JP2011013252A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus carrying out image formation of high quality, by detecting light with high accuracy without being influenced by a change of ambient temperature and preventing a lag of scanning timing.SOLUTION: The image forming apparatus 1 is equipped with: a control part 16; a light source 32 irradiating the surface of a photoreceptor drum 41 which is a scanned surface, with laser beams for exposure; a PD sensor 70 for measuring the scanning timing; a thermistor 15 for detecting an atmospheric temperature in the apparatus; and a power source unit 17 for the thermistor 15. The PD sensor 70 has: a photodiode 71; an amplifier 72; a comparator 73; and a first external terminal 74. The thermistor 15 is connected to the first external terminal 74. An input voltage to the amplifier 72 is thereby lowered, and the tendency of a response speed drop of the PD sensor 70 caused by the rise of ambient temperature is eliminated. The PD sensor 70 thereby detects light with high accuracy, coping with the change of ambient temperature.

Description

  The present invention relates to an image forming apparatus typified by a copying machine, a printer, and a facsimile, in which an optical scanning device for exposing and scanning an image carrier surface (scanned surface) with a light beam (for example, laser light) is mounted.

  An optical scanning device mounted on an image forming apparatus such as a copying machine, a printer, or a facsimile is generally exposed while scanning the surface of an image carrier represented by a photosensitive drum, that is, a scanned surface. A predetermined electrostatic latent image is formed on the drum surface. The optical scanning device includes a housing and an optical device that irradiates the surface to be scanned with a light beam such as a light source, an optical deflector, a lens, and a reflection mirror. In the optical scanning device, a light beam emitted from a light source, such as a laser beam, is deflected in the main scanning direction by an optical deflector and emitted toward a surface to be scanned by a reflection mirror.

  Specifically, the optical scanning device includes a light source such as a laser diode, and laser light emitted from the light source is incident on a polygon mirror that is a rotating polygon mirror of the optical deflector. The polygon mirror reflects the laser beam on its reflecting surface and deflects it in the main scanning direction. Each laser beam deflected in the main scanning direction is then deflected at a constant speed parallel to the axial direction of the photosensitive drum by an fθ lens, and is emitted toward the surface of the photosensitive drum through a reflection mirror to form an image. The Note that in an optical scanning device that supports color printing, laser light may be irradiated onto the same reflecting surface of a polygon mirror simultaneously from a plurality of light sources.

  Some optical scanning devices include a PD sensor (BD sensor) that is a light sensor that receives and detects laser light outside the effective exposure area of the surface to be scanned in order to measure the timing of scanning with laser light. is there. An example of an image forming apparatus provided with such a sensor can be seen in Patent Document 1. The image forming apparatus described in Patent Document 1 includes a horizontal synchronous light receiving unit 7 as the PD sensor (BD sensor).

Japanese Patent Laid-Open No. 5-96778 (page 3, FIG. 1)

  A photo IC used as a PD sensor may be affected by changes in ambient temperature on which the photo IC is mounted. That is, the response speed of the photo IC decreases as the ambient temperature rises, and the falling time of the output signal from High to Low or vice versa tends to be longer. As a result, the light detection by the PD sensor is delayed, and there is a possibility that the scanning timing shift (jitter) increases. As a result, there is a possibility that the output image is distorted or that the optical scanning device is determined to be abnormal and the image forming operation is stopped. Further, in a color printing type image forming apparatus, the scanning timing of laser light corresponding to each of a plurality of colors is shifted, and there is a possibility that a color misregistration occurs in the color image and the image quality is deteriorated. .

  Such a temperature characteristic of the photo IC may be eliminated by lowering the input voltage to the amplifier built in the photo IC.

  The present invention has been made in view of the above points, and when irradiating a surface to be scanned with a light beam for exposure, the photo IC detects light with high accuracy without being affected by changes in ambient temperature. Another object of the present invention is to provide an image forming apparatus capable of performing high-quality image formation that can prevent a deviation in scanning timing.

  In order to solve the above-described problems, the present invention provides an image forming apparatus that controls an operation of the entire apparatus, a light source that irradiates and exposes a light beam to the surface to be scanned, and the effective surface to be scanned. A photo IC for receiving and detecting a light beam outside the exposure region and measuring a scanning timing; a thermistor for detecting an ambient temperature inside the apparatus; and a power supply device for supplying power to the thermistor. Includes a photodiode that receives the light beam, an amplifier that amplifies the photocurrent signal generated by the photodiode, a comparator that compares the signal voltage amplified by the amplifier with a reference voltage, and a wire connecting the photodiode and the amplifier. A first external terminal connected to the first external terminal, and the thermistor is connected to the first external terminal.

  According to this configuration, it is possible to reduce the input voltage to the amplifier using a thermistor whose electric resistance changes with temperature, and to eliminate the tendency of the response speed of the photo IC to decrease due to an increase in ambient temperature. Is possible. Therefore, the photo IC can detect light with high accuracy in response to a change in ambient temperature. As the thermistor, a general thermistor prepared for detecting the atmospheric temperature inside the image forming apparatus can be used. Since a separate thermistor is not provided only for temperature compensation of the photo IC, it is possible to provide a simple configuration in which the cost and size of the apparatus are suppressed.

  In the image forming apparatus having the above-described configuration, a switch that is controlled by the control unit to turn on / off the power supply to the thermistor is provided between the power supply device and the thermistor.

  According to this configuration, the power supply to the thermistor can be turned on when the ambient temperature inside the image forming apparatus is detected, and the power supply to the thermistor can be turned off when temperature compensation of the photo IC is performed. Accordingly, the thermistor can be utilized more suitably to make the photo IC respond to changes in ambient temperature, and light can be detected with higher accuracy.

  In the image forming apparatus having the above configuration, the amplifier is a differential amplifier, and before the photocurrent is generated in the photodiode between the photodiode and the first external terminal and the differential amplifier. A differential unit for holding the internal voltage of the photo IC is provided.

  According to this configuration, even when the differential amplifier always receives an input signal, it is possible to detect a change in signal voltage when a photocurrent is generated in the photodiode. Therefore, the photo IC can detect light with higher accuracy in response to a change in ambient temperature.

  In the image forming apparatus having the above-described configuration, a second external terminal provided in the photo IC and capable of inputting the reference voltage of the photo IC, and connected to the second external terminal and controlled by the control unit. / A converter.

  According to this configuration, the reference voltage of the photo IC can be arbitrarily changed even if the input voltage to the amplifier becomes higher or lower as a whole due to the influence of the ambient temperature. Therefore, the photo IC can be more suitably adapted to changes in the ambient temperature, and light can be detected with higher accuracy.

  In the image forming apparatus having the above configuration, the thermistor is arranged in a series circuit of a resistor and a thermistor, and is arranged in the order of the power supply device, the resistor, the thermistor, and the ground, and between the resistor and the thermistor. The voltage is input to the first external terminal.

  According to this configuration, it is possible to reduce the input voltage to the amplifier by using a thermistor whose resistance value decreases as the temperature rises, and to eliminate the tendency of the photo IC to decrease in response speed due to an increase in ambient temperature. Is possible. Therefore, the photo IC can detect light with high accuracy in response to a change in ambient temperature.

  According to the configuration of the present invention, when exposure is performed by irradiating a surface to be scanned with a light beam, the photo IC can detect light with high accuracy without being affected by a change in ambient temperature, and scanning timing can be obtained. Therefore, it is possible to provide an image forming apparatus that is capable of performing high-quality image formation.

1 is a schematic vertical sectional front view of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a vertical sectional front view of the periphery of the optical scanning device of the image forming apparatus shown in FIG. 1. FIG. 3 is a top view of the optical scanning device shown in FIG. 2. FIG. 4 is a circuit diagram of a thermistor for detecting an ambient temperature of the image forming apparatus shown in FIG. 2 and a PD sensor of the optical scanning device shown in FIG. 3. It is a block diagram concerning light detection by a PD sensor. It is a timing chart concerning light detection by a PD sensor. FIG. 6 is a circuit diagram of an ambient temperature detection thermistor of an image forming apparatus according to a second embodiment of the present invention and a PD sensor of an optical scanning device. FIG. 5 is a circuit diagram of an ambient temperature detection thermistor of an image forming apparatus according to a third embodiment of the present invention and a PD sensor of an optical scanning device. FIG. 6 is a circuit diagram of an ambient temperature detection thermistor of an image forming apparatus and a PD sensor of an optical scanning device according to a fourth embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  First, the image output operation of the image forming apparatus according to the first embodiment of the present invention will be described while explaining the outline of the structure with reference to FIG. FIG. 1 is a schematic vertical sectional front view of an image forming apparatus. This image forming apparatus is of a color printing type in which a toner image is transferred onto a sheet using an intermediate transfer belt.

  As shown in FIG. 1, a paper feed cassette 3 is disposed below the inside of the main body 2 of the image forming apparatus 1. The paper feed cassette 3 stores and accommodates paper P such as cut paper before printing. The sheets P are separated and sent one by one toward the upper left of the sheet cassette 3 in FIG. The paper feed cassette 3 can be pulled out horizontally from the front side of the main body 2.

  A first paper transport unit 4 is provided inside the main body 2 and to the left of the paper feed cassette 3. The first paper transport unit 4 is formed substantially vertically along the left side surface of the main body 2. The first paper transport unit 4 receives the paper P sent out from the paper feed cassette 3 and transports the paper P vertically upward along the left side surface of the main body 2 to the secondary transfer unit 9.

  A manual paper feed unit 5 is provided above the paper feed cassette 3 at a location on the right side which is the side opposite to the left side of the main body 2 where the first paper transport unit 4 is formed. Yes. In the manual paper feed unit 5, paper of a size that is not in the paper feed cassette 3, or paper that is to be manually fed, such as thick paper and OHP sheets, is placed.

  A second paper transport unit 6 is provided on the left side of the manual paper feed unit 5. The second paper transport unit 6 is located immediately above the paper feed cassette 3, extends substantially horizontally from the manual paper feed unit 5 to the first paper transport unit 4, and joins the first paper transport unit 4. The second paper transport unit 6 receives the paper sent out from the manual paper feed unit 5 and transports it to the first paper transport unit 4 substantially horizontally.

  On the other hand, the image forming apparatus 1 receives document image data from an external computer (not shown). The information of the image data is sent to the optical scanning device 30 that is an exposure unit disposed above the second paper transport unit 6. The laser beam L controlled based on the image data by the optical scanning device 30 is emitted toward the image forming unit 40.

  A total of four image forming units 40 are provided above the optical scanning device 30, and an intermediate transfer belt 7 using an intermediate transfer member in the form of an endless belt is provided above each image forming unit 40. The intermediate transfer belt 7 is supported by being wound around a plurality of rollers, and is rotated clockwise in FIG. 1 by a driving device (not shown).

  As shown in FIG. 1, the four image forming units 40 are of a so-called tandem type that are arranged in a line from the upstream side to the downstream side in the rotational direction along the rotational direction of the intermediate transfer belt 7. The four image forming units 40 are, in order from the upstream side, a yellow image forming unit 40Y, a magenta image forming unit 40M, a cyan image forming unit 40C, and a black image forming unit 40B. These image forming units 40 are replenished with a developer (toner) by a developer supply container and a conveying unit (not shown) corresponding to each color. In the following description, the identification symbols “Y”, “M”, “C”, and “B” are omitted unless particularly limited.

  In each image forming unit 40, an electrostatic latent image of a document image is formed by the laser light L emitted by the optical scanning device 30, and a toner image is developed from the electrostatic latent image. The toner image is primarily transferred onto the surface of the intermediate transfer belt 7 by the primary transfer unit 8 provided above each image forming unit 40. Then, as the intermediate transfer belt 7 rotates, the toner image of each image forming unit 40 is transferred to the intermediate transfer belt 7 at a predetermined timing, so that the surface of the intermediate transfer belt 7 has four colors of yellow, magenta, cyan, and black. A color toner image is formed by superimposing the color toner images.

  A secondary transfer unit 9 is disposed at a position where the intermediate transfer belt 7 is suspended on the sheet conveyance path. The color toner image on the surface of the intermediate transfer belt 7 is transferred to the paper P sent in synchronization by the first paper transport unit 4 at the secondary transfer nip portion formed in the secondary transfer unit 9.

  After the secondary transfer, deposits such as toner remaining on the surface of the intermediate transfer belt 7 are cleaned for the intermediate transfer belt 7 provided on the upstream side of the intermediate transfer belt 7 in the rotational direction of the image forming unit 40Y for yellow. It is cleaned and collected by the apparatus 10.

  A fixing device 11 is provided above the secondary transfer unit 9. The sheet P carrying the unfixed toner image in the secondary transfer unit 9 is sent to the fixing device 11 where the toner image is heated and pressed by a heat roller and a pressure roller to be fixed.

  A branch portion 12 is provided above the fixing device 11. The sheet P discharged from the fixing device 11 is discharged from the branching unit 12 to the sheet discharging unit 13 provided at the upper part of the image forming apparatus 1 when double-sided printing is not performed.

  The discharge port portion from which the paper P is discharged from the branch portion 12 toward the paper discharge portion 13 functions as the switchback portion 14. When performing duplex printing, the switchback unit 14 switches the transport direction of the paper P discharged from the fixing device 11. Then, the sheet P is sent downward through the branching unit 12, the left side of the fixing device 11, and the left side of the secondary transfer unit 9, and again passes through the first sheet transport unit 4 to the secondary transfer unit 9. Sent.

  Next, an outline of the structure of the periphery of the optical scanning device 30 of the image forming apparatus 1 will be described with reference to FIGS. 2 and 3. 2 is a vertical sectional front view of the periphery of the optical scanning device, and FIG. 3 is a top view of the optical scanning device.

  As described above, the optical scanning device 30 is designed to be mounted on the tandem type image forming apparatus 1 including four photosensitive drums corresponding to four colors of yellow, magenta, cyan, and black. Is.

  As shown in FIGS. 2 and 3, the optical scanning device 30 includes an optical device including a light source 32, an optical deflector 50, an optical member group 60, and a PD sensor 70 that is a photo IC inside a housing 31. I have.

  The housing 31 has a box shape with an upper surface formed as an open portion. A thin plate-shaped lid member (not shown) is attached to the upper surface portion of the housing 31 so as to cover and close the open portion. Both the housing 31 and the lid member are made of synthetic resin.

  The light source 32 is provided on one end side of the housing 31, that is, on the right end side in FIG. The optical scanning device 30 corresponds to four colors of yellow, magenta, cyan, and black, and four independent light sources 32 are provided. The light source 32 is configured by a laser diode having a specification for irradiating a visible region light beam, for example, a laser beam of about 670 nm. The optical scanning device 30 irradiates the surface of the photosensitive drum 41, which is the surface to be scanned, with the laser light from the light source 32 and exposes it.

  The optical deflector 50 is provided in the vicinity of the light source 32 and on one end side of the housing 31, that is, on the right end side in FIG. The optical deflector 50 includes a polygon mirror 51 that is a rotary polygon mirror and a motor 52. The motor 52 rotates the polygon mirror 51 having a regular polygonal plane shape around the axis in the vertical direction in FIG. A plurality of reflecting surfaces that reflect light are provided around the polygon mirror 51 that rotates about the axis.

  The laser beams LY, LM, LC, and LB emitted from the four light sources 32 are incident on the reflecting surface around the polygon mirror 51 while being shifted by a minute angle in the sub-scanning direction (vertical direction in FIG. 2). . While rotating, the polygon mirror 51 reflects each laser beam on its reflecting surface and deflects it in the main scanning direction (vertical direction in FIG. 3), while at the other end in the housing 31, that is, the left in FIGS. Lead towards the direction.

  The optical member group 60 is provided in a region in the housing 31 where the laser light reflected by the optical deflector 50 travels. The optical member group 60 includes a first fθ lens 61, a second fθ lens 62, and a reflection mirror 63.

  The first fθ lens 61 is disposed at a position just ahead of which the laser beams LY, LM, LC, and LB reflected by the optical deflector 50 travel. The first fθ lens 61 is shared by the laser beams LY, LM, LC, and LB, and one first fθ lens 61 is provided. In the first fθ lens 61, the laser beams LY, LM, LC, and LB are deflected at a constant speed in the main scanning direction. Further, the first fθ lens 61 corrects the adverse effects on the scanning such as the incident angles of the laser beams LY, LM, LC, and LB to the polygon mirror 51 and the surface tilt of the polygon mirror 51, while correcting the laser beams LY, LM, and LC. , Slightly increase the angle of LB in the sub-scanning direction.

  The yellow laser light LY that has passed through the first fθ lens 61 is reflected by the reflection mirror 63Ya in the vicinity of the inner bottom surface of the housing 31, and is folded back toward the first fθ lens 61. Thereafter, the laser beam LY passes through the second fθ lens 62Y, is reflected by the reflection mirror 63Yb near the upper end of the housing 31, and reaches the surface of the yellow photosensitive drum 41Y, which is the surface to be scanned, to form an image.

  Similarly to the yellow laser light LY, the magenta laser light LM that has passed through the first fθ lens 61 is reflected by the reflection mirror 63Ma in the vicinity of the inner bottom surface of the housing 31, and is folded back toward the first fθ lens 61. Thereafter, the laser beam LM passes through the second fθ lens 62M, is reflected by the reflection mirror 63Mb near the upper end of the housing 31, and reaches the surface of the magenta photosensitive drum 41M, which is the scanning surface, to form an image.

  The cyan laser light LC that has passed through the first fθ lens 61 is reflected substantially vertically upward by the reflecting mirror 63Ca in the vicinity of the inner bottom surface of the housing 31, and then substantially in the horizontal direction by the reflecting mirror 63Cb in the vicinity of the upper end of the housing 31. Then, it is folded in the direction of the first fθ lens 61. Thereafter, the laser beam LC passes through the second fθ lens 62C, is reflected by the reflection mirror 63Cc, and reaches the surface of the cyan photosensitive drum 41C, which is the surface to be scanned, to form an image.

  The black laser beam LB that has passed through the first fθ lens 61 passes through the second fθ lens 62B directly without passing through the reflection mirror. Thereafter, the laser beam LB is reflected by the reflection mirror 63B and reaches the surface of the black photosensitive drum 41B, which is the surface to be scanned, and forms an image.

  As shown in FIG. 3, the PD sensor 70 is disposed in the vicinity of the reflection mirror 63Ya and the second fθ lens 62M and closer to the outside in the main scanning direction. The PD sensor 70 receives laser light reflected by the polygon mirror 51 of the optical deflector 50 that is outside the effective exposure area of the surface to be scanned. The laser beam received by the PD sensor 70 is reflected toward the PD sensor 70 by the reflection mirror 33 provided in the vicinity of the second fθ lens 62B. The PD sensor 70, which is a photo IC, is a synchronous detection sensor for measuring the scanning timing of the laser beams LY, LM, LC, and LB corresponding to each of the four colors, and is also called a BD (Beam Detect) sensor.

  On the other hand, as shown in FIG. 2, a thermistor 15 is provided in the vicinity of the optical scanning device 30 and the photosensitive drum 41. The thermistor 15 detects the ambient temperature inside the image forming apparatus 1 that affects the image quality. The temperature information detected by the thermistor 15 is transmitted to the control unit 16 of the image forming apparatus 1 and processed.

  Next, the configuration and operation of the PD sensor 70 will be described in detail with reference to FIGS. 4 to 6 in addition to FIGS. 2 and 3. 4 is a circuit diagram of a thermistor for detecting the ambient temperature of the image forming apparatus and a PD sensor of the optical scanning device, FIG. 5 is a block diagram relating to light detection by the PD sensor, and FIG. 6 is a timing chart relating to light detection by the PD sensor. .

  The PD sensor 70 is a photo IC generally used as an optical sensor, and is configured as shown in the circuit diagram of FIG. The PD sensor 70 includes a photodiode 71, an amplifier 72, a comparator 73, and a first external terminal 74 as main components.

  The PD sensor 70 is held by the housing 31 of the optical scanning device 30 so that the laser beam is vertically incident on the photodiode 71. When laser light enters the photodiode 71, a photocurrent is generated. This photocurrent signal is amplified by the amplifier 72. The signal voltage amplified by the amplifier 72 is input to the comparator 73 and compared with the internal reference voltage Vref. For example, the PD sensor 70 outputs High as the output signal Vout when the internal signal input to the comparator 73 is smaller than Vref, and outputs Low as the output signal Vout when larger than Vref. That is, the PD sensor 70 outputs High when the laser beam is not incident on the photodiode 71, and outputs Low when the laser beam is incident (see FIG. 6).

  An example of the amplifier 72 is an operational amplifier and a transistor, and an example of the comparator 73 is a hysteresis circuit.

  On the other hand, the PD sensor 70 includes a first external terminal 74 connected to an electric wire connecting the photodiode 71 and the amplifier 72. As shown in FIG. 4, the first external terminal 74 is connected to a thermistor 15 for detecting ambient temperature.

  The thermistor 15 is a temperature sensor that is widely and generally used to measure temperature by utilizing the fact that the electrical resistance varies with temperature. The thermistor 15 is arranged in a series circuit of a resistor R and the thermistor 15. The power supply device 17 for supplying power to the thermistor 15, the resistor R, the thermistor 15, and the ground (GND) are arranged in this order. To be precise, the voltage between the resistor R and the thermistor 15 is input to the first external terminal 74 of the PD sensor 70.

  The thermistor 15 is of a type whose resistance value decreases as the temperature rises. Thus, since the resistance value of the thermistor 15 changes as the temperature rises, the voltage between the resistor R and the thermistor 15 also changes as the temperature rises. A voltage signal between the resistor R and the thermistor 15 is transmitted to the control unit 16 as temperature information.

  Next, scanning timing detection in the optical scanning device 30 will be described with reference to FIGS. 5 and 6 in addition to FIG. 4.

  The image forming apparatus 1 includes the above-described control unit 16 configured with a CPU 18 and other electronic components (not shown) in the main body 2 for controlling the operation of the entire apparatus. The control unit 16 uses the CPU 18 as a central processing unit, and controls a series of operations such as paper conveyance, image formation, and fixing based on programs and data stored and input in the storage unit 19.

  One of the data input to the storage unit 19 is the ambient temperature inside the image forming apparatus 1. This ambient temperature is detected by the thermistor 15 (see FIG. 2) disposed in the vicinity of the optical scanning device 30 and the photosensitive drum 41. In the storage unit 19, the relationship between the voltage between the resistor R and the thermistor 15 arranged in series as shown in FIG. 4 and the detected temperature of the thermistor 15 is tabulated and stored in advance. The controller 16 can recognize the detected temperature of the thermistor 15 based on this table.

  The timing of optical scanning in the optical scanning device 30 is measured based on the detection of laser light by the PD sensor 70. At this time, the photo IC used as the PD sensor 70 may be affected by a change in ambient temperature where the photo IC is mounted.

  A timing chart of the output signal Vout with respect to the incident light intensity to the PD sensor 70 is depicted in FIG. In the case of the ambient temperature during the normal image forming operation, the output signal Vout of the PD sensor 70 changes as shown by the solid line in FIG. However, as the ambient temperature rises, the output signal Vout tends to increase in the fall time from High to Low and vice versa, as indicated by the dotted line in FIG.

  By connecting the thermistor 15 to the first external terminal 74, the PD sensor 70 reduces the input voltage to the amplifier 72 using the thermistor 15 whose electrical resistance changes with temperature, that is, the resistance value decreases with increasing temperature. Can be made. Thereby, it is possible to eliminate the tendency of the PD sensor 70 to decrease the response speed due to the ambient temperature increase as described above. Therefore, the PD sensor 70 can detect light with high accuracy in response to a change in ambient temperature.

  As the thermistor 15, a general thermistor prepared for detecting the ambient temperature inside the image forming apparatus 1 can be used. Since a separate thermistor is not prepared only for temperature compensation of the PD sensor 70, the image forming apparatus 1 can have a simple configuration in which an increase in cost and an increase in size are suppressed.

  According to the configuration of the above embodiment, the PD sensor 70 can detect the light with high accuracy without being affected by the change in the ambient temperature when irradiating the surface to be scanned with the laser light for exposure. It is possible to provide an image forming apparatus 1 that can appropriately measure the scanning timing of the laser light corresponding to each of the four colors and can form a high-quality color image without color misregistration.

  Next, the detailed configuration of the image forming apparatus according to the second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a circuit diagram of the thermistor for detecting the ambient temperature of the image forming apparatus and the PD sensor of the optical scanning device. The basic configuration of this embodiment is the same as that of the first embodiment described with reference to FIGS. 1 to 6, and therefore the configuration common to the first embodiment is described in the drawings, and The description will be omitted.

  As shown in FIG. 7, the image forming apparatus according to the second embodiment includes a switch 20 between a power supply device 17 that supplies power to the thermistor 15 and the thermistor 15. The switch 20 turns ON / OFF the power supply to the thermistor 15 and is controlled by the control unit 16.

  As a result, when the ambient temperature inside the image forming apparatus 1 is detected, the power supply to the thermistor 15 can be turned on, and when the temperature compensation of the PD sensor 70 is performed, the power supply to the thermistor 15 can be turned off. . Therefore, the thermistor 15 can be utilized more suitably to make the PD sensor 70 respond to changes in the ambient temperature, and light can be detected with higher accuracy.

  Next, a detailed configuration of the image forming apparatus according to the third embodiment of the present invention will be described with reference to FIG. FIG. 8 is a circuit diagram of the thermistor for detecting the ambient temperature of the image forming apparatus and the PD sensor of the optical scanning device. The basic configuration of this embodiment is the same as that of the first embodiment described with reference to FIGS. 1 to 6, and therefore the configuration common to the first embodiment is described in the drawings, and The description will be omitted.

  As shown in FIG. 8, the image forming apparatus according to the third embodiment uses a differential amplifier 75 as an amplifier in the PD sensor 70, and includes a photodiode 71, a first external terminal 74, and a differential amplifier. The differential part 76 is provided between the terminal 75 and the terminal 75. The differential unit 76 holds the internal voltage of the PD sensor 70 before the photocurrent is generated in the photodiode 71.

  Thereby, even when the differential amplifier 75 is constantly receiving an input signal, it is possible to detect a change in signal voltage when a photocurrent is generated in the photodiode 71. Therefore, the PD sensor 70 can detect light with higher accuracy in response to changes in the ambient temperature.

  Next, the detailed configuration of the image forming apparatus according to the fourth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a circuit diagram of the thermistor for detecting the ambient temperature of the image forming apparatus and the PD sensor of the optical scanning device. The basic configuration of this embodiment is the same as that of the first embodiment described with reference to FIGS. 1 to 6, and therefore the configuration common to the first embodiment is described in the drawings, and The description will be omitted.

  As shown in FIG. 9, the image forming apparatus according to the fourth embodiment includes a D / A converter 21, and the PD sensor 70 includes a second external terminal 77. The D / A converter 21 is controlled by the control unit 16. The second external terminal 77 can receive a reference voltage for comparison with the signal voltage amplified by the amplifier 72 in the comparator 73.

  Thereby, even if the input voltage to the amplifier 72 increases or decreases as a whole due to the influence of the ambient temperature, the reference voltage of the PD sensor 70 can be arbitrarily changed. Accordingly, the PD sensor 70 can be more suitably adapted to changes in the ambient temperature, and light can be detected with higher accuracy.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  For example, in the embodiment of the present invention, a tandem color printing image forming apparatus provided with four photosensitive drums has been described as an example. However, an image forming apparatus to which the invention is applied is in this form. The present invention is not limited to this, and other types of image forming apparatuses for color printing, monochrome printing, and the like may be used.

  The thermistor 15 may be arranged in the order of the power supply device 17, the thermistor, the resistor R, and the ground. In this case, the thermistor 15 is desirably of a type whose resistance value increases as the temperature rises, whereby the input voltage to the amplifier 72 of the PD sensor 70 can be reduced. Therefore, as in the above embodiment, it is possible to eliminate the tendency of the PD sensor 70 to decrease the response speed due to the increase in the ambient temperature, and to detect light with high accuracy corresponding to the change in the ambient temperature. it can.

  The present invention can be used in an image forming apparatus provided with an optical sensor for receiving a light beam and measuring a scanning timing.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 15 Thermistor 16 Control part 17 Power supply device 20 Switch 21 D / A converter 30 Optical scanning device 31 Housing 32 Light source 40 Image forming part 41 Photosensitive drum (surface to be scanned)
70 PD sensor (Photo IC)
71 Photodiode 72 Amplifier 73 Comparator 74 First External Terminal 75 Differential Amplifier 76 Differential Portion 77 Second External Terminal R Resistance

Claims (5)

A control unit for controlling the operation of the entire apparatus;
A light source that irradiates and exposes a light beam onto the surface to be scanned;
A photo IC for receiving and detecting a light beam outside the effective exposure area of the surface to be scanned and measuring the scanning timing;
A thermistor that detects the ambient temperature inside the device;
A power supply for supplying power to the thermistor,
The photo IC is
A photodiode for receiving a light beam;
An amplifier that amplifies the photocurrent signal generated by the photodiode;
A comparator that compares the signal voltage amplified by the amplifier with a reference voltage;
An image forming apparatus comprising: a first external terminal connected to an electric wire connecting a photodiode and an amplifier; and the thermistor connected to the first external terminal.   The image forming apparatus according to claim 1, further comprising: a switch that is controlled by the control unit to turn on / off power supply to the thermistor between the power supply device and the thermistor.   The amplifier is a differential amplifier and holds the internal voltage of the photo IC before photocurrent is generated in the photodiode between the photodiode and the first external terminal and the differential amplifier. The image forming apparatus according to claim 1, further comprising a differential unit.   A second external terminal provided in the photo IC and capable of inputting the reference voltage of the photo IC; and a D / A converter connected to the second external terminal and controlled by the control unit. The image forming apparatus according to claim 1.   The thermistor is arranged in a series circuit of a resistor and a thermistor, and is arranged in the order of the power supply device, the resistor, the thermistor, and the ground, and a voltage between the resistor and the thermistor is input to the first external terminal. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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