Generalized Maxwell-slip Friction Model Research Articles

Application of switched-dynamics friction models in feedback control

In the last decades, several friction models suitable for control purposes have been proposed, which are able to represent most of the observed friction behavior. However, this comes at the cost of an increased complexity, presenting in some cases switched dynamics, as in the generalized Maxwell-slip friction model. Thus, consideration of these models in control design certainly increases the complexity of stability proofs, and thus, their use in control design except for feedforward compensation. The purpose of this work is to provide stability results to facilitate the application of these models in feedback control. First, results are given for a more general model with switched dynamics, and then results are given for the particular case of the generalized Maxwell-slip model. Then, the application of these developments is illustrated for the case of a deterministic robust control design for a linear motor drive. In this case, controllers with feedforward and feedback friction compensation are implemented in an experimental setup, showing the improvement in performance that can be achieved using the latter.

Piston-Seals Friction Modeling Using a Modified Maxwell Slip Formation and Genetic Identification Algorithm

Improving spontaneity, shifting control, and efficiency are the main goals of actuators for hydraulic automated transmissions. Friction losses of piston-seals play an essential role in achieving these goals. Therefore, modeling the complex friction behavior of piston seals leads to a better understanding of the determinant factors of energy losses and, consequently, the realization of more efficient transmission actuators. This paper proposes a piston-seal friction model based on the Generalized Maxwell-Slip model. The proposed model introduces an additional hydraulic-pressure dependency that emulates the influence of cylinder-pressure on the displacement variable while accounting for various piston-seal structures. A Genetic Algorithm is also applied to identify and optimize the parameters of the proposed friction model. Simulations with O-Ring, D-Ring, and Bonded Piston seals were developed to show the validity of the proposed model in practical scenarios. The results were also compared with the original Generalized Maxwell Slip friction model to show the superiority of the proposed model in representing the experimental data.

The generalized Maxwell-slip friction model applied to starting of small wind turbines

The generalized Maxwell-slip friction model applied to starting of small wind turbines

Adaptive feedforward control of a collaborative industrial robot manipulator using a novel extension of the Generalized Maxwell-Slip friction model

Collaborative industrial robots often use strain-wave transmissions which display a highly nonlinear behavior. In particular, the friction torque depend on the load torque and the hysteresis characteristics were recently found to depend on the joint angular position.This paper presents a novel extension of the Generalized Maxwell-Slip friction model to describe said phenomena in a combined framework. The method overcomes the discontinuity around zero velocity of existing models. Experiments on the Universal Robots UR5e manipulator show superior performance in terms of torque prediction accuracy and tracking performance of the proposed method.An adaptive feedforward friction compensator is proposed based on the extended Generalized Maxwell-Slip friction model to compensate the time-variations of the Coulomb and viscous friction due to, respectively, wear and mispredictions of the lubricant temperature. The adaptive estimator relies on the sensing hardware readily available in the joints of the Universal Robots manipulators, i.e. two absolute rotary encoders; one at each side of the transmission, current sensing for the electric actuator, and a temperature sensor. Results show a considerable reduction of the torque prediction error and tracking error.

Comprehensive modeling and identification of nonlinear joint dynamics for collaborative industrial robot manipulators

For collaborative robots, the ability to accurately predict the actuator torques required to realize the desired task is highly important. This will improve and guarantee the safety, motion and force control performance, and smooth lead-through programming experience. Thus, this paper presents the investigation towards comprehensive modeling and identification of nonlinear joint dynamics for collaborative robots. The proposed joint dynamics model and identification describes the most dominant dynamic characteristics of robot joints that comprise strain-wave transmissions, such as nonlinear friction, nonlinear stiffness, hysteresis, and kinematic error. Position-dependent backlash characteristics is observed and quantified using our proposed identification method and the Generalized Maxwell-Slip friction model is extended to describe the observed phenomena. The developed dynamic modeling and identification procedures provides insightful guidance for the design and model-based control of collaborative robots.

Finite-time adaptive sliding mode force control for electro-hydraulic load simulator based on improved GMS friction model

Abstract This paper addresses the force tracking problem of electro-hydraulic load simulator under the influence of nonlinear friction and uncertain disturbance. A nonlinear system model combined with the improved generalized Maxwell-slip (GMS) friction model is firstly derived to describe the characteristics of load simulator system more accurately. Then, by using particle swarm optimization (PSO) algorithm ​combined with the system hysteresis characteristic analysis, the GMS friction parameters are identified. To compensate for nonlinear friction and uncertain disturbance, a finite-time adaptive sliding mode control method is proposed based on the accurate system model. This controller has the ability to ensure that the system state moves along the nonlinear sliding surface to steady state in a short time as well as good dynamic properties under the influence of parametric uncertainties and disturbance, which further improves the force loading accuracy and rapidity. At the end of this work, simulation and experimental results are employed to demonstrate the effectiveness of the proposed sliding mode control strategy.

GMS friction model approximation

The paper deals with the research of sigmoid smooth curve application to the approximation of GMS (Generalized Maxwell-Slip) friction model. The study provides an analysis of the influence of the curves on the effectiveness of friction property modelling and computational efficiency. The smooth curves have been used to replace switching instructions in the differential equation of the state variables in GMS model, thus allowing the simulation of a smooth transition between two friction regimes: stiction and sliding. The new modified friction model facilitates production of continuous derivatives and maintenance of all the GMS model friction properties. The M-GMS model can be used to solve dynamic machine systems applying the methods designed for continuous systems, e.g. during the Lyapunov exponent calculation with standard methods to determine the system chaoticity or to be applied to gradient optimization techniques.