# Study on Overturn Proof Monitoring System of Mobile Crane
## 2 A Simulator of Mobile Crane
### Dynamic Characteristic Analysis  
In order to investigate dynamic characteristics, actual parameters such as weight, length, relief angle, working radius and outrigger length of the crane are reflected in the analysis. The dynamic analysis was applied to the movement of the boom's turning, ascending and descending (center of gravity change). The outrigger reaction force value, which is the support point, was derived and analyzed. Moreover, crane operation was simulated considering the constraint, contact and load conditions and the result was derived for the entire crane model through dynamic analysis.  
The limit of overturning has been analyzed according to the working radius of the crane through dynamic simulation. The simulation was performed to find a situation where the undulation angle was fixed at 0\({}^{\circ}\) and the boom length was adjusted (work radius change) to invert when a limit load was applied at each work radius. The total analysis time was 45 s and a simulation was performed sequentially, turning 90 degrees from the rear to the lateral direction (counterclockwise) and then descending from a maximum angle of 78 to 0 degrees. At this time, the total length of the boom was 21.6 m and the loading weight was set to 4 tons.  
As for the results of the analysis from Figure 4, the graph confirmed that the size of the reaction force was almost the same in all four positions of the front and rear outriggers due to the large body weight of 26 tons compared to the 3 tons load weight. The load weight is insignificant, so the magnitude of the four-point reaction force is not significantly different. As the analysis progressed, the rear outrigger reaction force gradually increased while the external force increased and the loading weight increased, while the front outrigger reaction force decreased; the overturning load was reached when the front outrigger reaction force became 0 N. The side overturning from load weight 48,070 N simulation is shown in Figure 5.  
Figure 3: 3D Modeling of mobile crane (Model No. SS7506).  
Table 2 shows the result of the reaction forces of the outrigger. The result confirmed that the larger the working radius, the smaller the filling load size in addition to the inversely related relationship with the falling moment value and the working radius. Table 2 summarizes the size of the initial outrigger reaction forces.  
Prior to the actual vehicle experiment, optimization considering the weight of the crane cabin and attachments was performed to compare the simulated values of the four outrigger points and the measured values at the points installed on the ground. While calibrating the simulation model based on the value of the outrigger reaction force, the error rate between the measured value of each outrigger and the analyzed value for each outrigger position was calculated to be 1.7%, 3.9%, 7.7%, 7.6% and the result was consistent with the measured value as shown in Table 3.  
Figure 4: The simulation result of rear overturning.  
Figure 5: The simulation result of side overturning.  
Since the center of gravity of the body of the crane modeling is almost similar to the actual crane, it was possible to develop a simulation model similar to the actual vehicle through optimal arrangement of auxiliary parts.