RU2807409C1 - Method and system of non-contact ranging and profilometry - Google Patents

Abstract

FIELD: measuring technology.

SUBSTANCE: invention is related to profilometers and rangefinders. A system implementing a method for ranging and profilometry includes at least one image recording device, a computing device and a projection device containing a spatially extended source of non-coherent light, first and second flat periodic gratings, which are located in parallel planes on one side of the light source and which are illuminated by said light source, wherein the second grating is illuminated by the light passed through the first grating, wherein the system uses at least one device for moving the isoline with the greatest contrast of the projection of the LM structure formed by the projection device along the surface of at least one object.

EFFECT: simplification of the ranging and profilometry system.

39 cl, 6 dwg

Description

Field of technology

The invention relates to the field of measuring technology and can be used for non-contact measurement of distances to objects, coordinates of points on their surface, as well as determining the shape of objects.

Prior Art

Determining the distance to points of an object (ranging), measuring their coordinates, as well as the shape of the surface of the object (profilometry) is necessary for solving many applied and scientific and technical problems. Non-contact methods of ranging and profilometry are used in construction, design, and reverse engineering. They are also used in computer vision systems, virtual and augmented reality, for controlling vehicles and robotic devices , in medicine, etc. There are many known methods for non-contact active optical measurements of the distance to objects, the coordinates of points on their surface and its shape (see, for example, [1 - 5]). A significant part of these methods are based on the use of laser devices. In particular, these include time-of-flight methods of ranging and profilometry, using, for example, lidars [1 - 6], as well as methods based on the use of laser triangulation, laser structured illumination, etc. (see, for example, [1 - 5, 7]). The disadvantages of these methods are the complexity and high cost of laser devices, the complexity of methods for processing the obtained data, the negative impact on the measurement results of the speckle structure of laser radiation, re-reflection and scattering of laser beams, the danger of laser radiation to the eyes and optical devices, etc.

There are known methods of active optical ranging and profilometry that do not use laser light sources. There is a known method for determining the shape of an object, based on measuring the sharpness of focusing images of flat periodic transparency on the surface of the object, which are installed in an optical projector and illuminated with incoherent light [8 - 13]. Periodic stripes of light are focused onto the surface of an object using a lens mounted at the output of an optical projection device. The contrast of the projection of light strips onto the surface is determined by the computing device from the image of the object recorded by an image recording device, for example, a television camera. The optical axes of the projector and the image recording device usually coincide. The maximum contrast of the image of the stripes is achieved in areas of the surface of the object that coincide with the focusing plane of the lens of the projection device. The distance to this plane is measured in advance when calibrating the device or calculated. The position of the plane where the contrast of the light stripes is maximum relative to the object is changed by moving the projector or object along the optical axis of the projector, or by changing the focal length of the projector lens. By moving the focal plane of the projector relative to the object, they scan the surface of the object with it, record images of the projection of stripes of light onto the surface, then, by processing the resulting images, determine the distance to various points on the surface of the object, as well as its shape. A measurement method and device similar to those described above are also used to perform profilometry of microobjects using a wide-field microscope [14, 15]. The disadvantages of this method of optical ranging, profilometry and microscopy are the need to use a complex optical projection device that includes a high-quality lens, the influence of imperfections in the lens of the projection device on the accuracy and reliability of measurements, and the limited field illuminated by the projection device.

Known optical phase and triangulation methods for measuring the 3D shape of an object, which are based on projecting periodic structured illumination onto the surface of the object, for example, periodic stripes of light, and recording an image of this surface (see, for example, [2, 16 – 20]). Illumination of the surface of an object, periodic in space, is created using a projector, in which an incoherent beam of light emitted by a light source is spatially modulated when passing through a transparency, the transmittance of which periodically depends on the coordinate transverse to the optical axis of the projector. Using a lens mounted at the output of this projector, the object is illuminated by a diverging spatially modulated beam of light. The use of computer-controlled optical projectors, such as those with LCDs or other spatial light modulators, allows dynamic control of the period and phase of spatial modulation of the intensity of light illuminating an object. The projection of periodic stripes of light on the surface of an object is recorded by an image recording device, for example, a television or photo camera. The angle between the optical axis of the projector and the optical axis of the image recording device is usually quite large. The projection pattern of periodic strips of light onto an object is affected by the shape of its surface, in particular, the variation in the phase of the projection of periodic strips of light and the displacement of a given strip depend on it. When using the triangulation method, the shape of an object and the distance to its points are determined by the angles at which stripes of a periodic light structure are projected onto the surface of the object and observed [1]. The disadvantage of the triangulation method is the low accuracy of determining these angles and the difficulty of determining the strip numbers of the projected periodic light structure. When using the phase measurement method, the projection phase of periodic stripes of light is determined by finding, for example, the spatial Fourier spectrum of the image of the surface of an object or by the method of step-by-step phase shift of these light stripes [2, 19]. Based on the measured dependence of the projection phase variation on the coordinates in the image of the object, its shape is determined. The disadvantage of phase methods is the ambiguity of calculating the phase from the image of the projection of periodically structured light onto the surface of the object. Various methods have been proposed to disambiguate the calculation of the image phase of a periodic structured backlight projected onto the surface of an object using an optical projector with a lens (see, for example, patents [21–24]). Using such methods, it is possible to measure the absolute values of the coordinates of points on the surface of an object, but this requires a more complex projection system, as well as methods for processing measurement results. In addition to the above specific disadvantages of phase and triangulation methods for measuring the 3D shape of objects using periodic structured illumination, their general disadvantages are:

• The complexity and high cost of an optical projector with a lens,

• Limited transverse size of the area surface illuminated by one projector,

• Difficulty measuring the shape of non-smooth surfaces, surfaces with discontinuities or changes in height,

• The need to calibrate the measuring system as a whole.

There are known methods for forming periodic structured beams of incoherent light without the use of complex and expensive projection devices with a lens [25 - 33]. To form periodically structured beams of incoherent light, these methods use a two-grid device, which includes a light source and two flat one-dimensional periodic gratings with the same stripe direction, which are located on one side of the light source in parallel planes distant from each other. The method for generating periodically structured light beams with such a two-grid device is based on the generalized effect of forming a pseudo-image of the grating. This effect consists in the fact that when incoherent light emitted by a source sequentially passes through two flat periodic gratings behind the grating farthest from the light source, light moiré structures appear, which have a periodic spatial modulation of the light intensity. This moiré structure is called a generalized pseudo-image of the grating [28, 32, 33]. A special case of the generalized effect of forming a pseudo-image of a grating is the Lau effect [27, 28, 31, 34–36]. In this particular case, a contrast pseudo-image of the grating appears at an infinite distance from the two-grid device, and to form periodic modulation of light at a finite distance, a lens is used, which is located behind the grating farthest from the light source. The publication [37] considers a method for determining the distance between two parallel gratings with different spatial periods, based on measuring the characteristics of the light moiré structure that appears after incoherent light passes through these gratings. An optical double-grating device is also known, designed to measure the amount of movement of one of the gratings, as well as the amount of movement of an object attached to it in the plane of this grating in the direction perpendicular to the direction of its stripes, the operation of which is based on the generalized effect of forming a pseudo-image of the grating (see, for example , [29, 38]). Such a device for measuring the amount of movement of an object is one of the options for a linear optical encoder. A two-grid linear encoder is not applicable to measuring the amount of displacement in a direction that is perpendicular to the planes of the gratings, and it cannot be used for non-contact measurement of the distance to objects, the coordinates of their points and the shape of the surface. There are known non-contact methods for measuring the shape of objects that use the generalized effect of forming a pseudo-image of a grating [39 - 42] or the Lau effect [43]. In these methods, the shape of the object is determined by the magnitude of the spatial variation of the projection phase on the surface of the object of a periodic moiré structure, which is formed using a double-grid projection device. The image of the surface of an object illuminated by the said projection device is recorded by an image recording device and processed by a computing device using, for example, the Fourier transform or the step-by-step phase shift method [40 - 43]. To determine the distance to object points, the triangulation measurement method can be used [39]. System for implementing the profilometry method using the generalized effect of forming a lattice pseudo-image [39] is a prototype of the system proposed in the present invention. The prototype system consists of an objectiveless projection device, as well as an image recording device and a computing device [39 - 41]. The projection device includes a source of incoherent light, two periodic gratings located in parallel planes distant from each other. The moiré structure (pseudo-image of the grating) formed by the prototype projection device is weakly localized in the direction of the optical axis of the projector, which is perpendicular to the planes of the gratings. The advantage of the double-grid projection device proposed in the patent [39] is that it is simpler and cheaper than structured light projectors with a lens. The profilometry method, which is described in the patent [39], is closest to the proposed method in terms of technical essence and set of elements for its implementation. This method is a prototype of the proposed method. The known measurement method [39 - 41] has disadvantages of phase and triangulation methods of profilometry and ranging, in particular, the difficulty of using the method to measure the shape of non-smooth surfaces, the limited width of the surface area illuminated by the projection device, and the need to calibrate the measuring system as a whole. In addition, the disadvantage of the triangulation method is its low accuracy and difficulty in determining the numbers of stripes of the periodic light structure projected onto the object. The use of the phase measurement method is complicated by the ambiguity of calculating the phase of the projection of the moiré structure onto the object and the inability to determine the distance to the points of the object. In particular, to determine the distance from the projection device at which the object should be placed, the patent [39] suggests the use of an additional range finder, for example, a laser.

Disclosure of the Invention

Taking into account the shortcomings of the methods and systems for ranging and profilometry described in the section Prior Art, the basis of the invention is to provide a method and system that will eliminate at least some of these shortcomings. In particular, the objective of this invention is to propose a method and system that allows wide-field measurements of the absolute value of the distance to points on the surface of objects, their coordinates, as well as the shape of objects, including objects with a non-smooth surface, using periodically structured light, emitted by a lensless projection device. The objective of this invention is also to propose a method for measuring the distance to points of objects and their shape, in the implementation of which there is no problem of unambiguously determining the value of the phase and the numbers of projection stripes on the object periodically structured light.

The essence of the proposed method, as well as the method that is a prototype, is to project onto the surface of an object a light periodic moiré structure formed using a two-grid projection device, which we will also call a two-grid projector, registration using at least one recording device of the image of the surface area of the object on which this moiré structure is projected, mathematical processing by the computing device of the resulting images and determining, based on the results of this processing, the shape of the surface of the object. What is new in the proposed method is that for ranging and profilometry, at least one moire structure (pseudo-image of the grating) is used, which is quite strongly localized in the longitudinal direction, which is perpendicular to the planes of the gratings installed in the projection device. Such a localized moire (LM) structure is formed, for example, using the double-grid projection device described in the invention. Projection of the mentioned localized moiré structure move along the surface of the object, combining the plane of greatest contrast of the moiré structure with the point on the surface of the object, the coordinates of which need to be measured. Using the known value of the distance to this plane from the plane of the output grating of the projection device, the distance to a given point of the object and its longitudinal coordinate are determined. Using this data, as well as the image of the object and the results of calibration of the image recording device, the lateral coordinates of a given point of the object are determined. By scanning the surface of an object with the projection of the mentioned localized moiré structure, by registering and mathematically processing images of the object obtained at different positions of the LM structure projection, the shape of the object is found. In the proposed method, unlike the prototype method, when determining the shape of an object and the distance to its points, it is not necessary to determine the number of the stripe or the value of the projection phase of the moiré structure and there is no need to eliminate the ambiguity of the value of this phase. New in the proposed way is also that, unlike its closest analogue, it can be used not only to determine the shape of an object, but also to measure the absolute value of the distance to its points and their coordinates. To implement the proposed method, either one or a larger number of localized moiré structures formed by at least one projection device can be used. The difference between the proposed method and the prototype method is also that it can be implemented with a parallel arrangement of the longitudinal axis of the projection device and the optical axis of the image recording device.

The proposed system, just like the system that is its prototype, contains a double-grid projection device, an image recording device and a computing device. The projection device contains a source of incoherent light, first and second flat periodic gratings, which are located one behind the other in non-coinciding parallel planes on one side of the light source, and which are illuminated by the said light source, and the light passing through the first grating falls on the second grating. What is new is that the width of the light source, the first and second gratings that are mounted in the projection device, and the width of the angular spectrum of light emitted by the light source are such that at least one localized moiré pattern is formed. Increasing the width of the working aperture of the light source and gratings installed in the projection device makes it possible to increase the width of the continuous area within which measurements can be taken with the least error. The difference from the prototype is also that in the proposed system a device is used to scan the surface of an object with a projection of the LM structure. Unlike the prototype system, where in the projection device the distance between the gratings and their periods are fixed, in the proposed system the distance between the gratings and their periods can be controlled in a controlled manner, and thus, in particular, the surface of an object can be scanned by the projection of the LM structure. In the proposed system, a device can also be additionally used to change the relative orientation of the stripes of the localized moiré structure and the object.

The technical result is a simplification of the ranging and profilometry system, including from the point of view of manufacturing and control, a simplification of the measurement data processing methodology, the absence of the problem of phase ambiguity, an increase in the width of the area available for measurements using a single projection device, the ability to determine the shape of non-smooth surfaces, surfaces with gaps and jumps in height.

The essence of the invention is illustrated by the following figures.

In fig. 1 schematically shows the optical rangefinding and profilometry system, as well as the object onto which the light localized moiré structure is projected.

In fig. Figure 2 shows a diagram of a projection device that forms a light moiré structure.

In fig. Figure 3 schematically shows the projection onto the y = 0 plane of the elements of the projection device, the image recording device, as well as the localized moiré structure, displaying the positional and angular relationships between the elements of the devices, light rays and spatial regions of the LM structure.

In fig. Figure 4 schematically shows the projection onto the y = 0 plane of the elements of the projection device and the localized moiré structure, displaying the positional and angular relationships between the elements of the device, light rays and spatial regions of the LM structure at (Fig. 4(a)) and when (Fig. 4(b)), where - angular size of half the working aperture of the illuminator, - half-width of the angular spectrum of light emitted by the illuminator.

In fig. Figure 5 shows images of two types of flat one-dimensional amplitude gratings: a grating with a sinusoidal dependence of the amplitude transmittance on the coordinate (Fig. 5(a)) and a periodic binary raster (Fig. 5(b)).

In fig. 6 is a schematic illustration of an optical ranging and profilometry system that uses multiple projection devices and multiple image recording devices.

Carrying out the invention

A method for non-contact ranging and profilometry and a system for implementing it will be discussed with reference to the above-mentioned figures, in which like reference numerals denote the same elements. The method can be implemented using a system, a schematic representation of which is shown in Fig. 1 (clause 16 of the claims). The system includes an objective-free projection device 1, at least one image recording device 2, a computing device 3, as well as at least one device for moving the projection of a localized moiré structure 4, formed by the projection device 1, along the surface of the controlled object 5. Scheme projection device 1 is shown in FIG. 2 (clause 17 of the claims). The projection device 1 according to claim 17 of the formula of the invention includes a spatially extended source of incoherent light 6, which we will also call an illuminator, and two parallel flat one-dimensional (1D) periodic gratings 7 and 8. The first, closest to the illuminator 6, grating 7 and the second , output, grating 8 are located on one side of the light source 6. The stripes of these gratings have the same direction. It is preferable that the gratings 7 and 8 have a rectangular shape. The luminous surface of the light source 6 faces the gratings 7 and 8. In a particular case, according to claim 18 of the claims, the spatially extended light source 6 installed in the projection device 1 is a source of diffuse light. Such a source of diffuse light, for example, can be the surface of a heated body, a fluorescent lamp, a fluorescent screen, the screen of a phone, TV, tablet or computer monitor, or the surface of an organic and inorganic light-emitting diode. The source of diffuse light can also be a section of the daytime sky, the surface of a random phase transparency, for example, frosted glass, a sheet of tracing paper or tissue paper, illuminated from the side opposite to the gratings, etc. The projection device 1 forms at least one light LM structure. A localized moiré structure can be formed in the geometric optics (GO) zone (claim 2 of the invention formula) or in the Fresnel diffraction zone of the projection device 1 (claim 3 of the invention formula). Symbolic image of the light intensity distribution The LM structure in a plane parallel to the planes of the gratings (see Fig. 2) or in a plane perpendicular to the direction of their strokes (see Figs. 3 and 4) is designated in the figures by the number 9. In Fig. 1 and 2 show a right orthogonal coordinate system with axesx,y Andz, which is connected to projection device 1. Coordinate axisz directed perpendicular to the planes of the gratings 7 and 8, in the direction from the light source 6 to the gratings. If the second lattice 8 has a rectangular shape, then the axisz passes through its center, and is called below the optical axis of the projection device 1. Axisydirected along the direction of the strips of gratings 7 and 8 (see Fig. 2). The transmission coefficients of gratings 7 and 8 depend periodically on the coordinatex. Axis directionz further in the text we will call longitudinal directions perpendicular to the axisz, we will call them transverse. We will call the dimensions of the object 5, the working apertures of the light source 6, the gratings 7 and 8 in the direction of the axisx – their width, in the direction of the axisy– height, in the direction of the axisz –length or thickness. Plane coincides with the plane of the first grating 7. The second, output grating 8 is located in the plane, i.e. the planes of the first and second gratings are separated from each other by a distance. The distance in the longitudinal direction from the second grating 8 at we will also call the distance from the projection device 1. In the particular case when the working surface of the illuminator 6 is flat and it is located parallel to the planes of the gratings, the distance between the working surface of the illuminator 6 and the plane of the first grating 7 will be denoted by L₀. It may be zero. Coordinate of the center of the working surface of the illuminator along the axis equal to. In fig. 1 also shows a global fixed coordinate system with axes, And. In a particular case (clause 19 of the claims), the system can additionally use a device for determining the coordinates and orientation of the projection device 1 in the global coordinate system.

The rangefinding and profilometry system includes at least one device designed to move and/or change the orientation of the LM structure and object 5 relative to each other. In fig. 1 and fig. 2 thick arrows show the directions of possible translational movements and rotations of the elements of the rangefinding and profilometry system and object 5 in various special cases of implementation of the method and system. In a particular case (clause 20 of the claims), a device can be used that changes the distance between the projection device 1 and object 5 by progressively moving the projection device 1 and/or object 5. In particular, bringing the projection device 1 and object 5 closer or further away can carried out at a given speed. In a particular case (clause 21 of the claims), to change the relative position of the LM structure and object 5, devices can be used to rotate the projection device 1 and/or object 5. As an example, in Fig. 1 schematically shows a device 10 designed to move and/or change the orientation in space of the projection device 1. In a particular case of implementation of the system (clause 22 of the claims), the projection device 1 can use a device that controllably changes the distance between the gratings 7 and 8 in longitudinal direction or carries out the approach or removal of gratings 7 and 8 in this direction at a given speed. Additionally, there may be a device for translational movement of at least one of the gratings 7 and 8 in its plane in the direction of the coordinatex, which leads to a change in the phase of the quasiperiodic moiré structure formed by the projection device 1 (clause 23 of the claims). Devices that, in various particular cases of system implementation, can carry out movement and rotation of object 5, movement of gratings 7 and 8, are not shown in the figures. Devices by which the relative position and orientation of the projection device 1 and the object 5 are changed, as well as the position of individual elements of the projection device 1 are changed, are well known and commercially available [44 - 47]. The ranging and profilometry system also contains at least one device designed to measure the amount of change in position and/or orientation of at least one item from a set including object 5, projection device 1, gratings 7 and 8. Such devices are well known and commercially available [ 44 - 46, 48]. In a particular case, a device for moving and/or changing the orientation of elements of a system or object 5 and a device for measuring the magnitude of their movement, as well as the angles of their rotation, can be combined in one device or be one device.

The image registration device 2 is designed to register an image of at least one object 5 (see Fig. 1). The image recording device 2 can be, for example, a television camera or a photo camera. The image sensor 11 in the image recording device 2 is, for example, a CCD (charge-coupled device) or a CMOS (complementary metal-oxide-semiconductor) matrix. The lens 12 projects the light incident on it onto the image sensor 11 of the image recording device 2 (see FIGS. 1 and 3). It is preferable to pre-calibrate the image recording device 2 using known methods, for example, using a checkerboard pattern [19, 49]. The image recording device 2 may be stationary, or it may be slidable and rotatable. To move and rotate the image recording device 2, as well as to determine its position and orientation, well-known devices (not shown in the figures) are used. In a particular case, at least one image recording device 2 can be rigidly connected to the projection device 1, then it moves and rotates with it. In a particular case (clause 24 of the claims), the optical axis of the image recording device 2 is parallel to the longitudinal axis of the projection device 1.

The computing device 3 is designed to calculate the distance to points on the surface of the object 5 and their coordinates, as well as the shape of the surface of the object 5 based on images obtained by the image recording device 2. The computing device 3 is, for example, a computer or mobile computing device. The computing device 3, in addition to storing and processing information received from the image recording device 2, processes and stores data received from other devices of the system, as well as manages the system devices and their elements. In particular, it can process and store data about the magnitudes of movement, speeds of movement and angles of rotation of the projection device 1, image recording device 2, object 5, gratings 7 and 8, which come from devices that record these values.

The amplitude transmittance coefficients of the gratings 7 and 8, which are installed in the projection device 1, in the general case can be complex. In a particular case of implementation of the system (clause 25 of the claims), at least one grating is installed in the projection device 1, which has a real positive amplitude transmittance, which is called an amplitude grating. In a particular case (clause 26 of the claims), at least one grating installed in the projection device 1 is a 1D amplitude grating with a sinusoidal dependence of the magnitude of the change in the amplitude transmittance on the x coordinate (see Fig. 5(a)) [37, 50, 51]. We will call such a grating an amplitude grating with sinusoidal transmission. In another special case (clause 27 of the claims), at least one grating can be a 1D amplitude grating, which has a binary dependence of the transmittance on the transverse coordinate, for example, it represents transparent and opaque parallel rectangular stripes periodically alternating along the x coordinate, which have sharp boundaries (see Fig. 5(b)) [31, 32, 41, 42, 44, 52, 53]. Such gratings are also called periodic binary rasters. The advantage of using periodic binary rasters in a projection device is the simplicity and low cost of manufacturing these gratings and their commercial availability [44, 48, 53]. In another particular case (clause 28 of the claims), at least one phase grating can be used in the projection device 1, i.e. a grating with a periodic dependence of the phase of the amplitude transmittance on the transverse coordinate and a constant modulus of this coefficient [52, 54]. As another alternative, the projection device can use at least one grating that combines an amplitude and a phase grating [52, 55, 56]. Amplitude, phase and amplitude-phase gratings are manufactured by known photographic, holographic, lithographic, printing and other methods. Some of the types of gratings mentioned are commercially available [44, 48, 54]. In a particular case (clause 29 of the claims), at least one grating can be used in the projection device 1, the characteristics of which can be changed. For example, at least one of the gratings installed in the optical projection device 1 may be an amplitude binary raster whose fill factor and/or period can be changed. In a particular case (clause 30 of the claims), a spatial light modulator can be used to form at least one of the gratings installed in the projection device 1 [57 - 59].

The projection device 1 in a particular case of its implementation (clause 31 of the claims), when the first grating 7 and the second grating 8 are 1D amplitude gratings, operates as follows. The light emitted by the illuminator 6 passes first through the first grating 7, then through the second grating 8. When light passes through the amplitude grating, a spatial modulation of its intensity occurs, therefore, periodic stripes of light and shadow are observed behind each of the gratings 7 and 8. When the grating is illuminated with incoherent light from an extended source or diffuse light, the contrast of the bands of light and shadow decreases with distance from the grating in the longitudinal direction. This happens because with a wide angular spectrum of light incident on the grating, the bands of light and shadow that appear after the passage of plane light waves propagating at different angles to its surface “mix” at some distance behind the grating. At a sufficiently large distance from the grating, the light intensity becomes almost constant in space.However, there are planes parallel to the planes of the gratings 7 and 8 and distant from them in the longitudinal direction at known distances, in the vicinity of which the projection device 1 can form light moiré structures, which are regions of light and shadow periodic in space [25 - 28, 31 - 33 , 60 - 63]. Projection of these light moire structures on a plane parallel to the planes of the gratings, has the form of periodic light and dark stripes that are directed along the axisy (see Fig. 2). The formation of a localized moiré structure can be interpreted, in particular, as the effect of a shadow echo [60, 62, 63], which is a special case of a modulation echo [61]. Moiré structures formed by a double-grid projection device with 1D gratings are designated by two indices (N,M) (see clause 4 of the claims), whereN AndM - integers. The distance from the plane of the output grating 8 of the projection device 1 to the plane where the contrast of the moiré structure (N,M) is maximum, calculated using the formula

Where, And - spatial periods of the first and the second lattice, respectively [27, 31, 33, 64, 65]. Coordinate of the plane where the contrast of the moiré structure (N,M) has the largest value, equal to, Where. Dependence of light intensity on coordinatesx near the plane of greatest contrast of the moire structure (N,M) described by a periodic function, spatial period which is calculated using the formula [27, 31, 33, 64, 65]

The contrast of the moire structure ( N , M ) is calculated using the formula

Where And - maximum and minimum value of light intensity in the planez= const [64, 66]. Distance in axis directionx between the points at which the quantities are determined And, equals, Where - a natural number, including zero. Spatial distribution of light intensity in a plane close to the line conventionally shown in Fig. 3 and 4 and indicated by the number 9. Depth of field of moire structure (N,M) we will denote. Depth of field equal to twice the length, when removed in the longitudinal direction from the plane contrast of moiré structure (N,M) decreases by half compared to the value of its contrast in the plane. The projection device 1 in the embodiment proposed in the invention forms light moiré structures that are quite strongly localized in the longitudinal direction. Locality of the moiré structure (N,M) means that its depth of field significantly less than the distance from the projection device 1 to the plane on which the contrast of this moiré structure is greatest. Specifically, we will assume that the localized moiré structure (N,M) relative depth of field LM must be at least less than 0.25.

An analysis of the characteristics of moiré structures formed by a projection device in various special cases of implementation of this device, consideration of the conditions under which localized moiré structures can be formed, assessment of the accuracy of the proposed method of ranging and profilometry, as well as a number of its other characteristics will be carried out after the description of special cases of implementation of the method.

The method in a particular case of its implementation for measuring the distance to at least one given point 13 of the surface of an object 5 (see Fig. 1) and the coordinates of this point is carried out as follows. The surface of the object 5 is illuminated with light emitted by the projection device 1. The projection device 1 uses elements, in particular gratings 7 and 8, with such parameters that at least one localized moiré structure appears. In particular, according to claim 5 of the claims, at least one of the LM structures can be used to implement the method: (1,3), (1,2), (1,1), (2,1) and (3, 1). It is preferable to use LM structures with a sufficiently high contrast for measurements, for example, according to claim 6 of the invention formula, the highest contrast value of the LM structure exceeds 0.2. According to claim 7 of the claims, several LM structures can be simultaneously formed by one projection device. To simplify the further description of the method of ranging and profilometry, we will assume that, unless otherwise indicated, one LM structure, index (N,M) which is known. Typically, at least one image recording device 2 is focused approximately onto the plane of greatest contrast of this LM structure. It is preferable, firstly, that the depth of field of the lens 12 of the image recording device 2 be at least twice that of the moiré pattern (N,M); secondly, so that the width of the LM structure (N,M), used for measurements, (see Fig. 4) exceeded the period of the moire structure at least twice. If the width of the projection onto the planeconst of the controlled part of the surface of the object 5 is significantly greater than the period used LM structure, as well as the tangent of the angle between the surface of the object and the plane in the areas of their intersection is less than, That the projection 4 of the LM structure onto the surface of the object 5 has the form of a region or several regions within which quasi-periodic coordinates are observedxlight and dark stripes (see Fig. 1). The shape of the area on the surface of the object 5, where the projection 4 of the LM structure has a relatively high contrast, depends on the shape of the surface of the object 5 and the depth of field of the moiré structure (N,M). Plane, where the contrast of the moire structure (N,M) is the largest, intersects with the surface of object 5 along a flat line, which we will call the isoline of the greatest contrast of the LM structure. For example, with flat surfaces the plane intersects along segments of straight lines (they are shown by dash-dotted lines 14 in Fig. 1), with spherical surfaces - in a circle or along an arc of a circle. The image of the surface of the object 5, illuminated by the projection device 1, is recorded by the image recording device 2. Using the computing device 3, the dependence of the quasiperiodic contrast in the direction of the axis is determinedx changes in the brightness of the image of object 5 from 2D coordinates in the image. To calculate contrast, well-known mathematical methods of image processing are used. In particular, Fourier or wavelet analysis of images can be used, interpolating the spatial distribution of changes in image brightness with a periodic or quasi-periodic function, for example, a sinusoid or wavelet. The well-known method of step-by-step phase shift of stripes of a periodic light structure that illuminates this surface can also be applied [2, 19]. The phase shift of the moiré structure, which is projected onto the surface of the object 5, is carried out, for example, by transverse displacement in the direction of the axisxprojection device 1 or according to claim 23 of the formula of the invention by displacement in the direction of the axisx one of the gratings installed in it. Using the results of calculating the distribution of the contrast value of the image of the surface of object 5 onto which the LM structure is projected (N,M), find the position of the isoline of the greatest contrast of this LM structure. To determine the coordinates of a given point 13 of the surface of an object 5, the isoline of the greatest contrast of the projection 4 of the LM structure is combined with this point. This is done, in particular, in the following ways:

1. By changing the distance between the projection device 1 and the object 5, for example, by progressively moving the projection device 1 in the longitudinal direction (clause 8 of the claims).

2. By rotating the projection device 1 and/or object 5 (clause 9 of the claims).

3. Changing the distance from the projection device 1 to the plane of the greatest contrast of the moiré structure (clause 10 of the claims), for example, by changing the distance between gratings 7 and 8 (see clause 11 of the claims) or the spatial period of at least one of them (see clause 12 claims).

You can use a combination of two or three of the above methods of moving the projection 4 of the LM structure and the isoline of its greatest contrast along the object 5. The movement is carried out until the isoline of the greatest contrast passes through a given point 13 of the surface of the object 5. Distance in the longitudinal direction from the plane of the second grating 8 of the projection device 1 to the isoline of the greatest contrast of the LM structure (N,M) is calculated using formula (1). The longitudinal coordinate of a given point 13 in the coordinate system associated with the projection device 1 is equal to . In this position, the isoline of the greatest contrast of the LM structure determines the transverse coordinates of the point 13, using the measured values of the coordinates of this point on the image of the surface of the object 5 and the results of calibration of the image recording device 2 [19, 49]. In a convenient and easy-to-process special case, when, firstly, according to claim 24 of the claims, the optical axis of the image recording device 2 is parallel to the optical axis of the projection device 1 and, secondly, the coordinates of the lens 12 of the image recording device 2 in the coordinate system , associated with projection device 1, are fixed and equal,, (see Fig. 1 and Fig. 3), then the coordinatesx Andy points on the surface of the object 5, belonging to the plane, calculated using the formulas

Where - focal length of the lens 12 of the image recording device 2, And - coordinates of the images of these points on the surface of the image sensor 11, - distance from the lens 12 of the image recording device 2 to the plane , which is equal (see Fig. 3). Coordinates of a given point 13 on the surface of object 5 in the global coordinate system , , determined, using the computing device 3, based on the data obtained about its coordinates in the x , y and z coordinate system associated with the projection device 1, as well as data on the position and orientation of the projection device 1 in the global coordinate system.

The peculiarity of the proposed method in the particular case of its implementation for measuring the shape of an object is that the isoline of the greatest contrast of the projection 4 of at least one LM structure is moved along the entire controlled or accessible part of the surface of the object 5. At each position of the projection 4 of the LM structure, an image of the surface object 5 is registered by an image recording device 2. Processing of the received images and control of the movement of the projection 4 of the LM structure along the surface of the object 5 is carried out using a computing device 3. The computing device 3 by processing images of the surface of the object 5 obtained by the registration device 2 at different positions of the projection 4 of the LM structure , determines the longitudinal and transverse coordinates of the set of points of the controlled part of the surface of the object 5. The determination of the coordinates of each of the set of points of the surface of the object 5 is carried out in the same way as in the above-described special case of implementing a method for measuring the coordinates of one given point 13 of the object . To reduce the measurement time, as well as the time and labor intensity of processing their results according to claim 13 of the claims, it is preferable that at each position of the projection 4 of the LM structure on the surface of the object 5, the coordinates of the set of points on the surface of the object 5 located on the isoline of the greatest contrast are determined and stored by the computing device this LM structure. The proposed method allows you to measure the shape of non-smooth surfaces, surfaces with discontinuities and sudden changes in height, the shape and distance to several objects that do not obscure each other from the light of the projection device.

Let us consider the use of a method for measuring the shape of a part of the surface of an object 5 using an example when scanning the projection 4 of an LM structure along the surface of an object 5 is carried out by progressively moving the projection device 1 in the longitudinal direction towards the object 5 . It is preferable to first combine the isoline of the greatest contrast of the LM structure with the area of the object 5 closest in the longitudinal direction to the projection device 1. Using the moving device 10, the projection device 1 is gradually brought closer in the longitudinal direction to the object 5. At each step, the distance in the longitudinal direction between the projection device 1 and object 5 is reduced by a fixed amount , whose value is less , For example, . In this case, the isoline of the greatest contrast of the projection 4 of the moire structure also moves along the surface of the object. Distance from the area of object 5 closest to the projector to the plane of greatest contrast of the moire structure when moving to steps will be equal . The approach of the projection device 1 and the object 5 can also be continuous at a constant speed , in this case the registration time of one image should be much less than . In this case calculated by the formula , Where - time, - the moment in time when the isoline of the greatest contrast coincided with the area of the object closest to the projector. Image of the surface of an object 5 at each step or at successive moments in time is recorded by the image recording device 2. By processing by the computing device 3 the image obtained by the recording device 2 in step or at a time , determine the transverse coordinates x and y of the points of the surface of the object 5 located on the isoline of the greatest contrast of the projection of the LM structure at this value . By processing images of the surface of the object 5, which were recorded at different distances in the longitudinal direction from the projection device 1 to the object 5 , isolines are calculated for different values , and based on this data the shape of the surface of the object is calculated .

The use of several LM structures with different indices ( N, M ), formed according to claim 7 of the claims by one projection device, allows you to expand the range of measurements of distances and coordinates, as well as reduce the time required to measure the shape of the surface of an object. The implementation of the method using several moiré structures will be similar to the above-described implementation of the method in the case of one LM structure. In the case of using several LM structures, it is preferable to use several image recording devices, each of which is focused on the plane of greatest contrast of one of the LM structures. In the case when several LM structures or one LM structure whose index ( N,M ) is unknown in advance are projected onto the surface of an object, it is necessary to distinguish between images of projections of moiré structures with different indices ( N,M ) or determine the values of the indices ( N,M ) from an image that is recorded by an image recording device. Images of projections of moiré structures with different indices ( N, M ) can be distinguished, for example, by their periods, by the magnitude of their contrast, by the order of arrangement in the longitudinal direction.

Surface area size object 5, within which its shape is measured, can be increased if, after scanning the part of the surface accessible for measurements, the object 5 is rotated by a known angle, for example, around an axis perpendicular to the axisz. This will allow the projection device 1 to illuminate a previously inaccessible area of the surface of the object 5 and then scan it with at least one LM structure 4. It is also possible to increase the size of the area of the surface of the object 5, within which its shape is measured, if, after measuring the profile of one part of the object , move the projector 1 and, if necessary, image recording devices around the object, and then scan another part of the object’s surface with at least one LM structure. The size of the area of an object's surface available for measuring its profile, as well as the speed of such measurements, can be increased by using multiple projection devices and multiple image recording devices (see FIG. 6). Scanning of the surface of an object by LM structures formed by each of the projection devices is carried out, for example, by translational movement of the projection devices in their longitudinal direction, or by changing the distance between the gratings in the projection devices and/or by rotating the object using a turntable 15.Preferably, the areas of the object's surface that can be observed by the image recording devices overlap. Using the computing device 3, profiles of different sections of the object's surface are calculated, as described above, and then they can be combined by known methods into a single panoramic 3D picture of the object's surface profile.

Below is a rationale for the fact that with the help of a projection device, special cases of implementation of which are proposed in the invention, moiré structures localized in the longitudinal direction can be formed, and the influence of the parameters of the projection device is considered on the number and characteristics of the moire structures formed by it, and also an assessment of the accuracy of the proposed method of ranging and profilometry is given.

Let's denote a function that describes the angular distribution of light intensity emitted by small elements of the working surface of the illuminator 6, i.e. describes their radiation pattern, where - the angle between the direction in which the light wave propagates and the planex = const, - the angle between the direction of the light wave and the plane .

For simplicity or certainty we will assume that

the working surface of the illuminator 6 is spatially homogeneous, i.e. its luminosity, as well as the angular and frequency spectrum of light emitted by its elements, are constant within the working aperture of the illuminator surface;

the width of the angular distribution of light intensity emitted by the elements of the working surface of the illuminator 6 in the x = const plane is much less than the width of the angular distribution of light in the plane , and therefore . In this case, the angle is the angle between the direction in which the light travels and the longitudinal direction (see Figs. 3 and 4). Such an angular distribution of diffuse light intensity can be formed, for example, if the working surface of the illuminator 6 is a one-dimensional random phase transparency onto which a plane wave of incoherent light falls from the side opposite to the gratings, and the 1D stripes along which the optical path length of the light through the transparency is constant are directed parallel to the y axis. Half-width in plane angular spectrum of light emitted by the working surface of the illuminator 6, by level from the maximum value of the function let's denote ;

• according to claim 31 of the claims, amplitude gratings 7 and 8 are installed in the projection device 1;

• according to claim 32 of the claims, lattices 7 and 8 are thin, i.e. when they pass through the light emitted by the illuminator 6, there is no significant narrowing of its angular spectrum, for example, a decrease in the width of the angular spectrum of light does not exceed 20%;

• according to claim 33 of the claims, the working surface of the illuminator 6 has the shape of a rectangle, the plane of which is parallel to the planes of the gratings 7 and 8, and its sides are parallel to the x and y axes (Fig. 2). The width of the working aperture of the illuminator 6 is equal to (see Fig. 3 and Fig. 4), its height is (see Fig. 2);

• grids 7 and 8 have the shape of rectangles, the sides of which are parallel to the x and y axes. The widths of the working aperture of gratings 7 and 8 are equal And respectively (see Fig. 3 and Fig. 4), and the height is equal to And respectively (see Fig. 2). The centers of the working surface of the illuminator 6, as well as the first grating 7 and the second grating 8, are located on the optical axis of the projection device, i.e. the centers of these elements of the projection device 1 have transverse coordinates x = 0, ;

• the transverse dimensions of the working aperture of the illuminator 6 and gratings 7 and 8 are so large that in the region where the LM structure is formed ( N , M ), the influence of light diffraction on the apertures of these elements can be neglected, which is carried out under the conditions , , , Where – the smaller of the quantities And , – the smaller of the quantities And , – the smaller of the quantities And , ; For example, , , ;

• the width of gratings 7 and 8 significantly exceeds their periods , ; For example , .

First, we will determine the characteristics of the LM structures formed by the projection device 1, in the particular case when its parameters and the parameters of its elements are such that, according to claim 2 of the claims, the influence of light diffraction on the amplitude gratings 7 and 8 on the characteristics of the LM structures is negligible. In this particular case, to describe the characteristics of moiré structures formed by double-grid projector 1, the geometric optics approximation is applicable. In the geometric optics approximation, the characteristics of moiré structures do not depend on the wavelength of light, therefore, in a projection device, a source of both monochromatic and non-monochromatic light, in particular, a source of broadband light, for example, white light, can be used as an illuminator. The influence of diffraction on gratings 7 and 8 on the characteristics of the LM structure ( N , M ) can be ignored if the first and second gratings are located close to each other; according to clause 34 of the claims, the distance between their planes must satisfy the condition

(see [26, 62, 63]), where the length calculated by the formula

magnitude equal to , Where - central wavelength of light emitted by the illuminator, - half-width of the light spectrum by wavelength by level .

As As a typical example, we will consider the properties and evaluate the characteristics of LM structures formed in the zone of geometric optics, in the particular case when, according to claim 35 of the claims, 1D amplitude gratings 7 and 8 with sinusoidal transmission are used in the projection device 1. Amplitude transmittance coefficients of the first grating 7 and second grid 8 are given accordingly by the formulas

Where , - modulation depth, , - wave number, , - phase of the amplitude transmittance of the first grating 7 and the second grating 8, respectively. We assume that gratings 7 and 8 are surrounded on the outer perimeter by opaque frames (not shown in the figures), so the transmittance of the first grating is 7 equal to zero at or , and the transmittance of the second grating is 8 equal to zero at or . Using a projection device with two 1D amplitude gratings with sinusoidal transmission, a maximum of four moire patterns (real pseudo-grating images) can be formed. , [65]. Four moiré structures ( N , M ), namely (1,2), (1,1), (2,2) and (2,1), arise if . They are located in the vicinity of three planes, which are removed from the second lattice 8 at a distance , which are calculated using formula (1). As follows from formula (1), . The spatial periods of moiré structures (1,2), (1,1), (2,2) and (2,1) are calculated using formula (2). There is the following relationship between the periods of these moiré structures: . The phases of the moiré structures (1,2) (1,1) (2,2) and (2,1) are equal, respectively , , , . If , then three moire structures are formed by the projection device, but the moire structure (2,1) does not appear. At only one moiré structure (1,2) appears. At no moiré structures appear.

If the LM structure ( N , M ) appears far enough from the projection device 1, then near the region of its localization there are no longer stripes of light and shadow from gratings 7 and 8. In particular, when And , the bands of light and shadow from the gratings in the region of localization of the moiré structure ( N , M ) have low contrast, for example, it is less than 0.1 if the conditions are met , And . In an important case for many potential applications of the method, when , moiré structures with different indices ( N , M ), formed by a projection device with two 1D amplitude gratings with sinusoidal transmission, almost do not overlap in space. The exception is the moiré structures (1,1) and (2,2), which are located near the same plane , Where . In the vicinity of this plane light intensity is

(see [65]), where is the intensity of incoherent light incident on the first grating 7. In the vicinity of the planes And , where the moiré structure (1.2) and (2.1) is respectively localized, the light intensity is calculated using the formula

(see [65]), where the subscript NM has the value 12 and 21 for the moiré structure (1,2) and (2,1), respectively, . For all moiré structures ( N , M ), the contrast value , If , And , If . The contrast of moiré structures ( N , M ) depends on the longitudinal coordinate z , and this dependence is described by the formula

Where - contrast value of the moiré structure ( N , M ) in the plane . The moire structure (1,1) is the most contrasting of the four. In the GO zone at And = 1 its contrast in the plane equals = 8/9 [56]. The contrast of the moiré structure (2,2) is the smallest, in the plane it is equal = 1/18. Maximum contrast of moiré structures (1,2) and (2,1) in the GO zone at = 1 is equal = 2/9 [65]. Functions describes the dependence of the contrast of the moire structure ( N , M ) on the longitudinal coordinate z . Its value at maximum and equal to 1, i.e. . Function decreases to 0 as we move away from the plane both towards and away from the projection device. Depth of field moiré structure ( N , M ) is equal to the full width at half maximum (FWHM) of the function , Where .

Let us estimate the depth of field of the moire structure ( N , M ), which is formed by the projection device 1 in some special cases of its implementation. We will assume that the frames limiting the first and second gratings do not vignette the illuminator in the direction of coordinate x when it is observed from the point , And (see figs. 3 and 4). This condition is met, for example, if the width of the working aperture of the gratings 7 and 8 is greater than or equal to the width of the working aperture of the illuminator 6

The angular size of half the working aperture of the light source 6 in the plane when observed from a point with coordinates , And let's denote (see figs. 3 and 4). It is equal , Where . From formula (11) it follows that the angular size of the first and second gratings in the plane greater than the angular size of the illuminator, where said angular dimensions of the illuminator and gratings are determined from the point , And . In the particular case when the angular size of the illuminator is less than the width of the angular spectrum of the light it emits (see Fig. 4(a)), i.e. , and also when the brightness of the illuminator does not depend on the angle at , function near the plane at equal to

Where (see [39, 67 - 69]). From formula (12) it follows that the depth of field of the moiré structure (N,M) near the plane can be calculated using the formula

Moiré structure ( N , M ) at is highly localized , if the condition is met

From formula (13) it follows that the depth of field of the moire structure ( N , M ) is less than a quarter of the distance at . At the moiré structure ( N , M ) is localized ( ), If . For example, when And the moiré structure (1,1) will be localized if the width of the working aperture of the illuminator more .

In the opposite case, when, according to claim 36 of the claims, the angular size of the working aperture of the illuminator 6 in the plane when observed from a point with coordinates, And greater than the width of the angular spectrum of light emitted by the surface elements of the illuminator 6, (see Fig. 4 (b)), depth of field moire structure (N,M) near the plane at can be estimated using the formula

Relative depth of field of the moire structure (N,M) at calculate according to the formula

Moiré structure ( N , M ) at is localized , if the condition is met

in particular, at. From inequality (17) and conditions, which can be written in the form, again the necessary condition (14) follows, during which the moiré structure will be localized. In particular, at. Thus, in order for the projection device 1, in which the first and second gratings with angular dimensions in the plane larger than the angular size of the working aperture of the illuminator, a localized moire structure was formed (N,M), in this projection device according to clause 37 of the formula of the invention, it is necessary to use an illuminator 6, whose tangent of the angular size in the plane half the working aperture, equal, as well as the tangent of the half-width in this plane of the angular spectrum of the light emitted by it are more than five times greater than the ratio.

In the particular case of implementation of projection device 1, when the half-width of the angular spectrum of light emitted by the elements of the illuminator surface is equal to , and the width of the working aperture of the illuminator exceeds the distance from it to the plane of greatest contrast of the moiré structure ( N , M ) by more than twice , i.e. , from formula (15) it follows that the depth of field of the moiré structure is approximately equal to . From this assessment , as well as formulas (1) and (2), it follows that the relative depth of field of the LM structure ( N , M ) is approximately equal to . Based on this estimate of the relative depth of field, we find that when = 1 mm for the moiré structure (1,1) in the zone of geometric optics, where condition (5) is satisfied, the quantities may be on the order of a percentage.

Width of moire pattern (N,M) in the plane equal to (see Fig. 4)

The contrast and depth of field of LM structures depend on the transverse coordinate x . Localized moiré structure ( N,M ) has the highest contrast and smallest depth of field near the plane . In the vicinity of this plane there is a region of width (see Fig. 4), within which the contrast and depth of field of the LM structure ( N,M ) do not change or change little, for example, less than 1.2 times. We will call this region the central region of the moire structure ( N,M ). Width of the central area can be estimated using the formula (see Fig. 4 (a, b))

To implement the proposed method of ranging and profilometry, it is preferable that .

Thus, according to claim 14 of the claims, if the frames delimiting the first and second gratings do not vignette the illuminator in the direction of the coordinatex when it is observed from the central region of this LM structure, then when depth of field LM structure (N,M) in area can be assessed according to formulas (13) or (15), which can be replaced by one generalized formula

Where - the smallest of the values And .

The absolute error in determining the distance from the projection device to a given point of the object 5 is proportional to the depth of field of the moiré structure and usually does not exceed . For ranging and profilometry, it is preferable to use LM structures with a shallow depth of field, for example, according to claim 15 of the invention, it is proposed to use LM structures whose relative depth of field in the central region is less than three percent. To increase the accuracy and reduce the measurement time, it is advisable to optimize the characteristics of the LM structure projected onto the surface of the object 5, in particular, to select the optimal period of the LM structure, its depth of field and the direction of the stripes. When ( see Fig. 4(b)), by increasing the width of the light source, as well as the width of the gratings, as follows from formulas (11) and (19), it is possible to increase the width of the central region almost unlimitedly , within which the accuracy of measuring the distance to the points of the object and its shape will be approximately the same as in the center of the LM structure . Thus, the method and system proposed in the invention allow for wide-field ranging and profilometry.

Let us give the first numerical example in which we determine the characteristics of moiré structures formed in the area of geometric optics by projection device 1 with thin amplitude gratings 7 and 8. We assume that the first and second gratings with sinusoidal transmission with periods are installed in the projection device = 2 mm and = 1 mm respectively. The modulation depth of the transmission function of these gratings is equal to = 1. The distance between the first grating 7 and the second grating 8 is = 20 cm. Illuminator 6 is located close to the first grille = 0. Light source 6, first and second gratings have equal width = 100 cm. Illuminator 6 emits diffuse light in the range µm. The half-width of the angular spectrum of light emitted by small incoherent elements of the illuminator surface is equal to 30 ^o . The projection device 1 with these parameters forms two moire structures with a contrast of more than 0.2: these are moire structures (1,1) and (1,2). The moiré structure (2,1) does not arise, because . Distances between gratings less than distance equal to 33 cm, therefore the influence of light diffraction on the characteristics of moiré structures (1,1) and (1,2) can be neglected. The spatial period of the moiré structure (1,1) is equal to = 2 mm. This moiré structure will have the greatest contrast in a plane distant from the second grating at a distance = 20 cm. The maximum value of its contrast is approximately equal to ≈ 0.9. The width of the central region of the LM structure (1,1) is equal to 54 cm. The depth of field of the moire structure (1,1) in its central area is equal to 2 mm. Moiré structure (1,2) with spatial period = 0.67 mm is localized near a plane distant from the second grating at a distance ≈ 6.7 cm. Its maximum contrast is approximately = 0.22. The width of the central region of the LM structure (1,2) is equal to 69 cm. Depth of field of this moire pattern in its central region is equal to 0.7mm. The relative depth of field of the moiré structures (1,1) and (1,2) is approximately 1%.

Note that formulas (13), (15), (19) and (20) provide only an approximate estimate of the depth of field of the moiré structure ( N , M ) and the width of its central region. To increase the accuracy of measurements using the proposed method of ranging and profilometry, it is preferable to first measure the dependence of the contrast of the moiré structure ( N , M ) on the longitudinal coordinate z and transverse coordinate x , and based on the data of these experiments, determine the measurement error of the distance and coordinates .

In a number of other special cases of implementation of the proposed ranging and profilometry system, it uses a projection device 1, in which at least one amplitude grating is installed with a periodic non-sinusoidal dependence of the transmittance on the coordinatex. Using a projection device 1, in which at least one amplitude grating with non-sinusoidal transmission is installed, it is possible to form moiré structures (N,M), which have maximum values of integer indicesN AndM not limited value two [27, 64, 66, 70]. The number of moire patterns formed by such a projection device is may be greater than in the particular case when two amplitude gratings with sinusoidal transmission are used. The distances from the projection device 1 to the plane where the contrast of these moiré structures is greatest are calculated using formula (1), their periods are calculated using formula (2). The contrast value of the moire structure (N,M) in the plane in the GO zone is determined, in particular, by the dependence of the transmittance coefficients of the first and second gratings from coordinatex. The depth of field of LM structures can be estimated using formula (20).

As an amplitude gratings with non-sinusoidal transmission (clause 27 of the claims), a periodic binary raster can be used (see Fig. 5 (b)). The fill factor of a binary raster is equal to, Where - lattice period, - the width of its transparent stripes, index denotes the grating number in the projection device 1. Amplitude binary raster with also called Ronchi grid. In the particular case where the first grating 7 and the second grating 8 in the projection device 1 are Ronchi gratings, relatively contrasting moiré structures (1,1), (1,3) and (3,1) can appear in the field of geometric optics. The condition for their occurrence is, HereN AndM equal to 1 or 3. The greatest contrast of the moire structure (1,1) at approximately the same as when using two amplitude gratings with sinusoidal transmission0.9. The highest contrast value of the moiré structures (1.3) and (3.1) is approximately 0.3. The remaining moiré structures (N,M), formed by a projection device with two Ronchi gratings, in the geometric optics zone have a contrast of less than 0.2. When using in a projection device at least one binary raster with a fill factor less than that of the Ronchi grating, i.e., the number of relatively contrasting moiré structures can be significantly more than three. For example, in the particular case when the first lattice in a projection device is a binary raster with, and the second grating is a Ronchi grating or a grating with sinusoidal transmission at contrasting moiré structures (1,4), (1,3), (1,2), (1,1), (2,1), (3,1) and (4,1) will be formed (with contrast). As follows from formula (1),.

Installation in a projection device at least one amplitude grating with non-sinusoidal transmission, in some cases makes it possible to better adapt the proposed method to the conditions of a specific ranging and profilometry problem. In particular, in the case when a projection device forms a large number of relatively contrasting LM structures, for example, their number is more than three, it is possible to expand the range and accuracy, as well as reduce the time for measuring distances, coordinates and shapes of objects. The advantage of using a projection device in which at least one binary grating is installed is also the ability to control the characteristics of LM structures, for example, their number and contrast, by changing the period and/or fill factor of the grating.

In a particular case (clause 3 of the claims), to implement the method of ranging and profilometry, one or more localized moire structures are used, the characteristics of which are influenced by the effect of light diffraction. The system diagram for implementing the method according to claim 3 of the formula of the invention is the same as the system diagram for implementing the method according to claim 2 of the formula, when the controlled objects are located in the zone of the GO projection device. It is shown in Fig. 1. The difference is that in the particular case of implementing the method according to claim 3 of the claims, the parameters of the projection device 1 and its elements, in particular, the types and periods of gratings 7 and 8, the distances between them are such that LM structures are formed in the zone Fresnel diffraction projection device. In the projection device, which is used to implement the method according to claim 3 of the formula of the invention, not only amplitude gratings can be used as the first and/or second grating, but also phase gratings according to claim 28 of the formula [69, 71, 72], and also amplitude-phase gratings [55, 56]. A two-grating device that forms moiré structures (grating pseudo-images) in the Fresnel diffraction zone is called a Talbot-Lau interferometer in a number of publications [55, 70, 73]. Some properties of moiré structures formed by a two-grating device (Talbot-Lau interferometer) in the Fresnel diffraction zone are considered in publications [28 - 30, 39, 64, 65, 69, 74, 75]. The width of the central regions of LM structures and their depth of field in the central region in the Fresnel diffraction zone can be estimated according to formulas (19) and (20). To achieve a relatively high contrast of moiré structures formed in the Fresnel diffraction zone, instead of condition (5), which is necessary for the applicability of the GO approximation, other conditions are required conditions that impose restrictions on projection device parameters. As an example, we will determine the conditions under which contrasting LM structures are formed in the Fresnel diffraction zone, in the particular case when the projection device according to claim 35 of the claims uses two amplitude gratings with sinusoidal transmission. We will assume that. In this case, in the neighborhood of three planes with coordinates, And moiré structures (1,2), (1,1), (2,2) and (2,1) appear, respectively. As shown in publications [27, 30, 32, 64, 65, 75], The dependences of the contrast of the LM structure on the distance between the first and second gratings and on the width of the frequency spectrum of light emitted by the illuminator are qualitatively different for moiré structures (N,M) with odd and even index valuesM. For this reason, we first determine the conditions for the formation of contrasting moiré structures (1,1) and (2,1), for whichM= 1, and then separately the conditions for the formation of a contrasting moiré structure (1,2), for whichM= 2. The contrast of the moire structure (2.2) is small, so we will not take it into account.

The contrast of moiré structures (1,1) and (2,1) in the Fresnel diffraction region depends, in particular, on the distance between the gratings and length (see [32, 33, 65, 67, 68]). By varying the distance between the gratings, their periods, wavelength and light spectrum width, it is possible to change the maximum contrast value of the moiré structures (1,1) and (2,1) from a small value, which is less than 0.1, to the highest value, which is close to the highest value of their contrast in the geometric optics approximation, in particular, the value maybe more , Where - contrast of the moiré structure ( N ,1) in the plane in the approximation of geometric optics, the index N is equal to 1 and 2 for moiré structures (1,1) and (2,1), respectively. Let us assume that the projection device 1 uses an illuminator that is located near the first grating ( ) and which emits monochromatic incoherent light with a wavelength , and the condition is also satisfied . In this case, the contrast of the moiré structure ( N ,1) in the plane will have a value that is not much less than the value of its contrast in the GO zone, if the value modulus is close to unity (see [65]). This requirement is met provided

Where = 0, 1, 2, 3, … . Special case = 0 is the case when the value small (for example, ); it corresponds to the geometric optics approximation for describing the characteristics of LM structures. At 1, i.e. in the Fresnel zone of the projection device, the contrast of moiré structures (1,1) and (2,1) in the planes will exceed accordingly And , if the distance between the gratings changes within the intervals before (see [65]). The contrast of the moire structures (1,1) and (2,1), formed by the projection device 1 in the Fresnel diffraction zone, when the gratings 7 and 8 are illuminated with non-monochromatic light, will be less than their contrast in the case when the gratings are illuminated with monochromatic light. The decrease in the contrast of moiré structures will not be very significant if the light emitted by the illuminator has a spectral half-width along the wavelength limited by the condition , for example, in the case less decrease in contrast compared to will be no more than twice [64, 67], here = 1, 2, 3, … . From this estimate it follows that when the distance between the gratings is 7 and 8 less moiré structures (1,1) and (2,1) with contrast can be formed when gratings are illuminated with non-monochromatic light with a spectral width of several tenths .

Thus, if an LM structure (1,1) is used for ranging and profilometry in the Fresnel diffraction zone of a projection device, then according to clause 38 of the claims, it is preferable that the distance between the amplitude gratings installed in the projection device with sinusoidal transmission be within the ranges from before , and the illuminator installed in the projection device emitted light with a half-spectrum wavelength less than . When using the LM structure (2,1) according to clause 39 of the claims, it is preferable that the distance between the first and second amplitude gratings with sinusoidal transmission be within the ranges from before , and the illuminator emitted light with a half-width spectrum along the wavelength less than .

The highest contrast value of the moire structure (1,2), in contrast to the moire structures (1,1) and (2,1), weakly depends on the distance between gratings 7 and 8 and their periods, as well as the wavelength and width of the light spectrum, emitted by the illuminator [65]. In a particular case, when the half-width of the angular spectrum of light emitted by the illuminator is less than 30 ^° and the light source is located close to the first grating , (For example, ) the magnitude of the contrast of the moiré structure (1,2) in the plane will be from 0.21 to 0.25 for arbitrary values of the width of the frequency spectrum of the light emitted by the illuminator, as well as the distance between the gratings and their periods [65].

In the second numerical example, we will determine the characteristics of moiré structures formed in the Fresnel diffraction zone by projection device 1 with two amplitude gratings with sinusoidal transmission. We assume that the period of the first lattice 7 is equal to 0.5 mm, the period of the second grating 8 is = 0.25 mm, . Both grilles are thin. The central wavelength of light emitted by the illuminator 6 is equal to = 0.5 µm, half-width of the light spectrum equal to 0.1 µm. The half-width of the angular spectrum of light emitted by the surface elements of the illuminator 6 is equal to = 20 ^o . Illuminator 6 is located close to the first grille = 0. Light source 6 and gratings 7 and 8 have a working aperture width equal to = 1 m. The distance between the gratings is . Length equal to 25 cm. With the above parameters of the projection device 1 LM, structures will be formed in the Fresnel diffraction zone, since . For the moiré structure (1,1) the parameter is equal to 1. The spatial period of the moiré structure (1,1) is equal to = 0.5 mm. This moiré structure will have the greatest contrast in a plane distant from the second grating at a distance = 22.5 cm. Size exceeds 0.6. Angular size of half of the illuminator aperture equals 48 ^o . It is greater than the half-width of the angular spectrum of light emitted by the elements of the working surface of the illuminator 6, > . The depth of field of the moiré structure (1,1) is approximately equal to =0.8 mm. The relative depth of field of the LM structure (1,1) is equal to 0.34 10 ^-2 . The width of the central region of the LM structure (1,1) is approximately 67 cm. The spatial period of the moire structure (1,2) is equal to = 0.17 mm. This moiré pattern has the greatest contrast at a distance = 7.5 cm from the projection device. The highest contrast value of the moire structure (1.2) is approximately equal to . The depth of field of the moire structure (1,2) is equal to = 0.3 mm, its relative depth of field is . The width of the central region of the LM structure (1,2) is equal to = 78 cm. If, without changing the other parameters of the projection device 1, the distance from the first grating 7 to the second grating 8 is made equal to 45 cm, then the moiré structure (1,2) will have maximum contrast in a plane located at a distance = 15 cm from the projection device. Angular size of half the working aperture of the illuminator in this case it is equal to 40 ^o . It is greater than the half-width of the angular spectrum of light emitted by the surface elements of the illuminator, . At = 45 cm the width of the central region of the LM structure (1,2) is equal to = 62 cm, its relative depth of field is .

Projection device with parameters, in which the LM structure according to claim 3 of the formula of the invention is formed in its Fresnel diffraction zone, it is preferable to use it for ranging and profilometry in cases where there is a need to minimize the period and relative depth of field of the LM structure, provided that the plane of greatest contrast of the LM structure is located at a given distance from the projection device. The advantage of implementing the method according to claim 3 of the claims may also be that in this case it is possible to form and use for LM ranging and profilometry a structure with a given, for example, optimal for measurements, spatial period, which is remote from the projection device at a relatively large distance, which is at least greater than the distance from the projection device to the border of his civil defense zone. Specific features of the implementation of the method according to claim 3 of the claims are associated, in particular, with restrictions for LM structures (N,M) with an odd index valueM on the width of the frequency spectrum of light, as well as on the range of changes in the distances between the gratings and/or their periods.

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Claims (39)

1. A method for non-contact ranging and profilometry, which includes projecting onto the surface of an object a light periodic moiré structure formed using a projection device containing a spatially extended light source, which is also called an illuminator, as well as the first, closest to the light source, and the second, output, flat gratings with a spatially periodic dependence of the transmittance, registration using an image recording device of the image of the surface of the object on which this periodic moiré pattern is projected structure, calculation by a computing device of the dependence of the brightness of an object surface image on the coordinates in the image, characterized in that at least one moire structure is formed and projected onto the object, localized in a direction that is perpendicular to the plane of the output grating and which is called longitudinal, where the localization of the moire structure means that the smallest depth of field of this moiré structure is at least four times less than the distance from the plane of the output grating of the projection device to the plane parallel to it, on which the contrast of this moiré structure is greatest, the isoline of the greatest contrast of the projection onto the object is found by mathematical processing of the image of the object surface localized moire (LM) structure, move the projection of the LM structure along the surface of the object, combine the isoline of the greatest contrast of the projection of the LM structure with one or more points on the surface object, determine the longitudinal coordinates of these points, using for this the known value of the distance from the plane of the output grating of the projection device to the plane of greatest contrast of the LM structure, find the values of the transverse coordinates of the points of the object’s surface and its shape, using for this purpose the found values of their longitudinal coordinates and image of an object. 2. The method according to claim 1, characterized in that at least one localized moiré structure is formed in the region of the geometric optics of the projection device. 3. The method according to claim 1, characterized in that at least one localized moiré structure is formed in the Fresnel diffraction region of the projection device. 4. Method according to claim 1, characterized in that on the surface object project a localized moiré structure, denoted by the indices (N,M), WhereNAndM - natural numbers, which are formed using a projection device that includes a spatially extended light source, as well as the first, closest to the light source, and the second, output, flat one-dimensional lattices, which are located in parallel planes on one side of the light source, and these gratings have the same direction of stripes along which the transverse axis is directedy, and the periodic dependence of the amplitude transmittance on the transverse coordinatex, perpendicular to the direction of their stripes, determine the dependence of the quasiperiodic contrast in the direction of the axisx changes in the brightness of the image of the object’s surface from the coordinates on the image, and take into account that the spatial period of change in the brightness of the object’s surface in the direction of the axisx equals period $$P_{NM}$$ moire structure (N,M), which is calculated using the formula $$P_{NM}=\frac{p_1/N}{R_{NM}-1}$$ , Where $$R_{NM}=M{p}_1/N{p}_2>1$$ , $$p_1$$ And $$p_2$$ - period of the first and the second grating, respectively, calculate the distance from the plane of the output grating to the plane where the contrast of the moiré structure (N,M) is maximum, according to the formula $$L_{NM}=\frac{L_1}{R_{NM}-1}$$ , Where $$L_1$$ -the distance between the planes of the first and second grating, based on these data, the longitudinal coordinates of the points located on the isoline of the greatest contrast of the projection of the moiré structure are determined (N,M). 5. The method according to claim 4, characterized in that for its implementation at least one of the LM structures is used: (1,3), (1,2), (1,1), (2,1) and (3 ,1). 6. The method according to claim 1, characterized in that for its implementation at least one LM structure is used, in which the highest contrast value exceeds 0.2. 7. The method according to claim 1, characterized in that, using one projection device, several localized moiré structures are formed, and their projections are simultaneously or sequentially moved along the surface of one or more objects. 8. The method according to claim 1, characterized in that the movement of the projection of one or more LM structures along the surface of the object is carried out by translational movement of the projection device or object . 9. The method according to claim 1, characterized in that the projection of one or more LM structures is moved along the surface of the object by rotating the projection device and/or the object. 10. The method according to claim 1, characterized in that the projection of one or more localized moiré structures is moved along the surface of the object by changing the distance from the plane of the output grating of the projection device to the plane of the greatest contrast of the LM structure. 11. The method according to claim 4 or 10, characterized in that the change in the distance from the plane of the output grating of the projection device to the plane of the greatest contrast of the LM structure is carried out by changing the distance between the first and second grids installed in the projection device. 12. The method according to claim 4 or 10, characterized in that the change in the distance from the plane of the output grating of the projection device to the plane of the greatest contrast of the LM structure is carried out by changing the spatial period of at least one of the gratings installed in the projection device. 13. The method according to claim 1, characterized in that the isoline of the greatest contrast of the projection of at least one LM structure is moved across the entire controlled part of the surface of the object, and at each position of the isoline of the greatest contrast, the coordinates of a plurality of surface points located on this isoline are determined. 14. The method according to claim 4, characterized in that a localized moire structure is formed (N,M), using for this purpose a projection device that includes first and second thin amplitude gratings, as well as an illuminator with a flat, uniform luminous surface that is parallel to the planes of the gratings and has the shape of a rectangle with sides parallel to the axesx Andy, and the half-width in the plane $$y=y_S$$ angular spectrum emitted by the light illuminator $${\theta }_{xm}$$ , less $$\frac{\pi }{4}$$ , and the frames limiting the first and second grilles do not vignett the illuminator in the direction of the axisx when observed from the central region of the LM structure (N,M), evaluate the depth of field of this LM structure at $$\left|x\right|<0.5D_{NM}^{-}$$ according to the formula $$\Delta L_{NM}\approx 0.6P_{NM}ctg{\theta }_{Ex}$$ , Where $$D_{NM}^{-}$$ - width of the central region of the moire structure (N,M), which is calculated by the formula $$D_{NM}^{-}\approx \left|H_x-2\left(L_0+L_1+L_{NM}\right)tg{\theta }_{xm}\right|$$ , $${\theta }_{Ex}$$ - the smallest of the values $${\theta }_{sx}$$ And $${\theta }_{xm}$$ , $${\theta }_{sx}$$ - angular dimension in plane $$y=y_S$$ half the aperture of the working surface of the illuminator, equal $${\theta }_{sx}=arctg\left(\frac{H_x}{2\left(L_0+L_1+L_{NM}\right)}\right)$$ , $$H_x$$ - aperture width working illuminator surfaces, $$L_0$$ - the distance between the plane of the working surface of the light source and the plane of the first grating, $$y_S$$ - coordinate of the center of the working surface of the illuminator along the axis $$y$$ . 15. The method according to claim 1, characterized in that for its implementation a localized moiré structure is formed, in which the smallest relative depth of field is less than three percent. 16. A ranging and profilometry system, including at least one image recording device, a computing device and a projection device containing a spatially extended source of incoherent light, first and second flat periodic gratings, which are located in parallel planes on one side of the light source and which are illuminated by the said light source, and the second grating receives the light that passed through the first grating, characterized in that the system uses at least one device for moving the isoline of the greatest contrast of the projection of the LM structure formed by the projection device along the surface of at least one object. 17. The system according to claim 16, characterized in that it uses a projection device in which one-dimensional periodic gratings are used as the first and second gratings, and their stripes are directed parallel. 18. The system according to claim 16, characterized in that the optical projection device uses a diffuse light source as an illuminator. 19. The system according to claim 16, characterized in that it additionally uses a device for determining the coordinates and orientation of the projection device in the global coordinate system. 20. The system according to claim 16, characterized in that it uses at least one device that carries out translational movement of the projection device and/or object and determines the magnitude of this movement. 21. The system according to claim 16, characterized in that it uses at least one device that rotates the projection device or object and determines the magnitude of this rotation. 22. The system according to claim 16, characterized in that it uses a device that controls the distance between the planes of the first and second gratings installed in the projection device. 23. The system according to claim 17, characterized in that a device is additionally used that moves at least one of the gratings installed in the projection device in a controlled manner along the transverse coordinate x perpendicular to the direction of the grating strips. 24. The system according to claim 16, characterized in that the optical axis of at least one image recording device is parallel to the longitudinal axis of the projection device. 25. The system according to claim 16, characterized in that it uses a projection device in which at least one amplitude grating is installed. 26. The system according to claim 17, characterized in that it uses a projection device in which at least one amplitude grating is installed with a sinusoidal dependence of the magnitude of the change in the amplitude transmittance on the transverse coordinate. 27. The system according to claim 17, characterized in that it uses a projection device in which an amplitude binary raster is used as at least one grating. 28. The system according to claim 16, characterized in that it uses a projection device in which at least one grating is a phase grating. 29. The system according to claim 16, characterized in that it uses a projection device in which the characteristics of at least one grating can be changed. 30. The system according to claim 16, characterized in that it uses a projection device in which a spatial light modulator is used to form at least one grating. 31. The system according to claim 17, characterized in that it uses a projection device in which the first and second gratings are amplitude gratings. 32. The system according to claim 16, characterized in that it uses a projection device in which thin first and second gratings are installed, when passing through which the angular spectrum of light emitted by the illuminator is narrowed by less than 20%. 33. The system according to claim 17, characterized in that the projection device uses an illuminator with a uniform flat luminous surface, which is parallel to the planes of the gratings and has the shape of a rectangle with sides parallel to the x and y axes. 34. The system according to claim 31, characterized in that for the formation of the LM structure (N,M) it uses a projection device in which the first and second gratings are located at a distance from each other $$L_1$$ less $$0.2\frac{L_T\left({\lambda }_m\right)}{NM}$$ , Where $$L_T\left(\lambda \right)=\frac{p_1{p}_2}{\lambda }$$ , $${\lambda }_m={\lambda }_0+\Delta \lambda$$ , $${\lambda }_0$$ - central wavelength of light emitted by the illuminator, $$\Delta \lambda$$ - half-width of its spectrum along the wavelength. 35. The system according to claim 31, characterized in that it uses a projection device in which the first and second gratings have a sinusoidal dependence of the magnitude of the change in the amplitude transmittance on the x coordinate. 36. The system according to claim 33, characterized in that the projection device uses an illuminator, first and second thin amplitude gratings with angular dimensions in the plane $$y=y_S$$ greater than the width in this plane of the angular spectrum of the light emitted by the illuminator, where said angular dimensions of the illuminator and gratings are determined from the center of the plane in which the contrast of the LM structure used for measurements is maximum. 37. The system according to claim 33, characterized in that it uses a projection device in which first and second thin amplitude gratings with an angular size in the plane are installed $$y=\text{const}$$ is larger than the angular size of the working aperture of the illuminator, and an illuminator is installed whose tangent of the angular size in the plane $$y=\text{const}$$ half of its working aperture and the tangent of the half-width in this plane of the angular spectrum of the light emitted by it are more than five times greater than the ratio $$\frac{P_{NM}}{L_{NM}}$$ . 38. The system according to claim 35, characterized in that it uses a projection device that uses a light source with a half-spectrum wavelength $$\Delta \lambda$$ less than $$0.4{\lambda }_0{\nu }_1^{-1}$$ , the first grating with a spatial period greater than the spatial period of the second grating $$p_1>p_2$$ , and the first and second gratings are located at a distance from each other within the ranges $$\left({\nu }_1-0.2\right)L_T\left({\lambda }_0\right)$$ before $$\left({\nu }_1+0.2\right)L_T\left({\lambda }_0\right)$$ , Where $${\nu }_1$$ = 1, 2, 3, … . 39. The system according to claim 35, characterized in that it uses a projection device that uses a light source with a half-spectrum wavelength $$\Delta \lambda$$ less than $$0.4{\lambda }_0{\nu }_1^{-1}$$ , the first grating with a spatial period greater than twice the spatial period of the second grating $$p_1>2p_2$$ , and the first and second gratings are located at a distance from each other within ranges from $$\left({\nu }_1-0.2\right)\frac{L_T\left({\lambda }_0\right)}{2}$$ before $$\left({\nu }_1+0.2\right)\frac{L_T\left({\lambda }_0\right)}{2}$$ .