JPH0783156B2 - Semiconductor laser drive circuit - Google Patents

Description

The present invention relates to a semiconductor laser drive circuit suitable for application to an electrophotographic color copying machine, a laser printer, and the like.

BACKGROUND OF THE INVENTION In an electrophotographic color copying machine or the like, there is one using a semiconductor laser as a means for forming an electrostatic latent image on a photosensitive image forming body by an image signal corresponding to an original.

FIG. 5 is a block diagram showing an example of such a color copying machine 10.

The figure is an example of a color copying machine. This copying machine divides the color information of a color document into about three types of color information to record a color image. In this example, three colors of black BK, red R, and blue B are exemplified as the color information to be separated.

In the figure, 11 denotes a drum-shaped image forming body, on the surface of which a photoconductive photosensitive member surface layer such as selenium is formed, and an electrostatic image (electrostatic latent image) corresponding to an optical image can be formed. It is done like this.

On the peripheral surface of the image forming body 11, members described below are sequentially arranged in the direction of rotation thereof.

The surface of the image forming body 11 is uniformly charged by the charger 12. The uniformly exposed surface of the image forming zone 11 is subjected to image exposure based on each color separation image (its optical path is shown by 14).

After the image exposure, it is developed by a predetermined developing device. The developing devices are arranged by the number corresponding to the color separation image. In this example, the developing device 15 filled with the red toner developer, the developing device 16 filled with the blue toner developer, and the developing device 17 filled with the black toner developer, These are arranged in this order in the direction of rotation of the image forming body 11 so as to face the surface of the image forming body 11 in order.

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 separation image is developed.

A pre-transfer charger 19 and a pre-transfer exposure lamp 20 are provided on the developing device 17 side to facilitate transfer of a color image onto the recording medium P. However, the pre-transfer charger 19 and the pre-transfer exposure lamp are provided as needed.

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

The transferred recording material P is fixed by the fixing device 22 in the subsequent stage, and then the recording material P is ejected.

It should be noted that the static eliminator 23, which is used as required, is composed of one or both of a static eliminator lamp and a corona discharger for static elimination.

The cleaning device 24 is composed of a cleaning blade and a fur brush, and removes the residual toner adhering to the drum surface after transferring the color image of the image forming body 11 by these.

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

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

This is because in the case of using the laser beam scanner device, a small and inexpensive semiconductor laser can be used as a light source of the image recording device, and a clear color image can be recorded.

The image exposure means shown in FIG. 6 shows an example of the laser beam scanner device 30.

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

The laser beam emitted from the laser 31 enters a mirror scanner 34 composed of a rotary polygon mirror (polygon) via a collimator lens 32 and a cylindrical lens 33.

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

The laser beam is scanned by the mirror scanner 34 on the surface of the image forming body 11 at a constant speed in the predetermined direction a, whereby image scanning corresponding to the color separation data is performed by such scanning.

Reference numeral 39 denotes a photo sensor, and by receiving the laser beam reflected by the mirror 38, an index signal indicating the start of scanning of the laser beam is obtained, and writing of image data for one line is performed based on this index signal. Will be done.

When the laser beam scanner device 30 is used, it is possible to easily form an electrostatic image for each color-separated image while shifting it, so that a clear color image can be formed.

FIG. 7 is a system diagram showing an example of the laser drive circuit 40.

The laser drive circuit 40 is provided with a light quantity stabilizing circuit for stabilizing the light quantity of the laser, in addition to a circuit for driving the laser by the modulation signal.

The reason why the light quantity stabilization circuit is provided in this way is that the temperature characteristics of the laser are extremely poor. Considering use in an environment in which the ambient temperature changes, a light quantity stabilization circuit that stabilizes the laser light quantity is provided. Is necessary.

The laser 31 is excited by the drive current (excitation current) output from the current generation circuit 48, and emits light with a light amount corresponding to the drive current. The light amount of the laser beam emitted from the laser 31 is detected by the photo sensor 41, and the current corresponding to the light amount is supplied to the current / voltage converter 42 to be converted into a voltage signal corresponding to the light amount. Therefore, the photo sensor 41 and the current-voltage converter 42 function as the light amount monitor circuit 60.

The voltage signal is the reference voltage from the reference voltage source 43 and the voltage comparison circuit.
The comparison is made at 44, and the comparison output is supplied to the up / down counter 45 as an up / down control signal.

The counter 45 is configured to count a clock having a predetermined frequency from the oscillator 46, and its clear terminal CLR is cleared by a clear signal Sc sent from a microprocessor (microcomputer) controlling the copying machine and is counted. The enable signal Se is supplied to its enable terminal EN.

The digital output of the counter 45 is converted into an analog signal by the D / A converter 47 in the subsequent stage, and then supplied to the current generation circuit 48 as a current control signal.

Now, when the count enable signal Se is obtained after the counter 45 is cleared by the clear signal Sc, the control signal (high level signal) from the microcomputer to the current generation circuit 48 via the OR circuit 55. )
Is supplied. At the same time, the count enable signal
The counter 45 starts counting up by Se,
Along with this, the drive current to the laser 31 gradually increases. When the laser 31 is excited, the laser light amount also gradually increases.

The comparison output is kept at a high level until the laser light amount reaches a predetermined level, whereby the counter 45 continues the count-up operation. When the laser light amount reaches a predetermined level, the comparison output is inverted to the low level and the counter 45 shifts to the down count mode. With this, the light amount is gradually decreased contrary to the above, but the comparison output is inverted. When the level drops to the level, the operation mode of the counter 45 is reversed again.

Therefore, if the count enable signal Se is turned off after a lapse of a predetermined time, the count 45 holds the output level immediately before turning off.
31 is always excited by a constant drive current, and the amount of light always maintains a constant level.

In this way, with the light quantity controlled to a constant level,
The laser 31 is modulated by the modulation signal supplied to 49,
An electrostatic latent image corresponding to the image information of the original is formed on the drum 11, which is an image forming body.

[Problems to be Solved by the Invention] By the way, as shown in FIG. 8, the relationship between the drive current supplied to the laser 31 and the emitted light amount is such that the light amount only extremely increases up to a predetermined drive current value Ith. . However, it has a characteristic that the light amount rapidly increases when the drive current Ith is exceeded.

On the other hand, in the light quantity stabilizing circuit shown in FIG. 7, since the count value of the counter 45 is incremented or decremented by one, the inflection point Ith described above changes from zero drive current. It takes quite a long time to reach.

Since the control operation for keeping the light amount constant is usually performed as one step of the pre-processing (warming-up process) before the printing of one page, it takes time to stabilize the laser light amount. Has the drawback that the output of the image to be recorded is delayed and the waiting time of the operator is inadvertently lengthened.

In view of this, the present invention proposes a semiconductor laser drive circuit that solves such a problem by a simple configuration and that can significantly reduce the time required for stabilizing the light amount.

[Technical Means for Solving Problems] In order to solve the above problems, the present invention monitors a semiconductor laser and the amount of light emitted from the semiconductor laser, and generates a voltage according to the amount of light emitted from the semiconductor laser. And a digital signal as an increment for decreasing the semiconductor laser drive current or a decrement for decreasing the semiconductor laser drive current based on the comparison. And a current control means for controlling the drive current of the semiconductor laser in accordance with the digital signal from the feedback control means so that light emission of an appropriate amount of light is performed.
With the light amount P1 lower than the appropriate light amount range (Pmax to Pmin) as a boundary, the digital signal is output as an increment or a decrement in the following relationship depending on whether the region is in the low region or in the high region. A semiconductor laser drive circuit characterized by comprising the feedback control means is proposed.

That is, when the digital amount of the digital signal in the low region is A and the digital amount of the digital signal in the high region is B, A> B is set.

[Action]

When the detected light amount is less than or equal to the set light amount, the count-up operation is sequentially performed for each increment A. When the detected light amount is greater than or equal to the set light amount, the count is incremented for each increment B, contrary to the above. The up operation is executed.

Therefore, even when the light amount is increased from the zero state until the light amount reaches a predetermined level, the time required to reach the predetermined level is significantly shortened.

[Embodiment] Next, an example of a semiconductor laser drive circuit according to the present invention will be described in detail with reference to FIG.

FIG. 1 shows an example of a semiconductor laser drive circuit 40 according to the present invention. A photosensor 41 detects a current corresponding to the amount of laser light, which is converted into a voltage signal by a current / voltage converter 42. This voltage signal is converted to a digital signal by the A / D converter 51 and then supplied to the microcomputer 52, so that the output signal for current control output to the D / A converter 47 is changed depending on the value of the digital signal. Judged and decided.

Therefore, the circuit system including the microcomputer 52 is
A means for controlling the digital amount given to the D / A converter 47 so that the output of the A / D converter 51 becomes constant, a means for comparing the A / D converted value with a predetermined value, and this comparison. Based on the result
Means for selecting the increment or decrement of the digital amount given to the D / A converter 47 are provided. The method of determining the data output from the microcomputer 52 will be described later.

This control signal is latched by the latch circuit 53 and then D / A
By being supplied to the converter 47, it is converted into an analog control signal (current control signal) according to its output signal. By supplying this current control signal to the current generation circuit 48, the excitation state of the laser 31 is controlled based on this current control signal, and the light amount thereof is changed.

The microcomputer 52 outputs the following signals according to the value of the input digital signal.

That is, as shown in FIG. 2A, when the maximum value of the light amount required for data writing is Pmax and the minimum value is Pmin, the light amount smaller than the minimum value Pmin by a predetermined value is P1.
The light amount between Pmin and Pmax becomes the proper light amount value.

When the detected light amount is P1 or less, the increment ΔV of the digital value given to the D / A converter 47 is set to A. When P1 or more and Pmin or less, the increment ΔV is set to B,
Otherwise, .DELTA.V is set to -B (therefore, the decrease amount in this case). However, the relationship between A and B is selected as A>B> 0.

Then, the digital value V output to the previous D-A converter 47
Then, V + ΔV is calculated, and this is controlled as new V and output to the D / A converter 47.

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

Therefore, when the control routine for stabilizing the light quantity starts, the laser 31 is excited by the current I1 corresponding to the initial value ΔV, and in the next step, 2ΔV is used as a new output signal for the D / A converter. It is output to the 47 side, and accordingly, the laser 31 is excited by the current I2 corresponding to 2ΔV.

After that, the same control operation is repeated until the detected light intensity is P1 or more Pm
When it becomes less than or equal to in, B is used as ΔV instead of A this time.

As a result, the amount of change in current becomes smaller than before, but the detected light amount gradually increases as the control routine is repeated, and when the maximum light amount value Pmax is exceeded, the excitation current is controlled by -B this time. It will be.

Thus, the detected light amount settles to a value near Pmin to Pmax.

A and B can be set as follows.

That is, first, when the current control step is repeated n times, A is set to a value that slightly exceeds Pmin, and B is 1
When the current control step is repeated once or several times, Pmax
Is set to a value that exceeds.

This is because when A and B are too large, they cannot be converged to Pmin to Pmax, and when they are too small, it takes time to converge.

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

First, when the control routine for stabilizing the light quantity is called, the presence or absence of the light quantity control request flag is checked. If not requested, exit this control routine (step
61, 62). In the light quantity control mode, the on state of the laser 31 is judged, and when it is off, the laser 31 is controlled to be turned on, and then the control routine is exited (steps 63 to 65).

When the laser 31 is in the ON state, the A / D conversion data corresponding to the detected light amount is input, and then it is determined whether or not there is a proper range of the detected light amount (steps 66 and 67). in this case,
When the detected light amount is within the proper range (Pmin to Pmax), 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 (steps 68 and 69). .

When the detected light quantity is not within the proper range, the detected light quantity level is compared with the set light quantity P1, and when it is P1 or less, the increment A is set as ΔV, and then V + ΔV is set as V and the D / A converter 47 is set. (Steps 71 to 73).

Here, in the first control routine, it is initialized to V.

When it is detected that the detected light amount is P1 or more, it is determined whether or not it is within the proper range (Pmin to Pmax). When it is equal to or less than Pmin, the increment B is set as ΔV, and then V + ΔV is output as V to the D / A converter 47 (steps 74, 75).

As a result of such control, when the detected light amount becomes Pmax or more,
This time, the process proceeds to step 76, and after the decrement -B is set as ΔV, V-ΔV is output to the D / A converter 47. Therefore, when the control routine 74 is called a plurality of times, the light amount of the laser 31 is controlled between Pmin and Pmax.

Therefore, the light amount of the laser 31 is always excited with a light amount value (appropriate light amount value) between Pmin and Pmax.

The control routine is performed by a timer interrupt.

The timer interrupt routine keeps the rotation of the drum 11 and the image data writing (electrostatic image writing) timing
This is a subroutine for maintaining a fixed relationship.

In this case, the light intensity control program described above is placed in this timer interrupt routine, or a flag is set when the timer is interrupted, the flag is checked in the main routine, and the control routine is executed only when the flag is set. To execute.

Here, since the output of the D / A converter 47 is likely to have a glitch (whisker-like noise), a low-pass filter is often used in 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. Therefore, it is convenient to perform the light amount control process by the timer interrupt.

By the way, in the above-described embodiment, the light amount control starts from zero, but the control routine can be configured to start from a predetermined value lower than the light amount P1.

That is, the initial value of the data given to the D / A converter 47 is V =
Instead of setting 0, V = V0 (0 <V0 <V1) can be set. Here, V1 is data to be given to the D / A converter 49 corresponding to the light amount P1 at a certain temperature.

In this case, as shown in FIG. 3, the control time until the light amount is stabilized to the proper value can be further shortened.

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

Also, if the microcomputer 52 itself has an A / D conversion function, an A / D converter that performs A / D conversion of the appropriate light amount value
51 can be omitted.

Similarly, in the case where the microcomputer 52 itself has a latch function or the D / A converter 47 has a latch function, the latch circuit 53 is, of course, required.
Can be omitted.

In this embodiment, the amount of light is I / V converted, and the value obtained by A / D conversion is compared with a predetermined value to determine the increment ΔV. However, ΔV is determined by comparing whether the light amount is larger or smaller than a predetermined value at the end. You may decide.

[Effects of the Invention] As described above, according to the present invention, the output current for controlling the drive current for the laser 31 is controlled based on the increments A and B or the decrement-B. As described above, by increasing or decreasing the output current for each clock obtained from the oscillator 46, the adjustment time can be significantly shortened by the means for converging the output current to the appropriate light amount value.

In this way, if the adjustment time required for stabilizing the laser light amount can be shortened, the time from the start of the copy operation to the time when the image is actually rotated is also shortened, and the waiting time of the operator is also shortened. This also has the side effect of eliminating operator frustration.

Therefore, as described above, the present invention is extremely suitable when applied to a simple color copying machine or the like.

[Brief description of drawings]

FIG. 1 is a system diagram of an essential part showing an example of a driving circuit for a semiconductor laser according to the present invention, FIGS. 2 and 3 are diagrams used for explaining the operation thereof, and FIG. 4 is a laser light quantity stabilization control operation. 5 is a control flow chart showing an example, FIG. 5 is a configuration diagram of a main part showing an example of a simple type color copying machine suitable for application to the present invention, and FIG. 6 is an example of a laser beam scanner device used for explaining the present invention. FIG. 7 is a system diagram of a semiconductor laser drive circuit, and FIG. 8 is a characteristic diagram showing the relationship between the laser excitation current and the amount of emitted light. 10 …… Color copier 11 …… Image forming drum 30 …… Laser beam scanner 31 …… Semiconductor laser 40 …… Driving circuit 41 …… Photo sensor 42 …… Current / voltage converter 47 …… D / A Converter 51 …… A / D converter 52 …… Microcomputer 53 …… Latch circuit 60 …… Light intensity monitor circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 15/043 H04N 1/113 1/23 103 Z B41J 3/00 D (56) References 60-115278 (JP, A) JP-A-57-162481 (JP, A)

Claims (1)

[Claims] 1. A semiconductor laser, a light quantity monitor means for monitoring the quantity of light emitted from the semiconductor laser, and generating a voltage according to the quantity of light emitted from the semiconductor laser, and comparing the output of the light quantity monitor means with a predetermined value. A feedback control unit that outputs a digital signal as an increment for increasing the semiconductor laser drive current or a decrement for decreasing the semiconductor laser drive current based on the comparison; and the semiconductor according to the digital signal from the feedback control unit. In the low region with a light amount P1 lower than the appropriate light amount range (Pmax to Pmin) as a boundary, and a current control means for controlling the laser drive current so that an appropriate amount of light is emitted. And in the high region, the feedback control means is configured to output the digital signal as an increment or a decrement in the following relationship. The semiconductor laser drive circuit, characterized in that the. When the digital amount of the digital signal in the low region is A and the digital amount of the digital signal in the high region is B, A> B