## 3 Simulation and Experiment
### Kinematics Simulation  
The transmission angle would affect the transmission efficiency, and the extrusion force on the lever shaft would increase. The model of the load-lifting device shown in Figure 2 was established and imported into Adams software. After simplifying the model, constraints and loads were applied to analyze the kinematics. When the angle between the initial position of the steering rod and the lever was at an ideal value of 90\({}^{\circ}\), the lever rod rotated more than 44.3\({}^{\circ}\), and the transmission angle \(\alpha\) was too large. Therefore, the initial transmission angle needed to be optimized.  
The initial hook transmission angle was, respectively, set at 60\({}^{\circ}\), 65\({}^{\circ}\), 70\({}^{\circ}\), 75\({}^{\circ}\), 80\({}^{\circ}\), and 85\({}^{\circ}\), and the analysis model was adjusted. The transmission angle during the lifting process was analyzed by using the software, and the variance of the transmission angle during the lifting process corresponding to different initial hook transmission angles was calculated, as shown in Figure 5. Based on the analysis results, it could be known that when the initial transmission angle between the _bc_ rod and the _cd_ rod was 80\({}^{\circ}\), the variance was the smallest. It showed that the change of the transmission angle \(\alpha\) in the lifting process was smaller than that in the lifting operation of other initial positions. When the initial hook transmission angle \(\alpha\) was 80\({}^{\circ}\), the range of \(\alpha_{1}\) and \(\alpha_{2}\) were 66.7\({}^{\circ}\)\(\sim\)109.65\({}^{\circ}\) and \(-\)1.25\({}^{\circ}\)\(\sim\)10.3\({}^{\circ}\), respectively.  
To maintain a constant load force of 40 kN on the lower link, a hydraulic loading cylinder was used for loading with variable force. The Adams software was used to calculate the load \(F\) applied by the hydraulic loading cylinder and the load \(F_{1}\) transmitted by the steering rod during the lifting process. The rotation angle of the lower link during the dynamic simulation analysis was one degree per second. The results were shown in Figure 6. \(F\) and \(F_{1}\) varied from 44,948-55,265 N and 40,001-43,554 N, respectively. These parameters could be used as the design basis for component strength calibration. Meanwhile, the load-lifting process could be carried out according to the parameters to ensure that the load force of the lower link was kept at 40 kN.  
According to the dynamic simulation analysis results, the function equation of the loading force of the hydraulic cylinder during the loading and lifting process was fitted to check the strength of the design device. The fitting equation was shown in Equation (5), the fitting coefficient was high. Hence, the fitting equation could be used as one of the boundary conditions of the finite element simulation analysis.  
\[F=0.0388\cdot t^{4}-3.3115\cdot t^{3}+94.692\cdot t^{2}-994.47\cdot t+45612, \ R^{2}=0.9919 \tag{5}\]  
where \(F\) is the loading force of the hydraulic cylinder, N; \(t\) is the time for the lower to rise to the set height, s. The range of t varies from 0 s to 47.6 s.  
Figure 5: The changes of angle during the lifting process.