Nonlinear Friction Phenomenon Research Articles

Adaptive feed-forward friction compensation through developing an asymmetrical dynamic friction model

This article presents an adaptive feed-forward method to compensate for the dynamic friction in the machine tool systems so that the tracking errors of the machine axes can be reduced. To achieve this aim, a dynamic friction model is firstly established by constructing a continuous and differentiable two-segmented arc tangent curve to characterize the asymmetrical and nonlinear static friction phenomenon in relation to the positive and negative velocity ranges of the machine axes. Subsequently, a new feed-forward method is proposed to compensate for the friction by constructing an adaptive controller with three advantages, i.e. no need of velocity and acceleration measurement, large adaptive rate and high steady-state accuracy. During the model establishment, a discontinuous projection mapping in the learning process is constructed. Especially, the stability of the adaptive controller is strictly proved by theoretical derivation. Besides, a new two-step adaptive method is formulated to analytically calculate the unobservable parameter z. Finally, both simulations and experiments confirm that the proposed compensation method can reach to lower tracking errors, especially in the velocity reversal area, by comparing with the existing approaches.

Actuators based on a controlled particle-matrix interaction in magnetic hybrid materials for applications in locomotion and manipulation systems

Abstract The paper deals with the investigation of magneto-sensitive elastomers (MSE) and their application in technical actuator systems. MSE consist of an elastic matrix containing suspended magnetically soft and/or hard particles. Additionally, they can also contain silicone oil, graphite particles, thermoplastic components, etc., in various concentrations in order to tune specific properties such as viscosity, conductivity and thermoelasticity, respectively. The focuses of investigations are the beneficial properties of MSE in prototypes for locomotion and manipulation purposes that possess an integrated sensor function. The research follows the principle of a model-based design, i.e. the working steps are ideation, mathematical modelling, material characterization as well as building first functional models (prototypes). The developed apedal (without legs) and non-wheeled locomotion systems use the interplay between material deformations and the mechanical motion in connection with the issues of control and stability. Non-linear friction phenomena lead to a monotonous forward motion of the systems. The aim of this study is the design of such mechanical structures, which reduce the control costs. The investigations deal with the movement and control of ‘intelligent’ mechanisms, for which the magnetically field-controlled particle-matrix interactions provide an appropriate approach. The presented grippers enclose partially gripped objects, which is an advantage for handling sensitive objects. Form-fit grippers with adaptable contour at the contact area enable a uniform pressure distribution on the surface of gripped objects. Furthermore, with the possibility of active shape adaptation, objects with significantly differing geometries can be gripped. To realise the desired active shape adaptation, the effect of field-induced plasticity of MSE is used. The first developed prototypes mainly confirm the functional principles as such without direct application. For this, besides the ability of locomotion and manipulation itself, further technological possibilities have to be added to the systems. The first steps are therefore being taken towards integrated MSE based adaptive sensor systems.

Experimental and numerical analysis of industrial warm forming of stainless steel sheet

In this paper, the development of the industrial forming process of drawpieces is investigated experimentally and numerically. The drawing process presented in this work was achieved with a form of 17-4PH stainless steel sheet with a sheet thickness of 1mm. Due to the high ratio of yield stress to ultimate tensile strength and large amount of springback of the formed material, to ensure that the shape and dimensions of drawpiece are suitably accurate, the forming process is divided into two stages: forming of the drawpiece using a rubber punch and calibration of the drawpiece at elevated temperature. A 3D finite element (FE) coupled thermo-mechanical model was built using the commercial FE-package eta/DynaForm 5.9.3. This package allows physical models of real processes to be analysed, placing special emphasis on non-linear material behaviour, large deformations, and complex friction phenomena. The distribution of the drawpiece shape error obtained by the GOM ATOS system and thickening measurements confirmed that the developed methodology is suitable for industrial manufacture of bearing housings for aircraft fan engines.

A complete strategy for efficient and accurate multibody dynamics of flexible structures with large lap joints considering contact and friction

This paper deals with the dynamics of jointed flexible structures in multibody simulations. Joints are areas where the surfaces of substructures come into contact, for example, screwed or bolted joints. Depending on the spatial distribution of the joint, the overall dynamic behavior can be influenced significantly. Therefore, it is essential to consider the nonlinear contact and friction phenomena over the entire joint. In multibody dynamics, flexible bodies are often treated by the use of reduction methods, such as component mode synthesis (CMS). For jointed flexible structures, it is important to accurately compute the local deformations inside the joint in order to get a realistic representation of the nonlinear contact and friction forces. CMS alone is not suitable for the capture of these local nonlinearities and therefore is extended in this paper with problem-oriented trial vectors. The computation of these trial vectors is based on trial vector derivatives of the CMS reduction base. This paper describes the application of this extended reduction method to general multibody systems, under consideration of the contact and friction forces in the vector of generalized forces and the Jacobian. To ensure accuracy and numerical efficiency, different contact and friction models are investigated and evaluated. The complete strategy is applied to a multibody system containing a multilayered flexible structure. The numerical results confirm that the method leads to accurate results with low computational effort.

Eluding the Physical Constraints in a Nonlinear Interaction Sound Synthesis Model for Gesture Guidance

In this paper, a flexible control strategy for a synthesis model dedicated to nonlinear friction phenomena is proposed. This model enables to synthesize different types of sound sources, such as creaky doors, singing glasses, squeaking wet plates or bowed strings. Based on the perceptual stance that a sound is perceived as the result of an action on an object we propose a genuine source/filter synthesis approach that enables to elude physical constraints induced by the coupling between the interacting objects. This approach makes it possible to independently control and freely combine the action and the object. Different implementations and applications related to computer animation, gesture learning for rehabilitation and expert gestures are presented at the end of this paper.

Actuator stiction compensation via model predictive control for nonlinear processes

The problem of valve stiction is addressed, which is a nonlinear friction phenomenon that causes poor performance of control loops in the process industries. A model predictive control (MPC) stiction compensation formulation is developed including detailed dynamics for a sticky valve and additional constraints on the input rate of change and actuation magnitude to reduce control loop performance degradation and to prevent the MPC from requesting physically unrealistic control actions due to stiction. Although developed with a focus on stiction, the MPC‐based compensation method presented is general and has potential to compensate for other nonlinear valve dynamics which have some similarities to those caused by stiction. Feasibility and closed‐loop stability of the proposed MPC formulation are proven for a sufficiently small sampling period when Lyapunov‐based constraints are incorporated. Using a chemical process example with an economic model predictive controller (EMPC), the selection of appropriate constraints for the proposed method is demonstrated. The example verified the incorporation of the stiction dynamics and actuation magnitude constraints in the EMPC causes it to select set‐points that the valve output can reach and causes the operating constraints to be met. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2004–2023, 2016

Identification of Two-Mass Mechanical Systems Using Torque Excitation: Design and Experimental Evaluation

This paper deals with methods for parameter estimation of two-mass mechanical systems in electric drives. Estimates of mechanical parameters are needed in the start-up of a drive for automatic tuning of model-based speed and position controllers. A discrete-time output error (OE) model is applied to parameter estimation. The resulting pulse-transfer function is transformed into a continuous-time transfer function, and parameters of the two-mass system model are analytically solved from the coefficients of this transfer function. An open-loop identification setup and two closed-speed-loop identification setups (direct and indirect) are designed and experimentally compared. The experiments are carried out at nonzero speed to reduce the effect of nonlinear friction phenomena on the parameter estimates. According to results, all three identification setups are applicable for the parameter estimation of two-mass mechanical systems.

Actuators for Motion Control: Fine Actuator Force Control for Electric Injection Molding Machines

Currently, most plastic products are manufactured using injection molding machines, where the product quality largely depends on the injection force. In a typical injection molding machines force control system, force information from the machine environment is obtained by a force sensor. However, these sensors have a few disadvantages in terms of signal noise, sensor cost, and narrow bandwidth, and thus a sensorless force detection method is desirable. The use of a reaction force observer, based on the two-inertia resonant model, has been proposed, but this method suffers from some estimation errors due to the influence of nonlinear characteristics in the holding process and the screw back-pressure process. This article proposes a new injection force estimation method based on a high-order reaction force observer (HORFO) with Coulomb friction compensation, which is not significantly influenced by the nonlinear friction phenomenon. Moreover, this article evaluates the possibility and versatility of a sensorless force control system using the proposed HORFO with Coulomb friction compensation.

Development of Sensorless Force Control System Based on Nonlinear Friction Phenomenon for Electric Injection Molding Machine

Currently, most of the plastic products are manufactured by using injection molding machines. The quality of the products depends largely on the injection force. In a typical force control system of an injection molding machine, the information about the force in the machine environment is obtained by a force sensor. However, force sensors have a few disadvantages such as signal noise, high sensor cost and narrow bandwidth. We have proposed the use of a reaction force observer based on the two-inertia resonant model. However, this method has some estimated error caused by a static friction in the holding process and a Coulomb friction in the screw back-pressure process. The estimation accuracy of the reaction force observer depends on parameter variations and the non-linear friction phenomenon. This paper proposes a new injection-force-estimation method based on the proposed high-order reaction force observer (HORFO), which is not influenced significantly by the nonlinear friction phenomenon. The effectiveness of the proposed method is confirmed by experimental results.

The Feedforward Friction Compensation of Linear Motor Using Genetic Learning Algorithm

This paper proposes a feedforward friction compensator based on LuGre friction model. The various parameters in both the friction model and the system plant model would be coarsely estimated by the various experiments, and then the genetic algorithm (GA) finely optimizes the key parameters by a single identification experiment. When compared with the conventional black box learning algorithm, this model-based compensator uses only five parameters to model the nonlinear friction phenomenon and the corresponding convergent rate of parameters is fast in the learning process. Finally, the friction compensated performance of proposed algorithm is evaluated and compared with the traditional uncompensated system. The simulated and experimented results show that the velocity tracking error is drastically improved by the feedforward friction compensator in a linear motor motion system.

SMC With Disturbance Observer for a Linear Belt Drive

Accurate position-tracking control in a belt-driven servomechanism can experience vibrations and large tracking errors due to compliance and elasticity introduced by force transmission through the belt and nonlinear-friction phenomenon. In this paper, a new control algorithm which is based on a sliding-mode control that is able to deal with these problems is proposed. In order to further optimize position-tracking performance, the control scheme has been extended by an asymptotic disturbance observer. It has been proven that robust and vibration-free operation of a linear-belt-driven system can be achieved. The experiments presented in this paper show improved position-tracking error response while maintaining vibration suppression.

Classical cascade and sliding mode control tracking performances for a xy feed table of a high-speed machine tool

The development of robust tracking controllers for linear feed drive, high speed machine tools is the primary objective of this work. Robustness implies the controller ability to preserve tracking accuracy in the presence of cutting forces and friction forces. This paper discusses the design and tracking performances of traditional cascade and sliding mode controllers for a xy feed table. Tracking performances are analysed through circular tests that are performed at selected tracking speeds and circle radius. For cascade P/PI controller, tracking error is proportional to the reference speed and is inversely proportional to the velocity gain value of the position loop controller. Speed and acceleration feed forward further reduce this tracking error. Quadrant glitches, a product of non-linear friction phenomena at the point of velocity reversal, are observed. Sliding mode controller, however, significantly reduces quadrant glitches and exhibits greater dynamic stiffness while its tracking accuracy is comparable to the cascade controller.

Structural topology optimization for crashworthiness

This paper presents a method to obtain optimum topologies of structures subject to impact loads that produce geometric and material nonlinear behavior, surface contact, friction, and other phenomena in shell and three-dimensional structures. The main feature of this method is an algorithm that does not use sensitivity (gradient) information and does not require large number of iterations. A criterion called prescribed plastic strain/stress is used to circumvent the lack of sensitivity information. Additionally, a controlled crash behavior (CCB) feature is included in the simulation phase allowing design engineers to prescribe an improved structural behavior. An application of this method in a vehicle front rail is presented.

Nonlinear friction phenomena in direct-drive robotic arms: an experimental set-up for rapid modelling and control prototyping

This paper considers the design and the experimental validation of digital control algorithms when both low and high velocity precision issues are important for the quality of the controlled equipment. At low velocities friction phenomena are dominant, while at high velocities the nonlinear coupled and configuration-dependent dynamics plays a major role. Since rapid control prototyping (RCP) requires “finely-tuned” models of the equipment under investigation, an accurate definition of the nonlinear friction model is of capital importance for assessing the qualification of the proposed algorithms. An experimental validation of the proposed models and control algorithms with friction compensation is presented and discussed for a two-arms planar manipulator with brushless directdrive actuators.

Describing Function Analysis of Mechanical Systems with Nonlinear Friction and Backlash Phenomena

This paper analyses the dynamical properties of systems with nonlinear friction and backlash phenomena based on the describing function method. The dynamics is illustrated using the Nyquist and Bode plots and the results are compared with those of standard models