scholarly journals Study on Stiffness-Oriented Cable Tension Distribution for a Symmetrical Cable-Driven Mechanism

Symmetry ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1158 ◽  
Author(s):  
Yang ◽  
Yang ◽  
Chen ◽  
Wang ◽  
Zhang ◽  
...  
Keyword(s):  
Optimization Problem ◽  
Variable Stiffness ◽  
Complex Method ◽  
Redundant Actuation ◽  
Spherical Joint ◽  
Cable Tension ◽  
Tension Distribution ◽  
Computation Efficiency ◽  
Stiffness Model ◽  
Position Regulation

In this paper, we focus on the issues pertaining to stiffness-oriented cable tension distributionfor a symmetrical 6-cable-driven spherical joint module (6-CSJM), which can be employed to constructmodular cable-driven manipulators. Due to the redundant actuation of the 6-CSJM, three cables areemployed for position regulation by adjusting the cable lengths, and the remaining three cables areutilized for stiffness regulation by adjusting the cable tensions, i.e., the position and stiffness can beregulated simultaneously. To increase the range of stiffness regulation, a variable stiffness device(VSD) is designed, which is serially connected to the driving cable. Since the stiffness model of the6-CSJM with VSDs is very complicated, it is difficult to directly solve the cable tensions from thedesired stiffness. The stiffness-oriented cable tension distribution issue is formulated as a nonlinearconstrained optimization problem, and the Complex method is employed to obtain optimal tensiondistributions. Furthermore, to significantly improve the computation efficiency, a decision variableelimination technique is proposed to deal with the equality constraints, which reduces decision variablesfrom 6 to 3. A comprehensive simulation study is conducted to verify the effectiveness of the proposedmethod, showing that the 6-CSJM can accurately achieve the desired stiffness through cable tensionoptimization.

scholarly journals Cable Tension Analysis Oriented the Enhanced Stiffness of a 3-DOF Joint Module of a Modular Cable-Driven Human-Like Robotic Arm

2020 ◽  
Vol 10 (24) ◽  
pp. 8871
Author(s):  
Kaisheng Yang ◽  
Guilin Yang ◽  
Chi Zhang ◽  
Chinyin Chen ◽  
Tianjiang Zheng ◽  
...  
Keyword(s):  
Objective Function ◽  
Optimization Model ◽  
Human Robot Interaction ◽  
Robotic Arm ◽  
Robot Interaction ◽  
Cable Tension ◽  
Tension Distribution ◽  
Stiffness Model ◽  
Redundantly Actuated ◽  
Objective Function Values

Inspired by the structure of human arms, a modular cable-driven human-like robotic arm (CHRA) is developed for safe human–robot interaction. Due to the unilateral driving properties of the cables, the CHRA is redundantly actuated and its stiffness can be adjusted by regulating the cable tensions. Since the trajectory of the 3-DOF joint module (3DJM) of the CHRA is a curve on Lie group SO(3), an enhanced stiffness model of the 3DJM is established by the covariant derivative of the load to the displacement on SO(3). In this paper, we focus on analyzing the how cable tension distribution problem oriented the enhanced stiffness of the 3DJM of the CHRA for stiffness adjustment. Due to the complexity of the enhanced stiffness model, it is difficult to solve the cable tensions from the desired stiffness analytically. The problem of stiffness-oriented cable tension distribution (SCTD) is formulated as a nonlinear optimization model. The optimization model is simplified using the symmetry of the enhanced stiffness model, the rank of the Jacobian matrix and the equilibrium equation of the 3DJM. Since the objective function is too complicated to compute the gradient, a method based on the genetic algorithm is proposed for solving this optimization problem, which only utilizes the objective function values. A comprehensive simulation is carried out to validate the effectiveness of the proposed method.

Adaptive Complex Method for Efficient Design Optimization

2007 ◽  
Author(s):  
Marcus Pettersson ◽  
Johan O¨lvander
Keyword(s):  
Design Optimization ◽  
Optimization Problem ◽  
Global Optimum ◽  
Direct Search ◽  
Complex Method ◽  
Efficient Design ◽  
Direct Search Methods ◽  
Simulation Based ◽  
Set Of Points ◽  
Quasi Newton

Box’s Complex method for direct search has shown promise when applied to simulation based optimization. In direct search methods, like Box’s Complex method, the search starts with a set of points, where each point is a solution to the optimization problem. In the Complex method the number of points must be at least one plus the number of variables. However, in order to avoid premature termination and increase the likelihood of finding the global optimum more points are often used at the expense of the required number of evaluations. The idea in this paper is to gradually remove points during the optimization in order to achieve an adaptive Complex method for more efficient design optimization. The proposed method shows encouraging results when compared to the Complex method with fix number of points and a quasi-Newton method.

An obstacle-avoiding and stiffness-tunable modular bionic soft robot

Robotica ◽  
2022 ◽  
pp. 1-15
Author(s):  
Zhaoyu Liu ◽  
Yuxuan Wang ◽  
Jiangbei Wang ◽  
Yanqiong Fei ◽  
Qitong Du
Keyword(s):  
Variable Stiffness ◽  
Air Pressure ◽  
Design Parameters ◽  
Soft Robot ◽  
Working Pressure ◽  
Obstacle Avoiding ◽  
Stiffness Model ◽  
Pass Through ◽  
Soft Actuators

Abstract The aim of this work is to design and model a novel modular bionic soft robot for crawling and crossing obstacles. The modular bionic soft robot is composed of several serial driving soft modules, each module is composed of two parallel soft actuators. By analyzing the influence of working pressure and manufacturing size on the stiffness of the modular bionic soft robot, the nonlinear variable stiffness model of the modular bionic soft robot is established. Based on this model, the spatial states and design parameters of the modular bionic soft robot are discussed when the modular bionic soft robot can pass through the obstacle. Experiments show that when the inflation air pressure of the modular bionic soft robot is 70 kPa, its speed can reach 7.89 mm/s and the height of obstacles passed by it can reach 42.8 mm. The feasibility of the proposed modular bionic soft robot and nonlinear variable stiffness model is verified by locomotion experiments.

scholarly journals Spring Effects on Workspace and Stiffness of a Symmetrical Cable-Driven Hybrid Joint

Symmetry ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 101 ◽  
Author(s):  
Shan Zhang ◽  
Zheng Sun ◽  
Jili Lu ◽  
Lei Li ◽  
Chunlei Yu ◽  
...  
Keyword(s):  
Variable Stiffness ◽  
Robotic Manipulator ◽  
Spring Model ◽  
Cable Tension ◽  
Stiffness Analysis ◽  
Hybrid Joint ◽  
Compression Spring ◽  
Spring Force ◽  
Basic Parameters ◽  
Stiffness Characteristics

This paper aims to investigate how to determine the basic parameters of the helical compression spring which supports a symmetrical cable-driven hybrid joint (CDHJ) towards the elbow joint of wheelchair-mounted robotic manipulator. The joint design of wheelchair-mounted robotic manipulator needs to consider lightweight but robust, workspace requirements, and variable stiffness elements, so we propose a CDHJ which becomes a variable stiffness joint due the spring under bending and compression provides nonlinear stiffness characteristics. Intuitively, different springs will make the workspace and stiffness of CDHJ different, so we focus on studying the spring effects on workspace and stiffness of CDHJ for its preliminary design. The key to workspace and stiffness analysis of CDHJ is the cable tension, the key to calculate the cable tension is the lateral bending and compression spring model. The spring model is based on Castigliano’s theorem to obtain the relationship between spring force and displacement. The simulation results verify the correctness of the proposed spring model, and show that the spring, with properly chosen parameters, can increase the workspace of CDHJ whose stiffness also can be adjusted to meet the specified design requirements. Then, the modelling method can be extended to other cable-driven mechanism with a flexible compression spring.

Tension distribution shaping via reconfigurable attachment in planar mobile cable robots

Robotica ◽  
2013 ◽  
Vol 32 (2) ◽  
pp. 245-256 ◽  
Author(s):  
Xiaobo Zhou ◽  
Seung-kook Jun ◽  
Venkat Krovi
Keyword(s):  
Mobile Robots ◽  
Configuration Space ◽  
Optimization Problem ◽  
Null Space ◽  
Experimental Studies ◽  
Analysis Framework ◽  
Tension Distribution ◽  
Fixed Base ◽  
Tension Direction ◽  
Cable Robots

SUMMARYTraditional cable robots derive their manipulation capabilities using spooling winches at fixed base locations. In our previous work, we examined enhancing manipulation capabilities of cable robots by the addition of base mobility to spooling winches (allowing a group of mobile robots to cooperatively manipulate a payload using cables). Base mobility facilitated the regulation of the tension-direction (via active coordination of mobile bases) and allowed for better conditioning of the wrench-feasible workspace. In this paper we explore putting idler pulleys on the payload attachment as alternate means to simplify the design and enable practical deployment. We examine analysis of the system using ellipse geometry and develop a virtual cable-subsystem formulation (which also facilitates subsumption into the previously developed mobile cable robot analysis framework). We also seek improvement of the tension distribution by utilizing configuration space redundancy to shape the tension null space. This tension distribution shaping is implemented in the form of a tension factor optimization problem over the workspace and explored via both simulation and experimental studies.

Nonlinear Stiffness Analysis of Spring-Loaded Inverted Slider Crank Mechanisms With a Unified Model

2020 ◽  
Vol 12 (3) ◽  
Author(s):  
Zhongyi Li ◽  
Shaoping Bai ◽  
Weihai Chen ◽  
Jianbin Zhang
Keyword(s):  
Variable Stiffness ◽  
Comprehensive Analysis ◽  
Unified Model ◽  
Nonlinear Stiffness ◽  
Stiffness Analysis ◽  
Constant Torque ◽  
Stiffness Model ◽  
Overall Performance ◽  
Crank Mechanism

Abstract A mechanism with lumped-compliance can be constructed by mounting springs at joints of an inverted slider crank mechanism. Different mounting schemes bring change in the stiffness performance. In this paper, a unified stiffness model is developed for a comprehensive analysis of the stiffness performance for mechanisms constructed with different spring mounting schemes. With the model, stiffness behaviors of spring-loaded inverted slider crank mechanisms are analyzed. Influences of each individual spring on the overall performance are characterized. The unified stiffness model allows designing mechanisms for a desired stiffness performance, such as constant-torque mechanism and variable stiffness mechanism, both being illustrated with a design example and experiments.

Determination of Variable Stiffness of a Human Elbow for Human-Robot Interaction

2014 ◽  
Author(s):  
Michael Boyarsky ◽  
Megan Heenan ◽  
Scott Beardsley ◽  
Philip Voglewede
Keyword(s):  
Experimental Data ◽  
Disturbance Rejection ◽  
Variable Stiffness ◽  
Important Variable ◽  
Human Motion ◽  
Human Robot Interaction ◽  
Robot Interaction ◽  
Constant Stiffness ◽  
Stiffness Model ◽  
Motor Model

This paper aims to emulate human motion with a robot for the purpose of improving human-robot interaction (HRI). In order to engineer a robot that demonstrates functionally similar motion to humans, aspects of human motion such as variable stiffness must be captured. This paper successfully determined the variable stiffness humans use in the context of a 1 DOF disturbance rejection task by optimizing a time-varying stiffness parameter to experimental data in the context of a neuro-motor Simulink model. The significant improved agreement between the model and the experimental data in the disturbance rejection task after the addition of variable stiffness demonstrates how important variable stiffness is to creating a model of human motion. To enable a robot to emulate this motion, a predictive stiffness model was developed that attempts to reproduce the stiffness that a human would use in a given situation. The predictive stiffness model successfully decreases the error between the neuro-motor model and the experimental data when compared to the neuro-motor model with a constant stiffness value.

scholarly journals Variable Stiffness Model Construction and Simulation Verification of Coupled Notch Continuum Manipulator

IEEE Access ◽  
2019 ◽  
Vol 7 ◽  
pp. 154761-154769
Author(s):  
Haodong Wang ◽  
Zhijiang Du ◽  
Wenlong Yang ◽  
Zhi Yuan Yan ◽  
Xiaolong Wang
Keyword(s):  
Variable Stiffness ◽  
Model Construction ◽  
Stiffness Model ◽  
Continuum Manipulator

Sparse Sum-of-Squares Optimization for Model Updating Through Minimization of Modal Dynamic Residuals

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Dan Li ◽  
Yang Wang
Keyword(s):  
Optimization Problem ◽  
Model Updating ◽  
Polynomial Optimization ◽  
Element Model ◽  
Optimization Method ◽  
Sum Of Squares ◽  
Global Optimality ◽  
Polynomial Optimization Problem ◽  
Computation Efficiency ◽  
Dynamic Residuals

This research investigates the application of sum-of-squares (SOS) optimization method on finite element model updating through minimization of modal dynamic residuals. The modal dynamic residual formulation usually leads to a nonconvex polynomial optimization problem, the global optimality of which cannot be guaranteed by most off-the-shelf optimization solvers. The SOS optimization method can recast a nonconvex polynomial optimization problem into a convex semidefinite programming (SDP) problem. However, the size of the SDP problem can grow very large, sometimes with hundreds of thousands of variables. To improve the computation efficiency, this study exploits the sparsity in SOS optimization to significantly reduce the size of the SDP problem. A numerical example is provided to validate the proposed method.

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