Distributed Collision-Free Motion Coordination on a Sphere: A Conic Control Barrier Function Approach

This letter studies a distributed collision avoidance control problem for a group of rigid bodies on a sphere. A rigid body network, consisting of multiple rigid bodies constrained to a spherical surface and an interconnection topology, is first formulated. In this formulation, it is shown that motion coordination on a sphere is equivalent to attitude coordination on the 3-dimensional Special Orthogonal group. Then, an angle-based control barrier function that can handle a geodesic distance constraint on a spherical surface is presented. The proposed control barrier function is then extended to a relative motion case and applied to a collision avoidance problem for a rigid body network operating on a sphere. Each rigid body chooses its control input by solving a distributed optimization problem to achieve a nominal distributed motion coordination strategy while satisfying constraints for collision avoidance. The proposed collision-free motion coordination law is validated via simulation

RSL ROVER: Robotic Systems Laboratory Rugged Offroad Vehicle for Experimental Research

The goal of this project was to build an autonomous vehicle testbed for the Robotics Systems Laboratory. This testbed will be used by undergraduate, graduate, and faculty researchers to test different control methods, sensor combinations, vehicle control laws, and eventually autonomous navigation. This paper documents our accomplishments to achieve this goal; we built a hierarchical control system, robust actuator mounts, and an effective safety system. The result is a capable 6-wheeled offroad vehicle that can be electronically controlled by remote or directly by wire. A feed-forward control law was incorporated for speed control, yielding predictable performance given a desired speed. Actuators were tuned for fast, reliable response and wiring was kept organized. The team believes the vehicle will be a useful asset to the Robotic Systems Lab for future research. To improve upon our testbed, global positioning and a compass should be integrated along with other sensors that came with the vehicle such as a Lidar unit. With these additional components, the vehicle should be able to run autonomously

CABLE-SUSPENDED CPR-D TYPE PARALLEL ROBOT

This paper deals with the analysis and synthesis of a newly selected Cable-suspended Parallel Robot configuration, named CPR-D system. The camera carrier workspace has the shape of a parallelepiped. The CPR-D system has a unique Jacobian matrix that maps the relationship between internal and external coordinates. This geometric relationship is a key solution for the definition of the system kinematic and dynamic models. Because of the CPR-D system complexity, the Lagrange principle of virtual work has been adapted. Two significant Examples have been used for the CPR-D system analysis and validation

Dynamic Control of a Novel Planar Cable-Driven Parallel Robot with a Large Wrench Feasible Workspace

Cable-Driven Parallel Robots (CDPRs) are special manipulators where rigid links are replaced with cables. The use of cables offers several advantages over the conventional rigid manipulators, one of the most interesting being their ability to cover large workspaces since cables are easily winded. However, this workspace coverage has its limitations due to the maximum permissible cable tensions, i.e., tension limitations cause a decrease in the Wrench Feasible Workspace (WFW) of these robots. To solve this issue, a novel design based in the addition of passive carriages to the robot frame of three degrees-of-freedom (3DOF) fully-constrained CDPRs is used. The novelty of the design allows reducing the variation in the cable directions and forces increasing the robot WFW; nevertheless, it presents a low stiffness along the x direction. This paper presents the dynamic model of the novel proposal together with a new dynamic control technique, which rejects the vibrations caused by the stiffness loss while ensuring an accurate trajectory tracking. The simulation results show that the controlled system presents a larger WFW than the conventional scheme of the CDPR, maintaining a good performance in the trajectory tracking of the end-effector. The novel proposal presented here can be applied in multiple planar applications

Modelling and Control of a Knuckle Boom Crane

Cranes come in various sizes and designs to perform different tasks. Depending on their dynamic properties, they can be classified as gantry cranes and rotary cranes. In this paper we will focus on the so called 'knuckle boom' cranes which are among the most common types of rotary cranes. Compared with the other kinds of cranes (e.g. boom cranes, tower cranes, overhead cranes, etc), the study of knuckle cranes is still at an early stage and very few control strategies for this kind of crane have been proposed in the literature. Although fairly simple mechanically, from the control viewpoint the knuckle cranes present several challenges. A first result of this paper is to present for the first time a complete mathematical model for this kind of crane where it is possible to control the three rotations of the crane (known as luff, slew, and jib movement), and the cable length. The only simplifying assumption of the model is that the cable is considered rigid. On the basis of this model, we propose a nonlinear control law based on energy considerations which is able to perform position control of the crane while actively damping the oscillations of the load. The corresponding stability and convergence analysis is carefully proved using the LaSalle's invariance principle. The effectiveness of the proposed control approach has been tested in simulation with realistic physical parameters and in the presence of model mismatch.Comment: This paper has been accepted to International Journal of Control on March 29th 2021. arXiv admin note: text overlap with arXiv:2103.0250