Network Representation and Passivity of Delayed Teleoperation Systems

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

Realizing low-impedance rendering in admittance-type haptic interfaces using the input-to-state stable approach

© 2017 IEEE. This paper proposes an approach to enlarge the impedance range of admittance-type haptic interfaces. Admittance-type haptic interfaces have advantages over impedance-type haptic interfaces in the interaction with high impedance virtual environments. However, the performance of admittance-type haptic interfaces is often limited by the lower boundary of the impedance that can be achieved without stability issue. Especially, it is well known that low value of inertia in an admittance model often causes unstable interaction. This paper extends recently proposed input-to-state stable approach [1] to further lower down the achievable impedance in admittance-type haptic interfaces with less conservative constraint compared with the passivity-based approaches. The primary challenge was identifying the nonlinear hysteresis components which are essential for the implementation of the input-to-state stable approach. Through experimental investigation and after separating and merging the admittance model and the position controller, the partial admittance model (from the measured human force to the desired velocity) and the velocity controller (from the velocity tracking error to the controller force) were found having counter-clockwise hysteresis nonlinear behavior. Therefore, it allows implementing the one-port input-to-state stable (ISS) approach for making both components dissipative and ISS. An additional advantage of the proposed ISS approach is the easiness of the implementation. No model information is required, and the network representation is not necessary, unlike the passivity-based approaches. Series of experiments verified the effectiveness of the proposed approach in term of significantly lowering the achievable impedance value compared with what the time-domain passivity approach can render

Ambiguity-Aware Multi-Object Pose Optimization for Visually-Assisted Robot Manipulation

6D object pose estimation aims to infer the relative pose between the object and the camera using a single image or multiple images. Most works have focused on predicting the object pose without associated uncertainty under occlusion and structural ambiguity (symmetricity). However, these works demand prior information about shape attributes, and this condition is hardly satisfied in reality; even asymmetric objects may be symmetric under the viewpoint change. In addition, acquiring and fusing diverse sensor data is challenging when extending them to robotics applications. Tackling these limitations, we present an ambiguity-aware 6D object pose estimation network, PrimA6D++, as a generic uncertainty prediction method. The major challenges in pose estimation, such as occlusion and symmetry, can be handled in a generic manner based on the measured ambiguity of the prediction. Specifically, we devise a network to reconstruct the three rotation axis primitive images of a target object and predict the underlying uncertainty along each primitive axis. Leveraging the estimated uncertainty, we then optimize multi-object poses using visual measurements and camera poses by treating it as an object SLAM problem. The proposed method shows a significant performance improvement in T-LESS and YCB-Video datasets. We further demonstrate real-time scene recognition capability for visually-assisted robot manipulation. Our code and supplementary materials are available at https://github.com/rpmsnu/PrimA6D.Comment: IEEE Robotics and Automation Letter

Multilateral teleoperation over communication time delay using the time-domain passivity approach

A general framework to stabilize multilateral teleoperation system over a communication time delay based on the well-known time-domain passivity approach (TDPA) is proposed. The uniqueness of this framework is that it is independent of the amount of communication time delay, the multilateral control architecture, and the number of masters and slaves. The multilateral system was first decoupled into subsystems with respect to each terminal by identifying the input signals' contributions to the output terminals, which was not straightforward due to the coupled nature of the multilateral teleoperation system. The decoupled subsystems were then converted into an electrical circuit using a mechanical-electrical analogy. Time-delay power network (TDPN) was introduced to clarify active energy sources from the time delay and passivity observer/passivity controller (PO/PC) was utilized to dissipate those active energies. A less-conservative method compared with prior work was proposed to guarantee the stability. Experiments with a trilateral teleoperation system and with a multilateral teleoperation system with a dual master and dual slave were conducted to validate the proposed framework

Enhancing the Command-Following Bandwidth for Transparent Bilateral Teleoperation

© 2018 IEEE. Enhancing transparency of a teleoperation system by increasing the command-following bandwidth has not received lots of attention so far. This is considered a challenging task since in a teleoperation system the command-following bandwidth of the slave robot motion controller cannot be increased with a conventional motion controller as the desired trajectory is instantaneously commanded by the human user and thus, cannot be considered to be given in a pre-computed, smooth second order derivative form. We propose a method to increase the command-following bandwidth by extending the previously introduced Successive Stiffness Increment (SSI) approach to bilateral teleoperation. The approach allows realizing a very high motion controller gain, which cannot be realized with a conventional bilateral teleoperation controller as confirmed by experimental results

A Robust Controller Design Method for a Flexible Manipulator with a Large Time Varying Payload and Parameter Uncertainties

Abstract. A new robust controller design method is proposed to obtain a less conservative feedback controller and it is applied to a single-link flexible manipulator. The objective is to maximize the control performance guaranteeing the robust stability when regulating the tip position of the flexible manipulator in the presence of a large time-varying payload and parameter uncertainties such as stiffness and joint friction. A descriptor form representation, which allows separate treatment of payload uncertainty from other parametric uncertainties, is used to reduce the conservatism of the conventional robust control approaches. Uncertainty of the payload in the inertia matrix is represented by polytopic approach and the uncertain parameters in the damping and stiffness matrices are treated with descaling techniques. Using aforementioned techniques, the robust LQ controller design problem for a flexible manipulator based on the guaranteed cost approach is formulated. Then, the formulated problem is solved by LMIs

Enhancing the rate-hardness of haptic interaction: Successive force augmentation approach

© 1982-2012 IEEE. There have been numerous approaches that have been proposed to enlarge the impedance range of haptic interaction while maintaining stability. However, enhancing the rate-hardness of haptic interaction while maintaining stability is still a challenging issue. The actual perceived rate-hardness has been much lower than what the users expect to feel. In this paper, we propose the successive force augmentation (SFA) approach, which increases the impedance range by adding a feed-forward force offset to the state-dependent feedback force rendered using a low stiffness value. This allows the proposed approach to display stiffness of up to 10 N/mm with Phantom Premium 1.5. It was possible to further enhance the rate-hardness by using the original value of virtual environment stiffness for feedback force calculation during the transient response followed by normal SFA. Experimental evaluation for multi-DoF virtual environment exhibited a much higher displayed stiffness and rate-hardness compared to conventional approaches. Two user studies revealed that the increase of rate-hardness due to SFA allowed the participants to have a faster reaction time to an unexpected collision with a virtual wall and accurately discriminate between four virtual walls of different stiffness

KONTUR-2: Force-feedback Teleoperation from the International Space Station

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