Autonomous robots path planning: An adaptive roadmap approach

Developing algorithms that allow robots to independently navigate unknown environments is a widely researched area of robotics. The potential for autonomous mobile robots use, in industrial and military applications, is boundless. Path planning entails computing a collision free path from a robots current position to a desired target. The problem of path planning for these robots remains underdeveloped. Computational complexity, path optimization and robustness are some of the issues that arise. Current algorithms do not generate general solutions for different situations and require user experience and optimization. Classical algorithms are computationally extensive. This reduces the possibility of their use in real time applications. Additionally, classical algorithms do not allow for any control over attributes of the generated path. A new roadmap path planning algorithm is proposed in this paper. This method generates waypoints, through which the robot can avoid obstacles and reach its goal. At the heart of this algorithm is a method to control the distance of the waypoints from obstacles, without increasing its computational complexity. Several simulations were run to illustrate the robustness and adaptability of this approach, compared to the most commonly used path planning methods

Nonlinear behavior of metallic material under constant acceleration loading

There is frequent confusion in literature and in published data of material properties between the strain rate effect and the inertia effect on the behavior of metallic materials. While the measured changes of material behavior due to dynamic loading are frequently referred to as strain rate effects, little emphasis has been given to separating the effects of material inertia. In this work, inertia effects have been investigated during elastic deformations using transient dynamic finite element simulations. The work presents a case study in which a metallic bar is dynamically loaded by constant acceleration in simple tension. The material is assumed to be simple linear elastic. The material behavior is assumed to be time independent, strain rate effect was not considered in the simulations. Controlled axial displacement loading is applied at constant acceleration. When loading the material in the elastic range at high accelerations, the deformation becomes more concentrated towards the point of load application and a larger load is required to achieve a pre-defined displacement at this point, thus resulting in an apparent elasticity modulus higher than that measured at quasi-static conditions. Moreover, the material apparent response becomes non-linear. Keeping in mind that time independent properties have been adopted in the simulation and no strain rate effects have been considered, the resulting changes can be referred to pure inertia effects. In experimental testing, these changes would have been referred to strain-rate effects

Optimization of Classical Hydraulic Engine Mounts Based on RMS Method

Based on RMS averaging of the frequency response functions of the absolute acceleration and relative displacement transmissibility, optimal parameters describing the hydraulic engine mount are determined to explain the internal mount geometry. More specifically, it is shown that a line of minima exists to define a relationship between the absolute acceleration and relative displacement transmissibility of a sprung mass using a hydraulic mount as a means of suspension. This line of minima is used to determine several optimal systems developed on the basis of different clearance requirements, hence different relative displacement requirements, and compare them by means of their respective acceleration and displacement transmissibility functions. In addition, the transient response of the mount to a step input is also investigated to show the effects of the optimization upon the time domain response of the hydraulic mount

A survey of wheel tyre cavity resonance noise

Noise, vibration, and harshness (NVH) are synonymous with quality factor in automotive engineering. This quality factor is influenced by the internal noise such as engine noise, and external noise such as aerodynamic noise and tyre-road noise. Whereas many studies have been done to identify noise sources and reduce the noise and vibration transmission from the engine and aerodynamic sources to the passenger compartment, the tyre-road noise reduction outside the compartment still remains challenging. It is known that the exterior tyre-road noise being regulated by European legislation under ECE R117 and EC R661/2009 but for the interior tyre-road noise, it is only regulated by market requirement (consumer orientated). Wheel-tyre structure and tyre acoustic cavity resonances have been identified in literatures as the culprits. In this paper, a comprehensive review will be made to tyre-road noise studies and specifically to the acoustic cavity resonance effects and countermeasures

Improved mathematical modeling of thermal effects in flexural microcantilever resonators dynamics

In a recent research the thermal dependency of material characteristics in dynamic response of microresonator systems is modeled using Lorentzian function and employing perturbation analysis. Thermal phenomena introduce two main effects: damping due to internal friction, and softening due to Young modulus-temperature relationship. The presented mathematical model provided effective equations to study the electrically actuated microbeam resonators. The mathematical model of thermal phenomena in microbeam vibration was introduced by Jazar (2009). In that analysis, using the Zener model, a positive frequency dependent damping and a negative frequency dependent stiffness terms were introduced to mode the effects of warming at resonance (Jazar 2009). In this investigation, the problem will be analyzed from a practical point of view. We introduce a better mathematical model by improving the presented model. The main difference would be including the strain distribution in the damping and stiffness model

Hydraulic engine mounts: a survey

An ideal engine mount should provide a dual behavior. It needs to be soft to reduce the transmitted force, and to be hard to limit the relative displacement. The constant parameter linear mounts are unable to provide a good isolation when the excitation frequency is variable. Hydraulic engine mounts were invented as smart isolators to passively produce a soft isolator at low amplitude and a hard isolator at high amplitude. Having a dual behavior puts the mounts in the domain of nonlinear systems which in turn causes many new phenomena which have never appeared in linear analysis. The dual behavior hydraulic engine mounts were introduced around 1980 and passed through many analytic and technical improvements. This article will review these improvements up to 2012 and discusses the technical problems and methods of remedy

Crashworthiness of tapered thin-walled S-shaped structures

In a vehicular crash, a higher level of energy absorption in the frontal structures of the vehicle leads to less transferred energy to the passengers and less possibility for injury. S-shaped front rails, also known as S-rails, are one of the main structural elements and energy absorbers in the body of a vehicle. To improve the safety of passengers, the S-rail design should be optimized to absorb higher levels of energy in a frontal crash. In this study, the impact of tapering S-rails on the energy absorption is investigated. Two S-rails, one without internal diagonal reinforcement (type-A) and one with internal diagonal reinforcement (type-B), are both tapered with 20 different tapering ratios ranging from 110% to 300% in 10% increments. All of the S-rail models are subjected to static and dynamic loading conditions. Finite element analysis is used to assess the effectiveness of tapering S-rails by investigating the energy absorption (EA) and specific energy absorption (SEA) variations. An equation is developed to verify the numerical results. In this study, the reinforcing and tapering S-rails are shown to improve the EA and SEA under both static and dynamic loading conditions. By combining reinforcing and tapering techniques, S-rails showed a noticeable improvement in SEA of more than 300% in the static loading condition and an improvement of 275% in the dynamic loading condition

Structural-acoustic coupling study of tyre-cavity resonance

The tyre cavity resonance induced cabin noise has been a major unsolved customer complaint issue for a long time. A study of coupled tyre-cavity structural-acoustic system using impedance compact mobility matrix is presented in this paper. This method offers a better physical interpretation and numerical prediction about a coupled tyre-cavity system than previous models. It can calculate the sound pressure inside the tyre cavity as well as the tread wall vibration velocity at the same time. The analytical results have been verified by the results of the VAOne vibro-acoustic model. The VAOne software was also validated by the results from a case study of a rectangular box-cavity system in previous literature. From the analytical calculation, the tyre cavity coupling modal frequency is found to be split into two close resonance frequencies if the tyre structural natural frequency is close to the fluid cavity resonance frequency. The geometric coupling coefficient has been calculated using Matlab code. This study provides a better insight into the resonance coupling phenomenon of the tyre cavity to the tyre structure and its root causes. It demonstrates more clear physical meaning of the tyre cavity coupling model and its inherent characteristics than that from 'black box' finite element software. This develops a better understanding of the problem and its root causes facilitates effective solutions for the problem. Even though the study was conducted in a tyre-cavity system, the solution and methodology are applicable to other toroidal shape structural-acoustic systems

Acoustic Holographic Analysis of Wing Mirror Power Fold Actuator for Sound Quality Control

The possibility of application of acoustic holographic analysis with statistical envelope analysis algorithm for vehicle side mirror power-fold (PF) noise diagnostic is explored. The aim of this paper is to establish whether the sound visualization contours derived from the measurements can be used as a basis for the power-fold quality differentiation, and whether the results of noise source localization can suggest the best locations for signal sensor placement(s). With use of the acoustic camera, the diagnostic algorithm of the statistical envelope analysis is developed and validated using a large number of power-fold actuators comprising of subjectively 'good' and 'bad' samples. These power-fold actuators were tested and measured for the sound pressure spectra over the 1/3rd octave band over the frequency range up to 6300 Hz. Power-fold noise was measured by use of the microphone array. For given frequency limits of 1/3rd octave bands, sound pressure levels are measured on given power-fold actuators, an envelope algorithm was formed for the subjectively 'good' actuators, thus allowing to develop a quality control acceptance boundary envelope, with which, sound pressure spectrum amplitude of each individual actuator was compared. When the actuators have sound pressure spectrum amplitude curves falling within this boundary envelope, a pass status is obtained, and when the sound pressure spectrum amplitude curves stay outside of this envelope, a fail status is given

Continuous-curvature bounded trajectory planning using parametric splines

This paper investigates trajectory generation for curvature continuous paths. A car-like wheeled robot platform is considered. Planning is performed using a single B-spline curve that maintains continuity through the path. Constraints such as bounded curvature, velocity, and acceleration limits are considered. We minimize the traversal time while maintaining continuity and obeying the robot's constraints. Simulation experiments were successfully conducted to verify the efficiency and robustness of this approach