JP2737197B2 - Semiconductor laser scanner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Field of the Invention The present invention relates to a semiconductor laser scanning device used for a digital copying machine or a write head of an optical disk.

(2) Prior Art FIG. 9 shows a schematic structure of a digital copying machine using a semiconductor laser, which is used for illuminating a document which moves along the lower surface of a document (not shown) placed on a platen 01. The reflected light from the original of the lamp 02 is converged on the image reading unit 06 via the moving mirror system 03, the lens 04, and the fixed mirror system 05, and is converted into an electric signal. It is converted into binary serial data for each scanning line. The laser beam emitted from the semiconductor laser device 08 operating according to the serial data is charged around the charger.
An electrostatic latent image is formed on the surface of a photosensitive drum 013 having a developing unit 09, a developing unit 010, a transfer charger 011 and a cleaner unit 012. After the electrostatic latent image on the photosensitive drum 013 is transferred to the sheet supplied from the sheet tray 014,
The paper is discharged to the paper discharge tray 016 through the fixing unit 015.

By the way, in the semiconductor laser used in the digital copying machine, the laser light emission efficiency is reduced due to the rise of the cavity temperature accompanying the irradiation of the laser beam, so that the output of the laser beam is reduced. This means that the output fluctuates, that is, the light quantity fluctuates due to the change in the cavity temperature due to the oscillation of the laser beam, and this causes the deterioration of the image quality.

This will be described with reference to an example of the [current-output-temperature] characteristics of the semiconductor laser shown in FIG. 15. When the current I supplied to the laser diode is 35 to 39, which is the threshold value of laser oscillation.
The output P is extremely small in the region of mA or less, and at this time, the laser diode generates natural light. When the supplied current I exceeds the threshold, the laser diode starts stimulated emission, and its output P increases sharply. Assuming that the current I supplied to the laser diode is 50 mA in the oscillation region of the laser beam, as the cavity temperature T increases to 25 ° C., 50 ° C., and 70 ° C.,
The output P gradually decreases to 5 mW, 4 mW, and 3 mW. This means that, in order to obtain a constant output P, the current I applied to the laser diode should be controlled so as to compensate for the variation in the cavity temperature T. That is, when the output P of the laser beam decreases due to the increase in the cavity temperature T, the output P can be kept constant by increasing the current I applied to the laser diode.

10 to 14 show a conventional example in which temperature compensation is performed by applying the above-described principle to a semiconductor laser scanning device 08 as a writing device of the digital copying machine.

As shown in FIG. 10, a collimator lens 018 and a cylindrical lens 01 are provided on an optical path of a laser array 017 as a semiconductor laser light source for simultaneously irradiating three laser beams.
9, an imaging optical system 024 including a mirror 020, a rotating polygon mirror 021, an fθ lens 022, and a cylindrical lens 023 is provided, and the photosensitive drum 013 as a scanning surface rotatably provided around a central axis. Is scanned. An optical sensor 025 is provided at an end of the photosensitive drum 013, and an output timing of an image signal described later is set by a beam position detection signal output from the optical sensor 025.

As shown in FIG. 11, the laser array 017 includes three write oscillation regions 029a, 029b, and 029c separated by an insulating portion 028 on an upper portion of a substrate 027 having an electrode 026 on a lower surface, which will be described later. By supplying a drive current from the output terminals a, b, and c via the electrode 030, each of the write oscillation regions 029a, 029b, and 029c emits a laser beam having a certain polarization direction indicated by an arrow. I have.

Returning to FIG. 10, three LD drivers 031a, 031b, 031c provided in the oscillation control means A of the laser array 017 are connected to output terminals a, b, c connected to the laser array 017 and two input terminals, respectively. Terminals a ₁ , a ₂ ; b ₁ , b ₂ ; c ₁ , c ₂ are provided, respectively.
The image memory 0 is connected to one of the input terminals a ₁ , b ₁ , c ₁ .
32 a line memory 033a, 033b, with 033c are connected in series, the light quantity control circuit 034a to the other input terminal a _2, b _2, c ₂ which controls the laser light intensity, 034b, 034c are connected. The laser array 017 detects the amount of the emitted laser beam by measuring the back beam leaking backward in the detector 035. The detected light amount signal is used as a light amount comparator 03.
At 6, the output is compared with the reference potential of the light quantity reference signal generator 037, and the output of the light quantity comparator 036 is input to each of the light quantity control circuits 034a, 034b, 034c as a light quantity control signal, and is temporarily held. Further, the optical sensor 025
Is connected to a controller 038, and the image memory 032, the line memories 033a, 033b, 033c, and the light amount control circuits 034a, 034b, 034c are controlled by a timing control signal output from the controller 038. .

As shown in FIG. 12, the output terminals a, b, c of the oscillation control means A of the laser array 017 are respectively provided with transistors Tr ₁ ,
The transistor Tr ₂ and the resistor R ₁ are connected in series, and the base of each of the transistors Tr ₁ and the input terminals a ₁ , b ₁ , c
Each level converter between _{1 039a, 039b,} with 039c is interposed, the base of each transistor Tr ₂ is connected to the input terminal _{a 2, b 2, c 2} .

 Next, the operation of the conventional example having the above-described configuration will be described.

Based on the timing control signal output from the controller 038, each LD driver 031a, 031b, 031c
Laser beams for setting the light amount are sequentially emitted from the three write oscillation regions 029a, 029b, and 029c of 017. The light amount signal obtained by measuring the back beam of the light amount setting laser beam with the detector 035 is fed back to the light amount comparator 036, where it is compared with the reference potential of the light amount reference signal generator 037. The light amount control signal output from the light amount comparator 036 is a light amount control circuit 034a, 034b, 03
Entered in 4c and temporarily stored.

Subsequently, a laser beam for position detection is emitted from the write oscillation region 029a based on the timing control signal output from the controller 038. This position detection laser beam is reflected by the rotating polygon mirror 021 of the imaging optical system 024,
025 is detected. Then, the beam position detection signal output from the optical sensor 025 is fed back to the controller 038.

On the other hand, 3N-2 lines output from the image memory 032, 3N
The image signals corresponding to the N1 line and the 3N line (where N = 1, 2,...) Are temporarily stored in the line memories 033a, 033b, 033c, respectively, and then the timing is adjusted to the beam position detection signal. The signals are simultaneously input to the input terminals a ₁ , b ₁ , and c ₁ of the oscillation control means A. At the same time, the input terminals a ₂ , b ₂ ,
The c _2, light quantity control circuit 034a, 034b, the light quantity control signal which is temporarily stored in 034c is input.

The image signal level converter 039a, 039b, is applied to the base of the transistor Tr ₁ through 039C, the transistor Tr ₁
Together with on or off, the light quantity control signal supplies a base current that varies the size of the in accordance with the light amount to the transistor Tr _2. Therefore, the collector current flowing through the transistors Tr ₁ and Tr ₂ , that is, the drive current Id supplied to the three write oscillation regions 029 a, 029 b, and 029 c changes according to each correction signal, and the laser array due to the temperature change. The output fluctuation of 017 is compensated.

In this way, the laser array 017 irradiates the image data for three lines with a constant output in synchronization with the rotation of the rotary polygon mirror 021 and the three lines on the photosensitive drum 013 are simultaneously scanned. When the scanning of the third line is completed, the above cycle is repeated, and the scanning of the fourth and subsequent lines is performed.

(3) Problems to be Solved by the Invention In the above-mentioned conventional example, it is possible to compensate for the output fluctuation for each scanning line due to the self-heating of the laser array 017. 029
Output fluctuation for each pixel due to thermal interference between a, 029b and 029c could not be compensated.

That is, as shown in FIG. 13, when the drive current Id is supplied to the three write oscillation areas 029a, 029b, 029c in accordance with the image signal, the write oscillation areas adjacent to each other in a certain time area Δt are 029a, 029b, and 029c simultaneously irradiate a laser beam. Then, as shown in FIG. 14, development in which the output Pd decreases from the position indicated by the broken line to the position indicated by the solid line in the time region Δt due to the heat generated by the adjacent write oscillation regions 029a, 029b, 029c, so-called crosstalk occurs. As a result, the light amount of the laser beam fluctuates, which causes a decrease in image quality and the like.

The present invention has been made in view of the above circumstances, and removes the influence of output fluctuation due to crosstalk between a plurality of write oscillation regions in a laser array, and performs scanning with a constant light amount from the start point to the end point of each scan line. An object of the present invention is to provide a semiconductor laser scanning device capable of performing the above.

B. Configuration of the Invention (1) Means for Solving the Problems In order to solve the above problems, the present invention provides a semiconductor laser scanning device having a laser array having a plurality of independently oscillating write oscillation regions. In an apparatus, an intermediate oscillation region is interposed between adjacent write oscillation regions of the laser array, and a compensation current equal to or less than a laser oscillation threshold value is supplied to the intermediate oscillation region.

(2) Operation According to the present invention having the above-described configuration, the intermediate oscillation region to which the compensation current equal to or less than the laser oscillation threshold is supplied generates natural light and generates heat. Thus, one of the adjacent write oscillation regions of the laser array, when it irradiates a laser beam, has the intermediate oscillation in the heating state regardless of whether the other write oscillation region irradiates the laser beam. The region is subject to steady thermal influence from the region, and the thermal effect from the other write oscillation region is reduced.

(3) Example Hereinafter, an example of the present invention will be described with reference to the drawings.

FIGS. 1 and 2 show an overall view of a first embodiment of the present invention, which is an improvement of the conventional example, and an enlarged view of the laser array. The same reference numerals have been applied except for the above.

In this embodiment, the laser array 17 shown in FIG. 2 further includes two intermediate oscillation regions 29d and 29e at intermediate positions between the three writing oscillation regions 29a, 29b and 29c. Are connected to the two LD drivers 31d and 31e provided in the oscillation control means A of the laser array 17 in FIG. 1, respectively. It is characterized in that it has a polarizing filter 40 having the same polarization direction as the direction, and the other configuration is the same as that of the conventional example.

FIG. 3 shows a circuit of the oscillation control means A of the laser array.
In addition to the drivers 31a to 31c, LD drivers 31d and 3 for driving the newly added intermediate oscillation regions 29d and 29e
1e is provided. These LD drivers 31d and 31e are transistors T connected in series to the intermediate oscillation regions 29d and 29e.
r ₃ and a resistor R _3. A predetermined voltage divided by the resistors R ₃ and R ₄ is applied to the base of the transistor Tr ₃ .

With this configuration, the two intermediate oscillation regions
29d, a constant compensation voltage Ic is supplied at all times through the transistor Tr ₃ which turned to 29e. The compensation current Ic is set slightly lower than a threshold value at which laser oscillation occurs. The compensation current Ic causes the intermediate oscillation regions 29d and 29e to generate weak natural light and to be in a heating state. Due to the heat generation, the cavity temperature in the intermediate oscillation regions 29d and 29e becomes substantially equal to the cavity temperature during laser beam oscillation in the other three writing oscillation regions 29a, 29b and 29c. Is compensated.

This will be described with reference to the drawings.
When a drive current Id as shown in FIG. 4 is supplied to 29a, 29b, 29c in accordance with the image signal, the two intermediate oscillation regions 29d, 29c
A constant compensation current Ic is always supplied to e. Then, as shown in FIG. 5, the cavity temperature of the intermediate oscillation regions 29d and 29e rises due to the irradiation of the natural light of the output Pc by the compensation current Ic, and the heat interference causes the adjacent write oscillation regions to be originally (intermediate). When there is no oscillation region 29d, 29e) the output of the laser beam, which should be at the position of the broken line, decreases to the position of the solid line, and the output of the laser beam when the image signal is ON is substantially constant Pd over the entire writing oscillation region. Will be retained. That is, when the two intermediate oscillation regions 29d and 29e do not exist, the three write oscillation regions 29a and 29
b, 29c, adjacent write oscillation areas 29a and 29b, and intermittent crosstalk between write oscillation areas 29b and 29c caused a change in image density. Since the intermediate oscillation regions 29d and 29e which are always in a heating state are interposed between the oscillation regions 29a and 29b and the write oscillation regions 29b and 29c, each of the write oscillation regions 29a, 29b and 29c becomes the intermediate oscillation region 29.
The laser beam is thermally affected by d and 29e, so that the output of the laser beam is maintained at a constant value indicated by a solid line.

By the way, the intermediate oscillation region 29d,
Since the output of natural light generated by 29e is so weak that it hardly interferes with scanning, it is desirable to remove the influence as much as possible. Polarizing filter in Fig. 2
40 is provided for this purpose.
According to 40, even though half of the natural light passing therethrough is cut, the laser beam having the same polarization direction is completely transmitted, thereby reducing the influence of the natural light generated by the compensation current Ic and reducing the contrast. High image quality can be obtained.

According to the above-described first embodiment, since the polarization filter having the same polarization direction as the laser beam is provided in the optical path of the laser beam, unnecessary natural light generated in the intermediate oscillation region can be cut. It is possible to prevent an adverse effect on writing scan by natural light.

FIG. 6 shows a circuit of the oscillation control means A according to the second embodiment of the present invention.

In this embodiment, two intermediate oscillation regions 29d and 29e
Compensation current Ic supplied to is controlled by the image signals 101, 102, 103 from the input terminal _{a 1, b 1, c 1} . That is, the image signals 101 and 102 from the input terminals a ₁ , b ₁ and c ₁ are supplied to the EX-OR gate 4
EX-OR signal 2 which passes through 1 and is output from this EX-OR gate 41
01 is inputted write oscillation region 29a via a level converter 39d, the base of Tr ₃ connected to the intermediate oscillating region 29d between 29b. Similarly, the image signals 102 and 103 from the input terminals b ₁ and c ₁
Passes through an EX-OR gate 41, and an EX-OR signal 202 output from the EX-OR gate 41 is connected to an intermediate oscillation region 29e between the write oscillation regions 29b and 29c via a level converter 39e. Entered into the base of ₃ .

As a result, as shown in FIG. 7, when one of the image signals 101 and 102 input to the adjacent write oscillation regions 29a and 29b is ON, the compensation current Ic is supplied to the intermediate oscillation region 29d.
Similarly, when one of the image signals 102 and 103 input to the adjacent write oscillation regions 29b and 29c is ON, the compensation current Ic is supplied to the intermediate oscillation region 29d. Therefore, as shown in FIG. 8, when only one of the write oscillation regions 29a and 29b or only one of the write oscillation regions 29b and 29c irradiates the laser beam, the intermediate portion interposed between them. Oscillation region 29d, 29
e cavity temperature rises. In this manner, the output of the laser beam, which should be at the position of the broken line in the write oscillation regions 29a, 29b, and 29c (when there are no intermediate oscillation regions 29d and 29e), is generated by the heat from the intermediate oscillation regions 29d and 29e. The power of the laser beam is reduced to the actual position, and the power is maintained at a substantially constant Pd over the entire area.

According to the above-described second embodiment, the adjacent oscillation regions 29a and 29a
By driving the intermediate oscillation regions 29d and 29e by the EX-OR signals of the image signals 101, 102 and 103 of b and 29c, when only one of the adjacent write oscillation regions 29a, 29b and 29c irradiates the laser beam, the intermediate oscillation region Can generate heat. As a result, the generation of natural light is minimized, the contrast is improved, and the deterioration of the laser array due to heat generation is prevented, and the life can be extended.

As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the embodiments, and various small design changes can be made without departing from the present invention stored in the claims. It is possible to do.

For example, the number of the write oscillation regions of the laser array 17 as the semiconductor laser light source is not limited to three, but may be any plural number. In this case, the number of the intermediate oscillation areas is required to be one less than that of the write oscillation area. The polarizing filter 40
Can be used instead of the transmission type.

C. Effects of the Invention According to the above-described semiconductor laser scanning device of the present invention, in a semiconductor laser scanning device including a laser array having a plurality of write oscillation regions that can be independently modulated, Intermediate oscillation area is interposed between oscillation areas,
Since a compensation current equal to or less than the threshold value of laser oscillation is supplied to the intermediate oscillation region, the intermediate oscillation region supplied with the compensation current generates natural light and becomes in a heating state. Therefore, irrespective of whether a write oscillation region adjacent to a certain write oscillation region is in a heat-generating state or not, a weak natural light is generated and a constant thermal oscillation is generated between the write oscillation region and the intermediate oscillation region in a heat-generating state. An influence can be caused, whereby the output of the laser beam can be kept constant, so that the image quality of the image reproducing apparatus can be improved or the reading error of the optical disk can be prevented.

[Brief description of the drawings]

FIG. 1 is an overall view of a first embodiment of a semiconductor laser scanning device according to the present invention, FIG. 2 is an enlarged view of the laser array, FIG.
Fig. 4 is a circuit diagram of the oscillation control means, Fig. 4 is a time chart of the drive current, Fig. 5 is a time chart of the output, Fig. 6 is a circuit diagram of the oscillation control means of the second embodiment of the present invention, FIG. 7 is a time chart of the drive current, FIG. 8 is a time chart of the output, FIG. 9 is a schematic structural diagram of a digital copying machine, FIG. 10 is an overall view of a conventional semiconductor laser scanning device, FIG. Is an enlarged view of the laser array, FIG. 12 is a circuit diagram of the oscillation control means, FIG. 13 is a time chart of the drive current, FIG. 14 is a time chart of the output, FIG.
The figure is a [current-output-temperature] characteristic diagram of the semiconductor laser. 17 ... Laser array, 29a, 29b, 29c ... Write oscillation area, 2
9d, 29e: Middle oscillation region, Ic: Compensation current

Claims (1)

(57) [Claims] 1. A semiconductor laser scanning device comprising a laser array (17) having a plurality of write oscillation regions (29a, 29b, 29c) each of which can be independently modulated; adjacent to the laser array (17). Write oscillation area (29a,
A semiconductor laser having an intermediate oscillation region (29d, 29e) interposed between the intermediate oscillation regions (29b, 29c) and supplying a compensation current (Ic) equal to or less than a laser oscillation threshold value to the intermediate oscillation region (29d, 29e). Scanning device.