Ball Screw Feed Research Articles

Research on Global Nonsingular Fast Terminal Sliding Mode Control Strategy of Ball Screw Feed System Based on Improved Double Power Reaching Law

Research on Global Nonsingular Fast Terminal Sliding Mode Control Strategy of Ball Screw Feed System Based on Improved Double Power Reaching Law

Active prediction compensation strategy: A new positioning compensation technique for improving the accuracy of the dual ball screw feed mechanism under load

The dual ball screw feed mechanism (DBSFM) is commonly employed in high-end machining applications. However, its accuracy is challenging to enhance due to variations in the axial stiffness of the dual actuators under load, making geometric error compensation (GEC) difficult. To address this, our research establishes a comprehensive error model that integrates geometric error and load-induced error (LIE) to improve feeding accuracy. The axial stiffness matrix of the DBSFM is identified using motor current information, and an active prediction error matrix is defined based on the geometric error model, milling force model, and axial stiffness matrix. We propose and analyze the active prediction compensation (APC) strategy as a new method to enhance accuracy under load. Experimental validation using a gantry-type machine tool demonstrates that the APC strategy can reduce the positioning error of the DBSFM to ±2 μm under load, representing significant improvements over the established GEC method. Specifically, the APC strategy achieves a 53.07% and 57.04% enhancement in accuracy along the two axes. This work illustrates the effectiveness of the APC strategy in reducing positioning errors and improving feeding accuracy in DBSFM machining processes.

Direct torque control for PMSM based on the RBFNN surrogate model of electromagnetic torque and stator flux linkage

Direct Torque Control (DTC) is widely used in motion control of motors. Classical DTC utilizes the Park transformation(dq-model) or observer to estimate the stator fluxlinkage and electromagnetic torque. However, the dq-model and observer lack descriptions of the cogging torque and magnetic saturation in permanent magnet synchronous motors (PMSM). This paper proposes a novel method based on the surrogate model to estimate stator fluxlinkage and torque for PMSM DTC. First, a finite element model (FEM) was established based on the parameters of PMSM. Using the FEM and Latin hypercube sampling (LHS), a surrogate model for estimating the stator fluxlinkage and torque of PMSM was constructed. The stator fluxlinkage and torque surrogate model, active flux observer, and dq current model under different control methods are constructed, respectively. The servo control parameters were tuned using the extended symmetric optimum algorithm, and simulation and experiments were conducted. Finally, electromechanical coupling models with a ball screw feed system were built based on various control and feedback methods. Simulation and experiment results indicate that the surrogate model reduces torque ripple, stator fluxlinkage offset, and feed system tracking error.

Research on axial nonlinear vibration characteristics of ball screw feed system considering segmented restoring force

Taking the ball screw feed system as the research object, the two degree of freedom axial dynamic model of the system is constructed firstly. Based on Hertz contact theory, when the ball screw pair adopts variable lead self-preloading to eliminate the assembly clearance between the ball and raceway, considering the nonlinear segmented axial elastic recovery force generated by the uneven contact deformation between the ball and raceway under the action of external excitation force, further derive the nonlinear dynamic equation group of the system. Next, the fourth-order Runge-Kutta method was used to numerically solve the equation system, obtaining the system’s two and three-dimensional phase diagrams, Poincaré sections, time-domain waveform diagrams, frequency spectra, and bifurcation diagrams. Then, the effects of damping constant, initial contact angle between ball and raceway in ball screw pairs, and number of balls on the system’s response characteristics were analyzed, and the influence of external excitation forces on system stability was further studied. Finally, it was verified through experiments that the axial vibration of the system is indeed nonlinear vibration, providing a theoretical basis for the study of the dynamic characteristics of the ball screw feed system.

Design and simulation of eco-friendly smartphone controlled forklift

The recent revolution in industrial technology increased the demand for unmanned forklifts that can be operated remotely. Unmanned forklifts eliminate the effort needed to train a highly qualified operator and reduce the accident rate due to driver fatigue. Currently, the operation of forklifts depends on either hydraulic systems or gasoline which has a negative impact on the environment. The increased awareness of the environmental threats urged the manufacturers to replace conventional forklifts with electrical ones. Unmanned electrical forklifts have a high cost that is considered a burden for developing countries, especially when being used in small warehouses. Thus, this paper presents an innovative approach for designing a semi-automated eco-friendly forklift suitable for small warehouses operated using a smartphone application. The forklift is designed to lift a maximum load of 200 N using a ball screw feed mechanism, characterized by its light weight and its ability to withstand corrosion. The structural stability of the forklift has been investigated using SolidWorks simulation. The designed model has been imported to MATLAB Simulink to estimate the suitable battery size required for forklifts’ operation in addition to calculating the total energy consumed during one complete work cycle. It is found that only 6.7 % of the energy is dissipated which promotes the energy-saving capabilities of the designed forklift.

Dynamic vibration modeling of the ball screw feed system considering travel deviation

The vibration problem of the ball screw feed system in working conditions limits its application in precision machinery. However, few studies have developed models to investigate the vibration mechanism of the ball screw feed system in running status. In this paper, a dynamic model considering travel deviation and ball motion is proposed to explain the vibration mechanism of the ball screw feed system. This model is numerically solved and experimentally verified. Simulation results showed that, the travel deviation mainly affects the vibration amplitude rather than the frequency when the rotation speed is constant. Higher travel deviation introduces higher vibration amplitude, and the vibration of the feed system is more sensitive to the travel deviation of low frequency.

An analysis of heat source contribution and design of optimal cooling method for ball screw feed system

ABSTRACT Fundamentally, the heat source in the ball screw feed system accounts for the thermal behavior of ball screw. Due to the fact that cooling resources are not always sufficient, the main objective of this paper is to allocate cooling resources for multiple heat sources. The network model of ball screw thermal deformation and temperature at the heat source is constructed based on wavelet neural network (WNN). Combined with the mathematical analysis results, the explicit mathematical expression of thermal deformation and heat source under this working condition is deduced, and the explicit mathematical expression of heat source contribution is further obtained. After that, keeping the total heat source contribution constant under this working condition, the particle swarm optimization (PSO) algorithm is used to determine the heat source contribution distribution that can minimize the thermal deformation of the ball screw. Finally, through the design of the ball screw cooling system, the minimum thermal deformation of various heat sources at different cooling ratios under constant cooling flow is explored. The contribution of heat source is basically consistent with the optimal cooling ratio, which not only verifies each other, but also shows that the uniform cooling of heat source can best inhibit thermal deformation.

Thermal error compensation for a fluid-cooling ball-screw feed system

Thermal deformation resulted from the heat generated by the motor and the frictional behavior between the moving pairs significantly reduces the positioning accuracy of feed systems and thus influences the machining quality of parts. The internal cooling ball screw takes advantage of the cooling liquid to strengthen the convection heat transfer actively and suppress the temperature rise. Owing to the intermittent starting and stopping operation modes of the cooling machine, the heat flux arising from various heat sources cannot be completely removed by the coolant; consequently, thermal errors still exist. In this study, K-means++ clustering and correlation analyses were used to select thermal key points. A difference equation model of the thermal error was established to describe the transient change relationship between the temperatures of the thermal key points and the ball-screw shaft elongation, which was separated from the thermal characteristic experimental data according to the linear superposition principle of geometric and thermal errors to constitute the positioning error. The model parameters were identified using the least-squares method, and a thermal error compensation strategy based on the origin offset method was implemented. Experiments comparing the thermal error compensation of the three models under different working conditions were conducted to confirm that the thermal error difference equation model can be applied to reduce the thermal error of the feed system effectively and maintain excellent robustness.

Dynamic signal analysis based monitoring for ball screws preload deterioration

The ball screw feed system has been an important part of precision machinery and machine tools. Its preload degradation affects machining accuracy and the issue should be first coped with per manufacturers’ suggestion. The study aims to apply the adaptive order tracking technique and other spectrum analysis schemes as well to differentiate the preload conditions of ball screws. Here varied preload conditions (4 %, 1 % preload and 12um backlash) were considered for monitoring during normal operation. The sideband energy of higher harmonics of ball pass frequency (BPF) are featured to highlight the preload degradation. The control charts together with sideband ratios were established to differentiate preload conditions and single out backlash ball screws.

The Design of a Tracking Controller for Flexible Ball Screw Feed System Based on Integral Sliding Mode Control with a Generalized Extended State Observer

This article proposes a servo control strategy for compensating matched and mismatched perturbations in flexible ball screw feed systems to improve their tracking performance. The perturbations that satisfy or dissatisfy the matching conditions include external disturbances, parameter uncertainties, and unmodeled dynamics. The flexible ball screw feed model includes both a rigid body and first-order axial structural dynamics. A generalized extended state observer is adopted to observe the matched and mismatched perturbations and various state variables of the system, and an improved integral sliding mode controller is proposed that can simultaneously compensate for the perturbations of the system that satisfy and dissatisfy the matching conditions. In addition, vibration compensation is designed for first-order axial vibration of the system to develop a controller that can quickly and accurately track the ideal reference trajectory, suppress system structural vibrations, and be robust to time-varying uncertainties and external disturbances. Finally, the tracking performance, anti-interference performance, and vibration suppression performance of the designed controller are verified via simulation and comparative experiments.

Research on load distributions for ball screw feed system with assembly errors

This paper proposes a load distribution model for the ball screw feed system with the assembly errors of the guide rails, which is used to predict the variation law of the load distributions for the ball screws and carriage-guide rail systems. Firstly, under the action of the contact loads of the ball screws, the bending deformation of the screw axis corresponding to each ball is derived. Secondly, a static model of the machine tool bearing system with the assembly errors is established. Then, the load distribution model of the ball screw feed system is proposed based on the load balance and deformation compatibility equation, and the solution process of the proposed model including judging the ball-raceway contact state is given. In addition, the results are compared with those of the existing models to demonstrate the validity of the proposed model. Finally, the relation between the curve shape of the load distribution and the bending of the screw shaft axis is explored, and the variation law of the load distributions for the feed system under the effects of the axial, radial loads, and assembly errors is discussed.

Time-varying thermoelastic coupling analysis of heat source of ball screw feed drive system

Time-varying thermoelastic coupling analysis of heat source of ball screw feed drive system

Research on the multi-physical coupling characteristics of the machine tool and milling process based on the systematically integrated model

Good machine tool precision and a stable milling process are important foundations for obtaining high-quality qualified parts. During the machining process, the machine tool and the milling process will impact each other, and further jointly affect the motion accuracy as well as part quality. This paper makes a deep analysis of the machine tool and milling process from a new perspective, which regards the machine tool and milling process as a coupled entirety, and studies the interaction between them from a systematic perspective. By establishing a systematically integrated model of the ball screw feed system and milling process, the multi-physical simulation of the whole system is realized with the consideration of multi-source harmonics. The electrical-magnetic-mechanical-kinematic coupling characteristics between the machine tool and the milling process are investigated based on the established model and experiments. The research results show that the servo system and the milling process are two major harmonic sources in the system that generate low-medium frequency and medium-high frequency harmonics, respectively. As the machining process progresses, these harmonics will be transmitted and coupled through the servo motor, mechanical structure, and feedback signals, leading to the fluctuation in the motion of the worktable and the influences on the surface quality of the final part. A type of part surface defect that can only be explained by integrated analysis of the whole system is also demonstrated. The research work indicates that the machine tool and milling process is an integrated system with strong coupling characteristics. It's of great significance to study them from a systematic perspective.

Temperature field modeling and vibratory-thermal coupling analysis of ball screw feed system

Thermal deformation and dynamic response are essential factors affecting the accuracy of the ball screw feed system. In this paper, the temperature field model of the thermal network of the system and the axial dynamic model are established. The relationship between the heat generation of components and system response is analyzed by coupling models. The temperatures of related components are obtained by solving the thermal balance equations. The obtained temperatures are substituted into the dynamic model to investigate the response of the system considering the thermal effect. According to the displacement response of the system, the contact forces of the balls are calculated and substituted into the thermal network model to explore the influence of the response on heat generation. This work also gives a method to solve the relatively stable temperatures of vibratory-thermal coupling. The models of the system are verified by experiments, and the influences of related parameters on heat generation and the response of the system are also discussed.

Dynamic analysis and modeling of ball screw feed system with a localized defect on the support bearing

Dynamic analysis and modeling of ball screw feed system with a localized defect on the support bearing

Influence of nonlinearity of servo system electrical characteristics on motion smoothness of precision CNC machine tools

The ball screw feed system of CNC machine tools is a typical mechatronic motion mechanism. During the operation of the machine tool, not only the dynamic characteristics of the mechanical structure will affect its performance, but also the electrical characteristics of the servo system will affect the movement of the worktable, which will lead to displacement fluctuation and bring adverse effects on the precision of the machine tool and even the quality of the processed parts. Therefore, the electrical system and the mechanical system are strongly coupled to each other due to their high integration. In this paper, the fluctuation of current, torque, and displacement during the motion of the worktable is studied. Firstly, the mechatronic model of the ball screw feed system, which not only consists of all components of the feed system but also takes different nonideal characteristics of each component into consideration, is established to realize the physical simulation of the whole system. Then, with the consideration of the impacts of inverter dead zone, motor cogging torque, rotor mixed-eccentricity, winding asymmetry, and collecting error of feedback current, the frequency components of fluctuations caused by the nonlinear electrical characteristics of inverter and servo motor in the servo drive system are obtained. Finally, the influences of load, feedrate, servo parameters, and dynamic characteristics of mechanical structure on fluctuation are analyzed in the time domain and frequency domain. The phenomenon of displacement fluctuation of the worktable caused by the electrical characteristics of the servo system indicates that it is necessary and meaningful to build the integrated model to study the ball screw feed system from the view of the whole system.

Calculation of the Heat Flux from a Ball Screw Nut to the Nut Raceway

In the field of precision machining, temperature fluctuation tends to cause the most significant machining errors. In particular, heat, which is generated in the nut of the ball screw feed system during movement, can deform the screw shaft significantly. In order to calculate and evaluate the thermal deformation of the ball screw shaft, the rate of the heat transfer from the nut to the screw shaft must be known. This rate can be calculated by subtracting the heat transfer rate to the nut raceway from the heat generation rate of the nut. Hence, it is necessary to calculate the heat flux from the nut to the nut raceway. This paper introduces a novel method to calculate the heat flux from the nut to the nut raceway. The new approach also enables calculations for different operating conditions. Furthermore, an experimental setup is established to measure the temperature increase, from 0 to 180 s after the nut starts moving, for various operating conditions. It is then theoretically shown that the 0–180 s temperature increase/heat flux curves for the nut are “universal”, i.e., the curve remains unchanged for the different operating conditions. Subsequently, a thermal model using the finite element method (FEM) is developed to simulate the nut temperature increase over time, which is then compared with the experimental data. As a result, it becomes possible to determine the heat flux from the nut to the nut raceway and calculate the 0–180 s temperature increase/heat flux curve (ΔT˜0~180s,Training Data) for the training group. Finally, the heat flux from the nut to the nut raceway is calculated for ten different operating conditions in the test group using the 0–180 s temperature increase/heat flux curve of the training group (ΔT˜0~180s,Training Data). The corresponding temperature curves are then calculated by inputting the values of the heat fluxes into the FEM model. The highest root mean square error (RMSE) between the calculated and experimentally measured temperature increase was 0.16 °C for Test 7 (the error was 10.7%). This result indicates that the new method is valid and feasible for calculating the heat flux from a ball screw nut to the nut raceway.

Variable-Coefficient Dynamic Modeling Method for a Ball Screw Feed System in the No-Extra-Load Running State

In a ball screw feed system of high-speed/high-acceleration machine tools, large frictional and inertial forces may change the real contact state of the kinematic joints, resulting in changes in the contact and transmission stiffnesses and, hence, changes in the dynamic characteristics of the system. In this study, a variable–coefficient dynamic modeling method for a ball screw feed system is proposed, considering the influence of changes in the no-extra-load running states, such as position, speed, and acceleration. Based on Timoshenko beam elements with two nodes and four DOFs, an equivalent dynamic model of a ball screw feed system is established using the hybrid element method. The expression for the equivalent axial stiffness of individual kinematic joints is derived, considering the influence of the feed speed/acceleration under the no-extra-load running state of the system. In addition, the stiffness and mass of the screw shafts on both sides of the screw nut are calculated, considering the influence of the system’s feed position. Hence, we obtain the total stiffness and mass of the system in the no-extra-load running state and analyze the natural frequency. Finally, we conduct validation experiments on a ball screw feed system of a large gantry-type machine tool with different no-extra-load running states.

Vertical Machining Center Feed Axis Thermal Error Compensation Strategy Research

CNC machine tools are a measure of national manufacturing and comprehensive national strength and how to reduce CNC machine errors in modern industry has received much attention from all walks of life. The thermal deformation of the feed axis of CNC machine tools is affected by the machine’s structure, installation, material properties, motion position, working conditions, and environmental temperature. Therefore, adopting a single thermal error model to the compensation implementation needs is difficult under changing motion parameters. In this paper, VMC655H is used as the research object and an embedded system is used as the control core. The model classification method is based on the approximate matching of the motion parameters of the thermal error model. Dynamic loading technology is used to fit multiple thermal error models as a technical means to reduce the impact of the machine feed axis’s thermal deformation on the positioning accuracy during the manufacturing process. The thermal error classification model for machine tool feed axes with variable motion parameters in an embedded environment can classify, identify, and load compensation device models within a limited range of motion parameters. This strategy can determine the current operating environment and compensate for the poor adaptability of a single thermal error model. The study of the actual operation effect of the compensation device under this strategy shows that the compensation strategy proposed in this paper can compensate for the thermal deformation of the ball screw feed axis under variable motion, and the X-axis positioning accuracy of its feed system can be improved by 53.11%. This study provides a new idea for the compensation method for thermogenic errors in machine tools.

Transient thermal error modeling of a ball screw feed system

The thermal behaviors of the ball screw feed system significantly affect the machining accuracy of the machine tool, which is widely valued by users and manufacturers. In the current ball screws thermal error models, the moving heat source at nuts is simplified to a fixed heat source to simplify the calculation, which can decrease the model’s prediction accuracy. A novel thermal error modeling method for the ball screw feed system is proposed by this paper based on the FEM. In the proposed method, the moving heat source at the nut is loaded into the model by changing the grid distribution at different time steps. Meanwhile, a series of thermal experiments are carried out to collect the thermodynamic data with the machine tool’s feed drive system operating at a different speed. And then the multi-objective optimization method is introduced to obtain the heat generated by the nuts and the convection coefficient between the air and the screw. The experimental results show that the thermal error of the ball screw feed system is different when the feed system runs in different intervals, even if the temperature rise at measuring points is the same. In the final, experiments under different conditions are carried out, and the proposed model is accurate enough to predict the thermal error of the ball screw feed system.