JP4556563B2 - Image printing apparatus, printing result inspection apparatus, and printing result inspection method - Google Patents

Description

  The present invention relates to an image printing apparatus including an inspection unit that inspects a printing result by a printing unit of an image printing apparatus, a printing result inspection apparatus that inspects a printing result by image printing, and a printing result inspection method.

  2. Description of the Related Art Conventionally, an image printing apparatus including an inspection unit that inspects a result of image printing by a printing unit is known. The inspection means is provided with an image acquisition device for acquiring an image printed on a sheet as inspection image data. Then, the quality of the print result is determined based on the inspection image data acquired by the image acquisition device. As a result, it is possible to automatically determine the printing result, and in the case of printing failure, it is possible to automatically take measures such as reprinting. As a result, the reliability of the image printing apparatus can be further improved.

  Here, the quality determination of the print result is made based on the inspection image data as described above. Therefore, the inspection accuracy of the print result is greatly influenced by the quality of the inspection image data. For this reason, it is necessary to obtain high-quality inspection image data in order to inspect the printing result with higher accuracy.

  One of the causes of the quality deterioration of the inspection image data is a paper conveyance speed. Usually, the image acquisition device is fixedly arranged on the conveyance path. Then, the printing result on the conveyed paper is sequentially scanned and read at a predetermined scanning timing, and an image printed on the paper is acquired as inspection image data. This scanning timing is set based on a preset sheet conveyance speed. However, if the conveyance speed changes for some reason and the scanning timing and the position on the paper to be operated deviate from the timing when the scanning position passes, the image printed on the paper cannot be scanned accurately, It is not possible to obtain inspection image data, and thus to perform high-precision print result inspection.

  In view of this, Japanese Patent Application Laid-Open No. 2004-151561 discloses an image forming apparatus that detects the conveyance speed of a sheet by disposing conveyance speed acquisition means before and after the image reading apparatus. Then, the scanning timing is set according to the detected conveyance speed. According to this, appropriate inspection image data can be acquired even if the sheet conveyance speed is different from that set in advance for various reasons, and an accurate print result inspection can be performed.

JP 2004-1112045 A

  Here, usually, many speed detection means cannot obtain a stable detection value immediately after the start of speed detection. In other words, there is a transient time in which the detected value is unstable from the start of detection until a stable detected value is obtained. For example, in the image forming apparatus described in Patent Document 1, an encoder provided on the conveyance path is used as a speed detection unit. This encoder is rotated by a frictional force generated between the encoder and the conveyed paper, and detects the rotation speed as the conveyance speed of the paper. In other words, in the case of this encoder, the timing for starting speed detection is when the front end of the conveyed paper reaches and contacts the encoder. Ideally, it is desirable that the sheet conveying speed can be detected immediately immediately after the start of the speed detection. However, in practice, a stable detection value cannot be obtained until a predetermined time elapses after the start of speed detection. This is due to a temporary decrease in the sheet conveyance speed caused by the contact of the sheet with the encoder, a low detection response of the encoder, and the like. An appropriate scanning timing cannot be calculated at the conveyance speed detected during such a transient time, which is an unstable time, and therefore an accurate print result inspection cannot be performed. However, in the image forming apparatus described in Patent Document 1, consideration is not given to the problem of this transition time. For this reason, there is a possibility that the inspection accuracy of the printed result is lowered.

  Accordingly, an object of the present invention is to provide an image forming apparatus, a print result inspection apparatus, and a print result inspection method that can further improve the inspection accuracy of a print result.

An image printing apparatus according to the present invention includes a printing unit that prints a document image on a sheet based on document image data, an inspection unit that inspects a printing result by the printing unit, and a conveyance unit that conveys the sheet downstream along a conveyance path. An image printing apparatus comprising: a scanning unit that scans and reads a print result on a sheet to be transported sequentially at a predetermined scanning timing, and acquires an image printed on the sheet as inspection image data; an image reading unit, in parallel with the reading by the image reading unit conveying a conveying speed detecting means for sequentially detecting the conveying speed of the sheet in the vicinity of the image reading position by the image reading means, Ru are sequentially acquired by the conveying speed detecting means based on the speed, and a control means for sequentially controlling the scanning timing of reading by the image reading means currently performed, based on the inspection image data obtained by the image reading means A determination means for determining the quality of printing results, the transport speed detecting means, an upstream rate detection means for detecting the conveying speed of the sheet in the upstream detection position located immediately before the image reading position, the image reading A downstream speed detection means for detecting the sheet conveyance speed at a downstream detection position located immediately after the position, and the distance between the upstream detection position and the image reading position is detected by the upstream speed detection means. length in the conveyance direction of the paper sheets during the transient time until stable detection value is obtained from the start of Ri der than the distance to be transported, the distance between the upstream detection position and the downstream detection position is to be conveyed From the start of speed detection by the downstream speed detecting means until the stable detection value is obtained, the distance that the paper is conveyed is smaller than the subtracted distance.

  In another preferred aspect, the conveyance speed detection means has switching means for switching from speed detection by the upstream speed detection means to speed detection by the downstream speed detection means, and the switching timing by the switching means is conveyed. This is immediately before the trailing edge of the sheet passes the upstream detection position. Preferably, when the detection value of the paper detection sensor that detects the presence or absence of paper immediately before the upstream detection position is switched from the presence of paper to the absence of paper, the switching means preferably detects the downstream side from the speed detection by the upstream speed detection means. Switch to speed detection by speed detection means.

  In another preferred aspect, the conveyance speed detection means moves at least one of the upstream speed detection means and the downstream speed detection means in the conveyance direction according to the size of the sheet to be conveyed, Moving means for changing the distance from the downstream detection position is provided.

  In another preferred aspect, the upstream speed detection means and the downstream speed detection means are provided to face the detection roller, contact with a part of the conveyed paper, and rotate as the paper is conveyed. In the encoder, the transition time is a period during which the rotation speed generated at the initial stage of the encoder rotation increases.

Another printing result inspection apparatus according to the present invention is a printing result inspection apparatus that inspects the printing result by the image printing apparatus, and sequentially scans and reads the printing result on the conveyed paper at a predetermined scanning timing. An image reading unit that acquires an image printed on a sheet as inspection image data, and a conveyance speed detection that sequentially detects the sheet conveyance speed near the image reading position by the image reading unit in parallel with the reading by the image reading unit. and means, based on the conveying speed that will be acquired sequentially by the conveying speed detecting means, and control means for sequentially controlling the scanning timing of reading by the image reading means currently performed, based on the inspection image data obtained by the image reading means Determination means for determining whether the print result is good or not, and the conveyance speed detection means is configured to convey a sheet at an upstream detection position located immediately before the image reading position. An upstream rate detection means for detecting the speed, has a downstream speed detection means for detecting a conveying speed of the sheet in the downstream detection position located immediately after the image reading position, the upstream detecting location and the image reading position the distance between the der distance or more stable detection value from the speed detection start by the upstream rate detection unit is transported paper during the transient time to be obtained is, an upstream-side detection position and the downstream detection position The distance of the sheet is subtracted from the length of the sheet to be conveyed in the transition time from the start of speed detection by the downstream speed detection means until a stable detection value is obtained. It is smaller than the distance.

Another printing result inspection method according to the present invention is a printing result inspection method for inspecting a printing result by an image printing apparatus, and sequentially scans and reads a printing result on a conveyed paper at a predetermined scanning timing, an image reading step of acquiring the image printed on the paper as an inspection image data, the transport speed in parallel with the reading in the image reading step, sequentially detects the conveying speed of the sheet in the vicinity of the image reading position by the image reading step a detecting step, on the basis of the conveying speed that will be successively acquired at a conveying speed detection step, a control step of sequentially controlling the scanning timing of the image reading currently performed, printing on the basis of the inspection image data obtained by the image reading step A determination step for determining whether the result is good or not, and the conveyance speed detection step is an upstream located immediately before the image reading position. It has an upstream rate detection step of detecting a conveyance speed of the sheet at the detection position, and the downstream speed detection step of detecting a conveyance speed of the sheet in the downstream detection position located immediately after the image reading position, the upstream detection distance between the position and the image reading position, der distance over which the paper during the transient time until stable detection value from the speed detection start on the upstream side speed detection step is obtained is transported is, the upstream side detection The distance between the position and the downstream detection position is the distance between the transport direction length of the transported paper and the transition time from the start of speed detection at the downstream speed detection step until a stable detection value is obtained. The transported distance is smaller than the subtracted distance .

  Here, the image printing apparatus refers to all types of models that print an image on paper, such as a printer, a copying machine, a facsimile, and a digital multifunction machine that combines these. In addition to normal printing paper, paper refers to all sheet-like printing media such as postcards, cardboard, cloth, and OHP sheets.

  According to the present invention, since the speed detection position takes the transient time into consideration, the scanning timing can be calculated based on a stable detection value. Thereby, the inspection accuracy of the printing result can be further improved.

  Hereinafter, a printer 10 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an overall configuration diagram of the printer 10. The printer 10 described below is assumed to be a relatively large high-speed printer. However, it may be applied to other image forming apparatuses such as a copying machine and a small printer by appropriately changing a part of the configuration.

  The printer 10 is controlled by an image printing control unit (not shown), and prints the same image as the original image data stored in the image printing control unit on paper. The paper stored in the storage unit 22 is transported along the main transport path 14 and an image is printed in the printing unit 12. The print result is inspected by an inspection device 16 provided downstream of the printing unit 12. When the inspection result is normal, the sheet is conveyed to the normal paper discharge tray 34 or the duplex conveyance path 18. On the other hand, when the inspection result is abnormal, the sheet is conveyed to the abnormal paper discharge tray 36. Hereinafter, the printer 10 will be described in detail.

  The conveyance path on which the sheet is conveyed is roughly divided into a main conveyance path 14, a duplex conveyance path 18, and a discharge conveyance path 21. The main conveyance path 14 is a conveyance path that guides paper from the storage unit 22 to the printing unit 12 and the inspection device 16. The main conveyance path 14 is branched downstream into a duplex conveyance path 18 and a discharge conveyance path 21. The double-sided conveyance path 18 is a conveyance path that turns the paper over and guides it to the main conveyance path 14 again. The paper discharge conveyance path 21 guides the printed paper to the paper discharge unit 24. Each of the transport paths 14, 18, and 21 is formed by a transport guide plate 38 that guides the movement of the paper. The transport guide plate 38 is provided with a plurality of feeding means 40 that sequentially feed the sheets downstream.

  The feeding means 40 includes a conveyance roller 42 and a conveyance idler 44. The transport roller 42 is rotated by a driving unit (not shown), and applies a transport force to the paper by contacting the paper. The conveyance idler 44 is provided at a position facing the conveyance roller 42 and cooperates with the conveyance roller 42 to sandwich the sheet and prevent the sheet from floating.

  The storage unit 22 includes two first paper supply trays 30 having a relatively small capacity and two second paper supply trays 32 having a relatively large capacity as paper supply trays for storing paper. Each of the trays 30 and 32 is connected to the main transport path 14 so that paper can be appropriately supplied to the main transport path 14.

  The printing unit 12 prints an image on a sheet based on the document image data. The printing unit 12 forms an electrostatic latent image on the photoconductor by a charging unit and an exposure unit (not shown), and forms a toner image by attaching toner to the surface of the photoconductor by electrostatic force. The toner image formed here is an image based on the document image. The transfer roller 26 on which the toner image is transferred from the photoconductor or the photoconductor is provided on the main conveyance path 14, and the toner is transferred onto the paper as the paper is conveyed here. A fixing roller 28 is provided downstream of the photoconductor or transfer roller 26. The sheet on which the toner is attached is heated and pressed by the fixing roller 28. As a result, the toner is fixed on the paper.

  Next, the inspection apparatus will be described with reference to FIGS. FIG. 2 is a schematic side view around the inspection apparatus 16, and FIG. 3 is a schematic top view around the inspection apparatus. The inspection device 16 includes an image reading device 17 that reads an image printed on the paper 50, encoders 52 and 54 that detect the paper conveyance speed, and an inspection control unit (not shown).

  The image reading device 17 reads an image printed on a sheet by the printing unit 12. The image reading device 17 is fixedly installed on the conveyance guide plate 38 and incorporates a lamp 45, an imaging lens 46, and a CCD line sensor 48. The image reading device 17 reads an image on the image reading position R on the conveyance guide plate 38 as a line-like image by one reading. Here, since the paper 50 is being conveyed at a predetermined speed, the portion of the image printed on the paper 50 that is located at the image reading position R changes sequentially with time. Therefore, if the image reading device 17 sequentially reads an image positioned at the image reading position R at a predetermined timing and combines the obtained plurality of line-shaped images, an image printed on a sheet can be obtained. In other words, the image reading device 17 sequentially scans and reads the paper surface of the paper 50 in the transport direction, and acquires an image printed on the paper. Note that the image reading device 17 of the present embodiment can read a line-like image by one reading, but may be an image reading device that reads a dot-like minute image by one reading. In this case, the CCD sensor is scanned in a direction (vertical direction in FIG. 3) orthogonal to the conveyance direction, and a plurality of minute images are acquired and combined. At this time, since the paper 50 is moving at a predetermined speed, as a result, an image printed on the paper 50 is acquired by sequentially scanning in both the transport direction of the paper 50 and the direction orthogonal to the transport direction. Become.

  The image reading device 17 is provided downstream of the fixing roller 28. However, it is desirable to be close to the fixing roller 28 in order to shorten the entire processing time and to reduce the size of the apparatus. The image acquired and synthesized by the image reading device 17 is output to the inspection control unit as inspection image data. In this embodiment, a CCD sensor is used as a reading device. However, another device such as a CMOS sensor may be used as long as it reads an image printed on paper.

  Immediately before the image reading position R, an upstream encoder 52 that functions as upstream speed detection means is provided, and immediately after the image reading position R, a downstream encoder 54 that functions as downstream speed detection means is provided. Yes. The two encoders 52 and 54 are arranged in a predetermined positional relationship as will be described in detail later. In addition, detection rollers 56 and 58 for pressing the surface of the conveyed paper are provided at positions facing the encoders 52 and 54. The detection rollers 56 and 58 prevent the paper 50 from floating, so that the paper 50 can reliably contact the surfaces of the encoders 52 and 54. Each of the encoders 52 and 54 generates a frictional force between the encoders 52 and 54 and the paper 50 being conveyed, and rotates with the conveyance of the paper 50 by the frictional force. Then, the rotation speed is detected as the paper transport speed. The detected conveyance speed is output to the inspection control device. In this embodiment, an encoder is used as the conveyance speed detection unit. However, any device other than the encoder may be used as long as the conveyance speed of the paper can be detected, and the arrangement position is not limited to the conveyance path.

  The inspection control device has a function as control means for controlling the scanning timing of the image reading device 17. The scanning timing is set according to the conveyance speed output from the encoders 52 and 54. For example, if the acquired transport speed is slower than the transport speed expected in advance, the scan timing interval is increased. On the other hand, if the acquired transport speed is slower than the transport speed expected in advance, the scan timing interval is narrowed. The calculated scanning timing is output to the image reading device 17. The image reading device 17 sequentially reads the surface of the paper 50 passing through the image reading position R at the scanning timing output from the inspection control device. Thereby, it is possible to always obtain appropriate inspection image data regardless of the conveyance speed of the paper 50.

  Note that the timing at which the image reading device 17 starts reading and the reading start timing are calculated according to the output value of the first sheet detection sensor 60 provided immediately before the image reading position R. The first paper detection sensor 60 is a sensor that detects whether or not there is a paper 50 immediately above it. When the first sheet detection sensor 60 provided immediately before the image reading position R detects that the sheet 50 is present, the reading start timing is set. Of course, the first sheet detection sensor 60 may not be provided, and the reading start timing may be calculated based on the conveyance speed of the sheet 50 acquired by the encoders 52 and 54. That is, the time at which the paper 50 reaches the image reading position R may be calculated from the conveyance speed of the paper 50 acquired by the encoders 52 and 54, and this arrival time may be used as the reading start timing.

  As will be described in detail later, the conveyance speed used for the scanning timing is switched from the conveyance speed detected by the upstream encoder 52 to the conveyance speed detected by the downstream encoder 54 during the image reading. That is, the scanning timing is calculated based on the conveyance speed detected by the upstream encoder 52 for a predetermined time from the start of image reading, and the scanning timing is calculated based on the conveyance speed detected by the downstream encoder 54 after the predetermined time has elapsed. To do. The switching timing of the encoders 52 and 54 is detected by a second paper detection sensor 62 provided immediately before the upstream encoder 52. The second paper detection sensor 62 is also a sensor that detects whether there is a paper 50 immediately above it. The timing at which the detection value of the second paper detection sensor 62 is switched from the presence of the paper to the absence of the paper, in other words, the time when the rear end of the paper 50 passes the second paper detection sensor 62 is the timing for switching the encoder. . The reason for this configuration will be described in detail later.

  The inspection control device also has a function corresponding to a determination unit, and determines whether the print result is good or not by comparing and comparing the inspection image data with the document image data stored in advance. As a result of the comparison and collation, when the difference amount between the two image data is small, it is determined that the printing has been normally performed, and when the difference amount is large, it is determined that the printing result is defective. The obtained inspection result is output to the image printing control unit.

  The paper discharge unit 24 includes a normal paper discharge tray 34 that discharges the paper on which image printing has been completed normally, and an abnormal paper discharge tray 36 that discharges paper that has been determined to have a poor print result. A switch provided at the branch point of each transport path determines whether the paper transported along the main transport path 14 is led to the normal paper discharge tray 34, the abnormal paper discharge tray 36, or the double-side transport path 18. (Not shown). This switch is controlled by the image printing control unit.

  Next, the arrangement positions of the upstream encoder 52 and the downstream encoder 54 will be described in detail. First, an example of the conveyance speed detected by each encoder 52, 54 is shown in FIG. The vertical axis represents the rotation speed (paper conveyance speed) of the encoders 52 and 54, and the horizontal axis represents time. In FIG. 4, time ta indicates the time when the front end of the paper 50 contacts the encoders 52 and 54, that is, the detection start time. From this detection start time ta, the encoders 52 and 54 start to rotate, and the rotation speed (paper conveyance speed) increases rapidly. Then, the rotation speed is stabilized around time tb after the predetermined time has elapsed. The detection ends at time tc when the trailing edge of the paper 50 passes through the encoders 52 and 54. That is, it can be seen that there is a time during which the detection value is unstable and a transition time T from when the detection of the conveyance speed is started until a stable detection value is obtained. The cause of the transition time T includes the detection characteristics (responsiveness) of the encoders 52 and 54 and the temporary reduction of the paper conveyance speed that occurs when the paper 50 contacts the encoders 52 and 54. When the conveyance speed detected in such a transition time T is used for calculating the scanning timing of image reading, it is not possible to obtain an appropriate scanning timing and obtain appropriate inspection image data. Further, while the paper passes the image reading position R, that is, while image reading is being performed, the paper conveyance speed is always detected, and if the scanning timing based on the conveyance speed is not calculated, an appropriate inspection is performed. Image data cannot be acquired.

  Therefore, in this embodiment, the encoders 52 and 54 are arranged so that the transport speed detected during the transition time T is not used for calculating the scanning timing. This will be described with reference to FIG. FIG. 5 is a diagram schematically showing the positional relationship between the encoders 52 and 54 and the image reading position R.

  In this embodiment, the distance W1 between the upstream detection position Sa, which is the conveyance speed detection position (contact position with the paper 50) in the upstream encoder 52, and the image reading position R is defined as the transient time T1 in the upstream encoder 52. The distance traveled by DT1 is greater than or equal to DT1 (W1 ≧ DT1). With such an arrangement, the conveyance speed detected by the upstream encoder 52 is stable at the time when the front end of the sheet 50 reaches the image reading position R, that is, the time when image reading is started. Appropriate scanning timing can be calculated. Thereby, a more accurate printing result inspection can be performed. Actually, the image reading start time is the time when the front end of the sheet 50 is detected by the first sheet detection sensor 60 provided immediately before the image reading position R. A minute distance M1 exists between the first sheet detection sensor 60 and the image reading position R. Therefore, strictly speaking, in order to obtain a stable conveyance speed at the start of image reading, it is necessary to satisfy W1 ≧ DT1 + M1. However, since M1 is an extremely small numerical value, in the following description, the position of the first sheet detection sensor 60 is substantially the same as the image reading position R, that is, the minute distance M1≈0.

  Even after the trailing edge of the sheet 50 passes the upstream detection position Sa, that is, after the conveyance speed cannot be detected by the upstream encoder 52, image reading on the sheet 50 is continued. Accordingly, it is necessary to detect the conveyance speed even after the rear end of the sheet 50 has passed the upstream detection position Sa. Therefore, in the present embodiment, the downstream encoder 54 is provided immediately after the image reading position R. Then, at least before the trailing edge of the sheet 50 passes the upstream detection position Sa (before the upstream encoder 52 can no longer detect the conveyance speed), the upstream encoder 52 detects the conveyance speed used for calculating the scanning timing. The conveyance speed detected by the downstream encoder 54 is switched from the conveyed speed. The distance W2 between the downstream detection position Sb and the upstream detection position Sa, which is the conveyance speed detection position in the downstream encoder 54, is smaller than the conveyance direction length Wp of the conveyed sheet (W2 ≦ Wp). . As a result, the front end of the sheet 50 always reaches the downstream detection position Sb when the rear end of the sheet 50 passes the upstream detection position Sa. That is, even if the upstream encoder 52 cannot detect the conveyance speed, the downstream encoder 54 can detect the conveyance speed, and the conveyance speed is always detected while the paper 50 passes the image reading position R. be able to.

  Here, the downstream encoder 54 also has a transition time T2 during which stable conveyance speed cannot be detected. The arrangement of the downstream encoder 54 is preferably such that the conveyance speed detected during the transition time T2 is not used for calculating the scanning timing. Therefore, in the present embodiment, the distance W2 between the downstream detection position Sb and the upstream detection position Sa is the distance that the sheet travels during the transition time T2 of the downstream encoder 54 from the conveyance direction length Wp of the conveyed sheet. The distance is obtained by subtracting DT2 (W2 ≦ Wp−DT2). With this arrangement, when the trailing edge of the paper 50 reaches the upstream detection position, the transition time T2 of the downstream encoder 54 is after the passage of time. As a result, it is not necessary to use the unstable conveyance speed detected during the transition time T2 of the downstream encoder 54 for the calculation of the scanning timing, and it is possible to acquire appropriate inspection image data and to accurately inspect the printing result. Become.

  The transport direction length Wp of the transported paper 50 varies depending on the paper size. Therefore, when the distance W2 between the downstream detection position Sb and the upstream detection position Sa is fixed, the distance W2 is obtained by subtracting the distance DT2 from the minimum paper conveyance direction length Wpmin of the paper handled by the printer 10. It is desirable to set the distance (W2 = Wpmin−DT2).

  As another form, the positions of the encoders 52 and 54 may be made variable, and the distance W2 may be changed according to the paper size being conveyed. This can be realized, for example, by providing a moving means for moving the downstream encoder 54 and the detection roller 58 corresponding thereto in the transport direction. Then, the paper size used for the printing is detected for each printing, and the downstream encoder 54 and the detection roller 58 are moved so that the distance W2 becomes an appropriate value according to the detected paper size. . The moving means is, for example, a drive source (motor, etc.) and a transmission mechanism (ball screw, rack, pinion, etc.) that transmits the force of the drive source to the rotary shafts of the downstream encoder 54 and the detection roller 58 as a linear motion in the transport direction. This can be achieved.

  Further, as described above, the conveyance speed used for calculating the scanning timing during the image reading is switched from the conveyance speed detected by the upstream encoder 52 to the conveyance speed detected by the downstream encoder 54. This switching timing is detected by the second sheet detection sensor 62 provided immediately before the upstream detection position Sa. That is, the switching timing is the time when the rear end of the paper 50 is detected by the second paper detection sensor 62 (the time when the paper is switched from being present to not being present). By providing the second sheet detection sensor 62 immediately before the upstream detection position Sa, the rear end of the sheet 50 always passes through the upstream encoder 52 regardless of the sheet size (in the upstream encoder 52). The encoder can be switched before the transport speed is detected. Thereby, the conveyance speed can always be detected regardless of the paper size, and an appropriate scanning timing can be obtained.

  Here, a minute distance M2 also exists between the second sheet detection sensor 62 and the upstream detection position Sa. In order for the detection value of the downstream encoder 54 to be stable at the time of encoder switching, it is necessary to consider this minute distance M2. More specifically, the distance W2 between the upstream side detection position Sa and the downstream side detection position Sb is, more strictly, W2 ≦ Wp−DT2−M2 (Wp is the length in the paper conveyance direction, and DT2 is the paper during the transition time T2. Travel distance). However, in this description, the second sheet detection sensor 62 and the upstream detection position Sa are regarded as substantially the same position, that is, M2≈0.

  Of course, any means other than the second sheet detection sensor 62 may be used as long as the timing at which the rear end of the sheet 50 passes the upstream detection position can be acquired. Also, the encoder switching timing can be fixed by adjusting the distance W2 and the size of the conveyed paper. For example, the encoder may be always switched after n seconds (n is a fixed value) from the image reading start timing regardless of the paper size.

  FIG. 6 is a diagram showing the conveyance speed detected by the upstream encoder 52 and the downstream encoder 54 in this arrangement. In FIG. 6, the upper side indicates the transport speed detected by the upstream encoder 52 and the lower side indicates the transport speed detected by the downstream encoder 54.

  The upstream encoder 52 starts conveying speed detection at time t0 when the front end of the sheet 50 reaches the upstream detection position Sa. An unstable transport speed is detected from time t0 to time t1 after the transition time T1 has elapsed, and a stable transport speed is detected after time t1. Then, at the time t6 when the trailing edge of the paper 50 passes the upstream detection position Sa, the conveyance speed cannot be detected by the upstream encoder 52.

  On the other hand, the downstream encoder 54 starts conveying speed detection at time t3 when the front end of the paper 50 reaches the downstream detection position Sb. An unstable conveyance speed is detected from time t3 to time t4 after the transition time T2 has elapsed, and a stable conveyance speed is detected after time t4. Here, the distance W2 between the downstream detection position Sb and the upstream detection position Sa is W2 = Wp−DT2−M2 (M2≈0) (Wp is the length in the sheet conveyance direction, and DT2 is during the transition time T2. Is the distance that the sheet travels, M2 is the distance between the second sheet detection sensor 62 and the upstream detection position Sa). Therefore, times t3 and t4 are always before time t6 when the trailing edge of the sheet passes the upstream detection position Sa.

  The image reading device 17 starts image reading at time t2 when the front end of the sheet 50 reaches the image reading position R. Here, the distance between the upstream detection position Sa and the image reading position R is greater than the distance DT1 that the paper travels during the transient time T1 of the upstream encoder (W1 ≧ DT1). Therefore, the image reading start time t2 is always after the time t1 after the transition time T1 has elapsed from the time t0. That is, when the image reading is started, a stable conveyance speed is detected by the upstream encoder 52. Therefore, an appropriate scanning timing can be calculated based on a stable conveyance speed, and more appropriate inspection image data can be acquired.

  Image reading by the image reading device 17 continues until time t7 when the rear end of the paper 50 passes the image reading position R. Between time t2 and time t7, there is a time t6 at which the transport speed cannot be detected by the upstream encoder 52. In order to perform scanning timing calculation based on the conveyance speed after time t6, the encoder is switched at time t5 immediately before time t6. The time from time t5 to time t6 is the time required for the paper 50 to travel the minute distance M2 between the second paper detection sensor 62 and the upstream side detection position Sa. Therefore, when M2 = 0, t5 = t6.

  After this time t5, the scanning timing is calculated based on the conveyance speed detected by the downstream encoder 54. As described above, since W2 = Wp−DT2−M2, the downstream encoder 54 detects a stable conveyance speed at the time t5 (≈t6). Therefore, the scanning timing can be calculated based on a stable conveyance speed even after the encoder is switched. As a result, more appropriate inspection image data can be acquired and more accurate printing result inspection can be performed. That is, with the arrangement as in the present embodiment, more accurate printing result inspection can be performed.

  Next, the flow of image printing in the printer 10 will be described. When image printing is performed on paper, document image data that is an image to be printed is input to the image printing control unit. The document image data is input, for example, by transmitting document image data from another computer or the like to the image printing control unit via a communication device. The input document image data is stored in the image printing control unit and output to the inspection control unit. The inspection control unit stores the document image data. Of course, original image data may be acquired by reading a sheet on which a predetermined image is printed.

  The image printing control unit develops the toner image on the photosensitive member by controlling the charging device, the exposure device, and the like based on the stored document image data. Further, the feeding means 40 is driven to feed paper from the predetermined paper feed trays 30 and 32 to the main transport path 14. The fed paper is transported along the main transport path 14, and the toner image is transferred by the photoreceptor or the transfer roller 26. Then, the toner is fixed by being heated and pressurized by the fixing roller 28. As a result, image printing based on the document image data is performed on the paper.

  The sheet on which the image is printed by the printing unit 12 is further conveyed to the image reading position R. When the front end of the sheet 50 reaches the upstream detection position Sa, the upstream encoder 52 starts to rotate, and detection of the sheet conveyance speed is started. The detected conveyance speed is output to the inspection control device. If the paper 50 further advances and the first paper detection sensor 60 can detect the front edge of the paper 50, the inspection control device instructs the image reading device 17 to start image reading. The scanning timing calculated based on the conveyance speed at this time is also output. As described above, the distance W1 between the upstream detection position Sa and the image reading position R is equal to or longer than the distance DT1 that the paper 50 travels during the transition time T1. Therefore, the conveyance speed at this time is a stable value, and the calculated scanning timing is an appropriate value. The image reading device 17 executes image reading according to the scanning timing. Thereafter, the upstream encoder 52 outputs the detected transport speed as needed, and the inspection control device calculates and instructs the scanning timing based on this transport speed. Therefore, even if the paper conveyance speed changes, image reading can be performed at an appropriate scanning timing.

  When the trailing edge of the sheet reaches the second sheet detection sensor 62 and the output value from the sensor switches from the presence of the sheet to the absence of the sheet, the inspection control device scans based on the conveyance speed detected by the downstream encoder 54. Switch to timing calculation. As described above, the distance W2 between the upstream detection position Sa and the downstream detection position Sb is W2 = Wp−DT2−M2 (M2≈0). Therefore, when the encoder is switched, the detection value at the downstream encoder 54 is stable. The inspection control device calculates the scanning timing based on the stable conveyance speed. That is, by setting W2 = Wp-DT2-M2, the scanning timing can always be calculated based on a stable conveyance speed.

  When the paper 50 is further conveyed and the rear end of the paper 50 passes the image reading position R, the image reading by the image reading device 17 is completed. The image reading device 17 combines a plurality of image data acquired so far, and acquires an image printed on the paper 50. Then, the acquired and synthesized image data is output as inspection image data to the inspection control device.

  The inspection control unit compares and collates inspection image data acquired by the image reading device 17 with previously stored document data. If the difference amount between the two images is lower than a predetermined threshold value, it is determined that the image has been printed normally. If the difference amount is larger than the predetermined threshold value, it is determined that the printing result is defective.

  The inspection result is output to the image forming control unit. The image formation control unit switches the transport destination of the paper 50 according to the inspection result. That is, when the printing result is normal, the sheet is conveyed on the normal paper discharge tray 34 or the duplex conveying path 18. On the other hand, if the printing result is defective, the paper is conveyed to the abnormal paper discharge tray 36. The printing is repeated until normal printing is possible. It should be noted that the printing process may be forcibly terminated when a printing result defect continues for a predetermined number of times or more.

  As described above, according to the present embodiment, it is possible to always obtain an appropriate paper conveyance speed, and thus it is possible to inspect the printing result with higher accuracy. Further, by providing a second paper detection sensor immediately before the upstream detection position Sa and switching the encoder according to the output of the sensor, the encoder can be always switched at an appropriate timing regardless of the paper size. it can.

1 is an overall configuration diagram of a printer according to an embodiment of the present invention. It is a schematic side view around an inspection apparatus. It is a schematic top view around an inspection device. It is a figure which shows an example of the conveyance speed detected by each encoder. FIG. 6 is a diagram schematically showing a positional relationship between an encoder and an image reading position R. It is a figure which shows the conveyance speed detected with an upstream encoder and a downstream encoder.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Printer, 12 Printing part, 14, 18, 21 Each conveyance path, 16 Inspection apparatus, 17 Image reading apparatus, 22 Storage part, 24 Paper discharge part, 30, 32 Paper feed tray, 38 Transport guide plate, 40 Feed means, 50 paper, 52 upstream encoder, 54 downstream encoder, 56, 58 detection roller, 60 first paper detection sensor, 62 second paper detection sensor, R image reading position, Sa upstream detection position, Sb downstream detection position .

Claims (7)

Printing means for printing a document image on paper based on document image data;
Inspection means for inspecting the result of printing by the printing means;
Transport means for transporting paper downstream along the transport path;
An image printing apparatus comprising:
Inspection means
Image reading means for sequentially scanning and reading the printing result on the conveyed paper at a predetermined scanning timing, and acquiring an image printed on the paper as inspection image data;
In parallel with the reading by the image reading means, a conveyance speed detecting means for sequentially detecting the conveyance speed of the paper in the vicinity of the image reading position by the image reading means,
Based on the conveying speed that will be acquired sequentially by the conveying speed detecting means, and control means for sequentially controlling the scanning timing of reading by the image reading means currently performed,
A judging means for judging the quality of the print result based on the inspection image data obtained by the image reading means;
Have
The conveyance speed detection means includes an upstream speed detection means for detecting the paper conveyance speed at the upstream detection position located immediately before the image reading position, and a paper conveyance speed at the downstream detection position located immediately after the image reading position. And downstream speed detecting means for detecting
The distance between the upstream detecting location and the image reading position state, and are more distance stable detection value from the speed detection start by the upstream rate detection unit is transported paper during the transient time to be obtained,
The distance between the upstream side detection position and the downstream side detection position is the distance between the length of the transported sheet in the transport direction and the transition time from when the speed detection is started by the downstream speed detection means until a stable detection value is obtained. The distance that the paper is transported is less than the subtracted distance,
An image printing apparatus. The image printing apparatus according to claim 1 ,
The conveyance speed detection means has a switching means for switching from speed detection at the upstream speed detection means to speed detection at the downstream speed detection means,
The image printing apparatus characterized in that the switching timing by the switching means is immediately before the trailing edge of the conveyed paper passes the upstream detection position. The image printing apparatus according to claim 2 ,
When the detection value of the paper detection sensor that detects the presence or absence of paper immediately before the upstream detection position is switched from the presence of paper to the absence of paper, the switching means changes from the speed detection by the upstream speed detection means to the downstream speed detection means. An image printing apparatus characterized by switching to speed detection. The image printing apparatus according to any one of claims 1 to 3 ,
The conveyance speed detection means moves at least one of the upstream speed detection means and the downstream speed detection means in the conveyance direction in accordance with the size of the paper to be conveyed, and the distance between the upstream detection position and the downstream detection position. An image printing apparatus comprising a moving means for changing the position. The image printing apparatus according to any one of claims 1 to 4 , wherein:
The upstream speed detection means and the downstream speed detection means are encoders that are provided opposite to the detection roller and that are in contact with a part of the conveyed paper and rotate as the paper is conveyed,
The image printing apparatus according to claim 1, wherein the transition time is a period in which a rotation speed generated at an early stage of rotation of the encoder is increased. A printing result inspection apparatus for inspecting a printing result by an image printing apparatus,
Image reading means for sequentially scanning and reading the printing result on the conveyed paper at a predetermined scanning timing, and acquiring an image printed on the paper as inspection image data;
In parallel with the reading by the image reading means, a conveyance speed detecting means for sequentially detecting the conveyance speed of the paper in the vicinity of the image reading position by the image reading means,
Based on the conveying speed that will be acquired sequentially by the conveying speed detecting means, and control means for sequentially controlling the scanning timing of reading by the image reading means currently performed,
A judging means for judging the quality of the print result based on the inspection image data obtained by the image reading means;
Have
The conveyance speed detection means includes an upstream speed detection means for detecting the paper conveyance speed at the upstream detection position located immediately before the image reading position, and a paper conveyance speed at the downstream detection position located immediately after the image reading position. And downstream speed detecting means for detecting
The distance between the upstream detecting location and the image reading position state, and are more distance stable detection value from the speed detection start by the upstream rate detection unit is transported paper during the transient time to be obtained,
The distance between the upstream side detection position and the downstream side detection position is the distance between the length of the transported sheet in the transport direction and the transition time from when the speed detection is started by the downstream speed detection means until a stable detection value is obtained. The distance that the paper is transported is less than the subtracted distance,
A printing result inspection apparatus characterized by that. A printing result inspection method for inspecting a result of printing by an image printing apparatus,
An image reading step of sequentially scanning and reading the printing result on the conveyed paper at a predetermined scanning timing, and acquiring an image printed on the paper as inspection image data;
In parallel with reading in the image reading step, and the conveyance speed detection step of sequentially detecting the conveying speed of the sheet in the vicinity of the image reading position by the image reading step,
Based on the conveying speed that will be successively acquired at a conveying speed detection step, a control step of sequentially controlling the scanning timing of the image reading currently performed,
A determination step for determining the quality of the print result based on the inspection image data obtained by the image reading step;
Have
The conveyance speed detection step includes an upstream speed detection step for detecting the paper conveyance speed at the upstream detection position located immediately before the image reading position, and a paper conveyance speed at the downstream detection position located immediately after the image reading position. A downstream speed detecting step for detecting
The distance between the upstream detecting location and the image reading position state, and are more than the distance the paper during the transient time until stable detection value from the speed detection start on the upstream side speed detection step is obtained is transported,
The distance between the upstream detection position and the downstream detection position is determined between the length of the transported paper in the transport direction and the transition time from the start of speed detection at the downstream speed detection step until a stable detection value is obtained. The distance that the paper is transported is smaller than the subtracted distance,
A printing result inspection method characterized by the above.

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