Profile error compensation in fast tool servo diamond turning of micro-structured surfaces

There is increasing use of ultra-precision components with micro-structured surfaces in a range of areas such as optical, biological, medical, metrology artifacts and data storage. Fast tool servo (FTS) diamond turning is superior in machining precision and complicated micro-structured surfaces with wavelength above tens of microns. However, the component errors in the FTS diamond turning machine cause profile error to the machined micro-structured surfaces. In this paper, the main sources of component errors and their effect on the profile accuracy of the machined micro-structured surfaces are identified and analyzed. Compensation methods are proposed to accordingly modify the tool path for each component error to pre-compensate the induced profile errors. Typical micro-structured surfaces, e.g. sinusoidal wave along radial direction, sinusoidal wave along x direction and micro-lens array, were machined to show the effect of the component errors on profile accuracy and the effectiveness of the proposed compensation methods. ► Sliding error and dynamic error are identified as two important causes of the profile errors. ► An indirect method has been proposed to obtain the sliding error from the measured surface profiles of a workpiece. ► An integral sliding mode controller has been proposed to control the FTS. ► A method to modify the tool path to pre-compensate the profile error.