JP2011090075A - Image forming apparatus provided laser fixing device and laser fixing control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a fixing temperature from being raised by controlling laser power in fixing a second face when fixing a first face of a recording sheet and fixing the second face in duplex printing. <P>SOLUTION: A color multifunction machine 100 includes a thickness detection means 70 which is provided for measuring thickness of a recording sheet on a conveying path of the recording sheet which has been delivered from a paper feed part and has not reached a fixing device 15 yet. When the recording sheet is thin, the image forming apparatus reduces laser power for output. Even when show-through occurs, the fixing temperature of a toner is maintained so as not to exceed a set temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a laser fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile, and a laser fixing control method.

  An electrophotographic image forming apparatus (for example, a printer) includes a fixing device that fixes a toner image formed on a recording member (recording paper or paper) onto the paper by heat melting. As an example of this fixing device, as disclosed in Patent Document 1, a roller-pair type fixing device including a fixing roller and a pressure roller is known.

  The fixing roller is a roller member in which an elastic layer is formed on the surface of a hollow metal core made of metal such as aluminum, and a halogen lamp is arranged as a heat source inside the core metal. Then, the temperature controller controls the temperature of the surface of the fixing roller by controlling the halogen lamp on / off based on a signal output from a temperature sensor provided on the surface of the fixing roller.

  The pressure roller is a roller member in which a heat-resistant elastic layer such as silicon rubber is provided as a coating layer on a cored bar. The pressure roller is pressed against the peripheral surface of the fixing roller, and a nip region is formed between the fixing roller and the pressure roller by elastic deformation of the elastic layer of the pressure roller.

  In the above configuration, the fixing device sandwiches the paper on which the unfixed toner image is formed in the nip region between the fixing roller and the pressure roller, and conveys the paper by rotating both the rollers, The toner image on the sheet is melted and fixed on the sheet by the heat of the peripheral surface of the fixing roller.

  However, in the conventional roller pair system, immediately after the power is turned on in the morning, the fixing roller and the pressure roller are at room temperature. Further, in the standby state in which the copying operation is not performed, the roller surface needs to be maintained at a predetermined temperature. Therefore, the heating must always be performed even when the copying operation is not performed. In addition to these copying operations, useless energy is consumed.

  In order to solve such a problem, a laser-type fixing device that performs fixing by irradiating an unfixed toner image formed on a recording sheet with a laser beam and melting the toner image is proposed in Patent Document 2. Has been.

  However, in a laser fixing device provided in a multifunction machine or the like having a duplex printing function, the laser power for the first surface of the paper and the laser power for the second surface are usually the same. FIG. 16 shows a conventional laser fixing device. The laser fixing apparatus 200 includes a laser element 201 and a lens 202, and fixes the unfixed toner 204 existing on the surface of the sheet 203 by irradiating the laser beam 205. This sheet 203 has already been fixed with the toner 206 on the first surface, and FIG. 16 shows a scene in which the toner 204 on the second surface is fixed by the laser fixing device 200.

  However, as shown in FIG. 16, when printing on both sides of the thin paper 203, the toner 206 printed on the first surface shows through 207 on the second surface, so the same laser power as the first surface is irradiated on the second surface. In this case, the portion that becomes black due to show-through absorbs more laser light, and accordingly, the fixing temperature becomes higher than the set temperature, which causes a problem of causing image degradation such as voids. Laser light can be selectively irradiated, and the method of irradiating only the part where the toner is present is effective in terms of energy saving. However, the irradiated light protrudes from the toner, or part of the light passes through and reflects the toner. As a result, the part of the paper is also exposed to light, so the part of the toner that is darker than the white paper has a higher temperature than the part that is not part of the paper. The toner temperature increases.

  Therefore, Patent Document 3 describes that the toner amount on the front surface is made smaller than the toner amount on the back surface in order to eliminate the difference in gloss between the front surface and the back surface.

Japanese Patent Laid-Open No. 11-38802 Japanese Patent No. 3016685 JP-A-5-216316

  However, in the above method, since laser fixing fixes toner by light, if the recording paper with a small thickness is black on the second surface due to the show-through of the toner on the first surface, the light absorption amount of the recording paper is small. As a result, the problem that the fixing temperature of the toner becomes higher than the setting cannot be improved.

  The present invention has been made in view of the above problems, and controls the laser power when fixing the second surface when fixing the first surface of the paper and fixing the second surface in double-sided printing. Thus, an image forming apparatus and a laser fixing control method provided with a laser fixing device that suppresses an increase in fixing temperature are provided.

The present invention provides an image forming apparatus having a laser fixing device having a double-sided printing function.
Means for predicting or detecting the degree of show-through of the recording paper due to fixing of the first surface, and a laser for fixing the second surface of the recording paper to the laser fixing device based on the prediction result or the detection result The power is controlled so as not to exceed a predetermined temperature.

  Here, the means for predicting or detecting the show-through of the recording paper is a means for detecting either the thickness or the transparency of the recording paper, and is based on the image information on the first surface for the laser fixing device. Thus, the laser power for fixing the second surface is controlled.

  Further, the means for predicting or detecting the show-through of the recording paper is means for detecting the image density of the recording paper on the second surface after the first surface fixing and before the second surface fixing with reflected light. Features.

  Further, the laser irradiation of the laser fixing device is performed in units of blocks formed of a spot diameter of laser light or a combination thereof.

  In addition, the laser irradiation of the laser fixing device is performed on a pixel basis.

The present invention also provides a laser fixing control method for controlling a laser fixing device provided in an image forming apparatus having a double-sided printing function.
Based on a prediction result or a detection result by a means for predicting or detecting the show-through of the recording paper, the laser power for fixing the second surface of the recording paper to the laser fixing device is controlled so as not to exceed a predetermined temperature. It is characterized by that.

  Here, the means for predicting or detecting the show-through of the recording sheet detects either the thickness, type, or transparency of the recording sheet, and makes the laser fixing device based on the image information on the first surface. The laser power for fixing the second surface is controlled.

  Further, the laser irradiation of the laser fixing device is performed in units of blocks formed of a spot diameter of laser light or a combination thereof.

  In addition, the laser irradiation of the laser fixing device is performed on a pixel basis.

According to the present invention, since the toner is fixed by light in the laser fixing, the recording paper having a small thickness is printed on the first side when the second side is black due to the show-through of the toner on the first side. When the toner is black toner, the color color of the color toner), the amount of light absorbed by the recording paper is increased by the light irradiated to the recording paper through the toner, etc. There is a problem that becomes higher. Accordingly, a means for predicting or detecting the show-through of the recording paper is provided in advance, and the laser power when fixing the second surface is controlled (reduced) based on the prediction result or the detection result. Fixability can be secured.
Here, show-through means that the state of the toner fixed on the first surface can be seen thinly from the second surface (the back surface) in the case of a recording paper with a small paper thickness. Like ink, ink itself does not penetrate paper.

  In addition, the degree of show-through of the recording paper can be predicted by the thickness (type) of the recording paper, and the portion of the second side that is show-through can be found from the image information on the first side. In contrast, by controlling the laser power, it is possible to perform optimum control in units of blocks or pixels.

  In addition, by directly measuring the portion of the recording sheet that is actually show-through, the degree and portion of the show-through can be accurately grasped, and appropriate laser power control is possible.

  Further, since the blacked out part is not necessarily the entire surface, fixing failure occurs when the laser power of the part that is not show-through is reduced. Therefore, fixing failure can be suppressed by performing the control in units of blocks. Here, the block unit means the spot diameter of the laser light, but a plurality of spot diameters may be combined to form one block unit.

  In addition, since the blacked out part (when the toner printed on the first surface is black toner) is not necessarily the entire surface, if the laser power of the part that is not show-through is reduced, fixing failure will occur. turn into. Accordingly, fixing failure can be suppressed by performing the control in units of blocks or in units of small pixels.

1 is a schematic configuration diagram illustrating a color multifunction peripheral of an image forming apparatus according to the present invention. It is sectional drawing which shows the structure of a laser fixing apparatus. It is structure explanatory drawing which looked at the laser head from the front. It is the structure explanatory view which looked at the laser head from the side. 1 is a schematic configuration diagram illustrating a color multifunction peripheral according to a first embodiment. It is composition explanatory drawing which shows a thickness detection means. It is a block diagram which shows the control system of Example 1. FIG. 6 is a graph showing show-through density and toner temperature when the same laser power is irradiated. 1 is a schematic configuration diagram of a scan-type laser fixing device. FIG. 3 is a specific control block diagram of the image forming apparatus according to the first exemplary embodiment. 3 is a flowchart illustrating fixing control in Embodiment 1. FIG. 3 is a schematic configuration diagram illustrating a color multifunction peripheral according to a second embodiment. FIG. 6 is a schematic configuration diagram illustrating a color multifunction peripheral according to a third embodiment. It is a block diagram which shows the control system of Example 3. 10 is a flowchart illustrating fixing control in Embodiment 3. It is a schematic block diagram of the conventional laser fixing apparatus.

  An embodiment of the present invention will be described below with reference to FIGS. In this embodiment, the image forming apparatus of the present invention is applied to a color multifunction peripheral. FIG. 1 is a schematic configuration diagram of the color multifunction peripheral, FIG. 2 is a cross-sectional view illustrating the configuration of the fixing device, and FIG. FIG. 4 is a structural explanatory view of the laser head viewed from the front, and FIG. 4 is a structural explanatory view of the laser head viewed from the side.

  As shown in FIG. 1, a color multifunction peripheral 100 that is an image forming apparatus according to the present embodiment includes an optical system unit E, four sets of visible image forming units pa, pb, pc, pd, an intermediate transfer belt 11, A secondary transfer unit 14, a fixing unit 15, an internal paper feed unit 16 and a manual paper feed unit 17 are provided.

  In the visible image forming unit pa, a charging unit 103a, a developing unit 102a, and a cleaning unit 104a are disposed around a photosensitive member 101a that serves as a toner image carrier. The primary transfer unit 13 a is disposed via the intermediate transfer belt 11. The other three sets of visible image forming units pb, pc, and pd have the same configuration as the visible image forming unit pa, and yellow (Y), magenta (M), and cyan (C) are included in the developing units of each unit. , Black (B) toners are accommodated.

  The optical system unit E is arranged so that the data from the light source 4 reaches the four sets of photoconductors 101a, 101b, 101c, and 101d. The intermediate transfer belt 11 is disposed without bending by the tension rollers 11a and 11b, and the waste toner box 12 is disposed on the tension roller 11b side, and the secondary transfer unit 14 is disposed on the tension roller 11a side. The fixing unit 15 includes a fixing member 15 a and a conveying member 15 b and is disposed downstream of the secondary transfer unit 14.

  The image forming process is as follows. After the surface of the photosensitive drum 101a is uniformly charged by the charging unit 103a, the surface of the photosensitive drum 101a is laser-exposed according to image information by the optical system unit E to form an electrostatic latent image. The charging unit 103a employs a charging roller system in order to charge the surface of the photosensitive drum 101a uniformly and without generating ozone as much as possible. Thereafter, a toner image is developed on the electrostatic latent image on the photosensitive drum 101a by the developing unit 102a, and the visualized toner image is converted by the primary transfer unit 13a to which a bias voltage having a polarity opposite to that of the toner is applied. Then, the image is transferred onto the intermediate transfer belt 11. The other three sets of visible image forming units pb, pc, and pd operate in the same manner, and are sequentially transferred onto the intermediate transfer belt 11. The toner image on the intermediate transfer belt 11 is conveyed to the secondary transfer unit 14 and is separately supplied to a recording sheet fed from the sheet feeding roller 16a of the internal sheet feeding unit 16 or the sheet feeding roller 17a of the manual sheet feeding unit 17. The toner is transferred by applying a bias voltage having a polarity opposite to that of the toner. The toner image on the recording paper is conveyed to the fixing unit 15, heated by laser irradiation, fused on the recording paper, and discharged to the outside.

  Next, the laser fixing device of the present invention will be described in detail with reference to FIGS.

  As shown in FIG. 2, the laser fixing device (fixing unit) 15 includes a laser head (laser irradiation means) L1 and a paper conveying device (paper conveying means) L2.

  The laser fixing device 15 of the present invention fixes an unfixed toner image formed on the surface of the recording medium (paper) 40 to the recording medium 40 by heat. Specifically, the recording medium 40 carrying the image of the unfixed toner 41 at a predetermined fixing speed and copying speed is conveyed to the laser irradiation unit 51 irradiated with the laser light 52 on the paper conveying device L2, and the laser light 52 Fixing is performed by the heat of. In the image forming apparatus of this embodiment, the maximum fixing speed is 225 mm / sec, the maximum copying speed is 50 sheets / minute (A4 lateral feed), and the fixing speed (copying speed) is variably controlled according to the image pattern as described later.

  An unfixed toner image is, for example, a toner contained in a developer such as a non-magnetic one-component developer containing a non-magnetic toner, a non-magnetic two-component developer containing a non-magnetic toner and a carrier, and a magnetic developer containing a magnetic toner. Formed with. Since color toners (yellow, magenta, cyan) have a lower absorption rate of laser light than monochrome toners, an infrared absorber is added (for example, infrared absorption with respect to 100 parts by weight of color toner menbinder resin). 1 to 5 parts by weight of the phthalocyanine, which is an agent, and polymethine, cyanine, onium, nickel complex, etc. can be used in addition to phthalocyanine, or they can be used in combination. The same absorption rate is secured.

The sheet conveying device L2 includes a conveying belt 31, a driving roller 32, a driven roller 33, a suction charger 34, a separation charger 35, a charge eliminating charger 36, a separation claw 37, and a driving motor (not shown). The conveyor belt 31 is made of a polyimide resin having a belt thickness of 75 μm and a volume resistivity of 10 ¹⁶ Ω · cm, and is stretched between the driving roller 32 and the driven roller 33. The driving roller 32 is configured to be driven to rotate at an arbitrary speed by a driving motor (not shown), and the conveying belt 31 rotates at an arbitrary speed in the direction of the arrow by the rotation of the driving roller 32. An adsorption charger 34, a separation charger 35, a charge removal charger 36, and a separation claw 37 are provided around the transport belt 31.

  In such an apparatus, the sheet 40 on which the unfixed toner image conveyed from the secondary transfer unit 14 is formed is conveyed between the conveyance belt 31 on the driven roller 33 and the suction charger 34. The driven roller 33 is made of a conductive material and is grounded. By applying an electric charge to the paper 40 by the suction charger 34, the paper 40 and the transport belt 31 cause dielectric polarization, and the paper 40 is placed on the transport belt 31. Electrostatic adsorption. The paper 40 is conveyed to the laser irradiation unit 51 by driving the driving roller 32. The image of the unfixed toner 41 on the paper 40 conveyed to the laser irradiation unit 51 is irradiated with a laser according to the image information by the laser head L1 and fixed. The paper 40 that has finished fixing the toner image in the laser irradiation unit 51 is conveyed between the separation charger 35 and the driving roller 32 while being electrostatically attracted to the conveyance belt 31. The drive roller 32 is made of a conductive material and is grounded, and the electrostatic adsorption force between the conveyance belt 31 and the paper 40 is weakened by removing the charge on the paper 40 by the separation charger 35. In this state, the conveyance belt 31 rotates along the driving roller 32 and has a large curvature. Therefore, the leading end of the paper 40 is lifted from the conveyance belt 31, and the paper 40 is completely separated from the conveyance belt 31 by the separation claw 37. To do. The transport belt 31 from which the paper 40 has been peeled is driven to the suction position of the paper 40 again after the outer surface and the inner surface of the transport belt 31 have been discharged by the charge removal charger 36.

  The laser head L1 is for the purpose of fixing the toner 41 to the paper 40 by irradiating the laser beam 52 to the image of the unfixed toner 41 in the laser irradiation unit 51. As shown in FIGS. 2, 3, and 4, the laser head L1 includes a semiconductor laser array 60 in which a plurality of semiconductor laser elements 61 are arranged in a line in the longitudinal direction, a heat sink (heat sink) 53, and a temperature sensor 54. ing. In the present embodiment, the semiconductor laser array 60 is one in which 1,000 laser elements 61 having a wavelength of 780 nm and one rated output of 150 mW are arranged. At this time, the arrangement pitch p of the laser elements 61 is 0.3 mm, and the laser spot diameter d is also 0.3 mm. As the heat sink 53, a total of 10 heat sinks (UB30-20B manufactured by Alpha Co., Ltd.), which are made of an aluminum alloy and have a base size of 30 mm × 30 mm, a height of 20 mm, and a heat resistance of 1.6 ° C./W, are arranged in a row. (Total thermal resistance 0.16 ° C./W) is used.

Further, the detailed configuration of the laser head L1 will be described with reference to FIGS.
A control circuit (not shown) for making the laser light output variable by the input signal or keeping the laser output constant by the signal from the monitoring photodiode 62 which is a light receiving element and the photodiode 62 are formed monolithically. A semiconductor laser element (chip) 61 is mounted on the silicon substrate 63, and electrical connection is made between the laser element 61 and the silicon substrate 63 by a wire bond line 64 or the like.

  Next, a plurality of the silicon substrates with laser elements 63 are mounted on the ceramic substrate 66, and electrical connection is made between the surface electrode 65 of the ceramic substrate 66 and the electrode on the silicon substrate 63 by wire bonding or the like. Finally, a lens holder 67 holding a heat radiating plate 53 and a plurality of convex lenses 68 as a plurality of condensing optical systems is attached to the ceramic substrate 66 on which the plurality of laser devices are arranged. Thereby, the laser head L1 according to the present embodiment is manufactured.

The plurality of convex lenses 68 and the lens holder 67 in the laser irradiation means (laser head) L1 are made of a lens-lens holder integrated molded product made of resin, or flat glass rather than a lens holder in which each convex lens 68 is incorporated. A lens array such as a flat microlens manufactured by ion exchange in a shape is more advantageous in terms of price, process, and assembly accuracy.
It is also possible to eliminate the condensing optical system and irradiate the toner image with a laser beam in a parallel light state.

  Further, a temperature sensor 54 made of a thermistor for measuring the temperature of the laser head L1 is mounted on the ceramic substrate 66. The temperature sensor 54 is arranged at the center with respect to the longitudinal position of the fixing device. Based on the temperature data detected by the temperature sensor 54, a control circuit (not shown) as the first control unit controls the voltage applied to the laser element 61.

Example 1
As shown in FIG. 5, the color multifunction peripheral 100 has a thickness for measuring the thickness of the paper in the middle of the paper conveyance path after being output from the paper supply unit and before being conveyed to the fixing device 15. Detection means 70 is provided. As shown in FIG. 6, the thickness detection means 70 includes an upper roller 71 and a lower roller 72 that is detachably connected to the upper roller 71 by a biased spring 73 during the conveyance of the paper to the transfer unit. The shaft 74 changes in inclination as the lower roller 72 moves away from and contacts, and the position sensor 75 detects the position of one end of the shaft 74. Based on the detection result of the position sensor 75, the thickness of the paper can be measured.

  The color multifunction peripheral 100 according to the first embodiment has a laser power conversion table for changing the laser power based on the measurement result of the thickness detector 70 and the printing information on the first surface, and performs fixing control. FIG. 7 shows a block diagram of the control system. A control unit 77 provided in the color multifunction peripheral 100 controls the laser fixing device 15 based on the detection results of the thickness detection unit 70 and the first surface image information detection unit 78. The first surface image information detection means 78 detects image information of the first surface, and the control unit 77 obtains a show-through image of the second surface based on this image information. Then, the control unit 77 obtains the show-through state based on the sheet thickness by the thickness detection unit 70.

  When the paper is thin and the toner show-through is severe, when irradiated with the same laser power, the temperature of the irradiated toner on the second surface increases as shown in FIG. Along with that, a void is generated, causing a problem of image quality degradation.

  Therefore, when the thickness of the paper is thin, it is preferable to reduce the output within the range of about 0.1% to 30% of the normal laser power. The laser power can be controlled by the control unit 77 by controlling the irradiation time, but the emission power may be controlled. The thickness of the normal paper is about 100 to 150 μm. For example, if the paper thickness is 60 μm based on the detection result of the thickness detection means 70, the control unit 77 uses the laser power of the laser fixing device 15. Is reduced by 1% to 20%. As a result, it is possible to maintain the toner fixing temperature so as not to exceed a set temperature (for example, 180 ° C.) even in the show-through portion.

  Of course, the part where the laser power is reduced may be controlled so that only the part where the show-through occurs is caused by the toner on the first surface. The laser power is reduced only for the portion where the print information on the first surface and the print portion on the second surface overlap, and for the portion where the print information on the first surface and the print portion on the second surface do not overlap, the laser power is Do not decrease.

  Further, according to the detection result of the thickness detection means 70, when the paper thickness is equal to or greater than a predetermined value, there is almost no show-through due to the toner on the first surface, so the control unit 77 reduces the laser power on the second surface. No control is performed. In this embodiment, the semiconductor laser array 60 shown in FIGS. 3 and 4 is adopted. The semiconductor laser array 60 has 1,000 laser elements 61 each having a wavelength of 780 nm and a rated output of 150 mW. Something is used. At this time, the arrangement pitch p of the laser elements 61 is 0.3 mm, and the laser spot diameter d is also 0.3 mm. Therefore, it is possible to control the laser power for each spot in the range of 0.3 mm. The spot range is desirably as small as possible, and it is preferable to control for each dot if possible. In this way, irradiation is performed in block units with the spot diameter or a combination thereof.

In that case, it is necessary to arrange the semiconductor lasers at a dot pitch, or to adopt a scanning method using a CO ₂ laser or the like shown in FIG. The laser fixing device 110 in FIG. 9 scans the recording paper (image recording medium) 115 in the lateral direction (main scanning direction) by a polyhedral mirror 112 that rotates laser light from a single laser light source 113, and the laser light A fθ lens or a condensing lens as a correction lens 114 that corrects the aberration caused by deflection is condensed on the entire area of the recording paper (image recording medium) 115, and the recording paper (image recording medium) 115 is longitudinally moved by the conveying device 116. By carrying it, it has a mechanism for irradiating the entire area of the recording paper (image recording medium) 115 with focused laser light.
The method for determining the thickness of the paper is not limited to the current configuration, and may be another configuration.

  As shown in FIG. 8, when the amount of light absorption differs between the case where the toner is black toner and the color toner such as cyan, the degree of increase in toner temperature due to the show-through of the toner on the second surface Will be different. Generally, in the case of a color toner, since the light absorption amount at a wavelength of 780 nm is small, the light absorption amount can be adjusted by adding a light absorbing agent that absorbs light absorption at 780 nm. However, due to cost (generally expensive light absorbers), absorption amount, and the like, the four toner colors may not have the same absorption amount. Therefore, for example, when the amount of light absorbed by color toner such as cyan is smaller than that of black toner, the second surface is obtained when the toner printed on the first surface is black toner and cyan toner as shown in FIG. When the toner printed on the black toner is black toner, even when the same laser power is irradiated, the heat generation temperature of the toner on the second surface is different, and the black toner has a higher toner temperature on the second surface. Therefore, the control unit 77 is more optimal by changing the degree to which the laser power of the laser fixing device 15 is reduced depending on whether the toner printed on the first surface is black toner, cyan toner, yellow toner, or magenta toner. It is possible to ensure a good fixing property.

  Further, when the toner on the first surface is fixed by the laser beam but is not yet sufficiently solidified, the laser beam irradiated at the time of fixing the second surface is transmitted through the paper, and the first surface is fixed. In order to prevent uncured toner from being melted and causing toner stains such as a paper guide, the following measures can be taken. According to the thickness of the paper detected by the paper thickness detecting means 70, the problem is solved by adjusting the time until the second surface is fixed after the first surface is fixed.

  FIG. 10 is a more specific control block diagram of the image forming apparatus according to the present embodiment.

  A reading unit 125 that reads an original image, an image processing unit 126 that converts the read original image into an appropriate electrical signal to generate image data, an image forming unit 127 that prints out the generated image data, and predicts or shows through A detection unit 130 for detecting, a fixing control unit 122 for controlling laser light irradiation of a fixing unit (not shown), and a recording member (paper) after receiving a print start signal based on a process speed and a signal of an actuator for detecting a paper conveyance start signal ) Stores the arrival time to the laser irradiation unit in the fixing device, the peripheral device control unit 128 that controls peripheral devices such as finishers and sorters that are post-processing devices, and the operation unit of the image forming apparatus 120. The input unit 123 and the display unit 124 are provided.

Control in this laser fixing will be described. FIG. 11 shows a flowchart of control in the present embodiment.
The control unit 121 detects the thickness of the sheet by the detection unit 130, compares the result with the laser power conversion table, and calculates the laser light output value (step S1). The image information on the first surface is analyzed based on the print position information of the image information received from the image processing unit 126 (refers to a signal indicating which position to print for each page with respect to the print job) (step 1 S2), obtaining the image information of the second surface offset. Data stored in advance in the storage unit 129 is collated. The control unit 121 calculates the print position information obtained by analyzing the image information on the second surface, the show-through image information, and the show-through detection information by the detection unit 130 using the laser power conversion table. Based on the laser light output value, the laser power for each block on the second surface is determined (step S3). The determination result is transmitted to the fixing control unit 122, and the fixing control unit 122 drives the recording paper conveyance belt 31 to irradiate the laser beam based on the received print position information and the calculated output value of the laser beam. Each on / off control is determined (step S4), and a laser beam output instruction signal and an output value are transmitted to the laser fixing device 15 (step S5).

In addition, the fixing control unit 112 monitors a signal of an actuator (not shown) that detects conveyance of the recording paper 40 and performs control to apply a bias voltage to the recording paper conveyance belt 31 based on this signal.
The laser fixing device 15 irradiates a laser for each block (step S6).

(Example 2)
The difference from the first embodiment is that a means 80 for detecting paper transparency is provided instead of the means for detecting the paper thickness as means for predicting the show-through of the paper. As shown in FIG. 12, the transparency detecting means 80 emits light by sandwiching the conveyed paper in the middle of the paper conveying path after the paper is fed out and before the fixing surface of the first surface is fixed. The element 81 and the light receiving element 82 are arranged facing each other. In the transparency detecting means 80 in the present embodiment, the light emitting element 81 is configured by an infrared light emitting diode, and the light receiving element 82 is configured by a photodiode.

A light receiving element (photodiode) 82 is provided for a light emitting element (LED) 81 having a center wavelength of 780 nm, and light incident on the photodiode 82 generates a current that depends on the amount of light received, and is converted into a voltage corresponding thereto. Are amplified and output as an image density signal.
The reason why the center wavelength is set to 780 nm is to increase the accuracy of prediction of the toner temperature rise due to the show-through of the toner by making it the same as the oscillation wavelength of the fixing laser.

  By the degree to which the infrared light emitted from the light emitting element 81 is received by the light receiving element 82, the transparency of the paper can be grasped, and the degree of toner show-through can be predicted. The method for discriminating the transparency of the paper is not limited to the current configuration, and another configuration may be used.

  In the second embodiment, the show-through of the second surface is predicted based on the transparency of the paper. Since the fixing control based on the detection result is the same as that in the first embodiment, the description thereof is omitted.

(Example 3)
In the present embodiment, the semiconductor laser array 60 shown in FIGS. 3 and 4 similar to that of the first embodiment is employed.

  As shown in FIG. 13, a show-through density measuring device 85 is provided for the second surface of the paper in the middle of conveyance before fixing the second surface after fixing the first surface, and toner show-through is provided for each block. Measure the degree of. The show-through density measuring device 85 includes a light emitting element 81 and a light receiving element 82 provided on a line. The light emitting element 81 is configured by an infrared light emitting diode, and the light receiving element 82 is configured by a photodiode.

  A linear light receiving element (photodiode) 82 is provided for a linear light emitting element (LED) 81 having a center wavelength of 780 nm, and light incident on the photodiode 82 generates a current depending on the amount of received light. Is then amplified and output as an image density signal.

  In accordance with the measurement result, the laser power is controlled for each block, and the output of the laser element is lowered to the portion where the show-through density is high by the above measurement. The extent of the range of each block depends on the number and pitch of the light emitting elements 81 and the light receiving elements 82 and the laser element pitch of the semiconductor laser array. Each block is finer and can be controlled more finely. However, since the cost is higher, the range of each block depends on the design concept. The laser method may be a scan method, and the scan method can be controlled with a higher resolution, but there is a problem that the cost is high.

  FIG. 14 shows a block diagram of the control system. The controller 91 controls the laser power of the laser fixing device 15 based on the result of the show-through density detecting device 85.

  FIG. 15 shows a flowchart of control in this embodiment. First, the image density on the second surface is measured for each block by the show-through density detector 85 (step S11). The controller 91 determines the laser power for each block on the second surface based on the detection result of the image density on the second surface (step S12). Further, on / off control for each block is determined based on the image information of the second surface (step S13). The control unit 91 transmits an output instruction signal and an output value of the laser beam to the laser fixing device 15 (step S14). The laser fixing device 15 irradiates a laser for each block (step S15).

  In this way, the degree of show-through of the paper is predicted or detected by measuring the thickness of the paper, and based on the prediction result or detection result, the laser power for fixing the second surface is controlled so as not to exceed a predetermined temperature. As a result, voids and the like that occur as the surface temperature of the toner increases can be prevented, and image quality can be maintained even in duplex printing.

4 Light source 11 Intermediate transfer belt 11a, 11b Tension roller 13a Primary transfer unit 14 Secondary transfer unit 15 Fixing unit (laser fixing device)
15a fixing member 15b conveying member 16 internal sheet feeding unit 16a sheet feeding roller 17 sheet feeding unit 17a sheet feeding roller 31 recording sheet conveying belt 32 driving roller 33 driven roller 34 suction charger 35 separating charger 36 discharging charger 37 separating claw 40 recording medium ( Recording sheet)
41 Unfixed toner 51 Laser irradiation part 52 Laser light 53 Heat sink (heat sink)
54 temperature sensor 60 semiconductor laser array 61 semiconductor laser element 62 photodiode 63 silicon substrate 64 wire bond wire 65 surface electrode 66 ceramic substrate 67 lens holder 68 convex lens 70 detection means 71 upper roller 72 lower roller 73 spring 74 shaft 75 position sensor 77 control Part 78 First surface image information detecting means 80 Transmissivity detecting means 81 Light emitting element (LED)
82 Light-receiving element (photodiode)
85 Density measuring device 91 Control unit d Laser spot diameter E Optical system unit L1 Laser head L2 Paper transport device

Claims (9)

In an image forming apparatus having a double-sided printing function and a laser fixing device,
Means for predicting or detecting the degree of show-through of the recording paper due to fixing of the first side;
An image forming apparatus characterized in that, based on the prediction result or detection result, the laser power for fixing the second surface of the recording paper to the laser fixing device is controlled so as not to exceed a predetermined temperature. The means for predicting or detecting the show-through of the recording paper is a means for detecting either the thickness or the transparency of the recording paper,
The image forming apparatus according to claim 1, wherein the laser power for fixing the second surface is controlled based on the image information on the first surface for the laser fixing device.   The means for predicting or detecting the show-through of the recording paper is means for detecting the image density of the recording paper on the second surface after the first surface fixing and before the second surface fixing with reflected light. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the laser irradiation of the laser fixing device is performed in units of blocks formed of a spot diameter of laser light or a combination thereof.   The image forming apparatus according to claim 1, wherein the laser irradiation of the laser fixing device is performed in units of pixels. In a laser fixing control method for controlling a laser fixing device provided in an image forming apparatus having a double-sided printing function,
Based on a prediction result or a detection result by a means for predicting or detecting the show-through of the recording paper, the laser power for fixing the second surface of the recording paper to the laser fixing device is controlled so as not to exceed a predetermined temperature. And a laser fixing control method. The means for predicting or detecting the show-through of the recording paper detects the thickness or type or transparency of the recording paper,
7. The laser fixing control method according to claim 6, wherein a laser power for fixing on the second surface is controlled based on image information on the first surface for the laser fixing device.   The laser fixing control method according to claim 6 or 7, wherein the laser irradiation of the laser fixing device is performed in units of blocks including a spot diameter of laser light or a combination thereof.   The laser fixing control method according to claim 6, wherein the laser irradiation of the laser fixing device is performed in units of pixels.

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