Publications

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Telerobotic and Biorobotic Systems Group
University of Alberta
Department of Electrical and Computer Engineering

Journal Papers:

1. Michael C. Yip, Mahdi Tavakoli, and Robert D. Howe, Haptic Performance Analysis of a Haptic Telemanipulation Task under Time Delay, Journal of Advanced Robotics, Accepted July 2010. To appear. [Preprint]

Abstract—There is ample research on the effect of haptic teleoperation under delayed communication channels in terms of stability and system performance. Little attention, however, has been paid to the effect of delayed force feedback on users´ task performance, and whether force feedback is beneficial under significant communication delays. This paper investigates whether force feedback improves user´s task performance in delayed teleoperation. We study peg-in-the-hole insertion/retraction, dexterous manipulation tasks involving high degrees of freedom and high forces at certain points during task execution. A user study involving unilateral (without force feedback), bilateral (with force feedback), and graphical-feedback teleoperation under various delays is presented. We observed that for all feedback modalities, task completion times increase as delay increases. Haptic feedback helps reduce contact forces and the occurrence of large robot/environment forces. Furthermore, graphical feedback helps users maintain the lowest range of forces at the cost of higher task completion times. With users mindful of minimizing contact forces, haptic/graphical feedback causes the task to take more time than unilateral control. Therefore, when short completion times are crucial given a tolerance for larger forces, force feedback only serves to increase the time required to perform the task; thus, unilateral control may be sufficient.

2. M. Tavakoli, R.D. Howe, Haptic Effects of Surgical Teleoperator Flexibility, International Journal of Robotics Research, Special Issue on Medical Robotics, 2009. To appear. [Preprint]

Abstract—Minimally invasive surgery systems typically involve thin and cable-driven surgical instruments. This introduces link and joint fexibility in the slave robot of a master-slave teleoperation system, reducing the effective stiffness of the slave and the transparency of teleoperation. In this paper, we analyze transparency under slave link and joint exibility (tool fexibility). We also evaluate the added benefits of using extra sensors at the tip of the fexible robot. It is shown that tip velocity (or position) feedback improves free-space position tracking performance in the presence of robot fexibility. Also, when the interaction forces with an environment are measured by a force sensor and fed back to the user's hand, tip velocity feedback improves hard-contact force tracking performance. During a hard contact task, tip velocity feedback can also eliminate the transmission of robot fexibility to the user's hand.

3. M.Tavakoli, A. Aziminejad, R.V. Patel, M. Moallem, Discrete-Time Bilateral Teleoperation: Modeling and Stability Analysis, IET Control Theory & Applications, vol. 2, no. 6, pp. 496-512, June 2008. [IEEEXplore] [pdf]

Abstract—Discretization of a stabilizing continuous-time bilateral teleoperation controller for digital implementation may not necessarily lead to stable teleoperation. While previous research has focused on the question of passivity or stability of haptic interaction with a discretely simulated virtual wall, this paper addresses the stability of master-slave teleoperation under discrete-time bilateral control. Stability regions are determined in the form of conditions involving the sampling period, control gains including the damping introduced by the controller, and environment sti.ness. Among the obtained stability conditions are lower and upper bounds on the controller damping in addition to upper bounds on the sampling period and the environment stiffness, implying that as the sampling period is increased, the maximum admissible stiffness of the environment with which a slave robot can stably interact is reduced. An outcome of the paper is a set of design guidelines in terms of selection of various control parameters and the sampling rate for stable teleoperation under discrete-time control. Due to the sampling period{environment stiffness tradeoff and the stability-transparency tradeoff, the obtained stability boundaries are of particular importance for hard-contact teleoperation or when the teleoperation system has near-ideal or ideal transparency. The results of the stability analysis are confirmed by a simulation study in which the bilateral controller is realized by z-domain transfer functions while the master, the slave and the environment are simulated in the s-domain.

4. M. Tavakoli, A. Aziminejad, R.V. Patel, M. Moallem, High-Fidelity Bilateral Teleoperation Systems and the Effect of Multimodal Haptics, IEEE Transactionson Systems, Man, and Cybernetics - Part B, vol. 37, no. 6, pp. 1512-1528, December 2007. [IEEEXplore] [pdf]

Abstract— In master-slave teleoperation applications that deal with a delicate and sensitive environment, it is important to provide haptic feedback of slave/environment interactions to the user's hand as it improves task performance and teleoperation transparency (fidelity), which is the extent of telepresence of the remote environment available to the user through the master-slave system. For haptic teleoperation, in addition to a haptics-capable master interface, often one or more force sensors are also used, which warrant new bilateral control architectures while increasing the cost and complexity of the teleoperation system. In this paper, we investigate the added benefits of using force sensors that measure hand/master and slave/environment interactions and utilizing local feedback loops on teleoperation transparency. We compare the two-channel and the four-channel bilateral control systems in terms of stability and transparency, and study the stability and performance robustness of the four-channel method against non-idealities arisen during bilateral control implementation including master-slave communication latency and changes in the environment dynamics. The next issue addressed in the paper deals with the case where the master interface is nothaptics-capable but the slave is equipped with a force sensor. In the context of robotics-assisted soft-tissue surgical applications, we explore through human factors experiments whether slave/environment force measurements can be of any help with regard to improving task performance. The last problem we study is whether slave/environment force information, with and without haptic capability in the master interface, can help improve outcomes under degraded visual conditions.

5. A. Aziminejad, M. Tavakoli, R.V. Patel, M. Moallem, Stability and Performance in Delayed Bilateral Teleoperation: Theory and Experiments, Control Engineering Practice, vol. 16, no. 11, pp. 1329-1343, November 2008. [ScienceDirect] [Pdf]

Abstract—In the presence of communication latency in a bilaterally controlled teleoperation system, stability and transparency are severely affected. In this paper, based on a passivity framework, admittance-type and hybrid-type delay-compensated communication channels, which warrant different bilateral control architectures, are introduced. We use wave transforms and signal filtering to make the delayed-communication channel passive and derive passivity/stability conditions based on the end-to-end model of the teleoperation system with and without incorporating force measurement data of the master and the slave manipulators' interactions with the operator and the remote environment in the control configuration. Based on analogies of the hybrid parameters of the teleoperation systems, it is demonstrated that using force sensor measurements about hand-master and/or slave-environment interactions in the control algorithm can significantly improve teleoperation transparency. Experimental results with a soft-tissue task for a hybrid-type architecture and for round-trip delays of 60 and 600~msec further substantiate the hypothesis that using slave-side force measurements considerably enhances the matching of the master and the slave forces and consequently the transparency compared to a position error-based configuration.

6. A. Aziminejad, M.Tavakoli, R.V. Patel, M. Moallem, Transparent Time-Delayed Bilateral Teleoperation Using Wave Variables, IEEE Transactions on Control Systems Technology, vol. 16, no. 3, pp. 548-555, May 2008. [IEEEXplore] [Pdf]

Abstract—Beside stability, a high degree of transparency is also an essential requirement in order to enable operators to safely and precisely perform bilateral teleoperation tasks. An existing approach based on the wave transformation technique can make a two-channel teleoperation system insensitive to time delays by making the time-delayed communication channel passive. In this paper, we propose a novel method for incorporating this technique in a four-channel architecture, which is the optimal architecture from a transparency point of view, and derive the corresponding absolute stability condition. It is analytically demonstrated that the proposed teleoperation architecture is capable of providing ideal transparency when transmission delays are present and criteria for its stable operation are derived. We also show that a three-channel variant of the proposed four-channel control architecture can offer a comparable performance with less implementation complexity. Experimental results in support of the developed theory are provided.

7. A. Aziminejad, M.Tavakoli, R.V. Patel, M. Moallem, Improving Transparency in Delay-free and Delayed Teleoperation: A Generalized 4-Channel Control Architecture. International Journal of Factory Automation, Robotics and Soft Computing, no. 1, pp.60-69, January 2008. [Journal]

Abstract—For haptic teleoperation, often one or more force sensors are also used, which warrant new bilateral control architectures while increasing the cost and complexity of the teleoperation system. In this paper, considering a four channel architecture, we investigate the added benefits of using force sensors that measure hand/master and slave/environment interactions and utilizing local feedback loops on teleoperation transparency. Furthermore, we propose a novel method for incorporating wave transformation delay compensation technique in the four channel architecture, which is the best architecture for providing transparency. It is demonstrated that the proposed teleoperation architecture is capable of providing absolute stability as well as ideal transparency under time delay. The corresponding conditions for each of these two operation modes have been derived. Experimental results in support of the developed theory are provided.

8. M. Tavakoli, R.V.Patel, M. Moallem, A Haptic Interface for Computer-Integrated Endoscopic Surgery and Training,Virtual Reality (special issue on Haptic Interfaces and Applications), vol. 9, no. 2-3, pp. 160-176, March 2006. [SpringerLink] [pdf]

Abstract—Haptic feedback has the potential to provide superior performance in computer-integrated surgery and training. This paper discusses the design of a user interface that is capable of providing force feedback in all the degrees of freedom available during endoscopic surgery. Using the Jacobian matrix of the haptic interface and its singular values, methods are proposed for analysis and optimization of the interface performance with regard to the accuracy of force feedback, the range of applicable forces, and the accuracy of control. The haptic user interface is used with a sensorized slave robot to form a master-slave test-bed for studying haptic interaction in a minimally invasive environment. Using the master-slave test-bed, teleoperation experiments involving a single degree of freedom surgical task (palpation) are conducted. Different bilateral control methods are compared based on the transparency of the master-slave system in terms of transmitting the critical task-related information to the user in the context of soft-tissue surgical applications.

9. M. Tavakoli, A. Aziminejad, R.V. Patel, M. Moallem, Methods and Mechanisms for Contact Feedbackin a Robot-Assisted Minimally Invasive Environment, Surgical Endoscopy and Other Interventional Techniques, vol. 10, no. 20, pp. 1570-1579, October 2006. [SpringerLink] [PubMed] [pdf]

Abstract—Providing a surgeon with information regarding contacts made between instruments and tissue during robot-assisted interventions can improve task efficiency and reliability. In this paper, different methods for feedback of such information to the surgeon are discussed. It is hypothesized that various modalities of contact feedback have the potential to enhance performance in a robot-assisted minimally invasive environment. To verify the hypothesis, novel mechanisms needed for incorporating contact feedback are designed including a surgeon-robot interface with full force feedback capabilities and a surgical end-effector with full force sensing capabilities, which are suitable for minimally invasive applications. These two mechanisms are used to form a robotic “master-slave” test-bed for studying the effect of contact feedback on the system and user performance. Using the master-slave system, experiments for surgical tasks involving soft-tissue palpation are conducted. The performance of the master-slave system is validated in terms of criteria that assess the accurate transmission to the surgeon of task-related information, which is critical in the context of soft-tissue surgical applications. Moreover, using a set of experiments involving human subjects, the performance of several users in carrying out the task is compared for different modalities of contact feedback.

10. M. Tavakoli, R.V. Patel, M. Moallem, Haptic Interaction in Robot-Assisted Endoscopic Surgery: A Sensorized End Effector, The International Journal ofMedical Robotics and Computer Assisted Surgery, vol. 1, no. 2, pp. 53-63, January 2005. [Wiley InterScience] [pdf]

Abstract—Conventional endoscopic surgery has some drawbacks that can be addressed by using robots. The robotic systems used for surgery are still in their infancy. A major deficiency is the lack of haptic feedback to the surgeon. In this paper, the benefits of haptic feedback in robot-assisted surgery are discussed. A novel robotic end-effector is then described that meets the requirements of endoscopic surgery and is sensorized for force/torque feedback. The endoscopic end-effector is capable of non-invasively measuring its interaction with tissue in all the degrees of freedom available during endoscopic manipulation. It is also capable of remotely actuating a tip and measuring its interaction with the environment without using any sensors on the jaws. The sensorized end-effector can be used as the last arm of a surgical robot to incorporate haptic feedback and/or to evaluate skills and learning curves of residents and surgeons in endoscopic surgery.

11. M. Tavakoli, H.D. Taghirad, M. Abrishamchian, Identification and Robust H∞ Control of the Rotational/Translational Actuator System, International Journal of Control, Automation, and Systems, vol. 3, no.3, pp. 387-396, September 2005. [Journal] [pdf]

Book Contributions Journal Papers:

1. M. Tavakoli, R.V. Patel, M. Moallem, A. Aziminejad, Haptics for Teleoperated Surgical Robotic Systems, New Frontiers in Robotics series, World Scientific, 2008. [Order a copy]

Abstract—The Rotational/Translational Actuator (RTAC) benchmark problem considers a fourth-order dynamical system involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem has been posed to investigate the utility of a rotational actuator for stabilizing translational motion. In order to experimentally implement any of the model-based controllers proposed in the literature, the values of model parameters are required which are generally difficult to determine rigorously. In this paper, an approach to the least-squares estimation of the parameters of a system is formulated and practically applied to the RTAC system. On the other hand, this paper shows how to model a nonlinear system as a linear uncertain system via nonparametric system identification, in order to provide the information required for linear robust H_inf control design. This method is also applied to the RTAC system, which demonstrates severe nonlinearities due to the coupling from the rotational motion to the translational motion. Experimental results confirm that this approach can effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block.

2. M. Tavakoli and R.V.Patel, Haptics in Telerobotic Systems for Minimally Invasive Surgery. In S.Kumar and J. Marescaux (Eds.), Telesurgery, Springer, ISBN 978-3-540-72998-3, 2008.

3. A. Aziminejad, M.Tavakoli, R.V.Patel, M. Moallem, Improving Transparency in Delay-free and Delayed Teleoperation: A Generalized 4-Channel Control Architecture. In S. Pennacchio (Ed.), Recent Advances in Control Systems, Robotics and Automation (2nd ed.), International Society for Advanced Research, ISBN 978-88-901928-3-8, 2008.

Patent:

M. Tavakoli, R.V. Patel, M. Moallem, “Force Reflective Robotic Control System and Minimally Invasive Surgical Device”. United States Patent Application published 01/25/2007.
R.V. Patel, A.L. Trejos, M. Tavakoli, M. Naish, "Training and Skills Assessment System for Minimally Invasive Endoscopic Surgery". Provisional Patent filed in 2008.

Conference papers:

1. Xia Liu, Mahdi Tavakoli, Qi Huang, Haptic Nonlinear Adaptive Bilateral Control of Teleoperation Systems with Uncertain Dynamics and Kinematics, Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems, Taipei, Taiwan, 2010. [pdf]

Abstract—Research so far on adaptive bilateral control of master-slave teleoperation systems considers dynamic uncertainties but stops short of considering kinematic uncertainties. However, when picking up objects of unknown lengths, orientations and gripping points, the overall kinematics of a robot in the teleoperation system becomes uncertain. Therefore, new controllers are required that can guarantee the stability and motion tracking performance of the overall system in the presence of both dynamic and kinematic uncertainties in the master and the slave robots. In this paper, first the uncertain dynamics of the human operator and the environment are incorporated into the dynamics of the master and the slave, respectively. Then, for a teleoperation system with both uncertain dynamics and kinematics, nonlinear adaptive controllers are designed for both the master and the slave. The controllers do not need exact knowledge of the dynamics of the master, the slave, the human, or the environment, or of the kinematics of the mater or the slave. The stability and position tracking convergence of the entire teleoperation system are studied. The validity of the theoretical results is verified by simulation.

2.      Michael Yip, Mahdi Tavakoli, Robert D. Howe, Haptic Performance Analysis of a Manipulation Task in Time-Delayed Teleoperation, Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems, Taipei, Taiwan, 2010. [pdf]

Abstract—There is ample research on the stabilization of haptic teleoperation systems under communication time delay. Little attention, however, has so far been paid to the usefulness of delayed haptic feedback on task performance. While the usefulness of haptic feedback in no-delay teleoperation has been previously established, this paper investigates whether haptic feedback helps to improve task performance in the presence of delay. We consider peg-inthe- hole insertion, which is a dexterous manipulation task requiring high force levels at certain points during the task execution. Through a user study involving unilateral and bilateral teleoperation experiments under different delays, it is observed that in both unilateral and bilateral teleoperation, the task completion time increases as delay increases. It is also seen that haptic feedback helps reduce the amount and rate of energy transfer to the environment and the occurrence of larger robot/environment interaction forces. However, with the users mindful of minimizing contact forces, haptic feedback causes the task to take more time compared to no haptic feedback regardless of the time delay. Therefore, for tasks where low completion times are crucial given a tolerance for larger forces, unilateral feedback may be sufficient.

3.      Minh-Quyen Le, Minh Tu Pham, Mahdi Tavakoli, Richard Moreau, Development of a hybrid control for a pneumatic teleoperation system using on/off solenoid valve, Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems, Taipei, Taiwan, 2010. To appear. [pdf]

Abstract—This paper presents a new predictive hybrid control law for the control of pneumatic teleoperation system using solenoid valves. Based on a predictive model of the mass flow rate of the valves, this method is used in a four-channel bilateral control architecture for teleoperation. An analysis of the parameter controllers is carried out in order to achieve acceptable performances. The simulation results show that a good accuracy for position and force tracking of a teleoperation system is obtained.

4.      Victor Mendez and Mahdi Tavakoli, A Passivity Criterion for N-Port Multilateral Haptic Systems, , 2010 IEEE Conference on Decision and Control, Atlanta, GA, December 2010. To appear. [pdf]

Abstract—This paper presents a criterion for passivity of n-port networks, which can be used to model multilateral systems involving haptic information sharing between a number of users. Such systems have recently found interesting applications in both cooperative haptic teleoperation and haptics-assisted training. The criterion presented in Theorem 1, which is necessary and sufficient for passivity of the n-port network, imposes 2n conditions on the immitance parameters of the network and on the residues of the immitance parameters at their imaginary-axis poles. It is shown that when n = 2, the proposed conditions reduce to the well-known Raisbeck´s passivity criterion for two-port networks. Another special case for which the proposed criterion has been simplified corresponds to three-port networks. As an example, the passivity of a dual-user haptic system for control of a single teleoperated robot is investigated.

5.      Ali Jazayeri and Mahdi Tavakoli, Absolute Stability Analysis of Sampled-Data Teleoperation Systems, 2010 IEEE Conference on Decision and Control, Atlanta, GA, December 2010. To appear. [pdf]

Abstract—In a haptic teleoperation system, closed-loop stability is influenced by the human operator and the environment dynamics, which are typically uncertain, time-varying or unknown. Therefore, in lieu of stability, the passivity of a teleoperation system as a sufficient condition for stability is investigated in the literature. The rationale for this is that, if the two-port network representing the teleoperator (comprising the master, the controller and communication channel, and the slave) is passive and is terminated to any passive but otherwise arbitrary operator and environment, the overall teleoperation system will also be passive. Instead of ensuring the passivity of the teleoperator in isolation, which is an overly-conservative requirement, in this paper we study the stability of the overall teleoperation system having assumed the passivity of the operator and the environment while permitting the teleoperator to be passive or nonpassive -- such relaxation of the passivity condition on the teleoperator is expected to reduce design conservatism and allow for higher teleoperation performance. The broader aim of this study is to find the conditions for the stability of a teleoperation system when its controllers are implemented in discrete-time -- it is known that discretization causes energy leaks and thus does not necessarily preserve passivity or stability. The absolute stability conditions for the sampled-data teleoperator are obtained using the Small Gain Theorem. The resulting condition for stability of the sampled-data teleoperation system imposes bounds on the controller parameters, the sampling period, and the master and slave robots damping terms.

6.      M. Tavakoli and Robert D. Howe, Improving Teleoperation Performance in the Presence of Non-ideal Robot Dynamics, 2008 IEEE International Conference on Technologies forPractical Robot Applications, Boston, MA, November 2008.

7.      M. Tavakoli and R.D. Howe, The Effect ofJoint Elasticity on Bilateral Teleoperation, In Proceedings of the 2007 International Conference on Intelligent RobotsandSystems, San Diego, CA, October/November2007. BEST PAPER AWARD FINALIST. [IEEEXplore] [pdf]

Abstract—In applications such as space and surgical robotics, the use of thin, lightweight manipulators and cable-driven end-effectors results in flexibility of the manipulator. In bilateral teleoperation, however, any flexibility in a link or joint of the robot reduces the transparency of teleoperation. In this paper, we analyze master-slave teleoperationtransparency under slave robot joint elasticity and evaluate the added benefits of using extra sensors at the end-effector of the elastic-joint robot. It is shown that velocity (or position) feedback from the output shaft of the elastic joint improves free-space position tracking performance, which in the absence of such feedback is hampered by the joint's anti-resonance. Also, when the interaction forces with an environment are measured by a force sensor and fed back to the user, end-effector velocity feedback improves hard-contact force tracking performance. If the operating trajectories correspond to low frequencies, both free-space position tracking and hard-contact force tracking are satisfactory regardless of end-effector feedback, yet the elasticity in the joint will be transmitted to the user during a hard contact task unless end-effector velocity feedback is used.

8.      M. Tavakoli, A. Aziminejad, R.V. Patel, M. Moallem, Stability of Discrete-Time Bilateral Teleoperation Control, In Proceedings of the 2007 International Conference on Intelligent Robots and Systems, SanDiego, CA, October/November 2007. [IEEEXplore] [pdf]

Abstract—Discretization of a stabilizing continuous-time bilateral teleoperation controller for digital implementation may not necessarily lead to stable teleoperation. While previous research has focused on the question of passivity or stability of haptic interaction with a discretely-simulated virtual wall, this paper addresses the stability of master-slaveteleoperation under discrete-time bilateral control. Stability regions are determined as a function of the sampling period, environment stiffness and control gains. Due to the tradeoff between stability and transparency in bilateral teleoperation, such stability boundaries are of particular importance when the teleoperation system is ideally transparent.

9.      M. Tavakoli, A. Aziminejad, R.V. Patel, M. Moallem, Enhanced Transparency in Haptics-Based Master-Slave Systems, In Proceedings of the 2007 American Control Conference,New York, NY, July 2007. [IEEEXplore] [pdf]

Abstract—Bilateral master-slave teleoperation, in addition to requiring a haptics-capable master interface, often requires one or more force sensors, which increases the cost and complexity of the system particularly for robot-assisted surgery. In this paper, we investigate the benefits of using force sensors that measure hand/master and slave/environment interactions, and study the effects of the bilateral control structure and in particular the presence of force feedforward and local force feedback on teleoperation transparency. Human factors experiments are performed to study how haptic feedback can help improve task performance under degraded visual conditions.

10.      A. Aziminejad, M. Tavakoli, R.V. Patel, M. Moallem, Wave-Based Time Delay Compensation in Bilateral Teleoperation: Two-Channel versus Four-Channel Architectures, In Proceedings of the 2007 American Control Conference, New York, NY, July 2007. [IEEEXplore] [pdf]

Abstract—In this paper, two different approaches have been proposed aiming to improve transparency of a passivity-based delay-compensated teleoperation system: direct force reflection in a two-channel wave-based control architecture, which uses the same number of channels as the traditional position error-based control scheme with wave variables and, four-channel wave-based control architecture, which is capable of achieving ideal transparency in the presence of time delay. In order to present a comprehensive performance comparison, we quantify the transparency of each approach through subjecting the experimental results of a bilateral master-slave system developed for endoscopic surgery applications to identification of the hybrid parameters of the equivalent two-port network.

11.      A. Aziminejad, M. Tavakoli, R.V. Patel, M. Moallem, Bilateral Delayed Teleoperation: The Effects of Passified Channel Model and Force Sensing, In Proceedings of the 2007 IEEE International Conference on Robotics and Automation, Rome, Italy, April 2007. [IEEE Xplore] [pdf]

Abstract—In this paper, based on a passivity framework, admittance-type and hybrid-type delay-compensated communication channel models are introduced, which warrant different bilateral control architectures for wave-based teleoperation under time delay. We utilize wave transforms and signal filtering for passivating the delayed-communication channel and passivity/stability conditions are derived using scattering theory based on an end-to-end model of the teleoperation system rather than the communication channel alone. Contrary to a commonly held view, it is proven that the teleoperation system can remain stable when force measurement data of the master and the slave manipulators interactions with the operator and the remote environment are used. Experimental results on a soft-tissue task for a hybrid-type architecture and for round-trip delays of 60 msec and 600 msec show that using slave-side force measurements considerably enhances teleoperation transparency.

12.      M. Tavakoli, A. Aziminejad, R.V. Patel, M. Moallem, Multi-Sensory Force/DeformationCues for Stiffness Characterization in Soft-Tissue Palpation, In Proceedings of the 28th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, pp. 837-840, New York, NY, August/September 2006. [IEEE Xplore] [pdf]

Abstract—In the commercially available robot-assisted surgical systems, camera vision constitutes the only flow of data from the patient side to the surgeon side. This paper studies how various modalities for feedback of interaction between a surgical tool and soft tissue can improve the efficiency of a typical surgical task. Utilizing a haptics-enabled master-slave test-bed for minimally invasive surgery, user performance during a telemanipulated soft tissue stiffness discrimination task is compared under visual, haptic, graphical, and graphical plus haptic feedback modes in terms of task success rate and completion time and the amount of energy transfer and consequently trauma to tissue. While no significant difference is found in terms of the task completion times, graphical cueing and visual cueing are found to lead to the highest success rate and the highest risk of tissue damage (proportional to energy), respectively.

13.      M. Tavakoli, A. Aziminejad, R.V. Patel, M. Moallem, Tool/Tissue Interaction Feedback Modalities in Robot-Assisted Lump Localization, In Proceedings of the 28th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, pp. 3854-3857, New York, NY, August/September 2006. [IEEE Xplore] [pdf]

Abstract—Providing a surgeon with information regarding contacts made between tools and tissue during robot-assisted interventions can improve task efficiency and reliability. It is hypothesized that various modalities of contact feedback have the potential to enhance performance in a robot-assisted minimally invasive environment. In this paper, (kinesthetic) haptic feedback is compared with visual feedback of haptic information in terms of several performance metrics. Using a haptics-capable master-slave test-bed for endoscopic surgery, experiments involving a lump localization task are conducted and the performance of human subjects is compared for these two modalities of contact feedback. It is shown that the two feedback modalities result in comparable localization accuracies -- an advantage of visual haptic feedback due to the lower system complexity required -- while the task completion times are significantly shorter with haptic feedback.

14. M. Tavakoli, R.V. Patel, M. Moallem, Bilateral Control of a Teleoperator for Soft Tissue Palpation: Design and Experiments, In Proceedings of the 2006 IEEE International Conference on Robotics and Automation, pp. 3280-3285, Orlando, FL, May 2006.[IEEE Xplore] [pdf]

Abstract—In robot-assisted interventions, providing a surgeon with haptic information regarding contacts made between surgical instruments and tissue can improve task performance and reliability. In this paper, a force-reflective user interface is used with a sensorized surgical instrument to form a master-slave test-bed for studying haptic interaction in a soft-tissue endoscopic surgery environment. After modeling and parametric identification of the master and the slave, bilateral controllers are designed and teleoperation experiments involving a single degree of freedom surgical task on soft tissue (palpation) are conducted. The transparency of the teleoperator in terms of transmitting the critical task-related information to the user in the context of soft-tissue surgical applications is investigated.

15. M. Tavakoli, R.V. Patel, M. Moallem, Adaptive Inverse Dynamics Control of a PHANToM Haptic Device, In Proceedings of the 2006 IEEE International Conference on Robotics and Automation, pp. 4354-4356, Orlando, FL, May 2006.

Abstract—The PHANToM haptic device is being commonly used in haptics-based master-slave teleoperation research. The dynamics of the PHANToM robot vary significantly depending on how it is mounted and whether a sensor or tool is attached at its endpoint. Moreover, it has been shown that fixed impedance-reflecting controllers cannot preserve master-slave position tracking when the environment impedance changes. In this paper, a neural network is used to implement adaptive inverse dynamics control of a PHANToM haptic device. Experimental results show that the neural network controller successfully represents the inverse dynamics of the PHANToM and can adapt to changes in the dynamics to maintain master-slave tracking.

16. M. Tavakoli, R.V. Patel, M. Moallem, Robotic Suturing Forces in the Presence of Haptic Feedback and Sensory Substitution, In Proceedings of the 2005 IEEE Conference on Control Applications, pp. 1-6, Toronto, Canada, August 2005. [IEEE Xplore]

Abstract—There has been some interest in recent years on how information about interactions happening between surgical instruments and tissue during robot-assisted surgery could improve the efficiency and reliability of a surgical task. In this paper, it is hypothesized that various modes of sensory feedback have the potential to enhance performance in robot-assisted surgery in terms of the amount of applied forces. User performance during telemanipulated suturing is compared for cases where force feedback is replaced or complemented by visual representation of the force levels. In addition to confirming the above hypothesis, the results indicate a trade-off between the magnitudes of applied forces and the time required to complete the task.

17. R. Rayman, S. Primak, R. Patel, M. Moallem, R. Morady, M. Tavakoli, V. Subotic, N. Galbraith, A.van Wynsberghe, K. Croome, Effects of Latency on Telesurgery: An Experimental Study, In Proceedings of the 8th International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI ’05), pp. 57-64, Palm Springs, CA, October 2005. [SpringerLink] [PubMed]

Abstract—The paper is concerned with determining the feasibility of performing telesurgery over long communication links. It describes an experimental testbed for telesurgery that is currently available in our laboratory. The testbed is capable of supporting both wired and satellite connections as well as simulated network environments. The feasibility of performing telesurgery over a satellite link with approximately 600 ms delay is shown through a number of dry and wet lab experiments. Quantitative results of these experiments are also discussed.

18. M. Tavakoli, R.V.Patel, M. Moallem, Haptic Feedback and Sensory Substitution during Telemanipulated Suturing, In Proceedings of the First Joint Eurohaptics Conference and Symposium on Haptic Interfaces forVirtual Environment and Teleoeprator Systems (World Haptics), Pisa, Italy, March 2005. [IEEE Xplore]

Abstract—Various modes of sensory feedback to user have the potential to enhance performance in robot-assisted surgery. In this paper, it is hypothesized that substituting or augmenting force feedback by visual representation of the force levels can potentially assist the user in limiting the amount of applied forces. In addition to confirming the above for a telemanipulated suturing task, the results indicate that there is a trade-off between the magnitudes of applied forces and the time required to complete the task.

19. M. Tavakoli, R.V.Patel, M. Moallem, Design Issues in a Haptics-Based Master-Slave System for Minimally Invasive Surgery, In Proceedings of the 2004 IEEE International Conference on Robotics and Automation, pp. 371-376, New Orleans, LA, April 2004. [IEEE Xplore]

Abstract—Minimally invasive surgery (MIS) is an alternative to open surgery where special instruments are inserted into the body cavity through tiny incisions in order to perform surgical procedures. In this paper, some design issues in a master-slave robotic system for use in MIS are discussed. First, we discuss the design of a user interface that can be used to incorporate haptic interaction in robot-assisted MIS. Then we discuss the design of a laparoscopic end effector that meets MIS requirements and is instrumented for haptic feedback.

20. M. Tavakoli, R.V. Patel, M. Moallem, A Force Reflective Master-Slave System for Minimally Invasive Surgery, In Proceedings of the 2003 IEEE/RSJ InternationalConference on Intelligent Robots and Systems, pp. 3077-3082, Las Vegas, NV, October 2003. [IEEE Xplore]

Abstract—Minimally invasive surgery involves inserting special instruments into the body cavity through tiny incisions in order to perform surgical procedures. In this paper, the design of a robotic master slave system for use in minimally invasive surgery is discussed. This system is capable of providing haptic feedback to the surgeon in all available degrees of freedom. System design as well as master and slave bilateral control and communication issues are discussed.

21. M. Tavakoli, H.D. Taghirad, M. Abrishamchian, Parametricand Nonparametric Identification and Robust Control of a Rotational/Translational Actuator, In Proceedings of the Fourth International Conference on Control and Automation, pp. 765-769, Montreal, Canada, June 2003. [IEEE Xplore]

Abstract—RTAC benchmark problem considers a nonlinear fourth-order dynamical system involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem has been posed to investigate the utility of a rotational proof mass actuator for stabilizing translational motion. In order to implement any of the model-based controllers proposed in the literature, the values of model parameters are required which are generally difficult to determine rigorously. In this paper, an approach to the least-squares estimation of system parameters is discussed and practically applied to the benchmark problem. Next, in order to design an H_inf controller, the nonlinear system is modelled as a perturbed linear system using an effective identification scheme. Experimental results confirm that this approach can effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block. Finally, an effective mixed-sensitivity problem is developed for the system to satisfy all performance requirements as well as robust stability despite actuator saturation.

22. S. Tavakoli, M. Tavakoli, Optimal Tuning of PID Controllers for First Order PlusTime Delay Models Using Dimensional Analysis, In Proceedings of the Fourth International Conference on Control and Automation, pp. 942-946, Montreal, Canada, June 2003. [IEEE Xplore]

Abstract—Using dimensional analysis and numerical optimisation techniques, an optimal method for tuning PID controllers for first order plus time delay systems is presented. Considering integral square error (ISE), integral absolute error (IAE) and integral time absolute error (ITAE) performance criteria, optimal equations for obtaining PID parameters are proposed. Simulation results show that the proposed method has a considerable superiority over conventional techniques. In addition, the closed loop system shows a robust performance in the face of model parameters uncertainty.

23. S. Tavakoli, M. Tavakoli, Stable Optimal Order Reduction via Combined Genetic Algorithms and Simulated Annealing, In Proceedings of the 7th Iranian Conference on Electrical Engineering, pp. 69-76, Tehran, Iran,June 1999.

24. M. Abrishamchian, H.D. Taghirad, M. Tavakoli, Identification for Control of a Rotational/Translational Actuator, In Proceedings of the 7th Iranian Conference on Electrical Engineering, pp. 81-86, Tehran, Iran, June 1999.

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