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This paper presents a fast tool servo (FTS) driven by a voice coil motor (VCM) with a function of self-sensing of cutting forces. Conventionally, cutting force measurement associated with a FTS system is made by integrating an additional force sensor or a dynamometer, which would make the system complicated and influence the dynamic performance of the FTS. Differing from the conventional method, the force measurement in the proposed system is achieved by detecting the current of the VCM and then obtaining the cutting force based on the electromagnetic field distribution of the VCM. Since it is not necessary to integrate additional force sensors, the main body of the FTS could be compact and the dynamics of the FTS would not be influenced by the added function of force measurement. The FTS mainly consists of an air bearing guide driven by a VCM with a stroke of 2.5 mm, an optical encoders feedback system for precision positioning and a hall current sensor for current measurement. To obtain forces from the measured currents, the magnetic field distribution of the VCM is figured out and the nonlinear relationship between the position and the magnetic field distribution is corrected. The basic performances of the FTS for positioning and force measurement were experimentally investigated. It is shown that the system could have a positioning resolution of 20 nm and a force self-sensing resolution of 5 mN based on the proposed method. The proposed method provides a new way for in-process cutting force measurement associated with FTS systems.

Detection of surface defects is critical in quality control of reflective optics. In this note, we propose a new surface defect detection method for reflective optics using the normalized reflectivity, which is calculated from the signal intensity of a chromatic confocal surface profiler. This detection method first scans the surface to acquire signal intensity data and then models the intensity data to calculate the normalized local reflectivity map. The reflectivity map is further processed by threshold segmentation to extract defects from normal areas. Measurement experiments on an Al-coated concave reflector with artificial defects were carried out to demonstrate the feasibility of the method. This detection method can provide existing optical surface profilers with defect detecting capabilities without extra equipment.

A new prototype non-contact profiler based on surface tracking has been specially developed. Surface tracking is carried out by a specially designed dual stage probe system with the aid of a four-Degree Of Freedom high-precision motion platform. The dual stage probe system keeps a short-range optical probe constantly tracking the surface by a self-developed voice coil motor servo, by which a wide measuring range of up to 10 mm is realized. The system performance evaluation including resolution, repeatability, and scanning speed proved the good capability of the new prototype non-contact profiler. To realize a full area covered 3D profile measurement of special-shaped optics within one scanning procedure, a signal intensity monitor integrated in the surface tracking controller is specially developed. In the experiment, a snip-single-corner-rectangular-shaped freeform surface was successfully measured over full area by the new non-contact profiler. This work provides an effective solution for 3D profile measurement of special-shaped optical surfaces over full reflecting area. Experimental results demonstrate that the proposed measuring system is of great significance in quality evaluation of optical surfaces.

Spiral scanning is a high-efficiency scanning mode for surface profile measurement systems. The most important priority to realize the spiral scanning mode is to accurately align the measuring probe with the rotational centre of the spindle. This paper proposes a novel centre alignment method of the measuring probe, which is considered to be suitable for any type of spiral scanning surface measurement systems. The proposed method, which only needs a tilted flat mirror as the artefact, makes the time-consuming centre alignment process of the measuring probe become much easier and faster. The operational steps of the proposed method are presented. Experiments have also been carried out based on a self-developed optical profiler with spiral scanning operation to verity the feasibility of the proposed method. The experimental results show that the proposed method is capable of conducting a fast alignment (only takes 3 min) while maintaining a high alignment accuracy. Evaluation of the alignment accuracy shows that the centering error is less than 10 µm on the mechanical guide rail stage and about 1.7 µm on the air-bearing stage.