Attributes of a sensor suite

Attributes of a sensor suite

Everett52 recommends that the following attributes should be considered for
the entire sensing suite:
1. Simplicity. As with any design, simple sensors which have straightforward
hardware and operating principles are more desirable than sensors
which are complex and require constant maintenance.
2. Modularity. In order to reconfigure a sensor suite (add new sensors,
remove ones that aren’t appropriate for the task), the designer must be able
to remove one sensor and/or its perceptual schema without impacting any
other sensing capability.
3. Redundancy. In most military and industrial applications, it is imperative
that the robot function correctly, since it would put people at risk to try

to retrieve the robot and fix it. Sensors are especially important because a
faulty sensor can cause the robot to “hallucinate.” As a result, sensor suites
may offer some sort of redundancy.
There are two types of redundancy. Physical PHYSICAL redundancy means that there
REDUNDANCY are several instances of physically identical sensors on the robot. Fig. 6.4
shows a robot with redundant cameras. In this case, the cameras are mounted
180 apart, and when one sensor fails, the robot has to “drive backwards” in
order to accomplish its task.
LOGICAL Logical redundancymeans that another sensor using a different sensing mo-
REDUNDANCY dality can produce the same percept or releaser. For example, the Mars Sojourner
mobile robot had a laser striping system for determining the range
to obstacles, which emitted a line of light. If the surface was flat, a camera
would see a flat line, whereas if the surface was rough the line would
appear jagged. The robot also carried a second camera which could do obstacle
detection via stereo triangulation. The laser striping sensor and the
stereo cameras are logically redundant. They are not physically redundant,
but they produce the same overall information: the location of obstacles relative
to the robot. However, logically redundant sensors are not necessarily
equivalent in processing speed or accuracy and resolution. A stereo range
sensor and algorithm computes the range much slower than a laser striping
system.
Physical redundancy introduces new issues which are the area of active
research investigation. Possibly the most intriguing is how a robot can determine
that a sensor (or algorithm) has failed and needs to be swapped out.
FAULT TOLERANCE Surviving a failure is referred to as fault tolerance. Robots can be programmed
in most cases to tolerate faults as long as they can identify when they occur.