Virtual maintenance simulation technology in civil aircraft engineering

Based on the requirements and characteristics of civil aircraft maintainability design, virtual simulation technology is introduced into aircraft maintainability design, analysis, and verification. This paper presents the flow of virtual maintenance simulation through visual analysis, physical accessibility analysis, and operational space analysis. A method of virtual maintenance simulation accessibility analysis is presented. The evaluation of virtual simulation design is realized. In the design stage, through the virtual maintenance simulation analysis, the design factors affecting maintenance and potential maintenance hazards are found in advance. A timely improvement is made to improve the level of aircraft maintainability design and reduce later maintenance costs.


Introduction
Maintainability is the inherent characteristic of the product that makes product maintenance simple, rapid, and economical; it is given by product design and must be considered in design [1].Although maintainability design is carried out in parallel with aircraft design, its defects are usually not discovered until the manufacturing stage or even the use and maintenance stage.
It is necessary to adopt advanced and effective maintainability analysis, verification, and evaluation techniques to find maintainability design defects in time from the overall design stage; in this way, we can avoid the time lag of maintainability work and provide basic information for maintenance support analysis, maintenance data compilation, maintenance training, and other work [2].
Virtual maintenance simulation analysis replaces the physical prototype with the computer-based prototype [3].It simulates the maintenance process of the aircraft with the digital prototype.It verifies and evaluates the maintainability of the aircraft.It overcomes the shortcomings of the physical prototype, such as a long manufacturing cycle, high cost, and difficult modification.It finds the possible maintainability problems in the aircraft design as early as possible.It is of great significance to ensure aircraft quality and reliability, reduce aircraft maintenance costs, and shorten aircraft design cycles [4].

Virtual maintenance simulation system
A virtual maintenance environment is a virtual place for maintenance operations.The virtual maintenance simulation design and verification of aircraft should be based on the establishment of a virtual maintenance environment, implemented according to maintainability analysis requirements [5].In this paper, a virtual maintenance system is developed by combining DELMIA software.

Overall framework
The method of "virtual human maintenance virtual product" is adopted to realize the simulation of the virtual maintenance process for the purpose of product maintainability analysis and verification [6].Therefore, a design-centered virtual maintenance system is established [7].A complete virtual maintenance system should include a virtual human model, maintenance objects realized based on digital prototype technology, maintenance tools, maintenance scenarios, maintenance process simulation model, human-computer interaction interface, etc.Its composition framework is shown in Figure 1.

Human body library
Tool model library

Human modeling
Tool modeling

Digital prototype
Maintenance scenario

Virtual maintenance process modeling
Maintenance process simulation analysis

Virtual maintenance environment
Maintenance process

Man-machine interaction interface
Human factor analysis index Human

Maintainability evaluation
Ergonomic evaluation

Virtual maintenance simulation process
The maintainability requirements of the analysis object and the components of the virtual environment are determined.The digital prototype model is imported.According to maintainability requirements and maintenance instructions of analysis objects, maintenance tasks are decomposed.Appropriate maintenance tools are selected to conduct maintenance simulation and analysis in a virtual environment, and a virtual maintenance analysis report is finally formed [8].The process is shown in Figure 2.

Virtual maintenance accessibility analysis
The core of virtual maintenance is the simulation of the maintenance operation process.In the process of virtual maintenance simulation, a series of key technologies need to be solved [9].This paper will conduct in-depth research on maintenance accessibility technology [10].Maintenance accessibility refers to the relative ease of accessing different components of a product when maintaining it [11].The reachability analysis of virtual maintenance includes visual reachability, physical reachability, and operational space.

Visual reachability
The feasible solution space of the visual position of the eye is determined by constructing the visual field of the maintenance part.On this basis, the visual cone is constructed from the physiological visual field area of the human eye.The visual reachability of the maintenance part is evaluated according to the area in the visual cone.The visibility evaluation is scored according to the distribution position of the repair part in the observed field of view.Specific scores are shown in Table 1 below.The higher the level of the final analysis, the less visibility.Table 1.Visual accessibility analysis.

Score Description Analysis level 1
The maintenance part is visible in the optimal cone area with good visibility.I 2 The maintenance part is located in the largest cone area, and the best visibility can be achieved by adjusting the attitude, and the visibility is good.3 The maintenance part is located in the largest cone area, and the best visibility in the cone cannot be achieved by adjusting the attitude, and the visibility is not good.II 4 The maintenance part is located in the invisible area, and the maximum cone visibility can be achieved by adjusting the attitude, and the visibility is general.5 The maintenance part is located in the invisible area, and the maximum cone visibility cannot be achieved by adjusting the attitude, and the visibility is poor.III

Physical reachability
In the process of virtual maintenance, it is often necessary to determine whether the maintenance is comfortable for people at this point according to the distance between the standing position of the person and the maintenance part, combined with ergonomic factors.Accessibility evaluation is scored according to the distance between maintenance objects and maintenance personnel and whether there are obstacles between personnel and equipment.Specific scores are shown in Table 2 below.The higher the level of the final analysis is, the worse the entity can reach.Table 2. Physical reachability analysis.

Score Description Analysis level 1
The equipment is located within the reachability range, and there are no obstacles between the equipment and personnel, and the reachability is good.

I 2
The equipment is located in the reachability range, and there are obstacles between the equipment and personnel.The reachability can be reached by adjusting the attitude.II 3 The equipment is located outside the reachability range and can be reachability by adjusting the attitude.4 The equipment is located in the reachability range, there are obstacles between the equipment and personnel, and it is also unreachable by adjusting the attitude.Other components need to be removed during maintenance, and the reachability is poor.III 5 The equipment is outside the reachability range and cannot be reachability by adjusting the attitude.

Operational space
Evaluation of operation space based on virtual maintenance environment Through the maintenance movement simulation and real-time collision detection of the tool, the satisfaction of the movement space is analyzed.Specific scores are shown in Table 3 below.The space analysis of arms and tools of maintenance personnel in the maintenance process is important.The higher the maintenance level is, the smaller the operating space is.Suggestions should be provided for the design of the operating space.The maintenance operation space and channel space are sufficient, and the maintenance operation is good.I 2 Maintenance operation space and channel space have enough space for personnel related maintenance operations, but they are relatively cramped.

II 3
Insufficient maintenance operation space and access space.III

Aircraft project application
Taking an enclosure in the wing box segment of an aircraft of a certain model as an example, a virtual maintenance environment was built.The accessibility of its interior was simulated by virtual maintenance simulation.The simulation object was the hydraulic pipeline connection joint, as shown in Figure 3. DELMIA software is used to simulate the Hydraulic line connecting connector and carry out a virtual simulation analysis, as shown in Figure 4.According to the results of the simulation analysis, they are scored, and the rating level is shown in Table 4.As can be seen from Table 4, when maintaining the connection joints in this area, the maintenance personnel have poor visibility, poor accessibility, and poor operating space.
Table 4. Accessibility analysis score level.

Score Description Analysis level
Visual accessibility When maintaining connecting connector 1, the visual field in the maximum cone is partially blocked by the pipeline, and the visibility is poor; When maintaining connecting connector 2, the field of view in the largest cone is blocked by the pipeline, resulting in poor visibility.

I Reachability, physical
When maintaining connecting connector 1, the maintenance personnel can reach it by adjusting the attitude, but there are obstacles in the middle, and the accessibility is normal; When maintaining connecting connector 2, the maintenance personnel can adjust the attitude, but there are obstacles in the middle, and the reachability is normal.

II Operational space
When maintaining connecting connector 1, the operation space of the maintenance personnel is limited, and the left and right hands interfere with the pipe.When maintaining connecting connector 2, the operation space of the maintenance personnel is limited, and the left and right hands interfere with the pipes.

Conclusion
Virtual maintenance is an effective method to improve the quality of aircraft maintainability design, and the key to its realization lies in the virtual design environment.In this paper, the maintainability accessibility of aircraft in the DELMIA environment is discussed qualitatively.It provides a technical approach for virtual maintainability design and visual and reachability analysis of aircraft systems and can be used as a reference for developing the virtual maintenance analysis and evaluation system.