Gabriel Arslan Waltersson, Systems and Control

Allowing controlled in-hand slip, rather than imposing rigid grasps, can substantially expand the manipulation capabilities of robotic systems equipped with parallel grippers. Such capabilities include more efficient object reorientation and increased effective reach. This thesis establishes the foundations for slip-aware in-hand manipulation with parallel grippers and demonstrates that such capabilities can be achieved using only a single-degree-of-freedom gripper and tactile sensing. To this end, the thesis contributes to advances in planar friction modeling and estimation, tactile sensing, gripper hardware design, and slip-aware control.

Robotic grippers interact with objects through the contact surface between their fingers and the object. We explore and model the friction at this interface, focusing on planar motion where translation and rotation occur simultaneously. This creates coupled tangential and torsional friction, which we model by extending the LuGre model using limit surface theory.

To experimentally realize slip-aware manipulation, we develop two generations of tactile sensors and gripper hardware. The first combines a high-performance force-controlled parallel gripper with commercial force/torque sensors and custom relative-velocity sensors based on optical mouse technology. This enables slip-aware manipulation using only in-hand perception. We use this system to estimate friction and contact properties and demonstrate several manipulation controllers, including gravity-assisted linear and rotational trajectory following, hinge control, and slip-avoidance. This framework is further extended with online estimation of contact properties, eliminating the need for a separate exploration phase.

The second-generation tactile sensor introduces a deformable sensing pad that measures sliding velocity, forces, torques, and pressure distribution. Using these sensors and an updated gripper, we demonstrate a variety of in-hand manipulation primitives by combining in-hand control with end-effector motion. Together, the extended friction model and contact-property estimation, tactile sensing and gripper hardware, and slip-aware manipulation controllers establish a unified basis for controlled slip and demonstrate versatile dexterous manipulation with simple parallel grippers.