tailieunhanh - [Psychology] Mechanical Assemblies Phần

Nguồn gốc của từ tâm lý học (psychology) là psyche (tâm lý) rất gần giống với "soul" (linh hồn) trong tiếng Hy Lạp, và tâm lý học trước đây đã được coi như một nghiên cứu về linh hồn (với ý nghĩa tôn giáo của thuật ngữ này), trong thời kỳ Thiên Chúa Giáo. | 270 10 ASSEMBLY OF COMPLIANTLY SUPPORTED RIGID PARTS FIGURE 10-15. Geometry of a Two-Point Contact. The variable c is called the clearance ratio. It is the dimensionless clearance between peg and hole. Figure 10-16 shows that the clearance ratio describes different kinds of parts rather well. That is knowing the name of the part and its approximate size one can predict the clearance ratio with good accuracy. The data in this figure are derived from industry recommended practices and ASME standard fit classes Baumeister and Marks . Equation 10-2 shows that as the peg goes deeper into the hole angle 0 gets smaller and the peg becomes more parallel to the axis of the hole. This fact is reflected in the long curved portion of Figure 10-12. Figure 10-17 plots the exact version of Equation 10-2 for different values of clearance ratio c. Note particularly the very small values of 0 that apply to parts with small values of c. Intuitively we know that small 0 implies difficult assembly. Combining Figure 10-17 with data such as that in Figure 10-16 permits us to predict which kinds of parts might present assembly difficulties. The dashed line in Figure 10-17 represents the fact that there is a maximum value for 9 above which the peg cannot even enter the hole. This value is given by ơmax V 10-4 It turns out in practice that the condition in Equation 10-4 is very easy to satisfy and that in fact a smaller maximum value for Q usually governs. This is called the wedging angle ow. Wedging and jamming are discussed next. . Wedging and Jamming Wedging and jamming are conditions that arise from the interplay of forces between the parts. To unify the discussion we use the definitions in Figure 10-9 Figure 10-10 and Figure 10-18. The forces applied to the peg by the compliances are represented by Fx. Fz and M at or about the tip of the peg. The forces applied to the peg by its contact with the hole are represented by 1 2 and the friction forces normal to the contacted surfaces.