JP2000085176A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a constant printing density of an image by finding a threshold current value among pages or among lines so as to drive a non-light emitting point by a current of the found out threshold current or lower. SOLUTION: In the case only a light emitting point 15a of a laser chip 15 is emitting light, the size of the output voltage 16a of a monitor photo diode 16 and the size of a standard voltage 24 are compared so that the comparison result is inputted into a current driving circuit 22 for controlling the size of the current value to be outputted from the current driving circuit 22. At the time, a current of the threshold current found out among pages or among lines or lower is outputted from a current driving circuit 23 to a non-light emitting point 15b for driving the non-light emitting point 15b. Accordingly, since the current amount can be corrected by real time so that fluctuation of the light output can be prevented, the printing density of an image can always be provided constantly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image using a laser scanner.

[0002]

2. Description of the Related Art Conventionally, a laser beam printer, which is one mode of an image forming apparatus, uses a single beam laser having a single beam from a beam source. For this reason, in order to obtain a high-speed output, high-resolution laser beam printer, a method of increasing the number of rotations of the polygon mirror or increasing the number of surfaces of the polygon mirror has been required.

[0003] However, when the rotation speed of the polygon mirror is increased, there are problems such as abrasion of the bearing, falling of the rotating shaft, generation of noise, and a problem that the durability of the polygon mirror itself is reduced. Further, increasing the number of surfaces of the polygon mirror causes a problem that the accuracy of beam irradiation on the image carrier deteriorates.

Therefore, in order to obtain a high-resolution laser beam printer, an image forming apparatus using a multi-beam laser has recently been developed. The multi-beam laser has a plurality of light emitting points and scans the plurality of light emitting points simultaneously. Therefore, the resolution of the laser beam printer can be increased without increasing the number of rotations of the polygon mirror or increasing the number of surfaces of the polygon mirror.

[0005]

However, the multi-beam laser is a so-called semiconductor laser using a semiconductor. Therefore, there is a characteristic that the threshold current value increases due to the temperature rise or deterioration. Therefore, when a multi-beam laser is used in the image forming apparatus, the light output fluctuates in the constant current operation, so that a constant print density may not be obtained.

Therefore, in order to obtain a constant light output while keeping the print density constant, the output light quantity of the light output is received (monitored) by a photodiode or the like, and the received light output voltage is compared with a reference voltage. It is necessary to provide the image forming apparatus with a feedback circuit for controlling the driving current.

A circuit for driving such a semiconductor laser is provided with an automatic optical power control (APC).
l. Hereinafter, referred to as APC) circuit. This A
The PC circuit also corrects light amount fluctuations due to variations in laser chip characteristics of the multi-beam laser.

However, in an image forming apparatus using a multi-beam laser, when a plurality of light emitting points are controlled by a single monitor photodiode, a plurality of light emitting points may emit light during main scanning. is there. Therefore, it is difficult to perform APC independently for each light emitting point. That is, there is a case where a problem occurs that the light amount decreases during the main scanning and the print density decreases in the latter half of the main scanning line.

Further, the plurality of light emitting points provided in the multi-beam laser are not thermally insulated. Therefore, heat generated by light emission at one light-emitting point may increase the temperature at another light-emitting point. Therefore,
When a certain light emitting point emits light, the light amount of another light emitting point may be reduced, and a problem may occur on an image.

(Object of the Invention) During main scanning, the amount of current for driving a plurality of light-emitting points of a laser is corrected in real time to prevent fluctuations in light output, thereby keeping the print density of an image constant. The purpose is to do.

[0011]

The above object can be attained by an image forming apparatus according to the present invention. The present invention is an image forming apparatus having the following configuration.

That is, in an image forming apparatus including a laser having a plurality of light emitting points, one optical sensor for monitoring the amount of laser output from the laser, and drive current control means for driving the laser, Means for performing real-time APC (automatic light output control) of light emitting points, means for calculating a threshold current value between pages or between lines, and means for driving non-light emitting points with a current equal to or less than the threshold current. The feature is provided.

A laser having a plurality of light emitting points;
One optical sensor that monitors the amount of output light output from the laser, a plurality of reference voltages for comparing output voltages output from the optical sensor, and the plurality of light-emitting points according to the number of light-emitting points that emit light. Selecting means for selecting one of the reference voltages, comparing means for comparing the output voltage with the selected reference voltage, and a current value for driving the laser based on difference data output from the comparing means And a light output control means including a current drive means for determining

(Operation) By using the image forming apparatus having the above-described configuration, the light amount fluctuation of a plurality of light emitting points emitting light during the main scanning can be corrected in real time, so that a necessary light amount can be obtained in each main scanning line. . In addition, by energizing the non-light emitting point to a value equal to or less than the threshold current value, the non-light emitting point is in a state where heat is generated, and the light quantity fluctuation due to thermal coupling between the light emitting points is reduced.

[0015]

(Embodiment 1) Hereinafter, an image forming apparatus using a double beam laser as an embodiment of the present invention will be described with reference to the drawings. A case where only real-time APC is performed during image formation will be described.

FIG. 3 is a diagram showing a main part of the image forming apparatus according to the present embodiment. In FIG. 3, reference numeral 1 denotes an organic photosensitive drum serving as an image carrier, 2 denotes a charging roller serving as a charging member for charging the image carrier 1, 3 denotes a laser exposure device that irradiates the image carrier 1 with laser light, and 4 denotes development. A developing device comprising a sleeve, a developing blade, and a one-component magnetic toner; 5, a cleaning blade for cleaning the toner on the image carrier 1; 6, a transfer roller for transferring an image onto an original; This is a fixing device for fixing the visible image to a document or the like.

Although the image forming apparatus according to this embodiment uses a double beam laser, the number of lasers may be three or more. As described later, N reference voltages are required for N lasers.

Next, the operation of the image forming apparatus having the above configuration will be described. First, the organic photosensitive drum 1
Is uniformly charged to a negative charge by the charging roller 2.
Then, an electrostatic latent image is formed on the organic photosensitive drum 1 by the laser beam from the laser exposure device 3. Next, the charged toner in the developing device 4 adheres to the electrostatic latent image on the organic photosensitive drum 1 to become a visible image. Thereafter, the toner image is transferred onto the paper on the transfer roller 6 and is fixed on the paper by the fixing device 7. Further, the cleaning blade 5 removes the toner remaining on the organic photosensitive drum 1. Each of the above units is operated to form an image.

Next, a process until an electrostatic latent image is formed in the image forming apparatus using the double beam laser as described above will be described with reference to FIG. As shown in FIG. 4, first, the double beam laser light sources 8 to 2
A book laser light is emitted. And the laser light
After passing through the collimator lens 9 and the cylindrical lens 10, it is deflected and scanned by the polygon mirror 11. Thereafter, the laser light passes through the scanning lens 12 and is scanned on the organic photosensitive drum 1.

At this time, since two lasers are emitted at the same time, scanning of two lines is performed. Further, a double beam laser light source 8, a collimator lens 9, a cylindrical lens 10, a polygon mirror 11, and a scanning lens 1
2, an exposure apparatus 3 is formed.

Next, the double beam laser light source 8 will be described with reference to FIG. FIG. 5 is a perspective view showing the vicinity of the double beam laser light source 8. In FIG. 5, a double beam laser light source 8 is connected to a stem 13. A base 14 is provided on one side of the stem 13, and a laser chip 15 having light emitting points 15 a and 15 b and a photodiode 16 are fixed on the base 14.

A cap 17 is attached to the stem 13 so as to cover the base 14 on which the laser chip 15 and the photodiode 16 are mounted, and the tip of the cap 17 is provided with laser beams La and Lb. A passing window 18 is provided.

On the other hand, on the opposite surface of the stem 13, an energizing terminal 19 for connecting the laser chip 15 and the photodiode 16 to a laser drive control system (not shown) is provided.

Next, an APC circuit for controlling the drive current of the double beam laser light source 8 will be described with reference to FIG. FIG. 6 is a block diagram showing the basic configuration of an APC circuit for controlling the drive current of the double beam laser light source 8.

In FIG. 6, reference numeral 15 denotes a laser chip,
5a and 15b are light emitting points of the laser chip 15, 16 is a monitor photodiode that receives a monitor beam from the light emitting points 15a and 15b, 16a is a monitor output voltage output from the monitor photodiode 16, and 24 is a monitor output voltage 16a. The reference voltage (Vr) for comparing the voltages
ef1) and 25 are reference voltages (Vref2) for comparing the voltage with the monitor output voltage 16a, and 21 is a CP for selecting the reference voltages 24 and 25 to be compared with the monitor output voltage 16a.
U and 22 are current drive circuits for outputting a current for driving the light emitting point 15a, and 23 is a current drive circuit for outputting a current for driving the light emitting point 15b.

Next, the operation of the APC circuit will be described. First, the light emitting points 15a and 15b of the laser chip 15
When is turned on, the monitor photodiode 16 is irradiated with laser light as a monitor beam. Then, it is converted to the monitor output voltage 16a. The magnitude of the monitor output voltage 16a corresponds to the magnitude of the drive current for driving the laser.

Subsequently, using the CPU 21, the magnitude of the monitor output voltage 16a and the reference voltage 24 (Vref
1) or monitor output voltage 16a and reference voltage 25
Compare with the magnitude of (Vref2). Where Vre
f1 is a reference voltage for comparison when only one of the two lasers of the double beam laser light source 8 emits light. Vref2 is a reference voltage for comparison when two lasers of the double beam laser light source 8 emit light simultaneously.

The CPU 21 determines whether only one of the two lasers of the double beam laser light source 8 emits light or both of the lasers emit light.
Done by Then, based on the determination result, selection of a reference voltage to be compared with the monitor output voltage 16a is performed.

The method of controlling the drive current of the laser will be described below for each case.

(1) When only the light emitting point 15a emits light As described above, when only the light emitting point 15a emits light, the magnitude of the monitor output voltage 16a and the reference voltage 24
Compare with (Vref1). Then, control is performed using the current drive circuit 22 so that they become equal. Specifically, the comparison result is input to the current driving circuit 22, and the magnitude of the current value output from the current driving circuit 22 is controlled. At this time, the light emitting point 15b is also driven. The current for that is output from the current drive circuit 23 to the light emitting point 15b. The intensity of the output current is equal to or less than the threshold current value of the light emitting point 15b.

(2) When only the light emitting point 15b emits light On the other hand, when only the light emitting point 15b emits light, the magnitude of the monitor output voltage 16a and the reference voltage 24 (Vref
Compare with the size of 1). Then, control is performed using the current drive circuit 23 so that they become equal. Specifically, the comparison result is input to the current drive circuit 23, and the magnitude of the current value output from the current drive circuit 23 is controlled.
At this time, a current for driving the light emitting point 15a is output from the current driving circuit 22 to the light emitting point 15a. The intensity of the output current is equal to or less than the threshold current value of the light emitting point 15a.

(3) When both the light emitting points 15a and 15b emit light When both the light emitting points 15a and 15b emit light, the magnitude of the monitor output voltage 16a and the reference voltage 25 (Vre
Compare with the magnitude of f2). Then, control is performed simultaneously using the current drive circuit 22 and the current drive circuit 23 so that they become equal. Specifically, the comparison result is input to each of the current driving circuits 22 and 23, and the magnitude of the current value output from each of the current driving circuits 22 and 23 is controlled.

In (1) and (2), energizing the non-light-emitting point to a value equal to or less than the threshold current value causes the non-light-emitting point to generate heat, and the light quantity fluctuation due to the thermal coupling between the light-emitting points. This is to reduce it.

Next, the algorithm of the real-time APC of the image forming apparatus using the double beam laser will be described with reference to FIG. FIG. 1 is a flowchart of the algorithm of the real-time APC of the image forming apparatus using the double beam laser according to the present embodiment.

Here, of the two lasers of the double beam laser, one laser will be referred to as laser 1 and the other laser will be referred to as laser 2.

First, in step S11, it is determined whether or not the image forming apparatus is forming an image. If it is time to form an image, the flow shifts to step S12 to perform real-time APC. When the APC is performed, the light emission states of the lasers 1 and 2 are checked and the cases are classified (S12).

That is, when only the laser 1 emits light, the process proceeds to step S13. Laser 2
If only light is emitted, the process proceeds to step S24.
If both lasers 1 and 2 emit light, the process proceeds to step S26. If both lasers 1 and 2 do not emit light, APC is not performed, and the process returns to step S11.

On the other hand, if it is determined in step S11 that the image forming apparatus has not formed an image,
Move to step S36.

In step S13, the laser 2 is energized at a threshold current value or less. Here, the current value of the current supplied to the laser 1 is the value determined by the previous APC. Further, the current value of the current applied to the laser 2 is a threshold current value measured between pages (including the pre-rotation when the laser beam printer starts up) or between lines.

Here, between pages means the organic photosensitive drum 1
The area between the lines is an area in the main scanning direction other than the image forming area provided on the organic photosensitive drum 1.

The measurement of the threshold current value is carried out for each of the lasers 1 and 2 sequentially between pages and between lines. Then, the threshold current values of the respective lasers 1 and 2 are stored in the memory 26 based on the measurement results, and the values are used the next time the lasers 1 and 2 are energized below the threshold current value. use. The algorithm for measuring the threshold current value will be described later.

Thereafter, while energizing the laser 2, the current value necessary for obtaining the optical output of the laser 1 is corrected by real-time APC. First, the CPU 21 associates the current value of the current supplied to the laser 1 with the number of bits. The digital value represented by the 8 bits of the CPU 21 is, for example, from 0 to 255 bits, and a current value corresponding to the digital value can be supplied to the laser.

The correspondence between the digital value and the current value is set, for example, such that the current value increases as the digital value increases. Then, the process proceeds to step S14, and it is determined whether or not the output of the photodiode 16 as the monitor input is smaller than the reference voltage 24 (Vref1) (S14).

If the output of the photodiode 16 is smaller than the reference voltage 24 (Vref1), the digital value of the CPU 21 is added by one step (S15). on the other hand,
The output of the photodiode 16 is applied to a reference voltage 24 (Vre
If not smaller than f1), the digital value of the CPU 21 is subtracted by one step (S19).

That is, when the output of the photodiode 16 is smaller than the reference voltage 24 (Vref1), the current value of the laser 1 is insufficient and the current value is increased. On the other hand, the output of the photodiode 16 is equal to the reference voltage 2
In the case of 4 (Vref1) or more, the current value of the laser 1 is decreased because the current value of the laser 1 is too large.

After updating the current value of the laser 1, the output of the photodiode 16 and the reference voltage 24 (Vref
1), the image formation is progressing even during the execution of the APC. Therefore, when the image formation is completed during the execution of the APC, or when the light emitting state of the laser 1 (the light emitting state is determined in step S12). When confirmed, both lasers 1,
2 does not emit light).

Therefore, a step (S16, S20) of monitoring whether or not an image is still being formed and a step (S17, S21) of monitoring whether the state that only the laser 1 emits light are not changed are required. Therefore, these steps were provided. When the image formation is completed, the APC
Is interrupted, and in order to store the emission data of the laser 1 in the memory 26 based on the bit number at that time, the process temporarily shifts to step S23 and returns to step S11.

On the other hand, if the image formation is not completed,
C is continued and the process proceeds to step S17 or S21.
In step S17 or S21, if the emission state of the laser has changed,
In order to temporarily suspend the PC and store the data in the memory 26 based on the number of bits at that time, the process temporarily shifts to step S23, and returns to step S12 via step S11.

Then, in step S12, APC corresponding to the laser emission state is performed. If the laser emission state has not changed, the AP for laser 1
Continue C. When the image formation is completed, the APC is performed regardless of whether the laser emission state is changing.
Interrupt. Then, the driving current value (current value I) of the laser 1 at that time is stored, and when the laser 1 is to emit light in the future, the laser 1 is driven by that value.

The current value I is different from the current value I ₁ required to obtain the required light output of the laser 1. But,
It is at least closer to the drive current value I 'of the laser 1 before APC is performed. That is, the relationship | I ₁ −I | <| I ₁ −I ′ | is satisfied.

Therefore, in order to emit a more accurate amount of laser light, even when APC is not completed, data is stored in the memory 26, and is temporarily used as a drive current value of the laser 1 in the future.

When the APC is continued without changing the light emission state of the laser light, the output of the photodiode 16 is compared with the reference voltage 24 (Vref1) (Sref).
18, S22). In step S18 or S22, the output of the photodiode 16 and the reference voltage 24 (Vr
As long as the magnitude relationship with ef1) is not reversed, step S1
5, or return to S19 to repeat addition or subtraction of digital values.

When the magnitude relationship between the output of the photodiode 16 and the reference voltage 24 (Vref1) is reversed (the comparison in step S18 includes the case where the output of the photodiode 16 and the reference voltage 24 (Vref1) are equal). ), Judging that the current value is necessary for the optical output of the laser 1,
The data is updated and stored in the memory 26 (S23), and when the laser 1 emits light in the future, the laser 1 is driven with the newly determined current value. This value is maintained until a new value is determined in the next APC for the laser 1 (including the APC when both are emitting). Step S
When 23 ends, the process returns to step S11, and if image forming is being performed, APC is continuously performed.

Next, APC when only the laser 2 emits light in step S12 (proceeding to step S24) will be described. Basically, APC is performed in the same manner as in the case where only the laser 1 emits light. The difference from the case where only the laser 1 emits light is that the laser 1 and the laser 2 are interchanged.

Accordingly, real-time APC of the laser 2 is performed while energizing the laser 1 to a value equal to or less than the threshold current value (S24). Here, step S14 of the flowchart of the APC when only the laser 1 emits light.
Steps from S22 to S22 are collectively referred to as step S1. Then, the light amount of the laser 2 is corrected (S1). When the laser 2 emits light, as in the case of the laser 1, the laser 2 is driven with the newly updated current value in step S25. This value is held until the new value is updated in the next APC for the laser 2 (including the APC when both are emitting).

In step S12, APC when both lasers are emitting (go to step S26)
Will be described with reference to FIG. In this case, APC is performed on both lasers 1 and 2 simultaneously based on the combined light amount of both lasers 1 and 2. Here, the value of the current supplied to the lasers 1 and 2 is the value updated in the previous APC.

When performing APC for the lasers 1 and 2, the CPU 21 first associates the current values of the current supplied to the lasers 1 and 2 with the number of bits. Then, it is determined whether or not the output of the photodiode 16 as the monitor input is smaller than the reference voltage 25 (Vref2) (S26). In this case, the photodiode 16
Detects the combined light amount of both lasers 1 and 2.
Therefore, Vref2 is used as the reference voltage.

When the output of the photodiode 16 is smaller than the reference voltage 25 (Vref2),
The digital values corresponding to the current values of 2 are each added by one step (S27). On the other hand, when the output of the photodiode 16 is not smaller than the reference voltage 25 (Vref2), the digital values corresponding to the current values of the lasers 1 and 2 are respectively subtracted by one step (S31).

Then, similarly to the case where the laser 1 or 2 emits light alone, here, the step (S28, S32) of monitoring whether an image is still being formed and the current state that both lasers are emitting light The process proceeds to steps (S29, S33) for monitoring whether or not the state has changed.

When the image formation is completed or when the laser emission state has changed, the APC is temporarily suspended, and the data is stored in the memory 2 based on the bit number at that time.
6 (S35). Thereafter, the process returns to step S11 described in FIG. At this time, in step S35, the drive current values of both the lasers 1 and 2 are provisionally determined. On the other hand, if the image formation is not completed and the light emission state has not changed,
C, the output of the photodiode 16 and the reference voltage 2
5 (Vref2) (S30, S34).

The output of the photodiode 16 and the reference voltage 25 are compared by comparing the output of the photodiode 16 with the reference voltage 25 performed in step S30 or S34.
As long as the magnitude relationship with (Vref2) does not reverse, the process returns to step S27 or S31, and the addition or subtraction of the digital value is repeated.

The output of the photodiode 16 and the reference voltage 2
The current value when the magnitude relationship with 5 (Vref2) is reversed for the first time (including the case where they are equal in the comparison in step S30) is determined as the current value required to obtain the necessary optical output of both the lasers 1 and 2. Then, this data is stored in the memory 26 (S35), and when the lasers 1 and 2 are to emit light in the future, the drive is performed with the updated current value.

This current value is maintained until the next APC for the lasers 1 and 2 is updated. Step S
Upon completion of step 35, the process returns to step S11, and if it is time for image formation, APC is continuously performed.

As described above, after all, in the present embodiment, at least one of the two lasers at the time of image formation is used.
When two lasers are emitting light, APC is performed. During non-image formation (between pages and between lines), only measurement of the threshold current value of each laser is performed. Further, at the time of image formation and measurement of the threshold current value of the laser, the laser which does not emit light is energized to a value equal to or less than the threshold current value of the laser.

Next, an algorithm for measuring the threshold current value of the laser executed between pages and between lines will be described with reference to FIG. FIG. 7 is a flowchart of an algorithm for measuring the threshold current value of the laser executed between pages and between lines in the present embodiment.

Each laser has a unique threshold current value. Therefore, it is necessary to measure the threshold current values for the lasers 1 and 2 in order.

In this embodiment, the threshold current value of the laser 1 is measured first, and then the threshold current value of the laser 2 is measured. First, in step S41, it is determined whether or not a page or a line exists. If it is between pages or between lines, the threshold current value is measured.

That is, the laser 2 is energized with the threshold current value updated in the previous measurement of the threshold current value or less (S42), and the laser 1 is energized with the previously measured threshold current value (S42). S43).

On the other hand, when it is determined in step S41 that the laser beam is not irradiated between the pages or between the lines, the process proceeds to step S56, and the measurement of the threshold current value is not performed.

Subsequently, the photodiode 16 detects whether or not the laser 1 emits light (S44). At this time, the current value supplied to the laser 1 is associated with the digital value of the CPU 21 as in the case of the real-time APC described above. If the laser 1 does not emit light, the digital value of the CPU 21 is added (S45),
It is detected again whether the laser 1 emits light (S4).
6).

If the laser 1 does not emit light, steps S45 and S46 are repeated until the laser 1 emits light. When laser 1 emits light, from the emission data of laser 1 at that time,
For example, a value obtained by subtracting 10% is stored in the memory 26 (S
50), this value is used as a new threshold current value of the laser 1. In addition, even if the algorithm described above is used,
If the threshold current has decreased, steps S47 to S49 are executed.

The reason why the value is subtracted by 10% and stored in the memory 26 is to prevent a situation in which the non-light emitting point emits light due to a malfunction because the threshold current value changes. Therefore, if the above situation can be prevented, the value does not need to be particularly 10%.

If the laser 1 emits light in step S44, the current value is high, so the digital value of the CPU 21 is subtracted (S47), and it is detected whether or not the laser 1 emits light (S48). Until the laser 1 stops emitting light, the digital value subtraction (S47) and the detection of whether the laser 1 emits light (S48) are repeated.

If the digital value at the time when the laser 1 stops emitting light is added by one step (S49) and the data at that time is subtracted by, for example, 10%, and stored in the memory 26 (S50), the laser 1 A new threshold current value is determined. The threshold current value of the laser 1 updated in step S50 is used when the laser 1 is to be supplied with a current equal to or less than the threshold current value in the future. Retained until the value is updated.

Next, the threshold current value of the laser 2 is measured. The measurement is basically the same as the measurement of the threshold current value of the laser 1 described above. That is, the difference from the measurement of the threshold current value of laser 1 is that laser 1 and laser 2
Is to be replaced.

While energizing the laser 1 to a value equal to or less than the threshold current value updated in the previous measurement of the threshold current value (S5).
1) The laser 2 is supplied with the previously measured threshold current value (S52). Here, steps S43 to S48 of the flowchart of measuring the threshold current value of the laser 1 are collectively referred to as step S2.

Then, in step S2, the photodiode 16 detects whether or not the laser 2 emits light (S44). At this time, the aforementioned real-time APC
As in the case of (1), the value of the current supplied to the laser 2 is associated with the digital value of the CPU 21. If the laser 2 does not emit light, the digital value of the CPU 21 is added (S45), and it is detected again whether the laser 2 emits light (S46).

If the laser 2 does not emit light, steps S45 and S46 are repeated until the laser 2 emits light. When the laser 2 emits light, from the emission data of the laser 2 at that time,
For example, a value obtained by subtracting 10% is stored in the memory 26 (S
50), this value is used as a new threshold current value of the laser 2.

As in the case of the laser 1, step S53
The threshold current value determined in step 2 is used when the laser 2 is to be supplied with a current equal to or smaller than the threshold current value in the future. The threshold current value is corrected next time, and the threshold current value is updated. Held until

When the threshold current values of the lasers 1 and 2 are determined, the power supply to the lasers 1 and 2 is turned off (S5).
4), the measurement of the threshold current value ends (S55).

As described above, since the image forming apparatus using the double beam laser and the single monitor photodiode according to the present embodiment can perform real-time APC, the required light amount can be obtained in each main scanning line. Thus, a constant printing density can always be realized.

Further, by applying a current equal to or less than the threshold current value to the non-light-emitting point, the non-light-emitting point generates heat. Therefore, the fluctuation of the light amount due to the thermal coupling between the light emitting points is reduced, and the laser light amount correction with high accuracy can be realized.

(Embodiment 2) Next, A for controlling the drive current of the double beam laser light source 8 according to the present embodiment will be described.
A basic block diagram of the PC circuit will be described with reference to FIG. FIG. 8 is a basic block diagram of the APC circuit according to the second embodiment. The laser drive current control can also be performed by the configuration shown in FIG. A circuit for measuring the threshold current of the laser is omitted and not shown.

In FIG. 8, 15 is a laser chip, 1
5a and 15b are light emitting points of the laser chip 15, 16 is a monitor photodiode that receives a monitor beam from the light emitting points 15a and 15b, 16a is a monitor output voltage output from the monitor photodiode 16, and 24 is a monitor output voltage 16a. The reference voltage (Vr) for comparing the voltages
ef1), 25 are reference voltages (Vref2) for comparing the monitor output voltage 16a with the voltage, 26 is a subtractor, 27 is an on / off signal 22a of the laser 15a,
b on / off signal 23a, the reference voltages 24, 25
Is an amplifier for amplifying the output from the subtractor 26, and 29 is a light emitting point 15
Reference numeral 30 denotes a sample and hold circuit for the light emitting point 15b.

Although the image forming apparatus according to the present embodiment uses a double beam laser, the number of lasers may be three or more.

Next, the operation of the APC circuit according to this embodiment will be described. Light emitting point 1 of laser chip 15
When the lamps 5a and 15b are turned on, the monitor photodiode 16 is irradiated with laser light as a monitor beam.
Then, it is converted to the monitor output voltage 16a. In addition,
The magnitude of the monitor output voltage 16a corresponds to the amount of drive current for driving the laser.

The monitor output voltage 16a is input to a subtracter 26, which subtracts the level of the reference voltage from the level of the monitor output voltage 16a and outputs the difference. Further, the determination circuit 27 determines which reference voltage of the reference voltages 24 (Vref1) and 25 (Vref2) is to be compared with the monitor output voltage 16a by the lasers 15a and 15b.
The determination is made based on the input of the n / off signals 22a and 23a.

As in the first embodiment, when only one laser emits light, the reference voltage 24 (Vref1) can be subtracted from the level of the monitor output voltage 16a. When both lasers are emitting light, the level of the monitor output voltage 16a is changed to the reference voltage 25 (Vref).
2) can be subtracted. Thereafter, the output of the subtracter 26 is amplified by the amplifier 28. Then, it is output to sample and hold circuits 29 and 30 for holding the value.

If both lasers are emitting at the same time, the output of the subtractor 26 is the current of the lasers 15a and 15b.
The output of the amplifier 28 is distributed according to the ratio of the amount of current supplied to the amplifiers and held by the sample and hold circuits 29 and 30, respectively. Then, the value of the current supplied to each laser is controlled in accordance with the outputs of the sample and hold circuits 29 and 30.

The real-time APC and the measurement of the threshold current value of each of the beams 1 and 2 are performed according to the procedure described in the first embodiment and the steps of the procedure.

(Embodiment 3) An image forming apparatus according to the present embodiment will be described with reference to a flowchart shown in FIG. The configuration of the image forming apparatus according to the present embodiment is a configuration using a double beam laser and a single monitor photodiode as in the first and second embodiments. That is, the image forming apparatus according to the present embodiment performs real-time APC when at least one of the two lasers emits light during image formation. At the same time, a laser that does not emit light during APC is energized to a value equal to or lower than the threshold current value of the laser.

Note that the image forming apparatus according to the present embodiment uses a double beam laser, but the number of lasers may be three or more.

However, the image forming apparatus according to the present embodiment not only measures the threshold current value of each laser performed in Embodiments 1 and 2 during non-image formation, but also performs independent measurement for each laser. Perform APC (AP between pages)
C or APC between lines). In addition, this page A
In the case of the PC or the inter-line APC, similarly to the real-time APC, the non-light emitting point is energized at a threshold current value or less of the laser.

FIG. 9 is a flowchart of an algorithm for measuring the threshold current value of the laser and APC between pages or APC between lines in this embodiment. The image forming apparatus according to the present embodiment continuously performs the measurement of the threshold current value and the APC for the laser 1 during non-image formation. After that, the measurement of the threshold current value and the APC for the laser 2 are continuously performed.

Hereinafter, the measurement of the threshold current value and the APC operation in this embodiment will be described with reference to the flowchart of FIG. First, it is determined whether or not there is between pages or between lines (S61). When between pages or between lines, measurement of threshold current value and AP
Perform C.

On the other hand, if it is determined in step S60 that the current is not between pages or between lines, the flow shifts to step S77 to measure the threshold current value and perform APC.
Is not performed.

First, while energizing the laser 2 to a value equal to or less than the threshold current value determined in the previous measurement of the threshold current value (S62), a new method is used as necessary by the same method as in the first embodiment. The threshold current value of the laser 1 is updated, and the updated data is stored in the memory 26 (S63).

Next, a current value I ₁ required to obtain the optical output updated by the previous APC is supplied to the laser 1 (S _1).
64). At this time, the laser 2 is continuously energized at a threshold current value or less. After that, laser 1
(S65-S69). S65 to S69
Are omitted to avoid redundant description.

The procedure of steps S65 to S69 is referred to as step S3. The above-described APC is performed at the time of non-image formation. Therefore, a step of monitoring whether or not an image is being formed by the real-time APC according to the first and second embodiments and a step of monitoring whether or not the light emission state of the laser has changed are not provided.

By executing the above operation, the measurement of the threshold current value of the laser 1 and the APC are completed.

Then, the measurement result obtained in step S3 is stored as a current value required to obtain the optical output of the laser 1 (S70). Next, steps S62 to S
The measurement of the threshold current value of the laser 2 and the APC are performed by the same method as that performed on the laser 1 in 70 (S71 to S74). When the measurement of the threshold current values of the lasers 1 and 2 and the APC are completed, the power supply to the lasers 1 and 2 is turned off (S75), and the measurement of the threshold current values and A
The PC ends (S78).

The threshold current values of the lasers 1 and 2 updated by the above-described procedure are held and used until the threshold current values are updated in the next non-image formation. The current value required for the light output of the lasers 1 and 2 updated by the above procedure is used from the first drive of the lasers 1 and 2 at the time of image formation, and is described in the first and second embodiments. Held until updated by the real-time APC.

The image forming apparatus according to the present embodiment can perform not only real-time APC during image formation but also APC between pages and lines during non-image formation. Therefore, more accurate laser light quantity correction can be realized.

(Embodiment 4) An image forming apparatus according to the present embodiment will be described with reference to FIG. The image forming apparatus according to the present embodiment uses a double beam laser and a single monitor photodiode as in the third embodiment to measure real-time APC during image formation, to measure the threshold current of the laser during non-image formation, and to set the page interval. APC or APC between lines is performed.

However, the configuration of the image forming apparatus according to this embodiment is different from the configuration of the image forming apparatus described above in that the light output of the laser 1 determined by APC when only one of the lasers emits light is used. The required current value I ₁ and the current value I ₂ required for the light output of laser 2 and the light output of laser 1 determined by APC when both lasers are emitting The configuration is such that the current value I ₁ ′ and the current value I ₂ ′ required for the optical output of the laser 2 can be stored separately.

In the third embodiment, the current value of the current for driving each laser is a value measured by the previous APC. In the first to third embodiments, the current value for driving the laser is a value measured by the previous APC, and the APC is performed when only one of the lasers emits light or when both lasers emit light. I did not distinguish what was done when I was.

However, in the present embodiment, a distinction is made with respect to the number of lasers that emit light. Specifically, the drive currents I ₁ and I ₂ output when only one laser emits light use values determined by APC performed when only one laser emits light. The drive currents I ₁ ′ and I ₂ ′ when both lasers emit light use values determined by APC performed when both lasers emit light.

In this embodiment, when performing inter-page APC or inter-line APC performed during non-image formation, APC for simultaneously emitting both lasers described in the first embodiment is also performed. The APC for emitting both lasers is performed after the measurement of the threshold current value for each of the lasers 1 and 2 described in the third embodiment and the completion of the APC.

FIG. 10 shows the measurement of the threshold current value of the laser, the APC between pages and the A between lines in this embodiment.
It is a flowchart of the algorithm of PC. Hereinafter, FIG. 10 will be described. First, it is determined whether it is between pages or between lines (S81). If it is between pages or between lines, step S82
In this case, the measurement of the threshold current values of the lasers 1 and 2 and the APC are sequentially performed (S82 to S85).

The above measuring method is the same as the method of measuring the threshold current value of the laser and the APC between pages or the APC between lines described in the third embodiment. The current values I ₁ and I ₂ are driving currents when one corresponding laser emits only one of them.

Next, drive currents I ₁ ′ and I ₂ ′ when both lasers emit light at the same time are measured. First, the current values I ₁ , I ₂ determined for the lasers 1 and 2 by APC
Is energized (S86). At this time, since the currents were adjusted in S83 and S85, the amounts of light when the lasers 1 and 2 each emitted light independently were the same.

In the APC in which the lasers 1 and 2 emit light independently, the non-emission point is energized at a threshold current value or less. Therefore, each of the lasers 1 and 2 at this time is in a state close to the case where both lasers 1 and 2 emit light thermally. Therefore, even if both lasers 1 and 2 are made to emit light, the light quantity of each of the lasers 1 and 2 is almost the same as when each is generated independently.

Further, in APC, the value of the current supplied to the lasers 1 and 2 is uniformly increased or decreased. Therefore, even after APC, the output light amounts of the lasers 1 and 2 are substantially equal. Therefore, when both lasers are emitting light simultaneously at the time of image formation, the difference in the amount of light between the two lasers is small. Therefore, the print density is not affected.

The flow shifts from step S86 to step S87 to correct the light quantity of the combined lasers 1 and 2 in the same manner as in the case where the lasers 1 and 2 emit light simultaneously as described in the first embodiment (S87). To S91). Then, the correction results are stored as drive currents I ₁ ′ and I ₂ ′ when the lasers 1 and 2 emit light simultaneously (S92). However,
Since the above-described APC is performed during non-image formation, the step of monitoring whether or not the image is being formed and the step of monitoring whether or not the light emission state of the laser has been changed as described in the real-time APC of the first embodiment are unnecessary. Not provided.

By the above procedure, the threshold current values of the lasers ₁ and ₂ and the drive currents I ₁ and I _{2 for} emitting only one of the lasers and the drive currents I ₁ ′ and I ₁ ′ for emitting both of the lasers simultaneously are obtained. When I ₂ ′ is determined, the power supply to the lasers 1 and 2 is turned off (S93), and the measurement of the threshold current value and the APC are completed (S94).

As described above, the updated lasers 1, 2
, The image formation for one main scan is completed,
The data is retained and used until the next non-image formation is updated. Further, the current values I ₁ , I ₂ , I ₁ ′, I ₂ ′ determined according to the present embodiment start to be used when only one laser or both lasers are driven at the beginning of image formation, Retained until updated by APC.

In this embodiment, the drive currents I ₁ and I ₂ when only one laser emits light use values updated by APC performed when only one laser emits light. On the other hand, the drive current I when both lasers emit light
₁ ', I _2' is for use values updated in APC went when both laser is emitting light, respectively, can be a higher degree of light amount correction.

In this embodiment, an image forming apparatus using a double beam laser has been described. However, the present invention can be applied to an image forming apparatus having three or more lasers.

[0119]

As described above, the image forming apparatus of the present invention corrects the amount of current for driving each light emitting point during main scanning in real time. Therefore, it is possible to always obtain a necessary light amount in each main scanning line. That is,
Fluctuations in light output can be prevented. Therefore, the print density of the image can be made constant.

Further, the image forming apparatus of the present invention measures a threshold current value at a non-light emitting point during non-image formation. Then, energization at a value equal to or less than the threshold current value is performed at the non-light emitting point. Therefore, it is possible to make the non-light emitting point generate heat. Therefore, the fluctuation of the output light amount caused by the thermal coupling between the light emitting points is reduced. That is, highly accurate laser light quantity correction can be realized.

Further, by performing light amount correction even during non-image formation, the accuracy of light amount correction can be further improved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an algorithm of a real-time APC according to the present invention.

FIG. 2 is a flowchart showing a real-time APC algorithm according to the present invention.

FIG. 3 is a diagram illustrating a main part of the laser beam printer.

FIG. 4 is a diagram showing a process until an electrostatic latent image is formed in an image forming apparatus using a double beam laser.

FIG. 5 is a perspective view of a double beam laser light source.

FIG. 6 shows A of the double beam laser according to the first embodiment.
It is a block circuit diagram of a PC circuit.

FIG. 7 is a flowchart showing an algorithm for measuring a threshold current of a laser according to the present invention.

FIG. 8 shows A of the double beam laser according to the second embodiment.
It is a block circuit diagram of a PC circuit.

FIG. 9 is a flowchart illustrating an algorithm of inter-page APC and inter-line APC based on the third embodiment.

FIG. 10 is a flowchart illustrating an algorithm of inter-page APC and inter-line APC based on Embodiment 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic photosensitive drum 2 Charging roller 3 Laser exposure device 4 Developing device 5 Cleaning blade 6 Transfer roller 7 Fixing device 8 Double beam laser light source 9 Collimator lens 10 Cylindrical lens 11 Polygon mirror 12 Scanning lens 15 Laser chip 16 Photodiode 19 Current supply terminal 21 CPU

Claims (7)

[Claims] 1. An image forming apparatus comprising: a laser having a plurality of light emitting points; one optical sensor for monitoring a laser output light amount output from the laser; and a drive current control unit for driving the laser. Means for performing real-time APC (automatic light output control) of a light-emitting point (hereinafter simply referred to as a light-emitting point) of the plurality of light-emitting points; means for calculating a threshold current value between pages or lines; Means for driving a light-emitting point that does not emit light (hereinafter, referred to as a non-light-emitting point) among the plurality of light-emitting points with a current equal to or less than the threshold current. 2. The image forming apparatus according to claim 1, wherein the detecting unit detects whether the light emitting point is a single light emission or a plurality of light emissions, and the real time is based on a detection result obtained by the detecting means. An image forming apparatus comprising: a switching unit that switches a reference voltage used for APC. 3. The image forming apparatus according to claim 2, wherein
An image forming apparatus, wherein the real-time APC is performed between the pages or between the lines. 4. The image forming apparatus according to claim 3, wherein the real-time APC is performed when each of the light-emitting points emits light alone between the pages or between the lines. 5. The image forming apparatus according to claim 4, wherein a plurality of drive currents obtained by the real-time APC when the light emitting points emit light alone between the pages or the lines are used. The image forming apparatus performs the real-time APC when the light emitting points emit light simultaneously. 6. A laser having a plurality of light emitting points, one optical sensor for monitoring an output light amount output from the laser, and a plurality of reference voltages for comparing output voltages output from the optical sensor. Selecting means for selecting one of the plurality of reference voltages according to the number of light emitting points to emit light; comparing means for comparing the output voltage with the selected reference voltage; An image forming apparatus, comprising: a light output control unit including: a current driving unit that determines a current value for driving the laser based on difference data output from the control unit. 7. The image forming apparatus according to claim 6, further comprising: an amplifying unit that amplifies the difference data output from the comparing unit; and a holding unit that holds the amplified data output from the amplifying unit. An image forming apparatus comprising: