JP6665549B2 - Tire contact surface analysis device, tire contact surface analysis system, and tire contact surface analysis method - Google Patents

Description

  The present invention relates to a tire contact surface analysis device, a tire contact surface analysis system, and a tire contact surface analysis method.

  2. Description of the Related Art A pneumatic tire (hereinafter, simply referred to as a "tire") comes into contact with a moving body such as a vehicle to move on a target surface, for example, a road surface. It is the only one that transfers power from the source to the target surface. Therefore, the performance of the tire has a great influence on the kinetic performance of the vehicle. Tire performance includes, for example, evaluation items such as noise performance, friction performance, steering stability performance, and braking performance, and these evaluation items change depending on tire contact characteristics. The tire contact characteristics include a contact area, an average pressure based on a load applied and a contact area, a maximum contact length in a tire circumferential direction (contact length direction), and a maximum contact width in a tire width direction (contact width direction). In order to accurately determine these tire contact characteristics, the tire contact shape when the tire comes into contact with the target surface, particularly the contour line that constitutes the tire contact surface when the tire comes into contact with the target surface, is determined, and the contact area is determined. It is important to obtain the value with high accuracy.

  Therefore, conventionally, a technique has been proposed in which image analysis of tire contact image data is performed to determine a tire contact shape, and a tire contact characteristic is determined. For example, Patent Document 1 discloses that a captured image of a tire tread is binarized based on a threshold set for luminance, and an inflating process and an eroding process are performed on the binarized image. A technique for determining a ground contact shape is described.

JP-A-5-196557

  Here, when analyzing the contact area by determining the tire contact shape, the shape of the groove in the contact area is also an important factor. Since the luminance of the ground contact image is different between the position where the tire is actually in contact with the ground and the position corresponding to the groove bottom in the contact region, the shape of the groove is extracted by binarizing the contact image based on the luminance. be able to. However, the groove may be chamfered at the opening, and the brightness of the chamfered portion is different from that of the groove bottom portion. May not be extracted. In this case, since the shape of the groove to be extracted is different from the shape of the actual groove, there is a problem that the analysis accuracy when analyzing the ground contact area is reduced.

  The present invention has been made in view of the above, and provides a tire tread analysis device, a tire tread analysis system, and a tire tread analysis method capable of reducing an analysis error in analyzing a tread region. The purpose is to:

  In order to solve the above-described problems and achieve the object, a tire contact surface analysis device according to the present invention includes a contact surface image acquisition unit that acquires an image of a contact surface of a pneumatic tire, and the contact surface image acquisition unit. A groove extracting unit that extracts a groove of the pneumatic tire from the acquired ground contact surface image, wherein the groove extracting unit sets a scan line on the ground contact surface image, and the scan line In the case where the average luminance in the region where is located is the land local luminance, and a value obtained by subtracting a certain value from the land local luminance is the groove local luminance, the luminance of the center pixel of the scan line and the groove are obtained. A brightness comparison unit that compares the local brightness, and when the brightness of the center pixel is smaller than the groove local brightness, the brightness is a predetermined length in both directions in the length direction of the scan line from the center pixel. Contact And determining a maximum luminance position in a range in both directions by scanning the surface image and extracting the luminance, and determining a range surrounded by the two maximum luminance positions as the groove. Features.

  Further, in the tire ground contact surface analysis device, the scan line setting unit includes, as the scan line, a circumferential scan line set in a direction extending along a tire circumferential direction of the pneumatic tire; It is preferable to set a width direction scanning line set in a direction extending along the tire width direction.

  Further, in the tire ground contact surface analysis device, the determination unit may determine a position where both of the two maximum luminance positions have a luminance equal to or higher than a luminance value obtained by adding a predetermined luminance value to the land portion local luminance. In this case, it is preferable that a range surrounded by the two maximum luminance positions is determined as the groove.

  Further, in the tire contact surface analysis device, the determination unit, of the two maximum luminance positions, only one of the maximum luminance positions, added a predetermined luminance value to the land local luminance. When the position has a luminance equal to or higher than the luminance value, it is preferable that a range surrounded by the maximum luminance position and the center pixel is determined as a component of the groove.

  In the tire contact surface analysis device, a total contact region calculation unit that determines a total contact region from the contact surface image, and the total contact region determined by the total contact region calculation unit, extracted by the groove extraction unit. And a real ground contact area calculation unit that obtains the real ground contact area by removing the groove.

  Further, in order to solve the above-described problems and achieve the object, a tire contact surface analysis system according to the present invention includes the tire contact surface analysis device, a transparent plate for pressing the pneumatic tire, and pressing the transparent plate. A plurality of light sources for irradiating the ground plane, and a photographing unit for photographing the ground plane via the transparent plate.

Further, to solve the problem described above and achieve the object, a tire contact surface analysis method according to the present invention includes the steps of acquiring an image of the ground surface of the pneumatic tire, the scan line with respect to contact the ground image Setting the average luminance in the area where the scanning line is located as the land local luminance, and subtracting a constant value from the land local luminance as the groove local luminance, the scanning line, Comparing the luminance of the central pixel with the local luminance of the groove, and when the luminance of the central pixel is smaller than the local luminance of the groove, in each of the two directions in the length direction of the scan line from the central pixel. The ground plane image is scanned at a predetermined length to extract the luminance, and the maximum luminance position in each of the scanned two-direction ranges is determined, and is surrounded by the two maximum luminance positions. And determining the circumference as the groove of the pneumatic tire, characterized in that it comprises a.

  ADVANTAGE OF THE INVENTION The tire contact surface analysis apparatus, the tire contact surface analysis system, and the tire contact surface analysis method according to the present invention have an effect that an analysis error in analyzing a contact region can be reduced.

FIG. 1 is a configuration diagram illustrating a tire ground contact surface analysis system according to the embodiment. FIG. 2 is a block diagram illustrating functions of the tire tread surface analysis device illustrated in FIG. 1. FIG. 3 is a flowchart showing a processing procedure when analyzing the contact surface with the tire contact surface analysis device according to the embodiment. FIG. 4 is an explanatory diagram of a ground contact surface image. FIG. 5 is a flowchart illustrating a processing procedure for extracting a groove. FIG. 6 is an explanatory diagram of a scanning line. FIG. 7 is a flowchart illustrating a processing procedure for performing the groove extraction processing. FIG. 8 is a detailed view of a portion A in FIG. FIG. 9 is an explanatory diagram of the center pixel. FIG. 10 is an explanatory diagram of the local maximum luminance and the maximum luminance position. FIG. 11 is an explanatory diagram of a case where the determination is performed without using the land local luminance + α. FIG. 12 is a diagram showing the correspondence between the position in the tire circumferential direction of FIG. 11 and the luminance. FIG. 13A is an explanatory diagram of how a scanning line advances. FIG. 13B is an explanatory diagram of how a scanning line advances. FIG. 13C is an explanatory diagram of how a scanning line advances. FIG. 13D is an explanatory diagram of how a scanning line advances. FIG. 13E is an explanatory diagram of how a scanning line advances. FIG. 14A is an explanatory diagram of how a scanning line in the width direction advances. FIG. 14B is an explanatory diagram of how the scanning line in the width direction advances. FIG. 14C is an explanatory diagram of how the scanning line in the width direction advances. FIG. 14D is an explanatory diagram of how the scanning line in the width direction advances. FIG. 14E is an explanatory diagram of how the scanning line in the width direction advances. FIG. 15 is an explanatory diagram of a groove image. FIG. 16 is an explanatory diagram of the contraction processing. FIG. 17 is an explanatory diagram of the expansion processing. FIG. 18 is an explanatory diagram of the total contact area image. FIG. 19 is an explanatory diagram of the actual ground area image. FIG. 20 is a modified example of the process performed by the tire contact surface analysis device according to the embodiment, and is an explanatory diagram in a case where lug grooves and main grooves are extracted by different methods.

  Hereinafter, embodiments of a tire contact surface analysis device, a tire contact surface analysis system, and a tire contact surface analysis method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by the embodiment. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art, and those that are substantially the same.

[Embodiment]
FIG. 1 is a configuration diagram illustrating a tire ground contact surface analysis system according to the embodiment. FIG. 2 is a block diagram illustrating functions of the tire tread surface analysis device illustrated in FIG. 1. In these figures, FIG. 1 schematically shows the entire configuration of the tire contact surface analysis system, and FIG. 2 shows main functions of the tire contact surface analysis device.

  The tire tread analysis system 1 according to the present embodiment is applied to a system that analyzes the tread 61 by acquiring an image of the tread 61 of the pneumatic tire. The tire contact surface analysis system 1 includes a tire testing machine 2, an imaging device 10, and a tire contact surface analysis device 20 (see FIG. 1).

  The tire testing machine 2 is a device that gives test conditions to a test tire 60 that is a pneumatic tire to be tested. In the configuration of FIG. 1, the tire testing machine 2 has a supporting device 3 and a driving device 5. The support device 3 is a device that rotatably supports the test tire 60 and has a rim 4 on which the test tire 60 is mounted. The driving device 5 is a device for applying a driving force to the test tire 60, and includes a motor 6 for driving the test tire 60 and a motor control device 7 for driving and controlling the motor 6.

  In the tire testing machine 2, the supporting device 3 mounts and supports the test tire 60 on the rim 4, and presses the test tire 60 against the upper surface 11 </ b> U, which is one main surface of the transparent plate 11 of the driving device 5. A load is applied to 60. In addition, the support device 3 adjusts the positional relationship between the test tire 60 and the transparent plate 11 by displacing the rim 4 to give the test tire 60 a slip angle or an angle. The drive device 5 can drive the motor 6 by the motor control device 7 to rotate the rim 4 by a predetermined angle. Thereby, the rolling state of the tire when the vehicle is running is reproduced with the surface of the transparent plate 11 as the road surface. Further, the test conditions can be changed by adjusting the load, the rotational speed, the slip angle, the angle, and the like by the support device 3 and the drive device 5.

  The transparent plate 11 is a light transmitting plate having a property of transmitting light. The transparent plate 11 does not need to transmit 100% of the light, and it is sufficient that the transparent plate 11 has a light transmittance that allows the surface of the tire to be photographed through the transparent plate 11. The transparent plate 11 is, for example, a flat plate made of acrylic resin or a flat plate made of glass. Since the contact state between the test tire 60 and the flat plate is photographed and image-analyzed, a more realistic contact state of the tire can be analyzed.

  The imaging device 10 includes a camera 15 that is an imaging unit that captures an image of the test tire 60 and an illumination lamp 16 that is a light source. The camera 15 is configured by, for example, a CCD (Charge Coupled Device) camera. The camera 15 captures an image of the test tire 60 via the transparent plate 11, thereby capturing an image of the contact surface 61 of the test tire 60 pressed against the transparent plate 11. More specifically, the camera 15 is disposed on the lower surface 11D side, which is the other main surface of the transparent plate 11, so that the optical axis is orthogonal to the lower surface 11D side, and a test is performed from the lower surface 11D side via the transparent plate 11. The tire 60 is photographed. Thereby, the camera 15 captures an image of the test tire 60 including at least the contact surface 61 and generates digital image data of the test tire 60 including the contact surface 61.

  The illumination lamp 16 is a lamp that illuminates the shooting range of the camera 15, and is configured by, for example, a halogen lamp. A plurality of the illumination lamps 16 are provided, and the grounding surface 61 of the test tire 60 pressed against the transparent plate 11 is placed on the lower surface 11D side of the transparent plate 11 via the transparent plate 11 or the transparent plate 11. Irradiation is performed from between the upper surface 11U side and the test tire 60. The plurality of illumination lamps 16 are respectively provided at positions other than the position where the transparent plate 11 that moves as the test tire 60 is rotated by the support device 3 moves.

  The number of these lighting lamps 16 may be varied according to the conditions of the test performed by the tire testing machine 2. For example, when the groove of the test tire 60 is not chamfered, it is not necessary to irradiate light in consideration of the chamfer, and therefore, the number of the illumination lamps 16 may be relatively small. On the other hand, when the groove of the test tire 60 is chamfered, since the luminance of the chamfered portion and the tread surface need to be greatly different, the number of the illumination lamps 16 is increased and the Irradiation with light is preferred. Further, these illumination lamps 16 may be of a constant lighting type or of a flash lighting type.

  The tire contact surface analysis device 20 is, for example, a PC (Personal Computer) in which a predetermined analysis program is installed, and processes an image of the test tire 60 input from the photographing device 10 to analyze the contact surface 61 of the test tire 60. Perform the following processing. The process of analyzing the contact surface 61 of the test tire 60 includes a process of calculating the contact surface 61 based on the captured image of the test tire 60. The tire contact surface analysis device 20 includes a processing device 30 that performs arithmetic processing such as analysis of the contact surface 61 and saves data, an input unit 21 where an operator performs an input operation to the tire contact surface analysis device 20, and an analysis result. And a display unit 22 for displaying various information. A keyboard or a pointing device such as a mouse is used for the input unit 21, and a display device such as a liquid crystal display is used for the display unit 22. The input unit 21 and the display unit 22 are electrically connected to the processing device 30, so that the tire contact surface analysis device 20 allows the operator to perform an input operation on the input unit 21 while visually recognizing the display unit 22. Has become possible. In addition, the camera 15 is connected to the processing device 30 of the tire contact surface analysis device 20, whereby the tire contact surface analysis device 20 can acquire an image captured by the camera 15.

  The processing device 30 included in the tire contact surface analysis device 20 includes a processing unit 31 having a CPU (Central Processing Unit) and the like, and a storage unit 50 such as a RAM (Random Access Memory). The processing unit 31 and the storage unit 50 configured as described above may be provided in the same housing, may be provided in different housings, or the plurality of storage units 50 may be provided in both forms. It may be provided.

  The processing unit 31 included in the processing device 30 functionally includes a contact surface image acquisition unit 32, a groove extraction unit 33, a total contact region calculation unit 38, and an actual contact region calculation unit 39. Among these, the contact surface image acquisition unit 32 acquires a contact surface image 80 (see FIG. 4) which is an image of the contact surface 61 of the test tire 60. Further, the groove extracting unit 33 can extract the groove 65 (see FIG. 4) of the test tire 60 from the contact surface image 80 acquired by the contact surface image acquiring unit 32. Further, the total contact area calculation unit 38 obtains the total contact area 85 (see FIG. 18) from the contact surface image. Further, the actual contact area calculation unit 39 obtains an actual contact area 87 (see FIG. 19) by removing the groove 65 extracted by the groove extraction unit 33 from the total contact area 85 obtained by the total contact area calculation unit 38.

  The groove extracting unit 33 includes a scanning line setting unit 34, a luminance comparing unit 35, a determining unit 36, and a groove image generating unit 37. The scanning line setting unit 34 sets a scanning line 70 (see FIGS. 6 and 14A) for the ground plane image 80. In addition, the luminance comparing unit 35 performs scanning when the average luminance in the area where the scanning line 70 is located is defined as the land local luminance, and a value obtained by subtracting a constant value from the land local luminance is determined as the groove local luminance. The luminance of the center pixel 74 of the line 70 (see FIG. 9) is compared with the groove local luminance. When the luminance of the center pixel 74 is smaller than the local luminance of the groove, the determination unit 36 scans the ground plane image 80 with a predetermined length from the center pixel 74 in each of the two longitudinal directions of the scanning line 70. Then, the maximum luminance position in each of the scanned ranges is determined, and the range surrounded by the two maximum luminance positions is determined as the groove 65. The groove image generation unit 37 generates a groove image (see FIG. 15) that is an image of the groove 65 extracted from the ground contact surface image 80 by combining the elements determined as the grooves 65 by the determination unit 36.

  The analysis program used in the tire contact surface analysis device 20 is stored in the storage unit 50 in advance, and when analyzing the contact surface 61 of the test tire 60, the program stored in the storage unit 50 is processed by the processing unit. Each function is executed by calling at 31 and executing the operation according to the program at the processing unit 31.

  The tire contact surface analysis system 1 and the tire contact surface analysis device 20 according to the present embodiment are configured as described above, and the operation thereof will be described below. When the contact surface 61 of the test tire 60 is analyzed by the tire contact surface analysis system 1, the test tire 60 is mounted on the support device 3 of the tire testing machine 2, and the test tire 60 is pressed against the transparent plate 11. While rotating or stopped, the camera 15 captures an image of the ground contact surface 61. At this time, the test tire 60 is photographed in a state where it is irradiated with light from a plurality of illumination lamps 16 from a plurality of directions. For this reason, the camera 15 can photograph the test tire 60 with a difference in luminance between the contact surface 61 and a portion other than the contact surface 61. The photographed image is acquired by the tire contact surface analysis device 20, and the tire contact surface analysis device 20 analyzes the contact surface 61 based on the acquired image.

  Next, a processing procedure when the tire contact surface analysis device 20 analyzes the contact surface 61 will be described. FIG. 3 is a flowchart showing a processing procedure when analyzing the contact surface with the tire contact surface analysis device according to the embodiment. FIG. 4 is an explanatory diagram of a ground contact surface image. When analyzing the contact surface 61 with the tire contact surface analysis device 20, first, a contact surface image 80 which is an image of the contact surface 61 of the test tire 60 is obtained (step ST11). The camera 15 photographs the test tire 60 pressed against the transparent plate 11 through the transparent plate 11, and obtains the image photographed by the camera 15 with the tire contact surface analysis device 20, thereby converting the photographed image. It is acquired as the ground plane image 80. The acquisition of the contact surface image 80 is performed by the contact surface image acquisition unit 32 included in the processing unit 31 of the processing device 30.

  Since the contact surface image 80 acquired by the contact surface image acquisition unit 32 is obtained by simply photographing the test tire 60 from the contact surface 61 side, the contact surface image 80 includes an area other than the contact surface 61 in the test tire 60. ing. The contact surface image 80 is acquired by the contact surface image acquiring unit 32 as an image whose luminance is represented by 256 gradations, for example. In the case where the contact surface 61 is photographed while rotating the test tire 60, the contact surface image acquisition unit 32 transmits the acquired contact surface image 80 to the storage unit 50, and stores the acquired contact surface image 80 one by one.

  Next, the groove 65 is extracted from the ground contact surface image 80 (step ST12). The groove 65 in this case is defined as a groove 65 that is recessed from the tire plane in the tread portion of the test tire 60. The groove 65 includes a lug groove 66 extending in the tire width direction and a main groove 67 extending in the tire circumferential direction. The extraction of these grooves 65 from the ground contact surface image 80 is performed by the groove extraction unit 33 included in the processing unit 31 of the processing device 30.

  FIG. 5 is a flowchart illustrating a processing procedure for extracting a groove. FIG. 6 is an explanatory diagram of a scanning line. When the groove extraction unit 33 extracts the groove 65 from the ground plane image 80, first, the scanning line 70 is set for the ground plane image 80 (step ST21). This setting is performed by the scanning line setting unit 34 included in the groove extracting unit 33. The scanning line 70 includes a circumferential scanning line 71 extending in the tire circumferential direction and scanning in the tire circumferential direction, and a width scanning line 72 extending in the tire width direction and scanning in the tire width direction (see FIG. 14A). . Among them, the circumferential scanning line 71 can extract the lag groove 66, and the width scanning line 72 can extract the main groove 67.

  The length of each of the circumferential scanning line 71 and the width scanning line 72 is at least twice as long as the maximum groove width of the groove 65 to be extracted. It has a width of one pixel. The groove width in this case is the width of the groove 65 with respect to the direction in which the scanning line 70 extends, and regardless of the inclination angle of the groove 65 in the tire circumferential direction or the tire width direction, the width of the lug groove 66 in the tire circumferential direction. And the width of the main groove 67 in the tire width direction. The extraction of the lag groove 66 using the circumferential scanning line 71 and the extraction of the main groove 67 using the width scanning line 72 are performed by the same method. However, in the following description, the scanning line 70 is used. The method of extracting the groove 65 will be described using the circumferential scanning line 71 as a representative.

  The circumferential scanning line 71 is set in a direction extending along the tire circumferential direction of the test tire 60 in the contact surface image 80 with respect to the contact surface image 80. The length is longer than the groove width of the lug groove 66. For example, in the case where the ground contact surface image 80 is an image composed of 1200 vertical pixels × 1600 horizontal pixels, the length of the circumferential scanning line 71 is long. The length is set at about 150 pixels. Since the width of the circumferential scanning line 71 is one pixel, the circumferential scanning line 71 extends as long as 150 pixels in the tire circumferential direction and forms a scanning line 70 having a width of one pixel in the tire width direction. This is set for the ground image 80.

  The scanning line 70 scans while moving on the image in one direction, and after moving from one end to the other end of the image, moves to an adjacent row and repeats scanning while moving in one direction again, so-called, Perform a raster scan. Therefore, when the groove 65 is extracted by the scanning line 70, the scanning line 70 is extracted while scanning near the corner of the image as a scanning start position. Therefore, when the scan line 70 is set by the scan line setting unit 34, the scan line 70 is actually set near one corner in the ground contact surface image 80. However, a method of extracting the groove 65 using the scan line 70 will be described. Therefore, in the following description, a case where the scanning line 70 is set on the groove 65 will be described.

  When the scanning line 70 is set in the ground contact surface image 80, the groove 65 is extracted using the scanning line 70 (step ST22). FIG. 7 is a flowchart illustrating a processing procedure for performing the groove extraction processing. FIG. 8 is a detailed view of a portion A in FIG. When performing the process of extracting the groove 65 on the ground contact surface image 80, first, a luminance calculation line 76 is set (step ST31). The luminance calculation line 76 is a line for calculating the land local luminance. The land local luminance is the average luminance in the scanning line 70 and the area in the vicinity thereof, that is, the average luminance in the area where the scanning line 70 is located, and the average luminance of the land 68 in the area where the scanning line 70 is located. Has become. The luminance calculation line 76 is set to have the same length as the length of the scanning line 70, and is shifted by one pixel from the scanning line 70 with respect to the scanning line 70 at each of both sides in the width direction of the scanning line 70. Set to position. That is, two luminance calculation lines 76 are set on each side of the scanning line 70 in the width direction, and a total of four lines are set. Accordingly, in the circumferential scanning line 71, two luminance calculation lines 76 are set on one side of the circumferential scanning line 71 in the tire width direction, and a total of four luminance calculation lines 76 are provided on both sides of the circumferential scanning line 71 in the tire width direction. Set. The area where the four luminance calculation lines 76 set on both sides in the width direction of the scanning line 70 are located is an area 77 near the scanning line 70. In addition, although the luminance calculation lines 76 are set to two lines on each side of the scanning line 70, that is, four in total, the luminance calculation lines 76 may be set to other numbers.

  Next, the determination unit 36 determines whether or not there is a scanning line 70 and a luminance calculation line 76 which are off the ground plane image 80 (step ST32). If it is determined that there is a scan line 70 or a luminance calculation line 76 that protrudes from the contact surface image 80 (step ST32, Yes determination), the process exits from the flow of the groove 65 extraction process. That is, when the scanning line 70 or the brightness calculation line 76 is protruding from the ground plane image 80, the extraction processing of the groove 65 is not performed at the current position of the scanning line 70.

  On the other hand, when it is determined that there is no scanning line 70 and no luminance calculation line 76 that protrude from the ground contact surface image 80 (step ST32, No determination), the land local luminance is calculated (step ST33). The land part local luminance is an area where the scanning line 70 is located on the ground plane image 80, and uses luminance information of a pixel located in a luminance calculation area 78 which is an area composed of the scanning line 70 and the neighboring area 77. calculate. That is, the average value of the pixels located in the luminance calculation area 78 is calculated, and the average value is set as the land-local luminance.

  In addition, since the land local luminance is the local luminance of the land 68, when calculating the land local luminance, the pixel corresponding to the groove 65 on the ground contact surface image 80 is excluded. Is preferred. Specifically, since the pixel corresponding to the groove 65 has low luminance, the pixel corresponding to the groove 65 is excluded by excluding the pixel whose luminance is lower than a predetermined threshold, and is excluded from the calculation of the average luminance. For example, when the luminance is represented by 256 gradations, the low luminance pixels having a luminance of 40 or less are excluded from the calculation of the average luminance, and the pixels corresponding to the grooves 65 are excluded from the calculation of the average luminance. exclude.

  Further, since the luminance of the non-grounded area 82 (see FIG. 6) is significantly different from the luminance of the grounded area 81, when calculating the land-local luminance, pixels corresponding to the non-grounded area 82 are also excluded. Preferably, the average brightness is calculated. Specifically, since the pixels corresponding to the non-grounded area 82 have higher luminance than the pixels corresponding to the grounded area 81 (see FIG. 6), pixels having a luminance higher than a predetermined threshold are excluded. , The pixel corresponding to the non-ground area 82 is excluded from the calculation of the average luminance. For example, when the luminance is represented by 256 gradations, the high luminance pixels having a luminance of 160 or more are excluded from the calculation of the average luminance, so that the pixels corresponding to the non-ground area 82 are excluded and the average luminance is calculated. Exclude from calculation.

  After the land local luminance is calculated, it is determined whether the luminance of the center pixel 74 of the scanning line 70 is smaller than the groove local luminance (step ST34). FIG. 9 is an explanatory diagram of the center pixel. The center pixel 74 of the scanning line 70 is a pixel located at the center in the length direction of the scanning line 70. In the circumferential scanning line 71, a pixel located at the center of the circumferential scanning line 71 in the tire circumferential direction. It has become. The groove local luminance is obtained by subtracting a fixed value from the land local luminance. When the luminance is represented by 256 gradations, for example, 30 is subtracted from the land local luminance. The obtained luminance is defined as the groove local luminance at the current position of the scanning line 70.

  The groove extracting unit 33 extracts the luminance of the central pixel 74 of the scanning line 70, and compares the luminance of the central pixel 74 with the local luminance of the groove by the luminance comparing unit 35. As a result of the comparison, when it is determined that the luminance of the center pixel 74 of the scanning line 70 is not smaller than the local luminance of the groove (step ST34, No determination), the process exits the flow of the groove 65 extraction processing. That is, when the luminance of the center pixel 74 is not smaller than the groove local luminance, it can be determined that the center pixel 74 at the current position of the scanning line 70 is not at the position corresponding to the groove 65, and thus the current scanning line At the position 70, the extraction processing of the groove 65 is not performed.

  On the other hand, when it is determined that the luminance of the central pixel 74 of the scanning line 70 is smaller than the groove local luminance (step ST34, Yes determination), the central pixel 74 is set as a component of the groove 65 in the storage unit. At step ST35, a local maximum luminance is extracted by scanning in both directions in the length direction of the scanning line 70 with the center pixel 74 as a base point, and a local maximum luminance is obtained.

  FIG. 10 is an explanatory diagram of the local maximum luminance and the maximum luminance position. When it is determined that the luminance of the central pixel 74 is smaller than the groove local luminance, scanning is performed from the central pixel 74 in a predetermined range in the length direction of the scanning line 70 to extract luminance and perform scanning. The maximum brightness within the range is extracted as the local maximum brightness. The local maximum luminance is extracted in each of the two directions in the length direction of the scanning line 70 starting from the center pixel 74. Further, the position where the pixel having the local maximum luminance is located in the length direction of the scanning line 70 is obtained as the maximum luminance positions PA and PB.

  The scanning range based on the center pixel 74 when extracting the local maximum luminance is preferably about half the maximum groove width GW of the groove 65 extracted using the scanning line 70. For example, in the circumferential scanning line 71, it is preferable to set the width to about half the maximum groove width GW of the lug groove 66 in the tire circumferential direction. In the present embodiment, since the maximum groove width GW of the lug groove 66 in the ground contact surface image 80 is about 60 pixels, the scanning range starting from the center pixel 74 is 5 pixels less than half of 60 pixels 25 Set to pixel. That is, the local maximum luminance is obtained by scanning 25 pixels each in the length direction of the scan line 70 with the center pixel 74 of the scan line 70 as a base point, extracting the luminance, and calculating the maximum luminance of the pixels located within the range. By extraction, local maximum luminances at two positions are extracted, and two maximum luminance positions PA and PB are obtained. By setting the scanning range to about half of the maximum groove width GW of the lug groove 66, erroneous detection of the maximum luminance positions PA and PB can be reduced.

  Next, it is determined whether at least one of the local maximum luminances is equal to or higher than the land local luminance + α (step ST36). Here, the luminance of the pixel is lower in the groove 65 than in the land portion 68, and the central pixel 74 is determined as a component of the groove 65 because the luminance is lower than the local luminance of the groove. Is in position. Therefore, when the local maximum luminance when scanning the luminance in the length direction of the scanning line 70 is equal to or greater than the land local luminance, the maximum luminance positions PA and PB are determined by the groove 65 and the land 68. Can be estimated. On the other hand, even if the local maximum luminance is equal to or higher than the land local luminance, the maximum luminance positions PA and PB may not be the boundary between the land 68 and the groove 65. In this case, the maximum luminance positions PA and PB may be used. If PB is determined to be the boundary between the groove 65 and the land portion 68, an erroneous determination is made.

  FIG. 11 is an explanatory diagram of a case where the determination is performed without using the land local luminance + α. FIG. 12 is a diagram showing the correspondence between the position in the tire circumferential direction of FIG. 11 and the luminance. Even when the brightness of the land portion 68 is relatively small and the difference between the brightness of the groove 65 and the land portion 68 is not large, the maximum brightness positions PA and PB can be obtained. In this case, the maximum brightness positions PA and PB are determined. , May be located at a position other than the boundary between the groove 65 and the land portion 68. For example, as shown in FIG. 11, the maximum luminance position PB may be located on the land portion 68. In this case, since the maximum luminance position PB is different from the actual boundary position PC between the groove 65 and the land portion 68, a range surrounded by the maximum luminance position PA and the maximum luminance position PB is defined as the groove 65. (FIG. 11: GWE), which is different from the actual groove 65 (FIG. 11: GWC), resulting in an erroneous determination. Therefore, in order to prevent this erroneous determination, in the present embodiment, it is determined whether or not the maximum luminance position PA, PB is the boundary portion between the groove 65 and the land portion 68 by a predetermined value for the land local luminance. The determination is made by comparing the value obtained by adding a certain value with the local maximum luminance. In this case, α may be set to a constant value in advance, or the value may be determined by examining the luminance distribution at a plurality of positions on the scanning line 70. In the present embodiment, α = 35 is set for the ground plane image 80 whose luminance is represented by 256 gradations.

  The land local luminance + α set as described above is compared with the local maximum luminances of the two maximum luminance positions PA and PB, and at least one of the local maximum luminances is the land local luminance. The determination unit 36 determines whether or not it is equal to or more than + α. If it is determined that none of the local maximum luminances is equal to or higher than the land local luminance + α (No in step ST36), the flow exits from the flow of the groove 65 extraction processing. That is, when it is determined that none of the local maximum luminances is equal to or higher than the land local luminance + α, the boundary between the groove 65 and the land 68 is not located in the scanning range, or the luminance is appropriately adjusted. Since the extraction has not been performed, in this case, the extraction processing of the groove 65 is not performed at the current position of the scanning line 70.

  On the other hand, if it is determined that at least one of the local maximum luminances is equal to or higher than the land local luminance + α (step ST36, Yes determination), then the local maximum luminances of both of the two locations are landed. It is determined whether or not the value is equal to or higher than the local luminance + α (step ST37). When it is determined that the local maximum luminance is equal to or higher than the land local luminance + α at both locations (step ST37, Yes determination), the range surrounded by the two maximum luminance positions PA and PB. Is determined as the groove 65 (step ST38). That is, the determination unit 36 determines that the two maximum luminance positions PA and PB have a luminance equal to or higher than the luminance value obtained by adding the predetermined luminance value α to the land local luminance. The range surrounded by the maximum luminance positions PA and PB is determined as the groove 65. In this case, a group of pixels arranged in a line in the tire circumferential direction and surrounded by the maximum luminance position PA and the maximum luminance position PB is stored in the storage unit 50 as a component of the groove 65.

  On the other hand, when it is determined that the local maximum luminance is not equal to or higher than the land local luminance + α at both locations (step ST37, No determination), it is surrounded by one of the maximum luminance positions and the center pixel 74. The range is determined as a component of the groove 65 (step ST39). That is, the determination unit 36 determines that only one of the two maximum luminance positions PA and PB has a luminance equal to or higher than the luminance value obtained by adding the predetermined luminance value α to the land local luminance. If it is a position, the range surrounded by the maximum luminance position and the center pixel 74 is determined as a component of the groove 65. For example, only in the maximum luminance position PA, the local maximum luminance is equal to or higher than the land local luminance + α, and the maximum luminance position PB is determined when the local maximum luminance is not equal to or higher than the land local luminance + α. A group of pixels arranged in a row in the tire circumferential direction and surrounded by the PA and the center pixel 74 is stored in the storage unit 50 as a component of the groove 65. Conversely, only the maximum luminance position PB has a local maximum luminance equal to or higher than the land local luminance + α, and a maximum luminance position PA has the maximum luminance when the local maximum luminance is not equal to or higher than the land local luminance + α. A group of pixels arranged in a line in the tire circumferential direction and surrounded by the position PB and the center pixel 74 is stored in the storage unit 50 as a component of the groove 65.

  As described above, in the process of extracting the groove 65, the luminance is scanned along the scanning line 70, and the components of the groove 65 are extracted based on the extracted luminance. Since the luminance changes at a portion where the angle with respect to the surface of the land portion 68 greatly changes, when the opening of the groove 65 is chamfered, the luminance at the boundary between the surface of the land portion 68 and the chamfer is obtained. Changes. Therefore, by extracting the components of the groove 65 based on the luminance, when the opening of the groove 65 is chamfered, the chamfered portion can also be extracted as a component of the groove 65.

  When the process of extracting the groove 65 at one position of the scanning line 70 is completed, it is next determined whether or not the position of the scanning line 70 is the end position (step ST23). That is, since the scan line 70 performs the raster scan, it is determined whether or not the current position of the scan line 70 is the end position.

  FIG. 13A to FIG. 13E are explanatory diagrams of how a scanning line advances. The manner in which the scanning line 70 advances when scanning is performed using the scanning line 70 will be described with reference to the circumferential scanning line 71. In step ST21, the circumferential scanning line 71 is located at, for example, the upper leftmost position of the ground plane image 80. The portion is set to extend in the left-right direction (FIG. 13A). After the groove 65 is extracted at this position, the circumferential scanning line 71 is moved one pixel to the right (FIG. 13B), and by repeating these, the circumferential scanning is performed while extracting the groove 65 at each position. The line 71 is moved rightward.

  Thus, when the circumferential scanning line 71 moves to the right end of the ground plane image 80 (FIG. 13C), the circumferential scanning line 71 is moved to the left end of the next lower row of pixels. (FIG. 13D). In this manner, the circumferential scanning line 71 is sequentially moved to the right by one pixel at a time, and after moving to the right end, the circumferential scanning line 71 is repeatedly moved to the left end of the next lower row of pixels. It is moved to the lower rightmost part of the contact surface image 80 (FIG. 13E). This position is the end position when the circumferential scanning line 71 is moved while extracting the groove 65.

  After the process of extracting the groove 65 at the current position of the scan line 70 is completed, it is determined whether or not the position of the scan line 70 is the end position (step ST23), and the position of the scan line 70 is not the end position. Is determined (step ST23, No determination), the scanning line 70 is moved (step ST24). In this case, the scanning line 70 is moved from the current position by one pixel in the length direction of the scanning line 70 or to the position of the end of the adjacent row. After moving the scanning line 70, the process returns to step ST22, and the groove 65 is extracted again. By repeating these steps, the groove 65 is extracted in the entire area of the ground contact surface image 80.

  In the above description, the case where the lug grooves 66 are extracted using the circumferential scanning lines 71 has been described. However, the case where the main grooves 67 are extracted using the width scanning lines 72 is also performed in the same manner. . That is, when it is determined that the luminance of the center pixel 74 at the current position of the width direction scanning line 72 is smaller than the groove local luminance, the local maximum luminance and the maximum luminance positions PA and PB are obtained. The components of the main groove 67 are extracted.

  Further, since the width direction scanning line 72 is set in a direction extending along the tire width direction of the test tire 60 and is provided in a direction orthogonal to the circumferential direction scanning line 71, the moving direction is also the circumferential direction scanning line 71. Is a direction orthogonal to the moving direction of 14A to 14E are explanatory diagrams illustrating how the scanning line in the width direction advances. In step ST21, for example, the width direction scanning line 72 is set so as to extend in the vertical direction at the uppermost left portion of the ground contact surface image 80 (FIG. 14A). After the main groove 67 is extracted at this position, the width-directional scanning line 72 is moved downward by one pixel (FIG. 14B), and by repeating these steps, the width of the main groove 67 is extracted at each position. The direction scanning line 72 is moved downward.

  Thereby, when the width direction scanning line 72 moves to the lower end of the ground plane image 80 (FIG. 14C), the width direction scanning line 72 is moved to the upper end of the right column of the pixel (FIG. 14C). (FIG. 14D). As described above, the width direction scanning line 72 is sequentially moved downward by one pixel at a time, and after moving to the lower end, the width direction scanning line 72 is repeatedly moved to the upper end of the one right column of the pixels, so that the width direction scanning line 72 is connected. The ground image 80 is moved to the lowest right position (FIG. 14E). This position is the end position when the width direction scanning line 72 is moved while extracting the main groove 67.

  Also in the width direction scanning line 72, after the main groove 67 extraction processing at the current width direction scanning line 72 position is completed, it is determined whether or not the position of the width direction scanning line 72 is the end position (step S1). In ST23), when it is determined that the position of the width direction scanning line 72 is not the end position (step ST23, No determination), the width direction scanning line 72 is moved (step ST24). In this case, the pixel is moved from the current position of the width direction scanning line 72 by one pixel in the length direction of the width direction scanning line 72 or to the position of the end of the adjacent row. After moving the scanning line 72 in the width direction, the process returns to step ST22, and the main groove 67 is extracted again. By repeating these, the extraction processing of the main groove 67 is performed in the entire region of the ground contact surface image 80.

  When it is determined that the position of the scanning line 70 is the end position in both the circumferential scanning line 71 and the width scanning line 72 (step ST23, Yes determination), the groove is formed in the entire area of the ground contact surface image 80. Since the extraction processing of 65 has been performed, the processing exits from the processing of extracting the groove 65.

  FIG. 15 is an explanatory diagram of a groove image. When the extraction of the groove 65 is completed, next, a groove image 83 is generated (step ST13). The generation of the groove image 83 is performed by the groove image generation unit 37 included in the groove extraction unit 33. The groove image generation unit 37 extracts using the circumferential scanning lines 71, extracts the components of the lug grooves 66 stored in the storage unit 50, and extracts using the width scanning lines 72, and stores the components in the storage unit 50. By composing all the components of the main groove 67 as black pixels, one groove image 83 is generated as an image of the entire groove 65 included in the ground contact surface image 80. That is, for example, in step ST39, a portion that is not extracted as a component of the groove 65 when viewed from the center pixel 74 in the length direction of the scan line 70 is also extracted as a component of the groove 65 when the scan line 70 moves. Therefore, by connecting these by the groove image generation unit 37, a groove image 83 with no excess or shortage can be obtained.

  When the groove image 83 is generated, the shape of the groove 65 is adjusted by repeating the contraction processing and the expansion processing, and a small block of black pixels on the groove image 83 is removed. This makes it possible to remove small bumps on the groove image 83, which are generated by extracting a portion other than the groove 65 as a component of the groove 65 due to luminance unevenness or the like when extracting the groove 65. 65 can be made to look good.

  FIG. 16 is an explanatory diagram of the contraction processing. FIG. 17 is an explanatory diagram of the expansion processing. In the contraction process, for example, when the target pixel is a black pixel, as shown in FIG. 16, if at least one white pixel exists around the target pixel, the target pixel is replaced with a white pixel. In other words, the contraction processing is performed by setting each of the black pixels as the center pixel and one of the eight surrounding pixels (one pixel at the upper left, upper, upper right, right, lower right, lower, lower left, and lower left nearest to the center pixel). However, if a white pixel exists, the center pixel is replaced with a white pixel. Conversely, as shown in FIG. 17, the expansion process is a process of replacing the target pixel with a black pixel if there is at least one black pixel around the target pixel. That is, the expansion process is performed by setting each white pixel as a center pixel and one of the eight surrounding pixels (one pixel at the upper left, upper, upper right, right, lower right, lower, lower left, and lower left nearest to the center pixel) However, if a black pixel exists, the center pixel is replaced with a black pixel.

  In the present embodiment, when the groove image 83 is generated, the contraction processing is performed three times, the expansion processing is performed three times, and then, in order to remove a small lump of black pixels, 500 consecutive black pixels are formed. A set of black pixels that are equal to or smaller than a pixel is removed. After that, the expansion process is performed three times, and the contraction process is performed three times. Thereby, a good-looking groove image 83 can be obtained. The number and order of these contraction processing and expansion processing, and the number of continuous black pixels as a reference when removing a lump of black pixels are determined by the tread pattern of the test tire 60, the test conditions, and the resolution of the image. It is preferable to set appropriately according to the conditions.

  Next, the total ground area 85 is determined (step ST14). FIG. 18 is an explanatory diagram of the total contact area image. The total contact area 85 is obtained by generating the total contact area image 84 from the contact surface image 80 by the total contact area calculation unit 38. When the total contact region image 84 is generated from the contact surface image 80 by the total contact region calculation unit 38, the total contact region image 84 is generated by performing a binarization process on the contact surface image 80. That is, in the contact area image 80, the contact area 81 has lower luminance than the non-contact area 82, and the groove 65 has a lower luminance than the land section 68 in the contact area 81. The binarization is performed using the luminance at a threshold value at which the land portion 68 of 81 and the non-ground area 82 can be separated. As a result, the non-ground area 82 becomes a white pixel, and in the ground area 81, both the land 68 and the groove 65 become black pixels. Therefore, the ground area 81 in the ground plane image 80 becomes the total ground area 85. A total contact area image 84 can be generated.

  Note that, in the present embodiment, the flow for obtaining the total contact area 85 after the extraction of the groove 65 is described. However, the processing for obtaining the total contact area 85 from the contact surface image 80 extracts the groove 65. The determination of the total contact area 85 and the extraction of the groove 65 may be performed in parallel.

  Next, the actual ground area 87 is obtained (step ST15). FIG. 19 is an explanatory diagram of the actual ground area image. The actual contact area 87 is obtained by removing the groove 65 extracted by the groove extraction section 33 from the total contact area 85 determined by the total contact area calculation section 38 by the actual contact area calculation section 39. That is, by replacing the portion corresponding to the groove 65 of the ground plane image 80 with a white pixel in the total ground region image 84 of the binary image in which the total ground region 85 is a black pixel, the portion corresponding to the groove 65 is changed. A real ground area image 86 that is an image of the real ground area 87 that has become a white pixel is generated.

  The tire contact surface analysis system 1 acquires a large number of contact surface images 80 with one test tire 60, and extracts the grooves 65 from these contact surface images 80 by the above-described tire contact surface analysis method. In the contact surface image 80, a highly accurate actual contact region image 86 can be easily acquired.

  When the luminance of the center pixel 74 of the scanning line 70 is smaller than the local luminance of the groove, the tire ground contact surface analysis device 20 according to the above-described embodiment sets the maximum luminance position in both directions in the length direction of the scanning line 70 from the center pixel 74. PA and PB are obtained, respectively, and a range surrounded by the two maximum luminance positions PA and PB is determined as the groove 65. For example, even if the groove 65 is chamfered, the groove including the chamfered portion is included. 65 can be determined. In other words, since the brightness of the chamfered portion is likely to be high, by extracting the groove 65 based on the maximum luminance position, it is possible to extract the region including the chamfered portion that is the high luminance as the groove 65. it can. As a result, it is possible to appropriately extract the shape of the groove 65, and it is possible to reduce an analysis error when analyzing the contact area.

  Further, as the scanning line 70, a circumferential scanning line 71 set in a direction extending along the tire circumferential direction of the test tire 60, and a width direction scanning line set in a direction extending along the tire width direction of the test tire 60 Since 72 is set, the groove 65 can be extracted using the circumferential scanning line 71 and the width scanning line 72 regardless of the direction of the groove 65 of the test tire 60. Thereby, even if the groove 65 extending in any direction of the tire circumferential direction and the tire width direction is chamfered, it can be extracted as a component of the groove 65 including the chamfered portion. As a result, an analysis error in analyzing the ground contact region can be reduced more reliably.

  In addition, when both of the two maximum luminance positions PA and PB have a luminance equal to or higher than a luminance value obtained by adding a predetermined luminance value α to the land local luminance, the two maximum luminance positions Since the range surrounded by PA and PB is determined as the groove 65, the width of the groove 65 can be accurately extracted. As a result, an analysis error in analyzing the ground contact region can be reduced more reliably.

  Further, when only one of the maximum luminance positions PA and PB has a luminance equal to or higher than a luminance value obtained by adding a predetermined luminance value α to the land-local luminance. Since the range surrounded by the maximum luminance position and the center pixel 74 is determined as a component of the groove 65, erroneous determination of the groove 65 can be suppressed. As a result, an analysis error in analyzing the ground contact region can be reduced more reliably.

  Further, when calculating the land-local brightness, not only the brightness of the pixels on the scanning line 70 but also the brightness of the pixels on the brightness calculation line 76 is used by setting the brightness calculation line 76. The local brightness can be calculated with high accuracy. That is, since the ground plane image 80 has luminance unevenness, it is difficult to calculate with high accuracy when the land local luminance is calculated only with the luminance of the pixel on the scanning line 70. The extraction accuracy of 65 also becomes unstable. On the other hand, when the luminance calculation line 76 is also used to calculate the land local luminance, the luminance can be calculated in a wider range of pixels, and thus the land local luminance is calculated with higher accuracy. be able to. As a result, the extraction accuracy of the groove 65 can be improved, and the analysis error in analyzing the ground contact area can be more reliably reduced.

  Further, the tire ground contact surface analysis system 1 according to the embodiment is configured such that the ground contact surface 61 of the test tire 60 pressed against the transparent plate 11 is illuminated by the plurality of illumination lamps 16, and the camera 15 passes through the transparent plate 11. Thus, the ground plane 61 can be photographed with a luminance difference between the ground plane 61 and the non-ground plane. At this time, since the test tire 60 is photographed in a state where light is emitted from the plurality of illumination lamps 16 from a plurality of directions, the groove 65 and a portion other than the groove 65 are photographed with a difference in luminance. can do. Thereby, the shape of the groove 65 can be specified more reliably, and the groove 65 can be more reliably extracted from the ground contact surface image 80. As a result, an analysis error in analyzing the ground contact region can be reduced more reliably.

  In addition, when the luminance of the center pixel 74 of the scanning line 70 is smaller than the local luminance of the groove, the tire ground contact surface analysis method according to the embodiment includes the maximum luminance position PA in both directions in the length direction of the scanning line 70 from the central pixel 74. , And PB are obtained, and the range surrounded by the two maximum luminance positions PA and PB is determined as the groove 65. For example, even when the groove 65 is chamfered, the groove 65 including the chamfered portion is also included. Can be determined. As a result, it is possible to appropriately extract the shape of the groove 65, and it is possible to reduce an analysis error when analyzing the contact area.

(Modification)
In the tire contact surface analysis device 20 according to the above-described embodiment, the lug groove 66 and the main groove 67 are both extracted using the scanning line 70, but the lug groove 66 and the main groove 67 are different. You may extract by a technique. FIG. 20 is a modified example of the process performed by the tire contact surface analysis device according to the embodiment, and is an explanatory diagram in a case where lug grooves and main grooves are extracted by different methods. When the lug groove 66 and the main groove 67 are extracted by different methods, for example, the lug groove 66 may be extracted by the method in the above-described embodiment, and the main groove 67 may be extracted based on the contour line 89. Good. A method for extracting the main groove 67 based on the contour line 89 will be described. First, the contact surface image 80 is binarized based on luminance. Explaining the luminance distribution of the contact surface image 80, in the contact surface image 80, the luminance of the contact region 81 is lower than the luminance of the non-contact areas 90 located at two places on both sides of the contact region 81 in the tire circumferential direction. Further, the brightness of the main groove 67 located in the non-contact area 90 tends to be lower than that of the land portion in the non-contact area 90. For this reason, when the contact surface image 80 is binarized based on luminance, the contact region 81 and the portion of the main groove 67 in the non-contact area 90 can be made the same color. , And the main groove 67 in the non-contact area 90 can be black pixels.

  After that, a contour line image 88 is generated by extracting a contour line 89 in the binarized image. The extraction of the contour line 89 from the binarized image is performed, for example, by scanning the image, detecting a portion having a tone difference as an edge, and performing the scanning from a plurality of directions to extract a contour. This is performed using a bell filter. As a result, in the image composed of black pixels in the binarized image, the boundary portion between the pixel and the white pixel is extracted as the contour 89, and the contour image 88 can be generated.

  The extraction of the contour line 89 may be performed by a method other than the extraction method using the Sobel filter. For example, a luminance difference (absolute value) between adjacent pixels in the horizontal direction or between adjacent pixels in the vertical direction in the binarized image is calculated, and the calculated value is output for each pixel of the binarized image. Thus, the outline 89 may be extracted.

  After the contour image 88 is generated, the main groove scan line 95 is set in the non-contact area 90 in the contour image 88. The main groove scanning line 95 is a line parallel to the contour 89 of the main groove 67 in the contour image 88, and is a line extending in the tire circumferential direction. In this modification, the width of the non-contact area 90 in the tire circumferential direction is set as a constant width in each of the two non-contact areas 90, and the main groove scanning line 95 is connected to the two non-contact areas. The setting is made for each of the regions 90. The two main groove scanning lines 95 have the same length in the tire circumferential direction as the width of the non-contact area 90 in the tire circumferential direction, and are set so that the positions in the tire width direction are the same.

  When the main groove scanning line 95 is set in the non-contact area 90, the main groove scanning line 95 is moved from one end 91 in the tire width direction to the other end 91, and the width of the pixel in the tire width direction is set as a reference. At each of the positions, the total number of black pixels overlapping the main groove scanning line 95 is determined for each position. When the total number of black pixels for each position in the tire width direction in the non-contact area 90 is determined, the position where the total number of black pixels is large in the tire width direction in order from the position where the total number of black pixels is the largest is determined as the number of main grooves 67. Select the corresponding number.

  In other words, at positions where the total number of black pixels is obtained, positions twice as many as the number of the main grooves 67 of the test tire 60 are extracted from the position where the total number of black pixels is the largest to the position where the total number of black pixels is smaller. For example, when the number of the main grooves 67 is three, from the position in the tire width direction where the total number of black pixels overlapping the main groove scanning line 95 is the largest, the total number of black pixels is the sixth largest in the tire width direction. Six positions in the tire width direction up to the position are extracted.

  Since the positions extracted as described above are positions where the contour line 89 of the main groove 67 is located in the tire width direction, a portion sandwiched between the extracted positions is extracted as a portion where the main groove 67 is located. Note that the portion sandwiched between the extracted positions also corresponds to the portion where the land portion is located. However, since the main groove 67 and the land portion have different intervals in the tire width direction and different positions in the tire width direction, these elements are different. Thus, the position of the main groove 67 in the tire width direction is extracted.

  By combining the main groove 67 extracted as described above with the lug groove 66 extracted by the method in the above-described embodiment, even if the lug groove 66 and the main groove 67 are extracted by different methods, one groove is formed. An image 83 can be generated. The generated groove image 83 can be used when obtaining the actual contact area 87 by removing the groove 65 in the groove image 83 from the total contact area 85 of the total contact area image 84 as in the above-described embodiment. it can.

REFERENCE SIGNS LIST 1 tire contact surface analysis system 2 tire testing machine 3 support device 5 drive device 10 photographing device 11 transparent plate 15 camera (photographing unit)
16 Lighting lamp (light source)
Reference Signs List 20 tire contact surface analysis device 30 processing device 31 processing unit 32 contact surface image acquisition unit 33 groove extraction unit 34 scan line setting unit 35 luminance comparison unit 36 determination unit 37 groove image generation unit 38 total contact area calculation unit 39 actual contact area calculation Part 50 storage part 60 test tire (pneumatic tire)
61 ground plane 65 groove 66 lug groove 67 main groove 68 land part 70 scanning line 71 circumferential scanning line 72 width direction scanning line 74 center pixel 76 luminance calculation line 77 neighborhood area 78 luminance calculation area 80 ground plane image 81 ground area 82 non Contact area 83 Groove image 84 Total contact area image 85 Total contact area 86 Actual contact area image 87 Actual contact area

Claims (7)

A contact surface image acquisition unit that acquires an image of the contact surface of the pneumatic tire,
A groove extraction unit that extracts the groove of the pneumatic tire from the contact surface image acquired by the contact surface image acquisition unit,
With
The groove extraction unit,
A scanning line setting unit that sets a scanning line for the ground plane image,
In the case where the average luminance in the region where the scanning line is located is the land local luminance, and a value obtained by subtracting a certain value from the land local luminance is the groove local luminance, the luminance of the central pixel of the scanning line is obtained. And a brightness comparison unit that compares the groove local brightness,
When the luminance of the central pixel is smaller than the local luminance of the groove, the ground plane image is scanned with a predetermined length in both directions in the length direction of the scan line from the central pixel to extract luminance. A determination unit that determines the maximum luminance position in each of the scanned ranges in both directions, and determines a range surrounded by the two maximum luminance positions as the groove.
A tire contact surface analysis device, comprising:   The scanning line setting unit is configured to set, as the scanning line, a circumferential scanning line set in a direction extending along a tire circumferential direction of the pneumatic tire and a direction extending along a tire width direction of the pneumatic tire. The tire ground contact surface analysis device according to claim 1, wherein the width direction scanning line to be set is set.   The judging unit, when both of the two maximum luminance positions are positions having a luminance equal to or higher than a luminance value obtained by adding a predetermined luminance value to the land local luminance, the two maximum luminance positions The tire contact surface analysis device according to claim 1, wherein a range surrounded by the luminance position is determined as the groove.   The determination unit is a position in which only one of the two maximum luminance positions has a luminance equal to or higher than a luminance value obtained by adding a predetermined luminance value to the land local luminance. The tire ground contact surface analysis device according to any one of claims 1 to 3, wherein in this case, a range surrounded by the maximum luminance position and the center pixel is determined as a component of the groove. A total contact area calculation unit for determining a total contact area from the contact surface image,
From the total contact area calculated by the total contact area calculation unit, an actual contact area calculation unit that removes the groove extracted by the groove extraction unit to determine an actual contact area,
The tire contact surface analysis device according to any one of claims 1 to 4, further comprising: A tire tread analysis device according to any one of claims 1 to 5,
A transparent plate for pressing the pneumatic tire,
A plurality of light sources that irradiate the ground plane pressed against the transparent plate,
A photographing unit that photographs the ground plane through the transparent plate,
A tire ground contact surface analysis system, comprising: Obtaining an image of the ground plane of the pneumatic tire ;
Setting a scan line relative to contact the ground image,
In the case where the average luminance in the region where the scanning line is located is the land local luminance, and a value obtained by subtracting a certain value from the land local luminance is the groove local luminance, the luminance of the central pixel of the scanning line is obtained. And comparing the groove local brightness with;
When the luminance of the central pixel is smaller than the local luminance of the groove, the ground plane image is scanned with a predetermined length in both directions in the length direction of the scan line from the central pixel to extract luminance. Determining the maximum luminance position in both scanned ranges in each direction, and determining a range surrounded by the two maximum luminance positions as the groove of the pneumatic tire ;
A tire ground contact surface analysis method, comprising: