高级算法最小化了精密运动控制应用中的步进电机噪声和振动亚博尊贵会员

高级算法最小化了精密运动控制应用中的步进电机噪声和振动亚博尊贵会员

由Dan Jacques，Startgro Microsystems Inc.的战略营销经亚博棋牌游戏理

Stepper Motors: Benefits and Challenges

步进电机在许多应用中提供直接电流（DC）和无刷直流（BLDC）电机的独特优势。亚博尊贵会员双极步进器提供精确的开环位置以及不使用控制回路或外部传感器的零速扭矩。通过控制的步进能力，步进电机非常适用于各种精密运动控制应用，包括闭路电视（CCTV），3D打印机，计算机数控（CNC），纺织制造设备和拾取机。亚博尊贵会员

Successful deployment of stepper motors requires effective management of noise and vibration. In CCTV applications, for example, vibration translates directly to the image sensor and gimbal. Large zoom combined with movement can distort the image. In 3D printing, motor resonance or overshoot caused by high torque ripple can result in many unwanted printing artifacts. In most cases, reducing motor vibration results in better image quality or more precise 3D printing. Reducing motor vibration also enables quieter overall operation.

Advanced technologies based on proprietary algorithms—such as QuietStep found in Allegro’s A5984 microstepping motor driver—are now available to minimize noise and vibration in stepper motor designs by reducing torque ripple and current distortion. Before delving into these motion control solutions, it’s helpful to understand what causes vibration and in turn audible noise, starting with how a stepper motor operates.

Stepper Fundamentals

A bipolar stepper motor is a DC motor with discrete pole positions constructed of multiple coils arranged in two groups called phases. The current ratio between the two phases determines how the rotor is positioned between the two windings. In this way, a stepper motor can divide its position between two poles into smaller increments called microsteps.

可以求和每个步进电机绕组中的电流来创建载体的大小是扭矩的矢量。通过检查极性空间中的两个阶段中的每一个中的每次，可以通过每个电循环旋转时来可视化向量。

Figure 1. Left - Phase current in each of two windings of a bipolar stepper motor in 1/8th step.
Right – Phase current in each of two windings of a bipolar stepper in 1/8th step but represented in the polar domain.

In the time-based domain (Figure 1, left), the torque is defined as the sum of the area under the two curves. In the polar domain (Figure 1, right), the magnitude of the vector is the torque. In these images, the torque can be seen as constant as the field moves through each electrical cycle. When torque is not constant, the system experiences vibration and audible noise.

Assuming the motor is not operating at resonance, torque ripple becomes the biggest source of audible noise and vibration in a stepper motor.

Controlling a Stepper Motor (Current Control)

脉冲宽度调制（PWM）电流控制是驱动步进器的最常见方法。通过实现电流控制，控制器PWM将输出排序，限制每次绕组中的电流以维持限定定义转子位置的比率。

The nature of PWM current control results in current ripple based on the applied duty cycle, the inductance of the motor, and the voltage across it. To minimize ripple, the controller can manage how the current decreases in the windings by implementing various decay modes.

Common decay modes for a single PWM cycle begin with drive current ramp-up.

Following the drive, shown in figure 2A, the decay mode is implemented during PWM off-time through two synchronous methods shown in figure 2B and 2C.

Figure 2: Current path in full bridge showing drive and decay modes.

快速衰减提供最佳电流控制，但导致高纹波。缓慢衰减导致低纹波，但衰减率受电机的背部电动势（BEMF），这在某些情况下可以产生电流的扭曲。

图3a显示了使用100％缓慢衰减时会发生什么。当绕线电流下降时，缓慢衰减不能足够快地减小电流，导致下降沿的失真。图3B显示了使用100％快速衰减的效果。纹波电流要大得多，但控制器保持对电流的准确控制。

图3A缓慢衰减会在负载电流降低时产生失真。
Figure 3B. Fast decay causes large ripple current, which can result in vibration and audible noise.

可以避免图1中所示的效果，同时通过达到折衷来保持合理的纹波电流。当电流在负载中减小时，驾驶员实现快速和慢衰减的组合，称为混合衰减。关闭时间被分成快速衰减的一部分和慢衰减的一部分，如图4所示。当负载中的电流增加时，慢衰减最小化纹波。

Figure 4. Mixed decay minimizes ripple while also maintaining control of the current in the winding.

Depending on a stepper motor’s characteristics and its LR time constant, slow decay on the rising edge can create issues at low currents where the rate of change in current is too fast for the PWM controller to regulate to low currents due to current sense amplifier blanking. This scenario can result in current distortion when the current in the load is increasing, as shown in Figure 5.

图5.上升沿的慢衰减可能导致具有某些LR特性的电机中的失真。

It’s difficult to achieve an easy compromise that works for all bipolar stepper motors. To solve these issues while maintaining the lowest ripple possible, the system must adapt to different motor characteristics.

A New Approach to Reducing Torque Ripple

Allegro has introduced a novel way to reduce torque ripple and current distortion for stepper motor applications. This innovation, QuietStep, is now available as an option on Allegro’s latest A5984 stepper motor driver.

安静的技术使用专有的算法，动态调整（向上或向下）在逐个周期的基础上进行快速衰减的百分比，以在不使用复杂软件的情况下在所有操作条件下实现最佳性能。

The algorithm reverses the traditional approach to mixed decay by implementing slow decay first, followed by fast decay. Figure 6A shows traditional mixed decay with the fixed portion of fast and slow decay and with fast decay starting the PWM off-time cycle. Figure 6B shows how slow decay starts when using QuietStep at the beginning of the PWM off-time cycle. QuietStep automatically adjusts the ratio of fast and slow decay to minimize current ripple while maintaining accurate current regulation.

Figure 6A. Traditional mixed decay where the ratio of fast and slow decay is fixed.
Figure 6B. Adaptive-PFD can dynamically adjust the ratio of fast and slow decay to maintain current control and minimize current ripple.

仅在电流调节所需时才能快速衰减，导致最低可能的纹波电流。图7显示了由固定的混合衰减产生的高纹波电流，随着电流的慢衰减，电流控制的电流和电流控制的电流和损耗导致。与混合衰减相比，安静的技术通过切割纹波电流，消除了这些效果。当电流正在增加时，安静的步骤将当前调节维护到零安培。

Figure 7. Traditional slow decay with increasing current and mixed decay for decreasing current results in loss of regulation on rising with increasing current and large ripple with decreasing current. Adaptive-PFD provides excellent current regulation with increasing current while maintaining low ripple current through the entire electrical cycle.

Reducing system-level current ripple and resonance minimizes vibration as well as audible noise caused by vibration. The result is better video imaging in CCTV systems and superior print quality in 3D printing.

从家庭自动化门锁和阀门控制到精密视觉系统和3D打印，降低了几乎每个电机控制应用都会增强噪音和振动。Allegro的EventStep技术消除了试图确定系统中噪音和振动源的麻烦。完全集成到IC中，静音易于实现，不需要编程或外部组件，并完全自动。

Deploying QuietStep with Allegro’s Bipolar Stepper Motor Driver

使用MicroStepping Motor驱动程序实现这种先进技术，如AllegroA5984, current waveforms are automatically optimized over a wide range of stepper motor speeds and characteristics. Stepper motor driver solutions, equipped with QuietStep technology, adjusts the amount of fast decay on-the-fly during a PWM cycle to minimize current ripple over various operating conditions. This feature improves system performance, resulting in reduced audible motor noise, lower vibration, and increased step accuracy. Utilizing this technology, the A5984 driver is designed to operate bipolar stepper motors from full-step up to 1/32 step modes and enables an output drive capacity of up to 40 V and ±2 A. Overall, an QuietStep algorithm allows for easier system design, implementation and operation.

了解有关A5984驱动程序和安静的技术，访问的更多信息www.wangzuanquan.com/a5984.

Allegro MicroSystems is a global leader in power and sensing solutions for motion control and energy-efficient systems. For more information, visitwww.wangzuanquan.com.。

基于文章，“Minimizing Stepper Motor Noise and Vibration in Precision Motion Control Applications“由Allegro Microsyste亚博棋牌游戏ms的Dan Jacques，最初发布All About Circuits, February 2021. The original article can befound here。Used with permission. For portions not copyrighted by original publisher, Copyright ©2021, Allegro MicroSystems, INC.