Hiroo Fujita

Three-dimensional surface profilometry using structured liquid crystal grating

This paper describes a device for measuring the three dimensional surface profile using a grating projection method. A phase shifting technique without any mechanical moving is expected for profile analysis. A grating that is a key component in this technique is made using an active controlled liquid crystal (LC). This LC grating has the performances of more than 8 bits of gray levels and its grating period is 50 micro-meters per line without any colored filters. Surface profiles of some samples are measured for the demonstration of the system.

Three-dimensional profilometry using liquid crystal grating

This paper describes a device for 3D profile measurement systems, which are based on grating projection method using phase shifting technique for fringe analysis. As a key component of these systems, we propose to apply a liquid crystal (LC) grating instead of a conventional ruled grating, which has difficulty in speedy and accurate shifting of the projected pattern. This LC grating consists of 960 lines of stripe pattern on the substrate of 60×40 mm2 in size and has such features as 8 bits of gray levels in dynamic range in use of mono-chromatic applications. A sinusoidal pattern as well as a binary pattern in realized by combining pulse width modulation control and frame ratio control technqiue. In addition, the period of the pattern is arbitrarily controlled and shifting of the projected pattern is also electrically realized. We demonstrate a few examples measured by the system which uses this LC grating inside.

Liquid crystal grating for profilometry using structured light

This paper describes a liquid crystal (LC) device for three dimensional profile measurement systems which are based on grating projection method using phase shifting technique. As a key component to these sytems, we propose to apply a liquid crystal (LC) grating instead of a conventional ruled grating because the grating ruled on the glass plate has difficulty in speedy and accurate shifting of the pattern. This LC grating consists of 960 lines of stripe pattern on the substrate of 60x40 mm2 in size and has such features as 8 bits of gray levels in dynamic range for mono-chromatic usage. A sinusoidal pattern as well as a binary pattern is realized by combining pulse width modulation control (PWMC) and frame ratio control (FRC) technique. The period of the pattern is arbitrarily controlled and, in addition, shifting of the projected pattern is also electrically realized. We present properties of the LC grating we have developed and demonstrate a few examples obtained by the system which has this LC grating built in.

Three-dimensional surface profile measurement by using liquid crystal grating with triangular intensity distribution patterns

This paper discusses a novel device for measuring 3D-surface profiles of objects using a grating pattern projection method. In particular, the configuration of a grating pattern generating and image processing system for calculating phase distribution from deformed grating images are described. In the grating pattern generating system, the grating is made from a liquid crystal (LC) with a stripe structure pattern which is driven by a pulse width modulation method. The intensity distribution made by the stripe LC grating is set to be triangular. The triangular distribution will be realized using low-bit gray levels. For instance, less than 11 gray levels will produce two patterns which is phase shifted by 1/4cycles; then, projection onto an object can be achieved twice. The deformed grating images posed by the object are detected by a CCD camera in the form of a two-phase image. The image processing system transforms the intensity distribution of the two-phase image into phase distribution which corresponds to the profile of the object. In this operation, linear regions are chosen where the intensities of the two-phase image change linearly by selecting the two-phase image alternately. The one cycle period is formed with four linear regions (quadrant), and the phase width in each quadrant is set to be π/2. Because the intensity distribution in the linear regions varies depending on the profile of the object, the phase distribution in each region is calculated using a simple linear operation using intensity variations or pixel number data.

Surface Profilometry Using Liquid Crystal Grating Projection

A specified liquid crystal (LC) device is shown for three dimensional profile measurement systems based on triangulation principle using phase shifting technique. Dual projection is available to improve problems in conventional pattern projection method.

Three-dimensional imaging using liquid crystal grating projection

This paper describes a device for 3D profile measurement systems which are based on grating projection method using phase shifting technique. As a key component to these systems, we propose to apply a liquid crystal (LC) grating instead of a conventional ruled grating which has difficulty in speedy and accurate shifting of the projected pattern. This LC grating consists of 960 lines of stripe pattern on the substrate of 60×40 mm2 in size and has such features as 8 bits of gray levels in dynamic range in mono-chromatic usage. A sinusoidal pattern as well as a binary pattern is realized by combining pulse width modulation control (PWMC) and frame ratio control (FRC) technique. The period of the pattern is arbitrarily controlled and, in addition, shifting of the projected pattern is also electrically realized. We demonstrate a few examples measured by the system which has this LC grating built in.

Development of High Resolution Displacement Measurement Apparatus using Linear Scale with Different Grating Pitches.

This paper discusses an apparatus for optically detecting dimension or displacement. In particular, the optical unit with compact in size and simpler in construction, and signal processing unit with resolution to be better than 0.1μm are described. The key device of the optical unit is linear scale. The scale consists of one moving and two stationary gratings, and these two types of grating have different grating pitch lengths. These two pitches are set to odd integer multiples. For example, moving and stationary. gratings set to 50μm and 10μm, respectively. The scale is directly irradiated by a divergent light emitted from a laser diode, and generates two sinusoidal-like signals with 10μm period. By using the divergent light, the need for a collimating lens is eliminated. This reduces the overall size of the optical unit The signal processing unit operates on the two signals for, detecting the signal phase at the stop position of the moving grating. The basis of the phase detection is a linear operation. By using the linear operation system, high resolution detection of the signal phase is accomplished by segmenting the one cycle period into more than 300 parts.

Three-dimensional profilometry using hybrid grating projection

This paper describes a grating projection method for the measurement of surface profiles of objects. In this kind of profilometry, a grating with binary transmittance distribution has been utilized usually. And in these cases such a problem is known as an error is caused due to the non-sinusoidal transmittance distribution of the grating. And another difficulty is also indicated that shifting of the grating is given by mechanical movement of the grating. Here we propose to use a hybrid grating is given by mechanical movement of the grating. Here we propose to us a hybrid grating which consists of a conventional binary grating and a liquid crystal binary grating. Then moire pattern is produced by superposing these two binary gratings. When two binary gratings are overlapped with an appropriate gap, the resultant more pattern becomes closely sinusoidal in intensity distribution. The, in the optical arrangement for profile measurement using this hybrid grating, when the LC gratin pattern is moved, the projected pattern is shifted arbitrarily in phase. Surface profiles of some samples are measured to show validity of the more pattern projection and utility of the prototype system.

Surface Profile Measurement by Optical Heterodyne Interferometry using Acousto-Optic Modulator.

音響光学素子の高周波側のキャリア周波数と低周波側の変調周波数を同時に制御することによって2ビームを任意に走査することを可能にした.この2ビーム光を用いて光ヘテロダイン法による表面形状計測を試みた.さらに, 回転テープルを利用することによって, 従来, ソマグレン型干渉計においては円周上の一断面のみの測定が可能であったのに対し, 本手法によると表面形状の計測を可能とした.このときの高さ方向の繰返し精度10n m, 平面ミラーとの比較でλ/20以下の精度が得られた.