Abstract
This paper details the implementation on the humanoid robot iCub of state-of-the-art algorithms for whole-body control. We regulate the forces between the robot and its surrounding environment to stabilize a desired robot posture. We assume that the forces and torques are exerted on rigid contacts. The validity of this assumption is guaranteed by constraining the contact forces and torques, e.g. the contact forces must belong to the associated friction cones. The implementation of this control strategy requires to estimate the external forces acting on the robot, and the internal joint torques. We then detail algorithms to obtain these estimations when using a robot with an iCub-like sensor set, i.e. distributed six-axis force-torque sensors and whole-body tactile sensors. A general theory for identifying the robot inertial parameters is also presented. From an actuation standpoint, we show how to implement a joint torque control in the case of DC brushless motors. In addition, the coupling mechanism of the iCub torso is investigated. The soundness of the entire control architecture is validated in a real scenario involving the robot iCub balancing and making contacts at both arms.
Highlights
Classical industrial applications employ robots with limited mobility
This is the typical case for legged robots, for which motion is constrained by rigid contacts with the ground
The force-regulation task at the arms is shown in Figures 9 and 10, which shows that the generation of forces at the arms does not affect the center of pressure at the feet
Summary
Classical industrial applications employ robots with limited mobility. assuming that the robot is firmly attached to the ground, interaction control (e.g., manipulation) is usually achieved separately from whole-body posture control (e.g., balancing). Foreseen applications involve robots with augmented autonomy and physical mobility. Within this novel context, physical interaction influences stability and balance. The problem becomes even more complex when these systems are constrained that is their dynamics are subject to a set of (possibly time-varying) non-linear constraints This is the typical case for legged robots, for which motion is constrained by rigid contacts with the ground. This section reviews previous literature on rigid contacts and their role in whole-body stability. This specific type of contacts is associated with a center of pressure that lies on the contact plane (Section 2.2.2) This property is exploited to give necessary and sufficient conditions for the stability of a planar unilateral contact (Section 2.2.3).
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