Page 328 - Sensing, Intelligence, Motion : How Robots and Humans Move in an Unstructured World

THE CASE OF THE PPP (CARTESIAN) ARM 303

Step 2 Motion Along the Intersection Curve Between a Type II Obstacle and
an M-Plane. Move along the intersection curve until one of the following
occurs:
(a) The M-line is encountered. If dist(P c (curr loc), P c (T )) >
5
dist(P c (H j ), P c (T )),go to Step 2. Otherwise, define L j = curr loc;
go to Step 1.
(b) A wall or a Type I obstacle is encountered. T cannot be reached—the
procedure terminates.
(c) Another Type II obstacle is encountered. T cannot be reached—the
procedure terminates.
(d) A Type III obstacle is encountered. Set local dir2 = downward or
upward if the obstacle is of Type III + (or III − ). Go to Step 4.

Step 3 Motion Along the Intersection Curve Between a Type III Obstacle and
a V-Plane. Move along the intersection curve until one of the following
occurs:
(a) The M-line is met. Go to Step 1.
(b) A wall or a Type I obstacle is encountered. T cannot be reached—the
procedure terminates.
(c) A Type II + obstacle is encountered. Set j = j + 1 and define H j =
curr loc;set F = 1and set local dir1 according to Rule 1. Go to
Step 4.
(d) A Type II − obstacle is encountered. Set j = j + 1 and define H j =
curr loc;set F = 1and set local dir1 according to Rule 2. Go to
Step 4.
(e) Another Type III obstacle is encountered. Set j = j + 1 and define
H j = curr loc;set F = 2and set local dir1 = right. Go toStep5.
Step 4 Motion along the intersection curve between a Type II obstacle and
a Type III obstacle. Move along the intersection curve until one of the
following occurs:
(a) A wall or a Type I obstacle is encountered. Target T cannot be
reached—the procedure terminates.
(b) The M-plane is encountered. Go to Step 2.
(c) The V-plane is encountered. If dist(P c (curr loc), P c (T )) >
dist(P c (H j ), P c (T )), thengotoStep 2.Otherwise,define L j =
curr loc;gotoStep 3.
(d) Another Type II obstacle is encountered. Target T cannot be
reached—the procedure terminates.
(e) Another Type III obstacle is encountered. Go to Step 5.

5 If l 3 S = l 3 T , this comparison will never be executed because the procedure will have terminated at
Step 1d.