Study on Automatic Centering Operations of Varieties of Workpieces Based on Non-linear Dynamic Analyzes of Contact Surfaces

工件的定心操作是计算机辅助制造（CAM）中尚未建立自动化的最耗时的工作之一。作为定心操作自动化的基础研究，提出了定心操作自动化所需的分析模型和方法。首先，使用实验设备观察当用锤子施加脉冲力时工件的运动行为，并测量所施加的力与工件的位移之间的关系。然后，工件与工作台之间的摩擦力被表示为工件速度的非线性函数。接下来，为了数值地获得工件在工作台上的位移行为，通过有限元法（FEM）模拟工件的移动，其中在工件和工作台之间的接触表面处应用非线性摩擦力模型。最后，提出了一种确定使工件定位误差最小的最佳冲击力的方法，并给出了数值结果。主要研究结果如下：（1）建立了由静摩擦系数、动摩擦系数和摩擦力函数上升速度两个参数组成的摩擦力模型。(2)采用摩擦力模型和有限元法对工件的位移行为进行了计算机模拟。模拟结果与实测结果吻合较好。(3)建立了一种确定工件在工作台上移动到所需位置时的最佳冲击力的方法，并通过数值计算对该方法进行了验证。

The centering operation of workpieces is one of the most time-consuming jobs for which automation has not been established in Computer-Aided Manufacturing (CAM). As fundamental research for automating the centering operations, analytical models and methodologies needed for automating centering operations were proposed. First, the movement behaviors of a workpiece when applying an impulse force with a hammer were observed using experimental equipment and the relationships between the applied force and the displacement of the workpiece were measured. Then, frictional forces between a workpiece and a table were formulated as a nonlinear function of the velocity of the workpiece. Next, to obtain a displacement behavior of the workpiece on a table numerically, the movement of the workpiece was simulated by the finite element method (FEM) in which a nonlinear frictional force model was applied at the contact surface between the workpiece and the table. Finally, a method was constructed for determining the optimal impulse force for displacing a workpiece to a required postion on a table so that the positional error of the workpiece was minimum and numerical results were given to demonstrate the method. The results obtained by this study are itemized as follows :(1) A frictional force model with four parameters of static frictional coefficient, dynamic frictional coefficient and two parametric values expressing the rising speed of the frictional force function was constructed.(2) Computer simulation of workpiece displacement behaviors was conducted using the frictional force model and the finite element method. The simulated results have a good agreement with the measured ones.(3) A method for determining the optimal impulse force for displacing a workpiece to a required position on a table was constructed and the method was demonstrated using numerical results.