Patent Publication Number: US-8967617-B2

Title: Printing apparatus and method for detecting origin of conveying roller

Description:
This application is a divisional of U.S. patent application Ser. No. 12/543,991, filed Aug. 9, 2009, now U.S. Pat. No. 8,622,388. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to conveyance control of a print medium. Especially, the present invention relates to a configuration for detecting an origin or phase of a conveying roller at the time of its rotation and a method for the same in a configuration of conveying the print medium using the conveying roller. 
     2. Description of the Related Art 
     In printing apparatuses in recent years, there is increased printing use of printing photographic images not only on plain papers but also on special purpose papers. In particular, in the ink jet printing apparatus, a trend of a decreased size of an ink drop has progressed and it has become possible to output an image comparative to or better than silver salt photographs with high resolution. With realization of such high resolution of images, higher precision of paper conveyance is also being advanced and there have been proposed a lot of methods whereby the conveying roller such that a metallic shaft is coated with grinding stone is used and methods for controlling conveyance of such a conveying roller with high precision. 
     For example, Japanese Patent Laid-Open No. 2006-240055 discloses a configuration where a code wheel is provided on the same axis of the conveying roller and slits formed on its circumferential part at equal intervals are detected by an encoder sensor fixed in the apparatus. According to this, a technology of performing drive control of a DC motor for rotating the conveying roller depending on a cycle at which the slits are detected, etc., is disclosed. Then, according to the same document, a method includes acquiring an origin of the conveying roller by having provided a pattern for rotation phase detection, separately from the slits on the code wheel, and detecting the pattern concerned with another sensor in order to correct a conveyance error resulting from eccentricity of the conveying roller. 
       FIG. 20  is a sectional view for explaining an installation state of the code wheel and the sensors. A film-like code wheel  2002  shares a rotation axis with a conveying roller  2001  and is disposed around its circumference in a spreading manner. Slits  2002   a  that are arranged at equal intervals and are used for detection of positional precision and a belt-like pattern  2002   b  used for phase detection of roller rotation are printed on the code wheel  2002 . An encoder sensor  2003  is installed at a position where the slits  2002   a  pass with rotation of the code wheel  2002 , and detects a rotation amount of the code wheel  2002 , i.e., the conveying roller  2001 . On the other hand, an edge sensor  2004  detects the edge of the pattern  2002   b  that moves with the rotation of the code wheel  2002 , and the printing apparatus is configured to be able to set the origin of the roller rotation using this detected timing. 
       FIG. 21  is a diagram showing another example of a configuration for detecting the origin of the conveying roller. In this example, a sensed part  2102  is attached to a part of the conveying roller  2101 , and moves in a circle with rotation of the conveying roller  2101 . A photo-interrupter  2103  is being fixed at a position where the sensed part  2102  in the apparatus passes and can detect the origin of the conveying roller  2101  from a timing at which the sensed part  2102  intercepts the photo-interrupter  2103 . 
     Thus, in order to perform the conveyance control in a high-precision state while correcting the conveyance error resulting from the eccentricity of the conveying roller, a mechanism for detecting the origin of the conveying roller also becomes necessary, apart from the mechanism for detecting the rotation amount of the conveying roller. 
     However, since the above-mentioned conventional configuration requires some electronic device elements, such a photo-interrupter for phase detection, and cable wiring for this newly, a cost of the apparatus cannot avoid increasing. 
     SUMMARY OF THE INVENTION 
     The present invention is made in order to solve the problems, and its object is to provide a printing apparatus capable of detecting an origin of the conveying roller with a relatively simple configuration, yet such that it does not accompany increase of a cost. 
     The first aspect of the present invention is a printing apparatus for printing an image on a print medium using a printing head, comprising: a driving unit configured to drive a conveying roller for conveying the print medium; a counting unit configured to count a rotation amount of the conveying roller; a locking unit configured to lock rotation of the conveying roller at a predetermined rotational position; and a detecting unit that uses a count value of the counting unit when the conveying roller is locked by the locking unit as a reference and detects a phase of rotation of the conveying roller obtained by the reference and the count value of the counting unit. 
     The second aspect of the present invention is a method for detecting an origin of a conveying roller for conveying a print medium in a printing apparatus for printing an image to the print medium using a printing head, comprising: a step of moving a trigger unit configured to lock the conveying roller to a lock position; a rotating step of rotating the conveying roller; a counting step of counting a rotation amount of the conveying roller from start of rotation of the conveying roller in the rotating step to a time when the conveying roller is locked; and a step of storing a count value acquired by the counting step. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (With reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a mechanical unit of a printing apparatus applicable to an embodiment of the present invention; 
         FIG. 2  is a sectional view for explaining in detail a conveying mechanism including a conveying unit in the printing apparatus of the embodiment of the present invention; 
         FIG. 3  is a perspective view for explaining in detail the conveying mechanism including the conveying unit in the printing apparatus of this embodiment; 
         FIG. 4  is a diagram for explaining a mechanism for detecting an origin in a conveying roller of the embodiment of the present invention; 
         FIG. 5  is a diagram for explaining the mechanism for detecting the origin in the conveying roller of the embodiment of the present invention; 
         FIG. 6  is a diagram showing a state of the carriage when being observed from its reverse side in the printing apparatus of the first embodiment; 
         FIGS. 7A to 7C  are sectional views for explaining concretely steps where a locking function acts through the mechanism explained by  FIGS. 4 to 6 ; 
         FIG. 8  is a diagram for explaining a direction of a resultant force F resulting from a driving force Fdrive of the conveying roller, a lock reaction force Flock from the stopping lever, and an angular moment Mlock of the lock ring; 
         FIGS. 9A and 9B  are diagrams showing a timing at which a conveying roller encoder sensor detects slits of a code wheel; 
         FIG. 10  is a diagram showing another example of shape of the lock ring in the first embodiment; 
         FIG. 11  is a block diagram for explaining a configuration of control of the printing apparatus of the embodiment of the present invention; 
         FIG. 12  is a flowchart for explaining steps of a processing that a CPU performs in detecting the origin of the conveying roller in the first embodiment; 
         FIGS. 13A to 13C  are diagrams for explaining a paper spacing switching mechanism of a second embodiment when the carriage is observed from its reverse side; 
         FIGS. 14A to 14C  are diagrams of a slide bearing when being observed from a carriage side; 
         FIGS. 15A to 15C  are diagrams showing a relation between the slide bearing and the conveying roller when the carriage moves to a lock position in the cases where a paper spacing is at a normal position, a thick paper position, and a maximum position, respectively; 
         FIGS. 16A and 16B  are diagrams for explaining a paper spacing position and a movement area of the carriage in a second embodiment; 
         FIGS. 17A and 17B  are diagrams for explaining a configuration in which a stroke area at a large-paper-spacing position is brought into correspondence with two positions of a paper spacing switching slider; 
         FIG. 18  is a flowchart for explaining steps of a processing that a CPU performs in detecting the origin of the conveying roller in the second embodiment; 
         FIGS. 19A and 19B  are sectional views for explaining steps where the locking function in the printing apparatus of a third embodiment acts; 
         FIG. 20  is a sectional view for explaining an installation state of the code wheel and the sensors; and 
         FIG. 21  is a diagram showing another example of a configuration for detecting the origin of the conveying roller. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereafter, the best forms for carrying out the present invention will be described with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a perspective view of a mechanical unit of a printing apparatus in this embodiment. 
     (A) Conveying Unit 
     A conveying unit has a configuration that a pressure plate  21  on which print medium is loaded, a feed roller  28  for feeding the print medium P one sheet by one sheet, a separation roller for separating the print medium (not illustrated), a return lever for returning the print medium to its loading position (not illustrated), etc. are attached on a conveying unit base  20 . A movable side guide  23  is provided to the pressure plate  21  in a movable manner and regulates the loading position of the print medium. The pressure plate  21  is pivotable about a rotation axis connected to the conveying unit base  20  and is energized in a direction of the feed roller  28  by an unillustrated pressure plate spring. The feed roller  28  has a rod-like shape whose cross section is a circular arc and feeds a print medium into the inside of the apparatus by rotating itself while keeping contact with a surface of the print medium. The print medium bumps against a nip part that is composed of the feed roller  28  and the separation roller, and is divided by this nip part; and only the print medium at the highest position is further conveyed into the inside. A torque of a feed motor  99  is obtained by a process in which a driving force of the feed motor  99  acting as feed driving means is transferred thereto through a drive transferring gear, a planetary gear, etc. The driving force of the feed motor  99  is also transferred to the cleaning unit that will be described later. 
     (B) Conveying Unit 
     Main elements of the conveying unit are attached to a metallic plate chassis  11  that is bent and raised and chassis  97 ,  98  of mold molding. The print medium sent to the conveying unit is guided by a paper guide and a pinch roller holder  30  that are arranged at specified positions of an inlet port, and is held between a roller pair consisting of a conveying roller  36  and a pinch roller  37 . The conveying roller  36  has a structure of a metallic shaft with minute particles of a ceramic coated thereon, and metallic portions at both ends thereof are supported by bearing parts fixed to the chassis  11 . A plurality of pinch rollers  37  each of which is energized to press the surface of the conveying roller  36  by a pinch roller spring  31  are held by the pinch roller holder  30 , and the each pinch roller  37  abuts against the surface of the conveying roller  36  and is driven by this. 
       FIGS. 2 and 3  are a sectional view and a perspective view for explaining in detail a conveying mechanism including the conveying unit in the printing apparatus of this embodiment. The torque of the conveying roller  36  is acquired by a process in which a driving force of a conveying motor  35  made up of a DC motor is transferred to a pulley gear  361  provided on the axis of the conveying roller  36  through a timing belt  39 . On the same axis of the conveying roller  36 , a code wheel  362  on which slits are formed with a pitch of 150 to 360 lpi is directly linked to it. Then, a conveying roller encoder sensor  363  is fixed at a position in the figure of the chassis  11  so as to read the number of times of passing of the slits on the code wheel  362  and its timing. 
     Referring to  FIG. 1  again, when the roller pair consisting of the conveying roller  36  and the pinch roller  37  is rotated by the conveying motor  35 , the print medium being held by this roller pair is conveyed in the inside of the apparatus. The pinch roller holder  30  is equipped with an edge sensor for detecting a top end and a rear end of the print medium and for positioning it. By detection with the edge sensor, the print medium is positioned on a platen  34  that is attached to the chassis  11  and is located in a printing unit. 
     (C) Carriage Unit 
     On the print medium supported by the platen  34  from below in a downstream side of the conveying roller  36 , an image based on print information is printed by a printing head  7  mounted on a carriage  50  that passes over an upper side of the print medium. 
     The carriage  50  carries the printing head  7  and an ink tank  71  for supplying ink to this, and is movable in the X direction of the figure. The printing head  7  of this embodiment is constructed so that a voltage pulse may be impressed to a heater provided at a position corresponding to the individual discharge port, and the ink may be discharged from the individual discharge port using pressure change produced by growth or contraction of an air bubble in generated film boiling. However, such a discharge method does not limit the present invention. 
     The carriage  50  is supported by a carriage rail  52  that is extended in a direction at right angles to the conveyance direction of the print medium and an upper guide rail  111  and is guided thereby with respect to its movement direction. The carriage rail  52  is attached to the chassis  11 , and the upper guide rail  111  is formed to be integral with the chassis  11 . Furthermore, the upper guide rail  111  holds the end of the carriage  50 , and also plays the role of maintaining a gap between the discharge port plane of the printing head  7  and the print medium. 
     The moving force of the carriage  50  is a driving force of a motor  54  attached to the chassis  11  which is supplied thereto through an idle pulley  542  and a timing belt  541  that is provided to the idle pulley  542  in a tensioned state and supported by it. A cord strip  561  in which markings were formed with a pitch of 150 to 300 lpi is provided in a tensioned state in a direction parallel to the timing belt  541 , and an unillustrated encoder sensor mounted on the carriage  50  detects the markings during movement of the carriage  50 . Thereby, a current position of the carriage  50  can be detected. A flexible cable  57  electrically connects a carriage board on the carriage  50  on which the encoder sensor, etc. is provided with an electric board  91  fixed in the apparatus while following reciprocation of the carriage  50 . A printing signal with which the printing head  7  performs printing is transferred thereto from the electric board  91  through the flexible cable  57  and the carriage board. According to this printing signal, individual heaters of the printing head  7  that is during movement are driven, and dots are printed on the print medium on the platen  34 . 
     (D) Discharging Unit 
     The torque of a discharging roller  40  is obtained by a process where the torque of the conveying roller  36  is transferred to a discharging roller gear  404  directly linked to the discharging roller  40  from the gear part of the pulley gear  361  directly linked to the conveying roller  36  through an idler gear  45 . Referring  FIG. 2  again, a discharging code wheel  402  is installed on the axis of the discharging roller  40 , and a rotation amount of the discharging roller  40  is detected by a discharging roller encoder  403 . 
     A plurality of spurs are attached to a spur holder  43 , and these spurs are pressed toward the discharging roller  40  by spur springs each of which is a coil spring provided in a rod-like shape. The print medium on which an image was formed by the printing head  7  is conveyed while being held between the discharging roller  40  and a plurality of nips of these spurs, and is discharged. 
     (E) Cleaning Unit 
     A cleaning unit  60  consists of a pump for cleaning the printing head  7 , a cap for suppressing drying out of the printing head  7 , a blade for cleaning the discharge port plane of the printing head  7 , etc. A main driving force of the cleaning unit is obtained by a force being transferred from the feed motor  99  being already explained. The cleaning unit  60  performs a suction operation of sucking unnecessary ink etc. from the printing head  7  by acting a pump with a cap adhered to the printing head  7 , a blade operation of cleaning a face surface of the printing head  7  by moving a blade, and the like. 
     Below, a characteristic configuration of this embodiment will be explained in detail. 
       FIGS. 4 and 5  are diagrams for explaining a mechanism for detecting an origin in the conveying roller  36  of this embodiment, wherein  FIG. 4  shows the pulley gear  361  on the conveying roller  36  when being observed from its front side, and  FIG. 4  shows the same when being observed from its reverse side. A lock ring  4001  is attached to the pulley gear  361 , has a circumferential part  4001   a  and a concave part  4001   b , and rotates integrally with the conveying roller  36 . By a stopping lever  4002  rotating about the rotation center  4002   a , it can stop the lock ring  4001  by bumping the lock part  4002   b  against the concave part  4001   b  of the lock ring  4001 . A lock link lever  4003  is a lever for pressing and pulling up the stopping lever  4002 , and a pressing force and a pulling up force between the lock link lever  4003  and the stopping lever  4002  is generated by a stopping lever spring  4004 . The force Ftg for turning the lock link lever  4003  is generated by the carriage  50  moving to a lock position that is opposite to the home position and is outside the scan area of printing (a left end part of  FIG. 1 ). 
       FIG. 6  is a diagram showing a state of the carriage  50  in the printing apparatus of this embodiment when being observed from its reverse side, which is opposite to  FIG. 1 . A protrusion part  50   a  is attached to the reverse side of the carriage  50 . When the carriage  50  moves to the lock position, the protrusion part  50   a  abuts against a slope  4003   a  of the lock link lever  4003 . When a predetermined force Fcr is added to the slope  4003   a  of the lock link lever  4003  by such abutment, referring to  FIG. 4  or  FIG. 5  again, a force Ftg that makes the lock link lever  4003  turn in a direction of an arrow of the figure will occur. 
       FIGS. 7A to 7C  are sectional views for concretely explaining steps where a locking function acts through the mechanism explained by  FIGS. 4 to 6 . 
       FIG. 7A  is a diagram showing a state where the carriage  50  is not located at the lock position. Since the lock link lever  4003  is not pressed, the lock ring  4001  and the lock ring lever  4002  are isolated from each other. If during the printing operation, the conveying roller  36  and the lock ring  4001  are rotating intermittently in a CW direction of the figure for conveying the print medium. 
       FIG. 7B  shows a state where the carriage  50  moves to the lock position, and the lock link lever  4003  is pressed by the protrusion part  50   a , a mechanical trigger being given to it. Occurrence of Ftg makes the lock link lever  4003  turn, and the stopping lever  4002  abuts against the circumferential part  4001   a  of the lock ring  4001  by a thrust of the stopping lever spring  4004 . At this time, the stopping lever  4002  is configured to be able to make a stroke into the lock link lever  4003  even when the stopping lever  4002  is given a pressure from the circumferential part  4001   a  of the lock ring. Therefore, damage by collision between the protrusion part  50   a  of the carriage  50  and the lock link lever  4003  does not occur. Moreover, with a procedure where the stopping lever  4002  and the lock link lever  4003  are constructed in advance with separate parts in this way, a stroke amount of the lock link lever  4003  and a swing amount of the lock link lever  4003  can be set up separately, respectively. As a result, it is possible to secure the stroke amount that does not depend on tolerances of these parts, just by which the stopping lever  4002  can penetrate positively into the concave part  4001   b  of the lock ring. 
       FIG. 7C  is a diagram showing a state where the conveying roller  36  is further rotated starting from the state of  FIG. 7B , and the rotation is locked by the lock ring  4001 . When the lock ring  4001  further rotates in the CW direction with the stopping lever  4002  being abutted against the circumferential part  4001   a  of the lock ring  4001 , a locking part of the stopping lever  4002  will enter into the concave part  4001   b  of the lock ring  4001 . Then, the locking part inhibits the rotation of the lock ring  4001  in the CW direction after this. That is, the lock ring  4001  and the conveying roller  36  are locked so as not to rotate. Incidentally, at this time, since the lock ring  4001  is being fixed to the pulley gear  361  for transferring a driving force from the conveying motor  35 , no torque occurs between the conveying roller  36  and the pulley gear  361 . 
     Such a locked state (stopping state) occurs only at one determined position among positions when the conveying roller  36  makes one rotation. Therefore, the position at which the conveying roller was locked (stopped) in this way can be assigned as the origin of the phase of the conveying roller. 
     Incidentally, it is preferable that the rotation direction of the conveying roller when the locked state is detected is a direction in which the print medium during printing is conveyed (the CW direction), as explained above. Moreover, in the locked state, referring to  FIG. 8 , the resultant force F resulting from a driving force Fdrive of the conveying roller  36 , and a lock reaction force Flock from the stopping lever  4002 , and an angular moment Mlock of the lock ring  4001  occurs. In doing this, in order to positively install the conveying roller  36  in the bearing so that reproducibility of conveyance may be secured, it is preferable that individual components are arranged so that the resultant force F may exert in a direction of a bearing  8001  that supports the shaft of the conveying roller  36 . 
     In the above, the lock ring  4001  also bears a function of preventing coming-off of the timing belt  39 , and was explained as of a separate configuration from the pulley gear  361  in a mold configuration. However, in the case where there is no possibility that the timing belt  39  may come off, and in the case where the apparatus is configured so that the conveying roller  36  is driven through gears, the lock ring  4001  and the pulley gear  361  may be a monolithic part. Anyway, the constituent components are required to be configured so that the driving force of the conveying motor  35  and the reaction force when the conveying roller  36  is locked may not bring about a shift of rotation phase between the conveying roller  36  and the pulley gear  361 , or between the conveying roller  36  and the code wheel  362 , or the like. At this time, it is also useful to set up an upper limit to the drive voltage and a pulse width to the conveying motor  35 , or to set up an upper limit to the torque in order to prevent damages to parts. 
     In this embodiment, the state where rotation of the conveying roller  36  is locked (stopped) is determined, referring to  FIG. 2 , by a state where the conveying roller encoder sensor  363  becomes not to detect the slits on the code wheel  362 . 
       FIGS. 9A and 9B  are diagrams each showing a timing at which the conveying roller encoder sensor  363  detects the slits of the code wheel  362  with respect to a time axis t shown as a horizontal axis.  FIG. 9A  shows a state where the conveying roller  36  is rotating at a predetermined speed. Here, a state where seven slits Sn to Sn+6 are detected within a predetermined time is shown. Since the slits are formed in the code wheel  362  at regular intervals, when the conveying roller  36  is rotating at a constant speed, the conveying roller encoder sensor  363  detects the slits at such fixed time intervals. On the other hand,  FIG. 9B  shows a state where the rotation of the conveying roller  36  is being locked on the way. Here, after the slits up to Sn+3 were detected, it becomes that even after the predetermined time has lapsed, the slits after them is not detected. At the timing when this situation occurs, a control unit of the printing apparatus can determine that the conveying roller  36  falls in the locked state. 
     To be concrete, in the case where the number of detected slits is less than or equal to 10 within a predetermined time of, for example, about 200 ms, it may be determined that the locked state occurs. Moreover, a state may be determined to be the locked state, for example, when the next slit cannot be detected within a predetermined time after the timing when one slit was detected. With such a configuration of this embodiment, it is possible to positively detect an origin position of the conveying roller by using an existing encoder that is constructed with high resolution, without installing a new electronic device. 
       FIG. 11  is a block diagram for explaining a configuration of control of the printing apparatus of this embodiment. The CPU  501  controls the mechanisms in the apparatus through a controller  502  according to various programs stored in ROM  504 . In doing this, RAM  503  is used as a work area at the time of saving various pieces of data primarily or performing a processing. The CPU  501  performs image processing for converting image data to a printing signal that can be printed by the printing apparatus for the image data received from a host device connected to the outside. Then, the CPU  501  drives a various motor  506  through a motor driver  507  and drives the printing head  7  through a printing head driver  509  to form an image on the print medium. In the figure, the motor  506  and motor driver  507  show collectively the conveying motor  35 , the carriage motor  54 , the feed motor  99 , and their respective drivers that were described previously. 
     Electrically writable EEPROM  508  stores set-up values at a factory and data to be updated, and this data is used as control parameters by the controller  502  and the CPU  501 . A sensor  505  collectively shows the temperature sensors and encoder sensors being set up in various locations in the apparatus, and the above-mentioned conveying roller encoder sensor  363  is one of them. The CPU  501  overwrites count information that was obtained by the conveying roller encoder sensor  363  in detecting the slits to ring buffer of the RAM  503  on an as-needed basis. When the origin is detected, the origin information is stored in another area of the RAM  503  or in the EEPROM. 
       FIG. 12  is a flowchart for explaining steps of the processing that the CPU  501  performs in detecting the origin of the conveying roller  36 . 
     When the origin detection processing is started, the CPU  501  moves the carriage  50  to the lock position by driving the carriage motor  54  at Step S 1201 . Thereby, the protrusion part  50   a  mounted on the carriage  50  bumps against the slope  4003   a  of the lock link lever, the lock link lever  4003  turns, and the stopping lever  4002  abuts against the circumferential part  4001   a  of the lock ring  4001 . 
     In the continuing Step S 1202 , the CPU  501  rotates the conveying roller  36  in a direction of conveying the print medium (the CW direction in  FIG. 7 ) by driving the conveying motor  35 . At this time, detection of the slits of the conveying roller encoder sensor is also performed simultaneously. If the CPU  501  detects the locked state of the conveying roller  36  by the count information of the conveying roller encoder sensor  363 , the CPU  501  halts the driving of the conveying motor  35  and stops the conveying roller  36  (Step S 1203 ). 
     In Step S 1204 , the CPU  501  stores a rotational position at which the conveying roller encoder sensor  363  detected the locked state in the RAM  503  or the EEPROM  508  as the origin information. 
     After this, the CPU  501  evacuates the carriage  50  from the lock position at Step S 1205 . Furthermore, the CPU  501  makes the conveying roller  36  rotate by a predetermined amount in a CCW direction by driving the conveying motor  35  in a direction opposite to the normal direction at Step S 1206 . Thereby, the concave part  4002   b  of the lock ring gets isolated from the stopping lever  4002 . By the above-mentioned way, this processing is completed. 
     A value that the conveying roller encoder sensor  363  counts for one rotation of the conveying roller  36  is a known fixed value, and this serves as one cycle when the phase is managed. Therefore, in printing operations after the origin detection processing explained above was performed, the phase of the conveying roller  36  can always be grasped from a count value that the conveying roller encoder sensor  363  detects after that, on the basis of the origin information stored at Step S 1204 . That is, the CPU  501  can convey the print medium in the high precision state, while correcting a conveyance error resulting from eccentricity of the conveying roller by using the rotation amount and the phase of the conveying roller obtained from the conveying roller encoder sensor  363 . 
     Incidentally, in the above, although the embodiment was explained to be configured so that the rotational position at which the conveying roller encoder sensor  363  detected the locked state was stored as the original information, the count value that is stored and upgraded at the timing at which this locked state is detected may be reset to zero. If the follow is modified in this way, the phase control after that can be performed in a state where the count value 0 is assumed as the original. 
     Note that the phase control after the processing of origin detection that was described above can be correctly performed during a time when the conveying roller encoder sensor  363  is operating. However, if the hard power-off is once done, the conveying roller encoder sensor  363  will become not to operate, and the information in the RAM will be erased; therefore, the origin information and the count values will be lost. Therefore, at the time of returning from the hard power-off, the printing apparatus of this embodiment shall newly re-acquire the origin information by performing a series of origin detection processing steps as shown in the flowchart of  FIG. 12 . 
     Moreover, even when the apparatus is in a state of hard power-on, if an emphasis is placed on power saving and extension of life of the encoder, there may be a case where the conveying roller encoder sensor  363  is not operated at the time of soft power-off or at the time of absence of the printing operation. In such a case, the series of origin detection processing steps as shown by the flowchart of  FIG. 12  may be performed each time the conveying roller encoder sensor  363  returns to the operation. Moreover, in the case where there is a less fear that the conveying roller  36  is rotated by an external force during stoppage of the conveying roller encoder sensor  363 , it is also effective to, just before stopping the operation of the conveying roller encoder sensor  363 , store the phase and the origin information at that time. 
     Furthermore, there is a case where it can be determined that the phase control of the conveying roller  36  is not needed to be performed depending on a kind of image data, a kind of the print medium, etc. In such a case, the above-mentioned origin detection processing may be performed at timing when the printing operation that needs the phase control of the conveying roller  36  is first performed after the soft power-on was done. 
     In this embodiment explained above, as explained in  FIG. 4  and  FIG. 5 , the locking function is such that the concave part  4001   b  is provided in the lock ring  4001  and a top end of the stopping lever  4002  protrudes into this, but a shape of the lock ring is not limited to this. For example, the same function can be realized by providing a protrusion part in a part of the circumferential part of the lock ring  4001  and configuring the protrusion part so that a top end of the stopping lever  4002  abuts against its side face  4001   c.    
     Moreover, although in the above, the embodiment was explained to be configured so that an event that the rotation of the conveying roller  36  is locked is detected using the information of the conveying roller encoder sensor  363 , the present invention is not limited to such a configuration. For example, in the case where a rotation ratio of the conveying roller  36  and the discharging roller  40  is 1:1, it is also possible to detect that the conveying roller  36  is in the locked state using the information of the discharging roller encoder  403 . Moreover, it is also possible to detect the locked state of the discharging roller  40  by providing a mechanism for locking the roller on the discharging roller  40  side, using the information of the conveying roller encoder sensor  363  and the information of the discharging roller encoder  403 . Similarly, gears used for transferring of the driving force, for example, the idler gear  45 , may be considered as an object to be locked (stopped), and means for detecting the rotation amount of one of these gears may be provided separately. 
     As explained in the foregoing, according to this embodiment, it is possible to acquire the origin of the conveying roller with high precision by assembling an existing encoder sensor that is constructed with high resolution and several pieces of cheap mechanical parts, without installing a new electronic device and cable wiring for this. 
     Second Embodiment 
     Also in this embodiment, the printing apparatus explained by  FIGS. 1 to 5  shall be used. However, in this embodiment, a paper spacing switching mechanism provided on the reverse side of the carriage  50  in advance is also used as means for pressing the lock link lever  4003 . This paper spacing switching mechanism is a mechanism that is provided to the carriage in order to adjust a distance between the discharge port plane of the printing head  7  and the print medium depending on a kind of the print medium. 
       FIGS. 13A to 13C  are diagrams for explaining the paper spacing switching mechanism of this embodiment, when the carriage  50  is observed from its reverse side.  FIGS. 14  A to  14 C are diagrams of a slide bearing  1301  of  FIGS. 13A to 13C  when being observed from a carriage side. 
     The slide bearing  1301  is an axial component that slides on the carriage rail  52  when the carriage  50  moves. A paper spacing switching slider  1302  slides in a direction A-B of the figure, being held by the carriage  50  and the slide bearing, whereby it changes a distance between the carriage  50  and the slide bearing  1301 , i.e., a height of the carriage  50 . 
       FIG. 13A  and  FIG. 14A  show a state of a narrow paper spacing (normal position) with the position used for printing on a plain paper or photographic special paper. If the carriage  50  is moved in the direction A from this state, since a protrusion part  1302   a  attached to the paper spacing switching slider  1302  is held down by an obstacle, only the carriage  50  and the slide bearing  1301  move in the direction A. That is, a relative position in the horizontal direction between the paper spacing switching slider  1302  and the slide bearing  1301  displaces, and a relative position in the height direction also changes by the mutual slopes. As a result, the carriage mounted on the paper spacing switching slider  1302  rises.  FIG. 13B  and  FIG. 14B  show a state where the carriage  50  has risen in this way by one step to be located at a position where the paper spacing is wide that is for printing on a thick paper, etc. (a thick paper position). Moreover, if the carriage  50  is further moved in the direction A by the same method, the carriage  50  will further rise by one more step.  FIG. 13C  and the  FIG. 14C  show a state where the carriage  50  further rises by one more step and is located at a position where the paper spacing is the widest (a maximum position), which is at the time of printing a disk such as CD-R. Incidentally, if in a state where the protrusion part  1302   a  is held down by the obstacle, the carriage  50  is moved in the direction B, the carriage  50  can be returned to an original position. The printing apparatus of this embodiment is configured to be able to adjust the paper spacing distance in three stages according to a kind of the print medium by using thus mechanism. 
       FIGS. 15A to 15C  are diagrams each showing a relation of the slide bearing  1301  and the lock mechanism of the conveying roller when the carriage has moved to the lock position in the case where the paper spacing is at the normal position, at the thick paper position, and at the maximum position, respectively. Referring to  FIGS. 15A and 15B , even if the carriage  50  has moved to the lock position in the state of the normal position or the thick paper position, the protrusion part  1302   a  keeps to be isolated from the lock link lever  4003 ; therefore, the lock link lever  4003  will not turn. That is, a function as trigger means has become invalid. On the other hand, referring to  FIG. 15C , in the case where the paper spacing is at the maximum position, when the carriage  50  has moved to the lock position, the protrusion part  1302   a  abuts against the slope  4003   a  of the lock link lever  4003 ; therefore, the lock link lever  4003  turns in the CW direction. That is, a function as the trigger means is kept valid. Incidentally, the apparatus is designed so that a force of turning the lock link lever  4003  may be sufficiently smaller that the slide force of the paper spacing switching slider  1302  in order that the paper spacing switching slider  1302  would not be shifted in turning the lock link lever  4003 . 
       FIGS. 16A and 16B  are diagrams for explaining a paper spacing position and a movement area of the carriage  50  in this embodiment. In the case where the print medium is of the fixed size, such as the plain paper, the photographic special paper, or the thick paper, in order to perform printing on the whole area of the print medium in its width direction, the carriage does reciprocation in a range indicated by an arrow of a solid line of  FIG. 16A . That is, the carriage  50  moves also to the lock position during the printing operation. However, since the paper spacing position is either the normal position or the thick paper position at this time, even when the carriage  50  reaches the lock position, the protrusion part  1302   a  dose not abut against the slope  4003   a  of the lock link lever  4003 , and consequently the lock link lever  4003  does not turn. 
     In the case where the print medium is CD-R, the carriage only needs to move in a range indicated by an arrow of a solid line of  FIG. 16B  and does not move to the lock position for printing operation. That is, there is no possibility that the conveying roller  36  may be locked in the midst of performing the printing operation to CD-R. On the other hand, in acquiring the origin information of the conveying roller  36 , the paper spacing is set to the maximum position and the carriage  50  is moved to the lock position indicated by an arrow of a broken line. 
       FIG. 18  is a flowchart for explaining steps of the processing that the CPU  501  performs in detecting the origin of the conveying roller  36 . 
     In this embodiment, when the origin detection processing is started, first the paper spacing distance is set to the maximum position at step S 1801 . This may be done by the CPU  501  automatically or the user may be requested to do so. At the continuing Step S 1802 , the carriage  50  moves to the lock position by driving the carriage motor  54 . Since the paper spacing is being set to the maximum position, at timing when the carriage  50  reaches the lock position, the protrusion part  1302   a  abuts against the slope  4003   a  of the lock link lever  4003 , which makes the lock link lever  4003  turn. Hereafter, the steps of Step S 1803  to Step S 1807  are the same as those of the flowchart of  FIG. 12  explained in the first embodiment. 
     In order not to lock the conveying roller  36  in the midst of a printing operation, it is needed that the lock link lever  4003  and the trigger means on the carriage  50  abutting against this abut against each other outside the movement area where the carriage  50  is in the printing operation. That is, in the case where the protrusion part  50   a  fixed on the reverse side of the carriage  50  is used as the trigger means like the first embodiment, an area that is the movement area necessary for the operation of printing on a fixed size print medium added with a width of the lock position is required as a moveable area of the carriage  50 . As a result, in the printing apparatus of the first embodiment, the width larger than the width shown in  FIG. 16  by an addition of the width of the lock position becomes necessary, which leads to a larger size of the apparatus compared to this embodiment. In the printing apparatus of this embodiment, the lock position of the printing apparatus is included in a usual printing area when the printing area is wide, and becomes as the lock position only when the printing area width is narrow. By this fact, the origin information of the conveying roller can be acquired without incurring enlargement of the printing apparatus, contrary to the first embodiment. 
     Incidentally, with the above-mentioned configuration, if the printing operation is done on the print medium of the fixed size with the paper spacing of the maximum position, it will become unable to divide the normal printing operation and the origin acquisition operation. However, even in the case like this, if the stroke area of the slider that realizes the same paper spacing may be further widened and the area is brought into correspondence with two positions of the paper spacing switching slider  1303 , the above-mentioned problem can be solved. 
       FIGS. 17A and 17B  show the configuration of realizing two stage paper spacing, and are diagrams for explaining a configuration in which the stroke area at the large-paper-spacing position is brought into correspondence with the two positions of the paper spacing switching slider  1303 .  FIG. 17A  is a diagram showing a positional relation of the paper spacing switching slider  1303  and the slide bearing  1301  in the case where the paper spacing is wide and the normal printing operation is performed. On the other hand,  FIG. 17B  is a diagram showing a positional relation of the paper spacing switching slider  1303  and the slide bearing  1301  at the time of acquiring the origin information. Although the paper spacing is in a wide state in either state, the printing apparatus is configured as follows: in the state of  FIG. 17A , when the carriage  50  moves to the lock position, the protrusion part does not abut against the lock link lever; and in the state of  FIG. 17B , the protrusion part abuts against the lock link lever so as to lock the conveying roller. 
     As described in the foregoing, according to this embodiment, the printing apparatus is configured so that the protrusion part mounted on the paper spacing switching slider can be used as the trigger means for locking the conveying roller, and the function of the trigger means can be switched to be valid or invalid by the paper spacing switching slider. Thereby, the same effect as that of the first embodiment can be realized, without incurring enlargement of the printing apparatus. 
     Third Embodiment 
     Also in this embodiment, the printing apparatus explained by  FIGS. 1 to 5  shall be used. However, in this embodiment, the conveying roller is locked by using a trigger component driven by the feed motor. Referring to  FIG. 1 , the printing apparatus of this embodiment is configured so that the feed roller  28  may rotate in a direction of feeding the print medium by the feed motor  99  making a positive rotation and subsequently the pressure plate  21  may rise. By this series of operations, one sheet of paper that is at the highest position among a plurality of print medium is fed into the inside of the apparatus. Thus, what is necessary in order to prevent the pressure plate  21  from going up until the feed roller  28  makes the predetermined forward rotation amount is just to provide the well-known drive delay mechanism and to secure an insensitive rotation amount. Note that in a state where the pressure plate  21  has not risen in this mechanism, as during waiting of print medium feeding, if the feed motor  99  rotates by a fixed amount in whichever direction, positive direction or reverse direction, the feed roller  28  does not contact with the print medium and the print medium does not move. In this embodiment, the trigger component is made to operate using the normal and reverse rotations of a predetermined amount by the feed roller  28  in a state where the pressure plate  21  does not rise, in this way, and the origin of the conveying roller  36  is acquired. 
       FIGS. 19A and 19B  are sectional views for explaining steps in which the locking function in the printing apparatus of this embodiment acts. The trigger component  1901  is jointed to the feed roller  28  by means of friction rotational joint (torque limiter joint) and is configured so that it may rotate to a position in  FIG. 19A  when the feed roller  28  rotates in a forward direction and may rotate to a position in  FIG. 19B  when the feed roller  28  rotates in a reverse direction. When acquiring the origin, if the feed roller  28  is rotated in the reverse direction by a predetermined amount in a state where the pressure plate  21  is lowered, a trigger component  1901  rotates in the CW direction. When the trigger component is rotated to a predetermined rotary position (the lock position), the lever part  1901   a  of the trigger component  1901  abuts against the protrusion part  4003   a  provided in the lock link lever  4003  and pushes this in the downward direction, which makes the lock link lever  4003  turn. If the conveying roller  36   a  is made to rotate in the CW direction in this state, the stopping lever  4002  of the lock link lever  4003  enters into the concave part  4002   a  of the lock ring  4001  by the same mechanism of the above-mentioned embodiment, the conveying roller  36   a  is locked (stopped), and thereby the origin information can be acquired. 
     After that, if the trigger component  1901  is set back to the position of  FIG. 19A  by making the feed roller  28  rotate in the forward direction, and subsequently the conveying roller  36  is made to rotate in the CCW direction, the locked state is canceled by an applied force of the stopping lever spring  4004 . 
     As described in the foregoing, according to this embodiment, it is possible to acquire the origin of the conveying roller with high precision by preparing the trigger means that is jointed to the feed roller  28  by means of friction rotational joint, without installing a new electronic device and cable wiring for this. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2008-215888, filed Aug. 25, 2008 which is hereby incorporated by reference herein in its entirety.