“…As shown in Figure 13, when an external load, 92000 N, is applied, an upward shift in the hysteresis curve occurs. According to the result presented in Figure 13 and consistent with the similar studies (Dunaj et al, 2019; Pawełko et al, 2014), any changes in the preload vary the nonlinearity of stiffness of the system and the roller contact. The coupling effects between the lubricated linear roller guideway’s normal and tangential dynamics affect horizontal stiffness and contact restoring forces because of vertical stiffness changes.Figure 13.Friction force versus sliding velocity.…”
Section: Resultssupporting
confidence: 89%
“…The important point is that in this study, each contact roller is modeled as EHL contact in mixed lubrication regime and has a nonlinear behavior. Changing the external load or preload causes stiffness nonlinearity in the contact interface (Dunaj et al, 2019; Pawełko et al, 2014). Increasing the preload in EHL contact affects the hydrodynamic, asperity, and oil film pressure distribution, that is, as the applied load increases, the oil film thickness decreases, leading to more load carrying share by asperity contact in the mixed lubrication regime.…”
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.
“…As shown in Figure 13, when an external load, 92000 N, is applied, an upward shift in the hysteresis curve occurs. According to the result presented in Figure 13 and consistent with the similar studies (Dunaj et al, 2019; Pawełko et al, 2014), any changes in the preload vary the nonlinearity of stiffness of the system and the roller contact. The coupling effects between the lubricated linear roller guideway’s normal and tangential dynamics affect horizontal stiffness and contact restoring forces because of vertical stiffness changes.Figure 13.Friction force versus sliding velocity.…”
Section: Resultssupporting
confidence: 89%
“…The important point is that in this study, each contact roller is modeled as EHL contact in mixed lubrication regime and has a nonlinear behavior. Changing the external load or preload causes stiffness nonlinearity in the contact interface (Dunaj et al, 2019; Pawełko et al, 2014). Increasing the preload in EHL contact affects the hydrodynamic, asperity, and oil film pressure distribution, that is, as the applied load increases, the oil film thickness decreases, leading to more load carrying share by asperity contact in the mixed lubrication regime.…”
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.
“…Then, analytically obtained results of stiffness model were compared with the experimental results. Also, Dunaj et al [8] presented a methodology to determine the stiffness of machine tool load-bearing system using substructuring method. They proposed a simplified model of stiffness of the linear guide with a preload (regardless of used types of carriages), moreover, they developed an equivalent contact model which allows to replace the ball with four rod elements of equivalent stiffness.…”
This paper presents an innovative system determining machine tool quasi-static stiffness in machining space, so-called Stiffness Workspace System (SWS). The system allows for the assessment of the accuracy of a machine which has become a vital aspect over past years for machine tool manufacturers and users. Since machine tools static stiffness is one of the main criteria using to evaluate the machines' quality, it is crucial to highlight the relevance of experimental and analytical stiffness determination methods. Therefore, the proposed method is applied to estimate the spatial variation of static stiffness in the machine tool workspace. This paper describes the SWS system—its design, working principle, mounting conditions and signal processing. The major advantage of the system is the capability to apply forces of controlled magnitude and orientation as well as simultaneously measure the resulting displacements. The obtained results give possibility to estimate and evaluate static stiffness coefficients depending on the position and direction under loaded conditions. The results confirm the validity of the analyses of spatial stiffness distribution in the machine workspace.
“…The guiding systems of the Y and Z axes were modeled in accordance with the method contained in [26]. The feed drive systems were modeled in accordance with [27] and [28].…”
Section: Formulation Of a Substructural Fem Modelmentioning
Designing machine tools for in situ machining is a challenging task due to their unique structures and restrictive functional requirements. Such a machine tool should be characterized by low mass, adequate machining accuracy and high machining stability. The paper presents the design of an ultra-light, axisymmetric, portable machine tool for in situ flange face milling. Due to a high compliance of the designed machine tool and a need of maintaining its low mass, structural modification aimed at stability increase were highly limited. Therefore, it was decided to select the spindle ensuring machining stability. The selection of the spindle was supported by finite element analysis. Based on numerical analyzes results a prototype with a proper spindle was build. Then, the accuracy of the finite element model and the predicted stability were experimentally verified, showing a good agreement with the real counterpart. Finally, two general conclusions were formulated: (i) in the case of machine tools characterized by high compliance and limited possibility of modifying their design a good choice may be the selection of a spindle that allows to obtain parameters that ensure stable machining, and (ii) it is possible to build low-dimensional, reliable finite element model without using substructuring or reduction methods, and a well-thought-out discretization and replacement elements of complex load bearing systems instead.
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