Abstract In recent years, time series classification with shapelets, due to the high accuracy and good interpretability, has attracted considerable interests. These approaches extract or learn shapelets from the training time series. Although they can achieve higher accuracy than other approaches, there still confront some challenges. First, they may suffer from low accuracy in the case of small training dataset. Second, they must manually set some parameters, like the number of shapelets and the length of each shapelet beforehand, and some hyper-parameters, like learning rate and regulation weight, which are difficult to set without prior knowledge. Third, extracting or learning shapelets incurs a huge computation cost, due to the huge search space. In this paper, we extend our previous shapelet learning approach ELIS to ELIS++. To improve the accuracy on the small training dataset, we propose a data augmentation approach. To learn the higher quality shapelets, based on the PAA shapelet candidates search technique proposed in ELIS, ELIS++ first propose a novel entropy-based approach shapelet candidate selection mechanism to discover shapelet candidates, and then applies the logistic regression model to adjust shapelets.To avoid setting other parameters manually, we propose a Bayesian Optimization based approach. Moreover, two techniques are proposed to improve the efficiency, coarse-grained shapelet adjustment and SIMD-based parallel computation. We conduct extensive experiments on 35 UCR datasets, and results verify the effectiveness and efficiency of ELIS++.

Coating rollers are widely popular in structural painting, in comparison with brushes and sprayers, due to thicker paint layer, better color consistency, and effortless customizability of holder frame and naps. In this paper, we introduce a cost-effective method to employ a general purpose robot (Sawyer, Rethink Robotics) for autonomous coating. To sense the position and the shape of the target object to be coated, the robot is combined with an RGB-Depth camera. The combined system autonomously recognizes the number of faces of the object as well as their position and surface normal. Unlike related work based on two-dimensional RGB-based image processing, all the analyses and algorithms here employ three-dimensional point cloud data (PCD). The object model learned from the PCD is then autonomously analyzed to achieve optimal motion planning to avoid collision between the robot arm and the object. To achieve human-level performance in terms of the quality of coating using the bare minimum ingredients, a combination of our own passive and builtin active impedance control is implemented. The former is realized by installing an ultrasonic sensor at the end-effector of robot working with a customized compliant mass-spring-damper roller to keep a precise distance between the end-effector and surface to be coated, maintaining a fixed force. Altogether, the control approach mimics human painting as evidenced by experimental measurements on the thickness of the coating. Coating on two different polyhedral objects is also demonstrated to test the overall method.

Recently, time series classification with shapelets, due to their high discriminative ability and good interpretability, has attracted considerable interests within the research community. Previously, shapelet generating approaches extracted shapelets from training time series or learned shapelets with many parameters. Although they can achieve higher accuracy than other approaches, they still confront some challenges. First, searching or learning shapelets in the raw time series space incurs a huge computation cost. For example, it may cost several hours to deal with only hundreds of time series. Second, they must determine how many shapelets are needed beforehand, which is difficult without prior knowledge. To overcome these challenges, in this paper, we propose a novel algorithm to learn shapelets. We first discover shapelet candidates from the Piecewise Aggregate Approximation (PAA) word space, which is much more efficient than searching in the raw time series space. Moreover, the concept of coverage is proposed to measure the quality of candidates, based on which we design a method to compute the optimal number of shapelets. After that, we apply the logistic regression classifier to adjust the shapelets. Extensive experimentation on 15 datasets demonstrates that our algorithm is more accurate against 6 baselines and outperforms 2 orders of magnitude in terms of efficiency. Moreover, our algorithm has fewer redundant shape-like shapelets and is more convenient to interpret classification decisions.