Showing papers by "Asokan Thondiyath published in 2020"

Muscle Fatigue Induced Hand Tremor Clustering in Dynamic Laparoscopic Manipulation

Abstract: Differentiating muscle fatigue induced hand tremor of surgeons into different discernible levels is important in laparoscopic surgery. Systematic clustering can be used as a method to assess the risk of hand tremor which can largely affect the surgical performance. The prime challenges lying here are the detection of fatigue onset and classification of fatigue induced tremor level in dynamic laparoscopic tool manipulation. Conventionally, muscle fatigue is assessed with frequency domain analysis of the surface electromyography (sEMG) signal, where the detection process is predominantly valid only for isometric contraction of muscles. Conventional methods cannot be used for assessment of fatigue level in case of dynamic activities as the task itself modulates the frequency content of the myoelectric response. In this paper, we have proposed a novel polynomial Hammerstein model-based clustering of fatigue induced tremor, employing sEMG, and joint torques. The sEMG signal, containing muscle fatigue information, gets fused in this model dynamically through a Kalman filter. Model parameter-based clustering of the fatigue induced tremor level was implemented on eight subjects. Optimal number of cluster centers were found to be appropriately coherent with the fatigue inducing task epochs of the experiment. In spite of the subjective variations, the model parameter-based clustering method was able to differentiate among the fatigue-inducing tasks for all the subjects. We have concluded that this model-based clustering can successfully differentiate between different levels of the fatigue induced tremor in dynamic activity of laparoscopic tool manipulation.

Design of a Variable Stiffness Joint Module to Quickly Change the Stiffness and to Reduce the Power Consumption

Abstract: Variable stiffness actuators (VSA) are finding wide applications in robotics to enhance safety during interactions with stiff environments. Researchers have proposed various design architectures like antagonistic actuation, which requires both the motors to be powered simultaneously for varying the stiffness or equilibrium position. In this paper, the design of a novel joint module, named as variable stiffness joint module (VSJM), is proposed, which consists of a lead-screw arrangement for varying the stiffness range and a cam based mechanism to change the stiffness within the set range quickly. The cam profile has been synthesized to maximize the stiffness variation as well as to maintain the cam and cam follower in static equilibrium when the output link is in the equilibrium position. This was achieved by properly positioning and orienting the friction cones at the contact points. By mechanically compensating the moment due to unbalanced forces at the contact points, the continuous usage of stiffness motor has been eliminated, leading to reduced power consumption. Details of the proposed mechanism are presented along with the mathematical model for cam profile synthesis and static analysis. A simplified prototype of the proposed design has been fabricated to perform the experiments. A hammering-a-nail experiment has been conducted to show the capability of the mechanism, and the results are presented.

Theoretical and Experimental Investigations on the Design of a Hybrid Depth Controller for a Standalone Variable Buoyancy System— vBuoy

Abstract: Design of controllers for underwater vehicles is challenging due to their nonlinear dynamics, time-varying model parameters, and environmental disturbances, which are difficult to measure or estimate. Conventional linear controllers sometimes fail to handle these issues effectively and hence it is necessary to design special controllers that are robust under such circumstances. Variable buoyancy (VB) engines are used in many underwater vehicles and standalone buoyancy modules are being developed for multiple underwater applications. Design and analysis of a hybrid depth controller for a single degree of freedom, standalone VB module, vBuoy, is presented in this paper. The design and mathematical model of the vBuoy is presented along with its open-loop performance analysis. A hybrid controller, which captures the best characteristics of a proportional–integral–derivative controller, a linear quadratic regulator, and a sliding mode controller, is designed for the depth control of the module. Based on the desired transient and steady-state behavior of the system, a supervisory controller is used to switch between the conventional controllers. The comparison of simulation results between the proposed hybrid controller and the conventional controllers shows a significant improvement in the closed-loop performance. The performance is evaluated using the parameters such as rise time, percentage overshoot, settling time, and root mean square error. The same has been implemented in an experimental vBuoy prototype to verify the performance of the hybrid controller and also to validate the robustness of the controller. Based on the simulation and experimental results, it was observed that the hybrid controller improves the trajectory tracking performance by 28%–33%.

Design of a Tether Driven Minimally Invasive Robotic Surgical Tool with Decoupled Degree‐of‐Freedom Wrist

Abstract: Background Dexterous surgical tool wrists used in tele-operated robotic surgery typically have mechanically coupled pitch and yaw degree of freedom (DoF). This leads to complex control requirements. Materials and methods The design of a robotic surgical tool with a mechanically decoupled dexterous wrist which uses stationary tether guides to guide drive tethers is presented. The tethers are routed through the plane of symmetry of the tool and follow law of belting to mechanically decouple the wrist. An optimization procedure for the placement of the stationary tether guides to minimize the change in tether length is presented. Results Experimental and analytical results confirm the decoupled motion capability of the wrist. Also, the change in length of tether segments over the operating range of motion was found to be very small. Conclusion A prototype has been fabricated through metal 3D printing and integrated to a tele-operated robotic setup to demonstrate its utility in surgical application.

Enhancement of Stability and Transparency in Teleoperated Robots Through Isotropy-Based Design

Abstract: The primary challenge in implementing teleoperated master-slave robots is that both of its objectives - stability and transparency, are conflicting to each other. This trade-off is usually attributed to the time-delay in the communication channel, and state-of-the-art controllers are proposed primarily to counteract the effects of this time delay. Despite such controllers, it is observed that the system suffers from instability and inaccurate force feedback (loss of transparency), at least under certain conditions. This is because issues other than time delay which cause oscillations and inaccurate force feedback are rarely addressed in the literature. In this paper, such issues are clearly identified and it is shown here that controller design cannot counteract these issues. It is proposed in this paper that an isotropy based design of robots is necessary for recovering the additional stable and transparent behavior of the system, apart from what a controller can achieve. Another significant contribution of this paper is that because of the proposed design, the need for two signals from the traditional four-channel teleoperation architecture is eliminated, thus reducing the complexity of the system. Experimental validation is carried out by implementing a two-channel architecture on the designed robots.