Recalcitrant VSS 1

[treddie]

Hi everyone.

I have a stubborn VSS that simply will not cooperate. Please see the attached image. In it, you will see a curved Origin Trajectory and another straight line which serves as the X-Trajectory. You will also see two axes. I know from double-checking, that one of those axes is tangent to the Origin Trajectory and lies in its plane (the Origin Trajectory lies in a flat plane). From there, the other axis and the X-Trajectory form an orthogonal frame. That second axis is normal to the cylinder on which the Origin Trajectory sits.

Now, the origin of the ortho-frame is NOT the start point of the Origin Trajectory and the VSS, although it begins there...There is another point (PNT3) that acts as the origin of the frame so that the frame can move along the Origin Trajectory from start to finish. The position of that point is governed by the relation, d136 = trajpar. d136 is the offset distance of PNT3 along the Origin Trajectory, and from the 1st endpoint of the Origin Trajectory (initially zero).

To check to make sure all of the above move correctly along the Origin Trajectory, I can change d136 manually, and the entire frame moves as it should along the trajectory.

But once I begin the VSS and get my trajectories selected, Creo will not let me into Sketcher, due to the error in the top left corner of the image. And since I cannot get into Sketcher, I also cannot set up the relation.

What the heck am I doing wrong?

Many thanks for any responses!

 

[laik]

Hi,

here is the definition of x-trajectory. X-Trajectory—X-axis of the section plane passes through the intersection point of the specified X-trajectory and the section plane along the sweep.

 

[treddie]

Hi laik,

Thanks for your response. It's been awhile since my last VSS, but I have done enough of them in the past and should have known better. Age I guess.
Thanks for the brain reset.

For anyone new to VSS's, the key mistake I made in my image is, notice that I have that straight line which is supposed to indicate the x-axis for the VSS sketch. The key there, is that that is the x-axis for the initial SKETCH, NOT for any other moment in time as the sketch is driven along the Origin Trajectory. The X-Trajectory can be imagined as the endpoint of a straight line (the x-axis) as that straight line is swept along with the sketch section from the start of the Origin Trajectory to its end. The result is the accumulation of all those endpoints each of which defines the x-axis at any given moment, all together being points that "scribe out" the X-Trajectory.

The key then, is that in many cases the shape of that X-Trajectory may not be known explicitly beforehand. You may have to use other Creo methods to build it.