Konrad Herrmann

A neural network approach to correcting nonlinearity in optical interferometers

Real interferometers with phase quadrature detecting subsystems usually demonstrate nonlinearity with length measurements. Conventional nonlinearity correction techniques based on elliptical fittings are reviewed and their limitation is investigated using computer simulations. A new approach based on neural networks (NNs) for correcting nonlinearity in optical interferometers for length and displacement measurements is introduced, the principle of which is given (including the architecture of the NN) and its training method. An experimental setup was developed based on a differential plane-mirror interferometer for testing the proposed method. The experimental results show that this new approach is successfully applicable to real, noisy interferometer signals.

A laser measurement system for the high-precision calibration of displacement transducers

A laser system for displacement measurements, based on the iodine-stabilized He - Ne laser wavelength standard at 633 nm, has been built up. Two resonator mirror moving systems with displacement ranges of 3 and respectively were investigated and the guidance deviations of the latter were corrected. An inductive displacement transducer was calibrated using the measuring laser. The overall measurement uncertainty was estimated for the calibration of the inductive transducer for a displacement length of .

Lateral scanning confocal microscopy for the determination of in-plane displacements of microelectromechanical systems devices

A method named lateral scanning confocal microscopy (LtSCM) is proposed with the aim of determining the in-plane displacement of microstructures, especially of those moving components within microelectromechanical systems (MEMS) actuators and sensors, which feature high aspect ratio and limited geometrical size in one or two dimensions within the surface plane. The principle of the LtSCM is presented and theoretically analyzed, which indicates that the LtSCM has the potential to determine with high resolution the in-plane displacement, position, and even the geometrical size of the object. Furthermore, in the case of in-plane displacement measurement, the measurement resolution of the LtSCM should be insensitive to the dynamic performance of the movable microstructures, i.e., from quasi-static to ultrahigh speed. In a proof-of-principle experiment, the voltage-displacement response of an electrostatic comb-drive actuator has been obtained with nanometric resolution.

Towards quantitative determination of the spring constant of a scanning force microscope cantilever with a microelectromechanical nano-force actuator

The calibration of the performance of an SFM (scanning force microscope) cantilever has gained more and more interest in the past years, particularly due to increasing applications of SFMs for the determination of the mechanical properties of materials, such as biological structures and organic molecules. In this paper, a MEMS-based nano-force actuator with a force resolution up to nN (10−9 N) is presented to quantitatively determine the stiffness of an SFM cantilever. The principle, structure design and realization of the nano-force actuator are detailed. Preliminary experiments demonstrate that the long-term self-calibration stability of the actuator is better than 3.7 × 10−3 N m−1 (1σ) over 1 h. With careful calibration of the stiffness of the actuator, the MEMS actuator has the capability to determine the stiffness of various types of cantilevers (from 100 N m−1 down to 0.1 N m−1) with high accuracy. In addition, thanks to the large displacement and force range (up to 8 µm and 1 mN, respectively) of the actuator, the calibration procedure with our MEMS nano-force actuator features simple and active operation, and therefore applicability for different types of quantitative SFMs.

Determination of the geometry of microhardness indenters with a scanning force microscope

In this paper, experience gathered during the measurement of the geometry of microhardness indenters using a scanning force microscope is discussed. Reasonable accuracy of the geometrical parameters of a microhardness indenter can be obtained only if the scanning force microscope has been calibrated. The effect of the geometrical deviations on the result measured for the universal hardness is discussed.

Characterisation of the geometry of indenters used for the micro- and nanoindentation method

In this paper, experience gathered during the measurement of the geometry of indenters for the micro- and nanoindentation test using a scanning force microscope is reported. A usable accuracy of the geometrical parameters of a microhardness indenter can be obtained only if the scanning force microscope has been calibrated. The evaluation of the indenter geometry is described according to two methods: On the one hand the determination of the geometrical parameters plane angle, tip radius and length of line of junction in the microhardness range and on the other hand the calculation of area functions which are suitable for the nanohardness range. The accuracy of these evaluation methods is estimated.

Traceability in hardness measurements: from the definition to industry

The measurement of hardness has been and continues to be of significant importance to many of the worlds manufacturing industries. Conventional hardness testing is the most commonly used method for acceptance testing and production quality control of metals and metallic products. Instrumented indentation is one of the few techniques available for obtaining various property values for coatings and electronic products in the micrometre and nanometre dimensional scales. For these industries to be successful, it is critical that measurements made by suppliers and customers agree within some practical limits.To help assure this measurement agreement, a traceability chain for hardness measurement traceability from the hardness definition to industry has developed and evolved over the past 100 years, but its development has been complicated. A hardness measurement value not only requires traceability of force, length and time measurements but also requires traceability of the hardness values measured by the hardness machine. These multiple traceability paths are needed because a hardness measurement is affected by other influence parameters that are often difficult to identify, quantify and correct. This paper describes the current situation of hardness measurement traceability that exists for the conventional hardness methods (i.e. Rockwell, Brinell, Vickers and Knoop hardness) and for special-application hardness and indentation methods (i.e. elastomer, dynamic, portables and instrumented indentation).

CIRP sponsored international comparison on nanoindentation

With the emergence of international standards for the instrumented indentation test, an international comparison on nanoindentation, sponsored by The International Academy for Production Engineering (CIRP), was performed. The objective of the comparison was to determine how well the ISO standards adopted in October 2002 (ISO 14577-1, -2, -3) could be realized. The exercise involved 12 participants throughout Europe, Asia and the USA. Results for hardness and elastic modulus of (1 0 0)Al were collected and analysed. A comparison of the results obtained by this exercise with those obtained from the first CIRP international comparison on ultra-microhardness and elasticity measurement held from 1993 to 1997 was made.

Two approaches for enhancing the accuracy of the Rockwell hardness test

Two approaches have been investigated in our study in order to develop indenter calibration methods with high accuracy. One approach is by establishing a group standard utilizing several indenters, which yields better statistical results than the calibration using only one indenter. The second approach is by correcting the hardness test values using the indenters area function determined by a highly accurate stylus profilometer. In the stylus profilometer developed in this study, the indenter is scanned in 3D and is detected by a position stationary stylus probe. The 3D geometry of the indenter is thus derived from the displacements of the indenter which are measured by three homodyne laser interferometers, offering direct measurement traceability. In addition, for achieving a better measurement performance a special radial scan function is designed where the indenter is scanned radially over its apex. A data evaluation method has been established for calculating the indenters area function from its measured 3D geometry. The correction method of hardness values based on the indenters area function is described. In this paper, a group of three Rockwell indenters has been investigated. The mean deviation of HRC values measured by this group of Rockwell indenters has been reduced from 0.11 HRC to 0.06 HRC by using the proposed correction method.

Investigation of a group standard of Rockwell diamond indenters

Abstract The specific hardness deviations of a Rockwell diamond indenter can be determined by a group standard, consisting of several indenters, using correction functions. In this paper the establishment of an HRC group standard in the PTB and comparative investigations of the group standards in the PTB and the calibration laboratory MPA NRW are reported. Above all the group standard is advantageous for maintaining the stability of the Rockwell hardness scales.