JP3548412B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer that forms an electrostatic latent image on an image carrier based on an input image signal and visualizes the latent image with a developing unit. .
[0002]
[Prior art]
2. Description of the Related Art Conventionally, for example, a known image forming method using an electrophotographic process including a process of forming an electrostatic latent image on a surface of an image carrier such as an electrophotographic photosensitive member, and developing the latent image with a developer to visualize the latent image. As the device, a device using a two-component developer having a toner and a magnetic carrier as a developer or a device using a one-component developer consisting of only a toner is widely used.
[0003]
In such an image forming apparatus, a developing device for developing a latent image has a developer accommodating portion accommodating a developer having a toner, and generally, a stirring member is provided in the developer accommodating portion. After the toner is supplied from the outside to the developer accommodating portion, the developer is conveyed to the developer carrier by the stirring member.
[0004]
Particularly, in a developing device using a two-component developer, the developer is agitated by the agitating member to uniformly disperse the toner in the magnetic carrier. Therefore, the toner causes friction between the toner and the magnetic carrier due to the agitation, and is charged to a desired charge amount.
[0005]
Further, in a developing device using a one-component developer, a configuration in which the toner conveyed onto the developer carrying member by the stirring member is applied to the developer carrying member by a developer applying member elastically in contact with the developing carrier is used. Thus, the toner is frictionally generated with the developer carrier and the developer application member, and is charged to a desired charge amount.
[0006]
[Problems to be solved by the invention]
However, the stirring operation and the toner applying operation of the developing device in the above-described conventional image forming apparatus are continuously performed during the developing process. Therefore, for example, when an image with extremely small toner consumption is continuously printed, the developer May be in an excessively agitated state or an excessively triboelectrically charged state. FIG. 17 shows an example of such an image.
[0007]
That is, when an image having the entire length L and the length of the printing portion I is formed on the image carrier rotating in the direction of arrow E, the area to be printed on the entire image is extremely small. Even in such a case, the stirring and coating operations have conventionally been performed continuously while the latent image having the length L passes through the facing region between the image carrier and the developer carrier. For this reason, the toner on the developer carrier is consumed only for the visualization of the latent image in the printing portion I, and the remaining non-printing portion is agitated and applied without consuming the toner. In the non-printing area, excessive stirring and excessive triboelectric charging occurred.
[0008]
When the developer is excessively stirred or excessively charged in such a manner, the deterioration of the developer, that is, a phenomenon such as an excessive increase in the charge amount of the toner and a destruction of the developer occurs, and the image density decreases and the fog is reduced. And the like, the quality of developed images deteriorates. In particular, non-magnetic toners containing a flexible polymer resin as a main component and having a high volume resistance have caused such problems remarkably. Further, if the developer carrier is continuously driven without consuming the toner, there is a problem that the toner on the developer carrier is released and scattered, thereby contaminating the inside of the apparatus.
[0009]
Therefore, an object of the present invention is to detect a printing portion by reading a document image, and calculate a time required for the printing portion to pass through the development area based on a signal of the detected printing portion,Of developer carrierUnnecessary agitation and coating operation are eliminated by controlling the rotation time, and deterioration of the developer due to excessive charging or damage of the toner is prevented.Also, it is possible to prevent the shock at the start and stop of rotation of the developer carrier from adversely affecting the developing operation of other developing means.Another object of the present invention is to provide an image forming apparatus capable of always stably obtaining a high-quality image.
[0010]
[Means for Solving the Problems]
The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:An image carrier on which an electrostatic latent image is formed;
First developing means for carrying a developer of a predetermined color on a first developer carrier and developing a latent image on the image carrier in a first development area;
The second developer carrying member is arranged on the downstream side of the first developing unit with respect to the image carrier moving direction, and carries a developer of a color different from the predetermined color on the second developer carrying member. Second developing means for developing a latent image on the image carrier;
Color determination means for determining a color included in an image to be formed;
A print portion detecting means for detecting a print portion and a non-print portion for each color,
A drive control unit that controls a rotation operation of the first developer carrier and the second developer carrier based on a signal from the printing unit detection unit;
In the image forming apparatus having
The drive control means includes:
In a case where the printing section of the predetermined color and the printing section of the different color coexist in one image area, the developing areas of the first developer carrier and the second developer carrier are provided. While the image area is passing, the first developer carrier and the second developer carrier are rotated,
In the case where only the printing portion of the predetermined color exists in one image area, the first developer carrier is rotated while the image area passes through the first development area, And not rotating the second developer carrier while the image area is passing through the second development area,
In the case where only one printing portion of the different color exists in one image region, the rotation operation of the first developer carrier is not performed while the image region passes through the first development region, And, while the image area is passing through the second development area, so as to perform the rotation operation of the second developer carrier,
The timing of stopping the rotation of the first developer carrier is when a non-image area on the image carrier is passing through the first development area, and the second developing means When the development operation by is not performed,
The start timing of the rotation operation of the second developer carrier is when the non-image area on the image carrier is passing through the second development area and the first developer means When the developing operation is not performed,
Control so thatAn image forming apparatus characterized in that:
[0015]
According to another embodiment of the present invention,In a case where a plurality of image formations are continuously performed while leaving a predetermined width of the image interval, the predetermined width of the image is formed between the first development area and the second development area on the image carrier. When the distance is shorter than the distance between the development areas,
When starting the rotation operation of the second developer carrier at an image interval,
The image interval is a width longer than the distance between the development areas by adding the non-image area width corresponding to one or more image widths to the predetermined width..
[0016]
According to another embodiment of the present invention,A member for holding the first developer carrier and the second developer carrier and the image carrier at a predetermined interval, wherein the member does not contact the image carrier;.
[0017]
In the present invention,The developer is a non-magnetic toner.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.
[0019]
Example 1
FIG. 1 shows an overall schematic configuration of an electrophotographic copying machine which is an embodiment of an image forming apparatus according to the present invention. According to the present embodiment, an electrophotographic copying machine has an electrophotographic photosensitive member 1 as an image carrier, and the electrophotographic photosensitive member 1 has a photoconductive layer provided on a cylindrical conductive substrate. Is rotatably supported in the direction of the arrow. The photoreceptor 1 is uniformly charged to a predetermined potential level by a well-known scotron charger 2, and then receives a laser exposure 3 modulated according to an image signal to form an electrostatic latent image. Next, a predetermined bias is applied to the electrostatic latent image to a developing roller 41 as a developing carrier of a developing device 4 having a two-component developer having a non-magnetic toner and a magnetic carrier. The toner is adhered to form a toner image on the photoconductor. The toner image is transferred onto the transfer paper P conveyed along the conveyance path 10 using the transfer corona charger 8, and then sent to the fixing device 11. In the fixing device 11, the toner image on the transfer paper P is fixed on the transfer paper P and becomes a permanent image.
[0020]
After the transfer step, the photoconductor 1 is rotated as it is, the residual toner on the surface of the photoconductor 1 is removed by the cleaning device 9, and the next image formation is repeated again.
[0021]
In the electrophotographic copying machine shown in FIG. 1, a portion 27 surrounded by a broken line is an image reader, which reads a document and converts an image signal into an electric signal. The document 13 loaded on the platen glass 12 in the image reader unit 27 is scanned by the illumination lamp 14, guided to mirrors 15 a, 15 b, and 15 c reflected from the document 13, and guided by the imaging lens 15 d to the CCD 16 serving as a light receiving element. An image is formed thereon, and the image information is extracted as an electric signal.
[0022]
The electric signal is digitized by the A / D converter 20 and then sent to the signal processing unit 21 where it is converted into an image signal of 256 gradations proportional to the image density. The image signal is sent to the laser driver 25, and the light emission of the semiconductor laser 18 is modulated according to the image signal. The laser beam modulated according to the image signal writes a latent image on the photoconductor 1 via the polygon mirror 17 and the mirror 15e as image information.
[0023]
According to the present invention, a printing unit detecting unit 22 that detects a printing unit and a non-printing unit of an original image, and a developing unit as a developer carrier provided in the developing device 4 according to a signal from the printing unit detecting unit 22 A drive motor 23 for turning on and off the driving of a roller 41 and stirring screws 43 and 45 as developer stirring means is provided. The drive control method of the developing roller 41 and the stirring screws 43 and 45 will be described later.
[0024]
2 and 3 show a more detailed configuration of the developing device 4. FIG. 2 is a side view of the developing device 4, and FIG. 3 is a top view.
[0025]
As shown in FIG. 2, the developing device 4 is divided by a partition wall 46 into a toner storage section D that stores toner and a developer storage section C that stores a two-component developer containing a magnetic carrier. The toner in the toner storage section D and the developer in the developer storage section C are omitted for clarity.
[0026]
The developer accommodating section C is divided by a partition wall 44 into a developer stirring section C1 and a developer supply section C2 for supplying the developer to the developing roller 41. The developer stirring section C1 and the developer supply section C2 Screws 45 and 43 are provided, respectively. The toner in the toner storage section D is supplied into the developer storage section C from the toner supply port 49 by rotating the toner conveying members 47 and 48.
[0027]
As shown in FIG. 3, the screws 43 and 45 are disposed in parallel to the developing roller 41, and the screws 43 and 45 are driven to rotate so that the developer is conveyed in the directions F and G opposite to each other. Has become. Openings 44a and 44b are formed at both ends of the partition wall 44, and transfer of the developer from the screw 45 to the screw 43 and transfer of the developer from the screw 43 to the screw 45 are performed, respectively. The toner supplied from the plurality of toner supply ports 49 is conveyed in the directions of arrows F and G while being sufficiently agitated and mixed with the two-component developer in the developer accommodating section C by the rotational driving of the screws 43 and 45. It is supplied to the roller 41.
[0028]
The developing roller 41 includes a developing sleeve 41a made of a hollow metal cylinder and a magnet roll 41b fixed inside the developing sleeve 41a. The developer containing the magnetic carrier supplied to the developing roller 41 is held on the developing sleeve 41a, and is conveyed in the arrow direction as the developing sleeve 41a rotates in the arrow direction. After the layer thickness of the agent layer is regulated to a predetermined thickness, the layer is conveyed to a developing area facing the photoconductor 1 and adheres to an electrostatic latent image formed on the photoconductor 1 in advance to make the latent image visible. Image.
[0029]
As described above, in the developing device 4, the developer is agitated by the rotational driving of the screws 43 and 45, and as a result, the toner is charged. Also, when the layer thickness is regulated by the rotation of the developing sleeve 41a, a turbulent flow occurs in the transport of the developer, and the developer is stirred, and the toner is similarly charged. The screws 43 and 45 and the developing sleeve 41a are connected by a drive gear (not shown), and are simultaneously rotated by the drive motor 23 as shown in FIG.
[0030]
Although the configuration of the developing device 4 using the two-component developer has been described above, FIG. 4 shows the configuration of the developing device 4 ′ using the one-component developer. The contents of the present invention described later can be similarly applied to a developing device using this one-component developer.
[0031]
The developing device 4 ′ has a developing container 56 that stores the toner T, and has a configuration in which a developing roller 51 is provided at an opening facing the photoconductor 1. The toner T is supplied onto the developing roller 51 by a toner supply roller 53 which comes into contact with the developing roller 51 and rotates in the same direction as the developing roller 51, and has a predetermined toner layer formed by an elastic rubber blade 52 which comes into contact with the developing roller 51. The thickness is regulated and applied onto the developing roller.
[0032]
The toner is frictionally charged when rubbed on the developing roller 51 by the blade 52, and is held on the developing roller 51 by a mirror force, which is an electrostatic attraction acting between the developing roller 51 and the toner. The toner applied on the developing roller 51 is conveyed to the developing area facing the photoreceptor 1 with the rotation of the developing roller 51, and adheres to the electrostatic latent image formed on the photoreceptor 1 in advance to form the latent image. Make it a visible image. In the developing container 56, conveying members 54 and 55 for supplying the toner to the toner supply roller 53 are provided. The developing roller 51, the supply roller 53, and the transport members 54 and 55 are connected by a drive gear (not shown), and are simultaneously rotated by a drive motor (not shown).
[0033]
Next, before describing the present invention in detail, a conventional configuration will be described with reference to FIG. 18 for comparison.
[0034]
FIG. 18 shows an example of the drive timing of the developing roller 41 (linked with the screws 43 and 45) and each device related to the image formation arranged around the photosensitive member. The drive timing is based on the time (t0 in FIG. 18) at which the image area on the rotating photoconductor (copy 1 in FIG. 18) passes through the position of each device. The deviation of the driving time is omitted.
[0035]
The photoreceptor starts rotating at the same time as the copy start operation key is turned on, and before the tip of the copy 1 area on the photoreceptor passes, the charging output, the transfer output, the developing bias, and the exposure laser are sequentially turned on to start image formation. The developing roller is turned on by the developing roller drive motor prior to the passage of the leading edge of the copy 1, and is kept on until the copy 1 and the second continuous image area, copy 2, have passed, and the copy 2 area passes. And then turn it off. Although the copy section passing times of the copy 1 and the copy 2 are only I1 and I2, conventionally, the developing roller was continuously rotated during the passage of not only the I1 and I2 but also the non-print section. For this reason, excessive stirring or excessive triboelectric charging of the toner has occurred.
[0036]
FIG. 5 shows an example of the drive timing according to the present invention in comparison with the above-described conventional configuration. The drive timing of the components other than the developing roller 41 is the same as that of FIG. 18, but the drive timing of the developing roller 41 is different from that of the related art. The developing roller 41 is moved by a predetermined time Δt before the printing section passage time I1 of the copy 1 (see FIG.5The rotation is turned on at t1). Δt is a rotation rising time required for the rotation speed of the developing roller 41 to reach a predetermined speed required for performing development after the rotation of the developing roller 41 is turned ON.
[0037]
FIG. 6 is an enlarged view of an opposing portion between the photoconductor 1 and the developing roller 41. The inclined portion J is a region where the flying motion of the toner occurs in the process of visualizing the latent image, and J corresponds to the developing region. The developing roller 41 turns on before Δt when the leading end of the printing unit I1 reaches the upper end h1 of the developing area J. As a result, the image can be normally visualized from the leading end of the printing unit I1. On the other hand, at the same time when the printing5At t2), the rotation of the developing roller 41 is turned off. That is, in FIG. 6, the rotation of the developing roller 41 is turned off at the same time that the rear end of the printing unit I1 has passed the lower end h2 of the developing area J. Since there is no printing portion after passing the rear end, it can be turned off simultaneously after passing the rear end. Similarly, for copy 2, the rotation is turned ON before Δt before the printing section passing time I2, and the rotation of the developing roller 41 is turned off at the same time when the passing of the printing section is completed.
[0038]
A method of calculating the rotation ON and OFF times t1 and t2 of the developing roller 41 will be described below.
[0039]
FIG. 7 is a schematic diagram illustrating an image configuration of a document. The original is read by the image reader unit 27 (FIG. 1) as a set (m rows × n columns matrix) of pixels Q (image constituent units) shown in FIG. The pixels are sequentially read from the front end of the image along the arrow H direction (photoconductor rotation direction) and the arrow K direction (perpendicular to the photoconductor rotation direction), and are extracted as an image signal for each pixel by the signal processing unit 21. . The image signal has 256 levels of gradation in proportion to the image density. The minimum value is 0 level (white background) and the maximum value is 256 levels (solid image). I (x, y) represents an image signal value of a pixel at x row and y column.
[0040]
Subsequently, in the printing unit detection unit 22, a pixel set (Ia, Ib, Ic in FIG. 7) of the entire image in which the image signal value is not 0 level is detected as a printing unit, and the remaining area is detected as a non-printing unit. Is done.
[0041]
The memory 24 (FIG. 1) is a storage device for temporarily storing an image signal and a print portion area of the entire image. At the time of image formation, an image signal and a print portion signal are taken out from the memory 24 as appropriate to perform an image forming operation. .
[0042]
Since the pixel set of the printing unit exists in the rows i1 and i2 along the rotation direction of the photoconductor, only the time required to pass the partial image development area corresponding to the rows i1 and i2 in the latent image formed on the photoconductor is used. Then, the developing roller 41 is rotated. The time T1 at which the row i1 starts passing through the developing area and the time T2 at which the row i2 ends passing through the developing area are defined assuming that the length of one pixel side is d and the rotation speed of the photoconductor is v.
T1 = t0 + (i1-1) · d / v, T2 = t0 + i2 · d / v
It is. Here, t0 is a time from when the photosensitive member 1 starts rotating until the leading end of the latent image passes the upper end h1 of the developing area J (FIG. 6), and is set to a predetermined value in advance.
[0043]
Therefore, the rotation ON and OFF times t1 and t2 of the developing roller 41 are
t1 = T1−Δt = t0 + (i1-1) · d / v−Δt
t2 = T2 = t0 + i2 · d / v
It becomes.
[0044]
The developing roller drive motor 23 is driven based on the signal of the rotation ON and OFF times calculated in this way, and the rotation of the developing roller 41 is controlled.
[0045]
FIG. 8 shows a control flow of the drive control of the developing roller 41 described above. In the portion surrounded by the broken line, the topmost row i1 and the last row i2 of a plurality of printing portions distributed in the image are detected. In order to prevent the image noise included in the non-printing portion from being erroneously recognized as the printing portion, the determining portion (1) for determining the presence or absence of printing determines the image signal value I (x, y) as the noise level value e. Compared to This noise level value is appropriately set to an optimum value according to the noise level of the document to be used.
[0046]
The setting values of the used apparatus are as follows.
d: about 42 μm
v: 100 mm / sec
Δt: 80 msec
[0047]
In the above flow, the developing roller 41 was continuously rotated while the printing sections were passing through the developing area even when a plurality of printing sections existed discretely along the photoconductor traveling direction. When the area between printing sections between printing sections is large, control may be performed so that the developing roller 41 is once turned off in the inter-printing area and then turned on again when the next printing section passes. .
[0048]
Figure9As shown in (2), in a document in which the printing units Ia and Ib are separated by a distance f along the photoconductor traveling direction, if f> Δt (= sleeve rotation rising time), the printing unit Ia and Ib are temporarily turned OFF in the region f. If f <△ t, the motor is not turned off and is continuously rotated.
[0049]
As described above, the original image is read to detect the print portion, and based on the signal of the detected print portion, the time during which the print portion passes through the development area is calculated, and only during the same time is the developing roller 41 and the screw 43, By rotating the 45, the stirring and coating operations were kept to a minimum and the deterioration of the developer could be suppressed.
[0050]
Example 2
In the above embodiment, the case where the present invention is applied to a single-color image forming apparatus, that is, an apparatus having only one developing device, has been described. However, a multi-color image forming apparatus that obtains an image composed of a plurality of colors, that is, a developing device Can be applied to an apparatus having a plurality of. For example, manuscripts in which the main text is written in black letters, such as proofreading documents, and red vermilion are partially included, and manuscripts such as confidential documents, which are partially redfaced with handling precautions, are red, The color is calibrated in two colors of black, and the area occupied by the red printing portion is often small. Of these, the problem of the conventional toner deterioration due to the low toner consumption easily occurs in the red image portion.
[0051]
FIG. 10 shows the overall configuration of a two-color image forming apparatus applied to the present invention. Components having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and the description of the functions is partially omitted.
[0052]
The photoreceptor 1 is uniformly charged to a predetermined potential level by a scotron charger 2, and then receives a laser exposure 3 modulated according to a first image signal to form a first electrostatic latent image. . Next, the first electrostatic latent image is developed by a first developing device 4 having a developer composed of a non-magnetic toner of the first color (red) and a magnetic carrier, and the first color toner is formed on the photoconductor 1. An image is formed. Subsequently, the photosensitive member 1 carrying the first color toner image is recharged by using the scorotron charger 5 to equalize the potential of the photosensitive member 1 and simultaneously charge the photosensitive member 1 to a predetermined potential level. Receives the laser exposure 6 modulated according to the above, a second electrostatic latent image is formed. Next, the second electrostatic latent image is developed by the second developing device 7 holding the non-magnetic toner of the second color (black), and a superimposed image of the first and second color toner images is formed on the photoreceptor 1. It is formed. The second color development is performed by non-contact development in which the toner carried on the developing roller 71 of the developing device 7 does not contact the photoconductor 1, so that the second color development is performed without disturbing the first color toner image. The first developing roller 41 and the second developing roller 71 are driven to rotate by drive motors 23 and 29, respectively.
[0053]
A portion 27 surrounded by a broken line is an image reader portion which reads a two-color original consisting of red and black and converts image information into an electric signal. The document 13 loaded on the platen glass 12 in the image reader unit 27 is scanned by the illumination lamp 14, and the reflected light from the document 13 is guided to mirrors 15a, 15b, and 15c to be filtered by the lens 15d for red and cyan filters. An image is formed on the built-in CCD 16, and red and cyan components are extracted as electric signals.
[0054]
After being digitized by the electric signal A / D converter 20 and sent to the color discriminating section 28 to be discriminated into red and black components, the signal processing section 21 performs 256-level processing in proportion to the image densities of red and black. Is converted into a tone image signal. The red image signal is sent to the laser driver 25, and the laser beam whose emission of the semiconductor laser 18 is modulated in accordance with the red image signal (R) becomes the first image information via the polygon mirror 17 and the mirror 15e as the first image information. Then, the first latent image is written. Similarly, the black image signal is sent to the laser driver 26, and the emission of the semiconductor laser 19 is modulated according to the black image signal (B). The laser beam modulated according to the black image signal writes a second latent image as second image information via the polygon mirror 17 and mirrors 15f and 15g.
[0055]
According to the present invention, the printing unit detection unit 22 detects the red printing unit and the black printing unit based on the image signals of red and black, and based on the result, turns the developing rollers 41 and 71 on and off. The time is calculated, and the rotation driving of the developing roller 41 and the developing roller 71 is controlled based on the calculated signal. The developing roller 41 is turned ON only while the red printing portion in the latent image passes through the developing region of the first developing device 4, while the developing roller 71 is configured such that the black printing portion changes the developing region of the second developing device 7. It is controlled so as to rotate only during the passing time. The method of detecting the printing unit and the method of calculating the rotation ON and OFF times are performed in the same manner as in the first embodiment.
[0056]
FIG. 11 shows an example of the drive timing of the first developing roller 41 and the second developing roller 71 in the second embodiment. The drive timings other than those for the developing roller are the same as in the first embodiment (FIG. 2).
[0057]
Of the two continuous image areas, the first sheet (copy) has a mixture of a red print section and a black print section, and the second sheet (copy 2) has only a black print section. The first developing roller 41 turns ON at time Δt before the red printing section passing time I1 of copy 1, and turns OFF at the same time as the red printing section has passed. Since the red print portion does not exist in the copy 2, the rotation of the first developing roller 41 remains OFF. On the other hand, the second developing roller 71 is turned on before Δt before each of the black printing portion passing time J1 of the copy 1 and the black printing portion passing time J2 of the copy 2, and the passing of each black printing portion is completed. At the same time, the rotation is turned off.
[0058]
Conventionally, in this type of two-color image forming apparatus, both the first developing roller 41 and the second developing roller 71 are always continuous during the operation, regardless of whether a red printing portion or a black printing portion exists in the document. Was rotating. For this reason, there was a problem of toner deterioration, but by applying the present invention, the deterioration could be suppressed.
[0059]
Example 3
In the above embodiment, as can be seen from FIG. 11, the rotation of the developing roller is turned ON and OFF during one copy image formation. However, if the mechanical drive shock at the time of ON or OFF is large, the vibration generated at the time of driving propagates to the photosensitive drum cylinder, and the first development process and the second development process interfere with each other, causing a toner image disturbance at the time of a visible image. Thatis there. For example, if the second developing roller 71 is turned ON and OFF during the formation of the first toner image, the first toner image may be disturbed by a drive shock. FIG. 12 shows the arrangement of the first and second developing devices 4 and 7 around the photoconductor. If the distance X between the two developing devices 4 and 7 along the photoconductor surface is smaller than the image length Z (not shown), the first development and the second development are performed simultaneously on the same image, which may cause the above problem. is there.
[0060]
In order to solve this problem, the drive of the developing roller may be turned on and off while the non-image area corresponding to a portion between successive images on the photoconductor 1 passes through the developing area. FIGS. 13 and 14 show the drive timing of the developing roller in the third embodiment. FIG. 13 shows a case where the non-image width W is larger than the distance X, and FIG. 14 shows a case where the non-image width W0 is smaller than the distance X.
[0061]
FIG. 13A shows an example of the drive timing when forming three continuous images. Driving timings other than the developing roller are omitted. Symbols X, Z, and W in FIG. 13A represent the time required for the photoconductor to move these distances.
[0062]
The ON and OFF of the first and second developing rollers are all performed in the non-image area. When the second developing roller 71 is turned on after the leading end of the image area Z has passed through the first developing roller 41 as shown in FIG. 13B, the first toner image is disturbed for the above-described reason. X time when the leading end of the image area Z passes through the first developing roller 41PreviousTo ON. If the first developing roller 41 is turned off before the rear end of the image area Z passes through the second developing roller 71 as shown in FIG. 13C, the second toner image is disturbed. It is turned off X hours after the rear end of the image area Z has passed through the second developing roller 71.
[0063]
FIG. 14 shows an example of the drive timing when the non-image width W0 is smaller than X. This corresponds to a case where the non-image width for increasing the number of prints per unit time is reduced.
[0064]
In this case, since the non-image width W0 is small, the ON / OFF operation as shown in FIG. 13 cannot be performed. In FIG. 14, the third image is usually formed with a non-image width W0 after the second copy 2 and a copy 3 ′. However, since the non-image width W0 is smaller than X, the T0 ( If the second developing roller 71 is turned on before <X), the first toner image is disturbed. In order to solve this, the image formation of the copy 3 'is usually delayed, the non-image width is enlarged to W1, the image is formed by the copy 3, and the second developing roller is formed before T1 (> X) of the copy 3. Is turned on. Here, the image forming time for one sheet is skipped and a new non-image width W1 is generated.
[0065]
By the above method, mutual interference between the first and second developments was eliminated, and unnecessary rotation of the development roller was eliminated. In order to eliminate not only the interference between the first and second developing steps but also the interference between the developing step and the exposing step or between the developing step and the transferring step, the non-image width W1 is set to Y (from the exposure 3 to the transfer 8) shown in FIG. Distance) or more.
[0066]
Further, the vibration of the rotation ON and OFF of the developing roller may not be transmitted to the photosensitive drum cylinder. Conventionally, in order to maintain the gap between the developing roller and the photosensitive member at a predetermined value, holding members are provided at both ends of the developing roller shaft, and the holding members are brought into contact with the photosensitive member. Vibrations at the time of rotation ON and OFF of the roller propagated to the photosensitive drum via the holding member. In order to avoid this, as shown in FIG. 15, the holding members 72a, 72b of the axis of the developing roller 71 are abutted against cylindrical members 73a, 73b which are coaxial with the photoconductor 1 and have the same outer diameter and do not contact the photoconductor 1. Accordingly, vibration propagation to the photoconductor 1 can be cut off.
[0067]
Example 4
The present invention is applicable not only to a two-color image forming apparatus but also to a full-color image forming apparatus. FIG. 16 shows a schematic configuration of such a full-color image forming apparatus.
[0068]
In this embodiment, the full-color image forming apparatus includes four image forming stations a, b, c, and d corresponding to respective colors of yellow, magenta, cyan, and black, and each station includes photoconductors 61a to 61d. At the center, latent image forming devices 62a to 62d, developing rollers 63a to 63d, and transfer devices 64a to 64d are provided around the center.
[0069]
The transfer belt 60 that sucks and conveys the transfer paper P sequentially superimposes the toner images of each color formed on each photoconductor on the transfer paper at each transfer device portion, and then transfers the toner images to the fixing device 11. The paper is transported and fixed. Note that components having the same functions as those of the image forming apparatus of the above-described embodiment are denoted by the same reference numerals, and descriptions of the functions are partially omitted.
[0070]
According to the present invention, a full-color original is read by a CCD (not shown) having red, green, and blue color separation filters in an image reader unit 27, and is read by a color discrimination unit 28 and a signal processing unit 21. , Cyan, and black color components. The image signal of each color is sent to the printing unit detector 22, and the printing unit and the non-printing unit of each color are detected, and the rotation ON and OFF times of the developing rollers 63a to 63d are calculated as in the second embodiment. You. The rotation drive of each developing roller is controlled based on this calculation signal.
[0071]
Conventionally, in the full-color image forming mode, the developing roller of the developing device holding the toner that is not necessary for reproducing the original color is also always the same as the developing roller of the developing device holding the toner necessary for the color reproduction. It was spinning continuously. However, in the present invention, by the above-described method, the developing device in which the printing portion of the retained toner does not exist is controlled so that the developing roller does not rotate, so that unnecessary toner agitation and coating are not performed, and the progress of toner deterioration is prevented. I was able to suppress it.
[0072]
【The invention's effect】
As explained above,The present invention relates to an image forming apparatus in which the rotation time of a developer carrier is controlled, a minimum necessary developing operation is performed, unnecessary stirring and coating operations are eliminated, and deterioration of the developer is prevented. By preventing the shock at the start and stop of rotation of the developing device from adversely affecting the developing operation of other developing means, it is possible to prevent toner image disturbance and obtain a stable image for a long period of time.
[Brief description of the drawings]
FIG. 1 is an overall view of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a sectional view of a developing device using a two-component developer.
FIG. 3 is a top view of a developing device using the two-component developer of FIG. 2;
FIG. 4 is a sectional view of a developing device using a one-component developer.
FIG. 5 is a diagram showing one embodiment of a developing roller drive timing according to the present invention.
FIG. 6 is an explanatory diagram of a development area.
FIG. 7 is an explanatory diagram of a pixel configuration of a document.
FIG. 8 is a control flowchart of developing roller driving.
FIG. 9 is a diagram showing a print portion distribution.
FIG. 10 is an overall view of a two-color image forming apparatus according to another embodiment of the present invention.
FIG. 11 is a diagram showing another embodiment of the developing roller drive timing according to the present invention.
FIG. 12 is a diagram showing an arrangement relationship of an exposure, development, and transfer device.
FIG. 13 is a diagram of another embodiment of the developing roller drive timing according to the present invention.
FIG. 14 is a diagram of another embodiment of the developing roller drive timing according to the present invention.
FIG. 15 is a perspective view showing support means for a developing roller.
FIG. 16 shows the present invention.ofFIG. 11 is an overall view of a full-color image forming apparatus according to another embodiment.
FIG. 17 is a diagram illustrating a relationship between a document and a printing unit.
FIG. 18 is a diagram illustrating a conventional drive timing of a developing roller.
[Explanation of symbols]
1 Image carrier (photoreceptor drum)
4, 4 ', 7 Developing means (developing device)
21 Color discriminator
22 Printing section detection section
23 Developing roller drive motor
24 memory
27 Image reader section (document reading section)
41, 51, 71 Developer Carrier (Developing Roller)
43, 45, 54, 55 Stirring means (stirring screw)

Claims (4)

An image carrier on which an electrostatic latent image is formed;
First developing means for carrying a developer of a predetermined color on a first developer carrier and developing a latent image on the image carrier in a first development area;
The second developer carrying member is arranged on the downstream side of the first developing unit with respect to the image carrier moving direction, and carries a developer of a color different from the predetermined color on the second developer carrying member. Second developing means for developing a latent image on the image carrier;
Color determination means for determining a color included in an image to be formed;
A print portion detecting means for detecting a print portion and a non-print portion for each color,
A drive control unit that controls a rotation operation of the first developer carrier and the second developer carrier based on a signal from the printing unit detection unit;
In the image forming apparatus having
The drive control means includes:
In a case where the printing section of the predetermined color and the printing section of the different color coexist in one image area, the developing areas of the first developer carrier and the second developer carrier are provided. While the image area is passing, the first developer carrier and the second developer carrier are rotated,
In the case where only the printing portion of the predetermined color exists in one image area, the first developer carrier is rotated while the image area passes through the first development area, And not rotating the second developer carrier while the image area is passing through the second development area,
In the case where only one printing portion of the different color exists in one image region, the rotation operation of the first developer carrier is not performed while the image region passes through the first development region, And, while the image area is passing through the second development area, so as to perform the rotation operation of the second developer carrier,
The timing of stopping the rotation of the first developer carrier is when a non-image area on the image carrier is passing through the first development area, and the second developing means When the development operation by is not performed,
The start timing of the rotation operation of the second developer carrier is when the non-image area on the image carrier is passing through the second development area and the first developer means When the developing operation is not performed,
An image forming apparatus characterized in that the image forming apparatus performs control so that In a case where a plurality of image formations are continuously performed while leaving a predetermined width of the image interval, the predetermined width of the image is formed between the first development area and the second development area on the image carrier. When the distance is shorter than the distance between the development areas,
When starting the rotation operation of the second developer carrier at an image interval,
2. The image forming apparatus according to claim 1, wherein the image interval is longer than the distance between the development areas by adding a non-image area width equal to or more than one image width to the predetermined width. 3. . A member for holding the first developer carrier and the second developer carrier and the image carrier at a predetermined interval, wherein the member does not contact the image carrier. The image forming apparatus according to claim 1 . The image forming apparatus according to claim 1, wherein the developer is a non-magnetic toner .

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