电动机通过转子和定子中的磁场的相互作用产生扭矩和旋转。在一个理想的电动机 - 机械部件，完美加工和组装的和电场，即建造和衰减即时 - 扭矩输出将是完全光滑的，没有变化。但在现实世界中，有多种因素导致扭矩输出不一致 - 即使只有少量。通电电动机的输出扭矩的这种周期性波动被称为扭矩脉动。
在数学上，扭矩脉动被定义为在电动机的一个机械旋转上产生的最大和最小扭矩之间的差异，除以一旋转产生的平均扭矩，表示为百分比。
In linear motion applications, the main effect of torque ripple is that it causes motion to be inconsistent. And because motor torque is required to accelerate an axis to a specified velocity, torque ripple can cause velocity ripple, or “jerky” motion. In applications such as machining and dispensing, this inconsistent motion can have a significant effect on the process or end product — such as visible variations in machining patterns or in the thickness of dispensed adhesives. In other applications, such as pick and place, the torque ripple and smoothness of motion may not be a critical performance issue. That is, unless the roughness is severe enough to cause vibrations or audible noise — especially if the vibrations excite resonances in other parts of the system.
The amount of torque ripple a motor produces depends on two main factors: the motor’s construction and its method of control.
电机结构和齿槽扭矩
在其转子中使用永磁体的电机 - 例如无刷直流电机，步进电机和synchronous AC motors- 体验称为齿槽或齿槽扭矩的现象。齿槽扭矩（通常在步进电机的上下文中称为制动扭矩）是由转子和定子齿的某些转子位置处的定子齿引起的。
图片信用：Kollmorgen
虽然通常与手动转动无动力的电动机时可以毡的“凹口”相关联，但是当电动机供电时也存在齿槽扭矩，在这种情况下，它有助于电动机的扭矩脉动，尤其是在慢速操作期间。
There are ways to mitigate cogging torque and the uneven torque production that results from it — by optimizing the number of magnetic poles and slots, and byskewing or shaping the magnets and slotsto create overlap from one detent position to the next. And a newer type of brushless DC motor — theslotless, or coreless, design — does away with cogging torque (although not torque ripple) by using a wound stator core, so there are no teeth in the stator to create periodic attractive and repulsive forces with the rotor magnets.
Image credit: Lin Engineering
齿轮扭矩也可以发生在交流感应电动机中，其中转子的磁场由定子的场引起，而不是由磁体产生。然而，为了避免齿槽，构造AC感应电动机，使转子槽与定子槽的比率是非整数倍数。
Motor commutation and torque ripple
永磁无刷直流(刷)和synchronous AC motors are often differentiated by the way their stators are wound and the commutation method they use. Permanent magnet synchronous AC motors have sinusoidally wound stators and use sinusoidal commutation. This means that current to the motor is continuously controlled, so torque output remains very constant with low torque ripple.
For motion control applications, permanent magnet AC (PMAC) motors may use a more advanced control method known as面向领域的控制（焦点）。通过面向磁场控制，可以独立地测量和控制每个绕组中的电流，因此甚至进一步降低扭矩脉动。用这种方法，带宽当前的控制回路和解决反馈设备的分辨率also affect the quality of torque production and amount of torque ripple. And advanced servo drive algorithms can further reduce or even eliminate torque ripple for extremely sensitive applications.
与PMAC电机相比，无刷直流电动机具有梯形伤口定子，通常使用trapezoidal commutation. With trapezoidal commutation, three Hall sensors provide information on the position of the rotor every 60 electrical degrees. This means that current is applied to the windings in a square waveform, with six “steps” per electrical cycle of the motor. But current in the windings can’t rise (or fall) instantaneously due to the windings’电感，因此在每个步骤中发生扭矩变化，或每60个电度发生。
Image credit: STMicroelectronics
Because the frequency of the torque ripple is proportional to the motor’s rotational speed, at higher speeds, the motor and load inertia can serve to smooth out the effects of this inconsistent torque. Mechanical methods to reduce torque ripple in BLDC motors include increasing the number of windings in the stator or the number of poles in the rotor. And BLDC motors — like PMAC motors — can use sinusoidal control or even field-oriented control to improve the smoothness of torque production, although these methods increase system cost and complexity.
提起：线性运动提示
