The inertia versine method measures track displacement based on the principle of the law of inertia, under which displacement can be obtained by double integration of acceleration. Track inspection devices using the law of inertia have already been used by some railway operators. However, one disadvantage of such devices is the difficulty of obtaining correct displacement values due to integration errors. The developed inertia versine method processes data to make errors equal to the inspection characteristics of the 10-m chord versine method used in the actual field of track maintenance. Since this device uses only one sensor unit to measure track displacement, it is less expensive than the conventional track inspection cars that require three sensors. In addition, a newly developed two-axle rail displacement meter performs contact-less measurement of vertical and lateral displacement at a point between the sensor unit and the rail, thus positioning of sensor installation is less restricted. If it is installed on a commercial service car truck, for example, track displacement can be monitored continuously during operation (Fig. 1).

A performance confirmation test was carried out on a prototype device manufactured for installation on commercial service Shinkansen cars. The test demonstrated in running at 20 km/h or more that the maximum value of repetition errors of data was 0.5 mm or less, with a standard deviation of 0.2 mm or less; these results are equal to the corresponding values obtained by the conventional inspection cars. For practical purposes, there are no problems with the precision of inspection at low speeds, which the normal inertia method is regarded as difficult to measure at (Fig. 2).

The durability will be checked with the prototype device mounted on Kyushu Shinkansen cars.