Julien Lépine

A Laboratory Excitation Technique to Test Road Bike Vibration Transmission

This paper describes a technique designed to measure the in-situ acceleration signals that will be used to drive a road simulator in the study of road bike vibration transmission in a laboratory setting. To measure the signals, a bike mounted by a cyclist and towed by a motor vehicle is used. A road simulator using actuators driven by a digital signal is described. The impulse response of the bike used to measure road data is convoluted with the road acceleration in order to obtain the required actuator signal. The reproduction capacity of the simulator is evaluated by comparing the frequency content as well as the time statistical parameters of the acceleration signal measurement with road to the acceleration obtained on the simulator. On a granular road with a broadband excitation spectrum, the vertical excitation obtained with the simulator adequately mimics the measured road acceleration. This technique can be used to compare vibration transmission characteristics among different road bikes.

Technique to Measure the Dynamic Behavior of Road Bike Wheels

In the quest to improve comfort in road cycling, a primary concern of the bike manufacturing industry is the vibration generated by the road and transmitted to the cyclist’s hands and buttocks. The bike wheels are considered to be one of the major components contributing to the bike’s vibration isolation. In this paper, we describe a technique that uses the measurement of a blocked force at the hub. A road simulator was used to impose a controlled white noise vertical displacement under the tire. Measurements were taken of the force under the tire and the blocked force at the wheel hub. Six different wheels were tested. When the force was applied at different locations on the wheel, some of the wheels showed important spatial variations of the blocked force. The results show that this technique is successful in differentiating and ranking the wheels. Each wheel was also characterized by its radial static stiffness. Preliminary results show that there is poor correlation R 2 = 0.41 between radial static stiffness and the blocked force at the dynamic hub.

Excitation techniques for testing bike vibration transmission in the laboratory

Vibrations generated by road surface defects are a significant source of discomfort for cyclists. This paper presents two very different laboratory techniques for studying road bike vibration. The first technique uses a treadmill with a modified belt surface. The second technique is based on the use of a road simulator that was developed specifically to generate displacement excitation under the wheels of the bike. Broadband excitation generated by coarse pavement surface is also evaluated in this study. The objective of this paper is to evaluate and compare the relative merits of these two approaches. For the purposes of evaluation, we have described a technique to obtain a realistic measurement of input in real road conditions. Our results demonstrate that the road simulator succeeds in producing adequate displacement profiles in the vertical axis resulting in a vibration frequency spectrum that closely resembles the measurements in real road conditions. Limitations in current actuator capacity prevent to reproduce very coarse road conditions. Finally, more work is needed to develop an appropriate belt surface that can generate sufficient energy excitation above the 25 Hz range.

Influence of Test Conditions on Comfort Ranking of Road Bicycle Wheels

In the past few years, the dynamic comfort of bicycles has become a hot topic in the cycling industry. To improve comfort, a wide variety of dynamic tests is used to characterize and compare bikes. Because these tests usually involve a cyclist, and since the tires have a non-linear effect on the system, test protocols are expected to have an impact on the dynamic characteristics and bicycle ranking. With the objective of establishing good practices when comparing wheel comfort, this paper presents the influence of several test parameters on the vibrations induced to the cyclist at the hands and buttocks. The influence of two excitation surfaces on bicycle dynamics is studied: a flat excitation surface and an irregular surface that locally deforms the tire. The type of excitation, such as white noise, impacts and typical road excitation, are also investigated. Results with regard to the effect of the cyclist’s mass are also presented. The conclusion of this study shows that even if those parameters have a significant influence on the vibration levels transmitted to the cyclist, they do not affect the transmissibility ranking of two wheelsets. It should be noted however that the changes observed in the cyclist’s posture and position on the bicycle can affect wheelset ranking. Great care is therefore advised in controlling the cyclist’s posture and attitude on the bicycle during the tests.

Evaluation of machine learning algorithms for detection of road induced shocks buried in vehicle vibration signals

Road surface imperfections and aberrations generate shocks causing vehicles to sustain structural fatigue and functional defects, driver and passenger discomfort, injuries, and damage to freight. The harmful effect of shocks can be mitigated at different levels, for example, by improving road surfaces, vehicle suspension and protective packaging of freight. The efficiency of these methods partly depends on the identification and characterisation of the shocks. An assessment of four machine learning algorithms (Classifiers) that can be used to identify shocks produced on different roads and test tracks is presented in this paper. The algorithms were trained using synthetic signals. These were created from a model made from acceleration measurements on a test vehicle. The trained Classifiers were assessed on different measurement signals made on the same vehicle. The results show that the Support Vector Machine detection algorithm used in conjunction with a Gaussian Kernel Transform can accurately detect shocks generated on the test track with an area under the curve (AUC) of 0.89 and a Pseudo Energy Ratio Fall-Out (PERFO) of 8%.

On the Use of Machine Learning to Detect Shocks in Road Vehicle Vibration Signals

The characterisation of transportation hazards is paramount for protective packaging validation. It is used to estimate and simulate the loads and stresses occurring during transport which are essential to optimise packaging and ensure that products will resist the transportation environment with the minimum amount of protective material. Characterising road transportation vibrations is rather complex due to the nature of the dynamic motion produced by vehicles. For instance, different levels of vibration are induced to freight depending on the vehicle speed and the road surface; which often results in nonstationary random vibration. Road aberrations (such as cracks, potholes, speed bumps...) also produce transient vibrations (shocks) that can damage products. Because shocks and random vibrations cannot be analysed with the same statistical tools, the shocks have to be separated from the underlying vibrations. Both of these dynamic loads have to be characterised separately because they have different damaging effects. This task is a challenging because both types of vibration are recorded on a vehicle within the same vibration signal.

Effect of Structural Damping on Vibrations Transmitted to Road Cyclists

Improving ride quality is a paramount concern for road cyclists who are subjected to road induced vibrations during long rides. It has been hypothesized that adding structural damping to the bicycle can decrease the vibration levels transmitted to the cyclist. The human body is most sensitive to vibrations in the frequency range of 0–60 Hz, and the amount of damping added by the cyclist when riding the bicycle is very large. This could potentially reduce the net benefit of small improvements provided by structural damping. This paper reveals the effects of structural damping modifications on the modal parameters of a bicycle frame and on the amount of vibrations transmitted to the cyclist due to road surface excitation. A bicycle frame originally designed with damping gel inserts was tested in three different configurations: (1) with its damping gel inserts, (2) with its damping gel inserts and additional damping material wrapped around the frame’s tubing and (3) without its damping gel inserts. Three different metrics were used to assess the damping material effect on vibrations transmitted to the cyclist at the hands and buttocks: acceleration, transmitted force and power absorbed by the cyclist. This paper shows that in all configurations and measurements, added damping did not reduce the vibrations transmitted to the cyclist.

A Laboratory Technique to Compare Road Bike Dynamic Comfort

Comfort is an important characteristic in road bikes, and a major source of discomfort is the vibration transmitted to the cyclist. Since human memory tends to forget the perceived vibration stimulus strength soon after the perception is no longer present, a comparison between two situations must be done rapidly. Laboratory testing is therefore frequently used to investigate and document perception. This paper presents a laboratory technique enabling us to subject the cyclist to various types of bike vibration stimuli. The technique is based on the use of a bicycle simulator that generates vertical displacement under both wheels of a bike. A commercial bicycle is used to replicate vibration outputs at the saddle and the stem of different bikes. The strategy to determine the appropriate driving signals of each simulator actuator is presented in this paper. This requires solving an inverse problem. The results indicate that the measured and the reproduced PSD spectrum shapes are very similar. The main factor influencing the quality of reproduction is cyclist intervariability.