Fringe projection profilometry (FPP) is a commonly used tool in the three-dimensional (3D) measurement of diffuse objects in reverse engineering, products online detection, medical diagnosis, etc. However, due to the limited depth-of-field (DOF) of projection-imaging lenses, the contrast of captured sinusoidal fringes will decrease with the increase of defocus, which affects the high-precision acquisition of axial 3D topography. Although the lenses can be designed based on Scheimpflug principle or double-telecentric optical path to extend the DOF, some problems such as off-axis aberration, fixed magnification and limited field-of-view are still existing. To overcome the aforementioned drawbacks, FPP with phase-coded optics is proposed in this paper, where the captured sinusoidal fringe patterns are modulated effectively and the projection-imaging DOF of the system is greatly extended. Experimental results demonstrate the effectiveness of the proposed technique.
This paper presents a mathematical model which can fit a parameter in an optimal position by measuring data. The model can synchronously correct the measurement error caused by the small rotation about X, Y and Z axes and the small deviation along X, Y and Z directions. The measurement results of the surface show that the model is reliable and effective, which provides loose conditions for placing mirrors and reliable measurement results for contact Coordinate Measuring Machine(CMM) off-axis surface contour measurement. The basic principle of the data analysis is also of high reference value for contour measurement of other non-contact free-form surfaces. The validity of the model is verified by mathematical simulation and practical engineering application, which is of great help to the measurement of high precision contact free-form surface.
The advantages of the freeform surface is obviously in optical system application: higher image quality, larger view field, simplified system and more design degrees of freedom. But, the large application of the freeform surface is limited by the difficulty of its manufacture. Measurement is the base of optical fabrication. In order to achieve the high precision freeform surface, the surface should be measured accurately. High precision freeform surface measurement technology is one of the most important problem in the field of optical fabrication. A new measurement method has been proposed which is different from the existing free-form surface measurement instruments, and it is proved in theory that can achieve high precision measurement for free-form surfaces. In this paper, a complete mathematical model is established for the probe part through ray tracing, so as to obtain the object-image relationship data of light passing through each optical element. Using the point set, the wave image of each surface is obtained, the optical path difference of the light is calculated, and the corresponding interference diagram is drawn. This process is principle verification. Contrary to the simulation process, in the process of measuring, the interferogram is obtained first, and then the deviation value is calculated.
A new noncontact detection method has been proposed in order to solve the problem that the accuracy of complex freeform surface detection is not high enough and the Poor adaptability, which using optical probe with standard reflective spherical shell lens of Tyman-Green interferometer. The probe is made up by laser beam, convergent lens, diaphragm and standard reflective spherical shell lens. The laser beam is converged to a guass focus, which is overlapped with the centre of the inner surface of translucent spherical shell. Ideally, the beam is converged onto the surface of the lens and reflected to the inner surface of the spherical shell, then returned to the original path. Wave front information, when the focal point is located at a different position of the detected surface including defocus, over-focus, and ideal focus, was obtained by ZEMAX. The longitudinal positioning accuracy of the surface is discussed and proved to 100nm, which is carried out by preliminary analysis of wavefront information.
Simultaneous realization of high-precision and universal detection of freeform surfaces is an important and urgent problem to be solved in optical inspection. To solve this problem, a Twyman-Gre e n interferometric optical probe in conjunction with a standard retroreflective spherical lens design is be proposed in this paper. The detection technology does not need to align the optical probe wit h the normal direction of the measured surface, and only two translational axes and one rotation axis are required for measurement, the location of the measured point is determined by the null interference fringes obtained by the interference of the reference light and the detection light, thereby obtaining the three-dimensional surface shape data of the measured surface. The basic parameters of the optical probe are determined by theoretical calculations and a mathematical model is established. The simulat ion was performed using matlab, and the feasibility of the system structure was verified by building experiments.
Virtual Reality (VR) products serve for human eyes ultimately, and the optical properties of VR optical systems must be consistent with the characteristic of human eyes. The monocular coaxial VR optical system is simulated in ZEMAX. A diffraction grating is added to the optical surface next to the eye, and the lights emitted from the diffraction grating are deflected, which can forming an asymmetrical field of view(FOV). Then the lateral chromatic aberration caused by the diffraction grating was corrected by the chromatic dispersion of the prism. Finally, the aspheric surface was added to further optimum design. During the optical design of the system, how to balance the dispersion of the diffraction grating and the prism is the main problem. The balance was achieved by adjusting the parameters of the grating and the prism constantly, and then using aspheric surfaces finally. In order to make the asymmetric FOV of the system consistent with the angle of the visual axis, and to ensure the stereo vision area clear, the smaller half FOV of monocular system is required to reach 30°. Eventually, a system with asymmetrical FOV of 30°+40° was designed. In addition, the aberration curve of the system was analyzed by ZEMAX, and the binocular FOV was calculated according to the principle of binocular overlap. The results show that the asymmetry of FOV of VR monocular optical system can fit to human eyes and the imaging quality match for the human visual characteristics. At the same time, the diffraction grating increases binocular FOV, which decreases the requirement for the design FOV of monocular system.
Low temperature glass molding technology is the main method on volume-producing high precision middle and small
diameter optical cells in the future. While the accuracy of the molding die will effect the cell precision, so the high
precision molding die development is one of the most important part of the low temperature glass molding technology.
The molding die is manufactured from high rigid and crisp metal alloy, with the ultrasonic vibration character of high
vibration frequency and concentrative energy distribution; abrasive particles will impact the rigid metal alloy surface
with very high speed that will remove the material from the work piece. Ultrasonic can make the rigid metal alloy
molding die controllable polishing and reduce the roughness and surface error. Different from other ultrasonic fabrication
method, untouched ultrasonic polishing is applied on polish the molding die, that means the tool does not touch the work
piece in the process of polishing. The abrasive particles vibrate around the balance position with high speed and
frequency under the drive of ultrasonic vibration in the liquid medium and impact the workspace surface, the energy of
abrasive particles come from ultrasonic vibration, while not from the direct hammer blow of the tool. So a nummular
vibrator simple harmonic vibrates on an infinity plane surface is considered as a model of ultrasonic polishing working
condition. According to Huygens theory the sound field distribution on a plane surface is analyzed and calculated, the
tool removing function is also deduced from this distribution. Then the simple point ultrasonic polishing experiment is
proceeded to certificate the theory validity.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.