Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

282 Chapter 11 Proprioceptive and Environmental Sensing Mechanisms and Devices
and below. This is due to the possibility that the robot might try to drive
under something that is not quite high enough, or try to drive up onto
something and get the bottom edge of the bumper stuck, before it trips
the sensor. Both of these cases are potential showstoppers if the robot has
no idea it has hit something. This is where a bumper compliant and sensitive
to bumps coming from any direction is very helpful. If there is a
chance the robot will be operating in an environment where this problem
will arise, this additional degree of freedom, with sensing, makes the
bumper’s suspension system more complex but vital. Let’s start by looking
at the simplest case, the one-dimension sensing bumper.
SIMPLE BUMPER SUSPENSION DEVICES
The one-dimension (1D) bumper only detects bumps that hit the bumper
relatively straight on, from one direction. Although this may seem too
limiting, it can be made to work well if there are several smaller
bumpers, each with their own 1D sensor. Together they can sense a large
area of bumps from many directions. There are also layouts that are basically
1D in design, but, by being compliant, can be made to sense bumps
from arbitrary directions.
Since straight-on or nearly straight-on bumps are the most common
and produce the largest forces, it is better to use a design that allows the
bumper to have the longest travel in that direction. Bumps can be
detected around the sides of the robot without as much motion from the
bumper. This is why a compliant 1D bumper suspension can be used for
2D detection. There are many ways to attach bumpers that are basically
1D bumpers, but that can also function as 2D bumpers.
Some of these methods, or variations of them, can be used as is, with
no additional devices required. Usually, though, a secondary device must
be incorporated into the layout to positively locate the nominal position
of the bumper. This facilitates repeatable sensing by the limit switch. The
spring-centered plate layout is shown in Figure 11-14. The moving plate
is so loosely positioned it requires a vibration damper or it will wobble
constantly.
The V-groove centering block shown in Figure 11-12, is a basic
method of realigning the bumper after encountering a bump, but there
are several others that work nearly as well. The V-groove layout is essentially
two reversed bump limit switch layouts at 90° to each other. It is
therefore effective for bumpers designed to detect bumps from straight or
nearly straight on.