While robotic manipulation of rigid objects is quite straightforward, coping with deformable objects is an open issue. More specifically, tasks like tying a knot, wiring a connector or even surgical suturing deal with the domain of Deformable Linear Objects (DLOs). In particular the detection of a DLO is a non-trivial problem especially under clutter and occlusions (as well as self-occlusions). The pose estimation of a DLO results into the identification of its parameters related to a designed model, e.g. a basis spline. It follows that the stand-alone segmentation of a DLO might not be sufficient to conduct a full manipulation task. This is why we propose a novel framework able to perform both a semantic segmentation and b-spline modeling of multiple deformable linear objects simultaneously without strict requirements about environment (i.e. the background). The core algorithm is based on biased random walks over the Region Adiacency Graph built on a superpixel oversegmentation of the source image. The algorithm is initialized by a Convolutional Neural Networks that detects the DLO’s endcaps. An open source implementation of the proposed approach is also provided to easy the reproduction of the whole detection pipeline along with a novel cables dataset in order to encourage further experiments.
Moving to the domain of knot-tying with , the basic approach still turns out to be background removal, like in @cite_12 , or its 3D counterpart -- plane removal-- like in @cite_9 and @cite_10 . All these methods produce a raw set of points on which a region growing algorithm is run to attain a vectorization of the target object. A different approach is used in @cite_32 , with the model of the object registered to the 3D point cloud in real-time in order to avoid the segmentation step. As described in @cite_16 , deep learning can also be used to track a deformable object: deep features are associated with rope configurations so to establish a direct mapping toward energy configurations without any explicit modeling step. This approach, however, may hardly work effectively in presence of complex and or unknown backgrounds.
@cite_9 @cite_32 @cite_16 @cite_10 @cite_12
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In this paper, we address the problem of manipulating deformable objects such as ropes. Starting with an RGB-D view of a tangled rope, our goal is to infer its knot structure and then choose appropriate manipulation actions that result in the rope getting untangled. We design appropriate features and present an inference algorithm based on particle filters to infer the rope's structure. Our learning algorithm is based on max-margin learning. We then choose an appropriate manipulation action based on the current knot structure and other properties such as slack in the rope. We then repeatedly perform perception and manipulation until the rope is untangled. We evaluate our algorithm extensively on a dataset having five different types of ropes and 10 different types of knots. We then perform robotic experiments, in which our bimanual manipulator (PR2) untangles ropes successfully 76.9 of the time. We introduce an algorithm for tracking deformable objects from a sequence of point clouds. The proposed tracking algorithm is based on a probabilistic generative model that incorporates observations of the point cloud and the physical properties of the tracked object and its environment. We propose a modified expectation maximization algorithm to perform maximum a posteriori estimation to update the state estimate at each time step. Our modification makes it practical to perform the inference through calls to a physics simulation engine. This is significant because (i) it allows for the use of highly optimized physics simulation engines for the core computations of our tracking algorithm, and (ii) it makes it possible to naturally, and efficiently, account for physical constraints imposed by collisions, grasping actions, and material properties in the observation updates. Even in the presence of the relatively large occlusions that occur during manipulation tasks, our algorithm is able to robustly track a variety of types of deformable objects, including ones that are one-dimensional, such as ropes; two-dimensional, such as cloth; and three-dimensional, such as sponges. Our implementation can track these objects in real time. Manipulation of deformable objects, such as ropes and cloth, is an important but challenging problem in robotics. We present a learning-based system where a robot takes as input a sequence of images of a human manipulating a rope from an initial to goal configuration, and outputs a sequence of actions that can reproduce the human demonstration, using only monocular images as input. To perform this task, the robot learns a pixel-level inverse dynamics model of rope manipulation directly from images in a self-supervised manner, using about 60K interactions with the rope collected autonomously by the robot. The human demonstration provides a high-level plan of what to do and the low-level inverse model is used to execute the plan. We show that by combining the high and low-level plans, the robot can successfully manipulate a rope into a variety of target shapes using only a sequence of human-provided images for direction. We consider the problem of teaching robots by demonstration how to perform manipulation tasks, in which the geometry (including size, shape, and pose) of the relevant objects varies from trial to trial. We present a method, which we call trajectory transfer, for adapting a demonstrated trajectory from the geometry at training time to the geometry at test time. Trajectory transfer is based on non-rigid registration, which computes a smooth transformation from the training scene onto the testing scene. We then show how to perform a multi-step task by repeatedly looking up the nearest demonstration and then applying trajectory transfer. As our main experimental validation, we enable a PR2 robot to autonomously tie five different types of knots in rope. This article describes a project undertaken to explore pro gramming physical operations on complex flexible objects. Uncertainty about the exact state of the object makes it im possible to precisel...