Changhyun Jun

Minimal Grasper: A Practical Robotic Grasper With Robust Performance for Pick-and-Place Tasks

In this paper, a flexible enveloping grasper is proposed for pick-and-place tasks with low manipulation and task planning complexity for practical applications. The proposed grasper has two main characteristics: self-adaptivity and flexibility. Self-adaptivity means that the proposed grasper can grip an object in a self-adaptive way such that various process complexities (e.g., sensing, force control, and sensor–motor coordination) are significantly reduced. By flexibility, we mean that, by using a flexible material, a stable grip can be implemented to cause increased friction between the grasper and the target object as a result of increased contact area. These two properties help the proposed grasper to minimize internal forces in a passive manner and to achieve successful force distribution with self-adaptivity when performing enveloping grasping. Three sets of experiments were performed with an average success rate of 93.2% in pick-and-place tasks.

Robust-PCA-based hierarchical plane extraction for application to geometric 3D indoor mapping

Purpose – The authors aim to propose a novel plane extraction algorithm for geometric 3D indoor mapping with range scan data. Design/methodology/approach – The proposed method utilizes a divide-and-conquer step to efficiently handle huge amounts of point clouds not in a whole group, but in forms of separate sub-groups with similar plane parameters. This method adopts robust principal component analysis to enhance estimation accuracy. Findings – Experimental results verify that the method not only shows enhanced performance in the plane extraction, but also broadens the domain of interest of the plane registration to an information-poor environment (such as simple indoor corridors), while the previous method only adequately works in an information-rich environment (such as a space with many features). Originality/value – The proposed algorithm has three advantages over the current state-of-the-art method in that it is fast, utilizes more inlier sensor data that does not become contaminated by severe sensor...

Convex Cut: A realtime pseudo-structure extraction algorithm for 3D point cloud data

In this paper, a realtime pseudo-structure extraction algorithm for 3D indoor point cloud data (PCD) is proposed. This algorithm is called Convex Cut (CC) because of its two main steps: cutting the PCD with arbitrary planes, and extracting convex parts. CC can be used as a preprocessing module for other existing algorithms to extract static parts in dynamic environments or to represent a principal 3D model of a given PCD. Its calculation time is 24 milliseconds for 50k PCD on a consumer PC, and it yields a precision value of 0.90 and a recall value of 0.99 on average in highly dynamic and cluttered environments. Some possible applications are explained such as simultaneous localization and mapping in dynamic environments, efficient dense map representation, robust 3D scan matching with plane features, and natural motion planning.

Method for Estimating Concentration Time and Storage Coefficient of the Clark Model Using Rainfall-Runoff Measurements

AbstractThis study proposed a method for estimating the concentration time and storage coefficient of the Clark model using the rainfall-runoff measurements. The proposed method is based on the analytically derived concentration time and storage coefficient of the Nash model along with the relationship between these two parameters. More fundamentally, the proposed method recursively searches the convergent concentration time and storage coefficient, or the number of linear reservoirs and storage coefficient of the linear reservoir of the Nash model. The proposed method was applied to the Bangrim stream gauge station of the Pyungchang River Basin, Korea. The results are summarized as follows. First, this study theoretically derived the basin storage coefficient and concentration time by using the Nash model. Especially, the relationship between the storage coefficient and concentration time could be expressed as a function of the number of linear reservoirs only. This result has a special meaning to unders...

Performance assessment model for robot-based automated construction systems

An adjusted assessment model based on benefit-cost analysis (BCA) is proposed for evaluating the economic efficiency of automated construction technologies. In contrast to conventional BCA, the model does not compare monetary values, but the differences in benefits and costs between traditional and automated construction methods. To verify the usefulness of the model, it was applied to a real-scale building construction project that used a fully automated building construction system, and the face validity of the model was confirmed. The results indicate that the model can support decision makers in identifying valuable benefit factors and in assessing the cost effectiveness of the system.

Application of the Beta Distribution for the Temporal Quantification of Storm Events

This study suggested the parameter estimation method for given rainfall events to be properly expressed by the beta distribution. For this purpose, this study compared the characteristics of probability density function with the parameter proposed considering the cases with and without addition to the rainfall peak, and the cases of using the real hyetograph and the rearranged hyetograph about the rainfall peak. As an example, this study analyzed the independent rainfall events at Seoul in 2010 and the annual maximum independent rainfall events from 1961 to 2010. The results derived are as follows. First, this study confirmed the necessity of additional consideration on rainfall peak to mimic the real hyetograph of rainfall events by the beta distribution. Second, this study confirmed the case of using rearranged hyetograph about the rainfall peak derived a better beta distribution to well mimic the characteristics of real rainfall than the case using the real hyetograph.

Evaluation of the Concept of Critical Rainfall Duration by Bivariate Frequency Analysis of Annual Maximum Independent Rainfall Event Series in Seoul, Korea

AbstractThis study investigated the possible problems of using the concept of critical rainfall duration (CRD) for estimating the design flood. The investigation focused on the evaluation of the difference between the annual maximum independent rainfall event series (IRES) and the annual maximum short-duration rainfall series in Seoul, Korea. Annual maximum IRES was determined by applying Freund’s bivariate exponential distribution, which were also used for frequency analysis by applying the Gumbel’s bivariate logistic model. Both the annual maximum IRES and the frequency analysis results were then compared with those of the conventional annual maximum fixed-duration rainfall series (FDRS). The results are summarized as follows. First, the mean rainfall intensity of the annual maximum IRES was found to be little changed regardless of their durations. Thus, most of the annual maximum short-duration rainfall series would be selected in the annual maximum IRES. Second, results of the bivariate frequency anal...

Effect of Rainfall Temporal Distribution on the Conversion Factor to Convert the Fixed-Interval into True-Interval Rainfall

AbstractIn this study, the Weiss approach to derive the CF (the conversion factor to convert the fixed-interval annual maximum rainfall into the true-interval one) was examined and revised to consider the rainfall temporal distribution. As examples, several rainfall temporal distribution models currently being used in the rainfall-runoff analysis, along with several simple distributions such as triangular or pentagonal, were considered to derive the CF. The resulting CFs were then compared with the CFs estimated by analyzing the observed rainfall data, both in Korea and in several other countries, such as the United States, the United Kingdom, Australia, and New Zealand. The findings from this study can be summarized as follows. First, the effect of the temporal distribution of rainfall is very significant on the estimation of the CF. The CF for the impulse rainfall was the smallest at 1.0, and that for the uniformly-distributed rainfall was the highest at 1.333. Second, the CFs derived for the temporal d...

The analysis of effect of observation models and data associations on the consistency of EKF SLAM

Analysis on causes of inconsistency of Extended Kalman Filter (EKF) Simultaneous Localization And Mapping (SLAM) is mentioned in this paper. The effect of noise models and observation models on the inconsistent behavior of EKF SLAM was examined. In addition, the effect of registration of the false landmarks on inconsistent behavior of the EKF SLAM is mentioned in this paper. This paper identifies several causes of inconsistency of EKF SLAM by observability analysis.

Towards a Realistic Indoor World Reconstruction: Preliminary Results for an Object-Oriented 3D RGB-D Mapping

AbstractA real world reconstruction that generates cyberspace not from a computer graphics tool, but from the real world, has been one of the main issues in two different communities of robotics and computer vision under different names of Simultaneous Localization And Mapping (SLAM) and Structure from Motion (SfM). However, there have been few trials that actively integrate SLAM and SfM for possible synergy. This paper shows the real world reconstruction can be enabled through this integration. As a result, the preliminary map has been generated of which five subgoals are: Realistic view (RGB), accurate geometry (depth), applicability to multi-floor indoor building, initial classification of a possible set of objects, and full automation. To this end, an engineering framework of “Acquire-Build-Comprehend (ABC)” is proposed, through which a sensor system acquires an RGB-Depth point cloud from the real world, builds a three-dimensional map, and comprehends this map to yield the possible set of objects. Its...