JP3368941B2 - Auto focus mechanism - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pinhole type autofocus mechanism. More specifically, the present invention relates to a pinhole type autofocus mechanism in which reflected light from an object is split into two lights, and pinholes are arranged in front of and behind the split reflected light.

[0002]

BACKGROUND ART For example, a pinhole system is known as one of autofocus mechanisms used for a measuring head of a surface roughness meter and a pickup of a flowpy disk driver. This is because the reflected light from the object is split into two lights, a pinhole is placed before and after the split reflected light, and a photodetector is placed immediately after that, and based on the output of the photodetector. This is a method of obtaining a focus error signal.

Specifically, an optical system including an objective lens for converging light on an object, a beam splitter for splitting the reflected light from the object into two lights, and a front of an image forming point of one of the divided reflected lights. And a pinhole plate having pinholes respectively arranged after the image formation point of the other divided reflected light, a photodetector arranged immediately after each pinhole plate, and an output of this photodetector. And a drive mechanism for moving the objective lens so that the objective lens always focuses on the object surface based on an output signal (focus error signal) from the detection circuit. It is a composition.

[0004]

In the case of the pinhole type autofocus mechanism described above, it is necessary to align the pinhole with the optical axis of the autofocus mechanism. However, at the time of initial assembly and adjustment, if the pinhole is not located near the optical axis, no light will enter the photodetector. Which direction should the pinhole plate be moved and adjusted? I do not know. Therefore, conventionally, the pinhole plate is made to coincide with the optical axis while the pinhole plate is moved and adjusted by trial and error, so that the adjustment is troublesome and time-consuming.

It is an object of the present invention to provide a pinhole type autofocus mechanism which can eliminate such drawbacks of the prior art and can easily and quickly align the pinhole with the optical axis. is there.

[0006]

According to a first aspect of the invention, an optical system including an objective lens for focusing light on an object, a beam splitter for splitting reflected light from the object into two lights, and one of the split reflections A pinhole plate having pinholes arranged before the image formation point of light and after the image formation point of the other divided reflected light, and a photodetector arranged immediately after each pinhole plate, In the autofocus mechanism including a detection circuit for detecting defocus based on the output of the photodetector and a drive mechanism for moving the objective lens based on the output signal from the detection circuit, the pinhole plate is , Multiple pinholes are arranged in the vertical and horizontal directions at regular intervals.
The pinhole plate is movably provided.

In the second invention, an optical system including an objective lens for converging light on an object, a beam splitter for splitting reflected light from the object into two lights, and an image forming point of one of the split reflected lights. A pinhole plate having pinholes respectively arranged before and after the image formation point of the other divided reflected light, a photodetector arranged immediately after each pinhole plate, and an output of this photodetector. In the autofocus mechanism including a detection circuit for detecting defocus based on the above, and a drive mechanism for moving the objective lens based on an output signal from the detection circuit, one pinhole is provided in the pinhole plate. And a guide long hole having a width substantially equal to or less than the diameter of the pinhole and having a predetermined length along the straight line passing through the pinhole.

[0008]

In the first aspect of the invention, since the plurality of pinholes are arranged on the pinhole plate in the vertical and horizontal directions at constant pitch intervals, the probability that the pinholes coincide with the optical axis at the time of initial assembly / adjustment is high. Increase. Even if they do not match during the initial assembly and adjustment, if you move the pinhole plate in any direction,
Since the adjacent pinholes are aligned with the optical axis, the pinholes can be aligned with the optical axis more easily and quickly than ever before.

In the second invention, one pinhole is provided in the pinhole plate, and a guide hole having a width which is substantially equal to or smaller than the diameter of the pinhole and has a predetermined length along a straight line passing through the pinhole. Is provided, the optical axis is positioned so that the optical axis is in a direction orthogonal to the guide slot and having a width corresponding to the length of the guide slot during the initial assembly and adjustment. This is easy due to the wide range. Therefore, first, when the pinhole plate is moved in the direction orthogonal to the guide slot, the optical axis enters the guide slot.
Next, when the pinhole plate is moved in the direction of the guide long hole, the guide long hole comes off the optical axis and the signal from the photodetector temporarily stops. An output is obtained from the photodetector with a pinhole. Therefore, the pinhole can be aligned with the optical axis more easily and quickly than in the conventional case.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical displacement meter using a pinhole type autofocus mechanism of the present invention will be described in detail below with reference to the drawings. Here, first, the configuration of the optical displacement meter common to each embodiment will be described, and then each embodiment will be described.

As shown in FIG. 1, the optical displacement meter includes a displacement meter body 1 and an objective lens 14 for the displacement meter body 1.
, An objective lens holder 2 for holding the objective lens holder 2 movably in the vertical direction, a voice coil 6 as a drive mechanism for driving the objective lens holder 2 in the vertical direction, and a linear for detecting the vertical position of the objective lens holder 2. The encoder 9 is included. The voice coil 6 is composed of a magnet 4 fixed to the displacement meter main body 1 and a coil 5 fixed to the objective lens holder 2. The linear encoder 9 includes a scale 7, one end of which is fixed to the objective lens holder 2, and the displacement gauge body 1.
And a detector 8 fixed to face the scale 7.

A semiconductor laser 11 is provided on the displacement meter main body 1.
And the light emitted from the semiconductor laser 11
A beam splitter 12 that reflects toward 0, a collimator lens 13 that directs the light whose traveling direction has been changed by the beam splitter 12 into a parallel beam, and a reflected light from the measurement surface 10 that forms an image. The image lens 15, the beam splitter 16 that splits the light that has passed through the imaging lens 15, and the beam splitter 16
Pinhole plates 17A and 17B arranged before and after the in-focus position of each divided reflected light
And photodetectors 18A, 18 for detecting the amount of split reflected light that has passed through the pinhole plates 17A, 17B, respectively.
B and are provided. In addition, here, the semiconductor laser 11, the beam splitter 12, and the collimator lens 1 are used.
An illumination optical system 19 is formed including the objective lens 14 that collects light on the measurement surface 3 and the measurement surface 10.

FIG. 2 shows the detection circuit 20. The detection circuit 20 includes a current-voltage (IV) converter 21A, which converts the output current of each photodetector 18A, 18B into a voltage.
21B, amplifiers 22A and 22B for amplifying the output voltages of the respective IV converters 21A and 21B, and both amplifiers 2
Difference calculator 23 that calculates the difference between the outputs of 2A and 22B and sum calculator 2 that calculates the sum of the outputs of both amplifiers 22A and 22B.
4 and a divider 25 that divides the output of the difference calculator 23 by the output of the sum calculator 24 to obtain a focus error signal S having an S-shaped curve.

Now, if the distances from the in-focus position of each divided reflected light to each pinhole plate 17A, 17B are set to be equal to each other, the output of each photodetector 18A, 18B becomes as shown in FIG. At that time, the focus error signal S obtained from the detection circuit 20 becomes an S-shaped curve as shown in FIG. 4, and becomes a signal corresponding to the displacement of the measurement surface 10. Therefore, based on the focus error signal S, the objective lens 14
So that the measurement surface 10 is always focused on by the voice coil 6
By controlling, the output of the linear encoder 9 at that time can be output as a measurement value. That is, measurement surface 1
The roughness of 0 can be obtained from the output of the linear encoder 9.

First Embodiment In the above optical displacement meter, each pinhole plate 17 is used.
As shown in FIG. 5, a plurality of pinholes 31 each having a pinhole function are arranged in A and 17B in the vertical and horizontal directions at regular intervals. As described above, since the pinhole plates 17A and 17B are provided with the plurality of pinholes 31, the pinholes 3 are initially assembled and adjusted.
The probability that 1 matches the optical axis increases. Even if they do not match at the time of initial assembly and adjustment, if the pinhole plates 17A and 17B are moved in either direction, the adjacent pinholes 31
Can be aligned with the optical axis. Therefore, according to the first embodiment, the pinhole can be easily and quickly aligned with the optical axis and the burden on the operator can be reduced, as compared with the related art.

In the first embodiment, the pinhole 3
The number of 1s and the arrangement method are not limited to those in the above embodiment. For example, for the number is arbitrary as long as it is two or more, advantages there the probability that a pinhole more you often coincides with the optical axis increases Ru.

Second Embodiment In the above optical displacement meter, each pinhole plate 17 is used.
A and 17B have one pinhole 3 as shown in FIG.
2 and a guide hole 33 having a width equal to the diameter of the pinhole 32 and a length several times the diameter are provided along a straight line passing through the pinhole 32. A band 3 having a width in a direction orthogonal to the guide slot 33 at the time of initial assembly and adjustment and corresponding to the length of the guide slot 33.
Position it so that the optical axis is inside 4. This is easy due to the wide range. Therefore, first, the pinhole plate 1
When 7A and 17B are moved in a direction orthogonal to the guide slot 33, the optical axis enters the guide slot 33. Next, when the pinhole plates 17A and 17B are moved in the direction of the guide elongated hole 33, the guide elongated hole 33 is disengaged from the optical axis and the signals from the photodetectors 18A and 18B are temporarily stopped. As you move it, the pinhole 32 on the optical axis
And the outputs are obtained from the photodetectors 18A and 18B. Therefore, according to the second embodiment, the pinhole can be easily and quickly aligned with the optical axis, and the burden on the operator can be reduced, and one pinhole 32 can be provided. Since it is only necessary to drill the guide long holes 33, the number of drilling processes can be reduced as compared with the first embodiment.

In the second embodiment, the width of the guide elongated hole 33 is made equal to the diameter of the pin hole 32, but the width of the guide elongated hole 33 may be slightly larger than the diameter of the pin hole 32. It may be smaller than the diameter of the pinhole 32. That is, the diameter may be substantially equal to or smaller than the diameter of the pinhole 32. The length may be determined in consideration of the movable range of the pinhole plates 17A and 17B. Further, another guide elongated hole is formed on the opposite side of the pin hole 32, that is, the two guide elongated holes 33, 33 are arranged on the straight line passing through the pin hole 32 so as to sandwich the pin hole 32. By doing so, the bands 34 on both sides can be adjusted during the initial assembly and adjustment.
Since it is only necessary to position it so that the optical axis can enter inside,
It is simpler than the case of the embodiment.

Further, in each of the above-described embodiments, the example applied to the optical displacement meter has been described, but the autofocus mechanism of the present invention is not limited to this. For example, the present invention can be used for a copying probe used when performing a copying operation in a coordinate measuring machine, a pickup of a flowpy disc driver, and the like.

[0020]

As described above, according to the autofocus mechanism of the present invention, in the pinhole focusing method, the pinhole can be easily and quickly aligned with the optical axis.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an optical displacement meter to which the present invention is applied.

FIG. 2 is a diagram showing a detection circuit of the optical displacement meter of FIG.

FIG. 3 is a diagram showing an output of a photodetector in the optical displacement meter of FIG.

4 is a diagram showing a focus error signal in the optical displacement meter of FIG.

FIG. 5 is a diagram showing a pinhole plate in the first embodiment of the present invention.

FIG. 6 is a diagram showing a pinhole plate according to a second embodiment of the present invention.

[Explanation of symbols]

11 Semiconductor laser 14 Objective lens 17A, 17B pinhole plate 18A, 18B photo detector 19 Optical system for illumination 20 detection circuit 31,32 pinhole 33 Guide long hole

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 55-65921 (JP, A) JP 4-265918 (JP, A) JP 58-102107 (JP, A) 34512 (JP, U) Actually open 5-33109 (JP, U) Actually open 54-66859 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01C 3/00-3 / 32 G01B 11/00-11/30 102 G02B 7/28-7/40 G03B 13/32-13/36

Claims (2)

(57) [Claims] 1. An optical system including an objective lens for condensing light on an object, a beam splitter for splitting reflected light from the object into two lights, and a beam splitter before and after an image forming point of one of the split reflected lights. A pinhole plate having pinholes arranged after and at the image formation point of the split reflected light, a photodetector arranged immediately after each pinhole plate, and a focus based on the output of this photodetector. In an autofocus mechanism including a detection circuit that detects a shift and a drive mechanism that moves the objective lens based on an output signal from the detection circuit, the pinhole plate has a plurality of pinholes vertically and horizontally. In a certain direction
An autofocus mechanism characterized in that the pinhole plates are arranged so that they can be moved, and the pinhole plates are movably provided. 2. An optical system including an objective lens for condensing light on an object, a beam splitter for splitting reflected light from the object into two lights, and a beam splitter before and after an image forming point of one split reflected light. A pinhole plate having pinholes arranged after and at the image formation point of the split reflected light, a photodetector arranged immediately after each pinhole plate, and a focus based on the output of this photodetector. In an autofocus mechanism including a detection circuit for detecting a shift and a drive mechanism for moving the objective lens based on an output signal from the detection circuit, the pinhole plate has one pinhole and its pin. An autofocus mechanism, characterized in that a guide long hole having a width of not more than the diameter of a pinhole and a length of a predetermined length is provided along a straight line passing through the hole.