This paper presents a new robot controller for space telerobotics missions specially designed to meet the requirements of KONTUR-2, a German & Russian telerobotics mission that addressed scientific and technological questions for future planetary explorations. In KONTUR-2, Earth and ISS have been used as a test-bed to evaluate and demonstrate a new technology for real-time telemanipulation from space. During the August 2015' experiments campaign, a cosmonaut teleoperated a robot manipulator located in Germany, using a force-feedback joystick from the Russian segment of the International Space Station (ISS). The focus of the paper is on the design and performance of the bilateral controller between ISS joystick and Earth robot. The controller is based on a 4-Channels architecture in which stability is guaranteed through passivity and the Time Delay Power Network (TDPN) concept. We show how the proposed approach successfully fulfills mission requirements, specially those related to system operation through space links and internet channels, involving time delays and data losses of different nature.
On-orbit servicing involves a new class of space missions in which a servicer spacecraft is launched into the orbit of a target spacecraft, the client. The servicer navigates to the client with the intention of manipulating it, using a robotic arm. Within this framework, this work presents a new robotic experimental facility which was recently built at the DLR to support the development and experimental validation of such orbital servicing robots. The facility allows reproducing a closeproximity scenario under realistic three-dimensional orbital dynamics conditions. Its salient features are described here, to include a fully actuated macro-micro system with multiple sensing capabilities, and analyses on its performance including the amount of space environment volume that can be simulated.
The paper proposes a general network based analysis and design guidelines for teleoperation systems. The electrical domain is appealing because it enjoys proficient analysis and design tools and allows a one step higher abstraction element, the network. Thus, in order to analyze the system by means of network elements the mechanical system must be first modeled as an electric circuit. Only then power ports become apparent and networks can be defined. This kind of analysis has been previously performed in systems with well defined causalities, specially in the communication channel. Indeed, a communication channel exchanging flow-like and effort-like signals, as for instance velocity and computed force, has a well defined causality and can thus be directly mapped as a two-port electrical network. However, this is only one of the many possible system architectures. This paper investigates how other architectures, including those with ambiguous causalities, can be modeled by means of networks, even in the lack of flow or effort being transmitted, and how they can be made passive for any communication channel characteristic (delay, package-loss and jitter). The methods are exposed in the form of design guidelines sustained with an example and validated with experimental results.
This article presents a method for passivating the communication channel of a symmetric position-position teleoperation architecture on the time domain. The time domain passivity control approach has recently gained appeal in the context of timedelayed teleoperation because passivity is not established as a design constraint, which often forces conservative rules, but rather as a property which the system must preserve during operation. Since passivity is a network property, the first design rule within this framework is to represent consistent and comprehensible circuit (i.e., network) representations of the mechanical teleoperation system. In particular, the energetic behavior of these networks is interesting because it allows straightforward conclusions about system stability. By means of so-called passivity observers (PO) and passivity controllers (PC) (Hannaford & Ryu, 2001), the energetic response of a delayed communication channel is captured and modulated over time so that the network in question never becomes nonpassive. The case analyzed in this paper tackles a communication channel that conveys position data back and forth. This type of channel does not offer intuitive network representation since only flows are actually being transmitted. Although energy clearly travels from one side to the other, port power identification, as defined by the correlated pair flow and effort, is not evident. This work first investigates how this kind of channel can be represented by means of circuit networks even with the lack of physical effort being transmitted through the channel, and identifies which networks are susceptible to become nonpassive due to the channel characteristics (i.e., time delay, discretization or package loss). Once achieved, a distributed control structure is presented based on a PC series that keeps the system at the verge of passivity (and therefore stability) independent from the channel properties. The results obtained by the simulation and by experiment sustain the presented approach.
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