# Design and Mechanical Behavior Research of Highway Guardrail Patrol Robot
## 4 Dynamic Simulation of Guardrail Inspection Robot
### Barrier Guardrail Section  
The obstacles of guardrail groups are theoretically divided into three types: straight obstacle section, slope obstacle section, and turning obstacle section. A straight obstacle refers to the distance \(d\) generated when two sections of the guardrail are spliced together due to shape limitations, generally ranging from 5 to 10 mm in size. The simulation uses four sections of the guardrail spliced, with d values of 7.5 mm, 10 mm, and 12.5 mm, as shown in Figure 6a. When the stiffness \(k_{1}\) of the active wheel side spring and the stiffness \(k_{2}\) of the driven wheel side spring are set according to the parameters of Groups 1-4, the displacement curve of the robot in the X-direction is shown in Figure 6b. It can be observed that when the spring parameters are set to Group 1, the robot experiences jamming during the return journey. This occurs because the stiffness of the spring on the driven wheel side is too weak to  
Figure 5: Simulation diagram of barrier-free guardrail section. provide sufficient force to maintain the robot's alignment with the guardrail. Over time, this misalignment accumulates, and once it reaches a critical level, the excessive angle between the robot and the guardrail causes jamming. As a result, the spring parameter settings of Group 1 are considered unreasonable and are excluded from further consideration. When the spring parameters are set to Groups 2-4, the robot successfully completes back-and-forth movement on the straight obstacle guardrail group, performing four obstacle-crossing behaviors: front auxiliary wheel obstacle crossing, rear auxiliary wheel obstacle crossing, non-driven rubber-coated wheel obstacle crossing, and driven rubber-coated wheel obstacle crossing. By observing the vertical (Y-direction) displacement curve of the robot under the parameter settings of Groups 2-3, as shown in Figure 6c, it is evident that the vertical displacement values are relatively small and exhibit no abrupt changes when the robot is not crossing obstacles. This demonstrates that the robot can maintain overall stability during the obstacle crossing. However, under different spring parameters, the vertical displacement of the robot varies when the rubber-coated wheel crosses obstacles, with the fourth group of parameters showing the least variation. This occurs because the force on the active side of the robot is relatively large, restricting its movement. Unlike in the obstacle-free section, a larger vertical displacement during the obstacle crossing is beneficial, as it reduces the robot's compression on the guardrail and better protects the guardrail's structural integrity. To comprehensively evaluate the robot's performance, it is also necessary to consider two additional types of obstacles: slope obstacles and turning obstacles. Turning obstacles occur on high-curvature curved sections and arise due to angular deviations of the guardrail in the vertical direction. It is reasonable to conclude that such deviations only affect the obstacle-crossing height and are essentially equivalent to straight obstacles. Therefore, they will not be analyzed separately. Figure 6: Simulation diagram of barrier section for level obstacles. (**a**) Schematic diagram of the straight obstacle guardrail section, where the obstacle marked by the red dashed line is 10 mm, which is the preset obstacle value mentioned above. (**b**) Displacement of the robot in the X-direction on the straight obstacle section. (**c**) Displacement of the robot in the Y-direction on the straight obstacle section. When the road environment of the expressway includes slopes, the angles between the guardrail groups must be adjusted. By accumulating multiple small angles, the guardrail groups can be aligned with the slope of the roadside. The slope obstacle is set at an angle of \(1^{\circ}\), which can be categorized into two scenarios: uphill and downhill, as illustrated in Figure 7a.