Error Of Spindle Research Articles

Research on thermal error of electric spindle based on ISCA-GRNN

Research on thermal error of electric spindle based on ISCA-GRNN

The influence of journal's roundness on rotating accuracy of aerostatic spindle and precision improvement by time-controlled grinding

The roundness of the journal directly affects the radial synchronous error (RSE) of the aerostatic spindle. However, the state-of-the-art ultra-precision grinding machine can only achieve a roundness of 0.2–0.3 µm, which limits the improvement of the rotating accuracy. Hence, novel time-controlled grinding (TCG) is proposed to further converge the rotor's roundness. To provide the machining basis and prediction, CFD is used to quantitatively analyze the effect of roundness on the flow field and a rotating trajectory model is established. Based on the model's guidance, the rotor's average roundness converged to 0.08 µm by TCG, even better than manual lapping, and the RSE decreased from ∼30 nm to ∼11 nm synchronously, proving the model's and TCG's feasibility and potential.

Robust modeling for thermal error of spindle of slant bed lathe based on error decomposition

Thermal error of spindle is critical to the slant bed CNC lathe towards high machining precision. The heat generated by the spindle itself contributes to the thermal error indeed. However, the thermal error is also influenced by the thermal deformation of other components such as the turret and lathe bed, especially in complex structured slant-bed CNC lathes where error coupling commonly exists. In order to achieve robust modeling of thermal error, a decomposition method was proposed in this paper to separate the contributions of spindle, turret and lathe bed from the overall measured thermal deformation. The thermal error coupling relationship was established from the perspective of machine tool construction. A specific testing scheme was designed to determine the parameters of decoupling model. Additionally, a comparative experiment was carried out by placing the sensor support horizontally and vertically to verify the effectiveness of thermal error decoupling. Taking T65-750 high-precision CNC lathe as the object, the relationship between thermal error and tilt angle in the X-direction of the headstock, bed, and other components was revealed, achieving robust prediction of thermal error irrespective of the ambient temperature subject to change. Finally, the thermal error model built based on error decomposition was applied to improve the machining accuracy of cylindrical parts dramatically in practice.

Segmented modeling and compensation of thermal error of gear grinding machine spindle based on variable thermal hysteresis

Segmented modeling and compensation of thermal error of gear grinding machine spindle based on variable thermal hysteresis

Thermal error modeling of high-speed electric spindle based on Aquila Optimizer optimized least squares support vector machine

The thermal error of electric spindle is an important factor affecting the machining accuracy of machine tools. To establish the thermal error prediction model, the thermal characteristics of A02 electric spindle were simulated and analyzed by ANSYS, to determine the best temperature measuring point. The temperature and thermal error of A02 electric spindle at different rotational speeds were obtained by thermal characteristics experiment. Through the combination of systematic clustering and grey relational analysis, four best temperature measuring points were selected from ten temperature measuring points. A prediction model of least squares support vector machine (LSSVM) optimized by Aquila Optimizer (AO) is established and compared with the model optimized by Particle Swarm Optimization (PSO), it is superior to the latter in prediction accuracy (η), goodness of fit (R2), root mean square error (RMSE) and mean absolute error (MAE). The AO-LSSVM prediction model based on experimental data has a prediction accuracy of more than 94% for the thermal error of motorized spindle and has good stability and generalization ability.

Thermal error modeling of electric spindle based on particle swarm optimization-SVM neural network

High-speed electric spindle is an important part of computer numerical control (CNC) machining equipment. The thermal displacement generated by the electric spindle during operation is the main reason that affects the machining stability and machining accuracy of the electric spindle. Compensating the thermal error of the high-speed electric spindle can effectively improve the CNC machining. Improve equipment processing performance. Therefore, it is particularly important to establish the accuracy of the thermal error prediction model. Taking the A02 high-speed electric spindle as the research object, ANSYS is used to analyze the thermal characteristics of the electric spindle, and the temperature and thermal displacement monitoring points of the electric spindle are arranged according to the simulation results, and the temperature and thermal displacement data of the monitoring points under different rotational speeds are collected; using K-means to classify temperature measurement points, uses the gray relation analysis degree to determine the correlation between the temperature measurement point and the thermal displacement data, and selects 4 temperature-sensitive points from 10 temperature measurement points. Finally, particle swarm optimization (PSO) is used to optimize the penalty factor and kernel function of support vector machine (SVM), and the PSO-SVM prediction model is established to compare with the neural network prediction model of SVM and genetic algorithm (GA) optimized SVM. The results show that PSO-SVM has better robustness, stability, and generalization ability.

Thermal Error Analysis of Five-Axis Machine Tools Based on Five-Point Test Method

The accuracy of five-axis machine tools is a key performance indicator. Among the various error sources of high precision five-axis machine tools, thermal and geometric errors occupy the majority. Thermal errors have become the largest error source of high precision five-axis machine tools, accounting for about 45% of the total errors. Accurate measurement of thermal errors plays a vital role in improving the accuracy of five-axis machine tools. Taking the Shenyang HTM50100 turning and milling machine tool as an example, this paper proposes a method to measure the thermal error of the machine tool spindle using the five-point test method. In the process of thermal error modeling, we select the temperature key point and analyze the collected data. Finally, we evaluate thermal error model. The method is verified by an experiment. The experiment results show that the method is highly accurate, fast, and easy to use. It provides a theoretical basis and practical method for the measurement of thermal errors on five-axis machine tools. By evaluating the method based on multiple linear regression, the predictive ability of the model is about 77%. Compared with LSTM, the prediction accuracy is improved by 5.08%.

Feedback control–based active cooling with pre-estimated reliability for stabilizing the thermal error of a precision mechanical spindle

The thermal error stability (STE) of the spindle determines the machining accuracy of a precision machine tool. The “active cooling-spindle” system is regarded as a feedback control system, and the data-driven thermal error model is utilized to output feedback. In this way, the spindle thermal error can be stabilized by the homeostasis ability of the feedback control system under disturbance. Structural temperature measurements are considerably interfered by the active cooling, so the regression models trained with experimental data might output inaccurate feedback in unseen work conditions. Such inaccurate feedbacks are the primary cause for excessive fluctuations and failures of the thermal error control processes. The independence of the thermal data is analyzed, and a V-C (Vapnik–Chervonenkis) dimension–based approach is presented to estimate the generalization error bound of the regression models. Then, the model which is most likely to give acceptable performance can be selected, the reliability of the feedback can be pre-estimated, and the risk of unsatisfactory control effect will be largely reduced. Experiments under different work conditions are conducted to verify the proposed strategy. The thermal error is stabilized to be within a range smaller than 1.637 μm, and thermal equilibrium time is advanced by more than 78.3%.

Measurement method of spindle motion error based on composite laser target

The primary component of ultra-precision machining machines and measuring instruments is a high-precision spindle, and spindle error affects the accuracy of these machines. Traditional spindle error measurement methods often require a standard device as a reference, which inevitably reduces the accuracy of spindle error measurement, while the error separation technique is tedious and time-consuming. This study proposed a spindle error measurement method based on a composite laser target, which can measure the motion error of the spindle, including axial, radial, and tilt error in terms of five degrees of freedom. In this method, a composite laser target containing a laser point source and laser collimated beam was constructed and mounted on the spindle as a reference frame to mark the position of the spindle during rotation. Consequently, the error of the spindle was obtained via measurements of the position and angle of the composite laser target. Differential confocal microscopy technique was employed for measuring the axial position of the laser point source to obtain the axial error of the spindle, whereas the radial position was measured using a conventional microscope optical path to obtain the radial error of the spindle. Further, the angle of laser collimation was measured using a collimation measurement optical path to obtain the tilt error of the spindle. The measurement resolution of the proposed method for spindle error was verified through suitable experiments, yielding resolutions of 4 and 2 nm for axial and radial errors, respectively, and 0.2 μrad in case of tilt error. In addition, the method was tested on an air spindle to demonstrate the feasibility of using the method on machines. Thus, it was demonstrated that the proposed method can be used to obtain the spindle error by optical standard devices without additional error separation techniques, particularly for a spindle in ultra-high precision measurement equipment. Further, it facilitates real time monitoring or evaluation and calibration of the spindle error. This method is expected to serve several important practical applications in the field of ultra-precision machining and measurement. • Spindle error measurement method based on a composite laser target proposed. • Method eliminates reliance of accuracy on standard device used. • Motion error of spindle: axial, radial, tilt in terms of five degrees of freedom. • Resolution of proposed method verified through suitable experiments. • Practical applications in the field of ultra-precision machining and measurement.

Axial Error of Spindle Measurements Using a High-Frequency-Modulated Interferometer

In this paper, a novel, compact, and high-precision axial error measurement using a frequency-modulated interferometer is developed. Normally, heterodyne interferometers are a powerful system for small displacement measurements due to their property of being less sensitive to temperature and pressure variations. However, the maximum measurement speed of the heterodyne interferometer is around 5 m/s because it is usually limited by the difference in frequency between the two components of the laser beam, which is no larger than 3 MHz or 20 MHz corresponding laser source based on the Zeeman effect and acousto-optic modulator, respectively. The proposed measuring system is realized by modulating the frequency of the laser diode source at a high modulation frequency and using lock-in amplifiers to extract the harmonics of the interference signal. The measurement speed is proportional to the modulation frequency. Thus, the higher the modulation frequency, the higher the measuring speed attains. The frequency-modulated interferometer is then applied to measure the axial error of an ultra-precision spindle. The proposed system can be a capable solution for noncontact and high-precision spindle error measurements in the machining process.

Study on vibration characteristics of motorized spindle based on multi-physics fields

Ceramic motorized spindle plays an important role on CNC machine tool. Its dynamic characteristic determines the machining quality of spindle. This paper established a dynamics model of ceramic bearing, and explored the relationship of bearing stiffness and vibration response. The temperature field model of ceramic motorized spindle was established to analyze the temperature field. The motorized spindle air gap influence on unbalanced magnetic pull was studied. The dynamic model of ceramic motorized spindle was established through considering the multiple physical fields influence factors, the changing law of dynamic characteristics was studied. It has been verified by experiments. The average error of ceramic spindle decreased from 5.1% to 2.1%. The establishment of multi-fields dynamic model provided an important guidance for spindle design.

Experiment and Analysis of Thermal Error of Boring-Milling Center Spindle

Taking the spindle of the boring-milling machining center as the research object, analyzes the heat source of the spindle, and uses FILR infrared camera and API spindle analyzer measurement system to design a thermal error experimental detection scheme for the spindle system. The temperature field and thermal deformation of the spindle system. Understanding and grasping the thermal deformation of the spindle system under different operating conditions during operation provides basic data support for the optimization design and compensation of the spindle system.

A Displacement Measuring Interferometer Based on a Frequency-Locked Laser Diode with High Modulation Frequency

Laser interferometers can achieve a nanometer-order uncertainty of measurements when their frequencies are locked to the reference frequencies of the atom or molecule transitions. There are three types of displacement-measuring interferometers: homodyne, heterodyne, and frequency modulation (FM) interferometers. Among these types of interferometer, the FM interferometer has many advantageous features. The interference signal is a series of time-dependent harmonics of modulation frequency, so the phase shift can be detected accurately using the synchronous detection method. Moreover, the FM interferometer is the most suitable for combination with a frequency-locked laser because both require frequency modulation. In previous research, low modulation frequencies at some tens of kHz have been used to lock the frequency of laser diodes (LDs). The low modulation frequency for the laser source means that the maximum measurement speed of the FM interferometers is limited. This paper proposes a novel contribution regarding the application of a high-frequency modulation for an LD to improve both the frequency stability of the laser source and the measurement speed of the FM interferometer. The frequency of the LD was locked to an I2 hyperfine component at 1 MHz modulation frequency. A high bandwidth lock-in amplifier was utilized to detect the saturated absorption signals of the I2 hyperfine structure and induce the signal to lock the frequency of the LD. The locked LD was then used for an FM displacement measuring interferometer. Moreover, a suitable modulation amplitude that affected the signal-to-noise ratio of both the I2 absorption signal and the harmonic intensity of the interference signal was determined. In order to verify the measurement resolution of the proposed interferometer, the displacement induced by a piezo electric actuator was concurrently measured by the interferometer and a capacitive sensor. The difference of the displacement results was less than 20 nm. To evaluate the measurement speed, the interferometer was used to measure the axial error of a high-speed spindle at 500 rpm. The main conclusion of this study is that a stable displacement interferometer with high accuracy and a high measurement speed can be achieved using an LD frequency locked to an I2 hyperfine transition at a high modulation frequency.

Characterization and Evaluation of Rotation Accuracy of Hydrostatic Spindle under the Influence of Unbalance

The paper studies the characterization and evaluation technology of rotation accuracy of hydrostatic spindle under the influence of unbalance. The dynamic model of the motion error of the hydrostatic spindle is established based on the dynamic parameters. The variation law of motion error of spindle rotor is analyzed under the unbalanced mass. The paper finds that with the increase of the spindle speed, the amplitude of the spindle error motion will increase, and the inclination angleθerror is more sensitive to the change in the rotational speed. In the total synthesis accuracy, the proportion of synchronization error decreases with the increase of the rotational speed. Finally, the least squares evaluation algorithm is used to evaluate the rotation error of the hydrostatic spindle, and a method for evaluating the rotation accuracy of the hydrostatic spindle with high calculation accuracy and calculation efficiency is proposed.

Robust machine tool thermal error compensation modelling based on temperature-sensitive interval segmentation modelling technology

Establishing a mathematical model that can reflect the relationship between temperature increase and thermal error during machining is the core of thermal error compensation technology for CNC machine tools. The collinearity between temperature-sensitive points and the correlation between temperature-sensitive points and thermal errors are important factors affecting the prediction accuracy and robustness of the thermal error compensation model. Based on the thermal error measurement experiments of the Leaderway-V450 CNC machine tool in different periods of the year, the principal component regression (PCR) modelling algorithm, which can eliminate the collinearity effect, is proposed to establish the thermal error compensation model of the machine tool on the basis of selecting the temperature-sensitive points by using the correlation coefficient. It is compared with the newly proposed ridge regression thermal error compensation modelling algorithm. The results show that the thermal error compensation modelling method proposed in this paper can basically control the Z-direction thermal error of the CNC machine tool spindle within 10 μm with only two temperature sensors and has higher engineering practicability. It is found that the thermal error compensation model of machine tools has a jump interval affected by the ambient temperature. This interval is called the temperature-sensitive interval, and a temperature-sensitive interval subsection point selection algorithm is proposed to build a subsection model on both sides of the segment point. The results show that the Z-direction thermal error of the spindle of CNC machine tools can be basically controlled within 5 μm with only two temperature sensors and that the model is highly robust and has great engineering application value.

Research on roundness error extraction method for precision machine tool spindle based on least square method

Based on the application requirement of online measurement and evaluation for roundness error of precision machine tool spindle, a specific method is proposed to fit the spindle roundness error based on the least square method according to the characteristics of the roundness error. Firstly, aiming to the radial vibration displacement signal of spindle, which collected by the sensor, a multi-harmonic signal with speed frequency of spindle as the fundamental frequency is constructed, and then the least square method is used to fit the amplitudes and phases of each harmonic signals. Finally, according to the fitting results, the rotation error and the interference of higher-order noise signals are eliminated, and the contour signal with only roundness error of the spindle is reconstructed, and then the roundness error of the spindle is evaluated by appropriate evaluation method. The simulation system of rotation and roundness errors separation for spindle system is developed, and the feasibility and accuracy of least square method to fit the spindle roundness error are verified by simulation analysis.

Thermal error modeling of machine tool spindle based on the improved algorithm optimized BP neural network

Thermal error of the machine tool spindle is one of the main factors affecting the machining accuracy. For the complex operating environment of the machine tool, the difficulty of thermal error prediction modeling, and the low accuracy of the traditional thermal error prediction model, a spindle thermal error prediction model based on the improved particle swarm optimization (IPSO) optimize back propagation (BP) neural network is established in this paper. The temperature measurement points are clustered by SOM neural network, and the correlation analysis method is used to explore the correlation between the thermal sensitive points and the thermal error of the spindle. The S-type function is used to improve the inertia weight coefficient of the IPSO algorithm so as to improve the particle optimization effect. IPSO is used to optimize the parameters of BP neural network, such as the initial weights and thresholds. Compared with the GA-BP prediction model, the modeling efficiency, robustness, and accuracy of IPSO-BP neural network prediction model are all superior GA-BP prediction model. Taking the thermal error of the electric spindle of precision CNC machining center as the research object, the intelligent temperature sensor and the laser displacement sensor are used to obtain the machine tool temperature values and the spindle thermal error values. The prediction accuracy of the GA-BP model for the spindle thermal error was 93.1%, and the prediction accuracy of the IPSO-BP model was 96.5%. The results show that the IPSO-BP model can accurately predict the thermal error of the spindle under different working conditions. The model can obtain higher thermal error prediction accuracy and is more suitable for the thermal error compensation model.

Influence of microscale effect on the radial rotation error of aerostatic spindle

This paper presents the influence of the microscale effect on the radial rotation error of aerostatic spindle, which is determined by the corresponding stiffness, damping, and unbalance mass. A microscale gas film flow model is used to simulate the static performance of the aerostatic bearing by introducing the microscale effect factor Q in this paper. Firstly, the radial stiffness and damping coefficients of aerostatic bearing were calculated considering microscale effect factor Q, therefore, the position of the rotating shaft in radial plane was deduced, and the corresponding rotation error was obtained. Finally, the simulation results of the stiffness and radial rotation error were verified by the experiment on the shaft test table, and the motion orbit was measured by a displace sensor with a high precision standard ball. The experimental results indicated that the simulated result considering the microscale effect factor Q was more consistent with the actual experimental value, which provided a reference for the design and optimization of the aerostatic spindle.

Analysis of aerostatic spindle radial vibration error based on microscale nonlinear dynamic characteristics

This paper presents a method of predicting the radial rotary error of an aerostatic spindle based on the microscale-effect to investigate the influence of gas film fluctuation on the rotation accuracy of the aerostatic spindle. First, the gas bearing of the spindle is simplified as a spring-damping system with two degrees of freedom perpendicular to each other. Additionally, the aerostatic spindle bearing-rotor system is established by considering the forced vibration and deflection vibration of the rotor. Subsequently, the microscale-effect is introduced into the dynamic model of the gas film flow, and the dynamic Reynolds equation of the gas film is established in the microscale. Moreover, the nonlinear dynamic stiffness and dynamic damping coefficient are obtained by the perturbation method. The nonlinear dynamic parameters in the microscale are introduced into the dynamic model of the bearing-rotor system and all the vibration errors are obtained. By comparison with the conventional case, it is found that the spindle gyration error increased and that the response delay occurred when the microscale-effect is considered. Moreover, the influence of the supply pressure and speed on the vibration of the spindle is also analyzed. An experiment measuring the spindle rotation error is carried out. The experimental results reveal that the prediction method of the nonlinear spindle rotation error in the microscale is more accurate, and that the errors are 5.8% and 9.6%.

Measurement of Spindle Tilt Error Based on Interference Fringe

The spindle rotation error is one of the important factors that affect the precision of the machined parts. The study of spindle rotation error is of great significance for finding the source of error, predicting the surface shape error of machining parts and improving the machining accuracy of ultra-precision machine tools. The structural of the aerostatic spindle this article focuses on is motorized spindle and the spindle tilt error has the maximum effect on the machining precision. A new method for measuring the rotation error of ultra-precision aerostatic spindle based on interference fringes is proposed in this paper. By using the principle of phase shifting interferometry, the mathematical model between the shape of interference fringes and the motion law of the spindle rotor is established by theoretical modeling. The interference fringes are processed with gray, smooth filtering, expansion corrosion, and edge detection and so on. The distance and direction of the interference fringes are calculated in the coordinate system, so as to get the spindle tilt error. Finally, the measurement system for the spindle rotation error of the aerostatic spindle is developed. The accuracy and effectiveness of this method are shown based on the experimental results.