JP2012121174A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To certainly prevent misalignment in print start timing, resulting from malfunction due to noise.SOLUTION: An LSU 6 includes three phototransistors 24A, 24B, 24C and a sensor output circuit 23. The phototransistors detect the quantity of light of respective light beams, and are arranged in the scanning direction on the outside of the printing area of a photoreceptor on the scanning start side. A sensor processing circuit 23 creates a pulse signal of fixed width by comparing the output signals from the phototransistors with each other. An image processing part 4 controls the LSU 6 by using the pulse signal as a print start signal when the width of the pulse signal falls within a predetermined range, otherwise by not using the pulse signal as a print start signal.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic printer or a copy that forms an image by scanning laser light on a photosensitive member with a polygon mirror or the like.

  In a printing apparatus using a laser scanning unit (LSU), a laser beam is scanned on a photosensitive member by a polygon mirror or the like. Therefore, a BD sensor is arranged outside the printing area on the main scanning start side of the photosensitive member, and the laser beam is BD. Based on the signal output when crossing the sensor, the printing start timing signal in the main scanning direction is generated to control the printing in the main scanning direction from a certain position (for example, Patent Literature 1).

  The output signal from the BD sensor is easily affected by changes in the amount of laser light (beam diameter) and noise, and the print start timing is determined based on the detection signal from the BD sensor. However, the print quality is adversely affected.

  In order to prevent this, measures have been taken conventionally. For example, with respect to changes in the amount of laser light, the BD sensor is composed of two optical sensors arranged adjacent to each other, and the result of relative comparison between the output signals is used as the print start timing signal. I was trying to eliminate the effects of.

  Also, for the influence of noise, when the BD sensor detects laser light, the BD sensor output is masked until just before the next laser light detection, and even if noise is applied to the BD sensor, this is ignored. The circuit was configured as follows.

JP-A-11-115240

  However, as a countermeasure for comparing the output signals of the two optical sensors, as shown in FIG. 10, the timing of the leading edge of the BD sensor output from the intersection of the waveforms when the optical sensors 124A and 124B detect the laser beam 151 is used. Although it is possible to define the timing, the timing of the trailing edge is affected by the amount of light, and the pulse width of the BD sensor output is not guaranteed. For this reason, the BD sensor output and noise cannot be distinguished, and it has not been possible to determine whether noise is present from the pulse width.

  Regarding the mask of the BD sensor output, there is some blurring (jitter) in the time (BD cycle) from detection of the BD sensor to the next detection. There is also an error in the frequency of the clock used to determine the mask period. The jitter of the BD cycle is caused by the influence of the fluctuation of the rotation speed of the polygon mirror and the error of the reflection angle of the plurality of reflecting surfaces. If the BD cycle is shortened and the BD sensor detects it during the mask period. There are problems that the print start signal is not generated or the print start timing is greatly deviated. For this reason, the mask period has to be suppressed to a time shorter than the BD cycle, and a complete noise countermeasure cannot always be achieved.

  An object of the present invention is to reliably prevent a shift in print start timing caused by a malfunction caused by noise.

  The image forming apparatus according to the present invention includes an optical scanning device and an image processing unit. The optical scanning device is configured to deflect the light beam output from the light source and scan the photoconductor. The image processing unit is configured to control the optical scanning device.

  In the present invention, the optical scanning device has at least three optical sensors and a sensor output processing unit. Each of the plurality of optical sensors detects the light amount of the light beam, and is arranged in the scanning direction outside the printing area on the scanning start side of the photosensitive member. The sensor output processing unit generates a pulse signal having a constant width by relatively comparing the output signals of the plurality of optical sensors.

  In this invention, the image processing unit uses the pulse signal as a print start signal when the width of the pulse signal is within a predetermined range, and the pulse signal is used as the print start signal when the width of the pulse signal is outside the predetermined range. The optical scanning device is controlled so as not to be used.

  The image forming apparatus configured as described above includes at least three photosensors arranged in the scanning direction outside the printing area on the scanning start side of the photoconductor, so that the beam diameter of the light beam output from the light source, that is, the light Even if the amount of light of the beam changes, a pulse signal having a constant width in which the timings of both the leading edge and the trailing edge are defined is generated by relatively comparing the output signals of the plurality of optical sensors by the sensor output unit. Then, by adopting the image processing unit as a print start signal only when the width is within a predetermined range, it is possible to prevent the print start timing from being shifted due to the influence of noise.

  As a specific configuration of the image processing unit, when the width of the pulse signal output from the sensor output processing unit is within a predetermined range, a print start signal is generated from the pulse signal and output from the sensor output processing unit. A pulse signal processing unit that does not generate a print start signal when the width of the pulse signal is outside the predetermined range, and a print control that determines the print start timing by the optical scanning device based on the print start signal output from the pulse signal processing unit Are provided.

  The pulse signal processing unit is preferably configured to count and process the width of the pulse signal output from the sensor output processing unit with a clock cycle. In particular, if the width of the pulse signal is set to 3 clock cycles or more, it can be executed with a count of at least 2 clocks to detect that it is not noise, and printing starts at the timing of the trailing edge of the pulse signal. However, the determination time for the print permission / prohibition process for at least one clock can be obtained.

  Here, if there is an error in the rotational speed of the polygon mirror that scans the light beam, the scanning speed of the light beam that passes over the optical sensor varies, so the width of the pulse signal is counted to absorb the variation. Need to have a margin. On the other hand, the rotational speed of the polygon mirror is determined by the reference oscillator and its frequency division ratio. Therefore, if the above clock is combined with the clock used to determine the rotation frequency of the polygon mirror that scans the light beam, the generated pulse width and count value can be obtained even if the clock frequency changes slightly. Changes relatively, so there is no need to provide a margin for the count value.

  According to the present invention, it is possible to generate a pulse signal having a constant width that does not depend on the light amount of the light beam, and by detecting that this width is within a predetermined range, it is possible to reliably prevent a shift in print start timing due to malfunction due to noise. I can do it.

1 is a schematic front sectional view of an image forming apparatus. It is a schematic block diagram which shows the printing control system of a laser scanning unit and an image process part. (A) is a schematic block diagram which shows the structure of a BD sensor. (B) is a time chart showing signal waveforms of the respective parts of the BD sensor when the laser beam diameter is large, and (c) when the laser beam diameter is small. It is a schematic block diagram which shows the structure of a BD signal processing circuit. It is a time chart which shows the signal waveform of each part of a BD signal processing circuit with a BD signal and a clock. 6 is a time chart showing a case where noise is applied to a BD signal in FIG. 5. It is a schematic block diagram which shows the other example of a structure of BD sensor. It is explanatory drawing explaining an example of the principle of this invention BD sensor, and its detection result. It is explanatory drawing which shows the case where the number of the phototransistors which comprise a BD sensor in FIG. 8 is five. It is explanatory drawing explaining an example of the principle of the conventional BD sensor, and its detection result.

  First, an overall configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. The image forming apparatus 1 is large and includes a document reading unit 2, an image processing unit 4, a laser scanning unit (an example of an optical scanning device of the present invention, hereinafter referred to as LSU) 6, and a print engine 5.

  The document reading unit 2 is configured to read an image of the document 3 with the CCD sensor 7 and transmit image data to the image processing unit 4. The original 3 is placed and read in the state shown in FIG. 1 or is read while being fed by a document feeder provided in the original reading unit 2.

  The image processing unit 4 converts the image data from the document reading unit 2 into a format suitable for printing by performing, for example, dither processing and the like, receives print data from a personal computer or the like, and receives image data for printing. Generate.

  The print engine 5 emits a laser diode (not shown) which is a light source of the LSU 6 according to the image data from the image processing unit 4, and exposes the photoconductor 8 to form an electrostatic latent image. Then, the developing unit 9 attaches toner to form a visible image (toner image). The formed visible image is transferred to the paper supplied from the paper cassette 10, fixed by the fixing unit 12, and discharged.

  The CPU that controls the print engine 5 is connected to a CPU (none of which is shown) of the image processing unit 4 via a communication line. When a print start request is received from the image processing unit 4, the photoconductor by the cleaning unit 13. 8, charging of the photosensitive member 8 by the charger 15, and paper feeding from the paper cassette 10 are performed. When printing can be started, the CPU of the image processing unit is notified that printing is possible.

  A synchronization signal (BD signal) 11 indicating the print start timing is output from the LSU 6, and the image processing unit 4 converts the image data into an LD on / off signal in accordance with this synchronization signal, and transfers it through the signal line 14. To start.

  Next, determination of the print start timing by the image forming apparatus 1 configured as described above will be described with reference to FIGS.

  First, the generation procedure of the BD signal 11 will be described with reference to FIGS. FIG. 2 is a schematic block diagram illustrating a print control system of the LSU and the image processing unit. As shown in FIG. 2, the image processing unit 4 includes a BD signal processing circuit (an example of the sensor output processing unit of the present invention) 20, an oscillator 34, and a print control unit 33. The LSU 6 includes a laser driver 30, an LD 31, a polygon mirror 29, an oscillator 37, an fθ lens 28, a mirror 27, a BD sensor mirror 26, and a BD sensor 25.

  The print control unit 33 converts the image data 36 into an on / off signal of the LD 31, and on / off of one line in synchronization with the signal 35 indicating the main scanning writing timing output from the BD signal processing circuit 20. A signal is sent to the laser driver 30 through the signal line 14.

  The laser driver 30 controls the current of the LD 31 according to the on / off signal to cause the LD 31 to emit light. The laser beam is reflected and scanned by the polygon mirror 29 to expose the photosensitive member 8 through the fθ lens 28 and the mirror 27. A BD sensor mirror 26 is provided on the start side of the main scanning (left hand side in the figure), and the laser light reflected by the BD sensor mirror 26 is reflected by the three phototransistors 24A to 24C of the BD sensor 25. An example of an optical sensor of the invention). The analog outputs of the phototransistors 24 </ b> A to 24 </ b> C are processed by the sensor output processing circuit 23, converted into on / off signals, and output to the image processing unit 4 as the BD signal 11.

  The BD signal processing circuit 20 performs processing characteristic of the present invention in order to remove noise of the BD signal 11 and also performs a conventional process of applying a mask for a certain period to the output of the BD sensor 25. The signal 35 after noise removal is output to the print control unit 33.

  The image processing unit 4 and the LSU 6 are provided with oscillators 34 and 35 that oscillate clocks, respectively. The clock of the oscillator 34 is used for controlling the print start timing in the print controller 33 and the BD signal processing circuit 20, and the clock of the oscillator 35 is used for driving control of a motor (not shown) that rotates the polygon mirror 29.

  FIG. 3 is a diagram schematically showing the configuration and signal waveforms of each part of the BD sensor embodying the present invention. As illustrated in FIG. 3A, the BD sensor 25 includes three phototransistors 24 </ b> A to 24 </ b> C and a sensor output processing circuit 23. The sensor output circuit 23 includes three amplifiers (hereinafter referred to as AMP) 40A to 40C, two comparators 41A and 41B, three determiners 42A to 42C, two AND gates 43A and 43B, and a flip-flop 44. .

  As shown in FIG. 3A, the three phototransistors 24A to 24C are arranged at equal intervals L in the main scanning direction outside the printing area on the main scanning start side of the photosensitive member 8 (see FIG. 1). As shown, the laser beam is scanned from the left to the right in the figure. The phototransistors 24A to 24C are connected to the corresponding AMPs 40A to 40C, respectively, and a voltage corresponding to the amount of incident laser light is input from the AMP to the comparators 41A and 41B.

  Each input to the comparators 41A and 41B is also input to the determiners 42A to 42C for determining that AMP output ≧ specified voltage, and together with the AND gates 43A and 43B, the comparator 41A is in a state where the laser beam 51 is not incident. , 41B controls EN (enable) of the comparator to output Low.

  The flip-flop 44 is set / reset by the outputs from the comparators 41A and 41B, and is output as the BD signal 11. Here, the beam diameter of the laser beam 51 is sufficiently large as shown in the figure with respect to the light receiving areas of the phototransistors 24A to 24C, and the phototransistors 41A to 41C receive light relatively simultaneously. To do. FIG. 3B shows the signal waveform of each part when the beam diameter of the laser light 51 is large, and FIG. 3C shows the signal waveform of each part when the beam diameter of the laser light is small.

  In FIG. 3B, waveforms 45A to 45C are the outputs of the phototransistors 24A to 24C or waveforms after they are amplified. The time when the maximum value of each waveform is reached is the time when the center of the laser beam passes through the center (one-dot chain line portion) of each of the phototransistors 24A to 24C. Reference numeral 46 denotes a specified voltage for determination performed in the determiners 42A to 42C. Based on the value of the specified voltage, the outputs of the AND gates 43A and 43B change to pulses as shown by waveforms 47A and 47B, respectively. Waveforms 48A and 48B are output pulses of the comparators 41A and 41B, respectively.

  The waveform 48A becomes High at the timing 49A where the waveforms 45A and 45B intersect, and returns to Low when the waveform 47A becomes invalid (Low). Similarly, the waveform 48B becomes High between the timing when the waveforms 45B and 45C cross each other and the timing when the EN47B becomes Low. Since these signals are input to the flip-flop 44, the waveform 50 of the BD signal 11 becomes High during the period (pulse width T) of the timings 49A and 49B.

  If the beam diameter of the laser beam 51 is reduced, the outputs of the phototransistors 24A to 24C change to narrow shapes like waveforms 45D to 45F as shown in FIG. As a result, the pulse widths and generation positions of the waveforms 47 and 48 change, but the final pulse width T of the BD signal and its position do not change as can be understood by comparing FIGS. 3B and 3C. . Therefore, the pulse width T of the BD signal 11 does not depend on the beam diameter (light quantity) of the laser light, and is a constant pulse width determined by the arrangement interval L of the phototransistor. If the scanning speed of the laser light is V, T = The relationship L / V is established.

  As will be described later, the BD signal generated as described above is counted and processed in the clock cycle in the subsequent signal processing as shown in FIG. Although the number of phototransistors is three in this embodiment, it may be three or more. In particular, when an odd number is set as shown in FIG. 9, a plurality of pulses having a uniform width can be obtained, which contributes to more precise signal processing.

  Next, a processing procedure of the BD signal generated as described above will be described with reference to FIGS. In the following description, it is assumed that the pulse width of the generated BD signal is input to the BD signal processing circuit 20 within a range of 3 clocks or more and less than 4 clocks of the oscillator 34.

  FIG. 4 shows the configuration of the BD signal processing circuit 20. The BD signal processing circuit 20 includes three flip-flops 60A to 60C, an inverting circuit 61, an AND circuit 62, a mask circuit 63, a falling edge detection circuit 69, a flip-flop 67, and an AND circuit 68. The mask circuit 63 includes a falling edge detection circuit 64, a counter 65, and a comparator 66.

  FIG. 5 shows the output of each part of the BD signal processing circuit. As shown in FIG. 5, the BD signal 11 is sequentially delayed by the flip-flops 60 </ b> A to 60 </ b> C and input to the AND circuit 62. However, only the flip-flop 60 </ b> C is inverted by the inversion circuit 61 and input to the AND circuit 62.

  The output of the AND circuit 62 becomes High when the output of the flip-flops 60A and 60B changes from Low → High → High → High at every clock, and the inversion of the output of the flip-flop 60C becomes Low. When it becomes, it becomes Low.

  The output of the AND circuit 62 is input to the set terminal of the flip-flop 67, and the output of the flip-flop 67 becomes High in synchronization with the clock. When the falling edge detection circuit 69 detects the falling edge of the BD signal, the output of the flip-flop 67 is set to Low.

  The mask circuit 63 is a circuit for masking noise conventionally used. When the falling edge detection circuit 64 detects the BD signal and the counter 65 counts the set value, the output of the comparator 66 is output. It is comprised so that it may become High. However, since the count value is relatively large, it is easily affected by uneven rotation of the polygon mirror 29 and it is difficult to set the count value just before the rising edge of the BD signal, so that it is about 99% of the predicted period of the BD signal. A count value is set in. That is, the output of the mask circuit 63 becomes High earlier than the rising edge of the BD signal, as indicated by reference numeral 73 in the rising edge. The output of the mask circuit 63 is input to the AND circuit 62, and noise during the printing period of approximately one line is masked.

  Since the output of the flip-flop 67 and the BD signal are input to the AND circuit 68, when the output of the flip-flops 60A and 60B changes from Low → High → High every clock, the output of the AND circuit 68 is output. Becomes High and becomes High during the period when the BD signal is High, and becomes Low simultaneously with the fall of the BD signal.

  As shown in FIG. 2, the output of the AND circuit 68, that is, the output signal 35 of the BD signal processing circuit 20, is transferred to the print control unit 33 and used for determining the print start timing.

  Next, the principle of removing noise on the BD signal by the BD signal processing circuit configured as described above will be described.

  FIG. 6 shows the output of each unit of the BD signal processing unit when noise is added to the BD signal after the mask period ends. In the following description, it is assumed that the noise pulse width is 1 clock or more and less than 2 clocks, and the noise is generated immediately before the rising edge of the BD signal.

  As shown in FIG. 6, in the case of the pulse 70 of the regular BD signal, since there is a pulse width of 2 clocks or more, the outputs of the flip-flops 60A and 60B are output every clock after the mask period by the mask circuit 63 is completed. At the time of changing from Low → High → High, the output of the AND circuit 62 becomes High. As a result, the output of the flip-flop 67 becomes High, and the change in the BD signal is output from the AND circuit 68 to the print control unit 33.

  On the other hand, in the case of the noise 71 on the BD signal, since the pulse width is less than 2 clocks, noise propagates to the inversion of the outputs of the flip-flops 60A and 60B and the output of the flip-flop 60C. In the portion, by taking the AND of each delay signal, noise does not propagate to the hatched portion 72 and does not become high. As a result, the output of the flip-flop 67 does not become High, and the change in the BD signal is not output from the AND circuit 68 to the print control unit 33. That is, the noise 71 on the BD signal is completely masked.

  Further, as in this embodiment, if the pulse width of the pulse 70 of the regular BD signal is set to 3 clocks or more, it can be executed with a count of at least 2 clocks in order to detect that it is not noise, and the pulse Even if the printing process is started at the trailing edge of the signal, the determination time for the print permission / inhibition process for at least one clock can be obtained.

  FIG. 7 shows another embodiment of the configuration of the BD sensor. The motor clock for rotating the polygon mirror 29 in the configuration of FIG. 2 is supplied from the oscillator 37 of the LSU 6, but in FIG. 7, it is supplied from the motor clock generation circuit 38 based on the clock of the oscillator 34 of the image processing unit 4. Configured to be

  In the example of FIG. 2, there is no frequency correlation between the oscillator 34 and the oscillator 37, but in the example of FIG. 7, the rotation speed control of the motor of the polygon mirror 29 and the BD signal processing circuit 20 with the same clock of the oscillator 34. Processing of the BD signal is performed.

  The rotational speed of the motor affects not only the printing magnification but also the pulse width of the BD signal. However, the rotational speed of the polygon mirror 29 is determined by the reference oscillator and its frequency dividing ratio. By using the same oscillator 34 for both motor speed control and BD signal processing as in the example, it is possible to avoid the influence of errors in a plurality of oscillators. As a result, it is not necessary to provide a margin for the count value of the BD signal.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 4 ... Image processing part 6 ... LSU (optical scanning device)
24A, 24B, 24C ... Phototransistor (light sensor)
23 ... Sensor output processing circuit (sensor output processing unit)
20 ... BD signal processing circuit (pulse signal processing unit)
33 ... Print control unit 34, 37 ... Oscillator

Claims (5)

An optical scanning device that deflects the light beam output from the light source and scans the photosensitive member;
An image processing unit for controlling the optical scanning device;
In an image forming apparatus comprising:
The optical scanning device includes:
At least three optical sensors arranged in the scanning direction outside the printing area on the scanning start side of the photoconductor, and detecting the amount of the light beam;
A sensor output processing unit that generates a pulse signal having a constant width by relatively comparing output signals of the plurality of optical sensors;
Have
When the width of the pulse signal output from the sensor output processing unit is within a predetermined range, the image processing unit uses the pulse signal as a print start signal, and the width of the pulse signal output from the sensor output processing unit An image forming apparatus that controls the optical scanning device so that the pulse signal is not used as a print start signal when the value is outside a predetermined range. The image processing unit
When the width of the pulse signal output from the sensor output processing unit is within a predetermined range, a print start signal is generated from the pulse signal, and the width of the pulse signal output from the sensor output processing unit is outside the predetermined range. A pulse signal processing unit that does not generate a print start signal in the case, a print control unit that determines a print start timing by the optical scanning device based on a print start signal output from the pulse signal processing unit,
An image forming apparatus according to claim 1.   The image forming apparatus according to claim 2, wherein the pulse signal processing unit counts and processes the width of the pulse signal output from the sensor output processing unit in a clock cycle.   The image forming apparatus according to claim 3, wherein a width of the pulse signal is set to a time equal to or longer than three clock cycles.   The image forming apparatus according to claim 3, wherein the clock is also used as a clock used for determining a rotation frequency of a polygon mirror that performs scanning of a light beam.

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