Author name cluster

Dinesh K. Pai

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

26 papers

1 author row

ICRA Conference 2011 Conference Paper

A biologically inspired controller for fast eye movements

Martin Lesmana
Dinesh K. Pai

We describe and test a non-linear control algorithm inspired by the behavior of motor neurons in humans and other animals during extremely fast saccadic eye movements. The algorithm is implemented on a robotic eye, which includes a stiff camera cable, similar to the optic nerve, which adds a complicated non-linear stiffness to the plant. For high speed movement, our "pulse-step" controller operates open-loop using an internal model of the eye plant learned from past measurements. We show that the controller approaches the performance seen in the human eye, producing fast movements with little overshoot. Interestingly, the controller reproduces the main sequence relationship observed in animal eye movements.

ICRA Conference 2003 Conference Paper

Post-stabilization for rigid body simulation with contact and constraints

Michael B. Cline
Dinesh K. Pai

Rigid body dynamics with contact constraints can be solved locally using linear complementarity techniques. However, these techniques do not impose the original constraints and need stabilization. In this paper we show how constraint stabilization can also be done in a complementarity framework. Our technique effectively eliminates the drift problem for both equality and inequality constraints and requires no parameter tweaking. We describe results from an implemented system, and compare the new technique to the well known Baumgarte stabilization.

ICRA Conference 2002 Conference Paper

Real Time Simulation of Multizone Elastokinematic Models

Doug L. James
Dinesh K. Pai

We introduce precomputed multizone elastokinematic models for interactive simulation of multibody kinematic systems which include elastostatic deformations. This enables an efficient form of domain decomposition, suitable for interactive simulation of stiff flexible structures for real time applications such as interactive assembly. One advantage of multizone models is that each zone can have small strains, and hence be modeled with linear elasticity, while the entire multizone/multibody system admits large nonlinear relative strains. This permits fast capacitance matrix algorithms and precomputed Green's functions to be used for efficient real time simulation. Examples are given for a human finger modeled as a kinematic chain with a compliant elastic covering.

ICRA Conference 2002 Conference Paper

Robotic Acquisition of Deformable Models

Jochen Lang 0001
Dinesh K. Pai
Robert J. Woodham

We describe techniques for automatically acquiring observations of a deforming object and for estimating a model of the deformation from these observations. A robotic system was developed for measuring deformation, and has been previously reported (Pai et al. , 2000, 2001). The present paper describes new techniques for the estimation of deformable models based on discrete Green's functions, from measurements acquired using stereo vision and a robot arm's position and force sensors. This kind of robotic measurement presents new challenges for measurement and estimation, that we address here. Our techniques for robotic acquisition of deformable, object models have potential applications in robotics, haptic interfaces, simulation, computer graphics and virtual reality.

ICRA Conference 2001 Conference Paper

Robotic Mapping of Friction and Roughness for Reality-based Modeling

John E. Lloyd
Dinesh K. Pai

This paper discusses the robotic acquisition and characterization of surface friction and roughness for real-world objects. Our motivation is the construction of detailed "reality-based" models for existing objects that can be used in haptic displays and other applications involving simulation. A key challenge addressed in this paper is the acquisition of these surface properties on real objects with nontrivial shape, and registration of these properties with respect to geometric models of the shape. We show how Coulomb friction may be effectively estimated in the presence of variations in surface normal. We also show how to estimate a stochastic process model of surface roughness. Finally, we demonstrate the robotic mapping of surface friction over an entire object, using the UBC Active Measurement Facility (ACME).

ICRA Conference 2000 Conference Paper

Active Measurement of Contact Sounds

Joshua L. Richmond
Dinesh K. Pai

We describe a system for robotic measurement of contact sounds. This system is well suited for acquiring impulse-response sound models. A brief explanation of the sound models is included. We also describe experimental results to illustrate the process of acquiring sound models using our system, and a brief analysis of the results. The initial results are promising and could lead to applications in reality-based modeling and object recognition.

ICRA Conference 2000 Conference Paper

Forward Dynamics Algorithms for Multibody Chains and Contact

Dinesh K. Pai
Uri M. Ascher
Paul G. Kry

We describe a framework for derivation of several forward dynamics algorithms used in robotics. The framework is based on formulating an augmented system and performing block matrix elimination on this system. Several popular algorithms such as the O(N) articulated body method, and the composite rigid body method can be easily derived. We also derive an algorithm for simulation of contact between smooth bodies of arbitrary shape, in contact coordinates. Finally, we discuss some potential numerical difficulties that could arise and their solution.

ICRA Conference 1999 Conference Paper

A Mobile Manipulator

Matthew T. Mason
Dinesh K. Pai
Daniela Rus
Lee R. Taylor
Michael A. Erdmann

This paper describes a mobile manipulator that uses its wheels for manipulation as well as locomotion. This robot, named the mobipulator, looks like a small car with four independently powered wheels, none of them steered. It is designed to manipulate paper and other objects on the surface of a desk. The wheels are used for locomotion or for manipulation, switching functions dynamically as the task demands. So far we have preliminary demonstrations of a variety of motions, and performance data for the task of moving a sheet of paper in a square while maintaining constant orientation.

ICRA Conference 1999 Conference Paper

Computing Fault Tolerant Motions for a Robot Manipulator

Scott K. Ralph
Dinesh K. Pai

We introduce a method of planning fault tolerant trajectories based on the least constraint (LC) framework. Fault tolerance is achieved in two ways: exploiting properties of LC itself, and using a performance measure which assess the fault tolerant potential of a given configuration. LC encourages designs which are based solely on salient constraints of the task, allowing the inherent redundancy of the robot to be used to maintain a safe configuration. We compute the effects of faults on the topology of the configuration space and construct optimal recovery motions for a set of faults. We describe an efficient algorithm for computing the optimal recovery motions for a large number of faults over the entire configuration space simultaneously. A performance measure, called longevity, quantifies the ability of the recovery motions to complete the task. From the performance measure fault tolerant paths are constructed. We look at the simple task of positioning the end effector of a Puma 560 at a given point in the workspace.

ICRA Conference 1999 Conference Paper

Green's Function Contact Maps for Accurate Real Time Collisions

C. Ullrich
Dinesh K. Pai

In this article, we discuss the application, of a Green's function approach to contact maps. We apply the contact map algorithm to the case of an elastic bar impacting on a massive foundation. It is demonstrated that the energy lost to elastic waves is an important factor in post-contact states.

ICRA Conference 1998 Conference Paper

Contact Response Maps for Real Time Dynamic Simulation

C. Ullrich
Dinesh K. Pai

We describe the generation and use of "contact response maps" for real time dynamic simulation. Contact response maps are geometry and material dependent maps on physical objects which describe the surface tractions associated with local deformations during contact. We develop a technique for precomputing contact response maps for elastic bodies using the boundary element method to solve the corresponding plane strain problem. Such maps can then be used in a real time simulation environment to accurately resolve collision dynamics.

ICRA Conference 1997 Conference Paper

Model-based telerobotics with vision

John E. Lloyd
Jeffrey S. Beis
Dinesh K. Pai
David G. Lowe

We describe an implemented model-based telerobotic system designed to investigate assembly and other tasks involving contact and manipulation of known objects. Key features of our system include ease of maintaining a world model at the operator site and a task-centric operator interface. Our system incorporates gray-scale model-based vision to assist in building and maintaining the local model. The local model is used to provide a task-centric operator interface, emphasizing the natural and direct manipulation of objects, with the robot's presence indicated in a more abstract fashion. The operator interface is designed to work with widely available and inexpensive desktop computers with low DOF input devices (such as a mouse). We also describe experimental results to date, which include performing assembly-like tasks over the Internet.

ICRA Conference 1996 Conference Paper

Constraint programming for Platonic Beast legged robots

Dinesh K. Pai
Roderick A. Barman

We describe the architecture of a system for programming the high degree-of-freedom Platonic Beast legged robot with constraints. This includes software for distributed control of the robot using the least constraint approach, and hardware for supporting this programming model with distributed computing and communication. We have implemented this system, and we describe results to date.

ICRA Conference 1996 Conference Paper

Haptic texturing-a stochastic approach

Juhani O. Siira
Dinesh K. Pai

All objects have a surface roughness which manifests itself as small forces when objects slide under load against each other. Simulating this roughness haptically enriches the interaction between a user and a virtual world, just as creating graphical textures enhances the depiction of a scene. As with graphical textures, a major design constraint for haptic textures is the generation of a sufficiently "realistic" texture given hard constraints on computational costs. The authors present a simple, fast algorithm to synthesize haptic textures from statistical properties of surfaces. The synthesized texture can be overlaid on other contact models, such as hard contact with Coulomb friction. The algorithm requires minimal hardware support, and can be implemented on a variety of force-feedback mechanisms. It has been successfully implemented on a two-degree-of-freedom haptic interface (the Pantograph).

IROS Conference 1995 Conference Paper

Detection and localization of unmodeled manipulator collisions

Scott K. Ralph
Dinesh K. Pai

Robotic tasks usually require some collision free motions, and there has been considerable work in methods for collision avoidance. However, noise in the sensor data, movement of the obstacles, and incomplete or inaccurate model of the surroundings all may lead to unexpected collisions. Detecting such collisions is necessary before recovery and/or replanning may take place. A means of detecting a collision, as well as the position of the collision on the manipulator has been developed. The detection scheme combines information from observed disturbance torques to detect collision and infer the location of contact with the environment. Knowledge of contact position allows for a more intelligent and less error-prone recovery scheme. A simulation using a three DOF manipulator shows that the collision identification and localization scheme is feasible and robust with respect to noise.

IROS Conference 1995 Conference Paper

Multiresolution rough terrain motion planning

Dinesh K. Pai
L. -M. Reissell

We describe a new approach to the problem of motion planning for mobile robots on natural, nonhomogenous terrain. Our approach computes a multiresolution representation of the terrain using wavelets, and hierarchically plans the path through sections which are well approximated on coarser levels and relatively smooth. Unlike most methods, the hierarchical approximation errors are used explicitly in a cost function to distinguish preferred terrain sections. The error is computed using the corresponding wavelet coefficients. The path planning algorithm uses a new nonscalar path cost measure based on the sorted terrain costs along the path. This measure can be incorporated into standard global path search algorithms and yields intuitively good paths. Additional constraints for specific robots can be integrated into this approach for efficient hierarchical motion planning on rough terrain. We present experimental results for real terrain data.

ICRA Conference 1995 Conference Paper

Numerical Solution of Differential Systems with Algebraic Inequalities Arising in Robot Programming

Raymond J. Spiteri
Uri M. Ascher
Dinesh K. Pai

Recently, new robot programming approaches have proposed the use of programmed constraints as an executable specification language for the desired behavior of a robot. The constraint-based approaches are intermediate level languages, promising a higher, more declarative level of programming than trajectory-based approaches, while being more tractable computationally than motion planning. This paper considers a numerical algorithm for solution of differential systems subject to algebraic inequality constraints. These are the mathematical structures behind the constraint-based approach. Our approach is based on a principle of 'least constraint', consisting of a dynamic integration of the equations of motion coupled with invocation of a control mechanism to ensure that the robot trajectory avoids all constraint boundaries. This is achieved by minimization of a barrier function defined using buffer zones near the constraint boundaries. Determination of the buffer zones is done dynamically, corresponding to a local planning strategy.

ICRA Conference 1995 Conference Paper

The Formulation Stiffness of Forward Dynamics Algorithms and Implications for Robot Simulation

Benoit P. Cloutier
Dinesh K. Pai
Uri M. Ascher

The authors identify an important phenomenon they call "formulation stiffness" in the numerical simulation of tree-structured multibody systems such as robot manipulators. The numerical simulation problem is usually treated as two separate problems: (i) the forward dynamics problem for computing system accelerations, and (ii) the numerical integration problem far advancing the state in time. The authors show that the interaction of these two problems leads to new conclusions about the overall efficiency of multibody simulation algorithms; in particular the fastest forward dynamics methods are not necessarily best when considered in conjunction with the popular adaptive stepsize integration methods. Specifically, the authors show that the articulated-body method is better suited to deal with certain types of numerical problems than the composite rigid body method. The authors present examples of simulations and discuss the practical implications of these results.

IROS Conference 1994 Conference Paper

Constructing performance measures for constrained systems

Kees van den Doel
Dinesh K. Pai

Investigates the construction of performance measures for robot manipulators with closed kinematic loops. For such systems, the equations for the forward kinematics and the constraints can not be solved explicitly in general. The authors extend a formalism introduced by them previously (1993, 1994) based on the construction of an "induced" metric tensor on the work space of the manipulator, to include systems with constraints (which may be non-holonomic). As an example of an application the authors compute the generalized Yoshikawa measure for a planar five-link closed linkage chain, which they use to compute some optimal postures. >

ICRA Conference 1994 Conference Paper

Constructing Performance Measures for Robot Manipulators

Kees van den Doel
Dinesh K. Pai

We introduce a formalism for the systematic construction of performance measures for robot manipulators in a unified framework based on differential geometry. We show how known measures arise naturally in our formalism and we construct some new measures. The new measures presented here are the effective inertia on workspace and the kinematic and dynamic anisotropy measures for redundant manipulators. >

ICRA Conference 1994 Conference Paper

Platonic Beasts: A New Family of Multilimbed Robots

Dinesh K. Pai
Roderick A. Barman
Scott K. Ralph

Describes class of spherically symmetric, high degree of freedom robots called "platonic beasts". A robot in this family is kinematically equivalent to a symmetric polyhedron, such as one of the platonic solids, with identical multi-purpose limbs attached to its vertices. The symmetry and regularity of the design have several advantages including robustness to toppling, novel gaits such as the rolling gait, and fault tolerance. The authors describe the design, simulation, and construction of a prototype platonic beast robot that the authors have built in their lab. The robot has four limbs, each with three degrees of freedom, and is controlled by a network of four embedded 32-bit microcontrollers. The authors also discuss the general features of these robots, including locomotion using the rolling gait and the implications of its novel features. >

ICRA Conference 1994 Conference Paper

Redundancy and Non-Linearity Measures for Robot Manipulators

Kees van den Doel
Dinesh K. Pai

We investigate two new classes of performance measures. The first class quantifies the ability of a redundant manipulator to reconfigure itself while keeping the end-effector at a fixed position. The second measures the nonlinearity of the manipulator. We derive these measures using the differential-geometric formalism we introduced previously (1993). >

IROS Conference 1993 Conference Paper

Simultaneous computation of robot kinematics and differential kinematics with automatic differentiation

Dinesh K. Pai
Tony H. S. Ser

Describes the computation of derivatives of functions defined on a robot's kinematic quantities using the efficient adjoint technique for automatic differentiation. Implemented software called RAD (Robot Automated Differentiation), which can generate optimized C programs for computing these quantities from concise descriptions of the robot and the required kinematic quantities, is also described. In addition to automatic differentiation, the RAD software provides a symbolic formulation of the kinematics and simplification of trigonometric algebraic expressions using Mathematica and pattern matching. The authors illustrate the utility of the software with a 2-link robot and a PUMA robot.

ICRA Conference 1990 Conference Paper

On the motion of compliantly-connected rigid bodies in contact. II. A system for analyzing designs for assembly

Bruce Randall Donald
Dinesh K. Pai

For pt. I see Cornell Computer Science Tech. Report (1989). A fully algorithmic, combinatorially precise approach to designing devices so that they are easy to assemble and (optional) hard to disassemble is presented. The analysis can be used to validate good designs and can be iterated to generate improved designs. The approach is based on an algorithm for predicting the motion of flexible objects in contact. Such objects are intended to model snap-fastener-type devices, which are very useful in assembly design. The authors describe the algorithm, its implementation in a system for predicting and analyzing the motion of snap-fastener-type devices, and experiments run using the system to analyze and design particular devices. The issues discussed include: the relevance of the approach to engineering, the computational methods employed, the algebraic techniques for predicting motions in contact with rotational compliance, and issues of robustness and stability of the geometric and algebraic algorithms. Subtle mechanical difficulties arise in predicting motions under rotational compliance. The authors discuss these problems and their solutions. >

ICRA Conference 1989 Conference Paper

Generic singularities of robot manipulators

Dinesh K. Pai
Ming C. Leu

The singularities of the differential kinematic map, i. e. of the manipulator Jacobian, are considered. The authors first examine the notion of a generic kinematic map, whose singularities form smooth manifolds of prescribed dimension in the joint space of the manipulator. For three-joint robots, an equivalent condition for genericity using determinants is derived. The condition lends itself to symbolic computation and is sufficient for the study of decoupled manipulators, i. e. manipulators that an be separated into a three-joint translating part and a three-joint orienting part. The results are illustrated by analyzing the singularities of two classes of three-joint positioning robots. >

ICRA Conference 1986 Conference Paper

INEFFABELLE - An environment for interactive computer graphic simulation of robotic applications

Dinesh K. Pai
M. C. Leu

This paper describes an environment developed for interactive computer graphic simulation of robotic applications. The goals of this environment are to make the development of application programs easier and to allow the same models to be used by a variety of application programs. In this environment, standard models of work cells, robots, sensors, and other entities can be created. These models can be extended to include user-defined properties of individual entities. Functions are provided to access the data in these models, to manipulate the data with computer graphic animation, and to perform other simulation tasks.