JPH06255172A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To make the intensity of beams or the like uniform thereby to form high-quality images by providing a controlling means for controlling the expos ing amount of a laser exposing means based on the detecting result of the intensity of laser beam in one scanning line on a photosensitive body. CONSTITUTION:The diameter of laser beams is adjusted as required by the signals from a laser driving circuit 2 and a collimator lens driving circuit 3. The diameter and the intensity of the adjusted laser light in one scanning line are detected by a photosensor array 36 and input to an A/D converter 4a of an image controlling circuit 1. The signal from the A/D converter 4a is, through a gain correcting memory 44 and a beam diameter correcting memory 46, fed back respectively to a gain correcting gate array 43 and a beam diameter correcting gate array 45. A reference clock is generated from a reference clock generating circuit 47 so as to control the timing of the whole printer head, which is transferred to the gain correcting gate array 43, beam diameter correcting gate array 45 and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image using a laser beam, and more particularly to an image forming apparatus capable of changing the beam diameter or the beam intensity of the laser beam.

[0002]

2. Description of the Related Art In a printer head of a laser printer as an example of a conventional image forming apparatus using a laser beam, a laser beam output from a laser diode is incident on a polygon mirror via a collimator lens. When the polygon mirror is rotated, the laser beam scans the mirror surface of the photoconductor in the main scanning direction, and as a result, an electrostatic latent image is formed on the photoconductor.

[0003]

In the printer head of the conventional laser printer, the electrostatic latent image is formed on the surface of the photoreceptor as described above. In a conventional printer head, for example, fluctuations in the reflectance of the polygon mirror within one scanning line and variations in the transmittance and reflectance of the optical system that sends the laser beam from the laser diode to the photoconductor through the polygon mirror cause The beam diameter and beam intensity on the photoconductor may change within one scanning line. As a result, there arises a problem that the image quality is deteriorated.

The present invention has been made to solve the above problems, and an object thereof is to provide an image forming apparatus capable of obtaining a high-quality image.

[0005]

An image forming apparatus according to a first aspect of the present invention is directed to a laser exposure means for exposing a photosensitive member with a laser beam, and a beam intensity of the laser beam in one scanning line on the photosensitive member. And a control means for controlling the exposure amount of the laser exposure means based on the detection result of the detection means.

According to another aspect of the image forming apparatus of the present invention, there are provided a laser exposure means for exposing the photoconductor with a laser beam, a detection means for detecting the beam diameter of the laser beam in one scanning line on the photoconductor, and a detection means. Control means for controlling the exposure amount of the laser exposure means based on the detection result.

According to a third aspect of the present invention, there is provided an image forming apparatus in which a laser exposure means for exposing a photoconductor with a laser beam and a surface potential on the photoconductor during one scanning line when the laser beam scans the photoconductor. Detecting means for detecting, and control means for controlling the exposure amount of the laser exposing means based on the detection result of the detecting means.

[0008]

In the image forming apparatus according to the present invention, when the photosensitive member is exposed by the laser beam, the beam intensity of the laser beam in one scanning line is detected, and the beam of the laser beam is detected based on the detection result. The exposure dose determined by the intensity is controlled. Therefore, it is possible to obtain a uniform beam intensity over one scanning line on the photoconductor.

In the image forming apparatus according to the second aspect,
The beam diameter of the laser beam in one scanning line on the photoconductor is detected, and the exposure amount determined by the beam diameter is controlled based on the detection result, so that a uniform beam diameter can be obtained over one scanning line on the photoconductor. Obtainable.

In the image forming apparatus according to claim 3,
When the laser beam exposes the photoconductor, the surface potential in one scanning line on the photoconductor is detected, and the exposure amount of the laser beam is controlled based on the detection result.
It becomes possible to perform exposure depending on the surface potential across the line.

The beam exposure amount includes the beam diameter, the beam intensity, and the beam emission time.

[0012]

【Example】

(1) First Embodiment (i) Device Configuration An embodiment of the present invention will be described below with reference to the drawings. Figure 1
FIG. 1 is a schematic diagram showing a schematic configuration of an image forming apparatus to which the present invention is applied.

Referring to FIG. 1, a laser beam printer as an example of an image forming apparatus includes an image forming unit 51, a paper feeding unit 52 for supplying copy paper, and a paper discharge for discharging the copied paper. And part 53. The image forming unit 51 includes a photoconductor drum 20, a charger 22 for applying a potential to the photoconductor drum 20 in advance, and a printer head (laser scanning system) 5 for forming an electrostatic latent image on the photoconductor 20.
A developing unit 24 provided on the downstream side of the printer head for developing an image, a transfer charger 28 for transferring an electrostatic latent image on the photoconductor 20 to a copy sheet, and a photoconductor 20 on the photoconductor 20 after the transfer. And a cleaning unit 31 for removing unnecessary electric potential, which are sequentially arranged in the rotation direction of the photoconductor 20.

The paper feed section 52 includes a paper feed guide 34 for guiding the copy paper 25, a paper feed unit 29, and a paper feed belt 33. The paper discharge unit 53 includes a paper discharge belt 32 and a paper discharge tray 27, and the copy paper 25 discharged from the paper discharge belt 32 is sent to the paper discharge tray 27 via a paper discharge roller 26.

The surface potential detecting device 60 surrounded by a dotted line in the figure is a device used in the second embodiment and is not included in the device according to the first embodiment.

Next, the details of the printer head shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a schematic diagram showing the configuration of a printer head to which the present invention is applied and whose beam diameter can be changed. Referring to FIG. 2, the printer head includes an LD package 8 including a laser diode 10 for emitting a laser beam and a pin diode 9 connected thereto, and a collimator for changing the diameter of the laser beam output from the LD package 8. It includes a lens 11 and a polygon mirror 14 for changing the laser beam output from the collimator lens 11. The polygon mirror 14 has a plurality of mirror surfaces 15, and the polygon motor 13
Is rotated in the direction of the arrow in the figure. The laser beam changed by the polygon mirror 14 is the fθ lens 16
And an electrostatic latent image is formed on the photoconductor 20 in accordance with the image data.

An optical sensor array 36 for detecting the beam diameter and the beam intensity of the laser beam is provided between the fθ lens 16 and the photosensitive member 20, and a laser beam for sending a beam signal for detection to the optical sensor array 36. The optical sensor array mirror 37 provided in the main scanning direction is provided in the path.

When an electrostatic latent image is formed on the photoconductor 20, the laser beam is first rotated by the polygon mirror 14 to start the SOS (Start of Scan) sensor 17.
Incident on the photosensitive member 2 in the main scanning direction indicated by the arrow in the figure.
Scan over 0. Output data from the SOS sensor 17 is sent to the waveform shaping circuit 18. The LD package 8 is driven by the laser drive circuit 2, and the collimator lens 11
Are driven by the collimator lens drive circuit 3. The laser drive circuit 2 and the collimator lens drive circuit 3 are controlled by the image control circuit 1 which inputs image data.

FIG. 3 is a block diagram showing the main part of the control unit of the printer head shown in FIG. Referring to FIG. 3, the printer head controller drives an image control circuit 1 for inputting image data from a host computer (not shown), a laser drive circuit 2 for driving a laser diode 10, and a collimator lens drive for driving a collimator lens 11. Circuit 3. The image control circuit 1 receives the image data Dn from a host computer (not shown) and outputs the laser drive signal L to the laser drive circuit 2 and the collimator lens drive circuit 3 according to the image data Dn. And a beam diameter correction gate array 45 for outputting beam diameter correction data C for forming a desired laser beam diameter, and the image control circuit 1.
It includes a CPU 41 for controlling the whole and an I / O 42 for receiving an SOS signal and other external signals.

The laser beam adjusted to a desired beam diameter by the signals from the laser driving circuit 2 and the collimator lens driving circuit 3 is detected by the optical sensor array 36 to have a beam diameter and a beam intensity within one scanning line. The (sensor light receiving amount P) is input to the A / D converter 4a of the image control circuit 1. The signal from the A / D converter 4a is used as a gain correction memory 44 and a beam diameter correction memory 46.
And is fed back to the gain correction gate array 43 and the beam diameter correction gate array 45, respectively.

In order to control the timing of the entire printer head, a reference clock generating circuit 47 generates a reference clock and sends it to the gain correction gate array 43, the beam diameter correction gate array 45 and the like. Also, a timing signal such as LDON indicating that the laser diode 10 is turned on is sent to each element as shown in the figure.

The laser drive circuit 2 receives the laser emission signal L and changes it into an analog signal.
a and a laser diode light emission control circuit 2b for controlling the light emission of the laser diode, the collimator lens drive circuit 3 receives the beam diameter correction data C and converts the signal into an analog signal. And a collimator lens drive control circuit 3b for driving 11.

The laser diode 1 will be described with reference to FIG.
The output from 0 is detected not only by the photosensor array 36 but also by the pin diode 9, but the photosensor array 36 is used to perform correction between pixels in one scanning line on the photoconductor 20 as described later. The pin diode 9 is provided and is used only for correcting the temperature characteristic.

The surface potential detecting device surrounded by a dotted line in the figure is included only in the second embodiment as described above.

Next, a mechanism for changing the beam diameter will be described with reference to FIG. The beam diameter is changed by moving the collimator lens 11 by the voice coil 21 in the optical axis direction. As this moving mechanism, a well-known optical disk pickup device can be applied.

When the collimator lens 11 is at the solid line position in the figure, the laser beam on the photoconductor 20 is set to have the minimum beam diameter D ₀ . When the collimator lens 11 is moved to the dotted line position by Δx by the voice coil,
Defocus occurs on the photoconductor 20 and the beam diameter increases. At this time, there is a relationship of D (Δx) = D ₀ √ [1+ {4λ (f / f _c0 ) ² Δx / πD ₀ ² } ² ]. Where λ is the oscillation wavelength of the laser diode f is the focal length of the scanning optical system (fθ lens) f _c0 is the focal length of the collimator lens.

Now, λ = 780 nm, f = 150 mm, f
_c0 = 6.0 mm, when the _{D 0 = 30μm, D = 0.03√} (1 + 4.76 × 10 5 · Δx 2) and made (mm).

The relationship between Δx and D is shown in FIG. That is, by shifting the collimator lens as shown in FIG. 5, the beam diameter can be shifted from 30 μm to 60 μm.

Next, details of the optical sensor array will be described. FIG. 6 is an equivalent circuit diagram of the optical sensor array. Referring to FIG. 6, photosensor array 36 includes a plurality of photodiodes connected in parallel, one end of which is connected to power supply voltage Vcc, and the other end of which is connected to output Vout. The other end of the photosensor array 36 is also connected via a node 56 to a load resistor 57 and an analog switch 55 connected to ground potential. The detection of the beam diameter and the detection of the beam intensity are switched by turning on or off the analog switch 55. As shown in the figure, about 8000 photodiodes are connected in parallel to the optical sensor array 36, and a voltage is generated at the output Vout when the beam hits one of the sensors.

FIG. 7 shows the positional relationship between the optical sensor array 36 and the beam diameter for scanning it in the main scanning direction and the output Vou.
It is a figure which shows the relationship with t. (A) corresponds to the case where the beam diameter is large, and (B) corresponds to the case where the beam diameter is small. Referring to FIGS. 7A and 7B, the optical sensor array 3
If any of the sensors that make up 6 hit the beam, Vou
Since a voltage is generated at t, it can be seen that the time period in which the voltage is output differs depending on the size of the beam diameter. Therefore, this can be utilized to detect the beam diameter.

(Ii) Detection of Beam Diameter Next, a specific method of detecting the beam diameter will be described. 2 to 7, when the printer head is turned on, the collimator lens 11 is first moved to set the beam diameter. At this time, as shown in the time chart of FIG. 8, the laser is turned off by 1 ON M (M is a real number). In the state of FIG. 8, it is 1 on 1 off. In the figure, (A) shows a state before the beam diameter is corrected, and (B) shows a state after the beam diameter is corrected.

Then, the image control circuit 1 measures the emission time of one dot of the laser beam. At this time, in the equivalent circuit of the optical sensor array 36 shown in FIG. 6, the analog switch 55 is turned on, the load resistance 57 is reduced, and the optical sensor array is used in a saturated state. The meaning of using this optical sensor in a saturated state will be described with reference to FIG. Since the analog switch 55 is turned on when the beam diameter is detected, the characteristic curve of the sensor light receiving amount P of the photosensor array 36 and the output Vout is as shown in FIG. At this time, it is detected only whether the output Vout of the optical sensor is equal to or larger than the predetermined value Vth or smaller than Vth.

On the other hand, when detecting the beam intensity, which will be described later, the analog switch 55 is turned off and the P-Vout characteristic curve of the photosensor array 36 is used in the state of. When the beam diameter / beam intensity is detected, the laser is driven at full power (near Pmax in FIG. 9). By emitting light in this portion, it is possible to detect the laser intensity and the beam diameter without any trouble.

The image control circuit 1 sets a correction value in the beam diameter correction memory 46 so that the beam diameter becomes a predetermined constant value.

Next, a specific method of obtaining the correction data will be described. After the power is turned on, the polygon mirror 14 rotates and the laser diode 10 is forced to emit light after a predetermined time.
After the SOS sensor 17 detects the SOS signal, the signal that turns on / off the laser diode 10 at full power is the CPU.
41. With this signal, a signal for driving the laser diode 10 with full power is output from the gain correction gate array 43, and the laser diode 10 is on / off driven with full power. Optical sensor array 36
Receives the signal. At this time, the analog switch 55 shown in FIG. 6 is on, and the output of the photosensor array 36 becomes as shown in FIG. 8 (A). If there is a difference in beam diameter, the output Vo of the optical sensor array 36 will be changed accordingly.
Since the on time of ut changes, it is detected. Specifically, the output of the photosensor array 36 is converted through the A / D converter 4a, and the output is counted to count the number of reference clocks when the photosensor array 36 is on. Thereby, the time when the photosensor array 36 is on can be known.

When the beam diameter is detected, the A / D
The converter 4a merely functions as a waveform shaping circuit. That is, it works as a 1-bit A / D converter.

By storing the count value thus obtained in the beam diameter correction memory 46, the beam diameter at a specific position in one line can be detected. For example, with a 400 DPI printer, one line has 33
It is composed of 07 pixels. If the laser diode 10 is turned on and off for each pixel repeatedly, the beam diameter can be known for every two pixels.
The beam diameter is known for each pixel. FIG. 10 shows a timing chart showing the relationship among the photosensor array output, the reference clock signal, the counter (FIG. 3, 46a) value, and the beam diameter correction memory when the pixel is repeatedly turned on and off for each pixel.

The beam diameter detected next is stored in the beam diameter correction memory 46. This stored state is shown in FIG. In this example, since the beam is repeatedly turned on and off for each pixel, the beam diameters for all pixels cannot be known. That is, for example, the values of C2, C4, and C6 are unknown. Therefore, the beam diameter for the adjacent pixel is set. Specifically, for example, C2 = C1, C4 = C
3 ...

Although the beam diameter fluctuates, it usually falls within the value at the time of design. That is, the beam diameter correction data C is Cm
Since it falls within the range of in <C <Cmax, a 3-bit code (c ₁ , c ₂ , c ₃ ) is assigned to the value of C.
If it does not fit, an error may occur. As a result, the value of C, the sign, and the defocus amount are stored in the beam diameter correction memory 46 as shown in FIG. Here, the defocus amount corresponds to the correction moving amount of the voice coil 21 described above.

As a result, the on-time of the output of Vout was changed due to the difference in beam diameter as shown in FIG. 8A, but the beam diameter was corrected by the correction data, as shown in FIG. 8B. A pulse with a pulse width equal to can be obtained. This is equivalent to making the beam diameters equal.

Next, a method of correcting the beam intensity will be described. First, the analog switch 55 of the photosensor array 36 shown in FIG. 6 is turned off so that the photosensor array 36 can detect the beam intensity as an analog value. Also, A
The output of the / D converter 4a is switched from 1 bit to 8 bits.

By driving the voice coil 21 according to the beam diameter detected by the above-mentioned method, the beam diameter is kept constant, for example, a value of 60 μm <C <65 μm, and the laser is emitted at a constant beam intensity over the image area. Make it emit light continuously. Then, the A / D of the optical sensor array 36
The output from the converter 4a is sequentially output to P1 and P for each pixel.
2, P3, ..., P3307 and the gain correction memory 44. Since the output from the A / D converter 4a is 8 bits, the sensor light receiving amount P = p0p1p2p3p4p
Represented as 5p6p7. Further, the value of P increases as the amount of received light increases. The correction data is stored in the gain correction memory 44 so that there is no variation in the value of P thus obtained.

FIG. 13 is a timing chart showing the relationship between the SOS signal and the LDON signal and the photosensor array output Vout when the laser beam is fully emitted in the printing area of the photoconductor 20. FIG. 7A is a diagram showing a state before correcting the intensity of the laser beam, and FIG. 9B is a diagram showing a state after correcting the intensity of the laser beam. In addition, here LDO
The N signal is a signal indicating the on / off state of the laser diode 10. Comparing (A) and (B), the beam intensity fluctuates in one scanning line before the correction, but it is kept constant after the correction.

In this embodiment, a half mirror is used to split the image light and the light to the photosensor array.
The photosensor array mirror may be inserted in the optical path when the beam diameter and the beam intensity are detected.

Further, in the present embodiment, the beam diameter is corrected before the beam intensity is corrected, but only the beam intensity may be detected and the beam intensity may be corrected accordingly.

Further, in this embodiment, the beam diameter and the beam intensity are changed to control the exposure amount, but the exposure amount may be controlled by changing the pulse width.

(2) Second Embodiment (i) Device Configuration Next, a second embodiment of the present invention will be described. The configuration of the second embodiment is basically the same as that of the first embodiment, but the following points are different. That is, in the second embodiment, the surface potential detecting device 60 surrounded by the dotted line in FIGS. 1 and 3 is provided, whereby the photoreceptor 2 is provided.
The surface potential on 0 is detected. In addition, in this case, FIG.
The optical sensor array 36 and the optical sensor array mirror 37 shown in FIG. 3 are omitted.

FIG. 14 is a block diagram showing details of the surface potential detecting device 60. Referring to FIG. 14, the surface potential detecting device 60 includes a surface potential sensor 61 for detecting a surface potential, an A / D converter 61a for converting an output signal from the surface potential sensor 61 into a digital signal, and a surface potential sensor 61a. Linear pulse motor 6 for driving the potential sensor 61
2 and a linear pulse motor driver 63 for driving the linear pulse motor 62.

(Ii) Detection of Surface Potential When detecting the surface potential of the photoconductor 20, FIG.
As shown in, while rotating the photosensitive drum 20, the surface potential sensor 61 is moved in the main scanning direction indicated by the arrow in the figure. As a result, a surface potential along the optical axis of the photoconductor 20 as shown in FIG. 15B is obtained.

(Iii) Correction of Surface Potential Next, a method of correcting variations in surface potential will be described.
As described above, the photoconductor 20 is rotated, the charging charger 22 is turned on, and the laser beam is guided to the photoconductor 20. At this time, the beam diameter BC and the beam intensity BP are read from the beam diameter correction memory 46 and the gain correction memory 44, respectively,
Image data 1111 with the corrected beam diameter and beam intensity
A latent image corresponding to 1111 (solid black) is formed.

The surface potential on the photoconductor 20, which is the electrostatic latent image potential (Vi) formed by laser irradiation, is detected. The detection method is the linear pulse motor 62 as described above.
Is performed by driving the surface potential sensor 61.
The series of operations is controlled by the CPU 41. The output from the surface potential sensor 61 is taken into the image control circuit 1 by the port of the I / O 42 via the A / D converter 61a and stored in the beam diameter correction memory 46. Next, beam diameter correction data C is created according to the surface potential detection output, and is similarly expanded in the beam diameter correction memory 46. The details will be described later. Next, the laser is turned off, and the charging charger 22 and the photoconductor 20 are turned off.

By the above steps, it is corrected that the beam diameter as the electrostatic latent image changes due to the contamination of the charging charger 22 and the change of the surface potential due to the characteristic change of the photoconductor 20,
It is possible to always obtain a uniform latent image spot.

Next, the creation of the beam diameter correction data C will be described. In this embodiment, a two-component developing method is used in which the charging potential V ₀ of the photoconductor 20 is −600 V, the proper post-exposure potential V _{i is} −80 V, and the developing bias voltage V _{B is} −250 V.

In FIG. 15B, the surface potential V _i when the electrostatic latent image is formed by laser exposure is obtained by charging the photoconductor 20 to the surface potential V ₀ (= −600 V) by the charger 22. FIG. As shown in the figure, the central portion of the photoconductor 20 has V _i = −80 V, but the both ends have V _i = −60 V. The reason for this is that both ends of the charge wire of the charger 22 are contaminated and the charge cannot be sufficiently applied to the photoconductor 20. That is, the photoconductor causes charging failure,
Both V ₀ and V _i have the potential lowered by −20 V (ΔV ₀ = ΔV _i = 20 V).

FIG. 16 is a graph showing the relationship between the laser beam diameter and the surface potential V _i . 15A shows the relationship between the surface potential of the central portion of the photoconductor 20 and the exposure laser beam diameter and latent image beam diameter shown in FIG. 15B. Here, the exposure beam diameter (true circle diameter) is D, and the developing bias voltage V
_If the latent image beam diameter at _B is a, this ratio a /
The relationship between D and the electrostatic latent image potential difference ΔV _i is shown in FIG.

In the case of FIG. 16A, since ΔV _i = 0V, a / D = 80% from FIG. 17, and the latent image beam diameter a is 80% of the exposure beam diameter D.

Next, in (B), ΔV _i = V _i ′ −
In the case of V _i = 20V, a ′ / D = 90 from FIG.
%, And the latent image beam diameter a ′ becomes thicker (10%) than in the normal case (A).

Therefore, it is necessary to reduce the exposure beam diameter D in order to obtain the latent image beam diameter a as shown in (C). Letting this exposure beam diameter be D ′, a ′ = 0.9D ′ (1) a ′ = a, a = 0.8D Substituting these values into the equation (1) gives 0.8D = 0.9D 'Thus, D' = (0.8 / 0.9 ) D = 0.89D next, the [Delta] V _i when the 20V, the exposure beam diameter may be set to the diameter of 89% of the normal setting.

Similarly, the latent image potential in the axial direction of the photoconductor 20 is measured by the surface potential sensor 61, and the exposure beam diameter is corrected from the graph of the relationship between the beam diameter and the electrostatic latent image potential difference ΔV _{i in} FIG. .

For example, in the case of a printer of 400 DPI, the exposure beam diameter D is D = 63.5 μm and the latent image beam diameter is a = 0.8D = 50.8 μm, so that the toner image is crushed during development, transfer and fixing. The dot diameter of the pixel obtained by is about 60 μm. Specifically, the weight becomes about 20%.

The beam shape may be a perfect circle or an ellipse. In the case of an ellipse, beam diameter correction data may be provided in each of the vertical and horizontal directions of the beam.

When the surface potential sensor 61 is driven, C
A start command is sent from the PU 41 to the linear pulse motor driver 63. The linear pulse motor driver 63 is a drive circuit for operating the linear pulse motor 62, and moves the surface potential sensor 61 in the axial direction of the photoconductor 20 to return it to the initial position (home position).

The detected surface potential data (corresponding to ΔV _i ) is stored in a specific area (area different from the beam diameter) of the beam diameter correction memory 46.

Specifically, it is stored as shown in FIG. Next, based on these data, the beam diameter is set based on the following equation.

R = 80 / (80 + 0.5Q) R ₀ This corresponds to the presupposed 0.8 / 0.9 × D. Here, R ₀ corresponds to the reference beam diameter = 60 μm. This method corresponds to the graph in FIG. 17 replaced with an equation.

As a result, the table shown in FIG. 19 is created and stored in the beam diameter correction memory 46. Here, the beam diameter correction data R is the same as C described in FIG. 12 (first embodiment).
It is 3-bit data of c ₁ , c ₂ and c ₃ . The corresponding defocus amount is the same as in FIG.

Next, the processing during actual image formation will be described. 8-bit image data Dn and control data are sent to the image control circuit 1 as image data from an image reader (not shown) or a host computer. A forced light emission signal is formed by the print start command, and the laser diode 10 is turned on. When the SOS signal of the first line is output, R1, R2, ..., R33 are set so that the beam diameter becomes constant according to the reference clock as described above.
The beam diameter is controlled for each pixel based on 07.
The input Ln (n is the pixel number) of the D / A converter of the laser drive circuit 2, which corresponds to the actual drive current of the laser diode 10, is Ln = Dn · K / Pn, where K is a gain correction gate array according to a constant The gain is corrected at 45. As a result, the gain is weakened for pixels with higher emission intensity, and a uniform beam spot can be obtained for uniform data between pixels on a line.

FIG. 20 shows a flow chart of the actual control procedure of the present invention described above. In the first embodiment, the beam diameter and the beam intensity are detected by the optical sensor array to correct the beam diameter and the beam intensity, and in the second embodiment, the surface potential is detected to correct the beam diameter. However, the present invention is not limited to this, and the beam intensity may be corrected by measuring the surface potential also in the second embodiment.

Although the beam diameter, the beam intensity and the surface potential are detected when the power is turned on, they may be detected on a job basis or a page basis. In particular, it is desirable to detect the beam diameter and the beam intensity on a job-by-job basis or on a page-by-page basis when the characteristics greatly change when a current is applied to the laser diode for a long time.

Further, in the flow chart showing the control procedure of the present embodiment shown in FIG. 20, the steps of # 1 and the analog switch off of # 2 to the step of driving the laser diode with full power may be omitted.

[0071]

As described above, according to the present invention, the beam intensity, the beam diameter, or the surface potential in one scanning line on the photoconductor is detected, and the detection result indicates the beam intensity, the beam diameter, the light emission time, or the like. Since the exposure amount of the laser exposure means is controlled, it is possible to obtain a uniform beam intensity and beam diameter over one scanning line on the photoconductor. As a result, it is possible to provide an image forming apparatus capable of obtaining a high quality image.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a laser beam printer to which the present invention is applied.

FIG. 2 is a perspective view of a printer head to which the present invention is applied.

FIG. 3 is a block diagram showing a main part of a control unit of the printer head.

FIG. 4 is a diagram showing a mechanism for changing a beam diameter.

FIG. 5 is a diagram showing a relationship between a moving amount of a collimator lens and a laser beam diameter.

FIG. 6 is an equivalent circuit diagram of the optical array sensor.

FIG. 7 is a diagram showing a relationship between a beam diameter and an output on the optical array sensor.

FIG. 8 is a time chart before and after beam diameter correction.

FIG. 9 is a graph showing a characteristic curve of the amount of light received by the sensor of the optical sensor array and the output voltage of the sensor.

FIG. 10 is a diagram showing a relationship between an optical sensor array output and a beam diameter.

FIG. 11 is a diagram showing an example of data stored in a beam diameter correction memory.

FIG. 12 is a diagram showing the contents of beam diameter data.

FIG. 13 is a time chart before and after laser intensity correction.

FIG. 14 is a block diagram showing a configuration of a surface potential detecting device.

FIG. 15 is a diagram showing a positional relationship between a surface potential sensor and a photoconductor and an output example of the surface potential sensor.

FIG. 16 is a diagram showing a relationship between a laser beam diameter and a surface potential.

FIG. 17 is a diagram showing the relationship between the beam diameter and the electrostatic latent image potential difference.

FIG. 18 is a diagram showing the contents of a beam diameter correction memory.

FIG. 19 is a diagram showing the contents of beam diameter correction data.

FIG. 20 is a flow chart showing a method of detecting a surface potential during image formation and a method of correcting the same.

[Explanation of symbols]

 1 Image Control Circuit 2 Laser Driving Circuit 3 Collimator Lens Driving Circuit 5 Printer Head 36 Optical Sensor Array 41 CPU 43 Gain Correction Gate Array 44 Gain Correction Memory 45 Beam Diameter Correction Gate Array 46 Beam Diameter Correction Memory

Claims (3)

[Claims] 1. A laser exposure unit that exposes a photoconductor with a laser beam, a detection unit that detects the beam intensity of the laser beam in one scanning line on the photoconductor, and a detection result of the detection unit. And a control unit for controlling the exposure amount of the laser exposure unit. 2. A laser exposure unit that exposes a photoconductor with a laser beam, a detection unit that detects the beam diameter of the laser beam in one scanning line on the photoconductor, and a detection result of the detection unit. And a control unit for controlling the exposure amount of the laser exposure unit. 3. A laser exposure means for exposing a photoconductor with a laser beam, and 1 when the laser beam scans the photoconductor.
A detection means for detecting the surface potential on the photoconductor in the scanning line; and a control means for controlling the exposure amount of the laser exposure means based on the detection result of the detection means, Image forming apparatus.