SENSOR PLACEMENT GUIDE FOR STRUCTURAL JOINT STIFFNESS MODEL IMPROVEMENT

1997 ◽  
Vol 11 (5) ◽  
pp. 651-672 ◽  
Author(s):  
H.B. Kim ◽  
Y.S. Park
Keyword(s):  
Sensor Placement ◽  
Joint Stiffness ◽  
Stiffness Model ◽  
Structural Joint ◽  
Model Improvement

An Improved Stiffness Model for Bolted Joints

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
Sayed A. Nassar ◽  
Antoine Abboud
Keyword(s):  
Joint Stiffness ◽  
Effective Area ◽  
Accurate Estimate ◽  
Diameter Ratio ◽  
Bolted Joints ◽  
Plate Material ◽  
Reliable Prediction ◽  
Novel Approach ◽  
Stiffness Model ◽  
Initial Assembly

An improved stiffness model is proposed for bolted joints made of similar and dissimilar plates. A novel approach is used to obtain an expression for the effective area used for determining the joint stiffness. More accurate estimate of the joint stiffness provides a more reliable prediction of the joint behavior both during its initial assembly, as well as under subsequently applied tensile loads in service. The effect of the grip length-to-diameter ratio, joint sizes, underhead contact radii ratio, hole clearance, and plate material/thickness ratio are investigated. Experimental data are used for determining the envelope angle α in the proposed analytical model. Finite element modeling is used for evaluating the accuracy of the proposed stiffness model.

EFFECTIVE DYNAMIC STIFFNESS MODEL AND ITS EFFECTS ON ROBOT SAFETY AND PERFORMANCE

2013 ◽  
Vol 37 (3) ◽  
pp. 395-403
Author(s):  
Dongjun Shin ◽  
Zhan Fan Quek
Keyword(s):  
Dynamic Stiffness ◽  
Joint Stiffness ◽  
Optimization Strategy ◽  
Design Guideline ◽  
Controller Gain ◽  
Stiffness Model ◽  
Effective Dynamic ◽  
Stiffness Characteristics ◽  
And Performance ◽  
The Impact

Due to the limited control bandwidth of pneumatic artificial muscles, joint stiffness characteristics and their effects on safety and performance of human-friendly robots should be considered in the frequency domain. This paper introduces the concept of effective dynamic stiffness and validates its model with the Stanford Safety Robot. Experimental results show that the dynamic stiffness demonstrates limited effects on the impact acceleration given the same impact velocity and controller gain, whereas it significantly affects control performance of position tracking due to pressure-induced non-linearities. A stiffness optimization strategy for safety and performance is discussed as a design guideline of human-friendly robots.

Joint Stiffness of 3D Space Frame Thin Walled Structural Joint Considering Local Buckling Effect

2014 ◽  
Vol 660 ◽  
pp. 773-777
Author(s):  
Mohd Shukri Yob ◽  
Shuhaimi Mansor ◽  
Razali Sulaiman
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Joint Stiffness ◽  
Element Model ◽  
Joint Effect ◽  
Experimental Result ◽  
Space Frame ◽  
3D Space ◽  
Structural Joint ◽  
Thin Walled

Thin walled structure is widely used in designing light weight vehicle. For automotive industry, weight is an important characteristic to increase performance of a vehicle. Vehicle structures are built from thin walled beams by joining them using various joining methods and techniques. For a structure, its stiffness greatly depends on joint stiffness. However, stiffness of thin walled beam is difficult to predict accurately due to buckling effect. Once the beams are joined to form a structure, it will expose to joint flexibility effect. A lot of researches had been done to predict the behaviors of thin walled joint analytically and numerically. However, these methods failed to come out with satisfactory result. In this research work, finite element model for 3D space frame thin walled structural joint is developed using circular beam element by validating with experimental result. Another finite element model using rigid element is used to represent 3D space frame behavior without joint effect. The difference between these 2 models is due to joint effect. By using same modelling technique, joint stiffness for different sizes can be established. Then, the relation between joint stiffness for 3D space frame and size of beam can be obtained.

Torsional Stiffness Model of an Industrial Robotic Joint Using Fractal Theory

2019 ◽  
Author(s):  
Jingjing Xu ◽  
Zhifeng Liu ◽  
Yongsheng Zhao ◽  
Qiang Cheng ◽  
Yanhu Pei ◽  
...  
Keyword(s):  
Prediction Accuracy ◽  
Fractal Theory ◽  
Great Influence ◽  
Joint Stiffness ◽  
Equilibrium Analysis ◽  
Torsional Stiffness ◽  
Tangential Stiffness ◽  
Proposed Model ◽  
Stiffness Model ◽  
Rv Reducer

Abstract It is known that mechanical connections have great influence on the dynamic characteristic of the assembly. In existing methods, the torsional stiffness of the robotic joint is calculated only considering the stiffness of components of the system, which largely reduces the prediction accuracy of the joint stiffness. In the paper, to predict the joint stiffness more accurately, a model is proposed considering influences of the stiffness of all connections existed in a joint system. The normal and tangential stiffness of the contact surface of each connection are calculated by combining the equilibrium analysis of the force and the fractal theory. Then the total stiffness of one robotic joint can be modelled by putting the torsional stiffness of all connections and that of the RV reducer and gear pair in parallel. To verify the proposed model, its simulation result is compared to the stiffness based on the previous technique without considering the influence of connections. The comparison result shows that the proposed model can improve the stiffness-prediction accuracy. This study can be extended to the stiffness modeling of other joint systems and provides a theoretical basis for the dynamic analysis of the robotic system.

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.

Structural Joint Stiffness of Automotive Body

1988 ◽  
Author(s):  
Toshiaki Sakurai ◽  
Yoshinobu Kamada
Keyword(s):  
Joint Stiffness ◽  
Automotive Body ◽  
Structural Joint

A Novel Wire-Driven Variable-Stiffness Joint Based on a Permanent Magnetic Mechanism

2019 ◽  
Vol 11 (5) ◽  
Author(s):  
Ming Zhang ◽  
Lijin Fang ◽  
Feng Sun ◽  
Koichi Oka
Keyword(s):  
Traditional Approach ◽  
Joint Stiffness ◽  
Variable Stiffness ◽  
The Novel ◽  
Adjustment Time ◽  
Stiffness Model ◽  
Wide Range ◽  
Driven System ◽  
The Relationship ◽  
Magnetic Mechanism

The variable-stiffness joint (VSJ) plays an important role in creating compliant and powerful motions. This paper presents a novel wire-driven VSJ based on a permanent magnetic mechanism (PMM). The proposed joint regulates the joint stiffness with lower energy consumption through a wide range via the permanent magnetic mechanism. This effect possibly depends on the novel nonlinear combination of a permanent magnet-spring and wire-driven system that achieves the same stiffness with lower wire tension. A trapezoidal layout of the joint is proposed. Because of the relationship among the stiffness, the position of the joint and the stiffness of the PMM, the stiffness model is also been established. Based on this model, the decoupling controller is built to independently control the position and stiffness of the joint. Experiments show that the VSJPMM achieves position and stiffness independently and also reduces energy and power required to regulate the stiffness compared with the traditional approach. In addition, the proposed mechanism displays a powerful motion and short stiffness adjustment time.

A Study on the Improvement of the Structural Joint Stiffness for Aluminum BIW

1997 ◽  
Author(s):  
Young Woong Lee ◽  
Yong Woo Kwon ◽  
Soon Yong Kwon ◽  
Won Suk Cho
Keyword(s):  
Joint Stiffness ◽  
Structural Joint
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