Page 198 - Anatomy of a Robot

07_200256_CH07/Bergren 4/10/03 3:30 PM Page 183
ENERGY CONTROL AND SOFTWARE 183
If a very brief power failure occurs, proper PFD software will preserve that infor-
mation and finish the movement when the power returns a few milliseconds later.
Certainly, if the power failure lasts longer, the motion will be ruined anyway. In
addition, if safety requires it, all motions must come to a fail-safe stop when the
power goes down. In all these instances, a complete PFD recovery of mechanical
states is impossible.

Mechanical Considerations: Software

for Energy Control

We’ll be discussing some mechanical engineering in Chapter 11. Many aspects of the
mechanical design of the robot hinge on the energy consumption. Certainly, if the robot
moves, then energy is expended to create that motion. The control system can monitor
the expenditure of mechanical energy and optimize things. This can happen in several
ways, which are listed here in no particular order of importance.

SHARING MOTORS

Motors tend to be among the heaviest of components. If the robot does not have to move
in multiple dimensions at once, consider putting in lightweight clutches and share the
motor between these mechanisms. The robot’s software may have to determine which
direction to move first.

POSITION PREDICTION

When the control software decides to move the robot, it expects it to wind up in the
proper position at the end of the move. But the truth is, the robot rarely winds up in the
exact right spot after an initial move. Another smaller movement is often necessary. To
the extent that these smaller corrective moves can be minimized, the robot can save
energy. Remember, it often takes extra energy just to get a robot moving at all. If the
robot’s control system is smart enough to adapt, it can predict the effect of a movement
even before it takes place. Further, as conditions change around the robot, the predic-
tion mechanism can be altered to fit the conditions. With the right algorithm, the robot’s
control software will continue to be efficient in its movements, coming close to the pre-
dicted position on the first try.