An Introduction to Active Vibration Control Systems for Effective Isolation

Isolation systems such as active vibration control systems, also referred as active vibration cancellation or active vibration isolation, react dynamically in response to incoming vibrations instead of passively decreasing the impact of vibrations by means of their mechanical structure.

Feedback and feed-forward are the two types of active vibration cancellation system. Feedback systems constantly sense incoming vibrations and react accordingly, whereas feed-forward systems are specially designed to offset routine periodic vibrations.

They sense incoming vibrations using a sensing mechanism and react to these vibrations by means of an actuator, which reduces the vibrations by tuning an isolator or negates them by producing a signal.

Table Stable Active Vibration Isolation Systems

Table Stable active vibration isolation systems are exclusively distributed by Herzan in the Americas, New Zealand, and Australia. They are hybrid systems consisting of active and passive isolation components.

These systems are manufactured in Table Stable’s workshop located in Zwillikon, Switzerland (Figure 1). Dr. John Sandercock developed the Table Stable active vibration control systems to support his Sandercock Interferometer, as interferometers are vulnerable to incoming vibrations.

The AVI Series and the TS Series are the two active isolation system lines offered by Herzan.

Table Stable's workshop in Switzerland

Figure 1. Table Stable's workshop in Switzerland

Working Principle of Table Stable Active Vibration Isolation Systems

The passive component of a Table Stable isolation system comprises stiff metal springs to support the load weight. These springs offer a basic level of vibration isolation in lower frequencies and outstanding vibration cancellation in higher frequencies. Besides supporting the load, they allow for actuator movement in the active component.

The role of an active isolation component is to augment and rectify the performance of the springs. Actuators, control electronics, and vibration sensors (piezo accelerometers) are part of the active isolation component.

Each isolation system consists of a minimum of eight sensors that are placed in different orientations to allow for sensing in all six degrees of freedom. The kinetic vibration energy is converted into electrical signals by the piezo accelerometers, which then transmit the signals to the control electronics.

The signals from the sensors are reconciled and processed by the electronics utilizing a proprietary algorithm. The actuators (piezo actuators) then receive a cancellation signal from the electronics.

Since they are connected to the various sensors, they are available in the same number, orientation and location as the sensors. The equivalent but out-of-phase vibrations created by the actuators cancel out the incoming vibrations, thereby allowing the load on the system intact (Figure 2). This process takes place within 5 to 20 milliseconds of a system sensing the vibration.

Illustration of vibration cancellation

Figure 2. Illustration of vibration cancellation

Advantages of the Feedback Loop

The feedback loop in a system consists of actuators, electronics and sensors. It not only reduces vibrations within the active range, but eliminates the low frequency resonance problem which affects all passive vibration isolation systems and removes incidental resonances which are intrinsic to simple mechanical structures.

The performance curve of the active systems shows a smooth roll-off progressing into the higher frequencies instead of a spiky curve representing deteriorated performance at certain frequencies.

The ability to use the stiff metal springs for the passive component is another advantage of the feedback loop. In passive isolation systems, soft springs are used to lower the low frequency resonance of the system to extend the isolator’s effective range. This approach leads to a very soft mount for the equipment that has a load on top of it.

The settling time is more for softer mounts. Conversely, Table Stable active isolation systems support the load through stiff metal springs, enabling them to settle out and start vibration cancellation within a second of a shock or impact (Figure 3).

Settling Time - TS vs. Passive

Figure 3. Settling Time - TS vs. Passive

Benefits of Table Stable Isolation Systems

The following are the key benefits of the Table Stable isolation system:

  • Compact, 5 to 20 millisecond response, and vibration cancellation in six degrees of freedom
  • No low frequency resonance and isolation in the low frequencies
  • Internal feedback loop damps all mechanical resonances
  • Tuning to vibration levels is not required for the feedback system
  • No air required and no ongoing maintenance

About Herzan

Herzan provides high performance environmental solutions for precision research instruments. They include acoustic enclosures, vibration isolation systems, Faraday cages, and site survey tools. Herzan specializes in supporting nanotechnology research, but also offers solutions for product testing, in-vitro fertilization, and many other applications.

Herzan understands that every application and environment is different, so it collaborates with customers to create comprehensive integrated solutions that satisfy their unique demands.

Herzan was founded in 1992 by Ann Scanlan in Orange County, California. Originally, Herzan was established as an American subsidiary of Herz Company Ltd., a Japanese company specializing in vibration control. The name Herzan comes from the amalgamation of 'Herz' and 'Ann'.

This information has been sourced, reviewed and adapted from materials provided by Herzan LLC.

For more information on this source, please visit Herzan LLC.

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