This paper presents a novel control architecture for controlling a moving remote center of motion in addition to the end-effector motion during robotic surgery. In minimally invasive surgery, it is common to require that the point at which the robot enters the body, called the incision point or the trocar, does not allow for any lateral motion. It is generally considered that no motion should be applied to this point in order to avoid inflicting damage to the patient's skin. However, in surgery, the patient's body may be moving, for example due to breathing or the beating of the heart. In order to compensate for this motion-or if we for some other reason want to leverage the possible motion of the incision point to improve performance in any other way-we derive a new framework which allows us to actively control the motion both at the incision point and the end effector. The novelty of the approach lies in the possibility of controlling both the incision point and the end effector to follow a trajectory, and that we find a Jacobian matrix that satisfies the velocity constraints in both the end-effector and the incision point frames. This allows us to formulate a framework that is not only suited for control, but also for analyzing the condition number of the Jacobian and avoid any singular configurations that may arise either as a result of the constrained motion or the manipulator geometry. The approach is verified experimentally on a redundant industrial manipulator.

Abstract:This paper presents a novel control architecture for operational space control when the end effector or the robotic chain is kinematically constrained. Particularly, we address kinematic control of robots operating in the presence of obstacles such as point, plane, or barrier constraints imposed on a point on the manipulator. The main advantage of the proposed approach is that we are able to control the end-effector motion in the normal way using conventional operational space control schemes, and by re-writing the Jacobian matrix we also guarantee that the constraints are satisfied. The most challenging problem of obstacle avoidance of robotic manipulators is the extremely complex structure that arises when the obstacles are mapped from the operational space to joint space. We solve this by first finding a new set of velocity variables for a point on the robot in the vicinity of the obstacle, and on these new variables we impose a structure which guarantees that the robot does not hit the obstacle. We then find a mapping denoted the Constrained Jacobian Matrix from the joint variables to these new velocity variables and use this mapping to find a trajectory in joint space for which the constraints are not violated. We present for the first time the Constrained Jacobian Matrix which imposes a kinematic constraint on the manipulator chain and show the efficiency of the approach through experiments on a real robot.

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This paper focuses on modelling and control of mass and heat transfer process for Wire Arc Additive Manufacturing (WAAM). It considers a nonlinear model for the deposited layer geometry of thin walls bases on process variables (wire feed speed, arc current, travel speed and contact tip to workpiece distance) and physical variables (arc power, inter-pass temperature) as inputs. The model is based on the Rosenthal solution for the temperature distribution due to a moving heat source in combination with a layer geometry parameterization, which is incorporated in a dynamic model of the GMAW process for control design. A closed-loop control is proposed to guarantee a more accurate deposition geometry considering the linearized model about a given operating point. Numerical simulation results illustrate the efficacy of the proposed control for the regulation and tracking of both layer height and wall width and a experimental setup for validating the control strategy is also proposed.

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Por descuido nosso, o nome de uma co-autora do trabalho "O efeito do laser de baixa energia no crescimento bacteriano in vitro", publicado na RBO do mês de agosto, estava alterado. Ao invés de Carolina Mariano dos Santos, o nome real é: Caroline Mariano dos Santos. Sendo assim, vimos por meio desta solicitar a retificação do nome da autora em próximo número da Revista. Desde já agradeço.

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In this paper we use the theory of mean-stable surfaces (stable minimal surfaces included) to explore the static Einstein-Maxwell space-time. We first prove that the zero set of the lapse function must be contained in the horizon boundary. Then, we explore some implications of it providing a rigidity result and a result of nonexistence of stable minimal surfaces for a static extension subject to a certain boundary data. We finish by proving that the ADM mass is bounded from above by the Hawking quasi-local mass.