Control Aware of Limitations of Manipulators with Claw for Aerial Robots Imitating Bird's Skeleton

Winged animals such as birds, flying mammals or insects have lightweight limbs which allow them to perform different tasks. Although in robotics there are some examples of winged robots (called ornithopters), it has not been yet studied how to add them some manipulation-like capabilities, similarly to the anatomy of animals limbs. Adding those capabilities to ornithopters will outperform multirotor platforms giving the possibility to perch in unaccessible places, grasp objects and perform some kind of manipulation while being in proximity to humans. The special manipulator imitates the anatomy of the birds, having a kinematic chain with actuated joints except the first passive one that resembles the claw of a bird with a grasping force. This work analyzes in depth these ornithopterlike manipulators and proposes a nonlinear controller aware of the limitation in the grasping force of the claw, modeled as static friction. The solution is based on a methodology to control constrained-nonlinear systems via diffeomorphisms providing an explicit controller with low torques demand to meet aerial requirements. It is verified on a realistic simulator with
5DOF links—claw, low/upp-er leg, body, neck and beak–, and experimentally validated in a simpler 3DOF prototype.