Abhijit Mahapatra

Energy-efficient inverse dynamic model of a Hexapod robot

A hexapod robotic system is a complex multi-body system that exhibits complex motion characteristics due to the effect of forces and torques (both internal and external). In the present study, inverse dynamics model using Newton-Euler approach was developed for the hexapod robotic system. It is assumed that the prescribed motion of the model is fully known and consistent with the kinematic constraints of the realistic model. The kinematic motion parameters (displacement, velocity and accelerations) obtained from the inverse kinematic analysis of the robotic system with specified path and gait planning for straight forward motion in varying terrain are substituted in the inverse dynamic model which is a set of algebraic equations. The equations are solved for to determine the joint torques and resulting reaction forces for the foot in contact with the ground that are responsible to generate the prescribed motion trajectories. The solution is not unique due to the redundant set of forces/ moments and/or constraints used. Therefore, the solution of the problem has been obtained by minimizing the total instantaneous power consumption of the system, considered as the objective function with respect to linear equality and inequality constraints. The simulated results of foot-ground contact and variation of instantaneous power consumption for the dynamical system are discussed thereafter.

Study of thermo-fluidic behavior of micro-droplet in inkjet-based micro manufacturing processes

Inkjet printing technology, a maskless, non-contact patterning operation, which has been a revelation in the field of micro and nano manufacturing for its use in the selective deposition of desired materials. It is becoming an exciting alternative technology such as lithography to print functional material on to a substrate. Selective deposition of functional materials on desired substrates is a basic requirement in many of the printing based micro and nano manufacturing operations like the fabrication of microelectronic devices, solar cell, Light-emitting Diode (LED) research fields like pharmaceutical industries for drug discovery purposes and in biotechnology to make DNA microarrays. In this paper, an attempt has been made to design and develop an indigenous Electrohydrodynamic Inkjet printing system for micro fabrication and to study the interrelationships between various thermos-fluidic parameters of the ink material in the printing process. The effect of printing process parameters on printing perfo...

Inverse Dynamics and Feet-Terrain Collision Model for Optimal Distribution of the Contact Forces During Crab Motion of a Hexapod Robot

The present study deals with the kinematics, dynamics and feet-ground contact modeling of a hexapedal robotic system. Feet-ground interaction generates contact forces, which play a very important role for locomotion on varying terrains. In this study, the constrained inverse dynamical model is formulated as a coupled dynamics problem using Newton-Euler approach with implicit constraints in Cartesian coordinates. The contact force distribution in the feet during interaction with the terrain is considered to be a constrained optimization problem. For a more realistic locomotion analysis, impact of feet-tip with the terrain is considered, which is assumed to be governed by a compliant normal contact force model. The paper also investigates the optimal feet forces’ distributions under body forces, total power consumption etc. without any external disturbance during the robot’s locomotion with wave-crab gait (duty factor = ½).

Motion Control Strategies based on PD Control for a Four Degree-of-Freedom Serial Robotic Manipulator to Mimic Human Index Finger Articulations

The present study is based on motion control of an articulated model of a human index finger that has been modeled as a four-degree-of-freedom serial robotic manipulator. Preliminary studies on position and tracking control have been carried out by testing various control strategies based on proportional-derivative (PD) control in a simulation environment wherein the manipulator has been modeled and simulated with a certain input signal and responses to various controllers have been shown. Model free and model based controllers have been designed simulated using MATLAB®/ Simulink®. Strategies like model free PD control have been improved upon by introducing auto-tuning and learning capabilities. A virtual plant modeled using Simmechanics® toolbox has been set up and used for simulation purposes. General Terms Degree of freedom, human hand articulations, serial manipulators

Trajectory based Recovery of Index Finger Articulated Pose during Palmar Grasp

This paper describes our experimental and analytical study of recovering index finger pose from tip trajectory during palmar grasp. Our study experimentally evaluates a kinematical model that can be used to reduce the number of surface markers in each finger for motion estimation and its segmental kinematics. We captured the trajectory of the index finger tip and joint angles in typical fist closing mode (palmar grasp), based on the concept of planar homology in projective space and then investigated the inverse kinematics solutions for the correlation. Jacobian based Damped Least Square (DLS) with variable damping parameter λ has been implemented. The DLS method, though iterative, shows reasonably fast convergence with in 3-10 iterations in feed forward mode and has better concurrence with the experimental values in recovery of articulated pose. General Terms Robotics, Computer Vision.

Modal response of 4-rod type radio frequency quadrupole linac

This paper deals with the analysis and experimental study of natural frequencies of vibration of a 4-rod type radio frequency quadrupole (RFQ) linear accelerator. The eigenvalue analysis of the structure has been done both analytically (multispan beam concept) as well as using blocked Lanczos eigenvalue finite element solver with an ability to extract the rigid body modes. This has been done in the mechanical design phase to find the level of agreement between the output of simplified analytical analysis results and the output of a commercial finite element method (FEM) solver, since a full scale RFQ structure is too complex to handle analytically. Experimental validation of the analysis results has been done on the physical 1.7 m RFQ at the installation site. The experimental data obtained were later analyzed and found to be in close agreement with the predicted frequencies in the lower frequency ranges. It gets more and more deviated in the higher frequency ranges. Also some frequencies were observed during experimentation, which were not found in the finite element analysis results. The source of those frequencies are to be further investigated as it may play a predominant role in the design high quality factor beam line cavities for higher operational efficiency.