JP2008089828A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which fuses and fixes an toner image on a sheet by irradiating the toner image with laser beam, in which excellent fixation can be performed by imparting necessary and sufficient energy (heat quantity) to the toner image with the laser beam. <P>SOLUTION: The toner image TA consisting of a character "A" is scanned as main scanning with laser beam H1 disposed downstream in a sub-scanning direction (as shown by an arrow S2) and having small output W1 and laser beam H2 disposed upstream and having large output W2 in sequence in a main scanning direction (as shown by an arrow S1) to thereby form a first line L1, a second line L2, and a third line L3. A region scanned with the laser beam H1 of a leading line is scanned again with the laser beam H2 of a following line to thereby heat the toner image stepwise, so that the toner image can excellently be fixed with the necessary and sufficient energy. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for fixing a toner image on a sheet by irradiating an unfixed toner image carried on the sheet with laser light.

  As a fixing device for fixing a toner image on a sheet in an image forming apparatus such as a copying machine, a printer, and a facsimile, a heat-pressing type is generally known. In this apparatus, a pressure roller is pressed against a fixing roller heated by a heater to form a fixing nip portion between both rollers, and a sheet carrying an unfixed toner image is inserted into the fixing nip portion. The toner image is heated and pressurized to be fixed on the sheet. According to this method, it takes a long time for the fixing device to reach a predetermined fixing temperature at which the toner can be melted, and it is necessary to heat the entire fixing roller in order to melt the toner image. There were many problems that thermal efficiency (energy efficiency) was bad.

  As a measure for solving such a problem, for example, Patent Document 1 proposes a method of fixing a toner image by irradiating a laser beam.

  In this apparatus, a toner image is melted and fixed on a sheet by irradiating a laser beam based on the same image information to a toner image formed on the surface of the photoreceptor based on the image information.

  According to this, since the laser image is irradiated on the toner image based on the image information, it is not necessary to irradiate the area without the toner image on the sheet with the laser beam. Improvements can be made.

JP 2000-338798 A

  However, according to Patent Document 1 described above, since one laser beam is used for fixing, it is necessary to increase the scanning speed of the laser beam in order to cope with the increase in the fixing speed in the recent image formation. is there. For this reason, it is impossible to apply a sufficient amount of heat to the toner image (hereinafter, energy is used for the laser beam and heat amount is used for the toner, which have almost the same meaning). There was a problem that fixing failure occurred. On the other hand, as a measure for imparting a sufficient amount of heat to the toner image, a method of increasing the output of laser light can be considered. In this case, although a large amount of heat is imparted to the toner in a short time, the toner Since the temperature of the toner does not rise rapidly, there is a problem that the amount of heat wasted without increasing the melting of the toner.

  Accordingly, the present invention provides an image forming apparatus including a fixing device that fixes a toner image with a laser beam, and causes improper fixing due to an insufficient amount of heat applied to the toner, or a rapid amount of heat applied to the toner. An object of the present invention is to provide an image forming apparatus that prevents waste of heat caused by it.

  According to a first aspect of the present invention, there is provided an exposure apparatus for forming an electrostatic latent image by exposing the surface of a uniformly charged photoreceptor in the main scanning direction and the sub-scanning direction based on image information, and the electrostatic latent image as a toner. The present invention relates to an image forming apparatus including a developing device that develops an image, a transfer device that transfers the toner image onto a sheet, and a fixing device that fixes the transferred toner image onto the sheet. In the image forming apparatus according to the present invention, the fixing device generates laser light from a plurality of laser light sources, each having a plurality of laser light sources that generate laser light that is ON / OFF controlled based on image information. Scanning means for scanning the sheet in the main scanning direction and in the sub-scanning direction by the laser beam and melting and fixing the toner image on the sheet, wherein the plurality of laser light sources emit laser light along the sub-scanning direction. One line is main-scanned in an aligned state, and the amount of heat applied to the toner by the laser light upstream in the sub-scanning direction is set to be larger than the amount of heat applied to the toner by the laser light downstream in the sub-scanning direction. It is characterized by being.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the plurality of laser light sources includes a region scanned by the downstream laser light in the preceding line and an upstream side in the subsequent line. The main feature is that the laser beam performs main scanning.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, each of the laser light generation units changes the output of the laser light generated from the plurality of laser light sources, thereby imparting the toner to each toner. The feature is that the amount of heat to be changed is changed.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the laser light generation unit changes the irradiation time of the laser light generated from the plurality of laser light sources to each toner. It is characterized in that the amount of heat applied is changed.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the laser light generating means uses the laser used in accordance with a toner amount of a toner image based on the image information. It is characterized by changing the number of light sources.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the laser light generating means emits a laser light having a wavelength substantially the same as an absorption wavelength of the toner to the plurality of laser light sources. It is characterized by being generated from.

  According to the first aspect of the present invention, the fixing device melts and fixes the toner image on the sheet by the laser light generating means and the scanning means based on the image information that forms the electrostatic latent image. Only the area necessary for fusing the toner image is scanned and the other unnecessary areas need not be scanned, so that unnecessary power consumption can be suppressed. Further, the fixing device performs main scanning on one line in a state where the laser beams are arranged along the sub-scanning direction, and is further on the upstream side in the sub-scanning direction than the amount of heat given to the toner by the laser beam on the downstream side in the sub-scanning direction. Since the amount of heat imparted to the toner by the laser beam is increased, the amount of heat imparted to the toner image can be varied within one line.

  According to the second aspect of the present invention, the plurality of laser light sources scan the area where the downstream laser beam in the preceding line is main scanned with the upstream laser beam in the succeeding line. Since the region that has been preheated by the main scanning of the downstream laser beam can be heated by the main scanning of the laser beam upstream of the subsequent line, heat can be efficiently applied to the toner image. When heating a toner image, since the toner has a relatively large heat capacity, even if a large amount of heat is applied to melt the toner image in a short time, the toner image cannot be heated suddenly, and wasteful heat is generated. Will be wasted. Therefore, according to the second aspect of the present invention, since the same region of the toner image can be heated in stages, waste of heat can be eliminated.

  According to the invention of claim 3, the amount of heat applied to the toner is changed by changing the output of the plurality of laser beams.

  According to the invention of claim 4, the amount of heat applied to the toner is changed by changing the irradiation time of the plurality of laser beams.

  According to the fifth aspect of the present invention, excessive heating of the toner image can be prevented by changing the number of laser light sources to be used in accordance with the toner amount of the toner image based on the image information.

  According to the invention of claim 6, since the laser light generating means generates laser light having a wavelength substantially the same as the absorption wavelength of the toner from the plurality of laser light sources, the energy of the laser light is favorably absorbed by the toner.

  Hereinafter, the best embodiment of the present invention will be described in detail with reference to the drawings. In addition, in each drawing, the member etc. which attached | subjected the same code | symbol are the same structures, The duplication description about these shall be abbreviate | omitted suitably. Moreover, in each drawing, members and the like that are not necessary for the description are omitted as appropriate.

<Embodiment 1>
The image forming apparatus 1 according to the present invention will be described with reference to FIGS. Among these, FIG. 1 is a diagram schematically showing the configuration of the image forming apparatus 1 according to the present invention. FIG. 2 is a diagram illustrating an example in which one line on the sheet P is scanned with two laser beams H1 and H2 having different outputs arranged in the sub-scanning direction. FIG. 3 is a diagram illustrating the relationship between the wavelength of the laser beam and the transmittance of the toner T.

  As shown in FIG. 1, the image forming apparatus 1 includes a sheet feeding unit 11 that feeds and transports a sheet P (a recording medium such as paper and a transparent film), and a toner image T (as an image on the sheet P that is fed and transported. In the following description, the image forming unit 12 for forming the toner image and the toner “T” is used, the sheet conveying unit 13 for conveying the sheet P after the image formation, and the image is fixed on the sheet P. And a fixing unit 14.

  The sheet feeding unit 11 includes a sheet feeding cassette 21, a sheet feeding roller 22, a feeding roller 23, a retard roller 24, a conveying roller pair 25, a registration roller pair 26, and the like. A plurality of sheets P stored in a stacked state in the sheet feeding cassette 21 are fed by the sheet feeding roller 22 in order from the topmost one, and separated one by one by the feeding roller 23 and the retard roller 24. And then conveyed downstream. Further, the sheet P is conveyed to the registration roller pair 26 by the conveyance roller pair 25, and after the skew feeding is corrected, the sheet P is supplied to the image forming unit 12 described below by the registration roller pair 26.

  The image forming unit 12 is provided with a photosensitive drum 31 (a drum-shaped photosensitive member), around which a charging roller 32 (charging device), an exposure device 33, a developing device 34, and a transfer roller 35 (transferring). Device), a cleaning device 36, and the like. The photosensitive drum 31 is rotationally driven at a predetermined process speed (circumferential speed) in the direction of arrow R31 by a driving unit (not shown). The surface (outer peripheral surface) of the photosensitive drum 31 is uniformly (uniformly) charged to a predetermined polarity and potential by the charging roller 32. An electrostatic latent image is formed on the surface of the photosensitive drum 31 after charging by the exposure device 33. For example, the exposure device 33 performs main scanning on the surface of the photosensitive drum 31 that has been uniformly charged by laser light that is ON / OFF controlled based on image information, and performs sub-scanning by rotation of the photosensitive drum 31. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 31. The electrostatic latent image is developed as a toner image T with the toner T attached thereto by the developing device 34. As will be described later, the toner image is transferred onto the sheet P by a transfer roller 35 that also serves as an electrostatic attraction roller. As the exposure apparatus, an apparatus in which a large number of LEDs are arranged in the main scanning direction and ON / OFF control is performed based on the image information can be used. The toner T will be described in detail later.

  The sheet conveyance unit 13 includes a transfer roller 35 disposed on the upstream side in the sheet conveyance direction, an electrostatic adsorption roller 37 disposed on the downstream side, and a conveyance belt 38 stretched over these rollers. Is arranged. The conveyance belt 38 is pressed against the photosensitive drum 31 by the transfer roller 35, and a transfer nip portion N is formed between the photosensitive drum 31 and the conveyance belt 38. The transfer nip N is disposed on a line segment connecting the center of the photosensitive drum 31 and the center of the transfer roller 35. The toner image T formed on the photosensitive drum 31 described above reaches the transfer nip portion N as the photosensitive drum 31 rotates in the direction of arrow 31. In synchronization with this, the sheet P is supplied from the registration roller pair 26 to the transfer nip portion N. At this time, a transfer bias is applied to the transfer roller 35, whereby the toner image T on the photosensitive drum 31 is transferred onto the sheet P. At this time, the sheet P is electrostatically attracted to the surface of the conveyance belt 38. In other words, when the sheet P passes through the transfer nip portion N, it is gradually attracted to the surface of the conveyor belt 38 from the leading end side in parallel with the transfer of the toner image T on the photosensitive drum 31. After the toner image is transferred, the transfer residual toner remaining on the surface of the photosensitive drum 31 is removed by the cleaning device 36 and is used for the next image formation. The transfer belt 38 rotates in the arrow R38 direction as the downstream electrostatic attraction roller 37 is driven and rotated in the arrow R37 direction by a driving unit (not shown). As a result, the sheet P is conveyed to the fixing unit 14 while maintaining the state of being electrostatically attracted to the surface of the conveying belt 38 and carrying an unfixed toner image on the surface. For this reason, the sheet P at the time of fixing, and thus the toner image T, can maintain high positional accuracy.

  A fixing device 40 is disposed in the fixing unit 14. 1B is a view of the fixing device 40 in FIG. 1A as viewed from above. The sheet P conveyed to the fixing unit 14 is fixed by the fixing device 40 with the toner image T melted and fixed. In the present embodiment, the fixing device 40 melts and fixes the toner image T using laser light. That is, the fixing device 40 scans the sheet P in the main scanning direction and the sub-scanning direction by using the laser light generating unit 41 having a plurality (two in the present embodiment) of laser light sources and the laser light generated from the plurality of laser light sources. Scanning means for scanning in the direction to melt and fix the toner image T to the sheet P. The scanning unit includes a collimator lens 42, a cylindrical lens 43, a polygon mirror 44, an imaging lens 45, folding mirrors 46 and 47, and the like, and thereby the laser light is directed in a direction orthogonal to the conveyance direction on the sheet P. Main scan. On the other hand, the sub-scanning by the laser beam is performed by the above-described conveyance belt 38 conveying the sheet P in the direction of arrow R38. The laser light generated from the laser light source is collimated by the collimator lens 42 and focused on the polygon mirror 44 by the cylindrical lens 43. The laser beam reflected by the polygon mirror 44 rotated at a high speed by a polygon motor (not shown) is imaged by the imaging lens 45, further reflected by the folding mirrors 46 and 47, and irradiated on the sheet P in the main scanning direction. To do. In parallel with the main scanning, the sheet P is conveyed by the conveying belt, and the sheet P is irradiated in the sub-scanning direction. That is, the fixing device 40 can irradiate (scan) the sheet P in the main scanning direction and the sub-scanning direction. The fixing device 40 will be described in detail later.

  The sheet P on which the toner image T is fixed by the fixing device 40 is separated from the transport belt 38, transported in the direction of the arrow Kp by the transport roller 48, and further discharged onto a discharge tray (not shown) by the discharge roller 49. The Thus, image formation on one side (front surface) of one sheet P is completed.

  The scanning of the sheet P by the fixing device 40 described above is performed based on the same image information as the image information used when the electrostatic latent image is formed on the photosensitive drum 31 described above. That is, as described above, the electrostatic latent image is formed when the exposure device 33 exposes the surface of the photosensitive drum 31 in the main scanning direction and the sub-scanning direction based on the image information, and toner is applied to the electrostatic latent image. A toner image is formed by adhesion. Based on the same image information, the fixing device 40 scans the sheet P with ON / OFF-controlled laser light. As a result, it is possible to irradiate the laser beam only to a region where the toner image T on the sheet P is present and not to irradiate the other region, so that waste of energy can be prevented. Here, when the fixing device 40 irradiates the laser beam based on the image information, the irradiation region is set wider than the exposure region by the exposure device 33. Thereby, even when there is an assembly error or an operation error of each member, the entire toner image T can be surely irradiated with the laser beam and fused and fixed.

  In the present embodiment, the laser generator 41 further includes a plurality of (two) laser light sources, and the toner image is obtained by simultaneously scanning the sheet P with a plurality of laser beams generated from the plurality of laser light sources. T is fixed.

  This point will be described in detail with reference to FIG. In this figure, a sheet P carrying an unfixed toner image TA with the letter “A” on the surface is conveyed in the direction of the arrow Kp and reaches the fixing portion, and this toner image TA is irradiated with laser beams H1 and H2. The example which receives is shown typically. Here, the black circles constituting “A” in the figure symbolize the toner. Further, the main scanning direction of the laser beams H1 and H2 is indicated by S1, and the sub-scanning direction (the direction opposite to the arrow Kp direction which is the conveyance direction of the sheet P) is indicated by S2.

  In the present embodiment, the laser generating means 41 has two laser light sources. The laser beams H1 and H2 generated from these laser light sources are arranged so that their spots are arranged adjacent to each other in the sub-scanning direction (arrow S2 direction) when the sheet P is irradiated by the polygon mirror 44 or the like. ing. However, arranging here includes cases where they are arranged so as to be in contact with each other and cases where they are arranged so as to partially overlap each other, but the latter is adopted in an actual machine.

  In the present embodiment, the two laser beams H1 and H2 are disposed downstream of the laser beam H1 along the sub-scanning direction, and the laser beam H2 is disposed upstream of the laser beam H1 and H2. By simultaneously moving in the main scanning direction, one line is scanned.

Here, assuming that the energy (heat amount) given to the toner by the laser beam is J, the output of the laser beam is W, and the irradiation time of the laser beam is t,
J = W · t
The relationship holds.

  In the present embodiment, the energy applied to the toner by the laser beams H1 and H2 is made different by giving the outputs W1 and W2 different for the plurality of laser beams H1 and H2. Specifically, the output W2 of the upstream laser beam H2 is configured to be larger than the output W1 of the downstream laser beam H1. In other words, when the laser beam H1 and the laser beam H2 irradiate the toner image T under the same conditions, the amount of heat applied to the toner image T by the laser beam H2 rather than the amount of heat applied to the toner image by the laser beam H1. Is getting bigger.

  Further, as shown in FIG. 2, the first line L1, the second line L2, the third line L3,..., N (n is a natural number) are sequentially formed by main scanning and sub scanning of the laser beams H1 and H2. At this time, the region on the downstream side in the sub-scanning direction of the preceding line is scanned so that the region on the upstream side in the sub-scanning direction of the subsequent line overlaps. More specifically, when forming the succeeding line (for example, the second line L2) in the region scanned by the laser beam H1 in the preceding line (for example, the first line L1), the laser beam H2 is generated. I'm trying to scan. These relationships are established between the second line L2 and the third rain L3, and also between two adjacent lines thereafter.

  As described above, the output W1 of the laser beam H1 is smaller than the output W2 of the laser beam H2. Therefore, in the present embodiment, the same area of the toner image TA is first raised to a certain temperature (preheated) by the laser light H1 of the preceding line, and then raised to a predetermined temperature by the laser light H2 of the subsequent line. I try to warm it up.

  Thereby, waste of energy of the laser beam can be prevented. That is, for example, when considering the case where the output of the laser beam H1 is equivalent to that of the laser beam H2, the toner T has a relatively large heat capacity. It will not rise rapidly. The amount of heat used to raise the temperature is less than the applied energy, and the remaining energy is wasted. Therefore, in the present embodiment, as described above, the output W1 of the laser beam H1 on the downstream side in the sub-scanning direction is made smaller than the output W2 of the laser beam H2 on the upstream side in the sub-scanning direction. In addition to reducing waste of waste, it has made it possible to establish a favorable settlement. In other words, necessary and sufficient energy (amount of heat) is applied to the toner image T by the laser beams H1 and H2, so that good fixing can be performed.

  Here, the toner used in this embodiment will be described. As the toner, a toner for flash fixing that has a clear melting point, that is, fluidity increases in a short time when the melting point is exceeded is used. Specifically, a light-absorbing strand such as styrene acrylic or polyester was used. Further, in the present embodiment, unlike the above-described fixing device of the heat and pressure type using the fixing roller and the pressure roller, there is no need to separate the sheet P on which the toner image is fixed from the fixing roller. Addition of a wax component or the like for promoting separation is unnecessary. In other words, the addition of external additives other than toner can be suppressed compared to a heat-pressing type fixing device, so that the toner can be selected based on the original function of the toner without any other restrictions. Can do.

  Furthermore, in this embodiment, the laser beam used has a wavelength close to the absorption wavelength of the toner. Increased photothermal conversion efficiency. FIG. 3 shows the relationship between the wavelength of the laser beam in the fixed laser and the transmittance of the laser beam. In the figure, the horizontal axis represents the wavelength (nm) of the laser beam, and the vertical axis represents the transmittance (%) of the laser beam. From the figure, the transmittance in the vicinity of the wavelength of the laser beam of 572 nm is the lowest, and therefore the absorption efficiency is the highest. The next highest absorption effect is in the vicinity of 527 nm. Note that the second harmonic of a solid-state laser exists at 530 nm. As described above, the light-to-heat conversion efficiency can be increased by using a laser beam whose wavelength is close to the absorption wavelength of the toner.

<Embodiment 2>
The second embodiment will be described with reference to FIGS. 4 (a) and 4 (b). FIG. 4A is a diagram for explaining an example in which one line on the sheet P is scanned with three laser beams with different outputs arranged in the sub-scanning direction, and FIG. 5 is a diagram for explaining an example of scanning one line on a sheet P while stopping the operation.

  In the present embodiment, the main scanning is performed with three or more laser beams arranged in the sub-scanning direction. In FIG. 4A, a case where there are three laser beams will be described as an example. However, in principle, the case where there are four or more laser beams can be applied in substantially the same manner.

The three laser beams are referred to as laser beams H1, H2, and H3 in order from the downstream side in the sub-scanning direction. These three laser beams H1, H2, and H3 are simultaneously main-scanned to form one line. Here, it is assumed that the output magnitude relationship is set to be smaller as the laser beam is on the downstream side. That is, when the outputs of the laser beams H1, H2, and H3 are W1, W2, and W3 in this order,
W1 <W2 <W3
The relationship was established.

  Furthermore, in this embodiment, as shown in FIG. 4A, one line is constituted by the laser beams H1, H2, and H3, and scanning is performed in the order of the first line L1, the second line L2, and the third line L3. To go. At this time, the region scanned by the laser beam H2 in the preceding first line L1 is scanned by the laser beam H3 in the following second line L2, and the region scanned by the laser beam H1 in the preceding first line L1 is scanned. Then, the subsequent laser light H2 of the second line L2 is scanned. Similarly, the area scanned by the laser beam H2 in the preceding second line L2 is scanned by the laser beam H3 in the subsequent third line L3, and the area scanned by the laser beam H1 in the preceding second line L2 is scanned. Then, the subsequent laser beam H2 of the third line L3 is scanned. That is, the area scanned by the laser beam H1 of the preceding first line L1 is scanned by the laser beam H2 of the succeeding second line L2, and the laser beam H3 of the third line L3 is further scanned by the same area. In this way, the same region is heated stepwise with the laser beam H1 with the output W1, then with the laser beam H2 with the output W2, and then with the laser beam H3 with the output 3, so that the toner undergoes a rapid thermal change. Since the toner can be melted gradually without giving it, it is possible to perform good fixing and to suppress wasteful energy consumption.

In the present embodiment, when the toner amount of the toner image carried on the sheet P is small, for example, as shown in FIG. 4B, the laser beam H1 is stopped and the laser beams H2, H3 are stopped. By scanning, one line may be scanned. For example, the letter “A” (toner image TA) shown in FIG. 4A has a toner amount of 1.5 mg / cm ² in the area inside the letter face F, and the letter “B” shown in FIG. (Toner image TB) has a toner amount of 0.6 mg / cm ² for the same letter face F. The toner amount can be calculated based on image data when the surface of the photosensitive drum 31 is exposed by the exposure device 33 described above.

  In the present embodiment, the toner image TA shown in FIG. 4A has a large amount of toner, and a large amount of heat is required to melt the toner. Therefore, one line is divided into three laser beams H1, H2, and H3. Scanned. On the other hand, the toner image TB having a small amount of toner does not have as much heat as necessary to melt the toner as in the case of (a). Therefore, if too much heat is applied, the toner image TB may become glossy between the toner image TA. Unevenness occurs. Furthermore, when the amount of heat is extremely excessive, heat accumulates in the vicinity of the surface of the toner image TB, and the toner surface layer may be heated by this heat, resulting in an image having a rough surface.

  Therefore, in this embodiment, when the amount of toner is small, one line is scanned with two laser beams H2 and H3. Actually, a threshold value is set for the toner amount, and when the toner amount exceeds the threshold value, one line is scanned by three laser beams H1, H2, and H3. One line may be scanned by the laser beams H2 and H3. Here, as examples of the outputs W1, W2, and W3 of the three laser beams H1, H2, and H3, for example, W2 is set to 3 times W1, and W3 is set to 6 times W1. In order to obtain an output equivalent to this by setting the outputs of the three laser beams H1, H2, and H3 in this way, for example, compared with a case where 10 laser beams having an output of W1 are simply arranged. Thus, the configuration can be simplified.

  In the above description, when one of the three laser beams H1, H2, and H3 is stopped and one line is scanned with the two laser beams, the laser beam H1 is stopped and the laser beam H2 is stopped. , H3 scan one line, but depending on how the output values of the laser beams H1, H2, H3 are set and the toner amount of the toner image, H3 is stopped instead. One line may be scanned by two laser beams H1 and H2. However, in this embodiment, the laser beam H2 cannot be selected as the laser beam to be stopped.

  In the above description, for simplification of description, the description has been made by paying attention to the toner amount in the letter face region. However, in practice, the laser light is reduced to three based on the toner amount in one sheet P. It is also possible to select whether to use two or not. Further, in one sheet P, an area with a large amount of toner can be scanned with three laser beams, and an area with a small amount of toner can be scanned with two laser beams. In addition, when the image formed on the sheet P is monochrome, scanning is performed with two laser beams. When the image is formed in color, scanning is performed with three laser beams based on a general increase in toner amount. It is also possible to use properly.

  In the above description, an example in which one line is scanned with the three laser beams H1, H2, and H3 arranged in the sub-scanning direction has been described. However, the present embodiment is not limited to this, and four or more lines are scanned. The present invention can be similarly applied to the case where one line is scanned with the laser beam.

<Embodiment 3>
The present embodiment will be described with reference to FIG. FIG. 5 is a diagram illustrating an example in which one line on the sheet P is scanned with three laser beams arranged in the sub-scanning direction and having different scanning times.

  In the first and second embodiments described above, a plurality of laser beams are arranged in the sub-scanning direction, and their outputs are changed so that the amount of heat applied to the toner by each laser beam has a difference. On the other hand, in this embodiment, by changing the irradiation time of a plurality of laser beams, the amount of heat applied to the toner by each laser beam is made different.

Hereinafter, a case where one line is scanned with three laser beams H1, H2, and H3 will be described as an example. In the present embodiment, three laser light sources are provided, one polygon mirror is provided for each laser light source, and the rotation speed is changed to change each of the laser beams H1, H2, and H3. Irradiation times t1, t2, t3 are
t1 <t2 <t3
It was made to become. As described above, the energy that the laser beam gives to the toner is
J = W · t
Therefore, when the output W is constant, the energy applied to the toner increases as the irradiation time t increases.

  In the above description, three polygon mirrors having different rotation speeds are used. Instead, three polygon mirrors having different outer diameters are combined to form one polygon mirror. Each laser beam may be applied to regions having different diameters so that the irradiation time varies.

  In the above description, the case where the image forming apparatus is a single color (monochrome) has been described as an example. However, the present invention is not limited to this, and a two-color image forming apparatus, and further a four-color full-color image formation. It can also be applied to devices and the like. For example, in the case of a four-color full-color image forming apparatus, a four-color toner image of Y (yellow), M (magenta), C (cyan), and K (black) is superimposed to form a color image on a sheet. In general, the amount of toner tends to increase compared to monochrome. According to the present invention, the number of laser beams, the output, and the irradiation are applied according to the amount of toner. By changing the time based on the image information, good fixing can be realized while suppressing waste of energy.

  The present invention can be applied to a case where an image formed based on image information is processed again based on the same image information.

1 is a diagram schematically illustrating a configuration of an image forming apparatus. It is a figure explaining the example which scans one line on a sheet | seat with two laser beams with which different outputs arranged in the subscanning direction. It is a figure which shows the relationship between the wavelength of a laser beam, and the transmittance | permeability of a toner. (A) is a figure explaining the example which scans 1 line on a sheet | seat with three laser beams with which the output differs arranged in the subscanning direction, (b) stops one of those laser beams. FIG. 6 is a diagram illustrating an example of scanning one line on a sheet. It is a figure explaining the example which scans 1 line on the sheet | seat P with the three laser beams with which scanning time arranged in the subscanning direction differs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 31 ... Photosensitive drum (photosensitive body), 33 ... Exposure apparatus, 34 ... Development apparatus, 35 ... Transfer roller (transfer apparatus), 40 ... Fixing apparatus, 41 ... Laser beam Generation means, H1, H2, H3... Laser light, L1... First line, L2... Second line, L3... Third line, P. Scanning direction, T... Toner, toner image, TA... Toner image with letter “A”, TB... Toner image with letter “B”,

Claims (6)

An exposure device that forms an electrostatic latent image by exposing the surface of the photoreceptor after uniform charging in the main scanning direction and the sub-scanning direction based on image information; and a developing device that develops the electrostatic latent image as a toner image; An image forming apparatus comprising: a transfer device that transfers the toner image to a sheet; and a fixing device that fixes the transferred toner image to the sheet.
The fixing device includes:
Laser light generating means having a plurality of laser light sources each generating laser light that is ON / OFF controlled based on image information;
Scanning means that scans the sheet in the main scanning direction and the sub-scanning direction by laser light generated from the plurality of laser light sources, and melts and fixes the toner image to the sheet;
The plurality of laser light sources perform main scanning on one line in a state in which the laser beams are arranged along the sub-scanning direction, and further upstream than the amount of heat imparted to the toner by the laser beam on the downstream side in the sub-scanning direction. The amount of heat applied to the toner by the laser beam on the side is set to be large,
An image forming apparatus. The plurality of laser light sources perform main scanning with the upstream laser light in the subsequent line in the region where the downstream laser light in the preceding line is main scanned.
The image forming apparatus according to claim 1. The laser light generating means changes the amount of heat applied to the toner by changing the output of the laser light generated from the plurality of laser light sources,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The laser light generation means changes the amount of heat applied to the toner by changing the irradiation time of the laser light generated from the plurality of laser light sources,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The laser light generating means changes the number of the laser light sources to be used according to the toner amount of the toner image based on the image information.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The laser light generating means generates laser light having substantially the same wavelength as the absorption wavelength of the toner from the plurality of laser light sources;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images