Xuanze Wang

Extended depth of field through an axicon

One of the main disadvantages of imaging systems is the limited depth of field. We present the ability of a refractive axicon for imaging with an extended depth of field. We design an imaging system with a two-step imaging approach that uses a CCD camera to capture intermediate images and uses a digital process to obtain the final images. The depth of field is analyzed based on the condition of the focal segment. In particular, the point spread functions (PSFs) are discussed in simulation in detail. The performed experiments validate the effect and feasibility of the axicon for imaging with an extending depth of field.

Algorithm for sine wave cure fit based on frequency precise estimation

In the process of curve fitting, the unknown relationship between the data sampling rate and the frequency of the measured signal as well as signals frequency fluctuations can cause remarkable error. In this paper, a sine curve fitting algorithm with frequency precise estimation is proposed to solve this problem. Firstly, ellipse fitting algorithm is used to estimate the measured signal frequency. On the basis of this, the three-parameter sine fitting calculation based on the least squares method is applied to the sampling data, and the accuracy of the sine curve fitting result is improved. The experimental results show that the algorithm proposed in this paper can avoid the problem of frequency fluctuation and error caused by the unknown relationship between the sampling frequencies. Moreover, the fitting has a good randomness after frequency estimation, and the fitting result has nothing to do with the signal amplitude. Compared without frequency accurate estimation, the fitting error is greatly reduced and the fitting precision is higher.

Image classification and recognition method to mechanical parts based on fractal dimension

Complex mechanical parts have characteristics of irregularity and certain statistical self-similarity, which can be described by fractal dimension. And the values of their fractal dimension can be used as an measurement to classify and recognize the mechanical parts. In addition, the values can guide robots to grab parts. However, the image obtained by a vision system, which contains part images main image and image background will affect the calculation of fractal dimension of main images. In order to solve the problem, an improved differential box-counting method is designed in this paper. The fractal dimension of part images which has been cut and rotated can be calculated using this differential box- counting method. The experimental result shows that the improved differential box-counting method can calculate the fractal dimension of different size-length images, and the values are more stable. The improved method solves the problem that traditional algorithm can only calculate the fractal dimension of image which side length is integer power of 2.

Imaging characteristics of the axicon imaging system

The depth of an image system can be extended by an axicon which can generate line focus. According to physical optical theory, the diffracting patterns of the defocus point spread function (PSF) for the imaging system with axicon are analyzed through the generalize pupil function. The expressions of the PSF for the imaging system illuminated by white light are described as the superposition of the intensities in individual monochromatic patterns. Experimental results show that the central portion contains the most energy of the diffraction pattern from the PSF produced by the white light, and the contrast of secondary outside circular rings decreased rapidly. Furthermore, the central spot radius varied slowly with the increase of defocus parameter, and the depth of field of the imaging system is effectively extended with a shortcoming that the images need further processing.

A high-accuracy signal processing algorithm for frequency scanned interferometry

A high-accuracy signal processing algorithm was designed for the absolute distance measurement system performed with frequency scanned interferometry. The system uses frequency-modulated laser as light source and consists of two interferometers: the reference interferometer is used to compensate the errors and the measurement interferometer is used to measure the displacement. The reference interferometer and the measurement interferometer are used to measure synchronously. The principle of the measuring system and the current modulation circuit were presented. The smoothing convolution was used for processing the signals. The optical path difference of the reference interferometer has been calibrated, so the absolute distance can be measured by acquiring the phase information extracted from interference signals produced while scanning the laser frequency. Finally, measurement results of absolute distances ranging from 0.1m to 0.5m were presented. The experimental results demonstrated that the proposed algorithm had major computing advantages.

Displacement measurement based on TWAIN interface

The standard of technology without an interesting name (TWAIN) was introduced and a displacement measurement method was presented. Based on the theories of image capture and image measurement, a displacement measurement system was developed and subpixel and centroid technique were used to improve the measurement precision. The Experiment results show that the proposed method has low cost and high precision.

Design of a probe for two-dimensional small angle detection

A novel two-dimensional small angle probe is introduced, which is based on principle of auto-collimation and utilizes quadrant Si-photoelectric detector (QPD) as detection device. AC modulation, AC magnification and absolute value demodulation are incorporated to restrain the DC excursion caused by background light and noise etc and to improve the sensitivity and stability of angle detection. To ensure that while the laser is shining, the current signal (converted into voltage signal) of QPD also is linear to the AC modulation voltage, this paper adopted AC modulation signal (5400Hz) with a DC offset. AC magnification circuit with reasonable parameters is designed to inhibit DC drift and the impact of industrial frequency noise and to ensure good amplification to signal frequency at the same time. A piezoelectric-driven micro-angle generator is designed to demarcate the angle. The calibration data are input to single chip, and the measurement of angles can be shown in SMC1602A.

Calibration method with grating grooves based on precision vision measurement

This paper presents a new method of high-precision calibration with grating grooves for precision vision measurement system of micro-size part. After an image of high precision grating grooves are grabbed by CCD, a black-and-white striped picture may be gotten. A group of data being similar to sinusoid is gotten by calculating the sum of gray-value of pixels in each column. These calculated data are elaborately showed a Lissajous figure in one plane by translation for pixel. The size mapping coefficient between the grating groove and their image pixels of the optical measurement system is calculated by analyzing and processing the Lissajous figure. It is not necessary to calculate the interior and exterior parameters of the camera for the calibration of measurement system when this method is adopted. Finally, this paper gives the result of calibration and its error analysis for one optical system.

Development of a novel optical alignment system for accurate leveling adjustment of a high-precision chip mounter

Automatic high-precision chip mounter have been applied frequently in high-precision and complex craft situations. The key to the equipment is the vision alignment system. The leveling adjustment is the important part and preconditin of the alignment. On the basis of a correlative leveling adjustment technlogy, a novel optical alignment system for leveling adjustment is presented. Its optical system is designed and its flow of image processing is discussed. To avoid the influence of interference, the polarization of the light is used skillfully in the optical system. The result of simulated experiments of the reticle-mark collected by a charge couple device (CCD) indicates that the system can meet the precision needs of an automatic chip mounter vision alignment system and it is reasonable.