Page 26 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine
P. 26
Measure Twice, Cut Once
little chance that we will maneuver between the two obstacles in Figure 1.4, even if
the distance between them is ample.
Timer Interrupt
Get Sonar
Ranges
Mode = OFF Mode
Test
Yes L >Dmax No
and
R >Dmax
Last State < 5 Last Last State = 6
State?
Last State = 5
L < R Range R < L
Test
Last Yes Last Yes
State=4? State=3?
No No
State= 1 State= 2 State=3 State=5 State= 4 State= 6
Decelerate Accelerate Decelerate Decelerate Decelerate Decelerate
to Halt Straight and Turn and Turn and Turn and Turn
Ahead Right Right Left Left
Run Motors
& Housekeeping
Return from Interrupt
Figure 1.5. State driven program flow with escape logic
When one begins to think of adding rules to help the robot achieve an objective,
and to maximize its circumnavigation performance, it becomes obvious that the
purely state-driven model will be very messy indeed. What is more, it will become
very difficult to maintain and modify the structure.
9
