Pyramid wavefront sensor (PWFS) without modulation is prevailing over one with modulation. So far how to describe
measured signals of non-modulation PWFS needs deeply research. In this paper, the theory of the non-modulation PWFS
is briefly presented according to wave optics. This paper analyses the existing four approaches in theory. By numerical
simulation this paper further verifies the performance of four approaches under the experiment condition. The result
shows that the approach with total intensity of pixels conjugate to the same spot in the pupil as signal denominator is the
best choice for the non-modulation PWFS in closed-loop correction.
To overcome the difficulty in the non-contact angle measurement especially for large-scaled workpieces, the paper presents a new angle measurement method based on Hough transform. The realization process of the method consists of workpiece image acquisition & preprocessing and angle measurement. With the preprocessing one can obtain an ideal binarized edge image of the workpiece image. The angle measurement is then carried out by employing the classical Hough transform. Except the discussion of measurement principle, both practical examples and simulated experiments are introduced to demonstrate the performance of the method proposed in the paper. The experiment results indicate that this method can be applied to measure the workpiece angle under many occasions and can achieve the aim of the non-contact angle measurement. At the same time, it does still possess great advantages in terms of reliability and noise rejection capability.
The paper firstly discusses the derivation of interference fringes and FFT method that is a conventional method for measuring fringes with equal spacing. And then, a new method for measuring the interference line fringes is presented. On the basis of Hough transform and digital image processing technology, this method accomplishes fringes image preprocessing (i.e., fringes skeletonizing) and fringes spacing measurement. It has been shown, with both theoretical analysis and experimental measurements, that this method is a universal method for fringes measurement and has more remarkable advantage than the FFT method because of the application of the former not being limited by some regulations such as equidistant fringes and sampling length, and so on. In addition, it also holds a good noise rejection capability and great reliability.