I. INTRODUCTION
The Simultaneous Localization and Mapping (SLAM) system [1]–[5] is the core of many robot-related tasks, such as robotic exploration and inspection [6]–[9]. The tightly coupled SLAM systems based on 3D Light Detection and Ranging (Lidar) and Inertial Measurement Unit (IMU) sensors have gained popularity due to high accuracy and robustness. In general circumstances, the systems employing an optimization framework often suffer from high computational cost, which limits their real-time applicability. To address this problem, utilizing Kalman Filter [10]–[12] for fusing Lidar and IMU data can significantly enhance calculation efficiency and increase the odometry output rate.