The complex world of vibration control systems can often be categorized into two main types: passive and active vibration control. These are critical considerations in applications that demand precision and stability, such as in the use of highly sensitive scientific instruments or heavy machinery. Passive vibration control is simpler and involves the use of materials…
The complex world of vibration control systems can often be categorized into two main types: passive and active vibration control. These are critical considerations in applications that demand precision and stability, such as in the use of highly sensitive scientific instruments or heavy machinery.
Passive vibration control is simpler and involves the use of materials like steel springs, rubber mounts, or air chambers that provide attenuation to vibration, primarily at very high frequencies. The degree of attenuation is heavily reliant on the resonant frequency of the material or spring used. For instance, rubber and steel springs, with resonant frequencies around 8-10 Hz and 4-7 Hz respectively, can only attenuate vibrations above these frequencies. The ease of setup and lack of height control make passive isolators suitable for applications with less sensitivity to floor vibration, such as low-power optical microscopes or machinery in a factory.
On the other hand, pneumatic isolation, a form of passive vibration control, offers superior performance because it operates at a lower resonant frequency, around 2 Hz, and starts attenuating vibrations at around 4-5 Hz. However, it’s more challenging to set up and requires a continuous supply of air or nitrogen. It typically involves a mechanical self-leveling system, which senses payload deflection and re-levels the payload. Some may mistake pneumatic isolation systems with self-leveling height control as active vibration control systems, but this is not accurate. These systems lack the essential components of an active vibration control system: an inertial sensor and an active feedback or feed-forward loop.
Active damping, often used in combination with a pneumatic spring, uses a sensor mounted to the payload, and a signal is sent back to the controller. The controller then controls the air flow into the isolator to reduce amplification at the air isolator’s resonance. This can be considered a form of active control, but it is important to note that this only reduces the resonance amplification and does not enhance the overall performance of the vibration isolation system.
In summary, while passive and active control systems each have their unique advantages and appropriate use cases, it is crucial to understand the specific requirements of the application in question to make an informed decision on the most suitable type of vibration control. Understanding the frequency range of vibration disturbances that need to be controlled and the required level of precision are critical factors in this decision-making process.
Video TranscriptExpand ↓
Hi there. I'm West Wigglesworth with TMC, and I'm here at our headquarters in Peabody, Massachusetts, just north of Boston. And today, I will be talking about vibration control, and the key differences related as compared to passive vibration control. So first, I thought I'd start off by talking about some of the key elements that are required to really call something active vibration control. So, really, the three key components are an inertial sensor that actually measures the vibration, a control system with a feedback loop. And an actuator. Alright. So one of the things about active vibration control and passive vibration control is that The terms can be interchanged and sometimes confused. So I wanted to just back up and give some examples about both types of systems. And I was going to start with something that the industry as a whole really agrees on, and that is that a simple spring is a passive isolator. So something like steel spring between two two steel plates, a rubber mount, and something like an air chamber that simply gets pumped up with air and you put your payload on top of these type these isolators, four of them typically. And it supports the payload, and it attenuates vibration but only a very high frequencies, and it's very dependent on the resonant frequency of the spring. So rubber springs could be an eight hertz isolator, ten hertz, even hertz isolator, and a steel spring could be something like four hertz or seven hertz. And, of course, an air spring is typically a little bit lower frequency, and that's important because anything below any vibration that is below that frequency coming from the floor will not get attenuated. So these simple simple rubber mount steel springs, they're easy to set up. There's no height control and their promote performance again, mainly because they're only attenuating for vibration that is above that resonant frequency. So very high frequencies are attenuated. Now typical applications for simple passive rubber mounts are things like simple optical microscopes, low power, low magnification, machinery in a factory if you're trying to reduce the impact of that machinery on the rest of the factory. These would be simple rubber mounts that are used in applications that. Very very low low low magnification type of instruments things that are not highly sensitive to to floor vibration. Now the next step up would be something known as pneumatic isolation. And one of the first differences is that it's a little bit more difficult to set up. So with a pneumatic isolation system, the vibration isolation performance is much better than a simple rubber mount or steel spring. Because it's a softer isolator. It has a resonant frequency of around two hertz, maybe a little bit less than that, maybe a little bit more, But it's attenuating floor vibration starting at around four or five hertz compared to a simple rubber spring that amplifying at that frequency or even amplifying at a higher frequency. So pneumatic system, little bit more difficult to set up than a passive spring but well worth it. And typically includes a mechanical self leveling system, which is a high control valve and a mechanical linkage to the payload, and that senses, you know, a deflection in the payload and re levels that payload. It does require continuous supply of air or nitrogen. And an option for the height control is electronic non contacting height control. And another option in combination with a pneumatic spring is an active damping system. Now some will consider pneumatic isolator with self leveling height control to be an active vibration control system, but it's really not. It is passively attenuating the floor vibration. Yes. There's a sensor, but it's a mechanical linkage to the payload. That is reacting to the deflection of the payload -- Mhmm. -- and then controlling the air in and out of the isolated to re level. The the isolator and the payload, but it's not active vibration control. There's no inertial sensor, and there's no active feedback loop or feed forward loop. With these other options, electronic height control. Again, some might consider that active vibration control, but it really is just to improve the precision of the height repeatability system and the the height control system. With active damping, we would add a sensor to the payload So it would be, you know, a sensor mounted to the payload, and a signal back to the controller, which then activates the air going in and out of the isolator to really only reduce the amplification at the resonance of the air isolator. So that is an active control system, but it's not improving the overall performance of the vibration isolation system. It's only attenuating the amplification of the resonance of the the air isolator.
