JP2004114397A - Image formation apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image formation apparatus capable of correctly detecting BD (beam detection) signals of a plurality of lasers by a relatively simple configuration. <P>SOLUTION: A scanner motor 111 generates a reference pulse (FG) synchronously with rotary driving of a polygon mirror. A BD signal timing detecting circuit 151 detects a differential signal ΔBD of a first and a second timings (/BD01 and /BD02) when a first and a second laser beams pass a predetermined position based on the reference pulse, respectively. At the time of forming an electrostatic latent image onto a photoreceptor drum, the second timing is generated with the differential signal ΔBD being taken into consideration for the first timing (/BD01). When the first and the second timings are to be measured, preferably, the measurement is carried out by temporarily setting a rotation control of the polygon mirror to be lower than a target speed, and the measured value may be converted to a difference corresponding to the target speed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus used for a facsimile, a copying machine, a printer, and the like.
[0002]
[Prior art]
An electrophotographic image forming apparatus scans a photosensitive drum by scanning a laser beam modulated in accordance with image data, forms a charged latent image on the surface of the photosensitive drum, and uses the latent image with a developer such as toner. An image is formed by developing and heat fixing. Among such image forming apparatuses, there is known an image forming apparatus using a plurality of laser beams in order to speed up the formation of a latent image on a photosensitive drum.
[0003]
In order to synchronize the scanning of each laser beam, a single light receiving element (usually called a BD light receiving element) for detecting the laser beam is shared by a plurality of laser beams.
[0004]
[Problems to be solved by the invention]
When a plurality of laser beams are received by one BD light receiving element and a plurality of BD signals are to be transmitted through one signal line, as shown in FIG. 11, a plurality of BD detection portions are formed on one signal waveform. BD detection signals / BD1 and / BD2 including the negative peak in the example of the drawing are obtained. This signal is converted into rectangular wave signals / BDO1, / BDO2 by waveform shaping.
[0005]
However, as the speed of the image forming apparatus increases, the BD detection portions of the respective laser beams come closer to each other and overlap. Therefore, there is a problem that it is difficult to accurately identify both pulses by waveform shaping.
[0006]
In addition, as the speed and size of the apparatus are reduced, the interval between a plurality of laser beams is reduced, which makes it more difficult to control with the conventional method.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of accurately detecting BD signals of a plurality of lasers with a relatively simple configuration.
[0008]
[Means for Solving the Problems]
The image forming apparatus according to the present invention scans the first and second laser beams during one scan to form an electrostatic latent image on the photosensitive drum, and makes the formed electrostatic latent image visible with a developer. An image forming apparatus for forming an image and transferring and fixing the image to a recording medium, comprising: scanning means for scanning first and second laser beams; and reference pulse generating means for generating a reference pulse in synchronization with rotation of the scanning means. Means for detecting first and second timings at which first and second laser beams pass through predetermined positions, respectively, based on the reference pulse when being scanned by the scanning means; and Means for measuring a difference between second timings; and timing generating means for generating the second timing in consideration of the difference in the first timing when forming the electrostatic latent image. And it features.
[0009]
As described above, in the present invention, instead of directly calculating the difference between the first and second timings, first, the first and second timings are measured with reference to a predetermined reference pulse, and the difference between the results is determined. Accordingly, even if the difference between the first and second timings is very small, the difference can be measured more accurately. Further, by using this difference, image data can be output more accurately in synchronization with scanning of both laser beams when the electrostatic latent image is formed.
[0010]
The apparatus further includes means for temporarily setting the rotation control of the rotation drive to be lower than a target speed at the time of measuring the first and second timings, performing measurement, and converting the measured value to a difference corresponding to the target speed. Is also good. Thereby, the resolution of the measurement can be substantially improved without changing the speed (frequency) of the clock used for the measurement.
[0011]
The measurement may be performed a plurality of times, and an average value of the plurality of measurement values may be used as a measurement result.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail.
[0013]
FIG. 1 shows a schematic internal configuration of an electrophotographic printer as an example of an image forming apparatus to which the present invention is applied. This printer includes a photosensitive drum 1 for forming an electrostatic latent image, a charging roller 2 for uniformly charging the photosensitive drum 1 with a high voltage, and an optical for scanning a plurality of laser beams on the photosensitive drum 1. A unit 3, a developing unit 5 for developing an electrostatic latent image formed on the photosensitive drum 1 with toner by a laser beam 4 emitted from the optical unit, and a toner image on the photosensitive drum 1 into a predetermined form; A transfer roller charger 6 for transferring to a sheet, a fixing device 7 for melting the transferred toner on the sheet and fixing it to a sheet 13 as a recording medium, a standard cassette 8 for stacking sheets for printing, a standard A standard cassette paper feed roller 9 for picking up paper from the cassette 8, a top sensor 10 for taking a leading edge resist for printing of the conveyed paper, and the paper is normally discharged to the fixing device. Sheet discharge sensor 11 for checking whether, comprises a paper detecting sensor 12 for detecting the presence or absence of paper in the standard tray.
[0014]
FIG. 2 is a block diagram showing a hardware configuration of a control unit of the printer in FIG. In the figure, a printer controller 101 communicates with a host computer 108, receives image data, converts the received image data into information that can be printed by a printer, and communicates with a printer engine unit described later. Send and receive signals and communicate. The engine controller 102 controls each unit of the printer engine via communication with the printer controller 101. For example, it exchanges signals such as / RDY and / PRINT and controls each unit of the printer engine via serial communication. The paper transport control unit 103 feeds paper from the cassette 8 by driving the solenoid 109 in accordance with an instruction from the engine controller 102 based on a print request from the printer controller 101, and transports the paper until the paper is discharged outside the machine. Of the main motor 110, or ON / OFF of a solenoid for stopping a predetermined roller drive, based on an instruction from the control unit. The optical system control unit 104 emits at least two laser beams based on image data from the printer controller 101, rotates the scanner motor 111, and detects a BD signal that is a horizontal synchronization signal from the BD sensor 112. And the process of turning on the lasers before the timing of detecting the BD signal of each laser is executed based on the instruction of the engine controller 102. The high-voltage control unit 105 executes each high-voltage output of the primary charging unit 115, the developing unit 116, and the transfer unit 117 based on an instruction from the engine controller 102. The fixing device controller 106 controls the temperature of the fixing device 7 to a predetermined temperature based on an instruction from the engine controller 102. That is, the temperature is controlled by the thermistor 118 and the heater 119 is turned on / off to control the temperature to a predetermined temperature. The sensor input unit 107 is an input unit of a sensor group for detecting the presence / absence of paper at each unit in the paper transport path such as the top sensor 10, the paper ejection sensor 11, and the paper presence / absence sensor 12.
[0015]
The engine controller 102 starts a printing operation in response to a command or a signal of the printer controller 101, and issues a predetermined instruction to various control units connected to the engine controller 102 until the printing operation is completed.
[0016]
An internal configuration of the optical unit 3 will be described with reference to FIG. In the figure, a semiconductor laser 301 is a multi-beam emission type semiconductor laser that receives an image signal to be transferred and emits light based on image information. The collimator lens 302 is a lens that converts light emitted from the semiconductor laser 301 into a parallel light beam. The cylindrical lens 303 is a lens that optically corrects the parallel light flux such as linearity. The polygon mirror 304 is a mirror having a polygonal reflection surface that rotates and scans a laser beam output from the cylindrical lens 303. A torrec lens 305 is a lens for correcting optical distortion of a laser beam scanned and output from the polygon mirror 304. The imaging lens 306 is a lens that condenses the output light beam of the torrec lens 305. The reflection mirror 308 is a mirror for changing the direction of the output light of the imaging lens 306 and directing the light toward the photosensitive drum 1. The parallel synchronization (BD) mirror 307 is a mirror arranged at the scanning start end or the end to detect the position of the beam main-scanned by the polygon mirror 304 (the timing at which the beam passes a predetermined position). The BD detector 309 is a light receiving element that receives the beam reflected by the BD mirror 307.
[0017]
Here, the configuration of a conventional optical system control unit is shown in FIG. 10 for reference. This optical system control unit corresponds to the engine controller 102 in FIG. 2, and includes a CPU 120, a BD signal detection circuit 152, and a laser control signal generation circuit 153 therein. The laser driver 154 corresponds to the optical system control unit shown in FIG. And the lighting control of the laser 113 (L1) and the laser 114 (L2). The photodiode 155 returns the detection signal PD to the laser driver 154 for stabilizing control of the amount of laser light. As shown in FIG. 11, the BD signal detection circuit 152 shapes the waveform of the BD signals / BD1 and / BD2 input from the BD sensor 112, and outputs them as rectangular wave signals / BDO1 and / BDO2. By transmitting video signals / VDO1 and / VDO2 synchronized with the rectangular wave signals / BDO1 and / BDO2 to the laser driver 154, the printer controller 101 can put target image information on the laser beam. However, the problem of placing two BD signals on one BD signal waveform is as described in the section of the related art.
[0018]
Therefore, in the present embodiment, an optical system control unit as shown in FIG. 4 is used. The same elements as those shown in FIG. 10 are denoted by the same reference numerals, and the basic configuration is the same, so only the differences will be described. FIG. 4 differs from FIG. 10 in that signals / BDO1 and / BDO2 are input to BD timing detection circuit 151. The BD timing detection circuit 151 is a circuit newly provided in the present embodiment, and measures the scanning positions (timings) of the signals / BDO1 and / BDO2 with reference to an FG signal described later. ΔBD, which is the difference time between the scanning positions, and a signal / BDO1 are output to the printer controller 101. The FG signal is output from the scanner motor 111. The scanner motor 111 is controlled by a control signal / MTRON from the CPU 120.
[0019]
FIG. 5 shows a method for detecting an FG signal which is a rotation signal of the scanner motor 111. The timing at which one corner of the polygon mirror 304 reaches a predetermined position (the position indicated by the black triangle mark in the figure) can be detected by a sensor 160 such as a Hall element. In this case, the FG signal is output at a rate of one pulse every one rotation of the polygon mirror 304. When the scanner motor 111 rotates at a constant speed, the FG signals are output at equal intervals. The FG signal is shaped into a waveform and input to the BD signal timing detection circuit 151.
[0020]
FIG. 6 is a block diagram showing the internal configuration of the BD signal timing detection circuit 151. When the signals / BDO1 and / BDO2 are input from the BD signal detection circuit 152, the signals are input to the BD signal difference detection circuit 157 and the BD separation circuit 156. The BD separation circuit 156 separates the signal / BDO1 and sends it to the printer controller 101. BD signal difference detection circuit 157 receives system clock SCLK, and generates difference time signal ΔBD from signals / BDO1 and / BDO2 with reference to signal / FG.
[0021]
FIG. 7 is a time chart showing the operation of the BD signal difference detection circuit 157. First, the scanner motor 111 is rotated at a constant target speed. Therefore, prior to the image forming operation, only the first laser 112 is turned on, and the time (BDin1) until the falling edge of the / BDO1 signal is measured based on the falling edge of the FG signal using the system clock SCLK. In the case of FIG. 7, BDin1 has three system clocks. Next, only the second laser 114 is turned on, and the time (BDin2) until the falling edge of the / BDO2 signal is measured based on the falling edge of the FG signal using the system clock / SCLK. In the case of FIG. 7, BDin2 has five system clocks. The difference between BDin1 and BDin2 is defined as ΔBD (2 system clocks). Next, data corresponding to ΔBD is output to the printer controller 101. The printer controller 101 keeps holding when ΔBD is input, outputs a video signal / VDO1 for the first laser 112 in synchronization with / BDO1 input for each surface of the polygon mirror 304 during image formation, and holds The video signal / VDO2 for the second laser 114 is transmitted to the laser driver 154 in synchronization with the timing delayed by ΔBD. This makes it possible to form an electrostatic latent image on the drum in which the writing start points of both lasers are exactly matched.
[0022]
It should be noted that if the detection of ΔBD is measured a plurality of times while the scanner motor 111 is stable at the target speed, and the average value is output as ΔBD, the accuracy can be further improved.
[0023]
According to the present embodiment, even when the falling edges of / BDO1 and / BDO2 are close to each other, by independently measuring / BDO1 and / BDO2 and taking the difference ΔBD, image data can be obtained. It is possible to output certain / VDO1 and / VDO2 accurately synchronized with / BDO1 and / BDO2.
[0024]
A second embodiment of the present invention will be described with reference to FIGS. FIG. 8 shows a configuration of an optical system control unit according to the second embodiment. The difference from the optical system control unit shown in FIG. 4 is that the difference value ΔBD to the printer controller 101 is transmitted to the printer controller 101 via the CPU 120 by serial communication. The other configuration is the same as that shown in FIG. 4, and a duplicate description will be omitted.
[0025]
FIG. 9 is a time chart illustrating the operation of the BD signal difference detection circuit 157 according to the second embodiment. In the present embodiment, this operation is performed by rotating the polygon mirror at half the target rotation speed. That is, the rotation speed of the polygon mirror differs from that of the first embodiment in measuring the time until the falling edge of the / BDO1 and / BDO2 signals with reference to the falling edge of the FG signal.
[0026]
Specifically, the scanner motor 111 is rotated at a constant rotation speed lower than the target speed, and only the first laser 112 is turned on, and the falling edge of the FG signal is used as a reference until the falling edge of the / BDO1 signal. BDin11 is measured by the system clock / SCLK. In the case of FIG. 9, BDin11 has six system clocks. Next, only the second laser 114 is turned on, and the BDin 22 is measured using the system clock / SCLK to measure the time until the falling edge of the / BDO2 signal based on the falling edge of the FG signal. In the case of FIG. 9, the BDin 22 has 11 system clocks. The difference between BDin11 and BDin22 is defined as ΔBD2 (5 system clocks). The ΔBD2 data is notified to the CPU 120.
[0027]
Since ΔBD2 is a difference when rotating at half the target speed, a value obtained by reducing the value of ΔBD2 to 1/2 becomes ΔBD at the target speed. In FIG. 9, since it is 1/2 of 5 system clocks, ΔBD is 2.5 system clocks, which means that the difference can be detected more accurately by 0.5 system clocks than in the first example. After the above calculation is performed by the CPU 120, the data is transmitted to the printer controller 101 by serial communication. In the subsequent printing operation, / VDO1 is output in synchronization with the input / BDO1, and / VDO2 is transmitted to the laser driver 154 in synchronization with the timing of delaying the time of ΔBD, so that the accuracy is displayed on the photosensitive drum. An electrostatic latent image is formed well. In this embodiment, the scanning position of each laser beam can be accurately measured even when the system clock is relatively slow with respect to the video clock.
[0028]
Note that the method of measuring the BDin 11 and the BDin 22 by lowering the rotation speed of the polygon mirror in the second embodiment can also be adopted in the configuration of FIG. The rate of rotation speed reduction was １ ／, but is not limited to this.
[0029]
【The invention's effect】
According to the present invention, when the laser beams are received by one light receiving element in order to detect the scanning positions of the first and second laser beams, the reference pulse generated in synchronization with the rotation drive of the scanning means is used as a reference. By independently measuring the scanning positions (or timings) of the two laser beams and taking the difference between them, image data can be output more accurately in synchronization with the scanning of the two laser beams.
[0030]
Further, by measuring the scanning position (or timing) of both laser beams at a speed lower than the target speed, each scanning position can be measured more accurately.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic internal configuration of an electrophotographic printer as an example of an image forming apparatus to which the present invention is applied.
FIG. 2 is a block diagram illustrating a hardware configuration of a control unit of the printer in FIG.
FIG. 3 is a diagram showing an internal configuration of an optical unit in the printer of FIG.
FIG. 4 is a block diagram illustrating a configuration of an optical system control unit according to the embodiment of the present invention.
FIG. 5 is a diagram for explaining a method of detecting an FG signal which is a rotation signal of the scanner motor shown in FIG. 3;
FIG. 6 is a block diagram showing an internal configuration of a BD signal timing detection circuit in FIG. 4;
FIG. 7 is a time chart showing the operation of the BD signal difference detection circuit in FIG. 6;
FIG. 8 is a block diagram illustrating a configuration of an optical system control unit according to a second embodiment of the present invention.
FIG. 9 is a time chart illustrating an operation of the BD signal difference detection circuit according to the second embodiment of this invention.
FIG. 10 is a block diagram illustrating a configuration of a conventional optical system control unit.
FIG. 11 is a waveform diagram showing BD detection signals / BD1 and / BD2 when a plurality of laser beams are received by one BD light receiving element and a plurality of BD signals are to be transmitted through one signal line.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 photosensitive drum 2 charging roller 3 optical unit 4 laser beam 5 developing device 6 transfer roller 7 fixing device 8 standard cassette 9 paper feed roller 10 registration sensor 11 paper discharge sensor 12 paper presence sensor 13 paper

Claims (4)

The first and second laser beams are scanned during one scan to form an electrostatic latent image on the photosensitive drum, and the formed electrostatic latent image is visualized with a developer and transferred and fixed on a recording medium. Image forming apparatus,
Scanning means for scanning the first and second laser beams;
Reference pulse generation means for generating a reference pulse in synchronization with the rotation drive of the scanning means,
Means for detecting first and second timings at which the first and second laser beams respectively pass through predetermined positions based on the reference pulse when being scanned by the scanning means;
Means for measuring a difference between the first and second timings;
An image forming apparatus comprising: a timing generating unit configured to generate the second timing in consideration of the difference in the first timing when the electrostatic latent image is formed. Means for measuring the first and second timings by temporarily setting the rotation control of the rotation drive to be lower than a target speed, performing a measurement, and converting the measured value into a difference corresponding to the target speed. The image forming apparatus according to claim 1, wherein: The image forming apparatus according to claim 2, wherein the measurement is performed a plurality of times, and an average value of the plurality of measurement values is used as a measurement result. 2. The image forming apparatus according to claim 1, wherein the scanning unit has a single polygon mirror.

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