JP5061445B2 - Printhead characteristic measuring apparatus and light quantity correction method - Google Patents

Description

  The present invention relates to a characteristic measuring apparatus for correcting the light quantity of a print head for performing optical writing, and more specifically, to a characteristic measuring apparatus for a print head used for correcting a variation in light quantity generated between a plurality of light emitting elements. About.

In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, first, for example, the surface of a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged by a charging device. The charged photosensitive drum is exposed by an exposure device controlled based on the image data, and an electrostatic latent image is formed on the surface thereof. Subsequently, the electrostatic latent image formed on the photosensitive drum is made a visible image (toner image) by the developing device, and then the toner image is conveyed to the transfer unit along with the rotation of the photosensitive drum to be recorded. Electrostatic transfer on paper. Then, the toner image carried on the recording paper is subjected to a fixing process to complete the toner image.
As an exposure apparatus used here, an optical scanning method has been used in which a laser diode and a polygon mirror are combined to scan and expose a laser beam in the main scanning direction. However, in recent years, exposure using an LED print head (LPH: LED Print Head) configured by arranging a large number of LEDs (Light Emitting Diodes) in the main scanning direction due to demands for downsizing of the apparatus. Many devices are also used.

  LPH generally includes an LED array in which a large number of LEDs are arranged in a line, and a rod lens array in which a large number of rod lenses for imaging light output from the LEDs on the surface of the photosensitive drum are arranged in a line. It is configured. In the image forming apparatus, each LED of the LPH is driven based on the input image data to output light toward the photosensitive drum, and the light is imaged on the surface of the photosensitive drum by the rod lens array. At the same time, the photosensitive drum is rotated in a predetermined direction (sub-scanning direction) and moved relative to LPH. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum.

However, in an LPH having a structure in which a plurality of light emitting elements (LEDs) are arranged in a line in the main scanning direction, variation in the amount of light of each light emitting element greatly affects image quality. That is, when there is a variation in the amount of light in each light emitting element, streaks in the sub-scanning direction and density unevenness in the main scanning direction occur, and image quality defects are likely to occur. For this reason, it is necessary to correct the light amount of each light emitting element arranged in the LPH so that the light amounts of all the light emitting elements are within a predetermined range.
Therefore, the following technique is disclosed as a conventional technique for correcting the light quantity of each light emitting element. That is, two correction values are given to each light emitting element to emit light, and the characteristic value in the exposure intensity distribution is measured with a two-dimensional CCD or the like for each correction value. Then, a correlation curve between the correction value and the characteristic value for each light emitting element is created from the measurement result, and a predetermined calculation process is performed based on the correlation curve to obtain a correction value for each light emitting element. There is a technique for obtaining the emitted light amount (see, for example, Patent Document 1). In addition, there is a technique for measuring the characteristic point of the light emitting element based on the light emission intensity distribution of the light emitting element obtained by the slit and determining the light amount correction value data (see, for example, Patent Document 2).

JP 2002-127492 A (page 7-9, FIG. 16) JP 11-227254 A (page 3-4, FIG. 9)

  By the way, for example, when the light quantity of each LED in the LPH is corrected using a technique such as Patent Document 1 and Patent Document 2 described above, it is necessary to accurately measure the light quantity of each LED. In this case, a sensor such as a CCD (Charge Coupled Device) or a PD (Photo Diode) is usually used as the light receiving element for measuring the light quantity of the LED.

However, a sensor such as a CCD or PD has a sensitivity characteristic that the sensitivity changes depending on the incident angle of incident light (incident light). Similarly, the photoreceptor that actually receives the exposure light in the image forming apparatus also has sensitivity characteristics depending on the incident angle of the incident light. The sensitivity characteristic with respect to the incident angle of the sensor is usually different from the sensitivity characteristic with respect to the incident angle of the photosensitive member.
On the other hand, even light emitted perpendicularly to the light receiving surface of the rod lens array from the LED passes through different optical paths in the rod lens due to the positional relationship between the rod lens and the LED. As a result, the incident angles of the light condensed on the focal plane of the rod lens array are different, and the incident light to the photosensitive member also has various incident angles within a predetermined range.

  Therefore, when measuring the light quantity of each LED in the LPH, if there is no correspondence between the incident angle of light incident on the sensor and the incident angle of light incident on the photosensitive member, Even if the light amount of each LED is corrected based on the measured light amount data, the surface potential on the uniformly charged photoconductor is set to a target value when the photoconductor is actually exposed in the image forming apparatus. It becomes difficult to set. As a result, there is a problem that an image formed by the image forming apparatus cannot obtain an appropriate image density and image gradation.

Accordingly, the present invention has been made to solve the technical problems as described above, and the object of the present invention is related to the sensitivity characteristics of the photoconductor mounted on the image forming apparatus with respect to the LED print head. It is to obtain light quantity correction value data.
Another object is to perform light quantity correction corresponding to the sensitivity characteristic of the photoreceptor in the LED print head.

  For this purpose, the printhead characteristic measuring apparatus according to the present invention includes a plurality of light emitting elements arranged in a line, and data for correcting the light amount of the printhead that condenses the light from the light emitting elements on the condensing surface. A characteristic measuring device for measuring the light emitting element disposed on the print head and measuring the amount of light of each light emitting element, and the incident angle of the light from the light emitting element on the light collection surface And an optical system that uniformly compresses and collects light on the sensor regardless of the image height.

Here, in the optical system, the incident angle θ of the light from the light emitting element to the light collecting surface and the incident angle θ ′ to the sensor do not depend on the image height on the light collecting surface, and θ ′ = αθ. It can be characterized by substantially satisfying the relationship (α is a constant). Further, the optical system may be configured by a double-sided telecentric optical system. In particular, the optical system includes a first lens, a second lens disposed so that an object-side focal point coincides with an image-side focal point of the first lens, an image-side focal point of the first lens, and a second lens. It is also possible to include a first aperture disposed at a position where the object side focal point of the lens coincides. Furthermore, the optical system may further include a second diaphragm that restricts light incident from the print head to light having an object height within a predetermined range at the object-side focal position of the first lens. .
In addition, the sensor may be configured by a line CCD or a photodiode.

  Further, the present invention is regarded as a light amount correction method for a print head. The light amount correction method for a print head according to the present invention is a print head in which a plurality of light emitting elements are arranged in a line and light from the light emitting elements is exposed to a photosensitive member. A light amount correction method using an optical system that focuses light incident at an incident angle within a predetermined range from a print head on a sensor at an incident angle uniformly compressed at a predetermined magnification without depending on the image height. The optical system that collects light on the sensor and calculates light amount correction value data for correcting the amount of light in each light emitting element based on the amount of light collected on the sensor. The magnification is set so that the sensitivity of the photosensitive member at the incident angle of the light incident from the head and the sensitivity of the sensor at the compressed incident angle of the light condensed on the sensor are substantially the same. It is.

Here, in the optical system, the incident angle of light incident from the print head is N °, the incident angle to the sensor showing the same sensitivity as the sensitivity of the photosensitive member at the incident angle N ° is M °, and the magnification α is α. = M / N can be set. Further, the optical system includes a first lens having a focal length f _1, and a second lens having a focal length f _2, and the image-side focal point of the first lens and the object side focal point of the second lens matches It is characterized by being arranged such that f ₂ / f ₁ = N / M. Furthermore, the optical system further includes a first diaphragm disposed at a position where the image side focal point of the first lens coincides with the object side focal point of the second lens, and the first diaphragm is incident from the print head. The incident angle θ of the emitted light may be set so as to pass light in a range of −N ° ≦ θ ≦ N °.

  Further, the present invention is regarded as a print head, and the print head of the present invention is a print head that exposes a photoreceptor to form an electrostatic latent image, and includes a plurality of light emitting elements arranged in a line, and the light emitting elements Based on the light amount correction data for correcting each light amount, the light amount correction data generated corresponding to the incident light angle dependency of the photosensitive member, and the light amount correction data stored in the memory The light amount correction data stored in the memory is measured by a sensor system having an incident light angle dependency substantially equal to the incident light angle dependency of the photosensitive member. It is generated based on the light quantity data.

  Here, the sensor system is a sensor that measures the amount of light, and the incident angle θ of the light from the light emitting element and the outgoing angle θ ′ to the sensor do not depend on the image height, and θ ′ = αθ (α is a constant). And an optical system that substantially satisfies the above relationship. In particular, the optical system of the sensor system can be characterized in that it is composed of a double-sided telecentric optical system. Further, the light emitting elements may be arranged in a staggered manner for each of the plurality of light emitting elements.

Further, the present invention is regarded as an image forming apparatus. The image forming apparatus of the present invention includes a photoconductor and a print head that exposes the photoconductor to form an electrostatic latent image, and the print heads are arranged in a line. A plurality of light emitting elements, a light amount correction data for correcting the light amount of each of the light emitting elements, and a memory storing light amount correction data generated corresponding to the incident light angle dependency of the photosensitive member, and a memory The light amount correction data stored in the memory is substantially equal to the incident light angle dependency of the photosensitive member. It is generated based on light amount data measured by a sensor system having light angle dependency.
Here, in the light amount correction data stored in the memory of the print head, the light amount of the light emitting element that emits light after being corrected by the light amount correction data and the potential of the electrostatic latent image formed on the photosensitive member are correlated. It can be characterized by being generated.

  According to the present invention, since the LPH is light amount corrected by the light amount correction value data corresponding to the sensitivity characteristic of the photoconductor, it is possible to achieve an appropriate image density and image gradation in the image forming apparatus.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an overall configuration of an image forming apparatus using an LED print head to be measured in the present embodiment. The image forming apparatus shown in FIG. 1 is a so-called tandem digital color printer 1, and includes an image forming process unit 10 that forms an image corresponding to image data of each color, a control unit 30 that controls the image forming process unit 10, For example, an image processing unit (IPS: Image Processing System) 40 that is connected to a personal computer (PC) 2 and an image reading device (IIT) 3 and performs predetermined image processing on image data received from these devices is provided. .

The image forming process unit 10 includes four image forming units 11Y, 11M, 11C, and 11K that are arranged in parallel at a predetermined interval. The image forming units 11Y, 11M, 11C, and 11K uniformly charge the surface of the photosensitive drum 12 as an image carrier that forms an electrostatic latent image and carries a toner image with a predetermined potential. The charger 13, the LED print head (LPH) 14 as an exposure device that exposes the photosensitive drum 12 charged by the charger 13, the developing device 15 that develops the electrostatic latent image obtained by the LPH 14, and the photosensitive after transfer A cleaner 16 for cleaning the surface of the body drum 12 is provided. Here, the image forming units 11Y, 11M, 11C, and 11K are configured in substantially the same manner except for the toner stored in the developing unit 15. The image forming units 11Y, 11M, 11C, and 11K respectively form yellow (Y), magenta (M), cyan (C), and black (K) toner images.
In addition, the image forming process unit 10 includes an intermediate transfer belt 21 to which the toner images of the respective colors formed on the photosensitive drums 12 of the image forming units 11Y, 11M, 11C, and 11K are transferred in a multiple manner, and the image forming units 11Y and 11Y. A primary transfer roll 22 as a primary transfer charger for sequentially transferring (primary transfer) each color toner image of 11M, 11C, and 11K to the intermediate transfer belt 21, and a superimposed toner image transferred onto the intermediate transfer belt 21 as a recording material (recording) A secondary transfer roll 23 serving as a secondary transfer charger that performs batch transfer (secondary transfer) on the paper P, which is a paper, and a fixing device 25 that fixes the secondary transferred image on the paper P.

  In the digital color printer 1 of the present embodiment, the image forming process unit 10 performs an image forming operation based on a control signal such as a synchronization signal supplied from the control unit 30. At that time, the image data input from the PC 2 or IIT 3 is subjected to image processing by the image processing unit 40 and supplied to each of the image forming units 11Y, 11M, 11C, and 11K via the interface. In the yellow image forming unit 11Y, for example, the surface of the photosensitive drum 12 uniformly charged at a predetermined potential by the charger 13 is exposed by the LPH 14 that emits light based on the image data obtained from the image processing unit 40. Thus, an electrostatic latent image is formed on the photosensitive drum 12. The formed electrostatic latent image is developed by the developing device 15, and a yellow toner image is formed on the photosensitive drum 12. Similarly, magenta, cyan, and black toner images are formed in the image forming units 11M, 11C, and 11K.

The color toner images formed by the image forming units 11Y, 11M, 11C, and 11K are sequentially electrostatically attracted by the primary transfer roll 22 onto the intermediate transfer belt 21 that rotates in the direction of arrow A in FIG. A toner image superimposed on the belt 21 is formed. The superimposed toner image is conveyed to a region (secondary transfer portion) where the secondary transfer roll 23 is disposed as the intermediate transfer belt 21 moves. When the superimposed toner image is conveyed to the secondary transfer unit, the paper P is supplied to the secondary transfer unit in accordance with the timing at which the toner image is conveyed to the secondary transfer unit. Then, the superimposed toner images are collectively electrostatically transferred onto the conveyed paper P by the transfer electric field formed by the secondary transfer roll 23 in the secondary transfer portion.
Thereafter, the sheet P on which the superimposed toner image has been electrostatically transferred is peeled off from the intermediate transfer belt 21 and conveyed to the fixing device 25 by the conveying belt 24. The unfixed toner image on the paper P conveyed to the fixing device 25 is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 25. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge mounting portion (not shown) provided in the discharge portion of the image forming apparatus.

  FIG. 2 is a view showing a configuration of an LED print head (LPH) 14 that is an exposure unit. 2, the LPH 14 includes a housing 61 as a support, a self-scanning LED array (SLED) 63 constituting a light emitting unit, and a drive circuit (signal generation circuit) 100 (drive signal generation means for driving the SLED 63 and SLED 63). The LED circuit board 62 and the rod lens array 64, which are optical members for forming an image of the light from the SLED 63 on the surface of the photosensitive drum 12, and the rod lens array 64 are supported from the outside. A shielding holder 65 and a leaf spring 66 for urging the housing 61 toward the rod lens array 64 are provided.

The housing 61 is formed of a block or sheet metal such as aluminum or SUS, and supports the LED circuit board 62. The holder 65 supports the housing 61 and the rod lens array 64, and is set so that the light emitting point of the SLED 63 and the focal point of the rod lens array 64 coincide. Furthermore, the holder 65 is configured to seal the SLED 63. Therefore, it is possible to prevent dust from adhering to the SLED 63 from the outside. On the other hand, the leaf spring 66 urges the LED circuit board 62 toward the rod lens array 64 via the housing 61 so as to maintain the positional relationship between the SLED 63 and the rod lens array 64.
The LPH 14 configured as described above is configured to be movable in the optical axis direction of the rod lens array 64 by an adjustment screw (not shown), and the imaging position (focal plane) of the rod lens array 64 is the surface of the photosensitive drum 12. It is adjusted so that it is located above.

As shown in FIG. 3 (plan view of the LED circuit board 62), the LED circuit board 62 includes, for example, SLEDs 63 composed of 58 SLED chips (CHIP1 to CHIP58) in parallel with the axial direction of the photosensitive drum 12. It is arranged in a row with high accuracy. In this case, as shown in FIG. 4 (a diagram for explaining a connecting portion of each SLED chip), each LED array is connected to each other at the end boundary of the LED array arranged in each SLED chip (CHIP1 to CHIP58). The SLED chips are alternately arranged in a staggered manner so as to be continuously arranged at the connecting portions. In FIG. 4, a connecting part of CHIP1, CHIP2, and CHIP3 is shown as an example.
The LED circuit board 62 includes a signal generation circuit 100, a level shift circuit 104, a three-terminal regulator 101 for stabilizing the output voltage, an EEPROM 102 for storing light amount correction value data in the SLED 63, the digital color printer 1 main body, and the like. Is provided with a harness 103 for transmitting and receiving signals.

Next, the wiring configuration on the LED circuit board 62 will be described.
FIG. 5 is a diagram showing a wiring diagram formed on the LED circuit board 62. As shown in FIG. 5, on the LED circuit board 62, a + 3.3V power line 105 that supplies power to each SLED chip, a grounded (GND) power line 106, and the signal generation circuit 100 to each SLED chip. Signal lines 107 (107_1 to 107_58) for transmitting lighting signals ΦI (ΦI1 to ΦI58), signal lines 108 (108_1 to 108_6) for transmitting transfer signals CK1 (CK1_1 to 1_6), and transfer signals CK2 (CK2_1 to 2_6) ) For transmitting signal lines 109 (109_1 to 109_6).
And the lighting signal (PHI) I with respect to CHIP1-CHIP58 is input into each SLED chip (CHIP1-CHIP58) via the signal line 107. FIG. Further, the transfer signal CK1 (CK1_1 to 1_6) is input to the CHIP1 to CHIP58 via the signal line 108, and the transfer signal CK2 (CK2_1 to 2_6) is input to the CHIP1 to CHIP58 via the signal line 109, respectively.

Next, the circuit configuration of the SLED 63 will be described.
FIG. 6 is a diagram for explaining the circuit configuration of the SLED 63. The SLED 63 of this embodiment is connected to the signal generation circuit 100 via the level shift circuit 104. The level shift circuit 104 has a configuration in which a resistor R1B and a capacitor C1, and a resistor R2B and a capacitor C2 are arranged in parallel, one end of which is connected to the input terminal of the SLED 63, and the other end of the signal generating circuit 100. Connected to the output terminal. Based on the transfer signals CK1R and CK1C and the transfer signals CK2R and CK2C output from the signal generation circuit 100, the transfer signal CK1 and the transfer signal CK2 are output to the SLED 63.
In addition, although 58 SLED chips are arranged in series in the SLED 63 of the present embodiment, only one SLED chip is shown in FIG. In the following description, the SLED chip is referred to as SLED 63 for convenience.

As shown in FIG. 6, the SLED 63 includes 128 thyristors S1 to S128 as switching elements, 128 LEDs L1 to L128 as light emitting elements, 128 diodes D1 to D128, and 128 resistors R1 to R128. In addition, the transfer current limiting resistors R1A and R2A are configured to prevent an excessive current from flowing through the signal line.
Here, a part mainly composed of thyristors S1 to S128 and diodes D1 to D128 for controlling supply of current to the LEDs L1 to L128 is referred to as a transfer unit.

In the SLED 63 of the present embodiment, the anode terminals (input terminals) A1 to A128 of the thyristors S1 to S128 are connected to the power supply line 105. A power supply voltage VDD (VDD = + 3.3 V) is supplied to the power supply line 105.
A transfer signal CK1 is transmitted from the signal generation circuit 100 to the cathode terminals (output terminals) K1, K3,..., K127 of the odd-numbered thyristors S1, S3,. Is done.
.., S128 to the even-numbered thyristors S2, S4,..., S128 from the signal generation circuit 100 through the level shift circuit 104 and the transfer current limiting resistor R2A. CK2 is transmitted.

On the other hand, gate terminals (control terminals) G1 to G128 of the thyristors S1 to S128 are respectively connected to the power supply line 106 via resistors R1 to R128 provided corresponding to the thyristors S1 to S128. The power supply line 106 is grounded (GND).
The gate terminals G1 to G128 of the thyristors S1 to S128 are connected to the gate terminals of the LEDs L1 to L128 provided corresponding to the thyristors S1 to S128, respectively.
Furthermore, the cathode terminals of the diodes D1 to D128 are connected to the gate terminals G1 to G128 of the thyristors S1 to S128. The gate terminals G1 to G127 of the thyristors S1 to S127 are connected to the anode terminals of the next-stage diodes D2 to D128, respectively. That is, the diodes D1 to D128 are connected in series with the gate terminals G1 to G127 interposed therebetween.
The anode terminal of the diode D1 is connected to the signal generation circuit 100 via the transfer current limiting resistor R2A and the level shift circuit 104, and the transfer signal CK2 is transmitted. Further, the cathode terminals of the LEDs L1 to L128 are connected to the signal generation circuit 100, and the lighting signal ΦI is transmitted.

  Further, the light shielding mask 50 is disposed in the SLED 63 so as to cover the thyristors S1 to S128 and the diodes D1 to D128 in the transfer unit. This is because during the image forming operation, light emission from the thyristors S1 to S128 in the on state and current is flowing, and from the diodes D1 to D128 in the current flow state is blocked, and unnecessary light is removed from the photoconductor. It is provided to suppress exposure of the drum 12.

Next, a signal (drive signal) for driving the SLED 63 output from the signal generation circuit 100 and the level shift circuit 104 will be described.
FIG. 7 is a timing chart showing drive signals output from the signal generation circuit 100 and the level shift circuit 104. Note that the timing chart shown in FIG. 7 shows a case where all LEDs perform optical writing (light emission).
(1) First, when a reset signal (RST) is input from the image forming apparatus to the signal generation circuit 100, the signal generation circuit 100 transfers the transfer signal CK1C to a high level (hereinafter referred to as “H”) and transfers. The signal CK1R is set to “H”, the transfer signal CK1 is set to “H”, the transfer signal CK2C is set to low level (hereinafter referred to as “L”), the transfer signal CK2R is set to “L”, and the transfer signal CK2 is set. Is set to a low level (“L”), and all thyristors S1 to S128 are set to an off state (FIG. 7A).
(2) Following the reset signal (RST), the line synchronization signal Lsync output from the signal generation circuit 100 becomes “H” (FIG. 7A), and the operation of the SLED 63 is started. Then, in synchronization with the line synchronization signal Lsync, as shown in FIGS. 7E, 7F, and 7G, the transfer signal CK2C and the transfer signal CK2R are set to “H”, and the transfer signal CK2 is set to “H”. (FIG. 7B).
(3) Next, as shown in FIG. 7C, the transfer signal CK1R is set to “L” (FIG. 7C).

(4) Subsequently, as shown in FIG. 7B, the transfer signal CK1C is set to “L” (FIG. 7D).
In this state, the gate current of the thyristor S1 starts to flow. At that time, the tri-state buffer B1R of the signal generation circuit 100 is set to high impedance (Hiz) to prevent current backflow.
Thereafter, the thyristor S1 starts to be turned on by the gate current of the thyristor S1, and the gate current gradually increases. At the same time, when a current flows into the capacitor C1 of the level shift circuit 104, the potential of the transfer signal CK1 also gradually increases.

(5) After a predetermined time (the time when the transfer signal CK1 potential becomes close to GND) elapses, the tristate buffer B1R of the signal generation circuit 100 is set to “L” (FIG. 7E). As a result, the potential of the signal line Φ1 and the potential of the transfer signal CK1 rise due to the rise of the gate G1 potential, and accordingly, a current starts to flow to the resistor R1B side of the level shift circuit 104. On the other hand, the current flowing into the capacitor C1 of the level shift circuit 104 gradually decreases as the potential of the transfer signal CK1 increases.
When the thyristor S1 is completely turned on and becomes a steady state, a current for maintaining the on state of the thyristor S1 flows to the resistor R1B of the level shift circuit 104, but does not flow to the capacitor C1.
At this time, as shown in FIG. 7B, the tri-state buffer B1C of the signal generating circuit 100 is set to high impedance (Hiz) (FIG. 7E).

  (6) With the thyristor S1 completely turned on, the lighting signal ΦI is set to “L” as shown in FIG. 7H (FIG. 7F). At this time, since the potential of the gate G1> the potential of the gate G2, the LED L1 having a thyristor structure is turned on earlier and lights up. As the LED L1 is turned on, the potential of the signal line Φ1 rises, so that the LEDs after the LED L2 are not turned on. That is, for the LEDs L1, L2, L3, L4,..., Only the LED L1 having the highest gate voltage is turned on (lighted).

(7) Next, as shown in FIG. 7 (F), when the transfer signal CK2R is set to “L” (FIG. 7 (g)), a current flows as in FIG. A voltage is generated across the capacitor C2 104.
(8) As shown in FIG. 7E, when the transfer signal CK2C is set to “L” in this state (FIG. 7H), the thyristor switch S2 is turned on.
(9) Then, as shown in FIGS. 7B and 7C, when the transfer signals CK1C and CK1R are simultaneously set to “H” (FIG. 7I), the thyristor switch S1 is turned off and passes through the resistor R1. As a result, the potential of the gate G1 gradually decreases. At that time, the thyristor switch S2 is completely turned on. Therefore, by turning on / off the lighting signal ΦI corresponding to the image data from the lighting signal terminal ID, the LED L2 can be turned on / off. In this case, since the potential of the gate G1 is already lower than the potential of the gate G2, the LED L1 is not turned on.

(10) The above-described operation is sequentially performed to sequentially turn on the LEDs L1 to L128.
Then, after the “transfer operation period” in FIG. 7 in which the terminal LED L128 is extinguished, the transfer signals CK1C and CK1R are set to “H”, the transfer signal CK1 is set to “H”, and the transfer signals CK2C and CK2R are set to “H”. The transfer signal CK2 is set to “H” as “H”, and both the transfer signal CK1 and the transfer signal CK2 are kept in the “H” state for a predetermined time (“transfer thyristor is turned off” in FIG. 7). As a result, all thyristors S1 to S128 are turned off. Therefore, in this state, no current flows through all the thyristors S1 to S128, so that the thyristors S1 to S128 are held in the off state (not lit).

(11) Further, after the transfer signals CK1 and CK2 are both kept at "H" for a predetermined time, the transfer signals CK2C and CK2R are set to "L" and the transfer signal CK2 is set to "L" (in FIG. 7, “Period during which no current flows through the transfer unit”). Thereby, since no current flows through the diodes D1 to D128, all the diodes D1 to D128 are also kept in the non-lighted state.
As a result, during the unsteady operation including the state where the photosensitive drum 12 (see FIG. 1) stops rotating after the lighting signal ΦI is output and the image formation is completed, the transfer unit of the SLED 63 is operated. No current is applied. For this reason, in a state where the photoconductor 12 is stopped from rotating, current does not flow through the thyristors S1 to S128 and the diodes D1 to D128 arranged in the transfer unit together with the LEDs L1 to L128, and the thyristors S1 to S128 and Since no light is emitted from the diodes D1 to D128, unnecessary exposure of the photosensitive drum 12 is suppressed.

Next, the configuration of the signal generation circuit 100 will be described in detail.
FIG. 8 is a block diagram showing a configuration of the signal generation circuit 100. The signal generation circuit 100 includes an image data development unit 110, a density unevenness correction data unit 112, a timing signal generation unit 114, a reference clock generation unit 116, and lighting time control / corresponding to each SLED chip (CHIP1 to CHIP58). The driving unit 118-1 to 118-58 constitutes a main part.
Image data is serially transmitted from the image processing unit (IPS) 40 to the image data development unit 110. The image data development unit 110 divides the transmitted image data into image data for each SLED chip (CHIP1 to CHIP58) and 1st to 128th dot, 129 to 256th dot,..., 7297 to 7424th dot. The image data developing unit 110 is connected to the lighting time control / drive units 118-1 to 118-58, and outputs the divided image data to the corresponding lighting time control / drive units 118-1 to 118-58.

The density unevenness correction data unit 112 generates density unevenness correction data for correcting image density unevenness at the time of image formation caused by variations in the amount of light for each LED in the SLED 63, and the lighting time control / drive unit 118- 1 to 118-58. This density unevenness correction data is formed, for example, for each LED as the number of pulses set according to variations in the amount of light by each LED.
The EEPROM 102 stores light amount correction value data for each LED, which is measured and calculated by a light profile measuring apparatus 200 described later, and other data for correcting density unevenness as necessary. When the machine power is turned on, light amount correction value data for each LED is downloaded from the EEPROM 102 to the density unevenness correction data unit 112. The density unevenness correction data unit 112 generates density unevenness correction data based on the acquired light amount correction value data for each LED, and further, based on the light amount correction value data and other data as necessary, It is output to the lighting time control / drive units 118-1 to 118-58.

The reference clock generation unit 116 is connected to the control unit 30, the timing signal generation unit 114, and the lighting time control / drive units 118-1 to 118-58 of the main body.
As shown in FIG. 9 (a block diagram illustrating the configuration of the reference clock generation unit 116), the reference clock generation unit 116 includes a crystal oscillator 140, a frequency divider 1 / M142, a frequency divider 1 / N144, and a phase comparator. 146 and a voltage controlled oscillator 148, and a lookup table (LUT) 132. The LUT 132 stores a table for determining the frequency division ratios M and N based on the light amount adjustment data from the control unit 30. The crystal oscillator 140 is connected to the frequency divider 1 / N144, oscillates at a predetermined frequency, and outputs the oscillated signal to the frequency divider 1 / N144. The frequency divider 1 / N 144 is connected to the LUT 132 and the phase comparator 146 and divides the signal oscillated by the crystal oscillator 140 based on the frequency division ratio N determined by the light amount adjustment data from the LUT 132. The phase comparator 146 is connected to the frequency divider 1 / M142, the frequency divider 1 / N144, and the voltage controlled oscillator 148, and the output signal from the frequency divider 1 / M142 and the frequency divider 1 / N144. Is compared with the output signal. The control voltage supplied to the voltage controlled oscillator 148 is controlled according to the comparison result (phase difference) by the phase comparator 146. The voltage controlled oscillator 148 outputs a clock signal at a frequency based on the control voltage. In the present embodiment, a control voltage corresponding to a frequency that divides the possible lighting period into 256 is supplied, a clock signal having this frequency is generated, and all the lighting time control / drive units 118-1 to 118-58 are supplied. Output. The voltage controlled oscillator 148 is also connected to the frequency divider 1 / M142, and the clock signal output from the voltage controlled oscillator 148 is also branched and input to the frequency divider 1 / M142. The frequency divider 1 / M 142 divides the clock signal fed back from the voltage controlled oscillator 148 based on the frequency division ratio M determined by the light amount adjustment data from the LUT 132.

The timing signal generation unit 114 is connected to the control unit 30 and the reference clock generation unit 116, and is synchronized with the horizontal synchronization signal (Lsync) from the control unit 30 based on the oscillation signal from the reference clock generation unit 116. The transfer signals CK1R and CK1C and the transfer signals CK2R and CK2C are generated. The transfer signals CK1R and CK1C and the transfer signals CK2R and CK2C are transferred to the LPH 14 through the level shift circuit 140 as the transfer signal CK1 and the transfer signal CK2.
The timing signal generation unit 114 is connected to the density unevenness correction data unit 112 and the image data development unit 110 and is synchronized with the Lsync signal from the control unit 30 based on the oscillation signal from the reference clock generation unit 116. Thus, a data read signal for reading image data corresponding to each pixel from the image data development unit 110 and a data read for reading density unevenness correction data corresponding to each pixel (each LED) from the density unevenness correction data unit 112. A signal is output to each. Further, the timing signal generation unit 114 is also connected to the lighting time control / drive units 118-1 to 118-58 and is synchronized with the Lsync signal from the control unit 30 based on the oscillation signal from the reference clock generation unit 116. Thus, a trigger signal for starting lighting of the SLED 63 is output.

The lighting time control / drive units 118-1 to 118-58 correct the lighting time of each pixel (each LED) based on the density unevenness correction data, and generate a control signal for lighting each pixel of the SLED 63.
Specifically, as shown in FIG. 10 (block diagram for explaining the configuration of the lighting time control / drive unit 118), the lighting time control / drive units 118-1 to 118-58 are presettable digital one-shot multi A vibrator (PDOMV) 160, a linearity correction unit 162, and an AND circuit 170 are included. The AND circuit 170 is connected to the image data development unit 110 and the timing signal generation unit 114. When the image data from the image data development unit 110 is 1 (ON), the trigger signal (TRG) from the timing signal generation unit 114 is displayed. ) Is output to the PDOMV 160, and when the image data is 0 (OFF), the trigger signal is set not to be output. PDOMV 160 is connected to AND circuit 170, OR circuit 168, density unevenness correction data unit 112, and reference clock generation unit 116, and a reference clock corresponding to density unevenness correction data in synchronization with a trigger signal from AND circuit 170. Generate a number of lighting pulses.

  The linearity correction unit 162 corrects and outputs the lighting pulse signal from the PDOMV 160 in order to correct the variation in the light emission start time of each LED in the SLED 63. Specifically, the linearity correction unit 162 includes a plurality of delay circuits 164 (eight in this embodiment, 164-0 to 164-7), a delay selection register 166, a delay signal selection unit 165, and an AND circuit 167. , An OR circuit 168, and a lighting signal selection unit 169. The delay circuits 164-0 to 164-7 are connected to the PDOMV 160, and different times for delaying the lighting pulse signal from the PDOMV 160 are set. The delay selection register 166 is connected to the delay signal selection unit 165 and the lighting signal selection unit 169, and the delay selection register 166 stores delay selection data for each LED in the SLED 63 and lighting signal selection data. . Delay selection data and lighting signal selection data for each LED are measured in advance and stored in the EEPROM 102. The delay selection data and lighting signal selection data stored in the EEPROM 102 are downloaded to the delay selection register 166 via the density unevenness correction data unit 112 when the machine power is turned on. Note that a flash ROM can also be used as the storage means, and in that case, the flash ROM itself can function as the delay selection register 166.

The delay signal selection unit 165 is connected to the AND circuit 167 and the OR circuit 168, and is one of outputs from the delay circuits 164-0 to 164-7 based on the delay selection data stored in the delay selection register 166. Select one. The AND circuit 167 is a logical product of the lighting pulse signal from the PDOMV 160 and the delayed lighting pulse signal selected by the delay signal selection unit 165, that is, both the lighting pulse signal before the delay and the lighting pulse signal after the delay are in the lighting state. If there is, output a lighting pulse. The OR circuit 168 is a logical sum of the lighting pulse signal from the PDOMV 160 and the delayed lighting pulse signal selected by the delay signal selection unit 165, that is, at least one of the lighting pulse signal before the delay and the lighting pulse signal after the delay is in the lighting state. If so, a lighting pulse is output.
The lighting signal selection unit 169 selects one of the outputs from the AND circuit 167 or the OR circuit 168 based on the lighting selection data stored in the delay selection register 166. The selected lighting pulse is output to the LPH 14 via the MOSFET 172.

  Further, as shown in FIG. 8, a three-terminal regulator 101 is connected to the LPH 14, and a stable + 3.3V voltage is supplied from the three-terminal regulator 101 to the LPH 14.

Next, a method for measuring and calculating light amount correction value data related to the LPH 14 stored in the EEPROM 102 will be described. As described above, the light amount correction value data is data for correcting variations in the amount of light generated for each LED in the SLED 63 during image formation, and the density unevenness correction data unit 112 generates density unevenness correction data. This data is used at the time.
First, an optical profile measuring apparatus 200 as a characteristic measuring apparatus for measuring the exposure energy distribution (light quantity distribution) of the LPH 14 will be described. FIG. 11 is a diagram showing a configuration of the optical profile measuring apparatus 200. As shown in FIG. 11, the optical profile measuring apparatus 200 is an example of a sensor. As an example of the sensor, a light receiving surface is provided facing the light emitting unit (SLED 63) of the LPH 14, and a line CCD (line CCD) Charge Coupled Device) 261, which includes this line CCD 261 and uses the output from the line CCD 261 to measure the light quantity distribution from the LPH 14, and expands the light from the light emitting part (SLED 63) of the LPH 14 to the surface of the line CCD 261 A magnifying optical system 260 as an optical system for image formation, a moving stage 262 for moving the CCD board 270 with the direction (main scanning direction) in which the SLEDs 63 of the LPH 14 are arranged as the moving direction, and a stage driver 263 for moving the moving stage 262 at a constant speed , The drive signal is output to the LPH 14 and each S And a CCD interface 280 for processing the data signal transferred ED63 from LPH driver 264, CCD board 270 to turn on the.
The line CCD 261 and the magnifying optical system 260 constitute a sensor system that is a measurement unit in the optical profile measurement apparatus 200. Moreover, PD (Photo Diode) can also be used as a sensor.

Processing of the obtained data signal, movement control of the moving stage 262, control of the LPH driver 264, and the like are executed by a personal computer (PC) 266 that is a processing unit. The PC 266 includes a frame grabber 267 for capturing image data, a digital I / O 268 that controls the input of status signals and data signals, the output of control signals, and the like, a motor controller 269 that controls the drive of the stage driver 263, and the like. Yes. The moving stage 262 has a non-contact structure using, for example, an air bearing and a linear motor, and the motor controller 269 performs PLL control by feedback from the linear encoder, thereby realizing constant speed movement control of the CCD board 270. is doing.
The optical profile measuring apparatus 200 converts the data into a digital value and takes it into the PC 266 while moving the CCD board 270 having the line CCD 261 at a constant speed in the main scanning direction.

Here, in the optical profile measuring apparatus 200 of the present embodiment, the magnifying optical system 260 is an optical system that is telecentric on both sides (double-sided telecentric optical system or optical system) with respect to the wavelength (780 nm) of light emitted from the SLED 63 of the LPH 14. (Focal optical system).
FIG. 12 is a diagram for explaining the configuration of the magnifying optical system 260. As shown in FIG. 12, the magnifying optical system 260 at the barrel K, the object-side lens Len1 focal length _{f 1,} and the image side lens Len2 focal length _{f 2,} along the optical axis, The image-side focal point F ₁ ′ of the object-side lens Len1 and the object-side focal point F ₂ of the image-side lens Len2 are arranged so as to coincide with each other. The first diaphragm S1 is disposed at a position where the image side focal point F ₁ ′ of the object side lens Len1 and the object side focal point F ₂ of the image side lens Len2 coincide.
The object-side focal point F1 of the object-side lens Len1 is disposed so as to coincide with the focal plane Q1 (focal length f) of the rod lens array 64 of the LPH ₁₄ . A second diaphragm S2 is disposed at the object-side focal point F ₁ (focal plane Q1 of the rod lens array 64) of the object-side lens Len1.
Further, the sensor surface of the line CCD 261 is disposed so as to coincide with a surface orthogonal to the optical axis at the position of the image side focal point F ₂ ′ of the image side lens Len2. Note that the surface orthogonal to the optical axis at the position of the image side focal point F ₂ ′ of the image side lens Len2 is the focal plane Q2 of the magnifying optical system 260.

  In this way, by configuring the magnifying optical system 260 as a double-sided telecentric optical system, when the light emitted from the SLED 63 of the LPH 14 is collected by the rod lens array 64, it enters the focal plane Q1 at an incident angle θ. The light is incident on the focal plane Q2 of the magnifying optical system 260, that is, the sensor plane of the line CCD 261 at an incident angle αθ (= θ ′: α is a constant) regardless of the image height h at the focal plane Q1. It is possible to form a unique relationship between the incident angle θ on the focal plane Q1 and the incident angle θ ′ on the sensor surface of the line CCD 261. Here, the incident angle refers to an angle formed by the light beam and the optical axis (the same applies hereinafter).

This relationship can be derived as follows. In the double-sided telecentric optical system, light emitted from the same point on the focal plane Q1 of the rod lens array 64 is always parallel light in a region between the object side lens Len1 and the image side lens Len2. Therefore, the incident angle θ of the light incident on the focal plane Q1 and the incident angle θ ′ when entering the focal plane Q2 (sensor surface of the line CCD 261) through the magnifying optical system 260 are shown in FIG. ,
f ₁ · tan θ = f ₂ · tan θ ′ (1)
Holds. Here, since θ and θ ′ may be considered to be sufficiently small,
f ₁ · θ = f ₂ · θ ′ (2)
And can be approximated. Therefore,
θ ′ = αθ (3)
Can guide you. Here, α = 1 / β, and β is β = f ₂ / f _1, which is the magnification (h ′ / h) of the magnifying optical system 260.

  That is, in the optical profile measuring apparatus 200 of the present embodiment, the light incident on the focal plane Q1 of the rod lens array 64 is incident on the focal plane Q1 by using the magnifying optical system 260 configured with a bilateral telecentric optical system. Regardless of what image height h is emitted, light with any incident angle θ is converted into light with an incident angle αθ (= θ ′) that is uniformly compressed at a predetermined magnification α on the sensor surface of the line CCD 261. Will be.

  When the magnifying optical system 260 is constituted by an optical system other than the double-sided telecentric optical system, for example, when a telecentric optical system is used on the object side, the incident angle θ ″ on the sensor surface of the line CCD 261 is: When θ ″ = α′θ, the magnification α ′ is a function α ′ (h) with the image height h at the focal plane Q1 of the rod lens array 64 as a variable. That is, in this case, even if the incident angle θ at the focal plane Q1 is the same, the incident angle θ ″ (= α ′) at the sensor plane of the line CCD 261 is different because the image height h at the focal plane Q1 is different. Therefore, when an optical system other than the both-side telecentric optical system is used for the magnifying optical system 260, the incident angle θ at the focal plane Q1 on the sensor surface of the line CCD 261 is used. Cannot be compressed uniformly.

Incidentally, FIG. 13 is a diagram showing the optical paths of the light B1 and the light B2 emitted from different light emitting points (LEDs) of the SLED 63, respectively. As shown in FIG. 13, the rod lens array 64 has a refractive index distribution around its central axis even with the two lights B1 and B2 irradiated perpendicularly from the light emitting point toward the rod lens array 64. Thus, the optical path follows a different path depending on which part of the incident surface of the rod lens array 64 is incident. Therefore, the light B1 and the light B2 have different incident angles when entering the focal plane Q1 of the rod lens array 64. For example, in the example shown in FIG. 13, the light B1 enters perpendicularly to the focal plane Q1, while the light B2 enters the focal plane Q1 at an incident angle γ.
In addition, the light emitted from the light emitting point (LED) of the SLED 63 is actually emitted with a spread as shown by the dotted line in FIG. 13, and forms an image on the focal plane Q1 through a plurality of rod lenses. . However, in FIG. 13, in order to facilitate understanding, the portion with the strongest light intensity (solid line) is described to clarify the difference in the optical path. Therefore, the actual condensed light on the focal plane Q1 has a light amount distribution such that the solid line portion has the highest light intensity and becomes weaker along the periphery.

On the other hand, the photosensitive drum 12 provided in the image forming units 11Y, 11M, 11C, and 11K (see FIG. 1) and the line CCD 261 are incident on light sensitivity (hereinafter also simply referred to as “sensitivity”). It has a sensitivity characteristic (incident light angle dependency) that changes depending on the incident angle of light. FIG. 14 is a diagram showing the relationship between the sensitivity of the photosensitive drum (photosensitive member) 12 and the sensitivity of the line CCD (sensor) 261 and the incident angle of light incident on each. As shown in FIG. 14, the photosensitive drum (photosensitive member) 12 and the line CCD (sensor) 261 have different sensitivity characteristics with respect to the light incident angle.
That is, even if the light set to the same light amount is irradiated to the photosensitive drum 12 and the line CCD 261, if the incident angle of the irradiated light is different, the photosensitive drum 12 and the line CCD 261 are different. It will have a different sensitivity.

  As described above, due to the characteristics of the rod lens array 64, light from the LPH 14 enters the focal plane Q1 of the rod lens array 64 with various incident angles. In particular, as shown in FIG. 4, in the LPH 14, since the SLED chips (CHIP1 to CHIP58) are alternately arranged in a staggered manner, the incident angle to the focal plane Q1 is greatly different for each SLED chip. Therefore, when the light collected on the focal plane Q1 is collected on the line CCD 261 by a conventional optical profile measuring device and the light amount data is measured, the incident angle θ on the focal plane Q1 and the line CCD 261 are measured. A relationship of θ ″ = α ′ (h) · θ having a coefficient α ′ (h) with the image height h at the focal plane Q1 as a variable is generated between the incident angle θ ″ on the sensor surface. Therefore, even if the incident angle at the focal plane Q1 is θ, the incident angle θ ″ at the sensor plane of the line CCD 261 varies depending on the image height h at the focal plane Q1 of the light. Will have the same value.

Therefore, the light incident on the focal plane Q1 of the rod lens array 64 at the incident angle θ enters the photosensitive drum 12 at the incident angle θ (in the image forming apparatus, the surface of the photosensitive drum 12 is the focal point of the rod lens array 64). Therefore, in the conventional optical profile measuring apparatus, the incident angle θ of light incident on the photosensitive drum 12 and the incident angle θ ″ of light incident on the sensor surface of the line CCD 261 are: It cannot be uniquely associated with one-to-one.
That is, in the conventional optical profile measuring device, light having an incident angle θ incident on the photosensitive drum 12 is incident on the sensor surface of the line CCD 261 as an incident angle, for example, θ ₁ ′, depending on the difference in image height h. It has a plurality of values such as θ ₂ ′, θ ₃ ′,. Therefore, as shown in FIG. 14, the sensitivity at the incident angles θ ₁ ′, θ ₂ ′, θ ₃ ′,... Therefore, the sensitivity characteristic of the photosensitive drum 12 and the sensitivity characteristic of the line CCD 261 cannot be uniquely associated one-to-one.

  Therefore, the conventional optical profile measurement device cannot measure the light quantity of the LPH 14 in association with the sensitivity characteristic of the photosensitive drum 12. Thereby, light amount correction value data is generated based on the light amount data measured by the conventional light profile measuring device, and when the light amount of the LPH 14 is corrected by the light amount correction value data, the actual image forming apparatus When the photosensitive drum 12 is exposed by the LPH 14 and an electrostatic latent image is formed, a divergence occurs between the light amount assumed to obtain a predetermined latent image potential and the light amount actually irradiated from the LPH 14. It will be. That is, a phenomenon that a desired latent image potential cannot be obtained even when a predetermined amount of light is output from the LPH 14 occurs. As a result, even if the light amount correction value data is generated by the conventional optical profile measuring device and the photosensitive drum 12 is exposed by the LPH 14 corrected based on the light amount correction value data, the proper image density and image gradation are obtained. The inconvenience that it was not possible to have obtained.

On the other hand, in the optical profile measuring apparatus 200 of the present embodiment, the magnifying optical system 260 composed of a bilateral telecentric optical system is used. Thereby, the light incident on the focal plane Q1 of the rod lens array 64 does not depend on the image height h at the focal plane Q1, and the incident magnification θ is uniformly a predetermined magnification on the sensor plane of the line CCD 261. It is converted into an incident angle αθ (= θ ′) compressed by α (constant). Therefore, the incident angle θ of light incident on the photosensitive drum 12 and the incident angle θ ′ of light incident on the sensor surface of the line CCD 261 can be uniquely associated.
That is, the incident angle θ of the light incident on the photosensitive drum 12 is, for example, an incident angle θ ₁ ′, regardless of the image height h at the focal plane Q1 of the light when entering the sensor surface of the line CCD 261. Will have only one value. Therefore, as shown in FIG. 15, the sensitivity characteristic of the photosensitive drum 12 and the sensitivity characteristic of the line CCD 261 can be uniquely associated one-to-one.

  Therefore, the following becomes possible. That is, the opening angle of the rod lens array 64 used for optical writing is normally 12 to 23 ° with the optical axis as the center, and the light incident on the focal plane Q1 of the rod lens array 64 from the LPH 14 is normally incident angle −23. Since it is set in the range of ° ≦ θ ≦ 23 °, the incident angle θ of the light incident on the photosensitive drum 12 in the actual image forming apparatus is in the range of −23 ° ≦ θ ≦ 23 °. Accordingly, with reference to FIG. 15, the sensitivity of the photosensitive drum (photosensitive member) 12 at an incident angle of −23 ° ≦ θ ≦ 23 ° is in the range of 1 to q (0 <q <1). At this time, the range of the incident angle θ ′ where the sensitivity of the line CCD (sensor) 261 indicates 1 to q is set to −m ° ≦ θ ′ ≦ m °. Then, in the magnifying optical system 260, if the magnification α is set so that light having an incident angle θ = 23 ° incident on the focal plane Q1 is converted to an incident angle θ ′ = m ° on the sensor surface of the line CCD 261, With respect to light in an incident angle range of −23 ° ≦ θ ≦ 23 °, the sensitivity of the photosensitive drum (photosensitive member) 12 and the sensitivity of the line CCD (sensor) 261 can be substantially matched.

More specifically, light incident on the photosensitive drum 12 at 23 ° is incident at m ° on the sensor surface of the line CCD 261 by the magnifying optical system 260. Therefore, the sensitivity at the incident angle | θ | = 23 ° at the photosensitive drum 12 and the sensitivity at the incident angle | θ ′ | = m ° at the line CCD 261 are both q and coincide with each other from FIG.
Even in the range of the incident angle −23 ° <θ <23 °, the linear relationship of θ ′ = αθ is obtained from the above-described equation (3). Therefore, the sensitivity of the photosensitive drum 12 and the sensitivity of the line CCD 261 are different from each other. It will be approximately the same.
Accordingly, in this case, α = m / 23, that is, α = 1 / β as described above, and β is β = f ₂ / f ₁ , so that f ₂ / f ₁ = 23 / m. have a relationship as, the object-side lens Len1 focal length _{f 1,} a double telecentric magnifying optical system 260 with the image-side lens Len2 focal length _{f 2,} the incident angle -23 of ° ≦ θ ≦ 23 ° With respect to the light in the range, the sensitivity of the photosensitive drum (photosensitive member) 12 and the sensitivity of the line CCD (sensor) 261 can be substantially matched.
Here, the method of matching the sensitivity at the maximum incident angle has been described. However, an error between the sensitivity of the photosensitive drum (photosensitive member) 12 and the sensitivity of the line CCD (sensor) 261 using the above-described magnifying optical system 260 is described. It is also possible to set the above-described magnification α at a position (angle) at which the sum of squares is minimized, and match the sensitivity.

Further, when α = m / 23 is set, the opening of the first aperture stop S1 is set to the rod lens array 64 so that light in the range of θ <−23 ° and θ> 23 ° does not enter the line CCD 261. Is set so that only the light incident on the focal plane Q1 in the range of the incident angle −23 ° ≦ θ ≦ 23 ° is allowed to pass (see FIG. 12). This is necessary because, when shading correction is performed using a uniform light source, if the shading correction is performed including the influence on the light of the angle of the eye that does not enter when the light quantity of the LPH 14 is measured, an error from the measurement of the light quantity of the LPH 14 increases. is there.
Further, with respect to the opening of the second aperture stop S2, in order to prevent unnecessary light from entering the magnifying optical system 260, for example, the object point heights h <−0.5 mm and h> 0.5 mm that are out of the field of view. Is set to prevent the incidence of light. Usually, light outside the field of view is necessary because it tends to cause stray light in the lens system.

As described above, the optical profile measuring apparatus 200 according to the present embodiment uses the magnifying optical system 260 configured by the both-side telecentric optical system, and also has a predetermined incident angle (for example, light incident on the photosensitive drum 12 from the LPH 14). The maximum incident angle) is N °, the incident angle at the line CCD 261 showing the same sensitivity as that of the photosensitive member at the incident angle N ° is M °, and the focal length f ₁ of the object side lens Len1 and the image side lens Len2 The focal length f ₂ is set to be f ₂ / f ₁ = N / M. Thereby, the sensitivity of the photosensitive drum 12 and the sensitivity of the line CCD 261 can be substantially matched with respect to light in the incident angle range of −N ° ≦ θ ≦ N °. In the present embodiment, it is configured so that f ₂ / f ₁ = 23 / m (m is an incident angle at the line CCD 261 showing the same sensitivity as that of the photosensitive member at an incident angle of 23 °). Thus, the sensitivity of the photosensitive drum 12 and the sensitivity of the line CCD 261 can be made to substantially coincide with each other with respect to light having an incident angle on the photosensitive drum 12 in the range of −23 ° ≦ θ ≦ 23 °.

Therefore, the light profile measuring apparatus 200 can generate light amount correction value data corresponding to the sensitivity characteristic of the photosensitive drum 12. In particular, even in the LPH 14 in which the SLED chips (CHIP1 to CHIP58) are alternately arranged in a staggered manner, light amount correction value data corresponding to the sensitivity characteristic of the photosensitive drum 12 can be generated.
As a result, the light quantity of the LPH 14 is corrected by the light quantity correction value data, so that when the photosensitive drum 12 is exposed by the LPH 14 to form an electrostatic latent image in an actual image forming apparatus, a predetermined latent image is formed. The amount of light assumed to obtain the potential and the amount of light actually emitted from the LPH 14 can be made substantially coincident. As a result, it is possible to obtain a desired latent image potential with respect to a predetermined amount of light, and to realize an appropriate image density and image gradation.

  Next, processing when light amount correction value data is generated by the optical profile measurement device 200 of the present embodiment will be described. FIG. 16 is a flowchart showing the flow of processing when generating light amount correction value data. Note that when performing the light amount correction value data generation processing, the LPH 14 used in the digital color printer 1 is held in advance in the optical profile measuring apparatus 200 by a holder member (not shown) and set at a predetermined position.

First, the PC 266 outputs a control signal instructing the LPH driver 264 to turn on the LPH 14 with 4 on 4 off from the digital I / O 268. Thereby, the LPH driver 264 turns on the LPH 14 with 4 on 4 off (S1).
Here, 4on4off lighting means that, as shown in FIG. 17, in the LED array arranged in the SLED 63 of the LPH 14, four adjacent LEDs are turned on, and further, the four adjacent LEDs are turned off. A lighting form. Thus, the reason why the LPH 14 is turned on 4 on 4 off is that when all the lights are turned on, the total light quantity becomes too large, and it is difficult to accurately measure the peak and valley coordinate points of the light quantity by each LED. In addition, as long as each LED is turned on / off alternately, it is possible to use 2on2off lighting in addition to 4on4off lighting.

Next, the PC 266 outputs a control signal for moving the moving stage 262 to the stage driver 263 via the motor controller 269, and moves the CCD board 270 and the magnifying optical system 260 in the arrangement direction of the SLED 63 (main scanning). Direction) (S2).
Further, the PC 266 outputs a control signal for instructing measurement of the light amount distribution of the LPH 14 to the CCD board 270 from the digital I / O 268 via the CCD interface 280. Then, the CCD board 270 measures the light quantity distribution of the LPH 14 using the line CCD 261 (S3).

Next, the PC 266 acquires the light amount distribution data measured in step 3 from the CCD board 270 via the CCD interface 280. Then, as shown in FIG. 18, with respect to the light amount distribution data, an integrated value in the sub-scanning direction (y) at each coordinate position (x) in the main scanning direction is calculated, and the light amount distribution (light profile) in the main scanning direction. Is obtained (S4).
At that time, black level correction and shading correction are performed. Here, the black level correction value and the shading correction value for the line CCD 261 are obtained in advance. When obtaining the black level correction value and the shading correction value, light is incident on the magnifying optical system 260 from the integrating sphere and measured. In this case, as the light source used for the integrating sphere, the same LED (wavelength 780 nm) as the LED of the SLED 63 disposed in the LPH 14 is used. In addition, the maximum value of the incident angle of light incident on the magnifying optical system 260 from the integrating sphere is 23 ° which is the maximum value of the incident angle incident on the magnifying optical system 260 from the LPH 14 in the actual optical profile measurement apparatus 200. Is set to be

Subsequently, the PC 266 detects a peak position and a valley position in the main scanning direction (x) for the light profile calculated in Step 4. Then, the light amount from the valley to the valley in the light profile is integrated, and the integrated value is divided by the distance from the valley to the valley, thereby calculating the light amount (exposure energy) density in the region between the valleys. The exposure energy density of each region obtained in this way is set as a correction characteristic value (%) of each light emitting point (LED) (see FIG. 19) (S5).
Further, the PC 266 increases or decreases the amount of light according to the error from the target value so that the correction characteristic value matches the predetermined target value, so that the correction characteristic value (%) in all regions is flat. To be. By such flattening processing, a light amount correction value for each region, that is, a light amount correction value for each LED is calculated (S6).
Then, the PC 266 stores light amount correction value data for each LED that is turned on with 4on4off lighting in the memory (S7).

Next, the PC 266 outputs a control signal instructing the LPH driver 264 to turn on the LPH 14 with 4off4on from the digital I / O 268. Thereby, the LPH driver 264 lights the LPH 14 with 4off4on (S9). That is, the setting is changed to a lighting mode in which the LED turned on in Step 1 is turned off and the LED turned off in Step 1 is turned on.
Then, Step 2 to Step 7 are performed in the same manner, and the PC 266 stores the light amount correction value data for each LED that is turned on when 4off4on is lit (S7).
After the measurement in the 4off4on lighting mode is completed (S8), the PC 266 stores the stored light amount correction value data for each LED that is lit by 4on4off lighting and the light amount correction value data for each LED that is lit by 4off4on lighting. Are rearranged in accordance with the arrangement order of the LEDs in the LPH 14 to be combined as light amount correction value data for all the LEDs in the LPH 14. And this is memorize | stored in memory as light quantity correction value data of LPH14 (S10).
In this way, light amount correction value data of the LPH 14 (SLED 63) is generated. The generated light amount correction value data is stored from the PC 266 into the EEPROM 102 disposed on the LED circuit board 62 (see FIGS. 2 and 3).

As described above, the optical profile measuring apparatus 200 according to the present embodiment uses the magnifying optical system 260 configured by a double-sided telecentric optical system and sets a predetermined incident angle of light incident on the photosensitive drum 12 from the LPH 14. N °, the incident angle of the line CCD261 showing the same sensitivity and the sensitivity of the photosensitive member at the incidence angle N ° as M °, the focal length _{f 1} of the object side lens len1, the focal length _{f 2} of the image side lens Len2 Are configured so that f ₂ / f ₁ = N / M. Thereby, the sensitivity of the photosensitive drum 12 and the sensitivity of the line CCD 261 can be substantially matched with respect to light in the incident angle range of −N ° ≦ θ ≦ N °.
Therefore, the light profile measuring apparatus 200 can generate light amount correction value data corresponding to the sensitivity characteristic of the photosensitive drum 12. In particular, even in the LPH 14 in which the SLED chips are alternately arranged in a staggered manner, light amount correction value data corresponding to the sensitivity characteristic of the photosensitive drum 12 can be generated.
As a result, the light quantity of the LPH 14 is corrected by the light quantity correction value data, so that when the photosensitive drum 12 is exposed by the LPH 14 to form an electrostatic latent image in an actual image forming apparatus, a predetermined latent image is formed. The amount of light assumed to obtain the potential and the amount of light actually emitted from the LPH 14 can be made substantially coincident. As a result, in the image forming apparatus, a desired latent image potential can be obtained for a predetermined amount of light, and an appropriate image density and image gradation can be obtained, so that the image forming apparatus is clear and rich in gradation. It is possible to form a high quality image.

It is the figure which showed the whole structure of the image forming apparatus using the LED print head used as a measuring object in this Embodiment. It is the figure which showed the structure of the LED print head (LPH). It is a top view of a LED circuit board. It is a figure explaining the connection part of each SLED chip. It is the figure which showed the wiring diagram currently formed on the LED circuit board. It is a figure explaining the circuit structure of SLED. It is a timing chart which shows the drive signal output from a signal generation circuit. It is a block diagram which shows the structure of a signal generation circuit. It is a block diagram explaining the structure of a reference clock generation part. It is a block diagram explaining the structure of lighting time control and a drive part. It is the figure which showed the structure of the optical profile measuring device. It is a figure explaining the structure of an expansion optical system. It is the figure which each represented the optical path of light B1 and light B2 which were radiate | emitted from LED from which SLED differs. It is the figure which showed the relationship between the sensitivity of a photosensitive drum (photosensitive body) and the sensitivity of a line CCD (sensor), and the incident angle of the light which injects into each. It is the figure which showed the relationship between the sensitivity of a photosensitive drum (photosensitive body) and the sensitivity of a line CCD (sensor), and the incident angle of the light which injects into each. It is a flowchart which shows the flow of the process at the time of producing | generating light quantity correction value data. It is a figure explaining the lighting form of 4on4off. It is a figure explaining the direction of integration of light quantity distribution data. It is a figure explaining a correction characteristic value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Digital color printer, 10 ... Image formation process part, 11Y, 11M, 11C, 11K ... Image formation unit, 12 ... Photosensitive drum, 14 ... LED print head (LPH), 30 ... Control part, 40 ... Image processing part (IPS), 62 ... LED circuit board, 63 ... self-scanning LED array (SLED), 64 ... rod lens array, 100 ... drive circuit (signal generation circuit), 102 ... EEPROM, 104 ... level shift circuit, 110 ... image Data development unit 112 ... Density unevenness correction data unit 114 ... Timing signal generation unit 116 ... Reference clock generation unit 118-1 to 118-58 ... Lighting time control / drive unit 200 ... Optical profile measurement device 260 ... Magnifying optical system, 261 ... line CCD, K ... barrel, Len1 ... object side lens, Len2 ... image side lens, S1 ... 1 stop, S2 ... second aperture

Claims (4)

Characteristic measurement in which multiple light-emitting elements are arranged in a line, and the light from the light-emitting elements is collected on the surface of the photoconductor by a rod lens array to measure the data for correcting the light amount of the print head that exposes the photoconductor A device,
A sensor that is disposed opposite to the light emitting element disposed in the print head and measures the amount of light of each of the light emitting elements;
An optical system composed of a bilateral telecentric optical system that uniformly compresses the incident angle of light from the light emitting element to the sensor to a predetermined magnification α without depending on the image height and collects the light on the sensor. ,
The optical system includes a first lens having a focal length f _1, and the first lens second lens having a focal length f ₂ of the image side focal point is disposed so as to match the object-side focal point of the first Incidence that is located at a position where the image side focal point of the first lens coincides with the object side focal point of the second lens, and is within the range of the opening angle N ° of the rod lens array among the light incident from the light emitting element. look including a first aperture passing only the light incident at the corner, the light incident in the sensitivity and the incident angle M ° in the photosensitive member to light incident at N ° is the aperture angle of the rod lens array When the sensitivity of the sensor with respect to the above is coincident, the first lens and the second lens are arranged so that f ₂ / f ₁ = N / M, whereby the magnification α becomes α = Printhead characterized by being set to M / N Device characteristic measuring device.   2. The optical system further includes a second diaphragm that restricts light incident from the print head to light having an object height within a predetermined range at an object-side focal position of the first lens. The printhead characteristic measuring apparatus as described.   2. The printhead characteristic measuring apparatus according to claim 1, wherein the sensor is composed of a line CCD or a photodiode. A light amount correction method for a print head in which a plurality of light emitting elements are arranged in a line, and light from the light emitting elements is condensed on the surface of the photoconductor by a rod lens array to expose the photoconductor,
As an optical system that forms an image of light from the plurality of light emitting elements on a sensor that measures the amount of light of each of the plurality of light emitting elements , the first lens having a focal length f ₁ and the image-side focal point of the first lens. a second lens having a focal length f ₂ which are arranged to match the object-side focal point, and the object-side focal point of the first lens image side focal point and the second lens is disposed in matching position, An aperture that allows only the light incident at an incident angle within the range of the aperture angle N ° of the rod lens array to pass through the light incident from the print head, and is the aperture angle of the rod lens array. When the sensitivity of the photoconductor with respect to light incident at ° matches the sensitivity of the sensor with respect to light incident at an incident angle M °, the first lens and the second lens are f ₂ / It is arranged to be f ₁ = N / M Using the set both-side telecentric optical system as magnification alpha is alpha = M / N by Rukoto, the light incident from the print head, which is compressed uniformly in the magnification alpha regardless of the image height condensed on the sensor at an angle of incidence,
Light quantity correcting method of a print head, wherein the early days including the step of calculating a light quantity correction value data for correcting the amount of light in the light-emitting element, respectively, based on the amount of light focused on the sensor.

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