An induction heating-assisted injection molding (IHAIM) process developed by the authors is used to replicate surfaces containing random nano-patterns. The injection molding setup is developed so that an induction heating system rapidly heats the cavity wall at rates of up to 10°C/s. In order to enable the optimization of the IHAIM process for nano-pattern replication, it is necessary to develop robust methods for quantitative characterization of the replicated nano-patterns. For this purpose, three different approaches for quantitative characterization of random nano-patterns are applied and compared. Results show that the use of IHAIM is an efficient way to improve replication quality. All three measurement methods are capable of detecting the trend of the replication quality of the surface changing the process condition.
This paper discusses tool-wear processes in the milling of carbon fiber-reinforced plastic (CFRP) laminates. Plane down-milling tests with unidirectional and cross-directional CFRP laminates were performed using two types of cutting tools made of tungsten carbide and polycrystalline diamond. Measurements of the changes in the cutting forces and tool-wear widths over the cutting distance revealed that the fiber orientation direction in the CFRP laminates relative to the tool-traveling direction is an important parameter to determine the tool-wear processes. Additionally, based on obtained experimental results, a wear parameter to characterize cutting tool wear is introduced. This parameter can accurately explain the relationship between the worn tool-edge profiles and the processed-surface quality.
This paper deals with the wear behavior of the mini-size diamond wheel used in Ultrasonic Assisted Grinding (UAG). The aim is to understand the wheel wear behavior. Sequential changes of the surface topography of the mini-size wheel, such as the number and shape of grains of the cutting edge, during the on-surface UAG process were observed and evaluated quantitatively using a Scanning Electron Microscope with four electron probes (3D-SEM). The obtained results show that a good wheel surface is maintained during the UAG process compared with the Conventional Grinding (CG) process. In particular, a number of sharp grain cutting edges are larger in the UAG process than those of the CG process. Additionally, these results are closely related to the stability of grinding forces and the reduction of the finished workpiece surface.
Because a large number of accidents with electric wheelchairs are due to operational errors, steering assistance systems for wheelchairs have been studied in a variety of ways. One of the basic systems is 3-D obstacle detection around the wheelchair. One method uses a stereo camera for detecting obstacles by image processing. However, this method is less reliable under varying light conditions. A laser range sensor is another useful device for obstacle detection. However, it requires a complex swinging mechanism for 3-D positioning which makes the measuring time too long. Therefore, this paper presents a 3-D obstacle detection system for electric wheelchairs using a 2-D laser range sensor. We set up only one 2-D laser range sensor over the wheelchair, and attached mirrors around it to reflect the laser light obliquely downwards. Then, we gathered obstacle points while the electric wheelchair was moving and made a 3-D obstacle map to assist steering. We built a prototype device and confirmed by experimentation that it is able to detect obstacles in 3-D.
We aim to realize a large-scale straightness evaluation using a gyro. It detects tangential angles to evaluate a profile without any references. However, fluctuations of angular signal, called gyro drift, are considered a major contributor of error. We adopted a reversal measurement for eliminating the drift. The reversal measurement has been widely used for eliminating stable error from ancient. Here, we periodically performed reversal measurements for eliminating drift of a commercially available fiber optic gyro (FOG) unit. As a result, an angle could be derived with a standard deviation of 0.4 mrad for 1 hour of repeated measurements with an interval of 60 s, even though the gyro has a drift of several mrad/h including the effects of the Earth’s rotation. This indicates that the reversal measurement is effective in reducing the drift.
The R-test measures the three-dimensional displacement of a precision sphere, attached to a machine spindle, by using three displacement sensors fixed to the machine’s table. Its application to error calibration for five-axis machine tools has long been studied. This paper presents software for analyzing the measured R-test trajectories for error diagnosis and numerical compensation for rotary axis location errors and error motions. The developed software first graphically presents the measured R-test trajectories to help a user intuitively understand error motions of the rotary axes. It also numerically parameterizes the rotary axis geometric error parameters, and then generates a compensation table that can be implemented in some latest-generation commercial CNC systems. An actual demonstration of its application to a five-axis machine tool with a universal head (two rotary axes on the spindle side) is presented.
Improving water repellency of a metal surface is required in a wide range of industrial applications. In this study, the water repellency control of an oxygen-free copper surface was attempted by generating micro V grooves on the surface by using ultraprecision cutting technology. The results showed that the maximum contact angle of a water drop on a micro V-grooved surface could be as high as approximately twice that of a flat surface. The contact angle depended strongly on the direction, depth, pitch of the grooves, and burr formation at the edges of the micro grooves. A method for controlling burr formation was proposed.
In recent years, 5-axis machine and multi-tasking machine have seen wide spread use. These tools can contribute to the enhancement of machining efficiency and precision. Conversely, their complex motion can cause numerous collision accidents between machines, tools, materials, and other parts. To prevent such accidents, it is now common to verify numerical control (NC) data using a machine motion simulator before performing the actual machining. However, the actual machining process is not always conducted in the expected manner. In some cases, the machining process is manually defined or altered, possibly causing a collision accident. In the present study, an online real-time collision free system was developed for the prevention of unexpected collisions. The effects of using this system are described in this article.
This present study describes a novel micro-fabrication technique using transfer-print of thin-film for micro-mechanical structure. Some thin-films of Au have been transferred from a stamp onto pre-structured micro-ridges of polymer substrate. These thin-films successfully form into an array of fixed micro-beams as a mechanical structure. The fabricated micro-beams typically have a thickness of less than 100 nm and a tens micro-meter long. This present paper also reports an investigation about effects of stamp surface properties. A modification of stamp surface wettability and roughness improves adhesive force (releasability) of thin-film to provide flat micro-beam without undesired deformations. Hydrophobic stamp with micro-roughness results in an increase of production yield of micro-beams to reach more than 90%. Simple mechanical test shows that the fabricated micro-beam is transversely tensioned by the supporting micro-ridges of substrate. It is clarified that the proposed process can be applied to fabricate micro/nano-mechanical elements.
The purpose of this study is to estimate ablated crater depth with sufficient numerical accuracy when multi-shot channels of ultra-short pulsed laser are executed for micro drilling processes on thin glass plates. In this analytical model, the plasma model, in which the free electron density and the complex dielectric function of the Lorentz model are evaluated, is applied to estimate the ablated regions and the regions damaged by laser ablation when glass is considered to be a dielectric material. The absorption coefficient and the threshold fluence are important parameters in the evaluation of the ablated crater depth and ablation rate. The parameters obtained in this numerical analysis are in agreement with the experimental results and are computed quantitatively to several laser irradiation conditions. The experimental results and analysis results are examined for multi-shot channels. In an experiment involving laser ablation using multi-shot laser beams, ablation rates for the initial shot are lower than subsequent ablation rates. The effectiveness of the modified absorption coefficient and modified threshold fluence for initial shots is confirmed for the reduction of ablation rate.
Due to rising energy requirements, the use of low-weight materials is becoming more important, especially in aerospace and automotive engineering. Because of their high strength-to-weight ratio, carbon fiber reinforced plastics (CFRP) are increasingly replacing metals. These materials are usually machined by milling operations. Their main problems are high tool wear, thermal damage, and surface integrity. This paper presents a machine concept and control strategy to substitute milling with laser cutting. Because a high, constant-trajectory velocity is required during laser cutting operations, a highly dynamic machine tool is needed. Conventional machine tools requiring large workspaces are inertial and therefore unsuitable for this task. Thus, a portal machine concept was investigated with an additional laser scanner and lightweight moving components. To increase path accuracy, two control strategies were implemented and analyzed in a multi-body simulation. One approach is to use a frequency-separating filter, while the second is based on estimation of tool center point positioning error using a Kalman filter. An acceleration sensor located near the tool center point (TCP) or the drive current signal can be used as input for the Kalman filter. Both input signals are investigated and compared in this paper. Results presented in this paper show that with these control strategies, highly dynamic trajectories can be realized with high precision.
A stereo camera system with digital image correlation (DIC) was developed for accurate measurement of the position and orientation of a precision positioning stage. Stereo correspondence was carefully calculated by sub-image matching based on the DIC method. Camera parameters for the triangulation were determined from the measurement results of x, y, and z translation of an accurate positioning stage. The measured root mean square random errors were 0.6 μm in the in-plane direction and 1.7 μm in the out-of-plane direction. The proportional errors in the in-plane and out-of-plane directions were 0.2 μm/10 mm and 0.5 μm/10 mm, respectively.