Displacement Sensor Calibration Research Articles

Self-Calibration Method of Displacement Sensor in AMB-Rotor System Based on Magnetic Bearing Current Control

Displacement sensors are the key components of the active magnetic bearing rotor (AMB-rotor) system to realize the closed-loop control of the rotor displacement. The aging and failure of the displacement sensor components will lead to the changes of sensor sensitivity and zero point, which can directly affect the suspension performance of the rotor and even cause the instability of the AMB-rotor system. Therefore, it is significant to calibrate the sensor regularly. This paper proposes a self calibration method based on the detection and control of the magnetic bearing current without additional calibration equipment and hardware circuits. In addition, a new control structure of the AMB-rotor system is proposed to achieve efficient calibration, which can control the rotor displacement based on current following control method. Finally, experimental results verify the effectiveness of the proposed method on the displacement sensor calibration.

On the Role of Contact and System Stiffness in the Measurement of Principal Variables in Fretting Wear Testing.

In this work, the role of the contact stiffness in the measurement of principal variables in fretting wear tests is assessed. Several fretting wear tribometers found in the literature, including one developed by the authors, are analysed and modelled using numerical methods. The results show the importance of the tribosystem stiffness and tangential contact stiffness in the displacement sensor calibration and in the correct numerical modelling of fretting wear tests, especially for flat-to-flat contact configuration. The study highlights that, in most cases, direct comparisons between fretting results with severe wear obtained with different tribometers cannot be performed if the contact stiffness is not properly considered during the development of the experiments.

A Long-Range High Applicability Length Comparator for Linear Displacement Sensor Calibration

In this article, a long-range length comparator, applicable for both static- and dynamic-index calibrations of a linear displacement sensor, is presented. The comparator consists of an air-floating linear motion generator (LMG) and an interferometric optical length calibrator (OLC). A novel design of the LMG made by multisegment splicing is introduced, in which a two-level vibration isolation arrangement, a multiple sliders' setup, and an exoskeleton framework are adopted. The resulting linear motion can be extremely ideal even with a large stroke. The angular error is within 11.89 μrad covering the -2m range. The maximum operating speed and the acceleration of the LMG are 10 m/s and 20 m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. A dual-path optical design of the OLC is displayed, resulting in high environmental tolerance and a small trigger delay of 4.75 ns. The best accuracy of the comparator can be ±(0.041+0.106L) μm with a resolution of 0.3 nm. The maximum error and operation speed of a 2-m range exposed encoder were successfully calibrated, and the grating pitch deviation was also found, by which the effectiveness of the comparator is proven. The proposed length comparator introduces a possible solution, for how a long-range linear displacement sensor, can be calibrated with high accuracy, efficiency, and applicability.

Development of a novel system for linear displacement sensor calibration

This paper presents the development of semi-autonomous metrological devices, capable of calibrating variety of linear displacement sensors, like Linear Variable Differential Transformers (LVDT), string potentiometers, laser displacement sensors and other. Data acquisition equipment that could be used for measuring objects of various shapes and sizes are already available; however, devices specifically tailored for the calibration of displacement sensors are not currently offered. Advantages of this new technology, that we are investigating and developing, include reduction of time, costs and human resources required to perform calibration. In addition to that, the advantages of an affordable calibration device will allow calibrations to be carried out internally, as opposed to outsourcing to dedicated facilities. The scope of the project encompasses research into the device’s compliance with ISO/IEC 17025 to obtain NATA accreditation, research into design, and selection of material and manufacturing processes to ensure an acceptable measurement of uncertainty is achievable across all varieties of linear displacement sensors. The sensors are used to measure suspension displacement, steered angle and various other geometries on vehicles and test equipment. Outcomes of this research project offer experimental evidence that proves the feasibility of developing and manufacturing devices that produce an acceptable uncertainty that meets testing standards requirements at a fraction of the cost of comparable measuring devices.

A Method for Measurement of Nonlinearity of Laser Interferometer Based on Optical Frequency Tuning.

A method for measuring the nonlinearity of laser interferometer using optical frequency tuning technique is presented in this paper. The basic principle of this method is to make the fractional part of an interference fringe change by tuning the laser frequency and determining the nonlinearity of interferometer by comparing the fractional fringe change measured by the interferometer to that calculated from the laser frequency change. An experimental interferometric system with a wavelength tunable laser source is set up and the nonlinearity of the interferometer is measured. Since it does not require the precise displacement mechanism to produce the optical path difference change, this method is more convenient to use and may achieve a higher accuracy than the conventional measurement methods. The nonlinearity of the arbitrary interferometric phase can be measured by changing the laser frequency with this method. Experiments results have shown that the repeatability of nonlinearity measurement is less than 0.2 nm. This method can be applied to interferometry-based high precision dimensional measurements, such as coordinate measurement and displacement sensor calibration.

Visualization Calibration System Design of Inductive Displacement Sensor

This paper describes the design of calibration system structure and program. Inductive displacement sensor calibration system based on virtual instrument is established by using LabVIEW8.5. It can complete the measured signal acquisition and calibration. In the measurement process, the inductive displacement sensor is a converter that measures a displacement and converts it into a electrical signal. By calibration, the system can be quickly translated the voltage signal into the original displacement signal. Compared with the traditional manual method, the calibration system has the advantage of simple structure and easy operation，and the visual linear fitting straight line can be obtained.

Research of Spindle Runout Testing Methods

The paper aims at the analysis of machine spindle runout characteristics and designs of a laser displacement sensor in non-contact spindle runout measurement system. To ensure accuracy, we designed the laser displacement sensor calibration device, and the test calibration experiment was carried out by using laser displacement sensor. Experimental results showed that the test methods met the accuracy requirements of test system.

Calibration of Displacement Sensors with High-Precision and Large Measurement Range Using Temporal Speckle Pattern Interferometry

In the present study, a real-time calibration method for micro displacement sensors is introduced, and a calibration system is developed. SPCM, the sequence pulse counting method previously proposed by us, is capable of automatically determining both the larger range displacement and the performance of a sensor, such as the nonlinear error and the displacement sensitivity within a quarter of the light source wavelength. The new calibration system consists of a programmable motor driven platform, an out-of-plane sensitive electronic speckle pattern interferometry (ESPI), and a sequence image acquisition system. The platform is used to provide displacement changes of a moving component and its displacement is measured by the ESPI and calibrated sensor synchronously. The calibration accuracy of the proposed method is in the submicrometer level and the displacement range can be from sub-micrometer to millimeters depending on the storage capacity of the computer and the correlation property of the interferometer. Three capacitance-type displacement sensors have been calibrated successfully, whose displacement ranges are –300μm to 300μm, –30μm to 30μm, and –3μm to 3μm, respectively.

Combined optical and X–ray interferometry for high–precision dimensional metrology

The requirement for calibrating transducers having subnanometre displacement sensitivities stimulated the development of an instrument in which the displacement is measured by a combination of optical and X–ray interferometry. The need to combine both types of interferometry arises from the fact that optical interferometry enables displacements corresponding to whole numbers of optical fringes to be measured very precisely, but subdivision of an optical fringe may give rise to errors that are significant at the subnanometre level. The X–ray interferometer is used to subdivide the optical fringes. Traceability to the meter is achieved via traceable calibrations of the lattice parameter of silicon and of the laser frequency. Polarization encoding and phase modulation allow the optical interferometer to be precisely set on a specific position of the interference fringe—the null point setting. The null point settings in the interference fringe field correspond to dark or bright fringes. Null measurement ensures maximum possible noise rejection. However, polarization encoding makes the interferometer nonlinear, but all nonlinearity effects are effectively zero at the fringe set point. The X–ray interferometer provides the means for linear subdivision of optical fringes. Each X–ray fringe corresponds to a displacement that is equal to the lattice parameter of silicon, which is ca .0.19 nm for the (220) lattice planes. For displacements up to 1 m the measurement uncertainties at 95% confidence level are ± 30 pm, and for displacements up to 100 m and 1 mm the uncertainties are ± 35 and ± 170 pm, respectively. Important features of the instrument, which is located at the National Physical Laboratory, are the silicon monolith interferometer that both diffracts X–rays and forms part of the optical interferometer, a totally reflecting parabolic collimator for enhancing the usable X–ray flux and the servo–control for the interferometers.

Calibration of displacement sensors up to 300 µm with nanometre accuracy and direct traceability to a primary standard of length

A new class of sensor has recently appeared: nanometre sensors. These sensors are characterized by nanometre or sub-nanometre resolution and an uncertainty of a few nanometres over a range of at least several micrometres. Instruments such as capacitive or inductive sensors, laser interferometers, holographic scales, and scanning probe microscopes belong to the class of nanometre sensors. Linearity errors and drift in the mechanical and electronic system limit the accuracy of all these sensors. In order to determine these errors in a traceable way, the instrumentation described in this paper was developed. The heart of the system consists of a Fabry-Perot cavity. One mirror of this cavity generates the required displacement. A so-called slave laser is stabilized to the cavity length. The frequency of this slave laser is compared with the frequency of a primary length standard. In this way the displacement is measured with a resolution of a few picometres, a range of 300 µm and an uncertainty of about 1 nm. Experiments confirm the performance of this instrument and show typical deviations of the probe systems investigated.