Patent Publication Number: US-2023145960-A1

Title: Image projection measuring apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2020-204911 filed on Dec. 10, 2020, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The disclosure relates to an image projection measuring apparatus and particularly relates to an image projection measuring apparatus that improves working efficiency by projecting image projection data obtained through conversion onto a work to enable checking of the measurement precision while acquiring measurement data of the work on the measurement site. 
     Japanese Unexamined Patent Application Publication No. 2015-114170 discloses a three-dimensional measuring apparatus of related art. The three-dimensional measuring apparatus primarily includes a probe used to measure a work, and an articulated arm mechanism with the probe at the distal end thereof. The three-dimensional measuring apparatus is coupled to, for example, a notebook personal computer (hereinafter referred to as a “personal computer”) and causes a display of the personal computer to display image data to which measurement data is converted. An operator checks the image data displayed on the display of the personal computer and compares it with an actual work to determine whether the measuring operation is being performed with good precision. 
     SUMMARY 
     An aspect of the disclosure provides an image projection measuring apparatus including a measurer, a storage, an image projection data generator, an image projector, and an image projection controller. The measurer is configured to measure a shape of a work by illuminating an outer surface of the work with a line laser from a laser emitter. The storage is configured to store measurement data acquired by the measurer. The image projection data generator is configured to generate image projection data from the measurement data. The image projector includes a camera and is configured to project the image projection data from the camera. The image projection controller is configured to cause the image projector to project the image projection data onto the outer surface of the work. 
     An aspect of the disclosure provides an image projection measuring apparatus including a measurer, an image projector, and circuitry. The measurer is configured to measure a shape of a work by illuminating an outer surface of the work with a line laser from a laser emitter. The image projector includes a camera and is configured to project image projection data from a camera. The circuitry is configured to store measurement data acquired by the measurer. The circuitry is configured to generate the image projection data from the measurement data. The circuitry is configured to cause the image projector to project the image projection data onto the outer surface of the work. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate an example embodiment and, together with the specification, serve to explain the principles of the disclosure. 
         FIG.  1    is a perspective view of an image projection measuring apparatus according to an embodiment of the disclosure; 
         FIG.  2    is a block diagram illustrating the image projection measuring apparatus according to the embodiment of the disclosure; 
         FIG.  3    is a flowchart illustrating a measuring operation performed by the image projection measuring apparatus according to the embodiment of the disclosure; 
         FIG.  4    schematically illustrates a measuring operation performed by the image projection measuring apparatus according to the embodiment of the disclosure; 
         FIG.  5    schematically illustrates a measuring operation performed by the image projection measuring apparatus according to the embodiment of the disclosure; 
         FIG.  6    schematically illustrates how the image projection measuring apparatus according to the embodiment of the disclosure performs measurement; 
         FIG.  7    schematically illustrates how the image projection measuring apparatus according to the embodiment of the disclosure performs measurement; 
         FIG.  8    schematically illustrates how the image projection measuring apparatus according to the embodiment of the disclosure performs measurement; and 
         FIG.  9    schematically illustrates how the image projection measuring apparatus according to the embodiment of the disclosure performs measurement. 
     
    
    
     DETAILED DESCRIPTION 
     The measuring method using the three-dimensional measuring apparatus of related art described above may involve operators working in pairs. One operator brings the tip of the probe into contact with the work while operating the articulated arm mechanism to measure the shape of the work. In coordination with the operation for measuring the shape of the work, the other operator checks image data displayed on the display of the personal computer to find areas of low measurement precision and gives appropriate instructions to the one operator. 
     In this measuring method, the instructions described above may not be given in a timely manner, or the two operators may have different criteria for determining the precision of measurement data. The resulting failure in communication between the two operators may degrade working efficiency. 
     To solve the problems described above, one operator may compare the image data displayed on the display of the personal computer with the shape of the work to be measured to determine the measurement precision while performing the measuring operation on the work. To check the measurement precision during the measuring operation on the work, the operator frequently stops the ongoing measuring operation and shifts the eyes from the work to the display of the personal computer. With this measuring method, therefore, it is difficult to ensure high working efficiency. 
     Additionally, in the measuring method described above, where the operator determines the precision of the measurement data while checking the image data displayed on the display of the personal computer, the determination of precision of the measurement data may vary depending on, for example, the experience and skill of the operator. 
     The disclosure has been made in view of the circumstances described above. It is desirable to provide an image projection measuring apparatus that improves working efficiency by projecting image projection data obtained through conversion onto a work to enable checking of the measurement precision while acquiring measurement data of the work on the measurement site. 
     First, an image projection measuring apparatus  10  according to an embodiment of the disclosure will be described in detail on the basis of the drawings. Note that the following description is directed to an illustrative example of the disclosure and not to be construed as limiting to the disclosure. Factors including, without limitation, numerical values, shapes, materials, components, positions of the components, and how the components are coupled to each other are illustrative only and not to be construed as limiting to the disclosure. Further, elements in the following example embodiment which are not recited in a most-generic independent claim of the disclosure are optional and may be provided on an as-needed basis. The drawings are schematic and are not intended to be drawn to scale. Throughout the present specification and the drawings, elements having substantially the same function and configuration are denoted with the same numerals to avoid any redundant description. 
       FIG.  1    is a perspective view of the image projection measuring apparatus  10  according to the present embodiment.  FIG.  2    is a block diagram illustrating the image projection measuring apparatus  10  according to the present embodiment.  FIG.  3    is a flowchart illustrating a measuring operation performed on a work  18  by the image projection measuring apparatus  10  according to the present embodiment.  FIG.  4    and  FIG.  5    each schematically illustrate a measuring operation performed on the work  18  by the image projection measuring apparatus  10  according to the present embodiment. 
     As illustrated in  FIG.  1   , the image projection measuring apparatus  10  primarily includes a main body  11 , a measurer  12  included in the main body  11 , an image projector  13  included in the main body  11 , a grip  14  with which to operate the main body  11 , an articulated arm  15  coupled to the grip  14 , a base  16  configured to support the articulated arm  15 , and a controller  17  configured to control the image projection measuring apparatus  10 . The image projection measuring apparatus  10  is used as a measuring apparatus that measures the shape of the work  18 , such as a body panel of a vehicle. The image projection measuring apparatus  10  is also used as an image projecting apparatus that projects image projection data generated from measurement data of the work  18  using a projection mapping technique. 
     The main body  11  is, for example, a rectangular housing configured to include therein the measurer  12  and the image projector  13 . A front surface  11 A of the main body  11  has thereon a laser emitter  12 A (see  FIG.  6   ) of the measurer  12  and cameras  13 A and  13 B (see  FIG.  7   ) of the image projector  13 . The laser emitter  12 A is configured to emit a line laser L (see  FIG.  6   ). The cameras  13 A and  13 B are configured to project image projection data. 
     The measurer  12  is, for example, a non-contact laser scanner. The measurer  12  is capable of measuring the three-dimensional shape of the work  18  by illuminating the outer surface of the work  18  with the line laser L. An operator  19  moves the line laser L, for example, from the lower end toward the upper end of one side of the work  18  in a desired measuring direction, so that, for the area passed through by the line laser L, measurement data constituted by coordinate data is acquired with respect to each line laser L. The acquired measurement data is stored in a storage  21  (see  FIG.  2   ). 
     The image projector  13  is a projector device, such as a digital light processing (DLP) projector or a liquid-crystal projector. Under the control of an image projection controller  23  (see  FIG.  2   ), the image projector  13  projects image projection data generated by an image projection data generator  22  (see  FIG.  2   ) onto the outer surface of the work  18 . While described in detail below, image projection data is data for image projection and is obtained by converting the measurement data. 
     The grip  14  is coupled to a back surface  11 B of the main body  11  and is also coupled to the articulated arm  15 . That is, the grip  14  is disposed between the main body  11  and the articulated arm  15 . To perform a measuring operation, the operator  19  holds the grip  14  and moves the front surface  11 A of the main body  11 , within the range of movement of the articulated arm  15 , along the outer surface of the work  18  to be measured. 
     The articulated arm  15  is constituted, for example, by a six-axis mechanism. The articulated arm  15  is coupled at one end thereof to the grip  14  and coupled at the other end thereof to the base  16 . The articulated arm  15  is movable in various directions in conjunction with movement of the grip  14 . With the grip  14 , the operator  19  can freely move the front surface  11 A of the main body  11  along the outer surface of the work  18 . The articulated arm  15  is supported in a stable state by the base  16 . 
     The controller  17  is, for example, an electronic controller (ECU) including a central processing unit (CPU), a read-only memory (ROM), and a random-access memory (RAM) and configured to execute various computations for controlling the image projection measuring apparatus  10 . As illustrated, the image projection measuring apparatus  10  is coupled to a personal computer, which is then used as the controller  17 . 
     The storage  21  of the controller  17  illustrated in  FIG.  2    is constituted, for example, by a non-volatile memory, such as an electrically erasable programmable read-only memory (EEPROM). The storage  21  stores measurement data acquired by the measurer  12  and image projection data and obscure image projection data generated by the image projection data generator  22 . The storage  21  also stores, for example, each threshold used by a measurement data determination unit  24  to determine precision, and computer-aided design (CAD) data of the work  18 . 
     From measurement data acquired by the measurer  12 , the image projection data generator  22  of the controller  17  generates image projection data to be projected onto the outer surface of the work  18  and stores the generated image projection data in the storage  21 . As necessary, the image projection data generator  22  generates image projection data from measurement data stored in the storage  21 . The image projection data generator  22  also generates obscure image projection data and stores it in the storage  21 . The obscure image projection data is constituted by a region of the image projection data determined to be obscure by the measurement data determination unit  24 . 
     The image projection controller  23  of the controller  17  controls the storage  21  and the image projector  13  and causes the image projector  13  to project the image projection data and the obscure image projection data generated by the image projection data generator  22  onto the outer surface of the work  18 . The image projection controller  23  adjusts the angle of view and the projection direction of the cameras  13 A and  13 B (see  FIG.  7   ) of the image projector  13 , so that the image projection data and the obscure image projection data that substantially coincide with a projection region R of the work  18  (see  FIG.  6   ) are projected onto the outer surface of the work  18 . 
     The image projection data generator  22  generates image projection data, as necessary, while measurement data is being acquired by the measurer  12 . This allows the image projection controller  23  to cause the image projector  13  to project the image projection data onto the work  18  while the work  18  is being measured by the measurer  12 . 
     The measurement data determination unit  24  of the controller  17  compares image projection data with CAD data of the work  18  stored in the storage  21  and determines a region where measurement data is not acquired with good precision. As described above, the image projection data generator  22  also generates obscure image projection data constituted by a region of image projection data determined to be obscure by the measurement data determination unit  24 . While described in detail below, the image projection controller  23  causes the image projector  13  to project the obscure image projection data onto the work  18 , so that the operator  19  can clearly recognize a region where measurement data is not acquired with good precision. 
     As illustrated in  FIG.  3   , in step S 10 , the operator  19  operates an operation unit of the personal computer, which serves as the controller  17 , and stores CAD data of the work  18  to be measured in the storage  21 . Then, while checking the CAD data displayed on the display of the personal computer, the operator  19  performs a coordinate setting operation of the measurer  12  using the CAD data to complete preparation for the measurement. The coordinate setting operation allows the image projection data to be projected in such a way that it substantially coincides with the measurement region of the work  18 . 
     For example,  FIG.  4    illustrates a measuring operation performed on a vehicle&#39;s door component  18 A, which is the work  18  to be measured. In this case, the operator  19  secures the door component  18 A onto a work table  31  and stores CAD data of the door component  18 A in the storage  21 . Then, while looking at the CAD data of the door component  18 A displayed on the display, the operator  19  performs the coordinate setting operation by illuminating the upper surface of the door component  18 A with the line laser L for measurement (see  FIG.  6   ) from the measurer  12 . A finely dotted region  32  represents the line laser L. 
     In step S 11 , the operator  19  determines the sequence of measurement on the work  18 . For example, the operator  19  moves the line laser L emitted from the laser emitter  12 A of the measurer  12 , from one end toward the other end of the measurement region, to acquire measurement data of the work  18  for each line laser L and stores the acquired measurement data in the storage  21 . 
     For example, to measure the upper surface of the door component  18 A as illustrated in  FIG.  4   , the operator  19  moves the line laser L from one end to the other end of the door component  18 A in the longitudinal direction to acquire the measurement data. For example, while operating the main body  11  with the grip  14  in such a way that the upper surface of the door component  18 A is substantially parallel to the front surface  11 A of the main body  11 , the operator  19  illuminates the upper surface of the door component  18 A with the line laser L across the short side. 
     In step S 12 , the image projection data generator  22  generates image projection data from the measurement data acquired by the measurer  12  and stores the generated image projection data in the storage  21 . 
     As an exemplary method of generating image projection data, the present embodiment adopts the following method. First, the image projection data generator  22  transforms coordinate data of measurement data of the work  18  into a world coordinate system (world matrix). Next, the image projection data generator  22  transforms the world coordinate system (world matrix) into a view coordinate system (view matrix), and then transforms the view coordinate system (view matrix) into a projection coordinate system. Last, the image projection data generator  22  transforms the projection coordinate system into a screen coordinate system to generate image projection data. 
     In step S 13 , the image projection controller  23  controls the storage  21  and the image projector  13 , calls the image projection data from the storage  21 , and outputs the image projection data to the image projector  13 . The image projector  13  projects the received image projection data onto the outer surface of the work  18 . Before the projection, the image projection controller  23  identifies the projection region R (see  FIG.  6   ) of the work  18  onto which an image representing the image projection data is to be projected. The image projection controller  23  then adjusts the angle of view and the projection direction of the cameras  13 A and  13 B (see  FIG.  7   ) of the image projector  13 , so that the image projection data that substantially coincides with the measurement region of the work  18  is projected by the image projector  13 . 
     Referring to  FIG.  4   , a diagonally shaded region  33  represents the projection region R of the image projection data. The image projector  13  projects the image projection data onto a region of the upper surface of the door component  18 A where measurement has been completed by the measurer  12 . The image projection controller  23  generates image projection data of the region defined in the direction of measurement and causes the image projector  13  to project the generated image projection data onto the upper surface of the door component  18 A. The image projection controller  23  repeats the generation of image projection data and causes the image projector  13  to project the generated image projection data onto the upper surface of the door component  18 A while following the line laser L emitted from the laser emitter  12 A (see  FIG.  6   ) of the measurer  12 . 
     In step S 14 , while performing the measuring operation on the work  18  using the measurer  12 , the operator  19  checks the image projection data projected onto the outer surface of the work  18  and determines whether the measurement data is acquired with good precision. 
     For example, the image projector  13 , which is a projector device as described above, projects the image projection data onto the upper surface of the door component  18 A using a projection mapping technique. As illustrated in  FIG.  4   , the upper surface of the door component  18 A is not a simple flat surface and has, for example, protrusions. Depending on the angle of the front surface  11 A of the main body  11  with respect to the upper surface of the door component  18 A, the presence of the protrusions creates shaded regions which are not properly illuminated with the line laser L and where measurement data cannot be acquired with good precision. Depending on how the door component  18 A is illuminated and how its material is plated, even a flat surface of the door component  18 A has some regions which are not properly illuminated with the line laser L and where measurement data cannot be acquired with good precision. 
       FIG.  5    illustrates image projection data projected onto an outer surface of the work  18  (which though is not the upper surface of the door component  18 A). For example, a region marked with a circle  34  is a region where measurement data is not acquired with good precision. The image projection data is projected, for example, in blue onto a region where measurement data is acquired with good precision. As illustrated, the image projection data is superimposed on the outer surface of the work  18 . On the other hand, image projection data is not generated for a region where measurement data is not acquired with good precision, and therefore, image projection data is not projected in blue onto this region. As a result, the outer surface of the work  18  is exposed in the region where measurement data is not acquired with good precision. That is, the image projection data is partially obscured and projected in blue in a patchy manner. This enables the operator  19  to determine the precision of the measurement data while checking how the image projection data is projected. 
     In step S 14 , the operator  19  checks the image projection data projected onto the upper surface of the work  18 . If the operator  19  determines that there is a region where measurement data is not acquired with good precision (NO in step S 14 ), the process proceeds to step S 15 , where, without ending the measuring operation on the work  18 , the operator  19  remeasures the region for which it has been determined that measurement data is not acquired with good precision. The measurement data acquired by the remeasurement is stored in the storage  21 . 
     The process then returns to step S 12 , where, as described above, the image projection data generator  22  generates image projection data from the measurement data acquired by the remeasurement and stores the generated image projection data in the storage  21 . In step S 13 , the image projection controller  23  causes the image projector  13  to project the image projection data obtained through the remeasurement onto the outer surface of the work  18 . Then, in step S 14 , the operator  19  checks the projected image projection data and determines whether measurement data is acquired with good precision in the remeasured region. The image projection data generator  22  may combine the measurement data acquired by the remeasurement with the measurement data acquired by the previous measurement to generate image projection data. 
     For example, while adjusting the angle of the front surface  11 A of the main body  11  with respect to the upper surface of the door component  18 A using the grip  14 , the operator  19  measures the region for which it has been determined that the measurement data is not acquired with good precision. For the measurement, the operator  19  illuminates the region with the line laser L, for example, in a direction different from the direction of measurement in the previous measurement. Then, as described above, the operator  19  checks the image projection data projected onto the upper surface of the door component  18 A subjected to the remeasurement and determines the precision of measurement data. 
     The operator  19  checks the image projection data projected onto the upper surface of the work  18 , and if determining that all measurement data are acquired with good precision (YES in step S 14 ), the process proceeds to step S 16 , where the operator  19  ends the measuring operation on the upper surface of the work  18 . The operator  19  then performs the same measuring operation as above on unmeasured sides of the work  18  to acquire measurement data of the entire work  18 . 
     If the operator  19  determines that the upper surface of the door component  18 A has a region where measurement data is not acquired with good precision, the operator  19  repeats the remeasuring operation involving steps S 15 , S 12 , and S 13  until no such region is found. 
       FIG.  6    to  FIG.  9    schematically illustrate a measuring operation performed on the work  18  by the image projection measuring apparatus  10  according to the present embodiment. 
       FIG.  6    illustrates a measuring operation performed when the laser emitter  12 A of the measurer  12  is disposed in substantially the center of the front surface  11 A of the main body  11  and one camera  13 B of the image projector  13  is disposed below the laser emitter  12 A in the vicinity of the lower end of the front surface  11 A of the main body  11 . An arrow  41  indicates a measuring direction in which the measuring operation on the work  18  proceeds. By holding the grip  14 , for example, the operator  19  performs the measuring operation while tilting the main body  11  forward. 
     The finely dotted region  32  represents the line laser L emitted from the laser emitter  12 A of the measurer  12 , and the diagonally shaded region  33  represents the projection region R of the image projection data projected from the camera  13 B. As described above, since image projection data is generated from measurement data acquired by the measurer  12 , the projection region R of the image projector  13  is located behind the line laser L in the measuring direction. 
     To allow the projection region R to be located behind the line laser L in the configuration with one camera  13 B, the operator  19  cannot perform the measuring operation while stretching and contracting the arm to move the main body  11  back and forth. Accordingly, within the range of movement of the articulated arm  15  (see  FIG.  1   ), the operator  19  moves around the work table  31  (see  FIG.  4   ) to which the work  18  is secured. Then, while performing the measuring operation on the work  18 , the operator  19  checks the projected image projection data to determine the precision of the measurement data. 
       FIG.  7    illustrates a measuring operation performed when the laser emitter  12 A of the measurer  12  is disposed in substantially the center of the front surface  11 A of the main body  11  and two cameras  13 A and  13 B of the image projector  13  are disposed above and below the laser emitter  12 A in the vicinity of the upper and lower ends of the front surface  11 A of the main body  11 . Arrows  51  and  52  each indicate a measuring direction in which a measuring operation on the work  18  proceeds. By holding the grip  14 , for example, the operator  19  performs the measuring operation while tilting the main body  11  forward. 
     When the work  18  is measured in the direction toward the operator  19  as indicated by the arrow  51 , image projection data is projected from the camera  13 A of the image projector  13  disposed near the upper end of the main body  11 . When the work  18  is measured in the direction away from the operator  19  as indicated by the arrow  52 , image projection data is projected from the camera  13 B of the image projector  13  disposed near the lower end of the main body  11 . 
     In the configuration with two cameras  13 A and  13 B, the operator  19  stretches and contracts the arm at one position of the work table  31  having the work  18  secured thereto to move the main body  11  back and forth within the range of movement of the articulated arm  15 . Thus, while performing the measuring operation on the work  18 , the operator  19  checks the projected image projection data to determine the precision of the measurement data. 
     The configuration is not limited to the one described above, in which the two cameras  13 A and  13 B of the image projector  13  are disposed above and below the laser emitter  12 A on the front surface  11 A of the main body  11 . For example, four cameras including two cameras on the right and left sides of the laser emitter  12 A as well as the two cameras  13 A and  13 B described above may be disposed on the front surface  11 A of the main body  11 . In this case, by appropriately switching the camera used for projection, the operator  19  can perform a measuring operation while image projection data is being projected from all directions within the range of movement of the articulated arm  15 , so that working efficiency is improved. 
       FIG.  8    and  FIG.  9    schematically illustrate how image projection data is projected onto the outer surface of the work  18 .  FIG.  8    illustrates how image projection data is projected through one camera  13 A near the upper end of the front surface  11 A of the main body  11 , and  FIG.  9    illustrates how image projection data is projected through two cameras  13 A and  13 B near the upper and lower ends of the front surface  11 A of the main body  11 . 
     As illustrated in  FIG.  8   , a dotted circle  61  indicates the projection region R projected by the image projector  13 . The outer surface of the work  18  to be measured has recessed portions. As illustrated, when image projection data is projected from the camera  13 A near the upper end of the main body  11 , areas indicated by dark regions  62  are in the shade of steps created by the recessed portions. Therefore, the image projection data may not be properly projected onto the outer surface of the work  18  and may be partially unclear. 
     As a result, even when measurement data is actually acquired with good precision, such an unclear region of the image projection data may be erroneously determined, by the operator  19 , as a region where measurement data is not acquired with good precision. 
     In the configuration illustrated in  FIG.  9   , two cameras  13 A and  13 B of the image projector  13  are disposed near the upper and lower ends of the front surface  11 A of the main body  11 , with the laser emitter  12 A of the measurer  12  in substantially the center of the front surface  11 A interposed therebetween. As illustrated, the camera  13 B on the lower side projects the same image projection data as the camera  13 A on the upper side onto the projection region R indicated by the dotted circle  61 . The image projection data is thus reliably projected even onto the areas (see the dark regions  62  in  FIG.  8   ) that are in the shade of the steps. 
     As described above, the image projector  13  projects the image projection data onto the outer surface of the work  18  from at least two cameras  13 A and  13 B that are opposite, for example, in the up and down direction or in the right and left direction, with the laser emitter  12 A interposed therebetween. This prevents the occurrence of an unclear region of image projection data caused by the outer shape of the work  18 . The operator  19  can thus determine the precision of measurement data while looking at image projection data clearly projected onto the outer surface of the work  18  and can be prevented from making an erroneous determination such as that described above. 
     That is, as described with reference to  FIG.  7   , the laser emitter  12 A of the measurer  12  is disposed in substantially the center of the front surface  11 A of the main body  11 , and a plurality of cameras  13 A and  13 B of the image projector  13  are disposed around the laser emitter  12 A. Then, by projecting image projection data using at least two cameras  13 A and  13 B disposed front and back in the measuring direction, it is possible to avoid creation of blind spots, such as those created during projection with one camera. The image projection data is thus clearly projected onto the outer surface of the work  18 . 
     In the present embodiment, the image projection controller  23  causes the image projector  13  to project image projection data onto the outer surface of the work  18 . The operator  19  checks the projected image projection data, determines a region where measurement data is not acquired with good precision, and performs a remeasurement on the region. However, the disclosure is not limited to this. 
     As described with reference to  FIG.  2   , the measurement data determination unit  24  of the controller  17  determines precision of the measurement data acquired by the measurer  12 . The measurement data determination unit  24  compares the image projection data generated by the image projection data generator  22  with CAD data of the work  18  stored in the storage  21 . For example, image projection data is not generated for a region where measurement data is not acquired with good precision, and the resulting image projection data is patchy. 
     Accordingly, a threshold for density of image data in a predetermined area is set in advance. The measurement data determination unit  24  selects a patchy region with reference to CAD data, makes a determination for the region using the threshold, and determines a region where measurement data is not acquired with good precision. From image projection data, the image projection data generator  22  also generates obscure image projection data constituted by a region determined to be obscure by the measurement data determination unit  24 . 
     In step S 13  described with reference to  FIG.  3   , the image projection controller  23  controls the storage  21  and the image projector  13 , calls obscure image projection data from the storage  21 , and outputs the obscure image projection data to the image projector  13 . The image projector  13  projects the received obscure image projection data onto the outer surface of the work  18 . 
     In step S 14  described with reference to  FIG.  3   , while performing a measuring operation on the work  18  using the measurer  12 , the operator  19  can determine, if obscure image projection data is projected onto the outer surface of the work  18 , that a region onto which the obscure image projection data has been projected is a region where measurement data is not acquired with good precision. In this case, the measurement data determination unit  24  mechanically determines the precision of measurement data on the basis of the threshold set in advance. This means that the determination of precision of measurement data is made consistently without being influenced, for example, by the experience and skill of the operator, and uniform precision of measurement data is achieved. 
     Other than projecting the obscure image projection data onto a region to be determined as described above, the obscure region may be highlighted with a red circle and superimposed on the entire image projection data being projected, so as to alert the operator  19 . Various other changes can be made without departing from the scope of the disclosure. 
     In the image projection measuring apparatus according to the aspect of the disclosure, image projection data generated from measurement data of the work acquired by the measurer is projected by the image projector onto the outer surface of the work. From the image projection data projected onto the outer surface of the work, the operator can determine the precision of the measurement data. 
     With the image projection measuring apparatus according to the aspect of the disclosure, the operator can check the image projection data projected onto the work and determine the precision of the measurement data while performing a measuring operation on the work. Upon determining that there is a region where the measurement data is obscure, the operator can immediately start remeasurement of the region. This significantly improves working efficiency. 
     In the image projection measuring apparatus according to the aspect of the disclosure, the image projection data may be projected onto a region of the work substantially coinciding with a region where the measurement data is acquired. The operator can thus immediately identify a region where measurement has not been performed with good precision and can perform a remeasuring operation on the region. 
     In the image projection measuring apparatus according to the aspect of the disclosure, a plurality of cameras of the image projector may be disposed around the laser emitter of the measurer. This significantly reduces areas that are likely to become blind spots during projection. The operator can thus determine the precision of measurement data while looking at image projection data clearly projected onto the outer surface of the work. 
     In the image projection measuring apparatus according to the aspect of the disclosure, the measurement data determination unit may determine the precision of the measurement data using the image projection data. The determination of precision of measurement data can thus be made consistently without being influenced, for example, by the experience and skill of the operator. 
     The controller  17  illustrated in  FIG.  2    can be implemented by circuitry including at least one semiconductor integrated circuit such as at least one processor (e.g., a central processing unit (CPU)), at least one application specific integrated circuit (ASIC), and/or at least one field programmable gate array (FPGA). At least one processor can be configured, by reading instructions from at least one machine readable tangible medium, to perform all or a part of functions of the controller  17  including the storage  21 , the image projection data generator  22 , the image projection controller  23 , and the measurement data determination unit  24 . Such a medium may take many forms, including, but not limited to, any type of magnetic medium such as a hard disk, any type of optical medium such as a CD and a DVD, any type of semiconductor memory (i.e., semiconductor circuit) such as a volatile memory and a non-volatile memory. The volatile memory may include a DRAM and a SRAM, and the non-volatile memory may include a ROM and a NVRAM. The ASIC is an integrated circuit (IC) customized to perform, and the FPGA is an integrated circuit designed to be configured after manufacturing in order to perform, all or a part of the functions of the modules illustrated in  FIG.  2   .