Re: Adaptive slicing problems.

From: C. Brock Rooney (
Date: Mon Feb 24 1997 - 20:40:46 EET

At 12:49 PM 2/24/97 +1000, Raymond Hope wrote
>Hi all;
>My name is Ray Hope. I've been working on slicing procedures for layered
>manufacturing, and am using layers with sloping boundary surfaces to
>eliminate the stair case effect. I have recently been working on adaptive
>slicing, and have come across some cases that can cause problems. So I
>thought I should call on the greater collective knowledge of the group and
>see if we can come up with some ideas.
>Note I am obtaining the definition of parts from B-spline surfaces. Layer
>error is approximated from the radius of curvature and angle of the
>surface normal.
>Problem 1.
> Joins between two or more surfaces, and vertices can cause the error
>approximation to give incorrect results. Previously published work (by
>others) has tried to solve this problem by slicing the part so that the
>surface joins coincide with layer joins. However this can only work if the
>surface joins are in the same plane as the layers. In many cases where a
>part is defined by two intersecting surfaces, the intersection curve is not
>in the layer plane. So what do we do?
>Problem 2.
> The method mentioned above to predict the error, produces a predicted
>error much less than the true value near inflection points. This is
>because at an inflection point the curvature becomes zero, and is also very
>small nearby. So how should we predict error near inflection points?
>I look forward to hearing some interesting suggestion from all of you.
These are some of the reasons why it is better to slice a set of
triangles with matching vertices, such as a well faceted, valid STL file.
C. Brock Rooney, Pres., Brock Rooney & Associates Inc. (Brockware)
       268 George St. Birmingham Michigan 48009 USA
(810) 645-0236 fax/bbs (810) 645-9020 email

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