JP2000355117A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus wherein speeding-up and high resolution of image forming is achieved without varying an emission quantity of a laser light source by the image forming mode, durability of a laser device is attained and change in registration of a laser light in a main scanning direction by an image forming mode does not occur. SOLUTION: This image forming apparatus forms an image on a photosensitive body in accordance with image information by introducing a laser light to the photosensitive body. A laser driving circuit in the image forming apparatus comprises a bias current superposing means 58 that applies a bias current to a laser light source 51 and a switch current applying means 57 that allows the laser light source 51 to emit a light in accordance with image information by applying a current corresponding to the image information in addition to the bias current. The light quantity of the laser light source 51 at a time when the image corresponding to the image information is formed on the photosensitive body is not changed but the quantity of the bias current to the laser light source from the bias current superposing means 58 is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copier, a printer, a facsimile machine, and the like, in which a laser beam modulated from a laser light source is guided to the surface of a photoreceptor to obtain an image corresponding to image information. To an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, for example, an image forming apparatus using an electrophotographic method has, for example, a drum-shaped electrophotographic photosensitive member as a photosensitive member serving as an image carrier, and the surface of the photosensitive member is charged by charging means. After being uniformly charged, the surface of the photoreceptor is exposed according to the image information by a laser beam modulated according to the image information, for example, from a laser light source as an exposure unit, and the surface is exposed to an electrostatic force corresponding to the image information. Form a latent image. Thereafter, a developing device containing a so-called toner, for example, using a resin as a base as a developer, transfers and attaches the toner to an image portion of an electrostatic latent image on the photoconductor, thereby visualizing the toner. A so-called toner image is formed. The toner image is subsequently transferred onto the recording material, for example, electrostatically by the action of the transfer unit. The unfixed toner image transferred onto the recording material is then fixed on the recording material by, for example, heat and pressure in a fixing device, and becomes a permanent image.

In an image forming apparatus using a semiconductor laser element as a laser light source as an exposure means as in the above-mentioned conventional image forming apparatus, the laser drive circuit controls light emission of the semiconductor laser element.

In a conventional laser drive circuit, a constant DC current is supplied to a semiconductor laser element, and a switch current (pulse current) for switching the semiconductor laser element according to image information is supplied in addition to the DC current. This is a general method.

[0005] A semiconductor laser element has a changing point which is a threshold current for emitting laser light. If a current smaller than this threshold current is applied only, the semiconductor laser element does not emit laser light and the phase is changed. Diode emission, which is discrete diffused light, is performed. The light quantity during this diode emission is
Extremely small compared to laser emission.

As described above, the semiconductor laser device emits laser light only when a current larger than the threshold value flows. This is because a semiconductor laser device performs laser oscillation.
This is because it is necessary to exceed a certain energy level inside the semiconductor laser element. If a current exceeding this energy level is passed through the semiconductor laser element, the amount of laser emission can be controlled by a slight increase or decrease in the amount of current thereafter.

Therefore, a DC current is supplied to the semiconductor laser device as described above (hereinafter, this current is referred to as a "bias current"), and the energy level inside the semiconductor laser device is increased, and laser emission is started from that state. In this case, the time required for exceeding the energy level for laser emission is shorter than that in the case where no bias current is supplied to the semiconductor laser device.

As described above, since the emission characteristics of the semiconductor laser device can be improved, a method in which a bias current and a switch current are supplied to the semiconductor laser device has been conventionally used in a laser driving circuit.

Conventionally, the amount of laser light emitted from a semiconductor laser element is detected, for example, by using a photodetector such as a photodiode, and is automatically controlled (APC: AUTO POWER CONTROL) to maintain a constant amount of light emitted. The semiconductor laser element and the photodiode can be a laser chip integrally unitized.

Here, the semiconductor laser element has a temperature characteristic, and the magnitude of the threshold current for laser emission largely depends on the ambient temperature of the semiconductor laser element (the temperature of the laser chip). In general, the output of a photodiode built into a laser chip for controlling the light emission amount of a semiconductor laser element is very small when the semiconductor laser element emits diode light (bias light emission). However, it was very difficult to control the amount of bias current.

For these reasons, if the bias current flowing through the semiconductor laser element is set to a fixed value near the threshold current for laser emission, there is a possibility that erroneous emission of laser light may occur due to a change in temperature. Conventionally, since it was not necessary to control a very high-speed minute pulse for laser emission, the bias current was fixedly set to less than half the threshold value, and a latent image was actually formed on the photoreceptor. Is controlled using the output of a built-in photodiode.

However, in recent years, the speed of the image forming apparatus and the definition of the formed image have been increased, and the ON / OFF frequency of the laser emission of the semiconductor laser device has been increased.
In some cases, emission control with a pulse width of (nanosecond) is required.

In order to control the laser emission having such a pulse width, it is necessary to raise the above-mentioned bias current to near the threshold value, in addition to the performance of the driver of the semiconductor laser device. So for that,
Circuits have been developed that can also control the bias current so that the bias current can be set near the threshold.

Further, in recent image forming apparatuses using, for example, an electrophotographic system, copiers, facsimile machines,
As printers (for example, as an output of a personal computer) are being integrated and compounded, various image quality is required for one engine (means for forming an image on a recording material). To cope with this, a method has been adopted in which the laser power (the amount of laser light emitted from the semiconductor laser element) is changed during image formation according to the image formation mode (for example, each mode of copying, printer, etc.).

In general, in an image forming mode as a printer, rather than in an image forming mode as a copying machine,
Increase laser power. This is because, when an image is formed as a printer, the resolution is higher than that of an image reading system at the time of forming an image as a copying machine based on bitmap data, such as CG (computer graphics) sent from a personal computer. This is because data is sent to the image forming apparatus.

Here, an example of a conventional laser driving circuit will be described with reference to FIG.
Is connected to a bias current source 58 and a pulse current source 57, and the bias current source 58 is connected to the semiconductor laser element 51.
Is supplied with a constant bias current. The current from the pulse current source 57 to the semiconductor laser element 51 is turned on / off by the pulse current switch 56 according to the image signal.
Thus, the laser emission of the semiconductor laser element 51 is controlled to form an electrostatic latent image on the photosensitive member according to the image information.

Conventionally, the amount of pulse current flowing through the semiconductor laser element 51 is controlled as follows to control the amount of laser light for actually writing an image on the photosensitive member. That is, the pulse current switch 56 is turned on, and the current of the pulse current source 57 is supplied to the semiconductor laser element 51 to turn on (laser emission).
In synchronization with this, the pulse current sample / hold circuit 54 is brought into a sample state. At this time, a part of the laser light of the semiconductor laser element 51 is detected by the photodiode 52, and the detection signal is converted into a voltage signal by the current-voltage converter 53. The output signal of the current / voltage converter 53 is sampled by a pulse current sample / hold circuit 54,
It is supplied to a pulse current operation amplifier 59.

The pulse current operation amplifier 59 compares the output signal of the pulse current sample / hold circuit 54 with the reference voltage output from the first reference voltage generator 67, and responds to the difference signal. The current of the pulse current source 57 is controlled. Thereafter, the pulse current sample / hold circuit 54 enters a hold state, and supplies a pulse current to the semiconductor laser element 51 while maintaining the controlled value.

Conventionally, when the image forming apparatus is, for example, a multifunction machine of a copying machine and a printer, as described above, the amount of laser emission (laser power) of the semiconductor laser element 51 is generally increased during printing. Therefore, at the time of the printer, as shown in FIG.
Is switched to a second reference voltage generator 68 that generates a voltage higher than the reference voltage generated by the semiconductor laser device 51.
Is controlled.

[0020]

However, the above-described conventional image forming apparatus has the following problems.

First, when the bias current flowing through the semiconductor laser device is raised to a value near the threshold value of laser light emission, a problem occurs in the life of the semiconductor laser device.

The life of a semiconductor laser device depends on the amount of current applied thereto, the application time, and the temperature.
In addition, there are two ways of deterioration of the semiconductor laser element: chemical deterioration of the mirror surface inside the laser chip due to laser emission, and electrical deterioration of the semiconductor caused by heat loss due to applied current.

In a laser driving circuit in which the bias current is set so as to be less than half of the threshold current, the amount of the bias current is very small and hardly contributes to electrical deterioration. Thus, the life of the semiconductor laser element was calculated.

However, in the case of a laser driving circuit that applies a bias current to near a threshold value to control a minute pulse at high speed, this amount of bias current is necessary for laser emission for actually forming a latent image. There is no significant difference from the current amount, and this bias current amount is a current amount that affects the life of the semiconductor laser device.

In an image forming apparatus in which the amount of bias current is increased to near the threshold value for laser emission, the actual laser emission time is only during the formation of a latent image on the photosensitive member, and is not required for image formation standby. The time during which bias current (diode light emission) is applied by applying a bias current to the semiconductor laser element is many times longer.

As described above, in the image forming apparatus in which the bias current is increased to the vicinity of the threshold value in order to realize high speed and high definition, conventionally, there is a problem that the life of the semiconductor laser element is extremely shortened.

Conventionally, a laser light source as an exposure means is disposed relatively inside a main body of an image forming apparatus as a laser scanner unit integrated with a rotary polygon mirror for scanning exposure and the like. Is a copier, it cannot be attached or detached without removing a number of components such as a platen glass, a CCD unit, a board cover, and an image processing board, and a considerable amount of time must be spent for replacing the laser scanner unit. Further, since the laser scanner unit requires optical adjustment, it is not possible to replace only the laser light source in the market, and replacement of each laser scanner unit is required, which considerably increases the cost. That is, as described above, the service life may be impaired due to the extremely short life of the laser light source.

In addition, the integration of the functions of the recent image forming apparatus described above also causes a reduction in the life of the semiconductor laser device. That is, as described above, for example, in the case of a multifunction machine of a copying machine and a printer, the laser power at the time of writing image information to the photoconductor when used as a conventional printer is to be increased.

Further, when the laser power at the time of writing image information on the surface of the photosensitive member is changed in accordance with the image forming mode in accordance with the integration of the image forming apparatus, raster scanning on the photosensitive member is performed. In order to generate the horizontal synchronizing signal, there is a problem that an output signal from a horizontal synchronizing signal detecting unit (hereinafter, referred to as a “beam sensor (BD sensor)”) installed near the photoconductor changes. Occurs.

This is because basically, when the laser power is high, the pulse width of the output signal of the beam detect sensor (BD sensor) tends to be wide. Therefore, when the laser power changes, the synchronization signal from the beam detect sensor is changed. This is because the registration in the main scanning direction (for example, the longitudinal direction of the photosensitive drum) changes when an image is formed on the photosensitive member on the basis of.

Accordingly, an object of the present invention is to realize high-speed and high-definition image formation without changing the amount of laser light emitted from a laser light source in an image forming mode, to extend the life of the laser light source, and An object of the present invention is to provide an image forming apparatus in which there is no change in registration in the main scanning direction of laser light in an image forming mode.

Another object of the present invention is to improve the serviceability by preventing the life of the laser light source from being shortened and by eliminating the replacement of the laser light source which is relatively difficult to replace. It is to provide.

[0033]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
In an image forming apparatus for guiding a laser beam modulated according to image information from a laser light source onto a photoconductor and forming an image on the photoconductor according to the image information, a laser controlling driving of the laser light source A driving circuit comprising: bias current superimposing means for applying a bias current to the laser light source; and applying a switch current for applying a current according to image information in addition to the bias current to cause the laser light source to emit laser light according to the image information. Means for forming an image in accordance with image information on the photoreceptor, without changing a laser light emission amount of the laser light source, and changing a bias current amount from the bias current superimposing means to the laser light source. An image forming apparatus characterized by being variable. According to a preferred embodiment of the present invention, the image forming apparatus has a plurality of image forming modes, and changes the amount of the bias current according to the plurality of image forming modes.

According to one embodiment of the present invention, the image forming apparatus detects a light emission amount of the laser light source and outputs a signal corresponding to the light emission amount; Bias emission target value setting means for outputting a desired signal corresponding to a bias emission target value that is a light emission amount target value of the laser light source, the bias light emission target value being provided with bias set value variable means, and a plurality of bias emission target values being variable; Bias emission target value setting means capable of outputting a desired signal corresponding to the bias emission target value; and a bias controlling the amount of bias current such that the output of the light emission amount detection means corresponds to the output of the bias emission target value setting means. Current control means. According to a preferred embodiment of the present invention, the image forming apparatus has the plurality of bias emission target values according to the plurality of image forming modes.

According to one embodiment of the present invention, the output of the light emission amount detecting means is connected to the bias current control means via a sample / hold circuit, and the sample / hold circuit connects the bias to the laser light source. The sample state is established in synchronization with the application of only the current, and the hold state is established in synchronization with the application of the switch current in addition to the bias current to the laser light source.

According to a preferred embodiment of the present invention, when a plurality of images are formed intermittently on the photoreceptor, at least first control of the bias current during each image formation is performed.
The image forming apparatus further includes a control sequence switching unit that switches a second bias current control sequence, and generally controls the bias current during each image formation in accordance with the first bias current control sequence, and performs image formation on the photoconductor. When the image forming mode is switched to the next, the bias current is controlled in accordance with the second bias current control sequence between the next image formation. According to a preferred embodiment of the present invention, during the image formation on the photoreceptor, after a lapse of a predetermined time from starting to control the bias current according to the second bias current control sequence, the first bias current control Return to the control of the bias current according to the sequence. Preferably, in the second bias current control sequence, the period in which the sample / hold circuit is set in a sample state and the output of the light emission amount detection means is connected to the bias current control means is controlled by the first bias current control. Make it longer than the sequence.

According to a preferred embodiment of the present invention, the plurality of image forming modes include at least a first image forming mode corresponding to an initial state of the image forming apparatus, and in the first image forming mode, The light emission target value setting means sets the bias light emission target value to a first bias light emission target value which is the minimum among the plurality of bias light emission target values. Preferably, when an image forming mode other than the first image forming mode is selected from among the plurality of image forming modes and the image forming apparatus is unused for a predetermined time, Returning to the first image forming mode, the bias light emission target value setting means sets the bias light emission target value to the first bias light emission target value.

According to one embodiment of the present invention, the laser light source is a semiconductor laser element, and the plurality of image forming modes have substantially different image definition.
Further, according to a preferred embodiment of the present invention, at least one of the plurality of bias emission target values corresponds to a bias current value near a current threshold value for laser emission of the laser light source.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus according to the present invention.

According to this embodiment, the present invention is embodied in an electrophotographic copying machine and a multifunction printer.
The present invention is not limited to the image forming apparatus described in the present embodiment, but may be any optical light modulated laser light from a laser light source may be guided to the photoreceptor surface to obtain an image corresponding to image information. It is to be understood that the present invention can be applied to the image forming apparatus.

First, the overall configuration and schematic operation of the image forming apparatus shown in FIG. 1 will be described. The image forming apparatus of FIG. 1 includes an image reading unit that irradiates a document with light and reads image information of the document by reflected light thereof, and an image forming unit that forms an image according to the image information read from the document by the image reading unit. Are roughly divided into

In the image reading section, the document feeder 1
Are transported one by one onto the surface of the document glass 2 one by one. When a document is conveyed onto the platen glass 2, the scanner lamp 3 of the scanner unit 4 is turned on, and the scanner unit 4 moves to irradiate the document. The reflected light from the original passes through the lens unit 8 via the mirrors 5, 6, and 7, and then forms an image on the image sensor unit 9 and is input. The image signal input to the image sensor unit 9 is directly or temporarily stored in an image memory (not shown) and read out again, and thereafter, an exposure control unit (laser scanner unit) 10 described later of the image forming unit. Is input to

In the image forming section, a drum-shaped electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive drum”) 11 is supported as an image bearing member so as to be rotatable in an arrow X direction. A corona charger 19 as a charging unit uniformly charges the surface of the photosensitive drum 11 with the rotation in the direction of the arrow X.

Subsequently, as will be described later in detail, the exposure control unit 10 controls the semiconductor laser device (LD: LD:
A laser chip 31 including a laser diode) 51 and a photodiode (PD) 52 as a light-emission amount detecting unit, and according to an image signal input to the exposure control unit 10 from an image reading unit. Laser light L is emitted from the laser chip 31 and the photosensitive drum 11 is scanned and exposed to form an electrostatic latent image on the photosensitive drum 11.

Thereafter, as the photosensitive drum 11 rotates,
Developing device 12 provided on the outer periphery of photosensitive drum 11
However, the developer (including toner) contained therein is transferred and adhered to the image portion of the electrostatic latent image, and a toner image is formed on the photosensitive drum 11. Further, the image forming apparatus of the present embodiment has a developing device 13 in addition to the developing device 12, and each of the developing devices 13 is brought close to the surface of the photosensitive drum 11 during image formation. The developing device 12 and 13 are capable of moving back and forth with respect to the surface of the developing device 11 so that different color images can be formed.

On the other hand, the recording material P is sent out from the recording material loading section 14 or 15 by the recording material supply roller 22 or 23, and synchronized with the formation of the toner image on the photosensitive drum 11. 11 and a transfer charger 16 as a transfer means are conveyed to a transfer site opposed to the transfer charger.

Thus, in the transfer section, the photosensitive drum 1
The toner image formed on the recording material P is electrostatically transferred onto the recording material P. Subsequently, the recording material P carrying the transferred unfixed toner image is transferred to the fixing device 1 by the recording material conveying means 21 or the like.
7, where the unfixed toner image is fixed on the recording material P by heat and pressure to become a permanent image.

Thereafter, the recording material P is discharged out of the image forming apparatus by the recording material discharge unit 18. Further, the so-called transfer residual toner remaining on the surface of the photosensitive drum 11 after the transfer is completed is removed by the cleaning unit 2 provided in the cleaning device 20.
0a is scraped off, and the photosensitive drum 11 is cleaned and repeatedly used for image formation.

Next, the exposure controller 10 will be further described. FIG. 2 shows a schematic configuration of the exposure control unit 10 included in the image forming apparatus of the present embodiment and the vicinity thereof.

The exposure control section 10 has a semiconductor laser element 51 as a laser light source as an exposure means. or,
The semiconductor laser element 51 is unitized as a laser chip 31 in which a photodiode 52 as a light emission amount detecting means for detecting a part of light emitted by the semiconductor laser element 51 is provided.

As will be described later, this photodiode 5
Automatic control of the light emission amount of the semiconductor laser element 51 (hereinafter referred to as “APC”: AUTO POWER CONTROL) is performed using the detection signal of No. 2.

The laser light L emitted from the laser chip 31 is converted into substantially parallel light by the collimator lens 35 and the stop 32, and is incident on the rotary polygon mirror 33 with a predetermined beam diameter.

The rotating polygon mirror 33 rotates at a constant angular velocity in the direction indicated by the arrow A, and the laser light L incident upon the rotation is reflected as a deflection beam whose angle continuously changes. The laser beam L that has become a deflected beam is condensed by the f-θ lens 34. At the same time, the f-θ lens corrects distortion so as to guarantee the temporal linearity of the scanning of the laser light L, and the light beam of the laser light L is
The photosensitive drum 11 as an image carrier is coupled and scanned at a constant speed in the direction of arrow B.

A beam detecting sensor (BD sensor) 36 for detecting the reflected light from the rotary polygon mirror 33 is provided near the photosensitive drum 11, in this embodiment, near one end of the photosensitive drum 11 in the longitudinal direction. The detection signal of the beam detection sensor 36 is used as a synchronization signal for synchronizing rotation of the rotary polygon mirror 33 and writing of image information on the photosensitive drum 11.

Next, the exposure control in this embodiment will be described. FIG. 3 shows a schematic circuit configuration of a laser drive circuit for controlling the drive of the semiconductor laser element 51.

As shown in FIG. 3, in this embodiment, the image control section 71 controls each section of the image forming apparatus. The image control unit 71 is a control circuit that processes an image signal read by the image sensor unit 9 and data transmitted from an external interface (I / F) 72.

The image control section 71 supplies an image signal from the image sensor section 9 to the laser drive circuit line by line in synchronization with an output signal of the beam detector sensor 36, for example. A timing signal required for APC of the semiconductor laser 51 is created.

According to this embodiment, the semiconductor laser element 51
A bias current source 58 as bias current superimposing means.
And a pulse current source 57 as a switch current applying means. From the pulse current source 57 to the semiconductor laser element 5
The pulse current switch 56 supplies the image signal (V
ON / OFF according to (IDEO DATA). The pulse current switch 56 is connected to the image signal (VIDEO DAT)
When a high-level (“H”) signal of A) is input, the signal is turned on and the current determined by the pulse current source 57 flows through the semiconductor laser element 51, and the semiconductor laser element 51 emits laser light. The pulse current switch 56 is turned off when a low level (“L”) signal is input, and the laser emission of the semiconductor laser element 51 ends. By controlling ON / OFF of the pulse current switch 56 according to the image signal, the semiconductor laser element 51 is driven, and the photosensitive drum 11
Image information is written thereon to form an electrostatic latent image.

In the image forming apparatus of this embodiment, the semiconductor laser device 5 is in a standby state in which no image forming operation is performed.
1 is off. Then, the semiconductor laser element 51 is turned on during the image forming operation, and APC is performed to keep the light emission amount at a desired value. In the APC, the laser beam L is scanned on the photosensitive drum 11 by the rotating polygon mirror 33.
Performed line by line. This is hereinafter referred to as “line APC”. The line APC is performed in a non-image area during the image forming operation so as not to affect image formation.

As described above, in the image forming apparatus of this embodiment, a bias current is supplied to the semiconductor laser element 51 in advance in addition to the switch current for turning on / off the laser emission. In this embodiment, a normal image quality mode and a high image quality mode are provided according to the image quality (fineness) required for the formed image. In the normal image quality mode, the bias current is set to about half the laser threshold value. In the high image quality mode, the bias current is set near the laser threshold value.

As described above, the image forming apparatus according to the present embodiment changes the light emission characteristics of the semiconductor laser element 51 by changing the amount of bias current without changing the laser power when writing image information to the photosensitive drum 11, thereby changing the minute pulse. The light emission reproducibility can be improved, and high-definition image information can be written on the photosensitive drum 11.

In this embodiment, two modes, that is, a normal image quality mode and a high image quality mode, are configured to be set. However, the present invention is not limited to this mode. It should be understood that it is of course possible to divide the image forming apparatus into a configuration having more stages of image forming modes. Further, since the image forming apparatus of the present embodiment is a multifunction machine of a copying machine and a printer, for example, when the copying machine mode and the printer mode are selected and used, respectively, the normal image quality mode is automatically set in the copying machine mode. In the printer mode, it is also possible to configure to set the high image quality mode.

Further, in this embodiment, in order to set the bias current near the threshold value, the photosensitive drum
APC is performed not only on the amount of laser emission used for forming a latent image on the semiconductor laser device 1 but also on bias emission (diode emission) when only a bias current is supplied to the semiconductor laser element 51.

Here, in this embodiment, a bias current and a switch current (pulse current) are applied to the semiconductor laser element 51.
APC of the laser emission amount when
APC of bias light emission (diode light emission) when only a bias current is applied to a semiconductor laser device
Are referred to as “biased APC” to distinguish them.

Referring to FIG. 3, the laser driving circuit of the present embodiment will be described in more detail.

First, a line APC performed during image formation
In order to set a bias current to be supplied to the semiconductor laser element (PD) 51 in a non-image area, a bias current switch 62 is set to a first bias reference in a bias light emission target value setting means described later in detail. The voltage is set to the voltage generator 63 side, and only the bias current is supplied to the semiconductor laser element 51 to light it (diode light emission). In synchronization with this, the bias current sample / hold circuit (S / H-B) 65 is brought into a sample state.

At this time, a part of the light emitted from the semiconductor laser element 51 is detected by the photodiode 52 which is the light emission amount detecting means, and the detection signal is supplied to the current / voltage converter (I /
V) 53 to be converted into a voltage signal. Current-voltage converter 53
Is amplified by an amplifier circuit (Amp) 55, sampled by a sample / hold circuit 65, and supplied to a bias current operation amplifier 61 as bias current control means.

Operation amplifier 61 for bias current
Then, the output signal of the bias current sample / hold circuit 65 is compared with the reference voltage of the first bias reference voltage generator 63, and the bias current source 58
To control the current. That is, the current of the bias current source 58 is controlled so that the target bias light emission amount set as the reference voltage by the first reference voltage generator 63 is performed, and the bias APC of the semiconductor laser element 51 is performed. When this control ends, the bias current sample / hold circuit 65
Is in a hold state, and supplies a bias current to the semiconductor laser element 51 while maintaining the controlled value.

After the bias APC, a total APC is performed. Naturally, this total APC is also performed in the non-image area. That is, after the end of the bias APC, the pulse current switch 56 is turned on, and the current of the pulse current source 57 is supplied to the semiconductor laser element 51 in addition to the bias current set by the above-described bias APC to turn on (laser emission).
Let it. In synchronization with this, the pulse current sample / hold circuit (S / HT) 54 is set to the sample state.

At this time, a part of the laser light of the semiconductor laser element 51 is detected by the photodiode 52, and the detection signal is converted into a voltage signal by the current-voltage converter 53. The output signal of the current / voltage converter 53 is a pulse current sample /
It is sampled by the hold circuit 54 and supplied to a pulse current operation amplifier 59 as pulse current control means.

The pulse current operation amplifier 59 compares the output signal of the pulse current sample / hold circuit 54 with the reference voltage of the total reference voltage generator 60 as a laser emission target value setting means, and obtains the difference signal. The current of the pulse current source 57 is controlled according to. That is, the pulse current source 57 is set so that the target laser emission amount set as the reference voltage by the total reference voltage generator 60 is obtained.
And the total APC of the semiconductor laser 51 is performed. When this control is completed, the pulse current sample /
The hold circuit 54 enters a hold state, and supplies a pulse current to the semiconductor laser element 51 while maintaining the controlled value.

On the other hand, in the image area, the output signal of the current / voltage converter 53 in the non-image area is held by the bias current sample / hold circuit 65 and the pulse current sample / hold circuit 54. The operation amplifier 59 and the pulse current operation amplifier 61 output the held signals,
A bias current and a pulse current are set by the first bias reference voltage generator 63 and the total reference voltage generator 60, respectively, and the light amount of the semiconductor laser element 51 is controlled.

FIG. 4 shows the timing of an input signal to each element in the line APC described above. Sample / hold circuit for bias current (S / H-B) 65,
Sample / hold circuit for pulse current (S / HT) 5
Reference numeral 4 denotes a sample state by a high level ("H") signal and a hold state by a low level ("L") signal. The bias current switch 62 is connected to a second bias reference voltage generator 64 by an "H" signal. , "L" signal to the first bias reference voltage generator 63.

In FIG. 4, in the non-image area, the image signal (VIDEO DATE) becomes "H" in synchronization with the input signal to the pulse current sample / hold circuit (S / HT) 54, and the pulse current switch 56 The reason why the signal is turned to “H” before the image area after turning ON is to obtain a synchronization signal by the above-described beam detect sensor (BD sensor) 36. The image signal (VIDEO)
DATE), the hatched portion is actually the photosensitive drum 11
Image data to be written on the top.

Next, a method of controlling a bias current applied to the semiconductor laser device 51 of this embodiment will be described. FIG. 5 shows a sequence when the image forming apparatus of the present embodiment is used as a copying machine to copy two A4-size sheets as the recording material P. In the sequence shown in FIG. 5, a case where the mode of image formation is switched from the normal image quality mode to the high image quality mode between the first and second sheets is taken as an example. In FIG. 5, the output of the semiconductor laser element 51 (PD output)
Indicates the presence or absence of laser emission.

The laser driving circuit of this embodiment can output a desired signal corresponding to a target value (bias emission target value) of a bias emission amount of the semiconductor laser element 51 in order to set a bias current. It has a light emission target value setting means.

The bias light emission target value setting means includes:
A signal corresponding to a plurality of bias emission target values can be generated. In the present embodiment, a first bias reference voltage generation for generating a signal corresponding to the bias emission target value when the normal image quality mode is selected. Container (Vref-B-1) 63
A second bias reference voltage generator (Vref-B-2) 64 for generating a signal corresponding to a bias light emission target value when the high image quality mode is selected; and these two bias reference voltage generators 63 and 64 And a bias current switch 62 as bias setting variable means for switching between the two.

First, the operation unit 7 of the image forming apparatus of the present embodiment
3 is pressed, a copy start signal (COPY START) is generated.
Is input to the image control unit 71. The "H" signal of the copy start signal indicates the start of copying.

This copy start signal is transmitted to the image control unit 71.
Is input to the image controller 71, the image controller 71 starts driving control of each part of the image forming apparatus, and the image forming apparatus starts an image forming operation. When the image forming operation starts, the laser drive circuit operates according to the following sequence.

That is, first, the laser drive circuit receives the copy start signal and starts pulling in the bias APC. At this time, if the normal image quality mode is selected on the operation unit 71, the bias current switch signal (B-POWE
R SW) becomes “L” level, and the bias current switch 62 is connected to the first bias reference voltage generator 63 side. At this time, if the high image quality mode is selected, the bias current switch signal (B-POWER SW) becomes “H” level, and the second bias reference voltage generator 6
4 is selected.

In consideration of the life of the semiconductor laser element 51,
In the initial state of the image forming apparatus, it is preferable that the minimum value of the bias emission target value is selected.

According to this embodiment, the output from the first bias reference voltage generator 63 is smaller than the output from the second bias reference voltage generator 64, that is, the bias current superimposed on the semiconductor laser element 51. Is less.

In the sequence example shown in FIG. 5, the normal image quality mode is selected by the operation unit 71 at the start of image formation, and the output from the first bias reference voltage generator 63 is input to the bias current operation amplifier 61. Have been. Therefore, the pull-in of the bias APC is started with the output of the first bias reference voltage generator 63 as a target. That is, the bias current switch signal (B-POWER SW) is set to "L", and the signal (S / H-B) to the bias current sample / hold signal circuit is set to "H" to turn on the semiconductor laser element 51 (diode light emission). Then, the bias A is adjusted so that the desired bias level, that is, the light emission amount of the semiconductor laser element 51 becomes the desired light amount.
Perform PC.

After a predetermined time, when the bias level reaches a desired level, the process shifts to pulling in the total APC. That is, the bias current switch signal (BP)
POWER-SW) and the signal (S / H-B) to the bias current sample / hold circuit are set to “L”, and the image signal (VIDEO DATA) and the pulse current sample / hold
The signal (S / HT) to the hold circuit is set to “H”,
The pulse current switch 56 is turned on to start the laser emission of the semiconductor laser element 51, and the total APC is started.

Here, since the hold capability of the sample / hold circuit is limited, the control of the bias APC is interposed even while the total APC is being pulled. Thus, the bias AP inserted between the total APCs
While C is performed, the total APC is in a hold state.

When the total APC pull-in is completed after a certain period of time, the process shifts to line APC control based on a synchronizing signal from the beam detect sensor (BD sensor) 36 and enters a standby state. The operation of the line APC is as described above.

Subsequently, during the period of forming a latent image on the photosensitive drum 11, image data actually written on the photosensitive drum 11 is loaded on the image signal (VIDEO DATE) while performing the line APC. In the image signal (VIDEODATE) of the image forming period in FIG. 5, the hatched portion is the image data actually written on the photosensitive drum 11.

Next, when the image forming mode is switched during the copying to the first recording material P in this way, the image forming mode is switched when the first copying is completed. , The bias current switch signal (B-POWER SW) is switched. For example, when the mode is switched from the normal image quality mode to the high image quality mode as in the sequence shown in FIG. 5, the bias current switch signal (B-POWER SW) changes from “L” to “H”, and the bias current operation amplifier 6
The input to 1 is switched to the output of the second bias reference voltage generator 64.

As a result, the amount of bias current supplied to the semiconductor laser element 51 changes. However, since APC is a feedback control, it takes some time to switch the current due to its characteristics. Therefore, between the first and second sheets, the output is switched from the first bias reference voltage generator 63 to the second bias reference voltage generator 64 immediately after the first copy is completed. .

Here, preferably, in the bias APC in the inter-sheet sequence after the image forming mode is switched during the image formation as described above, the normal line AP
The sample time is set longer than the sample time of the bias APC in C. By doing so, the switching of the bias current amount can be performed in a short time.

The image control unit controls the timing of the APC sequence. However, when the image forming mode is changed during image formation as described above, a plurality of bias current control sequences such as extending the bias APC sampling time are used. It also has a function as a means for switching between sequences.

Thereafter, after a lapse of a predetermined time, the process returns to the normal line APC, returns to the standby state, and prepares for the second image formation. In the second latent image forming period, the laser drive circuit is controlled in the same sequence as that for the first copy to form an image. After completion of image formation, the laser is turned off.

The image forming apparatus of this embodiment is similar to that of FIGS.
As is clear from the above, this is a so-called multifunction peripheral having both an image reading unit and an external interface (IF). In the case of such a multifunction peripheral, a plurality of jobs such as copying and printing may inevitably overlap. Further, the level of image quality required for each image formation is also different, and generally a higher definition image is required at the time of printing.

For example, when printing is performed immediately after copying, if the image forming mode at the time of copying is the normal mode, it is preferable, but not limited, that the high quality mode be set at the time of printing. In the example image forming apparatus, the amount of bias current is switched in the same manner as when the image forming mode is changed during copying as described above.

Further, in the image forming apparatus of the present embodiment, the previous user may leave the apparatus without resetting the setting of the use state. In such a case, if the previous user was copying in the high image quality mode and the next user made a copy without changing the settings, for example, despite the fact that it was just a text document copy, It is possible to copy in mode. This is disadvantageous in view of the life of the laser element. Therefore, it is preferable to return to the normal mode when the image forming apparatus is not used for a predetermined time.

As described above, according to the present invention, the semiconductor laser device 5 can be used in accordance with a plurality of image forming modes having different image qualities without changing the light emission amount of the semiconductor laser device 51 during image formation.
1 can be changed, the bias current can be increased for high-speed image formation and high-definition image, and the integrated current for driving the semiconductor laser element 51 can be increased. And the life of the semiconductor laser element 51 can be prolonged. Further, since the amount of laser light emitted from the semiconductor laser element 51 during image formation is not changed depending on the image forming mode, the registration of the laser beam L on the photosensitive drum 11 in the main scanning direction does not change.

[0098]

As described above, the image forming apparatus of the present invention guides a laser beam modulated according to image information from a laser light source onto a photoreceptor, and places a laser beam on the photoreceptor according to the image information. In an image forming apparatus for forming an image, a laser driving circuit for controlling driving of a laser light source includes a bias current superimposing means for applying a bias current to the laser light source; and applying a current corresponding to image information in addition to the bias current. Switch current applying means for causing the laser light source to emit laser light according to the image information; and forming a bias current without changing the laser light emission amount of the laser light source when forming an image corresponding to the image information on the photosensitive member. Since the amount of bias current from the means to the laser light source is made variable, it is possible to increase the bias current in order to increase the speed of image formation and increase the definition of the image in accordance with the image forming mode. Can, and it is possible to prevent impairing the lifetime of the laser light source. Therefore, the laser light source
Serviceability can be improved without setting parts such as service parts in the laser scanner unit, which are relatively difficult to replace. Further, the registration of the image in the main scanning direction does not change depending on the image forming mode.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram illustrating an example of the vicinity of a photoconductor and an exposure control unit according to the present invention.

FIG. 3 is a schematic circuit diagram showing one embodiment of a laser drive circuit according to the present invention.

FIG. 4 is a timing chart illustrating a sequence of automatic light emission control (APC) according to the present invention.

FIG. 5 is a timing chart for explaining an embodiment of an automatic light emission control (APC) sequence when an image forming mode is changed during image formation according to the present invention.

FIG. 6 is a schematic circuit diagram showing an example of a conventional laser drive circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Exposure control part 11 Photosensitive drum (photoreceptor) 12 Developing device 16 Transfer charger 17 Fixing device 19 Charging means 31 Laser chip 51 Semiconductor laser element (laser light source, LD) 52 Photodiode (light emission amount detecting means, PD) 62 Bias Current switch (bias setting value changing means) 63 First bias reference voltage generator (bias emission target value setting means) 64 Second bias reference voltage generator (bias emission target value setting means)

Continued on the front page F-term (reference) 2C362 AA03 AA53 AA54 AA56 AA61 AA63 AA72 AA75 BB33 CB05 5C072 AA03 BA03 BA04 BA05 CA06 CA14 HA02 HA13 HB02 HB04 HB06 UA05 5C074 AA02 AA12 AA15 BB03 BB03 DD06 CC03 AB27 BA07 EA28 FA02 GA03 GA12 GA18 GA24 GA38

Claims (13)

[Claims] 1. An image forming apparatus for guiding a laser beam modulated according to image information from a laser light source onto a photoreceptor and forming an image on the photoreceptor according to the image information. A laser driving circuit for controlling driving, a bias current superimposing means for applying a bias current to the laser light source, and applying a current corresponding to image information in addition to the bias current to cause the laser light source to emit a laser according to the image information. A switch current applying means for emitting light, wherein the laser light emission amount of the laser light source when forming an image according to image information on the photoconductor is not changed, and Wherein the amount of bias current is variable. 2. The image forming apparatus according to claim 1, further comprising a plurality of image forming modes, wherein said bias current amount is changed according to said plurality of image forming modes. 3. A light emission amount detecting means for detecting a light emission amount of the laser light source and outputting a signal corresponding to the light emission amount, and a bias light emission target value which is a light emission target value of the laser light source only by the bias current. Bias emission target value setting means for outputting a desired signal corresponding to the bias emission target value, wherein the bias emission target value is variable by providing a bias setting value variable means, and the desired signal for a plurality of bias emission target values can be output. A bias light emission target value setting means; and a bias current control means for controlling the bias current amount so that an output of the light emission amount detection means corresponds to an output of the bias light emission target value setting means. Item 3. The image forming apparatus according to item 1 or 2. 4. The image forming apparatus according to claim 3, wherein said plurality of bias light emission target values correspond to said plurality of image forming modes. 5. The output of the light emission amount detecting means is connected to the bias current control means via a sample / hold circuit, and the sample / hold circuit applies only the bias current to the laser light source. 5. The image forming apparatus according to claim 3, wherein a sample state is established in synchronization with the laser light source, and a hold state is established in synchronization with application of the switch current in addition to the bias current to the laser light source. 6. A control sequence switching means for switching at least a first and a second bias current control sequence for controlling the bias current during each image formation when a plurality of images are intermittently formed on the photoconductor. Have more,
Normally, the bias current during each image formation is controlled according to the first bias current control sequence, and when the image formation mode is switched during the image formation on the photoconductor, the image forming apparatus performs the next image formation. 5. The image forming apparatus according to claim 2, wherein the bias current is controlled in accordance with the second bias current control sequence. 7. A bias current according to the first bias current control sequence after a lapse of a predetermined time from the start of controlling the bias current according to the second bias current control sequence during image formation on the photoconductor. 7. The image forming apparatus according to claim 6, wherein the control is returned to said control. 8. The second bias current control sequence includes a period in which the sample / hold circuit is set in a sample state and an output of the light emission amount detection unit is connected to the bias current control unit. 8. The image forming apparatus according to claim 6, wherein the image forming apparatus is longer than the sequence. 9. The image forming mode according to claim 1, wherein the plurality of image forming modes include at least a first image forming mode corresponding to an initial state of the image forming apparatus. 5. The image forming apparatus according to claim 4, wherein the bias light emission target value is set to a first bias light emission target value which is the minimum among the plurality of bias light emission target values. 10. In a state where an image forming mode other than the first image forming mode among the plurality of image forming modes is selected, when a predetermined time has elapsed without using the image forming apparatus, 10. The image forming apparatus according to claim 9, wherein returning to the first image forming mode, the bias light emission target value setting means sets a bias light emission target value to the first bias light emission target value. 11. The image forming apparatus according to claim 1, wherein said laser light source is a semiconductor laser device. 12. The image forming apparatus according to claim 2, wherein the plurality of image forming modes substantially differ in definition of an image to be formed. 13. The method according to claim 3, wherein at least one of the plurality of bias emission target values corresponds to a bias current value near a current threshold value for laser emission of the laser light source. Image forming apparatus.