Yizhong Wang

Data reduction in integrated reverse engineering and rapid prototyping

In reverse engineering, a digitizer usually generates a large cloud of 3D points data, many of which are not necessary for subsequent applications. When a digitized part is to be manufactured by means of rapid prototyping machines, e.g. stereolithography apparatus (SLA) and selective laser sintering equipment (SLS), etc. there is no need to construct the CAD model of the digitized part. This will be described by the proposed novel method which can construct an STL file (the de facto file format for rapid prototyping machines) directly from digitized part data. In order to reduce storage space and increase computational efficiency for subsequent processes, e.g. slicing, data reduction is achieved based on two criteria: One is the desired percentage data reduction; the other is the maximum bounded error.

Study on Welder Training by Means of Haptic Guidance and Virtual Reality for Arc Welding

Gaining and improving welding skill is important for welders. The advent of virtual reality (VR) technology provides a new kind of medium for skill training. In this paper, a haptic arc welding training method is proposed based on VR and haptic guidance. The training method is designed to emulate the presence of a human tutor which feedbacks forces to a welder to show the proper force/position relation within pre-defined trajectories for attaining hand-mind-eye coordination skills in a virtual environment. Three basic welding operation skills, namely maintaining the proper arc length, maintaining the proper electrode angle, and maintaining the proper traverse speed are selected for training. The Phantom haptic device is used as the haptic interface. The haptic guidance is realized with proportional-plus-derivative (PD) feedback control of the error between the current and ideal trajectory. The proposed method is cost-less, effective, and environment-friend for the training of both novice and skilled welders.

An investigation of parting direction based on dexel model and fuzzy decision making

This paper presents a method for automatic mould parting direction selection in computer-aided design of moulds and dies. When given a three-dimensional CAD model, the minimum volume bounding box of the model is found first. Three pairs of possible parting directions are defined based on the bounding box surface normal vectors. They are in the length direction, the width direction and the height direction of the bounding box. Now, a dexel model is constructed along each parting direction. Parting lines corresponding to the three possible parting directions are estimated using a slice method. Finally, criteria such as undercut, draw, projected area and flatness in all parting directions are quantified using the dexel model of the part. A designers preferences, coded as fuzzy weighting factors, are set-up for the evaluation of the most promising parting direction. Uncertainty that is assumed to be inherent in the assessments of the ratings and weights is accounted for by the proposed fuzzy heuristic.

A web-based fuzzy mass customization system

Mass customization attempts to give customers the product they want, when and where they want it, at a cost comparable to that of mass-produced goods. With the increasing popularity of the Internet and broadband, it is now possible to let mass household consumers be involved in the design of a product that reflects their preferences or personalities. As such an application is targeted at the general public, a descriptive or linguistic input style is preferred. The concept of fuzzy customization is therefore proposed and investigated. A prototype system is implemented on a web client/server architecture, namely CyberFGC, which consists of a fuzzy geometric customization (FGC) program, Virtual Reality Modeling Language (VRML), and common gateway interface (CGI) programs. In this system, household consumers can customize products using their preferred linguistic description such as big, small, normal, etc., over the World Wide Web. Examples of customization of wine glasses and furniture are described in detail.

Haptic modeling for a virtual coordinate measuring machine

Introducing a haptic device into coordinate measuring machine (CMM) inspection path planning leads to the proposal of a novel CMM off-line inspection path planning environment, a haptic virtual coordinate measuring machine (HVCMM), which makes use of the haptic modeling technique for CMM off-line programming. The HVCMM is an accurate model of a real CMM, which simulates a CMMs operation and its measurement process in a virtual environment with haptic perception. In this paper, a simple and effective mechanics model is implemented for the proposed HVCMM. The HVCMM enables CMM off-line programming to take place exactly as if an operator were in front of a real CMM and moving a real CMM probe. Even more, operators can feel the collision between the CMM and a part. Since there is a force feedback when the probe reaches the surface of the part, besides showing the contact in the HVCMM environment, it is much easier to generate a collision-free probe path than using other off-line inspection planning methods. The HVCMM not only facilitates inspection path planning, but also speeds it up because the operator does not need to slow the probe down when it is approaching an object. Combined visual and force feedback is the best indicator for selecting measurement points.

Study on underwater wet arc welding training with haptic device

Underwater wet arc welding is hard and sometime involves risks to welder divers. To help welder divers gain their underwater wet arc welding skills, a new underwater wet arc welding training method is proposed in this paper based on haptic device. In this method, self-consuming technique is focused on, and fillet welding in different positions is mainly discussed. The haptic device simulates the impacts of seawater acted on an electrode holder, and also guides a trainee to maintain the virtual electrodes proper moving path, proper travel speed, proper compensation speed, proper work angle and the lead angle, and proper arc length. The proposed system is implemented using a Phantom Desktop, and its feasibility is verified. The introduction of a haptic device makes the welder divers training for underwater wet arc welding risk free, convenient and efficient.

Accessibility analysis for CMM inspection planning by means of haptic device and STL representation

Inspection planning plays one of important roles in examining a manufactured part in 3D sizes, positions and forms using coordinate measuring machine (CMM). Accessibility Analysis must be done during CMM inspection planning. Usually, accessibility analysis is based on the computation of a parts computer-aided design (CAD) model and the model of a probe. In this paper, a new accessibility analysis method for CMM inspection planning is proposed based on a haptic device and STL representation. Different collision modes are analyzed. A quick collision detection algorithm is given, which is based on the STL representation. Force response is analyzed to distinguish between an occurred collision and a normal contacting of the tip to an inspection point. Using STL representation, the virtual CMM probe unit model is more precise, which results in the accessibility analysis implemented precisely. With the force feedback generated by a Phantom Desktop haptic device, the accessibility analysis is performed much easier.

Independent Component Automatic Clustering and its application on multi-trails imaginary hand movement related EEG

How to extract task-relevant components from spontaneous electroencephalogram background is an open problem in EEG signal analysis. An Independent Component Automatic Clustering (ICAC) method, which combined Independent Component Analysis (ICA) with automatic clustering, is developed in this paper. In ICAC, the ICA decomposed components were grouped into several clusters and sorted automatically. A majority of task-relevant components could be grouped into one cluster and be recognized easily, which can compensate the traditional ICA limitation of component sorting without any task specialized orders. We adopted this method on multi trails EEG signals during imaginary hand movement, results showed that ICAC can automatically extract task-relevant component and increase the Fisher Criterion (FC) separability significantly. Furthermore, we show that the residual mutual information between task-relevant components is not useless as previously regarded but very useful on components recognition.

Study on virtual coordinate measuring machine based on augmented virtuality

In this paper, a new method for constructing a virtual coordinate measuring machine (VCMM) is proposed based on augmented virtuality. The VCMM consists of two main parts: hardware and software. An operation-simulating mechanism and a binocular-stereo vision system compose the hardware, which are used to the extract operation information of an operator. There are four modules in software, including hand-segmentation, motion-analysis, model-render and augmented-virtual module, which are used to integrate the physical information into the VCMM environment. To verify the proposed VCMM, experiments are conducted and the result shows it feasible and reliable.

Feature recognition of multi-class imaginary movements in brain-computer interface

Feature recognition of multi-class imaginary movements is an important subject of brain-computer interface based on imaginary movement. In this paper, using the method of two-dimensional time-frequency analysis combined with Fisher separability analysis to study multi-channel synchronization, multi-class imaginary movements potential information of typical subjects. Also we have extracted the feature data of event related resynchronization/synchronization that could be used to identify different classes, and then use the support vector machine to establish classifiers, and have completed a higher accuracy rate of classification for multi-motor patterns. The result shows that the identification accuracy could basically satisfy the requirements of BCI systems under the circumstances that the subjects are better trained.