Active Vibration Cancellation Technology

Interview conducted by Will SoutterJan 4 2016

In this interview, Wes Wigglesworth from TMC talks about the technology and applications of their active vibration cancellation systems.

Could you provide our readers with a brief overview of TMC and the industries that you operate in?

TMC designs and manufactures advanced active and passive floor vibration cancellation systems as well as magnetic field cancellation systems and acoustic enclosures.

We continue to lead the industry with sophisticated active, inertial vibration cancellation systems featuring piezoelectric actuators and digital controllers.

Our passive products range from simple, desk style isolated microscope tables, to virtually any size optical table systems. We also have a new active benchtop system I would like to discuss.

TMC products enable ultra-precision research, measurements, and manufacturing in the fields of photonics, semiconductor manufacturing, materials sciences, life sciences, drug discovery, and nanotechnology.

Our products are designed and manufactured at our state-of-the-art, vertically integrated manufacturing facility and are backed by a commitment to provide superior global service.

TMC Everstill™ K-400 benchtop in use with a Taylor Hobson bearing measurement system

How do active vibration cancellation systems work?

The term “active” is often misused in the world of vibration isolation. When TMC talks about active vibration cancellation (VC), we really mean “inertial” active vibration cancellation.

This means the isolation system includes vibration, not position sensors, which continuously measure mechanical vibration with respect to the Earth, and actuators in a closed-loop feedback system which act with an opposing force to cancel the measured vibration.

A pneumatic vibration isolation system with self-leveling height control is not an inertial “active” vibration isolation or cancellation system. While passive pneumatic systems are very good at attenuating high frequency (above 10 Hz) vibration, this is essentially a mass-spring damper acting as a low pass filter. TMC is a leader in this field with our Gimbal Piston technology designed into our line of Micro-g^® products.

Only an inertial, active VC system, however, will aggressively cancel vibration or motion originating in the isolated payload, and/or vibration coming from the floor or frame supporting the isolators. TMC designs and manufactures both such active VC systems, known as parallel and serial type respectively.

In parallel-type active VC, the sensor-actuator control loop is in parallel with a spring; the spring is attenuating the floor vibration while the active control system is coupled to the payload to cancel payload motion, such as that induced by a moving stage. TMC provides such a solution with our Electro-Damp^® technology.

In serial-type active VC, the sensor-actuator is in series with a spring. This is the approach in TMC’s unique serial architecture employed in our Stacis^® technology, and now in the new Everstill technology. Only such a serial-type inertial active VC design can provide highly aggressive low frequency (below 10 Hz) vibration cancellation.

Specifically, these unique technologies operate with an active bandwidth from as low as 0.6 Hz and up to 150 Hz and deliver 50% cancellation at 1 Hz and 90% starting at 2 Hz. This is achievable due to two key design features.

First, the active control loop is decoupled from payload. This allows us to maximize the bandwidth in spite of payload resonances without the need for payload-dependent tuning, retuning, or even de-tuning as is the case with parallel-type technologies.

Second, velocity-type sensors, with sensitivity down to levels below 1 Hz, are combined with high capacity actuators for low frequency vibration cancellation unmatched in the industry.

In what fields is active vibration cancellation used and why is it necessary?

A researcher, design engineer or facility manager may require active vibration cancellation due to the harsh environment in which they work, or because of the sensitivities of the instrument, procedure or device they are working with - or both.

Typically, a precision inspection or imaging tool is inherently sensitive to vibration, and often is designed with passive air isolators or springs internally. As such, many precision instruments achieve their high level of performance in a ground-floor lab or relatively quiet building or development lab.

But when installed in a semiconductor fab, research hospital (particularly an upper floor), or high-traffic materials research facility, for instance, the highest performance and resolution are not achievable due to low frequency ambient vibration and transient events.

Very often, a point-of-use active inertial VC platform with Everstill or Stacis technology is needed to support the instrument and enable high resolution imaging and sensitive procedures.

Our customers are most often working with scanning probe microscopes (including atomic force microscopes), scanning and transmission electron microscopes, other charged-beam instruments, mask alignment tools, wafer metrology, and failure analysis instruments used in the fields of photonics, semiconductor manufacturing, life sciences, drug discovery, and nanotechnology.

TMC Everstill K-400 isolating an optical microscope

TMC offers the Everstill™ K-400. What are the advantages of using this system?

Everstill is a new technology developed by TMC. TMC has been known as the leader in vibration isolation, and Everstill is the next generation in active inertial vibration cancellation. The patented technology delivers aggressive vibration cancellation starting at 0.7Hz, in a compact serial-type design.

The K-400 is the first benchtop system with the Everstill technology. The best-in-class vibration cancellation in the 1-10Hz range is a significant advantage for researchers, technicians and designers who are pushing the limits of their small precision instruments.

The K-400 is very easy to set up and start using. Simply plug in the power cord and power on the unit with one press of a button. The unit senses an off-center payload, levels the top plate and automatically closes all the sensor-actuator control loops to initiate active inertial vibration cancellation, all within a matter of seconds.

Could you tell our readers about how the geophone-type velocity sensors, used by the Everstill™ K-400, work?

TMC has been working with velocity-type sensors in active VC since the mid-1990s. Vibration cancellation benefits from geophone sensors due to their sensitivity well below 1Hz. To achieve the aggressive attenuation which Everstill delivers, a velocity-type sensor is required.

The signal from the absolute velocity sensor is amplified, then processed via sophisticated algorithms, then sent to the actuators to counteract the floor or table vibration starting at approximately 0.7 Hz.

What do you believe gives TMC a competitive advantage within the market?

Remember, Everstill employs serial-type architecture, very similar to our Stacis technology. Stacis is highly regarded in our industry for supporting some of the most sensitive electron-beam and ion-beam based instruments in semiconductor fabs and research facilities worldwide. In the K-400, we now have a very similar solution for much smaller, yet still very demanding instruments in a compact and portable package.

The competitive advantages become clear for two reasons: vibration cancellation at low frequency, and stability. Serial-type active systems achieve better overall vibration isolation because payload resonances are mechanically filtered from the vibration sensors. This allows for high gain settings with no sacrifice in system stability.

The added stability from the stiff springs inside of Everstill enables longer hold times for critical procedures. No other commercial product can provide such a solution.

Where can our readers find out more about the Everstill™ technology, the K-400 and TMC’s work in the field of active vibration cancellation?

The best place is our website, www.techmfg.com. We also have applications engineers available by phone at our headquarters in Peabody MA who can be reached at 1-800-542-9725.

About Wes Wigglesworth

Wes Wigglesworth has been with TMC since 1997, and is currently the Product Manager for TMC’s flagship line of Active Vibration and Noise cancellation systems, including Stacis, Stacis iX, Mag-NetX and the new Everstill.

Wes has previously held positions in Application Engineering, Sales Engineering, and OEM Account Management in the scientific and technology industry over a period of over 24 years. He holds a bachelor's degree in Electrical Engineering from Tufts University in Medford, MA.