Research of data transmission path of neutral file between Pro/E and ADAMS*

Mei-fa HUANG，Bao-feng MO，Meng-meng XIAO

School of Mechatronic Engineering，Guilin University of Electronic Technology，Guilin 541004，China

1.Introduction

VPT(virtual prototyping technology)is a new technology in the current areas of design and manufacture，which can establish three-dimensional entity model and kinematics model of mechanical system by using computer software.Meanwhile it can analyze and evaluate the performance of the mechanical system，providing the basis for design and manufacture of mechanical products［1-2］.ADAMS(automatic dynamic analysis of mechanical systems)，and Pro/E software are commonly used in the virtual prototype technology.

ADAMS has a powerful post-processing module and friendly man-machine interface，whose simulation analysis is in the important significance of reference value.Pro/E is comprehensive three-dimensional software that integrates the function of CAD/CAM/CAE，possessing very strong three-dimensional modeling capabilities.Among the current development of complex mechanical system，the more popular solution is to use Pro/E to construct 3D modeling，then import it into the ADAMS to conduct kinematics and dynamics analysis，which can meet the research needs well［3］.Due that CAD software and dynamic simulation software are two different kinds of products，a series of problems such as graphical information data exchange will occur in the process of passing model.How to choose graphic data transmission path between Pro/E and ADAMS to avoid the shortcomings mentioned above and get the best result is an inevitable problem，especially for technician to conduct the development of VPT by using Pro/E and ADAMS.

The ways of importing the model into ADAMS from Pro/E can be generally divided into kinds.One way is to conduct seamless connection by Mechanism/Pro，a special data interface between Pro/E and ADAMS.The other way is to save the model as a neutral file supported by two software，and then import it into ADAMS by reading［4］.The advantage of first kind of method is to define model to conduct simulation analysis without quitting Pro/E interface，while the shortcoming is that it will often cause trans-mission failure because of being unable of identifying reading path when transport model is complex.The advantage of the second kind of method is to provide a variety of neutral files for users to choose，while the shortcoming is that it will cause the phenomenon of lacking of line and angle，which can’t ensure the quality of model strictly.Now，for the transmission path of special data interface，there have been more professional teaching books and video to consult.The further introduction won’t be discussed here.Taking the model of five-axis linkage milling head as an example，this paper mainly discuss the transmission between the Pro/E and ADAMS software for the model in kinds of the neutral files.

2.The neutral file supported by Pro/E and ADAMS

The neutral files supported by Pro/E and ADAMS software are mainly:* .stp，* .slp，* .stl，* .igs，* .x_t，* .obj.

2.1.The* .stp file

Stp，a kind of CAD file format conforming to STEP international standard(ISO 10303)，is internationally recognized as the global uniform standard of CAD data file exchange.Our country also formulates the corresponding national standards based on STEP international standard like many countries in the world，whose standard is GB16656［5］.The problems existing in the STEP standard are that too tremendous entire system，slow process of setting standard，and larger generated data than the file of IGES format.

Figure 1.Five-axis milling head model in Pro/E

STP format is more commonly used in the design of 3D CAD，because it has good compatibility for each CAD software and the basic data will not lost when transmitted in the CAD software which will be easy to lose data between CAD and other software.From the Figure 2，it can be seen that part information of electric spindle of five-axis linkage milling head mode，breaking surface and losing surface will appear when the data is transmitted by using the STP format between Pro/E and ADAMS which will damage the model.What’s more，it takes a long time when STP file format is imported into ADAMS，especially unsuitable for the large transduction and complex model.

Figure 2.Five-axis milling head model of stp format

2.2.The* .slp file

Slp file is a common standard format of data exchange.The parts precision outputted by Pro/E can be adjusted by deviation control，the smaller the deviation value is set，the higher the precision of the model.The higher the model accuracy，the greater the output file，the time will also be longer.So the deviation control should be set reasonably，usually by selecting the default values.

The precision is higher and surface quality is better when data is exchanged in the form of slp between Pro/E and ADMS，and there is no occurrence of wrinkled surface and lost surface.But it is just suitable for transmitting parts;the information will lose when transmitting assembly，which will lead to the failure of transmission，as shown in Figure 3.

Figure 3.Five-axis milling head model of slp format

2.3.The* .stl file

Since stl file was developed by three-dimensional systems company，it used triangular facets to represent three-dimensional solid model.Now it has become a standard file of CAD/CAM system interface formats，and most modeling systems can support and generate such a format［6］.

There are two ways to generate stl files of Pro/E，one is a binary format，the other is the ASC Ⅱcode format.Special attention should be paid to the output file in Pro/E，which cannot be identified by ADAMS when files generate a binary format，so ASCⅡcode must be chosen to transfer data smoothly between two software.Stl files are imported into the ADAMS in the form of shell，and material properties of spare parts can’t be defined after importing.As shown in Figure 4，five-axis milling head model becomes a whole，but can’t be simulated.

Figure 4.Five-axis milling head model of stl format

2.4.The* .igs file

Igs files are generated by Iges standard，mainly used for conversion and transmission of file，such as three-dimensional surface model and three-dimensional solid model between different three-dimensional software.Our country has recommended the IGES 3.0 as a national standard in September，1993.

The surface quality is relatively smooth after the five-axis milling head model is imported into ADAMS by the form of igs，basically no loss of pattern features.But surface quality is unstable after conversion，sometimes phenomenon of wrinkled surface appears.And only simple geometric model information can be imported，while additional information can be lost easily.As shown in Figure 5，we pay more attention to the selection of export form between entity and shell when importing the model into ADAMS.If imported by the form of housing，the material properties can’t be defined and simulated effectively，so models of igs format generally use the"entity"form when imported.

Figure 5.Five-axis milling head model of igs format

2.5.The* .x_t file

X_T file as the earliest neutral file，outputted by parasolid module of UG，can be used in the other software supported by other format.As x_t file has good compatibility，and the converted file is relatively small，easy to transport and use.It’s now commonly used as a neutral file supported by a variety of softwares.

Pro/E will automatically create a file to save the each part information and assembly information for model when the model is imported into ADAMS.After defining and adding the constraint of material properties for assembly，the required analysis can be conducted.From Figure 6，it can be seen that the surface quality of the imported model is not perfect，the original smooth round surface turns into a polygon surface and wrinkled surface appears，but this does not affect the subsequent analysis.

Figure 6.Ive-axis milling head model of x_t format

2.6.The* .obj file

Obj file is a three-dimensional file format，mainly supporting polygon model，the surface above three points，normal and texture coordinates［7］.It can be directly opened by Word Pad to edit and modify，and is very useful for data transduction between models in the three-dimensional software.Obj file is a broad applicability neutralfile，almostallwell-known three-dimensional software support the reading and writing of obj files，but many of them need the plug to achieve.

Due to the version and system，sometime wrinkle will appear on the surface after the model is imported into ADAMS in the form of obj.But after many trials，there is no occurrence of information leakage and it does not affect the subsequent analysis research，as shown in Figure 7.Before defining the material properties of the parts，we can merge unimportant parts into a whole and define the material properties by using Boolean operation.Then we add the Marker points，constraints，power supply，etc.，and analyze at last，which can effectively reduce the total work and improve the work efficiency.

Figure 7.Five-axis milling head model of obj format

3.Analysis of experimental results

This paper jointly set up 3D model for the research of dynamic analysis by using Pro/E and ADAMS，firstly considering the problem of data transfer between them.And the most important thing in the process of transmitting data is to ensure the integrity，continuity and stability of the model information and balance transmission efficiency.Its main features as below:

① The phenomenon of wrinkled surface，crumpled surface，and lost surface can’t appear after model transmission as much as possible.

②The phenomenon of the error information or missing information can not appear before and after transmitting the information of model.

③The work can be done after finishing the model transmission，which makes analysis and research work go on in rapid succession between them.

④ The processofmodeltransconductance should be convenient and quick，efficient and reliable in order to improve the work efficiency.

Taking the model of five-axis linkage milling head as an example，several neutral files supported by Pro/E and ADAMS are analyzed and studied specifically.Establish a model of five-axis linkage milling head in software of Pro/E，and define the properties of components.Add constraints and verify the accuracy of the model through the interference checking.Then the model is separately saved to working directory in the neutral file format of* .stp，* .slp，* .stl，* .igs，* .x_t，* .obj.Finally，copy the saved neutral files to the ADAMS working directory and use the key of import in the file menu of ADAMS to read each neutral file.Click the button of model in the view and the file is displayed in the ADAMS.

The Stp format is the slowest considering the conversion speed when Stp Slp Stp are transferred to ADAMS，and the others are relatively fast.The surface quality is very good after SLP and STL format conversion，but the assembly information of model is lost，leading to the failure of simulation.The situation is mainly used in the simple conversion of parts and assembly，not for turning surface.Parts model established in Pro/E can be imported into ADAMS in the format of SLP and STL format one by one to conduct assembly simulation.This kind of practice is feasible for the simple assembly.However，it will be amount of workload and wasting of resources for complex assembly model.

The conversion speed of Igs format is slow and must be in the form of an entity when imported.Otherwise，it is unable to define material properties，leading to the failure of simulation.The information of quality and color is not easier to lose，which is not suitable for transmitting file between Pro/E and ADAMS.Igs format is often used to convert surface，whose surface quality is better，but not for entities.

The transmission speed of x_t file and obj file is faster and the transmission won’t lose the assembly information of model.And it will automatically create the information of a separate part to distinguish each entity，making sure to get the feature information of assembly effectively.Sometimes wrinkled surface appears in the transformation model，but this does not affect its overall quality and follow-up studies，as shown in Table 1.

Table 1.The results of data exchange for each neutral file

4.Conclusion

In the case of five-axis linkage milling head，this paper mainly studies and analyzes many kinds of the neutral file supported by the Pro/E and ADAMS software，summarizing the characteristics of data transmission of the neutral file，the problems that should be paid attention to when used and the applicability after conversion.In addition，the superiority of data conversion between Pro/E and ADAMS software for* .x_t file and* .obj file is shown，which has certain guiding significance for those who use Pro/E and ADAMS for unite-modeling to conduct dynamics analysis.

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