed increases, and it drops sharply at higher speeds, so its working speed is generally around300～600RPMThe AC servo motor outputs a constant torque at its rated speed (usually2000RPMor3000RPM）It can output rated torque within, and constant power output above rated speed.

4、 Different overload capacities

Stepper motors generally do not have overload capacity. AC servo motors have strong overload capacity. Taking Sanyo AC servo system as an example, it has the ability to handle speed overload and torque overload. Its torque is two to three times the rated torque and can be used to overcome the inertia moment of the inertial load at the moment of starting. Stepper motors do not have this overload capacity. In order to overcome this inertia torque during selection, it is often necessary to choose motors with larger torque. However, machines do not require such large torque during normal operation, resulting in torque waste.

5、 Different operational performance

The control of stepper motors is open-loop control. If the starting frequency is too high or the load is too large, it is easy to cause step loss or stalling. If the speed is too high when stopping, it is easy to cause overshoot. Therefore, in order to ensure its control accuracy, the problem of speed increase and decrease should be handled well. The AC servo drive system is a closed-loop control system, and the driver can directly sample the feedback signal of the motor encoder. The internal structure consists of a position loop and a speed loop, and generally does not cause step loss or overshoot of the stepper motor, making the control performance more reliable.

6、 Different speed response performance

The stepper motor needs to accelerate from static to working speed (usually several hundred revolutions per minute)200～400millisecond. The acceleration performance of the communication servo system is good, as demonstrated by Shanyang400WTaking AC servo motor as an example, accelerate from static to its rated speed3000RPMIt only takes a few milliseconds and can be used for control situations that require fast start stop.

In summary, AC servo systems outperform stepper motors in many performance aspects. But in some situations where the requirements are not high, stepper motors are often used as executive motors. Therefore, in the design process of the control system, it is necessary to comprehensively consider various factors such as control requirements and costs, and select appropriate control motors.