JP4059370B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an image forming apparatus in an electrophotographic printer, a photosensitive drum as an image carrier is charged by a charging roller, and an electrostatic latent image is formed by exposing the surface of the photosensitive drum. The electrostatic latent image is developed by a developing device comprising a toner image to form a toner image, and the toner image is transferred to a sheet by a transfer roller. The sheet on which the toner image has been transferred is sent to a fixing roller, where the toner image is fixed and becomes an image. The toner remaining on the photosensitive drum after the transfer is removed from the photosensitive drum and collected by a cleaning blade, a cleaning roller, or the like.
[0003]
By the way, each roller such as the charging roller, the developing roller, the transfer roller, the cleaning blade, and the cleaning roller is formed of an elastic rubber material and pressed against the photosensitive drum. As the rubber material used for the developing roller, dimethyl silicone rubber having high environmental stability and easily charging the toner to a negative polarity is used.
[0004]
[Problems to be solved by the invention]
However, in the conventional image forming apparatus, the developing roller is used in a state where it is constantly pressed against the photosensitive drum, so that if the image forming apparatus is left for a long time without printing, the developing roller Low molecular components (hereinafter referred to as “oligomers”) are deposited and adhere to the surface of the photosensitive drum.
[0005]
In particular, the dimethyl silicone rubber has a structure in which low-molecular-weight siloxane is more likely to precipitate as an oligomer than other rubber materials, so that the amount of oligomer adhering to the surface of the photosensitive drum increases and the exposure by the LED head is blocked. The toner adheres to the oligomer. As a result, horizontal streaks such as white streaks and black streaks are formed in the image, and the image quality deteriorates.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the conventional image forming apparatus and to provide an image forming apparatus capable of improving image quality without forming horizontal stripes in an image.
[0007]
[Means for Solving the Problems]
For this reason, in the image forming apparatus of the present invention, a carrier rotation process for rotating the image carrier is performed in accordance with the leaving time when the image forming apparatus is left without being printed. Yes.
An image carrier, a toner carrier that is provided in constant contact with the image carrier, and supplies toner to the image carrier, toner supply means for supplying toner to the toner carrier, and the carrier In the rotation process, the voltage applied to the toner carrier and the voltage applied to the toner supply means are set to 0 [V], and the image is carried by the number of rotations increased as the standing time is increased without forming an image. And a carrier rotation processing means for rotating the body.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0009]
FIG. 2 is a conceptual diagram of the image forming apparatus according to the first embodiment of the present invention.
[0010]
As shown in the figure, the image forming apparatus includes an LED head 13 as an exposure unit, a transfer roller 14 as a transfer unit, a photosensitive drum 16 as an image carrier, a charging roller 17 as a charging unit, and a developing unit. The developing device 18 includes a cleaning roller 58 as a cleaning unit, and the developing device 18 includes a developing roller 19 as a toner carrier and a rotating member, a developing blade 55, a toner supply roller 56 as a toner supply unit, and the like. In this embodiment, the LED head 13 is used as the exposure means, but a laser, a liquid crystal shutter, or the like can be used instead of the LED head 13.
[0011]
In the image forming apparatus configured as described above, the surface of the photosensitive drum 16 is uniformly and uniformly charged by the charging roller 17, and the photosensitive drum 16 is exposed by the LED head 13 to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 18 and the toner 57 is adhered to the photosensitive drum 16 to form a toner image. The toner 57 is supplied to the developing roller 19 by the toner supply roller 56, and is made into a thin layer having a uniform thickness on the surface of the developing roller 19 by the developing blade 55.
[0012]
Subsequently, the transfer roller 14 transfers the toner image onto a sheet (not shown) serving as a recording medium, and the sheet after the toner image is transferred is supplied to a fixing device (not illustrated) serving as a fixing unit to fix the toner image. Image. Further, the toner remaining on the photosensitive drum 16 after the transfer is removed from the photosensitive drum 16 and collected by the cleaning roller 58 or the like.
[0013]
By the way, each of the rollers such as the charging roller 17, the developing roller 19, the transfer roller 14, and the cleaning roller 58 is formed of an elastic rubber material and is pressed against the photosensitive drum 16. For example, dimethyl silicone rubber that has high environmental stability and easily charges the toner 57 to a negative polarity is used as the rubber material used for the developing roller 19.
[0014]
Since the developing roller 19 is used in a state where it is constantly pressed against the photosensitive drum 16, if the image forming apparatus is left for a long time without printing, oligomers as foreign matters precipitate from the developing roller 19. Then, the precipitated oligomer adheres to the surface of the photosensitive drum 16. In particular, since the dimethyl silicone rubber has a structure in which low-molecular siloxane is more likely to precipitate as an oligomer than other rubber materials, the amount of oligomer attached to the surface of the photosensitive drum 16 increases.
[0015]
The oligomer is locally attached to a portion of the surface of the photosensitive drum 16 that contacts the developing roller 19. Therefore, before starting the image forming operation, the photosensitive drum 16 is rotated a predetermined number of times, the oligomer adhering to the surface of the photosensitive drum 16 is thinned, and another roller, for example, the above-mentioned The charging roller 17, the transfer roller 14, the cleaning roller 58, and the like are dispersed. In this case, the photosensitive drum 16 can be rotated continuously or intermittently.
[0016]
In the charging roller 17, the transfer roller 14, the cleaning roller 58 and the like, oligomers are similarly deposited and locally adhered to the surface of the photosensitive drum 16. The oligomer also rotates the photosensitive drum 16. To make it thinner and dispersed on other rollers. In this case, the charging roller 17, the transfer roller 14, the cleaning roller 58, and the like constitute a rotating body.
[0017]
FIG. 1 is a block diagram of an image forming apparatus according to a first embodiment of the present invention.
[0018]
In the figure, 81 is a main CPU as a main control unit, 82 is a main power switch, 83 is an information device terminal such as a host computer for generating a print command signal, 84 is a time counter for measuring the time for leaving, and 87 is a photosensitive drum. 16 is a drum counter for calculating a drum count value corresponding to the total number of revolutions (FIG. 2), 85 is a drum count table recording means for recording the drum count value as a table value, and 88 is connected to the photosensitive drum 16. The main CPU 81 includes a drum count determination processing unit 86. The motor driving unit drives a motor (not shown).
[0019]
The drum counter 87 is arranged for judging the life of the image forming apparatus, and when the photosensitive drum 16 is rotated by a predetermined amount for printing in the vertical direction on one sheet of A4 size paper. The drum count value is incremented. Therefore, in the present embodiment, the total number of rotations of the photosensitive drum 16 does not match the drum count value. The drum count value can also be calculated in a one-to-one correspondence with the total number of rotations of the photosensitive drum 16.
[0020]
Next, the image forming apparatus is allowed to stand for a long time without printing, and the oligomer adhering to the surface of the photosensitive drum 16 is thinned and dispersed to other rollers. The relationship with the drum count value until the horizontal streak disappears will be described.
[0021]
FIG. 3 is a diagram showing a relationship between the image forming apparatus leaving time and the drum count value until the horizontal streak disappears in the first embodiment of the present invention. Note that the horizontal axis represents the standing time, and the vertical axis represents the drum count value.
[0022]
The horizontal streaks use pulverized toner and are high by 1by1 (method of forming one dot on four ridges), 2by2 (method of forming four dots on 16 ridges), and the like. It is known that it is likely to occur when printing with a resolution pattern. Therefore, when dimethyl silicone rubber is used as the developing roller 19 (FIG. 2) and pulverized toner is used as the toner 57, printing is performed with a dot density of 1200 DPI and a high resolution pattern of 1 by 1. Show.
[0023]
In this case, as the standing time becomes longer, the drum count value until the horizontal streak disappears becomes larger. When the standing time becomes 60 [minutes] or more, the slope of the drum count value becomes gradual, and the drum count value becomes approximately 20 times. It can be seen that the horizontal stripe disappears at ˜22 or more.
[0024]
Therefore, a drum count table is set corresponding to the characteristics shown in FIG. 3, and the drum count table is recorded in the drum count table recording means 85 (FIG. 1).
[0025]
FIG. 4 is a diagram showing the relationship between the image forming apparatus leaving time and the drum count table value according to the first embodiment of the present invention. The horizontal axis represents the standing time TC, and the vertical axis represents the table value DCt.
[0026]
As shown in the figure, the leaving time TC is
0 <TC ≦ 10 [minutes]
, The table value DCt representing the number of rotations of the photosensitive drum 16 (FIG. 2) until the image forming operation is started is 10, and the leaving time TC is
10 <TC ≦ 30 [minutes]
In this case, the table value DCt is set to 15, and the leaving time TC is
30 <TC ≦ 60 [minutes]
In this case, the table value DCt is set to 20, and the leaving time TC is
60 <TC [minutes]
In this case, the table value DCt is set to 25. These table values DCt differ depending on the types of the developing roller 19 and the toner 57, the pressing amount of the developing roller 19 against the photosensitive drum 16, and the like.
[0027]
Next, the operation of the image forming apparatus when it is left for a long time without being printed will be described.
[0028]
FIG. 5 is a flowchart showing the operation of the image forming apparatus according to the first embodiment of the present invention.
[0029]
First, a leaving determination processing unit (not shown) of the main CPU 81 (FIG. 1) performs a leaving determination process to determine whether the image forming apparatus has been left for a predetermined time without printing.
[0030]
When the power is turned on, that is, when the main power switch 82 is turned on, or when the main power switch 82 is already turned on and a print command is sent from the information equipment terminal 83, the abandonment determination process is performed. The means determines that the image forming apparatus has been left without printing for a predetermined time, that is, for a long time, and the carrier rotation processing means (not shown) of the main CPU 81 performs carrier rotation processing corresponding to the leaving time TC. And prevent the formation of horizontal streaks.
[0031]
In this case, when the main power switch 82 is turned on, the leaving determination processing means determines that the image forming apparatus has been left for a sufficiently long time without printing, and the carrier rotation processing means A signal is sent to the drum count table recording means 85, and the table value DCt is read from the drum count table recording means 85. In this case, the table value DCt is set to 25 which is the maximum value.
[0032]
On the other hand, when the main power switch 82 is already turned on and a printing command is sent from the information equipment terminal 83, the leaving determination processing unit is left for a sufficiently long time without printing the image forming apparatus. The carrier rotation processing means reads the standing time TC from the time counter 84, and reads the table value DCt corresponding to the standing time TC from the drum count table recording means 85.
[0033]
Next, the carrier rotation processing means reads the drum count value before the photosensitive drum 16 starts rotating from the drum counter 87 as the reference drum count value DC0, and operates the motor driving unit 88 to drive the motor. Then, the rotation of the photosensitive drum 16 is started.
[0034]
The drum count determination processing means 86 reads the drum count value DC incremented with the rotation of the photosensitive drum 16, and based on the drum count value DC, the reference drum count value DC0, and the table value DCt, Whether or not the image forming operation start condition is satisfied is determined based on whether or not the following expression (1) is satisfied.
[0035]
DCt <DC-DC0 (1)
When the image forming operation start condition is satisfied, the main CPU 81 stops the photosensitive drum 16 and ends the carrier rotating process, and an image forming processing unit (not shown) of the main CPU 81 performs the image forming process, and The forming operation is started. At this time, the main CPU 81 resets the drum counter 87 and sets the reference drum count value DC0 to the drum count value DC. Accordingly, it is possible to prevent the drum count value DC for determining the life of the image forming apparatus from being increased by the rotation of the photosensitive drum 16 not involved in actual image formation.
[0036]
As described above, when the image forming apparatus is left for a long time without printing, the photosensitive member is formed by a predetermined amount, that is, a predetermined number of rotations without forming an image before starting the image forming operation. Since the drum 16 is rotated, the oligomer adhering to the surface of the photoconductive drum 16 is thinned and other rollers such as the charging roller 17, the transfer roller 14, and the cleaning roller 58 are also formed. Etc. can be dispersed.
[0037]
Therefore, exposure by the LED head 13 is not blocked, and the toner 57 does not adhere to the oligomer. As a result, horizontal stripes such as white stripes and black stripes are not formed on the image, and the image quality can be improved.
[0038]
Further, since the photosensitive drum 16 is rotated by the number of rotations corresponding to the leaving time TC, the photosensitive drum 16 is not meaninglessly rotated for a long time. Accordingly, the waiting time until the image forming operation is started can be shortened, so that the printing throughput can be improved.
[0039]
Next, a flowchart will be described.
Step S1: It is determined whether or not the main power switch 82 is turned on. If the main power switch 82 is turned on, the process proceeds to step S4. If the main power switch 82 is not turned on, the process proceeds to step S2.
Step S2 It waits for a print command to be sent from the information equipment terminal 83.
Step S3 Read the standing time TC.
Step S4: Read the table value DCt.
Step S5: The reference drum count value DC0 is read.
Step S6 The rotation of the photosensitive drum 16 is started.
Step S7: The drum count value DC is read.
Step S8: It is determined whether the table value DCt is smaller than a value obtained by subtracting the reference drum count value DC0 from the drum count value DC. If the table value DCt is smaller than the value obtained by subtracting the reference drum count value DC0 from the drum count value DC, the process proceeds to step S9. If the table value DCt is greater than or equal to the value obtained by subtracting the reference drum count value DC0 from the drum count value DC. Return to step S7.
Step S9: An image forming operation is started, the drum counter 87 is reset, and the process is terminated.
[0040]
Next, a second embodiment of the present invention will be described. In this case, a color image forming apparatus is used as the image forming apparatus.
[0041]
FIG. 6 is a first conceptual diagram of a color image forming apparatus according to the second embodiment of the present invention, and FIG. 7 is a second conceptual diagram of the color image forming apparatus according to the second embodiment of the present invention.
[0042]
As shown in the figure, in the color image forming apparatus 11, four sets of first to fourth printing mechanisms P1 to P4 are arranged in a tandem type in order along the conveyance direction of the paper 21 as a recording medium. Each of the first to fourth printing mechanisms P1 to P4 includes an electrophotographic LED printing mechanism.
[0043]
The first printing mechanism P1 is formed by a yellow image forming unit 12Y, an LED head 13Y as an exposure unit that exposes the surface of the photosensitive drum 16 as an image carrier according to image data, and the image forming unit 12Y. And a transfer roller 14Y as transfer means for transferring the yellow toner image onto the paper 21.
[0044]
The second printing mechanism P2 includes a magenta image forming unit 12M, an LED head 13M as an exposure unit that exposes the surface of the photosensitive drum 16 as an image carrier according to image data, and the image forming unit 12M. It comprises a transfer roller 14M as transfer means for transferring the formed magenta toner image onto the paper 21.
[0045]
The third printing mechanism P3 includes a cyan image forming unit 12C, an LED head 13C as an exposure unit that exposes the surface of the photosensitive drum 16 as an image carrier according to image data, and the image forming unit 12C. It comprises a transfer roller 14 </ b> C as transfer means for transferring the formed cyan toner image onto the paper 21.
[0046]
Further, the fourth printing mechanism P4 includes a black image forming unit 12BK, an LED head 13BK as an exposure unit that exposes the surface of the photosensitive drum 16 as an image carrier according to image data, and the image forming unit 12BK. It comprises a transfer roller 14BK as transfer means for transferring the formed black toner image onto the paper 21.
[0047]
The image forming units 12Y, 12M, 12C, and 12BK all have the same structure, and the photosensitive drum 16 that is rotated about the shaft 15 in the direction of arrow a and the surface of the photosensitive drum 16 are uniform. The charging roller 17 serves as a charging means for uniformly and uniformly charging, and the developing device 18 serves as a developing means. The developing device 18 includes a toner carrying member and a developing roller 19 as a rotating member. The developing roller 19 is made of a semiconductive rubber material, and includes a developing blade (not shown) and the developing roller 19. A toner supply roller (not shown) serving as a toner supply means for supplying the toner is brought into pressure contact, and a toner container (not shown) is disposed around the toner supply roller.
[0048]
A cleaning blade 59 as a cleaning unit is disposed in pressure contact with the photosensitive drum 16 to scrape off toner remaining on the surface of the photosensitive drum 16 after transfer. The scraped toner is stored in a waste toner box (not shown) by the spiral screw 60.
[0049]
Next, the function of the developing device 18 in each of the image forming units 12Y, 12M, 12C, and 12BK will be described.
[0050]
The non-magnetic one-component toner supplied from the toner container is sent to the developing roller 19 via a toner supply roller, and is thinned on the surface of the developing roller 19 by the developing blade. Reach the contact surface. When the toner is thinned, the toner is rubbed (rubbed) strongly by the developing roller 19 and the developing blade and charged. In the present embodiment, the toner is charged to a negative polarity and reversal development is performed.
[0051]
Next, the LED heads 13Y, 13M, 13C, and 13BK will be described.
[0052]
The LED heads 13Y, 13M, 13C, and 13BK include an LED array (not shown), a drive IC (not shown) that drives the LED array, a substrate (not shown) that mounts the drive IC, and a rod (not shown) that collects light from the LED array. The LED array is composed of a lens array or the like and selectively emits light according to color image data transmitted from the information device terminal via an interface unit (not shown), and the surface of the photosensitive drum 16 is exposed to form an electrostatic latent image. To do. Then, the toner on the developing roller 19 is attached to the electrostatic latent image by electrostatic force to form a toner image. Each LED head 13Y, 13M, 13C, 13BK is pressed downward in FIGS. 6 and 7 by a spring 17a.
[0053]
The transfer portions where the photosensitive drums 16 of the image forming portions 12Y, 12M, 12C, and 12BK and the transfer rollers 14Y, 14M, 14C, and 14BK face each other are moved along the image forming portions 12Y, 12M, 12C, and 12BK. Then, an endless conveyance belt 20 as a recording medium conveyance member is caused to travel, and the conveyance belt 20 conveys the sheet 21 while being sandwiched between the photosensitive drums 16 and the transfer rollers 14Y, 14M, 14C, and 14BK. .
[0054]
The developing device 18 of the image forming unit 12Y has yellow toner, the developing device 18 of the image forming unit 12M has magenta toner, and the developing device 18 of the image forming unit 12C has cyan toner. The black toner is accommodated in the developing device 18 of the unit 12BK.
[0055]
Further, the yellow image data of the color image data is stored in the LED head 13Y of the first printing mechanism P1, and the magenta image data of the color image data is stored in the LED head 13M of the second printing mechanism P2. The cyan image data of the color image data is transmitted to the LED head 13C of the third printing mechanism P3, and the black image data of the color image data is transmitted to the LED head 13BK of the fourth printing mechanism P4. The
[0056]
The conveyor belt 20 is made of a high-resistance semiconductive plastic film, is formed in a seamless endless shape, and is stretched between the driving roller 31, the driven roller 32, and the tension roller 33. The resistance value of the conveyor belt 20 is such that the static electricity remaining on the conveyor belt 20 is naturally neutralized when the sheet 21 is attracted to the conveyor belt 20 by electrostatic force and the sheet 21 is separated from the conveyor belt 20. The range is set to
[0057]
The driving roller 31 is connected to a motor (not shown) as belt driving means, and is rotated in the direction of the arrow f by the motor to drive the conveyor belt 20. Further, the tension roller 33 is urged in the direction of arrow g by a spring (not shown), and applies tension to the conveyor belt 20.
[0058]
The upper half 20a of the conveyor belt 20 is stretched through the transfer portions of the first to fourth printing mechanisms P1 to P4, and the lower half 20b of the conveyor belt 20 is between the tension roller 33 and the cleaning blade 34. It is stretched between the tip. The cleaning blade 34 is made of a flexible rubber material or plastic material, and scrapes the toner remaining on the surface of the conveying belt 20 into a waste toner tank 35.
[0059]
When the motor is driven in the reverse direction, the transport belt 20 is caused to travel in the reverse direction. Further, in the present embodiment, each photosensitive drum 16 and each transfer roller 14Y, 14M, 14C, 14BK are in contact with the conveyance belt 20. Further, camshafts 22 are rotatably supported with respect to the main body of the color image forming apparatus 11 on the downstream side of the image forming units 12Y, 12M, 12C, and 12BK in the traveling direction of the conveyor belt 20, respectively. An eccentric cam 23 is attached to the cam shaft 22. Therefore, by oscillating the eccentric cam 23, the image forming units 12Y, 12M, 12C, and 12BK are oscillated around the fulcrum and the photosensitive drum 16 and the conveying belt 20 are in contact with each other. The photosensitive drum 16 and the conveyor belt 20 can be placed at a retracted position where they do not contact.
[0060]
A sheet feeding mechanism 36 is disposed on the right side of the color image forming apparatus 11 in FIG. The paper feed mechanism 36 includes a paper storage cassette, a hopping mechanism, and a registration roller 45, and the paper storage cassette includes a recording medium storage box 37, a push-up plate 38, and a pressing means 39. The hopping mechanism includes a discriminating means 40, a spring 41 and a paper feed roller 42, and the discriminating means 40 is pressed against the paper feed roller 42 by a spring 41.
[0061]
In this case, the paper 21 stored in the recording medium storage box 37 is pressed against the paper feed roller 42 by the pressing means 39 via the push-up plate 38 and drives a paper feed motor (not shown) to feed the paper feed roller 42. Are rotated one by one by the discriminating means 40 pressed against the paper feed roller 42 by the spring 41 and fed one by one, guided by the guides 43 and 44, and sent to the registration roller 45. .
[0062]
Subsequently, when the registration roller 45 is rotated by a motor (not shown), the sheet 21 is further guided by the medium guide 46 and sent between the suction roller 47 as an aging member and the transport belt 20. The suction roller 47 is in pressure contact with the driven roller 32 via the transport belt 20, charges the paper 21 sent from the paper feed mechanism 36, and attracts it to the transport belt 20 by electrostatic force. Therefore, the suction roller 47 is made of a high resistance semiconductive rubber material. The medium guide 46 is provided with a photo sensor (not shown) for detecting the front end of the paper 21 and a photo sensor 52 for detecting the front end of the paper 21 between the suction roller 47 and the image forming unit 12Y. .
[0063]
Further, a static eliminator (not shown) is disposed so as to face the driving roller 31 via the conveyor belt 20. The static eliminator neutralizes the sheet 21 that has been sucked and sent by the conveyor belt 20 and releases the attracted state to facilitate separation from the conveyor belt 20. A photo sensor (not shown) for detecting the rear end of the paper 21 is disposed downstream of the static eliminator in the transport direction of the paper 21.
[0064]
Further, on the downstream side of the static eliminator and the photosensor in the conveyance direction of the paper 21, the toner images of the respective colors transferred to the paper 21 in the respective transfer portions of the first to fourth printing mechanisms P1 to P4 are fixed. A fixing device 48 is provided. The fixing device 48 includes a heat roller 49 that heats the toner on the paper 21, and a pressure roller 50 that presses the paper 21 against the heat roller 49.
[0065]
The heat roller 49 is formed by coating an elastic body such as silicone rubber on a mandrel such as aluminum and coating the surface of the elastic body with a fluororesin for preventing offset. The pressure roller 50 is formed by coating an elastic body such as silicone rubber on a mandrel such as aluminum. A thermistor (not shown) is disposed so as to face the heat roller 49, and the temperature of the heat roller 49 is detected by the thermistor so that the heat roller 49 reaches a predetermined fixing temperature according to the detected temperature. A heater (not shown) in the heat roller 49 can be controlled on and off. The offset prevention liquid can be supplied to the surface of the heat roller 49 by an oil roller, an oil pad, or the like.
[0066]
A discharge port 51 and a photosensor 53 for detecting the rear end of the paper 21 are disposed downstream of the fixing device 48 in the conveyance direction of the paper 21, and a discharge stacker (not shown) is disposed outside the discharge port 51. Established. After the recording, the sheet 21 is discharged to the discharge stacker through the discharge port 51. Reference numeral 54 denotes an operation unit.
[0067]
Next, the control unit of the color image forming apparatus 11 having the above configuration will be described.
[0068]
FIG. 8 is a block diagram of the control unit of the color image forming apparatus according to the second embodiment of the present invention.
[0069]
In the figure, reference numeral 61 denotes a control circuit comprising a microprocessor or the like, and the control circuit 61 controls the entire color image forming apparatus 11 (FIGS. 6 and 7). The control circuit 61 includes a toner supply bias power source for applying a voltage to each toner supply roller of each developing device 18 of the first to fourth printing mechanisms P1 to P4, that is, an SP bias power source 62, and each of the first to first printing mechanisms P1 to P4. A developing bias power source that applies a voltage to each developing roller 19 of the fourth printing mechanisms P1 to P4, that is, a DB bias power source 63, and a voltage is applied to each charging roller 17 of each of the first to fourth printing mechanisms P1 to P4. Charging power supply 64, transfer power supplies 65Y, 65M, 65C, 65BK for applying voltages to the transfer rollers 14Y, 14M, 14C, 14BK of the first to fourth printing mechanisms P1 to P4, respectively, and the suction roller 47. An adsorption charging power source 66 for applying a charging voltage to each is connected. Reference numeral 95 denotes a power supply system. The driven roller 32 is grounded, and the sheet 21 is attracted to the transport belt 20 by electrostatic force due to a potential difference between the driven roller 32 and the suction roller 47. Then, it is possible to apply a voltage to the driven roller 32 and ground the suction roller 47.
[0070]
Each SP bias power source 62, DB bias power source 63, charging power source 64, transfer power sources 65Y, 65M, 65C, 65BK, and adsorption charging power source 66 are controlled to be turned on / off by instructions from the control circuit 61. .
[0071]
Further, print control circuits 68Y, 68M, 68C, and 68BK are connected to the control circuit 61 so as to correspond to the first to fourth printing mechanisms P1 to P4, respectively. The print control circuits 68Y, 68M, 68C, and 68BK are respectively yellow image data, magenta image data, cyan image data, and black image data among the color image data from the memories 69Y, 69M, 69C, and 69BK. The image data is received and transferred to the LED heads 13Y, 13M, 13C, and 13BK according to an instruction from the control circuit 61, and the exposure time of each LED element of the LED array is controlled. A latent image is formed.
[0072]
For this purpose, when the interface unit 70 receives color image data transmitted from an information device terminal such as a host computer (not shown), the interface unit 70 separates the color image data for each color by an image data decomposition unit (not shown), and outputs yellow data. Image data, magenta image data, cyan image data, and black image data are generated, the yellow image data is stored in the memory 69Y, the magenta image data is stored in the memory 69M, and the cyan image data is stored in the memory 69C. The black image data is stored in the memory 69BK.
[0073]
The control circuit 61 is connected to a fixing device driver 71, a motor drive circuit 72, a sensor receiver driver 76, and an operation unit 54 for an operator to input necessary information to the color image forming apparatus 11. The fixing device driver 71 turns on and off a heater (not shown) in the heat roller 49 so as to keep the heat roller 49 at a predetermined temperature. Further, the motor drive circuit 72 includes the transfer rollers 14Y, 14M, 14C, and 14BK, the photosensitive drums 16, the charging rollers 17, the developing rollers 19, and the toner supply rollers. 42, the sheet feeding motor 73 that rotates the registration roller 45, the belt traveling motor 74 that rotates the driving roller 31, and the motor 75 that rotates the heat roller 49 are driven.
[0074]
The transfer rollers 14Y, 14M, 14C, and 14BK rotated by the motors 28 and 73 to 75, the photosensitive drums 16, the charging rollers 17, the developing rollers 19, the toner supply rollers, the driving rollers 31, and the supply rollers The paper roller 42, the registration roller 45, and the heat roller 49 are connected by a gear or a belt (not shown). Then, the sensor receiver driver 76 operates each of the photosensors 30, 52, 53 and sends the output waveform of each of the photosensors 30, 52, 53 to the control circuit 61 as a detection signal.
[0075]
When the motor 73 is driven in the forward direction, only the paper feed roller 42 is rotated in the direction of arrow h, and when the motor 73 is driven in the reverse direction, the paper feed roller 42 is not rotated and only the registration roller 45 is rotated. A one-way bearing (not shown) is provided so that the paper 21 can be fed to the medium guide 46.
[0076]
Next, in the color image forming apparatus 11 having the above-described configuration, an operation when a low-speed color image forming operation is shifted to a high-speed monochrome image forming operation will be described.
[0077]
First, after the color image forming apparatus 11 is turned on and predetermined initial settings are made, when the interface unit 70 receives color image data sent from the information equipment terminal, the control circuit 61 An instruction is given to the interface unit 70 and each of the memories 69Y, 69M, 69C, and 69BK. Based on the instruction, the image data decomposing means decomposes the received color image data for each color, and converts the yellow image data into the memory 69Y. The magenta image data is stored in the memory 69M, the cyan image data is stored in the memory 69C, and the black image data is stored in the memory 69BK.
[0078]
At the same time, the control circuit 61 drives the motor 74 by the motor drive circuit 72, rotates the drive roller 31 in the direction of arrow f, and causes the conveyor belt 20 to travel. The control circuit 61 drives the motor 75 by the motor drive circuit 72, rotates the heat roller 49, and drives the fixing device driver 71 to warm up the heat roller 49 until the fixing temperature is reached. Thereafter, the temperature of the heat roller 49 is controlled so as to always be maintained at a constant value.
[0079]
When each page of image data is stored in each of the memories 69Y, 69M, 69C and 69BK and the heat roller 49 reaches the fixing temperature, the control circuit 61 drives the motor 73 in the forward direction by the motor drive circuit 72. Then, the paper feed roller 42 is rotated in the direction of arrow h. With the rotation of the paper feed roller 42, only one paper 21 stored in the recording medium storage box 37 is fed out and sent to the guides 43 and 44, and the front end of the paper 21 reaches the registration roller 45. Then, a small amount is further conveyed thereafter. As a result, the front end of the paper 21 abuts between the rollers of the registration rollers 45 and is slightly bent (bent), and the skew of the paper 21 is corrected by this bending.
[0080]
Then, the control circuit 61 drives each motor 28 via a motor drive circuit 72, and each transfer roller 14Y, 14M, 14C, 14BK, each photosensitive drum 16, each charging roller 17, each developing roller 19, and each toner supply. Rotate each roller.
[0081]
Thereafter, when the motor 73 is driven in the reverse direction to rotate the registration roller 45, the paper 21 is guided by the medium guide 46 and sent between the suction roller 47 and the transport belt 20. When the front end of the sheet 21 reaches between the suction roller 47 and the conveyance belt 20, the control circuit 61 turns on the suction charging power supply 66 and applies a voltage to the suction roller 47. At this time, the sheet 21 is attracted to the transport belt 20 by the electrostatic force generated between the attracting roller 47 and the driven roller 32. Subsequently, the sheet 21 is conveyed while being attracted to the conveyance belt 20.
[0082]
Then, after a short period of time has elapsed since the start of the motors 28, a high voltage is applied to the charging roller 17, the developing roller 19 and the toner supply roller of each of the first to fourth printing mechanisms P1 to P4. Therefore, the control circuit 61 turns on the respective power sources 64, the DB bias power source 63, and the SP bias power source 62.
[0083]
In this embodiment, the charging roller 17 has a voltage of -1350 [V], the developing roller 19 has a voltage of -300 [V], and the toner supply roller has a voltage of -450 [V]. When applied, the surface of the photosensitive drum 16 is brought to a surface potential of −800 [V]. In this way, the surface of the photosensitive drum 16 of each of the first to fourth printing mechanisms P1 to P4 is uniformly and uniformly charged by the charging roller 17, respectively.
[0084]
Next, the control circuit 61 issues an instruction to the memory 69Y, reads yellow image data for one line from the memory 69Y, and sends the yellow image data to the print control circuit 68Y. The print control circuit 68Y changes the sent yellow image data into a form that can be transferred to the LED head 13Y of the first printing mechanism P1, and transfers it to the LED head 13Y.
[0085]
The LED head 13Y turns on the LED element (not shown) corresponding to the yellow image data transferred from the print control circuit 68Y to perform exposure, and the photosensitive drum charged to −800 [V]. An electrostatic latent image for one line corresponding to the yellow image data is formed on the surface 16. At this time, the voltage of the image portion of the electrostatic latent image is in the vicinity of 0 [V].
[0086]
In this manner, electrostatic latent images are sequentially formed on the surface of the photosensitive drum 16 based on yellow image data sent from the memory 69Y for each line, and electrostatic latent images corresponding to the length in the sub-scanning direction are formed. When the image is formed, the exposure is finished. Then, yellow toner is adhered to the surface of the photosensitive drum 16 on which the electrostatic latent image is formed by the electrostatic force of the charged developing roller 19. Therefore, as the photosensitive drum 16 rotates, the electrostatic latent image is sequentially developed with yellow toner to become a yellow toner image.
[0087]
When the front end of the paper 21 reaches the transfer portion of the first printing mechanism P1, the control circuit 61 turns on the transfer power supply 65Y of the first printing mechanism P1, and transfers the transfer roller of the first printing mechanism P1. A voltage is applied to 14Y. In the present embodiment, a voltage of +1500 [V] is applied to the transfer roller 14Y. As a result, the yellow toner image on the photoconductive drum 16 is transferred to the paper 21 line by line by the transfer roller 14Y. As the photoconductive drum 16 rotates, the yellow toner image for one page is transferred to the paper. 21 is transferred. In this manner, the transfer of the yellow toner image onto the paper 21 (yellow transfer) by the image forming unit 12Y is completed.
[0088]
Then, the conveyor belt 20 is continuously run, and the paper 21 moves from the first printing mechanism P1 to the second printing mechanism P2, and the magenta toner image is transferred to the paper 21 in the second printing mechanism P2. Is done.
[0089]
That is, the control circuit 61 issues an instruction to the memory 69M, reads out one line of magenta image data from the memory 69M, and sends the magenta image data to the print control circuit 68M. The print control circuit 68M changes the sent magenta image data into a form that can be transferred to the LED head 13M of the second printing mechanism P2, and transfers it to the LED head 13M.
[0090]
Then, the LED head 13M turns on the LED elements of the LED array (not shown) corresponding to the magenta image data transferred from the print control circuit 68M to perform exposure, and on the surface of the charged photosensitive drum 16, An electrostatic latent image corresponding to one line corresponding to magenta image data is formed.
[0091]
In this manner, electrostatic latent images are sequentially formed on the surface of the photosensitive drum 16 based on magenta image data sent from the memory 69M for each line, and electrostatic latent images corresponding to the length in the sub-scanning direction are formed. When the image is formed, the exposure is finished. Then, magenta toner is adhered to the surface of the photosensitive drum 16 on which the electrostatic latent image is formed by the electrostatic force of the charged developing roller 19. Therefore, as the photosensitive drum 16 rotates, the electrostatic latent image is sequentially developed with magenta toner to become a magenta toner image.
[0092]
When the front end of the paper 21 reaches the transfer portion of the second printing mechanism P2, the control circuit 61 turns on the transfer power supply 65M of the second printing mechanism P2, and transfers the transfer roller of the second printing mechanism P2. A voltage is applied to 14M. In the present embodiment, a voltage of +1500 [V] is applied to the transfer roller 14M. As a result, the magenta toner image on the photosensitive drum 16 is transferred to the paper 21 line by line by the transfer roller 14M, and as the photosensitive drum 16 rotates, the magenta toner image for one page is transferred to the paper. 21 is transferred onto the yellow toner image on 21. In this manner, the transfer of the magenta toner image onto the paper 21 by the image forming unit 12M (magenta transfer) is completed.
[0093]
Next, the paper 21 moves from the second printing mechanism P2 to the third printing mechanism P3, and the cyan toner image is similarly transferred (cyan transfer) to the paper 21 in the third printing mechanism P3.
[0094]
When the cyan toner image is transferred to the paper 21, the paper 21 moves from the third printing mechanism P3 to the fourth printing mechanism P4, and in the fourth printing mechanism P4, a black toner image is similarly formed. Transferred (black transferred) onto the paper 21.
[0095]
In this way, the color toner images are transferred onto the paper 21 so as to form a color toner image.
[0096]
In the fixing device 48, the color toner image is fixed on the paper 21 by the heat roller 49 and the pressure roller 50 that have already reached the fixing temperature, and becomes a color image, that is, a color image. When the fixing is completed, the sheet 21 is discharged from the discharge port 51 to the outside of the color image forming apparatus 11. The control circuit 61 knows that the paper 21 has been discharged when the photosensor 53 detects the trailing edge of the paper 21.
[0097]
The transfer power supplies 65Y, 65M, 65C, and 65BK are turned off when the rear end of the sheet 21 passes through the photosensitive drums 16. The motor 73 is stopped when the rear end of the paper 21 passes through the suction roller 47, that is, when the photosensor 52 detects the rear end of the paper 21.
[0098]
Further, the motors 28 and 74 are temporarily stopped once the rear end of the paper 21 is detected by the photosensor 53, and then are driven in the reverse direction to form the image forming units 12Y, 12M, 12C, and 12BK. In the retracted position.
[0099]
When the paper 21 is discharged, the control circuit 61 stops the motor 75 by the motor driving circuit 72 and ends the image forming operation.
[0100]
In this way, a color image can be recorded on the paper 21 fed out from the paper feed mechanism 36.
[0101]
By the way, each of the rollers such as the charging roller 17, the developing roller 19, the transfer rollers 14Y, 14M, 14C, and 14BK is formed of an elastic rubber material and is pressed against the photosensitive drum 16. For example, dimethyl silicone rubber having high environmental stability and easily charging the toner to a negative polarity is used as the rubber material used for the developing roller 19.
[0102]
Since the developing roller 19 is used while being constantly pressed against the photosensitive drum 16, if the color image forming apparatus 11 is left for a long time without printing, the developing roller 19 generates an oligomer as a foreign substance. Is deposited, and the deposited oligomer adheres to the surface of the photosensitive drum 16.
[0103]
Therefore, when the color image forming apparatus 11 is left for a long time without printing, the carrier rotation processing means (not shown) of the control circuit 61 performs the carrier rotation processing and performs the photosensitive operation before starting the image forming operation. The body drum 16 is rotated by a predetermined number of revolutions, and the oligomer adhering to the photosensitive drum 16 is scraped off by the cleaning blade 59. In the charging roller 17, the developing roller 19, and the transfer rollers 14Y, 14M, 14C, and 14BK, oligomers are similarly deposited and locally adhere to the surface of the photosensitive drum 16, but the photosensitive drum 16 is attached to the surface of the photosensitive drum 16. By rotating, the oligomer adhering to the photosensitive drum 16 is scraped off by the cleaning blade 59.
[0104]
Therefore, when the main power switch of the color image forming apparatus 11 is turned on or when the main power switch is already turned on and a print command is input from the information equipment terminal, the color image forming apparatus 11 is longer than the threshold value, the carrier rotation processing means starts the carrier rotation processing, rotates the photosensitive drum 16 in the direction of arrow a, and causes the conveyor belt 20 to travel. . A time counter (not shown) is connected to the control circuit 61, and the control circuit 61 reads the leaving time from the time counter.
[0105]
In this case, the paper feed roller 42 is not rotated and the paper 21 is not fed. Further, the transfer power supplies 65Y, 65M, 65C, and 65BK are kept off. The contact position on the photosensitive drum 16 where the developing roller 19 was in contact before the rotation of the photosensitive drum 16, that is, the position slightly upstream from the oligomer adhesion position, is the LED heads 13Y, 13M. , 13C, and 13BK, the print control circuits 68Y, 68M, 68C, and 68BK send image data for solid printing to the LED heads 13Y, 13M, 13C, and 13BK. Exposure. In addition, since the number of steps of one turn of the photosensitive drum 16 is known, the control circuit 61 determines whether the position slightly upstream from the oligomer attachment position has reached just below the LED heads 13Y, 13M, 13C, and 13BK. It can be easily judged.
[0106]
Subsequently, when the exposed position on the photosensitive drum 16 reaches the developing portion between the photosensitive drum 16 and the developing roller 19, the toner on the developing roller 19 is attached to the surface of the photosensitive drum 16. . As described above, since the transfer power supplies 65Y, 65M, 65C, and 65BK are off, the toner adhering to the surface of the photosensitive drum 16 passes through the transfer portion, and remains as it is, the photosensitive drum 16 and the cleaning blade 59. Reach the cleaning part between. In the cleaning unit, the surface of the photosensitive drum 16 is rubbed by the cleaning blade 59.
[0107]
As a result, the toner becomes a lubricant, and the oligomer on the surface of the photosensitive drum 16 is scraped off together with the toner. In this case, since the photosensitive drum 16 is rotated by a predetermined number of rotations, the oligomer is almost completely removed. Thereafter, an image forming processing unit (not shown) of the control circuit 61 starts an image forming operation.
[0108]
As described above, when the color image forming apparatus 11 is left for a long time without printing, the photosensitive drum 16 is rotated by a predetermined number of rotations before starting the image forming operation. The oligomer adhering to the photosensitive drum 16 can be scraped off by the cleaning blade 59.
[0109]
Therefore, the exposure by the LED heads 13Y, 13M, 13C, and 13BK is not blocked, and the toner does not adhere to the oligomer, so that no horizontal stripes are formed in the color image and the image quality is improved. Can do.
[0110]
By the way, normally, a predetermined peripheral speed difference is set between the peripheral speed of the photosensitive drum 16 and the peripheral speed of the developing roller 19, and the peripheral speed of the developing roller 19 is made higher than the peripheral speed of the photosensitive drum 16. As a result, the toner on the developing roller 19 easily moves to the photosensitive drum 16, so that a sufficient amount of toner becomes a lubricant, and the oligomer on the surface of the photosensitive drum 16 is sufficiently scraped off.
[0111]
Next, a third embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st Embodiment, the description is abbreviate | omitted by providing the same code | symbol.
[0112]
FIG. 9 is a block diagram of an image forming apparatus according to the third embodiment of the present invention.
[0113]
In this case, the carrier rotation processing means (not shown) of the main CPU 81 as the main control unit includes a drum count determination processing means 86 and a motor rotation speed change processing means 89, and the drum count determination processing means 86 is a drum count determination processing. Based on the drum count value DC, the reference drum count value DC0, and the table value DCt, it is determined whether or not the image forming operation start condition is satisfied based on whether or not the expression (1) is satisfied, and the motor rotation The speed change processing means 89 performs a motor rotation speed change process, and rotates the photosensitive drum 16 while the carrier rotation process for preventing the formation of horizontal stripes in the color image is performed. The rotation speed of the motor, that is, the motor rotation speed is changed. When the motor is a stepping motor, the motor rotation speed can be changed by changing the voltage applied to the stepping motor.
[0114]
Next, the operation of the image forming apparatus having the above configuration will be described.
[0115]
FIG. 10 is a flowchart showing the operation of the image forming apparatus in the third embodiment of the present invention, and FIG. 11 is a diagram showing the relationship between the rotational speed of the photosensitive drum and the standby time in the third embodiment of the present invention. It is.
[0116]
First, when the main power switch 82 (FIG. 9) is turned on, or when the main power switch 82 is already turned on and a print command is sent from the information equipment terminal 83, the carrier rotation processing means. Starts the carrier rotation process.
[0117]
In the present embodiment, as in the first embodiment, when the main power switch 82 is turned on, the carrier rotation processing means sends a signal to the drum count table recording means 85 to record the drum count table. The table value DCt is read from the means 85. In this case, the table value DCt is set to 25 which is the maximum value.
[0118]
On the other hand, when the main power switch 82 is already turned on and a printing command is sent from the information equipment terminal 83, the carrier rotation processing means reads the standing time TC from the time counter 84 and records the drum count table. The table value DCt corresponding to the leaving time TC is read from the means 85. When there is no table value DCt corresponding to the standing time TC, the carrier rotation processing means immediately stops the carrier rotation processing and does not perform the carrier rotation processing.
[0119]
Next, the carrier rotation processing means reads the drum count value before the photosensitive drum 16 starts rotating from the drum counter 87 as the reference drum count value DC0, and operates the motor driving unit 88 to set in advance. The motor is driven at the motor rotation speed Nm for the carried carrier rotation processing, and the rotation of the photosensitive drum 16 is started.
[0120]
Next, the drum count determination processing means 86 reads the drum count value DC incremented with the rotation of the photosensitive drum 16, and based on the drum count value DC, the reference drum count value DC0, and the table value DCt, Whether or not the image forming operation start condition is satisfied is determined based on whether or not the expression (1) is satisfied.
[0121]
When the image forming operation start condition is satisfied, the carrier rotation process is terminated, and the image forming processing unit (not shown) of the main CPU 81 performs the image forming process and starts the image forming operation. At this time, the main CPU 81 resets the drum counter 87 and sets the reference drum count value DC0 to the drum count value DC.
[0122]
As described above, when the carrier rotation process is started, the drum count value DC is incremented with the rotation of the photosensitive drum 16, and the drum count value DC, the reference drum count value DC0, and the table value are increased. Whether or not the image forming operation start condition is satisfied is determined based on DCt, and the image forming operation is started when the image forming operation start condition is satisfied. Therefore, the standby time from the start of rotation of the photosensitive drum 16 for the carrier rotation processing to the start of the image forming operation varies in accordance with the table value DCt and the rotation speed of the photosensitive drum 16. . For example, when the table value DCt is 20, as shown in FIG. 11, when the rotational speed of the photosensitive drum 16 is 4 [RPM], the standby time is 5 [minutes] and the rotational speed is 16 When it is [RPM], the standby time is 1.25 [minute], and when the rotational speed is 20 [RPM], the standby time is 1 [minute].
[0123]
Accordingly, the lower the rotational speed of the photosensitive drum 16, the longer the standby time and the lower the print throughput. Therefore, in the present embodiment, when the rotation of the photosensitive drum 16 is started, the motor rotation speed changing unit 89 changes the motor rotation speed to the motor rotation speed Nm. The motor rotation speed Nm is set so that the rotation speed of the photosensitive drum 16 is higher than the rotation speed of the photosensitive drum 16 during the image forming operation, that is, the printing speed.
[0124]
Note that if the motor rotation speed is increased, the motor becomes larger and the cost increases. Therefore, the motor rotation speed Nm is set in consideration of the motor dimensions, cost, and the like.
[0125]
Thus, before the image forming operation is started, the motor is driven at the motor rotation speed Nm and the photosensitive drum 16 is rotated by a predetermined number of rotations, so that horizontal stripes are formed in the image. The image quality can be improved.
[0126]
In addition, since the motor rotation speed Nm during the carrier rotation process is set so that the rotation speed of the photosensitive drum 16 is higher than the printing speed, the standby time can be shortened and the printing throughput can be shortened. Can be improved.
[0127]
Next, a flowchart will be described.
Step S11: It is determined whether or not the main power switch 82 is turned on. If the main power switch 82 is turned on, the process proceeds to step S14. If the main power switch 82 is not turned on, the process proceeds to step S12.
Step S12 It waits for a print command to be sent from the information equipment terminal 83.
Step S13 Read the standing time TC.
Step S14: The table value DCt is read out.
Step S15: The reference drum count value DC0 is read.
Step S16: The motor rotation speed is changed.
Step S17 The rotation of the photosensitive drum 16 is started.
Step S18 The drum count value DC is read.
Step S19: It is determined whether the table value DCt is smaller than a value obtained by subtracting the reference drum count value DC0 from the drum count value DC. If the table value DCt is smaller than the value obtained by subtracting the reference drum count value DC0 from the drum count value DC, the process proceeds to step S20. If the table value DCt is equal to or greater than the value obtained by subtracting the reference drum count value DC0 from the drum count value DC. The process returns to step S18.
Step S20 The image forming operation is started, the drum counter 87 is reset, and the process is terminated.
[0128]
Next, a fourth embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st Embodiment, the description is abbreviate | omitted by providing the same code | symbol.
[0129]
FIG. 12 is a conceptual diagram of an image forming apparatus according to the fourth embodiment of the present invention, and FIG. 13 is a time chart showing the operation of the image forming apparatus according to the fourth embodiment of the present invention.
[0130]
In the figure, reference numeral 18 denotes a developing device as a developing means, and the developing device 18 is provided with a developing roller 19 as a toner carrier and a rotating member, a developing blade 55, and a toner supply roller 56 as a toner supply means. The A DB bias power source 91 for applying a DB bias voltage to the developing roller 19 and an SP bias power source 92 for simultaneously applying an SP bias voltage to the developing blade 55 and the toner supply roller 56 are connected. The developing blade 55 and the toner supply roller 56 are connected by a metal contact 93.
[0131]
In FIG. 13, the rotation of the photosensitive drum 16 as the image carrier in the carrier rotation process is started at the timing t1, the image forming operation is started at the timing t2, and the cleaning sequence is performed until the timing t3. Is called. Meanwhile, the motor is driven at timing t1, stopped at timing t3, and the charging voltage, DB bias voltage, SP bias voltage, cleaning bias voltage, and transfer voltage are changed as shown in the figure.
[0132]
By the way, in this embodiment, the longer the standing time, the greater the number of rotations that the photosensitive drum 16 is rotated in the carrier rotation process, and the longer the standby time.
[0133]
Therefore, when the DB bias voltage and the SP bias voltage are changed as shown by the broken lines in the figure, the developing roller 19 depends on the types of the toner 57, the developing roller 19, the toner supply roller 56, and the like used, and the usage environment. The potential of the thin layer of the toner 57 (hereinafter referred to as “toner layer potential”) becomes high, and the toner 57 adheres to the photosensitive drum 16 to cause a stain phenomenon. This is because the toner 57 is rubbed more than usual on the developing roller 19 and the charge amount of the toner 57 increases as the number of rotations of the photosensitive drum 16 in the carrier rotation process increases. In the meantime, the toner 57 continues to be supplied from the toner supply roller 56 to the developing roller 19, and the absolute amount of the toner 57 increases.
[0134]
Therefore, the voltage applied to the developing roller 19 and the voltage applied to the developing blade 55 and the toner supply roller 56 are lowered to prevent the toner layer potential from increasing.
[0135]
In the present embodiment, the DB bias voltage and the SP bias voltage are set to 0 (zero) from timing t1 to timing t2 and until a predetermined time elapses from timing t2. Note that the DB bias voltage and the SP bias voltage can be made lower than the DB bias voltage and the SP bias voltage during the image forming operation.
[0136]
Then, as shown in FIG. 13, a cleaning sequence is performed from timing t2 to timing t3, and the cleaning bias voltage is set to a negative polarity for a predetermined time. As a result, the toner 57 adhering to the charging roller 17 serving as the charging unit, the cleaning roller 58 serving as the cleaning unit, the transfer roller 14 serving as the transfer unit, and the like can be removed and collected by the developing device 18. Subsequently, after the motor is stopped and the photosensitive drum 16 is stopped, the image forming operation is started.
[0137]
As described above, in this embodiment, the DB bias voltage and the SP bias voltage are set to 0 or lower than those during the image forming operation until the image forming operation is started. It can be prevented from becoming high. Therefore, the toner 57 does not adhere to the photosensitive drum 16, the occurrence of the smear phenomenon can be prevented, and the image quality can be improved.
[0138]
Next, a fifth embodiment of the present invention will be described. In addition, about the thing which has the same structure as 4th Embodiment, the description is abbreviate | omitted by providing the same code | symbol.
[0139]
FIG. 14 is a conceptual diagram of an image forming apparatus according to the fifth embodiment of the present invention, and FIG. 15 is a time chart showing the operation of the image forming apparatus according to the fifth embodiment of the present invention.
[0140]
In this case, in order to scrape off the toner 57 remaining on the photosensitive drum 16 as the image carrier after the transfer, a cleaning blade 59 as a cleaning unit is provided in contact with the photosensitive drum 16.
[0141]
As shown in FIG. 15, the photosensitive drum 16 is rotated by a predetermined number of rotations while the carrier rotation process from the timing t11 to the timing t16 is performed, and subsequently, from the timing t16 to the timing t17. In the meantime, the cleaning sequence is performed.
[0142]
The toner adhesion processing means (not shown) of the main CPU 81 is positioned between the developing roller 19 as the rotating body and the LED head 13 as the exposure means when left unattended between the timing t11 and the timing t16 that change depending on the leaving time. Based on the relationship, the time τ1 until the oligomer adhesion position on the photosensitive drum 16 at the timing t11 reaches the exposure portion where the photosensitive drum 16 and the LED head 13 face each other is calculated, and the time τ1 from the timing t11 is calculated. When the time elapses, exposure is performed only at the oligomer adhesion position from timing t12 to timing t13, and the toner 57 is adhered to the oligomer adhesion position.
[0143]
Then, the transfer voltage is set to 0 between timing t14 and timing t15 when the oligomer adhesion position passes through the transfer portion so that the toner 57 adhered to the oligomer adhesion position is not transferred by the transfer roller 14. . The transfer voltage can be a negative value. Although not shown in FIG. 15, during the rotation of the carrier, exposure by the LED head 13 can be performed each time the photosensitive drum 16 is rotated, and the transfer voltage can be set to zero. .
[0144]
At timing t16, when the oligomer attachment position reaches the cleaning portion where the photosensitive drum 16 and the cleaning blade 59 face each other, the cleaning blade 59 scrapes off the toner 57 attached to the oligomer attachment position. In this case, since the oligomer is lubricated by the toner 57, the oligomer can be efficiently removed together with the toner 57.
[0145]
Since the scraped toner 57 is discarded, it is not preferable that the toner 57 is excessively consumed. Therefore, exposure by the LED head 13 is performed in a 1by1 pattern with high resolution. Also, for example, when the image forming apparatus is left for 10 minutes and then the image forming operation is started and printing is performed, the image is displayed when the toner 57 is attached to the oligomer attaching position and when the toner 57 is not attached. Comparing the drum count values until the horizontal streaks disappeared, the number of printed sheets 21 is about 3 to 5 less when the toner 57 is attached to the oligomer attachment position than when the toner 57 is not attached. can do.
[0146]
Next, a sixth embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st Embodiment, the description is abbreviate | omitted by providing the same code | symbol.
[0147]
FIG. 16 is a time chart showing the operation of the image forming apparatus according to the sixth embodiment of the present invention.
[0148]
In this case, while the carrier rotation processing from timing t21 to timing t22 is being performed, the photosensitive drum 16 (FIG. 2) as the image carrier is rotated by a predetermined number of rotations, and subsequently from timing t22. A cleaning sequence is performed until timing t24. Then, during the period from timing t23 immediately before the photosensitive drum 16 is stopped to timing t24, the SP bias voltage is increased by −100 [V] or more (larger in absolute value) than the value during the image forming operation. Therefore, it is possible to prevent the toner 57 on the developing roller 19 as a rotating body from adhering to the oligomer adhesion position. At timing t21, the charging voltage is set to -1300 [V], the DB bias voltage is set to -250 [V], the SP bias voltage is set to -450 [V], and the transfer voltage is set to +1000 [V]. The transfer voltage is set to -1000 [V] for a predetermined time. The DB bias voltage is set to −250 [V] and the SP bias voltage is set to −550 [V] from timing t23 to timing t24. Note that the value of each voltage is changed depending on the type of the toner 57 used, the developing roller 19, the toner supply roller 56 as a toner supply unit, and the like.
[0149]
If the time from the timing t23 to the timing t24 is long, the amount of the toner 57 on the developing roller 19 is excessively increased, and the toner 57 adheres to the photosensitive drum 16 to cause a stain phenomenon. The printing throughput of the apparatus is reduced.
[0150]
Therefore, the time between the timing t23 and the timing t24 is such that the photosensitive drum 16 can be moved by a distance equal to or larger than the contact width (nip width) between the developing roller 19 and the photosensitive drum 16 at least at the oligomer adhesion position. It is preferable to set the time required for the developing roller 19 to make one rotation at the maximum.
[0151]
Then, the image forming operation is started at timing t25, the photosensitive drum 16 is rotated, and when the oligomer adhesion position reaches the transfer portion at timing t26, the transfer voltage is changed to a negative value from timing t26 to timing t27. It is changed to a positive value at timing t27. Note that the time from timing t23 to timing t24 is equal to the time from timing t26 to timing t27. Therefore, even if the toner 57 on the developing roller 19 adheres to the photosensitive drum 16, the toner 57 on the photosensitive drum 16 does not adhere to the transfer roller 14, and the cleaning roller 58 or the cleaning blade 59 ( 14), the toner 57 can be collected.
[0152]
For example, when printing is performed after the image forming apparatus is left for 10 minutes, when the SP bias voltage is increased by −250 [V] from timing t23 to timing t24, It can be seen that the horizontal streaks formed in the image disappear. In addition, when the image forming apparatus is left for 1 [day] and then the image forming operation is started and printing is performed, the SP bias voltage is increased by −250 [V] from timing t23 to timing t24. When the drum count value until the horizontal streaks formed in the image disappear is compared with the case where it is not increased, the number of printed sheets of paper 21 when the value is increased by −250 [V] is higher than when the value is not increased. About 5 to 7 sheets can be reduced.
[0153]
As described above, since the SP bias voltage is set higher than the value during the image forming operation from the timing t23 immediately before the photosensitive drum 16 is stopped to the timing t24, the toner 57 on the developing roller 19 is at the oligomer adhesion position. Adhesion can be prevented.
[0154]
Next, a seventh embodiment of the present invention will be described.
[0155]
FIG. 17 is a block diagram showing the main part of the control unit of the color image forming apparatus according to the seventh embodiment of the present invention.
[0156]
As shown in the figure, the control circuit 61 includes an intermittent operation control unit 95, a counter 96, a register 97, a comparison unit 98, and a motor control unit 99. The motor control unit 99 sends an instruction to the motor drive circuit 72. To drive the motor.
[0157]
In this case, while the color image forming apparatus 11 (FIGS. 6 and 7) is left for a long time without being printed, the standing time is counted by the counter 96, and when one hour has elapsed from the start of timing, The carrier rotation processing means (not shown) of the intermittent operation control unit 95 drives the motors 28 that drive the image forming units 12Y, 12M, 12C, and 12BK via the motor drive circuit 72, and each photosensitive member as an image carrier. The body drum 16, each charging roller 17 as a charging unit, and each developing roller 19 as a rotating body are rotated about 2 mm at a distance on the outer peripheral surface. During this time, the paper feed mechanism 36, the conveyance belt 20 as the recording medium conveyance member, the power supply system, and the like are not operated.
[0158]
Therefore, in the carrier rotation process, the photosensitive drum 16 is rotated about 2 [mm] per hour. For example, when the diameter of the photosensitive drum 16 is 30 [mm], the photosensitive drum 16 is It is rotated once over 47 hours (about 2 days). Thus, in the carrier rotation process, the photosensitive drum 16 is rotated so that the contact position between the photosensitive drum 16 and the developing roller 19 changes with time, and the photosensitive drum 16 and the developing roller 19 are moved. The time left in contact is only one hour. As a result, oligomers as foreign matters deposited from the developing roller 19 are attached little by little over the entire surface of the photosensitive drum 16, so that it is possible to prevent horizontal stripes from being formed in the color image.
[0159]
Further, since the idling amount of each photosensitive drum 16, each charging roller 17, and each developing roller 19 in the image forming units 12Y, 12M, 12C, and 12BK is small, the reliability of the color image forming apparatus 11 is not lowered. .
[0160]
Note that the toner on the developing roller 19 slightly adheres to the photosensitive drum 16 due to a slight rotation of the photosensitive drum 16, but the toner on the photosensitive drum 16 does not move because the conveyor belt 20 is not running. 59 is removed and accumulated on the conveyor belt 20. Therefore, the oligomer can also be removed.
[0161]
As described above, in the present embodiment, in the carrier rotation process, the photosensitive drum 16 is rotated little by little without causing the conveyor belt 20 to travel, so that the oligomer deposited from the developing roller 19 is not removed from the photosensitive drum 16. It is possible to prevent the formation of horizontal streaks on the color image. Further, since the oligomer adhering to the photosensitive drum 16 is removed by the conveying belt 20 and the cleaning blade 59, it is possible to further prevent the formation of horizontal stripes in the color image.
[0162]
In the present embodiment, the photosensitive drum 16 is rotated about 2 [mm] per hour, but the power is on and the printer is left without printing, that is, When the non-printing state continues for a predetermined time, or when the power is off and the state of being left without printing is continued for a predetermined time, the photosensitive drum 16 and the developing roller 19 are exposed to different positions. The body drum 16 can also be rotated.
[0163]
Next, the operation of the control circuit 61 will be described.
[0164]
The intermittent operation control unit 95 is connected to the counter 96, the comparison unit 98, the register 97, and the motor control unit 99, and performs control for rotating the photosensitive drum 16 intermittently. The counter 96 measures the time for intermittently rotating the photosensitive drum 16, receives the counter reset signal a and the counter clock signal b from the intermittent operation control unit 95, and sends the count value e to the comparison unit 98. In the counter 96, the count value e is reset by receiving the counter reset signal a, and then the count value e is incremented according to the counter clock signal b.
[0165]
The count value e represents the duration when the photosensitive drum 16 and the developing roller 19 are stopped. For example, in the counter clock signal b sent from the intermittent operation control unit 95 to the counter 96, the count value e is 100 [ms]. When there is one pulse input, if the count value e (8CA0 [H]) for 36000 pulses is counted, one hour has passed.
[0166]
In the intermittent operation control unit 95, a time for stopping the photosensitive drum 16 and the developing roller 19 is set in advance, and a signal c corresponding to the time is sent to the register 97. Then, the register 97 generates a set value d corresponding to the signal c and sends the set value d to the comparison unit 98. The comparison unit 98 compares the count value e with the set value d, and when the count value e becomes equal to or greater than the set value d, generates the interrupt signal f and sends the interrupt signal f to the intermittent operation control unit 95. .
[0167]
When receiving the interrupt signal f, the intermittent operation control unit 95 sends an instruction to the motor control unit 99 to rotate the photosensitive drum 16 and the developing roller 19 by a predetermined amount. The motor control unit 99 sends the instruction to the motor drive circuit 72, drives the motor 28 for a preset time, and then stops it. Accordingly, the photosensitive drum 16 is rotated by a predetermined amount and stopped. The motor control unit 99 notifies the intermittent operation control unit 95 that the rotation of the photosensitive drum 16 is stopped.
[0168]
Subsequently, when the motor control unit 99 notifies that the rotation of the photosensitive drum 16 is stopped, the intermittent operation control unit 95 sends the counter reset signal a and the counter clock signal b to the counter 96 again.
[0169]
In this embodiment, the conveyance belt 20 is prevented from traveling, but the traveling of the conveyance belt 20 can be synchronized with the rotation of the photosensitive drum 16. In this case, it is possible to prevent the photosensitive drum 16 from being worn.
[0170]
Next, an eighth embodiment of the present invention will be described. In addition, about the thing which has the same structure as 2nd Embodiment, the description is abbreviate | omitted by providing the same code | symbol.
[0171]
18 is a perspective view of the image forming unit placed in the operating position in the eighth embodiment of the present invention, and FIG. 19 is a perspective view of the image forming unit placed in the retracted position in the eighth embodiment of the present invention. FIG.
[0172]
In the figure, reference numeral 24 denotes a frame of each of the image forming units 12Y (FIG. 6), 12M, 12C (FIG. 7), and 12BK. 24 a is formed, and the protrusion 24 a is rotatably engaged with a guide groove (not shown) formed on the main body of the color image forming apparatus 11. Accordingly, the image forming units 12Y, 12M, 12C, and 12BK can be swung around the protrusion 24a. Further, a protruding plate portion 24 b is formed at the downstream end portion of the frame 24 in the conveyance direction of the paper 21.
[0173]
Further, camshafts 22 are rotatably supported with respect to the main body of the color image forming apparatus 11 on the downstream side of the image forming units 12Y, 12M, 12C, and 12BK in the conveyance direction of the paper 21, respectively. An eccentric cam 23 is fixed in the vicinity of both ends of the camshaft 22 so as to face the protruding plate portion 24b.
[0174]
Each frame 24 is pressed downward by the spring 17a through the LED heads 13Y, 13M, 13C, 13BK as exposure means. When the camshaft 22 is rotated, the eccentric cam 23 rotates to push up the protruding plate portion 24b, resist the urging force of the spring 17a, and each frame 24 has an amount of eccentricity of the eccentric cam 23 with the protrusion 24a serving as a fulcrum. Rotate clockwise.
[0175]
The camshaft 22 is provided with a gear 25 via a one-way bearing 22a, and the gear 25 is fixed to a rotating shaft of a motor 28 as a driving means for contact / separation via a two-stage gear 26. Is engaged with the motor gear 27. On the other hand, a gear 16a is disposed at the end of the photosensitive drum 16 as an image carrier, and the two-stage gear 26 and the gear 16a are selectively meshed with each other. The camshaft 22, the one-way bearing 22a, the eccentric cam 23, the gear 25, the two-stage gear 26, the motor gear 27, and the motor 28 constitute an image forming unit moving unit.
[0176]
By the way, normally, the image forming units 12Y, 12M, 12C, and 12BK are placed in an operating position as shown in FIG. 18, and the two-stage gear 26 and the gear 16a are engaged with each other at the operating position. The motor 28 is driven in the positive direction. As a result, the photosensitive drum 16 is rotated in the arrow a direction at a predetermined speed. At this time, although the gear 25 rotates, the camshaft 22 and the eccentric cam 23 do not rotate because the one-way bearing 22a idles. A spring 23a is disposed between the eccentric cam 23 and the main body of the color image forming apparatus 11, and the spring 23a moves the eccentric cam 23 so that the eccentric portion 23b of the eccentric cam 23 always faces in the direction of arrow e. Energize.
[0177]
Further, a gear is provided at the end of the developing roller 19 as a rotating member by fitting with a gear 16 a provided at the end of the photosensitive drum 16, and as the photosensitive drum 16 rotates. The developing roller 19 rotates. At this time, the gear 16 a disposed at the end of the photosensitive drum 16 is made larger than the photosensitive drum 16, and the gear disposed at the end of the developing roller 19 is made smaller than the developing roller 19, thereby The peripheral speed of the drum 16 and the peripheral speed of the developing roller 19 can be made different. In the present embodiment, the peripheral speed of the developing roller 19 is made higher (1.28 times) than the peripheral speed of the photosensitive drum 16.
[0178]
When the motor 28 is driven in the opposite direction as the carrier rotation process starts, the one-way bearing 22a is locked and the camshaft 22 and the eccentric cam 23 are moved against the urging force of the spring 23a. Rotated. At this time, as shown in FIG. 19, the image forming units 12Y, 12M, 12C, and 12BK are rotated clockwise with the protrusion 24a as a fulcrum and placed in the retracted position. The meshing between the step gear 26 and the gear 16a is released.
[0179]
A slit disk 29 is fixed to the camshaft 22, and a slit 29 a is formed in the slit disk 29. The position of the eccentric cam 23 can be known by detecting the slit 29a by the photosensor 30. Note that the slit 29a is in a position detected by the photosensor 30 when each of the image forming units 12Y, 12M, 12C, and 12BK is placed at the retracted position.
[0180]
Each frame 24 is formed with a window hole 13a for allowing the LED heads 13Y, 13M, 13C, and 13BK to face the respective photosensitive drums 16, and the LED holes 13Y, 13M, and 13C are formed by the window hole 13a. , 13BK can be positioned with respect to the image forming units 12Y, 12M, 12C, 12BK. When the carrier rotation process is completed, the image forming units 12Y, 12M, 12C, and 12BK are rotated clockwise around the protrusions 24a and placed in the operating positions.
[0181]
In this case, while the carrier rotation processing is performed, the image forming units 12Y, 12M, 12C, and 12BK are placed at the retracted positions, and the photosensitive drum 16 and the conveyance belt 20 are not brought into contact with each other. Therefore, it is possible to prevent the photosensitive drum 16 from being worn.
[0182]
In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.
[0183]
【The invention's effect】
As described above in detail, according to the present invention, in the image forming apparatus, the carrier that rotates the image carrier in accordance with the leaving time when the image forming apparatus is left without being printed. Rotation processing is performed.
An image carrier, a toner carrier that is provided in constant contact with the image carrier, and supplies toner to the image carrier, toner supply means for supplying toner to the toner carrier, and the carrier In the rotation process, the voltage applied to the toner carrier and the voltage applied to the toner supply means are set to 0 [V], and the image is carried by the number of rotations increased as the standing time is increased without forming an image. And a carrier rotation processing means for rotating the body.
[0184]
In this case, when the image forming apparatus is left unattended, before the image forming operation is started, the image carrier is rotated in accordance with the leaving time, so that the foreign matter adhering to the surface of the image carrier is smoothed. And can be dispersed in other rotating bodies.
Therefore, the exposure by the exposure means is not blocked, and the toner does not adhere to foreign matter. As a result, horizontal stripes such as white stripes and black stripes are not formed in the image, and the image quality can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a conceptual diagram of an image forming apparatus according to the first embodiment of the present invention.
FIG. 3 is a diagram illustrating a relationship between a standing time of the image forming apparatus according to the first embodiment of the present invention and a drum count value until a horizontal stripe disappears.
FIG. 4 is a diagram illustrating a relationship between a leaving time of the image forming apparatus and a table value of a drum count table according to the first embodiment of the present invention.
FIG. 5 is a flowchart showing an operation of the image forming apparatus according to the first embodiment of the present invention.
FIG. 6 is a first conceptual diagram of a color image forming apparatus according to a second embodiment of the present invention.
FIG. 7 is a second conceptual diagram of a color image forming apparatus according to a second embodiment of the present invention.
FIG. 8 is a block diagram of a control unit of a color image forming apparatus according to a second embodiment of the present invention.
FIG. 9 is a block diagram of an image forming apparatus according to a third embodiment of the present invention.
FIG. 10 is a flowchart showing an operation of the image forming apparatus according to the third embodiment of the present invention.
FIG. 11 is a diagram showing the relationship between the rotational speed of the photosensitive drum and the standby time in the third embodiment of the present invention.
FIG. 12 is a conceptual diagram of an image forming apparatus according to a fourth embodiment of the present invention.
FIG. 13 is a time chart illustrating the operation of the image forming apparatus according to the fourth embodiment of the present invention.
FIG. 14 is a conceptual diagram of an image forming apparatus according to a fifth embodiment of the present invention.
FIG. 15 is a time chart showing the operation of the image forming apparatus in the fifth embodiment of the present invention.
FIG. 16 is a time chart illustrating an operation of the image forming apparatus according to the sixth embodiment of the present invention.
FIG. 17 is a block diagram illustrating a main part of a control unit of a color image forming apparatus according to a seventh embodiment of the present invention.
FIG. 18 is a perspective view of an image forming unit placed in an operating position according to an eighth embodiment of the present invention.
FIG. 19 is a perspective view of an image forming unit placed in a retracted position according to an eighth embodiment of the present invention.
[Explanation of symbols]
11 Color image forming apparatus
12Y, 12M, 12C, 12BK Image forming unit
14, 14Y, 14M, 14C, 14BK Transfer roller
16 Photosensitive drum
17 Charging roller
19 Developing roller
20 Conveyor belt
57 Toner
58 Cleaning roller
61 Control circuit
81 Main CPU

Claims (1)

(A) In an image forming apparatus that performs a carrier rotation process for rotating an image carrier in accordance with a leaving time when the image forming apparatus is left without printing.
(B) an image carrier;
(C) a toner carrier that is disposed in constant contact with the image carrier and supplies toner to the image carrier;
(D) toner supply means for supplying toner to the toner carrier;
(E) in the carrying body rotation process, the voltage applied to the toner carrying member, and a voltage applied to the toner supply means in the 0 [V], without forming the images, increases as the standing time is longer An image forming apparatus comprising: a carrier rotation processing unit that rotates the image carrier by the rotated number of rotations .

Images