Analysis of various manipulator configurations based on multi-objective black-box optimization

Branching structure in arborescent animals: Models of relative growth

I‐shaped links in eccentrically braced frames (EBFs) are susceptible to lateral or lateral torsional buckling when subjected to cyclic link rotations. Lateral bracing should be provided at the ends of the I‐shaped links in order to prevent these failures. Requirements for such braces are available in widely used design specifications such as the AISC Seismic Provisions for Structural Steel Buildings (AISC341‐16) and EC8. These requirements limit the use of I‐shaped links in bridge piers and elevator shafts. A combined experimental and numerical study was undertaken to investigate the behavior of laterally unsupported I‐shaped links under cyclic loading. The experimental study consisted of testing of six nearly full‐scale EBFs where the link length, link length ratio, and presence of lateral supports were considered as the prime variables. The test results demonstrated that short links with link length ratios less than 1.22 can experience inelastic link rotations greater than the codified limit of 0.08 rad even without lateral bracing. A numerical parametric study was conducted to develop more generalized design recommendations for laterally unsupported I‐shaped shear links. Stability of one‐story one‐bay EBFs was studied using geometrically and materially nonlinear finite element analysis including imperfections. The numerical results showed that I‐shaped links without lateral bracing can provide a stable response when the link length ratio is less than 1.15. In addition to this limit, the ratio of the elastic critical buckling capacity to the plastic shear capacity should be greater than 3.5 and 2.5 for links with and without axial force, respectively.

This paper presents an optimal performance design for the kinematics and dynamics indices of serial manipulators, with an integrated approach that combines differential evolution with local search method. The proposed method can generate the optimization solutions of both joint configuration and link length, which divided into two sub-procedure. While the Global Conditioning Index (GCI), Structural Length Index (SLI) and Modified Dynamic Conditioning Index (MDCI), corresponding to kinematic and dynamic feature separately, are utilized as objective function of the method to calculate the design parameters. Finally a case study is included to illustrate the optimal design method with fewer iterations on 6-DOF manipulator.

In designing a crank rocker four bar mechanism with a uniform input rotation typical input parameters are the required total output oscillation angle and the timing ratio of the advance to return cycle time. In determining an optimum design the parameters of interest are usually the extreme transmission angles and the ratio of the longest to shortest link length occuring in the mechanism. This work first develops an analytic construction of the link lengths and worst transmission angles based on the necessary geometry for a given output angle of oscillation and required timing ratio. The resulting equations are programmed and graphs developed which give the variation of extreme transmission angle and maximum link length ratio as a function of the specified output angle of oscillation, timing ratio, and geometric construction variables. Using these graphs a designer will be able to easily select optimum designs based on worst transmission angles and link length ratios. Examples are included.

Mobile manipulators are highly versatile and are used across various fields due to their flexibility, reach, and adaptability. Hence it finds applications that involve complex environments or require high precision. The mobile manipulation tasks require the manipulators to retain good manipulation capability, which calls for reasonable motion planning. Manipulability, a crucial metric indicating the robot’s ability to perform effective and efficient manipulation tasks, serves as the central criterion for the design of redundant mobile manipulators (MM). In addition to this, for applications where the mobile base and manipulator are moving simultaneously, a design configuration with good manipulability measure is preferred. This study fills a significant gap in the literature by offering an analysis of the design considerations for a redundant MM for improved manipulability measure. In this paper, the end effector of a 6 DoF MM is made to move through a predefined trajectory, and the manipulability measure and manipulability ellipsoid are computed at various points in the workspace. The analysis is done based on various link length ratios, mounting positions of the arm, and mobile base speeds. The manipulability ellipsoids at various locations in the task space were analyzed which is indicative of maximum and minimum velocities achievable by the end effector. Based on the analysis, the best configuration is identified and a kinematic controller is designed for this configuration which traces the reference trajectory with high manipulability. An exhaustive simulation study shows the benefits of the suggested design principles and control techniques, reaffirming the significance of optimized link lengths, mounting positions, and mobile base speeds in enhancing manipulability. Although this study is carried out in a 6 DoF MM, the novelty of this research lies in its emphasis on enabling design of redundant MM for better manipulability which lays a strong foundation for future applications.

Experimental study on the cyclic behaviour of shear links made of BLY160 steel

A method estimating the queue length in city street networks was proposed using the data of roll time occupancy. The key idea of this paper is that when the queue length in front of the queue detector becomes longer, the speeds of the following vehicles to pass through the detector will become smaller, resulting in higher occupancy with constant traffic intensity. Considering the relationship between queue lengths and roll time occupancy affected by many factors, such as link length, lane width, lane number, and bus ratio, twelve different conditions were designed, and the traffic data under different conditions was obtained using VISSIM simulation. Based on the analysis of simulation data, an S‐type logistic model was decided to develop for the relationship between queue lengths and roll time occupancy, and the fitting equations were obtained under the twelve simulation situations. The average model for the relationship between queue lengths and roll time occupancy was presented by successive multiple linear regression with the fitting equation parameters and simulation parameters, and the estimation model for queue length was presented through analyzing the equation of the average relation model.

Active-Passive Hybrid Cable-Driven Robots (APHCDRs) are a novel type of cable-driven robots with the design of active-passive-linkage segments. Compared with tradition ones, they are more flexible and have higher maneuverability in confined environment, thus, are widely researched in recent years. However, the workspace and stiffness performance of APHCDRs which are two important properties were rarely studied. In this paper, the generalized kinematic model of APHCDRs is established first. Then, the resolved workspace and stiffness model are proposed. Workspace radius and stiffness are analyzed by considering link length and linkage ratio respectively. Finally, particle swarm optimization (PSO) is used to search for the optimal configurations of APHCDRs which reach maximum workspace area, working radius and maximum stiffness respectively. The analysis results on the workspace and stiffness are useful for optimizing of APHCDRs’ structural design.

Numerical parameters study on seismic performance of short replaceable link with perforated web: Bearing capacity and overstrength

Dynamic modeling and analysis of flexible manipulators play an essential role in optimizing mechanical design parameters and control law of real robot systems. In this paper, a nonlinear dynamic model of a manipulator is formulated based on the Finite Element Method. To analyze the dynamic behavior effectively, a numerical simulation scheme is proposed by taking full advantages of MATLAB and SIMULINK toolboxes. In this manner, the effect of varying payload and link length ratio of the manipulator to its elastic displacement is dynamically taken into account. The simulation results show that the payload and length link ratio have significant influences on the elastic displacements of the system. In particular, a proper spectrum of the link length ratio, in which the flexural displacement of the end point of the manipulator is smallest, is demonstrated. To this end, the proposed methodology could be used further to select optimal geometric parameters for the links of new robot designs.

The existence of groups of highly intercorrelated variables among the large number of parameters widely used for quantifying drainage basin morphology suggests the possibility of reducing them to fewer dimensions. Through principal axis factor analysis of 37 morphometric properties of 52 third-order basins in the Udi-Awgu cuesta of south-eastern Nigeria, six factors identified as measures of intensity of dissection, stream network size, relief, shape, link length ratio and bifurcation ratio, are found to account for 92 per cent of the variance in the data. The factor-defining variables are total drainage density, total stream length, relief ratio, lemniscate ratio, link length ratio and bifurcation ratio respectively.These findings are essentially similar to those obtained for the third-order basins of southern Uganda, western U.S.A., southern Indiana, Barbados and Tobago. These studies suggest that, irrespective of differences in climate, lithology and vegetation cover, the morphology of drainage basins may be adequately quantified by measurement and analysis of these six variables which thus constitute the parameters of the reduced rank model of the morphology of drainage basins. Explanations are offered for the orthogonality of these dimensions, and their geomorphic and hydrologic importance are briefly reviewed.The identification of these underlying dimensions will not only simplify future morphometric work but also provide criteria for an objective multi-dimensional morphological classification of drainage basins.

Overstrength factor of short low-yield-point steel shear links

To improve reachability of a snake-like robot depending on the problem, the links of the robot need to be resizable. In such a case folding links of the robot help to better plan obstacle avoidance. Optimum folding of the robot is the aim of our paper. We introduce a practical idea to construct reconfigurable and resizable snake robots which can be folded and an approximation algorithm to find near-optimum folding for the robot. Since an open chain is an abstract model of a snake-like robot, folding algorithms for the proposed robot are given in terms of an open chain. Ruler folding is a well-known NP-Complete problem. It considers folding of an n-link open chain linkage to the minimum length. The best previously known approximation algorithm for this problem has been developed by Hopcroft et al. They achieved the upper bound of 2m 1 for the length of the folded chain in all cases, where m 1 is the length of the longest link of the given chain. Already there are no any algorithms for open chain folding which guarante that the folded length of the open chain is less than 2m 1. In this paper, we introduce an approximation algorithm which runs in O (n log n) using O (n) space. We introduce a function for the upper bound of the folded chain which depends to the lengths of all links in the given chain. Our experimental results show that for more than 95% of the problem instances we can achieve the same results in O (n) time. Using our folding algorithm, we can design the length of each link in an open chain to get x · m 1 folded length where 1 < x < 2 is given and m 1 is the length of the longest link of the chain. We introduce how to design a snake-like robot for which it can be folded in the given interval.

SUMMARYIn this paper, a walking pattern optimization procedure is implemented to yield the optimal heel-strike and toe-off motions for different goal functions. To this end, first, a full dynamic model of a humanoid robot equipped with active toe joints is developed. This model consists of two parts: multi-body dynamics of the robot which is obtained by Lagrange and Kane methods and power transmission dynamic model which is developed using system identification approach. Then, a gait planning routine is presented and consistent parameters are specified. Several simulations and experimental tests are carried out on SURENA III humanoid robot which is designed and fabricated at the Center of Advanced Systems and Technologies located in the University of Tehran. Afterward, a genetic algorithm optimization is adopted to compute the optimal walking patterns for five different goal functions including energy consumption, stability margin, joint velocity, joint torque and required friction coefficient. Also, several parametric analyses are performed to characterize the effects of heel-strike and toe-off angle and toe link mass and length on these five goal functions. Finally, it is concluded that walking pattern without heel-strike and toe-off motions requires less friction coefficient than the pattern with heel-strike and toe-off motions. Also, heavier toe link lowers tip-over instability and slippage occurrence possibility, but requires more energy consumption and joint torque.

Manipulator dynamics on the velocity-dependent nonlinear joint torques due to the Coriolis and centrifugal forcesis investigated. The nonlinear mapping from the velocity space to the joint torque space is characterized by geomet-rically describing a joint torque set as an image of a velocity set with a constant norm. The geometry represents the characteristics of the nonlinear joint torques independent of velocity directions. The characteristics are investigated in two cases: 2DOF and more than 2DOF. 2DOF manipulators have the characteristic that the image of the isotropic velocity set has the shape of an ellipse in the joint torque space. In the case of more than 2DOF, the image is included in an ellipsoid. These characteristics are verified with numerical manipulator models.