Issues, concerns, and initial implementation results for space based telerobotic control

Telerobotic control for space based assembly and servicing tasks presents many problems in system design. Traditional force reflection teleoperation schemes are not well suited to this application, and the approaches to compliance control via computer algorithms have yet to see significant testing and comparison. These observations are discussed in detail, as well as the concerns they raise for imminent design and testing of space robotic systems. As an example of the detailed technical work yet to be done before such systems can be specified, a particular approach to providing manipulator compliance is examined experimentally and through modeling and analysis. This yields some initial insight into the limitations and design trade-offs for this class of manipulator control schemes. Implications of this investigation for space based telerobots are discussed in detail

Sensors Allocation and Observer Design for Discrete Bilateral Teleoperation Systems with Multi-Rate Sampling

This study addresses sensor allocation by analyzing exponential stability for discrete-time teleoperation systems. Previous studies mostly concentrate on the continuous-time teleoperation systems and neglect the management of significant practical phenomena, such as data-swap, the effect of sampling rates of samplers, and refresh rates of actuators on the system’s stability. A multi-rate sampling approach is proposed in this study, given the isolation of the master and slave robots in teleoperation systems which may have different hardware restrictions. This architecture collects data through numerous sensors with various sampling rates, assuming that a continuous-time controller stabilizes a linear teleoperation system. The aim is to assign each position and velocity signals to sensors with different sampling rates and divide the state vector between sensors to guarantee the stability of the resulting multi-rate sampled-data teleoperation system. Sufficient Krasovskii-based conditions will be provided to preserve the exponential stability of the system. This problem will be transformed into a mixed-integer program with LMIs (linear matrix inequalities). These conditions are also used to design the observers for the multi-rate teleoperation systems whose estimation errors converge exponentially to the origin. The results are validated by numerical simulations which are useful in designing sensor networks for teleoperation systems

Adaptive Neural Network Fixed-Time Control Design for Bilateral Teleoperation With Time Delay.

In this article, subject to time-varying delay and uncertainties in dynamics, we propose a novel adaptive fixed-time control strategy for a class of nonlinear bilateral teleoperation systems. First, an adaptive control scheme is applied to estimate the upper bound of delay, which can resolve the predicament that delay has significant impacts on the stability of bilateral teleoperation systems. Then, radial basis function neural networks (RBFNNs) are utilized for estimating uncertainties in bilateral teleoperation systems, including dynamics, operator, and environmental models. Novel adaptation laws are introduced to address systems' uncertainties in the fixed-time convergence settings. Next, a novel adaptive fixed-time neural network control scheme is proposed. Based on the Lyapunov stability theory, the bilateral teleoperation systems are proved to be stable in fixed time. Finally, simulations and experiments are presented to verify the validity of the control algorithm

Control systems with network delay

In this paper motion control systems with delay in measurement and control channels are discussed and a new structure of the observer-predictor is proposed. The feature of the proposed system is enforcement of the convergence in both the estimation and the prediction of the plant output in the presence of the variable, unknown delay in both measurement and in the control channels. The estimation is based on the available data – undelayed control input, the delayed measurement of position or velocity and the nominal parameters of the plant and it does not require apriori knowledge of the delay. The stability and convergence is proven and selection of observer and the controller parameters is discussed. Experimental results are shown to illustrate the theoretical prediction

Robust teleoperation of mechanical systems based on active disturbances compensation control structure

[EN] We present a control strategy to guarantee the stability of teleoperation systems formed by mechanical systems of nDOF with parametric uncertainties, external disturbances, a partial measure of state vectors, and without the use of force sensors. We neglected time delays in the communication channel, because we assume that mechanical systems are close enough. The control strategy is based on the disturbances active compensation structure, which incorporates discontinuous state observers and low-pass filters to estimate state variables and all nonmeasured signals needed to implement the controller. The controller is robust such that guarantees the tracking control objective. The teleoperation strategy’s performance is illustrated by experiments with mechanical systems of one and two degrees of freedom.[ES] Se presenta una estrategia de control para garantizar la estabilidad de sistemas de teleoperación formados por mecanismos de n grados de libertad (nGDL), con incertidumbres paramétricas, perturbaciones externas, medición parcial de los vectores de estado y sin el uso de sensores de fuerza. Se asume que los mecanismos se encuentran lo suficientemente cercanos uno del otro, de tal forma que el problema de retardos ocasionados por el medio de comunicación es despreciable. La estrategia se basa en la aplicación de la estructura de control con compensación activa de perturbaciones, la cual incorpora observadores de estado discontinuos y filtros paso bajo que permiten la estimación de las variables de estado y otras señales no medidas, así como los términos de perturbación presentes en ambos sistemas, que permiten la implementación de los controladores. El desempeño de la estrategia de teleoperación se ilustra a través de experimentos con mecanismos de uno y dos grados de libertad.Rosas Almeida, D.; González Solis, E.; Raya Díaz, G. (2021). Teleoperación robusta de sistemas mecánicos basada en la estructura de control con compensación activa de perturbaciones. Revista Iberoamericana de Automática e Informática industrial. 18(3):218-229. https://doi.org/10.4995/riai.2021.14433OJS218229183Almeida, D. I. R., Álvarez, J., Peña, J., 2011. Control structure with disturbance identification for lagrangian systems. International Journal of Non-Linear Mechanics 46, 486-495. https://doi.org/10.1016/j.ijnonlinmec.2010.08.005Almeida, D. I. R., Cárdenas, J. A. C., Díaz, J. d. D. O., Valdez, H. M., 2019. Control robusto de un actuador neumático basado en la estructura de control con compensación activa de perturbaciones para seguimiento de trayectorias. Revista Iberoamericana de Automática e Informática industrial 16, 138-146. https://doi.org/10.4995/riai.2018.9073Chan, L., Naghdy, F., Stirling, D., 2014. Application of adaptive controllers in teleoperation systems: A survey. IEEE Transactions on Human-Machine Systems 44, 337-352. https://doi.org/10.1109/THMS.2014.2303983De Lima, M. V., Mozelli, L. A., Neto, A. A., Souza, F. O., 2020. A simple algebraic criterion for stability of bilateral teleoperation systems under timevarying delays. Mechanical Systems and Signal Processing 137, 106217. https://doi.org/10.1016/j.ymssp.2019.06.035Erickson, D., Weber, M., Sharf, I., 2003. Contact stiffness and damping estimation for robotic systems. The International Journal of Robotics Research 22, 41-57. https://doi.org/10.1177/0278364903022001004Fink, N., 2019. Model reference adaptive control for telemanipulation. Hungarian Journal of Industry and Chemistry 47, 41-48. https://doi.org/10.33927/hjic-2019-07Li, Y., Liu, K., He, W., Yin, Y., Johansson, R., Zhang, K., 2019. Bilateral teleoperation of multiple robots under scheduling communication. IEEE Transactions on Control Systems Technology. https://doi.org/10.1109/TCST.2019.2923788Mohammadi, A., Tavakoli, M., Marquez, H. J., 2012. Control of nonlinear teleoperation systems subject to disturbances and variable time delays. In: Editor (Ed.), 2012 IEEE/RSJ International Conference on Intelligent Robots and Systems. Vol. II. IEEE, Ch. 7, pp. 3017-3022. https://doi.org/10.1109/IROS.2012.6385461Passenberg, C., Peer, A., Buss, M., 2010. A survey of environment-, operator- , and task-adapted controllers for teleoperation systems. Mechatronics 20, 787-801. https://doi.org/10.1016/j.mechatronics.2010.04.005Rasouli, P., Forouzantabar, A., Moattari, M., Azadi, M., 2020. Fault-tolerant control of teleoperation systems with flexible-link slave robot and disturbance compensation. Iranian Journal of Science and Technology, Transactions of Electrical Engineering, 1-13. https://doi.org/10.1007/s40998-020-00309-5Rodriguez-Angeles, A., Nijmeijer, H., 2004. Mutual synchronization of robots via estimated state feedback: a cooperative approach. IEEE Transactions on control systems technology 12, 542-554. https://doi.org/10.1109/TCST.2004.825065Rosas, D. I., Álvarez, J., Cantú Cárdenas, J. A., 2019. Application of the active disturbance rejection control structure to improve the controller performance of uncertain pneumatic actuators. Asian Journal of Control 21, 99-113. https://doi.org/10.1002/asjc.2026Rosas, D. I., Álvarez, J., Fridman, L., 2007. Robust observation and identification of ndof lagrangian systems. International Journal of Robust and Nonlinear Control: IFAC-Affiliated Journal 17, 842-861. https://doi.org/10.1002/rnc.1156Sánchez-Sánchez, P., Gutiérrez-Giles, A., Pliego-Jiménez, J., Arteaga-Pérez, ' M., 2019. Seguimiento de trayectorias con incertidumbre del modelo usando un diferenciador robusto. Revista Iberoamericana de Automática e Informática. 16, 423-434. https://doi.org/10.4995/riai.2019.10265Utkin, V., 1977. Variable structure systems with sliding modes. IEEE Transactions on Automatic control 22, 212-222. https://doi.org/10.1109/TAC.1977.1101446Yang, H., Liu, L., Wang, Y., 2019. Observer-based sliding mode control for bilateral teleoperation with time-varying delays. Control Engineering Practice 91, 104097. https://doi.org/10.1016/j.conengprac.2019.07.01

Generalized Scattering-Based Stabilization of Nonlinear Interconnected Systems

The research presented in this thesis is aimed at development of new methods and techniques for stability analysis and stabilization of interconnections of nonlinear systems, in particular, in the presence of communication delays. Based on the conic systems\u27 formalism, we extend the notion of conicity for the non-planar case where the dimension of the cone\u27s central subspace may be greater than one. One of the advantages of the notion of non-planar conicity is that any dissipative system with a quadratic supply rate can be represented as a non-planar conic system; specifically, its central subspace and radius can be calculated using an algorithm developed in this thesis. For a feedback interconnection of two non-planar conic systems, a graph separation condition for finite-gain L2-stability is established in terms of central subspaces and radii of the subsystems\u27 non-planar cones. Subsequently, a generalized version of the scattering transformation is developed which is applicable to non-planar conic systems. The transformation allows for rendering the dynamics of a non-planar conic system into a prescribed cone with compatible dimensions; the corresponding design algorithm is presented. The ability of the generalized scattering transformation to change the parameters of a system\u27s cone can be used for stabilization of interconnections of non-planar conic systems. For interconnections without communication delays, stabilization is achieved through the design of a scattering transformation that guarantees the fulfilment of the graph separation stability condition. For interconnected systems with communication delays, scattering transformations are designed on both sides of communication channel in a way that guarantees the overall stability through fulfilment of the small gain stability condition. Application to stabilization of bilateral teleoperators with multiple heterogeneous communication delays is briefly discussed. Next, the coupled stability problem is addressed based on the proposed scattering based stabilization techniques. The coupled stability problem is one of the most fundamental problems in robotics. It requires to guarantee stability of a controlled manipulator in contact with an environment whose dynamics are unknown, or at least not known precisely. We present a scattering-based design procedure that guarantees coupled stability while at the same time does not affect the robot\u27s trajectory tracking performance in free space. A detailed design example is presented that demonstrates the capabilities of the scattering-based design approach, as well as its advantages in comparison with more conventional passivity-based approaches. Finally, the generalized scattering-based technique is applied to the problem of stabilization of complex interconnections of dissipative systems with quadratic supply rates in the presence of multiple heterogeneous constant time delays. Our approach is to design local scattering transformations that guarantee the fulfilment of a multi-dimensional small-gain stability condition for the interconnected system. A numerical example is presented that illustrates the capabilities of the proposed design method

Sliding mode control for a surgical teleoperation system via a disturbance observer

To obtain accurate trajectory tracking with robustness and faithful force feedback in a practical application, a sliding mode controller (SMC) combined with a compensation controller based on a nonlinear disturbance observer (DOB) is proposed. The DOB estimates the disturbances arising mainly from the uncertain dynamic model of a surgical manipulator, frictional forces and external interaction forces, and compensates for these disturbances in the control law. Accordingly, it alleviates the chattering problem caused by t

T-S Fuzzy H∞ Tracking Control of Input Delayed Robotic Manipulators

Time delays are often encountered by practical control systems while they are acquiring, processing, communicating, and sending signals. Time delays may affect the system stability and degrade the control system performance if they are not properly dealt with. Taking the classical robot control problem as an example, the significant effect of time delay on the closed-loop system stability has been highlighted in the bilateral teleoperation, where the communication delay transmitted through a network medium has been received widespread attention and different approaches have been proposed to address this problem (Hokayem and Spong, 2006). In addition, examples like processing delays in visual systems and communication delay between different computers on a single humanoid robot are also main sources that may cause time delays in a robotic control system (Chopra, 2009), and the issue of time delay for robotic systems has been studied through the passivity property. For systems with time delays, both delay dependent and delay independent control strategies have been extensively studied in recent years, see for example (Xu and Lam, 2008) and references therein. For the control of nonlinear time delay systems, model based Takagi- Sugeno (T-S) fuzzy control (Tanaka and Wang, 2001; Feng, 2006; Lin et al., 2007) is regarded as one of the most effective approach because some of linear control theory can be applied directly. Conditions for designing such kinds of controllers are generally expressed as linear matrix inequalities (LMIs) which can be efficiently solved by using most available software like Matlab LMI Toolbox, or bilinear matrix inequalities (BMIs) which could be transferred to LMIs by using algorithms like iteration algorithm or cone complementary linearisation algorithm. From the theoretical point of view, one of the current focus on the control of time delay systems is to develop less conservative approaches so that the controller can stabilise the systems or can achieve the defined control performance under bigger time delay