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

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.

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 A novel stiffness model for a wall-climbing hexapod robot based on nonlinear variable stiffness

2018 ◽  
Vol 10 (1) ◽  
pp. 168781401775248 ◽  
Author(s):  
Bin He ◽  
Shoulin Xu ◽  
Zhipeng Wang
Keyword(s):  
Structural Parameters ◽  
Variable Stiffness ◽  
Load Force ◽  
Nonlinear Stiffness ◽  
Hexapod Robot ◽  
Maximum Stiffness ◽  
Stiffness Model ◽  
Linear And Nonlinear ◽  
Serial Mechanism ◽  
Selection Of

In this article, the most contribution is to propose a novel general stiffness model to analyze the stiffness of a wall-climbing hexapod robot. First, we propose a new general stiffness model of serial mechanism, which includes the linear and nonlinear stiffness models. By comparison, the nonlinear stiffness model is a variable stiffness model which introduces the external load force as a variable, obtaining that the nonlinear stiffness model can greatly improve the accuracy of stiffness model than linear stiffness model. Then, the stiffness model of one leg of the robot and the overall stiffness model of the robot are derived based on the general stiffness model. Next, to improve the stiffness of the robot, a new minimum and maximum stiffness are introduced, which provide with effective reference for the selection and optimization of the structural parameters of the robot. Finally, we develop a new wall-climbing hexapod robot based on selection and optimization of the structural parameters, then the experiments are used to show that the selection of structure parameters of the robot effectively improve the stiffness of the robot.

Comparing model-based control methods for simultaneous stiffness and position control of inflatable soft robots

2020 ◽  
pp. 027836492091196
Author(s):  
Charles M. Best ◽  
Levi Rupert ◽  
Marc D. Killpack
Keyword(s):  
Dynamic Models ◽  
Position Control ◽  
Sliding Mode ◽  
Joint Stiffness ◽  
Variable Stiffness ◽  
Soft Robots ◽  
End Effector ◽  
Simultaneous Control ◽  
Stiffness Model ◽  
Stiffness Control

Inflatable robots are naturally lightweight and compliant, which may make them well suited for operating in unstructured environments or in close proximity to people. The inflatable joints used in this article consist of a strong fabric exterior that constrains two opposing compliant air bladders that generate torque (unlike McKibben actuators where pressure changes cause translation). This antagonistic structure allows the simultaneous control of position and stiffness. However, dynamic models of soft robots that allow variable stiffness control have not been well developed. In this work, a model that includes stiffness as a state variable is developed and validated. Using the stiffness model, a sliding mode controller and model predictive controller are developed to control stiffness and position simultaneously. For sliding mode control (SMC), the joint stiffness was controlled to within 0.07 Nm/rad of a 45 Nm/rad command. For model predictive control (MPC) the joint stiffness was controlled to within 0.045 Nm/rad of the same stiffness command. Both SMC and MPC were able to control to within 0.5° of a desired position at steady state. Stiffness control was extended to a multiple-degree-of-freedom soft robot using MPC. Controlling stiffness of a 4-DOF arm reduced the end-effector deflection by approximately 50% (from 17.9 to 12.2cm) with a 4 lb (1.8 kg) step input applied at the end effector when higher joint stiffness (40 Nm/rad) was used compared with low stiffness (30 Nm/rad). This work shows that the derived stiffness model can enable effective position and stiffness control.

Static Force Model-Based Stiffness Model for Pneumatic Muscle Actuators

2015 ◽  
Vol 18 ◽  
pp. 207-214 ◽  
Author(s):  
József Sárosi ◽  
Ján Piteľ ◽  
Jaroslav Šeminský
Keyword(s):  
Variable Stiffness ◽  
Relative Displacement ◽  
Time Variable ◽  
Force Model ◽  
Power Weight ◽  
Static Force ◽  
Pneumatic Muscle ◽  
Stiffness Model ◽  
Muscle Actuators ◽  
And Control

Pneumatic muscle actuators (PMAs) differ from general pneumatic systems as they have no inner moved parts and there is no sliding on the surfaces. During action they reach high velocities, while the power/weight and power/volume rations reach high levels. The main drawbacks of PMAs are limited contraction (relative displacement), nonlinear and time variable behaviour, existence of hysteresis and step-jump pressure (to start radial diaphragm deformation) and also antagonistic connection of PMAs to generate two-direction motion. These make PMAs difficult to modelling and control. In this paper a new stiffness model and the variable-stiffness spring-like characteristics are described and tested using two Fluidic Muscles made by Festo Company. The muscles have the same diameter, but different length.

Analysis of a novel manipulator with low melting point alloy initiated stiffness variation and shape detection for minimally invasive surgery

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Xiaoyong Wei ◽  
Feng Ju ◽  
Bai Chen ◽  
Hao Guo ◽  
Dan Wang ◽  
...  
Keyword(s):  
Minimally Invasive Surgery ◽  
Melting Point ◽  
Detection Method ◽  
Variable Stiffness ◽  
Shape Detection ◽  
Content Type ◽  
Continuum Robot ◽  
Stiffness Variation ◽  
Continuum Manipulator ◽  
The Continuum

Purpose There is an increasing popularity for the continuum robot in minimally invasive surgery owing to its compliance and dexterity. However, the dexterity takes the challenges in loading and precise control because of the absence of the shape tracking for the continuum robot. The purpose of this paper is to propose a new type of continuum manipulator with variable stiffness that can track the bending shape timely. Design/methodology/approach The low-melting-point alloy (LMPA) is used to implement the stiffness variation and shape detection for the continuum manipulator. A conceptual design for a single module is presented, and the principle of stiffness control based on the established static model is formulated. Afterward, a shape detection method is introduced in which the shape of the continuum manipulator can be detected by measuring the resistance of every LMPA. Finally, the effect of the proposed variable stiffness method is verified by simulation; the variable stiffness and shape detection methods are evaluated by experiments. Findings The results from the simulations and experiments indicate that the designed continuum manipulator has the ability of stiffness variation over 42.3% and the shape detection method has high precision. Originality/value Compared with conventional structures, the novel manipulator has a simpler structure and integrates the stiffness variation and shape detection capabilities with the LMPA. The proposed method is promising, and it can be conveniently extended to other continuum manipulators.

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.

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