JP2002303814A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner which can maintain excellent images with simple constitution even when a beam diameter varies owing to the influence of temperature variation, etc. SOLUTION: A detecting means detects beam diameter variation in a vertical scanning direction (100, 102) and when the detection result exceeds a permissible value, stationary light intensity is adjusted (104, 106) by changing the reference voltage of an LD driving circuit. Then the detecting means detects beam diameter variation in a horizontal scanning direction (108); when the detection result exceeds a permissible value, the RLC circuit constant of the LD driving circuit is obtained and resistance R is varied to vary the overshoot quantity in the rising of an LD driving current waveform, thereby adjusting the rising light intensity (110, 112).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly, to a light source such as a semiconductor laser (LD) which is turned on based on image information, and a photoreceptor is irradiated with a light beam output from the light source. The present invention relates to an optical scanning device provided in an electrophotographic apparatus such as a laser beam printer and a digital copying machine that forms an image by scanning.

[0002]

2. Description of the Related Art Recent laser beam printers and digital copiers are provided with an optical scanning device for scanning a light beam on a photosensitive material or a photosensitive member. FIG. 8 shows an example of this type of optical scanning device. The optical scanning device shown in FIG. 8 irradiates a light beam emitted from a light source 200 to a rotating polygon mirror 204 via a condenser lens group 202 and also irradiates the light beam emitted to the rotating polygon mirror 204 to the rotating polygon mirror 204. By being reflected by the reflecting surface 204A that moves with the rotation of the polygon mirror 204, the imaging lens 20
The scanning exposure is carried out along the axial direction of the photosensitive drum 208 via the reference numeral 6. In addition, the rotating polygon mirror 2
The direction in which the light beam is scanned by the rotation of 04 is called the main scanning direction, and the direction orthogonal to the main scanning direction is called the sub-scanning direction.

[0003] With the recent progress of digitization technology and image processing technology, the resolution of optical scanning devices has been further increased, and dots smaller than the beam diameter of a general optical scanning device of 50 μm to 80 μm have been developed. There is an increasing demand for forming an image on a computer. For example, to obtain a resolution of 1200 dpi, an image resolution of 21 μm is required in units of 11 μm to obtain a resolution of 2400 dpi. Therefore, such an optical scanning device is a semiconductor laser (hereinafter referred to as L
By adjusting the light intensity, lighting time, and the like with high precision, it is possible to form an image with high resolution.

[0004] In an image forming apparatus such as a laser printer or a digital copier, the focal position of a light beam fluctuates due to deformation of an optical scanning device or distortion of a lens due to temperature fluctuation or the like. When the focal position fluctuates, the beam diameter on the photoreceptor changes, and as image quality, reproducibility of fine lines and halftones that form an image with dots smaller than the beam diameter of the optical scanning device deteriorates.

FIG. 9 shows light intensity distributions at various beam diameters when the light emission power of the LD is kept constant. FIG.
As shown in the graph, even if the light emission power of the LD is constant, if the focus position is shifted and the beam diameter is increased, the light intensity at the center of the light beam is reduced.

FIG. 10A shows a drawing state when the beam diameters in the main scanning direction and the sub-scanning direction are appropriate.
FIG. 10B shows a drawing state when the beam diameter in the main scanning direction becomes large, and FIG. 10C shows a drawing state when the beam diameter in the sub-scanning direction becomes large.

As shown in FIG. 10A, the line width in the main scanning direction depends on the beam diameter in the sub scanning direction, and the line width in the sub scanning direction depends on the beam diameter in the main scanning direction and the laser lighting time. . When the line width in the sub-scanning direction is 1 dot or less, the central light intensity of the light beam differs depending on the laser lighting time.

As shown in FIG. 10B, when the beam diameter in the main scanning direction increases, the center intensity of the light beam for the same laser lighting time decreases, and the image forming width decreases. The width becomes thin.

As shown in FIG. 10C, when the beam diameter in the sub-scanning direction increases, the center intensity of the light beam decreases,
Since the width in which an image is formed becomes narrow, the line width in the main scanning direction becomes narrow.

Further, if the beam diameter becomes larger than that shown in FIGS. 10B and 10C, there is a problem that a thin line cannot be drawn. Further, for the same reason, when the beam diameter increases, the reproducibility of the highlight portion and the reproducibility of the halftone also deteriorate.

Therefore, in order to solve this kind of problem,
JP-A 1-292211 and JP-A 7-20395
In the technology described in Japanese Patent Application Laid-Open No. H11-260, the beam diameter of a scanning beam is detected by a beam detecting unit, and based on the detection result, an optical component inside the optical scanning device is moved to adjust the focal position of the light beam and to expose the light. The beam diameter on the body is stabilized.

In the technique described in Japanese Patent Application Laid-Open No. 1-292311, as shown in FIG. 11, a CCD 212 is disposed at a position equivalent to the photosensitive member 210, and a laser element 216 is disposed as shown in FIG.
A light beam is applied to the CCD 212 by inputting an ON / OFF signal as shown in FIG. CCD2
As shown in FIG. 12B, the exposure distribution on the light source 12 is a strong and weak distribution according to the spot diameter of the laser beam.
The output of each pixel 212 has a distribution as shown in FIG. 12C, and based on the signal (output signal of each pixel), a contrast ratio is calculated to detect a beam diameter variation of the light beam. Then, based on the result, the collimator lens 21
4 is moved in the optical axis direction by a stepping motor as a focus adjusting unit 218 to stabilize the beam diameter on the photoconductor 210.

In the technique described in Japanese Patent Application Laid-Open No. 7-20395, as shown in FIG.
22, the beam diameter fluctuation in the main scanning direction and the sub-scanning direction are detected from the output signals.
The beam diameter fluctuation in the sub-scanning direction is controlled by the cylindrical lens 22.
8 are moved by a piezoelectric element in the optical axis direction to stabilize the beam diameter on the photosensitive member.

[0014]

However, in each of Japanese Patent Application Laid-Open Nos. 1-292311 and 7-20395, since an optical component is mechanically moved, the movement of a piezoelectric element, a stepping motor, or the like is required. Since a mechanism is required and the configuration of the device becomes complicated, it is difficult to reduce the size and cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an optical scanning device capable of maintaining good image quality with a simple configuration even if the beam diameter fluctuates due to a change in temperature or the like. The purpose is to provide.

[0016]

In order to achieve the above object, according to the present invention, a light source for outputting a light beam based on image information is turned on, and a light beam output from the light source is emitted. An optical scanning device that optically scans a photosensitive member by using a light emitting device that detects a state of the light beam; and the light emitting device changes a light intensity of the light beam based on a detection result of the light emitting device. Control means for controlling the light emitting source so that the light intensity at the rise of the light beam changes after controlling the light source.

According to the first aspect of the present invention, the detecting means detects a state (for example, light intensity, beam diameter, etc.) of a light beam output from a light emitting source such as a semiconductor laser. The control unit controls the light source so that the steady light intensity of the light beam output from the light source changes based on the detection result of the detection unit. For example, when there is a change in the detection result of the detection unit, the drive current or the drive voltage of a light emitting source such as a semiconductor laser is increased or decreased based on the detection result of the detection unit, thereby causing a change due to a beam diameter change or a light amount change. The light intensity at the center of the light beam can be maintained in an appropriate state.

Subsequently, the control means controls the light emitting source so that the light intensity at the rising of the light beam changes. For example, by changing the amount of overshoot at the rise of the drive current waveform for driving the light emitting source, it is possible to improve the decrease of the light intensity at the rise due to the fluctuation of the beam diameter.

Therefore, by controlling the semiconductor laser by the control means as described above, the light beam output from the light emitting source can be maintained in an appropriate state without mechanically moving the optical components. With a simple configuration, high-resolution fine line reproducibility and halftone reproducibility can be maintained, and good image quality can be maintained.

Further, if the light emitting source is controlled first so that the light intensity at the rising of the light beam changes, the light intensity at the rising time will be changed when controlling so that the steady light intensity of the light beam changes. However, as described above, after the light source is controlled so that the steady light intensity of the light beam changes, the control accuracy is deteriorated by controlling the light source so that the light intensity at the rising edge of the light beam changes. Adjustment to the beam diameter can be performed without the need.

According to a second aspect of the present invention, in the first aspect, the detecting means detects a beam diameter variation in a main scanning direction and a sub-scanning direction as a state of the light beam, and the control means After controlling the light-emitting source so that the steady light intensity of the light beam changes based on the detection result of the beam diameter variation in the sub-scanning direction by the detection unit, the variation of the beam diameter in the main scanning direction by the detection unit is controlled. The light source is controlled so that the light intensity at the rising of the light beam changes based on the detection result.

According to the invention of claim 2, according to claim 1,
In the invention described in (1), the detecting means detects a beam diameter variation in the main scanning direction and the sub-scanning direction as a state of the light beam output from the light emitting source.

The control means controls the light emission source so that the steady light intensity of the light beam changes if the beam diameter in the sub-scanning direction detected by the detection means fluctuates. That is, when the beam diameter in the sub-scanning direction increases, the driving current of the light emitting source such as a semiconductor laser increases, and when the beam diameter in the sub-scanning direction decreases, the driving current of the light emitting source such as a semiconductor laser decreases. Is reduced, the light intensity at the center of the light beam, which fluctuates due to fluctuations in the beam diameter and the amount of light in the sub-scanning direction, can be maintained in an appropriate state. Can be prevented.

Subsequently, the control means controls the light emitting source so that the rising light intensity of the light beam changes if the beam diameter in the main scanning direction detected by the detecting means changes. That is, when the beam diameter in the main scanning direction increases, the rising overshoot amount of the drive current waveform of the light emitting source such as a semiconductor laser increases when rising, and when the beam diameter in the main scanning direction decreases, By reducing the amount of overshoot at the rise of the drive current waveform of the light-emitting source such as a semiconductor laser, it is possible to improve the decrease in light intensity at the rise due to the fluctuation of the beam diameter in the main scanning direction. Characteristics and halftone reproducibility can be maintained, and good image quality can be maintained.

If the beam diameter in the main scanning direction is adjusted (adjustment of the rising light intensity) first, the steady light intensity is changed when adjusting the beam diameter in the sub-scanning direction. Is changed at the time of adjustment in the sub-scanning direction. However, as described above, the adjustment accuracy deteriorates by adjusting the beam diameter in the sub-scanning direction and then adjusting the beam diameter in the main scanning direction. Adjustment to the beam diameter can be performed without the need.

According to a third aspect of the present invention, in the first aspect, the detecting means detects a light intensity fluctuation of the light beam and a beam diameter fluctuation in a main scanning direction as the state of the light beam. The control means controls the light emitting source so that the steady light intensity of the light beam changes based on the detection result of the light intensity fluctuation by the detection means, and then controls the beam diameter in the main scanning direction by the detection means. The light emitting source is controlled so that the light intensity at the rise of the light beam changes based on the detection result of the fluctuation.

According to the invention described in claim 3, according to claim 1
In the invention described in (1), the detecting means detects the light intensity of the light beam and the beam diameter variation in the main scanning direction as the state of the light beam output from the light emitting source. That is, the detecting means detects the fluctuation amount of the beam diameter as the fluctuation of the light amount.

Then, the control means controls the light emitting source so as to adjust the steady light intensity of the light beam based on the fluctuation of the light amount, thereby preventing the deterioration of the image quality due to the fluctuation of the beam diameter in the sub-scanning direction. it can.

Subsequently, the control means controls the light emitting source so that the rising light intensity of the light beam changes if the beam diameter in the main scanning direction detected by the detecting means fluctuates. That is, when the beam diameter in the main scanning direction increases, the rising overshoot amount of the drive current waveform of the light emitting source such as a semiconductor laser increases when rising, and when the beam diameter in the main scanning direction decreases, By reducing the amount of overshoot at the rise of the drive current waveform of the light-emitting source such as a semiconductor laser, it is possible to improve the decrease in light intensity at the rise due to the fluctuation of the beam diameter in the main scanning direction. Characteristics and halftone reproducibility can be maintained, and good image quality can be maintained.

Further, if the beam diameter in the main scanning direction is adjusted (adjustment of the rising light intensity) first, the steady light intensity is changed at the time of adjusting for the fluctuation of the light amount, so that the rising light intensity adjusted earlier is adjusted. However, as described above, the beam diameter changes in the main scanning direction after performing the adjustment for the fluctuation in the light amount, so that the beam accuracy is not deteriorated. Adjustments to the diameter can be made.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a schematic configuration of an optical scanning device according to an embodiment of the present invention.

The optical scanning device 10 shown in FIG. 2 employs an overfilled optical system in which a light beam wider than the deflecting surface is incident on a deflecting surface of a rotary polygon mirror described later.

In FIG. 2, the light source unit includes a semiconductor laser (hereinafter, referred to as an LD) 12 as a light emitting source according to the present invention which emits a light beam having a substantially Gaussian distribution. When a light beam having a divergence angle is emitted from its focal position, a collimator lens 14 has the function of turning the light beam into substantially parallel light, a beam shaping slit 16 for passing only the light beam at the center, and incidence. A cylindrical lens 18 that converges the obtained light beam in the sub-scanning direction near the deflection surface of a rotary polygon mirror described later is arranged.

The LD 12 is connected to a control device described later, and the control device controls the light beam output of the LD 12 to modulate based on image information.

The collimator lens 14 is provided with an LD 12
Is approximately 1 time smaller than the focal length of the collimator lens 14.
mm shorter, and with this arrangement,
The light beam that has passed through the collimator lens 14 does not become substantially parallel light but becomes divergent light.

At the extension of the cylindrical lens 18 on the light beam emission side, a plane mirror 20 for reflecting the emitted light beam is arranged. The reflection side of the plane mirror 20 has a shape of a regular polygonal prism having a plurality of deflecting surfaces (mirror surfaces) having the same surface width on the side surface, and is driven by a driving unit (not shown) with the center axis being the rotation center in the direction of the arrow. A rotating polygon mirror 22 that rotates at an angular velocity is arranged.

An fθ lens 24 composed of a pair of lenses 24a and 24b is arranged between the plane mirror 20 and the rotary polygon mirror 22. In the case of the overfilled optical system, the fθ lens 24 converges the gentle divergent light reflected by the plane mirror 20 as an elongated line image wider than the image width of the rotary polygon mirror 22 in the main scanning direction. Thereby, the light is converged so as to straddle a plurality of deflection surfaces.

Further, the fθ lens 24 includes a rotating polygon mirror 22.
Is arranged so as to pass through the fθ lens 24 again, and converges the light beam that has passed again as a light spot on a photosensitive member, which will be described later.
It has a function of moving the light spot on the photoreceptor at a substantially constant speed in the main scanning direction.

On the side of the rotary polygon mirror 22 where the fθ lens 24 is disposed, a plane mirror 2 for reflecting the image recording light beam deflected by the rotary polygon mirror 22 is provided.
6 and a cylindrical mirror 28, and the light beam is reflected by the cylindrical mirror 28, and then reaches a photoreceptor 30 disposed below. Although the cylindrical mirror 28 is used in FIG. 2, a plane mirror or a cylindrical lens may be used. The cylindrical mirror 28 and the cylindrical lens have the power to converge the light beam in the sub-scanning direction, and correct the positional deviation (surface tilt) in the sub-scanning direction on the photoconductor 30 caused by the variation of the deflection surface of the rotary polygon mirror 22. It is preferable because it has the function of performing

The photosensitive member 30 has an elongated columnar shape with a photosensitive material responsive to a light beam applied to its surface, and is arranged such that the main scanning direction coincides with the longitudinal direction of the photosensitive member. Have been. That is, the light spot converged on the photoconductor 30 together with the rotation direction of the rotary polygon mirror 22 is:
It moves on the photoreceptor 30 along the main scanning direction, and the image can be recorded by the scanning line.

The photosensitive member 30 is rotated at a constant rotation speed by a driving means (not shown) about its rotation axis to sequentially move the scanning lines on the photosensitive member 30 in the sub-scanning direction.

Further, in order to set a write start position at which image recording is performed on these scanning lines, a plane mirror 32 which folds a light beam is formed on a path passing through the fθ lens 24, and a beam is formed in the sub-scanning direction. A cylindrical lens 34 to be operated and an SOS sensor 36 are arranged.

The SOS sensor 36 is connected to a control device, which will be described later. The control device starts modulating the image signal after a lapse of a predetermined time from when the output signal of the SOS sensor 36 is detected.

Further, on the optical path after scanning the SOS sensor 36 and on the path that reflects the cylindrical mirror 28 outside the area where an image is formed on the photosensitive member, the fluctuation of the beam diameter of the light beam is detected. A plane mirror 38 that folds the light beam and a detection unit 40 are arranged. Since the detection means 40 is arranged at a position substantially equivalent to the photoconductor 30, the amount of change in the beam diameter on the photoconductor 30 and the detection means 4
The change amount of the beam diameter on 0 becomes equal. That is, the beam diameter fluctuation can be detected by the detecting means 40.

The LD 12, which is a light source, modulates an image signal based on image information to perform optical scanning. The detecting means 40 detects an SOS for setting an image writing position.
After the sensor 36 is scanned by the LD 12, the sensor 36 is arranged in an area before an area where an image is formed.

As shown in FIG. 3, the detecting means 40 has a one-dimensional CCD sensor 44 and a photo sensor 46 arranged inside the holder 42 so that the direction of the element row is the same as the sub-scanning direction. Slit 4 in front of photo sensor 46
8 is provided.

FIG. 4 shows a one-dimensional CC with respect to the variation of the beam diameter.
FIGS. 4A and 4B show output signals of the D sensor 44 and the photo sensor 46. FIG. 4A shows a current signal with a proper beam diameter, and FIG. 4B shows a case where the beam diameter in the main scanning direction becomes large. FIG. 4C shows a current signal when the beam diameter in the sub-scanning direction becomes large.
(D) shows a current signal when the beam diameter in the main scanning direction and the beam diameter in the sub-scanning direction is increased. Thus, the beam diameter of the light beam incident on the detecting means 40 is determined by the detecting means 40.
Can be easily determined from the output signal of Based on this output signal, the steady light intensity and the rising light intensity of the light beam can be adjusted.

The detection means 40 is connected to the control device 80 as shown in FIG. 5, and the detection result of the detection means 40 is output to the control device 80. The control device 8
Reference numeral 0 denotes a microcomputer including a ROM, a RAM, a CPU, and a peripheral device, and as described above, an optical scanning device for controlling the modulation of the light beam output of the LD 12 based on image information and adjusting a light beam diameter to be described later. Of various controls. Further, the control device 80 is connected to an LD drive circuit 90 described later, and is configured to control the LD drive circuit 90.

FIG. 6 is a diagram for explaining an LD drive circuit 90 for adjusting the steady light intensity and the rising light intensity of the light beam. Note that the control device 80 and the LD drive circuit 90 correspond to control means of the present invention.

As shown in FIG. 6, the LD drive circuit 90 includes
A bias current source 50 for flowing a bias current having a predetermined current value to the LD 12 and a switching current source 52 for flowing a switching current having a predetermined current value to the LD 12 are provided.

The bias current source 50 and the switching current source 52 are grounded via resistors R1 and R2, respectively. The bias current source 50 and the switching current source 5
2 are connected to an enable (ENB) terminal 54, respectively, and function by receiving an ENB signal from the ENB terminal 54.

The bias current source 50 is connected to the LD 12. The LD 12 is connected to a power supply terminal 58 via an RLC circuit 56 for changing the rising light intensity, and a predetermined voltage is applied from the power supply terminal 58.

That is, the bias current source 50
A bias current having a predetermined current value flows through D12. The bias current source 50 is connected to the LD 12
Is set to be less than a threshold current required for outputting coherent light.

A load resistor RL is connected to the power supply terminal 58 in parallel with the LD 12. The LD 12 and the load resistor RL are connected to the collectors of npn transistors 60 and 62, respectively. The emitters of the transistors 60 and 62 are both connected to the switching current source 52,
The base is connected to the switch 64. Switch 64
Controls ON / OFF of the current flowing from the collector to the emitter by controlling the base currents of the transistors 60 and 62.
OFF is controlled.

The switch 64 is connected to the VIDEO terminal 66. The switch 64 is driven by a VIDEO terminal 66.
This is performed based on the VIDEO signal from. Thus, a light beam modulated based on the image data is generated.

On the other hand, the LD 12 package contains an LD
12 is a photodiode P for monitoring the amount of output light.
D is provided, and the diode and the diode PD are connected to the LD12.
And outputs a current corresponding to the output light quantity. This current is converted into a monitor voltage by a current-to-voltage converter (not shown) and input to the plus terminal of the comparator 68.

The minus side of the comparator 68 is connected to a reference voltage terminal 70, and a predetermined reference voltage is input from the reference voltage terminal 70. That is, the comparator 68 compares the monitor voltage with the reference voltage and outputs the result.

That is, by changing the reference voltage by the control means 80 based on the detection result of the detection means 40,
The steady light intensity of the light beam can be changed.

The output of the comparator 68 is supplied to the S / H circuit 7
S / H circuit 72 is connected to switching current source 5
2 is connected. The S / H circuit 72 changes the switching current set by the switching current source 52 based on the output of the comparator 68, and generates a switching current such that the monitor voltage matches the reference voltage. .

The LD 12 outputs coherent light when the threshold current is exceeded, and the light intensity has a characteristic proportional to the current (drive current) flowing through the LD 12. Therefore, S / H
The circuit 72 changes the switching current so that the monitor voltage coincides with the reference voltage, and outputs an optical beam having a predetermined light intensity set by the reference voltage.
Twelve light output controls can be performed.

Further, the S / H circuit 72 outputs the S / H (Samp
le / Hold) terminal 74, and a Sample signal or a Hold signal is input from the S / H terminal 74. The S / H circuit 72 is Sampl
The optical output of the LD 12 is controlled during the period when the signal e is input, and the result of the optical output control is held during the other period, that is, during the period when the Hold signal is input.

The resistance R of the RLC circuit 56 connected to the LD 12 is connected to a resistance value control terminal 57.
On the basis of the detection result of 0, the light intensity at the rising edge can be changed by changing the resistance value of the resistor R under the control of the control means 80.

Next, a procedure for changing the steady light intensity and the rising light intensity of the light beam in the optical scanning device configured as described above will be described. FIG. 1 is a flowchart showing a procedure for correcting the steady light intensity and the rising light intensity of the light beam in the control device 80 of the optical scanning device according to the present embodiment.

As shown in FIG. 1, after turning on the LD 12 in step 100, the control device 80 proceeds to step 102. In step 102, the detecting means 40, in the present embodiment, a one-dimensional CC in which the element rows are arranged in the sub-scanning direction.
The D sensor 44 detects a change in the beam diameter in the sub-scanning direction, and the detection result is input to the control device 80. The beam diameter variation in the sub-scanning direction depends on the CCD sensor 4 as shown in FIG.
4 and the number of CCD cells that have received the beam (in FIG. 4, described as the position in the sub-scanning direction). That is, by using the CCD sensor 44,
The change in the beam diameter in the sub-scanning direction can be detected as a change in the beam diameter, or can be detected as a change in the amount of light.

In step 104, the detection result in step 102 is stored in a memory (not shown)
It is determined whether or not the allowable value stored in the ROM or the like is exceeded. If the determination is affirmative, the routine proceeds to step 106, where the adjustment Look Up Ta is used.
The reference voltage of the LD drive circuit is obtained using ble (LUT), and the steady light intensity is adjusted by changing the reference voltage. That is, when the beam diameter in the sub-scanning direction increases, the reference voltage input to the reference voltage terminal 70 is changed so as to increase the drive current of the LD 12, and when the beam diameter decreases, the drive current of the LD 12 increases. By changing the reference voltage input to the reference voltage terminal 70 so as to reduce the light intensity, the light intensity at the center of the light beam that has fluctuated due to the fluctuation of the beam diameter or the light quantity can be maintained in an appropriate state. By doing so, it is possible to prevent the image quality from deteriorating due to the beam diameter fluctuation in the sub-scanning direction. If the determination in step 104 is negative, the process proceeds to step 108.

In this embodiment, the beam diameter fluctuation in the sub-scanning direction is detected by using the one-dimensional CCD sensor 44. However, the sensor is not limited to the one-dimensional CCD, but may be a two-dimensional CCD sensor. Other detection devices such as a photo sensor and a photo sensor may be used. The detection target may detect the maximum (peak) light amount when the light beam for one dot is turned on instead of the fluctuation of the beam diameter, and obtain the steady light intensity adjustment value from the maximum light amount. .

In step 108, the beam diameter variation in the main scanning direction is detected and detected by the detecting means 40, in this embodiment, the photosensor 46 having a slit 48 having a longitudinal opening in the sub-scanning direction disposed on the front side. The result is the controller 8
Input to 0.

In step 110, the detection result in step 108 is stored in a memory (not shown)
M, etc.) is determined. If the determination is affirmative, the routine proceeds to step 112, where a LookUp Table (LUT) for adjustment is used.
Is used to determine the RLC circuit constant of the LD drive circuit 90,
In the case of the present embodiment, the value of the resistor R is changed by inputting a signal for changing the resistance value of the resistor R to the resistance value control terminal 57, and the amount of overshoot at the rise of the LD drive current waveform is changed. Adjust the rising light intensity. That is, when the beam diameter in the main scanning direction increases, the LD
By increasing the amount of overshoot at the rise of the drive current waveform and decreasing the overshoot at the rise of the LD drive current waveform when the beam diameter becomes smaller, the light at the rise due to beam diameter fluctuation in the main scanning direction is reduced. The decrease in strength can be improved. By doing so, high-resolution fine-line reproducibility and half-tone reproducibility can be maintained. If the determination in step 110 is negative, the series of processing ends.

More specifically, as an example of the adjustment for the beam diameter fluctuation shown in FIG. 7, the nominal beam diameter shown in FIG.
As shown in (B), when the drawing state has changed (the line width has become narrower), the steady light intensity is adjusted by adjusting the LD drive current to correct the beam diameter in the sub-scanning direction. . Then, by adjusting the overshoot amount of the drive current waveform to adjust the light intensity at the time of light rising and correcting the beam diameter in the main scanning direction (FIG. 7C), the main scanning direction and the sub-scanning direction are adjusted. Can be corrected for the variation in the beam diameter. FIG. 7A shows the nominal drawing state, LD drive waveform, and light intensity characteristics.
(B) Drawing state when beam diameter becomes large, LD
FIG. 7C shows driving waveforms and light intensity characteristics, and FIG.
FIG. 14 shows a drawing state, an LD drive waveform, and a light intensity characteristic when (B) is corrected.

By adjusting the beam diameter in the main scanning direction after adjusting the beam diameter in the sub-scanning direction, even if the beam diameter changes due to a change in temperature or the like, the main scanning direction can be adjusted. The beam diameter in the scanning direction and the sub-scanning direction can be adjusted with high accuracy. In other words, if the adjustment in the main scanning direction (adjustment of the rising light intensity) is performed first, the steady light intensity is changed during the adjustment in the sub-scanning direction, so that the previously adjusted rising light intensity is adjusted in the sub-scanning direction. (The steady light intensity fluctuation is added to the rising light intensity). Therefore, if the order of adjustment in the main scanning direction and the sub-scanning direction is interchanged, the adjustment accuracy will deteriorate. However, in the present embodiment, as described above, after the adjustment for the beam diameter variation in the sub-scanning direction is performed, Since the adjustment for the fluctuation of the beam diameter in the scanning direction is performed, the adjustment can be performed without deteriorating the adjustment accuracy, whereby the fine line reproducibility of high resolution and the reproducibility of the halftone can be maintained, and a favorable Image quality can be maintained.

In the above-described embodiment, the beam diameter fluctuation in the main scanning direction is detected by the photo sensor 46. However, the sensor is not limited to the photo sensor 46, but may be another type such as a two-dimensional CCD sensor. A detection device may be used. When a two-dimensional CCD sensor is used, the light beam is pulsed on the light receiving surface of the CCD for a time corresponding to one dot to detect the beam diameter in the main scanning direction and the beam diameter in the sub-scanning direction from the received image. It is possible.

In the above embodiment, the CCD sensor 44 detects the beam diameter fluctuation in the sub-scanning direction. However, the present invention is not limited to this. For example,
Photosensor 46 for detecting beam diameter variation in the main scanning direction
It is also possible to arrange the slit 48 provided on the front surface of the photosensor at an angle with respect to the scanning direction, and to detect the beam diameter in the sub-scanning direction from the relationship between the time and current obtained from the photosensor.

The detecting means 40 may directly detect the fluctuation of the beam as in the above-described embodiment, or may detect the fluctuation of the temperature by a temperature sensor or the like. When a temperature sensor is used, the beam diameter variation with respect to the temperature variation is determined in advance, and the relational value is set to LU.
By storing in the memory as T, it becomes possible to estimate the beam diameter fluctuation amount, that is, the light intensity at the steady light rising to be adjusted, from the temperature fluctuation amount.

Further, in the above-described embodiment, the detecting means 40 is arranged on the scanning start side. However, the present invention is not limited to this. The detecting means 40 may be arranged outside the image forming area on the scanning end side. , SOS sensor 36 may be provided on the optical path before scanning.

[0076]

As described above, according to the present invention, the state of the light beam output from the light emitting source is detected, and the light emitting source is changed so that the steady light intensity of the light beam changes based on the detection result. After controlling the light source, the light intensity at the center of the light beam can be maintained in an appropriate state by controlling the light emission source so that the light intensity at the rising of the light beam changes, and at the time of rising due to fluctuation in the beam diameter. Therefore, even if the beam diameter fluctuates due to a change in temperature or the like, good image quality can be maintained with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure for correcting a steady light intensity and a rising light intensity of a light beam in an optical scanning device according to the present embodiment.

FIG. 2 is a perspective view showing a schematic configuration of an optical scanning device according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a detection unit.

4A and 4B are diagrams showing output signals of a one-dimensional CCD sensor and a photosensor with respect to a change in a beam diameter. FIG. 4A shows each output signal in a state where a beam diameter is appropriate, and FIG. Each output when the beam diameter becomes large,
(C) shows each output when the beam diameter in the sub-scanning direction increases, and (d) shows each output when the beam diameter in the main scanning direction and the sub-scanning direction increases.

FIG. 5 is a block diagram showing a control system for correcting a beam diameter variation.

FIG. 6 is a diagram for explaining an LD drive circuit for adjusting a steady light intensity and a rising light intensity of a light beam.

FIGS. 7A and 7B are diagrams illustrating an example of adjustment with respect to beam diameter fluctuation, wherein FIG. 7A illustrates a nominal writing state, an LD drive current waveform, and light intensity characteristics, and FIG. 7B illustrates writing when the beam diameter is increased; (C) shows a drawing state when (B) is corrected, and shows an LD driving current waveform and light intensity characteristics.
7 shows a drive current waveform and light intensity characteristics.

FIG. 8 is a diagram illustrating an example of a conventional optical scanning device.

FIG. 9 is a diagram showing light intensity distributions at various beam diameters when the light emission power of the LD is fixed.

10A and 10B are diagrams illustrating a drawing state due to a change in beam diameter in the main scanning direction and the sub-scanning direction. FIG. 10A illustrates a drawing state when the beam diameter in the main scanning direction and the sub-scanning direction is appropriate. (b) shows the drawing state when the beam diameter in the main scanning direction becomes large, and (c) shows the drawing state when the beam diameter in the sub-scanning direction becomes large.

FIG. 11 is a diagram illustrating an example of a beam diameter correcting unit in a conventional optical scanning device.

12A and 12B are diagrams for explaining correction of a beam diameter in a conventional optical device, in which FIG. 12A shows a signal from a laser driver, and FIG. 12B shows the relationship between the laser beam diameter and exposure distribution. (C) shows an output signal from the CCD.

FIG. 13 is a diagram showing another example of the beam diameter correcting means in the conventional optical scanning device.

[Explanation of symbols]

 Reference Signs List 10 optical scanning device 12 semiconductor laser 40 detection means 44 one-dimensional CCD sensor 46 photo sensor 48 slit 50 bias current source 52 switching current source 56 RLC circuit 68 comparator 70 reference voltage terminal 72 S / H circuit 80 control device 90 LD drive circuit PD F and diode R resistance

Continued on the front page F term (reference) 2C362 AA03 AA20 AA28 AA29 AA32 AA33 AA54 AA61 2H045 CB22 CB41 DA02 5C072 AA03 BA13 HA02 HB02 HB04 HB10 XA01 XA05

Claims (3)

[Claims] 1. An optical scanning device that turns on a light emitting source that outputs a light beam based on image information, and optically scans a photosensitive member with the light beam output from the light emitting source. Detecting means for detecting, after controlling the light emitting source so that the steady light intensity of the light beam changes based on the detection result of the detecting means, the light intensity at the rising edge of the light beam changes. An optical scanning device comprising: a control unit configured to control a light emitting source. 2. The method according to claim 1, wherein the detecting unit detects a beam diameter variation in a main scanning direction and a sub-scanning direction as a state of the light beam,
The control unit controls the light emitting source so that the steady light intensity of the light beam changes based on the detection result of the beam diameter variation in the sub-scanning direction by the detection unit, and then controls the light source in the main scanning direction by the detection unit. The optical scanning device according to claim 1, wherein the light emitting source is controlled so that the light intensity at the rising of the light beam changes based on the detection result of the beam diameter fluctuation. 3. The detecting means detects a light intensity fluctuation of the light beam and a beam diameter fluctuation in a main scanning direction as a state of the light beam, and the control means detects a light intensity fluctuation detected by the detecting means. After controlling the light emission source so that the steady light intensity of the light beam changes based on the light intensity at the rising of the light beam based on the detection result of the beam diameter fluctuation in the main scanning direction by the detection means. The optical scanning device according to claim 1, wherein the light source is controlled to change.