JP2015060009A - Optical scanning device, light source emission method of optical scanning device, and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a same print quality even if light quantity changes by preventing surface stain and improving reproducibility of pulse width.SOLUTION: An optical scanning device 40 includes: a light source; a light source emission device 101 which makes the light source illuminate; and a scanning optical system which deflects, for scanning, the light emitted from the light source on a scanned surface of a photosensitive body. It includes: a first bias current control part 50(1); a modulation current control part 50(3); and a second bias current control part 50(2). A bias current that is inputted in the light source includes a first bias current and a second bias current. A first bias current value is a constant value, and the second bias current has a feature in which a total value of the first bias current and the second bias current is changed according to a target light emission amount within a range of less than a threshold value current of the light source so that reproducibility of pulse width is maintained regardless of the target light quantity.

Description

  The present invention relates to an optical scanning device, a light source emission method of the optical scanning device, and an image forming apparatus.

  In an electrophotographic image forming apparatus such as a laser printer, a digital copying machine, and a facsimile apparatus, an image is written by a light beam scanning method. In this light beam scanning method, for example, a semiconductor laser is used as a light source, and a laser beam emitted from the semiconductor laser is scanned in a main scanning direction on a scanned surface of a photoconductor to be image-written by a scanning means such as a polygon mirror. To write an image line by line on the photoreceptor. In this case, the light quantity of the laser beam irradiated to the photoconductor is changed according to, for example, the rotation speed of the photoconductor or deterioration due to aging of the photoconductor.

By the way, when changing the light quantity of the semiconductor laser, it is known that when the driving current of the semiconductor laser is low, that is, the light emission amount is small, the rise of the semiconductor laser light is delayed as compared with the case where the light emission amount is large. . Such a phenomenon of the semiconductor laser is called an oscillation delay.
When an oscillation delay occurs between the pulse waveforms of a plurality of emitted laser beams, a difference occurs in the pulse width in the pulse waveform of the semiconductor laser, and the pulse width reproducibility (here, the pulse width of the ideal waveform of the emission signal) A difference occurs in the ratio of the pulse width of the actually obtained light amount).
If the pulse width reproducibility varies depending on the amount of light emission, there arises a problem that printing cannot be performed with the same line width, that is, the same print quality cannot be maintained.

  As a method for improving the repetition rate of the oscillation delay or pulse width, in a device for driving a semiconductor laser (referred to as a semiconductor laser light emitting device), a current that does not exceed the threshold current before the semiconductor laser emits light (referred to as a bias current). Is known to be applied to a semiconductor laser light emitting device and the drive current is made up of a modulation current and a bias current to increase the drive current.

  However, in this method, a bias current close to the threshold current is input to the semiconductor laser light emitting device in addition to the modulation current. For this reason, the semiconductor laser emits light spontaneously (bias light emission) due to the bias current, and a latent image is formed on the photosensitive member due to the light emission, which causes another problem of so-called scumming.

Here, regarding the problem of soiling, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2004-153118), the bias current is configured in two stages in a semiconductor laser starting device or the like, and the first bias current is grounded. It is described that a constant current value smaller than a threshold current at which no contamination occurs is generated, and a second bias current is superimposed and output for a short time immediately before light emission of the semiconductor laser. In this case, the sum of the first and second bias current values does not exceed the threshold current, so that the problem of oscillation delay and the problem of soiling due to the bias current are reduced.
However, in the semiconductor laser light emitting device described in Patent Document 1, the first and second bias currents are constant regardless of the light amount of the semiconductor laser activation device, and therefore, there is a difference in the pulse width recall due to the oscillation delay. The problem that appears can not be solved.

On the other hand, in relation to this problem, for example, an image forming apparatus described in Japanese Patent Application Laid-Open No. 2004-268436 is known.
The purpose of this image forming apparatus is to ensure a stable halftone gradation even if the amount of light of the semiconductor laser is changed by adjusting one bias current. Although there is no expression of width reproducibility, it is understood that the oscillation delay has been improved.
However, in this image forming apparatus, for the purpose of adjusting one bias current, the current value has to be close to the threshold current, and it is difficult to suppress the occurrence of soiling due to bias emission.

  As described above, the problem of oscillation delay and the problem of preventing scumming are known, and the respective solutions are also known. However, in the optical scanning device equipped with the conventional semiconductor laser device, these problems were solved at the same time. There is nothing.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to prevent scumming and improve the reproducibility of the pulse width, so that the same print quality can be obtained even if the amount of light changes. Is to maintain.

  The present invention is an optical scanning device comprising: a light source; a light source light emitting device that emits the light source; and a scanning optical system that deflects and scans light irradiated from the light source on a scanned surface of a photoreceptor. A light source light emitting device generates a first bias current and outputs the light source according to a light emission signal input to the light source light emitting device, and outputs the first bias current control unit to the light source before emitting light. A modulation current control unit that generates a modulation current and outputs it to the light source; a second current that generates a second bias current and outputs the first bias current to the light source and then outputs the modulation current to the light source A bias current control unit, wherein a bias current input to the light source is configured by the first bias current and the second bias current, the first bias current value is a constant value, and the second bias current Depending on the target light emission amount, the sum of the first bias current and the second bias current is less than the threshold current of the light source so that the pulse width reproduction rate is maintained regardless of the target light amount. The optical scanning device is characterized by being changed.

  According to the present invention, it is possible to maintain the same print quality even when the amount of light is changed by preventing the background stain and improving the reproducibility of the pulse width.

1 is a diagram schematically illustrating an image forming apparatus including an optical scanning device according to an embodiment. It is a figure shown about the structure of the optical scanning device shown in FIG. It is a block diagram which shows schematically the control part of an optical scanning device. It is a flowchart which shows the output procedure of a 2nd bias current and 2nd bias current application time. It is a table | surface which shows the relationship between target light emission amount, a 2nd bias current value coefficient, and a 2nd bias current application time coefficient. It is the figure which represented the result of the pulse width reproduction rate for every target luminescence amount. It is the figure which represented the result of the pulse width reproduction rate for every target luminescence amount. It is a figure which shows the pulse width for demonstrating the reproduction rate of a pulse width. It is a figure which shows the time change of the drive current with respect to different target light emission amount P1, P2. It is a figure which shows the time change of the emitted light amount of a semiconductor laser when each drive current which changes with time with respect to different target emitted light amount P1, P2 is applied to a semiconductor laser light-emitting device. It is a figure which shows the time change of the drive current of the same target light emission amount P2 in case environmental temperature differs. It is a figure which shows the time change of the emitted light amount of a semiconductor laser when the drive current which changes with time in the same target emitted light amount P2 in case environmental temperature differs is applied to a semiconductor laser light-emitting device. It is a figure which shows the time change of the emitted light amount of a semiconductor laser by the drive current of the method of making the 2nd bias current immediately before the modulation current output constant, irrespective of the emitted light amount of the conventional semiconductor laser.

Next, an embodiment of the optical scanning device of the present invention will be described with reference to the drawings.
Here, first, the entire image forming apparatus including the optical scanning device according to the present embodiment will be schematically described.
FIG. 1 is a diagram schematically illustrating an image forming apparatus including an optical scanning device according to the present embodiment.
The image forming apparatus includes a photosensitive drum 10, a charging unit 12, a toner cartridge 14 of a developing unit, a transfer roller 16, and a cleaner (not shown) that removes toner on the photosensitive drum 10. Further, the intermediate transfer belt 20, the intermediate transfer roller 22, the intermediate transfer belt cleaning device 24, the transfer device 26, the paper feed registration sensor 28, the fixing device 30, the paper discharge roller 32, and the optical scanning device 40. It is composed of

  In this image forming apparatus, during operation, the optical scanning device 40 exposes a timing-controlled light beam onto the photosensitive drum 10 to form an electrostatic latent image. The formed electrostatic latent image is developed with toner supplied from the toner cartridge 14. The toner image on the photosensitive drum 10 is transferred onto the intermediate transfer belt 20 by the transfer roller 16.

  On the other hand, the transfer sheet S is fed between the intermediate transfer belt 20 and the transfer device 26 in synchronization with the conveyance of the toner image on the intermediate transfer belt 20. Here, the transfer device 26 transfers the toner image onto the transfer paper S, and the fixing device 30 applies heat and pressure to the transfer paper S on which the toner image is transferred to fix it. After fixing, the transfer paper S is discharged by a paper discharge roller 32 attached to a paper discharge device and stacked on a paper discharge tray (not shown).

FIG. 2 is a diagram showing the configuration of the optical scanning device 40 shown in FIG.
The optical scanning device 40 includes a semiconductor laser (light source) light emitting device 101, a coupling lens 102, an aperture 103, a cylindrical lens 104, a polygon mirror 105, lenses 106 and 107, and a mirror 108. In addition, a photosensitive member 109 as a photosensitive medium, a synchronous mirror 110, a synchronous lens 111, a synchronous sensor 112, and a control unit 60 are included. These constitute a scanning optical system that deflects the light emitted from the semiconductor laser and guides it to the photoreceptor 109.

The light source light emitting device 101 is a semiconductor laser element that emits a light beam for optical scanning, and is driven by the control unit 60 according to image data. When the light beam that has passed through the coupling lens 102 passes through the opening of the aperture 103, a portion having a low light intensity at the periphery of the light beam is blocked, that is, the beam is shaped, and the cylindrical lens 104 that is a linear imaging optical system. Is incident on.
The cylindrical lens 104 condenses the incident light beam in the sub-scanning direction, and condenses it in the vicinity of the deflection reflection surface of the polygon mirror 105 that is an optical deflector.

The light beam reflected by the deflecting and reflecting surface of the polygon mirror 105 passes through the two lenses 106 and 107 constituting the scanning optical system while being deflected at a constant angular velocity as the polygon mirror 105 rotates at a constant speed. Further, the optical path is bent by the mirror 108, and the light is condensed and scanned as a light spot on the surface that is the photosensitive surface of the photoconductive photosensitive member 109 that forms the surface to be scanned. As a result, an electrostatic latent image is formed on the photoconductor 109.
Prior to scanning, the light beam enters the reflection mirror 110 and is reflected, and is collected by the synchronization lens 111 onto the synchronization sensor 112, which is a light receiving element. The timing of optical writing with the light beam to the photoconductor 109 is determined by a semiconductor laser light emitting device to be described later based on the output signal of the synchronization sensor 112.

Next, the second bias current control in the optical scanning device according to the present embodiment will be schematically described, and then components for performing the control will be described.
The image forming apparatus equipped with this optical scanning device maintains the same print quality even when the amount of light changes, by preventing smudges and eliminating the difference in pulse width recall (referred to as improved reproducibility). The purpose of this is as follows.

In other words, this optical scanning device has a pulse width of the laser pulse when the semiconductor laser emits light according to the target light emission amount based on the target light emission amount (the optimum light amount for the photosensitive member at that time) and the ambient temperature of the semiconductor laser. Control so that it can be kept constant. That is, good reproducibility of the pulse width is obtained.
For this reason, here, when a bias current is applied to the semiconductor laser light emitting device 101, the bias current value does not exceed the threshold current value of the semiconductor laser, and the occurrence of soiling is minimized. In addition, the second bias current value is adjusted so that good reproducibility of the pulse width can be obtained.
As will be described later, the adjustment first determines the current value of the first bias current that always takes a constant value, and then determines the second bias current according to the light emission amount of the semiconductor laser light emitting device.
For the second bias current, a reference current value and a reference second bias current value are determined by a method to be described later, and the amount of laser light output from the semiconductor laser light emitting device and the environmental temperature with respect to the reference second baice current value. Change the parameter determined by
A method of obtaining the reference second bias current value and parameters will be described later.

FIG. 3 is a block diagram schematically illustrating a control unit of the optical scanning device.
The control unit 60 of the optical scanning device includes an ASIC (Application Specific Integrated Circuit) constituting a semiconductor laser light emitting circuit (LD driver) 50, a semiconductor laser (LD) light emitting device 101, a temperature sensor 53, and a CPU 51. An image input device 52 is connected. The LD driver 50 includes a first bias current control unit 50 (1), a second bias current control unit 50 (2), a modulation current control unit 50 (3), and a drive current control unit 50 (4).

The first bias current control unit 50 (1) always generates a constant (or predetermined) current value (referred to as the first bias current Ib1), and the second bias current control unit 50 (2) determines the light emission amount or the environmental temperature. In response to this, a predetermined current value (referred to as second bias current Ib2) is generated.
Further, the modulation current control unit 50 (3) generates the modulation current Im according to the light emission command signal from the image input device 52.
The drive current controller 50 (4) receives the first bias current Ib 1, the second bias current and Ib 2, and the modulation current Im, and sums these currents and outputs them as a drive current to the semiconductor laser light emitting device 101.

The CPU 51 outputs a control signal (initialization command signal) to the LD driver 50, and the image input device 52 outputs various signals such as a light emission command signal (light emission signal) and a bias current setting signal to the LD driver 50. Further, temperature information for detecting the temperature (environment temperature) of the semiconductor laser usage environment is input from the temperature sensor 53 to the CPU 51.
The LD is provided with a monitor photodiode (PD) (not shown) that detects the light emission amount of the semiconductor laser light emitting device 101. Further, a storage unit (not shown) is provided for storing a table (table) (FIG. 5) for obtaining a program executed by the CPU 51, a second bias current value, and the like.

Next, a method for setting a second bias current for performing laser emission by the control unit 60 of the present optical scanning device will be described.
FIG. 4 is a flowchart showing an output procedure of the second bias current value and the second bias current application time.
The control unit 60 (CPU 51) of the optical scanning device outputs a target light emission amount (laser light amount optimum for the sensitivity of the photosensitive member 109 at that time) to the LD driver 50 (S101).

Next, the CPU 51 reads temperature information from the temperature sensor 53 and stores the ambient temperature of the semiconductor laser in a storage unit (not shown) (S102).
In addition, the CPU 51 stores a table (to be described later) corresponding to the target light emission amount and the environmental temperature (a table recording parameters for determining the application time of the second bias current value and the second bias current value corresponding to the target light emission amount; 5A and 5B are read (S103).
The second bias current value and the second bias current application time are calculated from the parameters (coefficients) of the read table, the reference second bias current value, and the reference second bias current application time (S104).
The calculated second bias current value and second bias current application time are output to the LD driver (S105).

Next, a method for determining each parameter of the table will be described.
First, a method for obtaining the reference second bias current value of the present embodiment will be described.
Here, the light emission amount when the light emission amount used in the present optical scanning device (semiconductor laser light emitting device 101) is the smallest is P0, and the second bias current value at this time is the reference second bias current value.
The reference second bias current value is the maximum value because the light emission amount is the minimum. Here, if the sum of the first bias current and the second bias current exceeds the threshold current, the background is contaminated with laser light. Therefore, the second bias current value needs to be a value that does not exceed a value obtained by subtracting the first bias current value that is a constant value from the threshold current value of the semiconductor laser (less than the threshold current).
In this case, the maximum value of the reference second bias current value is a value obtained by subtracting a first bias current value that is a constant value from the threshold current value of the semiconductor laser light emitting device 101. This value can be uniquely determined because the threshold current value and the first bias current value of the semiconductor laser light emitting device 101 are constant.
It should be noted that in the processing by the execution of the program in the optical scanning device, the reference second bias current value calculated from the threshold current value may be rounded down to be the reference second bias current value.

Next, a ratio (Harus width reproduction ratio) between the pulse waveform width of the laser beam at the light emission amount P0 and the pulse waveform width in the rectangular wave which is an ideal value is obtained, and this is obtained in the semiconductor laser light emitting device 101. The target recall rate is N.
In this way, after obtaining the target reproducibility N of the semiconductor laser light emitting device 101, next, when the target light emission amounts P1, P2,... Pn other than the reference light emission amount P0 in the semiconductor laser light emitting device 101 are obtained. In addition, a second bias current value necessary to obtain the target recall N is obtained.

That is, here, at room temperature (for example, 25 ° C.), the application time of the second bias current value to the semiconductor laser light emitting device 101 is constant, and for each target light emission amount (P1, P2,... Pn), The pulse width reproduction rate obtained at that time is obtained by changing the second bias current value (a specific method for obtaining the pulse width reproduction rate will be described later).
FIG. 6A. B is a graph showing the results for each target light emission amount. The pulse width recall rate (%) is on the vertical axis and the second bias current value is on the horizontal axis. Is the second bias current value when the target reproduction ratio N (for example, N = 96%) is reached.
Next, the ratio of the second bias current value at each light quantity (P1, P2,... Pn) and the reference second bias current value is obtained.

Next, similarly, at a normal temperature (for example, 25 ° C.), the second bias current value applied to the semiconductor laser light emitting device 101 having the second bias current value is made constant, and the target light emission amount (P1, P2,... Pn). Each time the second bias current application time is changed, the pulse width recall obtained at that time is obtained.
FIG. 7A. B is a graph showing the result for each target light emission amount. The pulse width recall rate (%) is on the vertical axis and the second bias current application time is on the horizontal axis. A second bias current application time when the recall reaches a target recall N (for example, N = 96%) is obtained.
Next, a ratio between the second bias current application time and the reference second bias current application time at each light amount (P1, P2,... Pn) is obtained.
The reference second baice current application time is the application time of the reference second baice current when the reference second bias current is applied and the target recall N is obtained.
A table summarizing the ratio between the second bias current value and the reference second bias current value at each light quantity, and the ratio between the second bias current application time and the reference second bias current application time at each light quantity. (Table of FIG. 5A) is created.

The table of FIG. 5B is obtained by repeating the same experiment in a state where the table of FIG. 5A is obtained and the temperature is increased (the temperature is increased by 20 ° C. from the state of Table 1).
Here, the pulse width reproducibility (%) is, for example, that the target light emission amount is P1, the first bias current and the second bias current application time are fixed, and image data with a pulse width of 1 dot and a constant temperature environment. Turn on the laser under. The width of the pulse waveform of the obtained laser beam is measured and calculated as a ratio between the measured value and the Halth width of the ideal optical pulse waveform.
FIG. 8 is a diagram showing a pulse width for explaining the recall ratio of the pulse width.
The pulse width obtained by measurement is t1 in FIG. 8B, which is obtained as a ratio (t1 / t0) to the time t0 in the rectangular wave that is an ideal waveform at the light amount P1 in FIG. 8A.

Next, a result of actually adjusting the second bias current corresponding to the target light emission amount will be described based on the tables of FIGS. 5A and 5B thus obtained. The coefficients in FIGS. 5A and 5B decrease at a predetermined ratio as the target light emission amount increases.
FIG. 9 is a diagram showing the change over time in the drive current for different target light emission amounts P1 and P2 (P1 <P2).
9A and 9B show that when the target light emission amounts P1 and P2, the second bias current Ib2 is superimposed on the first bias current Ib1 that is always applied, and then the modulation current Im is superimposed. 9A and 9B, as is clear from the comparison with FIGS. 9A and 9B, in the case of P2 larger than the target light emission amount P1, the second bias current value is large and the application time of the second bias current value is also long. long.

FIG. 10 shows temporal changes in the light emission amount of the semiconductor laser when the drive currents varying with time for different target light emission amounts P1 and P2 are applied to the semiconductor laser light emitting device.
As shown in FIG. 10, by changing the second bias current value and the second bias current value application time according to the target light emission amount, the pulse width of the laser light becomes substantially constant regardless of the light emission amount.

FIG. 11 is a diagram illustrating a change over time of the drive current with respect to the same target light emission amount P2 when the environmental temperatures are different.
11A and 11B show that when the target light emission amount P2, the second bias current value to be applied is larger when the temperature is high (here, 60 ° C.) than when the temperature is low (here, 25 ° C.). This indicates that the application time is long.
FIG. 12 shows a temporal change in the light emission amount of the semiconductor laser when a time-varying drive current at the same target light emission amount P2 is applied to the semiconductor laser light emitting device when the ambient temperature is different.
As shown in FIG. 12, by adjusting the second bias current value and the application time thereof, the pulse width of the laser light waveform almost completely matches. The reproducibility of the width is very good.

FIG. 13 is a diagram illustrating a temporal change in the light emission amount of the semiconductor laser due to the drive current when the second bias current immediately before the modulation current output is constant regardless of the light emission amount of the conventional semiconductor laser.
The second bias current of the conventional semiconductor laser shown in FIG. 13 has the same current value and the same current application time in both cases of the target light emission amounts P1 and P2. Therefore, in FIG. 13, when the target light emission amount P1 is low, the pulse width of the light emission amount is shorter than that of the high target light emission amount P2 (compared with the rising waveform of the target light emission amount P2). That is, a time difference Δt2 is generated, and the pulse width of the pulse waveform of the light emission amount is shortened.
On the other hand, FIG. 10 shows that the time difference is small compared to FIG. 13 and the reproducibility of the pulse width is good as is clear when compared with FIG. 13 shown in the conventional example.

In the present embodiment, by changing the second bias current value and the second bias current application time tb2 according to the target light emission amount, the pulse width of the pulse waveform of the light emission amount as shown in FIG. 6 can be realized. Even if the target light emission amount is different, that is, even when the light intensity is low, the rise of the pulse waveform of the light emission amount is the same as in the case of the high light emission amount, and the reproducibility of the pulse width when used with a low light amount can be improved. it can.
By improving the reproducibility of the pulse width, it is possible to maintain the pulse width of the emitted laser light constant even if the target light emission amount changes due to, for example, changing the printing speed or updating the photoreceptor. Can maintain the print quality.

  50 ... LD driver, 50 (1) ... first bias current control unit, 50 (2) ... second bias current control unit, 50 (3) ... modulation current control unit, 50 (4 ) ... Driving current control unit, 51 ... CPU, 52 ... Image input device, 53 ... Temperature sensor, 60 ... Control unit, 101 ... Semiconductor laser (LD) light emitting device, Ith ... threshold current, Iη ... light emission current, Ib ... bias current, Ib1 ... first bias current, Ib2 ... second bias current, Im ... modulation current, tb2 ... first Two bias current application time, LD ... Semiconductor laser (PD: Including photodiode)

JP 2004-153118 A JP 2004-268436 A

Claims (6)

An optical scanning device comprising: a light source; a light source light emitting device that emits light from the light source; and a scanning optical system that deflects and scans light irradiated from the light source on a surface to be scanned of a photoreceptor.
The light source light emitting device generates a first bias current and outputs the light source according to a light emission signal input to the light source light emitting device, and outputs the first bias current control unit to the light source before emitting light. A modulation current control unit that generates and outputs a modulation current to the light source, and a second bias current that is generated and output to the light source after the first bias current is output to the light source and before the modulation current is output. A two-bias current control unit;
With
The bias current input to the light source is composed of the first bias current and the second bias current, the first bias current value is a constant value, and the second bias current is independent of the target light emission amount. The sum of the first bias current and the second bias current is changed in accordance with a target light emission amount within a range in which the sum of the first bias current and the second bias current is less than a threshold current of the light source so that a pulse width reproduction rate is maintained. Optical scanning device. The optical scanning device according to claim 1,
The second bias current is defined as a reference second bias current value obtained by subtracting the first bias current from the threshold current value when the light source has the smallest target light emission amount, and the reference second bias current value is applied. An optical scanning device that reduces the reference second bias current value and the reference second bias current application time at a predetermined ratio based on a target light emission amount of the light source, with time being a reference second bias current application time. The optical scanning device according to claim 1 or 2,
A light having a table that stores predetermined ratios of the second bias current value with respect to the reference second bias current value and the second bias current application time with respect to the reference second bias current application time for each target light emission amount. Scanning device. The optical scanning device according to claim 3,
The optical scanning device, wherein the table is created for each environmental temperature of the light source.   An image forming apparatus comprising the optical scanning device according to claim 1. A light source emission control method for an optical scanning device having a light source, a light source light emitting device that emits light from the light source, and a scanning optical system that deflects and scans light irradiated from the light source on a scanned surface of a photoreceptor,
A first bias current output step of generating a first bias current and outputting to the light source before emitting light; and generating a second bias current and outputting the first bias current to the light source; A second bias current generating step for outputting to the light source before outputting; a modulation current outputting step for generating a modulated current for causing the light source to emit light in accordance with a light emission signal input to the light source light emitting device and outputting the modulated current to the light source; ,
Have
The first bias current value is set to a constant value, and the second bias current is a sum of the first bias current and the second bias current so that the pulse width reproducibility is maintained regardless of the target light emission amount. A light source emission control method for controlling to change according to a target emission amount within a range in which a value is less than a threshold current of the light source.

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