Key Engineering Materials Vol. 516

Abstract: This research applied a stylus probe without balance and lever arm as in the previous design of a contact-force-controlled Scanning Probe Microscope (SPM) system. The controller integrated both Ziegler-Nichols-based and intelligent fuzzy methods; thus the systems relative stability can be reserved under the nominal conditions. In addition, one can see that both hysteresis and parameter variation effects of the force actuator can be reduced. Comparing the results with the traditional Ziegler-Nichols-based controller by simulation, one can see that the proposed systems are much more robust.

Abstract: This paper aims to develop a cost-effective diamond turning process to obtain nanosmooth CaF₂ optics. Diamond tool wear was also carried out through a number of cutting trials. Three CaF₂ specimens (diameter of 50 mm and thickness of 5 mm, crystal orientation of (111)) were diamond turned on an ultra precision lathe (Moore Nanotech 350UPL) by a number of facing cuts. In the cutting trials feed rate varied from 1 μm/rev to 10 μm/rev. White spirit mist was used as the coolant. Cutting forces were measured by a dynamometer (Kistler BA9256). Surface roughness of the CaF₂ optics and tool flank wear were measured by a white light interferometer (Zygo Newview 5000) and a scanning electron microscope (FEI Quanta 3D FEG), respectively. It was found that using a feed rate of 1 μm/rev surface roughness Ra of 2 nm could be obtained. When the ratio of the normal cutting force to the tangential cutting force was lower than 1 tool wear would initiate. In diamond turning of calcium fluoride abrasive wear was the main tool wear mechanism. Using white spirit mist as thecoolant could avoid generation of thermal type brittle fracture on the machined CaF₂ surfaces.

Abstract: In this work, two kinds of freeform micro optics were successfully fabricated by using focused ion beam machining. A divergence compensation method was applied to optimize the machining process. Both dynamic variation of the sputter yield and the extra ion flux contributed by the beam tail were taken into consideration. Measurement results on the surface topography indicated that 3-fold improvement of the relative divergence was achieved for both optics when compared with conventional focused ion beam milling without any corrections. Furthermore, investigations on the influences of scanning strategies, including raster scan, serpentine scan and contour scan, were carried out. The serpentine scan is recommended for the fabrication of freeform optics by focused ion beam technology owing to the minimal beam travelling distance over the pattern area.

Abstract: In this paper a novel 4 Degree-of-Freedom (DOF) parallel mechanism with the configuration of 4PUS-1RPU is applied for a 5-axis Hybrid Kinematic Machine (HKM), combined with an additional linear motion. The Parallel Kinematic Mechanism (PKM) is composed of four symmetrical driving chains and one central passive sub-chain. Firstly, the mechanism is described, and the mobility is analyzed. Then the inverse kinematics of the 4-DOF PKM and the direct kinematics for the serial central sub-chain are then presented. The dexterity and the workspace analysis for the mechanism are also carried out. Finally, machining experiment research is presented to verify the effect of the prototype. The research provides the basis for the further parametric design with consideration of kinematic and dexterity performance.

Abstract: In the present study, we experimentally investigated the roll stability recovery performance of a vehicle at various tilting angles. The vehicle was ultimately targeted to contain a velocity-field measurement system in underwater conditions, which should confirm stationary buoyancy during measurement. We employed two small gear-rack ax mountings on a weighted mass as the actuating system inside the bluff-body. Speed and movement were feedback controlled by the activating electronic motor system. The feedback algorithm used tilting action signals from an inclinometer sensor installed in the central region of the vessel shell. As a result, the bluff-body vessel effectively recovered self-stabilizing positions against the tilting action.

Abstract: To effectively reduce the friction in machines operating under lubrication, the sliding surfaces should be fully fluid-film lubricated. Under the full fluid-film lubricated conditions, the upper surface is completely supported by the lubrication film formed in the gap between the surfaces, resulting in low friction and no wear. Surface texuturing is a promising way to modify the tribological properties of sliding surfaces, and a technique for fabricating surface textures with a nanometre-order depth using a femtosecond laser can be used to easily and quickly produce periodic grooves in metal surfaces. It can thus be applied to industrial sliding surfaces to improve their tribological properties. The purpose of the study is to verify the effect of surface nanotextures fabricated using a femtosecond laser to reduce friction under lubrication. As a result, the two disks continued to operate under full fluid-film lubricated conditions even when the bearing clearance became quite small, less than 200 nm. Our testing showed that grooves with a nanometre-order depth can support a higher load than ones with a micrometre-order depth, and we proved that nanotexture can expand the full-lubricated condition.

Abstract: Diamond turning of steel parts is conventionally not possible due to the high tool wear. However this process would enable several different applications with high economical innovative potential. One technology that enables the direct manufacturing of steel components with monocrystalline diamond is the ultrasonic assisted diamond turning process. This technology has been investigated over the years within the Fraunhofer IPT and is now commercialized by its spin-off company son-x. Surface roughness in the range of Ra < 5 nm can be achieved and the diamond tool wear is reduced by a factor of 100 or higher. In order to prove the industrial suitability of the process, two aspherical shapes and one large spherical geometry have been manufactured. The possible form accuracies and surface roughness values will be described in this paper, as well as the tool wear. The goal was to achieve optical surface roughness and a shape accuracy below 300 nm.

Abstract: A novel combined metal-fused silica resonator for the cylinder vibrating gyroscope is proposed in this paper. The cylinder wall of the resonator is made of fused silica, while the bottom is made of metal, and then the two parts are connected by strong glue. With this method, the manufacturing difficulty of the fused silica resonator can be reduced significantly and the performance can be retained without remarkable degeneration. In this paper, the novel metal-fused silica resonator is analyzed, including the structural optimization design and fabrication, testing of the stability of the resonance frequency and the Q factor. The preliminary experimental results show that the low-cost combined metal-fused silica resonator has potential good performance to achieve high accuracy in a cylinder shell vibrating gyroscope.

Abstract: A simple and novel self-assembly based process is presented in this paper for the fabrication of gold triangular nanocavity arrays. This process combines nanosphere lithography (NSL) with some standard MEMS technologies. A carboxylated polystyrene (PS) nanosphere bilayer with a relatively large area is fabricated on silicon wafer as the starting template by spin-coating. Oxygen plasma etching, metal deposition and lifting-off of the PS upper layer are then orderly carried out for the formation of triangular space, which is made up of Cr film and the remaining PS nanoparticles. Then silicon etching is used to transfer the triangle pattern onto the silicon wafer. Finally, a 50 nm thick gold layer is deposited on the pattern to fabricate gold triangular nanocavity arrays. With this strategy, both the period and the cavity size can be adjusted independently. This will allow the tuning of the optical properties for desired application.

Abstract: We have developed a novel planarization method called catalyst-referred etching (CARE), which can planarize SiC substrates without the use of an abrasive. In this method, platinum is used as an oxidation catalyst. The surface of CARE-processed 4H-SiC (0001) substrates are atomically flat all over the wafer. It is found that the surface of CARE-processed substrates is composed of alternating wide and narrow terraces with single bilayer-height steps, regardless of the off-cut angle. This unique structure is induced by the differences in the chemical stabilities of the terraces.