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.

Drift Reduction of a 4-DOF Measurement System Caused by Unstable Air Refractive Index.

Laser beam drift greatly influences the accuracy of a four degrees of freedom (4-DOF) measurement system during the detection of machine tool errors, especially for long-distance measurement. A novel method was proposed using bellows to serve as a laser beam shield and air pumps to stabilize the refractive index of air. The inner diameter of the bellows and the control mode of the pumps were optimized through theoretical analysis and simulation. An experimental setup was established to verify the feasibility of the method under the temperature interference condition. The results indicated that the position stability of the laser beam spot can be improved by more than 79% under the action of pumping and inflating. The proposed scheme provides a cost-effective method to reduce the laser beam drift, which can be applied to improve the detection accuracy of a 4-DOF measurement system.

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.

A Differential Resonant Accelerometer with Low Cross-Interference and Temperature Drift.

Presented in this paper is a high-performance resonant accelerometer with low cross-interference, low temperature drift and digital output. The sensor consists of two quartz double-ended tuning forks (DETFs) and a silicon substrate. A new differential silicon substrate is proposed to reduce the temperature drift and cross-interference from the undesirable direction significantly. The natural frequency of the quartz DETF is theoretically calculated, and then the axial stress on the vibration beams is verified through finite element method (FEM) under a 100 g acceleration which is loaded on x-axis, y-axis and z-axis, respectively. Moreover, sensor chip is wire-bonded to a printed circuit board (PCB) which contains two identical oscillating circuits. In addition, a steel shell is selected to package the sensor for experiments. Benefiting from the distinctive configuration of the differential structure, the accelerometer characteristics such as temperature drift and cross-interface are improved. The experimental results demonstrate that the cross-interference is lower than 0.03% and the temperature drift is about 18.16 ppm/°C.

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.

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.

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.

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.

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 resonant sensor composed of quartz double ended tuning fork and silicon substrate for digital acceleration measurement.

Presented in this paper is a micro-resonant acceleration sensor based on the frequency shift of quartz double ended tuning fork (DETF). The structure is silicon substrate having a proof mass supported by two parallel flexure hinges as doubly sustained cantilever, with a resonating DETF located between the hinges. The acceleration normal to the chip plane induces an axial stress in the DETF beam and, in turn, a proportional shift in the beam resonant frequency. Substrate is manufactured by single-crystal silicon for stable mechanical properties and batch-fabrication processes. Electrodes on the four surfaces of DETF beam excite anti-phase vibration model, to balance inner stress and torque and imply a high quality factor. The sensor is simply packaged and operates unsealed in atmosphere for measurements. The tested natural frequency is 36.9 kHz and the sensitivity is 21 Hz/g on a nominally ±100 g device, which is in good agreement with analytical calculation and finite element simulation. The output frequency drifting is less than 0.5 Hz (0.0014% of steady output) within 1 h. The nonlinearity is 0.0019%FS and hysteresis is 0.0026%FS. The testing results confirm the feasibility of combining quartz DETF and silicon substrate to achieve a micro-resonant sensor based on simple processing for digital acceleration measurements.