Synchronization of tool tip and tool orientation contour errors in five-axis machining

In current CNC machines, each axis is generally controlled by an individual controller, which tries to minimize the axial position tracking error. However, eliminating the tracking errors of each individual axis in multi-axis feed drive systems may not guarantee the desired contouring accuracy. Tracking errors in individual driving axis result in tool tip contour error and tool orientation contour error during five-axis machining. Based on the conventional definition of the tool orientation contour error, which is defined as deviation in the normal direction from the desired orientation in spherical coordinates, even if the tool tip contour error and tool orientation contour error are very small, a mismatch between the tool tip position and tool orientation causes an overcut or undercut when these errors are treated independently. In order to avoid this mismatch, this paper presents a new definition of the actual tool orientation contour error that considers the synchronization between the tool tip contour error and tool orientation contour error. In addition, an estimation model for the tool orientation contour error is proposed. Simulation results demonstrate that the proposed model gives a better indication of the actual tool orientation contour error than the conventional definition.