Re: Adaptive slicing problems.

Date: Mon Feb 24 1997 - 20:42:34 EET

In a message dated 97-02-23 23:29:41 EST, you write:

 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?

Of course your slices could have any edge shape and could be assembled to
create any requred form. Today, however, I assume the "adaptive slices" you
contemplate are limited to cross sections which have edges which define
"compound curves"- which could be visualized as having been cut by a laser
beam (a straight edge, at a varying angle from vertical).

If this is correct, it may be helpful to look at a relatively simple example
before getting too involved with software details. Consider modeling or
fabricating a threaded shaft (simple "triangular threads"), with layers
sliced perpendicular to the shaft . Such a threaded shaft is just one
example to illustrate the general need to be able to create sharply defined
details (in addition to flat planes) at ANY elevation.

To minimize "stairstepping" and enable such general "Z" capability, how can
one avoid either: 1.) using fine layer thicknesses (perhaps varied
according to the needs of the particular geometry) , or 2.) resorting to even
more complex edge shapes?

Norm Kinzie
(617) 444-6910
Laminar Systems, Inc.
45 Brentwood Circle
Needham, MA 02192

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