Key Engineering Materials Vol. 516

Abstract: A binocular robot vision system reconstructs 3D scenes from right and left images by using triangulation. However when using triangulation, the corresponding problems have to be resolved. To resolve the corresponding problems easily, authors have proposed a binocular robot vision system with an autonomously moving active viewpoint. By using this active viewpoint, the system constructs the correspondence between images of feature points of an object on the right and left images and calculates the spatial coordinates of the feature points. However the system cannot achieve correspondence between right and left images for smooth surface without feature points like corners. In this paper, we propose a method to extract feature points on a smooth surface virtually. To extract the feature points on the smooth surface of an object virtually, we use an active viewpoint of our system and vergence motion of the right and left cameras. In this system, the right and left cameras viewpoints are corresponded mechanically by the active viewpoint and vergence motion of both cameras. As the virtual feature point, a contact point between the smooth surface and tangential line from the epipole on the baseline of right and left cameras is extracted from the camera images. Because the right and left cameras viewpoints are fixed by the active viewpoint, the active viewpoint becomes the constraint for the extraction of the virtual feature points. The information of the virtual feature points on the smooth surface of an object is used for the calculation of the spatial coordinates of the object. The effect of the proposed method to extract the feature points virtually is shown experimentally by using a sphere as an object.

Abstract: Micro end mills, for example, smaller than 0.5 mm in diameter have low strength and stiffness. They are rather difficult to be re-sharpened by grinding. Therefore they are usually used until their breakage or are exchanged for a new one when the machining results lose quality. In the previous study [, tool life up to breakage was experimentally investigated under various feed rates and some useful information was obtained to predict tool life considering a sort of bending fatigue. For each experiment, a new tool was used to machine slots till it broke due to fatigue and/or wear. In this study, in order to measure tool life based upon another point of reference, the machining accuracies of the above slots were investigated. The main results obtained are as follows: (1) Slot depth first increased due to thermal deformation of the spindle and then decreased due to tool wear, (2) Slot width decreased as the tool wear increased, (3) Slot bottom corner radius increased as the tool wear increased, (4) Burr size increased as the tool wear increased, (5) Surface roughness of the slot bottom seemed to be influenced by feed rate, tool wear and chatter.

Abstract: The Atmospheric Pressure Plasma Jet (APPJ) is an innovative technology in advanced optics manufacturing; it is a non-contact precision machining method based on the chemical reaction between a reactive neutral radical generated by the plasma and substrate surface atoms for atom-scale material removal. The APPJ involves a complicated process; therefore, the controllability of the technical process was investigated to describe the accuracy of machining efficiency that is the uniformity and repeatability for machining systems, the linearity relation between the removal rates and dwell time. Moreover, the experimental result of the fused quartz removal function variation trend with different processing parameters was discussed. The results of experimentation indicate that the APPJ method has good repeatability within a short dwell time, the removal depth increases with the dwell time and a linearity relation seems appropriate, and the radio frequency (RF) power and the flux of assistant gas oxygen have a great influence on removal efficiency. However, the removal rate remains stable under small perturbation of flux of plasma gas He and reactive gas SF₆. And the surface roughness is improved from Ra 9.3nm to Ra 3.7nm.

Abstract: Aspherical supermirrors are some of the most useful neutron-focusing optics. We aim to develop multiple aspherical supermirror devices using high-precision figured aspherical focusing supermirrors to focus neutron beams with high intensities, because multiple mirrors collect a very large beam divergence. Thin mirrors with millimetre thickness are required to minimize the absorption loss of incident neutron beams since the thickness of a mirror shadows the reflective area of other mirrors. However, it is difficult to fabricate thin mirror substrates with a form accuracy at the sub-micrometre level by conventional machining. Conventional machining deforms a substrate by machining force and spring back after machining causes figure error. Furthermore the deposition of supermirrors deforms the mirror substrate by film stress. Thus, we developed a new process of fabricating a precise millimetre-thick elliptical supermirror. This process consists of non-contact figuring by the numerically controlled local wet etching technique, the minimization of surface roughness without degrading form accuracy by low-pressure polishing with a polishing pressure less than about 7 kPa (1psi), and the ion beam sputter deposition of NiC/Ti multilayers on both sides of the mirror substrate to compensate for film stress. In this paper, we report on the fabrication results of aplano-elliptical mirror substrate with a thickness of 1 mm.

Abstract: This study investigated phenomena of ultrasonic cutting in the case of high-speed conditions. Ultrasonically assisted cutting techniques were developed by Kumabe in the 1950s. He found a critical cutting speed that limits cutting speed to obtain ultrasonically assisted effects and is calculated by frequency and amplitude of oscillation. In general, ultrasonically assisted cutting is not suitable for high-speed cutting conditions because the effects of ultrasonic application are cancelled due to tool contacts with the workpiece during the cutting operation. Present ultrasonically assisted cutting cannot allow increased cutting speed because cutting speed is limited by a critical cutting speed that is less than that compared with general cutting speed. And ultrasonically assisted cutting cannot improve productivity due to long processing time. We conducted high-speed ultrasonic cutting, and the maximum cutting speed in this research was 300 m/min which is higher than general critical cutting speed. The workpiece material was A5056 and cemented carbide tool inserts were employed in this research. Without ultrasonic oscillation, machined surface retained some built up edge and surface roughness is 28 μmRz. In the case of ultrasonic cutting, surface hasnt built up edge and periodically marks due to ultrasonic oscillation remained on the surface. The roughness of conventionally cut surface is better than in ultrasonic cutting. The cutting phenomena of ultrasonic cutting are different compared with those under conventional cutting conditions.

Abstract: In this paper, a novel sensing cutting tool for precision turning is presented, which has a self-sensing function to monitor the cutting force in real-time cutting conditions. The basic idea is the integration of the sensors using piezoelectric film onto the rake face of the tool to measure the main cutting force. Piezoelectric film generates electrical signals according to the piezoelectric effect when it is subjected to small movements, due to the deflection and vibration of the tool during machining operations. The output electrical signal of the piezoelectric film is amplified and capable of transmitting cutting force signals to the measuring system. In particular, the results of a calibration experiment using a dynamometer illustrate the performance of the sensing cutting tool and the relationship between cutting force and electrical signals, which can be used reliably to monitor the cutting force. The paper concludes with further discussions on the potential and application of the smart cutting tool for real-time condition monitoring and adaptive machining purposes.

Abstract: To maximize cutting performance of elliptical vibration cutting (EVC) (also known as two-dimensional vibration assisted cutting), the elliptical trajectory of a cutting tool needs to be corrected. In this study, the effect of the shape of the elliptical trajectory on the machining characteristics of EVC is investigated. Various elliptical trajectories were created by modulating the relative phase and magnitude of the sinusoidal input voltages to the piezoelectric actuators and the effect of tilt angle of the elliptical trajectory on the machining quality such as the cutting resistance and machining quality is experimentally observed in successive micro-V grooving as the tilt angle is changed between 0^o, 30^o, -30^o, and 90^o. It is found that the tilt angle significantly affects both the cutting resistance and machining quality.

Abstract: As advancing technologies increase the demand for yield and planarity in integrated circuits, wafers have become larger and their specifications more stringent. Flatness, thickness variation and nanotopography have emerged as important concerns in the wafering process. Double side polishing has been adopted as a solution to these problems. This paper focuses on the material removal characteristics and wafer profile variation during Si double side polishing. A polishing experiment to investigate Si removal characteristics according to process parameters was carried out in a single head rotary polisher equipped with a monitoring system for friction force. It was found that the material removal rate is related to friction energy rate, and the polishing state was transited and divided into three conditions according to pressure. On the basis of the experimental results, the wafer profile variation in double side polishing was modelled and simulated according to pressure. The friction energy was calculated to find the material removal amount across the wafer. With the conversion of calculated friction energy to the material removal amount, wafer profile variation was simulated. As a result, the wafer profile variation and its range were increased with a pressure increase, and originated from the position near the wafer edge.

Abstract: Ultrasonic-magnetorheological combined finishing (UMCF) is a new technique for the ultra precision machining of aspheric surfaces, especially for high quality work pieces with small curvature radius concave surfaces. The goal with UMCF is to minimize surface figure errors by optimizing the dwell time and tool path, and the current approach typically results in low amplitude form errors. However, discrepancies exist between the predicted and observed form errors. The major sources of such errors are machine axes positioning errors and unpredicted variations of the removal function. Errors that can produce discrepancies between actual and predicted removal profiles were modelled. A diagnostic method was developed to determine the residual error induced by two types of error. Their effects were examined with numerical simulations and the simulation result was presented. Finally, UMCF experiments are performed on a variety of optical surfaces. The final residual error after polishing is less than 2.6 nm PV values. The successful figuring results prove the validity and advantages of UMCF.

Abstract: We developed a real-time nanomanipulation system based on high-speed atomic force microscopy (HS-AFM). During manipulation, the operation of the manipulation is momentarily interrupted for a very short time for high-speed imaging; thus, the topographical image of the fabricated surface is periodically updated during the manipulation. By using a high-speed imaging technique, the interrupting time could be much reduced during the manipulation; as a result, the operator almost does not notice the blink time of the interruption for imaging during the manipulation. As for the high-speed imaging technique, we employed a contact-mode HS-AFM to obtain topographic information through the instantaneous deflection of the cantilever during high-speed scanning. By using a share motion PZT scanner, the surface could be imaged with a frame rate of several fps. Furthermore, the high-speed AFM was coupled with a haptic device for human interfacing. By using the system, the operator can move the AFM probe into any position on the surface and feel the response from the surface during manipulation. As a demonstration of the system, nanofabrication under real-time monitoring was performed. This system would be very useful for real-time nanomanipulation and fabrication of sample surfaces.