Interferometric Measurement System Research Articles

二元伪随机光栅与台阶校准检测系统传递函数的影响分析

二元伪随机光栅与台阶校准检测系统传递函数的影响分析

Analysis of trajectory deviation during high speed robotic trimming of carbon-fiber reinforced polymers

Abstract Although carbon-fiber reinforced polymers (CFRPs) are used extensively in the aerospace industry, trimming of CFRPs in high speed robotic end milling has however not yet received its due attention within the research community. For such an application, the robot should be very stiff for the machining operation to be generated. If the robot is not sufficiently stiff, deviations in shape and position of the workpieces will occur. In this paper, a methodology has been developed and implemented for quantifying the relative contributions of cutting parameters (feed, speed) and robot configuration to workpiece accuracy during robotic trimming of CFRP laminates. Trajectory deviation and part accuracy are evaluated with respect to robot configurations and cutting conditions using data from two sources. The first set of data is obtained through the laser interferometer measurement system, while the second set of data is obtained from measurements carried out on the trimmed specimens using the coordinate measuring machine (CMM). Results from the laser interferometer system show that the observed errors are consistent with gear transmission errors. This is revealed by periodic shapes along the measured path. It was observed also that joint 1 has an important influence on the robot accuracy. The less the joint 1 displaced, the better the performance of the robot. Machining results show that a lack of stiffness in the robot causes large deviations in shape and position and, further, that these deviations are affected by the cutting force and the machining parameters. Results show also that the robot configuration which is optimally suited to perform the task is reached by using a relatively folded configuration and a minimal displacement of the joint 1. Furthermore, the optimum cutting conditions leading to a minimum trajectory deviation are achieved at a low feed rate (0.2 mm/rev) and a moderate cutting speed (400 m/min).

Control of an equipment for fabricating periodic nanostructure

Abstract This study presents the control for an equipment that is designed for fabricating periodic nanostructures. This equipment can generate the patterns required for nanostructure production using direct writing laser lithography. The equipment incorporates a direct writing laser lithography instrument, a linear motor-driven long-stroke stage ( X , Y ), a piezoelectric-driven two degrees of freedom (2-DOF) nano-stage ( Y , θ z ), a 3-DOF laser interferometer measurement system, and a system control unit. The working stage of this equipment is combined by a long-stroke stage and a nano-stage; therefore, it can provide long-stroke and high-precision positioning. The feedback signal for this stage is obtained using a 3-DOF laser interferometer measurement system. Integral sliding-mode controllers are used to control the linear motor-driven stage and PID controllers are used to control the piezo-stage for precision positioning. This paper presents the design of the controllers and the control results. Experimental results show that satisfactory writing results can be obtained at a 100 mm/s scan speed.

Fabry–Perot displacement interferometer for the measuring range up to 100 mm

Current commercial laser interferometers have demonstrated outstanding measuring performances for high precision measurements, but they are very sensitive to environmental or mechanical effects. Owing to the fact that the most laser interferometers are based on the structure of Michelson interferometer, the above-mentioned influences from measuring arms will undisputedly lead to significant errors. To realize the high precision measurement, the environmental conditions must be strictly demanded. As a result of that limit, it’s inconvenient for industrial applications. In comparison with such non-common optical path structure, conventional Fabry–Perot interferometer with common optical path can effectively reduce the measuring errors resulting from environmental disturbances.To minimize the environmental and mechanical effects, a new interferometric displacement system with the structure of common optical path is proposed. By the optical interference principle and the corner cube reflector, the novel system with the common optical path can be designed. Hence, the novel interferometer can hold the advantage of large measurement range, and the signal pattern is nearly the same with that of Michelson interferometer. Because of the folded optical cavity, the resolution of the multi-interference interferometer with corner-cube can be enhanced to λ/16.Through this development, a high accurate interferometric displacement measurement system can be available under ordinary environmental conditions without the compensation requirement of the tilt angles and its prominent measurement characterizations have been proven. It will be demonstrated that measurement range is larger than 100mm and the standard deviation of the comparison experiment is about 0.211μm (within half wavelength) in the whole measuring range.

Absolute distance measurement using frequency-sweeping heterodyne interferometer calibrated by an optical frequency comb

We present a frequency-sweeping heterodyne interferometer to measure an absolute distance based on a frequency-tunable diode laser calibrated by an optical frequency comb (OFC) and an interferometric phase measurement system. The laser frequency-sweeping process is calibrated by the OFC within a range of 200 GHz and an accuracy of 1.3 kHz, which brings about a precise temporal synthetic wavelength of 1.499 mm. The interferometric phase measurement system consisting of the analog signal processing circuit and the digital phase meter achieves a phase difference resolution better than 0.1 deg. As the laser frequency is sweeping, the absolute distance can be determined by measuring the phase difference variation of the interference signals. In the laboratory condition, our experimental scheme realizes micrometer accuracy over meter distance.

Proposal for eliminating the external disturbance via digital PGC technique in a multiplexed fiber interferometer measurement system

We demonstrate a multiplexed fiber interferometer measurement system for eliminating the external disturbance using the digital phase generated carrier (PGC) demodulation technique. By applying two fiber Bragg gratings (FBG) and two fiber interferometers that share the reference arm and part of the sensing arm in this measurement system, we find that the system can be used for detecting the useful signal and the external disturbances is reduced by 26dB. Thus, our work may provide some new possibilities for technological applications in vibration measurement.

Holographic method for topography measurement of highly tilted and high numerical aperture micro structures

This paper presents an analysis of the topography characterization of a tilted sample by interferometric measurement systems in transmission and reflection configurations. The developed analytical expressions permit the direct reconstruction of the three-dimensional shape of a tilted sample. The first method presented in this paper, the so-called Thin Tilted Element Approximation (TTEA) method, is an extension of the well-known Thin Element Approximation for tilted geometry, which can be applied to the case of large sample tilts, but it requires the numerical aperture (local shape gradients) of the sample to be low. The second method presented here, the so-called Tilted Local Ray Approximation (TLRA) algorithm, is based on the analysis of local ray transition through a measured object. The method can be applied for the accurate shape characterization of tilted samples with high shape gradient. The developed algorithms require focused images, while in the inclined sample configuration the image plane is tilted relatively to the detection plane. To overcome this problem we propose the application of an efficient algorithm for the numerical propagation between tilted planes. The accuracy of TTEA and TLRA algorithms is successfully proven with simulations and experimental measurements for the case of low and high NA microlenses.

레이저 간섭계를 이용한 직각도 측정에 관한 분석

The squareness measurement of driving axes of a machine tool is very important to evaluate the performance of the machine. Laser interferometer measurement system is one of the most reliable equipment to measure the squareness. However, squareness measurement using laser system with an optical square result in restriction of straightness optics setup and Abbe’s offset. This offset combines with angular errors during the motion of an axis to cause Abbe’s error. In addition, the difficulty in optical square setup causes restriction of other optics and limitation of measurable range. In this paper, mathematical approaches are presented to eliminate the Abbe’s error and to estimate squareness for full range by using the best fit of straightness data measured without an optical square. Experiments for squareness measurement of 3 axis machine tool were conducted and the proposed techniques were used for squareness evaluation with elimination of Abbe’s error and squareness estimation for the full travel range.

Experimental validation of dual/modified dual arm locking for LISA

The laser frequency stabilization subsystem is one of the most significant parts within the interferometric measurement system of LISA. Arm locking as a proposed frequency stabilization technique synthesizes an adequately filtered linear combination of the interferometry signals as a frequency reference. Until now all the benchtop experiments on arm locking verified only the basic single arm locking configuration with unrealistic short signal travel times. At the University of Florida we developed the hardware-based University of Florida LISA Interferometer Simulator (UFLIS) to study and verify laser frequency noise reduction and suppression techniques under realistic LISA-like conditions. These conditions include the Doppler shifts between the spacecraft, LISA-like signal travel times, realistic laser frequency and timing noise. In this paper we will report about preliminary experiments on advanced arm locking schemes including dual arm locking and modified dual arm locking with realistic 33 s light travel times. In our experiments the implementation of a dual/modified dual arm locking sensor and controller is realized using several digital signal processing boards. We demonstrated the closed-loop stability of arm locking setup and measured the noise suppression in these experiments.

Large range and high resolution on-line displacement measurement system by combining double interferometres

A stabilized interferometric displacement measurement system, which is suitable for on-line measurement and is endowed with large measurement range and high resolution, is proposed. The system is stabilized by a feedback loop which compensates the influences induced by the environmental disturbances and makes the system stabile enough for on-line measurement. Two different wavelengths are working simultaneously in the system. The measurement range which is determined by the synthetic-wavelength interferometric signal is expanded to the order of millimeter, while the measurement resolution which is determined by one of the single-wavelength interferometric signal is the order of sub-nanometer.

Elimination of drift in a fiber-Bragg-grating-based multiplexed Michelson interferometer measurement system

Random phase drift in single-mode optical fiber interferometers used with measurement systems, which is resulted from various types of environmental disturbances, should be eliminated in order to obtain high measurement precision. We propose an optical fiber interferometric measurement system which has the function of self-eliminating the random phase drift and is stable and robust enough for real-time precision measurement. By employing the characteristics of fiber Bragg gratings, the system interleaves two fiber Michelson interferometers together that share the common-interferometric-optical path. The signal of one of the interferometers is used to stabilize the system while the signal of the other interferometer is used for measurement. An electronic feedback loop for the stabilizing action is designed. The bandwidth of the feedback loop is 5 kHz, sufficiently wide to eliminate random phase drift resulted from various environmental disturbances. The system is endowed with high stability and therefore suitable for real-time precision measurement. By means of an active phase tracking technique to measure displacement, the linear regression coefficient of the displacement measurement results is 0.9998.

Design of a long stroke translation stage for AFM

A new metrological AFM is developed for the Dutch standards laboratory. This instrument consists of a translation stage with a stroke of 1×1×1 mm and a custom-designed AFM measurement head. Here the design of the translation stage, consisting of elastic straight guides, Lorentz-actuators with weight and stiffness compensation and interferometric translation measurement systems, will be discussed. Some preliminary results on the performance of the actuation system are presented.

Stitching interferometric measurement system for hard x-ray nanofocusing mirrors

We have developed an advanced type of relative angle determinable stitching interferometry (RADSI) for hard x-ray nanofocusing mirrors. The surface metrology system consists of two types of optical interferometers. One is a microscope Michelson interferometer, which measures the local figure profile of the mirror surface, and the other is a large-area Fizeau interferometer, which determines the stitching angles between neighboring shots using a flat mirror. The surface figure profile of each of the one-shots and the stitching angles are measured at the same time. Precise measurement of local surface area and the stitching angles of 1×10-8 rad order were achieved using the developed system. To demonstrate the accuracy of the developed measurement system, we measured an elliptically figured mirror for hard x-ray nanofocusing. The mirror's surface shape has a curvature radius of a few meters. As a result, measurement reproducibility and reliability of less than PV 3 nm was achieved by using a 25 nm focusing mirror.

High stability interleaved fiber Michelson interferometer for on-line precision displacement measurements

A self-reference fiber Michelson interferometer measurement system, which employs fiber Bragg gratings (FBGs) as in-fiber reflective mirrors and interleaves together two fiber Michelson interferometers that share the common-interferometric-optical path, is presented. One of the fiber interferometers is used to stabilise the system by the use of an electronic feedback loop to compensate the influences resulting from the environmental disturbances, while the other one is used to perform the measurement task. The influences resulting from the environmental disturbances have been eliminated by the compensating action of the electronic feedback loop, this makes the system suitable for on-line precision measurement. By means of the homodyne phase-tracking technique, the linearity of the measurement results of displacement measurements has been very high.

The Application of the Dual-Beam Laser Interferometer for Calibration Precision Machine ToolsAnwendung eines Zweistrahl-Laserinterferometers zur Kalibrierung von Präzisionswerkzeugen

Abstract In this paper, a dual-beam laser interferometer measurement system for precision machine tools was presented. The straightness measurement module and the angular measurement module were combined to form this measurement system such that the operations of precision machine tools, the positioning, vertical straightness, horizontal straightness, pitch and yaw, can be obtained. The resolution of the positioning, straightness and angle has achieved 0.1 nm, 1 nm and 0.1 arcsec, respectively. The performance of this measurement system has been proved by experiments.

Design and analysis of a highly stabilised optical fiber Michelson interferometer measurement system

Single-mode optical fiber interferometers used with measurement or sensing systems should be stabilised to achieve high measurement accuracy and linearity in the presence of differential phase drift in their arms resulting from temperature fluctuations and other types of environmental disturbances. We propose an optical fiber interferometric measurement system which has the function of self-compensating the influences induced by the environmental disturbances and is stable and robust enough for on-line precision measurement or sensing. By employing the characteristics of fiber Bragg gratings (FBGs), the system interleaves two fiber Michelson interferometers together that share the common-interferometric-optical path. One of the fiber interferometers is used to stabilise the system while the other one is used to perform the measurement or sensing task. An electronic feedback loop for stabilising the measurement system is designed. The bandwidth of the feedback loop is 5 kHz, sufficiently wide to compensate various disturbances from environment. By these means, the system is endowed with high stability in various environments and suitability for on-line precision measurement or sensing.

Frequency-tunable pre-stabilized lasers for LISA via sideband locking

Laser frequency noise mitigation is one of the most challenging aspects of the LISA interferometric measurement system. The unstabilized frequency fluctuations must be suppressed by roughly 12 orders of magnitude in order to achieve stability sufficient for gravitational wave detection. This enormous suppression will be achieved through a combination of stabilization and common-mode rejection techniques. The stabilization component will itself be achieved in two stages: pre-stabilization to a local optical reference followed by arm locking to some combination of the inter-spacecraft distances. In order for these two stabilization stages to work simultaneously, the lock-point of the pre-stabilization loop must be frequency tunable. The current baseline stabilization technique, Pound–Drever–Hall locking to an optical cavity, does not provide tunability between cavity resonances. Here we present a modification to the baseline technique that allows the laser to be locked to a cavity resonance with an adjustable frequency offset. This technique requires no modifications to the optical cavity itself, thus preserving the stability of the frequency reference. We present measurements of the system performance and demonstrate that the offset locking techniques are compatible with arm locking.

Near optimum sampling design and an efficient algorithm for single tone frequency estimation

Work on single tone frequency estimation has focused on uniformly sampled data. However, it has been shown that, for a given number of samples, more information on the frequency of a signal can be gained by non-uniform sampling schemes [M. Wieler, S. Trittler, F.A. Hamprecht, Optimal design for single tone frequency estimation, Digital Signal Process., in press]. Unfortunately, an optimum sampling pattern (that, for example, minimizes the Cramer-Rao bound) does not automatically have a fast and simple algorithm for frequency estimation associated with it. For application in an interferometric measurement system, an algorithm is needed that gathers as much information as possible from a low number of samples, while at the same time keeping the computational effort sufficiently low to process millions of time series in a few seconds. This paper proposes a simple approximation to the optimum sampling pattern by using uniformly sampled blocks of data and further proposes to estimate phase and frequency in each of these blocks and to exploit these intermediate results in the final estimation. An approach to do so is investigated in detail. Results are compared to the Cramer-Rao bound (CRB), and it is shown that this algorithm almost reaches this limit on the variance of unbiased estimators, at a computational complexity lower than that of a typical FFT-based approach. For M=32 samples and a signal-to-noise ratio of 10, the standard deviation of the frequency estimate is lower by more than 50% compared to uniform sampling. In addition, the algorithm can easily be applied to poorly characterized systems, e.g. systems for which the noise is not known exactly. Finally, we demonstrate that the proposed strategy yields results that are within 3% of the theoretically achievable accuracy for the theoretically optimum sampling pattern.

An All Fiber White Light Interferometric Absolute Temperature Measurement System.

Recently the author of this article proposed a new signal processing algorithm for an all fiber white light interferometer. In this article, an all fiber white light interferometric absolute temperature measurement system is presented using the previously proposed signal processing algorithm. Stability and absolute temperature measurement were demonstrated. These two tests demonstrated the feasibility of absolute temperature measurement with an accuracy of 0.015 fringe and 0.0005 fringe, respectively. A hysteresis test from 373K to 873K was also presented. Finally, robustness of the sensor system towards laser diode temperature drift, AFMZI temperature drift and PZT non-linearity was demonstrated.

Modeling and Formulation of a Novel Microoptoelectromechanical Gyroscope

This paper proposed a novel design of microgyroscope based on MEMS structures and optic interferometric microdisplacement measurement technique. The gyroscope consists of microvibrator and interferometric readout. Using Coriolis force, the vibrator transfers the system rotation into a forced vibration; the induced vibration can be sensed by the interferometric microdisplacement measurement system. The optic measurement system has two mirrors which will reflect two rays into a detector. The comprehensive studies on the formulation and analysis of the proposed gyroscope have been undertaken; two key sensor equations have been derived in the first time in the world: (1) relation between rotation and phase shift of light Δφ = (4πl0/λ) + (8π/λ)(xmax Qy/ωy)Ω(t)sin (ωdt), (2) relation between rotation and interferometric intensity of light I(t) ≈ (8π/λ)(xmax Qy/ωy)Ω(t)sin (ωdt)sin (4πl0/λ). The comparison of the proposed gyroscope and well‐know Sagnac formulation has been investigated; it shown that the proposed model is much better than Sagnac ones. The new model has finally get rid of needing very long fiber in the case of Sagnac gyroscope. The innovative model gives a new hope to fabricate high accurate and cheaper gyroscope. To date, the proposed gyroscope is the most accurate gyroscope.