Seyed Farokh Atashzar

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.

Robust Motion Control of Ultrasonic Motors Under Temperature Disturbance

This paper presents a practical robust controller that solves the problem of accurate motion control of ultrasonic motors (USMs) over prolonged durations, where temperature increases pose a significant challenge. This paper focuses on USMs with driver circuits that have a single user-controllable input. Prior to developing the robust controller, a nonlinear model of the system was identified by experimentally measuring the temporal relationship between motor speed and temperature to the applied input control signal. A linear approximation of this model was used to design two robust inverse dynamic controllers: one used temperature feedback and the other did not. Both control methods were implemented on a custom designed embedded control system and achieved highly consistent and accurate performance while under load over a range of working frequencies. Step-response experiments (1 rad) demonstrated a rise time of 0.1 s without any overshoot or steady-state error. A normalized RMSE below 3% with a delay of 25 ms was achieved for reference inputs with frequencies up to 1 Hz. This performance was maintained during prolonged continuous dynamic operation of several minutes, despite the great variation in the motors dynamics due to the temperature effects (over a range 25 °C-45 °C) and modeling uncertainties.

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 Passivity-Based Approach for Stable Patient–Robot Interaction in Haptics-Enabled Rehabilitation Systems: Modulated Time-Domain Passivity Control

In this paper, a novel passivity-based technique is proposed to 1) analyze and 2) guarantee the stability of haptics-enabled robotic/telerobotic systems when there is a possibility of having a source of nonpassivity (namely, a nonpassive environment) in addition to the conventional nonpassive component in teleoperation systems (namely, a delayed communication channel). The need for the proposed technique is motivated by safe and optimal implementation of the haptics-enabled robotic, cloud-based, and remote rehabilitation systems. The objective of the controller proposed in this paper is to perform minimum alteration to the system transparency, in a dynamic and patient-specific manner, by utilizing quantifiable biomechanical capability of the user’s limb (i.e., excess of passivity) in dissipating interactive energies to guaranteeing human–robot interaction safety, in the context of the strong passivity theorem. The proposed controller is named modulated time-domain passivity control (M-TDPC) approach and is a new member of the family of the state-of-the-art TDPC techniques. Simulations and experimental results are presented in support of the proposed technique and the developed theory.

A new set of desired objectives for dual-user systems in the presence of unknown communication delay

In this paper, new sets of desired objectives will be introduced for dual user systems. It will be shown that the existing set of objectives leads to eliminate the effect of dominance factor from the picture, while this is an important factor in dual user system. Consequently, in this paper, two sets of desired objective containing the dominance factor are presented, which can be used in variety of applications. Then, an adaptive control methodology is presented to satisfy the desired objectives in the presence of unknown communication delay. Towards this end, new desired impedance equations are introduced for each set of desired objectives. Subsequently, the adaptive impedance control strategy is applied which brings the closed-loop system in the form of the desired impedances. The stability of closed-loop system is investigated through passivity theory and it has been shown that the controller maintains system stability despite of the undesired effects of communication delays. The main feature of the controller is that it does not require a-priori information of delay. In fact, the controller uses delayed signals sent through the communication channels and consequently, there is no necessity to know the delay value. The performance of the proposed control methodology as well as the importance of the proposed sets is validated through experiments.

Telerobotics-Assisted Platform for Enhancing Interaction with Physical Environments for People Living with Cerebral Palsy

In this paper, the design and implementation of a new telerobotics-assisted platform is proposed for individuals who have cerebral palsy (CP). The main objective of the proposed assistive system is to modulate capabilities of individuals through the proposed telerobotic medium and to enhance their control over interaction with objects in a real physical environment. The proposed platform is motivated by evidence showing that lack of interaction with real environments can develop further secondary sensorimotor and cognitive issues for people who grow up with CP. The proposed telerobotic system assists individuals by (a) mapping their limited but convenient motion range to a larger workspace needed for task performance in the real environment, (b) transferring only the voluntary components of the hand motion to the task-side robot to perform tasks and (c) kinaesthetically dissipating the energy of their involuntary motions using a viscous force field implemented in high frequency domain. Consequently, using...

A Small-Gain Approach for Nonpassive Bilateral Telerobotic Rehabilitation: Stability Analysis and Controller Synthesis

In this paper, the design of a novel bilateral telerobotic architecture for rehabilitation purposes is proposed and the related feasibility, stability, and control challenges are studied. The objective is to incorporate the supervision of a local/remote human physiotherapist into haptics-enabled rehabilitation systems and allow the therapist to provide nonpassive nonlinear assistive/resistive forces in response to the patients movements. This can address a challenge of conventional software-based rehabilitation systems, i.e., limited capability in adjusting the therapy. To guarantee human–robot interaction safety, a new design framework and a stabilizing controller are developed based on the small-gain approach. System stability and transparency are analyzed in the presence of the nonpassive, nonlinear, and nonautonomous behavior of the terminals (the therapist and the patient) and time-varying delays for the case of remote and cloud-based therapy. Several practical considerations have been taken into account to match the clinical needs and minimize the implementation cost. Simulation studies, practical implementation, and experimental evaluations are presented.