Virtual Assembly Process Simulation for Hybrid Car Battery based on DELMIA

In view of the disadvantages of low assembly efficiency and poor quality of hybrid car battery, this paper researches on the virtual assembly process simulation technology. This paper analyzes the assembly process of the battery firstly. Then, based on the principle that detachable parts can be also assembled orderly, the assembly sequence and path planning of parts and components are implemented in the assembly process simulation platform DPM of DELMIA software, and the simulation process is simultaneously completed in DPM platform. The assembly process is verified, and the interference detection is carried out. Lastly, the ergonomics assembly process simulation is implemented in the Ergonomics module of DELMIA. The assembly motion setting and planning for workers are completed, the walking route is determined, and the relationship between the assembly simulation process of the battery and action of workers is established. The feasibility of assembly process and the reachability of workers are verified. The virtual assembly simulation process proposed in this paper improves assembly quality and assembly efficiency of hybrid car battery.


Introduction
The assembly is a bridge between the design and manufacture, the assembly process design directly affects the product quality and production efficiency.Currently, computers are being applied more and more in the assembly process design.The product design, assembly, analysis and detection are carried out in virtual environment, which gets rid of the traditional product design and development process.Virtual assembly technology can shorten the product development time, improve product quality and reduce product cost and price.At present, many research institutes and teaching institutions in developed countries have made a lot of progress in virtual assembly.In Germany, the FRAUNHOFER industry research institute developed a virtual assembly planning system, which can consider the influence of assembly condition, assembly feature and other factors on the assembly, and realize the man-machine interactive assembly operation and analyze the assembly time and cost [1].Jung et al. developed the virtual assembly system CODY, which is combined with artificial intelligence technology and virtual reality technology, and the product designers can make products by simple language commands or three-dimensional assembly operation based on knowledge and 3D interactive [2].Hermansson et al. of Sweden proposed a low-dimensional path planning algorithm for automatically planning and finding a smooth and collision-free mounting of connectors in a wiring harness installation [3].Garbaya el of France focused on modeling the dynamic behavior of mechanical parts during the execution of virtual assembly operation [4].In America, The NIST institute developed a kind of virtual assembly design environment named as VADE, which explored the virtual manufacturing in virtual environment through assembly planning and assembly evaluation [5].The VPL company developed RB2, DIVISION developed the DVS system, AUTODESK company developed CTL [6].Vyawahare et al. developed a new interaction technique 'Bimanual Stretched String Control of Haptic Workspace Mapping' using a unique combination of spatial interaction device in the domain of virtual assembly [7].
The automotive industry of today is focusing on electrified and hybrid solutions, where both conventional combustion engines and battery supplied electrical engines need to fit in an already densely packed vehicle [3].The clearance of each component must be evaluated with other disciplines and their components.There are some research on the field of path planning [8,9].
In this paper, virtual assembly technology for hybrid car battery is researched.As an important part of the hybrid car, battery is the power supply with the powerful energy.It is not only as a driving power energy, but also provides power to the air conditioning system, power steering system, ignition system, lighting and signal system, wiper and sprinkler, vehicle entertainment music and communications.The design of hybrid car battery, especially the design and verification of assembly process, has always been paid attention to.DELMIA is the digital software developed by French Dassault System, which faces manufacturing process, maintenance process and ergonomic, provides all kinds of definition, simulation and analysis of the manufacturing process, and covers the application of automobile manufacturing, aircraft design, ship manufacturing and other various industry fields.
This paper analyzes battery assembly process, describes assembly process simulation and ergonomics assembly process simulation for hybrid car battery based on DELMIA.

Hybrid car battery structure and assembly process analysis
The hybrid car battery structure is shown in Figure 1.Overall, the battery is mainly composed of two parts: the front part including part covered by the front cover, the rear part including part covered by the upper cover.The part covered by the front cover mainly contains blower, junction box and service pin, which is simple to assemble from the scene feedback.There are many parts in the part covered by the upper cover, the structure is more complex, and so the assembly process is complex.The hierarchical assembly design is adopted in battery assembly, which is the design concept of assembly oriented to improve the assembly ability of the battery.The hierarchical assembly design can reduce the insertion operation and replace it with placement operation.The number of parts has increased somewhat, but the assembly operation becomes simple, and an assembly operation can be completed basically by only one worker.The bracket plate is divided into three parts of the bracket base, the bracket layering piece and the top of the bracket.A trapezoidal groove is processed on both sides of the bracket layering piece, and the trapezoidal groove is longitudinally inserted through the trapezoidal groove on the bracket base.The trapezoidal groove is processed on both sides of the bracket, and the trapezoidal groove is transversally inserted through the lateral trapezoidal groove on the bracket base.The drainage plate is horizontal, and it is mainly positioned with four positioning plates between two bracket layer pieces.The drainage plate is formed by injection molding, deformation is easily generated, so there is the locating pin hole in the drainage plate to prevent the twist deformation of the drainage plate.The drainage plate which is located between the two layers of the battery pack mainly plays the role of guiding the airflow direction.When assembled, the front and rear fixing plate and the bracket layering pieces are fixed firstly, then the drainage plate is inserted, the baffle plate is installed lastly.The hierarchical assembly of the battery is simple and efficient.

Virtual Assembly process simulation
In the virtual environment, the assembly process of battery is simulated by DELMIA software, and the rationality of the assembly process is verified.Figure 2 is the simulation flow of hybrid car battery assembly process.The process of assembly simulation is shown as follows: 1. Three-dimension modeling of battery components and related resources.Before assembly process simulation, the battery parts, the 3D entity model and related resources are established in the three-dimensional mapping software firstly, and assembly hierarchy and assembly constraint relations between battery parts and components are determined.In this way, the 3D solid model of the battery parts and components and related resources can be called directly when the assembly process is simulated.2. Create a virtual assembly environment.The whole simulation process is carried out in virtual environment.The battery parts and components the 3D solid model of related resources are called in the virtual environment, assembly process documents are established, and the production line and tooling equipment are distributed and so on.3. Planning of virtual assembly sequence and assembly path.In the DELMIA assembly process simulation platform, the battery is wholly shown as a product.The location of each part and component is obvious.According to the principle that detachable parts can be also assembled orderly, parts and components of the battery are dissembled, the reverse route of disassembly process is namely the assembly route.
The virtual assembly process of the battery is based on the base plate.The various parts and components of the battery is closed to the base plate from the different space position, and then fixed.
The assembly path of the battery parts and components is created.At the same time, the interference of parts and components is detected to see if there is collision among parts and components.In the process of removing the battery, we get the assembly sequence and assembly path, as shown in Figure 3.

Simulation of assembly process.
The assembly process of battery is simulated in DPM platform of DELMIA software.The simulation includes three processes.Firstly, we initialize the simulation environment.Secondly, the assembly sequence and path are planned.Finally, the assembly process is simulated, and the interference is synchronously detected.The method combining user manual guidance and software automatic search is adopted to plan the battery assembly path.After the assembly process simulation, the relevant reports are generated to guide the actual production process.Figure 4 is the result of the simulation of hybrid car battery assembly process in DELMIA software.5. Simulation analysis.The simulation results of hybrid car battery assembly are analyzed.From Figure 3, the assembly simulation process can directly determine the virtual assembly sequence and assembly path.The assembly body explosion diagram also clearly shows the main sub assembly and components structure.If the assembly sequence and path are not satisfied, it can be modified according to simulation results and actual assembly, until it is satisfied.
The interference detection in the assembly simulation process is carried out by using static, dynamic and movement interference detection method of DELMIA software itself.At the same time, the assembly constrains and assembly error can be detected, and the influence of parts deformation to assembly process can be analyzed.

Ergonomics assembly process simulation
The car battery is assembled with manual assembly, so the staff labor intensity, the commodious operating space and the comfort of gesture become evaluation criteria of assembly process rationality.This work can be completed in the Ergonomics module of DELMIA.In the Ergonomics module, the assembly motion setting and planning for the workers is completed, the walking route is determined, the work task is established and workers assembly process is simulated to analysis labor intensity of workers and assembly reachability.Figure 5 is the ergonomics simulation flow of hybrid car battery assembly process.The 3D solid model of related resources of the battery parts and components are called into DPM platform of DELMIA software firstly.The XY plane is as the datum plane in this paper.Then the contact position and orientation of the products and resources to the floor are determined.In this way, the preparation of the battery assembly is completed, as shown in Figure 6.Worker's movement is planned in ergonomics simulation platform (Human Tast Simulation) of DELMIA.After getting assembly simulation process of the battery in assembly process simulation platform, the movement of workers are inserted into the assembly process simulation platform to connect the battery simulation assembly process with workers.The walking route of workers is shown in Figure 7. Figure 8 is the result of movement execution.
The reachability of workers movement and commodious operating space are verified by ergonomics assembly process simulation of battery, and the assembly process is reasonable in ergonomics.

Conclusion
This paper describes virtual assembly process simulation for hybrid car battery.Based on the principle that detachable parts can be also assembled orderly, the assembly sequence and path planning of parts and components are implemented in the assembly process simulation platform DPM of DELMIA software, and the simulation process is simultaneously completed in DPM platform.The assembly process is verified, and the interference detection is carried out.
The ergonomics assembly process simulation is implemented in the Ergonomics module of DELMIA.In the Ergonomics module, the assembly motion setting and planning for the workers are completed, the walking route is determined, and the relationship between the assembly simulation process of the battery and action of workers is established.The feasibility of assembly process and the reachability of workers are verified.The virtual assembly simulation process put forward in this paper improves assembly quality and assembly efficiency of hybrid car battery.
In the future, we will further research on assembly path planning method to realize the automatic and rapid assembly path planning of hybrid car battery.

Figure 1 .
Figure 1.Parts decomposition diagram of battery structure.

Figure 2 .
Figure 2. The simulation flow of hybrid car battery assembly process.

Figure 3 .
Figure 3.The assembly path of battery parts and components.

Figure 4 .
Figure 4.The result of assembly process simulation of battery.

Figure 5 .
Figure 5.The ergonomics simulation flow of hybrid car battery assembly process.

Figure 6 .
Figure 6.The preparation result of ergonomics simulation.

Figure 7 .
Figure 7.The walking route of workers.

Figure 8 .
Figure 8.The result of movement execution.