# Motion Simulation and Human-Computer Interaction System for Lunar Exploration
## 2 Materials and Methods
### Modeling of Lunar Environment and Rover
#### 2.2.2 Motion Simulation of the Rover  
Due to the limitations of the mechanical structure, the translation range of the 6-DOF platform is limited [17]. Therefore, in the process of simulating the actual movement of the rover, the platform cannot track the 6-DOF attitude. To achieve high-fidelity posture following, the output data needs to be processed. The human vestibular perception system is composed of otoliths and semicircular canals. The driver feels linear acceleration through otoliths, and angular velocity through semicircular canals. When the data is greater than the threshold, the driver will sense movement. To be perceived by humans, the longitudinal and lateral acceleration must be greater than 0.17 m/s\({}^{2}\), the vertical acceleration must be greater than 0.28 m/s\({}^{2}\), and the pitch, roll, and yaw angular velocity must be greater than 3.6\({}^{\circ}\)/s, 3.0\({}^{\circ}\)/s, 2.6\({}^{\circ}\)/s. The platform moves at an angular velocity lower than the human perception threshold, and the longitudinal and lateral linear acceleration are simulated by the gravity component. Based on this principle, we designed a motion simulation system. The motion parameters of the rover and the linear acceleration perceived by the otolith were used as the input data of the algorithm to obtain the displacement and attitude angle. The flow of the somatosensory feedback algorithm is shown in Figure 6.  
Figure 4: Simulation model of the lunar environment. Figure 5: Simulation model of the lunar rover. Otoliths cannot distinguish the influence of gravity on motion, and the perceived linear acceleration exists in the form of the specific force \(f_{AA}\):  
\[f_{AA}=a-g \tag{3}\]  
where \(a\) is the absolute linear acceleration of human body and \(g\) is the gravitational acceleration. It is difficult for the human body to perceive tiny angular velocities, so tilt coordination cannot simulate excessively high linear acceleration. It is necessary to scale the kinematic parameters through the scale link. Taking into account the relative position of the vehicle centroid and the vestibule, \(L_{s}\) is the coordinate transformation matrix from the human body coordinate system to the inertial coordinate system, and \(T_{s}\) represents the transformation matrix from the angular velocity to the Euler angle change rate. The linear acceleration and angular acceleration in the human body coordinate system was converted to the inertial coordinate system:  
\[f_{2}=L_{s}f_{1} \tag{4}\]  
\[\dot{\beta}_{2}=T_{s}\omega_{1} \tag{5}\]  
where \(f_{1},f_{2}\) are the specific force in the human body coordinate system and the inertial coordinate system, respectively. \(\omega_{1},\dot{\beta}_{2}\) are the angular velocity signals in the human body coordinate system and the inertial coordinate system. The speed of the rover was low, and the posture change was small. The 6-DOF platform could easily track the high-frequency components of linear acceleration and angular velocities. The motion simulation system tracked high-frequency linear acceleration and used tilt coordination to simulate longitudinal and lateral linear acceleration. We designed the angular velocity-limiting link to ensure that it would be difficult for the human body to perceive posture changes caused by tilt coordination. We limited the angular displacement caused by the low-frequency angular velocity to ensure that the 6-DOF platform was not affected by interference factors. It is necessary to ensure that the platform returned to the initial position without being perceived after the pose change occurred. We designed a third-order high-pass filter to filter the linear acceleration in the inertial coordinate system.