# Control Design and Validation for Floating Piston Electro-Pneumatic Gearbox Actuator
## 4 Controller Testing and Tuning on Test Bench
### Discussion on Results  
Table 5 presents the intervals of the controller performances measured with supply pressure between 6 and 9 bar. Similarly to the simulations, the LQR controller failed in all Gear to Neutral shifts, as it either gets stuck in an intermediate position of the cylinder or clearly exceeds one of the given  
Figure 10: LQR controller—Neutral to High gear changes (measurement). limits (for instance it achieves 6 mm overshoot or 200 ms shift time); thus, there is no need to analyze these cases, whereas the PID controller meets all the requirements in these test cases. To find the explanation of the failure of the LQR controller is an important task. The linearized models are both controllable and observable, and all individual controllers are stable. The high speed of the system may cause large transients during switching between the controllers around Neutral, which cannot be handled with the given control frequency in practice. However, as the controller achieved Neutral to Gear shifts with acceptable overall performances, it can be used for the high accuracy control of single-piston actuators. Therefore, in the current industrial application, this approach is not applied in this control task. During Neutral to Low gear changes, both controllers performed well, but at first sight, the LQR control slightly exceeded the collision speed in the case of 9 bar supply pressure, while switching the actuator to Low. However, oppositely to the simulations, the exact position of collision is not known, as the movement of the mechanism is limited outside of the cylinder, thus the collision speed was assumed to be equal to the piston velocity at reaching 90% of the reference position. This way, the impact velocity is clearly overestimated, while its direct measurement was also not possible; therefore, against the small excess of the collision speed, the LQR controller shall be accepted. In the case of Low to Neutral and High to Neutral gear changes, only the PID controller were able to meet the requirements. Based on the results, there is a massive difference between the two gear change regarding shift time, which can be explained by the geometry of the cylinder. Due to the Floating Piston, the difference of the piston areas affected by the chamber pressures is much bigger between Neutral and High position of the actuator. Therefore, the High to Neutral gear changes are much faster, which causes overshoot. The last case is the Neutral to High gear change. As it was shown in Figures 9 and 10, there is no significant difference between the controllers, the LQR controller achieves slightly faster gear changes and higher collision speeds. In industrial application, such systems are often controlled by Open-loop controllers, where the solenoid valve commands are determined as follows. * Switching to Neutral is achieved by loading both chambers at the same time. * Switching to Gear is achieved by the asymmetric activation of the solenoid valves, thus the collision speed can be minimized by increasing the opposite chamber's pressure. Open-loop methods designed along these principles perform well concerning the collision speed and overshoot, as they significantly increase the counter-side chamber's pressure. Although, as this damping effect is applied at the start of the gear change, it will affect the whole movement, instead of only slowing down the piston at a later position, which results in slower overall movement and higher shift time. However, they always use two solenoid valve commands to achieve gear change. However, gear changes can be achieved much faster with a single valve activation due to the natural damping caused by the decreasing counter-side chamber volume and still meeting all of the requirements with the presented closed-loop controllers, while if it is needed they activate the counter-side chamber's valve at later position to prevent overshoot or high collision speed.