JPH01164915A - Image recorder - Google Patents

Abstract

PURPOSE:To constantly control the outputs of laser light beams by forcing a semiconductor laser to emit light out of period for recording images and performing the detection of synchronizing signals and the sampling of outputs from a light detection means. CONSTITUTION:Before scanning a photosensitive body 7, a main beam is made vertically incident on a deflection surface 5. The output signals from the light detection means 22 are identified between the time when only sub-beam is made incident and the time the main beam reflected by the deflection surface 5 is also reflected and the synchronizing signal of every scanning line is generated. And a current is supplied to the semiconductor laser 21 so that the outputs of the laser light beams become constant corresponding to the sampling values of the outputs from the light detection means 22. Thus, the detection of the synchronizing signals and the constant control of the outputs of the laser light beams are performed based on the detection signals of the light detection means 22 and the constant control of the light output can be performed without receiving the effect of the detection of the synchronizing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a recording device using a semiconductor laser in a laser printer.

(Prior Art) In a laser printer, a rotating polygon motor deflects a laser beam to write (record) one line of image data on a photoreceptor.

In order to synchronize the image writing position for each line, conventionally a photodiode is placed in a non-image area in the optical path of the laser beam, and each time the laser beam passes through this photodiode, the output signal of this photodiode is 1 more
Detects the image writing synchronization signal for each line. Further, an optical fiber is arranged at the position where this photodiode is arranged, and a photodiode for receiving light is provided at the other end of the optical fiber, so that synchronization is achieved indirectly.

(Problems to be Solved by the Invention) Conventional synchronization signal detection requires a dedicated light receiving section (photodiode).

An object of the present invention is to provide an image recording device with a simple configuration in a laser printer.

(Means for Solving the Problems) An image recording apparatus according to the present invention includes: a semiconductor laser that generates a main beam of laser light; a rotational deflection means having a deflection surface that deflects this beam as it rotates; In an image recording apparatus having a photoconductor on which an image irradiated by a beam deflected by a beam is recorded line by line, the semiconductor laser described above has a secondary beam in addition to the main beam that irradiates the photoconductor. The semiconductor laser described above includes a light detection means for generating a beam and detecting the amount of light of this sub-beam,
The main beam is installed at a position where the main beam is perpendicularly incident on the photoreceptor to be scanned by the deflection of the rotational deflection means before being deflected, is reflected, and is incident on the light detection means for detecting the amount of light of the sub-beam. An identification circuit for discriminating between the output signal of the photodetecting means described in ``-'' when only the sub beam is incident and when the main beam reflected by the deflection surface is incident, and generates a synchronizing signal for each scanning line. and sample-hold means for sample-holding the output of the photo-detecting means; current supply means for supplying current to the semiconductor laser so that the laser light output is constant in accordance with the sampling value of the sample-hold means; A current is supplied to the current supply means for causing the semiconductor laser to emit light for at least the period required for synchronization signal detection, and the sampling value during this period is kept small to record an image signal on the photoreceptor during the synchronization signal detection period. The present invention is characterized by comprising current supply control means for causing the sample and hold means to hold the period.

(Function) During the period of recording an image signal, the laser light output of the semiconductor laser is generated intermittently at high speed in response to the image signal, so it is difficult to control the light output at a constant level. Therefore, the semiconductor laser is forced to emit light during a period including at least the synchronization signal detection period outside the image recording period, and the synchronization signal is detected and the output of the light detection means is sampled. During the image recording period, this sampling value is held to control the optical output of the semiconductor laser.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 schematically shows the optical system of the laser printer. The main beam 1 emitted from the semiconductor laser 1 is collimated into parallel light by a collimator lens 2, and further focused onto one deflection surface 5 of a polygon mirror 4 by a norlindrical lens 3. The main beam focused on the deflection surface 5'' is deflected according to the rotation of the polygon mirror 4 (clockwise in the drawing), passes through the rO lens 6, and is scanned while being focused on the photoreceptor 7.

The positional relationship between the main beam emitted from the semiconductor laser l and the deflection surface 5 is such that the main beam or non-image area is perpendicular to the deflection surface 5 before the main beam is scanned onto the photoreceptor 7 by the deflection surface 5. Set it like this. Therefore, when the deflection surface 5 becomes perpendicular to the main beam, the light is focused on the deflection surface 5 and the reflected main beam! , passes through the lindrical lens 3 and the collimator lens 2 and enters the semiconductor laser 1 again. Note that conventionally, the main beam from the semiconductor laser 1 was not incident perpendicularly to the deflection surface 5. This is because when the main beam returns to the laser diode 1, laser generation becomes unstable.

As shown in FIGS. 3(a)' and 3(b), the semiconductor laser l includes a laser diode chip 2 that emits laser light.
1, a photodiode 22 for detecting the amount of laser light is provided on the side opposite to the aperture window 23. The main beam of the laser diode chip 21 is emitted in two directions to an aperture window 23 and a photodiode 22 for monitoring the amount of light. The main beam passing through the aperture window 23 reaches the photoreceptor 7 as shown in FIG.

On the other hand, the sub beam directed toward the photodiode 22 is used to keep the amount of light emitted from the laser diode deep 21 constant. That is, since the intensity of the light beam emitted from the laser diode chip 21 is indirectly detected through the photodiode 22 based on the intensity of the sub beam,
The current flowing through the laser diode chip 21 is decreased or increased in response to an increase or decrease in the amount of light detected by the photodiode 22.

As shown in FIG. 4, the relationship between the output and current of the semiconductor laser 1 is significantly dependent on temperature. Therefore, a photodiode 22 is placed inside to compensate for the temperature drop in output due to self-development and stabilize the output.

By the way, if this photodiode 22 can be used to detect the synchronizing signal for each scanning line, there is no need to separately provide a photodiode dedicated to detecting the synchronizing signal. Therefore, in this embodiment, as shown in FIG. 2 and FIG. Let it enter the semiconductor laser 1 again. This re-entering main beam is simultaneously superimposed on the sub-beam emitted from the laser diode depth 21 and enters the photodiode 22. Therefore, by distinguishing and extracting the intensity of the sub beam detected by the photodiode 22 and the intensity of the main beam superimposed on the sub beam and re-entering, it is possible to detect each scanning line necessary for drawing an image on the photoreceptor 7. It can be used as a synchronization signal.

FIG. 1 shows a circuit diagram for controlling the light amount of the semiconductor laser I and detecting a synchronizing signal, and FIG. 6 shows a timing chart thereof.

The synchronization signal is detected as follows. Photodiode 2
2 is a photoelectric converter, and the current flowing through the photodiode 22 changes depending on the intensity of the light beam. The current is converted into a voltage, but since this voltage is minute, it is amplified by the operational amplifier 101. Next, the amplified voltage a is compared with the threshold voltage g by the comparator 102. The output voltage of the comparator 102 becomes a synchronization signal and is sent to a laser printer control system (not shown). This comparator! 0
The threshold voltage g of 2 is, as shown in FIG. 6(a),
It is set so that the output voltage of the comparator 102 when only the sub beam is incident on the photodiode 22 and the output voltage of the comparator 102 when the main beam is incident on the photodiode 22 again can be distinguished. Therefore, as shown in FIG. 6(b), while the main beam is re-entering the semiconductor laser l, the output voltage of the comparator 102 is at a high level and is used as a synchronizing signal for each scanning line. be able to.

Laser output control is performed as follows. The current flowing through the laser diode chip 21 flows through two transistors II.
+, +12. As shown in FIG. 6(f), image data f necessary for drawing is sent from a host computer, etc., and input to OR gate II3, and when the image data is at a high level, a constant current is applied to transistor 21. Flow.

On the other hand, current is always allowed to flow through the other transistor 112 as well. This is because if the current flowing through the laser diode chip 21 is switched from Ov only by the transistor III, the responsiveness of the optical output will deteriorate due to the transient characteristic of the optical output. Therefore, it is necessary to cause a certain current to flow through the transistor 112. The light output value at this time is set so that when only the transistor 112 is sending current to the laser diode chip 21, the light emission state is at a low level that is insufficient to draw an image on the photoreceptor 1. . Specifically, level E in Figure 4
, set below (the level before the output increases). When current flows through both transistors I11 and I112,
A light output sufficient to fully expose the photoreceptor 7 (level E in FIG. 4) should be generated.

As shown in FIG. 7, an example of control for keeping the laser light output constant is that the current flowing through the transistor 112 (hatched in FIG. (The current flowing through the transistor Il+ is not controlled.) in accordance with the amount of light received by the photodiode 22. That is, both transistors 11
The voltage detected by the photodiode 22 with current flowing through the transistors 1 and 112 is amplified by the operational amplifier 101 and then applied to the base of the transistor 112 via the sample bold circuit. Therefore, transistor 112
Then, the collector current is controlled so that the output voltage a of the operational amplifier 101 is constant, that is, the intensity of the light beam emitted from the laser diode deep 21 is constant.

The sample hold circuit is an analog switch 121, C
It consists of 11 circuits + 22 and an operational amplifier 123. The sample and hold circuit consists of an amplifier 101 and a transistor 112.
The reason for intervening between them is to control the light output only outside the image recording area.

In the image recording area, drawing is performed by generating or ceasing generation of the main beam in accordance with the image signal. However, the light output immediately after the semiconductor laser 1 is activated is unstable, and there is also a delay in the control circuit to keep the light output constant. It is very difficult to perform control to keep the advance output constant during

Therefore, as will be explained later, the analog switch 121 is closed outside the image recording area, sampling is performed, and the analog switch 12+ is closed when the song enters the image recording area (that is, when the main beam re-enters the semiconductor laser l). Open and hold the sampled and constant light output. In the image recording area, an image is recorded using this held optical output.

The CR circuit 122 in the sample and hold circuit is used to delay the response of the feedback system. In this embodiment, the optical output is held when the main beam enters the semiconductor laser 1 again. If there is no CR circuit +22,
Since the photodiode 22 is held when receiving an optical output equal to or greater than a specified value, the current value is bolded to the value when feedback acts in the direction of reducing the current of the transistor 112. Therefore, the time constant of CR is determined so as not to hold the output of the photodiode 22 upon re-incidence, and the response of the feedback system is delayed. In this way, the output e of the operational amplifier 123 is stabilized as shown in FIG. 6(e), and the synchronization signal detection circuit is prevented from affecting the laser light output control circuit.

Next, the timing of light output control will be explained. Use one-shot multi-by-break 124 and OR gate 125 to provide this timing. The synchronizing signal output from the comparator 102 is sent to the one-shot multivibrator 124 and the OR gate +25, and the output C of the one-shot multivibrator 124 is
It is sent to analog switch 121 and 01z gate 125.

As shown in Figure 6 (C), one shot multi-bye break! 24 is the positive advancing edge of the synchronization signal, that is, it becomes 0 when the main beam re-enters, and after the image recording period has elapsed and a predetermined time j+ has elapsed, it becomes high level due to forced emission of the laser. Return to Therefore, the analog switch 121 is open during the image recording period and does not perform feedback control to keep the previous output constant.

On the other hand, the OR gate 125 takes the logical sum d of the synchronizing signal C and the signal C, and the transistor 1
11. This allows analog switch +21
closes and while sampling the laser light output, the laser diode depth 2I is forcibly brought into a light emitting state, and while the main beam is re-entering the semiconductor laser 1, the light emitting state of the laser is maintained; Accurately extract the synchronization signal.

(Effects of the Invention) Based on the detection signal of the light detection means, synchronization signal detection and laser first-out car window control can be performed. The front car window can be controlled without being affected by synchronization signal detection.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an output control circuit of a semiconductor laser. FIG. 2 is a diagram schematically showing the optical system of the laser printer. FIGS. 3(a) and 3(b) are a plan view and a cross-sectional view of a semiconductor laser, respectively. FIG. 4 is a graph of the current dependence of the output of the semiconductor laser. FIG. 5 is a diagram schematically showing the state of re-incidence of the main beam. FIG. 6 is a timing chart of the output control circuit. FIG. 7 is a graph of an example of current control. l... Semiconductor laser, 4... Polygon mirror, 5... Deflection surface, 7... Photoreceptor, 21
...Laser diode chip, 22...Photodiode, +02...Comparator, Ill, 112...Transistor, 121-123
...Sample and hold circuit. Figure 3 Figure 5

Claims (1)

[Claims] (1) A semiconductor laser that generates a main beam of laser light;
In the image recording device described above, the image recording device includes a rotary deflection means having a deflection surface that deflects the beam as it rotates, and a photoreceptor on which an image irradiated with the beam deflected by the rotary deflection means is recorded line by line. The semiconductor laser generates a sub beam in addition to the main beam for irradiating the photoreceptor, and includes a photodetection means for detecting the amount of light of the sub beam, and the semiconductor laser is configured to deflect Before scanning the photoreceptor by deflection by the surface, the main beam is perpendicularly incident on the deflection surface, is reflected, and is installed at a position where it enters the light detection means for detecting the amount of light of the sub-beam; Regarding the output signal, an identification circuit that discriminates between when only the sub beam is incident and when the main beam reflected by the deflection surface is also incident, and generates a synchronization signal for each scanning line; and the output of the photodetecting means described above. sample-and-hold means for holding the sample; current supply means for supplying current to the semiconductor laser so that the laser light output is constant in accordance with the sampling value of the sample-and-hold means; Current supply control means causes the current supply means for causing the semiconductor laser to emit light to supply current, and causes the sample hold means to hold the sampled value during this period at least during the synchronization signal detection period and the period during which the image signal is recorded on the photoreceptor. An image recording device comprising: