Jiing-Yih Lai

Sweep-surface reconstruction from three-dimensional measured data

The purpose of this work was to present a surface fitting algorithm for sweep surface reconstruction from three-dimensional measured data. The sweeping rule considered in this work was essentially translational sweeping in which the generators traverse about the directors to form the desired sweep surface. The sweep-surface fitting was formulated as a nonlinear least-squares minimization problem for which an error expression was minimized which yields the optimized generators, the directors and the parameter values corresponding to each measured data. An algorithm was presented also to convert the sweep surface model into a composite spline surface which could be imported into most CAD/CAM systems. Effective experimental results were provided to illustrate the feasibility of the proposed strategy.

Reconstruction of surfaces of revolution from measured points

Abstract The objective of this work was to propose a surface fitting algorithm for the reconstruction of surfaces of revolution from three-dimensional measured points. A surface of revolution can be described by a two-dimensional cross-section curve rotating about an axis. An iterative optimization process was proposed to minimize the root-mean-squares error between each of the measured data and the fitted surface, which yields the optimized rotating axis and the best-fit cross-section curve. This surface fitting algorithm was combined with a B-spline surface fitting algorithm and a surface blending algorithm for the modeling of complex rotational parts. Several examples were presented to demonstrate the feasibility of the proposed strategy.

VIRTUAL 3D PLANNING OF PELVIC FRACTURE REDUCTION AND IMPLANT PLACEMENT

In pelvic surgery, CT images are commonly used for diagnosis and surgical planning. The images are often displayed and manipulated in a 2D environment, which is insufficient owing to the complex geometry of a pelvic structure. Moreover, a pre-bend of the reconstruction plates is necessary, but difficult to complete, because of the lack of appropriate templates. In this study, an integrated preoperative planning system is developed to provide 3D models and physical templates so that the surgeon can simulate and observe his planning and prepare better-fitted curved plates before surgery. The proposed method can be divided into the following four stages: 3D display, bone segmentation, bone reduction, and implant placement. As for the designed curved plates, they can be fabricated as templates by means of rapid prototyping technology. Several examples, including artificial bones, real CT images and real pelvic surgery, have been presented to demonstrate the feasibility of the proposed method.

A nurbs curve interpolator with jerk‐limited trajectory planning

Abstract The control of the maximum acceleration and jerk in the trajectory planning of the CNC controller is very important because it affects the smoothness of the machined surface substantially. We proposed a parametric interpolator composed of a look‐ahead stage and a real‐time sampling stage for jerk‐limited acceleration planning. A pre‐sampling process was implemented in the look‐ahead stage to identify the segment points, where the acceleration changed across zero. A check of the acceleration and jerk was implemented and the feedrate was modified accordingly. In addition, a backtracking process was carried out during the deceleration stage to ensure that the modified feedrate was satisfied. In the real‐time sampling stage, an acceleration profile based on constant jerk was implemented for each region between two segment points. With this algorithm, we ensured that both the chord error and the maximum acceleration and jerk were within the allowable limits. Also, it kept the similarity of the speed profiles for adjacent cutting paths in zigzag machining.

Development of a Virtual Simulation System for Crane-Operating Training

The purpose of this work is to develop a virtual simulation system for crane-operating training. It includes an operating chamber to simulate the driving chamber of a truck crane and a motion chair to offer additional vibrating effect. The virtual scenes, generated by a VR software, is displayed on a screen in front of the operating chamber through a 3D projector. A data communication structure is proposed to deliver the information among three personal computers. The hardware configuration of the simulator is discussed and the VR techniques used to generate the virtual scenes are addressed. A performance evaluation in terms of the frame rate is provided also.Copyright

Automatic reconstruction of B-spline surfaces with constrained boundaries

The aim of this study is to present an automatic surface reconstruction method that can take practical restrictions on scanned points into consideration and efficiently and reliably output a group of G^1 surfaces. The proposed method is mainly composed of three phases: quadrangle frame generation, point and curve networks planning, and surface patches reconstruction. In the first phase, the original triangle mesh is reduced and converted into a quadrangle mesh, the edges of which serve as the frame of the surfaces. In the second phase, the boundary data of the surfaces are prepared. These include a network of serial points, frame curves and surface normals which are also expressed as curves. In the final phase, surface initialization, harmonization mapping and surface warping are presented to yield the desired surfaces. The main advantage of the proposed method is that it can relax the pre-processing of a scanned triangle mesh, and hence, increase the efficiency and quality of the surface reconstruction. Several examples of various types of air bags are presented to demonstrate the feasibility of the proposed method.

Three-dimensional CAD model reconstruction from image data of computer tomography

Three‐dimensional (3D) shape reconstruction from 2D image data has been receiving extensive attention in medical engineering. It can enhance accurate diagnosis of the disease from medical images of computer tomography (CT) and magnetic resonance imaging (MRI). An algorithm based on reverse engineering technique was proposed in this work for 3D surface reconstruction of CT images. Several image processing techniques were applied first to detect the 2D contour of the object for each of the CT images. A surface lofting approach was then employed to fit the 2D contours into a 3D surface model. A brain example was presented to demonstrate the feasibility of the proposed method.

A sweep-surface fitting algorithm for reverse engineering

The issue of surface reconstruction from three-dimensional measured data has been receiving extensive attention recently. In order to reflect the original shape design of an existing part geometry, it needs different surface-fitting algorithms to reconstruct appropriate surface models. The objective of this work is to establish a sweep-surface fitting strategy for three-dimensional measured data. The sweep surface was formed by traversing cross-section curves along a profile curve. A nonlinear parameter optimization process was employed to evaluate the unknown parameters of the sweep-surface model. The feasibility of the proposed method has been verified by computer simulation and experimental results. A comparison study with proposed methods, a B-spline surface fitting and a lofted surface fitting, was also provided.

Recognition of virtual loops on 3D CAD models based on the B-rep model

Loops are critical elements in boundary representation (B-rep) models because they link all edges corresponding to a face. Loops can be used in feature recognition for identifying depressions or protrusions. In real 3D CAD models, however, features typically lie across multiple faces, which is beyond the data structure of current B-rep models. This study presents a virtual loop concept to account for all loop types used in CAD models, and develops algorithms for recognizing them. In accordance with the complexity of the recognition algorithm, this study defines three types of loop: single, virtual, and multivirtual. A single loop is the current loop recorded in the B-rep model. A virtual loop lies across faces that are at least G1 continuous. Finally, a multivirtual loop lies across faces that are either G0 or G1 continuous. The proposed loop structure provides a more complete data structure for recognizing various types of features in feature-recognition modules. Several realistic CAD models are presented to confirm the feasibility of the proposed loop-recognition and feature-recognition methods.

Recognition of depression and protrusion features on B-rep models based on virtual loops

ABSTRACTLoops are vital elements in B-rep models and are used to describe the boundary contours of faces. A loop is only defined on a single face, which does not reflect real situations in which features mostly lie across multiple faces. The objective of this study is to detect virtual loops across multiple faces and subsequently use them for recognizing depression and protrusion features in computer-aided design models. Three loop types are defined: single, virtual, and multivirtual loops; virtual and multivirtual loops lie across multiple faces with different boundary conditions across faces. The data of the detected loops are then used to develop a feature recognition algorithm for identifying various depression and protrusion types, ranging from simple circular holes on a face to complex irregular pockets on multiple faces with fillets. This paper provides a detailed description of the proposed algorithm and presents several examples to illustrate its feasibility.