JP2000141756A - Image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To transmit horizontal synchronous signals without influences of noises by making a fall edge of a pulse frequency divided from a detection output pulse the horizontal synchronous signal to a laser of an odd number and transmitting a rise edge of the pulse as the horizontal synchronous signal to a laser of an even number. SOLUTION: Generated horizontal synchronous signals corresponding respectively to first and second lasers are frequency divided by an IC4 and transmitted as BDT signals to an IC3. The IC3 judges a fall edge of the transmitted BDT signal as the horizontal synchronous signal corresponding to the first laser and a rise edge as the horizontal synchronous signal corresponding to the second laser, and controls an image write position or the like. Since a pulse width of the BDT signal can be made twice a pulse width of a normal BD signal, even if countermeasures against extraneous noises are more intensely carried out to a transmission line for the BDT signal thereby making a signal waveform dull, the correct horizontal synchronous signal can be transmitted owing to the large pulse width.

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 beam printer, for forming an image with a laser beam.

[0002]

2. Description of the Related Art Conventionally, a method of increasing the printing resolution of a laser beam printer is to use a plurality of laser light emitting elements, emit a plurality of laser beams, and emit the plurality of laser beams onto a photosensitive drum. In the method in which each laser beam scans the photosensitive drum and a laser horizontal synchronization signal is generated by one photodetector, the number of laser elements in one horizontal scanning period corresponds to the number of laser beams. The number of laser horizontal synchronizing signals thus generated is transmitted to the device control ASIC downstream of the detecting element.

[0003]

However, in the above conventional example, when the transmission distance from the detection element to the ASIC for controlling the device is long, noise is superimposed on the signal by external noise such as radiation noise and electrostatic noise. , Device control A
In some cases, the SIC erroneously detected the laser horizontal synchronization signal. In such a case, it is general that the ASIC detects only a normal horizontal synchronizing signal by cutting unnecessary noise by a filter using a damper resistor, a capacitor, or the like. In order to increase the resistance to noise, it is necessary to increase the damper resistance and the capacitor so as to have a filtering effect on the noise and to smooth the waveform to be transmitted.

[0004] However, in order to transmit two pulses, unless a filter having a certain degree or less is used, the second pulse may not be detected due to a rounded waveform. This is more likely to occur with smaller pulses. Therefore, the higher the frequency of the horizontal synchronization signal, the lower the cutoff frequency of the filter must be. That is, the higher the pulse frequency of the horizontal synchronization signal, the more difficult it is to take measures against external noise.

It is an object of the present invention to provide an image forming apparatus capable of transmitting a signal to a control ASIC without being affected by horizontal synchronization signal noise detected by a detection element.

[0006]

According to the present invention, a main body A is provided.
Before transmission to the SIC, the two pulses are frequency-divided into one pulse, the falling edge of this pulse is a horizontal synchronization signal for the first laser, and the rising edge for this pulse is the horizontal synchronization signal for the second laser. By transmitting as a signal, the device control ASIC can obtain a desired horizontal synchronizing signal even when a signal is blunted and transmitted by inserting a capacitor or the like as a measure against external noise.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 5 is a sectional view for explaining the structure of an image forming apparatus, for example, showing a case of a laser printer. Hereinafter, the configuration and operation will be described.

The laser printer 101 (hereinafter referred to as the main body 10)
1) has a cassette 102 having a function of detecting the presence or absence of the recording paper S.
Cassette paper presence sensor 1 for detecting the presence or absence of recording paper S
03, a cassette size sensor 104 (comprising a plurality of micro switches) for detecting the size of the recording paper S in the cassette 102, a paper feed roller 105 for feeding out the recording paper S from the cassette 102, and the like are provided.

A pair of paper feed rollers 106 for feeding the recording paper S is provided downstream of the paper feed roller 105. Further, a paper feed sensor 107 for detecting the conveyance state of the fed recording paper is provided downstream of the paper feed roller pair 106, and the recording paper S is provided on the recording paper S based on the laser beam from the laser scanner unit 108. Is provided with an image forming section 109 for forming a toner image.

Further, a fixing unit 110 for thermally fixing the toner image formed on the recording paper S is provided downstream of the image forming unit 109, and a paper conveyance state of a paper discharge unit is provided downstream of the fixing unit 110. , A discharge roller 112 for discharging the recording paper S, and a loading tray 113 for loading the recording paper S on which recording has been completed.

The laser scanner unit 108 receives an image signal (image signal VD) sent from an external device 128 described later.
O), a laser unit 114 that emits a laser beam modulated based on O), a polygon motor 115 for scanning the laser beam from the laser unit 114 onto a photosensitive drum 118 described later, an image forming lens group 116, and a folding mirror 117. And the like.

The image forming unit 109 includes a photosensitive drum 117, a primary charging roller 119, a developing unit 120, a transfer charging roller 121,
It is composed of a cleaner 122 and the like. In addition, the fixing device 1
Reference numeral 10 denotes a ceramic heater 110a as a heating source, a thermistor 110b for detecting the temperature thereof, a polyimide film 110c including the ceramic heater 110a and the thermistor 110b, and rotating together with recording paper conveyance, the ceramic heater 110a, thermistor 110b, and a polyimide film. A stay 110d for holding 110c,
And a pressure roller 110 in pressure contact with the ceramic heater 110a via the polyimide film 110d.
e.

The main motor 123 applies a driving force to the paper feed roller 105 via a paper feed roller clutch 124. Further, each of the image forming section 109 including a paper feed / conveyance roller pair 106 and a photosensitive drum 118 is provided. Unit, fuser 1
10. The driving force is also applied to the paper discharge roller 112.

FIGS. 1 and 2 show a first embodiment of the present invention, and FIGS. 1 and 2 show the features of the present invention best. In FIG. A horizontal synchronization signal of a beam, 2 is a laser power voltage signal, 3 is a sample and hold signal (hereinafter, referred to as SH signal), 4 is a switching signal of a laser diode (hereinafter, LD ON).
/ OFF signal), 5 is a scanner motor drive signal (hereinafter, referred to as SCANNER MOTOR ON / OFF signal), 6 is a scanner motor rotation state signal (hereinafter, referred to as SCNRDY signal), AMP1, and AMP.
2 is a laser power voltage buffer circuit, AMP3 is an I / V conversion circuit for converting the output from the horizontal synchronization signal, C1 is a capacitor for sampling and holding the output voltage of AMP2, and CMP1 is the output from AMP3. A comparison circuit with hysteresis for shaping, IC1 performs a switching operation of a laser diode according to an LD ON / OFF signal 4, and a laser driver circuit that drives a constant current according to the output voltage of the AMP1, and IC2 forms a scanner motor A motor driver circuit for servo-controlling the DC motor is a semiconductor integrated circuit (hereinafter referred to as an ASIC) that controls all the sequences of the engine.
, LD1 and LD2 are semiconductor laser diodes, PD1 is a photodiode for detecting the light amount of the LD1 and LD2, BD1 is a beam detection photodiode for detecting light from a horizontal synchronization signal detector, and R1 is A resistor for detecting the current of PD1, SW1 is a switch circuit for discharging the C1, and SW2 is a C
This is a switch circuit for controlling one sample and hold.

In the above configuration, this embodiment will be described with reference to FIG. IC3 when engine is not in print state
By SCANNER MOTOR ON / OFF 5
Is turned off to turn off the MTR1, and the switch SW1 is turned on by the inverting circuit INV1 to put the C1 into a discharge state. When the engine is in the printing state, the SCANNER MOTOR ON / OFF 5 is turned on by the IC 3 to turn on the MTR 1, and the IN 3
SW1 is turned off by V1 to put C1 in a chargeable state. The IC 3 monitors the SCNRDY signal 6 and outputs
When it is detected that R1 has reached the specified number of revolutions, the SH signal 3 is turned ON and the LD ON / OFF signal 4 is turned ON in order to detect the horizontal synchronization signal and set the laser light amount to an arbitrary value. As a result, the switching circuit in the IC 1 is turned on, and the LD 1 is in a state capable of emitting light.
Since the SW2 is also turned on, a laser light amount adjustment control system is established. Since the voltage of the capacitor C1 is discharged in the initial state, the voltage amplified with respect to Vref by the AMP1 is input to the constant current circuit of the IC1, and the LD1 starts emitting light. The laser light amount is detected by the photodiode PD1, and a current responsive to the light amount flows through the resistor R1 to generate a voltage and charge the capacitor C1 via the AMP2. By repeating this operation, the SH capacitor voltage of the capacitor C1 gradually rises,
The light amount of the light also increases. When the light amount reaches a predetermined light amount (Vbd), a current flows to the photodiode BD1, and AMP3
, And the waveform is shaped by CMP1 and input to IC3 as a horizontal synchronization signal.

The IC 3 monitors the voltage of the AMP 1 by A / D conversion, and upon detecting an arbitrary voltage (Vready), turns off the SH signal 3 and the previous LD ON / OFF signal 4 to perform a forced light quantity sampling process, and The laser forced emission processing means is terminated (hereinafter, referred to as initial APC). Here, assuming that the voltage value of the SH capacitor of the capacitor C1 corresponding to the prescribed laser light amount is Vtarget, the following relationship needs to be established. Vbd ≦ Vready <Vtarget
t. Vready needs to be set to a high voltage within a range that does not develop on the photoconductor drum surface, or a voltage that becomes Vtarget by the timing of developing an image to be printed on the photoconductor drum. In this way, once Vr
Upon detecting the "easy", the IC 3 is raised to a specified light amount by controlling the laser light amount adjustment outside the image area. In the present embodiment, laser light amount adjustment (hereinafter, referred to as line APC) is performed for each horizontal scanning cycle, and a laser forced emission area (hereinafter, referred to as an outside image area) for detecting a horizontal synchronization signal (hereinafter, referred to as a BD signal). , Referred to as the unblanking area)
It is performed using. Also, it is needless to say that the adjustment of the laser light amount can be performed every horizontal scanning cycle in the non-image area other than the unblanking area. Here, all non-image areas other than the unblanking area are possible. Here, the case of adjusting the laser light amount in the unblanking region will be described. IC3 measures the time from the BD signal detected in the initial APC process, and sets T before the prescribed horizontal scanning period.
SH signal 3, LD ON / OFF signal 4 from unblk
Turn ON. As a result, the above-described laser light amount control system is established, and a light amount sample state is established to increase the laser light amount. When the BD signal is detected, the SH signal 3 is turned off and the light quantity holding state is set. By this line APC process, the sample and the hold are repeatedly increased to a specified light amount Vtarget necessary for image exposure. In this case the laser is 2
First, only the LD1 is turned on, the horizontal synchronizing signal BD1 corresponding to the LD1 is detected, and then the LD1 is turned off.
D2 is turned on to detect BD2.

Next, the configuration of the IC 3 will be described with reference to FIG. The IC3 has an internal data bus,
CPU 10, ROM 11, RAM 12, A / D converter 1
3. A microcomputer having an I / O 14, a register 16 connected to the internal bus, and a logic circuit 1.
5, 17, 18, 19, 20, 21, 22, 23. In the initial APC process, the LD
By writing "1" to the forced ON and forced SAMPLE, the outputs of 22 and 23 are set to "1". In the line APC process, when a BD signal is input, a reset signal from a synchronous reset pulse generator 15 is divided by a 16 frequency divider 17 and a counter 1.
Input to 8 to initialize. Then, the data corresponding to Tunblk stored in the ROM 11 is stored in the UB of the register 16.
Write to LK start, UBLK end, SAMPLE start. The comparator 19 compares this data with the output value of the counter 18 to generate the timing of the line APC.

Next, a description will be given of a method of transmitting a laser horizontal synchronization signal according to the present invention. The horizontal synchronization signals respectively corresponding to the first laser and the second laser generated as shown in FIG. 2 are divided by the IC 4 and transmitted to the IC 3 as BDT signals. The IC 3 determines that the falling edge of the transmitted BDT signal is a horizontal synchronization signal corresponding to the first laser and the rising edge is a horizontal synchronization signal corresponding to the second laser,
The image writing position and the like are controlled.

Thus, the pulse width of the BDT signal can be made twice as large as that of a normal BD signal pulse.
The ASIC for the engine controller is correct because the original pulse width is large (slow pulse frequency) even if the signal waveform becomes dull by taking extra measures against external noise such as radiation noise and electrostatic noise on the transmission line of the DT signal. A horizontal synchronization signal can be obtained.

The photodiode BD1 and the amplifier A
By storing the MP3, the comparator CMP1, and the flip-flop IC4 in a single-chip IC, a BDT signal can be generated from a BD signal on which noise is not superimposed.

(Second Embodiment) A second embodiment will be described with reference to FIGS. 6, 7 and 8.

The difference from the first embodiment is that a comparator which compares a signal obtained by converting a current flowing through BD1 into a voltage by AMP3 has a threshold voltage Vth and has a threshold voltage Vth.
In addition to MP1, a threshold voltage Vth ′ (Vth ′
<Vth) and the short-time one-shot IC5, the delay circuit DL1, the RS flip-flop IC6, and the AND gate IC7, so that an erroneous signal is output in an unnecessary period. The signal is transmitted to the ASIC in the IC3 engine controller only during the period in which the horizontal synchronization signal is to be detected as shown in FIG. This time Ta is determined by the delay circuit.

Since the time for detecting the horizontal synchronizing signal is very short with respect to the period, it is possible to prevent the IC 4, which is generally not resistant to noise, from being inverted at an incorrect timing.

The photodiode BD1 and the amplifier A
By placing MP3, comparator CMP1, one-shot IC5, delay circuit DL1, RS flip-flop IC6, flip-flop IC4 and AND gate IC7 in a single-chip IC, a BDT signal can be generated from a BD signal on which noise is not superimposed. it can.

[0025]

As described above, according to the present invention,
Before transmitting the horizontal synchronization signal detected by the horizontal synchronization signal detection circuit to the ASIC for engine control,
By dividing the two pulses into one pulse and transmitting the falling edge of this pulse as a horizontal synchronization signal for the first laser and the rising edge for this pulse as a horizontal synchronization signal for the second laser, The device control ASIC can obtain a desired horizontal synchronizing signal even if a signal is blunted and transmitted by inserting a capacitor or the like as a measure against external noise.

[Brief description of the drawings]

FIG. 1 is a laser control circuit diagram according to a first embodiment of the present invention.

FIG. 2 is a timing chart of a laser control circuit diagram according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram of the inside of an IC 3 shown in FIG. 1;

FIG. 4 shows a signal waveform according to the first embodiment of the present invention.

FIG. 5 is a configuration diagram of a laser printer according to first and second embodiments of the present invention.

FIG. 6 is a laser control circuit diagram according to a second embodiment of the present invention.

FIG. 7 is a timing chart of a laser control circuit diagram according to a second embodiment of the present invention.

FIG. 8 shows a signal waveform according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Horizontal sync signal of laser beam 2 Laser power voltage signal 3 Sample hold signal 4 Switching signal of laser diode 5 Drive signal of scanner motor 6 Scanner motor rotation state signal AMP1, AMP2, AMP3 Amplifier BD1, PD1 Photodiode C1 Capacitor CMP1 Comparator DL1 delay circuit IC1 laser driver IC2 motor driver IC3 engine controller IC4, IC4 D-type flip-flop circuit IC5 one-shot circuit (monostable flip-flop) IC6 RS flip-flop IC7 AND gate INV1 inverter LD1, LD2 laser diode R1 resistance SW1, SW2 switch

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 BA69 BA70 BB32 BB37 DA41 EA11 2H045 AA01 AA52 CA97 CB61 5C072 AA03 BA11 FB08 FB27 HA02 HA06 HA13 MB09 XA05

Claims (4)

[Claims] 1. An optical scanning means for deflecting a plurality of laser beams modulated according to an image signal by a rotary polygon mirror to optically scan an image carrier with the plurality of laser beams, and detecting a laser horizontal synchronization signal. Detection circuit, a laser output adjustment mechanism for adjusting the output of the laser, a detection output allowable range setting means for recognizing a detection output output from the detection circuit only within a predetermined time range, and the detection output allowable range. Means for changing the timing of outputting
A laser forcible light emitting unit for forcibly emitting a laser, a printing start timing in a main scanning direction is determined based on a plurality of detection output pulses of the detection circuit, and the laser beam is formed on the image carrier by the optical scanning unit. An image forming apparatus for forming an image using a latent image, further comprising: means for dividing a plurality of detection output pulses output from the detection circuit, wherein the divided pulse signal is transmitted through a transmission path. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the detection circuit for detecting the laser horizontal synchronization signal and the frequency dividing circuit for dividing the plurality of detection outputs are one-chip ICs. Image forming device. 3. The image forming apparatus according to claim 1, wherein an odd-numbered detection output pulse of a plurality of detection outputs is made to correspond to the falling of the divided pulse, and an even-numbered detection output pulse is made to correspond to the even-numbered detection output pulse. An image forming apparatus further comprising: means for responding to a rise of a divided pulse. 4. The image forming apparatus according to claim 1, further comprising: means for preventing the frequency-divided pulse from being generated outside a range in which the detection output pulse is detected. apparatus.