Page 199 - Anatomy of a Robot

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184 CHAPTER SEVEN
Consider a real example. Suppose the robot must put fence poles in the ground. The
control software has been turning on the forward motor for three seconds each time the
robot must move to the next pole. However, as the robot begins to enter sandy soil, trac-
tion becomes a problem and it takes extra motor time to reach the next position. The
control software should be able to sense this from the last fence post, and turn the motor
on longer when moving to the next post. As the traction gets better, the duration can be
decreased.

MINIMUM ENERGY ROUTES

The control system software, given a command to move the robot in multiple dimen-
sions, should be able to minimize the amount of energy required to make the motions.
This can take place in multiple ways. In some cases, the robot can effectively make the
required motion in any number of different ways. Suppose, for example, that the robot
must move its hand to a new location to perform a task. The robot could retract its hand,
move itself to a comfortable spot in front of the object to be manipulated, and extend
its hand to grasp the object. This set of motions might well be wasteful. Moving the
hand to the required position may only take a rotation at the waist or an extension of the
arm. The same task can be carried out in this manner at a great savings in energy.
The control software can decide which movement will minimize energy consump-
tion in a few different ways. The software can contain a simple static model of the cost
for moving in each dimension, or it can adaptively change the movement costs by
observing the costs of previous movements. Certainly, these algorithms can become
complex. If one portion of the robot breaks, rendering motion in one dimension impos-
sible, simply raise the cost of motion in that dimension to a very high value. The energy
minimization software should then bypass any movement in the dimension containing
the broken components.

BRAKING
Anyone who has driven down a very long, steep hill knows that braking takes energy.
The brake pedal is held down, requiring energy from the leg muscles. Common driving
lore holds that the brakes should be let up now and then to avoid overheating. This is
something I still do to this day, not knowing if it’s needed. In any event, the design of
the braking system should be carefully done instead of waiting until the last second.
First of all, just what are brakes? We’ll discuss the types of brakes shortly. Defined
in a general manner, brakes are a mechanism for slowing down the robot in one or more
dimensions. Following the theory that every component must be justified, we should
ask the following question. Why might braking be required at all?