JP2017156573A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can reduce a manufacturing cost and simplify a configuration.SOLUTION: An image forming apparatus comprises: a photoconductor drum 3a; a scanner unit 5 that irradiates the photoconductor drum 3a with light to form a latent image; a developing unit 4 that includes a developing roller developing the latent image formed by the scanner unit 5 to form a toner image, and can move between a contact position and a separation position; a driving part that drives the developing unit 4; a transfer roller that is in contact with the photoconductor drum 3a; a transfer current detection part 202 that detects a current flowing in the transfer roller; and a main control part 301 that determines whether or not a latent image is formed on the photoconductor drum 3a on the basis of a result of detection performed by the transfer current detection part 202.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus such as an electrophotographic printer, a copying machine, and the like, and more particularly to an image forming apparatus that determines the presence / absence and position of a developing unit having a plurality of stop positions.

  In image forming apparatuses such as electrophotographic copying machines and printers, the presence or absence of process cartridges and the presence or absence of photosensitive drums are detected using electrical processing instead of means using mechanical parts such as switches and sensors. Has been proposed. For example, Patent Document 1 proposes an image forming apparatus that applies a voltage to a transfer roller disposed to face a photosensitive drum and detects a current flowing through the transfer roller. For example, Patent Document 2 proposes an image forming apparatus that detects a current flowing through a charging roller by applying a voltage to a charging roller disposed opposite to the photosensitive drum.

  In order to suppress wear of the photosensitive drum and the developing roller in the developing unit, an image forming apparatus in which the developing unit for developing toner has a plurality of stop positions has been proposed. For example, in Patent Document 3, in order to detect the position of the developing unit, the position of the developing unit is detected using a phase sensor.

Japanese Patent Publication No. 07-060288 Japanese Patent Laid-Open No. 06-003891 JP 2012-128017 A

  However, in the case of an image forming apparatus in which the developing unit has a plurality of stop positions, means using mechanical parts such as sensors are used when detecting the position of the developing unit. There is a problem that the structure of the image forming apparatus is complicated accordingly.

  SUMMARY An advantage of some aspects of the invention is to simplify the configuration of an image forming apparatus.

  In order to solve the above-described problems, the present invention has the following configuration.

  (1) A photoconductor, an exposure unit that irradiates light to the photoconductor to form a latent image, and a developing unit that develops the latent image formed by the exposure unit to form a toner image. , A developing unit capable of moving between a first position in contact with the photosensitive member and a second position separated from the photosensitive member, driving means for driving the developing unit, and the photosensitive member Whether or not a latent image is formed on the photoconductor based on a detection result by the first detection unit, a first detection unit that detects a current flowing through the conductive member, An image forming apparatus comprising: a latent image determination unit that determines

  (2) a photoconductor, an exposure unit that irradiates light to the photoconductor to form a latent image, and a developing unit that develops the latent image formed by the exposure unit to form a toner image, the developing unit , A developing unit capable of moving between a first position in contact with the photosensitive member and a second position separated from the photosensitive member, driving means for driving the developing unit, and the photosensitive member Based on the detection result by the first detection means, the first detection means for detecting the current flowing through the conductive member, An image forming apparatus comprising: position determination means for determining that the position is present.

  According to the present invention, the configuration of the image forming apparatus can be simplified.

Sectional drawing of the image forming apparatus of Examples 1-3, The figure which shows the transfer current detection part of Example 1. FIG. 1 is a block diagram of an image forming apparatus according to a first embodiment. Sectional drawing of the developing unit of Examples 1-3 Flowcharts for explaining development unit presence / absence determination processing, separation determination processing, and latent image presence determination processing according to the first embodiment. Flowchart for explaining contact determination processing in the first and third embodiments The figure which shows the charging current detection part of Example 2, The block diagram of an image forming apparatus Flowchart for explaining latent image presence / absence determination processing according to the second embodiment. Block diagram of the image forming apparatus of Embodiment 3 Flowchart for explaining latent image presence / absence determination processing according to the third embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail by way of examples with reference to the drawings.

[Image forming apparatus]
In the first embodiment, an image forming apparatus that makes it possible to determine the presence / absence and position of a developing unit by detecting a transfer current will be described. FIG. 1A is a cross-sectional view schematically illustrating the image forming apparatus according to the present exemplary embodiment. The printer main body 1 includes a photosensitive drum 3 a that is a photosensitive member, a charging roller 14 that is a charging unit, a photosensitive drum 3 a, and a photosensitive drum unit 3 that holds the charging roller 14. Further, in the printer main body 1, a developing roller 4a that is a developing unit for developing a latent image on the photosensitive drum 3a (on the photosensitive member) with toner, a developing unit 4 that holds the developing roller 4a, and the photosensitive drum 3a. The scanner unit 5 is an exposure means for exposing the light. The developing unit 4 is a unit that can be attached to and detached from the printer main body 1. The developing unit 4 only needs to hold at least the developing roller 4a. The photosensitive drum unit 3 and the developing unit 4 are not integrated and are independent. Further, in the printer main body 1, a paper feed roller 6, a transport roller pair 7, a transfer roller 8, a heating device 9, a pressure roller 10, and a paper discharge roller pair 11 are installed as rollers for paper transport. .

[Image formation and paper transport]
The sheets S that are recording media stacked and stored in the sheet feed tray 12 are fed one by one by the sheet feed roller 6 and the separation pad 39. The sheet S is transported by the transport roller pair 7 and sent to the nip portion between the photosensitive drum 3 a and the transfer roller 8. The photosensitive drum 3a is rotated in the direction of the arrow (clockwise direction) in the figure, and the surface of the photosensitive drum 3a is uniformly charged by the charging roller 14 and is latentized by the laser light 5a irradiated from the scanner unit 5. An image is formed. The latent image formed on the photosensitive drum 3a is developed by the developing roller 4a, and a toner image is formed on the photosensitive drum 3a. The toner image formed on the photosensitive drum 3 a is transferred to the sheet S sent to the nip portion between the photosensitive drum 3 a and the transfer roller 8. Further, the sheet S on which the toner image is transferred is sent to the nip portion between the heating device 9 and the pressure roller 10, where it is heated and pressed to fix the toner image on the sheet S. The sheet S on which the toner image has been fixed is discharged to a discharge tray 13 by a discharge roller pair 11.

[Development unit contact and separation]
The developing unit 4 can be stopped at two positions. Hereinafter, the stoppable position is referred to as a stop position. The developing unit 4 can be moved between two stop positions by a driving unit (not shown) as driving means. One of the two stop positions of the developing unit 4 is a position where the developing roller 4a held by the developing unit 4 and the photosensitive drum 3a come into contact. Hereinafter, the stop position is a contact that is the first position. It is called position. The other of the two stop positions of the developing unit 4 is a position where the developing roller 4a and the photosensitive drum 3a are relatively far from the photosensitive drum 3a than the contact position. This is called a separation position. FIG. 1A shows a state where the developing unit 4 is in the contact position. The contact position is a position that the developing unit 4 takes when forming an image for forming a toner image mainly on the photosensitive drum 3a. The separation position does not form a toner image in order to suppress the deterioration of the photosensitive drum 3a and the developing roller 4a and the change in the shape of the developing roller 4a due to the rotation of the photosensitive drum 3a and the developing roller 4a. This is the position to take.

[Development unit presence / absence execution timing]
In the image forming apparatus of this embodiment, in order to determine whether or not image formation is possible, whether or not a unit or apparatus necessary for the image forming operation is mounted, and the mounted unit or apparatus can operate normally. An initialization operation is performed to check whether or not. Since it is necessary to check the presence / absence of the developing unit 4 in the initialization operation, the presence / absence determination of the developing unit 4 is executed in the initialization operation. The initialization operation is performed immediately after the power is turned on or after the opening / closing of a cartridge door (not shown) in which the developing unit 4 may be attached or detached. The cartridge door is a door that is provided on the side surface of the printer main body 1 and for accessing removable parts (developing unit 4 and the like) inside the printer main body 1.

[Development unit contact timing execution timing]
Since the image forming apparatus of this embodiment needs to take a contact position when performing image formation, the contact determination of the developing unit 4 is performed at the time of image formation. Further, when the interval for feeding the paper S during image formation is widened, the development unit 4 is once moved to the separation position, and the development unit 4 is again moved to the contact position in accordance with image formation. At this time, the contact of the developing unit 4 is determined. If it is not possible to determine that the development unit 4 has moved to the contact position even if it is instructed to move the development unit 4 to the contact position, the development unit 4 is moved to the contact position again if possible. Control (retry).

[Development unit separation determination execution timing]
In the image forming apparatus according to the present exemplary embodiment, after the initial rotation performed at the contact position or after the image formation, the developing unit 4 is moved to the separated position in order to suppress deterioration of the photosensitive drum 3a and the developing roller 4a. Implement control to move. Therefore, the separation of the developing unit 4 is determined after initial rotation and image formation. Also, when the interval for feeding the paper S during image formation is increased, the separation of the development unit 4 is determined in order to move the development unit 4 to the separation position. If it is not possible to determine that the developing unit 4 has moved to the separated position even if it is instructed to move the developing unit 4 to the separated position, if possible, control to move the developing unit 4 to the separated position again (if possible) Retry).

[Current detector]
FIG. 1B shows the electrical configuration of the charging roller 14, the transfer roller 8 and the photosensitive drum 3a used in this embodiment. The transfer voltage power supply 201 as the second application means and the charging voltage power supply 203 as the first application means apply the designated voltages to the transfer roller 8 and the charging roller 14, respectively. The transfer current detection unit 202 as the first detection means detects the transfer current It flowing through the transfer roller 8 with the direction of the current flowing from the transfer roller 8 as a conductive member to the photosensitive drum 3a being positive. The transfer current detection unit 202 is mounted for the purpose of detecting transfer current It and applying an optimum transfer voltage to transfer the toner image on the photosensitive drum 3a to the paper S during image formation. Yes. In this embodiment, the transfer current detection unit 202 is also used to determine the presence / absence of the developing unit 4 and the stop position.

[Block diagram of image forming apparatus]
FIG. 2 is a block diagram illustrating a control configuration of the image forming apparatus according to the present exemplary embodiment. The main control unit 301 of this embodiment will be described. An exposure control unit 302 serving as a control unit controls the scanner unit 5 to perform exposure by irradiating the photosensitive drum 3a with a laser beam with a predetermined light amount or with a light amount according to image data. The development movement control unit 303 moves the development unit 4 from the contact position to the separation position or from the separation position to the contact position. The drive control unit 304 controls the photosensitive drum 3a to rotate in the clockwise direction (see FIG. 1A) at a constant rotational speed. The charging output control unit 305 and the transfer output control unit 306 control the charging voltage power source 203 and the transfer voltage power source 201, respectively, and apply specified voltages to the charging roller 14 and the transfer roller 8, respectively.

  The current detection unit 307 controls the transfer current detection unit 202 to detect the transfer current It flowing between the photosensitive drum 3 a and the transfer roller 8. The detection result of the current detection unit 307 has a larger value as the current flowing in the positive direction is larger. The presence / absence determination unit 311, the contact determination unit 312, and the separation determination unit 313 of the developing unit 4 make a determination based on the detection result of the current detection unit 307. Here, the main control unit 301 functions as a mounting determination unit and a position determination unit. Specifically, the presence / absence determination unit 311 of the main control unit 301 functions as a mounting determination unit, and the contact determination unit 312 and the separation determination unit 313 of the main control unit 301 function as position determination units. The main control unit 301 includes a storage unit 314 that stores various types of information.

[Development unit]
FIG. 3 is a cross-sectional view showing the developing unit 4 used in this embodiment. FIG. 3A shows a case where the developing unit 4 takes a contact position. When the developing unit 4 is in the contact position shown in FIG. 3A, the laser light 5a emitted from the scanner unit 5 is not shielded but is irradiated onto the surface of the photosensitive drum 3a. On the other hand, FIG. 3B shows a case where the developing unit 4 takes a separated position. When the developing unit 4 is in the separated position shown in FIG. 3B, the laser light 5b irradiated from the scanner unit 5 is shielded by the developing unit 4 and is not irradiated onto the surface of the photosensitive drum 3a. When the developing unit 4 is not attached to the printer main body 1, a latent image is formed on the photosensitive drum 3a by the laser light 5a emitted from the scanner unit 5.

  As described above, when the laser light is irradiated from the scanner unit 5, the developing unit 4 is not attached to the printer main body 1, or the developing unit 4 is attached to the printer main body 1 and is in the contact position. In this case, a latent image is formed on the photosensitive drum 3a. On the other hand, when the developing unit 4 is attached to the printer main body 1 and is in the separated position when the laser light is irradiated from the scanner unit 5, a latent image is not formed on the photosensitive drum 3a.

[Development unit presence / absence judgment processing]
FIG. 4 is a flowchart for explaining the presence / absence determination and separation determination of the developing unit 4 according to this embodiment. The presence / absence determination process of the developing unit 4 in FIG. This embodiment is based on the premise that the photosensitive drum unit 3 is mounted on the printer main body 1, and the same applies to the following embodiments. In a state where the presence or absence of the developing unit 4 is not determined, it cannot be determined that the developing unit 4 is in the contact position even if a latent image is formed on the photosensitive drum 3a. As described above, a latent image is formed on the photosensitive drum 3 a because the developing unit 4 is in the contact position, and a latent image is formed on the photosensitive drum 3 a because the developing unit 4 is not attached to the printer main body 1. This is because an image may be formed. In either case, it is determined that a latent image is formed on the photosensitive drum 3a. Therefore, the development movement control unit 303 changes the stop position of the development unit 4 and determines whether the development unit 4 is present based on whether the development unit 4 is in the separated position. As described above, the presence / absence determination of the developing unit 4 is performed during the initialization operation.

  When the main control unit 301 is instructed to determine the presence or absence of the development unit 4, the development movement control unit 303 starts the movement of the development unit 4 to the separated position. Further, the main control unit 301 resets and starts a timer (not shown), initializes the value of the number of retries, which is a predetermined number of times described later, and starts the following processing. In step (hereinafter referred to as S) 501, the main control unit 301 causes the drive control unit 304 to rotate the photosensitive drum 3a. In step S <b> 502, the main control unit 301 causes the charge output control unit 305 to start outputting the charging voltage to the charging voltage power source 203, and causes the scanner unit 5 to start exposure using the exposure control unit 302. In step S503, the main control unit 301 performs exposure by the scanner unit 5 regardless of the position of the developing unit 4, and determines whether or not a latent image is formed on the photosensitive drum 3a (hereinafter simply referred to as detection of a latent image). ). In step S504, the main control unit 301 determines whether or not a latent image has been formed on the photosensitive drum 3a (hereinafter, whether there is a latent image). Details of the processing of S504 will be described with reference to FIG.

  In step S505, the main control unit 301 reads the determination result of the presence / absence of a latent image on the photosensitive drum 3a in step S504 from the storage unit 314, and determines whether there is a latent image on the photosensitive drum 3a. If the main control unit 301 determines in step S505 that there is no latent image on the photosensitive drum 3a, the process proceeds to step S510. In this case, the main control unit 301, more specifically, the presence / absence determination unit 311 of the main control unit 301, causes the developing unit 4 to apply the laser light 5b emitted from the scanner unit 5 as shown in FIG. Since the light is shielded, it is determined that no latent image is formed on the photosensitive drum 3a. In step S510, the main control unit 301 stores information indicating that the development unit 4 is present (development unit presence information) in the storage unit 314, and ends the process.

  If the main control unit 301 determines in step S505 that there is a latent image on the photosensitive drum 3a, the process advances to step S506. The main control unit 301 detects whether a latent image is formed on the photosensitive drum 3a because the developing unit 4 is in the contact position, or the latent image on the photosensitive drum 3a because the developing unit 4 is not attached to the printer main body 1. It cannot be judged whether an image is formed. Therefore, in step S506, the main control unit 301 performs a retry if the number of retries that moved the developing unit 4 to the separated position (hereinafter referred to as the number of retries) does not exceed a preset threshold value. In addition, it is determined whether the number of retries is less than or equal to a threshold value. The threshold value of the number of retries is set in advance according to, for example, a mechanism for performing contact and separation by the driving of the image forming apparatus, deterioration of the photosensitive drum 3a, and the starting position of the developing unit 4. Even when the developing unit 4 is mounted, it is uncertain where the developing unit 4 is located at the start of movement. For this reason, the threshold for the number of retries is set in consideration of the number of retries when it is assumed that the position at the start of movement is at the contact position farthest from the separated position. The same applies when moving to a contact position described later.

  If the main control unit 301 determines in S506 that the number of retries is less than or equal to the threshold value, the main control unit 301 increments the number of retries in S507. In step S508, the main control unit 301 causes the development movement control unit 303 to move the development unit 4 to the separation position, resets and starts a timer (not shown), and returns the process to step S503. If the main control unit 301 determines in S506 that the number of retries has exceeded the threshold value, it determines in S509 that the development unit 4 is not attached to the printer body 1, and information indicating that the development unit 4 is not in the storage unit 314. (Development unit absence information) is stored, and the process is terminated.

  Note that in the presence / absence determination processing of the developing unit 4 in FIG. 4A, when it is determined that there is no developing unit 4, the following may be performed. For example, a configuration may be adopted in which the fact that the developing unit 4 is not present is displayed on a display unit (not shown) and the user is notified to attach the developing unit 4 to the printer main body 1.

[Development unit separation determination processing]
The separation determination process of the developing unit 4 in FIG. 4B will be described. The separation determination process in FIG. 4B is performed on the assumption that the developing unit 4 is attached to the printer body 1. The process shown in FIG. 4B is performed after the initial rotation or after the image formation as described above. The difference between the separation determination process in FIG. 4B and the presence / absence determination process of the developing unit 4 in FIG. 4A is that information stored when there is no latent image on the photosensitive drum 3a and the threshold of the number of retries. And information stored when the retry count threshold is exceeded. When the main control unit 301 is instructed to determine the separation of the development unit 4, the development movement control unit 303 starts the movement of the development unit 4 to the separation position. Further, the main control unit 301 resets and starts a timer (not shown), initializes the value of the number of retries, and starts processing. In FIG. 4B, the same process as the process described in FIG. 4A is assigned the same step number, and the description is omitted.

  If the main control unit 301 determines in step S505 that there is no latent image on the photosensitive drum 3a, the process proceeds to step S524. Here, in the presence / absence determination process of FIG. 4A, if there is no latent image on the photosensitive drum 3a, the main control unit 301 stores the development unit presence information in the storage unit 314 in S510. On the other hand, in the separation determination process of FIG. 4B, it is assumed that the developing unit 4 is attached to the printer main body 1. For this reason, the main control unit 301, more specifically, the separation determination unit 313 of the main control unit 301, indicates that there is no latent image on the photosensitive drum 3a because the developing unit 4 is separated as shown in FIG. It is determined that the laser beam 5b is in the position and shields the laser beam 5b. In step S524, the main control unit 301 stores in the storage unit 314 information indicating that the developing unit 4 is in the separated position (hereinafter, referred to as separated position confirmation information), and ends the process.

  In step S521, the main control unit 301 determines whether the number of retries is equal to or less than a threshold value. The threshold value of the number of retries here is set according to, for example, a mechanism for performing contact and separation by the driving of the image forming apparatus, deterioration of the photosensitive drum 3a, and the like. If the main control unit 301 determines in S521 that the number of retries is less than or equal to the threshold, the process proceeds to S522. If the main control unit 301 determines in S521 that the number of retries has exceeded the threshold, the process proceeds to S523. Here, in the case of the presence / absence determination process in FIG. 4A, the main control unit 301 stores the development unit absence information in the storage unit 314. On the other hand, in the case of the separation determination process in FIG. 4B, it is assumed that the developing unit 4 is attached to the printer main body 1. Therefore, if the developing unit 4 is operating normally, the developing unit 4 should be moved to the separated position and no latent image should be formed on the photosensitive drum 3a. In step S523, the main control unit 301 determines that the developing unit 4 cannot move between the separation position and the contact position, and stores, for example, information indicating that the developing unit 4 has failed (hereinafter referred to as failure information). The data is stored in the unit 314 and the process is terminated.

  FIG. 4B is a process based on the assumption that the developing unit 4 is attached to the printer main body 1. However, the separation determination process may be executed even when the presence or absence of the developing unit 4 is not determined. it can. In that case, the separation determination process of FIG. 4B is executed together with the presence / absence determination process of FIG. In this case, when the main control unit 301 determines that there is no latent image on the photosensitive drum 3a in S505 in the flowchart of FIG. 4A, in addition to the development unit presence information in S510, the separation position determination information is also stored. This is a process to which control stored in the unit 314 is added.

[Latent image presence / absence judgment processing]
The latent image presence / absence determination process of FIG. 4C, which is the process of S504 of FIGS. 4A and 4B, will be described. In this embodiment, the main control unit 301 serving as a latent image determination unit determines the presence or absence of a latent image on the photosensitive drum 3 a based on the transfer current It detected by the current detection unit 307. Table 1 is a table showing the charging voltage [V] and the transfer voltage [V] to be used.

表１に示す帯電電圧（−１４００Ｖ）で感光ドラム３ａを帯電した場合について説明する。この場合、感光ドラム３ａを露光して潜像が形成されたときの感光ドラム３ａの表面電位と、潜像が形成されていないときの感光ドラム３ａの表面電位とを比べると、潜像が形成されたときのほうが感光ドラムの３ａの表面電位は高い。表１に示す転写電圧（＋１５００Ｖ）を印加する場合、感光ドラム３ａ上に潜像が形成されなかった場合のほうが、感光ドラム３ａ上に潜像が形成された場合よりも、電流検知部３０７はより大きな電流を検知できる。そこで、感光ドラム３ａ上の潜像の有無の判断は、転写電流Ｉｔの閾値をあらかじめ設定しておき、電流検知部３０７により検知した転写電流Ｉｔが閾値より大きい場合には潜像なし、転写電流Ｉｔが閾値以下である場合には潜像あり、と判断することができる。なお、閾値は、例えば設計段階や出荷段階において測定され、記憶部３１４に記憶されているものとする。

A case where the photosensitive drum 3 a is charged with the charging voltage (−1400 V) shown in Table 1 will be described. In this case, the latent image is formed by comparing the surface potential of the photosensitive drum 3a when the latent image is formed by exposing the photosensitive drum 3a with the surface potential of the photosensitive drum 3a when the latent image is not formed. When this is done, the surface potential of the photosensitive drum 3a is higher. When the transfer voltage (+1500 V) shown in Table 1 is applied, the current detection unit 307 is more effective when the latent image is not formed on the photosensitive drum 3a than when the latent image is formed on the photosensitive drum 3a. Larger current can be detected. Therefore, the determination of the presence or absence of a latent image on the photosensitive drum 3a is performed by setting a threshold value of the transfer current It in advance, and when the transfer current It detected by the current detection unit 307 is larger than the threshold value, there is no latent image, and the transfer current If It is less than or equal to the threshold value, it can be determined that there is a latent image. It is assumed that the threshold value is measured, for example, in the design stage or the shipping stage and stored in the storage unit 314.

  In step S531, the main control unit 301 applies the transfer voltage (+1500 V) specified in Table 1 by the transfer output control unit 306. In S532, the main control unit 301 determines whether or not a predetermined time (development position determination time) has elapsed by referring to a timer (not shown). If the main control unit 301 determines in S532 that the development position determination time has not elapsed, the process returns to S532, and if it is determined that the development position determination time has elapsed, the process proceeds to S533. Here, the development position determination time is as follows. That is, considering the possibility that the development unit 4 is between the contact position and the separation position, the position of the development unit 4 is determined to be either the contact position or the separation position, and the photosensitive drum according to the position of the development unit 4 is determined. This is the time during which the current detection unit 307 can determine whether or not there is a latent image on 3a. For example, a time obtained by adding the maximum time required for the developing unit 4 to move from the contact position to the separated position and the time required for the surface exposed on the photosensitive drum 3a to reach the transfer roller 8 is set.

  In step S <b> 533, the main control unit 301 detects the transfer current It flowing between the photosensitive drum 3 a and the transfer roller 8 by the transfer current detection unit 202, and acquires the detection result of the transfer current It from the current detection unit 307. In step S534, the main control unit 301 determines whether the transfer current It detected in step S533 is greater than a first threshold value. If the main control unit 301 determines in step S534 that the transfer current It is greater than the first threshold, the process proceeds to step S535. In step S535, the main control unit 301 stores in the storage unit 314 information indicating that there is no latent image on the photosensitive drum 3a, and the process proceeds to step S505 in FIGS. 4A and 4B. Proceed. If the main control unit 301 determines in S534 that the transfer current It is equal to or smaller than the first threshold value, in S536, information indicating that there is a latent image on the photosensitive drum 3a (information with latent image) is stored in the storage unit 314. The process is stored, and the process proceeds to S505 in FIGS. 4 (a) and 4 (b).

[Development unit contact determination processing]
FIG. 5 is a flowchart showing the contact determination process of this embodiment. FIG. 5 will be described. When the contact determination of FIG. 5 is performed, it is necessary to confirm in advance that the developing unit 4 is attached to the printer main body 1. If mounting of the developing unit 4 is not confirmed, the developing unit 4 presence / absence determination process described with reference to FIG. 4A is performed to determine that the developing unit 4 is mounted. When the contact determination is instructed, the main control unit 301 starts the movement of the development unit 4 to the contact position by the development movement control unit 303, resets and starts a timer (not shown), and tries again later. The number of times is initialized and the following processing is started. Note that the processing from S601 to S603 in FIG. 5 is the same as the processing from S501 to S503 in FIG.

  In step S604, the main control unit 301 determines whether there is a latent image, and determines whether there is a latent image on the photosensitive drum 3a. The latent image presence / absence determination in S604 uses the latent image presence / absence determination process described with reference to FIG. In step S605, the main control unit 301 reads the information stored in the storage unit 314 in step S604, and determines whether there is a latent image on the photosensitive drum 3a. If the main control unit 301 determines in S605 that there is a latent image on the photosensitive drum 3a, the process proceeds to S610. In step S610, the main control unit 301 stores information indicating that the developing unit 4 is in the contact position (hereinafter referred to as contact position determination information) in the storage unit 314, and ends the process.

  If the main control unit 301 determines in step S605 that there is no latent image on the photosensitive drum 3a, the process advances to step S606. In step S606, the main control unit 301 determines whether the number of retries is equal to or less than a threshold value. Note that the threshold for the number of retries is determined in the same manner as in FIG. If the main control unit 301 determines in S606 that the number of retries is less than or equal to the threshold value, the main control unit 301 increments the number of retries in S607. In step S608, the main control unit 301 executes the movement of the development unit 4 to the contact position by the development movement control unit 303, resets and starts a timer (not shown), and returns the process to step S603.

  If the main control unit 301 determines in S606 that the number of retries has exceeded the threshold, the process proceeds to S609. The process of FIG. 5 is a process that is executed after it is determined that the developing unit 4 is attached to the printer main body 1. Therefore, if the developing unit 4 is operating normally, the developing unit 4 should be moved to the contact position and a latent image should be formed on the photosensitive drum 3a. In step S <b> 609, the main control unit 301 stores information (failure information) indicating that the development unit 4 or the like is in failure in the storage unit 314, and the process ends.

  In this embodiment, the transfer current It is detected after waiting for the time until the position of the developing unit 4 is determined in the process of FIG. 4C. However, the developing unit 4 can form a latent image from the contact position to the third position between the contact position and the separation position, and cannot form a latent image from the third position to the separation position. The following control is also possible. That is, in order to optimize the moving time of the developing unit 4 at the time of separation determination or contact determination, the current detection unit 307 continues to detect the transfer current It even while the developing unit 4 is moving. Further, it is possible to control to wait for a predetermined time from the third position to the separated position.

  As described above, in this embodiment, a latent image can be formed on the photosensitive drum 3a by the scanner unit 5 when the developing unit 4 is in contact, and a latent image cannot be formed at the time of separation. The position of the developing unit 4 is determined based on the presence or absence. By performing exposure regardless of the position of the developing unit 4, a latent image is formed on the photosensitive drum 3a when the developing unit 4 takes the contact position, and a latent image is formed on the photosensitive drum 3a when taking the separated position. An image is not formed. Therefore, by detecting the presence or absence of the latent image on the photosensitive drum 3a and the transfer current It, the presence and position of the developing unit 4 can be determined by electrical processing without using a sensor.

  As described above, according to this embodiment, the manufacturing cost can be reduced and the configuration can be simplified.

  In the first embodiment, as shown in FIG. 4C, the presence / absence of a latent image on the photosensitive drum 3a is determined based on the detection result of the transfer current It. In the second embodiment, an example in which the determination is based on the detection result of the charging current, not the detection result of the transfer current It will be described.

[Charging current detector]
FIG. 6A shows the electrical configuration of the charging roller 14, the transfer roller 8 and the photosensitive drum 3a used in this embodiment. In addition, the same code | symbol is attached | subjected to the same structure as the structure demonstrated in FIG.1 (b), and description is abbreviate | omitted. A charging current detection unit 701 serving as a first detection unit detects the charging current Ip with the direction of the current flowing from the charging roller 14 serving as a conductive member to the photosensitive drum 3a being positive. The charging current detection unit 701 is mounted for the purpose of controlling the charging current Ip during image formation in order to form a toner image on the photosensitive drum 3a. However, in this embodiment, the charging current detection unit 701 is also used for determining the presence or position of the developing unit 4.

[Block diagram of image forming apparatus]
FIG. 6B is a block diagram illustrating a control configuration of the image forming apparatus according to the present exemplary embodiment. In the first embodiment, the current detection unit 307 is used as a means for detecting current. However, in this embodiment, the current detection unit 801 is used. The current detection unit 801 controls the charging current detection unit 701 to detect the charging current Ip flowing between the photosensitive drum 3 a and the charging roller 14. The detection result of the current detection unit 801 has a larger value as the current flowing in the positive direction increases. The presence / absence determination unit 811, the contact determination unit 812, and the separation determination unit 813 each make a determination based on the detection result of the current detection unit 801. In addition, the same code | symbol is attached | subjected to the same structure as the structure demonstrated in FIG. 2, and description is abbreviate | omitted.

[Latent image presence / absence judgment processing]
FIG. 7 is a flowchart showing the presence / absence determination of a latent image in this embodiment. The instruction for determining the latent image is performed from the same processing as in the first embodiment. That is, the latent image presence / absence determination shown in FIG. 7 is a process performed in S504 at the time of the presence / absence determination of the developing unit 4 in FIG. 4A or the separation determination in FIG. 4B. The latent image presence / absence determination shown in FIG. 7 is also a process performed in S604 at the time of contact determination of the developing unit 4 in FIG. Further, the transfer voltage and the charging voltage shown in Table 1 are used.

(Judgment of presence or absence of latent image)
FIG. 7 is a flowchart of the presence / absence determination of the latent image at the time of the presence / absence determination of the developing unit 4, the determination of the separation, or the contact determination. Unlike FIG. 4C, the latent image on the photosensitive drum 3a is determined based on the detection result of the charging current Ip. Note that the processing in S901 in FIG. 7 is the same as the processing in S532 in FIG. In step S <b> 902, the main control unit 301 detects the charging current Ip with the charging current detection unit 701, and acquires the detection result of the charging current Ip from the current detection unit 801.

  Here, the surface potential of the photosensitive drum 3a when the latent image is formed on the photosensitive drum 3a is higher than the surface potential when the latent image is not formed. Since the charging voltage is −1400 [V] from Table 1, the charging current Ip detected by the current detection unit 801 is larger when the latent image is formed on the photosensitive drum 3a. Smaller than when not formed. Therefore, a threshold value for detecting the charging current Ip is provided, and the presence or absence of a latent image is determined by comparing the detected charging current Ip with the threshold value.

  In step S903, the main control unit 301 determines whether the charging current Ip detected in step S902 is equal to or smaller than a second threshold value. If the main control unit 301 determines in step S903 that the charging current Ip is equal to or less than the second threshold value, the main control unit 301 determines that a latent image is formed on the photosensitive drum 3a, and advances the process to step S904. In step S904, the main control unit 301 stores the latent image presence information in the storage unit 314, and advances the processing to step S505 in FIGS. 4A and 4B or step S605 in FIG. If the main control unit 301 determines in step S903 that the charging current Ip is greater than the second threshold value, the main control unit 301 determines that a latent image is not formed on the photosensitive drum 3a, and advances the process to step S905. In step S905, the main control unit 301 stores the no latent image information in the storage unit 314, and advances the processing to step S505 in FIGS. 4A and 4B. Note that the second threshold value used for the determination in S903 is set in the same manner as in the first embodiment, and thus the description thereof is omitted.

  As described above, in this embodiment, the image forming apparatus capable of determining the position of the developing unit 4 based on the detection result of the charging current Ip has been described. However, in the case of an image forming apparatus including both the charging current Ip detection unit and the transfer current It detection unit, the present embodiment and the first embodiment may be used in combination. For example, detection of the charging current Ip is used to determine the presence / absence of a latent image when determining the separation of the developing unit 4, and detection of the transfer current It described in the first embodiment is used to determine whether there is a latent image when determining contact. The position of the developing unit 4 may be determined.

  As described above, according to this embodiment, the manufacturing cost can be reduced and the configuration can be simplified.

  In the third embodiment, the charging voltage, the transfer voltage, and the laser light amount are set according to a change (hereinafter referred to as deterioration) due to the use of the photosensitive drum 3a, and the position of the developing unit is determined. This is because if the same charging voltage, transfer voltage, and laser light amount are used, the current value that can be detected changes due to deterioration of the photosensitive drum 3a, and therefore the position determination of the developing unit 4 may not be performed correctly. Because there is. As a method for estimating the degree of deterioration of the photosensitive drum 3a, estimation of the film thickness of the photosensitive drum 3a based on the driving time of the photosensitive drum 3a is known. The film thickness of the photosensitive drum 3a becomes thinner as the driving time (usable time) of the photosensitive drum 3a becomes longer. Also in the present embodiment, description will be made using estimation of the film thickness of the photosensitive drum 3a based on the driving time of the photosensitive drum 3a. In this embodiment, the position determination of the developing unit 4 based on the detection result of the transfer current It by the transfer current detection unit 202 described in the first embodiment is used. For estimation of the film thickness of the photosensitive drum 3a, for example, the number of printed sheets S, the charging time, the contact time of the developing roller 4a, or the like may be used.

[Block diagram of image forming apparatus]
FIG. 8 is a block diagram illustrating a control configuration of the image forming apparatus according to the present exemplary embodiment. In addition to the configuration of the first embodiment, a deterioration determining unit 1001 for determining a change in the film thickness of the photosensitive drum 3a is provided. The deterioration determining unit 1001 determines the deterioration of the photosensitive drum 3a based on the driving time of the photosensitive drum 3a stored in the nonvolatile memory 1011. In this embodiment, the deterioration determining unit 1001 determines the film thickness of the photosensitive drum 3a. The exposure control unit 302, the charging output control unit 305, and the transfer output control unit 306 are respectively adapted to the amount of laser light and charging according to the film thickness (in other words, deterioration) of the photosensitive drum 3 a determined by the deterioration determination unit 1001. Change the voltage and transfer voltage settings. In addition, the same code | symbol is attached | subjected to the same structure as the structure demonstrated in FIG. 2, and description is abbreviate | omitted.

[Latent image presence / absence judgment processing]
FIG. 9 is a flowchart for explaining the presence / absence determination of the latent image at the time of the presence / absence determination of the developing unit 4 or the separation determination and the contact determination according to the present embodiment. Table 2 shows set values of the laser light quantity [μJ / cm ² ], the charging voltage [V], and the transfer voltage [V] corresponding to the film thickness [μm] of the photosensitive drum 3a. For example, when the film thickness of the photosensitive drum 3a determined by the deterioration determination unit 1001 is 14 μm, the main control unit 301 from Table 2 indicates that the amount of laser light is 440 μJ / cm ² , the charging voltage is −1370V, and the transfer Set the voltage to + 1480V.

  In the image forming apparatus according to the present exemplary embodiment, the scanner unit 5 emits laser light with the light amount specified by the exposure control unit 302. Further, the charging voltage designated by the charging output control unit 305 is applied by the charging voltage power source 203. Further, the transfer voltage specified by the transfer output control unit 306 is applied by the transfer voltage power supply 201.

  Table 2 shows the amount of laser light, the charging voltage, and the transfer voltage according to the film thickness of the photosensitive drum 3a. In the image forming apparatus of this embodiment, by using these values, even if the film thickness of the photosensitive drum 3a is thin, current detection is performed in the same manner as when the film thickness is large, and the latent image on the photosensitive drum 3a is detected. Can be determined. The relationship between the film thickness of the photosensitive drum 3a, the amount of laser light, the charging voltage, and the set value of the transfer voltage, in other words, the information in Table 2 is determined when the image forming apparatus is designed and stored in the nonvolatile memory 1011. .

  In this embodiment, the presence / absence determination of the latent image is performed from the same processing as that in the first embodiment. That is, the presence / absence determination of the latent image in FIG. 9 is performed in S504 at the time of the presence / absence determination of the developing unit 4 in FIG. 4A or at the separation determination in FIG. 4B or at S604 at the time of contact determination in FIG. Each process is performed. In FIG. 9, when the presence / absence determination of a latent image is instructed, the processing after S1101 is executed.

(Judgment of presence or absence of latent image)
In step S <b> 1101, the main control unit 301 causes the deterioration determination unit 1001 to estimate the film thickness of the photosensitive drum 3 a based on the driving time of the photosensitive drum 3 a stored in the nonvolatile memory 1011. In step S1102, the main control unit 301 determines the charging voltage and the transfer voltage from Table 2 according to the film thickness of the photosensitive drum 3a estimated in step S1101, and sets the charging voltage by the charging voltage power source 203 and the transfer voltage by the transfer voltage power source 201. , Respectively. In S1103, the main control unit 301 determines the laser light amount from Table 2 according to the film thickness of the photosensitive drum 3a estimated in S1101, and changes the laser light amount. Since the processing after S532 in FIG. 9 is the same as the processing described in FIG. 4C of the first embodiment, the same step number is assigned and the description is omitted.

  As described above, in this embodiment, when determining the position of the developing unit 4 by the transfer current It, an appropriate laser light amount, charging voltage, and transfer voltage are used according to the film thickness of the photosensitive drum 3a. As a result, even when the deterioration of the photosensitive drum 3a progresses, the position of the developing unit 4 can be determined based on the detection result of the transfer current It. In the present embodiment, an appropriate laser light amount, charging voltage, and transfer voltage are set according to the film thickness of the photosensitive drum 3a, but the first used in S534 of FIG. 9 according to the film thickness of the photosensitive drum 3a. The threshold value may be set appropriately. Further, instead of the detection result of the transfer current It, the detection result of the charging current Ip according to the second embodiment may be used. When the detection result of the charging current Ip is used, an appropriate laser is used according to the film thickness of the photosensitive drum 3a. What is necessary is just to set a light quantity and a charging voltage.

  In the first to third embodiments, the image forming apparatus illustrated in FIG. 1 has been described. However, the configuration of the image forming apparatus is not limited to such a configuration. That is, if the developing unit is detachable and the light emitted from the scanner unit is blocked or not blocked according to the mounting / demounting / abutment / separation position of the developing unit. Good. For example, the image forming apparatus may include a plurality of process cartridges for a plurality of colors.

  As described above, according to this embodiment, the manufacturing cost can be reduced and the configuration can be simplified.

3a Photosensitive drum 4 Development unit 5 Scanner unit 8 Transfer roller 202 Transfer current detection unit 301 Main control unit

Claims (16)

A photoreceptor,
Exposure means for irradiating the photoreceptor with light to form a latent image;
A developing unit configured to develop a latent image formed by the exposure unit to form a toner image; a first position where the developing unit contacts the photoconductor; and a second position spaced apart from the photoconductor; A development unit capable of moving between,
Driving means for driving the developing unit;
A conductive member in contact with the photosensitive member;
First detection means for detecting a current flowing through the conductive member;
A latent image judging means for judging whether or not a latent image is formed on the photoconductor based on a detection result by the first detecting means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, further comprising: a mounting determination unit that determines whether the developing unit is mounted based on a determination result by the latent image determination unit.   The mounting determination unit is configured to determine that a latent image is formed on the photoconductor by the latent image determination unit when the driving unit moves the developing unit to the second position. Determines that the developing unit is not mounted, and if the latent image determining unit determines that a latent image is not formed on the photoconductor, determines that the developing unit is mounted. The image forming apparatus according to claim 2.   The developing unit is in the first position or the second position based on the determination result by the latent image determining means in a state where the developing determining unit determines that the developing unit is mounted. The image forming apparatus according to claim 3, further comprising a position determining unit that determines   The mounting determination unit determines whether or not the developing unit is mounted when the power of the image forming apparatus is turned on or when the developing unit is attached or detached. 5. The image forming apparatus according to 4. A photoreceptor,
Exposure means for irradiating the photoreceptor with light to form a latent image;
A developing unit configured to develop a latent image formed by the exposure unit to form a toner image; a first position where the developing unit contacts the photoconductor; and a second position spaced apart from the photoconductor; A development unit capable of moving between,
Driving means for driving the developing unit;
A conductive member in contact with the photosensitive member;
First detection means for detecting a current flowing through the conductive member;
Position determining means for determining that the developing unit is at the first position or the second position based on a detection result by the first detecting means;
An image forming apparatus comprising: A latent image judging means for judging whether or not a latent image is formed on the photosensitive member;
The image forming apparatus according to claim 6, wherein the position determining unit determines that the developing unit is in the first position or the second position based on a determination result by the latent image determining unit.   When the position determining means determines that a latent image is formed on the photosensitive member by the latent image determining means when the developing unit is moved to the first position by the driving means. The image forming apparatus according to claim 4, wherein the developing unit is determined to be in the first position.   The position determining means does not form a latent image on the photoreceptor by the latent image determining means even if the driving means moves the developing unit to the first position a predetermined number of times. The image forming apparatus according to claim 8, wherein if it is determined that there is no failure, it is determined that the developing unit is out of order.   When the position determining means determines that a latent image is not formed on the photosensitive member by the latent image determining means when the developing unit is moved to the second position by the driving means. The image forming apparatus according to claim 4, wherein the developing unit is determined to be in the second position.   Even if the position judging means causes the driving means to move the developing unit to the second position a predetermined number of times, a latent image is formed on the photoconductor by the latent image judging means. The image forming apparatus according to claim 10, wherein if it is determined that the developing unit is faulty, it is determined that the developing unit is out of order. Charging means for charging the photoreceptor;
First application means for applying a charging voltage to the charging means;
Control means for controlling the amount of light emitted from the exposure means;
Transfer means for transferring a toner image formed on the photoreceptor;
Second application means for applying a transfer voltage to the transfer means;
Second detection means for detecting the degree of deterioration of the photoreceptor;
With
The latent image determining means determines whether the latent image is formed on the photoconductor according to the degree of deterioration of the photoconductor detected by the second detecting means. The first detection unit applies the charging voltage applied by one application unit, the transfer voltage applied by the second application unit, and the amount of light irradiated by the exposure unit to the conductive member. The image forming apparatus according to claim 4, wherein a flowing current is detected.   The image forming apparatus according to claim 12, wherein the second detection unit detects a degree of deterioration of the photoconductor according to a film thickness of the photoconductor.   The image forming apparatus according to claim 13, wherein the second detection unit estimates a film thickness of the photoconductor based on a driving time of the photoconductor. The conductive member is the transfer means;
The latent image determining unit determines that a latent image is not formed on the photoconductor when the current flowing through the transfer unit is determined to be larger than a first threshold value, and the first threshold value is determined. The image forming apparatus according to claim 12, wherein if it is determined that the latent image is below, it is determined that a latent image is formed on the photosensitive member. The conductive member is the charging means;
The latent image determining unit determines that a latent image is not formed on the photoconductor when the current flowing through the charging unit is determined to be larger than a second threshold value, and the second threshold value is determined. The image forming apparatus according to claim 12, wherein if it is determined that the latent image is below, it is determined that a latent image is formed on the photosensitive member.

Images