Research On Tool Path Planning With Constant Scallop Height For Turning Of Freeform Optics

Freeform optics possess numerous advantages such as: simplifying thearchitecture of optical system, improving optical performances and enhance theefficiency, etc. Therefore they have received extensively applications inmicro-electronics, aerospace, communication, and so on. Diamond turning, includingSlow Slide Servo and Fast Tool Servo, is the main method for the formation offreeform optics. Tool path planning has important impact on processing efficiency andsurface quality. Good tool path planning method should have high calculation speedand processing efficiency as well as good surface quality. This thesis has researchedtool path planning with constant scallop height for diamond turning, which couldimprove processing efficiency while meeting the requirement of surface quality.This thesis summarizes the mainly used freeform optics with their mathematicalexpression, and then introduces the contour shape of diamond tool nose. A newmethod is proposed to avoid the difficult calculation in the resolving of cutter locationpoint from the known cutter contact point. In this method, the cutting edge isprojected to the base plane, therefore the cutting tool with non-zero rake angle can beapproximately recognized as cutting tool with zero rake angle. Then, the tool pathplanning algorithm with constant scallop height for diamond turning is researched fortwo types of cutting edges, round and ellipse, respectively.This thesis proposes the simulation algorithm for scallop height topography andsurface topography with polar grid. The tool path with constant scallop height and itsscallop height topography is calculated and contrasted with constant radial feedmethod in two different radial feeds, the average radial feed in constant scallop heightmethod and the radial feed to insure the allowed value of scallop height. Then we use two-dimensional wavelet analysis on different surface topographies to extract thesurface roughness element and reconstruct it to acquire the roughness topographywhich is contrasted with each other.The tool path made up of micro-line segments which is generated directly fromthe tool path planning method is not suitable for processing, because its large amountof cutter location points, high time cost and low processing quality. These problemscan be resolved by fitting the discrete points to NURBS curves.This thesis introduces the basic knowledge of NURBS, then chooses theapplicable data parameterization algorithm and node vector algorithm. A novelsectional NURBS curve fitting algorithm for tool path of diamond turning is proposedin this thesis. In this algorithm, two adjacent sections are end-to-end, the number ofcontrol points in each section is fixed, and the number of cutter location points in eachsection is adjusted to ensure the fitting precision with the largest number of points.Then the validity of the algorithm is proved by fitting the tool path generated in theprevious chapter using this method.