Precision Rotary Stage Research Articles

Vertical Marginal Discrepancy Performance of a CAD-CAM System with Multiple Users.

The purpose of this evaluation was to evaluate the vertical marginal discrepancies of a computer-aided design-computer-aided manufacture (CAD-CAM) system used by different providers at separate time intervals. Lithium disilicate monolithic crowns on mandibular third molars were fabricated by three different providers inexperienced in digital dentistry. Using a precision rotary stage mounted on a digital recording microscope, the crown vertical marginal discrepancy was assessed using 160× magnification at 5-degree intervals around the crown marginal circumference for a total of 72 measurements per specimen. In addition to mean vertical marginal discrepancy, the maximum vertical marginal discrepancy, and its location as well as the percent of closed marginal assessments, were assessed. Mean data was analyzed using Kruskal-Wallis and Dunn post hoc testing at a 95% level of confidence (α=0.05). The mean marginal vertical discrepancy for all specimens was 21.1 ± 5.5 μm and a significant difference (p=0.0016) existed between groups but with noted wide similarity overlap. No difference (p=0.65) was observed with the mean closed margin percentage, but a significant difference (p=0.0012) existed in the observed maximum marginal discrepancy between groups. The 2-mm axial wall height (AWH), 20-degree total occlusal convergence (TOC) had significantly less (p<0.017) mean vertical marginal discrepancies than the 4-mm AWH, 20-degree TOC, and the 3-mm AWH, 16-degree TOC groups with the remaining groups similar (p>0.147). The plotted location of the specimen's maximum vertical discrepancy suggests a potential pattern amid the 360-degree margin circumference. Under the conditions of this study, CAD-CAM-derived monolithic lithium disilicate ceramic crowns fabricated by different clinicians demonstrated mean vertical marginal discrepancy results that were less than the suggested maximum clinically acceptable values. A potential for patterns of marginal discrepancy results was identified and deserves further evaluation. Results should be interpreted with caution as in vitro methodologies vary and do not directly correlate with clinical conditions.

A precision positioning rotary stage driven by multilayer piezoelectric stacks

The precision rotary stage plays a prominent role in the operation of precision drive equipment and mechatronics. However, the existing precision rotary stages are challenging to juggle the characteristics of low-voltage drive and high precision. This paper represents a precision positioning rotary stage driven by multilayer piezoelectric stacks, which can achieve stage rotating with low voltage and high precision. The rotary stage is driven by the interaction between a cylinder-type stator and a rotor, utilizing the third-order in-plane traveling wave vibrations. The contact model between the stator and the rotor is built. The prototype of the stage was made and the test experiment was completed. The experimental results show that the stage considers comprehensively the characteristics of high precision (the resolution is 27.53 μrad), and low-voltage drive(driving voltage as low as 5 Vp-p). The maximum speed of the proposed stage is 1039 r/min and the speed under a 200-g load is 30.23 r/min. The rotary stage shows tremendous potential in the field of the precision drive.

A method for simultaneously measuring 6DOF geometric motion errors of a precision rotary stage based on absolute position-distance measurement

In this paper, an absolute position-distance measurement based method for simultaneous measurement of six-degree-of-freedom (6DOF) errors of a precision rotary stage is proposed. This method uses the multi-wavelength phase-shifting interferometry technology and high-speed CCD camera to measure the instantaneous absolute spatial posture of the specially designed micro structure feature following the movement of a measured rotary stage. By analyzing the spatial posture of a series of instantaneous micro structure features, the 6DOF errors of the precision rotary stage are separated. The simultaneous, high precision and dynamically continuous measurement of 6DOF errors of the precision rotary stage is achieved. To improve the accuracy of error analysis, a model of 6DOF errors of the precision rotary stage is established to determine the mapping relationship between the 6DOF errors and the spatial posture of the micro structure feature. A test platform for 6DOF geometric motion errors of the precision rotary stage is built. The measurement results demonstrate the effectiveness and accuracy of the proposed method.

6 DOF calibration of profile sensor locations in an inspection station

Traditional coordinate measuring systems rely on the accurate kinematics of moving a sensor to the workpiece. This paper describes an instrument using a precision rotary stage to rotate a workpiece with respect to a set of three laser line sensors. The accuracy of the point cloud obtained from a single rotation of the workpiece is dependent on the rotational accuracy of the stage and knowledge of the location of the line sensors with respect to the rotary axis and each other. The calibration procedure required to locate these line sensors utilizes a precision artefact placed on the rotary stage.

Exclusion of Linear Acceleration Signal in the MEMS Thermal Gyroscope

This letter identifies the source of linear acceleration signal in the microelectromechanical systems (MEMS) thermal gyroscope and provides a real-time solution to exclude it. The main culprit of the undesired acceleration signal is found to be lack of rotational symmetry due to Manhattan sensor topology. A higher level of symmetry is obtained by constructing a hybrid gyroscope using two individual devices operating in tandem but 180° out-of-phase. A precision rotary stage is used to test the duo. The experiments confirmed that higher symmetry is promising in excluding the acceleration signal. Compared with a single device, the hybrid gyroscope demonstrated 16-fold reduction in the acceleration signal and 5-fold improved acceleration to rotation sensitivities. [2017-0171]

Method for correction of rotation errors in Micro-CT System

In Micro-CT (Computed Tomography) system, a series of projection data of sample are collected by the detector as the precision stage rotates step by step. However, the accuracy of projection images is limited by rotation errors during the acquisition process. Therefore, evaluating the performance of precision rotary stage and developing corresponding compensation method are necessary in Micro-CT system. In this paper, a metered system is designed which is composed of four precision capacitive sensors, a precision machined steel cylinder and four flexible hinges. Based on the metered system, a method to calibrate and correct the errors when the precision stage turns is proposed. Firstly, the theoretical analysis is proposed and the imperfect situations are considered. And then, the method has been applied to correct experimental data taken from a microscope type of Micro-CT system. Successful results are shown through evaluating MTF (Modulation Transfer Function) of Micro-CT system. Lastly, a sample of tungsten wire is scanned and the reconstructed images are compared before and after using the calibrated method.

A rotary stage in a vacuum using an air bearing

We present a design for a precision rotary air-bearing stage that can be used as a positioning system in vacuum applications, and evaluate its performance. The rotary stage used a vacuum-compatible air bearing, direct-drive motor, and high-resolution encoder to move precisely in a vacuum. The air bearing used a differential exhaust scheme with optimally designed parameters to minimize the air leakage into the vacuum chamber. The vacuum level was estimated from a theoretical leakage analysis and verified experimentally. The results show that a vacuum of 4 × 10−4 Pa was achieved during operation of the air-bearing stage, with an increase in the pressure of 0.5% at a velocity of 300 rpm, and a rotational resolution of 0.162 μrad and rotational accuracy of 0.23 μm in the radial direction.

Robust MEMS Gyroscope Based on Thermal Principles

Two variants of a novel single-axis thermal gyroscope without seismic mass are designed, fabricated, and characterized in this paper. The operating principle of the device is differential temperature detection due to the Coriolis effect on an oscillatory gas stream created by alternating two resistive microheaters. The fabrication process is based on a bulk micromachining technology on a silicon substrate using platinum as the only conductor layer. The device structure consists of two resistive temperature detectors equally spaced from the two microheaters. The 170-nm-thick platinum heater and detector microstructures are freely suspended over a cavity etched into the substrate, with minimal structural support. A computer-controlled precision rotary stage is constructed to accurately measure the device performance. The devices demonstrate excellent linearity within the tested ±3.5 revolution per second angular rate of rotation and show sensitivities of 0.947 and 1.287 mV/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> /s at 20 mW heater powers. The robustness of the devices has been validated by the drop shocks of 2,722 to 16,398g (9.81 m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ).

Successful fabrication of a convex platform PMMA cell-counting slide using a high-precision perpendicular dual-spindle CNC machine tool

This study presents a novel approach to the fabrication of a biomedical-mold for producing convex platform PMMA (poly-methyl-meth-acrylate) slides for counting cells. These slides allow for the microscopic examination of urine sediment cells. Manufacturing of such slides incorporates three important procedures: (1) the development of a tabletop high-precision dual-spindle CNC (computerized numerical control) machine tool; (2) the formation of a boron-doped polycrystalline composite diamond (BD-PCD) wheel-tool on the machine tool developed in procedure (1); and (3) the cutting of a multi-groove-biomedical-mold array using the formed diamond wheel-tool in situ on the developed machine. The machine incorporates a hybrid working platform providing wheel-tool thinning using spark erosion to cut, polish, and deburr microgrooves on NAK80 steel directly. With consideration given for the electrical conductive properties of BD-PCD, the diamond wheel-tool is thinned to a thickness of 5 µm by rotary wire electrical discharge machining. The thinned wheel-tool can grind microgrooves 10 µm wide. An embedded design, which inserts a close fitting precision core into the biomedical-mold to create step-difference (concave inward) of 50 µm in height between the core and the mold, is also proposed and realized. The perpendicular dual-spindles and precision rotary stage are features that allow for biomedical-mold machining without the necessity of uploading and repositioning materials until all tasks are completed. A PMMA biomedical-slide with a plurality of juxtaposed counting chambers is formed and its usefulness verified.

Sensitivity Improvement of Micromachined Convective Accelerometers

The sensitivity of a micromachined convective accelerometer filled with different gases at various conditions is theoretically and experimentally investigated. It is shown that the sensitivity of the accelerometer is proportional to the Rayleigh number for the contained gas. The Rayleigh numbers for nine gases are calculated, and the corresponding sensitivity improvements are predicted. To test our predictions, bulk silicon micromachining technology is used to fabricate and package several thermal accelerometers. A precision rotary stage is set up enclosing a packaged device into a gas chamber and rotating its sensitive axis against gravity. Data acquisition is done by a high-precision digital multimeter over full cycle rotations for seven candidate gases: nitrogen (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), argon (Ar), carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), sulfur hexafluoride (SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ), hexafluoroethane (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ), octafluoropropane ( C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> ), and octafluorocyclobutane ( C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> ). The measured sensitivities are in good agreement with the theoretical predictions. An upper limit to the sensitivity improvement by boosting the Rayleigh number for the contained gas is measured. Sensitivity decline beyond a critical Rayleigh number is reported for the first time since the advent of the convective accelerometers without proof mass.

Rapid Measurement of Involute Profiles for Scroll Compressors

Scroll compressors are widely used in air conditioners, vacuum pumps and so on. Rapid measurement of flank profile of a scroll compressor is important to improve the compression efficiency and decrease noises. A contact probe made of ruby was used for measurement of flank profile. The probe was moved by a linear slide along the X axis at a constant speed. The scroll workpiece was fixed on a precision rotary stage. The relationship between the stage rotational speed and the X axis moving speed complies with the Archimedean curve. The measurement data of the rapid measurement system were analyzed and measurement errors were removed by compensation of the offset between the coordinates of the rotary stage center and those of workpiece center. The measurement results were compared with those measured by a commercial coordinate measuring machine (CMM). The measurement time for the involute profile of the scroll is shortened to 153 seconds by the developed rapid measurement system from the 10 minutes measurement time by the CMM while the measurement accuracy is kept the same.

The Analysis of Radial/Axial Error Motion on a Precision Rotation Stage

Rotating stages in semiconductor, display industry and many other fields require challenging accuracy to perform their functions properly. Especially, Axis of rotation error on rotary system is significant; such as the spindle error motion of the aligner, wire bonder and inspector machine which result in the poor state of manufactured goods. To evaluate and improve the performance of such precision rotary stage, unessential movements on the other 5 degrees of freedom of the rotary stage must be measured and analyzed. In this paper, we have measured the three translations and two tilt motions of a rotating stage with high precision capacitive sensors. To obtain the radial error motion from T.I.R (Total Indicated Reading) of radial direction, we have used Donaldson's reversal technique. And the axial components of the spindle tilt error motion can be obtained accurately from the axial direction outputs of sensors by Estler face motion reversal technique. Further more we have defined and measured the sensitivity of positioning error to the five error motions. Keywords—Donaldson's reversal methods, Estler face motion reversal method, Error motion, sensitivity, T.I.R (Total Indicated Reading).

Sci‐PM Sat ‐ 01: Imaging performance of a bench‐top megavoltage CT scanner

The ultimate goal of this project is to create a focused 2D MV detector with high detective quantum efficiency so reasonable low contrast resolution (LCR) at low dose can be obtained in MVCT. As an initial step an 80‐element detector is fabricated by tiling 8‐element (element size 0.275 × 0.8 × 1 cm3) and photodiode arrays on an arc (radius = 110 cm). A precision rotary stage and its control are added to create a third generation CT scanner. The attenuation of and 6 MV beams are measured as a function of solid water thickness, fit to a second order polynomial to correct for spectral hardening artifacts. A calibration procedure was established to remove ring artifacts caused by distinctly asymmetric line spread functions at the ends of 8‐element blocks. Low contrast resolution as a function of dose and object size, the signal to noise ratio (SNR) as a function of dose, and linearity of CT numbers with density were quantified. Throwing away one‐ninth of collected projection angles to reduce the dose per image adversely affects the resolution in 6 MV images; 15 mm targets at 1.5% are visible at 7cGy. Low contrast target of 1.5% at 6 mm is visible in at 2cGy. LCR in objects stays approximately constant while dose is reduced from 17 to 2cGy. Contrast decreases with diameter decrease. SNR2 from a uniform phantom increases linearly with dose (R2=0.9977). CT numbers as a function of the density show a linear trend (R2=0.9923).

Po-Poster - 01: A bench-top megavoltage CT scanner

The purpose of this project was to design, fabricate and test the data acquisition timing control, precision rotary stage control, and analog data multiplexer unit for a prototype megavoltage computed tomography (MVCT) detector. An 80-element prototype detector array is made with (element size 0.275 × 0.8 × 1 cm3) scintillators and photodiodes on an arc (radius of 110 cm). In addition to designing and fabricating an in-house data acquisition system (front-end integrators, data multiplexer unit, and timing control), a precision rotary stage and its control are added to create a third generation MVCT scanner. Data acquisition is synchronized with radiation pulses from a linac. Response of detector as a function of dose rate was studied by varying the source to detector distance. A narrow slit beam, at five locations, was used to measure the pre-sampled MTF. Detector signal in open beam was measured for a number of radiation pulses to use the periodogram method for NPS estimation. Using the measured MTF, NPS, and photon fluence impinging on detector, DQE was calculated. Detector response is linear as a function of dose rate, however shows a non-linear component while measuring the attenuation by solid water due to the polyenergetic spectrum. Beam-hardening correction is necessary before image reconstruction. MTF at the Nyquist frequency (0.16 mm−1) is 0.48. Zero-frequency DQE in 6 MV at 21% is higher than any experimental MVCT detector. The basic performance of the prototype detector is satisfactory for producing reasonable low contrast resolution in MVCT images with low dose.

SU‐FF‐I‐05: A Bench‐Top Megavoltage CT (MVCT) Scanner with Cadmium Tungstate‐Photodiode Detectors

Purpose: To design, fabricate and test the data acquisition timing control, precision rotary stage control, and an analog data multiplexer unit for a prototype megavoltage computed tomography (MVCT) detector. To measure the basic detector characteristics such as linearity with dose rate, the pre‐sampled modulation transfer function (MTF), the noise power spectrum (NPS) and the detective quantum efficiency (DQE). Method and Materials: The 80‐element prototype detector array is made with CdWO4 (element size 0.275 × 0.8 × 1 cm3) scintillators and photodiodes placed on an arc with a radius of 110 cm. In addition to designing and fabricating an in‐house data acquisition system (front‐end integrators, data multiplexer unit, and timing control), a precision rotary stage and its control are added to create a third generation MVCT scanner. The data acquisition is synchronized with radiation pulses from a linear accelerator. The response of the detector as a function of dose rate was studied by varying the source to detector distance. A narrow slit beam, at five locations, was used to measure the pre‐sampled MTF. The detector signal in open beam was measured for a number of radiation pulses to use the periodogram method for NPS estimation. Using the measured MTF, NPS, and the photon fluence impinging on the detector, the DQE was calculated. Results: Detector response is linear as a function of dose rate, however, shows a non‐linear component while measuring the attenuation by solid water due to the poly‐energetic spectrum. Therefore, beam‐hardening correction is necessary before MVCT image reconstruction. The MTF at the Nyquist frequency (0.16 mm−1) is approximately 0.48. The zero‐frequency DQE in 6 MV beam at 21% is higher than any experimental MVCT detector. Conclusion: The basic performance of the prototype detector was found to be satisfactory for producing reasonable low contrast resolution in MVCT images with low dose.

TU‐EE‐A3‐03: Performance of a Bench‐Top, Megavoltage CT (MVCT) Scanner Using Cadmium Tungstate‐Photodiodes

Purpose: To evaluate the imaging performance of a prototype fan‐beam megavoltage CT (MVCT) scanner in and 6 MV beams. Method and Materials: The 80‐element detector is fabricated by tiling 8‐element (element size 0.275 × 0.8 × 1 cm3) and photodiode arrays and arranging them on an arc (radius = 110 cm). A precision rotary stage and its control are added to create a third generation CT scanner. The attenuation of and 6 MV beams was measured as a function of solid water thickness, and fit to a second order polynomial to correct for spectral hardening artifacts. A calibration procedure was established to remove ring artifacts caused by the distinctly asymmetric line spread functions at the ends of 8‐element blocks. The low contrast resolution (LCR) as a function of dose and object size, the signal to noise ratio (SNR) as a function of dose, and the linearity of CT numbers with density were quantified. Results: Throwing away one‐ninth of collected projection angles to reduce the dose per image adversely affects the resolution in 6 MV images; however, 15 mm targets at 1.5% level are still visible at 7 cGy. The low contrast target of 1.5% at 6 mm diameter is visible in images at 2cGy. The LCR in the objects stays approximately constant with the dose reduced from 17 to 2 cGy. In general, the contrast decreases as the target diameter decreases. The SNR2 obtained from a uniform phantom increases linearly with dose (R2=0.9977). CT numbers as a function of the density show a linear trend (R2= 0.9923). Conclusion: The prototype detector performance is satisfactory to achieve the ultimate goal of this project of creating a focused 2‐D MV detector with high detective quantum efficiency such that reasonable LCR at low dose can be obtained in MVCT.

Precision goniometer equipped with a 22-bit absolute rotary encoder.

The calibration of a compact precision goniometer equipped with a 22-bit absolute rotary encoder is presented. The goniometer is a modified Huber 410 goniometer: the diffraction angles can be coarsely generated by a stepping-motor-driven worm gear and precisely interpolated by a piezoactuator-driven tangent arm. The angular accuracy of the precision rotary stage was evaluated with an autocollimator. It was shown that the deviation from circularity of the rolling bearing utilized in the precision rotary stage restricts the angular positioning accuracy of the goniometer, and results in an angular accuracy ten times larger than the angular resolution of 0.01 arcsec. The 22-bit encoder was calibrated by an incremental rotary encoder. It became evident that the accuracy of the absolute encoder is approximately 18 bit due to systematic errors.

3-D x-ray mirror metrology with a vertical scanning long trace profiler (abstract)

The long trace profiler (LTP) was originally developed at Brookhaven National Laboratory for the specific purpose of measuring the surface figure of large cylindrical mirrors used at grazing incidence in synchrotron radiation (SR) beamlines. In its original configuration, it could measure only along one line down the center of the cylinder. A single linear profile is often sufficient to gauge the quality of the optical surface on these kinds of mirrors. For some applications it is necessary to measure the topography of the entire surface, not just along one line but over a grid that covers the entire surface area. We have modified a standard LTP to enable measurement of the complete surface of Wolter telescope optics in a vertical configuration. The vertical scanning LTP (VSLTP) is capable of producing a complete 3-D map of the surface topography errors relative to the ideal desired surface on complete segments of paraboloids and hyperboloids. The instrument uses a penta prism assembly to scan the probe beam in the longitudinal direction parallel to the mirror symmetry axis and uses a precision rotary stage to provide scans in the azimuthal direction. A Risley prism pair and a dove prism are used to orient the probe beam in the proper direction for the azimuthal scans. The repeatability of the prototype instrument is better than 20 nm over trace lengths of 35 mm with a slope measurement accuracy of about 1 microradian.