JPH11166881A - Eccentricity measuring method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eccentricity measuring device and method suited for measuring the eccentricity of an optical system of rotation symmetry, such as a lens surface or a reflecting surface, and an aspherical surface, etc. SOLUTION: A measuring surface consisting of a surface of rotation symmetry is mounted on a rotating shaft so that their respective axes of rotation symmetry are coincident. Two coherent light beams 2a, 2b are made to pass through different areas of a variable-focal-distance condensing lens 5 whose optical axis 12 coincides with that of the rotating shaft, to collect the two light beams 2a, 2b at the apparent center of curvature of the measuring surface and to make the beams cross each other. The two light beams 2a, 2b diverging from the center of curvature are made to impinge on different areas of the measuring surface, and the two light beams 2a, 2b reflected by the measuring surface are made to overlap each other to form interference fringes. Then the fluctuation of interference fringe information which is caused when the measuring surface is rotated about the rotating shaft 12 is detected by a light detection means 9, so that when the eccentricity of the measuring surface with respect to the rotating shaft 12 is calculated, the condensing lens 5 changes at least either one of its focal distance or focal position depending on the magnitude of the radius of curvature of the measuring surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eccentricity measuring apparatus and an eccentricity measuring method, and more particularly to an axis (for example, an optical system) which is a reference of a center of curvature of a rotationally symmetric optical member such as a lens surface, a reflecting surface, and an aspheric surface. It is suitable for measuring the distance from the optical axis, that is, the eccentricity. In particular, it is suitable for measurement with a plurality of optical members held in a lens barrel.

[0002]

2. Description of the Related Art Various eccentricity measuring devices for measuring the eccentricity of a lens optical member or the like have been proposed. Figure 2 shows the Japanese Patent Publication No. 51-4
It is a principal part schematic diagram of the eccentricity measuring device disclosed by No. 2495. In the figure, the eccentricity of the lens surface is measured using two-beam interference.

In FIG. 1, a coherent light beam 2 from a light source 1 is converted into a coherent two light beam 2 by a splitting surface 3 a of a light beam splitting element 3.
a and 2b, and the light is guided to the condenser lens 5. Then, the two light beams 2a and 2b are made to converge and intersect in the vicinity of the center of curvature 13 of the surface 8 to be measured before being incident on the surface 8 to be measured. Thereafter, the light reflected by the surface 8 to be measured is returned to the original optical path, and is superimposed on the surface of the light detecting means 9 via the dividing surface 3a to generate interference fringes. Then, the phase difference between the two light beams reflected by the measurement surface 8 is measured from the fluctuation of the interference fringe generated when the device 8 is rotated about the reference axis 12, and the eccentricity of the surface 8 is detected from the result. ing.

[0004]

However, in the conventional eccentricity measuring apparatus, it is necessary to use condensing lenses having focal lengths corresponding to each other due to the difference in the radius of curvature of the measurement surface. It was necessary to prepare various kinds. For this reason, the load of lens replacement was large, and the working efficiency was poor. In addition, with one type of condenser lens, the measurement diameter of the surface to be measured is fixed, and the measurement accuracy may not be sufficient.

Further, in the measurement of eccentricity of an aspherical surface as a measurement surface, it is necessary to measure at least two different diameters, and the measurement range is limited with one condenser lens. was difficult.

The present invention has been made to solve the above-mentioned problem, and can reduce the number of types of condenser lenses even if the lens surface or the reflection surface has various radii of curvature. An object of the present invention is to provide an eccentricity measuring device and an eccentricity measuring method in which the entire device can be simplified and high-precision measurement with high working efficiency can be performed.

[0007]

An eccentricity measuring method according to the present invention comprises the steps of: (1-1) mounting a measurement surface composed of a rotationally symmetric surface on a rotational axis such that the rotationally symmetric axis coincides with the rotational surface; The luminous flux passes through different regions of a variable focal length condensing lens whose optical axis is coincident with the rotation axis, is condensed at the apparent center of curvature of the measurement surface, intersects, and diverges from the center of curvature. When the two light beams thus obtained are incident on different areas of the measurement surface, the two light beams reflected on the measurement surface are superimposed to form an interference fringe, and the measurement surface is rotated about the rotation axis. When the amount of eccentricity of the measurement surface with respect to the rotation axis is obtained by detecting the fluctuation of the interference fringe information caused by the light detection means, the condenser lens focuses on the basis of the radius of curvature of the measurement surface. That at least one of the distance and the focal position has been changed. Features.

In particular, (1-1-1) the condensing lens changes the condensing position of the two light beams.

(1-1-2) The focal length of the condenser lens is changed by changing a predetermined lens interval among a plurality of lenses constituting the condenser lens.

(1-1-3) The condenser lens is a zoom lens. And so on.

The eccentricity measuring apparatus of the present invention is characterized in that (2-1) the eccentricity measuring method of the constitution (1-1) is used.

[0012]

FIG. 1 is a schematic view of a main part of an eccentricity measuring device according to the present invention. In the figure, reference numeral 1 denotes a laser light source which emits a coherent light beam 2. Reference numeral 3 denotes a light beam which is divided into two light beams 2a, 2a
b, and is an optical path dividing means for superposing the two light beams reflected from the measurement surface (measured surface). Reference numeral 5 denotes a condensing lens (zoom lens) having a variable focal length, and converges and intersects the two light beams 2a and 2b from the light beam splitting element 3 with the curvature center position 13 of the surface 8 'to be measured.

When the focal length of the condenser lens 5 is changed, the entire condenser lens is moved in the direction of the optical axis 11.
Reference numeral 9 denotes light detecting means (light receiving means), which detects interference fringes formed by the two light beams 2a and 2b reflected by the measurement surface 8 and returned.

Reference numeral 7 denotes a turntable for rotating the object 8 to be measured. Reference numeral 12 denotes a rotation axis of the turntable 7, which corresponds to the optical axis (reference axis) of the optical system. Reference numeral 14 denotes a rotation direction detecting unit for the turntable 7. Reference numeral 8 denotes an object to be measured. Reference numeral 8 'denotes a surface to be measured in the object 8 under measurement, and reference numeral 13 denotes a center of curvature (apparent center of curvature) of the surface 8' to be measured.

In FIG. 1, since the measurement surface 8 'is the first surface, the positions of the apparent center of curvature 13 and the center of curvature coincide with each other. Although one measured object 8 is shown in FIG. 1, many measured objects are usually arranged before and after the measured object 8 with the optical axes 11 aligned. Therefore, the center of curvature of the measurement surface 8 ′ is optically displaced when viewed from the condenser lens 5 side, and is located at the apparent center of curvature. An arithmetic unit 10 calculates the amount of eccentricity from the rotation axis 12 of the surface 8 'to be measured based on signals from the light detection means 9 and the rotation direction detection means 14.

Next, the operation of this embodiment will be described. A light beam 2 from a laser 1 as a light source is split by a light beam splitting element 3 (light splitting surface 3a) into light beams 2a and 2b parallel to the optical axis 11 of the condensing lens 5, and enters the condensing lens 5. The two luminous fluxes 2a and 2b incident on the condenser lens 5 are located at the center of curvature (apparent center of curvature) 1 on the surface 8 'of the object 8 to be measured.
The focal length of the condenser lens 5 and the entire condenser lens 5 are adjusted by moving the entire condenser lens 5 in the direction of the optical axis so as to approximately cross the condenser lens 3.

Since the position where the two light beams 2a and 2b converge and intersect roughly coincides with the center of curvature 13 of the surface 8 'to be measured, the two light beams reflected in the area of the surface 8' to be measured The light returns to the light beam splitting element 3 via the condensing lens 5 while traveling backward along the same optical path as the path, and is superimposed on the surface of the light detecting means 9 to generate interference fringes. The interference fringes of the two light beams include a phase difference. The phase difference is detected by the light detecting means 9, and an output signal is sent to the calculating means 10.

Observing the output signal from the light detecting means 9,
Condensing lens 5 so that the contrast of interference fringes is maximized.
Has been fine-tuned. The position where the two luminous fluxes 2a and 2b converge and intersect almost completely coincides with the center of curvature of the measured surface 8 '. In this state, the turntable 7 is rotated, and the signal from the light detecting means 9 and the signal from the rotational azimuth detecting means 14 are processed by the calculating means 10 so that the eccentricity of the surface 8 'to be measured (here, the reference axis ( The magnitude and direction of the eccentricity amount from the optical axis 11 are obtained.

FIG. 3 shows a paraxial refractive power arrangement of a condenser lens having a variable focal length. In this example, the focal lengths are f ₁ and f ₂
Has two lenses L ₁ and L ₂ ,
Lens L ₂ of the focal length f ₂ is movable in the optical axis 11 direction. Assuming that the distance between the _two lenses L ₁ and L ₂ is Da, the distance f _t from the lens L ₁ having the focal length f _{1 to} the intersection of the two light beams and the focal length f of the entire system are paraxial theory. _Ft = {− Da ² + f ₁ Da + f ₁ f ₂ } / (f ₁ + f
₂₋ Da) f = f ₁ f ₂ / (f ₁ + f ₂ −Da)

That is, the distance Da between the two lenses L ₁ and L ₂
, The focal position f _{t of the two} light beams and the focal length f of the entire system can be made continuously variable. This means that one kind of condenser lens can measure various kinds of objects having different curvatures.

In FIG. 3, the condenser lens 5 has a configuration of _two lenses L ₁ and L _{2 having} a positive refractive power. However, a configuration of positive and negative lenses, and a configuration of negative and positive lenses are also possible. Any number of lenses can be used as long as the number of lenses is two or more.

As shown in FIGS. 4A and 4B, the focal length f of the condenser lens 5 is changed, and
By moving the whole in the direction of the optical axis 11, an arbitrary measurement diameter of the measured surface 8 'can be measured.

[0023] Figure 4 when measuring the convex surface as in (A) is and to reduce the focal length f _t of the condenser lens 5, to reduce the distance between the condenser lens 5 and the measured surface 8 ' The measurement diameter is increased, and conversely, as shown in FIG. 4 '(B), the focal length _ft is increased and the distance between the condenser lens 5 and the surface to be measured 8' is increased. since it is also possible to reduce the diameter, while changing the focal position f _t the condenser lens 5, the distance between the condenser lens 5 to be measured surface 8 'also by changing, it can be measured in any size.

Incidentally, the condenser lens 5 in the present embodiment has two lenses.
A back focus lens having two focal lengths may be used. Further, the focal point (13) may be changed while changing the focal length of the condenser lens 5. Further, in the present embodiment, the position of the condenser lens 5 may be changed so that only the focal position changes without changing the focal length of the condenser lens 5.

[0025]

As described above, according to the present invention, the number of condenser lenses can be reduced even when the radius of curvature of the measurement surface changes variously by forming the condenser lens from a lens system having a variable focal length. An eccentricity measuring device and an eccentricity measuring method capable of performing measurement, reducing the load of lens replacement, simplifying the entire device, and performing highly accurate measurement with high work efficiency can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an eccentricity measuring device of the present invention.

FIG. 2 is a schematic diagram of a conventional eccentricity measuring device.

FIG. 3 is an explanatory diagram showing a configuration of a condenser lens according to the present invention.

FIG. 4 is an explanatory diagram for explaining variable eccentricity measurement diameter in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser 2 Light beam 2a, 2b Light beam 3 Light beam splitting element 5 Focal length condensing lens 6 Turntable 7 Rotation azimuth detecting means 8 Optical system to be measured 8 'Measurement surface 9 Light detecting means 10 Arithmetic unit 11 Optical axis of condensing lens 12 Rotary table rotation axis 13 Apparent center of curvature of measured surface

Claims (5)

[Claims] 1. A variable focal length variable measuring apparatus comprising: a measuring surface comprising a rotationally symmetric surface mounted on a rotational axis such that the rotational symmetric axis coincides therewith; and two coherent light beams having an optical axis coincident with the rotational axis. Passing through different areas of the condenser lens to converge and intersect at the apparent center of curvature of the measurement surface, causing two light beams diverging from the center of curvature to enter different areas of the measurement surface, An interference fringe is formed by superimposing two light beams reflected by the measurement surface, and a change in the interference fringe information generated when the measurement surface is rotated about the rotation axis is detected by a light detection unit. When obtaining the amount of eccentricity of the measurement surface with respect to the rotation axis, the condensing lens changes at least one of a focal length and a focal position based on a radius of curvature of the measurement surface. Eccentricity measurement method. 2. The eccentricity measuring method according to claim 1, wherein said condensing lens changes a condensing position of said two light beams. 3. The eccentricity measuring method according to claim 1, wherein the condensing lens changes a focal length by changing a predetermined lens interval among a plurality of lenses constituting the condensing lens. 4. The eccentricity measuring method according to claim 1, wherein said condenser lens is a zoom lens. 5. An eccentricity measuring apparatus using the eccentricity measuring method according to claim 1. Description: