JP4939139B2 - Image forming apparatus and image forming method for forming image on sheet-like medium - Google Patents

Description

The present invention relates to an image forming apparatus capable of detecting distribution information of a state of a sheet-like medium to be printed by non-contact high-frequency electromagnetic wave sensing and automatically adjusting an image forming condition using the detection result, and an image It relates to a forming method. Typically, the electromagnetic wave to be used is an electromagnetic wave including a component having a frequency in the range of 30 GHz to 30 THz (also referred to as a THz wave or a terahertz wave in this specification).

Generally, in a copying machine, an ink jet printer, a laser printer, and the like, image forming conditions are controlled so that an optimum image can be formed according to a printing medium. The sensing contents are paper type, moisture content (moisture content), etc., and various sensors are provided for that purpose, and feedforward control or feedback control of image forming conditions is performed based on the sensing results. .

In particular, in recent image forming devices called high-quality print-on-demand (POD) machines, the amount of moisture absorbed by the print media, which changes depending on the environment, and the effect of gaps on the print media surface are affected. Studies have been made to improve the printing state by avoiding as much as possible. As for the former, a method of arranging a thermo-hygrometer around the image forming system and a method of irradiating light and judging the amount of water by the reflected light have been proposed (see Patent Document 1). In general, the gap is not a method of incorporating a sensor for detecting this, but an estimation is made based on the difference in the amount of reflected light depending on the direction of the gap to provide a curl correction means (patent) Reference 2).
JP-A-8-137145 Japanese Unexamined Patent Publication No. 2000-227694

In order to form a high-quality image similar to that of a printing apparatus such as a POD machine, the distribution of the state of the print medium in the in-plane direction becomes a problem. For example, when the ambient humidity is high, the print medium set in the cassette may have a higher moisture content in the peripheral part and a smaller amount in the central part. The distribution of this state changes in a complicated manner depending on the environmental temperature and humidity, the moisture content of the print medium when set in the cassette, the elapsed time from the set, and the like. In such a case, even if only one point of the medium is measured and the print control is performed, the state of the entire print medium may not be reflected, and the printing cannot be optimized.

On the other hand, the gap is not constant unless special paper is used, and correction based on the difference in the amount of reflection alone cannot cope with changes in the amount of reflection due to stray light, print medium tension, or creases. There was a problem that could not be enough.

In view of the above problems, the image forming apparatus of the present invention is
Sheet feeding means capable of stacking and arranging sheet-like media;
Conveying means for conveying the sheet-like medium disposed in the sheet feeding means in an in-plane direction of the sheet-like medium;
At a plurality of sheet-like medium that will be conveyed by said conveying means, and illuminating means for illuminating a same electromagnetic waves including at least a part of the frequency of the following frequency domain above 30 GHz 30 THz,
Detection means for detecting the intensity of the electromagnetic wave reflected or transmitted at the irradiation position by the irradiation means in the sheet-like medium;
Storage means for storing the relationship between the intensity of electromagnetic waves reflected or transmitted by the sheet medium and the state of the sheet medium;
Using the intensity detected by the detection means and the relationship stored by the storage means, the state of the sheet-like medium before the image formation is acquired for each irradiation position, and the surface of the sheet-like medium Means for obtaining a distribution of said state with respect to an inward direction;
Means for acquiring an image forming condition for each irradiation position related to an in-plane direction of the sheet-like medium before the image formation based on the acquired distribution of the state;
Image forming means for forming an image under the acquired image forming conditions for each irradiation position of the sheet-like medium conveyed by the conveying means .

In view of the above problems, the image forming method of the present invention includes the following steps. In the first step, high-frequency electromagnetic waves are irradiated at a plurality of locations onto a sheet-like medium for printing. In the second step, a change in the propagation state of the electromagnetic wave at a plurality of locations on the sheet-like medium is detected. In the third step, based on the data on the distribution of the state of the sheet-like medium obtained based on the data relating to the change in the propagation state of the electromagnetic wave received depending on the state of the sheet-like medium for printing and the detected data The image forming conditions for printing are determined. In the fourth step, image forming conditions are adjusted based on the determined result in accordance with the state of each location of the sheet-like medium for printing irradiated with the electromagnetic wave. Here, for example, the distribution information of the sheet-like medium is acquired by changing the position where the plurality of places are irradiated in synchronization with the conveyance of the sheet-like medium to the image forming unit, and the image forming unit also forms an image. In this process, the image forming conditions can be adjusted using information for controlling the image forming conditions at the same place as determined based on the distribution information in synchronization with the conveyance of the sheet-like medium.

In the present invention, the distribution in the in-plane direction of the sheet-like medium (such as the amount of moisture and the direction of the gaps) can be sensed. For example, it is possible to adjust image formation relatively finely even within one medium, and relatively high A quality image can be obtained on a sheet-like medium. In particular, for example, by adjusting the image forming conditions every several lines according to the difference between the print medium edge and the center of the moisture amount, or by adjusting the image forming conditions corresponding to the direction of the gap, Stable image formation is always possible without being affected by the surrounding environment.

An embodiment of the present invention will be described with reference to FIG. One embodiment of the image forming apparatus of the present invention includes an irradiation unit, a detection unit, a data acquisition unit, a distribution information acquisition unit, a calculation unit, and a control unit. The irradiation unit irradiates a terahertz wave at a plurality of places on a sheet-like medium such as paper. The detection means detects a change in the propagation state of the terahertz wave at a plurality of locations on the sheet-like medium. The data acquisition means acquires data relating to a change in the propagation state of the terahertz wave received depending on the moisture content of the sheet-like medium, the gap, and the like. The distribution information acquisition unit acquires the distribution information of the state of the sheet-like medium based on the acquired data and the data detected by the detection unit. The computing means determines image forming conditions for printing based on the distribution information of the state of the sheet-like medium. The control means adjusts the image forming conditions based on the determined result according to the state of each location of the sheet-like medium. As the image forming conditions, for example, in an electrophotographic image forming apparatus, there are a heating temperature at the time of fixing, a bias voltage of toner at the time of transfer, and the like. Further, for example, in an inkjet image forming apparatus, there are the number of ink ejection nozzles driven, a driving voltage pulse pattern, and the like.

In the present embodiment, transmission of THz waves and reflected waves are used instead of the conventional method of irradiating light and utilizing the reflected light. There is no problem of stray light from the outside, and the wavelength of electromagnetic waves is as long as several hundreds of μm, so there is no influence of unevenness on the surface of the print medium, so when viewing the in-plane distribution of the sheet-like medium state while scanning the beam direction Can be detected with high accuracy.

In this embodiment, while relatively moving the sheet-like print medium and the THz wave beam, the transmission wave or the reflected wave, and in some cases, both are detected, and the in-plane distribution of the state of the print medium is contactless. To detect. Further, when an image is formed, the printing conditions are controlled based on the detection result of the in-plane distribution of the state even in one printing medium.

Since the THz wave has a property of being absorbed by moisture, the amount of transmission or reflection varies depending on the amount of moisture. If a calibration curve using this is made into a database according to the type of printing medium and the environment, the distribution of moisture content in the printing medium can be acquired. As for the gap, since the gap direction gives polarization dispersion to the propagation of the THz wave, it can be estimated based on the database by detecting the amount of transmission and reflection.

Further details will be described. In the image forming apparatus or method shown in FIG. 1, reference numeral 1 denotes a sheet-like print medium, and FIG. 1 (a) shows a state in which one medium 1 starts to be conveyed from the laminate 2. Reference numeral 3 denotes a THz wave generation source, such as a quantum cascade laser, a resonant tunneling diode, or a Gunn diode with harmonic generation means attached. If it becomes relatively large, a parametric generator using a backward traveling wave tube or a nonlinear crystal element may be used. Also, a THz wave generation source using a method of generating a femtosecond laser by irradiating a photoconductive element may be used.

The THz wave emitted from the generation source 3 is scanned by a beam deflecting unit (not shown) in a direction (indicated by an arrow 11) substantially perpendicular to the conveyance direction (indicated by an arrow 9) of the sheet-like print medium 1. The THz wave beam 5 emitted from the generation source 3 and applied to the sheet-like print medium 1 from the front is typically adjusted to a parallel beam of a spot of about 1 cmΦ. When the THz wave beam 5 is deflected as indicated by reference numeral 10, the irradiation position is scanned in the direction of the arrow 11 on the print medium 1. The THz wave beam 5 becomes a transmitted beam 6 after passing through the printing medium 1 and reaches the detector 4 through the cylindrical lens 7. As the detector 4, a DLATGS detector which is a pyroelectric detector, a Golay cell, or the like can be used. When using these detectors, generally, synchronous detection by modulating the light intensity with an optical chopper (not shown) is used as a conventional means for improving S / N.

When the print medium 1 is conveyed in the direction of arrow 9, if the beam scan is performed in the direction of arrow 11 as described above, the beam spot is swept in a zigzag manner as indicated by reference numeral 8 in FIG. Information on the state distribution of the medium 1 can be acquired.

Here, the transmitted THz wave 6 is attenuated according to the amount of water contained in the print medium 1 as shown by the calibration curve in FIG. Therefore, if the type of the printing medium 1 is known, the intensity of the transmitted THz wave 6 can be detected and the in-plane distribution of the moisture amount can be acquired. FIG. 6 is an image diagram of an example of the water content distribution obtained by such means. This is an example in which the amount of water increases from the central portion 611 to the peripheral portion 612 of the sheet-like print medium 1.

In the image forming apparatus 700 as shown in FIG. 7, the acquisition information of the moisture content distribution of such a sheet-like medium is determined based on the difference in moisture content, such as the heating temperature during fixing and the toner bias voltage during transfer. The image forming conditions are reflected in the image forming conditions of the image forming control unit 707 that controls the image forming conditions. This enables high-quality image formation without unevenness on the sheet-like print medium 710 separated and conveyed from the sheet-like medium laminate 709 of the paper feeding unit 701. More specifically, for the state distribution information of the print medium 710 acquired by the distribution detection unit 706 in synchronization with the transport unit 712, the arithmetic processing unit 705 performs information such as the amount of water (such as a calibration curve as described above). Comparison is performed based on data in the storage unit 704 that stores information. Then, an information signal based on the comparison result is sent to the image formation control unit 707. The image formation control unit 707 generates a control signal related to image formation conditions from this information signal. In the image forming unit 708, on the basis of the signal relating to the image forming condition from the image forming control unit 707, the print medium 710 conveyed to the image forming unit 702 is synchronized with the conveying unit 712, for example, several lines. Image formation is performed while adjusting the image formation conditions every time. Thereby, high-quality image formation without unevenness according to the state distribution of the print medium 710 can be performed. The image-formed printing medium 710 is sent to the paper discharge unit 703 and laminated there as indicated by reference numeral 711.

Hereinafter, more specific examples will be described.

(Example 1)
The first embodiment according to the present invention controls image forming conditions by transporting a sheet-like print medium and simultaneously scanning a THz wave to examine the moisture distribution of the entire print medium.

In the configuration of the present embodiment shown in FIG. 1, the THz wave generation source 3 includes a light source that generates an electromagnetic wave at 600 GHz by a resonant tunneling diode and a galvano mirror that deflects the beam 5 in the direction of an arrow 10. The diameter of the beam 5 is adjusted to about 1 cm. By deflecting by the galvanometer mirror, the beam 5 is scanned in the direction of the arrow 11 on the surface of the print medium 1. The THz wave 6 transmitted through the sheet-like print medium 1 is condensed and detected by the cylindrical lens 7 on the DLATGS detector 4.

When such a scan is performed while the print medium 1 is conveyed in the direction of the arrow 9, a THz wave is irradiated / detected along a zigzag locus as indicated by reference numeral 8 in FIG. As a result, the moisture content distribution of the printing medium 1 is acquired together with the transport position information.

FIG. 5 shows an image diagram of the transmitted electromagnetic wave intensity depending on the moisture content of the printing medium 1. It can be seen that the intensity of electromagnetic waves detected by the distribution detecting means decreases because the amount of THz waves absorbed by the water increases as the amount of water increases. Since the amount of moisture absorption also varies depending on the type of print medium (A, B, and C for convenience), it is necessary to acquire data using this as a parameter. Information on the type of the print medium may be input by an operator or stored in the apparatus using another detection means such as a light method.

FIG. 6 shows an example in which the distribution of moisture content in the sheet-like print medium 1 is detected by the arithmetic processing unit using such a calibration curve stored in the storage unit. Here, for example, the white portion 611 in the central portion of the print medium 1 has a low water content of 3% or less, and the water content gradually increases in the region of the peripheral portion 612 as it goes to the periphery, reaching about 6%. It has become. When the place where the printing medium 1 is stored is dry and the humidity of the environment when the printing medium 1 is set is high, such distribution occurs when sufficient time has not passed. Such an in-plane distribution could not be obtained by the conventional detection method.

In the case of such a printing medium 1, if it is conveyed in the direction of the arrow 9, the amount of water is large in the first part, decreases in the center, and the amount of water increases in the final part. Become. If the image forming control unit adjusts the image forming conditions of the image forming means in the same print medium 1 in accordance with the difference in the state in the same print medium 1, the print state and the curl status of the print medium 1 Etc. can be optimally controlled.

The entire image forming apparatus 700 will be described with reference to FIG. A print medium 709 is set in the paper supply unit 701, and a part of the print medium 710 is supplied to the image forming unit 702 by the conveying unit 712 together with a print command. The distribution detecting means 706 has been described with reference to FIG. 1, and the electromagnetic wave detection information obtained there is sent to the arithmetic processing unit 705 together with the transport position information of the print medium 710 by the transport means 712. In the arithmetic processing unit 705, the obtained information is compared with information in the storage unit 704 in which the electromagnetic wave intensity information related to the type of print medium and the amount of water is stored as a database, and the state of the print medium corresponding to the position is compared. Determine the distribution of. Then, image formation control information based on this is sent to the image formation control means 707. Alternatively, the distribution information of the state of the print medium may be sent to the image formation control unit 707 and the image formation control unit 707 may obtain the image formation control information. The image formation control unit 707 reflects the image formation control information as a heating temperature during fixing and a toner bias voltage during transfer. And this reflected signal. Based on the transport position information of the print medium 710 from the transport unit 712, the image is formed on the print medium 710 by sequentially sending it to the image forming unit 708. Thereafter, the print medium 710 on which the image is formed is held as a stacked body 711 in the paper discharge unit 703.

By providing an image forming apparatus that appropriately adjusts image forming conditions within the surface of such a single sheet-like print medium, printing irregularities and curls are reduced, and a high-quality image is obtained on the print medium. be able to.

(Example 2)
A second embodiment according to the present invention will be described with reference to FIG. In the first embodiment, the beam scan is performed in order to finely detect the state distribution of the sheet-like medium, but in the second embodiment, a fixed plurality of pairs of generators and detectors are installed, and a beam scanning system is installed. It is a thing that lost.

In FIG. 2, 23a to 23c are electromagnetic wave generation sources similar to the electromagnetic wave generation source 3 of the first embodiment, and 24a to 24c are detectors similar to the detector 4 of the first embodiment. As for the electromagnetic wave generation source, the electromagnetic wave beam from one generator may be branched into a plurality of beams. Each beam 25 is transmitted through a sheet-like print medium 27 separated and conveyed from the laminate 29 to become a transmitted beam 26. The transmitted beam 26 is detected by detectors 24a to 24c, and the state of the print medium 27 is changed. You will get in points.

By conveying the printing medium 27 in the direction of the arrow 28, information on each point of the sheet-like medium 27 irradiated with each beam 25 is linearly scanned to obtain state distribution information. As described in the first embodiment, there are many patterns in which there is a difference between the periphery and the center as described in the first embodiment, and it is often unnecessary to acquire information from the entire surface of the sheet-like medium 27. In such a case, the image forming conditions of the image forming apparatus can be adjusted based on the thinned state information as in this embodiment. The control method of the present embodiment is the same as that of the first embodiment.

In this embodiment, the cost can be reduced by reducing optical components such as a cylindrical lens.

(Example 3)
A third embodiment according to the present invention will be described with reference to FIG. In the present embodiment, when the sheet-like print medium is paper, paper gap information is acquired. In general, the gaps in the paper are randomly oriented depending on the paper unless it is a special paper. However, if there is a certain degree of directionality in a single sheet of paper, the transmitted beam from the paper 37 being conveyed in the direction of the arrow 38 using the single THz wave beam 35 shown in FIG. If you see 36 intensity changes, you can estimate the direction of the gap. That is, the paper gap can cause polarization dispersion for the THz wave, and if the electromagnetic wave 35 from the THz wave light source 33 is irradiated to the print medium 37 as linearly polarized light by the polarizer 31, it corresponds to the gap direction. The electromagnetic wave intensity is acquired by the detector 34.

If the polarization is parallel to the transport direction 38, the intensity of the transmitted light 36 becomes stronger when the gap direction coincides with the polarization direction, and becomes weaker when orthogonal to the polarization direction. When the signal detected by the detector 34 is small as a change, an average gap direction can be determined by integrating signals in a certain region.

The information on the distribution of the gap direction can be used as follows for adjusting the image forming conditions. For example, in an ink jet printer, the ink infiltration direction varies depending on the gap direction, and the landing pattern may not be stable. If the gap direction of the paper is known in advance by the method of this embodiment, the landing pattern on the paper is controlled by adjusting the image forming means by the image forming control unit, and a high-quality stable image can be obtained. .

If necessary, a plurality of electromagnetic wave detection elements may be provided as in the second embodiment in order to acquire the distribution in the gap direction in one print medium.

(Example 4)
A fourth embodiment according to the present invention will be described with reference to FIG. In this embodiment, the reflected wave 45 on the print medium 47 is also used as shown in FIG.

In this embodiment, the output of the THz wave generator 40 is converted into a linearly polarized wave 44 by the polarizer 43, and after irradiating the sheet-like print medium 47, the transmitted wave 46 is detected by the detector 42 and the reflected wave 45 is detected by the detector 41. Detected. The reflected wave 45 and the transmitted wave 46 are affected by both the moisture content of the print medium 47 and the gap direction. Therefore, if a database for preliminarily estimating the correspondence between the information obtained by the two detectors 41 and 42, the amount of moisture and the gap is stored in the storage unit, the distribution of both the amount of moisture and the gap is obtained. Can be acquired. Also, if necessary, a plurality of pairs of generators and detectors may be prepared, and the entire distribution of the sheet-like medium conveyed in the direction of the arrow 48 may be acquired.

If the polarization direction of the linearly polarized light 44 is changed by rotating the polarizer 43, the intensity ratio of reflection and transmission can be changed. Therefore, if the signal is acquired by synchronous detection in synchronization with the rotation of the polarizer 43, the sensitivity can be improved.

In the method of the present embodiment, for example, when printing on both sides in a POD machine, the fixing temperature and the distribution based on the moisture content and the distribution of the gaps are adjusted so as to adjust the amount of curling that occurs when fixing the printing medium. High-quality image formation can be performed by adjusting the fixing time.

1A and 1B are diagrams for explaining an embodiment and a first example of an apparatus for detecting a state distribution of a sheet-like medium according to the present invention. The perspective view which shows the apparatus which detects the state distribution of the sheet-like medium of 2nd Example by this invention. FIG. 10 is a perspective view showing an apparatus for detecting a state distribution of a sheet-like medium according to a third embodiment of the present invention. FIG. 10 is a perspective view showing an apparatus for detecting a state distribution of a sheet-like medium according to a fourth embodiment of the present invention. The figure explaining the example of the calibration curve of the detection using a terahertz wave. The top view which shows the example of the moisture content distribution of a sheet-like medium. 1 is a block diagram illustrating an entire image forming apparatus according to the present invention.

Explanation of symbols

1, 2, 27, 29, 37, 47, 709, 710, 711 ... Sheet media (printed media, laminate of sheet media)
3, 23a to 23c, 33, 40 ... Irradiation means (electromagnetic wave generator, source)
4, 24a to 24c, 34, 41, 42 ... Detection means (detector)
5, 6, 25, 26, 35, 36, 44, 45, 46 ... Electromagnetic beam (transmitted wave, reflected wave)
31, 43 ... Polarizer
700 ... Image forming device
704 ... Data acquisition means (storage unit)
705 ... Distribution information acquisition means (arithmetic processing unit)
706 ... Detection means (distribution detection means)
707 ... Control means, calculation means (image formation control unit)
708 ... Image forming means

Claims (7)

An image forming apparatus,
Sheet feeding means capable of stacking and arranging sheet-like media;
Conveying means for conveying the sheet-like medium disposed in the sheet feeding means in an in-plane direction of the sheet-like medium;
At a plurality of sheet-like medium that will be conveyed by said conveying means, and illuminating means for illuminating a same electromagnetic waves including at least a part of the frequency of the following frequency domain above 30 GHz 30 THz,
Detection means for detecting the intensity of the electromagnetic wave reflected or transmitted at the irradiation position by the irradiation means in the sheet-like medium;
Storage means for storing the relationship between the intensity of electromagnetic waves reflected or transmitted by the sheet-like medium before image formation and the state of the sheet-like medium;
Using the intensity detected by the detection means and the relationship stored by the storage means, the state of the sheet-like medium before the image formation is acquired for each irradiation position, and the surface of the sheet-like medium Means for obtaining a distribution of said state with respect to an inward direction;
Means for acquiring an image forming condition for each irradiation position related to an in-plane direction of the sheet-like medium before the image formation based on the acquired distribution of the state;
Image forming means for forming an image under the acquired image forming conditions for each irradiation position of the sheet-like medium conveyed by the conveying means;
An image forming apparatus comprising: The irradiation means includes a light source,
Configured to deflect the electromagnetic wave generated from the light source,
The image forming apparatus according to claim 1, wherein the irradiation position is moved in an in-plane direction of the sheet-like medium and in a direction substantially perpendicular to a conveyance direction by the conveyance unit. The storage means stores the relationship between the intensity of electromagnetic waves reflected or transmitted by the sheet-like medium before image formation , the state of the sheet-like medium, and the type of the sheet-like medium,
The means for acquiring the state distribution uses the intensity detected by the detection means, the type of sheet-like medium arranged in the paper feeding means, and the relationship stored in the storage means. The image forming apparatus according to claim 1, wherein the distribution of the state is acquired. The state of the sheet-like medium before image formation is an amount of moisture contained in the sheet-like medium or a gap direction in the in-plane direction. Image forming apparatus. The irradiation means includes a light source,
Comprising a polarizer for making the electromagnetic wave generated from the light source linearly polarized light,
The polarizer polarizes the electromagnetic wave so as to have a polarization direction substantially parallel to the transport direction by the transport means,
The image forming apparatus according to claim 4, wherein the state of the sheet-like medium before the image formation is a gap direction in the in-plane direction. The irradiation means includes a light source,
Comprising a polarizer for making the electromagnetic wave generated from the light source linearly polarized light,
The detection means is configured to detect a reflected wave reflected at an irradiation position by the irradiation means and a transmitted wave transmitted through the irradiation position by the irradiation means,
The state of the sheet-like medium before the image formation is the amount of moisture contained in the sheet-like medium and a gap direction in the in-plane direction. Image forming apparatus. The image forming conditions are:
In the case of electrophotography, this is the heating temperature during fixing or the toner bias voltage during transfer.
The image forming apparatus according to claim 1 , wherein in the case of an ink jet system, the number of ink ejection nozzles is driven or a pattern of driving voltage pulses.

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