JP5067007B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  An electrophotographic image forming apparatus such as a copying machine, a printer, or a facsimile machine transfers a toner image from a surface of an image carrier such as a photosensitive member or an intermediate transfer member onto a recording medium, and fixes the transferred toner image. An image is formed on a recording medium. In such an image forming apparatus, it is important for improving the image quality that the density of the image transferred onto the recording medium is always properly controlled.

  Therefore, as a means for appropriately controlling the image density, for example, a toner image for density measurement (referred to as a patch image) for measuring the density of the toner image is formed on the photoconductor, and the density of the patch image is detected by optical density detection. A stable image is obtained by performing image density control in which the detection result is fed back to the exposure amount exposed by the writing means and the developing bias.

  The optical density detection means comprises a light emitting element such as an LED, a light receiving element such as a photodiode, and a holder for holding both elements, and irradiates the patch image on the photoreceptor with light from the light emitting element. The density of the patch image is measured by measuring the reflected light of the patch with a light receiving element.

  However, in the optical density detector, the amount of emitted light is reduced compared to the initial state due to deterioration of the light emitting element, or the measurement surface (sensor surface) of the element (sensor) is contaminated with toner, and the light received by the light receiving element is input. The amount of light changes.

Therefore, it is necessary to adjust the amount of emitted light so that the amount of received light is the same as in the initial state. As an adjustment method, for example, in Patent Document 1, the intermediate transfer drum surface is irradiated with the light amount of the initial light amount value Aoh of the correction density sensor, and the density Vmes of the intermediate transfer drum is measured. Next, when Vmes = V0 as compared with the reference density V0, Aoh is set as the irradiation light quantity (light emission quantity) of the density sensor at the time of image density control. A method is described in which when Vmes is greater than or smaller than V0, the output Vmes is increased or decreased by a certain amount until V0 reaches V0, and the light amount when Vmes = V0 is set as the light emission amount of the density sensor at the time of image density control. Has been.
Japanese Patent Laid-Open No. 10-268591

  However, as described in Patent Document 1, a method of adjusting the amount of emitted light by a certain amount and adjusting it to a target value (referred to as a staircase search adjustment method) When the amount of change, which is the difference from the initial light amount, is small compared to the initial state, the adjustment time can be completed in a relatively short time even using a means called the staircase search adjustment method.

  However, if the inside of the device is cleaned or the material is replaced while the power is off, the dirty sensor surface may be cleaned, or conversely, a large amount of toner may adhere due to machine vibration. There is a possibility that the amount of change in the amount of received light is larger than the initial state with respect to a certain amount of emitted light. When such a change amount is large, there is a problem that adjustment takes time in the method in which the amount of emitted light is increased or decreased by a fixed amount by the staircase search adjustment method.

  An object of the present invention is to provide an image forming apparatus having an adjusting unit that adjusts the amount of light emitted from a light emitting unit without deteriorating print productivity even when the sensor surface of the optical density detecting unit is soiled with toner or the like. is there.

The above object can be achieved by the following configurations.
1. An electrostatic latent image carrier and a toner image for density measurement are formed on the electrostatic latent image carrier, and the density of the toner image is measured by an optical density detector having a light emitting part and a light receiving part. An image forming control unit that controls image forming conditions according to a measurement result, and a control unit that adjusts a light emission amount of the light emitting unit,
The image forming apparatus characterized in that the control means performs adjustment by a binary search adjustment method during a warm-up operation and performs adjustment by a staircase search adjustment method during an image forming operation .

  According to the present invention, the control means for adjusting the light emission amount of the light emitting unit is adjusted without reducing print productivity because the adjustment operation for adjusting the light emission amount is different between the warm-up operation and the image forming operation. Is possible.

An embodiment of the present invention will be described. In addition, although this invention is demonstrated based on embodiment of illustration, this invention is not restricted to this embodiment. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.
(Body structure)
FIG. 1 is a cross-sectional configuration diagram as an example of an image forming apparatus of the present invention.

  In FIG. 1, reference numeral 50 denotes a photosensitive member (photosensitive drum). In the photosensitive drum 50, a photosensitive layer is applied on a drum, and a resin layer is provided thereon. Furthermore, it is grounded and rotated clockwise. Reference numeral 52 denotes a scorotron charger (charging means) for uniformly charging the circumferential surface of the photosensitive drum 50 by corona discharge. Prior to the charging by the charger 52, the peripheral surface of the photosensitive member may be discharged by performing exposure by the pre-charging exposure unit 51 using a light emitting diode or the like in order to eliminate the history of the photosensitive member in the previous image formation.

  After uniform charging of the photoreceptor, image exposure based on the image signal is performed by an image exposure unit 53 as an image exposure unit. The image exposure unit 53 in this figure uses a laser diode (not shown) as an exposure light source. Scanning on the photosensitive drum is performed by the light whose optical path is bent by the reflection mirror 532 through the rotating polygon mirror 531 and the fθ lens, and an electrostatic latent image is formed.

  Here, in this embodiment, a reversal development process is used. In the reversal development process, the surface of the photoreceptor is uniformly charged by the charger 52, and the exposed area of the photoreceptor, that is, the exposed area potential (exposed area) of the photoreceptor is visualized by the developing process (means). This is an image forming method. On the other hand, the unexposed portion potential is not developed by the developing bias potential applied to the developing sleeve 541.

  The electrostatic latent image is then developed by a developing device 54 as developing means. A developing device 54 containing a developer composed of toner and carrier is provided at the periphery of the photosensitive drum 50, and development is performed by a developing sleeve 541 that contains a magnet and rotates while holding the developer. At this time, usually, development is performed by applying a DC bias between the photosensitive drum 50 and the developing sleeve 541 and, if necessary, an AC bias voltage. Further, the developer is developed in contact with or not in contact with the photoreceptor. The potential of the photosensitive member is measured by providing a potential sensor 547 above the development position as shown in FIG.

  Further, as will be described later, an optical density detecting means 80 for detecting the density of the patch image formed on the surface of the photosensitive drum is provided. The optical density detection means 80 is disposed between the developing position and the transfer position with a predetermined distance from the photosensitive drum, and has a light emitting element 81 that irradiates light to the light emitting section. Is a reflective optical sensor having a light receiving element 82 that receives light and measures the amount of light received.

  The transfer paper P as a recording medium is fed to the transfer area by the rotation operation of the paper feed roller 57 at the time when the transfer timing is ready after image formation.

  In the transfer area, a transfer electrode (transfer means: transfer device) 58 is operated on the peripheral surface of the photosensitive drum 50 in synchronization with the transfer timing, and the charged recording paper P is charged with a polarity opposite to that of the toner. Transfer the toner.

  Next, the transfer paper P is neutralized by a separation electrode (separator) 59, separated by the peripheral surface of the photosensitive drum 50 and conveyed to the fixing device 60, and the toner is removed by heating and pressurizing the heat roller 601 and the pressure roller 602. After the welding, the sheet is discharged to the outside of the apparatus via the sheet discharge roller 61. The transfer electrode 58 and the separation electrode 59 stop the primary operation after the transfer paper P passes and prepare for the next toner image formation. In FIG. 1, a transfer band electrode of corotron is used as the transfer electrode 58. The transfer electrode setting conditions vary depending on the process speed (peripheral speed) of the photosensitive member and cannot be specified. For example, the transfer current is set to +100 to +400 μA, and the transfer voltage is set to +500 to +2000 V. can do.

  On the other hand, after the transfer paper P is separated, the photosensitive drum 50 removes and cleans residual toner by pressure contact of a blade 621 of a cleaning device (cleaning means) 62, and again performs charge removal by the pre-charge exposure unit 51 and charging by the charger 52. Then, the next image forming process is started.

  Reference numeral 70 denotes a detachable process cartridge in which a photoconductor, a charger, a transfer device, a separator, and a cleaning device are integrated.

All the operations described above are controlled and managed by a control means MC (not shown) included in the image forming apparatus used in the present embodiment.
(Density detection means)
Next, the optical density detector 80 according to the present invention will be described. As described above, when the element surfaces (sensor surfaces) of the light emitting element 81 and the light receiving element 82 of the optical density detector 80 are contaminated with toner or paper dust, the amount of received light changes with respect to the initial value as a design standard. Yes (mainly reduced). Therefore, means for adjusting the amount of emitted light is required so that the amount of received light is the same as the initial value. The adjusting means will be described below.

  FIG. 2 shows a schematic characteristic curve of an optical density detector 80 having an LED as the light emitting element 81 and a photodiode as the light receiving element 82. The horizontal axis in FIG. 2 indicates the light emission voltage (referred to as Vout) applied to the light emitting element 81, and the vertical axis indicates the light reception voltage (referred to as Vin) when the light receiving element 82 receives light.

  FIG. 2 shows a reference voltage (referred to as Vobject) as a design reference voltage (initial value). Since it takes time to accurately adjust Vobject so that it becomes Vobject, it has an adjustment range ± α as a range that does not affect the reference voltage within a certain range (no problem). (Referred to as Object ± α).

  In FIG. 2, when the characteristic curve of the reflective optical sensor when the sensor surface is not dirty is a1, it is expected that the characteristic curves gradually become a2 and a3 when the sensor surface becomes dirty.

  When the sensor surface becomes dirty and the reflective optical sensor enters the state of the characteristic curve a2, the light emission voltage must be changed from Vout (0) to Vout (1) as the reference light emission voltage in order to obtain Vobject. However, since the characteristic curve of the reflection type optical sensor changes depending on the degree of contamination on the sensor surface, it is not known how much Vout (1) is set to Vobject, and Vout cannot be obtained easily.

Therefore, Vout was obtained using the following method. That is, the amount of change (Vobject-Vin) in which the amount of received light generally changes is
1) It is large when a print job is started after the power is turned on after the power is turned off and the apparatus is warmed up.
2) There are few cases during the operation of outputting an image.
It is known.

  In the case of 1), if the inside of the device is cleaned or the material is replaced while the power is turned off, the dirty sensor surface may be cleaned, or conversely, a large amount of toner may adhere. The amount of change is considered large. In the case of 2), since the toner or the like gradually adheres to the sensor surface, the amount of change is considered to be small.

  Therefore, as an adjustment method when the amount of change is large as in the case of 1), a binary search adjustment method for repeatedly searching for an intermediate value between the upper value and the lower value of Vout including Vobject and performing a search so as to approach Vobject, When the amount of change is small as in the case of 2), it is known that there is a staircase search adjustment method in which a search is performed by changing a certain amount from either the upper value or the lower value of the object to approach the object. ing.

Here, the binary search adjustment method and the staircase search adjustment method will be described. FIG. 3 is a conceptual diagram regarding the binary search adjustment method, and FIG. 4 is a conceptual diagram regarding the staircase search adjustment method.
(Binary search adjustment method)
In FIG. 3, the characteristic curve a2 when the sensor surface is dirty will be described as an example. Note that the object has an adjustment width ± α, but is represented by a solid line here.

  First, the upper limit value (upper value 1) and lower limit value (lower value 1) of the voltage are determined in consideration of the allowable withstand voltage and safety factor of the LED as the light emitting element, and an intermediate value Vout (1) between the upper value 1 and the lower value 1 of Vout. ) The numbers in parentheses indicate the number of searches (adjustments).

  It is determined whether Vin (1) when output at Vout (1) is lower or higher than Vobject (first search). If lower, Vout (1) is set to the lower value 2 and the intermediate value Vout from the upper value 1 of Vout Find (2). When Vin (2) when output at Vout (2) is lower than Vobject (second search), Vout (2) is set to the lower value 3 and an intermediate value Vout (3) from the upper value 1 is obtained. When Vin (3) when output at Vout (3) is higher than Vobject (third search), this time, Vout (3) is set to an upper value of 2, and a lower value of 3 is set to Vout (2). Output with the value Vout (4) to obtain Vin (4). If Vin (4) is within the allowable range of the object, the binary search adjustment method is terminated.

A method of obtaining the Vobject by repeatedly performing the act of obtaining the intermediate value in this way is called a binary search adjustment method.
(Staircase search adjustment method)
Next, the staircase search adjustment method will be described with reference to FIG.

  An upper limit value (upper value v1) and a lower limit value (lower value v2) are set as design criteria in the vicinity of Object ± α, and the adjustment range of Vout is set to d [V]. In the present embodiment, the adjustment width d [V] is divided into 10 steps, and the light emission voltage is given so as to step up by a constant voltage vc (vc = d / 10), so that the object becomes Vobject when Vout (0). Pre-stored in the control means MC.

  A value five steps before Vout (0) is set as Vout (−5), and Vout (−4) (Vout (−4) = Vout (−5) + vc), Vout ( -3), Vout (−2)... And Vout are switched and output like a staircase, and Vin is measured each time, and the adjustment is finished when Vin enters the adjustment target, Object ± α. If it does not enter even after 10 adjustments, an error will occur. Alternatively, V ±± may be obtained by starting from the upper value v1 and switching in order.

  A method for obtaining a target value (Voject) while stepping up or down by a certain amount in this way is called a staircase search adjustment method.

  As described above, the binary search adjustment method always repeats the process of obtaining the intermediate value, and therefore has a feature that the time required to obtain the obtained value is almost constant regardless of the amount of change. The staircase search adjustment method is characterized in that the time for searching for a value to be obtained differs depending on the amount of change, and the search time is short when the change is small, and the search time is long when the change is large.

  It is preferable that the method of adjusting the light emission amount of the light emitting portion is performed quickly so as not to affect the image forming operation. Therefore, it is necessary to determine which adjustment method is preferable in order to perform faster, considering the features of the staircase search adjustment method and the binary search adjustment method.

  Therefore, an experiment was conducted to compare whether the staircase search adjustment method or the binary search adjustment method is preferable when the change amount is large or small.

  In the experiment, first, the LED applied voltage change amount (Vout (1) −Vout (0) in FIG. 2) during the warm-up immediately after the sensor surface was cleaned and the photoconductor was replaced and after 1000 copies was measured. Next, the time required to become a Vobject (referred to as correction time) was measured for the staircase search adjustment method and the binary search adjustment method, respectively. The results are shown in Table 1.

  From Table 1, the amount of change in the LED applied voltage during warm-up after the photoconductor replacement was 1V, and the amount of change in the LED applied voltage after 1000 copies was 0.1V. The correction time when the amount of change is 1 V takes 5 seconds or more in the staircase search adjustment method, but only 1 sec in the binary search adjustment method. However, the correction time when the amount of change is 0.1 V ends in 0.5 sec in the staircase search adjustment method, whereas it takes 1 sec in the binary search adjustment method.

  That is, it can be said experimentally that the binary search adjustment method has a constant correction time regardless of the amount of change, and that the staircase search adjustment method changes the correction time depending on the change amount. Therefore, when adjusting the amount of light emitted from the light emitting unit, use the binary search adjustment method when warming up, and use the staircase search adjustment method during image output operation to correct without reducing print productivity. It can be said that this is an excellent adjustment method.

Hereinafter, the adjustment method will be described with reference to the flowcharts of FIGS.
(flowchart)
FIG. 5 is a flowchart showing a flow in which the control means MC of the image forming apparatus used in the present embodiment determines whether to execute the staircase search adjustment method or the binary search adjustment method. FIGS. 6 and 7 are subroutines thereof. FIG.

  In FIG. 5, the control means MC determines whether or not the state of the machine is in a warm-up (WU) state (step S1). When in the WU state (step S1: Yes), the binary search adjustment method (step S2) is performed. When not in the WU state (step S1: No), it indicates that the staircase search adjustment method (step S3) is performed.

  FIG. 6 shows a subroutine for the binary search adjustment method (step S2). The reflection type optical sensor can change the amount of emitted light by 256 steps from 00h to FFh (h is hexadecimal) according to an instruction from the control means MC. The control means MC performs the following control.

  The upper limit of voltage = 255 and the lower limit of voltage = 0 are set (step S21), and (upper limit + lower limit) / 2 is applied to the LED (step S22). After 100 msec from the application, reading of the light amount of the LED is started (step S23), and it is determined whether the light amount is within the target value range (step S24). If within the range (step S24: Yes), the process proceeds to step S25. If it is out of range (step S24: No), the process proceeds to step S26. A step S25 stores the LED set voltage in the nonvolatile memory and ends the binary search adjustment method.

  In step S26, it is determined whether the amount of light is equal to or greater than the target position. If it is equal to or greater than the target value (step S26: Yes), the process proceeds to step S27. If it is lower than the target value, the process proceeds to step S28.

  In step S27, the power supply lower limit value is corrected to the current output value, and the process proceeds to step S29. In step S28, the power supply upper limit value is corrected to the current output value, and the process proceeds to step S29. In step S29, it is determined whether or not the number of corrections has reached 10. When it has reached 10 times (step S29: Yes), the process proceeds to step S25. When it has not reached 10 times (step S29: No), it returns to step S22.

  FIG. 7 shows a subroutine for the staircase search adjustment method (step S3). The control means MC performs the following control.

  That is, the initial setting is set to (current value−5step) (step S31), the output value is applied to the LED (step S32), and the light quantity reading of the LED is started after 100 msec (step S33). In step S34, it is determined whether the amount of light is within the target value range. If it is within the range (step S34: Yes), the process proceeds to step S35. If it is out of range (step S34: No), the process proceeds to step S36.

  A step S35 stores the LED set voltage in the nonvolatile memory and ends the staircase search adjustment method. In step S36, it is determined whether the number of corrections has reached 10. When it has reached 10 times (step S36: Yes), the process proceeds to step S37. When it has not reached 10 times (step S36: No), it returns to step S32. In step S37, errors are counted and the process proceeds to step S38. In step S38, it is determined whether or not the error count has reached 10 consecutive times. If it has reached 10 times (step S38: Yes), the process proceeds to step S39. When it has not reached 10 times (step S38: No), it progresses to step S40. A step S39 displays a service call (SC) and ends the staircase search adjustment method.

  A step S40 changes the LED light quantity to the previous value and ends the staircase search adjustment method.

1 is an image forming apparatus according to the present embodiment. It is a figure which shows the characteristic curve of an optical sensor. It is a schematic diagram explaining a binary search adjustment method. It is a schematic diagram explaining the staircase search adjustment method. It is a main flowchart. It is a subroutine figure of a binary search adjustment method. It is a subroutine figure of the staircase search adjustment method.

Explanation of symbols

50 photoconductor drum (or photoconductor)
DESCRIPTION OF SYMBOLS 51 Pre-charge exposure part 52 Charging device 53 Image exposure device 54 Development device 541 Development sleeve 543,544 Developer stirring conveyance member 547 Potential sensor 57 Paper feed roller 58 Transfer electrode 59 Separation electrode (separator)
60 Fixing device 61 Paper discharge roller 62 Cleaning device 70 Process cartridge

Claims (1)

An electrostatic latent image carrier and a toner image for density measurement are formed on the electrostatic latent image carrier, and the density of the toner image is measured by an optical density detector having a light emitting part and a light receiving part. In an image forming apparatus having an image forming control means for controlling image forming conditions according to a measurement result,
Control means for adjusting the light emission amount of the light emitting unit;
The image forming apparatus characterized in that the control means performs adjustment by a binary search adjustment method during a warm-up operation and performs adjustment by a staircase search adjustment method during an image forming operation .

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