JP2013113672A - Rubber friction test method and rubber friction test device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber friction test method and a rubber friction test device for appropriately evaluating frictional abrasion characteristics of a rubber test piece by obtaining the contact surface shape of the rubber test piece and calculating distortion distribution in the contact surface.SOLUTION: A rubber friction test method includes: a pattern formation process of forming a pattern 13 for image analysis on the outer peripheral surface 11 of a doughnut-like rubber test piece 1; a friction test process of rotating the rubber test piece 1 and a rotary drum 2 the cylindrical part 21 of which is formed of a transparent material while bringing the outer peripheral surface 11 of the rubber test piece 1 into contact with the rotary drum 2; an image acquisition process of photographing the outer peripheral surface 11 through the cylindrical part 21 simultaneously with the friction test process to acquire an outer peripheral surface image 11P; and an evaluation process of evaluating frictional abrasion characteristics of the rubber test piece 1 by obtaining the contact surface shape of the rubber test piece 1 from the acquired outer peripheral surface image 11P and calculating distortion distribution in the contact surface of the rubber test piece 1 on the basis of the pattern 13 for image analysis included in the outer peripheral surface image 11P.

Description

  The present invention relates to a rubber friction test method and a rubber friction test apparatus for evaluating the friction and wear characteristics of rubber test pieces.

  In order to examine the friction and wear characteristics of a tire, a friction test apparatus and a friction test method for contacting a sample tire with a rotary drum are known. The frictional wear characteristics of the tire are affected by the deformation of the tire during the friction test, specifically, the shape of the tire contact surface, the strain distribution in the contact surface, and the like. For this reason, observation of the contact surface shape, calculation of the strain distribution in the contact surface, and the like are important for appropriate evaluation of the friction and wear characteristics of the tire.

  In Patent Document 1 below, in order to photograph the ground contact surface of a tire with respect to an ice road surface, a transparent plate having an ice layer formed on the surface thereof, and light substantially parallel to the transparent plate and / or the inside of the ice layer is provided. There is disclosed a tire ground contact surface measuring device including light irradiating means for irradiating and photographing means for photographing a tire ground contact surface from the opposite side of the ice layer. According to the tire contact surface measuring apparatus, the contour of the tire contact surface shape can be photographed with high accuracy, but the strain distribution in the contact surface cannot be calculated.

  In Patent Document 2 below, a grid surface is provided on the surface of the side portion of the tire, and images of the grid surface are acquired by two cameras in a state where the tire is rotated and intermittently illuminated by a strobe device. Discloses a tire shape measuring method for regenerating the shape of the side portion at the time of rolling of the tire. However, according to this tire shape measuring method, it is possible to obtain the shape and strain distribution of the tire side part, but since the ground contact surface of the tire cannot be observed, the ground contact surface shape and the strain distribution in the ground contact surface are obtained. I can't.

JP 2005-24365 A Japanese Patent Laid-Open No. 10-38533

  The present invention has been made in view of the above circumstances, and its purpose is to obtain a contact surface shape of a rubber test piece and calculate a strain distribution in the contact surface when evaluating the frictional wear characteristics of the rubber test piece. Accordingly, an object of the present invention is to provide a rubber friction test method and a rubber friction test apparatus capable of appropriately evaluating the friction and wear characteristics of a rubber test piece.

The above object can be achieved by the present invention as described below. That is, the rubber friction test method according to the present invention is a rubber friction test method for evaluating the friction and wear characteristics of a rubber test piece,
A pattern forming step of forming an image analysis pattern on the outer peripheral surface of the doughnut-shaped rubber test piece;
A friction test step of rotating the rubber test piece and the rotary drum while bringing the outer peripheral surface of the rubber test piece into contact with the rotary drum having a cylindrical portion formed of a transparent material;
Simultaneously with the friction test step, an image acquisition step of taking an image of the outer peripheral surface of the rubber test piece through the cylindrical portion of the rotary drum and acquiring an outer peripheral surface image;
By obtaining the contact surface shape of the rubber test piece from the acquired outer peripheral surface image, and calculating the strain distribution in the contact surface of the rubber test piece based on the image analysis pattern included in the outer peripheral surface image. And an evaluation step for evaluating the frictional wear characteristics of the test piece.

  According to such a configuration, since the cylindrical portion of the rotary drum is formed of a transparent material, the outer peripheral surface of the rubber test piece in contact with the cylindrical portion is photographed through the cylindrical portion to acquire an outer peripheral surface image. be able to. By acquiring the outer peripheral surface image, the shape of the contact surface of the rubber test piece can be obtained, and the strain distribution in the contact surface of the rubber test piece is calculated based on the image analysis pattern formed on the outer peripheral surface. Therefore, the friction and wear characteristics of the rubber specimen can be appropriately evaluated.

  In the rubber friction test method of the present invention, in the pattern formation step, an image analysis pattern is further formed on the side surface of the rubber test piece, and in the image acquisition step, the side surface of the rubber test piece is photographed to obtain a side image. And it is preferable that the said evaluation process includes the process of evaluating the deformation | transformation of a rubber test piece by matching the image analysis pattern contained in the said outer peripheral surface image, and the image analysis pattern contained in the said side surface image. According to such a configuration, since it is possible to evaluate the distortion of the outer peripheral surface and the side surface of the rubber test piece in the contact state, that is, the deformation of the entire rubber test piece, the frictional wear characteristics of the rubber test piece can be more appropriately evaluated. .

  In the rubber friction test method of the present invention, it is preferable that the image analysis pattern is a point pattern in which dots are regularly arranged vertically and horizontally. According to this configuration, it is easy to form the image analysis pattern on the rubber test piece, and it is also easy to analyze the image analysis pattern included in the acquired outer peripheral surface image and / or side surface image. Therefore, the friction and wear characteristics of the rubber test piece can be appropriately evaluated.

On the other hand, a rubber friction test apparatus according to the present invention is a rubber friction test apparatus for evaluating the friction and wear characteristics of a rubber test piece,
A rotary drum having a cylindrical portion formed of a transparent material and capable of being driven to rotate;
A test piece contact means capable of contacting a donut-shaped rubber test piece having an image analysis pattern formed on the outer peripheral surface thereof in a rotating state with the cylindrical portion of the rotary drum;
Photographing means for photographing the outer peripheral surface of the rubber test piece through the cylindrical portion of the rotary drum to obtain an outer peripheral surface image;
An evaluation means for evaluating the friction and wear characteristics of the rubber test piece based on the acquired outer peripheral surface image,
The evaluation means includes strain distribution calculation means for calculating a strain distribution in the contact surface of the rubber test piece based on the image analysis pattern included in the outer peripheral surface image.

  According to such a configuration, since the cylindrical portion of the rotary drum is formed of a transparent material, the outer peripheral surface of the rubber test piece in contact with the cylindrical portion is photographed through the cylindrical portion to acquire an outer peripheral surface image. be able to. By acquiring the outer peripheral surface image, the shape of the contact surface of the rubber test piece can be obtained, and the strain distribution in the contact surface of the rubber test piece is calculated based on the image analysis pattern formed on the outer peripheral surface. Therefore, the friction and wear characteristics of the rubber specimen can be appropriately evaluated.

  In the rubber friction test apparatus according to the present invention, a mirror is further provided on the inner surface side of the cylindrical portion of the rotary drum, and the photographing means is brought into contact with the outer surface side of the cylindrical portion of the rotary drum via the mirror. It is preferable to photograph the outer peripheral surface of the rubber test piece. According to this configuration, since it is not necessary to arrange the test piece contact means and the photographing means inside the rotary drum, the size of the rotary drum can be reduced.

Perspective view showing the outline of the friction test of rubber specimens Side view of rubber friction test equipment Top view of rubber friction test equipment Front view and side view showing details of rubber test piece Schematic configuration diagram showing the overall configuration of a rubber friction test apparatus according to the present invention The figure which shows an example of the outer peripheral surface image which image | photographed the outer peripheral surface of the rubber test piece (A) Speed distribution at the contact surface of the rubber test piece, (b) Strain distribution at the contact surface of the rubber test piece

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an outline of a friction test of a rubber test piece. FIG. 2 is a side view of the rubber friction test apparatus, and FIG. 3 is a plan view of the rubber friction test apparatus. FIG. 4 is a front view and a side view showing details of the rubber test piece. FIG. 5 is a schematic configuration diagram showing the overall configuration of the rubber friction test apparatus according to the present invention.

  The rubber friction test method and the rubber friction test apparatus of the present invention are for evaluating the friction and wear characteristics of rubber test pieces. As shown in FIG. 1, the rubber test piece friction test is performed by rotating and contacting the rubber test piece 1 and the rotary drum 2 with a rotary drive device.

  As shown in the figure, the rubber friction test apparatus according to the present invention includes a rotary drum 2 in which a cylindrical portion 21 is formed of a transparent material and can be driven to rotate, and a donut in which an image analysis pattern 13 is formed on an outer peripheral surface 11. The test piece contact means 3 capable of rotating the rubber test piece 1 in contact with the cylindrical portion 21 of the rotary drum 2 and the outer peripheral surface 11 of the rubber test piece 1 through the cylindrical portion 21 of the rotary drum 2. A photographing unit 41 for acquiring an outer peripheral surface image, and an evaluation unit 51 for evaluating the frictional wear characteristic of the rubber test piece 1 based on the acquired outer peripheral surface image.

  The rubber test piece 1 has a donut shape or a cylindrical shape, and includes an outer peripheral surface 11 and a side surface 12. For example, the rubber test piece 1 has an outer diameter of 50 mm, an inner diameter of 23 mm, and a width of 10 mm. In the present embodiment, image analysis patterns 13 and 14 are formed on the outer peripheral surface 11 and the side surface 12, respectively.

  The image analysis pattern 13 formed on the outer peripheral surface 11 is a point pattern in which the points 13a are regularly arranged vertically and horizontally. The image analysis pattern 13 may be provided on the entire outer peripheral surface 11 or only on a part thereof. The points 13a have a diameter of 0.3 to 0.4 mm, for example, and the distance between the points 13a is 1 mm. When the rubber test piece 1 is black, the point 13a is formed of white or the like in order to improve visibility.

  The image analysis pattern 14 formed on the side surface 12 is a point pattern in which the points 14a are regularly arranged vertically and horizontally. The image analysis pattern 14 may be provided on the entire side surface 12 or only on a part thereof, and in this example, only two dot sequences are provided. The points 14a have a diameter of 0.2 mm, for example, and the interval between the points 14a is 0.5 mm. When the rubber test piece 1 is black, the point 14a is formed of white or the like in order to improve visibility.

  The rubber test piece 1 is brought into rotational contact with the rotary drum 2 by the test piece contact means 3. The test piece contact means 3 includes a test piece rotation shaft 31 to which the rubber test piece 1 is fixed, and a test piece rotation drive device 32 that rotationally drives the test piece rotation shaft 31. As the test piece rotation drive device 32, an electric motor or the like is exemplified, and the rotating shaft 31 can be driven by the electric motor and can be braked by applying a braking torque. Further, a separate brake means may be provided to brake the rotating shaft 31.

  Moreover, it is preferable that the test piece contact means 3 has a load loading mechanism that applies a force perpendicular to the rotary drum 2 so that a predetermined load is applied to the rubber test piece 1. Examples of this mechanism include a hydraulic device and a device using an elastic restoring force. Moreover, you may provide the measuring device for measuring a load.

  The rotary drum 2 includes a cylindrical portion 21 and a disc portion 22 and has a bottomed cylindrical shape as a whole. The outer peripheral surface of the cylindrical portion 21 of the rotary drum 2 is in rotational contact with the outer peripheral surface of the rubber test piece 1, and a rubber friction test is performed.

  The cylindrical portion 21 has a cylindrical shape with a constant thickness. The cylindrical portion 21 has, for example, an outer diameter of 250 mm, a width of 40 mm, and a thickness of 10 mm. The width of the cylindrical portion 21 is at least larger than the width of the rubber test piece 1. The cylindrical portion 21 is made of a transparent material. The transparent material may be colorless and transparent or colored and transparent, but it is preferable to use a colorless and transparent material. Examples of the transparent material include inorganic glass such as tempered glass, plastic such as polyvinyl chloride, polystyrene, acrylic resin, and polycarbonate resin, and acrylic resin is preferable from the viewpoint of strength and workability.

  The disc portion 22 has a plate shape having a predetermined radius, and is fixed to the end portion of the cylindrical portion 21. As shown in the figure, the disk portion 22 is provided with an observation hole 22a. The center of the disc portion 22 is supported by the drum rotation shaft 61 via the support portion 23. The drum rotation shaft 61 is rotationally driven by a drum rotation driving device 62. Thereby, the rotary drum 2 can be rotationally driven in the same manner as the rubber test piece 1. The drum rotation driving device 62 and the test piece rotation driving device 32 are controlled by the rotation control means 52 to start, stop, and the number of rotations.

  The photographing means 41 is disposed at a position where the outer peripheral surface 11 of the rubber test piece 1 can be photographed from the opposite side of the rubber test piece 1 through the cylindrical portion 21 of the rotary drum 2. In the present embodiment, the mirror 7 is provided on the inner surface side of the cylindrical portion 21 of the rotary drum 2, and the photographing means 41 photographs the outer peripheral surface 11 of the rubber test piece 1 through the mirror 7 and the outer peripheral surface image 11P. Can be obtained. However, the mirror 7 may not be provided, and the photographing means 41 may be disposed on the inner surface side of the cylindrical portion 21 of the rotary drum 2 so as to directly photograph the outer peripheral surface 11 of the rubber test piece 1.

  The rubber friction test apparatus according to the present embodiment includes an imaging unit 42 in addition to the imaging unit 41. The photographing means 42 is disposed at a position where the side surface 12 of the rubber test piece 1 can be photographed. The photographing means 42 can photograph the side surface 12 of the rubber test piece 1 to obtain a side image 12P. The photographing means 41 and the photographing means 42 are preferably synchronized and photograph the rubber test piece 1 at the same time.

  As the photographing means 41 and 42, a CCD camera, a video camera, a high-speed camera, or the like can be used. In the present invention, it is preferable to use a high-speed camera so that the image analysis patterns 13 and 14 can be photographed in detail. . The outer peripheral surface image 11P and the side surface image 12P respectively photographed by the photographing means 41 and the photographing means 42 are taken into the evaluation means 51, and the frictional wear characteristics of the rubber test piece 1 are evaluated based on the outer peripheral surface image 11P and the side surface image 12P. Is done. The outer peripheral surface image 11P and the side surface image 12P are stored in the memory 53 and then analyzed by the evaluation unit 51.

  The evaluation unit 51 includes a strain distribution calculation unit 54 that calculates a strain distribution in the contact surface of the rubber test piece 1 based on the image analysis pattern 13 included in the outer peripheral surface image 11P. Specifically, the strain distribution calculating unit 54 compares the image analysis pattern 13 at a certain point in time with the reference image analysis pattern 13 and measures the displacement of each corresponding point 13a. A strain distribution can be calculated.

  A more specific method for calculating distortion is as follows. First, the barycentric coordinates are calculated by binarization for each point 13a of the image analysis pattern 13. This is repeated, and time-series data when one point 13a flows in the rotation direction is acquired (for example, 80 frames in the range of FIG. 6). Next, for each point 13a, the change in the distance between the two points at the center of gravity of the adjacent point 13a is calculated. Then, distortion is calculated in comparison with the reference image analysis pattern 13. The distortion in two directions is calculated separately for the rotation direction and the width direction.

  The strain distribution calculating means 54 can also calculate the strain distribution on the side surface 12 of the rubber test piece 1 based on the image analysis pattern 14 included in the side image 12P. When the strain distribution on the outer peripheral surface 11 of the rubber test piece 1 and the strain distribution on the side surface 12 are made to correspond to each other, it is not possible to perform from one direction by comparing the stepping of the contact surface in each direction, the kicking position, and the strain variation. 3D evaluation is possible.

  The processing control device 5 includes an evaluation unit 51, a rotation control unit 52, a memory 53, a strain distribution calculation unit 54, and the like, and is connected to an input / output device 55 such as a personal computer. The operator can operate the processing control device 5 via the input / output device 55 and can browse and analyze images and data in the processing control device 5.

  The illumination 8 is disposed on the side of the rotary drum 2, particularly on the side of the cylindrical portion 21. The illumination 8 is arranged so that light substantially parallel to the width direction of the cylindrical portion 21 can be irradiated to the inside of the cylindrical portion 21. Therefore, the light is totally reflected inside the cylindrical portion 21, and the light hardly comes outside except the contact surface of the rubber test piece 1. Thereby, the contact surface of the rubber test piece 1 becomes particularly bright and can be clearly distinguished from the other portions.

  This makes it possible to acquire the coordinates of the contact surface end from the outer peripheral surface image 11P, and determine the stepping position and kicking position of the contact surface. The speed and strain can be evaluated in more detail by considering the positional relationship between the inside and outside of the contact surface, the stepping-in, and the kicking-out.

  Next, the rubber friction test method of the present invention using the rubber friction test apparatus as described above will be described. The rubber friction test method of the present invention is a rubber friction test method for evaluating the friction and wear characteristics of the rubber test piece 1 and forms a pattern 13 for image analysis on the outer peripheral surface 11 of the doughnut-shaped rubber test piece 1. A friction test step of rotating the rubber test piece 1 and the rotary drum 2 while bringing the outer peripheral surface 11 of the rubber test piece 1 into contact with the rotary drum 2 having the cylindrical portion 21 formed of a transparent material, Simultaneously with the test process, the outer peripheral surface 11 of the rubber test piece 1 is photographed through the cylindrical portion 21 of the rotary drum 2 to acquire the outer peripheral surface image 11P, and the rubber test piece 1 is obtained from the acquired outer peripheral surface image 11P. The frictional wear characteristic of the rubber test piece 1 is obtained by obtaining the contact surface shape and calculating the strain distribution in the contact surface of the rubber test piece 1 based on the image analysis pattern 13 included in the outer peripheral surface image 11P. Includes a worthy evaluation process, the.

  Further, in the rubber friction test method of the present invention, the image analysis pattern 14 is further formed on the side surface 12 of the rubber test piece 1 in the pattern formation step, and the side surface 12 of the rubber test piece 1 is photographed in the image acquisition step. The side image 12P is acquired, and the evaluation step evaluates the deformation of the rubber test piece 1 by associating the image analysis pattern 13 included in the outer peripheral surface image 11P with the image analysis pattern 14 included in the side image 12P. It is preferable to include a process.

  Image analysis patterns 13 and 14 are formed in advance on the outer peripheral surface 11 and the side surface 12 of the rubber test piece 1. The rubber test piece 1 is fixed to the test piece rotating shaft 31 of the test piece contact means 3, and while the rubber test piece 1 is in contact with the rotary drum 2, both are rotated to perform a rubber friction test. At this time, the rubber test piece 1 is photographed by the photographing means 41 and 42, and the outer peripheral surface image 11P and the side image 12P of the rubber test piece 1 are acquired.

  FIG. 6 shows an example of the outer peripheral surface image 11P. When the outer peripheral surface 11 of the rubber test piece 1 is rotating in the direction of the arrow, the first half of the contact surface forms an adhesion zone Pa in which no slip occurs with respect to the rotary drum 2, and the second half rotates. A slip region Ps that is in a slip state with respect to the expression drum 2 is formed. Thus, the area | region which united the adhesion area | region Pa and the sliding area | region Ps is a contact surface, and the contact surface shape of the rubber test piece 1 can be obtained from the outer peripheral surface image 11P.

  Further, the outer peripheral surface image 11P includes an image analysis pattern 13. By comparing the image analysis pattern 13 at a certain time point with the image analysis pattern 13 after a lapse of a minute time, the speed of each point 13a. Can be calculated. The boundary point between the adhesion area Pa and the slip area Ps can be determined from the calculated speed fluctuation. If there are a plurality of points in the width direction as in the image analysis pattern 13, the boundary points calculated for each of them can be connected to determine the boundary line BL between the adhesion area Pa of the contact surface and the sliding area Ps. Further, the distortion distribution can be calculated by comparing the image analysis pattern 13 at a certain point in time with the reference image analysis pattern 13 and measuring the displacement of each corresponding point 13a.

  The velocity distribution at the contact surface of the rubber test piece 1 calculated according to the present invention is shown in FIG. 7 (a), and the strain distribution at the contact surface of the rubber test piece 1 is shown in FIG. 7 (b). In the adhesion area Pa, the speed of the rubber test piece 1 is substantially the same as that of the rotary drum 2, and the distortion of the rubber test piece 1 is compressed (minus direction) and does not change significantly. In the sliding region Ps, the speed of the rubber test piece 1 increases as the distance from the adhesion region Pa increases, and temporarily exceeds the reference rotational speed of the rubber test piece 1 at the end of the sliding region Ps. The distortion of the rubber test piece 1 changes in tension (in the positive direction), and the direction is reversed between the stepping side and the kicking side.

[Other Embodiments]
(1) In the above-described embodiment, the photographing means 41 and the photographing means 42 are used to photograph the outer peripheral surface 11 and the side surface 12 of the rubber test piece 1, but it is not always necessary to provide two photographing means. The outer peripheral surface 11 and the side surface 12 may be photographed separately using only the photographing means 41. In this case, the outer peripheral surface 11 and the side surface 12 of the rubber test piece 1 may be marked, and the acquired outer peripheral surface image 11P and the side image 12P may be associated with each other after acquiring the images.

  (2) In the above-described embodiment, the rubber test piece 1 having a relatively small size is used. However, by increasing the size of the rotary drum 2, the sample tire is used as the rubber test piece 1 and the tire is frictionally worn. Properties can also be evaluated directly.

  (3) When photographing the outer peripheral surface 11 of the rubber test piece 1, one photographing means 41 is used, but by further photographing the outer peripheral surface 11 using another photographing means arranged so as to be adjacent to each other, The displacement in the depth direction (thickness direction of the rubber test piece 1) can also be evaluated, and more detailed data can be obtained. The same applies to the side surface 12 of the rubber test piece 1.

DESCRIPTION OF SYMBOLS 1 Rubber test piece 2 Rotary drum 3 Test piece contact means 7 Mirror 8 Illumination 11 Outer peripheral surface 11P Outer peripheral surface image 12 Side surface 12P Side surface image 13 Image analysis pattern 13a Point 14 Image analysis pattern 14a Point 21 Cylindrical portion 22 Disc portion 41 photographing means 42 photographing means 51 evaluating means 54 strain distribution calculating means

Claims (5)

A rubber friction test method for evaluating the friction and wear characteristics of a rubber test piece,
A pattern forming step of forming an image analysis pattern on the outer peripheral surface of the doughnut-shaped rubber test piece;
A friction test step of rotating the rubber test piece and the rotary drum while bringing the outer peripheral surface of the rubber test piece into contact with the rotary drum having a cylindrical portion formed of a transparent material;
Simultaneously with the friction test step, an image acquisition step of taking an image of the outer peripheral surface of the rubber test piece through the cylindrical portion of the rotary drum and acquiring an outer peripheral surface image;
By obtaining the contact surface shape of the rubber test piece from the acquired outer peripheral surface image, and calculating the strain distribution in the contact surface of the rubber test piece based on the image analysis pattern included in the outer peripheral surface image. A rubber friction test method comprising: an evaluation step for evaluating the friction and wear characteristics of the test piece.   In the pattern formation step, an image analysis pattern is further formed on the side surface of the rubber test piece. In the image acquisition step, the side surface image is obtained by photographing the side surface of the rubber test piece. The rubber friction according to claim 1, further comprising a step of evaluating deformation of the rubber test piece by associating the image analysis pattern included in the surface image with the image analysis pattern included in the side image. Test method.   The rubber friction test method according to claim 1, wherein the image analysis pattern is a point pattern in which dots are regularly arranged vertically and horizontally. A rubber friction test device for evaluating the friction and wear characteristics of a rubber test piece,
A rotary drum having a cylindrical portion formed of a transparent material and capable of being driven to rotate;
A test piece contact means capable of contacting a donut-shaped rubber test piece having an image analysis pattern formed on the outer peripheral surface thereof in a rotating state with the cylindrical portion of the rotary drum;
Photographing means for photographing the outer peripheral surface of the rubber test piece through the cylindrical portion of the rotary drum to obtain an outer peripheral surface image;
An evaluation means for evaluating the friction and wear characteristics of the rubber test piece based on the acquired outer peripheral surface image,
The rubber friction test apparatus characterized in that the evaluation means includes a strain distribution calculation means for calculating a strain distribution in the contact surface of the rubber test piece based on the image analysis pattern included in the outer peripheral surface image. A mirror is further provided on the inner surface side of the cylindrical portion of the rotary drum,
5. The rubber friction test apparatus according to claim 4, wherein the photographing unit photographs the outer peripheral surface of the rubber test piece that is in contact with the outer surface side of the cylindrical portion of the rotary drum via the mirror. .

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