JPH11201720A - Focus detecting method and device for projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus detecting method and a device for a projector having reproducibility on the measured result with a relatively simple and inexpensive structure. SOLUTION: An object image is formed on the surface of a screen 6 by a projecting lens 1 facing an object W, and the surface of the object W is illuminated by the reflected light from a half-mirror 13 located in the projection light path of the projecting lens 1 in this projector. The image of a reticle 11 located on the illumination light path from an illumination light source 9 to the half-mirror 13 is projected on the surface of the object W by the light flux displaced from the optical axis of the half-mirror 13, the image of the reticle 11 is converted into a side drift image against the optical axis by a focus action, and the moving state of the image is detected by an edge detecting element 7 located on the screen 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring microscope or a projector used as a shape measuring device for a part, and more particularly to a method and an apparatus for detecting a focus of the projector.

[0002]

2. Description of the Related Art As is well known, in a measuring microscope or a projector used as a shape measuring device for a part, since the focus accuracy of a projected image of an object to be measured directly has a significant influence on the measurement accuracy, it has conventionally been known. Various focus detection methods and devices have been proposed.

That is, this type of projector uses a so-called triangulation method in which an object to be measured is positioned below a projection lens, and the surface of the object to be measured is spot-irradiated with a laser beam or the like to perform point measurement. However, since this method has a two-axis optical system of a light projecting and a detecting system, a shadow portion that cannot be measured is generated due to "vignetting" of the light used (Japanese Patent Publication No. No. 17934).

In order to solve such a problem of the conventional two-axis optical system, conventionally, a laser beam is passed through a non-center portion of a projection lens, and the position of light reflected from the surface of the object to be measured is detected by a line sensor or a position sensor. (JP-A-4-36603 and JP-A-8-1456)
No. 21).

[0005]

However, in this improved focusing device, since the light of the laser or the light emitting element is reflected on the surface of the object to be measured, the reflected light depends on the properties of the surface of the object to be measured. The state changes greatly. For this reason, the visual measurement with the same focus device requires not only skill but also a tendency for individual differences among the measurers, and the reliability of the focus accuracy itself cannot be maintained.

An object of the present invention is to provide a focus detection method for a projector which has a relatively simple and inexpensive structure and has a reproducible measurement result in view of the above-described problems of the conventional focus detection apparatus for a projector. And to get the device.

[0007]

According to the present invention, there is provided the following objects: 1) an image of an object to be measured is formed on a surface of a screen by a projection lens facing the object to be measured, and a projection optical path of the projection lens; In a projector that illuminates the surface of the DUT with reflected light from a half mirror positioned therein, an image of a reticle located on an illumination optical path from an illumination light source to the half mirror is converted into an optical axis of the half mirror. Is projected on the surface of the object to be measured with a light beam displaced from the optical axis, and the image of the reticle is converted into a laterally displaced image with respect to the optical axis by a focus operation, and the moving state of this image is detected by an edge detection element located on the screen. A focus detection method of the projector, 2) an image of the object to be measured is formed on the surface of the screen by a projection lens facing the object to be measured, and a half positioned in a projection optical path of the projection lens. A reticle located in an illumination optical path from an illumination light source to the half mirror, and a reticle that is displaced with respect to the optical axis in the illumination optical path. A light beam mask, an edge detecting element for detecting an image of a reticle on the surface of the screen projected on the surface of the object to be measured by a displacement light beam passing through the light beam mask, and monitoring by the edge detecting element. Means for precisely adjusting the relative distance between the projection lens and the object to be measured.

In the following description of a preferred embodiment of the present invention, 1) a structure in which the projector is a shape measuring device for components, 2) a position adjusting means, a driving circuit for operating a driving means, and the projection lens And a structure provided with an autofocus mechanism having a feedback circuit for receiving a relative current position signal of the device under test.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a first embodiment of the present invention applied to a projector of a contour measuring device for a component. A measuring stage 2 on which a measuring object W can be fixed on an upper surface of a measuring object 2 of a projecting lens 1 is provided. It is located on one optical axis.

The measuring stage 2 is used to measure an arbitrary position on the surface of the object W to be mounted, and has any strictness in a horizontal plane (XY direction) perpendicular to the plane of FIG. Can be adjusted to the position. The measuring stage 2 can detect the moving distance in the vertical direction (Z direction) by the precise length measuring scale 3, and the moving amount of the length measuring scale 3 in the vertical direction is input to the length measuring counter 4. The amount of movement is displayed on the display 5 by the calculated output of the length counter 4. In addition,
As will be described later, a signal of an edge detection circuit 8 for processing an output signal from an edge detection element 7 to be described later attached to the screen 6 is input to the length measurement counter 4 described above. Is detected, the moving distance in the vertical direction is displayed on the display 5 via the length measuring counter 4.

An illumination light source 9 having an optical axis directed in the horizontal direction is arranged on the side of the projection lens 1, and is arranged on an output optical axis of a condenser lens 10 for condensing illumination light of the illumination light source 9. A reticle 11 having a light transmitting portion 11a (in the illustrated case, a rectangular transmitting portion) is disposed, and the transmitted light of the reticle 11 is incident on the above-described projection lens 1 via the illumination lens 12 and the half mirror 13. The illumination lens 1
2 is provided with a light flux mask 14 having a light transmission window 14a displaced from the optical axis.
The image of the light transmitting portion 11a is projected on the surface of the workpiece W through an optical path indicated by oblique lines in the figure, and projected onto the screen 6 via the half mirror 13 by the operation of the projection lens 1. Become.

At the center of the screen 6 on which an enlarged image of the object W is projected, an edge detecting element 7 whose center coincides with the optical axis is located. The focus state of the light transmitting portion 11a of the reticle 11 projected on the surface is monitored. As the edge detecting element 7 used for this purpose, a known element having a double concentric photosensitive portion is suitable as shown in the upper part of the figure, but other types known as a line sensor and a position sensor are suitable. Can also be used.

Since the focus detecting device of the projector according to the first embodiment has the above-described structure, the vertical position (Z direction) of an arbitrary position on the surface of the object to be measured W by the following focus operation. Can be calculated. That is, the image forming position of the light transmitting portion 11a of the reticle 11 on the screen 6 is determined by the cross line indicating the optical axis in the back focus state, the just focus state, and the front focus state, as shown in the lower right of FIG. To the left and right.

Therefore, if the measuring stage 2 is moved up and down while measuring the moving distance by the length measuring scale 3, the just-focused state is detected by the edge detecting element 7. And height.

Further, the focus detecting device of the projector according to the first embodiment has a reticle 11 and a light flux mask 14 arranged in an illumination optical path from an illumination light source 9 to a half mirror 13.
Since the configuration is such that the image of the reticle 11 on the surface of the screen 6 is detected by the edge detection element 7, the apparatus can be configured without using expensive detection elements and parts, etc. A measurement can be made. Since the measurement in this case uses the image of the reticle 11, the surface of the workpiece W may be either a mirror surface or a diffusion surface.

FIG. 2 shows a focus detecting device of a projector according to a second embodiment of the present invention. The focus detecting device includes a driving mechanism 1 for driving a measuring stage 2 in a vertical direction.
5, a so-called auto-focus mechanism including a drive circuit 16 for controlling the drive mechanism 15 and a feedback circuit 17 to which an output signal of the edge detection circuit 8 is input. That is, in the focus detection device of FIG. 2, the same parts as those of FIG. 1 are denoted by the same reference numerals, and the output signal of the length measuring scale 3 is input to the feedback circuit 17 via the counter 4. .

Therefore, in such a focus detection device for a projector, the vertical position of the measurement stage 2 changes in response to the detection signal of the edge detection element 7, and the just-focused state is detected by the edge detection element 7. Then, the current height in the vertical direction is displayed on the display 5.

The focus detecting device of the projector according to the present invention comprises:
Although it can be applied as a dimension measuring device, a position determining device, and a shape determining device for detecting an edge of an object to be measured, in the case of such a device, measurement is performed at the focus position displayed by the length measuring counter 4 described above. After the stage 2 is moved, the illumination format may be switched to, for example, transmissive illumination. In this case, it is necessary to use a non-directional edge detection element 7 for detecting an optical image.

[0019]

As is apparent from the above description, according to the present invention, it is possible to obtain a focus detection method and apparatus using relatively inexpensive parts and having little difference in measurement results due to individual differences between operators. The focus detection device of the invention includes:
It can be incorporated into a measuring microscope or shape measuring instrument, and can be easily put into practical use as an autofocus mechanism.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a focus detection device of a projector according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram of a focus detection device of a projector according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Projection lens 2 Measurement stage 3 Measurement scale 4 Measurement counter 5 Display 6 Screen 7 Edge detection element 8 Edge detection circuit 9 Illumination light source 10 Condenser lens 11 Reticle 12 Illumination lens 13 Half mirror 14 Light flux mask 15 Driving mechanism 16 Drive circuit 17 Feedback circuit

Claims (4)

[Claims] 1. An image of an object to be measured is formed on a surface of a screen by a projection lens facing the object to be measured, and the object to be measured is reflected by a half mirror positioned in a projection optical path of the projection lens. In a projector that illuminates the surface of the
An image of a reticle located on an illumination optical path from an illumination light source to the half mirror is projected onto the surface of the object to be measured with a light beam displaced from the optical axis of the half mirror, and the image of the reticle is focused on the optical axis by a focus operation. A focus shift method for a projector, wherein the shift state of the image is converted into a laterally shifted image, and a moving state of the image is detected by an edge detecting element positioned on the screen. 2. An image of an object to be measured is formed on a surface of a screen by a projection lens facing the object to be measured, and the object to be measured is reflected by a half mirror positioned in a projection optical path of the projection lens. In a projector that illuminates the surface of the
A reticle positioned in the illumination light path from the illumination light source to the half mirror, a light flux mask displaced with respect to the optical axis in the illumination light path, and the measurement target with the displaced light flux passing through the light flux mask; An edge detection element for detecting an image of a reticle on the surface of the screen projected on the surface of the object, and strictly adjusting the relative distance between the projection lens and the object under monitoring by the edge detection element A focus detection device for a projector. 3. The focus detecting device for a projector according to claim 2, wherein said projector is a measuring microscope or a part shape measuring device. 4. The apparatus according to claim 1, wherein the position adjusting means includes a driving circuit for operating the driving means, and an autofocus mechanism having a feedback circuit for inputting a relative current position signal between the projection lens and the device under test. 4. The focus detecting device for a projector according to claim 2, wherein