Modeling and Animating Human Figures - Computer Animation: Algorithms and Techniques - page 292

of the object and the task. The model developed by Kondo [ 38 ] for this computation makes use of a
spherical coordinate system. A set of angles for the shoulder and elbow is calculated from the desired
hand and shoulder position and then adjusted if joint limitations are violated. Finally, a wrist orientation
is calculated separately. The method is described, along with a manipulation planner for trajectories of
cooperating arms, by Koga et al. [ 36 ] .
9.2.2 The shoulder joint
The shoulder joint requires special consideration. It is commonly modeled as a ball joint with three
coincident DOFs. The human shoulder system is actually more complex. Scheepers [ 57 ] described
a more realistic model of the clavicle and scapula along with a shoulder joint, in which three separate
joints with limited range provide very realistic-looking arm and shoulder motion. Scheepers also pro-
vided an approach to the forearm rotation problem using a radioulnar (mid-forearm) joint (see
Figure 9.9 ) .
9.2.3 The hand
To include a fully articulated hand in the arm model, one must introduce many more joints (and thus
DOFs). A simple hand configuration may consist of a palm, four fingers, and a thumb, with joints and
DOFs as shown in Figure 9.10 .
clavicle joint
shoulder complex
scapula
elbow
radioulnar joint
wrist
FIGURE 9.9
Conceptual model of the upper limb.