JP2675051B2 - Optical non-contact position measuring device - Google Patents

Description

The present invention relates to a position measuring device, and more particularly to an optical non-contact position measuring device for optically measuring the position of a surface to be measured in a non-contact manner.

[Conventional technology]

Conventionally, this type of device uses the principle of triangulation to measure the change in angle due to the change in the position of the measured surface using a photoelectric conversion element, and the deviation (displacement) of the position of the measured surface from a fixed point. There is a device according to a compensation method in which the deviation of the image point caused by (1) is detected by a photoelectric conversion element, the device is moved by a servo mechanism so as to compensate the deviation, and the amount of movement is measured.

Among these devices, the one that uses the principle of triangulation is
The angle ψ (0 ≦ ψ ≦ 90 between the direction in which the measurement laser beam is incident and the straight line connecting the measured position and the photoelectric conversion element
The larger the angle is, the higher the measurement sensitivity becomes, but if the angle ψ is large, the laser beam reflected by the surface to be measured is blocked by the projections near the position to be measured and cannot enter the photoelectric conversion element. There is a drawback that In addition, since the device using the compensation method requires the use of a servo mechanism, not only is the device complicated and costly, but also the measured surface is inclined and the intensity distribution of the reflected light beam is axisymmetric with respect to the optical axis. If it does not, there is a drawback that a highly accurate measured value cannot be obtained.

FIG. 6 shows an optical non-contact position measuring device disclosed in Japanese Patent Application No. 62-27084, which overcomes the above-mentioned drawbacks.

The laser beam output from the He-Ne laser light source 9 is reflected by the mirror 8 and the minute mirror 7, and is reflected by the surface S to be measured via holes 37 and 35 formed in the centers of the shielding plate 34 and the convex lens 31, respectively. Then, the reflected light again enters the convex lens 31, passes through the slits 36A and 36B provided in the shielding plate 34,
After being refracted by the cylindrical lens 33, it enters the CCD line sensor 10 placed at the focus of the cylindrical lens 33. CCD line sensor
Reference numeral 10 is arranged parallel to the generatrix in the plane of mirror symmetry including the generatrix of the cylindrical lens 33. Therefore, slit 36A,
The light passing through 36B is refracted by the cylindrical lens 33 in the plane perpendicular to the arrangement direction of the CCD line sensor elements (CCD pixels), and is focused on the CCD line sensor 10. The output of the CCD line sensor 10 is input to a calculation means (not shown), and the displacement of the surface to be measured is calculated.

In this device, the optical path through which the laser beam is incident on the surface to be measured and the optical path through which the reflected light is detected are both along the optical axis (the axis of the convex lens 31), so the shadow effect does not occur. Further, since the displacement of the surface to be measured is detected by the change of the CCD line sensor pixel number on which the reflected light is incident, an error does not occur even if the intensity distribution of the reflected light is not axisymmetric with respect to the optical axis. Therefore, the drawbacks of the device using the principle of triangulation and the device using the compensation method are overcome.

[Problems to be solved by the invention]

The optical non-contact position measuring device disclosed in the above-mentioned Japanese Patent Application No. 62-27084 has the following drawbacks.

1. Since the CCD pixel array direction is parallel to the generatrix direction of the cylindrical lens 33, light rays which are not converged in the CCD pixel array direction (and thus have a wide width in the CCD pixel array direction) are detected in the CCD line sensor 10. Incident. as a result,
The output curve of the CCD line sensor becomes flat, and the position of the maximum intensity of the incident light beam becomes unclear, and errors easily occur.

2. With a set of optical systems (slits 36A, 36B, cylindrical lens 33, CCD line sensor 10) having a specific geometrical optical arrangement, the position where the reflected light from the measured surface is incident on the CCD line sensor 10 is determined. Since it is detected, for example, when the normal line of the surface to be measured is largely deviated from the plane including the generatrix of the cylindrical lens 33 and the optical axis 2 (the paper surface of FIG. 6), the reflected light from the surface to be measured is The CCD line sensor 1 will move when it is deviated from the transmission line of light by a set of optical systems with a specific geometrical optical arrangement.
At 0, reflected light can no longer be detected.

Further, if there is an error (alignment error) in the array of each element of this optical system, the error must be corrected by a separate correction experiment.

[Means for solving the problem]

The optical non-contact position measuring device of the present invention comprises: a convex lens (1) that emits an incident parallel light beam to a surface to be measured and receives a light beam reflected from the surface to be measured; ) Irradiation device (7,8,9) for making the parallel rays incident on the convex lens (1) along the axis (2), and the first symmetry plane including the generatrix of the cylindrical lens (3). The symmetry plane (21) and the mirror symmetry plane perpendicular to the generatrix are the second mirror symmetry plane (22), and the line of intersection of the first and second mirror symmetry planes (21, 22) is the cylindrical lens (3). 1st spindle (23), 1st spindle (2
3) Draw a straight line parallel to the generatrix through the optical center above the second main axis (2
4), the first principal axis of each is a convex lens (1)
Oriented parallel to the axis (2) of the convex lens (1), each second principal axis is positioned in the focal plane (5) of the convex lens (1) opposite to the surface to be measured, and the axis (2) of the convex lens (1) is A plurality of cylindrical lenses (3A, 3A) that are oriented perpendicularly to a straight line connecting the intersection between the first main axis and the second main axis and the intersection of the focal plane (5) with
B, 3C) and the focal plane (5) parallel to the focal plane (5) of the convex lens (1)
Placed in front of each cylindrical lens (3A, 3B, 3C)
Slits (6A, 6B, 6C) at positions facing the cylindrical lenses (3A, 3B, 3C) along the line of intersection with the first mirror symmetry plane of
In the second mirror symmetry plane of each of the cylindrical lenses (3A, 3B, 3C) and the shielding plate 4 provided with, the focal plane is equal to the focal length of the cylindrical lenses (3A, 3B, 3C). Position detecting line sensors (10A, 10B, 10) arranged behind (5) and parallel to the focal plane (5).
C) and an arithmetic means for inputting the outputs of the line sensors (10A, 10B, 10C) and calculating the position of the surface to be measured.

[Action]

 The principle of the present invention will be described with reference to FIG.

FIGS. 5 (A) and 5 (B) are optical element layouts of essential parts of the optical non-contact position measuring device of the present invention.

As shown in FIG. 5 (A), the parallel rays transmitted from the rear side (left side in FIG. 5) of the convex lens 1 on the axis 2 of the convex lens 1 are reflected at the point P on the surface to be measured, One of the reflected light rays L ₁ is refracted by the convex lens 1, and the refracted light L ₂ enters the cylindrical lens 3 through the slit 6 of the shielding plate 4. Fifth
In the figure, the paper surface is the second mirror symmetry plane 22 of the cylindrical lens 3, and the slit 6 is oriented perpendicular to the paper surface. Slit 6
Since the width of is very small compared to the focal length f ₁ of the convex lens 1, the light ray L ₂ is incident on the cylindrical lens 3 almost in parallel (the fifth
(B)), a position which is refracted in a plane parallel to the second mirror symmetry plane 22 of the cylindrical lens 3 and is located at the focal length f ₂ of the cylindrical lens 3 in the mirror symmetry plane. Line sensor for detection 10
It converges to the upper point H.

Now, the light emitted from the focal point F of the convex lens 1 is refracted by the convex lens 1 and passes through the slit 6 and the cylindrical lens 3 to form an image on the line sensor 10, and R is the distance between the axis 2 of the convex lens 1 and the point R. a, the displacement of the measuring point P relative to the focus F is z ₁ ,
The image point for the measuring point P of the convex lens 1 is Q, and the point Q
And the focal plane 5 of the convex lens 1 is z ₂ , and the intersection of the first and second principal axes of the cylindrical lens 3 is O, and the angle ROQ
Where α is α and the length of the line segment RH is x, tan α ＝ x / f ₂ ＝ a / z ₂ …… (1) From the convex lens formula Eliminating α and z ₂ from equations (1) and (2) gives Since the proportionality constant k can be known from the constant of the optical system,
By finding x from the line sensor pixel number ξ
You can know z ₁ .

In the case of only one set, the optical system consisting of the slit 6, the cylindrical lens 3 and the line sensor 10 in FIG. 5 has a normal to the measured surface which is the second reflection symmetry of the cylindrical lens 3 (the plane of the paper in FIG. 5). ), The reflected light from the surface S to be measured is not refracted in the generatrix direction of the cylindrical lens 3 (direction perpendicular to the paper surface of FIG. 5) even if it enters the cylindrical lens 3, so the CCD line sensor 10 It will not be incident on the top. Therefore, by using a plurality of sets of optical systems around the axis 2, it is possible to prevent the measurement from being obstructed no matter what direction the surface normal of the surface to be measured is inclined. Value x obtained for the same displacement z ₁ from multiple sets of optical line sensors
Are almost equal, but they are not exactly equal due to alignment and measurement errors. Therefore, if the arithmetic unit obtains the most probable value of x using the method of least squares,
The error-corrected measurement value is obtained.

In this device, since the light rays are converged in the pixel array direction of the line sensor 10, the output of the line sensor 10 has a sharp peak, and as a result, it becomes easy to detect the light receiving position of the line sensor. Further, by using a plurality of optical systems each consisting of a slit, a cylindrical lens, and a line sensor, it is possible to perform measurement regardless of the direction in which the normal to the surface to be measured at the measurement point is inclined with respect to the optical axis of the device. it can. In addition, since the probability that the measurement errors due to the plurality of sets of optical systems are strengthened is very small, a highly reliable measurement result can be obtained without performing a separate correction experiment.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

1 is a block diagram of an embodiment of the optical non-contact position measuring device of the present invention, FIG. 2 is a diagram showing the arrangement of the slit 6, the cylindrical lens 3 and the CCD line sensor 10 of the device of FIG. FIG. 3 is a sectional view taken along the line AA of the apparatus shown in FIG.

The convex lens 1 emits an incident parallel light beam with a focal length f ₁ of 70 mm to the surface to be measured and receives a light beam reflected from the surface to be measured. The He-Ne laser beam 9, the mirror 8 and the minute mirror 7 constitute an irradiation device, and the output laser light of the He-Ne laser light source 9 is reflected by the mirror 8 and passes through a hole 15 provided in the side wall of the housing 14. And enters the housing 14 so as to be orthogonal to the optical axis (axis of the convex lens 1) 2. This laser beam is reflected along the optical axis 2 by the minute mirror 7 provided on the optical axis 2, and is irradiated onto the surface S to be measured via the convex lens 1.

3 sets of slit, cylindrical lens, CCD line sensor (6A, 3A, 10A), (6B, 3B, 10B), (6C, 3C, 10C)
As shown in the figure, three-fold symmetry (1 /
Symmetry that makes the same figure every three rotations).
Now, the mirror symmetry planes parallel and perpendicular to the generatrices of the cylindrical lenses 3 of each set (hereinafter, the set names A, B, and C will be omitted when describing the arrangement within each set) are respectively defined as the first , And the second mirror symmetry planes 21 and 22. The first and second
The line of intersection of the mirror symmetry planes 21 and 22 of is the first principal axis 2 of the cylindrical lens 3.
3, a straight line passing through the optical center O on the first main axis 23 of the cylindrical lens 3 and perpendicular to the first main axis 23 is the second main axis 24. Cylindrical lens 3
Is positioned such that its second main axis 24 is contained within the focal plane 5 of the convex lens 1, the first main axis 23 is oriented parallel to the optical axis 2, and the second main axis 24 is aligned with the focal plane 5 and the optical axis 2. It is oriented so as to be perpendicular to the straight line TO connecting the intersection point T with the optical center O. In this embodiment, the length of the line segment TO (distance between the first main axis 23 and the optical axis 2) a = 20 mm. The shield plate 4 is arranged immediately in front of the cylindrical lens 3 perpendicularly to the optical axis 2 and has a slit 6 having a width of 1 mm. The slit 6 includes the first mirror symmetry plane 21 and the shield plate 4.
It is provided at a position facing the cylindrical lens 3 along the line of intersection with. The CCD line sensor 10 is arranged along the second mirror symmetry plane 22 perpendicularly to the first main axis 23 at a focal distance f ₂ = 150 mm from the cylindrical lens 3.

The arithmetic unit 11 calculates the displacement z _{1 of the} point P with respect to the focus F from the outputs of the CCD line sensors 10A, 10B, 10C.

 Next, the operation of this embodiment will be described.

When the measurement point of the surface S to be measured is at the focal point F of the convex lens 1, the light rays reflected at the point F and passing through the convex lens 1 and the slits 6A, 6B, 6C (in FIG. 1, for the sake of simplicity, Only rays passing through 6A are shown), cylindrical lenses 3A, 3
The CCD line sensor 10A, 1 passes through the optical centers of B, 3C O _A , O _B , O _C.
The light enters the pixels R _A , R _B , and R _C of 0B and 10C, which are separated by a from the optical axis. The arithmetic unit 11 associates the output maximum pixel number at this time with the displacement z ₁ = 0 of the surface S to be measured. When the measured point P is displaced from the focus F by z ₁ , it is reflected at the point P,
Light passing through convex lens 1 and slits 6A, 6B, 6C is also a cylindrical lens
The CCD line sensor 1 passes through the optical centers O _A , O _B and O _{C of} 3A, 3B and 3C.
It is incident on the pixels separated by x _A , x _B , x _C from the pixels R _A , R _B , R _{C of} 0A, 10B, 10C.

FIG. 4 is a diagram showing an example of an output curve with respect to the pixel number of the CCD line sensor 10.

Since the incident rays are focused in the pixel array direction,
The output curve shows a sharp peak at pixel number ξ.
Normally, the lengths x _A , x _B , and x _C corresponding to the pixel numbers of the maximum outputs of the CCD line sensors 10A, 10B, and 10C are almost equal, but they are not equal because of an error. The calculation means 11 is equation (3)
And x _A, x _B, obtains the most probable value of z ₁ by the least square method from x _C. In this embodiment, k = f ₁ ² / (af ₂ ) = 1.63 in the equation (3).
When CCD line sensors 10A, 10B, and 10C having 7 μm × 2059 elements are adopted, the measurement range is z = −11.7 to +11.7 mm with reference to the focal point F of the convex lens 1, and the resolution is
It is 11.4 μm.

The present invention is not limited to the above-described embodiments, and various modifications can be made.

In this embodiment, the optical system composed of three sets of slits, cylindrical lenses, and CCD line sensors is symmetrically arranged three times around the optical axis 2, but the number of optical systems is not necessarily three sets. The arrangement also does not necessarily have to be rotationally symmetrical. However, the symmetry of the arrangement of the optical system not only allows the measurement error to be treated as a systematic error by operating the device for measurement or processing the measurement value, but also facilitates other calculations. Further, by selecting the focal lengths f ₁ and f ₂ of the lens, as can be seen from the equation (3), it is possible to take a very long measuring range to a very large measuring range. Further, although the CCD line sensor is used in the embodiment, it can be replaced regardless of analog or digital if the light receiving position is converted into an electric signal. Further, the light source that generates parallel rays is not limited to the He-Ne laser. In the present embodiment, only the device for detecting the displacement of the surface to be measured in the z-axis direction along the irradiation laser beam has been described, but this device is arranged on a table movable in the x- and y-axis directions, and each x , z displacement of measured surface at y coordinate
Then, three-dimensional data of the surface to be measured can be obtained.

〔The invention's effect〕

 As described above, the present invention has the following effects.

1. By arranging the cylindrical lens on the focal plane of the objective lens and arranging the line sensor on the focal point of the cylindrical lens, the relationship between the displacement of the surface to be measured and the light receiving position of the line sensor becomes linear, and the device adjustment is easy. Also, the calculation for obtaining the displacement of the surface to be measured from the light receiving position of the line sensor becomes easy.

2. By arranging the light rays incident on the cylindrical lens to converge in the pixel array direction of the line sensor, the intensity distribution of the light incident on the line sensor has a sharp peak,
As a result, it is possible to easily detect the light receiving position of the line sensor.

3. A plurality of sets of optical systems consisting of a cylindrical lens and a line sensor arranged as in 1 and 2 above, and a slit arranged in parallel with the generatrix immediately before the cylindrical lens are arranged around the optical axis of the device. By doing so, it is possible to obtain the measured value regardless of the direction of the normal line of the surface to be measured at the measurement point with respect to the optical axis. In addition, the probability that measurement errors due to a plurality of sets of optical systems will intensify each other is very small, and therefore highly reliable measurement results can be obtained without performing separate correction experiments.

[Brief description of the drawings]

1 is a block diagram of an embodiment of the optical non-contact position measuring device of the present invention, FIG. 2 is a diagram showing the arrangement of the slit 6, the cylindrical lens 3 and the CCD line sensor 10 of the device of FIG. 3 is a sectional view taken along the line AA of the device of FIG. 1, FIG. 4 is a diagram showing an example of an output curve of a CCD line sensor, and FIGS. 5 (A) and 5 (B) are optical non-contact position measuring devices of the present invention. FIG. 6 is a layout diagram of an optical element of the main part of FIG. 6, and FIG. 6 is a configuration diagram of a conventional example of an optical non-contact position measuring device. 1 ... convex lens, 2 ... optical axis, 3,3A, 3B, 3C ... cylindrical lens, 4 ... shield plate, 5 ... focal plane, 6,6A, 6B, 6C ... slit, 7 ... small Mirror, 8 ... Mirror, 9 ... He-Ne laser light source, 10, 10A, 10B, 10C ... CCD line sensor, 11 ... Arithmetic unit, 14 ... Housing, 15 ... Hole, 21,22 ... Mirror plane of symmetry, 23 ... primary spindle, 24 ... secondary spindle.

Claims (1)

(57) [Claims] 1. A convex lens (1) which emits an incident parallel light beam to a surface to be measured and receives a light beam reflected from the surface to be measured, and a parallel light beam which is generated on an axis (2) of the convex lens (1). An irradiation device (7,8,9) along which the parallel rays are incident on the convex lens (1), and a mirror symmetry plane including a generatrix of the cylindrical lens (3) is a first mirror symmetry plane (21), The mirror symmetry plane perpendicular to the is defined as the second mirror symmetry plane (22), and the line of intersection of the first and second mirror symmetry planes (21, 22) is defined as the first principal axis (23) of the cylindrical lens (3). , 1st spindle (23)
When a straight line passing through the above optical center and parallel to the generatrix is the second main axis (24), each first main axis is oriented parallel to the axis (2) of the convex lens (1), and each second main axis is The convex lens (1) is positioned in the focal plane (5) on the side opposite to the surface to be measured, and the intersection of the axis (2) of the convex lens (1) and the focal plane (5), the first principal axis and the second principal axis are measured. Multiple cylindrical lenses (3A, 3A) oriented perpendicular to a straight line connecting the intersection with the main axis
B, 3C) and the first mirror symmetry plane of each cylindrical lens (3A, 3B, 3C) which is arranged in front of the focal plane (5) in parallel with the focal plane (5) of the convex lens (1). The shielding plate 4 having slits (6A, 6B, 6C) at positions facing the cylindrical lenses (3A, 3B, 3C) along the intersection line, and the cylindrical lenses (3A, 3B, 3C) Position detection which is arranged in the second mirror symmetry plane behind the focal plane (5) by a distance equal to the focal length of the cylindrical lens (3A, 3B, 3C) and parallel to the focal plane (5). Line sensor (10A, 10B, 10
C) and an optical non-contact position measuring device having an arithmetic means for calculating the position of the surface to be measured by inputting the outputs of the line sensors (10A, 10B, 10C).