JP2010117253A - Device for capturing image invariant optical speckle and method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for capturing an image invariant optical speckle capable of avoiding shape variation and intensity fluctuation of a speckle and a method for the same. <P>SOLUTION: A highly coherent light is used to illuminate a surface and is scattered by the surface, and is captured from the direction with a ±10° from the angle of specular reflection. When the speckle capturing device relatively moves with respect to the surface, a light restrictive module is designed to confine the view angle of the sensor, and the speckle only moves on the image so that the shape and the intensity thereof are almost kept constant. With this structure, it is possible to perform high accuracy optical pattern recognition and positioning. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image invariant light spot in which coherent diffracted light is generated, and more particularly to an apparatus and method for capturing a light spot generated when scattered light passes through a small aperture light limiting element.

  When two highly coherent light beams overlap in space and the optical path length difference is smaller than the coherent length, interference fringes are generated. Optical interference is classified as amplifying interference and destructive interference, where amplifying interference produces a bright spot, while destructive interference produces a dark spot. Therefore, the result of the interference is a spatial pattern with scattered bright spots and dark spots, called a speckle pattern or speckle image. Interference is related to wavelength and optical path length difference. If two light beams overlap in space and the optical path length difference between the two beams is an odd integer multiple of a half wavelength, destructive interference occurs. If the optical path length difference between these two beams is an integral multiple of that wavelength, amplifying interference occurs. The sensitivity of this interference is therefore half that wavelength. The wavelength of light is considerably short. For example, the wavelength range of visible light is 0.4 μm to 0.7 μm. Because half-wavelength sensitivity is very accurate, interference effects are widely used in many different fields.

  When highly coherent light is incident on an optical rough surface, scattered light is generated and propagates in an arbitrary direction in space. When these scattered lights overlap in space with an optical path difference shorter than the coherence length of the light, stable interference occurs. The result of this interference is an image having scattered bright areas and dark areas, called light spots.

  The light spot was recognized as noise and was considered a destructive factor for the optical system. Spots of light were found to be associated with movement, but were used as a type of detection technique. Recently, unique light spots have been used as detection technology for movement detection. U.S. Pat. No. 6,642,506 B1 published in 2003 (hereinafter referred to as Patent 506) discloses the detection of one-dimensional displacement and captures an optical speckle pattern by a device comprising coherent light, an optical aperture and an imaging lens. In Japanese Patent No. 506, a spot having a preferable size can be captured using an aperture having an appropriate size so as to match the pixel size of the image sensor. In Patent 506, the aperture further needs to be placed at the focal point of the imaging lens, and the optical axis of the imaging lens and the aperture are perpendicular to the surface so that vertical fluctuations in height on the surface hardly affect the spots. It was stressed to do. In another US Patent No. 20050024623 (hereinafter referred to as Patent 623), a method and apparatus for detecting optical displacement was disclosed. A highly coherent light source is used to radiate a coherent light beam to irradiate the surface, the light is reflected by the surface, and specularly reflected light is received by a sensor arranged in the reflection direction. When the angle with the surface of the reflected light is equal to the angle with the surface of the incident light, it is called regular reflection. The sensor receives specularly reflected light and scattered light simultaneously, and the received light interferes with each other to generate a large number of spots on the sensor. The displacement direction and the displacement amount can be determined by comparing the speckle pattern after movement with the speckle pattern before movement.

  Another related technique was published in US Patent Application No. WO2004075040 (hereinafter referred to as Case 040), which disclosed an optical signal processing method and apparatus using an optical mouse with digital signal processing. By collecting the speckle movement signal, the relative displacement of the mouse with respect to the surface where the scattered light is generated can be obtained. The mouse includes an electric signal amplification modeling module, a direction determination counting module, a computer interface, a laser light source, and a laser speckle image receiving sensor. The speckle image received by the sensor is converted into an electrical signal and sent to the signal amplification modeling module.

  All of the above signal analysis is related to the counting analysis of the number of bright spots and dark spots of the speckle image captured by the sensor, and then converted into the moving direction and the displacement amount. The structure of the case 040 is simple. However, when the surface is smooth, the size of the generated spots is very small, which is inconvenient for analysis of bright and dark areas of the spots. Therefore, the resolution and sensitivity of this system is low.

In Japanese Patent No. 623, regular reflection is received by a sensor, and then the received light signal is divided into a direct current portion and an alternating current portion. The direct current portion is the smooth brightness of the reflected light, and the alternating current portion is the bright and dark areas of the spots. If the size of the spot is too small, it is difficult to recognize the AC signal, making analysis difficult.
In Japanese Patent No. 506, the stop needs to be placed at the focal point of an imaging lens that is a telecentric projection system. Although this system is not sensitive to vertical height displacement, the aperture of this structure is not capable of limiting the image capture area on its surface. This means that this structure cannot confine the sensor viewing angle to the scattered light on the surface. Although the structure of the patent 506 can be used to control the size of the spots, the ability to avoid spot fluctuations during relative motion between the surface and the imaging system is limited.

  Therefore, the key factors for correctly and correctly recognizing the two-dimensional speckle pattern are the appropriateness of the size of the speckles and the sharpness of the speckle pattern, and in particular, speckle pattern image invariant spots. The image invariant light speckle pattern is unique and favors correct navigation and accurate positioning and can be widely used in devices such as laser mice, finger navigation, intelligence cards, and 3D fingerprint identification.

  In order to solve the above problems, an object of the present invention is to provide an image invariant light spot capturing apparatus and method. Using the technology developed in the present invention, problems such as smaller size spots, spot shape changes and spot intensity variations can be reasonably solved.

  A speckle pattern in a non-specular reflection direction can be captured using a two-dimensional image invariant light spot capturing device. For example, light having an angle of ± 10 ° from regular reflection is captured. A light limiting aperture is introduced into the optical path to limit the viewing angle of the scattered light, i.e. to confine the image capture area on this surface. By combining factors such as the size of the spots, the focal length of the image capture lens, the image capture angle, and the image capture area on the surface, the light spots captured by the spot capture device become image invariant. An image-invariant light spot means that when this spot capturing device moves relative to the surface, the captured light spot moves only on the image plane without deformation, i.e., the spot capturing device is continuously on the surface. Although moving, the light spot moves continuously from one side of the image sensor until it disappears to the other side of the sensor, meaning that the shape and intensity of this light spot remain the same. Since the spots captured by the spot capturing device are image invariant, the image invariant light spot capturing device of the present invention is very useful for accurate optical pattern recognition and positioning.

  The advantages and spirit of the invention may be understood from the following detailed description in conjunction with the accompanying drawings.

  The following paragraphs describe how to obtain image invariant light spots when there is relative motion between the light spot capturing device of the present invention and the surface. The calculation of the optical path difference before and after this relative motion will be described in detail.

  The laser speckle of the present invention is formed by interference of light scattered by the irradiated surface and diffracted by the elements of the spot capturing device. The speckle pattern produced by an image sensor is basically related to factors such as the nature of the light source, the characteristics of the illuminated surface, the location of the spot capturing device, and the pixel size of the two-dimensional image sensor. It is difficult to analyze all the factors in detail, and in the present invention, an appropriate model is developed to analyze speckle pattern formation. The laser is a highly coherent source and meets the decisive condition of producing spots due to interference. Surface properties are the most difficult to handle and it is impossible to analyze all surface properties. One key point that needs to be emphasized in the present invention is an appropriate size and high brightness spot for image analysis, and a small size and low brightness spot is always abandoned because of noise. Therefore, the analysis of the present invention focuses on spots with high brightness and large size. The brightness of the spots depends on the interference conditions, and the high brightness spots are caused by amplifying interference. However, the average size of the spots is related to the characteristics of the spot capture device. The average size of the spots can be written as 2δ = 2Lλ / D, where 2δ is the average diameter of the spots, λ is the wavelength of the laser beam, D is the diameter of the aperture of the spot capturing device, and L is the distance from the aperture to the image sensor. It is. When the light from a scattering point and its adjacent scattering points combine to generate amplifying interference on the image sensor, bright, large-sized spots are produced. On the other hand, if the light from the scattering point and the adjacent scattering point causes destructive interference on the image sensor, a blurred spot or a spot does not occur. Cross-correlation is used to match the speckle pattern produced before and after the relative movement between the surface and the speckle capture device. Assuming that a first light speckle pattern is recorded and there is a special spot with high brightness, what will happen to this spot after the spot capture device has moved a distance d relative to the surface. The analysis is as follows.

(I) In order to minimize the scale of the system, the 4f lens imaging system is selected for convenient analysis, where f is the focal length of the lens used in the imaging system. The object distance is equal to the image distance of the 4f system, and the magnification M of the system is equal to 1. Referring to FIG. 1A, γ _A = γ _B , γ _{A ′} = γ _{B ′} , and γ _{A ″} = γ _{B ″} .

  (Ii) The size of the spot at position B on the image plane can be assumed to be an average size 2δ generated by diffraction. Since the magnification of this system is 1, all points in a region centered on point A on the surface with radius δ surround a point B on the image plane with a diffraction-limited Airy disk having a size of 2δ≈2Lλ / D. Occurs at the corresponding position. This Airy disk overlaps with other Airy disks generated at other scattering points and generates interference. Point B is a luminance that means that scattered light from each point in a region centered on point A with radius δ reaches point B having an optical path difference of 0 or an integer multiple of a wavelength. Assuming that the speckle capture device moves a distance d with respect to the surface and the point A on the object plane moves to point A ′ or A ″ with respect to this speckle capture device, the corresponding image points are B ′ or B ″, respectively. Become.

Let γ _A ≈ 2f and reasonably assume γ _A >> d >> δ. As shown in FIG. 1B, the maximum optical path length difference, γ _{A + δ} and γ _A−δ, generated at a point in a region centered on point A with a radius δ is evaluated (represented by γ, θ _A , δ, where in δ is the mean radius of the light spot, theta _a image capture angle between the normal direction of the light-limiting module optical axis and the surface, d is variable from zero at the moving distance to the diameter of the image capturing area, the image is unchanged Γ is the vertical distance from the imaging lens to this surface.)

Using Taylor series expansion, ignoring the second and higher order terms,

As shown in FIG. 1C, when the spot capturing device has relative motion with respect to the surface, point A moves a distance d to reach point A ′ (corresponding image point of B ′), and point A ′ with radius δ. The maximum optical path length difference from all points in the center area is calculated. The difference between γ _{A ′ + δ} and γ _A′−δ is γ _{A ′ + δ−} γ _A′−δ ≈2δ sin θ _{A ′}
As shown in FIG. 1C, the point A on the surface moves by a distance d to reach the point A ′, and the maximum optical path length difference of all points in the region centered on the point A ′ with the radius δ, γ _{A ′ + δ} − γ _A′−δ is compared with the maximum optical path length difference of all points in the region centered on the point A with the radius δ, and γ _{A + δ} −γ _A−δ . _{γ a '+ δ -γ A'-} δ) - (γ a + δ -γ a-δ), but can be calculated as follows.

Assuming that θ _{A ′} = θ _A + Δθ, where Δθ is a very small angular displacement,

So in _{Δθ ≒ dcosθ A / γ A γ} A = γ / cosθ A,

Assuming that the scattered light from the surface point A passing through the 4f lens forms an image at the point B on the photosensor, then the scattered light at the surface points A ′ and A ″ are similarly point B ′ on the photosensor. And B ″. Due to the diffraction effect, each point on the image plane within the radius δ (the radius of the Airy disk and the average radius of the spot) centered on the point B is energy coupled with the point B, that is, each point contributes to the interference at the point B. It is shown. Further, under the condition where the magnification is equal to 1, the point B is a bright point, which means that scattered light at each point within the radius δ centered on the point A on the surface causes amplifying interference at the point B. An equivalent optical path length difference from each point within the radius δ centered on the point A to each point within the radius δ centered on the point B is considered to be zero. The initial phase of each scattered light is incorporated into an equivalent optical path length difference. In other words, the maximum optical path length difference from each point within the radius δ centered on the point A to each point within the radius δ centered on the point B, n (γ _{A + δ} + γ _{B + δ} ) −n (γ _A−δ + γ _B−δ ) ≈4δsinθ _A (n is assumed to be 1 because of air) is automatically compensated by the natural fine structure of the region surrounding the point A. When there is a relative motion of d between the light source and the irradiated surface and the initial surface condition is maintained, each point in the radius δ centered on the point B ′ from each point in the radius δ centered on the point A ′ The maximum optical path length difference to the point is (γA _{′ + δ} + γB _{′ + δ} ) − ( _γA′−δ + _γB′−δ ). This new maximum optical path length difference needs to be compared with the first to determine the change in maximum optical path length difference, and the change in maximum optical path length is a key factor for fluctuations in speckle intensity. . If the change in the maximum optical path length difference is half that wavelength, the first amplifying interference becomes destructive interference after its relative movement. Change of the maximum optical path length difference due to relative movement d _{is, [γ A '+ δ +} γ B' + δ) - (γ A'-δ + γ B'-δ)] - [(γ A + δ + γ B + δ) - (γ A-δ + γ _B-δ)] is ≒ 4δdcos ³ θ _a / γ. When 4δdcos ³ θ _A / γ << λ is satisfied, the change in the maximum optical path length difference due to the relative motion d is very small. Under the condition that the point B is a bright spot, the point B ′ is still a bright spot because of the amplifying interference. The spots move to the image plane, but neither shape nor intensity changes under this special condition that is important for image recognition. The change in the maximum optical path length difference of the present invention was calculated as 4δdcos ³ θ _A / γ <λ / 5, and there was no observed spot shape change or intensity variation.

  FIG. 2A is a structural drawing of one exemplary embodiment disclosing an image invariant light spot capturing device. The apparatus includes a light source 10, a light limiting module 12, and a light sensor 14. A parallel light wave 100 is emitted from the light source 10 and the converging lens 11 to irradiate the surface 2. The light source is coherent, for example a laser. The light source 10 is therefore a vertical cavity surface emitting laser VCSEL, an edge emitting laser EFL, a highly coherent solid state laser, or a narrowband highly coherent light emitting diode LED. The area of the surface 2 irradiated with the parallel light wave 100 is adjusted by adjusting the distance between the light source 10 and the converging lens 11 according to a predetermined value. The light limiting module 12 includes a plurality of light limiting elements. In this embodiment, the light limiting module 12 includes a diaphragm 121, and the imaging lens 122 having the diaphragm 121 is disposed between the imaging lens 122 and the surface 2. A photosensor 14 is placed behind the light limiting module 12 and is a one-dimensional or two-dimensional charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) array.

  The light source 10 emits a parallel light wave 100 and irradiates the surface 2 and then generates scattered light 102. The characteristics of the scattered light 102 are determined by the properties of the surface 2. When the surface is very smooth, regular reflection occurs from the surface. All of the scattered light 102 propagates in the same direction, and the parallel light wave 100 contains the same energy. Scattered light 102 is distributed in different directions, assuming that surface 2 is an optically rough (scattering) surface.

  Further, at least one of the scattered light 102 is a spot that is easily recognized after being propagated in an arbitrary direction under the condition that the surface 2 is irradiated and rough.

Further, when the light source 10 emits the parallel light wave 100 and illuminates the surface 2, scattered light 102 is generated, and at least one of the scattered light 102 is collected by the light limiting module 12, which includes a diaphragm 121. The imaging lens 122 having the imaging lens 122 is disposed behind the diaphragm 121, which means that the imaging lens 122 is disposed between the diaphragm 121 and the optical sensor 14. The light limiting module 12 limits the incident viewing angle of the optical sensor 14 for the scattered light 102, and the incident viewing angle is determined by the distance between the diaphragm 121 and the imaging lens 122, the diameter of the diaphragm 121, and the imaging lens. Due to the diameter of the stop 121, at least one of the scattered light 102 passes through the stop to generate a plurality of diffracted lights, and the plurality of diffracted lights pass through the imaging lens 122 to generate spots. The average size of the spots can be manipulated by the diameter of the diaphragm 121, and then a plurality of spots are imaged on the photosensor 14. By appropriately adjusting parameters such as the size of the spots, the focal length of the imaging lens, the image capture angle, and the image capture area of the surface, the change in the maximum optical path length difference is 4δdcos ³ θ _A / γ <λ / 5 And an image invariant light speckle pattern is produced on the image surface.

In order to obtain an image invariant light speckle pattern from the three-dimensional surface having the finest appearance, a parallel light wave 100 is incident on the surface 2 at an incident angle θ _i , and the scattered light 102 is deviated from the regular reflection of the present invention by a deviation angle ± 10 °. Condensate. The light limiting module 12 of the present invention is designed to accurately collect the scattered light 102 at an angle θ _i ± 10 °. When a substantially parallel light beam illuminates the surface, most of the scattered light is concentrated in the direction of θ _r = θ _i , and the scattered light decreases with the scattering direction deviated from θ _r = θ _i . The scattered light in the direction θ _r = θ _i includes two components, the main component is derived from surface regular reflection, and the subcomponent is derived from scattered light due to the natural fine structure of the surface. Although specularly reflected light waves have the same phase, scattered light has a random phase and interference occurs, but these light waves overlap. By analyzing the relationship between the interference fringes before and after the relative movement between the spot capturing device and the surface, quantitative data of the relative movement can be obtained. If this surface is sufficiently optically rough, specular reflection is reduced, random scattering is increased, and the phase changes rapidly, which is inconvenient for cross-correlation pattern recognition. When the angle θ _r = θ _i ± 10 ° is selected as the scattered light wave condensing direction of the present invention, specular reflection can be avoided and more scattered light waves can be collected, and the optical speckle pattern generated in the three-dimensional appearance of the surface can be obtained. Effectively recorded and accurate recognition and positioning is obtained.

FIG. 2B is a drawing of an optical path showing the relationship between the position of the stop and the incident viewing angle of the sensor with respect to scattered light. Referring to this figure, the light limiting module 12 includes a stop 121 and an imaging lens 122 just as in FIG. 1A, and the stop 121 can be placed at point G or H. Compared with the light limiting module 12 having the diaphragm 121 at the point G, the light limiting module 12 having the diaphragm 121 at the point H blocks scattered light far from the optical axis. The optical path in this figure shows that the stop 121 is positioned behind the focal point of the imaging lens but in front of the sensor 14, and the image capture region is defined on this surface by controlling the incident viewing angle using the exact position of the stop 121. Restrict to above. In this embodiment, when light waves are incident on points E and F on the surface 2 and at least scattered light 102 is generated, the scattered light 102 passes through the imaging lens 122 and the scattered light 102 at points E and F is Under the condition that the diaphragm 121 is arranged at the point G, it passes through the imaging lens 122 and forms an image at the points E ′ and F ′ on the sensor 14, indicating that the luminous flux of F ′ is higher than the luminous flux of E ′. . For the stop 121 arranged at H, scattered light at a point F close to the optical axis passes through the imaging lens 122 and forms an image at F ′ on the sensor 14, and scattered light at a point E far from the optical axis is detected by the sensor. No image can be formed with E ′ on the image 14. In the present embodiment, the function of the stop 121 is an aperture stop, but the function of the imaging lens 122 is a field stop. In the present embodiment, as an example, a light limiting component by adjusting the aperture diameter and position of the light limiting module 12 of the present embodiment is proposed, and the operation of the spot size and the viewing angle of the sensor 14 with respect to the scattered light 102 are proposed. Limits can be made at the same time. The size of the spots, the focal length of the imaging lens, the factors such as the parameters of the image capture angle and surface appropriately Kumiawashi, change of the maximum optical path length difference of condition that _{^{4δdcos 3 θ A / γ <λ}} / 5 Filling generates an image invariant optical speckle image in the image plane.

  FIG. 2C is a drawing of the structure of another preferred embodiment according to the present invention. 2A, the light limiting module 12 also includes an imaging lens 122 and a diaphragm 121. The imaging lens 122 is disposed in front of the diaphragm 121, and the diaphragm 121 is different from the imaging lens 122. It means that it is arranged between the sensors 14. In order to effectively obtain the purpose of limiting the viewing angle of the sensor so as to receive scattered light, the normal stop 121 is usually disposed behind the focal point of the imaging lens 122 and in front of the sensor 14.

  FIG. 2D is a drawing of the structure of another exemplary embodiment according to the present invention. The difference of this embodiment compared to FIG. 2A is that the light limiting module 12 is a microlens 123 surrounded by a light shielding plate 124. The function of the opaque plate 124 is the same as that of the diaphragm 121 in FIG. 2A, and is to diffract at least the scattered light 102 to generate a diffracted light wave. By using the micro lens 123 and the light shielding plate 124 in combination with the irradiation region on the surface 2, the viewing angle of the sensor 14 can be confined to the scattered light 102, and an image invariant light speckle image can be generated on the sensor 14.

  FIG. 3 is a drawing of the structure of another preferred embodiment according to the present invention. The difference of this embodiment compared to FIG. 2A is that the light limiting module 12 includes an imaging lens 122, a first aperture 125 and a second aperture 126. The imaging lens 122 is disposed behind the first diaphragm 125 and the second diaphragm 126, which means that the imaging lens 122 is disposed between the second diaphragm 126 and the sensor 14. In this arrangement, the first diaphragm 125 is first arranged, then the second diaphragm 126 is arranged, then the imaging lens 122 is arranged, and finally the sensor 14 is arranged. When the light source 10 emits the light wave 100 and irradiates the surface 2 to generate at least scattered light 102, the first diaphragm 125 blocks a part of the scattered light 102 and restricts the scattered light 102 from entering the sensor 14. To do. When a part of the scattered light 102 passes through the first diaphragm 125, the second diaphragm 126 further blocks a part of the scattered light 102 from entering the sensor 14. The viewing angle of the sensor 14 with respect to the scattered light 102 is determined by the diameters of the first diaphragm 125 and the second diaphragm 126 and the distance between them, that is, the image capturing area is limited on the surface thereof. The scattered light 102 within the viewing angle is further diffracted, passes through the imaging lens 122, forms an image on the sensor 14, and generates an image invariant light speckle pattern. In other arrangements, the light limiting module 12 also includes an imaging lens 122, a first aperture 125, and a second aperture 126, which can also be positioned in front of the first aperture 125 and the second aperture 126, and the first It means that the diaphragm 125 and the second diaphragm 126 are disposed between the imaging lens 122 and the sensor 14. In other arrangements, the imaging lens 122 can also be located between the first diaphragm 125 and the second diaphragm 126.

FIG. 4A is a diagram illustrating generation of secondary scattered light by a general-purpose package of an image sensor. Unlike FIG. 2C, the light limiting module 12 includes an imaging lens 122 and a diaphragm 121, and is configured to surround the sensor 14 with a sleeve 141. From this figure, position I on surface 2 is outside the viewing angle of sensor 14. At least scattered light 102 is generated at point I, and the scattered light is incident on I ′ on the inner surface of the sleeve 141 to generate secondary scattered light 104. The secondary scattered light 104 passes through a diaphragm 121 located at H and is sensor. 14 is reached. Under conditions where the secondary scattered light 104 is not excluded, it is difficult to generate an image-invariant light speckle pattern. If the secondary scattered light 104 overlaps the scattered light 102 on the image plane, The phase change of the next scattered light is random and difficult to handle, and the generated spots often flicker. In this state, no image invariant light spots can be obtained.
FIG. 4B shows another preferred embodiment according to the present invention. Compared to FIG. 4A, in order to prevent the scattered light 102 incident on the inner surface of the sleeve 141 and further scattered secondary scattered light 104 from entering the sensor 14, the prestage light limiting element 16 is placed in front of the light limiting module 12. To place. The prestage light limiting element 16 of the present embodiment is a light limiting diaphragm 161, and the prestage light limiting diaphragm 161 is disposed between the surface 2 and the light limiting module 12, and the light limiting module 12 includes the imaging lens 122 and the diaphragm 121. Therefore, the prestage light limiting diaphragm 161 is located between the surface 2 and the imaging lens 122, and the diaphragm 121 is arranged between the imaging lens 122 and the sensor 14. When parallel light waves are incident on positions F and I on the surface 2, the scattered light 102 at position F passes through the prestage light limiting diaphragm 161, imaging lens 122, and diaphragm 121, and then forms an image directly on the sensor 14. To do. Scattered light 102 at position I outside the imaging region is blocked by the prestage light limiting diaphragm 161. A part of the non-blocking light 103 enters the inner surface of the sleeve 141 and generates secondary scattered light, but does not reach the sensor 14. The background noise is effectively reduced, and the signal to noise ratio of the sensor 14 is enhanced, resulting in an image invariant light spot.

  FIG. 4C is a drawing of the structure of another preferred embodiment according to the present invention. Compared to FIG. 2C, the difference in this embodiment is that each light limiting module 12 includes an imaging lens 122 and a diaphragm 121, and a prestage diaphragm 161 is introduced between the imaging lens 122 and the surface 2. The pre-stage diaphragm 161 is used to prevent the secondary scattered light generated on the surface 2 by the scattered light 102 from entering the sensor 14. As a result, the background noise of the sensor 14 is reduced, and an image invariant light spot is obtained.

All of the structures described in FIGS. 2A-4C are representative embodiments of the present invention, and the image-invariant light spot capturing device includes a light source, a light limiting module 12, and a sensor. The light limiting module 12 confines the viewing angle of the sensor 14 to the scattered light 102, i.e. limits the image capture area on its surface. By appropriately combining parameters such as speckle size, focal length of imaging lens, image capture angle, and imaging area on the surface, the change in maximum optical path length difference is 4δdcos ³ θ _A / γ <λ / An image invariant optical speckle image is obtained on the image plane. The image invariant optical speckle image can also be applied to devices such as a laser mouse, finger navigator, intelligent card, three-dimensional status identification, machine tool or high precision positioning device for mechanical arm. The speckle image captured by the laser speckle optical capture device made based on the structure of FIG. 4C of the present invention is shown in FIG. 5, the surface of which is a hard mouse test plate, and the moving distance between each frame is 60 μm. Yes, continuous moving frames are shown from left to right in the figure. In order to observe this frame continuously, the speckle image appears from one side of the image sensor and moves continuously until it comes out of the image sensor, and the spots just move, there is no shape change and no intensity fluctuation, As a result, an image invariant optical speckle image is shown.

  Therefore, the image invariant light spot capturing device of the present invention can be applied to a laser mouse. FIG. 6A is a drawing of a laser mouse according to the present invention, where both the light source 10 and the sensor 14 are placed in a container 310 of the laser mouse 300. The light source 10 emits a light wave, passes through a converging lens 11, generates a parallel light wave, and enters the surface 2 to generate a scattered light wave 102. At least the scattered light 102 is appropriately adjusted including an imaging lens 122 and a diaphragm 121. The light limiting module 12 is passed. The scattered light 102 is diffracted through the imaging lens 122 and the stop 121, producing speckles of an appropriate size on the image sensor 14, and the stop also limits the viewing angle of the sensor 14 to the scattered light 102. The sensor 14 records a first speckle image before the container 310 moves, and after the container 310 moves relative to the surface 2, the sensor 14 records a second speckle image. By comparing the first speckle image and the second speckle image, the moving direction and moving distance of the container 310 relative to the surface 2 can be calculated, which becomes a basic signal of the laser mouse.

  With reference to FIG. 6B, the light source 10 and the sensor 14 are disposed in the container 310 of the laser mouse 300. The light source 10 emits a light wave, passes through a converging lens 11 to generate a parallel light wave, enters the surface 2 to generate a scattered light wave 102, and the scattered light 102 passes through the prestage light limiting aperture 161 and is then secondarily scattered. Although light is generated, the secondary scattered light is blocked and cannot reach the sensor 14. At least the scattered light 102 passes through a prestage light limiting diaphragm 161 and further passes through a suitably adjusted light limiting module 12 including an imaging lens 122 and a diaphragm 121. The scattered light 102 is diffracted through the imaging lens 122 and the aperture 121 to produce an appropriately sized spot on the image sensor 14, which also limits the surface image capture area that the sensor 14 receives. The sensor 14 records a first speckle image before the container 310 moves, and after the container 310 moves relative to the surface 2, the sensor 14 records a second speckle image. By comparing the first speckle image and the second speckle image, the moving direction and moving distance of the container 310 relative to the surface 2 can be calculated, which becomes a basic signal of the laser mouse.

  The image invariant spot capturing apparatus and method described above will be introduced. Referring to FIG. 7A, a highly coherent light beam is first emitted (step 500). The highly coherent light beam is incident on the surface and generates scattered light (step 511). An aperture is positioned behind the imaging lens focus and in front of the sensor, and the aperture and imaging lens are included as a light limiting module (step 522). When the scattered light passes through the light limiting module, the viewing angle of the sensor with respect to the scattered light is limited by the light limiting module, and the scattered light is further diffracted by the light limiting module (step 531). The diffracted lights interfere with each other to generate spots (step 540). This spot is recorded as an image (step 550). The movement of the speckle image is recognized by pattern recognition of the image, and the relative motion between the spot capturing device and the surface can be determined (step 560).

  With reference to FIG. 7B, a highly coherent light beam is first emitted (step 500). The highly coherent light beam is incident on the surface and generates scattered light (step 511). The scattered light passes through the first diaphragm (step 521). The scattered light further passes through the second aperture and the imaging lens, where the first aperture and the second aperture include a light limiting module that limits the viewing angle of the sensor with respect to the scattered light with the light limiting module. Diffracted by the light limiting module (step 530). The diffracted lights interfere with each other to generate spots (step 540). This spot is recorded as an image (step 550). The movement of the speckle image is recognized by pattern recognition of the image, and the relative motion between the spot capturing device and the surface can be determined (step 560).

  Referring to FIG. 7C, a highly coherent light beam is first emitted (step 500). The highly coherent light beam is incident on the surface and generates scattered light (step 511). A pre-stage light limiting element is placed between the surface and the imaging lens (step 512). The scattered light passes through the prestage light limiting element and is incident on the sleeve to generate secondary scattered light, but this secondary scattered light is blocked and is not received by the sensor (step 513). An aperture is disposed between the imaging lens and the sensor, and the aperture and imaging lens include a light limiting module (step 522). When the scattered light passes through the light limiting module, the viewing angle of the sensor with respect to the scattered light is limited by the light limiting module, and the scattered light is further diffracted by the light limiting module (step 531). The diffracted lights interfere with each other to generate spots (step 540). This spot is recorded as an image (step 550). The movement of the speckle image is recognized by pattern recognition of the image, and the relative motion between the spot capturing device and the surface can be determined (step 560).

Overall, an apparatus and method for capturing image invariant spots has been disclosed in the present invention. The light limiting module is placed in front of the sensor and changes in the maximum optical path length difference by appropriately adjusting parameters such as speckle size, focal length of imaging lens, image capture angle, and surface image capture area Satisfies the condition of 4δdcos ³ θ _A / γ <λ / 5, and an image invariant optical speckle image is obtained on the image plane.

  If there is relative motion between the speckle capture device and the surface, the resulting speckle will move accordingly, but is invariant to relative motion, which is convenient for accurate positioning and recognition. Therefore, the image invariant spot capturing device and method can be applied to devices such as laser mouse, finger navigator, intelligent card, 3D fingerprint identification, machine tool or precision positioning device for mechanical arm.

  The characteristics and spirit of the present invention have been hopefully well explained using the above examples and descriptions. Those skilled in the art will readily recognize that numerous modifications and variations of this device can be made while retaining the teachings of the present invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

It is the schematic of the relative optical path difference between the speckle images used for the theoretical calculation of this invention. It is the schematic of the relative optical path difference between the speckle images used for the theoretical calculation of this invention. It is the schematic of the relative optical path difference between the speckle images used for the theoretical calculation of this invention. 1 is a preferred embodiment structure according to the present invention. FIG. 3 is a schematic diagram of an optical path of a second exemplary embodiment according to the present invention. 2 shows the structure of another preferred embodiment according to the present invention. 2 shows the structure of another preferred embodiment according to the present invention. 2 shows the structure of another preferred embodiment according to the present invention. It is the schematic of secondary scattering. FIG. 6 is a schematic diagram of another exemplary embodiment according to the present invention. Figure 6 is another preferred embodiment structure according to the present invention. 2 shows a photograph of an image invariant light spot captured by an image invariant light spot capturing device according to the present invention. It is the schematic of the laser mouse based on this invention. It is the schematic of the laser mouse based on this invention. Fig. 4 shows a procedure for producing capture of image invariant light spots according to the invention. Fig. 4 shows a procedure for producing capture of image invariant light spots according to the invention. Fig. 4 shows a procedure for producing capture of image invariant light spots according to the invention.

Claims (20)

An image invariant light spot capturing device,
A light source that emits highly coherent light to illuminate the surface and generate multiple scattered light; and
A light limiting module that confines an incident viewing angle to the scattered light and generates a plurality of spots by causing the diffracted light to interfere with each other by generating a plurality of diffracted lights from the scattered light;
A sensor that receives the spots and generates a first speckle image, and generates a second speckle image after the light limiting module and the sensor move relative to the surface, and determines the moving direction and moving distance of the sensor relative to the surface. A sensor determined by comparing the first speckle image and the second speckle image;
A capture device comprising: a prestage light limiting device disposed between the light limiting module and the surface to prevent secondary scattered light of the scattered light from entering the sensor. 2. The image invariant light spot capturing device according to claim 1, wherein the prestage light limiting device is an aperture. The light limiting module includes an imaging lens and a diaphragm, the diaphragm is disposed behind the imaging lens focal point and in front of the sensor, and the scattered light passes through the imaging lens and the diaphragm of the light limiting module. The image-invariant optical spot capturing device according to claim 1, wherein when imaging is performed on the sensor, the light limiting module limits the viewing angle of the sensor to limit the scattered light from entering the sensor. The apparatus for capturing image invariant light spots according to claim 1, further comprising a converging lens arranged in front of the light source so that parallel light is generated from highly coherent light and irradiates the surface. The optical axis of the optical limiting module is arranged in the direction of θ _r ≧ θ _i + 10 °, where θ _r is the angle between the optical axis of the optical limiting module and the normal direction of the surface, and θ _i is the incident light. The image invariant light spot capturing device according to claim 1, which is an angle between the direction of the surface and the normal direction of the surface. The optical axis of the optical limiting module is arranged in the direction of θ _r ≦ θ _i −10 °, where θ _r is the angle between the optical axis of the optical limiting module and the normal direction of the surface, and θ _i is The image invariant light spot capturing device according to claim 1, which is an angle between a direction of the incident light and a normal direction of the surface. The change in relative optical path length difference, 4δdcos ³ θ _A / γ, is less than λ / 5, where δ is the average radius of the light spots,
θ _A is the image capture angle between the optical axis of the light limiting module and the normal direction of the surface,
d is the diameter of the image capture area, equal to the maximum travel distance when the image is unchanged,
γ is the vertical distance interval from the imaging lens to the surface,
The image invariant light spot capturing device according to claim 1, wherein λ is a wavelength of the highly coherent light. The light limiting module includes a diaphragm and an imaging lens, the diaphragm is disposed in front of the imaging lens, and the scattered light passes through the diaphragm and the imaging lens of the light limiting module and is coupled onto the sensor. 2. The image invariant light spot capturing device of claim 1, wherein, when imaging, the light limiting module limits the incident viewing angle of the sensor by limiting the scattered light to enter the sensor. 9. The image invariant light spot capturing device according to claim 8, further comprising a second aperture disposed near the surface, limiting the incident viewing angle of the sensor for receiving the scattered light, and changing a relative optical path length difference. 4δdcos ³ θ _A / γ is less than λ / 5, where δ is the average radius of the light spots,
θ _A is the image capture angle between the optical axis of the light limiting module and the normal direction of the surface;
d is the diameter of the image capture area, equal to the maximum travel distance when the image is unchanged,
γ is the vertical distance interval from the imaging lens to the surface,
A device in which λ is the wavelength of highly coherent light. 2. The image invariant light spot capturing device according to claim 1, wherein the light limiting module is a microlens. The image invariant light spot capturing device according to claim 10, wherein the light limiting module further includes an opaque plate surrounding the microlens and blocking unwanted scattered light. Laser mouse
A light source that emits highly coherent light to illuminate the surface and generate multiple scattered light; and
A light limiting module that confines an incident viewing angle to scattered light, and generates a plurality of diffracted lights from the scattered light, whereby the diffracted lights interfere with each other to generate a plurality of spots;
A sensor that receives speckles to generate a first speckle image, and the light limiting module and the sensor generate a second speckle image after moving relative to the surface,
A prestage light limiting device disposed between the light limiting module and the surface, to prevent secondary scattered light of the scattered light from entering the sensor; and
The first speckle image and the second speckle image are received, and the first speckle image and the second speckle image are compared to determine the moving direction and moving distance of the sensor relative to the surface. A laser mouse that includes a processing device. The light limiting module includes an imaging lens and an aperture, the aperture is disposed behind the imaging lens focal point and in front of the sensor, and the scattered light passes through the imaging lens and the aperture of the light limiting module. 13. The laser mouse according to claim 12, wherein when the image is formed on the sensor, the light limiting module limits an incident viewing angle of the sensor to limit the scattered light from entering the sensor. The change in relative optical path length difference, 4δdcos ³ θ _A / γ, is less than λ / 5, where δ is the average radius of the light spots,
θ _A is the image capture angle between the optical axis of the light limiting module and the normal direction of the surface,
d is the diameter of the image capture area, equal to the maximum travel distance when the image is unchanged,
γ is the vertical distance interval from the imaging lens to the surface,
The laser mouse according to claim 12, wherein λ is a wavelength of the highly coherent light. 13. The laser mouse according to claim 12, wherein the light limiting module includes a diaphragm and an imaging lens, and the diaphragm is disposed in front of the imaging lens. The laser mouse of claim 12, wherein the light limiting module combines a microlens and an opaque plate around it. In the method of capturing image invariant light spots,
Emits highly coherent light,
Irradiate the surface with highly coherent light to generate multiple scattered light,
Passing the pre-stage light limiting device so that the scattered light blocks the secondary scattered light of the scattered light,
The scattered light passes through a light limiting module to limit the incident viewing angle of the sensor to generate a plurality of diffracted lights,
The diffracted light interferes with each other to generate a plurality of spots,
A capture method comprising recording said spots to produce an image. 18. The method of capturing an image invariant light spot of claim 17 further comprising comparing images to determine movement relative to a surface to monitor movement of the spot. The light limiting module includes an imaging lens and an aperture, the aperture is disposed behind the imaging lens focal point and in front of the sensor, and the scattered light passes through the imaging lens and the aperture of the light limiting module. 18. The method of capturing image invariant light spots according to claim 17, wherein when the image is formed on the sensor, the light limiting module limits a viewing angle of the sensor to restrict the scattered light from entering the sensor. Using the light limiting module, the change in relative optical path length difference, 4δdcos ³ θ _A / γ, is limited to less than λ / 5, where δ is the average radius of the light spot,
θ _A is the image capture angle between the optical axis of the light limiting module and the normal direction of the surface,
d is the diameter of the image capture area, equal to the maximum travel distance when the image is unchanged,
γ is the vertical distance interval from the imaging lens to the surface,
18. The method of capturing image invariant light spots according to claim 17, wherein λ is the wavelength of the highly coherent light.

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