Bimanual human robot cooperation with adaptive stiffness control

Abstract

We propose a human-robot cooperation scheme for bimanual robots. After the initial task demonstration, the human co-worker can modify both the spatial course of motion as well as the speed of execution in an intuitive way. To achieve this goal, speed-scaled dynamic motion primitives are applied for the underlying task representation. The proposed adaptation scheme adjusts the robot's stiffness in path operational space, i. e. along the trajectory. It allows a human co-worker to be less precise in the parts of the task that require high precision, as the precision aspect can be provided by the robot. The required dynamic capabilities of the robot were obtained by decoupling the bimanual robot dynamics in operational space, which is attached to the desired trajectory. The proposed scheme was validated in a task where two Kuka LWR-4 robot arms cooperate with a human to carry an object.

Modeling and Control of Multi-Arm and Multi-Leg Robots: Compensating for Object Dynamics During Grasping

“…To follow a desired trajectory with an operational point x ∈ R 6 associated to the robot by the Jacobian J o and realizing an Cartesian impedance behaviour [13], [15] where the desired inertia is identical to the robot inertia, we choose the motion control law as in our previous work for bimanual grasping (without object dynamics) [21]…”

“…In the case of decoupled motion and contact wrench control, and assuming that motion control requires all actuated DOF of the robot, we may still be able to satisfy (15) by adding constraint wrenches to resolve underactuation, without inducing any additional motion. In…”

“…In that specific situation the contacts are coplanar and the grasp matrix degenerates [27]. [22] and [23] solve the equality constraint imposed by underactuation (15) for controlling contact wrenches based on quadratic programming. We instead solve it analytically.…”

“…However, grasping situations are typically treated as fixed-base multi-arm robot systems without virtual joints, e.g. [11]- [15]. Inspired by virtual model control [16] and the idea of additional virtual contacts in the grasp matrix [17], we realize that treating the object as an additional link virtually attached to the robot, turns the multi-arm robot into an underactuated system.…”

Admittance control for collaborative dual-arm manipulation

“…Recently, the cooperative task-space representation has been used to perform physical human-robot collaboration [12], [13]. A cooperative control scheme based on an impedance law allows performing kinesthetic guiding operations.…”