JP2004028914A - Optical displacement sensor - Google Patents

Abstract

An optical displacement sensor capable of measuring the shape of the inner surface of a hole or a groove having a diameter smaller than an opening diameter of an objective lens with high accuracy.
An optical displacement sensor of a coaxial focusing system, comprising: a sensor head section (10) including an objective lens; and a sensor head section (10) disposed in front of the objective lens of the sensor head section at a predetermined distance from the sensor head section. A reflecting mirror member (30) smaller than the opening diameter, and supporting members (22, 23) for supporting the reflecting mirror member with respect to the sensor head portion. The reflecting mirror member is disposed in a bare state without being surrounded by a lens barrel, and the support member has a cross-sectional profile of a predetermined distance portion from the reflecting mirror member side to the sensor head portion side. Are within a circle corresponding to the aperture of the objective lens, and further, the numerical aperture of the objective lens is not substantially reduced.
[Selection] Fig. 2

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical displacement sensor of a coaxial focusing system, and more particularly to an optical displacement sensor suitable for measuring displacement of an inner peripheral surface of a small hole or an inner surface of a narrow groove.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. 5-99631 discloses a hole shape light measuring device for measuring the inner surface shape of a hole formed in a metal by a drill or the like. This hole shape light measuring device includes a first means for emitting a beam-like light beam, a second means for bending the light beam by an angle slightly deviated from 90 degrees, and a method in which the bent light beam is centered on the original light beam. Third means for rotating, fourth means for condensing irregularly reflected light of a light spot formed when the bent light beam hits the inner surface of the hole, and an image of a light spot formed by the light condensed by the fourth means. A fifth means for detecting the position and a sixth means for calculating the light spot position from the image position detected by the fifth means according to the principle of triangulation are included.
[0003]
According to this hole shape light measuring device, the mechanical movement can continuously measure the inner surface shape over the circumference of the hole only by rotation, there is no friction and wear because there is no contact between the measuring device and the inner surface of the hole, , So that various advantages such as a reduction in measurement time as compared with the conventional method can be obtained.
[0004]
Further, Japanese Patent Application Laid-Open No. Hei 5-164556 discloses a non-contact displacement meter of a focusing system suitable as a non-contact surface roughness meter, a non-contact scanning probe for a three-dimensional coordinate measuring instrument, and the like.
[0005]
According to this displacement meter, it is possible to measure the surface shape of a deep groove or a hole, and there is an advantage that the objective lens can be replaced. In addition, FIGS. 2 and 6 of the publication also disclose a technique for measuring the inner surface of a hole by disposing a reflecting mirror in a lens barrel reaching an objective lens and bending the optical axis by 90 degrees. .
[0006]
[Problems to be solved by the invention]
However, in the hole shape light measuring device disclosed in Japanese Patent Application Laid-Open No. 5-99631, since displacement measurement is performed based on the principle of triangulation, the optical axis of incident light from the measuring device toward the object to be measured is measured. A parallax angle equal to or more than a certain value corresponding to the required resolution is required between the light beam and the optical axis of the reflected light reflected by the measurement object and returned to the measurement device. Therefore, when trying to measure the inner surface of a hole with a large depth for the diameter or a groove with a large depth for the width, the hole that can be measured by the parallax angle between the incident optical path and the reflected optical path described above Is limited in depth. On the other hand, if the parallax angle between the optical axis of the incident light and the optical axis of the reflected light is reduced, it is possible to cope with a deeper groove or hole, but this will reduce the measurement resolution and reduce the minuteness of the inner surface of the hole or groove. The shape change cannot be measured accurately. Furthermore, since the spot diameter of the incident light on the measurement object is not always narrowed, it is not possible to measure the displacement of the minute shape.
[0007]
On the other hand, according to the in-focus type non-contact displacement meter disclosed in Japanese Patent Application Laid-Open No. 5-164556, a so-called coaxial epi-optical system is employed, so that the incidence / reflection as in the case of employing the principle of triangulation is adopted. No inconvenience occurs due to the parallax angle between the optical paths. However, in the inner surface measurement technique shown in FIGS. 2 and 6 of the publication, a configuration is adopted in which a reflecting mirror is arranged in a lens barrel from a light source to an objective lens and an optical axis is bent substantially at a right angle. Therefore, the inner diameter of the measurable hole must necessarily be larger than the outer diameter of the lens barrel, in other words, it cannot be applied in principle to holes and grooves smaller than the aperture of the objective lens. .
[0008]
The present invention has been made in view of the above-mentioned conventional problems, and the object thereof is to provide an inner surface of a hole or a narrow groove smaller than the opening diameter of an objective lens. An object of the present invention is to provide an optical displacement sensor capable of measuring a shape with high accuracy.
[0009]
Another object of the present invention is to provide a fixture for a reflecting mirror member suitable for the above-mentioned optical displacement sensor.
[0010]
Still other objects and operational effects of the present invention will be easily understood by those skilled in the art by referring to the description in the following specification.
[0011]
[Means for Solving the Problems]
The optical displacement sensor of the present invention employs, as a principle of displacement detection, a coaxial focusing method described in, for example, JP-A-5-164556 and JP-A-7-113617. Therefore, for example, there is no problem of a measurement limitation caused by a parallax angle as in an optical displacement sensor employing a triangulation method described in Japanese Patent Application Laid-Open No. 5-99631.
[0012]
The optical displacement sensor includes a sensor head portion including an objective lens, and a reflecting mirror disposed at a predetermined distance in front of the objective lens of the sensor head portion and sufficiently smaller than an opening diameter of the objective lens. And a support member for supporting the reflecting mirror member with respect to the sensor head section.
[0013]
The “reflecting mirror member” is a member having a mirror surface for changing the optical axis by a predetermined angle by reflecting measurement light coming from the objective lens. It is a matter of design to determine the angle of change of the optical axis by the reflecting mirror member. However, when measuring the displacement of the inner peripheral surface of the hole / the inner surface of the groove, the optical axis change angle is 90 degrees or approximately 90 degrees. Will be taken. The reason why the reflecting mirror member is set to “smaller than the opening diameter” is that in the optical displacement sensor of the present invention, in order to measure the displacement of the inner peripheral surface of the hole or the inner surface of the groove, it is necessary to use the hole or This is because, while the reflecting mirror member must be inserted into the groove, the size of the reflecting mirror member determines the insertable hole diameter or groove width. The measuring light has the shape of a conical light beam connecting the effective diameter of the objective lens (a circle equivalent to an aperture) and the focal point on the measurement object, and the reflecting mirror member is arranged in front of the objective lens. Therefore, the size of the cross section is smaller than the effective diameter of the objective lens, and the size of the reflection surface is large enough to cover all the luminous fluxes of the measurement light at that position. (Here, the cross section refers to a plane perpendicular to a line connecting the center of the objective lens and the focal point on the object to be measured.) Also, there is "a predetermined distance in front of the objective lens". It is needless to say that the "predetermined distance" is before the converging point generated in front of the objective lens.
[0014]
In addition, the reflecting mirror member must be disposed in a bare state without being surrounded by the lens barrel. For example, as shown in FIG. 2 or FIG. 6 of JP-A-5-164556, when a configuration in which a reflecting mirror member is surrounded by a lens barrel is adopted, a hole diameter and a groove width which can be applied depending on the outer diameter of the lens barrel. Is limited. However, if the outer diameter of the lens barrel is made smaller than the aperture diameter of the objective lens, the lower limit of the applicable hole shape and groove width becomes smaller, but in this case, the hole diameter and groove width are reduced by the inner diameter of the lens barrel. Regardless, the numerical aperture of the objective lens is uniquely limited, and the measurement resolution is reduced.
[0015]
On the other hand, if the reflecting mirror member is exposed without being surrounded by the lens barrel, as long as the reflecting mirror member can be inserted, the numerical aperture of the objective lens is used to the full extent, and the inner peripheral surface (hole) is used. ) And the displacement of the inner surface (in the case of a groove) can be measured. That is, after the reflection mirror member is inserted from the entrance of the hole or groove into the inside, until the outer peripheral edge of the conical light beam from the objective lens to the reflection mirror member is blocked by the entrance of the hole or groove, the objective Since the numerical aperture of the lens does not decrease, displacement measurement can be performed with the maximum resolution. On the other hand, when the reflecting mirror member is inserted deep inside the hole or groove, when the outer peripheral edge of the conical light beam starts to be blocked by the entrance of the hole or groove, the numerical aperture of the objective lens starts decreasing for the first time, As a result, the measurement resolution is reduced, but even so, as long as the reflecting mirror member can be inserted, the displacement cannot be measured.
[0016]
In order to realize such a bare structure of the reflecting mirror member, the supporting member has a cross-sectional contour of a predetermined distance portion (preferably, the entire length) from the reflecting mirror member side to the sensor head portion side. It must be within the circle corresponding to the aperture of the objective lens. Otherwise, the support member itself interferes and the reflecting mirror member cannot be inserted deeply into a hole or a narrow groove smaller than the opening diameter of the objective lens. In order to allow insertion of the reflecting mirror member even for a hole diameter and a groove width of the same size as the reflecting mirror member, the area occupied by the cross section of the supporting member should be closer to the center of the circle. Needless to say, this is preferable.
[0017]
In addition, the support member must be a non-light-shielding structure that does not substantially reduce the numerical aperture of the objective lens. Even if the support member does not hinder the insertion of the reflector member into the hole or groove, if it greatly blocks the light from the objective lens, the numerical aperture will decrease substantially, and the measurement resolution will decrease. Is reduced. In a preferred embodiment, the non-light-shielding structure constituting the support member is formed of one or two or more wires extending along the optical axis and parallel to each other.
[0018]
According to the above-described optical displacement sensor of the present invention, the shape of the inner surface of a hole or a groove having a diameter smaller than the opening diameter of the objective lens can be measured with high accuracy.
[0019]
Next, in the optical displacement sensor of the coaxial focusing system, a reflecting mirror member sufficiently smaller than the aperture diameter of the objective lens is surrounded by a lens barrel at a position at a predetermined distance in front of the objective lens in the sensor head. The present inventors propose a suitable fitting in order to dispose it in a bare state without being performed.
[0020]
The mounting tool includes a mounting portion adapted to a predetermined portion of the sensor head portion, a holding portion for holding the reflecting mirror member, and a supporting portion for supporting the holding portion with respect to the mounting portion, Contains. The support section has a cross-sectional contour falling within a circle corresponding to the aperture of the objective lens over the entire length from the sensor head section side to the reflecting mirror member side, and further substantially reduces the numerical aperture of the objective lens. This is a non-light-shielding structure that is not reduced in nature. For the reasons described above, in a preferred embodiment, the non-light-shielding structure constituting the support portion is constituted by one or two or more wires extending along the optical axis and parallel to each other. It may be something.
[0021]
The predetermined portion of the sensor head may be the tip of a lens barrel that houses the objective lens of the sensor head, or the head case itself of the sensor head.
[0022]
According to such a mounting tool, in the optical displacement sensor of the coaxial focusing system, a reflecting mirror member sufficiently smaller than the aperture diameter of the objective lens is provided at a predetermined distance in front of the objective lens in the sensor head. Can be arranged in a bare state without being surrounded by the lens barrel, whereby the optical displacement sensor of the present invention can be easily realized. In addition, by exchanging the reflecting mirror member together with the fixture, it is easy to deal with various measuring objects.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a coaxial focusing type optical displacement sensor and a mounting member for a reflecting mirror member according to the present invention will be described below in detail with reference to the accompanying drawings.
[0024]
FIG. 1 shows a configuration diagram (first embodiment) of an optical displacement sensor according to the present invention. As shown in FIG. 1, the optical displacement sensor 1 has a sensor head unit 10 and a reflector mount 20. In the drawing, reference numeral 40 denotes an object to be measured, and reference numeral 40a denotes a vertically penetrated hole drilled in the object to be measured. In the following description, it is assumed that the displacement sensor 1 of the present invention performs displacement measurement on the inner peripheral surface of the hole 40a.
[0025]
The sensor head unit 10 includes a head case 11 and a lens barrel 12. In the illustrated example, the shape of the head case 11 is illustrated as a rectangular parallelepiped, and the shape of the lens barrel 12 is illustrated as a cylindrical body. However, it should be understood that this is merely an example for explanation.
[0026]
Although not shown, an optical system, an electric circuit, and the like constituting a coaxial focusing type optical displacement sensor are built in the head case 11. On the other hand, an objective lens (not shown) is held in the lens barrel 12. Although the optical system of the optical displacement sensor of the coaxial focusing system is well known to those skilled in the art, an example thereof will be described later with reference to FIGS.
[0027]
Next, a description will be given of the reflector mounting member 20 which is a main part of the present invention. In FIG. 1, the details of the part II surrounded by a circle drawn by a dotted line are shown in FIG.
[0028]
As shown in FIG. 1, a mounting member 20 for a reflecting mirror member includes a cap 21 attached to a tip portion (a lower end portion in the figure) of the lens barrel 12 of the sensor head portion 12 and a mirror holding member for holding the reflecting mirror member 30. A member 24 and two support members 22 and 23 having one end (the upper end in the figure) fixed to the cap 21 and the other end (the lower end in the figure) fixed to the mirror holding member 24 are provided.
[0029]
The cap 21 is formed in a circular dish shape conforming to the distal end shape of the lens barrel 12, and a fixing means for fixing the cap 21 and the lens barrel 12 is, for example, a permanent fixing structure using an adhesive, or a screw or a press-fit fitting. A possible structure is adopted. A circular opening 21 a is formed in the center of the cap 21 so as to face an objective lens (not shown) in the lens barrel 12. The inner diameter of the opening 21a defines the opening diameter of the objective lens.
[0030]
In this example, the reflecting mirror member 24 is a cylindrical body whose upper end surface is inclined at an angle of approximately 45 degrees with respect to the optical axis A of the objective lens, and the inclined surface is a reflecting mirror surface 30a. . Therefore, in the figure, light incident on the mirror surface 30a vertically downward from directly above the reflecting mirror member 24 is reflected by the mirror surface 30a, changes its direction in the horizontal direction, and travels toward the inner peripheral side surface of the hole 40a. Further, the light reflected on the inner peripheral side surface of the hole 40a goes back on the same optical path as the outward path and returns to the objective lens. As is well known, in this type of the displacement sensor of the coaxial focusing system, by operating one component of the optical system in the head case 11 (for example, the objective lens itself or other optical components), The focal point is adjusted so that the focal point always coincides (focussed) on the inner peripheral side surface of the hole 40a. Conversely, the displacement of the measured surface is obtained via the operation amount of the optical component in the focused state. As is clear from the figure, the size of the reflecting mirror member 30 is sufficiently smaller than the opening 21a of the cap 21 corresponding to the opening of the objective lens. The reflecting mirror member 30 is in a so-called bare state without being surrounded by a lens barrel or the like. Further, the reflecting mirror member 30 is held by the mirror holding member 24 at a position separated by a predetermined distance forward (downward in the figure) of the objective lens in the optical axis direction.
[0031]
In this example, the mirror holding member 24 is formed as a cylindrical body having a slightly larger diameter than the reflecting mirror member 30, and the reflecting mirror member 30 is positioned and held at the center thereof. As a means for positioning and holding the reflecting mirror member 30 at the center of the mirror holding member 24, various known members such as a press-fitting structure and screwing can be arbitrarily adopted. The mirror holding member 24 is supported by the cap 21 via two support members 22 and 23 in the illustrated example.
[0032]
In this example, the supporting members 22 and 23 have a rigidity that does not cause a problem in measurement so that the truncated cone-shaped light beam 50 from the opening 21a of the cap 21 to the mirror surface 30a of the reflecting mirror member 30 is not blocked as much as possible. (For example, metal prisms, metal cylinders, metal wires, etc.) having These support members 22 and 23 extend parallel to each other along the optical axis of the objective lens. The upper ends of the support members 22 and 23 are bent in an L-shape, and the bent portions 22a and 23a are connected to an annular bottom 25 corresponding to the inner peripheral edge of the opening 21a of the cap 21 by appropriate bonding means such as bonding. It is fixed at. The lower ends of the support members 22 and 23 are fixed to the outer peripheral edge of the mirror holding member 24 by an appropriate connecting means such as adhesion. The interval between the support members 22 and 23 is made as narrow as possible so as not to hinder the insertion of the mirror holding member 24 into the assumed hole 40a. The length of the support members 22 and 23 is determined such that a spot of a certain size before the light condensing point is formed on the mirror surface 30a of the reflecting mirror member 30.
[0033]
In other words, the support members 22 and 23 have their cross-sectional outlines substantially at the center of a circle corresponding to the opening 21a of the objective lens over the entire length from the sensor head section 10 side to the reflecting mirror member 30 side. Further, the non-light-shielding structure does not substantially reduce the numerical aperture of the objective lens.
[0034]
Next, the operation of the present invention will be described. According to the reflector mounting fixture 20 having the above-described configuration, even if the inner diameter of the hole 40a of the measurement target 40 is smaller than the opening 21a of the objective lens, only the reflector member 30 is inserted into the hole 40a. Thus, displacement measurement of the inner peripheral side surface can be performed. Moreover, after the insertion of the reflecting mirror member 30 from the entrance of the hole 40a into the inside, until the outer peripheral edge of the conical light beam 50 from the objective lens to the reflecting mirror member 30 is blocked by the entrance of the hole 40a, Since the numerical aperture of the objective lens does not decrease, displacement measurement can be performed with the maximum resolution. On the other hand, when the outer peripheral edge of the conical light beam 50 starts to be blocked by the entrance of the hole due to the insertion of the reflecting mirror member 30 deep inside the hole, the numerical aperture of the objective lens starts decreasing for the first time, Although the measurement resolution is reduced, the displacement cannot be measured even if the reflecting mirror member 30 can be inserted.
[0035]
That is, according to the present invention, since the reflecting mirror member 30 is exposed without being surrounded by the lens barrel, the numerical aperture of the objective lens is maximized as long as the reflecting mirror member 30 can be inserted. Displacement measurement of the inner peripheral surface (in the case of a hole) or the inner surface (in the case of a groove) becomes possible.
[0036]
In the above embodiment, the support members 22 and 23 may be directly fixed to the head case 11 instead of the lens barrel 12 via an appropriate bracket. Further, the support members 22 and 23 may be fixed to the head case 11 instead of the lens barrel 12 via a square cap. As described above, various configurations can be adopted for the connection mode between the support members 22 and 23 and the sensor head unit 10.
[0037]
Finally, the optical system of the coaxial focusing type displacement sensor built in the head case 11 will be briefly described. As is well known, a coaxial focusing type optical displacement sensor employs a so-called coaxial epi-illumination type optical system and operates one optical component constituting the optical system to measure an object to be measured. A focused state where the surface and the focal point of the objective lens coincide with each other is created, and the displacement of the measurement surface is determined in reverse from the operation amount of the optical component in that state. In order to create a focused state, a method of operating the objective lens itself (hereinafter, referred to as a first method) and a method of operating the objective lens as disclosed in JP-A-7-113617 and JP-A-5-164556 are disclosed. As disclosed in the gazette, there is a method (hereinafter, referred to as a second method) in which another optical component of an optical system leading to the objective lens is operated while the objective lens is fixed. In the present invention, any of the first and second methods may be adopted.
[0038]
FIG. 3 shows an optical system of a first type of coaxial focusing type optical displacement sensor described in JP-A-7-113617. In the figure, 501 is a laser diode, 502 is a beam splitter, 503 is a collimating lens, 504 is an objective lens, 505 is an object to be measured, 506 is an optical diaphragm, 507 is a photodiode, 508 is an amplifier, and 509 is a laser power control circuit. , 510 is a tuning fork, 511 is a tuning fork detector, 512 is an amplifier, 513 is a solenoid, 514 is a tuning fork amplitude control circuit, 515 is a calculation unit, 516 is a distance conversion unit, X is a received light amount signal, and Y is an amplitude signal. . Since the operation of the optical system and the circuit is described in detail in the publication, the description is omitted. In short, while the objective lens is vibrated through the tuning fork 510, the operation is performed based on the state of the received light amount signal X. The focus state is detected, and a target displacement amount is calculated based on the state of the amplitude signal Y obtained at that time.
[0039]
FIG. 4 shows an optical system of an optical displacement sensor of a second type of coaxial focusing system described in Japanese Patent Application Laid-Open No. 5-164556. In the figure, 601 is a semiconductor laser, 602 is a deflection beam splitter, 603 is a collimator lens, 604 is a relay lens, 605 is a relay lens, 605 is an objective lens, 606 is a measurement surface, 607 is a measurement surface, 608 is an imaging lens, and 609 is a beam splitter. , 610 is a light receiving element, 611 is a light receiving element, L1 is the amount of operation of the relay lens, and L2 is the amount of movement of the focal point of the objective lens. The operation of this optical system is described in detail in the publication, so that the description is omitted. In short, as is clear from the comparison between FIG. By moving only the relay lens 605 upward while keeping the fixed, the position of the condensing point can be moved downward.
[0040]
In the above embodiment, if the measurement target 40 and the reflecting mirror member 30 are relatively three-dimensionally moved and rotated, as in the apparatus described in Japanese Patent Application Laid-Open No. 5-99631, for example, the measurement target Needless to say, it is possible to measure displacement at an arbitrary position in the 40 hole 40a. In order to realize the relative movement, the table on which the measurement object 40 is placed may be moved and rotated three-dimensionally, or the sensor side may be moved and rotated three-dimensionally.
[0041]
In addition, the number of wires constituting the support members 22 and 23 is not limited to the embodiment, but in short, it is appropriate within a range that does not substantially block the conical light beam 50 (does not reduce the numerical aperture of the objective lens). Can be changed.
[0042]
Further, the support members 22 and 23 themselves do not necessarily need to be formed of linear members, and may have any shape within a range that does not substantially block the above-mentioned conical light beam 50 (does not reduce the numerical aperture of the objective lens). And materials (net, spiral, transparent, etc.) could be adopted.
[0043]
【The invention's effect】
As is apparent from the above description, according to the present invention, an optical displacement sensor capable of measuring the inner surface shape with high accuracy even for a hole or a groove having a diameter smaller than the opening diameter of the objective lens. Can be realized.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an optical displacement sensor according to the present invention.
FIG. 2 is an enlarged view of a main part of the present invention.
FIG. 3 is a basic configuration diagram (part 1) of an optical system of an optical displacement sensor of a coaxial focusing system.
FIG. 4 is a basic configuration diagram (part 2) of an optical system of an optical displacement sensor of a coaxial focusing system.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 optical displacement sensor 10 sensor head unit 11 head case 12 lens barrel 20 reflector mounting fixture 21 cap 21a openings 22, 23 support members 22a, 23a bent parts 22c, 23c bracket 24 mirror holding member 25 annular bottom part 26 square cap 30 reflection Mirror member 40 Object to be measured 40a Hole 50 Conical luminous flux

Claims (5)

An optical displacement sensor of a coaxial focusing system,
A sensor head section including an objective lens, a reflecting mirror member disposed at a predetermined distance in front of the objective lens of the sensor head section and smaller than an opening diameter of the objective lens; and A support member for supporting the head portion,
The reflecting mirror member is disposed in a bare state without being surrounded by a lens barrel, and the supporting member has a sectional contour at a predetermined distance portion from the reflecting mirror member side to the sensor head portion side. Is within a circle corresponding to the aperture of the objective lens. The optical displacement sensor according to claim 1, wherein the support member is one or two or more wires extending along an optical axis. In a coaxial focusing type optical displacement sensor, a reflecting mirror member smaller than the aperture diameter of the objective lens is exposed at a predetermined distance in front of the objective lens of the sensor head without being surrounded by the lens barrel. It is a fixture of the reflecting mirror member to be arranged in a state,
A mounting portion adapted to a predetermined portion of the sensor head portion,
A holding unit for holding the reflecting mirror member,
And a supporting portion for supporting the holding portion with respect to the mounting portion,
The support portion is characterized in that, at a predetermined distance portion from the reflective mirror member side to the sensor head portion side, a cross-sectional contour falls within a circle corresponding to an opening of the objective lens, Fixture. 4. The fixture of claim 3, wherein the support portion is one or more wires extending along an optical axis. 5. 5. The fixture for a reflecting mirror member according to claim 3, wherein the predetermined portion of the sensor head is a tip of a lens barrel that accommodates an objective lens of the sensor head. 6.

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