Off on a tangent... Part 2

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  Off on a tangent... Part 2
  March 28, 2008, 03:47 PM Jay Tedeschi

  Once we have created all four boundary patches, we need only stitch the 5 surfaces into a quilt which will get us setup for our next step which is to evaluate the curvature of the model. For this we will use the Zebra Analysis tool… I know that for most of you, this is something that you probably saw once in a demonstration, or maybe you were looking for the Draft Analysis tool and hit this one by mistake… either way, that was about it. Well, it is for working on parts such these that this tool was implemented.

  

  The quickest way to get started is to select the “Quilt” that I created in the previous step and then Apply or OK.

  

  What results is a display which highlights any surface irregularities in an exaggerated manner by projecting parallel “stripes” onto the selected surface. Industrial Design tools such as AliasStudio use this as one of their default diagnostic shading modes. The reason for this is simple… the human eye is very good at detecting extremely minute imperfections or discontinuities in surface smoothness. This tool highlights those areas for you, which allows you to correct for any unplanned surface characteristics prior to going to manufacturing.

  In the first example below, I set the boundary patch blend conditions to “Free” which if you recall gives us a G0 condition at the edge where the patch and the rest of the surface join. As you can see, the “Zebra Stripes” do not align, which indicates that there is a lack of tangency and curvature between these surfaces.

  

  When the boundary patch conditions are set for “Tangency” you can see from the image below that the resultant Zebra Analysis shows the edges of the stripes lining up, which confirms that we do in fact have tangency, or a G1 condition. If the curvature continuity requirement were greater, say for something like Class A surfaces which is defined as G2 and higher, we would have to have used a different workflow as the boundary patch only allows us to define G0 or G1. The fact that there are still slight “jogs” on the stripes at the intersection of the patch and the parent surface are an indicator of this… on a set of G2 surfaces, there would be a completely smooth transition between the two.

  

  Now that we have our smooth offset surface, we can start to define one of our conformal buttons. In the assembly, if I set the edit target to the outer button housing and execute the Copy Object command I can create an associative copy of the offset surface from the upper housing in my button housing file. There are quite a few options when using Copy Object but in the interest of simplicity I will select Body as opposed to Face, as this will let me select the Quilt instead of the individual surfaces. I will also make sure that the Output is set to give me an associative surface.

  

  The result as you can see from the image of my browser below is an adaptive surface.

  

  This surface can now be used with the Split command to give me the conformal “cut” we are looking for.

  

  The split gives us curvature which exactly matches that of the controller housing and as you can see in the image below is exactly what we were trying to accomplish.

  

  

  2 Comments | Add Comment The Gear Box > Tips, Inventor 2008

Comments

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  April 2, 2008 03:26 PM Larry Heavner

  Great use of the tool. This really demonstrates how far Inventor has come and what you can do today to create an asthetically pleasing design.

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  April 5, 2008 10:11 AM Rhys Evans

  Thanks Jay, this is exactly the type of tip that I look for. I teach product design to 11 to 19 year old students and the products they design have increasingly complex forms. This is a resource I will use directly with my older students and I am sure it will encourage them to keep an eye on your blog. Great stuff!