Robot Builders

In this paper we generate gaits for two types of underactuated mechanical systems: principally kinematic and purely mechanical systems. Our goal is to specify inputs in the form of gaits, that is, a sequence of controlled shape changes of a multi-bodied mechanical system that when executed would produce a desired change in the unactuated position or orientation variables of the entire mechanical system. In other words, we want to indirectly control the unactuated degrees of freedom of the mechanical system utilizing a controlled “internal” shape change. More precisely, in this paper we develop a gait evaluation tool which easily measures the change of position, computed in a body-attached coordinate frame, due to any closed curve in the shape space. This evaluation tool is simple enough that we can use it to generate gaits or to design curves that move the mechanical system along a desired direction. Finally, we verify that this gait analysis technique applies to two seemingly different classes of mechanical systems, purely mechanical and principally kinematic systems, and unify the gait generation problem for both classes.

Researchers at Princeton University are currently working on two projects to reduce jet travel’s role in global warming. The first one, a major project funded by the U.S. Air Force with $7.5 million, is focused on developing computational models that accurately simulate the burning of jet fuel, a complex process not well understood today. The second one, funded by NetJets, a company providing business jets, will help to develop new jet fuels with near-zero net greenhouse gas emissions.

In this paper a novel Polar Scan Matching (PSM) approach is described that works in the laser scanner’s polar coordinate system, therefore taking advantage of the structure of the laser measurements and eliminating the need for an expensive search for corresponding points in other scan match approaches. PSM belongs to the family of point to point scan matching approaches with its matching bearing association rule. The performance of PSM is thoroughly evaluated in a simulated experiment, in experiments using ground truth, in experiments aimed at determining the area of convergence and in a SLAM experiment. All results are compared to results obtained using an iterated closest point (ICP) scan matching algorithm implementation. It is found that PSM is superior to the ICP implementation in processing speed and that PSM converges to a correct solution from a larger range of initial positions.

The reason some people don’t get post-traumatic stress disorder or depression from chronic stress, while others do, may lie in specific molecular differences in the brain. This study mapped them out in mice responding to stressful situations, in mechanisms also found in human brain. It turns out that the ability to withstand stress isn’t just the absence of brain mechanisms that underlie the tendency to buckle under; a different, adaptive molecular engine gets fired up to drive resilience. -more-

This paper presents a distributed control algorithm for multi-target surveillance by multiple robots. Robots equipped with sensors and communication devices discover and track as many evasive targets as possible in an open region. The algorithm utilizes information from sensors, communication, and a mechanism to predict the minimum time before a robot loses a target. Workload is shared locally between robots using a greedy assignment of targets. Across long distances robots cooperate through explicit communication. The approach is coined Behavioral Cooperative Multi-robot Observation of Multiple Moving Targets. A formal representation of the proposed algorithm as well as proofs of performance guarantee are provided. Extensive simulations confirm the theoretical results in practice.

Stents are tiny tubes inserted into diseased arteries to keep them open. The stent being tested is intended to act as a temporary scaffold to support the blood vessel during the healing process and maintain blood flow. It subsequently dissolves, leaving the patient free of any permanent implant.

In this paper, an algorithm for autonomous stair climbing with a tracked vehicle is presented. The proposed method achieves robust performance under real-world conditions, without assuming prior knowledge of the stair geometry, the dynamics of the vehicle’s interaction with the stair surface, or lighting conditions. The approach relies on fast and accurate estimation of the robot’s heading and its position relative to the stair boundaries. An extended Kalman filter is used for quaternion-based attitude estimation, fusing rotational velocity measurements from a 3-axial gyroscope, and measurements of the stair edges acquired with an onboard camera. A two-tiered controller, comprised of a centering- and a heading-control module, utilizes the estimates to guide the robot rapidly, safely, and accurately upstairs. Both the theoretical analysis and implementation of the algorithm are presented in detail, and extensive experimental results demonstrating the algorithm’s performance are described.

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This paper develops a motion planning algorithm which exploits symmetries in distributed systems to reduce motion planning computation complexity. Symmetries allow for algebraic manipulations that are computationally costly, which normally must be carried out for each component in a distributed system, to be related among various symmetric components in a distributed system by a simple algebraic relationship. This leads to a large reduction in the complexity of the overall motion planning problem for a group of distributed mobile robotic agents. In particular, due to the manner in which a symmetric system is defined, the structure of the Chen—Fliess—Sussmann differential equations has a simple relationship among various symmetric components of a distributed system. Essentially, symmetries are defined in a manner which preserves the Lie algebraic structure of each component. In a system with distributed computational capability, the motion planning computations may be distributed throughout formation in such a way that the objectives of the formation are satisfied and collision avoidance is guaranteed. The algorithm maintains a rigid body formation at the beginning and end of the trajectory, as well as possibly specified intermediate points. Due to the generally nonholonomic nature of mobile robots, guaranteeing a rigid body formation during the intermediate motion is impossible. However, it is possible to bound the magnitude of the deviation from the rigid body formation at any point along the trajectory. Simulation and experimental results are provided to demonstrate the utility of the algorithm.

If don’t like the concept of ‘Frankenfoods,’ I have bad news for you. U.S. researchers have developed an artificial chromosome for corn plants. The Chicago Tribune reports that researchers can now make chromosomes to order. These artificial chromosomes are accepted as natural by the plants and passed through generations. As the Monsanto Company bought rights to use this mini-chromosome stacking technology in corn, cotton, soybeans, and canola, I guess we’ll soon eat food made from permanently genetically modified organisms (PGMOs?). read story

The objective of this paper is to propose a new homography-based approach to image-based visual tracking and servoing. The visual tracking algorithm proposed in the paper is based on a new efficient second-order minimization method. Theoretical analysis and comparative experiments with other tracking approaches show that the proposed method has a higher convergence rate than standard first-order minimization techniques. Therefore, it is well adapted to real-time robotic applications. The output of the visual tracking is a homography linking the current and the reference image of a planar target. Using the homography, a task function isomorphic to the camera pose has been designed. A new image-based control law is proposed which does not need any measure of the 3D structure of the observed target (e.g. the normal to the plane). The theoretical proof of the existence of the isomorphism between the task function and the camera pose and the theoretical proof of the stability of the control law are provided. The experimental results, obtained with a 6 d.o.f. robot, show the advantages of the proposed method with respect to the existing approaches.