Estimation and compensation of geometric errors for rotary axes are among methods to improve machining accuracy of five-axis machine tools. Studies have been conducted on various methodologies for estimating geometric errors for rotary axes, which are essential for improving machining accuracies of five-axis CNC machine tools. This paper presents a method for estimating geometric errors of a rotating/tilting table using a cross-shaped calibration artifact with a touch trigger probe. The proposed method includes rotary axes error estimation equations for angles of each rotary and tilt axis based on locations of probing points. Computer simulations were performed based on a MATLAB/Simulink and ADAMS cosimulation system using the probing cycle process to verify the proposed method. Computer simulation results confirmed the usefulness of the proposed method in terms of volumetric errors.
Tool-center-point (TCP) calibration and geometric error identification procedures are proposed to improve the accuracy of a 6-axis manipulator with a tilting rotary table. The accuracy of a 6-axis manipulator is affected by the accuracy of TCP calibration. In general, TCP calibration of the 6-axis manipulator uses a conical fixture provided by the manufacturer. However, since a TCP cannot be accurately positioned to the tip of the conical fixture repeatedly, a large positional deviation occurs at the calibration depending on the worker proficiency. Thus, accuracies of TCP calibration and the 6-axis manipulator are reduced. In this paper, a 3-DOF measuring device, consisting of a nest with three dial gauges and a precision ball, is developed to calibrate the TCP and to improve the accuracy of the 6-axis manipulator. Then, geometric errors of a tilting rotary table are identified via double ball-bar measurements according to the ISO 10791-6 with TCP initial alignment using an extension fixture. Finally, proposed TCP calibration and geometric error identification procedures are validated experimentally, and they show improvements in positional accuracy by 55 and 90%, respectively.
ISO 10791-6 specifies test conditions, BK1 and BK2, including circularly interpolated motions by simultaneous control of two linear axes and a rotary/tilting axis, for five-axis machine tools with a tilting-rotary table. Eccentricities of measured motions are used to identify position-independent geometric errors of the rotary/tilting axis. However, time-consuming alignments of measurement devices are required to execute the circular motions due to large geometric errors of the tilting axis. In this paper, a simple method is proposed to align an initial position of a tool-center-point (TCP) relative to the actual tilting axis of five-axis machine tools for application of ISO 10791-6. A ball at the tool nose with an extension fixture, supplied commercially by a double ball-bar manufacturer, is used to measure positional deviations of a ball on workpiece table at 90° command angle of a tilting axis. An alignment error of a TCP is identified simply by using a geometric relationship of the TCP and measured deviations. Then, identified alignment errors are used to calculate initial position of a TCP for fine measurements of position-independent geometric errors specified in ISO 10791-6. The proposed method is applied to a five-axis machine tool and verified experimentally.
Citations
Citations to this article as recorded by
A Study on the Estimation of Geometric Errors for Rotary Axes of a Five-Axis Machine Tool Using a Cross-Shaped Calibration Artifact Jeongmo Kang, Dayoung Kim, Sungchul Jee Journal of the Korean Society for Precision Engineering.2023; 40(1): 87. CrossRef
A TCP Calibration of a 6-Axis Manipulator and Geometric Errors Identification of a Tilting-Rotary Table Kwang-Il Lee, Do-Hun Kim, Hoon-Hee Lee, Seung-Han Yang Journal of the Korean Society for Precision Engineering.2022; 39(4): 253. CrossRef
A new technique based on the reversal method, is suggested to measure squareness error of the two-linear axes system. The technique uses the L-type steel bar, a capacitive sensor, and three experimental installations required to measure squareness error and two horizontal straightness errors. Profile and squareness of the L-type steel bar are estimated, by using the principle of the reversal method. Also, setup errors inevitable at installation, are separated from measured data using the least square method. Multi-DOF errors of two-linear axes system are measured and analyzed, using the suggested technique. Also, the reference mirror with flatness of 30 nm is used to verify the suggested measurement technique. Difference between the two measurement methods is 3.25 arcsec, a value within measurement repeatability.
In the manufacture of mechanical components, volumetric errors of a machine tool should be checked and reduced to meet the required tolerance levels. In this paper, we propose a quick and simple method of measurement for checking and compensating geometric errors which include scaling and squareness errors. During the measurement, which usually takes approximately 5 minutes to complete, the machine tool is first commanded into four vertices sequentially on a virtual regular tetrahedron. Subsequently, the six lengths between four vertices are measured using a double ball-bar and geometric errors are calculated from the measured lengths. In order to verify the measurement result, the measured geometric errors are compensated using NC-code and the six lengths are re-measured to confirm the error correction. In conclusion, a double ball-bar circular test on XY-, YZ-, ZX-plane is done, first without compensation and then with the compensation of the measured geometric errors to check the effect of compensation practically.
Citations
Citations to this article as recorded by
Use of a Virtual Polyhedron for Interim Checking of the Volumetric and Geometric Errors of Machine Tools Kwang-Il Lee, Heung-Ki Jeon, Jae-Chang Lee, Seung-Han Yang International Journal of Precision Engineering and Manufacturing.2022; 23(10): 1133. CrossRef
Measurement of Location Errors in a Horizontal 4-axis Machine Tool using a Touch Trigger Probe Ji Hun Jeong, Gyungho Khim, Jeong Seok Oh, Sung-Chong Chung Journal of the Korean Society for Precision Engineering.2019; 36(8): 745. CrossRef
A fine stage is developed for the 3-DOF error compensation of a linear axis in order to improve the positioning accuracy. This stage is designed as a planar parallel mechanism, and the joints are based on a flexure hinge to achieve ultra-precise positioning. Also, the effect of Abbe’s offsets between the measuring and driving coordinate systems is minimized to ensure an exact error compensation. The mode shapes of the designed stage are analyzed to verify the desired 3-DOF motions, and the workspace and displacement of a piezoelectric actuator (PZT) for compensation are analyzed using forward and inverse kinematics. The 3-DOF error of a linear axis is measured and compensated by using the developed fine stage. A marked improvement is observed compared to the results obtained without error compensation. The peak-to-valley (PV) values of the positional and rotational errors are reduced by 92.6% and 91.3%, respectively.
Citations
Citations to this article as recorded by
A new method to identify the position-independent geometric errors in the rotary axes of five-axis machine tools Seth Osei, Wei Wang, Qicheng Ding Journal of Manufacturing Processes.2023; 87: 46. CrossRef
Development and Performance Evaluation of a Fine Stage for Compensating 6-DOF Motion Errors of an Ultra-Precision Linear Stage Hoon-Hee Lee, In-Seok Lee, Kwang-Il Lee, Seung-Han Yang Journal of the Korean Society for Precision Engineering.2021; 38(2): 123. CrossRef
Optimal On-Machine Measurement of Position-Independent Geometric Errors for Rotary Axes in Five-Axis Machines with a Universal Head Kwang-Il Lee, Jae-Chang Lee, Seung-Han Yang International Journal of Precision Engineering and Manufacturing.2018; 19(4): 545. CrossRef
Error Compensation Using Variable Stiffness in Orbital Grinding Joon Jang, Woo Chun Choi International Journal of Precision Engineering and Manufacturing.2018; 19(3): 317. CrossRef
Face- and Body-Diagonal Length Tests using a Double Ball-Bar for Squareness Errors of Machine Tools Seung-Han Yang, Hoon-Hee Lee, Kwang-Il Lee International Journal of Precision Engineering and Manufacturing.2018; 19(7): 1039. CrossRef
First
Prev
