Papers by Keyword: Error Identification

Abstract: Geometric errors of a machining center can cause great influence on machining accuracy, and these geometric errors should be identified and compensated in the actual working conditions. Taking a three-axis vertical machining center as example, 21 geometric errors of the machine tool were solved. By using the 12-line method based on a laser interferometer, identification principle of the positioning errors, straightness errors, pitch errors, yaw errors, roll errors and squareness errors are presented, and all of the 21 geometric errors of the machining center were identified. Geometric errors having great influence effect on machining accuracy can be identified. The research results provide guidance for analyze of geometric errors of machining center.

Abstract: Aiming at tedious of parameters identification in the process of robot calibration, this paper proposed a method to directly establish parameter error equations based on relative distance error by using the kinematics model in which the parameters error were considered, employing a laser interferometer to measure a 6R robot end-effector displacement distance along its Cartesian coordinates system axis direction, and respectively recorded the joint angle position data to the measured points, then taking all recorded data as basis for the robot kinematics parameter errors identifying equations and employing a hybrid genetic algorithm to solve the equations. The result shown that incomplete distance info can be used to identify kinematics parameters error in robot calibration process.

Abstract: In this study, a small, 6-DOF (degree of freedom) parallel mechanism worktable for machine tool was developed. There are a lot of factors that affect the positioning error and the accuracy of the machine tools. The uncertainty in position is mainly due to the rigidity of the structure, the geometric error of parts and assembly errors. It is very difficult to estimate the assembly errors and the link parameter of each part. In this paper, the uncertainty factor in positioning of the worktable was investigated and compensated based on measurement of movement error by using coordinate measuring machine (CMM).

Abstract: The worldwide competition calls for higher precision machine tool, so how to improve the machining precision is a hot topic. Error identification, as the first basic step of enhancing precision ,is paid expecially attention to. In this paper, two different but important kinds of identification methods—direct identification and indirect identification are introduced, what special is that these methods are achieved just by one equipment—laser interferometer named laser Doppler displacement measurement(LDDM).Through experiments, we can gain the errors of 3-axis machine tool including 3 displacement errors, 6 straightness errors,3 squareness errors, axis spike, backlash, circularity value, cyclic error and so on. The results will benefit for later accuracy improvement.

Abstract: Geometric errors identification of revolving axle of multi-axis machine tool has encountered a great difficulty in geometric errors compensation. This paper describes a new method to identify geometric errors inherent to revolving axle of multi-axis machine tool based on a ball-bar system. Under RTCP (Rotation Around Tool Center Point) or RPCP (Rotation Around Part Center Point) function, the displacement errors of revolving axle in X, Y and Z direction can be obtained by the ball-bar system respectively at every measurement angle. With the corresponding identification algorithm proposed in this paper, the whole six geometric errors of revolving axle can be identified. This new method is suitable for any type of multi-axis machine tool and without structural constraints. To confirm the validity of the proposed method, an experiment has been conducted on a five-axis machine tool, and the results show that this method is effective and applicable.

Abstract: In NC machining, the precision of the final parts is affected by many factors, including geometric deviation of machine tool components and structures, deformation of process system caused by cutting force and cutting heat, servo delay, tool wear and so on. Among which geometric error of machine tool is one of the most important factors. This study focused on geometric error identification and compensation of rotation axes of five-axis machine tools. A new method was proposed to identify the 6 geometric error parameters of each rotation axes of five-axis machine tools based on a ball-bar system. Regarding the machine tool as a rigid multi-body system (MBS), a geometric error model was established based on homogeneous transfer matrix (HTM). Finally, the geometric errors were compensated by correcting NC codes by the prototype software system developed in this study. An experiment and an application were conducted and the results show that the proposed method is effective to improve the machining accuracy.

Abstract: A computational model for position and posture error of 6-DOF parallel machines is proposed based on D-H transformation matrix and the inverse kinematics. The model is used to construct a linear least-square identification model for geometric parameter errors. Error identification program and compensation method are also presented. Simulation results indicate that the effects on position and posture of machines are almost equivalent from calculated least-square solution and from real values. The pose error of moving platform can be decreased up to 90% if error compensation is performed by modifying the input kinematic parameters of driving joints.

Abstract: It is inefficient and complicate to detect geometric errors of a heavy machine tool with large scale dimensions by using traditional laser interferometer. With the development of the laser tracker convenient for measuring large scale dimension, the accuracy of the laser tracker can meet the accuracy requirements for geometric error measurement of heavy machine tools. In this paper a method of using laser tracker for detecting and identifying the error of a heavy NC boring and milling machine tool is introduced. The measuring experiment demonstrates that this new method can improve the measurement efficiency.