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Input/output (I/O) delays in a closed-loop robotic system can significantly deteriorate both its stability and performance. In this paper, we study the position control problem for robotic manipulators under I/O delays, where the delays manifest as a result of communication with a non-collocated controller. Previous research on this topic has assumed the gravitational torque to be pre-compensated in a collocated manner. This paper studies the stability and regulation performance of the closed-loop system when the compensation for the gravitational torque is provided by a non-collocated controller. We demonstrate that simply utilizing scattering transformation for robotic systems under I/O communication delays results in position drift due to gravity compensation. Hence, a new control algorithm incorporating delayed position feedback and scattering variables is studied subsequently. Stability and performance margins dependent on the round-trip delays and the gravitational model are proposed to guarantee stable position regulation. Since the control architecture with scattering transformation does not address the stability problem due to sensing-actuation delays, a new controller is developed to cope with robotic control systems under time-varying sensing-actuation delays. The proposed control algorithms are studied in this paper via experiments on a manipulator with three degrees of freedom. [ABSTRACT FROM AUTHOR]

The problem of controlling a group of networked mechanical systems to synchronize and follow a common trajectory is studied in this paper. We first address the results for net worked mechanical systems to achieve synchronization when the interagent communication graph is balanced and strongly connected with communication delays. Subsequently, a control law is developed to guarantee synchronization and trajectory tracking for net worked mechanical systems communicating on regular graphs when there are constant time delays in communication and the interconnection topology is time-varying. The case when a human operator input is introduced in the closed-loop system is also considered. It is demonstrated that a bounded human operator input results in bounded tracking and synchronization errors, even when there are constant time delays in communication. The simulation and experimental results are presented by utilizing the kinematic and dynamic models of PHANToM Omni derived in this paper. [ABSTRACT FROM AUTHOR]

Input/output delays in a control system can pose significant impediments to the stabilization problem and potentially degrade the performance of the closed-loop system. In this paper, we study the classical set-point control problem for rigid robots with input–output communication delays in the closed-loop system. We demonstrate that if there are transmission delays between the robotic system and the controller, then the use of the scattering variables can stabilize an otherwise unstable system for arbitrary unknown constant delays. It is also demonstrated that the proposed algorithm results in guaranteed set-point tracking. In the case of time-varying delays, scattering variables together with additional gains can be utilized to stabilize the closed-loop system that is composed of the robotic manipulator and the controller. Furthermore, a scattering representation-based design with position feedback is proposed to improve closed-loop performance under time-varying delays. The proposed algorithms are validated via experiments in this paper. [ABSTRACT FROM AUTHOR]