Abstract:
A printing apparatus free from the problem of vibration due to a head maintenance process when a recording head is maintained in the middle of a recording operation. The printing apparatus performs control so that a recording medium is conveyed subsequent to a head maintenance process, when the recording head is maintained in the middle of a recording operation. Even if the position of the recording medium suffers from an error due to the vibration of the apparatus in the course of the maintenance of the recording head, the error in the recording medium position is eliminated by conveying the recording medium in succession to the maintenance. A disturbance-free high-quality image is thus recorded on the recording medium.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a control method for a printing apparatus that performs printing by moving a recording head in a direction perpendicular to the direction of conveyance of a copy sheet. More particularly, the present invention relates to a control method for a printing apparatus in a head maintenance operation to restore a recording state of a recording head in the middle of a recording operation. 
     2. Description of the Related Art 
     FIG. 3 shows one example of printing apparatus. The printing apparatus shown is a so-called serial printer, which performs printing by moving a recording head in a main scan direction in perpendicular to a direction of paper conveyance (i.e., a sub scan direction). The printing apparatus thus repeats the process of printing in the main scan direction and moving a recording medium in the sub scan direction. FIG. 4 is a sectional view of a major portion of the printing apparatus of FIG.  3 . An automatic paper feeder  1  feeds a recording medium to a recording position where the recording head performs printing. Although the automatic paper feeder  1  usually stores a stack of recording media, only one of the recording medium is picked up by a paper feed roller  5  at one time and is supplied to a recording area  8  within a printing apparatus in operation. The recording medium  4 , interposed between a pressure roller  6  and a paper conveyance roller  7 , advances in an intermittent manner while a recording head (not shown) installed on a carriage  2  performs printing in the course of movement in a main scan direction (namely a direction in perpendicular to the direction of paper conveyance). A diversity of recording heads carry out different printing methods, and an ink-jet recording head, for example, has a portion with a plurality of discharge nozzles mounted therein. In operation, a head maintenance operation to be described later is carried out as necessary. The recording medium  4  that has undergone the printing is then discharged into a discharge tray  3 . 
     The paper conveyance roller  7  rotates when supplied with drive power by a drive motor through a drive gear train (not shown). The pressure roller  6 , in contact with the paper conveyance roller  7  or the recording medium  4 , also rotates in combination therewith. 
     In the drive gear train, gears must be meshed with each other with a high degree of precision to accurately transfer the drive power of the drive motor. If the gears abut tightly each other with some load working therebetween, the gears may be damaged due to a mesh degradation and generate mechanical noise. To improve durability and increase low-noise performance, the gear train is typically provided with a backlash. 
     Specifically, a maintenance unit  9  for carrying out the above maintenance operation may be a suction unit for an ink jet head, a wiping unit for cleaning the face of the ink jet head (where discharge nozzles are arranged), an extra discharging unit for the ink jet head for discharging ink without printing, or some other similar unit. The maintenance unit  9  thus performs the function required to stabilize the printing operation of the ink jet head. Since such a maintenance unit is typically arranged outside the recording area, the maintenance operation is carried out after moving the recording head to the position of the maintenance unit. The maintenance operation typically involves moving the recording head, namely, the carriage  2 , out of the recording area. The frequency of maintenance operations changes depending on the pattern to be printed in the printing operation (or a “print pattern”) and environmental conditions such as temperature and humidity. To perform a high quality printing, the maintenance operation is performed several times during the printing of a single page. 
     Referring to FIG. 5, a sequence of the head maintenance process, in the middle of a printing operation, is discussed. The following example is a so-called single direction recording system in which an image is formed when the carriage  2  goes in the main scan and no image formation is carried out when the carriage  2  returns. 
     In the recording operation, the recording head discharges ink while the carriage  2  scans, and an image is formed on the recording medium  4  (step S 501 ). The paper conveyance roller  7  rotates by a predetermined quantity of rotation to convey the copy sheet while the carriage  2  moves in its back scan direction (in the return direction), and the recording head is prepared to print a next line (step S 502 ). 
     It is determined in step S 503  whether the recording head needs maintaining. When it is determined that a head maintenance operation job is needed, the process goes to step S 504  to execute a head maintenance operation. The process returns to step S 501  as necessary subsequent to the head maintenance, and steps S 501  through S 504  are repeated. 
     When a head maintenance job is performed in the above conventional sequence, the carriage  2  is transferred to a maintenance position prior to the head maintenance operation. The range of scan in the head maintenance operation is different from that in a normal recording operation without performing the head maintenance job. In the head maintenance, the apparatus suffers from a vibration different from the vibration which is generated when the entire apparatus repeatedly scans in the normal printing operation. When a recording operation is executed in immediate succession to the execution of a head maintenance job, a printed image is subject to disturbance. The following causes of the disturbance are contemplated. 
     The entire apparatus vibrates due to the operation of a drive system that executes the head maintenance. Under such vibration, the paper conveyance roller  7  rotates by a small quantity of rotation corresponding to the backlash of the gear train, causing the recording head to be subject to a relative position error, and thereby leading to a landing error of an ink jet in the direction of paper conveyance. As a result, the printed image is disturbed. When the entire apparatus vibrates due to the operation of the drive system that executes the head maintenance, the vibration is transferred to the recording medium, causing it to vibrate, changing a distance to the recording head (i.e., the distance between the head and the copy sheet), and leading a landing error in the scan direction of the carriage  2  and a disturbance in the printed image. 
     SUMMARY OF THE INVENTION 
     In view of the above problem, the present invention has been developed. It is an object of the present invention to provide a printing apparatus and a control method for the printing apparatus, which outputs a good quality image by controlling a position error of a recording medium taking place in a head maintenance job in the middle of a printing operation and a vibration of the apparatus. 
     To resolve the above problem, the present invention provides a control method of a printing apparatus including a conveying unit for conveying a recording medium, a carriage with a recording head mounted thereon, and a maintenance unit for performing a maintenance job on the recording head, wherein the printing apparatus performs recording by intermittently operating the conveying unit to intermittently convey a recording medium by a predetermined travel and by causing the carriage to scan with the conveying unit stopped. When the recording head is maintained by the maintenance unit in the middle of the printing operation, the apparatus controls so that the operation of the conveying unit is stopped subsequent to the finish of a maintenance job. 
     A printing apparatus of the present invention includes a conveying unit for conveying a recording medium, a carriage with a recording head mounted thereon, and a maintenance unit for performing a maintenance job on the recording head, wherein the printing apparatus performs recording by intermittently operating the conveying unit to intermittently convey a recording medium by a predetermined travel and by causing the carriage to scan with the conveying unit stopped. The printing apparatus includes a control unit for performing control so that the operation of the conveying unit is stopped subsequent to the finish of a maintenance job when the recording head is maintained by the maintenance unit in the printing operation. 
     In accordance with the present invention, when the maintenance of the recording head becomes necessary in the middle of printing operation to the recording medium, the conveying unit is controlled so that the conveying unit is operated subsequent to the maintenance job. Even if the apparatus suffers from a vibration in the course of the maintenance of the recording head, the entire apparatus is set to a normal printing state, namely, a state as if no maintenance job were done, before the apparatus resumes a printing operation. The image disturbance due to the vibration of the apparatus is thus prevented. Even if the recording medium is in position error due to the vibration subsequent to the maintenance, the error of the recording medium is covered because the conveying unit has operated subsequent to the maintenance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow diagram of the operation of a printing apparatus which executes a head maintenance job in the middle of a printing operation in accordance with a first embodiment of the present invention; 
     FIG. 2 is a flow diagram of the operation of a printing apparatus which executes a head maintenance job in the middle of a printing operation in accordance with a second embodiment of the present invention; 
     FIG. 3 is a perspective view of a printing apparatus of the present invention; 
     FIG. 4 is a sectional view of the printing apparatus; 
     FIG. 5 is a flow diagram of the operation of a conventional printing apparatus which executes a head maintenance job in the middle of a printing operation; and 
     FIG. 6 is a block diagram showing a control system of an ink jet printing apparatus in which the present invention is implemented. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Throughout the description of this invention, the term “recording” refers to transferring not only an image of texts and drawings, which have themselves meaning, but a pattern, which itself is meaningless. The terms “recording” and “printing” are interchangeably used in this specification. 
     The present invention applies to a variety of apparatuses which perform recording onto printing media including sheets of paper, threads, fibers, fabric, hides, metals, plastics, glass, wood, ceramics, etc. These apparatuses include printers, copying apparatuses, facsimiles having a communication system, a printer system in which a communication system and a printer are combined, an apparatus, such as a word processor, with a printer section, and an industrial recording apparatus in which a diversity of processing devices are combined. 
     The printing apparatus and the control method for the printing apparatus of the present invention are now discussed, referring to the drawings. 
     First Embodiment 
     The construction of a recording apparatus, in which the present invention is implemented, remains unchanged from that discussed in conjunction with the conventional art shown in FIG.  3  and FIG.  4 . The recording apparatus of a first embodiment of the present invention is the one that records an image onto a recording medium using an ink-jet type recording head for discharging ink (also called an ink-jet head). 
     A variety of known techniques may be employed as an ink discharging method. For example, the present invention may employ a bubble jet technique which discharges ink by applying thermal energy with an electricity-heat converting body such as a heater element as an means for discharging ink, or a technique which employs an element, such as an piezoelectric element, which generates mechanical pressure by applying an electrical signal thereto. 
     As already discussed, available as a maintenance unit  9  for carrying out the above maintenance operation may be a suction unit for an ink jet head, a wiping unit for cleaning the face of the ink jet head (where discharge nozzles are arranged), an extra discharging unit for the ink jet head for discharging ink without printing, or some other similar unit. The head maintenance unit is the one for restoring a full discharging capability of the ink-jet head, and may be referred to as a “restoring unit”. 
     The suction unit may include a cap member for covering a discharge nozzle face of the recording head, a mechanism for generating a negative pressure within the cap member using a pump or the like, and a drive mechanism for moving the cap member to the discharge nozzle face of the recording head. In the operation of the suction unit, the carriage  2  having an ink-jet head mounted thereto is transferred to the position of the head maintenance unit. The discharge nozzle face is capped with the cap member by moving the cap member to the discharge nozzle face. A negative pressure is then generated within the cap member. 
     The wiping unit may include a wiping member for wiping the recording head. The carriage  2  having the ink-jet head mounted thereon scans with respect to the wiping member to wipe its discharge nozzle face. 
     The head maintenance operation in accordance with the present invention may incorporate the above techniques, alone or in combination. 
     FIG. 6 is a block diagram roughly showing a control system of an ink-jet recording apparatus, in which the present invention is implemented. 
     The control system shown in FIG. 6 drives and controls each block in the recording apparatus. A control unit  10  includes CPU  10   a  that executes a process for controlling each block, ROM  10   b  for storing a program and the like to be executed by CPU  10   a,  and RAM  10   c  for storing a diversity of data. 
     CPU  10   a  may be a central processing unit, for example, and reads the program and diverse data from ROM  10   b  to be described later, and an external apparatus  20 , such as a host apparatus, performs necessary computations and determinations, and controls each block in the printing apparatus. 
     ROM  10   b  is a read-only memory, and stores the program to be executed by CPU  10   a,  and a diversity of data needed to control the recording apparatus and to perform recording on the recording apparatus, such as character codes and dot patterns. 
     RAM  10   c  is a memory to and from which data is written or read (also referred to as a “read-write memory”), and is constructed of a working area for temporarily storing data currently under processing and computation results, a buffer area for storing a diversity of data input from the external apparatus  20 , and a text area for storing text and the like. 
     The control unit  10  receives an image signal from the external apparatus  20  through an interface  11 , and diverse pieces of information from an operation panel  12 , including those about a recording density, the number of copies, and the size of copying area. The control unit  10  outputs a drive signal to a motor driver  13  which controls and drives motors. The control unit  10  further outputs an image signal and the like to a head driver  14  that controls and drives a recording head  15 . The motors driven by the motor driver  13  are a carriage motor  16  for moving the carriage  2  and a conveyance motor  17  for conveying a recording medium. 
     One example of the control sequence of the printing apparatus of the present invention is now discussed, referring to FIG.  1 . 
     FIG. 1 illustrates the operational flow of the head maintenance that is carried out in the middle of a recording operation. 
     Step S 101  is a processing step for recording. In the recording operation, the recording head is driven in response to the image signal with the carriage  2  moved in the scan direction, and an image is formed on the recording medium  4 . The recording head in the embodiments of the present invention is an ink-jet type recording head. With the recording head driven, ink is discharged through nozzles arranged on the recording head. 
     In step S 101 , the carriage  2  scans in a predetermined direction. It is determined in step S 102  whether a head maintenance job needs to be carried. When it is determined in step S 102  that the recording head needs maintaining, the process goes to step S 104 . 
     In step S 104 , the carriage  2  is moved to a predetermined position in a return direction (hereinafter referred to as a “back scan direction”) with a conveyance roller  7  as means for conveying the recording medium  4  not rotated. The head maintenance (in step S 105 ) and the conveying of the recording medium by a predetermined distance by the conveying unit (in step S 106 ) are executed. 
     When it is determined in step S 102  that the recording head needs no maintenance, the process goes to step S 103 . In step S 103 , the paper conveyance roller  7  is rotated by a predetermined quantity of rotation to convey the recording medium  4  by a required distance while the carriage  2  scans in the return direction. When the back scan of the carriage  2  and the conveyance of the recording medium  4  are completed, the process returns to step S 101  and the recording operation is resumed. Steps S 101  through S 106  are hereinafter repeated. 
     The above sequence is executed by the control system in the above-referenced printing apparatus. 
     Since the recording medium  4  is conveyed by the paper conveyance roller  7  subsequent to the head maintenance, the position of the recording medium  4 , if deviated due to the vibration of the apparatus during the head maintenance, is corrected. Since the mode of vibration of the entire apparatus immediately prior to the resuming of the recording becomes the normal mode of vibration, no image disturbance takes place even subsequent to the head maintenance in the middle of the recording operation. 
     The present invention is effective particularly in an arrangement, such as the above-referenced suction unit or wiping unit, involving a mechanical operation, i.e., the movement of the cap member or the generation of the negative pressure or in an arrangement involving the movement of the carriage  2  different from its movement for the recording. 
     The temperature of the recording head, the ambient temperature, the number of drivings of the recording head, the amount of recording about a recorded area serve alone or in combination as a criterion in the determination in step S 102  of whether the head maintenance is required. Alternatively, known techniques relating to the timing for carrying out the restoring operation of the recording head may be used. 
     In the flow diagram shown in FIG. 1, a determination of whether the recording head needs maintaining is performed each time the carriage  2  scans for printing. The present invention is not limited to this method. Alternatively, a determination of whether the recording head needs maintaining is performed every predetermined number of scans of the recording head. Alternatively, a determination of whether the recording head needs maintaining may be performed referring to the number of recorded dots or detected temperature in the middle of the printing by the recording head. 
     Second Embodiment 
     A second embodiment is now discussed, referring to the drawings. 
     FIG. 2 is a flow diagram showing the head maintenance process in the middle of the recording operation. Each of this process is now discussed. 
     Step S 201  is a processing step for recording. In the same way as in the first embodiment, the recording head is driven for printing while the carriage  2  scans. In step S 202 , the carriage  2  scans in the return direction, while the paper conveyance roller  7  is rotated by a predetermined quantity of rotation to convey the recording medium  4 . Through the process in step S 202 , the next line succeeding to the line that has undergone the printing is ready for next printing. In step S 203 , a determination is performed of whether the recording head needs maintaining. When it is determined in step S 203  that the recording heads needs maintaining, the process goes to step S 204 . 
     In step S 204 , the head maintenance process is performed. In step S 205 , the paper conveyance roller  7  is rotated by the predetermined quantity of rotation in a reverse direction, and is then rotated again by the predetermined quantity of rotation in the paper conveyance direction (step S 206 ). The process then returns to step S 201  and the recording operation is resumed. 
     The rotation of the paper conveyance roller  7  in step S 205  is opposite in direction to the paper conveyance direction. Through the rotations of the paper conveyance roller  7  in step S 205  and step S 206 , the paper conveyance roller  7  is stopped at the same position as if no head maintenance took place. Even if the gear train rotates in response to the vibration of the apparatus due to the head maintenance process, the relative position of the recording medium  4  with respect to the recording head is set to be back to its original one. 
     When it is determined in step S 203  that no head maintenance is required, the process returns to step S 201 , and the recording is resumed. 
     Steps in S 201  through S 206  are repeated, and the recording operation is performed. 
     The sequence in the second embodiment is performed by the control system in the printing apparatus in the same way as in the first embodiment. 
     The same factors as those in the first embodiment are accounted for as the criteria of the determination of whether the recording head needs maintaining. The same timing for the determination of whether the recording head needs maintaining, discussed in conjunction with the first embodiment, is also applicable. 
     In accordance with the present invention, the paper conveyance roller  7  is rotated by a predetermined quantity of rotation in a direction reverse to the paper conveyance direction, subsequent to the head maintenance, and is then rotated by the predetermined quantity of rotation in the paper conveyance direction. Through this process, the paper conveyance roller  7  and the gear train for driving the paper conveyance roller  7  are set back to the same state as if no head maintenance job were made. Even if the apparatus vibrates in the head maintenance process and suffers from a mechanical position error, possibly leading to an image disturbance, such a image disturbance due to the head maintenance job in the middle of the recording operation is controlled. 
     Even if the head maintenance is carried out in the middle of the recording operation, the conveying unit for conveying the recording medium is activated to eliminate the effect caused in the head maintenance, and the image quality is maintained.