A. Aziminejad

High-Fidelity Bilateral Teleoperation Systems and the Effect of Multimodal Haptics

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 users 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 the 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 of utilizing local feedback loops on the 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 nonidealities that arise during bilateral control implementation, which include 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 not haptics 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.

Transparent Time-Delayed Bilateral Teleoperation Using Wave Variables

Besides 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 implementational complexity. Experimental results in support of the developed theory are provided.

Methods and mechanisms for contact feedback in a robot-assisted minimally invasive environment

Providing a surgeon with information regarding contacts made between instruments and tissue during robot-assisted interventions can improve task efficiency and reliability. In this report, different methods for feedback of such information to the surgeon are discussed. It is hypothesized that various methods 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 were designed, including a surgeon–robot interface with full force feedback capabilities and a surgical end-effector with full force sensing capabilities, that are suitable for minimally invasive applications. These two mechanisms were 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 were conducted. The performance of the master–slave system was validated in terms of criteria that assess the accurate transmission of task-related information to the surgeon, 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 was compared among different methods of contact feedback.

Enhanced Transparency in Haptics-Based Master-Slave Systems

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.

Multi-sensory force/deformation cues for stiffness characterization in soft-tissue palpation.

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

Wave-Based Time Delay Compensation in Bilateral Teleoperation: Two-Channel versus Four-Channel Architectures

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.

Tool/tissue interaction feedback modalities in robot-assisted lump localization

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

Stability of discrete-time bilateral teleoperation control

Discretization of a stabilizing continuous-time bilateral teleoperation controller for digital implementation may not necessarily lead to stable teleoperation. 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 stiffness. Due to the tradeoff between stability and transparency in bilateral teleoperation, such stability boundaries are of particular importance when the teleoperation system has good transparency.

Bilateral Delayed Teleoperation: The Effects of a Passivated Channel Model and Force Sensing

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.

A Study of Transparency in Wave-based Teleoperation

Transparency and stability are two key issues in bilateral teleoperation. This paper develops an analytical framework for investigating transparency of a position error-based teleoperator without and with time delay and derives criteria for optimum transparent operation in each case. The analysis is based upon two-port network modelling of the teleoperation system. For stabilizing this teleoperator in the presence of communication latencies, the Niemeyer-Slotine wave based approach is employed and its performance with respect to transparency is investigated. In order to improve transparency in a wave-based teleoperator, two different methods are rigorously studied and compared. Numerical simulation results have been included in order to support the theoretical analysis