A Psychophysical Model of Motorcycle Handlebar Vibrations

In this study, we developed a perception-based quantitative model to relate broadband vibrations transmitted through a motorcycle handlebar to a rider’s hands. The test apparatus consisted of the handlebar of a motorcycle rig assembly driven by a computer-controlled actuator. Participants were instructed to hold the handlebar and maintain a sitting posture as they would while riding a motorcycle. In Exp. 1, psychophysical detection thresholds for 10 participants were estimated at ten test frequencies between 20–300 Hz using a two-interval one-up two-down adaptive procedure. The interpolated threshold vs. frequency function specified the minimum acceleration required before a user could perceive the vibration at a particular frequency. In Exp. 2, participants were asked to rate 15 representative handlebar vibrations using a magnitude estimation procedure. The vibration patterns were measured on an actual motorcycle handlebar while the motorcycle traveled at speeds ranging from 25 to 75 mph. Several weighting functions, including the ISO-5349 standards, were applied to the broadband vibration signal in the frequency domain to estimate the total vibration energy by summing up all weighted components. The best weighting function, in the sense that the estimated total energy correlated linearly with the subjective magnitude ratings obtained in Exp. 2, were based on the detection threshold data obtained in Exp. 1. Specifically, the strength of each vibration component was calculated relative to the human detection threshold at the same frequency, thereby taking into account human sensitivity to vibration signals at different frequencies. The resulting weighting function can be applied to other recorded vibration signals to predict user rating of perceived vibration intensities.