# Time of Flight Distance Sensor-Based Construction Equipment Activity Detection Method
## 3 Methodologies
### Data Collection and Participants  
An excavator's arm comprises three articulation points, each of which is equipped with a piston that contracts and expands. The arm moves to the maximum/minimum angle of each articulation point according to the length of the piston's contraction and expansion. In other words, the displacement of the piston corresponds in a 1:1 ratio with the angle of the articulation point; thus, measuring the position of the articulation point and the maximum/minimum displacement of the piston from the equipment specifications or directly collected data allows us to evaluate the current movement of the excavator based solely on the piston's motion. In this study, a distance sensor was installed for each piston of the three articulation points, which allowed us to measure the piston displacement of the boom, arm, and bucket, thereby capturing the equipment's movements as relevant data.  
The experiment was conducted using a scale model of an excavator (one-twelfth scale). The differences between the minimum and maximum displacement of the boom, arm, and bucket pistons were 13.2 cm, 15.3 cm, and 11.5 cm, respectively, and the measured ranges of the rotation angles were 97\({}^{\circ}\), 110\({}^{\circ}\), and 207\({}^{\circ}\). Here, three sensors were mounted on a single Arduino Mega 2560 compatible board to measure the piston displacement of the three points, as shown in Figure 1.  
The sensor used in this study was the VL53L0X-V2 equipped with the VL53L0X time of flight (ToF) module. This sensor is very small, and the distance detection function within a stable range--which was measured targeting a specific point in the experiment--exhibited a detectable distance range of 10 to 300 mm. The technical specifications of the VL53L0X-V2 ToF sensor are given in Table 2. The meanings of each feature item are as follows: Package indicates the type of housing for the sensor module equipped with the ToF sensor; Size indicates the dimensions of the sensor module; Operating Voltages indicates the range of voltages required for the sensor to operate normally; Operating Temperature indicates  
Figure 1: Installed sensors and boards: (**a**) One-twelfth scale model and sensor system configuration; (**b**) ToF sensor and reflector; (**c**) hydraulic piston installation.  
the range of temperatures within which the sensor can function properly; I2C indicates the type of interface used for communication between the sensor and a microcontroller; Detectable Distance indicates the minimum and maximum distances that the sensor can detect; Infrared emitter indicates the wavelength of the infrared light-emitting diode used for distance detection.  
The connection details of the sensors are shown in Figure 2. Each sensor was connected to the controller to acquire the respective distance values. The controller received the individual sensor values, which were stored based on predetermined waiting times. Here, the measurement time and distance values were recorded in a matrix and transmitted to the host computer. The data measurement interval was set to 20 frames per second. The model was trained in the MATLAB 23.2.0 (R2023b) environment, 64-bit Windows 11 system with the following hardware configuration: an NVIDIA GeForce GTX 1080 GPU, 16 gigabytes, and Intel(R) Core (TM) i7-13650 HX.