Are object detection assessment criteria ready for maritime computer vision?

Maritime vessels equipped with visible and infrared cameras can complement other conventional sensors for object detection. However, application of computer vision techniques in maritime domain received attention only recently. The maritime environment offers its own unique requirements and challenges. Assessment of the quality of detections is a fundamental need in computer vision. However, the conventional assessment metrics suitable for usual object detection are deficient in the maritime setting. Thus, a large body of related work in computer vision appears inapplicable to the maritime setting at the first sight. We discuss the problem of defining assessment metrics suitable for maritime computer vision. We consider new bottom edge proximity metrics as assessment metrics for maritime computer vision. These metrics indicate that existing computer vision approaches are indeed promising for maritime computer vision and can play a foundational role in the emerging field of maritime computer vision

Theoretical Model Construction of Deformation-Force for Soft Grippers Part I: Co-rotational Modeling and Force Control for Design Optimization

Compliant grippers, owing to adaptivity and safety, have attracted considerable attention for unstructured grasping in real applications, such as industrial or logistic scenarios. However, accurately modeling the bidirectional relationship between shape deformation and contact force for such grippers, the Fin-Ray grippers as an example, remains stagnant to date. To address this research gap, this article devises, presents, and experimentally validates a universal bidirectional force-displacement mathematical model for compliant grippers based on the co-rotational concept, which endows such grippers with an intrinsic force sensing capability and offers a better insight into the design optimization. In Part I of the article, we introduce the fundamental theory of the co-rotational approach, where arbitrary large deformation of beam elements can be modeled. Its intrinsic principle allows taking materials with varying stiffness, various connection types, and key design parameters into consideration with few assumptions. Further, the force-displacement relationship is numerically derived, providing accurate displacement estimations of the gripper under external forces with minor computational loads. The performance of the proposed method is experimentally verified through comparison with Finite Element Analysis (FEA) in simulation, obtaining a fair degree of accuracy (6%), and design optimization of Fin-Ray grippers is systematically investigated. Part II of this article demonstrating the force sensing capabilities and the effects of representative co-rotational modeling parameters on model accuracy is released in Arxiv

Theoretical Model Construction of Deformation-Force for Soft Grippers Part II: Displacement Control Based Intrinsic Force Sensing

Force-aware grasping is an essential capability for most robots in practical applications. Especially for compliant grippers, such as Fin-Ray grippers, it still remains challenging to build a bidirectional mathematical model that mutually maps the shape deformation and contact force. Part I of this article has constructed the force-displacement relationship for design optimization through the co-rotational theory. In Part II, we further devise a displacement-force mathematical model, enabling the compliant gripper to precisely estimate contact force from deformations sensor-free. The presented displacement-force model elaborately investigates contact forces and provides force feedback for a force control system of a gripper, where deformation appears as displacements in contact points. Afterward, simulation experiments are conducted to evaluate the performance of the proposed model through comparisons with the finite-element analysis (FEA) in Ansys. Simulation results reveal that the proposed model accurately estimates contact force, with an average error of around 3% and 4% for single or multiple node cases, respectively, regardless of various design parameters (Part I of this article is released in Arxiv1

Robotic perception and grasp in unstructured environments

Perception and grasp are crucial capabilities for robots to perform desired services in unstructured environments. This thesis presents important insights and concepts related robotic perception and grasp in unstructured scenarios. In this thesis, three specific problems related to this topic have been studied, viz., tracking of cylindrical objects, grasping of static and dynamic cylindrical objects based on the proposed ellipse detection, pose estimation of multiple objects and occluded objects in cluttered environments and the optimal design of under-actuated robotic gripper for realizing stable grasps. For the problem of the ellipse detection, two critically important problems have been addressed. The proposed detector provides either faster or more accurate ellipse detection results than the current state-of-the-art methods, irrespective of challenging scenarios such as occluded or overlapping ellipses. For the problem of pose estimation of objects, we propose a highly efficient learning approach integrated by the contextual information to estimate pose of the textured or texture-less objects for grasping purposes in a cluttered environment where the objects might be partially occluded. It has been indicated that the proposed method is superior to several state-of-the-art works. The proposed perception algorithms impose the constraints in the scenarios where the severe occlusions result in the lack of visibility. For the problem of the optimal design of under-actuated robotic gripper, the mathematical model between the active and contact forces has been expressed and the geometric model of transmission characteristics determined by the tendon routes for reducing the resistance has been explored for determining the dimension parameters of the gripper. Practical experiments are performed by the designed gripper to validate the proposed designed approach. The utility of these algorithms has been shown using several series of robotic grasp experiments with successful rates of over 80% in various difficult scenarios, including tracking cylindrical objects, grasping static and dynamic cylindrical objects, grasping textured and texture-less by estimating poses of multiple objects and occluded objects.Doctor of Philosoph

An Improved Sorting Algorithm for Periodic PRI Signals Based on Congruence Transform

Recently, a signal sorting algorithm based on the congruence transform has been proposed, which is effective in dealing with the staggered Pulse Repetition Interval (PRI) signals. It can effectively sort the staggered PRI signals and obtain the sub-PRI sequence directly without sub-PRI ranking, and it is less affected by interfered pulses and pulse loss. Nevertheless, we find that the algorithm causes pseudo-peaks in the remainder histogram when sorting signals such as sliding PRI, sinusoidal PRI, etc. (collectively referred to as periodic PRI signal in this paper) and pseudo-peaks will cause errors in signal sorting. To solve the issue of pseudo-peaks when sorting periodic PRI signals, an improved sorting algorithm based on congruence transform is proposed. According to the analysis of the congruence characteristics of the periodic PRI signal, a novel method is proposed to identify pseudo-peaks based on the histogram peak amplitude and symmetric difference set. The signal sorting algorithm based on congruence transform is improved to achieve a good sorting effect on periodic PRI signals. Simulation experiments demonstrate that the novel algorithm can effectively sort periodic PRI signals and improve Precall, Pd, and Pf by 6.9%, 5.1%, and 3.2%, respectively, compared to the typical similar algorithms

Are object detection assessment criteria ready for maritime computer vision?

Maritime vessels equipped with visible and infrared cameras can complement other conventional sensors for object detection. However, application of computer vision techniques in maritime domain received attention only recently. The maritime environment offers its own unique requirements and challenges. Assessment of the quality of detections is a fundamental need in computer vision. However, the conventional assessment metrics suitable for usual object detection are deficient in the maritime setting. Thus, a large body of related work in computer vision appears inapplicable to the maritime setting at the first sight. We discuss the problem of defining assessment metrics suitable for maritime computer vision. We consider new bottom edge proximity metrics as assessment metrics for maritime computer vision. These metrics indicate that existing computer vision approaches are indeed promising for maritime computer vision and can play a foundational role in the emerging field of maritime computer vision

Robust ellipse detection via duality principle with a false determination control

In this paper, we propose a novel ellipse detection approach that eliminates false detection-based parameter space decomposition, principal of symmetric tangents, and a novel geometric constraint utilizing properties of tangents of ellipses. The principle of symmetric tangents provides better computational efficiency through confirmation of the ellipse center in the decomposed parameter space. The geometric constraint is used for alleviating the false detection probability. The experimental results confirm that the approach detects ellipse with an excellent accuracy at a high speed

Grasp analysis and optimal design of robotic fingertip for two tendon-driven fingers

In this work, we focus on building the model of optimization design of the fingertip to evaluate the best fingertip shape and determining the size range of objects grasped by fingertips steadily. We describe the effect of fingertip dimension on the stability of fingertip grasp, while other existing works mostly paid close attention to stability analysis for existing fingertip designs or prototypes. First, we elaborate on a versatile force-form analysis approach to quantifying the grasp stability by constructing a series of mathematical models under rolling constraints. Second, the best performing fingertip shape is indicated for realizing stable fingertip grasps. Next, the relations between the dimension of the fingertip, the size of objects, and the posture of the fingertip relative to a stable contact point are expressed by mathematical formulations in geometric constraints. Finally, an under-actuated gripper with two 3-link fingers is designed and performs practical experiments to demonstrate for verifying the presented analysis and models