JP2008064953A - Image forming apparatus and control method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of highly accurately detecting a toner image formed on an image carrier, with a simple configuration. <P>SOLUTION: Toner adhesion amount detecting patches of a plurality of densities are formed on a transfer belt (S403). The light quantity of the light emitting element of a reflection type sensor is set to a predetermined value A (S405), the patch of a low adhesion area is detected and a toner adhesion amount is calculated from the output value of the sensor (S407). Then, the patch of a middle adhesion amount area is detected at an emitted light quantity B which is prescribed times the emitted light quantity A (S409), and the adhesion amount is calculated from the correction value of the emitted light quantity and the output value of the sensor (S411). Then, the patch of a high adhesion amount area is detected at an emitted light amount C which is prescribed times the emitted light quantity A (S413), and the adhesion amount is calculated from the correction value of the emitted light quantity and the output value of the sensor (S415). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming apparatus control method, and more particularly to an image forming apparatus capable of detecting a toner image formed on an image carrier and determining a toner adhesion amount based on the result. The present invention relates to an apparatus control method.

  Conventionally, image forming apparatuses such as an MFP (Multi Function Peripheral), a full color printer, a copying machine, and a facsimile machine are known. The image forming apparatus is equipped with an image (toner) density sensor (IDC sensor) in order to detect the toner density on the intermediate transfer belt (an example of an image carrier).

  That is, a conventional image forming apparatus receives a light emitting element that emits irradiation light that irradiates a control reference toner image (toner patch) formed on an intermediate transfer belt, and light reflected from the reference toner image. A light receiving element to be arranged is provided on a support, and this is used as a photo sensor (IDC sensor). The density of the toner image is detected based on the output (the amount of reflected light) of the light receiving element in the photosensor, and density correction control is executed.

  In order to increase the accuracy of density correction control, there is also a sensor having two light receiving elements. The reflected light from the toner patch contains a regular reflection component and an irregular reflection component. By detecting both of these characteristics separately, the accuracy of density detection can be increased, and therefore, two light receiving elements for specular reflection component light reception and irregular reflection component light reception are individually mounted.

  In performing density correction control, before measuring the amount of reflected light from the reference toner image (toner patch), the light emitting element of the photo sensor (IDC sensor) emits light, and the bare surface (underground) of the image carrier (transfer belt). The amount of reflected light from the light is measured, and the amount of light emitted from the light emitting element is adjusted so that the value becomes a predetermined value (bare surface correction control). In this state, accurate density measurement is realized by measuring the reflected light amount of the toner patch.

  Patent Document 1 below discloses an image density detection device that changes the amount of LED light and the amplification factor so that the detection value on the surface of the photoreceptor is constant, and then reads the pattern density.

  Patent Document 2 discloses an image forming apparatus that adjusts the amplification factor at predetermined time intervals so that the detected value on the surface of the photoreceptor is constant.

Patent Document 3 discloses an image forming apparatus that detects the surface of a photoconductor with a predetermined light amount, changes the light amount if the detected value is not a predetermined value, and performs measurement again.
Japanese Unexamined Patent Publication No. 7-43298 JP-A-9-96930 JP 2004-117807 A

  The IDC sensor must detect from a state where there is no toner adhesion to a low adhesion and a high adhesion. However, since the IDC sensor uses a reflective optical sensor, the change in reflected light becomes smaller and the change in sensor output becomes smaller as the amount of adhesion increases. For this reason, there is a problem that the detection accuracy is lowered in an area where there is a lot of toner.

For example, the change in the amount of reflected light as the toner patch is high deposition is reduced, becomes saturated at a coverage of around 7 g / m ^2, the high-adhesion region in the vicinity of 5 g / m ^2, the amount of reflected light with respect to the adhesion amount of change Since the change becomes small, there is a problem that detection accuracy is low.

  In order to solve such a problem, it can be considered that a high adhesion sensor and a low adhesion sensor are separately provided in the IDC sensor. However, cost reduction has progressed due to the lower price of printers, and it is required to detect the entire area with one sensor.

  Further, the power supply voltage for control inside the printer is from 5V to 3.3V or lower, and it is necessary to lower the power supply of the IDC sensor, but it is necessary to increase the detection accuracy of the sensor.

  The present invention has been made to solve the above problems, and provides an image forming apparatus capable of accurately detecting a toner image formed on an image carrier with a simple configuration, and a control method for the image forming apparatus. The purpose is to do.

  In order to achieve the above object, according to one aspect of the present invention, an image forming apparatus includes: an image carrier; an optical sensor that includes a light emitting portion and a light receiving portion facing the image carrier; and a toner for detection on the image carrier. An image forming unit; an optical sensor that detects a toner image on the image carrier; a conversion unit that converts an output value of the optical sensor into a toner adhesion amount; and a density of the toner image formed by the forming unit. And changing means for changing the sensitivity of the optical sensor.

Preferably, the changing unit changes the light amount of the light emitting unit of the optical sensor.
Preferably, the image forming apparatus further includes setting means for setting the light amount of the light emitting portion of the optical sensor so that the reflected light from the surface on which the toner image is not formed on the image carrier has a constant value. When detecting a region where the density of the toner image on the image carrier is high and the change in the output of the optical sensor is small, the light amount of the light emitting part of the optical sensor is increased. The toner adhesion amount is calculated from the increase amount of the light amount and the output value of the optical sensor.

  Preferably, the image forming apparatus forms a toner image on the image carrier, changes the light amount of the light emitting portion of the optical sensor, measures the toner image, and detects a change in the output of the light receiving portion of the optical sensor at that time. Detecting means for determining the amount of change in the light amount of the light emitting portion detected by the detecting means and the actual amount of light received by the light receiving portion, and determining the relationship between the light emitting portion of the sensor when detecting the toner adhesion amount. Correct the amount of light.

Preferably, the changing means changes the gain of the output of the optical sensor.
According to another aspect of the present invention, there is provided a control method for an image forming apparatus including an image carrier and an optical sensor that includes a light emitting unit and a light receiving unit facing the image carrier. A forming step for forming an image, a toner image on the image carrier by an optical sensor, a conversion step for converting an output value of the optical sensor into a toner adhesion amount, and a density of the toner image formed in the forming step. And a changing step for changing the sensitivity of the optical sensor.

  According to the present invention, it is possible to provide an image forming apparatus capable of accurately detecting a toner image formed on an image carrier with a simple configuration, and a control method for the image forming apparatus.

  FIG. 1 is a diagram showing a schematic configuration of a color laser beam printer according to one embodiment of the present invention.

  When a print start request is transmitted from an image controller (not shown) to the printer, a printing operation is started. The printer feeds paper from the paper feed cassette 1 by the paper feed roller 2, moves the paper along the paper feed path 3, and waits for the paper at a position where it reaches the timing sensor 30.

  The printer rotates an intermediate transfer belt 8 that is an image carrier by a transfer belt driving roller 9. Images are formed on the intermediate transfer belt 8 by the process units Y, M, C, and K that form images of the respective colors. Each process unit includes image bearing rollers 11, 16, 21, 26, charging devices 14, 19, 24, 29, exposure devices 13, 18, 23, 28, developing devices 12, 17, 22, 27, Transfer devices 10, 15, 20, and 25 are provided.

  Control is performed to match the leading edge position of the sheet and the image position by driving the timing roller 4 in accordance with the timing at which the position of the image formed on the intermediate transfer belt 8 reaches the position of the secondary transfer roller 5. Done. By applying a transfer voltage (about +2000 V) to the secondary transfer roller 5, toner that forms an image on the intermediate transfer belt 8 (in this printer, negatively charged toner) is transferred to the opposing roller 6 and the secondary roller 6. The image is transferred onto a sheet passing through the transfer roller 5.

  The transferred toner image is fixed on the sheet by the fixing roller 7 and discharged to a discharge tray at the top of the printer.

  The above-described printer is provided with a toner concentration detection sensor 31 in the apparatus so that the toner concentration in printing is constant. This is an optical sensor facing the transfer belt 8. Image stabilization control is performed when the main switch of the apparatus main body is turned on, when the toner cartridge is replaced, or when a predetermined number of sheets are printed.

  In the image stabilization control, several patches are formed on the transfer belt 8 for toner density detection (about 10 mm square) printed by changing the toner density by changing the development output of the developing device. The toner density detection sensor 31 detects the density of these toner patches. By providing feedback to the development output of the developing device according to the detection result, a stable toner density can always be obtained during printing. Note that image stabilization control is performed for each color in the case of a color printer.

FIG. 2 is a diagram showing the configuration of the toner concentration sensor 31 installed in the apparatus.
The toner density of the toner patch 33 formed on the transfer belt 8 is measured by a toner density sensor 31 disposed opposite to the transfer belt 8. The toner concentration sensor 31 includes an LED light emitting element 31b and two photodiodes 31c and 31d which are light receiving elements. Each of the light emitting element and the light receiving element irradiates the toner patch 33 with the condensed LED light Pa from the windows 31j, 31k, 31l of the housing 31m, receives the regular reflection light Pb and the irregular reflection light Pc, and photoelectrically converts the light quantity. By converting, the density of the toner patch is detected. That is, the output value of the sensor is converted into the toner adhesion amount.

  The printer also has a function of changing the light emission amount of the toner density sensor 31. The amount of light is set so that the reflected light from the surface on which the toner image is not formed on the transfer belt 8 has a constant value. When detecting an area where the density of the toner patch is high and the change in the output of the toner density sensor is small, the amount of light is increased by a predetermined amount for each toner adhesion amount of the toner patch, and detection is performed by increasing the output value of the sensor. . The toner adhesion amount is calculated from the sensor light emission increase amount and the detected value.

  By changing the amount of light emitted from the sensor according to the amount of toner to be detected, the reflected light from the toner patch is changed and detected by the sensor, thereby increasing the amount of toner from the state where no toner is attached. In the entire area up to the adhered state, it is possible to detect the amount of adhesion without reducing accuracy.

FIG. 3 is a diagram illustrating a light emission amount control unit and a toner concentration detection unit of the toner concentration sensor.
Referring to the figure, a toner concentration sensor 31 includes a light emitting element 31b, a regular reflection light receiving element 31c, a diffuse reflection light receiving element 31d, a transistor 31a for controlling the current of the light emitting element 31b, and a PWM for controlling the light amount of the light emitting element. A CR smoothing circuit 31j for smoothing a signal, a current limiting resistor 31e, a base resistor 31f, a regular reflection light amount photoelectric conversion resistor 31g, a diffuse reflection light amount photoelectric conversion resistor 31h, and a DC power input 31i are provided.

  A PWM signal is input to the toner density sensor 31 through the PWM output port 102 of the CPU 101 of the main body control board 100. The PWM duty is converted into a voltage by the smoothing circuit 31j and controls the base current of the transistor 31a. Thereby, the amount of current to the light emitting element 31b is determined, and the light quantity of the light emitting element 31b is controlled.

  When the light emitting element 31b emits light with a predetermined light amount and light is irradiated onto the toner surface to be measured on the transfer belt 8, the reflected light from the toner surface is received by the regular reflection light receiving element 31c and the irregular reflection light receiving element 31d. . A current flows through the light receiving elements 31c and 31d in accordance with the amount of received light, and photoelectric conversion is performed by the photoelectric conversion resistors 31g and 31h, and a detection voltage is input to the arithmetic circuit unit 31k.

  The arithmetic circuit unit 31k calculates a difference between the detection voltage 104a corresponding to the amount of light received by the regular reflection light receiving element 31c and the detection voltage 105a corresponding to the amount of light received by the irregular reflection light receiving element 31d, and obtains a sensor output.

  When the toner density is small, the amount of specular reflection from the surface of the transfer belt 8 is large and the amount of irregular reflection is small. That is, the photoelectric conversion output voltage 104a for the regular reflection light amount is large, and the photoelectric conversion output voltage 105a for the irregular reflection light amount is small.

  When the toner density is high, the amount of specular reflection from the surface of the transfer belt 8 is small and the amount of irregular reflection is large. That is, the photoelectric conversion output voltage 104a with the regular reflection light amount is small, and the photoelectric conversion output voltage 105a with the irregular reflection light amount is large.

  The sensor output after the difference calculation is detected as an analog voltage with an 8-bit resolution by the A / D input port 104 of the CPU 101 of the main body control board 100. The main body control board 100 includes a memory 103 that stores various numerical values and a correction control unit 151 that performs correction control based on the detection result of the toner image.

FIG. 4 is a diagram illustrating the relationship between the toner adhesion amount on the transfer belt and the sensor output voltage.
In this characteristic, the light amount of the light emitting element is adjusted so that the sensor output becomes 3.0 V in a state where the toner is not attached to the transfer belt (belt bare surface). When detecting an adhesion amount (low adhesion region) of a toner adhesion amount of 4 g / m ² or less, the sensor output changes greatly according to a change in the adhesion amount. As sensor characteristics, the sensor output decreases and the change amount decreases as the toner adhesion amount increases. That is, as the amount of toner adhesion increases, the variation in the toner adhesion amount with respect to the resolution of the A / D port increases, and the detection accuracy deteriorates.

  Therefore, in the present embodiment, in the middle adhesion region and the high adhesion region, reading is performed with the light amount of the light emitting element increased and the sensor sensitivity increased.

  FIG. 5 is a diagram illustrating the relationship between the toner adhesion amount on the transfer belt in the middle adhesion region and the sensor output voltage.

When detecting toner medium attachment region (region of ^{4g / m 2 ~5.2g / m 2} ) is the light intensity of the sensor light emitting device was adjusted in a state in which the above-described toner is not adhered (the belt bare surface) quantity In contrast, detection is performed at a predetermined multiple (TL multiple). S2 in FIG. 5 is a diagram showing the characteristics at that time.

  The output (S2) of the sensor is an output obtained by multiplying the sensor output (S1) with the light amount adjusted in a state where the toner is not attached by TL times with the offset voltage as a reference. As a result, the amount of change in sensor output increases in the vicinity of the toner adhesion amount to be detected, and the detection accuracy can be increased. That is, when the sensor output in FIG. 4 is VL1, the sensor output VL2 in FIG. 5 is expressed by the following equation (1).

VL2 = (VL1-offset) × TL + offset (1)
FIG. 6 is a diagram illustrating the relationship between the toner adhesion amount on the transfer belt in the high adhesion region and the sensor output voltage.

When detecting toner in a high adhesion area (5.2 g / m ² or more), the light quantity of the sensor light emitting element is a predetermined multiple of the light quantity adjusted in the state where the toner is not adhered (belt bare surface). Detection is performed (TH> TL). S3 in FIG. 6 is a diagram showing the characteristics at that time.

  When the sensor output in FIG. 4 is VL1, the sensor output VH2 in FIG. 6 is expressed by the following equation (2).

VH2 = (VL1-offset) × TH + offset (2)
FIG. 7 is a diagram for explaining control of sensor output (LED light emission amount).

  The light amount (and sensor output) of the sensor light emitting element can be adjusted by changing the PWM duty (LED duty). FIG. 7 shows the sensor output characteristics when the toner adhered on the transfer belt is constant and the PWM duty is changed. In order to acquire this characteristic, it is not necessary to move the transfer belt, and a specific patch (such as a constant high density toner image) may be detected while changing the PWM duty.

  The characteristics shown in FIG. 7 and the like obtained by the detection are stored in the memory 103 of the control board, and the PWM duty necessary for multiplying the light amount of the sensor light emitting element by a predetermined value (TL or TH) is determined.

  For example, assume that the sensor output is measured when the PWM duty is a in a state where toner is not attached (belt bare surface), and a measured value A is obtained.

  In order to multiply the amount of light by TL when detecting the toner in the intermediate adhesion region, the PWM duty that can obtain the sensor output B obtained by multiplying A by TL is set to b.

  Similarly, when highly adhering toner is detected, a PWM duty that can obtain a sensor output C obtained by multiplying A by TH is set to c.

  As described above, with reference to the light amount of the sensor light emitting element set with no toner attached to the transfer belt (belt bare surface), the sensor output is changed by changing the light amount by a predetermined amount according to the toner attached amount to be detected. obtain. Thereby, according to each toner adhesion amount, it becomes possible to raise sensor output and sensor sensitivity, and to raise detection accuracy.

FIG. 8 is a flowchart of density correction control executed by the printer.
Referring to the figure, in step S101, the light amount of the sensor on the bare surface of the transfer belt is adjusted. In step S103, the sensor light emission amount is detected. In step S105, the toner adhesion amount is detected, and based on the result, density correction is controlled in step S107.

  FIG. 9 is a flowchart showing sensor light emission amount adjustment processing (S101) on the bare surface of the transfer belt in FIG.

  In step S201, the transfer belt is driven, and in step S203, the sensor light emitting element is turned on. In step S205, the amount of light received by the sensor on the bare belt surface is detected. In step S207, the amount of light emitted from the sensor light emitting element is increased, and in step S209, it is determined whether or not a predetermined amount of regular reflection light is received. If NO, the process from step S207 is repeated.

  If the predetermined light receiving amount is reached, in step S211, the light emitting amount A of the sensor light emitting element and the PWM duty (a) at that time are stored in memory.

  FIG. 10 is a flowchart showing the process (S103) for detecting the sensor light emission amount characteristic of FIG.

  Referring to the figure, in step S301, a detection patch is formed on the transfer belt and moved to a sensor position. In step S303, the sensor light emitting element is turned off, and in step S305, the amount of received light from the sensor is detected.

  Next, in step S307, the PWM duty of the light emitting element is increased by a predetermined amount, and the measurement from step S305 is repeated until the PWM duty becomes 100% (S309).

  In step S311, the characteristics of the PWM duty and the light emission amount (sensor light reception amount) are stored in the memory.

  FIG. 11 is a flowchart showing the processing (S105) for detecting the toner adhesion amount of FIG.

Referring to the drawing, in step S401, the transfer belt is driven, and in step S403, a toner adhesion amount detection patch is formed on the transfer belt. Toner adhesion amount detection patch is made of seven patches increased deposition amount at 0.5 g / ^{m 2} unit area of about 3 g / ^{m 2} of 6.5 g / ^{m 2.}

  In step S405, the light emission amount = A and the PWM duty = a are set. In step S407, a patch in the low adhesion region is detected, and the toner adhesion amount is calculated from the output value of the sensor.

  Next, in step S409, from the light emission amount obtained in the flow of FIG. 10 and the PWM duty characteristic, PWM duty = b, which is B corrected by a predetermined multiple from the light emission amount A, is set. The amount of adhesion is calculated from the correction value (increase amount) of the light emission amount and the output value of the sensor.

  Next, in step S413, from the characteristic of the light emission amount and the PWM duty obtained in the flow of FIG. 10, PWM duty = c that is C corrected by a predetermined multiple from the light emission amount A is set, and in step S415, the patch of the high adhesion amount region The amount of adhesion is calculated from the correction value (increase amount) of the light emission amount and the output value of the sensor.

[Effects of the embodiment]
As described above, the light emission amount of the sensor is adjusted so that the sensor output on the bare belt surface becomes a predetermined value. Based on the light emission amount, the light emission amount of the sensor is multiplied by a predetermined value depending on the amount of toner to be detected. It is corrected. Reflected light from the toner patch is detected by the sensor, and the toner adhesion amount is calculated from the correction amount and the output value of the sensor. Accordingly, the light emission amount of the sensor can be switched from a preset light emission amount based on the detected toner adhesion amount, and the sensitivity of the sensor output can be increased in the adhesion amount region to be detected, and the detection accuracy can be improved.

[Modification]
In the above embodiment, the CPU sets the PWM duty depending on the toner adhesion amount to be detected. However, an amplifier may be provided in the arithmetic circuit 31k, and the gain of the amplifier may be changed by the CPU port. That is, the sensor characteristics shown in FIGS. 4 to 6 are obtained by increasing the amplification degree according to the toner adhesion amount to be detected. The CPU calculates the toner adhesion amount (density) based on the sensor output and the gain increase amount.

[Others]
The present invention can be applied to an image forming apparatus such as an MFP, a facsimile machine, a copying machine, an electrophotographic copying machine capable of full color printing, and an electrophotographic printer.

  Further, the processing in the above-described embodiment may be performed by software or by using a hardware circuit.

  In addition, a program for executing the processing in the above-described embodiment can be provided, and the program is recorded on a recording medium such as a CD-ROM, a flexible disk, a hard disk, a ROM, a RAM, and a memory card and provided to the user. You may decide to do it. The program may be downloaded to the apparatus via a communication line such as the Internet.

  In addition, it should be thought that the said embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a diagram showing a schematic configuration of a color laser beam printer in one embodiment of the present invention. FIG. FIG. 3 is a diagram illustrating a configuration of a toner density sensor 31 installed in the apparatus. It is a figure which shows the emitted light amount control part of a toner density sensor, and a toner density | concentration detection part. FIG. 5 is a diagram illustrating a relationship between toner adhesion amount on a transfer belt and sensor output voltage. FIG. 6 is a diagram illustrating a relationship between a toner adhesion amount on a transfer belt in a middle adhesion region and a sensor output voltage. FIG. 6 is a diagram illustrating a relationship between a toner adhesion amount on a transfer belt and a sensor output voltage in a high adhesion region. It is a figure for demonstrating control of a sensor output (LED light emission amount). 6 is a flowchart of density correction control executed by a printer. FIG. 9 is a flowchart illustrating sensor light emission amount adjustment processing (S101) on the bare surface of the transfer belt in FIG. 8; FIG. It is a flowchart which shows the process (S103) which detects the sensor light emission amount characteristic of FIG. FIG. 9 is a flowchart showing processing (S105) for detecting the toner adhesion amount in FIG. 8; FIG.

Explanation of symbols

  8 Intermediate transfer belt, 31 Toner density detection sensor, 31b LED light emitting element, 31c, 31d Light receiving element, 31k arithmetic circuit, 33 toner patch, 101 CPU, 102 PWM output port, 103 memory, 104 A / D input unit, 151 correction Control unit.

Claims (6)

An image carrier;
An optical sensor including a light emitting portion and a light receiving portion facing the image carrier;
Forming means for forming a toner image for detection on the image carrier;
Conversion means for detecting a toner image of the image carrier by the optical sensor and converting an output value of the optical sensor at that time into a toner adhesion amount;
An image forming apparatus comprising: a changing unit that changes the sensitivity of the optical sensor in accordance with a density of a toner image formed by the forming unit.   The image forming apparatus according to claim 1, wherein the changing unit changes a light amount of a light emitting unit of the optical sensor. Further comprising setting means for setting the light quantity of the light emitting part of the optical sensor so that the reflected light from the surface on which the toner image is not formed on the image carrier has a constant value;
When the change means detects a region where the density of the toner image on the image carrier is high and the change in the output of the optical sensor is small, the light amount of the light emitting unit of the optical sensor is increased,
The image forming apparatus according to claim 2, wherein the conversion unit calculates a toner adhesion amount from an increase amount of a light amount of a light emitting unit of the optical sensor and an output value of the optical sensor. Detection means for forming a toner image on the image carrier, measuring the toner image by changing the light amount of the light emitting portion of the optical sensor, and detecting a change in the output of the light receiving portion of the optical sensor at that time In addition,
The change unit obtains a relationship between the change amount of the light amount of the light emitting unit detected by the detection unit and the actual received light amount of the light receiving unit, and corrects the light amount of the light emitting unit of the sensor when detecting the toner adhesion amount. The image forming apparatus according to claim 2, wherein:   The image forming apparatus according to claim 1, wherein the changing unit changes a gain of an output of the optical sensor. An image carrier;
A control method of an image forming apparatus provided with an optical sensor including a light emitting unit and a light receiving unit facing the image carrier,
Forming a detection toner image on the image carrier;
A conversion step of detecting a toner image of the image carrier by the optical sensor and converting an output value of the optical sensor at that time into a toner adhesion amount;
And a changing step of changing the sensitivity of the optical sensor in accordance with the density of the toner image formed in the forming step.

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