JP2013257187A5 - Detection apparatus and multicolor image forming apparatus - Google Patents

Description

The present invention relates to a detection device and a multicolor image forming apparatus.
The “multicolor image forming apparatus” of the present invention can be implemented as a digital copying machine, a laser printer, a laser plotter, a laser facsimile, or a complex machine thereof.

The present invention was made in view of the above circumstances, adopt a cross-correlation function using discrete Fourier transform as an evaluation value, detecting apparatus suitable for real-time detection, and multi-color image forming apparatus using the same The realization of

The movement information detection apparatus according to the present invention is a detection apparatus that detects at least one of speed and displacement of a moving body as movement information, and includes a light source unit that irradiates the moving body and a plurality of pixels. An image sensor unit that outputs a two-dimensional image, an optical system that guides scattered light scattered by the moving member onto the image sensor unit , and an image pattern that acquires a time-series image pattern from the image sensor unit And obtaining at least one of the speed and displacement of the moving member by a cross-correlation function of the image pattern P1 and the image pattern P2, which are two image patterns having different times obtained by the image pattern obtaining unit. the cross-correlation function is a discrete Fourier transform, and the background removal processing in a frequency space, and inverse discrete Fourier transform, to include And butterflies.

The mobile information detecting apparatus of the invention, the detection apparatus suitable for real-time detection, and realization of multi-color image forming apparatus can be using the same.

It is a figure which shows one example of a correlation mutual function. It is sectional drawing of the correlation mutual function of FIG. It is a figure for demonstrating movement information detection. The flowchart of the procedure which calculates a peak position is shown. It is a figure which shows the example of two image patterns acquired continuously in time. It is a flowchart which shows the procedure which calculates | requires the deformed cross correlation function. It is a figure which shows one example of the low frequency removal pattern LC. It is a figure for demonstrating the effect of a background removal process. It is a figure which shows the example of two image patterns acquired as preliminary operation | movement before detecting a speed and a displacement. It is a figure which shows three examples of the low frequency removal pattern LC. It is a figure which shows the example of the two image patterns acquired. It is a figure which shows correlation pattern PS1, PS2, PS3 calculated | required using the low frequency removal pattern LC1, LC2, LC3 shown in FIG. It is a figure which shows another two examples of a low frequency removal pattern. It is a figure explaining that this invention is effective with respect to a subpixel process. It is a figure which shows the graph of the correlation peak position PP which performed the sub pixel process with respect to two adjacent image patterns, when a background removal process is performed. It is a figure which shows the graph of correlation peak position PP when not performing a background removal process. It is a figure for demonstrating one Embodiment of a multicolor image forming apparatus. It is a figure for demonstrating another form of implementation of a multi-color image forming apparatus. It is a figure for demonstrating an example of a structure of an optical scanning device. It is a figure which shows the schematic diagram of the structure of a liquid-crystal deflection element. FIG. 6 is a diagram illustrating an embodiment when the movement information detection device is applied to the detection of the speed fluctuation of the intermediate transfer belt of the multicolor image forming apparatus. 1 is a diagram illustrating an embodiment of a multicolor image forming apparatus that prints and records pixels with an ink discharge head. FIG. It is a figure for demonstrating a prior art.

Hereinafter, embodiments will be described.
First, the detection of the movement information of the moving body will be described with reference to FIG.
The movement information is “at least one of speed and displacement of the moving body ” as described above.
Hereinafter, “at least one of speed and displacement” may be abbreviated as “speed or displacement” or “displacement or velocity”.
That is, only one of the displacement / velocity of the moving body can be detected as movement information, or both can be detected as movement information.

In FIG. 3, symbol LS indicates “linear stage”, symbol VCP indicates “air suction plate”, symbol S indicates “paper”, symbol LTS indicates “semiconductor laser”, and symbol CL indicates “coupling lens”.
Reference sign LN indicates an “imaging lens”, reference sign IS indicates an “image sensor of an image sensor unit ”, reference sign PSN indicates “image pattern acquisition means”, and reference sign CON indicates “speed / displacement calculation means”.

The sheet S is a sheet-like recording medium used in the multicolor image forming apparatus, specifically, the above-described “standard sheet, postcard, cardboard, OHP sheet, etc.”, and “the moving body whose movement information is to be detected ( Hereinafter also referred to as “moving member”) .

The portions excluding the paper S, the linear stage LS, and the air suction plate VCP constitute one embodiment of the “detection device that detects movement information”.

“Displacement and speed” of the paper S by the linear stage LS is movement information.
The semiconductor laser LTS is a “light source”, specifically a “red semiconductor laser” having an emission wavelength of 658 nm.
The coupling lens CL is a positive lens having a focal length of 4 mm, collects the beam from the semiconductor laser LTS, and irradiates the paper S. The semiconductor laser LTS, which is a light source, and the coupling lens CL constitute a “light source unit that irradiates the moving body”.
The “irradiation angle” is inclined 45 degrees with respect to the paper surface.

Of course, the present invention is not limited to this, but the contrast of the speckle pattern is reduced, but a “lower cost LED light source” can also be used.
The linear stage LS performs “moving operation at a speed of 100 mm / second in the moving direction”.
Since the speckle pattern on the light receiving surface of the image sensor IS forms an inverted image, it moves in the direction opposite to the paper S at the “speed obtained by multiplying the paper moving speed by the imaging magnification” as the paper S moves. Moving.
During this movement, the image sensor IS continuously captures a speckle pattern at a constant time interval (frame rate 504 fps), and acquires the speckle pattern by the image pattern acquisition means PSN.
The speckle pattern acquired by imaging in this way is an “image pattern”.
That is, the image sensor unit outputs a two-dimensional image in time series.

Next, determine the "cross-correlation function as the evaluation value" from the acquired image pattern, a procedure for obtaining the peak position (also referred to as "correlation peak position".).
The correlation peak position can be converted into a displacement amount using the imaging magnification and the pixel pitch of the image sensor IS.
That is, as described above, in the process of calculating the displacement amount from two image patterns acquired sequentially in time, the two image patterns are updated as needed to accumulate the displacement amount, and the “cumulative displacement amount” of the moving object Can be calculated.

Hereinafter, the embodiment of the invention will be described by taking the case of FIG. 3 as an example.
FIG. 4 shows a flowchart of the “procedure for obtaining the peak position”.
In “image pattern acquisition 201”, two temporally continuous image patterns (speckle patterns for two frames) at a certain time are acquired.

The “cross-correlation function” obtained by the “calculation using discrete Fourier transform / inverse discrete Fourier transform” in the equation (2) described above is not subjected to “background removal processing”.

In the present invention, in order to remove the influence of background portion overlapping the peak portion, by adding a "background removal processing in a frequency space" Request "deformed cross-correlation function."

The "peak position calculation 203" of FIG. 4, obtaining a correlation peak position.

In the detection apparatus of the present invention, unlike the prior art, there is no “addition of arithmetic processing in real space before and after evaluation value calculation”. Therefore, the “calculation processing time” hardly increases.

Hereinafter, each procedure will be described.
FIG. 5 shows two image patterns acquired successively in time at a certain point in the step of “image pattern acquisition 201” in FIG.
5A shows the image pattern P1 at time t1 (before movement), and FIG. 5B shows the image pattern P2 at time t2 subsequent to time t1 (after movement).
In the example in the description, the time difference between time: t1 and t2 is “time between adjacent frames (1 second / 504): 1.98 ms” according to the frame rate (504 fps).
Using these two image patterns P1 and P2, a “deformed cross-correlation function” is obtained .

FIG. 6 is a flowchart showing a procedure for obtaining a “modified cross-correlation function”.
Image patterns P1 and P2 are acquired in real space. Then, a Fourier pattern F1 by the discrete Fourier transform of the image pattern P1.
Similarly, obtaining the Fourier pattern F2 by the discrete Fourier transform of the image pattern P2.

A complex conjugate F2 ^* of the Fourier pattern F2 is obtained , and a composite Fourier pattern F3 is obtained by the product of the complex conjugate F2 ^* and the Fourier pattern F1.
Synthesized Fourier pattern F3 to "background removal processing in the frequency space (background processing in the frequency space)" is subjected to, determining the BG removed Fourier pattern F4.
In this way, a “deformed cross-correlation function” is obtained by performing “inverse discrete Fourier transform” on the “BG-removed Fourier pattern F4 subjected to background removal processing in the frequency space”.

The case where the difference of the background removal pattern FB is performed will be described as “another example of obtaining a deformed cross-correlation function (background removal processing in a frequency space)”.

Against above-mentioned image pattern P1 and P2, when describing the case of applying the background removal pattern FB, "BG removed by obtaining a difference between the background removal pattern FB" synthetic Fourier pattern F3 "above for each pixel A Fourier pattern F4 "can be obtained.

As shown in FIG. 9, two image patterns (referred to as Q1 and Q2) are acquired (image pattern acquisition 301) as “preliminary operation before detecting speed and displacement”.
On the acquired image pattern Q1 and Q2, the low frequency rejection pattern LC1, LC2, ..., are sequentially applied LCn, a ..., correlation pattern PS1, PS2, determined ..., PSn, a ... .
Of the correlation patterns PSn calculated in this way, the “correlation pattern PS (best) from which the background portion is well removed” is selected.
Then, the low frequency removal pattern LC (best) used for the calculation of the correlation pattern PS (best) is selected and used when “actually detecting speed and displacement”.

Actually, an example is shown in which correlation patterns PS1, PS2, and PS3 are obtained for image patterns Q1 and Q2 using three types of low-frequency removal patterns LC1, LC2, and LC3.

Correlation patterns PS1, PS2, and PS3 obtained by using the low frequency removal patterns LC1, LC2, and LC3 for these image patterns Q1 and Q2 are shown in FIGS.

The three correlation patterns PS1, PS2, and PS3 obtained are compared as follows.
When the correlation patterns PS1 and PS2 are compared, the “peak part” in these is substantially the same, but in the correlation pattern PS2, the background part is better removed.

As another embodiment, “performing background removal processing in a frequency space” is effective for the so-called sub-pixel processing for obtaining the correlation peak position PP on the correlation pattern PS with a resolution equal to or less than the pixel unit of the image sensor. Explain what to do.

As a comparative example, FIGS. 16A and 16B show “results similar to the above” when the background removal process is not performed.
The cumulative displacement amount when the background removal process is performed is 50.020 mm, and the cumulative displacement amount when it is not performed is 49.736 mm.
The error with respect to the moving distance of 50 mm is 20 μm for the former and 264 μm for the latter. The error in the former is 0.8% of the error in the latter, and the effect of 10 times or more is seen for highly accurate detection. .
The cross correlation function of the adjacent image patterns P1 and P2 having the acquisition times has been described above. However, the image patterns P1 and P2 giving the cross correlation function are acquired by the time-series image patterns acquired by the image pattern acquisition unit. It is also possible to use two image patterns having different times.

In the multicolor image forming apparatus of FIG. 18 as well, each of the photoreceptors 1Y, 1M, 1C, and 1K is uniformly charged by the chargers 2Y, 2M, 2C, and 2K.

For this purpose, a detection device that detects the speed fluctuation and displacement of these belts as movement information is important.

The “ detection device ” described above can be used to detect speed fluctuations in the circumference of the belt of the intermediate transfer belt or the conveyance belt used in the multicolor image forming apparatus. Speed fluctuation can be detected.

Further, with respect to a belt-like member or a roller-like member used as a fixing device, it is also possible to detect and correct a speed variation using the above-described detection device .

The movement information detection device A which is the detection device in FIG. 21 is installed in the vicinity of the drive roller 105 </ b> A of the intermediate transfer belt 105.

As in the case of the movement information detection device B, which is another detection device, if it is arranged corresponding to the “strained portion” of the intermediate transfer belt 105, it is easily affected by the above-mentioned belt fluttering.

The detection device 255 is arranged at the position shown in the figure, detects a predetermined feed amount of intermittent feed as movement information of the actual recording paper S itself as a moving body, and realizes highly accurate paper feed by controlling conveyance. it can.

Claims (9)

A detection device for detecting at least one of speed and displacement of a moving body as movement information,
A light source unit for irradiating the moving body ;
An image sensor unit having a plurality of pixels and outputting a one-dimensional or two-dimensional image;
An optical system for guiding the scattered light scattered by the moving member onto the image sensor;
Image pattern acquisition means for acquiring a time-series image pattern from the image sensor unit ;
Have
Obtain at least one of the speed and displacement of the moving member by the cross-correlation function of the image pattern P1 and the image pattern P2, which are two image patterns having different times acquired by the image pattern acquisition means ,
The cross-correlation function, discrete Fourier transform and the detection apparatus which comprises a background removal processing in a frequency space, and inverse discrete Fourier transform, a. The detection device according to claim 1,
The cross-correlation function is
Determining a Fourier pattern F1 by discrete Fourier transforming the image pattern P1,
Determining a Fourier pattern F2 by discrete Fourier transforming the image pattern P2,
Wherein a Fourier pattern F1, by obtaining the product of the complex conjugate of the Fourier pattern F2, determining a synthesized Fourier pattern F3,
With respect to the synthesized Fourier pattern F3, by removing the background of the frequency space, determining a Fourier pattern F4,
Detecting device comprising the steps of: obtaining a correlation pattern PS, in that it consists by inverse discrete Fourier transform of the Fourier pattern F4. The detection device according to claim 2, wherein
The background removal processing, detection device and obtains the product of the synthesized Fourier pattern F3 and low frequency rejection pattern LC. The detection device according to claim 2, wherein
The background removal processing, detection device and obtains a difference between the synthesized Fourier pattern F3 and the background removal pattern FB. The detection device according to claim 3 or 4,
Wherein at least one of the low frequency removal pattern LC and the background removal pattern FB is, a plurality of patterns prepared,
In response to said at least one image pattern P1 and the image pattern P2, one of the plurality of removed patterns said prepared is selected and you and performs the background removal processing detector. The detection apparatus according to any one of claims 1 to 5,
Wherein when more obtain the velocity or displacement of the moving member in the cross-correlation function, the detection device and obtains the correlation peak position PP in the correlation pattern PS in pixels following the resolution of the image sensor unit. A plurality of image carriers, a charging device that uniformly charges the plurality of image carriers, and an optical scanning device that forms an electrostatic latent image by optically scanning the plurality of uniformly charged image carriers with a beam spot; The electrostatic scanning image formed on the plurality of image carriers by the optical scanning device is visualized with toner of a predetermined color, and can be moved to face the plurality of image carriers. An intermediate transfer belt, a first transfer device, a second transfer device, and a fixing device.
The color toner images visualized on the plurality of image carriers are transferred onto the intermediate transfer belt by the first transfer device, and the color toner images are superimposed on the intermediate transfer belt. The respective color toner images thus transferred are transferred onto a sheet-like recording medium by the second transfer means, and the respective color toner images transferred onto the sheet-like recording medium are fixed on the sheet-like recording medium by the fixing device. In a multicolor image forming apparatus for forming a color or color image,
7. A multicolor image forming apparatus comprising: the detection device according to claim 1; and detecting a speed of the intermediate transfer belt. A plurality of image carriers, a charging device that uniformly charges the plurality of image carriers, and an optical scanning device that forms an electrostatic latent image by optically scanning the plurality of uniformly charged image carriers with a beam spot; The electrostatic scanning image formed on the plurality of image carriers by the optical scanning device is visualized with toner of a predetermined color, and can be moved to face the plurality of image carriers. A conveyance belt that conveys a sheet-like recording medium, a transfer device, and a fixing device,
Each color toner image visualized on the plurality of image carriers is directly transferred to the sheet-like recording medium conveyed by the conveying belt by the transfer device, and each color toner image is transferred onto the sheet-like recording medium. In a multicolor image forming apparatus that forms a multicolor or color image by superimposing and fixing each color toner image superimposed on the sheet-like recording medium on the sheet-like recording medium by the fixing unit.
7. A multicolor image forming apparatus comprising: the detection device according to claim 1; and detecting a speed of the conveyance belt. In a multicolor image forming apparatus that prints and records pixels on a sheet-like recording medium with an ink ejection head,
A multicolor image forming apparatus comprising: the detection device according to claim 1, wherein the movement amount of the sheet-like recording medium is detected.