JPH01164914A - Image recorder - Google Patents

Abstract

PURPOSE:To eliminate the need for a light receiving part only for detecting a synchronizing signal by determining the positions of a laser light source and a rotary deflection means so that a main beam reflected from a deflecting surface is made incident on a light detection means, detecting the incidence and outputting a synchronizing signal. CONSTITUTION:The laser light source 1 is set on such a position that the main beam is vertically incident on the deflecting surface 5 with the deflection by the deflecting surface 5 of the rotary deflection means 4 before scanning a photosensitive body 7 and a reflected to be made incident on the light detection means 22 for detecting the light quantity of a sub-beam. An identification circuit identifies concerning the output signal from the light detection means 22 between the time when only sub-beam is made incident and the time when the main beam reflected by the deflecting surface 5 is also made incident with the sub- beam and generates the synchronizing signal every scanning line. Since the synchronizing signal is generated by using the light detection means for monitoring the light quantity in the laser light source, the constitution of a laser optical system can be simplified.

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.

Conventionally, in order to synchronize the image writing position for each line, 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 placed at the position where this photodiode is placed, and a photodiode for receiving light is provided at the other end of the optical fiber, and a 4, 1I7 configuration is used for indirect synchronization.

(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 that does not require a light receiving section (photodiode) dedicated to detecting a synchronization signal.

(Means for Solving the Problems) An image recording apparatus according to the present invention includes: a laser light source 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 photoreceptor on which an image irradiated with a beam deflected by a means is recorded line by line, the laser light source described above emits a sub beam in addition to a main beam for irradiating the photoreceptor. The laser light source is provided with a photodetecting means for detecting the light intensity of the sub-beam, and the laser light source is configured such that the main beam is perpendicular to the deflection surface before scanning the photoreceptor by deflection by the deflection surface of the rotational deflection means. incident on and reflected,
It is installed at a position where the above-mentioned sub-beam is incident on the light detection means for detecting light m, and regarding the output signal of the above-mentioned light-detection means, when only the sub-beam is incident and when the main beam reflected by the deflection surface is also incident. The present invention is characterized in that it includes an identification circuit that identifies each scanning line and generates a synchronizing signal for each scanning line.

(Function) When the main beam emitted from the laser light source enters the deflection surface perpendicularly and the reflected light enters the light detection means for monitoring the light amount provided inside the laser light source, the identification circuit is activated. This is detected and a synchronization signal is output. For this reason, the positions of the laser light source and the rotary deflection means are determined so that the main beam is reflected from the deflection surface and enters the photodetection means.

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

FIG. 1 schematically shows the optical system of a laser printer. The main beam emitted from the semiconductor laser I is corrected into parallel light by a collimator lens 2, and further focused onto one deflection surface 5 of a polygon mirror 4 by a cylindrical 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 an fθ lens 6, and is scanned while being imaged on the photoreceptor 7.

The positional relationship between the main beam emitted from the semiconductor laser I and the deflection surface 5 is such that the main beam is perpendicular to the deflection surface 5 in the non-image area before the main beam is scanned onto the photoreceptor 7 by the deflection surface 5. stipulated in Therefore, when the deflection surface 5 becomes perpendicular to the main beam, the main beam is focused on the deflection surface 5 and reflected, and then passes through the cylindrical lens 3 and the collimator lens 2 and enters the semiconductor laser l again. Become.

Note that conventionally, the main beam from the semiconductor laser 1 was prevented from entering 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. 2(a) and 2(b), the semiconductor laser 1 includes a laser diode chip 21 that emits laser light.
In addition, a photodiode 2 for detecting the laser beam m
2 is provided on the side opposite to the opening window 23. The main beam of the laser diode depth 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 is directed to the photoreceptor 7 as shown in FIG.
reach.

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, the intensity of the light beam emitted from the laser diode depth 21 is detected indirectly 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. 3, the relationship between the output and current of the semiconductor laser I is significantly dependent on temperature. Therefore, a photodiode 22 is placed inside to compensate for the decrease in output due to self-heating and stabilize the output.

By the way, if this photodiode 22 can be used to detect a synchronizing signal for each scanning line, there is no need to separately provide a photodiode dedicated to detecting a synchronizing signal. Therefore, in this embodiment, as shown in FIGS. 1 and 4, before the main beam scans the photoreceptor 7, the main beam is incident perpendicularly on the deflection surface 5, and the main beam reflected on the deflection surface 5 is redirected. It is made incident on the semiconductor laser 1. This re-entering main beam is simultaneously superimposed on the sub-beam emitted from the laser diode chip 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, each scanning line necessary for drawing an image on the photoreceptor 7 can be detected. It can be used as a synchronization signal.

FIG. 5 shows a circuit diagram for controlling the light amount of the semiconductor laser 1 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 IX voltage 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). As shown in FIG. 6(a), the threshold voltage g of the comparator 102 is the output voltage of the comparator 102 when only the sub beam is incident on the photodiode 22, and the output voltage when the main beam is incident again on the photodiode 22. It is set so that it can be distinguished from the output voltage of the comparator 102. Therefore, (b
), while the main beam is re-entering the semiconductor laser 1, the output voltage of the comparator 102 is at a high level and can be used as a synchronizing signal for each scanning line.

Laser output control is performed as follows. The current flowing through the laser diode chip 21 flows through two transistors Il.
l, 112. As shown in FIG. 6(f), the image data r necessary for drawing is sent from a host computer, etc., and input to the OR gate 113, and when the image data is at a high level, a constant current is applied to the transistor 111. flows.

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 using only the transistor III, the responsiveness of the optical output will deteriorate due to the transient characteristics of the optical output. So, transistor! It is necessary to keep the current flowing in step 12. The light output value at this time is
Only the transistor 112 is the laser diode chip 2I
When current is flowing through the photoreceptor l, the setting is such that the level of light emitted is low enough to draw an image on the photoreceptor l. Specifically, it is set below level E in FIG. 3 (the level before the output increases). When current flows through both transistors 111 and 112, the light output is sufficient to fully expose the photoreceptor 7 (level E in FIG. 3).
t) is 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 111 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 transistor ! Applied to the base of +2. Therefore, transistor 112
Here, 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 chip 21 is constant.

The sample hold circuit is analog switch 121, C
It consists of an R circuit 122 and an operational amplifier 123. The reason why the sample and hold circuit is interposed between the amplifier 101 and the transistor 112 is to perform optical output control 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 extremely difficult to perform control to keep the optical output constant during the period of

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 before entering the image recording area (that is, when the main beam re-enters the semiconductor laser I). 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 I again. If there is no CR circuit 122,
Since the photodiode 22 is held when receiving an optical output equal to or greater than a specified value, the current value is held at the current 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 at the time of 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. To provide this timing, a one-shot multi-by-break 124 and an OR gate 125 are used. The synchronizing signal output from the comparator 102 is also sent to the one-shot multi-by break 124 and the OR gate 125, and the output C of the one-shot multi-by break 124 is
The signal is sent to an analog switch 121 and an OR gate 125.

As shown in FIG. 6(C), the one-shot multi-by-break [24] becomes "0" at the forward advancing edge of the synchronizing signal, that is, at the time of re-incidence of the main beam, and ensures that the image recording period is over. , after a predetermined time t+'e has elapsed,
Returns to high level due to forced emission of laser. Therefore, the analog switch 121 is open during the image recording period and does not perform feedback control to keep the optical output constant. On the other hand, the OR gate 125 calculates the logical sum d between the synchronizing signal and the signal C, and drives the transistor 111 via the OR gate 13. As a result, while the analog switch +21 is closed and the laser light output is being sampled, the laser diode depth 2I is forced to emit light, and while the main beam is re-entering the semiconductor laser 1, the laser is emitted. maintain the state and reliably extract the synchronization signal.

(Effects of the Invention) Since the synchronization signal is generated using the light detection means for monitoring the amount of light inside the laser light source, the construction of the laser optical system is simplified. Moreover, costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing an optical system of a laser printer. FIGS. 2(a) and 2(b) are a plan view and a cross-sectional view, respectively, of a semiconductor laser. FIG. 3 is a graph of the current dependence of the output of the semiconductor laser. FIG. 4 is a diagram schematically showing the state of re-incidence of the main beam. FIG. 5 is an output control circuit diagram of a semiconductor laser. FIG. 6 is a timing diagram of the output control circuit. FIG. 7 is a graph of an example of current control. ! ... Semiconductor laser, 4 ... Polygon mirror, 5 ... Deflection surface, 7 ... Photoreceptor, 21
...Laser diode depth, 22...Photodiode, 102...Comparator, Ill, +12...Transistor, 121-123...Sample and hold circuit. Patent applicant Minolta Camera Co., Ltd. agent Patent attorney Aoyama Ao Two idiots Figure 2
Figure 4 Figure 3'. “020” Denmo

Claims (1)

[Claims] (1) A laser light source that generates a main beam of laser light, a rotational deflection means having a deflection surface that deflects this beam as it rotates, and an image irradiated by the beam deflected by the rotational deflection means line by line. In an image recording apparatus having a photoconductor for recording, the laser light source generates a sub beam in addition to a main beam for irradiating the photoconductor, and a photodetector is provided for detecting the light intensity of the sub beam. In the laser light source, the main beam is incident perpendicularly to the deflection surface before scanning the photoreceptor by deflection by the deflection surface of the rotary deflection means, and is reflected, and a photodetector for detecting the amount of light of the sub-beam is used. It is installed at a position where the output signal of the photodetecting means is incident on the light detecting means, and distinguishes between when only the sub beam is incident and when the main beam reflected by the deflection surface is also incident, and synchronizes each scanning line. An image recording device characterized by comprising an identification circuit that generates a signal.