JP2005084212A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of highly accurately detecting a toner patch against a secular change in sensor characteristics such as soiling without additionally installing a toner dust proofing mechanism such as a shutter or a mechanism of cleaning the detecting surface of a sensor. <P>SOLUTION: The image forming apparatus is provided with a luminous current switching means for switching the luminous current of an optical reflection density sensor in accordance with the case of detecting the reflection output of the toner patch and the case of detecting the reflection output of a non-image part on an image carrier, and the luminous current of the optical reflection density sensor is adjusted based on the detection result of the reflection output of the non-image part on the image carrier. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus that visualizes an image using colored particles of a toner such as a printer, a facsimile machine, and a copying machine.

  An image forming apparatus using an electrophotographic system includes a printing process in which colored particles are visualized as an image on the surface of a recording body, and a transfer and fixing process in which the visualized colored particle image is fixed to the recording body. First, the photosensitive member is uniformly charged by a charger. Next, a narrowed laser is irradiated onto the photosensitive member to form an electrostatic latent image. The charged toner is developed on the latent image to make the latent image noticeable. Next, a transfer charger supplies a reverse charge to the toner on the back side of the paper, and the toner adhering to the photoconductor is transferred onto a recording medium such as paper, an OHP sheet, or an intermediate transfer body to obtain an image. The electrophotographic process is well known.

  In this type of image forming apparatus, as a consideration to enable stable reproduction of high-quality image quality over a long period of time, before the start of printing work, after the end of printing work, or between sheets during printing work, It is known to incorporate a mechanism that forms a patch on the surface of a photoreceptor and controls various parameters related to printing based on information obtained from the patch. Here, the patch used for the control as described above has a configuration in which control is performed using a “potential patch” formed as a latent image without attaching toner on the photoreceptor, and is formed by attaching toner. There is a configuration in which control is performed using a “toner patch”.

  In the former, the latent image potential is detected by a potential sensor that is installed directly opposite the photoconductor. On the other hand, the latter detects the degree of toner adhesion by an optical reflection density sensor having a light emitting part and a light receiving part. FIG. 2 shows a schematic diagram of an optical reflection density sensor. Hereinafter, the optical reflection density sensor is referred to as a sensor. Since black toner mainly composed of carbon black has the property of absorbing infrared light, a light source that emits infrared light is used. Infer. FIG. 3 shows the sensor output result when the toner patch is measured. As a result, the sensor output decreases in the region where the toner is attached to the sensor output of the non-photosensitive portion of the photoconductor. The difference in the voltage value of the sensor output is the difference between the reflected output by the toner patch and the reflected output of the non-photosensitive portion of the photoconductor. When the toner adhesion amount increases, infrared light is absorbed more, so that the sensor output at the light receiving portion acts in the direction of decreasing.

  Next, as an example of the sensor characteristic change, the influence when the detection surface of the sensor becomes dirty will be described. FIG. 4 is a diagram in which the reflected output of the non-photosensitive portion of the photoconductor is actually measured by changing the light emission current. When the detection surface of the sensor becomes dirty, the sensor output when detecting the non-image portion of the photosensitive member is lowered even when the same light emission current is applied. This is a phenomenon that occurs because the transmittance of the sensor detection surface decreases. In order to prevent such erroneous detection of the toner adhesion amount, not only the reflected output from the toner patch but also the reflected output from the non-image portion of the photoconductor where no toner patch is formed is detected, and the sensor is based on the detection result. A method for adjusting the gain of the light receiving unit has been proposed (see, for example, Patent Document 1). If this method is used, even if the sensor is somewhat dirty, the amount of toner patch attached can be detected correctly without being affected by the stain, and the above-mentioned drawbacks can be eliminated. However, the reflected output from the non-image area of the photoconductor is very high compared to the reflected output from the toner patch. The detection sensitivity will be reduced. FIG. 5 shows the relationship between the light emission current and the reflection output of the non-image portion of the photoreceptor.

  On the other hand, measures are taken to prevent contamination by toner or paper dust by closing the sensor detection surface except for attaching a dustproof shutter to the detection surface of the adhesion amount sensor and making adjustments during control. Furthermore, a cleaning member is attached to the back side of the shutter so that cleaning is performed simultaneously with opening and closing of the shutter. However, if such a cleaning mechanism is added to the sensor, the increase in size and cost of the apparatus cannot be avoided, and ensuring the reliability of the mechanism is also a major problem.

Japanese Patent Laid-Open No. 56-164355

JP 09-006203 A

  An object of the present invention is to provide an image that can detect a toner patch with high accuracy against changes in sensor characteristics over time such as dirt without adding a toner dustproof mechanism such as a shutter or a sensor detection surface cleaning mechanism. It is to provide a forming apparatus.

  The above object has a light emission current switching means for switching the light emission current of the optical reflection density sensor between when detecting the reflection output of the toner patch and when detecting the reflection output of the non-image portion of the image carrier, and This is achieved by adjusting the light emission current of the optical reflection density sensor based on the detection result of the reflection output of the non-image portion of the image carrier.

  According to the present invention, by adjusting the light emission current of the optical reflection density sensor at the non-image portion of the photoreceptor, it is possible to detect a large amount of toner adhesion with high accuracy without mounting a complicated mechanical mechanism. I can do it.

  Embodiments of the present invention will be described below with reference to FIGS. 1 and 6 to 8.

  1 is a charging device, 2 is an exposure device, 3 is a developing device, 4 is a transfer charging device, 5 is a fixing device, 6 is a cleaner, 7 is a registration roller, 8 is a conveyor belt, 9 is a photoreceptor, 10 is a sensor, 11 Is a control device, 12 is a reflected output comparison device, 13 is a light emission current switching device, and 14 is a light emission current storage unit.

  The movement of the paper in the apparatus will be described with reference to FIG. The paper passes through the resist path and is sent to the printing unit by the resist roller 7, and the toner image formed on the surface of the photoconductor 9 is given a charge of corona discharge having a polarity opposite to that of the toner by the transfer charger 4. Let them transcribe. Thereafter, it passes through the fixing device 5 and is discharged to the stacker. When detecting the toner patch, the toner patch image data sent from the controller is formed into a test patch latent image determined in advance by the exposure device 2, and the test patch latent image is imaged by the developing device 3. The reflection density of the toner patch area is detected by the sensor 10, and the grid voltage of the charger 1, the developing bias of the developing device 3, and the laser power of the exposure device 2 can be adjusted by the control device 11 based on the detected value. .

  As shown in FIG. 1, the position of the sensor 10 is a region where the toner developed on the photoreceptor 9 is directly detected, so that the toner is largely scattered. In addition, since the paper passes directly under the sensor, it is also a part that receives contamination by paper dust. In the embodiment, the reflected output of the non-image part of the photoconductor is detected, the change in the sensor characteristic is detected from the change in the output, and when it is determined that the light has changed, the light emission current is changed to an optimal value, This is a method for detecting a toner patch.

  Next, a method for detecting changes in sensor characteristics will be described. FIG. 7 shows a flowchart of sensor characteristic change detection. First, prior to the toner patch detection, the reflected output of the non-photosensitive portion of the photoreceptor is detected. For this reason, the light emission current switching device 13 switches to the light emission current P0 of the non-image portion of the photoreceptor previously stored in the CPU. Thereafter, the photosensitive member is rotated to capture the reflected output of the non-image portion. The reflected output is obtained by taking data for one rotation of the photoreceptor and averaging the data. This is a measure for reducing such errors as much as possible because the distance between the sensor and the object to be detected varies due to uneven reflection output in the circumferential direction of the photosensitive member, or vibration and jitter of the photosensitive member driving portion, and the captured data varies. Here, the sensor output value after the averaging process is defined as Vs1. Next, a difference ΔV (= | Vs0−Vs1 |) with respect to the reflection output Vs0 of the non-photosensitive portion of the photosensitive member stored in advance in the CPU is calculated. Next, ΔV is compared with a threshold voltage ΔV0 stored in advance in the CPU. If the output voltage difference ΔV is equal to or larger than the threshold voltage ΔV0, it is determined that the sensor characteristics have changed. In this case, a sequence for adjusting the light emission current is started. The reflected output comparison device 12 is a part that calculates the difference between the sensor output values Vs1 and Vs0 and the output voltage difference ΔV and compares them with the threshold voltage ΔV0 stored in advance in the CPU. The detection timing of this sequence may be any time before the detection of the toner patch, but is preferably performed immediately before the detection of the toner patch as much as possible.

  FIG. 8 shows a flowchart of light emission current adjustment. The light emission current is changed until the output voltage difference ΔV detected by the reflected output comparator 12 becomes smaller than the threshold voltage ΔV0. Here, the light emission current when ΔV <ΔV0 is assumed to be P0 ′. The light emission current P 0 ′ is stored in the light emission current storage unit 14. Regarding the method of changing the light emission current, Vs1 is calculated by changing the light emission current every time the photoconductor 9 makes one turn, and the output voltage difference ΔV is calculated. The output voltage difference ΔV and the threshold voltage ΔV0 are compared, and the light emission current is changed until ΔV <ΔV0. Next, the expression P1 '= (P0' / P0) * P1 is calculated by using the P0 'and P0 and the light emission current P1 for the toner patch stored in the CPU in advance. The calculation result P1 'of the equation is used as a light emission current for toner patch detection.

  For example, if the sensor surface is dirty, P0 '/ P0> 1 and P1'> P1. When there is no dirt on the sensor surface, that is, when P0 '= P0, the above equation becomes P1' = P1, and the light emission current is not changed. By adjusting the light emission current using the above equation, it is possible to detect the toner patch with high accuracy even if the sensor characteristic changes. In this embodiment, the light emission current is described, but P1 in the above formula is also applicable to the light emission voltage. In this embodiment, the reflection output of the non-image portion of the photosensitive member or the toner patch formed on the photosensitive member is detected. However, the detection target is a toner patch transferred from the photosensitive member onto the intermediate transfer member, and the intermediate patch. The same effect can be obtained even if the reflected output of the non-image portion on the transfer body is detected.

1 is a schematic view of an image forming apparatus showing an embodiment of the present invention. Schematic of an optical reflection density sensor. The figure which showed the sensor output waveform when a toner patch is detected. The figure showing the reflection output change of the photoconductor non-image part when a sensor detection surface becomes dirty. The figure which showed the relationship between light emission current and the reflected output of a photoreceptor non-image part. The schematic of the peripheral circuit of the sensor in the Example of this invention. The control flowchart which detects the sensor characteristic change in the Example of this invention. The control flowchart which adjusts the light emission current in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Charging device, 2 ... Exposure device, 3 ... Developer, 4 ... Transfer charging device, 5 ... Fixing device, 6 ... Cleaner, 7 ... Registration roller, 8 ... Conveying belt, 9 ... Photoconductor, 10 ... Optical reflection Density sensor 11 ... Control device 12 ... Reflection output comparison device 13 ... Light emission current switching device 14 ... Light emission current storage unit 15 ... Light emission unit 16 ... Light receiving unit 17 ... Toner patch 18 ... Photoconductor non-image Reflection output of the part, 19 ... reflection output of the toner patch.

Claims (12)

  At least an image carrier, a charger, an exposure device, a developing machine, and an optical reflection density sensor, and a solid image developed on the image carrier by the optical reflection density sensor and a halftone image other than solid The optical reflection density sensor when detecting the reflected output of the non-image portion of the image carrier and detecting the toner patch based on the detection result of the reflected output of the non-image portion of the image carrier. In the image forming apparatus that adjusts the detection condition, the emission current of the optical reflection density sensor is switched between when the reflected output of the toner patch is detected and when the reflected output of the non-image portion of the image carrier is detected. An image forming apparatus comprising: a current switching unit; and adjusting a light emission current of the optical reflection density sensor based on a detection result of a reflection output of a non-image portion of the image carrier.   A reflection output comparing device that compares the reflection output of the non-image portion of the image carrier stored in advance with the reflection output value of the non-image portion of the image carrier detected by the optical reflection density sensor; The image forming apparatus according to claim 1.   In the reflection output comparison device, the output voltage difference between the reflection output of the non-image portion of the image carrier stored in advance and the reflection output of the image carrier non-image portion detected by the optical reflection density sensor is calculated, The image forming apparatus according to claim 2, wherein the output voltage difference is compared with a threshold voltage stored in advance.   When the output voltage difference is equal to or larger than the threshold voltage, the light emission current for detecting the non-image portion of the image carrier is changed so that the output voltage difference becomes smaller than the threshold voltage. The image forming apparatus according to claim 3, further comprising: a light emission current storage unit that stores the light emission current of the light emission current.   The image forming apparatus according to claim 3, wherein when the output voltage difference is equal to or larger than the threshold voltage, a light emission current for detecting a toner patch is changed.   When the output voltage difference is equal to or larger than the threshold voltage, P0 is a pre-stored light emission current for detecting a non-image portion of the image carrier, P1 is a pre-stored light emission current for the toner patch, and When the light emission current when the output voltage difference is smaller than the threshold voltage is P0 ′, the light emission current P1 ′ of the optical reflection density sensor when detecting the toner patch is P1 ′ = P0 ′ / P0 ×. The image forming apparatus according to claim 5, wherein the image forming apparatus is represented by P <b> 1.   At least an image carrier, a charger, an exposure device, a developing machine, and an optical reflection density sensor, and a solid image developed on the image carrier by the optical reflection density sensor and a halftone image other than solid Of the optical reflection density sensor when detecting the reflection output of the non-image portion of the image carrier and detecting the toner patch based on the detection result of the reflection output of the non-image portion of the image carrier. In the image forming apparatus that adjusts the detection condition, the light emission voltage that switches between the light emission voltage of the optical reflection density sensor when detecting the reflection output of the toner patch and the reflection output of the non-image portion of the image carrier. An image forming apparatus comprising a switching unit and adjusting a light emission voltage of the optical reflection density sensor based on a detection result of a reflection output of a non-image portion of the image carrier.   In the image forming apparatus, the reflection output comparison device for comparing the reflection output of the non-image portion of the image carrier stored in advance with the reflection output value of the non-image portion of the image carrier detected by the optical reflection density sensor. The image forming apparatus according to claim 7, further comprising:   In the reflection output comparison device, the output voltage difference between the reflection output of the non-image portion of the image carrier stored in advance and the reflection output of the image carrier non-image portion detected by the optical reflection density sensor is calculated, The image forming apparatus according to claim 8, wherein the output voltage difference is compared with a threshold voltage stored in advance.   When the output voltage difference is equal to or larger than the threshold voltage, the light emission voltage for detecting the non-image portion of the image carrier is changed so that the output voltage difference becomes smaller than the threshold voltage. The image forming apparatus according to claim 9, further comprising: a light emission voltage storage unit configured to store the light emission voltage.   The image forming apparatus according to claim 9, wherein when the output voltage difference is equal to or larger than the threshold voltage, a light emission voltage for detecting a toner patch is changed. When the output voltage difference is equal to or larger than the threshold voltage, P0 is a pre-stored light emission voltage for detecting a non-image portion of the image carrier, P1 is a pre-stored light emission voltage for the toner patch, and When the light emission voltage when the output voltage difference is smaller than the threshold voltage is P0 ′, the light emission voltage P1 ′ of the optical reflection density sensor when detecting the toner patch is P1 ′ = P0 ′ / P0 ×. The image forming apparatus according to claim 11, wherein the image forming apparatus is represented by P <b> 1.

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