Reza N. Jazar

Continuous Path Smoothing for Car-Like Robots Using B-Spline Curves

A practical approach for generating motion paths with continuous steering for car-like mobile robots is presented here. This paper addresses two key issues in robot motion planning; path continuity and maximum curvature constraint for nonholonomic robots. The advantage of this new method is that it allows robots to account for their constraints in an efficient manner that facilitates real-time planning. B-spline curves are leveraged for their robustness and practical synthesis to model the vehicle’s path. Comparative navigational-based analyses are presented to selected appropriate curve and nominate its parameters. Path continuity is achieved by utilizing a single path, to represent the trajectory, with no limitations on path, or orientation. The path parameters are formulated with respect to the robot’s constraints. Maximum curvature is satisfied locally, in every segment using a smoothing algorithm, if needed. It is demonstrated that any local modifications of single sections have minimal effect on the entire path. Rigorous simulations are presented, to highlight the benefits of the proposed method, in comparison to existing approaches with regards to continuity, curvature control, path length and resulting acceleration. Experimental results validate that our approach mimics human steering with high accuracy. Accordingly, efficiently formulated continuous paths ultimately contribute towards passenger comfort improvement. Using presented approach, autonomous vehicles generate and follow paths that humans are accustomed to, with minimum disturbances.

In the Passenger Seat: Investigating Ride Comfort Measures in Autonomous Cars

The prospect of driverless cars wide-scale deployment is imminent owing to the advances in robotics, computational power, communications, and sensor technologies. This promises highway fatality reductions and improvements in traffic and fuel efficiency. Our understanding of the effects arising from commuting in autonomous cars is still limited. The novel concept of the loss of driver controllability is introduced here. It requires a reassessment of vehicles comfort criteria. In this review paper, traditional comfort measures are examined and autonomous passenger awareness factors are proposed. We categorize path-planning methods in light of the offered factors. The objective of the review presented in this article is to highlight the gap in path planning from a passenger comfort perspective and propose some research solutions. It is expected that this investigation will generate more research interest and bring innovative solutions into this field.

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.

Mathematical Theory of Autodriver for Autonomous Vehicles

Introducing an independent four-wheel-steering (4WS) system, we are able to design an autodriver to keep an autonomous vehicle on a given road. The kinematic condition of steering can be used to set the steer angles such that the kinematic center of rotation be at any desired point. The road and tire characteristics, along with the dynamics of a moving vehicle cause the vehicle to turn about an actual point that is not necessarily at the road curvature center. The position of the dynamic turning center can be controlled by adjusting the steer angles such that it coincides with the road curvature center. Such a vehicle will move on the desired road autonomously.

Randomized Bidirectional B-Spline Parameterization Motion Planning

This paper presents a motion planner tailored for particular requirements for robotic car navigation. We leverage B-spline curve properties to include vehicles constraint requirements, thus lowering the search dimensionality. An algorithm, which combines competent exploratory nature of the randomized search methods with vector-valued parameterization steering, is developed here. Vehicles limitations, along with obstacles constraints, are satisfied without being hindered by numerical integration and control space discretization of traditional randomized kinodynamic planners. We rely on newly developed theoretical underpinnings to overcome performance issues in rapidly exploring random tree (RRT) solutions. Rigorous simulations and analysis demonstrate that this new approach outperforms recently proposed planners by using an efficient bidirectional RRT-based search, by maintaining continuous state and control spaces, and generating C2 continuous paths, which are realistic inputs suited for mobile robotic applications and passenger vehicles.

Effects of seat structural dynamics on current ride comfort criteria

The ISO 2631-1 (1997) provides methodologies for assessment of the seated human body comfort in response to vibrations. The standard covers various conditions such as frequency content, direction and location of the transmission of the vibration to the human body. However, the effects of seat structural dynamics mode shapes and corresponding resonances have not been discussed. This study provides important knowledge about the effects of vehicle seat structural vibration modes on discomfort assessment. The occupied seat resonant frequencies and corresponding vibration modes were measured and comfort test was carried out based on the paired comparison test method. The results show that the ISO 2631-1 (1997) method significantly underestimates the vibration discomfort level around the occupied seat twisting resonant frequencies. This underestimation is mainly due to the ISO suggested location of the accelerometer pad on the seatback. The centre of the seatback is a nodal point at the seat twisting mode. Therefore, it underestimates the total vibration transferred to the occupant body from the seatback. Practitioner Summary: The effects of the vehicle seat structural dynamics have not been discussed in the human body vibration ISO . The results of this research show that the current measurement method suggested by ISO 2631-1 (1997) can significantly underestimate the vibration discomfort level at around the seat structural vibration mode.

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.

Smart Flat Ride Tuning

Flat ride is the condition that the unpleasant pitch oscillation of the vehicle body turns into more tolerable bounce oscillation, when a car hits a bump in forward motion. Based on experimental results, Maurice Olley discovered and introduced two conditions for flat ride: 1. The radius of gyration in pitch should be equal to the multiplication of the distance from the mass centers \(a_{1},a_{2}\) of the front and rear wheels of the car (\({r}^{2} = a_{1}a_{2}\)). 2. The rear suspension should have around 20% higher rate than the front. The equation \({r}^{2} = a_{1}a_{2}\) makes the car to be considered as two separated uncoupled mass-spring systems of front and rear suspensions.

Time Optimal Control

The most important job of industrial robots is moving between two points rest-to-rest. Minimum time control is what we need to increase industrial robots productivity. The objective of time-optimal control is to transfer the end-effector of a robot from an initial position to a desired destination in minimum time. Consider a system with the following equation of motion: