A practical procedure for angular resampling applied to motion measurements on a motorbike valvetrain

An experimental test campaign was performed on the valve train of a racing motorbike engine in order to get insight into the dynamic of the system. In particular the valve motion was picked up in cold test conditions by means of a laser vibrometer able to acquire displacement and velocity signals. As usual for rotary machines, the analysis of the experimental data is more significant if performed in the angle domain rather than in the time domain, so that referring the valve time-dependent measurements to the camshaft angular position was required. To this purpose the camshaft was fitted with a zebra tape whose dark and light stripes were tracked by means of an optical probe. Unfortunately, the employed zebra tape presented stripes with slightly different widths, thus precluding the possibility to directly obtain the correct relationship between camshaft angular position and time. In order to overcome this problem, a practical procedure for the zebra tape identification was developed and is the focus of the present paper.