JP2007271657A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus where the responsiveness of a laser element is made compatible with restraint of the optical fatigue of an image carrier. <P>SOLUTION: The image forming apparatus is equipped with: the laser element to form an electrostatic latent image on the image carrier by irradiating with light; a current control means to cause a predetermined current to follow to the laser element when a laser irradiation position by the laser element is a non-image part; a detection means to detect the surface potential of the image carrier; and an analysis means to obtain a boundary current I<SB>b</SB>between an area where the surface potential of the image carrier changes gently and an area where it changes suddenly according to the level of the current applied to the laser element based on the result of detection by the detection means. The current control means sets the predetermined current flowing when the laser irradiation position by the laser element is the non-image part to the boundary current I<SB>b</SB>obtained by the analysis means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and in particular, for a laser element that irradiates light to form an electrostatic latent image on an image carrier, a current flows even when the laser irradiation position of the laser element is a non-image portion. The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, image forming apparatuses such as printers, copiers, fax machines, and multi-function machines have been provided with an image carrier such as a photosensitive drum, and the image carrier is irradiated with laser light from an exposure device. As a result, an electrostatic latent image is formed on the image carrier, and a toner image is formed based on the electrostatic latent image.

  The exposure apparatus is provided with a laser element (laser diode: LD) for irradiating laser light. Since the amount of light to be output from the laser element changes with temperature and changes over time, stable output is performed by automatic control (APC: Auto Power Control).

  Here, when the current that flows is increased, the laser element emits light as a simple light emitting diode (LED) at first, and the amount of emitted light increases at an accelerated rate as a certain amount of current flows. Laser emission starts.

Therefore, in the technique disclosed in Patent Document 1, even when the laser irradiation position is a non-image part, the current flowing through the laser element is not reduced to 0, and the current for forming the minimum density, that is, the threshold value when the laser element starts laser emission. A current is supplied as a bias current to the laser element so as to improve the response of the laser element when irradiating the image portion with light. The magnitude of this current that forms the minimum density is obtained by detecting the potential of the image carrier relative to the current flowing through the laser element.
JP 2000-187374 A

  However, even when the laser irradiation position is in the non-image portion as described above, causing the laser element to emit current and causing light emission causes light fatigue in the image carrier.

  The present invention has been made in view of this point, and an object of the present invention is to provide an image forming apparatus capable of satisfying both responsiveness of a laser element and suppression of light fatigue of an image carrier.

  The image forming apparatus according to claim 1, wherein a laser element that irradiates light to form an electrostatic latent image on an image carrier, and the laser element is predetermined when the laser irradiation position of the laser element is a non-image portion. Current control means for causing current to flow, detection means for detecting the surface potential of the image carrier, and the detection result of the detection means, based on the detection result of the detection means, Analyzing means for obtaining a boundary current between a region where the surface potential changes slowly and a region where the surface potential changes abruptly, and the current control means flows when the laser irradiation position of the laser element is a non-image portion. In the image forming apparatus, the predetermined current is equal to or less than the boundary current obtained by the analysis unit.

  With this configuration, light is irradiated from the laser element, an electrostatic latent image is formed on the image carrier, and the laser irradiation position of the laser element with respect to this laser element is predetermined even when the laser irradiation position is a non-image portion. As the electric current flows, the surface potential of the image carrier is detected, and based on the detection result, the surface potential of the image carrier rapidly changes depending on the magnitude of the current passed through the laser element. The boundary current with the region where the change occurs is determined, and the predetermined current that flows to the laser element when the laser irradiation position of the laser element is a non-image portion is set to be equal to or less than the determined boundary current.

  Therefore, even when the laser irradiation position of the laser element is a non-image part, the responsiveness of the laser element when starting to irradiate light on the image part is improved by passing a current through the laser element. The surface potential of the image carrier is made less than or equal to the boundary current between the region where the surface potential of the image carrier slowly changes and the region where it suddenly changes according to the magnitude of the current flowing through the laser element, so that an excessive amount of light is applied to the image carrier. Since it is made not to irradiate, suppression of light fatigue and the responsiveness of a laser element can be made compatible.

  The analyzing means may identify the boundary current based on the detection potential of the detecting means corresponding to the current by causing the laser element to emit light with a predetermined current, or for image formation. The boundary current may be specified on the basis of the potential detected by the detection means when the laser element emits light and the magnitude of the current passed through the laser element at that time.

  The detecting means may identify the surface potential by detecting the amount of light emitted from the laser element that has formed a potential on the surface of the image carrier, or may be formed according to the surface potential of the image carrier. The surface potential may be specified by detecting the density of the toner image.

  The current control means preferably causes the predetermined current to flow through the laser element as a bias current constantly flowing through the laser element. In this way, the device configuration can be simplified.

  The image forming apparatus according to claim 1, wherein the current control unit causes the boundary current to flow through the laser element when a laser irradiation position of the laser element is a non-image portion.

  With this configuration, when the laser irradiation position of the laser element is a non-image portion, a boundary current flows through the laser element, and thereby, a sufficiently large amount of current flows through the laser element to ensure high response. The element can be realized with certainty, whereby both the responsiveness of the laser element and the avoidance of light fatigue of the image carrier can be reliably achieved.

  The image forming apparatus according to claim 3, wherein the current control unit switches a current flowing through the laser element to a plurality of magnitudes, and the analysis unit sends a current flowing through the laser element through the current control unit. By switching to a magnitude, the laser element emits light with the plurality of magnitudes of current, and the detection means detects each surface potential generated in the image carrier, and the detection means obtains a detection result. 3. The image forming apparatus according to claim 1, wherein a current at a boundary between two of the currents is specified.

  In this configuration, the current flowing through the laser element by the current control unit is switched to a plurality of magnitudes, and the current flowing through the laser element is switched to the plurality of magnitudes by the current control unit. A detection result obtained by the detection means detecting each surface potential generated in the image carrier by the laser element emitting light with a plurality of magnitudes of current is obtained, and two of the plurality of magnitudes of the current are obtained. The current that is the boundary between the regions is identified.

  In this way, both suppression of light fatigue and responsiveness of the laser element can be achieved.

  According to the present invention, it is possible to achieve both high responsiveness of the laser element and suppression of light fatigue of the image carrier.

  A copying machine 100 according to an embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram schematically illustrating a copying machine 100 according to an embodiment of the present invention. The copier 100 is an electrophotographic image forming apparatus.

  The copying machine 100 includes a photosensitive drum 200, a charger 210, an exposure device 220, a potential detector 230, a developing device 240, and a toner detector 250 provided in the vicinity of the photosensitive drum 200, and the above-described exposure device 220. A bias current control circuit 225 for controlling a bias current passed through the laser element and a control device 300 for controlling each of the above components.

  The charger 210 imparts a charge to the surface of the photosensitive drum 200. The exposure device 220 forms an electrostatic latent image on the surface of the photosensitive drum 200 to which the electric charge is applied by the charger 210. Then, based on the electrostatic latent image, the developing device 240 forms a toner image on the photosensitive drum 200. In FIG. 1, illustration of a transfer portion and the like for transferring the formed toner image onto a recording sheet is omitted.

  The exposure apparatus 220 has a laser element 221 (laser diode: hereinafter simply abbreviated as LD (Laser Diode)), and irradiates the photosensitive drum 200 to which a charge is applied from the LD 221 with laser light. An electrostatic latent image is formed on the surface of the photosensitive drum 200. The exposure apparatus 220 is also provided with a drive IC 222 for automatically controlling (APC: Auto Power Control) the current flowing through the LD 221.

  FIG. 2 is an explanatory diagram showing the relationship between the current flowing through the LD 221 and the amount of light emitted by the LD 221.

As the flowing current increases, the LD 221 gradually increases the amount of emitted light. LD221 while the current is less than the threshold current _{I th} increases gently quantity as mere LED. This current region where the LD 221 operates as a simple LED is referred to as an LED light emitting region. In contrast, current LD 221 exceeds the threshold current _{I th,} LD 221 is started laser emission increases rapidly emission amount. When an electrostatic latent image is formed on the photosensitive drum 200, a current in the LD light emitting region where the LD 221 emits laser light is caused to flow to the LD 221 by the driving IC 222.

  In FIG. 2, the relationship between the current of the LD 221 and the amount of light is schematically shown.

  Returning to FIG. 1, the potential detector 230 detects the amount of light emitted by the LD 221 by detecting the surface potential of the photosensitive drum 200 irradiated with light by the LD 221.

  The toner detector 250 will be described in a modified example.

  The bias current control circuit 225 includes seven current control resistors R1 to R7 and an analog switch 226 that selectively connects the resistors R1 to R7 to the RS terminal of the drive IC 222. The resistors R1 to R7 are provided between the RS terminal of the driving IC 222 and the ground, and have a function of causing a current corresponding to the resistance value of the resistor selected by the analog switch 226 to flow through the bias current of the LD 221. The bias current is a current that is supplied to the LD 221 by the drive IC 222 when the laser irradiation position of the LD 221 is a non-image portion (a portion that does not form a toner image) (hereinafter, referred to as non-image formation). The LD 221 is constantly supplied with this bias current, and an additional current is supplied in addition to the bias current according to the density of the toner image to be formed.

  The control device 300 is an information processing device, and controls the operation of each component described above to execute an image forming process. The control device 300 implements an analysis processing unit 301, an exposure light amount control unit 302, and a resistance selection processing unit 303 by executing software.

  The exposure light quantity control unit 302 controls the light emission quantity of the LD 221 by a pulse width modulation method by inputting a pulse signal to the drive IC 222 provided in the exposure apparatus 220. The exposure light quantity control unit 302 obtains a control signal corresponding to the image data of the image to be formed by the copying machine 100 from an image formation processing unit (not shown), thereby generating a pulse signal to be input to the drive IC 222. Identify.

  The resistance selection processing unit 303 inputs the control signal to the analog switch 226 to select the magnitude of the bias current that flows through the LD 221.

  In the following, when any one of the resistors R1 to R7 is selected by the analog switch 226, the different bias currents that are passed through the LD 221 according to the selected resistor are respectively corresponding to the resistors R1 to R7. Called current.

  The analysis processing unit 301 analyzes the detection result based on the detection result of the potential detector 230, and thereby uses the corresponding current of any one of the seven resistors R1 to R7 as the bias current of the LD 221. Identify what is best for you. When the optimum corresponding current is specified by the analysis processing unit 301, the optimum current is continuously set to the bias current of the LD 221 by the resistance selection processing unit 303 thereafter.

  The above-described processing in which the analysis processing unit 301 specifies the optimum bias current will be described in detail with reference to FIGS.

  FIG. 3 is a flowchart showing the operation of the copying machine 100.

  In step S1, the user turns on the power to the copying machine 100, and the copying machine 100 starts supplying power to each unit. The copying machine 100 sets the magnitude of the bias current of the LD 221 to an appropriate magnitude by executing the illustrated process when the power is turned on.

  In steps S <b> 2 to S <b> 5, the analysis processing unit 301 sequentially causes the corresponding currents of the resistors R <b> 1 to R <b> 7 to flow through the LD 221 and acquires the detection potential of the potential detector 230 when the respective currents flow through the LD 221.

  In step S <b> 2, the analysis processing unit 301 selects one of the resistors R <b> 1 to R <b> 7 and causes a corresponding current corresponding to the resistor to flow through the LD 221.

  In step S <b> 3, the LD 221 emits a light amount corresponding to the flowing current and irradiates the photosensitive drum 200. At this time, prior to light emission, a charge is applied in advance from the charger 210 (FIG. 1) to the region of the photosensitive drum 200 to which light is applied.

  In step S4, the potential of the surface of the photosensitive drum 200 irradiated with light in step S3 is detected by the potential detector 230.

  The analysis processing unit 301 repeatedly executes the processing of steps S2 to S4 (step S5: NO) until the potential detection (steps S2 to S4) is completed for all the resistors R1 to R7 (step S5: NO). When the detection is finished, the processing after step S6 is started (step S5: YES).

  The potential detection (steps S2 to S4) for the resistors R1 to R7 may be performed in any order. For example, the potential detection may be performed in descending order of resistance value or in ascending order.

  In steps S6 to S7, the analysis processing unit 301 analyzes the detection result of the potential detector 230 with the corresponding currents of the resistors R1 to R7 obtained in the processes of steps S2 to S5.

  In step S6, the analysis processing unit 301 specifies the potential function V (i) based on the detection potential of the potential detector 230 at the corresponding current of the resistors R1 to R7 detected in step S4.

  FIG. 4 is an explanatory diagram showing the potential function V (i).

  Black circles shown in FIG. 4 indicate, in order from left to right, the detection potentials in step S4 of FIG. 3 for the corresponding currents of the resistors R1 to R7. For example, the potential indicated by the symbol V5 is a detection potential at the corresponding current of the resistor R5. Each potential at the resistors R1 to R7 is lower as the potential is detected when a large current is passed through the LD 221, that is, as the potential indicated by the black circle on the right side. This is because as the larger current flows through the LD 221, the LD 221 emits a larger amount of light and removes charges from the photosensitive drum 200.

  Based on the black circle data in FIG. 4 detected in step S4 of FIG. 3, the analysis processing unit 301 detects the potential function V (i) indicated by the dashed line graph in FIG. A potential function V (i) indicating a correspondence relationship with the surface potential of the body drum 200 is specified.

In this potential function V (i), across a boundary currents I _b, the small current from the demarcation current I _b, in the slowly voltage (vertical axis) is changed, a current larger than the demarcation current I _b, the potential ( The vertical axis) changes rapidly. Analysis processing unit 301, after identifying the potential function V (i), according obtaining this boundary current I _b.

  In step S6 of FIG. 3, the analysis processing unit 301 specifies the potential function V (i).

Then, in step S7, the analysis processing unit 301 calculates a boundary current _{I b.} However, not necessarily, the demarcation current I _b is the one of the corresponding current of the resistor R1 to R7, does not necessarily completely strictly match, the analysis processing unit 301, the value of the exact boundaries current I _b nearest to either the corresponding current of the resistor R1 to R7, identified as the demarcation current _{I b.} Hereinafter, such a demarcation current I _b specified in the will be described with equated with demarcation current I _b in the strict sense. Analysis processing unit 301, by determining the boundary current _{I b,} the resistance of the demarcation current _{I b} and the corresponding current is determined from among the resistors R1 to R7.

In Figure 4, the analysis processing unit 301, shown for the case of specifying the resistor R5 as resistance demarcation current I _b.

Note that the boundary current I _b, in the threshold current I _th as described in FIG. 2, the smaller the boundary current I _b. Moreover, than the current which flows through the LD221 when the copying machine 100 to form an image of the minimum density to the recording paper, the smaller the boundary current I _b.

In step S8 in FIG. 3, the resistance selection processing unit 303, a signal for selecting the analysis processing unit 301 identified as a resistance of the boundary current I _b resistor is inputted to an analog switch 226, a corresponding current in the resistance LD221 Set to the bias current.

  In step S9, image formation is performed under the appropriate bias current thus set.

If the copying machine 100 described above, while the responsiveness of the LD221 by current LD221 even during non-image formation is made to flow is improved, since the demarcation current I _b which flows through the LD221 during non image formation is small, While ensuring the responsiveness of the LD 221, light fatigue of the photosensitive drum 200 can be avoided, and both can be made compatible.

  A modification of the present embodiment will be described below.

  (A) In the description of the above-described embodiment, the bias current is determined by the potential detector 230 detecting the potential of the photosensitive drum 200 irradiated with light from the LD 221. However, the present invention is limited to this case. For example, instead of the potential detector 230, a light amount measuring device that directly measures the amount of light emitted by the LD 221 may be used, or the toner detector 250 (FIG. 1) may be used.

  The toner detector 250 detects the density of the toner image formed on the photosensitive drum 200 by the developing device 240 based on the electrostatic latent image, thereby forming an electrostatic latent image based on the toner image of that density. The potential of the photosensitive drum 200 thus detected is detected.

  The density of the toner image is determined according to the amount of light of the LD 221 in the same manner as the potential of the photosensitive drum 200 shown on the vertical axis of FIG. Instead of the potential of the photosensitive drum 200, the processing described with reference to FIGS. 3 to 4 may be performed by the analysis processing unit 301 and the exposure light amount control unit 302 based on the toner density.

In this case, in step S4 of FIG. 3, the toner detector 250 detects the toner density instead of the potential detector 230 detecting the potential. However, in this step S4, it is essential that the developing device 240 executes the developing process. Based on the thus detected toner density, a step S6, the analysis processing unit 301 identifies the demarcation current I _b.

  The same applies to the case where a light amount measuring device that directly measures the amount of light emitted by the LD 221 is used.

  Note that the magnitude of the bias current may be determined by comprehensive determination based on at least two detection results of the potential detector 230, the toner detector 250, and the light amount measuring device.

The potential detection in step S2~S5 of (B) 3, necessarily, not have to detection of all of the resistors R1 to R7, necessary for obtaining the demarcation current _{I b} (step S6～S7) It is enough to go within the range. Therefore, in step S5, even if detection with all resistors is not completed, it may be determined that the detection has been completed within a necessary range, and the process may proceed to step S6 and subsequent steps (step S5: YES).

(C) The number of current control resistors provided in the bias current control circuit 225 is not limited to seven as in the resistors R1 to R7, but at most, it is at least better. Also, instead of switching the bias current stepwise by a plurality of resistors as described above, a bias current control circuit that continuously changes the bias current steplessly is provided, and the potential of the photosensitive drum 200 corresponding to the change is provided. by detecting a change in electric potential detector 230, more precisely the current of the current value close to the demarcation current I _b may be those in the bias current of the LD 221. By doing so, it is possible to achieve both the avoidance of light fatigue and the responsiveness of the LD 221 more accurately.

(D) is not limited to the current equal to the demarcation current I _b, or as the bias current is the demarcation current I _b is smaller than current. For example, if a degree of light-induced fatigue to the photosensitive drum 200 is already occurring, such as when the risk of adverse effects due to light fatigue is high, the resistance is selected resistance to flow in LD221 even less current than the demarcation current I _b It may be selected by the processing unit 303 and the corresponding current of the resistor is used as the bias current.

  (E) Once the bias current of the LD 221 set in the step of FIG. 3 is set once, the power to the copying machine 100 is turned on again, that is, the processing of FIG. 3 is executed again. Until it is not changed. In this way, the processing of the copying machine 100 can be simplified.

  However, the processing of steps S2 to S8 in FIG. 3 may be performed based on a user instruction or the like, so that the bias current may be appropriately adjusted before the power is turned on again.

  Note that the processing of steps S2 to S8 in FIG. 3 in which an appropriate bias current is specified and set in the copying machine 100 is performed when the copying machine 100 is turned on or when a user's instruction is given. For example, the copying machine 100 may automatically start this processing at regular intervals to adjust the bias current.

1 is a diagram schematically showing a copying machine 100 according to an embodiment of the present invention. It is explanatory drawing which shows the relationship between the electric current which flows into LD221, and the light quantity which LD221 light-emits. 3 is a flowchart showing the operation of the copying machine 100. It is explanatory drawing which shows electric potential function V (i).

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Copier 200 Photosensitive drum 210 Charger 220 Exposure apparatus 221 Laser element 222 Drive IC
225 bias current control circuit 226 analog switches 230 potential detector 240 developing device 250 toner detector 300 controller 301 analyzer processing unit 302 exposure light amount control unit 303 resistor selecting section I _b demarcation current I _th threshold current R1~R7 current-controlling Resistor V (i) Potential function V5 Potential at bias current by resistor R5

Claims (3)

A laser element that irradiates light to form an electrostatic latent image on the image carrier;
Current control means for causing a predetermined current to flow through the laser element when the laser irradiation position of the laser element is a non-image portion;
Detection means for detecting a surface potential of the image carrier;
An analysis for obtaining a boundary current between a region where the surface potential of the image carrier slowly changes and a region where the surface potential changes abruptly according to the magnitude of the current flowing through the laser element based on the detection result of the detection means. Means and
The image forming apparatus, wherein the current control unit sets the predetermined current that flows when the laser irradiation position of the laser element is a non-image portion to be equal to or less than a boundary current obtained by the analysis unit.   The image forming apparatus according to claim 1, wherein the current control unit causes the boundary current to flow through the laser element when a laser irradiation position of the laser element is a non-image portion. The current control means switches the current flowing through the laser element to a plurality of magnitudes,
The analyzing unit causes the current control unit to switch the current flowing through the laser element to the plurality of magnitudes, whereby each of the laser elements emits light with the plurality of magnitudes and is generated in the image carrier. 3. The image forming apparatus according to claim 1, wherein a detection result obtained by detecting the surface potential by the detection unit is acquired, and a current at a boundary between the two regions among the plurality of currents is specified.

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