JP3809304B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that performs image scanning using a plurality of lasers and performs masking control so that an image is not written in a non-image area.
[0002]
[Prior art]
Conventionally, an image forming apparatus that scans an image using a plurality of lasers is configured as disclosed in Japanese Patent Application Laid-Open No. 57-67375 filed by the present applicant.
[0003]
Even if the lasers are arranged vertically, they can be arranged only at an interval wider than the interval between the main scanning lines. For this reason, it is necessary to arrange the lasers obliquely in the main scanning direction so that the intervals between the lasers have the determined line density of the main scanning lines.
[0004]
By the way, the image forming apparatus has an image writing range determined according to the paper size. When the image writing range is exceeded, the image sticks out of the paper, and the toner adhering to the protruding portion is applied to the transfer roller while adhering to the photosensitive drum. And contaminates the transfer roller. This is described in Japanese Patent Application Laid-Open No. 2-226262 filed by the present applicant. However, there is only written about prevention of image sticking in the sub-scanning direction, that is, the sheet conveyance direction. For example, FIG. 2 of JP-A-2-226262 describes a time chart of the ENBL signal, which is a signal masking the image signal VDO in the sub-scanning direction, and allows the image signal to pass only during the true period of the ENBL signal. .
[0005]
However, the protrusion of the image also occurs in the main scanning direction. When the image in the main scanning direction protrudes, the end of the transfer roller 9 in FIG. 1 of JP-A-2-226262 is contaminated with toner. The toner adhering to the transfer roller adheres to the back side of the next larger sheet and causes a phenomenon called back stain. In particular, when printing on both sides of the paper, it becomes a very serious contamination image.
[0006]
[Problems to be solved by the invention]
In the above-mentioned conventional example, Japanese Patent Laid-Open No. 57-67375, the timing at which each laser starts writing an image in the main scanning direction is different.
[0007]
As described above, when there are a plurality of writing laser beams, there are as many image signals as there are laser beams, and even if masking is performed so that the image signals do not protrude, if one laser beam is out of phase, one masking signal is generated. It turned out that it was difficult to mask accurately.
[0008]
Recently, there is a strong demand for writing images to the edge of the paper and using the paper effectively. For this reason, it is necessary to perform image masking with higher accuracy than in the past, and to prevent overrun of image writing accurately at the edge of the sheet when the image protrudes from the image area.
[0009]
The present invention has been made in view of the above problems, and in an image forming apparatus that forms an image by scanning a plurality of light beams on a photoconductor, image writing prohibition / permission of each light beam is controlled with high accuracy. With the goal. Another object is to realize it with a simple configuration.
[0010]
[Means for Solving the Problems]
An image forming apparatus according to the present invention scans a plurality of light beams to be modulated on a photosensitive member, and detects and detects each of the plurality of light beams in an image forming device that forms an image on the photosensitive member. A single detection means for sequentially outputting pulses; a distribution means for sequentially distributing and outputting the detection pulses to different signal lines by counting the detection pulses sequentially output from the single detection means; and the distribution means Each of the light beams is masked at different timings by comparing a plurality of count means for starting a clock count operation in synchronization with a detection pulse outputted from the counter and a count value of the count means and a predetermined value. A plurality of masking signal generating means for generating a masking signal for generating the masking signal, and the mask generated by each of the plurality of masking signal generating means. And king signal by a modulation signal for modulating said light beam to a logical operation, and having a masking means for masking at each different from each other timing of the light beam.
[0011]
The image forming apparatus control method according to the present invention is a method for controlling an image forming apparatus that scans a plurality of modulated light beams onto a photoconductor to form an image on the photoconductor. A detection step of detecting each of the plurality of light beams by using a detector of the plurality of detectors and sequentially outputting detection pulses, and counting the detection pulses sequentially output from the single detector, thereby detecting the detection pulses. A distribution step for sequentially distributing and outputting to different signal lines, and a clock count operation in synchronization with each of the detection pulses distributed in the distribution step, and comparing the count value with a predetermined value, thereby the light beam Generating a masking signal for masking each of them at different timings, and modulating the generated masking signal and the light beam A modulation signal of order by logical operation, and having a masking step of masking each a different timing of the light beam.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
The image forming apparatus of this embodiment will be described with reference to the drawings.
[0013]
FIG. 2 is a perspective view for explaining a laser scanning optical system of the image forming apparatus according to the embodiment.
[0014]
In FIG. 2, reference numeral 1 denotes a multi-beam laser having a plurality of light emitting sources, which emits four substantially parallel laser beams. 3 is a collimator lens, 3 is a polygon mirror for scanning four laser beams emitted from a multi-beam laser, 4 is an F-θ lens, and 5 is irradiated with a laser beam to be scanned to form an electrostatic latent image. A photosensitive drum to be formed, 6 is a reflecting mirror, and 7 is a beam detector that detects that the laser beam has passed at one point on the scanning path of the laser beam in order to control the timing of starting main scanning. 8 is a slit. Further, the four laser beams collected by the F-θ lens 4 are assigned symbols B1, B2, B3, and B4, respectively. The laser beam converged through the collimator lens 2 is deflected in the direction of the arrow by the polygon mora 3, collected by the F-θ lens, and then scanned on the photosensitive drum 5. A part of the laser beam that has been flared is reflected by the reflecting mirror 6 at the main scanning start position and guided to the beam detector 7.
[0015]
FIG. 3 is a block diagram of a circuit for processing a signal output from the beam detector 7.
[0016]
In FIG. 3, 10 is an amplifier that amplifies the signal received by the beam detector, 11 is a slicer, and converts the analog signal into a square wave by slicing the output of the amplifier 11 with the voltage set by the variable resistor 12. To the terminal 13.
[0017]
FIG. 4 is a diagram showing the inclination of the multi-beam, and shows the irradiation position of the beam at a certain moment. In FIG. 4, a line perpendicular to the main scanning line SL direction is denoted by LL ′. When each beam interval of the four beams is Pl, by tilting the line LL ′ by an angle α, the scan line interval on the photosensitive drum becomes Ps, which can be narrower than Pl. However, tilting in this way shifts the irradiation position of each beam in the main scanning direction. The deviation in the main scanning direction between the beams is about 0.5 mm. Therefore, the modulation of each beam by the image signal must be performed by shifting a predetermined time corresponding to the irradiation position deviation.
[0018]
On the other hand, masking control of these image signals has not been performed as severely as beam modulation control. That is, the masking control is for controlling the beam not to be emitted unnecessarily outside the image area. However, as in the conventional case, about 3 mm from each end of the paper is taken as a blank portion, and the inside is imaged. In the case of a region, even if a masking signal is generated at a timing common to each beam, the influence of the deviation of each beam of about 0.5 mm does not matter so much.
[0019]
However, when it is desired to write an image to the edge of the sheet, the amount of deviation of the beam irradiation position cannot be ignored. This is the theme to be solved in this embodiment.
[0020]
FIG. 5 is a diagram illustrating a situation in which each beam passes through the slit 8. In FIG. 5, the beam diameter of each beam is dd, the interval between the slits 8 is ds, the interval between the centers of the beams in the main scanning direction is db, and the length of the gap between each beam and the beam in the main scanning direction is da. And By making the slit interval ds larger than the beam diameter dd and sufficiently narrower than the beam gap da, each beam passing through the slit 8 can be separated and guided to the beam detector 7.
[0021]
FIG. 6 is a cross-sectional view of the main part of the image forming apparatus. In this figure, a folding mirror 30 is added to the optical system. Reference numeral 31 denotes a paper feed cassette, and reference numeral 32 denotes a paper size sensor. The paper size sensor 32 reads special information corresponding to the paper size provided in the paper feed cassette 31 as bit information using a microswitch or the like. Reference numeral 33 denotes a paper feed roller, 34 denotes a registration roller, 35 denotes a transfer roller, 36 denotes a developing roller, 37 denotes a fixing roller, and 38 denotes a paper discharge tray.
[0022]
Next, the characteristic part of a present Example is demonstrated based on FIG.
[0023]
In FIG. 1, reference numeral 40 denotes a detection circuit which outputs pulses when four light beams B1 to B4 enter the beam detector 7 of FIG. Since the light beams B1 to B4 are scanned at intervals in the main scanning direction as described above, the beam detector 7 sequentially receives them with a time difference. As a result, the detection circuit 40 sequentially outputs four pulses with a time difference. Reference numeral 41 denotes a distributor, which decomposes the four pulses output from the detection circuit 40 and outputs them as BD1 to BD4. BD1 to BD4 correspond to the light beams B1 to B4, respectively, and serve as main scanning start timing signals.
[0024]
Details of the distributor 41 are shown in FIG. In FIG. 7, 14 is an input terminal to which the output from the detection circuit 40 is inputted, 15 to 18 are gate circuits, 19 is a quaternary counter, 20 is a decoder, 21 to 24 are decomposed BD signals BD1 to BD4. Output terminal. These operations will be described with reference to FIG. In FIG. 8, four pulses are sequentially input to the input terminal 14 with a time difference. The counter 19 advances each time each pulse is applied. When the counter output is decoded by the decoder 20, signals corresponding to the output of the counter 19 are obtained at the output sections of C 0, C 1, C 2, and C 3 of the decoder 20. When the gate circuits 15 to 18 are sequentially turned through with this signal, the BD signals BD1 to BD4 corresponding to the light beams B1 to B4 are respectively decomposed at the output terminals 21 to 24 as shown in FIG. Is output.
[0025]
Returning to FIG. 1 again, the description will be continued. In FIG. 1, reference numeral 42 denotes an image signal generator for outputting four image signals for modulating light beams in synchronization with the four BD signals described above, and 43 to 46 denote images generated by the image signal generator 42. Gate circuits 47 to 50 as masking means for masking a signal with a masking signal to be described later are used to emit laser beams L1 to L4 from the laser 1 by driving the laser 1 in accordance with each image signal. It is a driver.
[0026]
Next, the most characteristic masking function in this embodiment will be described. In FIG. 1, 51 is a flip-flop, 52 is a counter, and 53 is a clock input terminal of the counter 52. When BD1 is input, the counter 52 starts counting up from zero and is input to the clock input terminal. The clock is counted up to the maximum value.
[0027]
Reference numeral 70 denotes a CPU, and 62 to 69 are registers whose values are set by the CPU 70. In the registers 62 and 63, the rise time and fall time of / MASK1 are set, respectively. The rise time and fall time of MASK2 are set, the rise time and fall time of / MASK3 are set in registers 65 and 66, respectively, and the rise time and fall time of / MASK4 are set in registers 67 and 68, respectively. Are set respectively. Reference numerals 54 to 61 denote digital comparators for comparing the values of the registers 62 to 69 with the count value of the counter 52, respectively. Reference numerals 71 to 74 denote flip-flops (hereinafter referred to as flip-flops), which are the outputs COMP1-1 and 55 of the comparator 54, the outputs COMP1-2 of 56, the outputs COMP2-1 of 56, the outputs COMP2-2 of 57, and the outputs COMP3-1 of 58, respectively. 59, the output COMP3-2 of 59, the output COMP4-1 of 60, and the output COMP4-2 of 61 are input, and the masking signals / MASK1 to / MASK4 are output. These masking signals / MASK1 to / MASK4 are input to the gate circuits 43 to 46, respectively, as described above.
[0028]
The operation of the above configuration will be described with reference to the timing chart of FIG. First, when BD1 output from the distributor 41 is input to the set terminal of the free flow 51 at time t0, the free flow 51 outputs an operation enable signal CNTENB to the counter 52 from the Q terminal. As a result, the counter 52 starts counting the clock applied to the clock terminal 53. When the count value of the counter 52 reaches the maximum value output later, it is returned to the reset terminal of the free flow 51, the free flow 51 is reset, and the CNTEB signal falls low. In this way, the period during which the CNTENB signal is high is the time during which the counter 52 is operating, and when the count value reaches the maximum value, the initial state of count zero is restored.
[0029]
The outputs of the counter are compared by the comparators 54 to 61 to determine whether or not they match the outputs of the registers 62 to 69, respectively. That is, as shown in FIG. 9, the comparator outputs COMP1-1 to COMP4-2 become high at the times indicated by the values stored in the corresponding registers.
[0030]
Thus, each of the flip signals outputs a masking signal / MASK1 to / MASK4 as shown in FIG. 9 by the comparator signal applied to the flip signals 71 to 74. For example, the masking signal / MASK1 is high during a period from time t1 indicated by the value stored in the register 62 to time t5 indicated by the value stored in the register 63. Further, other masking signals / MASK2 to / MASK4 also become high during the period from each time t2 to t4 to each time t6 to t8, as shown in FIG.
[0031]
The symbol “/” in front of the signal name of the masking signal indicates that the function of the signal is valid when the signal is at a low level. That is, / MASK1 is for masking the image signal when it is low, and when it is high, it indicates that the image signal is passed from the gate circuit 43 without being masked. Therefore, the masking signal can be said to be a permission signal according to the opposite view. In any case, it is a design matter in which case it becomes high or low, and it still realizes a function for controlling prohibition (masking) or permission of light beam modulation by an image signal.
[0032]
Further, the CPU 70 can arbitrarily set the value stored in each register. Specifically, the difference between the masking signals at the rise time and the fall time corresponds to the deviation in scanning timing caused by the positional deviation in the main scanning direction of each laser beam, as indicated by db shown in FIG. Of course, it is determined. This misalignment can be further corrected in detail by separately providing the CPU 70 with an adjustment amount. Further, the length of the period during which each masking signal is high is a length corresponding to the paper size detected by the paper size sensor 32.
[0033]
The count value of the counter 52 is used not only for generating a masking signal but also for generating a forced lighting signal (unblanking) for forcibly turning on the laser to obtain another signal such as a BD signal. Is called. It is also used for monitoring the period of the BD signal.
[0034]
In this embodiment, only the BD signal BD1 extracted by the distributor 41 is input to the free flow 51 to instruct the start of the counting operation of the counter 52. However, the output of the distributor 41 is not used in this way. In addition, the output of the detection circuit 40, that is, the BD signal having four pulses BD1 to BD4, may be input to the free flow 51 as it is. This is because once the flip-flop 51 is triggered and set by the S terminal, the Q output does not change until a reset signal is input to the R terminal, and therefore, it is not affected by the pulses of the BD signals BD2 to BD4.
[0035]
As described above, it is possible to perform accurate masking of an image signal by generating masking signals at different timings corresponding to each of a plurality of laser beams.
[0036]
(Second embodiment)
In the first embodiment, an example in which only one counter is used has been shown. Such a configuration is effective if the individual difference is small in the distance between the beams. However, when the distance between the beams needs to be adjusted, for example, when the F-θ lens 4 is distorted, the angle α for rotating the laser 1 in FIG. 4 is adjusted. In this case, since the interval between the scanning lines is adjusted to a specified value, the distance db between the beams is different for each apparatus. In the first embodiment, it is possible to input correction values to the CPU 70 and correct them for each device, but the number of adjustment steps increases. Therefore, in the second embodiment, a configuration is proposed in which adjustment is not required even if the distance between the beams changes.
[0037]
FIG. 10 is a block diagram showing the second embodiment, and FIG. 11 is a time chart thereof. In FIG. 10, parts having the same functions as those in FIG.
[0038]
In FIG. 10, 80 is a flip-flop, 81 is a counter, and 82 is a clock input terminal of the counter 81. When BD1 is input, the counter 81 starts counting up from zero and is input to the clock input terminal. The clock is counted up to the maximum value. Reference numerals 85 and 86 are registers whose values are set by the CPU 70. In the registers 85 and 86, the rising time and falling time of / MASK1 are set, respectively. Reference numerals 83 and 84 denote digital comparators for comparing the values of the registers 85 and 86 with the count value of the counter 81, respectively. Reference numeral 87 denotes a flip-flop (hereinafter referred to as flip-flop), which receives the outputs COMP1-1 and COMP1-2 of the comparator 83 and outputs a masking signal / MASK1. Reference numeral 88 denotes a masking signal generation circuit constructed as described above, and is indicated by a one-dot chain line in the drawing. The masking signal generation circuit 88 generates / MASK1 corresponding to the laser beam L1. Reference numerals 89, 90 and 91 denote masking signal generation circuits for generating / MASK2, / MASK3 and / MASK4 corresponding to the laser beams L2, L3 and L4, respectively. Has been. In the second embodiment, the outputs BD1 to BD4 from the distributors are used as BD signal inputs to the respective masking signal generation circuits. Masking signals / MASK1 to / MASK4 generated from the masking signal generating circuits 88 to 91 in this way are input to the gate circuits 43 to 46, respectively, as in the first embodiment.
[0039]
These timing charts are shown in FIG.
[0040]
Also in the second embodiment, as in the first embodiment, the count value of the counter is not only for generating a masking signal but also forcibly turns on the laser to obtain another signal such as a BD signal. It may also be used to generate a forced lighting signal (unblanking) for generating the signal. Of course, in this case, the forcible lighting signals of the four laser beams are generated based on the respective counters in the corresponding masking signal generation circuit, so that the error in the distance between the beams is similar to the masking signal. Regardless of this, forced lighting can be performed at an accurate timing.
[0041]
According to the second embodiment, since the masking signal is generated by operating the counter for each laser beam based on the timing of the BD signal corresponding to each laser beam, the distance between the beams is an arbitrary distance. However, since it is not necessary to correct this, man-hours are not increased.
[0042]
(Other examples)
In the above embodiments, an example in which a laser is used as a light source for forming a latent image on the photosensitive member has been described. However, the light source is not limited to this, and various types of light sources may be used. Further, although an example in which four light beams are used has been described, the present invention is not limited to this value, and can be applied to any number of light beams as long as the number is two or more. .
[0043]
【The invention's effect】
According to the present invention, in an image forming apparatus that scans a plurality of light beams to be modulated on a photoconductor and forms an image on the photoconductor, each of the plurality of light beams is detected and a detection pulse is generated. A single detection means for sequentially outputting, a distribution means for sequentially distributing and outputting the detection pulses to different signal lines by counting the detection pulses sequentially output from the single detection means, and an output from the distribution means A plurality of counting means for starting a clock counting operation in synchronization with the detected pulse, and comparing the count value of the counting means with a predetermined value to mask each of the light beams at different timings. A plurality of masking signal generating means for generating a masking signal; and the masking signal generated by each of the plurality of masking signal generating means; Masking means for masking each of the light beams at different timings by performing a logical operation on the modulation signal for modulating the light beam, so that image writing inhibition / permission of each light beam can be controlled with high accuracy. As a result, it is possible to perform image writing up to the edge of the sheet.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a first embodiment. FIG. 2 is a perspective view of a laser scanning optical system of an image forming apparatus. FIG. 3 is a block diagram of a circuit for processing a signal received by a beam detector. FIG. 5 is a diagram showing the inclination of the multi-beams. FIG. 5 is a diagram showing a situation where each beam passes through the slit 8. FIG. 6 is a cross-sectional view of the main part of the image forming apparatus. 8] Time chart of distributor 41 [FIG. 9] Time chart of circuit of FIG. 1 [FIG. 10] Circuit block diagram showing the second embodiment [FIG. 11] Time chart of the second embodiment [Explanation of symbols]
1 Multi-beam laser 3 Polygon mirror scanner 4 F-θ lens 5 Photosensitive drum 6 Reflecting mirror 7 Beam detector BD
8 Slit 32 Paper size detection 40 Beam detection circuit 41 Distributor 42 Image signal generators 43, 44, 45, 46 Gate circuits 47, 48, 49, 50 Laser drive circuit 51 Flip-flop 52 Counter 53 Counter clock input terminals 54-61 Digital comparator 62-69 Register 70 CPU
71-74 Flip-flop 80 Flip-flop 81 Counter 82 Counter clock input terminal 83, 84 Digital comparator 85, 86 Register 87 Flip-flop

Claims (5)

In an image forming apparatus that scans a plurality of light beams to be modulated on a photoconductor and forms an image on the photoconductor,
A single detection means for detecting each of the plurality of light beams and sequentially outputting a detection pulse;
Distributing means for sequentially outputting the detection pulses to different signal lines by counting the detection pulses sequentially output from the single detection means;
A plurality of counting means for starting a clock counting operation in synchronization with a detection pulse output from the distributing means;
A plurality of masking signal generating means for generating a masking signal for masking each of the light beams at different timings by comparing the count value of the counting means with a predetermined value ;
Masking means for masking each of the light beams at different timings by performing a logical operation on the masking signal generated from each of the plurality of masking signal generating means and a modulation signal for modulating the light beam. An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, further comprising means for changing a width of the masking signal. 3. The image forming apparatus according to claim 2, further comprising means for changing a width of the masking signal in accordance with a paper size. Claims, characterized in that for generating a forced lighting signal for forcibly generating the light beam to obtain said detection pulse, based on the clock count value from the detection pulse generation timing generated in the previous scan Item 2. The image forming apparatus according to Item 1 . A method of controlling an image forming apparatus that scans a plurality of light beams to be modulated on a photoconductor and forms an image on the photoconductor,
A detection step of detecting each of the plurality of light beams using a single detector and sequentially outputting detection pulses;
A distribution step of sequentially distributing the detection pulses to different signal lines by counting the detection pulses sequentially output from the single detector;
Masking for masking each of the light beams at different timings by starting a clock count operation in synchronization with each of the detection pulses distributed in the distribution step and comparing the count value with a predetermined value. A generation step for generating a signal;
An image forming apparatus comprising: a masking step of masking each of the light beams at different timings by performing a logical operation on the generated masking signal and a modulation signal for modulating the light beam . Control method.

Images