Yau-Zen Chang

Practical and flexible path planning for car-like mobile robot using maximal-curvature cubic spiral

Abstract This paper presents a nonholonomic path planning method, aiming at taking into considerations of curvature constraint, length minimization, and computational demand, for car-like mobile robot based on cubic spirals. The generated path is made up of at most five segments: at most two maximal-curvature cubic spiral segments with zero curvature at both ends in connection with up to three straight line segments. A numerically efficient process is presented to generate a Cartesian shortest path among the family of paths considered for a given pair of start and destination configurations. Our approach is resorted to minimization via linear programming over the sum of length of each path segment of paths synthesized based on minimal locomotion cubic spirals linking start and destination orientations through a selected intermediate orientation. The potential intermediate configurations are not necessarily selected from the symmetric mean circle for non-parallel start and destination orientations. The novelty of the presented path generation method based on cubic spirals is: (i) Practical: the implementation is straightforward so that the generation of feasible paths in an environment free of obstacles is efficient in a few milliseconds; (ii) Flexible: it lends itself to various generalizations: readily applicable to mobile robots capable of forward and backward motion and Dubins’ car (i.e. car with only forward driving capability); well adapted to the incorporation of other constraints like wall-collision avoidance encountered in robot soccer games; straightforward extension to planning a path connecting an ordered sequence of target configurations in simple obstructed environment.

A Hybrid Search Algorithm for Porous Air Bearings Optimization

The study deals with the development of a hybrid search algorithm for efficient optimization of porous air bearings. Both the compressible Reynolds equation and Darcys law are linearized and solved iteratively by a successive-over-relaxation method for modeling parallel-surface porous bearings. Three factors affecting the computational efficiency of the numerical model are highlighted and discussed. The hybrid optimization is performed by adopting genetic algorithm (GA) for initial search and accelerated by simplex method (SM) for refined solution. A simple and useful variable transformation is presented and used to convert the unconstrained SM to a constrained method. In this study, the hybrid search algorithm for a multi-variable design exhibits better efficiency compared with the search efficiency by using the SM. The proposed hybrid method also eliminates the need of several trials with random initial guesses to ensure high probability of global optimization. This study presents a new approach for optimizing the performance of porous air bearings and other tribological components. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002

A Simple Fuzzy Motion Planning Strategy for Autonomous Mobile Robots

This paper presents a fuzzy motion planning strategy that will enable a mobile robot to navigate in unknown indoor environments. The strategy is sensor-based and simple enough to be implemented in most low-cost systems, yet capable to demonstrate behaviours only found in high-end systems, such as wall-following and obstacle-avoidance. The strategy is composed of three modes: the normal mode, the wall-following mode, and the sub-target mode. Switch between these modes is decided by the conditions of whether the target is reached and/or within the direction of allowable steering bounds, and whether the robot is surrounded or in a dead lock situation. Distance information for motion planning is acquired using a Scanning Laser Range Finder (URG-04LX). Simulation results of some benchmark scenarios demonstrate performance of the proposed motion planning strategy.

A comparative study of smooth path planning for a mobile robot by evolutionary multi-objective optimization

This paper studies the evolutionary planning strategies for mobile robots to move smoothly along efficient collision-free paths in known static environments. The cost of each candidate path is composed of the path length and a weighted sum of penetration depth to vertices of polygonal obstacles. The path is composed of a pre-specified number of cubic spiral segments with constrained curvature. Comparison of the path planning performance between two Pareto-optimal schemes, the parallel genetic algorithm scheme based on the island method (PGA) and the non-dominated sorting genetic algorithm (NSGA-II), are conducted in terms of success rate in separate runs and path length whenever collision-free paths are found. Numerical simulation results are presented for three types of obstacles: polygons, walls, and combinations of both.

Biomechanical evaluation of an orthodontic miniimplant used with revolving (translation and rotation) temporary anchorage device by finite element analysis and experimental testing.

Purpose:To evaluate the biomechanical interactions of a miniimplant using a temporary anchorage device (TAD) for orthodontic traction. Materials and Methods:A miniimplant was designed with dual thread (DT) with a TAD that can be connected optionally onto the miniimplant with 60-degree switching unit and an extended arm for tying orthodontic wire. Finite element analysis was used to calculate the relative miniimplant displacement and bone strain under immediate load (500 gW) on behalf of the maximum lateral force during orthodontic treatment. The TAD removal forces were measured by pullout testing. Results:Simulated results showed that the maximum von Mises bone strain concentrated at the cervical regions around the miniimplant. The corresponding strain value in DT miniimplant assembled with TAD was greater than those for DT and single-thread implants with 2.24 and 1.73 times, respectively. Small relative miniimplant displacement (<20 &mgr;m) was found in all cases. The TAD removal force remained larger than 2 times the finger-pulling force (9.3 N) after 5 repeated removal tests. Conclusion:The DT miniimplant connected with TAD can provide translation and rotation features to change the angles and directions of orthodontic tractions for most effective anchorage preparation.

Collision Detection of Deformable Polyhedral Objects via Inner-outer Ellipsoids

For deformable polyhedral objects undergoing vertex repositioning, this paper develops a collision detection procedure by virtue of inner-outer ellipsoidal bounds of deformation. A new design of collision detector with tunable accuracy, defined by a linear inequality for easily computed and updated parameters, is presented. It utilizes and tracks a measure of proximity/penetration between two objects in the direction of shortest path between two inner ellipsoids. Moreover, it does not incur additional computational expenses since no costly updating process and heavy dependence on the geometric details of the deformed polyhedral objects is needed, so that the efficiency is comparable to that of rigid cases. Numerical experiments on pairs of randomly scaling convex polyhedra, lacking geometry coherence, demonstrated that the efficiency of the new collision detector is comparable to the rigid case

The Application of Nearly Embarrassingly Parallel Computation in the Optimization of Fluid-Film Lubrication©

The combination of powerful, yet inexpensive PCs and readily available open sources for parallel computation marks a new era of easy access to massive computation for the tribology community. The study demonstrates the applicability of embarrassingly parallel computation in the optimization of air-lubricated porous bearings with four design variables. To achieve high speedup without increasing the coding complexity, the master computer implements the lattice method to allocate the near-the-same computational load in the master-slave cluster. The effect of master capability on the cluster performance is also presented. The results are compared with that of an unparallelized simplex method and indicate a significant reduction in execution time due to parallelism. In a simulated analysis, a high speedup can also be obtained in dealing with a problem with many design variables. This study provides the framework for optimization of applications with complex tribological models to be solved with minimum execution time.

Application of non-destructive impedance-based monitoring technique for cyclic fatigue evaluation of endodontic nickel–titanium rotary instruments

This study investigates the application of non-destructive testing based on the impedance theory in the cyclic fatigue evaluation of endodontic Ni-Ti rotary instruments. Fifty Ni-Ti ProTaper instruments were divided into five groups (n=10 in Groups A to E). Groups A to D were subjected to cyclic fatigue within an artificial canal (Group E was the control group). The mean value of the total life limit (TLL), defined as the instrument being rotated until fracture occurred was found to be 104 s in Group A. Each rotary instrument in Groups B, C and D were rotated until the tested instruments reached 80% (84 s), 60% (62 s) and 40% (42 s) of the TLL. After fatigue testing, each rotary instrument was mounted onto a custom-developed non-destructive testing device to give the tip of the instrument a progressive sideways bend in four mutually perpendicular directions to measure the corresponding impedance value (including the resistance and the reactance). The results indicated that the impedance value showed the same trend as the resistance, implying that the impedance was primarily affected by the resistance. The impedance value for the instruments in the 80% and 60% TLL groups increased by about 6 mΩ (about 7.5%) more than that of the instruments in the intact and 40% TLL groups. The SEM analysis result showed that crack striations were only found at the tip of the thread on the cracked surface of the instrument, consistent with the impedance measurements that found the impedance value of the cracked surface to be significantly different from those in other surfaces. These findings indicate that the impedance value may represent an effective parameter for evaluating the micro-structural status of Ni-Ti rotary instruments subjected to fatigue loading.

Human face detection with neural networks and the DIRECT algorithm

Based on Rowley’s approach, this article proposes a new architecture that uses a specific optimization technique, the DIRECT (DIviding RECTangle) algorithm, to improve the efficiency of face detection in images. The system consists of two main parts: a neural network-based face detection arbitrator, and a search strategy based on an integer-handling DIRECT algorithm. By the architecture, the number of arbitrations is dramatically reduced, and human faces, if they are present in an image, are not restricted to predetermined resolutions and aspect ratios. Experimental results show that the proposed architecture is efficient in terms of both speed and robustness.

3D registration of human face using evolutionary computation and Kriging interpolation

This paper proposes a fast and robust 3D human face geometric data registration strategy dedicated for image-guided medical applications. The registration scheme is composed of a coarse transformation stage and a fine-tuning stage. In the first stage, fuzzy c-mean is used to reduce the data amount of template 3D image, and evolutionary computation is implemented to find optimal initial pose for the Iterative Closest Point plus k-dimensional (KD) tree scheme. In the second stage, the huge reference image data are replaced by a Kriging model. The time-consuming search for corresponding points in evaluating the degree of misalignment is substituted by projecting the points in the template image onto the model. To illustrate the validity and applicability of the proposed approach, a problem composed of 174 635 points reference image and an 11 280 points template image is demonstrated. Computational results show that our approach accelerates the registration process from 1361.28 seconds to 432.85 seconds when compared with the conventional ICP plus K-D tree scheme, while the average misalignment reduces from 11.35 mm to 2.33 mm.