Miniature composite dual-frequency fringe projection module based on liquid crystal display

Abstract

The present application belongs to the technical field of 3D detection, and provides a micro composite double-frequency fringe projection module based on liquid crystal display, which is particularly suitable for the field of miniaturization and high-precision dynamic detection of complex objects. The present application forms a liquid crystal display module through the design of binary filling composite multi-frequency fringe pattern, and then projects a single-frame composite double-frequency fringe field through the liquid crystal display module and a cylindrical lens. The three-dimensional surface shape of a moving complex object can be detected with high precision by using Fourier transform profilometry or deep learning. The present application has the advantages of single-frame display and non-linear scanning refresh display, and does not produce line scanning shadows when using a camera for structured light detection. Furthermore, the present application has a simple structure, can greatly reduce the volume and significantly reduce the production cost, and is expected to realize commercial production. At the same time, the volume of the present application is limited, and miniaturization, mobility and portability can be realized, which has good mobile electronic terminal application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of 3D detection, and relates to a fringe projection profile detection technology, and particularly provides a micro composite double-frequency fringe projection module based on liquid crystal display, which is suitable for a structured light detection system based on fringe projection, can realize high-precision detection for complex objects and dynamic scenes, and is miniaturized. BACKGROUND

[0002] With the continuous development of science and technology and industrial processing level, the detection demand for complex object dynamic scenes is also increasing; among numerous detection methods, the optical detection method based on structured light illumination (such as fringe projection profile, phase measurement deflection and structured light modulation analysis technology) has the advantages of non-contact, full-field detection, high precision and the like, and is thus widely applied to surface quality detection and three-dimensional surface shape measurement of various elements. However, how to quickly and accurately obtain three-dimensional topographic information of dynamic objects or transient change scenes is a problem to be solved in the field of fringe projection profile, and high-quality sinusoidal fringe projection technology capable of being applied to dynamic acquisition scenes is an important factor limiting the dynamic measurement of fringe projection profile.

[0003] At present, the projection display mode commonly used in fringe projection profile adopts a line scanning refreshing mechanism, which can meet the projection demand when the acquisition rate of the acquisition device is low, but when the acquisition rate of the acquisition device is high, the line scanning refreshing process is captured to appear a stroboscopic phenomenon, as shown in FIG. 1, thereby resulting in poor quality of the captured fringe, which not only has a negative impact on the subsequent reconstruction result, but also sacrifices the acquisition characteristics of the acquisition device. Figure 1 How to obtain high-precision three-dimensional data of complex objects and dynamic scenes on a miniaturized and low-cost platform and accurately restore the biological features and details of a face is still a great technical problem of "three-dimensional face recognition", and is also a key scientific and technological problem urgently to be solved in the national economic and social development. Common fringe projection technologies include binary defocusing projection, array projection, mechanical rotating grating projection and time coding projection, which can meet the experimental demand of the corresponding application scenes, but are not easy to realize miniaturization and low cost; therefore, it has high practical value to research a simple and efficient projection module technology suitable for complex objects and dynamic scenes. SUMMARY

[0004] The application aims to provide a new composite multi-frequency fringe projection module based on liquid crystal display for single-frame complex object and dynamic object detection scenes, which can be well integrated with deep learning technology in terms of single-frame, and can fully play the acquisition characteristics of the acquisition device in terms of projection mode, and is suitable for a fringe projection profile dynamic detection system.

[0005] To achieve the above object, the technical scheme adopted by the application is that:

[0006] A composite double-frequency fringe projection module based on liquid crystal display, comprising: a liquid crystal display module, a cylindrical lens and an imaging lens; characterized in that, under the irradiation of a backlight source, the liquid crystal display module displays a pair of binary-filled composite multi-frequency fringe patterns, which are projected onto the cylindrical lens after passing through the projection imaging lens, and form a composite double-frequency fringe light field after passing through the cylindrical lens.

[0007] Further, the composite multi-double-frequency fringe is composed of a first fringe with a frequency of 1 and a second fringe with a frequency of f, and the binary-filled composite multi-frequency fringe pattern is mathematically expressed as:

[0008]

[0009] wherein I is a function image of the pattern, x is the pixel position along the X-axis, h is the height (vertical direction: Y-axis) of the liquid crystal display module (ITO electrode layer), and L is the length (horizontal direction: X-axis) of the liquid crystal display module (ITO electrode layer).

[0010] Further, the liquid crystal display module comprises, from top to bottom: a backlight source, a first polarizer, a first glass substrate, a first ITO electrode layer, liquid crystal molecules, a second ITO electrode layer, a second glass substrate and a second polarizer, and the binary-filled composite multi-frequency fringe pattern is arranged on the first ITO electrode layer.

[0011] Further, the liquid crystal display module is rectangular, with a height of twice the amplitude of the composite double-frequency fringe field and a length of 10 times the height.

[0012] Based on the above technical solution, the present application has the following advantages:

[0013] The present application provides a composite multi-frequency fringe projection module based on liquid crystal display, which uses a non-refreshing liquid crystal display method to etch a specially designed pattern on the ITO electrode that controls the liquid crystal display, and utilizes the characteristic of the cylindrical lens that only magnifies the image on a single optical axis, so that the module can stably and clearly project a composite double-frequency fringe pattern. The present application has the advantage of being able to stably and single-frame project a composite double-frequency fringe, and can use Fourier phase profilometry and deep learning technology to achieve high-precision detection of complex objects and dynamic scenes, which has good application prospects in transient scenes. At the same time, the projection module of the present application has a simple structure and low component cost, and its manufacturing cost is much lower than that of traditional liquid crystal display projectors, and its volume is also easier to miniaturize. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The present application is to solve the problem of frequency flicker that occurs when the projection frame rate of an existing commercial projector does not match the camera shooting frame rate.

[0015] Figure 2 This is a schematic diagram of the structure of the micro composite dual-frequency stripe projection module based on liquid crystal display in this invention.

[0016] Figure 3 This is the binary filled composite multi-frequency stripe pattern in this invention.

[0017] Figure 4 This is a composite dual-frequency fringe pattern obtained using Matlab simulation technology in an embodiment of the present invention.

[0018] Figure 5 This is a one-dimensional light intensity distribution map of composite dual-frequency fringes obtained using Matlab simulation technology in an embodiment of the present invention.

[0019] Figure 6 This is a one-dimensional light intensity distribution map of dual-frequency composite stripes obtained using Zemax ray tracing technology in an embodiment of the present invention.

[0020] Figure 7 This is a schematic diagram of the structure of the liquid crystal display module in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] This embodiment provides a composite dual-frequency stripe projection module based on a liquid crystal display, the structure of which is as follows: Figure 2 As shown, it specifically includes: a backlight source, a first polarizer, a first glass substrate, a first ITO electrode layer, liquid crystal molecules, a second ITO electrode layer, a second glass substrate, and a second polarizer (such as...). Figure 7 The liquid crystal display module (shown) comprises a cylindrical lens and an imaging lens. A set of controllable electrodes is located on the first ITO electrode layer. When a driving voltage is applied, the liquid crystal display module displays a binary-filled composite multi-frequency fringe pattern under the influence of a backlight. This pattern is projected onto the cylindrical lens through the projection imaging lens. Utilizing the characteristic of the cylindrical lens to magnify the image along a single optical axis, the projected pattern transforms into a composite dual-frequency fringe light field after passing through the cylindrical lens. The single-frame composite multi-frequency fringe generated by the module is suitable for high-precision detection in dynamic and complex scenes, and the module is compact, facilitating the miniaturization of three-dimensional sensing systems.

[0023] Furthermore, the composite multi-frequency stripe is composed of a first stripe with a frequency of 1 (i.e., the entire period length is the same as the length of the liquid crystal panel) and a second stripe with a frequency of f; therefore, the binary-filled composite multi-frequency stripe pattern is as follows: Figure 3 As shown, it can be expressed mathematically as follows:

[0024]

[0025] Wherein, with the midpoint of the left boundary of ITO electrode layer as the origin, I is the function image of binary filling composite multi-frequency fringe pattern, x is the pixel position along the X axis, h is the height (vertical direction: Y axis) of the liquid crystal display module (ITO electrode layer), and L is the length (horizontal direction: X axis) of the liquid crystal display module (ITO electrode layer);

[0026] Further, the liquid crystal display module is rectangular, the height is twice the amplitude of the composite double-frequency fringe field, and the length is 10 times the height; a binary filling composite double-frequency fringe pattern artificially designed is etched on the ITO electrode layer through a photoetching process, so that the liquid crystal of the pattern part can be made to be transparent when the electrode is connected, and an equal proportion pattern style is formed on the liquid crystal surface; the cylindrical lens has an image magnification only on one optical axis, the optical axis is perpendicular to the amplitude variation direction of the etched pattern, and the composite double-frequency fringe field can be obtained; under the requirement, the size of the projection negative is not limited, and miniaturization, mobility and portability can be achieved.

[0027] Further, the composite double-frequency fringe projection module uses liquid crystal display technology, but the driving technology does not use the commonly used TFT as a driver device, does not use linear array scanning technology for pattern display, but uses electrode full plate pattern etching method to directly display the whole pattern, and will not produce line scanning shadow in application and collection work. Under this technology, high-precision measurement of dynamic scenes can be realized.

[0028] From the practical application:

[0029] Based on the above composite double-frequency fringe projection module, first, according to the detection needs of scene complexity, the frequencies of the two kinds of fringes used for composition are determined, and a binary filled composite multi-frequency fringe pattern is generated; then, the generated pattern is etched on an ITO electrode layer through a process such as photolithography, and the ITO electrode layer is divided into two parts; then, the ITO electrode layer is used as a control switch for liquid crystal display, and is combined into a TN type liquid crystal display in the order of backlight 1, first polarizer 2, first glass substrate 3, first ITO electrode layer 4, liquid crystal molecules 5, second ITO electrode layer 6, second glass substrate 7, and second polarizer 8 from top to bottom, and the binary filled composite multi-frequency fringe pattern is arranged on the first ITO electrode layer; finally, the pattern displayed by the liquid crystal display will form a composite double-frequency fringe after passing through a cylindrical lens. In use, first, the projection module is used to project a fringe pattern onto the object to be measured, and the pattern will be deformed in the area projected on the object, and an image acquisition device is used to acquire the deformed fringe pattern, and the acquired image is subjected to Fourier transform processing to obtain a frequency spectrum of the image. Since the phase of the object surface is modulated by two frequencies of the fringe, the frequency spectrum will have two fundamental frequencies. The two fundamental frequency components are filtered, and the truncated phase is calculated using Fourier profilometry. The truncated phase with a fringe frequency of 1 is used as a reference to unwrap the other phase pattern. Under this technology, multiple phase shifts are not required, and a single frame can be captured. Furthermore, deep learning technology can be combined to detect the three-dimensional topography of dynamic complex objects with high precision. Based on the above composite double-frequency fringe projection module, other frequency double-frequency combinations can be set to generate a multi-frequency fringe field or even a more frequency fringe field.

[0030] From the working principle:

[0031] The application controls the electrode engraved with a special pattern to control the liquid crystal display module to display a binary filled composite double-frequency pattern. The pattern itself is an electrode, which can form a stable voltage difference and achieve a stable non-scanning display effect. Taking the horizontal direction as the X coordinate direction and the upward direction as the Y coordinate direction, the display direction of the binary filled composite double-frequency pattern on the liquid crystal base is X. Adding an imaging lens in front of the liquid crystal display module will display the inverted image of the binary filled composite double-frequency pattern on the image plane. Adding a cylindrical lens in front of the projection imaging lens will expand the Y direction of the projection pattern. Each light transmission point will be expanded into a straight line, and each straight line corresponds to a unique X coordinate. Under the condition of uniform backlight, the light field illumination of the imaging area is proportional to the width of the Y direction transmission. Assuming that the light field of the pattern displayed by the liquid crystal is I(x, y), and the point spread function of the cylindrical lens is PSF(x, y), the final light field of the imaging area is as shown in Figure 4 The theoretical one-dimensional light intensity diagram and the result obtained by applying the ray tracing technology in Zemax are as shown in Figure 5 , 6As shown, the light field can be expressed as conv2(I(x,y),PSF(x,y)), which is true in most areas of the final imaging area, and only needs to add a suitable diaphragm to make the displayed pattern completely a composite multi-frequency fringe pattern; since the projection generation does not need to refresh the display by line scanning, it can participate in 3D measurement work for a long time under the premise of good heat dissipation.

[0032] The above is only a specific implementation of the present application, any feature disclosed in the specification can be replaced by other equivalent or similar purpose alternative features unless specifically described; all features disclosed, or steps in all methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A composite dual-frequency fringe projection module based on liquid crystal display, comprising: The application relates to a liquid crystal display module, a cylindrical lens and a projection imaging lens, characterized in that the liquid crystal display module displays a binary filling composite multi-frequency fringe pattern, the pattern is projected onto the cylindrical lens through the projection imaging lens, and a composite double-frequency fringe field is formed after the pattern passes through the cylindrical lens. The composite multi-double-frequency fringe is composed of a first fringe with a frequency of 1 and a second fringe with a frequency of f, and the binary filling composite multi-frequency fringe pattern is expressed in a mathematical way as follows: Wherein, I is a function image of the binary filling composite multi-frequency fringe pattern, x is a pixel position along the X axis, h is the height of the liquid crystal display module, and L is the length of the liquid crystal display module.

2. The composite dual-frequency fringe projection module based on liquid crystal display according to claim 1, characterized in that, The liquid crystal display module comprises, from top to bottom, a backlight source, a first polarizer, a first glass substrate, a first ITO electrode layer, liquid crystal molecules, a second ITO electrode layer, a second glass substrate and a second polarizer, and the binary filling composite multi-frequency fringe pattern is arranged on the first ITO electrode layer.

3. The composite dual-frequency fringe projection module based on liquid crystal display according to claim 1, characterized in that, The liquid crystal display module is rectangular, the height is twice the amplitude of the composite double-frequency fringe field, and the length is 10 times the height.

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