This note presents a modification of the integrated friction model structure proposed by Swevers et al. (2000), called the Leuven model. The Leuven model structure allows accurate modeling both in the presliding and the sliding regimes without the use of a switching function. The model incorporates a hysteresis function with nonlocal memory and arbitrary transition curves. This note presents two modifications of the Leuven model. A first modification overcomes a recently detected shortcoming of the original Leuven model: a discontinuity in the friction force which occurs during certain transitions in presliding. A second modification, using the general Maxwell slip model to implement the hysteresis force, eliminates the problem of stack overflow, which can occur with the implementation of the hysteresis force.

Technical Note: modification of the Leuven integrated friction model structure

In this paper, we present an analytical method to investigate the behavior of a two-degree-of-freedom oscillator excited by dry friction. The system consists of two masses connected by linear springs. These two masses are in contact with a driving belt moving at a constant velocity. The contact forces between the masses and the belt are obtained assuming Coulomb's friction law. Two families of periodic motions are found in closed form. The first one includes stick-slip oscillations with two switches per period, the second one is also composed of stick-slip motion, but includes three switches per period. In both cases, the initial conditions and the time duration of each kind of motions (stick or slip phases) are obtained in analytical form.

Dynamics of coupled oscillators exited by dry friction

Control-oriented friction modeling of hydraulic actuators based on hysteretic nonlinearity of lubricant film

Owing to the harsh environment of underground mines, autonomous underground articulated vehicles (UAVs) with precise control and positioning system are particularly important. However, the ambiguity of steering characteristics hinders the development of UAVs. This study presents a model-based method to uncover the steering characteristics of a UAV. Firstly, a hybrid model of UAV was established, which included a dynamic model of articulated frames and a model of the hydraulic power steering system. Secondly, a field test of a typical UAV, a load-haul-dump (LHD) with 4 m3 capacity, was carried out. In order to verify the correctness of the established model and the accuracy of the involved parameters, the field test results were used to verify the dynamic model in time and frequency domains. Then, the steering characteristics of the UAV were uncovered based on the verified hybrid model, and the results showed that the increased load would increase ‘oversteering’ under the same articulation angle and that the error of trajectory exceeded 0.3 m. In addition, the deviations of trajectories between the two frames were revealed during the transient steering process, and the maximum deviation reached 0.21 m when the velocity was 2 m/s and the articulation angle was 15°. The comprehensive results indicate that the steering characteristics of UAVs cannot be ignored in regard to precise autonomous control and positioning.

Hybrid Model-Based Analysis of Underground Articulated Vehicles Steering Characteristics

Received: 5 October 2020 Accepted: 26 December 2020 The stability and reliability of hydraulic control system have a direct bearing on the overall dynamic performance of the press machine. Hydromechanical analysis on the hydraulic control system is of theoretical and practical significance to improving the transmission performance and structural design of the entire press machine. From a quantitative perspective, this paper firstly analyzes the fluid transmission features of the hydraulic control system for the press machine, and presents the fluid transmission route and design drawings of the hydraulic control system. The next step is the design of the hydraulic control system. The authors specified the steps of design and calculation for the hydraulic control cylinder, and the principles for determining the power of the diesel engine. After that, experiments were carried out to verify the dynamic and static features of the designed system, and prove that our system is scientific and rational.

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Design of Hydraulic Control System for Press Machine and Analysis on Its Fluid Transmission Features

In this paper, stick–slip phenomenon of hydraulic forging press machine (HFPM), a nonlinear manufacturing system subjected to weak rigidity and negative friction velocity gradient, was investigated in slow-motion process. Dynamic characteristics of non-smooth motion were investigated experimentally under various operating conditions in slow-motion process. Taking into account the quadratic and cubic nonlinearities, the governing equation of the HFPM was derived. The method of multiple scales was employed to obtain approximate solution for velocity oscillation during slow motion. The steady-state responses for each case (i.e., non-resonance, primary, super-harmonic and sub-harmonic oscillation) were examined to investigate the correlation between velocity oscillation and nonlinear vibration in slow motion. The effects of viscous damping coefficient, hydraulic stiffness, friction parameters, excitation amplitude and frequency on the amplitude–frequency response characteristics were studied, and the interaction between system dynamics and tribological effects were presented. The stability of operational conditions and the critical velocity of the forging process were analyzed through the bifurcation techniques. Experimental results conducted on the HFPM verify the effectiveness of the proposed method.

Estimation of dynamic behaviors of hydraulic forging press machine in slow-motion manufacturing process

The viscous damping coefficient (VDC) of hydraulic actuators is crucial for system modeling, control and dynamic characteristic analysis. Currently, the researches on hydraulic actuators focus on behavior assessment, promotion of control performance and efficiency. However, the estimation of the VDC is difficult due to a lack of study. Firstly, using two types of hydraulic cylinders, behaviors of the VDC are experimentally examined with velocities and pressure variations. For the tested plunger type hydraulic cylinder, the exponential model $$B = \alpha \upsilon^{ - \beta } ,(\alpha > 0,\beta > 0)$$
 or $$B = \alpha_{1} e^{{ - \beta_{1} \upsilon }} + \alpha_{2} e^{{ - \beta_{2} \upsilon }} (\alpha_{1} ,\alpha_{2} > 0,\beta_{1} ,\beta_{2} > 0)$$
 , fits the relation between the VDC and velocities for a given pressure of chamber with high precision. The magnitude of the VDC decreases almost linearly under certain velocities when increasing the chamber pressure from 0.6 MPa to 6.0 MPa. Furthermore, the effects of the chamber pressures on the VDC of piston and plunge type hydraulic cylinders are different due to different sealing types. In order to investigate the VDC of a plunger type hydraulic actuator drastically, a steady-state numerical model has been developed to describe the mechanism incorporating tandem seal lubrication, back-up ring related friction behaviors and shear stress of fluid. It is shown that the simulated results of VDC agree with the measured results with a good accuracy. The proposed method provides an instruction to predict the VDC in system modeling and analysis.

Peng-Da Ma

Papers

Estimation of dynamic behaviors of hydraulic forging press machine in slow-motion manufacturing process

Theoretical Investigation of the Viscous Damping Coefficient of Hydraulic Actuators