Form error analysis of mould insert for large angle lens with ICP algorithm

Form measurement and form error analysis of high precision moulding lens of large angle have been immersed due to recent demands of some optical applications, such as mobile cellular phones with digital camera and daily disposable contact lens. The image dilation and distortion of measuring mould insert of soft contact lens needs to be compensated because of its steep-side features. This paper aims to utilize the iterative closest point (ICP) algorithm to stitch two curves which are measured on the different reference datum with a certain rotational angle. Measuring data is rotated back by a rotation matrix to improve the accuracy of ICP algorithm. Experiments have been conducted on a Mitutoyo profile analyzer with a Contracer CV-1000 and tip of radius 25 μm, angle 12° to measure a steel mould insert of soft contact lens. A sine bar and gauge blocks are used to measure twice on different sides of the reference datum with specified tilt angle. Results have demonstrated that the profile of a large angle lens can be reconstructed successfully and form error can then be calculated from the reconstructed profiles. Future work is to focus on exploring 3D measurement of non-symmetric lens.