Friction tester

Abstract

To provide a friction tester capable of measuring frictional force, detecting lubrication conditions related to oil film thickness, and measuring surface roughness.SOLUTION: A friction tester 1 includes a movement mechanism 20, a friction force measurement unit 30, a lubrication state detection unit 40, and a surface roughness measurement unit 50. The movement mechanism 20 causes a pair of test pieces T1 and T2 to move relative to each other and slide against each other. The friction force measurement unit 30 measures the frictional force between the pair of test pieces T1 and T2. The lubrication state detection unit 40 measures the oil film thickness between the pair of test pieces T1 and T2. The surface roughness measurement unit 50 measures the surface roughness of a sliding mark M formed on the second test piece T2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a friction tester. [Background technology]

[0002] Patent Document 1 discloses a conventional friction tester. This friction tester is a pin-on-disk type and is equipped with a motor that rotates and slides a disk, which is one test piece, against a pin, which is the other test piece, a torque detector that detects the torque generated by the motor, and an oil film sensor that measures the oil film thickness between the pin and the disk. This friction tester can obtain the friction force between the pin and the disk from the difference between the torque under no load detected by the torque detector and the torque when the pin and the disk are slid against each other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-26581 Summary of the Invention [Problem to be solved by the invention]

[0004] The friction tester in Patent Document 1 can measure the friction force between test pieces and the oil film thickness between the test pieces, but cannot measure the surface roughness of the test pieces. Surface roughness is closely related to friction. Therefore, in order to elucidate friction phenomena, it is desirable to automatically measure the friction force, oil film thickness, and surface roughness.

[0005] The present invention has been made in view of the above-mentioned conventional circumstances, and an object to be achieved by the present invention is to provide a friction tester that can measure friction force, detect the lubrication state related to oil film thickness, and measure surface roughness. [Means for solving the problem]

[0006] The friction tester of the present invention comprises a moving mechanism, a friction force measuring unit, a lubrication state detecting unit, and a roughness measuring unit. The moving mechanism moves a pair of test pieces relative to each other to cause them to slide. The friction force measuring unit measures the friction force between the pair of test pieces. The lubrication state detecting unit detects the lubrication state between the pair of test pieces. The roughness measuring unit measures the surface roughness of the sliding marks made on one of the test pieces. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram showing the configuration of a friction tester according to a first embodiment. [Figure 2] 1 is a schematic diagram showing a main part of a friction tester according to a first embodiment. [Figure 3] FIG. 2 is a diagram showing roughness measurement points in the first embodiment. [Figure 4] 10A and 10B are schematic diagrams showing a friction tester according to another embodiment, in which (A) is a plan view and (B) is a front view. DETAILED DESCRIPTION OF THE INVENTION

[0008] First, embodiments of the present invention will be listed and described. Any combination of the following embodiments without causing any contradiction is also included in the form for carrying out the present invention. [1] The friction tester of the present invention includes a moving mechanism for moving and sliding a pair of test pieces relative to one another, a friction force measuring unit for measuring the friction force between the pair of test pieces, a lubrication state detecting unit for detecting the lubrication state between the pair of test pieces, and a roughness measuring unit for measuring the surface roughness of the sliding marks made on one of the test pieces. Because this friction tester includes a friction force measuring unit, a lubrication state detecting unit, and a roughness measuring unit, it can measure friction force, lubrication state, and surface roughness. In other words, this friction tester can measure surface roughness while maintaining lubrication. The data regarding friction force, lubrication state, and surface roughness obtained by this friction tester can be used to predict friction characteristics using machine learning. [2] The friction tester described in [1] above includes a control unit that controls the movement mechanism with respect to the relative movement of the pair of test pieces. The control unit performs measurements by the friction force measurement unit and detection by the lubrication state detection unit while driving the movement mechanism to slide the pair of test pieces, and performs measurements by the roughness measurement unit when the movement mechanism is stopped. The friction tester can repeatedly perform measurements by the friction force measurement unit, detection by the lubrication state detection unit, and measurements by the roughness measurement unit. In this case, the friction tester can stop the relative movement of the pair of test pieces at a predetermined timing or change sliding conditions such as the movement speed and acceleration. In this way, the friction tester repeatedly stops and moves the pair of test pieces relative to each other, measuring the friction force and detecting the lubrication state during movement, i.e., during sliding, and measuring the surface roughness when stopped. Furthermore, the friction tester can change sliding conditions to measure friction force, detect the lubrication state, and measure surface roughness. Therefore, a person who uses this friction tester to measure friction force, detect lubrication state, and measure surface roughness (hereinafter referred to as "measurer") can understand the changes in friction force, lubrication state, and surface roughness over time depending on the sliding conditions. [3] In the friction tester described in [2] above, the movement mechanism is configured to move one of the test pieces to be measured by the roughness measurement unit, and the control unit can control the movement mechanism so that one of the test pieces stops at a predetermined position relative to the roughness measurement unit, thereby controlling the roughness measurement unit to measure the surface roughness of the sliding marks. In this case, the surface roughness of the sliding marks measured by the roughness measurement unit of this friction tester is not affected by variations in the measurement position. This allows the person making the measurement to accurately understand changes in surface roughness due to friction. [4] In the friction tester described in any one of [1] to [3] above, the roughness measurement unit can measure the surface roughness in the sliding direction in which the pair of test pieces move and slide relative to each other, and the surface roughness in the direction perpendicular to the sliding direction. In this case, the measurer can determine the surface roughness related to friction from the surface roughness in the sliding direction measured by the roughness measurement unit of the friction tester, and can determine the amount of wear from the surface roughness in the direction perpendicular to the sliding direction. [5] In the friction tester according to any one of [1] to [4] above, the roughness measuring unit may be a contact type. In this case, the friction tester can accurately evaluate the surface quality of the test piece even in a lubricated state.

[0009] <Embodiment 1> A first embodiment of the friction tester of the present invention will be described with reference to the drawings. As shown in FIG. 1 , the friction tester 1 of the first embodiment includes a base 10, a moving mechanism 20, a friction force measuring unit 30, a lubrication state detecting unit 40, a roughness measuring unit 50, a data acquisition system 60, and a personal computer 70. A pair of test pieces T1 and T2 are attached to the friction tester 1, with the pin-shaped first test piece T1 and the disk-shaped second test piece T2 moving and sliding relative to each other. In other words, the friction tester 1 is a pin-on-disk type. The first test piece T1 and the second test piece T2 are made of conductive metal such as aluminum or steel.

[0010] The movement mechanism 20 rotates the second test piece T2, sliding the bottom surface of the first test piece T1 over the top surface of the second test piece T2. The movement mechanism 20 includes a stepping motor 21, a motor driver 23, a rotary table 25, and a slip ring 27. The rotation shaft of the stepping motor 21 extends vertically. Upon receiving a pulse signal, the motor driver 23 rotates the rotation shaft of the stepping motor 21 by a fixed angle in a set direction. In this way, the motor driver 23 rotates the rotation shaft of the stepping motor 21 to a predetermined rotation angle and stops it depending on the number of pulses. The motor driver 23 can also change the rotation speed and acceleration of the stepping motor 21 by controlling the pulse frequency.

[0011] The motor driver 23 is connected to a personal computer 70. The personal computer 70 transmits pulse signals to the motor driver 23 and controls the movement mechanism 20 with respect to the rotation, stopping, rotation speed, acceleration, etc. of the stepping motor 21. The personal computer 70 corresponds to a control unit.

[0012] The turntable 25 is disk-shaped. The outer diameter of the turntable 25 is approximately the same as the outer diameter of the disk-shaped second test piece T2. The turntable 25 has an electrode plate 25A forming the upper surface and an insulating plate 25B stacked below the electrode plate 25A. The turntable 25 is connected to the rotating shaft of the stepping motor 21. The turntable 25 is rotatable on the base 10 of the friction tester 1. The turntable 25 can hold the second test piece T2 on its upper surface. When the turntable 25 holds the second test piece T2, the upper surface of the electrode plate 25A comes into contact with the lower surface of the second test piece T2. The second test piece T2 held on the turntable 25 rotates together with the turntable 25 in accordance with the rotation of the rotating shaft of the stepping motor 21. The electrode plate 25A is connected to an LCR meter 41 (described later) via a slip ring 27. That is, the lead wire L1 connected to the electrode plate 25A is connected to the rotating side of the slip ring 27. The lead wire L2 connected to the fixed side is connected to one measurement terminal of the LCR meter 41.

[0013] The friction force measuring unit 30 measures the friction force between the lower end surface of the first test piece T1 and the upper surface of the second test piece T2. The friction force measuring unit 30 has a metal arm 31 and a displacement meter 33. The displacement meter 33 is equipped with a strain gauge 35 (see FIG. 2). One end of the metal arm 31 is connected via a hinge to the upper end of a first support column P1 that stands up from the base 10. The metal arm 31 extends horizontally in a straight line from the upper end of the first support column P1. The metal arm 31 is movable vertically along an arc with one end as the center. The other end of the metal arm 31 is located above the rotary table 25. The other end of the metal arm 31 holds the upper end of the pin-shaped first test piece T1. The first test piece T1 held at the tip of the metal arm 31 extends vertically. A downward pressure force F is applied to the first test piece T1 by placing a weight on the other end of the metal arm 31. The pressure force F causes the lower end surface of the first test piece T1 to come into contact with the upper surface of the second test piece T2.

[0014] As shown in FIG. 2, a strain gauge 35 constituting a displacement meter 33 is attached to the side of the metal arm 31. The friction force measuring unit 30 uses the strain gauge 35 to detect strain when the friction force applied to the first test piece T1 due to the rotation of the second test piece T2 held on the turntable 25 is transmitted to the metal arm 31, causing the metal arm 31 to deform. The strain data detected by the strain gauge 35 is collected by a data collection system 60. A personal computer 70 connected to the data collection system 60 calibrates the relationship between the bending stress and strain generated by the load in the direction of the friction force, and calculates the friction force between the first test piece T1 and the second test piece T2 from the strain data collected by the data collection system 60. In this way, the friction force measuring unit 30 can measure the friction force between the first test piece T1 and the second test piece T2 using the displacement meter 33 equipped with the strain gauge 35.

[0015] As shown in FIGS. 1 and 2, in the friction tester 1, an oil film S is formed between the lower end surface of the first test piece T1 and the upper surface of the second test piece T2. The lubrication state detection unit 40 detects the lubrication state between the lower end surface of the first test piece T1 and the upper surface of the second test piece T2. The lubrication state detection unit 40 includes an LCR meter 41. The LCR meter 41 has a pair of measurement terminals. One measurement terminal of the LCR meter 41 is connected to a lead wire L2 connected to the fixed side of the slip ring 27. The rotating side of the slip ring 27 is connected to a lead wire L2 connected to the electrode plate 25A. The upper surface of the electrode plate 25A is in contact with the lower surface of the second test piece T2. Therefore, one measurement terminal of the LCR meter 41 is electrically connected to the second test piece T2. The other measurement terminal of the LCR meter 41 is connected to the first test piece T1 via a lead wire L3 and is electrically connected to the first test piece T1. Therefore, the LCR meter 41 can measure the impedance and phase angle that change depending on the thickness of the oil film S between the lower end surface of the first test piece T1 and the upper surface of the second test piece T2.

[0016] The LCR meter 41 is connected to a personal computer 70. The personal computer 70 calculates the oil film thickness and contact ratio (oil film rupture rate) between the lower end surface of the first test piece T1 and the upper surface of the second test piece T2 by an electrical impedance method from the impedance and phase angle measured by the LCR meter 41. The personal computer 70 instructs the LCR meter 41 to measure the impedance and phase angle only while the second test piece T2 held on the turntable 25 is rotating and sliding on the first test piece T1, and controls the lubrication state detection unit 40.

[0017] The movement mechanism 20 rotates the second test piece T2, sliding the top surface of the second test piece T2 against the bottom surface of the first test piece T1, leaving a circular sliding mark M on the top surface of the second test piece T2, as shown in FIG. 3. The roughness measurement unit 50 measures the surface roughness of the sliding mark M on the top surface of the second test piece T2. As shown in FIGS. 1 and 2, the roughness measurement unit 50 is a contact type in which a probe 53B moves while making contact with the top surface of the second test piece T2 to detect its surface roughness. Because the roughness measurement unit 50 is a contact type, it can accurately measure surface roughness even when the sliding surface is wet with lubricant. The roughness measurement unit 50 includes an arm 51, a detection unit 53, and a controller 55. The arm 51 is attached to a second support P2 that extends from the base 10 so as to be freely movable in the vertical direction. The arm 51 extends horizontally in a straight line from the second support P2. The detection unit 53 includes an extension 53A and a probe 53B. The extension 53A extends from the tip of the arm 51 in the same direction as the extension of the arm 51. The extension 53A is movable in the extending direction, and the length by which it protrudes from the tip of the arm 51 changes. The probe 53B is provided at the tip of the extension 53A. As shown in FIG. 3, the probe 53B is movable in the radial direction R of the second test piece T2 as the extension 53A moves relative to the arm 51.

[0018] As shown in FIG. 1, the controller 55 controls the vertical movement of the arm 51 and the horizontal movement of the extension 53A. When the lower end of the probe 53B moves in the radial direction R of the second test piece T2 while contacting the upper surface of the second test piece T2, the controller 55 acquires height data of the lower end of the probe 53B at the movement position of the probe 53B. In other words, the roughness measuring unit 50 is capable of freely moving the probe 53B in a direction perpendicular to the sliding direction C between the first test piece T1 and the second test piece T2, and can measure the surface roughness in the direction perpendicular to the sliding direction C (see FIG. 3). Furthermore, when the roughness measuring unit 50 brings the probe 53B into contact with any position of the sliding mark M made on the upper surface of the second test piece T2 and rotates the rotation shaft of the stepping motor 21 by a predetermined angle, it can measure the surface roughness in the sliding direction C within that rotation range (see FIG. 3).

[0019] The controller 55 is connected to a personal computer 70. The personal computer 70 instructs the controller 55 to measure the surface roughness of the sliding mark M while the second test piece T2 held on the rotary table 25 is stopped at a predetermined position, thereby controlling the roughness measurement unit 50. The data measured by the roughness measurement unit 50 is saved in the personal computer 70 as cross-sectional curve (profile) data each time a measurement is performed. Based on the saved cross-sectional curve data, the personal computer 70 calculates parameters indicating surface roughness specified in JIS B 0601 and the like, such as Ra (arithmetic mean roughness), Rq (root mean square height), Rpk (protruding peak height), Rvk (protruding valley depth), and Rk (level difference of the core portion), using roughness analysis software.

[0020] Next, the measurement of friction force, detection of lubrication state, and measurement of surface roughness by this friction tester 1 will be described. This friction tester 1 uses the movement mechanism 20 to repeatedly rotate and stop the second test piece T2 for a predetermined period of time. For example, the movement mechanism 20 stops the second test piece T2 every 60 seconds of rotation. At this time, the movement mechanism 20 controls the stepping motor 21 by a program so that the measurement position where the roughness measurement unit 50 measures the surface roughness is always the same, and stops the rotation of the second test piece T2 at a predetermined position.

[0021] In this friction tester 1, while the second test piece T2 is rotating, the friction force measurement unit 30 measures the friction force between the bottom end surface of the first test piece T1 and the top surface of the second test piece T2, and the circulation state detection unit detects the lubrication state between the bottom end surface of the first test piece T1 and the top surface of the second test piece T2. The friction force measurement and lubrication state detection are performed, for example, every 100 msec. While the second test piece T2 is stationary, the roughness measurement unit 50 measures the surface roughness of the sliding marks M made on the top surface of the second test piece T2 in a direction R perpendicular to the sliding direction C (see Figure 3). The roughness measurement unit 50 measures, for example, an 8 mm measurement length in the direction perpendicular to the sliding direction C at 0.5 μm intervals. The cross-sectional curve data, which is point cloud data of 16,000 measured points, is saved to the personal computer 70 in CSV format or the like after each measurement.

[0022] In this friction tester 1, while the second test piece T2 is stationary, the probe 53B of the roughness measuring unit 50 is brought into contact with a predetermined position of the sliding mark M on the top surface of the second test piece T2, and the stepping motor 21 is controlled by a program to rotate the second test piece T2 by a predetermined angle so as to obtain the desired arc length. This allows the surface roughness of the sliding mark M in the sliding direction C to be measured within that rotation range (see FIG. 3). In this case, too, the roughness measuring unit 50 measures, for example, a measurement length of 8 mm in the arc direction at 0.5 μm intervals. The cross-sectional curve data, which is point cloud data of the measured 16,000 points, is saved in CSV format or the like to the personal computer 70 after each measurement.

[0023] The computer 70 calculates parameters Ra, Rq, Rpk, Rvk, Rk, etc., which indicate surface roughness as defined in JIS B 0601 and the like, using roughness analysis software based on the saved profile curve data.

[0024] The friction tester 1 of the first embodiment described above includes a moving mechanism 20 that rotates the second test piece T2 and slides it against the first test piece T1; a friction force measuring unit 30 that measures the friction force between the bottom end surface of the first test piece T1 and the top surface of the second test piece T2; a lubrication condition detecting unit 40 that detects the lubrication condition between the bottom end surface of the first test piece T1 and the top surface of the second test piece T2; and a roughness measuring unit 50 that measures the surface roughness of the sliding marks M left on the top surface of the second test piece T2. Because the friction tester 1 includes the friction force measuring unit 30, the lubrication condition detecting unit 40, and the roughness measuring unit 50, it can automatically measure the friction force, lubrication condition, and surface roughness. In other words, the friction tester 1 can measure surface roughness while maintaining the lubrication condition. Data regarding the friction force, lubrication condition, and surface roughness obtained by the friction tester 1 can be used to predict friction characteristics using machine learning.

[0025] The friction tester 1 includes a personal computer 70 that controls the movement mechanism 20 with respect to the rotation of the second test piece T2. The personal computer 70 performs measurements by the friction force measurement unit 30 and detection by the lubrication state detection unit 40 while driving the movement mechanism 20 to cause the first test piece T1 and the second test piece T2 to slide against each other. When the movement mechanism 20 is stopped, the personal computer 70 performs measurements by the roughness measurement unit 50. The friction force measurement unit 30, detection by the lubrication state detection unit 40, and measurement by the roughness measurement unit 50 are repeated. Therefore, the friction tester 1 can stop the rotation of the second test piece T2 at a predetermined timing or change sliding conditions such as the rotation speed and rotation acceleration. In this way, the friction tester 1 repeatedly rotates and stops the second test piece T2, thereby measuring the friction force and detecting the lubrication state during rotation, i.e., during sliding, and measuring the surface roughness when stopped. Furthermore, this friction tester 1 can measure frictional force, detect lubrication state, and measure surface roughness by changing sliding conditions, allowing the person performing the measurement to understand changes over time in frictional force, lubrication state, and surface roughness depending on the sliding conditions.

[0026] In this friction tester 1, the movement mechanism 20 is configured to move the second test piece T2 to be measured by the roughness measurement unit 50, and the personal computer 70 controls the movement mechanism 20 so that the second test piece T2 stops at a predetermined position relative to the roughness measurement unit 50, and controls the roughness measurement unit 50 so that the surface roughness of the sliding mark M is measured. Therefore, the surface roughness of the sliding mark M measured by the roughness measurement unit 50 of this friction tester 1 is not affected by variations in the measurement position. This allows the person making the measurement to accurately understand changes in surface roughness due to friction.

[0027] In this friction tester 1, the roughness measurement unit 50 measures the surface roughness in a sliding direction C in which the second test piece T2 rotates and slides against the first test piece T1, and the surface roughness in a direction R perpendicular to the sliding direction C. The person measuring can determine the surface roughness related to friction from the surface roughness in the sliding direction C measured by the roughness measurement unit 50 of the friction tester 1, and can determine the amount of wear from the surface roughness in the direction R perpendicular to the sliding direction C.

[0028] In this friction tester 1, the roughness measuring unit 50 is of a contact type. Therefore, this friction tester 1 can accurately evaluate the surface texture of the second test piece T2 even in a lubricated state.

[0029] The present invention is not limited to the first embodiment described above with reference to the drawings, and the following embodiments are also included within the technical scope of the present invention. (1) In the first embodiment, the friction tester 1 is a pin-on-disk type. However, it may be a ball-on-disk type, a thrust cylinder type, a block-on-disk type, or other type. For example, as shown in FIG. 4, it may be a friction tester 2 in which the outer surfaces of a pair of ring-shaped test pieces T3 and T4 slide against each other. In this friction tester 2, the rotation axes of the test pieces T3 and T4 extend parallel to the horizontal direction. In this friction tester 2, oil L is supplied from above the sliding portion of the test pieces T3 and T4, and an oil film S is formed on the outer surfaces of the test pieces T3 and T4. The movement mechanism of this friction tester 2 is a motor (not shown) that rotates one of the test pieces around the rotation axis. The friction force measurement unit of this friction tester 2 calculates the friction force from the torque of the motor. The lubrication state detection unit of this friction tester 2 calculates the oil film thickness and contact ratio between the pair of ring-shaped test pieces T3, T4 from the impedance and phase angle measured by the LCR meter 141 connected to each of the test pieces T3, T4. The roughness measurement unit of this friction tester has a pair of probes 153B that contact the outer circumferential surface of each of the test pieces T3, T4, and measures the surface roughness of the outer circumferential surface while each of the test pieces T3, T4 is rotating.

[0030] (2) In the first embodiment, there is one roughness measuring unit 50. However, the surface roughness in the sliding direction and the surface roughness in the direction perpendicular to the sliding direction may be measured by two different roughness measuring units. (3) In the first embodiment, the second test piece T2 is rotated and slid on the first test piece T1. Alternatively, the first test piece may be moved circumferentially around the central axis of the second test piece to slide on the second test piece. (4) In the first embodiment, the frictional force measuring unit 30 measures the frictional force using the displacement meter 33 that uses the strain gauge 35. However, the frictional force measuring unit may measure the frictional force using other methods. (5) In the first embodiment, the oil film thickness and contact ratio were calculated using the electrical impedance method. However, other methods may be used to calculate the oil film thickness, etc. Furthermore, methods that can determine the lubrication state even if the oil film thickness cannot be quantitatively measured may also be used. Other electrical methods, such as capacitance or contact electrical resistance, may be used. In this case, the oil film thickness is unknown, but the contact ratio α is. In this case, α = 1 for boundary lubrication, α = 0 for hydrodynamic lubrication, and 1 > α > 0 for mixed lubrication. When considering the Stribeck curve, friction coefficient data alone is insufficient to distinguish between boundary lubrication and hydrodynamic lubrication even when the friction coefficient value is the same. Introducing the contact ratio α makes this possible. This is extremely important when using machine learning to analyze data and predict friction coefficients. (6) In the first embodiment, the surface roughness parameters are calculated using roughness analysis software based on the profile curve data. However, the profile curve data may be filtered to calculate waviness and surface shape, which are surface characteristics from a more macroscopic perspective than surface roughness.

[0031] (7) In the first embodiment, the frictional force is measured using a strain gauge. However, for example, a capacitance-type displacement meter may be used to detect the amount of displacement of the metal arm elastically deformed by the frictional force, and the relationship between the amount of displacement and the frictional force may be calibrated, and then the amount of displacement may be converted into the frictional force. (8) In the first embodiment, the second test piece T2 is rotated, and the first test piece T1 is slid over the second test piece. However, the second test piece may be reciprocated by a linear actuator, and the first test piece may be slid over the second test piece. (9) In the first embodiment, the first test piece T1 is pin-shaped. However, the first test piece may be ball-shaped. (10) In the first embodiment, the first test piece T1 was a pin-like piece that did not move. In contrast, the first test piece T1 may rotate or swing while sliding against the second test piece. The friction and wear characteristics are affected by the surface roughness of both test pieces. For this reason, the first test piece may be made rotatable and swingable, and the roughness of the first test piece may be measured in addition to the roughness of the second test piece. [Explanation of symbols]

[0032] 1, 2... friction tester, T1, T2, T3, T4... test pieces (T1... first test piece, T2... second test piece), 20... moving mechanism, 21... stepping motor, 30... friction force measuring unit, 40... lubrication state detecting unit, 50... roughness measuring unit, 70... personal computer (control unit), M... sliding mark

Claims

1. a moving mechanism that moves and slides the pair of test pieces relative to one another; a friction force measuring unit that measures the friction force between the pair of test pieces; a lubrication state detection unit that detects a lubrication state between the pair of test pieces; a roughness measuring unit that measures the surface roughness of the sliding marks made on one of the test pieces; A friction testing machine equipped with:

2. a control unit that controls the movement mechanism with respect to the relative movement of the pair of test pieces; 2. The friction testing machine according to claim 1, wherein the control unit performs measurement by the friction force measuring unit and detection by the lubrication state detecting unit while driving the moving mechanism to slide the pair of test pieces, and performs measurement by the roughness measuring unit when the moving mechanism is stopped, and repeatedly performs measurement by the friction force measuring unit, detection by the lubrication state detecting unit, and measurement by the roughness measuring unit.

3. the moving mechanism is configured to move one of the test pieces to be measured by the roughness measuring unit, 3. The friction testing machine according to claim 2, wherein the control unit controls the moving mechanism so that one of the test pieces stops at a predetermined position relative to the roughness measuring unit, and controls the roughness measuring unit so as to measure the surface roughness of the sliding mark.

4. 2. The friction tester according to claim 1, wherein the roughness measuring unit measures the surface roughness in a sliding direction in which the pair of test pieces move and slide relative to each other, and in a direction perpendicular to the sliding direction.

5. 5. The friction tester according to claim 1, wherein the roughness measuring unit is a contact type.

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