JP4604890B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a laser printer.

In a laser printer, a laser beam emitted from a laser diode is irradiated onto a charged photosensitive drum, and is generated between a portion (bright portion) that has been irradiated with laser light and a portion that has not been irradiated (dark portion). An invisible image based on the potential difference, that is, an electrostatic latent image is formed. The electrostatic latent image is developed with a developer such as toner and transferred to a recording medium to form an image.
Conventionally, a laser printer having a function of automatically adjusting the light intensity of such a laser diode has been disclosed. For example, in the following Patent Document 1, the applied current is adjusted so that the light intensity of the laser diode becomes a predetermined level by measuring and feeding back the light intensity when the laser diode is turned on. In this device, an abnormality occurring in a laser diode or the like is detected by detecting the value of the applied current.
JP-A-6-031975 JP 2004-342655 A

(First issue)
By the way, in such an image forming apparatus, when an inappropriate signal is input to the laser diode due to software runaway or the like, the laser diode is turned on even though it is a non-image forming area. Exposure may be performed and a normal image may not be formed (for example, a black image is formed). Since such a situation cannot be detected by the above-described conventional technology, the abnormality is confirmed only after the user confirms the printed sheet, and the sheet and toner are consumed wastefully until the user notices the abnormality. There was a problem.

(Second problem)
In addition, when the laser diode is not irradiated, if the laser diode is turned on slightly by passing a small current smaller than that at the time of irradiation, the response (rise) of the laser diode is improved, and irradiation / non-irradiation is performed at high speed. It is known that it has the characteristic that irradiation can be switched. For this reason, for example, in the device described in Patent Document 2, the laser diode is controlled so that a lighting current for turning on the laser diode and a fine lighting current for slightly turning on the laser diode are alternately supplied.

  On the other hand, an image forming apparatus having a function of changing the resolution of an image to be formed according to a use is known. For example, in an image that can form an image with a low resolution of 600 dpi and a high resolution of 1200 dpi, a 1200 dpi image has twice as many dots as the 600 dpi image in the main scanning direction and twice in the sub-scanning direction. . Therefore, at 1200 dpi, the photosensitive member moving speed (moving in the sub-scanning direction) is reduced to half the speed. As for the light intensity at the time of turning on the laser light, if the same light intensity is used at 1200 dpi and 600 dpi, the amount of irradiation per unit area on the photosensitive member becomes large and the print density becomes too high. As shown in A), the light intensity P1200 at 1200 dpi is made smaller than the light intensity P600 at 600 dpi. In this case, as shown in the figure, the lighting current I1200 supplied to the laser diode at 1200 dpi is controlled to be smaller than the lighting current I600 at 600 dpi.

By the way, in the image forming apparatus having the function of changing the resolution as described above, no proposal has been made regarding the control of the fine lighting current. Conventionally, for example, the light intensity at the time of the fine lighting is uniform at the time of lighting. It is adjusted to be one hundredth of the light intensity. That is, as shown in FIGS. 6A and 6B, the light intensity PM600 at the time of fine lighting at 600 dpi decreases at a constant rate with respect to the light intensity P600 at the time of lighting, and at the time of fine lighting at 1200 dpi. The light intensity PM1200 is smaller than the light intensity P1200 at the time of lighting at the same rate as at 600 dpi. Adjusted.
However, if the current value of the fine lighting current becomes too small, the response of the laser diode may be deteriorated. Conversely, if the current value of the fine lighting current is too large, the light intensity of the laser light increases and the photosensitive member is There was a problem of exposure.

  The present invention has been completed based on the above situation, and a first object of the present invention is to eliminate a problem caused by an abnormality that a laser beam is lit at a non-image forming timing. The purpose of is to control the fine lighting current appropriately regardless of the resolution setting.

As means for achieving the above object, an image forming apparatus according to the invention of claim 1 is a photoconductor, a laser light emitting means for emitting a laser beam irradiated on the photoconductor, and light emission from the laser light emitting means. Measuring means for measuring the light intensity of the laser light to be supplied, supplying a current for emitting the laser light to the laser emitting means, and determining the current value of the current based on the measurement result of the measuring means A laser driving unit that adjusts the light intensity of the laser light between a high level for forming a latent image on the photoconductor and a low level for forming no latent image on the photoconductor; and the laser driving unit On the other hand, a light level switching means for outputting a high level signal for supplying a current for increasing the light intensity of the laser light to the laser light emitting means and a low level signal for supplying a current for decreasing the light level. And when the low level signal is output by the light level switching means, the light intensity of the laser light measured by the measuring means corresponds to a predetermined light intensity at which a latent image is formed on the photoconductor. And when it is determined that the light intensity of the laser light measured by the measuring means does not correspond to the predetermined light intensity, the light intensity of the laser light further measured by the measuring means Is determined to be equal to or greater than a threshold value indicating deterioration of the laser emission means, and the determination means determines that the light intensity of the laser light measured by the measurement means corresponds to the predetermined light intensity. If it is, a stopping means for stopping the image forming operation, the judgment unit Therefore, when the light intensity of the laser beam is determined to be equal to or more than the threshold value, the light emitting means Characterized in place with a notification means for notifying the deterioration, the.

According to a second aspect of the present invention, there is provided an image forming apparatus comprising: a photosensitive member; a laser emitting unit that emits a laser beam applied to the photosensitive member; and a measurement that measures a light intensity of the laser beam emitted from the laser emitting unit. And a current for causing the laser light emission means to emit the laser light, and adjusting a current value of the current based on a measurement result of the measurement means, thereby adjusting a light intensity of the laser light. Laser driving means for switching between a high level for forming a latent image on the photoconductor and a low level for not forming a latent image on the photoconductor, and the laser driving means for the laser light to the laser driving means. A light level switching means for outputting a high level signal for supplying a current for increasing the light intensity and a low level signal for supplying a current for decreasing the light intensity; Judging means for judging whether or not the light intensity of the laser beam measured by the measuring means corresponds to a predetermined light intensity at which a latent image is formed on the photosensitive member when a bell signal is output; And when the determination means determines that the light intensity of the laser beam measured by the measurement means corresponds to the predetermined light intensity, and a stop means for stopping an image forming operation, and formed on the photoreceptor. Resolution setting means for setting the resolution of the latent image to low resolution or high resolution, and the laser driving means outputs the laser light when the high level signal is output by the light level switching means. The laser is supplied when a lighting current for emitting light at a high level of light intensity for forming a latent image on the photosensitive member is supplied and the low level signal is output by the light level switching means. Wherein not form a latent image on a photosensitive member comprising supplies a fine lighting current to emit light at a low level of light intensity, setting of the resolution setting means when the high resolution, low current value of the lighting current It is characterized in that it is smaller than the resolution and the current value of the fine lighting current is the same as that at the low resolution .

A third aspect of the present invention, there is provided a connector described in claim 2, in the laser driving means, and a circuit for supplying the fine lighting current when the setting is a low resolution the resolution setting unit, when the high-resolution It is characterized in that the circuit for supplying the fine lighting current is common.

According to a fourth aspect of the invention, there is provided the second or third aspect of the invention, wherein the light emitting means is configured to irradiate a single laser beam to the photoconductor, and the resolution setting means. And a speed adjusting means for adjusting the moving speed of the photosensitive member at a high resolution so as to be smaller than the moving speed of the photosensitive member at a low resolution.

A fifth aspect of the present invention, there is provided a connector described in claim 4, the current value of the lighting current supplied by the laser driving means on the basis of the moving speed of the photosensitive member to be adjusted by the speed adjustment means adjusting It is characterized by

According to a sixth aspect of the present invention, there is provided an image forming apparatus comprising: a photosensitive member; a laser emitting unit that emits a laser beam applied to the photosensitive member; and a measurement that measures a light intensity of the laser beam emitted from the laser emitting unit. And a current for causing the laser light emission means to emit the laser light, and adjusting a current value of the current based on a measurement result of the measurement means, thereby adjusting a light intensity of the laser light. Laser driving means for switching between a high level for forming a latent image on the photoconductor and a low level for not forming a latent image on the photoconductor, and the laser driving means for the laser light to the laser driving means. A light level switching means for outputting a high level signal for supplying a current for increasing the light intensity and a low level signal for supplying a current for decreasing the light intensity; Judging means for judging whether or not the light intensity of the laser beam measured by the measuring means corresponds to a predetermined light intensity at which a latent image is formed on the photosensitive member when a bell signal is output; And a stopping means for stopping an image forming operation when the determining means determines that the light intensity of the laser light measured by the measuring means corresponds to the predetermined light intensity, and the laser driving means Supplies a lighting current that causes the laser beam to emit light at a high level of light intensity that forms a latent image on the photoreceptor when the high level signal is output by the light level switching means, When the low level signal is output by the level switching means, a fine lighting current for supplying the laser beam with a low level light intensity that does not form a latent image on the photosensitive member is supplied. The laser driving means can switch the current value of the lighting current between high and low, and supplies the fine lighting current having the same current value when the current value of the lighting current is high and low. However, it has characteristics.

A seventh aspect of the present invention is the laser device according to the sixth aspect , wherein the laser driving means supplies a circuit for supplying the fine lighting current when the current value of the lighting current is high, and a current value of the lighting current. This is characterized in that the circuit for supplying the fine lighting current is common when the voltage is low.

According to an eighth aspect of the present invention, there is provided the apparatus according to the sixth or seventh aspect , further comprising speed adjusting means for adjusting a moving speed of the photoconductor, wherein a current value of the lighting current supplied by the laser driving means is Further, it is characterized in that it can be switched based on the moving speed of the photosensitive member adjusted by the speed adjusting means.

<Inventions of Claims 1 , 2 , and 6 >
When the light intensity of the laser beam measured by the measuring means is a predetermined light intensity at which a latent image is formed on the photosensitive member even though the low level signal is output by the light level switching means The image forming operation is stopped. Accordingly, it is possible to prevent a situation in which paper and toner are wasted due to erroneous emission of laser light during non-image formation.

<Invention of Claim 1 >
When it is determined that the light intensity of the laser beam is equal to or higher than a predetermined threshold value indicating the deterioration of the light emitting means when the low level signal is output by the light level switching means, the deterioration of the light emitting means is notified. . As a result, the failure location is specified, so that maintenance can be performed quickly.

<Invention of Claim 2 >
If the fine lighting current at the low resolution is different from the fine lighting current at the high resolution, if one of the fine lighting currents is too large, the photoconductor may be exposed. There is a risk of getting worse. On the other hand, in this configuration, the fine lighting current at the time of low resolution and the fine lighting current at the time of high resolution are set to the same current value, so that the fine lighting current can always be kept at an optimum value.

<Invention of Claim 3 >
The laser driving means can be constructed at low cost because the circuit for supplying the fine lighting current is common between the low resolution setting and the high resolution setting of the resolution setting means.

<Invention of Claim 4 >
In order to change the resolution, a configuration in which the number of laser beams applied to the photoconductor is appropriately switched according to the resolution is also conceivable, but this increases the cost. In addition, a configuration in which the scanning speed of the laser beam in the main scanning direction is changed according to the resolution is conceivable, but is often technically difficult. On the other hand, according to this configuration, the resolution can be easily changed by adjusting the moving speed of the photoconductor according to the resolution setting.

<Invention of Claim 5 >
By adjusting the current value of the lighting current according to the moving speed of the photosensitive member, the density level of the image at each resolution can be made appropriate. It is also possible to reduce damage to the photoconductor by preventing the photoconductor from being irradiated with laser light having an excessive light intensity.

<Invention of Claim 6 >
When the lighting current level is changed by switching the lighting current level, the photoconductor may be exposed if the lighting current is too large, and if it is too small, the response of the laser emitting means will deteriorate. There is a risk that. On the other hand, in this configuration, the fine lighting current can always be kept at an optimal value by setting the fine lighting current to a constant current value regardless of the level of the lighting current.

<Invention of Claim 7 >
The laser driving means can be configured at low cost because the circuit for supplying the fine lighting current is common between when the lighting current is high and when the lighting current is low.

<Invention of Claim 8 >
By adjusting the current value of the lighting current according to the moving speed of the photosensitive member, it is possible to make the density level of the formed image appropriate. It is also possible to reduce damage to the photoconductor by preventing the photoconductor from being irradiated with laser light having an excessive light intensity.

<Embodiment 1>
Embodiment 1 of the present invention will be described with reference to the drawings.
(Whole structure of laser printer)
FIG. 1 is a side sectional view of an essential part showing an embodiment of a laser printer 1 as an image forming apparatus of the present invention. The laser printer 1 includes a feeder unit 4 for feeding a sheet 3 as a recording medium and an image forming unit 5 for forming an image on the fed sheet 3 in a main body casing 2. ing.

  The feeder unit 4 includes a paper feed tray 6 that is detachably attached to the bottom of the main casing 2, a paper feed roller 8 and a separation pad 9 that are provided above the front end of the paper feed tray 6, and a paper feed roller 8, a pickup roller 11 provided on the rear side of the paper feed roller 8, a pinch roller 10 disposed oppositely on the lower front side of the paper feed roller 8, a registration roller 12 provided on the upper rear side of the paper feed roller 8, and the like.

  Inside the paper feed tray 6, there is provided a paper pressing plate 7 on which the paper 3 can be stacked. The sheet pressing plate 7 is supported at the rear end so as to be swingable, so that the front end is movable in the vertical direction. Further, a lever 14 for lifting the front end portion of the paper pressing plate 7 upward is provided at the front end portion of the paper feed tray 6. When the lever 14 is driven to rotate clockwise in the drawing, the rear end of the lever 14 lifts the front end of the paper pressing plate 7, and the uppermost paper 3 on the paper pressing plate 7 is pressed by the pickup roller 11. By the rotation of the pickup roller 11, the conveyance is started between the paper feed roller 8 and the separation pad 9.

  When the sheet 3 fed out between the sheet feeding roller 8 and the separation pad 9 by the pickup roller 11 is sandwiched between the sheet feeding roller 8 and the separation pad 9 by the rotation of the sheet feeding roller 8. Each sheet is reliably fed and fed. The fed paper 3 passes between the paper feed roller 8 and the pinch roller 10 and is conveyed to the registration roller 12.

  The registration roller 12 includes a pair of rollers facing each other, and after the registration of the sheet 3, the registration roller 12 is transferred to a transfer position P (a nip position between a photosensitive drum 27 and a transfer roller 30 described later) of the image forming unit 5. Transport toward.

  A scanner unit 16 for exposing a photosensitive drum 27 described later is provided in the upper part of the main casing 2. The scanner unit 16 includes a laser light emitting unit 17 that emits laser light, a polygon mirror 19 that is rotationally driven by a scanner motor 18, an fθ lens 20, reflecting mirrors 22 and 23, a lens 21, and the like. After the laser light emitted from the laser light emitting unit 17 is deflected by the polygon mirror 19 and passes through the fθ lens 20 as indicated by a broken line, the optical path is turned back by the reflecting mirror 22 and further passes through the lens 21. The optical path is further bent downward by the reflecting mirror 23, so that the surface of the photosensitive drum 27 (described later) of the process cartridge 25 is irradiated at high speed.

  The scanner unit 16 is provided with a BD (Beam Detector) sensor 24 configured to be able to detect the laser light reflected by the polygon mirror 19. This BD sensor 24 is normally used for adjusting the writing timing of each line of laser light, and is configured to detect reflected light when the polygon mirror 19 reaches a predetermined angle, that is, laser light. The irradiation of the laser beam to one position in the main scanning direction is detected. When the laser light is detected, the BD sensor 24 outputs a beam detection signal (hereinafter referred to as a BD signal) corresponding to the detection of the reflected light to the scanner control unit 56 of the control device 50 described later.

The image forming unit 5 includes a process cartridge 25, a fixing unit 39, and the like.
The process cartridge 25 is detachably attached to the main body casing 2 below the scanner unit 16. The process cartridge 25 includes a drum cartridge 26 and a developing cartridge 28 that is detachably attached to the drum cartridge 26.

  The drum cartridge 26 has a developing cartridge 28 mounted on the front side thereof, and a photosensitive drum 27, a scorotron charger 29, a transfer roller 30 and the like on the rear side thereof.

  The photosensitive drum 27 is rotatably supported by covering a drum body formed by a positively chargeable photosensitive layer whose outermost layer is made of polycarbonate or the like around a metal drum shaft.

  The scorotron charger 29 is disposed oppositely and spaced apart from the rear side of the photosensitive drum 27 so as not to contact the photosensitive drum 27. The scorotron charger 29 is a positively charged scorotron charger that generates corona discharge from a charging wire such as tungsten, and can uniformly charge the surface of the photosensitive drum 27 to a positive polarity. It is provided as follows.

  The transfer roller 30 is rotatably supported on the lower side of the photosensitive drum 27, and forms a nip with the photosensitive drum 27. The transfer roller 30 is configured by covering a metal roller shaft with a roller body made of a conductive rubber material. A transfer bias is applied to the transfer roller 30 during transfer.

  The developing cartridge 28 has a box shape opened rearward, and a toner storage chamber 34 filled with a positively chargeable non-magnetic one-component toner is provided as a developer at the inner front portion thereof. Examples of the toner include polymerizable monomers such as styrene monomers such as styrene, and acrylic monomers such as acrylic acid, alkyl (C1 to C4) acrylate, and alkyl (C1 to C4) methacrylate. Polymerized toner obtained by copolymerization by suspension polymerization or the like is used. Such a polymerized toner has a substantially spherical shape, has extremely good fluidity, and can achieve high-quality image formation. On the front side of the toner storage chamber 34, a supply roller 33, a developing roller 31, a layer thickness regulating blade 32, and the like are provided. An agitator 35 for agitating the toner is rotatably provided in the toner storage chamber 34.

  The supply roller 33 is configured by covering a metal roller shaft with a roller made of a conductive foam material, and is rotatably supported.

  The developing roller 31 is rotatably supported by the developing cartridge 28 in a state in which the developing roller 31 is in contact with the supply roller 33 so as to be compressed with respect to the upper rear side of the supply roller 33. Further, the developing roller 31 contacts and contacts the photosensitive drum 27 in a state where the developing cartridge 28 is mounted on the drum cartridge 26. The developing roller 31 is configured by covering a metal roller shaft with a roller body made of a conductive rubber material.

  The layer thickness regulating blade 32 includes a pressing portion made of insulating silicone rubber at the tip of a metal leaf spring material. The layer thickness regulating blade is supported above the developing roller, and the pressing portion is pressed against the developing roller 31 by the elastic force of the leaf spring material.

  The toner discharged from the toner storage chamber 34 is supplied to the developing roller 31 by the rotation of the supply roller 33, and at this time, the toner is positively frictionally charged between the supply roller 33 and the developing roller 31. The toner supplied onto the developing roller 31 enters between the pressing portion of the layer thickness regulating blade 32 and the developing roller 31 as the developing roller 31 rotates, and forms a thin layer with a constant thickness on the developing roller 31. It is carried on.

  As the surface of the photosensitive drum 27 rotates, the surface of the photosensitive drum 27 is first uniformly charged positively by the scorotron charger 29 and then exposed by high-speed scanning of the laser light L from the scanner unit 16 to form on the paper 3. An electrostatic latent image corresponding to the image to be formed is formed.

  Next, when the developing roller 31 rotates, the positively charged toner carried on the developing roller 31 is formed on the surface of the photoconductive drum 27 when it contacts the photoconductive drum 27. It is supplied to the electrostatic latent image. As a result, the electrostatic latent image on the photosensitive drum 27 is visualized, and a toner image by reversal development is carried on the surface of the photosensitive drum 27. Thereafter, the toner image carried on the surface of the photosensitive drum 27 is transferred to the transfer roller 30 while the paper 3 passes through the transfer position P between the photosensitive drum 27 and the transfer roller 30. It is transferred to the paper 3 by the voltage. The sheet 3 having the toner image transferred thereon is then conveyed to the fixing unit 39.

  The fixing unit 39 is provided on the rear side of the process cartridge 25, and includes a fixing frame 40, and a heating roller 41 and a pressure roller 42 in the fixing frame 40. The heating roller 41 includes a metal tube whose surface is coated with a fluororesin, and a halogen lamp for heating in the metal tube, and is provided rotatably.

  The pressure roller 42 is disposed opposite the heating roller 41 so as to press the heating roller 41. The pressure roller 42 is configured by covering a metal roller shaft with a roller made of a rubber material, and is driven to rotate in accordance with the rotation drive of the heating roller 41.

  In the fixing unit 39, the toner transferred onto the paper 3 at the transfer position P is thermally fixed while the paper 3 passes between the heating roller 41 and the pressure roller 42. Then, the sheet 3 on which the toner is fixed is conveyed to a sheet discharge path 44 that is curved and extends toward the upper surface of the main casing 2. The sheet 3 conveyed to the sheet discharge path 44 is discharged onto a sheet discharge tray 46 formed on the upper surface of the main casing 2 by a discharge roller 45 provided at the upper end position of the sheet discharge path 44.

(Electric configuration of the entire laser printer)
Next, the electrical configuration of the laser printer 1 according to this embodiment will be described. FIG. 2 is a block diagram conceptually showing the electrical configuration of the laser printer 1.

  The laser printer 1 includes a control device 50 including a well-known microcomputer that includes a CPU 51, a ROM 52, a RAM 53, a bus line 54 that connects these units, and the like. The control device 50 also includes a scanner control unit 56 for controlling the scanner unit 16, an image formation control unit 57 for controlling the image forming unit 5, a motor drive unit 59 for driving the main motor 58, and a display. A display control unit 61 for displaying the operation state of the laser printer 1 and error display on a display unit 60 (corresponding to “notification means” of the present invention) composed of a lamp and the like, an external information processing apparatus (personal) via a network A network interface 62 for performing data communication with a computer or the like is provided, and these units are connected to the CPU 51, ROM 52, and RAM 53 via the bus line 54. The main motor 58 is a motor that rotationally drives the paper feeding roller 8, the pickup roller 11, the registration roller 12, the photosensitive drum 27, the heating roller 41, and the like described above in synchronization.

  When the CPU 51 receives a print command from the external information processing apparatus via the network, the CPU 51 then controls the scanner control unit 56, the image formation control unit 57, the motor drive unit 59, and the like according to the print data transmitted via the network. By controlling the drive, a process of forming an image based on the print data on the paper 3 while carrying the paper 3 is performed. The CPU 51 corresponds to the light level switching means, determination means, stop means, abnormal location determination means, resolution setting means, and speed adjustment means of the present invention.

(Configuration of laser drive circuit)
The scanner control unit 56 includes a scanner motor driving circuit (not shown) for controlling the rotation of the scanner motor 18 and a laser driving circuit 70 for controlling the driving of the laser light emitting unit 17 (“laser driving means of the present invention”). For example). Next, the configuration of the laser drive circuit 70 will be described with reference to the circuit diagram of FIG.

  The laser driving circuit 70 is activated by the LD enable signal output from the CPU 51, and reduces the change in the light emission output due to the change in the temperature characteristics of the laser diode LD and the change over time when the laser diode LD emits light. Automatic light quantity control (APC) is performed.

  A laser emission unit 17 provided in the scanner unit 16 receives a laser diode LD (corresponding to the “laser emission unit” of the present invention) and laser light emitted from the laser diode LD and detects the light intensity thereof. The photodiode PD (corresponding to the “measuring means” of the present invention) is sealed in the same package. The anode of the laser diode LD is connected to the power supply Vcc and the cathode of the photodiode PD. The anode of the photodiode PD is connected to the variable resistor R1 whose one end is grounded, the CPU 51, and the sample hold circuit 72. The current generated when the photodiode PD receives the laser beam generated from the laser diode LD is converted into a voltage by the variable resistor R1, and is output to the CPU 51 and the sample hold circuit 72 as the monitor signal S1. In addition to the monitor signal S1, the BD signal S2 from the BD sensor 24 described above is also input to the CPU 51. The sample hold circuit 72 outputs the voltage value Vmon held by the monitor signal S1 to the differential amplifier circuit 73. The differential amplifier circuit 73 outputs a voltage corresponding to the deviation between the held voltage value and the reference voltage Vref input from the CPU 51 to the positive phase input of the operational amplifier op2 described later.

  On the other hand, the cathode of the laser diode LD is connected to the collector of the transistor Tr1 and the collector of the transistor Tr2. The emitter of the transistor Tr1 is connected to the variable resistor R2 whose one end is grounded and the reverse phase input of the operational amplifier Op1. A voltage dividing circuit 74 including a pair of resistors R3 and R4 is connected to the positive phase input of the operational amplifier Op1, and the differential output of the operational amplifier Op1 is connected to the base of the transistor Tr1. As a result, the differential output of the operational amplifier Op1 is fed back via the base-emitter of the transistor Tr1, so that the positive phase input voltage and the negative phase input voltage of the operational amplifier Op1 are substantially the same. It has become. For this reason, the voltage of the emitter of the transistor Tr1 becomes constant, and a constant current Ibias flows from the collector to the emitter of the transistor Tr1.

  The base of the transistor Tr2 is connected to the CPU 51, and the transistor Tr2 is connected to the light level signal S3 from the CPU 51 (a signal output based on the print data or the like for turning on or turning off the laser diode LD). Operates as a switch. The emitter of the transistor Tr2 is connected to the collector of the transistor Tr3. The emitter of the transistor Tr3 is connected to the resistor R5 whose one end is grounded and the negative phase input of the operational amplifier Op2. As a result, the operational amplifier Op2 is also in an imaginary short state in which the positive phase input voltage and the negative phase input voltage are substantially the same. The voltage from the differential amplifier circuit 73 described above is input to the positive phase input of the operational amplifier Op2, and this voltage value and the voltage of the emitter of the transistor Tr3 are substantially equal. Therefore, when the transistor Tr2 is on, a current Iop corresponding to the output voltage from the differential amplifier circuit 73 flows from the collector of the transistor Tr3 to the emitter side.

  With the above configuration, in the laser driving circuit 70, when the light level signal output from the CPU 51 is L (low level signal), the transistor Tr2 is turned off, and the laser diode LD has a constant current Ibias. Flowing. When the optical level signal is H (high level signal), the transistor Tr2 is turned on, and in addition to the current Ibias, the current Iop corresponding to the output voltage from the differential amplifier circuit 73 flows through the laser diode LD. .

  The current Iop + Ibias flowing through the laser diode LD when the optical level signal is H is a lighting current for turning on the laser diode LD, and the light intensity of the laser light generated from the laser diode LD is the photosensitive drum 27. It is adjusted by the value of the reference voltage Vref output from the CPU 51 to the differential amplifier circuit 73 so that the electrostatic latent image is formed on the upper side. Here, in this laser printer 1, it is possible to form an image with two kinds of resolutions of a low resolution of 600 dpi and a high resolution of 1200 dpi. As shown in FIG. 6, the current I1200 flowing through the laser diode LD at 1200 dpi is shown. The value is made smaller than the current value of the current I600 at 600 dpi. As a result, the light intensity P1200 of the laser light in the lighting state at 1200 dpi is smaller than the light intensity P600 at 600 dpi. As will be described later, this corresponds to the rotational speed of the photosensitive drum 27 being half that at 600 dpi at 1200 dpi.

  The current Ibias flowing through the laser diode LD when the light level signal is L is a slight lighting current for setting the laser diode LD in a slightly lighted state, and the light intensity of the laser light emitted from the laser diode LD is Adjustment is made so that the electrostatic latent image is not formed on the photosensitive drum 27. The current value of the fine lighting current IM600 at 600 dpi is set so that the light intensity PM600 at the time of fine lighting at 600 dpi is a predetermined ratio (about 1/300 to 1/200) with respect to the light intensity P600 at the time of lighting. Is done. On the other hand, the current value of the fine lighting current IM1200 ′ at 1200 dpi is the same as the current value of the fine lighting current IM600 at 600 dpi. Therefore, the light intensity PM1200 ′ at the time of fine lighting is also the same as that at the time of the fine lighting at 600 dpi. It is the same as the light intensity PM600.

(Control action by laser printer)
The control device 50 of the laser printer 1 receives a print command from an external information processing apparatus operated by the user, and starts various printing operations. The CPU 51 receives resolution information for specifying the resolution of the image to be printed together with the print data from the external information processing apparatus, and sets the resolution based on this (specifically, the set resolution is stored in the RAM 53 together with the print data). To do.) Then, the CPU 51 outputs a speed designation signal based on the resolution setting to the motor control unit 56, and the motor control unit 56 drives the main motor 58 at a speed according to the speed designation signal. Specifically, the main motor 58 is driven to rotate at a speed half that of 600 dpi at 1200 dpi. As a result, the paper feed roller 8, the pickup roller 11, the registration roller 12, the photosensitive drum 27, the heating roller 41 and the like are rotationally driven at a speed corresponding to the speed of the main motor 58.

  Further, the CPU 51 outputs a scanner motor drive signal to the scanner control unit 56 to activate the scanner motor 18. When the rotation of the scanner motor 18 is stabilized at a predetermined speed, an LD enable signal is output to put the laser drive circuit 70 into an operating state. The CPU 51 generates the light level signal S3 and the reference voltage Vref based on the resolution setting and the print data, and outputs them to the laser drive circuit 70, thereby starting the laser diode LD. Then, formation of an electrostatic latent image on the photosensitive drum 27 is started.

  FIG. 4 illustrates the relationship between the light level signal S3 and the light intensity of the laser light emitted from the laser diode LD. When the resolution setting is low resolution (600 dpi), when the light level signal S3 output from the CPU 51 is H, a laser beam having a high level (P1) light intensity is emitted, and the electrostatic latent image is formed on the photosensitive drum 27. An image is formed. When the light level signal S3 is L, the light intensity of the laser light is low (P2), and an electrostatic latent image is hardly formed on the photosensitive drum 27. When the resolution is set to high resolution (1200 dpi) and the light level signal S3 is H, laser light having a light intensity of a high level (P3) lower than that at the time of low resolution is emitted and is applied onto the photosensitive drum 27. An electrostatic latent image is formed. At this time, since the rotational speed of the photosensitive drum 27 is half that at the time of low resolution, the irradiation amount of the laser light per unit area to the photosensitive drum 27 is not significantly different from that at the time of low resolution. When the resolution setting is high resolution (1200 dpi) and the light level signal S3 is L, the light intensity of the laser light becomes a low level (P2) equal to that at the time of low resolution. An electrostatic latent image is not formed.

(Abnormality detection processing)
Next, the abnormality detection process executed when the laser diode LD is activated will be described with reference to the flowchart of FIG.
First, in S101, the CPU 51 outputs an LD enable signal to start the operation of the laser driving circuit 70. In step S102, the laser diode LD is started up. Specifically, the CPU 51 alternately outputs H and L as the light level signal S3 at predetermined intervals, and gradually increases the value of the reference voltage Vref output to the differential amplifier circuit 73 from a small value toward a target value. Increase to. As a result, the laser diode LD is repeatedly turned on and slightly turned on, and the current value of the lighting current gradually increases, so that the light intensity of the laser light at the time of lighting gradually increases. At this time, the CPU 51 starts counting the LD start timer configured as a software timer.

  Subsequently, in S103, an initial value 0 is input to the counter i for preventing erroneous detection. In S104, the monitor voltage Vmon when the light level signal S3 is L becomes the voltage when the laser diode LD is slightly lit. It is determined whether it corresponds. When comparing the voltages, for example, if the monitor voltage Vmon is in the range of 0 to 10 mV, it is determined that the voltage corresponds to the voltage at the time of slight lighting. A range of values is selected (the same applies to the following description). Here, when it is determined that the monitor voltage Vmon when the light level signal S3 is L does not correspond to the voltage when the laser diode LD is slightly lit (S104: No), the value of the counter i is determined in S105. In step S106, it is determined whether or not the value of the counter i has reached the predetermined number X. If not (S106: No), the process proceeds to step S104 again. Thereby, when a negative determination is made in S104, the determination in S104 is repeated a plurality of times until an affirmative determination is made, thereby preventing erroneous detection. When the negative determination in S104 is repeated a predetermined number of times X (S106: Yes), an error detection process for the laser drive circuit 70 is performed in S107, and an error code indicating the failure location is stored in the RAM or the like. The Subsequently, a printing operation stop process is performed in S108. In this stop process, the CPU 51 outputs a stop signal to each unit, thereby turning off the laser driving circuit 70 and stopping the driving of the scanner motor 18 and the main motor 58, and so on, so that all printing operations are stopped. In step S109, an error notification process for displaying an error on the display unit 60 is performed. In this error notification process, for example, the error location may be displayed on a liquid crystal screen provided in the display unit 60, or the error location may be notified to an external information processing apparatus via a network. good.

  When it is determined in S104 that the monitor voltage when the light level signal is L corresponds to the voltage when the laser diode LD is slightly lit (S104: Yes), in S110, the aforementioned LD It is determined whether or not the BD detection preparation period has elapsed with reference to the activation timer. This BD detection preparation period is a period in which the light intensity at the time of lighting of the laser diode LD that gradually increases from the start of the start-up of the laser diode LD is expected to be a light intensity that can be detected by the BD sensor 24. It is. In S110, if the BD detection preparation period has not elapsed (S110: No), the same processing is repeated until the BD detection preparation period has elapsed. If the BD detection preparation period has elapsed (S110: Yes), the BD is determined in S111. It is determined whether or not the BD signal S2 is input from the sensor 24. If it is determined that the BD signal S2 is not input (S111: No), it is detected in S112 that an abnormality has occurred on the optical path of the laser light in the BD sensor 24 or the scanner unit 16. In the same manner as described above, error detection processing is performed. Similarly, the printing operation is stopped in S113, and error notification is performed in S114.

  If it is determined in S111 that the BD signal S2 has been input from the BD sensor 24 (S111: Yes), it is determined in S115 whether or not the LD startup period has elapsed with reference to the LD start timer described above. To be judged. During this LD startup period, the laser diode LD has been started up and the light intensity of the laser light at the time of lighting reaches the target light intensity and is constant (the increase in the reference voltage Vref is stopped). ) Expected period. In S115, when the LD startup period has not elapsed (S115: No), the same processing is repeated until the LD startup period has elapsed, and when the LD startup period has elapsed (S115: Yes), the light is transmitted in S116. It is determined whether or not the monitor voltage Vmon when the level signal S3 is L corresponds to the voltage when the laser diode LD is slightly lit. Here, when it is determined that the monitor voltage V when the light level signal S3 is L corresponds to the voltage when the laser diode LD is slightly lit (S116: Yes), the laser diode LD, the laser Since it is considered that the drive circuit 70, the BD sensor 24, etc. are operating normally, formation of an electrostatic latent image on the photosensitive drum 27 is subsequently started.

  If it is determined in S116 that the monitor voltage Vmon when the light level signal S3 is L does not correspond to the voltage when the laser diode LD is slightly lit (S116: No), in S117, It is determined whether or not the monitor voltage Vmon when the optical level signal S3 is L corresponds to the voltage when the laser diode LD is turned on (that is, the reference voltage Vref). Here, when it is determined that the monitor voltage Vref when the light level signal S3 is L corresponds to the voltage (reference voltage Vref) when the laser diode LD is turned on (S117: Yes), that is, FIG. As shown in FIG. 4, when the light intensity of the laser beam is high when the light level signal S3 is L (P4 when the resolution is low, P4 ′ when the resolution is high), the laser diode LD is normal, It is considered that a lighting current flows through the laser diode LD due to an abnormality in the switching operation of the laser driving circuit 70. Therefore, error detection processing of the laser drive circuit 70 is performed in S118. Then, the printing operation is stopped in S119, and error notification is performed in S120. The light intensity at the high level (P4 when the resolution is low and P4 ′ when the resolution is high) corresponds to the “predetermined light intensity” of the present invention.

  When it is determined in S117 that the monitor voltage Vmon when the light level signal S3 is L does not correspond to the voltage (reference voltage Vref) when the laser diode LD is turned on (S117: No). In S118, the deterioration detection process of the laser diode LD is performed. This is because when the laser diode LD deteriorates and the output drops, the laser drive circuit 70 gradually supplies a large current Iop to the laser diode LD, and the current value of the current Iop eventually becomes the switching value of the transistor Tr2. When the size exceeds the capacity, the current Iop flows to some extent in the laser diode LD when the transistor Tr2 is off (that is, when it is slightly lit). In this case, for example, as shown in FIG. 4, the light intensity of the laser light emitted when the light level signal S3 is L is an intermediate level P5 between the light intensity at the high level and the light intensity at the low level. (P4> P5> P2 at low resolution, P4 ′> P5> P2 at high resolution). In this deterioration detection process, the fact that the laser diode LD has deteriorated is stored in the RAM or the like. Subsequently, in S122, it is determined whether or not the monitor voltage Vmon when the light level signal S3 is L is equal to or lower than a predetermined threshold value. This threshold value is determined to be, for example, 1/150 of the reference voltage Vref. When the monitor voltage Vmon is equal to or lower than this threshold value (S122: Yes), the degradation of the laser diode LD is not problematic in operation. Therefore, formation of an electrostatic latent image on the photosensitive drum 27 is subsequently started. If the monitor voltage Vmon is greater than this threshold value (S122: No), it is considered that there is a possibility that the degradation of the laser diode LD will cause an operational problem, so the printing operation is stopped in S123, An error notification is performed in S124.

(Effect of this embodiment)
As described above, according to the present embodiment, an electrostatic latent image is formed on the photosensitive drum 27 with the light intensity of the laser light measured by the photodiode PD, even though the light level signal S3 is L. When the predetermined light intensity (P4 or P4 ′) is reached, the image forming operation is stopped. Accordingly, it is possible to prevent a situation in which the paper 3 and toner are wasted due to erroneous laser light emission during non-image formation.

  Further, when a laser beam having a light intensity corresponding to a high level (P4 or P4 ′) is emitted when the optical level signal S3 is L, there is no problem in the laser diode LD, the photodiode PD, and the like. Since it is considered that there is an abnormality in the laser drive circuit 70, it is possible to identify the failure location.

  Furthermore, when the light level signal S3 is L, when it is determined that the light intensity of the laser light is equal to or higher than a predetermined threshold value indicating the deterioration of the laser diode LD, the deterioration of the laser diode LD is notified. As a result, the failure location is specified, so that maintenance can be performed quickly.

  In addition, it is possible to easily identify the cause of the failure by determining which one of the laser diode LD and the BD sensor 24 is abnormal based on the signals from the photodiode PD and the BD sensor 24, thereby identifying the failure location. It can be investigated and maintenance can be performed quickly. In particular, the abnormality detection by the BD sensor 24 and the photodiode PD is efficient because the existing configuration can be used as it is. In addition, when the laser diode LD is activated, detection by the photodiode PD is performed before detection by the BD sensor 24, so that the laser light reaches an early time before reaching the light intensity that can be detected by the BD sensor 24. Abnormality can be detected.

In addition, if the fine lighting current at the low resolution and the fine lighting current at the high resolution are different, there is a possibility that the photosensitive member may be exposed if one of the fine lighting currents is too large. The response may get worse. On the other hand, in this configuration, the fine lighting current at the time of low resolution and the fine lighting current at the time of high resolution are set to the same current value, so that the fine lighting current can always be kept at an optimum value.
Furthermore, the laser driving circuit 70 can be configured at low cost because the circuit for supplying the fine lighting current Ibias is common between the low resolution setting and the high resolution setting.

  In order to change the resolution, a configuration in which the number of laser beams applied to the photoconductor is appropriately switched according to the resolution is also conceivable, but this increases the cost. In addition, a configuration in which the scanning speed of the laser beam in the main scanning direction is changed according to the resolution is conceivable, but is often technically difficult. On the other hand, according to this configuration, the resolution can be easily changed by adjusting the moving speed of the photosensitive drum 27 in accordance with the resolution setting.

  Further, by adjusting the current value of the lighting current according to the rotation speed of the photosensitive drum 27, the density level of the image at each resolution can be made appropriate. Further, it is possible to reduce damage to the photosensitive drum 27 by preventing the photosensitive drum 27 from being irradiated with laser light having an excessive light intensity.

In addition, when the lighting current level is changed in accordance with the switching of the lighting current level, the photosensitive member may be exposed if the lighting current is too large. There is a risk of getting worse. On the other hand, in this configuration, the fine lighting current can always be kept at an optimal value by setting the fine lighting current to a constant current value regardless of the level of the lighting current.
Further, the laser driving circuit 70 can be configured at low cost because the circuit for supplying the fine lighting current Ibias is common between the high and low lighting currents.

  Further, by adjusting the current value of the lighting current according to the rotational speed of the photosensitive drum 27, it is possible to make the density level of the formed image appropriate.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.
(1) The present invention can also be applied to an image forming apparatus having, for example, a scanner function and a facsimile function. In particular, in the case of an image forming apparatus having a facsimile function, a black image is formed, for example, when a printing operation is started even though there is an abnormality such that a laser diode is turned on when a low level signal is output. The original FAX data (print data) may not remain, but such a situation can be prevented beforehand by applying the present invention.
(2) Although the abnormality detection process of the above embodiment is performed when the laser diode is started up, according to the present invention, the abnormality detection process such as S116 to S124 in FIG. You may make it carry out over.

(3) In the above embodiment, the predetermined light intensity is the light intensity at the time of high level (when lighting). However, according to the present invention (claim 1), the predetermined light intensity is at the time of high level (when lighting). Detection may be performed at a level different from the light intensity.
(4) According to the present invention (claims 1 to 4), the current value of the current supplied at the low level may be set to 0, and the laser light emitting means may be turned off.

1 is a side sectional view of an essential part of a laser printer according to Embodiment 1 of the present invention. Block diagram showing the electrical configuration of the laser printer Circuit diagram of laser drive circuit Graph showing the relationship between the optical level signal and the light intensity of the laser beam Flow chart showing laser diode abnormality detection processing (A) Graph showing light intensity-current characteristic curve of laser diode (B) Graph showing an enlarged part thereof

1. Laser printer (image forming device)
24 ... BD sensor (laser light detection means)
27. Photosensitive drum (photosensitive member)
51 ... CPU (light level switching means, determination means, stop means, abnormal location determination means, resolution setting means, speed adjustment means)
60. Display section (notification means)
70 ... Laser drive circuit (laser drive means)
LD ... Laser diode (Laser emission means)
PD ... photodiode (measuring means)

Claims (8)

A photoreceptor,
Laser light emitting means for emitting laser light applied to the photosensitive member;
Measuring means for measuring the light intensity of the laser light emitted from the laser light emitting means;
A current for causing the laser light emission means to emit the laser light is supplied, and a current value of the current is adjusted based on a measurement result of the measurement means, and the light intensity of the laser light is adjusted to the photoconductor. Laser driving means for switching between a high level for forming a latent image thereon and a low level for not forming a latent image on the photoreceptor;
Light level switching for outputting a high level signal for supplying a current for raising the light intensity of the laser light to the laser light emitting means and a low level signal for supplying a current for lowering the laser driving means. Means,
Whether the light intensity of the laser light measured by the measuring means corresponds to a predetermined light intensity at which a latent image is formed on the photoreceptor when the low level signal is output by the light level switching means And determining that the light intensity of the laser light measured by the measuring means does not correspond to the predetermined light intensity, the light intensity of the laser light measured by the measuring means is A judging means for judging whether or not the threshold value indicates a deterioration of the laser emitting means ;
Stop means for stopping the image forming operation when the determination means determines that the light intensity of the laser beam measured by the measurement means corresponds to the predetermined light intensity;
It said determination means Therefore, when the light intensity of the laser beam is determined to be equal to or greater than the threshold value, and informing means for informing the deterioration of the light emitting means,
The image forming apparatus you comprising the. A photoreceptor,
Laser light emitting means for emitting laser light applied to the photosensitive member;
Measuring means for measuring the light intensity of the laser light emitted from the laser light emitting means;
A current for causing the laser light emission means to emit the laser light is supplied, and a current value of the current is adjusted based on a measurement result of the measurement means, and the light intensity of the laser light is adjusted to the photoconductor. Laser driving means for switching between a high level for forming a latent image thereon and a low level for not forming a latent image on the photoreceptor;
Light level switching for outputting a high level signal for supplying a current for raising the light intensity of the laser light to the laser light emitting means and a low level signal for supplying a current for lowering the laser driving means. Means,
Whether the light intensity of the laser light measured by the measuring means corresponds to a predetermined light intensity at which a latent image is formed on the photoreceptor when the low level signal is output by the light level switching means A determination means for determining whether or not,
Stop means for stopping the image forming operation when the determination means determines that the light intensity of the laser beam measured by the measurement means corresponds to the predetermined light intensity;
Resolution setting means for setting the resolution of the latent image formed on the photoreceptor to a low resolution or a high resolution;
With
The laser driving means supplies a lighting current for emitting the laser light at a high level of light intensity that forms a latent image on the photosensitive member when the high level signal is output by the light level switching means. When the low level signal is output from the light level switching means, a fine lighting current for supplying the laser beam with a low level light intensity that does not form a latent image on the photosensitive member is supplied. There,
When setting of the resolution setting means of high resolution, you wherein the current value of the lighting current is smaller than when the low resolution, the current value of the fine lighting current to the same in the case of low resolution Image forming apparatus. In the laser driving unit, the circuit that supplies the fine lighting current when the setting of the resolution setting unit is low resolution and the circuit that supplies the fine lighting current when the resolution setting is high are common. The image forming apparatus according to claim 2 . The light emitting means is configured to irradiate one laser beam to the photoconductor,
Based on the resolution setting by the resolution setting means, a speed adjusting means for adjusting the moving speed of the photoconductor at a high resolution to be smaller than the moving speed of the photoconductor at a low resolution is provided. the image forming apparatus according to claim 2 or claim 3, characterized. 5. The image forming apparatus according to claim 4 , wherein a current value of the lighting current supplied by the laser driving unit is adjusted based on a moving speed of the photosensitive member adjusted by the speed adjusting unit. . A photoreceptor,
Laser light emitting means for emitting laser light applied to the photosensitive member;
Measuring means for measuring the light intensity of the laser light emitted from the laser light emitting means;
A current for causing the laser light emission means to emit the laser light is supplied, and a current value of the current is adjusted based on a measurement result of the measurement means, and the light intensity of the laser light is adjusted to the photoconductor. Laser driving means for switching between a high level for forming a latent image thereon and a low level for not forming a latent image on the photoreceptor;
Light level switching for outputting a high level signal for supplying a current for raising the light intensity of the laser light to the laser light emitting means and a low level signal for supplying a current for lowering the laser driving means. Means,
Whether the light intensity of the laser light measured by the measuring means corresponds to a predetermined light intensity at which a latent image is formed on the photoreceptor when the low level signal is output by the light level switching means A determination means for determining whether or not,
Stop means for stopping the image forming operation when the determination means determines that the light intensity of the laser beam measured by the measurement means corresponds to the predetermined light intensity;
With
The laser driving means supplies a lighting current for emitting the laser light at a high level of light intensity that forms a latent image on the photosensitive member when the high level signal is output by the light level switching means. When the low level signal is output from the light level switching means, a fine lighting current for supplying the laser beam with a low level light intensity that does not form a latent image on the photosensitive member is supplied. There,
The laser driving means can switch the current value of the lighting current between high and low, and supplies the fine lighting current of the same current value when the current value of the lighting current is high and low. and to that image forming apparatus. In the laser driving means, a circuit that supplies the fine lighting current when the current value of the lighting current is high and a circuit that supplies the fine lighting current when the current value of the lighting current is low are common. The image forming apparatus according to claim 6 , wherein the image forming apparatus is an image forming apparatus. A speed adjusting means for adjusting the moving speed of the photosensitive member;
Current value of the lighting current supplied by the laser driving means, according to claim 6 or claim 7, characterized in that it is switched based on the moving speed of the photosensitive member to be adjusted by the speed adjustment means Image forming apparatus.

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