The noise size in the motor depends on motor type, environmental conditions and specific applications. Permanent magnet motors and mixed stepping motors are usually quite quiet because their rotation is relatively stable. The variable magnetic blocking motor is the most no matter where it is used. In order to better understand the source of noise, we need to think about how the rotational movement is generated. When the step motor is stepped, it will not stop immediately, but will continue to move slightly before and after, and then stop. This problem can be overcome by using a specific control logic in the motor drive. During the motor run, the motor is started after the motor is completed but stopped, the drive issues the next step. This continuous and regular motor proceeds can reduce noise and vibration. Also note that each stepper motor has a resonant frequency, typically resonance when the motor is moved at a speed of 150 to 300 per second. Many designers tend to avoid the operating frequency range to minimize noise and vibration. However, the slower reducer inserts appropriately designed and adjusts the size can also reduce vibration. There is also a traditional solution that installs the rear damper on the crankshaft, which can also reduce vibration. Most stepper motors of noise reduction are controlled by pulse width modulation (PWM) signal, which continuously forces H bridges to switch between switching states, and adjust the current of the motor. Based on this technique-based driver circuit is often referred to as a chopper driver because it will subtop the output voltage to the output voltage to the PWM waveform, thereby providing a constant current for the motor windings. In contrast, the L / R technology is intended to keep the voltage applied to the winding constant, and the advantage of current chopping is that it is a very efficient, compact and economical solution that only produces little heat. It should be noted that the modulation signal applied to the stepper motor generates an audio signal, which is more serious when the PWM frequency falls within the audio band. Through experiments, it is easy to verify how the stepper motor generates noise, even when the motor is stopped or held in a certain location. This phenomenon is mainly generated when the switching frequency is less than 20 kHz. Therefore, the first method of reducing noise is to increase the switching frequency. Most chopper drivers can increase the switching frequency by modifying the value of an external resistor or capacitor. Its purpose is to change the duration of the PWM signal for current-regulated PWM signals in the closed state, the shorter the duration, the higher the switching frequency. However, the frequency does not have to be too high, because the switching loss will increase by more than a certain limit. A more appropriate switching frequency value is between 30 and 50 kHz. If this is not yet, the current applied to the motor winding can be reduced. In fact, lower current means reducing vibration, of course, noise is reduced. However, this method also has side effects, that is, torque will decrease. If the torque is too low, it will cause operation to fail. Since the motor is open-loop control, it is necessary to provide a current sufficient to cover all of its operating conditions, even under the most harsh conditions. A good compromise is to reduce current during the motor stop. Typically, the current required for the motor hold position is large below the current required to accelerate or rotate the motor at a constant rate. In fact, all stepper motor drivers can set the current value by modifying an analog reference voltage Vref. The trip current ITrip is a function of external RSENSE resistors and VREF reference voltages. Once the designer selects the RSENSE resistor, the value is fixed at runtime, so it can modify the ITrip by dynamically change VREF. If you need to further reduce noise, the motor can be run at a slow attenuation mode (not a fast or mixed attenuation mode). This model minimizes the drive current ripple, thereby reducing noise and improving the efficiency of the drive. However, slow attenuating mode is not always the best solution, especially when using microclocking techniques. Stepping Drive Integrated Drivers are intended to provide simple configuration and advanced control functions for various types of applications. The integrated encoder option makes a stepper motor a best choice for synchronous location applications. Just connect the coil to the power transistor and connect the transistor to the control circuit, the stepper motor can be driven. Figure 1: Block diagram of a3982. (Source: allegromicrosystems) AlleGromicrosystems is a leader with brush DC motor and stepper motor driver design and manufacturing, providing a range of secure and reliable solutions for integrated MOSFET gate drivers. The company's A3982 is a complete stepper motor drive, built-in converter, easy to operate, is suitable for low power and high power applications. The A3982 is used to run a bipolar stepper motor in full step and half step mode, which provides up to 35V and ± 2A output signals. Current attenuation mode (slow attenuation or mixing attenuation) can be selected by applying a signal on the STEP input pin, as shown in the schematic block diagram of Figure 1. In the mixed mode, chopping control is initially set to fast attenuation mode, and the duration is 31.25% of the fixed shutdown time, and then set to slow attenuation during the remaining time. This current attenuation control mechanism reduces motor noise that can be heard, improves step precision and reduces power consumption. The characteristics of the converter greatly simplify the design of the motor control system. Simply apply a pulse on the STEP input pin, the motor is driven, no preface table or high frequency control line. Therefore, in applications where the host microcontroller is unavailable or loaded, the A3982 is the best choice. Toshiba Electronic Components and Storage companies also offer a variety of stepper motor drivers. Its TB67S128 / 249/279/289 device adopts proprietary active gain control (AGC) technology. The AGC can dynamically adjust the drive current of the stepper motor to deal with the large torque state and restore normal current values in real time and open-loop design. AGC technology can greatly reduce power consumption and reduce or avoid more complex closed-loop design. Figure 2: Typical application of TB67S128 motor driver (Source: Toshiba) TB67S128 / 249/279 / 289FTG device operating voltage is 10V to 42V, which can provide 5.0A, 4.5A, 2.0A and 3.0A current, respectively. These devices also provide 32 steps and 128 steps in a quadrant to make them suitable for extensive industrial precision motor control applications (Figure 2). Conclusion Stepper motors have a simple structure and is easy to control. As a digital electronic component, the stepping motor is widely used in various open-loop control systems. However, the noise generated by the drive circuit and the resonant mechanical structure affects overall performance. Most stepper motor applications require smooth operation. In order to achieve smooth running effect, the designer can modify the voltage, current, or more commonly to modify the microcreen settings. Responsible Editor: LQ
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