JPH0663764B2 - Optical ring type non-contact measuring sensor - Google Patents

Description

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

[Conventional technology]

3 and 4 are views showing conventional examples of this type of non-contact length measuring sensor.

The one shown in Figure 3 uses the principle of triangulation,
The photoelectric conversion element is used to measure the change in the incident angle θ due to the change in the position of the surface to be measured. According to this principle, the measurement sensitivity increases as the angle φ formed by the irradiation optical axis of the laser beam and the straight line connecting the non-measurement position and the photoelectric conversion element increases, but when the angle φ is large, it is reflected on the surface to be measured. There is a drawback in that the laser beam is blocked by the protrusions near the measured position and causes a shadow effect that prevents the laser beam from entering the photoelectric conversion element. Further, when the surface to be measured is tilted, the laser spot becomes an ellipse when viewed from the photoelectric conversion element, so that there is a drawback that the measurement accuracy is poor depending on where the center is located.

FIG. 4 shows an optical non-contact sensor designed to overcome the drawback of the principle of FIG. Therefore, the light received by the CCD line sensor is the fifth
As shown in FIG. 5A, sufficient strength and good distribution are not obtained, and as shown in FIG. 5B, the measurement accuracy may deteriorate. As a practical measure in this case, in order to adopt only good light, a plurality of optical path systems and CCDs are symmetrical with respect to the optical axis.
It has the drawback of having to use a line sensor.

An object of the present invention is to provide an optical ring type non-contact sensor which is a non-contact length measuring sensor without the above-mentioned drawbacks.

[Means for Solving the Problems]

The optical ring type non-contact length measuring sensor of the present invention emits an incident parallel laser beam to a surface to be measured, generates a parallel laser beam, and a first convex lens which receives a laser beam reflected from the surface to be measured. An irradiation device for making the parallel laser beam along the optical axis of the first convex lens incident on the first convex lens, and a focal length of the first convex lens on the opposite side of the surface to be measured with respect to the first convex lens. An annular slit disposed on a surface perpendicular to the optical axis and having a predetermined radius with the optical axis as a center, and an opposite side of the first convex lens with respect to the slit centered on the optical axis And a second convex lens placed at a position on the surface opposite to the slit with respect to the second convex lens on the surface perpendicular to the optical axis with the focal length of the second convex lens separated. A plate-shaped optical sensor centered on the axis, Receiving a signal from the serial light sensor,
And an arithmetic unit for obtaining the radius of the image of the slit formed on the optical sensor.

[Action]

The laser light reflected from the target surface for distance measurement is condensed by the first convex lens, and only the light corresponding to the annular slit is further condensed by the second convex lens, which corresponds to the annular slit on the CCD area sensor. Form an annular image that
A signal based on this image formation is read from the CCD area sensor, and the arithmetic unit calculates the radius of the image formation that changes corresponding to the distance from the target surface.

Further explaining this principle in detail with reference to FIG.
The annular slit is separated by the focal length f ₁ of the first convex lens,
It is placed on a surface perpendicular to the optical axis of the first convex lens, and has an annular shape with a radius a around the optical axis. The second convex lens is placed at a distance l from the annular slit such that the optical axis of the second convex lens overlaps the optical axis of the first convex lens. The image forming surface of the second convex lens is set to be perpendicular to the optical axis with the focal length f ₂ of the second convex lens being separated. In such an optical system, when the surface to be measured is displaced by the distance z ₁ from the focal length f _{1, the} formula (1) is established from the Newton's image formation formula in the first convex lens.

Equation (2) is established from the analogy of △ SCQ and △ FES.

Expression (3) is established from Expressions (1) and (2).

Since the position where the image in the slit S is formed by the second convex lens is the virtual image point V, the formula (4) is established by using the Newton's image formation formula.

Equation (5) is established from the analogy of ΔCRT and ΔVUT.

Equation (6) is established from the analogy of ΔPQR and ΔPVU.

Equation (7) is established from the analogy of ΔPQR and ΔPWT.

The expression (8) is established from the expressions (4), (5), (6), and (7).

Further, equation (9) is derived from equations (3) and (8).

This expression (9) indicates that the displacement z ₁ and the radius r of the ring image have a linear relationship. Therefore, Z ₁ can be easily obtained from r.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of an optical ring type non-contact length measuring sensor of the present invention.

The laser beam 12 emitted from the He-Ne laser 9 is reflected by the minute mirrors 10 and 11, emitted on the optical axis 2 of the first convex lens 1 (focal length f ₁ ), and the measured surface of the measuring object 13 is measured. S is reflected as scattered light. Of this reflected light, a ring slit 4 which is an annular slit provided on the slit plate 3 (a radius of 20 mm around the optical axis 2 and a slit width
Only the circular light that has passed through 0.2 mm) is the second convex lens 5
A ring-shaped image is formed on the CCD area sensor 7 attached to the vertical plate 6 that passes through the (focal length f ₂ ) and is perpendicular to the optical axis 2.

The intervals between the surface to be measured S, the first convex lens 1, the slit plate 3, the second convex lens 5, and the CCD area sensor 7 are z ₁ + f ₁ , f ₁ , l, f ₂ , respectively, and in this embodiment, f ₁ = 70mm, f
₂ = 120 mm and l = 30 mm. Therefore, the equation (10) is obtained by using the above equation (9).

r = 0.49z ₁ (10) As a CCD area sensor, 1/2 inch 380,000 pixels (13.
7μm / 1 pixel) and resolution is 786 (H) × 48
It is 8 (V). Therefore, from formula (10), measuring range The sensor of is obtained.

The radius r is calculated from the ring image obtained by the CCD area sensor by the arithmetic unit 8, but excludes the reflected light that does not have sufficient intensity and the inappropriate value that is interfered by the speckle phenomenon. , High-accuracy measurement values can be obtained from the remaining good quality data by using the least squares method.

Therefore, z ₁ is obtained from the obtained r, and f ₁ is known, so the distance (z ₁ + f ₁ ) is also obtained.

In the present invention, the plate-like optical sensor for image formation extraction may be a flat photoelectric sensor, CCD
It is not limited to area sensors.

〔The invention's effect〕

As described above, according to the present invention, an annular slit is provided between the first and second convex lenses arranged so that their optical axes coincide with each other, and the plate-shaped light is provided at the focal length position of the second convex lens. A sensor is provided, and the laser beam reflected from the surface to be measured is passed through the first convex lens, the annular slit, and the second convex lens to determine the size of the radius of the image of the annular slit formed on the optical sensor. The following effects can be obtained by calculating with a computing device.

1. The radius of the image formed on the optical sensor and the displacement of the surface to be measured have a linear relationship, which facilitates the adjustment of the device and facilitates the calculation of the displacement from the radius.

2. By using an annular slit and a plate-shaped optical sensor, information about the radius can be obtained at all angles of 360 °, so depending on the properties of the surface to be measured (roughness, etc.), there may be angles where good reflected light cannot be obtained. Even if there is such data, it is possible to measure with high accuracy by excluding such data.

3. Since the axis for emitting laser light and the axis for receiving light are the same, the shadow effect in triangulation and the deterioration of accuracy on steep slopes do not occur.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an optical ring type non-contact length measuring sensor of the present invention, FIG. 2 is a diagram for explaining the principle of the present invention, and FIGS. 3 and 4 are conventional examples. FIGS. 5 (a) and 5 (b) are views for explaining the operation of FIG. 1 ... First convex lens, 2 ... Optical axis, 3 ... Slit plate, 4 ... Ring slit, 5 ... Second convex lens, 6 ... Vertical plate, 7 ... CCD area sensor, 8 ... Arithmetic unit, 9 ... He-Ne laser, 10, 11 ... Micro mirror, 12 ... Laser beam.

Claims (1)

[Claims] 1. A first laser which emits an incident parallel laser beam to a surface to be measured and receives a laser beam reflected from the surface to be measured.
Irradiation device (9) that generates a parallel laser beam and causes the parallel laser beam along the optical axis (2) of the first convex lens (1) to enter the first convex lens (1). 10 and 11) and the first convex lens (1) on the opposite side of the surface to be measured
Is disposed on a surface (3) perpendicular to the optical axis (2) at a focal distance (f ₁ ) of the convex lens (1), and the optical axis (2)
An annular slit (4) having a predetermined radius (a) centered at, and a position on the opposite side of the first convex lens (1) with respect to the slit (4) centered on the optical axis (2) ( l) and the second convex lens (5), and the second convex lens (5) is separated from the second convex lens (5) on the opposite side of the slit (4) by the focal length (f ₂ ). ,
A plate-shaped optical sensor (7) disposed on a surface (6) perpendicular to the optical axis (2) and centered on the optical axis (2), and a signal from the optical sensor (7). Therefore, an optical ring type non-contact length measuring sensor having an arithmetic unit (8) for obtaining a radius (r) of an image formed by the slit (4) formed on the optical sensor (7).