Measuring head and eccentricity measuring device including the same

A measuring head includes a light source unit, a first image pickup element, a second image pickup element, an objective optical system, an optical path splitting element, a common optical path, a first optical path, and a second optical path. The common optical path is located on one side of the optical path splitting element, and the first optical path and a second optical path are located on the other side. The optical path splitting element is disposed at a position where the first optical path and the second optical path intersect. The light source unit and the first image pickup element are disposed at predetermined positions. The second image pickup element is disposed at a position different from the predetermined positions. Each of the predetermined positions is a focal position of the objective optical system or a position conjugate to the focal position of the objective optical system.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a measuring head with a wide measurement range in the measurement axis direction and an eccentricity measuring device including the same.

Description of the Related Art

An eccentricity measuring device is a device for measuring the amount of eccentricity in a subject. Eccentricity can be represented by tilt and shift. For example, when the subject is a plane parallel plate, the amount of tilt can be represented by the angle between the normal to a surface of the plane parallel plate and the reference axis. Furthermore, the amount of shift can be represented by the amount of displacement between the center of the plane parallel plate and the reference axis.

The device that measures the amount of tilt is called autocollimator. As an angle measuring device with an autocollimator, a device described in Japanese Patent No. 3089261 is available.

The device described in Japanese Patent No. 3089261 includes two CCD cameras. One of the CCD cameras is disposed at the focal position of a convex lens. The other CCD camera is disposed at a position different from the focal position of the convex lens. Furthermore, a beam splitter is disposed between an object to be measured and the convex lens. In the device described in Japanese Patent No. 3089261, the amount of tilt and the amount of shift can be obtained.

SUMMARY OF THE INVENTION

In one aspect, a measuring head of the present invention comprises a light source unit, a first image pickup element, a second image pickup element, an objective optical system, an optical path splitting element, a common optical path, a first optical path, and a second optical path, wherein

the common optical path is formed from the optical path splitting element toward the objective optical system,

the first optical path is formed from the optical path splitting element toward the first image pickup element,

the second optical path is formed from the optical path splitting element toward the second image pickup element,

the common optical path is located on one side and the first optical path and the second optical path are located on the other side, with the optical path splitting element interposed therebetween,

the optical path splitting element is disposed at a position where the first optical path and the second optical path intersect,

the light source unit is disposed in the first optical path,

the light source unit and the first image pickup element are disposed at predetermined positions,

the second image pickup element is disposed at a position different from the predetermined positions, and

the predetermined positions are each a focal position of the objective optical system or a position conjugate to the focal position of the objective optical system.

Furthermore, in another aspect, an eccentricity measuring device of the present invention comprises a body, a moving mechanism, a measuring head, a holding member, and a processing device, wherein

the measuring head, the holding member, and the moving mechanism are provided in the body,

the measuring head and the holding member are positioned such that the measuring head and a subject held by the holding member are located on a measurement axis,

the moving mechanism moves at least one of the measuring head and the holding member in a direction along the measurement axis,

the processing device is connected to the moving mechanism and the measuring head, and

the measuring head is the measuring head of the former aspect.

DETAILED DESCRIPTION OF THE INVENTION

Prior to the explanation of examples, action and effect of embodiments according to certain aspects of the present invention will be described below. In the explanation of the action and effect of the embodiments concretely, the explanation will be made by citing concrete examples. However, similar to a case of the examples to be described later, aspects exemplified thereof are only some of the aspects included in the present invention, and there exists a large number of variations in these aspects. Consequently, the present invention is not restricted to the aspects that will be exemplified.

A measuring head of the present embodiment includes a light source unit, a first image pickup element, a second image pickup element, an objective optical system, an optical path splitting element, a common optical path, a first optical path, and a second optical path. The common optical path is formed from the optical path splitting element toward the objective optical system. The first optical path is formed from the optical path splitting element toward the first image pickup element. The second optical path is formed from the optical path splitting element toward the second image pickup element. The common optical path is located on one side and the first optical path and the second optical path are located on the other side, with the optical path splitting element interposed therebetween. The optical path splitting element is disposed at a position where the first optical path and the second optical path intersect. The light source unit is disposed in the first optical path. The light source unit and the first image pickup element are disposed at predetermined positions. The second image pickup element is disposed at a position different from the predetermined positions. Each of the predetermined positions is a focal position of the objective optical system or a position conjugate to the focal position of the objective optical system.

FIG. 1AandFIG. 1Bare diagrams showing a measuring head of the present embodiment, in whichFIG. 1Ais a diagram showing the entire configuration andFIG. 1Bis a diagram showing the configuration of an optical system.

A measuring head1includes a housing2. In the housing2, a light source unit3, a first image pickup element4, a second image pickup element5, an objective optical system6, and an optical path splitting element7are disposed. Furthermore, in order to dispose these elements and the like, a common optical path OPC, a first optical path OP1, and a second optical path OP2are formed.

The common optical path OPC is formed from the optical path splitting element7toward the objective optical system6. The first optical path OP1is formed from the optical path splitting element7toward the first image pickup element4. The second optical path OP2is formed from the optical path splitting element7toward the second image pickup element5.

The common optical path OPC is located on one side and the first optical path OP1and the second optical path OP2are located on the other side, with the optical path splitting element7interposed therebetween.

The objective optical system6and the optical path splitting element7are disposed in the common optical path OPC. Furthermore, a subject9is disposed in the common optical path OPC. Here, since the objective optical system6is disposed closer to the subject9side than the optical path splitting element7, the objective optical system6is located closest to the subject9. That is, nothing is present except the subject9in the space from the objective optical system6to the subject9side.

The light source unit3, the first image pickup element4, and a beam splitter8are disposed in the first optical path OP1. The second image pickup element5is disposed in the second optical path OP2. Furthermore, the optical path splitting element7is disposed at the position where the first optical path OP1and the second optical path OP2intersect.

The light source unit3is disposed in the first optical path OP1. The light source unit3is disposed at a predetermined position. The predetermined position is the focal position of the objective optical system6or the position conjugate to the focal position of the objective optical system6. The predetermined position may be displaced approximately by a few hundred micro meters from the focal position of the objective optical system6or the position conjugate to the focal position of the objective optical system6, for example, depending on the amount of aberration produced by the objective optical system6. The accuracy of these positions may vary with the accuracy required for the measuring head1.

For example, a laser, a light-emitting diode, a halogen lamp, or a xenon lamp may be used for the light source unit3. The light source unit3preferably includes a point light source. When a surface light source is used for the light source unit3, an image of the light emitting unit is formed by an optical system and a pin hole is disposed at the image position of the light emitting unit. Also when a point light source is used for the light source unit3, an image of the point light source is formed and a pin hole may be disposed at the image position of the point light source.

InFIG. 1B, a light-emitting diode is used as the light source unit3. The wavelength of light emitted from the light-emitting diode is not limited to particular values. Here, red light is emitted from the light-emitting diode.

The beam splitter8is disposed in the first optical path OP1. An optical path on the light source unit3side and an optical path on the first image pickup element4side are formed by the beam splitter8. A light flux L1emitted from the light source unit3is incident on the beam splitter8.

The beam splitter8is a prism having a half mirror surface. In the half mirror, incident light is split into reflected light and transmitted light. The wavelength band of the reflected light and the wavelength band of the transmitted light are the same. Furthermore, the light intensity of the reflected light and the transmitted light intensity are determined by the reflection characteristics of the half mirror. The beam splitter8may be a plane parallel plate having a half mirror surface.

The light flux L1reflected by the beam splitter8is incident on the optical path splitting element7. The optical path splitting element7has an optical surface that separates the incident light into two. An example of such optical surfaces is a half mirror. Here, a prism having a half mirror surface is used as the optical path splitting element7. The light flux L1reflected by the optical path splitting element7is incident on the objective optical system6disposed in the common optical path OPC.

FIG. 2is a diagram showing a specific example of the objective optical system. As shown inFIG. 2, the objective optical system6is configured with four lenses. More specifically, the objective optical system6includes a negative meniscus lens20, a biconvex positive lens21, a biconvex positive lens22, and a negative meniscus lens23. Here, the negative meniscus lens20and the biconvex positive lens21are cemented together. Furthermore, the biconvex positive lens22and the negative meniscus lens23are cemented together.

Returning toFIG. 1AandFIG. 1B, a further description will be provided. Alight flux L2is emitted from the objective optical system6. Here, the light source unit3is disposed at the focal position of the objective optical system6. More specifically, the light emitting unit of the light source unit3or the image of the light emitting unit is positioned at the focal position of the objective optical system6. Thus, the light flux L2emitted from the objective optical system6is a parallel light flux parallel to the measurement axis10.

The subject9is disposed on the common optical path OPC. For the adjustment of the distance from the objective optical system6to the subject9, at least one of the subject9and the measuring head1is moved.

The subject9is irradiated with the light flux L2. At the subject9, at least part of the light intensity of the irradiating light flux L2is reflected by the surface of the subject9. The light flux L3reflected by the surface of the subject9travels through the common optical path OPC toward the objective optical system6.

The light flux L3passes through the objective optical system6and is incident on the optical path splitting element7. Part of the light intensity of the light flux L3is reflected by the optical path splitting element7. The reflected light flux L3is incident on the beam splitter8. Part of the light intensity of the light flux L3is transmitted through the beam splitter8. The light flux L3transmitted through the beam splitter8is incident on the first image pickup element4. The first image pickup element4is, for example, a CCD or a CMOS.

A semiconductor position detecting element may be used instead of the first image pickup element4. The semiconductor position detecting element has a single light-receiving surface. In the semiconductor position detecting element, the output current value changes depending on the position of light incident on the light-receiving surface.

The first image pickup element4is disposed at a predetermined position. As described above, the predetermined position is the focal position of the objective optical system6or the position conjugate to the focal position of the objective optical system6.

Although the first image pickup element4is disposed in the first optical path OP1, the first image pickup element4is disposed at a position indicated by the rectangle defined by dotted lines when the position of the first image pickup element4is illustrated on the second optical path OP2inFIG. 1A. As shown inFIG. 1A, this position coincides with the focal position of the objective optical system6. Therefore, the light flux L3is collected on the first image pickup element4. That is, the image of the light source unit3is formed on the first image pickup element4.

Furthermore, since the subject9is irradiated with the light flux L2, it follows that the subject9is illuminated with light flux L2. Then, when attention is given to a point on the subject9, a light flux also travels from this point toward the objective optical system6. InFIG. 1AandFIG. 1B, a light flux L4travels from a point on the measurement axis10toward the objective optical system6.

The light flux L4passes through the objective optical system6and is incident on the optical path splitting element7. Part of the light flux L4is transmitted through the optical path splitting element7. The transmitted light flux L4is incident on the second image pickup element5. The second image pickup element5is, for example, a CCD or a CMOS.

The second image pickup element5is disposed at a position different from the predetermined positions. As described above, each of the predetermined positions is the focal position of the objective optical system6or the position conjugate to the focal position of the objective optical system6. Therefore, the subject9and the second image pickup element5are optically conjugate. Since the subject9is irradiated with the light flux L2, the image of the subject9is formed on the second image pickup element5.

In this way, in the measuring head1, the image of the light source unit3is formed on the first image pickup element4, and the image of the subject9is formed on the second image pickup element5. Using these two images, it is possible to measure the amount of tilt and the amount of shift in the subject9. In the following description, a plane parallel plate is used as the subject9.

When the angle formed between the normal to a surface of the plane parallel plate (hereinafter referred to as “the normal to the surface”) and the measurement axis10is zero, tilt does not occur. In this case, the light flux L3reflected by the surface of the plane parallel plate is identical to the light flux L2except that the travelling direction of the light flux L3is opposite to that of the light flux L2. That is, the light flux L3is a parallel light flux and travels in parallel with the measurement axis10. The light flux L3is incident on a certain position in the first image pickup element4. As a result, the image of the light source unit3is formed at the certain position in the first image pickup element4.

By contrast, when the angle formed between the normal to the surface and the measurement axis10is not zero, a tilt occurs. In this case, the light flux L3is a parallel light flux but travels at an angle that is not zero relative to the measurement axis10. Thus, the light flux L3is incident on a position displaced from the certain position in the first image pickup element4. As a result, the image of the light source unit3is formed at a position displaced from the certain position in the first image pickup element4.

In this way, it is possible to obtain the amount of tilt by measuring the amount of displacement from the certain position in the first image pickup element4for the image of the light source unit3. The certain position in the first image pickup element4can be set, for example, at the center of the first image pickup element4.

Reflected light is also produced from the back surface of the plane parallel plate. Therefore, the image of the light source unit3is formed by the reflected light from the back surface. However, the light intensity of this reflected light is very small. Therefore, the image of the light source unit3formed by the reflected light from the back surface can be considered to be undetectable with the first image pickup element4.

When the amount of displacement between the center of the plane parallel plate and the measurement axis10is zero, no shift occurs. By contrast, when the amount of displacement between the center of the plane parallel plate and the measurement axis10is not zero, a shift occurs. The position of the image of the light source unit3formed on the first image pickup element4does not change whether the amount of displacement is zero or the amount of displacement is not zero. Therefore, it is impossible to detect a shift with the first image pickup element4.

By contrast, in the second image pickup element5, the image of the surface of the plane parallel plate serving as the subject9is formed. Therefore, it is possible to detect the displacement between the center of the plane parallel plate and the measurement axis10with the second image pickup element5. However, since the image of the surface of the plane parallel plate has low contrast, it is difficult to measure the amount of displacement precisely.

Based on this, it is preferable to form an indicator with high contrast at the center of the surface of the plane parallel plate. An example of such indicators is a reticle drawn in black. By doing so, it is possible to acquire the image of the reticle with high contrast with the second image pickup element5. The indicator is not limited to particular shapes.

When the amount of displacement between the center of the reticle and the measurement axis10is zero, no shift occurs and therefore the amount of shift is zero. In this case, the image of the reticle is formed at a certain position in the second image pickup element5. By contrast, when the amount of displacement between the center of the reticle and the measurement axis10is not zero, a shift occurs. In this case, the image of the reticle is formed at a position displaced from the certain position in the second image pickup element5.

In this way, it is possible to obtain the amount of shift by measuring the amount of displacement from the certain position in the second image pickup element5for the image of the reticle. The certain position in the second image pickup element5can be set, for example, at the center of the second image pickup element5.

In this way, according to the measuring head of the present embodiment, it is possible to measure the amount of shift and the amount of tilt of the subject at the same time.

In addition, in the measuring head of the present embodiment, the objective optical system is disposed closest to the subject. That is, nothing is present except the subject in the space from the objective optical system to the subject side. Therefore, according to the measuring head of the present embodiment, it is possible to increase the measurement range in the measurement axis direction. As a result, even when a subject is long in the measurement axis direction, it is possible to measure the amount of shift and the amount of tilt of the subject at the same time.

Furthermore, in the measuring head of the present embodiment, it is preferable that the distance from the subject disposed on the common optical path to the objective optical system be twice the focal length of the objective optical system.

As shown inFIG. 1A, in the measuring head of the present embodiment, the distance from the objective optical system6to the subject9is twice the focal length of the objective optical system6. The second image pickup element5is disposed accordingly such that the distance from the objective optical system6to the second image pickup element5is about twice the focal length of the objective optical system6. By doing so, it is possible to accurately detect the reticle image located at a finite distance.

The distance from the objective optical system6to the subject9may deviate minutely (to a degree of a few hundred micro meters) from twice the focal length of the objective optical system6, for example, depending on the amount of aberration produced by the objective optical system6. The accuracy of these positions may vary with the accuracy required for the measuring head1.

Furthermore, it is preferable that the measuring head of the present embodiment include a reflective member in the second optical path.

The second optical path OP2shown inFIG. 1AandFIG. 1Bis an optical path that is straight from the optical path splitting element7to the second image pickup element5. Thus, the size of the measuring head1is large. It is then preferable that a reflective member be provided in the second optical path.

FIG. 3AandFIG. 3Bare diagrams showing arrangement examples of the reflective member, in whichFIG. 3Ais a diagram showing a first modification andFIG. 3Bis a diagram showing a second modification. The same configuration as inFIG. 1Ais denoted with the same reference numerals and a detailed description thereof will be omitted.

In the first modification, a mirror30is disposed in the second optical path OP2. The mirror30is disposed whereby the second optical path OP2is bent once. With this bending, the second optical path OP2from the optical path splitting element7toward the second image pickup element5is bent to the first image pickup element4side. Therefore, it is possible to reduce the size of the measuring head1both in the direction along the measurement axis10and in the direction orthogonal to the measurement axis10.

In the second modification, a pentagonal prism31is disposed in the second optical path OP2. The optical path is bent twice by the pentagonal prism31. With the first bending, the second optical path OP2from the optical path splitting element7toward the second image pickup element5is bent to the optical path splitting element7side. Then, with the second bending, the second optical path OP2is bent to the first image pickup element4side.

In the second modification, the bend is made to the optical path splitting element7side. Thus, in the second modification, it is possible to further reduce the size of the measuring head1in the direction along the measurement axis10.

Furthermore, it is preferable that the measuring head of the present embodiment include a magnifying optical system in the second optical path.

As described above, the amount of shift is obtained by picking up the image of the subject9with the second image pickup element5and measuring the amount of displacement from the certain position in the second image pickup element5. Therefore, it is possible to obtain the more precise amount of shift by measuring the position of the image of the subject9more precisely. It is then preferable that a magnifying optical system be disposed in the second optical path.

FIG. 4is a diagram showing an arrangement example of the magnifying optical system. The same configuration as inFIG. 3Bwill be denoted with the same reference numerals and a detailed description thereof will be omitted.

As shown inFIG. 4, a magnifying optical system40is disposed in the second optical path OP2. More specifically, the magnifying optical system40is disposed between the pentagonal prism.31and the second image pickup element5. For example, a teleconverter can be used as the magnifying optical system40. Furthermore, the magnification by the magnifying optical system40is, for example, two.

The image of the subject9formed on the second image pickup element5is enlarged by the magnifying optical system40. Accordingly, it is possible to measure the position of the image of the subject9more precisely. When the magnifying optical system40is disposed, the pentagonal prism31may not be necessarily disposed. That is, the magnifying optical system40may be disposed in the second optical path OP2inFIG. 1AandFIG. 1BorFIG. 3A.

Furthermore, in the measuring head of the present embodiment, it is preferable that the optical path splitting element be formed with a plane parallel plate and a cylindrical lens is provided in the second optical path.

InFIG. 1A, a prism having a half mirror surface is used for the optical path splitting element7. However, a plane parallel plate having a half mirror surface may be used as the optical path splitting element7. Here, when the degree of flatness of the half mirror surface is low, it is difficult to bring the light flux emitted from the objective optical system6into parallelism, and, moreover, aberration occurs in the image of the light source unit3formed on the first image pickup element4. Therefore, in order to keep the degree of flatness of the half mirror surface high, it is desirable that the thickness of the plane parallel plate is as large as possible.

However, the optical path splitting element7is disposed at a position where the light flux converges. If the plane parallel plate is disposed at an angle in the converging light flux, astigmatism occurs. The amount of astigmatism produced increases as the thickness of the plane parallel plate increases. In this case, since the aberration of the image of the subject also increases, it is difficult to measure the position of the image of the subject precisely. It is then preferable that a cylindrical lens be disposed in the second optical path.

FIG. 5is a diagram showing an arrangement example of the cylindrical lens. The same configuration as inFIG. 3Bwill be denoted with the same reference numerals and a detailed description thereof will be omitted.

InFIG. 5, a plane parallel plate50having a half mirror surface is used as the optical path splitting element7, and a cylindrical lens51is disposed in the second optical path OP2. More specifically, the cylindrical lens51is disposed between the pentagonal prism31and the second image pickup element5.

With the cylindrical lens51, it is possible to favorably correct the astigmatism produced in the plane parallel plate50. As a result, it is possible to measure the position of the image of the subject9more precisely even using the plane parallel plate50having a large thickness. Furthermore, it is also possible to make the image of the light source unit3formed on the first image pickup element4with little aberration.

When the plane parallel plate50and the cylindrical lens51are disposed, the pentagonal prism31may not necessarily be disposed. That is, inFIG. 1AandFIG. 1BorFIG. 3A, the plane parallel plate50may be disposed instead of the optical path splitting element7, and the cylindrical lens51may be disposed in the second optical path OP2.

Furthermore, in the measuring head of the present embodiment, it is preferable that the optical path splitting element have a dichroic mirror surface.

When an optical element having a half mirror surface is used for the optical path splitting element7, loss of light intensity occurs in the half mirror surface. An optical element having a dichroic mirror surface is then used for the optical path splitting element7. Accordingly, it is possible to prevent loss of light intensity in all of light fluxes L1, L2, and light flux L3.

In the dichroic mirror, the incident light is split into reflected light and transmitted light. The wavelength band of the reflected light and the wavelength band of the transmitted light as well as the light intensity of the reflected light and the light intensity of transmitted light are determined by the spectral characteristics of the dichroic mirror.

When red light is used as the light flux L1, the spectral characteristics of the dichroic mirror are set such that light in the wavelength band corresponding to red is reflected and light in the other wavelength band is transmitted. By doing so, the light flux L1is reflected by the optical path splitting element7with almost no loss of light intensity. As a result, the subject9can be irradiated with the light flux L2in a brighter state than when a half mirror is used.

Furthermore, the light flux L3reflected by the subject9is also reflected by the optical path splitting element7with almost no loss of light intensity. As a result, the light flux L3can be incident on the first image pickup element4in a brighter state than when a half mirror is used. Accordingly, the image of the light source unit3that is brighter than when a half mirror is used is obtained.

Furthermore, it is preferable that the measuring head of the present embodiment include an illumination light source in the second optical path.

When an optical element having a dichroic mirror surface that reflects light in the wavelength band corresponding to red is used for the optical path splitting element7, and red light is used as the light flux L4, the light is reflected by the optical path splitting element7. In this case, the light flux L4is not incident on the second image pickup element5and therefore it becomes impossible to measure the amount of shift.

In order to measure the amount of shift, the wavelength band of light in the light flux L4is made different from the wavelength band in the light flux L1. For this, an illumination light source for producing a light flux L4is prepared. The light flux L4is then no longer reflected by the optical path splitting element7. The illumination light source is not limited as long as the wavelength band of light in the light flux L4differs from the wavelength band in the light flux L1. For example, a white light source may be used as an illumination light source.

FIG. 6AandFIG. 6Bare diagrams showing an arrangement example of the illumination light source, in whichFIG. 6Ais a diagram showing a first arrangement example andFIG. 6Bis a diagram showing a second arrangement example. The same configuration as inFIG. 1Bwill be denoted with the same reference numerals and a detailed description thereof will be omitted.

In the first arrangement example, the illumination light source is separate from the measuring head. Specifically, as shown inFIG. 6A, an illumination light source60is disposed on the opposite side to the measuring head1with the subject9interposed therebetween.

Illumination light is emitted from the illumination light source60. When the light flux L1is red light, the wavelength band of the illumination light is different from the wavelength band of red light. For example, the wavelength band of the illumination light is the wavelength band corresponding to green light. The illumination light from the illumination light source60is applied to the subject9. Since illumination is performed from the opposite side to the objective optical system6, the subject9is subjected to trans-illumination.

The light flux L4produced from the subject9passes through the objective optical system6and is incident on the optical path splitting element7. Here, since the light flux L4is green light, when the optical path splitting element7having a dichroic mirror surface that reflects light in the wavelength band corresponding to red is used, the light flux L4passes through the optical path splitting element7. The transmitted light flux L4is incident on the second image pickup element5. As a result, the image of the subject9is formed on the second image pickup element5.

In the first arrangement example, since the light flux L4is light transmitted through the subject9and the optical path splitting element7, loss of light intensity is little. Therefore, when a reticle is formed on the subject9, it is possible to acquire the image of the reticle with high contrast with the second image pickup element5. However, it takes time for position adjustment because the illumination light source60is separate from the measuring head1.

In the second arrangement example, the illumination light source is disposed in the measuring head1. Specifically, as shown inFIG. 6B, the illumination light source61is disposed in the second optical path OP2.

Illumination light is emitted from the illumination light source61. When the light flux L1is red light, the wavelength band of the illumination light differs from the wavelength band of red light. For example, the wavelength band of the illumination light is the wavelength band corresponding to blue light. The illumination light is reflected by the beam splitter62and is incident on the optical path splitting element7. Here, since the light flux L4is blue light, the illumination light is transmitted through the optical path splitting element7. In addition, the illumination light passes through the objective optical system6and is applied to the subject9. Since illumination is performed from the same side as the objective optical system6, the subject9is subjected to reflected light illumination.

The light flux L4produced from the subject9passes through the objective optical system6and is incident on the optical path splitting element7. Here, since the light flux L4is blue light, the light flux L4is transmitted through the optical path splitting element7. The transmitted light flux L4is incident on the second image pickup element5. As a result, the image of the subject9is formed on the second image pickup element5.

In the second arrangement example, since the light flux L4is light reflected by the subject9, the loss of light intensity is larger than that of the first arrangement example. However, the illumination light source61is integrated with the measuring head1and therefore it does not take time for position adjustment.

Furthermore, the eccentricity measuring device of the present embodiment includes a body, a moving mechanism, a measuring head, a holding member, and a processing device. The measuring head, the holding member, and the moving mechanism are provided in the body. The measuring head and the holding member are positioned such that the measuring head and the subject held by the holding member are located on the measurement axis. The moving mechanism moves at least one of the measuring head and the holding member in the direction along the measurement axis. The processing device is connected to the moving mechanism and the measuring head. The measuring head is the measuring head described above.

FIG. 7is a diagram showing the eccentricity measuring device of the present embodiment. An eccentricity measuring device70includes a body71, a moving mechanism72, a measuring head73, a holding member74, and a processing device75. The moving mechanism72, the measuring head73, and the holding member74are provided in the body71.

The moving mechanism72is fixed to the body71. The moving mechanism72is, for example, a linear stage. The measuring head73is placed on the moving mechanism72with the adjustment mechanism76interposed therebetween. The holding member74is fixed to the body71with the adjustment mechanism77interposed therebetween. The holding member74holds a subject (not shown).

The measuring head73and the subject are located on the measurement axis79. The measuring head73and the holding member74are positioned so as to achieve this configuration. The adjustment mechanism.76and the adjustment mechanism77are used for this positioning.

However, the measuring head73may be directly attached to the moving mechanism72and the holding member74may be replaced for each subject. By doing so, it is possible to locate the measuring head73and the subject held by the holding member74on the measurement axis79. In this case, the adjustment mechanism76and the adjustment mechanism77become unnecessary.

The moving mechanism72moves the measuring head73in the direction along the measurement axis. It is thus possible to adjust the distance between the measuring head73and the subject. As a result, it is possible to form the image of the subject on the second image pickup element5. The moving mechanism72may be disposed on the holding member74side. Furthermore, the moving mechanism may be provided both on the measuring head73and on the holding member74.

The processing device75is connected with the moving mechanism72and the measuring head73. Upon an instruction from the processing device75, the moving mechanism72is driven whereby the position of the measuring head73is adjusted. Furthermore, information obtained by the measuring head73is sent to the processing device75and undergoes a variety of processing by the processing device75.

When an illumination light source is not disposed in the measuring head73, an illumination light source78is provided in the body71. The illumination light source78is disposed at a position opposed to the measuring head73with the holding member74interposed therebetween. When the illumination light source78is provided, the illumination light source78is connected to the processing device75. It is thus possible to control the illumination light source78.

An example of measurement by the eccentricity measuring device70will be described. The subject is the barrel of a single focus optical system. It is assumed that the single focus optical system is configured with five single lenses. Furthermore, in the following description, “linear stage72” is used instead of “moving mechanism72”.

FIG. 8is a diagram showing an example of the barrel. Since the single focus optical system is configured with five single lenses, the number of lens frames that hold the lenses is also five. As shown inFIG. 8, in a barrel80, a lens frame81, a lens frame82, a lens frame83, a lens frame84, and a lens frame85are inserted.

An opening that holds the lens is formed in the lens frame81. A surface that receives a lens (hereinafter “receiving surface”) is formed in this opening. It is desirable that the angle formed between the normal to the receiving surface and the center axis of the lens frame81is zero. However, if there is a machining error, the angle formed between the normal to the receiving surface and the center axis of the lens frame81is not zero. In this case, a tilt occurs in the opening.

Furthermore, it is desirable that the opening is formed in the center of the lens frame81. However, if there is a machining error, the opening is formed at a position displaced from the center of the frame81. In this case, a shift occurs in the opening.

In this way, tilt and shift occur in the opening of the lens frame81due to a machining error. If an image is formed in a state in which the lens is held by the lens frame81, aberration occurs in the formed image. The lens frame82, the lens frame83, the lens frame84, and the lens frame85are similar to the lens frame81.

If the lens frames are inserted into the barrel80in a state in which lenses are held by the lens frames81to85, the imaging performance of the single focus optical system is reduced. It is then important to measure the amount of tilt and the amount of shift in each lens frame.

When the amount of tilt and the amount of shift in each lens frame can be measured, it is possible to machine the lens frame again based on the measurement result. It is thus possible to reduce the amount of tilt and the amount of shift in the lens frame. Alternatively, the measurement result is fed back to the initial machining process. By doing so, it is possible to reduce the amount of tilt and the amount of shift in the lens frame fabricated in the initial machining process.

To obtain the amount of tilt and the amount of shift in the lens frame, a plane parallel plate having a reticle formed thereon (hereinafter referred to as “measurement flat plate”) is used in the measurement by the eccentricity measuring device70.FIG. 9is a diagram showing the measurement flat plate.

A measurement flat plate100is a transparent plane parallel plate101. A reticle102is formed on one surface of the plane parallel plate101. The reticle102is formed exactly in the center of the plane parallel plate101.

Such a measurement flat plate100is held by the lens frames81to85. InFIG. 8, a measurement flat plate86is held by the lens frame81, a measurement flat plate87is held by the lens frame82, a measurement flat plate88is held by the lens frame83, a measurement flat plate89is held by the lens frame84, and a measurement flat plate90is held by the lens frame85.

Accordingly, the position of the reticle in the measurement flat plate is substantially equivalent to the amount of shift in the lens frame. Furthermore, the direction of the normal to the surface in the measurement flat plate is substantially equivalent to the amount of tilt in the lens frame.

In the lens frame81, the opening is shifted rightward, and the normal to the receiving surface faces obliquely upward to the left. In the lens frame82, the opening is not shifted, and the normal to the receiving surface faces obliquely upward to the left. In the lens frame83, the opening is shifted rightward, and the normal to the receiving surface faces obliquely upward to the left. In the lens frame84, the opening is shifted leftward, and the normal to the receiving surface faces obliquely upward to the right. In the lens frame85, the opening is not shifted, and the normal to the receiving surface faces obliquely upward to the right. As used herein, left, right, up, and down mean top and bottom in the drawing sheets.

Furthermore, a jig91is disposed on one side of the barrel80. The jig91is configured with a lens frame92and a measurement flat plate93. The opening of the lens frame92is formed with high accuracy. Therefore, the amount of tilt and the amount of shift in the lens frame92are both almost zero.

Prior to measurement, the barrel80and the jig91are held by the holding member74. In doing so, the barrel80and the jig91are held such that the barrel80is located closer to the measuring head73side than the jig91.

The measuring head73is disposed at a position directly facing the barrel80. The measuring head73is moved along the measurement axis79by the linear stage72at a time of measurement. The linear stage72and the measuring head73are attached to the body71such that the measurement axis79forms the right angle relative to the surface of the measurement flat plate93on the jig91. In order to form the right angle, each of the jig91, the linear stage72, and the measuring head73may be provided with a mechanism for inclination adjustment. This adjustment is performed as necessary. By doing so, it is possible to perform measurement while ensuring the right angle of the measurement flat plate93and the measuring head73. The linear stage72is also provided with an adjustment mechanism.

The measuring head73is moved to a reference position on the linear stage72. This reference position is a position representing a mechanical origin. It is thus possible to return the measuring head73to the mechanical origin.

A light flux is applied toward the holding member74. The light flux L1is emitted from the light source unit3of the measuring head73, and the light flux L2is applied to the barrel80and the jig91. When an illumination light source is disposed in the measuring head73, illumination light is applied from this illumination light source to the barrel80and the jig91. When an illumination light source is not disposed in the measuring head73, illumination light is applied from the illumination light source78to the barrel80and the jig91.

For each of the jig91and the barrel80, measurement of the position of the reticle image and measurement of the position of the image of the light source unit3are performed.FIG. 10is a flowchart of a measuring method.

In step S100, the number of surfaces to be measured is set. The number of surfaces to be measured is determined by the number of measurement flat plates. It is noted that the number of surfaces to be measured does not include the measurement flat plate of the jig. Since the number of measurement flat plates in the barrel80is five, N=5 is set. Then, in step S101, the measuring head73is moved to the reference position on the linear stage72. Thus, measurement is ready.

First, measurement is performed for the jig91. Illumination light is applied to the jig91whereby an image Io of the reticle102on the measurement flat plate93(hereinafter referred to as “reticle image Io”) can be formed. Then, in step S102, the measuring head73is moved so that the reticle image Io is formed on the second image pickup element5. Here, the contrast of the reticle image Io may be obtained while the measuring head73is moved, and the movement of the measuring head73may be stopped when the contrast of the reticle image Io is largest. By doing so, it is possible to automatically focus on the reticle102.

In this state, a clear reticle image Io is formed on the second image pickup element5. Then, the image of the reticle image Io is picked up, and the coordinates So(δxo, δyo) of the reticle image Io are obtained. In step S103, the obtained So(δxo, δyo) is stored.

By contrast, in the first image pickup element4, the image of the light source unit3(hereinafter referred to as “spot image”) is formed. Since the number of measurement flat plates is six, the number of spot images is six. The six spot images are produced by reflection at the surfaces of the measurement flat plates86to90and93. The light intensity of the light flux L2decreases every time it passes through the measurement flat plate. Therefore, the brightness varies among the six spot images.

The brightest spot image of the six spot images is the image produced by reflection from the measurement flat plate located closest to the measuring head73. By contrast, the darkest spot image is the image produced by reflection from the measurement flat plate located farthest from the measuring head73.

The measurement flat plate93is located farthest from the measuring head73. Then, the darkest spot image is specified from among the six spot images, and the coordinates To(εxo, εyo) of the darkest spot image are obtained. In step S104, the obtained To(εxo, εyo) is stored.

Furthermore, the position Zo(zo) of the measuring head73on the measurement axis79is stored. The measurement of the position of the reticle image on the jig91and the measurement of the position of the spot image are thus finished.

As described above, the amount of shift and the amount of tilt are almost zero in the jig91. Therefore, it is possible to use So(δxo, δyo) as the shift origin. Furthermore, it is possible to use To(εxo, εyo) as the tilt origin.

Subsequently, measurement is performed for the barrel80. In measurement for the barrel80, a variable n is used to count the number of times of measurement in the barrel80. Then, in step S105, the value of n is initialized.

In a state in which the measurement in the jig91is finished, the reticle102on the measurement flat plate93is in focus. Therefore, efficient measurement can be performed when measurement of the position of the reticle image and measurement of the position of the spot image are performed from the measurement flat plate located closest to the measurement flat plate93. It is noted that the measurement flat plates may be measured in the order from the measurement flat plate located farthest from the measurement flat plate93, or in a random order.

The measurement flat plate located closest to the measurement flat plate93is the measurement flat plate90. The measurement flat plate90is located closer to the measuring head73side than the measurement flat plate93. Then, in step S106, the measuring head73is moved in the direction away from the barrel80so that a reticle image I1is formed on the second image pickup element5. The reticle image I1is the image of the reticle formed on the measurement flat plate90. Also at this time, the contrast of the reticle image I1is obtained, and when the contrast of the reticle image I1is largest, the measuring head73may be stopped moving.

In this state, a clear reticle image I1is formed on the second image pickup element5. Then, the reticle image I1is picked up, and the coordinates S1(δx1, δy1) of the reticle image I1on the measurement flat plate90are obtained. In step S107, the obtained S1(δx1, δy1) is stored.

Furthermore, the position of the measurement flat plate90is the second farthest position from the measuring head73. Then, the second darkest spot image is specified from among the six spot images, and the coordinates T1(εx1, εy1) of the second darkest spot image are obtained. In step S108, the obtained T1(εx1, εy1) is stored.

In step S109, the number of times of measurement is confirmed. When n does not agree with N−1, the measurement has not yet finished for all of the measurement flat plates. In this case, step S110is executed. In step S110, the value of the variable n is incremented.

Here, the coordinates To1(εxo1, εyo1) of the darkest spot image may be obtained, and the obtained To1(εxo1, εyo1) may be stored. In this case, step S111is executed. Step S111is executed as necessary.

The coordinates of the darkest spot image have already been obtained in the measurement in the measurement flat plate93(step S104). However, the measurement in the measurement flat plate90and the measurement in the measurement flat plate93are different in position of the measuring head73. Therefore, the coordinates measured for the measurement flat plate90and the coordinates measured for the measurement flat plate93do not always agree. This point will be described later.

Furthermore, the position Z1(z1) of the measuring head73on the measurement axis79is stored. The measurement in the measurement flat plate90is then finished.

Thereafter, the processing performed for the measurement flat plate90is repeatedly performed in the order of the measurement flat plate89, the measurement flat plate88, the measurement flat plate87, and the measurement flat plate86.

When the coordinates of the reticle in the measurement flat plate86and the coordinates of the spot image are finished being stored, the measurement of the position of the reticle image in the barrel80and the measurement of the position of the spot image are finished.

The measurement data of the position of the reticle image and the measurement data of the position of the spot image are stored together with the position data of the measuring head73into the processing device75.

It is possible to obtain the amount of tilt and the amount of shift in each lens frame from the measurement data stored in the processing device75.

The normal to the surface of the measurement flat plate93and the measurement axis79are preferably parallel to each other. However, it is extremely difficult to bring them into perfect parallelism. In a state in which the normal to the surface of the measurement flat plate93and the measurement axis79intersect, when the measuring head73moves along the measurement axis79, the measuring head73moves also in the direction orthogonal to the normal to the surface of the measurement flat plate93. Such movement results in an error in measurement of the position of the reticle image and measurement of the position of the spot image. The factors in the error resulting from the movement of the measuring head73include pitching and yawing in the measuring head73.

As described above, when the coordinates of the darkest spot image are measured in the measurement of the measurement flat plate86to measurement flat plate90, it is possible to detect the amount of displacement due to pitching and the amount of displacement due to yawing in the measuring head73, using the measurement data of the coordinates of the darkest spot image. It is possible to perform eccentricity measurement with high accuracy by correcting the amount of tilt and the amount of shift using the detected amount of displacement.

Although eccentricity measurement in the barrel of the single focus optical system has been described above, it is possible to perform similar eccentricity measurement also for a zoom lens frame.

Furthermore, by using the measuring head73, it is possible to measure the degree of parallelism and the degree of concentricity of a cylinder internal structure in a noncontact manner and in a simple way.

Furthermore, by using the common optical path OPC and the first optical path OP1in the measuring head73, it is possible to use the measuring head73as an autocollimator. That is, the eccentricity measuring device70may be a device that measures the amount of tilt in a lens frame without obtaining the amount of shift in a lens frame. In this case, it is possible to measure the amount of tilt for a plurality of measurement flat plates at the same time.

According to the present invention, it is possible to provide a measuring head with a wide range of measurement in the measurement axis direction and an eccentricity measuring device including the same.

As described above, the present invention is suitable for a measuring head with a wide range of measurement in the measurement axis direction and an eccentricity measuring device including the same.