## 3 Simulation Results and Analysis
### Analysis of the Differences in Acceleration Effects between the Two Configurations  
In Figures 8 and 9, the velocity variation curves of the armature from the first to the fourth stage in the PP and PN configurations of the launching device are shown in Figures 8a and 9a, respectively. The axial force variation curves are shown in Figures 8b and 9b. The current curves of each drive coil in the PP configuration are shown in Figures 8c and 9c, and the current curves in the PN configuration are shown in Figures 8d and 9d. The armature triggering is performed according to the optimal \(P_{1}\), \(T_{2}\), \(T_{3}\), and \(T_{4}\) obtained from the previous simulation experiments for both the PP and PN configurations. It is observed that in the coil launching device with an inter-stage distance of \(D\) = 15 mm, the optimized PN configuration achieves higher velocity than the PP configuration, which is consistent with the conclusions obtained by scholars in recent years (i.e., reverse current in the coil helps to improve the exit velocity of the armature). However, in the coil launching device with an inter-stage distance of \(D\) = 5 mm, the velocity of the PN configuration does not surpass that of the PP configuration. The following analysis is conducted to explain these phenomena. From Figures 8a and 9a, it can be observed that the armature in the PP configuration of the launching device does not exhibit the armature capture effect after being accelerated by the first three drive coils, but experiences significant deceleration due to a large braking force after leaving the fourth-stage coil. Conversely, the armature in the PN configuration experiences a certain armature capture effect after being accelerated by the first three drive coils, resulting in a decrease in velocity after each stage. However, when it leaves the final-stage coil, there is almost no decrease in velocity. This leads to the PP configuration having a higher exit velocity than the PN configuration for D = 5 mm. The electromagnetic forces acting on the armature in Figures 8b and 9b during the launch process can be correlated with the results in Figures 8a and 9a. For example, the armature in the PN configuration experiences a period of smaller braking forces after being driven by the first three coils, while the armature in the PP configuration only experiences significant deceleration after leaving the final-stage coil. Additionally, the electromagnetic forces acting on each drive coil in the PP configuration occur earlier than in the PN configuration, matching the armature velocity curves. Comparing (c) and (d) in Figures 8 and 9, it can be found that in the PN configuration of the coil launching device, there is a relatively small induced current generated in the subsequent drive coil after the triggering of the drive coil, and when the subsequent drive coil is energized, the current in that coil is enhanced. In the PP configuration, however, a different phenomenon occurs. The energization of the drive coils does not affect the generation of induced currents in the subsequent drive coils but instead rapidly decreases the induced current in the previous drive coil. This is because there are diodes in the drive coils that restrict the flow of current. In the PN configuration of the coil launching device, the current directions in adjacent drive coils are opposite, resulting in the diodes conducting due to the induced electromotive force. In the PP configuration, the current  
Figure 9: The launching situation of the device with an inter-stage distance of \(D\) = 15 mm: (**a**) velocity variation curve; (**b**) force variation curve; (**c**) current curve of PP configuration; and (**d**) current curve of PN configuration. directions in adjacent drive coils are the same, resulting in the induced electromotive force hindering the conduction of the diodes, thus no induced current is generated.