JP2015001557A - Displacement measurement device, displacement measurement method and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a displacement measurement device that makes it easy to reduce an influence of a measuring environmental temperature variation in a displacement measurement of a kinetic measured surface using a speckle pattern.SOLUTION: In a displacement measurement device illuminating a kinetic measured surface Ob with coherent light by an illumination optical system 3 having a laser beam source 1 and a coupling lens 2 as irradiation light, guiding detection light upon the kinetic measured surface to an image pickup element 7 via an imaging optical system 5, acquiring a speckle pattern upon the kinetic measured surface at a prescribed frame rate, performing a mutual correlation computation among the speckle patterns acquired at a prescribed time interval, and measuring at least one of a movement distance of the kinetic measured surface and a movement velocity thereof on the basis of the computation result, an illumination mode of the kinetic measured surface by the illumination optical system and a position relation between the imaging optical system and the image pickup element with respect to the kinetic measured surface are set so that a distance Db between a boiling surface BM of the kinetic measured surface Ob and a Gauss surface GM by the imaging optical system 5 of the kinetic measured surface, and an interval D between the Gauss surface and a light reception surface 7A of the image pickup element satisfy a condition (1) D/Db≒0.

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 in the direct transfer method and the intermediate transfer belt in the intermediate transfer belt method are moved with high accuracy.

  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 driving control of a recording medium, a conveyance belt, and an intermediate transfer belt (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 the speckle pattern moves when the test surface irradiated with coherent light moves in the plane direction. A test surface that moves in the plane direction is referred to as a “dynamic test surface”.

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

  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.

  This invention makes it a subject to implement | achieve the displacement measuring apparatus which can reduce the influence of a measurement environment temperature fluctuation easily in the displacement measurement of the dynamic test surface using a speckle pattern in view of the situation mentioned above.

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. In the displacement measuring apparatus for measuring at least one of the moving distance and the moving speed of the dynamic test surface based on the calculation result, the boiling surface of the dynamic test surface and the imaging of the dynamic test surface The distance from the Gauss surface by the optical system: Db, the distance between the Gauss surface and the light receiving surface of the image sensor: D, the conditions:
(1) D / Db≈0
The illumination aspect of the dynamic test surface by the illumination optical system and the positional relationship between the imaging optical system and the image sensor with respect to the dynamic test surface are set so as to satisfy the above.

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

It is a figure for demonstrating one Embodiment. It is a figure for demonstrating another embodiment. It is a figure for demonstrating a part of characteristic of embodiment of FIG. It is a figure for demonstrating the characteristic part of other embodiment. It is a figure for demonstrating one Embodiment of an image forming apparatus.

  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 movement amount 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 following three factors can be cited as influences of fluctuations in the measurement environment temperature.

  A. Variation of the distance between the image plane (Gaussian plane) imaged by the imaging optical system on the dynamic test surface and the “light-receiving surface of the imaging optical system” with temperature.

  B. Variation of 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 due to temperature.

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

  As described above, there are three factors A to C as the cause of the error that occurs in the detection length due to the fluctuation of the measurement environment temperature.

  Therefore, it is necessary to take these three factors into consideration when measuring the detection length.

  Consider a state in which coherent light is irradiated onto a dynamic test surface that moves at a moving speed V1, and an image of the dynamic test surface is formed on the light receiving surface of the image sensor by the imaging optical system.

  In this state, a “speckle pattern” is imaged on the light receiving surface.

  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 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 illumination optical system” obtained through the coupling lens of the illumination optical system and the imaging optical system.

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

  Hereinafter, embodiments will be described. In order to avoid complications, the same symbols are used in the following figures for those that are not likely to be confused.

  FIG. 1 is a diagram for explaining one embodiment of a displacement measuring apparatus.

  In FIG. 1A, reference numeral 0 denotes a moving body, reference numeral 1 denotes a laser light source, reference numeral 2 denotes a coupling lens, reference numeral 5 denotes a lens, and reference numeral 6 denotes a lens barrel.

  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, 81 and 82 are housings, 83 is a bottom plate, 9 is a calculation unit, and 10 is a light source driving unit.

  A laser light source 1 (hereinafter 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 light (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.
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.

  Hereinafter, the laser light emitted from the illumination optical system 3 is also referred to as “irradiation light”.

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

  The moving body 0 is, for example, the above-described intermediate transfer belt and moves in the direction of the arrow at a predetermined speed: V1.

  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 lens 5 constitutes an “imaging optical system” and is 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 lens 5 that is the imaging optical system, and the imaging element 7 are in a predetermined positional relationship while being held by 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.

  As described above, the positional relationship among the illumination optical system 3, the imaging optical system 5, and the imaging element 7 is determined by the housings 81 and 82, and is 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, that is, a well-known “cross-correlation calculation” based on the output of the image sensor 7, and calculates the detection length 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. 1A, 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.

  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 5.

  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 5 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”.

  Then, the cross-correlation calculation between the speckle patterns acquired at a predetermined time interval is performed in the calculation unit 9, and based on the calculation result, the moving speed Ob of the dynamic test surface Ob is measured.

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

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

  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.

  In the displacement measuring apparatus as shown in FIG. 1A, the measurement environment temperature is the temperature of the illumination optical system 3, the imaging optical system 5, the imaging element 7, etc. at the time of measurement.

As a cause of the rise in the measurement environment temperature, heat generation in the imaging device 7, the LD driving driver IC (light source driving unit 10), the FPGA (calculating unit 9), the LD (light source 1), or the like can be considered.
By mounting the calculation unit 9 and the light source driving unit 10 on the same bottom plate 83 and integrating them with the housings 82 and 83, the displacement measuring device can be reduced in size.

  However, measurement environment temperature rises by integrating a plurality of exothermic parts.

The heat transfer from these heat sources to the illumination optical system 3, the image pickup optical system 5, and the image sensor 7 has different transfer paths, so that the amount of temperature rise and the rise timing are generally not the same.
Therefore, the variation in the measurement environment temperature is not the same in the illumination optical system 3, the imaging optical system 5, and the imaging element 7.

When the position of the imaging optical system 5 varies, the imaging magnification: M on the right side of the equation (a) varies.
When the positional relationship between the imaging optical system 5 and the imaging element 7 varies, “D” on the right side of the equation (a) varies.

  When the positional relationship between the illumination optical system 3 and the imaging optical system 5 varies, “Db” on the right side of the equation (a) varies.

These “M”, “D”, and “Db” variations caused by variations in the measurement environment temperature also have different timings, and it is not easy to align the timings of these variations.
In order to reduce the “detection length error” associated with the change in the measurement environment temperature, it is preferable that the factors causing the error are small, and it is preferable that the characteristics are not complicated.

  The ratio of the moving speed of the dynamic test surface Ob: V1 and the moving speed of the speckle pattern: V2: V2 / V1 depends on the imaging magnification: M and the distances: D, Db according to the above formula (a).

  The value of “Db” in equation (a) is defined by “the distance between the Gaussian image plane position and the imaging plane position of the light source 1 obtained via the coupling lens 2 and the imaging optical system 5”.

  Therefore, it is considered that the value of “Db” is influenced by “positional variations of the light source 1, the coupling lens 2, and the imaging optical system 5”.

  In addition, since the value of “D” is “the distance between the Gaussian image plane and the light receiving surface of the image sensor”, the value of “D” is affected by the position fluctuations of the imaging optical system 5 and the image sensor 7. it is conceivable that.

  Accordingly, it is considered that the position variation of the four portions of the light source 1, the coupling lens 2, the imaging optical system 5, and the imaging element 7 affects the detection length.

  FIG. 1B illustrates the optical positional relationship among the illumination optical system 3, the dynamic test surface Ob, the imaging optical system 5, and the imaging element 7 in the displacement measuring apparatus shown in FIG. It is a figure for doing.

As shown in FIG. 1B, the irradiation light emitted from the illumination optical system 3 is a parallel light beam 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. 1B, the “dotted line” indicates the imaging light ray of this imaging.

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

  As shown in FIG. 1B, the distance between the Gaussian surface GM and the light receiving surface 7A of the image sensor 70 is “D”, and the distance between the Gaussian surface GM and the boiling surface BM is “Db”.

  In FIG. 1B, 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. However, even if it fluctuates in this way, the value of “D” is as small as about 100 μm at most.

  In the embodiment of FIG. 1, each unit is set so that “D / Db≈0”.

  As described above, since “D = 0” is satisfied in the design, the above condition “D / Db≈0” is satisfied if the distance: Db is set to a finite value. Above satisfied.

If “D / Db≈0” holds, the equation (a) becomes
(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 on the imaging optical system 5 out of the four parts of the “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 fluctuations 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, as shown in FIG. 1C, 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. In order to increase “distance: Db”, there are the following measures.
The first measure is to “increase the focal length of the imaging optical system 5”.
In FIG. 1B, when the focal length of the imaging optical system 5 increases, the position of the boiling surface BM gradually moves to the right in the drawing.
When the focal length becomes sufficiently large, the position of the boiling surface BM moves to the right beyond the Gaussian surface GM, and the distance: Db increases to an extent that “Expression (b) is satisfied”.

  However, in this case, the power of the imaging optical system 5 is reduced, the distance between the dynamic test surface Ob and the Gaussian surface GM is increased, and the displacement measuring apparatus is increased in size.

  Within the practical size range of the displacement measuring device, there is a limit to increasing the focal length of the imaging optical system 5, and it is not easy to sufficiently suppress the influence of the displacement of the illumination optical system 3.

  The second measure is “to make the irradiation light emitted from the illumination optical system 3 into a condensed light flux”.

  Considering the case of FIG. 1B, the position of the boiling surface BM moves to the left in the drawing as the condensing property of irradiation light increases, and the distance: Db increases.

  When the irradiation light emitted from the illumination optical system 3 is focused on the object side focal position of the imaging optical system 5, the light beam that has passed through the imaging optical system 5 becomes a parallel light beam.

  Therefore, the position of the boiling surface BM is + ∞ (the light traveling direction is positive).

  That is, at this time, the distance: Db is “∞”, and “D / Db = 0 regardless of the value of D” is established.

  The third policy, like the second policy, is to set the distance: Db to “∞”, but this is realized by the configuration of the imaging optical system.

  That is, the light source 1 is disposed at the focal position of the coupling lens 2 and the irradiation light is emitted from the illumination optical system 3 as a parallel light beam.

This parallel light beam is once condensed in the imaging optical system to generate a first conjugate plane, and is converted again into a parallel light beam. In this case, the position of the second conjugate plane is + ∞ by design, and Db≈ + ∞.
The displacement measuring device shown in FIG. 2 is an example in this case.
That is, the imaging optical system is constituted by two groups of lenses 51 and 52, and the irradiation light emitted from the illumination optical system 3 is a parallel light flux.

  The parallel light beam from the dynamic test surface Ob is converged by the lens 51, condensed at the object side focal position of the lens 52, becomes divergent light, passes through the lens 52, and becomes a parallel light beam.

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

  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 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 coherent light from the laser light source 1 into a parallel beam by the coupling lens 2.

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

  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 “Gauss surface by the imaging optical system” of the dynamic test surface Ob.

  That is, the displacement measuring apparatus shown in FIG. 2 uses coherent light from the illumination optical system 3 having the laser light source 1 and the 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 illumination optical system 3 converts coherent light from the laser light source 1 into a parallel beam by the coupling lens 2.

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

  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 zero in the embodiment of FIG.

  FIG. 2B illustrates the optical positional relationship between the illumination optical system 3, the dynamic test surface Ob, the imaging optical system, and the imaging element 7 in the displacement measuring apparatus shown in FIG. FIG.

As shown in FIG. 2B, the irradiation light emitted from the illumination optical system 3 is a parallel light flux and illuminates the dynamic test surface Ob.
Light (detection light) reflected by the dynamic test surface Ob is imaged by the imaging optical system using the Gaussian surface GM as an imaging surface. Thereby, the speckle pattern by the dynamic test surface Ob is imaged.

  In FIG. 2B, the “dotted line” indicates the imaging light ray of this imaging.

  On the other hand, the laser light from the light source 1 forms an image by the coupling lens 2 and the imaging optical system 5, and the imaging light in this case is emitted in parallel from the lens 52 which is the second group of the imaging optical system.

  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 at most about 100 μm or less as described above even when manufacturing errors are taken into consideration.

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

Therefore, the variation factor of the detection length is only the variation of the imaging magnification: M.
For this reason, even if the “response to the change in the measurement environment temperature” is deviated between the imaging optical system and the illumination optical system, it is not affected by the change in the measurement environment temperature in the illumination optical system 3.

  That is, it is only necessary to consider the influence of the fluctuation of the measurement environment temperature on the imaging optical system among the four parts “light source, coupling lens, imaging optical system, imaging element” that affect the detection length.

  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.

  Further, the imaging optical system is “telecentric on both the object side and the image side”, so that the variation in magnification due to defocusing of the dynamic test surface Ob and the light receiving surface 7A is small, and the variation in detection length can also be reduced.

  As described above, the value of the distance: D is 0 by 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 varies at the component tolerance level, the distance: Db varies on the order of several meters to several hundred meters.

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

  Therefore, the influence of “change in the positional relationship between the light source 1 and the coupling lens 2” in the illumination optical system 3 can be suppressed, and the change in the “detection length” can be suppressed.

  In the embodiment of FIG. 2, as described above, 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 are obtained synergistically, the “variation in detection length” can be further reduced as compared with the embodiment described with reference to FIG.

  FIG. 3 shows portions of the imaging optical system, the lens barrel 60, and the imaging element 7 in the embodiment shown in FIG.

  The first group (lens 51) and the second group (lens 52) are arranged in a common lens barrel 60.

  As shown in FIG. 2A, the lens barrel 60 is held by housings 81 and 82.

  The lens barrel 60 is disposed such that an end on the image sensor 7 side (an end on the lower side in the figure) is in contact with the image sensor 7.

  It is conceivable that the lens barrel 60 expands and contracts when the measurement environment temperature fluctuates. By utilizing this point, it is possible to suppress the variation in telecentricity in the imaging optical system.

  That is, the lens barrel 60 is held by frictional coupling so that it can “slide” with respect to the housings 81 and 82.

  The group interval between the first group (lens 51) and the second group (lens 52) held in the lens barrel 60 is set to “L”. Further, the coefficient of linear expansion of the material substance forming the lens barrel 60 is “α”.

  When the measurement environment temperature changes by “ΔT”, the change amount ΔL of the group interval between the first and second groups becomes “α · L · ΔT”.

  The lens barrel 60 can “slid in the optical axis direction” relative to the housings 81 and 82, and can thermally expand and contract independently of the housings 81 and 82.

  Accordingly, the thermal expansion / contraction amount ΔL of the group interval L of the imaging optical system can be controlled by the linear expansion coefficient α of the lens barrel 60 without being affected by the housings 81 and 82.

  Further, the change amount of the focal length f of the imaging optical system due to the temperature change ΔT is assumed to be “Δf”.

  Therefore, it is possible to optimize the change in the measurement environment temperature: the change in the focal length due to ΔT: Δf, and to compensate for the detection length error caused by the change in the group interval: ΔL.

Since the lens barrel 60 and the image sensor 7 are in “contact arrangement”, the amount of displacement of the image sensor in the optical axis direction is added to the amount of expansion / contraction of the lens barrel 60 in the optical axis direction.
Therefore, the amount of change in the distance between the image sensor and the image pickup optical system can be controlled by the expansion and contraction of the lens barrel 60 regardless of the change in the image sensor 7.

  The imaging magnification: M of the “telecentric imaging optical system” having the two-group configuration as in the embodiment of FIG. It is.

  When the measurement environment temperature T changes by ΔT within the fluctuation range, the interval between the first and second groups: L changes by “α · L · ΔT”.

  The focal lengths f1 and f2 change by Δf1 and Δf2, respectively.

  Therefore, the focal length changes: Δf1 and Δf2 satisfy the following condition (2) with respect to the change in the group spacing of the first and second groups with the change in the measurement environment temperature: ΔL.

(2) ΔL = Δf1 + Δf2
That is, the materials of the lenses 51 and 52 of the first group and the second group and the linear expansion coefficient of the lens barrel 60 are selected so that the condition (2) is satisfied.

  In this way, even if the measurement environment temperature changes, the “telecentricity” of the imaging optical system is preserved, and fluctuations in the imaging magnification: M are suppressed.

  That is, when the change in the principal point interval and the change in the focal length are balanced, even if the group interval changes due to the change in the measurement environment temperature, the change in the imaging magnification: M is effectively suppressed.

  As a result, the variation in detection length is also effectively suppressed.

  If the variation (Δf1, Δf2) of the focal lengths of the first and second groups can be minimized while satisfying the condition (2) and maintaining the telecentricity, the fluctuation of the imaging magnification: M is also minimized.

  FIG. 4 is a modification of the embodiment shown in FIG.

  In this embodiment, two groups of lenses 51 and 52 constituting the imaging optical system are held in separate lens barrels.

  That is, the lens 51 forming the first group of positive power is held by the first lens barrel 61, and the lens 52 forming the second group of positive power is held by the second lens barrel 62.

  Both of the lens barrels 61 and 62 on the image sensor 7 side are fixed in contact with the image sensor 7.

  That is, the imaging element 7 side of the lens barrels 61 and 62 is fixed in the vicinity of the imaging surface 7A.

  The distance from the light receiving surface 7A of the image sensor 7 to the first group 51 is L1, and the distance from the light receiving surface 7A to the second group 52 is L2. L1> L2.

  The linear expansion coefficient of the first lens barrel 61 is α1, the linear expansion coefficient of the second lens barrel 62 is α2, and the linear expansion coefficients α1 and α2 are different from each other.

  The first lens barrel 61 can slide relative to the housings 81 and 82 (not shown in FIG. 4) that hold the first lens barrel 61, and the second lens barrel 62 can slide relative to the first lens barrel 61. .

  Therefore, when the measurement environment temperature changes, the first and second lens barrels 61 and 62 expand and contract independently of each other.

  In the embodiment shown in FIG. 3, since both the first group 51 and the second group 52 are provided in a common lens barrel 60, the group spacing change between the first and second groups accompanying the change in the measurement environment temperature. Is uniquely determined.

  As shown in FIG. 4, if the first group 51 and the second group 52 are held in separate lens barrels 61 and 62 having different linear expansion coefficients, the change in the group interval due to the change in the measurement environment temperature can be freely set. .

  For example, it is easy to satisfy the above condition (2).

  In particular, the distances L1 and L2 and the linear expansion coefficients α1 and α2 can be determined so as to satisfy the following condition (3).

(3) L1 × α1 = L2 × α2
That is, the positions of the lenses of the first group and the second group and the materials of the lens barrels 61 and 62 are set so that the condition (3) is satisfied.

  When the condition (3) is satisfied, the distance between the first and second groups constituting the imaging optical system can be kept unchanged regardless of the change in the measurement environment temperature.

  Here, a specific example is given.

"Concrete example"
The lenses of the first group and the second group (lenses 51 and 52 shown in FIGS. 2 and 3) are each set to “two-lens lens configuration” so as to “minimize the amount of change in focal length of each group”. did.
That is, the first group is a cemented lens of the positive lens L1 and the negative lens L2 from the object side, and the second group is a cemented lens of the negative lens L3 and the positive lens L4 from the object side.

The lens L1 has a focal length of 5.991 mm, the glass material is “E-C8” made by HOYA, the lens L2 has a focal length of −11.838 mm, and the glass material is “PCD4” made by HOYA.
The lens L3 has a focal length of −9.471 mm, the glass material is “PCD4” manufactured by HOYA, and the lens L4 has a focal length of 4.793 mm and the glass material is “E-C8” manufactured by HOYA.

“E-C8” and “PCD4” are trade names.
At this time, at the design reference temperature: 25 ° C., the focal length f1 of the first group is 12.5 mm, and the focal length f2 of the second group is 10.0 mm.

Therefore, the imaging magnification (= f2 / f1) is 0.8.
Maximum fluctuation amount of the measurement environment temperature with respect to the imaging optical system: ΔT = + 65 ° C.
In this case, the focal length: variation amount of f1 is ^-2 × ¹⁰ -2 (μm), a focal length: variation amount of f2 could be minimized to ^-2 × ¹⁰ -2 (μm).

  The designed principal point distance between the first and second groups is 22.5 mm.

  Therefore, the imaging optical system can preserve the telecentricity with respect to the maximum fluctuation amount of the measurement environment temperature: + 65 ° C. as follows.

That is, as L1-L2 = 22.5 mm, the condition:
L1 × α1 × 65−L2 × α2 × 65 = −4 × 10 ⁻² (μm)
In order to satisfy the above, the material of the lens barrels 61 and 62 may be selected.
In this way, the telecentricity of the imaging optical system is preserved regardless of the change in the measurement environment temperature, and the change in the imaging magnification: M is minimized.

Note that the change in the group interval (= −4 × 10 ⁻² μm) accompanying the change in the focal lengths f1 and f2 can be regarded as 0 in practice, and the change in the group interval may be zero.

  That is, in this case, it is only necessary to satisfy the condition (2).

  By using the first and second groups of the two-lens laminated lenses, the focal length variation was minimized, and the variation in the group interval: L was set to 0, whereby the variation in the detection length could be 0.05% or less.

  In the specific example described above, both the first and second groups have the “two-lens laminated structure”. However, the present invention is not limited to this, and at least one of the first group and the second group may be composed of one lens. Good.

  The main factor of fluctuation due to temperature fluctuation of the focal length of the imaging optical system is the temperature fluctuation coefficient of the refractive index of the glass material: dN / dT.

  Therefore, using “glass material satisfying dN / dT≈0”, a two-group two-sheet configuration is also possible.

  However, the degree of freedom in design with respect to the constraint on the conjugate length of the imaging optical system and the improvement of aberrations is low.

  By using a laminated lens configuration, such disadvantages can be eliminated, an achromatic effect can be obtained, and fluctuations in focal length associated with wavelength fluctuations of the light source can be suppressed.

  As described above, the displacement measuring apparatus of the present invention can realize “stable displacement measurement” with extremely small variation in detection length with respect to changes in geodetic environmental 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 the frame frequency for acquiring the speckle pattern.
For models with different dimensional configurations, the temperature variation of the detection length can be reduced if optimization is performed in the same manner as in the above embodiment.

  A displacement measuring method for measuring the displacement of the dynamic test surface can be implemented using the displacement measuring apparatus of the above embodiment.

  FIG. 5 shows an embodiment of a color image forming apparatus.

  This color image forming apparatus is of a tandem type using an electrophotographic process, and has four photoreceptors 11Y, 11M, 11C, and 11K that are also received 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 11Y, the formed electrostatic latent image is developed by the developing device GK, and a black toner image is formed on the photoreceptor 11K.

  The toner images of the respective colors formed on the photoconductors 11Y to 11K in this way are transferred onto the intermediate transfer belt 17.

  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 photoconductor 11C by the transfer charger 15C, and a black toner image is transferred from the photoconductor 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”.

  Then, in the transfer portion, the color toner image on the intermediate transfer belt 17 is transferred by being sandwiched 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 regularly controlled by a control driving unit (not shown).

  The displacement measuring means 31 is of the various embodiments described above, and uses the surface of the intermediate transfer belt 17 as a dynamic test surface to measure the moving speed with high accuracy.

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

Ob dynamic test surface
1 Laser light source (LD)
2 Coupling lens
3 Illumination optics
5 Imaging optical system
7 Image sensor
81 housing
82 Housing
9 Calculation unit
10 Light source drive

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

Laser Research 1980 Volume 8 Issue 2 Page 45 “Dynamic Speckle Characteristics and Application to Speed Measurement (I)”

Claims (9)

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 distance: Db between the boiling surface of the dynamic test surface and the Gaussian surface of the dynamic test surface by the imaging optical system: D: The distance: D between the Gaussian surface and the light receiving surface of the imaging element is:
(1) D / Db≈0
The displacement measuring device is characterized in that the illumination aspect of the dynamic test surface by the illumination optical system and the positional relationship between the imaging optical system and the image sensor with respect to the dynamic test surface are set so as to satisfy the above. 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 illumination optical system converts coherent light from a laser light source into a parallel beam by a coupling lens.
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 the image-side focal plane of the first group. And provided at a position that is the object-side focal plane of the second group,
A displacement measuring apparatus, wherein a light receiving surface of an image sensor is matched with a Gaussian surface of the dynamic test surface by an imaging optical system. The displacement measuring device according to claim 2, wherein
A displacement measuring apparatus characterized by minimizing the amount of fluctuation of the focal length of the first group and the second group of the imaging optical system due to fluctuation of the measurement environment temperature. The displacement measuring device according to claim 2 or 3,
A displacement measuring apparatus characterized by minimizing a fluctuation amount due to a fluctuation of a measurement environment temperature of a group interval between a first group and a second group of an imaging optical system. The displacement measuring device according to claim 3,
The first group and the second group of the imaging optical system are both lenses and are arranged in a common lens barrel. The focal length of the first group is f1, the focal length of the second group is f2, and the length of the lens barrel. The amount of change: Δf1, Δf2, and ΔL accompanying the change of the measurement environment temperature is substantially within the fluctuation range of the measurement environment temperature.
(2) ΔL = Δf1 + Δf2
A displacement measuring device, wherein the material of each lens of the first group and the second group and the linear expansion coefficient of the lens barrel are selected so as to satisfy the above. The displacement measuring device according to claim 4 or 5,
In the imaging optical system, the first group and the second group are both lenses, the first group is held by the first lens barrel, the second group is held by the second lens barrel,
The image sensor side of the first and second lens barrels is fixed in the vicinity of the light receiving surface of the image sensor,
Distance from the light receiving surface to the first group: L1, Distance from the light receiving surface to the second group: L2, Linear expansion coefficient of the first lens barrel: α1, Line of the second lens barrel Expansion coefficient: α2 is the condition:
(3) L1 × α1 = L2 × α2
A displacement measuring device in which the positions of the lenses of the first group and the second group and the linear expansion coefficients of the first and second lens barrels are set so as to satisfy the above. 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 any one of claims 1 to 6. 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,
With the surface of the moving body as a dynamic test surface, it has a displacement measuring device that measures the displacement,
An image forming apparatus using the displacement measuring apparatus according to any one of claims 1 to 6 as the displacement measuring apparatus. The image forming apparatus according to claim 8.
An electrostatic latent image is formed on a photoconductive photosensitive member using an electrophotographic process, the electrostatic latent image is visualized as a toner image, and the obtained toner image is transferred to a transfer target. Image forming apparatus.

Images