3D曲线扫描（sweep)问题

依我的经验来看，有的3D曲线可以扫描，而有的不可以，有人说：用Through points做的3D曲线不可以扫描。我认为不是这样，例如：林清安的《pro/engineer零件组合》（2000年4月第一版）第130页，第2章第2.5节“以Map part设计配件”中的3D曲线就是用Through points做出来的，可以扫描。下图我做的这个曲线亦可以扫描。
因此，到底什么样的曲线不可以扫描呢？有谁知道啊！

欢迎在论坛讨论此类问题，
以后凡是能提出有见解的问题的必奖励！
如果还能通过分析研究得到结论的重奖！！
  
支持！　好的问题也是不容易提出的，但关键要总结出结果阿！ by idesign

下面这条曲线不可以扫描，仅管还是2D的平面曲线。

Rules for Defining a Trajectory
  
A constant section sweep can use either a trajectory sketched at the time of feature creation or a trajectory made up of selected datum curves or edges. As a general rule, the trajectory must have adjacent reference surfaces or be planar.  
  
When you define a sweep, the system checks the specified trajectory for validity and establishes normal surfaces. A normal surface is the surface whose normal is used to establish the Y-axis of the trajectory. When ambiguity exists, the system prompts you to select a normal surface.
  
Depending on the type of chain selected as a trajectory, the system behaves as follows:
  
-   All chain segments reference edges桾he normal surfaces are the adjacent surfaces of the edges. If the edges are two-sided, the system prompts you to choose one set of surfaces.
  
-   All chain segments reference entities that belong to a datum curve, created by referencing surfaces (for example, by using the Projected option)桾he normal surfaces are reference surfaces of the curve. If the curve references two sets of surfaces, the system prompts you to choose one.  
  
-   All chain segments reference a sketched datum curve梩he normal surface is the sketching plane of the curve.
  
-   The chain of edges/curves is planar (other than a straight line)桾he normal surface is the plane defined by the chain.
  
-   Datum curves that you select for the trajectory must be created with one of the following options:
  
Sketch
  
Intr. Surfs
  
Use Xsec
  
Projected
  
Formed
  
OffsetfromSrf
  
2 Projections from any curve that lies in a plane
  
Consider the following special cases:
  
-   If a datum curve and its adjacent surfaces were bent by a toroidal bend feature, you can use that curve as a trajectory.
  
-   If you extend the chain with Trim/Extend in the CHAIN menu, the system accepts that chain if it is planar.
  
Note that a sweep may fail if
  
-   A trajectory crosses itself
  
-   You align or dimension a section to fixed entities, but the orientation of the section changes when its is swept along the 3-dimensional trajectory
  
-   An arc or a spline radius is too small, relative to the section, and the feature intersects itself traversing around the arc.

上面这个Rules for Defining a Trajectory 明显没有解释为什么我所附的两幅图中的用Thru points 做出来的trajectory，一条可以扫描，而另一条不可以的问题。
按照上面这个Rules for Defining a Trajectory所讲，用Thru points做的曲线从根本上来讲是没有办法扫描的了。但依据是什么呢？

可以把你的part贴上来吗？

当然可以啦！愿意的话还可以将part文件传给你试一下.

呵呵

https://www.tallrain.com/htm/myworks/proe/proe2001_tallrain.rar