Influence the structure of the road surface on the measurement of distance and speed using optical head

The optical head is a linear vehicle speed sensor. Its action is based on image analysis of the moving road surface. A special algorithm converts it on the speed signal. Because the image of a road is analyzed, therefore the change in structure of the road surface causes change of the signal from the optical head. Therefore, for each type of surface, it is necessary to calibrate the optical head. Calibration consists of measuring, using an optical head, the length of the measurement distance, which was previously precisely measured with another reference device. Based on these two values the calibration factor is calculated, and entered afterwards in the optical head control software. This optical head is used in several the road tests, and its speed measurement function is used in the measurement of vehicle acceleration, braking distance, the total vehicle road load. This device, connected to the recorder, is also used in research on motion parameters of vehicle under real driving conditions. During these tests may occur the change of the road surface, therefore it is particularly important to know the influence of road surface structure on the signal from the optical head. This paper presents the results of optical head tests on the road with different structure and surface quality.