Static Analysis of Spherical nR Kinematic Chains With Joint Friction

1992 ◽  
Author(s):  
Pierre Larochelle ◽  
J. M. McCarthy
Keyword(s):  
Static Analysis ◽  
Bending Moment ◽  
Iterative Solution ◽  
Friction Model ◽  
Friction Torque ◽  
Force Balance ◽  
External Loading ◽  
Linear System Of Equations ◽  
Kinematic Chains ◽  
Joint Friction

Abstract This paper presents the static analysis of general spherical nR simple open or closed kinematic chains with joint friction. The internal loading on each link is found to consist of a bending moment and a torsional moment. The goal of this analysis is to determine these moments which are then used in designing the link. The moment and force balance equations for each link yields a linear system of equations which define the internal moments of the mechanism and the output torque on the driven crank for a given input torque. A Coulomb model of joint friction is used to determine the friction torque along the axis of a joint. The joint friction model requires an iterative solution. The purpose of this algorithm is to provide a means of computing the complete internal and external loading on the members of spherical chains while including frictional effects in order to facilitate the design of a functional spherical mechanisms.

scholarly journals A Novel Virtual Sensor for Estimating Robot Joint Total Friction Based on Total Momentum

2019 ◽  
Vol 9 (16) ◽  
pp. 3344 ◽  
Author(s):  
Xu ◽  
Fan ◽  
Fang ◽  
Wang ◽  
Zhu ◽  
...  
Keyword(s):  
Performance Improvement ◽  
Trajectory Tracking ◽  
Friction Model ◽  
Friction Torque ◽  
Joint Torque ◽  
Tracking Performance ◽  
Step Response ◽  
Virtual Sensor ◽  
Joint Friction ◽  
Velocity Tracking

Robot joint friction is an important and complicated issue in improving robot control performance. In this paper, a virtual sensor based on the total generalized momentum concept is proposed to estimate the total friction torque, including both the motor-side and link-side friction, of robot joints without joint torque sensors. The proposed algorithm only requires a robot joint dynamics model and not a complex friction model dependent on factors such as time and velocity. By compensating for the estimated friction torque with a robot joint controller, the trajectory tracking performance of the controller, especially the velocity tracking performance, can be improved. To verify the effectiveness of the developed algorithm, 2-DOF planar manipulator simulations and single-joint system experiments are conducted. The simulation and experimental results show that the designed virtual sensor can effectively estimate the total joint friction disturbance and that the controller trajectory tracking performance is improved after observed friction compensation. However, the position tracking performance improvement of the controller is less than that for the velocity tracking performance improvement during the experiments. In addition, the velocity step response ability and velocity tracking performance of the controller are improved more at low velocities than that at high velocities in the experiments. The proposed algorithm has engineering and theoretical significance for estimating robot joint friction and improving the performance of robot joint controllers.

On the Application of the Lu-Gre Model to Simulate Joint Friction in Multi-Body Systems

2011 ◽  
Author(s):  
Kedar Gajanan Kale ◽  
Rajiv Rampalli
Keyword(s):  
Friction Model ◽  
Lugre Model ◽  
Friction Forces ◽  
Joint Friction ◽  
Modeling Techniques ◽  
Static Regime ◽  
Increasing Demand ◽  
Automotive Suspension ◽  
Multi Body

Advances in the application of multi-body simulation technology to real world problems have led to an ever increasing demand for higher fidelity modeling techniques. Of these, accurate modeling of friction is of strategic interest in applications such as control system design, automotive suspension analysis, robotics etc. Joints (sometimes referred to as constraints) play an important role in defining the dynamics of a multi-body system. Hence, it is imperative to accurately account for friction forces arising at these joints due to the underlying interface dynamics. In this paper, we discuss the application of LuGre, a dynamic friction model to simulate joint friction. We choose the LuGre model due to its ability to capture important effects such as the Stribeck effect and the Dahl effect. The native 1-d LuGre model is extended to formulate friction computations for non-trivial joint geometries and dynamics in 2 and 3 dimensions. It is also extended to work in the quasi-static regime. Specific applications to revolute, cylindrical and spherical joints in multi-body systems are discussed. Finally, an engineering case study on the effects of joint friction in automotive suspension analysis is presented.

Direct Sensitivity Analysis of Spatial Multibody Systems With Joint Friction Using Index-1 Formulation

2021 ◽  
Author(s):  
Adwait Verulkar ◽  
Corina Sandu ◽  
Daniel Dopico ◽  
Adrian Sandu
Keyword(s):  
Sensitivity Analysis ◽  
Dynamic Systems ◽  
Multibody Systems ◽  
Friction Model ◽  
Design Parameters ◽  
Adjoint Sensitivity ◽  
Joint Friction ◽  
Multibody Dynamic ◽  
Model Dynamics ◽  
Direct Sensitivity

Abstract Sensitivity analysis is one of the most prominent gradient based optimization techniques for mechanical systems. Model sensitivities are the derivatives of the generalized coordinates defining the motion of the system in time with respect to the system design parameters. These sensitivities can be calculated using finite differences, but the accuracy and computational inefficiency of this method limits its use. Hence, the methodologies of direct and adjoint sensitivity analysis have gained prominence. Recent research has presented computationally efficient methodologies for both direct and adjoint sensitivity analysis of complex multibody dynamic systems. The contribution of this article is in the development of the mathematical framework for conducting the direct sensitivity analysis of multibody dynamic systems with joint friction using the index-1 formulation. For modeling friction in multibody systems, the Brown and McPhee friction model has been used. This model incorporates the effects of both static and dynamic friction on the model dynamics. A case study has been conducted on a spatial slider-crank mechanism to illustrate the application of this methodology to real-world systems. Using computer models, with and without joint friction, effect of friction on the dynamics and model sensitivities has been demonstrated. The sensitivities of slider velocity have been computed with respect to the design parameters of crank length, rod length, and the parameters defining the friction model. Due to the highly non-linear nature of friction, the model dynamics are more sensitive during the transition phases, where the friction coefficient changes from static to dynamic and vice versa.

scholarly journals TRANSMITTED POWER AND ENERGY FLOW BEHAVIOR OF DEGRADING WET FRICTION CLUTCHES

2012 ◽  
pp. 286-291
Author(s):  
SHOAIB IQBAL ◽  
THIERRY JANSSENS ◽  
WIM DESMET ◽  
FARID AL- BENDER
Keyword(s):  
Energy Flow ◽  
Relative Velocity ◽  
Normal Load ◽  
Flow Behavior ◽  
Friction Material ◽  
Friction Model ◽  
Friction Torque ◽  
Phase Changes ◽  
Transmitted Power ◽  
Wet Friction

Experiments and simulations performed in the framework of accelerated-life tests of wet friction clutches reveal that with the progression of degradation of clutches, the transmitted power decreases together with a change in the energy flow behavior, mainly in the pre-lockup phase. In addition, the engagement duration increases and the relative velocity fluctuation in post-lockup phase changes. These degradation effects are due to the reduction in friction torque and the change in the relative velocity profile caused by the changing friction characteristics of the clutch friction material with degradation. Simulations are performed in a bond graph methodology incorporating an adapted form of the Generalized Maxwell Slip (GMS) friction model, which calculates the friction torque taking into account the dynamic variation in relative velocity and the normal load.

scholarly journals The Effect of Stick Stiffness of Friction Models on the Bending Behavior in Non-Bonded Flexible Risers

2017 ◽  
Author(s):  
Tianjiao Dai ◽  
Naiquan Ye ◽  
Svein Sævik
Keyword(s):  
Shear Deformation ◽  
Numerical Study ◽  
Bending Moment ◽  
Friction Stress ◽  
Friction Model ◽  
Stiffness Reduction ◽  
Friction Models ◽  
Flexible Risers ◽  
Bending Behavior ◽  
Full Scale Tests

This paper investigates the effect of stick stiffness on the bending behavior in non-bonded flexible risers. The stick stiffness was normally implemented in the friction model for calculating the friction stress between layers in such structures. As the stick stiffness may be too small to achieve the plane-surfaces-remain-plane assumption under low contact pressure in some friction models [1], a new friction model was proposed for maintaining the constant stick stiffness in the present work. Less stick stiffness than that obtained by the plane-surfaces-remain-plane assumption was observed in test data. It was assumed that the stick stiffness reduction is caused by shear deformation of plastic layers. A numerical study on stick stiffness by including the shear deformation effect was carried out and verified against full scale tests with respect to the bending moment-curvature relationship.

The Study of FEM for Internal Force Analysis of the Sluice Structure

2011 ◽  
Vol 71-78 ◽  
pp. 3275-3279
Author(s):  
Xiao Na Li ◽  
Tong Chun Li ◽  
Yuan Ding
Keyword(s):  
Cross Section ◽  
Bending Moment ◽  
Internal Force ◽  
Force Balance ◽  
Shearing Force ◽  
Force Analysis ◽  
Reconstruction Project ◽  
Unit Stress ◽  
Reinforcement Design

This paper takes a sluice reconstruction project as an example. The constraint internal force, the related axis force, bending moment, and shearing force at the corresponding section are solved according to the unit stress and internal force balance. Furthermore, technology of mesh auto-generation in cross-section is utilized to plot the internal force graph of the structure directly, which will provide reference for reinforcement design and make it more convenient.

scholarly journals A new joint friction model for parameter identification and sensor-less hand guiding in industrial robots

2020 ◽  
Vol 47 (6) ◽  
pp. 847-857
Author(s):  
Guanghui Liu ◽  
Qiang Li ◽  
Lijin Fang ◽  
Bing Han ◽  
Hualiang Zhang
Keyword(s):  
Industrial Robot ◽  
Angular Displacement ◽  
Weighted Least Squares ◽  
Friction Model ◽  
Industrial Robots ◽  
Model Parameters ◽  
Dynamic Parameters ◽  
Content Type ◽  
Joint Friction ◽  
Six Dof

Purpose The purpose of this paper is to propose a new joint friction model, which can accurately model the real friction, especially in cases with sudden changes in the motion direction. The identification and sensor-less control algorithm are investigated to verify the validity of this model. Design/methodology/approach The proposed friction model is nonlinear and it considers the angular displacement and angular velocity of the joint as a secondary compensation for identification. In the present study, the authors design a pipeline – including a manually designed excitation trajectory, a weighted least squares algorithm for identifying the dynamic parameters and a hand guiding controller for the arm’s direct teaching. Findings Compared with the conventional joint friction model, the proposed method can effectively predict friction factors during the dynamic motion of the arm. Then friction parameters are quantitatively obtained and compared with the proposed friction model and the conventional friction model indirectly. It is found that the average root mean square error of predicted six joints in the proposed method decreases by more than 54%. The arm’s force control with the full torque using the estimated dynamic parameters is qualitatively studied. It is concluded that a light-weight industrial robot can be dragged smoothly by the hand guiding. Practical implications In the present study, a systematic pipeline is proposed for identifying and controlling an industrial arm. The whole procedure has been verified in a commercial six DOF industrial arm. Based on the conducted experiment, it is found that the proposed approach is more accurate in comparison with conventional methods. A hand-guiding demo also illustrates that the proposed approach can provide the industrial arm with the full torque compensation. This essential functionality is widely required in many industrial arms such as kinaesthetic teaching. Originality/value First, a new friction model is proposed. Based on this model, identifying the dynamic parameter is carried out to obtain a set of model parameters of an industrial arm. Finally, a smooth hand guiding control is demonstrated based on the proposed dynamic model.

scholarly journals Study on the Low Velocity Stability of a Prostate Seed Implantation Robot’s Rotatory Joint

Electronics ◽  
2020 ◽  
Vol 9 (2) ◽  
pp. 284 ◽  
Author(s):  
Bing Li ◽  
Yongde Zhang ◽  
Lipeng Yuan ◽  
Xiaolin Xi
Keyword(s):  
Prostate Cancer ◽  
Parameter Identification ◽  
Control Method ◽  
Friction Model ◽  
Friction Torque ◽  
Low Velocity ◽  
Seed Implantation ◽  
Compensation Control ◽  
Lugre Friction Model ◽  
Lugre Friction

Prostate cancer has one of the highest incidences of male malignant tumors worldwide. Its treatment involves the robotic implantation of radioactive seeds in the perineum, a safe and effective procedure for early, low-risk prostate cancer. In order to ensure precise positioning, the seed implantation needle is set at low terminal velocity. In this paper, the motion output position instability caused by the friction torque of the robot’s motor and rotating joint during low velocity motion was analyzed and studied. This paper also presents a compensation control method based on the LuGre friction model, which offers piecewise parameter identification with GA-PSO. First, based on an analysis of its structure and working principle, the friction torque model of the robotic system and the torque model of the driving motor are established, and the influence of friction torque on motion stability analyzed. Then, based on experimental data of the relationship between velocity and friction torque for no-friction compensation, the velocity point of the minimum torque of the rotating joint and the critical Stribeck velocity point were used for segmental parameter identification; cubic spline interpolation was used for segmental fitting. Furthermore, on the basis of the LuGre model identification method, parameter identification of the genetic algorithm-particle swarm optimization, and compensation control of the LuGre friction model, a control method is analysed and set forth. Malab2017a/Simulink simulation software was used to simulate and analyze the control method, and verify its feasibility. Finally, the cantilever prostate seed implantation robot system was tested to verify the effectiveness of the segmented identification method and the compensation control strategy. The results reveal that motion output position stability at low velocity meets the requirements of the cantilever prostate seed implantation robot, thus providing a vital reference for further research.

Modelling and Identification of a Six Axes Industrial Robot

2005 ◽  
Author(s):  
Rob Waiboer ◽  
Ronald Aarts ◽  
Ben Jonker
Keyword(s):  
Least Squares ◽  
Industrial Robot ◽  
Equations Of Motion ◽  
Experimental Parameter ◽  
Friction Model ◽  
Unknown Parameters ◽  
Joint Friction ◽  
Inertia Parameters ◽  
Value Decomposition ◽  
Least Squares Techniques

This paper deals with the modelling and identification of a six axes industrial Sta¨ubli RX90 robot. A non-linear finite element method is used to generate the dynamic equations of motion in a form suitable for both simulation and identification. The latter requires that the equations of motion are linear in the inertia parameters. Joint friction is described by a friction model that describes the friction behaviour in the full velocity range necessary for identification. Experimental parameter identification by means of linear least squares techniques showed to be very suited for identification of the unknown parameters, provided that the problem is properly scaled and that the influence of disturbances is sufficiently analysed and managed. An analysis of the least squares problem by means of a singular value decomposition is preferred as it not only solves the problem of rank deficiency, but it also can correctly deal with measurement noise and unmodelled dynamics.

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