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

在计算机辅助制造（CAM）中，工件定心是最耗时且尚未实现自动化的工作之一。作为对定心自动化的基础性研究，提出了定心自动化所需的分析模型和方法。首先，利用实验设备观察了锤击冲击作用下工件的运动特性，并测量了冲击作用与工件位移的关系。然后，将工件与工作台之间的摩擦力表示为工件速度的非线性函数。其次，为了获得工件在工作台上的位移特性，采用有限元法（FEM）对工件在工作台与工件接触面处的运动进行了模拟，并建立了非线性摩擦力模型。最后，构造了一种确定工件位移到工作台所需位置的最优冲力的方法，使工件的位置误差最小，并给出了数值结果。研究结果如下：(1)构建了静摩擦系数、动摩擦系数4个参数和表示摩擦力函数上升速度的2个参数值的摩擦力模型。(2)采用摩擦力模型和有限元法对工件位移行为进行了计算机仿真。模拟结果与实测结果吻合较好。(3)构造了一种确定工件位移到工作台所需位置的最佳冲力的方法，并用数值结果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.