Ellipsis

Off on a tangent... Part 2

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.

Off on a tangent... Part 1

I want you to think for a moment of the obstacles that need to be overcome when creating conformal objects of any type for consumer electronic products. In the case presented here we have buttons on a game controller that must match the contours of the controller housing, however must also be raised slightly above the housing surface for easy actuation.

To achieve this we will use an offset surface from the controller housing itself, however there is a problem with this approach as the resultant surface has holes which match those areas in the housing surface where the button cutouts and blends are.

We need to patch these holes, but need these new surfaces to have the same curvature as the housing itself. So, how do we get a clean, contoured surface, which can be used to give us the conformal cut we are looking for, and that will be associative to any modifications to the housing itself? The boundary patch will give us the results we need, but we will have to set the proper conditions to get the desired results. Take a look at the image below.

The only input that is needed from the user is to select an edge boundary which defines a closed area. As you can see, the edge need not be planar, and in this example I have selected the most extreme hole to patch from a standpoint of curvature. Once selected, if I rotate the model you will see that in the default “Free Condition” the contour of the boundary patch does not match that of offset surface. This is due to the fact that the continuity of the patch in the “Free Condition” is G0, which quite simply means the the curves or in this case surfaces touch at the join point. Obviously, as you can see from the image, this is “slightly less” [grin] than what we probably had in mind when we were thinking of conformity.

“Tangent Condition” will give us a boundary patch with a continuity of G1, which is as the name implies is tangent, or more specifically will result in a set of curves or surfaces which both touch and share a common tangent direction at the join points. As you can see above, changing to a “Tangent Condition” gives us a much better result, and most likely more in line with what we were looking for in the first place.

Thinking Globally...

The next time you are thinking about using Excel for dispensing global parameters throughout your assembly I would like you to consider the following proposal… use a derived part instead. Yep, a derived part. Many of you have probably noticed that when you create a derived part, there is a folder in the Derived Part dialog box which is labeled “Parameters”. Those of you who did, and who investigated further are probably already using this workflow… if this is you, kudos, you can stop reading now. If not, then continue on…

Take a look at the image below. There are several interesting topics that could be covered with this example, e.g., skeletal modeling, component position, sketch properties, however we are going to focus on using derived parts for pushing global parameters throughout the assembly. Take a look at the User Parameters in the dialog box shown in the image. There are two parameters in particular, which we want to share amongst several of the parts which make up this F1 rear wing assembly, BRKT_RECESS and WIDTH_INSIDE. To facilitate this we need only enable parameter export by checking the radio button as shown in the image. Once this is done, these parameters will be accessible to any part file which uses this .ipt file as a base component.

Upon opening the rear wing assembly, and creating a new part for the upper airfoil section we exit the base sketch and start the Derived Component command. You will be prompted to select a part for the Base Component, and if we select the part that we just flagged with the two exported User Parameters then what we see when we expand the Parameters/User Parameters folders in the Derived Part browser should look very similar to what I am showing below.

These two parameters are now available for use and will function exactly like any other user parameter. At this point let’s select the Extrude command and pick the magenta section in the image above. We will select Distance for our Extents, a midplane direction and as our termination we will choose “List Parameters” as shown below…

From the following dialog box we select the user parameter WIDTH_INSIDE…

The result is a component with its length driven by a global parameter, which is controlled in a single .ipt file along with the sketch elements needed to create all of the components which are similar to this one, e.g., all of the interior wing airfoils. This is extremely powerful, as all of these parts can be updated by simply editing the source .ipt file and then issuing a global update at the assembly. It is more importantly a clean alternative to using Excel, and can significantly cut down on the number of files required to be linked to achieve similar results.

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