JP6143548B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic recording system such as a laser printer or a copying machine.

  An electrophotographic image forming apparatus has an optical scanning device that focuses light on a lens with laser light emitted from a laser diode, forms an image on a photosensitive member, and exposes the image. In the optical scanning device, in order to maintain a desired image quality under various exposure conditions, adjustment is performed so that the amount of laser light emitted from the laser diode becomes a desired value.

  Specifically, when the photosensitive member is exposed with light emitted from the front side of the chip of the laser diode, laser light emitted from the rear side of the chip is received by a photodiode disposed behind the chip. Then, based on the output from the photodiode, so-called APC (Auto Power Control) for adjusting the light emission amount of the laser light is performed. Regarding this APC, Patent Document 1 feeds back a comparison value between a value obtained by voltage-converting a monitor current generated based on the amount of received light detected by a photodiode and a reference voltage value set by the duty value of the PWM signal. Thus, a method for adjusting the light emission amount of the laser diode is described. The amount of laser light emitted is adjusted by receiving the light behind the chip, which is emitted from the back of the laser diode chip. The amount of light received by the photodiode is emitted from the front of the chip. This is because it is assumed to be proportional to the amount of light. That is, detecting the laser beam emitted from the back of the chip is substantially the same as detecting the light emitted from the front of the chip and imaged on the photosensitive member.

  Incidentally, in recent electrophotographic image forming apparatuses, there is a demand for higher image quality. In Patent Document 2, a laser beam is irradiated at a normal light emission level for normal printing on a portion of the photoconductor where toner is adhered. In addition, by suppressing the occurrence of fog phenomenon etc. by irradiating laser light at a minute light emission level lower than the light emission level for normal printing so that the toner does not adhere to the portion where the toner on the photoconductor does not adhere, Form high-quality images.

JP 2003-305882 A JP 2012-137743 A

  When performing minute emission, the amount of light applied to the photoconductor when the laser diode chip emits minute light may not be the same depending on the optical scanning device due to individual differences of the laser diode chip, its drive circuit, lens, etc. is there. For this reason, in some cases, it is not possible to emit a small amount of light with an appropriate amount of light, and the potential of the portion of the photoconductor that has performed a small amount of light emission is not optimized, which may cause image defects.

  In view of the above problems, an object of the present invention is to perform minute light emission with an appropriate amount of light.

The present invention includes a photoreceptor, a light irradiating means for irradiating light source emitted laser beam on the photosensitive member, a developing unit for attaching toner to the photosensitive member, the image portions of the previous SL photoconductor, laser emission A drive current obtained by adding the first drive current and the second drive current is supplied to the light irradiating means so as to emit laser light with a normal light emission amount in the region, and the normal image is applied to the non-image portion of the photoconductor. Switching means for supplying the second drive current to the light irradiating means without adding the first drive current so as to emit laser light with a minute light emission amount in a laser emission region smaller than the light emission amount ; When the second drive current is supplied at a first value, the first light amount of the laser light emitted from the light irradiation means and the second drive current at a second value different from the first value Laser light emitted from the light irradiation means when supplied A second light amount, based on, and further comprising a determining means for determining a third value of the second driving current for said micro-emission amount of the third amount of light irradiated from the light irradiation unit To do.

The present invention also provides a photoconductor, a light irradiating unit for irradiating the photoconductor with laser light emitted from a light source, a developing unit for attaching toner to the photoconductor , and a laser for an image portion of the photoconductor. to emit laser light in a normal light emission quantity of the light emitting region, a drive current obtained by adding the first drive current and the second drive current is supplied to the light irradiation unit with respect to the non-image portion of the photosensitive member, wherein Switching means for supplying the second drive current to the light irradiation means without adding the first drive current so as to emit laser light with a minute light emission amount in a laser emission region smaller than the normal light emission amount ; The first value supplied as the second drive current so that the laser light emitted from the light irradiation means becomes the first light quantity, and the laser light emitted from the light irradiation means becomes the second light quantity. The second drive current is supplied as Based on a different second value from said first value, determining a third value of the second driving current for said micro-emission amount of the third amount of light irradiated from the light irradiation unit It has a determination means.

  According to the present invention, minute light emission can be performed with an appropriate amount of light.

Schematic perspective view of optical scanning device Schematic sectional view of the image forming apparatus Diagram showing the laser drive circuit The figure which shows the relationship between the electric current which flows into the laser diode, and the light emission quantity The figure which shows the light quantity range which is used in the minute emission Flow chart of light intensity adjustment process The figure which shows the relationship between the Duty value of PWM2 signal, and measurement light quantity Graph showing the relationship between the duty value of the PWM2 signal and the measured light quantity Flow chart of light intensity adjustment process The figure which shows the relationship between target light quantity and Duty value of PWM2 signal

  Specific configurations of the present invention for solving the above-described problems will be described based on the following examples. However, the constituent elements described in this embodiment are merely examples, and the scope of the present invention is not limited to them.

[Image forming apparatus]
FIG. 2 is a schematic sectional view of the color image forming apparatus. In the following description, a color image forming apparatus is used for description, but the present invention is not limited to this. The minute light emission of the non-image portion, which will be described in detail later, can be applied to, for example, a monochromatic image forming apparatus. In the following description, an inline color image forming apparatus will be described as an example. However, a rotary color image forming apparatus may be used, for example. Hereinafter, an inline type color image forming apparatus will be described in detail as an example.

  As shown in FIG. 2, the color laser printer 50 has a plurality of photosensitive drums 5 (5Y, 5M, 5C, and 5K) that are photosensitive members, and sequentially performs multiple transfer onto the intermediate transfer belt 3 in order to achieve full color. This is a printer for obtaining a print image.

  The intermediate transfer belt 3 is an endless endless belt, suspended on a driving roller 12, a tension roller 13, an idler roller 17, and a secondary transfer counter roller 18, and rotated at a process speed of 115 mm / sec in the direction of the arrow in the figure. doing. The drive roller 12, the tension roller 13, and the secondary transfer counter roller 18 are support rollers that support the intermediate transfer belt 3. The drive roller 12 and the secondary transfer counter roller 18 have a configuration of φ24, and the tension roller 13 has a configuration of φ16. It has become.

  Four photosensitive drums 5 (5Y, 5M, 5C, 5K) are arranged in series in the moving direction of the intermediate transfer belt 3. The photosensitive drum 5Y having the developing unit 8Y is uniformly charged to a predetermined polarity and potential by the primary charging roller 7Y during the rotation process, and then irradiated with the laser beam 4Y by the optical scanning device 9Y as a light irradiation unit. . Thereby, an electrostatic latent image corresponding to the first color (yellow) component image of the target color image is formed. Next, yellow toner as the first color is attached to the electrostatic latent image by the first developing means (yellow developing device) 8Y and developed. As a result, the image is visualized. A system in which toner is developed in a portion where an electrostatic latent image is formed by irradiating light is referred to as a “reversal development system”.

  The yellow toner image formed on the photosensitive drum 5Y enters the primary transfer nip portion with the intermediate transfer belt 3. In the primary transfer nip portion, a voltage application member (primary transfer roller) 10Y is brought into contact with and contacted with the back side of the intermediate transfer belt 3. A primary transfer bias power source (not shown) is connected to the voltage applying member 10Y to enable bias application. First, a yellow toner image is transferred to the intermediate transfer belt 3 at the first color port.

  Next, the magenta, cyan, and black toner images are sequentially transferred to the yellow toner image from the photosensitive drums 5M, 5C, and 5K on which the magenta, cyan, and black toner images are formed through the same process as that for the yellow. The The four color toner images transferred onto the intermediate transfer belt 3 rotate and move in the direction of the arrow (clockwise) in FIG.

  On the other hand, the recording material P stacked and stored in the paper feed cassette 1 is fed by the paper feed roller 2, conveyed to the nip portion of the registration roller pair 6, and temporarily stopped. The recording material P once stopped is supplied to the secondary transfer nip by the registration roller pair 6 in synchronization with the timing at which the four color toner images formed on the intermediate transfer belt 3 reach the secondary transfer nip. Then, the toner image on the intermediate transfer belt 3 is transferred onto the recording material P by voltage application (about +1.5 kV) between the secondary transfer roller 11 and the secondary transfer counter roller 18.

  The recording material P onto which the toner image has been transferred is separated from the intermediate transfer belt 3 and sent to the fixing device 14 via the conveyance guide 19 where it is heated and pressurized by the fixing roller 15 and the pressure roller 16. Thus, the toner image is melted and fixed on the surface. Thereby, a four-color full-color image is obtained. Thereafter, the recording material P is discharged from the pair of discharge rollers 20 to the outside of the apparatus, and one printing cycle is completed. On the other hand, the toner remaining on the intermediate transfer belt 3 without being transferred to the recording material P in the secondary transfer portion is removed by the cleaning unit 21 disposed on the downstream side of the secondary transfer portion.

  The above is the description of the image forming apparatus and its operation.

  The image forming apparatus according to the present embodiment is configured so that the optical scanning device 9 (9Y) is applied to a portion (non-image portion) where the toner on the surface of the photosensitive drum 5 is not adhered in order to suppress fogging, reversal fogging, or other image defects. , 9M, 9C, 9K) irradiates light with a minute light emission amount. By irradiating the photosensitive drum 5 with this small amount of light, the electric potential on the surface of the photosensitive drum 5 after charging is changed to an appropriate potential such that toner does not adhere. The optical scanning device 9 (9Y, 9M, 9C, 9K) changes the charged surface potential of the photosensitive drum 5 to the potential to which the toner adheres to the portion of the photosensitive drum 5 on which the toner adheres. For this purpose, the light emitted normally is irradiated.

  Next, in the following, first, an external view of the optical scanning device 9 as the optical scanning device 9 (9Y, 9M, 9C, 9K) will be described in relation to the laser driving system, and then the laser driving system will be described. The circuit configuration will be described in detail.

[Optical scanning device]
FIG. 1 shows a schematic diagram of an optical scanning device 9 as a light irradiation means. Since the optical scanning devices 9Y, 9M, 9C, and 9K have the same configuration, the following description will be made on behalf of the optical scanning device 9. A drive current is applied (flowed) by the laser drive circuit 130 to the laser diode element 110 which is a light emitting element. The laser diode element 110 emits laser light with a light emission amount corresponding to the applied drive current. As will be described later, the laser drive circuit 130 is a circuit electrically connected to the engine controller 122 and the video controller 123 and is a circuit for driving the laser diode element 110.

  The laser light emitted from the laser diode element 110 is incident on the rotating polygon mirror 133 after the beam shape is shaped by the collimator lens 134 and converted into parallel light. Then, the light is reflected by the polygon mirror 133, passes through the fθ lens 132, and forms an image as a dot-like spot on the photosensitive drum 5. As the polygon mirror 133 rotates, the laser light is deflected, and the spot of the laser light moves on the photosensitive drum 5 in the direction of the rotation axis of the photosensitive drum 5. In addition to the laser beam deflection caused by the rotation of the polygon mirror 133, the photosensitive drum 5 itself rotates to scan the photosensitive drum 5 with the laser beam to form a latent image.

  On the other hand, assuming that a portion through which the laser beam reflected by the polygon mirror 133 passes when irradiated onto the photosensitive drum 5 is a scanning region, the scanning region is related to the scanning direction of the laser beam (rotational axis direction of the photosensitive drum 5). A mirror 131 is provided adjacent to one end of the mirror 131. A BD sensor 121 is disposed on the optical path of the laser light reflected by the mirror 131. The BD sensor 121 outputs a signal when it detects the incidence of the laser light. Thus, the rotational phase of the polygon mirror 133 can be detected by detecting the laser beam with the BD sensor 121. Then, in order to start scanning with a laser beam from a desired position on the photosensitive drum 5, the light emission start timing of the laser beam for starting the scanning is determined based on the output from the BD sensor 121 described above.

  While scanning the latent image by rotating the polygon mirror 133, a laser beam is incident on the BD sensor 121 to obtain an output from the BD sensor 121 for each reflection surface of the polygon mirror 133. Forcibly emit light for a certain period from the timing of. The predetermined timing is a timing at which the polygon mirror 133 rotates by a predetermined angle on the basis of the timing when the previous output is obtained from the BD sensor 121 and the laser beam can enter the BD sensor 121 again. This predetermined angle substantially corresponds to an angle range in which one of the plurality of reflecting surfaces of the polygon mirror 133 reflects the laser light. As shown in FIG. 1, when the polygon mirror 133 is a six-sided polygon mirror, the angle range scanned by one reflecting surface is 60 ° (= 360 ° ÷ 6), and the predetermined angle described above is set to a little less than 60 °. The Accordingly, the following output can be obtained from the BD sensor 121 by forcibly causing the laser diode element 110 to emit light for a certain period of time at a predetermined timing after obtaining the output from the BD sensor 121.

  While the laser diode element 110 is forced to emit light, APC (Auto Power Control) control, which is automatic light amount control for adjusting the laser light emission amount at the same time, is performed. This APC will be described in detail later.

[Laser drive circuit diagram]
FIG. 3 is a diagram showing a laser driving circuit and its connection relationship. Laser drive circuits 130a, 130b, 130c, and 130d shown in FIG. 3 correspond to the laser drive circuit 130 described with reference to FIG. 1, and all have the same circuit configuration. Therefore, in the following description, the laser drive circuit 130a will be described as a representative.

  The laser drive circuit 130a is a circuit as an adjustment unit that can adjust the light emission amount of the laser diode element 110 when minute light is emitted so as not to cause toner adhesion on the surface of the photosensitive drum 5. A laser diode element 110, an engine controller 122, and a video controller 123 are connected to the laser drive circuit 130a. The synchronization detection signal element (BD detection element) 121 is connected to the laser drive circuit 130a via the engine controller 122.

  The laser drive circuit 130a includes comparator circuits 101 and 111, variable resistors 102 and 112, sample / hold circuits 103 and 113, hold capacitors 104 and 114, operational amplifiers 105 and 115, and transistors 106 and 116. Further, the laser drive circuit 130a includes switching current setting resistors 107 and 117, switching circuits 108, 109, 118 and 119, inverters 141 and 151, and resistors 142 and 152, PWM1 and PWM2 for smoothing the PWM1 and PWM2. Capacitors 143 and 153 for smoothing and pull-down resistors 144 and 154 are provided. As will be described in detail later, portions 101 to 109 and 141 to 144 correspond to the light amount adjusting means for the first light emission level, and portions 111 to 119 and 151 to 154 are the light amount adjusting means for the second light emission level. It corresponds to.

  The laser diode element 110 includes a laser diode 110a (hereinafter referred to as LD 110a) as a light source, and a photodiode 110b (hereinafter referred to as PD 110b) as a light receiving means. The light emitted from the front of the chip of the LD 110a passes through the collimator lens 134, reaches the surface of the photosensitive drum 5 through the polygon mirror 131 and the fθ lens 132, and forms an image. On the other hand, the light emitted from the rear of the chip of the LD 110a is received by the PD 110b.

  The engine controller 122 includes an ASIC, CPU, RAM, and EEPROM, and controls the printer engine. The engine controller 122 also performs communication control with the video controller 123. In the OR circuit 124, the Ldrv signal of the engine controller 122 and the VIDEO signal from the video controller 123 are connected to the input, and the output signal DATA is connected to the switching circuit 108. The VIDEO signal is generated based on print data sent from an external device such as a reader scanner connected to the outside or a host computer.

  The VIDEO signal output from the video controller 123 is input to the buffer 125 with an enable terminal, and the output of the buffer 125 is connected to the OR circuit 124 described above. At this time, the enable terminal is connected to the Venb signal from the engine controller 122. Further, the engine controller 122 is connected so as to output an SH1 signal, an SH2 signal, an SH3 signal, an SH4 signal, a BASE signal, an Ldrv signal, and a Venb signal, which will be described later.

  The first reference voltage Vref11 and the second reference voltage Vref21 are input to the positive terminals of the comparator circuits 101 and 111, respectively, and the outputs are input to the sample / hold circuits 103 and 113, respectively. The reference voltage Vref11 is set as a target voltage for causing the LD 110a to emit light with a light emission amount for normal light emission (first light emission level). The reference voltage Vref21 is set as a target voltage for the light emission amount for minute light emission (second light emission level lower than the first light emission level). PWM1 (Duty value) and PWM2 (Duty value), which are reference values for setting the voltages of the reference voltage Vref11 and the reference voltage Vref21, are input from the engine controller 122, respectively. Hold capacitors 104 and 114 are connected to the sample / hold circuits 103 and 113, respectively. The outputs of the hold capacitors 104 and 114 are input to the positive terminals of the operational amplifiers 105 and 115, respectively.

  The negative terminal of the operational amplifier 105 is connected to the switching current setting resistor 107 and the emitter terminal of the transistor 106, and the output is input to the base terminal of the transistor 106. A switching current setting resistor 117 and an emitter terminal of the transistor 116 are connected to the negative terminal of the operational amplifier 115, and an output is input to the base terminal of the transistor 116. The collector terminals of the transistors 106 and 116 are connected to the switching circuits 108 and 118, respectively. These operational amplifiers 105 and 115, transistors 106 and 116, and current setting resistors 107 and 117 determine the drive currents Idrv and Ib of the LD 110a according to the output voltages of the sample / hold circuits 103 and 113.

  The switching circuit 108 is turned on / off by the pulse modulation data signal Data. The switching circuit 118 is turned on / off by the input signal Base.

  The output terminals of the switching circuits 108 and 118 are connected to the cathode of the LD 110a and supply drive currents Idrv and Ib. The anode of the LD 110a is connected to the power supply Vcc. The cathode of the PD 110b that monitors the amount of light of the LD 110a is connected to the power supply Vcc, and the anode of the PD 110b is connected to the switching circuits 109 and 119, and the monitor current Im flows through the variable resistors 102 and 112 during APC control Thus, the monitor current Im is converted into the monitor voltage Vm. The monitor voltage Vm is input to the negative terminals of the comparators 101 and 111.

  In FIG. 3, the engine controller 122 and the video controller are shown separately, but the present invention is not limited to this form. For example, part or all of the engine controller 122 and the video controller may be constructed with the same controller. In addition, for example, part or all of the laser drive circuits 130a, 130b, 130c, and 130d may be built in the engine controller 122.

[APC for minute emission]
A case where APC control is performed with a light emission amount for minute light emission will be described with reference to FIG. The engine controller 122 sets the sample / hold circuit 103 to the hold state according to the instruction of the SH1 signal, and sets the switching circuit 108 to the OFF operation state based on the input signal Data. Regarding this input signal Data, the engine controller 122 disables the Venb signal connected to the enable terminal of the buffer 125 with enable terminal, controls the Ldrv signal, and turns off the input signal Data. Further, the engine controller 122 sets the sample / hold circuit 113 during the sampling operation according to the instruction of the SH2 signal, and turns off the switching circuit 109 according to the instruction of the SH3 signal. Further, the switching circuit 119 is turned on in response to an instruction from the SH4 signal. The switching circuit 118 is turned on by the input signal Base, and the LD 110a is set to be in a minute light emission state.

  In this state, when the LD 110a enters a minute light emission state, the PD 110b receives the light emitted behind the chip of the LD 110a and generates a monitor current Im proportional to the amount of received light (outputs a signal). Here, since substantially the same light is emitted from the front and rear of the chip of the LD 110a, the monitor current Im is proportional to the amount of light emitted from the front of the chip of the LD 110a. The monitor current Im is converted into the monitor voltage Vm2 by flowing the monitor current Im through the variable resistor 112. Further, the comparator 111 adjusts the drive current Ib of the LD 110a through the operational amplifier 115 or the like so that the monitor voltage Vm2 and the reference voltage Vref21 set by the reference value PWM2 match. Furthermore, the capacitor 114 is charged and discharged. During non-APC operation, that is, during normal image formation, the sample / hold circuit 113 is in the hold state, so that the voltage charged in the capacitor 114 is maintained, and a constant drive current Ib is supplied to emit light from the LD 110a. Is maintained in a minute light emission state with a desired light emission amount. The desired light emission amount (micro light emission level) P (Ib) is a light emission amount for preventing the fogging, reversal fogging and the like from causing the toner on the photosensitive drum 5 to adhere to the photosensitive drum 5. is there.

[APC for normal light emission]
Next, a case where APC control is performed with a light emission amount for normal light emission will be described with reference to FIG. When the LD 110a emits light with the light emission amount for normal light emission, the circuit of FIG. 3 is operated as follows. The sample / hold circuit 103 is set to the sample state, and the sample / hold circuit 113 is set to the hold state. Further, the switching circuit 109 is turned on by the instruction of the SH3 signal, and the switching circuit 119 is turned off by the instruction of the SH4 signal. Then, the switching circuits 108 and 118 are turned on. In this state, when the LD 110a enters the normal light emission state, the PD 110b monitors the light emission amount of the LD 110a and generates a monitor current Im proportional to the light emission amount. The monitor current Im is converted into the monitor voltage Vm1 by flowing the monitor current Im through the variable resistor 102. The comparator 101 controls the drive current of the LD 110a via the operational amplifier 105 or the like so that the monitor voltage Vm1 and the reference voltage Vref11 set by the reference value PWM1 match. Further, the capacitor 104 is charged and discharged. During the non-APC operation, that is, during image formation, the sample / hold circuit 103 and the sample / hold circuit 113 are in the hold state, thereby maintaining the voltage charged in the capacitor 104 and maintaining the light amount of the LD 110a. . That is, the drive current Idrv + Ib is supplied to the LD 110a. Thus, the light emission amount of the LD 110a is set to emit light with a desired light emission amount (normal light emission level) P (Idrv + Ib). The normal light emission level is a light emission amount for making the surface of the photosensitive drum 5 have a potential for attaching toner onto the photosensitive drum 5 by irradiating light of the light emission level.

  By operating the laser drive circuit 130 in this manner, the engine controller 122 performs APC for the minute light emission amount and the normal light emission amount, respectively, and the minute light emission amount P (Ib) and the normal light emission amount P ( It becomes possible to cause the LD 110a to emit light with a two-level light emission amount of (Idrv + Ib).

[Operation during image formation]
Next, the operation of the laser drive circuit 130 during image formation will be described in more detail. At the time of image formation, based on the output from the BD sensor 121, a pulse modulation data signal Data as a VIDEO signal is transmitted from the video controller 123 to the switching circuit 108 of the laser driving circuit 130. The switching circuit 108 is switched on and off by the pulse modulation data signal Data. As a result, the drive current Idrv is supplied to the LD 110a or not. Then, the switching circuit 108 is turned on for the image portion which is a portion to which the toner on the surface of the photosensitive drum 5 is attached, and the LD 110a to which the drive current Idrv + Ib is supplied emits light with the normal light emission amount P (Idrv + Ib). Irradiate light. In addition, the switching circuit 108 is turned off with respect to the non-image portion which is a portion where the toner on the surface of the photosensitive drum 5 is not attached, and the LD 110a to which only the driving current Ib is supplied without being supplied with the driving current Idrv P (Ib) emits light and is irradiated with light.

  As described above, by emitting a minute amount of light, it is possible to optimize the potential of a portion (non-image portion) where the toner on the surface of the photosensitive drum 5 does not adhere, and fog or reversal fog or an electric field at the end of the image portion is involved. It is possible to suppress image defects such as thinning of the toner adhesion region due to the toner.

[Problems related to minute emission]
There are individual differences in the laser diode element 110, its laser drive circuit 130a, each optical component (collimator lens 134, polygon mirror 133, fθ lens 132, etc.), and there are also errors in their relative positions. For this reason, when performing minute light emission, the light quantity irradiated to the photosensitive drum 5 when the laser diode chip emits minute light may not be the same for each optical scanning device 9. For this reason, in some cases, it is not possible to emit a small amount of light with an appropriate amount of light, and the potential of the portion of the photoconductor that has performed a small amount of light emission is not optimized, which may cause image defects.

  In particular, the minute light emission has a smaller light amount than the normal light emission, and the drive current Ib flowing through the LD 110a is small. For this reason, the influence of the error of the drive current Ib on the amount of light is large, and it is necessary to set the drive current Ib with high accuracy in each optical scanning device 9.

  FIG. 4 is a diagram showing the relationship between the drive current I supplied to the laser diode and the light emission amount P of the laser diode driven thereby. Generally, a laser diode emits LED in a low current region with a threshold value Ith as a boundary, and emits laser in a high current region. The drive current Ib when causing the laser diode to emit light with the minute light emission amount Pb at the minute light emission level is set to be larger than the threshold current Ith.

  However, when minute light emission is performed with the drive current Ib in the vicinity of the threshold current Ith, the light emitted from the LD 110a is close to LED light emission, and the spread angle of the light emitted from the light emitting point of the laser diode to the front and rear of the chip increases. As the divergence angle increases, the light emitted from the front of the chip is less likely to be collected on the collimator lens 134 and the like, and finally the ratio of the light that reaches the surface of the photosensitive drum 5 and forms an image is the divergence angle. Compared to when it is small.

  On the other hand, even if the light emitted to the rear of the chip has a large divergence angle, the ratio of light that reaches the PD 110b and is received is not much different from that when the divergence angle is small. For this reason, as the drive current Ib decreases and approaches the threshold current Ith, the proportional relationship between the amount of light received by the PD 110b and the amount of light reaching the surface of the photosensitive drum 5 is broken. That is, even when the driving current Ib is adjusted so that the amount of light received by the PD 110b becomes a desired amount of light when performing APC for minute light emission, the amount of light actually imaged on the surface of the photosensitive drum 5 is as follows. There is a risk that the light intensity will be lower than the desired amount of light.

[Light intensity adjustment process]
Next, the light amount adjustment process on the surface of the photosensitive drum 5 will be described. The light amount adjustment process on the surface of the photosensitive drum 5 is a process performed in the manufacturing / assembly process of the optical scanning device. This light quantity adjustment step is performed by placing the optical scanning device 9 on a dedicated jig (not shown). This jig is provided with a light receiving element, and can receive light emitted from the optical scanning device 9. The positional relationship between the optical scanning device 9 disposed on the jig and the light receiving element is the positional relationship between the optical scanning device 9 mounted in the color laser printer 50 and the laser beam irradiation position on the surface of the photosensitive drum 5. The light receiving elements are arranged so as to have the same relationship. Therefore, detecting the laser beam from the optical scanning device 9 with the light receiving element of the jig is equivalent to detecting the laser beam from the optical scanning device 9 at the laser beam irradiation position on the surface of the photosensitive drum 5. FIG. 5 shows the maximum use light amount and the minimum use light amount on the surface of the photosensitive drum 5 at the time of minute light emission used in the color laser printer 50.

  In the light amount adjustment step, first, the duty value of the PWM2 signal, which is the reference value of the light emission amount for minute light emission, is set to 0%, and APC is performed. At this time, the light amount is measured by the light receiving element of the jig, and the variable resistor 112 (see FIG. 3) is adjusted so that the light amount is larger than the above-mentioned maximum light amount of 45 μW on the surface of the photosensitive drum 5 in FIG. .

  Next, the process of measuring the correspondence between the duty value of the PWM2 signal and the amount of light on the surface of the photosensitive drum 5 and finally storing it in the color laser printer 50 will be described. This process is shown in the flowchart of FIG. 6 and is mainly divided into the following two processes. (1) A light amount storage step for measuring the light amount of the minute light emission on the surface of the photosensitive drum 5 and storing it in the optical scanning device 9, and (2) the data stored in the optical scanning device 9 to the storage means of the color laser printer 50. Storage data writing process for writing.

  First, (1) the light quantity storage step will be described. The light quantity storage process is a process performed in the manufacturing / assembly process of the optical scanning device 9. In the light quantity storage step, in the duty value setting S701 of the PWM2 signal, a plurality of different PWM2 signals serving as predetermined reference values are output, and the processes of S701 to S703 are executed.

  In S701, when the duty value of the PWM2 signal, which is a predetermined reference value for minute light emission, is set to 60%, when the PWM2 signal is output, the reference voltage Vref21 (see FIG. 3) is smoothed to 0.5V. It becomes. In S702, APC is performed in the state of Vref21 set in S701, and laser emission is performed. In S703, the amount of light is measured with the light receiving element of the jig in the APC operation state performed in S702, and a measurement result of 19.2 μW is obtained.

  Similarly, the processing from S701 to S703 is performed even when the duty value of the PWM2 signal, which is another predetermined reference value for minute light emission, is 80% and 0% so that N = 3 in S704. The amount of light is measured by the light receiving element, and measurement results: 8.6 μW and 48.0 μW are obtained, respectively. FIG. 7 shows the correspondence between the duty value of the PWM2 signal for minute light emission, the reference voltage Vref21, and the amount of light at the position (photosensitive drum surface position) corresponding to the surface of the photosensitive drum 5 measured by the light receiving element of the jig. It is a table which shows. FIG. 8 is a graph showing the relationship between the duty value of the PWM2 signal for minute light emission and the amount of light at the position (photosensitive drum surface position) corresponding to the surface of the photosensitive drum 5 measured by the light receiving element of the jig. In this embodiment, the duty value of the PWM2 signal shown below is set as a plurality of predetermined reference values. (1) Duty value (60%) corresponding to the drive current Ib in which the proportional relationship between the amount of light received by the PD 110b and the amount of light reaching the surface of the photosensitive drum 5 is broken. (2) Duty value (0%) corresponding to the amount of light that is greater than or equal to the maximum amount of light used for minute light emission (on the surface of the photosensitive drum 5). (3) Duty value (80%) corresponding to a light amount equal to or smaller than a minimum light amount for minute light emission (on the surface of the photosensitive drum 5).

  In S704, it is confirmed whether S701 to S703 have been performed on the duty values of a plurality of PWM2 signals for minute light emission determined in advance. In S705, the duty values measured in S703 (0%, 60%, 80%) Then, the corresponding light quantity data (48.0 μW, 19.2 μW, 8.6 μW) is stored in a barcode label which is a temporary storage means, and the barcode label is attached to the optical scanning device 9.

  Next, (2) the stored data writing process to the storage means of the color laser printer 50 will be described. This process is performed in the manufacturing / assembly process of the color laser printer 50.

  In S706, the light quantity data stored in the barcode label in S705 is read by a barcode reader as a reading means. In step S707, the stored data writing process is completed by writing the light amount data read in step S706 to the EEPROM in the engine controller 122 as a final storage unit.

[Setting method of duty value of PWM2 signal]
Next, a method for setting the duty value of the PWM2 signal when the optical scanning device 9 emits minute light will be described. When performing image formation, the light emission amount Pb of minute light emission is set according to various conditions. The conditions for determining the light emission amount Pb of the minute light emission include, for example, the usage amount of the photosensitive drum 5 and the rotational speed (process speed) of the photosensitive drum 5.

  The engine controller 122 calculates the duty value of the PWM2 signal for irradiating the surface of the photosensitive drum 5 with laser light with the desired light emission amount Pb using the light amount data written in the EEPROM in S707 described above. Specifically, the calculation is performed by a CPU as a calculation unit in the engine controller 122.

For example, if the desired light emission amount Pb is 15 μW, the condition of Pb <19.2 μW is satisfied. Therefore, the duty value of the PWM2 signal for setting the light amount Pb: 15 μW is 2 points (60%, 19.2 μW). ), (80%, 8.6 μW) linear linear interpolation.
In particular,
(PWM2 signal duty value)
= (15 μW-19.2 μW) × (60% -80%) / (19.2 μW−8.6 μW) +60
= 67.92%
Is calculated.

  When the desired light emission amount Pb satisfies the condition of Pb> 19.2 μW, the duty value of the PWM2 signal is 2 points (0%, 48.0 μW) and (60%, 19.2 μW). Calculation is performed by primary linear interpolation.

  As described above, the engine controller 122 detects the photosensitive drum when the light source (LD 110a) emits light based on the predetermined reference value (Duty value: 0%, 60%, 80%) and the predetermined reference value. The duty value of the PWM2 signal that is a reference value to be input to the optical scanning device 9 is determined based on the information regarding the relationship between the light quantity at position 5 (48.0 μW, 19.2 μW, and 8.6 μW). That is, the engine controller 122 is a determination unit that determines the duty value of the PWM2 signal that is a reference value input to the optical scanning device 9.

  As described above, according to the present embodiment, light is emitted at a predetermined duty value of the PWM2 signal, the light amount is measured at a position corresponding to the surface of the photosensitive drum 5, and is stored in the color laser printer 50. Then, by setting the duty value of the PWM2 signal for obtaining a desired minute light emission amount based on the stored light amount, the surface of the photosensitive drum 5 can be minutely emitted with a desired light amount.

  In this embodiment, the duty values of the three light emission PWM signals are calculated by linear interpolation based on the light amount data obtained by measuring the light amount. However, the duty values of the minute light emission PWM signals for measuring the light amount are three. Not limited to. In other words, it is sufficient to measure the amount of light with a plurality of duty values corresponding to the required accuracy to create light amount data, and if more accuracy is required, the amount of light may be measured with four or more duty values. If a certain degree of accuracy is acceptable, the light quantity may be measured using only two duty values.

  Further, the light amount data and duty value calculation method is not limited to linear linear interpolation. As another method, a function approximating the relationship between the duty value and the light amount as shown in FIG. 8 (a value corresponding to the duty value, a value corresponding to the light amount is a variable) is stored, and a predetermined point or It is also possible to determine a constant of this function from the relationship between the Duty values at a plurality of points and the measured light quantity, write the constant into the storage means of the color laser printer 50, and calculate the Duty value based on this function.

  In this embodiment, the light amount data is created using the duty value and light amount of the PWM signal for minute light emission, which is a value related to the drive current Ib, as parameters, and the light amount of minute light emission is set. Not limited. That is, data is created with a value related to the drive current Ib and a value related to the light emission amount of the minute light emission on the surface of the photosensitive drum 5 measured when the light is emitted at that value, and the light emission amount of the minute light emission is determined based on the data. You only have to set it. For example, the value related to the actually measured light amount on the surface of the photosensitive drum 5 may be a difference between the measured light amount and the reference light amount.

Further, the light amount data is stored in the barcode label of the optical scanning device 9 and written in the EEPROM in the engine controller 122, so that the light amount data is finally stored in the color laser printer 50. However, the method for storing the light amount data is not limited to this. For example, a non-illustrated non-volatile memory as a storage unit is provided in the optical scanning device 9, and light amount data is stored in the non-volatile memory in the optical scanning device 9 in the manufacturing / assembly process of the optical scanning device 9. Then, when actually setting the duty value of the PWM2 signal, the light amount data may be read from the nonvolatile memory in the optical scanning device 9 to calculate the duty value. In this case, the light quantity adjustment process described above ends in S705 of the flowchart of FIG. in this way,
When the light amount data is read out from the storage means provided in the optical scanning device 9 when calculating the duty value, the light amount data is read out in the manufacturing / assembly process of the color laser printer 50 and another final storage means. There is no need to write to. For this reason, the manufacturing and assembling process of the color laser printer 50 can be simplified.

  In the first embodiment, the light amount corresponding to the predetermined duty value of the PWM2 signal for minute light emission is measured and stored. In the second embodiment, the PWM2 for minute light emission corresponding to the predetermined light amount is stored. The difference is that the duty value of the signal is obtained and stored. In the following description, only differences from the first embodiment will be described, and other descriptions will be given the same reference numerals and description thereof will be omitted.

  FIG. 9 is a flowchart illustrating the light amount adjustment process of the second embodiment. (1) In the light amount storage step, the duty value of the PWM2 signal is determined so that the light amount detected by the light receiving element of the jig becomes a predetermined light amount. In this embodiment, the predetermined target light amount is set to three values of 45.0 μW, 19.2 μW, and 8.6 μW.

  In step S901, the duty value of the PWM2 signal is set. When obtaining a duty value at which the target light quantity is 19.2 μW, it is known that the duty value is about 19.2 μW at around 60%, so it is assumed that, for example, a duty value of 61% is set as an initial value. When the duty value is 61%, the reference voltage Vref21 (see FIG. 3) is smoothed to 0.4875V. In S902, APC is performed in the state of the reference voltage Vref21 set in S901, and laser emission is performed. In S903, the light quantity is measured by the light receiving element of the jig in the APC operation state performed in S902. In this case, it is assumed that a measurement result of 18.8 μW is obtained.

  In S904, the result of division between the target light amount (19.2 μW) on the surface of the photosensitive drum 5 shown in FIG. 10 and the light amount on the surface of the photosensitive drum 5 measured in S903 is used as a comparison value, and this comparison value is 0. It is confirmed whether or not 995 ≦ (comparison value). In this case, (comparative value) = (light quantity measured in S903) / (target light quantity (19.2 μW)) = 18.8 μW / 19.2 μW = 0.799 <0.995. For this reason, S904 becomes NO, the process proceeds to S905, and the duty value of the PWM2 signal is lowered by 1%.

  When the duty value of the PWM2 signal is set to 60% again in S901, the reference voltage Vref21 is smoothed to 0.5V. In S902, APC is performed in the state of Vref21 set in S901, and laser emission is performed. In S903, the amount of light on the surface of the photosensitive drum 5 after passing through the collimator lens 134 and the like in the optical scanning device is measured in the APC operation state performed in S902, and a measurement result of 19.2 μW is obtained.

  In S904, (comparative value) = (light amount on the surface of the photosensitive drum 5 measured in S903) / (target light amount on the surface of the photosensitive drum 5 shown in FIG. 10 (19.2 μW)) = 19.2 μW / 19.2 μW = 1, 0.995 ≦ (comparison value) is satisfied. For this reason, the process proceeds to S906. In S906, (comparison value) = 1 ≦ 1.01 is satisfied. For this reason, the process proceeds to S908, and the duty value of the PWM2 signal for which the light amount on the surface of the photosensitive drum 5 is the target light amount (19.2 μW) is determined to be 60%. The above steps S901 to S908 are repeated until the duty value (reference value) of the PWM2 signal corresponding to each of the three target light quantities 45.0 μW, 19.2 μW, and 8.6 μW is found (until N = 3). . As a result, the duty value (reference value) of the PWM2 signal for which the target light amounts are 45.0 μW and 8.6 μW are determined to be 6% and 80%, respectively.

  FIG. 10 is a table of the target light amount and the duty value of the PWM2 signal obtained correspondingly. In the present embodiment, as in the first embodiment, a predetermined target light amount is set to a light amount (19.2 μW) in which the proportional relationship between the amount of light received by the PD 110b and the amount of light reaching the surface of the photosensitive drum 5 is broken. ), The maximum amount of light used for minute light emission (on the surface of the photosensitive drum 5) (45.0 μW), and the minimum amount of light used for minute light emission (on the surface of the photosensitive drum 5) (8.6 μW).

  In step S908, it is confirmed whether the duty value of the PWM2 signal for causing the LD 110a to emit light to the target light amount is determined for all the predetermined target light amounts (45.0 μW, 19.2 μW, and 8.6 μW). In step S909, the duty value data (6%, 60%, 80%) of the PWM2 signal is stored in the barcode label, and the barcode label is attached to the optical scanning device 9. Since the subsequent storage data writing steps S910 to S911 to the storage means of the color laser printer 50 are the same as S706 to S707 in the first embodiment, description thereof will be omitted. The method for setting the duty value of the PWM2 signal in the color laser printer 50 is also the same as that in the first embodiment, and a detailed description thereof will be omitted.

  In any case, in this embodiment, the engine controller 122 determines a predetermined light amount (45.0 μW, 19.2 μW, 8.6 μW) and a predetermined light amount at the position of the photosensitive drum 5. The reference value (duty value of the PWM2 signal) to be input to the optical scanning device 9 is determined based on information on the relationship between the reference value (6%, 60%, 80%) for causing the light source (LD 110a) to emit light. To do.

  Thus, even if the duty value of the PWM2 signal for minute light emission corresponding to the predetermined light quantity is obtained and stored, the same effect as in the first embodiment can be obtained. That is, the light quantity is actually measured at a position corresponding to the surface of the photosensitive drum 5 to obtain the duty value of the PWM2 signal corresponding to the predetermined light quantity and stored in the color laser printer 50. Then, by setting the duty value of the PWM2 signal for obtaining a desired minute light emission amount based on the stored duty value, minute light emission with a desired light amount can be performed on the surface of the photosensitive drum 5.

  In this embodiment, the duty value data is created using the duty value of the PWM signal for minute light emission that is a value related to the target light amount and the drive current Ib as a parameter, and the light amount of minute light emission is set. It is not limited to these. That is, as long as the value corresponds to the drive current Ib, the duty value of the minute light emission PWM signal does not have to be, and the duty value obtained by the duty value is not the duty value itself but the reference duty value and the obtained duty value. It may be a value corresponding to the difference.

5 Photosensitive drum 8 Developing means 9 Optical scanning device 110a Laser diode (LD)
110b Photodiode (PD)
122 engine controller

Claims (6)

A photoreceptor,
Light irradiating means for irradiating the photosensitive member with laser light emitted from a light source;
Developing means for attaching toner to the photoreceptor;
The image portion before Symbol photoreceptor, to emit laser light in a normal light emission amount of the laser emitting region, and provides drive current obtained by adding the first drive current and the second drive current to said light emitting means, The second drive current is added to the non-image portion of the photoconductor without adding the first drive current so that laser light is emitted with a minute light emission amount in a laser emission region smaller than the normal light emission amount. Switching means for supplying to the light irradiation means;
A first light amount of the laser light emitted from the light irradiation unit when the second drive current is supplied at a first value, and a second value different from the first value for the second drive current. The second drive current for setting the minute light emission amount emitted from the light irradiation means as a third light amount based on the second light amount of the laser light emitted from the light irradiation means when supplied at An image forming apparatus comprising: a determining unit that determines a third value of The determining means sets the relationship between the second driving current and the light amount of the laser light to 1 based on the first value, the second value, the first light amount, and the second light amount. The image forming apparatus according to claim 1 , wherein the third value is determined using a result obtained by performing linear interpolation . The determining means approximates a relationship between the second drive current and the light amount of the laser light based on the first value, the second value, the first light amount, and the second light amount. using the function, the image forming apparatus of claim 1, wherein determining the third value. A photoreceptor,
Light irradiating means for irradiating the photosensitive member with laser light emitted from a light source;
Developing means for attaching toner to the photoreceptor;
A drive current obtained by adding a first drive current and a second drive current is supplied to the light irradiation means so that laser light is emitted with a normal light emission amount in a laser emission region with respect to the image portion of the photoconductor, the relative non-image portion of the photoreceptor, the normal to emit laser light with small emission amount of small lasing region than the light emission amount, the second drive current without adding the first drive current Switching means for supplying to the light irradiation means;
The first value supplied as the second drive current so that the laser light emitted from the light irradiation means becomes the first light quantity, and the laser light emitted from the light irradiation means becomes the second light quantity. Thus, based on the second value different from the first value supplied as the second driving current, the first light emission amount emitted from the light irradiating means is used as the third light amount. An image forming apparatus comprising: a determination unit that determines a third value of the two drive currents . The determining means sets the relationship between the second driving current and the light amount of the laser light to 1 based on the first value, the second value, the first light amount, and the second light amount. The image forming apparatus according to claim 4 , wherein the third value is determined using a result obtained by performing a linear interpolation . The determining means approximates a relationship between the second drive current and the light amount of the laser light based on the first value, the second value, the first light amount, and the second light amount. The image forming apparatus according to claim 4 , wherein the third value is determined using the function obtained .

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