Rencheng Zheng

Study on Emergency-Avoidance Braking for the Automatic Platooning of Trucks

In developing automatic platooning of trucks as an energy-saving technology, the reliable driving of the platooned trucks is a primary objective for public implementation and future applications. At the same time, there is also an emergency requirement to ensure the safety of the driving experiment in the automatic platooning of trucks, including the conditions of a system failure. This paper presents a detailed experimental study on emergency avoidance braking for the automatic platooning of trucks using a driving simulator (DS) and an actual-vehicle experiment. In addition, a modification on the braking capability of the trucks of a platoon was applied for safety control. Therefore, human drivers can brake without risking a rear-end collision, in the case of an emergency for a failure in automatic platooning. Initially, an experimental platform was built to reproduce the automatic platooning of trucks in an advanced DS system. Assuming system failure and the emergency deceleration of the preceding truck without warning, the behavior of the driver in the following truck was studied in terms of emergency avoidance of a collision. In particular, with different settings for the mean maximum decelerations of the brake system of the following truck, the stopping gap distances and driver reaction times were analyzed in the driving experiment using the advanced DS and an actual vehicle. The experimental results indicated that emergency braking is an effective method for avoiding a rear-end collision when there is a system failure in the automatic platooning, resulting in the mean maximum deceleration for the following truck being higher than that for the preceding truck.

Evaluation of Sternocleidomastoid Muscle Activity of a Passenger in Response to a Car's Lateral Acceleration While Slalom Driving

Human factors are becoming one of the most important factors that are considered for automobile design and test. However, the ride comfort of a passenger or driver is mainly dependent on a subjective assessment by a test driver or questionnaire investigation, and, therefore, a quantitative evaluation of the ride comfort is being pursued as one of the research goals in the automobile industry. In this paper, actual-vehicle and driving simulator (DS) experiments were carried out to evaluate the sternocleidomastoid (SCM) muscle activity of a passenger in response to a cars lateral acceleration while slalom driving. Interestingly, the SCM muscle of the passenger on the side opposite the direction of the cars lateral acceleration contracts to keep the head stable against the body shaking. The electromyography (EMG) signal of the SCM muscle in a modified car was significantly lower than in a normal car, because the 1-10 Hz low-frequency vibrations of the body frame of the modified car during the slalom driving were decreased through improvements of the rigidity of cars body frame. A passenger feels more discomfort when the EMG signal of the SCM muscle increases, and less as the signal decreases. The DS experiment, with the addition of more experimental conditions, arrived at the same conclusion, which testified that the DS is a powerful tool with which to evaluate passenger discomfort. In conclusion, the EMG of the SCM muscle can be considered as an objective and effective method with which to quantify the effect of vehicle properties on human discomfort in both actual-vehicle and DS experiments for slalom driving.

Eye-Gaze Tracking Analysis of Driver Behavior While Interacting With Navigation Systems in an Urban Area

With the advent of global positioning system technology, smart phones are used as portable navigation systems. Guidelines that ensure driving safety while using conventional on-board navigation systems have already been published but do not extend to portable navigation systems; therefore, this study focused on the analysis of the eye-gaze tracking of drivers interacting with portable navigation systems in an urban area. Combinations of different display sizes and positions of portable navigation systems were adopted by 20 participants in a driving simulator experiment. An expectation maximum algorithm was proposed to classify the measured eye-gaze points; furthermore, three measures of glance frequency, glance time, and total glance time as a percentage were calculated. The results indicated that the convenient display position with a small visual angle can provide a significantly shorter glance time but a significantly higher glance frequency; however, the small-size display will bring on significantly longer glance time that may result in the increasing of visual distraction for drivers. The small-size portable display received significantly lower scores for subjective evaluation of acceptability and fatigue; moreover, the small-size portable display on the conventional built-in position received significantly lower subjective evaluation scores than that of the big-size one on the upper side of the dashboard. In addition, it indicated an increased risk of rear-end collision that the proportion of time that the time-to-collision was less than 1 s was significantly shorter for the portable navigation than that of traditional on-board one.

Biosignal Analysis to Assess Mental Stress in Automatic Driving of Trucks: Palmar Perspiration and Masseter Electromyography

Nowadays insight into human-machine interaction is a critical topic with the large-scale development of intelligent vehicles. Biosignal analysis can provide a deeper understanding of driver behaviors that may indicate rationally practical use of the automatic technology. Therefore, this study concentrates on biosignal analysis to quantitatively evaluate mental stress of drivers during automatic driving of trucks, with vehicles set at a closed gap distance apart to reduce air resistance to save energy consumption. By application of two wearable sensor systems, a continuous measurement was realized for palmar perspiration and masseter electromyography, and a biosignal processing method was proposed to assess mental stress levels. In a driving simulator experiment, ten participants completed automatic driving with 4, 8, and 12 m gap distances from the preceding vehicle, and manual driving with about 25 m gap distance as a reference. It was found that mental stress significantly increased when the gap distances decreased, and an abrupt increase in mental stress of drivers was also observed accompanying a sudden change of the gap distance during automatic driving, which corresponded to significantly higher ride discomfort according to subjective reports.

Effectiveness Testing of a Piezoelectric Energy Harvester for an Automobile Wheel Using Stochastic Resonance

The collection of clean power from ambient vibrations is considered a promising method for energy harvesting. For the case of wheel rotation, the present study investigates the effectiveness of a piezoelectric energy harvester, with the application of stochastic resonance to optimize the efficiency of energy harvesting. It is hypothesized that when the wheel rotates at variable speeds, the energy harvester is subjected to on-road noise as ambient excitations and a tangentially acting gravity force as a periodic modulation force, which can stimulate stochastic resonance. The energy harvester was miniaturized with a bistable cantilever structure, and the on-road noise was measured for the implementation of a vibrator in an experimental setting. A validation experiment revealed that the harvesting system was optimized to capture power that was approximately 12 times that captured under only on-road noise excitation and 50 times that captured under only the periodic gravity force. Moreover, the investigation of up-sweep excitations with increasing rotational frequency confirmed that stochastic resonance is effective in optimizing the performance of the energy harvester, with a certain bandwidth of vehicle speeds. An actual-vehicle experiment validates that the prototype harvester using stochastic resonance is capable of improving power generation performance for practical tire application.

On electrical optimisation using a Duffing-type vibrational energy harvester

There has been much recent interest in the response analysis and optimisation of the linear energy harvester under ambient vibrations. To transfer maximum power to an electrical load in a resonant system, the load resistance should be equal to the sum of the electrical analogue of mechanical damping and internal resistance. However, principally because of the limited bandwidth offered by the linear energy harvester, the potential benefit of nonlinearity has recently been applied to improve the effectiveness of energy harvesting devices. For example, a Duffing-type oscillator can provide a wider bandwidth and greater effectiveness when subject to periodic excitations. The motivating hypothesis has been that the nonlinear Duffing energy harvester can also be optimised to maximise the available electrical power. This paper presents theoretical optimisation and numerical studies under three different conditions with the designed Duffing-type devices. First, the simplest model without any transmission mechanism and optimisation constraints is considered. Second, a device operated under low frequency and large force excitations using a ball screw to convert low-speed linear motion to high-speed rotation is analysed, where the optimum lead and load resistance are derived. Finally, considering the limitation of some dimensions in practical implementation, the constrained optimisation subjected to the maximum displacement of the seismic mass is also shown in this paper.

On square-wave-driven stochastic resonance for energy harvesting in a bistable system

Stochastic resonance is a physical phenomenon through which the throughput of energy within an oscillator excited by a stochastic source can be boosted by adding a small modulating excitation. This study investigates the feasibility of implementing square-wave-driven stochastic resonance to enhance energy harvesting. The motivating hypothesis was that such stochastic resonance can be efficiently realized in a bistable mechanism. However, the condition for the occurrence of stochastic resonance is conventionally defined by the Kramers rate. This definition is inadequate because of the necessity and difficulty in estimating white noise density. A bistable mechanism has been designed using an explicit analytical model which implies a new approach for achieving stochastic resonance in the paper. Experimental tests confirm that the addition of a small-scale force to the bistable system excited by a random signal apparently leads to a corresponding amplification of the response that we now term square-wave-driven stochastic resonance. The study therefore indicates that this approach may be a promising way to improve the performance of an energy harvester under certain forms of random excitation.

An experimental study of stochastic resonance in a bistable mechanical system

Potential applications for stochastic resonance have developed strongly in recent years. This paper presents a study of an application of stochastic resonance in a mechanical system. Since a linear system cannot normally exhibit stochastic resonance, a cantilever beam with an end magnet was used to constitute a bistable nonlinear oscillator. Excited by ambient random vibration, the elastic beam undergoes a modulation of the potential well by means of a periodic excitation and flips between bistable states as a result of this. By adjusting the distance between the end magnet and a fixed magnet it is possible to drive the system controllably between bistable states. An electromagnet was used to provide the periodical parametric excitation which can result in stochastic resonance. The conditions for the occurrence of stochastic resonance are also discussed in the paper. Furthermore, simulations and experimental studies have been implemented to illustrate the application. The experimental results prove that stochastic resonance can occur, and that it can be usefully applied in such a mechanical system under specific conditions.

Stabilisation of the high-energy orbit for a non-linear energy harvester with variable damping

The non-linearity of a hardening-type oscillator provides a wider bandwidth and a higher energy harvesting capability under harmonic excitations. Also, both low- and high-energy responses can coexist for the same parameter combinations at relatively high excitation levels. However, if the oscillator’s response happens to coincide with the low-energy orbit then the improved performance achieved by the non-linear oscillator over that of its linear counterpart, could be impaired. This is therefore the main motivation for stabilisation of the high-energy orbit. In the present work, a schematic harvester design is considered consisting of a mass supported by two linear springs connected in series, each with a parallel damper, and a third-order non-linear spring. The equivalent linear stiffness and damping coefficients of the oscillator are derived through variation of the damper element. From this adjustment the variation of the equivalent stiffness generates a corresponding shift in the frequency–amplitude response curve, and this triggers a jump from the low-energy orbit to stabilise the high-energy orbit. This approach has been seen to require little additional energy supply for the adjustment and stabilisation, compared with that needed for direct stiffness tuning by mechanical means. Overall energy saving is of particular importance for energy harvesting applications. Subsequent results from simulation and experimentation confirm that the proposed method can be used to trigger a jump to the desirable state, thereby introducing a beneficial addition to the performance of the non-linear hardening-type energy harvester that improves overall efficiency and broadens the bandwidth.

The Effect of a Haptic Guidance Steering System on Fatigue-Related Driver Behavior

Prolonged driving on monotonous roads often leads to a reduction in task load that causes drivers passive fatigue. Passive fatigue results in loss of driver alertness and is detrimental to driver safety. This paper focuses on the effect of a haptic guidance steering system on improving behaviors of passively fatigued drivers. By continuously exerting active torque on a steering wheel, the haptic system guides drivers to follow the centerline of a lane; meanwhile, the drivers sense the torque and interact with it while operating the steering wheel. An experiment was conducted with 12 healthy participants in a high-fidelity driving simulator. A monotonous driving course was designed, and vehicle speed was fixed in order to induce drivers’ passive fatigue. A treatment session was arranged with the haptic guidance steering system, and a control session was conducted as a comparison. Driving performance, assessed by standard deviation of lane position, mean absolute lateral error, and time-to-lane crossing, was significantly improved when haptic guidance was activated. Results of physiological measures, including heart rate variability and percentage of eye closure, revealed that passively fatigued drivers were aroused when they were aware of the active torque on the steering wheel. In conclusion, the activation of haptic guidance can be regarded as an effective countermeasure for the passively fatigued drivers who have performed a prolonged monotonous driving task.