Author name cluster

Varun Agrawal

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.

5 papers

1 author row

ICRA Conference 2024 Conference Paper

A Group Theoretic Metric for Robot State Estimation Leveraging Chebyshev Interpolation

Varun Agrawal
Frank Dellaert

We propose a new metric for robot state estimation based on the recently introduced SE 2 (3) Lie group definition. Our metric is related to prior metrics for SLAM but explicitly takes into account the linear velocity of the state estimate, improving over current pose-based trajectory analysis. This has the benefit of providing a single, quantitative metric to evaluate state estimation algorithms against, while being compatible with existing tools and libraries. Since ground truth data generally consists of pose data from motion capture systems, we also propose an approach to compute the ground truth linear velocity based on polynomial interpolation. Using Chebyshev interpolation and a pseudospectral parameterization, we can accurately estimate the ground truth linear velocity of the trajectory in an optimal fashion with best approximation error. We demonstrate how this approach performs on multiple robotic platforms where accurate state estimation is vital, and compare it to alternative approaches such as finite differences. The pseudospectral parameterization also provides a means of trajectory data compression as an additional benefit. Experimental results show our method provides a valid and accurate means of comparing state estimation systems, which is also easy to interpret and report.

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ICRA Conference 2023 Conference Paper

Constraint Manifolds for Robotic Inference and Planning

Yetong Zhang
Fan Jiang
Gerry Chen
Varun Agrawal
Adam Rutkowski
Frank Dellaert

We propose a manifold optimization approach for solving constrained inference and planning problems. The approach employs a framework that transforms an arbitrary nonlinear equality constrained optimization problem into an unconstrained manifold optimization problem. The core of the transformation process is the formulation of constraint manifolds that represent sets of variables subject to equality constraints. We propose various approaches to define the tan-gent spaces and retraction operations of constraint manifolds, which are crucial for manifold optimization. We evaluate our constraint manifold optimization approach on multiple constrained inference and planning problems, and show that it generates strictly feasible results with increased efficiency as compared to state-of-the-art constrained optimization methods.

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ICRA Conference 2021 Conference Paper

Continuous-time State & Dynamics Estimation using a Pseudo-Spectral Parameterization

Varun Agrawal
Frank Dellaert

We present a novel continuous time trajectory representation based on a Chebyshev polynomial basis, which when governed by known dynamics models, allows for full trajectory and robot dynamics estimation, particularly useful for high-performance robotics applications such as unmanned aerial vehicles. We show that we can gracefully incorporate model dynamics to our trajectory representation, within a factor-graph based framework, and leverage ideas from pseudo- spectral optimal control to parameterize the state and the control trajectories as interpolating polynomials. This allows us to perform efficient optimization at specifically chosen points derived from the theory, while recovering full trajectory estimates. Through simulated experiments we demonstrate the applicability of our representation for accurate flight dynamics estimation for multirotor aerial vehicles. The representation framework is general and can thus be applied to a multitude of high-performance applications beyond multirotor platforms.

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ICRA Conference 2010 Conference Paper

Control of cable actuated devices using smooth backlash inverse

Varun Agrawal
William J. Peine
Bin Yao
SeungWook Choi

Cable conduit actuation provides a simple yet dexterous mode of power transmission for remote actuation. However, they are not preferred because of the nonlinearities arising from friction and cable compliance which lead to backlash type of behavior. Unlike most of the current research in backlash control which generally assumes no knowledge of one of the intermediate states, the controller design in this case can be significantly simplified if output feedback of the system is available. This paper uses a simple feedforward control law for backlash compensation. A novel smooth backlash inverse is proposed, which takes the physical limitations of the actuator in consideration, unlike other designs, and thus makes it more intuitive to use. Implementation of this inverse on physical systems can also improve the system performance over the theoretical exact inverse, as well as other existing smooth inverse designs. Improvement in the performance is shown through experiments on a robot arm of Laprotek surgical system as well as on an experimental setup using polymeric cables for actuation.

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ICRA Conference 2008 Conference Paper

Modeling of a closed loop cable-conduit transmission system

Varun Agrawal
William J. Peine
Bin Yao

Many surgical robots use cable-conduit pairs in a pull-pull configuration to actuate the instruments and transmit power into the patient’s body. Friction between the cable and the conduit makes the system nonlinear and accounts for major losses in tension transmission across the cable. This paper proposes an analytical model for a similar cable-conduit system and formulates the load transmission characteristics. The dynamic model uses discrete elements with friction losses and cable stretch calculated for each of the segments. The simulations predict backlash, cable slacking, and other nonlinear behavior. These results are verified with an experiment using two DC motors coupled with a cable-conduit pair. The drive motor is run in position control mode, while the load motor simulates a passive environment torsional spring. Experimental results are compared with the simulation and various implications are discussed.

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