Grading plate holding inspection procedure

Abstract

A graduation plate holding inspection procedure includes an image acquisition step to capture image data on the graduation plate from the camera, a range calculation step to extract a first contrast range and a second contrast range from the image data, and a contrast processing step to contrast the first contrast range with the second contrast range based on brightness or color. The contrast processing step involves calculating a difference between pixel values ​​or luminance values ​​of adjacent pixels in each of the first and second contrast ranges to contrast a magnitude of difference in the first contrast range with a magnitude of difference in the second contrast range. The relative holding between the camera and the graduation plate is inspected based on a contrast result obtained in the contrast processing step.

Description

INCLUSION BY REFERENCE

[0001] This application is based on and claims priority from patent application JP 2023-108962 A (DAS code E4C0), filed on June 30, 2023, the disclosure of which is incorporated herein by reference in its entirety. BACKGROUND OF THE INVENTION 1. Field of the Invention

[0002] The present invention relates to a graduation plate holding inspection method. 2. Description of the state of the art

[0003] Dial gauges, for example, are measuring instruments that display measured values ​​in analog form. Precision measuring instruments such as dial gauges are inspected by instrument manufacturers or inspection bodies before product shipment or periodically to ensure measurement accuracy and precise calibration.

[0004] Patent Literature 1: JP 2017-067628 A SUMMARY OF THE INVENTION

[0005] In the inspection of dial gauges, the spindle of a dial gauge to be inspected is displaced by a predetermined amount by a dial inspection device (master gauge), and the readings are compared between the dial gauge to be inspected and the master gauge to measure the reading error. However, even if this inspection method determines that a dial gauge has a reading error, it cannot be determined whether the error is caused by the dial gauge itself or by a problem with the inspection process.If there is a problem with the inspection procedure, even a gauge that originally passed inspection will fail inspection for defects in the graduation plate or the accuracy of the gauge, and this causes problems such as time and expense for investigating the cause of the problems and replacing parts that were originally unnecessary.

[0006] A purpose of the present invention is to provide a graduation plate posture inspection method for inspecting a relative posture between a camera and a graduation plate.

[0007] A graduation plate posture inspection method according to an exemplary embodiment of the present invention is a graduation plate posture inspection method for inspecting a relative posture between a camera and a graduation plate, the method comprising: an image data acquiring step for acquiring image data on the graduation plate from the camera; a region calculation step for extracting a first contrast region and a second contrast region in the image data; and a contrast processing step for contrasting the first contrast area with the second contrast area based on brightness or color, wherein the relative attitude between the camera and the graduation plate is inspected based on a contrast result in the contrast processing step.

[0008] In an exemplary embodiment of the present invention, it is preferable that the first contrast area and the second contrast area are positioned on opposite sides of each other with a center of the graduation plate or a virtual straight line passing through the center of the graduation plate between the first contrast area and the second contrast area.

[0009] In an exemplary embodiment of the present invention, it is preferred that the first contrast region and the second contrast region each include a background-colored portion of the graduation plate and a printed or engraved mark.

[0010] In an exemplary embodiment of the present invention, it is preferable that the contrast processing step includes calculating a difference between pixel values ​​or luminance values ​​of adjacent pixels in each of the first contrast range and the second contrast range to contrast a magnitude of the difference in the first contrast range with a magnitude of the difference in the second contrast range.

[0011] In an exemplary embodiment of the present invention, it is preferable that the graduation plate holding inspection method further includes: before the area calculation step is performed, a brightness adjusting step of adjusting the illumination and the camera exposure in such a manner that an exposure time of the camera is the longest within a range in which the luminance of pixels in the image data is not saturated, and that the number of pixels having a brightness above a predetermined threshold is a predetermined fixed count or more.

[0012] In an exemplary embodiment of the present invention, it is preferred that the area calculation step includes: a center point calculation step of calculating a center point of the graduation plate, and The center point calculation step includes: Calculating a line connecting a first pair of graduations at point-symmetric positions with respect to a midpoint between the first pair of graduations and a line connecting a second pair of graduations at point-symmetric positions with respect to a midpoint between the second pair of graduations; and Specify an intersection point of the line connecting the first pair of graduations and the line connecting the second pair of graduations as the center point of the graduation plate.

[0013] In an exemplary embodiment of the present invention, it is preferred that the center point calculation step includes: Searching for edge coordinates on one side of each graduation in a width direction using a predetermined algorithm and edge coordinates on the other side of the other side of the graduation in the width direction using the same algorithm with an orientation different from the predetermined algorithm; and Calculating the line connecting each pair of graduations by setting a midpoint between the edge coordinates on one side and the edge coordinates on the other side as the midpoint coordinates of a width of each graduation and connecting the midpoint coordinates of each pair of graduations.

[0014] A graduation plate holding inspection program according to an exemplary embodiment of the present invention, causing a computer to execute: an image data acquiring step for acquiring image data on a graduation plate from a camera; a region calculation step for extracting a first contrast region and a second contrast region in the image data; and a contrast processing step for contrasting the first contrast area with the second contrast area based on brightness or color, wherein a relative attitude between the camera and the graduation plate is inspected based on a contrast result in the contrast processing step.

[0015] A graduation plate posture inspection device according to an exemplary embodiment of the present invention is a graduation plate posture inspection device that inspects a relative posture between a camera and a graduation plate, the device comprising: an image data acquisition unit that acquires image data on the graduation plate from the camera; an area calculation unit that extracts a first contrast area and a second contrast area in the image data; and a contrast processing unit that contrasts the first contrast area with the second contrast area based on brightness or color, wherein the relative attitude between the camera and the graduation plate is inspected based on a contrast result by the contrast processing unit.

[0016] In an exemplary embodiment of the present invention, it is preferable that a base plate extending from a stand part holding a measuring device to be inspected including the graduation plate to be inspected is provided, and the camera is installed on the base plate.

[0017] In an exemplary embodiment of the present invention, it is preferable that the tripod part is installed on a master gauge to enable a relative position and posture of the measuring device to be inspected, the master gauge and the camera to be fixed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a system configuration diagram showing a measuring instrument inspection device; Fig. 2 shows a functional block diagram illustrating an arithmetic processor device; Fig. 3 is a block diagram illustrating a graduation plate position checking unit; Fig. 4 is a flowchart for explaining an overall flow of a graduation plate holding inspection process; Fig. 5 is a flowchart for explaining a procedure of a brightness adjustment step; Fig. 6 is a flowchart showing an area calculation step; Fig. 7 is a flowchart showing a procedure for calculating the center point of a graduation plate; Fig. 8 is a flowchart for explaining a procedure for calculating a center coordinate value of a graduation in the width direction; Fig. 9 is a flowchart for explaining the procedure for calculating the center coordinate value of the graduation in the width direction; Fig. 10 is a flowchart for explaining a procedure of a contrast area extraction step; Fig. 11 is a flowchart for explaining a procedure of a contrast processing step; Fig. 12 is a flowchart for explaining a flow of a filter processing step; Fig. 13 is a flowchart for explaining a procedure of an inclination determining step; Fig. 14 is a diagram showing an example of the procedure for calculating the center point of the graduation plate; Fig. 15 shows an enlarged view of a graduation; Fig. 16 is a diagram illustrating examples of a first contrast area and a second contrast area; Fig. 17 is a diagram schematically illustrating a change in luminance difference when a one-dimensional difference filter is applied along a graduation line crossing in the longitudinal direction; Fig. 18 is a diagram illustrating an example of a guide display; and Fig. 19 is a diagram illustrating an example of the guide display. DETAILED DESCRIPTION

[0018] An embodiment of the present invention will be illustrated and described with reference to the reference numerals assigned to the elements in the figures. (First exemplary embodiment)

[0019] A measuring device inspection apparatus according to a first exemplary embodiment of the present invention will be described below.

[0020] A measuring device inspection device 100 inspects a measuring device 10 that displays a measured value in analog form, for example, with a disc-shaped graduation plate 200 and a rotating pointer, such as an (analog display type) dial gauge. (Dial gauges may be referred to as indicators or test indicators.)

[0021] The precision measuring instrument 10, such as a dial gauge, is periodically inspected by gauge manufacturers or inspection bodies to ensure measurement accuracy and precise calibration. The gauge inspection device 100 according to the present exemplary embodiment inspects whether the installation posture of the gauge inspection device 100 and the gauge 10 is appropriate (performs a graduation plate posture inspection) before inspecting the gauge 10 itself (performs a defect inspection or a reading error inspection of the disc-shaped graduation plate 200).

[0022] Fig. 1 shows a system configuration diagram illustrating the measuring device inspection apparatus 100.

[0023] The gauge inspection device 100 includes a master gauge 20 serving as a reference for gauge readings, a tripod part 30 for installing the gauge 10 to be inspected on the master gauge 20, a camera 40 imaging an analog display unit 200 of the gauge 10 to be inspected, an illumination unit 50 illuminating the analog display unit 200 of the gauge 10 to be inspected, and an arithmetic processor device 300.

[0024] The master gauge 20 includes a reference spindle 22 that moves forward and backward and a precisely calibrated high-precision encoder (displacement detector) 23. The reference spindle 22 displaces a contact point 11 of the measuring device 10 to be inspected, and the high-precision encoder 23 detects the displacement of the reference spindle 22. The difference between the reading of the master gauge 20 (the detection value of the high-precision encoder 23) and the reading of the measuring device 10 to be inspected is the error of the measuring device 10 to be inspected.

[0025] In the present exemplary embodiment, the measuring device inspection apparatus 100 includes the master gauge 20 assuming that a reading error inspection is to be performed after a graduation plate holding inspection and a graduation plate defect inspection. However, if the graduation plate defect inspection is performed only as an inspection of the measuring device 10 and the reading error inspection using the master gauge 20 is not performed, the master gauge 20 is not required. That is, the master gauge 20 is an additional element in the present invention and is not essential.

[0026] The stand part 30 includes a column 31 and a console part 32. The column 31 is installed on a cover part 21 of the master gauge 20, and the console part 32 is provided to be movable along the column 31. The console part 32 includes an arm part that extends orthogonally to the column 31 and holds the measuring device 10 to be inspected at the tip of the arm part. In particular, a part of the measuring device 10 to be inspected (in Fig. 1 the shaft of the scale measuring device) is held at the tip of the console part 32.

[0027] When the master gauge 20 is not used, a so-called tripod is prepared, which includes the column 31 provided standing on a base, and the tripod (base) is installed on a workbench or the like.

[0028] The camera 40 includes an optical lens system and an image sensor, such as a CCD or CMOS. The camera 40 is installed to image the graduation plate 200 of the measuring device 10 to be inspected from the front. That is, the camera 40 is installed to image the graduation plate 200 of the measuring device 10 to be inspected, which is held by the tripod part 30, from the front. In the present exemplary embodiment, the camera 40 is fixedly installed, and it is assumed that the relative posture and relative position between the camera 40 and the measuring device 10 to be inspected are adjusted by adjusting the orientation (tilt) and position of the measuring device 10 to be inspected. Since the ultimate goal is to adjust the posture so that the camera 40 and the measuring device 10 to be inspected (graduation plate 200) face each other, the orientation (tilt) and position of the camera 40 may also be adjustable.

[0029] Here, the fact that the camera 40 and the measuring device 10 (graduation plate 200) ideally face each other means that the graduation plate 200 is orthogonal to the optical axis of the camera 40, with the surface of the graduation plate 200 being considered a plane. It can also be said that the normal of the graduation plate 200 and the optical axis of the camera 40 are parallel.

[0030] The illumination unit 50 is, for example, a ring illumination and illuminates the graduation plate 200 of the measuring device 10 to be inspected in such a way that uneven luminance due to shadows does not occur.

[0031] In the present exemplary embodiment, a long plate-shaped base plate 33 is attached to the column 31 of the tripod part 30, and the camera 40 and the illumination unit 50 are installed on the base plate 33. That is, a lighting installation stand 34 and a camera installation stand 35 are provided on the base plate 33 to firmly install the illumination unit 50 and the camera 40 with respect to the tripod part 30 that holds the measuring device 10 to be inspected. Preferably, the lighting installation stand 34 and the camera installation stand 35 can move back and forth or left and right to the extent that their positions can be adjusted with respect to the base plate 33, and their positions can be fixed with set screws or the like.

[0032] When the tripod part 30 is installed on the master gauge 20, the relative position and posture between the master gauge 20, the measuring device 10 to be inspected, the illumination unit 50, and the camera 40 can be fixed. When inspecting the accuracy of the measuring device 10 to be inspected, the accuracy can be inspected in various postures, such as vertical, horizontal, and inverted postures. In this case, the master gauge 20 and the measuring device 10 to be inspected are tilted to a horizontal posture, rotated to an inverted posture, or changed to various other postures. In this case, the illumination unit 50 and the camera 40 are moved together with the master gauge 20, the tripod part 30, and the measuring device 10 to be inspected. Therefore, once the brightness and posture are adjusted, there is no need to readjust them even if the inspection posture is changed.

[0033] In the present exemplary embodiment, it is assumed that the base plate 33 is attached to the column 31 at a right angle, the camera installation stand 35 is attached to the base plate 33 at a right angle, and the camera 40 is attached to the camera installation stand 35 at a right angle. Thus, when the measuring device 10 to be inspected (for example, a scale measuring device) is attached to the stand part 30, the vertical axis of the measuring device 10 to be inspected (the axis parallel to the spindle and the shaft) is orthogonal to the optical axis of the camera 40. In the present exemplary embodiment, the inclination in the left-right direction (rotation using the axis parallel to the spindle and the shaft as the rotation axis) is to be checked. The method in the present exemplary embodiment can also be applied to the vertical direction to correct the inclination in the vertical and horizontal directions.

[0034] The arithmetic processing device 300 is typically a small computer with a keyboard, a mouse, a microphone, a display, a printer, and a speaker built into or outside the computer body as input / output devices. Alternatively, the arithmetic processing device 300 may be a tablet device or a smartphone (portable high-performance phone).

[0035] Fig. 2 shows a functional block diagram illustrating the arithmetic processor device 300.

[0036] The arithmetic processor device 300 includes a central processing unit (CPU), a memory (ROM, RAM), and the like, and performs functions of functional units through the CPU, which executes an inspection program. The inspection program can be distributed by recording it on a non-volatile recording medium (a CD-ROM, a memory card, or the like) or by downloading it via an Internet connection or the like.

[0037] The arithmetic processor device 300 includes an inspection execution unit 310 that performs various inspections of the measuring device 10. The inspection execution unit 310 includes a graduation plate position checking unit 400, a graduation plate defect detection unit 320, and a display value defect evaluation unit 330.

[0038] Here, the graduation plate posture inspection unit 400 inspects the relative posture between the camera 40 and the graduation plate 200 from the image data on the graduation plate 200 imaged by the camera 40. Details of this will be described later.

[0039] The graduation plate defect detection unit 320 detects defects such as distortions, scratches, missing graduations, and graduation intervals on the graduation plate 200 from the image data on the graduation plate 200 imaged by the camera 40.

[0040] At this time, if the graduation plate 200 is tilted relative to the camera 40, the graduation plate 200 or the graduations cannot be accurately inspected based on the image data. That is, even if there is an error in the graduation plate 200 or the graduations in the image data, it is necessary to distinguish whether the error exists in the measuring device to be inspected itself or whether the image data is originally distorted. The display value error evaluation unit 330 evaluates the discrepancy between the display value of the master gauge 20 (detection value of the high-precision encoder 23) and the display value of the measuring device 10 to be inspected. At this time, it is assumed that the analog display unit 200 of the measuring device 10 to be inspected is imaged by the camera 40, and the display value is automatically read from the image data.In this case, if the graduation plate 200 is tilted relative to the camera 40, the image data will exhibit parallax for the tilt amount, and the reading of the pointer's reading will exhibit a discrepancy. If there is a discrepancy between the reading of the pointer of the measuring device 10 under inspection and the reading of the master gauge 20, it is necessary to distinguish whether the discrepancy is due to a fault in the internal mechanism of the measuring device 10 under inspection or a parallax problem at the time of image data acquisition.

[0041] Since the measuring device 10 to be inspected displays a measured value with a resolution of the order of micrometers, if the relative posture between the camera 40 and the measuring device 10 to be inspected deviates by approximately 5° from the facing posture, this will interfere with graduation plate defect detection or indication value error evaluation. According to the inventors' verification, it is considered ideal to keep the deviation of the relative posture between the camera 40 and the measuring device 10 to be inspected within 3°. Such a deviation of 3° or 5° is imperceptible to the human eye. For this reason, a graduation plate posture inspection step is performed before graduation plate defect detection or indication value error evaluation.

[0042] Fig. 3 shows a block diagram illustrating the graduation plate position checking unit 400.

[0043] The graduation plate position checking unit 400 includes a brightness adjustment unit 410, an image data acquisition unit 420, an area calculation unit 430, a contrast processing unit 440, and a guide unit 450. The area calculation unit 430 includes a center calculation unit 431 and a contrast area extraction unit 432. The contrast processing unit 440 includes a filter processing unit 441 and an inclination determination unit 442.

[0044] The operation of each functional unit is described later with reference to a flowchart.

[0045] A flow of a graduation plate holding inspection method according to the first embodiment will be described sequentially. Before performing the graduation plate holding inspection method, an operator installs the measuring device 10 to be inspected on the tripod part 30 and adjusts the measuring device 10 to be inspected and the camera 40 to be opposite each other as far as possible. The camera 40 can be focused on the graduation plate 200 of the measuring device 10 to be inspected, the illumination and exposure can be set to preset standard settings, and automatic adjustment (automatic focus and exposure adjustment) of the camera 40 can be enabled as an initial adjustment. The installation (replacement) of the measuring device 10 to be inspected on the tripod part 30 and the setup of the camera 40 can be automated by a robot instead of manual work by the operator.

[0046] Fig. 4 is a flowchart for explaining an overall flow of the graduation plate holding inspection method according to the first embodiment.

[0047] As in Fig. 4, the graduation plate holding inspection method includes a brightness adjustment step ST1000, an imaging step ST2000, an area calculation step ST3000, a contrast processing step ST4000, and a guide display step ST5000.

[0048] The steps are described below in order.

[0049] Fig. 5 shows a flowchart for explaining a procedure of the brightness adjustment step ST1000.

[0050] Considering the following steps, it is desirable that the image data on the graduation plate 200 utilize the widest possible luminance range. Therefore, the illumination and exposure are adjusted in such a way that the image data is brightened to the limit within a range where the luminance of the pixels in the image data is not saturated.

[0051] First, the brightness of the illumination unit 50 is set to a predetermined initial value (ST1100), and the exposure time of the camera 40 is set to a minimum (ST1200). Minimizing the exposure time of the camera 40 means minimizing the exposure time within the specifications of the camera 40, in other words, setting the shutter speed to the fastest possible speed. Setting the brightness of the illumination unit 50 to the initial value can be considered, for example, as setting the current or voltage value to be applied to the illumination unit 50 to a predetermined initial value. Alternatively, an illuminometer can be placed near the measuring device 10 to be inspected, and the current value (voltage value) applied to the illumination unit 50 can be automatically adjusted to achieve a preset illuminance.With this setting, the graduation plate 200 of the measuring device 10 to be inspected is imaged as an attempt to acquire image data (ST1300). The acquired image data is recorded in the image data acquisition unit 420.

[0052] In the test image data, it is checked whether there are pixels with saturated luminance values ​​(ST1400). If there are no pixels with saturated luminance values ​​(ST1400: NO), the exposure time of camera 40 is increased by one unit (ST1500). One unit of the exposure time of camera 40 is appropriately set in units of 1 / 1000 second, 1 / 100 second, or 1 / 10 second, taking into account the specifications of camera 40, the inspection accuracy of graduation plate 200, and the time required for inspection. Since the exposure of camera 40 is set to a minimum, the luminance is not saturated from the beginning, and imaging is repeated as one trial (ST1300) while increasing the exposure time of camera 40 (ST1500) until the first pixel with a saturated luminance value appears (ST1400).

[0053] When the first pixel with a saturated luminance value appears (ST1400: YES), the exposure time is reduced by one unit from the exposure time at that point (ST1600). This means that the exposure time is now set to the maximum exposure time within the range where the luminance of the pixels in the image data is not saturated.

[0054] With this illumination and exposure time adjustment, it is checked whether the image data exceeds a predetermined standard brightness (ST1700). The luminance distribution (histogram) of the image data is calculated, and the number of pixels with a brightness (luminance value) above a predetermined threshold is counted. If the count exceeds a predetermined number, it is assumed that the brightness adjustment was successful. If the number of pixels with a brightness (luminance value) above the predetermined threshold is insufficient, the brightness of the illumination unit 50 is increased by one unit (the applied current value or the illumination intensity is increased) (ST1800), and the process returns to ST1200 to perform the brightness adjustment again.

[0055] This brightness setting ensures that the luminance distribution of the image data is optimal every time and that the posture inspection is stable every time.

[0056] If the brightness adjustment is successful (ST1000), the procedure returns to the flow chart in Fig. 4, and the graduation plate 200 is imaged by the camera 40 (image sensor) to acquire image data (ST2000) and record the image data in the image data acquisition unit 420 as image data for inspection.

[0057] Since graduation plate image data has been acquired for inspection, the relative posture between the graduation plate 200 and the camera 40 is inspected based on the graduation plate image data. For the inspection, a contrast region extraction step (ST3500 in Fig. 6) is performed to extract a first contrast region and a second contrast region to be contrasted in the image data. The first contrast region and the second contrast region are regions in the image data that are in a point symmetry relationship with the center of the graduation plate 200 as the center of symmetry, or are regions positioned on opposite sides of each other with a virtual straight line passing through the center of the graduation plate 200 therebetween, as shown in Fig. 16. By contrasting the pixel value (color and luminance) in the first contrast range with that in the second contrast range, the relative attitude of the camera 40 and the graduation plate 200 is checked.

[0058] Fig. 6 is a flowchart for explaining a procedure for extracting the contrast areas (the area calculation step ST3000).

[0059] When calculating the contrast areas (area calculation step ST3000), the center point of the graduation plate 200 in the image data is first calculated (a center point calculation step ST3100). There are various methods for calculating the center point of the graduation plate 200. For example, by viewing the graduation plate 200 in the image data as a circle, the center of the circle can be calculated. In addition, the external shape of the graduation plate (circle) 200 can be extracted by image recognition to calculate the center point of the circle from multiple points on the circumference. When the graduation plate 200 is tilted with respect to the camera 40, the graduation plate 200 is strictly speaking imaged as an ellipse, but this distortion is very small, and the center point can be calculated by viewing the ellipse as a circle.Even if the graduation plate 200 is considered as an ellipse, the center point can be calculated from the intersection of the major diameter and the minor diameter.

[0060] Here, considering that the graduations of the graduation plate 200 are one of the important elements in the subsequent graduation plate error detection and display value error evaluation, the center point of the graduation plate 200 is calculated based on the graduations with a procedure (the center point calculation step ST3100) in the flowchart in Fig. 7 calculated.

[0061] Fig. 14 is a diagram illustrating an example of the center point of the graduation plate 200, and reference is also made thereto.

[0062] By detecting two graduations parallel to the y-axis from the graduation plate image data in two-dimensional Cartesian coordinates (x, y), a 0° graduation and a 180° graduation are found (ST3200) (see Fig. 14). In addition, by detecting two graduations parallel to the x-axis from the graduation plate image data in two-dimensional Cartesian coordinates (x, y), a 90° graduation and a 270° graduation are found (ST3200). Then, the center coordinates of the 0° graduation in the width direction are calculated, and the center coordinates of the 180° graduation in the width direction are calculated (ST3300). Similarly, the center coordinates of the 90° graduation in the width direction are calculated, and the center coordinates of the 270° graduation in the width direction are calculated (ST3300).

[0063] Once the center coordinates of each graduation in the latitude direction are calculated, the center coordinates of the 0° graduation and the center coordinates of the 180° graduation are connected to form a y1 line. Similarly, the center coordinates of the 90° graduation and the center coordinates of the 270° graduation are connected to form an x1 line. The intersection point of the y1 line and the x1 line is set as the center point of the graduation plate 200 (ST3400).

[0064] However, since the graduations each have a width, the coordinate value of the center point of the width of each graduation is used as the graduation position (ST3300). For example, if the center point of the width of the graduation is set to 0°, the center point of the coordinate value of the left edge of the graduation and the coordinate value of the right edge of the graduation are used. To prevent the center point coordinates from shifting to either the left or right side within the graduation width, the left edge and the right edge are searched using the same procedure and the same threshold.

[0065] Fig. 8 and Fig. 9 show flowcharts for explaining a procedure for calculating the center coordinate value of a graduation in the width direction. Here, the case of calculating the center coordinate value of the 0° graduation in the width direction is described as an example. Fig. Figure 15 shows an enlarged view of the graduation, and reference is also made to it. The same procedure can be applied to the case of calculating the center of the graduation width at 180°. In addition, by changing the orientation (exchanging the x-axis with the y-axis), the same procedure can be applied to the case of calculating the center of the graduation width at each of 90° and 270°.

[0066] In ST3311, a line parallel to the x-axis is extracted from a 0° graduation area. The graduation parallel to the y-axis and on the positive side of the y-axis (or the graduation with the larger y-coordinate value) is recognized as the 0° graduation. Since the background is white and the graduation is black, the area of ​​pixels with a luminance of less than half (128) of the maximum luminance (255), for example, can be set as a graduation area. Alternatively, the area of ​​pixels with a luminance of less than 0.7 (179) of the maximum luminance (255) can be set as the graduation area, or the area of ​​pixels with a luminance of less than 0.65 (166) can be set as the graduation area. Here, the graduation area includes both the graduation itself and the background around the graduation.In other words, the graduation area is defined as the area in which a graduation crossing line, which will be described later, can cross from the background to the graduation to the background.

[0067] Then, to calculate the center coordinate value of the graduation width (here, the width in the x-direction), a line crossing the graduation area in a direction (parallel to the x-direction) orthogonal to the graduation and parallel to the y-direction is extracted. This line is called the graduation crossing line. Fig. 15, the graduation crossing line is shown as a long line for clarity.

[0068] The graduation crossing line is only required to safely cross the graduation, and there are no particular restrictions on where on the graduation the line crosses (which line is extracted). Here, as an example, a line that crosses the center of the graduation area in the y direction (the center of the graduation in the vertical direction) is extracted.

[0069] For the graduation crossing line extracted in this way, the same algorithm with different orientations is used to search for the coordinates of the left edge (the coordinates of the edge in the direction where the x-coordinate value is small) and the coordinates of the right edge (the coordinates of the edge in the direction where the x-coordinate value is large). First, the coordinates of the left edge (the coordinates of the edge in the direction where the x-coordinate value is small) in ST3312 to ST3320 are Fig. 8 wanted.

[0070] In ST3312, the pixel with the smallest x-coordinate value on the graduation crossing line is set as the pixel of interest, and the luminance value of this pixel of interest is detected. The detected luminance value is represented as L0.

[0071] In ST3313, a stability counter N is reset to 0 (zero). The stability counter N is described later.

[0072] In ST3314, the pixel of interest is moved one pixel to the positive side in the x-direction (adjacent pixel on the positive side), and the luminance value of this new pixel of interest is detected, which is represented as L(k) using an index number k. Here, the new pixel of interest is represented as L1. In ST3315, the luminance difference L(k) - L(k - 1), specifically L1 - L0, between two adjacent pixels in the x-direction is calculated, and the magnitude of the luminance difference |L1 - L0| is compared with a preset stability determination threshold to determine whether the luminance difference |L1 - L0| ≤ stability determination threshold is satisfied. Satisfying the luminance difference |L1 - L0| ≤ stability determination threshold concludes that the pixel of interest is not located on the transition boundary between the background and the pitch, but is located on or within the pitch.If the luminance difference |L1 - L0| ≤ stability determination threshold is satisfied, the stability count N is incremented by 1 (N = N + 1) (ST3317). Until the stability count N reaches a preset stability count threshold (for example, 5) (ST3318), ST3314 to ST3318 are repeated while moving the pixel of interest in the positive direction of the x-direction (ST3319, ST3314). If the luminance difference L(k) - L(k - 1) of neighboring pixels is continuously stable and the number of stability counts N reaches the stability count threshold (for example, 5), the coordinate value of the pixel of interest at that time (here, the x-coordinate value) is stored as the left side edge coordinates ELmin.

[0073] Failure to satisfy the luminance difference |L1 - L0| ≤ stability determination threshold (ST3315:NO) concludes that the pixel of interest is located on the transition boundary between the background and the pitch and not on the pitch, therefore the stability count is reset to zero (ST3313) and the search continues.

[0074] In Fig. 9, ST3321 to ST3329 are the procedure for searching for the right edge coordinates (the coordinate of the edge in the direction where the x coordinate value is large).

[0075] The difference between ST3312 and ST3320 in Fig. 8 is that the search is performed from right to left (from a larger x-coordinate value to a smaller x-coordinate value). First, in ST3312, the pixel with the largest x-coordinate value in the graduation crossing line is set to the pixel of interest, and the luminance value L0 of this pixel of interest is acquired (ST3321). Then, in ST3323, the luminance value L(j) of the neighboring pixel on the negative side is acquired. When searching for the right edge coordinates (the flowchart in Fig. 9) an index number j is used. For the other procedures, both the stability determination threshold and the stability count are the same as in ST3312 to ST3320 in Fig. 8. The same algorithm with different orientation is used to search for the right edge coordinates, and the searched right edge coordinates are stored as right edge coordinates ELmax (ST3329).

[0076] The center coordinate value CLx of the graduation is the midpoint between the left edge coordinates ELmin and the right edge coordinates ELmax, that is, (ELmin + ELmax) / 2 (ST3330).

[0077] In this way, by searching for the edges from both the left and right sides using the same method, any deviation in center point detection within the width of the graduation is eliminated.

[0078] Alternatively, two or more graduating crossing lines may be extracted, and the center coordinate values ​​of these lines in the width direction may be calculated to determine the mean value.

[0079] The center point of the graduation plate 200 has been calculated at this point (ST3100), and the contrast area extraction step (ST3500) is performed, returning to the flowchart in Fig. 6 (the area calculation step ST3000).

[0080] Fig. 10 is a flowchart for explaining a procedure of the contrast area extraction step (ST3500). Fig. 16 shows a diagram illustrating an example of the first contrast area and the second contrast area, and reference will also be made to it. In ST3510, the previously calculated center coordinate value of the graduation plate 200 is read. Then, an area of ​​a predetermined size including the graduation on the negative side in the x-direction from the center point is extracted (ST3520). (The area is searched for the negative side along the line parallel to the x-axis passing through the center point to find the 270° graduation.) This area is set as the first contrast area (ST3530). Here, the area including the graduation at 270° is the first contrast area. As this contrast area, the area assumed to include both the graduation and the background is extracted.

[0081] Next, a region of the predetermined size is extracted at a position symmetrical to the first contrast region (ST3540). This region is set as the second contrast region (ST3550). Here, it is assumed that the first contrast region and the second contrast region are point-symmetrical with respect to the center point, but also line-symmetrical with respect to a virtual line parallel to the y-axis and passing through the center point.

[0082] It is checked whether the first contrast area and the second contrast area each contain the background and the graduation (ST3560). Since the graduation plate 200 is circular, the two graduations are positioned symmetrically with respect to the center point, and the first contrast area and the second contrast area each contain the graduation and the background as long as the second contrast area is extracted symmetrically with respect to the first contrast area. If at least one of the first contrast area and the second contrast area does not contain both the graduation and the background (ST3560: NO), the extraction is retried by expanding the extraction area range (ST3570). If the first contrast area and the second contrast area are not successfully extracted after a predetermined number of retries, an error notification is performed, and the procedure is suspended.

[0083] After the first contrast area and the second contrast area are extracted, the contrast processing step (ST4000) of contrasting the first contrast area with the second contrast area based on the luminance is performed, referring to the flowchart in Fig. 4 (the graduation plate holding inspection procedure). Fig. 11 is a flowchart showing a flow of the contrast processing step (ST4000). The contrast processing step (ST4000) includes a filter processing step (ST4100) of performing filter processing (in this case, difference filtering) on ​​the first contrast area and the second contrast area to obtain the luminance difference in each contrast area, and an inclination determination step (ST4200) of comparing the luminance difference data obtained in the filter processing step (ST4100) to evaluate the inclination of the graduation plate 200.

[0084] Fig. 12 shows a flowchart for explaining the operation of the filter processing step. The filter processing step ST4100 includes a first contrast luminance difference calculation step (ST4110) of performing filter processing on the first contrast region to obtain a first contrast luminance difference, and a second contrast luminance difference calculation step (ST4120) of performing filter processing on the second contrast region to obtain a second contrast luminance difference. The first contrast luminance difference calculation step (ST4110) and the second contrast luminance difference calculation step (ST4120) have different calculation objectives but the same processing content.

[0085] In the first contrast luminance difference calculation step (ST4110), the maximum value among the luminance differences of respective adjacent pixels in each row of the first contrast region is first calculated (ST4111). Since the first contrast region is the region containing the 270° graduation, and the 270° graduation is parallel to the x-axis, a line that crosses the graduation longitudinally along the x-direction is referred to as a longitudinally crossing graduation line. Fig. 16 is also referred to. A one-dimensional difference filter is applied to each graduation line that intersects in the longitudinal direction. For example, the pixel value (luminance value) of each pixel is multiplied by (1, -1) along the x-direction to calculate the luminance difference between the pixel of interest and its neighboring pixel. Fig. Figure 17 shows a diagram schematically illustrating the change in the luminance difference when the one-dimensional difference filter is applied along the graduation line crossing in the longitudinal direction, and reference will also be made to it. For example, if the luminance value of the pixel of interest is L1 and the luminance value of its neighboring pixel is L2, the luminance difference DL is |L1 - L2|. Finally, it is sufficient to contrast the "magnitude" of the luminance difference obtained in the first contrast region with that in the second contrast region, and the luminance difference is regarded here as the magnitude (absolute value) of the luminance difference. For each line (each graduation line crossing in the longitudinal direction), a maximum value of the luminance difference DLmax is calculated.

[0086] When calculating the maximum value of the luminance difference DLmax in the first contrast luminance difference calculation step (ST4110), only one line (graduation line crossing in the longitudinal direction) can be used for the calculation, but it is desirable to calculate the maximum value of the luminance difference DLmax for each of multiple lines (graduation lines crossing in the longitudinal direction). Then, in ST4112, the average of the calculated multiple maximum values ​​of the luminance differences DLmax is calculated to be used as a first contrast luminance difference DL1 (ST4112).

[0087] For the second contrast area (in this case, the area containing the 90° graduation), the maximum value DLmax among the luminance differences of respective adjacent pixels in each line is also calculated (ST4121), and the average of the maximum values ​​DLmax is calculated to be used as a second contrast luminance difference DL2 (ST4122).

[0088] Since the first contrast luminance difference DL1 in the first contrast area and the second contrast luminance difference DL2 in the second contrast area are calculated in the filter processing step ST4100, the inclination determination step (ST4200) is performed next, and the flowchart in Fig. 11 (the contrast processing step ST4000). As shown in the flow chart in Fig. As shown in Figure 13, first, the difference between the first contrast luminance difference DL1 in the first contrast region and the second contrast luminance difference DL2 in the second contrast region is calculated to be used as a difference in luminance differences ΔDL (= DL1 - DL2) (ST4210). If the magnitude |ΔDL| of the difference in luminance differences ΔDL is less than or equal to a preset tilt determination threshold (ST4220: YES), it means that the left and right sides of the graduation plate 200 are imaged similarly and that the graduation plate 200 has no tilt (or a tilt within the acceptable range) (ST4230).

[0089] On the other hand, if the difference between the first contrast luminance difference DL1 and the second contrast luminance difference DL2 is larger (ST4220: NO), it is determined that the graduation plate 200 is tilted with respect to the optical axis of the camera 40. The larger difference between the first contrast luminance difference DL1 and the second contrast luminance difference DL2 means that there is a difference in the sharpness of the left and right graduations in the image data. However, since the focus of the camera 40 is on the graduation plate 200, which means that the graduation plate 200 is in focus within the depth of field range, there is a difference in the sharpness between the left and right graduations in detail.Although the difference may be small, this causes a difference in the recognition of the graduations and the pointer on the left and right sides in the image data when the graduation error inspection and display value error inspection are subsequently performed based on the image data.

[0090] If the magnitude |ΔDL| of the luminance difference ΔDL exceeds the tilt determination threshold, the first contrast luminance difference DL1 and the second contrast luminance difference DL2 are stored. The first contrast luminance difference DL1 can be compared with the second contrast luminance difference DL2 to store which is larger (or smaller).

[0091] Additionally, in ST4250, the magnitude of the luminance difference ΔDL (= DL1 - DL2) is converted into the tilt amount. This can be tabulated by calculating the relationship between the magnitude of the tilt angle of the graduation plate 200 with respect to the camera's optical axis and the magnitude of the luminance difference ΔDL in advance through preliminary experiments. Alternatively, instead of strictly converting the luminance difference ΔDL into tilt angles at 0.1° intervals, an evaluation index can be used that classifies the luminance difference ΔDL into, for example, 10 levels according to magnitude.

[0092] Next, the guidance display step (ST5000) will be described. In the guidance display step (ST5000), the inclination (or inclination level) of the graduation plate 200 is visualized and displayed on a display device (monitor) to provide the operator with assistance for adjusting the posture of the graduation plate 200. Fig. 18 and Fig. 19 show examples of the guidance display. In the examples in Fig. 18 and Fig. 19, the graduation plate 200 is displayed on the monitor screen, and the balance of the inclination of the graduation plate 200 is indicated by the lengths of bars with colors (for example, blue and yellow) below the graduation plate 200. When the graduation plate 200 has no inclination, the left (yellow) bar and the right (blue) bar are the same length, as in Fig. 19. When the graduation plate 200 has a tilt, the lengths of the left and right bars are changed to represent the magnitude of the tilt. Here, the bar on the side with the smaller luminance difference (the first contrast luminance difference DL1 or the second contrast luminance difference DL2) is expressed longer. The operator refers to this guide display, adjusts the posture of the graduation plate 200, and repeats the graduation plate posture inspection several times so that the graduation plate 200 reaches the Fig. 19. This allows the measuring device 10 to be installed such that the graduation plate 200 directly faces the camera 40, and the operator confirms that the graduation plate 200 and the camera 40 face each other.

[0093] It was not possible to strictly determine whether the graduation plate 200 and the camera 40 were facing each other simply by visually observing the measuring device 10 (graduation plate 200) or by visually observing the image data obtained by imaging the measuring device 10 (graduation plate 200) on the screen. Therefore, it was not possible to install the graduation plate 200 such that the graduation plate 200 and the camera 40 were strictly facing each other. For this reason, even the measuring device 10 that originally passed inspection failed the inspection for defects in the graduation plate 200 or the accuracy of the measuring device 10, and this caused problems such as time and cost for investigating the cause of the problems and replacing parts that were originally unnecessary.In this regard, the inventors carefully investigated why the inspection for defects in the graduation plate 200 or the accuracy of the measuring device 10 is often unsuccessful, and after careful investigation, they realized that the basis of the problem is the installation posture of the measuring device 10 (graduation plate 200) and the camera 40. Therefore, the present invention was made to strictly inspect the relative posture between the camera 40 and the graduation plate 200 by paying attention to the pixel values ​​or the difference in pixel values ​​(difference in pixel values ​​of adjacent pixels) in the contrast areas (the first contrast area and the second contrast area) at symmetrical positions.

[0094] The present invention is not limited to the above exemplary embodiment and can be appropriately modified without departing from the gist.

[0095] The graduation plate 200 may be an analog graduation plate (analog scale meter) with graduations engraved or printed on an actual plate, or a graduation plate displayed on a digital display panel, such as an LCD or OLED panel.

[0096] In the above exemplary embodiment, the contrast is performed using graduations that are point-symmetric with respect to the center of the graduation plate 200 or symmetric with respect to a virtual line passing through the center, but marks (for example, numbers, symbols, or the like) at symmetrical positions may be used instead of graduations.

[0097] Although a one-dimensional difference filter is used in the above description, the processing is not limited to this as long as it can emphasize the pixel value (luminance value) of the boundary between the background of the graduation plate and the print on the graduation plate (for example, marks such as graduations).

[0098] In the above exemplary embodiment, luminance values ​​are used as pixel values, but color tones (black and white tones or RGB tones) can be used for contrast. 100 measuring device inspection device 10 Measuring device (measuring device to be inspected) 200 graduation plate 12 hands 11 Contact point 20 Mastergauge 21 Lid part 22 Reference spindle 23 encoders 30 Tripod part 31 Column 32 Console part 33 Base plate 34 Lighting installation tripod 35 Camera installation tripod 40 Camera 50 lighting units 300 arithmetic processor unit 310 Inspection Execution Unit 400 Graduation Plate Position Testing Unit 410 Brightness adjustment unit 420 Image data acquisition unit 430 Area calculation unit 431 Center calculation unit 432 Contrast area extraction unit 440 Contrast processing unit 441 Filter processing unit 442 Inclination determination unit 450 guide unit QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2023-108962 A

[0001] JP 2017-067628 A

[0004]

Claims

[1] A graduation plate posture inspection method for inspecting a relative posture between a camera and a graduation plate, the method comprising: an image data acquiring step for acquiring image data on the graduation plate from the camera; a region calculation step for extracting a first contrast region and a second contrast region in the image data; and a contrast processing step for contrasting the first contrast area with the second contrast area based on brightness or color, wherein the relative attitude between the camera and the graduation plate is inspected based on a contrast result in the contrast processing step. [2] The graduation plate holding inspection method according to claim 1, wherein the first contrast area and the second contrast area are positioned on opposite sides of each other with a center of the graduation plate or a virtual straight line passing through the center of the graduation plate between the first contrast area and the second contrast area. [3] The graduation plate holding inspection method according to claim 1, wherein the first contrast area and the second contrast area each include a background colored portion of the graduation plate and a printed or engraved mark. [4] The graduation plate holding inspection method according to claim 1, wherein the contrast processing step comprises calculating a difference between pixel values or luminance values of adjacent pixels in each of the first contrast area and the second contrast area to contrast a magnitude of the difference in the first contrast area with a magnitude of the difference in the second contrast area. [5] The graduation plate holding inspection method according to claim 1, further comprising: before the area calculation step is performed, a brightness adjusting step of adjusting the illumination and the camera exposure in such a manner that an exposure time of the camera is the longest within a range in which the luminance of pixels in the image data is not saturated, and that the number of pixels having a brightness above a predetermined threshold is a predetermined fixed count or more. [6] The graduation plate holding inspection method according to claim 1, wherein the area calculating step comprises: a center point calculation step of calculating a center point of the graduation plate, and The center point calculation step includes: Calculating a line connecting a first pair of graduations at point-symmetric positions with respect to a center point of the graduation plate and a line connecting a second pair of graduations at point-symmetric positions with respect to a center point of the graduation plate; and Specify an intersection point of the line connecting the first pair of graduations and the line connecting the second pair of graduations as the center point of the graduation plate. [7] The graduation plate posture inspection method according to claim 6, wherein the center point calculation step comprises: Searching for edge coordinates on one side of each graduation in a width direction using a predetermined algorithm and edge coordinates on the other side of the other side of the graduation in the width direction using the same algorithm with an orientation different from the predetermined algorithm; and Calculating the line connecting each pair of graduations by setting a midpoint between the edge coordinates on one side and the edge coordinates on the other side as the midpoint coordinates of a width of each graduation and connecting the midpoint coordinates of each pair of graduations. [8] Recording medium storing a graduation plate holding inspection program that causes a computer to execute: an image data acquiring step for acquiring image data on a graduation plate from a camera; a region calculation step for extracting a first contrast region and a second contrast region in the image data; and a contrast processing step for contrasting the first contrast area with the second contrast area based on brightness or color, wherein a relative attitude between the camera and the graduation plate is inspected based on a contrast result in the contrast processing step. [9] A graduation plate posture inspection device configured to inspect a relative posture between a camera and a graduation plate, the device comprising: an image data acquisition unit configured to acquire image data on the graduation plate from the camera; a region calculation unit configured to extract a first contrast region and a second contrast region in the image data; and a contrast processing unit configured to contrast the first contrast range with the second contrast range based on brightness or color, wherein the relative attitude between the camera and the graduation plate is inspected based on a contrast result by the contrast processing unit. [10] Graduation plate holding inspection device according to claim 9, wherein a base plate extending from a tripod part configured to hold a measuring device to be inspected including the graduation plate to be inspected, and the camera is installed on the base plate. [11] The graduation plate holding inspection device according to claim 9, wherein the tripod part is installed on a master gauge to enable a relative position and posture of the gauge to be inspected, the master gauge and the camera to be fixed.

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