To analyze the turning characteristics of a large-scale skid-steered unmanned ground vehicle (UGV), a mathematical model based on geometric characteristics and kinematics was developed in this work. The turning characteristics, as well as some important geometric and moving features, were seriously considered in the model. A self-designed UGV was employed to conduct targeted experiments. Initial experiment showed that the width of UGV was much larger than that of actual value, because slippage phenomenon made the errors of actual velocity and trajectory length between two sides of the UGV were lower than those obtained from direct wheel velocities measurements and calculations. Further experiments which obtained moving velocity of the UAV by means of a highly accurate Inertial Navigation System (INS) were conducted. Combining this velocity, the slippage levels of the four wheels can be quantitatively measured. In addition, using standard velocities derived from the accurate moving velocity, a true turning radius can be accurately calculated in real time when the slippage characteristics were seriously considered, hence, the mathematical model can be sufficiently validated. The work can realize modelling and dynamic analysis and estimation of the slippage characteristics of this type of UGV.
This work is about the influence rule of inclination of welding torch on the formation and characteristics of weld bead during the pulsed-gas metal arc welding (GMAW) process based on the robotic operation. The inclination of welding torch was an important operation condition during the pulsed-GMAW process, because it can affect the formation and quality of weld bead, which was the output of the process. In this work, the different inclination modes and values were employed to conduct actual welding experiments, and some influence rules can be obtained according to examine the surface topography and cross section. Then, to obtain further rules, serious measurements for the geometry characteristic parameters were conducted and corresponding curve fitting equations between inclination angles and the bead width, penetration and bead height were obtained, and the largest error of these curve fitting equations was 0.117 mm, whose corresponding mean squared error (MSE) was 0.0103. Corresponding verification experiments validated the effectiveness of the curve fittings and showed the second order polynomials were proper, and the largest errors between measurements and curve fitting equations for inclination angle under backward mode were larger than those under forward mode, and were 0.10 mm and 0.15 mm, respectively, which corresponded to the penetration and were below 10%, therefore the equations can be used to predict the geometry of the weld bead. This work can benefit the process and operation optimization of the pulsed-GMAW process, both in the academic researches and actual industrial production.
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