JP2002067382A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent mistake to take a beam detection signal by a foregoing beam for a beam detection signal by a following beam. SOLUTION: In an image forming device that does a deflection scanning of several optical beams 2a and 3a that are modulated in response to an image signal generated from several LD units 2 and 3 by a polygon mirror 4, forms image on a photoreceptor drum 1 at a specific interval in main scanning direction, and generates and records the image signal based on the beam detection signal by a beam detector 6 arranged in front of an effective writing area of the main scanning direction, a foregoing light beam 2a is turned on before a light beam 2a that precedes the beam detector 6 reaches, it is turned off after the beam detector 6 activates the beam detection signal, a following light beam 3a is turned on after the beam detector 6 stops activating the beam detection signal, and it is turned off after a beam detection means activates the beam detection signal again.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser printer, a digital copying machine, and a facsimile machine equipped with a writing optical system for simultaneously recording a plurality of lines by using a plurality of independently modulating recording light sources. Related to the device.

[0002]

2. Description of the Related Art Hitherto, a multi-beam image forming apparatus equipped with a writing optical system for simultaneously recording a plurality of lines using a plurality of light beams has been proposed. Such a multi-beam image forming apparatus can write an image of a plurality of lines on one surface of a polygon mirror, so that high-speed writing can be performed using a low-speed rotating polygon motor and a low-output laser diode. have.

In a multi-beam image forming apparatus, in order to simultaneously record data for a plurality of lines using a plurality of light beams, it is necessary to align the scanning timing of each beam. Therefore, a method is adopted in which laser light is incident on the photodetector before writing of an image is started at the beginning of scanning, and a writing start position is controlled by an output signal thereof.

In the image forming apparatus using one light beam, the same write start position control is performed because the write position needs to be constant for each line. However, in an image forming apparatus using a plurality of light beams, it is necessary to control the second and subsequent light emission timings, so that some measures are required, and various methods have been proposed.

[0005] First, in the simplest case, if the scanning beam positions of a plurality of light beams are aligned in the main scanning direction, it is not necessary to take the timing of the remaining beams by setting the timing with one beam. It can be easily realized. However,
After aligning a plurality of beams in the main scanning direction, the beam interval in the sub-scanning direction is kept constant, for example, 63.5 μm (400 dp).
It is optically difficult to keep in i). In addition, a function of a variable writing density is also required, and therefore, it is necessary to switch a beam pitch in the sub-scanning direction, which is further difficult.

Therefore, a method has been proposed in which the scanning position of the light beam is separated to some extent in the main scanning direction, and the laser pitch is adjusted or switched in the sub-scanning direction by rotating the laser emitting unit. JP-A-57-647
Japanese Patent Application Publication No. 18-182173 discloses one detector for detecting a scanning position of one light beam among a plurality of light beams having a known interval in the main scanning direction, and another detector based on an output of the detector. A laser printer provided with a delay circuit for controlling the start of recording of a light beam is described.

[0007] Also, Japanese Patent Application Laid-Open No. 2-42413 discloses that
It is described that a digital copying machine is provided with separating means for separating and outputting a light beam for generating an image writing timing signal from a plurality of light beams incident on a beam detecting means.

Japanese Patent Laid-Open Publication No. Hei 6-344593 discloses that a photodetector is provided with a plurality of slits in a multi-beam recording apparatus. In 2
It has been proposed to attach a polarizing plate having a polarization direction different by 90 degrees to two photodetectors. In addition, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 796 describes a method of detecting a scanning position by a plurality of light beams with a single detector in a multi-beam image forming apparatus.

[0009]

However, the method described in Japanese Patent Application Laid-Open No. 57-64718 has a problem that when the interval in the main scanning direction fluctuates due to the environment and the variation of the machine,
Adjustment is difficult because there is no feedback. Further, when the beam pitch changes when the writing density is changed, it is necessary to change the delay time.

The digital copying machine described in Japanese Patent Application Laid-Open No. 2-42413 has disadvantages in that it is difficult to set the threshold level of the light beam separating means and the circuit is complicated. The one described in JP-A-6-344591 requires a slit plate having a special shape.
Since two photodetectors and a polarizing plate are required, the cost is high.

Further, in the case of the method described in Japanese Patent Application Laid-Open No. 10-151796, a delay time from when a light beam is incident on the beam detecting means until the beam detection signal becomes active, There is a delay time from when the light beam incident on the laser beam passes or when the light beam is turned off until the beam detection signal becomes negative.

Therefore, if the time from turning off the preceding beam to turning on the succeeding beam is too short, the beam detection signal may not be negative even if the preceding beam is turned off. Therefore, the beam detection signal of the preceding beam may be erroneously detected as the beam detection signal of the following beam.

The problem of this conventional example will be described with reference to FIG. FIG. 10 is a timing chart of an abnormal operation caused by the conventional multi-beam imaging apparatus. As shown in this figure, the forcible lighting signal BD of the preceding light beam
1 for a while, the beam detection signal XD
ETP remains active. In this specification and the drawings, the symbol “X” at the beginning of a signal signifies a low active signal.

The timing for activating the forcible lighting signal BD2 of the succeeding light beam is set by the CPU immediately before the succeeding light beam reaches the beam detecting means, but it follows the preceding light beam. When the interval between the light beams is short, the forcible lighting signal BD of the succeeding light beam while the beam detection signal XDETP is in the active state
2 will be active. Then, the beam detection signal of the preceding light beam is erroneously detected as the beam detection signal of the following beam, and is output as XDETP2.

Since XLDSYNC2 is activated by XDETP2, the compulsory lighting signal BD2 of the succeeding light beam is negated, and the following light beam is turned off. No detection signal is generated, and no pulse is generated at the timing indicated by the dotted line that would occur during normal operation.

As will be described later, XLDSYNC1, XLD
The SYNC2 signal is output to the image input unit, and is used as a synchronization signal for synchronizing the image data from the image input unit with the image writing. An image having a shifted position is formed.

The present invention has been made to solve this problem, and can be manufactured at a low cost and with high accuracy with a simple structure, and detects a beam detection signal of a preceding beam by a succeeding beam. An object of the present invention is to provide an image forming apparatus that does not erroneously detect a signal.

[0018]

According to the present invention, in order to achieve the above object, a plurality of light beam generating means and a light beam generated by each of the light beam generating means according to an image signal are modulated. A plurality of modulating means; a deflecting means for deflecting and scanning the light beam generated by each light beam generating means; and an image forming apparatus for condensing the plurality of deflected and scanned light beams at predetermined intervals in the main scanning direction. Means, and a beam detection means disposed at a position before the effective writing area in the main scanning direction and activating a beam detection signal when each light beam is received, and a beam detection signal output from the beam detection means In the image forming apparatus which performs the recording operation by generating the image signal based on the above, the following first or second light beam control means is provided.

The first light beam control means turns on the preceding light beam before the preceding light beam reaches the beam detection means, and activates the beam detection signal after the beam detection means activates the beam detection signal. Turns off the preceding light beam, turns on the succeeding light beam after the beam detection means no longer activates the beam detection signal, and turns on the subsequent light beam after the beam detection means generates the beam detection signal again. This is a means for controlling the plurality of light beam generating means so as to turn off the beam.

The second light beam control means turns on the preceding light beam before the preceding light beam reaches the beam detection means, and activates the beam detection signal after the beam detection means activates the beam detection signal. The preceding light beam is turned off, and after a predetermined time elapses after the beam detection unit does not activate the beam detection signal and after a lapse of a predetermined time from when the beam detection unit activates the beam detection signal, the following light beam is activated. This is a means for controlling the plurality of light beam generating means so as to be turned on, and after the beam detecting means generates a beam detection signal again, the subsequent light beam is turned off.

In this image forming apparatus, it is preferable to provide a means for changing a predetermined time from turning off the preceding light beam to turning on the following light beam in accordance with the scanning speed. Further, it is preferable to provide means for separating a beam detection signal by a plurality of pulses from the beam detection means into a beam detection signal of each light beam by using any one of the signals for lighting the plurality of light beams.

If the beam detection means does not activate the beam detection signal within a predetermined time after the subsequent light beam is turned on, means for turning off the subsequent light beam may be provided. If the beam detection unit does not activate the beam detection signal within a predetermined time after the subsequent light beam is turned on, a unit for performing error processing and displaying an error message may be provided.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. In the multi-beam image forming apparatus shown in FIG. 1, reference numerals 2 and 3 denote LD units each incorporating a semiconductor laser (hereinafter abbreviated as "LD") for generating a light beam modulated according to modulation data. It is.

Reference numeral 4 denotes a polygon mirror, which is a deflecting means for deflecting and scanning the light beam generated from each of the LD units 2 and 3. The polygon mirror 4 is rotated at a constant rotation speed by a motor (not shown). Reference numeral 5 denotes an fθ lens, which focuses two light beams deflected and scanned by the polygon mirror 4 on the photosensitive drum 1 at a predetermined interval in the sub-scanning direction to form an image, and It is an image forming means for scanning. Reference numeral 6 denotes a photodetector, which is disposed at a position before the effective writing area in the main scanning direction and generates a beam detection signal XDETP when receiving a light beam. 7, a beam splitter; and 8, a cylinder lens.

Reference numerals 9 and 10 denote a first LD modulator and a second LD modulator, which are modulation means for modulating and driving the LDs included in the LD units 2 and 3. Reference numeral 11 denotes a print control unit which receives a beam detection signal XDETP from the photodetector 6 and outputs modulation data to the first LD modulation unit 9 and the second LD modulation unit 10 based on image data from an image data input unit (not shown). I do.

In this multi-beam image forming apparatus,
The light beams respectively generated from the LD units 2 and 3 are combined by a beam splitter 7 and then transmitted through a cylinder lens 8 to be incident on a polygon mirror 4 rotating at a predetermined rotation speed, where it is deflected. After being scanned, the light is focused on the photosensitive drum 1 and the photodetector 6 via the fθ lens 5. The light beam 2a emitted from the first LD unit 2 is deflected by the same surface of the polygon mirror as the second light beam 2a.
Is scanned earlier than the light beam 3a emitted from the LD unit 3 of FIG.

Although an example using two LD units has been described here, an LD array in which a plurality of laser light sources are housed in one package may be used. Each of the two converged light beams has a diameter of 5 in the main scanning direction.
0 to 80 μm, diameter in the sub-scanning direction is 70 to 10
It is an ellipse of about 0 μm. The distance between the centers of the beams in the sub-scanning direction corresponds to the writing density.
At pi, it is adjusted to 63.5 μm. The center-to-center distance of the converged light beam in the main scanning direction is determined by the optical system, but is less accurate than adjustment in the sub-scanning direction, and is about 1 ± 0.2 mm in this example.

As shown in FIG. 3, the photodetector 6 includes a PIN photodiode 61 which is a light receiving element for performing photoelectric conversion,
A digital signal conversion circuit 62 converts the output into a binary digital signal, and outputs a beam detection signal XDETP which goes low when light is received. An IC in which the light receiving element and the electric circuit are contained in one package may be used, or the light receiving element and the electric circuit may be separated. Alternatively, the received light may be guided to a light receiving element using a fiber.

The shape of the light receiving portion 6a of the photodetector 6 is a rectangle long in the sub-scanning direction as shown in FIG. 2, and the light from the first LD unit 2 is located immediately before the effective writing area in the main scanning direction. The beam 2a and the light beam 3a by the second LD unit 3 are located at positions where both beams are incident.
The reason why the length of the light beam is long in the sub-scanning direction is to reliably catch the light beam even if the incident position of the light beam is slightly shifted due to a variation in mounting the photodetector or a variation in the mechanical of the optical system. Here, it is a rectangle of 0.5 mm × 3.0 mm. here,
An example in which the light receiving portion 6a of the photodetector 6 is rectangular will be described. However, the light receiving portion 6a may not be rectangular as long as the front edge of the light receiving portion 6a is substantially perpendicular to the main scanning direction.

When the two light beams illuminating the light receiving portion 6a of the photodetector 6 scan and cross, the beam detection signal XDETP of two pulses as shown in FIG. Is obtained. This beam detection signal XDE
When the light beam preceding in the main scanning direction reaches the light receiving portion 6a, a current flows through the PIN photodiode 61,
It goes low. Next, when the beam passes through the light receiving section 6a or when the light beam is turned off, no current flows through the PIN photodiode 61, and the PIN photodiode 61 becomes high level.
Further, when the light beam that follows in the main scanning direction reaches the light receiving section 6a, a current flows through the PIN photodiode 61, and the PIN photodiode 61 goes low again. After that, when the beam passes through the light receiving portion 6a or when the light beam is turned off, no current flows through the PIN photodiode 61, and the PIN photodiode 61 goes high again.

Assuming that the distance between the centers of the converged light beams in the main scanning direction is 1 mm and the diameter of the light beams in the main scanning direction is 80 μm, the gap in the main scanning direction of the light beams is 0.9.
2 mm. Since the width of the light receiving portion 6a of the photodetector 6 in the main scanning direction is 0.5 mm, the beam detection signal XDETP of two pulses is obtained as described above. The beam detection signal XDETP is input to the print control unit 11, and the print control unit 11 combines the image data from the image input unit (not shown) with the forced lighting signal of each LD unit for obtaining the synchronization detection signal. And outputs the modulated data of the two LD units 2 and 3 to the first and second LD modulators 9 and 10.

FIG. 5 shows an example of a circuit block of the print control unit 11.
Shown in The function of the print control unit is not limited to this, but only the part related to the present invention will be described here.
First, the clock generation circuit 12 includes a crystal oscillator and a PLL frequency synthesizer, and generates a print pixel clock LDCLK. Print pixel clock LDCLK
Is the first clock synchronization circuit 14 and the second clock synchronization circuit 15 which are separated by the pulse separation circuit 13
Are synchronized with the timings of the light beam synchronization detection pulse signal XDETP1 and the second light beam synchronization detection pulse signal XDETP2, and the first light beam modulation clock LDCLK1 and the second light beam modulation clock LDCLK2. Becomes

The first and second light beam synchronization detection pulse signals XDETP1 and XDETP2 are respectively the first and second synchronization detection pulse signals XDETP1 and XDETP2.
Light beam modulation clocks LDCLK1 and LDCLK
2 and become XLDSYNC1 and XLDSYNC2 having a predetermined pulse width. These LDCLK1,
LDCLK2 and XLDSYNC1, XLDSYNC
2 are output to an image input unit (not shown), and are used as a clock and a synchronization signal for synchronizing image data from the image input unit with image writing. Furthermore, X
The LDSYNC1 signal is also output to the reset terminal of the main scanning counter 16 to reset the main scanning counter 16.

The main scanning counter 16 has an XLDSYNC1
A binary counter that is reset by a signal and incremented by LDCLK1 allows the main scanning position of the light beam to be determined from the count value. The main scanning counter 16 has a number of bits that does not overflow during scanning of one line. The number of bits is 29
When printing an image on a 7 mm printing paper at 800 dpi, 14 bits are required.

The main scanning counter 16 has 3
The comparators 17 to 19 are connected to each other, and the first comparator 17 includes a BD 1 for forcibly driving the first LD unit 2 to detect synchronization of the first LD unit 2.
(Beam Detect) signal is generated. Therefore, the first comparator 17 is provided with CP which is a numerical value setting means for setting a numerical value variably thereto.
U (Central Processing Uni)
t) 20 is an I / F (Interface) register 21
, A count value A of the main scanning counter 16 and a numerical value B variably set by the CPU 20 in advance.
When the count value A exceeds the set value B, the output becomes active.

This output is ORed with the image data for the first LD unit 2 by the OR gate 22, which is a logical OR means, as a BD1 signal, and is output to the first LD modulator 9 shown in FIG. The first LD unit 2 that generates the light beam 2a preceding in the scanning direction is forcibly driven to emit light. At this time, the timing of the forced driving of the first LD unit 2 is such that the main scanning light scanned on the next surface of the polygon mirror after the main scanning light passes through the effective print area is received by the light receiving portion of the photodetector 6. Since it is necessary to be before reaching the light receiving portion 6a and it is necessary to prevent flare, the set value B is set to be immediately before the light receiving portion 6a of the photodetector 6.

When the preceding light beam 2a in the main scanning direction forcibly driven enters the light receiving portion 6a of the photodetector 6, the beam detection signal XDETP output from the photodetector 6 is output. Becomes active. When the beam detection signal XDETP is input to the pulse separation circuit 13, the first light beam synchronization detection pulse signal XDET
P1 is separated and output, and its signal is synchronized with the print pixel clock LDCLK by the first clock synchronization circuit 14, output as the XLDSYNC1 signal, and the main scanning counter 16 is reset.

BD for forcibly driving the first LD unit 2
The 1 signal is an output of the first comparator 17, and this comparator compares the count value A of the main scanning counter 16 with a numerical value B variably set by the CPU 20, and the set value B is used as the count value. When the main scanning counter 16 is reset, the BD1 signal is negated and the first LD unit 2 that generates the light beam 2a preceding in the main scanning direction is turned off when the main scanning counter 16 is reset. Then, when the main scanning counter 16 is reset, the counting is restarted, and this counting is repeated for each surface of the polygon mirror.

The second comparator 18 is provided for defining the start position of the BD2 signal for forcibly driving the second LD unit 3 for detecting the synchronization of the second LD unit 3, The CPU 20 compares a numerical value C set variably in advance with the count value A of the main scanning counter 16. When the count value A matches the set value C, the output signal becomes active.

The third comparator 19 is provided for defining a forced ending position of the BD2 signal for forcibly driving the second LD unit 3, and is provided with a numerical value D which is variably set in advance by the CPU 20 and a main value. The count value A of the scan counter 38 is compared. When the count value A matches the set value D, the output signal becomes active. An OR gate 19 whose output becomes active when either this output signal or the aforementioned XLDSYNC2 signal becomes active.
Is input to a reset terminal of a first SR flip-flop 24 described later.

The first SR flip-flop 24 is connected to the second
, And is reset when either the output of the third comparator 19 or the XLDSYNC2 signal becomes active. The output of the first SR flip-flop 24 is input to the AND gate 27. The other input of the AND gate 27 is the output of the second SR flip-flop 26. Second S
The output of the R flip-flop 26 is set when the XDETP signal goes negative (high), and the XLDSYNC
It is reset when one signal becomes active (low).
Therefore, the beam detection signal X by the preceding light beam 2a
When the DETP signal becomes active, the pulse separation circuit 13 and the first clock synchronization circuit 14
After the LDSYNC1 signal becomes active, its XD
Until the ETP signal returns to negative, the output of the second flip-flop 26 is low, otherwise it is high.

The output of the AND gate 27 is a BD2 signal for forcibly driving the second LD unit 3 for detecting the synchronization of the second LD unit 3. This BD2 signal is logically ORed with the image data for the second LD unit 3 by the OR gate 25 which is a logical OR means, and is output to the second LD modulator 10 shown in FIG. With this output, the second LD unit 3, which generates the light beam 3a following in the main scanning direction, is forcibly driven to emit light.

At this time, the timing of the forcible driving of the second LD unit 3 needs to be before the light beam 3a by the second LD unit 3 reaches the light receiving section 6a of the photodetector 6. Therefore, the set value C is set immediately before the light receiving unit 6a of the photodetector 6. Then, when the light beam 3a following in the main scanning direction forcibly driven as described above is incident on the light receiving portion 6a of the photodetector 6, the beam detection signal XDETP output from the photodetector 6 becomes active. become.

An outline of the time from when the preceding light beam 2a is detected to when the following light beam 3a reaches the light receiving portion of the photodetector can be obtained. Therefore, after detecting the preceding light beam 2a, By starting lighting of the following light beam 3a after a predetermined time, the lighting time of the following light beam 3a can be suppressed. Further, the time from when the preceding light beam 2a is detected to when the following light beam 3a reaches the light receiving portion 6a of the photodetector 6 varies depending on the scanning speed. When the scanning speed changes due to a change in the writing density or the like, the lighting start timing of the succeeding light beam 3a can be optimized to suppress the lighting time of the following light beam 3a.

Further, by providing the second RS flip-flop 26 and the AND gate 27, the BD2 signal is generated before the beam detection signal XDETP returns to negative (high) after the preceding light beam 2a is turned off. The subsequent light beam is not turned on. Therefore, unlike the conventional example shown in FIG. 10, the beam detection signal XDETP by the preceding light beam is not erroneously recognized as the beam detection signal XDETP by the following light beam.

The beam detection signal XDETP generated by the succeeding light beam 3a is separated and output by the pulse separation circuit 13 as a second light beam synchronization detection pulse signal XDETP2, and this signal XDETP2 is output to the second clock synchronization circuit 15 As a result, it is synchronized with the print pixel clock LDCLK and output as the XLDSYNC2 signal.

The XLDSYNC2 signal causes the first S
The R flip-flop 24 is reset, the BD2 signal for forcibly driving the second LD unit 3 is negated, and the second LD that generates the light beam 3a following in the main scanning direction is generated.
The unit 3 is turned off. The timing of turning off the succeeding light beam 3a is such that the beam detection signal XDETP of two separate pulses is provided if the second pulse goes low.
It is desirable to turn off the light immediately after the pulse goes low for the second time, because unnecessary light emission can be reduced and the influence of flare light can be reduced.

On the other hand, if the beam detection signal by the following light beam 3a is not detected for a certain period of time, the main scanning counter 1
6 becomes equal to the set value D, the output signal of the third comparator 19 becomes active, and the first R
The S flip-flop 24 is reset and the second LD
The BD2 signal for forcibly driving the unit 3 is negated,
The second LD unit 3 is turned off.

The set value D is set by the CPU 20 so that the output signal of the third comparator 19 becomes active after the timing when the synchronizing signal XLDSYNC2 becomes active if the operation is normal. Therefore, even when a failure occurs due to a failure of the second LD unit 3, unnecessary light can be prevented from being generated, and a situation in which writing is performed on the entire surface can be avoided.

The CPU 20 detects that the output signal of the third comparator 19 becomes active and turns off the second LD, thereby detecting the subsequent second LD.
Detecting that the photodetector 6 does not generate the beam detection signal XDETP within a predetermined time after the unit 3 is turned on,
The user is warned by performing error processing and displaying an error message on the display unit. Therefore, the user can immediately know the occurrence of the trouble, and can perform the repair quickly.

Next, an example of the circuit of the pulse separation circuit 13 is shown in FIG. The beam detection signal XDETP is the first LD
BD1 signal and second LD for forced drive of unit 2
By taking the logic of the BD2 signal for forced driving of the unit 3 and the NAND gates 31 and 32, respectively, as shown in FIG. 6, the synchronization detection pulse signal X for the first light beam is obtained.
DETP1 and synchronization detection pulse signal X for second light beam
DETP2 is separated and output. This is because when the BD1 signal for forcibly driving the first LD unit 2 is active, X
This is because the DETP signal is a beam detection signal by the first light beam, and the XDETP signal when the BD2 signal for forcibly driving the second LD unit 3 is active is a beam detection signal by the second light beam. .

FIG. 9 is a diagram showing each signal in this embodiment.
A timing chart similar to FIG. When the BD1 signal for forcibly lighting the preceding light beam is activated, the preceding light beam is turned on. When the preceding light beam reaches the light detector 6, the light detector 6 activates the beam detection signal XDETP. Then, the BD1 signal and the beam detection signal XDETP are supplied to the NAND gate 3 shown in FIG.
The logic is taken by 1 and the synchronization detection pulse signal XDETP
Activate 1

Further, the clock is synchronized with the clock by the clock synchronizing circuit 14, the XLDSYNC1 signal becomes active, and the main scanning counter 16 is reset by the signal, so that the BD1 signal is negated. Even if the BD1 signal is negated, the beam detection signal XDETP remains active for a while. After the beam detection signal XDETP becomes negative, the BD2 signal for forcibly lighting the following light beam is activated when the timing before the following light beam arrives at the photodetector 6 is determined. The running light beam is turned on. This timing is set by the set value C of the second comparator 18, but when the beam detection signal XDETP is active, B
A second flip-flop circuit 26 and an AND gate 27 are provided so that the D2 signal does not become active.

When the following light beam reaches the photodetector 6, the beam detection signal XDETP becomes active again. Then, the BD2 signal and the beam detection signal XDETP are
The logic is taken by the NAND gate 32 shown in FIG. 6 to activate the synchronization detection pulse signal XDETP2. Further, the clock synchronizing circuit 15 outputs the print pixel clock LDC
Synchronized with LK1, the XLDSYNC2 signal becomes active, which resets the first SR flip-flop 24 and negates the BD2 signal.

[Modification of Embodiment] In the above embodiment,
Second RS flip-flop 26 and AND gate 27
The logic circuit consisting of prevents the BD2 signal for forcibly driving the second LD unit 3 from being generated while the beam detection signal XDETP by the preceding light beam 2a is active. If the set value C can be set to an appropriate value, this logic circuit need not be provided.

If the beam detection signal XDETP due to the light beam 3a of the succeeding second LD unit 3 is not detected for a certain period of time, if the second LD unit does not need to be turned off and error processing and warning are not required, The XLDSYNC2 signal may be inverted and directly input to the reset terminal of the first flip-flop 24 without providing the third comparator 19 and the OR gate 23. Even with such a configuration, the other functions operate without any problem.

As the pulse separation circuit 13, in addition to the configuration shown in FIG. 6 already described, a configuration shown in FIGS. 7 and 8 can be used. First, the configuration shown in FIG. 7 will be described. In this configuration, unlike the configuration shown in FIG. 6, the beam detection signal XDETP is separated only by the BD1 signal for forcibly driving the first LD unit 2. The NAND gate 33 is the same as the NAND gate 31 shown in FIG. 6, except that the NAND gate 34 is the NAND gate 32 shown in FIG.
And different. In the configuration shown in FIG. 7, the negation of the BD1 signal is input to the NAND gate 34. Since the XDETP signal is generated by the second LD unit 3 while the BD1 signal is negative, the XDETP signal can be separated even with such a configuration.

Next, the configuration shown in FIG. 8 will be described.
In this configuration, contrary to the configuration shown in FIG.
The beam detection signal XDETP is separated only by the BD2 signal for forced driving of the unit 3. The NAND gate 36 is shown in FIG.
, But the NAND gate 35 is different from the NAND gate 31 in FIG. FIG.
In the configuration shown in FIG. 7, the negation of the BD2 signal is input to the NAND gate 35. Since the XDETP signal is generated by the first LD unit 2 while the BD2 signal is negative, even with such a configuration, the XDET signal can be obtained.
Separation of P signals can be performed.

In this embodiment, a multi-beam image forming apparatus using two light beams has been described as an example, but the present invention can also be applied to a multi-beam image forming apparatus using three or more light beams.

[0060]

As described above, according to the present invention, after the beam detection signal of the preceding light beam becomes negative, the succeeding light beam is turned on. There is no possibility that the beam detection signal is erroneously detected as a beam detection signal by the succeeding beam.

Further, by changing the predetermined time from turning off the preceding light beam to turning on the succeeding light beam in accordance with the scanning speed, even if the writing density is changed, the following light is emitted. The lighting time of the beam can be minimized, and the generation of flare light can be minimized. Further, the beam detection signal of a plurality of pulses from the beam detection unit can be separated into the beam detection signals of the respective light beams by using any one of the signals for lighting the plurality of light beams.

If the beam detection means does not activate the beam detection signal within a predetermined time after the subsequent light beam is turned on, the light beam generation means is turned off by turning off the subsequent light beam. However, even if a failure occurs, unnecessary light can be prevented from being generated. If the beam detection unit does not activate the beam detection signal within a predetermined time after turning on the subsequent light beam, the user performs error processing and displays an error message, so that the user can operate the light beam generation unit. You can know the failure quickly.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating a relationship between a light receiving unit of a photodetector and two light beams in the image forming apparatus.

FIG. 3 is a block diagram showing a configuration of the photodetector.

FIG. 4 is a waveform diagram of a beam detection signal XDETP output from the photodetector.

FIG. 5 is a block diagram illustrating a configuration example of a print control unit in FIG. 1;

FIG. 6 is a logic circuit diagram showing a configuration example of a pulse separation circuit in FIG. 1;

FIG. 7 is a logic circuit diagram showing another configuration example of the pulse separation circuit.

FIG. 8 is a logic circuit diagram showing still another configuration example of the pulse separation circuit.

9 is a timing chart illustrating waveforms of respective signals of a print control unit in the image forming apparatus illustrated in FIG.

FIG. 10 is a timing chart showing waveforms of respective signals of a print control unit of a conventional multi-beam image forming apparatus.

[Explanation of symbols]

 1: Photosensitive drum 2, 3: LD unit 4: Polygon mirror 5: fθ lens 6: Photodetector 6a: Light receiving unit 7: Beam splitter 8: Cylinder lens 9: First LD modulator 10: Second LD modulator 11: Print control unit 12: Clock generation circuit 13: Pulse separation circuit 14: First clock synchronization circuit 15: Second clock synchronization circuit 16: Main scanning counter 17 to 19: Comparator 20: CPU 21: I / F register 22, 23, 25: OR gate 24, 26: SR flip-flop 27: AND gate 31-36: NAND gate

Continued on the front page F-term (reference) 2C362 BA56 BA67 BA69 BB31 BB32 BB33 BB38 CB02 CB13 DA43 EA06 EA07 2H045 AA01 BA22 BA32 CA88 CA92 DA41 5C072 AA03 BA04 BA13 HA02 HA06 HA13 HB08 HB11 XA01 XA15 5CB07 A06 EA CC GG02 GG03 GG09 HH02

Claims (6)

[Claims] A plurality of light beam generating means, a plurality of modulating means for modulating a light beam generated by each of the light beam generating means according to an image signal, and a plurality of light beam generating means. Deflecting means for deflecting and scanning a light beam; imaging means for condensing a plurality of light beams deflected and scanned by the means at predetermined intervals in the main scanning direction; And a beam detection unit that activates a beam detection signal when each of the light beams is received, and generates the image signal based on the beam detection signal output from the beam detection unit to perform a recording operation. In the image forming apparatus performing, before the light beam preceding the beam detection means reaches,
Turning on the preceding light beam, turning off the preceding light beam after the beam detection means activates the beam detection signal, and further turning off the preceding light beam after the beam detection means no longer activates the beam detection signal. Light beam control means for controlling the plurality of light beam generation means so as to turn on the light beam to be turned on, and after the beam detection means generates a beam detection signal again, to turn off the subsequent light beam. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein
The light beam control unit turns off the preceding light beam, after the beam detection unit does not activate the beam detection signal, and after a lapse of a predetermined time from when the beam detection unit activates the beam detection signal. An image forming apparatus for controlling the plurality of light beam generating means so as to turn on the following light beam. 3. The image forming apparatus according to claim 2, wherein
An image forming apparatus comprising: means for changing a predetermined time from turning off the preceding light beam to turning on the following light beam in accordance with a scanning speed. 4. The image forming apparatus according to claim 1, wherein the plurality of light beams are used to turn on the plurality of light beams, respectively, and the plurality of light beams are used to emit light from the beam detection unit. An image forming apparatus comprising: means for separating a detection signal into a beam detection signal of each light beam. 5. The image forming apparatus according to claim 1, wherein the beam detection unit activates a beam detection signal within a predetermined time after the subsequent light beam is turned on. An image forming apparatus, further comprising means for turning off the following light beam when not performed. 6. The image forming apparatus according to claim 5, wherein
If the beam detection means does not activate the beam detection signal within a predetermined time after the subsequent light beam is turned on, means for performing error processing and displaying an error message is provided. Image forming apparatus.