JP2007118521A - Optical writing control method and image forming apparatus - Google Patents

Abstract

An object of the present invention is to prevent scumming even when an LD temperature rises.
[Solution]
In an image forming apparatus including an LD control unit 107 that controls a bias current of the LD 101 when optical writing is performed on an image carrier using a semiconductor laser (LD) 101 as a light source, the LD control unit 107 is configured to perform continuous printing. The characteristics of the LD 101 are detected during the sub-scanning paper interval (period in which the LD 101 is not turned off in the non-image area), and the bias current of the LD 101 is corrected based on the detected characteristics. As the characteristic detection of the LD 101, for example, a threshold current is detected, and the threshold current is detected by detecting the differential quantum efficiency of the LD 101.
[Selection] Figure 1

Description

  The present invention relates to an optical writing control method applied to an optical writing apparatus that performs optical writing with a semiconductor laser, and an image forming apparatus that performs optical writing with the optical writing control method, and in particular, detects the characteristics of the semiconductor laser between papers. The present invention relates to an optical writing control method that corrects optical writing and an image forming apparatus that performs optical writing using the method.

  Laser diodes (hereinafter also referred to as LDs), which are semiconductor lasers, are small in size and can perform high-speed optical modulation with a drive current. LD drive circuits are roughly classified into a non-bias system and a bias system. The no-bias method is a method in which the bias current is zero and the laser diode LD is driven with a pulse current corresponding to the input signal. On the other hand, the biased method is a method of driving the laser diode LD by adding a pulse current corresponding to the input signal while flowing a bias current smaller than the threshold current Ith through the laser diode LD. Compared to the non-bias method, the biased method can reduce the delay time until a carrier capable of laser oscillation is generated, so the delay time from the application of the pulse current corresponding to the input signal to light emission is reduced. Can be used nowadays.

  However, in the conventional biased LD driver IC, the bias current is fixed to a certain value. Therefore, in a new system such as a tandem color machine or a multi-beam machine using a plurality of laser diodes LD, the laser diode LD is used. The threshold current difference due to manufacturing variations of the product and the threshold current difference due to temperature during use cannot be absorbed, resulting in a problem that the light pulse width cannot be stably obtained and the image quality is affected. (For example, refer to Patent Document 1).

  With the recent increase in resolution of printers and the like, the realization of a system using a 650 nm red laser diode and a 400 nm ultraviolet laser diode has also begun. However, these laser diodes have a feature that it takes a long time to generate carriers having a concentration capable of laser oscillation, as compared with those having a long wavelength such as 780 nm and 1.3 μm. The conventional biased LD driver IC has a problem that only a pulse narrower than a desired pulse width can be obtained. Furthermore, with the recent increase in speed of printers and the like, the required optical pulse width is becoming increasingly narrow, and stable pulse width output is expected.

  Therefore, the present applicant has proposed the invention disclosed in Patent Document 2 so that a stable pulse width can be output.

  The present invention includes a light amount detection circuit unit that monitors a light amount of a semiconductor laser that emits light with a light amount corresponding to a supplied current, generates and outputs a voltage Vm corresponding to the light amount, and outputs the light amount detection circuit unit In a semiconductor laser driving circuit including a sample-and-hold type APC circuit that controls the light amount of the semiconductor laser to a predetermined value based on the voltage Vm, a pulse current that is a modulation current of a set current value is generated, The pulse current generation circuit unit that supplies the pulse current to the semiconductor laser in response to an external control signal Sd and the voltage Vm from the light amount detection circuit unit is a direct current so that a set voltage is obtained. A bias current generation circuit unit that generates a bias current and supplies it to the semiconductor laser, and an oscillation circuit that generates and outputs a clock signal CLK having a frequency set from outside And a control circuit for performing a predetermined operation for detecting the differential quantum efficiency of the semiconductor laser in accordance with the clock signal CLK from the oscillation circuit unit, and setting a current value of the obtained pulse current in the pulse current generation circuit unit The control circuit unit changes the time required for detecting the differential quantum efficiency of the semiconductor laser in accordance with the frequency of the clock signal CLK.

  Patent Document 2 exemplifies a configuration example of a semiconductor laser driving circuit as shown in FIG. 11, a semiconductor laser driving circuit 501 includes operational amplifiers AMP1 and AMP2, switches SW1 and SW2, S / H capacitors 502 that store output voltages of the operational amplifiers AMP1 and AMP2, a voltage-current conversion circuit 503, a variable resistor VR1, and A reference voltage generation circuit 504 that generates and outputs a predetermined reference voltage Vref is provided. Further, the semiconductor laser drive circuit 501 switches the switches SW1, SW2 and the APC signal Sapc which is a signal for controlling the input APC and the reset signal RES for starting the reset operation for forcibly turning off the laser diode LD. A control circuit 505 for controlling the operation of the operational amplifier AMP2 and a photodiode PD are provided. Further, the semiconductor laser driving circuit 501 includes a pulse current generation circuit 506 that outputs a current having a value corresponding to the data signal CODE from the control circuit 505 according to a signal input from the outside, and a half of the reference voltage Vref. A voltage control circuit 507 that generates a voltage and outputs a voltage of Vref or Vref / 2 in accordance with a control signal Vcon from the control circuit 505. Further, the control circuit 505 includes a logic circuit 511, a selector 512, an oscillation circuit 513 that generates a clock signal CLK and supplies the clock signal CLK to the logic circuit 511, and a resistor 514 for setting the frequency of the clock signal CLK from the oscillation circuit 513. I have.

  The voltage-current conversion circuit 503, the pulse current generation circuit 506, the voltage control circuit 507, the operational amplifiers AMP1 and AMP2, the switches SW1 and SW2, the logic circuit 511, the selector 512, and the oscillation circuit 513 are integrated into one IC and are subjected to differential quantum efficiency. It constitutes a detection unit, and the reset signal RES is a signal for resetting the IC. The APC signal Sapc is an enable signal for APC control in a normal state. When the APC signal Sapc is at a high level, the switch SW1 is turned on to be in a conductive state, and when at a low level, the switch SW1 is turned off to be in a cut-off state. The reference voltage Vref is a voltage for setting the light quantity of the laser diode LD. The S / H capacitor 502 is a capacitor that stores a voltage that is a result of APC control. The voltage-current conversion circuit 503 is a current source that generates a bias current Ib to be supplied to the laser diode LD, and corresponds to the high voltage side voltage (hereinafter referred to as the voltage of the S / H capacitor 2) VSH of the S / H capacitor 502. The generated current is generated and supplied to the laser diode LD as a DC bias current. The pulse current generation circuit 506 is a current source that generates and outputs a pulse current ip that is a modulation current supplied to the laser diode LD, and performs output control of the pulse current ip generated according to the control signal Sd from the outside. . The pulse current generation circuit 506 sets a current value generated by the data signal CODE input from the logic circuit 511 when performing an operation (hereinafter referred to as initialization) for detecting the differential quantum efficiency of the laser diode. .

  The reference voltage Vref from the reference voltage generation circuit 504 is input to the voltage control circuit 507, and the control signal Vcon is input from the logic circuit 511. The voltage control circuit 507 generates a reference voltage signal for setting the light quantity of the laser diode LD, for example, a voltage of Vref / 2, and each of the operational amplifiers AMP1 and AMP2 is generated by the control signal Vcon from the logic circuit 511 at the time of initialization. A voltage of Vref / 2 is output to the non-inverting input terminal, and after initialization, the reference voltage Vref from the reference voltage generation circuit 504 is output to the non-inverting input terminals of the operational amplifiers AMP1 and AMP2. The output ends of the operational amplifiers AMP1 and AMP2 are connected, and the connecting portion is connected to one end of the switch SW1. The other end of the switch SW1 is connected to a voltage-current conversion circuit 503, and an S / H capacitor 502 and a switch SW2 are connected in parallel between the connection portion and the ground voltage. The switch SW1 receives the control signal CTL1 from the selector 512 of the control circuit 505 and performs switching according to the input control signal CTL1. The switch SW2 receives the control signal CTL2 from the logic circuit 511 of the control circuit 505. Then, switching is performed according to the input control signal CTL2. As a result, the switch SW1 controls disconnection between the S / H capacitor 502 and the output terminals of the operational amplifiers AMP1 and AMP2 in order to hold the voltage VSH of the S / H capacitor 502. The switch SW2 discharges the S / H capacitor 2 when the laser diode LD is forcibly turned off, for example, when the power is turned on.

  At the time of initialization, while the reset signal RES is at a high level, the logic circuit 11 is in a reset state, and the drive current Iop is not supplied to the laser diode LD. That is, the switch SW2 is turned on, the charge of the S / H capacitor 2 is discharged, the bias current Ib supplied by the voltage-current conversion circuit 3 becomes zero, and the pulse current generation circuit 6 receives the pulse current ip from the logic circuit 11. The data signal CODE indicating = 0 is input, and the pulse current ip supplied to the laser diode LD becomes zero regardless of the control signal Sd. Such a reset state may be immediately after power-on of the system, at the time of resetting, or when some abnormality occurs in the system, and initialization is performed immediately after the reset is released.

Since the semiconductor laser drive circuit itself shown in FIG. 11 is known, its operation and other details are omitted. The semiconductor laser driving circuit shown corresponds to an LD control unit in an embodiment described later, the LD corresponds to the LD 101, and the PD receives light emitted from the LD 101 in FIG. 1 described later.
JP 2003-154705 A JP 2005-129842 A

  FIG. 8 is a characteristic diagram showing the relationship between the LD (semiconductor laser) drive current Iop and the amount of light. As can be seen from this figure, when the drive current Iop is increased, the light emission efficiency changes at the threshold current Ith. That is, the slope of the characteristic indicating the amount of light changes. When the threshold current Ith is lower than the threshold current Ith, spontaneous emission (LED light emission) starts, and when the threshold current Ith is higher than the threshold current Ith, LD oscillation by stimulated emission is started and LD light emission is performed. In addition, as the temperature characteristics, “Ith” increases (30 ° C., 50 ° C.), efficiency decreases (30 ° C. for 20 ° C. characteristics, 50 ° C.) maximum output decreases (20 ° C., 50 ° C. for 30 ° C. Phenomenon).

  On the other hand, when performing normal LD control, as shown in the characteristic diagram of FIG. 9, the bias current steadily flows the bias current Ib below the threshold current Ith to improve the output rise characteristic of the LD. Further, at the time of lighting, a necessary amount of light is obtained by flowing a current of Ib (bias current) + Id (lighting current). In FIG. 9, the horizontal axis represents the lighting current, and the vertical axis represents the amount of light.

  When the LD is driven with such characteristics and the required light quantity is set, the threshold current Ith is detected at 20 ° C., for example, as shown in FIG. 10, and the bias current Ib and the lighting current Id are determined. Until the next threshold current Ith is detected, the lighting current Id is fixed, and during normal operation, the bias current Ib is changed by APC (automatic power control) for each scanning line to control the set light amount. Yes. APC is a known technique, and is configured using, for example, a sample hold circuit. However, if the temperature rises during continuous printing, the LD output efficiency decreases as shown in FIG. 10, and the bias current Ib increases due to APC. Then, when the bias current Ib exceeds the threshold current Ith, the amount of bias light is increased correspondingly, and background contamination occurs.

  That is, in the conventional control method for driving the LD with a bias method, the threshold current detection inherent to the laser is performed at the time of power-on or before the start of the print job. The threshold current increased due to the rise, which caused soiling.

  The present invention has been made in view of such a state of the art, and an object of the present invention is to prevent scumming even when the LD temperature rises.

  In order to achieve the object, the first means is an optical writing control method for controlling a bias current of the semiconductor laser when optical writing is performed on an image carrier using a semiconductor laser as a light source. And detecting a characteristic of the semiconductor laser during a sub-scanning non-image area and not turning off the semiconductor laser, and correcting a bias current of the semiconductor laser based on the detected characteristic. To do.

  The second means is characterized in that, in the first means, the characteristic of the semiconductor laser is a threshold current.

  3. The optical writing control method according to claim 1, wherein the third means starts the correction in the first or second means using a negation of an FGATE signal indicating that an image is being created as a trigger. 4.

  A fourth means is an image forming apparatus comprising a control means for controlling the bias current of the semiconductor laser when optical writing is performed on the image carrier using the semiconductor laser as a light source, and the control means is adapted for continuous printing. The characteristic of the semiconductor laser is detected between the two sheets of paper, and the bias current of the semiconductor laser is corrected based on the detected characteristic.

  A fifth means includes a light writing means for performing line scanning by a light beam emitted from a light emitting source controlled to be turned on according to image data and writing an image in the fourth means, and the light beam on the scanning line. A light beam detecting means for detecting, and a differential quantum efficiency detecting means for detecting the differential quantum efficiency of the semiconductor laser, wherein the control means is based on detection results of the light beam detecting means and the differential quantum efficiency detecting means. Then, the bias current is corrected.

  A sixth means is characterized in that, in the fourth or fifth means, the characteristic of the semiconductor laser is a threshold current.

  In a seventh means, in any one of the fourth to sixth means, the control means detects a threshold current between the sheets without changing a printing condition and an operating condition, and corrects the bias current. It is characterized by.

  An eighth means is any one of the fourth to seventh means, wherein the control means detects the threshold current by using a negation of an FGATE signal indicating that an image is being created as a trigger, and a bias current of the laser. The correction is started.

  A ninth means is any one of the fourth to eighth means, an intermediate transfer belt for primary transfer of an image on the image carrier, and secondary transfer for transferring the image on the intermediate transfer belt to a recording medium. Means, a contact / separation means for contacting and separating the secondary transfer means with respect to the intermediate transfer belt, a pattern density detection means for detecting a density of a pattern formed on the intermediate transfer belt, and the pattern density detection means A process correction unit that performs process correction based on the detection result of the step, wherein the secondary transfer unit is separated from the intermediate transfer belt during the pattern formation, and the process correction unit performs process correction between the sheets. The threshold current is detected and the bias current is corrected.

  According to a tenth means, in any one of the fourth to eighth means, an intermediate transfer belt that primarily transfers the image on the image carrier, and a secondary that transfers the image on the intermediate transfer belt to a recording medium. A transfer means; a contact / separation means for bringing the secondary transfer means into and out of contact with the intermediate transfer belt; a pattern density detection means for detecting the density of a pattern formed on the intermediate transfer belt; and the pattern density detection. A positional deviation correction unit that corrects a positional deviation based on a detection result of the unit, and separates the secondary transfer unit from the intermediate transfer belt during the formation of the pattern, and the positional deviation correction unit between the sheets The threshold current is detected and the bias current is corrected when the positional deviation correction is performed.

  The eleventh means is characterized in that, in the ninth or tenth means, initialization is performed after the pattern is formed on the intermediate transfer belt between the sheets.

  A twelfth means is characterized in that, in any of the sixth to eleventh means, the threshold current detection and correction timing is managed by the number of printed sheets.

  A thirteenth means includes a measuring means for measuring the temperature inside the machine in any one of the sixth to eleventh means, and the threshold current detection and correction timing is kept at a constant temperature after the previous correction. It is managed by change.

  In the embodiments described later, the semiconductor laser is the LD 101, the image carrier is the photosensitive member 200, the control means is the writing control system 12, the optical writing means is the writing optical system 11, and the light beam detecting means is the synchronization detection plate. 106, the writing control system 12, the differential quantum efficiency detection means is the LD control section 107, the intermediate transfer belt is denoted by reference numeral 208, the secondary transfer means is the secondary transfer section (secondary transfer roller) 209, and the contact / separation means is A pattern density detection unit corresponds to a pattern detection sensor 210, a process correction unit and a positional deviation correction unit correspond to a CPU 320, and a measurement unit corresponds to a temperature sensor (not shown).

  According to the present invention, the characteristics of the semiconductor laser are detected between the papers, and the bias current of the semiconductor laser is corrected based on the detected characteristics, so that no soiling occurs even if the temperature of the semiconductor laser rises. be able to.

  The best mode for carrying out the invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an optical writing device in an image forming apparatus according to an embodiment of the present invention. The optical writing device 1 according to the present embodiment includes a writing optical system 11 and a writing control system 12. The writing optical system 11 is provided outside a writing scanning range to a photoconductor (not shown), a semiconductor laser (hereinafter referred to as LD) 101 as a light source, a polygon mirror 102 as a scanning means, an Fθ lens 103 as a scanning speed conversion means. The reflection mirror 105, the synchronization detection plate 106 to which the scanning light reflected by the reflection mirror 105 is input, and the dustproof glass 104 provided at the boundary to the image forming unit and preventing dust from entering the image forming unit side. , And a polygon control unit 108 that controls the driving of a polygon motor that rotationally drives the polygon mirror 102. The synchronization detection plate 106 detects an effective writing start position and controls the writing position in the main scanning direction to be constant.

  The write control system 12 includes a write control unit GADV 310 and an LD control unit 107, and the write control unit GADV 310 includes a timing control unit 120, an LD drive data generation unit 110, a pixel clock generation unit 111, and an image processing unit 113. Yes. The timing control unit 120 controls various image forming timings by a main scanning counter and a sub scanning counter (not shown). The pixel clock generation unit 111 generates a pixel clock synchronized with the output signal of the synchronization detection plate 106 and supplies it to the image processing unit 113 and the laser drive data generation unit 110. The image processing unit 113 generates image data based on the pixel clock, and generates a process pattern from the timing signal from the timing control unit 120. The LD drive data generation unit 110 similarly generates laser drive data (modulation data) based on the pixel clock for the input image data, and drives the LD 101 via the LD control unit 107. The LD control unit 107 has the same configuration as the known example shown in FIG. 11 described above, and also functions as a differential quantum efficiency detection unit that detects the differential quantum efficiency of the semiconductor laser. The LD control unit 107 detects the differential quantum efficiency of the semiconductor laser to detect a threshold current unique to the laser, and controls the laser bias current according to the output result. Since the configuration of the optical writing apparatus itself shown in FIG. 1 is known, detailed description thereof is omitted.

  In the optical writing apparatus schematically configured as described above, the laser beam from the LD 101 is scanned in the main scanning direction by the polygon mirror 102, converted from the uniform angular velocity deflection to the uniform velocity deflection by the Fθ lens 103, and is produced from the dust-proof glass 104. The light is emitted to the image device side. The polygon control unit 108 controls the rotation of the polygon mirror 102, and the synchronization writing plate 106 detects the effective writing start position of the scanning laser beam. The detected position detection information is input to the timing control unit 120 and the LD drive data generation unit 110.

  FIG. 2 is a diagram showing a schematic configuration of the image forming unit. The image forming unit includes a photosensitive member 200, a charging unit 201, a writing unit 202, a developing unit 203, a primary transfer unit (not shown), a cleaning unit 207, a midpointer belt 208, a secondary transfer unit 209, a paper feeding unit 204, a fixing unit. The unit 205 and the control unit including the CPU 320 shown in FIG. In the writing unit 202, four optical writing devices 1 shown in FIG. 1 are provided for each color of YMCK, and optical writing is performed for each color. Hereinafter, one color, K color in the figure, will be described as an example.

  When forming an image, the photosensitive member 200 is charged by the charging unit 201, and the photosensitive member 200 is irradiated with LD light modulated in accordance with image data from the writing unit 202, and an electrostatic latent image is formed on the surface of the photosensitive member 200. Form. The developing unit 203 develops the electrostatic latent image on the photoconductor 200 by attaching toner of a color corresponding to the photoconductor 200, and the visualized toner image is primarily transferred to the intermediate transfer belt 208. In the present embodiment, the image is transferred to the intermediate transfer belt 208 in the order of Y → C → M → K and superimposed to form a full color image. On the other hand, the transfer paper is fed from the paper feed unit 204, and the full-color image is secondarily transferred from the intermediate transfer belt 208 onto the transfer paper in the secondary transfer unit 209. The color image transferred onto the transfer paper is fixed by the fixing unit 205 at the next stage. Further, an excessive toner image remaining on the surface of the photoconductor 200 is removed by the cleaning unit 207.

  FIG. 3 is a functional block diagram illustrating an outline of an electrical configuration of the image forming apparatus according to the present embodiment. In FIG. 1, the image forming apparatus includes an image reading unit, an image writing unit, and a control unit. The image reading unit includes a scanner unit 300 and an IPU 301. The image writing unit includes a write control unit GAVD 310, an LD control unit 107, and an LD 101. Including. The control unit includes a CPU 320, NVROM 328 and RAM 322, image memory 324, RAM 323, and operation unit 327, and can send and receive signals via a system bus 325. Further, the image reading unit and the image writing unit are connected by a local bus 329, and are connected to the system bus 325 by a local I / F 326, and a system including an image reading unit, an image writing unit, and a control unit is constructed.

  The IPU 301 is called an image processing unit, and converts image data read by the scanner unit 300 and converted from digital signals into image data suitable for printing. The CPU 320 executes predetermined processing based on the operation information input from the operation unit 327 and using the RAM 322 as a work area based on a program stored in the NVROM 328. The image data read by the scanner unit 300 and converted into digital data by the IPU 301 is normally sent to the RAM 323, compressed, and stored in the image memory 324. When printing an image, the image data is read from the image memory 324, decompressed and written in the RAM 323, and the written image data is sent to the write control unit GAVD310. As the input image data, data for controlling the lighting of the LD 101 by the writing control unit GAVD 310 is generated and input to the LD control unit 107. Then, the LD control unit 107 drives the LD 101 to perform optical writing.

  When printing image data previously written in the image memory 324, the image data from the image memory 324 is written in accordance with an instruction from the CPU 320 in accordance with an operation input from the operation unit 327 in the same manner as described above. 310, the LD control unit 107 drives the LD 101, and optical writing is performed.

  FIG. 4 is a timing chart showing threshold current detection and correction timing. XPFGATE is Low and indicates an image area in the sub-scanning direction. XPFGATE is input to the CPU 320 from the write control unit GAVD 310 as an interrupt signal and performs various controls. In XPFGATE, an LD lighting signal corresponding to image data is input from the GAVD 310 to the LD control unit 107 during the Low period, and the LD control unit 107 lights the LD 101 in accordance with the LD lighting signal. The writing control unit GAVD 310 performs timing control by turning a sub-scanning counter that counts the same detection signal from the negation (rising) of each color XPFGATE, and performs a density correction pattern (hereinafter referred to as a P pattern), a blade wobbling prevention pattern (hereinafter referred to as a pattern). , B pattern), and a positional deviation correction pattern (hereinafter referred to as M pattern). The generation timing of these patterns is output from the timing control unit 120 to the LD drive data generation unit 110, and the LD drive data generation unit 110 generates LD drive data for writing the P pattern, the B pattern, and the M pattern. The generation timing of the P pattern, B pattern, and M pattern can be set at an arbitrary position in units of sub-scanning dots. The pattern is a non-image area of sub-scanning, and is formed between so-called papers during a period in which the semiconductor laser is not turned off. The pattern formed between the papers is read, and if necessary, density, misregistration, etc. Is corrected.

  The CPU 320 polls the status flag indicating the P pattern generation state of the write control unit GAVD 310 in a certain period, and outputs the initialization start signal to the LD control unit 107 at the timing when the generation of the M pattern is completed, thereby detecting the threshold current. And correct. When the correction is completed, the writing control unit GAVD 320 automatically returns the flag to Low. The initialization here is an operation for detecting the differential quantum efficiency of the laser diode as described above.

  Detailed timings of threshold current detection and correction at this time are shown in FIG. As described above, XPFGATE indicates an image area with Low, XPFGATE is input to the port of the CPU 320 from the write control unit GAVD 310, and the CPU 320 detects the fall of the XPFGATE of each color and corrects the threshold current Ith and corrects the write control unit GAVD310. Set the initialization start flag. The write control unit GAVD 310 outputs an initialization start signal to the LD control unit 107 at the rise (negation) of each color XPFGATE, and performs threshold current detection and correction. When the correction is completed, the writing control unit GAVD 320 automatically returns the initialization start flag to Low.

  The secondary transfer unit 209 includes a secondary transfer roller that can be separated from and brought into contact with the intermediate transfer belt 208. The contact timing of the secondary transfer roller is controlled by turning a timer from an XPFAGE interrupt signal to the CPU 320. When the time when the recording paper passes the secondary transfer roller by the timer measurement has elapsed, the secondary transfer roller is separated from the intermediate transfer belt 208 side (shown as the secondary transfer roller contact / separation timing in FIG. 4), and the intermediate transfer belt 208 is reached. After the toner image (P, B, M pattern) by the above initialization passes through the secondary transfer roller, the secondary transfer roller is brought into contact. Although not described in detail, the contact / separation (contact / separation) mechanism of the secondary transfer roller includes a drive mechanism including a motor and a cam. Further, the P, B, and M patterns are formed by a pattern detection sensor 210 provided at a position facing the intermediate transfer belt 208 on the downstream side of the secondary transfer unit 209 in the rotation direction of the intermediate transfer belt. The position of the pattern is detected as timing. The detected data is sent to the CPU 320 and processed by the CPU 320 to detect density unevenness and positional deviation. Then, based on the detected density unevenness and position deviation, density correction is performed from the P pattern, cleaning blade wobbling prevention correction from the B pattern, and position deviation correction from the M pattern.

  On the other hand, the threshold current detection and the correction timing are managed by, for example, the number of prints. The processing procedure at this time is shown in the flowchart of FIG. In this procedure, first, the number counter N is reset to 0 (step S101). Next, XPFGATE is polled (step S102). When XPFGATE becomes H, the number counter N is incremented (step S103), the number of sheets is determined (step S104), and if N = P, bias correction is performed (step S105). ), If N ≠ P, the process returns to step S102 and the subsequent processing is repeated. As a result, bias correction (pattern writing and correction) is performed for each preset number of sheets P, it is possible to prevent the occurrence of background contamination, and normal image output is possible.

  Further, since the temperature rise of the LD 101 (rise in the in-machine temperature) causes the image shift, it can be managed according to the temperature change. That is, an in-machine temperature measuring means such as a temperature sensor is installed in the vicinity of the image forming unit of the image forming apparatus, and the bias is detected when a certain temperature change occurs after the previous correction of the threshold current detection and correction timing. Make corrections. The processing procedure at this time is shown in the flowchart of FIG. In this procedure, first, an initial temperature Ta in the machine is detected by a temperature sensor (not shown) and stored in a memory (for example, RAM 322) (step S201). Next, initial setting (bias correction or the like) is performed (step S202), the temperature T is detected and stored in the memory (step S204), and the difference (X ≧ T−Ta) from the initial temperature Ta is set as the reference value X. Compare (step S204). If the difference (T-Ta) is larger than the reference value X, bias correction is performed (step S205). If smaller, the process returns to step 203, and the subsequent processing is repeated. As a result, it is possible to prevent the occurrence of background contamination due to temperature, and normal image output is possible.

As described above, according to this embodiment,
1) During continuous printing, threshold current detection and bias current correction are performed without system shutdown, so that a normal image with no background stain can always be output without reducing productivity.
2) In a system that does not include a bias mechanism for preventing toner adhesion to the secondary transfer roller, when the toner pattern is formed on the intermediate transfer belt without transferring to the recording paper, the paper due to contamination of the secondary transfer roller It is necessary to separate the secondary roller in order to prevent the backside dirt on the surface. Similarly, threshold detection and correction also emit LD light, so that the toner adheres to the intermediate transfer belt, so the secondary transfer roller needs to be separated. If the P, B, and M patterns are formed between sheets as shown in the above-described embodiment, the secondary transfer roller must be separated between the sheets, which reduces productivity. However, in this embodiment, since operations that require the separation of the secondary transfer roller are collectively performed between sheets, productivity is improved as compared with the case where the secondary transfer roller is separated for each pattern formation and correction operation. Can be made.
3) Pattern formation at the time of sheet spacing is performed by counting the synchronization signal based on the previous FAGTE negation reference and controlling the timing, and when performing threshold current detection, in systems where it is necessary to turn off LD, before pattern and between patterns When the threshold current is detected, the synchronization signal is not input and the pattern cannot be formed normally. On the other hand, in the present embodiment, since threshold current detection and bias current correction are performed after various patterns are imaged, pattern formation failure due to no synchronization signal input can be prevented.
4) Since bias correction is performed for each preset number of sheets P, a normal image free from background contamination can always be output.
5) Since bias correction is performed every time a preset temperature change occurs, it is possible to prevent the occurrence of background contamination caused by temperature, and always output a normal image.
There are effects such as.

1 is a diagram illustrating a schematic configuration of an optical writing device in an image forming apparatus according to an embodiment of the present invention. It is a figure which shows schematic structure of the image creation part in this embodiment. It is a block diagram which shows the detail of the LD control part in this embodiment. 6 is a timing chart showing a relationship between threshold current detection, correction, and secondary transfer roller contact / separation timing between sheets in the present embodiment. 5 is a timing chart showing details of threshold current detection and correction timing in FIG. 4. 6 is a flowchart illustrating a processing procedure when threshold current detection and the correction timing are managed according to the number of prints in the present embodiment. It is a flowchart which shows the process sequence when managing the threshold current detection and correction timing in this embodiment by a temperature change. It is a characteristic view which shows the relationship between the drive current of LD and light quantity for demonstrating the conventionally known threshold current. It is a characteristic view which shows the relationship between the lighting current and light quantity of LD for demonstrating the conventionally known bias current. It is a characteristic view which shows the relationship between the drive current and light quantity for demonstrating the soil contamination generation mechanism known conventionally. It is a figure which shows an example of the circuit structure of the semiconductor laser drive circuit which concerns on a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical writing apparatus 11 Writing optical system 12 Writing control system 101 LD
DESCRIPTION OF SYMBOLS 102 Polygon mirror 103 F (theta) lens 105 Reflection mirror 106 Synchronization detection plate 107 LD control part 110 LD drive data generation part 111 Pixel clock generation part 113 Image processing part 120 Timing control part 200 Photoconductor 201 Charging part 202 Writing unit 203 Development part 204 Supply Paper unit 205 Fixing unit 207 Cleaning unit 208 Intermediate transfer belt 209 Secondary transfer unit 210 Pattern detection sensor 320 CPU

Claims (13)

In an optical writing control method for controlling a bias current of the semiconductor laser when optical writing is performed on an image carrier using a semiconductor laser as a light source,
Detect the characteristics of the semiconductor laser between the paper during continuous printing,
An optical writing control method, comprising: correcting a bias current of the semiconductor laser based on detected characteristics.   The optical writing control method according to claim 1, wherein the characteristic of the semiconductor laser is a threshold current.   3. The optical writing control method according to claim 1, wherein the correction is started with a negation of an FGATE signal indicating that an image is being created as a trigger. In an image forming apparatus comprising a control means for controlling a bias current of the semiconductor laser when optical writing is performed on an image carrier using a semiconductor laser as a light source,
The image forming apparatus, wherein the control unit detects the characteristics of the semiconductor laser between sheets during continuous printing, and corrects the bias current of the semiconductor laser based on the detected characteristics. A light writing unit that performs line scanning by a light beam emitted from a light source that is controlled to be turned on according to image data, and writes an image;
A light beam detecting means for detecting the light beam on a scanning line;
Differential quantum efficiency detection means for detecting the differential quantum efficiency of the semiconductor laser;
With
The image forming apparatus according to claim 4, wherein the control unit corrects the bias current based on detection results of the light beam detection unit and the differential quantum efficiency detection unit.   6. The image forming apparatus according to claim 4, wherein the characteristic of the semiconductor laser is a threshold current.   7. The image according to claim 4, wherein the control unit detects a threshold current between the sheets without changing a printing condition and an operation condition, and corrects the bias current. 8. Forming equipment.   8. The control unit according to claim 4, wherein the control unit detects the threshold current using a negation of an FGATE signal indicating that an image is being created as a trigger, and starts correction of a laser bias current. 2. The image forming apparatus according to item 1. An intermediate transfer belt for primary transfer of an image on the image carrier;
Secondary transfer means for transferring an image on the intermediate transfer belt to a recording medium;
Contact / separation means for contacting / separating the secondary transfer means to / from the intermediate transfer belt;
Pattern density detecting means for detecting the density of the pattern formed on the intermediate transfer belt;
Process correction means for correcting the process based on the detection result of the pattern density detection means;
And detecting the threshold current and correcting the bias current when the process correction unit performs process correction between the sheets by separating the secondary transfer unit from the intermediate transfer belt during the formation of the pattern. The image forming apparatus according to claim 4, wherein the image forming apparatus is performed. An intermediate transfer belt for primary transfer of an image on the image carrier;
Secondary transfer means for transferring an image on the intermediate transfer belt to a recording medium;
Contact / separation means for contacting / separating the secondary transfer means to / from the intermediate transfer belt;
Pattern density detecting means for detecting the density of the pattern formed on the intermediate transfer belt;
A positional deviation correction unit that corrects a positional deviation based on a detection result of the pattern density detection unit;
And detecting the threshold current and the bias current when the secondary transfer unit is separated from the intermediate transfer belt during the pattern formation and the positional shift correction unit performs positional shift correction between the sheets. The image forming apparatus according to claim 4, wherein correction is performed.   The image forming apparatus according to claim 9, wherein initialization is performed after the pattern is formed on the intermediate transfer belt between the sheets.   12. The image forming apparatus according to claim 6, wherein the threshold current detection and correction timing is managed by the number of prints.   12. A measuring means for measuring the temperature inside the machine, wherein the threshold current detection and correction timing is managed by a constant temperature change since the previous correction was performed. The image forming apparatus described in the item.

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