Papers by Keyword: Error Modeling

Abstract: The positioning error of ultra-precision machine tools is the primary factor directly affecting the machining accuracy. It mainly depends on the machine tools guide. And its variation trend contains the same inertia as that of the machine tools movement. The variation trend of the positioning error is the derivative of a function fitted with the positioning errors of three adjacent testing points. The variation trends function is fitted with the variation trend of many points. The model of positioning error is the integral of the variation trends function. Because the variation trend of positioning error has certain inertia, the model of positioning error which is obtained in this way is more precise and more reliable than error function model which is directly fitted with limited discrete data.

Abstract: A new method compensating geometric error components of a four-axis horizontal machine tool is presented in this paper. Homogeneous transformation matrices (HTMS) and error conversion are integrated in the compensation strategy. A mathematical model which contains 29 geometric error components is established based on HTMS and the errors in X, Y and Z directions are obtained through calculation. The errors in three directions are compensated by shifting the corresponding axis. But the configuration of this machine tool is X-axis, Z-axis, B-axis, C-axis without Y-axis, so the errors in X, Y and Z directions need to be converted into X, Z and C directions which is different from the traditional machine tools. The errors after conversion are used to compensation directly. This approach is significant for the error modeling and compensation which is an easy and efficient way to improve the precision of the four-axis machine tools.

Abstract: The objective of this paper is to describe the calibration test method and conditions for MEMS-based IMUs including accelerometers and gyroscopes. This method is mainly used to derive deterministic error bounds within the acceptable range of accuracy. After a detailed description of the error model, the calibration process, test procedure, and test results as well as practical challenges are discussed. The presented method is simple, cheap and fast that takes only a few hours for calibration and validation of these sensors.

Abstract: Coordinate Measuring Machines (CMM's) have attributes to provide results with accuracy and repeatability in measurements, so they are considered equipment with potential for application in industrial environments, specifically in inspection processes. However, as in a machine tools the knowledge of the errors in CMM is needed and allows applying techniques of error compensation. This study aimed to develop a mathematical model of the kinematic errors of a bridge type CMM in "X", "Y" and "Z" directions. Modeling of the errors was accomplished using coordinate transformations applied to the rigid body kinematics; the method of the homogeneous transformation was used for the development of the model. The position and angular errors for the three axes of CMM, in addition to errors related to the absence of orthogonality between them were equated. This study allowed to conclude that modeling of errors applied to CMM allied to calibration is able to evaluate the metrological performance of equipment with displacement on guides, thus is possible to use this technique as error budget analysis in machines.

Abstract: This paper reviews the development history of parallel machine tool and new achievements in China and abroad. Typical methods of error modeling, error detection and error compensation are introduced. After analyzing the biggest problem of recent error compensation technology, this paper prospects the further research trends.

Abstract: A 3-PUU parallel mechanism was studied, which can perform one-dimensional translation about z-axis and two-dimensional rotations about y-axis and x-axis. This paper shows the study about the precision analysis, the dimensional analysis and the synthesis problem of the parallel mechanism having less degree of freedom. First, the closed-loop vector model was built based on analyzing the branched-chains of 3-PUU, the pose error model was built through the differential geometry, and the error model of positive solutions was obtained which contains all the structural parameters errors. For the error of structural parameters given, the pose output error can be solved out by application of this model, the area of maximum error is found out. And the influence of pose output error was analyzed with postures changed. The dimensional analysis of 3-PUU was also done by this error model, and the reasonable selection of mechanism parameters was discussed. And then the rationality of structure dimensional design was discussed in this paper. Finally, this method also may be used in the dimensional analysis of other less freedom parallel mechanisms.

Abstract: Focus on the problems of calculation complexity and abstractness in the traditional analysis methods of serial-parallel mechanism, the complete kinematic product of exponentials formula of serial-parallel mechanism was established in the paper based on the screw representation of spatial rigid motion. The errors of 4 D-H parameters were equivalent to error screw and the practical screw coordinate containing error screw of every joint axis was established. After the practical kinematic product of exponentials formula of serial-parallel mechanism being derived, the pose error model of tool coordinate system was established. According to the above screw method, numerical calculation of cutting machine about kinematic and error analysis was performed with MATLAB and the calculation results were compared with the simulation results of ADAMS. The comparison results show that relative error of the two groups of calculation results is within the 0.001 orders of magnitude and the correctness of screw methods application in the analysis of serial-parallel mechanism.

Abstract: With the increasing requirements of the machining accuracy of CNC machine tools, the impact of thermal deformation is growing. Thermal error compensation technology can predict and compensate the thermal errors in real-time, and improve the machining accuracy of the machine tool. In this paper, the research objects of thermal error compensation is expanded to the volumetric error of the machine tool, the volumetric error modeling of a three-axis machine tool is fulfilled and a compensator is developed for the compensation experiment, which provides scientific basis for the improvement of the machining accuracy.

Abstract: The forward kinematics of manipulator was studied to analyze the positive position of the novel 2UPS-RPU parallel mechanism with series connection inputs. With the restrict condition of the lengths of three actuated limbs as constraint conditions, the constrained equations were established, and the four nonlinear equations were obtained to solve forward positional problems of the mechanism. Based on the elimination method, a two-dimensional equation is obtained by eliminating the four-dimensional equation. The search method based on the least square method of the MATLAB software was utilized to analyze forward position of 2UPS-RPU parallel mechanism. The results of numerical verification showed that through this method all forward solutions can be found which are basically coincident with the inverse ones, and the little error was caused by the accumulating calculation error. An error model was established based on differential theory and kinematics equations .This model simplified the installation error as the manufacturing error. Finally the error value was obtained by MATLAB ,which proved the error model was correct.

Abstract: To bring a new technological revolution, CNC technology and machines give the birth of a new era of control and production. The rapid development of CNC has considerably advanced the precision and ultra-precision machining technology to improve a new level and great attention. From error prevention and compensation, researches of the CNC machines precision at home and abroad were introduced. Key reasons for error compensation hardly use in the domestic widely were pointed out. Finally, the necessity and main contents of error compensation technology were presented according to the actual situation of enterprises.