# Main Factors on Effect of Precise Measurement and Precise Tamping Based on BP Neural Network
## 1 Introduction  
The application of heavy-duty track maintenance machinery to realize digitally-controlled tamping operation and repairing the tracks by sections is an effective means to eliminate the ballasted track irregularities at the longitudinal level and the alignment [1; 2; 3]. Owing to the high mechanization, excellent operation quality, intelligent control and other advantages, it has become a popular maintenance practice accepted by railways all over the world. In 2021, in order to effectively improve the operation effect of heavy-duty tamping machines on ballasted tracks to remove track geometry irregularity, the technology of track PMPT was promoted and rolled out in China. The PMPT technology uses measuring equipment to accurately measure the track profile, optimizes to eliminate the track irregularity and formulate the tamping operation scheme based on the measurement results, inputs the tamping scheme to the heavy-duty machine before maintenance, and carries out precise digital tamping operations. In the PMPT of a ballasted track, precise track measurement and precise tamping with the heavy-duty machine are two important links. Precise track measurement can quickly and accurately obtain the static track geometry state and control position information with the track geometry measurement trolley (TGMT), such as the three-dimensional coordinates of the track center line and the left and right rails [4]. It guides the track geometry adjustment performance, which is the premise to ensure the high smoothness and stability of the track. In line with the different measurement principles and methods, it can be classified into three modes of measurement: absolute measurement, relative measurement [5], and\"relative + absolute\" combined measurement. There are certain differences in measurement accuracy. Among them, the representative measuring equipment are the inertial navigation system (INS), the trolley and total station (TS) [6], the INS trolley, and the INS trolley and GNSS [7]. The INS trolley with TS configuration can provide 3D tamping surveying solutions for ballasted track works, as is shown in Figure 1a. Its 3D positioning data acquisition adopts the IMS measuring module and TS. The TS is used for leveling and free station setting on the track, thereby observing the surrounding CPIII control points (generally 4-8) and obtaining the 3D coordinates of the station setting position. The INS trolley with GNSS configuration adopts position and attitude measurements with a multi-antenna combination and INS real-time data fusion technology, thereby possessing a non-stop continuous measurement function, as is shown in Figure 1b. Precise tamping with a heavy-duty machine is to guide heavy-duty track maintenance machinery to carry out digitally controlled tamping operations on ballasted tracks by using the measurement results. The tamping machine conducts track lifting, leveling, and alignment lining so as to improve the compactness of the track bed [8; 9; 10], and make the track geometry parameters meet the requirements of track design standards or maintenance codes [11], such as longitudinal level, cross level, and alignment of the track. At present, the main models of tamping machines used in China are the DCL-32 and DWL-48, which have some differences in the operating system, operation accuracy, and heavy-duty tamping machine parameter settings. DCL-32 [12] is a double-sleeper continuous tamping machine, which needs to be equipped with a dynamic track stabilizer, as is shown in Figure 2a. DWL-48 is a three-sleeper continuous tamping machine that integrates tamping and stabilization [13] and features high efficiency, high precision, and low energy consumption [14], as is shown in Figure 2b. DCL-32 and DWL-48 are produced using two tamping models produced by Plasser & Theurer as prototypes, which respectively include the 09-32 and 09-3X. Both the DCL-32 and DWL-48 models adopt Automatischer Leit Computer (ALC) control system and can achieve precise tamping.