Novel Signal Processor Eliminates Self-Generated Vibration
PI holds Exclusive License for Novel Technology Based on
Research at the Massachusetts Institute of Technology (MIT)
Download Technote on Mach in MEMS Testing (1 MB, PDF)

A growing number of processes in manufacturing and testing require positioning resolution and accuracy in the nanometer and sub-nanometer realm. Apart from accuracy, the time factor is becoming more and more critical, especially in automated high-tech applications.

PI now offers the Mach™ Throughput Coprocessor, a unique plug-and-play solution for all processes requiring highest precision and ultra-fast response ("Nanometer- Precision in Milliseconds").

PI's Mach™ Signal Processor, a "black box" system upgrade, implements a patented real-time feedforward technology called Input ShapingTM that was developed based on research at the MIT (Massachusetts Institute of Technology). PI holds an exclusive license agreement with Convolve, Inc. (the technology's commercialization company) for marketing Input Shaping™ with piezoelectric NanoAutomation™ products. The solution to the problem "Nanometer-Precision in Milliseconds" can usually not be achieved by "simply" improving the accuracy and responsiveness of the Nanopositioning system.

Fig. 9

For example, the force that a NanoStage applies to its load and fixturing will cause them to vibrate in their resonant modes. At the same time, the recoil force that the stage confers to its supporting structure (which is equal and opposite to the force applied to the load) will in turn excite resonances in the supporting structure.

Usually these vibrations can take hundreds of milliseconds to damp away, which is several orders of magnitude longer than the settling time of the unloaded Nanopositioning stage. Conventional control techniques cannot significantly improve this situation, since the main problem is caused by the reaction of elements outside the servo loop. In addition, most systems show several resonant frequencies. All these problems can be solved by plugging the Mach™ Coprocessor inline between the controlling computer or function generator and the PI controller. It's patented technology simply stops the Nanopositioning stage from exciting resonances in the supporting structure or payload. Therefore, the point of interest in the positioning system can settle in 1/f0 where f0 is the lowest resonant frequency in the system.

Fig. 10, Laser Vibrometer measurement of fixture resonance, excited by the rapid movement of the Nanopositioning Stage (which is not overshooting!) without Mach™
Mach™ is installed outside the feedback loop (Fig. 9) and, in operation, receives no information from the motion de-vice, computer or other system elements. It requires no modification to the customer's setup, application software or servo parameters which is why open loop positioning systems also benefit from Mach™'s unique performance. Setting up Mach™ is very easy. First, the vibration frequencies created by the Nanopositioner's actuation are measured (e.g. by a Polytec non contact Laser Vibrometer) at the point of interest. Next the frequencies are fed into a coefficient- generating utility running on a World Wide Web page and the resulting coefficients are then downloaded into the flash RAM in the Mach™ Box. The Coprocessor is now capable of modifying all input signals (in real-time!) in a way that resonances at the point of interest cannot be excited. Mach™ is not to be confused with a filter. It works with random signals as well as with periodic waveforms such as sine, triangular or square waves. Mach™ even neutralizes transients with the same efficiency.

Fig. 11, Mach™ nullifies the fixture's resonant recoil behavior. The servo parameters are the same as with Fig. 10

More information at PI Nanopositioning Technologies

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