JP4804153B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to detection accuracy of a paper edge in an image forming apparatus that detects an edge position of a paper in order to form an image at predetermined positions on both sides of the paper and corrects a start position of image formation.

  Conventionally, in an electrophotographic image forming apparatus, duplex printing is often performed as follows. A sheet is fed from a sheet feeding unit to a predetermined image forming position through a conveyance path, and an image on the first surface of the sheet is formed at the image forming position. Thereafter, the paper is turned upside down through another conveyance path (so-called circulation conveyance path or switchback conveyance path), and the sheet is fed again to the image forming apparatus. Then, the second surface is formed at the image forming position.

  As described above, when a sheet is conveyed, the sheet may be displaced in the direction perpendicular to the conveying direction due to mechanical skew or slip. In electrophotographic image formation, the paper is heated to fix the unfixed toner image formed on the first surface of the normal paper. Next, when the sheet is sent again to the image forming position to form an image on the second surface of the sheet (at the time of refeeding), the sheet temperature is higher than the temperature at the first sheet feeding. It becomes a state. In other words, when the toner is fixed at the time of fixing, the paper is heated to evaporate moisture and the like, so that the paper contracts and the print position in the direction perpendicular to the paper transport direction may be different.

  For this reason, if no measures are taken, even if the user tries to place an image of the same size on both sides of the paper and uses the same size image, the horizontal print start position between the both sides of the paper Different results.

  Because of such a problem, for example, a method disclosed in Patent Document 1 is proposed. In this method, a sensor for detecting the edge of the paper is arranged on the paper conveyance path to detect the paper edge position in the direction perpendicular to the paper conveyance direction, calculate the deviation amount of the paper edge, and based on the calculated deviation amount. The image export position is corrected.

  The paper edge detection method is usually performed as follows. When the apparatus is initialized, the light source is turned off with no paper between the light source and the line sensor, and the output voltage Vb (dark voltage) of the line sensor is measured. Next, the on-duty of the light source is controlled so that the peak voltage of the line sensor becomes a voltage (Vp) lower by a predetermined value than the saturation voltage (the voltage at which the sensor output voltage does not increase even if the light source light quantity is increased further). The light intensity is adjusted. When the sheet is conveyed between the contact image sensor and the LED array as the light source in the printing mode, the end position of the sheet is detected.

  FIG. 13 shows the output waveform of the sensor when there is a sheet under the sheet end detection sensor. As shown in the figure, the change in the level of the sensor output voltage near the end of the sheet has a gradient from the non-paper portion to the paper presence portion. The detection position of the paper edge is determined by the slice level voltage Vth (threshold voltage for detecting the paper edge) = (Vp + Vb) / 2 + Vb. Then, a falling edge position where the sensor level becomes Vth from a voltage equal to or higher than Vth is detected, and this is used as a paper edge detection position.

JP 2002-292960 A

  As shown in FIG. 13, the paper edge sensor has an error between the paper edge detection position and the actual paper edge position due to wraparound by light from the LED array. In addition, when there is a sheet between the LED array (light source) and the contact image sensor, it is desirable that the voltage Vs (hereinafter referred to as a shading voltage) at the portion shielded by the sheet is equal to the dark voltage Vb.

  However, if the paper does not approach the sensor and light wraps around it, light from the light source passes through the paper when the paper has a low basis weight or paper with high light transmission. The voltage sometimes increased (Vs ′). Furthermore, the slice level Vth may be lower than the light shielding voltage Vs ′ due to the paper due to the sensitivity of the contact image sensor, the variation in the light amount of the light source, the unevenness of the light distribution characteristic, and the like, and the case where the paper edge cannot be detected may occur.

Even if the slice level Vth is set appropriately, if multiple edges that are regarded as paper edges are detected due to dust (such as paper dust) on the optical path, the paper edges are detected incorrectly, and appropriate print correction is performed. There was something that could not be done.
Further, even if the slice level Vth is set appropriately, the actually detected paper edge detection position may exceed the upper and lower limit values to be measured from the paper edge design position set for each paper size. Conventionally, since correction is not performed when it is detected outside the paper edge search range, a formed image on the paper may be lost, or unfixed toner may be scattered in a place where there is no paper, thereby contaminating the inside of the apparatus. It was.

A first object of the present invention is to appropriately detect the end of a sheet even for a highly transmissive sheet and perform print writing correction so as to print at a predetermined position.
A second object of the present invention is to prevent misdetection due to noise or dust, and to perform print writing correction so as to appropriately detect the paper edge and print at a predetermined position.
A third object of the present invention is to perform print writing correction so that printing is performed at a predetermined position even when the actual sheet edge is in a position exceeding the upper and lower limit values to be measured from the sheet edge design position. .

  In order to solve the above-described problems, the present invention provides a conveyance path that conveys a sheet, and a line sensor that is arranged in the conveyance path, and in which a plurality of light receiving elements are arranged in a line perpendicular to the conveyance direction of the sheet. Including a detection value in a state where the paper is not conveyed to the paper edge detection means, and the paper is conveyed to the paper edge detection means. A threshold value for detecting the sheet edge using a detection value in the state, and detecting the sheet edge based on the determined threshold value; and a sheet edge detection unit that detects the sheet edge in the conveyance path. Calculation means for calculating a deviation amount of the paper edge detected by the paper edge detection means with respect to the conveyance reference position to be passed, and reading means for sequentially reading output values of the plurality of light receiving elements from the conveyance reference position Paper edge detection range setting means for setting the paper edge detection range according to the paper size, and correction means for correcting the image formation start position of the image formed on the paper based on the deviation amount. In the image forming apparatus, the correction unit may detect the output values sequentially read in the detection range when the paper end is not detected in the detection range set by the paper end detection range setting unit. When the final output value is a detection value in a state where the paper is conveyed to the paper edge detection means, the start position of the detection range is determined as the paper edge, and the sequential reading in the detection range is performed. If the final output value is a detection value in a state where the paper is not conveyed to the paper edge detection means, the end position of the detection range is determined as the paper edge, and the image shape And correcting the corrected position.

  According to the first invention relating to the present application, the slice level is appropriately set even when the S / N is reduced by the highly permeable paper. In other words, it is possible to prevent the detection value of the paper edge detection sensor when the light is shielded from being higher than the slice level and detecting the paper edge when using a highly transmissive paper. The paper edge can be detected more accurately than the method.

  According to the second invention related to the present application, it is possible to prevent erroneous detection of the paper edge due to paper dust, dust, and noise, and to correct the print writing so that the paper edge is accurately detected and printed at a predetermined position. Can do.

  According to the third invention relating to the present application, even when the actual paper edge is at a position exceeding the upper and lower limit values to be measured from the paper edge design position, the print writing correction can be performed so as to print at a predetermined position. Thus, it is possible to reduce the error of the printing position.

Example 1
The configuration of the first embodiment according to the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram showing the configuration of the image forming apparatus 4 in the embodiment, including an external device 47.

  In FIG. 1, 15 is a CPU that controls the entire image forming apparatus 4. Reference numeral 33 denotes a ROM which stores a control program for the CPU 15 and a control table. Reference numeral 10 denotes a pre-registration sensor, which is a sensor for detecting the leading edge of the sheet in order to align the sheet by the registration roller 16. A laser drive circuit 25 irradiates a laser in accordance with image data from the image control means 24. Reference numeral 9 denotes a paper edge detection sensor which detects a paper edge (paper edge) perpendicular to the paper conveyance direction and measures a deviation position of the paper perpendicular to the conveyance direction from the conveyance reference position. When the paper end in the width direction (perpendicular to the transport direction) of the paper passes the transport reference position when the paper is transported, the print position of the second side is set with the write correction value in the main scanning direction = 0. Is set to print at the specified position.

  The paper end detection sensor 9 is composed of a contact image sensor 34 and an LED array 36 and is output to the edge determination means 17 for detecting the paper end. When the edge of the sheet is determined by the edge determining unit 17, the distance from the conveyance reference position to the sheet end is measured by the edge position measuring unit 18. The measurement result is stored in the RAM 20.

  The CPU 15 requests the image control means 24 to correct the print writing timing with the distance from the conveyance reference position to the sheet edge as the amount of sheet misalignment. A paper feed driving unit 23 designates one of the manual feed tray 43, the paper feed cassette A8, the paper feed cassette B30, and the paper feed cassette C31 to feed paper. In the first exemplary embodiment, the reference of the mounting, conveyance, and printing position of the paper in each paper feed cassette is configured on the premise of the one-side reference, and the reference of each paper size is on the conveyance reference position side as shown in FIG. Is set to Reference numerals 38, 39, and 40 denote sensors for detecting the size of the paper filled in each of the paper feed cassette A8, the paper feed cassette B30, and the paper feed cassette C31. An image forming unit 26 prints on the fed paper by an electrophotographic process.

  A conveyance driving unit 27 conveys the fed sheet to the image forming position and conveys it to the paper discharge or double-side conveyance path (sheet reversing unit) 5. The sheet reversing drive means 21 performs reversal of the sheet conveyed to the duplex conveying path 5 to perform duplex printing, and drives the conveyance and refeeding to the image forming unit. The conveyance sensor 11 is a sensor provided in the double-side conveyance path 5 and detects the conveyance of the paper. Reference numeral 44 denotes fixing heater driving means for driving the fixing heater 19. Reference numeral 29 denotes print setting means for setting the print mode, paper size designation, etc. from the user, and the CPU 15 can detect the size of the paper fed for printing.

Next, the configuration will be described with reference to FIG. 2 showing a cross-sectional view of the image forming apparatus 4.
When the print start command is sent from the image control means 24, the CPU 15 picks up the paper set in the paper feed slot selected from the paper feed cassette A8, paper feed cassette B30, paper feed cassette C31, and manual feed tray 43. It controls so that it may be guide | induced to a conveyance path with a roller. After the leading edge of the sheet is detected by the pre-registration sensor 10 and registered, the transfer roller 1 and the photosensitive drum 6 are conveyed to the nipped image transfer position. In parallel with this, the laser drive means 25 is driven according to the image data sent from the image control means 24. As a result, the laser is irradiated from the laser scanner 2 onto the photosensitive drum 6 uniformly charged by the charging roller 7.

  The laser scanner 2 rotates a polygon mirror (not shown) at a constant speed to scan the laser from the left to the right in the main scanning direction of the paper. Further, a toner (not shown) image is visualized on the photosensitive drum 6 by the developing device 3. As a result, the toner nipped by the transfer roller 1 and developed on the photosensitive drum 6 is transferred onto the sheet. The sheet on which the toner has been transferred is fixed through a heat fixing roller pair 13 heated by a heater 19 in the roller.

  In the case of single-sided printing, the sheet is continuously conveyed and discharged to the FD tray 28. In the case of duplex printing, after the trailing edge of the sheet is detected by the paper discharge sensor 14, the sheet is reversed and driven by the sheet reversing drive unit 21 to be introduced into the duplex conveying path 5 in order to print the back side. A sheet is detected by a conveyance sensor 11 installed on the conveyance path of the duplex conveyance path 5. After a predetermined timing after the front end of the paper is detected by the transport sensor 11, the paper left end position is detected by the paper end detection sensor 9.

  The sheet edge detection sensor 9 is installed on the left side in the sheet conveyance direction, and includes a contact image sensor 34, an LED array 36, and a rod lens array 35 as shown in FIG. The contact image sensor 34 has light receiving elements 37 arranged in a line in the main scanning direction, and measures how much the left edge of all paper sizes that can be conveyed by the image forming apparatus 4 is conveyed with respect to the conveyance reference. It has a sensor length as possible.

  Further, the paper end detection sensor 9 is arranged so that light is emitted from the LED array 36 and transmitted light is received by the light receiving element 37 via the rod lens array 35. The LED light is directly irradiated to the image sensor at a portion where the paper is not conveyed. When there is a sheet, the LED light is blocked by the sheet, and the sensor level decreases. By detecting the position where the sensor level changes at the sheet edge, the position is determined as the sheet edge.

  After the sheet end position is detected by the sheet end detection sensor 9, the sheet is fed again to the image transfer position. The edge determination unit 17 detects the sheet edge, and the edge position measurement unit 18 measures the amount of deviation in the main scanning direction from the conveyance reference position. The amount of deviation in the main scanning direction from the paper conveyance reference position is transmitted to the image control means 24 by a CMD / STS signal.

  Based on the amount of misalignment in the main scanning direction of the paper, the image control means 24 starts the printing start timing so that the printing start position of the second surface in the main scanning direction starts from the specified position (position 5 mm from the left end). Adjust. The corrected image data is transmitted to the laser driving means 25. The laser driving means 25 starts laser irradiation based on the corrected image. The irradiated laser forms a latent image on the photosensitive drum 6 through a polygon mirror rotating at a constant speed so as to scan from the left to the right of the paper, is developed with toner, and is fed again from the double-sided conveyance path 5. After being transferred to and fixed on the sheet, the paper is discharged to the FD tray 28.

  Next, image writing start correction by the image control means 24 will be described with reference to FIGS.

  The image control means 24 receives image information sent from an external device 47 such as a host computer and develops dots. A communication signal (CMD / STS) for performing command / status communication between the CPU 15 and the image control means 24, a sub-scanning direction synchronization signal (TOPSYNC) output from the CPU 15 to the image control means 24, and main scanning There is a direction synchronization signal (BD). Further, the image control means 24 transmits an image signal, which is dot-developed internally in synchronization with the image transfer clock (VCLK), to the laser driving means 25.

  FIG. 14 is a timing diagram of each signal and a diagram showing the printing position of the paper. As shown in FIG. 14, the laser is configured such that an image is formed by scanning the paper from the left to the right in the main scanning direction for each line by the laser scanner 2. On the other hand, a paper edge detection sensor 9 is also installed on the left side of the paper and detects how much the left edge of the paper is shifted in the main scanning direction from the conveyance reference. Further, the resolution of the sheet edge detection sensor 9 and the printing density in the horizontal direction are the same.

  The image control means 24 outputs an image signal for each dot in synchronization with VCLK at a predetermined timing R with reference to the rising edge of the BD signal output from the CPU 15 in synchronization with the laser scanner 2. Here, the predetermined timing R means that in printing on the second side of the paper, the left edge of the paper is conveyed along the conveyance reference and Δ (the number of difference pixels between the paper left edge detected by the paper edge sensor and the paper conveyance reference position) = In the case of 0, the print timing is from a position 5 mm from the left end of the paper.

  In this embodiment, since the left side is the reference, the timing R is a timing common to all paper sizes. The left edge of the paper is detected by the paper edge detection sensor 9 and the like, and the calculated difference pixel number Δ from the conveyance reference position to the left edge of the paper is transmitted to the image control means 24 through the CMD / STS signal. The image control unit 24 changes the timing of outputting the image data based on the transmitted sheet deviation amount. Since the amount of deviation (number of pixels) from the conveyance reference position is the same as the resolution of the paper edge detection sensor and the horizontal printing density, the image signal start timing (image signal from the rising edge of the BD) is equal to the number of dots of the paper edge deviation. Adjust the time until output starts.

  When the left edge of the image signal is detected to the right of the transport reference position by the paper edge detection sensor 9 or the like, the start timing of the image signal is adjusted to a timing delayed by a deviation amount × VCLK from the predetermined timing R. On the other hand, when the left end of the sheet is detected to the left of the transport reference position, the timing is adjusted to be earlier than the predetermined timing R by a deviation amount × VCLK. FIG. 14 is a timing diagram in which the print start timing is corrected when the paper is transported so as to be separated by 3 dots from the paper transport reference. The paper edge detection sensor 9 detects that the paper edge has shifted by 3 dots in the main scanning printing direction from the transport reference, and the image control means 24 detects 1 dot from the falling edge of the BD signal 3 VCLK after the predetermined timing R. Correction is made to output the image signal of the eye.

  Next, details of the configuration and operation will be described with reference to FIG. 4 which is an electrical block diagram specifically showing the edge determination unit 17, the edge position measurement unit 18, and the sheet end detection sensor 9 and FIG. 5 which is a timing chart.

  A timing generation circuit 41 generates a timing signal for driving the contact image sensor 34 and the like. A contact image sensor 34 receives a CLK signal and a RESET signal from the timing generation circuit 41. The CLK signal is a synchronization signal for serially transferring the output of each light receiving element, and the RESET signal is a signal for resetting the output of the sensor. As shown in FIG. 5, in the contact image sensor 34, the light receiving elements 37 are arranged in one row, and are arranged so that the conveyance reference position and the position of the first pixel of the effective pixels of the light receiving element 37 coincide.

  The output of the sensor is reset when the RESET signal becomes “High”, and after the blanking output of a predetermined section, in synchronization with the rising edge of the CLK signal, the pixels are sequentially output from the first pixel of the effective pixels of the light receiving element 37, Read every line. An LED array 36 controls the pulse width of the LED drive signal having a pulse waveform from the CPU 15 to adjust the amount of light of the LED. A D / A converter 42 converts digital data Dth set by the CPU 15 into an analog voltage Vth. A comparator 45 compares the output from the contact image sensor 34 with the slice level voltage Vth (threshold voltage for detecting the paper edge) set by the D / A converter.

  Reference numeral 46 denotes an edge position detection counter which is reset by the RESET signal and is counted up at the rising edge of the CLK signal during the enable valid period output from the comparator 45. As shown in FIG. 5, the sensor output is higher than the slice level Vth at a location where there is no sheet between the LED array 36 and the contact image sensor 34, so that the comparator output becomes “High” and the edge position detection counter 46 is enabled. Dcnt (count value = n) counted up when enable is valid is output to the CPU 15. This count value is the number of pixels of the light receiving element from the conveyance reference position to the sheet edge.

  The output from the contact image sensor 34 is input to the A / D port of the CPU 15. The A / D port incorporates an A / D converter and converts an analog voltage output from the contact image sensor 34 into digital data. The output of the contact image sensor 34 is sampled by the A / D_CLK signal output from the timing generation circuit 41 and converted into digital data Dsamp (A / D value). The A / D_CLK signal is flexibly generated from the timing generation circuit according to the setting from the CPU 15.

  At the time of initialization light amount adjustment, the timing generation circuit 41 outputs an A / D_CLK signal over the reading time for one line of the contact image sensor 34 to sample the output levels of all the pixels of the sensor. When sampling the light-shielding voltage Vs of the paper during paper conveyance, the A / D_CLK signal is generated as follows. That is, the A / D_CLK signal is generated so as to sample the sensor output of the location where the paper shields between the LED array 36 and the contact image sensor 34 regardless of the size of paper usable in the image forming apparatus 4. ing.

  Next, the operation of paper edge detection and print position correction will be described based on the flowchart of FIG.

  When the power of the image forming apparatus 4 is input or an initialization command is issued, the CPU 15 starts adjusting the light amount of the LED (LED array 36) for initialization (S1, 2). The pulse width of the LED driving signal is driven to the maximum to irradiate the contact image sensor 34 with the maximum amount of light, and the output signal for one line from the sensor is read. At this time, the timing generation circuit is set so that the A / D_CLK signal is always output (AD_CLK1 in FIG. 5) during the reading time of one line of the contact image sensor 34 (S3).

  Control is performed to lower the light amount by lowering the lighting duty of the LED drive signal until the peak value for one line of the contact image sensor 34 starts to fall (S4, 5). The peak voltage Vp when the peak value for one line of the contact image sensor 34 starts to drop and the pulse width of the LED drive signal at that time are recorded in the RAM 20 (S6). In the case of a single-sided printing command according to an instruction from the user, the first side is finished after printing (S22).

  If there is a duplex printing command, the sheet is fed and printed on the first side, and then the sheet is conveyed to the duplex conveyance path 5 (S7, 8). When the leading edge of the sheet is detected by the conveyance sensor 11, after a predetermined time, the LED is turned on with the pulse width recorded in the RAM 20 with the LED drive signal. In S9 and 10, the first line of the contact image sensor 34 is read to detect the light shielding voltage Vs. The shading voltage Vs is sampled so that the sensor output of the point at which the paper shields the LED light is always read regardless of the paper size, and the sampled shading voltage Vs is recorded in the RAM 20. At this time, the timing generation circuit is set so that A / D_CLK becomes the timing (AD_CLK2 in FIG. 5) for sampling the light shielding voltage Vs of the paper.

  The slice level Vth is calculated from the shading voltage Vs read in S11 and the peak voltage Vp recorded in the RAM 20 when adjusting the amount of light (calculation formula: Vth = Vs + (Vp + Vs) / 2). When the contact image sensor 34 starts reading the second line, digital data Dth corresponding to Vth is output to the D / A converter 42 in order to set the calculated Vth as a reference of the comparator 45. Since the comparator output is enabled for the sensor output at the portion where there is no paper, the counting by the edge position detection counter 46 is activated.

  In S13, the value n of the edge detection counter is set to 0 by the RESET signal. When the enable is enabled, the edge position detection counter 46 starts counting (S14). Since the enable is valid from the start of counting to the edge detection position, the pixel data is sequentially read and the count up is continued (S15 to 17).

  Since the falling edge of the image data is detected at the sheet edge position and the enable becomes invalid, the edge position detection counter 46 stops counting (S18). The final count value n of the edge position detection counter 46 becomes the difference pixel number Δ from the conveyance reference position to the sheet edge, and the image control means 24 is notified of the difference pixel number Δ (= n) (S19). The image control means 24 converts the time axis by the above-described control based on the notified difference pixel number Δ, adjusts the image writing timing of the second side (S20), and prints the second side (S21).

(Example 2)
FIG. 7 is an electrical block diagram specifically illustrating the edge position determination unit, the edge position measurement unit, and the sheet end detection sensor according to the second embodiment.

  In the second embodiment, the reference for the mounting, transport, and printing position of the paper in each paper feed cassette is based on the central reference. In the configuration based on the center reference, as shown in FIG. 12B, the reference of each sheet is at the center, so the reference position of the sheet edge differs for each sheet size, and the calculation method of the deviation amount of the sheet edge is also different.

  As shown in FIG. 15, Area is an internal signal for confirming the presence / absence of a paper edge within a set range (detection range). Area is set by the CPU 15 so as to enable a period corresponding to a range of ± 4 mm around the paper edge design value of each paper size. In the present embodiment, the operation will be specifically described assuming that the contact image sensor 34 has a printing density of 600 dpi and a paper size of A4 size paper. As shown in FIG. 15, the A4 size paper left edge design value is 2478 dots (105 mm) to the left from the center reference, and 236 pixels (10 mm) to the right from the conveyance reference position. Area (paper edge search range) is set between 142 pixels and 331 pixels from the conveyance reference position (first pixel of effective pixels).

In the second embodiment, the CPU 15 generates a CLK signal and a RESET signal for driving the contact image sensor 34, and inputs the output of the contact image sensor 34 to the A / D port.
The CPU 15 samples the value of the A / D port in synchronization with the CLK signal. The first line of the reading line refers to the data m of the Mth pixel at the location shielded by the paper in order to sample the light shielding voltage Vs in order to determine the slice level of the paper. A slice level Dth (A / D conversion value of Vth) is calculated from the data m.

  In the second reading line, in order to detect the paper edge, the data sampled at the A / D port is sequentially compared with the slice level Dth from the paper edge search range start pixel of the effective pixel to the paper edge search range end pixel. If there are a plurality of pixels (paper edge candidates) that are equal to or smaller than Dth in the paper edge search range, the final paper edge candidate in the search range is set as the paper edge detection position.

Next, the operation of A4 size paper edge correction will be described based on the flowchart of FIG.
FIG. 8 is a flowchart in which S9 to S21 in FIG. In addition, the flow part of S9-S21 differs, and the other part is the same process as FIG.

  First, the CPU 15 reads the first line of the contact image sensor 34 (S1). In order to measure the light shielding voltage Vs, the output of the pixel (M pixel) corresponding to the light shielding position of the paper is sampled by reading the sensor (S2). A slice level Dth (A / D conversion value of Vth) is calculated from the light shielding voltage Vs and the peak voltage Vp at the time of adjusting the light amount (S3).

  Next, the CPU 15 reads the second line of the contact image sensor 34 (S4). The CPU 15 confirms that the size designated by the print setting means 29 or the like is A4 size paper, and sets the area between the 142nd pixel and the 331st pixel as the paper edge search range (Area) in synchronization with the CLK cycle. (S5).

  First, the memory C of the pixel number at the paper edge candidate position numbered from the first sensor effective pixel on the RAM 20 is set to zero. The pixel number n from which data is read is set to 1, and the output of the contact image sensor 34 is sequentially taken from the first effective pixel (S6, 7). When the pixel number is after the 142nd pixel, each pixel data and the slice level Dth are sequentially compared, and the falling edge pixel position from Dth to Dth is investigated as a paper edge candidate. If it is the 142th pixel or less, the count-up is continued for each pixel until it becomes 142 pixels (S7-9).

  If a paper edge candidate is detected after the paper edge search is started, the value of the paper edge candidate pixel number memory C is updated to the detected pixel number n (S12). When the pixel data is read out at the 331st pixel, the detection of the paper edge candidate is finished. By repeating S10 to S14, the final value of the pixel number memory C becomes the paper edge candidate at the location closest to the end of the range in the paper edge search range.

  If no paper edge candidate is detected between the 142nd pixel and the 331st pixel, the value in the pixel number memory C remains 142 and the difference pixel number Δ is processed as 0 (S15, 17). On the other hand, if the pixel number memory C is not 142, there is a paper edge candidate, and the difference pixel number Δ from the paper edge detection position to the paper edge design value is calculated as a correction value. Since the paper edge candidate pixel number memory C is n and the A4 size paper edge design value is the 236th pixel, the difference pixel number Δ is calculated from Δ = n−236 (S15, 16). The calculated difference pixel number Δ is notified to the image control means 24 by a CMD / STS signal. The image control unit 24 converts the time axis by the above-described control based on the notified difference pixel number Δ and adjusts the image writing timing of the second surface.

  FIG. 9 shows a timing chart regarding the second embodiment. In the search within the paper edge search range, the detected paper edge candidates are sequentially updated, and the paper edge candidate closest to the end of the range in the paper edge search range is adopted. Even if an error due to dust or the like occurs in a nonexistent location, the edge of the paper can be detected correctly.

(Example 3)
FIG. 10 is a flowchart for explaining the operation of the third embodiment.
Steps S1 to S5 are the same as those in FIG.

  In S6 and 7, the value of the memory C for recording the largest pixel number among the paper edges detected in the paper edge search range is set to 142, and the pixel number n for reading data is set to 1. Then, the output of the contact image sensor 34 is sequentially captured from the first effective pixel (S6, 7).

  Next, pixel data is sequentially read out for each pixel, and counting up is continued for each pixel until n becomes 142 (S8, 9). When n reaches 142, pixel data is sequentially read, and each pixel data is compared with the slice level Dth (S10, 11). If the pixel data of pixel number n is larger than Dth, the memory C is updated to n (S12). If the pixel data is not larger than Dth, the value of the memory C is not changed and the next pixel data is read.

  The flow of S10 to S14 is repeated until the image data n reaches 331 (the end of the paper edge search range). After the data comparison for the 331st pixel is completed, if the value n in the memory C is a value from 142 to 331, the paper edge exists in the paper edge search range. When the value n of the memory C is 142, it is assumed that the actual paper edge is at a position below the 142th pixel of the paper edge search range start, and the paper edge is set to the 142nd pixel. That is, when the paper edge is not detected in the paper edge search range, and the final detection value of the paper edge detection sensor 9 in the paper edge search range is a detection value when the paper is shielded by the paper, the paper edge search is performed. The range start position is regarded as the paper edge.

  On the other hand, when the value n of the memory C is 331, it is assumed that the actual paper edge is the 331st pixel or more at the end of the paper edge search range, and the paper edge is set to the 331st pixel. That is, when the paper edge is not detected in the paper edge search range, and the final detection value of the paper edge detection sensor 9 in the paper edge search range is the detection value when there is no paper, the paper edge search range end position Is considered the edge of the paper. FIG. 11 is a timing chart when the paper edge is outside the paper edge search range.

  Next, in S15, the pixel number memory C value (= n) is used as the paper edge detection position, and the difference pixel number Δ (= n−236) up to the paper edge design value (236th pixel) is calculated. To notify. The image control unit 24 converts the time axis by the above-described control based on the notified difference pixel number Δ and adjusts the image writing timing of the second surface.

It is a block diagram which shows the structure of Example 1 by this invention. It is a figure which shows the apparatus cross section (outline) of Example 1 by this invention. It is a figure which shows the structure of the paper end detection sensor of Example 1 by this invention. FIG. 3 is an electrical block diagram of a sheet end detection sensor, an edge determination unit, and an edge position measurement unit according to the first exemplary embodiment of the present invention. It is a timing chart of Example 1 by the present invention, and is a figure showing the relation between a paper edge detection sensor and paper. It is an operation | movement flowchart of Example 1 by this invention. It is an electrical block diagram of the paper end detection sensor, the edge determination means, and the edge position measurement means of Embodiment 2 according to the present invention. It is an operation | movement flowchart of Example 2 by this invention. It is a timing chart of Example 2 by the present invention. It is an operation | movement flowchart of Example 3 by this invention. It is a timing chart of Example 3 by the present invention. FIG. 6 is a diagram illustrating a sheet edge position based on a sheet reference for each sheet size. It is a figure which shows the paper edge detection waveform by the conventional slice level setting. FIG. 6 is a timing diagram illustrating a method for correcting image writing timing for a shifted paper edge by a paper edge detection sensor. It is the figure which showed A4 paper size and the paper edge search range of Example 2 by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transfer roller 2 ... Laser scanner 3 ... Developing device 4 ... Image forming apparatus 5 ... Double-sided conveyance path 6 ... Photosensitive drum 7 ... Charging roller 8 ... Paper feed cassette A
DESCRIPTION OF SYMBOLS 9 ... Paper edge detection sensor 10 ... Pre-registration sensor 11 ... Conveyance sensor 12 ... Fixing discharge sensor 13 ... Fixing roller pair 14 ... Discharge sensor 15 ... CPU
16: Registration roller 17 ... Edge determining means 18 ... Edge position measuring means 19 ... Heater 20 ... RAM
DESCRIPTION OF SYMBOLS 21 ... Paper inversion drive means 23 ... Paper feed drive means 24 ... Image control means 25 ... Laser drive means 26 ... Image forming means 27 ... Conveyance drive means 28 ... FD tray 29 ... Print setting means 30 ... Paper feed cassette B
31: Paper cassette C
33 ... ROM
34 ... Contact image sensor 35 ... Rod lens array 36 ... LED array 37 ... Light receiving element 38 ... Cassette A size sensor 39 ... Cassette B size sensor 40 ... Cassette C size sensor 41 ... Timing generation circuit 42 ... D / A converter 43 ... Manual feed Tray 44 ... Fixing heater driving means 45 ... Comparator 46 ... Edge position detection counter

Claims (1)

A transport path for transporting paper,
A paper edge detection means for detecting a paper edge of the paper , comprising a line sensor arranged in the conveyance path and having a plurality of light receiving elements arranged in a line in a direction orthogonal to the paper conveyance direction , Determining a threshold value for detecting the paper edge using a detection value when the paper is not conveyed to the paper edge detection unit and a detection value when the paper is conveyed to the paper edge detection unit; Paper edge detecting means for detecting the paper edge with reference to the determined threshold ;
Calculation means for calculating a deviation amount of the paper edge detected by the paper edge detection means with respect to a conveyance reference position through which the paper edge should pass in the conveyance path;
Read means for sequentially reading output values of the plurality of light receiving elements from the transport reference position;
A paper edge detection range setting means for setting a detection range of the paper edge according to the size of the paper;
An image forming apparatus comprising: a correction unit that corrects an image formation start position of an image formed on the sheet based on the shift amount;
The correction means is a case where a paper edge is not detected in the detection range set by the paper edge detection range setting means, and a final output value of the sequentially read output values in the detection range is the paper Is a detection value in a state where it is conveyed to the paper edge detection means, the start position of the detection range is determined as the paper edge, and the final output value of the sequentially read output values in the detection range is When the detected value is in a state where the paper is not conveyed to the paper edge detecting means, the end position of the detection range is determined as the paper edge, and the image formation correction position is corrected. Image forming apparatus.

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