Virtual Proxy Research Articles

Leader-Following Connectivity Preservation and Collision Avoidance Control for Multiple Spacecraft with Bounded Actuation

This paper investigates the distributed formation control of a group of leader-following spacecraft with bounded actuation and limited communication ranges. In particular, connectivity-preserving and collision-avoidance controllers are proposed for the leader with constant or time-varying velocity, respectively. The communication graph between the spacecraft is modeled via a distance-induced proximity graph. By designing a virtual proxy for each spacecraft, the spacecraft–proxy couplings address the actuator saturation constraints. The inter-proxy dynamics incorporated with a bounded artificial potential function fulfill the coordination of all proxies. In addition, the bounded potential function can simultaneously tackle connectivity preservation and collision avoidance problems. The distributed formation controllers are proposed for multiple spacecraft with constant or time-varying velocities relative to the leader. A sliding mode control approach and the proxies’ dynamics are used in the design of a distributed cooperative controller for spacecraft to address the cooperative problem between the followers and the leader. Numerical simulations confirm the effectiveness of the anti-saturation distributed connectivity preservation controller.

Connectivity preservation control for multiple unmanned aerial vehicles in the presence of bounded actuation

This paper proposes a novel multi-unmanned aerial vehicle (UAV) connectivity preservation controller, suitable for scenarios with bounded actuation and limited communication range. According to the hierarchical control strategy, controllers are designed separately for the position and attitude subsystems. A distributed position controller is developed, integrating an indirect coupling control mechanism. The innovative mechanism associates each UAV with a virtual proxy, facilitating connections among adjacent UAVs through these proxies. This structuring assists in managing the actuator saturation constraints effectively. The artificial potential function is utilized to preserve network connectivity and fulfill coordination among all virtual proxies. Additionally, an attitude controller designed for finite-time convergence guarantees that the attitude subsystem adheres precisely to the attitude specified by the distributed position controller. Simulation results validate the efficacy of this distributed formation controller with connectivity preservation under bounded actuation conditions. The simulation results confirm the effectiveness of the distributed connectivity preservation controller with bounded actuation.

Mapping Online Community Spaces Through Online Focus Group Discussions Among Gay, Bisexual, and Other Men Who Have Sex With Men in Guangdong, China: Implications for Human Immunodeficiency Virus/Sexually Transmitted Disease Prevention Services.

Chinese gay, bisexual, and other men who have sex with men (GBMSM) face discrimination in many facility-based health services, thus increasing the importance of online engagement. The purpose of this study was to examine online GBMSM community spaces and implications for HIV/sexually transmitted disease prevention services. We conducted a total of 6 online focus group discussions with Chinese GBMSM from Guangdong province on the chat-based platform WeChat in 2021. Focus group discussions were asynchronous, and participants were able to provide and map out online spaces that they had participated in and share their perspectives on online engagement. Data were analyzed through framework analysis. Overall, 48 participants participated. Most were mainly sexually attracted to men (n = 43; 90.0%) and never participated in in-person LGBTQ-related events (n = 29; 60.4%). Participants articulated a typology of online spaces along the axes of whether such spaces were Chinese platforms (vs. non-Chinese) or whether they were GBMSM-specific (vs. non-GBMSM-specific). Participants articulated several advantages of online spaces, including greater anonymity, opportunities for community building, sharing of sexual health information, and being able to meet other GBMSM more efficiently. Drawbacks included the lack of personal connection, lack of safety measures for youth, encountering deception and the use of fake profile pictures, and needing a virtual proxy network to access some websites. Participants provided suggestions to further improve their experiences of online spaces. Although broad-based, GBMSM-specific messaging can be implemented in Chinese, GBMSM-specific spaces, sexual health messaging may also reach niche GBMSM communities in a variety of non-GBMSM spaces.

Adaptive proxy-based sliding mode control for a class of second-order nonlinear systems and its application to pneumatic muscle actuators

The human-centered robotic systems demand safe and robust controllers in many applications. This paper proposes an adaptive proxy-based sliding mode control approach for a class of typical second-order nonlinear systems. A new PID-type virtual coupling is designed between a virtual proxy and the physical object. Considering the unknown bound of lumped disturbances, an adaptation law is applied to online adjust the gain of a sign function which ensures the proxy to track the reference accurately. By using the Lyapunov theorem, the closed-loop system stability is proved. Both simulations and experiments are conducted to verify the proposed method based on a real-world pneumatic muscle actuator control platform. The results show that the proposed adaptive proxy-based sliding mode control approach presents better tracking accuracy, safety, and robustness than the conventional PID control and sliding mode control.

An Anonymous System Based on Random Virtual Proxy Mutation

An Anonymous System Based on Random Virtual Proxy Mutation

Adaptive Proxy-Based Robust Control Integrated With Nonlinear Disturbance Observer for Pneumatic Muscle Actuators

In pneumatic muscle actuators (PMAs)-driven robotic applications, there might exist unpredictable shocks which lead to the sudden change of desired trajectories and large tracking errors. This is dangerous for physical systems. In this article, we propose a novel adaptive proxy-based robust controller (APRC) for PMAs, which is effective in realizing a damped response and regulating the behaviors of the PMA via a virtual proxy. Moreover, the integration of the APRC and the nonlinear disturbance observer further handles the system uncertainties/disturbances and improves the system robustness. According to the Lyapunov theorem, the tracking states of the closed-loop PMA control system are proven to be globally uniformly ultimately bounded through two motion phases. Extensive experiments are conducted to verify the superior performance of our approach, in multiple tracking scenarios.

Bio-inspired knitted fabric development using 3D modelling and image processing

The principles of biomimicry were used to develop novel textile structures inspired from the Morpho butterfly’s wing scale, primarily for technical applications. Bio-mimetic virtual abstract 3D proxy models of knitted structures were developed. The models were mapped onto the original biological templates and then on the knitted fabrics. Image segmentation methods such as binarize, local adaptive threshold and morphological threshold were employed concurrently to ‘digitise’ the biological template, 3D models and knitted fabrics. Eight samples mimicking the Morpho scales were knitted. Euclidean distance measurement and pixel values, established that the biological template, selected 3D geometrical models and physical knitted fabrics have a high degree of similarity. Local adaptive threshold gave better results for pixel intensity differences while the morphological threshold method generated better results when measuring Euclidean distance.

Continuous Collision Detection for Virtual Proxy Haptic Rendering of Deformable Triangular Mesh Models.

Most haptic systems suffer from what is known as the "tunneling" problem, which arises when a virtual object moves or deforms largely towards a small virtual tool. This problem occurs because the displacement of the virtual object is not considered during collision detection and can be solved with Continuous Collision Detection (CCD). Originally, haptic rendering with CCD was proposed for applications with 6 Degrees-of-Freedom (DoF) only. However, 3-DoF is simple to use in, and sufficient for, many applications. In this paper, we focus on CCD with a 3-DoF point-object haptic rendering of dynamic and deformable objects. Since we use the virtual proxy method, we propose a triangle-proxy CCD approach with a complementary process called Proxy Pop-Out to solve this problem. The results show that we are able to solve the "tunneling" problem, even for a small proxy against thin and deformable objects with large motions. In addition, we present probing haptic interactions with deformable objects in a multi-rate haptic rendering system. By using Oriented Particles and Position Based Dynamics, our system is efficient and stable.

Connectivity-Preserving Synchronization of Time-Delay Euler-Lagrange Networks With Bounded Actuation.

This paper proposes a strategy to overcome the threats posed to connectivity-preserving synchronization of Euler-Lagrange networks by time-varying delays and bounded actuation. It first introduces a suitable distributed negative gradient plus damping injection controller, based on which it establishes that the local connectivity of time-delay Euler-Lagrange networks can be preserved by appropriately regulating the interagent connections and increasing the damping injection locally. Yet, actuator saturation may impede the proper modulation of the interagent connections and the injection of sufficient damping and, thus, may threaten the maintenance of connectivity. This paper then develops an indirect coupling control framework which integrates the bounded actuation constraints into the control design. The framework endows every agent with a virtual proxy and couples initially adjacent agents through their virtual proxies. The interproxy couplings then tackle the time-varying delays while the agent-proxy couplings account for the saturation of actuators. Lyapunov-Krasovskii analysis proves that the indirect coupling strategy can drive time-delay Euler-Lagrange networks with bounded actuation to connectivity-preserving synchronization by limiting the energy of the agent-proxy and interproxy couplings according to the actuation constraints. Experiments with Geomagic Touch haptic robots validate the proposed designs compared to a conventional proportional plus damping controller.

Virtual coupling triggering for interaction force reduction of haptic free-motion using surface EMG

Haptic systems render virtual reality by providing kinesthetic, tactile senses to an operator through a haptic device. Previous researchers analyzed haptic systems’ stability and performance issues. On haptic frameworks, a virtual coupling network that provides compliance between the haptic device and the virtual proxy for passivity distorts realistic interaction with virtual environment. That is, the operator will experience resistance even when the environment simulates free-motion. This paper suggests a virtual coupling triggering algorithm for improving free-motion performance of a haptic interface. A 1DOF exoskeleton for a knee joint is designed, and admittance control is used instead of compensating device dynamics to enable wide implementation of the haptic interface, up to a heavy and bulky haptic device. The algorithm utilizes surface EMG (sEMG) signal, which is easily collected from operators. Proper virtual coupling is designed according to previously derived guidelines for unconditional stability criteria. A method for pattern recognition of sEMG signal and a triggering algorithm corresponding to the recognized patterns are explained. The suggested algorithm successfully reduces peak of interaction force between the device and the operator by about half when the haptic interface simulates free-motion. Corresponding simulations and experiments are presented.

Improving transparency of virtual coupling for haptic interaction with human force observer

SUMMARYRelying solely on virtual springs and dampers, the transparency of standard virtual coupling suffers from the device-proxy coordination error when a large interaction force is engaged (e.g., contact tasks) and also from the unmodifiable inertias of the haptic device and the virtual proxy. To overcome these limitations, we propose a novel virtual coupling scheme, which, utilizing passive decomposition and a human force observer, can maintain the device-proxy coordination error even during contact tasks, while also allowing for scaling down (or up) the apparent inertia of the coordinated device-proxy system, thereby, substantially improving transparency of the standard virtual coupling. Experiments are performed to show the performance and passivity of the proposed virtual coupling. Minimum-possible passive inertia scaling is also theoretically established via some positive-real analysis.

6-DOF extension of memory-based passivation approach for stable haptic interaction

This paper extends previously proposed memory-based passivity approach (MBPA) to 6 degrees-of-freedom (DOF) haptic interactions. By introducing 6-DOF virtual proxy and virtual object, connected with haptic interaction point (HIP), we can extend MBPA to 6-DOF, including torque vs. orientation passivity. To find a passive relationship between positions vs. force graph, instead of position itself, we use position error between the center of mass of the virtual proxy and virtual object. For the angle vs. torque graph, we use angular displacement between the unit vector of the virtual proxy and virtual object instead of angle itself. After the extension, position/angular resolution became a problem, since it depends on configuration of the haptic device. Position resolution should be fixed, and real-time monitoring of every single position change is strongly required in previous MBPA. However, those are difficult requirements when the approach is extended to multi-DOF, especially 6-DOF including orientation. This paper revises the data saving procedure and force bounding mechanism to allow variable position resolution. Position value instead of simple incremental integer is saved together with matched force data into memory space, which allows to interpolate corresponding force value at the releasing trajectory even though it is not in the saved data list. This generalized framework of 6-DOF haptic rendering is evaluated according to simulation results.

Callisto Basic and Callisto Pro

Callisto Basic and Callisto Pro

Memory-Based Passivation Approach for Stable Haptic Interaction

Inspired from the graphical interpretation of passivity in a position versus force xy graph, this paper proposes a new concept of passivation method to increase the dynamic range of impedance in which a haptic interface can passively interact. The position versus force graph represents the energy behavior in a one-port haptic interface while the haptic interface is traveling in (pressed) or out of (released) a virtual environment (VE). It interprets that to make the one-port system passive, it is sufficient to bound the releasing path below the pressing path in the position versus force graph. To realize the bound, the computed force output from the VE is saved into a designated memory, addressed by current position, while the haptic interface is pressed. Thereafter, the saved force can be reused to upper-bound the releasing path below the saved pressing path while the haptic interface is released. The proposed method is generalized from preliminary work by including interaction with a moving virtual object and multi-DOF extension, together with more systematic and detailed explanations about the methods. In particular, we reconfigure the one-port moving virtual object as a two-port haptic controller and a connected one-port moving inertia. This reconfiguration allows implementation of the preliminary approach including the interaction with moving virtual objects by using an error versus force passivity instead of a position versus force passivity. This two-port extension also allows generalization of the proposed method to multi-DOF interactions by introducing virtual proxy as a virtual moving object. The proposed method is tested with a single and a multi-DOF haptic interface and shows better performance than the recently proposed field-programmable gate array-based time-domain passivity approach .

컨택트 작업 시 햅틱 인터렉션의 투명성 향상을 위한 Virtual Coupling 기법의 설계

Since its introduction (e.g., [4, 6]), virtual coupling technique has been de facto way to connect a haptic device with a virtual proxy for haptic rendering and control. However, because of the single dependence on spring-damper feedback action, this virtual coupling suffers from the degraded transparency particularly during contact tasks when large device/proxy-forces are involved. In this paper, we propose a novel virtual coupling technique, which, by utilizing passive decomposition, reduces device-proxy position deviation even during the contact tasks while also scaling down (or up) the apparent inertia of the coordinated device-proxy. By doing so, we can significantly improve transparency between multiple degree of freedom (possibly nonlinear) haptic device and virtual proxy. In other to use passive decomposition, disturbance observer of [3] is adopted to estimate human force with some dead-zone modification to avoid "winding-up" force estimation in the presence of device torque saturation. Some preliminary experimental results are also given to illustrate efficacy of the proposed technique.

Stateful Virtual Proxy for SIP Message Flooding Attack Detection

VoIP service is the transmission of voice data using SIP protocol on an IP-based network. The SIP protocol has many advantages, such as providing IP-based voice communication and multimedia service with low communication cost. Therefore, the SIP protocol disseminated quickly. However, SIP protocol exposes new forms of vulnerabilities to malicious attacks, such as message flooding attack. It also incurs threats from many existing vulnerabilities as occurs for IP-based protocol. In this paper, we propose a new virtual proxy to cooperate with the existing Proxy Server to provide state monitoring and detect SIP message flooding attack with IP/MAC authentication. Based on a proposed virtual proxy, the proposed system enhances SIP attack detection performance with minimal latency of SIP packet transmission.

Cooperative Proxy Caching for Wireless Base Stations

This paper proposes a mobile cache model to facilitate the cooperative proxy caching in wireless base stations. This mobile cache model uses a network cache line to record the caching state information about a web document for effective data search and cache space management. Based on the proposed mobile cache model, a P2P cooperative proxy caching scheme is proposed to use a self‐configured and self‐managed virtual proxy graph (VPG), independent of the underlying wireless network structure and adaptive to the network and geographic environment changes, to achieve efficient data search, data cache and date replication. Based on demand, the aggregate effect of data caching, searching and replicating actions by individual proxy servers automatically migrates the cached web documents closer to the interested clients. In addition, a cache line migration (CLM) strategy is proposed to flow and replicate the heads of network cache lines of web documents associated with a moving mobile host to the new base station during the mobile host handoff. These replicated cache line heads provide direct links to the cached web documents accessed by the moving mobile hosts in the previous base station, thus improving the mobile web caching performance. Performance studies have shown that the proposed P2P cooperative proxy caching schemes significantly outperform existing caching schemes.

幾何学的力覚提示アルゴリズムの力学的解釈とインピーダンス型およびアドミッタンス型の実装法

Geometric haptic rendering algorithms, in which virtual proxy positions are determined according to input device positions, are widely used for impedance-type haptic rendering. Such methods are intuitively simple because they reduce mechanistic problems of determining reaction forces into geometric problems of updating proxy positions. Aiming to extend the scope of application of geometric haptic algorithms, this paper presents a mechanistic interpretation of geometric algorithms and proposes two techniques. One is a technique to combine geometric algorithms and viscous damping in impedance-type haptic rendering. The other is a technique to utilize geometric algorithms in admittance-type haptic rendering. The results of implementation experiments are presented.

Haptic Rendered Virtual Modelling of Gear Assembly

Development of a haptic rendered virtual model for automatic gear assembly is reported. The overall objective of the project is to develop a new paradigm for programming of robotics manipulator performing complex constrained motion tasks. The virtual model is used by the human operator to perform the task in a virtual environment. Position and contact force and torque data generated in the virtual environment combined with a priori knowledge about the task is used to identify and learn the skills in the newly demonstrated tasks and then to perform the assembly by a robotic manipulator. The two metric module spur gears meshing engagement problem is used as a case study. The gears are modelled using virtual proxy algorithm. The operators’ control traces are recorded from the virtual environment and are used to acquire manipulation skills by machine learning algorithms. The development platform consists of a six degree-of-freedom PHANToM Premium 1.5 and Reachin API. An overview of the whole project is provided and the development carried out to construct the haptic rendered virtual model is described. The progress up-to-date is provided.

Spatial Constraint Method: A New Approach to Real-Time Haptic Interaction in Virtual Environments

In this paper, we propose an approach to real-time haptic interaction based on the concept of simulating the constraining propertes of space. Research on haptic interaction has been conducted from the points of view of both surface and volume rendering. Most approaches to surface rendering—such as the constraint-based god-object method, the point-based approach, and the virtual proxy approach—have dealt only with the interaction with an object surface. Whereas, in volume rendering approaches, algorithms for representing volume data through interactions in space have been investigated. Our approach provides a framework for the representation of haptic interaction with both surface and space. We discretize the space using a tetrahedral cell mesh and associate a constraining property with each cell. The interaction of the haptic interface points with a volume is simulated using the constraining properties of the cells occupied by this volume. We implemented a fast computation algorithm that works at a haptic rate. The algorithm is robust in that any sudden or quick motion of the user does not disturb the computation, and the computation time for each cycle is independent of the complexity of the model as a whole. To demonstrate the performance of the proposed method, we present experimental results on the interaction with models of varying complexity. Also, we discuss some problems that need to be solved in future work.