JPS62284748A - Luminosity controllable semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To enable luminous energy to be controlled very easily by controlling the luminosity of a laser beam with a voltage regulation means. CONSTITUTION:In a luminosity monitoring circuit 60, a resistor 62 is connected to a positive terminal for a current/voltage conversion means 42, and a photosensor 41 to both ends of the resistor. A detection current corresponding to the luminosity of the laser beam is converted to a proportional voltage. In addition, resistors 63-65 are connected between a negative terminal and its output side, and a variable resistor 65 obtains an output voltage VM which has proportional relations with a detection current. Since the output voltage VM is input to a voltage regulation means 70, a voltage VM' proportional to the output voltage VM is available with an output terminal 80 through the control of a variable resistor 71. Consequently the value of an input digital signal entered into a microcomputer 52 is apparently controlled, thus enabling control of the luminosity of a laser beam 31.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Industrial Field of Application 1 This invention relates to a semiconductor laser drive circuit capable of adjusting the amount of light suitable for application to electrophotographic color copying machines, laser printers, etc. .

[Background of the Invention] Some electrophotographic color copying machines use a semiconductor laser as a means for forming an electrostatic latent image on a photosensitive image forming member using an image signal corresponding to a document.

FIG. 3 is a configuration diagram showing an example of such a color copying machine 10. As shown in FIG.

The figure shows an example of a simple color copying machine. This copying machine attempts to record a color image by separating the color information of a color original into approximately three types of color information. In this example, the color information to be separated is black BK, red R, and blue B.
Illustrate colors.

In the figure, 11 indicates a drum-shaped image forming body,
A photoconductive photoreceptor surface layer made of selenium or the like is formed on the surface thereof, and is cut out so that an electrostatic image (electrostatic latent image) corresponding to an optical image can be formed.

The following members are sequentially arranged on the circumferential surface of the image forming body 11 in the direction of rotation thereof.

The surface of the image forming body 11 is uniformly charged by the charger 12. The surface of the charged image forming body 11 is exposed to light (the light is indicated by 14) based on each color separation image.

After image exposure, the image is developed by a predetermined developing device.

The developing devices are arranged in a number corresponding to the color separated images.

In this example, developing device 1 is completely filled with red toner developer.
5, a developing device 16 filled with a blue toner developer,
The developing devices 17 filled with a black toner developer are sequentially arranged facing the surface of the image forming body 11 in this order in the rotational direction of the image forming body 11.

The developing devices 15 to 17 are sequentially selected in synchronization with the rotation of the image forming body 11. For example, by selecting the developing device 17, a black color separated image (ordinary monochrome image) is developed.

A pre-transfer charger 19 and a pre-transfer exposure lamp 20 are provided on the developing device 17 side, and these make it easy to transfer the color image onto the recording medium P. However, the pre-transfer charger 1
9 and a pre-transfer exposure lamp are provided as necessary.

The color image developed on the image forming body 11 is completely transferred onto the recording body P by the transfer device 21.

The transferred recording medium P undergoes the fixing process by the fixing device 22 at the subsequent stage, and then the recording medium P is discharged.

Note that the static eliminator 23 includes one or a combination of a static eliminator lamp and a corona discharger for defrosting.

The cleaning device 24 includes a cleaning blade and a fur brush, and is used to remove residual toner adhering to the drum surface after the color image of the image forming member 11 has been transferred.

As the charger 12 described above, a scorotron corona discharger or the like can be used. This is because stable charging can be applied to the image forming body 11 with less influence from previous charging.

As the image exposure, image exposure obtained by a laser beam scanning device is used.

This is because when using a laser beam scanning device, not only can a small and inexpensive semiconductor laser be used as the light source of the image recording device, but also a clear color image can be recorded.

The image exposure means shown in FIG. 4 is an example of this laser beam scanning device 30.

The laser beam scanning device 30 includes a semiconductor laser 31, and the laser 31 is optically modulated based on a color separation image (for example, binary data).

The laser beam emitted from the laser 31 enters a mirror scanner 34 made of a rotating polygon mirror via a collimator lens 32 and a cylindrical lens 33.

A laser beam is deflected by the mirror scanner 34 and irradiated onto the surface of the image forming body 11 through an f-θ lens 35 and a cylindrical lens 36 for image formation.

The laser beam is directed to the image forming body 1 by the mirror scanner 34.
1 is scanned at a constant speed in a predetermined direction a, image exposure corresponding to a color separation image is performed by such scanning.

In addition, 39 indicates a photosensor, and by receiving the laser beam reflected by the mirror 38, an index signal indicating the start of laser beam scanning is obtained, and one line of image data is written based on this index signal. It will be done.

When using the laser beam scanning device 30, it is possible to form electrostatic images while shifting them for each color separation image.
Capable of recording clear color images.

FIG. 5 is a system diagram of essential parts showing an example of a laser drive circuit 40 suitable for use in the above-mentioned color copying machine.

The laser drive circuit 40 is provided with a light amount stabilizing circuit for stabilizing the laser light amount to a proper light amount value in addition to a circuit that drives the laser using a modulation signal.

The reason for providing this light intensity stabilization circuit is that the temperature characteristics of lasers are very poor, and considering that the laser is used in an environment where the ambient temperature changes, a light intensity stabilization circuit that stabilizes the laser light intensity is required. This is because it becomes necessary.

Note that this example is a case where the appropriate light amount value is controlled by a microcomputer.

Then, the laser 31 is excited by the drive current (excitation current) output from the current generation circuit 48, and emits light with an amount of light corresponding to the drive current. The laser beam emitted from the laser 31 is sent to a photosensor (photodiode, etc.) 4
1 detects the amount of light, and a current corresponding to the amount of light can be supplied to the current/voltage conversion means 42, thereby converting it into a voltage signal corresponding to the amount of light. Therefore, the photosensor 41 and the current/voltage conversion means 42 function as a light amount monitor circuit 60.

The voltage signal is converted into a digital signal by the A/D converter 51 and then supplied to the microcomputer 52, whereby a predetermined output signal for the current side corresponding to the value of the digital signal is output. .

This control signal is latched by the latch circuit 53 and then supplied to the D/A converter 47, where it can be converted into an analog control signal (current control signal) according to the output signal. By being able to supply this current control signal to the current generation circuit 48, the laser 31
The excited state of the light is controlled, and the amount of light changes.

By the way, as shown in FIG. 6, the relationship between the drive current supplied to the laser 31 and the amount of emitted light is determined by a predetermined drive current value It.
Up to h, the amount of light is extremely small and does not become very large. but,
It has a characteristic that the amount of light increases rapidly when the drive current Ith is exceeded.

Therefore, until the drive current reaches this inflection point rth from zero, the range of change in the value of the limiting current supplied to the current generating circuit 48 is large, and after that, the limiting current is controlled in small steps. This is because the time it takes for the light amount to converge to an appropriate value can be significantly shortened.

Taking this into consideration, the microcomputer 52
Depending on the value of the input digital signal supplied to it, the following signal is output.

That is, as shown in FIG. 7A, the maximum value of the amount of laser light required for data writing is P max, and the minimum value is Pm1.
When n, let Pl be a light amount smaller than this minimum value P min by a predetermined value. The light amount between Pmin and Pmax becomes the appropriate light amount value.

When the detected light amount is less than P1, the D/A converter 47
The increment ΔV of the digital value given to is 8. and,
When it is 21 or more and Pm1n or less, the increase Δ
V is set to 8, and in other cases, ΔV is set to -B (therefore, in this case, the amount of decrease). However, A, [
3 is assumed to be selected as A>B>0.

Then, V+ΔV is calculated from the digital value V that was previously output to the D/A converter 47, and this is controlled to be output to the D/A converter 47 as a new {circle around (2)}.

Note that ■ is set to an initial value of 0 in the initialization routine when the power is turned on.

For this reason, when the control routine for stabilizing the light amount starts, the laser 31 is excited by the current 1 corresponding to the initial value Δ■, and in the next step, the laser 31 is excited by the current 1 corresponding to the initial value Δ■.
V is output as a new output signal to the D/A converter 47 side, and accordingly, the laser 31 outputs a current I2 corresponding to 2Δ■.
You will be encouraged by this.

Thereafter, the same control ii operation is repeated, and when the detected light amount becomes less than P1 or less and less than min, this time B or ΔV is used instead of A.
used as.

As a result, the amount of current change is smaller than before, but as the control routine is repeated, the detected light amount gradually increases, and when it exceeds the maximum light amount value P max, the excitation current is controlled by -B ( It will be sold wholesale.

In this way, the amount of detected light settles down to a value around Pm1n to Pmax.

A and B can be set as follows.

That is, first, when the electricity amount control step is repeated once, A is set to a value that slightly exceeds Pm1n, and B is set to a value that slightly exceeds Pm1n.
is set to a value that exceeds P max @ when the current control step is repeated once or several times.

This is because if A and B are too large, it will not be possible to converge to Pmin-Pmax, and if A and B are too small, it will take time to converge.

Next, an example of the control program for stabilizing the amount of light described above will be explained with reference to FIG.

First, when a control routine for stabilizing the amount of light is called, it is checked whether there is a request for controlling the amount of light. The presence or absence of a light amount control request can be determined by the presence or absence of a flag obtained from a control routine that controls the main body of the apparatus.

If there is no request, exit from this control routine (step 1).

62). In the case of the light amount control mode, it is possible to determine whether the laser 31 is on, and when it is off, the laser 31 is controlled to turn on, and then exits from this control routine (steps 3 to 65).

When the laser 31 is in the on state, A/D conversion data corresponding to the detected light amount is input, and then it is determined whether the detected light amount is within the appropriate range (steps 66 and 67). In this case, the detected light amount is within the appropriate range (P m1n = P ma
x), the laser 31 is turned off and the light amount control request flag is reset, and then the control routine returns to the main processing control routine (step 6).
8.69).

When the detected light amount is not within the appropriate range, the level of the detected light amount is compared with the set light ff1P1, and if it is less than P1, the increase A is set as ΔV, and then V
+ΔV is output as ■ to the D/A converter 47 (steps 71 to 73).

Here, in the first control routine, initialization has been completed to ■=○.

When it is detected that the detected light amount is equal to or greater than P1, it is determined whether it is within the appropriate range (P m1n = P max). When Pm1n or less, the increase B is
Set it as V, then set V + ΔV as ■ and set it as D.
/A converter 47 (steps 74 and 75).

As a result of such control, when the detected light amount exceeds P max, the process moves to step 76, and the decrease -B becomes ΔV.
After being set as ■-ΔV in the D/A converter 47
is output. Therefore, when this control routine 74 is called, the light amount of the laser 31 changes from Pm1n to Pm
It will be controlled between i1+ and ax.

Therefore, the light intensity of the laser 31 is always from Pm1n to Pm
It will be excited with any light amount value (appropriate light amount value) between ax and ax.

The control routine is performed by timer interrupts.

In this case, either the light amount control program described above is placed in this timer interrupt routine, or a flag is set at the timer interrupt, the flag is checked in the main routine, and only when the flag is fully set, the control program Execute.

Here, since the output of the D/A converter 47 is prone to glitches (whisker-like noise), a low-pass filter is often used at the output stage of the D/A converter. Therefore, the response of the circuit is slow and the conversion time of the A/D converter is required, so it is convenient to control the amount of light by using a timer interrupt.

Although the light amount control is started from zero, the control routine can also be configured to start from a predetermined value lower than the light amount P1.

In other words, instead of setting the initial value to v=O, V=VO
(○<VO<Vl) can also be set. here,
(2) 1 is data to be given to the D/A converter corresponding to the light ff1P1 at a certain temperature.

In this case, as shown in FIG. 8, the control time required to stabilize the light amount to an appropriate value can be significantly shortened.

Incidentally, the light amount monitor circuit 60 used in the drive circuit 40 shown in FIG. 5 can have the configuration shown in FIG. 10.

As mentioned above, the light amount monitor circuit 860 is composed of the photosensor 41 and the current/voltage conversion means 42,
As the voltage conversion means 42, an operational amplifier is used as shown. Hereinafter, for convenience of explanation, the current/voltage conversion means 42 will be referred to as an operational amplifier.

A detection current corresponding to the amount of light detected by the photosensor 41 can be converted into a voltage corresponding to the detection current by a resistor 62 connected to a child terminal of the operational amplifier 42, and this voltage signal can be amplified by the operational amplifier 42.

The amplification factor of the operational amplifier 42 is determined by the values of the plurality of resistors 63 to 65 connected between one terminal and the output side.

What is the relationship between the amount of laser light and the detected current?The light of the photosensor 41! ! There is considerable variation depending on the current conversion characteristics, but this variation can be reduced by adjusting the variable resistor 65 provided in the operational amplifier 42.
2 can always be maintained in a constant proportional relationship (for example, when the amount of laser light is 31, the output voltage VM is 3V (volt)).

The output voltage VM is supplied to the microcomputer 52 to monitor the amount of light.

The reason why the output voltage VM is used as a signal for monitoring the amount of light is because the collimator lens 32 is placed close to the laser 31, so the amount of light from the laser 31 cannot be directly measured with an optical power meter or the like. be. Therefore,
It is extremely important to obtain an output voltage VM that has a constant proportional relationship with the amount of light.

[Problems to be Solved by the Invention] By the way, as described above, even if the amount of laser light is made constant, during long-term copying use, the photoconductive surface layer of the photoreceptor that is completely formed on the surface of the drum 11 will deteriorate. deteriorates or
Alternatively, the amount of laser light may need to be changed due to dirt on the optical system.

In such a case, the ROM containing the control program
It may be possible to modify the data (Pmin-PmaX) indicating the appropriate light intensity range of This will make maintenance more complicated.

Instead of such a means, a variable resistor 6 shown in FIG.
5, it is also possible to change the apparent upper output voltage VM.

However, in this case, since it is no longer possible to monitor the true amount of light emitted by the laser, the amount of light emitted by the laser 31 may be erroneously set to a light amount that is greater than the absolute rating.

Therefore, the present invention solves these problems by providing a semiconductor laser drive circuit that can easily adjust the optical Ji and that can adjust the amount of light emitted to prevent the amount of emitted light from exceeding the rated amount. This is a proposal.

Technical means for solving the L problem] In order to solve the above-mentioned problems, the present invention provides a light amount monitor circuit that monitors the amount of light emitted from a semiconductor laser, and converts the output voltage of this light amount monitor circuit into a digital amount. A/D conversion means for
The D/A converting means has control means for controlling the D/A converting means, and current generating means for causing a predetermined drive current to flow through the semiconductor laser in response to an analog signal from the D/A converting means.

The light amount monitoring circuit is comprised of current/voltage conversion means for obtaining a voltage proportional to the amount of light from the semiconductor laser, and voltage adjustment means for obtaining a voltage proportional to the output of the current/voltage conversion means.

As the voltage adjustment means, a variable resistor voltage divider circuit or an operational amplifier whose amplification factor can be adjusted is used.

[Function] If the output voltage is varied by the voltage adjustment means, the drive current flowing through the laser 31 is controlled, and as a result, the amount of laser light can be easily controlled.

In addition, since the current/voltage conversion means outputs a voltage VM proportional to the amount of light emitted by the semiconductor laser, by monitoring this output voltage V)4, it can be determined whether the amount of laser light has been controlled to exceed the absolute rating or not. can be checked accurately.

[Embodiment] Next, an example of a semiconductor laser drive circuit according to the present invention capable of increasing the amount of light will be described in detail with reference to FIG. 1 and subsequent figures.

Since the embodiment shown in FIG. 1 is applied to the semiconductor laser drive circuit shown in FIG. 5, a description of the structure and operation of the drive circuit 40 itself will be omitted.

FIG. 1 shows an example suitable for application to a light amount monitor circuit 60 used in this drive circuit 40, and the light amount monitor circuit 60 includes a photosensor 41 which is a photoelectric conversion element as described above, It is composed of current/voltage conversion means 42.

As the current/voltage conversion means 42, an operational amplifier is used in this example. For convenience of explanation, the current/voltage conversion means 42
will be referred to as an operational amplifier hereafter.

A resistor 62 that functions as a current/voltage converter is connected to the ten terminal of the operational amplifier 42, and this resistor 6
A photosensor 41 is connected to both ends of 2, and the detection current corresponding to the amount of laser light is converted into a detection current or a voltage proportional to this.

In addition, an operational amplifier 4 is connected between one terminal side and its output side.
A plurality of resistors 63 to 65 are connected to determine an amplification factor of 2. The variable resistor 65 is an adjustment element for obtaining an output voltage VM having a constant proportional relationship with the detection tube HQ.

The output voltage VM is supplied to the voltage adjusting means 7o connected at the subsequent stage. In this example, a pair of resistors 71 are connected in series as the voltage adjusting means 70.

72 is used, which is configured as a resistive voltage divider circuit.

In this case, one of the resistors 71 is of a variable type, and an output terminal 80 is led out from its movable terminal. By adjusting the variable resistor 71, the value of the output voltage VM is adjusted, and the adjusted output voltage VH' is supplied to the A/D converter 51 shown in FIG.

In this configuration, since the output voltage VM proportional to the amount of detected light is input to the voltage adjustment means 70,
By adjusting the variable resistor 71, a voltage VM' proportional to the output voltage VM is obtained at the output terminal 80. Therefore, by adjusting the variable resistor 71, the value of the input digital signal input to the microcomputer 52 is apparently adjusted, and as a result, the amount of light emitted by the laser 31 can be adjusted.

For this reason, when changing the amount of laser light due to deterioration of the photoreceptor provided on the drum 11 or dirt on the optical system, all you need to do is adjust the voltage adjustment means 70.
A desired appropriate light amount value can be obtained.

Also, the resistor 72 is set to VM' after adjusting the variable resistor 71.
This is adopted to avoid accidentally setting the value to ○V.

Even after the light amount is adjusted, the output voltage VM is proportional to the adjusted light amount, so just by monitoring this output voltage V14, it is possible to reliably check whether the light amount has been adjusted to exceed the absolute rating.

FIG. 2 shows another embodiment of the invention.

In this example, an operational amplifier is used as the voltage adjustment means 70, and the output voltage VM is supplied to the terminal of the operational amplifier 74, and its output stage is connected to the output terminal 80. A pair of resistors 75 are connected between one terminal and the output terminal 80.

Among the resistors 76, one resistor 76 adjusts its amplification factor.

Therefore, by adjusting this resistor 76, the value of the input digital signal supplied to the microcomputer 52 can be varied, and accordingly, the amount of light emitted by the laser 31 can be adjusted to an extreme value.

In the embodiments described above, the microcomputer 52 may be provided as a dedicated microcomputer for stabilizing the amount of light, or may be a microcomputer that controls illumination of the main body of the apparatus.

In addition, the microcomputer 52 also performs A/D conversion (
For cases where there is some shallowing, the A/D converter 51 for A/D converting the appropriate light amount value can be omitted.

Similarly, if the microcomputer 52 itself has a latch function or if the D/A converter 47 has a latch function, the latch circuit 53 can of course be omitted.

[Effects of the Invention] As explained above, the present invention provides the light amount monitor circuit 60.
Since the voltage adjusting means 7o is provided in the 100 and the amount of light emitted from the laser 31 is adjusted by this voltage adjusting means 70,
It has the following characteristics.

First, since the amount of laser light can be adjusted by the voltage adjustment means 70, even if the amount of light is adjusted due to deterioration of the drum photoreceptor or dirt on the optical system, the amount of light can be adjusted very easily. Thereby, the light amount adjustment time can be significantly shortened.

Second, even if the light intensity is adjusted to exceed the absolute rating of the laser 31 by mistake, the output voltage V)l
By monitoring the value of , this misadjustment can be checked and, if such an adjustment is made, it is possible to immediately readjust the light intensity below the absolute rating.

Thereby, it is possible to prevent the laser life from being deteriorated due to driving above the absolute rating.

Third, the ROM provided in the microcomputer 52
Since the light intensity of the laser 31 can be adjusted to a desired value without changing the data indicating the appropriate light intensity value, maintenance and inspection are extremely easy.

Therefore, as described above, the present invention is extremely suitable for application to simple color copying machines, laser drive circuits used in laser printers, and the like.

[Brief explanation of the drawing]

1 and 2 are connection diagrams of essential parts showing an example of a drive circuit for a semiconductor laser capable of adjusting light intensity according to the present invention, and FIG. 3 is an example of a simple color copying machine suitable for applying the present invention. 4 is a configuration diagram showing an example of a laser beam scanning device used to explain the present invention. The fifth factor is a system diagram of a semiconductor laser drive circuit, and FIG. 6 is a diagram showing the excitation current of a laser Figures 7 and 8 are graphs that explain the operation of the stabilization adjustment of the light intensity, respectively, and Figure 9 is a graph showing the relationship between the stability adjustment of the laser light intensity (an example of wholesale operation). The control flowchart, FIG. 10 is a connection diagram showing an example of a light amount monitor circuit provided in the drive circuit. 1o...Color copying machine 11...Drum 3o as an image forming body...Laser beam scanning device 31 ... Semiconductor laser 40 ... Drive circuit 41 ... Photo sensor 42 ... Current/voltage conversion means 47 ... D/A converter 51 ... A/D converter 52 ... Microcomputer 53...Latch circuit 60...Light level monitor circuit 70...Voltage adjustment means Patent applicant Company agent who closed Konishiroku Photo Industry Co., Ltd.
Patent attorney Kuni Yamaguchi 4; (i ≧ ＼ Fig. 4 β Q; Le r Kubo to Bote [ Fig. 5 concave: wL kanmaku λ Fig. 6 Fig. 10 Fig. 7 Fig. 8

Claims (4)

[Claims] (1) A semiconductor laser, a light amount monitoring circuit that monitors the amount of light emitted from this semiconductor laser, an A/D conversion means that converts the output voltage of this light amount monitoring circuit into a digital amount, and an output of this A/D conversion means. , comprising a control means for controlling a digital value given to the D/A conversion means, and a current generation means for causing a predetermined drive current to flow through the semiconductor laser in accordance with an analog signal obtained from the D/A conversion means, The light amount monitoring circuit is characterized by comprising current/voltage conversion means for obtaining a voltage proportional to the light amount of the semiconductor laser, and voltage adjustment means for obtaining a voltage proportional to the output of the current/voltage conversion means. Semiconductor laser drive circuit with adjustable light intensity. (2) The control means is characterized in that the digital amount given to the D/A conversion means is controlled by a microcomputer so that the output value of the A/D conversion means falls within a certain range. A semiconductor laser drive circuit capable of adjusting the amount of light according to claim 1. (3) The light amount adjustable semiconductor laser according to claims 1 and 2, wherein the voltage adjusting means is a resistive voltage dividing circuit whose voltage dividing ratio is adjustable. drive circuit. (4) The semiconductor laser drive capable of adjusting light intensity according to claims 1 and 2, characterized in that the voltage adjusting means is an operational amplifier whose amplification factor is adjustable. circuit.