JPS6347607A - Apparatus for measuring curved surface of optical parts - Google Patents

Abstract

PURPOSE:To inspect and measure the radius of curvature and surface power of a surface to be inspected from a specific calculation formula with high accuracy, by bringing surface to be inspected into contact with a fixed opening to read the change of the distance between a secondary beam source and an objective lens. CONSTITUTION:Laser beam is allowed to be incident on a curved surface 105 to be inspected present at the focal position F' of an objective lens 103 and is in contact with a fixed opening 104 and the reflected beam from said curved surface is formed into an image on a screen 106. When a frame 109 containing a condenser lens 102 is moves so that the condensing point of the condenser lens 102 is conjugated with the center O of curvature of the curved surface 105 and the lens 103, the automatic collimation image of the surface 105 is formed on the screen 106. When the distance between the condensing point and the focus F of the lens 103 is set to (x), formula I holds and the radius of curvature of the surface 105 can be calculated from the moving distance of the lens 102. When the refractive index of the surface 105 is set to (n) and both members of the formula I are multiplied by (n-1), formula II holds and the left member thereof imparts the power of a refractive surface. Therefore, all of the radii of curvature and surface powers can be measured easily.

Description

Detailed Description of the Invention: a. Technical Field The present invention relates to an apparatus for measuring and inspecting the refractive surface power, radius of curvature, and surface accuracy of a curved surface (test surface) having a smooth optical reflection surface such as an optical component. It is.

b. Prior Art and its Problems Various apparatuses for measuring and inspecting the radius of curvature and surface accuracy of optical reflective surfaces have been proposed and put into practice. Figure 2 is a diagram of the principle of measurement that is most commonly used among these measuring devices, and is a diagram of the principle of measurement that is most commonly used among these measuring devices.
Page 39 and ISO/TC172/SC7/WG
4 N22 (dated July 1, 1985).

FIG. 2(a) is a diagram illustrating an apparatus for measuring the radius of curvature of a concave surface. The light source (or secondary light source) 201 and the screen 206 are in a mutually conjugate positional relationship with respect to the half mirror 202, so that the image of the light source (or secondary light source) 201 is formed on the screen 206 by reflection from the concave surface. , the concave surface is the light source (or secondary light source) 2o1 is the objective lens 20
By measuring the distance between these positions 204 and 205, which must be either the position 204 imaged by 3 or the position 205 of autocollimation, the radius of curvature of the concave surface is known.

Furthermore, by performing RW4 on the deformation state of the reflected light 'g image on the screen 206 while the concave surface is placed at the autocollimation position 205, the local surface accuracy of the concave surface can be determined. Similarly, the radius of curvature of the convex surface can be measured, and FIG. 2(b) shows the pattern. The difference from the concave case is that the positions 204 and 20
The point is that the relative positional relationship with No. 5 has been swapped. Other than that difference, the measurement and inspection of the radius of curvature and degree of area are exactly the same as for concave surfaces.

Now, the measuring device shown in FIG. 2 has a serious problem. The point is that not all radii of curvature can be measured.For example, in the case of a concave surface, if the radius of curvature is 5.00 km, the distance between positions 204 and 205 is 5,000 mm, making the measuring device extremely large. On the other hand, in the case of convex surfaces.

Only between the objective lens 203 and the position 204 is the position 205
cannot exist, so the radius of curvature of the convex surface is also limited.

C1 Purpose Therefore, it is an object of the present invention to provide a compact curved surface measuring device for optical components, etc., which can measure all radii of curvature and simultaneously inspect and measure surface accuracy and refractive surface power.

d. Configuration of Embodiment FIG. 1 is an explanatory diagram showing an embodiment of the present invention. A laser beam with an appropriate wavelength is used as a light source, and the beam passes through a half mirror 101 and a condenser lens 10.
After being narrowed down by 2.

Diverge. Then, an objective lens 103 placed at the rear
After passing through the fixed aperture 104, the light is reflected by the curved surface 105 of an optical component or the like to be detected, travels backward, is bent at 90° by the half mirror 101, and reaches the screen 106. In order to eliminate reflected light from the measurement optics, the laser beam may be linearly polarized, in which case λ/4
Insert plate 1 and C7 between objective lens 103 and fixed aperture 104.

A polarizing plate 1 is placed between the half mirror 101 and the screen 106.
08, and adjust each polarization direction to find the place where the stray light is least. Also, if a polarizing beam splitter is used for the half mirror 101, the loss of light amount can be reduced. ．． Condenser lens 1o2. Frame 1 including polarizing plate 108 and screen 106
09 can be moved along the optical axis (in the direction of the arrow) by a moving means (not shown), and the interval (distance) between the condenser lens 102 and the objective lens 103 can be changed, and the change in the interval can be read. A reading means (not shown) is provided for this purpose.

The test surface 105 is configured to be set on the image-side focal point F' of the objective lens 103 when it abuts against the fixed aperture 104.

e. Assume that the working frame 109 of the embodiment is moved so that the focal point of the beam by the condenser lens 102 is set at a position that is conjugate with respect to the center of curvature ◯ of the test surface 105 and the objective lens 103. At this time, an autocollimation image from the surface to be inspected 105 is formed on the screen 106.

Here, from the object side focal point F of the objective lens 103.

Assuming that the distance to the convergence point of the beam by the condenser lens 102 is straddle, the focal length of the objective lens 103 is f, and the radius of curvature of the surface to be measured 105 is r, Newton's formula can be applied from Fig. 1. , x-r=-f''. Therefore, r f'', and it can be seen that the reciprocal 1/r of the radius of curvature of the surface to be inspected 105 is proportional to X. If the coordinate origin of frame 109 is
If O1 is defined as when the convergence point of the beam by the condenser lens 102 coincides with the object side focus F of the objective lens 103, then read the amount of movement of the frame 109 from the coordinate origin and substitute it for X in equation (1). Then, the radius of curvature r can be easily found.

Now, let n be the refractive index of the surface to be inspected 105.

Multiplying n-1 by both sides of equation (1), we get The left side is the equation that gives the power of the refractive surface.

Therefore, the device of the present invention can be directly said to be a device for measuring the power of a refractive surface.

Note that if the amount of movement of the frame 109 is read with a positive or negative sign depending on the direction of movement, it will correspond to the unevenness of the test surface 105.
It is possible to calculate the radius of curvature r with a sign.

Furthermore, if X is fixed at an appropriate value, all optical elements except the surface to be inspected 105 can be moved integrally in the same direction as the moving direction of the frame 109, and the amount of movement can be measured. It is equivalent to a conventional curvature radius measurement device. It should be noted that since the laser beam is incident on the present device as a parallel beam, it is obvious that when moving together, there is no need to move to the laser light source (not shown in the figure) at the same time.

From the above, the range of the radius of curvature r measured from the fifth part of the present invention is set as lrl≧lr, 1, and rIIl is the radius of curvature having the minimum absolute value determined by the limit of the movement amount X of the frame 109.

On the other hand, the measurement range of the radius of curvature r by the conventional method is Irl≦
lf'ml and rM is the radius of curvature with the maximum absolute value determined by the limit of the amount of movement that can be made as a unit, then if 1r, 1
If ≦Irm1 is satisfied, the objective of providing a compact device capable of measuring all radii of curvature is achieved.

In fact, it is easily possible to satisfy the condition lr, 1≦lrml. Furthermore, since the apparatus according to the present invention constantly searches for the autocollimation position, it is the same as always detecting the surface accuracy of the surface to be inspected 105 by WA. In other words, it can be said that all the objects of the present invention have been achieved.

Note that since the laser beam is a parallel beam up to the condenser lens 102, the half mirror 101
It is clear that, as long as a sufficient distance is secured between the frame 109 and the condenser lens 102, the measurement can be achieved by simply moving the condenser lens 102 alone, rather than by moving the frame 109.

f. Effect As mentioned above, the position where the secondary light source generated by the condenser lens is reimaged by the objective lens,
In contrast to conventional devices that calculate the radius of curvature of the surface to be measured from the distance between the surface and the autocollimation position,
A fixed aperture is installed on the image side focal point of the objective lens, and the distance between the secondary light source and the objective lens can be changed. By reading that distance, the curvature of the surface to be measured that is applied to the fixed aperture can be determined. By adding the function to calculate the radius and refractive surface power from equations (1) and (2),
It has become possible to measure all radii of curvature. Furthermore, it has become possible to observe local surface accuracy over all radii of curvature with one device.

Furthermore, it has been found that the device according to the present invention is compact and can be easily handled on a desktop.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing one embodiment of the present invention, Figure 2 (a
) is a diagram of the principle of measurement when a concave surface is the surface to be tested using a conventional device for measuring the radius of curvature, and FIG. 2(b) is a diagram of the principle of measurement when the surface to be tested is a convex surface. Procedure Amendment Book May 29, 1986

Claims (1)

[Claims] 1. The radius of curvature of the test surface is determined from the distance between the position where the secondary light source generated by the condenser lens is reimaged by the objective lens and the autocollimation position of the test surface. The device includes a fixed aperture installed above the image-side focal point of the objective lens so that the distance between the secondary light source and the objective lens can be changed, and means for reading the distance, and a fixed aperture covered by the fixed aperture. Apply the test surface to the surface, change the distance between the secondary light source and the objective lens, read the distance where the autocollimation position is determined, and obtain (n-1)/r=-[
(n-1)/f^2]x or 1/r=-(x/f^2)
A curved surface measuring device for optical components, etc., characterized in that the refractive surface power and the radius of curvature of a surface to be inspected are determined from the following equation. here,
f is the focal length of the objective lens, r is the radius of curvature of the test surface, n
is the refractive index of the surface to be inspected, and x is the distance from the object side focal point of the objective lens to the focal point of the beam by the condenser lens. 2. In claim 1, a linearly polarized laser is used as a light source, a λ/4 plate is placed between the objective lens and the fixed aperture, and a polarizing plate is placed close to the screen to eliminate stray light. An apparatus for measuring curved surfaces of optical components, etc., characterized in that the direction of polarization is adjusted to remove.