Luc Le-Tien

DLR MiroSurge: a versatile system for research in endoscopic telesurgery.

PurposeResearch on surgical robotics demands systems for evaluating scientific approaches. Such systems can be divided into dedicated and versatile systems. Dedicated systems are designed for a single surgical task or technique, whereas versatile systems are designed to be expandable and useful in multiple surgical applications. Versatile systems are often based on industrial robots, though, and because of this, are hardly suitable for close contact with humans.MethodTo achieve a high degree of versatility the Miro robotic surgery platform (MRSP) consists of versatile components, dedicated front–ends towards surgery and configurable interfaces for the surgeon.ResultsThis paper presents MiroSurge, a configuration of the MRSP that allows for bimanual endoscopic telesurgery with force feedback.ConclusionsWhile the components of the MiroSurge system are shown to fulfil the rigid design requirements for robotic telesurgery with force feedback, the system remains versatile, which is supposed to be a key issue for the further development and optimisation.

The DLR MIRO: a versatile lightweight robot for surgical applications

Purpose – Surgical robotics can be divided into two groups: specialized and versatile systems. Versatile systems can be used in different surgical applications, control architectures and operating room set‐ups, but often still based on the adaptation of industrial robots. Space consumption, safety and adequacy of industrial robots in the unstructured and crowded environment of an operating room and in close human robot interaction are at least questionable. The purpose of this paper is to describe the DLR MIRO, a new versatile lightweight robot for surgical applications.Design/methodology/approach – The design approach of the DLR MIRO robot focuses on compact, slim and lightweight design to assist the surgeon directly at the operating table without interference. Significantly reduced accelerated masses (total weight 10 kg) enhance the safety of the system during close interaction with patient and user. Additionally, MIRO integrates torque‐sensing capabilities to enable close interaction with human beings ...

A hands-on-robot for accurate placement of pedicle screws

This paper presents a novel system for accurate placement of pedicle screws. The system consists of a new light-weight (<10 kg), kinematically redundant, and fully torque controlled robot. Additionally, the pose of the robot tool-center point is tracked by an optical navigation system, serving as an external reference source. Therefore, it is possible to measure and to compensate deviations between the intraoperative and the preoperatively planned pose. The robotic arm itself is impedance controlled. This allows for a new intuitive man-machine-interface as the joint units are equipped with torque sensors: the robot can be moved just by pulling/pushing its structure. The surgeon has full control of the robot at every step of the intervention. The hand-eye-coordination problems known from manual pedicle screw placement can be omitted

The DLR MiroSurge - A robotic system for surgery

This video presents the in-house developed DLR MiroSurge robotic system for surgery. As shown, the system is suitable for both minimally invasive and open surgery. Essential part of the system is the MIRO robot: The soft robotics feature enables intuitive interaction with the robot.

Adaptive friction compensation in trajectory tracking control of DLR medical robots with elastic joints

In this paper we introduce an adaptive control scheme for robots with elastic joints (in particular for the DLR medical robot) in order to increase the positioning accuracy and the performance of control with respect to uncertainties of the parameters of the robot dynamics. In order to design control and analyze system stability a static friction model is applied which describes Coulomb, viscose and load dependent friction. A stability analysis is done for this adaptive control scheme, allowing a Lyapunov based convergence analysis in the context of the nonlinear robot dynamics. Experimental results validate the practical efficiency of the approach.

Improving tracking accuracy of a MIMO state feedback controller for elastic joint robots

In this paper a control scheme is addressed to improve the tracking accuracy of flexible joint robots without replacing the structure of a MIMO state feedback controller which is used effectually with the DLR medical robots. By using the desired position, the new desired link torque, as well as their derivatives the effects of nonlinear dynamics are compensated and the tracking accuracy is thereby increased. Hereby, the new desired link torque takes the whole rigid body dynamics into account, not only the friction and gravitation compensation terms. A stability analysis based on the Lyapunov theory and Barbalat’s lemma is given for this new MIMO state feedback control scheme. Experimental results validate the practical efficiency of the approach.In this paper a control scheme is addressed to improve the tracking accuracy of flexible joint robots without replacing the structure of a MIMO state feedback controller which is used effectually with the DLR medical robots. By using the desired position, the new desired link torque, as well as their derivatives the effects of nonlinear dynamics are compensated and the tracking accuracy is thereby increased. Hereby, the new desired link torque takes the whole rigid body dynamics into account, not only the friction and gravitation compensation terms. A stability analysis based on the Lyapunov theory and Barbalats lemma is given for this new MIMO state feedback control scheme. Experimental results validate the practical efficiency of the approach.

Robust Adaptive Tracking Control Based on State Feedback Controller With Integrator Terms for Elastic Joint Robots With Uncertain Parameters

This brief addresses a robust adaptive control scheme based on a cascaded structure with a full state feedback controller with integrator terms as inner control loop and computed torque as outer control loop for flexible joint robots. Together with integrator effect, the adaptive control law can enhance position accuracy under uncertainties of the robot model, especially, the high friction caused by harmonic drive with high gear ratio. In this brief, the adaptive friction compensation is designed based on the LuGre friction model, which exhibits some advantages compared with the static friction model (e.g., no chattering effect at zero motor velocity). Furthermore, structural oscillations of the link side can be effectively damped by using joint torque feedback in the state feedback controller. Therefore, the proposed adaptive control approach can simultaneously provide high control performance both in terms of the dynamic behavior and the position accuracy. Global asymptotic tracking is achieved for the complete controlled system. The system stability is derived using Lyapunov approaches and Barbalat’s lemma. Experimental results validate the practical efficiency of the approach.

Decoupling and tracking control for elastic joint robots with coupled joint structure

Graphical Abstract The paper deals with the modeling, identification, and control of a flexible joint robot developed for medical applications at the German Aerospace Center (DLR). In order to design anthropomorphic kinematics, the robot uses a coupled joint structure realized by a differential gearbox, which however leads to strong mechanical couplings inside the coupled joints and must be taken into account. Therefore, a regulation MIMO state feedback controller based on modal analysis is developed for each coupled joint pair, which consists of full state feedback (motor position, link side torque, as well as their derivatives). Furthermore, in order to improve position accuracy and simultaneously keep good dynamic behavior of the MIMO state feedback controller, a cascaded tracking control scheme is proposed, based on the MIMO state feedback controller with additional feedforward terms (desired motor velocity, desired motor acceleration, derivative of the desired torque), which are computed in a computed torque controller and take the whole rigid body dynamics into account. Stability analysis is shown for the complete controlled robot. Finally, experimental results with the DLR medical robot are presented to validate the practical efficiency of the approaches.The paper deals with the modeling, identification and control of a flexible joint robot developed for medical applications at the German Aerospace Center (DLR). In order to design anthropomorphic kinematics, the robot uses a coupled joint structure realized by a differential gear-box, which however leads to strong mechanical couplings inside the coupled joints and must be taken into account. Therefore, a regulation MIMO state feedback controller based on modal analysis is developed for each coupled joint pair, which consists of full state feedback (motor position, link side torque, as well as their derivatives). Furthermore, in order to improve position accuracy and simultaneously keep good dynamic behavior of the MIMO state feedback controller, a cascaded tracking control scheme is proposed, based on the MIMO state feedback controller with additional feedforward terms (desired motor velocity, desired motor acceleration, derivative of the desired torque), which are computed in a computed torque controller and take the whole rigid body dynamics into account. Stability analysis is shown for the complete controlled robot. Finally, experimental results with the DLR medical robot are presented to validate the practical efficiency of the approaches.

Entkopplungsregelung und Reibungskompensation für einen Roboter mit elastischen verkoppelten Gelenken

Zusammenfassung Dieser Beitrag beschreibt die Regelung und Reibungskompensation von Robotern mit elastischen und differentiell getriebenen Gelenken (implementiert am Beispiel des DLR-Medizinroboters). Unter Berücksichtigung der Gelenkverkopplung wird ein MIMO-Zustandsregler (multi-input-multi-output) für die Doppelgelenkstruktur des Medizinroboters eingeführt, der auf der Rückführung der gemessenen Motorpositionen, abtriebsseitigen Drehmomente und deren Ableitungen basiert. Um die Positioniergenauigkeit des Roboters zu verbessern, wird zusätzlich ein Störgrößenbeobachter für die Reibungskompensation entwickelt. Es wird gezeigt, dass der Roboter mit dem MIMO-Zustandsregler und dem Störgrößenbeobachter global asymptotisch stabil ist. Abschließend werden experimentelle Ergebnisse mit dem DLR-Medizinroboter zur Validierung des Ansatzes vorgestellt. Abstract The paper describes the control and friction compensation of a robot with flexible joints (the DLR medical robot), which has strong mechanical couplings within pairs of joints realized with a differential gear-box. In consideration of this coupling, a MIMO state controller is designed for the strongly coupled joints. In addition a disturbance observer is developed to compensate the nonlinear effects of the friction and to improve the position accuracy of the robot. It is shown that the system is global asymptotically stable for the MIMO controller and the disturbance observer. Finally, experimental results with the DLR medical robot are presented validating the proposed concept.