S. N. Shome

Time Delay Sliding Mode Control of Nonholonomic Wheeled Mobile Robot: Experimental Validation

In this endeavor, a hybrid control strategy has been proposed for composite path tracking control of a nonholonomic wheeled mobile robotic (WMR) system under parametric and nonparametric uncertainties. A WMR, often in practical circumstances, undergoes through various parametric changes. Moreover, modeling of WMR in presence of friction, slip or skid, backlash etc. is very difficult. These factors, which make the system model more cumbersome, are normally ignored but their effects are compensated through appropriate control methods. Conventional Sliding Mode Control (SMC) is such a method but it is susceptible to chattering due to high switching gains and reasonable tracking accuracy is sacrificed to avoid chattering. On the other hand, Time Delay Control (TDC) technique is highly efficient to assure robustness against unknown dynamics but it is unable to eliminate approximation errors that arise due to introduced delay. Considering the aforesaid difficulties of SM and TD controllers a hybrid control methodology christened as Time Delay Sliding Mode Control (SMC-TD) is adopted in this work for accurate path tracking of nonholonomic WMR. The SMC-TD is absolutely a judicious blending of SMC and TDC strategies aiming at elimination of the individual shortcomings while retaining the positive advantages. Detail features and advantages of the proposed controller are presented in greater length along with the experimental results, which are very promising.

Error modeling of Laser Range Finder for robotic application using time domain technique

Present day mobile robots are meant for very precise applications. For very precise applications of mobile robots, accurate estimation of inertial parameters depends upon the accuracy of mathematical model & as well as accuracy (error characteristics) of the individual sensor measurements. Sensor measurements are prone to various errors, which necessitates the detail modeling of sensors for estimation of useful signals from the noisy sensor measurements. Detail error modeling is essential to understand, identify & characterize the different types of noises present in the measured data using available mathematical techniques. This paper illustrates the frequency and time domain analysis techniques for characterization and identification of various noises present in the Laser Range Finder (Model: LMS200, SICK, Germany) measurements and their contribution to the overall noise statistics. A detailed methodology based on stochastic discrete time model is presented for Laser Range Finder error modeling.

Inverse kinematics of redundant serial manipulators using interval method in handling uncertainties

The paper presents an application of Interval method to solve the inverse kinematics of a serially connected redundant manipulator, aiming its use in design optimization of manipulators. The article attempts to solve inverse kinematics, when the lengths of the links of the manipulator are not precisely known. The sources of uncertainties include manufacturing tolerances, approximations for complex link geometries, inaccuracies in joint angle measurements etc. The inverse kinematics is intended to produce solutions for joint variables in interval of tolerances for specified end effector accuracy range. The redundancy resolution is cast as an optimization problem with arm isotropy as performance metric. In solving for the inverse kinematics, two stage interval optimization method is implemented, where, in the first stage, bisection technique is applied and in the second stage interval discrete random variable method is used. As exemplar problem solving, two cases, namely a planar3-degrees-of-freedom and a spatial 5-degrees-of-freedom serial link manipulators are considered.

Modeling and simulation of a jumping frog robot

In nature, several animals and insects use jumping locomotion in rough terrains. Jumping locomotion is useful for ground robots as jumping provide high speed movement with enhanced energy efficiency. It also helps in overcoming obstacles relatively larger than their body sizes. Jumping needs coordination and large instantaneous forces within a very short duration. In this paper, a method of jumping by using a four-bar spring/linkage mechanism integrated with spool winding and ratchet release mechanism has been presented. Inspired by the frogs, we have modeled and simulated a simple and efficient four legged jumping frog robot.

Robust control of nonholonomic wheeled mobile robot with past information: Theory and experiment

In this article, a robust hybrid control method is presented for efficient path tracking control of a nonholonomic wheeled mobile robotic system under parametric and nonparametric variations. The present control law is a paradigm shift to control a wheeled mobile robot over a predefined trajectory by fusing the best features of the switching control logic as well as time-delayed control logic. The proposed hybrid control strategy aims at reducing the effort required for modeling the complex wheeled mobile robotic systems by approximating the unknown dynamics using input and feedback information of past time instances. Furthermore, the proposed methodology significantly reduces the approximation error arising from finite time-delay through the switching logic without any prior knowledge of the uncertainty bound. A new stability analysis for the time-delayed control is proposed which establishes an analytical relation between the controller performance and the approximation error. Performance of the proposed hybrid controller is tested with a real-life wheeled mobile robot and improved tracking performance is observed compared to conventional robust control strategies even with the incorporation of dynamic parametric uncertainties.

A modular approach to detailed dynamic formulation and control of wheeled mobile robot

Presently, nonholonomic mobile robots driven by wheels are being used for variety of applications where high velocity maneuvering control is very essential. The need for accurate formulation of system dynamics incorporating each & every moving parts of the robot is very important for faster movement & precise applications. This paper represents the detailed dynamic formulation based on overall robots kinetic energy along with an advanced control scheme. Actuator dynamics have been also considered to achieve precise motion control and to design a simple controller with a low cost sensor suite. A modular approach has been adopted to derive the kinetic energy of the robot accurately & thereafter to evaluate required equations of motion. A feedback linearization based path following controller with online gain scheduling has been designed to control the mobile robot through various paths. The methodology adopted for path following control deals explicitly with detail robot-actuator dynamics and it overcomes stringent initial condition constraints. The simulation has been carried out with the parameters of a real robot and the simulation results illustrate very promising performance due to incorporation of detail robot-actuator dynamics.

Autonomous Underwater Vehicle for 150m Depth–Development Phases and Hurdles Faced

This paper describes the various development phases and the associated hurdles faced during the design, fabrication, sub-system level testing, assembly, integration and overall system testing of an Autonomous Underwater Vehicle (AUV). This AUV has been designed for a depth of 150 m with multi-thruster actuation for shallow water applications. The AUV is having onboard power, electronics and advanced control module, navigation and payload sensors and modular software architecture. During the development of AUV various hurdles like how to power on AUV from outside, loose connections, isolation and grounding, water leakage, battery tripping, etc. have been faced and resolved. The present paper describes the complete development aspects in brief and highlights the various hurdles with remedies throughout the development. The AUV has been tested successfully for various missions at Idukki Lake, Cochin, India up-to a depth of 5m.

Application of Particle Filtering Technique for sensor fusion in mobile robotics

Accurate position estimation is very essential for successful operation of any autonomous mobile robots. Generally, Extended Kalman Filter (EKF) is used to fuse multiple low cost sensor information for better position estimation of mobile robots. However, due to the first-order approximation while performing linearization of the nonlinear model in the EKF, it will introduce large estimation errors over the time. In order to reduce the significant estimation errors, the Particle Filter (PF) is presently used as a modern sensor fusion methodology applied to mobile robotics due to its generic nature to tackle uncertainty & nonlinearity. This paper illustrates application of Particle Filtering Technique for reliable estimation of the state vector of a mobile robot in association with proprioceptive (Odometry) and exteroceptive (Laser Range Finder) sensors for efficient control. The paper also presents a comparison of the performance of the EKF & PF techniques for the estimation of the states & control of the mobile robot and establishes the superiority of PF over EKF.

An investigation on the performance of an oscillating flat plate fin with compliant joint for underwater robotic actuation

Fishes are very good swimmers possessing impeccable maneuverability, efficiency, and stealth. Understanding the fish propulsion and mimicking the same is important in obtaining improved performance by non-conventional types of underwater robot/vehicle actuators. The role of the caudal fin in fish locomotion is predominant at higher swimming speeds producing most of the thrust force. Generally the fin motions are oscillatory in nature. In oscillatory trajectories, where reversal of motion is required, a normal actuator has to spend energy to accelerate as well as to decelerate(braking). During braking phase, a normal actuator, without any energy storage mechanism, dissipates energy. Ubiquitous presence of compliance in biological actuation system can store some energy which otherwise get dissipated. Fishes are evolved to tune their compliant joint stiffness according to the swimming conditions. The elastic joint(contributed by compliant muscle) can store energy in part of a cycle during fin oscillation and interaction with surrounding fluid in the form of potential energy and can release in next part of the cycle. This article investigates the role of compliance in the fin joint on propulsion performance through simulations. The analysis considers a rigid body model of trapezoidal flat fin with elastic joint and presents hydrodynamic force modeling for interacting fluid in Newton-Euler rigid body framework using blade element technique.

Caudal fin load characteristics with different motion patterns toward developing biorobotic fish-fin actuator

Traditionally underwater vehicles use thrusters as propulsion devices and achieve high speed. These thrusters come with their own limitations such as turbulence, cavitations etc. resulting into low efficiency and noise; the vehicles severely suffer from lack of efficiency in low speed operations. Maneuverability of vehicles using thrusters or jet propulsion devices is inherently limited. On the other hand, nature provides fins to fishes and aquatic animals for underwater locomotion with proven greater maneuverability, agility and efficiency in low speed motion, achieving a highly desirable quality of stealth. To adapt the biological mechanisms of thrust production to man-made underwater robotic vehicles, understanding of biomechanics and load characteristics of the natural fins is very important. In this paper, we consider the caudal fin of a fish, being the main propulsive actuator. This article aims to understand the load characteristics of different motion patterns of the fin in water through fluid-structure interaction (FSI) simulations and does not intend to access the performance of the fin propulsion as a whole. Numerical simulations have been carried out for determining the load characteristics of different motion patterns of the chosen caudal fin and the results are presented. The simulations are based on simple kinematic fin model and do not describe any working prototype. The simulations will eventually lead to the design and development of reduced order biorobotic replica of a caudal fin.