JP2005150547A - Method for driving photosensor and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for driving a photosensor for shortening a rising time since a light emitting diode emits the rays of lights until detecting precision is made stable; and an image forming apparatus for reducing the constraint of a detection time by the photosensor, and for realizing highly precise detection and high quality output. <P>SOLUTION: Currents I<SB>0</SB>are made to flow through the light emitting diode of a photosensor, and an object to be detected is irradiated with the rays of light outgoing from the light emitting diode so that the object to be detected can be detected. Prior to this, currents I<SB>1</SB>larger than the currents I<SB>0</SB>flowing in the detection process are made to flow through the light emitting diode in a predetermined time Tc. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of driving an optical sensor in which light emitted from a light emitting diode is reflected by an object to be detected and then received by a light receiving element, and an image forming apparatus using the same.

  Conventionally, in an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a composite machine thereof, for the purpose of stabilizing the image density in an output image, a photosensitive drum, an intermediate transfer belt, etc. In many cases, a reflection type optical sensor (P sensor) is installed at a position facing the image carrier (see, for example, Patent Document 1).

Various types of image density adjustment control using an optical sensor have been disclosed. An example is described below.
First, a plurality of patch patterns (substantially rectangular patterns of electrostatic latent images) are formed on the image carrier. Then, the latent image potential of each patch pattern is measured by a potential sensor. Further, after developing each patch pattern, the toner adhesion amount on the patch pattern (image portion) is measured by an optical sensor. Further, the non-image portion on the image carrier on which no patch pattern is formed is also measured by the optical sensor.
Then, a development potential for obtaining the maximum toner adhesion amount is obtained from the latent image potential detected by the potential sensor and the toner adhesion amount detected by the optical sensor. Then, based on the obtained development potential, the image forming conditions (charging potential, exposure potential, development voltage, etc.) are adjusted.

Such adjustment control, that is, detection by the optical sensor is performed at a predetermined timing (for example, every predetermined number of output sheets).
Here, the optical sensor includes a light emitting element and a light receiving element. The light emitting element is a light emitting diode, and the light receiving element is a photodiode (PD) or a phototransistor (PTr).

Each time detection is performed by the optical sensor, a predetermined current flows into the light emitting diode. When a current flows into the light emitting diode, light is emitted from the light emitting diode. The light emitted from the light emitting diode reaches the object to be detected (image portion or non-image portion on the image carrier) and is reflected there. This reflected light is incident on the light receiving element. The toner adhesion amount on the object to be detected is determined by the light amount (photosensor output) of the specularly reflected light (incident light) detected by the light receiving element. That is, when the detected light amount at the light receiving element is large, the toner adhesion amount is small, and when the detected light amount at the light receiving element is small, the toner adhesion amount is large.
In addition, inflow of the current into the light emitting diode is performed only at the time of detection in order to extend the life of the light emitting diode.

Japanese Unexamined Patent Publication No. 2000-221760

  The conventional optical sensor described above has a problem that it takes some time until the detection accuracy is stabilized after the light emitting diode emits light. Therefore, when an optical sensor is used in an image forming apparatus that requires high image quality, there is a time restriction in order to ensure sufficient detection accuracy.

In other words, in the above-described image forming apparatus in which a plurality of patch patterns having different toner adhesion amounts are formed on the image carrier, the accuracy is required unless a difference in toner adhesion amounts in each patch pattern (image portion) is clearly detected. High image forming conditions cannot be set. Therefore, a stable and high detection accuracy is required for the optical sensor.
On the other hand, in conventional photosensors, it takes time for the output value of the photosensor to stabilize after the current flows into the light-emitting diode. Therefore, it is necessary to detect the density of the patch pattern after the output value has stabilized. was there.

As a result of repeated researches to solve the above problems, the present inventor has come to know the following matters.
That is, the reason why the output value of the optical sensor is initially unstable is that it takes a certain amount of time for the light emission of the light emitting diode to stabilize after the current flows into the light emitting diode. The light emission efficiency (light emission stability) of the light emitting diode depends on the temperature fluctuation of the light emitting diode itself.

FIG. 5A is a graph showing the change with time of the output value (output voltage) of the optical sensor. In FIG. 5A, the horizontal axis represents time, and the vertical axis represents the output voltage of the light receiving element in the optical sensor. In FIG. 5B, the vertical axis indicates the value of current flowing into the light emitting diode. Further, FIG. 5C is a graph conceptually showing temperature fluctuation of the light emitting diode itself at this time.
In the optical sensor of FIG. 5, the current flowing into the light emitting diode is adjusted so that the output voltage of the light receiving element is 4 volts. Further, the optical sensor of FIG. 5 is one in which the light emitting diode is left unlit (stop driving) for 1 hour after it is turned off.

As shown in FIGS. 5A and 5B, after a predetermined current I ₀ flows into the light emitting diode of the photosensor, the output voltage of the photosensor varies within a range of about 0.2 volts, and the output It takes about 6 seconds (indicated by the arrow Ts in the figure) for the voltage to stabilize.
As shown in FIG. 5C, this is considered to correspond to the time from when the current I ₀ flows into the light emitting diode until the temperature of the light emitting diode itself increases by ΔT and stabilizes.

That is, immediately after the current I ₀ flows into the light emitting diode, the light emitting diode itself receives a heat amount corresponding to its heat capacity or thermal resistance and the temperature rises. Thereafter, the balance between heat reception and heat dissipation in the light emitting diode becomes constant, and the temperature of the light emitting diode itself is stabilized.
Here, when the temperature of the light emitting diode varies, the light emission efficiency also varies. Specifically, the luminous efficiency decreases as the temperature increases. Therefore, the light emission efficiency becomes unstable until the temperature of the light emitting diode is stabilized, and the output voltage of the photosensor varies. Thereafter, as the temperature of the light emitting diode is stabilized, the light emission efficiency is also stabilized, and variations in the output voltage of the optical sensor are eliminated.

  The present invention has been made to solve the above-described problems, and provides a method for driving an optical sensor with a short rise time from when a light emitting diode emits light until the detection accuracy is stabilized. An object of the present invention is to provide an image forming apparatus that can output high-quality images with high-precision detection with few detection time restrictions.

  According to a first aspect of the present invention, there is provided a method for driving an optical sensor using a light emitting diode as a light emitting element, wherein a current flows into the light emitting diode and is emitted from the light emitting diode. A detection step of irradiating an object to be detected; and a preparation step of flowing a current larger than a current flowing in the detection step into the light emitting diode before the detection step.

  According to a second aspect of the present invention, there is provided a method for driving an optical sensor according to the first aspect of the present invention, wherein the time for performing the preparation step is varied according to the time at which the optical sensor is stopped. is there.

  According to a third aspect of the present invention, there is provided the method for driving an optical sensor according to the first or second aspect of the invention, wherein the time for performing the preparation step is set to the magnitude of the current flowing during the preparation step. It is made to fluctuate accordingly.

  According to a fourth aspect of the present invention, there is provided the method for driving an optical sensor according to any one of the first to third aspects, wherein the time for the preparation step is determined according to the ambient temperature of the optical sensor. To fluctuate.

  According to a fifth aspect of the present invention, there is provided the method for driving an optical sensor according to any one of the first to fourth aspects, wherein the optical sensor is positioned opposite to the image carrier of the image forming apparatus. And the detected object is an image portion or a non-image portion formed on the image carrier.

  According to a sixth aspect of the present invention, there is provided an image forming apparatus comprising: an optical sensor having a light emitting diode as a light emitting element; and a control unit for adjusting a magnitude of a current flowing into the light emitting diode, Before a current flows into the light emitting diode and the object to be detected is irradiated with light emitted from the light emitting diode, a current larger than the current flows into the light emitting diode.

  According to a seventh aspect of the present invention, there is provided the image forming apparatus according to the sixth aspect, wherein the memory for storing the value of the current flowing into the light emitting diode when the object to be detected is irradiated with light. And the control unit determines the value of the large current based on the value of the current stored in the memory.

  The image forming apparatus according to an eighth aspect of the present invention is the image forming apparatus according to the sixth aspect, wherein the control unit sets a value of a current flowing into the light emitting diode before irradiating the object to be detected with light. In addition to the adjustment, the large current value is determined based on the adjusted current value.

  An image forming apparatus according to a ninth aspect of the present invention is the image forming apparatus according to the eighth aspect, wherein the light receiving element of the light sensor flows into the light emitting diode so that the amount of light received by the light receiving element is not less than a predetermined value. The value of the current to be adjusted is adjusted.

  An image forming apparatus according to a tenth aspect of the present invention is the image forming apparatus according to the eighth aspect, wherein the light receiving element of the photosensor flows into the light emitting diode so that the amount of light received by the light receiving element approximates a predetermined value. The value of the current to be adjusted is adjusted while changing the magnitude.

  An image forming apparatus according to an eleventh aspect of the present invention is the image forming apparatus according to any one of the sixth to tenth aspects, wherein the control unit drives the optical sensor for a time during which the large current flows. Is changed according to the time of stopping.

  The image forming apparatus according to a twelfth aspect of the present invention is the image forming apparatus according to any one of the sixth to eleventh aspects, wherein the control unit determines the time during which the large current flows in the magnitude of the current. It is made to fluctuate according to.

  According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the sixth to twelfth aspects, the control unit determines a time during which the large current flows in around the photosensor. It is varied according to the temperature.

  An image forming apparatus according to a fourteenth aspect of the present invention is the image forming apparatus according to any one of the sixth to thirteenth aspects, further comprising an image carrier, wherein the optical sensor faces the image carrier. The object to be detected is set as an image portion or a non-image portion formed on the image carrier.

  In the present invention, since the current value flowing into the light emitting diode of the optical sensor is controlled to be initially increased, the rise time from when the light emitting diode emits light until the detection accuracy is stabilized can be shortened. . Furthermore, it is possible to provide an image forming apparatus that has few restrictions on the detection time by the optical sensor and that can output high-quality images by high-precision detection.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
1 and 2, the first embodiment of the present invention will be described in detail. FIG. 1 is a schematic perspective view showing an optical sensor.
In FIG. 1, 1 is a specular reflection light receiving type optical sensor, 2 is a light emitting diode (LED) as a light emitting element of the optical sensor 1, 6 is a light receiving element (PD or PTr) of the optical sensor 1, and 10 is an optical sensor 1. Indicates the object to be detected by.
Here, the magnitude of the current flowing into the light emitting diode 2 of the optical sensor 1 is variable by the control unit 15.

Hereinafter, a method for driving the optical sensor 1 when performing density detection (or position detection, etc.) of the detection object will be described.
First, referring to FIG. 2 (B), current I ₁ is allowed to flow into light emitting diode 2 for a predetermined time Tc during a preparatory step before detecting object 10 (before the detecting step). Thereafter, a current I ₀ (current value at the time of detection) smaller than the current I ₁ flows into the light emitting diode 2.
The detected object 10 is detected after a predetermined time Ts has elapsed since the start of the current flow into the light emitting diode 2.

Specifically, referring to FIG. 1, emission light M <b> 1 emitted from light-emitting diode 2 by the inflow of current passes through the lens surface and enters the surface of detection object 10 at an incident angle θ. A part of the emitted light M1 incident on the surface of the detection object 10 travels toward the light receiving element 6 as regular reflected light (incident light M2) having a reflection angle θ. Thereafter, the incident light M <b> 2 enters the lens surface and is condensed on the light receiving element 6.
During the detection process, an output corresponding to the amount of incident light M2 incident on the light receiving element 6 is transmitted to the control unit 15. Furthermore, based on the magnitude of the output value transmitted to the control unit 15, the concentration of the detected object 10 is detected.

  In the optical sensor 1 driven as described above, the time Ts from when a current flows into the light emitting diode 2 until the output is stabilized is greatly shortened. The effect will be described with reference to FIGS.

FIG. 2A is a graph showing a change with time of the output value (output voltage) of the optical sensor 1. In FIG. 2A, the horizontal axis indicates time, and the vertical axis indicates the output voltage of the light receiving element 6 in the optical sensor 1. In FIG. 2B, the vertical axis indicates the value of current flowing into the light emitting diode 2. Further, FIG. 2C is a graph conceptually showing the temperature fluctuation of the light emitting diode 2 itself at this time.
2A to 2C respectively correspond to FIGS. 5A to 5C for the conventional optical sensor described above.

As shown in FIG. 2B, in the first embodiment, during the preparation process, a current I ₁ larger than the current I ₀ at the time of detection flows into the light emitting diode 2 for a predetermined time Tc. 2C is compared with FIG. 5C, the time Ts until the temperature of the light emitting diode itself rises by ΔT and stabilizes is shortened. That is, the amount of heat received by the light emitting diode increases in response to the large current I ₁ , so that the rate of temperature increase increases and reaches the vicinity of the temperature T + ΔT at an early stage. And just before reaching temperature T + ΔT, by adjusting the large current I ₁ to the normal current I ₀ , the balance between heat reception and heat dissipation in the light emitting diode 2 becomes constant, and the temperature of the light emitting diode 2 itself is stabilized. .
Here, if the large current I ₁ is within the specification range of the light emitting diode 2, the time Ts can be shortened as the current value increases.

In the first embodiment, the output of the optical sensor 1 varies as shown in FIG.
That is, at the time Tc when the large current I ₁ flows, the output of the optical sensor 1 increases according to the current value. Thereafter, when the inflowing current is changed from the large current I ₁ to the normal current I ₀ , the output of the optical sensor 1 approaches the target value V ₀ according to the current value. Then, after time Ts, the output of the optical sensor 1 is stabilized at V ₀ .
Comparing FIG. 2A and FIG. 5A, it can be seen that the time Ts until the output voltage of the optical sensor 1 is stabilized is greatly shortened.

  As described above, in the optical sensor 1 according to the first embodiment, since the current value flowing into the light emitting diode 2 is controlled to be initially increased before the detection process, the light emitting diode 2 emits light. The rise time Ts until the detection accuracy becomes stable is shortened. That is, the optical sensor 1 with high accuracy and high operability can be provided.

  In the first embodiment, when the detection by the optical sensor 1 is continuously performed, that is, when the time for which the driving of the optical sensor 1 is stopped (leaving time) is shortened, the temperature (T + ΔT) of the light emitting diode 2 is reduced. ) Is small, the next current inflow occurs. In this case, the time Ts until the temperature of the light emitting diode 2 is saturated is further shortened. Therefore, it is preferable to adjust and set the preparatory process time Ts before detection according to the drive stop time of the optical sensor 1. Specifically, the drive stop time of the optical sensor 1 is obtained by detecting the on / off time of the current flowing into the light emitting diode by the timer of the control unit 15.

  In the first embodiment, when the ambient temperature of the optical sensor 1 is relatively high, the temperature T of the light emitting diode 2 when driving is stopped is also high. In this case, the time Ts until the temperature of the light emitting diode 2 is saturated is further shortened. Therefore, it is preferable to adjust and set the preparatory process time Ts before detection according to the ambient temperature of the optical sensor 1. Specifically, the ambient temperature of the optical sensor 1 is detected by a temperature sensor connected to the control unit 15.

Further, in the first embodiment, when the current I ₁ that flows initially during the preparation process can be set relatively high, the time Ts until the temperature of the light emitting diode 2 is saturated is further shortened. Therefore, it is preferable to adjust and set the preparatory process time Ts before detection in accordance with the magnitude of the initial flowing current I ₁ .

In the first embodiment, the present invention is applied to the regular reflection light receiving type optical sensor 1. On the other hand, the present invention can also be applied to a diffuse reflection light receiving type optical sensor.
Specifically, in the diffuse reflection light receiving type optical sensor, diffuse reflection light is received by the light receiving element 6 of FIG. In this case, since the incident light M2 incident on the light receiving element 6 is diffusely reflected light, the reflection angle thereof does not coincide with the incident angle θ of the emitted light M1. Further, in this diffuse reflection light receiving type optical sensor, the output form is opposite to that of the regular reflection light receiving type. That is, when the object to be detected 10 is a color toner image, the amount of light detected by the light receiving element 6 is small when the amount of adhered toner is small, and the amount of light detected by the light receiving element is large when the amount of adhered toner is large. This is because diffuse reflection occurs due to the presence of toner particles.
Also in the diffuse reflection light receiving type optical sensor, the same effect as in the first embodiment can be obtained by controlling the current value flowing into the light emitting diode 2 to be initially increased before the detection step. Can do.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 3 is a configuration diagram illustrating a main part of the color image forming apparatus according to the second embodiment. 4 is a circuit diagram of the optical sensor 1 installed in the image forming apparatus of FIG. In the second embodiment, the optical sensor 1 of the first embodiment is installed in an image forming apparatus.

  In FIG. 3, 1 is an optical sensor for detecting the density of an image portion (or non-image portion) formed on the photosensitive drum 200, 200 is a photosensitive drum as an image carrier, and 201 is not transferred to the intermediate transfer unit. A photoconductor cleaning device that collects untransferred toner on the photoconductor drum 200, 202 a neutralizing lamp that resets the potential on the photoconductor drum 200, 203 a charging unit that uniformly charges the surface of the photoconductor drum 200, and 204 2 shows a potential sensor that detects a potential on the photosensitive drum 200.

  Reference numeral 230 denotes a revolver developing unit equipped with four color developing units 231K, 231Y, 231M, and 231C, and 500 denotes an intermediate transfer as an image carrier for superimposing toner images of the respective colors formed on the photosensitive drum 200. A unit 600 is a secondary transfer unit for transferring the color image formed by the intermediate transfer unit 500 to the transfer paper. A reference numeral 650 is a pair of registration rollers that convey the transfer paper toward the secondary transfer unit 600 in time. Show.

Here, the optical sensor 1 is the one shown in the first embodiment. Then, the plurality of patch patterns formed on the surface of the photosensitive drum 200 are detected objects 10, and their toner adhesion amounts are detected by the optical sensor 1.
The optical sensor 1 is located at a position facing the photosensitive drum 200 and at three positions (both ends and a central portion) in the axial direction of the photosensitive drum 1 (the direction perpendicular to the paper surface). Is provided.

Specifically, referring to the circuit diagram of FIG. 4, one-emission, one-reception type photosensors 1 </ b> L and 1 </ b> R are installed at both ends in the axial direction of the photosensitive drum 200. That is, each of these optical sensors 1L and 1R includes one light emitting diode 2L and 2R and one light receiving element 6L and 6R, respectively. These optical sensors 1L and 1R are specular reflection light receiving type optical sensors, and regular reflection light is incident on the light receiving elements 6L and 6R.
In addition, a one-emission two-reception type optical sensor 1 </ b> C is installed at the axial center of the photosensitive drum 200. That is, the optical sensor 1C includes one light emitting diode 2C and one light receiving element 6C1, 6C2. This optical sensor 1C is a specular reflection light receiving type / diffuse reflection light receiving type optical sensor, and regular reflection light is incident on one light receiving element 6C1, and diffuse reflection light is incident on the other light receiving element 6C2. The
These optical sensors 1L, 1C, and 1R detect the patch pattern density on the photosensitive drum 200, respectively, and obtain the axial density deviation based on the detection results. If the density deviation is not obtained, the optical sensor for density detection may be only the central one-emission two-light-receiving optical sensor 1C.

Referring to FIG. 3, potential sensor 204 is installed so as to face a region on photosensitive drum 200 where a patch pattern is formed. The potential sensor 204 is installed at a position corresponding to the installation position of the optical sensor 1 on the circumferential surface of the photosensitive drum 200.
Then, a development potential for obtaining the maximum toner adhesion amount is obtained from the latent image potential detected by the potential sensor 204 and the toner adhesion amount detected by the optical sensor 1. Then, based on the obtained development potential, the image forming conditions (charging potential, exposure potential, development voltage, etc.) are adjusted.

The image forming apparatus configured as described above operates as follows.
First, color image information of a color document placed on a document table is read by a color image reading device (not shown). The color image information is color-converted into four color image information of black, cyan, magenta, and yellow by the image processing unit. Then, the four color image information is transferred to the writing optical unit of the color image recording apparatus.

The writing optical unit first irradiates the surface of the photosensitive drum 200 uniformly charged by the charging unit 203 with the laser light L corresponding to any color in the color image information. Then, an electrostatic latent image corresponding to any one of black, cyan, magenta, and yellow is formed on the surface of the photosensitive drum 200.
The writing optical unit includes a semiconductor laser as a light source, a laser emission drive control unit, a polygon mirror and its rotation motor, an f / θ lens, a reflection mirror, and the like.

  On the other hand, the photosensitive drum 200 rotates in the direction of the arrow in FIG. The surface of the photosensitive drum 200 is arranged around the charging unit 203, the potential sensor 204, the selected developing unit 231C of the revolver developing unit 230, the optical sensor 1, the intermediate transfer unit 500, and the photosensitive member cleaning device. 201 and the charge removal lamp 202 are sequentially passed.

Here, the revolver developing unit 230 includes a black developing unit 231K, a cyan developing unit 231C, a magenta developing unit 231M, a yellow developing unit 231Y, and a revolver rotation driving unit that rotates each developing unit in the direction of the arrow in FIG. ing.
Each of the developing units 231K, 231C, 231M, and 231Y includes a developing sleeve that develops an electrostatic latent image by bringing a developer ear into contact with the surface of the photosensitive drum 200, and a developer paddle that pumps and stirs the developer. Etc.
The toner in each of the developing units 231K, 231C, 231M, and 231Y is negatively charged by stirring with the ferrite carrier. A developing bias is applied to each developing sleeve by a power source (not shown). As a result, a desired developing electric field is formed between the developing sleeve and the surface of the photosensitive drum 200.

The operation of each developing unit in the revolver developing unit 230 will be described using the black developing unit 231K as an example.
First, the black developing unit 231K is adjusted by the revolver rotation driving unit so as to be positioned upstream of the developing position facing the photosensitive drum 200 in the standby state before the start of copying. Then, as the copying operation is started and the laser light L corresponding to the black image data by the writing optical unit is irradiated onto the photosensitive drum 200, the black developing unit 231K is developed by the revolver rotation driving unit. Driven to position. Specifically, before the electrostatic latent image by the laser beam L reaches the development position, the movement of the black development unit 231K to the development position is completed.

In this way, the electrostatic latent image corresponding to the black image information on the photosensitive drum 200 is developed.
Note that the development of the electrostatic latent image corresponding to other colors is also achieved by moving the corresponding developing unit to the developing position in a timely manner by the revolver rotation driving unit in the same manner as the black developing unit 231K. .

Thereafter, the surface of the photosensitive drum 200 on which the electrostatic latent image is developed reaches a portion facing the intermediate transfer unit 500.
The intermediate transfer unit 500 includes an intermediate transfer belt 501 stretched around a plurality of rollers. On the outer periphery of the intermediate transfer belt 501, a secondary transfer unit 600, a belt neutralizing unit 503, a belt cleaning blade 504, a lubricant application brush 505, and the like are disposed. On the other hand, a primary transfer bias roller 507, a belt driving roller 508, a belt tension roller 509, a secondary transfer counter roller 510, a cleaning counter roller 511, and an earth roller 512 are disposed on the inner periphery of the intermediate transfer belt 501. The intermediate transfer belt 501 is stretched around these rollers. Each roller is made of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded.

A predetermined transfer voltage is applied to the primary transfer bias roller 507 by a primary transfer power source 801 in accordance with the number of superimposed toner images. Further, the intermediate transfer belt 501 is driven in the direction of the arrow by the rotational driving of the belt driving roller 508 in the direction of the arrow in the drawing.
In such an intermediate transfer unit 500, the toner image formed on the photosensitive drum 200 is transferred onto the intermediate transfer belt 501.

On the other hand, the surface of the photoconductor drum 200 after passing through the intermediate transfer unit 500 reaches a portion facing the photoconductor cleaning device 201. Then, after the untransferred toner on the photoconductive drum 200 is collected by the photoconductive cleaning device 201, it reaches the position of the static elimination lamp 202. Here, after the potential on the surface of the photosensitive drum 200 is cleared, the surface of the photosensitive drum 200 reaches the position of the charging unit 203.
Such a series of image forming processes is performed for each color of black, cyan, magenta, and yellow.

  In the above-described intermediate transfer unit 500, the toner images corresponding to the respective colors on the photosensitive drum 200 are sequentially transferred onto the intermediate transfer belt 501 in a superimposed manner. A color image corresponding to the color original is formed on the intermediate transfer belt 501.

The color image formed on the intermediate transfer belt 501 is then transferred onto the transfer paper K by the secondary transfer unit 600.
Here, the secondary transfer unit 600 includes a secondary transfer belt 601 stretched around three support rollers 602 to 604 and the like. The support roller 602 is controlled to move so that the belt portion of the secondary transfer belt 601 between the two support rollers 602 and 603 can be brought into and out of contact with the secondary transfer counter roller 510.

A predetermined transfer voltage is applied to the secondary transfer bias roller 605 by a secondary transfer power source 802. On the other hand, the secondary transfer belt 601 is driven in the direction of the arrow in FIG.
The color image on the intermediate transfer belt 501 is transferred to the transfer sheet K conveyed on the secondary transfer belt 601 from a paper feeding device (not shown) by the secondary transfer unit 600 configured as described above. Specifically, the transfer sheet K is conveyed at a predetermined timing by the registration roller pair 650 toward the secondary transfer bias roller 605 and the secondary transfer counter roller 510. The transfer sheet K attracts the toner on the intermediate transfer belt 501 by the voltage of the secondary transfer bias roller 605.

Thereafter, the transfer sheet K on which the color image has been transferred reaches the position of the transfer sheet discharger charger 606 by the secondary transfer belt 601. The transfer sheet K, which has been released from electrostatic attraction with the secondary transfer belt 601 here, is separated from the secondary transfer belt 601 and conveyed toward a fixing device (not shown).
On the other hand, the surface of the secondary transfer belt 601 after separating the transfer paper K sequentially passes through the positions of the belt charge removal charger 607 and the cleaning blade 608.
The transfer paper K that has reached the fixing device is discharged out of the image forming apparatus after the color image is fixed by the fixing device.
Thus, a series of image forming processes is completed.

Here, in the image forming apparatus according to the second embodiment, the density of the patch pattern formed on the photosensitive drum 200 is detected at a predetermined timing using the optical sensor 1 described in the first embodiment. ing.
That is, a large current I ₁ flows into the light emitting diode 2 of the optical sensor 1 for a time Tc several seconds before the patch pattern density detection (before the time Ts). Thereafter, the current value is changed to the normal current I ₀ . Then, after the time Ts elapses, the patch pattern density is detected.

  Referring to FIG. 4, the current control of the light emitting diodes 2L, 2C, and 2R in each of the optical sensors 1L, 1C, and 1R is a potential difference formed in the circuit (Vcc-LEDL, Vcc-LEDC, Vcc-LEDR). It is achieved by adjusting.

In the second embodiment, the value of the normal current I ₀ flowing into the light emitting diode 2 of the optical sensor 1 can be determined by various methods.
The first method is as follows.
First, the normal current value I ₀ flowing into the light emitting diode 2 is determined under a predetermined condition, for example, by adjustment based on a non-image portion (background portion) on the photosensitive drum 200. Then, the determined current value I ₀ is stored in the memory of the control unit 15. This current value I ₀ is used every time the concentration is detected until an output abnormality of the optical sensor 1 is detected. If an output abnormality of the optical sensor 1 is detected, the normal current I ₀ is adjusted again and stored in the memory.
In such a case, the initial current I ₁ during the preparation process is determined based on the normal current I ₀ stored in the memory. That is, the initial current I ₁ is set to be larger than the normal current I ₀ stored in the memory.

The second method is as follows.
Each time the detection process is performed, the normal current value I ₀ flowing into the light emitting diode 2 is adjusted before the detection process. Specifically, the output of the optical sensor 1 (the amount of incident light M2 received by the light receiving element 6) becomes a predetermined value or more (for example, 4 volts or more) while changing the inflowing current value. The normal current value I ₀ is determined.
In such a case, the initial current I ₁ during the preparation process is determined based on the normal current I ₀ adjusted for each detection process. That is, the initial current I ₁ is set to be larger than the adjusted normal current I ₀ .

The third method is as follows.
Each time the detection process is performed, the normal current value I ₀ flowing into the light emitting diode 2 is adjusted before the detection process. Specifically, the output of the optical sensor 1 (the amount of incident light M2 received by the light receiving element 6) approaches the target value (for example, 4 volts) while swinging the inflowing current value. A normal current value I ₀ is determined. At this time, the amplitude of the inflowing current value is gradually narrowed to finally determine the normal current value I ₀ . This is called a two-division method.
In such a case, the initial current I ₁ during the preparation process is determined based on the normal current I ₀ adjusted for each detection process. That is, the initial current I ₁ is set to be larger than the normal current I ₀ adjusted by the two-division method.

  As described above, in the image forming apparatus according to the second embodiment, since the current value flowing into the light emitting diode 2 of the optical sensor 1 is controlled to be initially increased before the detection process, the light emitting diode The rise time Ts from when 2 emits light until the detection accuracy is stabilized is shortened. As a result, it is possible to provide an image forming apparatus in which there are few restrictions on the detection time by the optical sensor 1 and high-quality output is possible by highly accurate detection.

  In the second embodiment, the optical sensor 1 described in the first embodiment is installed so as to face the photosensitive drum 200 of the image forming apparatus. However, the detection object of the optical sensor 1 of the present invention is not limited to this, and can be the intermediate transfer belt 501 of FIG. In this case, the optical sensor 1 is installed facing the intermediate transfer belt 501, and the toner adhesion amount of the image portion formed on the intermediate transfer belt 501 is detected with high accuracy in a short time by the optical sensor 1. Become.

Further, the detected object of the optical sensor 1 of the present invention can be a transfer belt or a photosensitive drum in a tandem color image forming apparatus. In this case, the optical sensor 1 is installed facing the transfer belt and the photosensitive drum of the tandem color image forming apparatus. Then, the toner adhesion amount and the positional deviation amount of the image portion formed on the transfer belt or the photosensitive drum are detected with high accuracy in a short time by the optical sensor 1.
The installation of the optical sensor 1 is not limited to the image forming apparatus, and can be applied to all objects to be detected that require high-precision detection capability in a short time.

In the second embodiment, the toner adhesion amounts of the patch pattern on the photosensitive drum 200 are detected by the three optical sensors 1L, 1C, and 1R, respectively. On the other hand, the amount of misregistration (color misregistration) can be detected by the three optical sensors 1L, 1C, 1R shown in FIG. 4 in addition to the toner adhesion amount of the patch pattern.
Specifically, line patterns are formed at the same timing at three positions (both ends and the center) on the photosensitive drum 200 in the axial direction. The positions of these line patterns are detected by the optical sensors 1L, 1C, and 1R, thereby detecting the amount of positional deviation in the axial direction on the photosensitive drum 200. In the center optical sensor 1C, a light receiving element 6C1 for regular reflection light is used. Also in this case, the positional deviation amount on the photosensitive drum 200 is detected with high accuracy in a short time by the optical sensor 1 as a line sensor.
Further, when it is desired to detect the amount of misalignment of the line pattern on the intermediate transfer belt 501, three optical sensors are provided at three positions in the width direction of the intermediate transfer belt 501, and the same control is performed.

  Furthermore, the present invention is not limited to the above-described embodiments, and it is apparent that each embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in each embodiment. It is. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like that are suitable for implementing the present invention can be used.

It is a perspective view which shows the optical sensor in Embodiment 1 of this invention. 2 is a graph showing (A) an output value change with time, (B) a change in current input to a light emitting diode, and (C) a temperature variation of the light emitting diode in the optical sensor of FIG. 1. It is a block diagram which shows the principal part of the image forming apparatus in Embodiment 2 of this invention. FIG. 4 is a circuit diagram illustrating an optical sensor installed in the image forming apparatus of FIG. 3. It is a graph which shows the time-dependent change of the output value in the conventional optical sensor, (B) Current change input to the light emitting diode, and (C) Temperature fluctuation of the light emitting diode.

Explanation of symbols

1, 1L, 1C, 1R optical sensor,
2, 2L, 2C, 2R light emitting diode (light emitting element),
6, 6L, 6C1, 6C2, 6R light receiving element,
10 detected object, 15 control unit,
200 Photosensitive drum (image carrier),
500 intermediate transfer unit (image carrier),
M1 emission light, M2 incident light.

Claims (14)

A method of driving an optical sensor using a light emitting diode as a light emitting element,
A detection step of irradiating the detected object with light emitted from the light emitting diode by flowing a current into the light emitting diode;
A method for driving an optical sensor, comprising: a preparatory step for flowing a current larger than a current flowing during the detection step into the light emitting diode before the detection step. The method for driving an optical sensor according to claim 1, wherein a time for performing the preparation step is varied according to a time for which the driving of the optical sensor is stopped. The method for driving an optical sensor according to claim 1, wherein a time for performing the preparation step is varied in accordance with a magnitude of a current flowing during the preparation step. The method for driving an optical sensor according to any one of claims 1 to 3, wherein a time for performing the preparation step is varied according to an ambient temperature of the optical sensor. The optical sensor is installed at a position facing the image carrier of the image forming apparatus,
The method of driving an optical sensor according to claim 1, wherein the object to be detected is an image portion or a non-image portion formed on the image carrier. An optical sensor using a light emitting diode as a light emitting element;
A controller that adjusts the magnitude of the current flowing into the light emitting diode,
An image forming apparatus, wherein a current larger than the current flows into the light emitting diode before a current flows into the light emitting diode and the object to be detected is irradiated with light emitted from the light emitting diode. A memory for storing a value of a current flowing into the light emitting diode when the object to be detected is irradiated with light;
The image forming apparatus according to claim 6, wherein the control unit determines the large current value based on a current value stored in the memory. The control unit adjusts the value of the current flowing into the light emitting diode before irradiating the object to be detected, and determines the value of the large current based on the adjusted current value. The image forming apparatus according to claim 6. The image forming apparatus according to claim 8, wherein a value of a current flowing into the light emitting diode is adjusted so that a light amount received by a light receiving element of the photosensor becomes a predetermined value or more. The image forming apparatus according to claim 8, wherein the value of the current flowing into the light emitting diode is adjusted to be large or small so that the amount of light received by the light receiving element of the photosensor approximates a predetermined value. . The image forming apparatus according to claim 6, wherein the control unit varies a time during which the large current flows in according to a time when the driving of the optical sensor is stopped. The image forming apparatus according to claim 6, wherein the control unit varies the time during which the large current flows in accordance with the magnitude of the current. The image forming apparatus according to claim 6, wherein the control unit varies the time during which the large current flows in according to an ambient temperature of the photosensor. An image carrier,
The optical sensor is installed at a position facing the image carrier,
The image forming apparatus according to claim 6, wherein the object to be detected is an image portion or a non-image portion formed on the image carrier.

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