Patent Publication Number: US-9420235-B2

Title: Measuring system for a 3D object

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a measuring system and, specifically, to a measuring system for a 3D object. 
     2. Description of the Related Art 
     Measuring a 3D object usually needs an optical system comprising a “projection device” and a “camera device”. Briefly, the projection device projects light onto the 3D object to generate a pattern of shadows. The camera device takes a picture of the 3D object and photographs the pattern of shadows of the 3D object at the same time to calculate the height of the 3D object and show a 3D image. 
     It is more and more common to apply a 3D measurement technique to the inspection of a circuit board during the manufacturing in-line process to improve productive efficiency. Currently, one of the methods of obtaining 3D information is to project a periodic fringe pattern onto an object to be measured. By shifting the phase of the periodic fringe pattern several times, an image corresponding to different fringe pattern phases from a position can be obtained. The primary principle is illustrated as follows: A light source is passed through a grating, and the resulting fringe pattern is projected onto the object to be measured through lenses. The grating itself is moved, or the object is moved relative to the projection system, to shift the phase of the fringe pattern. Thus, the surface contour of the object to be measured can be calculated. These techniques have been disclosed. For example, they are disclosed in U.S. Pat. Nos. 4,212,073 and 4,641,972. 
     In the above-mentioned documents, a periodic fringe pattern is generated by a projection device composed of a light source, a sinusoidal grating, and projection lenses. The periodic fringe pattern is then projected onto the surface of a certain region of the object to be measured. The phase of the periodic fringe pattern relative to the surface of the object to be measured can be shifted by moving the grating with a mechanism. These techniques are disclosed in U.S. Pat. Nos. 5,636,025 and 7,453,580. Moreover, the phase can also be shifted by changing the relative distance between the projection device and the certain region of the object to be measured, as disclosed in U.S. Pat. Nos. 5,646,733; 6,501,554; 6,509,559; 7,397,550; and 6,750,899. 
     Please refer to  FIG. 1 , which illustrates a prior art optical system  100 . The camera device  15  is a tri-linear camera. A projection system  18  generates periodic fringe patterns  16   a - 16   c  and projects the same onto an object  14  to be measured, and an image is focused onto the camera device  15 . The phases of fringe patterns  16   a ,  16   b , and  16   c  are different from each other. The camera device  15  comprises a plurality of linear detectors  15   a ,  15   b , and  15   c . Linear detectors  15   a ,  15   b , and  15   c  are separated from each other by a distance of several pixels. The object  14  to be measured moves relative to the optical system  100  in a direction indicated by an arrow  200  to allow the phase to be shifted. The illumination area of the fringe pattern  16   a  can be imaged onto the linear detector  15   a . When the illumination area is moved to the fringe pattern  16   b  that can be imaged onto the linear detector  15   b , and when the illumination area is moved to the fringe pattern  16   c  that can be imaged onto the fringe pattern  15   c , different image information of different phases of fringe patterns and different areas of the same object can be acquired. 3D information with substantially the same size as one single linear detector is then obtained accordingly. The geometric information of the object can be obtained by continuous line scanning. 
     However, the aforementioned technique is limited by the bandwidth of the tri-linear camera. That is, when the “camera device” operates, the minimal unit is the field of view (FOV). Because the line rate of the camera of the aforementioned technique is up to several thousand Hz, it is difficult to use a flash light source. Instead, a constant light source must be used. The consumed power of a constant light source is much greater than that of a flash light source. Also, the usage life-span of a constant light source is shorter, and the maintenance charges of a constant light are higher. 
     Furthermore, U.S. Pat. No. 6,750,899 discloses another method of generating a 3D image. The system structure is illustrated in  FIG. 2A . A projection system  81  comprises a flashlamp  82 , a condenser  83 , a grating  84 , and a projector  85 . A fringe pattern is generated for projection onto a board  86  to be measured and an object  87  to be measured. A camera system  88  comprises a CCD camera  89  and a camera lens  93 . The resolution of the CCD is 1024×1024. A light source  97  projects a light-spot onto an intersection of the optic axis of the CCD camera  89  and the board  86  to be measured, and the CCD camera  89  takes images for calculation of the distance between the board  86  and the camera system  88  accordingly. 
     The movement of the board  86  is controlled by an X-Y system  95 . Please also refer to  FIG. 2B  for another traditional system. The movement direction is indicated by an arrow  300 . When the board  86  moves to a region to be measured, the light source  97  is triggered, the CCD camera  89  takes images, and the imaging distance is adjusted accordingly. As shown in  FIG. 2B , the CCD camera  89  takes an image  801  first and then takes images  802 ,  803 , and  804  in order. The displacement between two taken images is about several pixels. All images can be taken within several milliseconds. The 3D information of an overlapped area  800  can be calculated from a part of the image  802  corresponding to the overlapped area  800 , a part of the image  803  corresponding to the overlapped area  800 , and a part of the image  804  corresponding to the overlapped area  800 . 
     In fact, the velocity of the traditional system while moving between different regions to be measured is different from that while images are being taken. Therefore, the traditional system has a problem of stable movement. It needs time to stabilize in a state of dynamic acceleration and deceleration. Moreover, only the overlapped parts of a plurality of images can be used for calculating 3D information. The other parts are useless. The problems mentioned above all cause a waste of the bandwidth of a camera. 
     Due to the issue of production costs, the density of components on a single unit of a circuit board is increasing. It thus is becoming increasingly necessary to measure a whole board under scanning-inspection to continuously improve the production capacity and the yield rate of production. Therefore, to meet market requirements, the measurement ability of the inspection device has to be good enough, and the inspection speed has to be relatively greater. 
     Additionally, the technique of using a telecentric lens as the projection device has been disclosed in the prior art, for example U.S. Pat. No. 6,577,405. However, in the prior art, additional hardware, such as a laser spot, has to be added in order to measure the distance of the object to be measured, and the distance between the whole set of the optical system and the object to be measured has to be changed in order to obtain clearer images. Thus, the system cannot overcome the movement limitation. 
     SUMMARY OF THE INVENTION 
     A primary objective of the present invention is to provide a measuring system for a 3D object. The system avoids the dynamic acceleration and deceleration change for movement. 
     Another objective of the present invention is to provide a measuring system for a 3D object. The system is able to decrease redundancy regions between images to fully utilize the bandwidth of a camera. 
     An additional objective of the present invention is to provide a measuring system for a 3D object that can meet the requirement of high inspection speed. 
     In order to achieve the above-mentioned objectives, the present invention discloses a measuring system used for measuring a 3D object. The measuring system for the 3D object comprises a base, a horizontal scanning device, a first light emitting device, a second light emitting device, an image capture device, and a control device. 
     The horizontal scanning device is disposed on the base. The image capture device is disposed between the first light emitting device and the second light emitting device. The first light emitting device is connected to the horizontal scanning device and is used for projecting a first light onto the 3D object. The second light emitting device is connected to the horizontal scanning device and is used for projecting a second light onto the 3D object. The image capture device is connected to the horizontal scanning device. When the first light or the second light is projected onto the 3D object, the image capture device captures a plurality of images of the 3D object. 
     In one embodiment, the first and second light emitting devices each use one projection lens respectively. The image capture device adopts a telecentric lens, and the telecentric lens adopts a double-sided telecentric lens. 
     The control device comprises a memory, a CPU, an image interface, a display screen, and an I/O unit electrically coupled to each other. The control device controls the horizontal scanning device to move horizontally relative to the base. Moreover, the measuring system for the 3D object further comprises a motor. The motor is electrically coupled to the I/O unit of the control device to drive the horizontal scanning device to move horizontally. 
     The control device can further control the first light emitting device and the second light emitting device such that the first light and the second light are projected onto the 3D object in alternating order. 
     In addition, the control device further controls the image capture device to capture the plurality of images of the 3D object when the first light or the second light is projected onto the 3D object. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of the structure of a prior art optical system. 
         FIG. 2A  is a schematic drawing of the appearance of another prior art optical system. 
         FIG. 2B  is a schematic drawing of images continuously taken by the optical system shown in  FIG. 2A . 
         FIG. 3  is a schematic drawing of a measuring system for a 3D object in accordance with the present invention. 
         FIG. 4  is a block diagram of the measuring system for a 3D object of the present invention. 
         FIG. 5  is a schematic drawing of light emitting devices and an image capture device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The advantages and innovative features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     Please refer to  FIG. 3  and  FIG. 4 .  FIG. 3  is a schematic drawing of a measuring system for a 3D object of the present invention.  FIG. 4  is a block diagram of the measuring system for a 3D object of the present invention. The present invention provides a measuring system  1  for measuring a 3D object  90  (e.g., a circuit board applied with solder paste). The measuring system  1  comprises a base  20 , a horizontal scanning device  30 , a first light emitting device  40 , a second light emitting device  50 , an image capture device  70 , and a control device  60 , which will be described in detail in  FIG. 4 . 
     The horizontal scanning device  30  is disposed on the base  20 . The horizontal scanning device  30  can move horizontally relative to the base  20 . In this embodiment, the horizontal scanning device  30  comprises a main body  31 , an X-axis track  30   b , and two Y-axis tracks  30   a . The first and second light emitting devices  40 ,  50  and the image capture device  70  are disposed on the main body  31 . The main body  31  can move along the X-axis track  30   b . The X-axis track  30   b  is able to move along the two Y-axis tracks  30   a ,  30   a . Briefly, the first and second light emitting devices  40 ,  50  and the image capture device  70  are connected to the horizontal scanning device  30  to allow the horizontal scanning device  30  to move the first and second light emitting devices  40 ,  50  and the image capture device  70  horizontally. Since the horizontal scanning device  30  can be a traditional device, further description is omitted for the sake of brevity. 
     The first light emitting device  40  is used for projecting a first light  41  onto the 3D object  90 . The second light emitting device  50  is used for projecting a second light  51  onto the 3D object  90 . When the first light  41  or the second light  51  is projected onto the 3D object  90 , the image capture device  70  captures a plurality of images of the 3D object  90 . 
     Please refer to  FIG. 5 , which is a schematic drawing of the structure of the first and second light emitting devices  40 ,  50  and the image capture device  70 . 
     The first light emitting device  40  comprises a first lighting component  42  and a first lens  43 . The first lighting component  42  projects a first light  41  onto the 3D object  90  through the first lens  43 . Moreover, those skilled in this art would understand that the first light emitting device  40  needs a grating element  43   a  to project a grating onto the 3D object  90  so that the 3D surface contour of the 3D object  90  can be calculated. In this embodiment, the first lens  43  is a projection lens. 
     The design of the second light emitting device  50  is the same as that of the first light emitting device  40 . The second light emitting device  50  comprises a second lighting component  52  and a second lens  53 . The second lighting component  52  projects a second light  51  onto the 3D object  90  through the second lens  53 . Moreover, those skilled in the art would understand that the second light emitting device  50  needs a grating element  53   a  to project a grating onto the 3D object  90  so that the 3D surface contour of the 3D object  90  can be calculated. In this embodiment, the second lens  53  is a projection lens. 
     The image capture device  70  is disposed between the first and second light emitting devices  40 ,  50 . A central axis  70   a  of the image capture device  70  and a central axis  40   a  of the first light emitting device  40  form an angle θ 1 . A central axis  70   a  of the image capture device  70  and a central axis  50   a  of the second light emitting device  50  form an angle θ 2 . The angle θ 1  and the angle θ 2  are suggested to be between 10 to 45 degrees. The image capture device  70  mainly comprises a sensing chip module  71  and a telecentric lens  72 . The telecentric lens  72  is a double-sided telecentric lens in this embodiment. Thus, there is no need to use any additional hardware to measure the dynamic distance between the 3D object  90  and the image capture device  70 . With simple movement of the sensing chip module  71  of the image capture device  70  (i.e., the camera), the dynamic imaging of the 3D object  90  can be obtained clearly, and the optical imaging magnification will not change accordingly. 
     For example, the 3D object  90  may be a circuit board to be inspected. The circuit board is placed on the base  20 . The horizontal scanning device  30  moves horizontally relative to the base  20 , which causes the first light emitting device  40 , the second light emitting device  50 , and the image capture device  70  to be moved relative to the base  20  horizontally, such as backwards and forwards in the X direction and also in the Y direction. Thus, the circuit board on the base  20  can be measured by the measuring system  1  of the present invention in order to detect soldering errors on the circuit board, for example. 
     Please refer to  FIG. 4 . Generally, the control device  60  comprises a memory  61 , a CPU  62 , an image interface  66 , a display screen  63 , and an I/O unit  64  electrically coupled to each other. The control device  60  controls the horizontal scanning device  30  to move horizontally relative to the base  20 . Moreover, the measuring system  1  further comprises a motor  65 . The motor  65  is electrically coupled to the I/O unit  64  of the control device  60  to drive the horizontal scanning device  30  to move horizontally. 
     Memory  61  stores a software program. The CPU  62  executes the software program to carry out instructions. Thus, the control device  60  is able to control the image capture device  70  to capture images. When the first light  41  or the second light  51  is projected onto the 3D object  90 , the image capture device  70  captures a plurality of images of the 3D object  90 . The plurality of images is then shown on the display screen  63  through the image interface  66 . 
     In addition, the control device  60  can further control the first light emitting device  40  and the second light emitting device  50  such that the first light  41  and the second light  51  are projected onto the 3D object  90  in an alternating pattern. For example, the control device  60  controls the first light  41  and the second light  51  to be alternately projected with a frequency of 2 Hz˜1000 Hz. With constant-velocity area progressive scanning, there is no change of dynamic acceleration and deceleration during the time of image taking, and redundant regions between images can be decreased (only at both ends requiring overlapped scanning) in order to fully utilize the bandwidth of the image capture device (e.g., a camera), to meet the requirement of higher inspection speed. 
     Because taking images in the present invention employs a “double-sided telecentric lens”, there is no need to use additional hardware to measure the distance between the object and the device. With simple movement of the sensing chip module of the image capture device (the camera), the 3D object can be obtained clearly, and the optical imaging magnification will not change. 
     As mentioned above, the inspection technique and system of the present invention can avoid the change of dynamic acceleration and deceleration and can also decrease redundant regions between images to fully utilize the bandwidth of the image capture device (e.g., a camera), to meet the requirement of high inspection speed. 
     It is noted that the above-mentioned embodiments are only for illustration. It is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. Therefore, it will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention.