Design and Analysis of a Cross Trapezoid Spatial Compliant Device With Variable Stiffness

2018 ◽  
Author(s):  
Zhuang Zhang ◽  
Genliang Chen ◽  
Lingyu Kong ◽  
Hao Wang
Keyword(s):  
Large Deflection ◽  
Variable Stiffness ◽  
Rigid Bodies ◽  
Main Concept ◽  
Compliance Matrix ◽  
Leaf Springs ◽  
Principal Axes ◽  
Great Force ◽  
Structural Compliance ◽  
Novel Design

This paper presents a novel design of spatial compliant device with variable stiffness. The main concept of the device is to have two elastic trapezoid four-bar linkages arranging in orthogonal. The tool side of the device can switch between totally stiff and compliant by changing the arrangement of leaf springs and passive joints. Based on the principal axes decomposition of structural compliance matrix, the leaf springs are approximated by hyper-redundant linkages with rigid bodies connected by passive elastic joints. Hence, the nonlinear large deflection problems of the leaf springs can be solved efficiently in a mechanism way. In order to demonstrate the compliance of the proposed device, a numerical simulation is provided using the proposed approach. The result shows that the leaf springs in the compliant device are easy to be deformed and can not generate great force. Due to these characteristics, as an end-of-arm tool, the device has the ability to prevent hard collisions under the compliant status and finish precise positioning under the stiff status.

scholarly journals A Stiffness Variable Passive Compliance Device with Reconfigurable Elastic Inner Skeleton and Origami Shell

2020 ◽  
Vol 33 (1) ◽  
Author(s):  
Zhuang Zhang ◽  
Genliang Chen ◽  
Weicheng Fan ◽  
Wei Yan ◽  
Lingyu Kong ◽  
...  
Keyword(s):  
Variable Stiffness ◽  
Rehabilitation Robotics ◽  
Human Robot Interaction ◽  
Main Concept ◽  
Robot Interaction ◽  
Switching Speed ◽  
Leaf Springs ◽  
Stiffness Variation ◽  
Low Stiffness ◽  
Large Deflection Problem

Abstract Devices with variable stiffness are drawing more and more attention with the growing interests of human-robot interaction, wearable robotics, rehabilitation robotics, etc. In this paper, the authors report on the design, analysis and experiments of a stiffness variable passive compliant device whose structure is a combination of a reconfigurable elastic inner skeleton and an origami shell. The main concept of the reconfigurable skeleton is to have two elastic trapezoid four-bar linkages arranged in orthogonal. The stiffness variation generates from the passive deflection of the elastic limbs and is realized by actively switching the arrangement of the leaf springs and the passive joints in a fast, simple and straightforward manner. The kinetostatics and the compliance of the device are analyzed based on an efficient approach to the large deflection problem of the elastic links. A prototype is fabricated to conduct experiments for the assessment of the proposed concept. The results show that the prototype possesses relatively low stiffness under the compliant status and high stiffness under the stiff status with a status switching speed around 80 ms.

Study on the stiffness property of a variable stiffness joint using a leaf spring

2018 ◽  
Vol 233 (3) ◽  
pp. 1021-1031 ◽  
Author(s):  
Lijin Fang ◽  
Yan Wang
Keyword(s):  
Geometric Nonlinearity ◽  
Large Deflection ◽  
Elliptic Integral ◽  
Joint Stiffness ◽  
Variable Stiffness ◽  
Leaf Spring ◽  
Stiffness Property ◽  
Force Structure ◽  
Leaf Springs ◽  
Application Requirements

Variable stiffness joints designed to ensure physical safety or adjust stiffness actively have attracted much attention in recent years. Springs are used in the internal kinematic structures of variable stiffness joints to achieve the compliance. In this paper, the stiffness property of a variable stiffness joint using a leaf spring is studied on the basis of geometric nonlinearity associated with large deflections of leaf springs. A new end structure is used in the variable stiffness joint to exert the external force on the leaf spring. Based on the elliptic integral solution to large deflection problems of cantilever beams, the effects of different end exertion force structures and geometric nonlinearity of leaf springs on the stiffness property are analyzed when the deflected angle of the joint is larger. It is found that the end exertion force structure and large deflection of leaf springs have a great impact on the changes of the joint stiffness during the joint deflection. A new variable stiffness joint using two leaf springs is proposed to meet different application requirements by changing the end exertion force structure. The experiment of the proposed joint is carried out to verify the validity of the stiffness analysis results.

scholarly journals An enhanced set of displacement parameter restraints in CRYSTALS

2018 ◽  
Vol 51 (4) ◽  
pp. 1059-1068 ◽  
Author(s):  
Pascal Parois ◽  
James Arnold ◽  
Richard Cooper
Keyword(s):  
Structural Model ◽  
Rigid Bodies ◽  
Model Parameters ◽  
Coordinate Systems ◽  
Principal Axes ◽  
Anisotropic Displacement Parameters ◽  
Set Up ◽  
Meaningful Relationships ◽  
Parameter Values ◽  
Total Model

Crystallographic restraints are widely used during refinement of small-molecule and macromolecular crystal structures. They can be especially useful for introducing additional observations and information into structure refinements against low-quality or low-resolution data (e.g. data obtained at high pressure) or to retain physically meaningful parameter values in disordered or unstable refinements. However, despite the fact that the anisotropic displacement parameters (ADPs) often constitute more than half of the total model parameters determined in a structure analysis, there are relatively few useful restraints for them, examples being Hirshfeld rigid-bond restraints, direct equivalence of parameters and SHELXL RIGU-type restraints. Conversely, geometric parameters can be subject to a multitude of restraints (e.g. absolute or relative distance, angle, planarity, chiral volume, and geometric similarity). This article presents a series of new ADP restraints implemented in CRYSTALS [Parois, Cooper & Thompson (2015), Chem. Cent. J. 9, 30] to give more control over ADPs by restraining, in a variety of ways, the directions and magnitudes of the principal axes of the ellipsoids in locally defined coordinate systems. The use of these new ADPs results in more realistic models, as well as a better user experience, through restraints that are more efficient and faster to set up. The use of these restraints is recommended to preserve physically meaningful relationships between displacement parameters in a structural model for rigid bodies, rotationally disordered groups and low-completeness data.

scholarly journals Novel Design of a Soft Lightweight Pneumatic Continuum Robot Arm with Decoupled Variable Stiffness and Positioning

Soft Robotics ◽  
2018 ◽  
Vol 5 (1) ◽  
pp. 54-70 ◽  
Author(s):  
Maria Elena Giannaccini ◽  
Chaoqun Xiang ◽  
Adham Atyabi ◽  
Theo Theodoridis ◽  
Samia Nefti-Meziani ◽  
...  
Keyword(s):  
Variable Stiffness ◽  
Robot Arm ◽  
Continuum Robot ◽  
Novel Design

scholarly journals The Stiffness Calculation and Optimization for the Variable Stiffness Load Torque Simulation System

2017 ◽  
Vol 2017 ◽  
pp. 1-8
Author(s):  
Zhe Ji ◽  
Xiaoxian Yao ◽  
Zuobao Liang
Keyword(s):  
Wind Tunnel ◽  
Calculation Method ◽  
Tracking Error ◽  
Wind Tunnel Test ◽  
Variable Stiffness ◽  
Simulation System ◽  
Load Torque ◽  
Loading System ◽  
Optimal Set ◽  
Novel Design

This paper presents a novel design for a variable stiffness load torque simulation system. The system is applied to the load torque on a rudder in a real-time hardware-in-the-loop system (HILS). Compared with the traditional loading method, in which unavoidable additional torque exists, the variable stiffness loading system employs a “first decomposed and then coupled” approach to output the load torque and to significantly reduce the additional torque. Based on experimental data obtained from a wind tunnel test, a calculation method is proposed to determine the loading parameters of the variable stiffness loading system. Since the load stiffness is related to a variety of factors, the stiffness values obtained from wind tunnel test data, such as the fixed Mach number and the rudder deflection angle, are not definite values. By analyzing the influencing factors of the loading parameters, an optimal set of load stiffness is obtained using an optimization algorithm, and exact tracking of the load torque is achieved. Using the calculation method to obtain a loading torque for the rudder as an example, the torque tracking error is less than 0.05 Nm. The simulation results indicate that the proposed calculation method for variable stiffness loading is effective.

Dynamic Analysis of Variable Stiffness Bracing System in Structure

2014 ◽  
Vol 704 ◽  
pp. 442-446 ◽  
Author(s):  
Amir Fateh ◽  
Farzad Hejazi ◽  
Mohd Saleh Jaafar ◽  
Izian Abd. Karim ◽  
Azlan bin Adnan
Keyword(s):  
Numerical Analysis ◽  
Dynamic Analysis ◽  
Variable Stiffness ◽  
Nonlinear Stiffness ◽  
Braced Frames ◽  
Earthquake Excitation ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Leaf Springs ◽  
Bracing System

In this paper, the application of a variable stiffness bracing (VSB) system in structures subjected to earthquake excitation is presented. The considered variable stiffness system is includes of four curve leaf springs. The nonlinear geometry of leaf springs which are acting as bending component lead to nonlinear stiffness performance. The variable stiffness bracing system does not act much for small to intermediate vibration amplitudes but it’s operated to control unpredictably large story displacement. It means this retrofit’s technique avoid an increase force in structural component due to ordinary brace action. The single degree of freedom system (SDOF) is considered and dynamic analysis of aforementioned system, with Bare and normal braced frames are conducted and the results are compared. The efficiency of the proposed system is discussed and proved in light of numerical analysis.

Sign in / Sign up

Export Citation Format

Share Document