JP2000183446A - Detector of degradation of semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To find out a degradation of a semiconductor laser in an earlier stage without being influenced by a change in a differential efficiency due to temperature and an irregular differential efficiency caused by a difference of a manufacturing lot of a semiconductor laser by providing a degradation judging means for judging the degradation of a semiconductor laser based on an initial differential efficiency and a differential efficiency at any time. SOLUTION: A CPU 14 calculates an initial differential efficiency at an environmental temperature stored in a RAM 18 based on an initial differential efficiency characteristic stored in a ROM 16. Then, the CPU 14 calculates a ration of a differential efficiency at any time to the initial differential efficiency to judge whether the ratio is at least a degradation reference value (for example, 0.75) or not. When the ratio is judged smaller than 0.75, the CPU 14 makes a display indicating that there is degradation. When the radio is 0.75 or above, and the accumulated printed number is judged less than a specified value, it is judged whether the ratio is 0.9 or above. When the ratio is 0.9 or above, the LD is judged normal, since a change of the ratio to the initial differential efficiency is less than 0.1, if the ratio is less than 0.9, the LD is judged degraded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting deterioration of a semiconductor laser, and more particularly to a device for detecting deterioration of a semiconductor laser used in an image forming apparatus such as a digital copying machine or a laser printer.

[0002]

2. Description of the Related Art Generally, an image forming apparatus such as a laser printer or an electrophotographic copying machine has a charging device 5 as shown in FIG.
An electrostatic latent image is formed by scanning a laser beam modulated on the basis of image data by the scanning device 50 on the photoreceptor 60 whose surface is uniformly charged by 2 and the obtained electrostatic latent image After the toner is supplied by a toner supply device 52 to form a visible image, the image is transferred onto a recording medium 48 such as a recording sheet in a transfer unit 54 and fixed by a fixing roller 55, so that an image is formed by a so-called electrophotographic method. .

The surface of the photoreceptor 60 after the transfer is cleaned by a cleaning unit 56 and is again charged.
As a result, the surface is uniformly charged, and the above-described processing is repeated.

As shown in FIG. 6, an optical scanning device 50 for scanning a laser beam on a photoreceptor has a laser diode 26 (hereinafter, referred to as an LD 26) as a semiconductor laser, a collimator lens 28, a polygon mirror 36, and fθ. It comprises a lens 40, a reflection mirror 42, and a cylinder mirror 44.

[0005] The LD 26 outputs a laser beam according to the blink timing modulated based on the image data. LD2
The laser beam from 6 enters the polygon mirror 36 via the collimator lens 28.

[0006] The polygon mirror 36 is used for the motor driving board 3.
The motor 8 is rotated at a constant angular speed by a drive motor (not shown) fixed on the motor 8. This rotation causes the polygon mirror 36
The reflection angle of the laser light incident on the photosensitive member is changed, and as a result, the main scanning of the laser light is performed along one direction on the photoconductor.

The fθ lens 40 sets the focal position of the laser beam, the irradiation position of which changes with the rotation of the polygon mirror 36, on the same plane, and collects the laser beam so as to main-scan the same plane at a constant speed. Light.

The laser light passing through the fθ lens 40 is reflected by a reflection mirror 42 and enters a cylinder mirror 44, and the optical path is deflected by the cylinder mirror 44 so as to be guided onto a photosensitive member (not shown). In recent years, L
D26, collimator lens 28, polygon mirror 36,
fθ lens 40, reflection mirror 42, cylinder mirror 44
ROS (Raster Output Scanner) has been proposed.

In general, in the optical scanning device having such a configuration, in order to obtain an image writing timing, a start-of-scan sensor 32 (hereinafter, referred to as an SOS sensor 48) including a light receiving element at a main scanning start position. Is provided.

In the optical path corresponding to the main scanning start position of the laser light, there is provided a reflection mirror 46 for adjusting an image writing timing, and the SOS sensor 48 receives the laser light reflected by the reflection mirror 46. It is arranged in the position to be. Therefore, the image writing timing is S
The falling edge of the detection signal of the OS sensor 48 is used as a start signal, and the clock is counted from the falling edge of the detection signal of the SOS sensor 48.

In such an optical scanning device, L
In order to maintain the light output value of the laser beam from D26 at a constant light output value, automatic output adjustment (APC; auto power control) is performed during one scan.

In the APC control, a monitor voltage obtained by converting a current of a photodiode (hereinafter, referred to as PD) which receives light from the LD 26 and outputs a current corresponding to the amount of received light, and a constant monitor voltage. The desired voltage reference value (Vref) corresponding to the light output value is sequentially compared, and the voltage reference value (Vref) is always compared.
This is control for adjusting the drive current of the LD 26 so that By this control, the light output value for image writing can be controlled to a required light output value. Such APC control is generally performed in a laser printer or a copying machine.

[0013]

Generally, as shown in FIG. 7, an LD used as a light source does not oscillate until a certain threshold current Ith regardless of the temperature environment. The light output value Po hardly increases because of the LED light emitting region (natural light emitting region).
When the threshold current Ith is exceeded, laser oscillation starts.
It has a characteristic (IL characteristic) that the optical output value Po of the laser light increases in proportion to the magnitude of the drive current given to D.

Therefore, the LD failure can be determined from the increase rate of the drive current determined during the APC control.
Generally, LD failures can be classified into three types (type 1 to type 3) as shown in FIG. In FIG. 8, the vertical axis represents the driving current If necessary to obtain a constant light output value, and the horizontal axis represents the LD lighting time h, and the driving current Ifb is 1.5 times the initial driving current Ifa. Is used as a failure criterion.

The type 1 fault is a type in which the current rapidly increases during a short lighting period and exceeds the drive current value of the fault determination reference, and is an initial fault caused by a manufacturing process. The main causes of this type 1 failure are defects in the formation of the light absorbing portion, such as flaws in the resonator mirror of the LD, dark portions (dark spots, etc.) inside the active layer of the LD, and defects during the production of the LD, such as electrode shorts.

The type 2 is a type that suddenly occurs during use of a machine, and the current suddenly increases to exceed a drive current value of a failure judgment criterion. Is applied, the resonator mirror is destroyed, or the light absorbing portion is multiplied by a minute defect existing at the time of manufacturing the resonator mirror of the LD.

Further, Type 3 belongs to a wear failure, and lattice defects are transferred to the inside of the active layer of the LD due to lattice mismatch. This is due to the formation of a dark portion, and in each case, the current injection-luminous efficiency gradually deteriorates.

Of these three types of LD faults, a type 1 LD fault can be removed by screening such as burn-in. In addition, the type 3 LD failure can be avoided by designing so that there is no problem with the required device life when used in a laser printer, a copying machine, or the like.

That is, type 1 LD failure and type 3
Can be avoided to some extent, but it is difficult to avoid a Type 2 LD failure that occurs suddenly during use of a machine because it cannot be predicted at all.
When the LD failure occurs, the operation of the machine stops, which causes a serious problem such as loss of image data.

Therefore, early detection of a type 2 LD failure is very important.
As described in Japanese Patent No. 1883181, a deterioration judgment method has been proposed by detecting a change in differential efficiency η, which is a ratio of a change in optical output of the LD to a change in drive current supplied to the LD.

In this deterioration judging method, the differential efficiency η becomes constant almost independent of the temperature change when the LD is normal.
This is a method utilizing the fact that the LD changes according to the degree of change with time, and the differential efficiency η before the LD changes with time is previously obtained as the initial differential efficiency η0 and stored in the recording unit.
When the device is started up or when it becomes necessary to check the deterioration state of the LD, the differential efficiency η calculated from the LD in the current state is compared with the initial differential efficiency η0 recorded in the recording unit. Then, when the calculated differential efficiency η falls outside the allowable range, it is a method of determining deterioration.

However, Japanese Patent Application Laid-Open No. 3-188181
According to the method disclosed in Japanese Patent Application Laid-Open No. H11-260, the differential efficiency η does not depend on the temperature change when the LD is in a normal state. However, the differential efficiency η of the LD actually increases with the temperature change as shown in FIG. And as the temperature increases, the differential efficiency η
Drops.

FIG. 9 shows the differential efficiency η for a plurality of LDs.
Is shown in the range of 15 ° C to 60 ° C. In FIG. 9, as an example, two LDs (LD # 1, LD #
2) shows the change of the differential efficiency η and the change of the differential efficiency η of the representative value Typical. Note that this temperature range is from 10 ° C. to 35 ° C.
When the temperature is set to ° C., the range of the temperature change in the optical scanning device in which the LDs are arranged is set to 15 ° C. to 60 ° C.

The range of this temperature change (15 ° C. to 60 ° C .; X
(The range in the axial direction), the variation in the differential efficiency η (range in the Y-axis direction) due to the difference between the production lots of the LDs is in the range of 0.1 to 0.6 shown in a dashed line as shown in FIG. Becomes The typical value is 0.1 to 0.1 in the dashed line.
Differential efficiency η for all LD temperatures in the range of 0.6
Are averaged, and when the temperature is 15 ° C., the differential efficiency η is 0.4, and when the temperature is 60 ° C., the differential efficiency η is 0.25.

Specifically, in the example shown by LD # 1, the differential efficiency η is 0.5 when the temperature is 15 ° C., and 0.15 when the temperature is 60 ° C. In the example shown by LD # 2, when the temperature is 15 ° C., the differential efficiency η is 0.55
When the temperature is 60 ° C., the differential efficiency η is 0.42.

Here, in the case where variation occurs due to temperature fluctuation, consider a deterioration criterion based on the above-mentioned Japanese Patent Application Laid-Open No. 3-188181 when considering an optical scanning device using LD # 1. .

First, when the temperature of LD # 1 is 15 ° C., the differential efficiency η is measured, and an initial value of 0.4 is obtained. It is assumed that a case where the differential efficiency η is halved with respect to this value (differential efficiency η = 0.2) is a deterioration reference.

Next, the differential efficiency η when the temperature of LD # 1 is 60 ° C. is measured. The obtained differential efficiency η is 0.15. That is, since the differential efficiency η when the temperature of the LD # 1 is 60 ° C. changes to 0.15, which is lower than the deterioration criterion of 0.2, when the deterioration is determined near 60 ° C. based on the differential efficiency. However, even though the LD itself has not deteriorated, it is determined to be in a deteriorated state.

In this case, in order to avoid erroneous detection, (differential efficiency η / initial differential efficiency η0) <(minimum value of variation range of differential efficiency η with respect to temperature of LD / variation range of differential efficiency η with respect to temperature of LD) = 0.1 / 0.
It is necessary to make 6 ≒ 0.17.

The conventional drive current value used as a criterion for determining a failure is 1.5 to 3 times the initial drive current value. This is because the measured differential efficiency η is 2/3 of the initial differential efficiency η0.
Until it is reduced to 故障, it means that it is not determined as a failure.

FIG. 10 shows a type 2 LD failure occurring during use of a machine and a type 3 L occurring due to wear of the LD.
The relation between the ratio of the differential efficiency η to the initial differential efficiency η0 in the case of the D failure and the LD lighting time h is shown.

The measured differential efficiency η is equal to the initial differential efficiency η0
Is about 2/3 to 1/3, the ratio of the differential efficiency η to the initial differential efficiency η0 is 0.67 to 0.34.
As can be seen from FIG. 10, a failure has already occurred. That is, from FIG. 10, the deterioration state (before the occurrence of the failure) until at least the ratio of the differential efficiency η to the initial differential efficiency η0 becomes 0.7 (that is, the state where the differential efficiency η is about 70% of the initial differential efficiency η0). ) Is meaningless and cannot be satisfied by the conventional criterion.

As described above, in the conventional semiconductor laser deterioration detection apparatus, the variation of the differential efficiency η due to the difference between the production lots of the semiconductor laser and the fluctuation of the differential efficiency η due to the temperature are required to detect the deterioration state of the semiconductor laser. Accuracy cannot be ensured, and it is not possible to prevent problems in the market from occurring.

From the above, the present invention provides a semiconductor device that can judge the state of deterioration of a semiconductor laser at an early stage without being affected by fluctuations in the differential efficiency η due to temperature and variations in the differential efficiency η due to differences in the production lot of the semiconductor laser. An object of the present invention is to provide a laser deterioration detection device.

[0035]

According to a first aspect of the present invention, there is provided a semiconductor laser deterioration detecting apparatus for detecting a temperature of an environment in which a semiconductor laser is disposed. The initial differential efficiency at the detected temperature is obtained by using an initial differential efficiency characteristic representing a relationship between the initial differential efficiency, which is a ratio of the optical output fluctuation of the semiconductor laser before the fluctuation to the fluctuation, and the temperature of the environment where the semiconductor laser is arranged. An initial differential efficiency calculating means for calculating; a calculating means for calculating a differential efficiency which is a ratio of a light output fluctuation of the semiconductor laser to a fluctuation of a driving current given to the semiconductor laser at the temperature detected by the temperature detecting means; A deterioration determining means for determining deterioration of the semiconductor laser based on the initial differential efficiency and the differential efficiency.

That is, in the first aspect of the present invention, the initial differential efficiency calculating means calculates the initial differential efficiency using the initial differential efficiency characteristics. That is, the initial differential efficiency characteristic is a one-to-one correspondence between the initial differential efficiency, which is the ratio of the optical output fluctuation of the semiconductor laser before the deterioration to the drive current fluctuation, and the temperature of the environment in which the semiconductor laser is arranged. The initial differential efficiency calculating means calculates the initial differential efficiency corresponding to the temperature detected by the temperature detecting means from the initial differential efficiency characteristic, thereby calculating the initial differential efficiency at the temperature of the environment where the semiconductor laser is arranged.

The calculating means calculates the differential efficiency of the semiconductor laser at the temperature detected by the temperature detecting means from the ratio of the light output fluctuation of the semiconductor laser to the fluctuation of the driving current applied to the semiconductor laser. The deterioration determining means determines deterioration of the semiconductor laser based on the initial differential efficiency calculated by the initial differential efficiency calculating means and the differential efficiency calculated by the circular loss means.

That is, according to the first aspect of the present invention, it is determined whether or not the deterioration judging means is in a deteriorated state based on the initial differential efficiency calculated according to the temperature change of the environment in which the semiconductor laser is disposed and the differential efficiency of the semiconductor laser. Therefore, even if the initial differential efficiency fluctuates due to a change in the temperature of the environment in which the semiconductor laser is arranged, a highly accurate deterioration determination can always be made.

Since the initial differential efficiency characteristic is determined in correspondence with each semiconductor laser, even if there is a variation in differential efficiency due to a difference in the production lot of the semiconductor laser, it is possible to always judge the deterioration with high accuracy.

The deterioration judging means may judge deterioration when the ratio of the differential efficiency to the initial differential efficiency is less than a predetermined value.

Further, the initial differential efficiency characteristic may be calculated at the time of manufacturing a semiconductor laser or at the time of manufacturing an optical device using the semiconductor laser.

Furthermore, in the semiconductor laser deterioration detecting device according to any one of claims 1 to 3, the deterioration judging means may determine that a ratio of the differential efficiency to the initial differential efficiency is the predetermined value. As described above, when the ratio between the ratio and the ratio of the differential efficiency to the initial differential efficiency before a predetermined period is less than a predetermined constant value, the deterioration may be determined.

Further, in the semiconductor laser deterioration detecting device according to any one of claims 2 to 4, as in claim 5, the deterioration judging means is adapted to increase as the operating time of the semiconductor laser increases. The predetermined value may be increased.

[0044]

FIG. 1 is an explanatory diagram showing a schematic configuration of an embodiment of a semiconductor laser deterioration detecting apparatus according to the present invention. As shown in FIG. 1, this semiconductor laser deterioration detecting device includes a thermometer 12 as a temperature detecting means, and a judging unit 10 including a CPU 14, a ROM 16, and a RAM 18. , An initial differential efficiency calculating means, a calculating means and a deterioration determining means.

The thermometer 12 is provided under the same environment as the environment where the LD 26 is arranged, and measures the temperature of the environment where the LD 26 is arranged and inputs the measured temperature to the input / output port. The temperature data measured by the thermometer 12 is stored in the A / D converter 11.
After being converted into digital data, the data is temporarily stored in the RAM 18 via the input / output port 20.

On the output side of the input / output port 20 of the judgment unit 10, a D / A converter 22, a semiconductor laser drive circuit 24 (hereinafter, referred to as an LD drive circuit 24), and a semiconductor laser 26.
(Hereinafter, referred to as LD 26).

The D / A converter 22 converts digital data output from a CPU described later into analog data and outputs the analog data to the LD drive circuit 24. The LD drive circuit 24 generates an LD drive current based on the input analog data and supplies the LD drive current to the LD 26. The LD emits a laser beam having a light intensity corresponding to the magnitude of the supplied drive current.

An A / D converter 34, an I / V converter 32, and a photodiode 30 (hereinafter referred to as PD 30) are sequentially connected to the input side of the input / output port 20 of the judging unit 10, and the temperature is also changed. A total of 12 are connected.

Upon receiving the laser beam from the LD 26, the PD 30 outputs a current having a magnitude corresponding to the optical output value of the received laser beam to the I / V converter 32 as a monitor current.

The I / V converter 32 converts the input monitor current into a voltage value and converts it into an analog voltage.
4 is output. The A / D converter 34 converts the input analog voltage into digital data and inputs the digital data to the input / output port 20 of the determination unit 10.

The CPU 14 constituting the determination unit 10
Recall the initial differential efficiency characteristic stored in M16,
Initial differential efficiency η corresponding to temperature stored in RAM 18
Calculate 0.

Here, the initial differential efficiency characteristics stored in the ROM 16 will be described. This initial differential efficiency characteristic is stored when a laser light source is incorporated in a manufacturing line of a laser scanning device, and is calculated, for example, as follows.

First, as shown in FIG.
When the ambient temperature of the LD 26 is t1 ° C., the LD 26
Is given so that the light output of the light source becomes the maximum light output value Pmax (mW).
The driving current value If2 and the light output value of the LD 26 are the maximum light output.
60% P of the value Pmax (mW)₆₀Drive power given to
The flow value If1 is measured. Next, the light output value of the LD 26
P_{6 0}, Pmax and the drive current values If1, If2
Rate η0 (t1) ≒ (Pmax−P ₆₀) / (If2-If1)
Confuse.

When the LD ambient temperature is changed to t2 ° C., the drive current If4 given so that the light output value of the LD 26 becomes the maximum light output value Pmax (mW), and the light output value of the LD 26 becomes The drive current value If3 given so as to be 60% P60 of the optical output value Pmax (mW) is measured, and the initial differential efficiency η0 (t2) P (Pmax) is obtained from these drive current values If3 and If4.
−P ₆₀ ) / (If4-If3).

As shown in FIG. 3, the horizontal axis represents the LD environment temperature (° C.), and the vertical axis represents the initial differential efficiency η 0, and the above two temperature values t 1 and t 2 and these two temperature values t 1 and t 2 are obtained. Differential efficiencies η0 (t1), η0 obtained correspondingly
(T2), the initial differential efficiency characteristic η0 (t) = (η0
(T2) −η0 (t1) / t2−t1) t + B = At +
B is calculated and stored in the ROM.

Here, the initial differential efficiency characteristic η0
(T) = At + B is stored.
Temperature values t1, t2 and these two temperature values t1, t2
2, the differential efficiency η0 (t1) obtained corresponding to
η0 (t2) can be stored.

Here, the determination routine of the determination unit 10 will be described with reference to FIG. Here, the optical scanning device is incorporated in a printer, and a predetermined number (1000 in the present embodiment) is used.
A description will be given of a case where the setting is made so as to determine the deterioration when the printing of (sheets) is completed. Step 108 corresponds to the initial differential efficiency calculating means, step 110 corresponds to the calculating means, and steps 114, 116, 118 and 120 correspond to the deterioration determining means.

First, in step 100, the judgment unit 1
0 determines whether printing of 1000 sheets has been completed. If it is determined in step 100 that printing of 1000 sheets has been completed, the count value n is incremented by one in step 102, and the process proceeds to step 104, where the temperature of the LD 26 detected and digitized by the thermometer 12 (temperature detecting means) is converted. The environmental temperature tn is taken. Step 1
At 06, the environmental temperature tn detected and digitized by the thermometer 12 is stored in the RAM 18.

At step 108, the CPU 14
16 is stored as the initial differential efficiency characteristic η0 (t) = At +
Based on B, the initial differential efficiency η0 (tn) = Atn + B at the environmental temperature tn stored in the RAM 18 is calculated.

In step 110, the differential efficiency η (tn) at the environmental temperature tn stored in the RAM 18 is calculated. The CPU 14 supplies at least two types of drive currents If5 and If6 to the LD 26, and the PD 30 corresponding to the at least two types of drive currents If5 and If6 and the respective drive currents If5 and If6. Then, the differential efficiency η (tn) ≒ (Pf6−Pf5) / (If6−If5) at the environmental temperature tn is calculated from the light output values Pf5 and Pf6 received by the above.

Here, the drive current Ifmax when the LD has the maximum light output of Pmax and the light output P _{60 at} which the LD is 60%.
The drive current If ₆₀ at which
(Tn) calculates ≒ the _{(Pmax-P 60) / (} Imax-I 60).

In step 112, the CPU 14 determines the differential efficiency η with respect to the initial differential efficiency η0 (tn) = Atn + B.
(Tn) and the ratio η (n, tn) are calculated, and step 11 is performed.
At 4, it is determined whether the ratio η (n, tn) is equal to or greater than a deterioration determination criterion (for example, 0.75). FIG. 3 shows, as an example, the initial differential efficiency η0 (tn) = At of LD # 1.
n + B and the differential efficiency η0 (tn) × 0.
75.

In step 114, 0.75 is set as a deterioration judgment criterion. The deterioration judgment criterion is based on the differential efficiency η0 (tn) shown in FIG.
It is determined based on the relationship between the ratio (tn) and the LD lighting time h, and is not limited to 0.75. Preferably, in FIG. 10, the ratio should be around 0.7 at which the ratio starts to decrease sharply, and more preferably 0.75.

In step 114, the ratio η (n,
If it is determined that (tn) is smaller than 0.75, the routine proceeds to step 122, where a display indicating deterioration is displayed on a display device (not shown), and this routine ends.

In step 114, the ratio η (n,
If it is determined that (tn) is 0.75 or more, the process proceeds to step 116 to determine whether the accumulated number of prints is less than a predetermined number (for example, 10,000) (n <10?).

If it is determined in step 116 that the accumulated number of prints is less than 10,000 (n <10), the process proceeds to step 118. In step 118, it is determined whether the ratio η (n, tn) is 0.9 or more. That is, if the ratio η (n, tn) is 0.9 or more, the change in the ratio of the differential efficiency to the initial differential efficiency is smaller than 0.1, so that the LD is normal, and conversely, the ratio η (n, tn). ) Is less than 0.9, the change amount of the ratio of the differential efficiency to the initial differential efficiency becomes larger than 0.1, so that the LD can be determined to be in a deteriorated state. Here, as an example, the ratio η (n, t
It is determined whether the LD is normal or deteriorated by determining whether n) is 0.9 or more.

The deterioration criterion for determining the deterioration state when the change amount of the ratio of the differential efficiency to the initial differential efficiency is 0.1 or more is determined when the cumulative number of prints is less than 10,000. , LD is less likely to wear out, and therefore the ratio η (n, tn) if the LD is in a normal state.
Is close to 1, because the ratio η (n, tn) suddenly decreases when the LD starts to deteriorate for some reason. Therefore, the 0.1 used here as the deterioration judgment criterion is not limited.

In step 118, the ratio η (n,
If tn) is determined to be 0.9 or more, step 1 is performed again.
Returning to 00, the above operation is repeated. Step 1
If it is determined in step 18 that the ratio η (n, tn) is not equal to or greater than 0.9 (that is, less than 0.9), the process proceeds to step 122, and a display indicating deterioration is displayed on a display device (not shown). This routine ends.

If it is determined in step 116 that the accumulated number of prints is not less than 10,000 (that is, it is equal to or more than 10,000), the process proceeds to step 120 and 1
The ratio η (n-10, t) of the differential efficiency η (t (n-10)) to the initial differential efficiency η0 (t (n-10))
(N−10)) and the ratio η (n, n) of the differential efficiency η (tn) to the initial differential efficiency η0 (tn) at the environmental temperature tn.
tn) is determined to be less than a predetermined value (for example, 0.9).

That is, the ratio η (n, tn) / η (n−1
0, t (n−10)) is less than 0.9, the ratio η (n−10, t) of the differential efficiency to the initial differential efficiency 10,000 sheets earlier
Since the amount of change between (n−10) and the ratio η (n, tn) of the differential efficiency to the current initial differential efficiency increases by 0.1 or more, the LD can be determined to be in a deteriorated state. Since the amount of change is smaller than 0.1, the LD can be determined to be normal.

That is, when static electricity or the like having a size exceeding the LD specifications is discharged to the LD, the optical scanning device may fail after 2 to 5 hours of the LD lighting time from the discharge, as shown in FIG. Has been confirmed.

For example, in the case of a printer, it is possible to print 10,000 to 100,000 sheets with an LD lighting time of 2 to 5 hours, so that the initial differential efficiency η0 (t (n (n
By setting to detect the deterioration state over time as compared with -10)), a failure of the LD can be detected early.

As a criterion for determining the change, here,
The ratio η (n−10) of the differential efficiency η (t (n−10)) to the initial differential efficiency η0 (t (n−10)) of 10,000 sheets before
t (n-10)) to the ratio η (n, tn)
(N, tn) / η (n−10, t (n−10)) is equal to 0.
The value is determined to be less than 9, but is not particularly limited to 0.9 when the change in the ratio is about 0.1 or more, since the possibility of LD deterioration is high.

At step 120, the differential efficiency η with respect to the initial differential efficiency η0 (t (n−10))
(T (n-10)) and the ratio η (n-10, t (n-1)
0)), if it is determined that the ratio of the ratio η (n, tn) is not less than 0.9, the process returns to step 100 again.
The above operation is repeated.

In step 120, the ratio η (n-10, t (n-10) of the differential efficiency η (t (n-10)) to the initial differential efficiency η0 (t (n-10)) of 10,000 sheets before −
If it is determined that the ratio of the ratio η (n, tn) to 10)) is less than 0.9, the routine proceeds to step 122, where a display indicating deterioration is displayed on a display device (not shown), and this routine ends. .

In the determination routine described above, 1000
A case has been described in which the determination of deterioration is made when printing of a sheet is completed (that is, every predetermined period). For example, the determination of deterioration may be made when instructed by an instruction unit (not shown). It is possible to make settings so that deterioration is determined at predetermined intervals and that deterioration is determined when instructed by an instruction unit (not shown).

The LD incorporated in the optical scanning device as described above
Since the deterioration state of the LD can be detected in accordance with the environmental temperature in which the LD is disposed every time, the deterioration state of the LD can be accurately detected.

Further, based on the judgment of the deterioration state, when the display device (not shown) indicates that the LD 26 is degraded, the LD is replaced, whereby the data of the sudden LD failure can be lost. Troubles such as disappearance and machine stoppage can be prevented.

The LD which is a key part of the optical scanning device
Is replaced, the optical scanning device can be used again, so that the optical scanning device can be recycled. Therefore, parts costs and readjustment costs can be kept low, and in addition to high reliability, low-cost, environmentally-friendly products can be manufactured.

Further, since the deterioration state of the LD can be detected in accordance with the environmental temperature where the LD is placed for each of the LDs incorporated in the optical scanning device, an LD provided with a plurality of light sources such as a semiconductor laser array can be detected. In this case, it is possible to avoid erroneous detection due to thermal crosstalk between light sources, which is a problem as a factor of fluctuation of the differential efficiency, and to accurately detect the deterioration state of the LD.

In the above embodiment, the semiconductor laser deterioration detecting device having an independent structure is described. However, the semiconductor laser deterioration detecting device is incorporated in another program such as a program for performing APC control. It is also possible to adopt a configuration.

[0082]

As described above, according to the present invention, the deterioration state of the semiconductor laser can be quickly controlled without being influenced by the fluctuation of the differential efficiency η due to the temperature or the variation of the differential efficiency η due to the difference in the production lot of the semiconductor laser. It is possible to provide a semiconductor laser deterioration detection device which can be determined in a short time.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of an embodiment of a semiconductor laser deterioration detection device of the present invention.

FIG. 2 is a graph showing a relationship between a drive current If and an optical output P when the ambient temperature of the LD is t1 ° C. and t2 ° C.

FIG. 3 is a graph showing initial differential efficiency characteristics obtained when the horizontal axis represents LD environmental temperature t (° C.) and the vertical axis represents differential efficiency η, and a deterioration determination criterion determined for the initial differential efficiency characteristics. It is.

FIG. 4 is a control routine for determining deterioration of a determination unit.

FIG. 5 is an explanatory diagram illustrating a general configuration of an image forming apparatus.

FIG. 6 is an explanatory diagram illustrating a general configuration of an optical scanning device.

FIG. 7 is a graph showing a relationship between an optical output P of an LD and a drive current If for each temperature.

FIG. 8 shows a drive current If in a type 2 and type 3 fault when the optical output P of the LD is adjusted to be constant.
6 is a graph showing the relationship between the power consumption and the lighting time h of the LD.

FIG. 9 is a graph showing variations in differential efficiency for each LD production lot.

FIG. 10 is a graph showing the relationship between the ratio of the differential efficiency η to the initial differential efficiency η0 of the LD and the lighting time of the LD.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Judgment part 11, 34 A / D converter 12 Thermometer 14 CPU 16 ROM 18 RAM 20 Input / output port 22 D / A converter 24 LD drive circuit 26 Semiconductor laser 30 Start of scan sensor 32 I / V converter

Claims (5)

[Claims] A temperature detecting means for detecting a temperature of an environment in which the semiconductor laser is arranged; Initial differential efficiency calculating means for calculating an initial differential efficiency at the detected temperature using an initial differential efficiency characteristic representing a relationship with the temperature of the environment; A calculating means for calculating a differential efficiency, which is a ratio of a light output fluctuation of the semiconductor laser to a fluctuation in the driving current; Semiconductor laser deterioration detection device. 2. The deterioration detecting device for a semiconductor laser according to claim 1, wherein said deterioration judging means judges deterioration when a ratio of said differential efficiency to said initial differential efficiency is less than a predetermined value. 3. The deterioration detecting device for a semiconductor laser according to claim 1, wherein the initial differential efficiency characteristic is calculated when a semiconductor laser is manufactured or when an optical device using the semiconductor laser is manufactured. 4. The deterioration determining means, wherein a ratio of the differential efficiency to the initial differential efficiency is equal to or greater than the predetermined value, and
4. The method according to claim 1, wherein when the ratio between the ratio and the ratio of the differential efficiency to the initial differential efficiency before a predetermined period is less than a predetermined constant value, it is determined that deterioration has occurred. Device for detecting deterioration of semiconductor laser. 5. The semiconductor laser deterioration detecting device according to claim 2, wherein said deterioration determining means increases said predetermined value as the operating time of said semiconductor laser increases.