JP6427857B2 - Displacement measuring device, displacement measuring method, and image forming apparatus - Google Patents

Description

  The present invention relates to a displacement measuring device, a displacement measuring method, and an image forming apparatus.

Measuring the speed and amount of movement of the surface of a rotating belt or the like is performed in various techniques.

For example, so-called tandem systems are the mainstream in color image forming apparatuses using an electrophotographic process in order to meet the demand for higher speed.

In the tandem color image forming apparatus, four photoconductors corresponding to toners of four colors (black, cyan, magenta, and yellow) are “arranged in parallel”.

Each color toner image formed on each photoconductor is finally superimposed on a recording medium such as paper (standard paper, postcard, cardboard, OHP sheet, etc.) to obtain a color image.

At that time, there are a direct transfer system in which each color toner image is directly superimposed on a recording medium and an intermediate transfer belt system.

In the intermediate transfer belt system, the toner images of the respective colors on the respective photoconductors are superimposed on the intermediate transfer belt and transferred to form a color image, and then transferred to a recording medium all at once.

In such a transfer, “color shift” occurs unless the conveying belt for feeding the recording medium is moved with high accuracy and the intermediate transfer belt is moved with high accuracy in the direct transfer method.

As a color image forming apparatus, there is known an ink jet type apparatus that forms a “color image by combining ink images of a plurality of colors” on a recording medium such as paper that moves in a fixed direction.

Even in such an ink-jet color image forming apparatus, color shift occurs unless the movement of the recording medium is controlled with high accuracy.

As described above, also in the image forming apparatus, in order to control the movement of the recording medium, the conveyance belt, and the intermediate transfer belt with high accuracy, it is necessary to measure the movement amount and movement speed thereof with high accuracy.

In an image forming apparatus, it has been proposed to use a speckle pattern for drive control of a recording medium, a conveyance belt, an intermediate transfer belt, and a photoreceptor (Patent Documents 1 to 3).

The speckle pattern is a random pattern generated by interference of light with reflected light or transmitted light when a coherent light such as laser light is irradiated onto a surface having fine irregularities.

It is known that when a surface irradiated with coherent light moves in the surface direction, the speckle pattern also moves.

Therefore, by measuring the displacement of the speckle pattern, the displacement (movement amount and movement speed) of the surface can be measured.

In this specification, “objects whose surface direction displacement is measured using speckle patterns”
Is called “dynamic test surface”.

Each of Patent Documents 1 to 3 discloses measurement of displacement of a dynamic test surface using a speckle pattern, but “influence of fluctuation in measurement environment temperature” is not considered.

The measurement environment temperature is a temperature related to the measurement of the displacement of the dynamic test surface.
Variations in the measurement environment temperature affect the measurement of the displacement of the dynamic test surface and cannot be ignored when high-precision measurement is required.

It is an object of the present invention to realize a displacement measuring apparatus that can easily reduce the influence of fluctuations in the measurement environment temperature in measuring the displacement of a dynamic test surface using a speckle pattern.

The displacement measuring apparatus of the present invention illuminates a dynamic test surface at a predetermined position using coherent light from an illumination optical system having a laser light source and a coupling lens as irradiation light, and detects detection light from the dynamic test surface. The light is guided to the image sensor through the imaging optical system, the speckle pattern by the dynamic test surface is acquired at a predetermined frame rate, and the cross-correlation between the speckle patterns acquired at a predetermined time interval is performed. based on the calculation result, the dynamic test surface, the displacement measuring device for measuring at least one of the moving distance and the moving speed, the imaging optical system includes, in order from the dynamic test surface side, the positive power of A first group, an aperture stop, and a second group having a positive power. The aperture stop is provided at a position that is the image side focal plane of the first group and the object side focal plane of the second group. is made, the said The light receiving surface of the image element is matched with a Gaussian surface by the imaging optical system of the dynamic test surface, a boiling surface of the dynamic test surface, and a Gaussian surface by the imaging optical system of the dynamic test surface; The distance: Db, the distance between the Gaussian surface and the light receiving surface of the image sensor: D , regardless of the variation of the measurement environment temperature in the measurement environment temperature change region , the condition:
(1) D / Db≈0
The illumination aspect of the dynamic test surface through the imaging optical system of the illumination optical system is defined so that the illumination optical system transmits light from the laser light source through the coupling lens. A first mirror that is a coherent parallel light beam, and each of the first group and the second group of the imaging optical system is composed of two or more lenses made of different materials, and holds the first group. A barrel, a third barrel that is slidable relative to the first barrel, and a second barrel that is slidable relative to the third barrel and holds the second group. One end of each of the first lens barrel and the third lens barrel is fixed to the image sensor .

In the displacement measuring apparatus of the present invention, when the condition (1) is satisfied, it becomes easy to reduce the influence of the fluctuation of the measurement environment temperature.

It is a figure for demonstrating embodiment. It is a figure for demonstrating one Embodiment of a displacement measuring device. It is a figure for demonstrating an Example. It is a figure for demonstrating an Example. It is a figure for demonstrating the principle of the displacement measurement by a speckle pattern. It is a figure for demonstrating one Embodiment of an image forming apparatus. It is a figure for demonstrating the specific example of a displacement measuring device. It is a figure for demonstrating another specific example of a displacement measuring device. It is a figure for demonstrating the other specific example of a displacement measuring device. It is a figure for demonstrating the other specific example of a displacement measuring device. It is a figure for demonstrating the other specific example of a displacement measuring device. It is a figure for demonstrating the other specific example of a displacement measuring device. It is a figure for demonstrating the other specific example of a displacement measuring device.

Hereinafter, embodiments will be described.
The object to be measured by the displacement measuring device is “at least one of the moving distance and the moving speed” of the dynamic test surface. In the following description, the moving distance of the dynamic test surface is referred to as “detection length”.

If the moving speed of the dynamic test surface is measured, the “detection length” has a relationship given by its time integration. Conversely, if the detection length is measured, the moving speed is given by its time derivative.

The detection length is not limited to the movement distance in the uniaxial direction of the dynamic test surface, but also refers to the movement distance in the biaxial direction.

In the measurement of “detection length”, the influence of fluctuations in the measurement environment temperature includes the following three factors: A to
C.

A. Image plane (Gaussian plane) of image formation by imaging optical system on dynamic test surface and "photosensitive surface of imaging optical system"
Variation due to temperature change in the interval between

B. Fluctuation due to temperature change in the distance from the image plane formed by the imaging optical system of the dynamic test surface to the “imaging plane of the illumination optical system” by the coupling lens of the illumination optical system and the imaging optical system.

  C. Imaging magnification of imaging optical system: Fluctuation due to temperature change of M.

  Therefore, in measuring the detection length, it is necessary to consider these three elements: A to C.

Movement speed: Coherent light is applied to the dynamic test surface moving at V1, and the imaging optical system
Consider a state in which an image of a dynamic test surface is formed on a light receiving surface of an image sensor.

Since speckles are generated very close to the dynamic test surface, a “speckle pattern” is imaged on the light receiving surface of the image sensor.

At this time, it is known that the movement speed V2 of the speckle pattern imaged by the image sensor is given by the following expression (a) where M is the imaging magnification of the imaging optical system (Non-patent Document 1).

(A) V2 / V1 = M {(D / Db) -1}
In Expression (a), “D” is the distance between the Gaussian plane (imaging plane) of the image obtained by the imaging optical system on the surface of the dynamic test surface and the light receiving surface of the imaging device.

“Db” is the distance between the boiling surface of the dynamic test surface and the Gaussian surface of the dynamic test surface by the imaging optical system.

The position of the “boiling surface” is the position of the “imaging surface of the laser light source” obtained through the coupling lens of the illumination optical system and the imaging optical system.

In the formula (a), what is affected by the measurement environment temperature is “interval: D (above (A))”,
“Distance: Db (above (B))” and “imaging magnification: M”.

Prior to the description of the embodiments of the invention, the above description will be described with reference to a specific optical arrangement example.

Please refer to FIG. In FIG. 5, reference numeral 1 is a laser light source, reference numeral 2 is a coupling lens,
Reference numeral 3 denotes an illumination optical system, reference numeral Ob denotes a dynamic test surface, and reference numeral 5 denotes an imaging optical system.

Reference numeral 7A denotes a light receiving surface of the image sensor. Hereinafter, the laser light source 1 is also simply referred to as the light source 1.

In FIG. 5, when the light source 1 of the illumination optical system 3 emits light, “laser light that is coherent light” is emitted, and the beam form is changed by the coupling lens 2.

  In FIG. 5, the laser beam that has passed through the coupling lens 2 becomes a “parallel beam”.

  This parallel light flux becomes “irradiation light” and illuminates the dynamic test surface Ob.

Light (detection light) reflected by the dynamic test surface Ob is imaged by the imaging optical system 5 using the Gaussian surface GM as an imaging surface. Thereby, the speckle pattern by the dynamic test surface Ob is imaged.

  In FIG. 5, “dotted lines” indicate the imaging light rays of this imaging.

On the other hand, the laser light from the light source 1 forms an “image of the light source 1” by the coupling lens 2 and the imaging optical system 5. This imaging surface is the boiling surface BM.

As shown in FIG. 5, the distance between the Gaussian surface GM and the light receiving surface 7A of the image sensor is “D”, and the Gaussian surface G
The distance between M and the boiling surface BM is “Db”.

In FIG. 5, the Gaussian surface GM and the light receiving surface 7A are drawn apart from each other, but the designed Gaussian surface GM is made to coincide with the light receiving surface 7A. That is, “D” in design is 0.

Actually, the value of “D” fluctuates due to an assembly error of each part of the displacement measuring device or a change with time. Further, as will be described later, the value of “D” also fluctuates due to a change in the measurement environment temperature.

However, even if it fluctuates in this way, the fluctuation range of the value of “D” is as small as about 100 μm at most.

Considering the ratio of the distance: D to the distance: Db: D / Db, as described above, “D =
“0” is satisfied.

Therefore, if the distance: Db is set to be “finite”, “D / Db≈0” stands upright.

If “D / Db≈0” holds, the above formula (a) is
(B) V2 / V1 = −M
It becomes.

That is, the change in the measurement environment temperature affects only the imaging magnification M of the imaging optical system 5.
Therefore, it is only necessary to consider the influence of temperature fluctuations on the imaging optical system 5 among the four parts “light source 1, coupling lens 2, imaging optical system 5, imaging element 7” that affect the detection length.

That is, if the “magnification due to variation in the measurement environment temperature” of the imaging magnification M by the imaging optical system 5 is reduced, the moving speed Ob of the dynamic test surface Ob can be accurately measured.

That is, among the four parts of the light source 1, the coupling lens 2, the imaging optical system 5, and the imaging element 7, only the error in the detection length by the imaging optical system 5 needs to be considered.

  Therefore, the design of the displacement measuring device is greatly simplified.

As described above, the value of “D” is 0 by design, and is about 100 μm or less even in consideration of the measurement environment temperature and changes with time.

  On the other hand, the distance: Db changes under various conditions.

For example, when the irradiation light emitted from the illumination optical system 3 becomes divergent, the boiling surface BM moves to the Gaussian surface GM side, and the distance: Db decreases.

In order for the above formula (b) to hold as a good approximation of the formula (a), it is better that “distance: Db” is larger.

The coupling lens 2 of the illumination optical system 3 has a positive power. The imaging optical system 5 also has positive power.

Therefore, the positive power of the combination of the coupling lens 2 and the imaging optical system 5 is adjusted, and the minimum value of “the fluctuation area of the boiling surface” due to the fluctuation of the measurement environment temperature is set to, for example, “1 m”.

In this case, “D / Db” even if the interval D is 100 μm due to a change in the measurement environment temperature or the like.
The maximum value of fluctuation of “1/10000” is considered to be negligible in the equation (a).

However, when the accuracy required for displacement measurement becomes extremely high, even the above “1/10000”
A case where it cannot be ignored in equation (a) is also conceivable.

Even in such a case, “distance: minimum value of Db fluctuation” due to fluctuation of the measurement environment temperature is several m.
If it is about, preferably about 10 m, sufficient measurement accuracy can be secured.

  The present invention has a characteristic feature in the configuration of the imaging optical system.

That is, the imaging optical system includes, in order from the dynamic test surface side, a first group of positive power, an aperture stop, and a second group of positive power.

The aperture stop is provided at a position that is the image side focal plane of the first group and the object side focal plane of the second group.

Then, the light receiving surface of the image sensor is matched with the “Gaussian surface by the imaging optical system” of the dynamic test surface.

FIG. 1A shows an example of this case following FIG. In order to avoid complications, common signs are used for those that are not likely to be confused.

In the example shown in FIG. 1A, the imaging optical system has a two-group configuration. In other words, the imaging optical system includes a first group 51, a second group 52, and an aperture stop S.
Both the first group 51 and the second group 52 have positive power.

In FIG. 1A, the irradiation light emitted from the illumination optical system 3 is a parallel light flux.
The dynamic test surface Ob matches the object side focal plane of the first group 51.

When the dynamic test surface Ob is illuminated by the irradiation light, the detection light from the dynamic test surface Ob is the first group 5
1 converges on the object side focal position of the second group 52.

  Then, it becomes divergent light and passes through the second group 52 to become a parallel light flux.

That is, in the embodiment shown in FIG. 1A, the dynamic test surface Ob is illuminated at a predetermined position using coherent light from the illumination optical system 3 having the light source 1 and the coupling lens 2 as irradiation light.

The “predetermined position” is, by design, “a position that is conjugate with the light receiving surface 7A of the image sensor 7” by the imaging optical system.

Then, the reflected light from the dynamic test surface Ob is guided as detection light to the image sensor 7 through the imaging optical system, and imaged on the light receiving surface 7A.

The illumination optical system 3 converts the coherent light from the laser light source 1 into a parallel beam by the coupling lens 2.

The imaging optical system includes a first group 51 having a positive power, an aperture stop S, and a second group 52 having a positive power in order from the dynamic test surface Ob side.

The aperture stop S is provided at a position that is the image side focal plane of the first group 51 and the object side focal plane of the second group 52.

The light receiving surface 7A of the image sensor 7 is matched with the “Gaussian surface GM by the imaging optical system” of the dynamic test surface Ob.

That is, the displacement measuring apparatus shown in FIG. 1A uses coherent light from an illumination optical system 3 having a laser light source 1 and a coupling lens 2 as irradiation light.

Then, the dynamic test surface Ob is illuminated at a predetermined position by the irradiation light, and the detection light from the dynamic test surface Ob is guided to the image sensor via the imaging optical system.

A speckle pattern by the dynamic test surface Ob is acquired at a predetermined frame rate, and a cross-correlation operation between the speckle patterns acquired at a predetermined time interval is performed.

Based on the calculation result, the moving distance (detection length) and moving speed: V1 of the dynamic test surface Ob are measured.

The “imaging optical system” includes, in order from the dynamic test surface Ob side, the first group 51 having a positive power and the aperture stop S.
The second group 52 of positive power is constituted.

The aperture stop S is provided at a position that is the image side focal plane of the first group 51 and the object side focal plane of the second group 52.

The light receiving surface 7A of the image sensor 7 is matched with the “Gaussian surface GM by the imaging optical system” of the dynamic test surface Ob.

Of course, the coincidence between the light-receiving surface 7A and the Gaussian surface GM is a “design” story, and in reality, it is not a precise coincidence due to various tolerances such as manufacturing, but the divergence amount between them is at most about 100 μm.

  That is, the value of “D” can be substantially 0 even in the embodiment of FIG.

  In FIG. 1A, a “dotted line” indicates an imaging light ray for imaging.

The laser light from the light source 1 forms an image by the coupling lens 2 and the imaging optical system. In this case, the imaging light is emitted from the second group 52 of the imaging optical system “parallel to the optical axis”.

For this reason, the position of the boiling surface BM, which is the image formation plane, is infinitely designed. Therefore,
The value of “Db” is infinite.

The value of “Db” is extremely large, and the value of “D” is as described above even when manufacturing errors are taken into consideration.
It is at most about 100 μm or less.

  That is, “D / Db” is substantially zero.

Therefore, the variation factor of the detection length is only the variation of the imaging magnification: M.
That is, it is only necessary to consider “the influence of fluctuations in the measurement environment temperature on the imaging optical system” among the four parts of “light source, coupling lens, imaging optical system, imaging device” that affect the detection length.

That is, as the “measurement environment temperature”, a temperature in the vicinity of the imaging optical system including the imaging optical system may be considered.

Of the four parts of the light source, the coupling lens, the imaging optical system, and the imaging device, only the detection length error due to the imaging optical system needs to be taken into account, so that the design of the displacement measuring apparatus is greatly simplified.

If it can be considered that “D / Db = 0”, if the moving speed of speckle pattern: V2 is obtained by cross-correlation calculation, the moving speed of dynamic test surface Ob: V1 is obtained as “−V2 / M”. .

The movement distance, which is the detection length, can be obtained by calculating “integration over time” on the movement speed: V1.

The imaging optical system in FIG. 1A is “telecentric on both the object side and the image side”, and the dynamic test surface O
b and the “imaging magnification due to defocus: variation in M” of the light receiving surface 7A are small.

  Accordingly, the influence of defocus on the detection length measurement is small.

As described above, the value of the distance: D is 0 in design, and can be set to a value smaller than 100 μm even if the dimensional tolerance of the actual machine is included.

Even if the positional relationship between the light source 1 and the coupling lens 2 in the illumination optical system 3 fluctuates at the component tolerance level, the variation of the distance: Db can be on the order of several meters to several hundred meters.

Even if D = 100 μm and Db = 10 m, D / Db is 1/100000,
The influence on the detection length error is as low as 0.001% or less in terms of percentage.

Accordingly, it is possible to suppress the influence of the fluctuation of the luminous flux form of the illumination light due to “the fluctuation of the positional relationship between the light source 1 and the coupling lens 2” in the illumination optical system 3 and to suppress the fluctuation of the “detection length”.

In the displacement measuring apparatus according to the present invention, the imaging optical system is provided with “both object side space and image side space” telecentricity.

For this reason, even if the dynamic test surface Ob is defocused in the optical axis direction of the imaging optical system, the imaging magnification: M of the imaging optical system hardly varies.

Similarly, even when the image pickup device 7 is defocused in the optical axis direction of the image pickup optical system, the change in the image pickup magnification: M hardly occurs.

Since these effects can be obtained synergistically, the “variation in detection length” can be further reduced as compared to “when using an imaging optical system having a one-group configuration” described with reference to FIG.

  FIG. 2 is a diagram for explaining one embodiment of the displacement measuring apparatus.

In FIG. 2, reference numeral 0 is a moving body, reference numeral 1 is a laser light source, reference numeral 2 is a coupling lens,
Reference numerals L51 and L52 denote lenses, and reference numeral 6 denotes a lens barrel.

  The lens L51 constitutes the first group 51, and the lens L52 constitutes the second group 52.

Reference numeral 7 denotes an image sensor, reference numeral 71 denotes a cover glass of the image sensor 7, and reference numeral 7 </ b> A denotes a light receiving surface of the image sensor 7.

Further, reference numerals 81 and 82 denote housings, reference numeral 83 denotes a bottom plate, reference numeral 9 denotes a calculation unit, and reference numeral 10 denotes a light source driving unit.

  A laser light source 1 (also simply referred to as a light source 1) is a semiconductor laser (hereinafter also referred to as an LD), and emits a divergent laser beam (which is coherent light).

  The emitted divergent laser light is weakened by the coupling lens 2.

In this embodiment, the divergent laser light is converted into a parallel light beam by the coupling lens 2 by design, and becomes irradiation light.
The coupling lens 2 and the light source 1 constitute “an essential part of the illumination optical system 3”. That is, the illumination optical system has a light source 1 and a coupling lens 2.

  The irradiation light illuminates the surface of the moving body 0 as shown in FIG.

The moving body 0 is, for example, the “intermediate transfer belt” described above, and has a predetermined speed V1 in the direction of the arrow.
It is supposed to move in.

The “surface illuminated by the irradiation light” of the moving body 0 is the dynamic test surface Ob, and the amount of movement is the “detection length”.

In the example in the description, the illumination aspect of the dynamic test surface by the illumination optical system 3 is “illumination with a parallel light beam” as described above.

The lenses L51 and L52 together with the aperture stop S constitute an “imaging optical system” and are assembled to the lens barrel 6.

The lens barrel 6 is held by housings 81 and 82 and is integrated with the light source 1 and the coupling lens 2 forming the illumination optical system 3.

  An imaging element 7 is fixedly provided at the position of the lower end of the lens barrel 6 in the drawing.

The illumination optical system 3, the lenses L51 and L52, which are the imaging optical system, the aperture stop S, and the imaging element 7 are in a predetermined positional relationship while being held in the housings 81 and 82.

The bottom plate 83 is integrated with the housings 81 and 82, and the arithmetic unit 9 and the light source driving unit 10 are attached to the outer surface thereof.
As the bottom plate 83, a “PCB substrate” can be preferably used.

Thus, the housings 81 and 82 define the positional relationship between the illumination optical system 3, the imaging optical system, and the imaging element 7, and are integrated with the bottom plate 83 to package the displacement measuring device.

The distance between the packaged displacement measuring device and the dynamic test surface Ob is controlled to a predetermined size by a “spacer” or the like.

The calculation unit 9 performs a predetermined calculation based on the output of the image sensor 7, that is, a well-known “cross-correlation calculation”.
And the detection length is calculated by calculation.

As the arithmetic unit 9, it is preferable to use “FPGA” that can appropriately rewrite the program contents, and FPGA is also assumed in the embodiment being described.

As the light source driving unit 10, a “LD driving driver IC” that drives the LD that is the light source 1 can be used. The driving by the light source driving unit 10 is also controlled by the calculation unit 9.

In FIG. 2, the light source 1 is driven and blinked by a light source driving unit 10 that is electrically connected. The displacement measurement is performed as follows.

The light source 1 is turned on to emit irradiation light from the illumination optical system 3, and the dynamic test surface Ob is illuminated at a predetermined position.

As described above, the “predetermined position” is a “position that is conjugate with the light receiving surface 7A of the image sensor 7” by the imaging optical system.

Then, the reflected light from the dynamic test surface Ob is detected as light and guided to the light receiving surface 7A of the image sensor 7 by the imaging optical system using the lenses L51 and L52 and the aperture stop S to form an image.

By this imaging, a speckle pattern formed by the dynamic test surface Ob is imaged on the light receiving surface 7A, and the dynamic test surface Ob moves at a moving speed V2 corresponding to the moving speed V1.

The image sensor 7 acquires a speckle pattern by the dynamic test surface Ob at a “predetermined frame rate”.

The “predetermined frame rate” can be appropriately selected within a range of several tens to several thousand, for example.

Then, the calculation unit 9 performs a cross-correlation calculation between speckle patterns acquired at a predetermined time interval (1 / frame rate).
Based on this calculation result, the moving speed Ob of the dynamic test surface Ob is measured.

Actually, the movement speed: V2 of the speckle pattern is determined, and based on this movement speed,
The moving speed V1 of the dynamic plane surface Ob is determined.

The “detection length” that is the movement distance can be obtained by time integration of the movement speed V1 determined in this way.

The “cross-correlation calculation” is a calculation that is already well known by Non-Patent Document 1, for example. The detection length can be calculated based on the movement amount of the “correlation peak” by this calculation.

  As an example of the cross-correlation calculation, the following is well known.

That is, two speckle patterns imaged at a predetermined frame rate are “f1” and “f2”.

Speckle pattern: F [f1] and F [f2] are Fourier transform operations for f1 and f2.
And the cross-correlation calculation is represented by “★”.

At this time, the cross-correlation calculation of the speckle patterns: f1 and f2 is given by the following calculation expression.

f1 * f2 ^* = F− ¹ [F [f1] · F [f2] ^* ]
“*” Represents a complex conjugate.

In the displacement measuring apparatus shown in FIG. 2, the arithmetic unit 9 and the light source driving unit 10 are mounted on the same bottom plate 83 and integrated with the housings 81 and 82 to realize miniaturization.

  Thus, the miniaturized displacement measuring apparatus includes a plurality of heat generating parts as its constituent elements.

In other words, heat generated by the image sensor 7, the LD driving driver IC (light source driving unit 10), the FPGA (calculating unit 9), the LD (light source 1), and the like can be considered as the cause of the rise of the “measurement environment temperature”.

However, as described above, if the distance: Db and the interval: D satisfy the condition (1), that is, “D / Db≈0”, the influence of the change in the measurement environment temperature is the imaging magnification of the imaging optical system: M It is only the fluctuation of.

The distance: Db and the interval: D can satisfy the condition (1) by setting “illumination mode in which the illumination optical system illuminates the dynamic test surface via the imaging optical system”. .

For example, as in the embodiment described above, the distance (Db) and the interval (D) can satisfy the condition (1) regardless of the “change in the measurement environment temperature”.

Therefore, by reducing the “variation amount due to the change in the measurement environment temperature” of the imaging magnification: M of the image pickup optical system, the variation in the accuracy of the displacement measurement due to the change in the measurement environment temperature can be reduced.

Imaging magnification of the imaging optical system: M is “insensitive to temperature change (not easily changed)”
It is possible to configure an imaging optical system.

For example, the lenses L51 and L52 constituting the first group 51 and the second group 52 are made of a glass material having a small “refractive index temperature variation” and “volume temperature variation”.

  The lens barrel 6 is also formed of a material having a sufficiently small volume expansion coefficient.

In this way, it is possible to realize an imaging optical system in which the variation amount of the imaging magnification: M is small with respect to the variation of the measurement environment temperature.

However, when high accuracy is required for displacement measurement, it is conceivable that such an “imaging optical system with a small variation amount of M: M” is insufficient.

  In the embodiment described below, in consideration of this point, a “group interval adjusting mechanism” is provided.

The group interval adjustment mechanism adjusts the group interval between the first group and the second group in accordance with the amount of variation of the focal lengths of the first group and the second group constituting the imaging optical system due to the variation in the measurement environment temperature. .

  The group interval adjustment between the first group and the second group is performed so that the “magnification due to the change in the measurement environment temperature” of the imaging magnification M is suppressed.

The imaging magnification of the imaging optical system is constant in the paraxial region, but in the actual imaging optical system,
It varies slightly depending on the height of the real image (referred to as “real image height”).

In the following examples, five object heights are taken, and it is examined how the average value of the magnifications at the five real image heights with respect to these five object heights changes depending on the measurement environment temperature.

  Examples will be described below.

As shown in FIG. 1B, the first group 51 of the imaging optical system is composed of two lenses L1 and L2, and the second group 52 is composed of two lenses L3 and L4.

The lenses L1 and L2 are bonded together to form the first group 51, and the lenses L3 and L4 are bonded together to form the second group 52.

The lens L1 on the object side of the first group 51 has a focal length of 5.991 mm, and the glass material is “E-C8” manufactured by HOYA.
The lens L2 on the aperture stop S side of the first group 51 has a focal length of −11.838 mm, and the glass material is “PCD4” manufactured by HOYA.

The lens L3 on the aperture stop S side of the second group 52 has a focal length of −9.471 mm, and the glass material is H.
The product was “PCD4” manufactured by OYA.

The lens L4 on the image side of the second group 52 has a focal length of 4.793 mm, and the glass material is made by HOYA.
E-C8 ".
Focal length of the first group 51: f1 is 12.5 mm, focal length of the second group: f2 is 10.0 mm
It is. These are values at a measurement environment temperature: 20 ° C.

The image-side focal position of the first group 51 and the object-side focal position of the second group 52 are matched, and an aperture stop S is disposed at the matching position of these focal points.

If this imaging device is used as shown in FIG. 1A, the dynamic test surface Ob is positioned at the object-side focal position of the first group 51, and the light receiving surface 7A is matched with the Gaussian surface, the image is formed. The magnification is 0.8.

In the embodiment, the distance relationship from the dynamic test surface Ob to the light receiving surface 7A is determined as shown in FIG.

  Moreover, the change range of the measurement environment temperature was determined as follows.

That is, at room temperature: 20 ° C., immediately after the current of the displacement measuring device is input, it is considered that the temperature rise of the displacement measuring device by the heat source is almost zero, and the temperature of the imaging optical system is also 20 ° C.
Room temperature: At an ambient temperature of 20 ° C., the temperature of the imaging optical system was 85 ° C. when an electric current was applied and the temperature rise of the displacement measuring device by the heat source was saturated.

Changes in the focal lengths of the first group 51 and the second group 52 when the temperature of the imaging optical system (measurement environment temperature) in this example was changed from 20 ° C. to 85 ° C. were as follows.

That is, the variation amount of the focal length: f1 is −2 × 10 ⁻² (μm), and the variation amount of the focal length: f2 is −2 × 10 ⁻² (μm).

That is, the amount of change in the focal lengths of the first group 51 and the second group 52 is extremely small, and is substantially “0”.
It can be regarded as.

Note that the cause that the focal lengths of the first group 51 and the second group 52 fluctuate due to the change of the measurement environment temperature is that “the emission wavelength of the light source 1 changes with temperature”.

In the example in the description, “wavelength: 649.9 nm to 668.532 nm” is assumed as the variation range of the emission wavelength of the light source 1 in the change region of the measurement environment temperature.

“Change in focal length with respect to wavelength fluctuation in the above range” of the first group 51 and the second group 52 of the embodiment
Is so small that it can be ignored.

Even with the “very small change in focal length” as described above, the magnification of the imaging optical system slightly changes.

In addition, high measurement accuracy may be required to such an extent that such a slight change in magnification causes an “error given to the detection length”.

The inventors have changed the first group 51 and the second group 5 in the imaging optical system in accordance with changes in the measurement environment temperature.
It was found that a change in magnification can be suppressed by adjusting the group interval with 2.

That is, the real image height corresponding to the maximum of the object height is normalized to 1.0, and other real image heights are compared with the image height ratio: 0.
The average of the magnifications at the image height ratios at these five points was determined as 2, 0.4, 0.6, and 0.8.

Then, the reference temperature at these image height ratios: the magnification at 20 degrees and the measurement environment temperature: the average change rate (%) of the magnification at 85 ° C. were obtained.

At the measurement environment temperature: 85 ° C., the group interval between the first group 51 and the second group 52 is set to “design standard 0”.
”In increments of 0.005 mm.

At this time, it was found that the group interval, the change amount of the magnification (the change amount of the average value), and the group interval “change in a linear relationship” as shown in FIG.

In FIG. 3, the “change amount of magnification” on the vertical axis indicates the reference temperature: 20 ° C. and the measurement environment temperature: 85 ° C.
The change rate (%) of the magnification at (the average value of the magnification at the five image height ratios).

  The horizontal axis in FIG. 3 represents the amount of change in the group interval between the first group 51 and the second group 52 of the imaging optical system.

If the vertical axis amount is y and the horizontal axis amount is x, the straight line in FIG.
y = 5.5016x-0.1139
It is expressed.

  Referring to FIG. 3, the value of x at which y becomes 0 is “about +20.71 μm”.

Therefore, when the measurement environment temperature is 85 ° C., if the group interval is longer than the design value by 20.71 μm, the change in the average magnification can be made extremely close to zero.

At this time, it was confirmed that the “magnification average fluctuation of the real image height” of the imaging optical system caused by the fluctuation of the measurement environment temperature of the displacement measuring apparatus can be 0.01% or less.

As described above, in the displacement measuring apparatus according to the present invention, since the parameter (1): D / Db = 0, the absolute values of “magnification change rate and detection length change rate” are equal.

  Therefore, the variation in detection length can be made 0.01% or less.

  The displacement measuring apparatus in the embodiment has a “group interval adjusting mechanism”.

The “group interval adjusting mechanism” is a group between the first and second groups in accordance with the variation amount of the focal lengths of the first group 51 and the second group 52 constituting the imaging optical system due to the variation of the measurement environment temperature. Adjust the interval.

The adjustment of the group interval by the group interval adjustment mechanism is performed so as to suppress the average fluctuation of the magnification at a plurality of real image heights of the speckle pattern due to the fluctuation of the measurement environment temperature.

In the embodiment being described, when the measurement environmental temperature changes from 20 ° C. to 85 ° C., the first
The group interval is adjusted so that the group interval of the second group is increased by +20.71 μm.

FIG. 4 shows an embodiment of the group interval adjusting mechanism. The group interval adjusting mechanism of the embodiment adjusts the group interval as follows.

  FIG. 4 shows a holding mechanism that holds the imaging optical system.

  This holding mechanism is configured by a combination of lens barrels.

In FIG. 4, reference numerals 51, 52, and S denote the first group, the second group, and the aperture stop as described above.

Each of the first group 51 and the second group 52 is depicted as a single lens for the sake of simplicity of illustration, but in the embodiment being described, each has a configuration in which two lenses are bonded together as described above.

When the measurement ambient temperature is 20 ° C., the focal length of the first group 51: f1 is 12.5 mm.
The focal length of the second group: f2 is 10.0 mm.

The positional relationship among the dynamic test surface Ob, the light receiving surface 7A of the light receiving element, the first group 51, the second group 52, and the aperture stop S when the measurement environment temperature is the reference temperature is as shown in FIG. It is.

The focal lengths of the first group 51 and the second group 52 are as follows when the measurement environmental temperature is 85 ° C.
Each changes by −2 × 10 ⁻² μm.

In FIG. 4, reference numeral 61 denotes a first lens barrel, reference numeral 62 denotes a second lens barrel, and reference numeral 63 denotes a third lens barrel.

The first lens barrel 61 holds the first group 51, and the second lens barrel 62 holds the second group 52. Third
The lens barrel 63 is provided between the first lens barrel 61 and the second lens barrel 62.

The first lens barrel 61 is held by housings 81 and 82 shown in FIG.
The first lens barrel 61 can slide relative to the housings 81 and 82, but is fixed to the housings 81 and 82 in the “direction of the position FX holding the first group 51” in the axial direction.

Accordingly, the first lens barrel 61 is thermally expanded and contracted by a change in the measurement environment temperature, and the housing 81,
Although it slides in the axial direction with respect to 82, the first group 51 is not displaced.
The open aperture stop S is also fixedly held by the first lens barrel 61.

The third lens barrel 63 is fitted on the inner periphery of the first lens barrel 61.
The second lens barrel 62 is fitted on the inner periphery of the third lens barrel 63. The second lens barrel 62 can slide with respect to the third lens barrel 63.

  However, the upper end portion of the second barrel 62 is fixed to the upper end portion of the third barrel 63.

In both the first lens barrel 61 and the third lens barrel 63, the lower end portion in the figure is fixed to the image sensor 7.

As shown in FIG. 4, the distances Z1, Z2, and Z3 are set with reference to the contact portions of the first lens barrel 61, the third lens barrel 63, and the image sensor 7.
A distance: Z1 is a distance from the contact portion to the first group 51, and a distance: Z2 is a distance from the upper end of the third lens barrel 63 to the second group 52.

  Distance: Z3 is a distance from the contact portion to the upper end portion of the third barrel 63.

The linear expansion coefficients of the respective materials constituting the first lens barrel 61, the second lens barrel 62, and the third lens barrel 63 are α1, α2, and α3, respectively.

Then, when the measurement environment temperature is raised from 20 ° C. to 85 ° C., the linear expansion amounts of the distances Z1, Z2, and Z3 are 65 · α1 · Z1, 65 · α2 · Z2, 65 · α3 · Z3.

Reference measurement environment temperature: At 20 ° C., the group interval between the first group 51 and the second group 52 is
Z1- (Z3-Z2) = Z1 + Z2-Z3
It is.

Therefore, when the measurement environment temperature is 85 ° C., the group interval is
Z1 (1 + 65 · α1) + Z2 (1 + 65 · α2) −Z3 (1 + 65 · α3)
It is.

Therefore, the change in group spacing: ΔL is
ΔL = 65 (α1 · Z1 + α2 · Z2−α3 · Z3)
It becomes.

65 · α1 · Z1 = ΔZ1, 65 · α2 · Z2 = ΔZ2, 65 · α3 · Z3 = ΔZ3,
ΔL = ΔZ1 + ΔZ2−ΔZ3
It is.

  In the example being described, this change amount: ΔL was set to +20.71 μm.

That is, the first lens barrel 61 and the third lens barrel 63 are both formed of “SUS430”, and the second lens barrel 62 is formed.
Was formed from “polyamideimide”.

The linear expansion coefficient (unit: 1 / K K is Kelvin temperature) of these materials is “1.04 × 10 ⁻⁵ ” for SUS430 and “3.8 × 10 ⁻⁵ ” for polyamideimide.

That is, α1 = α3 = 1.04 × 10 ⁻⁵ (1 / K) and α2 = 3.8 × 10 ⁻⁵ (1 / K).

  Based on this, the distances: Z1 to Z3 were set as follows.

Z1 = 27.060mm, Z2 = 0.419mm, Z3 = 21.78mm
As a result, ΔZ1 = 18.29 μm with respect to the change in the measurement environment temperature from 20 ° C. to 85 ° C.
m, ΔZ2 = 7.805 μm, and ΔZ3 = 5.381 μm were obtained.

That is, ΔZ1 + ΔZ2−ΔZ3 = + 20.71 μm
Was able to be realized.

As a result, the “average rate of change in magnification at the five real image heights” is set to “−1.54 × 10 ^−
6 (%) ”.

As already explained, since “D / Db = 0” is satisfied in the embodiment, the magnification is:
The change rate of M is equal to the change rate of the detection length.

Therefore, the variation of the detection length could be −1.54 × 10 ⁻⁶ (%).
This can be regarded as substantially “the variation in the detection length was zero”.

When the displacement measuring apparatus of the embodiment is actually manufactured, the “detection length error due to the dimensional tolerance between the manufacturable lens barrel part and the lens part” is larger than the above-mentioned design median value.

However, the detection length error due to this dimensional error is "about + 0.008% to -0.005%"
Therefore, it can be said that the actual machine performance at a manufacturable tolerance level is also excellent.
Since the dimensional tolerance is 10 μm, the “Newton number” of lens parts is 3 or less, and the grade of glass material is “Class 2”, it is a sufficiently manufacturable tolerance.

The displacement measuring apparatus described in the above embodiment uses coherent light from the illumination optical system 3 having the laser light source 1 and the coupling lens 2 as irradiation light.

The illumination light illuminates the dynamic test surface Ob at a predetermined position, and guides the detection light from the dynamic test surface Ob to the image sensor 7 via the imaging optical system.

The image sensor 7 acquires a speckle pattern by the dynamic test surface Ob at a predetermined frame rate, and performs a cross-correlation calculation between the speckle patterns acquired at a predetermined time interval.

Based on the calculation result, at least one of the moving distance and the moving speed of the dynamic test surface Ob is measured.

The imaging optical system includes a first group 51 having a positive power, an aperture stop S, and a second group 52 having a positive power in order from the dynamic test surface Ob side.

The aperture stop S is provided at a position that is the image-side focal plane of the first group 51 and the object-side focal plane of the second group 52.

The light receiving surface 7A of the image sensor 7 is matched with the Gaussian surface GM by the imaging optical system of the dynamic test surface Ob.

The distance between the boiling surface BM of the dynamic test surface Ob and the Gaussian surface GM of the dynamic test surface by the imaging optical system: Db, the distance between the Gaussian surface GM and the light receiving surface 7A of the image sensor: D is a condition ( The “illumination mode of the dynamic test surface through the imaging optical system” is defined so as to satisfy 1).

In the embodiment of the displacement measuring apparatus described above, the first group 51 and the second group 52 of the imaging optical system are used.
Are composed of two or more lenses L1, L2, L3, and L4 made of different materials.

The distance: Db and the interval: D are the conditions:
(1) D / Db≈0
Satisfied.

In the above embodiment, the group spacing of the first and second groups is adjusted according to the amount of fluctuation due to the variation in the measurement environment temperature of the focal lengths of the first group 51 and the second group 52 constituting the imaging optical system. Adjust with the mechanism.

The group interval adjustment mechanism suppresses fluctuations in the “average magnification at a plurality of real image heights” of the speckle pattern due to fluctuations in the measurement environment temperature.

The group interval adjusting mechanism of the embodiment has a plurality of lens barrels including at least a first lens barrel 61 that holds the first group 51 and a second lens barrel 62 that holds the second group 52.

The first lens barrel 61 and the second lens barrel 62 have different linear expansion coefficients, and one end of each of the first lens barrel 61 and the second lens barrel 62 is fixed to the image sensor 7.

And by the expansion and contraction of the plurality of lens barrels accompanying the change in the measurement environment temperature, the average change in magnification at the plurality of real image heights of the speckle pattern due to the change in the measurement environment temperature is suppressed.

In the displacement measuring apparatus of the embodiment, the group interval adjusting mechanism includes a first lens barrel 61 that holds the first lens group 51, a third lens barrel 63 that can slide with respect to the first lens barrel 61, and a third mirror. A second lens barrel 62 that holds the second group 52 and that can slide with respect to the tube 63 is provided.

  One end of the first lens barrel 61 and the third lens barrel 63 is fixed to the image sensor 7.

By the expansion and contraction of the first lens barrel 61 to the third lens barrel 63 accompanying the variation in the measurement environment temperature, the average variation of the magnifications of the plurality of real image heights of the speckle pattern due to the variation in the measurement environment temperature is minimized.

1st group 51 and 2nd group 5 which comprise the image sensor used for the above-mentioned example of a displacement measuring device.
2, the change of the focal length with respect to the maximum change of the measurement environment temperature is 0.001% or less of the focal length.

As is clear from the above description, the first lens barrel 61 and the third lens barrel 63 used in the embodiment are formed of the same material.

Therefore, these may be integrated as one unit without being separated.
The number of lens barrels used to hold the first group and the second group may be further increased to 4 or more. If it does in this way, the freedom degree of the combination of the material from which a linear expansion coefficient differs will increase.

As a result, the group interval can be easily adjusted.
Although the embodiment of the displacement measuring apparatus has been described above, a specific configuration example of the first to third lens barrels will be described below with reference to FIG.

  In FIG. 7, reference numeral 61A denotes a first lens barrel, reference numeral 62A denotes a second lens barrel, reference numeral 63A denotes a third lens barrel, reference numeral S denotes an aperture stop, and reference numeral 7 denotes an image sensor.

Reference numeral 51 denotes a first group of the imaging optical system, and reference numeral 52 denotes a second group of the imaging optical system.
The first lens barrel 61A, the second lens barrel 62A, and the third lens barrel 63A are all rotationally symmetric with respect to the axis AX.

The first lens barrel 61A holds the first group 51, and the second lens barrel 62A holds the second group 52.
The axis AX is a common optical axis of the first group 51 and the second group 52 held by the first lens barrel 61A and the second lens barrel 62A, that is, an optical axis of the imaging optical system.

As described above, the axis AX is also the “rotary symmetry axis” of the first to third lens barrels 61A to 63A.
Therefore, the axis AX is called a “lens barrel axis” in the relationship with the lens barrel, and is called the “optical axis” in the relationship with the imaging optical system. When these are not distinguished, they are simply referred to as “axis AX”.

The first to third lens barrels 61 </ b> A to 63 </ b> A are fitted to each other so as to be able to “slid” in the direction of the lens barrel axis AX as shown in the figure.
The “lower end portion in the drawing” of the first lens barrel 61A and the third lens barrel 63A is abutted against and fixed to the upper surface 7a of the image sensor 7.

The first lens barrel 61A has a planar portion 61a that is orthogonal to the axis AX in its internal structure.
The second lens barrel 62A has planar portions 62a, 62b, and 62c that are orthogonal to the axis AX.

  The planar portions 62a and 62b form a step in the axis AX direction on the first group 51 side, and the aperture stop S is provided in the planar portion 62b.

  Further, the flat portion 62a has a “gap” between the flat portion 61a of the first lens barrel 61A. This gap is referred to as “gap a” for convenience.

  The planar portion 62c that forms the lower end in the drawing of the second lens barrel 62A has an “interval” between the upper surface 7a of the image sensor 7. This interval is referred to as “interval a” for convenience.

  In addition, a space is formed between the flat portion 61a of the first lens barrel 61A and the flat portion 62b of the second lens barrel 62A. This void portion is referred to as “void portion a” for convenience.

  First, regarding the distance a, the second lens barrel 62A thermally expands downward in FIG. 7 in relation to the third lens barrel 63A.

  When the interval a is reduced by this thermal expansion and the flat portion 62b of the second lens barrel 62A comes into contact with the upper surface 7a of the image pickup device 7, the amount of elongation due to the thermal expansion of the second lens barrel 62a is restricted.

As a result, a desired amount of displacement of the second group 52 in the axis AX direction cannot be obtained.
Accordingly, the interval a is set to a size such that the second lens barrel 62A and the image sensor 7 do not contact each other regardless of fluctuations in the measurement environment temperature.
In this way, the flat surface portion 62a, which is the outermost surface portion on the first group 51 side in the lens barrel axis AX direction of the second lens barrel 62A, has the above-described configuration of the first lens barrel 61A regardless of the variation in the measurement environment temperature. It does not contact the flat surface portion 61a which is the surface facing the endmost surface portion.

  Next, regarding the gap a, when the measurement environment temperature rises, both the second lens barrel 62A and the third lens barrel 63A thermally expand.

  At this time, the planar portion 62a of the second lens barrel 62A extends toward the planar portion 61a of the first lens barrel 61A.

When the flat portion 62a comes into contact with the flat portion 61a due to this elongation, the amount of elongation caused by the heat of the second lens barrel 62A is restricted, and a desired displacement amount cannot be obtained.
As a result, a desired group interval displacement amount cannot be obtained.

  Therefore, the size of the interval a is set such that the flat surface portion 62a on the first group 51 side of the second lens barrel 62A does not come into contact with the flat surface portion 61a regardless of the variation of the measurement environment temperature.

  FIG. 8 is a modification of FIG. In order to avoid complications, the same symbols are used in FIG.

  A spring member SP1, which is a compressible elastic member, is disposed in the space a between the flat portion 61a of the first lens barrel 61A and the flat portion 62b of the second lens barrel 2A.

  In other words, a repulsive elastic member SP1 is provided between the first lens barrel 61A and the second lens barrel 62A to apply an elastic force that presses the second lens barrel 62A against the third lens barrel 63A.

  The spring member SP1 is “repulsive”, and its elastic force acts to press the second lens barrel 62A downward in the drawing.

  This concave pressure presses the second lens barrel 62A against the third lens barrel 63A to ensure contact between the second lens barrel 62A and the third lens barrel 63A, and also applies the third lens barrel 63A to the image sensor 7. Guarantees contact.

  At the time of displacement measurement, if the third lens barrel 63A is separated from the image sensor 7 due to disturbances such as vibration, there is a risk that it will deviate from the thermal displacement amount of the desired group interval.

  The spring member SP <b> 1 presses the second lens barrel 62 </ b> A toward the image sensor 7, thereby obtaining an effect of preventing the third lens barrel 63 </ b> A from being separated from the image sensor 7.

  FIG. 9 shows a state where the specific example shown in FIG. 8 is arranged in the housings 81A and 81B. Reference numeral 83A denotes a bottom plate.

  In this example, the image sensor 7 and the housing 81A are fixed to the bottom plate 83A in the lower part of the figure, and the first lens barrel 63A and the third lens barrel 63A are fixed to the image sensor 7.

  Therefore, the first lens barrel 61A and the third lens barrel 63A are thermally expanded with reference to the upper surface of the image sensor 7, and at that time, slide relative to the housings 81A and 82A.

  In the specific example of FIG. 9, a space SP is provided between the housings 81 </ b> A and 82 </ b> A and the first lens barrel 61 </ b> A in the portion above the axis AX.

  Therefore, the elongation accompanying the thermal expansion of the first lens barrel 61A is not hindered by the housings 81A and 82A.

  Therefore, the problem that the “displacement amount of a desired group interval” cannot be obtained by restricting the “displacement amount due to heat” of the first lens barrel 63A by the housings 81A and 82A is avoided.

  In other words, the space SP is set to a size such that “the housings 81A and 81A and the first lens barrel 61A are not in contact with each other in the direction of the lens barrel axis AX regardless of variations in the measurement environment temperature”.

The specific example of FIG. 10 is a modification of the specific example of FIG. 9, and a spring member SP2 that is a compressible elastic member is arranged in the space SP shown in FIG.
That is, the spring member SP2 is disposed between the housings 81A and 82A that hold the first lens barrel 61A and the opposed surfaces of the first lens barrel 61A.

  Since the spring member SP2 is “compressible”, an elastic force is applied to press the first lens barrel 61A downward in the axis AX direction.

  The first lens barrel 61A is pressed against the image sensor 7 by the resultant force of “downward elastic force” by the spring member SP2 and “upward elastic force” by the spring member SP1.

  The third lens barrel 63A is pressed against the image pickup device 7 by the resultant force of the downward elastic force of the drawing by the spring members SP1 and SP2.

  Accordingly, in the example of FIG. 10, it is not necessary to fix the “lower end portion in the drawing” of the first lens barrel 61 </ b> A and the third lens barrel 63 </ b> A to the image sensor 7.

  Also in the specific example of FIG. 10, it is possible to avoid the “problem deviating from the amount of thermal displacement at a desired group interval” due to the first lens barrel 61 </ b> A being separated from the image sensor 7 due to disturbance such as vibration.

  If two spring members SP1 and SP2 are used as in the specific example shown in FIG. 10, the first lens barrel 61A and the third lens barrel 63A need only be pressed against the image sensor 7 as described above.

In this case, by appropriately setting the spring strengths of the spring members SP1 and SP2, the “contact between the first lens barrel 61A and the third lens barrel 63A and the image sensor 7” under the action of gravity is performed. It can be secured.
In relation to claims 13 and 14, the spring member SP1 is "spring member A" and the spring member SP2 is "spring member B".

  The example described with reference to FIG. 10 is “when the displacement measuring device is arranged below the dynamic test surface”. Hereinafter, the acceleration of gravity is assumed to be “G”.

  The masses of the first lens barrel 61A, the second lens barrel 62A, and the third lens barrel 63A are M1, M2, and M3, respectively.

  Then, in each of the specific examples described above, downward gravity (M1G, M2G, M3G) acts on the first lens barrel 61A, the second lens barrel 62A, and the third lens barrel 63A.

The spring constant of the spring member SP1 is K1, the deflection amount is n1, the spring constant of the spring member SP2 is K2, and the deflection amount is n2.
In this way, the force acting on the first lens barrel 61A is “upward positive in each figure”
K1, n1-K2, n2-M1, G
It becomes.

The force acting on the third lens barrel 63A is
-K1, n1-K2, n2-M2, G-M3, G
It becomes.

At this time, in order for the first lens barrel 61A not to be separated from the image sensor 7,
K1, n1-K2, n2-M1, G <0 (1)
If it is. This is because the resultant force acting on the first lens barrel 61A is directed downward in each figure.

In order for the third lens barrel 63A not to be separated from the image sensor 7,
-K1, n1-K2, n2-M2, G-M3, G <0 (2)
If it is good.

  Therefore, according to the masses of the first to third lens barrels: M1 to M3, the spring constants and deflection amounts of the spring members SP1 and SP2 are set so that the above expressions (1) and (2) are satisfied at the same time. That's fine.

  On the contrary, when the displacement measuring device is arranged “above the dynamic test surface”, the image sensor 7 is at the top.

At this time, in order for the first lens barrel 61A not to be separated from the image sensor 7,
-K1 · n1 + K2 · n2-M1 · G> 0 (3)
If it is.

In order for the third lens barrel 63A not to be separated from the image sensor 7,
K1, n1-M3, G> 0 (4)
If it is good.

  Therefore, in this case, the spring constants and deflection amounts of the spring members SP1 and SP2 are set so that the expressions (3) and (4) are satisfied simultaneously according to the masses M1 to M3 of the first to third lens barrels. Set.

  FIG. 11 shows only the main part of another specific example. The specific example of FIG. 11 can be applied to the features described above with reference to FIGS. 4 and 7 to 10 described above.

7 to 10 denote the same parts as those in these drawings.
In FIG. 11, a “portion surrounded by a broken circle” indicated by reference numeral 11 </ b> P is a characteristic portion.

  That is, the feature of the specific example shown in FIG. 11 is that the contact surface SF between the second lens barrel 62B and the third lens barrel 63B is a surface (conical surface) inclined with respect to the lens barrel axis AX. There is in point.

  For example, in the specific example shown in FIG. 10, the surface where the second lens barrel 62A and the third lens barrel 63A contact each other in the axis AX direction is a flat surface.

  For this reason, when a “some factor” is applied to the second lens barrel 62A and the third lens barrel 63A in a direction parallel to the plane, there is a possibility that a deviation occurs.

  Such “deviation” causes “optical axis deviation” between the first group 51 and the second group 52 and causes the imaging magnification to change.

  As shown in FIG. 11, when the contact surface SF where the second lens barrel 62B and the third lens barrel 63B are in contact with each other in the axis AX direction is inclined to the axis AX, this problem can be solved.

  That is, the inclined surface (conical surface) SF suppresses the “shift in the direction in which the axis AX is orthogonal” of the second lens barrel 62B and the third lens barrel 63B.

The second lens barrel 62B and the third lens barrel 63B are brought into contact with and pressed against the inclined surface SF, thereby obtaining an effect of aligning the second lens barrel 62B and the third lens barrel 63B.
Note that the inclination of the contact surface SF may be lowered toward the side away from the axis AX.

FIG. 12 shows a main part of another specific example. The specific example of FIG. 12 can be applied to the features described above with reference to FIGS. 4 and 7 to 11 described above.
FIG. 12 shows a case where the present invention is applied to the specific example of FIG.

In FIG. 12, a “portion surrounded by a broken circle” indicated by reference numeral 12P is a characteristic portion.
That is, the third lens barrel is divided into two portions 63c1 and 63c2 in the axis AX direction.

  As described above, the first lens barrel, the second lens barrel, and the third lens barrel are combined with materials having a predetermined linear expansion coefficient.

However, there is not always a suitable material with the desired coefficient of linear expansion.
In such a case, the condition can be satisfied by composing the lens barrel with two or more materials having different linear expansion coefficients.

  In the specific example shown in FIG. 12, the third lens barrel is composed of two lens barrel portions 63c1 and 63c2, and the linear expansion coefficients of the materials constituting these lens barrel portions are β1 and β2, respectively.

  The lengths of the lens barrel portions 63c1 and 63c2 are Z31 and Z32, respectively, and the amount of change in the length of the third lens barrel required for the change in measurement environment temperature: ΔT is Δ30.

In this case, depending on the linear expansion coefficient: β1, β2,
Δ30 = (β1 · Z31 + β2 · Z32) ΔT
Z31 and Z32 may be set so as to satisfy the above.

  It goes without saying that not only the third lens barrel but also the first lens barrel 61A and the second lens barrel 62A can be configured by connecting two or more types of lens barrel members having different linear expansion coefficients in the direction of the lens barrel axis.

  The imaging optical system has an “aperture stop” as described above.

  When measuring the displacement of the dynamic test surface, if the “reflectance or displacement speed” of the dynamic test surface varies, the contrast of the acquired speckle pattern changes.

  Such a variation in the contrast of the speckle pattern affects the measurement accuracy. Therefore, the acquired speckle pattern is preferably a “pattern with good contrast”.

  A “speckle pattern with good contrast” has a ratio of a bright part to a dark part of about 1: 1.

The specific example shown in FIG. 13 addresses this problem.
That is, this specific example includes the aperture variable mechanism 70.

  The aperture variable mechanism 70 detects the luminance signal of the acquired speckle pattern based on the output of the image sensor 7 and adjusts the aperture of the aperture aperture S according to “change in luminance”.

This adjustment is preferably performed so as to “detect the luminance distribution and control the aperture so as to cancel the change in the luminance distribution”.
When the adjustment is performed in this way, the contrast is stabilized.

  However, the present invention is not limited to this, and it is also possible to perform control such that the aperture is changed by one step when the change amount of the luminance distribution exceeds a predetermined threshold value.

  As a mechanism for changing the aperture of the aperture stop S, various conventionally known mechanisms can be applied.

  However, in consideration of the configuration of the lens barrel and the size of the imaging optical system, the aperture stop S is configured with a liquid crystal filter so that the size of the aperture can be switched in stages, It is preferable to switch the size of the opening.

  First, using the displacement measuring apparatus using the imaging optical system described in the examples, displacement measurement was performed using the surface of the printing adhesive sheet adhered to the linear stage as the dynamic test surface.

  The dynamic test surface was measured with the moving amount when moved 50 mm at a linear velocity of 100 mm / sec as the “moving distance”, that is, the detection length.

  The positioning accuracy of the linear stage itself is 0.2 μm, and the error with respect to the feed amount of 50 mm is 0.0004%.

  As described above, the error range of the displacement measuring apparatus of the example is “about + 0.008% to −0.005%”.

  As a result of continuous measurement, it was confirmed that the error range was within the above range regardless of the fluctuation of the measurement environment temperature, and that the influence of the fluctuation of the measurement environment temperature was effectively suppressed.

  By using the displacement measuring apparatus described in the above embodiment and examples, the following displacement measuring method can be implemented.

That is, in this displacement measuring method, the dynamic test surface is illuminated at a predetermined position using coherent light from an illumination optical system having a laser light source and a coupling lens as irradiation light.

Then, the reflected light from the dynamic test surface is guided to the image sensor via the imaging optical system, and a speckle pattern from the dynamic test surface is acquired at a predetermined frame rate.

A cross correlation calculation between speckle patterns acquired at a predetermined time interval is performed, and at least one of the moving distance and the moving speed of the dynamic test surface is measured based on the calculation result.

In addition, the displacement measuring apparatus described above in the embodiment and examples is an image forming apparatus that forms an image on the surface of a moving body that moves at a constant speed in a fixed direction. As described above, it can be used to measure at least one of the moving distance and moving speed.

This image forming apparatus uses an electrophotographic process to form an electrostatic latent image on a photoconductive photoreceptor, visualize the electrostatic latent image as a toner image, and transfer the obtained toner image to a transfer target The image forming apparatus can be a transfer type image forming apparatus.

In this case, the displacement measuring device measures at least one of the moving distance and moving speed of the surface of the transfer object as a moving object.

As described above, the displacement measuring apparatus of the present invention can realize “stable displacement measurement” with extremely small fluctuations in the detection length with respect to changes in the measurement environment temperature.

Therefore, the displacement measuring device of the present invention can be used as a sensor for controlling the paper conveyance speed and the speed of the intermediate transfer belt of an ink jet type or electrophotographic type color image forming apparatus.

Since the displacement measuring apparatus of the present invention performs the measurement using the speckle pattern, the measurement can be carried out if there are fine irregularities on the dynamic test surface that is the measurement target.

Since it is a requirement that a speckle pattern be generated, the measurement target does not need to be marked with an encoder pattern, and a wide variety of objects can be measured.

In the embodiment described above, the measurement target is the “detection length having a dimension of length”, but speed information can also be obtained by time-differentiating the measurement length.
It is also possible to capture minute time speed fluctuations by appropriately selecting a frame rate for acquiring speckle patterns.
For models with different dimensional configurations, if optimization is performed in the same manner as in the above embodiment,
The temperature fluctuation of the detection length can be reduced.

  FIG. 6 shows an embodiment of a color image forming apparatus using a displacement measuring device.

This color image forming apparatus is a tandem method using an electrophotographic process,
It has four photoconductors 11Y, 11M, 11C, and 11K provided in parallel.

Y, M, C, and K in reference numerals 11Y and the like represent the colors of toner that forms a toner image. That is, Y represents yellow, M represents magenta, C represents cyan, and K represents black.

  The photoconductors 11Y to 11K are photoconductive and have a drum shape.

Around the photoreceptors 11Y to 11K, charging rollers TY to TK, developing devices GY to GK, transfer chargers 15Y to 15K, and cleaners BY to BK are provided so as to surround them.

An intermediate transfer belt denoted by reference numeral 17 is disposed below the photoconductors 11Y to 11K, and the surface thereof is close to the photoconductors 11Y to 11K.

In FIG. 5, reference numeral 13 denotes an optical scanning image writing apparatus, reference numeral 19 denotes a sheet cassette, reference numeral 21 denotes a transfer roller, reference numeral 23 denotes a fixing device, and reference numeral 25 denotes a discharge roller.

Reference numeral 27 denotes an exterior part, reference numeral 29 denotes a belt cleaning device, and reference numeral 31 denotes a displacement measuring device.

  The formation of a color image will be briefly described.

When image formation is started, the photoconductors 11Y to 11K rotate at a constant speed clockwise at a predetermined timing.

  The photoreceptors 11Y to 11K are uniformly charged by the corresponding charging rollers TY to KY.

Each of the uniformly charged photoconductors is written with an electrostatic latent image for each photoconductor by optical scanning by the image writing device 13, developed, and visualized as a toner image of a different color.

That is, an image of “yellow image component” is written on the photoreceptor 11Y, and the formed electrostatic latent image is developed by the developing device GY, so that a yellow toner image is formed on the photoreceptor 11Y.

An image of “magenta image component” is written on the photoreceptor 11M, and the formed electrostatic latent image is developed by the developing device GM, so that a magenta toner image is formed on the photoreceptor 11M.

An image of “cyan image component” is written on the photoconductor 11C, and the formed electrostatic latent image is developed by the developing device GC to form a cyan toner image on the photoconductor 11C.

An image of “black image component” is written on the photoreceptor 11K, and the formed electrostatic latent image is developed by the developing device GK, and a black toner image is formed on the photoreceptor 11K.

Thus, the toner images of the respective colors formed on the photoconductors 11Y to 11K are transferred to the intermediate transfer belt 1.
7 is transferred.

The intermediate transfer belt 17 is driven to rotate as a transfer target at a speed in accordance with the surface speed of the photoconductors 11Y to 11K according to the rotation of the photoreceptors 11Y to 11K.

Then, the yellow toner image is transferred from the photoconductor 11Y by the transfer charger 15Y, and the magenta toner image is transferred from the photoconductor 11M by the transfer charger 15M.

Similarly, a cyan toner image is transferred from the photoreceptor 11C by the transfer charger 15C, and
A black toner image is transferred from the photoreceptor 11K by the transfer charger 15K.

The transferred toner images of the respective colors are superimposed on each other on the intermediate transfer belt 17 to form a color toner image.

The transfer sheet P to which the color toner image is transferred is distributed from the sheet cassette 19 below the intermediate transfer belt 17 and heads toward the “transfer section”.

In the transfer portion, the color toner image on the intermediate transfer belt 17 is transferred by being nipped and conveyed by the intermediate transfer belt 17 and the transfer roller 21, and is directed to the fixing device 23.

The transfer paper P is fixed with the color toner image by the fixing device 23, and is discharged onto a tray formed as an upper portion of the exterior portion 27 by the discharge roller 25.

“Intermediate transfer toner and paper dust” is removed from the intermediate transfer belt 17 having the color toner image transferred onto the transfer paper P by the belt cleaning device 29.

The intermediate transfer belt 17 needs to pass through a position where the toner image of each color is transferred at a predetermined speed and timing. Therefore, the moving speed needs to be controlled with high accuracy.

The displacement measuring device 31 measures the moving speed of the surface of the intermediate transfer belt 17 toward the position where the toner image from each photoconductor is transferred with high accuracy.

Based on the measured moving speed, the moving speed of the intermediate transfer belt 17 is controlled to a constant speed by a control driving unit (not shown).

The displacement measuring means 31 is that of the embodiment or example described above, and the intermediate transfer belt 17.
The moving speed is measured with high accuracy using the surface of the surface as a dynamic test surface.

In this way, each color toner image is appropriately transferred, and a color image without color misregistration is formed.

As in the case of the embodiment, when the variation amount of the detection length is extremely small such as −1.54 × 10 ⁻⁶ (%), for example, high-speed image formation that obtains 60 color images per minute Even in the device "
It is possible to obtain a good color image without “color shift”.

In the above description, the surface of the intermediate transfer belt has been described as an example of the dynamic test surface. However, it goes without saying that the displacement of the surface of the photosensitive member can be measured by the displacement measuring apparatus described above.

Moreover, although the case where the reflected light from the dynamic test surface is used as the detection light has been described, of course, the transmitted light can also be used as the detection light.

It should be noted that FIG. 1, FIG. 2, FIG. 4, and FIG. 5 are all diagrams for explanation, and do not accurately represent the F number and other optical values in the actual optical system.

1 Laser light source
2 Coupling lens
3 Illumination optics
Ob dynamic test surface
51 First group of imaging optical system
52 Second group of imaging optical system
S Aperture stop of the imaging optical system
GM Gaussian surface
BM Boiling surface
7A Light receiving surface of light receiving element

JP 2003-267591 A JP 2010-55064 A JP 2009-15240 A

Laser Research 1980, Vol. 8, No. 2, p. 45 “Dynamic Speckle Characteristics and Application to Speed Measurement (I)”

Claims (14)

The coherent light from the illumination optical system having a laser light source and a coupling lens is used as illumination light, the dynamic test surface is illuminated at a predetermined position, and the detection light from the dynamic test surface is imaged via the imaging optical system. Guide to the element, acquire a speckle pattern by the dynamic test surface at a predetermined frame rate, perform cross-correlation between the speckle patterns acquired at a predetermined time interval, based on the calculation results, In a displacement measuring apparatus for measuring at least one of a moving distance and a moving speed of a dynamic test surface,
The imaging optical system includes, in order from the dynamic test surface side, a first group having a positive power, an aperture stop, and a second group having a positive power. The aperture stop is an image-side focal point of the first group. And at a position that is the object-side focal plane of the second group,
Receiving surface of the imaging element, wherein the dynamic allowed to conform to a Gaussian surface by the test surface imaging optical system, the Gaussian surface by dynamic and Boiling surface of the test surface, the imaging optical system of the dynamic test surface The distance: Db, the distance between the Gaussian surface and the light receiving surface of the image sensor: D , regardless of the variation of the measurement environment temperature in the measurement environment temperature change region , the condition:
(1) D / Db≈0
The illumination aspect of the dynamic test surface through the imaging optical system of the illumination optical system is defined,
The illumination optical system is a system in which light from the laser light source is converted into a coherent parallel light beam by the coupling lens,
Each of the first group and the second group of the imaging optical system is composed of two or more lenses made of different materials,
A first lens barrel that holds the first group, a third lens barrel that can slide relative to the first lens barrel, and that can slide relative to the third lens barrel and hold the second lens group A second lens barrel,
One end of each of the first lens barrel and the third lens barrel is fixed to the image pickup device. The displacement measuring device according to claim 1,
The displacement measuring apparatus, wherein the second lens barrel and the image sensor do not contact each other regardless of fluctuations in the measurement environment temperature . The displacement measuring apparatus according to claim 1 or 2 ,
The end surface of the second lens barrel on the first group side in the direction of the lens barrel axis does not come into contact with the surface facing the end surface of the first lens barrel, regardless of variations in the measurement environment temperature. Displacement measuring device characterized by. The displacement measuring apparatus according to any one of claims 1 to 3 ,
A displacement measuring device having a repulsive elastic member for applying an elastic force that presses the second lens barrel against the third lens barrel between the first lens barrel and the second lens barrel . In the displacement measuring device according to any one of claims 1 to 4 ,
A displacement measuring apparatus , wherein the housing that holds the first lens barrel and the first lens barrel do not contact each other in the direction of the lens barrel axis of the first lens barrel, regardless of a change in measurement environment temperature . The displacement measuring device according to claim 5, wherein
The housing for holding the first lens barrel and the first lens barrel have opposing surfaces facing each other in the lens barrel axis direction of the first lens barrel,
A displacement measuring apparatus comprising a compressible elastic member between the facing surface of the first lens barrel and the facing surface of the housing . The displacement measuring device according to claim 4 , wherein
The housing for holding the first lens barrel and the first lens barrel have opposing surfaces facing each other in the lens barrel axis direction of the first lens barrel, and the opposing surface of the first lens barrel. And having a compressible elastic member between the opposing surface of the housing,
The repulsive elastic member for applying an elastic force that presses the second barrel against the third barrel, and the compressible elastic member are both spring members,
When the repulsive elastic member is a spring member A and the compressive elastic member is a spring member B,
Spring constant of the spring member A: K1, deflection amount: n1, mass of the first lens barrel: M1, spring constant of the spring member B: K2, deflection amount: n2, mass of the second lens barrel: M2, mass of the third lens barrel: M3, acceleration of gravity: G, conditions:
K1, n1-K2, n2-M1, G <0 (1)
-K1, n1-K2, n2-M2, G-M3, G <0 (2)
Is satisfied, and is disposed below the dynamic test surface . The displacement measuring device according to claim 4 , wherein
The housing for holding the first lens barrel and the first lens barrel have opposing surfaces facing each other in the lens barrel axis direction of the first lens barrel, and the opposing surface of the first lens barrel; A compressible elastic member between the opposing surface of the housing;
Both the repulsive elastic member that exerts an elastic force that presses the second barrel against the third barrel and the compressible elastic member are spring members,
When the repulsive elastic member is a spring member A and the compressive elastic member is a spring member B,
Spring constant of the spring member A: K1, deflection amount: n1, mass of the first lens barrel: M1, spring constant of the spring member B: K2, deflection amount: n2, mass of the third lens barrel: M3, gravity Acceleration: G, conditions:
-K1 · n1 + K2 · n2-M1 · G> 0 (3)
K1, n1-M3, G> 0 (4)
Is satisfied, and is disposed above the dynamic test surface . In the displacement measuring device according to any one of claims 1 to 8 ,
At least one of the first to third lens barrels is configured by connecting two or more types of lens barrel members having different linear expansion coefficients in the direction of the lens barrel axis. . In the displacement measuring device according to any one of claims 1 to 9 ,
A displacement measuring apparatus , wherein a surface of the second lens barrel and the third lens barrel contacting with each other in the lens barrel axis direction is inclined with respect to the lens barrel axis . In the displacement measuring device according to any one of claims 1 to 10 ,
A displacement measuring device having a diaphragm variable mechanism that varies an aperture of the aperture diaphragm of the imaging optical system . Using coherent light from an illumination optical system having a laser light source and a coupling lens as illumination light, the dynamic test surface is illuminated at a predetermined position, and the reflected light from the dynamic test surface is imaged via the imaging optical system. Guide to the element, acquire a speckle pattern by the dynamic test surface at a predetermined frame rate, perform cross-correlation between the speckle patterns acquired at a predetermined time interval, based on the calculation results, In a displacement measuring method for measuring at least one of a moving distance and a moving speed of a dynamic test surface,
A displacement measuring method performed by the displacement measuring device according to claim 1 . In an image forming apparatus that forms an image on the surface of a moving body that moves at a constant speed in a constant direction,
A displacement measuring device for measuring at least one of a moving distance and a moving speed of the moving body as a dynamic test surface;
An image forming apparatus using the displacement measuring apparatus according to claim 1 as the displacement measuring apparatus. The image forming apparatus according to claim 13.
Using an electrophotographic process, an electrostatic latent image is formed on a photoconductive photosensitive member, the electrostatic latent image is visualized as a toner image, the obtained toner image is transferred to a transfer target, and the transfer target is transferred. An image forming apparatus , wherein a body is a moving body and at least one of a moving distance and a moving speed of the surface is measured .

Images