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80 Chapter
5. General Concepts, Toolkits, and Frameworks instructions
can be integrated directly into objects, such that the objects themselves
can tell how they have to be assembled (see Figure 5.2).
(a) (b)
Figure 5.2: (a)
Smart-Its sensor measuring the user’s actions, (b) Perception
model Artifact
Layer. We chose the actual boards of the furniture
as the artifacts in the perception
model. Besides the boards we included a screwdriver on the artifact
layer. The screwdriver is enhanced with a gyroscope
to detect when someone is tightening a
screw. Here, the artifact based approach proved highly valuable and
appropriate, as these objects all have their own typical
context and are the smallest computing
entities in the application. The low level perception methods in the
artifacts determine the orientation of the boards (accelerometer),
if they are moving or not, whether they
are being hammered on, and if they are experiencing force (force
sensors at edges) from another board. The screwdriver
simply detects (gyroscope), whether someone
is loosening or tightening a screw. These perception primitives
define the output of the artifact layer. Equally, they
are the input to the setting layer. All
perception primitives are calculated locally on each artifact. Setting
Layer. In this layer the perception primitives
from a tightly coupled group
of artifacts are combined. In the proactive furniture example the boards and
tools involved in the momentary stage of the assembly
form this group of artifacts. This may
create a large number of overlapping settings in the overall assembly plan.
However, the actual settings of interest are determined
by the current state of the assembly. The
setting layer infers the performed assembly steps by combining the
perception primitives from the artifact layer. In detail,
it determines whether two boards are aligned
and if they have been joined or not. Furthermore, it can detect
on which board, the screws are tightened. In principle
our model allows several settings are at
a time representing preliminary distinct compounds of boards, e.g.
if two people cooperatively do the assembly. In a last
step they would join their
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