Abstract: This paper uses CAXA drawing software and ADAMS mechanical system simulation analysis software to conduct dynamic analysis of a six-bar linkage. Compared with traditional graphical and analytical methods, both computer-aided methods have higher calculation speed and accuracy. By comparing the analysis results of the two software programs, the advantages and disadvantages of each computer-aided method in dynamic analysis of mechanisms are pointed out. However, ADAMS software shows its powerful advantages of high efficiency and high accuracy, especially for the analysis of complex mechanisms. Keywords: Dynamic analysis; Computer-aided method; CAXA; ADAMS Introduction: In mechanical design, the dynamic analysis of mechanisms plays an important role in the design of machinery, and analysis is the foundation of design. Common analysis methods include graphical and analytical methods, the theoretical basis of which is the relevant theory of kinematics and dynamics in theoretical mechanics. The graphical method is characterized by its visual and intuitive nature, and is easy to understand. It has always been widely used as an important method for analyzing and solving problems. However, in the past, when using manual graphical methods to analyze mechanisms, the second-order cumulative error was very large. This error was related to the drawing tools, the scale of the graphics, the order of drawing, and the experience of the designers, resulting in problems such as low accuracy and low efficiency. Moreover, analyzing a series of positions of the mechanism required repeated drawing, which was quite tedious and greatly limited the application of graphical methods. The characteristic of analytical methods is that they express the known parameters and motion variables and the unknown motion variables in the mechanism using mathematical formulas, establish a mathematical model of the mechanism, and then solve it. Therefore, once the analytical formula is established, the calculation of motion variables of the mechanism at various positions is very convenient and can achieve high calculation accuracy. Its disadvantages are that it is not as visual and intuitive as the graphical method, the mathematical model of the problem is more difficult to establish, the formula derivation process is tedious, and the equations of the model are sometimes difficult to solve. For these two basic methods, this paper applies computer-aided analysis, using CAXA drawing software and ADAMS mechanical system dynamics simulation analysis software to effectively solve the shortcomings of each method. The following is a dynamic analysis of a six-bar linkage as an example. 1 Computer-Aided Graphical Method The computer-aided graphical method fully utilizes the computer's high-speed and accurate calculation capabilities and powerful graphic display capabilities. By using general two-dimensional or three-dimensional CAD graphics software, geometric figures can be drawn and a small amount of analysis and calculation can be performed to obtain highly accurate analysis results. Taking the six-bar linkage shown in Figure 1 as an example, the method and main steps of using CAXA drawing software for kinematic and dynamic analysis are explained. Among them, component 1, namely crank OA, rotates counterclockwise at a speed of n=200 rpm. A load P of 500N is applied at the bottom of the slider. The direction of P is always opposite to the direction of movement of the slider. The basic structural parameters and performance parameters of the mechanism are shown in Table 1 and Table 2. 1) Determine the speed and acceleration of the slider; 2) Determine the driving torque of the crank. [align=center] Figure 1 Schematic diagram of the mechanism[/align] The method and main steps are as follows: (1) Analyze the composition and motion of the mechanism and draw a simplified kinematic diagram of the mechanism. Set an appropriate length scale, determine the relative position of each kinematic pair, take six positions for analysis, and draw simplified kinematic diagrams of the mechanism at the six positions respectively. (2) First, perform kinematic analysis on the six positions. Based on the principle of motion composition, establish the velocity vector equation, set an appropriate velocity scale, draw the velocity polygon, and solve for the angular velocity of the driven member and the velocity of the points on the component; then establish the acceleration vector equation, set an appropriate acceleration scale, draw the acceleration polygon, and solve for the angular acceleration of the driven member and the acceleration of the points on the component. (3) Then, perform dynamic analysis on the six positions. According to d'Alembert's principle, the inertial force can be regarded as a general external force applied to the component that generates the inertial force, and the mechanism can be regarded as an equilibrium state. Then, the static method is used to perform force analysis. When calculating the inertial force and the inertial torque, the results of the kinematic analysis are used, namely the acceleration of the center of mass and the angular acceleration of each component. Then, according to the simplification method of the inertial force system, a principal inertial vector is synthesized, and its point of application does not pass through the center of mass. When constructing the force polygon, the velocity polygon lever method is used. The entire velocity polygon is rotated (clockwise or counterclockwise). Then, according to the principle of the velocity image method, all external forces and inertial forces of the mechanism are applied to the corresponding positions on the velocity polygon diagram. An appropriate force scale is set, and the velocity polygon after the rotation is treated as a rigid lever. With the pole as the fulcrum, according to the lever equilibrium condition, the moments of each force about the velocity pole are calculated to obtain the balancing forces and moments acting on the crank. When using CAXA software for plotting, the functions of copying, translating, rotating, scaling, dimensioning, and precise point selection should be fully utilized to achieve efficient and accurate plotting and ensure solution accuracy. Finally, through measurement and calculation, the velocity, acceleration, and balancing moments acting on the crank of the slider are obtained. These data are recorded in EXCEL (note: save as .csv format), then imported into ADAMS software to generate curves for comparison with the simulation analysis results of ADAMS software. 2. Computer-Aided Analysis Method The following analysis of the six-bar linkage is performed using ADAMS mechanical system dynamics simulation analysis software. ADAMS uses the Lagrange equation method in the widely popular multi-rigid-body system dynamics theory to establish the dynamic equations of the system. It uses the Cartesian coordinates of the center of mass of the rigid body and the Euler angles or generalized Euler angles that reflect the displacement of the rigid body as generalized coordinates. It uses the Lagrange equation with multipliers to deal with complete or non-holonomic constrained systems with redundant coordinates and derives the kinematic equations with Cartesian generalized coordinates as variables. The calculation program of ADAMS uses Gear's rigid integral algorithm and sparse matrix algorithm, which greatly improves the calculation efficiency [3]. The core of ADAMS software is the kinematic and dynamic modeling theory of multi-body systems and its technical implementation. Through geometric modeling, the mechanism is concretized into a solid model with physical characteristics of mass and rotational inertia. Then, loads and constraints are applied to determine the connection between objects and how objects move relative to each other. Then, through simulation, the entire motion process is simulated to check whether the motion interferes and whether the mechanism has definite motion. After simulation, the velocity, acceleration and force of each component are obtained by measurement. Then, the measurement results are analyzed by calling the post-processing module ADAMS/PostProcessor. Figure 2 shows the simulation results using ADAMS software, including the geometric model of the six-bar linkage, the velocity and acceleration curves of the slider, and the driving torque curve acting on the crank. During modeling, special attention must be paid to whether the positions of the kinematic pairs at the connections of each component coincide. This must be determined by checking the coordinate values; otherwise, interference or errors in the operation results may occur. When applying force to the slider, because it is a production resistance, the direction of the force is always opposite to the direction of slider movement. Therefore, it must be defined using the function expression SIGN(500, -vy(slider.cm, MARKER_32, slider.cm)), where slider.cm is the component to which the force is applied, and MARKER_32 is the marker point of the force application. Figure 3 shows the curve of the production resistance acting on the slider over time. Through the analysis of the entire process, the key to using ADAMS software is to correctly perform geometric modeling, apply loads and constraints. Once the model is established, the kinematic and dynamic data of each component can be easily obtained through measurement without the need for complex mathematical modeling and calculation. Figure 2 Simulation analysis results Figure 3 Production resistance curve acting on the slider Figure 3 Result analysis and comparison In the ADAMS/PostProcessor interface, import the data from the graphical analysis. Generate corresponding graphical curves of velocity, acceleration, and driving torque acting on the crank as a function of the crank angle on the curves corresponding to the simulation analysis results, as shown in Figures 4 and 5. The solid lines represent the simulation result curves, and the dashed lines represent the graphical result curves. Overlapping the two curves in one figure allows for clear analysis and comparison. Figures 4 and 5 show that the results of velocity and acceleration analysis using the two methods are very close, indicating that the graphical method using CAXA plotting software can achieve the accuracy of the analytical method. However, in dynamic analysis, the results of the two methods differ significantly. The main reasons are: Figure 4 Comparison of velocity and acceleration of the slider Figure 5 Comparison of driving torque acting on the crank 1) When performing force analysis using the graphical method, the results of motion analysis are used. Due to the accumulation of multiple errors during plotting and calculation, the difference becomes larger. 2) When using graphical analysis, to simplify the plotting, the mass and moment of inertia of some components are often ignored. In this example, the masses of components 1 and 4 are ignored. However, when using ADAMS software, each component must have mass and moment of inertia; otherwise, an error message will pop up. This is a major reason for the difference in results. 3) Graphical analysis can only be performed on a limited number of locations. This example uses six points, which inevitably leads to a large error in the resulting curve. ADAMS software, on the other hand, uses 500 data points during one crank revolution to produce the curve, hence the difference in curves between the two methods. Clearly, the analysis results from ADAMS software are much more accurate. 4. Conclusion When performing velocity and acceleration analysis on the mechanism, the results from both methods are very close, with high accuracy. However, when performing force analysis, the results from the two methods differ significantly. The main reason is that ADAMS software considers more comprehensive factors, thus resulting in higher accuracy. However, using ADAMS simulation software requires high precision in modeling, constraint application, motion, and load handling. The mathematical modeling and calculation process is not always clear, and problems can be difficult to detect if not handled properly. Both methods have their advantages. The graphical method is easier to understand, so it can be used to qualitatively verify the results of ADAMS operation. ADAMS software, on the other hand, offers higher computational efficiency and accuracy, and can perform parametric modeling and dynamic analysis of flexible bodies—functions that the graphical method cannot achieve. The author's innovation lies in comparing the two methods of computer-aided analysis of mechanism dynamics, highlighting their respective advantages and disadvantages. With the development of modern machinery, higher demands are placed on machine speed and accuracy, and system structures have become more complex. ADAMS software demonstrates strong advantages in mechanism motion and dynamic analysis, but the computer-aided graphical method remains a useful approach for the motion analysis of simple planar mechanisms. References [1] Theoretical Mechanics Teaching and Research Group of Harbin Institute of Technology. Theoretical Mechanics. Beijing: Higher Education Press, 2001 [2] Wang Guoqiang, Zhang Jinping, Ma Ruoding. Virtual Prototype Technology and Its Practice in ADAMS [M]. Xi'an: Northwestern Polytechnical University Press, 2002 [3] Li Jun, Xing Junwen, Qin Wenjie. ADAMS Example Tutorial [M]. Beijing: Beijing University of Science and Technology Press, 2002 [4] Zhu Youmin, Jiang Yujin. Mechanical Principles. Chongqing: Chongqing University Press, 1986 [5] Du Yuming, Cui Xiangqun. Virtual Prototype Technology and Its Application in Mechanism Design [J]. Journal of Xingtai Vocational and Technical College, 2003, 10 (5): 33-36. [6] Ding Shoubin, Chang Zongyu. Interface between ADAMS and Commonly Used CAD Software [J]. Microcomputer Information, 2005, 10X: 202-204. About the author: Sun Hongxia (1970-), female (Han nationality), from Weinan, Shaanxi Province, is a doctoral candidate at China Agricultural University and an associate professor at Ningxia University. Her main research area is mechanical CAD.