Page 67 - Human Inspired Dexterity in Robotic Manipulation

Modeling and Human Performance in Manipulating Parallel Flexible Objects 63

Although the invariant features may be different in different dynamic
environments, the fundamental organizing principles are not expected to
change. But if they do, what are the corresponding optimization models
going to look like? This question has been originally raised in [15], where
the so-called object-crackle model was developed and verified under exper-
iments with a single mass-flexible object by using a virtual-reality-based
setup. Later on, this research line was extended in [16], where the minimum
hand-jerk model was derived and verified under experiments with multiple
flexible objects connected sequentially.
Recently, a novel model, named “the minimum acceleration of the
center of mass,” has been proposed and tested against experimental data
for a single mass-flexible object [17]. In the theoretical justification of this
model, it is argued that neither the minimum hand-jerk model nor its
dynamic counterpart, the minimum hand-force-change model, are applica-
ble to the modeling of reaching movements with parallel flexible objects
(such as the one shown in Fig. 5.1). Contrary to the previous statement,
in this chapter we show that the invariant features of hand trajectories in
the manipulation of parallel flexible objects can be captured by the minimum
hand-jerk and hand-force-change models. As in [15–17], we employ a sim-
plified, one-dimensional model of human movements. In this model the
configuration dependence of the human arm is ignored and the motion is
considered at the hand level.
The presentation is organized as follows. In Section 5.2 we formulate
the minimum hand-jerk model of reaching movements in the manipula-
tion of two-mass flexible objects with parallel connection of the springs.
A dynamic version of the minimum hand-jerk model—the minimum
hand-force-change model—is developed in Section 5.3.A method for
estimation of the hand mass, featured in the minimum hand-force-change
model, is described in Section 5.4. Initial experiments, validating the the-
oretical models with the use of a haptic simulator, are presented in
Section 5.5. The models developed and the experimental results obtained
are discussed in Section 5.6.Finally,conclusions aresummarized in
Section 5.7.

5.2 MINIMUM HAND-JERK MODEL

It is well known that for unconstrained reaching movements, the trajectory
of the human hand can be predicted with a reasonable accuracy by the min-
imum hand-jerk criterion [10]: