Chapter 2. Prehension

Chapter 4 - Planning of Prehension 93
Task Obiect
Determine which combination of omositions:
If task width = small then opposition 1 =pad
If task forces = heavy then opposition 1 =palm
If opposition 1 = pad then its VFI = thumb
If opposition 1 = palm then its VFI = palm
eVF2-
If opposition 1 = side then its VF2 = index
If opposition 1 = palm and
task length < three finger widths
then its VF2 = index or index-middle
Figure 4.12 Sample rules in knowledge-based system for selecting
an opposition space from object and task requirements. Three types
of rules are used. First, oppositions are chosen. Then, for each
opposition, the mappings from real fingers to virtual fingers are
made. Task width refers to the length of the opposition vector.
Task length refers to the height of the object. VF=virtual finger
(from Iberall et al., 1988).
on the number of constraints being modelled in the system. Again, the
human brain controlling the hand is working with a large multidimen-
sional constraint space, as outlined in Chapter 8.
An expert system can combine choosing oppositions and virtual
finger mappings (Iberall, 1987c; Iberall, Jackson, Labbe & Zampano,
1988). As seen in Figure 4.12, the system had three types of rules.
Similar to the GRASP-Exp rules, the first set of rules in this system
chose which oppositions were needed depending on object properties
(size, weight, surface characteristics) and task properties (anticipated