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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]

Abstract: In teleoperation systems operating in complex environments, due to the cognitive limitations of the human operator and lack of complete information about the remote environment, safety and performance of such systems can potentially be comprised. In order to ensure the safety and enhance the efficiency of complex teleoperation systems operating in cluttered environments, in this paper we investigate a semi-autonomous control framework for bilateral teleoperation. The semi-autonomous teleoperation system is composed of heterogeneous master and slave robots, where the slave robot is assumed to be a redundant manipulator. Considering robots with different configurations, and in the presence of dynamic uncertainties and asymmetric communication delays, we first develop a control algorithm to ensure position and velocity tracking in the task space. Additionally in the absence of dynamic uncertainty, and in the presence of human operator and environmental forces, all signals of the proposed teleoperation system are proven to be ultimately bounded. The redundancy of the slave robot is then utilized for achieving autonomous sub-task control, such as singularity avoidance, joint limits, and collision avoidance. The control algorithms for the proposed semi-autonomous teleoperation system are validated through numerical simulations on a non-redundant master and a redundant slave robot. [Copyright &y& Elsevier]

In this brief, we propose a passivity-based framework for control of bilateral teleoperators under time-varying delays and data loss. The usual scattering formalism which guarantees passivity for any constant time delay is extended in several important ways to handle adverse network dynamics. Communication management modules (CMM) are proposed to reconstruct the scattering variables while guaranteeing passivity of the bilateral teleoperator and asymptotic stability of the master/slave velocities under time-varying delays and data losses. The results are also extended to the discrete domain, in particular to the case where communication between the master and slave robots occurs over a packet-switched network. We show that passivity can be maintained in the face of varying delay and packet loss but that it depends fundamentally on the mechanism used to handle missing packets. Our framework unifies several existing results in the continuous and discrete time domain. We develop novel algorithms for the CMM which not only preserve passivity and stability, but have been shown through experiments to improve tracking performance in a single-degree-of-freedom teleoperator system. [ABSTRACT FROM AUTHOR]

This paper considers the multi-agent linear least-squares problem in a server–agent network architecture. The system comprises multiple agents, each with a set of local data points. The agents are connected to a server, and there is no inter-agent communication. The agents' goal is to compute a linear model that optimally fits the collective data. The agents, however, cannot share their data points. In principle, the agents can solve this problem by collaborating with the server using the server–agent network variant of the classical gradient-descent method. However, when the data points are ill-conditioned , the gradient-descent method requires a large number of iterations to converge. We propose an iterative pre-conditioning technique to mitigate the deleterious impact of the data points' conditioning on the convergence rate of the gradient-descent method. Unlike the conventional pre-conditioning techniques, the pre-conditioner matrix used in our proposed technique evolves iteratively. We show that our proposed algorithm converges linearly with an improved rate of convergence in comparison to both the classical and the accelerated gradient-descent methods. For the special case, when the solution of the least-squares problem is unique, our algorithm converges to the solution superlinearly. Through numerical experiments on benchmark least-squares problems, we validate our theoretical findings, and also demonstrate our algorithm's improved robustness against process noise. [ABSTRACT FROM AUTHOR]

Introduction: Vasculobiliary and vascular injuries following cholecystectomy are the most serious complications requiring complex surgical management resulting in greater patient morbidity and mortality.Methodology: The study was performed at a tertiary teaching hospital of North India. Records of patients referred for biliary or vascular injury sustained during cholecystectomy were reviewed retrospectively to identify patients with vascular injury between January 2009 and March 2018. Clinical profile, hospital course and outcome of these patients were analysed.Results: Over nine years, 117 patients were referred for cholecystectomy related complications. Total incidence of vascular injury was 5.1% (6/117). Combined vasculobiliary injury (VBI) occurred in 3.4% (4/117) while isolated vascular injury was present in 1.7% patients (2/117). Most (5/6) patients were operated for uncomplicated gall stone disease. Incidences of portal vein (PV) and right hepatic artery (RHA) injuries were equal (3/6). PV injuries were repaired either during cholecystectomy (1/3) or during re-exploration after damage control packing (2/3). RHA injuries presented as pseudoaneurysm and were managed surgically (2/3) or by coil embolization (1/3). All VBI referrals (4/117) were following open cholecystectomy. In VBI patients, vascular injury was diagnosed intra-operatively in two while it was diagnosed several weeks after cholecystectomy in two others. Biliary injury manifested as bile leak post-operatively in all four of them. Nature of biliary injury could be characterized in only 50% (2/4) patients. Definitive repair of biliary injury was performed in one patient only. There was one mortality in our series.Conclusion: Vascular injury is an uncommon complication of cholecystectomy with catastrophic outcome if not managed timely and properly. Adequate surgeon training, keeping the possibility of aberrant vasculobiliary anatomy in all cases, and proper surgical technique is crucial for prevention of such injuries. However in such an event, proper documentation and referral to tertiary centre will help in decreasing morbidity and further litigation. [ABSTRACT FROM AUTHOR]