Spindle Error Research Articles

고정밀 스핀들의 회전정밀도 측정 오차 분리법에 관한 연구

The rotation of a spindle unit must be accurate for high-quality machining and to improve the quality of the machine tools.Therefore, the proper measurement of the rotation accuracy and ensuring a proper analysis are very important. Separate processes are necessary because spindle errors and roundness errors associated with the test balls can both factor into the measured rotation error values. We used three methods to discern test ball errors and analyzed which could be deemed as the most proper technique in a test of the rotation accuracy of the main spindle of a machine tool.

A sub-nanometre spindle error motion separation technique

Abstract This work designs and validates a spindle error motion separation technique having a sub-nanometre measurement uncertainty. This technique overcomes typical measurement error sources arising from sensor, indexing or the repositioning of the artifact. We compare and assess various known reversal and multiprobe techniques by means of a novel error analysis method. From this, we develop an improved implementation of the multiprobe technique, which by-passes accurate indexing of the artifact and sensor(s) during testing, as well as unequal sensor sensitivities, in case multiple sensors are used. This is achieved by measuring the error motion consecutively under three different orientations by rotating the stator of the spindle utilising a high-precision indexing table. These modifications result in a measurement uncertainty that is four times smaller than the conventional multiprobe technique. Furthermore, the suppression of the low-order harmonics is reduced by an optimisation of measurement angles. Finally, several experimental tests are performed to quantify the measurement uncertainty and the influence of the measurement angles on the error separation. Repeatability tests on the radial error motion of an aerostatic rotary table show a measurement uncertainty of 0.455 nm.

Rapid Machine Tool Verification

This paper describes work carried out to develop methods of verifying that machine tools are capable of machining parts to within specification, immediately before carrying out critical material removal operations, and with negligible impact on process times. A review of machine tool calibration and verification technologies identified that current techniques were not suitable due to requirements for significant time and skilled human intervention. A ‘solution toolkit’ is presented consisting of a selection circular tests and artefact probing which are able to rapidly verify the kinematic errors and in some cases also dynamic errors for different types of machine tool, as well as supplementary methods for tool and spindle error detection. A novel artefact probing process is introduced which simplifies data processing so that the process can be readily automated using only the native machine tool controller. Laboratory testing and industrial case studies are described which demonstrate the effectiveness of this approach.

Nano-level instrumentation for analyzing the dynamic accuracy of a rolling element bearing

The rotational performance of high-precision rolling bearings is fundamental to the overall accuracy of complex mechanical systems. A nano-level instrument to analyze rotational accuracy of high-precision bearings of machine tools under working conditions was developed. In this instrument, a high-precision (error motion < 0.15 μm) and high-stiffness (2600 N axial loading capacity) aerostatic spindle was applied to spin the test bearing. Operating conditions could be simulated effectively because of the large axial loading capacity. An air-cylinder, controlled by a proportional pressure regulator, was applied to drive an air-bearing subjected to non-contact and precise loaded axial forces. The measurement results on axial loading and rotation constraint with five remaining degrees of freedom were completely unconstrained and uninfluenced by the instrument's structure. Dual capacity displacement sensors with 10 nm resolution were applied to measure the error motion of the spindle using a double-probe error separation method. This enabled the separation of the spindle's error motion from the measurement results of the test bearing which were measured using two orthogonal laser displacement sensors with 5 nm resolution. Finally, a Lissajous figure was used to evaluate the non-repetitive run-out (NRRO) of the bearing at different axial forces and speeds. The measurement results at various axial loadings and speeds showed the standard deviations of the measurements' repeatability and accuracy were less than 1% and 2%. Future studies will analyze the relationship between geometrical errors and NRRO, such as the ball diameter differences of and the geometrical errors in the grooves of rings.

Investigate the spindle errors motions from thermal change for high-precision CNC machining capability

As the demand for high speed and highly accurate machines has significantly increased, error motions from thermal change, which is up to 70 % of the total machining error, is found to be the main hurdles to overcome in improving the accuracy of CNC machine tools. In this research work, the authors installed four eddy current displacement sensors in the spindle structure near to the front bearing to monitor the spindle offset in the bearing level, which is mainly attributable to the thermal error motions of the spindle. In addition, another three capacitance sensors are mounted on the machine table level and aligned with the x-, y-, and z-axis of the machine to monitor the spindle shift in the table level to find out the correlation between temperature change and the thermal error motions of the spindle. To measure the temperature changes, we attached thermal sensors in the machine and cooling system. The estimation of the spindle thermal displacement based on temperature data from these thermal sensors can provide more information for the monitoring of thermal error motions of the spindle.

Research on the Online Test of the Fly Cutting Machine Tool Spindle

The online test system of the vertical spindle motion error of the ultra-precision fly cutting machine tool was established. And then using the online test system established to test and analyze the state of the rotary motion of the spindle under the idling condition. The axial synchronous motion error value of the spindle under 390rpm is about 61 nm, and the asynchronous error motion is about 33nm. The radial error motion value is about 91nm, and the asynchronous error is about 35nm. Through the test, we found that the axial and radial spindle error motion accuracy under idling speed can been improved with the spindle speed increases.

Research of Spindle Error Separation Mixed Method

This paper introduces a spindle error separation technique called orthogonal mixed method. The problem of harmonic suppression is solved by the orthogonal mixed method, which exists in the process of measurement based on three point method.The measuring system consisting of a displacement sensor and a angle sensor is developed for spindle error and roundness measurement. Two sensors, which are placed in the same plane perpendicular to the spindle axis, are mutual into 900. The principle of the critical angle method of total reflection are used by two sensors to separate rotation error from spindle error. Above all, the measured results show that this method indeed solve the problem of harmonic suppression, make the results of measurement more accurate.

Development of an automatic cumulative-lead error measurement system for ballscrew nuts

Ballscrew is a precision mechanical component used to convert rotational motion to linear motion in the precision linear stage. The precision measuring system for the screw's cumulative-lead error is already well known. Up to now, however, there is no suitable measuring equipment for internal cumulative-lead error of the nut. For a matching pair, it is not reasonable to understand the quality of only one piece. This paper presents a developed automatic cumulative-lead error measuring system for ballscrew nuts. The nut is clamped by a rotational stage, in which the moving angle is detected by a rotary encoder. The probing ball is inserted into the nut and remains in contact with the thread groove of the nut. The probe arm is mounted on a linear slide so that when rotating the nut, the probing ball will be pushed by the groove wall and moved axially. A high-resolution diffraction scale is employed to detect the linear movement of the probe to nanometer resolution. Combining the angular and linear motions, the cumulative-lead error of the nut can be realized. In practice, however, the nut will cause typical spindle errors during rotating, including axial slip, radial run out, and tilt motions. These errors have to be compensated in order to guarantee the accuracy of measurement results. A multi-sensor error compensation system is thus developed. Experimental results show the applicability of this developed measuring system.

Nanometer-level axis of rotation metrology for a high-precision macromolecular X-ray diffractometer

The availability of micro-focused beams at 3rd generation synchrotrons makes collecting X-ray data from macromolecular crystals down to a fraction of micron size possible. This requires using goniometers with nanometer-level errors. Crystal positioning is typically realized with a multi-axis goniometer designed to minimize error motion during rotation of the crystal by the data-collection axis. In this paper, five degree-of-freedom error motions of an air bearing diffractometer data-collection axis are evaluated using a multiprobe method. As spindle errors and artifact out-of-roundness approach equal magnitudes, techniques must be used to distinguish and separate each error. A purpose-built fixture orients a single capacitive sensor in three asymmetrical positions to separate artifact form error from spindle error motion. Metrology results of this air bearing Omega spindle demonstrate synchronous errors of 16 nm radial, 4 nm axial and 0.28 μrad tilt.

Roundness Measurement and Error Separation Technique

A new three-point method for spindle roundness error measuring was introduced, three capacitive sensors were installed on the measured shaft circularly, and with a certain angle each other, while the spindle was rotating with a certain speed, the capacitive sensors had measurement on the circular profile simultaneously, then through linear combination for three-sensor output signals, the roundness error was effectively separated from the spindle error. There were no strict requirement to initial installation position by using capacitive sensors, as long as ensuring the change of measured rotor error within the linear range of sensors, we could realize effective measurement. The experiment results have verified the effectiveness of roundness error measuring system based on three capacitive sensors.

A New Capacitive Sensing System for Roundness Measurement

A capacitive sensing system for measuring spindle roundness was proposed in this paper, it was different with the past method using inductive sensors and laser displacement sensors. Three capacitive displacement probes were installed circularly on the measured shaft, because of capacitive sensor with average effect in two electrode plates, it is able to overcome the affect of microscopic factors. while the shaft was rotating with a certain speed, the probes measured the shaft’s profile in non-contact mode simultaneously, then through linear combination for three output signals, the spindle error of the rotating shaft was eliminated, and the roundness error was effectively separated from the measurement results. The experiment results have verified the effectiveness of roundness error measuring system based on mutiple capacitive probes, this capacitive sensing system can be used for rotating shaft roundness measurement.

An Integrated Modeling Approach for ANN-Based Real-Time Thermal Error Compensation on a CNC Turning Center

Thermally induced errors play a critical role in controlling the level of machining accuracy. They can represent a significant proportion of dimensional errors in produced parts. Since thermal errors cannot totally be eliminated at the design stage, active errors compensation appears to be the most economical and realistic solution. Accurate and efficient modeling of the thermally induced errors is an indispensable part of the error compensation process. This paper presents an integrated and comprehensive modeling approach for real-time thermal error compensation. The modeling process is based on multiple temperature measurements, Taguchi’s orthogonal arrays, artificial neural networks and various statistical tools to provide cost effective selection of appropriate temperature variables and modeling conditions as well as to achieve robust and accurate thermal error models. The experimental results on a CNC turning center confirm the feasibility and efficiency of the proposed approach and show that the resultant model can accurately predict the time-variant spindle thermal drift errors under various operating conditions. After compensation, the thermally induced spindle errors were reduced from 19m to less than 1 m. The proposed modeling optimization strategy can be effectively and advantageously used for real-time error compensation since it presents the benefit of straightforward application, reduced modeling time and uncertainty.

Modeling and Analysis on the Rotation Accuracy of Lathe Spindle

The rotation accuracy of the machine spindle is an important accuracy index, and has numerous influence factors. According to the structure characteristic of the spindle system, an integrated model of the spindle rotation error is established in this paper. By this model, the impact law and cumulative effect of various error sources on spindle rotation accuracy can be analyzed. Taking the lathe spindles as an example, the modeling and analysis method for spindle error are introduced. Visualization of spindle center track is achieved by programming.

A newly conceived cylinder measuring machine and methods that eliminate the spindle errors

Advanced manufacturing processes require improving dimensional metrology applications to reach a nanometric accuracy level. Such measurements may be carried out using conventional highly accurate roundness measuring machines. On these machines, the metrology loop goes through the probing and the mechanical guiding elements. Hence, external forces, strain and thermal expansion are transmitted to the metrological structure through the supporting structure, thereby reducing measurement quality. The obtained measurement also combines both the motion error of the guiding system and the form error of the artifact. Detailed uncertainty budgeting might be improved, using error separation methods (multi-step, reversal and multi-probe error separation methods, etc), enabling identification of the systematic (synchronous or repeatable) guiding system motion errors as well as form error of the artifact. Nevertheless, the performance of this kind of machine is limited by the repeatability level of the mechanical guiding elements, which usually exceeds 25 nm (in the case of an air bearing spindle and a linear bearing). In order to guarantee a 5 nm measurement uncertainty level, LNE is currently developing an original machine dedicated to form measurement on cylindrical and spherical artifacts with an ultra-high level of accuracy. The architecture of this machine is based on the ‘dissociated metrological technique’ principle and contains reference probes and cylinder. The form errors of both cylindrical artifact and reference cylinder are obtained after a mathematical combination between the information given by the probe sensing the artifact and the information given by the probe sensing the reference cylinder by applying the modified multi-step separation method.

Orthogonal polynomials-based thermally induced spindle and geometric error modeling and compensation

The spindle error and geometric error are the main sources of inaccuracy in CNC machining. With the rising of the machine tool parts' temperature, the spindle error and geometric error increase continually, and the error curves have a nonlinear distribution. To analyze the thermal effects on spindle error and geometric error, an experiment is carried out. To improve the machining accuracy of a CNC machine, an error model is proposed based on orthogonal polynomials. With the application of the orthogonal polynomials, the polynomial regression can be transformed into multiple linear regressions which are easier to calculate. In order to implement the real-time error compensation for the thermally induced spindle error and geometric error, an error compensation method is proposed based on the external coordinate offset. The thermally induced spindle and geometric error are compensated by 90 % compared with no compensation.

Spindle error motion measurement of a large precision roll lathe

This paper describes a spindle error motion measurement system to evaluate the performance of the spindle of a large precision roll lathe, which is under development for fabrication of large-scale roll dies of micro-structured surfaces. The measurement system employed a large-scale roll workpiece with a diameter of 320 mm and a length of 1800 mm as a measurement artifact instead of a master object to figure out the spindle error motion over the entire fabrication length. To separate the spindle error motion and the out-of-roundness of the roll workpiece, the reversal method was employed. Two capacitive type displacement probes were mounted on the designed probe holders which were arranged to be faced to each other with the roll workpiece between them. Spindle error motion measurement was conducted at several sections of the roll workpiece along the roll axis to verify the tilt error motion of the spindle as well as the radial error motion. As the rotational speed was different for the mirror finishing fabrication of the roll workpiece and fabrication of the micro-structures on the roll workpiece, the spindle error motion was measured at rotational speeds of 5 and 300 rpm, respectively. Experimental results of the out-of-roundness of the roll workpiece as well as the spindle error motion measurement are presented in this paper.

Harmonic-analysis-based method for separation of form error during evaluation of high-speed spindle radial errors

The measurement and evaluation of spindle errors is an important task in the assessment of the accuracy of machine tools. The commonly followed capacitive-sensor-based measurement technique requires a comprehensive error separation method for the identification of the unwanted contributions of centering error, the form error of the artifact and thermal drift. This paper presents a method for form error separation that is suitable for the evaluation of the radial error of high-speed spindles. In the present work, a fixed sensitive radial error motion test is conducted using a capacitive sensor and a cylindrical artifact at different spindle speeds. A mathematical model consisting of a second-order polynomial and Fourier series function is used to interpret the data measured in the time domain. The form profile of the artifact is measured separately in a roundness tester using a capacitive sensor. A harmonic analysis method is proposed to identify and separate the dominant harmonic components in the form profile of the artifact. A mathematical description of the proposed method is described and experimental results are presented. Application of the proposed method to the evaluation of the synchronous radial error of a high-spindle is provided for measured data. The proposed method analyzes the data measured in the time domain and is suitable for the identification of the spindle errors at high-speed conditions.

Measurement of Radial and Axial Error Motion in a High Precision Spindle

The performance of a spindle is critical for high precision machining. In this paper, the spindle error motion in a high precision milling center was measured. The spindle is driven by air turbine with rotation speed of 120,000rpm. The radial and axial error motion of the axis of rotation was measured. The capacitive displacement sensors with nanometer resolution were mounted against the master gauge pin through the dedicated setup. Tlusty method was adopted to synchronize angular position of the spindle and data sampling. The measured radial and axial error motion of the spindle were 2.73μm and 2.59μm respectively. Despite of motion errors, the better machining accuracy still can be achieved. It seems that cutting force may improve the rotation performance of a spindle with aerostatic bearing.

Study on the Spindle Error Test and Analysis System of Numerical Control Machine Tools

It’s always an important means of measuring and improving the performance of machine tools with spindle error test and error analysis. Based on the analysis of the dynamic and thermal performance of spindle, the study is focused on how to get thermal deformation and temperature field by experimental methods. First of all, spindle error analysis methods are researched. Furthermore, developed a spindle error test and analysis system, established a set of complete structure system for spindle error test and analysis. Finally, tests are performed to demonstrate the feasibility of the error test and analysis system of the spindle, which laid foundation for the further research on the experimental analysis of machine tools.

Modeling, measurement, and evaluation of spindle radial errors in a miniaturized machine tool

Miniaturized machine tools have been established as a promising technology for machining the miniature components in wider range of materials. Spindle of a miniaturized machine tool needs to provide extremely high rotational speed, while maintaining the accuracy. In this work, a capacitive sensor-based measurement technique is followed for assessing radial errors of a miniaturized machine tool spindle. Accuracy of spindle error measurement is affected by inherent error sources such as sensor offset, thermal drift of spindle, centering error, and form error of the target surface installed in the spindle. In the present work, a model-based curve-fitting method is proposed for accurate interpretation and analysis of spindle error measurement data in time domain. Experimental results of the proposed method are presented and compared with the commonly followed discrete Fourier transform-based frequency domain-filtering method. Proposed method provides higher resolution for the estimation of fundamental frequency of spindle error data. Synchronous and asynchronous radial error values are evaluated in accordance with ANSI/ASME B89.3.4M [9] standard at various spindle speeds and number of spindle revolutions. It is found that the spindle speed and number of spindle revolutions does not have much influence on synchronous radial error of the spindle. On the other hand, asynchronous radial error motion exhibits a significant speed-dependant behavior with respect to the number of spindle revolutions.