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 MachTM Throughput Coprocessor, a unique plug-and-play solution for all processes requiring
highest precision and ultra-fast response ("Nanometer-Precision in Milliseconds").
PI's MachTM 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 ShapingTM
with piezoelectric NanoAutomationTM 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.
|
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.
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 pageand 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. |
| 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 TM Coprocessor |
Fig. 10, Laser Vibrometer measurement of
fixture resonace, excited by the rapid
movement of the NanoPositioning Stage
(which is not overshooting!) without Mach
Fig. 11, Mach nullifies the fixture´s resonant
recoil behavior. The servo parameters
are
the same as with Fig. 10 |
