JP2007327819A - Heterodyne laser interferometric measuring machine, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact heterodyne laser interferometric measuring machine for measuring a wavelength precisely, capable of forming an image of high quality by enhancing resolution to eliminate an influence of a dead path, and an image forming device. <P>SOLUTION: This heterodyne laser interferometric measuring machine includes a polarization beam splitter 2 for separating a laser beam from a heterodyne laser light source 1 into two measuring beams, two measuring mirrors 3, 4 fixed onto a measured object 102 to be directed to an opposed direction on a virtual straight line 101, two measuring optical paths 5, 6 for guiding the measuring beams to the measuring mirrors 3, 4 along the virtual straight line 101, 1/4 wavelength plates 7, 8 arranged in the respective measuring optical paths 5, 6, two reflecting mirrors 9, 10 positioned between the 1/4 wavelength plates 7, 8 and the measuring mirrors 3, 4 to reflect respectively one parts of measuring beam cross sections, and a computing means 11 for calculating a displacement corresponding to a difference between two beat signals by the measuring mirrors 3, 4 and the reflecting mirrors 9, 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heterodyne laser interferometer and an image forming apparatus equipped with the heterodyne laser interferometer, and more specifically, a laser used for precision manufacturing, processing of precision machines, semiconductors, optical disks, and the like. Heterodyne laser interferometer for measuring the displacement of an object to be measured using light, and an ink jet printer of a printing apparatus for forming a recorded image on a recording medium equipped with the heterodyne laser interferometer, electrostatic recording system or electronic The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, or a complex machine for forming a toner recording image in an image forming process such as a photographic system.

In a conventional heterodyne laser interferometer and an image forming apparatus equipped with the heterodyne laser interferometer, a typical method used as a laser interferometer is a highly accurate and stable heterodyne laser interferometer. It is a length measuring instrument.
As rotational shake measurement using a heterodyne laser interferometer, it has also been proposed to perform highly accurate displacement measurement that is not affected by fine irregularities on the surface to be measured (see Patent Document 5).
FIG. 6 is a block diagram of a basic configuration of a conventional heterodyne laser interferometer 1000.
In FIG. 6, a heterodyne laser light source 1001 emits two linearly polarized outgoing beams having slightly different frequencies and orthogonal planes of polarization.

The linearly polarized outgoing beam emitted from the heterodyne laser light source 1001 and branched by the beam splitter 1020 converts the interference state into an electrical signal by the photodetector 1021, and the beat signal is detected by the reference signal circuit 1022.
The beam that has passed through the beam splitter 1020 is split into a reference beam 1005 and a measurement beam 1006 by a polarization beam splitter 1002.
The reference beam 1005 passes through the quarter-wave plate 1007, is reflected by the reference mirror 1003 whose position is fixed, and returns to the polarization beam splitter 1002 through the quarter-wave plate 1007.
The measurement beam 1006 passes through the quarter-wave plate 1008, is reflected by the movable measurement mirror 1004, and returns to the polarization beam splitter 1002 through the quarter-wave plate 1008.

The reference beam 1005 and the measurement beam 1006 reflected by the reference mirror 1003 and the measurement mirror 1004 pass through the quarter-wave plate 1007 and the quarter-wave plate 1008 twice, respectively, so that the polarization plane is rotated and emitted from the polarization beam splitter 1002. It is separated from the beam, and the interference state is converted into an electric signal by the photodetector 1009, and the beat signal is detected by the measurement signal circuit 1010.
The polarizing beam splitter 1002, the two quarter wavelength plates 1007, and the quarter wavelength plate 1008 can be integrated.
The outputs of the reference signal circuit 1022 and the measurement signal circuit 1010 are processed by the calculation circuit 1019.
When the measurement mirror 1004 mounted and fixed on the measurement object moves, the beat signal phase of the measurement signal circuit 1010 changes and the frequency is Doppler shifted in accordance with the speed. Therefore, the arithmetic circuit 1019 causes the reference signal circuit 1022 to move. The movement distance can be measured by calculating these values.

The movement distance is measured not by absolute value measurement but by relative value measurement, and the measurement value is reset to zero at an arbitrarily determined measurement origin (Z). The difference in optical path length between the reference beam 1005 and the measurement beam 1006 at the measurement origin (Z) is a dead bus.
In general, it is difficult to make this dead bus zero because of restrictions on the arrangement of the optical system. It is known as Edren's formula that the wavelength of laser light changes depending on the ambient temperature, humidity, and atmospheric pressure, so the measured value of laser interferometry also changes, but the amount of change in the dead path is calculated from the measured value. Since it cannot be separated, there is a problem that the moving distance measurement accuracy of the movable measuring mirror 1004 is lowered as a result.

Therefore, various methods and apparatuses for reducing the influence of the dead bus as described below have been proposed.
First, a design dead path amount is obtained in advance, and a change in dead bus amount due to an environmental change is calculated to correct an actual length measurement result including a dead path (see Patent Documents 1 and 2).
That is, the dead bus length (Ld) is measured by some means, for example, a measure, the length measurement result measured using laser interference is (L), and the sign dash is corrected by Edren's formula considering the environment such as temperature. As a later measurement result, the true movement distance (La) = L ′ − (Ld−Ld ′) is assumed (see Patent Document 1).
Then, a detection unit for environmental conditions such as temperature is provided, and an operator inputs a dead path length (Cd) (correctly a count value corresponding to a distance) to the input unit of the dead bus, and is automatically corrected by the Edren equation. The true movement distance is C = Cp− (Cd−Cd ′) with respect to the measured movement distance (Cp) value (see Patent Document 2).

In addition, a quarter-wave plate of the reference optical path is partially inserted into the reference beam, a part of the surface of the quarter-wave plate of the measurement optical path is used as a mirror and placed at the measurement origin, and the reference signal is the reference optical path. Generated by interference between the part reflected from the reference mirror without passing through the quarter wavelength plate and the part reflected from the quarter wavelength plate surface of the measurement optical path, and the measurement signal passes through the quarter wavelength plate in the reference optical path. Since it is generated by interference between the part reflected from the reference mirror and the part reflected by the quarter-wave plate of the measurement optical path and reflected from the measurement mirror, the length of the dead path is measured with the reference signal, and the measurement mirror position Is measured with the measurement signal, and the change in the dead bus amount is offset from the length measurement result of the measurement mirror (see Patent Document 3).
Furthermore, the reference and measurement optical path is provided with an expansion / contraction mechanism so that the distance between the reference mirror / measurement object and the polarization beam splitter can be increased / decreased, and based on the reference signal from the light source corresponding to dead path zero, the reference and measurement optical path The dead bus itself is removed from the optical system by calculating the phase difference, expanding and contracting the length of the reference optical path, and actually adjusting the dead path length to zero (see Patent Document 4).

Further, there is a method for improving resolution by using a reference optical path as a measurement optical path in the laser interferometer.
FIG. 7 is a block diagram of a basic configuration of a conventional laser interferometer 2000 that improves resolution.
In FIG. 7, a laser interferometer 2000 has a shape in which a reference mirror 1003 and a measurement mirror 1004 facing in opposite directions are mounted and fixed on a device under test 2001.
The reference beam 1005 to the reference mirror 1003 is guided from the quarter wave plate 1007 through three mirrors 2002, 2003, and 2004 for changing the direction. The reference beam 1005 and the measurement beam 1006 are on the same straight line, and the reference mirror 1003 and the measurement mirror 1004 are arranged perpendicular to the two reference beams 1005 and the measurement beam 1006.

Compared with the heterodyne laser interferometer 1000 shown in FIG. 6, the laser interferometer 2000 measures the object to be measured so that the reference mirror 1003 faces the direction opposite to the measuring mirror 1004 with respect to a straight line corresponding to the optical axis. The difference is that it is mounted and fixed on the measurement object 2001.
In this configuration, since the optical path length is differentially detected and doubled with respect to the movement amount of the object to be measured 2001 in the optical axis direction, the resolution is improved twice.
In such a configuration of the differential detection optical system, the functions of the reference mirror 1003 and the measurement mirror 1004 are exactly the same.
However, in the optical differential detection, since it is necessary to configure an optical system that sandwiches the object to be measured 2001, the optical path basically becomes an unequal length optical path that is the amount of movement added to the object to be measured 2001, and the dead path is This is larger than the normal optical system shown in FIG.
For this reason, it becomes necessary to eliminate a decrease in measurement accuracy due to a further dead path.

In Patent Documents 1 and 2 taken up as conventional techniques, a dead path amount is obtained in advance, a change in the dead bus amount due to an environmental change is calculated, and a length measurement result including the dead path is corrected.
However, this is indirect, and there is a problem that the accuracy of the dead path amount obtained in advance is low.

In Patent Document 3, the dead bus amount change is offset by performing optical length measurement of the dead path portion together with the object, but it is assumed that the reference mirror is fixed in position.
If the reference mirror is allowed to move and applied to the differential detection optical system, the position of the measurement optical path is reversed with respect to the optical axis between the two optical paths, so that the measurement optical path is aligned with the same straight line of the measurement mirror. Has a problem that it is necessary to shift the optical path, and an extra mechanism is required.
Furthermore, in Patent Document 4, the dead path amount is actually obtained to eliminate itself, but an optical path expansion / contraction mechanism necessary for that purpose is necessary, and it is difficult to mount on an actual device, and there is a lot of installation space even when mounted. There is a bug.
JP-A-6-58711 Japanese Patent Laid-Open No. 9-287917 Japanese Patent Laid-Open No. 11-257915 JP 2003-287403 A JP 2003-329408 A

Conventional heterodyne laser interferometers and image forming apparatuses equipped with such heterodyne laser interferometers are not only low in accuracy to eliminate the effects of dead paths, but also require extra mechanisms as well as large sizes. There has been a problem that the image quality that forms a large amount of installation space also deteriorates.
Therefore, an object of the present invention is to solve such problems. That is, a heterodyne laser interferometer that forms a small, high-quality image that improves resolution and eliminates the effects of dead paths and performs high-accuracy measurement, and image formation that includes the heterodyne laser interferometer An object is to provide an apparatus.

  In order to achieve the above object, the invention described in claim 1 is a heterodyne laser interferometer that measures the displacement of an object to be measured using laser light, and uses two linearly polarized lights whose polarization planes are orthogonal at different frequencies. A heterodyne laser light source that generates a laser beam, a polarization beam splitter that separates the laser beam from the heterodyne laser light source into two measurement beams, and two measurement mirrors that are fixed on the object to be measured in opposite directions on a virtual line And two measurement optical paths for guiding the measurement beam along a virtual straight line to the measurement mirror, a quarter-wave plate disposed in each measurement optical path, and a position between the quarter-wave plate and the measurement mirror The two reflection mirrors that reflect a part of the cross section of the measurement beam, and the reflected light from the measurement mirror and the reflection mirror are divided into two to reduce the interference light intensity by the measurement mirror. Characterized in that it is a heterodyne laser interferometer length measuring apparatus comprising a calculating means for calculating a corresponding displacement to the difference between the two beat signals over preparative signal and the beat signal of the interference light intensity due to reflection mirror.

  The invention according to claim 2 is the heterodyne laser interferometer according to claim 1, wherein the polarization beam splitter is a heterodyne laser interferometer with an integrated quarter wave plate. To do.

  A third aspect of the present invention is the heterodyne laser interferometer according to the first or second aspect, wherein the measurement mirror is a heterodyne laser interferometer that doubles as an end face of the object to be measured. It is characterized by that.

  According to a fourth aspect of the present invention, in the heterodyne laser interferometer according to any one of the first to third aspects, the two reflection mirrors are the same so as to reflect a part of the measurement beam in the measurement optical path. It is a heterodyne laser interferometer that has a shape and is arranged at the same position with respect to the optical axis of the measurement optical path.

  A fifth aspect of the present invention is the heterodyne laser interferometer according to any one of the first to fourth aspects, wherein the heterodyne laser interferometer is located between the reflection mirror and the measurement mirror and condenses the measurement beam to measure the measurement mirror. The heterodyne laser interferometer is equipped with a lens for irradiating the light.

  The invention according to claim 6 is the heterodyne laser interferometer according to claim 5, wherein the lens is a heterodyne laser interferometer having a reflecting mirror formed on a part of the incident surface. And

  The invention according to claim 7 is the heterodyne laser interferometer according to claim 6, wherein the lens is a heterodyne laser interferometer having a reflecting mirror formed concentrically around the optical axis. It is characterized by.

  The invention according to claim 8 is the heterodyne laser interferometer according to claim 6, wherein the lens is provided with a reflecting mirror formed concentrically around the optical axis at the periphery. It is characterized by being.

  According to a ninth aspect of the present invention, in the heterodyne laser interferometer according to any one of the first to eighth aspects, the calculation means includes a beam splitter that divides the reflected light beam from the measurement mirror and the reflection mirror into two. A heterodyne laser interferometer is provided.

  According to a tenth aspect of the present invention, in the heterodyne laser interferometer according to any one of the first to ninth aspects, the calculation means selectively transmits interference light from the two measurement mirrors from the reflected light beam. It is a heterodyne laser interferometer that includes an aperture, a photodetector that electrically detects the intensity of interference light transmitted through the aperture, and a measurement circuit that generates a beat signal from the output of the photodetector.

  According to an eleventh aspect of the present invention, in the heterodyne laser interference length measuring device according to any one of the first to tenth aspects, the computing means selectively transmits the interference light from the two reflecting mirrors from the reflected light beam. It is a heterodyne laser interferometer that includes an aperture, a photodetector that electrically detects the intensity of interference light transmitted through the aperture, and a measurement circuit that generates a beat signal from the output of the photodetector.

  According to a twelfth aspect of the present invention, in the heterodyne laser interferometer according to any one of the first to eleventh aspects, the computing means has a displacement corresponding to the difference between the beat signals generated by the two measurement circuits. It is a heterodyne laser interferometer that includes an arithmetic circuit for performing calculation.

  According to a thirteenth aspect of the present invention, there is provided an image forming apparatus for forming a recorded image of toner on a recording medium, an image forming unit for forming a recorded image on the recording medium, and any one of the first to twelfth aspects. An image forming apparatus comprising the heterodyne laser interferometer described above.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to the thirteenth aspect, the image forming unit is an image forming apparatus that forms a toner recording image by an electrophotographic image forming process. .

  According to the present invention, a heterodyne laser interferometer that forms a small, high-quality image that improves resolution and eliminates the effects of dead paths and performs high-precision length measurement, and the heterodyne laser interferometer is provided. Can be provided.

Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a block diagram of a basic configuration of a heterodyne laser interferometer 100 according to an embodiment of the present invention.
In FIG. 1, a heterodyne laser interferometer 100 that measures the displacement of an object to be measured using laser light includes a heterodyne laser light source 1 that generates two linearly polarized laser beams having different planes of polarization at different frequencies, A polarization beam splitter 2 that separates the laser beam from the heterodyne laser light source 1 into two measurement beams, two measurement mirrors 3 and 4 that are fixed to the object 102 to face in opposite directions on the virtual straight line 101, and measurement Two measurement optical paths 5 and 6 for guiding a measurement beam to the mirrors 3 and 4 along a virtual straight line 101, quarter wave plates 7 and 8 disposed in the respective measurement optical paths 5 and 6, and 1 / Two reflection mirrors 9 and 10 which are located between the four-wavelength plates 7 and 8 and the measurement mirrors 3 and 4 and reflect a part of the cross section of the measurement beam, and the measurement mirrors 3 and 4 and the reflection mirrors 9 and 10 Is calculated by calculating a displacement corresponding to the difference between the two beat signals of the beat signal of the interference light intensity by the measurement mirrors 3 and 4 and the beat signal of the interference light intensity by the reflection mirrors 9 and 10 by dividing the reflected light beam into two. Means 11 are provided.

The heterodyne laser light source 1 emits two linearly polarized outgoing beams having slightly different frequencies and orthogonal planes of polarization, and is split into two measurement beams at the center point I (0) of the polarizing beam splitter 2, These are designated as measurement optical path 5 and measurement optical path 6, respectively.
The measurement beam passing through the measurement optical path 5 passes through the quarter-wave plate 7, then passes through the mirrors 103, 104, and 105 for changing the direction, is guided to the measurement mirror 3, is reflected there, and passes through the reverse path, It returns to the polarizing beam splitter 2 through the quarter wavelength plate 7.
A reflection mirror 9 that reflects a part of the measurement beam passing through the measurement optical path 5 is disposed at a predetermined position before the measurement mirror 3, and a part of the measurement beam passing through the measurement optical path 5 reaches the measurement mirror 3. Without being reflected by the reflecting mirror 9, the light returns to the polarizing beam splitter 2 through the quarter-wave plate 7.

The measurement beam passing through the measurement optical path 6 passes through the quarter wavelength plate 8, is reflected by the measurement mirror 4, and returns to the polarization beam splitter 2 through the quarter wavelength plate 8.
Similarly to the measurement beam passing through the measurement optical path 5, a reflection mirror 10 for reflecting a part of the measurement beam passing through the measurement optical path 6 is disposed at a predetermined position in front of the measurement mirror 4.
A part of the measurement beam passing through the measurement optical path 6 does not reach the measurement mirror 4 but is reflected by the reflection mirror 10 and returns to the polarization beam splitter 2 through the quarter-wave plate 8.
By integrating the polarizing beam splitter 2 and the two quarter-wave plates 7 and the quarter-wave plate 8, adjustment work and the like are reduced, and the accuracy and cost are further reduced.

The measurement beam passing through the measurement optical paths 5 and 6 is adjusted to be in a straight line, and the two measurement mirrors 3 and 4 are perpendicular to the optical axis of the measurement beam passing through the measurement optical paths 5 and 6 and are directed in opposite directions. In this state, it is installed and fixed on the object to be measured 102 which is a movable measuring object.
The reflection mirrors 9 and 10 have the same shape so as to reflect a part of each measurement beam passing through the measurement optical paths 5 and 6 and are disposed at the same position with respect to the optical axis of the measurement beam passing through the measurement optical paths 5 and 6. To do.
The positions of the reflection mirrors 9 and 10 are arranged as close to the measurement mirrors 3 and 4 as possible.
As the measurement mirrors 3 and 4 and the reflection mirrors 9 and 10, a plane mirror or a corner cube is used.
Further, the measurement mirrors 3 and 4 are formed by using the end face of the object to be measured 102, which is a movable measurement object, as a mirror, so that adjustment work and the like can be reduced, and the accuracy and cost can be further reduced.

The reflection mirrors 9 and 10 only have to reflect a part of the respective measurement beam beams passing through the measurement optical paths 5 and 6, and a glass plate or the like in which a reflection film pattern is formed on the mirror part can be used.
In the measurement optical path 5, the distance from the center point I (0) of the polarizing beam splitter 2 to the measurement mirror 3 and the distance to the reflection mirror 9 are (MP1) and (DP1), respectively.
Similarly, in the measurement optical path 6, the distance from the center point I (0) of the polarization beam splitter 2 to the measurement mirror 4 and the distance to the reflection mirror 10 are (MP2) and (DP2), respectively.
Since the measurement beams of the measurement optical paths 5 and 6 reflected by the measurement mirrors 3 and 4 and the reflection mirrors 9 and 10 pass through the quarter-wave plate 7 and the quarter-wave plate 8 respectively twice, the plane of polarization rotates. After the outgoing beam from the polarization beam splitter 2 is separated, the reflected light from the measurement mirrors 3 and 4 and the reflection mirrors 9 and 10 is divided into two by the calculation means 11 and the beat of the interference light intensity by the measurement mirrors 3 and 4 is obtained. The displacement corresponding to the difference between the two beat signals of the signal and the beat signal of the interference light intensity by the reflection mirrors 9 and 10 is calculated.

The calculation means 11 separates the measurement beams in the measurement optical paths 5 and 6 reflected by the measurement mirrors 3 and 4 and the reflection mirrors 9 and 10 from the polarization beam splitter 2 and then passes through the beam splitter 12. After being branched, the opening 13 and the measurement optical path 6 of each measurement optical path 5 are bent by a mirror 23 and guided to the photodetectors 15 and 16 through the opening 14.
An opening 14 for selectively transmitting the reflected light interference state from the reflection mirrors 9 and 10 is disposed in front of the photodetector 16, and the interference state is converted into an electrical signal by the photodetector 16, and the measurement signal The beat signal is detected and output by the circuit 18, and the beat signal of the measurement signal circuit 18 corresponds to (DP1-DP2), which corresponds to the dead path amount in the differential detection optical system.

Similarly, an opening 13 that selectively transmits the reflected light interference state from the measurement mirrors 3 and 4 is disposed in front of the photodetector 15. The photodetector 15 converts the interference state into an electrical signal. The measurement signal circuit 17 detects and outputs a beat signal. The beat signal of the measurement signal circuit 17 corresponds to (MP1-MP2), which is a measurement target including a dead path in the differential detection optical system. This corresponds to the moving distance of the object 102.
That is, since the moving distance of the object to be measured 102 including the dead path and the dead path amount can be electrically detected, the arithmetic circuit 19 calculates the difference between the output of the measurement signal circuit 17 and the output of the measurement signal circuit 18. In addition, it is possible to obtain the moving distance (MP1-MP2)-(DP1-DP2) of the object to be measured 102 that does not include the dead path amount in the differential detection optical system.

As a calculation method of the difference between the output of the measurement signal circuit 17 and the output of the measurement signal circuit 18 by the arithmetic circuit 19, the measurement signal circuit 18 is used as a reference beat signal, and the difference between the beat signals of the measurement signal circuit 17 is obtained. A linearly polarized outgoing beam emitted from the heterodyne laser light source 1 and branched by the beam splitter 20 is converted into an electrical signal by the photodetector 21 and a beat signal detected by the reference signal circuit 22 is used. The measurement signal circuit 17 and the measurement signal circuit 18 obtain the difference of the beat signal from the reference signal circuit 22 and actually calculate the data corresponding to (DP1-DP2) and (MP1-MP2). There is a way to calculate the difference.
This heterodyne laser interferometer 100 can be applied, for example, to measuring the amount of movement of a linear motion stage.

As a specific example, if it is applied to a precision linear motion stage for semiconductor or optical disk pattern fabrication, the stage movement can be measured with high accuracy without being affected by a dead path. And the accuracy of the fabrication pattern can be improved.
Therefore, this heterodyne laser interferometer 100 measures the length of the object 102 to be measured with an optical differential detection configuration, and at the same time, installs the reflecting mirrors 9 and 10 in the vicinity of the object 102 to be measured. Dead path length measurement is also performed on a part of each measurement beam in the optical paths 5 and 6, and the dead bus value is removed from the final length measurement result. Can be eliminated.

FIG. 2 is a block diagram of a basic configuration including the lenses 24 and 25 of the heterodyne laser interferometer 100 according to the embodiment of the present invention.
FIG. 3 is an enlarged view of the front and side of the basic configuration of a lens / reflecting mirror integrated element in which the reflecting mirrors 9 and 10 of the heterodyne laser interferometer 100 according to the embodiment of the present invention are formed at the center of the light beam. .
FIG. 4 is an enlarged view of the front and side of the basic configuration of the lens / reflecting mirror integrated element forming the reflecting mirrors 9 and 10 in the periphery of the heterodyne laser interferometer 100 according to the embodiment of the present invention.
In FIG. 2, the heterodyne laser interferometer 100 of this embodiment is obtained by mirroring the end surface itself of the object to be measured 102 in which the measurement mirrors 3 and 4 are movable as compared with the heterodyne laser interferometer 100 of FIG. The measurement mirrors 30 and 40 are formed and used together, and the measurement beams of the measurement optical paths 5 and 6 are condensed and irradiated by the lenses 24 and 25, and the other parts are the same. It is.
In this example, the measurement mirrors 3 and 4 are mirrored on the end face of the object 102 to be measured to form the measurement mirrors 30 and 40. However, the measurement mirrors 3 and 4 are independent measurements like the heterodyne laser interferometer 100 in FIG. The mirrors 3 and 4 may be installed and fixed on the object to be measured 102.

By condensing the measurement beams in the measurement optical paths 5 and 6 with the lenses 24 and 25, the area under the measurement mirrors 3 (30) and 4 (40) smaller than the beam diameter of the heterodyne laser light source 1 can be taken. Measurement is also possible for the object 102 and the object 102 to be measured in which the measurement mirrors 3 (30) and 4 (40) are curved.
Usually, the cross section of the outgoing beam of the heterodyne laser light source 1 is circular, and in addition, since the lenses 24 and 25 are also many rotationally symmetric with respect to the optical axis, the measurement beams of the measurement optical paths 5 and 6 are transmitted by the lenses 24 and 25, respectively. When condensing, the shape of the reflecting mirrors 9 and 10 is advantageously a concentric reflecting mirror shape with respect to the optical axis so that the center or periphery of the light beam is reflected.
Further, if the reflecting surfaces are arranged on the incident surfaces of the lenses 24 and 25 as the positions of the reflecting mirrors 9 and 10, it is advantageous because the distance between the reflecting mirrors 9 and 10 can be maximized.

In that case, if the lens / reflecting mirror integrated element shown in FIG. 3 in which the reflecting mirrors 9 and 10 of the plane mirror are formed in the central portions of the lenses 24 and 25 is used, the distance between the reflecting mirrors 9 and 10 can be secured to the maximum. In addition, the lenses 24 and 25 and the reflecting mirrors 9 and 10 can be adjusted at the same time, which is more preferable.
In the heterodyne laser interferometer length measuring device 100 including the lens / reflecting mirror integrated element that forms the reflecting mirrors 9 and 10 at the center of the light beam, the center of the incident surface of the lenses 24 and 25 that collect the measuring beams in the measuring optical paths 5 and 6 is used. Since the reflecting mirrors 9 and 10 that are concentric plane mirrors with respect to the optical axis are formed in the part, the interval between the reflecting mirrors 9 and 10 is ensured to the maximum, and in addition to the above-described effects, the influence of the dead path is maximized. Can be eliminated.
Furthermore, since the positions of the lenses 24 and 25 and the reflecting mirrors 9 and 10 can be adjusted simultaneously, handling becomes easy.

Alternatively, use of the lens / reflecting mirror integrated element shown in FIG. 4 in which the reflecting mirrors 9 and 10 of the plane mirror are formed in the peripheral portions of the lenses 24 and 25 is also suitable.
In the heterodyne laser interferometer length measuring device 100 including a lens / reflecting mirror integrated element that forms the reflecting mirrors 9 and 10 in the periphery, peripheral portions of the incident surfaces of the lenses 24 and 25 that collect the measurement beams of the measurement optical paths 5 and 6 are provided. Since the reflecting mirrors 9 and 10 are formed as concentric plane mirrors with respect to the optical axis, the distance between the reflecting mirrors 9 and 10 is ensured to the maximum, and in addition to the above-described effects, the influence of dead path is eliminated to the maximum. can do.
Furthermore, since the positions of the lenses 24 and 25 and the reflecting mirrors 9 and 10 can be adjusted simultaneously, handling becomes easy.

The heterodyne laser interferometer 100 provided with such lenses 24 and 25 can be applied to, for example, measurement of the rotational shake amount of the rotary stage.
As a specific example, if applied to a precision turntable for optical disc pattern production, the turntable rotational runout is measured with high accuracy without being affected by dead paths, so the amount of rotational runout is fed back to the laser beam position for pattern production. Therefore, the accuracy can be improved by creating a track pattern with no runout.
Therefore, in this heterodyne laser interferometer 100, the measurement beams in the measurement optical paths 5 and 6 are collected by the lenses 24 and 25 and irradiated on the object to be measured 102. In addition to the above-described effects, It is also possible to measure the measurement object 102 having only a beam reflection surface smaller than the measurement beam diameter of each of the measurement optical paths 5 and 6 and the measurement object 102 having a curved beam reflection surface.

FIG. 5 is a basic configuration diagram of an image forming apparatus 200 including the heterodyne laser interferometer 100 according to the embodiment of the present invention.
In FIG. 5, an image forming apparatus 200 includes an image forming unit 201 that forms an image on a recording medium (P), and a document image reading device 202 disposed above the image forming unit 201. The image forming unit 201 is held on the recording medium feeding unit 203.
The image forming unit 201 is configured to form a high-speed, high-quality toner recording image on a recording sheet of a recording medium (P), which is excellent in convenience and versatility in an electrophotographic image forming process.

In the document image reading apparatus 202, a document (O) placed on the document table 220 includes a first scanner 223 on which a light source 221 and a first mirror 222 are mounted by a driving unit (not shown), a second mirror 224, and a third mirror. The second scanner 226 on which the mirror 225 is mounted moves to the right in the direction of the arrow (A) shown in the figure. At this time, the document image surface is illuminated by the light source 221, and the document image is photoelectrically converted via the reading optical system 227. Reading is performed by the CCD of the element 228.
An object to be measured 102 of a second scanner 226 that operates in conjunction with a first scanner 223 in which a document image of an original (O) set on a document table 220 is read by a CCD of a photoelectric conversion element 228 via a reading optical system 227. The shift is measured by the heterodyne laser interferometer 100, and a high-quality original image is always read at an accurate reading position.

A high-quality original image read by the photoelectric conversion element 228 is imaged on the drum-shaped photosensitive drum 210 by the writing device 212 of the image forming unit 201.
The photosensitive drum 210 rotates clockwise in the direction of the arrow (B) shown in the figure. At this time, the surface of the photosensitive drum 210 is uniformly charged by the charger 211, and a high-quality original image is formed on the charged surface by the laser beam of the writing device 212. Is formed. As a result, an electrostatic latent image is formed on the photosensitive drum 210, and the electrostatic latent image is visualized as a high-quality toner image by the developing device 213.

On the other hand, the recording medium (P) recording paper is fed from the recording medium feeding unit 203 toward the photosensitive drum 210, and a high-quality toner recording image on the photosensitive drum 210 is received by the transfer unit 214. Transferred to the recording medium (P).
The recording medium (P) passes through the fixing device 215, and the high-quality toner recording image transferred to the surface is fixed on the recording medium (P). Then, the recording medium (P) is placed on the discharge tray 216. It is discharged and stored. The toner remaining on the photosensitive drum 210 is removed by the cleaning unit 217 and prepared for the next process.
Accordingly, it is possible to provide the image forming apparatus 200 including the heterodyne laser interferometer 100 that forms a small and high-quality image that improves the resolution and eliminates the influence of the dead path and performs high-precision length measurement.

It is a block diagram of the basic composition of the heterodyne laser interference length measuring device concerning the example of an embodiment of the invention. It is a block diagram of a basic composition provided with the lens of the heterodyne laser interferometer length measuring device concerning the embodiment of this invention. It is the front and side enlarged view of the basic composition of the lens and reflection mirror integrated element which forms the reflection mirror of the heterodyne laser interferometer length measuring device concerning the embodiment of this invention in the light beam center. It is the front and side enlarged view of the basic composition of the lens and reflection mirror integrated element which forms the reflection mirror of the heterodyne laser interference length measuring device concerning the embodiment of the present invention in the circumference. 1 is a basic configuration diagram of an image forming apparatus including a heterodyne laser interferometer according to an embodiment of the present invention. It is a block diagram of the basic composition of the conventional heterodyne laser interferometer. It is a block diagram of the basic composition of the laser interference length measuring device which improves the conventional resolution.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heterodyne laser light source 2 Polarizing beam splitter 3, 4 Measuring mirror 5, 6 Measuring optical path 7, 8 1/4 wavelength plate 9, 10 Reflecting mirror 11 Calculation means 12 Beam splitter 13, 14 Aperture 15, 16 Photo detector 17, 18 Measurement signal circuit 19 Arithmetic circuit 20 Beam splitter 21 Photo detector 22 Reference signal circuit 23 Mirror 24, 25 Lens 30, 40 Measurement mirror 100 Heterodyne laser interferometer 101 Virtual line 102 Measured object 103 4, 4, 5 Mirror 200 Image Forming device 201 Image forming unit 202 Document image reading device 203 Recording medium feeding unit 210 Photosensitive drum 211 Charger 212 Writing device 213 Developing device 214 Transfer device 215 Fixing device 216 Discharge tray 217 Cleaning unit 220 Document 221 Light source 222 First mirror 223 First scanner 224 Second mirror 225 Third mirror 226 Second scanner 227 Reading optical system 228 Photoelectric conversion element 1000 Heterodyne laser interferometer 1001 Heterodyne laser light source 1002 Polarizing beam splitter 1003 Reference mirror 1004 Measurement Mirror 1005 Reference beam 1006 Measurement beam 1007, 8 1/4 wavelength plate 1009 Photo detector 1010 Measurement signal circuit 1019 Arithmetic circuit 1020 Beam splitter 1021 Photo detector 1022 Reference signal circuit 2000 Heterodyne laser interferometer 2001 Measurement object 2002, 3, 4 mirror

Claims (14)

In a heterodyne laser interferometer that measures the displacement of an object to be measured using laser light,
A heterodyne laser source that generates two linearly polarized laser beams with different planes of polarization orthogonal to each other;
A polarization beam splitter for separating the laser beam from the heterodyne laser light source into two measurement beams;
Two measuring mirrors which are fixed to the object to be measured in opposite directions on a virtual straight line;
Two measurement optical paths for guiding a measurement beam along the virtual straight line to the measurement mirror;
A quarter-wave plate disposed in each of the measurement optical paths;
Two reflecting mirrors positioned between the quarter-wave plate and the measuring mirror and reflecting a part of the cross section of the measuring beam;
Calculation of displacement corresponding to the difference between two beat signals of the beat signal of the interference light intensity by the measurement mirror and the beat signal of the interference light intensity by the reflection mirror by dividing the reflected light beam from the measurement mirror and the reflection mirror into two Computing means for performing
A heterodyne laser interferometer, comprising: The heterodyne laser interferometer of claim 1,
A heterodyne laser interferometer, wherein the polarizing beam splitter includes the quarter-wave plate in an integrated manner. The heterodyne laser interferometer according to claim 1 or 2,
The heterodyne laser interferometer is characterized in that the measurement mirror has a mirrored end face of the object to be measured. The heterodyne laser interferometer according to any one of claims 1 to 3,
The two reflection mirrors are provided with the same shape so as to reflect a part of the measurement beam in the measurement optical path and at the same position with respect to the optical axis of the measurement optical path. Long device. The heterodyne laser interferometer according to any one of claims 1 to 4,
A heterodyne laser interferometer, comprising a lens positioned between the reflection mirror and the measurement mirror, and condensing a measurement beam and irradiating the measurement mirror. The heterodyne laser interferometer of claim 5,
The heterodyne laser interferometer, wherein the lens is provided with the reflecting mirror formed on a part of an incident surface. The heterodyne laser interferometer according to claim 6,
The heterodyne laser interferometer, wherein the lens is provided with the reflecting mirror formed concentrically around an optical axis. The heterodyne laser interferometer according to claim 6,
The heterodyne laser interferometer is characterized in that the lens is provided with the reflecting mirror formed in a concentric circle centered on the optical axis at the periphery. The heterodyne laser interferometer according to any one of claims 1 to 8,
The heterodyne laser interferometer is characterized in that the calculation means includes a beam splitter that divides a reflected light beam from the measurement mirror and the reflection mirror into two. The heterodyne laser interferometer according to any one of claims 1 to 9,
The calculation means includes an opening that selectively transmits interference light from the two measurement mirrors from a reflected light beam, a photodetector that electrically detects interference light intensity transmitted through the opening, and an output of the photodetector A heterodyne laser interferometer, comprising a measurement circuit for generating a beat signal from a laser. The heterodyne laser interferometer according to any one of claims 1 to 10,
The calculation means includes an opening that selectively transmits interference light from the two reflecting mirrors from a reflected light beam, a photodetector that electrically detects interference light intensity transmitted through the opening, and an output of the photodetector A heterodyne laser interferometer, comprising a measurement circuit for generating a beat signal from a laser. The heterodyne laser interferometer of any one of claims 1 to 11,
The heterodyne laser interferometer is characterized in that the arithmetic means includes an arithmetic circuit that calculates a displacement corresponding to a difference between beat signals generated by the two measurement circuits. In an image forming apparatus for forming a toner recording image on a recording medium,
An image forming unit for forming a recorded image on a recording medium;
A heterodyne laser interferometer measuring device according to any one of claims 1 to 12,
An image forming apparatus comprising: The image forming apparatus according to claim 13.
The image forming unit forms a recorded image of toner by an electrophotographic image forming process.

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