Contact-type Displacement Sensor Research Articles

Geometrical consideration for mechanical contact between rolling circle and surface roughness as an improvement to the surface profile

This paper describes measurement methods of surface profiles that improve contact-type displacement sensor outputs by focusing on the contact point between the sphere tip of the sensor and the rough surface. We examined the geometry of a surface profile model and compared measurements using various methods with the measurement using a roughness meter. The spherical tip of the contact type displacement sensor touches the measurement surface and detects the displacement. The sphere tip radius of a typical contact-type displacement sensor ranges from 1–3 mm, causing the roughness curve to be “filtered” by the radius of the sphere. Three methods for estimating the valley portion of the surface profile are evaluated in this study: a) linear approximation of the concave portion of the surface profile, b) function approximation of the concave portion, and c) using the known nose radius of the machining tool. The following sphere tip radii were used to measure actual surface profiles: 0.25 mm, 0.5 mm, 1.0 mm and 1.5 mm. Given the conditions of the experimental model, we found that surface profiles with a roughness that approximates a predictable curve can be measured with a high degree of accuracy.

Effective thermal elastic plastic finite element computation for welding distortion investigation of pozidriv-type welded structure with rectangular pipes and its mitigation

Welding distortion of pozidriv-type welded structure with rectangular pipes by 20 welding passes was examined with experimental and computational approaches, and mitigation techniques were also investigated for precision fabrication. Welding experiment to fabricate pozidriv type welded structure was conducted beforehand, and out-of-plane welding distortion was measured with contact type displacement sensor. Effective thermal elastic plastic finite element computation with iterative substructure method and parallel computation was developed, and then employed to examine the thermal-mechanical response during the entire welding process and predict the residual out-of-plane welding distortion. Good agreement between computed results and measurement data was observed with comparison. The influences of welding sequence and clamping constraint with tack welding on welding distortion were considered, which were also practiced for out-of-plane welding distortion mitigation. Both experiment and finite element computation show that out-of-plane welding distortion with welding sequence optimization and clamping constraint can be significantly reduced with about 38% and 56% magnitude of original welding distortion, respectively, while their mechanisms were also clarified by means of stiffness variation of solving welded structure.

Evaluation of Vision-Based Measurements for Shake-Table Testing of Nonstructural Components

AbstractDuring an earthquake, freestanding equipment and contents in a building may experience large complex 3D motion. Depending on the geometry, mass distribution, and support mechanism (e.g., wheels, casters, legs) of the object, this motion may include rolling, sliding, twisting, and rocking—potentially resulting in overturning or impact with building occupants, neighboring walls or other objects. Measuring this complex motion by traditional, contact-type displacement sensors is challenging. Owing to recent advances in video capture sensors and image processing techniques, vision-based motion tracking and measurement have been introduced as a practical, economical, and fairly accurate measuring method. This paper presents a procedure utilized to evaluate the accuracy of a consumer-grade camera for the purpose of measuring the motion of a piece of medical equipment during shake-table testing. The fixed-focal length camera considered in this study can capture video recordings with different resolution a...

The Effect of Niobium Doping on the Electrical Properties of 0.4(Bi0.5K0.5)TiO₃-0.6BiFeO₃ Lead-Free Piezoelectric Ceramics.

Ceramics in the system (Bi0.5K0.5)TiO3-BiFeO3 have good electromechanical properties and temperature stability. However, the high conductivity inherent in BiFeO3-based ceramics complicates measurement of the ferroelectric properties. In the present work, doping with niobium (Nb) is carried out to reduce the conductivity of (Bi0.5K0.5)TiO3-BiFeO3. Powders of composition 0.4(K0.5Bi0.5)Ti1−xNbxO3-0.6BiFe1−xNbxO3 (x = 0, 0.01 and 0.03) are prepared by the mixed oxide method and sintered at 1050 °C for 1 h. The effect of Nb doping on the structure is examined by X-ray diffraction. The microstructure is examined by scanning electron microscopy. The variation in relative permittivity with temperature is measured using an impedance analyzer. Ferroelectric properties are measured at room temperature using a Sawyer Tower circuit. Piezoelectric properties are measured using a d33 meter and a contact type displacement sensor. All the samples have high density, a rhombohedral unit cell and equiaxed, micron-sized grains. All the samples show relaxor-like behavior. Nb doping causes a reduction in conductivity by one to two orders of magnitude at 200 °C. The samples have narrow P-E loops reminiscent of a linear dielectric. The samples all possess bipolar butterfly S-E loops characteristic of a classic ferroelectric material. Nb doping causes a decrease in d33 and Smax/Emax.

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...

Error calibration of five-axis machine tools by on-machine measurement system using a laser displacement sensor

An on-machine measurement system to measure the workpiece’s geometry or dimension plays an important role in manufacturing processes. A laser displacement sensor recently attracts more attention which enables on-machine high-speed continuous scanning measurement. We developed an on-machine measurement system using a triangulation-based laser displacement sensor for five-axis machine tools. By driving the machine’s rotary axes to tilt or rotate the workpiece, the object’s geometry can be measured from all the directions in the three-dimensional space without being detached from a machine table. In such a measurement, location errors and error motions of the machine’s rotary axes clearly become major contributors for the measurement uncertainty. To identify location errors of rotary axes by using the on-machine laser measurement system itself, this paper presents its application to the R-test, where the three-dimensional displacement of a precision sphere, attached to a rotary table, is measured in the machine tool coordinate system. In the present laser measurement system, the position and the orientation of the laser displacement sensor must be calibrated in advance by using the motion of the machine’s rotary axes. The location errors of rotary axes cause their identification error. Unlike the conventional R-test, where the sphere’s displacement is measured by three contact-type displacement sensors, the formulation to identify location errors must consider the influence of this calibration error. Experimental demonstration is presented.

Non-contact R-test with laser displacement sensors for error calibration of five-axis machine tools

Abstract The R-test is an instrument to measure three-dimensional displacement of a precision sphere attached to a spindle relative to a work table by using three displacement sensors. Its application to error calibration for five-axis machine tools has been studied in both academia and industry. For the simplicity in calculating the sphere center displacement, all conventional R-test devices use contact-type displacement sensors with a flat-ended probe. Conventional contact-type R-test may be potentially subject to the influence of the friction or the dynamics of supporting spring in displacement sensors particularly in dynamic measurement. This paper proposes a non-contact R-test with laser displacement sensors. First, a new algorithm is proposed to calculate the three-dimensional displacement of sphere center by using non-contact displacement sensors. The compensation of measurement error of a laser displacement sensor due to the curvature of target sphere is incorporated. Then, the measurement uncertainty of four laser displacement sensors with different measuring principles is experimentally investigated in measuring the geometry of a sphere in order to select the laser displacement sensor most suitable for the application to a non-contact R-test. A prototype non-contact R-test device is developed for the verification of the proposed algorithm for non-contact R-test. Experimental case studies of error calibration of (1) static and (2) dynamic error motions of rotary axes in a five-axis machine tool with the developed non-contact R-test prototype are presented. Its measurement performance is compared to the conventional contact-type R-test device.

A spiral scanning probe system for micro-aspheric surface profile measurement

This paper presents a novel spiral scanning probe measurement system which is developed to achieve precise profile measurements of micro-aspheric surfaces. The system consists of a scanning stage (a spindle and a linear slide) and a contact-type displacement sensor. The contact-type sensor is employed for the scanning of the micro-aspheric surface. The micro-aspheric object is set on the spindle, and the contact-type displacement sensor is set on the linear slide. The motions of the spindle and the linear slide are controlled synchronously so that the micro-aspheric object is scanned spirally for high-speed measurement. The motions of the stage are used as the scanning datum for the profile measurement. Because the error motions of the stage are estimated to be on the order of tens of nanometer, these errors are measured and compensated to achieve precise measurements. The alignment error between the spindle rotation axis and the probe tip of the contact-type displacement sensor, which is called the centering error, is confirmed to cause considerable measurement error of the micro-aspheric surface profile. Methods are proposed to make the alignment accurately. Experiments of surface profile measurement of a micro-aspheric lens are also carried out in the measurement system.