JPH10166644A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the quantity of light can be controlled constantly for a plurality of laser light sources regardless of electrical or thermal crosstalk. SOLUTION: The image forming apparatus comprises a plurality of laser light sources 41a, 41b and forms a latent image on a photosensitive drum by scanning the drum linearly and simultaneously with a plurality of laser lights emitted from respective laser light sources in response to respective image signals therefrom. The plurality of laser light sources are provided, respectively, with photodiodes 42, 43 for detecting a part of laser light and drive current for each laser light source is controlled based on the output signal from a corresponding photodiode and a predetermined reference voltage thus controlling the quantity of light of each laser light source in real time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam writing type image forming apparatus for performing optical writing using a plurality of light beams.

[0002]

2. Description of the Related Art In recent years, a multi-beam writing type image forming apparatus for performing optical writing using a plurality of light beams has been studied. FIG. 7 shows an example of a laser printer using such a multi-beam writing method. 7, the laser printer 1 is connected to an external device 31 such as a computer, and prints on a recording sheet under the control of the external device 31. The external device 31 supplies various control signals and image information to the video controller 27. The video controller 27 develops the image information into a dot image,
Output as a video signal. The print control unit 26 is a control circuit for controlling each unit in the apparatus.

FIG. 8 shows the operation timing of the image forming apparatus shown in FIG. The video controller 27 corresponds to FIG.
As shown in (a), the RDY signal from the external device 31 is T
When it becomes RUE, the PRINT signal is set to TRUE as shown in FIG. When the PRINT signal becomes TRUE, the print control unit 26 starts driving the main motor 23 and the polygon motor 14 as shown in FIGS.
The photosensitive drum 1 is driven by driving the main motor 23.
7. The fixing roller of the fixing unit 9 and the paper discharge roller 11 start rotating. Thereafter, the print control unit 26 sets the semiconductor laser 1
At the same time, the light amount control of 3 is started, and the primary charger 19, the developing device 20, and the transfer charger 21 are sequentially driven at high voltage.

The print control unit 26 has passed a time T1 from the start of driving of the polygon motor 14 as shown in FIG.
When the rotation of the polygon motor 14 reaches a steady state, FIG.
As shown in (h), the paper feed clutch 24 is turned on to drive the paper feed roller 5, and the recording paper S in the paper feed cassette 2 is fed toward the registration roller 6. Then, the print control unit 26
8C outputs a VSREQ signal to the video controller 27 as shown in FIG. 8C at the timing when the leading end of the recording paper S reaches the registration roller 6, and turns off the paper feed clutch 24 as shown in FIG. The driving of the paper feed roller 5 is stopped.
On the other hand, when the video controller 27 completes the preparation of the output of the VDO signal after completing the development of the image information from the external device 31 into a dot image, after confirming that the VSREQ signal in FIG. As shown in FIG. 8D, the VSYNC signal is set to TRUE. Then, in synchronization with this, the output of the VDO signal is started as image data for one page after the time TV as shown in FIG.

At this time, the print control unit 26
Time T from the rising of the VSYNC signal as shown in (i).
After three, the registration roller clutch 25 is turned on, and the registration roller 6 is driven. The driving of the registration roller 6 is performed for a time T4 until the rear end of the recording sheet S passes through the registration roller 6 as shown in FIG. During this time, the print control unit 26 sends the VDO from the video controller 27
The semiconductor laser 13 is driven according to the signal.

As will be described later, two semiconductor lasers 13 are provided. The print controller 26 drives each of the semiconductor lasers in accordance with the VDO signal, and the laser light emitted from the two semiconductor lasers is transmitted to the scanner 7. The rotation is converted into a linear scan by the rotation of the polygon mirror 15. Then, the laser beams of the two semiconductor lasers are irradiated on the photosensitive drum 17 by the mirror 16. Thus, each V
The two laser beams modulated according to the DO signal are simultaneously scanned on the photosensitive drum 17 so that
A two-line latent image is formed thereon, and the same operation is repeated thereafter to form a one-page latent image on the photosensitive drum 17.

The latent image formed on the photosensitive drum 17 is developed by a developing device 20, and thereafter, a toner image is transferred to a recording sheet S by a transfer charger 21. When the transfer is completed, the recording paper S is conveyed to the fixing device 9 and the toner image is fixed on the recording paper S, and then discharged out of the apparatus by the discharge rollers 11. If you want to print the next page,
The print control unit 26 sets the PRINT signal to TRUE again after the time T5 as shown in FIG. 8B, and performs the same control as the printing of the first page.

FIG. 9 shows a detailed configuration of the semiconductor laser 13. In FIG. 9, two semiconductor lasers 51 and 52 are provided side by side as a semiconductor laser oscillator 53, and one photodiode 54 is arranged in the vicinity thereof. The photodiode 54 is configured to detect the backward light of each of the two semiconductor lasers 51, 52 so that the semiconductor lasers 51, 5 can be detected.
2 are arranged facing the boundary. Semiconductor laser 5
The forward lights 1 and 52 are converted into linear scans by the polygon mirror 15 and irradiated onto the photosensitive drum 17 as described above.

FIG. 10 shows a drive circuit for driving the semiconductor lasers 51 and 52. In FIG. 10, constant current circuits 61a and 61b are voltage-current converters for converting a voltage into a current, and supply a current corresponding to a light amount signal from the CPU 69 to the semiconductor lasers 51 and 52, respectively. The switching circuits 62a and 62b are circuits for switching the semiconductor lasers 51 and 52 according to the laser lighting signal (VDO signal) from the CPU 69, respectively. Semiconductor lasers 51 and 52
Are driven on and off according to the laser lighting signal, respectively.
When turned on, a drive current is supplied from the constant current circuit.
The light emission amounts of the semiconductor lasers 51 and 52 are each detected as a current value by the photodiode 54 and converted into a voltage signal by the resistor 68. After this voltage signal is amplified by the amplifier 63, it is taken into the CPU 69 as a light emission amount signal. CP
In U69, the levels of the light amount control signals 64a and 64b are varied according to the light emission amount signals of the semiconductor lasers 51 and 52, and the APC control is performed so that the light emission amount of the semiconductor lasers 51 and 52 becomes a desired light emission amount. Do.

[0010]

In the above-described conventional semiconductor laser driving circuit, since only one photodiode is provided for a plurality of semiconductor lasers, APC of a plurality of laser beams can be performed simultaneously. Instead, APC is performed in a time sharing manner. That is, two semiconductor lasers emit light in a non-image area between papers or lines in a time-division manner, hold the value of the light amount signal at that time, and drive the semiconductor laser according to the light amount signal held in the image area. Supplying current.

However, in such a method, APC of a plurality of semiconductor lasers cannot be performed at the same time, so that the amount of light of the semiconductor laser changes due to the influence of electric crosstalk and thermal crosstalk between the semiconductor lasers. FIG. 11A shows a signal for controlling ON / OFF of one of the semiconductor lasers, and FIG. 11C shows the light amount. FIG. 11B shows a signal for controlling on / off of the other semiconductor laser, and FIG. 11D shows the light amount. Normally, since the input signal (2) is constant as shown in FIG. 11B, the light quantity (2) in FIG. 11D should also be constant. However, FIG.
Since the light amount (1) of the other semiconductor laser changes as shown in FIG.
The light quantity (2) of the other semiconductor laser changes as shown in 1 (d).

When a surface emitting laser is used as a light source, heat is generated during a period in which the laser is turned on, and the heat output causes a blunt light output waveform of the other semiconductor laser. FIG. 12 shows this state. FIG.
(A) is a signal for controlling on / off of one surface emitting laser, FIG. 12 (c) is a light amount of the laser, and FIG. 12 (b) is a signal for controlling on / off of the other surface emitting laser. 1
2 (d) is the light amount of the laser. When one surface emitting laser is turned on as shown in FIG. 12C, it has heat as described above.
(2) as shown in FIG. Therefore, when optical writing is performed using a plurality of laser light sources, there is a difference in the amount of light between the lasers as described above, which has a problem of affecting the printed image quality.

In view of the above problems, the present invention provides an image forming apparatus capable of controlling the light amounts of a plurality of laser light sources to be constant irrespective of electrical or thermal crosstalk. It is intended for that purpose.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plurality of laser light sources, each of the plurality of laser light sources is driven in accordance with an image signal, and a plurality of laser light emitted from each of the laser light sources is imaged. In an image forming apparatus for forming a latent image on an image carrier by simultaneously linearly scanning on a carrier, a detection element for detecting a part of laser light corresponding to each of the plurality of laser light sources And controlling the drive current based on the output signal of the detection element corresponding to each laser light source and a predetermined reference voltage, thereby controlling the light amount of each laser light source to a desired light amount in real time. Is achieved by the image forming apparatus described above.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a laser diode used in the image forming apparatus of the present embodiment. In the present embodiment, the laser diode of FIG. 1 is provided as a recording light source in the image forming apparatus of FIG. 7, and a latent image is formed on the photosensitive drum 17 using the laser diode of FIG. Since the configuration and operation of the image forming apparatus of FIG. 7 have been described above, detailed description will be omitted.

Referring to FIG. First, reference numeral 41 denotes an edge-emitter type laser diode array in which two light emitting points (laser diodes) 41a and 41b are formed on one chip. In the vicinity of the laser diode array 41, photodiodes 42 and 43 are arranged corresponding to the light emitting points 41a and 41b, respectively. The laser diode array 41 and the photodiodes 42 and 43 include a case 46.
It is provided within. The photodiodes 42 and 43 are sensors for detecting two rear lights 44 and 45 of the light emitting points 41a and 41b, respectively, and the two rear lights 44 and 45 of the light emitting points 41a and 41b do not interfere with each other and correspond to the corresponding photo. The distance between the light emitting points and the distance between the light emitting points and the photodiodes are set so as to be incident on the sensor.

More specifically, two light emitting points 41
In order for the two laser beams a and 41b to enter the corresponding photodiodes without interfering with each other, the laser beams may be incident on the photodiodes before the bases of the two laser beams overlap. For this purpose, the distance between the two light emitting points 41a and 41b is H, and the full width at half maximum of the laser beam (the width at which the light intensity becomes half of the peak value when the light intensity is measured at a certain distance from the laser light emitting point) is Assuming that θ and the distance from the light emitting point to the photodiode are L, the spread Ltan θ of the laser light on the photodiode needs to be １ ／ or less of the distance H between the light emitting points.

Therefore, in this embodiment, Ltanθ <H
/ 2, that is, L <H / (2 tan θ), so that the two light emitting points 41a and 41b and the photodiodes 42 and 43
Is set. When the light emitting point and the photodiode are arranged so as to satisfy this condition, the distance between the light emitting point and the photodiode is shortened, so that the return light reflected from the photodiode and the laser light from the light emitting point may resonate. However, in order to avoid this, it is desirable to arrange the photodiodes 42 and 43 at an angle to the laser beam as shown in FIG.

FIG. 2 shows a drive circuit for driving the laser diode of FIG. The drive circuit in FIG. 2 is provided in the print control unit 26 of the image forming apparatus in FIG. In FIG. 2, first, in the present embodiment, the photodiodes 42 and 43 are arranged corresponding to the two light emitting points (laser diodes), respectively, as described above. APC control is performed for each of the two laser diodes in real time. FIG.
101, two laser diodes 41a, 41
1b is a laser driver IC for driving each laser diode according to the VDO signal, and has a function of performing APC control of each laser diode in real time. The laser driver IC 101 is provided with two terminals 110 and 120, and the video controller 27 shown in FIG.
20 is supplied with a VDO signal. When the input signals of the terminals 110 and 120 become TRUE, a drive current is supplied to each of the laser diodes 41a and 41b.

The VDO signal supplied to the terminal 110 is converted into a desired analog level by the logic input unit 102, and then gain is applied by the gain control unit 105 according to the characteristics of the laser diode. More specifically, the gain control unit 105 includes an amplifier, and the gain is previously adjusted using an external resistor or the like at the time of adjustment so that the light emission amount of the laser diode becomes a desired light emission amount. The output signal of the gain control unit 105 is input to the control amplifier 104, and the output signal of the photodiode 42
Detects the laser beam of the laser diode 41a, and the detection signal is fed back to the control amplifier 104.
In the control amplifier 104, these signals are compared with the reference voltage of the reference voltage generator 103, and a control voltage corresponding to the difference is supplied to the base terminal of the transistor 106.

Accordingly, when the light emission amount of the laser diode 41a has not reached the prescribed light amount, the base current of the transistor 106 is increased to increase the laser diode 41a.
The control works to increase the drive current of the laser diode 41, and the light amount of the laser diode 41 is controlled to a desired light amount. When the light emission amount of the laser diode 41a is larger than a predetermined light amount, control is performed so as to reduce the base current of the transistor 106, and the light amount of the laser diode 41a is controlled to a desired light amount. In this way, when the VDO signal at terminal 110 becomes TRUE, A
The PC operates, and the light amount of the laser diode 41a is maintained at a predetermined light amount.

Similarly, the VDO signal supplied to the terminal 120 is converted into a predetermined analog level by the logic input unit 112 and then input to the control amplifier 114 through the gain control unit 115. Similarly, the gain of the gain control unit 115 is previously adjusted so that the light amount of the laser diode 41b becomes a desired light amount. Further, the laser light of the laser diode 41 b is detected by the photodiode 43, and the detection signal is fed back to the input terminal of the control amplifier 114. Reference numeral 113 denotes a reference voltage generator that generates a reference voltage. With this configuration, a control voltage corresponding to the detection signal of the photodiode 43 is supplied from the control amplifier 114 to the base terminal of the transistor 116, and APC is performed in real time also in the laser diode 41b.

The laser beams emitted from the laser diodes 41a and 41b are converted into linear scans by the polygon mirror 15 as described with reference to FIG. As a result, a two-line latent image is formed on the photosensitive drum 17, and the same operation is repeated to form a one-page latent image on the photosensitive drum 17. Then, printing is completed by performing development, transfer to recording paper, and fixing as described above, and the print is discharged outside the apparatus.

In this embodiment, a photodiode is provided corresponding to each of two laser diodes, and APC control of each laser diode is performed in real time using an output signal of each corresponding photodiode. It is possible to control the light amount of each laser diode to a desired light amount irrespective of electrical and thermal crosstalk between them. FIG. 3A shows a signal for turning on / off one of the laser diodes, and FIG.
FIG. 3B shows a signal for turning on and off the other laser diode, and FIG. 3D shows the light amount. The broken line of the light amount in FIG. 3D is a change in the light amount due to the conventional electric and thermal crosstalk. In this embodiment, since each laser is controlled in real time, as shown by the solid line in FIG. There is no change in light quantity, and the light quantity of each laser can be controlled to be constant.

FIG. 4 shows another example of a laser diode. FIG. 4 shows an example in which two edge-emitter type laser diodes 71 and 72 are constituted by separate chips. In the vicinity of the laser diodes 71 and 72,
Photodiodes 73 and 74 are arranged corresponding to the laser diodes 71 and 72, respectively. The photodiodes 73 and 74 correspond to the respective laser diodes 7.
The laser diodes 71 and 7 are detected by detecting the backward light of the laser diodes 1 and 72 and feeding back the detection signals.
The second light amount is controlled to a desired light amount.

In the case of the laser diode shown in FIG.
When the distance between the light emitting points is H, the distance between the light emitting point and the photodiode is L, and the full width at half maximum of the laser light is θ, the rear lights of the laser diodes enter the corresponding photodiodes without interfering with each other. L <H /
(2 tan θ). In the case of FIG. 4, since the laser diode is constituted by separate chips, the distance between the light emitting point and the photodiode can be increased as compared with the case of FIG. 1, but also in this case, It is desirable to arrange each photodiode at an angle to the laser light so that resonance does not occur due to the return light.

FIG. 5 shows still another example of a laser diode. FIG. 5 uses two surface emitting lasers 81 and 82. Since the surface emitting laser does not emit backward light, the surface emitting lasers 81 and 82 are used by using the beam splitters 87 and 88.
Are divided into recording and APC laser beams. A divided by the beam splitters 87 and 88
The laser beams for PC are photodiodes 83 and 8 respectively.
4 is detected by the control amplifier 10 shown in FIG.
4, 114. Also in FIG.
As in FIGS. 1 and 4, when the distance between the light emitting points is H, the full width at half maximum of the laser is θ, and the distance between the light emitting points and the beam splitter (corresponding to the distance between the light emitting points and the photodiode) is L, The surface emitting lasers 81 and 82, the beam splitters 87 and 88, and the photodiodes 83 and 84 are arranged so as to satisfy L <H / (2 tan θ). Further, in order to prevent resonance due to return light from the photodiodes 83 and 84, as shown in FIG.
3, 84 are arranged obliquely.

When the laser diodes of FIGS. 4 and 5 are used, APC control of each laser diode can be performed in real time by the driving circuit of FIG. 2 just like the laser diode of FIG. Therefore, since APC is applied to each laser diode in real time,
Each laser diode can be controlled to a desired light amount irrespective of electrical crosstalk or thermal crosstalk between the laser diodes. Further, when the surface emitting laser shown in FIG. 5 is used, it is possible to correct the blunt rising as described above. FIG. 6 shows a waveform of an optical output when a surface emitting laser is used. Conventional time-sharing A
In the case of the PC control, as shown by the broken line, the light output waveform becomes dull and rises during the period when the other laser diode is turned on, and narrows.

In this embodiment, since each laser diode is controlled in real time, the APC operates at the time of the rise of the light output, and the dull rise of the light output can be corrected as shown by the solid line in FIG. When a surface emitting laser is used, a drive current having a peak value corresponding to each element is supplied to each laser before inputting an ON / OFF signal to a drive circuit to form a laser resonance mirror. There is a need to. For this purpose, it is necessary to individually set circuit constants for setting a peak value according to the variation of each element. In such a case, in the present embodiment, the blunt rising of the light output of the surface emitting laser is corrected and lighting is performed with a rectangular wave, so that it is not necessary to adjust the constant according to the variation of each element. ,
It is possible to easily manufacture the device.

[0030]

As described above, according to the present invention, a detection element is provided corresponding to each laser light source, and APC control is performed in real time using an output signal of the detection element corresponding to each laser light source. Thus, each laser light source can be controlled to a desired light amount regardless of electrical crosstalk or thermal crosstalk between the laser light sources. Therefore, since the light amount of each laser light source can always be maintained at a desired light amount, the image quality can be improved as compared with the conventional time-division control. Further, when a surface emitting laser is used, it is possible to correct the blunting of the rise of the optical output, and also to improve the image quality.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a laser diode used in an image forming apparatus of the present invention.

FIG. 2 is a diagram illustrating an example of a circuit that drives and controls a laser diode.

FIG. 3 is a diagram showing a change in light amount when an edge-emitter type laser diode is used, in comparison with a conventional case.

FIG. 4 is a diagram showing another example of a laser diode.

FIG. 5 is a diagram showing still another example of a laser diode.

FIG. 6 is a diagram showing the rise of the optical output in the case where a surface emitting laser is used, in comparison with the conventional example and the present invention.

FIG. 7 is a diagram illustrating a conventional image forming apparatus.

FIG. 8 is a time chart for explaining the operation of the device of FIG. 7;

FIG. 9 is a diagram showing a laser diode used in the device of FIG. 7;

FIG. 10 is a diagram showing a laser diode drive circuit of the device of FIG. 7;

FIG. 11 is a diagram for explaining a change in the amount of light due to the influence of electrical and thermal crosstalk between lasers when a plurality of semiconductor lasers are used.

FIG. 12 is a diagram for explaining a blunt rising of an optical output waveform when a surface emitting laser is used.

[Explanation of symbols]

 Reference Signs List 5 paper feed roller 6 registration roller 9 fixing device 15 polygon mirror 17 photosensitive drum 20 developing device 21 transfer charger 41 laser diode array 41a, 41b light emitting point (laser diode) 42, 43 photodiode 71, 72 laser diode 73, 74 photo Diodes 81, 82 Laser diodes 83, 84 Photodiodes 87, 88 Beam splitters 102, 112 Logic input units 103, 113 Reference voltage generators 104, 114 Control amplifiers 105, 115 Gain control units

Claims (3)

[Claims] A plurality of laser light sources, each of which is driven in accordance with an image signal, and which simultaneously scans a plurality of laser lights emitted from each of the plurality of laser light sources linearly on an image carrier. Accordingly, in an image forming apparatus for forming a latent image on an image carrier, a detection element for detecting a part of laser light corresponding to each of the plurality of laser light sources is provided, and a detection element is provided for each laser light source. An image forming apparatus for controlling the amount of light of each laser light source to a desired amount of light in real time by controlling a driving current based on an output signal of a detecting element and a predetermined reference voltage. 2. The image forming apparatus according to claim 1, wherein the distance between the laser light sources is H, the full width at half maximum of the laser light is θ, and the distance between the laser light sources and the detection element is H. L <H / (2 tan)
θ). 3. The image forming apparatus according to claim 1, wherein the detection element is configured to control the incident laser light so that the laser light from the laser light source and the return light reflected from the detection element do not resonate. An image forming apparatus, which is arranged to be inclined with respect to the image forming apparatus.