看看国外的高手是如何运用“自顶向下”
这是我从SW官方论坛翻译过来的一个讲“自顶向下”设计的一个贴子，个人觉得有一定参考与借鉴价值，故转发与各位社友共享一下，如翻译有误，还请各位大侠不吝指正：We do all our models "Top-Down" and here iswhat we found so far to be the best (in 我们发现下面所介绍的“自顶向下”设计方法对大多情况是最好的（适用most cases, since there are some assemblies that willrequire another structure). 于绝大多数情况，除了某些特殊结构的装配体）：
1.- Create a Part inside your Top-Level Assembly andcall it "Ref_Geometry" and define it as "not show on BOM" 1.在顶层装配体中新建一零件后把它命名为“参考几何体”，并在属性中设置成“不在BOM表中显示”
2.- Inside that Part, create all the sketches, planes,axis, points, etc. you need to drive your entire assembly. Aslo you can driveall that geometry from a single DT inside that part2.在这个零件中，创建要驱动整个模型的所有草图，平面，轴，点等，当然也可以用这个零件中的设计表来驱动装配体
3. Create Sub-assemblies as you need to create yourparts and insert a copy (an instance) of the Ref_Geometry" part on thosesub-assemblies.3.创建所必须的子装配体并把“参考几何体”插入到这些子装配体中。
4.- Create parts inside the sub-assemblies, and relatethe sketches needed to create the parts to the geometry on the"Ref_Geometry" part (that way all the in-context relations will be"inside" each sub-assembly level. 4.在这些子装配体中创建零件并将零件中的草图参考到“参考几何体”的元素中。（这样做的话就可以使顶层零件的参考约束也可以作用到子装配单元）
5.- This will create a Top-Down structure that willallow you top work with a single sub-assembly open, but on which any changesmade to the referencial geometry (or to the DT) will be reflected on any othersub-assembly and on the complete assembly when opened. 5.这种自顶向下的结构可以做到：仅在子装配体打开的情况下编辑子装配体而不会使参考失效。但是参考几何体如有任何改动，都会影响到任何子装配体以及打开时的整个装配体。
You need to create referencial geometry sketches assimple as possible in order to not create a "monster referencial geometrypart" that will degrade machine performance. That is, just create theesential geometry (for example to define a rectangular shape do not draw therectangle, just draw two points positioned with relations to another geometryor by dimensions, To define a circular shape, just define the points needed tocreate the circle at the part that will use that shape. Remember that you arecreating "referencial geometry" not a drawing. 创建的参考几何体要尽量地简单，一个复杂的“参考几何体”会使运行速度变慢.这样的话，只要创建一些关键的元素就可以了（比如说画一个直角形而不是矩形，只要画两个点，用尺寸或其它几何体定义位置，通过定义几个模形中要用到的点来定义一个圆）要记住你画的是参考几何体而不是工程图！
Do not do large referencial geometry sketches withlosts of relations, divide the referencial geometry in smaller sketches relatedone to each other (since they are inside the same part will not increase the"load", but when you open one for editing you will not be working ona 2000 entities sketch that will take 15 minutes to close and rebuild. 不要在一个大的草图里设置大量的几何关系，把这些参考几何分散到相互联系的小草图里，（这样的话因为这些几何体都在一个个小的草图内，从而不会增加模型载入的时间，从而不发这样的事：打开一个包含一个两千个实体的草图，并且需要花15分钟关闭与重建）
One last issue, try to avoid as much as possible"global variables", use "equal" relations between sketchesand place a dimension on one of the entities, that one will drive all theothers without getting into the "inefficient" Equations SW module. Ifyou have a DT on the Referencial Geometry part do all your complex calculationsinside the DT (Excel is a lot more powerfull that the VB equations ability ofSW. 最后一个问题是：尽量避免“全局变量”，这样的话在使用“相等”关系定义两个草图或加尺寸到某个实体时就不会驱动所有其它实体时进入到“低效”的SW方程式模块了。如果在参考几何体中设置有设计表时，你可以利用它来完成所有复杂的计算（EXCEL的计算能力比SW自带的VB关系式更强大）
没图哦 从今个起 发表于 2011-4-3 12:35 static/image/common/back.gif
没图哦
纯文字技术贴，无图
搬板凳，占位，学习。。。 精髓啊！是在别的地方学不到的 这是采用以上方法所做的一个实例：
学习啊！好东西支持支持
很有借鉴价值！学习中 这个真是好东西，一定要学习的。 好像比官方的自顶向下好用，学习了