JPH05164556A - Focusing type non-contact displacement gage - Google Patents

Abstract

PURPOSE:To enable the measurement of a surface shape of a deep groove and a hole without decreasing the response speed by making an objective lens part unmovable and making the objective lens exchangeable according to measuring application. CONSTITUTION:Relay lenses 52 and 54 are disposed between a collimator lens 24 and an objective lens 14 of an imaging optical system and one of the relay lenses is moved by a servo system to adjust the focus. Thus, the displacement of an object to be measured is determined from the position of the relay lens when the focusing point is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focusing type non-contact displacement meter, and more particularly to a deep groove suitable for use as a non-contact surface roughness meter or a non-contact scanning probe for a three-dimensional coordinate measuring machine. The present invention relates to a focusing type non-contact displacement meter capable of measuring the surface shape of a hole and exchanging an objective lens.

[0002]

2. Description of the Related Art As a non-contact displacement meter using a light beam, there are an apparatus using a triangulation method and an apparatus using an astigmatic method, a critical angle method, a Foucault method, a pinhole method, and the like. is there.

However, in the displacement meter using the triangulation method, there is a drawback in principle that the measurement range is narrowed when the resolution is increased.

Further, in the displacement meter using the in-focus method, the position of the objective lens in the in-focus state is detected as a displacement signal by using, for example, the principle of auto-focus of the optical disk, but most of them are objective lens driving means. Since the value of the current flowing through the moving coil used as is used as the displacement signal, the accuracy of displacement detection is low. Therefore, for example, a wide measurement range of 1 mm or more and 0.01 μ
It was difficult to achieve a high resolution of about m.

In order to solve such a problem, the applicant has already proposed in Japanese Patent Application No. 3-91573 (unknown) that the displacement can be detected with high resolution over a wide measuring range. Proposing a displacement meter.

As shown in FIG. 1, the objective lens 14 is servo-controlled so as to always focus on the surface 11A of the measuring object 10, and the displacement amount of the objective lens 14 is scaled by a scale 16.
And a linear encoder including a detector 18 or a differential transformer, and the displacement of the measurement surface 11A is measured.

In FIG. 1, 20 is a semiconductor laser as a light source, 22 is a polarization beam splitter for reflecting the light emitted from the semiconductor laser 20 toward the measurement surface 11A, and 24 is the polarization beam splitter 22. The collimator lens 26 for converting the light whose traveling direction is changed into a parallel beam by 26 prevents the scattered reflection light from the measurement surface 11A from returning to the semiconductor laser 20, and, in combination with the polarization beam splitter 22, forms a half beam. 1/4 wavelength delay plate for higher efficiency than when using a mirror, 2
Reference numeral 8 denotes an image forming lens for forming an image of the reflected light transmitted through the polarization beam splitter 22, and 30 denotes the image forming lens 2
A beam splitter for splitting the light transmitted through 8;
2A and 32B are pinhole plates arranged before and after the in-focus position of each reflected light split by the beam splitter 30, and 34A and 34B are reflected light that has passed through the pinhole plates 32A and 32B. Is a light-receiving element (for example, a photodiode) for detecting the respective light amounts of the above, and an imaging optical system is formed by the polarization beam splitter 22, the collimator lens 24, the objective lens 14, the quarter wavelength delay plate 26, and the imaging lens 28. It is configured.

The objective lens 14 has a movable lens barrel 38.
Moving coil 40 such as voice coil attached to the
And by the magnet 42, it is driven in the vertical direction of the figure,
The position of the movable lens barrel 38 when focused (that is, the objective lens 1
4 position) is detected by reading the displacement of the scale 16 with the detector 18.

According to the displacement meter proposed by the applicant, the displacement can be detected with high resolution over a wide measurement range.

[0010]

However, in the method of directly servoing the objective lens 14 with the moving coil 40 or the like, the deep groove 1 as shown in FIG. 1 is used.
In the measurement of the bottom surface 11A of No. 1, the lens barrel 38 of the objective lens 14 is used.
Becomes longer and the moving parts become heavier. Further, in the measurement of the inner surface 12A of the hole 12 as shown in FIG. 2, the lens barrel 38 has a complicated shape, and the movable portion also becomes heavy. Therefore, there is a problem that the response speed becomes slow.

Further, even if the objective lens unit is to be replaced depending on the application, if the weight of the movable portion fluctuates for that purpose, the objective lens cannot be controlled, and the objective lens cannot be replaced. .

The present invention has been made to solve the above-mentioned conventional problems. It is possible to measure the surface shape of a deep groove or a hole without reducing the response speed, and the objective lens can be changed depending on the measurement application. An object is to provide a focusable non-contact displacement meter that can be replaced.

[0013]

DISCLOSURE OF THE INVENTION The present invention relates to a focusing type non-contact displacement meter, which irradiates a light source and light emitted from the light source onto the surface of an object to be measured, and reflects the light of the light source. An image forming optical system for forming an image, a relay lens inserted in the optical path of the image forming optical system, a drive unit for changing the position of the relay lens, and an encoder for detecting the relay lens position. An in-focus point detecting means for detecting that the image position coincides with a predetermined position is provided, and the output of the encoder when the in-focus point is detected by the in-focus point detecting means by operating the driving means is measured. The object is achieved by outputting as a displacement signal.

[0014]

According to the present invention, the relay lens is inserted in the optical path of the imaging optical system for irradiating the surface of the object to be measured with the light emitted from the light source and forming the image of the light source by the reflected light. Then, the position of the relay lens is moved by a driving means such as a moving coil to adjust the distance between the relay lenses,
The objective lens is not moved but focused on the surface of the object to be measured, and the displacement of the relay lens at that time is detected by an encoder such as a scale or a differential transformer to determine the displacement of the surface to be measured.

Therefore, when measuring the bottom surface of the deep groove or the inner surface of the hole, even if the movable portion becomes heavy due to the length of the objective lens barrel becoming complicated, there is no need to move the objective lens. Since the relay lens can be moved, the weight is light and the response speed is fast.

Further, even if the objective lens is exchanged depending on the measurement application, the weight of the movable portion does not change, so that the control can be easily performed.

Particularly, when the relay lens is composed of a plurality of lenses and only the position of the specific lens is changed by the driving means, the structure is simple.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings.

The first embodiment of the present invention is one in which the present invention is applied to a non-contact displacement meter for measuring deep grooves by the pinhole method. In the same configuration as the comparative example shown in FIG. A pair of upper and lower relay lenses 52 and 54 are inserted between the collimator lens 24 and the objective lens 14 of
In the drawing, the movable portion 50 including the lower relay lens 54 is driven in the vertical direction of the drawing by the driving means including the voice coil 40 and the magnet 42, and the objective lens 14 is fixed to the case 58 via the fixed lens barrel 56. It is the one.

The relay lenses 52 and 54 and the objective lens 14 are all the same.

Since the other structure is the same as that of the comparative example shown in FIG. 1, detailed description thereof will be omitted.

In the movable part 50, as shown in FIG. 4, for example, only the lower relay lens 54 is moved in the vertical direction in the figure, and the upper relay lens 52 and the objective lens 14 are fixed. Therefore, if the displacement of the measurement surface 11A is a and the displacement of the lower relay lens 54 is b, then the following relationship is established between the displacements a and b.

B = a / {1+ (a / f)} (1)

Here, f is the focal length of the lens.

Therefore, the relationship between the displacement a of the measuring surface 11A and the displacement b of the relay lens 54 is not necessarily linear, but when the displacement a of the measuring surface 11A is small, there is no problem in use. For example, when f = 10 mm, b = 0.00999 mm when a = 0.01 mm, b = 0.099 mm when a = 0.1 mm.

When the displacement of the measurement surface 11A is large, it is possible to use it after function processing according to the relation of the above-mentioned expression (1).

In this embodiment, since the two relay lenses 52 and 54 and the objective lens 14 are all the same, there is an advantage that the displacement of the measuring surface 11A can be transmitted in a one-to-one manner.
By providing a signal processing circuit, it is possible to increase or decrease the measured displacement amount in the optical system.

Further, in this embodiment, the upper relay lens 52 near the collimator lens 24 is fixed and the lower relay lens 54 is moved, so that the structure is simple. As in the second embodiment shown in FIG. 5, the lower relay lens 54 is fixed and the upper relay lens 5 is fixed.
2 may be moved.

Next, with reference to FIG. 6, a third embodiment of the present invention applied to a non-contact displacement meter for measuring the surface shape of a hole will be described in detail.

In the third embodiment, in the same non-contact displacement meter as the comparative example shown in FIG. 2, a pair of left and right relay lenses 52 are provided between the collimator lens 24 and the objective lens 14 as in the first embodiment. , 54 are inserted, and on the other hand, the movable part 50 including the relay lens 54 on the right side in the figure is driven in the left-right direction in the figure by the driving means composed of the voice coil 40 and the magnet 42, and the objective lens 14 is fixed. 56
It is adapted to be fixed to the case 58 via.

The other structure and the basic operation are the same as those of the comparative example of FIG. 1 or the first embodiment of FIG. 3, and therefore detailed description will be omitted.

In each of the above-mentioned embodiments, since the movable portion 50 is driven by the voice coil 44, the responsiveness is fast. The driving method of the movable portion 50 is not limited to this, and for example, a linear motor or a feed screw and a rotary motor can be used.

In the above embodiment, the pinhole method is used to detect the measurement surface, but the method for generating the focus position signal when the measurement surface reaches the focus position of the objective lens is not limited to this. Not, for example, the astigmatism method, the critical angle method,
Other focusing methods such as the Foucault method may be used.

In each of the above embodiments, the beam splitter 30 is disposed between the imaging lens 28 and the pinhole plates 32A and 32B, but the position of the beam splitter 30 is not limited to this. There is no limitation, and it may be provided between the imaging lens (two required) and the polarization beam splitter 22. A half mirror may be used instead of the polarization beam splitter 22.

The encoder for detecting the position of the movable portion 50 is not limited to the linear encoder, and a rotary encoder may be used, for example.

[0036]

As described above, according to the present invention, since the objective lens is not moved but the relay lens is moved, the weight is light and the response speed is fast.

Further, even if the objective lens section is exchanged, the weight of the movable section including the relay lens does not change depending on the measurement application, so that it has an excellent effect that it can be easily controlled.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a situation where a bottom surface of a deep groove is measured using a comparative example proposed by the applicant in Japanese Patent Application No. 3-91573 (unknown).

FIG. 2 is a cross-sectional view showing a state where the inner surface of a hole is being measured by the same comparative example.

FIG. 3 is a cross-sectional view showing a state where the bottom surface of the deep groove is being measured according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the principle of the relay lens in the first embodiment.

FIG. 5 is a diagram showing the principle of the relay lens in the second embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a state in which the inner surface of a hole is being measured according to the third embodiment of the present invention.

[Explanation of symbols]

 10 ... Object to be measured, 11 ... Deep groove, 11A ... Bottom surface (measurement surface), 12 ... Hole, 12A ... Inner side surface (measurement surface), 14 ... Objective lens, 16 ... Scale, 18 ... Detector, 20 ... Semiconductor laser, 22 ... Polarizing beam splitter, 24 ... Collimator lens, 28 ... Imaging lens, 34A, 34B ... Light receiving element, 38 ... Movable lens barrel, 40 ... Voice coil, 42 ... Magnet, 50 ... Movable part, 52, 54 ... Relay lens , 56 ... Fixed lens barrel, 58 ... Case.

Claims (2)

[Claims] 1. A light source, and the surface of an object to be measured is irradiated with light emitted from the light source,
An image forming optical system for forming an image of the light source by the reflected light, a relay lens inserted in the optical path of the image forming optical system, a drive unit for changing the position of the relay lens, and a relay lens of the relay lens. An encoder for detecting a position and an in-focus point detecting means for detecting that the image forming position coincides with a predetermined position are provided, and the driving means is operated to operate the in-focus point detecting means to detect the in-focus point. A focusing non-contact displacement meter characterized by outputting the output of an encoder as a displacement signal of an object to be measured. 2. The focusing type non-contact displacement meter according to claim 1, wherein the relay lens is composed of a plurality of lenses, and only the position of the specific lens is changed by the driving means.