JPS6138506A - Focusing point deciding method of interference measuring machine - Google Patents

Abstract

PURPOSE:To decide on a focusing point (FP) automatically, clearly, and speedily by moving a mask on an optical axis when the quantity of light on an area sensor is maximum and making the decision from the rate of variation in the quantity of light. CONSTITUTION:The output signal of the area sensor is inputted to a light quantity detecting circuit 11 and then inputted to a lens driving circuit 12. The circuit 12 put a lens moving device 13 in operation to move a lens 4 to be measured in the optical axis direction. When the circuit 11 detects the maximum quantity of light in this feedback loop (FBR), a mask moving circuit 14 operates and the mask 15 moves between a converter lens 3 and the lens 4 to the center of the optical axis. When the mask 15 is FB during the measurement through this FBR, incident reflected light is cut off by a half by the mask 15 and the quantity of light of the sensor 10 is reduced to about half. Further, the quantity of light is reduced almost to zero at a cat-eye point. Thus, the maximum point of the quantity of light of the sensor 10 is detected while the lens 4 is moved and the mask 15 is moved to the center of the optical axis to calculate the FB from variation in the quantity of light, so automatic and manual decision making operations are performed clearly and speedily.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a method for determining a focusing point in an interferometer that measures, for example, a spherical surface, an aspherical surface, a shape, etc. The present invention relates to a method that enables the determination.

(Prior Art) In an interferometer that measures a spherical or aspherical surface of an object to be measured, a focusing point is detected in order to form an image of the object on an area sensor. here,
The imaging conditions on the area sensor are established at two locations: the focusing point and the cat's eye point. What we really want to find is the focusing point, and the cat's eye point images the wavefront of another optical system, resulting in incorrect measurements. Therefore, a method of separating the focusing point and the cat's eye point has been proposed. FIG. 5 shows an example.

In FIG. 5, a laser light source 1 and a collimator lens 2 are shown.
, a converter lens 3, and a lens 4 as an object to be measured.
are arranged in this order, and two beam splitters 5 and 6 are arranged between the collimator lens 2 and the converter lens 3 to respectively reflect the reflected light from the lens to be measured 4 to the sides. The reflected light from the beam splitter 5 is guided to the first area sensor 8 through the lens 7, and an image of the lens 4 to be measured is formed on the area sensor 8. The light is focused onto a second area sensor 10 by a lens 9. The constant a lens 4 can be moved in the optical axis direction.

In the above conventional example, the laser light emitted from the laser light source 1 becomes parallel light spread by the collimator lens 2, and passes through the converter lens 3 through the beam splitter 5.6.
incident on . The light converted into a spherical wave by the converter lens 3 is focused on one point. A lens to be measured 4 is arranged near this condensing position, and the reflected light from the lens to be measured 4 passes through the converter lens 3, is reflected by two beam splitters 5 and 6, and is sent to the area sensor 10. The light is focused upward and an image of the lens 4 to be measured is formed on the area sensor 8. Here, while visually checking the focal spot diameter of the area sensor 10, move the lens 4 to be measured in the optical axis direction to achieve a focal spot as shown by the solid line in FIG. 1 or as shown in FIG. When the light position is adjusted to match the top of the convex front surface of the lens 4 to be measured, the entire luminous flux incident on the top of the lens 4 to be measured is reflected, and as shown by C in FIG. 6, the area sensor The spot diameter on 10 becomes the minimum and the light amount becomes the maximum. This is the cat's eye point, and at this time, the wavefront of the optical system in front of the lens to be measured 4 forms an image on the area sensor 8. By further moving the lens 4 to be measured, as shown by the dashed line 4A in FIG. 5, and as shown in FIG. When the light is focused on a predetermined point, for example, the spherical center of the convex surface of the lens 4, the reflected light from the lens 4 to be measured passes through the converter lens 3, is reflected by the beam 4 splinter 6, and is focused on the area sensor 10. , again the spot diameter is the smallest and the light amount is the largest. This is the focusing point, and at this time the wavefront of the lens 40 to be measured forms an image on the area sensor 8. At positions other than the focusing point, as shown by a and b in FIG. 6, the spot diameter is large and the amount of light is small. What we are trying to find is only the focusing point, but if we only detect the point where the spot on the area sensor 10 is the smallest, we may end up detecting the cat's eye point instead of the focusing point. This results in measuring the wavefront of an optical system other than the object to be measured. Therefore, conventionally, when the spot diameter on the area sensor 10 is the smallest, the light flux on the surface of the lens to be measured 4 is observed, and if the light flux is focused on the surface of the lens to be measured 4, the cat's eye point (see Figure 3) is observed. ), and if it spread out, it was determined by visual inspection as the focusing point (see Figure 2). However, according to the conventional method described above, the discrimination has to be done visually; automatic discrimination is impossible, and it is difficult to clearly and quickly distinguish between the cat's eye point and the focusing point. there were.

(Objective) The object of the present invention is to identify a focusing point in an interferometer, which makes it possible to automatically determine a focusing point and to clearly and quickly distinguish between a focusing point and a cat's eye point. The purpose is to provide a method.

(Structure) The method for determining the focusing point in the interferometer of the present invention is to re-guide the reflected light from the object to be measured to the rear sensor by a beam splitter placed between the collimator lens and the converter lens, and focus the light on the area sensor. When the light intensity of the light spot reaches its maximum, the mask placed between the converter lens and the object to be measured is moved toward the center of the optical axis, and the reflected light from the object to be measured is focused on the area sensor. Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

The embodiment shown in FIG. 1 has common components with the conventional example shown in FIG. I decided to do it. In FIG. 1, the output signal of the area sensor 10 is input to the light amount detection circuit 11, the output of the light amount detection circuit 11 is input to the lens drive circuit 12, and the lens movement device 13 is driven by the lens drive circuit 12 to be measured. The lens 4 can be moved in the optical axis direction. In this way, the area sensor 10, the light amount detection circuit 11, the lens drive circuit 12, and the lens moving device 13 form a feedback loop, and the lens driving circuit 12 moves the lens moving device 13 so that the amount of light on the area sensor 10 is maximized. is driven to move the lens 4 to be measured in the optical axis direction. A signal is input from the light amount detection circuit 11 to the mask moving circuit 14. When the light amount detection circuit 11 detects the maximum light amount, the mask moving circuit 14 is activated and the mask 15 is moved between the converter lens 3 and the lens to be measured. 4 to the center of the optical axis.

Now, the point where the amount of light on the area sensor 10 is maximized is determined while moving the constant lens 4 using the feedback loop. Then, when the amount of light on the area sensor 10 reaches the maximum, the mask moving circuit 14 is driven to move the mask 15 to the center of the optical axis as shown in FIGS. 2 and 3. At this time, if it is the focusing point, the light that enters the lens to be measured 4 from the converter lens 3 is at a predetermined point in the lens to be measured 4, for example, the spherical center of the convex surface of the lens 4, as shown in FIG. Since it is reflected and returns along the same optical path as the incident optical path, the upper half of the incident reflected light in FIG. 2 is blocked by the mask 15, and therefore the amount of light on the area sensor 10 is as shown in FIG. Light i without inserting the mask as shown in b
It is about half of 1a.

In addition, if it is a cat's eye point, the light incident on the lens 4 to be measured will be reflected at the apex of the lens 4 as shown in Figure 3, so the light incident from above will be reflected downward and downward. Light incident from the is reflected upward. Therefore, in the figure, the light that is about to enter from above is blocked by the mask 15, and the light that is incident from below and reflected by the lens 4 is also blocked by the mask 15, so the amount of light on the area 7 sensor 10 is It almost disappears. In this way, while moving the lens 4 to be measured, the point where the amount of light on the area sensor IO becomes maximum is detected, and then when the mask 15 is moved and the amount of light on the area sensor IO is halved, the point is detected. is the focusing point, and it is sufficient to find the wavefront imaged on the other area sensor 8 at that time.

Note that the mask 15 does not necessarily have to be moved to the center of the optical axis, and the area sensor 1
It is also possible to distinguish between the focusing point and the cat's eye point by looking at the rate of decrease in the amount of light above zero. Furthermore, if a feedback loop is formed as in the embodiment shown in FIG. 1, it is possible to automatically determine the focusing point, but it is not necessarily necessary to automatically distinguish El" By manually moving the mask 15 when the light intensity reaches the maximum and observing the change in the light intensity on the area sensor IO at that time, it is possible to determine whether it is a focusing point or a cast eye point. It is possible to determine the distance clearly and quickly compared to the conventional method.The moving distance between the two points, the cat's eye point and the focusing point, can be determined on a linear scale or by the feed amount of the lens moving amount 'fl13. For example, the lens to be measured 4
The radius of curvature can be found.

(Effect) According to the present invention, when the amount of light reflected from the object to be measured on the area sensor reaches the maximum, the mask placed between the converter lens and the object to be measured is moved toward the center of the optical axis. Since the focusing point is determined based on the rate of change in the amount of light on the area sensor at that time, the focusing point can be determined automatically without visual inspection. Even in the case of discrimination, since the discrimination can be made based on the change in the amount of light on the area sensor, the discrimination can be made clearly and quickly.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the optical arrangement and control system showing an embodiment of the present invention, Fig. 2 is a diagram of the main optical system when detecting a focusing point according to the above embodiment, and Fig. 3 is a diagram showing the main parts when detecting a cat's eye point. FIG. 4 is a diagram showing an example of the light amount distribution in the area sensor in the above embodiment,
FIG. 5 is an optical layout diagram showing an example of a method for determining a focusing point in a conventional interferometric measuring device, and FIG. 6 is a diagram showing an example of a light amount distribution in an area sensor of the interferometric measuring device. 1.-Light source, 2-Collimator lens, 3.
-Inverter lens, 4.-Lens as object to be measured, 6-.-Beam splitter, 10.--Area sensor, 15-.-Mask. (Figure 2)

Claims (1)

[Claims] In an interferometric measuring instrument in which a light source, a collimator lens, a converter lens, and a measured object are arranged in this order, the reflected light from the measured object is guided to an area sensor by a beam splitter placed between the collimator lens and the converter lens. When the light intensity of the focused spot on the area sensor reaches its maximum, the mask placed between the converter lens and the object to be measured is moved toward the center of the optical axis, and the light is focused on the area sensor. A method for determining a focusing point in an interferometer, characterized by determining a focusing point and a cat's eye point based on the rate of decrease in reflected light from a body.