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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?

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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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