# Collaborative Robotics: Enhance Maintenance Procedures on Primary Flight Control Servo-Actuators
## 5 Advantages and Disadvantages of the Proposed Application  
Since each servo-actuator must be repaired according to precise instructions reported on its maintenance manual, the tasks commanded to the robot are very similar to the ones currently performed by the technicians in the test field. The goal of a partial automation of the repair process is to increase the operators' safety and to acquire more data to be used, together with the ones obtained with the HyDiag entry and exit tests, for health features extraction. With respect to standard manual procedures, the economic advantage of this approach does not rely on repairing the single faulty unit with a robot, but on the better estimate of its operating conditions. This leads to a better fault detection, a more reliable maintenance of EHSAs, and a decrease in the number of times a servo-actuator must be dismounted from the aircraft and repaired. By detecting the root cause of a failure, the repair operations would be more efficient since the technician would know exactly which component must be replaced. In addition, the implementation of prognostics algorithms would help to identify elements of the unit that, even if still in nominal conditions, are likely to fail soon. Replacing these components when the EHSA is already dismounted from the aircraft would increase the Mean Time Between Failures (MTBF), eventually preventing the occurrence of unanticipated failures.  
The research campaign proved the feasibility of performing complex tasks, such as repairing servo-actuators used to regulate the position of primary flight control surfaces, with collaborative manipulators. The preliminary results suggest that, by using an industrial manipulator, it is possible to have a more accurate adjustment of the servo-actuator. The control algorithm is designed to bring a desired quantity within a specific threshold and to reach the optimal target value. This is often a critical aspect in manual operations, due to the high correlation between the control quantity and the adjustment in the rotation of the regulation mechanism. As an example, in the case study of the RVDT sensor, the difference between the voltages of its secondary coils must be within the range of \(\pm 15\) mV. However, since the dependency of the \(\Delta\)U voltage with the orientation of the RVDT has been estimated to be about 120 mV/\({}^{\circ}\), to bring \(\Delta\)U as close as possible to the center of the acceptability interval would require exact actions. Using the proportional control algorithm described in Figure 9, this is possible with a robot, while it requires high efforts to a technician.  
On the other hand, these components are not subjected to scheduled maintenance, but they are only repaired when a failure occurs, and the root cause is often unknown. Moreover, especially for old units, it can happen that a safety screw is stuck and so it cannot be loosened by the robot, compromising its adjustment. Moreover, the EHSA has to be manually prepared by the operator before launching the automatic adjustment. This process comprehends tasks such as cutting the safety-wires, which assures the screws not to be loosened, and mounting the unit on the fixture.