JPS6353043A - Laser diode driving control circuit of laser printer - Google Patents

Abstract

PURPOSE:To enhance printing quality, by storing correction data for correcting the variation in the beam receiving intensity of the laser beam in a scanning direction generated by a lens and correcting laser output intensity during scanning. CONSTITUTION:A laser diode driving control circuit is equipped with a laser driving circuit 40 for performing the ON/OFF control of a laser diode on the basis of an image signal and an output control circuit 42 detecting the output intensity of laser beam and outputting a reference voltage signal for holding said output intensity to reference intensity to the laser driving circuit 40. Data for correcting the variation in beam receiving intensity generated by the passage of laser beam through a lens is stored in a correction data memory means at every scanning position, and the reference voltage signal from the output control circuit 42 is corrected at every scanning position by an output correction circuit. Therefore, the beam receiving intensity of laser beam at each scanning position on a photosensitive drum becomes a constant value over an entire scanning width and printing density becomes uniform.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention scans a laser beam output from a laser diode in the axial direction of the photosensitive drum using a rotating polygon mirror and an fθ lens. The present invention relates to a laser diode drive control circuit for a laser printer that forms an image corresponding to an image support signal.

[Prior Art] Generally, in a laser printer, for example, a charging section that charges the photosensitive drum along the circumference of the photosensitive drum rotating at a constant speed, and an image signal corresponding to character data input from the outside are used. Exposure section that scans the laser beam in the axial direction of the photosensitive drum in response; A developing section that develops the image formed on the photosensitive drum.

A transfer section that transfers the developed image onto paper supplied from the outside, a defrosting section that erases the image on the transfer section, and the like are provided.

The exposure section of such a laser printer is configured as shown in FIG. 9, for example. That is, 1 in the figure is a case formed in a flat isosceles triangular shape to prevent laser beams from leaking to the outside and to protect internal components. For example, an octagonal rotating polygon mirror 2 is disposed near the apex of the triangle in the case 1, and a reflecting mirror 3 is disposed along the base of the triangle. Note that the case 1 is positioned so that the reflecting mirror 3 is parallel to the axis of a photosensitive drum (not shown). In addition, a rotating polygon mirror (
An fθ lens 4 consisting of a combination of a plurality of lenses is disposed between the polygon mirror 2 and the reflecting mirror 3. The laser beam 6 output from the laser diode 5 attached to the inner surface of the case 1 is reflected by one reflective surface 7 of the rotating polygon mirror 2, passes through the fθ lens 4, and is reflected! I
The light is reflected by I3 and irradiated onto the photosensitive drum. When the rotating polygon mirror 2 rotates by 1/8 of a revolution, the laser beam 6
is scanned from one end of the reflecting mirror 3 to the other end. That is, the photosensitive drum is scanned by one width in the axial direction. A scan start position detection mirror 8 for detecting that the laser beam 6 is located at the scan start position is disposed near the scan start side end of the reflecting mirror 3. When this occurs, the laser beam 6 is reflected by the scan start position detection mirror 8 and input to the bin diode 9.

[Problems to be Solved by the Invention] However, the laser printer in which the rotating polygon mirror 2 and the fθ lens 4 are used to scan the laser beam 6 as described above also has the following problems. That is, the received light intensity of the laser beam 6 at each scanning position in the scanning direction on the photosensitive drum naturally needs to be constant at each scanning position. However, even if the laser diode 5
Even if the output intensity of the laser beam 6 output from the fθ lens 4 is constant during one scanning period, the passing efficiency of the laser beam at each scanning position in the scanning direction of the fθ lens 4 is not a constant value over the entire scanning width. Therefore, the intensity of the laser beam received at each scanning position X of the reflecting mirror 3 becomes a chevron curve as shown in FIG. That is, the received light intensity becomes high at the center of the reflection 1113 (the center of the fθ lens 4).

If the received intensity of the laser beam 6 cannot be maintained at a constant value at each scanning position @X, uneven exposure will occur between the center and the periphery of the photosensitive drum, which will affect the print quality of images obtained by this laser printer. There is a problem that the value decreases.

The present invention has been made based on these circumstances, and its purpose is to store correction data for correcting fluctuations in received light intensity in the scanning direction caused by the fθ lens, and to use this correction data to To provide a laser diode drive control circuit for a laser printer, which can always control the received intensity of a laser beam on a photosensitive drum to a constant value by correcting the laser output intensity during scanning, and can improve printing quality.

[Means for Solving the Problems] The laser diode drive control circuit of the laser printer of the present invention includes a laser drive circuit that controls on/off the laser diode based on an image signal, and an output intensity control circuit of the laser beam output from the laser diode. an output adjustment circuit that detects this and outputs a base Q voltage signal to the laser drive circuit in order to maintain the output intensity at the reference intensity when the image signal is turned on, and an output adjustment circuit that detects the A correction data storage means that stores correction data for each scanning position to correct fluctuations in the received intensity of the laser beam in the scanning direction, and is inserted between the laser drive circuit and the output adjustment circuit, and outputs the output from the output adjustment circuit. and an output correction circuit that corrects the reference voltage signal corresponding to the scanned position using correction data.

[Function] With the laser diode drive 11 control circuit of the laser printer configured as described above, the correction data storage means adjusts the received intensity of the laser beam in the scanning direction of the photosensitive drum, which is generated when the laser beam passes through the fθ lens. Correction data for correcting variations in is stored for each scanning position. Then, the output correction circuit corrects the reference voltage signal output from the output adjustment circuit using correction data for each scanning position. Therefore, the intensity of the laser beam received at each scanning position on the photosensitive drum is a constant value over the entire scanning width, so that the printing density becomes uniform over the entire width of the photosensitive drum.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic cross-sectional view showing the general configuration of a laser printer incorporating the laser diode drive control circuit of the present invention. In the figure, reference numeral 11 denotes a housing that covers the entire body, and a photosensitive drum 12 having a photosensitive surface formed on its outer circumferential surface is disposed at the center of the housing 11. This photosensitive drum 12 is connected to a main drive motor 13. It is rotated clockwise at a constant speed. Along the outer periphery of the photosensitive drum 12, there is a charging section 149 consisting of a charging charger; an exposing section 15 that outputs a laser beam 6 in response to an image signal; A developing edge section 16 that develops the image formed on the photosensitive drum 12 in the exposure section 15. A transfer section 18 consisting of a transfer charger which transfers the normalized image onto the paper 17 supplied from the cassette is provided.One charge eliminating section consisting of a charge eliminating lamp for erasing the image on the transfer section is provided.

Furthermore, a cassette 20 for continuously supplying paper 17 to the transfer section 18 is inserted into the bottom of the housing 11 from outside the housing 11 . Paper 17 stored in the cassette 20
are pulled out one by one from the cassette 20 by the CF roller 21 and guided to the transfer section 18 via PF (paper feed) rows 522a, 22b, and 22c. The image on the photosensitive drum 12 is transferred at this transfer section 18 . Paper 17 on which the image has been transferred
is a heat constant roller 23. The paper is discharged from the paper discharge port 25 to the outside of the casing 11 via the discharge rows 524a and 24b.

Note that the paper 17 is held between rollers 22b, 24a, and 24b on the conveyance path of the paper 17 from when the paper 17 is pulled out of the cassette 20 until it is ejected from the paper ejection port 25. The jams 26a and 26b detect the occurrence of the jam.

26c is installed. Furthermore, a paper end (PF) sensor 27 is disposed within the insertion opening of the cassette 20 in the cassette 11 to detect when the number of remaining sheets of paper 17 in the cassette 20 becomes less than or equal to a predetermined number.

The exposure section 15 is configured as shown in FIG. 3, for example. Since the configuration of this exposure section 15 is the same as that of the general exposure section shown in FIG. 9, the same reference numerals will be given and redundant explanation will be omitted. However, the laser beam 6 output from the laser diode 5 is close to the laser diode 5.
A bin diode (not shown) is installed in order to detect the output intensity.

FIG. 4 is a block diagram showing the schematic structure of the laser printer. A CPLI (central processing unit) 31 that executes various recitation processes is connected to a ROM 33 for storing control programs and correction data, a RAM 34 for storing variable data such as input character data, etc. via a pass line 32. An interface 35 through which character data to be printed is input from an external host computer. It controls an input/output port 37 that inputs and outputs various commands and data to and from various constituent members. This input/output port 37 has a photosensitive drum 12
A main drive motor 13. Charging section 14 consisting of a charging charger. Transfer section 18 consisting of a transfer charger. Static eliminator 19 consisting of a static eliminator lamp. Drive motors for various rollers and a laser diode drive control circuit 38 that drives and opens the laser diode 5 of the exposure section 15. The jams 26a to 26c of the paper end sensor 27.3@ are connected.

For example, as shown in FIG. 1, the laser diode drive ν1 hitting circuit 38 includes a laser drive circuit 40 that controls on/off the laser diode 5 based on an image signal input from the input/output port 37, and a laser diode drive circuit 40 that is located close to the laser diode 5. Laser beam 6 detected by arranged bin diode 41
An output adjustment circuit 42 outputs a reference voltage signal for maintaining the output intensity of the laser beam 6 at the reference intensity when the image signal is on based on the output intensity of the laser beam P16, and a control circuit 42 that outputs a reference voltage signal to maintain the output intensity of the laser beam 6 at the reference intensity when the image signal is on. A timing circuit 43 that detects with a bin diode 9 and sends a sample hold (S/H) signal to an output adjustment circuit 42, an arithmetic circuit 44, a clock oscillator 45 shown in FIG. 5, and three counters 46a, 4.
6b, 46c and a D/A converter 47, and a correction data memory 48 formed in the ROM 33 shown in FIG.

In the laser drive circuit 40, the image signal input from the input/output port 37 is input to the base of the transistor 52 via the driver 51.
The signal at the collector of is input to the base of a transistor 53 connected in parallel to the laser diode 5. Further, the anode terminal of the laser diode 5 is connected to a drive voltage terminal of +12V, and the cathode terminal is grounded via a resistor and a transistor 54 for current control. A corrected reference voltage signal output from the arithmetic circuit 44 of the output correction circuit is input to the base of the transistor 54.

Therefore, when the image signal becomes H level, the transistor 52 becomes conductive and the transistor 53 is cut off, so that a driving current flows through the laser diode 5 and a laser beam 6 is output. The output intensity of the laser beam 6 is determined by the corrected base rp-voltage signal applied to the base of the transistor 54.

In the output adjustment circuit 42, a current corresponding to the output intensity of the laser beam 6 output from the laser diode 5 flows through the bin diode 41, but this current is converted into a voltage value by the operational amplifier 55 and then sent to the differential amplifier 5G. Group 11 consisting of a variable resistor and a Zener diode! It is compared with the reference voltage from voltage setter 57 and input to the input terminal of sample hold circuit 58 . This sample-and-hold circuit 58 samples the output voltage of the differential amplifier 56 that is input to the input terminal when the sample-and-hold (S/H) signal from the timing circuit 43 that is input to the S/Hm element becomes H level. Then, it is sent as a reference voltage signal to the one-stroke input terminal of the arithmetic circuit 44 of the output correction circuit. Furthermore, after the S/H terminal changes to L level, is the ceramic capacitor charged? The output voltage is held at the reference voltage by iJ for a time corresponding to one scan of the laser beam 6.

In the timing circuit 43, when the laser beam 6 is located at the scanning start position, a current flows through the bin diode 9. This current is converted into a voltage value by five operational amplifiers,
Furthermore, it is converted into an H-level logic signal by the voltage comparator 60, and is input to the trigger terminal of the monostable circuit 61 and sent to the CPU 31 via the input/output port 37.
i is sent as an end signal. When the monostable circuit 61 receives an H level signal from the voltage comparator circuit 60, it generates a sample hold (S/H) signal that remains at the H level for a predetermined time determined by the time constant of the resistor and capacitor from the signal input time. It is sent to the sample hold circuit 58 of the output adjustment circuit 42. This predetermined time is set to the time when the laser beam 7 is located at the scanning start position.

Therefore, the output intensity of the laser beam 6 when the laser beam 6 is located at the scanning start position is output to the arithmetic circuit 44 of the output correction circuit.

Then, a scanning start signal is sent from the CPLI 31, the rotating polygon mirror 2 rotates, and the laser beam 6 is scanned while being controlled on and off by the image signal.

The laser output intensity of the laser diode 5 at this time is controlled by a corrected reference voltage signal output from the arithmetic circuit 44 and described later.

Next, the output correction circuit will be explained. In Figure 5, ROM
AO to A1 of the correction data memory 48 formed in the
In order to correct the laser light intensity received by the fθ lens 4 shown in FIG. 10, the correction data shown in FIG. 6, which has a characteristic opposite to that shown in FIG. 10, is stored in each address of 1. That is, let the scanning start position of the fθ lens 4 be AO,
Correction data at each scan position X, which is obtained by dividing the fθ lens 4 into 12 equal parts whose scan end position is A11, is stored.

Then, from the clock oscillator 45, each counter 46a to 4
The period of the clock signal sent to 6C is set to the travel time when the laser beam 6 moves between each scanning position. Therefore, when a scanning start signal is input from the input/output boat 37, the laser beam 6 sequentially scans the anti-INf 13 (photosensitive drum 12), and at the same time the counter 46a
~46C is counting up. As a result, the addresses where each correction data corresponding to each scanning position x is stored are sequentially designated, and the correction data stored at the address is transferred from the data output terminals Do to D7 to the D/A converter 47.
sent to. The D,/A converter 47 converts the input digital correction data into analog correction data and sends it to the + side input terminal of the arithmetic circuit 44 in FIG. 1 via the buffer 62.

Since a reference voltage signal that maintains a constant voltage value during the scanning period from the output adjustment circuit 42 is input to one input terminal of the arithmetic circuit 44, the arithmetic circuit 44 is connected to the transistor 54 of the laser drive circuit 40. The output signal (corrected reference voltage signal) to be sent out is corrected at each scanning position X to have a signal waveform similar to the characteristics shown in FIG. Therefore, since the current flowing through the laser diode 5 during one scanning period has a waveform as shown in FIG. 6, the output intensity waveform of the laser beam 6 also has a waveform as shown in FIG. However, as described above, when the output intensity of the laser diode 5 is constant, the received light intensity characteristics at each scanning position X in the scanning direction of the photosensitive drum 12 are as shown in FIG. 9, as described above.
The received light intensity at each scanning position X on the photosensitive drum 12 has a substantially constant value as shown in FIG.

The average level of the received light intensity on the photosensitive drum 12 is automatically controlled by the output adjustment circuit 42 to the reference intensity set by the reference voltage setting device 57 based on the output intensity detected by the bin diode 41. Ru.

Therefore, the laser beam on the photosensitive drum 12 is $516.
The exposure intensity becomes constant over the entire scanning width, and the density of the image formed on the photosensitive drum 12 by exposure becomes uniform. Therefore, the printing quality of the entire laser printer can be improved without causing unevenness in the image transferred to the paper 17.

FIG. 8 is a circuit diagram showing a laser diode drive control circuit for a laser printer according to another embodiment of the present invention. Note that the same parts as those in the embodiment shown in FIG. 1 are given the same reference numerals and redundant explanations will be omitted.

In the output adjustment circuit 71 in this embodiment, the output intensity of the laser beam 6 is determined not by the bin diode 41 disposed close to the laser diode 5, but by the bin diode 9, which detects when the laser beam 6 is located at the scanning start position. To detect. That is, the output signal of the operational amplifier 59 of the timing circuit 43 is input to the differential amplifier 56 of the output adjustment circuit 71. Further, in the timing circuit 43, the output signal of the voltage comparator circuit 60 is inputted to the monostable circuit 61 described above, and also inputted to another monostable circuit 61a having the same configuration. The output signals outputted from the different output terminals Q and d are inputted to the S/H terminal of the sample and hold circuit 58 of the output adjustment circuit 71 as a sample and hold (S/H) signal via the AND gate 72.

Even in this configuration, fluctuations in the received light intensity of the laser beam 6 at each scanning position X in the scanning direction by the fθ lens 4 are corrected by the movement of the output correction circuit, so that the same effect as in the previous embodiment can be obtained. Is possible. Further, the reference voltage signal outputted from the output adjustment circuit 71 to the arithmetic circuit 44 of the output correction circuit is the reference voltage signal after the laser beam iI6 is reflected by each reflecting surface 7 of the rotating polygon mirror 2 when located at the scanning start position. It corresponds to the intensity of the laser beam 16. Therefore, this reference voltage signal is also corrected at the same time for minute differences in reflectance and the like on each reflecting surface 7Ll.

[Effects of the Invention] As explained above, according to the present invention, correction data for correcting fluctuations in the received intensity of the laser beam in the scanning direction generated by the fθ lens is stored, and the laser output during scanning is adjusted using this correction data. I am trying to correct the intensity. Therefore, the intensity of the laser beam received on the photosensitive drum can always be controlled to be constant, and the printing quality of the entire laser printer can be improved.

[Brief explanation of the drawing]

1 to 7 show a laser diode drive control circuit of a laser printer according to an embodiment of the present invention, FIG. 1 is a circuit diagram showing the laser diode drive control circuit, and FIG. 2 is a circuit diagram of the laser printer. 3 is a sectional view showing the exposure section, FIG. 4 is a block diagram showing the entire laser printer, and FIG. 5 is a block diagram showing the main parts of the laser diode drive control circuit. FIG. 6 is a characteristic diagram showing the correction data at each scanning position stored in the correction data memory, and FIG. 7 is a characteristic diagram showing the laser light reception intensity on the photosensitive drum for explaining the effect.
FIG. 8 is a circuit diagram showing a laser diode drive control circuit according to another embodiment of the present invention, FIG. 9 is a diagram showing the configuration of a general exposure section, and FIG. 10 is a circuit diagram showing a conventional laser diode drive control circuit. FIG. 3 is a characteristic diagram showing the intensity of light received on the drum. 1... Case, 2... Rotating polygon mirror, 3... Reflector, 4... fθ lens, 5... Laser diode, 6
...Laser beam, 8...Scanning start position detection reading, 9,
41... Bin diode, 11... Housing, 12...
・Photosensitive drum, 14...Charging section, 15...Exposing section,
16... Developing section, 17... Paper, 18... Transfer section, 19... Static elimination section, 20... Cassette, 31...
CPU, 33...ROM, 34...RAM, 37
... Input/output boat, 38... Laser diode drive control circuit, 40... Laser drive circuit, 42... Output adjustment circuit, 43... Timing circuit, 44... Arithmetic circuit, 45... - Clock oscillator, 46a. 46b, 46c... Counter, 47... D/A converter, 48... Correction data memory, 58... Sample hold circuit, 61... Monostable circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Figure 4 (JOOmm) (0) (100
mm) Running distance bond'l! X Figure 6 Start/End/End (-100mm) (0) (100
mm) Fig. 7 ii ¥ = fX No. 8 Fig. 9 Fig. □ 1 ノ □ Scanning method χ Fig. 10

Claims (3)

[Claims] (1) At least a charging section, an exposure section, a developing section, and a transfer section are sequentially arranged along the circumference of the photosensitive drum, the charging section charges the photosensitive drum, and the exposure section turns on and off using an image signal. An image corresponding to the image signal is formed on the photosensitive drum by scanning the laser beam output from the off-controlled laser diode in the axial direction of the charged photosensitive drum using a rotating polygon mirror and an fθ lens. , in a laser printer that develops the formed image in a developing section and transfers the developed image to paper in a transfer section, a laser drive circuit that controls on/off the laser diode according to the image signal; an output adjustment circuit that detects the output intensity of the laser beam output from the laser diode and outputs a reference voltage signal to the laser drive circuit for maintaining the output intensity at a reference intensity when the image signal is turned on; a correction data storage means for storing correction data for each scanning position for correcting fluctuations in received intensity of the laser beam in the scanning direction of the photosensitive drum caused by the laser beam passing through the fθ lens; and the laser drive The present invention is characterized by comprising an output correction circuit that is inserted between the circuit and the output adjustment circuit and corrects a reference voltage signal corresponding to the scanning position output from the output adjustment circuit using the correction data. Laser diode drive control circuit for laser printers. (2) The laser according to claim 1, wherein the correction data storage means is a ROM that stores each correction data at each scanning position at each address corresponding to each scanning position. Printer laser diode drive control circuit. (3) The output correction circuit includes a clock oscillator that outputs a clock signal synchronized with the speed at which the laser beam moves between the scanning positions, and counts the clock signal in response to a scanning start signal of the laser beam. a counter circuit that starts and outputs a count value as a read address signal of the ROM; a D/A converter that converts each correction data read from the ROM into an analog value;
The laser according to claim (2), further comprising an arithmetic circuit that corrects the reference voltage signal output from the output adjustment circuit with analog correction data output from the /A conversion circuit. Printer laser diode drive control circuit.