JP3948438B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that prevents abnormal image defects that are likely to occur over time when developing by contact charging or contact development using toner containing an external additive.
[0002]
[Prior art]
Conventionally, there is an electrophotographic image forming apparatus. In this image forming apparatus, the image carrier is uniformly charged and initialized, an electrostatic latent image is formed on the image carrier by optical writing, the electrostatic latent image is converted into a toner image, and the toner image is converted into a toner image. It is transferred to a transfer material such as paper and fixed by a fixing device.
[0003]
In the past, corona discharge-type chargers and transfer devices were used for the above charging and transfer, but in recent years, contact-type chargers and transfer devices have increased due to the problem of deterioration of the usage environment due to ozone generation. .
For example, a contact-type charger is known in which a conductive foam is formed on a metal core, and a polyurethane skin layer is formed on the surface of the conductive foam. (For example, refer to Patent Document 1.)
Similarly, as a contact-type charger, a small-size and long-life charger in which a conductive foam having a cored bar is covered with a conductive resin tube has been proposed. (For example, see Patent Document 2.)
As a developing device, there is known a non-magnetic one-component developing device in which a non-magnetic one-component toner is used as a toner to be used and the inside of the toner hopper is partitioned in a double manner so that the size can be increased. (For example, refer to Patent Document 3.)
[0004]
[Patent Document 1]
JP 07-092774 ([0019], FIG. 1)
[Patent Document 2]
Japanese Patent Laid-Open No. 11-129556 ([Summary], FIG. 1)
[Patent Document 3]
JP 2001-194 483 A ([Summary], FIG. 2)
[0005]
[Problems to be solved by the invention]
Incidentally, a conventional electrophotographic image forming apparatus is equipped with a cleaning device for cleaning untransferred toner remaining on the image carrier. In addition, in order to improve toner fluidity and to prevent toner aggregation, an external additive made of fine particles of alumina, for example, is added to the non-magnetic one-component toner. Normally, the external additive adheres firmly to the toner, but the external additive added for the purpose of preventing aggregation is relatively large in particle size and often has a weak charging polarity, so it is easily detached from the toner. Tend.
[0006]
Therefore, particularly when an image having a pattern with a high printing rate is continuously printed, a large amount of toner is developed on the image carrier, and thus remains on the image carrier without being transferred to the transfer material. The amount of untransferred toner increases, and the external additive detached from the toner increases in the cleaning device. Although the cleaning device can clean the toner, the external additive cannot be cleaned by the cleaning device because the particles are too fine to slip through the cleaning blade.
[0007]
For this reason, the external additive remains attached to the image carrier, and the external additive attached to the image carrier now adheres to the contact charger. When the external additive adheres to the contact charger as described above, there is no problem in the charging ability as long as the external additive is small.
[0008]
The image forming unit of the image forming apparatus includes a drum unit and a developing unit. However, if the life of the drum unit and the developing unit is the same, the above-described problems may occur even if printing with a high printing rate is performed continuously. At the time of occurrence, there is no problem because the toner on the developing unit side is exhausted. However, if the drum unit and the development unit are separated, and the development unit that has run out of toner is replaced with a new development unit and printing with a high printing rate is performed many times, the contact charger is installed on the drum unit side. Therefore, the amount of the external additive attached to the contact charger continues to increase, and the above problem occurs.
[0009]
Further, in many cases, the external additive that has passed through the cleaning blade adheres in the form of streaks in the rotation direction of the image carrier. In such a case, the external additive adhering to the streaks previously obstructs optical writing, forming a non-development part, and white lines on the transfer material, as well as adversely accumulating on the contact charger. It becomes a factor causing image defects.
[0010]
Contrary to the above, in the case where printing with a very low printing rate is repeated, such as white printing, for example, the cleaning device has little or no toner. The additive is insufficient, the friction between the image carrier and the cleaning blade increases, the edge of the cleaning blade is damaged, and unevenness occurs at the edge. The untransferred toner and the external additive on the image carrier pass through the unevenness of the edge without being cleaned, and in this case, the toner adheres to the contact charger and causes a development failure, which causes a defective image.
[0011]
However, in Patent Documents 1 to 3 described above, appropriate consideration is not given to the development failure caused by the toner external additive as described above.
An object of the present invention is to provide an image forming apparatus that appropriately prevents a development failure caused by an external additive of toner in view of the above-described conventional situation.
[0012]
[Means for Solving the Problems]
The image forming apparatus of the present invention includes an image carrier, a charging unit that charges the image carrier to a predetermined potential, and the image carrier charged by the charging unit according to an image signal. Light irradiation An electrostatic latent image forming means for forming an electrostatic latent image; a developing means for applying a developer to the electrostatic latent image formed on the image carrier to form a toner image corresponding to the image signal; Transfer means for executing printing on the transfer material by transferring the toner image formed by the means to the transfer material, and the developing means is provided to contact the image carrier. Negatively charged non-magnetic one-component toner and positively charged polarity relative to the non-magnetic one-component toner A developing roller carrying and rotating the developer having externally added fine particles; a developer supply roller that presses the developing roller and supplies the developer to the developing roller upstream of the developing roller in the rotational conveying direction; The developing roller and the developer supply roller Between In A potential difference is generated in the direction in which the toner is attracted to the developing roller side. Bias voltage The An image forming apparatus comprising at least a bias voltage applying means for applying, a print dot number storage means for storing the number of print dots per page on the transfer material based on the image signal, and the transfer by the transfer means Printed page number storage means for counting and storing the number of printed pages on the material, and the print dot number storage means and the information stored in the printed page number storage means for preventing an abnormal image failure And controlling the light irradiation by the electrostatic latent image forming means to be inoperative so as not to form the electrostatic latent image on the image carrier while operating at least the image carrier and the charging means, and the developing roller And externally added particulate collection control means for controlling the bias voltage applying means so as to increase the potential difference between the developer supplying roller and the developer supplying roller to recover the externally added fine particles from the developing roller to the developer supplying roller. It is configured with.
[0013]
For example, the charging unit includes a contact-type charging unit that contacts the image carrier and charges the image carrier to the predetermined potential.
Further, the developing means is constituted by a contact-type developing means for forming the toner image by contacting the image carrier and applying the developer to the electrostatic latent image. Is done.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view illustrating an internal configuration of an image forming apparatus (hereinafter referred to as a printer) 1 according to an embodiment of the present invention. As shown in FIG. 1, the printer 1 includes an image forming unit 2, a duplex printing transport unit 3, and a paper feeding unit 4. The image forming unit 2 has a configuration in which four image forming units 5 (5-1, 5-2, 5-3, 5-4) are arranged in a multistage manner.
[0016]
Of the four image forming units 5, the three image forming units 5-1, 5-2, and 5-3 on the upstream side in the sheet conveying direction are magenta (M) and cyan (C ), A monochrome image is formed with yellow (Y) color toner, and the image forming unit 5-4 forms a monochrome image mainly with black (K) toner such as characters.
[0017]
Each of the image forming units 5 includes a drum set C1 and a toner set C2, and has the same configuration except for the developer (color) stored in the developing container. Therefore, the configuration of the yellow (Y) image forming unit 5-3 will be described below as an example.
[0018]
The drum set C1 is provided with a photosensitive drum 6, and a cleaner 7 and a charging roller 8 that surround the vicinity of the peripheral surface of the photosensitive drum 6 and constitute the drum set C1 together with the photosensitive drum 6 are provided. ing. Further, a print head 9 supported by a frame of the main body device is disposed in the vicinity of the upper peripheral surface of the photosensitive drum 6, and is in contact with the lower peripheral surface of the photosensitive drum 6 so as to sandwich the transport belt 10. The transfer device 11 is arranged.
[0019]
A developing container 12 and a developing roller 13 are disposed in the toner set C2. The developing container 12 contains toner therein and supports the developing roller 13 in the opening on the lower side surface. In order to prevent toner aggregation, aluminum oxide fine particles are added to the toner as an external additive. Aluminum oxide has a weaker negative potential than the weak negative potential of the toner, and is relatively positive with respect to the toner and adheres to the toner.
[0020]
The photosensitive drum 6 rotates in the clockwise direction in the figure, the peripheral surface is cleaned by the cleaner 7, and the peripheral surface of the photosensitive drum 6 is uniformly charged by the charge application from the charging roller 8. Next, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 6 by optical writing based on the print information from the print head 9. The electrostatic latent image is converted into a toner image by yellow (Y) toner stored in the developing container 12 by the developing process by the developing roller 13.
[0021]
The toner image formed on the peripheral surface of the photosensitive drum 6 in this way reaches the transfer portion where the photosensitive drum 6 and the transfer device 11 face each other as the photosensitive drum 6 rotates. The toner image that has reached the transfer portion is transferred onto a sheet that moves from the upstream side to the downstream side in the sheet conveyance direction immediately below the photosensitive drum 6.
[0022]
The sheet is carried out of the sheet feeding cassette 15 by one rotation of the sheet feeding roller 14, and is fed to the standby roller pair 19 through the guide roller pair 16, the guide path 17, and the feeding roller pair 18. Alternatively, the paper is fed by the paper feed roller 22 from the MPF tray 21 mounted on the opened mounting portion cover 20.
[0023]
The standby roller pair 19 feeds the sheet onto the conveying belt 10 at a timing when the sheet printing start position coincides with the leading edge of the toner image on the photosensitive drum 6 of the image forming unit 5-1 at the most upstream in the sheet conveying direction.
The conveyor belt 10 is stretched between a driving roller 23 and a driven roller 24, driven by the driving roller 23, and circulated in the counterclockwise direction in the figure. The sheet is electrostatically adsorbed and conveyed on the upper surface of the circulating and conveying belt 10, and a magenta (M) toner image is transferred by the transfer unit of the image forming unit 5-1, and the image forming unit 5-2. The cyan (C) toner image is transferred at the transfer portion, the yellow (Y) toner image is transferred at the transfer portion of the image forming unit 5-3, and the black ( The toner image of K) is transferred.
[0024]
The paper onto which the four color toner images are transferred in this manner is carried into a fixing unit 25 which is a fixing device. The fixing unit 25 is composed of a heat roller 26, a pressure roller 27, an oil application roller 28, and the like. While the paper is nipped and conveyed between the heat roller 26 and the pressure roller 27, the toner image is melted and pressed onto the paper surface. And fix. The oil application roller 28 has a function of applying toner releasing oil to the peripheral surface of the heat roller 26 and removing toner remaining on the heat roller 26.
[0025]
As described above, the sheet on which the toner image is fixed by the fixing unit 25 forms an image from the side discharge port 32 by the carry-out roller pair 31 when the switching plate 29 is rotated upward as shown by the solid line in the figure. When the switching plate 29 is rotated downward as indicated by the broken line in the figure, it is guided upward by the conveying roller pair 33 and the sheet discharge roller 34 moves the image forming surface. The paper is discharged downward to the paper discharge unit 35.
[0026]
The double-sided printing transport unit 3 is configured to be detachable from the apparatus main body, and is a unit that is mounted when performing double-sided printing by the printer 1 of this example, and a plurality of transport rollers 36a to 36e are disposed therein. Has been.
In the case of duplex printing, the paper is once sent upward by the switching plate 29. For example, when the trailing edge of the paper reaches the conveyance roller pair 33, the conveyance of the paper is stopped and the paper is further conveyed in the reverse direction. . By this control, the sheet is conveyed downward on the left side of the switching plate 29 set at the position indicated by the dotted line, is carried into the sheet conveyance path of the duplex printing conveyance unit 3, and is conveyed by the conveyance rollers 36a to 36e. It reaches the standby roller pair 19 via the guide path 17 and the feed roller pair 18 and is sent to the transfer unit at the same timing as the toner image as described above, and the toner image is transferred to the back surface of the paper.
[0027]
The density sensor 37 provided in the vicinity of the drive roller 23 is composed of, for example, a near-infrared regular reflection type sensor, and is composed of a light-emitting unit formed by LEDs and a light-receiving unit including a light-receiving element that detects the amount of LED light. ing.
The density sensor 37 is directly formed on the end of the peripheral surface of the conveyor belt 10 for measuring the toner density and the print position of a toner image directly formed on the central portion of the peripheral surface of the conveyor belt 10 as a resist patch. It is arranged for measuring a white band check patch of a toner image.
[0028]
FIG. 2 is a side cross-sectional view showing the internal configuration of the image forming unit only taken out. In the figure, the same components as those shown in FIG. 1 are denoted by the same reference numerals as those in FIG.
As shown in the figure, the image forming unit 5 is configured by integrally assembling a drum set C1 and a toner set C2. One drum set C1 includes the photosensitive drum 6, the cleaner 7, and the charging roller 8 shown in FIG. 1, and further includes a drum cover 38 that can be moved back and forth (left and right in FIG. 2). The cleaner 7 includes a cleaning blade 7 a, and the edge of the lower end portion of the cleaning blade 7 a is in pressure contact with the peripheral surface of the photosensitive drum 6.
[0029]
The other toner set C2 has a support portion (not shown) that supports the drum set C1, a toner hopper 41 that contains toner 39 as a developer, and a part of the peripheral surface exposed from the opening of the toner hopper 41. The toner hopper 41 is further provided with a toner stirring member 42, a toner supply roller 43, a doctor blade 44, a scooping sheet 45, and the like so as to be buried in the toner 39.
[0030]
FIG. 3 is a diagram showing a bias voltage system of each part of the image forming unit 5 in the printer 1 having the above configuration. For the sake of brevity, only one image forming unit 5 is shown in the figure, and the same components as those shown in FIGS. 1 and 2 are assigned the same numbers as those in FIGS. It shows.
[0031]
The photosensitive drum 6 is usually formed by uniformly depositing an organic photoconductor on the surface of a conductive metal roller, and the metal roller portion is grounded. The charging roller 8 has a white printing state charging potential (an initialization potential applied uniformly, a method of applying with a positive polarity and a method of applying with a negative polarity by a high voltage power source 46. In this example, a negative high voltage is applied. ) Is applied to the photosensitive drum 6.
[0032]
By this application, the photosensitive layer on the peripheral surface of the photosensitive drum 6 is uniformly charged to a minus high potential of, for example, “−650 V (volt)”. The print head 9 includes a laser light source or an LED light source, and selectively exposes the peripheral surface of the photosensitive drum 6 charged to a minus high potential according to image information. By this exposure, a negative low potential portion whose potential is attenuated to about “−70 V” is formed on the surface of the photosensitive drum 6, and the low potential portion of “−70 V” and the high potential of “−650 V” charged in advance. An electrostatic latent image is formed by the portion.
[0033]
The toner set C <b> 2 contains non-magnetic one-component toner 39 inside the toner hopper 41, and the developing roller 13 is applied with a developing bias of “−350 V” from the high voltage power supply 47. The toner supply roller 43 is applied with a supply bias of, for example, “−600 V” from another high voltage power supply 48. The doctor blade 44 is further supplied with a supply bias of, for example, “−400 V” from another high-voltage power supply 49.
[0034]
On the other hand, the toner 39 adheres to the surface of the developing roller 13 due to the potential difference from the toner supply roller 43, and then is regulated to a constant layer pressure by the doctor blade 44, and is negatively applied from the high voltage power supply 48 through the doctor blade 44. It is charged to a weak negative potential by the high voltage potential and adheres to the surface of the developing roller 13 with a certain thickness.
[0035]
The toner 39 is conveyed to a portion facing the photosensitive drum 6 while the developing roller 13 rotates. At the facing portion between the developing roller 13 and the photosensitive drum 6, a potential difference of “−280 V” is formed between the low potential portion of the “−70 V” electrostatic latent image and the developing roller 13. That is, the low potential portion of the electrostatic latent image forms a positive polarity potential relative to the developing roller 13. Due to the electric field due to this potential difference, the nonmagnetic toner 39 charged to the negative polarity is transferred to the positive potential electrostatic latent image low potential portion of the photosensitive drum 6 to form a toner image. This toner image is conveyed to the facing portion between the photosensitive drum 6 and the transfer sheet 11 by the rotation of the photosensitive drum 6.
[0036]
The transfer sheet 11 is formed of a conductive sheet and is connected to a positive high voltage power source 50. The transfer sheet 11 is opposed to and pressed against the photosensitive drum 6 to form a transfer portion. The transfer sheet 11 applies a transfer bias with a positive potential to the paper P conveyed to the transfer unit by the conveyance belt 10 via the conveyance belt 10. The negative toner image on the photosensitive drum 6 is transferred to the paper P that has become a positive potential by the application of this voltage.
[0037]
The toner image transferred to the paper P is fixed on the paper surface by the fixing unit 25 shown in FIG. On the other hand, a small amount of toner 39 that has not been transferred remains on the photosensitive drum 6. The remaining toner 39 is removed by the cleaner 7. FIG. 4 is a diagram illustrating an internal circuit configuration in the printer 1 having the above-described configuration. In the figure, the circuit configuration includes an interface (I / F) 51, a printer controller unit 52, an EEPROM 53, a ROM 54, an operation panel 55, and a head controller unit 56.
[0038]
The printer controller 52 is connected to a temperature / humidity sensor 57 disposed at an appropriate position inside the main body apparatus 1 and the density sensor 37 shown in FIG. 1, and although not shown in FIG. A paper counter 58 disposed on the path 17 is connected, and further, a high voltage unit 59 including the high voltage power sources 46 to 50 shown in FIG. 3 is connected. Further, the four print heads 9 shown in FIG. 1 are connected to the other head controller unit 56.
[0039]
An interface (I / F) 51 inputs print data sent from a host device (not shown), outputs image data in the print data to the head controller unit 56, and sends commands in the print data to the printer controller unit. To 52.
The EEPROM 53 stores supply biases for mode 1 and mode 2, which will be described later, the limit printing rate, the limit number of sheets, adjustment values for position and density correction, and the ROM 54 stores a printing program and a control program.
[0040]
Although not particularly shown, the head controller unit 56 includes a frame memory composed of four areas corresponding to yellow (Y), magenta (M), cyan (C), and black (K). The head controller unit 56 creates bitmap data of yellow (Y), magenta (M), cyan (C), and black (K) based on the image data input from the interface (I / F) 51.
[0041]
The yellow (Y) bitmap data is stored in the yellow (Y) storage area of the frame memory, and the magenta (M) bitmap data is stored in the magenta (M) storage area of the frame memory. The bitmap data C) is stored in the cyan (C) storage area of the frame memory, and the black (K) bitmap data is stored in the black (K) storage area of the frame memory.
[0042]
The printer controller unit 52 is a central control unit including a CPU that performs print control and system control of the printer 1 of the present example. Although not particularly illustrated, a time counter, a numeric counter, a register, and the like are built in and stored in the ROM 54. Each part is controlled according to the program. The printer controller 52 receives an operation signal from a key operation unit (not shown) provided on the operation panel 55, and also outputs a display signal to a display unit (not shown).
[0043]
The printer controller 52 sends a print command to the head for each of yellow (Y), magenta (M), cyan (C), and black (K) based on a command supplied from the interface (I / F) 51. Output to the controller unit 56.
Based on the print command, the head controller unit 56 supplies yellow (Y) print data to the print head 9 of the image forming unit 5-3 and supplies magenta (M) print data to the image forming unit 5-1. , The cyan (C) print data is supplied to the print head 9 of the image forming unit 5-2, and the black (K) print data is supplied to the print head 9 of the image forming unit 5-3. To do. Then, the above-described printing of each color is performed by the drum set C1 and the toner set C2.
[0044]
The head controller unit 56 supplies the print data to each print head 9 and notifies the printer controller unit 52 of the actual number of print dots.
FIG. 5 is a diagram showing a data configuration of a combination of the mode 1 and mode 2 bias voltages stored in the EEPROM 53. As shown in the figure, the standard value is -350v for the developing bias, -600v for the supply bias, and -400v for the doctor bias as described in FIG.
[0045]
Then, when the control process is in mode 1 to be described later, as shown in FIG. 5, only the supply bias is set to change to -700v. In mode 2, only the supply bias is further changed to -800v.
<First Embodiment>
FIG. 6 is a flowchart for explaining mode 1 processing during printing processing executed as described above while the head controller unit 56 is controlled by the printer controller unit 52.
[0046]
In addition, when the printing rate of a solid image is assumed to be 100%, it is standard that the printing rate is 5% in normal character printing. However, in this example, the image printing is taken into consideration. The standard printing rate is set to 15%.
The printing rate during the printing process is determined based on the actual number of print dots notified from the head controller unit 56 and the number of sheets (number of pages) used for printing input from the sheet counter 58. Calculated by the unit 52.
[0047]
The printer controller unit 52 uses a built-in numerical counter as an overprint rate counter.
In FIG. 6, when the printing process is started (S1), the printer controller 52 monitors the printing rate (S2).
[0048]
In this process, the printer controller 52 is notified from the head controller 56 while driving the print head 9 via the head controller 56 by a print signal (image signal) in order to calculate the printing rate in a later process. Count the number of printed dots.
[0049]
Then, it is determined whether or not printing for one page has been completed (S3). If the printing has not been completed (N in S3), the monitoring of the printing rate (counting the number of printing dots) is continued, and the printing is completed. If so (S3 is Y), then the overprint rate is calculated (S4).
In this process, first, the printing rate of the page that has just been printed is calculated from the total number of printing dots counted in process S2. Then, “15%” set as the standard print rate in this example is subtracted from the calculated print rate. Thus, how much the standard printing rate is exceeded is calculated as a printing rate excess value per page with a plus or minus sign.
[0050]
Subsequently, the calculated print rate excess value per page is added to the overprint rate counter (S5).
As a result, the print rate excess value per page during the printing process is accumulated as the total print rate every time one page is printed.
[0051]
Next, it is determined whether or not the accumulated overprint rate is “5000%” or more (S6).
In this process, when the overprint rate accumulated as described above is “5000%”, the image defect due to the external additive remaining attached to the surfaces of the photosensitive drum 6, the charging roller 8, and the developing roller 13. It has been empirically found that is likely to occur. Therefore, the “overprint rate of 5000%” is a timing for removing the residual external additive from the photosensitive drum 6, the charging roller 8, and the developing roller 13 to restore the whole to an appropriate state.
[0052]
If the overprint rate is not “5000%” or more in the determination of the process S6, it is not the timing to restore the whole to an appropriate state, so the process returns to the process S2 and the processes S2 to S6 are repeated.
If the overprinting rate becomes “5000%” or more in the determination in step S6 (Y in S6), first, a time counter is set (S7).
[0053]
In this process, in this example, “2 minutes” (120 seconds) is set in the time counter.
Subsequently, the supply bias value is set (S8).
In this processing, mode 1 combination data is selected from the bias voltage combination data shown in FIG. 5 stored in the EEPROM 53, the high voltage unit 59 is controlled, and “−700 v” is set as the supply bias value. A high voltage power supply 48 applies to the toner supply roller 43.
[0054]
In this state, idling is performed (S9).
In this process, actual printing is not performed. That is, exposure by the print head 9 is not performed, the sheet P is not transported, and the whole is simply driven by applying an applied bias.
[0055]
Then, the time counter refers to determine whether or not the set time has become 0 (S10). If the time counter has not become 0 (N in S10), the process returns to step S9 to continue idling. Thereby, idling continues for 2 minutes.
As described above, the aluminum oxide added to the toner 93 as an external additive has a weak positive potential. As a result, during idling for 2 minutes in mode 1 as described above, a difference in potential between the developing roller 13 and the toner supply roller 43 is formed in the direction from the developing roller 13 toward the toner supply roller 43 due to a stronger potential difference than usual. The external additive released from the toner 39 on the developing roller 13 is collected by the toner supply roller 43 by the electric field.
[0056]
Further, the free external additive adhering to the photosensitive drum 6 is also collected by the developing roller 13 and further collected from the developing roller 13 to the toner supply roller 43. Further, the free external additive adhering to the charging roller 8 also moves onto the photosensitive drum 6 which has been recovered by removing the free external additive as described above, and further passes through the developing roller 13 from the photosensitive drum 6. Then, the toner is collected by the toner supply roller 43.
[0057]
The free external additive collected on the toner supply roller 43 is stirred together with the toner 39 in the toner hopper 41 by the toner stirring member 42 and adheres to the toner particles, thereby releasing the release and returning to a normal state. .
As described above, according to this example, the overprinting rate is always monitored, and the developing environment of the image forming unit is restored to an appropriate state by changing the bias applied to the toner supply roller at an appropriate timing and rotating the entire unit idly. Therefore, it is possible to provide a highly reliable image forming apparatus capable of always obtaining a good image.
[0058]
If it is determined in step S10 that the time counter is 0 (Y in S10), the process ends. That is, the above restoration process is performed for 2 minutes and is completed.
Although not particularly described in the above process, the restoration process for removing the free external additive may be applied to a monochrome printing apparatus or a tandem type color printing apparatus. In the case of a tandem type color printing apparatus, when the overprinting rate reaches a specified limit value for each color, the whole may enter the blank printing mode (idle rotation).
[0059]
In this case, if the overprinting rate counters for other colors are reset, it is possible to avoid unnecessary frequent idling.
FIG. 7 is a flowchart for explaining processing in mode 1 and mode 2 during printing processing executed while the head controller unit 56 is controlled by the printer controller unit 52.
[0060]
In FIG. 7, the processes S101 to S105 are the same as the processes S1 to S5 described above. In FIG. 7, following the process S105, the paper counter is referred to, and it is determined whether or not the count value of the paper counter is 1000 or more (S106). As a result, it is determined whether the number of printed sheets has reached 1000 or more.
[0061]
If the number of printed sheets is still less than 1000 (N in S106), the processes S102 to S106 are repeated.
On the other hand, if the number of printed sheets is 1000 or more (S106 is Y), it is then determined whether or not the overprint rate counter n (%) is “5000 ≦ n <15000” (S107).
[0062]
If “n <5000”, the process returns to step S101 to repeat steps S101 to S107.
Thus, in this example, first, it is determined whether or not the number of printed sheets has exceeded 1000, and the overprint rate is monitored every 1000 sheets.
[0063]
If it is determined in step S107 that “5000 ≦ n <15000”, steps S108 to S111 are executed. The processes S108 to S111 are the same as the processes S7 to S10 shown in FIG.
On the other hand, if “15000 ≦ n” is determined in the processing S107, the processing of processing S112 to S115 is executed. In the processing in steps S112 to S115, the supply bias value set for the toner supply roller 43 in step S113 is the same as the processing in steps S108 to S111, except that “−800v” in mode 2 shown in FIG. It is.
[0064]
In this way, the development environment restoration start timing is divided into two stages, and two types of special supply bias to be applied to the toner supply roller 43 are prepared. Since the start timing of restoration to an appropriate state is performed with priority given to the number of printed sheets, the idling operation is not entered before the fixed number of sheets is reached, and therefore an operation giving priority to the printing work is possible. In this way, the processing procedure of this example may be configured.
<Second Embodiment>
By the way, as described above, for example, when printing with a very low printing rate such as white printing is repeated, the edge of the cleaning blade is damaged, and this causes development failure. In this example, the development environment is restored to an appropriate state by removing the cause of the development failure due to the repetition of such a low printing rate.
[0065]
FIG. 8 is a flowchart for explaining processing for removing the cause of development failure due to repetition of a low printing rate during printing processing executed while the head controller unit 56 is controlled by the printer controller unit 52.
First, in FIG. 8, the processes of steps S201 to S204 are the same as the processes of steps 101 to S104 (or steps S1 to S4) described above.
[0066]
Subsequent to the above-described processing S204, it is determined whether or not the overprint rate n of one page is “n ≦ −14” (S205).
In this process, it has been empirically found that if the overprint rate n continues to be “n ≦ −14”, the above-described development failure due to the low print rate occurs. Therefore, the development environment restoration start timing in the case of a low printing rate is set to “n ≦ −14”.
[0067]
If it is not “n ≦ −14” in the determination in the above-described process S205 (N in S205), the process returns to the process S202, and the processes S202 to S205 are repeated. Thereby, the printing process is continued.
On the other hand, if “n ≦ −14” is determined in step S205 (Y in S205), toner discharge processing is performed (S206).
[0068]
In this process, a toner image corresponding to a printing rate of about 0.05% when converted to a printing rate is developed on the photosensitive drum 6. The image forming unit 5 is controlled by the head controller unit 56 so that this toner image becomes a toner image having a density and a uniform dot arrangement so that the printing rate is about 0.05%.
[0069]
The above-mentioned printing rate of about 0.05% is a numerical value obtained empirically based on various experiments. Thus, printing with a printing rate of about 0.05% can be used as a lubricant. It has been confirmed that the additive can be supplied to the cleaning blade and has a sufficient effect for eliminating development defects.
[0070]
In addition, the method of developing a small amount of toner as described above is performed by a normal printing process and is not special, so that it is easy to realize.
As described above, according to this example, the printing rate is constantly monitored, and when the predetermined low printing rate is obtained, the development with a uniform density using a small amount of toner enables the printing with a very low printing rate. Since development defects caused by damage to the edge of the cleaning blade in the case of repeated operations can be eliminated in advance and the development environment can be restored, high reliability is always obtained in this respect as well. An image forming apparatus can be provided.
<Third Embodiment>
By the way, in general, in the developing device of an electrophotographic printer, the developing width of the developing roller is wider than the printing area of the paper and further wider than the maximum printable paper width.
[0071]
FIG. 9 is a diagram showing the relationship between the developing width of such a developing roller and the paper. In the figure, the developing roller 13, the paper P, and the doctor blade 44 and the side seal 61 in the toner hopper are also shown.
As shown in the figure, the developing width 13a of the developing roller 13 is wider than the printing area p1 of the paper P and further wider than the width p2 of the maximum printable paper P (for example, A3 size paper). Yes.
[0072]
In other words, at both ends of the developing roller 13, there are non-printing area portions 62 that do not contribute to image formation at all beyond the printing area p1 of the paper P beyond the width p2 of the paper P. The toner is also supplied from the toner supply roller 43 to the non-printing area portion 62.
[0073]
However, since the toner supplied to the non-printing area portion 62 is not used for development and is not consumed, the toner in this portion only goes back and forth between the developing roller 13 and the toner supply roller 43. repeat.
As a result, the toner composed of a relatively soft resin is gradually deformed or adhered to the toner surface due to the pressure of the doctor blade 44 or friction with the scooping sheet 45 (see FIG. 2). The external additive is released.
[0074]
As described above, when the external additive adhering to the toner surface is liberated, when printing is performed with such an image forming unit 5, there is little toner 39 remaining in the toner hopper 41, or the printing rate is high. When the toner 39 is consumed at a high speed, there is no problem because the toner 39 is consumed before it is damaged, but the toner 39 in the toner hopper 41 is large, the printing rate is low, and the single-shot (printing When printing is performed with a low frequency), the toner 39 is repeatedly consumed without being consumed for a long time, so that the toner 39 is damaged in various ways.
[0075]
As the damage received by the toner 39, for example, the toner 39 is rounded. When the toner 39 is rounded, it is difficult for the developing roller 13 to convey the toner, causing a problem that the density is lowered. Further, when the external additive is exhausted, an undesirable influence is exerted on the image formation, such as being unable to transfer to the paper P.
[0076]
Such damage to the toner 39 is particularly remarkable in the non-printing area 62 that does not contribute to printing at all. The toner 39 deteriorated due to the damage in the non-printing area 62 gradually enters the printing area p1 to cause a problem that the image quality at the edge of the formed image is deteriorated.
[0077]
Therefore, we decided to investigate these problems through experiments. First, in the experiment, 600 g of nonmagnetic one-component toner was prepared, filled in the toner hopper 41 of the image forming unit 5, and printing was performed by changing the printing conditions in various ways. As the non-magnetic one-component toner, four colors of full-color toner having a Tg of 59 ° C. and a softening point of 120 ° C. were used. In addition, a full color printer with a printing speed of about 30 ppm was used, and the state of image formation was confirmed by changing the printing conditions in various ways.
<Experimental example 1>
Intermittent printing every two sheets at a printing rate of 0.1% (after printing two sheets, when the machine operation stops, the next two sheets are printed. This is repeated). The image density at both ends from the vicinity of the sheet became thin, the transferability decreased, and the image started to deteriorate in image quality.
[0078]
At the time of 30000 sheets, the image quality at both ends of the image was clearly degraded, and the image was unusable. In the central part, there was no degradation to the point of problem.
<Experimental example 2>
Similarly, intermittent printing is performed every two sheets, and every 1000 sheets, solid printing is performed over the entire width of the outside of the print area 62 over the length of 210 mm in the feeding direction of the paper P, so that the area outside the print area 62 is printed. It was operated so that the toner was consumed.
[0079]
As a result, density reduction and blurring at both ends of the image did not occur even with 20000 sheets. Furthermore, even 30000 sheets could be printed without any problem. Before the 40,000 sheets were maintained, the experiment was completed because there was no toner in all the colors, but all were completed at a level where there was no problem.
[0080]
From the above results, it has been confirmed that the toner 39 outside the print frame area 62 is consumed regularly to prevent deterioration of the printed image edge.
<Experimental example 3>
The timing for consuming the toner outside the print area 62 is determined every operation time of 120 minutes, and solid printing is performed outside the print area 62 with a length of 210 mm in the paper feed direction every 120 minutes. In this case, the term “solid printing” means that there is no unevenness, and the solid image has a rough dot arrangement such that the printing rate of the solid image is 0.1%. As described above, since the work time of 120 minutes is a preferential measure regardless of the number of printed sheets, the number of printed sheets at the timing of starting toner consumption is random.
[0081]
Even in the result of this experiment, a good image was obtained until no toner was detected (until the toner of the image forming unit was used up).
<Experimental example 4>
The toner outside the printing area 62 is consumed for each printing, and is converted from the length of 210 mm for every 1000 sheets, and is 0.2 mm each time printing is completed. Printing was performed before printing on the next sheet (between intermittent conveyances). Also in this case, a good image was obtained until no toner was detected.
[0082]
As described above, in any case, by periodically consuming toner outside the printing frame area of the developing roller, it is possible to prevent image quality deterioration at the edge of the printed image that occurs when printing is performed for a long time at a low printing rate. it can.
In the case of solid printing with a length of 210 mm for every 1000 sheets, the effect for preventing image quality deterioration is greater if the printing is longer than 210 mm. However, toner consumption increases. In addition, when the printing rate is high, the toner runs out early and the use of the image forming unit ends. In such a case, the above processing is not necessary. Further, in the case of intermittent printing for each sheet at a lower printing rate, it is necessary to consume more non-printing area. In such a case, it is desirable to determine the toner consumption amount outside the print amount range and the consumption timing from the print rate and the operation time.
<Fourth Embodiment>
By the way, as described above, when an image having a high printing rate is continuously printed, the external additive alumina is released from the toner. However, this released alumina is generally unevenly distributed in a specific portion on the developing roller. . Although the unevenly distributed portion depends on the configuration of the image forming unit, when the toner hopper 41 is large and has a partition wall inside, free alumina is unevenly distributed at the center and both ends on the developing roller.
[0083]
When the free alumina is unevenly distributed in this way, there is a problem that the toner development amount of the image formed in that portion is lowered and the reflection density of the image is lowered. If a solid image is printed in such a case, the image density of the portion where free alumina is unevenly distributed becomes thin, and an image failure (so-called white band) occurs as if a vertical white band was printed. To do.
[0084]
In this example, a density patch is formed on the normally carried conveyor belt 10, and the density sensor 37 for correcting the density by detecting the density is utilized to repair the white band image failure in advance.
Here, the density patch and the density correction will be briefly described.
[0085]
FIG. 10 is a perspective view schematically showing the conveyance belt unit and the density sensor. As described with reference to FIG. 1, the conveyor belt 10 is stretched between the driving roller 23 and the driven roller 24, driven by the driving roller 23, and circulated in the counterclockwise direction indicated by arrow B in the drawing.
[0086]
A density check patch 63 is formed not only on the sheet but directly on the center of the paper transport surface 10a of the transport belt 10 by the image forming unit 5 periodically or as necessary. Is detected by the density sensor 37.
The density sensor 37 emits light when a voltage is applied to the LED of the light emitting unit, and the light receiving unit detects the reflected reflected light that is irradiated to the density check patch 63, and the analog detection amount is converted into a numerical value. The data is sent to the printer controller 52 and reflected in the high voltage unit 59 based on the result calculated by the printer controller 52.
[0087]
FIG. 11A is a diagram showing the above-described density confirmation patch, and FIG. 11B is a flowchart of processing for performing density adjustment based on the density detected from the density confirmation patch. First, in FIG. 10B, when the density adjustment process is started (S301), the density check patch 63 shown in FIG. 10A is formed on the conveying belt 10 as shown in FIG. The density sensor 37 detects the confirmation patch 63 and measures its density (S302).
[0088]
As shown in FIG. 11 (a), the density check patch 63 is composed of a total of 8 patches, each having two shades of light and dark, using magenta (M), cyan (C), yellow (Y), and black (K) toners. A patch is formed.
Subsequently, the output of the density sensor 37 that measures the density of the density check patch 63 is compared with a preset target density value (S303). If the output of the density sensor 37 is a target density value, it is determined that density adjustment is unnecessary, and the process ends.
[0089]
On the other hand, if the output of the density sensor 37 is higher or lower than the target density value, it is determined that adjustment is necessary, and density adjustment is performed (S304).
In this density adjustment, when the output of the density sensor 37 is higher than the target density value, the printer controller 52 instructs the high-pressure unit 59 to lower the developing bias to lower the density. Conversely, when the output of the density sensor 37 is lower than the target density value, the printer controller 52 instructs the high voltage unit 59 to increase the developing bias to increase the density.
[0090]
This adjustment is repeated until the output of the density sensor 37 reaches the target density value. As a result, the amount of toner to be developed is controlled to be constant, and a stable image density is constantly maintained.
It should be noted that such a density check patch 63 for density adjustment is typically selected at one central portion in the main scanning direction of the conveyor belt 10 as shown in FIG. A density check patch 63 having a pattern as shown in FIG.
[0091]
In this example, by utilizing the conventional density adjustment mechanism as described above, first, the density sensor 37 that has been conventionally fixed at the center is shown by arrows C and C ′ in FIG. The transport belt 10 is configured to be movable in the width direction.
Next, a white band check patch is directly formed at both ends of the transport belt 10 or at one of the ends, and the density of the white band check patch is measured by the density sensor 37.
[0092]
FIG. 12 (a) is a diagram showing the white band check patch of this example, and FIG. 12 (b) removes the cause of the image failure in advance based on the density detected from the white band check patch. It is a flowchart of a process.
As shown in FIG. 5A, the white band check patch 64 is formed by five patches of four colors of magenta (M), cyan (C), yellow (Y), and black (K). Yes. Since the white band has a relatively darker patch, it is easier to discern whether or not the white band has occurred. Therefore, the white band check patch 64 forms only five patches of the aforementioned darkness check patch in succession. To do.
[0093]
Further, as described above, since the white band appears at the central portion and both end portions, the central portion serves as a density adjustment patch region, and the white band check patch 64 is provided at both end portions of the transport belt 10 or either one thereof. It is made to form in the edge part.
In FIG. 5B, when the printing process starts (S401), the printing rate is monitored (S402). This process is basically the same as the process S2 in FIG. 6, the process S102 in FIG. 7, and the process S202 in FIG. 8, but in this case, the printing rate is determined from the ratio information of the lighting / non-lighting of the print head. Is calculated each time.
[0094]
Subsequently, the printing rate is checked (S403). In this process, the printing rate and the number of printed sheets are referred to.
In this example, conditions that may cause white bands are set in advance. That is, the above-mentioned condition is that printing is performed at a printing rate of 50% or more with 50 sheets of printing as A4 size paper as a break.
[0095]
Then, it is determined whether the printing rate is 50% and the number of printed sheets is 50 or more in A4 size (S405).
If this determination is No, printing continues (S409), but if the determination is Yes, a white band check is performed (S406).
[0096]
In this process, as described above, the white band check patch 64 is formed on both ends or one of the ends of the conveyor belt 10, and the density sensor 37 is moved from the central portion to the end portion to check the white band. This is a process for measuring the density of the patch 64 for use.
Subsequently, the measurement data is compared with a target value in advance to determine whether a white band has occurred (S407).
[0097]
In this example, the output of the density sensor is 3v when there is no toner on the conveyor belt 10, and the output when the white band check patch is normally formed is 1v. It is determined that a white band is about to occur.
If a white band is not generated (S407: No), printing is continued (S409). If a white band is being generated (S407: Yes), the process proceeds to an alumina release sequence (S408).
[0098]
This process is performed by performing normal white printing without paper. In general, toner is charged to a relatively strong negative potential, but alumina as an external additive is charged to a relatively weak negative potential. The higher the alumina concentration on the developing roller, the more the material adheres to the drum. Therefore, the white printing without paper, so-called idling, eliminates the uneven distribution of alumina in the portion where the alumina is unevenly distributed and a white band is formed.
[0099]
The idling time varies depending on the difference between the read output value of the density sensor and the target density value at the time of white band check. For example, when the difference is 1v, 10 sheets of time corresponding to white printing A4 is performed, and when 2v, 20 sheets are processed.
[0100]
At this time, when the alumina release sequence is performed for the color developing device, the conveying belt is rotated downward as in the monochrome printing mode to separate it from the photosensitive drum of the color developing unit. It is possible to prevent the alumina from adhering to the conveyor belt.
[0101]
After this alumina release sequence is executed, the white band check in step S406 is performed again. If there is no possibility of white band generation, the process returns to the printing operation in step S409.
Thus, in order to repair the white band image failure caused by the uneven distribution of external additives such as alumina, which occurs when printing a large amount of images with a high toner consumption and high printing rate, the paper feeding operation is performed. A sequence for performing white paper printing is provided, and particles such as alumina are discharged from the developing unit other than during image formation to prevent image deterioration due to the generation of white bands in advance.
[0102]
In the first embodiment, the printing rate is calculated by the number of printing dots per page. However, the present invention is not limited to this. For example, the number of lighting elements of the print head and the motor being lit You may make it calculate from the rotation time of (the motor which drives a photoconductive drum or a conveyance belt). In short, any method may be used as long as the printing rate can be calculated.
[0103]
In any of the embodiments, the case of developing with a non-magnetic one-component toner has been described. However, the present invention is not limited to this, and can be applied to the development with two-component toner.
In the fourth embodiment, the formation position of the white band check patch is determined in advance as the end portion of the transport belt. However, the present invention is not limited to this. For example, the same density as that of the white band check patch is used in the main scanning direction. When the patch is formed on the conveyor belt and the patch reaches the sensor position, the conveyor belt is stopped and the sensor is moved in the main scanning direction. A white band check patch may be formed again at the position in the main scanning direction after selecting a likely portion.
[0104]
【The invention's effect】
As described above, according to the present invention, when the printing rate is high and a large amount of toner is consumed, an image such as a white band is released from the toner and remains on the charger, the image carrier, the developing roller, or the like. Image defects caused by free external additives are removed because free external additives that cause defective defects are removed by changing the bias applied to the toner supply roller at the recovery start timing that has been previously known and rotating the entire roller idly. It is possible to provide a highly reliable image forming apparatus in which occurrence defects are eliminated and a good image is always obtained.
[0105]
Also, by constantly monitoring the printing rate and performing development with a uniform density using a small amount of toner when the predetermined printing rate is low, cleaning is performed when printing with a very low printing rate is repeated. Since development defects caused by damage to the blade edge can be eliminated in advance and the development environment can be restored, it is also possible to provide a highly reliable image forming apparatus capable of always obtaining a good image in this respect. It becomes possible.
[0106]
Further, by periodically consuming the toner outside the printing frame area of the developing roller, it is possible to prevent image quality deterioration at the edge of the printed image that occurs when printing is performed for a long time at a low printing rate.
In addition, a white band check patch is formed on the conveyor belt, and the cause of image failure is removed in advance based on the density detected from the white band check patch. It is possible to provide an image forming apparatus with high image quality.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an internal configuration of a printer according to an embodiment of the present invention.
FIG. 2 is a side cross-sectional view showing an internal configuration of only the image forming unit of the printer in the embodiment of the present invention.
FIG. 3 is a diagram illustrating a bias voltage system of each unit of an image forming unit of a printer according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating an internal circuit configuration of a printer according to an embodiment of the present invention.
FIG. 5 is a diagram showing a data configuration of a combination of mode 1 and mode 2 bias voltages stored in an EEPROM in the circuit configuration;
FIG. 6 is a flowchart illustrating a mode 1 process during a printing process that is executed while the head controller unit is controlled by the printer controller unit in the circuit configuration according to the first embodiment.
FIG. 7 is a flowchart illustrating processing in mode 1 and mode 2 during printing processing executed while the head controller is controlled by the printer controller in the circuit configuration.
FIG. 8 is a flowchart for explaining processing for removing a cause of development failure due to repetition of a low printing rate, which is executed while controlling the head controller by the printer controller according to the second embodiment.
FIG. 9 is a diagram illustrating a relationship between a developing width of a developing roller and paper in a third embodiment.
FIG. 10 is a perspective view schematically showing a conveyance belt unit and a density sensor according to a fourth embodiment.
11A is a diagram showing a density patch, and FIG. 11B is a flowchart of a process for performing density adjustment based on the density detected from the density patch.
FIG. 12A is a diagram showing a white band check patch according to the fourth embodiment, and FIG. 12B is a diagram showing a process for removing a factor of image failure in advance based on the density detected from the white band check patch. It is a flowchart.
[Explanation of symbols]
1 Printer
2 Image forming unit
3 Transport unit for duplex printing
4 Paper feeder
5 (5-1, 5-2, 5-3, 5-4) Image forming unit
C1 drum set
C2 toner set
6 Photosensitive drum
7 Cleaner
7a Cleaning blade
8 Charging roller
9 Print head
10 Conveyor belt
10a Paper transport surface
11 Transfer device
12 Developer container
13 Development roller
13a Development width
14 Feed roller
15 Paper cassette
16 Guide roller pair
17 Guideway
18 Feeding roller pair
19 Waiting roller pair
20 Mounting part cover
21 MPF tray
22 Feed roller
23 Drive roller
24 Followed roller
25 Fixing unit
26 Heat roller
27 Pressure roller
28 Oil application roller
29 Switching plate
31 Unloading roller pair
32 Side outlet
33 Pair of transport rollers
34 Paper discharge roller
35 Output section
36a to 36e Conveying roller
37 Concentration sensor
38 Drum cover
39 Toner
41 Toner Hopper
42 Toner stirring member
43 Toner supply roller
44 Doctor Blade
45 scooping sheet
46, 47, 48, 49, 50 High voltage power supply
51 Interface (I / F)
52 Printer Controller
53 EEPROM
54 ROM
55 Operation panel
56 Head controller
57 Temperature and humidity sensor
58 Paper counter
59 High pressure unit
P paper
p1 print area
p2 paper width
61 Side seal
62 Non-printing area
63 Density confirmation patch
64 White band check patch

Claims (3)

An image carrier, a charging unit that charges the image carrier to a predetermined potential, and an electrostatic latent image that forms an electrostatic latent image by irradiating the image carrier charged by the charging unit with light according to an image signal. A latent image forming unit; a developing unit that applies a developer to the electrostatic latent image formed on the image carrier to form a toner image according to the image signal; and the toner image formed by the developing unit. Transfer means for executing printing on the transfer material by transferring to the transfer material, and the developing means is provided so as to contact the image carrier, and the nonmagnetic one-component toner having a negatively charged polarity and the nonmagnetic A developing roller that carries the developer having externally added fine particles having a positively charged polarity relative to a one-component toner and that rotates and conveys the developer roller, and is in pressure contact with the developing roller on the upstream side of the developing roller in the rotation and conveying direction. A developer supply roller for supplying the developer to the roller. La and the developing roller and the developer the toner at least comprising an image forming apparatus comprising a bias voltage applying means for applying a bias voltage to generate a potential difference in a direction to be attracted to the developing roller side between the supply roller In
Print dot number storage means for storing the number of print dots per page on the transfer material based on the image signal;
Printed page number storage means for counting and storing the number of printed pages on the transfer material by the transfer means;
Based on the information stored in the print dot number storage means and the print page number storage means to prevent an abnormal image failure, the electrostatic latent image is applied to the image carrier while operating at least the image carrier and the charging means. The bias voltage application unit is controlled so that the potential difference between the developing roller and the developer supply roller becomes larger, while controlling the light irradiation by the electrostatic latent image forming unit so as not to form an image. And external addition particulate collection control means for collecting the external addition particulates from the developing roller to the developer supply roller side,
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the charging unit is a contact type charging unit that contacts the image carrier and charges the image carrier to the predetermined potential.   2. The image according to claim 1, wherein the developing unit is a contact-type developing unit that contacts the image carrier and applies the developer to the electrostatic latent image to form the toner image. Forming equipment.

Images