Geometric Errors Of Rotary Axis Research Articles

Influence of NC Program Quality and Geometric Errors of Rotary Axes on S-Shaped Machining Test Accuracy

An S-shaped machining test is proposed for the ISO 10791-7 standard to verify the performance of five-axis machining centers. However, investigation of the factor that has the most influence on the geometrical accuracy of finished S-shaped workpieces has not been undertaken. Determination of the influence of NC program tolerance and geometric errors concerning the rotary axes on the accuracy of the finished S-shaped workpiece forms the main objective of the study. Actual cutting experiments as well as simulations were performed during the proposed investigation. Our results clarify that NC-program tolerance has a significant influence on the end quality of the machined surface. Although geometric errors pertaining to rotary axes also have a significant influence on machined-surface quality, it is difficult to evaluate the influence of each individual error, because all geometric errors make glitches at the same point on the machined surface. The proposed S-shaped machining test can be used to provide a complete demonstration of available machining techniques.

Identification of geometric errors of rotary axis on multi-axis machine tool based on kinematic analysis method using double ball bar

Abstract Accuracy identification of geometric errors of rotary axis is important for error compensation of the multi-axis machine tool. However, it is not easy because of the influence of setup error of measurement instrument, and there exists angular errors and displacement errors need to be identified simultaneously. In this paper, a decoupled method based on double ball bar is proposed to identify the geometric errors of rotary axis including both position independent geometric error (PIGE) and position dependent geometric error (PDGE). A formulation for ball bar measurement is derived from kinematic analysis to reveal the relationship between sensitivity direction and setup position of ball bar. The angular errors and displacement errors can be identified separately when choosing the appropriate setup position and direction of ball bar. It can effectively reduce the interaction influence between them and improve the accuracy. To identify the 4 PIGEs, a method by averaging the measured results of ball bar to compute the eccentricity and slant of rotary axis is proposed. And, the PDGEs are leaved to mainly describe the oscillation of geometric errors of rotary axis. It is useful to correct the deviation error resulting from setup error of ball bar. For the identification of 6 PDGEs, by means of adjusting setup position and direction of ball bar, they can be identified one by one along the sensitivity direction of ball bar. Furthermore, in order to reduce the influence of setup error of ball bar, the sensitivity analysis is performed to obtain the sensitivity of measured results of ball bar with respect to setup error. According to the sensitivity characteristics of setup error, a method is presented to correct the PDGEs. Finally, several numerical simulations and experiments are conducted to verify the theoretical model and the proposed identification method. The results from the simulations and experiments demonstrate that the method can identify the geometric errors of rotary axis effectively and accurately.

The tool following function-based identification approach for all geometric errors of rotary axes using ballbar

This paper proposes a tool following function-based identification approach (TFFIA) for geometric errors of two rotary axes for one five-axis machine tool. It is comprehensive to identify all geometric errors of rotary errors. Firstly, synthetic error formulas of ballbar originate from the geometric error model of machine tools in order to consider the influences of 21 errors of three translational axes. It makes the approach more reasonable and precise. Secondly, the structures of three measurement patterns of TFFIA are described. Thirdly, in each pattern, errors of rotary axes affecting the accuracy of the sensitive direction are identified. As the result, the identification equations of all 20 errors coincide with the geometric properties of errors. Moreover, the impacts of setup errors of ballbar are eliminated with least square method to improve the precise of TFFIA. According to the structures of three patterns, only three installation of workpiece ball of ballbar are needed in the whole identification of two rotary axes to obtain the required ballbar readings. It greatly shortens the measurement time. Twenty geometric errors of two rotary axes are calculated with identification equations and ballbar readings. Finally, TFFIA is applied to a SmartCNC500 five-axis vertical machining center. The corresponding comparisons are proposed to verify the effectiveness and accuracy of TFFIA.

五轴机床旋转轴误差的在机测量与模糊径向基神经网络建模

五轴机床旋转轴误差的在机测量与模糊径向基神经网络建模

Identification of different geometric error models and definitions for the rotary axis of five-axis machine tools

Geometric errors are the major error sources of machine tools. Different geometric error models have been used in published studies according to the different definitions of geometric errors of the rotary axis. This is considerably dangerous as it makes the definition of geometric errors ambiguous and may reduce the effect of geometric error identification and compensation. This phenomenon has not been noticed yet. In this paper, another two used geometric error models of rotary axis are firstly introduced and analyzed, named as “Error first model” and “Motion first model”. These two models were both verified correctly by an example. After a detailed comparison, errors identified with these two models are discovered to have a certain relationship. “Error first model” is preferred for the modeling and definition of geometric errors of rotary axis. An experiment has been conducted on a 5-axis machine tool to demonstrate the correctness of our research. The results show that the identified geometric errors of rotary axis according to the two error models are greatly different and deserved to be concerned.

Identification of geometric errors of rotary axes on 5-axis machine tools by on-machine measurement

Geometric error is among the most important fundamental elements that significantly affect the machining accuracy of multi-axis machine tools. This paper developed an efficient, accurate, and automatic geometric error measurement and identification method for rotary axis of a five-axis machine tool based on on-machine measurement by using a touch-trigger probe with a test piece. Before on-machine measurement, the test piece is installed and pre-machined to a designated geometry. Then, the coordinates of the reference points on the test piece are indirectly measured at different rotary axis positions. The geometric errors of each rotary axis then can be identified individually and the calculation algorithm is easy to establish and solve. Due to the special features of this method, neither the geometric inaccuracy of the test piece nor its installation error on the workbench affects the geometric error measurement and identification results. Geometric errors of a five-axis machine tool with double table rotary axes are measured as an example to validate the efficiency and effectiveness.

Identification of two different geometric error definitions for the rotary axis of the 5-axis machine tools

Geometric errors are clearly among the critical error sources in 5-axis machine tools and directly contribute to the machining inaccuracies. According to the definition of geometric errors of the rotary axis, different understandings have been exist in published studies. It is extremely dangerous as it makes the comprehension of the geometric errors ambiguous and may make the geometric error identification and compensation less effective. This phenomenon has not been noticed so far. In this paper, two different commonly used geometric error definition and modeling methods are firstly identified and analyzed, named as “Rotary axis component shift” and “Rotary axis line shift”. The features and relationships of these two error modeling methods are analyzed. After a detailed comparison, “Rotary axis component shift” is more suitable to definite the geometric errors of rotary axis. An experiment has been conducted on a 5-axis machine tool to show the correctness of our work. The results show that the identified geometric errors of rotary axis based on the two error models are greatly different and need to be concerned.

A Modified Sequential Multilateration Scheme and its Application in Geometric Error Measurement of Rotary Axis

Geometric error compensation becomes an essential technology for improving the accuracy of multi-axes machine tools. Laser tracker has been has been considered as an enabling instrument which can be used to measure the geometric error of machine tools due to its high accurate and feasible measurement capability. This paper presents a modified sequential multilateration method for measuring the geometric errors of rotary axes of the machine tools. The method is developed based on a single laser tracker and three targets fixing on the rotary stage. The coordinates of the three targets are measured based on the modified sequential multilateration method using a single laser tracker when the rotary stage is rotated. Then geometric error components are identified based on established geometric error model which takes the positioning error of the targets as input. The validity of the proposed method is verified through both computer simulation and experiments conducted on a multi-axis machine tool.

Identification and compensation of geometric errors of rotary axes on five-axis machine by on-machine measurement

The geometric errors of rotary axes are the fundamental errors of a five-axis machine tool. They directly affect the machining accuracy, and require periodical measurement, identification and compensation. In this paper, a precise calibration and compensation method for the geometric errors of rotary axes on a five-axis machine tool is proposed. The automated measurement is realized by using an on-the-machine touch-trigger technology and an artifact. A calibration algorithm is proposed to calibrate geometric errors of rotary axes based on the relative displacement of the measured reference point. The geometric errors are individually separated and the coupling effect of the geometric errors of two rotary axes can be avoided. The geometry error of the artifact as well as its setup error has little influence on geometric error calibration results. Then a geometric error compensation algorithm is developed by modifying the numeric control (NC) source file. All the geometric errors of the rotary errors are compensated to improve the machining accuracy. The algorithm can be conveniently integrated into the post process. At last, an experiment on a five-axis machine tool with table A-axis and head B-axis structure validates the feasibility of the proposed method.

A machining test to calibrate rotary axis error motions of five-axis machine tools and its application to thermal deformation test

This paper proposes a machining test to parameterize error motions, or position-dependent geometric errors, of rotary axes in a five-axis machine tool. At the given set of angular positions of rotary axes, a square-shaped step is machined by a straight end mill. By measuring geometric errors of the finished test piece, the position and the orientation of rotary axis average lines (location errors), as well as position-dependent geometric errors of rotary axes, can be numerically identified based on the machine׳s kinematic model. Furthermore, by consequently performing the proposed machining test, one can quantitatively observe how error motions of rotary axes change due to thermal deformation induced mainly by spindle rotation. Experimental demonstration is presented.

A Machining Test to Evaluate Geometric Errors of Five-axis Machine Tools with its Application to Thermal Deformation Test

This paper proposes a machining test to calibrate position-dependent geometric errors, or “error map,” of rotary axes of a five-axis machine tool. At given sets of angular positions of rotary axes, a simple straight side-cutting using a straight end mill is performed. By measuring geometric errors of the machined test piece, position and orientation of rotary axis average lines (location errors), as well as position-dependent geometric errors of rotary axes, can be numerically identified based on the machine's kinematic model. Furthermore, by repeating the proposed machining test consequently, one can quantitatively observe how the position and the orientation of rotary axes change with respect to the tool spindle due to thermal deformation induced mainly by tool spindle rotation. Experimental demonstration is presented.

Influence of position-dependent geometric errors of rotary axes on a machining test of cone frustum by five-axis machine tools

A machining test of cone frustum, described in NAS (National Aerospace Standard) 979, is widely accepted by machine tool builders to evaluate the machining performance of five-axis machine tools. This paper discusses the influence of various error motions of rotary axes on a five-axis machine tool on the machining geometric accuracy of cone frustum machined by this test. Position-independent geometric errors, or location errors, associated with rotary axes, such as the squareness error of a rotary axis and a linear axis, can be seen as the most fundamental errors in five-axis kinematics. More complex errors, such as the deformation caused by the gravity, the pure radial error motion of a rotary axis, the angular positioning error of a rotary axis, can be modeled as position-dependent geometric errors of a rotary axis. This paper first describes a kinematic model of a five-axis machine tool under position-independent and position-dependent geometric errors associated with rotary axes. The influence of each error on machining geometric accuracy of a cone frustum is simulated by using this model. From these simulations, we show that some critical errors associated with a rotary axis impose no or negligibly small effect on the machining error. An experimental case study is presented to demonstrate the application of R -test to measure the enlargement of a periodic radial error motion of C -axis with B -axis rotation, which is shown by present numerical simulations to be among potentially critical error factors for cone frustum machining test.