JP5909879B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a developing roller that supplies a developer to a photoreceptor.

  2. Description of the Related Art Conventionally, an image forming apparatus is known that includes a photosensitive drum on which an electrostatic latent image is formed, a toner storage chamber that stores toner, and a developing roller that supplies toner in the toner storage chamber to the photosensitive drum (patent). Reference 1).

JP 2000-250378 A (FIG. 1)

  In recent years, it has been desired to increase the rotation speed of the developing roller and the photosensitive drum in order to increase the printing speed. However, if the rotation speed of the developing roller or the like is increased in this way, a phenomenon may occur in which the toner cannot be held by the developing roller and the toner is ejected from the nip portion between the developing roller and the photosensitive drum. It was. Specifically, this phenomenon does not occur when the toner in the toner storage chamber is not deteriorated, but occurs when the toner deteriorates and the fluidity is deteriorated.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of suppressing the ejection of toner (developer) accompanying an increase in printing speed.

In order to solve the above problems, an image forming apparatus according to the present invention controls a photosensitive member on which an electrostatic latent image is formed, a developing roller that supplies a developer to the photosensitive member, and a rotation speed of the developing roller. And a control device.
Then, the control device decreases the rotation speed of the developing roller according to an increase in a parameter corresponding to the total rotation amount of the developing roller, and decreases the peripheral speed ratio of the developing roller with respect to the photosensitive member. The ratio reduction control is executed.

  According to such an image forming apparatus, when the parameter corresponding to the total rotation amount of the developing roller increases and the deterioration of the developer progresses, the rotating speed of the developing roller decreases and the peripheral speed ratio of the developing roller becomes Therefore, the developer can be prevented from being ejected from the nip portion between the developing roller and the photosensitive member.

Further, the image forming apparatus includes a humidity measuring unit that measures humidity, and the control device determines whether or not the humidity measured by the humidity measuring unit is smaller than a first threshold value. run the speed ratio decrease control, if not smaller Ru is configured not to execute the peripheral speed ratio decreasing control.

  According to this, since the peripheral speed ratio reduction control is not executed under an environment where the humidity is not low (an environment where the developer fluidity is hardly deteriorated), the photosensitive member is exposed to the photosensitive member from the developing roller which is generated as the peripheral speed ratio decreases. Accordingly, it is possible to suppress a decrease in the amount of developer conveyed to the photosensitive member, and to suppress a decrease in developer concentration on the photoreceptor.

In addition, the control device may change a developing bias applied to the developing roller when the peripheral speed ratio of the developing roller is changed from the first peripheral speed ratio to a second peripheral speed ratio smaller than the first peripheral speed ratio. the absolute value Ru is configured to be larger than the previous value.

  According to this, even if the developer transport amount decreases by lowering the peripheral speed ratio from the first peripheral speed ratio to the second peripheral speed ratio, the developer transport is increased by increasing the absolute value of the developing bias. Since the amount can be increased, a decrease in developer concentration on the photoreceptor can be suppressed.

Further, the control device, the parameter Ru is configured to execute the peripheral speed ratio decreasing control on the basis of the peripheral speed ratio is gradually becomes smaller such peripheral speed ratio map with increasing.

  According to this, since it is possible to obtain an appropriate peripheral speed ratio according to the total rotation amount of the developing roller, it is possible to set the developer conveyance amount and density to appropriate values according to the total rotation amount.

In addition, when the humidity measured by the humidity measuring unit is not smaller than the first threshold, the control device changes the developing bias applied to the developing roller with a predetermined inclination as the parameter increases. When the developing bias is determined based on one map and the humidity measured by the humidity measuring unit is smaller than the first threshold, the developing bias applied to the developing roller is increased from the predetermined slope as the parameter increases. Ru is configured to determine the developing bias on the basis of the second map also is varied in a large tilt of the absolute value.

  According to this, when the humidity is smaller than the first threshold value, the developing bias is determined based on the second map having a larger slope than the first map, so that the absolute value of the developing bias increases and the peripheral speed ratio is increased. It is possible to suppress a decrease in developer density by suppressing a decrease in the developer conveyance amount that occurs with the decrease in the developer.

  Further, the parameter may be a total number of printed sheets.

  According to this, since the rotation speed of the developing roller can be controlled based on the total number of prints that can be grasped from a print command or the like, a sensor for detecting the total rotation amount of the developing roller becomes unnecessary, and the cost can be reduced. it can.

  Further, the image forming apparatus includes a drive source for rotating the developing roller, two transmission mechanisms having different speed transmission ratios, and an output unit coupled to the drive source via the two transmission mechanisms. A one-way clutch provided between one of the two transmission mechanisms and the output unit; and an electromagnetic clutch provided between the other transmission mechanism having a smaller speed transmission ratio than the one transmission mechanism and the output unit. The control device may be configured to control the electromagnetic clutch to switch the transmission mechanism so as to reduce the rotation speed of the developing roller.

  According to this, since the rotation speed of the developing roller can be changed without changing the rotation speed of the drive source, the drive source can be shared with other members (photoconductors, etc.), and the cost can be reduced. it can.

  According to the present invention, it is possible to suppress the ejection of the developer accompanying the increase in the printing speed.

It is a figure which shows the laser printer which concerns on embodiment of this invention. It is a figure which shows two transmission mechanisms and a peripheral speed switching mechanism. It is sectional drawing which shows a peripheral speed switching mechanism, (a) which shows the state from which the driving force is transmitted to the output gear from the transmission mechanism for slow peripheral speeds, and the driving force to the output gear from the transmission mechanism for normal peripheral speeds It is a figure (b) showing the state where is transmitted. It is a flowchart which shows operation | movement of a control apparatus. FIG. 6 is a map (a) showing the relationship between the peripheral speed ratio and the total number of printed sheets, and a map (b) showing the relationship between the developing bias and the total number of printed sheets when toner whose charge amount does not change due to deterioration is adopted. The map (a) showing the relationship between the peripheral speed ratio and the total number of printed sheets, the map (b) showing the relationship between the developing bias and the total number of printed sheets when the toner whose charge amount decreases due to deterioration is adopted, and the deterioration It is a map (c) showing the relationship between the developing bias and the total number of printed sheets when toner with increasing charge amount is employed. A map (a) showing a mode in which the peripheral speed ratio is gradually reduced as the total number of printed sheets increases, and a map (b) showing a form in which the developing bias when performing the peripheral speed ratio reduction control is gradually reduced in accordance with the total number of printed sheets. ). A map (a) showing a mode in which the peripheral speed ratio is gradually lowered as the total number of printed sheets increases, and a map (b) showing the relationship between the development bias and the total number of printed sheets when toner whose charge amount decreases due to deterioration is adopted. ) And a map (c) showing the relationship between the developing bias and the total number of printed sheets when a toner whose charge amount increases due to deterioration is employed.

<Overall configuration of laser printer>
Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, first, the overall configuration of a laser printer as an example of an image forming apparatus will be described, and then the features of the present invention will be described in detail.

  In the following description, the direction will be described with reference to the user when using the laser printer. That is, in FIG. 1, the left side toward the paper surface is “front side (front side)”, the right side toward the paper surface is “rear side (back side)”, the back side toward the paper surface is “left side”, and it faces the paper surface. Let the near side be the “right side”. In addition, the vertical direction toward the page is defined as the “vertical direction”.

  As shown in FIG. 1, the laser printer 1 includes an apparatus main body 2, a feeder unit 3, an image forming unit 4, a control device 100, and a drive unit 20. The control device 100 and the drive unit 20 will be described in detail later.

  The feeder unit 3 includes a paper feed tray 31 that is detachably attached to the lower portion of the apparatus main body 2 and a paper feed mechanism 32 that feeds the paper P in the paper feed tray 31 toward the image forming unit 4. Yes.

  The image forming unit 4 includes a scanner unit 5, a process cartridge 6, a transfer roller TR, and a fixing device 7.

  The scanner unit 5 is provided in an upper part in the apparatus main body 2 and includes a laser light emitting unit, a polygon mirror, a lens, a reflecting mirror, and the like (not shown). The scanner unit 5 irradiates a laser beam on a surface of a photosensitive drum 81 as an example of a photosensitive member described later by high-speed scanning.

  The process cartridge 6 is detachable from the apparatus main body 2, and includes a drum cartridge 8 having a photosensitive drum 81, a toner as an example of a developer, and a developing cartridge including a developing roller 91 that contacts the photosensitive drum 81. 9 and. The developing cartridge 9 can be attached to and detached from the drum cartridge 8. In the present embodiment, toner having a property that the charge amount becomes substantially constant even when deteriorated is adopted.

  In the process cartridge 6, the surface of the rotating photosensitive drum 81 is uniformly charged by a charger (not shown) and then exposed by high-speed scanning of a laser beam from the scanner unit 5. As a result, the potential of the exposed portion is lowered, and an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 81.

  Next, after the toner in the developing cartridge 9 is carried by the developing roller 91, the toner on the developing roller 91 is supplied to the electrostatic latent image on the photosensitive drum 81, and a toner image is formed on the surface of the photosensitive drum 81. The

  Thereafter, the paper P is conveyed between the photosensitive drum 81 and the transfer roller TR, whereby the toner image carried on the surface of the photosensitive drum 81 is transferred onto the paper P.

  The fixing device 7 includes a heating roller 71 and a pressure roller 72 that is disposed to face the heating roller 71 and presses the heating roller 71. In the fixing device 7 configured as described above, the toner transferred onto the paper P is thermally fixed while the paper P passes between the heating roller 71 and the pressure roller 72.

  The paper P heat-fixed by the fixing device 7 is conveyed to a paper discharge roller R disposed on the downstream side of the fixing device 7, and is sent out from the paper discharge roller R onto the paper discharge tray 2A.

<Configuration of drive unit>
Next, the drive unit 20 will be described in detail.
As shown in FIG. 2, the drive unit 20 decelerates the drive force output from the electric motor Mo, the peripheral speed switching mechanism 30, and the electric motor Mo as an example of a drive source that rotates the developing roller 91, and rotates the peripheral portion. Gears 21 to 24 for transmitting to the speed switching mechanism 30 and a gear 25 for transmitting the driving force output from the peripheral speed switching mechanism 30 to the developing roller 91 are provided. The electric motor Mo is configured to transmit the driving force to the developing roller 91 and also to the photosensitive drum 81 via another transmission mechanism (not shown).

  The gear 21 is a driving gear that receives a driving force from the electric motor Mo and transmits the driving force to the distribution gear 22. The distribution gear 22 is formed by integrating three types of gears 22 </ b> A to 22 </ b> C arranged coaxially. It is a three-stage gear, and the driving force transmitted from the drive gear 21 is transferred to a normal peripheral speed transmission mechanism MB (see solid line arrow) and a slow peripheral speed transmission mechanism MC (see two-dot chain line arrow). Distribute.

  Here, the “normal peripheral speed transmission mechanism MB” refers to a transmission mechanism configured with a speed transmission ratio for rotating the developing roller 91 at a predetermined speed (a speed transmission ratio smaller than that for the slow circumferential speed). In this embodiment, the gears 22B, 23, and 30B are used. The “slow circumferential speed transmission mechanism MC” refers to a transmission mechanism having a speed transmission ratio for rotating the developing roller 91 at a speed slower than the predetermined speed. In the present embodiment, the gear 22C is a gear. , 24, 30C. In FIG. 2, the gears 21 to 24 and 30A to 30C are depicted with different diameters to make the transmission mechanisms MB and MC easy to understand. However, the relationship of the speed transmission ratio as described above is satisfied. The diameter of each gear may be configured in any way.

  The gear 22 </ b> A of the distribution gear 22 is a driven gear that meshes with the drive gear 21. The gear 22 </ b> B is a driven gear that transmits a driving force to the first input gear 30 </ b> B of the peripheral speed switching mechanism 30 via the first intermediate gear 23. The gear 22 </ b> C is a driven gear that transmits a driving force to the second input gear 30 </ b> C of the peripheral speed switching mechanism 30 via the second intermediate gear 24.

  For this reason, when the electric motor Mo rotates / stops, the gears 21 to 24, 30B, 30C rotate / stop in conjunction with the rotation / stop. That is, the first input gear 30B and the second input gear 30C rotate / stop in conjunction with the rotation / stop of the electric motor Mo regardless of the state of the peripheral speed switching mechanism 30 (electromagnetic clutch 50).

  As shown in FIG. 3A, the peripheral speed switching mechanism 30 includes an output gear 30A, a first input gear 30B, a second input gear 30C, a one-way clutch 40, And a clutch 50.

  The output gear 30A is a gear that outputs a driving force to the developing roller 91 side (gear 25), and integrally includes a rotation shaft 30D that extends in the axial direction thereof. The rotating shaft 30D of the output gear 30A is connected to the electric motor Mo through the two transmission mechanisms MB and MC described above.

  The one-way clutch 40 is provided between the slow peripheral speed transmission mechanism MC (second input gear 30C) and the rotation shaft 30D of the output gear 30A, and rotates the second input gear 30C rotated by the electric motor Mo. The driving force is transmitted only in the direction. That is, only when the second input gear 30C rotates faster than the rotating shaft 30D, the driving force is transmitted to the rotating shaft 30D, and when the rotating shaft 30D rotates faster than the second input gear 30C, the second input gear. Transmission of driving force from 30C to the rotating shaft 30D is cut off.

  The electromagnetic clutch 50 includes a movable iron core 50A around which a coil is wound and a fixed iron core 50B, and a transmission mechanism MB for normal peripheral speed having a smaller speed transmission ratio than the transmission mechanism MC for slow peripheral speed described above. It is provided between the (first input gear 30B) and the rotary shaft 30D of the output gear 30A.

  Since the movable iron core 50A is engaged with the rotary shaft 30D via a spline or serration, the movable iron core 50A can move in the axial direction with respect to the rotary shaft 30D and can rotate integrally with the rotary shaft 30D. .

  The fixed iron core 50B is fixed to the end face of the first input gear 30B, and the first input gear 30B is assembled so as to be rotatable with respect to the rotary shaft 30D via a bearing (not shown).

  As a result, when the coil of the movable iron core 50A is energized, as shown in FIG. 3B, the movable iron core 50A moves and is attracted to the fixed iron core 50B by the electromagnetic attractive force, so that it is transmitted from the first input gear 30B. The driving force is transmitted to the rotary shaft 30D. At this time, since the rotation shaft 30D rotates faster than the second input gear 30C, transmission of the driving force from the second input gear 30C to the rotation shaft 30D is blocked by the one-way clutch 40.

  As described above, when the electromagnetic clutch 50 is energized, as shown in FIG. 3B, the driving force is transmitted from the normal peripheral speed transmission mechanism MB (first input gear 30B) to the output gear 30A. When the roller 91 rotates at a predetermined speed and the electromagnetic clutch 50 is de-energized, as shown in FIG. 3 (a), the transmission mechanism MC (second input gear 30C) for the slow peripheral speed changes to the output gear 30A. By transmitting the driving force, the developing roller 91 rotates at a speed slower than a predetermined speed.

<Control device>
Next, the control device 100 will be described in detail.
As shown in FIG. 1, the control device 100 includes, for example, a CPU, a RAM, a ROM, and an input / output circuit, and inputs from a temperature sensor 110 and a humidity sensor 120 as an example of humidity measurement means, and a print command. Control is executed by performing arithmetic processing based on the contents and programs and data stored in the ROM.

  Here, the temperature sensor 110 is provided in the vicinity of the developing roller 91 and detects the temperature of the air around the developing roller 91. The humidity sensor 120 is provided in the vicinity of an inlet (not shown) for taking outside air into the apparatus body 2 and detects the absolute humidity outside the apparatus body 2.

  The control device 100 is configured to execute peripheral speed ratio reduction control that decreases the rotational speed of the developing roller 91 and decreases the peripheral speed ratio of the developing roller 91 with respect to the photosensitive drum 81 in accordance with an increase in the total number of printed sheets. ing. Here, the total number of printed sheets is the total number of printed sheets from the start of use of one developing cartridge 9 to the present time. The control device 100 counts the total number of prints based on the print number data included in the print command, and resets the total number of prints when the developing cartridge 9 is replaced.

  Since the total number of printed sheets is a parameter that increases as the total rotation amount of the developing roller 91 increases, the control device 100 counts the total number of printed sheets so that the toner due to the increase in the total rotation amount of the developing roller 91 is obtained. Indirectly grasps deterioration.

  Specifically, in the peripheral speed ratio reduction control, the control device 100 determines whether or not the total number of printed sheets has exceeded the second threshold value T2 (see FIG. 4), and if not, develops the photosensitive drum 81. The rotation speed of the developing roller 91 is controlled so that the circumferential speed ratio of the roller 91 becomes a first circumferential speed ratio R1 as shown in FIG. Here, the second threshold value T2 may be determined in advance by experiments, simulations, or the like. When the total number of printed sheets exceeds the second threshold T2, the control device 100 changes the peripheral speed ratio of the developing roller 91 from the first peripheral speed ratio R1 to the second peripheral speed smaller than the first peripheral speed ratio R1. Change to speed ratio R2.

  By configuring the control device 100 in this manner, when the total number of printed sheets increases and toner deterioration progresses, the rotational speed of the developing roller 91 decreases and the peripheral speed ratio of the developing roller 91 decreases. Further, it is possible to prevent the toner from being ejected from the nip portion between the developing roller 91 and the photosensitive drum 81.

  Further, as shown in FIGS. 5A and 5B, when the peripheral speed ratio is the first peripheral speed ratio R1, the control device 100 sets the developing bias applied to the developing roller 91 to a first value that is a constant value. The bias value is B1. Then, when the peripheral speed ratio is changed from the first peripheral speed ratio R1 to the second peripheral speed ratio R2, the control device 100 increases the absolute value of the developing bias applied to the developing roller 91 from the previous value. The second bias value B2 is larger than the first bias value B1.

  As a result, even if the toner conveyance amount is reduced by lowering the peripheral speed ratio, the toner conveyance amount can be increased by increasing the developing bias. Therefore, it is possible to suppress a decrease in toner density on the photosensitive drum 81. it can.

  Further, the control device 100 corrects the absolute humidity detected by the humidity sensor 120 based on the temperature detected by the temperature sensor 110 to calculate relative humidity (hereinafter simply referred to as “humidity”). Then, the control device 100 executes the circumferential speed ratio reduction control described above when the calculated humidity is smaller than the first threshold T1 (see FIG. 4), and the circumferential speed when the humidity is not smaller than the first threshold T1. The ratio reduction control is not executed.

  That is, as shown in FIGS. 5A and 5B, even when the total number of printed sheets exceeds the second threshold value T2, in an environment where the humidity is not smaller than the first threshold value T1, that is, at low humidity. If there is no environment, the peripheral speed ratio and the developing bias are maintained at the first peripheral speed ratio R1 and the first bias value B1, which are initial values. Note that the first threshold T1 may be determined in advance through experiments, simulations, or the like.

  According to this, since the peripheral speed ratio reduction control is not executed under an environment where the humidity is not low (an environment where the fluidity of the toner hardly deteriorates), the developing roller 91 generates the photosensitive drum from the photosensitive drum. A decrease in the amount of toner transported to 81 can be suppressed, and a decrease in toner density on the photosensitive drum 81 can be suppressed.

  Next, the control of the control device 100 will be described in detail using the flowchart shown in FIG. In the initial state before starting this control, the control device 100 sets the peripheral speed ratio and the developing bias of the developing roller 91 to the first peripheral speed ratio R1 and the first bias value B1, which are initial values. ing.

  As shown in FIG. 4, the control device 100 first determines whether or not a print command has been received (S1). When the print command is received in step S1 (Yes), the control device 100 determines whether or not the humidity is smaller than the first threshold value T1 (S2).

  When the humidity is smaller than the first threshold value T1 in step S2 (Yes), the control device 100 proceeds to the process of step S3, and when it is not smaller (No), this control is finished as it is. Here, the processing in steps S3 and S4 is the above-described peripheral speed ratio reduction control. Therefore, the control device 100 is configured to execute the circumferential speed ratio reduction control when the humidity is smaller than the first threshold T1, and not to execute the circumferential speed ratio reduction control when the humidity is not smaller.

  In step S3, the control device 100 determines whether or not the total number of printed sheets has exceeded the second threshold value T2, and if it exceeds (Yes), in order to reduce the peripheral speed ratio of the developing roller 91 to be lower than normal. The energization state of the electromagnetic clutch 50 is turned off, and the transmission mechanism is switched from the transmission mechanism MB for normal peripheral speed to the transmission mechanism MC for slow peripheral speed (S4). That is, in step S4, the control device 100 changes the peripheral speed ratio of the developing roller 91 from the first peripheral speed ratio R1 to the second peripheral speed ratio R2 that is smaller than the first peripheral speed ratio R1.

  After step S4, the control device 100 changes the developing bias applied to the developing roller 91 to a second bias value B2 that is larger than the first bias value B1 applied at the first circumferential speed ratio (S5). This control is terminated. After the end of this control, the control device 100 controls the developing roller 91 by the peripheral speed ratio and the developing bias set by the main control, and controls the scanner unit 5 and the like by a known control, thereby controlling the printing. Run.

According to the present embodiment, in addition to the effects described above, the following effects can be obtained.
By switching the transmission mechanisms MB and MC by controlling the electromagnetic clutch 50, the rotation speed of the developing roller 91 can be changed without changing the rotation speed of the electric motor Mo. Therefore, the electric motor Mo is shared with the photosensitive drum 81. Cost reduction.

  Since the rotation speed of the developing roller 91 is controlled based on the total number of printed sheets that can be easily grasped from the number of printed sheets included in the print command, for example, based on a signal from a sensor that detects the total amount of rotation of the developing roller, Compared to a mode in which the rotation speed is controlled, no sensor is required, and the cost can be reduced.

In addition, this invention is not limited to the said embodiment, It can utilize with various forms so that it may illustrate below.
In the above embodiment, the developing bias applied to the developing roller 91 at the first circumferential speed ratio R1 and the second circumferential speed ratio R2 is set to a constant value (B1, B2), but the present invention is limited to this. It is not a thing. For example, when a toner having a property that the charge amount gradually decreases due to deterioration is employed, as shown in FIGS. 6A and 6B, the first peripheral speed ratio R1 and the second peripheral speed ratio R2 are used. At this time, the developing bias applied to the developing roller 91 may be changed so as to gradually decrease as the total number of printed sheets increases.

  That is, in this embodiment, when the first peripheral speed ratio R1 is decreased to the second peripheral speed ratio R2, the developing bias that gradually decreases from when the total number of printed sheets is zero is made larger than the previous value, After that, it should be gradually lowered from the increased value. According to this, in addition to the same effects as in the above embodiment, the amount of toner transport from the developing roller to the photosensitive drum increases due to the decrease in the toner charge amount due to deterioration, and the development bias is gradually lowered. Can be suppressed.

  Further, for example, when a toner having a property that the charge amount gradually increases due to deterioration is employed, as shown in FIGS. 6A and 6C, the first circumferential speed ratio R1 and the second circumferential speed are used. The developing bias applied to the developing roller 91 at the ratio R2 may be changed so as to gradually increase as the total number of printed sheets increases.

  That is, in this embodiment, when the first peripheral speed ratio R1 is lowered to the second peripheral speed ratio R2, the developing bias that gradually increases from when the total number of printed sheets is zero is made larger than the previous value, Then, gradually increase from the increased value. According to this, in addition to the same effects as in the above embodiment, the amount of toner transport from the developing roller to the photosensitive drum decreases due to the increase in the toner charge amount due to deterioration, and the development bias is gradually increased. Can be suppressed.

  In the above-described embodiment, the peripheral speed ratio of the developing roller 91 is switched in two stages. However, the present invention is not limited to this, and for example, development is performed with a dedicated motor different from the motor for driving the photosensitive drum 81. When the roller 91 is driven, it may be switched in three or more stages, or the peripheral speed ratio may be gradually decreased as the total number of printed sheets increases as shown in FIG. That is, the control device may be configured to execute the peripheral speed ratio reduction control based on the peripheral speed ratio map RM that gradually decreases the peripheral speed ratio as the total number of printed sheets increases. Further, in this case, as shown in FIG. 7B, the control device is configured to gradually increase the developing bias applied to the developing roller during the peripheral speed ratio decrease control as the total number of printed sheets increases. Also good.

  Specifically, the process of steps S3 and S4 in FIG. 4 is replaced with a step of determining the peripheral speed ratio based on the peripheral speed ratio map RM, and the process of step S5 is set based on the development bias map. What is necessary is just to replace with a step. According to this, when the humidity is not smaller than the first threshold value T1 in step S2 (No), the control device determines the peripheral speed ratio based on the reference map BM indicated by a broken line in FIG. At the same time, the developing bias is determined based on the first map M1 indicated by a broken line in FIG.

  Here, the reference map BM is a map that makes the peripheral speed ratio constant regardless of the increase in the total number of printed sheets. The first map M1 is a map that keeps the developing bias constant regardless of the increase in the total number of printed sheets. In other words, the first map M1 is a map that changes the developing bias with a predetermined inclination (0) as the total number of printed sheets increases. More specifically, the first map M1 in FIG. 7B is a map used when a toner whose charge amount becomes substantially constant even when deteriorated is employed.

  If the humidity is lower than the first threshold value T1 in step S2 (Yes), the control device is a peripheral speed corresponding to the total number of prints based on the peripheral speed ratio map RM indicated by the solid line in FIG. The ratio is determined, and the developing bias is determined based on the second map M2 indicated by the solid line in FIG. Here, the second map M2 is a map in which the developing bias is changed with an inclination having a larger absolute value than the inclination of the first map M1 as the total number of printed sheets increases.

  According to this, since it is possible to set an appropriate peripheral speed ratio according to the total number of printed sheets, it is possible to set the toner transport amount and density to appropriate values according to the total number of printed sheets. Further, when the humidity is smaller than the first threshold T1, that is, when the circumferential speed ratio reduction control is executed, the developing bias is determined based on the second map M2 having a larger slope than the first map M1, and therefore the circumferential speed ratio. Therefore, a decrease in the toner conveyance amount due to the decrease in toner can be suppressed, and a decrease in toner density can be suppressed.

  Note that when a toner whose charge amount decreases due to deterioration is employed, the first map M11 and the second map M12 shown in FIG. 8B may be used. Here, the first map M11 is a map for decreasing the developing bias with a predetermined inclination as the total number of printed sheets increases, and the second map M12 is a map for developing the developing bias as the total number of printed sheets increases. This is a map that is changed with an inclination larger than the inclination.

  That is, when the peripheral speed ratio is determined using the reference map BM shown in FIG. 8A, the developing bias is determined using the first map M11, and when the peripheral speed ratio is determined using the peripheral speed ratio map RM, the second map is used. The development bias may be determined from the map M12. Even in this case, it is possible to obtain the same effect as that of the embodiment shown in FIGS.

  Further, when adopting toner whose charge amount increases due to deterioration, the first map M21 and the second map M22 shown in FIG. 8C may be used. Here, the first map M21 is a map for increasing the developing bias with a predetermined slope as the total number of printed sheets increases, and the second map M22 is the developing bias for the first map M21 as the total number of printed sheets increases. This is a map that is changed with an inclination larger than the inclination.

  That is, when the peripheral speed ratio is determined by the reference map BM shown in FIG. 8A, the development bias is determined by the first map M21, and when the peripheral speed ratio is determined by the peripheral speed ratio map RM, The development bias may be determined from the map M22. Even in this case, it is possible to obtain the same effect as that of the embodiment shown in FIGS.

  In the above-described embodiment, the positively charged toner is used as the developer. However, the present invention is not limited to this, and a negatively charged toner may be used. In this case, for example, when the peripheral speed ratio is changed from the first peripheral speed ratio to the second peripheral speed ratio, a negative second bias value (a bias value having a large absolute value) that is smaller than the negative first bias value. ).

  In the above-described embodiment, the photosensitive drum 81 is employed as the photosensitive member. However, the present invention is not limited to this, and for example, a belt-shaped photosensitive member may be employed.

  In the embodiment, the total number of printed sheets is adopted as a parameter corresponding to the total rotation amount of the developing roller. However, the present invention is not limited to this, and may be, for example, the total rotation amount of the developing roller itself, It may be the number of dots printed on.

  In the above embodiment, the temperature sensor 110 and the humidity sensor 120 are employed as the humidity measuring means. However, the present invention is not limited to this, and for example, the humidity sensor may be configured only by a humidity sensor that detects relative humidity.

  In the above embodiment, the present invention is applied to the laser printer 1. However, the present invention is not limited to this, and the present invention may be applied to other image forming apparatuses such as a copying machine and a multifunction machine.

DESCRIPTION OF SYMBOLS 1 Laser printer 81 Photosensitive drum 91 Developing roller 100 Control apparatus 110 Temperature sensor 120 Humidity sensor B1 1st bias value B2 2nd bias value R1 1st circumferential speed ratio R2 2nd circumferential speed ratio T1 1st threshold value T2 2nd threshold value

Claims (4)

A photoreceptor on which an electrostatic latent image is formed;
A developing roller for supplying a developer to the photoreceptor;
A humidity measuring means for measuring humidity;
A control device for controlling the rotation speed of the developing roller,
The controller is
Peripheral speed ratio reduction control for decreasing the peripheral speed ratio of the developing roller with respect to the photosensitive member by decreasing the rotational speed of the developing roller in accordance with an increase in a parameter corresponding to the total rotation amount of the developing roller. Configured,
Wherein determining the humidity measured by the humidity measurement means or less or not than the first threshold value, executes the peripheral speed ratio decreasing control when small, if not smaller so as not to execute the peripheral speed ratio decreasing control Composed of
When the peripheral speed ratio of the developing roller is changed from the first peripheral speed ratio to a second peripheral speed ratio that is smaller than the first peripheral speed ratio, the absolute value of the developing bias applied to the developing roller is set to be less than the previous value. An image forming apparatus that is enlarged . A photoreceptor on which an electrostatic latent image is formed;
A developing roller for supplying a developer to the photoreceptor;
A humidity measuring means for measuring humidity;
A control device for controlling the rotation speed of the developing roller,
The controller is
Peripheral speed ratio reduction control for decreasing the peripheral speed ratio of the developing roller with respect to the photosensitive member by decreasing the rotational speed of the developing roller in accordance with an increase in a parameter corresponding to the total rotation amount of the developing roller. Configured,
Wherein determining the humidity measured by the humidity measurement means or less or not than the first threshold value, executes the peripheral speed ratio decreasing control when small, if not smaller so as not to execute the peripheral speed ratio decreasing control Composed of
The circumferential speed ratio reduction control is executed based on a circumferential speed ratio map such that the circumferential speed ratio gradually decreases as the parameter increases,
If the humidity measured by the humidity measuring means is not smaller than the first threshold value, the developing bias applied based on the first map in which the developing bias applied to the developing roller is changed with a predetermined inclination as the parameter increases. Decide
When the humidity measured by the humidity measuring means is smaller than the first threshold value, the developing bias applied to the developing roller is changed with a slope having a larger absolute value than the predetermined slope as the parameter increases. An image forming apparatus, wherein a developing bias is determined based on two maps . The parameters, the image forming apparatus according to claim 1 or claim 2, characterized in that the total number of printed sheets. A drive source for rotating the developing roller;
Two transmission mechanisms with different speed transmission ratios;
An output unit coupled to the drive source via the two transmission mechanisms;
A one-way clutch provided between one of the two transmission mechanisms and the output unit;
An electromagnetic clutch provided between the other transmission mechanism having a smaller speed transmission ratio than the one transmission mechanism and the output unit,
The controller is
Wherein by controlling the electromagnetic clutch switches the transmission mechanism, an image forming apparatus according to claim 1, characterized in that lowering the rotational speed of the developing roller.

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