Mahya Shahbazi

A control architecture for dual user teleoperation with unknown time delays: A sliding mode approach

This paper presents a sliding mode-based impedance controller for delayed dual user teleoperation system with unknown delay. The latency which has considerable undesirable effects on system stability and performance is compensated through this control approach. The nonlinear gain of the controller is achieved independent of time delay caused by communication channels. Therefore, the necessity of measurement or estimation of the time delay is relaxed. In addition, the stability analysis is presented for the closed-loop system employing the passivity theory. The validity of the proposed controller scheme is demonstrated via simulations performed on a delayed dual user system.

A novel shared structure for dual user systems with unknown time-delay utilizing adaptive impedance control

In this paper, a novel decentralized multilateral structure is proposed for the dual user systems in the presence of communication delay. The proposed structure utilizes adaptive impedance control approach in order to overcome the destructive effect of the time-delay on system desired-objectives, which is a disregarded issue in the previous studies on dual user system. The proposed control strategy, which utilizes three desired impedance surfaces defined in the paper, satisfactorily brings the system hybrid matrix close to the ideal one that guarantees the system stability and transparency. The controller is designed in a way that eliminates the necessity of the delay estimation as one of its outstanding characteristics; consequently, the unknown communication time-delay can be handled via this structure while previous studies have disregarded the issue of time delay in dual user system. Furthermore, the adaptive structure of the controller promises to overcome the uncertainties on robots dynamics. In addition, the efficiency of the controller in guaranteeing the system stability in the presence of unknown communication delay is investigated through passivity theory and the presented analysis illustrates complete independency of the closed-loop system stability on time delay value applying the proposed controller. Experimental results performed on a delayed dual user system demonstrate validity of the proposed scheme.

Tracking control of flexible-link manipulators based on environmental force disturbance observer

In this paper, a composite tracking controller for single-link flexible manipulators is proposed. An Extended Kalman Filter (EKF) is utilized to observe the environmental forces (as disturbances) and a Lyapunov redesign robust control to alleviate the destructive effects of the observation errors in noisy situations. The observed forces can also be used in many applications such as tele-surgical robotics as interaction data. Utilizing this method, the necessity of additional force sensors is removed. It enhances structural miniaturization of the robots and reduces the costs. It should be noted that the singularity of jacobian matrix related to the flexible link, causes extreme difficulties in observation procedure which is dealt with in this paper. Moreover, control strategy is based on the common near to tip output to avoid the difficulties associated with non-minimum phase behavior of flexible link manipulators. Simulation results performed on a single-link flexible manipulator (with parameters of an experimental setup) are presented to illustrate the significant improvement in performance of the proposed controller as well as force-disturbance observation ability in noisy situations.

A dual-user teleoperated system with Virtual Fixtures for robotic surgical training

This paper proposes a teleoperated dual-user system incorporating Virtual Fixtures (VFs) that allows concurrent performance of a robotic surgical task by an expert and a trainee. In order to guide the trainee through the procedure, an adaptive VF is created in the trainees workspace according to the motion generated by the expert who is performing the surgery at the same time. The VF gets adaptively adjusted based on the level of expertise the trainee shows during the surgery. In addition, the trainees level of expertise is used to adaptively adjust the dual-user dominance factor in an online fashion, which gives the trainee some authority over the task based on his/her skill level. To quantify the trainees expertise level, a performance measure is proposed, based on the force generated by the VF. Three performance measures from the literature are also used. To satisfy the desired objectives of the proposed system, an impedance-based control methodology is adopted. Stability of the closed-loop system is investigated using the small-gain theorem. A sufficient stability condition is derived that guarantees stability in the presence of time-varying communication delay. Experimental results are given to validate the performance of the system.

A sliding-mode controller for dual-user teleoperation with unknown constant time delays

Robotica / Volume 31 / Issue 04 / July 2013, pp 589 598 DOI: 10.1017/S0263574712000604, Published online: 19 October 2012 Link to this article: http://journals.cambridge.org/abstract_S0263574712000604 How to cite this article: Mahya Shahbazi, S. Farokh Atashzar, H. A. Talebi, F. Towhidkhah and M. J. Yazdanpanah (2013). A sliding-mode controller for dual-user teleoperation with unknown constant time delays. Robotica, 31, pp 589-598 doi:10.1017/S0263574712000604 Request Permissions : Click here

Control of time-delayed telerobotic systems with flexible-link slave manipulators

This paper focuses on control challenges caused by the slave-arm flexibility in master-slave telerobotic systems. Apart from time delay, the nonlinear non-minimum phase deflection of flexible-link slave manipulators creates extra challenges for control of telerobotic systems. These challenges have forced most of the prior research to use basic simplifications. In this paper, we try to remove most of the simplifications using a more realistic model for slave deflections. The degrading effects of flexibility on stability and performance of conventional telerobotics architectures are analyzed. Then, the standard Extended Lawrence Four-Channel (ELFC) control architecture is modified to obtain the stability condition and to enhance performance. Finally, the input-to-output stability (IOS) Small-Gain Theorem is used to generalize the stability criteria for varying delay and to remove the restrictive assumption of deflection-linearity. The proposed architecture consists of a local Partial Feedback Linearization scheme embedded into a modified ELFC architecture. This study is motivated by the use of light-weight cable driven tools in telerobotic surgery.

Robotics-Assisted Mirror Rehabilitation Therapy: A Therapist-in-the-Loop Assist-as-Needed Architecture

This paper presents a therapist-in-the-loop framework for robotics-assisted mirror rehabilitation integrated with adaptive assist-as-needed therapy (ANT) that is adjusted based on the impairment level of the patients affected limb. The framework, which is designed for patients with hemiparesis and/or hemispatial neglect, uses a patients functional limb as the medium to transfer therapeutic training from the therapist to the patients impaired limb (PIL). This allows the patient to use his/her functional limb to adjust the desired trajectory generated by the therapist if the trajectory is painful or uncomfortable for the PIL. In order to realize the adaptive patient-targeted therapy, two motor-function assessment metrics, performance symmetry and level of guidance, are proposed, providing real time, task-independent, and objective assessment of the PILs motor deficiency. An adaptation law is also presented to adjust the intensity of the therapy delivered to the patient in real time and based on the aforementioned estimation of the impairment level of the PIL. Closed-loop system stability has been investigated in the presence of communication delays to facilitate tele/in-home rehabilitation. For this purpose, a combination of the Circle Criterion and the Small-Gain theorem has been applied to account both for communication time delays and the time-varying adaptive ANT. Results of experiments to investigate the performance of the proposed framework are reported.

Characterization of Upper-Limb Pathological Tremors: Application to Design of an Augmented Haptic Rehabilitation System

In this paper, an adaptive filtering technique is proposed to estimate and characterize pathological tremors caused by Parkinsons Disease (PD) and Essential Tremor (ET). The technique is based on the formulation of band-limited multiple Fourier Linear Combiners (BMFLC) and is called Enhanced-BMFLC (E-BMFLC). The effectiveness of the designed filter is statistically evaluated through a clinical study involving 14 PD and 13 ET patients. The hand tremors of the participants are studied in three Degrees Of Freedom (DOF). Using statistical analysis, it is shown that the new design of the filter significantly enhances the accuracy in comparison with the performance of conventional BMFLC filtering. In addition, E-BMFLC significantly reduces the sensitivity to parameter tuning and intrapatient variabilities. The observed improvements are achieved by modulating the memory of the proposed filter, and by enriching the utilized harmonic model. The proposed filter is then used to develop a safe haptics-enabled robotic rehabilitation architecture, designed for patients having hand tremors. The architecture is entitled Augmented Haptic Rehabilitation (AHR), which enables adaptive management of the involuntary components of the hand motion while delivering assist-as-needed haptic therapy (for the voluntary component) and avoiding unsafe amplification of hand tremors. Experimental evaluations are provided to evaluate the efficacy of the proposed AHR system.

Novel Cooperative Teleoperation Framework: Multi-Master/Single-Slave System

In this paper, a novel multi-master/single-slave (MM/SS) teleoperated framework is proposed. The desired objectives for the MM/SS system are presented in such a way that both cooperative and training applications, e.g., surgical teleoperation and surgical training, can benefit. Passivity of the system is investigated, and it is shown that an ideal MM/SS system, depending on its structure, may not always be passive unlike a conventional SM/SS system. An impedance-based control methodology is developed to satisfy the desired objectives of the MM/SS system in the presence of communication delays. The small-gain theorem is used to analyze the closed-loop stability, deriving a sufficient condition to guarantee system stability in the presence of time delays. Experimental results conducted on an MM/SS system are presented to evaluate the performance of the proposed methodology.

A framework for supervised robotics-assisted mirror rehabilitation therapy

In this paper, a novel robotics-assisted rehabilitation framework is proposed for bilateral mirror-image therapy. For this purpose, a customized dual-user teleoperation architecture is designed incorporating Guidance Virtual Fixtures (GVFs) to deliver the appropriate therapeutic movements to the patients impaired limb by providing an assist-as-needed treatment strategy. In addition, the therapist is provided with informative haptic feedback that is generated based on the patients movements, allowing the therapist to decide in real-time on the level and format of the therapy required for the patient. Stability of the closed-loop system is also investigated using the small gain theorem, in the presence of communication time delays, facilitating the case of remote tele-rehabilitation. Experimental results are given to validate the performance of the proposed platform.