JP6459928B2 - Optical scanning device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to an optical scanning device that scans a surface to be scanned with light rays, and an image forming apparatus using the same.

  For example, a general optical scanning device used in, for example, a laser printer or a copying machine includes a light source that emits a laser beam, a deflector that deflects the laser beam and scans a surface to be scanned by the laser beam, and a photoconductor that deflects the laser beam. And a scanning lens that forms an image on the peripheral surface (scanned surface) of the drum. Such an optical scanning device includes a synchronization sensor that detects a laser beam outside the range of the scanning width in order to determine the writing start timing of the scanning line by the laser beam. Writing of the scanning line to the surface to be scanned is started after a lapse of a certain time after the synchronous sensor detects the laser beam.

  A BD (beam detect) sensor that receives the laser beam and outputs a synchronization signal is generally used as the synchronization sensor. The BD sensor includes a photoelectric conversion element that converts incident light into a detection voltage, and a comparison unit that outputs the synchronization signal when the detection voltage exceeds a preset threshold voltage. Since the scanning line writing timing is determined based on the synchronizing signal, it is important that the BD sensor does not erroneously output the synchronizing signal other than the original light detection timing. Japanese Patent Application Laid-Open No. 2004-133867 discloses a technique for suppressing an erroneous output of a BD sensor caused by flare caused by irradiating a laser beam to an edge portion of a scanning lens.

JP-A-6-3609

  However, the cause of erroneous output of the BD sensor is not limited to that caused by the edge portion of the scanning lens. For example, a photoelectric conversion element of a BD sensor is generally packaged with a translucent resin. When the laser beam is irradiated near the edge of the package, the photoelectric conversion element generates a detection voltage exceeding the threshold voltage due to the flare generated in the package, and the comparison unit erroneously outputs a synchronization signal. May end up. This problem of erroneous output becomes prominent in cases where the linear velocity is decreased to increase the resolution of the image while the amount of laser light is decreased.

  An object of the present invention is to provide an optical scanning device capable of preventing erroneous output of a synchronous sensor, and an image forming apparatus using the same.

An optical scanning device according to one aspect of the present invention includes a light source that emits a light beam, a deflecting body that deflects the light beam emitted from the light source, and that scans the surface to be scanned in the main scanning direction with the light beam, and the deflecting body. A scanning lens that forms an image of the light beam deflected by the scanning surface on the surface to be scanned, and a synchronization signal when the light beam that has passed through the scanning lens is incident and the detection value corresponding to the amount of the incident light beam exceeds a threshold value A control unit that controls writing of a scanning line on the surface to be scanned by the light beam based on the synchronization signal, and a changing unit that changes the threshold value of the synchronization sensor. The synchronous sensor includes a photoelectric conversion element that converts an incident light beam into a detection voltage, and a package layer made of a translucent resin that covers the photoelectric conversion element, and the package layer includes the light beam. An incident surface, and the incident surface includes a facing region facing the light receiving surface of the photoelectric conversion element and a peripheral region of the facing region, and the control unit converts the light amount of the light beam to a first light amount. Scanning in the low resolution mode set to 2 and scanning in the high resolution mode set to the second light quantity lower than the first light quantity can be executed, and the synchronization sensor can scan the low resolution mode. A light beam including a first voltage peak generated when a light beam incident on the facing region is received by the photoelectric conversion element and a flare generated in the package layer by the light beam incident on the peripheral region. And the second voltage peak generated when the photoelectric conversion element receives light, the first voltage peak outputs the detection voltage higher than the second voltage peak, and the scanning in the high resolution mode is performed. Enter the facing area. When a light beam including a third voltage peak generated when a light beam to be received is received by the photoelectric conversion element and a flare generated in the package layer by the light beam incident on the peripheral region is received by the photoelectric conversion element A fourth voltage peak that occurs, wherein the third voltage peak is higher than the fourth voltage peak, the third voltage peak is lower than the first voltage peak, and the fourth voltage peak is the second voltage peak. The detection voltage lower than the detection voltage, and the change means changes the threshold voltage to be compared with the detection voltage as the threshold, and in the scanning in the low resolution mode, The threshold is set to a first threshold voltage between the first voltage peak and the second voltage peak, and in the high-resolution mode scanning, the threshold is set to the third voltage peak and the fourth voltage peak. A second threshold voltage that is lower than the first threshold voltage is set to a voltage between the pressure peaks.

  According to this optical scanning device, the threshold value that serves as a reference for the synchronization sensor to output the synchronization signal can be changed by the changing means. For this reason, for example, when the light amount of the light beam is changed, it is possible to set an appropriate threshold value that can exclude the influence of flare or the like according to the light amount. Therefore, the synchronization signal can be accurately output to the synchronization sensor.

  In the above optical scanning device, the synchronization sensor compares the photoelectric conversion element that converts an incident light beam into a detection voltage, the detection voltage and a threshold voltage, and the detection voltage exceeds the threshold voltage. A comparison unit that outputs the synchronization signal, and the changing unit applies the threshold voltage to the comparison unit from the outside of the synchronization sensor, and changes the threshold voltage according to the amount of light. It is desirable to do.

  According to this optical scanning device, the threshold voltage serving as a reference for the comparison unit to output the synchronization signal is not fixedly set inside the synchronization sensor, but is determined according to the amount of light from the outside of the synchronization sensor. Given. Therefore, the comparison unit can accurately output the synchronization signal based on the threshold voltage sequentially set according to the light amount.

  In the above optical scanning device, a light source driving unit that is controlled by the control unit and drives the light source to emit light at a predetermined timing and a specified light amount, and a reference light amount corresponding to the light amount specified by the control unit A light amount adjusting unit that generates a signal, and the light source driving unit compares a monitor signal corresponding to a light amount of a light beam currently emitted from the light source with the reference light amount signal, and the monitor signal is the reference The light source is driven so as to match a light amount signal, and the changing unit includes the light amount adjustment unit and a wiring unit that inputs the reference light amount signal to the comparison unit as the threshold voltage. be able to.

  According to this optical scanning device, in the operation in which the control unit controls the light source driving unit to adjust the light amount of light, the reference light amount signal generated by the light amount adjusting unit is used to respond to the comparison unit of the synchronous sensor according to the light amount. Threshold voltage is given. That is, in conjunction with the light amount adjustment operation by the control unit, a threshold voltage serving as a reference for outputting the synchronization signal is set. Accordingly, it is possible to reliably set an appropriate threshold voltage following the change in the amount of light.

  The optical scanning device includes a light source driving unit that is controlled by the control unit and drives the light source to emit light at a predetermined timing and a predetermined light amount, and the light source driving unit is provided from the control unit. A light amount self-setting unit that determines the light amount of the emitted light based on a control signal; and a signal generation unit that generates a reference light amount signal according to the light amount determined by the light amount self-setting unit, the changing means The signal generation unit and a wiring unit that inputs the reference light amount signal as the threshold voltage to the comparison unit may be included.

  Also in this optical scanning device, in the operation in which the control unit controls the light source driving unit to adjust the light amount of the light beam, the reference light amount signal generated by the signal generation unit is used to respond to the comparison unit of the synchronous sensor according to the light amount. A threshold voltage can be provided. Further, according to this optical scanning device, since the interface between the synchronization sensor and the control unit can be used only for transmitting the synchronization signal, the control configuration can be simplified.

  In the above optical scanning device, the synchronization sensor further includes a package layer made of a translucent resin that covers the photoelectric conversion element, the package layer having an incident surface for the light beam, and the incident surface is the photoelectric sensor. It is desirable to include a facing area that faces the light receiving surface of the conversion element and a peripheral area of the facing area.

  In the synchronous sensor having the above configuration, flare is likely to occur in the package layer when a light beam enters the peripheral region. Therefore, the merit of changing the threshold voltage according to the amount of light is great.

  An image forming apparatus according to another aspect of the present invention is the above-described optical scanning device that irradiates light with an image carrier that carries an electrostatic latent image, and the peripheral surface of the image carrier as the scanned surface. And comprising.

  According to the present invention, erroneous output of the synchronization sensor can be prevented by appropriately changing the threshold value serving as a reference for the synchronization sensor to output the synchronization signal. Therefore, it is possible to provide an optical scanning apparatus and an image forming apparatus that can appropriately perform scanning line writing timing and perform high-quality image formation.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is an optical path diagram which shows the structure of the main scanning cross section of the optical scanning device which concerns on embodiment. It is a typical top view which shows the incident condition of the laser beam to BD sensor. It is typical sectional drawing which shows the incident condition of the laser beam to BD sensor. (A) is a graph which shows the relationship between the detection voltage according to the light intensity which a BD sensor detects, and a threshold voltage, (B) and (C) are the figures which show the output state of a synchronizing signal. It is a block diagram which shows the control structure of the optical scanning device which concerns on 1st Embodiment. It is a block diagram which shows the structure of a BD sensor. 3 is a flowchart illustrating a control operation of the optical scanning device according to the first embodiment. It is a block diagram which shows the control structure of the optical scanning device which concerns on 2nd Embodiment.

  Hereinafter, an optical scanning device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a configuration of an image forming apparatus 1 including an optical scanning device 11 according to an embodiment of the present invention. The image forming apparatus 1 includes an optical scanning device 11, a developing device 12, a charger 13, a photosensitive drum 14 (image carrier), a transfer roller 15, a fixing device 16, and a paper feed cassette 17.

  The photosensitive drum 14 is a cylindrical member, and carries an electrostatic latent image and a toner image on its peripheral surface. The photosensitive drum 14 receives a driving force from a motor (not shown) and is rotated in the clockwise direction in FIG. The charger 13 charges the surface of the photosensitive drum 14 substantially uniformly.

  The optical scanning device 11 includes a light source such as a laser diode, a deflecting body, a scanning lens, an optical element, and the like, and is applied to the peripheral surface (scanned surface) of the photosensitive drum 14 that is substantially uniformly charged by the charger 13. A laser beam corresponding to the image data is irradiated to form an electrostatic latent image of the image data. The optical scanning device 11 will be described in detail later.

  The developing device 12 supplies toner to the peripheral surface of the photosensitive drum 14 on which the electrostatic latent image is formed, thereby forming a toner image. The developing device 12 includes a developing roller that carries toner and a screw that conveys the toner while stirring. The toner image formed on the photosensitive drum 14 is transferred from the sheet feeding cassette 17 to the recording paper conveyed through the conveyance path P. The developing device 12 is supplied with toner from a toner container (not shown).

  A transfer roller 15 is disposed below the photosensitive drum 14 so as to face each other, and a transfer nip portion is formed by both. The transfer roller 15 is made of a conductive rubber material or the like and is given a transfer bias to transfer the toner image formed on the photosensitive drum 14 onto the recording paper.

  The fixing device 16 includes a fixing roller 160 incorporating a heater, and a pressure roller 161 that forms a fixing nip portion with the fixing roller 160. As the recording paper on which the toner image is formed passes through the fixing nip portion, the toner image is fixed on the recording paper.

  Next, an image forming operation of the image forming apparatus 1 will be briefly described. First, the surface of the photosensitive drum 14 is charged almost uniformly by the charger 13. The peripheral surface of the charged photosensitive drum 14 is exposed by the optical scanning device 11, and an electrostatic latent image of an image formed on the recording paper is formed on the surface of the photosensitive drum 14. The electrostatic latent image is made visible as a toner image by supplying toner from the developing device 12 to the peripheral surface of the photosensitive drum 14. On the other hand, the recording paper is fed from the paper feed cassette 17 to the transport path 170. The toner image is transferred to the recording paper as the recording paper passes through the transfer nip portion. After this transfer operation is performed, the recording paper is conveyed to the fixing device 16 (the fixing nip portion), and the toner image is fixed to the recording paper.

  Hereinafter, the optical scanning device 11 will be described in detail. FIG. 2 is an optical path diagram showing the configuration of the main scanning section of the optical scanning device 11. The optical scanning device 11 includes a semiconductor laser 21 (light source), a collimator lens 22, a cylindrical lens 23, a micro electro mechanical systems (MEMS) mirror 24 (deflector), a first scanning lens 25, a second scanning lens 26, and a BD lens 27. And a BD sensor 30 (synchronous sensor). FIG. 1 shows an example in which the scanning lens is composed of two lenses, but the scanning lens may be a single scanning optical system.

  The semiconductor laser 21 is a light source that emits a laser beam LB (light beam) having a predetermined wavelength (for example, 780 nm). The semiconductor laser 21 is driven by an LD driver 28 (FIG. 6) provided with drive circuit components. The amount of the laser beam LB emitted from the semiconductor laser 21 is determined by the drive current applied to the semiconductor laser 21 by the LD driver 28.

  The collimator lens 22 converts the laser beam LB emitted from the semiconductor laser 21 and diffused into parallel light. The cylindrical lens 23 converts the laser beam LB emitted from the collimator lens 22 into linear light that is long in the main scanning direction and forms an image on the MEMS mirror 24.

  The MEMS mirror 24 deflects (reflects) the laser beam LB emitted from the semiconductor laser 21 and scans the peripheral surface 14S of the photosensitive drum 14 in the main scanning direction by the deflected laser beam LB. 2 indicates an effective scanning area by the laser beam LB. The MEMS mirror 24 is of a piezoelectric drive type, and includes a mirror part that reflects the laser beam LB and a drive part that causes the mirror part to swing about the swing axis. In place of the MEMS mirror 24, a polygon mirror may be used.

  The first scanning lens 25 and the second scanning lens 26 collect the laser beam LB deflected by the MEMS mirror 24 and form an image on the circumferential surface 14S of the photosensitive drum 14. The first and second scanning lenses 25 and 26 are lenses having an arc sine characteristic and are long in the main scanning direction. Although the BD lens 27 passes through the first scanning lens 25, the laser beam LB outside the effective scanning region R in the main scanning direction is imaged on the light receiving surface of the BD sensor 30.

  The BD sensor 30 detects the laser beam LB outside the effective scanning region R in order to determine the writing start timing, which is the timing for starting the irradiation of the laser beam LB on the peripheral surface 14S of the photosensitive drum 14 for one main scanning line. To do. The BD sensor 30 converts the incident laser beam LB into a detection voltage (a detection value corresponding to the light amount), and outputs a synchronization signal when the detection voltage exceeds a predetermined threshold voltage. Specifically, the BD sensor 30 outputs a high level signal when the laser beam LB exceeding the threshold is not detected, and outputs a low level signal (synchronization) while detecting the laser beam LB exceeding the threshold. Signal).

  The laser beam LB emitted from the semiconductor laser 21 is incident on the MEMS mirror 24 through the collimator lens 22, a diaphragm (not shown), and the cylindrical lens 23. Thereafter, the laser beam LB is deflected by the MEMS mirror 24 that swings around the axis, passes through the first and second scanning lenses 25 and 26, and travels toward the drum circumferential surface 14S. As the MEMS mirror 24 swings, the laser beam LB draws a scanning line in the effective scanning region R on the drum peripheral surface 14S. Before the effective scanning region R is scanned, the laser beam LB is incident on the BD sensor 30. Based on the synchronization signal output from the BD sensor 30, the scanning line writing timing by the laser beam LB is determined.

  As described above, since the scanning line writing timing is determined based on the synchronizing signal output from the BD sensor 30, the BD sensor 30 outputs the synchronizing signal at a timing expected originally, and outputs the synchronizing signal at other timings. (Incorrect output) must be avoided. However, the synchronization signal may be erroneously output due to various factors of the BD sensor 30. One of the major factors will be described with reference to FIGS.

  FIG. 3 is a schematic plan view showing a state of incidence of the laser beam LB on the BD sensor 30, and FIG. 4 is a cross-sectional view thereof. The BD sensor 30 includes a photoelectric conversion element 31 and a package layer 32 that is sealed so as to cover the photoelectric conversion element 31. The photoelectric conversion element 31 is an element that converts received light into a voltage, and generates a detection voltage according to the amount of the incident laser beam LB. The package layer 32 is made of a light-transmitting resin mold layer for protecting the photoelectric conversion element 31, and here, the package layer 32 has a shape made of a rectangular parallelepiped in plan view.

  The package layer 32 has an incident surface 321 that is a plane on which the laser beam LB is incident. The incident surface 321 is a surface facing the emission surface of the BD lens 27, a facing region 32 </ b> C facing the light receiving surface of the photoelectric conversion element 31, and a peripheral region 32 </ b> E (near the edge portion of the incident surface 321) of the facing region 32 </ b> C. ).

  As shown in FIG. 3, the laser beam LB having a laser spot LS having a predetermined diameter crosses the incident surface 321 in the main scanning direction. The arrows in the figure are crossing paths. This transverse path is set on the arrangement position of the photoelectric conversion element 31. Originally, when the laser spot LS passes immediately above the photoelectric conversion element 31, the amount of light received by the photoelectric conversion element 31 reaches a peak, and the photoelectric conversion element 31 is assumed to generate a detection voltage exceeding the threshold voltage. That is, as shown in FIG. 4, the BD sensor 30 outputs a synchronization signal at the timing when the laser beam LB1 incident on the facing region 32C of the incident surface 321 is received by the photoelectric conversion element 31. This is the original operation.

  However, the peak of the received light amount may occur at a stage where the laser spot LS does not reach directly above the photoelectric conversion element 31. As illustrated in FIG. 4, for example, a state is assumed in which the laser beam LB <b> 2 has reached the peripheral region 32 </ b> E of the incident surface 321. The laser beam LB2 is a beam that enters the incident surface 321 at a timing earlier than the laser beam LB1. The laser beam LB2 is irregularly reflected at the edge of the package layer 32, and flare is generated in the package layer 32, so that the beam may enter the photoelectric conversion element 31. The flare is also generated when the laser beam LB is reflected by an article such as a lead wire existing near the edge of the package layer 32. The flare may unintentionally generate a peak in the amount of received light.

  FIG. 5A is a graph showing the relationship between the detection voltage corresponding to the light intensity detected by the BD sensor 30 and the threshold voltage. As shown in FIG. 3, the horizontal axis of this graph indicates the time that the laser beam LB crosses the incident surface 321 of the package layer 32 in the main scanning direction, and the vertical axis indicates that the photoelectric conversion element 31 generates the laser beam LB by photoelectric conversion. The detected voltage is shown. The first profile A1 drawn with a solid line in the drawing shows the change over time of the detection voltage when the light amount of the laser beam LB emitted from the semiconductor laser 21 is a predetermined first light amount.

  The first profile A1 has first and second voltage peaks P1 and P2 resulting from the occurrence of two light receiving peaks. The first voltage peak P1 is a peak that occurs when the laser beam LB1 incident on the facing region 32C is received by the photoelectric conversion element 31 (see FIG. 4). On the other hand, the second voltage peak P2 is a useless peak for the BD sensor 30 that is generated by a flare or the like generated in the package layer 32 by the laser beam LB2 incident on the peripheral region 32E.

  In FIG. 5A, the threshold voltage Th is set in the middle between the first voltage peak P1 and the second voltage peak P2 of the first profile A1. In the time axis on the horizontal axis, time t11 is the time when the detected voltage starts to exceed the threshold voltage Th for the first profile A1, and time t12 is the time when the threshold voltage Th has been exceeded. In this case, as shown in FIG. 5B, the output of the BD sensor 30 changes from the high level to the low level between times t11 and t12. That is, the synchronization signal SA1 is output between times t11 and t12.

  On the other hand, the second profile A2 drawn by a dotted line in FIG. 5A is a detection voltage when the light amount of the laser beam LB is a second light amount larger than the first light amount of the first profile A1. The time change of is shown. Similarly, the second profile A2 has first and second voltage peaks P1 ′ and P2 ′. In addition to the first voltage peak P1 ′, the second voltage peak P2 ′ is also at a voltage level exceeding the threshold voltage Th.

  In the time axis of FIG. 5A, time t21 is the time when the detected voltage starts to exceed the threshold voltage Th for the second profile A2, and time t22 is the time when the threshold voltage Th has been exceeded. Time t21 is the time when an event that exceeds the threshold voltage Th occurs due to the second voltage peak P2 ′ caused by flare. In this case, as shown in FIG. 5C, the output of the BD sensor 30 changes from a high level to a low level between times t21 and t22. That is, the synchronization signal SA2 is output between time t21 earlier than time t11 and time t22 later than t12.

  For example, when the scanning line writing timing is determined at the rise time (t11 or t21) of the synchronization signal, an appropriate writing timing can be set as long as the laser beam LB is a light amount that forms the first profile A1. However, when the laser beam LB is changed to the amount of light that forms the second profile A2, the writing start timing is set at a time earlier than the original time. This is because the threshold voltage Th does not match the second profile A2. In the case of the second profile A2, the voltage level is intermediate between the first voltage peak P1 'and the second voltage peak P2'. In addition, the threshold voltage Th ′ should be set.

  In the optical scanning device 11, the light quantity of the laser beam LB is finely adjusted depending on environmental conditions and the like, and may be greatly changed depending on image forming conditions. For example, the light quantity of the laser beam LB is changed depending on the scanning speed (the swing speed of the MEMS mirror 24), the rotational speed (linear speed) of the photosensitive drum 14, and the resolution and density of the image to be formed. In particular, when the resolution is changed between the low resolution mode and the high resolution mode, the light amount is greatly changed.

  For example, it is assumed that image formation is performed at the linear speed V1 in the low resolution mode and image formation is performed at the half linear speed V2 = V1 / 2 without changing the scanning speed in the high resolution mode. . In this case, in the high resolution mode, the linear velocity is reduced to ½. Therefore, when the laser beam LB is irradiated with the same light amount as in the low resolution mode, the light amount per unit area is doubled. Therefore, in the high resolution mode, it is necessary to reduce the light amount of the laser beam LB to half that in the low resolution mode.

  When such a light amount change is applied to the graph of FIG. 5A, the first profile A1 is created in the high resolution mode, and the second profile A2 is created in the low resolution mode. In the conventional BD sensor 30, the threshold value that is a reference for generating the synchronization signal is fixed to a constant value. For example, a fixed threshold voltage is set by connecting a fixed resistor to the threshold input terminal of the comparator. For example, when the threshold is set to the threshold voltage Th in FIG. 5A, the BD sensor 30 can output an accurate synchronization signal in the high resolution mode. However, in the low resolution mode, the synchronization signal may be output earlier than the original timing depending on the occurrence of flare.

  On the other hand, when the threshold value is set to the threshold voltage Th ′, an accurate synchronization signal can be output in the low resolution mode, but the synchronization signal may not be output in the high resolution mode. Even if the threshold voltage Th ′ is set to a low level so that the first voltage peak P1 of the first profile A1 can be detected, the second voltage peak P2 ′ caused by the flare of the first voltage peak P1 and the second profile A2 Therefore, there is a problem that it becomes difficult to separate the two.

  In view of the above problems, the optical scanning device 11 of the present embodiment includes a changing unit that changes a threshold value that serves as a reference for the BD sensor 30 to output a synchronization signal. Thereby, for example, when the light quantity of the laser beam LB is changed according to the image resolution, it is possible to set an appropriate threshold value that can exclude the influence of flare or the like according to the light quantity. Accordingly, the BD sensor 30 can accurately output the synchronization signal, and high-quality image formation can be achieved. Hereinafter, specific examples of the changing means will be described.

  FIG. 6 is a block diagram illustrating a control configuration of the optical scanning device 11 according to the first embodiment. The optical scanning device 11 includes an LD driver 28 (light source drive unit) in addition to the semiconductor laser 21 and the BD sensor 30 described above. Further, the image forming apparatus 1 includes a controller 40 (control unit) and a light amount adjustment unit 41 (changing unit) for driving control of the optical scanning device 11.

  The LD driver 28 is controlled by the controller 40 and performs light emission control for causing the semiconductor laser 21 to emit light at a predetermined timing designated by the controller 40 and at a designated light quantity. The LD driver 28 is supplied with a monitor current indicating the current light emission state of the semiconductor laser 21. In other words, the semiconductor laser 21 incorporates a light receiving element for monitoring light emission. The light receiving element receives a part of the light beam emitted from the semiconductor laser 21 and outputs a monitor current (monitor signal) obtained by photoelectrically converting the light to the LD driver 28.

  As described above, the BD sensor 30 receives the laser beam LB and generates a synchronization signal. This synchronization signal is output to the controller 40. FIG. 7 is a block diagram showing a configuration of the BD sensor 30. The BD sensor 30 includes a photoelectric conversion element 31 and a comparison unit 33. As described above, the photoelectric conversion element 31 receives the laser beam LB and generates a detection voltage corresponding to the amount of the laser beam LB.

  The comparison unit 33 is a so-called comparator, and includes a negative input terminal, a positive input terminal, and an output terminal. A detection voltage supplied from the photoelectric conversion element 31 inside the BD sensor 30 is input to the negative input terminal. A threshold voltage given from the outside is input to the positive input terminal. The output terminal is connected to the controller 40. The comparison unit 33 compares the detection voltage with the threshold voltage, and outputs a Hi-Low signal from the output terminal based on the comparison result. In the present embodiment, when the detected voltage exceeds the threshold voltage, a low level signal corresponding to the synchronization signal is output.

  The controller 40 controls the operation of forming the electrostatic latent image on the drum peripheral surface 14S by the optical scanning device 11 based on the image data of the image formed by the image forming apparatus 1. Specifically, the controller 40 generates light emission data based on the image data and outputs it to the LD driver 28. The timing of outputting the light emission data is determined based on a synchronization signal given from the BD sensor 30. That is, the controller 40 controls the writing timing of the scanning line on the drum peripheral surface 14S by the laser beam LB based on the synchronization signal. In addition, the controller 40 provides the LD driver 28 with light emission data that is not based on image data, for example, a light emission calibration required for light amount calibration or the initialization of the LD driver 28.

  The controller 40 also performs control to change the light quantity of the laser beam LB. The change in the amount of light is performed, for example, when the linear velocity for image formation is changed by changing the printing speed or the change between the high resolution mode and the low resolution mode, or when the light amount is calibrated. When changing the light amount, the controller 40 outputs a control signal corresponding to the light amount change to the light amount adjusting unit 41.

  The light amount adjustment unit 41 generates a reference light amount signal corresponding to the light amount specified by the control signal supplied from the controller 40. The reference light amount signal is a voltage signal that increases as the specified light amount increases. The light amount adjustment unit 41 is electrically connected by the LD driver 28 and the first wiring 411 by the BD sensor 30 and the second wiring 412 (wiring unit; part of the changing unit). Therefore, the reference light amount signal generated by the light amount adjustment unit 41 is given to the LD driver 28 and the BD sensor 30 in parallel. The light amount adjustment unit 41 may be a circuit unit built in the controller 40 or may be a DA converter that converts a digital instruction signal given from the controller 40 into an analog signal corresponding to the reference light amount signal. .

  The LD driver 28 compares the voltage conversion value of the monitor current given from the semiconductor laser 21 with the voltage value of the reference light quantity signal given from the light quantity adjusting unit 41, and drives the semiconductor laser 21 so that they match. . That is, the monitor current has a value corresponding to the light amount of the laser beam LB emitted from the semiconductor laser 21 at present. By matching this with the reference light amount signal, the semiconductor laser 21 is controlled with the light amount specified by the controller 40. Can emit light.

  The end of the second wiring 412 toward the BD sensor 30 is connected to the positive input terminal of the comparison unit 33. That is, the second wiring 412 is a wiring for inputting the above-described reference light amount signal to the comparison unit 33 as a threshold voltage to be compared with the detection voltage. When viewed from the BD sensor 30 side, the threshold voltage input to the positive input terminal is not a constant voltage generated by a fixed resistor or the like, but is supplied from the external light amount adjustment unit 41, and the light amount of the laser beam LB specified by the controller 40 The threshold voltage varies depending on In the first embodiment, the light amount adjustment unit 41 that generates the reference light amount signal and the second wiring 412 that supplies the reference light amount signal to the comparison unit 33 function as a changing unit that changes the threshold voltage of the BD sensor 30. To do.

  Since the threshold voltage applied to the comparison unit 33 is changed according to the light amount of the laser beam LB, the comparison unit 33 can output a synchronization signal at an appropriate timing according to the light amount. In the example shown in FIG. 5A, when the controller 40 specifies the amount of light that creates the first profile A1 in the high resolution mode, the threshold voltage Th is set by the reference light amount signal, When the second profile A2 in the resolution mode is designated, a threshold voltage Th ′ that is higher than the threshold voltage Th is set. The threshold voltage Th in the high resolution mode is set between the first voltage peak P1 when the laser beam LB incident on the facing region 32C is received and the second voltage peak P2 created by flare or the like ( P1> Th> P2). Similarly, the threshold voltage Th ′ in the low resolution mode is set so as to satisfy P1 ′> Th ′> P2 ′. As a result, it is possible to eliminate an erroneous output of the synchronization signal, an output leakage, or the like due to an inappropriate threshold voltage level.

  As a method for inputting a threshold voltage in an appropriate range to the positive input terminal of the comparison unit 33, there is a method for appropriately selecting the resistance value of the voltage dividing resistor incorporated in the first wiring 411. For example, when a voltage in the range of 0 to 1 V is input to the LD driver 28 and a voltage in the range of 0 to 0.5 V is intended to be input to the comparison unit 33, the voltage corresponding to the reference light amount signal is such The resistance value of the voltage dividing resistor is selected so as to be distributed at a voltage dividing ratio. Note that the reference light amount signal may be directly given to the positive input terminal by setting the comparison unit 33 without depending on the voltage dividing resistor.

  According to the above configuration, the comparison unit 33 is dynamically given a threshold voltage proportional to the reference light amount signal for determining the light amount. For this reason, the ratio of the original detection voltage (first voltage peaks P1, P1 ′) of the BD sensor 30 and the threshold voltage is kept constant. Further, flare generated in the package layer 32 covering the photoelectric conversion element 31 is also substantially proportional to the amount of the laser beam LB. Therefore, for example, as shown in the above example, the threshold voltage is changed from Th to Th ′ under the conditions satisfying the conditions of P1> Th> P2 and P1 ′> Th ′> P2 ′. It is possible to reliably prevent erroneous output.

  In addition, while the drum circumferential surface 14S is being scanned with the laser beam LB, the light amount of the laser beam LB may be rapidly decreased. In this case, since the threshold voltage given to the comparison unit 33 by the reference light amount signal also rapidly decreases, the detection voltage of the photoelectric conversion element 31 causes the threshold voltage to be caused by flare generated for some reason in the housing of the optical scanning device 11. There may be cases where it is exceeded. This inconvenience can be avoided by performing a mask process so that the controller 40 does not accept the synchronization signal except for the timing when the laser beam LB scans the vicinity of the position where the BD sensor 30 is disposed.

  FIG. 8 is a flowchart showing the control operation of the optical scanning device 11 according to the first embodiment. When the image forming operation is started, the controller 40 receives the image data of the image to be formed, and specifies the light amount of the laser beam LB accordingly. The light amount adjustment unit 41 generates a reference light amount signal C <b> 1 corresponding to the designated light amount from the controller 40. The reference light amount signal C1 is given to the LD driver 28 and to the comparison unit 33 of the BD sensor 30 as a threshold voltage Th1 (step S1).

  At the same time, the controller 40 generates light emission data based on the image data and outputs it to the LD driver 28 (step S2). Then, the semiconductor laser 21 is driven by the LD driver 28 at a timing based on the synchronization signal of the BD sensor 30 and at a light amount based on the reference light amount signal C1, and the drum circumferential surface 14S is scanned by the laser beam LB (step). S3).

  Next, the controller 40 determines whether or not the light amount of the laser beam LB needs to be changed by changing the resolution mode or the printing speed (step S4). When the light amount is not changed (NO in step S4), the reference light amount signal is not changed from C1, and the process is repeated without changing the threshold voltage from Th1.

  On the other hand, when the light amount needs to be changed (YES in step S4), the controller 40 sends a control signal for changing the designated light amount to the light amount adjusting unit 41. In response to this, the light amount adjusting unit 41 generates a new reference light amount signal C2 having a voltage value different from that of C1. Along with this. The threshold voltage given to the comparison unit 33 is also changed from Th1 to Th2 (step S5).

  The controller 40 generates light emission data based on the image data and outputs it to the LD driver 28 (step S6). Then, the LD driver 28 drives the semiconductor laser 21 based on the light emission data based on the synchronization signal output based on the threshold voltage = Th2 with the light amount based on the changed reference light amount signal C2 (step S7). . And the controller 40 determines whether the light quantity change of the laser beam LB is required (step S8). When the light amount change is not performed (NO in step S8), the reference light amount signal = C2 and the threshold voltage Th2 are maintained, and when the light amount change is necessary (YES in step S8), a new reference light amount signal and threshold voltage are set. Is set. Thereafter, such processing is repeated.

  According to the optical scanning device 11 according to the first embodiment described above, the threshold voltage serving as a reference for the BD sensor 30 to output the synchronization signal is changed in conjunction with the reference light amount signal generated by the light amount adjustment unit 41. It has a configuration. For this reason, when the light quantity of the laser beam LB is changed, a threshold voltage capable of excluding the influence of flare or the like can be set according to the light quantity. Therefore, it is possible to cause the BD sensor 30 to output the synchronization signal at an appropriate timing. Further, in conjunction with the light amount adjustment operation of the LD driver 28 by the controller 40, a threshold voltage serving as a reference for outputting a synchronization signal is set. Therefore, it is possible to reliably set an appropriate threshold voltage following the change in the light amount of the laser beam LB.

  FIG. 9 is a block diagram illustrating a control configuration of the optical scanning device 11A according to the second embodiment. The optical scanning device 11A includes the same semiconductor laser 21 and BD sensor 30 as those in the first embodiment, and an LD driver 28A (light source driving unit) having a light quantity determination function. The image forming apparatus 1 includes a controller 40A (control unit) for driving control of the optical scanning device 11A. The difference from the first embodiment is that the reference light amount signal is not generated on the controller 40A side and the reference light amount signal is generated on the LD driver 28A side in the second embodiment.

  The LD driver 28 </ b> A is controlled by the controller 40 and performs light emission control for causing the semiconductor laser 21 to emit light at a predetermined timing designated by the controller 40 and with a predetermined light amount determined by itself. The point that the monitoring current is given from the semiconductor laser 21 to the LD driver 28A is the same as in the first embodiment.

  The LD driver 28A further includes a light amount self-setting unit 281 and a signal generation unit 282 functionally. The light amount self-setting unit 281 determines the light amount of the laser beam LB emitted from the semiconductor laser 21 based on the control signal given from the controller 40. The light amount self-setting unit 281 receives, for example, a control signal related to a change in resolution as the control signal, and sets a specified light amount. The signal generation unit 282 generates a reference light amount signal corresponding to the designated light amount determined by the light amount self-setting unit 281. The LD driver 28A compares the voltage conversion value of the monitor current given from the semiconductor laser 21 with the voltage value of the reference light amount signal generated by the signal generator 282, and drives the semiconductor laser 21 so that they match. .

  The reference light amount signal generated by the signal generator 282 is input to the BD sensor 30. Specifically, the LD driver 28 </ b> A and the comparison unit 33 of the BD sensor 30 are electrically connected by the third wiring 413. The reference light amount signal generated by the signal generator 282 is input to the positive input terminal (see FIG. 7) of the comparator 33 as a threshold voltage via the third wiring 413. The comparison unit 33 compares the threshold voltage with the detection voltage of the photoelectric conversion element 31, and outputs a synchronization signal when the detection voltage exceeds the threshold voltage. In the second embodiment, the signal generation unit 282 that generates the reference light amount signal and the third wiring 413 that supplies the reference light amount signal to the comparison unit 33 function as a changing unit that changes the threshold voltage of the BD sensor 30.

  Also in the optical scanning device 11A according to the second embodiment, in the operation in which the controller 40A controls the LD driver 28A to adjust the light amount of the laser beam LB, the BD sensor is used by using the reference light amount signal generated by the signal generation unit 282. A threshold voltage corresponding to the amount of the laser beam LB can be given to the thirty comparison units 33. Further, according to the optical scanning device 11A, the BD sensor 30 is configured to acquire the reference light amount signal through the third wiring 413 from the LD driver 28A provided internally in the optical scanning device 11A. As in the first embodiment, when the reference light amount signal is acquired from the controller 40 side, an interface is required between the two, but according to the second embodiment, this can be omitted and the wiring can be simplified. There are advantages.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various deformation | transformation embodiment can be taken. For example, in the above-described embodiment, the reference light amount signal is used as the threshold voltage. However, there is no particular limitation as long as the signal changes according to the light amount of the laser beam LB. Further, the change of the threshold voltage is not limited to the change of the linear velocity or the light amount calibration. For example, the threshold voltage may be changed with a substantial change in the amount of light on the surface to be scanned accompanying a change in the profile of the laser spot LS of the laser beam LB.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Optical scanning apparatus 14 Photosensitive drum (image carrier)
14S peripheral surface (surface to be scanned)
21 Semiconductor laser (light source)
24 MEMS mirror (deflector)
25, 26 First and second scanning lenses 28, 28A LD driver (light source driving unit)
281 Light quantity self-setting unit 282 Signal generation unit (changing means)
30 BD sensor (synchronous sensor)
31 Photoelectric conversion element 32 Package layer 321 Incident surface 32C Face-to-face area 32E peripheral area 33 Comparison section 40, 40A Controller (control section)
41 Light intensity adjustment unit (changing means)
411, 412, 413 1st, 2nd, 3rd wiring (change means; wiring part)
LB laser beam

Claims (6)

A light source emitting light,
A deflector that deflects the light emitted from the light source and scans the surface to be scanned in the main scanning direction with the light;
A scanning lens that forms an image of the light beam deflected by the deflector on the surface to be scanned;
A synchronization sensor that outputs a synchronization signal when a light beam that has passed through the scanning lens is incident and a detection value corresponding to a light amount of the incident light beam exceeds a threshold;
A control unit that controls writing of a scanning line on the surface to be scanned by the light beam based on the synchronization signal;
Changing means for changing the threshold value of the synchronous sensor;
Equipped with a,
The synchronous sensor includes a photoelectric conversion element that converts an incident light beam into a detection voltage, and a package layer made of a translucent resin that covers the photoelectric conversion element, and the package layer has an incident surface for the light beam, The incident surface includes a facing region facing the light receiving surface of the photoelectric conversion element, and a peripheral region of the facing region,
The control unit is capable of executing a low-resolution mode scan for setting the light amount of the light beam to a first light amount and a high-resolution mode scan for setting a second light amount lower than the first light amount,
The synchronous sensor is
When the scanning in the low resolution mode is performed, the package is formed by a first voltage peak generated when a light beam incident on the facing region is received by the photoelectric conversion element and the light beam incident on the peripheral region. A second voltage peak generated when a light beam including flare generated in the layer is received by the photoelectric conversion element, and the first voltage peak outputs the detection voltage higher than the second voltage peak,
When the high-resolution mode scan is performed, the package is formed by a third voltage peak generated when a light beam incident on the facing region is received by the photoelectric conversion element and the light beam incident on the peripheral region. A fourth voltage peak generated when a light beam including a flare generated in the layer is received by the photoelectric conversion element, the third voltage peak is higher than the fourth voltage peak, and the third voltage peak is Outputting the detection voltage lower than the first voltage peak, wherein the fourth voltage peak is lower than the second voltage peak,
The changing means is
The threshold voltage to be compared with the detection voltage is changed to be treated as the threshold,
In scanning in the low resolution mode, the threshold is set to a first threshold voltage between the first voltage peak and the second voltage peak;
In the scanning in the high resolution mode, the threshold is set to a second threshold voltage that is a voltage between the third voltage peak and the fourth voltage peak and lower than the first threshold voltage. Scanning device. The optical scanning device according to claim 1,
Wherein the synchronization sensor,
Comparing the pre-Symbol detection voltage and the threshold voltage, and a comparator unit for the detected voltage to output the synchronization signal when exceeded the threshold voltage,
The optical scanning device, wherein the changing unit applies the threshold voltage to the comparison unit from the outside of the synchronous sensor, and changes the threshold voltage according to the amount of light. The optical scanning device according to claim 2,
A light source driving unit that is controlled by the control unit and drives the light source to emit a light beam at a predetermined timing and with a specified light amount;
A light amount adjustment unit that generates a reference light amount signal according to the light amount designated by the control unit,
The light source driving unit compares the monitor signal corresponding to the light amount of light currently emitted from the light source with the reference light amount signal, and drives the light source so that the monitor signal matches the reference light amount signal. Is,
The changing unit includes the light amount adjustment unit and a wiring unit that inputs the reference light amount signal as the threshold voltage to the comparison unit. The optical scanning device according to claim 2,
A light source driving unit that is controlled by the control unit and that drives the light source to emit light at a predetermined timing and a predetermined amount of light;
The light source driving unit generates a light amount self-setting unit that determines a light amount of emitted light, and a reference light amount signal corresponding to the light amount determined by the light amount self-setting unit, based on a control signal given from the control unit. A signal generator,
The changing unit includes the signal generation unit and a wiring unit that inputs the reference light amount signal as the threshold voltage to the comparison unit. In the optical scanning device according to any one of claims 1 to 4 ,
The control unit includes a mask processing unit that prevents the control unit from accepting the synchronization signal other than the timing at which the light beam scans near the arrangement position of the synchronization sensor.
Optical scanning device. An image carrier for carrying an electrostatic latent image;
The optical scanning device according to any one of claims 1 to 5, wherein a light beam is irradiated with the circumferential surface of the image carrier as the surface to be scanned.
An image forming apparatus comprising: