Development of DMD Reflection-Type CCD Camera for Phase Analysis and Shape Measurement

Noncontacting shape measurement for 3-D objects is important in automated manufacturing, component quality control, reverse engineering, etc. Phase-shifting method effectively attains high resolution and high accuracy in analyzing phase information on a projected grating. This technique, however, is difficult to be applied to dynamic condition since usually it requires several images. We developed a digital micromirror device (DMD) camera for phase analysis. In this paper, an one-shot shape and deformation measurement method using a DMD camera is proposed. The DMD camera consists of a DMD, a CCD, and two imaging lenses. In optics of the DMD camera, individual DMD mirrors correspond to individual CCD pixels. The DMD on-off binary pattern can be changed more than 6900 times in one second using an accessory light modulator package (ALP) controller board. Individual DMD mirrors operate as controllable high-speed shutters for corresponding CCD pixels. The four phase-shifted images can be recorded within one frame of the CCD camera. Therefore, shape measurement in dynamic condition can be realized without using a high-speed camera. In order to obtain the 3-D information of shape, multiple reference planes are used to calibrate the relationship between phase value and 3D coordinates. The principle and hardware are presented. In an experiment under dynamic condition, 3D shape information can be analyzed from only one captured image.

Pixel-to-Pixel Correspondence Adjustment in DMD Camera by Moiré Methodology

A camera based on the digital micromirror device (DMD) technology has been previously developed. In this optical system, the correspondence of each mirror of the DMD to each pixel of the CCD cannot readily be done since the pixel sizes of the DMD and the CCD are very small. An accurate pixel-to-pixel correspondence adjustment in the DMD camera by means of the phase-shifting moiré method is proposed. To perform high accurate adjustment of the optical system, the phase distribution of a moiré fringe pattern is analyzed when the CCD pixels and the DMD mirrors have a mismatch and/or misalignment with each other. This technique does not need a complicated setting or complex image processing to generate the moiré fringe pattern, and it needs only one captured image. In the adjustment experiment, the proposed method provided very accurate adjustment whose error was less than 1/25 pixel. An experiment of phase analysis to demonstrate the usefulness was performed.

Polarization aberration analysis and suppression of an infrared remote sensing optical system based on a digital micro-mirror device

System calibration is crucial for any 3-D shape measurement system. An accurate method is proposed to calibrate a 3-D shape measurement system based on a structured light technique. The projector is treated as a camera to unify the calibration procedures of a structured light system and a well-established stereo vision system. The key to realizing this method is to establish a highly accurate correspondence between camera pixels and projector pixels and generate digital micromirror device (DMD) image sets for projector calibration. A phase-shifting method is used to accomplish this task. A precalibrated lookup table and a linear interpolation algorithm are proposed to improve the accuracy of the generated DMD image, and accordingly improve the accuracy of the projector calibration and the 3-D measurement. Some experimental results are presented to demonstrate the performance of the system calibration.

Photolithography is one of the core technologies of micro-nano fabrication. Recently, lithography technology is applied to diverse field of technologies. These technologies include MEMS (micro electro mechanical system) devices, FPD (flat panel display), and semiconductor industry. When it comes to the typical exposure process of lithography technology, photomask costs is occupying large portion of the optical system. So, how to reduce the cost of the mask and employing maskless lithography technology has become an important issue to engineers. Although there being both advantages and disadvantages, maskless lithography is a receiving substantial attention from engineers in the fileds of micro-nano fabrication. With the development of technology, low cost, flexibility, efficiency in the fabrication of device are in high demand in maskless lithography technology. How to generate line/space patterns is gaining considerable attention in terms of maskless lithography exposure process. In order to achieve the accurate alignments of numerous optical heads within a reasonable amount of tack time, installing autonomous position align micro parallel manipulator system in each optical heads required. Applied parallel manipulator that consists of four 2-DOF (degree of freedom) decoupled actuator gives chances to provide 6-DOF independence motion, and has strength in high accuracy. It is thus, this parallel manipulator is suitable for the experiment. This paper covers the follows: First, we reported the DMD (Digital Micro mirror Device)-based makless lithography system to introduce spot array method in maskless digital exposure process. Second, applying a redundant parallel micro manipulator and analyzing kinematic characteristic of the 4-[PP]PS parallel manipulator is described. After that, comparing benefits and drawbacks of 4-[PP]PS parallel and 4-DOF serial manipulator is covered. Third, proposing a suitable error model of the system and applying the genetic algorithm to alignment spot array concerning position correction. Finally, we designed experiment which has vision sensor and align unit to verify positioning algorithm. Simulation and experimental result will be shown with the regard to parallel manipulator can find the optimal solution based on genetic algorithm and carry out the problem of spot array alignment by reducing the position error of the system.

Structured light devices are commonly used in many measurements by emitting certain illuminating patterns on objects or scenes, enabling the acquisition of object information. To achieve high-speed and high-accuracy measurements, researchers are focusing on improving the performance of structured light devices. LEDs, with their fast response times, have great potential in high-speed structured light devices. However, the current LED array driver circuits face challenges to balance high power and high speed. In this paper, we propose a driver circuit and a pattern display scheme that support high-power LED arrays to refresh structured light patterns at ultra-high rates. We have fabricated a prototype of the driver and used it to drive a 128×128 LED chip array. Experimental results demonstrate that the proposed driver outputs over 40W and supports the LED chip array refresh patterns at rates of up to 25MHz, which is approximately 1000 times faster than the fastest commercially available structured light device (i.e., the Digital Micromirror Device, DMD). The ultra-high-speed LED array device based on the proposed driver can be applied in computational ghost imaging, structured illumination microscopy, Fourier ptychographic imaging and other imaging fields.

In the case of phase-shifted grating projection method, there is a problem that the measurement error becomes larger when the object is moving more speedily. In order to solve this problem, we developed a DMD reflection-type CCD camera that we call a DMD camera. In this paper, we develop an algorithm to apply the phase-shifting method using correlation to the shape measurement using the DMD camera and high-speed phase-shifting method using the DMD camera. The four step phase-shift can be performed within 1/7,500 seconds because the pattern on the DMD can be changed theoretically 30,000 times in a second. The principle and the experimental result are shown.

In contrast to imaging using position-resolving cameras, single-pixel imaging uses a bucket detector along with spatially structured illumination to compressively recover images. This emerging imaging technique is a promising candidate for a broad range of applications due to the high signal-to-noise ratio (SNR) and sensitivity, and applicability in a wide range of frequency bands. Here, inspired by single-pixel imaging in the spatial domain, we demonstrate a time-domain single-pixel imaging (TSPI) system that covers frequency bands including both terahertz (THz) and near-infrared (NIR) regions. By implementing a programmable temporal fan-out gate based on a digital micromirror device, we can deterministically prepare temporally structured pulses with a temporal sampling size down to 16.00 ± 0.01 f s . By inheriting the advantages of detection efficiency and sensitivity from spatial single-pixel imaging, TSPI enables the recovery of a 5 fJ THz pulse and two NIR pulses with over 97 % fidelity via compressive sensing. We demonstrate that the TSPI is robust against temporal distortions in the probe pulse train as well. As a direct application, we apply TSPI to machine-learning-aided THz spectroscopy and demonstrate a high sample identification accuracy (97.5%) even under low SNRs (SNR ∼ 10 ).

Optical full-field measurement techniques have been widely studied in academia and applied to many actual fields of automated inspection, reverse engineering, cosmetic surgery, and so on. With the advent of color CCD cameras and DMD (Digital Micromirror Device) based color DLP (Digital Light Processing) projectors, their major red, green, and blue channels have been used as a carrier to code fringe patterns. Since three fringe patterns can be simultaneously projected and captured at one shot, the acquisition time reduces to 1/3 of the value by the gray fringe pattern projection. This chapter will introduce two kinds of applications of red, green, and blue as a carrier: 1) modulation and demodulation method of coding sinusoidal fringe patterns into RGB channels of a composite color image; and 2) modulation and demodulation method of coding sinusoidal and binary fringe patterns into RGB channels of multiple composite color images. Experiments on testing the two kinds of applications were carried out by measuring the shape of objects’ surface. The results confirm that red, green, and blue channels can be used as a carrier to reduce the acquisition time.

Active illumination mode with checkerboard pattern in focus variation microscopy: Analysis and application

Blade is the key component of the aero-engine. In generally, it requires precise size and accurate shape, so the three-dimensional shape measurement of the blade is very important. Fringe projection profilometry is generally used to measure the 3D shape of an object, because of the advantages of non-contact operation, full-field acquisition, high resolution, and fast data processing. In this paper, 3D shape measurement method based on surface structured light that combination of gray-code and phase-shift projection is proposed. The wrapped phase of the blade is got by the four-step phase-shift method. In the projection process of the gray-code, due to the ambient light, different surface reflectance and surface physical discontinuous, the edge of gray-code becomes smooth, leading to decode error, so that the gray-code pattern must be binaried before decode. Through the accurate binarization of the blade gray-code pattern, the decoding cycle of the blade is achieved, and the unwrapped phase is achieved by phase unwrapping. Then the unwrapped phase difference between the blade and reference plane is got, the height of the blade can be obtained by the relationship between the phase difference and the height. The experimental and simulation results show that the proposed method can achieve a high precision, high speed and low cost 3D shape measurement of the blade. The measurement accuracy reaches 0.03 mm. The proposed method extends the reliability and practicality of the fringe projection profilometry.

3D shape measurement systems that use contactless methods are required for quality inspection of metal molds and electronic parts in industrial fields. A fringe projection method with phase-shifting method offers the advantages of high precision and high speed. Recently, since the size of electronic parts has become smaller, the pitch of a grating pattern projected onto a specimen should also become smaller. In this paper, a small pitch fringe projection method using Talbot effect with an SLD (Super luminescent diode) and a method to incline the appearing area of the fringe pattern are proposed. A linear fiber array with four cores is prototyped. A phase-shifting method using the linear fiber array is also proposed. The effectiveness is confirmed with the experimental results of shape measurement using a 3D shape measurement setup built with proposed method.

Phase-shifting shadow moire is an efficient technique for three-dimensional (3-D) shape measurement, but the technique is always suffered from the error of phase shifter. A three-frame random phase-shifting algorithm is proposed to relax the requirements of repeatability and accuracy of the phase shifter in a shadow moire system. The proposed method can act as a bridge between the three phase-shifting analysis methods and two-shot phase-shifting methods. The value of introduced arbitrary and unknown phase shift can be calculated by a determinate formula. The algorithm has the advantages of being free from the disturbance of background elimination and less computation. In addition, the proposed method is immune to nonsinusoidal fringe patterns and can be implemented easily in many applications. Both simulation and optical experimental results verify the feasibility of this method.

Under the dynamic working conditions of a star sensor, motion blur of the star will appear due to its energy dispersion during imaging, leading to the degradation of the star centroid accuracy and attitude accuracy of the star sensor. To address this, a restoration method of a blurred star image for a star sensor under dynamic conditions is presented in this paper. First, a kinematic model of the star centroid and the degradation function of blurred star image under different conditions are analyzed. Then, an improved curvature filtering method based on energy function is proposed to remove the noise and improve the signal-to-noise ratio of the star image. Finally, the Richardson Lucy algorithm is used and the termination condition of the iterative equation is established by using the star centroid coordinates in three consecutive frames of restored images to ensure the restoration effect of the blurred star image and the accuracy of the star centroid coordinates. Under the dynamic condition of 0~4°/s, the proposed algorithm can effectively improve the signal-to-noise ratio of a blurred star image and maintain an error of the star centroid coordinates that is less than 0.1 pixels, which meets the requirement for high centroid accuracy.