In the high-end optical instrument application, aspherical lenses have replaced spherical lenses and became a key component owing to the aberration correction characteristic it benefits. Though aspherical lenses truly provide multiple advantages, as long as the uncertainty and time-taking issue remain unsolved in CNC polishing process, the term “mass production” will still be far from realization. In this paper, we have developed a method based on Preston’s equation and the Hertz-Contact theorem (HCT) to construct the tool influence function (TIF), hoping to increase the convergence of the process result. We will also discuss how different tool offsets affect the polishing force against the workpiece. We firstly obtained velocity distribution between bonnet and workpiece from dynamics in polar coordinates, then applied the equivalent contacting-Young’s modulus in Hertz-Contact theorem to calculate the pressure distribution model. Subsequently, we conducted a series of experiments under IRP1000 by Zeeko Ltd. and avoided unstable outcomes caused by both machine vibration and deficient tool offset. We modified the parameters into five different feed rates while remaining the equivalent dwelling time, to create more observable features of material removed and further proved the linearity relationship between the dwell time and the removal depth. We applied LP66 as the polishing pad and fused silica as the workpiece to acquire the experiment result.
Spherical lenses lead to forming spherical aberration and reduced optical performance. Consequently, in practice optical system shall apply a combination of spherical lenses for aberration correction. Thus, the volume of the optical system increased. In modern optical systems, aspherical lenses have been widely used because of their high optical performance with less optical components. However, aspherical surfaces cannot be fabricated by traditional full aperture polishing process due to their varying curvature. Sub-aperture computer numerical control (CNC) polishing is adopted for aspherical surface fabrication in recent years. By using CNC polishing process, mid-spatial frequency (MSF) error is normally accompanied during this process. And the MSF surface texture of optics decreases the optical performance for high precision optical system, especially for short-wavelength applications. Based on a bonnet polishing CNC machine, this study focuses on the relationship between MSF surface texture and CNC polishing parameters, which include feed rate, head speed, track spacing and path direction. The power spectral density (PSD) analysis is used to judge the MSF level caused by those polishing parameters. The test results show that controlling the removal depth of single polishing path, through the feed rate, and without same direction polishing path for higher total removal depth can efficiently reduce the MSF error. To verify the optical polishing parameters, we divided a correction polishing process to several polishing runs with different direction polishing paths. Compare to one shot polishing run, multi-direction path polishing plan could produce better surface quality on the optics.
Lasers are a promising high accuracy tool to make small holes in composite or hard material. They offer advantages over the conventional machining process, which is time consuming and has scaling limitations. However, the major downfall in laser material processing is the relatively large heat affect zone or number of molten burrs it generates, even when using nanosecond lasers over high-cost ultrafast lasers. In this paper, we constructed a nanosecond laser processing system with a 532 nm wavelength laser source. In order to enhance precision and minimize the effect of heat generation with the laser drilling process, we investigated the geometric shape of optical elements and analyzed the images using the modulation transfer function (MTF) and encircled energy (EE) by using optical software Zemax. We discuss commercial spherical lenses, including plano-convex lenses, bi-convex lenses, plano-concave lenses, bi-concave lenses, best-form lenses, and meniscus lenses. Furthermore, we determined the best lens configuration by image evaluation, and then verified the results experimentally by carrying out the laser drilling process on multilayer flexible copper clad laminate (FCCL). The paper presents the drilling results obtained with different lens configurations and found the best configuration had a small heat affect zone and a clean edge along laser-drilled holes.
The conventional measurements of the speed of light were performed before the early twentieth century. Only few used extraterrestrial sources and got the result with large uncertainty. We design a transmitter to modulate the rays from the local infrared light source and the extraterrestrial sources simultaneously into pulses. Both are received by a distant receiver. We have the white light travelling exactly along the path of the starlight pulses for calibration. It is found that the travel times of Aldebaran and Capella pulses are longer than that of Vega pulses. The results indicate that the speeds of starlights are different.
The speed of light is an important physical parameter. Currently it is a common belief of the constance of the speed of light regardless of the relative velocity between the source and the observer. Because the speed of light is very fast, if the relative velocity is small compared with the speed of light, it is difficult to detect the effect of the relative velocity on the measurement of the speed of light. In this paper we present a method of comparing the speeds of starlight and the light emitting from a terrestrial source. We use a telescope to collect the light from the star having significant relative velocity with respect to the earth, e.g. Capella. Then we modulate the starlight and the light emitted from the local source into pulses i.e. these pulses leave the modulator simultaneously. After travelling 4.2 km, these pulses are detected by a receiver. If the starlight and the terrestrial light have the same speed, then these pulses must arrive at the receiver at the same time. Our results show that the arrival times of the pulses of starlight are different from that of the local light. For example, the Capella is leaving away from the earth. The Capella pulses arrive later than the local light pulses. It indicates that the speed of Capella starlight is slower than the common believed value, c. The presented method uses one clock and one stick, so the clock synchronization problem and any physical unit transformation can be avoided.
The objective of this research is to develop a non-contact measurement system for micro-scale 3D geometry. The core of the system is based on Shape-from-Focus method. Corresponding digital images were taken at different heights with predefined step interval. The images taken were enhanced by image processing techniques including discrete Gaussian filtering and histogram equalization. The degree of the focused image was quantified and, then the height of each pixel was determined with Gaussian Interpolation. 3D geometry model of the specimen can be reconstructed. The system developed was verified with a standard sphere of radius 225 μm. The result gave the average radius of 221.56 μm with the standard deviation 8.95 μm. Feasibility of the measuring system was confirmed with satisfactory precision level.