JP7119727B2 - Tire contact shape analysis device and tire contact shape analysis method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a tire ground contact shape analysis device and a tire ground contact shape analysis method.

Techniques for analyzing the shape of the contact portion of a tire are disclosed in Patent Documents 1 and 2. In the technique disclosed in Patent Document 1, a satin-finished sheet is placed on a glass plate, a tire is pressed against the satin-finished surface of the satin-finished sheet and grounded, light is emitted from the glass plate, and light is emitted from the contact portion of the satin-finished surface. The grounded image is obtained by utilizing the fact that the reflectance is smaller than the reflectance from the non-grounded portion. The technology disclosed in Patent Literature 2 generates a binary image based on brightness from an image obtained by photographing a tire footprint.

JP-A-2003-14428 JP-A-5-196557

The technique disclosed in Patent Document 1 uses a satin-finished sheet. For this reason, when obtaining dynamic ground contact characteristics in a state where the tire is rolling, the sheet is peeled off from the glass plate when the rotating tire comes into contact with the sheet. According to the technology disclosed in Patent Document 2, when the tire is rotated in the grounded state, the footprint may be lost, and it is difficult to obtain the dynamic grounding characteristics of the tire. Therefore, the techniques disclosed in Patent Document 1 and Patent Document 2 have room for improvement in terms of obtaining dynamic ground contact characteristics of tires.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and its object is to provide a tire contact shape analysis device and a tire contact shape analysis method capable of accurately analyzing the dynamic contact characteristics of a tire in a short time. That is.

In order to solve the above-described problems and achieve the object, a tire contact shape analysis apparatus according to one aspect of the present invention measures the brightness of the edge of a groove provided in a tire tread portion on the contact surface of a tire to be analyzed. a tread image acquisition unit that acquires a photographed image of the tread of the tire by the light emitted from the illuminating unit; and the tread image acquired by the tread image acquisition unit. a ground contact characteristics analysis unit that analyzes a ground image and obtains ground contact characteristics , wherein the contact characteristics analysis unit includes a groove extraction unit that extracts a groove image from the captured image; and a contact characteristic calculating section that subtracts the groove image from a rough contact area image obtained by the binarization process. A chamfered image extracting unit for extracting a chamfered image showing a chamfered portion, a groove bottom extracting unit for extracting a portion having luminance lower than a predetermined luminance from the photographed image as a groove bottom image showing the bottom of the groove, and the photographed image. a main groove bottom extracting unit for extracting a low-luminance portion surrounded by a portion having a luminance higher than a predetermined luminance as a main groove bottom image showing the bottom of the main groove, the chamfered image, and the groove bottom image; a synthesizing unit for synthesizing the main groove bottom image and the groove image to obtain the groove image.

The tire is in contact with one main surface of a transparent plate, and the illumination unit includes a one main surface side lamp provided on one main surface side of the transparent plate so as to surround the ground contact surface of the tire; and a other-principal-surface-side lamp provided on the other-principal-surface side of the transparent plate, wherein the other-principal-surface-side lamp is a width-direction lamp that irradiates the ground contact surface with light from the outside to the inside in the tire width direction. is preferably included.

It is preferable that a camera for photographing the contact patch of the tire is further included, and the camera photographs the contact patch of the tire from a normal direction of a center point of the contact patch of the tire.

Preferably, the camera is provided in a range surrounded by a line extending from the contour of the ground contact surface of the tire in a direction perpendicular to the other main surface of the transparent plate.

It is preferable that the other-main-surface-side lamp includes a circumferential lamp that irradiates the ground contact surface with light from the outer side to the inner side in the tire circumferential direction.

It is preferable that the ground contact characteristic calculation unit uses a portion of the image obtained by the binarization process, excluding a portion corresponding to the stamp included in the captured image, as the rough ground contact area.

The main groove bottom extracting unit includes a smoothing processing unit that performs smoothing processing on the captured image in the tire circumferential direction, and a binary value on the smoothed image smoothed by the smoothing processing unit using a predetermined first luminance threshold. a first candidate image extracting unit that extracts a first candidate image that has undergone a normalization process; and a second candidate image that has been binarized from the smoothed image using a second luminance threshold lower than the first luminance threshold and extracts a second candidate image. a second candidate image extracting unit, a superposition processing unit for obtaining the main groove bottom image by superimposing an image of an isolated object that is included in the first candidate image and does not include a contact block with the second candidate image; is preferably included.

It is preferable that the chamfered image extracting unit uses, as the chamfered image, a portion of the photographed image that has luminance higher than the predetermined luminance, excluding a portion corresponding to the stamp included in the photographed image.

In order to solve the above-described problems and achieve the object, a tire ground contact shape analysis method according to one aspect of the present invention provides a method of irradiating a ground contact surface of a tire to be analyzed, and irradiating an edge of a groove provided in a tire tread portion. A contact patch image acquisition step of acquiring a photographed image of the contact patch of the tire with light that increases brightness; and the step of analyzing the contact characteristics includes a groove extraction process for extracting a groove image from the photographed image, and a rough contact area image obtained by binarizing the photographed image using a predetermined luminance as a threshold. The groove extraction process includes a chamfered image extraction process of extracting a portion having luminance higher than a predetermined luminance from the photographed image as a chamfered image showing the chamfered portion of the groove. a groove bottom extraction process for extracting a portion having a luminance lower than a predetermined luminance from the photographed image as a groove bottom image showing the bottom of the groove; main groove bottom extraction processing for extracting the low-luminance portion as a main groove bottom image showing the bottom of the main groove; and a compositing process that obtains

INDUSTRIAL APPLICABILITY The tire ground contact shape analysis device and tire ground contact shape analysis method according to the present invention can accurately analyze the dynamic contact characteristics of a tire in a short time.

FIG. 1 is a configuration diagram schematically showing a tire contact shape analysis device according to an embodiment. FIG. 2 is a block diagram showing functions of the tire contact shape analysis device shown in FIG. FIG. 3 is a diagram for explaining the movement of the transparent plate and the operation of the trigger device. FIG. 4 is a diagram for explaining the movement of the transparent plate and the operation of the trigger device. FIG. 5 is a flowchart showing the operation of the tire ground contact shape analysis device 1. As shown in FIG. FIG. 6 is a diagram showing an example of a specific arrangement of cameras and illumination lamps when a ground plane image is acquired by the ground plane image acquisition unit. FIG. 7 is a diagram showing an example of specific arrangement of cameras and lighting lamps when a ground plane image is acquired by the ground plane image acquisition unit. FIG. 8 is a diagram showing an example of a specific arrangement of cameras and illumination lamps when a ground plane image is acquired by the ground plane image acquisition unit. FIG. 9 is a diagram for explaining the inclination angle of the ramp with respect to the tire circumferential direction. FIG. 10 is a diagram for explaining the inclination angle of the ramp with respect to the tire circumferential direction. FIG. 11 is a view of the arrangement of the illumination lamps viewed from the direction along the rotation axis of the tire. FIG. 12 is a view of the arrangement of the lighting lamps from a direction perpendicular to the rotation axis of the tire. FIG. 13 is a view of the arrangement of the illumination lamps viewed from the upper surface side of the transparent plate. FIG. 14 is a diagram for explaining the inclination angle of the ramp with respect to the tire width direction. FIG. 15 is a diagram for explaining the inclination angle of the ramp with respect to the tire width direction. FIG. 16 is a diagram showing an example of light irradiation from a lamp that enhances the brightness of chamfering of sub-grooves. FIG. 17 is a diagram showing an example of light irradiation from a lamp that enhances the brightness of chamfering of sub-grooves. FIG. 18 is a diagram showing an example of light irradiation from a lamp that enhances the chamfered brightness of the sub-groove. FIG. 19 is a diagram showing an example of irradiation of light from a lamp that enhances the brightness of chamfering of sub-grooves. FIG. 20 is a diagram showing an example of light irradiation from a lamp that enhances the brightness of chamfering of sub-grooves. FIG. 21 is a diagram showing an example of light irradiation from a lamp that enhances the chamfered brightness of the sub-groove. FIG. 22 is a diagram illustrating an arrangement example of cameras. FIG. 23 is a diagram illustrating an arrangement example of cameras. FIG. 24 is a flowchart illustrating an example of processing by a grounding characteristic analysis unit; FIG. 25 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 26 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 27 is a diagram showing an example of an image acquired or created by the processing of the grounding property analysis unit. FIG. 28 is a diagram showing an example of an image acquired or created by the processing of the grounding property analysis unit. FIG. 29 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 30 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 31 is a diagram showing an example of an image acquired or created by the processing of the grounding property analysis unit. FIG. 32 is a diagram showing an example of GCA FIG. 33 is an explanatory diagram of the dilation process. FIG. 34 is an explanatory diagram of contraction processing. FIG. 35 is a diagram showing an example of a reference image. FIG. 36 is a diagram showing an example of a comparison image. FIG. 37 is a diagram showing an example of a comparison image. FIG. 38 is a diagram showing an example of the result of performing local binarization processing on the image shown in FIG. FIG. 39 is a flow diagram showing an example of processing by the main groove bottom extracting section. FIG. 40 is a diagram showing an example of a smoothed image. FIG. 41 is a diagram showing an example of the first candidate image. FIG. 42 is a diagram showing an example of the second candidate image. FIG. 43 is a diagram explaining the processing of the first candidate image extraction unit. FIG. 44 is a diagram explaining the processing of the first candidate image extraction unit. FIG. 45 is a diagram for explaining the processing of the superimposition processing unit. FIG. 46 is a diagram for explaining the processing of the superimposition processing unit. FIG. 47 is a diagram for explaining the processing of the superimposition processing unit; FIG. 48 is a diagram showing an example of an image obtained by extracting a high-brightness portion of a captured image. FIG. 49 is a diagram showing an example of a stamp image extracted by the stamp extraction unit. FIG. 50 is a diagram showing an example of a rough ground area image in which a high-luminance portion is white, and medium- and low-luminance portions are black, based on a predetermined threshold value. FIG. 51 is a flowchart showing a tire contact shape analysis method implemented by the tire contact shape analysis apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described in detail based on the drawings. In the description of each embodiment below, the same reference numerals are given to components that are the same as or equivalent to those of other embodiments, and description thereof will be simplified or omitted. The present invention is not limited by each embodiment. In addition, the components of each embodiment include those that can be easily replaced by those skilled in the art, or those that are substantially the same. In addition, the multiple modifications described in this embodiment can be arbitrarily combined within the scope obvious to those skilled in the art. Note that the configurations described below can be combined as appropriate. Also, omissions, substitutions, or changes in configuration can be made without departing from the scope of the invention.

FIG. 1 is a configuration diagram schematically showing a tire ground contact shape analysis device 1 according to an embodiment. FIG. 2 is a block diagram showing the functions of the tire ground contact shape analysis device 1 shown in FIG. In these figures, FIG. 1 schematically shows the overall configuration of the tire ground contact shape analysis device 1 , and FIG. 2 shows the main functions of the tire ground contact shape analysis device 1 .

The tire ground contact shape analysis device 1 according to the present embodiment is applied to a system that analyzes the ground contact surface 61 by acquiring an image of the contact surface 61 of the pneumatic tire 60 . The tire contact patch shape analysis device 1 includes a tire testing machine 2 , an imaging device 10 , and a tire contact patch analysis device 20 .

The tire testing machine 2 is a device that applies test conditions to a pneumatic tire 60 (hereinafter referred to as a tire 60) to be analyzed. In the configuration of FIG. 1 , the tire testing machine 2 has a support device 3 , a drive device 5 and a transparent plate 11 . The support device 3 is a device that rotatably supports the tire 60 and has a rim 4 on which the tire 60 is mounted. The driving device 5 is a device that applies driving force to the tire 60 and the transparent plate 11 . The driving device 5 is composed of a motor 6 that drives the tire 60 and the transparent plate 11 and a motor control device 7 that controls the motor 6 . The drive device 5 includes gears (not shown) and the like, and drives the transparent plate 11 horizontally.

In this tire testing machine 2, the support device 3 supports the tire 60 mounted on the rim 4, and the tire 60 is pressed against the upper surface 11U, which is one main surface of the transparent plate 11, to apply a load to the tire 60. The transparent plate 11 reproduces a flat road surface. The tire 60 pressed against the transparent plate 11 deforms its contact surface 61 in the same manner as when the vehicle is running on a flat road surface. By horizontally driving the transparent plate 11, the rolling state of the tire 60 during vehicle travel is reproduced using the surface of the transparent plate 11 as a road surface, and dynamic ground contact characteristics can be analyzed. Further, the support device 3 displaces the rim 4 to adjust the positional relationship between the tire 60 and the transparent plate 11, thereby giving the tire 60 a slip angle or an angle angle. Further, the driving device 5 can drive the motor 6 by the motor control device 7 to rotate the rim 4 by a predetermined angle. Moreover, the test conditions can be changed by adjusting the load, rotation speed, slip angle, angle angle, and the like of the supporting device 3 and the driving device 5 .

The transparent plate 11 is a light transmitting plate having a property of transmitting light. The transparent plate 11 does not have to transmit 100% of the light, as long as it has a light transmittance that allows the surface of the tire 60 to be photographed through the transparent plate 11 . The transparent plate 11 is, for example, a plane plate made of acrylic resin or a plane plate made of glass. Since the state of contact between the tire 60 and the plane plate is imaged and analyzed, the contact state of the tire 60 can be analyzed more realistically. Regarding the transparent plate 11, there is no designation of specifications such as plate thickness and refraction angle.

The photographing device 10 has a camera 15 as a photographing unit for photographing the tire 60 , an illumination lamp 16 as a light source, and a trigger device 17 . The camera 15 is configured by, for example, a CCD (Charge Coupled Device) camera. The camera 15 is fixed inside the photographing device 10 . The camera 15 photographs the tire 60 through the transparent plate 11 to photograph the ground contact surface 61 of the tire 60 pressed against the transparent plate 11 . Specifically, the camera 15 is arranged on the lower surface 11D side, which is the other main surface of the transparent plate 11, with its optical axis perpendicular to the lower surface 11D side. Shoot 60. Thereby, the camera 15 photographs the tire 60 including at least the contact patch 61 and generates digital image data of the tire 60 including the contact patch 61 .

The illumination lamp 16 is a lamp that illuminates the photographing range of the camera 15, and is composed of, for example, a halogen lamp. The illumination lamp 16 is a general term for a plurality of lamps 161 to 168 provided as described later. The illumination lamp 16 irradiates the ground contact surface 61 of the tire 60 pressed against the transparent plate 11 with light. The illumination lamp 16 emits light from the lower surface 11D side of the transparent plate 11 through the transparent plate 11 or from between the upper surface 11U side of the transparent plate 11 and the tire 60 . A plurality of illumination lamps 16 are arranged at positions other than the position where the transparent plate 11 moves. It should be noted that the camera 15 and the lighting lamp 16 in the imaging device 10 move together with the movement of the imaging device 10 .

The number of illumination lamps 16 may be changed according to the test conditions of the tire testing machine 2 . For example, when the load applied when the tire 60 is pressed against the transparent plate 11 is small, the contact area becomes narrow, and the difference in brightness between the contact surface 61 and the non-contact surface becomes clear. Therefore, in this case, the number of illumination lamps 16 may be relatively small, and may be arranged at only two locations oblique to the moving direction of the transparent plate 11 . On the other hand, when the tire 60 is pressed against the transparent plate 11 with a large load, the contact area is widened, so that the contact surface 61 needs to be irradiated with light from more directions. Therefore, in this case, the lighting lamps 16 are arranged at four or more locations surrounding the ground plane 61 . Further, these illumination lamps 16 may be of a constant lighting type or of a flash lighting type.

The trigger device 17 is a device that outputs a trigger signal indicating the timing of photographing by the camera 15 . The trigger device 17 outputs a semiconductor laser and outputs a trigger signal when its reflected light is detected. In this example, a retroreflective sheet 18 is attached to the side surface of the transparent plate 11, the semiconductor laser output from the trigger device 17 is reflected by the retroreflective sheet 18, and the detector 171 of the trigger device 17 detects the reflected light. Outputs a trigger signal when is detected. If the relationship between the pasting position of the retroreflective sheet 18 and the position of the camera 15 is fixed, the ground contact surface 61 at the same position of the tire 60 can be photographed even when photographing is performed multiple times.

The tire contact patch analysis device 20 is, for example, a PC (Personal Computer) in which a predetermined analysis program is installed, and processes an image of the tire 60 input from the imaging device 10 to analyze the contact patch 61 of the tire 60. I do. The process of analyzing the contact patch 61 of the tire 60 includes the process of calculating the contact patch 61 based on the captured image of the tire 60 . The tire contact patch analysis device 20 includes a processing device 30 that performs arithmetic processing such as analysis of the contact patch 61 and data storage, an input unit 21 that allows an operator to perform an input operation to the tire contact patch analysis device 20, and an analysis result and a display unit 22 for displaying various information. The input unit 21 uses a keyboard and a pointing device such as a mouse, and the display unit 22 uses a display device such as a liquid crystal display. The input unit 21 and the display unit 22 are electrically connected to the processing device 30 , so that the operator can perform an input operation on the input unit 21 while viewing the display unit 22 . is possible. The camera 15 is also connected to the processing device 30 of the tire patch analysis device 20 , so that the tire patch analysis device 20 can acquire the image captured by the camera 15 .

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

A processing unit 31 included in the processing device 30 functionally includes a contact surface image acquisition unit 32 , a contact characteristics analysis unit 33 , and a mark extraction unit 40 . Among these, the contact patch image acquisition unit 32 acquires a photographed image of the contact patch 61 of the tire 60 to be analyzed. The captured image is a digital image of the contact patch 61 of the tire 60 captured by the camera 15 . Further, the contact characteristic analysis unit 33 creates a contact area image indicating the contact area of the tire 60 based on the contact patch image acquired by the contact patch image acquisition unit 32 . In the following description, all images are assumed to consist of 256 gradations, and black is defined as luminance "255" and white as luminance "0".

The ground contact characteristic analysis section 33 includes a groove extractor 34 and a ground contact characteristic calculator 35 . A groove extractor 34 extracts a groove image from the photographed image. The contact characteristic calculator 35 subtracts the groove image from the rough contact area image obtained by binarizing the photographed image using a predetermined luminance as a threshold value. The ground contact characteristic calculator 35 may, for example, perform smoothing processing on the captured image, and then perform binarization processing with a luminance threshold of “220” to obtain a rough ground area image. For the smoothing process, for example, a process using a median filter (hereinafter referred to as a median process) may be used in which a region within a radius of 4 pixels from the pixel of interest is used as peripheral pixels. As will be described later, the groove extracting section 34 may extract the groove image by performing a process of removing the portion corresponding to the stamp included in the photographed image. Further, as will be described later, the contact characteristic calculation unit 35 may perform a process of excluding a portion corresponding to the stamp contained in the photographed image to extract a rough contact area image.

The groove extracting section 34 includes a chamfer image extracting section 34A, a groove bottom extracting section 34B, a main groove bottom extracting section 34C, and a synthesizing section 34D. The chamfered image extraction unit 34A extracts a chamfered image representing a chamfered portion provided on the edge of the groove of the tire 60 from the photographed image. The chamfered image extraction unit 34A extracts a portion having luminance higher than a predetermined luminance from the photographed image as a chamfered image. The groove bottom extraction unit 34B extracts a portion having luminance lower than a predetermined luminance from the photographed image as a groove bottom image indicating the bottom of the groove. The main groove bottom extraction unit 34C extracts a low-luminance portion surrounded by a portion having a luminance higher than a predetermined luminance from the photographed image as a main groove bottom image showing the bottom of the main groove. The synthesizing unit 34D obtains a groove image by synthesizing the chamfer image, the groove bottom image, and the main groove bottom image.

(Main groove bottom extraction part)
The main groove bottom extractor 34</b>C includes a smoothing processor 341 , a first candidate image extractor 342 , a second candidate image extractor 343 , and a superimposition processor 344 . The smoothing processing unit 341 smoothes the captured image in the tire circumferential direction. The first candidate image extraction unit 342 extracts a first candidate image obtained by binarizing the smoothed image smoothed by the smoothing processing unit 341 using a predetermined first luminance threshold. The second candidate image extraction unit 343 extracts a second candidate image obtained by binarizing the smoothed image smoothed by the smoothing processing unit 341 using a second luminance threshold lower than the first luminance threshold. The superposition processing unit 344 superimposes the image of the isolated object that is included in the first candidate image and does not include the contact block with the second candidate image to obtain the main groove bottom image.

Here, the groove of the tire 60 is a general term for main grooves, sub-grooves provided on the tread surface of the tire 60, and chamfers provided at the openings of these grooves. A main groove is a groove that has an obligation to display a wear indicator defined by JATMA. Further, the sub-groove is a lateral groove extending in the tire width direction, and functions as a groove by opening when the tire touches the ground.

The analysis program used in the tire tread analysis device 20 is stored in advance in the storage unit 50, and when analyzing the tread 61 of the tire 60, the program stored in the storage unit 50 is executed by the processing unit 31. , and the processing unit 31 executes an operation according to the program to execute each function.

The tire ground contact shape analysis device 1 according to the present embodiment is configured as described above. The operation of the tire ground contact shape analysis device 1 will be described below. When analyzing the contact patch 61 of the tire 60 by the tire contact shape analysis device 1, the tire 60 is mounted on the support device 3 of the tire testing machine 2, and the tire 60 is rotated while being pressed against the transparent plate 11. , the ground plane 61 is photographed by the camera 15 . At that time, the tires 60 are photographed while being irradiated with light from a plurality of illumination lamps 16 from a plurality of directions. Therefore, the camera 15 can photograph the tire 60 with a difference in brightness between the ground contact surface 61 and the portion other than the contact surface 61 . The photographed image is acquired by the tire contact patch analysis device 20, and the tire contact patch analysis device 20 analyzes the contact patch 61 based on the acquired image.

A distance sensor that detects a difference in height (depth) using a triangulation method can also be used to extract the groove portion of the tire 60 . However, in order to detect the groove portion on the entire ground plane 61, it is necessary to scan the detection range of the distance sensor. Therefore, it is difficult to analyze dynamic ground contact characteristics when the tire 60 is rolling only by using a distance sensor.

(Lighting conditions for shooting)
When acquiring an image of the contact area of the ground contact surface 61 of the tire 60, the illumination lamp 16 can be arranged on the upper surface 11U side of the transparent plate 11 so as to surround the contact surface 61. preferable. When acquiring an image of the contact area of the contact surface 61 of the tire 60, it is preferable to acquire the image by irradiating the tire 60 with light from the illumination lamp 16 arranged so as to surround the contact portion on the upper surface 11U side. .

(Movement of transparent plate and operation of trigger device)
3 and 4 are diagrams for explaining the movement of the transparent plate 11 and the operation of the trigger device 17. FIG. FIG. 3 shows the state before the transparent plate 11 moves and the state before the trigger device 17 detects the light reflected by the retroreflective sheet 18 . FIG. 4 shows the state after the transparent plate 11 has moved and the state when the trigger device 17 detects the light reflected by the retroreflective sheet 18 .

In FIG. 3, the upper surface 11U of the transparent plate 11 is flat, and the upper surface 11U serves as a flat road surface on which the tire 60 rolls. In FIG. 3, the tire 60 is fixed to the rim 4 of the support device 3 while being in contact with the upper surface 11U of the transparent plate 11. As shown in FIG. Therefore, the tire 60 rotates as the transparent plate 11 moves. The tire ground contact shape analysis device 1 moves the transparent plate 11 in the direction of the arrow Y1. As the transparent plate 11 moves in the direction of the arrow Y1, the tire 60 rotates in the direction of the arrow Y2. In the state shown in FIG. 3, the detection section 171 of the trigger device 17 does not detect the light reflected by the retroreflective sheet 18 . Unless the trigger device 17 detects light reflected by the retroreflective sheet 18, the transparent plate 11 continues to move in the direction of the arrow Y1. Since the photographing device 10 is fixed to the transparent plate 11 , the photographing device 10 also moves as the transparent plate 11 moves. The moving speed of the transparent plate 11 is, for example, 0.5 km/h. A rotating drum having a transparent outer peripheral surface may be used instead of the transparent plate 11 .

When the transparent plate 11 moves in the direction of arrow Y1 and enters the state shown in FIG. When the detector 171 of the trigger device 17 detects the reflected light, the tire ground contact shape analysis device 1 outputs a signal to the camera 15 to instruct photography. Thereby, the contact surface 61 of the tire 60 can be photographed. The transparent plate 11 may be transparent in the portion 110 corresponding to the photographing range of the camera 15, and the portion other than the portion 110 may be opaque. That is, the entire transparent plate 11 may be transparent, or only the portion 110 corresponding to the photographing range may be transparent.

(Operation of tire contact shape analysis device)
FIG. 5 is a flowchart showing the operation of the tire ground contact shape analysis device 1. As shown in FIG. When analyzing the tire 60, the tire ground contact shape analysis apparatus 1 irradiates the tire 60 pressed against the transparent plate 11 with light from the lighting lamp 16 (step S201). Next, the tire ground contact shape analysis device 1 starts driving the motor 6 by the motor control device 7 (step S202). When the motor 6 continues to be driven (step S203), the tire ground contact shape analyzer 1 determines whether or not the trigger device 17 has detected the retroreflective sheet 18 (step S204). If the trigger device 17 does not detect the retroreflective sheet 18, the tire contact shape analyzer 1 continues driving the motor 6 (step S204, No→S203).

When the trigger device 17 detects the retroreflective sheet 18, the tire ground contact shape analyzer 1 photographs the tire 60 with the camera 15 (step S204, Yes→S205). After that, the tire contact patch shape analysis device 1 stops driving the motor 6 and irradiating light (step S206).

(Example of specific arrangement and example of photographed image)
Next, a specific arrangement example of the camera 15 and the lighting lamp 16 will be described. 6 to 8 are diagrams showing examples of specific arrangements of the camera 15 and the illumination lamps 16 when the ground plane image acquisition unit 32 acquires the ground plane image. FIG. 6 is a diagram of the arrangement of the lighting lamps 16 viewed from the direction along the rotation axis of the tire 60. As shown in FIG. FIG. 7 is a view of the arrangement of the illumination lamps 16 viewed from the upper surface 11U side of the transparent plate 11. As shown in FIG. FIG. 8 is a view of the arrangement of the lighting lamps 16 viewed from a direction perpendicular to the rotation axis of the tire 60. As shown in FIG. In the following description, the direction along the rotation axis of the tire 60 is called the tire width direction, and the direction perpendicular to the rotation axis is called the tire circumferential direction.

In photographing with this device, the tire 60 to be analyzed had an air pressure of 230 kPa, a load of 6 kN, a rotational speed of 0.5 km/h, and a slip angle of 0°. For the camera 15, the camera gain was set to 3 dB, the F number was set to 4, and the exposure time was set to 1 ms.

6 to 8, the tire 60 is in contact with the upper surface 11U of the transparent plate 11. As shown in FIG. A camera 15 is provided on the lower surface 11D side of the transparent plate 11 . The camera 15 is arranged so that its optical axis 151 is positioned on the normal line of the center point of the ground contact surface 61 of the tire 60 . By arranging the optical axis 151 of the camera 15 to pass through the center point of the ground plane 61 , the ground plane 61 can be photographed from the normal direction of the center point of the ground plane 61 . As a result, stable analysis accuracy can be ensured. The closer to the edge of the captured image, the greater the influence of lens aberration, the more the spatial resolution fluctuates, and the more unstable the analysis accuracy becomes. By arranging the camera 15 in this way, the effect of lens aberration can be minimized.

6 to 8, lamps 161, 162, 163 and 164 are arranged on the upper surface 11U side of the transparent plate 11 as one main surface side lamps. Further, lamps 165 and 166 and a camera 15 are arranged as other main surface side lamps on the 11D side of the transparent plate 11 . Ramps 161 and 162 are arranged at positions separated from tire 60 in the tire circumferential direction. The ramps 161 and 162 are provided on different sides of the tire 60 . Ramp 163 and ramp 164 are arranged at positions separated from tire 60 in the tire width direction. The ramps 163 and 164 are provided on different sides of the tire 60 . Thus, the ramps 161-164 are arranged to surround the ground contact surface 61 of the tire 60. As shown in FIG. If the four sides of the ground contact surface 61 of the tire 60 are not irradiated, it will be difficult to obtain the contour of the ground contact shape, and there is a possibility that the analysis accuracy will decrease. On the other hand, by arranging the lamps 161 to 164 so as to surround the ground contact surface 61 of the tire 60 and irradiating the light on all four sides of the contact surface 61, the contour of the contact shape can be clarified, and the analysis accuracy is improved. can be improved.

6 and 8, the heights from the centers of the light emitting surfaces of the lamps 161 to 164 to the upper surface 11U of the transparent plate 11 are H1 to H4. 6 and 8, the inclination angles of the lamps 161 to 164, ie, the angles formed by the light irradiation direction with respect to the upper surface 11U of the transparent plate 11, are θ1 to θ4. In FIG. 7, distances in the tire circumferential direction from the centers of the light emitting surfaces of the lamps 161 and 162 to the center of the tire 60 are distances D1 and D2. In FIG. 7, distances in the tire width direction from the centers of the light emitting surfaces of the lamps 163 and 164 to the center of the tire 60 are D3 and D4. In FIG. 7, the centers of the light emitting surfaces of the lamps 161 and 162 match the center of the tire.

The heights H1 to H4 are preferably 0 mm or more and 201 mm or less. The minimum value of heights H1 to H4 is 0 mm. This is for placing the illumination lamp 16 on the transparent plate 11 . If the heights H1 to H4 exceed 201 mm, the light from the illumination does not enter the ground plane 61 well, and the outline of the ground plane becomes inaccurate, resulting in a decrease in analysis accuracy, which is not preferable.

The distances D1 and D2 in the tire circumferential direction are preferably larger than half the maximum contact length of the tire 60 and smaller than 1345 mm. However, it is necessary to prevent each lighting lamp 16 from contacting the tire 60 . It is not preferable to make the minimum value of the distances D1 and D2 smaller than half the maximum contact length of the tire 60 . This is to prevent the lighting lamp 16 from contacting the tire 60 . If the distances D1 and D2 exceed 1345 mm, the amount of illumination light impinging on the ground plane 61 is insufficient, the contour of the ground plane 61 becomes inaccurate, and the accuracy of analysis decreases, which is not preferable.

The distances D3 and D4 in the tire width direction are preferably larger than half the maximum contact width of the tire 60 and smaller than 300 mm. However, it is necessary to prevent each lighting lamp 16 from contacting the tire 60 . It is not preferable to make the minimum value of the distances D3 and D4 smaller than half of the maximum contact width of the tire 60 . This is to prevent the illumination lamps 16 from coming into contact with the tire 60 . If the distances D3 and D4 exceed 300 mm, the amount of illumination light impinging on the ground plane 61 is insufficient, the contour of the ground plane 61 becomes inaccurate, and the accuracy of analysis decreases, which is not preferable.

The inclination angles θ1 to θ4 of the lighting lamps 16 are preferably Atan(Hn/Dn)/π*180−0.6° or more and Atan(Hn/Dn)/π*180+0.6° or less ( n=1-4). For θ1 to θ4, it is preferable that each illumination lamp 16 irradiate light toward the center of the ground plane 61 . By irradiating the light in this manner, the light enters the ground plane 61 well. Therefore, the inclination angles θ1 to θ4 of the illumination lamp 16 are preferably Atan(Hn/Dn)/π*180 (n=1 to 4). However, a measurement error of ±0.6° was allowed.

In this embodiment, H1=H2=30 mm, H3=H4=13 mm, D1=D2=260 mm, D3=D4=230 mm, θ1=9.7°, θ2=11.6°, θ3=θ4=0°. did.

By arranging the lamps 161 to 164 as described with reference to FIGS. 6 to 8, light is emitted so as to surround the contact patch 61 of the tire 60, and a contact patch image can be obtained.

6 to 8, lamps 165 and 166 are arranged on the lower surface 11D side of the transparent plate 11 as other main surface side lamps. Both the lamps 165 and 166 are line lights whose longitudinal direction is the tire circumferential direction. The ramps 165 and 166 are arranged at positions separated from each other in the tire width direction of the tire 60 . The ramps 165 and 166 are provided on different sides of the tire 60 . In other words, the lamps 165 and 166 are width direction lamps that irradiate the ground contact surface 61 with light from the outside to the inside in the tire width direction. Thus, the lamps 165 and 166 are arranged so as to irradiate the ground contact surface 61 of the tire 60 with light in the tire width direction. The light from the lamps 165 and 166 can illuminate the edges of the main groove, making it easier to determine the main groove.

Here, in FIG. 8, the heights from the centers of the light emitting surfaces of the lamps 165 and 166 to the lower surface 11D are H5 and H6. In FIG. 8, the inclination angles of the lamps 165 and 166, that is, the angles formed by the light irradiation direction with respect to the lower surface 11D of the transparent plate 11 are θ5 and θ6. In FIG. 7, distances in the tire width direction from the centers of the light emitting surfaces of the lamps 165 and 166 to the center of the tire are D5 and D6. The angles θ5 and θ6 are preferably in the range of 19.4° or more and 22.4° or less. If the heights H5 and H6 change, then the appropriate angles θ5 and θ6 also change. In this case, the images obtained by the camera 15 are displayed live, and the angles θ5 and θ6 are adjusted so that the edge of the main groove shines the most while confirming the displayed contents. In this embodiment, H5=H6=62 mm, D5=D6=215 mm, θ5=21.8°, and θ6=20.1°.

9 and 10 are diagrams for explaining the inclination angles of the ramps 165 and 166 with respect to the tire circumferential direction. In FIG. 9, arrows Y5 and Y6, which are directions of light from lamps 165 and 166, are along the tire width direction. If the light from the lamps 165 and 166 travels in the tire width direction, the edge of the main groove extending in the tire circumferential direction can be illuminated with high brightness.

The longitudinal angle θ15 of the ramp 165 with respect to the tire circumferential direction and the longitudinal angle θ16 of the ramp 166 with respect to the tire circumferential direction shown in FIG. 10 are both preferably 0°. If both the angles θ15 and θ16 are 0°, the longitudinal direction of the lamp 165 and the longitudinal direction of the lamp 166 are parallel, and the brightness of all the chamfers of the main grooves present on the ground contact surface 61 is increased satisfactorily. Stable analysis accuracy can be secured. If the angles θ15 and θ16 are 0°±1°, there is no problem in increasing the chamfered brightness of the main groove. When the angles θ15 and θ16 exceed the range of 0°±1°, it becomes impossible to increase the brightness of all the chamfers of the main grooves present on the ground contact surface 61. It may not be possible, and the accuracy of the analysis may be degraded.

Here, when the edges of the sub-grooves are chamfered, it is preferable that a lamp is provided under the transparent plate so that the light travels in the tire circumferential direction. FIG. 11 is a view of the arrangement of the illumination lamps 16 viewed from the direction along the rotation axis of the tire 60. As shown in FIG. As shown in FIG. 11, lamps 167 and 168 are preferably provided as other-principal-surface side lamps on the lower surface 11D side of the transparent plate 11, which is the other principal surface of the transparent plate 11. As shown in FIG. Both of the lamps 167 and 168 are line lights whose longitudinal direction is the tire width direction. The ramps 167 and 168 are arranged at positions apart from each other in the tire circumferential direction of the tire 60 . Ramp 167 and ramp 168 are provided on different sides of tire 60 . That is, the lamps 167 and 168 are circumferential lamps that irradiate the ground contact surface 61 with light from the outer side to the inner side in the tire circumferential direction. Thus, the lamps 167 and 168 are arranged so as to irradiate the ground contact surface 61 of the tire 60 with light in the tire circumferential direction. The lamps 167, 168 can increase the brightness of the chamfering of the sub-grooves. That is, the lamps 167 and 168 irradiate the ground surface 61 with light that increases the brightness of the edges of the sub-grooves.

In FIG. 11, H7 and H8 are the heights from the centers of the light emitting surfaces of the lamps 167 and 168 to the lower surface 11D. In FIG. 11, the inclination angles of the lamps 167 and 168, that is, the angles formed by the light irradiation direction with respect to the lower surface 11D of the transparent plate 11 are θ7 and θ8. FIG. 12 is a view of the arrangement of the lighting lamps 16 viewed from a direction perpendicular to the rotation axis of the tire 60. As shown in FIG. FIG. 13 is a view of the arrangement of the illumination lamps 16 viewed from the upper surface 11U side of the transparent plate 11. As shown in FIG. In order to maximize the chamfering of the sub-grooves, the angles θ7 and θ8 are preferably 3.5° or more and 6.0° or less. In this embodiment, H7=H8=30 mm, θ7=4.2°, and θ8=4.9°.

In FIG. 13, distances in the tire circumferential direction from the centers of the light emitting surfaces of the lamps 167 and 168 to the center of the tire 60 are D7 and D8. Light from the lamps 167 , 168 can enhance the brightness of the sub-groove chamfers present in the ground plane 61 . In this embodiment, D7=D8=183 mm.

14 and 15 are diagrams for explaining the inclination angles of ramps 167 and 168 with respect to the tire width direction. In FIG. 14, arrows Y7 and Y8, which are directions of light from lamps 167 and 168, are along the tire circumferential direction. If the light from the lamps 167 and 168 travels in the tire circumferential direction, the edges of the sub-grooves extending in the tire width direction can be illuminated with high brightness.

Both the longitudinal angle θ17 of the ramp 167 with respect to the tire width direction and the longitudinal angle θ18 of the ramp 168 with respect to the tire width direction shown in FIG. 15 are preferably 0°. If both the angles θ17 and θ18 are 0°, the longitudinal direction of the lamp 167 and the longitudinal direction of the lamp 168 are parallel to each other, and the brightness of all the chamfered sub-grooves on the ground surface 61 can be increased satisfactorily. Stable analysis accuracy can be secured. If the angles θ17 and θ18 are 0°±1°, there is no problem in increasing the brightness. When the angles θ17 and θ18 exceed the range of 0°±1°, it becomes impossible to increase the brightness of all the chamfers of the sub-grooves present on the ground plane 61. For example, the brightness of only some of the chamfers can be increased. It may not be possible, and the accuracy of the analysis may be degraded.

FIGS. 16 to 21 are diagrams showing examples of illumination of light from lamps 167 and 168 that enhance the brightness of chamfering of sub-grooves. FIG. 16 shows an example of a captured image when the light from the lamps 167 and 168 is strong. FIG. 16 shows an example of a photographed image when the ground plane 61 is irradiated with light having an illuminance of approximately 1,300,000 lux. FIG. 17 is an enlarged view of the sub-groove portion 201 in FIG. In FIG. 17, the edge E1 of the sub-groove shines white, indicating that the amount of light in the tire circumferential direction is sufficient. FIG. 18 is an enlarged view of the sub-groove portion 202 in FIG. In FIG. 18, the edge E2 of the sub-groove shines white, indicating that the amount of light in the tire circumferential direction is sufficient. As shown in FIGS. 17 and 18, when the light from the lamps 167 and 168 is strong and the edges E1 and E2 of the sub-grooves shine white, the difference between the luminance of the grounded portion and the luminance of the edges of the sub-groove is Since it is large, the edge portion of the sub-groove can be easily separated from the photographed image.

FIG. 19 shows an example of a captured image when the light from the lamps 167 and 168 is rather weak. FIG. 19 shows an example of a photographed image when the ground plane 61 is irradiated with light having an illuminance of approximately 600,000 lux. FIG. 20 is an enlarged view of the sub-groove portion 201' in FIG. In FIG. 20, the edge E1' of the sub-groove is not very bright, indicating that the amount of light in the tire circumferential direction is insufficient. FIG. 21 is an enlarged view of the sub-groove portion 202' in FIG. In FIG. 21, the edge E2' of the sub-groove is not very bright, indicating that the amount of light in the tire circumferential direction is insufficient. As shown in FIGS. 20 and 21, when the light from the lamps 167 and 168 is weak and the edges E1' and E2' of the sub-grooves are not very bright, the luminance of the grounded portion and the luminance of the edges of the sub-groove are different. The difference is small, and it is difficult to separate the edge portions of the sub-grooves from the captured image.

As can be seen from FIGS. 16 to 21, it is preferable to set the light from the lamps 167 and 168 to a strong illuminance of about 1,300,000 lux to obtain a photographed image in which the edges of the sub-grooves are illuminated.

6 to 15, the illuminance in the tire width direction and the illuminance in the tire circumferential direction by the lamps 161 to 164 may be of the same degree, or one of them may be greater. As for the lamps 165 to 168, it is preferable to set the illuminance in the tire circumferential direction larger than the illuminance in the tire width direction. Otherwise, the chamfering of the sub-grooves existing on the ground contact surface 61 cannot be made clear, and the analysis accuracy is lowered. The illuminance of each of the lamps 161 to 164 must be equal to or higher than the illuminance of each of the lamps 165 to 168. Otherwise, the contour of the tire ground contact shape cannot be determined and accuracy is reduced.

22 and 23 are diagrams showing examples of the arrangement of the camera 15. FIG. FIG. 22 is a diagram of the camera 15 viewed from the direction along the rotation axis of the tire 60. FIG. FIG. 23 is a view of the camera 15 viewed from a direction perpendicular to the rotation axis of the tire 60. FIG. As shown in FIGS. 22 and 23, camera 15 is preferably provided below ground plane 61 . As shown in FIGS. 22 and 23 , camera 15 is preferably provided below range W1 of ground contact surface 61 in the tire circumferential direction and below range W2 of ground contact surface 61 in the tire width direction. In other words, the camera 15 is provided in a range surrounded by a line extending from the contour of the ground plane 61 in a direction perpendicular to the lower surface 11D of the transparent plate 11 . By arranging the camera 15 in this range, stable analysis accuracy can be ensured. If the camera 15 is moved away from the ground contact surface 61, the groove wall will interfere with the observation of the edge of the main groove, and the accuracy of the analysis will be lowered. 22 and 23, the distance L in the tire radial direction from the lower surface 11D of the transparent plate 11 to the camera 15 is preferably 121 mm or more and 240 mm or less. The distance L in the tire radial direction is, for example, 206 mm. However, the optimum value of the distance L differs depending on the groove width existing in the ground plane 61 .

(Processing of grounding characteristic analysis section)
An example of the processing by the grounding property analysis unit 33 and an image acquired or created by the processing will be described. FIG. 24 is a flowchart showing an example of processing by the grounding characteristic analysis unit 33. As shown in FIG. FIG. 24 shows an example of processing by the processing unit 31 centering on the grounding characteristic analysis unit 33. As shown in FIG. 25 to 31 are diagrams showing examples of images acquired or created by the processing of the grounding characteristic analysis unit 33. FIG.

In FIG. 24, first, the tread image acquisition unit 32 acquires a photographed image of the tread 61 of the tire (step S31). For example, the photographed image shown in FIG. 25 can be acquired by the process of step S31.

Next, the chamfered image extracting unit 34A of the groove extracting unit 34 extracts a portion having luminance higher than a predetermined luminance from the photographed image as a chamfered image indicating the chamfered portion of the groove (step S32). For example, the chamfered image shown in FIG. 26 can be acquired by the process of step S32.

A groove bottom extracting section 34B of the groove extracting section 34 extracts a portion having luminance lower than a predetermined luminance from the photographed image as a groove bottom image indicating the bottom of the groove (step S33). For example, the groove bottom image shown in FIG. 27 can be acquired by the process of step S33.

A main groove bottom extraction unit 34C of the groove extraction unit 34 extracts a low-luminance portion surrounded by a portion having a luminance higher than a predetermined luminance from the photographed image as a main groove bottom image showing the bottom of the main groove (step S34). ). By the process of step S34, for example, the main groove bottom image shown in FIG. 28 can be acquired.

The synthesizing section 34D of the groove extracting section 34 synthesizes the chamfer image, the groove bottom image, and the main groove bottom image to obtain a groove image (step S35). For example, the groove image shown in FIG. 29 can be acquired by the process of step S35.

Next, the grounding characteristic calculator 35 obtains a rough grounding area image by separating high-luminance portions into white and middle- and low-luminance portions into black based on a predetermined threshold value in the captured image (step S36). By the processing in step S36, for example, a rough contact area image shown in FIG. 30 is obtained from the photographed image shown in FIG. This provides a rough ground contact area image, for example, with non-ground contact blocks, groove chamfers and imprints in white, and groove bottoms and contact block portions in black.

Further, the ground contact characteristic calculator 35 subtracts the groove image (FIG. 29) from the rough ground contact area image (FIG. 30) to obtain an actual contact area image (hereinafter abbreviated as ACA) (step S37). By the processing of step S37, for example, the ACA shown in FIG. 31 can be obtained.

Here, "subtracting the groove image from the rough ground area image" refers to subtracting the luminance value of the groove from the luminance value of the rough ground area image for each identical pixel position. However, if the value after subtraction is lower than "0", it is replaced with "0". In this example, after the subtraction process, the erosion process is performed once, the dilation process is performed twice, the erosion process is performed once, the area occupied by the black object of 100 pixels or less is deleted (=replaced with white pixels; the same shall apply hereinafter), the erosion process is performed twice, The expansion treatment was performed four times and the contraction treatment was performed twice in this order. After that, the area occupied by 200 pixels or less of the white object is deleted (=replaced with black pixels; the same applies hereinafter), and the area occupied by the black object of 200 pixels or less is deleted to obtain the ACA shown in FIG.

ACA shown in FIG. 31 is the total area of the blocks that are in contact with the road surface. Based on the ACA shown in FIG. 31, for example, a ground contact area image (hereinafter abbreviated as GCA) shown in FIG. 32 can be obtained.

GCA is the total area of ACA surrounded by the outer ring line when the groove is filled. FIG. 32 is a diagram showing an example of GCA. For the ACA shown in FIG. 31, for example, the order of expansion processing 5 times, contraction processing 10 times, expansion processing 12 times, contraction processing 14 times, expansion processing 17 times, contraction processing 20 times, expansion processing 109 times, contraction processing 99 times , the GCA of FIG. 32 can be obtained.

FIG. 33 is an explanatory diagram of the dilation process. FIG. 34 is an explanatory diagram of contraction processing. As shown in FIG. 33, the expansion process is a process of replacing the target pixel with a black pixel if there is even one black pixel around the target pixel. In other words, dilation processing is performed by using a white pixel as the center pixel, and one of the eight surrounding pixels (upper left, upper, upper right, right, lower right, lower, lower left, and left pixels closest to the center pixel). However, if there is a black pixel, this process replaces the central pixel with the black pixel. Conversely, contraction processing is processing for replacing a target pixel with a white pixel if, for example, a target pixel is a black pixel and there is even one white pixel around the target pixel, as shown in FIG. In other words, the erosion process is performed by using a black pixel as the center pixel and one of the eight surrounding pixels (upper left, upper, upper right, right, lower right, lower, lower left, and left pixels closest to the center pixel). However, if a white pixel exists, the center pixel is replaced with a white pixel.

(Processing of chamfer image extraction unit)
Next, an example of processing of the chamfered image extraction unit 34A will be described. The chamfered image extraction unit 34A performs local binarization processing and extracts a chamfered image indicating the chamfered portion of the groove. The local binarization process is a process in which a weak smoothing process and a strong smoothing process are performed on the ground plane image, and both images are used to obtain the result. 34 A of chamfering image extraction parts perform a smoothing process by a median process in this example.

The chamfered image extracting unit 34A performs a weak smoothing process on the photographed image of the ground plane shown in FIG. 25 to obtain, for example, a reference image shown in FIG. FIG. 35 is a diagram showing an example of a reference image. For the weak smoothing process, for example, a median process using an area within a radius of 4 pixels from the pixel of interest as peripheral pixels can be applied.

Further, the chamfered image extraction unit 34A performs strong smoothing processing on the photographed image of the ground plane shown in FIG. 25, and obtains, for example, the contrast image shown in FIG. FIG. 36 is a diagram showing an example of a comparison image. For the strong smoothing processing of this example, for example, median processing that uses an area within a radius of 40 pixels from the pixel of interest as peripheral pixels can be applied.

Finally, at the same pixel position of the reference image shown in FIG. 35 and the comparison image shown in FIG. By replacing with white pixels, the image shown in FIG. 26 can be obtained. FIG. 26 is a diagram showing an example of the result of performing local binarization processing on the image shown in FIG. For example, let "50" be the above constant. The image shown in FIG. 26 reflects the result of noise removal. For example, black pixel aggregates occupying an area of 500 pixels or less are removed.

(Treatment of Groove Bottom Extraction Part)
Next, an example of the processing of the groove bottom extraction section 34B will be described. The groove bottom extraction unit 34B performs global binarization processing and local binarization processing, respectively, and superimposes the images of the processing results. That is, the brightness of corresponding pixels in the image subjected to the global binarization process and the image subjected to the local binarization process are added.

The global binarization process performed by the groove bottom extraction unit 34B is a process of binarizing the photographed image of the ground surface shown in FIG. After binarization, for noise removal, for example, one contraction process and one expansion process may be performed.

The local binarization processing performed by the groove bottom extracting section 34B is processing in which weak smoothing processing and strong smoothing processing are performed on the ground contact surface image, and the result is obtained using both images. In this example, the groove bottom extraction unit 34B performs smoothing processing by median processing.

The groove bottom extraction unit 34B performs a weak smoothing process on the photographed image of the ground contact surface shown in FIG. 25 to obtain, for example, a reference image shown in FIG. FIG. 35 is a diagram showing an example of a reference image. For the weak smoothing process, for example, a median process using an area within a radius of 4 pixels from the pixel of interest as peripheral pixels can be applied.

Further, the groove bottom extraction unit 34B performs a strong smoothing process on the photographed image of the contact surface shown in FIG. 25, and obtains, for example, a comparison image shown in FIG. FIG. 37 is a diagram showing an example of a comparison image. In the strong smoothing process of this example, for example, an area within ±100 pixels in the tire circumferential direction (horizontal direction of the image) and within ±5 pixels in the tire width direction (vertical direction of the image) from the pixel of interest is A median process can be applied that utilizes as

Next, at the same pixel position of the reference image shown in FIG. 35 and the comparison image shown in FIG. 37, if the luminance value of the reference image is below the threshold obtained by adding a constant to the luminance value of the comparison image, it is a black pixel. By replacing with white pixels, the image shown in FIG. 38 can be obtained. FIG. 38 is a diagram showing an example of the result of performing local binarization processing on the image shown in FIG. For example, let "-40" be the above constant. The image shown in FIG. 38 reflects the result of noise removal. For example, black pixel aggregates occupying an area of 100 pixels or less are removed.

It should be noted that favorable results can be obtained if the absolute value of the above constant is "40" or more. If the absolute value of the difference between the luminance of the bottom of the sub-groove and the average luminance of the surrounding area is "40" or more, the above constant can be set to "-40", and favorable results can be obtained. If the absolute value of the above luminance difference cannot be ensured to be "40" or more, the value of the above constant must be set to, for example, "-20", and grounding error judgment (for example, grounding block is mistaken as "ungrounded") judgment, etc.) occur, and favorable results cannot be obtained.

Finally, the groove bottom extracting unit 34B applies the global binarization processing to the photographed image of the contact surface shown in FIG. 25 and the image shown in FIG. The brightness of pixels at the same position in both images is added to the image after being processed in order. If the added luminance exceeds the upper limit of luminance "255", it is replaced with luminance "255". Through the above processing, the groove bottom extraction unit 34B obtains the groove bottom image shown in FIG.

(Processing of Main Groove Bottom Extracted Portion)
Next, an example of the processing of the main groove bottom extraction section 34C in step S34 of FIG. 24 will be described in more detail. FIG. 39 is a flow diagram showing an example of processing by the main groove bottom extraction section 34C.

In FIG. 39, first, the smoothing processing unit 341 performs smoothing processing on the captured image in the tire circumferential direction (step S341). For example, the smoothed image shown in FIG. 40 is obtained by the processing in step S341. FIG. 40 is a diagram showing an example of a smoothed image. Smoothing processing in the tire circumferential direction is processing for smoothing luminance using a peripheral region that is long in the tire circumferential direction. For example, when smoothing by applying a median filter, a region of ± 100 pixels in the tire circumferential direction (horizontal direction of the image) and ± 2.5 pixels in the tire width direction (vertical direction of the image) from the pixel of interest is a peripheral region , to smooth.

Next, the first candidate image extraction unit 342 extracts a first candidate image obtained by binarizing the smoothed image obtained in the process of step S341 using a predetermined first luminance threshold (step S342). By the process of step S342, for example, the first candidate image shown in FIG. 41 is obtained. FIG. 41 is a diagram showing an example of the first candidate image. In the process of step S342, for example, the first candidate image is obtained by setting the high-luminance portion to white and the medium- and low-luminance portions to black based on the first luminance threshold for the smoothed image. As shown in FIG. 41, the first candidate image is an image obtained by extracting isolated object portions G2, G3, and G4 separated by the edge of the main groove as the main groove bottom.

Further, the second candidate image extraction unit 343 extracts a second candidate image obtained by binarizing the smoothed image obtained in the process of step S341 using a second luminance threshold lower than the first luminance threshold (step S343). ). By the process of step S343, for example, the second candidate image shown in FIG. 42 is obtained. FIG. 42 is a diagram showing an example of the second candidate image. In the processing of step S343, for example, a second candidate image is obtained by separating the smoothed image into high-luminance and medium-luminance portions as white and low-luminance portions as black based on the second luminance threshold. Thereby, for example, the groove bottom can be extracted for the main groove having a relatively narrow groove width. As shown in FIG. 42, the second candidate image is an image obtained by extracting the portion that could not be extracted as the edge of the main groove, that is, the portion G1 in FIG. 41 as the main groove bottom.

Furthermore, the superimposition processing unit 344 superimposes the image of the isolated object that is included in the first candidate image (FIG. 41) and does not include the ground block such as the land area with the second candidate image (FIG. 42) to obtain the main image. A groove bottom image is obtained (step S344). By the process of step S344, for example, the main groove bottom image shown in FIG. 28 can be acquired. In the process of step S344, the brightness of pixels at the same position in both images is added. If the added luminance exceeds the upper limit of luminance "255", it is replaced with luminance "255". Through the above processing, the superposition processing unit 344 obtains the main groove bottom image shown in FIG.

(Processing of First Candidate Image Extraction Unit)
43 and 44 are diagrams for explaining the processing of the first candidate image extraction unit 342. FIG. First, the first candidate image extraction unit 342 performs the above-described smoothing process in the tire circumferential direction as the weak smoothing process on the captured image of the ground contact surface. The first candidate image extracting unit 342 also performs median processing using regions within a radius of 100 pixels from the pixel of interest as peripheral pixels as strong smoothing processing on the captured image of the ground plane. The first candidate image extraction unit 342 uses the image obtained by the weak smoothing process as a reference image and the image obtained by the strong smoothing process as a comparison image. At the same pixel position of the comparison image, if the luminance value of the reference image exceeds the threshold value obtained by adding a constant to the luminance value of the comparison image, it is replaced with a black pixel. If not, it is replaced with a white pixel. be able to. For example, let "30" be the above constant.

Further, the first candidate image extraction unit 342 performs global binarization processing with a brightness threshold value of “220” on the image obtained by the above-described smoothing processing in the tire circumferential direction, thereby obtaining the image shown in FIG. get The first candidate image extraction unit 342 subtracts the image shown in FIG. 43 from the image shown in FIG. 43 and 44, the luminance value is subtracted for each identical pixel position. However, if the value after subtraction is lower than "0", it is replaced with "0". The first candidate image extraction unit 342 can obtain the image shown in FIG. 41 by performing the above processing.

(Processing of Second Candidate Image Extraction Unit)
The second candidate image extraction unit 343 extracts the second candidate image by local binarization processing. As a weak smoothing process, the second candidate image extraction unit 343 uses, as peripheral pixels, areas within a radius of 4 pixels from the pixel of interest in the image obtained by, for example, the above-described smoothing process in the tire circumferential direction. A median process can be applied to obtain a reference image. As strong smoothing processing, the second candidate image extraction unit 343 uses, as peripheral pixels, regions within a radius of 40 pixels from the pixel of interest in the image obtained by the above-described smoothing processing in the tire circumferential direction. Median processing can be applied to obtain contrast images.

The second candidate image extraction unit 343 extracts a black pixel if the brightness value of the reference image is below a threshold obtained by adding a constant to the brightness value of the comparison image at the same pixel position of the reference image and the comparison image, and otherwise Replace with white pixels. At this time, for example, "-40" is set as the above constant. Finally, the second candidate image extraction unit 343 removes, for example, black objects occupying an area of 3000 pixels or less in the image to obtain a second candidate image for noise removal.

(Processing of superimposition processing unit)
45 to 47 are diagrams for explaining the processing of the overlay processing unit 344. FIG. First, the superposition processing section 344 designates the position of the main groove in the first candidate image, as shown in FIG. "X" in FIG. 45 indicates the position of the designated main groove. In FIG. 45, portions G1, G2, G3 and G4 are designated.

The main groove may be specified by the operator of the apparatus manually operating the input unit 21 while checking the screen of the display unit 22, or by using AI (Artificial Intelligence) or the like. . Also, for each portion in FIG. 45, a portion in which the ratio of the number of pixels in the horizontal direction (horizontal direction) to the number of pixels in the vertical direction (vertical direction) exceeds a predetermined threshold is designated as the main groove. may

Next, the superimposition processing unit 344 displays the image in which the positions of the main grooves are specified, with the outline emphasized, as shown in FIG. In FIG. 46, the outline is indicated by a dashed-dotted line for convenience of drawing, but it is preferable to emphasize the outline by displaying it in red, for example.

Furthermore, the superimposition processing unit 344 extracts the portion whose contour is emphasized as the main groove bottom if it does not include a contact block such as a land portion. As a result, the overlay processing unit 344 obtains an image including portions G2, G3 and G4 as shown in FIG. The image shown in FIG. 47 is an image obtained by extracting portions G2, G3 and G4 in FIG. A portion G1 in FIG. 45 is a portion including a ground block such as a land portion, so it is not extracted as the main groove bottom portion.

Here, whether or not the portion includes the ground block is determined by, for example, whether or not the number of pixels in the vertical direction (vertical direction) of the image forming the portion exceeds a predetermined threshold. For example, the number of pixels "150" is set as a threshold, and if the number of pixels in the vertical direction (vertical direction) of the rectangular image surrounding the part with the contour emphasized exceeds the threshold "150", it is determined that the part includes the ground block. , is not extracted as the main groove bottom. 47 and the second candidate image (FIG. 42) to obtain a main groove bottom image (FIG. 28).

(Processing of engraving extractor)
By the way, the tread surface of the tire 60 may be provided with markings. Inscriptions are identification lines and article numbers. When there is a mark on the tread surface of the tire 60, the luminance is high, and it may affect the ground contact image and cause an analysis error.

If the tread surface of the tire 60 has markings, it is preferable that the chamfered image extraction unit 34A and the contact characteristic calculation unit 35 process an image in which the markings are corrected. For this purpose, it is preferable that the image of the stamp is extracted by the stamp extraction unit 40 and the correction is performed using the extracted image.

FIG. 48 is a diagram showing an example of an image obtained by extracting a high-brightness portion from the captured image (FIG. 25). As shown in FIG. 48, when the marking extraction unit 40 extracts the chamfered portion of the groove as the high-brightness portion, the marking portion 203 is extracted as the high-brightness portion. After local binarization processing is performed on the photographed image (FIG. 25), the engraving extraction unit 40 removes a group of black pixels occupying an area of 100 pixels or less for noise removal, designates the engraving position, and extracts the engraving image. to extract

In the local binarization process, the stamp extraction unit 40 applies, as a weak smoothing process, a median process that uses an area within a radius of 4 pixels from the pixel of interest to the captured image (FIG. 25) as peripheral pixels. be able to. In the local binarization process, the mark extraction unit 40 can apply median processing that uses a region within a radius of 40 pixels from the pixel of interest as peripheral pixels as strong smoothing processing. In the local binarization process, the stamp extraction unit 40 replaces the luminance value of the reference image with a black pixel if it exceeds a threshold obtained by adding a constant to the luminance value of the comparison image, and replaces it with a white pixel if it does not. For example, let "50" be the above constant.

FIG. 49 is a diagram showing an example of a stamp image extracted by the stamp extraction unit 40. As shown in FIG. The designation of the marking position by the marking extraction unit 40 may be made manually by the operator of the apparatus while checking the screen, or may be designated using AI or the like. The stamp extracting unit 40 may designate a portion as a stamp when a specific character is included in the binarized image of the photographed image.

After extracting the high-brightness portion of the photographed image (FIG. 25), the stamp extracting unit 40 performs a subtraction process of subtracting the image of FIG. 49 from the image of FIG. 48, for example. More specifically, for each pixel corresponding to the image shown in FIG. 48 and the stamp image shown in FIG. 49, the luminance of the pixels forming the latter image is subtracted from the luminance of the pixels forming the former image. At this time, between the image shown in FIG. 48 and the engraved image shown in FIG. 49, the marking extracting unit 40 subtracts the brightness of pixels at the same position in both images. If the value after subtraction is lower than "0", it is replaced with "0". A chamfered image shown in FIG. 26 is obtained by the processing of the mark extraction unit 40 . The chamfered image shown in FIG. 26 has the stamped portion 203 of the image shown in FIG. 48 removed. Therefore, the chamfered image extraction unit 34A can extract the chamfered image from which the stamp has been removed. In other words, the chamfered image extraction unit 34A obtains a chamfered image by excluding the portion corresponding to the stamp included in the captured image, among the portions having brightness higher than the predetermined brightness, from the captured image.

FIG. 50 is a diagram showing an example of a rough ground area image in which the high-luminance portion is white and the medium- and low-luminance portions are black based on a predetermined threshold for the captured image (FIG. 25). As shown in FIG. 50, the stamped portion 204 is extracted as a high-brightness portion when creating a rough grounding area image. Therefore, the stamp extracting unit 40 performs addition processing for superimposing the image in FIG. 50 and the image in FIG. 49 . More specifically, for each corresponding pixel in the image shown in FIG. 50 and the stamp image shown in FIG. 49, the brightness of the pixels forming both images is added. At this time, the mark extraction unit 40 adds the brightness of pixels at the same position in the image shown in FIG. 50 and the image shown in FIG. 49 . If the added luminance exceeds the upper limit of luminance "255", it is replaced with luminance "255". A rough contact area image shown in FIG. 30 is obtained by the processing of the mark extraction unit 40 . The rough ground area image shown in FIG. 30 has the imprinted portion 204 of the image shown in FIG. 50 removed. Accordingly, the ground contact characteristic calculator 35 can obtain a rough ground contact area image from which the imprint has been removed. In other words, the ground contact characteristic calculation unit 35 converts the portion of the image obtained by binarizing the captured image using the predetermined luminance as a threshold value, excluding the portion corresponding to the stamp included in the captured image, into a rough contact area image. and

(Tire contact shape analysis method)
The tire ground contact shape analysis device 1 described above implements the following tire ground contact shape analysis method shown in FIG. FIG. 51 is a flowchart showing a tire contact shape analysis method implemented by the tire contact shape analysis apparatus.

In FIG. 51, first, a photographed image of the ground contact surface of the pneumatic tire to be analyzed is acquired with light that increases the brightness of the edge of the groove (step S41). Next, the contact surface image obtained in step S41 is analyzed to obtain contact characteristics (step S42). By adopting this tire ground contact shape analysis method, it is possible to accurately analyze the dynamic ground contact characteristics of a tire in a short time.

1 tire contact shape analysis device 2 tire testing machine 3 support device 4 rim 5 drive device 6 motor 7 motor control device 10 photographing device 11 transparent plate 11D lower surface 11U upper surface 15 camera 16 illumination lamp 17 trigger device 20 tire contact surface analysis device 21 Input unit 22 Display unit 30 Processing unit 31 Processing unit 32 Contact patch image acquisition unit 33 Contact property analysis unit 34 Groove extraction unit 34A Chamfer image extraction unit 34B Groove bottom extraction unit 34C Main groove bottom extraction unit 34D Synthesis unit 35 Contact property calculation unit 40 marking extraction unit 50 storage unit 60 tire 61 tread 161 to 168 lamp 171 detection unit 341 smoothing processing unit 342 first candidate image extraction unit 343 second candidate image extraction unit 344 superimposition processing unit

Claims (9)

An illumination unit that irradiates the tread surface of the tire to be analyzed with light that enhances the brightness of the edge of the groove provided in the tire tread portion, and the tread surface of the tire was photographed by the light emitted from the illumination unit. a ground plane image acquisition unit that acquires a captured image; and a ground plane image acquisition unit that analyzes the ground plane image acquired by the ground plane image acquisition unit and obtains a ground plane characteristic ,
The grounding characteristic analysis unit
a groove extraction unit for extracting a groove image from the photographed image;
a contact characteristic calculation unit that subtracts the groove image from a rough contact area image obtained by binarizing the photographed image using a predetermined luminance as a threshold;
The groove extracting part is
a chamfered image extraction unit for extracting a portion having a luminance higher than a predetermined luminance from the photographed image as a chamfered image showing a chamfered portion of the groove;
a groove bottom extraction unit that extracts a portion having luminance lower than a predetermined luminance from the photographed image as a groove bottom image indicating the bottom of the groove;
a main groove bottom extraction unit that extracts a low-luminance portion surrounded by portions having luminance higher than a predetermined luminance from the photographed image as a main groove bottom image showing the bottom of the main groove;
a synthesizing unit for synthesizing the chamfer image, the groove bottom image, and the main groove bottom image to obtain the groove image;
including
Tire contact shape analyzer. The tire contacts one main surface of the transparent plate,
The illumination unit
including one principal surface side lamp provided on one principal surface side of the transparent plate and another principal surface side lamp provided on the other principal surface side of the transparent plate so as to surround the ground contact surface of the tire. ,
2. The tire ground contact shape analysis device according to claim 1, wherein the other principal surface side lamp includes a width direction lamp that irradiates the ground contact surface with light from the outside to the inside in the tire width direction. 3. The tire ground contact shape analysis device according to claim 2, further comprising a camera for photographing the contact patch of the tire, wherein the camera photographs the contact patch of the tire from a normal direction of a center point of the contact patch of the tire. . The camera is
4. The tire contact shape analysis device according to claim 3, which is provided in a range surrounded by a line extending in a direction perpendicular to the other main surface side of the transparent plate from the contour of the contact patch of the tire. The tire contact patch shape according to any one of claims 2 to 4, wherein the other principal surface side lamp includes a circumferential lamp that irradiates the contact surface with light from the outer side to the inner side in the tire circumferential direction. analysis equipment. 6. The rough ground contact area is defined by the ground contact characteristic calculation unit, in the image obtained by the binarization process, by excluding a portion corresponding to the stamp contained in the captured image. The tire contact shape analysis device according to any one of. The main groove bottom extraction portion is
A smoothing processing unit that smoothes the photographed image in the circumferential direction of the tire; a first candidate image extraction unit for extracting; a second candidate image extraction unit for extracting a second candidate image obtained by binarizing the smoothed image using a second luminance threshold lower than the first luminance threshold; 7. A superposition processing unit for obtaining the main groove bottom image by superimposing an image of an isolated object that is included in the first candidate image and does not include the ground contact block and the second candidate image. The tire contact shape analysis device according to any one of. The chamfered image extraction unit
8. The chamfered image is defined as a portion of the photographed image obtained by excluding a portion corresponding to the stamp included in the photographed image from among portions having luminance higher than the predetermined luminance . 3. The tire contact shape analysis device according to 1. a contact patch image acquiring step of acquiring a photographed image of the contact patch of the tire, which is an analysis target, by light that is irradiated onto the contact patch of the tire and increases the brightness of edges of grooves provided in the tire tread portion; a ground contact characteristics analysis step of analyzing the ground contact image acquired by the contact face image obtaining step to determine the ground contact characteristics ,
The ground characteristic analysis step includes:
a groove extraction process for extracting a groove image from the photographed image;
a contact characteristic calculation process of subtracting the groove image from a rough contact area image obtained by binarizing the captured image using a predetermined luminance as a threshold;
The groove extraction process includes
A chamfered image extraction process for extracting a portion having a brightness higher than a predetermined brightness from the photographed image as a chamfered image showing a chamfered portion of the groove;
Groove bottom extraction processing for extracting a portion having luminance lower than a predetermined luminance from the photographed image as a groove bottom image showing the bottom of the groove;
Main groove bottom extraction processing for extracting a low-luminance portion surrounded by portions having luminance higher than a predetermined luminance from the photographed image as a main groove bottom image showing the bottom of the main groove;
Synthesis processing for synthesizing the chamfer image, the groove bottom image, and the main groove bottom image to obtain the groove image;
including
Tire contact shape analysis method.

Images