Conventional Displacement Sensor Research Articles

Deformation Monitoring of a Building Structure Using a Motion Capture System

Conventional 1-D or 2-D displacement sensors are occasionally used to measure the deformation of a structure. However, a motion capture system (MCS) can measure the 3-D movements of markers attached to a target structure with high accuracy and a high sampling rate. Because markers can be easily attached to a structure, an MCS is useful for monitoring the dynamic motions of complex structures, such as buildings, using multiple markers. This study proposes a deformation measurement method for building structures using an MCS. The suggested measurement method consists of four stages: 1) setup of the MCS; 2) data acquisition; 3) coordinate transformation into a structural coordinate system; and (4) generation of the deformed shape. The feasibility of the suggested MCS-based measurement method was validated using a free-vibration test of a three-story experimental frame model. The displacement and deformed shape that were measured using an MCS were compared to the displacement and deformed shape measured using a laser displacement sensor, which is a conventional displacement sensor. The comparison results indicated that the MCS can overcome the limits of 1-D displacement sensors and easily and accurately obtain the deformed shape of a structure.

A Vision-Based Sensor for Noncontact Structural Displacement Measurement.

Conventional displacement sensors have limitations in practical applications. This paper develops a vision sensor system for remote measurement of structural displacements. An advanced template matching algorithm, referred to as the upsampled cross correlation, is adopted and further developed into a software package for real-time displacement extraction from video images. By simply adjusting the upsampling factor, better subpixel resolution can be easily achieved to improve the measurement accuracy. The performance of the vision sensor is first evaluated through a laboratory shaking table test of a frame structure, in which the displacements at all the floors are measured by using one camera to track either high-contrast artificial targets or low-contrast natural targets on the structural surface such as bolts and nuts. Satisfactory agreements are observed between the displacements measured by the single camera and those measured by high-performance laser displacement sensors. Then field tests are carried out on a railway bridge and a pedestrian bridge, through which the accuracy of the vision sensor in both time and frequency domains is further confirmed in realistic field environments. Significant advantages of the noncontact vision sensor include its low cost, ease of operation, and flexibility to extract structural displacement at any point from a single measurement.

Nontarget Vision Sensor for Remote Measurement of Bridge Dynamic Response

AbstractDisplacements of railroad bridges under trainloads need to be closely monitored, but conventional displacement sensors have limitations for use in the field. This paper presents a new vision-based sensor system developed for remote measurement of structural dynamic displacements without requiring a specially installed target-marker panel. By implementing a robust object-search algorithm, the displacement can be accurately measured by tracking existing bridge surface features from a remote distance. The accuracy of measured dynamic displacements was first evaluated using a shaking table test. Then field tests were carried out on two railroad bridges subjected to freight trainloads traveling at various speeds. Measurements were taken remotely during the daytime and also at night from different distances with and without a target panel. Through comparison with a conventional contact-type displacement sensor, the high accuracy of the proposed nontarget remote-sensor system was demonstrated in the real...

Reflective displacement sensors with monolithically integrated VCSELs and RCEPDs

Micro-scale, reflective-type optical displacement sensors have been developed by monolithic integration of vertical cavity surface-emitting lasers (VCSELs) and resonant cavity-enhanced photodetectors (RCEPDs). This compact sensor (700 × 700 μm) consists of an oxide-confined VCSEL that is surrounded by an RCEPD and can measure the linear distance with a measurement range of ~10 mm, which is comparable to that of conventional displacement sensors. Fabrication details and sensor performances are discussed.

長周期・大振幅地震動の測定を目指した小型絶対変位振動計の開発研究

This paper proposes a novel seismometer-type absolute displacement sensor aimed at detecting earthquake waves with a large magnitude and long period. However, since the measuring range of the conventional displacement sensor is higher than the natural frequency of itself, it is difficult to detect a low frequency vibration below 1Hz using conventional seismic-type displacement sensors. In order to provide an absolute displacement detection which is capable of lowering the natural frequency and enlarging the detectable amplitude without causing a structural defect, the relative signals of displacement, velocity, and acceleration between a detected object and the auxiliary mass of the sensor are fed back into the sensor. In addition, a phase lag compensation is inserted to adjust phase angles, which are below a frequency lower than 1Hz. Theoretically, this sensor is able to detect a lower frequency range from 0.2Hz to 10Hz and large amplitude with 100 times to the movable range of the sensor. It has been demonstrated by experiments that the developed sensor with a small size and lightweight has a detecting range from 0.2 Hz to 10Hz for absolute displacement and velocity. As an additional advantage, the measurement displacement amplitude has been expanded to about 40dB (100 times) for detecting earthquake waves with large magnitude and long period. As the typical application example of the developed absolute displacement sensor, a seismic wave based on Hachinohe wave is used with well observation results.

Accurate full-field optical displacement measurement technique using a digital camera and repeated patterns.

In this study, a novel, fast, and accurate in-plane displacement distribution measurement method is proposed that uses a digital camera and arbitrary repeated patterns based on the moiré methodology. The key aspect of this method is the use of phase information of both the fundamental frequency and the high-order frequency components of the moiré fringe before and after deformations. Compared with conventional displacement methods and sensors, the main advantages of the method developed herein are its high resolution, accuracy, speed, low cost, and easy implementation. The effectiveness is confirmed by a simple in-plane displacement measurement experiment, and the experimental results indicate that an accuracy of 1/1000 of the pitch can be achieved for various repeated patterns. This method is useful for various applications ranging from the study of displacement and strain distributions in materials science, the biomimetics field, and mechanical material testing, to secure the integrity of infrastructures.

1C11 Amazing ability of the developed seismometer-type absolute displacement sensor for measuring earthquake waves with large magnitude and long period(The 12th International Conference on Motion and Vibration Control)

This paper demonstrates an amazing ability of a developed seismometer-type absolute displacement sensor aimed at detecting earthquake waves with a large magnitude and long period. Since the measuring range of the displacement sensor is higher than the natural frequency of itself, it is difficult to detect a low frequency vibration below 1 Hz using conventional seismic-type displacement sensors. Therefore, for detecting earthquake waves with a long period, acceleration sensors are used commonly. However for obtaining absolute displacements by the acceleration sensor, it is necessary to integrate twice of the acceleration signal. Then the drift problem guided to signal saturation will be happen essentially in the acceleration process by unknown signals. This seismometer-type absolute displacement sensor is consisted of a sensor body with a moving mass and its supporting springs, feedback control circuits and a third order phase lag compensator. The natural frequency of the sensor body located at 6.8Hz originally is reduced to 0.23 Hz using by acceleration feedback mainly and then moving stroke of the moving mass is compressed to 1mm to 1/630mm. Moreover the new natural frequency of 0.23Hz developed by feedback control is sifted to 0.065Hz by the third order phase lag compensator. Therefore the sensor has a measuring range from 0.08Hz to 10Hz, in addition to no drift problems by the use of feedback control way. In this way, the seismometer-type absolute displacement sensor with the amazing ability has been realized to measure the long period over 10 second of earthquake waves. In addition, the large magnitude to measure 630mm is expected, nevertheless a small size with moving stroke of 1mm. So far as we know, such a sensor for measuring absolute displacement is very novel in the world. In this paper the ability of the sensor will be shown by simulation and experiment.

A novel laser displacement sensor with improved robustness toward geometrical fluctuations of the laser beam

The measuring accuracy of conventional laser displacement sensors reduces over time as a result of geometrical fluctuations of the laser beam. Accordingly, the present study proposes a new laser displacement sensor in which the effects of geometrical fluctuations of the laser beam are minimized by means of a high-speed rotating optical diffuser. The performance of the proposed sensor is evaluated experimentally using a laboratory-built prototype. The experimental results show that the sensor achieves a higher measuring accuracy than a conventional laser displacement sensor based on a triangulation method. As a result, the proposed sensor provides an ideal solution for a wide range of automatic optical inspection and industrial applications.

C20 フィードバック制御を用いた長周期絶対変位センサ(M-OS4-2 制御用センサと空気圧アクチュエータの応用,M-OS4 制御用センサ・アクチュエータ,「海を越え,国を越え,世代を超えて!」)

This paper reports new results for developing absolute displacement sensor in order to measure a long period and large magnitude. Measuring of the absolute displacement of vibration objects, the natural frequency of sensor must be lower than the dominant frequency of the object. Therefore, it is difficult to measure a low frequency vibration below 1 Hz using conventional displacement sensors. In order to be lower the natural frequency, the sensor with the low natural frequency is realized by using feedback control. It has been demonstrated that a developed sensor has a detecting range from about 0.2 Hz to 10Hz for absolute displacement. In addition, the measurement displacement amplitude has been expanded to about 700 times. Moreover, by using the second order lag compensator measuring lower frequency range is expanded to 0.1 Hz.

Fiber optic displacement sensor with a large extendable measurement range while maintaining equally high sensitivity, linearity, and accuracy

This paper presents a fiber optic displacement sensor composed of a transmissive grating panel, a reflection mirror, and two optical fibers as a transceiver. The proposed fiber optic displacement sensor guarantees a stable reflected signal acquisition for application in real industrial fields. Through a parametric study of the grating pitch of the transmissive grating panel, the signal-to-noise ratio, linearity, resolution, accuracy error, and sensitivity of the proposed sensor were investigated. The measured bidirectional movement demonstrated a peak to peak accuracy of 10.5 μm, high linearity of 0.9996, resolution of 3.1 μm at the full bandwidth, signal-to-noise ratio of 27.7, and high sensitivity of 31.8 μm/rad during a movement of 16,004.0 μm using the transmissive grating panel, which had a grating pitch of 200 μm. Even for an extended measurement range, the proposed scheme enables the same accuracy, linearity, and sensitivity to be maintained when compared with conventional laser displacement sensors and fiber optic displacement sensors.

703 長周期・大振幅の動的計測を目指した絶対変位振動計の開発

This paper proposes a novel seismometer-type absolute displacement sensor aimed at detecting earthquake waves with a large magnitude and long period. However, since the measuring range of the displacement sensor is higher than the natural frequency of itself, it is difficult to detect a low frequency vibration below 1Hz using conventional seismic-type displacement sensors. In order to provide an absolute displacement detection which is capable of lowering the natural frequency and enlarging the detectable amplitude without causing a structural defect, the relative signals of displacement, velocity, and acceleration between a detected object and the auxiliary mass of the sensor are fed back into the sensor. In addition, phase lag compensation is inserted to adjust phase angles, which are below a frequency lower than 1Hz. It has been demonstrated that a developed sensor with a small size and lightweight has a detecting range from 0.2Hz to 10Hz for absolute displacement and velocity. As an additional advantage, the measurement displacement amplitude has been expanded to about 40dB (100 times) for detecting earthquake waves with large magnitude and long period

Long distance fiber-optic displacement sensor based on fiber collimator

A simple fiber-optic displacement sensor based on reflective intensity modulated technology is demonstrated using a fiber collimator. The sensing range is over 30 cm, which is over 100 times that of the conventional fiber-optic displacement sensor based on the normal single-mode fiber. The measured data are fitted into linear equation very well and the values of R-square are more than 0.995. The sensitivity of the device achieves 0.426 dB∕cm over the range of 5-30 cm. By applying the relative technique, the errors resulted from the fluctuation of light source and influences of environment are effectively eliminated, and the stability for wide range measurement can be improved. The simplicity of the design, high dynamic range, stability and the ease of the fabrication make it suitable for applications in industries.

Measuring true electromechanical strain of electroactive thermoplastic elastomer gels using synchrotron SAXS

The true electric actuation thickness strain of poly (styrene-b-ethylbutylene-b-styrene) (SEBS) gel was measured using an in situ synchrotron SAXS. The thermoplastic elastomer SEBS gel was microphase-separated to form a disordered styrene micelle nanostructure in an oil-swollen ethylbutylene matrix. The SEBS gel showed reversible cyclic load–unload compression behavior without permanent residual strain. The electromechanical strain of the SEBS gel with carbon paste electrodes could be evaluated by means of a nanostructure dimensional change traced by using the in situ synchrotron SAXS during actuation. The strain measured with SAXS was compared with the strain measured using conventional laser displacement sensor systems. The optical laser sensor method was likely to overestimate the thickness strain due to the bending movement of the dielectric elastomer. To our knowledge, the thickness strain value measured by the synchrotron SAXS is the closest to the true strain ever measured in the field of dielectric elastomer studies, because the nanostructure dimensional change depends on the thickness dimension change, not on the translational movement like the bending motion. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Vision-based displacement measurement method for high-rise building structures using partitioning approach

The horizontal displacement of a high-rise building structure is usually considered as one of the major indicators to assess the structural safety. It is, however, difficult to directly measure the displacement of such a flexible structure due to the inaccessibility to a reference point usually needed for conventional displacement sensors and the huge size of the structure. In order to resolve this issue, a novel vision-based displacement measurement technique is proposed by employing a partitioning approach (i.e., successive estimation of relative displacements and rotational angles throughout a large flexible structure). A series of the experimental tests using two webcams installed on a flexible steel column structure have been conducted to validate the feasibility of the proposed method. The test results showed that the difference between the displacement measured from the proposed method and the exact value is less than 0.5%. Therefore, the proposed method could be considered as one promising candidate for measuring the displacement of high-rise building structures.

Investigation of two different types of displacement transducers in the cryogenic environment

This paper presents the investigation of two different types of conventional displacement sensors applied in the cryogenic environment for instrumentation of superconducting fusion magnets and its test facilities. The first one is a wire-wound potentiometer and the second one is a strain gauge displacement sensor. These sensors were tested at different temperature levels between 300 and 6 K. Another test at high magnetic fields between 0 and 9 T was performed as well. The most important sensor properties such as sensitivity, linearity and hysteresis were derived and calculated.

A novel cell for the study of phase transitions using liquid dilatometry

An inexpensive Teflon dilatometry cell, using an integral movable diaphragm allows high-sensitivity scanning differential dilatometry to be carried out on liquids using any conventional displacement sensor, such as a capacitance dilatometer, strain gauge or LVDT. It is most suitable for the study of phase transitions in liquids, or solids immersed or suspended in liquids. The authors have studied the phase transitions of unsonicated dispersion of dipalmitoyl-phosphatidylcholine and water using a capacitance dilatometer.

Cyclic Triaxial Test of Dynamic Soil Properties for Wide Strain Range

Dynamic material properties of soil needed for the nonlinear analysis of earthquake response of the ground have usually been measured in the laboratory using the torsional column shear device. The cyclic triaxial test, despite its easier accessibility and handling for practicing engineers, has seldom been looked upon as a rational way to make a reliable measurement of dynamic properties. In this experimental study a highly sensitive gap sensor and a sealed load transducer are introduced inside the triaxial cell to eliminate the frictions of the conventional displacement sensor and the loading piston. A series of cyclic triaxial tests featuring these improvements have been carried out for saturated Toyoura sand with various void ratios and confining pressures, disclosing the following facts. (i) Reliable measurements of the shear modulus and its strain dependent variation within a wide strain range of the order of 10 -6 to 10 -3 are possible with the improved cyclic loading test, permitting a direct connection with the insitu shear wave velocity. (ii) An essentially good agreement of the modulus is quantitatively recognizable between the triaxial test and the torsional shear test, implying that the different stress and confining conditions inherent to the individual testing devices give no significant effect on the evaluation of the modulus. (iii) This test gives a reasonable hysteretic damping ratio as well as its strain dependency although the damping ratios measured by other researchers with different testing devices widely differ from each other indicating the difficulties for evaluating accurate damping ratio.