基于工件稳定性的全区域夹紧力变向迭代规划算法

研究机械加工过程中夹紧力的合理规划是保证加工质量的核心环节,对于实现加工过程的可靠性和精密化至关重要,为此构建了全区域夹紧力变向迭代规划算法。根据工件在装夹布局中的受力状态以及工件与装夹元件之间接触力的方向约束条件,分别依据夹紧力大小与夹紧点位置的未知和已知情况,结合线性规划技术建立了力的存在性和力的可行性分析方法。在夹紧力存在的条件下,通过离散夹紧表面为点集的方法,逐点地以一定步长正向从最小值开始选取夹紧力的大小,根据当前值与上一次取值之间可行性的差异,确定下一次取值的步长及其方向,若可行性相同则以相同步长继续正向取值,否则步长减半、反向取值,直至步长的绝对值在阈值范围之内,建立全区域内夹紧力的变向迭代规划算法。该算法将连续型的夹紧力设计问题转化为离散型,不仅适合于形状复杂的工件,而且还利于计算机实现夹紧力的自动化设计。

A Reverse Direction Iterative Planning Algorithm of Clamping Forces in Entire Active Region Based on Workpiece Stability

The reasonable planning of clamping forces in the machining process is a key issue for guaranteeing the machining quality, which is of great significance to ensure the machining reliability and accuracy. For this purpose, a reverse direction iterative planning algorithm of clamping forces in entire active region is established. In addition to the direction constraint to contact force between workpiece and fixture, the force state of workpiece in fixturing layout is analyzed. According to unknown and known conditions of magnitude of clamping forces and clamping placement, the analysis methods of force existence and force feasibility are established based on the linear programming technology. Under the condition of existence of clamping forces, a clamping surface is discretized into points, and the magnitude of clamping force is chosen, beginning with the minimum value at each point with a certain step length along the positive direction. The selection of the next magnitude of clamping force depends on the difference between the feasibilities of clamping forces at two adjacent points. According to the difference between the feasibilities of the current clamping force and the last one, the step length and its direction can be determined for the next selection. If the feasibility of the current magnitude is same as the feasibility of the previous magnitude, the step length and its direction for the next magnitude are the same as those for the current magnitude. Otherwise, a half of step length along the negative direction is chosen. The selection procedure for the magnitude of clamping force is exceeded until the absolute value of the current step length is within the given threshold value. The proposed method can be used to transform the continuous design issue of clamping forces into a discrete one. It can be used for the development of computer aided clamping force design as well as the determination of clamping forces for workpieces with complex surfaces.