• International Journal of CAD/CAM
• /
• 제6권1호
• /
• pp.139-148
• /
• 2006

Catmull-Clark subdivision scheme provides a powerful method for building smooth and complex surfaces. But the number of faces in the uniformly refined meshes increases exponentially with respect to subdivision depth. Adaptive tessellation reduces the number of faces needed to yield a smooth approximation to the limit surface and, consequently, makes the rendering process more efficient. In this paper, we present a new adaptive tessellation method for general Catmull-Clark subdivision surfaces. Different from previous control mesh refinement based approaches, which generate approximate meshes that usually do not interpolate the limit surface, the new method is based on direct evaluation of the limit surface to generate an inscribed polyhedron of the limit surface. With explicit evaluation of general Catmull-Clark subdivision surfaces becoming available, the new adaptive tessellation method can precisely measure error for every point of the limit surface. Hence, it has complete control of the accuracy of the tessellation result. Cracks are avoided by using a recursive color marking process to ensure that adjacent patches or subpatches use the same limit surface points in the construction of the shared boundary. The new method performs limit surface evaluation only at points that are needed for the final rendering process. Therefore it is very fast and memory efficient. The new method is presented for the general Catmull-Clark subdivision scheme. But it can be used for any subdivision scheme that has an explicit evaluation method for its limit surface.

• International Journal of CAD/CAM
• /
• 제7권1호
• /
• pp.21-30
• /
• 2007

The inverse offset method (IOM) is widely used for generating cutter paths from the point-based surface where the surface is characterised by a set of surface points rather than parametric polynomial surface equations. In the IOM, cutter path planning is carried out by specifying the grid sizes, called the step-forward and step-interval distances respectively in the forward and transverse cutting directions. The step-forward distance causes the chordal deviation and the step-forward distance produces the cusp. The chordal deviation and cusp are also functions of local surface slopes and curvatures. As the slopes and curvatures vary over the surface, different step-forward and step-interval distances are appropriate in different areas for obtaining the machined surface accurately and efficiently. In this paper, the chordal deviation and cusp height are calculated in consideration with the surface slopes and curvatures, and their combined effect is used to estimate the machined surface error. An adaptive grid generation algorithm is proposed, which enables the IOM to generate cutter paths adaptively using different step-forward and step-interval distances in different regions rather than constant step-forward and step-interval distances for entire surface.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 1998년도 Proceedings of International Symposium on Remote Sensing
• /
• pp.268-273
• /
• 1998

This study applies an on-line system, which employes an adaptive reconstruction technique to monitor and forecast ocean surface changes. The system adaptively generates an appropriate synthetic time series with recovering missing measurements for sequential images. The reconstruction method incorporates temporal variation according to physical properties of targets and anisotropic spatial optical properties into image processing techniques. This adaptive approach allows successive refinement of the structure of objects that are barely detectable in the observed series. The system sequentially collects the estimated results from the adaptive reconstruction and then statistically analyzes them to monitor and forecast the change in surface characteristics.

• 한국정밀공학회지
• /
• 제17권1호
• /
• pp.185-191
• /
• 2000

Direct ＆ adaptive slicing of sculptured surfaces in RP improves, quality ＆ accuracy of the final product, compared to the slicing with uniform layer thickness or the slicing of facets (ie, STL). Present D＆A slicing procedures adaptively compute the next layer thickness based on the surface information of current sliced contour, which assumes constant normal curvature values. In some cases, however. such assumption leads to intolerable slicing result which cannot correctly consider the entire local feature shape. We propose improved adaptive slicing algorithms which can determine near-optimal layer thickness, including illustrated examples.

• Journal of Electrical Engineering and Technology
• /
• 제3권2호
• /
• pp.207-212
• /
• 2008

This paper presents a robust and computationally efficient optimal design algorithm for electromagnetic devices by combining an adaptive response surface approximation of the objective function and($1+{\lambda}$) evolution strategy. In the adaptive response surface approximation, the design space is successively reduced with the iteration, and Pareto-optimal sampling points are generated by using Latin hypercube design with the Max Distance and Min Distance criteria. The proposed algorithm is applied to an analytic example and TEAM problem 22, and its robustness and computational efficiency are investigated.

• 제어로봇시스템학회논문지
• /
• 제8권9호
• /
• pp.719-727
• /
• 2002

We proposed a decoupled adaptive fuzzy sliding-mode control scheme for a class of fourth-order nonlinear systems. The system is decoupled into two second-order systems such that each subsystem has a separate control target expressed in terms of sliding surface. For these sliding surfaces, we define main and sub target conditions. and, we made intermediate variables which are interconnected both surface conditions from the sub target sliding surface. Then, Two sets of fuzzy rule bases are utilized to represent the equivalent control input with unknown system functions of the main target sliding surface including intermediate variables. The membership functions of the THEN-part, which is used to construct a suitable equivalent control of sliding-mode control, are changed according to the adaptive law. With such a design scheme, we not only maintain the distribution of membership functions over state space but also reduce the computing time considerably. We apply the decoupled adaptive sliding-mode control to a nonlinear Cart-Pole system and confirms the validity of the proposed approach.

• 대한기계학회논문집B
• /
• 제29권5호
• /
• pp.568-576
• /
• 2005

A 3-D finite element model combined with a volume tracking method is presented in this work to simulate the mold filling for casting processes. Especially, the analysis involves an adaptive grid method that is created under a criterion of element categorization of filling states and locations in the total region at each time step. By using an adaptive grid wherein the elements, finer than those in internal and external regions, are distributed at the surface region through refinement and coarsening procedures, a more efficient analysis of transient fluid flow with free surface is achieved. Adaptive grid based on VOF method is developed in tetrahedral element system. Through a 3-D analysis of the benchmark test of the casting process, the efficiency of the proposed adaptive grid method is verified. Developed FE code is applied to a typical industrial part of the casting process such as aluminum road wheel.

• Journal of Electrical Engineering and Technology
• /
• 제13권3호
• /
• pp.1304-1316
• /
• 2018

An adaptive sliding-mode observer for speed estimation in sensorless vector controlled induction machine drives is proposed in this paper to balance the dilemma between the requirement of fast reaching transient and the chattering phenomenon reduction on the sliding-mode surface. It is well known that the sliding-mode observer (SMO) suffers from the chattering phenomenon. However, the reduction of the chattering phenomenon will lead to a slow transient process. In order to balance this dilemma, an adaptive exponential reaching law is introduced into SMO by optimizing the reaching way to the sliding-mode surface. The adaptive exponential reaching law is based on the options of an exponential term that adapts to the variations of the sliding-mode surface and system states. Moreover, the proposed sliding-mode observer considering adaptive exponential reaching law, which is called adaptive sliding-mode observer (ASMO), is capable for reducing the chattering phenomenon and decreasing the reaching time simultaneously. The stability analysis for ASMO is achieved based on Lyapunov stability theory. Simulation and experimental results both demonstrate the correctness and the effectiveness of the proposed method.

• 전기학회논문지
• /
• 제60권11호
• /
• pp.2139-2146
• /
• 2011

In this paper, a robust adaptive controller is proposed for trajectory tracking of robot manipulators with the unknown friction coefficient and bounded disturbance. A new adaptive control law is developed based on sliding mode and derived from the Lyapunov stability analysis. The introduction of a boundary layer solves the problem of chattering. The proposed adaptive controller is globally asymptotically stable and guarantees zero steady state error for joint positions. The estimated friction coefficients can also approach the actual coefficients asymptotically. A simulation example is provided to demonstrate the performance of the proposed algorithm.

• 대한기계학회논문집B
• /
• 제28권11호
• /
• pp.1348-1358
• /
• 2004

The filling pattern and an adaptive grid refinement based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible transient viscous flow with free surfaces. The governing equation fur flow analysis is Navier-Stokes equation including inertia and gravity effects. The mixed FE formulation and predictor-corrector method are used effectively for unsteady numerical simulation. The flow front surface and the volume inflow rate are calculated using the filling pattern technique to select an adequate pattern among seven filling patterns at each tetrahedral control volume. By adaptive grid refinement, the new flow field that renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. The collapse of a water dam and the filling of a fluidity spiral have been analyzed. The numerical results have been in good agreement with the experimental results and the efficiency of the adaptive grid refinement and filling pattern techniques have been verified.