Patent Publication Number: US-11024049-B2

Title: Image measurement apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims foreign priority based on Japanese Patent Application No. 2018-162780, filed Aug. 31, 2018, the contents of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image measurement apparatus for imaging a workpiece and for measuring the workpiece. 
     2. Description of Related Art 
     By measuring dimensions of a predetermined portion of a product (workpiece) manufactured in a factory, an image inspection apparatus (image measurement apparatus) for inspecting whether or not the workpiece is a good product can greatly reduce the inspection burden on an inspector. 
     According to JP-A 2018-081115, an image measurement apparatus having a high-magnification camera and a low-magnification camera is proposed. 
     SUMMARY OF THE INVENTION 
     However, by further increasing the magnification of the two cameras mounted on the image measurement apparatus, it is possible to measure a smaller workpiece or a smaller measurement point in the workpiece. On the other hand, even a camera having relatively lower magnification, out of the two cameras, cannot put the whole workpiece in a single image. Generally, an image showing the whole workpiece is displayed in order to set the measurement point on the workpiece, so that the user can accurately set the measurement point. Accordingly, the camera with higher magnification may deteriorate the usability on setting of the measurement point. It is therefore an object of the present invention to further improve the usability of an image measurement apparatus. 
     The present invention is to provide, for example, an image measurement apparatus including: 
     a stage on which a workpiece is placed; 
     an imaging section that generates an image in an imaging field-of-view on the stage; 
     a driving section that switches the imaging field-of-view on the stage by moving the stage relative to the imaging section in an XY direction; 
     a determination section that determines whether or not the workpiece is included in the image generated by the imaging section; 
     a control section that controls the imaging section, the driving section, and the determination section,
         in which, when it is determined by the determination section that the workpiece is not included in the image, the control section performs a first stage operation to repeat a workpiece searching process in which the imaging section generates an image in each imaging field-of-view while moving the stage by controlling the driving section in accordance with a predetermined sequence, and the determination section determines whether or not the workpiece is included in each image,   in which, when it is determined by the determination section that the workpiece is included in the image, the control section performs a second stage operation to move the stage by the driving section so that the imaging section generates images in one or more imaging field-of-views located in a direction in which the workpiece extends, among a plurality of imaging field-of-views located around the imaging field-of-view on the stage, in which the image has been obtained, and   in which, when the image including the workpiece is found in the first stage operation, the control section performs switching from the first stage operation to the second stage operation;       

     an image joining section that joins a plurality of images generated in the second stage operation to generate a joined image including the whole workpiece; and 
     a display section that displays the joined image. 
     According to the present invention, since the joined image including the whole workpiece is generated and displayed, the usability of the image measurement apparatus is further improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an outline of an image measurement apparatus; 
         FIG. 2  is a cross-sectional view of a measurement unit; 
         FIG. 3  is a diagram illustrating an arrangement of a bird&#39;s eye view camera; 
         FIG. 4  is a diagram illustrating a method of generating bird&#39;s eye view images; 
         FIG. 5A  is a diagram illustrating a joined image; 
         FIG. 5B  is a diagram illustrating application examples of the bird&#39;s eye view images; 
         FIG. 6A  is a diagram illustrating a controller; 
         FIG. 6B  is a diagram illustrating the controller; 
         FIG. 7  is a flowchart showing a main process; 
         FIG. 8  is a flowchart showing a setting mode; 
         FIG. 9  is a flowchart showing a continuous measurement mode; 
         FIG. 10  is a flowchart showing a process of generating the bird&#39;s eye view images; 
         FIG. 11  is a diagram showing a method of setting a measurement point; 
         FIGS. 12A-D  is a diagram illustrating a method of generating the bird&#39;s eye view images; and 
         FIGS. 13A-F  is a diagram illustrating a method of generating the bird&#39;s eye view images. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     One embodiment of the present invention will be described below. Individual embodiments described below will facilitate to understand various concepts, such as superordinate, median and subordinate concepts, of the present invention. The technical scope of the present invention is defined by the claims, and is not limited to the following specific embodiments. 
     &lt;Image Measurement Apparatus  1 &gt; 
       FIG. 1  is a perspective view showing an exemplified configuration of an image measurement apparatus  1 . The image measurement apparatus  1  is an apparatus for capturing an image of a workpiece to generate a workpiece image, and for measuring a dimension of the workpiece in the workpiece image. In  FIG. 1 , the image measurement apparatus  1  includes a measurement unit  10 , a control unit  20 , a keyboard  31 , and a pointing device  32 . The workpiece is a measuring object of which shape and dimension are measured by the image measurement apparatus  1 . 
     The measurement unit  10  includes a display device  11 , a movable stage  12 , an XY-adjustment knob (not shown), a Z-adjustment knob  14   b , a power switch  15 , and an execution button  16 . The measurement unit  10  irradiates the workpiece placed on the movable stage  12  with detection light, and receives the transmitted light of the workpiece or the reflected light from the workpiece to generate the workpiece image. The workpiece is placed in a detection area  13  of the movable stage  12 . The measurement unit  10  displays the workpiece image on a display screen  18  of the display device  11 . 
     The display device  11  is a display device for displaying the workpiece image, measurement results, and a setting UI (user interface) on the display screen  18 . The user operates the keyboard  31  and the pointing device  32  while looking at the workpiece image displayed on the display device  11 , thereby setting a feature position for positioning, a measurement point for measuring a dimension, and the like. The movable stage  12  is a mounting table for mounting a workpiece. The detection area  13  is a region formed by a glass having translucency. The movable stage  12  moves in a Z-axis direction parallel to an imaging axis of the camera, and moves in an X-axis direction and a Y-axis direction, which are perpendicular to the imaging axis. 
     The XY-adjustment knob moves the movable stage  12  in the X-axis direction or in the Y-axis direction, thereby adjusting a position of the movable stage  12  relative to a camera (i.e., a position in the X-axis direction and a position in the Y-axis direction, of the movable stage  12 ). The Z-adjustment knob  14   b  moves the movable stage  12  in the Z-axis direction to adjust the position of the movable stage  12  relative to the camera (i.e., a position in the Z-axis direction). The power switch  15  is an operation section for switching a main power of the measurement unit  10  and the control unit  20  to be an on-state or an off-state. The execution button  16  is an operation section for starting dimension measurement. 
     The control unit  20  is a controller that controls imaging and screen displaying by the measurement unit  10 , analyzes the workpiece image, and measures a dimension of the workpiece. The control unit  20  is connected to a keyboard  31  and a pointing device  32 , and accepts user input through the keyboard  31  and the pointing device  32 . The keyboard  31  and the pointing device  32  form an operation section  30 . The control unit  20  activates the measurement unit  10  in a case where the power switch  15  is switched on. When the execution button  16  is operated, the control unit  20  controls the measurement unit  10  in accordance with setting data prepared in advance, searches for the workpiece in the detection area  13 , and measures the dimension of the workpiece. 
     &lt;Measurement Unit  10 &gt; 
       FIG. 2  is a cross-sectional view schematically showing a configuration example of the measurement unit  10 . Here, a cutting plane in a case where the measurement unit  10  is cut by a vertical plane (YZ-plane) parallel to the imaging axis is shown. The measurement unit  10  includes the display device  11 , the movable stage  12 , a housing  100 , a stage driving section  101 , a barrel section  102 , an illumination position adjusting section  103 , cameras  110  and  120 , a coaxial epi-illumination  130 , a ring illumination  140 , and a transmissive illumination  150 . 
     The stage driving section  101 , the barrel section  102 , the cameras  110  and  120 , the coaxial epi-illumination  130 , and the transmissive illumination  150  are arranged in the housing  100 . The stage driving section  101  moves the movable stage  12  in the X-axis direction, the Y-axis direction, or the Z-axis direction in accordance with a driving signal from the control unit  20 , and adjusts a position of the movable stage  12  with respect to the cameras  110  and  120 . Since the workpiece is placed on the movable stage  12 , the positional adjustment of the movable stage  12  corresponds to the positional adjustment of the workpiece. 
     The camera  110  is an imaging device having lower imaging magnification than the camera  120 . The camera  110  includes an imaging element  111 , an imaging lens  112 , a diaphragm plate  113 , and a light-receiving lens  114 . The imaging element  111  receives the detection light and generates the workpiece image. The imaging element  111  is arranged such that a light-receiving surface faces downward. The imaging lens  112  is an optical member for imaging the detection light on the imaging element  111 . The diaphragm plate  113  is an optical diaphragm that limits a transmitted light volume of the detection light, and is arranged between the imaging lens  112  and the light-receiving lens  114 . The light-receiving lens  114  is an optical member that collects the detection light from the workpiece, and is arranged so as to face the movable stage  12 . The imaging lens  112 , the diaphragm plate  113 , and the light-receiving lens  114  are arranged about a center axis extending in a vertical direction. 
     The camera  120  is an imaging device having higher imaging magnification than the camera  110 . The camera  120  includes an imaging element  121 , an imaging lens  122 , a diaphragm plate  123 , a half mirror  124 , and the light-receiving lens  114 . The imaging element  121  receives the detection light and generates the workpiece image. The imaging element  121  is arranged such that a light-receiving surface is oriented in a horizontal direction. That is, the light-receiving surface and the horizontal direction are orthogonal to each other. The imaging lens  122  is an optical member for imaging the detection light on the imaging element  121 . The diaphragm plate  123  is an optical diaphragm that limits a transmitted light volume of the detection light, and is arranged between the imaging lens  122  and the half mirror  124 . The light-receiving lens  114  is same as that of the camera  110 . The detection light transmitted through the light-receiving lens  114  is folded in the horizontal direction by the half mirror  124 , and forms an image on the imaging element  121  via the diaphragm plate  123  and the imaging lens  122 . 
     As the imaging elements  111  and  121 , for example, image sensors such as CCD (charge coupled device) and CMOS (complementary metal-oxide semiconductor) are used. As the light-receiving lens  114 , a telecentric lens having a property that a size of the workpiece image is not varied even when a distance between the light-receiving lens  114  and the workpiece is varied is used. That is, the optical systems of the cameras  110  and  120  respectively have telecentricity. A distortion of the workpiece in the workpiece image acquired by a telecentric optical system is very small as compared to a distortion of the workpiece in the workpiece image acquired by a non-telecentric optical system. Therefore, the workpiece can be measured with high accuracy. 
     The coaxial epi-illumination  130  is an illumination device that irradiates the workpiece on the movable stage  12  with illumination light from above. An optical axis of irradiation light of the coaxial epi-illumination  130  coincides with the imaging axis. The coaxial epi-illumination  130  includes a light source  131  arranged so as to output the illumination light in the horizontal direction, and a half mirror  132  that bends downwardly the illumination light emitted from the light source  131 . The illumination light of the coaxial epi-illumination  130  is advantageous when obtaining unevenness or patterns of a workpiece surface. 
     The imaging lenses  112  and  122 , the diaphragm plates  113  and  123 , the half mirrors  124  and  132 , and the light-receiving lens  114  are arranged in the barrel section  102 . 
     The transmissive illumination  150  is an illumination device that irradiates the workpiece on the movable stage  12  with illumination light from below. The transmissive illumination  150  includes a light source  151 , a mirror  152 , and a condensing lens  153 . The light source  151  is arranged so as to output illumination light in the horizontal direction. The illumination light emitted from the light source  151  is reflected by the mirror  152  and condensed by the condensing lens  153 . The illumination light passes through the movable stage  12  and irradiates the workpiece. Part of the illumination light is blocked by the workpiece, and the other part of the illumination light enters the light-receiving lens  114 . The illumination light of the transmissive illumination  150  is advantageous when acquiring an edge of a contour of the workpiece. 
     The ring illumination  140  is an illumination device that irradiates the workpiece on the movable stage  12  with illumination light from above or from the side. A plurality of light sources forming the ring illumination  140  are arranged to surround the imaging axes of the cameras  110  and  120 . LED (light emitting diode) or a halogen lamp is used as each light source of the coaxial epi-illumination  130 , the ring illumination  140 , and the transmissive illumination  150 . The illumination position adjusting section  103  adjusts a relative position of the ring illumination  140  with respect to the movable stage  12  by moving the ring illumination  140  in the Z-axis direction. 
     A bird&#39;s eye view camera  17  is an imaging device used to acquire a bird&#39;s eye view image of the movable stage  12 . The bird&#39;s eye view image is an image that encompasses almost the whole movable stage  12 . An imaging field-of-view of the bird&#39;s eye view camera  17  is wider than the imaging field-of-views of the cameras  110  and  120 . Therefore, the bird&#39;s eye view camera  17  is suitable for acquiring a wider range of images as compared with the cameras  110  and  120 . On the other hand, telecentricity of the bird&#39;s eye view camera  17  is low as compared to the telecentricity of the cameras  110  and  120 . Therefore, the bird&#39;s eye view camera  17  may be referred to as a non-telecentric camera. Since a shape of the workpiece is distorted in the workpiece image acquired by the bird&#39;s eye view camera  17 , the bird&#39;s eye view camera  17  is not suitable for measuring the workpiece as compared with the cameras  110  and  120 . An optical system has a circular field-of-view, and a subject in the field-of-view, as an image circle, forms an image on the imaging element. On the other hand, the imaging element can image in a rectangular range. That is, an imaging region is a partial rectangular region within the image circle. In this detailed description, the rectangular region on the movable stage  12  corresponding to the imaging region of the imaging element is called “imaging field-of-view.” 
     &lt;Bird&#39;s Eye View Camera&gt; 
     As shown in  FIG. 2 , the light-receiving lens  114  and the ring illumination  140  cover quite an area of the movable stage  12 . Therefore, the bird&#39;s eye view camera  17  is arranged at a position avoiding the light-receiving lens  114  and the ring illumination  140 . The bird&#39;s eye view camera  17  may be implemented by a single camera, or may be implemented by a plurality of cameras. 
       FIG. 3  is a diagram illustrating an arrangement of the bird&#39;s eye view camera  17  when the bird&#39;s eye view camera  17  is viewed from a front side of the measurement unit  10 . W indicates the workpiece. In this example, a bird&#39;s eye view camera  17 L is arranged on a left side of the light-receiving lens  114 , and a bird&#39;s eye view camera  17 R is arranged on a right side of the light-receiving lens  114 . R 1  indicates a visual field range of the camera  110 . R 2 L indicates a visual field range of the bird&#39;s eye view camera  17 L. R 2 R indicates a visual field range of the bird&#39;s eye view camera  17 R. By employing the two bird&#39;s eye view cameras  17 R and  17 L, it is possible to image the majority of the movable stage  12  at once. Nevertheless, other than the visual field range R 2 L of the bird&#39;s eye view camera  17 L, a blind spot range R 3  not covered by the visual field range R 2 L of the bird&#39;s eye view camera  17 L is formed on the movable stage  12 . If the light-receiving lenses of the bird&#39;s eye view cameras  17 R and  17 L are replaced with lenses covering a wider angle, the blind spot range R 3  is not formed. However, such a wide-angle lens is expensive. By arranging the bird&#39;s eye view camera  17 R and the bird&#39;s eye view camera  17 L farther from the movable stage  12 , the visual field ranges R 2 R and R 2 L will be widened. However, in this case, the visual field ranges R 2 R and R 2 L will be limited by the ring illumination  140 . Therefore, in the present example, a method of creating a bird&#39;s eye view image covering the whole movable stage  12  is proposed. 
       FIG. 4  is a diagram illustrating a method of creating a bird&#39;s eye view image. The control unit  20  moves the movable stage  12  so that a center between the imaging axis of the bird&#39;s eye view camera  17 L and the imaging axis of the bird&#39;s eye view camera  17 R coincide with a center of the movable stage  12 , and allows the bird&#39;s eye view cameras  17 L and  17 R to perform the imaging. A bird&#39;s eye view image  41   a  is an image acquired by the bird&#39;s eye view camera  17 L. A bird&#39;s eye view image  41   b  is an image acquired by the bird&#39;s eye view camera  17 R. Since the bird&#39;s eye view camera  17 R and the bird&#39;s eye view camera  17 L have the blind spot range R 3 , a part of the workpiece W located within the blind spot range R 3  does not appear in the bird&#39;s eye view images  41   a  and  41   b.    
     The control unit  20  moves the movable stage  12  so that the imaging axis of the bird&#39;s eye view camera  17 L (or the bird&#39;s eye view camera  17 R) coincides with the center of the movable stage  12 , and allows the bird&#39;s eye view camera  17 L (or the bird&#39;s eye view camera  17 R) to perform the imaging. Thus, a bird&#39;s eye view image  41   c  is generated. The bird&#39;s eye view image  41   c  shows a part of the workpiece W located within the blind spot range R 3 . The control unit  20  combines the bird&#39;s eye view images  41   a  and  41   b  with the bird&#39;s eye view image  41   c  to generate a bird&#39;s eye view image  41   d  including the whole movable stage  12 . A left portion of the bird&#39;s eye view image  41   c  overlaps with the bird&#39;s eye view image  41   a , and thus is removed. A right portion of the bird&#39;s eye view image  41   c  overlaps with the bird&#39;s eye view image  41   b , and thus is removed. 
     There are various methods of generating the bird&#39;s eye view image  41   d . When focusing on acquisition speed of the bird&#39;s eye view image, the number of bird&#39;s eye view images used for synthesis may be reduced. When focusing on suppressing distortion of the bird&#39;s eye view image, the number of images used for synthesis may be increased. The bird&#39;s eye view image is used for position detection, which will be described later. Therefore, when the large distortion occurs, even rough position detection may be compromised. Therefore, distortion of the bird&#39;s eye view image may be reduced. 
     &lt;Automatic Workpiece Detection&gt; 
       FIG. 5A  and  FIG. 5B  are diagrams illustrating automatic detection of the workpiece. As shown in  FIG. 5A , a single workpiece W is generally placed on the movable stage  12 . In this case, since the user places the workpiece W near the center of the movable stage  12 , the control unit  20  searches for the workpiece W with reference to the center of the movable stage  12 . In a case where the movable stage  12  is located at a home position, an optical axis of the light-receiving lens  114  passes through the center of the movable stage  12 . In this example, the control unit  20  acquires four workpiece images with the low-magnification camera  110 , thereby acquiring position and orientation of the workpiece W on the movable stage  12 , i.e., a rotation angle with respect to a reference model. In particular, the control unit  20  acquires a low-magnification image  43   a , extracts the workpiece W existed within the low-magnification image  43   a , and analyzes an extending direction of the workpiece W. In the detailed description, the extending direction of the workpiece W is referred to as a direction in which a portion has a luminance value equal to or lower than a predetermined luminance value (that is, a portion that corresponds to a so-called shadow), which is obtained by analyzing the low-magnification image  43   a.    
     The low-magnification image  43   a  has an upper side, a right side, a bottom side, and a left side. Since the edge is connected to the bottom side, among these, the control unit  20  determines that the workpiece W exists in a downward direction of the low-magnification image  43   a . The control unit  20  moves the movable stage  12  so as to acquire a low-magnification image  43   b  located in the downward direction of the low-magnification image  43   a , and allows the camera  110  to perform the imaging. Thus, the low-magnification image  43   b  is generated. The control unit  20  analyzes the extending direction of the workpiece W in the low-magnification image  43   b . Since the contour of the workpiece W is connected to a right side of the low-magnification image  43   b , the control unit  20  determines that the workpiece W exists in a right direction of the low-magnification image  43   b . Moreover, the contour of the workpiece W is also connected to an upper side of the low-magnification image  43   b , however, the low-magnification image  43   a  located above the low-magnification image  43   b  has already been analyzed. Therefore, the low-magnification image  43   a  is not considered as an acquisition target. The control unit  20  moves the movable stage  12  so as to acquire a low-magnification image  43   c  located to the right of the low-magnification image  43   b , and allows the camera  110  to perform the imaging. Thus, the low-magnification image  43   c  is generated. The control unit  20  analyzes the extending direction of the workpiece W in the low-magnification image  43   c . Since the contour of the workpiece W is connected to an upper side of the low-magnification image  43   c , the control unit  20  determines that the workpiece W exists in an upward direction of the low-magnification image  43   c . The control unit  20  moves the movable stage  12  so as to acquire a low-magnification image  43   d  located above the low-magnification image  43   c , and allows the camera  110  to perform the imaging. When the control unit  20  joins the low-magnification images  43   a  to  43   d  to generate a joined image and confirms that the contours of the workpiece W are connected to form a single contour in the joined image, the joined image is completely generated. In a setting mode, the control unit  20  accepts setting of positioning (pattern searching), setting of measurement point, and the like, with respect to the joined image. In a measurement mode, the control unit  20  detects position and orientation of the workpiece W from the joined image. The control unit  20  specifies measurement points on the workpiece W based on the position and orientation of the workpiece W, and measures the specified measurement points. 
     In the above paragraph, it is assumed that the workpiece W is included in the image when the control unit  20  acquires the low-magnification image  43   a  at first. As described in detail later, but actually, after a first stage operation, which is a workpiece searching operation, is performed, a second stage operation for searching the whole body (contour) of the workpiece is performed as described in the above paragraph. 
     However, as shown in  FIG. 5B , if a plurality of workpieces W (W 1  to W 8 ) can be measured only by pressing the execution button  16  once, work burden of the user is reduced. In this case, since the workpiece W also exists at a position other than the center of the movable stage  12 , a process of searching for the workpiece W existed at a position other than the center is required. If the plurality of workpieces W are searched while acquiring a low-magnification image as the low-magnification image  43   b , the longer search time is required. Consequently, the control unit  20  generates a bird&#39;s eye view image  41   d , specifies approximate positions of the plurality of workpieces W using the bird&#39;s eye view image  41   d , and acquires a low-magnification image with reference to the specified positions. It will be appreciated that the measurement time for the plurality of workpieces W is greatly shortened. It is called a multiple batch measurement mode, and the details thereof will be described later. 
     &lt;Controller&gt; 
       FIG. 6A  is a diagram illustrating functions of a controller  60  mounted on the control unit  20 .  FIG. 6B  shows optional functions required for generating the bird&#39;s eye view image  41 . The controller  60  consists of a CPU or the like, and controls the measurement unit  10 . “CPU” is an abbreviation of “central processing unit”. Some or all of the functions of the controller  60  may be implemented by hardware such as ASIC or FPGA. “ASIC” is an abbreviation of “application specific integrated circuit”. “FPGA” is an abbreviation of “field programmable gate array”. An illumination control section  81  is mounted on the control unit  20  or the measurement unit  10 , and controls the coaxial epi-illumination  130 , the ring illumination  140 , and the transmissive illumination  150  in accordance with a control signal from the controller  60 . An imaging control section  82  is mounted on the control unit  20  or the measurement unit  10 , and controls the cameras  110  and  120  and the bird&#39;s eye view cameras  17 R and  17 L, for measurement, in accordance with a control signal from the controller  60 . A storage device  70  includes a memory, a hard disk drive and the like, and stores setting data  71 , the low-magnification image  43 , the bird&#39;s eye view image  41  and the like. 
     A setting section  61  generates the setting data  71  for measuring the workpiece W in accordance with a user input from the keyboard  31  or the like. The setting data  71  includes, for example, setting information related to the searching (positioning) of the workpiece W, setting information related to the measurement point, a quality threshold value, imaging conditions (imaging magnification and illumination conditions), and the like. 
     A measurement control section  62  turns on any one of illumination units through the illumination control section  81  and allows any one of camera units to perform the imaging through the imaging control section  82  in accordance with the setting data  71 . 
     A workpiece determination section  63  extracts edges from images acquired by the cameras  110  and  120 , and determines whether or not the edges exist. The workpiece determination section  63  obtains the extending direction of the edge, and determines coordinates of an imaging position at which the next imaging is to be performed. An image joining section  64  joins a plurality of low-magnification images  43  including the edges of the workpiece W to generate a joined image  42 . 
     As shown in  FIG. 6B , a bird&#39;s eye view image generating section  65  joins the bird&#39;s eye view images  41   a  to  41   c  acquired by the bird&#39;s eye view cameras  17 R and  17 L to generate the larger bird&#39;s eye view image  41   d . A coordinate conversion section  68  converts the coordinates of the workpiece W within the bird&#39;s eye view image  41   d  into the coordinates of the camera  110 . A calibration section  69  calibrates a coordinate system of the bird&#39;s eye view camera  17  using calibration information  72 . The coordinate conversion section  68  and the calibration section  69  may be parts of the bird&#39;s eye view image generating section  65 . 
     A searching section  66  specifies position and orientation of the workpiece W from the bird&#39;s eye view image  41   d  and the joined image  42  based on the setting data  71 . For example, the searching section  66  roughly specifies a position of the workpiece W from the bird&#39;s eye view image  41   d  based on the setting data  71 , and specifies a detailed position and an orientation of the workpiece W based on the setting data  71  from the joined image  42  acquired on the basis of the position roughly specified. 
     A measurement section  67  performs various measurements on the workpiece W within the workpiece image in accordance with the setting data  71 . The workpiece image may be the joined image  42 , or may be a high-magnification image near the measurement point, acquired by the camera  120  based on the detailed position and the orientation of the workpiece W, or may be the low-magnification image. The measurement section  67  may compare the measurement results with the quality threshold to determine whether or not the workpiece W has sufficient quality. 
     A display control section  83  displays a user interface (UI) for creating the setting data  71  on the display device  11  in accordance with an instruction from the controller  60 , displays various images, and displays the measurement results. 
     &lt;Flowchart&gt; 
       FIG. 7  is a flowchart showing a main process executed by the controller  60  when the power switch  15  is turned on. 
     In S 701 , the controller  60  determines whether or not the setting mode is selected by the user through the operation section  30 . If the setting mode is not selected, the controller  60  skips S 702  and proceeds to S 703 . On the other hand, if the setting mode is selected, the controller  60  proceeds to S 702 . 
     The controller  60  (the setting section  61 ) executes the setting mode in S 702 . The setting mode will be described later in detail with reference to  FIG. 8 . 
     In S 703 , the controller  60  determines whether or not the measurement mode is selected by the user through the operation section  30 . The measurement mode may include a single measurement mode for measuring a single workpiece W and a multiple batch measurement mode for measuring a plurality of workpieces W. In the single measurement mode, since the workpiece W is usually arranged near the center of the movable stage  12 , the measurement unit  10  starts searching for the edge of the workpiece W from the center of the movable stage  12 . On the other hand, in the multiple batch measurement mode, as shown in  FIG. 5B , it is likely that the plurality of workpieces W are scattered over the whole movable stage  12 , so that positions of the respective workpieces are roughly specified using the bird&#39;s eye view images, and searching for the edge of the workpieces W is executed at the specified positions. For convenience of description, it is assumed that the measurement mode is a continuous measurement mode in the detailed description. If the measurement mode is not selected, the controller  60  returns to S 701 . On the other hand, if the measurement mode is selected, the controller  60  proceeds to S 704 . 
     In S 704 , the controller  60  determines whether or not the execution button  16  is operated by the user. When the execution buttons  16  are operated by the user, the controller  60  proceeds to the S 705 . 
     In S 705 , the controller  60  (the measurement control section  62 ) executes the continuous measurement mode. The continuous measurement mode will be described later in detail with reference to  FIG. 9 . 
     Setting Mode 
       FIG. 8  is a flowchart showing the setting mode. S 800  is the first stage operation for searching for the workpiece. S 800  may include S 801  to S 803 . S 810  is a second stage operation for searching the whole body (contour) of the workpiece. S 810  may include S 811  to S 817 . As the first stage operation and the second stage operation, an example of searching with the low-magnification camera  110  will be described. However, the searching may be performed using the high-magnification camera  120 , or alternatively, the searching may be performed using the low-magnification camera  110  and the high-magnification camera  120  in combination as appropriate. 
     In S 801 , the controller  60  (the measurement control section  62 ) moves the movable stage  12  in accordance with a predetermined sequence. In general, in the setting mode, the workpiece W with good quality (reference) is placed near the center of the movable stage  12 . Therefore, the controller  60  controls the stage driving section  101  so that the imaging field-of-view of the low-magnification camera  110  is located on a grid near the center of the movable stage  12 . The predetermined sequence is a sequence in which the movable stage  12  is sequentially moved to a plurality of predetermined stage coordinate positions. The predetermined sequence is defined by coordinate information of the movable stage  12 , and is stored in the storage device  70 . Since the image obtained by imaging within the imaging field-of-view has a rectangular shape, the whole movable stage  12  can be covered by a plurality of rectangular images. A plurality of rectangular images are arranged on the whole movable stage  12  in a shape of the grid. Therefore, the coordinates of each of the plurality of rectangular images can be managed as the coordinates of the grid. Since the grid is generally a grid point, four corners in the image correspond to the grid. A rectangle surrounded by four corners is the imaging field-of-view in a narrow sense. Therefore, each imaging field-of-view (imaging position) may be specified based on the coordinates of the upper left corner of the image. Alternatively, center coordinates of the image may be managed as the imaging position. 
     In S 802 , the controller  60  (the measurement control section  62 ) allows the camera  110  to perform the imaging through the imaging control section  82 , and acquires the low-magnification image  43 . The low-magnification image  43  is stored in the storage device  70 . The low-magnification image  43  may be stored in a storage device in the measurement unit  10  and processed instead of being stored in the storage device  70  of the control unit  20 . 
     In S 803 , the controller  60  (the workpiece determination section  63 ) determines whether or not edges exist within the low-magnification image  43 . In the low-magnification image  43 , the edge is a portion where the luminance value between adjacent pixels largely changes. If no edge exists within the low-magnification image  43 , the controller  60  returns to S 801  and moves the movable stage  12  to the next grid. If the edges are found within the low-magnification images  43 , the controller  60  proceeds to S 811 . In other words, the controller switches the workpiece searching sequence in S 800  to the contour searching sequence in S 810 . 
     In S 811 , the controller  60  (the measurement control section  62 ) adjusts operation conditions of the imaging control section  82  and operation conditions of the illumination control section  81  so that the edge of the workpiece W is emphasized. These operation conditions are referred to as the imaging conditions. The imaging conditions may include, for example, a position (in-focus position) of the movable stage  12  in the Z direction, an illumination mode (transmissive illumination/coaxial epi-illumination), exposure time, illumination light volume, and the like. Moreover, subsequent steps may be performed under predetermined conditions without adjusting the imaging conditions. 
     In S 812 , the controller  60  (the workpiece determination section  63 ) determines the extending direction of the edge. As described above, the extending direction may be determined based on one of the four sides with which the edge is in contact. Alternatively, a vector of the edge may be calculated. 
     In S 813 , the controller  60  (the measurement control section  62 ) determines the next imaging coordinates. For example, the measurement control section  62  obtains coordinates of the adjacent grid existed in the extending direction of the edge. 
     In S 814 , the controller  60  (the measurement control section  62 ) sets the coordinates of the adjacent grid existed in the extending direction of the edge on the stage driving section  101  and moves the movable stage  12 . 
     In S 815 , the controller  60  (the measurement control section  62 ) allows the camera  110  to perform the imaging through the imaging control section  82 , and acquires the low-magnification image  43 . The low-magnification image  43  is stored in the storage device  70 . 
     In S 816 , the controller  60  (the workpiece determination section  63 ) extracts an edge of the workpiece from the low-magnification image  43 . In this manner, the workpiece determination section  63  may serve as a determination section that determines the edge of the workpiece. 
     In S 817 , the controller  60  (the measurement control section  62 ) determines whether or not termination conditions are satisfied based on the extracted edges. For example, the workpiece determination section  63  determines whether or not all contour edges of the workpiece W have been extracted. Alternatively, the workpiece determination section  63  may determine the extending direction of the edge extracted from the low-magnification image  43 , and determine that the termination conditions are satisfied when the grid existed in the extending direction is the grid that the low-magnification image  43  has already been acquired. If the termination conditions are not satisfied, the controller  60  returns to S 811  (or alternatively, the controller may return to S 812 ). On the other hand, if the termination conditions are satisfied, the controller  60  proceeds to S 821 . 
     In S 821 , the controller  60  (the image joining section  64 ) reads and joins the low-magnification images  43  of the workpiece W from the storage device  70  and generates the single joined image  42 . The joined image  42  is also stored in the storage device  70 . For example, as shown in  FIG. 5A , the joined image  42  is generated from the four low-magnification images  43   a  to  43   d.    
     The controller  60  (the setting section  61 ) displays the joined image  42  on the display device  11  in S 822 , and accepts the setting of the measurement point, etc., for the workpiece W included in the joined image  42 . For example, the setting section  61  accepts designation of a feature point for pattern searching, designation of two edges for measuring a certain dimension (distance), and the like. The setting section  61  may superimpose and display a rectangular or circular designated region for designating a feature point or an edge on the joined image  42  in accordance with the user input from the operation section  30 . As shown in  FIG. 11 , two designated regions  1101   a  and  1101   b  may be designated in order to measure a length D of the workpiece W within the joined image  42 . In the detailed description, the length D is defined as a distance from the edge in the designated region  1101   a  to the edge in the designated region  1101   b . The setting section  61  may move the movable stage  12  by setting the positions of the designated regions  1101   a  and  1101   b  on the stage driving section  101 , and may allow the camera  120  to acquire high-magnification images within the regions  1101   a  and  1101   b . The setting section  61  may superimpose and display the high-magnification images on the designated regions  1101   a  and  1101   b . In other words, the high-magnification image may be displayed in the designated region arranged on the low-magnification image. In this manner, the image of the workpiece W may be displayed in more detail in the designated regions  1101   a  and  1101   b . The setting section  61  may accept imaging conditions (illumination conditions, magnification, focus and the like) for each of the designated regions  1101   a  and  1101   b . That is, the imaging conditions may be different for each of the designated regions  1101   a  and  1101   b . The setting section  61  may superimpose and display the images acquired from the designated regions  1101   a  and  1101   b  on the joined image  42 . For example, the setting section  61  may superimpose and display the images acquired by resetting the shooting conditions for measurement, with the joined image  42  acquired automatically in advance as a background image. The setting section  61  creates the setting data  71  in accordance with the user input and stores the setting data  71  in the storage device  70 . 
     Measurement Mode 
       FIG. 9  is a flowchart showing the continuous measurement mode. Steps equivalent or similar to those already described are referred with the same reference numerals. In the detailed description, a bird&#39;s eye view mode (S 901  to S 903 ) for acquiring the bird&#39;s eye view image  41  and for roughly specifying position and orientation of the workpiece W is described; however, this step is not essential. 
     In S 901 , the controller  60  (the measurement control section  62 ) refers to the setting data  71  and determines whether or not the bird&#39;s eye view mode is set to be enabled. As shown in  FIG. 5B , the bird&#39;s eye view mode is a mode advantageous for measuring a plurality of workpieces W. If the bird&#39;s eye view mode is enabled, the controller  60  proceeds to S 902 . If the bird&#39;s eye view mode is not enabled, the controller  60  skips S 902  and S 903  and proceeds to S 800 . 
     The controller  60  (the measurement control section  62 ) generates a bird&#39;s eye view image in S 902 . The process of generating the bird&#39;s eye view image  41  will be described in detail later with reference to  FIG. 10 . 
     In S 903 , the controller  60  (the measurement control section  62 ) uses the bird&#39;s eye view image to roughly specify a position of the workpiece W. The workpiece determination section  63  extracts the workpiece included in the bird&#39;s eye view image, and roughly obtains the position of the workpiece W. There are various methods for specifying the position of the workpiece. A method of roughly determining the position of the workpiece W as follows may be employed; in this method, a first bird&#39;s eye view image is acquired, the stage is slightly moved in the X direction or in the Y direction, a second bird&#39;s eye view image is acquired, and the position of the workpiece W is roughly determined based on a difference image between the first bird&#39;s eye view image and the second bird&#39;s eye view image. A method of roughly determining the position of the workpiece W as follows may be employed; in this method, the position of the workpiece W is roughly determined based on the difference image between the first bird&#39;s eye view image captured before placing the workpiece W and the second bird&#39;s eye view image captured after placing the workpiece W. Alternatively, a method may be employed in which the edges included in the bird&#39;s eye view image are extracted and the position of the workpiece W is roughly obtained based on the extracted edges. As shown in  FIG. 5B , the workpiece determination section  63  may extract contour edges of a plurality of workpieces W and may roughly determine barycentric positions of the respective contour edges as the positions of the workpieces W. The number of workpieces W may be set in advance through the operation section  30 . The workpiece determination section  63  may determine the position of each workpiece W in accordance with the number of workpieces W. For example, when four workpieces W are placed on the movable stage  12 , four contour edges have to exist within the bird&#39;s eye view image  41 . Therefore, the workpiece determination section  63  may extract the contour edges in accordance with the number of workpieces, and may determine the position of each contour edge. In the detailed description, the position of each workpiece W is a position within the bird&#39;s eye view image. The position of the workpiece W within the bird&#39;s eye view image exists in the coordinate system of the bird&#39;s eye view camera  17 . Therefore, the workpiece determination section  63  may convert the position of the workpiece W in the coordinate system of the bird&#39;s eye view camera  17  into the position in the coordinate system of the camera  110  using the coordinate conversion section  68 . Accordingly, the low-magnification image of each workpiece W can be acquired more easily. 
     Each process from S 800  to S 913  is performed for each of the plurality of workpieces W. 
     In S 800 , the controller  60  performs the first stage operation and detects the edges of the workpiece W. The first stage operation is as described above with reference to  FIG. 8 . 
     In S 810 , the controller  60  performs the second stage operation to generate a plurality of low-magnification images covering the workpiece W. The second stage operation is as described above with reference to  FIG. 8 . 
     In S 821 , the controller  60  (the image joining section  64 ) joins the plurality of low-magnification images to generate the joined image. The joined image may be generated by joining a plurality of high-magnification images. 
     In S 911 , the controller  60  (the searching section  66 ) specifies the detailed position and the orientation of the workpiece W in the joined image based on the setting data  71  for positioning. 
     In S 912 , the controller  60  (the measurement section  67 ) specifies the measurement point in the joined image and measures the measurement point based on the position and orientation of the workpiece W, and further based on the setting data  71  of the measurement point. A position of each measurement point is set with respect to a position of a reference feature point on the workpiece W. Therefore, the position of each measurement point in the joined image is determined by rotating the position of each measurement point in accordance with the orientation of the workpiece W with respect to the reference feature point. As described above, in order to improve the measurement accuracy, a high-magnification image of the measurement point may be acquired by the camera  120 , and the measurement may be performed based on the high-magnification image. 
     In S 913 , the controller  60  (the measurement section  67 ) compares the measurement results of the workpiece W with predetermined quality thresholds (e.g., tolerances), and determines whether or not the workpiece W has sufficient quality. The measurement section  67  may display the measurement results on the display device  11  together with the image of the workpiece W used for the measurement. 
     Generation of Bird&#39;s Eye View Image 
       FIG. 10  is a flowchart showing a process of generating the bird&#39;s eye view image. 
     In S 1001 , the controller  60  (the calibration section  69 ) calibrates the coordinate system of the bird&#39;s eye view camera  17 R and the coordinate system of the bird&#39;s eye view camera  17 L based on calibration information  72  previously stored in the storage device  70 . The bird&#39;s eye view camera  17 R has individual differences in a mounting position and orientation with respect to the measurement unit  10 . The bird&#39;s eye view camera  17 L has individual differences in a mounting position and orientation with respect to the measurement unit  10 . For example, an edge of the image acquired by the bird&#39;s eye view camera  17 R may not be parallel to an edge of the image acquired by the camera  110 . Therefore, upon assembling the measurement unit  10  in the factory, deviation amounts of the mounting position and mounting orientation are measured for each of the bird&#39;s eye view cameras  17 R and  17 L, and thus the calibration information  72  is created based on the measurement results and then stored in a ROM of the storage device  70 . By calibrating the coordinate system of the bird&#39;s eye view camera  17 R based on the calibration information  72 , it is possible to accurately convert a specific position of the bird&#39;s eye view camera  17 R in the coordinate system into a specific position of the camera  110  or the camera  120  in the coordinate system. Similarly, by calibrating the coordinate system of the bird&#39;s eye view camera  17 L based on the calibration information  72 , it is possible to accurately convert a specific position of the bird&#39;s eye view camera  17  L in the coordinate system into a specific position of the camera  110  or the camera  120  in the coordinate system. 
     In S 1002 , the controller  60  (the bird&#39;s eye view image generating section  65 ) sets the imaging position on the stage driving section  101 , and moves the movable stage  12  to the imaging position. For example, as shown in  FIG. 4 , the movable stage  12  moves so as to acquire bird&#39;s eye view images  41   a  and  41   b , which correspond to partial bird&#39;s eye view images. 
     In S 1003 , the controller  60  (the bird&#39;s eye view image generating section  65 ) allows the bird&#39;s eye view cameras  17 R and  17 L to perform the imaging through the imaging control section  82 , thereby acquiring partial bird&#39;s eye view images. 
     In S 1004 , the controller  60  (the bird&#39;s eye view image generating section  65 ) determines whether or not all bird&#39;s eye view images  41   a  to  41   c , required for synthesizing the bird&#39;s eye view image  41   d  (whole bird&#39;s eye view image), are acquired. If all of the bird&#39;s eye view images  41   a  to  41   c  have been acquired, the controller  60  proceeds to S 1005 . On the other hand, if all of the bird&#39;s eye view images  41   a  to  41   c  have not been acquired, the controller  60  returns to S 1002 . For example, when the bird&#39;s eye view images  41   a  and  41   b  are acquired but the bird&#39;s eye view image  41   c  is not acquired yet, the controller  60  returns to S 1002 . The movable stage  12  is moved to the imaging position of the bird&#39;s eye view image  41   c  in S 1002 . The bird&#39;s eye view image  41   c  is acquired in S 1003 . 
     In S 1005 , the controller  60  (the bird&#39;s eye view image generating section  65 ) combines a plurality of partial bird&#39;s eye view images to generate the whole bird&#39;s eye view image. In an example shown in  FIG. 4 , the bird&#39;s eye view image  41   d  is generated from the bird&#39;s eye view images  41   a  to  41   c.    
     Multiple Batch Mode Using Bird&#39;s Eye View Images 
     As shown in the  FIG. 5B , the multiple batch measurement mode will be further described, in which a plurality of workpieces W (W 1  to W 8 ) are placed on the stage and the user can measure the plurality of workpieces by pressing the execution button once. 
     According to the  FIG. 5B , the plurality of workpieces W 1  to W 8  are scattered and placed over the whole movable stage  12 . The controller  60  (the bird&#39;s eye view image generating section  65 ) allows the bird&#39;s eye view cameras  17 R and  17 L to perform the imaging through the imaging control section  82 , and acquires the bird&#39;s eye view image. The workpiece determination section  63  roughly specifies coordinate positions (for example, center coordinates, center-of-gravity coordinates, etc.) of the respective workpieces W 1  to W 8  using the bird&#39;s eye view image. The workpiece determination section  63  measures the coordinate positions of the respective workpieces W 1  to W 8  in accordance with a predetermined rule (for example, in the order of raster scanning from the upper left to the right, in the order from the workpiece closer to the center, and the like), or in accordance with an input by the user. 
     In the detailed description, a case where the coordinate positions of the workpieces W 1 , W 2 , W 3 , . . . , W 8  are measured in this order will be described. The controller  60  allows the bird&#39;s eye view cameras  17 R and  17 L to perform the imaging through the imaging control section  82 , thereby acquiring the bird&#39;s eye view image. The controller  60  specifies the coordinate positions of the workpieces W 1 , W 2 , W 3 , . . . , W 8 . The controller  60  stores the respective coordinate positions. Thus, the controller  60  determines a measurement order. Since the workpiece W 1  is first measured, the controller  60  moves the movable stage  12  toward the coordinate position of the workpiece W 1 . When the movable stage  12  reaches the coordinate position of the workpiece W 1 , the controller  60  executes a first stage operation for searching for the workpiece W 1 . Thereafter, the controller  60  executes the second stage operation for searching the whole body (contour) of the workpiece W 1 . When the measurement of one workpiece W 1  among the plurality of workpieces is completed through the second stage operation, the controller  60  shifts to the measurement of the next workpiece. The next workpiece is W 2 . The controller  60  moves the movable stage  12  toward the coordinate position of the workpiece W 2  and performs the first stage operation for searching for the workpiece W 2 . Furthermore, the controller  60  measures the workpiece W 2  through the second stage operation for searching for the whole body (contour) of the workpiece W 2 . In the same manner, the controller  60  measures the workpieces W 3 , W 4 , . . . , W 8 . 
     In this manner, it is possible to collectively execute the measurement of the workpieces W 1  to W 8  by using the bird&#39;s eye view cameras  17 R and  17 L. 
     After reaching the workpiece W 1 , the controller  60  may execute the second stage operation for searching for the whole body (contour) of the workpiece W 1  without executing the first stage operation for searching for the workpiece W 1 . This is because the workpiece W has already been found without performing the searching operation. For example, if the workpiece W 1  has already been found, the controller  60  may omit the first stage operation and perform the second stage operation. 
     It is described above that the workpiece determination section  63  measures the coordinate positions of the respective workpieces W 1  to W 8  in accordance with the predetermined rule, or alternatively, in accordance with the input by the user; however, it is a mere example. The workpiece determination section  63  may calculate a moving route each time (for example, at the coordinate position of each of the workpieces W 1  to W 8 ) to find the shortest moving distance, and then measure the coordinate position of each of the workpieces W 1  to W 8 . For example, when the coordinate position of a certain workpiece W is measured, the workpiece determination section  63  may determine another workpiece W which is at the shortest distance from the certain workpiece W and of which the coordinate position has not yet been measured, as the next measurement target. 
     &lt;Summary&gt; 
     The movable stage  12  is an example of the stage on which the workpiece W is placed. The camera  110  is an example of the imaging section that generates the image within the imaging field-of-view on the stage. The stage driving section  101  is an example of the driving section that switches the imaging field-of-view on the stage by moving the stage relative to the imaging section in the XY direction. The stage driving section  101  may move the cameras  110  and  120  with respect to the movable stage  12 , or may move the movable stage  12  with respect to the cameras  110  and  120 . The workpiece determination section  63  is an example of the determination section that determines whether or not the workpiece is included in the image generated by the imaging section. The controller  60  and the measurement control section  62  are examples of the control section for controlling the imaging section, the driving section, and the determination section. As described with reference to S 800 , when it is determined by the determination section that the workpiece W is not included in the image, the measurement control section  62  performs the first stage operation to repeat the workpiece searching process in which the imaging section generates an image in each imaging field-of-view while moving the stage by controlling the driving section in accordance with a predetermined sequence, and the determination section determines whether or not the workpiece is included in each image. As described with reference to S 810 , when it is determined by the determination section that the workpiece W is included in the image, the measurement control section  62  performs the second stage operation to move the stage by the driving section so that the imaging section generates images in one or more imaging field-of-views located in a direction in which the workpiece W extends, among a plurality of imaging field-of-views located around the imaging field-of-view on the stage, in which the image has been obtained. When the image including the workpiece W is found in the first stage operation, the measurement control section  62  switches from the first stage operation to the second stage operation. The image joining section  64  is an example of the image joining section that joins the plurality of images generated in the second stage operation to generate the joined image including the whole workpiece W. Thus, the present invention is particularly useful in a case where the imaging magnification of the cameras  110  and  120  is higher and the workpiece W is not accommodated in the imaging field-of-views of the cameras  110  and  120 . According to the present invention, the workpiece W is detected from the image acquired by the camera  110 , and the joined image  42  including the whole workpiece W is generated based on the workpiece W. Therefore, the usability of the image measurement apparatus  1  is further improved. 
     The measurement control section  62  may adjust the imaging conditions of the imaging section based on the image when the image including the workpiece W is found in the first stage operation, and may use the adjusted imaging conditions in the second stage operation. Consequently, the workpiece W is extracted more easily, and thus the image covering the whole workpiece W is generated more easily. 
     When it is determined by the determination section that at least a part of the workpiece is not included in the imaging field-of-view, the measurement control section  62  may continue to generate the joined image according to the predetermined sequence in accordance with the imaging conditions of the imaging section. For example, the default imaging conditions may be continuously used until the workpiece W is initially found in the first stage operation. The imaging conditions may include at least one of in-focus position, optical magnification, diaphragm conditions, illumination conditions, and exposure time of the optical system of the imaging section. The in-focus position with respect to the workpiece W may be changed by, for example, moving the movable stage  12  in the Z direction with respect to the cameras  110  and  120 . 
     The measurement control section  62  may have the setting mode for setting the measurement point of the workpiece W and the measurement mode for performing measurement on the measurement point set by the setting mode. The image joining section  64  may generate the joined image  42  in the setting mode. Consequently, the user will easily set the various settings while checking the whole workpiece W using the joined image  42 . 
     The transmissive illumination  150  is an example of the transmissive illumination that irradiates the workpiece W with light from below the stage having translucency. The coaxial epi-illumination  130  is an example of the epi-illumination that irradiates the workpiece with light from above the stage. The image joining section  64  may generate the joined image  42  by joining images of the workpiece W irradiated with light by the epi-illumination. The epi-illumination helps the user to visually observe patterns on the surface of the workpiece W. The workpiece determination section  63  may determine whether or not the workpiece W is included in the image of the workpiece W irradiated with light by the transmissive illumination. The transmissive illumination helps to highlight the edges of the workpiece W. 
     The display device  11  is an example of the display section that displays the joined image  42  in the setting mode. The operation section  30  may serve as the acceptation section that accepts designation of the extraction region of the edge serving as the measurement point and the imaging conditions of the image with respect to the workpiece W included in the joined image  42  displayed on the display section. Since the imaging conditions of the camera  110  and the imaging conditions of the camera  120  are different from each other, the imaging conditions of any one of the camera  110  and the camera  120  may be designated. The setting section  61  may serve as the setting section sets the number of images required for extracting the edge serving as the measurement point based on the imaging conditions accepted by the acceptation section. 
     In the measurement mode, the searching section  66  may specify the stage coordinates of the measurement point set in the setting mode by performing the pattern searching on the joined image  42 . The measurement control section  62  may allow the imaging section to image the measurement point again using the imaging conditions set at the measurement point in the setting mode with the stage coordinates specified by the searching section  66 . The measurement section  67  and the workpiece determination section  63  may extract the edge of the measurement point using the image generated by imaging again. 
     The workpiece determination section  63  may determine the boundary portion of the workpiece W as the edge based on the luminance value in the image. That is, the contour of the workpiece W may be extracted as the edge. 
     The storage device  70  is an example of a storage section that stores information relating to the stage coordinates of each imaging field-of-view in the stage. The measurement control section  62  may determine the moving direction of the stage in the second stage operation based on stage coordinates of the imaging field-of-view of the image including at least a part of the workpiece W found in the first stage operation, and information relating to the direction in which the workpiece W extends, and information relating to the stage coordinates (for example, the grid coordinates) of each imaging field-of-view stored in the storage section. 
     The measurement control section  62  may allow the image joining section to generate the joined image while the imaging section generates the image and the driving section moves the stage in the second stage operation. The measurement control section  62  may allow the image joining section to generate the joined image after a plurality of images are completely generated by the imaging section in the second stage operation. 
     The measurement cameras  110  and  120  are examples of a first camera that images the workpiece placed on the stage and generates the workpiece image. The bird&#39;s eye view camera  17  is an example of a second camera having the imaging field-of-view wider than that of the first camera, which images the workpiece placed on the stage and generates the bird&#39;s eye view image. The workpiece determination section  63  is an example of a detection section that detects the position of the workpiece W on the stage based on the bird&#39;s eye view image. The stage driving section  101  is an example of a driving section that moves the stage relative to the first camera in an XY direction. The measurement control section  62  controls the driving section based on the position of the workpiece W detected from the bird&#39;s eye view image by the detection section so that the workpiece is located in or near the imaging field-of-view of the first camera, and allows the first camera to image the workpiece to generate the workpiece image. Moreover, the workpiece W located in or near the imaging field-of-view of the first camera means that the whole or at least a part of the workpiece W is accommodated in the imaging field-of-view. Furthermore, the workpiece W may be not located in the imaging field-of-view, but located close to the imaging field-of-view. The searching section  66  is an example of a specifying section that specifies the detailed position and the orientation of the workpiece in the workpiece image generated by the first camera. The measurement section  67  is an example of an inspection section that determines an inspection point of the workpiece W in the workpiece image based on the detailed position and the orientation of the workpiece W specified by the specifying section, and executes a predetermined inspection process. The designated regions  1101   a  and  1101   b  of the measurement points are examples of the inspection points. Since the position of the workpiece W is obtained using the bird&#39;s eye view image in this manner, the position of the workpiece W is determined in a shorter time. For example, even if the workpiece W is not placed at the center of the movable stage  12 , the position of the workpiece W can be determined in a short time. Moreover, if the plurality of workpieces W are mounted on the movable stage  12 , the position of each workpiece W can be determined in a short time. 
     The coordinate conversion section  68  is an example of a coordinate conversion section that converts the coordinates in the coordinate system of the second camera into the coordinates in the coordinate system of the first camera. The coordinate conversion section  68  may convert the coordinates of the position of the workpiece detected from the bird&#39;s eye view image by the detection section into the coordinates in the coordinate system of the first camera. The measurement control section  62  may control the driving section based on the position of the workpiece in the coordinate system of the first camera acquired by the coordinate conversion section  68 . 
     As shown in  FIG. 3 , when viewed from a stage side, the second camera may include one or more bird&#39;s eye view cameras, and may be provided in a peripheral portion of the first camera. The second camera may include a first bird&#39;s eye view camera and a second bird&#39;s eye view camera. The first camera may be provided between the first bird&#39;s eye view camera and the second bird&#39;s eye view camera when viewed from the stage side. Furthermore, the imaging field-of-view of the first bird&#39;s eye view camera and the imaging field-of-view of the second bird&#39;s eye view camera may be different. The storage device  70  may function as a storage section that stores information relating to the mounting position and the mounting orientation of the first bird&#39;s eye view camera with respect to the image inspection apparatus, and information relating to the mounting position and the mounting orientation of the second bird&#39;s eye view camera with respect to the image inspection apparatus. Such information may be stored in the storage device  70  as the calibration information  72 . The calibration section  69  is an example of a calibration section that calibrates the coordinate system of the first bird&#39;s eye view camera on the basis of the information relating to the mounting position and the mounting orientation of the first bird&#39;s eye view camera, and calibrates the coordinate system of the second bird&#39;s eye view camera on the basis of the information relating to the mounting position and the mounting orientation of the second bird&#39;s eye view camera. 
     The bird&#39;s eye view image generating section  65  is an example of a generating section that generates the bird&#39;s eye view image including the whole stage by joining the image acquired by the first bird&#39;s eye view camera and the image acquired by the second bird&#39;s eye view camera. 
     The measurement control section  62  controls the driving section so that the bird&#39;s eye view image including the whole stage is generated by joining the image acquired by the first bird&#39;s eye view camera and the image acquired by the second bird&#39;s eye view camera. Thus, the stage moves relatively to the first bird&#39;s eye view camera and the second bird&#39;s eye view camera. 
     The telecentricity of the second camera may be lower than that of the first camera. That is, the second camera may be advantageous for creating the bird&#39;s eye view image. The first camera may be advantageous for measuring the workpiece W. 
     A method of creating the bird&#39;s eye view image using two bird&#39;s eye view cameras has been described with reference to  FIG. 3 . However, it is also possible to create the bird&#39;s eye view image using a single bird&#39;s eye view camera. In this case, the wide-angle lens is employed as the optical system used in the bird&#39;s eye view camera. 
     In the method of creating the bird&#39;s eye view image described with reference to  FIG. 4 , the movable stage  12  moves so that the center between the imaging axis of the bird&#39;s eye view camera  17 L and the imaging axis of the bird&#39;s eye view camera  17 R coincide with the center of the movable stage  12 , and the bird&#39;s eye view cameras  17 L and  17 R perform the imaging. The method of creating the bird&#39;s eye view image is not limited to this.
         As shown in  FIG. 12A , the controller  60  moves the movable stage  12 .   As shown in  FIG. 12B , the controller  60  allows a bird&#39;s eye view camera  12 R to perform the imaging, thereby acquiring the partial bird&#39;s eye view image  41   a.      As shown in  FIG. 12C , the controller  60  moves the movable stage  12  in a left direction and allows a bird&#39;s eye view camera  12 L to perform the imaging, thereby acquiring the partial bird&#39;s eye view image  41   b.      As shown in  FIG. 12D , the controller  60  combines the bird&#39;s eye view image  41   a  and the bird&#39;s eye view image  41   b  to generate the bird&#39;s eye view image  41   d  showing the whole movable stage  12 .       

     As described above, since the optical systems of the bird&#39;s eye view cameras  17 L and  17 R employ the wide-angle lenses, the large distortion occurs in the peripheral portion of the imaging field-of-view as compared with the central portion of the imaging field-of-view. Therefore, the bird&#39;s eye view may be generated only from the vicinity of the center of the imaging field-of-views of the bird&#39;s eye view cameras  17 L and  17 R.
         As shown in  FIG. 13A , the controller  60  moves the movable stage  12  and allows the bird&#39;s eye view camera  12 R to perform the imaging, thereby acquiring the partial bird&#39;s eye view image  41   a.      As shown in  FIG. 13B , the controller  60  moves the movable stage  12  in the left direction and allows the bird&#39;s eye view camera  12 R to perform the imaging, thereby acquiring the partial bird&#39;s eye view image  41   b.      As shown in  FIG. 13C , the controller  60  moves the movable stage  12  in the left direction and allows the bird&#39;s eye view camera  12 L to perform the imaging, thereby acquiring the partial bird&#39;s eye view image  41   c.      As shown in  FIG. 13D , the controller  60  moves the movable stage  12  in the left direction and allows the bird&#39;s eye view camera  12 L to perform the imaging, thereby acquiring the partial bird&#39;s eye view image  41   e.      As shown in  FIG. 13E , the controller  60  moves the movable stage  12  in the left direction and allows the bird&#39;s eye view camera  12 L to perform the imaging, thereby acquiring the partial bird&#39;s eye view image  41   f.      As shown in  FIG. 13F , the controller  60  combines the bird&#39;s eye view images  41   a ,  41   b ,  41   c ,  41   d ,  41   e , and  41   f  to generate a bird&#39;s eye view image  41   d  showing the whole movable stage  12 .