JP5121990B2 - Sheet transport device - Google Patents

Description

  The present invention relates to a sheet conveying apparatus, and more particularly, to a sheet conveying apparatus that performs accurate conveyance control even when, for example, the leading and trailing ends of a recording medium enter or exit a conveying roller.

  In recent years, recording apparatuses such as printers have increased opportunities to print photographic images using recording media such as photographic paper as well as plain paper. In particular, in an ink jet printer, ink droplets used for recording have a smaller size, and an image quality equivalent to or higher than that of a silver salt photograph has been obtained.

  At the same time, higher precision is required for transport of the recording medium, and a high precision roller such as a roller in which a metal shaft is coated with a grindstone is used as the transport roller. In addition to this, the DC motor used to drive the transport roller is also controlled by a code wheel and an encoder sensor provided on the shaft so as to achieve both high precision and high speed transport.

  Further, since the image cannot be correctly recorded up to the rear end portion of the recording medium only by using one pair of conveying rollers, another conveying roller pair is arranged downstream in the conveying direction of the recording medium in order to realize borderless recording. A configuration is also proposed in which the above is provided. However, in such a configuration, when the trailing edge of the recording medium is removed from the conveying roller pair on the upstream side in the conveying direction, the conveyance amount of the recording medium may change, and the image may be uneven. Therefore, in order to ensure the conveyance accuracy up to the rear end of the recording medium, the amount of conveyance is reduced by limiting the nozzles used in the recording head when recording is performed on the rear end of the recording medium. In addition, it has been proposed to maintain the recording quality by controlling the conveyance of the trailing edge of the recording medium in combination with the restriction of the nozzles used in the recording head (see Patent Document 1). Furthermore, the conveyance accuracy is ensured for the conveyance roller pair on the downstream side in the conveyance direction by increasing the mechanical accuracy.

JP 2002-225370 A

  In recent years, there has been an increasing demand for higher image quality and high-speed recording of recorded images. In order to meet this requirement, the recording width of the recording head is increased, the number of passes in multi-pass recording is reduced, and the recording medium conveyance length for each pass recording is also increased. In addition, in order to further improve image quality, ink droplets used for recording have become even smaller. This also means that the recording medium is required to be conveyed with higher accuracy.

  However, in the above conventional example, the performance of the recording head is not fully utilized when recording is performed on the rear end portion of the recording medium, and this has become a major obstacle to high-speed recording, which is a demand from the market.

  That is, in order to cope with borderless recording and the like, in the configuration in which another conveyance roller is provided downstream in the conveyance direction of the recording medium, the downstream conveyance roller is moved after the trailing end of the recording medium passes through the upstream conveyance roller. When transporting only by itself, drive transmission by idler gear etc. enters the middle. For this reason, it is difficult to ensure conveyance accuracy, and the number of nozzles used in the recording head must be limited to ensure accuracy, which is a major obstacle to increasing the recording speed.

  The present invention has been made in view of the above-described conventional example, and an object of the present invention is to provide a sheet conveying apparatus capable of performing accurate recording medium conveyance control even in a configuration in which a plurality of conveyance rollers are provided in a recording medium conveyance path. It is said.

  In order to achieve the above object, the sheet conveying apparatus of the present invention has the following configuration.

  That is, the first conveyance roller that conveys the sheet, the second conveyance roller that is provided downstream of the first conveyance roller in the conveyance direction, and conveys the sheet, and conveyance by the first conveyance roller. A first encoder sensor that outputs a first pulse signal in response to rotation of the first transport roller for detecting information; and a second encoder for detecting transport information by the second transport roller. And a second encoder sensor that outputs a second pulse signal according to the rotation of the first and second conveying rollers and at least one of the first pulse signal and the second pulse signal to control the conveyance of the sheet. And when the sheet is conveyed in a direction from the first conveyance roller toward the second conveyance roller, the control unit is arranged at a rear end position of the conveyed sheet. Thus, the signal used for the conveyance control is switched from the first pulse signal to the second pulse signal, and the conveyance information detected by the first pulse signal at the time of the switching is used for the second pulse signal. The subsequent transfer control is taken over.

  Also, a first conveying roller that conveys the sheet, and a second conveying roller that is provided downstream of the first conveying roller in the conveying direction and conveys the sheet, and conveying by the first conveying roller. A first encoder sensor that outputs a first pulse signal in response to rotation of the first transport roller for detecting information; and a second encoder for detecting transport information by the second transport roller. And a second encoder sensor that outputs a second pulse signal according to the rotation of the first and second conveying rollers and at least one of the first pulse signal and the second pulse signal to control the conveyance of the sheet. And when the sheet is conveyed in a direction from the first conveyance roller toward the second conveyance roller, the control unit is arranged at a rear end position of the conveyed sheet. Thus, the signal used for transport control is switched from the first pulse signal to the second pulse signal, and the phase difference between the first pulse signal and the second pulse signal is stopped in the transport control after the switching. It can also be characterized in that it is reflected in the target position or timing.

  Therefore, according to the present invention, an encoder sensor is provided for each of the two conveyance rollers provided in the conveyance path of the recording medium, and recording is performed by selectively using one of the output signals from these according to the position on the conveyance path of the recording medium. Media transport control is performed. As a result, it is possible to realize more accurate conveyance control, and as a result, it is possible to realize good image recording.

1 is a schematic perspective view of a recording apparatus that performs recording using an ink jet recording head that is a typical embodiment of the present invention. FIG. 2 is a schematic perspective view showing an internal structure of the recording apparatus with an outer case removed from the recording apparatus shown in FIG. 1. FIG. 3 is a side sectional view showing a recording medium transport mechanism in the internal structure of the recording apparatus shown in FIG. 2. FIG. 6 is a side cross-sectional view illustrating a state in which two encoders are provided on each of a conveyance roller and a paper discharge roller constituting a recording medium conveyance mechanism. FIG. 5 is a block diagram illustrating a control configuration of the recording apparatus illustrated in FIGS. 1 to 4. It is a figure explaining the control area of a plurality of encoders. FIG. 6 is a diagram for explaining conveyance control of a recording medium according to the first embodiment. It is a figure which shows the time transition of the pulse signal from the encoder sensor 363 according to Example 1, and the pulse signal from the encoder sensor 403. FIG. It is a figure which shows the time transition of the pulse signal from the encoder sensor 363 according to Example 2, and the pulse signal from the encoder sensor 403. FIG. It is another figure which shows the time transition of the pulse signal from the encoder sensor 363 according to Example 2, and the pulse signal from the encoder sensor 403. FIG. It is another figure which shows the time transition of the pulse signal from the encoder sensor 363 according to Example 2, and the pulse signal from the encoder sensor 403. FIG. FIG. 10 is a diagram illustrating a relationship between a pulse signal from an encoder sensor 363 according to a third embodiment, a pulse signal from an encoder sensor 403, and a conveyance amount of a recording medium. It is a figure which shows the time transition of the pulse signal from the encoder sensor for virtual conveyance rollers, and the pulse signal from the encoder sensor 403. FIG. , It is a figure which shows the time transition of the pulse signal from the encoder sensor 363 with high position detection resolution according to Example 4, and the pulse signal from the encoder sensor 403 with low position detection resolution. It is a figure which shows the time transition of the pulse signal from the encoder sensor 363 with low position detection resolution according to Example 4, and the pulse signal from the encoder sensor 403 with high position detection resolution. It is a figure explaining a mode that the amount of phase shifts according to Example 5 is detected and averaged several times.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings.

  In this specification, “recording” (sometimes referred to as “printing”) does not represent only the case of forming significant information such as characters and graphics. In addition to this, an image, a pattern, a pattern, or the like is widely formed on a recording medium regardless of whether it is significant involuntary, or whether it is manifested so that a human can perceive it visually, or It also represents the case where the medium is processed.

  “Recording medium” refers not only to paper used in general recording apparatuses but also widely to cloth, plastic film, metal plate, glass, ceramics, wood, leather, and the like that can accept ink. Shall.

  Further, “ink” (sometimes referred to as “liquid”) should be interpreted widely as in the definition of “recording (printing)”. That is, by being applied on the recording medium, it is used for forming an image, pattern, pattern, etc., processing the recording medium, or processing the ink (for example, solidification or insolubilization of the colorant in the ink applied to the recording medium). It shall represent a liquid that can be made.

  Furthermore, unless otherwise specified, the “nozzle” collectively refers to an ejection port or a liquid channel communicating with the ejection port and an element that generates energy used for ink ejection.

  FIG. 1 is a schematic perspective view of a recording apparatus that performs recording using an ink jet recording head according to a typical embodiment of the present invention.

  FIG. 2 is a schematic perspective view showing the internal structure of the recording apparatus with the outer case removed from the recording apparatus shown in FIG. As an operation of the recording apparatus, for example, an image is formed on the recording medium by repeatedly carrying a certain amount of recording medium and scanning a carriage equipped with the recording head.

  FIG. 3 is a side sectional view showing a recording medium transport mechanism in the internal structure of the recording apparatus shown in FIG.

  FIG. 4 is a side cross-sectional view showing a state where two encoders are provided on each of the transport roller and the paper discharge roller constituting the recording medium transport mechanism.

  The configuration of the recording apparatus will be described below with reference to FIGS.

  The recording apparatus 1 shown in FIGS. 1 to 4 includes a paper feed unit, a transport unit, a carriage unit, and a paper discharge unit. In the following, these outlines will be sequentially described by item.

(A) Paper Feed Unit The paper feed unit 2 shown in FIG. 1 is configured to stack a sheet-like recording medium (not shown) such as cut recording paper on the pressure plate 21 as shown in FIG. Yes. A pressure plate 21, a paper feed roller 28 for feeding a recording medium, a separation roller 241 for separating the recording medium one by one, and the like are attached to the base 20 in the paper feeding unit 2.

  A paper feed tray 26 for holding the loaded recording medium is attached to the base 20 or the exterior. The paper feed tray 26 is a multi-stage type and is pulled out for use.

  The feed roller 28 has a cylindrical shape with a circular cross section. The driving force of the paper feed roller 28 is transmitted from a motor shared with the cleaning unit provided in the paper feed unit 2 by a drive transmission gear (not shown) and a planetary gear (not shown).

  A movable side guide 23 is movably provided on the pressure plate 21 to regulate the recording medium stacking position. The pressure plate 21 can rotate around a rotation shaft coupled to the base 20, and is urged by the pressure plate spring 212 to the paper feed roller 28. A separation sheet (not shown) made of a material having a high coefficient of friction such as an artificial leather that prevents double feeding of recording media near the last sheet of the stacked recording media is provided at a portion of the pressure plate 21 that faces the paper feed roller 28. Is provided. The pressure plate 21 is configured to be able to contact and separate from the paper feed roller 28 by a pressure plate cam 241.

  Further, the separation roller 241 is provided with a clutch spring (not shown), and a portion where the separation roller 241 is attached can rotate when a load exceeding a predetermined value is applied.

  In a normal standby state, the loading port is closed so that the loaded recording medium does not enter the inside of the recording apparatus. When paper feeding starts from this state, first, the separation roller 241 contacts the paper feeding roller 28 by driving the motor. Then, the pressure plate 21 contacts the paper feed roller 28. In this state, feeding of the recording medium is started, and only a predetermined number of recording media are sent to the nip portion constituted by the feeding roller 28 and the separation roller 241. The sent recording medium is separated at the nip portion, and only the uppermost recording medium is fed into the recording apparatus.

  When the recording medium reaches the conveyance roller 36 and the pinch roller 37, the pressure plate 21 returns to its original position by a pressure plate cam (not shown). At this time, the recording medium that has reached the nip portion constituted by the paper feed roller 28 and the separation roller 241 can be returned to the stacking position.

(B) Conveying unit A conveying unit is attached to the chassis 11 made of a bent metal sheet. The transport unit includes a transport roller 36 that transports a recording medium and a PE sensor 32. The transport roller 36 has a configuration in which ceramic fine particles are coated on the surface of a metal shaft, and the metal portions of both shafts are received by bearings and attached to the chassis 11. A conveyance roller tension spring (not shown) is provided between the bearing and the conveyance roller 36 in order to apply a load during rotation to the conveyance roller 36 so that stable conveyance can be performed. Is given.
A plurality of driven pinch rollers 37 are provided in contact with the conveying roller 36. The pinch roller 37 is held by a pinch roller holder (not shown), and is urged by a pinch roller spring (not shown), so that the pinch roller 37 is pressed against the transport roller 36 and generates a transport force of the recording medium. At this time, the rotating shaft of the pinch roller holder is attached to the bearing of the chassis 11 and rotates around the shaft. Further, a platen 34 is disposed at the entrance of the transport unit where the recording medium is transported. The platen 34 is attached to the chassis 11 and positioned.

  In the above configuration, the recording medium sent to the transport unit is guided by a pinch roller holder (not shown) and a paper guide flapper, and is sent to a roller pair of the transport roller 36 and the pinch roller 37. At this time, the leading end of the recording medium conveyed by the PE sensor 32 is detected, and thereby the recording position of the recording medium is obtained. The recording medium is conveyed on the platen 34 by rotating the roller pairs 36 and 37 by a conveyance motor (not shown). On the platen 34, a rib serving as a conveyance reference surface is formed, and the gap with the recording head is managed, and control is performed so that the extent of the recording medium does not become large, together with a paper discharge unit described later. doing.

  As shown in FIG. 4, the transport roller 36 is driven by transmitting the rotational force of the transport motor 35 formed of a DC motor to a pulley 361 provided on the shaft of the transport roller 36 via a timing belt 39. A code wheel 362 on which markings are formed at a pitch of 150 to 300 lpi for detecting the amount of conveyance by the conveyance roller 36 is provided on the axis of the conveyance roller 36. An encoder sensor 363 that reads the marking is attached to the chassis 11 at a position adjacent to the code wheel 362.

  As described above, a plurality of code wheels and encoder sensors are provided in the same transport system, and the control target is changed according to the transport area of the recording medium P based on the output from the plurality of encoder sensors. In this embodiment, the recording medium P is conveyed.

  Advantages of such a configuration include a single drive source and low cost. In addition, the necessary control target can be directly controlled in the area where high-precision control is required, and the drive train is connected, so the behavior when switching the control target is stable and required for configurations with multiple drive sources. Another advantage is that it does not require sophisticated synchronization control of multiple rollers.

  Further, a recording head 7 that forms an image based on image information is provided on the downstream side of the conveying roller 36 in the recording medium conveying direction.

  As the recording head 7, an ink jet recording head equipped with a replaceable ink tank 71 for each color ink tank is used. The recording head 7 ejects ink from the nozzles by a pressure change caused by the growth or contraction of bubbles generated by boiling the ink film by applying heat to the ink with a heater or the like, and forms an image on the recording medium. At this time, the recording medium is held by the platen 34, and the distance from the nozzle to the recording surface of the recording medium is maintained at a predetermined amount.

  Further, the platen 34 is provided with a platen absorber 344 that absorbs ink that protrudes from the end of the recording medium when full-surface printing (edgeless printing) is performed. All the ink protruding from the four side edges of the recording medium is absorbed here.

(C) Carriage unit The carriage unit 5 includes a carriage 50 to which the recording head 7 is attached. The carriage 50 holds a guide shaft 52 for reciprocating scanning in a direction perpendicular to the recording medium conveyance direction (different directions) and the rear end of the carriage 50 to maintain a gap between the recording head 7 and the recording medium. It is supported by a rail (not shown). The guide shaft 52 is attached to the chassis 11. The guide rail is formed integrally with the chassis 11.

  The carriage 50 is driven via a timing belt 541 by a carriage motor 54 attached to the chassis 11. The timing belt 541 is coupled to the carriage 50 via a damper made of rubber or the like, and reduces image unevenness by attenuating vibration of the carriage motor 54 or the like. A code strip 561 in which markings are formed at a pitch of 150 to 300 lpi for detecting the position of the carriage 50 is provided in parallel with the timing belt 541. Further, an encoder sensor (not shown) for reading it is provided on a carriage substrate (not shown) mounted on the carriage 50. Further, the carriage 50 is provided with a flexible substrate 57 for transmitting various control signals and recording signals from a control circuit (described later) to the recording head 7.

  In order to fix the recording head 7 to the carriage 50, a head set lever 51 is provided. The head set lever 51 is rotated around the rotation fulcrum to fix the recording head 7 to the carriage 50.

  When forming an image on the recording medium, the roller pairs 36 and 37 convey the recording medium to the ink ejection position in the recording medium conveying direction by the recording head 7. At the same time, the carriage motor 54 moves the carriage 50 to the ink discharge position in the carriage movement direction. Thereafter, the recording head 7 ejects ink toward the recording medium according to a signal from the control circuit, and an image is formed.

(D) Paper discharge unit The paper discharge unit is a spur (not shown) configured to be rotated by being driven by a predetermined pressure against the two paper discharge rollers 40 and 41 and the paper discharge rollers 40 and 41, and transported. It is composed of a gear train for transmitting the driving of the rollers to the discharge rollers 40 and 41. The paper discharge rollers 40 and 41 are attached to the platen 34. The paper discharge roller 40 is provided with a plurality of rubber portions on a metal shaft.

  As shown in FIG. 4, the discharge roller 40 is driven by the drive from the conveying roller 36 acting on the discharge roller gear 404 directly connected to the discharge roller 40 via the idler gear 45. Further, the discharge roller 41 provided on the downstream side of the discharge roller 40 in the conveyance direction of the recording medium is made of resin. The drive to the paper discharge roller 41 is transmitted from the paper discharge roller 40 via another idler gear. On the shaft of the paper discharge roller 40, a code wheel 402 on which markings are formed at a pitch of 150 to 300 lpi for detecting the transport amount by the paper discharge roller 40 is provided. The encoder sensor 403 that reads the marking is attached to the chassis 11 at a position adjacent to the code wheel 402.

  The spur is attached to a spur holder 43.

  With the above configuration, the recording medium recorded by the recording head 7 is sandwiched between the nip between the paper discharge roller 41 and the spur, conveyed, and discharged to the paper discharge tray 46. The paper discharge tray 46 is configured to be housed in the front cover 95. The paper discharge tray 46 is pulled out for use. The discharge tray 46 increases in height toward the leading end, and both ends thereof are configured to be high in height so that the stackability of the discharged recording medium can be improved and the recording surface can be prevented from rubbing.

  FIG. 5 is a block diagram showing a control configuration of the recording apparatus shown in FIGS.

  As shown in FIG. 5, the controller 600 includes an MPU 601, a ROM 602, a special purpose integrated circuit (ASIC) 603, a RAM 604, and an A / D converter 606. The ROM 602 stores a program corresponding to a control sequence described later, a required table, and other fixed data. The ASIC 603 generates control signals for controlling the carriage motor 54, the transport motor 35, and the recording head 7. The RAM 604 is provided with an image data development area, a work area for program execution, and the like. The MPU 601, the ASIC 603, and the RAM 604 are connected to each other via a system bus 605 to exchange data. The A / D converter 606 inputs analog signals from the sensor group described below, performs A / D conversion, and supplies the digital signals to the MPU 601.

  In FIG. 5, reference numeral 610 denotes a computer (or a reader for image reading, a digital camera, or the like) serving as a supply source of image data, and is collectively referred to as a host device. Image data, commands, status signals, and the like are transmitted and received between the host apparatus 610 and the recording apparatus 1 via an interface (I / F) 611.

  Further, the switch group 620 instructs to start the power switch 621, the print switch 622 for instructing the start of printing, and the process (recovery process) for maintaining the ink ejection performance of the recording head 7 in a good state. Recovery switch 623 and the like. With these switches, the recording apparatus receives a command input from the operator. The sensor group 630 includes a position sensor 631 such as a photocoupler for detecting the home position h, a temperature sensor 632 provided at an appropriate location of the recording apparatus for detecting the environmental temperature, and the like.

  The encoder sensors 363 and 403 read the markings on the code wheels 362 and 402 provided on the conveyance roller 36 and the paper discharge roller 40, respectively, and generate encoder signals (analog signals). Then, in the encoder sensors 363 and 403, the signal edge is detected from the generated encoder signal to generate an edge signal, and the edge signal is A / D converted to generate a digital pulse signal. . Since the markings on the code wheels 362 and 402 are provided at regular intervals, the pulse signal generation cycle is constant as long as the transport rollers 36 and 40 normally rotate at a constant rotational speed.

  Accordingly, such pulse signals are output from the encoder sensors 363 and 403 and input to the ASIC 651. The ASIC 651 counts the number of pulses of the pulse signals from the encoder sensors 363 and 403 under the control of the MPU 601, detects the phase difference between these pulse signals, and measures the period of each pulse signal. These measurement and detection results are output to the MPU 601.

  Further, 640 is a carriage motor driver that drives the carriage motor 54 for reciprocating the carriage 50, and 642 is a transport motor driver that drives the transport motor 35 for transporting the recording medium.

  The ASIC 603 transfers printing element (ejection heater) drive data (DATA) to the print head while directly accessing the storage area of the RAM 602 during print scan by the print head 7.

  The configuration shown in FIGS. 1 to 4 is a configuration in which the ink cartridge 71 and the recording head 7 can be separated, but a replaceable head cartridge may be configured by integrally forming them. Further, the ASIC 651 may be omitted, and the ASIC 603 may process the pulse signals from the encoder sensors 363 and 403 instead of the ASIC 651.

  Next, several embodiments for controlling the conveyance of a recording medium based on outputs from a plurality of encoder sensors provided in the conveyance mechanism of the recording apparatus will be described in detail.

  FIG. 6 is a diagram for explaining a control area of a plurality of encoders.

  As shown in FIG. 6, in this embodiment, the control of the encoder sensors 363 and 403 is switched according to the rear end position of the recording medium P, or the conveyance control of the recording medium P is performed in cooperation.

  In this embodiment, the rear end position of the recording medium P is detected by the PE sensor 32. Actually, the detection is performed based on whether the leading end of the recording medium P is in contact with the PE sensor lever 321 provided in the pinch roller holder that holds the pinch roller 37 or the trailing end thereof is not in contact.

  As shown in FIG. 6, in this embodiment, one of the output signals from the two encoder sensors 363 and 403 is selected according to the rear end position of the recording medium P, and the recording medium P is conveyed based on the selected signal. Take control. When the recording medium P is conveyed, the rear end position of the recording medium P is detected by the PE sensor lever 321 and the PE sensor 32 according to the conveyance, and the nip position of the conveying roller 36 on the upstream side can be estimated from this detection information. It becomes. Basically, in the area where the recording medium P is conveyed by the conveyance roller 36, the conveyance motor 35 is controlled based on information obtained from the encoder sensor 363 to perform a line feed operation. Thereafter, after the recording medium P passes through the nip of the conveying roller 36, that is, in the area where the recording medium P is conveyed by the downstream discharge roller 40, the conveying motor 35 is controlled based on information obtained from the encoder sensor 403. To perform a line feed operation.

  This conveyance control will be further described with reference to the drawings.

  FIG. 7 is a diagram for explaining the conveyance control of the recording medium.

  FIG. 7A shows a state in which the recording motor P is controlled based on information obtained from the encoder sensor 363. In this state, the factors affecting the feeding accuracy of the transport roller 36 are the eccentricity of the transport roller 36 and the transport code wheel 362, and the eccentric phase difference between the two, excluding the friction slip of the transport roller 36. is there.

  FIG. 7B and FIG. 7C show a state in which the conveyance motor 35 is controlled on the recording medium P based on information from the encoder sensor 403. In this state, the factors affecting the feeding accuracy of the paper discharge roller 40 are the eccentricity of the paper discharge roller 40, the eccentricity of the code wheel 402, and the eccentric positions of both, excluding the friction slip of the paper discharge roller 40. It is a phase difference.

  In the conveyance control, it is desirable to switch from the control based on information obtained from the encoder sensor 363 to the control based on information obtained from the encoder sensor 403 in the state shown in FIG. However, such control has drawbacks as will be described later. For this reason, in this embodiment, in the line feed operation immediately before the state shown in FIG. 7B occurs, the information used for the conveyance control is switched from the information obtained from the encoder sensor 363 to the information obtained from the encoder sensor 403. Subsequent conveyance control is performed based on information obtained from the encoder sensor 403 until the recording of the page is completed.

  In the state shown in FIG. 7B, in the case of a blank line feed operation in which image recording is not continuous, based on information obtained from the encoder sensor 403 after the state shown in FIG. You may switch to conveyance control.

  In the case of the conventional configuration in which the downstream side conveyance roller 40 is not provided with an encoder sensor, in the state shown in FIG. 7C, the factor that affects the feeding accuracy of the paper discharge roller 40 is the friction of the paper discharge roller 40. Excluding slip, it is as follows. That is, the eccentricity of the code wheel 402, the gear feed error of the pulley 361 (similar to eccentricity), the idle gear 45 feeding error (similar to eccentricity), the feeding error of the roller gear 404 (similar to eccentricity), the paper discharge These are the eccentricity of the roller 40 and the eccentric phase difference of each. Therefore, with the configuration of this embodiment, the eccentricity error for the three gears can be improved. In reality, we have succeeded in reducing the transport error to about half from simulations and experiments.

  Next, control for intermittently conveying a recording medium by servo-controlling a DC motor (conveyance motor) based on information obtained from an encoder sensor will be described.

  In the servo control, the conveyance speed of the recording medium is accelerated and decelerated toward a stop target position designated in advance. In the vicinity of the stop target position, the speed is controlled to a constant speed at an extremely low speed just before the stop. Thereafter, at the moment when the stop target position is reached, the supply of drive power to the DC motor is cut off, and the recording medium stops as a result of inertia and the balance between the inertia of the mechanism and the frictional resistance.

  The example described below is directed to an area in which the conveyance of the recording medium is controlled to an extremely low speed just before the stop of the line feed operation executed when the information obtained from the above two encoder sensors is switched for the conveyance control. .

  First, switching of the pulse signal from the encoder sensor will be described.

  In this embodiment, the MPU 601 and the ASIC 651 cooperate to switch the pulse signal from the encoder sensor used for transport control.

  FIG. 8 is a diagram showing temporal transitions of the pulse signal from the encoder sensor 363 and the pulse signal from the encoder sensor 403.

  As shown in FIG. 8, the ASIC 651 detects the pulse signals EA-3, EA-2, EA-1, and EA0 using the pulse signal EA0 as the target stop timing of the conveying roller. On the other hand, the pulse signals EB-2, EB-1, and EB0 from the encoder sensor 403 are similarly detected. The pulse signals EA + 1 and EB + 1 are described for convenience as pulse signals detected in the future.

  As described above, the ASIC 651 includes two counters: a counter that counts pulse signals from the encoder sensor 363 and a counter that counts pulse signals from the encoder sensor 403. When the detection of the pulse signal reaches the target stop timing of the conveying roller, the count value of the counter that counts the pulse signal from the encoder sensor 363 is overwritten with the count value of the counter that counts the pulse signal from the encoder sensor 403. To do. At the same time, the ASIC 651 switches to input a pulse signal from the encoder sensor 403 under the control of the MPU 601, and thereafter performs conveyance control based on the pulse signal from the encoder sensor 403.

  If such control is performed, it is recognized that the pulse signal EA0 from the encoder sensor 363 is equal to the pulse signal EB0 from the encoder sensor 403, and thereafter, conveyance control is performed based on the count value of the pulse signal from the encoder sensor 403. .

  In this embodiment, the count value of the pulse signal EB0 is overwritten with the count value of the pulse signal EA0. However, the count value of the pulse signal EB0 may be left as it is, and the target stop value of the recording medium after switching the pulse signal input destination may be changed to be based on the count value of the pulse signal from the encoder sensor 403.

  Here, if necessary, the control parameter can be changed at the same time as the control target is changed. Such a change is effective, for example, when the resolution of the encoder sensor 363 on the recording medium P and the resolution of the encoder sensor 403 on the recording medium P are different. Specifically, since the amount of information per unit time is different, it is possible to obtain a stable pre-stop speed by changing the command speed in the low-speed control area just before stopping the transport motor or changing the gain. It is also possible to cope with optimization (shortening) of the stop time.

  The timing at which the pulse signal is transferred from the encoder sensor 363 to the encoder sensor 403 is ideal because the moment when the recording medium P passes through the nip of the conveying roller 36 can minimize the eccentric error of the drive train connected downstream. It is. However, in reality, when passing through the nip, a force that causes the pair of conveying rollers 36 and 37 to advance the recording medium P mechanically by the spring force of the pinch roller 37 works. In order to eliminate this disturbance, it is preferable that this takeover is performed before the recording medium P passes through the nip of the conveying roller. Furthermore, since the hand-over in a state where the conveyance speed is high contributes largely to disturbance due to mechanical elasticity of the drive train, moment of inertia, counter time resolution, and control followability, the conveyance speed is preferably low or when stopped. Among them, in order to eliminate the influence of backlash at the time of stop and the uncertain operation between the stop operation and the stop, it is more preferable to take over at the start of the stop operation or in some cases just before the stop operation. .

  Therefore, according to the embodiment described above, it is possible to dramatically improve the conveyance accuracy after the recording medium passes through the conveyance roller. Thereby, higher quality image recording becomes possible. In addition, it is possible to perform higher-speed recording by relaxing the restriction on the nozzles used in the recording head, which has been necessary in the past, and increasing the amount of line feed.

  In the first embodiment, the example of the pulse signal output from the two encoder sensors has been described. In this embodiment, the conveyance control in consideration of the phase difference between the two pulse signals will be described.

  If the position detection resolution for the conveyance of the recording medium by the two encoder sensors is equal, for example, both have a resolution of 1800 dpi quadruple (both edges of both phases), the pulse signal is 7200 dpi pitch = about 3.5 μm. Detected. This means that when the pulse signal input from the encoder sensor 363 to the encoder sensor 403 is taken over, a maximum deviation of 3.5 μm may occur depending on the phase difference of the pulse signal.

  In this embodiment, in order to halve this shift, the ASIC 651 detects the phase difference between the two pulse signals, and determines and selects a nearby pulse signal at the timing of taking over the count value of the pulse signal.

  FIG. 9 is a diagram showing temporal transitions of the pulse signal from the encoder sensor 363 and the pulse signal from the encoder sensor 403.

  As shown in FIG. 9, the pulse signal from the encoder sensor 363 is detected as EA-3, EA-2, EA-1, and EA0 using the pulse signal EA0 as the stop timing of the conveying roller 36. On the other hand, pulse signals from the encoder sensor 403 are detected as EB-2, EB-1, and EB0. In FIG. 9, pulse signals EA + 1 and EB + 1 are expressed for convenience as signals detected in the future.

  Here, the time difference TB1 between the pulse signals EB-1 and EA-2 and the time difference TB2 between the pulse signals EA-1 and EB0 are measured. From these two values, it is determined which of the pulse signals EB-1 and EB0 is closer to the pulse signal EA-1.

  In this example, since TB1> TB2, it is determined that the pulse signal EA-1 is close to EB0, and processing is performed as EA-1 = EB0. That is, the measurement value up to the pulse signal EA-1 is overwritten on the measurement value of the pulse signal EB0. On the other hand, when TB1 <TB2, the same processing may be performed as EA-1 = EB-1.

  As a result, an error caused by the phase difference between the pulse signals from the two encoder sensors when taking over the measured value of the pulse signal can be suppressed within ½ of the resolution of the encoder sensor 403. As described above, when the two encoder sensors have the same resolution, the error due to the phase difference can be suppressed to 7200 dpi pitch × 1/2 = about 1.8 μm, and more accurate conveyance can be realized.

  In this embodiment, only the time difference between pulse signals is used as a determination material in order to determine which of the neighboring pulse signals is. This is based on the fact that when the conveyance of the recording medium is stopped by servo control, the speed just before the stop is generally controlled to a very low constant speed, but if the control including the acceleration is intentionally performed. Compares the pulse signals with the acceleration taken into account. That is, the phase difference between the pulse signals from both encoder sensors can be obtained by considering the speed information (and the estimated value) and using the distance (time × speed) as a comparison index.

  In addition, in order to prevent any eccentric error of the roller, the pulse signal measurement value takeover position from the encoder sensor is brought close to the stop target position of the transport roller, and a pulse near or immediately before the stop target position of the transport roller. It is desirable to determine which signal is.

  FIG. 10 is another diagram showing temporal transitions of the pulse signal from the encoder sensor 363 and the pulse signal from the encoder sensor 403.

  As shown in FIG. 10, the time difference PB between the pulse signals EB-1 and EB0 and the time difference TB3 between the pulse signals EB0 and EA0 are measured, and TB3 and PB-TB3 are compared. Here, PB-TB3 is considered to be a time difference between the pulse signal EA0 and the pulse signal EB + 1 that will be detected in the future. After that, based on the comparison result, as described above, it is determined which of the pulse signals in the vicinity is the same as or just before the stop target position of the transport roller.

  FIG. 11 is still another diagram showing the temporal transition of the pulse signal from the encoder sensor 363 and the pulse signal from the encoder sensor 403.

  As shown in FIG. 11, it is possible to determine which of the neighboring pulse signals is by changing the time count base point. That is, pulses that are closer to each other based on a time difference TA1 from the pulse signal EA-1 and a time difference TA2 between the pulse signal EB0 and the pulse signal EA0 in the next cycle of the pulse signal EA-1 based on the pulse signal EA-1. The count values of the signals EA-1 and EB0 can be combined. In this case, the pulse signal from the nearby encoder sensor 363 is determined and selected with respect to the pulse signal from the encoder sensor 403. For this reason, the error due to the phase difference can be suppressed within ½ of the resolution of the encoder sensor 363 of the transport roller 36.

  Further, the timing for obtaining the phase difference and the timing for taking over the count value of the pulse signal are not necessarily the same, but in order to achieve highly accurate conveyance, it is preferable that these timings are the same.

  Furthermore, the control according to this embodiment has an advantage that it has a relatively small effect on servo control and recording medium stop control itself, and can be realized relatively easily.

  In the control according to this embodiment, if the phase difference between the pulse signals from the two encoder sensors can be detected and the adjacent pulse signal can be selected and determined, the method for detecting the phase difference and the method for selecting the nearby pulse are limited to the above methods. Other methods may be used.

  In this embodiment, a method for executing the count value of the pulse signal from the encoder sensor with higher accuracy and stopping the conveyance of the recording medium with higher accuracy as compared with the second embodiment will be described.

  FIG. 12 is a diagram illustrating the relationship between the pulse signal from the encoder sensor 363, the pulse signal from the encoder sensor 403, and the conveyance amount of the recording medium. In FIG. 12, the horizontal axis represents the transport amount (X) of the recording medium P, and the broken line of the horizontal line schematically shows an enormous pulse signal output from the encoder sensor. The example shown in this drawing shows a case where the recording medium conveyance position detection resolutions by the encoder sensor 363 and the encoder sensor 403 are equal and conveyance is performed with an equal feed amount P.

  According to FIG. 12, before the encoder switching point (left side in the drawing), based on the pulse signal from the encoder sensor 363, the stop target position is set with the position X-1 and the position X0 and the uniform feed amount P. When the stop target position is reached, the conveyance of the recording medium is stopped.

  Here, let us consider a case where the pulse signals from the two encoder sensors are shifted by ΔX in terms of the carry amount at the switching point. In this case, after the switching point (right side in the drawing), when the stop target position of the recording medium is determined based on the pulse signal from the encoder sensor 430, a deviation occurs as shown in FIG. That is, deviations ΔX + 1 and ΔX + 2 occur with respect to the positions X + 1 and X + 2, respectively. Under these conditions, ΔX = ΔX + 1 = ΔX + 2 is obtained.

  In order to eliminate this deviation, the phase difference (TB) between the pulse signal from the encoder sensor 363 and the pulse signal from the encoder sensor 403 is measured in this embodiment as in the second embodiment. Then, after the switching point shown in FIG. 12, this information is reflected on the stop target position of the paper discharge roller controlled based on the pulse signal from the encoder sensor 403.

  Specifically, as described in the second embodiment, the phase difference between the pulse signals from the two encoder sensors is detected. For example, as shown in FIG. 9, it is possible to grasp where the pulse signal EA-1 from the encoder sensor 363 is located between the pulse signals EB-1 and EB0 from the encoder sensor 403 from the phase differences TB1 and TB2. . For example, the measurement unit of the pulse signal is set finely from the encoder sensor 403 so that the pulse signal can be measured virtually even at a place where the pulse signal does not exist (it may be time). Thus, it can be defined as a measured value of the pulse signal that the pulse signal EA-1 is present at a position corresponding to the ratio of TB1: TB2 with respect to the pulse signals EB-1 and EB0.

  In other words, as shown in FIG. 13, the pulse signal from the virtual feed roller encoder sensor can be identified between the two pulse signals from the encoder sensor 403. This measurement value may be a virtual measurement value that assumes the position of the recording medium P, not the measurement of the pulse signal from the encoder sensor 403 itself.

  Similarly, it goes without saying that the results of phase difference detection shown in FIGS. 10 to 11 of the second embodiment can be easily realized.

  FIG. 13 is a diagram showing temporal transitions of the pulse signal from the virtual transport roller encoder sensor and the pulse signal from the encoder sensor 403.

  When the measurement target value is used to determine the stop target position (timing) of the paper discharge roller as shown in FIG. 13, the delay distances ΔX + 1 and ΔX + 2 from the pulse signal from the encoder sensor 403 can be determined. Regarding the stop at the position X + 1, as shown in FIG. 13, the pulse signal EB1- immediately before the stop target timing of the paper discharge roller from the speed information VB just before the conveyance stop based on the pulse signal from the encoder sensor 403 and the delay distance ΔX + 1. A time delay TD based on 0 is obtained. Based on this time delay, the stop operation is performed after the time TD has elapsed from the pulse signal EB1-0.

  This makes it possible to stop the conveyance of the recording medium at the stop target position X + 1 so that the ideal feed pitch P is in a place where no pulse signal exists. Similarly, the stop operation is performed with respect to the position X + 2 with a time delay TD = VB / (ΔX + 2).

  When the position detection resolutions of the encoder sensors 363 and 403 are the same, the value of the time phase difference between these two pulse signals is directly used as the conveyance stop delay value using the pulse signal from the encoder sensor 403 after the switching point. However, almost the same accuracy can be obtained.

  Japanese Patent Laid-Open No. 2005-132028 has already disclosed a technique for performing a stop operation at a target position other than the pulse signal position by adding a time delay to the pulse signal from the encoder sensor. Therefore, the feature of this embodiment is that the phase error of the pulse signals from the two encoder sensors is detected based on the pulse signal from the encoder sensor 403 used for the subsequent conveyance control, and this is reflected in the conveyance control. The phase error is being corrected.

  Therefore, according to the embodiment described above, the phase difference between the pulse signals from the two encoder sensors is detected when the measured value of the pulse signal is taken over, and the phase difference is detected based on the phase difference thereafter by the sheet discharge roller. The position (and timing) can be reflected. This makes it possible to realize an ideal conveyance stop.

  In the first to third embodiments, the recording medium conveyance position detection resolutions of the encoder sensor 363 and the encoder sensor 403 are assumed to be equal to simplify the description, but the present invention is not limited to this. For example, the resolution of the encoder sensor 403 may be made lower than that of the encoder sensor 363 by reducing the diameter of the discharge code wheel 402 due to the limitation of the housing size of the recording apparatus. On the contrary, when the eccentricity accuracy of the paper discharge roller 40 is not sufficiently secured, the diameter of the paper discharge code wheel 402 is increased to suppress the eccentricity, and the resolution of the encoder sensor 403 is set to the encoder sensor 363. The control stability may be improved by increasing the control value.

  14 to 15 are diagrams showing temporal transitions of a pulse signal from the encoder sensor 363 having a high position detection resolution and a pulse signal from the encoder sensor 403 having a low position detection resolution.

  FIG. 16 is a diagram illustrating a temporal transition of a pulse signal from the encoder sensor 363 having a low position detection resolution and a pulse signal from the encoder sensor 403 having a high position detection resolution.

  In these drawings, the position detection resolutions of the two encoder sensors are different from each other by a factor of two.

  First, the example shown in FIG. 14 will be described.

  In this example, the time from the encoder signal 363 to the pulse signal from the next encoder sensor 403 is measured based on the pulse signal from the encoder sensor 363, and the time from the pulse signal to the pulse signal from the next encoder sensor 363 is measured. To do. However, when two pulse signals from the encoder sensor 363 are detected in succession (for example, when detecting the pulse signals EA-2 and EA-1), the time measurement between them is cancelled.

  Thus, in the example of FIG. 14, between the pulse signals EA-3 and EB-1 (TAA-3), between EB-1 and EA-2 (TAB-2), and between EA-1 and EB0. The time between (TAA-1) and EB0 and EA0 (TAB0) can be detected. These times can be applied to the second and third embodiments described above.

  Next, the example shown in FIG. 15 will be described.

  In this example, the pulse signal from the encoder sensor 403 is used as a base point.

  First, the time from a pulse signal from the encoder sensor 403 to the next pulse signal from the encoder sensor 403 is measured, and the time from the pulse signal to the next pulse signal is also measured. If the next detected pulse signal is a signal from the encoder sensor 403, the measurement process ends. On the other hand, if the next detected pulse signal is a signal from the encoder sensor 363 (for example, EA-1 follows EA-2), the time from this pulse signal to the next pulse signal is measured. (For example, EB0 follows EA-1.)

  In this way, the time between the pulse signals EB-1 and EA-2 (TBA-1), between EA-2 and EA-1 (TB-1_0), and between EA-1 and EB0 (TBB0). Can be detected. Similarly, the time between the pulse signals EB0 and EA0 can be detected.

  Also, a measurement method different from the time measurement as described above can be used.

  That is, the time from the encoder sensor 403 to the pulse signal from the encoder sensor 363 is measured as a base point, and the time from the encoder signal 403 to the next pulse signal from the encoder sensor 403 (for example, EA-2 To EB0). According to this method, unlike the above-described method, it is not necessary to store the measurement value when the pulse signal EA-1 is detected.

  Furthermore, as another method, for example, a counter that counts the time to pulse signals EA-2, EA-1, and EB0 in FIG. 15 may be prepared.

  Finally, the example shown in FIG. 16 will be described.

  In this example, the reverse operation of the example shown in FIG. 14 may be performed. That is, based on the pulse signal from the encoder sensor 403, between the pulse signals EB-2 and EA-1 (TBA-2), between EA-1 and EB-1 (TBB-1), and EB0 and EA0. (TBA0) can be detected.

  Similarly, in the time measurement using the pulse signal from the encoder sensor 363 as a base point, a desired time can be detected by performing the reverse operation of the example shown in FIG.

  Note that the method for measuring time between pulse signals is not limited to the above-described method, and any method may be used as long as it can detect the phase difference of encoders having different resolutions.

  According to the embodiment described above, even if the position detection resolutions of the two encoder sensors are different, time measurement between pulse signals can be performed, and the obtained time is applied to the second and third embodiments. Accurate transfer control can be executed. This enables high-precision transport control while flexibly responding to such situations even if the resolution of the encoder sensor is different to improve space efficiency due to the size and structure of the recording device housing. Is done.

  Here, an example of obtaining the phase difference deviation amount with higher accuracy will be described.

  In the above-described embodiment, the example in which the phase shift amount detection timing is set when the transport operation is stopped or immediately before the stop operation has been described. However, in order to increase the detection accuracy of the phase shift amount, here, in the vicinity of the transport stop, A phase shift amount is detected a plurality of times, and a value obtained by averaging the detected values is defined as a phase shift amount.

  FIG. 17 is a diagram for explaining how the phase shift amount is detected and averaged a plurality of times.

  First, as shown in FIG. 17, the deviation amounts (distances) between the pulse signal from the upstream encoder sensor 363 and the pulse signal from the downstream encoder sensor 403 in the transport direction are expressed as ΔBA0, ΔBA1,..., ΔBB0, Let ΔBB1,. In this example, the shift amount is a distance, but it may be a time corresponding to the distance.

  Now, assuming that the ideal pitch of quadruple of the pulse signal from the encoder sensor 403 on the downstream side is PB, the phase shift amount (ΔB) of the pulse signal from the encoder sensor 363 with respect to the pulse signal from the encoder sensor 403 is as follows: become.

That is,
ΔB = PB × Σ (ΔBAx) / Σ (ΔBAx + ΔBBx), (x = 0 to N)
It is.

  Here, the amount of deviation is obtained as the distance, but this may be obtained as time.

  Thus, by averaging the phase shift amounts obtained over a plurality of pulse signals, it is possible to reduce mechanical behavior variations and speed control variations. Furthermore, by averaging at least four adjacent phase shift amounts, it is possible to reduce variations in encoder sensor characteristics. An encoder sensor usually obtains an output with a total of four phases, A phase and B phase, and rising and falling edges. There is a meaning.

  The average phase difference amount obtained in this way can be applied to the third embodiment, or the comparison of the values of Σ (ΔBAx) and Σ (ΔBBx) can be applied to the determination in the second embodiment. By doing so, it contributes to obtaining stable line feed accuracy.

  Of course, if the position detection resolutions of the encoder sensor 363 and the encoder sensor 403 are the same, the phase shift amount may be simply averaged as described above. However, if the resolutions are different, it is obtained from each pulse signal. The phase shift amount may be normalized and averaged. Then, when the count value of the pulse signal from the encoder sensor 363 is handed over to the count of the pulse signal from the encoder sensor 403, the averaged phase shift amount may be converted into a resolution to be used.

  Assuming that the quadruple pitch of the resolution of the encoder sensor 363 is RP1 and the quadruple pitch of the resolution of the encoder sensor 403 is RP2, the deviation amount of (RP1-RP2) is different from the phase deviation every time one detected pulse signal is shifted. Add (or subtract). It is only necessary to treat this amount as a normalized phase shift amount. Needless to say, if the resolutions of the two are different by about twice or more, it is necessary to consider whether or not the counterpart pulse signal for detecting the phase shift does not jump over the adjacent pulse signal.

  Further, the averaging method referred to in this embodiment is not limited to the above-described example, and includes information on a pulse signal at the stop target timing of the transport roller in order to add information immediately before the transport stop. You can also. Alternatively, in order to cancel the phase characteristics of the encoder sensor, only the in-phase pulse signal information may be used. As described above, as long as a representative phase difference is obtained from a plurality of pieces of phase difference information, it does not depart from the spirit of the present invention.

  By deriving a typical phase difference from such a large amount of phase difference information, the characteristics of the encoder sensor, the behavior of the mechanism, and unstable elements of control can be smoothed to obtain a more accurate phase difference. By applying this to the second and third embodiments, more accurate transport control can be realized.

Claims (9)

A first conveying roller for conveying a sheet;
A second conveyance roller that is provided downstream of the first conveyance roller and conveys the sheet with respect to the conveyance direction;
A first encoder sensor that outputs a first pulse signal in response to rotation of the first conveyance roller for detecting conveyance information by the first conveyance roller;
A second encoder sensor that outputs a second pulse signal according to rotation to the second conveyance roller for detecting conveyance information by the second conveyance roller;
Control means for controlling conveyance of the sheet based on at least one of the first pulse signal and the second pulse signal;
When the sheet is transported in the direction from the first transport roller toward the second transport roller, the control unit sends a signal used for transport control according to a rear end position of the transported sheet. The first pulse signal is switched to the second pulse signal, and the carrier information detected by the first pulse signal at the time of the switching is handed over to the subsequent carrier control using the second pulse signal. Sheet transport device. The control means includes a first counter that counts pulses included in the first pulse signal, and a second counter that counts pulses included in the second pulse signal,
2. The sheet conveying apparatus according to claim 1, wherein at the time of the switching, the control unit controls the second counter to overwrite the count value of the first counter. The control means includes detection means for detecting a phase difference between the first pulse signal and the second pulse signal,
The sheet conveying apparatus according to claim 1, wherein the control unit reflects the phase difference on a stop target position or timing in conveyance control after the switching. The detection means includes: (1) one pulse included in one of the first pulse signal and the second pulse signal, and the other of the first pulse signal and the second pulse signal. A first time difference that is a time difference from the pulse immediately before the one pulse included in the pulse signal of (2), (2) the one pulse included in the one pulse signal, and the other pulse signal included in the other pulse signal Detecting a second time difference, which is a time difference from the pulse immediately after the one pulse,
The sheet conveying apparatus according to claim 3, wherein the detecting unit obtains the phase difference by comparing the first time difference and the second time difference.   The sheet conveying apparatus according to claim 3, wherein the control unit reflects the phase difference on a stop target position or timing in each of a plurality of conveyance controls after the switching. A first conveying roller for conveying a sheet;
A second conveyance roller that is provided downstream of the first conveyance roller and conveys the sheet with respect to the conveyance direction;
A first encoder sensor that outputs a first pulse signal in response to rotation of the first conveyance roller for detecting conveyance information by the first conveyance roller;
A second encoder sensor that outputs a second pulse signal according to rotation to the second conveyance roller for detecting conveyance information by the second conveyance roller;
Control means for controlling conveyance of the sheet based on at least one of the first pulse signal and the second pulse signal;
When the sheet is transported in the direction from the first transport roller toward the second transport roller, the control unit sends a signal used for transport control according to a rear end position of the transported sheet. The first pulse signal is switched to the second pulse signal, and the phase difference between the first pulse signal and the second pulse signal is reflected in the stop target position or timing in the transport control after the switching. Sheet transport device. The detection means includes (1) one pulse included in one of the first pulse signal and the second pulse signal, and one of the first pulse signal and the second pulse signal. A first time difference that is a time difference from a pulse immediately before the one pulse included in the other pulse signal; and (2) the one pulse included in the one pulse signal and the other pulse signal included in the other pulse signal. Detecting a second time difference, which is a time difference from a pulse immediately after the one pulse,
The sheet conveying apparatus according to claim 6, wherein the detecting unit obtains the phase difference by comparing the first time difference and the second time difference.   The sheet conveying apparatus according to claim 6, wherein the control unit reflects the phase difference on a stop target position or timing in each of a plurality of conveyance controls after the switching.   The sheet conveying apparatus according to claim 1, wherein the first and second conveying rollers are driven by the same motor.

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