Patent Publication Number: US-6991312-B2

Title: Print head maintenance mechanism

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 2002-80961 filed in JAPAN on Mar. 22, 2002, which is (are) herein incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a maintenance mechanism for cleaning and protecting a print head of a printing machine of the ink jet printing system wherein printing is performed by jetting ink droplets onto a receiving medium. 
   2. Description of the Related Art 
   Ink-jet printing machines generally have three modes of operations which include a printing operation for printing on a receiving medium, a capping operation for protecting a print head and preventing nozzles from drying, and a wiping operation for cleaning by wiping surfaces of the nozzles of the print head.  FIGS. 11A  to  11 C illustrate an example of the conventional print head maintenance mechanism, while an example of such an arrangement of the maintenance mechanism is disclosed in Japanese Unexamined Patent Publication JP-A 2000-233517 (2000). 
     FIG. 11A  shows a state where a nozzle portion disposed at a respective bottom of a first and a second print head  3 ,  4  (lower portions as seen in the figure) is sealed by a respective cap  7   a,    7   b.  The first and second print heads  3 ,  4  are mounted to a carriage  2  adapted to reciprocate along a primary scanning direction as carried on a carriage shaft  5  extended transversely of a main frame  1 . At this time, a slide case  6  provided with the caps  7   a,    7   b  is positioned at a left end of the main frame  1  as operatively connected with the carriage  2  as shown in  FIG. 11A , the left end of the main frame  1  defining one end of a primary scanning movement. That is, the slide case  6  is placed at an uppermost position (a top dead center) by means of a function of sliding projections C slidably engaged with slanted cam grooves B formed in a base portion  9  of the printing machine, so that the print heads  3 ,  4  are sealed by the caps  7   a,    7   b.    
     FIG. 11B  shows a state where the wiping operation is being carried out for cleaning by wiping the nozzle surfaces at the print heads  3 ,  4 . At this time, the slide case  6  has the sliding projections C thereof fixed to a respective intermediate position of the cam grooves B by means of a lock mechanism (not shown), so that the caps  7   a,    7   b  are spaced away from the nozzle surfaces at the print heads  3 ,  4 . The carriage  2  passing over wipers  8  permits the wipers  8  to wipe and clean the nozzle surfaces at the print heads  3 ,  4 . 
     FIG. 11C  shows a state where the printing operation is being carried out. At this time, the carriage  2  is further moved rightward from the position shown in  FIG. 11B  or moved toward the other end of the primary scanning movement relative to the main frame  1  by a distance L 1  from the one end of the primary scanning movement, thus entering a printing region for performing the printing operation. In this state, the slide case  6  is released from the locked state while the sliding projections C rest at a respective right end of the cam grooves B in conjunction with the movement to the other end of the primary scanning movement relative to the main frame  1 . The slide case  6  is at a lowermost position (a bottom dead center) or at such a height as to bring the wipers  8  and caps  7   a,    7   b  out of interference with the operating print heads  3 ,  4 , so that a normal printing operation is allowed. 
   According to the conventional example mentioned above, a main body of the printing machine requires a further widthwise (the primary scanning direction) increase of space, such that the slide case  6  may be allowed to move a distance L 2  from the one end of the primary scanning movement relative to the main frame  1  thereby permitting a sequence of oblique sliding movements of the maintenance mechanism. Specifically, the space represented by L 2  in the figure is required to permit the slide case  6  to move up and down or to permit the sliding projections C in loose fit with the cam grooves B to slidably move in conjunction with the movement of the carriage  2 . This requires the further widthwise increase of space of the printing machine, which results in an increased widthwise dimension of the machine. 
   As a solution to this problem, for example, Japanese Unexamined Patent Publication JP-A 2000-203042 (2000) discloses an arrangement wherein a maintenance station is disposed within the printing region. In this case, a motor conventionally provided for driving a sheet feed roller or feed roller is utilized for driving the maintenance station. However, such an arrangement encounters a complicated structure of a drive force transmission mechanism and an increased number of components thereof. Consequently, a driving system has a complicated structure of a complicated control, which results in increased costs. 
   On the other hand, U.S. Pat. No. 5,455,609 discloses an arrangement employing the following drive force transmission mechanism for vertically moving the maintenance station. The transmission mechanism is arranged such that a worm gear mounted to an output shaft of a motor is meshed with a wheel gear, which is meshed with a rack. Unfortunately, this arrangement also suffers the complicated structure of the driving system. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, an object of the invention is to provide a less costly print head maintenance mechanism accomplishing a compact and simple construction by negating the need for the further widthwise increase of space for permitting the print head maintenance mechanism to move up and down. 
   The invention provides a print head maintenance mechanism for use in an ink jet printing machine in which printing is carried out by driving a carriage carrying a print head, the maintenance mechanism comprising: 
   a cap for preventing a nozzle provided at the print head from drying; 
   a cap holder retaining the cap and allowed to move along directions orthogonal to a primary scanning direction and a secondary scanning direction of the print head; 
   a first cam which is rotated at a predetermined position; 
   first biasing means for biasing the cap holder against the first cam; 
   a wiper for cleaning by wiping a surface of the nozzle provided at the print head; 
   a second cam which is rotated at a predetermined position; 
   a wiper holder retaining the wiper and allowed to move along directions orthogonal to the primary scanning direction and the secondary scanning direction of the print head; and 
   second biasing means for biasing the wiper holder against the second cam, 
   wherein the first and second cams are mounted to a single cam shaft, and 
   wherein the cam shaft is rotated through one revolution for switching the cap holder and wiper holder between a printing mode position for permitting a normal printing operation, a capping mode position for sealing the surface of the nozzle at the print head with the cap, and a wiping mode position for cleaning by wiping the nozzle surface with the wiper. 
   According to the invention, the cam shaft assembled with the two cams is rotated through one revolution thereby permitting the maintenance mechanism to be switched to the three mode positions. Therefore, the maintenance mechanism may be constructed in a simple structure of an easy control, which results in a low cost fabrication of the maintenance mechanism. 
   Thus, the invention is adapted to shift the cap holder and the wiper holder along the directions orthogonal to the primary scanning direction and the secondary scanning direction by way of rotation of the first and second cams. Specifically, in a case where the ink jet printing machine is disposed in a horizontal position, the cap holder and the wiper holder are shifted vertically so as to be switched to the printing mode position for permitting the normal printing operation, the capping mode position for sealing the surface of the nozzle at the print head, and the wiping mode position for cleaning by wiping the nozzle surface. Hence, the invention only needs to provide a space allowing for the vertical movements of the cap holder and the wiper holder, negating the need for the further widthwise increase of space. The provision of the print head maintenance mechanism does not require the ink jet printing machine to be further increased in the widthwise dimension so that the printing machine can accomplish a compact design. In addition, the rotation of a single cam shaft brings the two cams into rotation to switch the maintenance mechanism to the three mode positions. This ensures positive maintenance operations. Furthermore, the invention implements the switching function in a simple construction of an easy control, contributing to the low cost fabrication of the maintenance mechanism. 
   In addition, the invention accomplishes the switching to the three mode positions by rotating the cam shaft assembled with the two cams through one revolution and hence, the maintenance mechanism may be constructed in a simple construction of an easy control, which results in the low cost fabrication of the maintenance mechanism. 
   In the invention, it is preferable that the first biasing means for biasing the cap holder against the first cam comprises a pair of tension springs disposed at places on one of the diagonal lines of the cap holder as equi-spaced from the cam shaft. 
   According to the invention, the pair of tension springs as the first biasing means are disposed at places on one of the diagonal lines of the cap holder as equi-spaced from the cam shaft so that the cap holder may be biased against the cam in a well-balanced fashion. In addition, the first biasing means has a simple construction, contributing to the low cost fabrication of the maintenance mechanism. 
   In the invention, it is preferable that the second biasing means for biasing the wiper holder against the second cam comprises a pair of tension springs disposed at places on opposite sides of the cam shaft as equi-spaced from an axis of the wiper holder orthogonal to the cam shaft. 
   According to the invention, the pair of tension springs as the second biasing means are disposed at places on the opposite sides of the cam shaft as equi-spaced from the axis of the wiper holder orthogonal to the cam shaft so that the wiper holder may be biased against the cam in a well-balanced fashion. In addition, the second biasing means has a simple construction, contributing to the low cost fabrication of the maintenance mechanism. 
   Thus, the invention permits the wiper holder to be biased against the cam in a well-balanced fashion because the pair or tension springs as the second biasing means are disposed at places on the opposite sides of the cam shaft as equi-spaced from the axis of the wiper holder. Furthermore, the invention implements the second biasing means in a simple construction, thus offering the less costly maintenance mechanism. 
   In the invention, it is preferable that the first biasing means for biasing the cap holder against the first cam comprises a pair of tension springs disposed at places on one of the diagonal lines of the cap holder as equi-spaced from the cam shaft, and that the second biasing means for biasing the wiper holder against the second cam comprises a pair of tension springs disposed at places on opposite sides of the cam shaft as equi-spaced from an axis of the wiper holder orthogonal to the cam shaft. 
   According to the invention, the pair of tension springs as the first biasing means for the cap holder are disposed at places on one of the diagonal lines of the cap holder as equi-spaced from the cam shaft while the pair of tension springs as the second biasing means for the wiper holder are disposed at places on the opposite sides of the cam shaft as equi-spaced from the axis of the wiper holder. Hence, the first and second biasing means are capable of biasing the cap holder and the wiper holder against the first cam and the second cam in a well-balanced fashion, respectively. Furthermore, the first and second biasing means have simple constructions, thus contributing to the low cost fabrication of the maintenance mechanism. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other and further objects, features, and advantages of the invention will be more explicit from the following detailed description taken with reference to the drawings wherein: 
       FIG. 1  is a front view showing a normal mode (during a printing operation) of a print head maintenance mechanism according to one embodiment of the invention; 
       FIG. 2  is a side view showing the mechanism of  FIG. 1 ; 
       FIG. 3  is a front view showing a wiping mode of the print head maintenance mechanism according the one embodiment of the invention; 
       FIG. 4  is a side view showing the mechanism of  FIG. 3 ; 
       FIG. 5  is a front view showing a capping mode of the print head maintenance mechanism according to the one embodiment of the invention; 
       FIG. 6  is a side view showing the mechanism of  FIG. 5 ; 
       FIG. 7  is a block diagram schematically showing an electrical configuration of the print head maintenance mechanism; 
       FIG. 8  is a flow chart representing steps of the wiping mode; 
       FIG. 9  is a flow chart representing steps of the capping mode; 
       FIGS. 10A and 10B  are diagrams for comparison between the print head maintenance mechanism according to the one embodiment of the invention and the prior art; and 
       FIGS. 11A  to  11 C are diagrams showing one example of the conventional print head maintenance mechanism. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Now referring to the drawings, preferred embodiments of the invention are described below. 
   A print head maintenance mechanism according to one embodiment of the invention will hereinbelow be described with reference to the accompanying drawings. 
     FIGS. 1  to  6  each shows a respective operation mode of the print head maintenance mechanism. As shown in these figures, a pair of print heads  23 ,  24  are mounted to a carriage  22  adapted to reciprocate on a carriage shaft  25  along a primary scanning direction, the carriage shaft  25  extended transversely of a main frame  21 . The print head  23  on one side is loaded with a color ink cartridge, whereas the other print head  24  is loaded with a monochromatic ink cartridge. 
   Caps  27   a,    27   b  for preventing nozzles (not shown) provided at the print heads  23 ,  24  from drying are mounted to cap holders  33   a,    33   b  as constantly biased upward by helical compression springs  31   a,    31   b.  The cap holders  33   a,    33   b  are vertically movably mounted to one L 6  of maintenance stations which is disposed on one side of the main frame  21  with respect to a primary scanning direction, or on the left side as seen in the FIG.  1 . 
   The maintenance station L 6  is allowed to move up and down as guided by a guide boss  36  standing upright from the main frame  21  and a guide rail  43  formed by bending a part of the main frame  21 . The maintenance station L 6  is biased toward a bottom of the main frame  21 , or downwardly as seen in  FIG. 1 , by means of a pair of tension springs  32  as first biasing means stretched between the maintenance station L 6  and the main frame  21 , so that the cap holders  33   a,    33   b  are constantly biased against first cams  34   a,    34   c  at their bottoms. 
   One  28   a  of wipers for cleaning by wiping surfaces of the nozzles is fixed to a wiper holder  29   a.  The wiper holder  29   a  is vertically movably retained and guided by a guide member standing upright from the maintenance station L 6  on one side. The wiper holder  29   a  is also biased toward the bottom of the main frame  21  or downwardly as seen in  FIG. 1  by a pair of tension springs  30   a  as second biasing means stretched between the wiper holder  29   a  and the maintenance station L 6 , so that the wiper holder  29   a  is constantly biased against a second cam  34   b  at its bottom. 
   The other wiper  28   b  is fixed to a wiper holder  29   b.  The wiper holder  29   b  is vertically movably retained and guided by a guide member standing upright from the other maintenance station R 21  fixed to place on the other side of the main frame  21  with respect to the primary scanning direction, or on the right side as seen in the FIG.  1 . The wiper holder  29   b  is constantly biased against a second cam  34   d  at its bottom by means of a pair of tension springs  30   b  as second biasing means stretched between the wiper holder  29   b  and the maintenance station R 21 . 
   The first cams  34   a,    34   c  and the second cams  34   b,    34   d  are fixedly mounted to a single cam shaft  34 . A motor  51  (dedicated to the maintenance mechanism) operatively connected with the cam shaft  34  is rotated thereby shifting the cap holders  33   a,    33   b  and the wiper holders  29   a,    29   b  in a direction orthogonal to the primary scanning direction or to a secondary scanning direction of the carriage  22 . Specifically, in a case where the main frame  21  is mounted in a horizontal position, the cap holders and wiper holders are shifted vertically, so as to be switched to three mode positions which include a printing mode position for permitting a normal printing operation (see FIGS.  1  and  2 ), a wiping mode position for cleaning by wiping the nozzle surfaces (see FIGS.  3  and  4 ), and a capping mode position for sealing the nozzle surfaces (see FIGS.  5  and  6 ). 
   The cap holders  33   a,    33   b  are formed, for example, in a square shape in section taken at right angles to its axis. The pair of tension springs as the pair of the first biasing means  32  are disposed at places on one of the diagonal lines of each cap holder  33   a,    33   b  in section taken at right angles to its axis as equi-spaced from the cam shaft  34 . The pair of tension springs  32  have the same spring constant. 
   The pair of tension springs as the pair of the second biasing means  30   a  are disposed at places on opposite sides of an axis L 1  of the wiper holder  29   a  orthogonal to the cam shaft  34  as equi-spaced from the cam shaft  34 . The pair of tension springs  30   a  have the same spring constant. 
   The pair of tension springs as the pair of the second biasing means  30   b  are disposed at places on opposite sides of an axis L 2  of the wiper holder  29   b  orthogonal to the cam shaft  34  as equi-spaced from the cam shaft  34 . The pair of tension springs  30   b  have the same spring constant. 
   The pair of the first biasing means  32  for biasing the maintenance station L 6  downwardly are disposed at symmetrical places with respect to an axis of the cam shaft  34  or equi-spaced from abutment places between the cap holders  33   a,    33   b  and the cams. Hence, the cap holders  33   a,    33   b  are biased against the first cams  34   a,    34   c  in a well-balanced fashion. Likewise, the wiper holder  29   a  on one side is also biased against the second cam  34   b  by means of the pair of the second biasing means  30   a  disposed at symmetrical places with respect to the axis of the cam shaft  34  or equi-spaced from an abutment place between the wiper holder  29   a  and the second cam  34   b.  Therefore, the wiper holder  29   a  is biased in a stable manner. Similarly, the other wiper holder  29   b  is also biased against the second cam  34   d  by means of the pair of the second biasing means  30   b,    30   b  disposed at symmetrical places with respect to the axis of the cam shaft  34  or equi-spaced from an abutment place between the wiper holder  29   b  and the second cam  34   d.  Therefore, the wiper holder  29   b  is biased in a stable manner. Such a simple construction ensures that the cap holders  33   a,    33   b  and the wiper holders  29   a,    29   b  are positively moved up and down, thus contributing to the low cost fabrication of the maintenance mechanism. 
   On the other hand, the cam shaft  34  is disposed directly under the maintenance station L 6  and the maintenance station R 21  and is rotated by the motor  51  via a cam gear  35  and a gear not shown. An initial position of the cam shaft  34  is detected by means of a position detection switch  42  disposed at a place corresponding to the cam gear  35 . The motor  51  is controlled based on a counted number of feed steps, so as to permit the mechanism to be switched to the three mode positions including the printing mode position, capping mode position and wiping mode position. 
     FIG. 7  is a block diagram schematically showing an electrical configuration of the print head maintenance mechanism. The operations of the print head maintenance mechanism are controlled by a control unit  50  so implemented as to include a central processing unit (CPU) and the like. The control unit  50  is electrically connected with the motor  51  for rotating the cam shaft  34  and is also electrically connected with the position detection switch  42 . 
   For a mere reference purpose, preferred rotational angles for the cam shaft  34  to assume the respective mode positions according to the embodiment are listed as below: From normal (printing) mode to wiping mode: 97.1°, From wiping mode to capping mode: 112.2°, and From capping mode to normal (printing) mode: 150.7°. 
   With such definitions of the rotational angles, rotating the cam shaft  34  through one revolution permits the maintenance mechanism to be switched to the three operation modes. Furthermore, the switching from one operation mode to another may be easily controlled. 
   The print head maintenance mechanism constructed as described above performs a sequence of operations which are switched from the normal printing mode to the wiping mode including purging of waste ink, and then to the capping mode. The following description explains these operations. 
   At an input of a print signal from a control system not shown, the control unit  50  firstly rotates the motor  51  to move down the caps  27   a,    27   b  and the wipers  28   a,    28   b  to places out of interference with the print heads  23 ,  24 , as shown in  FIGS. 1 and 2 . Thus, the mechanism takes a position to permit the printing operation (the printing mode position). Subsequently, a sheet fed from a rear side of the main frame  21  is subjected to the printing operation which is performed by ejecting ink based on the print signal while the carriage  22  reciprocates on the carriage shaft  25  along the primary scanning direction. The printing operation is continued with the sheet intermittently advanced precisely along the secondary scanning direction by means of a conveyor roller (not shown). 
   During the printing operation, a cleaning operation is performed at given time intervals for ensuring a print quality, the cleaning operation including the wiping of the nozzle surfaces and purging cleaning for removing waste ink adhered to nozzle apertures by jetting the ink therethrough. As shown in  FIGS. 3 and 4 , the wiping of the nozzle surfaces is performed by raising the wipers  28   a,    28   b  of the maintenance stations R 21  and L 6  to bring the wipers into abutment against the print heads  23 ,  24  (the wiping mode position). Whenever the wiping operation is finished, the wipers  28   a,    28   b  are lowered so as to be spaced away from the print heads  23 ,  24 . The purging cleaning is performed by jetting the ink toward a waste ink receiving portion of the maintenance station R 21 . 
   After completion of the printing operation, the sheet is discharged by a discharge roller (not shown) toward the front side with respect to the drawing surface of  FIG. 1 , for example. Then, the carriage  22  is moved to a standby position on the left side of the figure. On the other hand, the motor is rotated to drive the cam shaft  34  thereby raising the caps  27   a,    27   b  which, in turn, seal the print heads  23 ,  24 , as shown in  FIGS. 5 and 6  (the capping mode position) . Thus is accomplished a capping operation for preventing the ink nozzles from drying. 
   In the state shown in  FIGS. 1 and 2  where the printing operation included in the operation sequence is being carried out, both the caps  27   a,    27   b  and the wipers  28   a,    28   b  are retracted to the bottom dead center where the caps and wipers are out of interference with the reciprocating print heads  23 ,  24 . At this point of time, the position detection switch  42  (contact type) for detecting the cam position is ON, contacting the cam gear  35 . 
   In the state shown in  FIGS. 3 and 4  where the wiping operation is being carried out, the cam shaft  34  is rotated to set the cams (the second cams)  34   b,    34   d  to operating positions where upper ends of both the wipers  28   a,    28   b  orthogonally overlap with the surfaces of the nozzles at the print heads  23 ,  24 . At this point of time, the position detection switch  42  is ON, contacting the cam gear  35 . 
   In this state, both the wipers  28   a,    28   b  operate as illustrated in the flow chart of  FIG. 8 , for example. That is, the wipers  28   a,    28   b  move up and down in conjunction with the reciprocal movement of the carriage  22 . Specifically, after the wipers  28   a,    28   b  are raised, the carriage  22  is moved for performing the wiping operation. Immediately after the wiping operation, the wipers  28   a,    28   b  are lowered to allow for the movement of the carriage  22 . The wiping operation is carried out by effecting these movements in combination. 
   More specifically, a wipe command signal triggers the wiping operation in Step a 1 . If the control unit  50  determines in the subsequent Step a 2  that the wipe command indicates the wiping of both a color ink and a monochromatic ink, the control proceeds to Step a 3  where the carriage  22  is moved from the printing region substantially of the same area as that of a sheet conveyance region shown in  FIG. 10A  to the one end of the primary scanning movement defined at the left end of the main frame  21  so as to be positioned directly above the maintenance station L 6  on one side. In the subsequent Step a 4 , the control unit  50  controllably drives the motor  51  to rotate the cam shaft  34  based on a number of feed steps and a signal from the position detection switch  42 , thereby bringing the second cams  34   b,    34   d  into rotation to raise the wipers  28   a,    28   b  to the wiping mode positions. 
   In Step a 5 , the carriage  22  at the left end is moved toward the printing region along the primary scanning direction, thereby performing the wiping of the color ink. Thus, the wiper  28   a  cleans by wiping the nozzle surface at the print head  23  for color ink. In the subsequent Step a 6 , the control unit  50  controllably drives the motor  51  to rotate the cam shaft  34  based on a number of feed steps and a signal from the position detection switch  42 , thereby bringing the second cams  34   b,    34   d  into rotation to lower the wipers  28   a,    28   b  to places out of interference with the print heads  23 ,  24 . In the subsequent Step a 7 , the carriage  22  is moved from the printing region to the other end of the primary scanning movement defined at the right end of the main frame  21 , so that the carriage  22  is positioned directly above the other maintenance station R 21 . 
   In the subsequent Step a 8 , the control unit  50  controllably drives the motor  51  to rotate the cam shaft  34  based on a number of feed steps and a signal from the position detection switch  42 , thereby bringing the second cams  34   b,    34   d  into rotation to raise the wipers  28   a,    28   b  to the wiping mode positions. In the subsequent Step a 9 , the carriage  22  at the right end is moved toward the printing region along the primary scanning direction, thereby performing the wiping of the monochromatic ink. Thus, the wiper  28   b  cleans by wiping the nozzle surface at the print head  24  for monochromatic ink. In the subsequent Step a 10 , the control unit  50  controllably drives the motor  51  to rotate the cam shaft  34  based on a number of feed steps and a signal from the position detection switch  42 , thereby bringing the second cams  34   b,    34   d  into rotation to lower the wipers  28   a,    28   b  to places out of interference with the print heads  23 ,  24 . In the subsequent Step a 11 , the carriage  22  is moved from the printing region to the right end of the main frame  21 , so that the carriage  22  is positioned directly above the other maintenance station R 21 . 
   In the subsequent Step a 12 , the print heads  23 ,  24  perform the purging cleaning by individually spitting the inks toward the waste ink receiving portion of the maintenance station R 21 . In the subsequent Step a 13 , the carriage  22  at the right end is moved to the printing region along the primary scanning direction, so that the printing operation is resumed. 
   If the control unit  50  determines in Step a 2  that the wipe command does not indicate the wiping of both the color ink and the monochromatic ink and then determines in Step a 14  that the wipe command indicates the wiping of the color ink, the same operations as in Steps a 3  to a 7  are performed in Steps a 15  to a 19  for cleaning by wiping the nozzle surface at the print head  23  for color ink. After the purging cleaning is performed in the subsequent Step a 12 , the printing operation is resumed in Step a 13 . 
   If the control unit  50  determines in Step a 2  that the wipe command does not indicate the wiping of both the color ink and the monochromatic ink and then determines in Step a 14  that the wipe command indicates the wiping of the monochromatic ink rather than the color ink, the same operations as in Steps a 7  to all are performed in Steps a 20  to a 24  for cleaning by wiping the nozzle surface at the print head  24  for monochromatic ink. After the purging cleaning is performed in the subsequent Step a 12 , the printing operation is resumed in Step a 13 . 
   In the state shown in  FIGS. 5 and 6  where the capping operation is being carried out, the carriage  22  rests at the standby position on the left side after completion of the printing operation or initialization, while the cam shaft  34  is rotated to set the cams (the first cams)  34   a,    34   c  to operation positions so that the maintenance station L 6  along with the cap  27  are raised to seal the nozzle surfaces at the print heads  23 ,  24 . At this point of time, the position detection switch  42  is OFF, placed out of contact with the cam gear  35 . 
   The capping operation may be performed as illustrated in the flow chart of  FIG. 9 , for example. Before the carriage  22  at the standby position is moved, the cap  27  is lowered to establish a state where the carriage  22  is allowed to move. On the other hand, after the carriage  22  is returned to the standby position from the printing region, the capping operation is carried out by raising the cap  27 . 
   More specifically, in response to a print start command given in Step b 1 , Step b 2  is performed where the control unit  50  controllably drives the motor  51  to rotate the cam shaft  34  based on a number of feed steps and a signal from the position detection switch  42 , thereby bringing the first cams  34   a,    34   c  into rotation to lower the caps  27   a,    27   b  from the capping mode positions to the printing mode positions. Thus, the caps  27   a,    27   b  are moved away from the nozzle surfaces at the print heads  23 ,  24 . In the subsequent Step b 3 , the carriage  22  at the standby position is moved to the printing region. In Step b 4 , the printing operation is started while the carriage  22  reciprocates along the primary scanning direction. 
   At termination of the printing operation in Step b 5 , the carriage  22  at the printing region is moved to the standby position in Step b 6 . In Step b 7 , the control unit  50  controllably drives the motor  51  to rotate the cam shaft  34  based on a number of feed steps and a signal from the position detection switch  42 , thereby bringing the first cams  34   a,    34   c  into rotation to raise the caps  27   a,    27   b  from the printing mode positions to the capping mode positions. Thus, the caps  27   a,    27   b  come into intimate contact with the nozzle surfaces at the print heads  23 ,  24  for sealing the nozzle surfaces. In the subsequent Step b 8 , the print heads stay at the standby positions to maintain a capped state until the next print start command is given. 
   As described above, the cap holders  33   a,    33   b  and the wiper holders  29   a,    29   b  can be vertically shifted by rotating the first cams  34   a,    34   c  and the second cams  34   b,    34   d,  whereby the maintenance mechanism can be switched to the printing mode position for permitting the normal printing operation, the capping mode position for sealing the nozzle surfaces at the print heads  23 ,  24 , and the wiping mode position for cleaning by wiping the nozzle surfaces. Hence, the mechanism only requires a space allowing for the vertical movement of the cap holders  33   a,    33   b  and the wiper holders  29   a,    29   b,  negating the need for the widthwise increase of space. With the print head maintenance mechanism according to one embodiment of the invention as shown in  FIG. 10A , the main frame  21  only needs to define a space for provision of the maintenance station L 6 , which is, as represented by X 1  in  FIG. 10A , substantially as large as to accommodate the carriage  22 . In contrast, the conventional arrangement shown in  FIG. 10B  requires a space, as represented by X 2  in  FIG. 10B , which is larger than the space X 1  in order to accommodate the carriage  22  as well as to allow the slide case  6  to move along the primary scanning direction. Thus, as shown in  FIGS. 10A and 10B , the provision of the print head maintenance mechanism of the invention does not require the widthwise (the primary scanning direction) expansion of the ink-jet printing machine, thus permitting the realization of the compact design thereof, provided that the sheet conveyance region through which a sheet to be printed is conveyed is of a constant size. In addition, one revolution of the single cam shaft  34  causes the two types of cams  34   a,    34   c;    34   b,    34   d  to rotate for switching the maintenance mechanism to the three mode positions, thus ensuring the positive maintenance operations. Furthermore, the switching function can be implemented in a simple construction of an easy control, contributing to the low cost fabrication of the maintenance mechanism. 
   The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and the range of equivalency of the claims are therefore intended to be embraced therein.