Independent Identification of Friction Characteristics for Parallel Manipulators

2006 ◽  
Vol 129 (3) ◽  
pp. 294-302 ◽  
Author(s):  
Houssem Abdellatif ◽  
Martin Grotjahn ◽  
Bodo Heimann
Keyword(s):  
Steady State ◽  
Degrees Of Freedom ◽  
Parallel Manipulators ◽  
Friction Model ◽  
Rigid Body Dynamics ◽  
Model Parameters ◽  
Friction Modeling ◽  
Friction Characteristics ◽  
Experimental Identification ◽  
Kinematic Coupling

The compensation for friction or joint losses in robotic manipulators contributes to an important improvement of the control quality. Besides appropriate friction modeling, experimental identification of the model parameters is fundamental toward better control performance. Conventionally steady-state friction characteristics are investigated for mechanical systems in the first step. However, and due to the high kinematic coupling, such procedure is already complicated for complex multiple closed-loop mechanisms, like parallel manipulators. Actuation friction of such mechanisms becomes configuration dependent. This paper presents a methodology that deals with such challenge. The kinematic coupling is regarded in the friction model and therefore in the design of the experimental identification. With the proposed strategy, it is possible to identify the steady-state friction parameters independently from any knowledge about inertial or rigid-body dynamics. Friction models for sensorless passive joints can also be provided. Besides, the method is kept very practical, since there is no need for any additional hardware devices or interfaces than a standard industrial control. The suitability for the industrial field is proven by experimental application to PaLiDA that is a six degrees of freedom parallel manipulator equipped with linear directly driven actuators.

scholarly journals Study on Friction in Automotive Shock Absorbers Part 1: Friction Simulation Using a Dynamic Friction Model in the Contact Zone of an FEM Model

Vehicles ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 212-232
Author(s):  
Ludwig Herzog ◽  
Klaus Augsburg
Keyword(s):  
Ride Comfort ◽  
Viscous Friction ◽  
Simulation Method ◽  
Friction Model ◽  
Model Parameters ◽  
Dynamic Friction ◽  
Friction Modeling ◽  
Shock Absorbers ◽  
Operation Conditions ◽  
Wide Range

The important change in the transition from partial to high automation is that a vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorber with two friction types: The intended viscous friction dissipates the chassis vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In this article, a simulation approach is introduced to model damper friction based on the most friction-relevant parameters. Since damper friction is highly dependent on geometry, which can vary widely, three-dimensional (3D) structural FEM is used to determine the deformations of the damper parts resulting from mounting and varying operation conditions. In the respective contact zones, a dynamic friction model is applied and parameterized based on the single friction point measurements. Subsequent to the parameterization of the overall friction model with geometry data, operation conditions, material properties and friction model parameters, single friction point simulations are performed, analyzed and validated against single friction point measurements. It is shown that this simulation method allows for friction prediction with high accuracy. Consequently, its application enables a wide range of parameters relevant to damper friction to be investigated with significantly increased development efficiency.

Experimental identification of the dynamics model for 6-DOF parallel manipulators

Robotica ◽  
2009 ◽  
Vol 28 (3) ◽  
pp. 359-368 ◽  
Author(s):  
Houssem Abdellatif ◽  
Bodo Heimann
Keyword(s):  
Degrees Of Freedom ◽  
Parallel Manipulators ◽  
Parallel Robots ◽  
Automatic Tuning ◽  
Data Filtering ◽  
Dynamics Model ◽  
Likelihood Estimator ◽  
Six Degrees Of Freedom ◽  
Experimental Identification ◽  
Dynamics Identification

SUMMARYThe paper presents a self-contained approach for the dynamics identification of six degrees of freedom (DOF) parallel robots. Major feature is the consequent consideration of structural properties of such machines to provide an experimentally adequate identification method. The known periodic excitation is modified and enhanced to take the actuator coupling as well as the numerical solution of the direct kinematics into account. The benefits of explicit frequency-domain data filtering are demonstrated. Additionally, a new implementation of the maximum-likelihood estimator allows for automatic tuning of the data filter. The issue of optimal input experiment design is also discussed and substantiated with extensive experiments.

scholarly journals Scaling and similarity of a stream-power incision and linear diffusion landscape evolution model

2018 ◽  
Vol 6 (3) ◽  
pp. 779-808 ◽  
Author(s):  
Nikos Theodoratos ◽  
Hansjörg Seybold ◽  
James W. Kirchner
Keyword(s):  
Steady State ◽  
Peclet Number ◽  
Degrees Of Freedom ◽  
Landscape Evolution ◽  
Initial Conditions ◽  
Evolution Model ◽  
Model Parameters ◽  
Stream Power ◽  
Linear Diffusion ◽  
Characteristic Scales

Abstract. The scaling and similarity of fluvial landscapes can reveal fundamental aspects of the physics driving their evolution. Here, we perform a dimensional analysis of the governing equation of a widely used landscape evolution model (LEM) that combines stream-power incision and linear diffusion laws. Our analysis assumes that length and height are conceptually distinct dimensions and uses characteristic scales that depend only on the model parameters (incision coefficient, diffusion coefficient, and uplift rate) rather than on the size of the domain or of landscape features. We use previously defined characteristic scales of length, height, and time, but, for the first time, we combine all three in a single analysis. Using these characteristic scales, we non-dimensionalize the LEM such that it includes only dimensionless variables and no parameters. This significantly simplifies the LEM by removing all parameter-related degrees of freedom. The only remaining degrees of freedom are in the boundary and initial conditions. Thus, for any given set of dimensionless boundary and initial conditions, all simulations, regardless of parameters, are just rescaled copies of each other, both in steady state and throughout their evolution. Therefore, the entire model parameter space can be explored by temporally and spatially rescaling a single simulation. This is orders of magnitude faster than performing multiple simulations to span multidimensional parameter spaces. The characteristic scales of length, height and time are geomorphologically interpretable; they define relationships between topography and the relative strengths of landscape-forming processes. The characteristic height scale specifies how drainage areas and slopes must be related to curvatures for a landscape to be in steady state and leads to methods for defining valleys, estimating model parameters, and testing whether real topography follows the LEM. The characteristic length scale is roughly equal to the scale of the transition from diffusion-dominated to advection-dominated propagation of topographic perturbations (e.g., knickpoints). We introduce a modified definition of the landscape Péclet number, which quantifies the relative influence of advective versus diffusive propagation of perturbations. Our Péclet number definition can account for the scaling of basin length with basin area, which depends on topographic convergence versus divergence.

scholarly journals A Bifurcation Analysis and Sensitivity Study of Brake Creep Groan

2021 ◽  
Vol 31 (16) ◽  
Author(s):  
Shaun Smith ◽  
James Knowles ◽  
Byron Mason ◽  
Sean Biggs
Keyword(s):  
Periodic Orbits ◽  
Degrees Of Freedom ◽  
Initial Conditions ◽  
Period Doubling ◽  
Nonlinear Behavior ◽  
Sensitivity Study ◽  
Friction Model ◽  
Model Parameters ◽  
Period Doubling Bifurcations ◽  
Simple Models

Creep groan is the undesirable vibration observed in the brake pad and disc as brakes are applied during low-speed driving. The presence of friction leads to nonlinear behavior even in simple models of this phenomenon. This paper uses tools from bifurcation theory to investigate creep groan behavior in a nonlinear 3-degrees-of-freedom mathematical model. Three areas of operational interest are identified, replicating results from previous studies: region 1 contains repelling equilibria and attracting periodic orbits (creep groan); region 2 contains both attracting equilibria and periodic orbits (creep groan and no creep groan, depending on initial conditions); region 3 contains attracting equilibria (no creep groan). The influence of several friction model parameters on these regions is presented, which identify that the transition between static and dynamic friction regimes has a large influence on the existence of creep groan. Additional investigations discover the presence of several bifurcations previously unknown to exist in this model, including Hopf, torus and period-doubling bifurcations. This insight provides valuable novel information about the nature of creep groan and indicates that complex behavior can be discovered and explored in relatively simple models.

scholarly journals Study on Friction in Automotive Shock Absorbers Part 2: Validation of Friction Simulations via Novel Single Friction Point Test Rigs

Vehicles ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 197-211
Author(s):  
Ludwig Herzog ◽  
Klaus Augsburg
Keyword(s):  
Ride Comfort ◽  
Viscous Friction ◽  
Friction Model ◽  
Operating Conditions ◽  
Model Parameters ◽  
Friction Modeling ◽  
Friction Behavior ◽  
General Applicability ◽  
Reliable Determination ◽  
Shock Absorbers

The most important change in the transition from partial to high automation is that the vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorbers with two friction types. The intended viscous friction dissipates the chassis’ vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In the current article, the simulation approach introduced in part 1 of this study is validated against a single friction point and full damper friction measurements. To achieve that, a friction measurement method with novel test rigs has been developed, which allows for reliable determination of the friction behavior of each single friction point, while appropriately resembling the operating conditions of the real damper. The subsequent presentation of a friction simulation using friction model parameters from different geometry shows the general applicability of the overall friction investigation methodology. Accordingly, the presented simulation and measurement approaches enable the investigation of dynamic friction in automotive shock absorbers with significantly increased development efficiency.

scholarly journals Scaling and similarity of a stream-power incision and linear diffusion landscape evolution model

2018 ◽  
Author(s):  
Nikos Theodoratos ◽  
Hansjörg Seybold ◽  
James W. Kirchner
Keyword(s):  
Steady State ◽  
Degrees Of Freedom ◽  
Characteristic Length ◽  
Initial Conditions ◽  
Model Parameters ◽  
Length Scale ◽  
Characteristic Length Scale ◽  
Stream Power ◽  
Linear Diffusion ◽  
Characteristic Scales

Abstract. Scaling and similarity of fluvial landscapes can reveal fundamental aspects of the physics driving their evolution. Here we perform dimensional analysis on a widely used landscape evolution model (LEM) that combines stream-power incision and linear diffusion laws. Our analysis assumes that length and height are conceptually distinct dimensions, and uses characteristic scales that depend only on the model parameters (incision coefficient, diffusion coefficient, and uplift rate) rather than on the size of the domain or of landscape features. We use a previously defined characteristic length scale, but introduce new characteristic height and time scales. We use these characteristic scales to non-dimensionalize the LEM, such that it includes only dimensionless variables and no parameters. This significantly simplifies the LEM by removing all parameter-related degrees of freedom. The only remaining degrees of freedom are in the boundary and initial conditions. Thus, for any given set of dimensionless boundary and initial conditions, all simulations, regardless of parameters, are just re-scaled copies of each other, both in steady state and throughout their evolution. Therefore, the entire model parameter space can be explored by temporally and spatially re-scaling a single simulation. This is orders of magnitude faster than performing multiple simulations to span multi-dimensional parameter spaces. The characteristic length, height, and time scales are geomorphologically interpretable; they define relationships between topography and the relative strengths of landscape-forming processes. The characteristic height scale specifies how drainage areas and slopes must be related to curvatures for a landscape to be in steady state, and leads to methods for defining valleys, estimating model parameters, and testing whether real topography follows the LEM. The characteristic length scale is roughly equal to the scale of the transition from diffusion-dominated to advection-dominated propagation of topographic perturbations (e.g., knickpoints). We introduce a modified definition of the landscape Péclet number, which quantifies the relative influence of advective versus diffusive propagation of perturbations. Our Péclet number definition can account for the scaling of basin length with basin area, which depends on topographic convergence versus divergence.

CFD Assisted Steady-State Modelling of Restrictive Counterbalance Valves

2020 ◽  
Author(s):  
Jannik H. Jakobsen ◽  
Michael R. Hansen
Keyword(s):  
Steady State ◽  
Friction Model ◽  
System Stability ◽  
Model Parameters ◽  
Cfd Modelling ◽  
Data Set ◽  
Load Pressure ◽  
Basic Model ◽  
And Performance ◽  
Approach To Steady State

The counterbalance valve is an important component in many hydraulic applications and its behaviour hugely impacts system stability and performance. Despite that, CBVs are rarely modelled accurately due to the effort required to obtain basic model parameters and the complexity involved in identifying expressions for flow forces and friction. This paper presents a CFD assisted approach to steady-state modelling of CBVs. It is applied to a 3-port restrictive commercially available counterbalance valve. The model obtained is based on detailed measurements of the valve geometry, a single data set and CFD modelling and includes flow forces and friction. The CFD assisted model is compared to experimental data at three temperatures and two versions of more classical steady-state model based on the orifice equation, uniform pressure distribution and experimental results. The results support the CFD assisted approach as a way to increase modelling accuracy. The load pressure corrected coulomb friction model used manages to capture the changes to hysteresis with temperature but not the changes with pilot pressure.

scholarly journals A Multivariable Adaptive Control Approach for Stabilization of a Cart-Type Double Inverted Pendulum

2011 ◽  
Vol 2011 ◽  
pp. 1-14 ◽  
Author(s):  
I. Hassanzadeh ◽  
A. Nejadfard ◽  
M. Zadi
Keyword(s):  
Steady State ◽  
Nonlinear Model ◽  
Degrees Of Freedom ◽  
Inverted Pendulum ◽  
Feedback Gain ◽  
Practical Implementation ◽  
Model Parameters ◽  
Lagrange Equations ◽  
Control Approach ◽  
Input Structure

This paper considers the design and practical implementation of linear-based controllers for a cart-type double inverted pendulum (DIPC). A constitution of two linked pendulums placed on a sliding cart, presenting a three Degrees of Freedom and single controlling input structure. The controller objective is to keep both pendulums in an up-up unstable equilibrium point. Modeling is based on the Euler-Lagrange equations, and the resulted nonlinear model is linearized around up-up position. First, the LQR method is used to stabilize DIPC by a feedback gain matrix in order to minimize a quadratic cost function. Without using an observer to estimate the unmeasured states, in the next step we make use of LQG controller which combines the Kalman-Bucy filter estimation and LQR feedback control to obtain a better steady-state performance, but poor robustness. Eventually, to overcome the unknown nonlinear model parameters, an adaptive controller is designed. This controller is based on Model Reference Adaptive System (MRAS) method, which uses the Lyapunov function to eliminate the defined state error. This controller improves both the steady-state and disturbance responses.

Holdup and holdup profiles in the reciprocating plate extractor VPE

1990 ◽  
Vol 55 (11) ◽  
pp. 2648-2661 ◽  
Author(s):  
Helena Sovová ◽  
Vladislav Bízek ◽  
Jaroslav Procházka
Keyword(s):  
Steady State ◽  
Experimental Results ◽  
Model Parameters ◽  
Dispersed Phase ◽  
Pulse Form ◽  
Sieve Plates

In this work measurements of mean holdup of dispersed phase, of axial holdup profiles and of flooding points in a reciprocating plate contactor with both the VPE-type plates and the sieve plates were carried out. The experimental results were compared with a monodisperse model of steady-state column hydrodynamics and the model parameters were evaluated. Important differences in the behaviour of the two plate types could be identified. Comparison was also made between two reciprocating drives of different pulse form.

Dynamic Analysis and Configuration Design of a Two-Component Wave-Energy Absorber

2012 ◽  
Author(s):  
Christophe Cochet ◽  
Ronald W. Yeung
Keyword(s):  
Wave Energy ◽  
Degrees Of Freedom ◽  
Outer Cylinder ◽  
Rigid Body Dynamics ◽  
Contact Forces ◽  
Energy Extraction ◽  
Energy Absorber ◽  
Compound Cylinder ◽  
Motion Study ◽  
Heave Motion

The wave-energy absorber being developed at UC Berkeley is modeled as a moored compound cylinder, with an outer cylinder sliding along a tension-tethered inner cylinder. With rigid-body dynamics, it is first shown that the surge and pitch degrees of freedom are decoupled from the heave motion. The heaving motion of the outer cylinder is analyzed and its geometric proportions (radii and drafts ratios) are optimized for wave-energy extraction. Earlier works of Yeung [1] and Chau and Yeung [2,3] are used in the present heave-motion study. The coupled surge-pitch motion can be solved and can provide the contact forces between the cylinders. The concept of capture width is used to characterize the energy extraction: its maximization leads to optimal energy extraction. The methodology presented provides the optimal geometry in terms of non-dimensional proportions of the device. It is found that a smaller radius and deeper draft for the outer cylinder will lead to a larger capture width and larger resulting motion.

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