JP6327945B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming process for forming a measurement image.

  The electrophotographic image forming apparatus rotates and drives a polygon mirror for deflecting the light beam emitted from the light source so that the light beam emitted from the light source scans the photosensitive member. The image forming apparatus includes a light receiving unit at a position for receiving light that is not irradiated on the photosensitive member among light deflected by the polygon mirror while the polygon mirror rotates. The light receiving means receives a part of the light deflected by the polygon mirror every time the light deflected by the polygon mirror scans the photosensitive member, and outputs a reference signal based on the received result. In the image forming apparatus, the rotation speed of the polygon mirror is controlled so that the reference signal from the light receiving means is output at a predetermined interval.

  For example, the light receiving means outputs a voltage according to the received light intensity, determines the threshold voltage based on the potential difference between both ends of the capacitor charged by this output voltage, and based on the output voltage of the light receiving means and the threshold voltage There is an image forming apparatus that generates a signal (Patent Document 1).

Japanese Patent Laid-Open No. 06-286217

  However, when the temperature around the image forming apparatus decreases, there is a problem in that the capacitor is not sufficiently charged or discharged, and the threshold voltage cannot be determined with high accuracy. Therefore, for example, when the electrostatic latent image is formed by reducing the intensity of the light beam, there is a possibility that the reference signal is not output.

  Therefore, an object of the present invention is to output a reference signal with high accuracy regardless of the ambient temperature of the image forming apparatus.

  In order to solve the above-described problem, an image forming apparatus according to claim 1 includes a photosensitive member, a light source, a polygon mirror that deflects a light beam emitted from the light source, and a driving unit that rotationally drives the polygon mirror. An exposure unit that exposes the photoconductor using the light beam emitted from the light source and deflected by the polygon mirror to form an electrostatic latent image on the photoconductor, and the exposure unit Image forming means for developing the formed electrostatic latent image to form an image, light receiving means for receiving the light beam deflected by the polygon mirror, and intensity of the light beam received by the light receiving means An output means for outputting a voltage corresponding to the output voltage, and a capacitor charged based on the voltage output from the output means, and based on a potential difference between both ends of the capacitor. Determining means for determining a threshold voltage; generating means for generating a reference signal based on the voltage output from the output means and the threshold voltage determined by the determining means; and the generated by the generating means Drive control means for controlling the drive means based on a reference signal, temperature detection means for detecting temperature, setting means for setting the intensity of a light beam emitted from the light source, and output from the light source to the setting means The intensity of the light beam to be set is set to the first intensity and the exposure unit forms an electrostatic latent image, and then the setting unit sets the intensity of the light beam emitted from the light source to the first intensity. In the case where the exposure unit forms an electrostatic latent image with a lower second intensity set, the setting unit sets the intensity of the light beam based on the temperature detected by the temperature detection unit. Characterized in that from the intensity of and a control means for controlling the timing of changing to the second intensity.

  According to the present invention, the reference signal can be output with high accuracy regardless of the ambient temperature of the image forming apparatus.

Schematic sectional view of the image forming apparatus Schematic diagram of main parts of intermediate transfer belt Schematic diagram of main parts of exposure equipment Control block diagram of image forming apparatus Schematic diagram of pattern image Schematic cross section of pattern detection sensor Diagram showing the characteristics of the peak hold section The figure which showed the detection result of the pattern image The figure which showed the detection result of the pattern image Flow chart of laser light quantity correction sequence Flow chart of delay time determination sequence

(Image forming device)
FIG. 1 is a schematic cross-sectional view of the image forming apparatus, and FIG. 2 is a schematic view of a main part showing the periphery of the intermediate transfer belt. The image forming units 10a to 10d include photosensitive drums 11a to 11d having photosensitive members formed on the surface, charging rollers 12a to 12d, developing devices 14a to 14d, and transfer rollers 17a to 17d. The image forming unit 10a forms a yellow image, the image forming unit 10b forms a magenta image, the image forming unit 10c forms a cyan image, and the image forming unit 10d forms a black image.

  The intermediate transfer belt 16 is stretched around a transfer counter roller 24 and a driving roller 25. The image forming units 10a to 10d are arranged side by side in the transport direction (arrow B direction) in which the intermediate transfer belt 16 is transported. Transfer rollers 17a to 17b are arranged at positions facing the photosensitive drums 11a to 11d via the intermediate transfer belt 16, respectively.

  The photosensitive drums 11a to 11d are rotationally driven in the direction of arrow A by motors 112a to 112d. After the photosensitive drums 11a to 11d are uniformly charged by the charging rollers 12a to 12d, the photosensitive drums 11a to 11d are exposed to light by the exposure device 13 according to image data. Thereby, an electrostatic latent image corresponding to the image data for each color component is formed on each of the photosensitive drums 11a to 11d. When the electrostatic latent images on the photosensitive drums 11a to 11d are developed by the developing units 14a to 14d, they are visualized as images of respective color components. Images on the photosensitive drums 11a to 11d are transferred onto the intermediate transfer belt 16 by transfer rollers 17a to 17d. As a result, a full-color image is formed on the intermediate transfer belt 16.

  The recording material P fed from the paper feed cassette 20 is transported toward the transfer roller 19 by the transport roller 23 so as to be synchronized with the image on the intermediate transfer belt 16. When the image on the intermediate transfer belt 16 and the recording material P pass through the nip portion between the transfer roller 19 and the transfer counter roller 24, a transfer electric field is applied to the transfer roller 19, and the recording material is transferred from the intermediate transfer belt 16 to the recording material. The image is transferred to P.

  Toner remaining on the photosensitive drums 11a to 11d without being transferred to the photosensitive drums 11a to 11d by the transfer rollers 17a to 17d is cleaned by the drum cleaners 15a to 15d. The toner remaining on the intermediate transfer belt 16 without being transferred from the intermediate transfer belt 16 to the recording material P by the transfer roller 19 is cleaned by the belt cleaner 18. The image transferred to the recording material P is conveyed to the fixing unit 21 and is fixed to the recording material P by the heat and pressure of the fixing unit 21. The recording material P on which the image is fixed is discharged from the image formation prosecution.

  The image forming apparatus corrects the intensity of the light beam when the paper type for forming an image is changed or when the temperature in the image forming apparatus changes by a predetermined temperature or more. In order to correct the intensity of the light beam, the image forming apparatus forms a measurement image (pattern image) on the intermediate transfer belt 16, and the intensity of the light beam is determined based on the result of detecting the pattern image by the pattern detection sensor 31. It is corrected. Details of the pattern detection sensor 31 will be described later.

  FIG. 3 is a schematic view of the main part of the exposure apparatus 13.

  The exposure apparatus 13 includes a laser light source 101, a collimator lens 102, an aperture stop 103, a cylindrical lens 104, a polygon mirror 105, a polygon motor 106, a toric lens 107, and a diffractive optical element 108. Further, the exposure apparatus 13 includes a reflection mirror 109 and a BD 114.

  As the laser light source 101, a semiconductor laser that is turned ON / OFF according to image data is used. The collimator lens 102 converts the light beam emitted from the laser light source 101 into a parallel light beam. The aperture stop 103 limits the luminous flux of the light beam. The cylindrical lens 104 focuses the light beam that has passed through the aperture stop 103 on the polygon mirror 105. The polygon mirror 105 is rotationally driven by the polygon motor 106 in the direction of the arrow C in the figure, and deflects the laser light imaged on the reflecting surface. As the polygon mirror 105 rotates in the direction of arrow C, the light deflected by the polygon mirror 105 scans the photosensitive drum 11. A direction in which the light deflected by the polygon mirror 105 scans the photosensitive drum 11 is a main scanning direction, a direction orthogonal to the main scanning direction, and a direction in which the surface of the photosensitive drum 11 moves is a sub-scanning direction.

  The toric lens 107 is an optical element having fθ characteristics. The diffractive optical element 108 is a diffractive portion having fθ characteristics. The reflection mirror 109 is provided at a position for receiving light that is not irradiated on the photosensitive drum 11 among the light deflected by the polygon mirror 105. The light beam reflected by the reflection mirror 109 is incident on the BD 114. In the configuration having the polygon mirror 105 for each of the photosensitive drums 11a to 11d, the BDs 114 are provided as many as the number of polygon mirrors 105. Regarding the laser light source 101 incident on the BD 114, in the case of a full-color image forming apparatus in which a plurality of color laser light sources 101 are incident on one polygon mirror 105, only one color of the laser light sources 101 incident on the polygon mirror 105 is used. It doesn't matter.

  The trajectory of the light beam deflected by the polygon mirror 105 is referred to as a scanning line. One scanning line writes an electrostatic latent image of a predetermined width. Since the photosensitive drum 11 is rotationally driven by the motor 112, an electrostatic latent image for one page is formed on the photosensitive drum 11 by scanning the rotated photosensitive drum 11 with the light beam deflected by the polygon mirror 105 a plurality of times. It is formed.

  FIG. 4A is a control block diagram of the image forming apparatus. When image data of a document read using a scanner (not shown) is input, the image generation unit 201 performs image processing on the image data to generate image data for printing. The image data for printing is transferred to the LD driving unit 203 via the video control 202. The video control 202 controls the writing timing in the main scanning direction and the writing timing in the sub scanning direction, and adjusts the timing at which data is transferred to the LD driving unit 203. The main scanning timing and the sub scanning timing are determined based on a reference signal (BD signal). The LD driving unit 203 controls the exposure time of the light beam so that the blinking timing according to the image data for printing is reached. The current control unit 205 sets the intensity (laser light amount) of the light emitted from the laser light source 101. The current supplied to the laser light source 101 is controlled so as to be a value.

  The polygon mirror 105 having a plurality of mirror surfaces is driven to rotate by driving a polygon motor 106. The polygon rotation control unit 204 applies a current to the polygon motor 106 based on the rotation control signal input from the CPU 120. The CPU 120 controls the current supplied from the polygon rotation control unit 204 to the polygon motor 106 so that the output timing of the reference signal output from the BD 114 becomes a predetermined timing. The CPU 120 and the polygon rotation control unit 204 function as a drive control unit that controls the rotation speed of the polygon mirror 105. The light beam emitted from the laser light source 101 scans the photosensitive drum 11 by the rotation of the polygon mirror 105. After the light beam emitted from the laser light source 101 is reflected by the collimator lens 102 and the reflection mirror 109, the light beam is detected by the BD 114. Based on the result of the BD 114 receiving the light beam, the BD 114 outputs a BD signal as a reference signal to the CPU 120. The temperature sensor 206 functions as a temperature detection unit that detects the temperature in the image forming apparatus. The pattern detection sensor 31 detects a pattern image on the intermediate transfer belt 16 and outputs the detection result to the CPU 120 as an analog signal. The temperature measured by the temperature sensor 206 and the detection result of the pattern detection sensor 31 are stored in the storage unit 121.

  FIG. 4B is a block diagram showing an internal configuration of the BD 114, and FIG. 4C shows a signal waveform inside the BD 114. FIG. A photodiode is used as a light receiving element in the BD 114, and a current value Ip corresponding to the amount of light beam reflected by the reflection mirror 109 (the intensity of light received during a predetermined detection time) flows. The current value Ip flowing through the photodiode is converted into the voltage Vip by the current-voltage conversion unit 211 and input to the peak hold unit 212 and the comparator 213, respectively.

  The peak hold unit 212 includes a peak hold circuit that holds a peak voltage of the voltage Vip (the lower side in the + direction and the upper side in the − direction in FIG. 4C) by a hold capacitor. In the present embodiment, charging is performed until the potential difference between both ends of the hold capacitor becomes equal to the maximum value of the voltage Vip. The peak hold unit 212 sets the voltage at a predetermined ratio (for example, output voltage when the BD 114 is in a non-light-receiving state + peak hold voltage × 30%) to the comparator 213 as the threshold voltage Vth with respect to the potential difference between both ends of the hold capacitor. Set. The comparator 213 compares the output voltage Vip of the photodiode with the threshold voltage Vth, and outputs a BD signal when the output voltage Vip is higher than the threshold voltage Vth.

  FIG. 5 shows the pattern image N transferred to the intermediate transfer belt 16. The pattern images y1, y2, y3, y4, and y5 are a yellow pattern image group Ny. The pattern images m1, m2, m3, m4, and m5 are a magenta pattern image group Nm. The pattern images c1, c2, c3, c4, and c5 are a cyan pattern image group Nc. The pattern images k1, k2, k3, k4, and k5 are a black pattern image group Nk.

  The patterns Ny, Nm, Nc, and Nk are transferred from the photosensitive drums 11a to 11d to the intermediate transfer belt 16. The patterns Ny, Nm, Nc, and Nk are formed using a predetermined laser intensity. The patterns Ny, Nm, Nc, and Nk are formed in an end region in a direction orthogonal to the direction in which the intermediate transfer belt 16 moves with a predetermined width and interval.

  Here, the black pattern Nk will be described. The pattern images k1, k2, k3, k4, and k5 are formed using light beams having different intensities. The intensity of the light beam at the time of forming each pattern image is set to satisfy k1> k2> k3> k4> k5. The higher the intensity of the light beam, the higher the density of the pattern image. The yellow pattern images y1 to y5, the magenta pattern images m1 to m5, and the cyan pattern images c1 to c5 are similarly formed with different light beam intensities.

  FIG. 6 is a diagram showing the relationship between the pattern detection sensor 31 and the pattern N transferred to the intermediate transfer belt 16.

  The pattern detection sensor 31 includes a light emitting element 311 and light receiving elements 312 and 313. The light emitting element 311 uses an LED, and the light receiving element 312 uses a phototransistor (Ptr). The light receiving element 312 is disposed at a position where regular reflection light from the intermediate transfer belt 16 and the pattern image N is received, and the light receiving element 313 is disposed at a position where irregular reflection light from the intermediate transfer belt 16 and the pattern image N is received. The

  FIG. 7A shows changes in the peak hold voltage when the light amount (intensity) of the light beam emitted from the laser light source 101 is changed from 100% to 10%. In FIG. 7A, the peak hold voltage V81 is higher than the peak hold voltage V82.

  When the light amount is reduced from 100% to 10% at time t1, the peak hold voltage V81 at the light amount 100% is reduced to the peak hold voltage V82. When the internal temperature of the image forming apparatus was the temperature T1, the peak hold voltage V82 was reached at time t2, as indicated by the solid line L81. On the other hand, when the internal temperature of the image forming apparatus is a temperature T2 lower than the temperature T1, the peak hold voltage V82 is reached at time t3 later than time t2, as indicated by a dotted line L82. That is, it can be seen that the peak hold voltage of the peak hold unit 212 increases as the internal temperature of the image forming apparatus decreases and the time required for the peak hold voltage to stabilize to a value corresponding to the amount of received light.

  FIG. 7B shows the relationship between the internal temperature of the image forming apparatus and the response time of the peak hold voltage when the laser light quantity is changed from 100% to 10%. At the temperature T1, the peak hold voltage is stabilized at Δt21 (= t2-t1), while at the temperature T2, the peak hold voltage is stabilized at Δt31 (= t3-t1). The lower the temperature of the BD 114, the lower the response of the peak hold voltage and the longer the response time is required. The difference in response time is considered to be caused by the time required for charging or discharging the hold capacitor varies depending on the temperature.

  FIG. 8A shows the output voltage of the pattern detection sensor 31 and the pattern image when the pattern image Nk formed on the intermediate transfer belt 16 is detected with the internal temperature of the image forming apparatus at the temperature T1. A part of the signal waveform inside the BD 114 is extracted during the period. FIG. 8A shows an output signal from the light receiving element 313 when the pattern detection sensor 31 detects the pattern image Nk, and a laser light quantity (intensity) when the black pattern image Nk is formed. Further, FIG. 8A shows the output voltage Vip of the photodiode of the BD 114, the peak hold voltage, the threshold voltage Vth determined based on the peak hold voltage, and the BD signal output from the comparator 213. Note that FIG. 8 illustrates a black pattern image Nk as an example, but each output value is similarly output when yellow, magenta, and cyan pattern images are formed.

  The amount of light emitted from the light emitting element 311 of the pattern detection sensor 31 is adjusted so that the voltage Vb is output when the light receiving element 312 receives the reflected light from the intermediate transfer belt 16. The amount of light emitted from the light emitting element 311 of the pattern detection sensor 31 may be adjusted so as to output the voltage Vc when the light receiving element 313 receives the reflected light from the intermediate transfer belt 16.

  The pattern image Nk is formed on the intermediate transfer belt 16 in the order of a pattern image k71, a pattern image k72, a pattern image k73, a pattern image k74, and a pattern image k75. That is, the laser light amount of the laser light source 101 is switched in the order of the laser light amount Dk1, the laser light amount Dk2, the laser light amount Dk3, the laser light amount Dk4, and the laser light amount Dk5.

  When the pattern image Nk71 formed using the laser light quantity Dk1 passes through the detection area of the pattern detection sensor 31, the pattern detection sensor 31 outputs a voltage Vk71. Similarly, when the patterns Nk72 to Nk75 formed using the laser light amounts Dk2 to Dk5 pass through the pattern detection region, the output voltage of the pattern detection sensor 31 is output in the order of voltages Vk72, Vk73, Vk74, and Vk75.

  The current flowing through the photodiode of the BD 114 changes according to the laser light amount of the light beam emitted from the laser light source 101. The output current of the photodiode is converted into the voltage Vip by the current-voltage converter 211. In FIG. 8A, the alternate long and short dash line is the peak hold voltage of the peak hold unit 212. In FIG. 8A, the broken line is a threshold voltage Vth that is a predetermined ratio with respect to the peak hold voltage. The BD signal is output if the output voltage Vip is higher than the threshold voltage Vth.

  FIG. 8B is a diagram showing the relationship between the laser light quantity of the light beam emitted from the laser light source 101 and the output voltage of the pattern detection sensor 31. The voltages Vk71 to Vk75 output from the pattern detection sensor 31 are voltages according to the density of the pattern image N (k71 to k75). In FIG. 8B, the laser light quantity of the light beam and the output voltage of the pattern detection sensor 31 are linearly interpolated by a straight line L71.

  The laser light source 101 changes the amount of laser light necessary to form an image with a predetermined density depending on the temperature and humidity of the image forming apparatus. Therefore, the CPU 120 uses the laser light amount when forming an image based on image data. It is necessary to determine Dtgt. As shown in FIG. 8B, the CPU 120 forms the pattern image N (k71 to k75) using the laser light amounts Dk1 to Dk5, and the laser when the output voltage of the pattern detection sensor 31 becomes the target voltage Vtgt. The light amount Dtgt is calculated using the straight line L71. Note that the output voltage of the pattern detection sensor 31 when an image of a predetermined density is detected becomes the target voltage Vtgt, and this value is stored in advance in the storage means 121 such as a memory.

  FIG. 9 shows the output voltage of the pattern detection sensor 31 when the pattern image Nk formed on the intermediate transfer belt 16 is detected in the state where the internal temperature of the image forming apparatus is the temperature T2, and the BD 114 during the pattern image formation period. A part of the internal signal waveform is extracted. FIG. 9 shows an output signal from the light receiving element 313 when the pattern detection sensor 31 detects the pattern image Nk, and a laser light amount (intensity) when the black pattern image Nk is formed. Further, FIG. 8A shows the output voltage Vip of the photodiode of the BD 114, the peak hold voltage, the threshold voltage Vth determined based on the peak hold voltage, and the BD signal output from the comparator 213. Note that FIG. 8 illustrates a black pattern image Nk as an example, but each output value is similarly output when yellow, magenta, and cyan pattern images are formed.

  The amount of light emitted from the light emitting element 311 of the pattern detection sensor 31 is adjusted so that the voltage Vb is output when the light receiving element 312 receives the reflected light from the intermediate transfer belt 16. The amount of light emitted from the light emitting element 311 of the pattern detection sensor 31 may be adjusted so as to output the voltage Vc when the light receiving element 313 receives the reflected light from the intermediate transfer belt 16.

  The pattern image Nk is formed on the intermediate transfer belt 16 in the order of the pattern image k91, the pattern image k92, the pattern image k93, the pattern image k94, and the pattern image k95. That is, the laser light amount of the laser light source 101 is switched in the order of the laser light amount Dk1, the laser light amount Dk2, the laser light amount Dk3, the laser light amount Dk4, and the laser light amount Dk5.

  When the pattern image Nk91 formed using the laser light quantity Dk1 passes through the detection area of the pattern detection sensor 31, the pattern detection sensor 31 outputs a voltage Vk91. Similarly, when the patterns Nk92 to Nk95 formed using the laser light amounts Dk2 to Dk5 pass through the pattern detection region, the output voltage of the pattern detection sensor 31 is output in the order of voltages Vk92, Vk93, Vk94, and Vk95.

  At this time, as described with reference to FIG. 7, the BD 114 cannot follow the change in the laser light amount due to a decrease in the response speed of the peak hold circuit. If the pattern image Nk is formed every predetermined time in this state, the output voltage Vip becomes a value lower than the threshold voltage Vth, and the BD signal may not be output. Therefore, after the pattern image k93 is formed, the timing for switching the laser light amount from Dk3 to Dk4 is delayed until the potential difference between both ends of the hold capacitor of the BD 114 is sufficiently reduced.

  During the period in which the change of the laser light amount is delayed, the laser light source 101 irradiates the light of the laser light amount Dk3 toward the BD 114, but the peak hold voltage gradually decreases as shown in FIG. After sufficient time has elapsed until the peak hold voltage of the BD 114 is sufficiently lowered and the output voltage Vip corresponding to the light of the laser light amount Dk4 becomes higher than the threshold voltage Vth, the formation of the remaining pattern images k94 and k95 is resumed. To do.

  The time at which the pattern image N starts to be formed is changed in accordance with the peak hold voltage of the BD 114 that changes depending on the temperature in the image forming apparatus, and the time to change the laser light amount is delayed, regardless of the temperature inside the image forming apparatus. The BD signal can be output with high accuracy.

  Although an example of waiting for the peak hold voltage to decrease when switching from the laser light amount Dk3 to the laser light amount Dk4 is described here, the peak hold voltage is changed when switching from Dk1 to Dk2 or when switching from Dk4 to Dk5. It is good also as a structure which waits for it to fall. Further, the configuration in which the timing at which the laser light amount is switched from Dk3 to Dk4 has been described only once, but the configuration in which the laser light amount is switched every time each pattern image is formed may be delayed.

  Next, a laser light quantity correction sequence for determining the laser light quantity in order to form an image with a predetermined density will be described with reference to FIG. The CPU 120 performs a laser light quantity correction sequence when the number of pages of an image printed by the image forming apparatus reaches a predetermined number or when the internal temperature of the image forming apparatus detected by the temperature sensor 206 changes by a predetermined temperature or more. carry out. The laser light quantity correction sequence is executed by the CPU 120 reading a program stored in the storage unit 121.

  When the laser light quantity correction sequence is started, the CPU 120 starts to rotate the polygon mirror (S1001). The CPU 120 inputs a drive signal to the polygon motor 106 to rotate the polygon mirror 105. Next, the CPU 120 causes the laser light source 101 to emit light with a predetermined light amount (for example, Dk1) (S1002). In step S1002, the CPU 120 controls the light amount of the light beam emitted from the laser light source 101 to a predetermined light amount using the current control unit 205 and the LD driving unit 203. Next, the CPU 120 stands by until the rotation speed of the polygon mirror 105 reaches a predetermined speed. In step S1003, the CPU 120 controls the value of the drive current supplied from the polygon rotation control unit 204 to the polygon motor 106 so that the BD signal output from the BD sensor 114 is output at a predetermined timing.

  After the rotation speed of the polygon mirror 105 is stabilized at a predetermined speed, the CPU 120 causes the light emitting element 311 of the pattern detection sensor 31 to emit light (S1004). And CPU120 adjusts the irradiation light quantity of the light emitting element 311 so that the output voltage of a pattern detection sensor may be set to Vb (or Vc) (S1005-S1006). After the light emitting element 311 of the pattern detection sensor 31 is adjusted, the CPU 120 performs a delay time determination sequence (S1007). Since the delay time determination sequence will be described with reference to FIG. 11, description thereof is omitted here.

  After executing the delay time determination sequence, the CPU 120 causes the image forming units 10a, 10b, 10c, and 10d to start forming pattern images Ny, Nm, Nc, and Nk (S1008). In step S <b> 1008, the CPU 120 inputs a timing signal for controlling the timing of changing the laser light amount based on the delay time determined by the delay time determination sequence, and the pattern image Ny, Nm, Nc, Nk on the intermediate transfer belt 16. To form. The LD driving unit 203 changes the laser light amount of the laser light source at a timing based on data input from the video control 202, and forms a predetermined pattern image at a predetermined timing.

  The CPU 120 starts measurement of the pattern images Ny, Nm, Nc, and Nk using the pattern detection sensor 31 (S1009), and determines whether measurement of all pattern images is completed (S1010). If all the pattern images have not passed through the detection area, the CPU 120 continues to measure the pattern images Ny, Nm, Nc, and Nk until the measurement of all the pattern images is completed.

  When measurement of all pattern images is completed in step S1010, the laser light amount for forming an image with a predetermined density is determined by calculation as described in FIG. 8, and the laser light amount correction sequence is terminated.

  Next, the delay time determination sequence shown in step S1007 of the laser light quantity correction sequence in FIG. 10 will be described with reference to FIG. When the delay time determination sequence is executed, the CPU 120 detects the internal temperature of the image forming apparatus using the temperature sensor 206 (S1021). The CPU 120 determines whether or not the detected temperature is higher than the predetermined temperature (S1022). If the detected temperature is higher than the predetermined temperature, the delay time is set to 0 (S1023). If the detected temperature is higher than the predetermined temperature, the CPU 120 sets the timing for changing the laser light amount to a predetermined timing. The predetermined timing is determined after the current control unit 205 changes the light amount of the light beam to a target light amount (for example, Dk2, Dk3, etc.) after the pattern image downstream in the conveyance direction in which the intermediate transfer belt 16 is conveyed is completed. This is the timing when the time required for setting has elapsed.

  On the other hand, if the detected temperature is lower than the predetermined temperature in step S1022, the delay time is determined with reference to the detected temperature / delay time correspondence table (Table 1) stored in advance in the storage means 121 (S1024). Table 1 is a correspondence table between the detected temperature and the delay time. In the correspondence table, the delay time is determined for each temperature range. Note that the delay time is not limited to the configuration determined by referring to the table, and may be a method of calculating using an arithmetic expression for calculating the delay time determined by experiment. When the delay time is determined, the delay time determination sequence is terminated, and the process proceeds to step S1008 in FIG.

  According to the present embodiment, the timing for switching the set value of the laser light amount is changed according to the temperature in the image forming apparatus, so that the BD signal can be accurately obtained even when the internal temperature of the image forming apparatus is lowered. Can be output.

11a, 11b, 11c, 11d Photosensitive drum 13 Exposure device 14a, 14b, 14c, 14d Developer 101 Laser light source 105 Polygon mirror 106 Polygon motor 114 BD
120 CPU
204 Polygon rotation drive unit 206 Temperature sensor

Claims (6)

A photoreceptor,
A light source; a polygon mirror that deflects a light beam emitted from the light source; and a driving unit that rotationally drives the polygon mirror, and is emitted from the light source to form an electrostatic latent image on the photosensitive member. Exposure means for exposing the photoreceptor using the light beam deflected by the polygon mirror;
Developing the electrostatic latent image formed by the exposure means, and forming an image; and
A light receiving means for receiving the light beam deflected by the polygon mirror;
Output means for outputting a voltage corresponding to the intensity of the light beam received by the light receiving means;
A determination unit that includes a capacitor that is charged based on the voltage output from the output unit, and that determines a threshold voltage based on a potential difference between both ends of the capacitor;
Generating means for generating a reference signal based on the voltage output from the output means and the threshold voltage determined by the determining means;
Drive control means for controlling the drive means based on the reference signal generated by the generation means;
Temperature detection means for detecting temperature;
Setting means for setting the intensity of the light beam emitted from the light source;
After the setting means sets the intensity of the light beam emitted from the light source to the first intensity and forms an electrostatic latent image on the exposure means, the setting means causes the light beam emitted from the light source to In the case where the intensity is set to a second intensity lower than the first intensity and the exposure unit forms an electrostatic latent image, the setting unit includes the setting unit based on the temperature detected by the temperature detection unit. An image forming apparatus comprising: a control unit that controls a timing of changing the intensity of the light beam from the first intensity to the second intensity.   The control means sets the timing at which the setting means changes the intensity of the light beam from the first intensity to the second intensity when the temperature detected by the temperature detecting means is higher than a predetermined temperature. If the detected temperature of the temperature detecting means is lower than a predetermined temperature, the timing at which the setting means changes the intensity of the light beam from the first intensity to the second intensity is higher than the predetermined timing. The image forming apparatus according to claim 1, wherein the image forming apparatus is delayed. The control means determines the timing at which the setting means changes the intensity of the light beam from the first intensity to the second intensity based on the detected temperature of the temperature detecting means,
The timing determined by the control means when the first temperature is detected by the temperature detection means is determined by the control means when the second temperature lower than the first temperature is detected by the temperature detection means. The image forming apparatus according to claim 1, wherein the image forming apparatus is later than the determined timing. The exposure unit forms a first electrostatic latent image with the setting unit setting the intensity of the light beam emitted from the light source to the first intensity, and the setting unit emits the light from the light source. Forming a second electrostatic latent image with the intensity of the light beam being set to the second intensity,
The control unit controls a time from when the first electrostatic latent image is formed to when the second electrostatic latent image is formed based on a detection result of the temperature detecting unit. The image forming apparatus according to any one of claims 1 to 3. The density of the first measurement image formed based on the first electrostatic latent image and the second measurement image formed based on the second electrostatic latent image by the image forming unit. Measuring means for measuring,
Correction means for correcting the intensity of the light beam emitted from the light source based on the density of the first measurement image and the density of the second measurement image measured by the measurement means. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 1, wherein the drive control unit controls the drive unit based on a timing at which the reference signal is output from the output unit.