Page 427 - Sensing, Intelligence, Motion : How Robots and Humans Move in an Unstructured World

402 SENSITIVE SKIN—DESIGNING AN ALL-SENSITIVE ROBOT ARM MANIPULATOR

board, the local control electronics occupies only a small physical area in it.
We obviously don’t want to cut off pieces of the board that contain control
electronics. This suggests that the control electronics should be put on the board
so as to simplify the cutting for typical surfaces. Another related problem is that,
electrically, sensors present a load on control electronics. Cutting off some sensors
changes that load, and so the control electronics should be able to handle this.
5. The arm’s interaction with its environment brings additional constraints.
Consider an environment where the robot arm may be hit by sharp hard objects.
Without extra precautions, this environment will likely rule out an infrared-
sensitive skin: Whereas these sensors have enviably high resolution and accuracy,
the tiny optical lenses sitting in front of every sensor make them brittle. A better
option then may be capacitance sensors: While not particularly accurate, they are
quite rugged.
On the other hand, covering the infrared sensitive skin with a layer of transpar-
ent epoxy or a similar compound may still warrant its use in a harsh environment.
The epoxy will pass sensors’ optical beams while mechanically protecting the
skin from the environment. This measure would also help in tasks where the
arm is periodically covered with dirt and has to be washed, such as in cleaning
chemical and nuclear dump sites. Because the content of such sites presents a
danger for human workers, robots are good candidates for the cleaning job. 4
Often the material that is to be evacuated from cleanup sites is inside large
metal or concrete tanks. The robot arm has to enter the tank through a relatively
small opening. Careful motion planning for the whole body of the arm is very
important: A small deviation from the opening’s center can spell a collision, and
this may happen at various points of the robot body, depending on how deep into
the tank opening the arm has to move. The operation calls for dextrous motion,
which in turn requires a good resolution of the sensitive skin. Infrared sensors
provide the requisite characteristics; the problem is, however, that sensors on the
skin will be quickly covered with dirt. A transparent layer of protective epoxy
will allow one to quickly wash off the dirt from the arm.
6. Specific applications can add their own constraints on the choice of sen-
sitive skin components. Given their decent accuracy and physical ruggedness,
arrays with tiny sonar sensors may be a good candidate for the skin. A sonar-
studded sensitive skin cannot be used, however, in space applications, for the
simple reason that sound does not spread outside the atmosphere.
The above need to wash off dirt from the skin is also such a constraint. Another
example is applications with unusual levels of radiation. Space robots must be
able to withstand space radiation. Hence only radiation-hardened components
will do the job for a sensitive skin intended for space applications.

Control Electronics. Depending on the physical principle of sensors chosen for
the sensitive skin, appropriate control schemes must be chosen. Ordinarily, skin

4 The multi-billion cleanup Superfund project in the United States in the mid-1990s had a provision
for utilizing robotics.