Design and experiment of multidimensional and subnanometer stage driven by spatially distributed piezoelectric ceramics.

Multidimensional microdriving stage is one of the key components to realize precision driving and high-precision positioning. To meet nanometer displacement and positioning in the fields of micro-/nano-machining and precision testing, a new six-degree-of-freedom microdriving stage (6-DOF-MDS) of multilayer spatially distributed piezoelectric ceramic actuators (PZTs) is proposed and designed. The interior of the 6-DOF-MDS is a hollow design. The flexure hinge is used as the transmission mechanism, and the series-parallel hybrid driving of the corresponding PZTs achieves the microtranslation in the X, Y, and Z directions and the microrotation around the three axes of the microdriving stage, forming a microdisplacement mechanism with high rigidity and simple structure, which can realize the microfeed of 6-DOF. The force-displacement theory and lug boss structure optimization of the 6-DOF-MDS are analyzed, while the strength checking and natural frequency of the 6-DOF-MDS are also simulated by the finite element method. In addition, the real-time motion control system of the 6-DOF-MDS is designed based on Advanced RISC Machines. Through a series of verification experiments, the stroke and resolution results of the 6-DOF-MDS are obtained, where the displacements in the X, Y, and Z directions are 20.72, 20.02, and 37.60 µm, respectively. The resolution is better than 0.68 nm. The rotation angles around X, Y, and Z are 38.96″, 33.80″, and 27.87″, respectively, with an angular resolution of 0.063″. Relevant coupling experiments were also performed in this paper; in the full stroke linear running of X-axis, the maximum coupling displacements of the Y- and Z-axes are 1.04 and 0.17 µm, respectively, with the corresponding coupling rates of ∼5.0% and 0.8%. The maximum coupling angles for the X-, Y-, and Z-axes are 0.33″, 0.14″, and 2.30″, respectively. Considering the coupling of the 6-DOF-MDS, decoupling measures and specific mathematical models have also been proposed. The proposed multidimensional microdriving stage achieves subnanometer resolution and can be used for the precise positioning and attitude control of precision instruments at the nano-/subnanometer level.

Directional region-based feature point matching algorithm based on SURF.

Feature point matching is one of the fundamental tasks in binocular vision. It directly affects the accuracy and quality of 3D reconstruction. This study proposes a directional region-based feature point matching algorithm based on the SURF algorithm to improve the accuracy of feature point matching. First, same-name points are selected as the matching reference points in the left and right images. Then, the SURF algorithm is used to extract feature points and construct the SURF feature point descriptors. During the matching process, the location relationship between the query feature point and the reference point in the left image is directed to determine the corresponding matching region in the right image. Then, the matching is completed within this region based on Euclidean distance. Finally, the grid-based motion statistics algorithm is used to eliminate mismatches. Experimental results show that the proposed algorithm can substantially improve the matching accuracy and the number of valid matched points, particularly in the presence of a large amount of noise and interference. It also exhibits good robustness and stability.

Development of submicron precision three-dimensional low cross-interference air-floating motion stage.

To meet the high requirements for positioning accuracy and multiple dimensions of positioning systems in the fields of precision measurement and precision machining, a new submicron-precision three-dimensional (3D) low cross-interference positioning system is designed and fabricated in this paper. The 3D motion stage mainly includes a mechanical structure, a support and guide system, and a driving system. The Abbe offset error is eliminated by adopting a coplanar structure in the X and Y directions, thus minimizing the mutual cross-interference of the motion stage. The X and Y motion stages are driven by a ball screw pair and an alternating current servo motor, which are supported and guided by an air-floating rail and slider. Moreover, the X and Y air-floating stages adopt a lateral structure and double rails, respectively. The Z-motion stage is directly driven by a high-precision piezoelectric motor. In addition, the system achieves high-precision motion by using the dual-loop control technology of secondary feedback combined with the high-resolution control characteristics of the servo motor. The performance of the positioning system is evaluated through a series of verification experiments. Results show that the stroke of the positioning system of the 3D air-floating motion stage can reach 100 × 100 × 100 mm3, and the repeated positioning accuracy is better than 0.41 µm (k = 2, k is defined by the International Organization for Standardization as the coverage factor). The maximum cross-interference of the X-stage is 180 nm, and the Y-stage reaches 320 nm when running with a full stroke of 100 mm in the Z-direction, demonstrating good repeatability, stable running, and high straightness. The submicron-precision 3D air-floating motion stage developed in this paper can be used as a suitable solution for coordinate measuring machines, microlithography, and micromachining applications when combined with an additional nanoprecision microstage.

A novel uncertainty evaluation method based on the particle filter and beta distribution for data with unknown distribution.

Uncertainty evaluation for unknown distribution data is a key problem to be solved in uncertainty evaluation theory. To evaluate the measurement uncertainty of data with unknown distributions, a novel uncertainty evaluation method based on the particle filter (PF) and beta distribution is proposed in this paper. A beta distribution with wide adaptability was adopted as the distribution type of measurement results, the parameters of the beta distribution were taken as the parameters to be estimated, and a state-space model was established. The PF method, suitable for non-Gaussian data, was utilized to obtain the estimates of the parameters of the beta distribution according to the measurement results. Finally, the best estimates of the measurement results and their uncertainty were calculated using the beta distribution parameters. Simulation results show that the proposed method is adaptive to accurately evaluate the measurement uncertainties of data, especially for non-Gaussian distribution data or asymmetrically distributed data. Multiple evaluation results show that the method has good robustness. The experimental results for the drift errors of a laser interferometer show that the uncertainty result of the proposed method is consistent with the Monte Carlo method. This method is suitable for a variety of distribution types that can be characterized through beta distribution and can solve the optimal estimation and uncertainty evaluation of most measurement results with unknown distribution types.

Large-scale and high-depth three dimensional scanning measurement system and algorithm optimization.

Tapping scanning mode is an important method for measuring surface topography at the nanometer scale. It is widely used because it can eliminate lateral force and reduce damage to the tested sample. Research on three dimensional (3D) scanning technology with a large range and high depth-to-width ratio has important practical significance and engineering application value because the current scanning probe microscope has the limitations of small measurement ranges and weak Z-direction measurement ability. The high-frequency resonance of the quartz tuning fork, combined with the tungsten stylus, is used in this paper. It has the ability to measure the surface profile of the microdevice with a large aspect ratio. The proposed 3D scanning measurement system has realized a microstructure measurement with a depth of ∼58 µm. The entire measuring range is 400 × 400 × 400 µm3, and the vertical resolution reaches 0.28 nm. The system can accurately obtain the 3D surface topography of the microfluidic biochip. In addition, a sliding window algorithm (SWA) based on errors in the scanning process and low scanning efficiency is proposed. Compared with the point-by-line scanning algorithm, the proposed SWA reduces the mean value of the squared residuals of the 3D profile by 7.70%, thereby verifying the feasibility of the algorithm. The 3D scanning measurement system and the algorithm in the tap mode provide an important reference for the 3D topography measurement of microstructures with large aspect ratios.

High-Precision Fabrication of Micro Monolithic Tungsten Ball Tips via Arc Discharge and the Taguchi Method.

A micro ball tip is a core component of high precision coordinate measuring machines. The present micro ball tips cannot satisfy the high-precision measuring requirements of high aspect ratio microstructures due to their large diameter and low accuracy. In the previous study, we fabricated a micro monolithic tungsten ball tip by using arc discharge and surface tension principles. However, the fabrication success rate of forming a micro ball tip is less than 10%. In the present study, the Taguchi method has been applied to increase the fabrication success rate, and it has increased to 57.5%. The output response is evaluated in terms of the diameter, roundness, and center offset of the tungsten probe ball tips. The smaller-the-better signal-to-noise ratio is applied to analyze the influence of various parameters. The proposed parameters can be used to increase the fabrication success rate and accuracy of the monolithic probe ball tip.

Independent driving method for significant hysteresis reduction of piezoelectric stack actuators.

Piezoelectric actuators are used extensively in precision positioning platforms. However, the positioning accuracy is severely affected by the hysteresis characteristics of piezoelectric ceramics. Piezoelectric stack actuators (PSAs) are usually composed of hundreds of thin piezoelectric ceramic layers connected in parallel, and their hysteresis quantity is the accumulation of that in each layer, which results in large nonlinear deformation. A new driving method is proposed for PSAs to drive each layer independently, and all the layers are driven in sequence. The independent driving logic is analyzed, and the scheme of the driving circuit is presented to replace the traditional voltage amplifier, which guarantees that there is no need to change the original driving signal. Experimental results show that the hysteresis of a homemade seven-layer PSA is reduced from approximately 12.5% to 2.7% compared with the traditional parallel driving method in various frequencies. The proposed independent driving method can reduce hysteresis significantly and achieve good linearity in an open-loop control, which does not need high-performance sensors or hysteresis models.

A method to correct hysteresis of scanning probe microscope images based on a sinusoidal model.

Piezoelectric actuators are widely used in scanning platforms of scanning probe microscopes (SPMs). However, the hysteresis of piezoelectric actuators reduces positioning accuracy and results in distorted SPM images. When regular raster scanning of SPM starts, the piezoelectric actuators move repeatedly at the same scanning range and frequency once the scanning parameters are set. In this study, a practical and simple mathematical model derived from experimental phenomenon, which is the combination of sinusoidal and linear functions, was proposed to describe the hysteresis behavior of piezoelectric actuators with repeated scanning. The model parameter was calculated from the coordinates of matched feature points in the trace and retrace images of ordinary sample obtained with an atomic force microscope (AFM). Experimental results show that the hysteresis of the scanned images is decreased from 107.46 pixels to 2.50 pixels after correction, with a width of 800 pixels. Hysteresis in other scanned images with different scanning frequencies and ranges was also corrected effectively using this model. The proposed model can be used to correct the hysteresis of AFM images without using any expensive displacement sensors or standard samples. The model is suitable and easy to be integrated into the scanning program of AFM without requiring hardware modifications.

Development of a Micro/Nano Probing System Using Double Elastic Mechanisms.

To meet the requirement of high precision measurement of coordinate measurement machine system, a compact microprobe has been designed for 3D measurement in this paper. Aiming to reduce the influences of signal coupling during the probing process, the probe has been designed by adopting two elastic mechanisms, in which the horizontal and vertical motions of the probe tip can be separated by differential signals of quadrant photodetectors in each elastic mechanism. A connecting rod has been designed to transfer the displacement of the probe tip in vertical direction from lower to upper elastic mechanisms. The sensitivity models in horizontal and vertical directions have been established, and the sensor sensitivity has been verified through experiments. Furthermore, the signal coupling of three axes has been analyzed, and mathematical models have been proposed for decoupling. The probing performance has been verified experimentally.

Fabrication and Study of Micro Monolithic Tungsten Ball Tips for Micro/Nano-CMM Probes.

Micro ball tips with high precision, small diameter, and high stiffness stems are required to measure microstructures with high aspect ratio. Existing ball tips cannot meet such demands because of their weak qualities. This study used an arc-discharge melting method to fabricate a micro monolithic tungsten ball tip on a tungsten stylus. The principles of arc discharge and surface tension phenomenon were introduced. The experimental setup was designed and established. Appropriate process parameters, such as impulse voltage, electro discharge time, and discharge gap were determined. Experimental results showed that a ball tip of approximately 60 µm in diameter with less than 0.6 µm roundness error and 0.6 µm center offset could be realized on a 100 µm-diameter tungsten wire. The fabricated micro ball tip was installed on a homemade probe, touched by high-precision gauge blocks in different directions. A repeatability of 41 nm (K = 2) was obtained. Several interesting phenomena in the ball-forming process were also discussed. The proposed method could be used to fabricate a monolithic probe ball tip, which is necessary for measuring microstructures.

Squeeze Film Air Damping in Tapping Mode Atomic Force Microscopy.

In dynamic plowing lithography, the sample surface is indented using a vibrating tip in tapping mode atomic force microscopy. During writing, the gap between the cantilever and the sample surface is very small, usually on the order of micrometers. High vibration frequency and small distance induce squeeze film air damping from the air in the gap. This damping can cause variations in the cantilever's vibrating parameters and affect the accuracy of the nanoscale patterning depth. In this paper, squeeze film air damping was modeled and analyzed considering the inclined angle between the cantilever and the sample surface, and its effects on the resonant amplitude and damping coefficient of the cantilever were discussed. The squeeze film air damping in the approaching curve of cantilever was observed, and its effect on fabricating nanopatterns was discussed.

A Scanning Probe Microscope for Surface Measurement in Nano-Scale.

A tapping mode scanning probe microscopy (TM SPM) system for surface measurement in nanoscale is developed, of which the main element is a scanning probe consisting of quartz tuning fork and a long sharp tungsten tip. Quartz tuning fork is a very good resonant element with piezoelectrical characteristic, and it acts as an actuator and a force sensor simultaneously in the probe. The vertical spatial resolution of the TM SPM is up to sub-nanometer (0.11 nm) and the measuring force is in micro Newton magnitude (about 30 µN). In the scanning operation, the probe vibrates at its resonant frequency, so that the amplitude or frequency (or phase) of the resonant tuning fork is very sensitive to external forces (Its quality factor in air is about 3138). Using the TM SPM constructed by this probe, silicon samples are scanned. Their topography and phase images which indicate the surface material characteristics are reconstructed effectively with a high resolution and low destructiveness. Soft materials, such as Protein structure can also be scanned theoretically without damage. In addition, because of the using of the long sharp tungsten tip, the system has the capacity of measuring micro structures with large aspect ratio, such as large micro steps, deep micro trenches, etc.

Fabrication of an Optical Fiber Micro-Sphere with a Diameter of Several Tens of Micrometers.

A new method to fabricate an integrated optical fiber micro-sphere with a diameter within 100 µm, based on the optical fiber tapering technique and the Taguchi method is proposed. Using a 125 µm diameter single-mode (SM) optical fiber, an optical fiber taper with a cone angle is formed with the tapering technique, and the fabrication optimization of a micro-sphere with a diameter of less than 100 µm is achieved using the Taguchi method. The optimum combination of process factors levels is obtained, and the signal-to-noise ratio (SNR) of three quality evaluation parameters and the significance of each process factors influencing them are selected as the two standards. Using the minimum zone method (MZM) to evaluate the quality of the fabricated optical fiber micro-sphere, a three-dimensional (3D) numerical fitting image of its surface profile and the true sphericity are subsequently realized. From the results, an optical fiber micro-sphere with a two-dimensional (2D) diameter less than 80 µm, 2D roundness error less than 0.70 µm, 2D offset distance between the micro-sphere center and the fiber stylus central line less than 0.65 µm, and true sphericity of about 0.5 µm, is fabricated.

Removing nonlinearity of a homodyne interferometer by adjusting the gains of its quadrature detector systems.

Most homodyne interferometers have a quadrature detector system that includes two polarizing beam splitters that cause nonlinearity of the order of a few nanometers by phase mixing. Detectors should have the same gains to reduce nonlinearity under the assumption that there is no loss in optical components. However, optical components exhibit some loss. We show that nonlinearity can be reduced to an order of 0.01 nm when the detector gains are adjusted by simulation to include the optical characteristics. The compensated nonlinearity is 18 times smaller than that when the four detector gains are set to be equal.