Fractal dimension is an important quantitative characteristic of a image, which can be widely used in image analysis. Differential box-counting method which is one of many calculation methods of a fractal dimension has been frequently used due to its simple calculation . In differential box-counting method, a window size M is limited in the integer power of 2. It leads to inaccurate calculation results of a fractal dimension. Aiming at solving the issues , in this paper, an improved algorithm is discussed that the window size M has been improved to be able to accommodate non-integer power of 2, and making the calculated fractal dimension error smaller. In order to verify superiority of the improved algorithm, the values of fractal dimension are regarded as parameters, and are applied for image segmentation combined with Ostu algorithm . Both traditional and improved differential box-counting methods are respectively used to estimate fractal dimensions and do threshold segmentation for a thread image . The experimental results show that image segmentation details by improved differential box-counting method are more obvious than that by traditional differential box-counting method, with less impurities, clearer target outline and better segmentation effect.
Differential box-counting (DBC) method has been widely used to calculate fractal dimension. analyzing the result of fractal dimension with background image by estimating this traditional method,we find that this algorithm has the limitation to estimate fractal dimension of images with background accurately. In order to solve this issue ,in this paper, an improved differential box-counting(IDBC) method has been proposed to eliminate influence of background on fractal dimension .The mainly improved steps of IDBC as follow: firstly ,the background pixels values G<sub>b</sub> of image need to be found out using probability .Secondly, the n<sub>q</sub> ( n<sub>q</sub> is the numbers of boxes in a grid) is set to zero when the maximum and minimum in a grid are equal to image background values. To validate IDBC method’s performance ,we designed an experiment that the fractal dimension of both original texture images and these ones put in different size frame with black-background are estimated and compared through four different algorithms, including DBC, relevant differential box-counting (RDBC) method, shifting differential box-counting (SDBC) method and IDBC method. The experimental results demonstrate that the IDBC method developed in this work has the ability to improve the measurement accuracy by avoiding the influence caused by background.
Single wavelength microscopic interferometry, driven by the Piezoelectric Transducer (PZT), is a common surface topography measurement method. Its measurement accuracy is directly determined by the original phase acquisition precision of every pixels in area array CCD. Traditional phase identification methods adopt 3 points or 4 points algorithm to obtain the phase. However, they require the displacement step, actuated by the PZT, to strictly keep the same to satisfy the 90° phase condition. Therefore, these methods are only suitable for the strict anti-vibration experimental environment or conditions with high precise closed-loop PZT actuator and strict calibration of interferometric wavelength. An auto-acquisition driving step method for the single wavelength microscopic interferometry is presented in this paper. Firstly, interference sequence diagrams, containing the surface topography information, are gathered by the CCD under open-loop PZT actuating. Next, two pixels whose phase difference is approximate 90° are selected as the calculating center to obtain smoothed gray values with regional gray average algorithm, which can reduce the influence of random noise. Finally, an optimal fitting algorithm for the ellipse, formed by the average gray values, is proposed to obtain the amplitudes and offsets of the two gray values array. According these fitting parameters and gray values, the drive step can be calculated by elliptic equations. Experiments have shown that this method can reduce the requirement conditions of measurement conditions and improve the measurement accuracy.
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.
A displacement sensor with controlled measuring force and its error analysis and precision verification are discussed in
this paper. The displacement sensor consists of an electric induction transducer with high resolution and a voice coil
motor (VCM). The measuring principles, structure, method enlarging measuring range, signal process of the sensor are
discussed. The main error sources such as parallelism error and incline of framework by unequal length of leaf springs,
rigidity of measuring rods, shape error of stylus, friction between iron core and other parts, damping of leaf springs,
variation of voltage, linearity of induction transducer, resolution and stability are analyzed. A measuring system for
surface topography with large measuring range is constructed based on the displacement sensor and 2D moving platform.
Measuring precision and stability of the measuring system is verified. Measuring force of the sensor in measurement
process of surface topography can be controlled at μN level and hardly changes. It has been used in measurement of
bearing ball, bullet mark, etc. It has measuring range up to 2mm and precision of nm level.
A five-degree-of-freedom (including two displace errors and three angular errors) online measuring system is proposed.
Two mutually perpendicular prisms are fixed on a workbench of guideway and move along with the workbench. The
measuring system consists of two independent left path and right path with same light structure and principle. The
principle of displacement and angular measurement is analyzed, and optical structure is established. The system has
many advantages such as small and simple structure, high-precision and cheap cost.
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.
A new five-degree-of-freedom measuring system was developed as a linear guide. According to the principle of
autocollimation, the system consisted of two semiconductor lasers, two right angle prisms, two lenses, two polarization
spectroscopes and four quadrant Si-photoelectric detectors(QPD). Two axial displacements and three angular rotation
degrees are measured by comparing the position of the spot center on the QPD. Repetitive simulations show that the
accuracy of the system is 3" for measurement of angle, which proves the feasibility of this system. The advantages of the
system include simple structure, easy operation, high accuracy, low cost and real-time work.
For the interference fringes' photodiode detection, its SNR can be improved by two ways to a great extent, one is space
arrangement of photodiodes, another is that photodiode operates without external reverse voltage. Despite application of
reverse voltage to photodiode is very useful in improving linearity and high frequency, it has the accompanying disadvantage of increasing dark current and noise levels along with the danger of damaging the device by excessive applied reverse voltage. In order to keep the high SNR and high frequency response of photodiode, we analyze the relation between movement frequency and photoelectric conversion of interference fringes when space arrangement of photodiodes are designed as a kind of high SNR detection method proposed in our previous article and photodiode operates in no reverse voltage state. On basis of the analysis, a combinative amplifier of DC (direct current) and AC (alternative current) is present to amplify the photoelectric difference signal. The input and feedback resistance of the amplifier are all replaced by the resistance and capacitance in parallel connection. When this amplifier is compared to the common one, it can greatly broaden the frequency response range of fringe signal and ensure the instrument can work normally at low and high frequency.
A new sub-pixel edge detection algorithm has been presented in this paper, which can be used in some high precision automatic alignment systems, such as automatic industrial measurement systems; integrate circuit encapsulation systems, micro-electromechanical systems, micro-optical electromechanical systems, three-dimensional encapsulation systems and so on. This algorithm uses the spatial moment to detect the location of edge within sub-pixel resolutions, and gains an advantage over the traditional pixel edge detection algorithms. Moreover, an extraction technology of region of interest is applied to reduce the time of analysis after rough pose estimation.
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.