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What are the ways to reduce and optimize structure-borne and air-borne noise of electric machines?

Views: 175     Author: Site Editor     Publish Time: 2022-08-02      Origin: Site

减少和优化电机的结构传播噪声和空气传播噪声的途径有哪些?

电机发生的运动振动是以空气传播噪声的形式从电机表面传播,在轴和电机固定底座处则以结构传播噪声的形式传播,在某种程度上,结构传播噪声转化为空气传播噪声进一步传播到环境中。为了降低噪声,一般的方法是中断从源到传输路径到耳朵的噪声链,或者直接在噪声源处减少噪声的产生。如果这是不可能的,至少可以尝试使噪音变得愉快或较少的反感,这项活动被称为“噪声优化”。通过对整个系统的优化来改变正在产生的噪声,所采取的措施必须始终考虑到经济因素。

绝缘和隔音

隔声屏障可以通过隔音和隔振来实现,绝缘层必须与阻尼层明确区分,阻尼层中的振动能转换为摩擦热。在固体中,这种摩擦热是由分子或相对较大的颗粒在体内相互运动引起的,也可由安装在设备外部的材料(如泡沫、无纺布材料、弹性体)引起,并表现出很大的内摩擦。为了使这种材料也具有阻尼效应,它必须附着在表面的振动波腹处。换句话说,附着在振动引起材料最大变形的位置,这种材料通常被称为绝缘材料,即使它不绝缘,也起阻尼作用。

 

对于液体,粘度具有阻尼效应,但仅与容器中液体的可压缩性或显著变形相结合,例如:水的阻尼能力很低,因为它的内耗很低,而且几乎是不可压缩的。油也几乎是不可压缩的,其显著较高的粘度只有在通过狭窄的开口时才会产生阻尼效果,换句话说就是改变形状,例如在减震器中。气体是可压缩的,但由于它们的粒子之间的距离很大,它们的内耗很低,因此阻尼能力很低。但是,如果气体流过如屏风、过滤器、泡沫,或者如果气体颗粒在这些屏障内振荡,那么摩擦、声压和声速就会增加,从而使声音体积减小,声能被“摩擦”成热。因此,屏风、过滤器和类似的装置都是消声器。一般来说,绝缘和阻尼措施必须分开考虑,它们往往是相互排斥的。然而,在许多情况下,采用绝缘和阻尼措施是有意义的,只有它们是在正确的位置才可行。


减少声辐射

通过封装整个电机,可以显著降低空气噪声对外部的辐射,在这种情况下,空气噪声的传播是有限的,而且是“阻塞的”。在这种情况下,必须考虑由封装本身引起的共振,以及空腔共振。通常,由于与驱动装置或环境的连接,整个电机无法完全密封。在开口的情况下,必须注意实现与声音传输有关的(声波)阻力的理想失配,并避免令人不快的反射。用隔音材料覆盖空腔有助于防止空腔共振,并有助于抑制空腔本身的振动。在消声的情况下,与隔声相反,声能被“破坏”(转化为摩擦)。在小型电机的情况下,由于与空间有关的原因,用绝缘材料覆盖密封舱通常是不可能的,或者是由于成本原因。

 

辐射噪声的表面可以通过为它们提供开口来减小,这会减小辐射表面的尺寸,也从根本上改变了表面的振动行为。这样,固有频率可以被移动,令人不快的振动模式连同它们的节点和波腹可以变得无害,附加的加强筋或支撑可以产生类似于开口的效果。


减少声振传递

减少声辐射而采取的措施也适用于防止电机振动通过轴和设备(或环境)中的电机安装系统传递,然而,有一些一般的“成功秘诀”:尽可能安装靠近最令人讨厌的振动运动的节点位置,最重要的节点位于轴承附近,仍然存在的振动运动应尽可能降低力振动。换句话说,在振动方向上尽可能地灵活安装系统,并且在给定的电机应用和其他条件(如传输冲击)下具有尽可能小的阻尼。如果力的震动很小,可以采用附加小振动运动的部件,即重量很小(轻型设备)。对于设备重量大,特别是在安装电机的区域,通常是有利的。当然,电机的振动质量、安装系统的弹性和电机安装附近设备的质量必须相互匹配,以便不会产生与不良运动频率的共振,调整系统使共振低于工作点。其他措施,如使用主动重量减振器或减震器,在理论上也是可行的。

 

减少声振激励

消除噪音和振动最好在它们产生的地方减少,即源头,在电机中,力和转矩是必需的,它们常常不可避免地包括不需要的部件(振荡转矩、齿槽转矩等),这是无法完全避免的。种类繁多,在目前遇到的电机概念中,其工作原理的变化也会导致各种噪声的激发。异步电动机的性能与同步电动机不同(包括电子换向电机和步进电动机),直流电机的性能与压电电机不同,因此,噪声和振动激励通常只能通过非常仔细地选择合适的电机和合适的电机尺寸来最小化。

 

结论:

优化是系统地影响声音和振动激励的努力,噪声优化的定义是系统地改变噪声的声学质量,以达到可能的最佳值。声学质量表示与听觉事件中单个需求的总体相关的需求得到满足的程度。理想的情况是,将令人不快的声场降低到听力阈值,通常在技术上或经济上是不可行的,我们可以试图影响噪声并改变它,从而消除令人不快的和令人不快的噪声成分。



What are the ways to reduce and optimize structure-borne and air-borne noise of electric machines?

The motion vibration generated by the motor is transmitted from the surface of the motor in the form of airborne noise, and is transmitted in the form of structure-borne noise at the shaft and the fixed base of the motor. To a certain extent, the structure-borne noise is converted into airborne noise and further spread to Environment. In order to reduce noise, the general approach is to interrupt the noise chain from the source to the transmission path to the ear, or reduce the noise generation directly at the noise source. If that's not possible, at least try to make the noise pleasant or less objectionable, an activity known as "noise optimization". The measures taken to change the noise being generated by optimizing the entire system must always take economical considerations into account.

Insulation and Soundproofing

The sound insulation barrier can be achieved by sound insulation and vibration isolation, the insulating layer must be clearly distinguished from the damping layer, and the vibration energy in the damping layer is converted into frictional heat. In solids, this frictional heat is caused by the mutual movement of molecules or relatively large particles in the body, and can also be caused by materials (such as foams, non-woven materials, elastomers) installed outside the device, and shows great large internal friction. In order for this material to also have a damping effect, it must be attached to the surface at the antinodes of the vibrations. In other words, attaching to the location where the vibration causes the most deformation of the material, this material is often referred to as an insulating material, acts as a damping even if it is not insulating.

For liquids, viscosity has a damping effect, but only in combination with the compressibility or significant deformation of the liquid in the container, e.g. water has a very low damping capacity because it has low internal friction and is almost incompressible. The oil is also almost incompressible, and its significantly higher viscosity produces a damping effect only when passing through narrow openings, in other words changing shape, such as in shock absorbers. Gases are compressible, but due to the large distance between their particles, they have low internal friction and therefore low damping capacity. However, if gas flows through e.g. screens, filters, foams, or if gas particles oscillate within these barriers, then friction, sound pressure and speed of sound increase, thereby reducing the volume of sound and the sound energy being "rubbed" into heat . Therefore, screens, filters and similar devices are all mufflers. In general, insulation and damping measures must be considered separately, and they are often mutually exclusive. However, in many cases it makes sense to employ insulation and damping measures, only if they are in the correct location.



reduce sound radiation

By encapsulating the entire motor, the radiation of airborne noise to the outside, where the propagation of airborne noise is limited and "blocked", can be significantly reduced. In this case, resonances caused by the package itself, as well as cavity resonances, must be considered. Often, the entire motor cannot be completely sealed due to the connection to the drive or the environment. In the case of openings, care must be taken to achieve an ideal mismatch of (sonic) resistance in relation to sound transmission and to avoid unpleasant reflections. Covering the cavity with soundproofing material helps prevent cavity resonance and helps dampen vibrations in the cavity itself. In the case of sound attenuation, as opposed to sound insulation, the sound energy is "destroyed" (transformed into friction). In the case of small motors, covering the capsule with insulating material is often not possible for space-related reasons, or for cost reasons.

Surfaces that radiate noise can be reduced by providing them with openings, which reduces the size of the radiating surface and also fundamentally changes the vibrational behavior of the surface. In this way, natural frequencies can be shifted, unpleasant vibration modes along with their nodes and antinodes can be rendered harmless, and additional stiffeners or supports can create an opening-like effect.


Reduce sound and vibration transmission

Measures taken to reduce acoustic radiation also apply to prevent motor vibrations from being transmitted through the shaft and the motor mounting system in the equipment (or environment), however, there are some general "recipes for success": mount as close as possible to the most annoying vibrational motion The node locations of the most important nodes are located near the bearing, and the vibration motion that still exists should reduce the force vibration as much as possible. In other words, mount the system as flexibly as possible in the direction of vibration and with as little damping as possible for a given motor application and other conditions such as transmission shocks. If the vibration of the force is small, a component with additional small vibrational movement, i.e. low weight (light equipment) can be used. It is often advantageous for heavy equipment, especially in the area where the motor is installed. Of course, the vibrating mass of the motor, the elasticity of the mounting system, and the mass of the equipment near where the motor is mounted must match each other so that resonance with undesirable motion frequencies does not occur, and the system is tuned so that the resonance is lower than the operating point. Other measures, such as the use of active weight dampers or shock absorbers, are also theoretically possible.

Reduce acoustic and vibration excitation

Elimination of noise and vibrations is best reduced where they are generated, i.e. the source, in electric machines forces and torques are necessary and they often inevitably include unwanted components (oscillating torque, cogging torque, etc.), This cannot be completely avoided. There are many kinds, and in the motor concepts encountered so far, changes in their working principles can also lead to the excitation of various noises. Asynchronous motors behave differently from synchronous motors (including electronically commutated motors and stepper motors), and DC motors behave differently from piezoelectric motors, so noise and vibration excitation can often only be achieved by very careful selection of the right motor and suitable motor size to minimize.

Conclusion

Optimization is the effort to systematically affect sound and vibration excitation, and noise optimization is defined as the systematic change in the acoustic quality of noise to achieve the best possible value. Acoustic quality represents the degree to which needs are met in relation to the population of individual needs in an auditory event. Ideally, reducing the unpleasant sound field to the hearing threshold, which is often not technically or economically feasible, we can try to influence the noise and change it, thereby removing the unpleasant and unpleasant noise components.