Human Machine Interaction and Communication in Cooperative Actions - Bioinspired Approaches for Human-Centric Technologies - page 247

arousal of a natural sense of collaboration in a robot guidance mechanism, it is
appropriate to supplement the haptic guidance with a role exchange mechanism,
which allows the computer to adjust the forces it applies to the user in response to
his/her actions. In general, a recent review on bilateral haptic interaction systems
(Passenberg et al 2010 ) shows that the incorporation of environment, operator, or
task-specific information in the controller structure can improve robustness and
performance, but such benefits are application dependent to a large extent.
In the rest of this section, we propose first a taxonomy for haptic interaction
which could potentially be used both for human-human and human-robot haptic
dyads. Then, we discuss in more detail the implications that the differences between
a musculo-skelettal system for humans and traditional actuators for robots bring
have from a motor control point of view, and the consequences for physical
interaction. A novel actuator, inspired by the structure of the musculo-skelettal
system is described. Finally, we consider one application domain - robot-assisted
physical therapy - where decoding the information in the physical interaction about
the state and interaction of the partner is of utmost importance to identify the right
level of assistance to the patient.
8.3.1 A Metrics to Measure Physical Interaction Complexity
To classify the various situations involving physical interaction and measure the
complexity of the challenge from a control point of view, we propose a metric based
on the well-known concept of compliance. More specifically, we propose to classify
physical-interaction scenarios according to two essential components of contacts:
external and internal compliance (see Fig. 8.2 ). The adjective internal as opposed to
external here refers to the interactive agent, in other words “the self” as opposed to
“the other.” For convenience, we will use the term self-compliance when referring
to internal compliance and the term external compliance when referring to “the
other” compliance. Self- and external compliance are the two sides of the interac-
tion. It is therefore crucial to understand how these two concepts become
intertwined once contacts are established. From here on, we will introduce the
concept of contact compliance, which corresponds to the overall compliance
obtained once the external and the self-compliance become coupled with the
contact establishment. At a coarse representational level, establishing a contact
can be seen as the serial connection of two compliances, one representing the
external compliance, the other representing the self-compliance. We propose to
classify physical interaction according to the degree of compliance involved on
both sides of the interaction and to measure the complexity of the interaction with
contact compliance. Remarkably, the compliance of a serial interconnection is
simply the linear sum of the individual compliances. 1 Therefore, roughly speaking,
1 If we consider the simple example of two springs serially interconnected, it is well known that the
stiffness of the serial interconnection k series is associated to the stiffness of the individual springs