Cooperative parameter estimation of a nonuniform payload by multiple quadrotors

Thispaper addresses the problem of carrying an unknown nonuniform payload by multiple quadrotor agents. The load is modeled as a rigid body with unknown weight and position of Center of Gravity (CG) for the agents, and is included in their dynamic equations of motion. The agents and the load are assumed to be connected to each other by taut ropes. The Udwadia–Kalaba equation is used to calculate the constraint forces on the ropes acting on each quadrotor. Inner-loop and outer-loop controllers for quadrotors position and attitude control are presented. For the outer loop, an estimation algorithm based on the invariance and immersion adaptive control is utilized to estimate the unknown physical parameters of the payload including mass and CG position without using multi-axes force/torque sensors. The inner-loop controller employs an adaptive controller. Simulation results, for two and four agents carrying a nonuniform rod and cubic payload, show the effectiveness of the proposed algorithm. A case study is also performed to investigate the effect of quadrotors positioning on flight endurance of the cooperative aerial team carrying a nonuniform payload.

Revisiting screw theory-based approaches in the constraint wrench analysis of robotic systems

This paper aims at shedding lights on two approaches that were recently proposed for the constraint wrench analysis of robotic manipulators. Both approaches benefit from the Newton–Euler equations, screw notations, and constraint transformation matrices (CTM) to cope with the inverse dynamic problem of multibody systems. In the first approach, which is called the joint-based method, the constraint transformation matrices are derived directly from the kinematic constraints which are imposed on the rigid links by kinematic pairs. In the second approach, which is referred to as the link-based method; however, the constraint matrices are obtained based on the wrench transfer formula of each rigid link. In this study, by resorting to the definition of reciprocal screws, the former methodology is further enhanced to a new version as well. Moreover, based on the proposed modified joint-based CTM, constraint forces and moments distribution indices are introduced. The three constraint wrench analysis methodologies, two joint-based and one link-based, result in different CTMs and set of equations as well, which will be discussed in detail. In the end, on two case studies, a spherical four-bar linkage and a Delta parallel robot, the pros and cons of all three constraint wrench analysis methodologies are discussed, and the proposed indices will be examined. The numerical results reveal that, although all three methods identically compute the magnitude of the applied and constraint force and moment vectors, the joint-based approaches do not report the constraint components with respect to a specific coordinate frame. Moreover, it is shown that the proposed indices can approximately predict the constraint forces and moments distribution at joints, which can be used as force transmission indicators in multibody systems.

On MBS Constraints and Projections

Constraints in multibody systems are usually treated by a Lagrange I - method resulting in equations of motion together with the constraint forces. Going from non-minimal coordinates to minimal ones opens the possibility to project the original equations directly to the minimal ones, thus eliminating the constraint forces. The necessary procedure is described, a general example of combined machine-process dynamics discussed and a specific example given. For a n-link robot tracking a path the equations of motion are projected onto this path resulting in quadratic form linear differential equations. They define the space of allowed motion, which is generated by a polygon-system.

An approach to tackle negative effects in project management

We introduce a model to support scenario analysis while managing costs of high-tech project. If the project results from joint efforts of firms with one per single stage the model suggests budget redistribution in case of funding shortage or exchange rate volatility. Given negative outer effects for the project the model requires the project to be completed and this constraint forces firms to diminish their profit or to make a loan if needed. The model proposed suggests human-machine (expert) interaction to build scenario for analysis but is simpler compared to method of successive concessions from computational point of view.

Analysis of a novel six-degree of freedom foldable parallel mechanism with optimized under-balance springs

The capacities of parallel mechanisms are limited by their height for the narrow space applications, such as the shipboard stability platforms, household simulators, aerospace mechanisms, etc. This paper proposes a novel foldable six-DOF parallel manipulator which has three main limbs with each actuated by two actuators. With the ability to fold in the vertical direction, this mechanism can be deployed from a height of about 0.278 m to 2.218 m, and the required driving stroke is only 0.67 m by the analysis results of the workspaces. However, this stroke enlargement leads to large driving forces. In order to improve the capacity for the heavy loading of this foldable mechanism, each leg is assisted by a balance spring. Static and dynamics models are built for the calculation of the driving forces and constraint forces. Two methods to calculate the optimal balance force for objective driving force are also proposed and based on the designed trace in the workspace, the springs’ linear stiffness is optimized. The simulation results demonstrate that the actuators’ driving forces are much reduced, and the homogeneity between the fully folded and deployed configuration is much improved by adding balance springs.

Experimental Characterization of High-Amplitude Fluid–Structure Interaction of a Flexible Hydrofoil at High Reynolds Number

A fluid–structure interaction (FSI) experiment was performed to study low-frequency (∼10 Hz), high-amplitude (±3.5% of the span) fin motion. This was achieved by placing an Inconel swept-fin at −9.6 deg angle-of-attack within the wake of a roughened cylinder. Speeds between 2.5 and 3.6 m/s produced cylinder diameter-based Reynolds numbers between 190,000 and 280,000, respectively. Detailed descriptions of the geometry, material/structural behavior, fluid properties, and initial conditions are provided to facilitate computational model development. Given the initial conditions, the resulting forced fin behavior was characterized with measurements of the mean and fluctuating velocity upstream of the fin (i.e., within the cylinder wake), fin tip/surface motion, and fin constraint forces/moments. This work provides a detailed experimental dataset of conditions mimicking a crashback event that is also a challenging FSI benchmark problem involving turbulent, vortex-induced structure motion. It has been used as a validation condition for FSI simulations, and it can be used to validate other FSI models as well as identifying strengths and weaknesses of various modeling approaches.

Towards Scale-Free Rain Streak Removal via Self-Supervised Fractal Band Learning

Data-driven rain streak removal methods, which most of rely on synthesized paired data, usually come across the generalization problem when being applied in real cases. In this paper, we propose a novel deep-learning based rain streak removal method injected with self-supervision to improve the ability to remove rain streaks in various scales. To realize this goal, we made efforts in two aspects. First, considering that rain streak removal is highly correlated with texture characteristics, we create a fractal band learning (FBL) network based on frequency band recovery. It integrates commonly seen band feature operations with neural modules and effectively improves the capacity to capture discriminative features for deraining. Second, to further improve the generalization ability of FBL for rain streaks in various scales, we add cross-scale self-supervision to regularize the network training. The constraint forces the extracted features of inputs in different scales to be equivalent after rescaling. Therefore, FBL can offer similar responses based on solely image content without the interleave of scale and is capable to remove rain streaks in various scales. Extensive experiments in quantitative and qualitative evaluations demonstrate the superiority of our FBL for rain streak removal, especially for the real cases where very large rain streaks exist, and prove the effectiveness of its each component. Our code will be public available at: https://github.com/flyywh/AAAI-2020-FBL-SS.