Cable robots form a class of parallel architecture robots with significant benefits including simplicity of construction, large workspace, significant payload capacity and end effector stiffness. While conventional cable robots have fixed bases, we seek to explore inclusion of mobility into the bases (in the form of gantries, and/or vehicle bases) which can significantly further enhance the capabilities of cable robots. However, this also introduces redundancy and complexity into the system which needs to be carefully analyzed and resolved. To this end, we propose a generalized modeling framework for systematic design and analysis of cooperative mobile cable robots, building upon knowledge base of multi-fingered grasping, and illustrate it with a case study of four cooperating gantry mounted cable robots transporting a planar payload.

Cable robots have seen considerable recent interest ensuing from their ability to combine a large workspace with significant payload capacity. However, the cables can apply forces to the end-effector only when they are in tension, and thus form a subclass of control problems requiring unilateral control inputs. Furthermore, actuation redundancy occurs when surplus cables are introduced within the system. On one hand, such redundancy needs to be carefully resolved for accurate tracking of the task. On the other hand, it allows the redistribution of the actuation forces to satisfy some secondary criteria. In this paper, we apply such redundancy for enhanced trajectory tracking by actively controlling the task stiffness of the end-effector. The scheme allow us to specify a lower bound of the task stiffness, which is intended to provide improved trajectory tracking and disturbance rejection performance. Finally, we illustrate the improved control performance within a virtual prototype cosimulation framework.

In this paper, we present a geometric method for motion planning for a fleet of differentially-driven wheeled mobile robots moving in formation, which explicitly takes into account their nonholonomic constraints. The relative position within the formation induces different motion plans for each individual wheeled mobile robot (WMR). We can quantitatively evaluate the performance of such induced motion plans using suitable metrics defined for the motions of each WMR. These performance metrics in cumulative form or individual form are used to optimize the overall formation (i.e., their relative positions) for performing a given task. The approach is well suited for online implementation and is demonstrated using case studies.

In this paper, we examine creation of a decentralized kinematic control scheme for a composite system of two (or more) wheeled mobile manipulators that can team up to cooperatively transport a common payload. Each mobile manipulator module consists of a differentially driven wheeled mobile robot (WMR) with a mounted planar two-degree-of-freedom (d.o.f) manipulator. A composite multi-degree-of-freedom system is formed when a payload is placed at the end effectors of multiple such modules with significant advantages. However, the nonholonomic/holonomic constraints and active/passive components within the composite vehicle need careful treatment for realizing the payload transport task. Hence, we first verify that arbitrary desired end-effector motions can be accommodated, within the feasible motion distributions of the articulations and the wheeled base. Then, we develop motion-plans by which this desired end-effector motion could be actively realized, using only the limited active motion-distribution of the differentially driven wheels. Finally, we deploy this in the form of a two-level hierarchical control framework, with an upper-level planning of the steerable active vector-fields and a lower-level posture stabilization control of the individual WMRs. Preliminary experimental results from the decentralized-control implementation for a two-module composite vehicle are also presented.