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[Psychology] Mechanical Assemblies Phần 3

Tâm lý học vừa được nghiên cứu một cách khoa học lẫn phi khoa học. Tâm lý học chủ đạo ngày nay đa phần đặt nền tảng trên thuyết thực chứng, thông qua những phân tích định lượng và sử dụng những phương pháp khoa học để thử và bác bỏ những giả thuyết. | 96 4 CONSTRAINT IN ASSEMBLY TABLE 4-11. Constraint Analysis of Pin-Hole and Pin-Slot Joint TU T1 T2 TU 0012-2 0 0016-2 0 0 0 0 0 1 0 1000 0-6 WR recip TU WR 0 0 1 6 0 0 0 0 0 0 1 0 FIGURE 4-32. Illustrating the Equivalence of Three Different Positions for the 2. Force in WRU in Table 4-11. The arrows for Fzi and Mx represent the original entries in the first row of WR and are equivalent to Fz2 without Mx and Fz3 also without Mx- measured about the global axis. Note that there is no corresponding problem regarding pin axis parallelism about the global X axis because the right pin can rock in the slot about its X axis. 4.F.4.b. Remarks A constraint analysis of a complex assembly may result in numerous reported overconstraints. Several reasons are possible The engineer made an error. The engineer intended that those features be overconstrained. The overconstraints are there in a mathematical sense but not in a practical sense. Let us consider these cases one at a time. The engineer made an error. In this case the error may be immediately obvious to the engineer who can correct it. In a complex assembly however this may not be easy especially in the presence of mathematical overconstraints. The engineer intended that those features be overconstrained. The engineer does not need to take any action in this case. The overconstraints are mathematical but not practical. This is the most interesting situation. It arises in particular in the case of two-sided constraints. These in turn can arise in several ways 1. The engineer can create a new two-sided feature by intersecting elementary surface contacts. For example as we saw in Section 4.F.2.C a pin-slot feature can be created by intersecting two plane surfaces with a cylinder. The result will contain a two-sided constraint which will generate an overconstraint report in the analysis. Possibly the report will be cluttered with overconstraint reports from such features. We avoided this clutter in the examples above by .