# Collaborative Robotics: Enhance Maintenance Procedures on Primary Flight Control Servo-Actuators
###### Abstract
If one or more tests, reported on the Maintenance Manual (MM) of the unit, fail, the EHSA is sent to the workshop where experienced technicians replace the non-functional components. The unit is then tested to be compliant with the requirements defined by the  
Figure 1: (**a**) Scheme of the actual maintenance procedures for EHSAs adopted by Lufthansa Technik AG; (**b**) Scheme of the enhanced maintenance procedures for EHSAs developed in the HyDiag project. Original Equipment Manufacturer (OEM). More in detail, the test procedure requires many manual adjustments to regulate specific outputs of the unit under test. Only when all the functional tests are passed, the servo-actuator is considered serviceable; if not, the entire testing process is repeated. Since this approach does not include an accurate analysis of the unit health status, it may require several adjustments and repair loops, resulting in a considerable loss of time and increment of the maintenance costs. To reduce the number of testing loops and, at the same time, have a better knowledge of the root cause of the failure, a new semi-automatic maintenance procedure, reported in Figure 1b, has been developed. The first step consists of an automatic entry test [13] where an excitation signal is commanded to the UUT to extract Health Features (HFs). These data will be later used to better identify the health status of the entire servo-actuator. Additional health features are obtained using a collaborative robot that regulates different elements (i.e., screws) on the faulty unit. This is done to evaluate the EHSA response to the aforementioned signal under different operating conditions. This approach not only guarantees the operators' safety, but it assures high repeatability of the process. The results of these tests are collected into an automatically generated trouble-shooting document. Since this information derives from a more accurate and reliable investigation on the overhaul status of the EHSA, it is more likely that the root cause of the failure is detected. The replacement of faulty sub-components is then performed by technicians, according to the instructions reported on the trouble-shooting document. The industrial manipulator is also used to achieve more accurate regulations of the EHSA during the adjustment procedure, leading to better respect the acceptability thresholds defined by the maintenance manual. Following the adjustments, an automatic exit test, which combines the HyDiag entry test and the robot features extraction, is performed. The last step is the OEM certification test that remains mandatory before being able to mount the unit back on the aircraft. On the contrary, if the HyDiag exit test is failed, a new trouble-shooting document is automatically generated, and the faulty servo-actuator is brought back to the workshop to be repaired. Nevertheless, due to more in-depth, and precise knowledge of the actual health status of the EHSA, given by the evaluation of the extracted health features, the project aims to avoid any iteration between testing and repairing operations, leading to a reduction in both maintenance costs and time.