**3. Constructing the track diagnosis system**

### **3.1 Track irregularities and track faults**

Major private railway companies and Japan Railways (JR) use track inspection vehicles to measure track displacement, and track management is based on such measurements. Track irregularities such as longitudinal level, alignment, gauge, cross level, and twist (depicted in **Figure 1**) should be controlled properly.

However, it is difficult for regional railway companies to introduce track inspection vehicles because of the cost. Moreover, manual inspection by track maintenance staff is inefficient and expensive.

#### **3.2 Overview of track management with proposed system**

**Figure 2** depicts the track management method used in this study. A 3-axis accelerometer mounted on a smartphone was used to measure the vibration of the carbody, a 3-axis Gyro sensor was used to measure the angular acceleration, and a GNSS sensor was used to collect information about the position and traveling speed; all data are then transmitted to the server. By analyzing the transmitted data, the condition of the track can be diagnosed, and, based on the result, railway operators can prioritize track maintenance and work.

### **3.3 Measurement devices**

A BL-02 IoT device for business use (hereafter referred to as Device B) and a commercial smartphone Galaxy S7-edge (hereafter referred to as Device G) were used for measurements. **Figure 3** shows a photograph of these devices, and **Table 1** details their specifications.

Both devices were equipped with a 3-axis accelerometer, a 3-axis Gyro sensor, a GNSS sensor that can determine the location and traveling speed, and 4G internet, which is required for data transmission and reception.

*Track structure and irregularities [5].*

*Track Condition Monitoring Based on In-Service Train Vibration Data Using Smartphones DOI: http://dx.doi.org/10.5772/intechopen.111703*

*Track condition management using car-body vibration.*

#### **Figure 3.**

*Appearance of the BL-02 IoT device for business use and the GalaxyS7-edge smartphone for general use.*


#### **Table 1.**

*Specifications of the device B and the device G.*

**Figure 4.** *Location of measurement devices.*

At the time of measurement, data from Device B were measured at 232 Hz and data from Device G were measured at 417 Hz; both were down-sampled to 80 Hz at the time of acquisition from the server to reduce the amount of processing required for analysis.

Using these devices, we can measure and diagnose the vibration of the car-body. Considering convenience and GNSS reception environment, we installed the smartphone near the driver's cab, as shown in **Figure 4**.

### **3.4 Identifying the areas of interest from the vibration measurements**

Smartphones are able to acquire latitude and longitude information; however, location detection errors increase when methods such as map matching are not employed. Therefore, we adopted a method to calculate the milage using the GNSS speed, which was, in turn, calculated using the Doppler effect of the GNSS carrier wave.
