• Title/Summary/Keyword: Volumetric Positioning Error

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The enhancement of 3-dimensional positioning accuracy by measuring error factors for CNC machine tools (공작기계의 오차요소 측정을 통한 3차원 위치정밀도 향상)

  • 손진욱;서석환;정세용;이응석;위현곤
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1994.10a
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    • pp.260-265
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    • 1994
  • Efforts have been devoted to developing rapid and accurate methods for measuring the errors of machine tools. The method os measurement and calibration of machine tool errors should be general and efficient. The objective of this study is to show in detail the full sequence from the measurement of errors factors to the verification of the positioning accuracy after compensation for the volumetric error. In this paper, we described the steps in measuring the volumetric error parameters, a general error model composed of error parameters, temperature, and the desired position. The validity of the error calibration methods proposed in this paper was tested using a vertical 3-axis CNC machine with a laser interferometer and a ball bar.

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Calibration of 6-DOF Parallel Mechanism Through the Measurement of Volumetric Error (공간오차 측정을 통한 6자유도 병렬기구의 보정)

  • Oh, Yong-Taek;Saragih, Agung S.;Kim, Jeong-Hyun;Ko, Tae-Jo
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.11 no.3
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    • pp.48-54
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    • 2012
  • This paper introduces the kinematic calibration method to improve the positioning accuracy of a parallel mechanism. Since all the actuators in the parallel mechanism are controlled simultaneously toward the target position, the volumetric errors originated from each motion element are too complicated. Therefore, the exact evaluation of the error sources of each motion element and its calibration is very important in terms of volumetric errors. In the calibration processes, the measurement of the errors between commands and trajectories is necessary in advance. To do this, a digitizer was used for the data acquisition in 3 dimensional space rather than arbitrary planar error data. After that, the optimization process that was used for reducing the motion errors were followed. Consequently, Levenberg-Marquart algorithm as well as the error data acquisition method turned out effective for the purpose of the calibration of the parallel mechanism.

A Useful Technique for Measuring the 3-dimensional Positioning of a Rotating Object (회전체의 효과적인 3차원 위치오차 측정방법)

  • Lee, Eung-Seok;Wi, Hyeon-Gon;Jeong, Ju-No
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.6
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    • pp.918-924
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    • 1997
  • A method for measuring the accuracy of rotating objects was studied. Rotating axis errors are significant; such as the spindle error of a manufacturing machine which results in the surface roughness of machined work pieces. Three capacitance type displacement sensors were used to measure the rotating master ball position. The sensors were mounted to the three orthogonal points on the spindle axis. The measurement data were analyzed and shown for rotating spindle accuracy, not only for average roundness error but also for spindle volumetric positional error during the revolutions. This method is simple and economical for industrial field use with regular inspection of rotating machines using portable equipment. Measuring and analyzing time using this method takes only a couple of hours. This method can also measure microscopic amplitude and 3-dimensional direction of vibrating objects.

Error Prediction Considering the Measurement Direction in OMM System (OMM 시스템에서 측정방향을 고려한 가공물의 오차평가)

  • 최진필;이상조;권혁동
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2002.05a
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    • pp.632-635
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    • 2002
  • In this paper, a general procedure to determine machine tool errors from the on-machine measurement (OMM) data is described. First, a parameterized error model of a machine tool is illustrated by approximating error components as linear function of axis positions, and a modified error model is proposed which includes backlash effects. To determine the unknown model coefficient vectors of the forward and backward error model, an artifact with 8 cutes is made and calibrated on CMM. Then, lower-left and upper-right cube corners are measured with a touch-trigger probe mounted on the machine tool spindle. Measured error data are used to determine the coefficient vectors. The positioning errors in the XY plane at the fixed z position are simulated for the forward and backward error model.

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Evaluation on the Usefulness of 6DoF Couch in V-MAT on Patients with Long length of Target (표적의 길이가 긴 환자의 용적회전변조 방사선치료 시 6DoF Couch의 유용성 평가)

  • Choi, Young Se;Park, Hyo Kuk;Kim, Se Young;Kim, Joo Ho;Lee, Sang Kyoo;Yoon, Jong Won;Cho, Jung Heui
    • The Journal of Korean Society for Radiation Therapy
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    • v.29 no.2
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    • pp.53-64
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    • 2017
  • Purpose: To evaluate the usefulness of the $HexaPOD^{TM}$ evo RT system(6DoF couch) and the tendency of dose difference according to size of rotational direction error for volumetric rotational modulated radiotherapy(V-MAT) in patients with long target lengths. Therefore, it is suggested to recommend the need for rotational error correction. Materials and Methods: Ten patients with Esophagus cancer or Breast cancer including SCL treated with HexaPOD 6DoF(Six-Degree of Freedom) couch were included in this study. 6DoF couch was used to measure the difference in dose according to the rotation error in the directions of Rx(pitch), Ry(roll), and Rz(yaw). Each rotation error was applied. Positioning variation on x, y and z axis was verified and random variations were made by 6DoF couch with positioning variation. Modified DQA is conducted and point dose and gamma value are analyzed and compared. In addition, after applying the rotation error every $1^{\circ}$ to treatment plans of each target with a diameter of 3 cm, 5, 10, 15, and 20 cm respectively, gamma passing rate is being monitored by its aspect of change according to types and sizes of the target length and rotation error. Results: Mean error of the point dose and Gamma passing rate when the position variation was applied were $2.50{\pm}1.11%$ and $84.1{\pm}7.39%$ in the Rx direction, $2.36{\pm}1.16%$, and $81.0{\pm}8.49%$ in the Ry, $2.35{\pm}1.10%$ and $84.4{\pm}6.99%$ in the Rz direction, respectively. As a result of analysis on gamma passing rate according to types and sizes of the target length and rotation error, the gamma passing rate tended to decrease with increasing rotation error in the Rx and Rz directions except Ry direction. In particular, the lowest gamma passing rate (74.2 %) was in the case of $2.5^{\circ}$ rotation error in Rz direction of the target of 10 cm. Conclusion: The correction of the rotational error is needed for volumetric modulated radiotherapy of the treatment area with a long target length, and the use of 6DoF couch will improve the reproducibility of the patient position and the quality of the treatment.

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