Bilateral Telemanipulation With Time Delays: A Two-Layer Approach Combining Passivity and Transparency
TL;DR: 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.
Abstract: 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.
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Abstract: 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].
216 citations
TL;DR: This paper presents a novel decentralized strategy able to enforce connectivity maintenance for a group of robots in a flexible way, 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.
Abstract: 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.
157 citations
Cites background or methods from "Bilateral Telemanipulation With Tim..."
..., the ‘two-layer approach’ discussed in detail in [39]): the augmentation of the system dynamics with the tank state xti makes it possible to exploit to the full extent any passivity margin already present in the system by taking into account the complete past evolution and not only a point-wise (at the current time) condition6....
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...…all of the approaches based on the exploitation of energy tanks for preserving passivity (see, e.g., the ‘two-layer approach’ discussed in detail by Franken et al. (2011)): the augmentation of the system dynamics with the tank state xti makes it possible to exploit to the full extent any…...
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...A first example of using such a technique (a controlled energy transfer) can be found in the work of Duindam and Stramigioli (2004), while extensions are proposed by, e.g., Secchi et al. (2006) and Franchi et al. (2011); Franken et al. (2011); Franchi et al. (2012b)....
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...To this end, we first introduce the fundamental concept of Energy Tanks [26], [38], [39], [29]: the Energy Tanks are artificial energy storing elements that keep track of the energy naturally dissipated by the agents, e....
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06 May 2013
TL;DR: By properly controlling the energy exchanged during the action, this paper guarantees the system passivity for any choice of the stiffness matrix, especially in case of time-varying stiffness, and therefore a stable behavior of the robot both in free motion and in interaction with an environment.
Abstract: In this paper, we present a new impedance control strategy that allows to reproduce a time-varying stiffness. By properly controlling the energy exchanged during the action, we guarantee the system passivity for any choice of the stiffness matrix, especially in case of time-varying stiffness, and therefore a stable behavior of the robot both in free motion and in interaction with an environment.
156 citations
Cites background from "Bilateral Telemanipulation With Tim..."
...Since its introduction, impedance control has seen a lot of applications in robotic manipulation [13], haptics [14] and teleoperation [15]....
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...This reservoir is called tank and it has been firstly introduced in [16] and then used in [17] in the field of haptic interfaces and in [15][18][19] in the field of teleoperation of single and multirobots....
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...However, tank can be used for making the system robust with respect to modelling errors and to cope with problems related to an imperfect knowledge of the model, as shown in [15][21]....
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TL;DR: This paper addresses the initial steps of the development of control concepts satisfying the basic safety requirements of robotic surgery, i.e., providing the robot with the necessary dexterity and a stable and smooth behavior of the surgical tool.
Abstract: Introducing some form of autonomy in robotic surgery is being considered by the medical community to better exploit the potential of robots in the operating room. However, significant technological steps have to occur before even the smallest autonomous task is ready to be presented to the regulatory authorities. In this paper, we address the initial steps of this process, in particular the development of control concepts satisfying the basic safety requirements of robotic surgery, i.e., providing the robot with the necessary dexterity and a stable and smooth behavior of the surgical tool. Two specific situations are considered: the automatic adaptation to changing tissue stiffness and the transition from autonomous to teleoperated mode. These situations replicate real-life cases when the surgeon adapts the stiffness of her/his arm to penetrate tissues of different consistency and when, due to an unexpected event, the surgeon has to take over the control of the surgical robot. To address the first case, we propose a passivity-based interactive control architecture that allows us to implement stable time-varying interactive behaviors. For the second case, we present a two-layered bilateral control architecture that ensures a stable behavior during the transition between autonomy and teleoperation and, after the switch, limits the effect of initial mismatch between master and slave poses. The proposed solutions are validated in the realistic surgical scenario developed within the EU-funded I-SUR project, using a surgical robot prototype specifically designed for the autonomous execution of surgical tasks like the insertion of needles into the human body.
153 citations
Cites background from "Bilateral Telemanipulation With Tim..."
...It is worth highlighting that the mentioned approaches do not consider autonomous modes and, therefore, always produce a bilateral action, moving both master and slave....
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...Nevertheless, when the surgeon switches the robot from an autonomous mode to a teleoperated mode, there is likely a kinematic mismatch between the pose of the master console and that of the surgical robot (i.e., the slave robot)....
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26 May 2015
TL;DR: A novel hybrid Cartesian force/impedance controller that is equipped with energy tanks to preserve passivity is proposed and a constructive way of initiating the energy tanks via the concept of task energy is proposed.
Abstract: In this paper we propose a novel hybrid Cartesian force/impedance controller that is equipped with energy tanks to preserve passivity. Our approach overcomes the problems of (hybrid) force control, impedance control, and set-point based indirect force control. It allows accurate force tracking, full compliant impedance behavior, and safe contact resemblance simultaneously by introducing a controller shaping function that robustly handles unexpected contact loss and avoids chattering behavior that switching based approaches suffer from. Furthermore, we propose a constructive way of initiating the energy tanks via the concept of task energy. This represents an estimate of the energy consumption of a given force control task prior to execution. The controller can be applied to both rigid body and flexible joint dynamics. To show the validity of our approach, several simulations and experiments with the KUKA/DLR LWR-III are carried out.
152 citations
Cites background from "Bilateral Telemanipulation With Tim..."
...Up to now, the concept of energy tanks has been mainly used in teleoperation [18], [19], [20] and was only recently applied to impedance control in terms of variable stiffness [21], [22]....
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References
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TL;DR: In this paper, a control law for teleoperators is presented which overcomes the instability caused by time delay by using passivity and scattering theory, a criterion is developed which shows why existing bilateral control systems are unstable for certain environments, and why the proposed bilateral control law is stable for any environment and any time delay.
Abstract: A control law for teleoperators is presented which overcomes the instability caused by time delay. By using passivity and scattering theory, a criterion is developed which shows why existing bilateral control systems are unstable for certain environments, and why the proposed bilateral control law is stable for any environment and any time delay. The control law has been implemented on a single-axis force-reflecting hand controller, and preliminary results are shown. To keep the presentation clear, a single-degree-of-freedom (DOF) linear time-invariant (LTI) teleoperator system is discussed. Nevertheless, results can be extended, without loss of generality, to an n-DOF nonlinear teleoperation system. >
2,131 citations
01 Oct 1993
TL;DR: It is shown that a proper use of an four channels is of critical importance in achieving high performance telepresence in the sense of accurate transmission of task impedances to the operator.
Abstract: Tools for quantifying teleoperation system performance and stability when communication delays are present are provided A general multivariable system architecture is utilized which includes all four-types of data transmission between master and slave: force and velocity in both directions It is shown that a proper use of an four channels is of critical importance in achieving high performance telepresence in the sense of accurate transmission of task impedances to the operator It is also shown that transparency and robust stability (passivity) are conflicting design goals in teleoperation systems The analysis is illustrated by comparing transparency and stability in two common architectures, as well as a recent passivated approach and a new transparency-optimized architecture, using simplified one-degree-of-freedom examples >
2,083 citations
"Bilateral Telemanipulation With Tim..." refers background in this paper
...Transparency is a performance measure of how well the complete system is able to convey to the user the perception of direct interaction with the environment [2]....
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TL;DR: This survey addresses the subject of bilateral teleoperation, a research stream with more than 50 years of history and one that continues to be a fertile ground for theoretical exploration and many applications.
1,584 citations
"Bilateral Telemanipulation With Tim..." refers background in this paper
...[5] have written extensive survey papers that discuss various approaches to implement bilateral telemanipulation....
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01 Aug 1989
TL;DR: It is shown that the hybrid model (as opposed to other two-port forms) leads to an intuitive representation of ideal teleoperator performance and applies to several teleoperator architectures.
Abstract: The application of a hybrid two-port model to teleoperators with force and velocity sensing at the master and slave is presented. The interfaces between human operator and master, and between environment and slave, are ports through which the teleoperator is designed to exchange energy between the operator and the environment. By computing or measuring the input-output properties of this two-port network, the hybrid two-port model of an actual or simulated teleoperator system can be obtained. It is shown that the hybrid model (as opposed to other two-port forms) leads to an intuitive representation of ideal teleoperator performance and applies to several teleoperator architectures. Thus measured values of the h matrix or values computed from a simulation can be used to compare performance with the ideal. The frequency-dependent h matrix is computed from a detailed SPICE model of an actual system, and the method is applied to a proposed architecture. >
966 citations
Additional excerpts
...by Hannaford [12], Mobasser et al....
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13 Sep 2001
TL;DR: A patent-pending, energy-based method is presented for controlling a haptic interface system to ensure stable contact under a wide variety of operating conditions and requires very little additional computation and does not require a dynamical model to be identified.
Abstract: A patent-pending, energy-based method is presented for controlling a haptic interface system to ensure stable contact under a wide variety of operating conditions. System stability is analyzed in terms of the time-domain definition of passivity. We define a "passivity observer" (PO) which measures energy flow in and out of one or more subsystems in real-time software. Active behavior is indicated by a negative value of the PO at any time. We also define the "passivity controller" (PC), an adaptive dissipative element which, at each time sample, absorbs exactly the net energy output (if any) measured by the PO. The method is tested with simulation and implementation in the Excalibur haptic interface system. Totally stable operation was achieved under conditions such as stiffness >100 N/mm or time delays of 15 ms. The PO/PC method requires very little additional computation and does not require a dynamical model to be identified.
744 citations