JPS5840723B2 - Jidoushyoutenkikou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focusing mechanism that makes use of the spherical aberration of a lens to measure minute irregularities on an object to be measured.

Conventional autofocus mechanisms are configured to drive the lens system to focus on the object to be measured, so the lens system is heavy, making it difficult to drive at high speed, and the responsiveness of the autofocus function is poor. However, the present invention aims to reduce the weight of the optical system to be driven and improve the responsiveness of the automatic focusing function.

In the present invention, the lens that focuses on the object is fixed, and the radial position of the lens of the incident light is adjusted by rotating the reflecting mirror that adjusts the position of the light incident on the lens. It is designed to automatically focus on the object.

The rotating mirror for adjusting the light incident on the lens is constantly vibrating at a small angle with a constant high frequency (sine wave).

When the reflected light from the object is focused on the object, it is in the most condensed state, and when it is not focused, the reflected light is more spread out than in the former case.

Therefore, by examining the sinusoidal reflected light intensity, the amount of deviation from the focus can be determined, and by feeding back the deviation signal to the rotating mirror drive unit, the focus can be automatically set on the object. .

In this manner, minute irregularities on the object to be measured can be measured depending on the position of the rotating reflecting mirror focused on the object.

FIG. 1 is for explaining the spherical aberration of the convex lens 1.

That is, the light ray 2 passing through the center of the lens 1 is focused far away, and as the incident light moves away from the center toward the outer periphery, the focus becomes closer.

The present invention utilizes the spherical aberration of this lens to automatically focus.

Hereinafter, one embodiment of the present invention will be explained with reference to FIGS. 2 to 4.

FIG. 2 is an explanatory diagram showing the configuration of the automatic focusing mechanism of the present invention.

Light projected from a point light source 10 such as a laser oscillator is reflected by a rotating mirror 3.

By controlling the rotating mirror 3 and moving the position of the incident light on the lens 1 in the diametrical direction of the lens, the focal position can be changed using the aberration of the lens.

The reflected light from the measurement object 9 passes through the same lens 1.)
- It is reflected by the mirror 4, passes through the slit plate 5, and reaches the light receiving element 6.

In the center of the slit plate 5, there is a slit 5a as shown in FIG. A slit is provided so that the light travels along the line.

When the focus is on the object 9, if the reflection point is placed exactly within the width of the sulin 5a (state 12 in Figure 3), the focus will be on the object. When there is no slit, the reflected light spreads on the width plate of the slit 5a, as shown by 11 in FIG.

Therefore, the output of the light receiving element 6 is maximum when the focus is on the object 9, and decreases as the focal point moves away from the object surface.

The output of the light receiving element 6 is input to the signal processing circuit 7, and the signal processing circuit 7
By inputting the output to the mirror drive unit 8 and controlling the mirror displacement, it is possible to automatically focus on the object 9.

An example of the signal processing circuit 7 is shown in FIG.

The oscillator 13 provides a frequency and amplitude for causing the rotating mirror 3 to vibrate by a minute angle.

The output (sinusoidal waveform) of the light receiving element 6 is amplified by the amplifier 14,
By performing multiplication by the oscillator output in a multiplier 15 and passing the result through a low-pass filter 16, a signal proportional to the amount of deviation from the focal position can be obtained.

This signal is added to the oscillator output by an adder 11, and then the gain is adjusted by a gain adjuster 18, and the signal is input to the mirror and drive unit 8.

As a result, the object 9 is automatically brought into focus.

As explained above, the automatic focusing mechanism of the present invention uses only the rotation of the reflecting mirror as a means to move the focal point of the optical system, so it has small inertia and can respond faster than conventional ones. Can be done.

Furthermore, since the device has a simple structure, it is excellent in both durability and practicality.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of lens aberrations, Fig. 2 is an explanatory diagram showing the automatic focusing mechanism of the present invention, Fig. 3 is an explanatory diagram of the slit plate in Fig. 2, and Fig. 4 is an explanatory diagram of the signal processing in Fig. 2. FIG. 2 is a block diagram showing an example of a circuit. 3...Rotating mirror, 4...-Fumirror, 5...Slit plate, 6...Photodetector,
I...Signal processing circuit, 8...Sharp moving part, 9...Measurement object, 10...Light source.

Claims (1)

[Claims] 1. An objective lens, a rotating reflector that adjusts the radial position of the incident light on the objective lens, and a rotating reflector that adjusts the radial position of the incident light to the objective lens, and a rotating reflector that adjusts the radial position of the light incident on the objective lens. and a means for automatically controlling the rotation angle of the rotating reflector so that the detection output of the light receiving element is maximized. An automatic focusing mechanism characterized in that it is configured to control and focus on an object to be measured.