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Phase calculation-based 3D imaging systems have been widely studied because of the advantages of non-contact operation, full-field, fast acquisition and automatic data processing. A vital step is calibration, which builds up the relationship between phase map and range image. The existing calibration methods are complicated because of using a precise translating stage or a 3D gauge block. Recently, we presented a simple method to convert phase into depth data by using a polynomial function and a plate having discrete markers on the surface with known distance in between. However, the initial position of all the markers needs to be determined manually and the X, Y coordinates are not calibrated. This paper presents a complete calibration method of phase calculation-based 3D imaging systems by using a plate having discrete markers on the surface with known distance in between. The absolute phase of each pixel can be calculated by projecting fringe pattern onto the plate. Each marker position can be determined by an automatic extraction algorithm, so the relative depth of each pixel to a chosen reference plane can be obtained. Therefore, coefficient set of the polynomial function for each pixel are determined by using the obtained absolute phase and depth data. In the meanwhile, pixel positions and the X, Y coordinates can be established by the parameters of the CCD camera. Experimental results and performance evaluation show that the proposed calibration method can easily build up the relationship between absolute phase map and range image in a simple way.

This paper presents an absolute phase calculation method from one composite RGB fringe pattern image by using Wavelet transform algorithm and the optimum fringe number selection. Three fringe patterns having optimum fringe numbers are projected simultaneously onto an object surface via the red, green and blue channels of a DLP (Digital Light Processing) projector. From a different viewpoint, a CCD camera captures the deformed fringe patterns with respect to the object shape to get a composite RGB image. After compensating for the crosstalk and chromatic aberration between color channels, three fringe patterns are extracted from the composite color image. Wavelet Transform algorithm is studied to calculate wrapped phase from one fringe pattern. Therefore, three wrapped maps are obtained from the three extracted fringe patterns. An absolute phase map is calculated pixel by pixel after applying the optimum three-fringe numbers selection method to the three obtained wrapped phase maps. Simulated and experimental data demonstrate the algorithm's validity of calculating the absolute phase and shape information. The proposed method can measure 3D shape information of moving objects since the system needs only one RGB fringe pattern image.

3D fringe projection measurement techniques are increasingly important in production for automation, quality control, reversal engineering, and biomedical engineering because of the advantages of non-contact operation, full-field acquisition and automatic data processing. With the advent of DLP (Digital Light Processing) projectors, digital fringe pattern projection techniques have been widely studied in academia and applied to industries. The experimental data from living profile of fringe patterns show that the obtained intensity has some fluctuation, which cause the calculated phase data inaccuracy. This paper presents one software method to eliminate the fluctuation between fringe patterns. Four-step phase-shifting algorithm is used to calculate the wrapped phase data, so four fringe pattern images having pi/2 shift in between need to be captured. Because of the fluctuation of intensity, the captured fringe patterns have an up or down shift among the four images. By considering the histogram of each fringe pattern, we present one compensation method to eliminate the fluctuation between fringe patterns. Simulated data are first tested by generating fringe patterns with fluctuation. Then experimental data from a 3D imaging system demonstrate the validity for calculating the phase and shape information with high accuracy. The results show that the proposed method eliminates the fluctuation between fringe pattern images to give accurate shape data information.

A compact self-sensing atomic force microscope (AFM) head is developed for the micro-nano dimensional measurement. This AFM head works in tapping mode equipped with a commercial self-sensing probe. This kind of probe can benefit not only from the tuning fork's stable resonant frequency and high quality factor but also from the silicon cantilever's reasonable spring constant. The head is convenient to operate by its simplicity of structure, since it does not need any optical detector to measure the bending of the cantilever. The compact structure makes the head ease to combine with other measuring methods. According to the probe's characteristics, a method is proposed to quickly calculate the cantilever's resonance amplitude through measuring its electro-mechanical coupling factor. An experiment system is established based on the nano-measuring machine (NMM) as a high precision positioning stage. Using this system, the approach/retract test is carried out for calibrating the head. The tests can be traced to the meter definition by interferometers in NMM. Experimental results show that the non-linearity error of this AFM head is smaller than 1%, the sensitivity reaches 0.47nm/mV and the measurement stroke is several hundreds of nanometers.

The wide variety of shapes, functions, and operational parameters of microelectromechanical systems (MEMS) moving into production requires high flexibility for any measurement instrument. A computer-controlled stroboscopic interferometer system is described in the paper for measuring out-of-plane motions of MEMS structures with nanometer resolution. This system introduces five-step phase-shifting interferometric measurement method with high accuracy and differential measurement mode by choosing a fixed area on the device as the reference point, which eliminates the effect of random errors efficiently and improves the measurement repeatability of the system. The repeatability of 10 measurements is 3.17 nm. The study on the dynamic behavior of a micro-resonator illustrates the powerful capabilities of the system.

White light interferometry(WLI) has grown to be a standard measurement method in the field of micro/nano manufacture. Vertical white light scanning interferometry(VSI), tilt white light scanning interferometry(TSI) and white light phase shifting interferometry(WLPSI) are introduced in this paper. A new algorithm based on the combination of VSI and image segmentation technology for measuring the film is presented in this paper. TSI is taken place of VSI for expanding its lateral measuring range and improving the testing efficiency as the vertical and lateral information of the samples are obtained after one time scan. Carré phase shifting is combined with vertical white light scanning which formed a white light phase shifting method. The measurement system equips a Mirau microscopic interferometer, and the scanning process is driven by nano-measuring machine(NNM) which is a high precision nano-positioner. At last, the testing results of some micro-structures illustrate the capabilities of the proposed algorithms.