In this paper, a two-layer approach is presented to guarantee the stable behavior of bilateral telemanipulation systems in the presence of time-varying destabilizing factors such as hard contacts, relaxed user grasps, stiff control settings, and/or communication delays. The approach splits the control architecture into two separate layers. The hierarchical top layer is used to implement a strategy that addresses the desired transparency, and the lower layer ensures that no “virtual” energy is generated. This means that any bilateral controller can be implemented in a passive manner. Separate communication channels connect the layers at the slave and master sides so that information related to exchanged energy is completely separated from information about the desired behavior. Furthermore, the proposed implementation does not depend on any type of assumption about the time delay in the communication channel. By complete separation of the properties of passivity and transparency, each layer can accommodate any number of different implementations that allow for almost independent optimization. Experimental results are presented, which highlight the benefit of the proposed framework.

Bilateral Telemanipulation With Time Delays: A Two-Layer Approach Combining Passivity and Transparency

Robustness and flexibility constitute the main advantages of multiple-robot systems with respect to single-robot ones as per the recent literature. The use of multiple unmanned aerial vehicles (UAVs) combines these benefits with the agility and pervasiveness of aerial platforms [1], [2]. The degree of autonomy of the multi-UAV system should be tuned according to the specificities of the situation under consideration. For regular missions, fully autonomous UAV systems are often appropriate, but, in general, the use of semiautonomous groups of UAVs, supervised or partially controlled by one or more human operators, is the only viable solution to deal with the complexity and unpredictability of real-world scenarios as in, e.g., the case of search and rescue missions or exploration of large/cluttered environments [3]. In addition, the human presence is also mandatory for taking the responsibility of critical decisions in high-risk situations [4].

Shared Control : Balancing Autonomy and Human Assistance with a Group of Quadrotor UAVs

In this paper, we propose a novel framework, passive set-position modulation (PSPM), which enables us to connect a (continuous-time) robot's position to a sequence of slowly updating/sparse (discrete-time) set-position signal via the simple (yet frequently used in practice) spring coupling with damping injection, while enforcing passivity of the closed-loop robotic system. The PSPM modulates the original set-position signal in such a way that the modulated signal is as close to the original signal as possible (i.e., maximum information recovery for better performance), yet only to the extent permissible by the available energy in the system (i.e., passivity constraints). We present its algorithm and theoretically show its passivity and performance. We also show how this PSPM can be applied for two applications, with some experimental results: Internet teleoperation with varying delay and packet loss; and haptics with slow and variable-rate data update.

Passive-Set-Position-Modulation Framework for Interactive Robotic Systems

Haptic teleoperation enables the human to perform manipulation tasks in distant, scaled, hazardous, or inaccessible environments. The human closes the control loop sending haptic command signals to and receiving haptic feedback signals from the remote teleoperator. The main research question is how to design the control such that human decision making and action is supported in the best possible way while ensuring robust operation of the system. The human in the loop induces two major challenges for control design: 1) the dynamics of the human operator and the teleoperation system are tightly coupled, i.e., stability of the overall system is affected by the human operator dynamics; and 2) the performance of the teleoperation system is subjectively evaluated by the human, which typically means that standard control performance metrics are not suitable. This paper discusses recent control design successes in the area of haptic teleoperation. In particular, the importance and need of dynamic human haptic closed-loop behavior models and human perception models for the further improvement of haptic teleoperation systems is highlighted and discussed for real-world problem domains.

Human-Oriented Control for Haptic Teleoperation

The design of decentralized controllers coping with the typical constraints on the inter-robot sensing/communication capabilities represents a promising direction in multi-robot research thanks to the inherent scalability and fault tolerance of these approaches. In these cases, connectivity of the underlying interaction graph plays a fundamental role: it represents a necessary condition for allowing a group or robots to achieve a common task by resorting to only local information. The goal of this paper is to present a novel decentralized strategy able to enforce connectivity maintenance for a group of robots in a flexible way, that is, by granting large freedom to the group internal configuration so as to allow establishment/deletion of interaction links at anytime as long as global connectivity is preserved. A peculiar feature of our approach is that we are able to embed into a unique connectivity preserving action a large number of constraints and requirements for the group: (i) the presence of specific inter-robot sensing/communication models; (ii) group requirements such as formation control; and (iii) individual requirements such as collision avoidance. This is achieved by defining a suitable global potential function of the second smallest eigenvalue I»2 of the graph Laplacian, and by computing, in a decentralized way, a gradient-like controller built on top of this potential. Simulation results obtained with a group of quadrotor unmanned aerial vehicles (UAVs) and unmanned ground vehicles, and experimental results obtained with four quadrotor UAVs, are finally presented to thoroughly illustrate the features of our approach on a concrete case study.

/pdf/a-passivity-based-decentralized-strategy-for-generalized-3stlx94yrp.pdf

A passivity-based decentralized strategy for generalized connectivity maintenance

In current video-assisted thoracic surgery, the endoscopic camera is operated by an assistant of the surgeon, which has several disadvantages. This paper describes a system which enables the surgeon to control the endoscopic camera without the help of an assistant. The system is controlled using head movements, so the surgeon can use his/her hands to operate the instruments. The system is based on a flexible endoscope, which leaves more space for the surgeon to operate his/her instruments compared to a rigid endoscope. The endoscopic image is shown either on a monitor or by means of a head-mounted display. Several trial sessions were performed with an anatomical model. Results indicate that the developed concept may provide a solution to some of the problems currently encountered in video-assisted thoracic surgery. The use of a head-mounted display turned out to be a valuable addition since it ensures the image is always in front of the surgeon's eyes.

Endoscopic camera control by head movements for thoracic surgery

Minimally invasive biopsies, drainages and therapies in the soft tissue organs of the thorax and abdomen are typically performed through a needle, which is inserted percutaneously to reach the target area. The conventional workflow for needle placement employs an iterative freehand technique. This article provides an overview of needle-placement systems developed to improve this method.
An overview of systems for needle placement was assembled, including those found in scientific publications and patents, as well as those that are commercially available. The systems are categorized by function and tabulated. Over 40 systems were identified, ranging from simple passive aids to fully actuated robots. The overview shows a wide variety of developed systems with growing complexity. However, given that only a few systems have reached commercial availability, it is clear that the technical community is struggling to develop solutions that are adopted clinically.

An overview of systems for CT- and MRI-guided percutaneous needle placement in the thorax and abdomen.

In this paper a structure will be given which in a remarkably simple way offers a solution to the implementation of different telemanipulation schemes for discrete time varying delays by preserving passivity and allowing the highest trans- parency possible. This is achieved by splitting the communication channel in two separate ones, one for the energy balance which will ensure passivity and one for the haptic information between master and slave and which will address transparency. The authors believe that this structure is the most general up to date which preserves passivity under discrete time varying delays allowing different control schemes to address transparency.

http://www.roboticsproceedings.org/rss05/p36.pdf

Bridging the gap between passivity and transparency

Background: Various systems exist for CT-guided needle placement in the thorax and abdomen, but widespread adoption is lacking. The goal of this work is to develop a system for precise needle placement with a design focus on clinical acceptability, applicability and usability. Methods: A system was outlined incorporating a needle guide on a mechanism with a remote centre of motion, manually placeable around the patient at the desired entry point and lockable by push-button to the CT table. System and patient are scanned for system-to-CT registration and target specification. The needle guide is automatically aimed at the target, for manual needle insertion to specified depth. Results: A fully functional prototype was realized, achieving 1.20.6 mm placement error at 79.0 +/- 8.4 mm depth and 2.1 +/- 0.7 mm at 156.0 +/- 6.9 mm for 2x12 in- and out-of-plane punctures in a gelatin phantom. Conclusions: The system enables precise needle placement in a single insertion and is ready for its first clinical deployment.

Michel Franken

Papers

Bilateral Telemanipulation With Time Delays: A Two-Layer Approach Combining Passivity and Transparency

Endoscopic camera control by head movements for thoracic surgery

An overview of systems for CT- and MRI-guided percutaneous needle placement in the thorax and abdomen.

Bridging the gap between passivity and transparency

System for CT-guided needle placement in the thorax and abdomen: A design for clinical acceptability, applicability and usability.