Image forming apparatus

Abstract

To properly adjust the feeding amount of a sheet-like medium toward a roller pair on the downstream side by a roller pair on the upstream side so as to suppress the quality deterioration of image formation while considering that the roller pair on the upstream side slips with respect to the sheet-like medium.SOLUTION: An image formation apparatus acquires one of the rotation frequency of an intermediate roller pair 22 and the feeding amount of sheets P when rotated at the rotation frequency as a theoretical value and acquires the other as an actual value. The image formation apparatus evaluates a difference in the feeding amount of the sheets P by the intermediate roller pair 22 between a case where the intermediate roller pair 22 slips with respect to the sheets P and a case where the intermediate roller pair 22 does not slip with respect to the sheets P, on the basis of the relation between the actual value and the theoretical value that have been acquired. The image formation apparatus adjusts the rotation frequency of the intermediate roller pair 22 per unit time, on the basis of the evaluation result, such that the feeding amount of the sheets P by the intermediate roller pair 22 becomes greater than that by a conveyance roller pair 23.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus for forming an image on a sheet-like medium. [Background technology]

[0002] In an image forming apparatus for forming an image on a sheet-like medium, there is a conventional technique in which the rotational speed of one pair of rollers among a plurality of roller pairs that transport the sheet-like medium is made different from the rotational speed of the other roller pairs. Patent Document 1 relates to such a conventional technique. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2015-168492 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] If the rotational speed of the upstream roller pair in the transport path is lower than that of the downstream roller pair, the amount of sheet-like medium that the upstream roller pair feeds will be less than that of the downstream roller pair. As a result, the sheet-like medium may be pulled upstream within the path between the two roller pairs, causing the downstream roller pair to slip against the sheet-like medium, which may degrade the quality of image formation performed downstream. Furthermore, if the upstream roller pair itself slips against the sheet-like medium, it may affect the amount of sheet-like medium that the upstream roller pair feeds, and consequently, the quality of image formation may also be affected.

[0005] The object of the present invention is to provide an image forming apparatus in which the amount of sheet-like medium fed by the upstream roller pair toward the downstream roller pair is appropriately adjusted to suppress deterioration of image forming quality, while taking into account that the upstream roller pair slides toward the sheet-like medium. [Means for solving the problem]

[0006] The image forming apparatus of the present invention comprises: a media storage unit for storing a sheet-like medium; a first pair of rollers that grips the sheet-like medium supplied from the media storage unit and feeds it along a predetermined transport path; a second pair of rollers that grips the sheet-like medium moved by the first pair of rollers and feeds it along the predetermined transport path downstream of the first pair of rollers with respect to the predetermined transport path; an image forming unit that forms an image on the sheet-like medium fed by the second pair of rollers downstream of the second pair of rollers with respect to the predetermined transport path; an acquisition means for acquiring the actual value of either the number of rotations of the first pair of rollers or the amount of sheet-like medium fed by the first pair of rollers when rotated by that number of rotations, relative to a theoretical value; and a control unit. The control unit performs a slip evaluation process, based on the relationship between the one theoretical value and the other actual value acquired by the acquisition means, to evaluate the difference in the amount of sheet-like medium fed by the first roller pair when the first roller pair slips against the sheet-like medium compared to when the first roller pair does not slip against the sheet-like medium, and an image forming process, while adjusting the number of rotations of the first roller pair per unit time based on the evaluation result in the slip evaluation process so that the amount of sheet-like medium fed by the first roller pair is greater than that of the second roller pair, to transport the sheet-like medium to the image forming unit with the first roller pair and the second roller pair, and to form an image on the sheet-like medium with the image forming unit. [Effects of the Invention]

[0007] The rotational speed (number of rotations per unit time) of the first roller pair located upstream is adjusted so that the amount of sheet-like medium fed by the first roller pair located upstream is greater than the amount fed by the second roller pair located downstream. As a result, the sheet-like medium is less likely to be pulled upstream within the path between the two roller pairs, and the risk of the downstream roller pair slipping against the sheet-like medium is suppressed. This suppresses the deterioration of image formation quality.

[0008] On the other hand, as a result of diligent research by the inventors, it has been found that in order to appropriately adjust the rotational speed of the first roller pair, it is particularly important to take into account the phenomenon of the first roller pair sliding against the sheet-like medium (slip). Due to factors upstream of the first roller pair, the sheet-like medium may be pulled upstream by the first roller pair, causing the first roller pair to slip. The amount of sheet-like medium that the first roller pair sends downstream is influenced by whether or not such slip occurs, and if so, the degree of slip.

[0009] Therefore, in this invention, either the number of rotations of the first roller pair or the amount of sheet-like medium fed out is set as a theoretical value, and the difference between the case where the first roller pair slips against the sheet-like medium (when slippage occurs) and the case where it does not slip is evaluated based on the relationship between the theoretical value and the actual value of the other obtained in relation to the theoretical value. Furthermore, the rotation speed of the first roller pair is adjusted based on the evaluation result. By appropriately reflecting the slip situation in the adjustment of the rotation speed of the first roller pair in this way, the amount of material fed out by the first roller pair can be ensured to be an appropriate size in relation to the amount of material fed out by the second roller pair. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic side view showing the internal structure of a printer according to a first embodiment, which is one embodiment of the present invention. [Figure 2] Figure 1 is a schematic plan view of the printer. [Figure 3] This is a magnified view of a portion of the area around the guide section in Figure 1. [Figure 4] This block diagram shows the electrical configuration of the printer shown in Figure 1. [Figure 5] Figure 3 is a schematic side view showing the excess paper generated around the guide section. [Figure 6] Figure 1 is a flowchart showing the processing flow executed by the control unit. [Figure 7] Figure 6 is a flowchart showing the image recording process. [Figure 8]Figure 3 is a schematic side view showing the various states of the paper around the guide section. [Figure 9] This is a schematic side view showing the internal structure of a printer according to a second embodiment, which is another embodiment of the present invention. [Modes for carrying out the invention]

[0011] [First Embodiment] A printer 100 (corresponding to the "image forming apparatus" of the present invention) according to the first embodiment, which is a preferred embodiment of the present invention, will be described below with reference to Figures 1 to 8. The vertical, horizontal, and front-to-back directions shown in Figure 1 refer to the vertical, front-to-back, and left-to-right directions of the printer 100.

[0012] As shown in Figures 1 and 2, the printer 100 mainly comprises a housing 100a, a feed tray 1, a transport mechanism 2, a cutter 3, a carriage 4, a head 5, a moving mechanism 6, an output tray 7, a cartridge mounting section 8, and a control unit 9.

[0013] The feeding tray 1 (corresponding to the "media storage section" of the present invention) is located below the head 5 within the housing 100a. The feeding tray 1 can be inserted into and removed from the housing 100a in the front-rear direction through an opening 101 formed in the front wall of the housing 100a.

[0014] The feeding tray 1 is capable of accommodating a roll body Rb and cut paper Kp (corresponding to the "short sheet-like medium" of the present invention). The feeding tray 1 may be capable of accommodating both the roll body Rb and cut paper Kp simultaneously, or it may be capable of selectively accommodating either the roll body Rb or cut paper Kp. The feeding tray 1 has a roll body support section 11 for supporting the roll body Rb and a mounting surface 12 on which the cut paper Kp is placed.

[0015] The roll body Rb consists of a long sheet of paper wound in a roll around the outer surface of a cylindrical core member Rc. The cut sheet Kp is a sheet of paper shorter than the long sheet of paper that makes up the roll body Rb, and is a standard size such as A4 or B5. The largest size of cut sheet Kp that can be used with the printer 100 of this embodiment is A4 size paper.

[0016] A roll sensor 71 is provided slightly behind the roll support section 11. The roll sensor 71 can detect whether or not a roll Rb is housed in the roll support section 11 of the feeding tray 1. More specifically, the roll sensor 71 detects that the roll Rb is supported by the roll support section 11 by detecting the roll paper Rp (corresponding to the "long sheet-like medium" of the present invention) that has been unwound from the roll Rb. The detection result from the roll sensor 71 is output to the control unit 9.

[0017] The transport mechanism 2 includes a feed roller unit 21, an intermediate roller pair 22, a transport roller pair 23, a paper discharge roller pair 24, and a guide section 25.

[0018] The feeding roller unit 21 includes a feeding motor 21a (see Figure 4), a feeding roller 21r, and an arm 21m. The feeding roller 21r feeds roll paper Rp unwound from a roll body Rb supported by a roll body support section 11, or cut paper Kp placed on a mounting surface 12, from the feeding tray 1. In the following description, when roll paper Rp and cut paper Kp are not distinguished, they will be referred to as "paper P" (corresponding to the "sheet-like medium" of the present invention). The feeding roller 21r is positioned above the bottom wall of the feeding tray 1. The feeding roller 21r is rotatably supported at the tip of the arm 21m and rotates when driven by the feeding motor 21a. The arm 21m is rotatably supported by a support shaft 21x. The support shaft 21x is supported by the housing 1a. The arm 21m is in contact with an elastic member (not shown) such as a leaf spring or a coil spring. This elastic member applies a force to the arm 21m that causes it to move towards the bottom wall of the feed tray 1. This force increases as the arm 21m moves counterclockwise in the diagram. Due to the action of this elastic member, the feed roller 21r is pressed against the paper P. Depending on the position of the feed roller 21r, the higher the feed roller 21r is positioned, the greater the force pressing the feed roller 21r against the paper P.

[0019] When the feed roller 21r rotates due to the drive of the feed motor 21a, a transport force is applied to the paper P in contact with the feed roller 21r in a direction from front to back. As a result, the paper P is fed out of the feed tray 1. The rear wall 15 provided at the rear end of the feed tray 1 is inclined such that its upper end is located behind its lower end. Therefore, the paper P fed out of the feed tray 1 is directed diagonally upward.

[0020] A feeding position sensor 72 is provided slightly behind the feeding roller unit 21. The feeding position sensor 72 can detect whether or not the paper P is positioned in a position where it can be fed by the feeding roller unit 21. The detection result from the feeding position sensor 72 is output to the control unit 9.

[0021] The intermediate roller pair 22 (corresponding to the "first roller pair" of the present invention) consists of a drive roller that rotates by the drive of an intermediate motor 22a (see Figure 4) and a driven roller that rotates along with the drive roller. When the intermediate motor 22a is driven by the control unit 9, the intermediate roller pair 22 rotates while gripping the paper P and transports the paper P. The intermediate roller pair 22 is located above the rear end of the feed tray 1. The intermediate roller pair 22 grips the paper P that is fed out of the feed tray 1 by the feed roller unit 21 and moving diagonally upward, and feeds it upward. The guide section 25 is located above the intermediate roller pair 22 and forms a path 25a in the paper P transport path, which is the part between the intermediate roller pair 22 and the transport roller pair 23. As shown in Figure 3, the path 25a extends upward from the intermediate roller pair 22 and curves from there toward the transport roller pair 23 in front. As the paper P is transported upward by the intermediate roller pair 22 passes through the path 25a, the paper P is guided along the path 25a towards the forward transport roller pair 23.

[0022] A tip position sensor 81 (corresponding to the "first tip sensor" of the present invention) is provided slightly below the intermediate roller pair 22. When the tip position sensor 81 detects the leading edge of the paper P, it outputs the detection result to the control unit 9. The timing at which the tip position sensor 81 detects the leading edge of the paper P is adjusted to coincide with, or nearly coincide with, the timing at which the leading edge of the paper P reaches the intermediate roller pair 22.

[0023] The transport roller pair 23 (corresponding to the "second roller pair" of the present invention) consists of a drive roller that rotates by the drive of the transport motor 23a (see Figure 4) and a driven roller that moves along with the drive roller. A rotary encoder 83 (corresponding to the "rotation sensor" of the present invention) is installed on the driven roller of the transport roller pair 23. The rotary encoder 83 can detect the amount of rotation of the transport roller pair 23 by detecting the amount of rotation of the driven roller. The rotary encoder 83 outputs a signal indicating the amount of rotation of the transport roller pair 23 to the control unit 9. The paper discharge roller pair 24 consists of a drive roller that rotates by the drive of the paper discharge motor 24a (see Figure 4) and a driven roller that moves along with the drive roller.

[0024] A tip position sensor 82 (corresponding to the "second tip sensor" of the present invention) is provided slightly behind the transport roller pair 23. When the tip position sensor 82 detects the leading edge of the paper P, it outputs the detection result to the control unit 9. The timing at which the tip position sensor 82 detects the leading edge of the paper P is adjusted to coincide with, or nearly coincide with, the timing at which the leading edge of the paper P reaches the transport roller pair 23.

[0025] When the transport motor 23a and the paper discharge motor 24a are driven by the control unit 9, the transport roller pair 23 and the paper discharge roller pair 24 rotate while gripping the paper P, transporting the paper P forward in the transport direction. The transport roller pair 23 is located behind the head 5 (upstream in the transport direction), and the paper discharge roller pair 24 is located in front of the head 5 (downstream in the transport direction). The transport roller pair 23 further feeds the paper P, which has been guided forward by the guide unit 25, toward the paper discharge roller pair 24. The paper discharge roller pair 24 further transports the paper P, which has been transported forward by the transport roller pair 23, while gripping it, and discharges it into the paper discharge tray 7.

[0026] As described above, the transport mechanism 2 transports the paper P from the feed tray 1, through the feed roller unit 21, the intermediate roller pair 22, the guide section 25, the transport roller pair 23, and the paper output roller pair 24 in order, along a transport path (corresponding to the "predetermined transport path" of the present invention) toward the paper output tray 7.

[0027] The cutter 3 is located between the rear end of the feed tray 1 and the intermediate roller pair 22. The cutter 3 consists of, for example, a disc-shaped rotating blade and a driven blade. The cutting motor 3a (see Figure 4) drives the rotating blade of the cutter 3, which also moves back and forth in the left-right direction. The roll paper Rp, which has been unwound from the roll body Rb and transported, is cut in the width direction by the cutter 3 when the cutting motor 3a is driven by the control unit 9. As a result, a rear end is formed on the roll paper Rp, and each sheet of paper is discharged into the output tray 7.

[0028] The print head 5 (corresponding to the "image forming unit" of the present invention) includes a plurality of nozzles 51 (see Figure 2) formed on its lower surface and a driver IC 52 (see Figure 4). When the driver IC 52 is driven by the control unit 9, ink is ejected from the nozzles 51. The ink reaches an area on the paper P at the image recording position opposite the lower surface of the print head 5. This forms an image on the paper P. The print head 5 is mounted on the carriage 4.

[0029] The moving mechanism 6 includes two guide rails 61 and 62 and a carriage motor 63 (see Figure 4). The two guide rails 61 and 62 are spaced apart from each other in the front-rear direction and each extends in the left-right direction. The carriage 4 is positioned to straddle the two guide rails 61 and 62. The carriage 4 is connected to the carriage motor 63 via a belt (not shown) or the like. When the carriage motor 63 is driven by the control unit 9, the carriage 4 moves along the guide rails 61 and 62 in the left-right direction (scanning direction).

[0030] The output tray 7 is located within the housing 100a, in front of the head 5 and above the feed tray 1. The output tray 7 can be inserted into and removed from the housing 100a in the front-to-back direction through an opening 102 formed in the front wall of the housing 100a. Paper P on which an image has been recorded by the head 5 is received by the output tray 7.

[0031] As shown in Figure 2, the cartridge mounting section 8 is located on one side (the right side) of the paper output tray 7 in the left-right direction, and in front of the movement mechanism 6 in the front-back direction. The cartridge mounting section 8 can be detachably fitted with four ink cartridges 10, each storing black, yellow, cyan, and magenta ink. Ink is supplied to the print head 5 from the ink cartridges 10 fitted in the cartridge mounting section 8 via tubes (not shown) or the like.

[0032] The control unit 9 controls the entire printer 100. As shown in Figure 4, the control unit 9 is electrically connected to the feed motor 21a, intermediate motor 22a, transport motor 23a, paper ejection motor 24a, cutting motor 3a, driver IC 52, carriage motor 63, roll sensor 71, feed position sensor 72, tip position sensors 81 and 82, rotary encoder 83, and the like.

[0033] As shown in Figure 4, the control unit 9 includes a CPU (Central Processing Unit) 91, ROM (Read-Only Memory) 92, RAM (Random Access Memory) 93, ASIC (Application Specific Integrated Circuit) 94, etc. The ROM 92 stores the program executed by the CPU 91 and ASIC 94, various fixed data, etc. The RAM 93 stores the data necessary for program execution (image data, X described later). MID It temporarily stores (buffer values, etc.).

[0034] Various fixed data stored in ROM92 are the number of rotations X of the transport roller pair 23. PF This includes data showing the following and data showing various setting values ​​for calculating the number of rotations of the intermediate rollers against 22. Set , X BF , T BF and B TGT This includes the following. In addition, the various fixed data also include data showing the conversion relationship between the number of rotations of the intermediate roller pair 22 and the amount of paper P fed (hereinafter referred to as "conversion data"). As described later, based on this conversion data, the amount of paper P fed by the intermediate roller pair 22 when the intermediate roller pair 22 rotates for a certain number of rotations is calculated. Note that the conversion relationship shown by the conversion data is based on the premise that the intermediate roller pair 22 does not slip relative to the paper P. In addition, the various fixed data also include the initial setting values ​​of the buffer values ​​described later.

[0035] Furthermore, the control unit 9 may perform various processes solely with the CPU 91, solely with the ASIC 94, or collaboratively with the CPU 91 and ASIC 94. Also, the control unit 9 may be performed by a single CPU 91, or by multiple CPUs 91 sharing the processing. Similarly, the control unit 9 may be performed by a single ASIC 94, or by multiple ASICs 94 sharing the processing. The various processes performed by the control unit 9 will now be described.

[0036] The control unit 9 determines whether the paper P fed from the feed tray 1 by the feed roller unit 21 is roll paper Rp or cut paper Kp as part of the paper type determination process. This determination is made based on the detection results of the roll sensor 71 and the feed position sensor 72. Specifically, if the roll sensor 71 detects that the roll paper Rp is supported by the roll support 11, and the feed position sensor 72 detects that the paper P is positioned at the feed position, then it is determined that the paper P fed by the feed roller unit 21 is roll paper Rp. On the other hand, if the roll sensor 71 detects that the roll paper Rp is not supported by the roll support 11, and the feed position sensor 72 detects that the paper P is positioned at the feed position, then it is determined that the paper P fed by the feed roller unit 21 is cut paper Kp.

[0037] Furthermore, the control unit 9 records an image on the paper P based on a recording instruction sent by the user from an external device (e.g., a PC or smartphone). Image recording is performed by repeatedly alternating between a transport process in which the transport mechanism 2 transports the paper P along a predetermined distance along the transport path, and a scanning process in which the movement mechanism 6 moves the carriage 4 in the scanning direction while ejecting ink from multiple nozzles 51 of the head 5 onto the paper P. If the paper P is roll paper Rp, the roll paper Rp receives ink ejected from the head 5 while being transported by the transport mechanism 2. Meanwhile, the roll paper Rp is cut to a desired length (e.g., the length indicated by the recording instruction) by the cutter 3. As a result, the roll paper Rp becomes individual sheets of paper with the desired length and has an image recorded on them, which are then discharged into the output tray 7. If the paper P is cut paper Kp, the cut paper Kp receives ink ejected from the head 5 while being transported by the transport mechanism 2. As a result, the cut paper Kp becomes a sheet of paper with an image recorded on it and is then discharged into the output tray 7.

[0038] The control unit 9 appropriately adjusts the rotation speed of each roller pair of the transport mechanism 2 so that image recording on the paper P is performed properly during the transport process described above. In particular, if the rotation speed of the intermediate roller pair 22 is smaller than the rotation speed of the transport roller pair 23, the amount of paper P that the intermediate roller pair 22 feeds out will be smaller than that of the transport roller pair 23. As a result, as shown in Figure 8(a), the paper P may come into contact with the guide section 25 and become taut. When the paper P is in this state, the transport roller pair 23 will try to feed out more paper P than the intermediate roller pair 22, and friction will occur between the paper P and the guide section 25, pulling the paper P upstream of the transport path. As a result, the transport roller pair 23 may slip relative to the paper P, and the quality of image formation by the head 5 may deteriorate. In order to suppress the occurrence of such a situation, it is necessary to appropriately adjust the rotation speed of the intermediate roller pair 22.

[0039] In view of the above, the present inventors have adopted a method in which the rotational speed of the intermediate roller pair 22 is greater than the rotational speed of the transport roller pair 23. As a result, the intermediate roller pair 22 feeds more paper P than the transport roller pair 23. Therefore, as shown in Figure 5, excess paper P is generated in the path 25a of the guide section 25, which is the part of the paper P transport path between the intermediate roller pair 22 and the transport roller pair 23. This control prevents the paper P from coming into contact with the guide section 25 and becoming taut. Thus, the transport roller pair 23 is prevented from sliding against the paper P, and the risk of deterioration in the image formation quality by the head 5 is also suppressed.

[0040] Furthermore, as a result of our diligent research on the control of the intermediate roller pair 22, we have concluded that it is particularly important to take into account the phenomenon of the intermediate roller pair 22 sliding relative to the paper P (hereinafter referred to as "slip") in order to appropriately adjust the rotational speed of the intermediate roller pair 22. Due to factors upstream of the intermediate roller pair 22, the paper P may be pulled upstream by the intermediate roller pair 22, causing the intermediate roller pair 22 to slip relative to the paper P. For example, when the paper P is roll paper Rp, if the amount of paper remaining in the roll body Rb is relatively large, the weight of the roll body Rb is large, and therefore the force required to pull the roll paper Rp from the roll body Rb is also relatively large. In addition, if the force required to pull the roll paper Rp from the roll body Rb is large, the roll paper Rp becomes taut and lifts the feed roller 21r, thereby increasing the force that the feed roller 21r applies to the roll paper Rp. As a result, when the amount of paper remaining in the roll Rb is relatively large, the force pulling the paper P upstream is greater compared to when the amount of paper remaining in the roll Rb is relatively small, making slippage between the intermediate rollers 22 more likely. Also, when the paper P is cut paper Kp, the position of the feed roller 21r changes according to the amount of paper remaining, and similarly, the force pulling the paper P upstream between the intermediate rollers 22 increases, which can make slippage more likely.

[0041] The control unit 9 executes the process of controlling the rotational speeds of the intermediate roller pair 22 and the conveyance roller pair 23 in consideration of the occurrence of slip as follows. First, a series of processes up to image recording by the control unit 9 will be described while referring to FIG. 6.

[0042] Based on the detection result of the leading edge position sensor 81, the control unit 9 feeds the sheet P to the sheet feeding roller unit 21 until the leading edge of the sheet P reaches the intermediate roller pair 22 (S1). Next, based on the detection result of the leading edge position sensor 82, the control unit 9 conveys the sheet P to the sheet feeding roller unit 21 and the intermediate roller pair 22 until the leading edge of the sheet P reaches the conveyance roller pair 23 (S2). At the same time, based on the detection result of the rotary encoder 83 during the execution of S2, the control unit 9 acquires the number of rotations (rotation amount) of the intermediate roller pair 22 from when the leading edge of the sheet P reaches the intermediate roller pair 22 until it reaches the conveyance roller pair 23 (S2).

[0043] Next, based on the following mathematical formulas 1 and 2, the control unit 9 obtains the number of rotations X of the intermediate roller pair 22 per conveyance process in the subsequent image recording MID (S3).

[0044] (Mathematical formula 1) TIFF0007852240000001.tif15170

[0045] (Mathematical formula 2) TIFF0007852240000002.tif7170

[0046] The slip rate R (corresponding to the "slip degree value" of the present invention) represented by Mathematical formula 1 is an evaluation value indicating the degree of slip occurring in the intermediate roller pair 22. L Act is the distance that the intermediate roller pair 22 has sent out the sheet P in S2 by quantity there is. L Act is the number of rotations of the intermediate roller pair 22 indicated by the detection result of the rotary encoder 83 (This corresponds to the "actual value" in this invention.) and is calculated based on the above conversion data stored in the ROM 92. L Set(This corresponds to the "theoretical value" of the present invention) is a reference value for the amount of paper P fed out when there is no slip, and is obtained from ROM92. Set It is preferable to set a practically appropriate value for R based on simulations and experiments so that R does not take a negative value. For example, assuming that the paper P passes approximately through the center in the width direction of the path 25a as shown in Figure 3, L is set according to the length from the intermediate roller pair 22 to the transport roller pair 23 in the paper P in that state. Set It may be set as described above. Set Since it is set so that R cannot be a negative value, R will be zero or greater. The larger R is, the greater L Act is L Set A larger value indicates a greater degree of slip. The process by which the control unit 9 calculates the slip ratio R corresponds to the "slip evaluation process" of the present invention.

[0047] X represented by equation 2 MID (corresponding to the "first slip correction count" of the present invention) is the number of rotations of the intermediate roller pair 22 used per transport process in image recording. PF (This corresponds to the "second reference rotation count" of the present invention) is the number of rotations of the transport roller pair 23 per transport process described above. BF This indicates the increase in the number of rotations of the intermediate roller pair 22 relative to the number of rotations of the transport roller pair 23 per single transport process described above. Due to this increase, excess paper P is generated in the path 25a with each transport process, and as the image recording transport process is repeated as described below, the excess accumulates. Hereafter, this accumulation of excess paper P in the path 25a will be referred to as the "buffer," and the value representing the amount of this accumulation will be referred to as the "buffer value." (1+R)(=L Act / L Set ≥1) represents the correction factor considering the slip between the intermediate roller and 22. Therefore, X MID The number of rotations of the conveyor rollers against 23 is X PF to X BF The number of rotations, including the slip ratio R, will correspond to the result of correction. If slip occurs between the intermediate rollers 22, (1+R) is greater than 1. Therefore, XMID is (X PF +X BF ) (corresponding to the "first reference rotation count" of the present invention) becomes larger than the calculated X. MID It is stored in RAM93.

[0048] Next, the control unit 9 performs a skew correction process (S4). The skew correction process is a process that prevents the paper P from being fed out by the transport roller pair 23 with its leading edge tilted at an angle to the direction in which the transport roller pair 23 extends (scanning direction). Specifically, the transport roller pair 23 is either not rotated, or rotated in the opposite direction to the rotation direction when feeding the paper P to the head 5, while the leading edge of the paper P is in contact with the transport roller pair 23 and a predetermined amount of paper P is fed to the intermediate roller pair 22. This causes the paper P to bend in the path 25a and be pressed against the transport roller pair 23, thereby making the leading edge of the paper P parallel to the direction in which the transport roller pair 23 extends.

[0049] Next, the control unit 9 performs a head-out process (S5). The head-out process involves feeding a predetermined amount of paper P to both the intermediate roller pair 22 and the transport roller pair 23. As a result, the paper P is fed out from the transport roller pair 23 and positioned for the first scanning process by the head 5. Here, by making the number of rotations of the intermediate roller pair 22 less than the number of rotations of the transport roller pair 23, the deflection of the paper P caused by the skew correction process is reduced. The remaining deflection of the paper P corresponds to the initial state of the buffer.

[0050] Next, the control unit 9 obtains the initial value of the buffer from the ROM 92 and stores it in the RAM 93 as the initial value of the buffer (S6). The initial value is set according to the initial size of the buffer corresponding to the deflection remaining in the path 25a after processing in S4 and S5. Specifically, it is set to a value obtained by subtracting the amount by which the buffer is reduced in the cueing process from the size of the buffer generated in the oblique correction process.

[0051] Next, the control unit 9 receives the X calculated in S3.MID Then, image recording is performed based on the initial buffer value set in S6 (S7). Details of image recording will be described later. When image recording is finished, the series of processes shown in Figure 6 is completed.

[0052] The details of image recording will be explained below with reference to Figure 7. In image recording, first, the control unit 9 performs a scanning process (S11). Next, the control unit 9 sets the buffer value stored in RAM 93 to a threshold T. BF The control unit 9 determines whether or not it exceeds the threshold T (S12). BF The size may be adjusted based on the paper type determination result. For example, if paper P is roll paper Rp, the threshold T may be adjusted compared to when paper P is cut paper Kp. BF It may be set to a large value. The buffer value is the threshold T. BF If it is determined that it does not exceed (S12, No), the control unit 9 will MID The transport process using is executed (S13). Hereinafter, this transport process will be referred to as the "normal transport process" (corresponding to the "first transport process" of the present invention).

[0053] In normal transport processing, the control unit 9 rotates the intermediate roller pair 22 X times. MID At the same time as it rotates, the transport roller pair 23 rotates X times. PF They are rotated. These pairs of rollers will rotate these number of times in the same period. Therefore, the rotational speed, i.e., the number of rotations per unit time, is X PF The conveyor rollers that rotated with X rotations were greater than the 23. PF Larger than X MID The ratio of the intermediate rollers that rotated for a certain number of rotations to 22 becomes larger. Also, using the slip ratio R, (X PF +X BF X has a value corrected for ) MID The intermediate roller pair 22 rotates at a number of rotations. Therefore, even if slip occurs in the intermediate roller pair 22, the certainty that the amount of paper P fed by the intermediate roller pair 22 will be greater than the amount of paper P fed by the transport roller pair 23 is improved. And the amount of paper P fed is when the intermediate roller pair 22 rotates (X) in a slip-free state.PF +X BF The amount of paper P fed out when rotated by the number of rotations of ) becomes close to the size of X. As a result, path 25a has X BF An excess amount of paper P, roughly corresponding to the size of the paper, is generated with each transport process.

[0054] Next, the control unit 9 sets the buffer value stored in RAM 93 to X BF The sum is calculated (S16). The sum is performed on the initial value set in S6 in Figure 6. As described above, X BF This roughly corresponds to the amount of excess paper P generated with each normal transport process in S13. Each time the normal transport process in S13 is completed, X is added to the buffer value in S16. BF These values ​​are then added together. Therefore, the buffer value reflects the size of the buffer in path 25a that is accumulated with each transport process.

[0055] Next, the control unit 9 determines whether image recording is complete by performing the required number of scanning and transport processes (S17). If the control unit 9 determines that image recording is complete (S17, Yes), the series of processes shown in Figure 7 ends. If the control unit 9 determines that image recording is not complete (S17, No), the processes from S11 onwards are executed to perform the next scanning and transport processes.

[0056] Returning to the process in S12, the buffer value stored in RAM93 is the threshold T. BF If it is determined that the value exceeds (S12, Yes), the control unit 9 will output X, which is represented by the following formula 4. * MID The transport process is executed using (corresponding to the "second slip correction count" of the present invention) (S14). S in Equation 3 BF This corresponds to the buffer value. Also, B TGT This corresponds to the target value of the buffer generated in path 25a immediately after the transport process in S14. Hereinafter, this transport process will be referred to as the "buffer clear transport process" (corresponding to the "second transport process" of the present invention). In this way, each time the normal transport process is executed, X BFThe value is accumulated in the buffer, and a buffer clear transport process is executed each time the buffer value exceeds a threshold. Therefore, the buffer clear transport process is executed each time the number of normal transport processes reaches a predetermined number (corresponding to the "predetermined number" in this invention).

[0057] (Equation 3) TIFF0007852240000003.tif8170

[0058] In the buffer clearing transport process, the control unit 9 rotates the intermediate roller pair 22 X times. * MID At the same time as it rotates, the transport roller pair 23 rotates X times. PF This rotates it. This makes it (1+R)*(S) different from the normal transport process in S13. BF -B TGT ) reduces the number of rotations between the intermediate roller and 22. BF The buffer value shown reflects the size of the buffer for path 25a, as described above. Therefore, (1+R)*S BF This corresponds to the number of rotations required to feed the amount of paper P corresponding to the buffer in path 25a to the intermediate roller pair 22, taking into account the case where slip occurs in the intermediate roller pair 22. Therefore, the number of rotations X of the intermediate roller pair 22 * MID When rotated, the buffer that has formed in path 25a is "-S BF The term *(1+R)* can temporarily resolve the issue, and the buffer after resolution can be adjusted to an appropriate amount (B TGT It can be set to the amount corresponding to [the value].

[0059] Next, the control unit 9 sets the buffer value stored in RAM 93 to B TGT The system is reset (S15). Then, the control unit 9 executes the processes from S16 onwards.

[0060] According to the first embodiment described above, the control unit 9 causes the paper P to be fed to the intermediate roller pair 22 from the time the leading edge of the paper P reaches the intermediate roller pair 22 until it reaches the transport roller pair 23, and L corresponds to the actual number of rotations of the intermediate roller pair 22. Act This is obtained based on the detection result of the rotary encoder 83. Then, the control unit 9 calculates the slip ratio R based on equation 1. Set This is the reference value (theoretical value) of the amount of paper P fed when the paper P is fed in the same manner as above with no slippage between the intermediate roller pair 22. The control unit 9 controls such L Set and L Act By calculating the slip ratio R that shows the relationship, we can evaluate the difference between when slip occurs and when it does not occur between the intermediate rollers 22.

[0061] Then, the control unit 9 calculates X, which is expressed by equation 2 using the slip ratio R, for each transport process. MID The intermediate roller pair 22 is rotated at the same time as X PF The conveyor roller pair 23 is rotated in the number of rotations shown in equation 2, using the slip ratio R, (X PF +X BF To compensate for this, even assuming that slip occurs in the intermediate roller pair 22, the number of rotations X of the conveyor roller pair 23 PF For comparison, the number of rotations of the intermediate roller is X (22). MID This can be appropriately set according to the slip conditions. By appropriately reflecting the slip conditions in the adjustment of the rotational speed of the intermediate roller pair 22 in this way, the amount of feed by the intermediate roller pair 22 can be ensured to be an appropriate size in relation to the amount of feed by the conveyor roller pair 23.

[0062] Furthermore, in this embodiment, a buffer is generated in the path 25a due to the normal transport process (S13 in Figure 7). Since this normal transport process is repeatedly executed, the buffer in the path 25a becomes larger. If the buffer becomes too large, as shown in Figure 8(b), the paper P may stick to the inner surface of the path 25a or be severely folded. In addition, the force with which the intermediate roller pair 22 pushes the paper P toward the transport roller pair 23 becomes excessive, and as a result of the amount of paper P that the transport roller pair 23 feeds toward the head 5 becoming excessive, the quality of image recording by the head 5 may deteriorate.

[0063] In response, the control unit 9 sets X as a buffer value each time the normal transport process is completed. BF The difference between the first reference rotation count and the second reference rotation count (corresponding to the "difference obtained by subtracting the second reference rotation count from the first reference rotation count" in this invention) is accumulated (S16 in Figure 7), and the buffer value reaches the threshold T. BF If it exceeds this limit, a buffer clear transport process (S14 in Figure 7) is executed. This allows the buffer that has accumulated in path 25a to be cleared. Therefore, the buffer does not become too large, and the degradation of image recording quality as described above is suppressed. Note that X is normally used for each transport process. BF Integrating these means that the number of times the transport process is executed is X BF This is equivalent to multiplying by X. Therefore, in determining whether or not to perform the buffer clear transport process, as in the process shown in Figure 7, X BF The buffer value obtained by accumulating these values ​​and the threshold T BF Instead of making a comparison, X BF Alternatively, the product obtained by multiplying by the number of executions of the normal transport process may be compared with another threshold. Here, if this other threshold is T BF If the initial value of the buffer is subtracted from the initial value, the former comparison and the latter comparison are equivalent. In other words, the number of normal transport operations performed before the buffer clear transport operation is executed is the same whether the former comparison is adopted or the latter comparison is adopted.

[0064] Furthermore, in the above embodiment, the initial value of the buffer value (S6 in Figure 6) corresponding to the initial state of the buffer generated by the skew correction process (S4 in Figure 6) and the cueing process (S5 in Figure 6) is X BF The values ​​are then accumulated. The buffer value then reaches the threshold T. BF If the buffer level exceeds a certain threshold, a buffer clearing and transport process is executed to reduce the buffer size. Therefore, the buffer can be reduced at the appropriate timing even when performing skew correction and head-out processing.

[0065] Furthermore, in the above embodiment, a threshold T is determined based on the paper type determination result. BF The following effects occur when the size is adjusted. Due to some factor not reflected in the slip ratio R, there is a risk that the amount of paper P transported may deviate from the expected value. Such factors include slippage in rollers other than the intermediate roller pair 22 that transport or feed the paper P, such as the transport roller pair 23. On the other hand, with roll paper Rp, the total amount each roller feeds when transporting one sheet of paper may be larger than with cut paper Kp. Therefore, if the above deviation occurs, the deviation is more likely to accumulate with roll paper Rp than with cut paper Kp due to the larger total feed amount, and the risk of insufficient buffer in path 25a increases. Therefore, as described above, the threshold T in the case of roll paper Rp is compared to the case of cut paper Kp. BF By increasing this value, the number of times the normal transport process is executed before the buffer clear transport process is performed (corresponding to the "predetermined number" in this invention) increases. This ensures that a relatively large buffer is secured in the former case. Therefore, buffer shortages that may occur in the case of roll paper Rp can be suppressed.

[0066] [Second Embodiment] A printer 200 (corresponding to the "image forming apparatus" of the present invention) according to a second embodiment, which is another embodiment of the present invention, will be described with reference to Figure 9. In printer 200, the difference from printer 100 according to the first embodiment is that a paper remaining amount sensor 271 is installed and that it is controlled by a control unit 209. The main difference in control unit 209 from control unit 9 is that instead of R in equation 1 used to control the rotation speed of the intermediate roller pair 22, R is represented by equation 4 described later. * This is what is used. In addition, this R * In calculating this, the control unit 209 performs the following determination and calculation processes based on each sensor. Other configurations and functions are common to both printer 100 and printer 200.

[0067] The paper remaining amount sensor 271 has multiple optical sensors, each consisting of a light-emitting unit and a light-receiving unit, arranged to sandwich the roll body Rb, which is supported by the roll body support unit 11, from the left and right directions. These multiple optical sensors are arranged along the vertical direction to form a sensor array. Each optical sensor detects whether or not the light-receiving unit has received the light emitted from the light-emitting unit, and transmits the detection result to the control unit 209. If the roll body Rb is in the path of the light of each optical sensor, the roll body Rb obstructs the reception of light by the light-receiving unit. Therefore, based on the detection result of the entire sensor array, the control unit 209 can determine the range in the vertical direction in which the roll body Rb is located. The range in which the roll body Rb is located changes according to the remaining amount of roll paper Rp wound around the core member Rc. Based on this, the control unit 209 can obtain the remaining amount of roll paper Rp on the roll body Rb according to the detection result of the paper remaining amount sensor 271.

[0068] Further, the control unit 209 calculates the cumulative usage length since the roll paper Rp on the roll body support portion 11 was first unwound and used. This calculation is performed based on the detection results of the roll body sensor 71, the rotary encoder 83, and the like. Specifically, the control unit 209 detects, based on the detection result of the roll body sensor 71, that the state has switched from a state where the roll paper Rp is not supported by the roll body support portion 11 to a state where the roll paper Rp is supported by the roll body support portion 11. Thereby, it is detected that the roll paper Rp was first unwound and used. Next, the control unit 209 accumulates the length of the roll paper Rp fed out by the intermediate roller pair 22 since the roll paper Rp was first unwound and used, based on the detection result of the rotary encoder 83. This accumulated result is used as the cumulative usage length.

[0069] And the control unit 209 calculates R represented by the following formula 4. * The calculated R * is used instead of R in the control of the control unit 9, and the control unit 209 executes the same processing as the control unit 9 based on formulas 1 to 3.

[0070] (Formula 4) TIFF0007852240000004.tif7170

[0071] In formula 4, R is the same as R represented by formula 1. α, β, γ, and δ are correction coefficients. These correction coefficients are used to correct the deviation from the assumed value regarding the amount of the sheet P conveyed due to some factor that cannot be fully reflected in the slip rate R of formula 1, such as slip occurring in the conveyance roller pair 23. The above deviation varies according to the characteristics and usage status of the sheet P, the quality of image recording, and the elapsed time since the start of use of the printer 100. The characteristics of the sheet P are, for example, the type for use of the sheet P (plain paper, glossy paper, etc.). Also, the usage status of the sheet P is the remaining amount of the roll paper Rp, the number of printed sheets of the sheet P, and the like. Each correction coefficient is set to adjust the slip rate R indicated by R according to these variation factors as follows.

[0072] α has a value corresponding to the type of paper P used. For example, when plain paper or glossy paper is selectively used as paper P, the value of α is set according to whether the material of these papers is prone to slipping. Also, β has a value corresponding to the quality of image recording. For example, when high-speed recording or high-resolution recording can be selected as the quality of image recording on paper P, the speed at which paper P is transported may be changed according to these selections. In such cases, β is set to a larger value because the risk of slipping increases as the transport speed of paper P increases.

[0073] Furthermore, when the paper P is roll paper Rp, γ has a value corresponding to the remaining amount of roll Rb obtained based on the detection result of the paper remaining amount sensor 271. For example, the larger the remaining amount, the greater the tension generated in the roll Rb or the pulled-out roll paper Rp, and the more likely slippage is to occur on the rollers. For this reason, γ is set to a larger value when the remaining amount is larger. Alternatively, the cumulative length used may be used instead of the remaining amount. When the cumulative length used is used, a larger cumulative length corresponds to a smaller remaining amount. Alternatively, the value of γ may be set according to the length conveyed by the intermediate roller pair 22 for a single sheet of paper P during image recording.

[0074] Furthermore, δ has a value corresponding to the number of printed pages and the elapsed time since the start of product use. For example, the control unit 209 stores the cumulative result of the number of printed pages in the ROM 92 and calculates the elapsed time since the start of product use based on the built-in timer. A large number of printed pages or a large elapsed time indicates that the various parts of the device are deteriorating due to aging. As deterioration progresses, slippage is more likely to occur in the rollers, and fluctuations in the roller diameter may occur, causing fluctuations in the operation of the rollers according to the control content based on equations 1 to 3. For this reason, the control unit 209 sets δ to a size corresponding to the number of printed pages and the elapsed time since the start of product use.

[0075] Based on the above, R can be appropriately corrected based on Equation 4 to reflect various factors that cannot be fully reflected in the slip ratio R of Equation 1.

[0076] <Variation> As described above, the embodiments of the present invention have been described based on the drawings. However, the specific configuration should be considered not to be limited to these embodiments. The scope of the present invention is indicated by the claims rather than the description of the above embodiments, and further includes all modifications within the meaning and scope equivalent to the claims.

[0077] For example, in Equation 1 of the above-described embodiment, L Act is the actual amount of the sheet P sent out by the intermediate roller pair 22 and is calculated based on the detection result of the rotary encoder 83. In contrast, instead of L Act , the number of rotations of the intermediate roller pair 22 itself indicated by the detection result of the rotary encoder 83 may be used. In this case, instead of L Set , a reference value regarding the number of rotations of the intermediate roller pair 22 may be used.

[0078] Also, in the above-described embodiment, when the sheet P is sent out by the intermediate roller pair 22 from the time the leading end of the sheet P reaches the intermediate roller pair 22 until it reaches the conveyance roller pair 23, L Act corresponding to the actual value of the number of rotations of the intermediate roller pair 22 is obtained based on the detection result of the rotary encoder 83. Then, the relationship between L Set which is the theoretical value of the amount of the sheet P sent out by the intermediate roller pair 22 in the above case and L Act is obtained as the slip rate R. In contrast, the number of rotations of the intermediate roller pair 22 may be used as the theoretical value, and the amount of the sheet P sent out by the intermediate roller pair 22 may be used as the actual value.

[0079] A specific configuration example is as follows: A paper status acquisition means is installed that acquires the status of the paper P in the path 25a, such as the amount of paper P fed into the path 25a, by irradiating the paper P and the path 25a with laser light. Then, the control unit 9 rotates the intermediate roller pair 22 for a number of rotations that is a preset value (theoretical value) after the leading edge of the paper P reaches the intermediate roller pair 22, and feeds the paper P into the intermediate roller pair 22. At this time, based on the status of the paper P in the path 25a acquired by the paper status acquisition means, the control unit 9 calculates the amount of paper P fed by the intermediate roller pair 22 (actual value). Furthermore, based on the calculation result, the control unit 9 evaluates the difference between the case where the intermediate roller pair 22 slips relative to the paper P and the case where it does not slip (corresponding to the "slip evaluation process" of the present invention). Specifically, the control unit 9 evaluates the difference based on the relationship between the calculated amount of paper P fed and the reference value of the amount of paper P fed when the intermediate roller pair 22 is rotated without slipping for the above preset number of rotations. In this regard, L in equation 1 Act The calculated paper feed amount P is used as L Set The above differences can also be evaluated by calculating the slip ratio R' when each of the following is replaced with the standard value of the discharge amount.

[0080] Furthermore, in the above-described embodiment, the slip ratio R is calculated for each image recording on a single sheet of paper P. In contrast, the slip ratio R may be acquired at the time of manufacturing the printer 100, or at the time of the first use of the printer 100 after manufacturing. In this case, the acquired R may be stored in the ROM 92, and the R stored in the ROM 92 may continue to be used in subsequent image recordings.

[0081] Furthermore, in the above embodiment, X * MID The buffer is temporarily cleared by a buffer clear transport process that rotates the intermediate roller pair 22 with a certain number of rotations. However, instead of the buffer clear transport process, X MID Smaller than X * MIDThe buffer may be temporarily reduced by rotating the intermediate roller pair 22 at a higher rotation speed.

[0082] In addition, while the above embodiments describe the application of the present invention to a printer 100, the invention is not limited thereto. The present invention can also be applied to any image recording device that ejects ink from a head, including inkjet, laser, and thermal image recorders, such as multifunction printers and copiers. [Explanation of Symbols]

[0083] 2. Conveying mechanism 4 carriages 5 heads 6 Moving mechanism 8. Cartridge mounting section 9, 209 Control Unit 10 Ink Cartridges 51 nozzles 100, 200 printers P Paper (recording medium)

Claims

1. A media storage section for containing a sheet-like medium, A first pair of rollers that grips a sheet-like medium supplied from the media storage unit and feeds it along a predetermined transport path, A second pair of rollers, while gripping the sheet-like medium moved by the first pair of rollers, feeds it along the predetermined transport path downstream of the first pair of rollers with respect to the predetermined transport path, With respect to the predetermined transport path, downstream from the second roller pair, an image forming unit forms an image on the sheet-like medium fed by the second roller pair, An acquisition means for acquiring the actual value of the other between the theoretical value of the number of rotations of the first roller pair and the amount of sheet-like medium fed by the first roller pair when rotated at that number of rotations, It is equipped with a control unit, The control unit, Based on the relationship between the one theoretical value and the other actual value obtained by the acquisition means, a slip evaluation process is performed to evaluate the difference in the amount of sheet-like medium fed by the first roller pair when the first roller pair slips against the sheet-like medium compared to when the first roller pair does not slip against the sheet-like medium. The process involves adjusting the number of rotations of the first roller pair per unit time based on the evaluation results in the slip evaluation process so that the amount of sheet-like medium fed out by the first roller pair is greater than that of the second roller pair, while simultaneously transporting the sheet-like medium to the image forming unit by the first roller pair and the second roller pair, and performing an image forming process to form an image on the sheet-like medium in the image forming unit. The acquisition means includes a first tip sensor capable of detecting when the leading edge of the sheet-like medium reaches the first roller pair, a second tip sensor capable of detecting when the leading edge of the sheet-like medium reaches the second roller pair, and a rotation sensor that detects the number of rotations of the first roller pair. The control unit, An image forming apparatus characterized in that, based on the detection results of the first tip sensor and the second tip sensor, the sheet-like medium is fed to the first roller pair at a feed amount corresponding to the theoretical value corresponding to the time from when the tip of the sheet-like medium reaches the first roller pair until it reaches the second roller pair, and the number of rotations of the first roller pair detected by the rotation sensor at that time is taken as the actual value, and the difference is evaluated in the slip evaluation process.

2. A media storage section for storing a sheet-like medium, A first pair of rollers that grips a sheet-like medium supplied from the media storage unit and feeds it along a predetermined transport path, A second pair of rollers, while gripping the sheet-like medium moved by the first pair of rollers, feeds it along the predetermined transport path downstream of the first pair of rollers with respect to the predetermined transport path, With respect to the predetermined transport path, downstream from the second roller pair, an image forming unit forms an image on the sheet-like medium fed by the second roller pair, An acquisition means for acquiring the actual value of the other between the theoretical value of the number of rotations of the first roller pair and the amount of sheet-like medium fed by the first roller pair when rotated at that number of rotations, It is equipped with a control unit, The control unit, Based on the relationship between the one theoretical value and the other actual value obtained by the acquisition means, a slip evaluation process is performed to evaluate the difference in the amount of sheet-like medium fed by the first roller pair when the first roller pair slips against the sheet-like medium compared to when the first roller pair does not slip against the sheet-like medium. The process involves adjusting the number of rotations of the first roller pair per unit time based on the evaluation results in the slip evaluation process so that the amount of sheet-like medium fed out by the first roller pair is greater than that of the second roller pair, while simultaneously transporting the sheet-like medium to the image forming unit by the first roller pair and the second roller pair, and performing an image forming process to form an image on the sheet-like medium in the image forming unit. The control unit, In the image forming process, the first transport process and the second transport process are performed. The first transport process is as follows: This process involves rotating the first roller pair with a first slip correction number, which is obtained by correcting the first reference number of rotations corresponding to the case when the first roller pair feeds the sheet-like medium without slipping, so that it becomes larger according to the evaluation result in the slip evaluation process, while simultaneously rotating the second roller pair with a second reference number of rotations smaller than the first reference number of rotations, thereby transporting the sheet-like medium to the image forming unit. The second transport process is as follows: An image forming apparatus characterized in that, after the first transport process has been performed once or more times, if the number of times the first transport process has been performed reaches a predetermined number of times, the first roller pair is rotated by a second slip correction number obtained by correcting a value smaller than the first reference rotation number according to the evaluation result of the slip evaluation unit, while the second roller pair is rotated by a second reference rotation number, thereby transporting the sheet-like medium to the image forming unit.

3. The control unit, in the image forming process, The process involves performing a skew correction process to feed the sheet-like medium to the first roller pair while the leading edge of the sheet-like medium is in contact with the second roller pair, a leading-out process to feed the sheet-like medium to both the first and second roller pairs such that the number of rotations of the first roller pair is less than the number of rotations of the second roller pair, and multiple first transport processes in this order. When executing the aforementioned multiple first transport processes, the difference between the first reference number of rotations and the second reference number of rotations is accumulated relative to the initial value each time the first transport process is executed, and the second transport process is executed when the accumulated result exceeds a threshold. The image forming apparatus according to claim 2, characterized in that the initial value is set based on the amount of feed by the first roller pair in the oblique correction process and the difference between the number of rotations of the first roller pair and the number of rotations of the second roller pair in the head-out process.

4. The media storage section has a first portion capable of accommodating a roll in which a long sheet-like medium is wound into a roll shape, and a second portion capable of accommodating multiple sheets of medium shorter than the long sheet-like medium in a stacked state. The long sheet-like medium and the short sheet-like medium are selectively fed from the medium storage section toward the first roller pair. The image forming apparatus according to claim 2 or 3, characterized in that the control unit performs the first transport process and the second transport process in such a way that the predetermined number of times is greater when the long sheet-like medium is used compared to when the short sheet-like medium is used.

5. comprising means for obtaining the number of rotations of the first roller pair, The control unit, in the slip evaluation process, The image forming apparatus according to any one of claims 1 to 4, characterized in that the slip value indicating the difference is calculated to increase in proportion to the magnitude of the difference between a reference value corresponding to the case when the first roller pair does not slip against the sheet-like medium and the number of rotations acquired by the rotation acquisition means.

6. The image forming apparatus according to claim 5, characterized in that the control unit corrects the slip value in the slip evaluation process according to at least one of the characteristics and usage conditions of the sheet-like medium, the quality of image formation by the image forming unit, and the elapsed time since the start of use of the apparatus.

7. The media storage section is capable of accommodating a roll in which a long sheet-like medium is wound into a roll shape. The image forming apparatus according to claim 6, characterized in that the usage status of the sheet-like medium corresponds to the cumulative amount used or remaining amount of the long sheet-like medium since it was first unwound from the roll body stored in the medium storage section and used.

Images