Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 11 Proprioceptive and Environmental Sensing Mechanisms and Devices 281
enough so that it contacts the object before any other part of the robot
does, otherwise the robot may not know it has hit something. Some robot
designs attempt to get around this by using a measure of the current
going to the drive wheels to judge if an object has been hit, but this
method is not as reliable.
A bumper, though seemingly simple, is a difficult sensor to implement
effectively on almost any robot. It is another case in which the shape of
the robot is important as it directly affects the sensor’s design and location.
The bumper is so tricky to make effective as to be nearly impossible
on some larger robots. Unfortunately, the larger the robot, the more
important it is to be able to detect contact with things in the environment,
since the large robot is more likely to cause damage to itself or the things
it collides with. In spite of this, most large teleoperated robots have no
collision detection system at all and rely on the driver to keep from hitting
things. Even large autonomous robots (robots around the size of
R2D2) are often built with no, or, at most, very small bumpers.
Simplifying any part of the robot’s shape, or its behaviors, that can
simplify the design of the bumper is well worth the effort. Making the
shape simple, like a rectangle or, better yet, a circle, makes the bumper
simpler. Having the robot designed so that it never has to back up means
the bumper only has to protect the front and possibly the sides of the
robot. Having the robot travel slowly, or slowing down when other sensors
indicate many obstacles nearby means the bumper doesn’t have to
respond as fast or absorb as much energy when an object is hit. All these
things can be vital to the successful design of an effective bumper.
There are several basic bumper designs that can be used as starting
points in the design process. The goal of detecting contact on all outer
surfaces of the robot can be achieved with either a single large bumper,
or several smaller ones, each of which with its own sensor. These smaller
pieces have the added benefit that the robot’s brain can get some idea of
where the body is hit, which can then be useful in determining the best
direction to take to get away from the object. This can be done with a single
piece bumper, but with less sensitivity.
A clever design that absolutely guarantees the bumper will completely
cover the entire outer surface of the robot is to float the entire shell of the
robot and make it the bumper, mounted using one of the techniques
described later. Place limit switches under it to detect motion in any
direction of this all-in-one bumper/shell. This concept works well for
small robots whose shells are light enough not to cause damage to themselves
but may be difficult to implement on larger robots.
Not only is it helpful to know the location of the bump, it is even better
to be able to detect bumps from any direction, including from above