JPH0883947A - Laser driving circuit for image forming apparatus - Google Patents

Abstract

PURPOSE: To reduce the overshoot of a light waveform generated at the time of switching a laser diode by selecting a switching circuit to be driven and decided according to a current value, a voltage value, a resistance value and a threshold value from a plurality of switching circuits of switching means. CONSTITUTION: A voltage between the terminals of a laser diode 100, a driving current are detected, recorded and calculated in light quantity control means, and the resistance component of the diode 100 is obtained. If the obtained value is larger than a reference value, the switching circuit 101 connected with no resistor is selected, while if the obtained value is smaller than the reference value (threshold value), the circuit 101 connected with the resistor is selected, and switched. Thus, the unevenness of the individual laser diode resistances are reduced, the light quantity change due to the overshoot can be suppressed to the minimum limit. Accordingly, an image of high image quantity and high accuracy can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reduces the influence of an optical waveform (overshoot) due to the resistance component of a semiconductor laser diode by executing laser drive control of a laser printer, thereby improving the quality of an image. Laser drive circuit of.

[0002]

2. Description of the Related Art Conventionally, a laser printer,
There is an LED printer, etc., and recording paper is fed from a recording paper storage unit such as a paper cassette in accordance with a print command from an external device such as a computer, and the timing of conveying the recording paper and an image from a video controller by a synchronous conveying means such as registration rollers. The image is recorded by conveying the information in synchronization with the information transmission timing.

FIG. 23 shows the configuration of a conventional laser printer 101, and FIG. 24 shows its main operation timing. Referring to FIGS. 23 and 24 together, the laser printer 10
The operation of No. 1 will be described.

When the video controller section 28 confirms that the RDY signal is TRUE (true), it sets the PRINT signal to TRUE. The print controller 26 uses the PRIN
When the T signal becomes TRUE, driving of the main motor 23 and the polygon motor 14 is started. Main motor 2
When 3 is driven, the photosensitive drum 17, the fixing roller and the paper discharge roller 11 rotate. After that, the light amount control and high-voltage driving of the primary charging 19, the developing device 20, and the transfer charging device 21 are also sequentially performed.

The printer control unit 26 uses the polygon motor 1
When the rotation of 4 is in a steady state, the paper feed clutch 24 is turned on to drive the paper feed roller 5 for t1 seconds, and the recording paper S is fed toward the registration roller pair 6. Then, the printer control unit 26 sends a VSREQ signal to the video controller unit 28 at the timing when the leading edge of the recording paper S reaches the registration roller pair, and also causes the paper feed roller clutch 24 to be OF.
Then, the driving of the paper feed roller 5 is stopped.

When the video controller section 28 finishes developing the image information into a dot image and is ready to output the VDO signal, it confirms that the VSREQ signal is TRUE, sets the VSYNC signal to TRUE, and synchronizes this. Then, after tv seconds, the output of the VDO signal as image data for one page is started.

At this time, the printer control unit 26 is
After 3 seconds from the rise of the C signal, the registration roller clutch 25 is turned on to drive the registration roller pair. The registration roller pair 6 is driven for a time t4 seconds until the trailing edge of the recording sheet S passes through the registration roller pair 6. Also,
During this time, the printer control unit 26 sends the HSYNC signal to the video controller unit 28 at a predetermined timing synchronized with the laser scanning, and modulates the laser light for scanning the photosensitive drum 17 based on the VDO signal.

When printing the next page, the PRINT signal is set to TRUE again after t5 seconds.
After that, the same operation as the first page is performed.

By the operations of the printer controller 26 and the video controller 28, the recording paper S is sequentially conveyed to the paper feed roller 5, the registration roller pair 6, the image recording unit 8, the fixing device 9, and the paper discharge roller 11. The image is recorded.

Next, the laser diode drive circuit will be described with reference to FIG. This laser drive circuit is composed of a constant current circuit 1, a switching circuit 2 and an amplifier circuit 3. The constant current circuit is a voltage-current converter, and supplies a current I ₁ according to the light amount signal 4 from the control device. This current I ₁
The switching circuit 2 is a circuit for switching the laser light by the laser lighting signal 5. The laser diode 6 emits light in accordance with the operation of the switching circuit 2. This light emission amount is taken out as a current value by the photodiode 7 and converted into a voltage signal by the resistor 8. The light emission amount extracted as the voltage value is amplified by the amplifier circuit 3 and becomes a light emission amount signal 9. The control device drives the laser diode while monitoring the light emission amount signal 9 and increasing the level of the light amount signal 4 until the specified light amount is reached.

FIG. 26 shows the internal structure of the switching circuit 2. The switching circuit 2 is mainly composed of a differential amplifier circuit 2A that generates mutually complementary modulation signals and a bias circuit 2B that improves switching characteristics, and includes a first transistor Q1 having a laser diode 3 as a load and a first transistor Q1. It is composed of one transistor Q1 and a second transistor Q2 whose one end is commonly connected. Then, this differential amplifier circuit complementarily drives ON / OFF of the transistors Q1 and Q2 in accordance with a laser lighting signal from the control device,
A current value obtained by adding a bias current and a current according to the light amount signal from the control signal is passed through the laser diode to emit laser light.

However, as is well known, the resistance component of the semiconductor laser element greatly differs depending on the individual element. Therefore, as shown in FIG. 27A, the optical waveform output from the semiconductor laser element has the same drive current. However, it varies greatly depending on individual devices. In the same semiconductor laser, when the power supply voltage fluctuates as shown in FIG.
The voltage between the terminals fluctuates, causing a difference in the optical waveform.

[0013]

In the above-mentioned conventional example, when the laser drive circuit is driven, variations in the resistance component of the laser diode, the threshold value, the operating current, and the power supply voltage are not taken into consideration. There was a difference in overshoot at. For this reason, the quality of the image is deteriorated by causing a density difference between the individual devices and a density difference due to an environmental change.

In view of the above points, an object of the present invention is to
An object of the present invention is to provide a laser drive circuit of an image forming apparatus having a simple structure by reducing an overshoot of an optical waveform generated when switching a laser diode.

[0015]

In order to achieve such an object, the present invention forms a latent image on a photoconductor by emitting light from a semiconductor laser, and the latent image is visualized by a developing device. In the laser drive circuit of the image forming apparatus to be changed, a switching means provided with a plurality of switching circuits in which a resistance is connected to the semiconductor laser, and a laser current drive means for driving the semiconductor laser with a current value based on a desired voltage. An operation for calculating a resistance value of the semiconductor laser based on a voltage detection means for detecting a terminal voltage of the semiconductor laser, a current value driven by the laser current driving means, and a voltage value detected by the detection means Means, threshold value detecting means for detecting the threshold value of the semiconductor laser, and a drive target determined by the current value, the voltage value, the resistance value and the threshold value Characterized in that the switching circuit and control means for selecting from a plurality of switching circuits in the switching means.

[0016]

The present invention is directed to a semiconductor laser (100) and a switching circuit (101A-101) in which a resistor is connected in series.
A plurality of C) are provided, and a suitable switching circuit determined by the laser drive current value, the inter-laser terminal voltage, the laser resistance value, and the threshold value is driven. As a result, it is possible to minimize the difference in the resistance component of the laser diode, the threshold value, the difference in the operating current, and the difference in the optical waveform due to the fluctuation in the power supply voltage, and high-quality image formation can be obtained.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a basic circuit configuration common to each embodiment.

In FIG. 1, A is a laser light source as an exposing means for forming an image using laser light. Reference numeral B is a laser light detecting means such as a photo sensor for monitoring the output of the laser light. C is a laser light amount control means for controlling the laser light source A so that a predetermined light output level is obtained by executing various control procedures described later based on the output of the laser light detection means B. D is the amount of laser light so that the timing of the laser light amount control means C is executed in the main scanning direction except for the maximum recordable region and in the sub-scanning direction in the image guarantee regions at the front and rear ends in the recording medium. The timing control means controls the timing of the control means C. The laser light amount control means C has a discrimination means for discriminating the output of the laser light detection means B and a light output level setting means for setting the laser light source level in accordance with the discrimination result. In addition,
The light amount control means C and the timing control means D are realized by the microprocessor executing software. Further, the laser drive circuit shown in the circuit diagram of each embodiment described later is included in the laser light source A.

(Embodiment 1) FIG. 2 shows a circuit configuration of a laser drive circuit of Embodiment 1. In FIG. 2, 101 is a switching circuit unit for turning on / off the laser drive current, 1
Reference numeral 02 denotes a laser current drive circuit section for setting a current value supplied to the laser diode 100 (laser light source A).
Reference numeral 103 is a detection circuit unit that detects the voltage (V _F ) between the terminals of the laser diode, and 104 is a switching control unit that drives an optimum switching circuit based on the resistance component of the laser diode 100.

The contents of the laser drive control will be described with reference to FIGS. 3 and 4. FIG. 3 shows laser light amount, APC voltage, V _F
The relationship of voltage is shown. FIG. 4 shows a processing procedure of laser drive control.

First, the rough adjustment AP by forced lighting at the time of pre-rotation
Start C (FIG. 4, A2). At the time point (A3) when the laser light amount reaches several percent of the specified light amount and the rough adjustment APC ends and the fine adjustment APC starts (timing T1) (A3), the terminal voltage of the laser diode 100 (laser light source A),
The drive current is detected and recorded in the light amount control means C (microprocessor) (A4). Further, also at the time when the specified light amount is reached (timing T2 in FIG. 3), the voltage between the terminals of the laser diode 100 and the drive current are similarly detected and recorded in the light amount control means C (A6). Then, the recording control means C calculates the recorded value, and the laser diode 100
The resistance component of is calculated (A8). When the obtained resistance value is larger than the reference value, the switching circuit to which the resistance of FIG. 2 is not connected is selected (A9), and when the resistance value is smaller than the reference value (threshold value), the resistance of FIG. Select the switching circuit to which is connected for switching operation (A
10).

By this switching process, variations in individual laser diode resistance components are reduced, and fluctuations in light quantity due to overshoot of the laser diode can be suppressed to a minimum limit.

Further, by controlling the laser diode resistance component as described above, it is possible to obtain a laser beam with a small light amount variation, so that it is possible to form a high-quality, high-definition and high-quality image.

(Second Embodiment) Next, a second embodiment of the present invention will be described.

FIG. 5 shows the circuit configuration of the laser drive circuit according to the second embodiment. FIG. 6 shows the change in the light amount in the second embodiment. FIG. 7 shows a laser control procedure in the second embodiment.

In FIG. 5, the same parts as those in the first embodiment shown in FIG. 2 are designated by the same reference numerals, and the duplicated description will be omitted. In FIG. 5, a plurality of switching circuits 101A to 101D to which resistors having different resistance values are connected are provided on the laser diode 100 side, and a switching circuit to be actually operated is selected by a switching control circuit 104.

A laser control procedure using the circuit of FIG. 5 will be described below with reference to FIG. Coarse adjustment APC by forced lighting is started at the time of previous rotation (FIG. 7, B2). At a point (B3) at which coarse adjustment APC ends and fine adjustment APC starts (see FIG. 6) when the prescribed amount of light is reached (B3), the terminal voltage and drive current of the laser diode 100 are detected and recorded (B4). Further, even when the prescribed light amount is reached, the terminal voltage and drive current of the laser diode 100 are similarly detected and recording is performed (B6). Then, the recorded value is calculated to obtain the resistance component of the laser diode 100 (B8). A switching circuit is selected so that a value obtained by adding the obtained resistance value and the resistance connected to the switching circuit becomes an appropriate value, and the switching operation is performed using the selected switching circuit (B9).

By executing the above processing, each laser diode can be set to a constant resistance component. Further, by controlling the resistance component of the laser diode in this way to obtain laser light with little fluctuation in light quantity, it is possible to form high-quality, high-definition and high-quality images.

(Third Embodiment) Next, a third embodiment of the present invention will be described.

The structure of the laser drive circuit is similar to that of the first embodiment shown in FIG. FIG. 8 shows the change in light amount in the third embodiment.
FIG. 9 shows a laser control procedure in the third embodiment.

The laser control contents of the third embodiment will be described below with reference to FIG. In FIG. 9, coarse adjustment APC by forced lighting is started during pre-rotation (FIG. 9, C2). At the time when the rough adjustment APC ends and the fine adjustment APC starts (C3), the voltage across the terminals of the laser diode 100 and the drive current are detected and recorded (C4). And
Laser diode 1 every n bits from fine adjustment APC start
00 terminal voltage and drive current are detected and recorded (C
7). Next, the recorded value is calculated to calculate the laser diode 10
The resistance component of 0 is obtained (C8). In the setting of the switching circuit without a resistance at that time, if the obtained resistance value is larger than the reference value, the switching circuit is not switched (C10). If the resistance value is smaller than the reference value, the resistance is connected. The selected switching circuit (C
10). It should be noted that the reverse operation is performed in the switching circuit having the setting of resistance.

By this control processing, it is possible to reduce variations in individual laser diode resistance components, and it is possible to suppress fluctuations in the amount of light due to overshoot of the laser diode to a minimum limit. Further, by controlling the resistance component of the laser diode in this way to obtain laser light with little fluctuation in light quantity, it is possible to form high-quality, high-definition and high-quality images.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described.

FIG. 10 shows the circuit configuration of the laser drive circuit according to the fourth embodiment. The same parts as those in the first embodiment shown in FIG. 2 are designated by the same reference numerals. FIG. 11 shows the change in light amount in the fourth embodiment. FIG. 12 shows the laser control procedure in the fourth embodiment.

In FIG. 10, 201 is a switching circuit section for turning on / off the laser drive current, and 202 is a laser current drive circuit section for setting the current value supplied to the laser diode. A switching control unit 204 drives an optimum switching circuit based on the resistance component of the laser diode.

Next, the contents of laser control will be described with reference to FIG. In FIG. 14, coarse adjustment APC by forced lighting is started during the previous multi-rotation (FIG. 12, D2). At a point (D3) when the coarse adjustment APC ends and the fine adjustment APC starts (D3), the laser diode 1 reaches a certain percentage of the specified light amount.
00 terminal voltage and drive current are detected and recorded (D
4). Further, even when the specified light amount is reached, the terminal voltage and drive current of the laser diode 100 are similarly detected and recording is performed (D7).

Then, the recorded value is calculated to obtain the resistance component of the laser diode (D8). In the setting of the switching circuit with no resistance at that time, if the obtained resistance value is larger than the reference value, the switching circuit is not switched (D10). If the resistance value is smaller than the reference value, the resistance is connected. The selected switching circuit is selected (D10), and the same operation is performed again. It should be noted that the reverse operation is performed in the switching circuit having the setting of resistance.

By executing the above control processing, it is possible to reduce variations in individual laser diode resistance components, and it is possible to suppress fluctuations in light quantity due to overshoot of the laser diode to a minimum limit. Also,
By thus controlling the resistance component of the laser diode and obtaining laser light with a small fluctuation in light quantity, it is possible to form a high-quality, high-definition, high-quality image.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described.

The laser drive circuit configuration in the fifth embodiment is similar to that of the first embodiment shown in FIG. FIG. 13 shows the change in light amount in the fifth embodiment. FIG. 14 shows a laser control procedure in the fifth embodiment.

The laser control contents of the fifth embodiment will be described with reference to FIG. In FIG. 14, initial APC by forced lighting is started at the time of previous rotation (FIG. 14, E1). At the time when the specified light amount is reached and the initial APC is completed (timing T10 in FIG. 13) (E2), the terminal voltage of the laser diode is detected and recorded (E3). Then, based on the recorded value, if the voltage is higher than the reference value, select the switching circuit that connects the laser diode and the resistor to the series (E5), and if it is lower than the reference value, connect the series resistor. Select a switching circuit that has not been turned on (E5).

By this processing, it is possible to reduce the influence of the V _F fluctuation of the laser diode due to the fluctuation of the power supply voltage,
The light quantity fluctuation of the light waveform is suppressed to the minimum limit.

(Sixth Embodiment) Next, a sixth embodiment of the present invention will be described.

The circuit configuration of the laser drive circuit of the sixth embodiment is the same as that of the first embodiment shown in FIG. FIG. 15 shows the change in light amount in the sixth embodiment. FIG. 16 shows the laser control contents of the sixth embodiment.

Referring to FIG. 16, within the laser control of the sixth embodiment
Explain the contents. In Fig. 16, the forced lighting is performed during the previous rotation.
The initial APC is started (FIG. 16, F). Reached the specified light intensity
Then, when the initial APC is completed (F2),
Voltage between terminals of the diode V _F Is detected and recorded (F3
-See Figure 15). Then, based on the recorded value, the reference value
If the voltage is higher than the
Select a switching circuit with a resistor connected to the
If not less than connected series resistor
A switching circuit is selected (F5). And selected
The first switching sheet is printed by the switching circuit
(F6).

In the unblanking APC performed by detecting the light amount after the printing of the first sheet, the terminal voltage V _F of the laser diode is detected and recorded at the time of the end (F8), as in the initial APC (see FIG. 15).

Based on the recorded value, a switching circuit in which a laser diode and a resistor are connected to the series is selected when the voltage is higher than the reference value, and a series resistor is connected when the voltage is lower than the reference value. A switching circuit that is not activated is selected (F11).

By the above processing, it is possible to reduce the influence of the fluctuation of V _F of the laser diode due to the fluctuation of the power supply voltage, and suppress the fluctuation of the light quantity of the optical waveform to the minimum limit.

(Embodiment 7) Next, a seventh embodiment of the present invention will be described. FIG. 17 shows the circuit configuration of the laser drive circuit according to the seventh embodiment. FIG. 18 shows the change in light amount in Example 7.
FIG. 19 shows the laser control procedure of the seventh embodiment.

In FIG. 17, reference numeral 301 is a switching circuit section for turning on / off the laser drive current, and 302 is a laser current drive circuit section for setting the current value supplied to the laser diode 300. Reference numeral 303 is a detection circuit unit that detects the threshold value of the laser diode 300, and 304 is a switching control unit that drives an optimum switching circuit based on the threshold value of the laser diode.

The laser control contents of the sixth embodiment will be described with reference to FIG. In FIG. 19, initial APC by forced lighting is started at the time of previous rotation (FIG. 19, G1). Two areas where certain spontaneous light emission is performed (n, n + 1 step: FIG. 1)
8)), the light amount variation value for one step during natural light emission is recorded by the light amount control means C, actually a microprocessor, from the two light amounts and set (G3). Next, increase the APC voltage value by one step,
The value of the light amount variation for one step UP is calculated and recorded (G4). The recorded value is compared with the set light amount fluctuation amount (G5). If it is equal, the value is increased by one step. If it is larger, it is confirmed that the time is the threshold value of the laser diode 300. Record the value (G
7). This processing corresponds to the function of the threshold detection circuit 303 in FIG.

Next, in the setting of the switching circuit having no resistance in the initial state of the current, when the obtained APC voltage value is smaller than the reference value, switching of the switching circuit is not performed (G9), and the APC voltage value is the reference value. If larger, select the switching circuit to which the resistor is connected (G
9). It should be noted that the reverse operation is performed in a switching circuit having a resistor as an initial setting.

By the above processing, the influence of the threshold value of each laser diode can be reduced, and the fluctuation of the light quantity due to the overshoot of the laser diode can be suppressed to the minimum limit.

(Embodiment 8) Next, an eighth embodiment of the present invention will be described. FIG. 20 shows the circuit configuration of the laser drive circuit according to the eighth embodiment. FIG. 21 shows the change in light amount according to the eighth embodiment.
FIG. 22 shows the laser control procedure of the eighth embodiment.

In FIG. 20, 401 is a switching circuit section for turning on / off the laser drive current, and 402 is a laser current drive circuit section for setting the current value supplied to the laser diode 400. A switching control unit 403 drives an optimum switching circuit based on the operating current value of the laser diode 400.

The laser control contents of the eighth embodiment will be described with reference to FIG. Initial APC by forced lighting is started during the previous rotation (FIG. 22, H1). At the time when the specified amount of light is reached and the initial APC is completed (H2), the laser diode 40
The terminal voltage of 0 is detected and recorded (H3). Then, based on the recorded value, when the voltage is higher than the reference value, a switching circuit in which a resistor is connected to the laser diode 400 and the series is selected (H4), and when it is lower than the reference value, the series resistor is connected. Select a switching circuit that is not activated (H5).

By the above processing, the influence of the operating current value of the laser diode due to the fluctuation of the power supply voltage can be reduced, and the fluctuation of the light quantity of the optical waveform can be suppressed to the minimum limit.

[0059]

As described above, according to the present invention, the optimum switching circuit can be driven based on the laser drive current value, the voltage value, and the threshold value. It is possible to obtain an optical waveform that is not affected by the difference in operating current and the fluctuation in power supply voltage.
As a result, it is possible to obtain the effect of obtaining a high quality and high definition image.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a laser drive circuit according to the first embodiment.

FIG. 3 is an explanatory diagram showing a light amount change of the first embodiment.

FIG. 4 is a flowchart showing a laser drive control procedure according to the first embodiment.

FIG. 5 is a block diagram showing a circuit configuration of a laser drive circuit according to a second embodiment.

FIG. 6 is an explanatory diagram showing a light amount change of the second embodiment.

FIG. 7 is a flowchart illustrating a laser drive control procedure according to the second embodiment.

FIG. 8 is an explanatory diagram showing a light amount change of the third embodiment.

FIG. 9 is a flowchart showing a laser drive control procedure according to the third embodiment.

FIG. 10 is a block diagram showing a circuit configuration of a laser drive circuit according to a fourth embodiment.

FIG. 11 is an explanatory diagram showing a light amount change of the fourth embodiment.

FIG. 12 is a flowchart showing a laser drive control procedure according to the fourth embodiment.

FIG. 13 is an explanatory diagram showing a light quantity change of the fifth embodiment.

FIG. 14 is a flowchart showing a laser drive control procedure of the fifth embodiment.

FIG. 15 is an explanatory diagram showing a light quantity change of the sixth embodiment.

FIG. 16 is a flowchart showing a laser drive control procedure according to the sixth embodiment.

FIG. 17 is a block diagram showing the circuit configuration of a laser drive circuit according to a seventh embodiment.

FIG. 18 is an explanatory diagram showing a light quantity change of the seventh embodiment.

FIG. 19 is a flowchart showing a laser drive control procedure according to the seventh embodiment.

FIG. 20 is a block diagram showing a circuit configuration of a laser drive circuit according to an eighth embodiment.

FIG. 21 is an explanatory diagram showing a change in light amount according to Example 8.

FIG. 22 is a flowchart showing a laser drive control procedure according to the eighth embodiment.

FIG. 23 is a side sectional view showing a mechanism of a conventional image forming apparatus.

FIG. 24 is a timing chart showing an image forming operation.

FIG. 25 is a block diagram showing a configuration of a conventional laser drive circuit.

FIG. 26 is a circuit diagram showing a configuration of a switching circuit.

FIG. 27 is an explanatory diagram showing changes in output of the semiconductor laser device.

[Explanation of symbols]

 100,300 Semiconductor laser (laser diode) 101,201,301,401 Switching circuit 102,202 Laser current drive circuit 104,204,304 Switching control circuit

Claims (1)

[Claims] 1. In a laser drive circuit of an image forming apparatus, which emits light from a semiconductor laser to form a latent image on a photoconductor and visualizes the latent image by a developing device, a resistor is connected in series with the semiconductor laser. Switching means provided with a plurality of switching circuits connected to each other, a laser current drive means for driving the semiconductor laser with a current value based on a desired voltage, a voltage detection means for detecting a terminal voltage of the semiconductor laser, the laser Calculating means for calculating the resistance value of the semiconductor laser based on the current value driven by the current driving means and the voltage value detected by the detecting means, and threshold detecting means for detecting the threshold value of the semiconductor laser. And a switching circuit to be driven that is determined by the current value, the voltage value, the resistance value, and the threshold value. The laser drive circuit of the image forming apparatus is characterized in that and control means for selecting from the etching circuit.