Ball Bar Research Articles

An Improvement Geometric Error Identification Method of CNC Machine Tool Based on Double Ball Bar

The double ball bar is widely used because it can quickly, easily and cost-effectively detect and evaluate the accuracy of CNC machine tools. But since the error recognition algorithm based on the double ball bar ignores the quadratic item, its recognition accuracy would be reduced. In this paper, an improved CNC verticality error and position error identification formula, combined with the machine tool error model to deduce a new error recognition model of double ball bar measurement is proposed. It can be drawn that the accuracy of the model are better than the existing methods because it keeps the second item in the derivation process of the model.

Using a double ball bar to identify position-independent geometric errors on the rotary axes of five-axis machine tools

A measuring method using a double ball bar (DBB) is proposed for identifying the eight position-independent geometric errors (PIGE) on the rotary axes of five-axis machine tools. Three measuring patterns are used, in which the translational axes are kept stationary and only two rotary axes move to obtain a circular trajectory. In this way, the effects of translational axes are totally excluded, and the measurement accuracy is improved. Motion equations, describing how the A-axis and C-axis move simultaneously to realize a circular trajectory, are presented. The influence of each deviation on the measurement patterns is simulated, and analytical solutions for the eight PIGEs are demonstrated. Finally, the measuring method is verified in a five-axis CNC machine tool. Experimental results confirm that the method provides precision results for the eight PIGEs.

Research on Precision Detection and Error Compensation Technology for 3-Axis CNC Milling Machine

Error detection and compensation technology is an economical and effective method for improving the precision of CNC machine tool. The paper established the geometric errors model of three-axis CNC milling machine based on homogeneous coordinates transformation theory. Error detection is tested by digital ball bar and error compensation software is developed for XK7132 milling machine, the compensation effect is evaluated by a laser interferometer. The results show that the precision of CNC milling machine is improved effectively by the proposed method.

Feed Rate Influence on Motion Error Characteristics of CNC Vertical Milling Machine

The increasing number of the Computer Numerical Control (CNC) machines usage in the manufacturing field appears to suggest that they are expected to be in good running condition. Machine tools such as CNC vertical milling machines are meant to produce precise work parts. Motion errors are factors which can directly affect the accuracy of the machine. This study presents an opportunity for interested parties to understand the characteristics of motion errors that exist in the CNC vertical milling machines with different feed rate settings. The purpose of this project is to find out any abnormalities apparent to the machine performance as the feed rate setting is increased. The motion errors of the CNC machines were examined by using a measuring device, namely Double Ball Bar (DBB). This equipment is designed to examine machine performance by measuring the accuracy of its movements. This device, which has two balls of identical size at the end of the bar, was mounted on a spindle and onto a special holder which is mounted on the working table. The machine is programmed to move in a circular motion, clockwise and anti-clockwise in three planes, XY, YZ and ZX. Any deviation from the standard data will represent the imperfection of the machines condition, especially mechanical components such as the slide bearing, spindle bearing or servo motor responses. By knowing the most significant error origin, the corrective countermeasures can then be carried out.

Geometric error modeling and compensation for large-scale grinding machine tools with multi-axes

Synthesis modeling of a geometric error-based traditional method for large-scale grinding machine tools with six axes is too complicated to perform in a real-time compensator with a built-in position control system, and it is difficult to obtain all of the error elements corresponding to the model. This paper proposed a novel strategy in which a machine may be considered as translation axes and rotary axes, and geometric errors of the translation axes and rotary axis are modeled and the geometric error models of the machine are very simple for real-time error compensation. The volumetric errors of the translation axes are measured using spatial circular curve ball bar test, and every element of the rotary axis is also obtained by a series of considerate ball bar tests. According to the characteristics of a position controller used in the machine, a synthesis error compensation system based on the NUM numerical control system was developed. Error compensation experiments were carried out, and the results show that the accuracy of the machine is improved significantly.

2 축 동시구동을 통한 볼바 측정용 원호경로 생성 방법

5 축 공작기계에서 회전축을 포함한 동시 구동에 대한 볼바 측정용 원호 경로 생성 및 NC 데이터 작성은 CAM 소프트웨어를 사용할 경우 공작기계의 구조, 사용되는 동시 구동축 종류 및 볼바 셋업 조건 등 다양한 시스템 구조와 변경된 측정 환경에 따라 매번 많은 시간과 노력을 수반해야 한다. 본 연구는 소프트웨어의 의존 없이 다양한 볼바 측정 조건에서도 항상 사용할 수 있는 두 축 동시 구동을 통한 원호 경로를 생성하는 기법을 소개하며 임의의 공작기계의 구조 및 동시 구동축의 종류, 볼바 셋업 조건 등을 고려한다. 제안한 원호 생성 기술을 이용하여 세 가지의 사례에 대한 원호 경로 생성용 수학식을 제시하며 더불어 볼바 부품간 물리적 간섭을 방지하기 위한 측정 가능성 사전 검사 방법을 제안한다. 제안한 기법의 타당성은 두 개의 회전축을 이용한 볼바 측정 실험을 통해서 검증한다.

Design of MK1432/H CNC Precision Cylindrical Grinding Machine

MK1432/H CNC precision cylindrical grinding machine is suitable for precision grinding IT6 to IT5 cylindrical or conical revolving workpiece, the table of the rail bed for the paste with plastic rail, the first holder of the rotating dial tone from the motor frequency speed, with Germany's Siemens 810D CNC two-axis system, built-in PLC, liquid crystal display. Servo motor is 1FK6 series; configure automatic measuring instrument line detection, automatic grinding work to achieve closed-loop cycle, ensuring high machining dimensional accuracy. Machine bed using a large round hole, fin-shaped reinforcement plates, Bench points up and down the table, you can grinding conical, bed and table in the guide rail for the laminating, the friction coefficient is small, table driven by a servo motor directly to the Deputy move the ball bar, smooth and reliable movement. Mainly used in automobile, motorcycle parts factory and other machinery manufacturing industry, for the grinding disc type, short axis, and taper shank type etc. parts.

Enhancement of geometric accuracy of five-axis machining centers based on identification and compensation of geometric deviations

The present paper describes the enhancement of kinematic accuracy of five-axis machining centers with a tilting rotary table. Geometric deviations inherent to the five-axis machine are calibrated through the actual trajectories measured by two different settings of a ball bar in simultaneous three axis motion. Measurement using a cylindrical coordinate system is superior to measurement using a Cartesian coordinate system from the viewpoint of the number of measurements. In order to verify the effectiveness of the calibration method, the inherent geometric deviations measured on the cylindrical coordinate system were corrected through the post processing of NC data for cutting the cone-frustum.The relative displacement between the tool center point and the workpiece was detected by the ball bar. Based on the experimental results, it is confirmed that the radius, center position, and roundness of the three-dimensional circular trajectory are improved when the inherent geometric deviations are corrected.

5 축 동시 구동을 통한 볼바 측정용 원추형 경로 생성 방법

본 연구는 원추대 가공과 등가인 동시 5 축 구동을 통한 볼바 측정용 경로 생성 기법을 소개하며 시스템 구조 형태(Structural configuration)에 관계없이 모든 5 축 공작기계에 대해 적용 가능한 일반화된 방법을 제시한다. 5 축 공작기계 시스템 정보와 원추형 정보, 그리고 볼바 측정 정보 등을 입력 받아 NC 코드 생성, 다양한 오차 평가 시뮬레이션 및 측정 시험을 쉽게 수행할 수 있도록 원호 경로 생성에 필요한 수학적 기계 입력 모델을 제시한다. 또한 제시된 원추형 경로 모델을 토대로 5 축 동시 구동 시 회전축의 이송 범위를 수학적으로 검토하며 반꼭지각 및 기울기각의 크기 차이, 볼바 틸팅 허용각 및 워크피스 볼의 오프셋 위치 등 여러 가지 조건이 이송 범위에 미치는 영향에 대해 분석한다.

S111043 パラレルメカニズムを用いた高速・高精度3次元計測システム(第26報) : ダブルボールバーを用いた校正([S111-04]第19回卒業研究コンテスト(4))

S111043 パラレルメカニズムを用いた高速・高精度3次元計測システム(第26報) : ダブルボールバーを用いた校正([S111-04]第19回卒業研究コンテスト(4))

Sensitivity Analysis in Ball Bar Measurement of Three-Dimensional Circular Movement Equivalent to Cone-Frustum Cutting in Five-Axis Machining Centers

Sensitivity Analysis in Ball Bar Measurement of Three-Dimensional Circular Movement Equivalent to Cone-Frustum Cutting in Five-Axis Machining Centers

Accuracy analysis of machine tools using Elastically Linked Systems

The paper introduces the concept of Elastically Linked Systems (ELS) to directly relate the machine tool positional and static accuracy to the machined part's geometric errors and form deviation. Practical implementation of the ELS concept resulted in a novel test equipment, Loaded Double Ball Bar (LDBB) which is a precision mechatronic device with variable load. The test method based on the device is able to reveal machine tool characteristics not obtainable with existing methods as for instance the variation of stiffness in the entire working space. The LDBB is used to experimentally evaluate the stiffness and the corresponding accuracy of five machine tools.

A Method for Measuring the Systematic Errors of CNC-Machine Tools

The method used for measurement and calibration of machine tool errors should be general and efficient. With this method, the machine tool status can be completely identified and its accuracy can be enhanced by software error compensation. The point compensation method can be used as a means for modifying the nominal tool path and on-machine inspection where the machine tool is used as a coordinate measuring machine. The validity of the error calibration method proposed in this' paper was shown using a vertical 3-axis CNC machine with a laser interferometer and a ball bar technique.

Analysis of circular trajectory equivalent to cone-frustum milling in five-axis machining centers using motion simulator

The present paper describes the effect of the half apex angle of the cone-frustum on the motion trajectory under simultaneous five-axis motion and the effect of the sensitive direction of the ball bar when the motion trajectory is measured along the three-dimensional circular conical path. In the present paper, simulation of the measurement by means of a ball bar instrument is mainly conducted using a motion simulator developed previously. In particular, a precise mathematical model was developed to express the pitch errors of the axes of rotation of the five-axis machining center having a tilting rotary table driven by worm gears. In the experiment and simulation, primarily the center position and half apex angle of the cone-frustum were varied. In addition, two sensitive directions of the ball bar were investigated. The motion simulator incorporating the pitch error model can express the detailed trajectories obtained by the ball bar, even if the half apex angle and center position of the cone-frustum and the sensitive direction of the ball bar were changed. Then, the influence of the frictional force of the linear axes of motion, and the backlash and pitch error of the axes of rotation on the circular trajectories were analyzed. In particular, for the case of a half apex angle of 45°, the trajectory due to the errors of the axis of rotation is strongly affected by the sensitive direction of the ball bar.

Ram spindle tolerance compensation for horizontal borer

Ram–Quill combination spindle has been applied widely in horizontal boring milling machine. It is a great benefit that the machine can be used for various applications. But as the report of experiment, the ram housing bent when it is moved for more than half of its maximum travel. The straightness of Ram housing is out of the tolerance and the runout of the spindle is way behind the requirement when spindle is at the maximum extension point. This paper proposes an electro-hydraulic monitoring and compensation system which will be able to adjust the pressure to the compensation mechanism in time. The experiments prove that the straightness of horizontal surface can meet the requirement, and a ball bar test at the extremely weak point shows an improvement of the roundness tolerance for 65.8 %. This can improve the tolerance of the machine, becoming a superior device.

Calibration of location errors of rotary axes on five-axis machine tools by on-the-machine measurement using a touch-trigger probe

As a basis to improve the motion accuracy of five-axis machining centers, it is important to develop a methodology to calibrate location errors of rotary axes, one of the fundamental error sources in the five-axis kinematics, in an accurate, efficient, and automated manner. This paper proposes a scheme to calibrate location errors of rotary axes by on-the-machine measurement of a test piece by using a contact-type touch-trigger probe installed on the machine's spindle. Compared to conventional calibration schemes described in latest revision of ISO standards (ISO/DIS 10791-1:2012 and ISO/DIS 10791-6:2012), where a precision sphere and a linear displacement sensor or the ball bar are used, the proposed approach is more suitable to efficient and automated calibration procedure of location errors, without requiring an experienced operator to perform the tests. The uncertainty analysis of the calibration of location errors is also presented with a particular interest in the influence of error motions of linear axes. The experimental demonstration is presented.

Ball Bar Measurement on Machine Tools with Rotary Axes

A ball bar is a very convenient device for measuring the motion accuracy of machine tools. Some trials have also been done for measuring motion accuracy of industrial robots. Nowadays, multi-axis machines such as five-axis machining centers are very popular, and therefore, there is increased demand for checking their accuracy. This paper introduces an idea for checking the motion accuracy of five-axis machining centers and diagnosing error sources by reviewing trial measurements on articulated industrial robots. There are two problems. The first problem is that the ball bar can measure only distances, and the second problem is that the ball bar is a linear device and therefore not suitable for the rotary axis motion of 5-axis machines and articulated robots. Finally, the test conditions for the measurement of the motion accuracy of a machine tool showing conical motion, by using the ball bar and ISO/DIS 10791-6 (which is currently being edited) are reviewed and verified.

Sensitivity Analysis in Ballbar Measurement of 3D Circular Interpolation Motion Equivalent to Cone-Frustum Cutting in Five-Axis Machining Centers

This paper describes the testing method for five-axis machining centers using three-dimensional circular interpolation movement equivalent to the cone-frustum cutting. It is assumed in the simulation that a ball bar system is used as a measuring device that can freely moves in 3D space. The ratio of a measurement value by the ball bar and a real error of each axis is defined as a sensitivity coefficient of axis. The sensitivity coefficient of each axis was calculated changing the apex angle and the center location of virtual cone-frustum. The 3D circular movements are simulated, and the effect of the pitch errors of the axes of rotation was investigated by changing the sensitive direction of the ball bar. From the view point of sensitivity coefficient, it is pointed out that if the measurement is conducted by the ball bar which is parallel to the bottom of a cone-frustum whose center is set away from the center line of the axis of rotation, it is possible to measure the movement errors of five axes.

A Model for Geometry-Dependent Errors in Length Artifacts.

We present a detailed model of dimensional changes in long length artifacts, such as step gauges and ball bars, due to bending under gravity. The comprehensive model is based on evaluation of the gauge points relative to the neutral bending surface. It yields the errors observed when the gauge points are located off the neutral bending surface of a bar or rod but also reveals the significant error associated with out-of-straightness of a bar or rod even if the gauge points are located in the neutral bending surface. For example, one experimental result shows a length change of greater than 1.5 µm on a 1 m ball bar with an out-of-straightness of 0.4 mm. This and other results are in agreement with the model presented in this paper.

A24 5軸マシニングセンタの円錐台試験法(OS1 最新工作機械(1))

ISO standards related to accuracy test of 5-axis machining center is currently undergoing the final stages. In this research, real cutting is performed by accuracy inspection about truncated cone cutting by the 5-axis simultaneous control under proposal, and cutting conditions and an evaluation method are examined. In addition, we also consider motion accuracy inspection by using ball bar interpolation accuracy of the proposed tests, simulating the cutting of the above mentioned truncated cone.