1. What is a stepper motor?
Stepping motor is an actuator that converts electrical pulses into angular displacement. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (ie step angle) in the set direction. You can control the angular displacement by controlling the number of pulses, so as to achieve the purpose of accurate positioning; at the same time, you can control the speed and acceleration of the motor rotation by controlling the pulse frequency, so as to achieve the purpose of speed regulation.
2. Classification of stepping motors:
There are three types of stepping motors: permanent magnet (PM), reactive (VR) and hybrid (HB):
Permanent magnet stepping is generally two-phase, with small torque and volume, and the stepping angle is generally 7.5 degrees or 15 degrees;
The reactive step is generally three-phase, which can achieve large torque output. The step angle is generally 1.5 degrees, but the noise and vibration are large.
Hybrid stepping refers to the combination of the advantages of permanent magnet and reactive. It is divided into two-phase, five-phase and three-phase: two-phase stepping angle is generally 1.8 degrees, this kind of stepping motor is the most widely used.
3. How to determine the DC power supply of the stepper motor driver:
3.1. Determination of voltage
The power supply voltage of the hybrid stepping motor driver is generally in a wide range (for example, the power supply voltage of the 2M530 is 24-45VDC), and the power supply voltage is usually selected according to the working speed and response requirements of the motor. If the motor has a high working speed or a fast response requirement, the voltage value is also high, but note that the ripple of the power supply voltage cannot exceed the maximum input voltage of the drive, otherwise the drive may be damaged.
B. Determination of current
The power supply current is generally determined according to the output phase current I of the driver. If a linear power supply is used, the power supply current can generally be 1.1 to 1.3 times I; if a switching power supply is used, the power supply current can generally be 1.5 to 2.0 times I.
4. Performance comparison of stepper motor and AC servo motor:
The stepper motor is a discrete movement device, which is essentially related to modern digital control technology. In the current domestic digital control system, stepper motors are widely used. With the advent 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, most of the motion control systems use stepper motors or all-digital AC servo motors as executive motors. Although the two are similar in control mode (pulse train and direction signal), there are big differences in performance and applications. Comparison of the performance of the two.
4.1 Different control accuracy
The step angle of the two-phase hybrid stepping motor is generally 1.8°, and the control accuracy of the AC servo motor is guaranteed by the rotary encoder at the back of the motor shaft. Take the Shinano all-digital AC servo motor as an example. For a motor with a standard 2000-line encoder, the pulse equivalent is 360°/8000=0.045° due to the quadruple frequency technology used inside the drive.
4.2 Different low frequency characteristics
Stepping motors are prone to low-frequency vibration at low speeds. The vibration frequency is related to the load condition and the performance of the drive. It is generally considered that the vibration frequency is half of the no-load take-off frequency of the motor. This low-frequency vibration phenomenon determined by the working principle of the stepper motor is very unfavorable to the normal operation of the machine. When stepping motors work at low speeds, damping technology should generally be used to overcome low-frequency vibration phenomena, such as adding a damper to the motor, or using subdivision technology on the drive.
The AC servo motor runs very smoothly, and there is no vibration even at low speeds. The AC servo system has resonance suppression function, which can cover the lack of mechanical rigidity, and the internal frequency analysis function (FFT) of the system can detect the resonance point of the machine, which is convenient for system adjustment.
4.3 Different moment frequency characteristics
The output torque of a stepping motor decreases with the increase of the speed, and will drop sharply at a higher speed, so its maximum working speed is generally 300-600RPM. AC servo motor has constant torque output, that is, it can output rated torque within its rated speed (generally 2000RPM or 3000RPM), and it is constant power output above the rated speed.
4.4 Different overload capacity
Stepper motors generally do not have overload capacity. AC servo motor has strong overload capacity. Take the Shinano AC servo system as an example, it has speed overload and torque overload capabilities. The maximum torque is three times the rated torque, which can be used to overcome the moment of inertia of the inertial load at the moment of starting. Because stepper motors do not have this overload capacity, in order to overcome this moment of inertia when selecting models, it is often necessary to select a motor with a larger torque, and the machine does not need such a large torque during normal operation, so a torque appears. The phenomenon of waste.
4.5 Different operating performance
Stepper motor control is open loop control. If the starting frequency is too high or the load is too large, it is easy to lose steps or stall. When the speed is too high, it is easy to overshoot. Therefore, to ensure its control accuracy, it should be handled well. Increase and decrease speed problems. The AC servo drive system is a closed-loop control. The drive can directly sample the feedback signal of the motor encoder. The position loop and speed loop are formed inside. Generally, stepping motors will not lose steps or overshoot, and the control performance is more reliable.
4.6 Different speed response performance
It takes 200 to 400 milliseconds for a stepping motor to accelerate from a standstill to a working speed (generally several hundred revolutions per minute). The acceleration performance of the AC servo system is better. Taking the Shinano HO CC 400W AC servo motor as an example, it only takes a few milliseconds to accelerate from a standstill to its rated speed of 3000RPM, which can be used in control situations that require fast start and stop.
In summary, the AC servo system is superior to stepper motors in many aspects of performance. However, stepper motors are often used as executive motors in some less demanding occasions. Therefore, in the design process of the control system, various factors such as control requirements and cost should be considered comprehensively, and an appropriate control motor should be selected.
5. Working speed of stepping motor:
Please refer to the torque-frequency characteristic diagram of each motor for details. Generally, the U3 H series can reach 3000 rpm without load, and the U3 series output rated torque is generally
Within 600 revolutions per minute, the U2 series output rated torque is generally within 300 revolutions per minute.
6. Heat problems of motors and drives:
The temperature that the motor can withstand is generally above 100 degrees, so it is normal for your hands to be hot during use. Small drive with large motor, such as 2M530 with 86
For the motor, pay attention to the heat dissipation of the driver, and it is best to work at low speed and intermittently.
7. Drive failure:
7.1 The motor is short-circuited between phases, or long-term overloaded operation, and burns the power module
7.2 The input control signal voltage is too high, reverse, or the high-frequency pulse stops suddenly, burning the input optocoupler
7.3 The input power voltage is unstable, or the regenerative current is too large, and the main power circuit is burned. Therefore, please pay attention to adding an isolation transformer, filter, and return.
Health absorption resistance, capacitance, etc.