-- [ From: Al Hastbacka * EMC.Ver #2.10P ] --
Raster may be faster in some cases, but there are VERY FEW cases where
raster is better than vector. When we started the Model Maker
development program in 1991, it was done because the raster techniques
that we examined DID NOT have the quality of surface finish(all sides--
not just the TOP) that we needed. The raster techniques that we
examined INCLUDED the printhead that is in the MJM. However, we wanted
precision, accuracy, and surface finish. If you are willing to give up
some of those parameters, the raster approach has some merit for
certain geometries (e.g., bricks--but then you could use a saw to cut a
block of wax to make even a faster prototype).
Regards,
Al Hastbacka
-------- REPLY, Original message follows --------
> Date: Monday, 04-Dec-95 11:34 AM
>
> From: M. Burns (marshall \ Internet: (mburns@netcom.com)
> To: Al Hastbacka \ PRODIGY: (KHVD07A)
>
> Subject: Re: Raster is faster
>
> Hi Folks,
>
> Sorry, I must disagree with Ulrich and Terry. Raster is not
> necessarily faster. It depends on the geometry. And in three
dimensions,
> that dependence is more pronounced than in two, so the history of 2-D
> plotters is not a good analog here. Some of the relative advantages
of the
> two scanning methods are:
>
> -- Raster: Easier and less expensive to adapt to multiple jets.
This
> makes it faster for shapes that cover wide swaths of space in each
layer.
>
> -- Vector: Can skip between regions that need processing,
without
> processing all of the empty space in between (except for one tool
motion
> between the regions). This makes it faster for shapes with wide open
> spaces in many layers. BPM takes advantage of this characteristic by
> always making only the shell of an object, so that every shape has
this
> characteristic. This is kind-of cheating, and they pay by having
dismally
> fragile models.
>
> -- Vector: For deposition processes (such as BPM and FDM, but
not
> SLA, SLS, or LOM, which also do vector scanning), easier and less
> expensive to adapt to aimed (instead of just downward) deposition.
The BPM
> fabricator is the only one that does this so far, with its two
rotational
> freedoms in the jets. The advantages of aimed deposition over
downward are
> (a) possibility of reducing dependence on support structures, which
has a
> whole set of further advantages, and (b) freedom, when the
appropriate
> software is developed, from today's constraint to building in flat
layers.
>
> -- Vector: The resolution of fabrication is limited by the
resolution
> of the motion control systems, not by the resolution of the raster
> pattern, so it can be better if the raster pattern is a constant of
the
> hardware, as it will usually be for a multi-jet head.
>
> I wouldn't write off vector deposition processes, like FDM and
BPM,
> just yet! Counterarguments welcome.
>
> (This is an independent technical opinion. Ennex Fabrication is
not
> engaged by either Stratasys or BPM. Copyright (c) 1995, Ennex Corp.)
>
> Best regards,
> Marshall Burns
> marshall@ennex.com
>
>
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-------- REPLY, End of original message --------
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