Image forming apparatus and transport control method

Abstract

To detect movement amounts of a recording medium with high accuracy to improve a printing quality.SOLUTION: An image forming device comprises: a conveying mechanism for a recording medium; a printing part that performs printing on the recording medium; an original point detecting part provided in the conveying mechanism; a movement amount calculating part that calculates movement amounts of the recording medium on the basis of correlation between photographed images photographed for each predetermined time by a photographing part, and cumulatively processes the calculated movement amounts sequentially to calculate a cumulative movement amount; a correcting part that performs operation to match the cumulative movement amount with a reference movement amount of the recording medium corresponding to a predetermined cycle obtained from a mechanical configuration of the conveying mechanism, for each predetermined cycle of the conveying mechanism that is detected by the original point detecting part; and a control part that controls the conveying mechanism on the basis of the cumulative movement amount corrected by the correcting part so that the recording medium is conveyed and controlled, and controls the printing part so that printing is performed on the recording medium conveyed and controlled.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus and a transport control method. [Background technology]

[0002] Today, a technology is known that corrects the timing of ink droplet ejection in accordance with the amount of movement of a rolled recording medium (web or roll of paper) detected by an encoder attached to a driven roller in front of the head, thereby preventing a deterioration in print quality.

[0003] Furthermore, Patent Document 1 (JP Patent Publication 2003-266828 A) discloses an image forming apparatus that allows for high-precision paper transport regardless of the type and condition of the paper. In this image forming apparatus, a motion sensor provided in the paper transport path irradiates laser light from a semiconductor laser onto the outer circumferential surface of an idle roller that rotates along with the transport of the paper. The motion sensor receives the reflected laser light with a two-dimensional semiconductor image sensor. A paper position detection section then detects the position of the paper based on a speckle pattern obtained from the reflected light. This allows for accurate detection of the paper position, enabling high-precision paper transport. Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional methods for detecting the amount of web movement, including the technology of Patent Document 1, have had the problem that when the driven roller thermally expands and changes its diameter, or when the driven roller becomes eccentric, it becomes difficult to detect the correct amount of web movement, resulting in reduced print quality.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an image forming apparatus and a transport control method that can detect the amount of movement of a recording medium with high accuracy, thereby improving print quality. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the present invention provides a recording medium conveying mechanism, a printing unit which prints on the recording medium, an origin detection unit provided in the conveying mechanism, a movement amount calculation unit which calculates a movement amount of the recording medium based on a correlation between captured images of the recording medium captured at predetermined time intervals by an imaging unit, and sequentially accumulates each calculated movement amount to calculate an accumulated movement amount, and a calculation unit which calculates an accumulated movement amount by multiplying a reference movement amount of the recording medium for a predetermined period obtained from the mechanical configuration of the conveying mechanism for each predetermined period of the conveying mechanism detected by the origin detection unit. Correct The recording medium conveying device includes a correction unit, and a control unit that controls the conveying mechanism based on the cumulative movement amount corrected by the correction unit to control the conveying of the recording medium, and also controls the printing unit to print on the recording medium whose conveying is controlled. Effect of the Invention

[0007] According to the present invention, it is possible to detect the amount of movement of the recording medium with high accuracy, thereby improving print quality. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing the appearance of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a schematic configuration of a main part of the image forming apparatus according to the embodiment. [Diagram 3] FIG. 3 is a block diagram of a sensor device provided in the image forming apparatus according to the embodiment. [Figure 4] FIG. 4 is a diagram showing the external appearance of the sensor device. [Diagram 5] FIG. 5 is a block diagram of a main part of the image forming apparatus according to the embodiment. [Figure 6] FIG. 6 is a functional block diagram of a calculation unit provided in the image forming apparatus according to the embodiment. [Figure 7] FIG. 7 is a diagram for explaining a peak value search technique in the peak position search section. [Figure 8] FIG. 8 is a diagram showing a correlation intensity distribution of a cross-correlation function. [Figure 9]FIG. 9 is a diagram showing the actual web transport position and the web transport position calculated based on the encoder signal. [Figure 10] FIG. 10 is a diagram showing the amount of deviation of the landing position of ink on the web. [Figure 11] FIG. 11 is a diagram for explaining the operation of calculating the accumulated movement amount. [Figure 12] FIG. 12 is a diagram for explaining the operation of correcting the accumulated movement amount. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an image forming apparatus according to an embodiment will be described with reference to the accompanying drawings.

[0010] (Overall composition) Fig. 1 is a perspective view showing the appearance of an image forming apparatus according to an embodiment, which forms an image by ejecting ink droplets onto a rolled recording medium (web or rolled paper). In Fig. 1, an image forming apparatus 110 adjusts the tension of a web 120 by means of a roller 130 or the like, and transports the web 120 in a transport direction 10. The image forming apparatus 110 then ejects ink of each of four colors, for example black (K), cyan (C), magenta (M), and yellow (Y), onto the transported web 120 to form a desired image. In the following description, a direction perpendicular to the transport direction 10 is referred to as an "orthogonal direction 20".

[0011] (Main part configuration) FIG. 2 is a diagram showing a schematic configuration of a main part of an image forming apparatus 110. As shown in FIG. 2, the image forming apparatus 110 has four liquid ejection head units for ejecting ink of four colors. Each liquid ejection head unit ejects a liquid of each color onto a web 120 transported in a transport direction 10. The web 120 is transported by two pairs of nip rollers and a transport roller 230 (an example of a transport mechanism). Hereinafter, of the two pairs of nip rollers, the nip rollers installed upstream of each liquid ejection head unit are referred to as "first nip roller NR1". Meanwhile, the nip rollers installed downstream of the first nip roller NR1 and each liquid ejection head unit are referred to as "second nip roller NR2".

[0012] The image forming apparatus 110 also has an encoder ENC (an example of an origin detector). The encoder ENC is a device equipped with a rotating plate and a rotation detection sensor that reads surface information of the rotating plate. The rotating plate of the encoder ENC is installed on the rotating shaft of the conveying roller 230. When the conveying roller 230 rotates, the rotating plate rotates, and the rotation detection sensor outputs an encoder pulse ENP, which is a pulse corresponding to the amount of rotation.

[0013] As will be described later, image forming apparatus 110 according to the embodiment corrects the calculated web movement amount based on encoder pulse ENP, for example, every time conveyance roller 230 makes one revolution (or every predetermined number of revolutions).

[0014] The liquid ejection head units (an example of a printing section) are arranged in the order of black (K), cyan (C), magenta (M) and yellow (Y) from the upstream side to the downstream side. That is, the black liquid ejection head unit 210K is provided at the most upstream side. The cyan liquid ejection head unit 210C is provided next to the black liquid ejection head unit 210K. The magenta liquid ejection head unit 210M is provided next to the cyan liquid ejection head unit 210C. The yellow liquid ejection head unit 210Y is provided at the most downstream side.

[0015] Based on image data, each liquid ejection head unit ejects ink of each color onto a predetermined location on the web 120. The landing position of the ink ejected onto the web 120 is approximately directly below the ejection position of the liquid ejection head unit.

[0016] In this example, black ink is ejected onto a black landing position PK of the black liquid ejection head unit 210K, and cyan ink is ejected onto a cyan landing position PC of the cyan liquid ejection head unit 210C. Similarly, magenta ink is ejected onto a magenta landing position PM of the magenta liquid ejection head unit 210M, and yellow ink is ejected onto a yellow landing position PY of the yellow liquid ejection head unit 210Y.

[0017] The ink ejection timing in each liquid ejection head unit and the actuator ACT provided in each liquid ejection head unit are controlled by a control unit 110F30 connected to each liquid ejection head unit.

[0018] Further, each liquid ejection head unit is provided with a plurality of driven rollers. The plurality of driven rollers are provided on the upstream side and downstream side of each liquid ejection head unit. That is, in the transport path of the web 120, a first roller that supports the web 120 is provided on the upstream side of each landing position for each liquid ejection head unit, and a second roller that supports the web 120 is provided on the downstream side of each landing position for each liquid ejection head unit.

[0019] That is, a first roller for black CR1K is provided upstream of the black landing position PK in the transport direction of the web 120. On the other hand, a second roller for black CR2K is provided downstream of the black landing position PK in the transport direction of the web.

[0020] Similarly, a first cyan roller CR1C and a second cyan roller CR2C are provided for the cyan liquid ejection head unit 210C. Furthermore, a first magenta roller CR1M and a second magenta roller CR2M are provided for the magenta liquid ejection head unit 210M. Furthermore, a first yellow roller CR1Y and a second yellow roller CR2Y are provided for the yellow liquid ejection head unit 210Y.

[0021] (Sensor device configuration) Next, in the image forming apparatus 110, as shown in Fig. 2, a sensor device SEN is provided between the conveying roller 230 and the first roller CR1K for black. Fig. 3 is a block diagram of the sensor device SEN. As shown in Fig. 3, the sensor device SEN has a light source LG, an imaging unit OS, a control circuit 52, a storage device 53, and a control unit 110F30. As the light source LG, a light source that emits infrared light, such as an LED (Light Emitting Diode) or an organic EL (Electro Luminescence) can be used.

[0022] The imaging unit OS may be a CCD (Charge Coupled Device) camera or a CMOS (Complementary Metal Oxide Semiconductor) camera. The imaging unit OS is preferably equipped with a global shutter. Compared to a rolling shutter, the global shutter can suppress so-called image shift, which occurs when the timing of releasing the shutter is not met for a subject that moves quickly.

[0023] The control circuit 52 controls the imaging unit OS, the light source LG, and the like inside the sensor device SEN. Specifically, the control circuit 52 outputs, for example, a trigger signal to the imaging unit OS to control the timing at which the imaging unit OS releases the shutter. The control circuit 52 also controls so that a two-dimensional image can be acquired from the imaging unit OS. The control circuit 52 then supplies the storage unit 53 with image information captured by the imaging unit OS at each time. The storage unit 53 stores the image information at each time supplied from the control circuit 52, etc.

[0024] The control unit 110F30 calculates and accumulates the amount of movement of the web 120 based on the correlation between images in the image information for each time stored in the storage unit 53. This makes it possible to accurately recognize the amount of movement of the web 120. This will be described in detail later.

[0025] Fig. 4 is a diagram showing the external appearance of the sensor device SEN. As shown in Fig. 4, the sensor device SEN irradiates detection light from a light source LG onto a web 120. Specifically, the sensor device SEN first has a light source (LG) such as a semiconductor laser or an LED (light emitting diode) and an optical system such as a collimating optical system. The sensor device SEN also has a CMOS image sensor, which is an example of an imaging unit OS, for capturing an image showing an imaging pattern, and a telecentric imaging optical system (TO) for focusing the imaging pattern on the CMOS image sensor.

[0026] (Detailed configuration of main parts) Fig. 5 is a block diagram of the main parts of the image forming apparatus 110. As shown in Fig. 5, the sensor device SEN of the image forming apparatus 110 has an imaging unit OS equipped with the above-mentioned light source LG, a control circuit 52, and a recording unit 53. The imaging unit OS captures an image of the web 120 transported in the transport direction 10.

[0027] The control circuit 52 has a shutter control unit 141A and an image acquisition unit 142A. The image acquisition unit 142A acquires image information of an image captured by the imaging unit OS at each time. The shutter control unit 141A controls the imaging timing of the imaging unit OS so as to capture an image at each time. The recording unit 53 stores the image information at each time acquired by the image acquisition unit 142A from the imaging unit OS.

[0028] As shown in FIG. 5, the image forming apparatus 110 includes a calculation unit 53F, a measurement unit 110F20, an adjustment unit 110F40, a cooling unit 250, and a notification unit 251.

[0029] Calculation unit 53F calculates the position of the pattern on web 120, the moving speed at which web 120 is transported, and the moving distance of web 120, based on the image information of the image at each time stored in storage unit 53. The output of the moving distance, etc. calculated by calculation unit 53F is supplied to adjustment unit 110F40 and control unit 110F30. Based on the output of the moving distance, etc. calculated by calculation unit 53F, adjustment unit 110F40 performs shutter control of imaging unit OS via shutter control unit 141A.

[0030] The control unit 110F30 (an example of a control unit) detects thermal expansion of the transport roller 230 based on the movement amount of the web 120 calculated by the calculation unit 53F, and cools the transport roller 230 via the cooling unit 250 when a predetermined amount of thermal expansion or more has occurred. Furthermore, the control unit 110F30 controls the image forming apparatus 110 to stop (system stop) when a predetermined amount of thermal expansion or more has occurred. Furthermore, the control unit 110F30 controls a predetermined notification, such as displaying a predetermined error message and / or sounding a warning sound, via the notification unit 251 when a predetermined amount of thermal expansion or more has occurred.

[0031] The measurement unit 110F20 counts the encoder pulses ENP output by the encoder ENC attached to the transport roller 230 shown in FIG. 2, thereby supplying a timing pulse to the calculation unit 53F every time the transport roller 230 rotates (or every several rotations). As described above, the calculation unit 53F calculates the movement amount of the web 120 based on the correlation of the images at each time and performs accumulation processing, but if this accumulation processing is continued, the difference from the actual behavior of the web between image acquisition cycles may become large. For this reason, the calculation unit 53F resets the difference from the actual behavior of the web between image acquisition cycles, for example, every time the transport roller 230 rotates once. This makes it possible to prevent accumulation of errors due to accumulation processing of the movement amount of the web 120.

[0032] (Imaging pattern) The web 120 is a member having scattering properties on the surface or inside thereof. Therefore, when the web 120 is irradiated with laser light, the reflected light is diffusely reflected. Due to this diffuse reflection, a spot pattern (image pattern) is formed on the web 120.

[0033] When the web 120 is transported, the imaging pattern of the web 120 is also transported together. Therefore, the calculation unit 53F calculates the movement amount of the web 120 based on the captured images of the same imaging pattern captured at different times. The calculation unit 53F also calculates the movement speed of the web 120 by converting this movement amount into a unit time.

[0034] (Functional block configuration of the calculation unit) Fig. 6 is a functional block diagram of the calculation unit 53F. As shown in Fig. 6, the calculation unit 53F performs a cross-correlation calculation on image data D1(n) and D2(n) acquired by the sensor device SEN at each predetermined time. Hereinafter, an image generated by the cross-correlation calculation is referred to as a "correlation image." The calculation unit 53F calculates the amount of deviation ΔD(n) based on the correlation image.

[0035] The cross-correlation calculation is calculated based on the following formula (1). In the following formula (1), image data D1(n) is the imaging data captured at the earlier time of two sets of image data captured consecutively at a predetermined time. In the following formula (1), image data D2(n) is the imaging data captured at the later time of two sets of image data captured consecutively at a predetermined time. In the following formula (1), "F[]" indicates Fourier transform, and "F-1[]" indicates inverse Fourier transform. In the following formula (1), "*" indicates complex conjugate, and "★" indicates cross-correlation calculation.

[0036] D1★D2*=F-1[F[D1]·F[D2]*]···(1)

[0037] As shown in formula (1), by performing a cross-correlation calculation "D1★D2" on image data D1 and D2, correlation image data showing the correlation between the images can be obtained. If the image data D1 and image data D2 are two-dimensional image data, the correlation image data will be two-dimensional image data. On the other hand, if the image data D1 and D2 are one-dimensional image data, the correlation image data will be one-dimensional image data.

[0038] In such correlation image data, when the problem is, for example, a luminance distribution with little difference between each region (broad luminance distribution), the phase-only correlation method shown in the following formula (2) may be used. In formula (2), "P[]" indicates that only the phase is extracted from the complex amplitude. Moreover, all amplitudes are set to "1".

[0039] D1★D2*=F-1[P[F[D1]]·P[F[D2]*]]···(2)

[0040] By using such a phase-only correlation method, it is possible to easily calculate the amount of deviation ΔD(n) based on the correlation image, even if the luminance distribution is broad.

[0041] The correlation image shows the correlation between the image data D1 and the image data D2. Specifically, the higher the degree of match between the image data D1 and the image data D2, the sharper the peak, the so-called correlation peak, of brightness is output at a position closer to the center of the correlation image. When the image data D1 and the image data D2 match, the center and the peak of the correlation image overlap.

[0042] (Correlation calculation example) The correlation calculation will now be described in detail.

[0043] 6, the calculation unit 53F has a first two-dimensional Fourier transform unit FT1, a second two-dimensional Fourier transform unit FT2, a correlation image data generation unit DMK, a peak position search unit SR, a calculation unit CAL, and a conversion result storage unit MEM. The calculation unit CAL is an example of a movement amount calculation unit, a correction unit, a comparison unit, and a detection unit.

[0044] The first two-dimensional Fourier transform unit FT1 transforms the first image data D1. Specifically, the first two-dimensional Fourier transform unit FT1 has a Fourier transform unit FT1a for the orthogonal direction and a Fourier transform unit FT1b for the transport direction.

[0045] The orthogonal Fourier transform unit FT1a performs a one-dimensional Fourier transform on the first image data D1 in the orthogonal direction. Then, the transport direction Fourier transform unit FT1b performs a one-dimensional Fourier transform on the first image data D1 in the transport direction based on the transformation result by the orthogonal Fourier transform unit FT1a. In this way, the orthogonal Fourier transform unit FT1a and the transport direction Fourier transform unit FT1b perform one-dimensional Fourier transform in the orthogonal direction and the transport direction, respectively. The first two-dimensional Fourier transform unit FT1 outputs the transformation result thus obtained to the correlation image data generation unit DMK.

[0046] Similarly, the second two-dimensional Fourier transform unit FT2 transforms the second image data D2. Specifically, the second two-dimensional Fourier transform unit FT2 includes an orthogonal Fourier transform unit FT2a, a transport direction Fourier transform unit FT2b, and a complex conjugate unit FT2c.

[0047] The orthogonal Fourier transform section FT2a performs a one-dimensional Fourier transform on the second image data D2 in the orthogonal direction. Then, the transport direction Fourier transform section FT2b performs a one-dimensional Fourier transform on the second image data D2 in the transport direction based on the transformation result by the orthogonal direction Fourier transform section FT2a. In this way, the orthogonal direction Fourier transform section FT2a and the transport direction Fourier transform section FT2b perform one-dimensional Fourier transforms in the orthogonal direction and the transport direction, respectively.

[0048] Next, the complex conjugate unit FT2c calculates the complex conjugate of the transformation results by the orthogonal Fourier transform unit FT2a and the transport direction Fourier transform unit FT2b. The second two-dimensional Fourier transform unit FT2 outputs the complex conjugate calculated by the complex conjugate unit FT2c to the correlation image data generation unit DMK.

[0049] Next, the correlation image data generation unit DMK generates correlation image data based on the transformation result of the first image data D1 output from the first two-dimensional Fourier transform unit FT1 and the transformation result of the second image data D2 output from the second two-dimensional Fourier transform unit FT2.

[0050] The correlation image data generating unit DMK includes an integrating unit DMKa and a two-dimensional inverse Fourier transform unit DMKb.

[0051] The accumulating unit DMKa accumulates the conversion result of the first image data D1 and the conversion result of the second image data D2, and supplies the accumulated output to the two-dimensional inverse Fourier transform unit DMKb. The two-dimensional inverse Fourier transform unit DMKb performs a two-dimensional inverse Fourier transform on the accumulation result by the accumulating unit DMKa. In this way, when the two-dimensional inverse Fourier transform is performed, correlation image data is generated.

[0052] Following the accumulation process of the conversion results of the first image data D1 and the second image data D2, the accumulation unit DMKa sequentially accumulates the conversion results of the second image data D2 and the conversion results of the third image data D3, the conversion results of the third image data D3 and the conversion results of the fourth image data D4, etc. The two-dimensional inverse Fourier transform unit DMKb sequentially performs two-dimensional inverse Fourier transform processing on the accumulation results supplied from the accumulation unit DMKa to generate correlation image data and supply it to the peak position search unit SR.

[0053] As an example, a matrix of luminance values ​​can be used as the correlation image data. The peak position search unit SR searches for the peak luminance (peak value) that rises most steeply in such correlation image data.

[0054] 7 is a diagram for explaining a method for searching for a peak value in the peak position search unit SR, in which the horizontal axis indicates the position in the transport direction in the image represented by the correlation image data, and the vertical axis indicates the brightness of the image represented by the correlation image data.

[0055] Hereinafter, three pieces of data, the first data value q1, the second data value q2, and the third data value q3, among the luminance values ​​indicated by the correlation image data, will be described as an example. That is, in this example, the peak position search unit SR searches for a peak position P on a curve k that connects the first data value q1, the second data value q2, and the third data value q3.

[0056] First, the peak position search unit SR calculates each difference in luminance of the image represented by the correlation image data, and then extracts the combination of data values ​​that has the largest difference value from among the calculated differences.

[0057] Next, the peak position search unit SR extracts a combination adjacent to the combination of data values ​​with the largest difference value. This allows three data to be extracted, such as a first data value q1, a second data value q2, and a third data value q3. The peak position search unit SR connects the three extracted data to calculate a curve k, and searches for the peak position P.

[0058] This reduces the amount of calculation required for sub-pixel processing and the like, and enables faster searching for peak position P. The position of the combination of data values ​​that produces the largest difference value is the steepest position.

[0059] Furthermore, the luminance used as the correlation image data is arranged at pixel pitch intervals (pixel size intervals) of the area sensor. For this reason, it is preferable to search for the peak value after so-called sub-pixel processing. By performing sub-pixel processing, the peak position can be searched for with high accuracy. This makes it possible to calculate the position, movement amount, movement speed, etc. with high accuracy.

[0060] Next, Fig. 8 is a diagram showing the correlation intensity distribution of the cross-correlation function. The X-axis and Y-axis in Fig. 8 indicate the serial numbers of pixels. The peak value shown as the "correlation peak" in Fig. 8 is searched for by the peak position search unit SR.

[0061] Next, the calculation unit CAL shown in Fig. 6 calculates the relative position, movement amount, movement speed, etc. of the web 120. For example, the calculation unit CAL calculates the difference between the positions of the peak values ​​of the correlation image data corresponding to the image data captured at predetermined times to calculate the relative position and movement amount, and accumulates the calculated movement amount for a predetermined amount. The calculation unit CAL also calculates the movement speed by dividing the movement amount by time. The calculation unit CAL supplies each piece of information on the relative position, movement amount, and movement speed thus calculated to the adjustment unit 110F40 and the control unit 110F30 shown in Fig. 5.

[0062] Here, a pair of first and second rollers CR1 and CR2 are provided below each liquid ejection head unit 210 to suppress flapping of the web 120 directly below each liquid ejection head unit 210. Also, an encoder ENC is provided on the rotation shaft of a transport roller 230 provided upstream of each liquid ejection head unit 210. When the transport roller 230 rotates to transport the web 120, an encoder signal is output from the encoder ENC. A control unit 110F30 shown in FIG. 5 controls the ink ejection timing of each liquid ejection head unit 210 based on this encoder signal.

[0063] Typically, each liquid ejection head unit 210 is provided at a position that is an integer multiple of the circumferential length of the transport roller 230 on which the encoder ENC is provided, making it possible to cancel misalignment due to the eccentricity of the transport roller synchronized with the rotation period of the transport roller 230. Also, mechanical positional misalignment of the liquid ejection head unit 210 is typically canceled by correcting the ink ejection timing based on the results of a test print performed before the start of printing.

[0064] However, there is usually a discrepancy between the position of the web 120 directly below the liquid ejection head unit 210 that ejects ink and the position calculated from the encoder signal due to factors such as thermal expansion of the transport roller 230, slippage between the web 120 and the transport roller 230, and stretching of the web 120 itself. The dotted line graph in Fig. 9 shows the actual transport position of the web 120, and the solid line graph shows the transport position of the web 120 calculated based on the encoder signal. As can be seen by comparing the dotted line graph and the solid line graph, when ejection of each liquid ejection head unit 210 is controlled based on the encoder signal, the ink will land at a position (δ) that is shifted from the desired landing position on the web 120.

[0065] 10 shows the amount of deviation of the ink landing position when eccentricity occurs in the transport roller 230 on which the encoder ENC is arranged. The dotted line shows the amount of deviation of the ink landing position when eccentricity and thermal expansion occur in the transport roller 230. The dashed-dotted line shows the amount of deviation of the ink landing position when eccentricity occurs in the transport roller 230 and slippage occurs between the web 120 and the transport roller 230.

[0066] Normally, the deviation due to eccentricity of the conveying roller 230 (dotted line graph in FIG. 10) has a period synchronized with the rotation period of the conveying roller 230, and the deviation occurs in the same manner every time. Also, the amount of deviation increases in proportion to the amount of eccentricity, but does not accumulate.

[0067] On the other hand, the linear expansion of the transport roller 230 and the slippage between the web 120 and the transport roller 230 accumulate and the state is different for each printing. For this reason, it is very difficult to correct the deviation of the ink landing position by the encoded signal from the encoder ENC provided on the transport roller 230.

[0068] In addition, the stretching of the web 120 caused by applying tension to suppress meandering of the web 120 is also a deviation whose state varies depending on the web thickness, web width, and amount of ink applied, and whose state varies for each print. For this reason, such deviations are also difficult to correct.

[0069] (Timing control of each part based on accumulated movement amount) For this reason, in the case of the image forming apparatus 110 according to the embodiment, the calculation unit CAL of the calculation unit 53F shown in Fig. 6 sequentially accumulates the movement amounts between the images calculated by the correlation calculation based on the images captured at each of the above-mentioned predetermined times, as shown in Fig. 11. Specifically, the movement amount between the captured image captured by the imaging unit OS and the immediately previous captured image captured by the imaging unit OS is calculated by the image correlation calculation, and each calculated movement amount is accumulated as follows.

[0070] Movement amount = (L1+L2+L3+L4+L5+...+Ln)

[0071] By using the movement amount calculated by the cumulative calculation in this way instead of the encoder signal, the movement amount of the web 120 can be recognized with high accuracy, and the timing of each part can be controlled accurately. That is, the movement amount calculated by the cumulative calculation is supplied to the adjustment part 110F40 and the control part 110F30.

[0072] The adjustment section 110F40 performs shutter control of the imaging section OS via the shutter control section 141A based on the amount of movement of the web 120. This allows the shutter control of the imaging section OS to be performed at optimal timing based on the accurate amount of movement of the web 120, so that the image of the web 120 can be captured at the accurate movement position of the web 120.

[0073] Furthermore, the control unit 110F30 controls the ejection of each liquid ejection head unit 210 via the movement unit 110F80 based on the amount of movement of the web 120. This allows the ink to land accurately at the target position on the web 120, improving printing accuracy.

[0074] (Detection of thermal expansion of conveyor roller) Next, the measurement unit 110F20 of the image forming apparatus 110 according to the embodiment supplies one encode pulse to the calculation unit 53F based on the encode signal from the encoder ENC of the conveyance roller 230 each time the conveyance roller 230 makes one revolution.

[0075] The calculation unit CAL of the calculation unit 53F stores the amount of paper movement (initial movement) per revolution of the roller, which is cumulatively calculated using a reference paper during adjustment, and detects the difference between the amount of paper movement per revolution calculated from the amount of movement cumulatively calculated at that time and the initial movement amount each time the measurement unit 110F20 is supplied. That is, the calculation unit CAL detects the difference between the amount of paper movement per revolution calculated from the current cumulative movement amount and the initial movement amount each time the transport roller 230 makes one revolution (or multiple revolutions), and supplies it to the control unit 110F30.

[0076] Control unit 110F30 determines that thermal expansion is occurring in conveyance roller 230 when the difference between the current accumulated movement amount and the initial movement amount is equal to or greater than a predetermined value.

[0077] (Discharge operation according to thermal expansion of the transport roller) When the control unit 110F30 determines that thermal expansion has occurred in the transport roller 230, it controls the ejection amount of each liquid ejection head unit 210 so that the ejection amount of ink corresponds to the degree of thermal expansion. This enables printing with an appropriate amount of ink, and improves printing accuracy.

[0078] (Thermal expansion warning) When the control unit 110F30 detects the occurrence of thermal expansion of the conveying roller 230, the control unit 110F30 performs notification control to notify the occurrence of thermal expansion via the notification unit 251 shown in FIG. 5. For example, when the notification unit 251 is a monitor device, the control unit 110F30 controls the monitor device to display an error message such as "The conveying roller is hot." When the notification unit 251 is a speaker unit, the control unit 110F30 notifies the user that thermal expansion has occurred in the conveying roller 230 by outputting an audio message or an electronic sound. This notification operation allows the user to take measures such as temporarily stopping the image forming apparatus 110 until the conveying roller 230 returns to the state before the thermal expansion.

[0079] The display control for the monitor device and the sound output control via the speaker unit may be used together. The control unit 110F30 may also notify an administrator or the like of the thermal expansion of the transport rollers 230 via a network.

[0080] (Cooling operation of the transport roller) Furthermore, when the control unit 110F30 detects the occurrence of thermal expansion of the conveying roller 230, it controls the cooling unit 250 to increase the cooling strength of the cooling unit 250 cooling the conveying roller 230 shown in Fig. 5 by a predetermined amount. This allows the conveying roller 230 to be cooled, and the conveying roller 230 to be returned to the state before the thermal expansion.

[0081] (System shutdown control) Furthermore, when the control unit 110F30 detects the occurrence of thermal expansion of the conveying roller 230, it controls, for example, to stop the power supply unit, or controls to stop the conveying roller 230 etc. via the power supply control unit. Note that it is also possible to control to stop only the conveying roller 230. This makes it possible to stop the progress of the thermal expansion of the conveying roller 230, and to return the conveying roller 230 to the state before the thermal expansion.

[0082] (Correction of accumulated travel amount) Next, in the case of the image forming apparatus 110 according to the embodiment, since only the relative movement amount of the captured image captured at each predetermined time is detected, if the paper behavior, slippage, speed fluctuation, etc. occurs less than the detection period, an error may occur with respect to the actual transport amount. If such an error is accumulated by the above-mentioned cumulative calculation, there is a risk that the difference with the actual behavior of the web 120 between the image acquisition periods may become large.

[0083] For this reason, the calculation unit CAL of the calculation unit 53F corrects the accumulated movement amount by the encoding pulse supplied from the measurement unit 110F20 every time the conveying roller 230 makes one revolution. In other words, the movement amount of the web 120 for one revolution of the conveying roller 230 is the movement amount calculated from the diameter of the conveying roller 230. For this reason, the calculation unit CAL performs a correction process, triggered by the encoding pulse, to make the accumulated movement amount coincide with the movement amount calculated from the diameter of the conveying roller 230.

[0084] Fig. 12 shows such a correction process, where the solid line is a graph of the accumulated movement amount, and the dotted line is the movement amount calculated from the diameter of the conveying roller 230. As shown in Fig. 12, the calculation unit CAL matches the accumulated movement amount of the solid line with the movement amount of the dotted line calculated from the diameter of the conveying roller 230 at the timing when the encoding pulse (output pulse signal) is supplied. This makes it possible to cancel the error each time the conveying roller 230 makes one revolution, so that the movement amount of the web 120 can be calculated with higher accuracy.

[0085] (Effects of the embodiment) As is clear from the above description, image forming apparatus 110 according to the embodiment calculates an accumulated movement amount by accumulating a predetermined amount of movement amounts calculated by performing correlation calculations on images of web 120 captured at predetermined times. A correction operation is performed to make this accumulated movement amount equal to the movement amount calculated from the diameter of transport roller 230 of web 120 each time transport roller 230 of web 120 makes one revolution (or multiple revolutions). This makes it possible to cancel errors occurring in the accumulated movement amount, and to control each section based on the more accurate movement amount of web 120.

[0086] (Modification) In the above-described embodiment, the “actual web movement amount” shown in FIG. 12 is obtained using the encode pulse (output pulse signal) for each revolution of the conveying roller 230, and the correction target value (dotted line in FIG. 12) is determined.

[0087] However, a cumulative value of the web movement amount detected by the image sensor may be calculated at the timing when the conveying roller 230 makes one revolution, and the average value of the multiple revolutions (e.g., 10 revolutions) may be taken as the correction target value. This allows the actual web movement amount including slip to be used as the correction target value, and each part can be controlled based on the more accurate movement amount of the web 120.

[0088] Finally, the above-described embodiment is presented as an example, and is not intended to limit the scope of the present invention. This novel embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. In addition, the embodiment and modifications of each embodiment are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0089] 110 Liquid ejection device 120 Web 210K Black Liquid Ejection Head Unit 210C Cyan liquid ejection head unit 210M Magenta liquid ejection head unit 210Y Yellow liquid ejection head unit SENK Black Sensor Device SENC Cyan sensor device SENM Magenta Sensor Device Sensor device for SENY Yellow 520 Controller [Prior art documents] [Patent documents]

[0090] [Patent Document 1] JP 2003-266828 A

Claims

1. A recording medium transport mechanism; a printing unit that prints on the recording medium; An origin detection unit provided in the transport mechanism; a movement amount calculation unit that calculates a movement amount of the recording medium based on a correlation between images of the recording medium captured by an imaging unit at predetermined time intervals, and calculates a cumulative movement amount by sequentially accumulating each calculated movement amount; a correction unit that corrects the accumulated movement amount to a reference movement amount of the recording medium for each predetermined period of the transport mechanism detected by the origin detection unit, the reference movement amount being obtained from a mechanical configuration of the transport mechanism; a control unit that controls the transport mechanism based on the cumulative movement amount corrected by the correction unit to transport and control the recording medium, and controls the printing unit to print on the recording medium that is transport-controlled; An image forming apparatus comprising:

2. a comparison unit that compares an initial value of the accumulated movement amount with a current accumulated movement amount at every predetermined cycle of the transport mechanism; The apparatus further includes a detection unit that detects thermal expansion of the transport mechanism when the current cumulative movement amount is equal to or greater than the initial value.

2. The image forming apparatus according to claim 1,

3. A cooling unit for the transport mechanism, The control unit controls a cooling intensity of the cooling unit to cool the transport mechanism when the detection unit detects thermal expansion of the transport mechanism.

3. The image forming apparatus according to claim 2,

4. The control unit controls at least the transport mechanism to stop when the detection unit detects thermal expansion of the transport mechanism.

4. The image forming apparatus according to claim 2, wherein:

5. the printing unit performs printing by ejecting ink onto the recording medium; The control unit controls an amount of ink ejected from the printing unit in accordance with an amount of thermal expansion of the transport mechanism detected by the detection unit.

5. The image forming apparatus according to claim 2, wherein:

6. The control unit performs a predetermined notification control via a notification unit when the detection unit detects a thermal expansion of the transport mechanism.

6. The image forming apparatus according to claim 2, wherein:

7. an imaging step of imaging the recording medium conveyed by the conveying mechanism at predetermined time intervals by an imaging unit; a movement amount calculation step in which a movement amount calculation unit calculates a movement amount of the recording medium based on a correlation of images of the recording medium captured by an imaging unit at predetermined time intervals, and calculates a cumulative movement amount by sequentially accumulating each calculated movement amount; a correction step in which a correction unit corrects the accumulated movement amount to a reference movement amount of the recording medium for a predetermined period of the transport mechanism, the reference movement amount being obtained from a mechanical configuration of the transport mechanism, for each predetermined period of the transport mechanism detected by an origin detection unit provided in the transport mechanism; a conveyance control step in which a control unit controls the conveyance mechanism based on the accumulated movement amount corrected in the correction step to perform conveyance control of the recording medium; The transport control method includes the steps of:

Images