A Projected Inverse Dynamics Approach for Multi-Arm Cartesian Impedance Control

Abstract

We propose a method for dual-arm manipulation of rigid objects, subject to external disturbance. The problem is formulated as a Cartesian impedance controller within a projected inverse dynamics framework. We use the constrained component of the controller to enforce contact and the unconstrained controller to accomplish the task with a desired 6-DOF impedance behaviour. Furthermore, the proposed method optimises the torque required to maintain contact, subject to unknown disturbances, and can do so without direct measurement of external force. The techniques are evaluated on a single-arm wiping a table and a dual-arm platform manipulating a rigid object of unknown mass and with human interaction. [1]

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

“…During grasping, the constraints should enforce a firm grasp without interfering the motion task. To satisfy this behavior, one should control the contact wrenches such that only the internal wrench is allowed [14] [21]. For this reason, the constraint Jacobian is…”

“…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]…”

“…The PIDC approach can be employed for optimization of contact wrenches considering friction cones [22], [23]. We demonstrated optimization of contact wrenches for multi-arm robots in [21] without compensating for object dynamics. However, these approaches are based on prior knowledge about contact surface friction coefficients.…”

“…In grasping situations we choose contact forces such that they point towards the center of all contact points. Combining [21] with the approach for object dynamics compensation presented in this paper remains future work.…”

“…Robot control is decoupled into two orthogonal subspaces, resulting in different and independent control laws for constraint consistent motion generation and realizing desired contact wrenches. The PIDC approach was validated with a torque-controlled manipulator for wiping a board [20] and dual-arm manipulating an object [21]. [22], [23] extend the framework to the underactuated case employing constrained optimization to maintain the contact.…”