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Interferometric calibration of microdisplacement actuators

Project Description

Precise positioning in nanometrology, scanning probe microscopy, and process control in nanofabrication needs of traceable displacement actuators operating in the micrometric and nanometric ranges of displacements. High sensitivity actuators have usually onboard position sensors in a closed-loop control of displacements.

The proposed cooperation in research is a pilot study on interferometric measurements of displacements (from the micrometric range down to the sub-wavelength range) of high-sensitivity actuators. The project has been re-proposed and discussed at the 2004 TC Length Meeting.

IMGC will circulate a commercial piezo-capacitive 10 µm actuator (with driver), which moves a 1“ flat mirror. Partners are asked to drive the analog input of the driver and relate this to the actuator displacements (possible from the micrometric full range down to the sub-wavelength range). Unwanted rotations should be measured to the extend possible.

The DPT-10  manual from the manufacturer will be provided.

Final Report 2018-02-28

Eleven laboratories from EURAMET and one laboratory from AFRIMETs participated in this “Co-operation in Research” project as a pilot study on interferometric calibration of microdisplace-ment actuators. Measurements reports have been submitted by all the laboratories. Measurements have been performed with homodyne and heterodyne interferometers, various optical and mechanical set-ups, and different orientations (horizontal, vertical up and vertical down) of the actuator. Compensation of the optical non-linearity made mostly use of own methods and associated software tools. Traceable instruments were used to measure temperature and ambient air parameters for air refractivity correction.

Some deviation of full range displacements occurred for a certain period covering the measurements by three labs and one by the pilot. It has no longer been observed with calibration measurements repeated by the pilot after about one year. A compensation for has not been introduced. The observed deviation is noticed in the results of these labs, likely with a contribution to the uncertainty of the artefact. Other contributions from hysteresis, drift and bending of the connecting cable have been considered, as well.

The overall reported results, corresponding to displacements vs. driving voltage of the actuator, have been analyzed either by weighted mean and simple mean approaches. The analysis makes use of a calculus sheet early proposed and contributed by partners. The En values are determined with reference to the positions calculated by the coefficients of a common third order polynomial with full scale displacements , and by a common average slope with short range displacements.

The En values of displacements up to ± 5 μm show some inconsistency of results with possible outliers, and some spread of results, thus requiring future steps to better highlight, quantify and compensate for errors not yet well identified or underestimated. Nevertheless, it is worth noting En values together with the ratio between the deviation of individual positions from the reference value and the associated uncertainty of the difference, ratio within 1 for most of the laboratories.

Meanwhile, a generally good consistency is obtained with short range displacements within ± 100 nm, as demonstrated by the En values (< 1) of all reported positions/labs, and by the ratio well within 1 between the deviation of individual positions from the reference value and the associated uncertainty of the difference. Some spread of results has been observed with the unwanted rotations (yaw and pitch) of the actuator driven up to the full range displacements. Changes of the maximum pitch and yaw by reorienting or by turning the actuator have been reported by some partners, whereas significant changes have not been observed by other partners.

Length (L)
Gian Bartolo Picotto, INRIM (Italy)
Coordinating Institute
INRIM (Italy)
Further Partners
NMISA (South Africa)


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