JPS63147644A - Output control apparatus of semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent the variation of beam output and to prevent inferior writing, by a method wherein a judge means is provided to judge whether the beam output of a semiconductor laser is fixed to a predetermined value in predetermined timing to store said beam output. CONSTITUTION:A beam detector 10 for detecting the beam output of semiconductor laser 1 and a laser driving circuit 9 allowing the current corresponding to the output signal of the detector 10 to flow to the semiconductor laser 1 are provided. A judge memory means for setting a timing signal permitting the alteration of the beam output of the semiconductor laser by a receiving permitting signal, an optical scanning permitting signal and a timing signal and judging whether the above-mentioned beam output is fixed to a predetermined value during the output of the timing signal to stored said beam output is provided. The beam scanning in an inferior state can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an output control device for a semiconductor laser for optical writing used in a BS6 laser printer or the like.

BACKGROUND OF THE INVENTION Generally, in laser printers and the like, images are formed by irradiating a photoreceptor with a light output corresponding to an image signal from a semiconductor laser. A characteristic of semiconductor lasers is that their output intensity is extremely unstable with respect to temperature. Therefore, in an environment where the ambient temperature of the semiconductor laser changes, it is necessary to stabilize the output intensity of the semiconductor laser using a semiconductor laser output control device or the like. For this reason, for example, Japanese Patent Application Laid-Open No. 60-17186 by the present applicant
Output control devices such as a counter type as shown in Publication No. 3 have been proposed.

However, no matter which output control method is used, the allowable time for the control is short in a scanning system such as a printer.

This is because the light output of the semiconductor laser must be performed at a timing in a region where the photoreceptor is not irradiated. As a result, when attempting to control the optical output of the semiconductor laser to a predetermined value using the output control device, it may not be possible to set the optical output to the predetermined value within a predetermined timing.

However, conventionally, even if the value is not set to a predetermined value, the image forming operation is performed as is. If optical writing scanning is performed in such a state, a good quality image cannot be obtained due to instability or insufficient light quantity, resulting in a erroneous image and a waste of printing paper.

Purpose The present invention has been made in view of the above points, and the present invention has been made to improve the output of a semiconductor laser, which can be used to prevent optical scanning in a defective state, detect an abnormality, etc. by recognizing the control state of the optical output. In order to achieve the above object, the present invention includes a light detection means for detecting the light output of a semiconductor laser, and a current that corresponds to the output signal of the light detection means to be transmitted to the semiconductor laser. In a semiconductor laser output control device, a semiconductor laser output control device is provided with a semiconductor laser drive circuit that allows a semiconductor laser to output a signal to a semiconductor laser, and a predetermined timing signal that allows a change in the optical output of the semiconductor laser is set, and the optical output is changed during output of a certain timing signal. The present invention is characterized in that a determination storage means is provided for determining and storing whether the value is fixed at a predetermined value.

Hereinafter, one embodiment of the present invention will be described based on the drawings. Voices, JP-A-60-171863, etc.

The basic configuration and operation of an optical writing device using a semiconductor laser as shown in FIG. 2 will be explained with reference to FIG.

The laser beam generated by the semiconductor laser 1 is collimated by the collimator lens 2 to form the rotating polygon #l113 and the rotating polygon #! The beam is deflected by an optical scanning device including a drive motor 4 that rotates the beam. The deflected laser beam is imaged by the fθ lens 5 onto the charged surface of the photoreceptor drum 6. The imaging spot of this laser beam moves repeatedly in the direction of arrow X by the rotation of the rotating polygon mirror 3 (
The photoreceptor drum 6 rotates at the same time (main scanning) (sub-scanning)
. A photodetector 7 is provided outside the upper writing area of the photosensitive drum 6, and detects the laser beam deflected by the rotating polygon mirror 3 to generate a synchronization signal BD. The signal processing circuit 8 applies the information signal to the semiconductor laser drive circuit 9, and its timing is controlled by the synchronization signal BD from the photodetector 7. This semiconductor laser drive circuit 9 drives the semiconductor laser 1 according to the information signal from the signal processing circuit 8. Therefore, the laser beam modulated by the information signal is irradiated onto the photosensitive drum 6 to form an electrostatic latent image. This electrostatic latent image is developed in a developing section according to an electrophotographic process or the like, and then transferred to paper or the like in a transfer section.

Further, the laser beam emitted backward from the semiconductor laser 1 is incident on the photodetector 1o, and its light intensity is detected. Then, the control circuit 11 controls the semiconductor laser drive circuit 9 according to the output signal of the photodetector 10, thereby controlling the output light amount of the semiconductor laser 1 to be constant.

1 shows the details of the semiconductor laser drive circuit 9 and the control circuit 11 in FIG. 2, and FIG. 3 shows the timing of signals at each part. A laser beam emitted backward from the semiconductor laser 1 is incident on a photodetector 10 constituted by a photodiode, and the photodiode 10 outputs a current proportional to the intensity of the laser beam. This detected current is amplified and converted into a voltage by an amplifier 12, and a comparator 13
It is compared with the reference voltage Vref at the same time. Here, the output voltage of the comparator 13 becomes a high level or a low level depending on the magnitude relationship between the two input voltages to the comparator 13, and controls the counter mode of the up/down counter 14. For example, when the intensity of the laser beam from the semiconductor laser 1 is weaker than the reference value, the output of the comparator 13 becomes a low level,
The up/down counter 14 is in a state where it operates as an up counter. This up/down counter 14 has D.
A semiconductor laser drive circuit 9 is connected via a /A converter 15 .

When a predetermined timing signal T8 is input to the edge detection circuit 16 as shown in Japanese Patent Application Laid-Open No. 60-171863, the JK flip-flop 17 is cleared by this timing signal T, and its output signal becomes low. By reaching the level, the up/down counter 14 becomes enabled. Further, the output signal of the comparator 13 is latched by the D flip-flop 18 using the clock signal from the oscillator 19, and the output signal of the second D flip-flop 18 is applied as a counting mode signal to the up/down counter 14 to change its counting mode. At the same time as controlling, the D flip-flop 20 latches the clock signal from the oscillator 19. The non-inverted output of the D flip-flop 18 and the inverted output of the D flip-flop 20 are input to a NOR circuit 21, and the JK flip-flop 17 is set by the output signal of the NOR circuit 21.

Now, assume that the output of the comparator 13 is at a high level (the optical output of the semiconductor laser I is greater than the reference value). In such a case, the timing signal T and the output down counter 14
is enabled, the up/down counter 14
operates as a down counter due to the high level output of the D flip-flop 18. Therefore, the driving current of the semiconductor laser 1 decreases, and the output voltage of the amplifier 12 decreases. Then, when the output of the comparator 13 is inverted from high level to low level, the output of the D flip-flop 18 becomes low level, the output of the NOR circuit 21 becomes high level, and the JK flip-flop 17 is set to up/down. counter 1
4 is disabled.

On the other hand, it is assumed that the output of the comparator 13 is at a low level (the optical output of the semiconductor laser 1 is smaller than the reference value). In such a case, the up/down counter 1 is controlled by the timing signal T.
4 is enabled, up/down counter 1
4 operates as an up counter due to the low level output of the D flip-flop 18. Therefore, the driving current of the semiconductor laser 1 increases, and the output voltage of the amplifier 12 increases.

Then, when the output of the comparator 13 goes from low level to high level, the output of the D flip-flop 18 goes high, and the up/down counter 14 starts to operate as a down counter. At this time, the output of the NOR circuit 21 remains at a low level, the JK flip-flop 17 is not reset, and the up/down counter 14 remains enabled.

That is, the up/down counter 14 is not disabled when the optical output of the semiconductor laser 1 increases and exceeds the reference value, but becomes disabled when the optical output of the semiconductor laser 1 decreases and exceeds the reference value. . Therefore, the holding current of the semiconductor laser 1 is always constant.

By the way, when the signal processing circuit 8 receives a frame signal T2 indicating the start of transmission of an information signal from an external device (not shown), the signal processing circuit 8 generates a synchronization signal BD obtained by amplifying and converting the detection signal from the photodetector 7 into a voltage using the amplifier 22. D at the timing according to
It is latched by the flip-flop 23 and outputs a signal T6 permitting reception of information data. Next, the signal processing circuit 8 outputs a signal L-5sync requesting information data after a predetermined timing based on the synchronization signal BD.

When the external device receives this L-5 sync signal, it sends one line of information data to the signal processing circuit 8 after a predetermined timing.
send to The signal processing circuit 8 receives this one line worth of information data and inputs it to a line buffer (not shown). Here, there is also a method in which the semiconductor laser 1 is directly driven to generate a modulation signal without taking the information data into the line buffer, and the modulated signal is irradiated onto the photosensitive drum 6 to form an electrostatic latent image. However, since the information data transfer speed capability of external devices differs depending on each external device, in order to provide versatility,
A common method is to provide a line buffer and temporarily store data in this line buffer as in this embodiment. More specifically, a so-called toggle line buffer system is adopted in which line buffers are provided for two lines and information data is received from an external device and read out for output to the semiconductor laser 1 alternately.

Next, the D flip-flop 24 latches the reception permission signal T in response to the synchronization signal BD and outputs a signal T permitting optical scanning. Further, the signal processing circuit 8 generates an optical scanning start signal T l after a predetermined timing based on the synchronization signal BD.
Output l. As a result, information data is read from the line buffer described above, and this information data is sent to the semiconductor laser drive circuit 9 to be used as a modulation signal. Incidentally, at time 2, the signal processing circuit 8 is receiving the second line of information data from the external device in parallel, and taking it into the other line buffer.

When the external device finishes sending information data for a predetermined line, it stops outputting the frame signal T. Therefore, the signal processing circuit 8 latches the frame signal T using the synchronization signal BD and stops outputting the reception permission signal T. Subsequently, as in the case described above, after a predetermined timing has elapsed from the synchronization signal BD, the optical scanning start signal T I 1 is outputted to read the information data from the line buffer and use it as a modulation signal. After one line of optical scanning is completed, the next synchronizing signal BD causes the D flip-flop 24 to output a reception permission signal T.

is latched, the output of the optical scanning permission signal T is stopped, and the series of optical scanning is completed.

The configuration and operation described above are similar to those shown in Japanese Patent Application Laid-Open No. 60-171863.

Since the light intensity of the semiconductor laser 1 varies depending on the temperature,
As mentioned above, the light intensity is detected and controlled to a predetermined value, but such control timing is determined by the semiconductor laser 1.
must be within a range in which the output light does not irradiate the photoreceptor drum 6. Also, a photodetector 10, an amplifier 12, a comparator 13
Considering the variation in the optical output of the semiconductor laser 1 due to the temperature characteristics of the D/A converter 15, resetting the optical output during the repetition of optical scanning for one page means that the optical output during optical scanning of the previous line A difference occurs between the intensity and the light intensity during optical scanning after resetting, and this difference becomes a difference in image density, which may make the image difficult to see. For this reason, it is preferable not to reset the optical output while repeating optical scanning for one page. Therefore, in this embodiment, in order to set the output light amount of the semiconductor laser 1, a timing signal T, which is a predetermined timing signal that allows a change in optical output, is used as a reception permission signal T, an optical scanning permission signal T, and which AND An inverted output signal T7 is created by inverting the AND signal from the circuit 25 by the NOT circuit 26, and this inverted output signal T, a timing signal T in a range in which the semiconductor laser 1 does not irradiate the photoreceptor drum 6 when outputting light, It is generated by the AND circuit 27 with the AND circuit 27. More specifically, the timing signal T8 is a short pulse signal for clearing the JK flip-flop 17, and the timing signal T,
is converted into a short pulse signal through the pulse generator 39 and then input to the AND circuit 27. Further, the pulse width of the timing signal T1 is preferably shorter than the pulse width of the signal output from the oscillator 19.

Note that the timing signal T3 for generating the timing signal T1 is generated by, for example, a circuit as shown in FIG. That is, in order to reset the light intensity within a range where the output light does not irradiate the photoreceptor drum 6, the pulse output from the oscillator 28 whose frequency is fixed is synchronized with the synchronization signal B.
Counting with counters 29 and 30 using D as a reference,
The count values of these counters 29 and 30 are stored in the control ROM 3.
1 as address data, the ROM 31 outputs data corresponding to the address and takes out the signal T j l. Therefore, at the timing of this signal TsI, the semiconductor laser 1 is brought into a light emitting state, and the photodetector 10 and the amplifier 1
A short timing signal for generating a signal T that clears the JK flip-flop 17 and permits resetting of the light intensity after a period of time when the states of the comparator 2 and the comparator 13 reach stable values corresponding to the output light. Output T. Thereby, the up-down counter 14 performs the above-described operation as an up-counter or a down-counter based on the output of the comparator 13.

A D flip-flop 32 serving as a determination storage means is connected to the JK flip-flop 17 of the edge circuit 16. This D flip-flop 32 inputs the timing signal Ts1, enables the up/down counter 14 by the timing signal T1, detects that the output signal of the comparator 13 is inverted in a predetermined direction, and disables the up/down counter 14. Able J
The timing signal T l l is latched by the output signal T of the K flip-flop 17 . That is, while the predetermined timing signal T l given for resetting the output light amount is being generated, the output signal of the comparator 13 is inverted in one predetermined direction, and the JK flip-flop 17 outputs an up/down counter. 14 is disabled and a signal T indicating that the optical output is fixed at a predetermined value;
It has a function to determine whether or not the output has been output.

If the determination result in the D flip-flop 32 is affirmative, a signal T is output to notify that the optical output has been fixed at a predetermined value, and an LED or the like is turned on by this signal T. The display 33 is the driver 34
It is provided through. On the other hand, D flip prop 3
If the determination result in step 2 is negative, a signal T is output.

Here, an AND circuit 35 and a D flip-flop 36 are provided to output the optical output abnormality signal T I 4 only when the timing signal T l l for starting optical scanning is generated. A display 37, such as an LED, is provided via a driver 38, and is turned on in response to an abnormality signal T l 4 from the second D flip-flop 36 to indicate the occurrence of an abnormality.

That is, at a predetermined timing T5 before optical scanning, the presence or absence of an abnormality is detected and stored in the D flip-flop 32, and the signal T is also at the L level as shown by the imaginary line in FIG. If there is an abnormality at the timing of the optical scanning start signal T I 1 for the actual optical scanning, the signal T I 3 and therefore the abnormality signal T I 4 are output based on the signal -, and measures such as write prohibition are taken. As a result, operations such as defective image formation are not performed while the amount of laser beam remains unstable, and the occurrence of defective images is prevented. Further, since an abnormality is displayed on the display 37 in parallel with such measures, it becomes easy to discover the location and cause of the abnormality during maintenance and inspection, and the time required for maintenance and inspection can be shortened.

The D flip-flop 32 is cleared by a pulse generator 39 which receives the information data reception permission signal T and generates a short pulse when the signal T6 is generated. That is, it is cleared in preparation for resetting the optical output immediately before starting optical scanning. Further, the D flip-flop 36 is set to be cleared by a return signal T l 6 inputted after the abnormal processing is completed.

Further, in this embodiment, the timing signal T, which allows changing the optical output, is the reception permission signal T. , the optical scanning permission signal T, and the timing signal T, but a short pulse signal output from the pulse generator 39 to which the predetermined timing signal T is input may be used as the timing signal T as it is.

This includes, for example, a photodetector 10, an amplifier 12, a comparator 13
In cases where fluctuations in the optical output of the semiconductor laser 1 due to the temperature characteristics of the D/A converter 15 can be ignored, 1
This is because it may be better to reset the optical output every time a line is optically scanned.

Furthermore, in this embodiment, the up/down counter 14 is enabled only when the optical output of the semiconductor laser 1 decreases and exceeds the reference value, but conversely, the optical output of the semiconductor laser 1 increases and exceeds the reference value. The up/down counter 14 may be enabled only when the value exceeds the value.

Effects As described above, the present invention controls the current flowing through the semiconductor laser to keep the optical output constant in order to prevent fluctuations in the optical output due to temperature. Since it is determined at a predetermined timing whether the output is fixed at a predetermined value and stored, this stored judgment result can be used to prevent defective writing in situations where the optical output is not fixed to a predetermined value. It can also be used for abnormality detection, and allows optical writing to be performed without producing defective images.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a block diagram, FIG. 2 is a schematic block diagram showing the configuration of a laser printer, FIG. 3 is a timing chart, and FIG. 4 is a block diagram. 1... Semiconductor laser,... Semiconductor laser drive circuit,
10... Photodetector (light detection means), 32... D flip-flop (judgment storage means) 33 Figure-゛

Claims (1)

[Claims] A semiconductor laser output control device comprising a photodetection means for detecting the optical output of a semiconductor laser, and a semiconductor laser drive circuit that causes a current to flow in the semiconductor laser according to an output signal of the photodetection means, A determination storage means is provided which sets a predetermined timing signal that allows a change in the optical output of the laser, and determines and stores whether the optical output is fixed at a predetermined value while a certain timing signal is being output. Semiconductor laser output control device.