Nonlinear Control of a Pneumatic Actuator Based on a Dynamic Friction Model

This paper presents a new controller for the position of a pneumatic actuator. The controller is designed based on the multiple-surface sliding control method in combination with a frictional compensator. The multiple-surface sliding control method is applied to deal with the nonlinear characteristics of the pneumatic system, and the frictional compensator is applied to compensate for the friction force in the pneumatic actuator. The friction force is estimated based on a dynamic friction model (the LuGre model). Both simulation and experimental studies are done to evaluate the new controller. The evaluation results indicate significant improvement in the tracking position error of the new controller comparing to the multiple-surface sliding controller without friction compensation and other nonlinear controllers.

Estimation of the tangential transverse vibrations effect on the friction force with the use of LuGre model

In this work, a novel dynamic computational model developed for the purpose of modelling the phenomenon of friction force reduction in a sliding motion at tangential transverse vibrations of elastic support is presented. In contrast to the currently used so-called kinematic models, this model takes into account the mass of a sliding and simultaneously subjected to vibrations body. It is based on the dynamic equations of motion of this body. For the description of the friction force, the LuGre model was used which considers both the compliance of the contact zone and its damping. Considered in this model are also compliance and damping of the drive. The model assumes that vibrations are not imposed directly on the shifting body but are transferred to it from the vibrating elastic support. The developed model has been implemented in the Matlab/Simulink environment and subsequently utilised in simulating analyses. The results of these were compared with the results of experiments which were carried out using a designated, in-house built, experimental rig. An excellent compliance has been achieved.

Efficiency comparison of various friction models of a hydraulic cylinder in the framework of multibody system dynamics

Dynamic simulation of mechanical systems can be performed using a multibody system dynamics approach. The approach allows to account systems of other physical nature, such as hydraulic actuators. In such systems, the nonlinearity and numerical stiffness introduced by the friction model of the hydraulic cylinders can be an important aspect to consider in the modeling because it can lead to poor computational efficiency. This paper couples various friction models of a hydraulic cylinder with the equations of motion of a hydraulically actuated multibody system in a monolithic framework. To this end, two static friction models, the Bengisu–Akay model and Brown–McPhee model, and two dynamic friction models, the LuGre model and modified LuGre model, are considered in this work. A hydraulically actuated four-bar mechanism is exemplified as a case study. The four modeling approaches are compared based on the work cycle, friction force, energy balance, and numerical efficiency. It is concluded that the Brown–McPhee approach is numerically the most efficient approach and it is well able to describe usual friction characteristics in dynamic simulation of hydraulically actuated multibody systems.

Modeling friction effects in lubricated roller guideways using a modified LuGre model

Guideways accommodate tool or workpiece translations, and their dynamic behavior and associated sliding effects have great impact on the precision, stability, and performance of the machine tool. During machining, guideway rollers experience oscillatory excitations because of cutting forces, which necessitate considering their pre-sliding behavior along with the sliding characteristics to compensate for the associated tracking errors using the position control system. This study considers friction effects in pre-sliding and sliding regimes of lubricated linear roller guideway systems to provide an accurate dynamic model of the machine tool element. To model the dynamic characteristics of frictional contact in the lubricated linear roller guideway, the LuGre model, commonly used in the machine tool positioning control system to estimate the compensating drive force, is modified considering the roller-raceway contact physics and the lubricant film dynamics. The proposed model also includes coupling effects between normal and tangential forces in the contact interface. Experimental studies were performed on a lubricated linear roller guideway to verify the performance of the presented modified LuGre model. In the experimental observations, the dynamic behavior of friction in the lubricated linear guideway is well illustrated. A comparison of the experimentally measured data and proposed modified LuGre model predictions shows the model can accurately predict dynamic behaviors of the frictional contact interface.