Abstract
Since a nonlinear relationship exists between the position coordinates of the rotation axes and components of the tool orientation, the tool will deviate from the required plane, resulting in nonlinear errors and deterioration of machining accuracy. Few attempts have been made to obtain a general formula and common rules for nonlinear error because of the existence of various kinematic structures of machine tools with orthogonal configuration. This paper analyzes the relationship between the deviation of cutter location points and motion of tool orientations. Five-axis CNC machine tools are divided into two groups according to the configuration of the two rotational joints and the home position. Motions of the tool are regarded as a combination of translation and rotation. A model for error calculation is then built. The maximum deviation of the tool with respect to the reference plane generated by the initial and the final orientation is used to quantify the magnitude of the errors. General formulas are derived and common change rules are analyzed. Finally, machining experiment is conducted to validate the theoretical analysis. The research has important implications on the selection of a particular kinematic configuration that may achieve higher accuracy for a specific machining task.
Highlights
Compared with the three-axis machine tool with three orthogonal translational axes, the five-axis machining center is equipped with two additional perpendicular rotational joints
The home position of the tool orientation cannot be parallel to the rotation axis specified by the second character, since it is not feasible for a tool to rotate about its own axis, which means that each type of rotary axis feature has two appropriate cutter orientations to enable five-axis machining
This study developed a general model to analyze the relationship between nonlinear errors and the movement of the rotation axes for various machine configurations
Summary
Compared with the three-axis machine tool with three orthogonal translational axes, the five-axis machining center is equipped with two additional perpendicular rotational joints. The papers mentioned above acknowledged that nonlinear errors in five-axis machining should focus on the configuration of machine tools and the variation of tool orientation, minimal attempts have been made to quantify their magnitude. To address this problem, a method was proposed [24] to evaluate the nonlinear errors induced by the motion of the rotary axes of vertical SR five-axis machine tools. A general model and common rules for nonlinear errors due to the motions of the rotation axes of five-axis machine tools with orthogonal configuration are still lacking.
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