JP3837276B2 - Film thickness measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a film thickness measuring device that measures the thickness of an oil film by an optical interference method.
[0002]
[Prior art]
An oil film is applied to the rolling and sliding surfaces for lubrication. Conventionally, the optical interference method has been widely used as a method for measuring the thickness of an oil film. In this type of measurement method, the surface of the oil film and the surface of the sample are irradiated by light irradiating means on the surface of the sample of the rolling member or the sliding member via, for example, a flat translucent plate whose back surface is in contact with the oil film. The interference light generated by the reflected light from the light is received through the light receiving means, and the thickness of the oil film is measured based on the phase difference of the interference light.
[0003]
When a bearing ball made of a steel ball having a relatively high light reflectance on the surface is used as a sample, the interference light accounts for about 90% of the light received by the light receiving means, whereas the light transmitting plate The reflected light from the surface is about 5% and can be ignored as an error.
[0004]
[Problems to be solved by the invention]
However, when using a sample such as a lip or O-ring of a rubber oil seal as a sliding member whose surface light reflectance is relatively small, the proportion of the interference light in the light received by the light receiving means is It becomes smaller and the reflected light from the surface of the light transmitting plate cannot be ignored as an error, and the thickness of the oil film cannot be measured accurately.
This invention aims at providing the film thickness measuring apparatus which can measure the thickness of an oil film correctly in view of the said subject.
[0005]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above object, the present invention comprises a translucent plate whose back surface is in contact with an oil film applied to the surface of the sample, and a light irradiation means for irradiating the surface of the sample through the translucent plate, Rotation that rotates the translucent plate in a film thickness measuring device that receives reflected light from the surface of the oil film and the surface of the sample through a light receiving means and measures the thickness of the oil film based on the interference light of both reflected lights. The translucent plate includes a flat rear surface, and the translucent plate is rotated around an axis perpendicular to the rear surface of the translucent plate by the rotation mechanism, and the sample is transmitted through the rotation. sliding or rolling the rear surface of the light plate contact, as reflected light from the surface of the transparent plate is not received by the light receiving means, the surface of the transparent plate is inclined with respect to the rear surface, the magnetic surface of the light plate, characterized in that it comprises a spherical or conical tapered surface A thickness measuring device.
[0006]
In this case, since the light receiving means mainly receives the reflected light from the surface of the oil film and the surface of the sample without receiving the reflected light from the surface of the translucent plate, a clean interference fringe can be obtained. Therefore, the thickness of the oil film can be measured more accurately regardless of the reflectance of the surface of the sample.
The surface of the translucent plate preferably includes a spherical surface or a conical tapered surface. This is because when the sample is a ball for a bearing, the direction of reflected light from the surface of the translucent plate does not change even if the ball and the translucent plate are brought into rolling contact.
[0007]
The present invention also includes a translucent plate whose back surface is in contact with an oil film applied to the surface of the sample, and a light irradiation means for irradiating the surface of the sample through the translucent plate, the surface of the oil film and the sample In the film thickness measuring device that receives the reflected light from the surface of the light through the light receiving means and measures the thickness of the oil film based on the interference light of the both reflected light, the rotating mechanism that rotates the translucent plate, The translucent plate is a flat plate whose front surface and back surface are parallel , and the translucent plate is rotated around an axis perpendicular to the back surface of the translucent plate by the rotation mechanism, and the sample is transmitted through the rotation. sliding or rolling the rear surface of the light plate contact, said light irradiation means irradiates light from obliquely with respect to the surface of the transparent plate, said light receiving means, reflected from the surface and the surface of the sample oil film Translucent so that it receives light and does not receive reflected light from the surface of the translucent plate Have set the thickness of the incident angle of the light from the light irradiation means to the surface of the translucent plate A, the thickness of the transparent plate t, a diameter of the irradiation opening of the light irradiation means as d1, the following The expression is satisfied,
t ≧ (d1 / 2) sinA
Assuming that the width of the contact area between the back surface of the light transmitting plate and the surface of the oil film is C, the maximum light receiving width of the light receiving means is d2, and the incident angle of light from the light emitting means to the surface of the light transmitting plate is A, The film thickness measuring apparatus is characterized in that the sample is pressed against the back surface of the translucent plate so as to be satisfied .
C = d2 / cosA
[0008]
In this case, since the light receiving means mainly receives the reflected light from the surface of the oil film and the surface of the sample without receiving the reflected light from the surface of the translucent plate, a clean interference fringe can be obtained. Therefore, the thickness of the oil film can be measured more accurately regardless of the reflectance of the surface of the sample.
Further, the inventor of the present application sets the incident angle A of light from the light irradiation means to the surface of the light transmission plate, the thickness t of the light transmission plate, and the diameter d1 of the irradiation port of the light irradiation means to satisfy the following formula. The knowledge that it is preferable to have been obtained was acquired.
[0009]
t ≧ d1 / 2sinA
In particular, the thickness of the translucent plate is made as thin as possible within the above range. That is, the thickness of the translucent plate is
t = d1 / 2sinA
The energy loss of light is the smallest, and the thickness of the oil film can be measured most accurately.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is an illustrative view showing a configuration of a film thickness measuring apparatus 1 according to an embodiment of the present invention. In FIG. 1, a film thickness measuring device 1 is a device that measures the thickness of an oil film 3 applied to the surface of a sample 2 by optical interferometry, and is arranged so that a back surface 4 a is in contact with the surface of the oil film 3. Light plate 4, light irradiating means 5 for irradiating the surface of sample 2 through light transmitting plate 4 and oil film 3, reflected light 6 from the surface of oil film 3, and reflected light 7 from the surface of sample 2 And a light receiving means 9 for receiving the interference light 8 generated by.
[0011]
The sample 2 may be, for example, a rubber O-ring as a sliding member. In this case, the sample 2 has elasticity and has a relatively low surface light reflectance. The sample 2 is held by a sample table (not shown), and a predetermined load is applied against the translucent plate 4. Therefore, the sample 2 is pressed into the back surface 4 a of the light transmitting plate 4 to form a parallel surface 2 a parallel to the back surface 4 a of the light transmitting plate 4.
The translucent plate 4 is a circular plate having a flat back surface 4a made of, for example, glass, and its front surface 4b has, for example, a spherical surface. Further, the back surface 4a of the translucent plate 4 is connected to the rotating shaft 10 at the center thereof, and when the film thickness measuring device 1 is operated, the rotating shaft 10 is rotated by a servo motor or the like, and is composed of, for example, an O-ring. The translucent plate 4 rotates relative to the sample 2 while sliding. On the other hand, when using the sample 2 made of a steel ball, the sample 2 rolls as the light transmitting plate 4 rotates. Here, the shape of the translucent plate 4 is not limited to the above-described shape. For example, if the direction of the reflected light from the surface 4b of the translucent plate 4 is not changed by the rotation of the translucent plate 4, for example, The surface 4b may be a conical tapered surface, and the outer shape may be an elliptical plate or a square plate instead of a circular plate. Moreover, the material of the translucent plate 4 is not limited to glass, but may be acrylic, for example.
[0012]
The light irradiation means 5 has, for example, an irradiation port 5a having a circular cross section at one end, and irradiates light, such as a laser, on the parallel surface 2a of the sample 2 obliquely from the irradiation port 5a. The irradiated light is divided into primary transmitted light 11 that is transmitted through the surface 4 b of the translucent plate 4 and primary reflected light 12 that is reflected from the surface 4 b of the translucent plate 4. For example, the primary reflected light 12 is reflected at the same angle as the incident angle with respect to the direction perpendicular to the surface 4 b of the translucent plate 4. Since the surface 4 b of the light transmitting plate 4 is spherical, the primary reflected light 12 is reflected in a direction sufficiently away from the light receiving means 9.
[0013]
When the primary transmitted light 11 reaches the back surface 4 a of the translucent plate 4 in contact with the surface of the oil film 3, the secondary transmitted light 13 that passes through the oil film 3 and the secondary reflected light 6 that reflects on the surface of the oil film 3 Divided into The secondary reflected light 6 is reflected at the same angle as the incident angle with respect to the surface of the oil film 3. Further, the secondary transmitted light 13 is reflected as the tertiary reflected light 7 on the surface of the parallel surface 2 a of the sample 2 at the same angle as the incident angle with respect to the parallel surface 2 a. Both reflected lights 6 and 7 interfere with each other, and interference light 8 is generated.
[0014]
The light receiving means 9 has, for example, a light receiving hole 9a having a circular cross section at one end. The light receiving hole 9a receives the interference light 8 generated by the secondary reflected light 6 and the tertiary reflected light 7, and 1 It arrange | positions so that the next reflected light 12 may not be received. Then, the thickness of the oil film 3 is measured based on the phase difference of the interference light 8 received by the light receiving means 9. In this embodiment, since the light receiving means 9 mainly receives the secondary reflected light 6 and the tertiary reflected light 7 without receiving the primary reflected light 12, a clean interference fringe can be obtained. Therefore, the thickness of the oil film 3 can be measured more accurately. In particular, it is very effective in that the thickness of the oil film 3 on the surface of the sample 2 having a low reflectance can be accurately measured. Moreover, the performance of the film thickness measuring apparatus can be improved at low cost only by changing the light transmitting plate of the existing film thickness measuring apparatus. However, the light irradiation means 5 may irradiate light substantially perpendicularly to the parallel surface 2a of the sample 2 if the light receiving means 9 does not receive the primary reflected light 12.
[0015]
FIG. 2 is an illustrative view showing a configuration of a film thickness measuring apparatus 1a according to another embodiment of the present invention. Referring to FIG. 2, this embodiment is mainly different from the embodiment of FIG. 1 in that a light-transmitting plate 15 made of flat plates whose back surface 4a and surface 4b are parallel to each other is used. is there. Since other configurations are the same as those of the embodiment of FIG. 1, the same reference numerals are given to the drawings and the description thereof is omitted.
The thickness t of the translucent plate 15 is the incident angle A formed by the light irradiated from the light irradiating means 5 onto the surface 15b of the translucent plate 15 with respect to the direction perpendicular to the translucent plate 15, and the irradiation of the light irradiating means 5. The following expression constituted by the diameter d1 of the port 5a and the diameter d2 of the light receiving port 9a of the light receiving means 9 is satisfied.
[0016]
t ≧ d1 / 2sinA (1)
The process that led to the derivation of the above equation will be described with reference to FIGS. 3 (a) and 3 (b). As shown in FIG. 3A, the primary reflected light 12 from the surface 15b of the translucent plate 15 and the secondary reflected light 6 from the surface of the oil film 3 in contact with the back surface 15a of the translucent plate 15 (into interference light). The light receiving means 9 receives both the reflected lights 12 and 6.
[0017]
In other words, in order for the light receiving means 9 not to receive the primary reflected light 12 but to receive the secondary reflected light 6, as shown in FIG. 3 (b), the both reflected lights 12 and 6 do not overlap. It is necessary.
The secondary reflected light 6 is parallel to the surface 15b of the translucent plate 15 with respect to the primary reflected light 12 of the irradiated light from the light irradiation means 5 having the beam diameter d1 (corresponding to the diameter d1 of the irradiation port 5a). The offset amount B is offset by 2t · tanA in the direction, and when viewed in the direction orthogonal to the two reflected lights 12 and 6, the offset amount B is B = 2t · tanA · cosA = 2tsinA (2)
It becomes.
[0018]
Here, in order that the reflected lights 12 and 6 do not overlap,
B ≧ d1 (3)
From the equations (2) and (3), the above equation (1) is derived.
In this embodiment, by setting the thickness t of the translucent plate 15 to a value satisfying the above formula (1), the light receiving means 9 does not receive the primary reflected light 12 and the secondary reflected light 6 and the tertiary reflected light. Since the light 7 is received, a clean interference fringe can be obtained. Therefore, the thickness of the oil film 3 can be measured more accurately. In particular, the thickness of the translucent plate 15 is
t = d1 / 2sinA
In this case, the energy loss of light is the smallest and the thickness of the oil film 3 can be measured most accurately.
[0019]
Referring to FIG. 4, the width C of the contact region 17 between the back surface 15 a of the translucent plate 15 and the surface of the oil film 3 corresponding to the maximum light receiving width d <b> 2 of the light receiving means 9 is calculated by the following equation.
C = d2 / cosA
For example, when d1 = 5 mm, d2 = 5 mm, and A = 20 °, the thickness t of the translucent plate 15 and the width C of the contact region 17 are as follows.
[0020]
t ≧ 6.9mm
C = 5.3mm
In this case, the thickness t of the translucent plate 15 may be a value studied at 6.9 mm or more, and a load may be applied to the sample 2 so that the width C of the contact region 17 is 5.3 mm. However, the shape of the translucent plate 4 is not limited to the above shape, and the outer shape may be an elliptical plate or a square plate instead of a circular plate. Moreover, the material of the translucent plate 4 is not limited to glass, but may be acrylic, for example.
[0021]
The present invention is not limited to the contents of the above embodiments, and various modifications can be made within the scope of the claims.
[Brief description of the drawings]
FIG. 1 is an illustrative view showing a configuration of a film thickness measuring apparatus according to an embodiment of the present invention.
FIG. 2 is an illustrative view showing a configuration of a film thickness measuring apparatus according to another embodiment of the present invention.
FIG. 3 is a schematic diagram for deriving a minimum value of the thickness of a light-transmitting plate.
FIG. 4 is a schematic diagram for deriving a width of a contact area.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Film thickness measuring apparatus 1a Film thickness measuring apparatus 2 Sample 3 Oil film 4 Translucent plate 4a Back surface 4b Front surface 5 Light irradiation means 6 Secondary reflected light 7 Tertiary reflected light 8 Interference light 9 Light receiving means 12 Primary reflected light 15 Translucent Plate 15a Back surface 15b Front surface A Incident angle t Plate thickness d1 Diameter of irradiation port

Claims (2)

A translucent plate whose back surface is in contact with an oil film applied to the surface of the sample;
A light irradiation means for irradiating the surface of the sample with light through the translucent plate,
In the film thickness measuring device that receives the reflected light from the surface of the oil film and the surface of the sample through the light receiving means, and measures the thickness of the oil film based on the interference light of both reflected lights,
A rotation mechanism for rotating the light transmitting plate;
The translucent plate includes a flat back surface,
The translucent plate is rotated around an axis perpendicular to the back surface of the translucent plate by the rotating mechanism, and with the rotation, the sample slides or rolls against the back surface of the translucent plate,
The surface of the light transmitting plate is inclined with respect to the back surface so that the reflected light from the surface of the light transmitting plate is not received by the light receiving means ,
The film thickness measuring device , wherein the surface of the light transmitting plate includes a spherical surface or a conical tapered surface . A translucent plate whose back surface is in contact with an oil film applied to the surface of the sample;
A light irradiation means for irradiating the surface of the sample with light through the translucent plate,
In the film thickness measuring device that receives the reflected light from the surface of the oil film and the surface of the sample through the light receiving means, and measures the thickness of the oil film based on the interference light of both reflected lights,
A rotation mechanism for rotating the light transmitting plate;
The translucent plate is a flat plate whose front and back are parallel ,
The translucent plate is rotated around an axis perpendicular to the back surface of the translucent plate by the rotating mechanism, and with the rotation, the sample slides or rolls against the back surface of the translucent plate,
The light irradiation means irradiates light obliquely with respect to the surface of the translucent plate,
The light receiving means receives the reflected light from the surface of the oil film and the surface of the sample, and sets the plate thickness of the light transmitting plate so as not to receive the reflected light from the surface of the light transmitting plate,
When the incident angle of light from the light irradiation means to the surface of the light transmission plate is A, the thickness of the light transmission plate is t, and the diameter of the irradiation port of the light irradiation means is d1, the following equation is satisfied:
t ≧ (d1 / 2) sinA
Assuming that the width of the contact area between the back surface of the light transmitting plate and the surface of the oil film is C, the maximum light receiving width of the light receiving means is d2, and the incident angle of light from the light emitting means to the surface of the light transmitting plate is A, The film thickness measuring apparatus, wherein the sample is pressed against the back surface of the light-transmitting plate so as to be satisfied.
C = d2 / cosA

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