JP2001308449A - Light source device and picture forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a laser light source capable of performing oscillation even with more than driving currents for outputting the maximum light quantity from being used beyond a light output range suitable for controlling the light quantity. SOLUTION: Lights outputted from a laser light source 12 are received by a light detecting part 14, and converted into a monitor voltage by an amplifier 16, and stored in an arithmetic judging part 20. Then, a difference between the newly stored monitor voltage and the previously stored monitor voltage is calculated by an arithmetic judging part 20, and the counter value of an up/down counter 22 is turned up until a difference between the differential voltage and a second reference voltage Vref is turned into almost 0 by a second comparing part 24 so that the driving currents can be increased. When the difference between the differential voltage and the second reference voltage Vref is turned into almost 0, the counter value of the up/down counter 22 at that time is stored as a counter upper limit value in an upper limit value storing part 34. Afterwards, the light quantity is controlled by using a first reference voltage Vref 1. When the counter value of the up/down counter 22 is turned to be more than the counter upper limit value, an abnormality detection signal is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source device and an image forming apparatus, and more particularly to a light source device provided with a laser light source capable of oscillating even when a driving current for outputting a maximum light amount is exceeded, and an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, an edge emitting laser has been used as a light source for a printer, an optical disk or the like. FIG. 7 shows the current-light output characteristics of this edge emitting laser.

As shown in FIG. 7, an edge emitting laser emits a current exceeding an oscillation threshold (hereinafter referred to as a “driving current”).
Is injected, the linearity is obtained in the current-light output characteristic, so that the light amount control is easy. However, when the driving current is increased, the transverse mode becomes unstable, and the current-light output characteristic is increased. Nonlinearity appears in When the drive current is further increased, the oscillation stops due to optical damage to the laser end face, and the oscillation becomes impossible even when the laser current returns to the low current region again. Normally, the light output used as a light source for a printer or the like is sufficiently smaller than a region where the light amount becomes unstable, and generally linearity is maintained.

In general, when such an edge emitting laser is used as a light source, the light amount is controlled by a control circuit shown in FIG. That is, the light beam output from the laser light source 100 is received by the light detection unit 102, and the light detection unit 102 outputs a photocurrent corresponding to the amount of the received light.
This photocurrent is amplified by the amplifier 104, converted into a voltage, input as a monitor voltage to the comparator 106, and compared with the reference voltage Vref. The comparison unit 106
Based on the comparison result, an up / down counter 108 for increasing or decreasing the output light amount of the laser light source 100 is controlled, and a laser drive circuit 112 is controlled via a D / A converter 110.
To give feedback. Monitor voltage is the reference voltage Vre
By repeating the above sequence until it becomes equal to f,
A desired light quantity is obtained. In some cases, instead of the up / down counter 108, analog control may be performed using a sample and hold circuit.

[0005] In recent years, in order to meet the demand for higher speed and higher resolution for a printer, and because it has become possible to produce an element having a plurality of light emitting points at low cost, Japanese Patent Application Laid-Open No. 5-294005 discloses this. As described above, it has been proposed to use a surface emitting laser as a light source for a printer. FIG. 9 shows general current-light output characteristics of this surface emitting laser.

The surface emitting laser is described in, for example, “Technical report of IEICE LQE98-14, IEICE Technical Report of IEICE LQE98-14.
1, P19-24 ”has the advantage that the lasing threshold current is lower than that of the edge emitting laser. However, as shown in FIG. 9, the output linear region is small. (The output light amount is at most about several mW at the maximum). Further, even if the drive current is increased beyond the maximum light amount, the output light amount changes to a decreasing tendency without destruction of the element, and oscillation is possible even when the current is returned to a lower current region than the current at the maximum light amount output. On the other hand, when the drive current is increased, the transverse mode may become unstable.

Therefore, in order to use such a surface emitting laser as a light source for a printer or the like, a light amount near the maximum light amount is required. Therefore, light amount control in a nonlinear region of current-light output characteristics is required.

[0008]

However, if the light amount control is performed in both the region where the output light amount increases and the region where the output light amount decreases with an increase in the driving current, the control becomes complicated, and the multi-mode oscillation becomes difficult. Could be. For example, when the monitor voltage at the time of maximum light output becomes lower than the reference voltage due to environmental temperature fluctuation, element deterioration, or the like, the drive current continues to increase in the conventional light control.

For this reason, the light amount is adjusted periodically (for example, before writing an image, between lines or between pages, etc.) so that the control does not exceed the maximum light amount, and the upper limit value of the drive current is reduced. It had to be stored in a memory or the like.

In addition, the surface emitting laser has a variation in current-light output characteristics due to a structural variation in a current confinement portion or the like for each light emitting point. For example, in a surface emitting laser, generally, as shown in FIG. 9, a light emitting point having a low maximum light amount tends to have a small driving current, but depending on the structure of the element, a maximum light amount The driving current may be smaller at a light emitting point with a higher. For this reason, it is necessary to obtain and store the current upper limit value for each light emitting point, and there is a problem that control time and cost increase and efficiency is poor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a laser light source capable of oscillating even when a driving current for outputting a maximum light amount is exceeded is used outside a light output range suitable for light amount control. It is an object of the present invention to provide a light source device and an image forming apparatus for preventing such a problem.

[0012]

According to a first aspect of the present invention, there is provided a light source device having a laser light source capable of oscillating even when a driving current for outputting a maximum light amount is exceeded. It is characterized by having lighting control means for lighting the laser light source at a drive current that outputs a maximum light amount or less.

According to the first aspect of the invention, when the laser light source capable of oscillating even when exceeding the drive current for outputting the maximum light amount is turned on by the lighting control means, the drive current for outputting the maximum light amount is provided. Hereinafter, the drive current value is limited. Accordingly, it is possible to prevent the use of the laser light source in a region where the output light amount decreases with an increase in the drive current, and it is possible to stably perform the light amount control.

According to a second aspect of the present invention, there is provided a detecting means for detecting an output light amount of the light source, and a detecting means for detecting the output light amount of the laser light source until the output light amount substantially equal to the maximum light amount is detected. A drive current control unit that increases a drive current; and a storage unit that stores a drive current value when an output light amount substantially equal to the maximum light amount is detected by the detection unit. However, the light output of the laser light source may be controlled with the drive current value stored in the storage means as an upper limit.

In this case, as described in claim 3, the drive current control means increases the drive current stepwise until the amount of increase in the amount of light detected by the detection means becomes smaller than a predetermined value. It is good to make it. Or,
Preferably, the drive current control means continuously increases the drive current until the amount of increase in the amount of light detected by the detection means becomes smaller than a predetermined value.

Also, as described in claim 5,
The storage means may store a drive current value when the amount of increase in the amount of light detected by the detection means becomes smaller than the predetermined value.

According to a sixth aspect of the present invention, when the laser light source has a plurality of light emitting points, the lighting control means outputs a drive current value for outputting the maximum light amount among the plurality of light emitting points. It is preferable to control the lighting of each light emitting point at a light emitting point at which the light amount is minimum or at a drive current for outputting the maximum light amount. For example, as described in claim 7, the laser light source may be a surface emitting laser.

According to an eighth aspect of the present invention, there is provided the light source device according to any one of the first to seventh aspects, wherein an image is formed on a photosensitive member by a light beam output from the light source device. It is characterized by doing.

According to the present invention, as a light source device for forming an image on a photosensitive member, the use of a laser light source in a region where the output light amount decreases with an increase in drive current is prevented. A light source device that can be used is used. That is, since the laser light source is used only within the light output range in which the light amount control can be performed stably, a desired output light amount can always be obtained from the light source device. Machine stop and the like can be prevented.

[0020]

Next, an example of an embodiment according to the present invention will be described in detail with reference to the drawings. <First Embodiment> FIG. 1 shows a control circuit configuration of a light source device to which the present invention is applied.

As shown in FIG. 1, the light source device 10 is provided with a laser light source 12 and a light detecting section 14 as detecting means of the present invention. The light detection unit 14 may be provided inside the package of the laser light source 12 or may be provided outside.

The light detector 14 receives the light beam output from the laser light source 12 and outputs a photocurrent according to the amount of light received. The photocurrent is amplified by the amplifier 16 and converted into a voltage, and is input to the first comparing unit 18 and the operation determining unit 20 as a monitor voltage.

The first comparing section 18 compares the input monitor voltage with the first reference voltage Vref1, and increases or decreases the counter value of the up / down counter 22 based on the comparison result. Note that the first reference voltage V
ref1 is set in advance by a control unit (not shown).

The operation determining unit 20 is a memory (not shown) for storing the input monitor voltage and a voltage value (hereinafter, referred to as “oscillation voltage”) for checking whether or not the laser is oscillating. It has. The operation determination unit 20 compares the input monitor voltage with an oscillation voltage stored in advance to determine whether the laser light source 12 is oscillating. Further, the input monitor voltage is compared with the previously input monitor voltage, and the difference (hereinafter, referred to as “difference voltage”) is output to the second comparing unit 24.

The second comparator 24 compares the input difference voltage with the second reference voltage Vref2, and increases or decreases the counter value of the up / down counter 22 based on the comparison result. This second reference voltage Vref
Reference numeral 2 is for comparing a difference between a monitor voltage when the value of an up / down counter 22 described later is n and a monitor voltage when the value is n + 1, and is set in advance by a control unit (not shown). Note that the drive current control means of the present invention includes an operation determination unit 20 and a second comparison unit 24.

The up / down counter 22 synchronizes with the pulse signal generated by the clock pulse generator 26,
The counter value incremented or decremented by the first comparing unit 18 or the second comparing unit 24 is output to the D / A converter 28 and the upper limit value monitoring unit 30.

The D / A converter 28 D / A converts the counter value from the up / down counter 22 and outputs it to the laser drive circuit 32. The laser drive circuit 32 supplies a drive current corresponding to the counter value to the laser light source 12. That is, in the light source device 10, by increasing or decreasing the counter value of the up / down counter 22, the drive current value of the laser light source 12 is changed, so that the output light amount can be controlled.

The upper limit monitor 30 includes an upper limit storage 34 as storage means of the present invention and an upper limit excess detector 36 as lighting control means of the present invention. The upper limit value storage unit 34 stores the up / down counter 22 during the light amount control.
Is stored (hereinafter referred to as “counter upper limit value”).

In the upper limit monitor 30, the first comparator 1
8, when the counter value of the up / down counter 22 is up or down,
According to 6, it is determined whether or not the counter value of the up / down counter 22 has exceeded the counter upper limit value stored in the upper limit value storage unit 34. Up / down counter 22
If the counter value exceeds the counter upper limit value, an abnormality detection signal is output to a control device (not shown).

On the other hand, when the counter value of the up / down counter 22 is up or down by the second comparing section 24, the upper limit value monitor section 30 outputs the upper limit value based on the counter value of the up / down counter 22. The counter upper limit value stored in the storage unit 34 is updated.

As described above, the light source device 10 according to the first embodiment is different from the control circuit for controlling the light amount used in the conventional light source device in the first comparison section 18 for controlling the light amount. Apart from (corresponding to the comparing unit 106 in FIG. 8), a function is provided for comparing the amount of increase in the amount of light (monitor voltage) when the current is increased with the second reference voltage Vref2.

Next, the operation of the first embodiment will be described.

In the light source device 10, after setting the upper limit value of the drive current by the drive current upper limit value setting process, the light amount control is performed. In the drive current upper limit value setting process, first, a signal indicating the second reference voltage Vref2 from the control unit (not shown) is input to the second comparison unit 24, and the value of the second reference voltage Vref2 is set. .

Next, injection of a drive current into the laser light source 12 is started by the laser drive circuit 32 in accordance with a lighting data signal from a control device (not shown).
Lights up. As in the conventional light quantity control, the output light quantity is increased by increasing the voltage value from a preset voltage value.

The light beam output from the laser light source 12 is received by the light detection unit 14, and a photocurrent corresponding to the amount of received light is output. The photocurrent is amplified by the amplifier 16 and converted into a monitor voltage by voltage conversion, and then stored in the operation determination unit 20.

The operation determination section 20 compares the monitor voltage with the oscillation voltage to determine whether the laser light source 12 is oscillating. When the monitor voltage is equal to or lower than the oscillation voltage, the counter value of the up / down counter 22 is increased via the second comparison unit 24, and the drive current of the laser light source 12 is increased. By repeating the above until the monitor voltage exceeds the oscillation voltage, the upper limit value of the drive current is prevented from being set to be equal to or less than the threshold current at which the laser light source 12 starts oscillating.

When the monitor voltage exceeds the oscillating voltage, the monitor voltage at this time is stored in the operation determining section 20. Further, the count value of the up / down counter 22 is increased by one, and the drive current of the laser light source 12 is increased. The monitor voltage after the increase of the drive current is also stored in the operation determination unit 20, and the operation determination unit 20 obtains a difference between the newly stored monitor voltage and the previously stored monitor voltage, and calculates the difference voltage. The data is input to the second comparison unit 24.

The second comparing section 24 compares the input difference voltage with the second reference voltage Vref2, and compares the difference voltage with the second reference voltage Vref2.
Until the difference from the reference voltage Vref2 becomes substantially 0, the counter value of the up / down counter 22 is increased, and the drive current is increased. When the difference from the second reference voltage Vref2 becomes substantially 0, the counter value of the up / down counter 22 at this time is stored in the upper limit value storage unit 34. Thereby, the upper limit of the drive current for turning on the laser light source 12 is set.

Next, the count value of the up / down counter 22 is reset to return the drive current value to the initial value. After that, light amount control is performed in the same manner as in the related art, and the first reference voltage Vref1 stored in the first comparing unit 18 in advance is used.
Obtain the desired amount of light.

At this time, in the upper limit monitor 30, the upper limit excess detector 36 monitors the counter value of the up / down counter 22 during light quantity control. When the counter value of the up / down counter 22 exceeds the counter upper limit value stored in the upper limit value storage unit 34, an abnormality detection signal is output to notify a controller (not shown) of an abnormality of the laser light source 12. In response to the abnormality detection signal, the control device (not shown) stops the driving of the light source device 10 or notifies the user to replace the laser light source 12, for example. The use of the laser light source 12 is prevented.

As described above, in the first embodiment, it is possible to easily set the upper limit value of the drive current suitable for the light amount control for the laser light source 12. After setting the upper limit,
The drive current for turning on the laser light source 12 can be limited to the set upper limit or less.

For example, if the value of the second reference voltage Vref2 is set to “0”, the upper limit of the drive current when the laser light source 12 is turned on is set to the drive current when the peak light amount is output. Therefore, it is possible to prevent the laser light source 12 from being used in a region in which the output light amount decreases as the drive current increases, exceeding the peak light amount. To prevent use near the peak light amount, the value of the second reference voltage Vref2 may be set to a value other than “0” (a value slightly larger than 0).

Thus, when the voltage at the time of maximum light output becomes lower than the reference voltage due to environmental temperature fluctuation, deterioration of the element, or the like, it is possible to prevent the drive current from being continuously increased and to stabilize the light control. A desired light output (output light amount) can be obtained.

When a laser light source 12 having a curvilinear current-light output characteristic such as a surface emitting laser is used, a plurality of first reference voltages Vref1 for controlling the amount of light and a plurality of first comparing sections 18 are provided. It is desirable.

Further, instead of the up / down counter 22, a sample-and-hold circuit may be used to perform analog control.

<Second Embodiment> Next, as a second embodiment, a light source device using a sample and hold circuit will be described.

FIG. 2 shows a control circuit configuration of the light source device 10 according to the second embodiment. In FIG. 2, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 2, the light source device 10 includes a differentiating circuit 40 and a sampler 40 in place of the operation determining unit 20 and the up / down counter 22 (see FIG. 1) in the first embodiment. A hold circuit 42 is provided.

In the differentiating circuit 40, the amount of change (increased voltage value) of the monitor voltage is obtained and output to the second comparing section 24.

The sample-and-hold circuit 42 compares the result of the comparison between the monitor voltage by the first comparing section 18 and the first reference voltage Vref1, or the difference between the increased voltage value and the second reference voltage Vref2 by the second comparing section 24. The output voltage is increased or decreased based on the comparison result. The voltage output from the sample and hold circuit 42 is input to the laser drive circuit 32 via the upper limit monitor 30. The laser drive circuit 32 changes the drive current of the laser light source 12 in accordance with the output voltage of the sample and hold circuit 42.

The upper limit value storage section 34 of the upper limit value monitor section 30 stores the upper limit value of the output voltage of the sample hold circuit 42. In the upper limit value monitor section 30, the output voltage of the sample and hold circuit 42 is monitored by the upper limit value excess detection section 36, and is input to the laser drive circuit 32. The upper limit value excess detection unit 36 updates the upper limit value of the output voltage stored in the upper limit value storage unit 34 and outputs an abnormality detection signal based on the monitoring result.

Next, the operation of the second embodiment will be described.

First, similarly to the first embodiment, a signal indicating the second reference voltage Vref2 is supplied to a control device (not shown).
To the second comparison unit 24, and the second reference voltage Vr
The value of ef2 is set.

Next, according to a lighting data signal from a control device (not shown), injection of a drive current into the laser light source 12 by the laser drive circuit 32 is started.
Lights up. At this time, the injected current is 0 m
The output light amount is increased by increasing the bias current value from A or the bias current value.

The light beam output from the laser light source 12 is received by the light detection unit 14, and a photocurrent corresponding to the amount of received light is output. This photocurrent is amplified by the amplifier 16 and converted into a monitor voltage by voltage conversion, and then an increased voltage value is obtained by the differentiating circuit 40.
The second comparator 24 compares the increased voltage value with the second reference voltage value Vref2, and increases the output voltage of the sample and hold circuit 42 according to the comparison result. In the laser drive circuit 32, the sample hold circuit 4
The driving current is changed according to the output voltage of the second driving voltage.

In the second comparing section 24, when the difference between the increased voltage value and the second reference voltage Vref2 becomes substantially 0, the second comparing section 24 supplies the laser driving circuit 32 corresponding to the upper limit value of the driving current to be injected into the laser light source 12 to the laser driving circuit 32. The output value of the sample and hold circuit 42 at this time is stored in the upper limit value storage unit 34 as the applied voltage upper limit value.

When performing light quantity control, the sample and hold circuit 42 is reset, and the drive current value is returned to the initial value. Thereafter, light amount control is performed in the same manner as in the related art, and a desired light amount is obtained using the first reference voltage Vref1 stored in the first comparing unit 18 in advance.

At this time, in the upper limit value monitor section 30, the output voltage of the sample and hold circuit 42 during light quantity control is monitored by the upper limit value excess detection section 36, and the output voltage is stored in the upper limit value storage section 34. If you exceed the upper limit,
An abnormality detection signal is output to notify a controller (not shown) of an abnormality of the laser light source.

As described above, the same effect as that of the first embodiment can be obtained even if analog control is performed using the sample and hold circuit 42 instead of the up / down counter 22.

The first and second embodiments have been described on the assumption that the laser light source 12 is an element having one light emitting point. May also be applied.

<Third Embodiment> Next, as a third embodiment, a light source device when a surface emitting laser having a plurality of light emitting points is used as a light source for a printer or the like will be described.

FIG. 3 shows a control circuit configuration of the light source device 10 according to the third embodiment. In FIG. 3, the same members as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 3, the light source device 10 includes a laser light source 12 having n (n: an integer of 2 or more) light emitting points 12A. A laser drive circuit 32 is provided for each. That is, twelve laser drive circuits 32 are provided,
Each light emitting point 12A is turned on by the corresponding laser drive circuit 32.

In addition to the light source device of the first embodiment, an upper limit comparing section 50 is added to the upper limit monitoring section 30, and a peak light quantity storage section 52 and a peak light quantity comparing section 54 are added.
Is additionally provided.

In the light source device 10, the same drive current upper limit value setting processing as that of the first embodiment is performed on each light emitting point 12A of the laser light source 12, and the second comparing section is performed for each light emitting point 12A. 24 and the second reference voltage Vref2
Up / down counter 22 when the difference from
Are sequentially obtained. In the upper limit comparison unit 50,
Each time the counter value of each light emitting point 12A is acquired, the count upper limit value stored in the upper limit value storage unit 34 is compared, and the count upper limit value of the upper limit value storage unit 34 is updated based on the comparison result. I do.

The output voltage value of the amplifier 16 when the difference between the difference voltage by the second comparing section 24 and the second reference voltage Vref2 becomes substantially zero, that is, the peak light quantity is output to the peak light quantity storage section 52. Monitor voltage when
"Peak monitor voltage" is stored. Each time the peak monitor voltage of each light emitting point 12A is obtained, the peak light comparator 54 compares the peak monitor voltage with the peak monitor voltage stored in the peak light storage unit 52, and based on the comparison result, determines the peak light monitor. The monitor voltage stored in the storage unit 52 is updated.

As described above, the light source device 10 according to the third embodiment has the function of setting the upper limit value of the driving current (for one light emitting point) in the first embodiment,
The configuration is such that a function of comparing the upper limit value of the drive current of 2 A and the peak light amount is added.

Next, the operation of the third embodiment will be described.

First, the principle of determining the upper limit of the drive current when using the laser light source 12 having a plurality of light emitting points 12A will be described. In the following, the laser light source 12 having two light emitting points 12A is used as an example, and one light emitting point 12A is used.
A description will be given assuming that the peak light amount of A (peak monitor voltage) is P1, the driving current at that time (that is, the upper limit of the driving current) is I1, the peak light amount of the other light emitting point 12A is P2, and the driving current at that time is I2. I do.

FIGS. 4 and 5 show the current-light output characteristics of these two light emitting points 12A. As shown in FIG.
When the relations of P1> P2 and I1> I2 are satisfied, the light emitting point 12A having the lower peak light amount (see FIG. 4) obtains the peak light amount at the light emitting point 12A having the higher peak light amount. Of the reference voltage (first
(Corresponding to the reference voltage Vref1) or more.

Therefore, the driving currents obtained for each light emitting point 12A are compared, and the minimum value may be set as the upper limit of the driving current for all the light emitting points 12A. In general, in a surface emitting laser, the relationship is P1> P2 and I1> I2.

On the other hand, as shown in FIG. 5, P1> P2, I
When the relationship of 1 <I2 holds, both light emitting points 12A
If the upper limit of the driving current for the light emitting point 12A (see FIG. 5) having the higher peak light quantity is set to the driving current I1 for obtaining the peak light quantity, the light emitting point 12A having the lower peak light quantity (see FIG. 5). ), It is not possible to obtain an output light quantity higher than the reference voltage (corresponding to the first reference voltage Vref1). Therefore, in this case, although the output light amount of the light emitting point 12A may decrease, the drive current I2 is set to the upper limit value of the drive current for both light emitting points 12A.

Next, the operation of the light source device 10 based on the above principle will be described.

In the light source device 10, first, as in the first embodiment, a signal indicating the second reference voltage Vref2 is input from the control device (not shown) to the second comparing section 24,
The value of the second reference voltage Vref2 is set.

Next, in accordance with the lighting data signal from the control device (not shown), the laser drive circuit 32 starts injecting a drive current to the first light emitting point 12A of the laser light source 12, and The drive current upper limit value setting process is performed on the light emitting point 12A in the same manner as in the first embodiment.

Thus, the counter value of the up / down counter 22 when the difference between the voltage difference by the second comparing section 24 and the second reference voltage Vref2 becomes substantially 0 (when the peak light quantity is obtained) is obtained. The upper limit value is stored in the upper limit value storage unit 34 as the counter upper limit value. Further, the output voltage value of the amplifier 16 at this time, that is, the monitor voltage is stored in the peak light amount storage unit 52 as the peak monitor voltage.

Next, the counter value of the up / down counter 22 is reset to return the drive current to the initial value. After the injection of the drive current to the first light emitting point 12A is stopped (light emission stop), the injection of the drive current to the second light emitting point 12A is started, and the second light emitting point 12A is started.
, A drive current upper limit value setting process is similarly performed.

When the difference between the difference voltage by the second comparing section 24 and the second reference voltage Vref2 becomes substantially zero, the upper limit value comparing section 50 causes the up / down counter 2 at this time.
The counter value of 2, that is, the counter upper limit value of the second light emitting point 12A is compared with the counter upper limit value stored in the upper limit value storage unit 34. If the counter upper limit value of the second light emitting point 12A is smaller than the counter upper limit value stored in the upper limit value storage unit 34, the content stored in the upper limit value storage unit 34 is changed to the counter value of the second light emitting point 12A. Update to the upper limit.

At this time, the peak light quantity comparing section 54 sets the difference voltage between the second comparing section 24 and the second reference voltage V
A comparison is also made between the monitor voltage when the difference from ref2 is substantially zero, that is, the peak monitor voltage of the second light emitting point 12A and the peak monitor voltage stored in the peak light amount storage unit 52. .

If the peak monitor voltage of the second light emitting point 12A is smaller than the peak monitor voltage stored in the peak light amount storage unit 52, the storage contents of the peak light amount storage unit 52 are changed to the second monitor amount. The monitor voltage value at the peak of the light emitting point 12A is updated. At the same time, the content stored in the upper limit value storage unit 34 is updated to the counter value of the up / down counter 22 at this time, that is, the counter upper limit value of the second light emitting point 12A.

For each of the third and subsequent light emitting points 12A,
The drive current upper limit value setting process is performed in the same manner as the second light emitting point 12A, and when the difference between the difference voltage by the second comparison unit 24 and the second reference voltage Vref2 becomes substantially zero, the up-down operation is performed. Based on the counter value of the counter 22 and the monitor voltage, the contents stored in the upper limit value storage unit 34 and the peak light amount storage unit 52 are updated. When it is completed up to the n-th light emitting point 12A,
The count value of the up / down counter 22 is reset, and the drive current value is returned to the initial value.

As a result, the light-emitting point 12A having a lower monitor voltage when the difference between the difference voltage by the second comparing section 24 and the second reference voltage Vref2 becomes substantially zero, the light-emitting point 12A of the up-down counter 22 at that time. When the counter value (counter upper limit value) is small, the minimum value of the counter upper limit value of each light emitting point 12A is stored in the upper limit value storage unit 34.

Further, although the monitor voltage is low when the difference between the difference voltage by the second comparing section 24 and the second reference voltage Vref2 becomes substantially zero, the counter of the up / down counter 22 at that time is low. When there is a light emitting point 12A having a large value, the upper limit value of the counter of the light emitting point 12A is stored in the upper limit value storage unit 34.

For example, in the case of the example shown in FIG.
The counter value of the up / down counter 22 corresponding to the drive current I2 is stored in the upper limit storage 34. Also, in the case of the example shown in FIG. 5, the counter value of the up / down counter 22 corresponding to the drive current I2 is stored in the upper limit value storage unit 3.
4 is stored.

After that, the light amount is controlled for each light emitting point 12A in the same manner as in the related art, and a desired light amount is obtained using the first reference voltage Vref1 stored in the first comparing section 18 in advance.

At this time, the counter upper limit value stored in the upper limit value storage unit 34 is used as a common counter upper limit value for all the light emitting points 12A. That is, each light emitting point 1
When 2A is emitted, the drive current is limited so as not to exceed the counter upper limit value. If the counter current exceeds the counter upper limit value, the upper limit value excess detection unit 36 outputs an abnormality detection signal, and the control device (not shown). ) Informs the laser light source 12 of the abnormality.

For example, in the case of the example shown in FIG.
Since the counter value of the up / down counter 22 corresponding to the drive current I2 is stored in the upper limit storage 34, the drive current I2 is set as the upper limit of the drive current for both light emitting points 12A. In this case, even when the light emitting point 12A having the higher peak light amount (see FIG. 4) and the driving current I2 when the light emitting point 12A having the lower peak light amount (see FIG. 4) obtains the peak light amount, the reference voltage ( First reference voltage Vref
1) The above output light quantity can be obtained. That is, a desired light amount can be obtained by the light amount control.

On the other hand, also in the example shown in FIG.
Is the upper limit of the drive current for both light emitting points 12A, so that even at the light emitting point 12A with the lower peak light amount (see FIG. 5), the output light amount of the reference voltage (first reference voltage Vref1) can be reached. Therefore, a desired light amount can be obtained by light amount control.

As described above, even when the laser light source 12 having a plurality of light emitting points 12A is used, all the light emitting points 12A
In common, the upper limit of the drive current suitable for the light quantity control can be easily set. After the upper limit is set, the drive current for turning on each light emitting point 12A can be limited to the set upper limit or less. Thereby, the light amount control of each light emitting point 12A can be stably performed, and a desired output light amount can be obtained.

In the third embodiment, an example has been described in which control is performed with priority given to obtaining a predetermined amount of light at all light emitting points 12A, but the present invention is not limited to this. Absent. For example, in the case of using a surface emitting laser, if giving priority to preventing multi-mode oscillation by increasing the drive current beyond the peak light amount rather than obtaining a predetermined light amount, each light emitting point 12
The minimum value may be selected from the upper limit values of the drive currents calculated for A, and set as the upper limit values of the drive currents for all the light emitting points 12A.

Further, by using the light source device of the first to third embodiments as a light source for a printer, an optical disk, or the like, the laser light source 12 is controlled only within the light output range where the light amount can be stably controlled. Therefore, the operation of a printer, an optical disk, or the like can be always performed with a desired light amount, and the deterioration of image quality, a writing error, and a machine stop due to an inability to control the light amount can be prevented.

Further, in particular, the light source device 10 of the third embodiment can be used for a printer using a surface emitting laser. FIG. 6 shows an example of a printer using a surface emitting laser.

More specifically, the printer 6 shown in FIG.
0 denotes a light beam output from each light emitting point 64 of the surface emitting laser 62,
8, the light is incident on the rotary polygon mirror 70. In addition,
Of course, the surface emitting laser 62 is
, And the light emitting point 64 corresponds to the light emitting point 12A described above.

Each light beam incident on the rotating polygon mirror 70 is
The light is deflected in the main scanning direction by the rotation of the rotary polygon mirror 70. At this time, the light beams are shifted in the sub-scanning direction to be incident, so that the writing by the plurality of scanning lines 72 is performed on the photosensitive drum 74 at the same time.

Each light beam reflected by the reflecting surface 70A of the rotary polygon mirror 70 is irradiated on the photosensitive drum 74 via the toroidal lens 76 and the scanning lens 78. That is, since the printer 60 can scan a plurality of lines simultaneously, it is possible to write an image on the photosensitive drum 74 at a high speed.

The reflection mirror 80 reflects a light beam before scanning the image area in each line scan, and detects a main scanning start timing, that is, a so-called SOS sensor, and detects the amount of light emitted from the surface emitting laser 62. Light detector 1
The light is guided to the photodetector 82 which also has the role of 4. By using the photocurrent output from the photodetector 82 to perform the above-described drive current upper limit value setting processing and light amount control, an image can be written on the photosensitive drum 74 by a light beam of a desired light amount. .

The present invention can of course be applied to any image forming apparatus other than the printer shown in FIG. 6 that writes an image on a photosensitive member by a light beam.

The drive current upper limit value setting process does not need to be performed each time the light amount is controlled, and may be performed, for example, at the start of a job or between pages according to the number of light emitting points and the control time.

[0099]

As described above, the present invention is to prevent a laser light source capable of oscillating even when exceeding a driving current for outputting a maximum light amount from being used outside a light output range suitable for light amount control. It has an excellent effect that it can be produced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a control circuit configuration in a light source device according to a first embodiment.

FIG. 2 is a block diagram illustrating a control circuit configuration in a light source device according to a second embodiment.

FIG. 3 is a block diagram illustrating a control circuit configuration in a light source device according to a third embodiment.

FIG. 4 is a graph showing an example of current-light output characteristics of a light source having a plurality of laser light sources (light emitting points).

FIG. 5 is a graph showing another example of current-light output characteristics of a light source having a plurality of laser light sources (light emitting points).

FIG. 6 is a configuration diagram illustrating an example of a printer using a surface emitting laser as a light source.

FIG. 7 is a graph showing current-light output characteristics of a general edge emitting laser.

FIG. 8 is a block diagram showing a control circuit configuration in a conventional light source device.

FIG. 9 is a graph showing current-light output characteristics of a general surface emitting laser.

FIG. 10 is a graph showing an example of current-light output characteristics of a surface emitting laser in a case where elements have structural variations.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 light source device 12 laser light source 14 light detection unit 18 first comparison unit 20 operation determination unit 22 up / down counter 24 second comparison unit 30 upper limit value monitor unit 32 laser drive circuit 34 upper limit value storage unit 36 upper limit excess detection unit Reference Signs List 40 Differentiating circuit 42 Sample hold circuit 50 Upper limit comparing section 52 Peak light quantity storing section 54 Peak light quantity comparing section 56 Peak light quantity monitoring section 60 Printer 62 Surface emitting laser 64 Light emitting point 74 Photosensitive drum 82 Photodetector

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H01S 5/18 B41J 3/00 D 5/40 G03G 15/04 120 H04N 1/036 F term (reference) 2C362 AA03 AA12 AA16 AA53 AA54 AA55 AA61 AA72 AA74 DA09 2H045 AA01 BA02 BA22 CB42 DA41 2H076 AB02 AB06 DA04 DA17 5C051 AA02 CA07 DA01 DA02 DB30 DE30 FA01 5F073 AB05 AB16 AB21 AB25 AB27 AB29 BA07 GA02 GA12 GA18 GA33 GA37

Claims (8)

[Claims] 1. A light source device comprising a laser light source capable of oscillating even when exceeding a driving current for outputting a maximum light amount, comprising a lighting control means for lighting the laser light source at a driving current for outputting the maximum light amount or less. A light source device characterized by the above-mentioned. 2. A detecting means for detecting an output light quantity of the light source, and a driving current control means for increasing a driving current of the laser light source until the detecting means detects an output light quantity substantially equal to the maximum light quantity. Storage means for storing a drive current value when an output light amount substantially equal to the maximum light amount is detected by the detection means, wherein the lighting control means is stored in the storage means. 2. The light source device according to claim 1, wherein the light output of the laser light source is controlled with the driving current value as an upper limit. 3. 3. The drive current control unit according to claim 2, wherein the drive current control unit increases the drive current stepwise until the amount of increase in the amount of light detected by the detection unit becomes smaller than a predetermined value. Light source device. 4. The apparatus according to claim 2, wherein the drive current control means continuously increases the drive current until the amount of increase in the amount of light detected by the detection means becomes smaller than a predetermined value. Light source device. 5. The storage unit according to claim 3, wherein the storage unit stores a drive current value when the amount of increase in the amount of light detected by the detection unit becomes smaller than the predetermined value. Light source device. 6. When the laser light source has a plurality of light-emitting points, the lighting control means outputs a light-emitting point having a minimum drive current value for outputting the maximum light amount among the light-emitting points, or The light source according to any one of claims 1 to 5, wherein lighting of each light emitting point is controlled when a light emitting point having a minimum maximum light amount is equal to or less than a drive current for outputting the maximum light amount. apparatus. 7. The light source device according to claim 6, wherein the laser light source is a surface emitting laser. 8. An image comprising the light source device according to claim 1, wherein an image is formed on a photosensitive member by a light beam output from the light source device. Forming equipment.