Search

The hydrostatic turntable is a critical component of numerous CNC machine tools, as it performs a supporting function and enables precise rotary motion. To ensure that high-precision CNC machines can operate under heavy loads, it is imperative to minimize power consumption. The power consumption of a hydrostatic turntable is affected by various factors, such as oil viscosity, initial oil film thickness, and oil pad structure. This study focuses on investigating a hydrostatic turntable with internal feedback. The Reynolds equation of the sector oil pad is solved using the finite difference method to establish the pressure distribution model. Subsequently, the study examines the power consumed by the axial oil pad at different initial oil film thickness, lubricating oil viscosity, and sealing edge width. To minimize power consumption caused by the axial oil pad, this paper employs the genetic algorithm to identify optimal design parameters within specified constraints. Additionally, the load-bearing performance of the optimized axial oil pad is checked to ensure that the load-bearing capacity and stiffness meet the requirements. Finally, the use of simulation software for oil pads in finite element simulation can preliminarily demonstrate the reliability of the proposed method. [ABSTRACT FROM AUTHOR]

FMS reliability cannot be accurately evaluated without considering coupling relations between system elements. This paper presented a hierarchical and quantitative evaluation index system for FMS based on Petri net models and judgment matrix construction. In the proposed system, influencing factors and their coupling relations related to system elements including human, control systems, and mechanical equipment are analyzed. Based on the above analysis, FMS is described as a hierarchical system composed of the whole-level system, processing system, and transfer system. Petri net for the running process of each system is modelled for reliability simulation analysis. And judgment matrices of indexes are constructed and combined with simulation of Petri net models to determine weighted values for influencing factors. Finally, an application example is completed to verify the effectiveness of the proposed system. Results indicate that the system can help to quantitatively evaluate the reliability of FMS based on availability indexes of elements and clearly show weaknesses of the system from element level, which is a significant basis for the FMS reliability improvement during the design stage. [ABSTRACT FROM AUTHOR]

In the reliability optimization design field of CNC machine tools, reliability allocation plays a significant part, which has the characteristics of high complexity and strong uncertainty. Traditionally, reliability allocation methods have the disadvantages of a single allocation influence factor, too subjective or too objective, not flexible enough, etc. To solve the related problems, a novel reliability allocation method for machine tools is proposed, which combines subjective and objective weightings, and a variety of influencing factors are considered comprehensively. To deal with the characteristic of uncertainty and fuzziness in machine tool reliability analysis, different intuitionistic trapezoidal fuzzy numbers (ITrFNs) are allocated according to the importance of influencing factors. As the subjective method, the analytic hierarchy process (AHP) can reflect the decision maker's subjective preferences of machine tool influence factors, while the grey relational method (GRA) can analyze the relationship between data which is adopted as an objective weighting method. The reliability of each subsystem is obtained by combining the two methods. Finally, the validity of the proposed method is proved by an illustration analyzing and comparing it with the traditional AHP method and fuzzy allocation methods. [ABSTRACT FROM AUTHOR]

In the state of machining service, to evaluate the machining accuracy reliability of multi-axis CNC machine tools, analyze the accuracy failure mode and the reliability sensitivity under the failure mode, this paper proposes a research method by the cross-correlation studies of geometric error parameters to improve and promote the accuracy reliability of CNC machine tools. Firstly, by multi-body system theory, the homogeneous coordinate transformation matrix between each body of the machine tool is established, and the spatial machining accuracy model is constructed. At the same time, considering the time series problem in the measurement process of geometric error parameters, this paper studies the correlation between the error parameters for reliability analysis and proposes a novel reliability analysis index for each measurement point in the machine tool workspace. To validation of the method, the analysis results of this paper are compared with those by Monte Carlo simulation. In addition, the accuracy failure conditions of the machine tool are studied, the failure state function of machine tool accuracy is established, and the accuracy failure modes that may occur are analyzed from this, to carry out the accuracy failure sensitivity analysis under the failure mode, and to identify key geometric errors which have a great impact on the machining accuracy reliability of machine tool in the failure mode. Finally, taking a 3-axis machine tool as an example, according to the analysis results, this paper puts forward measures to improve the accuracy reliability and verifies the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Bolted connections are widely used in the machine tool manufacturing and equipment. As it is well known, bolt preload will be attenuated by the vibration of machine tools, which will degenerate the working life of machine tools. In this paper, a new experimental design method is introduced into the study on bolt preload attenuation: the quadratic general rotary unitized design. The dynamic analysis of the bolted connection is carried out based on a finely fragmented numerical model to interpret the generation of fretting slip and the reason for the loosening of bolts. The alternating load cyclic vibration test, implemented on the bolted joints, can provide the vibration response under the influence of different working factors. Statistical test and analysis are performed on the quadratic regression mathematical model of the bolt preload attenuation, and the principal working factor that affecting the bolt preload attenuation under vibration can be obtained. Based on the analytical result, the combination of the working factors at the lowest bolt preload attenuation rate, which can effectively slow the bolt looseness, is investigated. The results of this study can provide an experimental basis for improving the machining stiffness of machine tools. [ABSTRACT FROM AUTHOR]

Meshing backlash mainly determines the transmission accuracy of harmonic drive, which is an important index in design. In this paper, a design method for short tooth involute profile is proposed. By intercepting part of the tooth profile, meshing interference of the addendum can be effectively avoided. Based on the dimensions of over pins of circular spline and flexspline, a calculation method of tooth thickness deviation is proposed, and the positive and negative tooth thickness deviation are defined. Involute functions need not be calculated by this method, which simplifies the solution process. By discretizing the teeth profile points of circular spline and flexspline, a calculation method of time-varying backlash is proposed, the variation of backlash in meshing in and out is analyzed, and the influence law of tooth thickness deviation on backlash is studied. On this basis, an algorithm for adjusting the radial deformation to compensate for the backlash is proposed. The results show that the excessive backlash in the meshing area can be reduced by increasing the radial deformation. When meshing interference occurs, the interference-free meshing can be realized by decreasing the radial deformation. [ABSTRACT FROM AUTHOR]

The superior performance of machining large parts with the free-form surface is demonstrated by a five-axis gantry machine tool composed of a gantry mainframe and a milling head. A turntable is used to adjust the position of the workpiece rather than a linear guideway when machining impellers or integral turbines. Furthermore, collisions between adjacent blades are almost unavoidable in the machining region, which is relatively narrow for milling heads. The majority of existing methods attempt to solve the problem by changing the tool's tilt angle. However, when an end-mill cutter is employed, this method will deteriorate surface quality and reduce efficiency. On the condition that the milling head has three rotary axes (TRA), a novel NC code generation method with a fixed tool orientation vector for narrow space surfaces is proposed in this paper. When the geometrical model, considered a supplementary condition, is combined with the kinematics model, an inverse kinematics solution to a general multi-axis gantry machine tool with a TRA milling head is obtained. The problem of multi-axis coupling in the inverse kinematics model is solved by combining the iteration method and geometrical model. In the narrow space for a milling head, the redundant degree of freedom, provided by a machine tool equipped with a TRA milling head, enables adjusting the posture of the milling head without changing the tool orientation vector. Feature points are extracted by preprocessing points selected from machined parts and the TRA milling head to choose the feasible posture and simulate the machining process. Collisions in the narrow space are successfully avoided throughout the cutting process. The NC code generation method is verified on CAM software and cut experiments, proven effective in this paper. [ABSTRACT FROM AUTHOR]

For the flat plastic parts with the size range of 200 to 1300 mm, the structural parameters decision model of injection mold gating system is established in this paper. Firstly, the relationship between the warpage and the structural parameters of gating system is fitted by Kriging model, and the minimum warpage is optimized by genetic algorithm (GA) to obtain the best structural parameters. Secondly, the best structural parameters of gating system corresponding to 16 groups of plastic parts are taken as samples, and the relationship between the structural parameters of gating system and the size parameters of plastic parts is established by Kriging model. In addition, K-means is used to reduce the number of the structural parameters of gating system from 5 to 2, in order to improve the accuracy of decision model. Finally, the size parameters of plastic parts are input to the decision model to obtain the structural parameters of gating system. Through the verification of mold flow analysis experiment, the structural parameters of gating system obtained by this method meet the design requirements and can effectively shorten the structural design cycle of injection mold. [ABSTRACT FROM AUTHOR]

Harmonic drive (HD) is one of the core components of the robot joint. Studies show that tooth shape design and meshing characteristics of the HD directly affect the motion control accuracy and vibration characteristics of the robot. In the present study, common coordinate systems are established for three tooth profiles to analyze the differences between them. To this end, expressions for the double circular arc common-tangent tooth profile (DCTP), cycloid common tangent tooth profile (CCTP), and the involute tooth profile (ITP) are established in the same coordinate system. By applying the envelope conjugate theory, the conjugate existent domain (CED) and conjugate tooth profile (CTP) of the HD transmission are solved independently for each profile. Furthermore, the influences of tooth profile parameters on both the CTP and CED are analyzed. Obtained results show that both the DCTP and CCTP have more robust envelope processes when compared with the ITP. Moreover, it is found that both profiles can achieve the second conjugate and two-point conjugate engagement through applying variations in the tooth shape design parameters. It is concluded that meshing performances of the DCTP and CCTP are better than that of the ITP, providing guidelines for the future development of the harmonic reducer tooth shape design. [ABSTRACT FROM AUTHOR]

In order to improve the printing quality, this study focused on the thermo-fluid-solid coupling process of ink roller-ink. One of the highlights of this study is to consider the influence of temperature on the rubber hyperelastic parameters, viscoelastic parameters, and ink viscosity. The other highlight is to improve the elastohydrodynamic lubrication theory and Hertz contact theory through the rubber elastic modulus, which is determined by the relaxation curve considering the temperature and working conditions. Furthermore, based on the improved theory, the thermo-fluid-solid coupling model of ink roller-ink was established. Finally, the effect of temperature on the coupling process was analyzed. The results show that under the working conditions, with increasing temperature from 20 °C to 40 °C, the contact half-width increases from 4.2335 mm to 4.4701 mm, and the minimum ink film thickness decreases from 0.5097 mm to 0.1410 mm, and the maximum ink pressure decreases from 0.6802 MPa to 0.6618 MPa. [ABSTRACT FROM AUTHOR]

The stiffness and damping modeling of joint surfaces are important for analyzing the dynamic characteristics of bolted joints, which has a great influence on the working precision of the machine tool. In this paper, a damping model is presented to predict the tangential damping of the joint accurately. The fractal theory is introduced to characterize the rough contact surface by using fractal dimension D and fractal roughness parameter G. For each micro-contact, the contact region can be divided into stick section and slip one. The energy dissipation of the micro-contact, which can be described as the tangential damping of bolted joint, emerges in the slip section. The physics-based friction coefficient is introduced to define the energy dissipation function based on the relationship between the deformation of micro-contact and the normal pressure. The energy dissipation factor and the proportional damping of the micro-contact can be obtained. The total tangential damping of bolted joint can be obtained by integrating the whole contact surfaces. Experimental set-up is designed to verify the proposed model. Compared with the constant friction coefficient damping model, the results show that the proposed model can more accurately describe the tangential damping of bolted joint. [ABSTRACT FROM AUTHOR]

Harmonic drives are the core components to enable movement in industrial robots. Unfortunately, the deformation of flexspline causes obvious partial axial load on gear engagement. This synthetic error leads to a series of additional problems, such as the deterioration of transmission quality, and the reduction of both precision and fatigue life. This study focuses on a harmonic drive with a double circular-arc tooth profile. A coordinate transformation is carried out based on the kinematics of harmonic drives. On this basis, the conjugate tooth profile of a circular spline is derived. A simulation model is developed based on the motion relationship for harmonic transmission. The effect of inhomogeneity of the load distribution on the surface of the gear teeth was investigated using the partial axial-load index. The effect of different factors on the partial axial load is analyzed. To reduce the effect of partial axial load of flexspline, we select a suitable material and wall thickness. For a certain practical range, both tooth width and chamfering of the flexspline teeth help reduce the partial axial load and increase the flexspline length. These conclusions enable improvements of future designs of reliable flexspline. [ABSTRACT FROM AUTHOR]

Grinding force is an important factor to consider in the field of precision manufacturing. In this study, a model of the thread grinding force in inner thread grinding that takes into account the thread helix angle and effect of grains overlapping is presented. The average undeformed chip thickness of a single abrasive grain can be obtained based on the Rayleigh probability density function. The contact length is assumed to be the arc contact length and is calculated based on the movement of an active grain. In addition, the effective grain overlap coefficient can be defined as the ratio of the effective area removed by a single grain to the cutting area without overlapping grains. The normal force is generated by material deformation and friction. Similarly, the tangential force is produced by material deformation and tangential friction. The normal and tangential forces can be calculated by considering a micro abrasive grain. Experiments were conducted to calculate the coefficients of the grinding force model in order to validate the model. Scanning electron microscopy was performed to determine the relationship between the normal force and the largest pit on the inner thread surface. Normal and tangential forces were analyzed under different spindle speeds, workpiece speeds, grinding depths, and thread helix angles. The numerical results suggest that grinding force is affected by the thread helix angle and friction forces; moreover, grain overlap cannot be ignored. Finally, a linear relationship between the normal force and the largest pit diameter was derived and used to determine the optimal normal force for generating improved inner thread surfaces. The proposed model provides a theoretical basis for the optimization of high-speed high-precision inner thread grinding. [ABSTRACT FROM AUTHOR]

Estimating the torsional stiffness has always been the primary issue in analyzing the dynamic characteristics of cycloid gears. The traditional method of obtaining torsional rigidity involves calculating the ratio of the input torque and rotation angle, treating the deformation of cycloid gear as a black box. In order to thoroughly understand the rotation angle caused by the local contact deformation of each cycloid pin gear, a Majumdar–Bhushan contact model and the finite element method are combined to express the normal contact stiffness. By multiplying the normal contact stiffness of each pin gear and the arm of normal contact force, the torsional stiffness of the cycloidal pin wheel system can be calculated. Experiments are conducted to establish the relationship between the torsional stiffness and roughness parameters of the machined tooth surface. The effect of input torque on the torsional stiffness has also been analyzed. This study formulates a relationship between the torsional stiffness and surface characteristics of cycloid gears, which can help improve their design and manufacture in the future. [ABSTRACT FROM AUTHOR]

The heavy-duty machine tool is usually assumed in the concrete foundation, in which the machine tool-foundation joints have a critical effect on the working accuracy and life of heavy-duty machine tool. This paper proposed a novel contact stiffness model of concrete-steel joint based on the fractal theory. The topography of contact surface exist in concrete-steel joint has a fractal feature and can be described by fractal parameters. Asperities are considered as elastic, plastic deformation in micro-scale. However, the asperities of concrete surface will be crushed when the stress is larger than their yield limit. Then, the force balance of contact surfaces will be broken. Here, an iteration model is proposed to describe the contact state of concrete-steel joint. Because the contact asperities cover a very small proportion (less than 1%), the load on crushed asperities is assumed carried by other no contact asperities. This process will be repeated again and again until the crushed asperities are not being produced under external load. After that, the real contact area, contact stiffness of the concrete-steel joint can be calculated by integrating the asperities of contact surfaces. Nonlinear relationships between contact stiffness and load, fractal roughness parameter G, fractal dimension D can be revealed based on the presented model. An experimental setup with concrete-steel test-specimens is designed to validate the proposed model. Results indicate that the theoretical vibration mode shapes agree well with the experimental variation mode shapes. The errors between theoretical and experimental natural frequencies are less than 4.18%. The presented model can be used to predict the contact stiffness of concrete-steel joint, which will provide a theoretical basis for optimizing the connection characteristic of machine tool-concrete foundation. [ABSTRACT FROM AUTHOR]

In the previous study, the minimum time and energy have been both considered to improve the efficiency and reliability of the manipulator operations. For further guaranteeing the tracking precision of end effector, a TE-E optimal planning technique is presented in this paper to optimize the trajectory of end effector. TE-E means two optimization objectives and one constraint condition: T is the total motion time, the first E is the total kinetic energy consumption and the second E is the motion error due to trajectory planning. In this technique, a local optimization process is completed to find a time-energy optimal trajectory, which could improve the movement efficiency and reliability. In this local process, the screw theory is used to obtain the forward and inverse kinematic models for simplifying the computation. The multi-solution situation in inverse kinematic is considered. The modified cubic spline interpolation is applied in the joint space to obtain the good motion stability. The objective function is defined as the weighted sum of two optimization objectives. The local optimal trajectory is obtained by using the particle swarm optimization (PSO) algorithm. Finally, the motion errors are considered as a condition to determine the number of the path points and obtain the final optimal trajectory that has good tracking precision. The simulation experiment for QJ-1 welding manipulator is completed to verify the reliability and validity of this technique. In the optimal trajectory, the relationships between the motion time and parameters for each joint show a good performance in the motion. The comparison of motion errors obtained by using the previous and presented methods proves the validity of this presented technique. [ABSTRACT FROM AUTHOR]

The solvent-shift method was used to identify appropriate polymers that inhibit the growth of felodipine crystals by monitoring particle size in supersaturated drug solutions in the presence of different polymers. We speculated that there would be an intermolecular interaction between the selected polymer (zein) and felodipine by extrapolating the inhibitory effect on crystal growth and then used the selected polymer as a carrier to prepare solid dispersions. The formulations were characterized by crystalline properties, thermodynamics of mixing, dissolution behavior, and physical stability. Powder x-ray diffraction and differential scanning calorimetry experiments indicated that amorphous solid dispersions were formed when the proportion of felodipine was < 30% (w/w). Stability tests showed that a solid dispersion with 20% felodipine remained in an amorphous state and was stable under accelerated storage conditions for 6 months. The dissolution rates of solid dispersions were significantly greater than those of the active pharmaceutical ingredient or physical mixtures. Analysis by Fourier-transform infrared spectroscopy and Raman microspectroscopy indicated the formation of intermolecular interactions between zein and felodipine. The study demonstrates the successful application of the chosen polymer as a carrier in solid dispersions and validates the concept of extrapolating the inhibitory effect on crystal growth to intermolecular interactions. [ABSTRACT FROM AUTHOR]

This work aims to propose a trajectory planning technique to minimize the end-effector synthesis error for industrial robots, while obtaining a stable movement. With ER3A-C60 robot as a research subject, the kinematic and dynamic models are established by using screw theory and Kane equations, and based on that, the end-effector synthesis error is modeled by considering the effects of interpolation algorithm and flexibilities of all joints. The septic polynomial is used to interpolate the via points in each joint space to obtain a stable movement. Finally, the PSO algorithm with suitable parameters is applied to find the minimum synthesis error under kinematic and dynamic constraints. The results show that the optimal synthesis error decreases by 88.94% compared with the initial one, the angular parameters are all far less than the limitations of joints and the optimal movement has a high stability, and this optimal trajectory has better overall performance than that based on the previous technique (with the minimum total motion time). The main contribution is that the proposed trajectory planning technique can significantly improve the tracking precision of the end effector while controlling the motion time within a given span under the requirements of continuous path control. [ABSTRACT FROM AUTHOR]

The stability of the tribological properties of polymer coatings is vital to ensure their long term use. The superlubricity of the poly(vinylphosphonic acid) (PVPA)-modified Ti6Al4V/polytetrafluoroethylene (PTFE) interface can be obtained when lubricated by phosphate-buffered saline (PBS, pH = 7.2), but not when lubricated by deionized water and ethanol. Therefore, the mechanisms for the superlubricity of PVPA coatings affected by lubricant were investigated in detail. The stability of the PVPA coatings and their compatibility with the lubricant are critical factors in realizing ideal tribological properties of PVPA coatings. Robust PVPA coatings are stable under a wide range of pH values (6-10) using PBS as the basic solution, and are also characterized by superlubricity. The hydrolysis kinetics of phosphate anhydride is the main reason for the pH responses. In addition, along with stability, PVPA coatings exhibit different friction coefficients in salt solutions which are composed of various ions, which indicates that the compatibility between PVPA coatings and the lubricant can be used to regulate the superlubricity properties. Based on a fundamental understanding of the mechanism of surperlubricity by considering the effects of the lubricant, PVPA coatings with stability and perfect tribological performance are expected to be applied in more aspects. [ABSTRACT FROM AUTHOR]