JPH04146465A - Electrophotographic recorder - Google Patents

Abstract

PURPOSE:To carry out recording with excellent printing position precision without having adjustment by carrying out arrangement so that a photodiode incorporated in a semiconductor laser unit is irradiated with laser light reflected by means of a polygon mirror, and producing an image writing out timing signal in a main scanning direction with the detection output of the reflected light and a reference clock for printing data. CONSTITUTION:A laser 2 is forcibly lighted, and when the polygon mirror 3 obtains regulated revolving speed, the forming wave form (h) of the light detecting wave form (g) of the photodiode 13 is compared with the count value of the output (i) of a reference clock generating circuit 28, on a timing generating circuit 18. In other words, the reference clock (h) is counted for a period that the forming wave form signal (h) receives reflected laser light, that is, for a low level period, the signal (h) for writing out an image in the mains canning direction, which is made incident after that, is delimited with a count value corresponding to the half of the counted value, and reference timing corresponding to a writing position is produced through the use of the delimiting timing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic recording apparatus that forms an image by an electrophotographic recording method by raster scanning a beam of a semiconductor laser.

[Prior Art] An example of the configuration of a laser scanner portion of such a conventional electrophotographic recording apparatus is shown in FIG. FIG. 8 is a view of the device from above, where 1 is a semiconductor laser unit, 2 is a semiconductor laser unit, and 2 is a semiconductor laser unit.
3 is a collimator lens that converts the laser beam into parallel light; 3 is a polygon mirror (rotating polygon mirror) that scans the beam; 5 is a toric lens; 6 is an fθ lens; and 7 is a photosensitive drum. Further, 30 is a reflecting mirror, and 31 is a photodetector.

The semiconductor laser in the semiconductor laser unit 1 blinks at a specified light intensity according to the ON/OFF state of the image signal. A laser front beam emitted from a semiconductor laser is converted into parallel light by a collimator lens 2, and is irradiated onto a polygon mirror 3. The light reflected by the polygon mirror 3 is passed through a toric lens 5. The light passes through the fθ lens 6 and is irradiated onto the photoreceptor drum 7, forming an electrostatic latent image. In order to make the laser light of the semiconductor laser a specified light intensity, the semiconductor laser back beam in the semiconductor laser unit 1 is also
It is detected by a photodiode inside and automatically controls the amount of light.

In order to determine the main scanning start position on the photosensitive drum 7, a semiconductor laser is forcibly turned on at a predetermined rotational position of the polygon mirror 3, and the reflection mirror 30 is irradiated via the polygon mirror 3. The laser beam reflected by the reflecting mirror 30 is guided to a photodetector 31. As a method for guiding this light, an optical fiber is often used in order to install the photodetector 31 at an arbitrary location that is less likely to be affected by external noise.

The photodetector 31 is composed of elements such as a PIN photodiode. The output of the photodetector 31 is shaped into a waveform and is used as a main scanning direction image writing timing signal. .

[Problems to be Solved by the Invention] However, in the conventional example as described above, in order to accurately align the image writing ratio position in the main scanning direction, that is, to ensure that the laser beam is incident on the photodetector 31, Delicate adjustments are required in the process of aligning the reflecting mirror 30 and the photodetector 31, and this adjustment has been a factor that significantly reduces production efficiency. Furthermore, since it is necessary to add an extra reflecting mirror and a photodetector, it is also disadvantageous in terms of manufacturing cost.

In view of the above-mentioned points, an object of the present invention is to eliminate the need for the above-mentioned reflecting mirrors and photodetectors and to achieve delicate alignment of them.
The object of the present invention is to provide an electrophotographic recording device that can improve production efficiency and reduce manufacturing costs without making adjustments.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a semiconductor laser and a photodiode for detecting the back beam of the laser.
a semiconductor laser unit enclosed in one case; a means for outputting print data in synchronization with a reference clock and driving the semiconductor laser based on the print data;
a rotating polygon mirror that raster-scans a front beam from the semiconductor laser onto a photoreceptor, and the reference clock according to a reflected light detection output of the photodiode indicating that a return beam reflected from the rotating polygon mirror has been received. and means for generating an image write timing signal in the main scanning direction based on the counted value of the reference clock.

[Function] In the present invention, a photodiode built into a semiconductor laser unit is arranged so as to be irradiated with laser light reflected by a polygon mirror, and a timing signal for writing an image in the main scanning direction is detected by detecting this reflected light. Since it is generated from the output and the reference clock for print data, it is possible to record with high print position accuracy without adjustment, without having to separately install a dedicated photodetector for the image writing signal in the main scanning direction. .

Therefore, the present invention eliminates the need for a delicate and highly accurate positioning process, so production efficiency can be improved without any adjustment, and manufacturing costs can also be reduced because an independent reflection mirror or photodetector is not required.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Similar! 1 and 2 show the configuration of a laser scanner portion of a first embodiment of the present invention, with FIG. 1 being a perspective view and FIG. 2 being a plan view showing the optical path accurately.

In the figure, IA is a semiconductor laser chip 1 to 2 with a built-in photodiode, 2 is a collimator lens, 3 is a polygon mirror, and 4 is a motor that rotates the polygon mirror 3 in the direction of the arrow in the figure. A toric lens 5 corrects the inclination of each reflective surface of the polygon mirror 3 and also serves as an imaging lens. 6 is an fθ lens, which corrects the optical distance to the photosensitive drum 7.

FIG. 3 shows the structure of the unit IA of the semiconductor laser shown in FIG. This semiconductor laser unit LA is generally commercially available. Also, the circuit symbol LD on the right side of the figure is a laser diode, P[) is a photodiode,
The cathode of the laser diode and the anode of the photodiode are commonly connected. Terminals a, b, and c in the circuit symbol correspond to leads a, b, and c in the same figure. 8 is a cap that isolates the laser diode and photodiode from the outside air. 9 is a window glass. IO is a mounting block made of metal such as iron or copper. 11 is a base, on which a laser diode 12 and a photodiode 13 are mounted.

The laser beam from the laser chip 12 is transmitted through the window glass 9.
The light is output in two directions: a front beam in the direction of , and a back beam in the direction of the photodiode 13 . By detecting the back beam with the photodiode 13, the amount of laser light can be monitored.

FIG. 4 shows the circuit configuration of the control circuit according to the first embodiment of the present invention. Here, an image controller 14 develops input print code data sent from a host computer (not shown) into dot image data and stores it in a buffer memory 15. The buffer memory 15 converts the image print data into the reference clock i of the reference clock generation circuit 28.
Output in sync with. 16 is related to image print data (
This is a forced lighting circuit that forces the laser to turn on, and is used when adjusting the amount of laser light. Reference numeral 17 denotes an OR circuit (logical sum circuit) which calculates the logical sum of the image print monitor 15 and the forced lighting signal. A timing generation circuit 18 generates a signal to the memory 15 for determining the image writing position in the main scanning direction. 19 is a waveform shaping circuit, which includes a photodiode (PD
) 13 is inputted through the amplifier circuit 25 and the comparison circuit 20, and is compared with the reference signal Vs to generate a waveform-shaped signal. 21 is a D/A (digital to analog) converter that converts the digital value determined by the counter circuit 22 into an analog signal. 23 is an amplifier circuit that amplifies the output of the D/A converter 21. 26 is a voltage/current converter that converts the voltage output e of the amplifier circuit 23 into a current. The laser diode (LD) 12 is driven by the 8-power current of the converter 26. 27 is a switch circuit, O
The output f of the R circuit 17 causes a laser diode (LD)
The current flowing through 12 is set to 0N10FF.

Here, the front beam from the laser diode (LD) 12 is FB, the back beam is BB, and the polygon mirror 3
The reflected beam from RB is expressed as RB. Further, although not shown here, a collimator lens 2 (see FIGS. 1 and 2) is present between the laser diode (LD) 12 and the polygon mirror 3. The reflected beam RB from the polygon mirror 3 passes through the window glass 8 shown in FIG. 3 and is irradiated onto a photodiode (PD) 13.

FIG. 5 shows details from the semiconductor laser unit IA to the polygon mirror 3 shown in FIGS. 1 and 2. In FIG. Here, 32 is a heat dissipation fin, which suppresses temperature fluctuations of the semiconductor laser unit IA and also serves as a holder for the collimator lens 2. The reflected beam from polygon mirror 3 is indicated by the chain line RB.
Indicated by The reflected beam RB passes through the collimator lens 2 and enters the semiconductor laser unit IA.

The mirror surface of the polygon mirror 3 is in the angle range from ρ to n,
The reflected beam RB is incident on the photodiode 13 within the semiconductor laser unit l. Therefore, the output of the photodiode 13 at this time changes as shown by signal g in FIG. The image export position in the main scanning direction! In order to accurately determine the laser emission position or collimator lens 2
It is better to accurately determine the angle of the polygon mirror 3 viewed from the beam exit position.

However, due to the limits of processing accuracy of the polygon mirror 3, the reflecting surface may be tilted to some extent, and although the angle of the reflecting surface is recognized by receiving the reflected beam from the polygon mirror 3, the beam spot is not narrowed down. Therefore, the angle of the reflecting surface cannot be recognized accurately. Therefore, in normal laser printers, in order to detect when the polygon mirror 3 has reached steady rotation, the laser is forcibly turned on and the laser beam is detected by a detection circuit that determines the image writing position in the main scanning direction. It is recognized that the time until detection 8, that is, the period of the photodetection signal, has become a constant value.

The same thing can be done with the photodiode 13 in the semiconductor laser unit IA in the laser printer of this embodiment.
This is done using That is, in this embodiment, when the laser 12 is forcibly turned on and the polygon mirror 3 reaches a specified rotation speed, the shaping waveform of the photodetection waveform g of the photodiode 13 and the counting of the output i of the reference clock generation circuit 28 are performed. The comparison with the value is performed by the timing generation circuit 18.

In other words, as shown in FIG. 6, the reference clock i is counted during the period when the shaped waveform signal is receiving the laser reflected light, in this example, during the low level period, and the count value corresponding to % of the counted value is counted. (If it is not divisible by 2, then before or after it) is used to separate the signals for starting the image in the main scanning direction that are subsequently incident, and this timing is used to generate a reference timing according to the writing start position. This function is the fourth
It is included in the timing generation circuit 18 shown in the figure. Here, it goes without saying that if the period of the reference clock i is made sufficiently smaller than the time for sending out one dot of image printing, the accuracy of the image writing position in the main scanning direction can be improved.

FIG. 7 shows the output timing of signals from each part of the circuit of FIG. 4. Here, the output signal of the amplifier circuit 23 is e, the output signal of the OR circuit 17 is f, the output signal of the amplifier circuit 25 is g,
The output signal of the waveform shaping circuit 19 is assumed to be h. When a print signal is received from a host computer (not shown),
Control is performed to adjust the amount of laser light to a specified value. Time t1
Then, the output signal f of the OR circuit 17 becomes high level by the forced lighting circuit 16. At the same time, the counter circuit 22 starts counting up, and the signal e gradually increases. As a result, the optical output of the laser diode 12 gradually increases, the reverse current of the photodiode 13 increases, and the level of the output signal g of the amplifier circuit 25 decreases. At time t2 when the level of the reference signal (voltage) Vref and the signal g become equal in the comparator circuit 20, the counter circuit 22 stops counting up, the hold circuit 24 holds the count value, and the signal e becomes a constant value. .

Considering the overshoot of the laser light output and the responsiveness of the photodiode 13, it is better to set the time t2 at which the signal e is held after a certain period of time has elapsed after the signal g becomes equal to the reference signal Vref. Common. Subsequently, at time t8, forced lighting is stopped, and at time t4, forced lighting is performed with a signal in order to obtain the image writing timing in the main scanning direction.

At this point, the polygon mirror 3 has already reached the specified rotation speed.

When the reflective surface (mirror surface) of the polygon mirror 3 comes to the position shown in FIG. Photodiode (PD) 13
detects the reflected light of the back beam and front beam,
The output signal g exhibits a voltage value even lower than the reference signal Vref. Therefore, a pulse-like low level is applied to the output signal by the waveform shaping circuit 19 having a reference signal of Vs.

At the next time t, the forced lighting is stopped, and the image print data is output to the switch circuit 27 a predetermined time t seconds after the timing generation circuit section 18 described above, that is, the timing of count 4 in FIG. Image print data is output until time t6, and line printing in the main scanning direction is completed.

From the next time t, the printing operation for the second line is performed in the same manner as described above. The same applies to the third and subsequent lines.

In this embodiment, the signal level, rising edge, and falling edge are determined as shown in FIG. 7, but these may vary depending on the control circuit system.

Australia's arrival Next, a second embodiment of the present invention will be described.

The device configuration of this embodiment is the same as that of the first embodiment of the present invention described above. In the first embodiment of the present invention, as shown in FIG. 6, by counting the reference clock i when the signal is at a low level, the image writing timing signal in the main scanning direction is generated using the predetermined count value. If the surface precision of each reflective surface of the polygon mirror 3 shown in FIG. 2 is not constant, the above-mentioned count value may also vary depending on each reflective surface. Therefore, in this second embodiment, the reference clock i is counted for each reflecting surface in the same way as in the first embodiment, and the count values of the reference clock 1 are detected which are an integral multiple of the number of surfaces of the polygon mirror 3. Then, based on the average value of the count values, a reference timing corresponding to the image writing position in the main scanning direction is generated as in the first embodiment. Thereby, it is possible to cope with the case where the surface precision of the above-mentioned irregular surface is not uniform.

Further, a third embodiment of the present invention will be described. The device configuration of this embodiment is the same as that of the first embodiment of the present invention described above. Normally, the device configuration is such that the positional relationships among the semiconductor laser unit, each lens system, and the polygon mirror do not change. Therefore, in this embodiment, the first
Alternatively, the count value of the reference clock i obtained by the method of the second embodiment is stored in the device's built-in storage device (for example,
The program is stored in the program ROM), and when printing, based on the stored count value, a reference timing is generated according to the image writing pressure position in the main scanning direction, similar to the first embodiment. .

[Effects of the Invention] As explained above, according to the present invention, the return beam of the laser front beam reflected from the polygon mirror is made incident on the photodiode built in the semiconductor laser unit, and the image writing timing in the main scanning direction is adjusted. Since the signal is generated by the reflected light detection output, which is the output of this photodiode, and the reference clock for print data, there is no need to newly provide a separate photodetector exclusively for the image writing signal in the main scanning direction. , it is possible to achieve the effect of making it possible to record with high print position accuracy without any adjustment.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of a laser scanner portion of a first embodiment of the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a diagram showing the structure of the semiconductor laser unit in FIGS. 1 and 2. FIG. 4 is a block diagram showing the configuration of a control circuit according to an embodiment of the present invention; FIG. 5 is a sectional view showing details of the irradiation section of the semiconductor laser unit in FIG. 3; FIGS. FIG. 7 is a timing chart showing the signal timing of the circuit shown in FIG. 4, and FIG. 8 is a plan view showing the configuration of a conventional laser scanner section. 1, IA... semiconductor laser unit, 2... collimator lens, 3... polygon mirror 4... motor, 5... toric lens. 6...fθ lens, 7...photosensitive drum, 12...laser chip (laser diode) 13...
·Photodiode. Figure 2 Figure 5 Cause Figure 6

Claims (1)

[Claims] 1) A semiconductor laser unit in which a semiconductor laser and a photodiode for detecting the back beam of the laser are enclosed in one case; means for driving the semiconductor laser based on data; a rotating polygon mirror that raster-scans a front beam from the semiconductor laser onto a photoreceptor; and a photoreceptor indicating that a return beam reflected from the rotating polygon mirror has been received. An electronic photograph characterized by comprising means for counting the reference clock according to the reflected light detection output of the diode, and means for generating an image writing timing signal in the main scanning direction based on the counted value of the reference clock. Recording device.