N. K. Philip

Bio: N. K. Philip is an academic researcher from Indian Space Research Organisation. The author has contributed to research in topics: Model predictive control & Rendezvous. The author has an hindex of 3, co-authored 8 publications receiving 39 citations.

Object detection and obstacle avoidance for mobile robot using stereo camera

Abstract: The objective of this research is to develop a real time obstacle detection and obstacle avoidance for autonomous navigation of mobile robots using a stereo camera in an unstructured environment. Autonomous navigation of mobile robots demands a) Exact determination of position and orientation of Robot and b) Accurate determination of size, shape, depth and range of potential obstacles in the environment. Simple kinematic model is used for mobile robot and stereo camera with pan and tilt provision is considered for long range operation. Complete 3D reconstruction of object/obstacle is obtained from the stereo matching algorithm and with triangulation method. The pose (position and orientation) of mobile robot is formulated from the static object observation with stereo reference matching points using RANSAC (RANdom SAmple Consensus) in successive frames. Potential field based obstacle avoidance formulation is carried out by using the obstacle range, size information, mobile robot position and orientation. Finally, proportional derivative navigation control loop along with obstacle avoidance algorithm is formulated and verified.

Trajectory optimization for Rendezvous and Docking using Nonlinear Model Predictive Control

Abstract: In this paper, MPC based constrained trajectory optimization algorithms has been applied for rendezvous and docking of two small satellites to achieve precise terminal soft docking with path constraints. A receding horizon MPC has been applied in order to reduce the computational load. The constraints such as thrust magnitude limit, chaser spacecraft positioning with in Line-of-Sight (LOS) while approaching the target spacecraft, and terminal velocity limit for soft-docking are considered. In addition debris avoidance constraints are considered and obstacles are assumed as spheres for simplicity. Nonlinear MPC optimization problem with constraints is solved by Sequential Quadratic Program (SQP) technique. The robustness of this control has been verified using nonlinear dynamics with perturbation model.

Autonomous terminal maneuver of spacecrafts for rendezvous using model predictive control

Abstract: Model Predictive Control (MPC) based relative motion control is developed for rendezvous of a follower spacecraft with a leader spacecraft. Debris Avoidance Maneuver operates in rendezvous phase and Line of Sight Maneuvers during terminal phase. In this approach, the optimal control sequence is generated over finite horizon by considering the measurement of the state in every guidance step for different rendezvous phases. Various equality and inequality constraints are included. These constraints are thrust magnitude limit, chaser spacecraft positioning with in Line-of-Sight (LOS) while approaching the target spacecraft, and chaser spacecraft terminal velocity limit for soft-docking with target spacecraft. In addition debris avoidance constraints are also considered along the rendezvous path. The robustness of this control has been verified using nonlinear dynamics with J2 perturbation model. Pulse Width and Pulse Frequency modulator (PWPFM) are used to generate the impulse velocity change by on/off thrusters as actuators. The MPC Controller is validated on nonlinear and elliptical orbit model by simulations.

Integrated Gimbal Dynamics model for Precise Gimbal Rate Control in Single Gimbal-CMG to achieve High Accuracy Pointing

Abstract: Modern Earth observation spacecrafts require high agility to maneuver with larger torque which eventually needs CMGs, as Reaction Wheels cannot meet the demand of such large torques. In order to obtain high-accuracy pointing control with CMG, extremely precise gimbal control is necessary. The current paper brings to light the degree of control precision achieved by gimbal control system with the high fidelity models of inaccuracies like Gimbal Friction, CMG Motor Ripple, structural compliance which hinder the level of accuracy obtainable from CMG attitude control. Proper compensation schemes based on the models help in facilitating an improved level of precision control with CMG. Simulations are carried out with periodic sinusoids as reference gimbal rate to 4 Single Gimbal Control Moment Gyros with roof-top configuration in MATLAB/SIMULINK.

Analytical optimal guidance algorithm for lunar soft landing with terminal control constraints

Abstract: In this paper it is proposed to augment an existing optimal analytical guidance algorithm for the purpose of achieving terminal angle constraint during the terminal powered descent phase of a lunar soft landing mission. Basic algorithm formulation caters to minimizing the acceleration due to onboard engines to minimize the fuel spend and reach the desired position with desired velocity. However, in order to cope up with terminal angle constraint, an augmentation is proposed in the objective function wherein the aim is not only to minimize the energy but also to minimize the terminal error in acceleration achieved and the desired acceleration specified by the designer. This inadvertently leads to the desired terminal angle. Simulations done for the fine braking phase of lunar soft landing mission prove that terminal attitude constraints are met with the modification in objective function.

A Review on Challenges of Autonomous Mobile Robot and Sensor Fusion Methods

Abstract: Autonomous mobile robots are becoming more prominent in recent time because of their relevance and applications to the world today. Their ability to navigate in an environment without a need for physical or electro-mechanical guidance devices has made it more promising and useful. The use of autonomous mobile robots is emerging in different sectors such as companies, industries, hospital, institutions, agriculture and homes to improve services and daily activities. Due to technology advancement, the demand for mobile robot has increased due to the task they perform and services they render such as carrying heavy objects, monitoring, search and rescue missions, etc. Various studies have been carried out by researchers on the importance of mobile robot, its applications and challenges. This survey paper unravels the current literatures, the challenges mobile robot is being faced with. A comprehensive study on devices/sensors and prevalent sensor fusion techniques developed for tackling issues like localization, estimation and navigation in mobile robot are presented as well in which they are organised according to relevance, strengths and weaknesses. The study therefore gives good direction for further investigation on developing methods to deal with the discrepancies faced with autonomous mobile robot.

Model predictive control for autonomous rendezvous and docking with a tumbling target

Abstract: In this paper, we investigate the application of model predictive control (MPC) strategy for controlling a chaser spacecraft to dock with a tumbling target in space. The CW-based model is used to predict the proximity trajectory, while a receding prediction horizon is employed to complete the specific docking manipulation in finite time, and a 2-norm cost index about control input is used to minimize the fuel consumption of the chaser during docking. To ensure the implementation of the docking procedure, several engineering constraints such as control input saturation, collision avoidance, velocity constraint, and dock-enabling condition are considered simultaneously. A time-varying linear inequality constraint is used rather than the original quadratic constraint, to achieve the collision-avoidance requirement. Therefore, the constrained optimal rendezvous trajectory in the case of such a MPC framework can be obtained by solving a quadratic program subject to linear constraints. To verify the feasibility of the proposed MPC strategy, four AR&D scenarios are simulated. The simulation results show that MPC strategy can be an effective approach to achieve rendezvous and proximity maneuvering between a chaser spacecraft and a tumbling target while satisfying various constraints, and provide robustness to disturbances.

Sampling-based 3-D Line-of-Sight PWA Model Predictive Control for Autonomous Rendezvous and Docking with a Tumbling Target.

Abstract: In this paper, a model predictive control (MPC) framework is employed to realize autonomous rendezvous and docking (AR&D) with a tumbling target, using the piecewise affine (PWA) model of the 3-D line-of-sight (LOS) dynamics and Euler attitude dynamics. Consider the error between the predictions obtained by the approximate linear model and the actual states of nonlinear dynamics, a sampling-based PWA MPC is proposed to sample the predictions in the closer neighborhood of the actual states. Besides, novel constructions of constraints are presented to reduce the on-board computation cost and time-delay. Furthermore, a singularity-free strategy is provided to realize crossing the singularity of angle states smoothly. Then, the mission is achieved by continuous 6-DOF pose (position and attitude) tracking of the target's docking port, with the coupling between the position and attitude of the target's docking port is taken into account. Finally, numerical results are presented to demonstrate the above theories.

An Overview of Nature-Inspired, Conventional, and Hybrid Methods of Autonomous Vehicle Path Planning

Abstract: Safe and smooth mobile robot navigation through cluttered environment from the initial position to goal with optimal path is required to achieve intelligent autonomous ground vehicles. There are countless research contributions from researchers aiming at finding solution to autonomous mobile robot path planning problems. This paper presents an overview of nature-inspired, conventional, and hybrid path planning strategies employed by researchers over the years for mobile robot path planning problem. The main strengths and challenges of path planning methods employed by researchers were identified and discussed. Future directions for path planning research is given. The results of this paper can significantly enhance how effective path planning methods could be employed and implemented to achieve real-time intelligent autonomous ground vehicles.

A Survey of Trajectory Planning Techniques for Autonomous Systems

Abstract: This work offers an overview of the effective communication techniques for space exploration of ground, aerial, and underwater vehicles. We not only comprehensively summarize the trajectory planning, space exploration, optimization, and other challenges encountered but also present the possible directions for future work. Because a detailed study like this is uncommon in the literature, an attempt has been made to fill the gap for readers interested in path planning. This paper also includes optimization strategies that can be used to implement terrestrial, underwater, and airborne applications. This study addresses numerical, bio-inspired, and hybrid methodologies for each dimension described. Throughout this study, we endeavored to establish a centralized platform in which a wealth of research on autonomous vehicles (on the land and their trajectory optimizations), airborne vehicles, and underwater vehicles, is published.