## 4 Result and Discussion
### Error Recognition  
Some ultrasonic and ToF sensors reported an error during certain tests and their data were excluded from the postprocess data. These errors can be categorized into two types: (1) Ultrasonic errors: Since the further inspection of the measuring device showed no faulty connections and no problem with the uploaded code, it was concluded that the flow of the electricity was causing issues in random sensors during some of the experiments. The ToF sensors draw more current from the device when they estimate the distance of an object which is located further away. Drawing more current from a multisensor device within a constant 400 mA current output (200 mA each Arduino [51]) resulted in a voltage drop. As already mentioned, the HC-SR04 could not work with a current lower than 3.6 V. The sensors indicated an error by either printing \"0\" or printing a value smaller than the actual distance. Unlike ToF sensors, ultrasonic sensors are low-frequency sensors with steady outputs. By plotting the results of ultrasonic sensors and studying them, these outliers are approximately 10% smaller than the estimated value. These values have been considered faulty values as well and have been excluded from the outputs. Figure 8 shows an example of this error. (2) ToF sensors: These sensors are sensitive to ambient light. Whenever a robust environmental light beam was focused on a sensor, the sensor was printing an error coded as \"8190\" instead of the measured distance. In addition, this type of sensor will print a coded value of \"65,535\" if it is burned, has a faulty connection, or the input power is not enough. To address the issues above, a code was used to exclude the faulty readings. This code first extracts the acquired HC-SR04, VL53L0X, and VL53L1X sensor data from the Raspberry Pi output in three different matrixes. In each matrix, the columns specify a given sensor and each row is a measurement cycle. Second, the code excludes the rows in which at least one of its values is faulty. Incorrect values are the coded errors mentioned above, including: 0, 8190, and 65,535. Table 3 displays the average results of all similar sensors with their standard deviations (STDEV) for each experiment with excessive ambient light (such as VL53L1X Light) and without it (such as VL53L1X). The first column lists the distance of the sensors from the  
Figure 8: Excluding the outliers of HC-SR04 estimations. targeted object, as measured by a steel measurement pattern. The column average then represents the average results of 25 distance sensors for 80 measurement cycles. The STDEV column represents the standard deviation of the same distance sensors on average for 80 data acquisition cycles in each experiment. The columns with no information show the incapability of distance measurement by the sensor type. Table 3 shows that ultrasonic sensors can measure higher distances more accurately. Moreover, ToF sensors decrease in accuracy as their distance from the target object increases. Further analysis of Table 3 shows that the standard deviation of all sensors in all situations rises with the increment of the object distance. Ambient light results in lower accuracy for ToF sensors and produces a more significant standard deviation. ToF sensors are also more sensitive to ambient light at larger distances. Table 3 also shows that even though VL53L0X measured distances up to 68 cm in the absence of the projector light, it only measured distances up to 48 cm when the projector light was on. VL53L0X sensors were also affected by ambient light. Subsequently, the VL53L0X can be introduced as the least effective distance sensor in this experiment due to its short distance range. This higher data fluctuation results in a significant standard deviation ratio and incorrect calibration. HC-SR04 and VL53L1x report very similar results on short distances, which demonstrates their accurate company calibration. For distances greater than 450 mm, the difference between the results of the ultrasonic sensor and VL53L1X is more than 3 mm.