Abstract:
An ink jet recording apparatus having a sheet forward roller  8  and a pump unit  11  connected to a single drive motor  7 , and a drive force is transmitted to the pump unit  11  through time lag mechanisms  33-34  that cause a time lag at the time of switching rotational directions. Sheet feeding/discharging operation and ink sucking operation are performed with the single drive motor by taking advantage of a timing at which there are no load fluctuations accompanied by the switching operation, without requiring any switching mechanism.

Description:
FIELD OF THE INVENTION 
     The invention relates to ink jet recording apparatuses in general, and more particularly to an ink jet recording apparatus featuring a mechanism that causes a single drive motor to perform both a recording head maintaining operation and a recording sheet feeding/discharging operation. 
     BACKGROUND OF THE INVENTION 
     An ink jet recording apparatus requires a drive system for performing a recording sheet feeding/discharging operation and a recording head maintaining operation, in addition to carriage travelling operation. Conventionally, printers have a switching mechanism that enables a single drive motor to perform these sheet feeding/discharging and recording head maintaining operations in order to miniaturize and reduce the price of the apparatus. 
     The switching mechanism switches a drive force of a sheet forward motor between a pump drive system and a sheet feed/discharge drive system when the carriage has moved from a home position to a printing region and when the carriage has moved from the printing region to the home position. This switching feature involves selectively meshing a switching gear with gears of the sheet feed/discharge system and with gears of the pump system such a switching feature is generally thought to be acceptable, however, it is not without shortcomings. In particular, the gears cannot be meshed with each other smoothly because they are not phased together. As a result, sheet feed timings may be disturbed. Furthermore, conventional apparatuses require a disadvantageously large number of components. 
     Further, an ink jet recording apparatus includes a cleaning mechanism be disposed in a region outside a data recording region to maintain a recording head in a satisfactory condition at all times. As a result, the width of the apparatus is necessarily increased. The increased width is especially disadvantageous in an ink jet recording apparatus dedicated to color printing. For example, same apparatuses use yellow, magenta, cyan, and black inks and further use two kinds of inks, dark and light, for each of these colors. Consequently, the recording head that jets these inks in the form of ink droplets is necessarily increased. Also, capping unit and the cleaning mechanism whose size depends on the size of the recording head are necessarily large-sized. As a result, if the carriage, the recording head, the capping unit, and the cleaning mechanism are disposed within the housing at a high density in an effort to miniaturize the recording apparatus, the printing margins disadvantageously are reduced. For example, the cleaning mechanism may inadvertently move into the carriage travelling path such that during the recording operation, the cleaning mechanism contacts the carriage, thereby disturbing the recording operation. 
     Further, the number of nozzle openings of the black recording head for jetting black ink and of the color recording head for jetting three kinds of color inks is increased in order to accommodate the needs for high-density and high-speed printing. In association therewith, if the sizes of the recording heads in the sheet forward direction and in the sheet width direction are increased, the sizes of the caps for sealing the respective recording heads are necessarily increased. As a result, the sealability of the caps is impaired due to displacements or the like at the time the caps come into contact with the recording heads. 
     SUMMARY OF THE INVENTION 
     The invention is applied to an ink jet recording apparatus wherein a single drive means capable of switching rotational directions between a forward direction and a reverse direction is coupled to recording sheet feed/discharge means and to ink sucking means so that a recording sheet discharging operation and an ink sucking operation are performed while the drive means is rotating in the reverse direction, the drive means being coupled to the ink sucking means through coupling means for causing a time lag at the time of switching the rotational directions. 
     Further, the invention is applied to an ink jet recording apparatus having a capping unit, the capping unit including: a slider being biased by a recording head or a carriage carrying the recording head and thereby following a movement of the carriage over a base table while vertically moving in coincidence with the movement of the carriage; a holder being held by the slider while urged toward the recording head by springs on both sides outside a sealing region of the recording head; and a cap for sealing a nozzle surface of the recording head, the cap being accommodated in the holder and being made of an elastic member. 
     Therefore, a first object of the invention is to provide an ink jet recording apparatus that can not only implement accurate sheet feeding/discharging operation without being affected by load fluctuations accompanied by the ink sucking operation by means of taking advantage of a time lag in transmitting a drive force to the ink sucking means, but also significantly simplify the drive system of the recording apparatus of this type, and thus curtail costs, miniaturize the apparatus, and reduce the time required for sequential operations by means of dispensing with a separately arranged drive force switching mechanism. 
     A second object of the invention is to provide an ink jet recording apparatus that can keep the ink sucking operation inoperative during recording operation by means of allowing both the sheet discharging operation by the sheet feed/discharge means and the ink sucking operation to be performed while the drive means is being rotated in a reverse direction. 
     A third object of the invention is to provide an ink jet recording apparatus that prevents disturbing the recording operation. That is, the apparatus can be further miniaturized by means of movably arranging the capping means of the recording head so as to enter into and overlap the cleaning means operating region. Therefore, the width of the capping means is reduced by a dimension equal to the overlap of the operating region of the cleaning means. At the same time, the apparatus can prevent the recording operation from being disturbed by having one side of the capping means function as a stopper surface to block the cleaning means from projecting. That is, the stopper surface prevents to the cleaning means from projecting and contacting the recording head as a result of the sheet forward motor having rotated in a direction opposite to the sheet forward direction. 
     Further, another object of the invention is to provide an ink jet recording apparatus that can record images at both side margins of a recording sheet, even in the case of using a large-sized carriage carrying a color ink tank, by allowing part of the carriage that is scanning to enter into the home position, while causing a guide means to locate the capping means having entered into the cleaning means operating region to a position where the capping means does not come in contact with the recording head. 
     Another object of the invention is to provide an ink jet recording apparatus that can implement highly accurate sheet forwarding by directly connecting the cleaning means or the ink sucking means to the sheet feed/discharge means through a transmission mechanism different from a transmission mechanism that transmits motive force to the sheet feed/discharge means. That is, as a result of such direct connection, backlashes caused by repetitive forward and reverse rotations of the train of gears and slippages caused by using friction clutches are eliminated, which in turn blocks load fluctuations caused by these transmission mechanisms themselves and load fluctuations accompanied by the operation of the ink sucking means from being transmitted to the sheet feed/discharge means. 
     Another object of the invention is to provide an ink jet recording apparatus that can increase the degree of freedom in sequencing the entire system of the recording apparatus by allowing the operation of initializing the cleaning means or the ink sucking means to be performed only by rotation of the sheet feed/discharge means in the sheet discharge operation direction, and further by means of allowing the ink sucking means to operate independently of from the location of the carriage. 
     Another object of the invention is to provide an ink jet recording apparatus having a capping unit that can seal the recording head reliably by means of reducing displacements of the capping unit from the recording head as far as possible. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing an ink jet recording apparatus, which is an embodiment of the invention; 
     FIG. 2 is a diagram showing a driving power transmitting system of the recording apparatus; and 
     FIG. 3 is an exploded perspective view showing a pump unit in the apparatus. 
     FIGS.  4 ( a ) and  4 ( b ) are perspective views showing an embodiment of a capping unit to be used in the apparatus as viewed from both sides, respectively; 
     FIG. 5 is an exploded perspective view showing the embodiment of the capping unit to be used in the apparatus. 
     FIGS.  6 ( a ) to  6 ( c ) are diagrams illustrative of the size of a slider and a cap frame and of the amounts of displacement caused at the time of capping, respectively; 
     FIGS.  7 ( a ) to  7 ( c ) are a top view of an embodiment of a cap holder with a cap attached thereto, a sectional view thereof with the cap removed therefrom; and a sectional view of an embodiment of the cap. 
     FIG.  8 ( a ) is a diagram illustrative of a load to be applied to the cap; 
     FIG.  8 ( b ) is a diagram illustrative of a load to be applied when the cap is initially coming into contact with a recording head; 
     FIG.  8 ( c ) is a diagram showing a relationship between the distance between the cap and the recording head and the load applied by the cap to the recording head, the relationship being observed between the cap of the invention and a cap that is located on the centerline inside the cap sealing region and that is held by two springs. 
     FIG. 9 is a sectional view showing an embodiment of a sheet feed mechanism of a cut sheet feeder. 
     FIGS.  10 ( a ) and  10 ( b ) are a plan view and a side view respectively showing a condition in which a carriage is locked by a cleaner unit out of operations of the cleaner unit and the capping unit. 
     FIGS.  11 ( a ) and  11 ( b ) are a plan view and a side view respectively showing a condition in which the carriage is unlocked out of the operations of the cleaner unit and the capping unit. 
     FIGS.  12 ( a ) and  12 ( b ) are a plan view and a side view respectively showing a flushing condition out of the operations of the cleaner unit and the capping unit. 
     FIGS.  13 ( a ) and  13 ( b ) are a plan view and a side view respectively showing a condition in which the cleaner unit is locked out of the operations of the cleaner unit and the capping unit. 
     FIGS.  14 ( a ) and  14 ( b ) are a plan view and a side view respectively showing a process for causing the carriage to lift the slider out of the operations of the cleaner unit and the capping unit. 
     FIGS.  15 ( a ) and  15 ( b ) are a plan view and a side view respectively showing a condition in which the recording head is sealed, out of the operations of the cleaner unit and the capping unit. 
     FIGS.  16 ( a ) and  16 ( b ) are a plan view and a side view respectively showing an idle sucking condition out of the operations of the cleaner unit and the capping unit. 
     FIGS.  17 ( a ) and  17 ( b ) are a plan view and a side view respectively showing a condition in which the cleaner unit has been set ready for cleaning out of the operations of the cleaner unit and the capping unit. 
     FIGS.  18 ( a ) and  18 ( b ) are a plan view and a side view respectively showing a cleaning condition out of the operations of the cleaner unit and the capping unit. 
     FIGS.  19 ( a ) and  19 ( b ) are a plan view and a side view respectively showing a condition in which the cleaner unit has been reset after cleaning out of the operations of the cleaner unit and the capping unit. 
     FIG. 20 is a flowchart showing a printing operation of the apparatus; 
     FIG. 21 is a flowchart showing the first half of the cleaning operation of the apparatus; and 
     FIG. 22 is a flowchart showing the latter half of the cleaning operation of the apparatus. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a diagram showing an embodiment of the invention. A carriage  1  is connected to a carriage motor  2  through a timing belt  3 , and moves to and from across the width of a recording sheet  4 . The carriage  1  carries an ink jet recording head  5  on the surface thereof confronting the recording sheet  4 , the ink jet recording head  5  serving to jet an ink droplet out of a nozzle opening while causing an actuator to apply pressure to ink. Further, the carriage  1  has an ink cartridge  6  releasably mounted on the upper surface thereof, the ink cartridge  6  serving to supply the ink to the recording head  5 . The recording sheet  4  is forwarded in a direction orthogonal to the carriage  1  moving directions at a predetermined pitch by a forward roller  8  that is connected to a sheet forward motor  7  through a drive force transmission mechanism to be described later. Outside a printing region are a capping unit  9  serving to seal the recording head  5  and a cleaner unit  10 . The cleaner unit  10  is disposed closer to the printing region than the capping unit  9 . 
     The capping unit  9  has not only the finction of sealing the recording head  5  during nonprinting periods in order to prevent the nozzle openings from clogging, but also the function of forcibly jetting the ink out of the recording head during ink charging periods and during unclogging periods while evacuated to a negative pressure by a pump unit  11 . It may be noted that reference numeral  12  denotes a cut sheet feeder. 
     FIG.  2  and FIG. 3 show an embodiment of the aforementioned drive force transmission mechanism. The forward roller  8  has a gear  13  on one end thereof, and is driven while receiving drive force from a pinion  14  on the shaft of the sheet forward motor  7  through an idler  15 . Further, a sheet feed roller drive shaft  16  has a gear  17  on one end thereof, and transmits motive power to the cut sheet feeder  12  while meshed with the gear  13  through a clutch mechanism  18 . The pump unit  11  is driven by a gear  22  disposed on one end of a sheet discharge roller  21  while receiving drive force from the pinion  14  of the sheet forward motor  7  through an idler  19  and a sheet discharge roller gear  20 . The clutch mechanism  18  is normally kept remote from the gears  13 ,  17  as shown in FIG. 2 by a not shown spring, and has the gears  13 ,  17  connected thereto when pressed by the carriage  1 . 
     Then, the construction of various parts and components will be described. The pump unit  11  is attached to a home position side surface of a pump frame  23  that is fixed in a direction orthogonal to the carriage  1  travelling directions. A gear  26  is rotatably disposed on a shaft  24  of the pump unit  11 , the gear  26  being meshable with the gear  22  of the sheet discharge roller  21  through an idler  25 . The gear  26  has a cleaner cam  29  attached to the back surface thereof so as to be idlably rotatable, the cleaner cam  29  having an arm  28  that frictionally rotates while urged by a spring  27 . The cleaner cam  29  moves a cleaner unit  10  with the arm  28  thereof. 
     Attached to the shaft  24  of the pump unit  11  are a rachet wheel  31 , an intermediate transmission wheel  32 , and a pump wheel  33 , such wheels being placed side by side in such a manner that the intermediate transmission wheel  32  can idlably rotate. The rachet wheel  31  has a projection  31   a  on the surface thereof confronting the intermediate transmission wheel  32 . The intermediate transmission wheel  32  has projections  32   a ,  32   b  on both surfaces thereof respectively. The pump wheel  33  has a projection  33   a  on the surface thereof confronting the intermediate transmission wheel  32 . 
     As a result of this construction, even if the rachet wheel  31  starts rotating, the rotation of the rachet wheel  31  is not transmitted to the intermediate transmission wheel  32  until the projection  31   a  of the rachet wheel  31  abuts against the projection  32   a  of the intermediate transmission wheel  32 . Further, even if the projection  31   a  of the rachet wheel  31  has abutted against the projection  32   a  of the intermediate transmission wheel  32 , the motive power is not transmitted to the pump wheel  33  until the projection  32   b  of the intermediate transmission wheel  32  abuts against the projection  33   a  of the pump wheel  33 . That is, upon switchover of the rotational direction of the sheet forward motor  7 , there is a rotation transmission lag equivalent to about a maximum of  2  revolutions between the rachet wheel  31  and the pump wheel  33 . 
     The pump wheel  33 , as known well, has two shaft holes  33   b ,  33   b , one end of each shaft hole extending toward the center and the other end extending toward the outer circumference. These shaft holes  33   b ,  33   b  allow rollers  34 ,  34  that are journaled thereby to move toward the outer circumference or toward the center in accordance with the rotational directions of the pump wheel  33 . That is, by rotating the sheet forward motor  7  either forwardly or reversely, pump operation or release operation can be selected, the pump operation applying pressure to a tube  35  with respect to a pump casing  36  and the release operation not applying pressure to the tube  35 . 
     The cleaner unit  10  has a groove  38  formed in the upper surface of a cleaner holder  37  so that a cleaning blade  39  is inserted into such groove  38 . The cleaning blade  39  is high enough to allow the distal end thereof to come in resilient contact with a nozzle plate of the recording head  5 . The cleaner holder  37  has a guide projection  40  formed on a side portion thereof, and such guide projection  40  is meshed with a guide groove  42  that extends in a direction orthogonal to the carriage  1  moving directions, the guide groove  42  being formed in the upper portion of the pump casing  36 . The cleaner holder  37  also has a vertically extending elongated hole  43  in a distal end thereof, and such elongated hole  43  is meshed with a projection  28   a  of the arm  28  of the cleaner cam  29 . Further, the cleaner holder  37  has a retaining projection  44  formed thereon between the cleaning blade  39  and the guide projection  40 , the retaining projection  44  meshing with a carriage stopper la disposed on a side surface of the carriage  1 . As a result of such construction, when the cleaner cam  29  rotates, the guide projection  40  shuttles along the guide groove  42 , so that the cleaner unit  10  is moved from an evacuation position to a cleaning position, i.e., from the right end position to the carriage  1  travelling region as viewed in FIG.  1 . Then, the cleaning blade  39  comes in resilient contact with the recording head  5 , so that the cleaning blade  39  not only wipes the nozzle surface, but also blocks a cap  80  to be described later from moving toward a start end. 
     FIG.  4  and FIG. 5 show an embodiment of the capping unit  9 . A cap frame  51  is attached to the pump frame  23  with two retaining projections  52 ,  52 , which project from one end thereof, meshed with retaining holes  23   b ,  23   b  of the pump frame  23 , so that the longitudinal direction of the cap frame  51  extends in the carriage  1  travelling directions. The cap frame  51  has cam grooves  53 ,  53  arranged on both sides thereof. Each cam groove  53 , consisting of an upwardly sloped portion  53   a  and a horizontal portion  53   b , extends from the start end portion side to the termination end portion side of the home position, i.e., from the left to the right as viewed in FIG.  5 . Projections  57  of a slider  56  are sidably attached to these cam grooves  53 ,  53 . 
     The slider  56  not only has, on the termination end portion side thereof, a contact piece  56   a  that comes in contact with the carriage  1 , but also has a holder receiving portion formed at a location that is apart from the contact piece  56   a  by a distance L S  as shown in FIG.  6 ( a ), the holder receiving portion serving to support the cap  80 . The distance L S  is equal to a length L C  that is the longitudinal length of the cap  80 . The slider  56  has, on both sides thereof, guide pieces  56   b ,  56   b  that guide the recording head  5 . The slider  56  also has the termination end portion side thereof supported with the projections  57  thereof attached to the cam grooves  53  of the cap frame  51 , and has the start end portion side thereof held by a lever  59  constituting a link that is rotatably urged toward the termination end portion side by a spring  58 . 
     As shown in FIG.  6 ( a ), each projection  57  is formed at a location substantially flush with a sealing surface  80   a  of the cap  80  (ΔH≈0). As a result of this construction, the displacement ΔL 1  can be minimized, ΔL 1  being the horizontal displacement resulting from the slider  56  rotating about the projections  57  at the time of sealing the recording head  5  after having moved to the capping position. Unlike this construction, if the projection  57  is formed at a different location ( 57 ′), higher or lower, a larger displacement ΔL 2  results, thereby making it more difficult to provide reliable sealing. 
     Further, the lever  59  that supports the lower portion of the slider  56  is designed as shown in FIG.  6 ( b ) so that the length of the arm provides a lift ΔH 1  which is greater than the lift ΔH 2  provide by the sloped portions  53   a  of the cam grooves  53 . It may be noted that loads to be applied during capping can be reduced by making the sloped portions  53   a  more horizontal. As a result, by reducing impact to the carriage  1  while reducing the current for driving the carriage motor  2 , trouble such as missing dots caused by the recording head  5  breaking the meniscuses is prevented. Therefore, printing reliability can be ensured. Further, the length of the lever  59  can be reduced by an amount corresponding to the reduced loads to be applied during capping, so that the horizontal displacement of the slider  56  which is determined by the distance rotated by the lever  59  can be restricted. As a result, the overall size of the capping unit can be reduced. 
     The slider  56  meshes with the distal end of the lever  59  through a meshing hole  60  that has a length L and that is formed in the lower portion thereof That is, the slider  56  is coupled to the lever  59  with a degree of freedom equivalent to the length L of the meshing hole  60  (FIG.  6 ( a )), so that the slider  56  can be drawn toward the start end portion side, i.e., the lower end portion side of the sloped portions  53   a  while maintaining the uncapped condition. As a result, wherein the uncapped condition, a stopper surface  63   b  of the cap holder  63  is displaced to a region confronting the front end face of the cleaner unit  10  by moving the lowest level region of the slider  56  up to such a location as to overlap the cleaner unit  10  operating region, which in turn prevents the cleaner unit  10  from projecting into the carriage  1  moving region. As a result, the capping unit  9  can be disposed as close to the recording sheet  4  side of the carriage  1  moving path as possible, i.e., without providing a large safety tolerance. Hence, the width of the recording apparatus can be reduced. 
     The slider  56  has spring receiving seats  62 ,  62  formed on the upper surface thereof. The spring receiving seats  62 ,  62  are scattered on left and right sides of the slider  56  so as to be symmetrical about the centerlines extending along the length and across the width of the cap  80 , and scattered in the carriage  1  moving direction. The slider  56  also has projections  65 ,  65 ′ formed on both sides of the start end portion side thereof, the projections  65 ,  65 ′ being meshable with grooves  64 ,  64 ′ of the cap holder  63 . Further, the slider  56  has a groove  67  formed along the longitudinal centerline on the termination end portion side thereof, the groove  67  being meshable with a projection  66  of the cap holder  63 . 
     The cap holder  63  has spring receiving portions  68 ,  68  that project from both sides thereof. It is in these spring receiving portions  68 ,  68  that spring receiving seats  69 ,  69  are arranged so as to be scattered in the carriage  1  moving directions. The cap holder  63  also has the grooves  64 ,  64 ′ formed on both sides of the start end portion side thereof, the grooves  64 ,  64 ′ being meshable with the projections  65 ,  65 ′ of the holder  56 . Further, the cap holder  63  has the projection  66  formed along the longitudinal centerline on the termination end portion side thereof, the projection  66  being meshable with the groove  67  of the slider  56 . The bottom surface of one of the grooves  64 ,  64 ′ is slightly higher than that of the other groove  64 ,  64 ′ or the bottom surface one of the projections  65 ,  65 ′ is slightly higher than that of the other projection  65 ,  65 ′. As a result, the cap holder  63  is supported at three points so as to allow one side of the start end portion side thereof to take a slightly lower position with respect to the slider  56 . Accordingly, the grooves  64 ,  64 ′ of the cap holder  63  mesh with the projections  65 ,  65 ′ of the slider  56 , with the projection  66  of the cap holder  63  meshes with the groove  67  of the slider  56 , and compression springs  70  are interposed between the respective spring receiving portions  62 ,  69  so that the cap holder  63  is urged upward. Specifically, the cap holder  63  is set so that one side of the cap holder  63  is at least lmm lower with respect to the slider  56 , or one side of the cap holder  63  is inclined with respect to the nozzle surface of the recording head  5  at an angle of 2 degrees or more. 
     Further, since the cap holder  63  is supported at the three points, the positioning height of the sealing surface of the cap  80  that is accommodated in the cap holder  63  can be adjusted more correctly. Further, the cap  80  can be easily removed from the recording head  5  by applying a peeling force to the cap holder  63  with a point outside the cap  80  as a fulcrum since the moment of the force is large, the cap  80  is easily removed, even when stuck to the recording head  5  due to solidification of the ink or the like. It must be appreciate that the cap holder  63  is resiliently urged toward the recording head  5  by the compression sprigs  70  which are located to the outside of the sealing region. Therefore, assuming that the compression forces to be applied by the compression springs  70  are Pa, Pb; the distances from the springs  70  to the cap  80  sealing points are La, Lb; and the distance between the sealing points, i.e., the width of the cap  80  is W, the reaction forces Ra, Rb at the respective sealing points are given as follows: 
     Ra={Pa (W+La)−Pb·Lb}/W; and 
     Rb={Pb (W+Lb)−Pa·La}/W. 
     Then, in order to allow the cap  80  to be in uniform contact with the recording head  5 , the reaction forces Ra, Rb applied to the respective sealing points must be identical to each other. Therefore, the conditions; 
     {Pa (W+La)−Pb·Lb}={Pb (W+Lb)−Pa·La}; and 
     Pa (W+2La)=Pb (W+2Lb). 
     that is, 
     Pa=Pb; and 
     La=Lb, 
     must be satisfied. 
     To satisfy the above conditions, the compression springs  70  having similar elastic properties are used on both sides, and these springs  70  are laid out so as to be symmetrical with respect to the cap  80 . 
     On the other hand, since the cap holder  63  is positioned with one side of the start end portion side being slightly lower than the other side, there is a disequilibrium in the loads to be applied when the cap  80  comes into contact with the recording head  5 . 
     As shown in FIG.  8 ( b ), reaction forces Ra, Rd at the support points A, D are given, respectively, as follows. 
     Ra={Pa (W′+La)−Pb·Lb′}/W′; and 
     Rd={Pb (W′+Lb′)−Pa·La}/W′. 
     Then, since the loads Pa, Pb are set to the same value as described above, 
     Ra=Pa+{Pa (La−Lb′)}/W′; and 
     Rd=Pa+{Pa (Lb′−La)}/W′. 
     Further, since La&gt;Lb′, it is axiomatic that {Pa (La−Lb′)}/W′&gt;0. 
     Hence, 
     Ra=Pa+{Pa (La−Lb′)}/W′&gt;Pa 
     When the cap  80  comes into contact with the recording head  5 , a load that is larger by {Pa (La−Lb′)}/W′ than the load Pa to be applied by the springs  70  themselves is applied to each contact point. As a result, self-aligning properties and contacting properties are increased. Although it is proposed to set W′ and Lb′ to smaller values and La to a larger value in order to increase the incremented load {Pa (La−Lb′)}/W′ to be applied at the initial stage of contact, it is more realistic to set La to a larger value and Lb′ to a smaller value since W′ depends on the size of the cap  80 . 
     FIG.  8 ( c ) shows a relationship between the distance between the cap and the recording head and the load to be applied by the cap to the recording head, the relationship being observed between the cap of the invention and a conventional cap that is held by two springs located along a centerline inside the cap sealing region. The cap of the invention whose characteristics are indicated by the solid line A can ensure that an adequate load can be given at the initial stage of contact, whereas the conventional cap whose characteristics are indicated by the dashed line B indicates that the full contact load is applied for the first time only immediately before the cap fully contacts the recording head. 
     The cap holder  63  has two projections  71  erected along the longitudinal centerline of the bottom surface  63   a  thereof, and two cylindrical bodies  72 ,  73  formed on the start end portion side thereof so as to be symmetrical about the longitudinal centerline. The cylindrical body  73  is connected to the tube  35  of the pump unit  11  while vertically extended to the outside. The cylindrical body  72  is connected to a valve seat  75  (described later) through a tube  74  while extended to the outside, the tube  74  extending in parallel to the bottom surface and bent toward the termination end portion side. Since the tubes  35 ,  74  are attached to the cap holders  64  at locations which are as close to the longitudinal centerline of the cap  80  as possible and are disposed vertically with respect to the cap and parallel to the moving direction of the cap, the bending moment to be applied to the cap  80  is advantageously reduced as much. 
     The valve seat  75  is fixed to the termination end portion of the slider  56 , and has a valve  77  fixed thereto. An operation rod  79  is attached to the slider  56  not only in such a manner as to be sidable in the carriage moving directions while coming in contact with a contact piece  76  disposed on the cap frame  51 , but also at a location confronting the valve  77  so that the valve  77  can maintain the closed position at all times while urged by a spring  78 . 
     The cap holder  63  holds the cap  80  therein with recesses  81 ,  82 , projections  71 , and claws  83  formed in and on the cap  80 . The cap is made of an elastic member such as rubber having ink resistance. The cap  80  has recesses  84 ,  85  formed in the bottom surface thereof, the recesses  84 ,  85  communicating with the cylindrical bodies  72 ,  73 , and holds two ink absorbing sheets  86 ,  87  with claws  83 . The ink absorbing sheets  86 ,  87  are made of a porous material having ink resistance. 
     FIG. 9 shows an embodiment of the cut sheet feeder  12  in the form of a cut sheet mechanism. The cut sheet feeder  12  includes a hopper  90 , a separation pad  94 , and a sheet feed roller  100 . The hopper  90  has the lower back surface thereof urged toward the sheet feed roller by a spring  92  that is interposed between a frame  91  and itself. Further, the separation pad  94  that is urged in a normal direction of the sheet feed roller  100  by a spring  93  is disposed on a lower hopper surface confronting the sheet feed roller  100 . The separation pad  94  is moved up and down by a cam (not shown) so as to be interlocked with the sheet feed operation while the sheet feed roller  100  is making a single revolution, the cam being disposed on the sheet feed roller drive shaft  16 . 
     The sheet feed roller  100  has an arcuate portion  100   a  and a straight portion  100   b , and is therefore D-shaped in cross section so that a high frictional force can be caused with respect to a recording sheet. The sheet feed roller  100  is attached to the sheet feed roller drive shaft  16  through a bushing  101 , and makes a single revolution during sheet feed operation while driven by the sheet forward motor  7  through the gear  17 . The bushing  101  has a cam surface  102  formed thereon so that the cam surface  102  extends around the central shaft excluding a bushing  101  region opposite to the straight portion  100   b  of the sheet feed roller  100 . The cam surface  102  allows an idle roller  103  to move therethrough. The idle roller  103  is rotatably held by a shaft  105  that is movable within an elongated hole  104  in the frame  91 , and is attached so as to be vertically movable with respect to the separation pad  94 . 
     As a result of such construction, when the sheet feed roller  100  reversely rotates (counterclockwise in FIG. 9) through a predetermined angle, the separation pad  94  is separated from the sheet feed roller  100  by a cam mechanism (not shown), and the recording sheet is bounced back to the hopper  90  by a not shown sheet return lever (not shown). Substantially simultaneously with the returning of the recording sheet to the hopper  90 , the separation pad  94  is pressed onto the sheet feed roller  100 . Then, when the sheet feed roller  100  rotates clockwise, the hopper  90  is instantaneously pushed up by the spring  92 , and sheets P are also pushed up, so that the arcuate portion  100   a  of the sheet feed roller  100  is pressed against the uppermost sheet. As the sheet feed roller  100  continues to rotate, such uppermost sheet is fed toward the separation pad  94 . By threading the recording sheet between the separation pad  94  and the sheet feed roller  100  through rotation of the arcuate portion  100   a , a single sheet is separated by the separation pad  94  out of a plurality of recording sheets, and the separated sheet is further forwarded to the forward roller  8 . At this point in time, the arcuate portion  100   a  of the sheet feed roller  100  has passed through the separation pad  94  and the straight portion  100   b  confronts the separation pad  94 . Therefore, it is the idle roller  103  pressed against the cam surface  102  that pushes the recording sheet onto the separation pad  94 , which in turn prevents a plurality of unseparated recording sheets from being forwarded to the forward roller  8  superfluously. Then, when the sheet feed roller  100  makes another revolution, the sheet feed mechanism is reset to the original condition, and therefore ready for next sheet feed operation. 
     A description of the operation of the apparatus according to the present invention follows. 
     During stoppage, the carriage  1  is locked with the retaining projection  44  of the cleaner unit  10  by pressing with the carriage stopper  1   a  as shown in FIG.  10 . Therefore, the sheet forward motor  7  is rotated forwardly to thereby evacuate the cleaner unit  10  from the recording head  5  and unlock the carriage as shown in FIG. 11 (S 100 ). As a result, the carriage  1  is movable, so that the carriage  1  is moved slightly toward the start end portion to thereby form a gap ΔG between the recording head  5  and the cap  80  as shown in FIG. 12 (S 101 ), and a flushing signal is supplied to the recording head  5  under this condition to thereby jet ink droplets onto the cap  80  out of nozzles (S 102 ). Since the cap  80  surface is inclined by an angle θ with respect to the nozzle surface of the recording head  5  under this condition, the possibility that ink splashes bounced back from the ink absorbing sheet  86  will deposit on the nozzle surface is significantly reduced. Since the slight movement of the carriage toward an end of the sheet is contained within the length L of the meshing hole  60  of the lever  59 , the lever  59  remains inoperative. Therefore, even if the carriage  1  comes into contact with the slider  56 , the resulting shock applied to the carriage  1  is absorbed, which in turn prevents the recording head  5  from damaging the meniscuses and hence ensures reliable printing operations. 
     Then, by moving the carriage  1  to the end portion confronting the home position, the gear  13  is meshed with the gear  17  of the sheet feed roller drive shaft  16  by the clutch mechanism  18  (S 103 ), and the sheet forward motor  7  is rotated reversely slightly to thereby cause the cut sheet feeder  12  to perform the sheet return operation (S 104 ). The drive force from the rachet wheel  31  is not transmitted to the pump wheel  33  since there is a transmission delay between the rachet wheel  31  and the intermediate transmission wheel  32 . Therefore, the cut sheet feeder  12  can perform the sheet return operation without applying unnecessary loads to the sheet forward motor  7 . Then, when the sheet forward motor  7  is rotated forwardly, the sheet feed roller  100  is rotated forwardly to thereby feed a recording sheet to the nipping region of the forward roller  8  (S 105 ). 
     Then, by moving the carriage  1  toward the home position, the gear  13  is unmeshed from the gear  17  of the sheet feed roller drive shaft  16  by the clutch mechanism  18  (S 106 ), and the sheet forward motor  7  is rotated reversely and the sheet is paid out of the forward roller  8  to thereby eliminate a skew of the recording sheet (S 107 ). 
     By moving the carriage  1  to the position at which the clutch mechanism  18  can perform the meshing operation, the gear  13  is meshed with the gear  17  of the sheet feed roller drive shaft  16  (S 108 ), and the sheet forward motor  7  is rotated forwardly to thereby forward the recording sheet to the forward roller  8 , and the cut sheet feeder  12  is reset (S 109 ). Then, by moving the carriage  1  toward the home position to thereby cause the clutch mechanism  18  to release the meshing of the gear  13  with the gear  17  of the sheet feed roller drive shaft  16  (S 110 ), and the sheet forward motor  7  is rotated reversely to thereby cause the forward roller  8  to locate the head end of the sheet to a predetermined position (S 111 ), and further the sheet forward motor  7  is rotated forwardly to thereby perform sheet positioning and backlash eliminating operations (S 112 ), and printing operation is thereafter started (S 113 ). Since forward and reverse rotations of the sheet forward motor  7  in these operations are made only slightly and alternately, a transmission delay caused by the intermediate transmission wheel  32  keeps the pump unit  11  inoperative. As a result, it is only loads necessary to forward the sheet that is applied to the sheet forward motor  7 . 
     When the printing operation has been started with the sheet thus set, the sheet forward motor  7  rotates forwardly to forward the sheet by a distance equivalent to a single line every time the recording head  5  ends printing a single line of data. Although there is no transmission delay caused by the intermediate transmission wheel  32  because of the successive forward rotation of the sheet forward motor  7 , the pump unit  11  rotates with the rollers  34  which are drawn toward the center. Therefore, the pump unit  11  does not function as a pump, so that there is no likelihood that the pump unit  11  will apply unnecessary loads to the sheet forward motor  7 . 
     While the recording head  5  is printing with the sheet forward motor  7  rotating forwardly and with the carriage  1  moving to and from within the printing region, not only the cleaner unit  10  in the reset position, i.e., in the evacuated position, which is out of the recording head  5  travelling region as shown in FIG. 13, but also the slider  56  of the capping unit  9  is lowered by the lever  59  that is urged by the spring  58 . Therefore, even if the recording head  5  has moved above the cap  80 , there is no likelihood that both will come in contact with each other. Further, the slider  56  has moved toward the printing region by a distance equivalent to the length L of the meshing hole  60  of the lever  59  while urged by a return spring  61 , so that the stopper surface  63   b  of the cap holder  63  confronts the cleaner unit  10 . As a result, even if the sheet forward motor  7  is rotated reversely, i.e., in such a direction as to drive out the cleaner unit  10  toward the recording head  5  travelling region, the cap holder  63  blocks the cleaner unit  10  from plunging into the recording head  5  travelling region. Hence, any situation affecting the recording operation can be prevented. 
     When the recording operation has been brought to an end, the carriage  1  is moved to the home position by the carriage motor  2 . During the movement of the carriage  1 , the carriage  1  comes into contact with the contact piece  56   a  of the slider  56  as shown in FIG. 14, so that slider  56  is moved toward the termination end portion against the return spring  61  while rotating the lever  59  against the spring  58 . During the movement of the slider  56 , the lever  59  is lifted in association with the movement of the carriage  1 , and the projections  57  of the slider  56  move along the sloped portions  53   a  of the cam grooves  53 . When the slider  56  pushed by the carriage  1  has the projections  57  thereof moved to the horizontal portions  53   b  of the cam grooves  53 , the cap  80  has, first of all, one point on the termination end portion side thereof come in contact with the nozzle surface of the recording head  5  with the compression force of all the compression springs  70  during such movement of the projections  57  along the horizontal portions  53   b , because the cap holder  63  is attached to the slider  56  so that one side on the start end portion side of the cap holder  63  takes a slightly lower position. 
     As shown in FIG. 15, when the slider  56  has reached the termination end portion, the entire circumference of the cap  80  receives the compression force from all the compression springs  70 , so that the cap  80  comes in contact with the nozzle surface of the recording head  5  to thereby seal the nozzle surface reliably. From the initial condition in which the cap  80  comes in contact with the nozzle surface to the final condition in which the cap  80  totally seals the nozzle surface, the projections  57  are substantially flush with the sealing surface  80   a  of the cap  80  (ΔH≈0). Therefore, the amount of horizontal displacement _L 1  is very small, i.e., the amount of displacement resulting from the slider  56  rotating about the projections  57  at the time of moving to the capping position as shown in FIG.  6 ( c ), so that the cap  80  can come in contact with the nozzle surface of the recording head  5  reliably, which in turn allows the cap  80  to seal the nozzle surface reliably. 
     In the thus sealed condition, the stopper surface  63   b  of the cap holder  63  is evacuated from the cleaner unit  10 . Therefore, when the sheet forward motor  7  is rotated reversely, the cleaner cam  29  that has rotated counterclockwise as viewed in FIG. 3 together with the gear  26  causes the cleaner unit  10  to project toward the recording head  5  travelling region by the arm  28  thereof. When the sheet forward motor  7  is rotated in the reverse direction so that the cleaning unit  10  comes immediately before the cleaning position, the retaining projection  44  of the cleaner unit  10  gets meshed with the carriage stopper  1   a  to thereby lock the carriage  1 , so that unnecessary movement of the carriage  1  is blocked as shown in FIG.  10 . 
     When the recording head  5  has been clogged due to the printing operation and the like performed over a long period of time, the recording head  5  must be cleaned. Not only the sheet forward motor  7  is rotated forwardly from the sealed condition shown in FIG. 10 to thereby discharge the recording sheet, but also the cleaner unit  10  is evacuated from the recording head  5  to thereby unlock the carriage as shown in FIG. 15 (S 114 ). Since the carriage  1  is set movable as a result of such operation, when the carriage  1  is moved further toward the termination end side up to a location shown in FIG. 16 from the capped condition shown in FIG. 15, the operation rod  79  disposed on the slider  56  comes in contact with the contact piece  76  of the cap frame  51  to thereby open the valve  77  of the valve seat  75  to the atmosphere (S 115 ). 
     When the sheet forward motor  7  is rotated reversely under this condition, the cleaner unit  10  comes to project into the recording head  5  travelling path, so that the cleaner unit  10  is set to the cleaning position as shown in FIG. 17 (Si 16 ). The current reverse rotation of the sheet forward motor  7  comes after the last forward rotation. Therefore, the current reverse rotation of the sheet forward motor  7  is not transmitted to the pump wheel  33  by the intermediate transmission wheel  32 , so that the pump unit  11  remains inoperative. 
     Then, by moving the carriage  1  toward the start end portion, the cleaning blade  39  comes into contact with the nozzle surface of the recording head  5  as shown in FIG.  18 . Therefore, by moving the carriage  1  to a wipe end position, the ink deposited on the nozzle surface can be wiped off (S 117 ). Since the cleaning blade  39  is in contact with the cap holder  63  at this time, the ink deposited onto the cleaning blade  39  as a result of the wiping operation is transferred to the cap holder  63  or to the cap  80 . Therefore, the amount of ink remaining on the cleaning blade  39  can be kept as small as possible, which in turn ensures reliability in the wiping operation. 
     Upon completing of the cleaning operation, the sheet forward motor  7  is rotated forwardly in an amount equal to the reverse rotation of the motor  7 , so that not only the cleaner unit  10  is returned to the evacuated position again as shown in FIG. 19 (S 118 ), but also the carriage  1  is moved to an idle sucking position to thereby move the slider  56  to the termination end portion and set the recording head  5  ready for idle sucking as shown in FIG. 16 (S 119 ). The sheet forward motor  7  is rotated in an amount equivalent to a transmission delay caused by the intermediate transmission wheel  32  (S 120 ), and the carriage  1  is moved slightly toward the start end portion to thereby set the recording head  5  in the sealed condition shown in FIG. 15 (S 121 ). As a result of this operation, the slider  56  moves away from the termination end portion, so that the operation rod  79  on the slider  56  also moves away from the contact piece  76  of the cap frame  51  and hence closes the valve  77  with the urging force of the spring  78 . 
     When the sheet forward motor  7  is rotated reversely under this condition, the motive force is transmitted to the pump unit  11 , and a sucking force is applied to the cap  80 . As a result, the ink is sucked from the recording head  5  at high pressure to be forcibly discharged therefrom, which in turn unclogs the nozzles (S 122 ). The carriage  1  is moved slightly toward the termination end portion to thereby set the recording head  5  in the idle sucking position shown in FIG. 16 (S 123 ), and the sheet forward motor  7  is rotated reversely at a low speed to thereby allow only the ink remaining in the cap  80  to be sucked without applying unnecessary sucking force to the recording head  5 , and the sucked ink is thereafter discharged into a waste ink tank (not shown) (S 124 ). Upon completing the idle sucking, the cleaner unit  10  is set in the position shown in FIG. 17, so that the sheet forward motor  7  is rotated forwardly to evacuate the cleaner unit  10  (S 125 ) and to move the carriage  1  to the wipe end position (S 126 ). 
     Upon completing the cleaning operation, the sheet forward motor  7  is rotated reversely to thereby eliminate a transmission delay of the intermediate transmission wheel  32  caused by the last forward rotation of the motor  7  (S 127 ) and to operate the pump unit  11 , so that the pump unit  11  sucks the ink remaining in the cap  80  with a strong sucking force without applying sucking force to the recording head  5  (S 128 ). 
     Then, the sheet forward motor  7  is rotated forwardly to thereby evacuate the cleaner unit  10  from the recording head  5  travelling path as shown in FIG. 16 (S 129 ). Further, the carriage  1  is moved toward the termination end portion again to thereby allow the cap  80  to seal the recording head  5  in the idle sucking condition as shown in FIG. 16 (S 130 ). Since the cleaner unit  10  has been evacuated from the recording head  5  travelling path, there is no likelihood that the cleaning blade  39  will come in contact with the nozzle surface of the recording head  5 . 
     The sheet forward motor  7  is rotated reversely to thereby eliminate a transmission delay caused by the intermediate transmission wheel  32  (S 131 ), and the carriage  1  is moved slightly toward the start end portion to thereby set the recording head  5  in the sealed condition shown in FIG. 15 (S 132 ). As a result of this operation, the slider  56  moves away from the termination end portion, so that the valve  77  is closed by the operation rod  79 . 
     When the sheet forward motor  7  is rotated reversely at a low speed under this condition, the motive force is transmitted to the pump unit  11  to thereby allow a weak sucking force to be applied to the cap  80 . As a result, the ink is forcibly discharged out of the recording head  5  with the weak sucking force, which in turn allows the meniscuses in the nozzles to be recovered (S 133 ). Upon completing the sucking operation, the carriage  1  is moved slightly toward the termination end portion to thereby set the recording head  5  in the idle sucking condition shown in FIG. 16 (S 134 ). Then, the sheet forward motor  7  is rotated reversely at a low speed, so that such a sucking force as not to cause the ink to be jetted out of the recording head  5  is applied to suck only the ink remaining in the cap  80 , and the sucked ink is thereafter discharged into the not shown waste ink tank (S 135 ). Upon end of the idle sucking operation, the cleaner unit  10  is set as shown in FIG. 17 by the low-speed reverse rotation of the sheet forward motor  7  performed in the aforementioned step (S 135 ). Therefore, when the carriage  1  is moved to the wipe end position as shown in FIG. 18, wiping operation is performed (S 136 ). 
     The sheet forward motor  7  is rotated reversely upon end of the cleaning operation. Since the current reverse rotation of the motor  7  is a succession of the last reverse rotation, the pump unit  11  is operated without having any transmission delay caused by the intermediate transmission wheel  32 . As a result, the ink remaining in the cap  80  is sucked at a high negative pressure without applying sucking force to the recording head  5  (S 137 ). The sheet forward motor  7  is rotated forwardly in an amount equivalent to a transmission delay caused by the intermediate transmission wheel  32  to thereby evacuate the cleaner unit  10  from the recording head  5  travelling path as shown in FIG. 19 (S 138 ). Further, the carriage  1  is moved toward the termination end portion again to thereby allow the cap  80  to seal the recording head  5  in the idle sucking condition as shown in FIG. 16 (S 139 ). Since the cleaner unit  10  has been evacuated from the recording head  5  travelling path, there is no likelihood that the cleaning blade  39  will come in contact with the nozzle surface of the recording head  5 . The sheet forward motor  7  is rotated reversely to thereby eliminate a transmission delay of the intermediate transmission wheel  32  caused by the last forward rotation of the motor  7  (S 140 ), and the carriage  1  is moved slightly toward the start end portion to thereby set the recording head  5  in the sealed condition shown in FIG.  15  and close the valve  77  (S 141 ). 
     When the sheet forward motor  7  is rotated reversely at a low speed under this condition, the motive force is transmitted to the pump unit  11  to thereby allow a weak sucking force to be applied to the cap  80 . As a result, the ink is forcibly discharged out of the recording head  5  with the weak sucking force, which in turn allows the meniscuses in the nozzles to be recovered (S 142 ). Upon completing the sucking operation, the carriage  1  is moved slightly toward the termination end portion to thereby set the recording head  5  in the idle sucking condition shown in FIG. 16 (S 143 ). Then, the sheet forward motor  7  is rotated reversely at a low speed, so that only the ink remaining in the cap  80  is sucked by such a sucking force as not to cause the ink to be jetted out of the recording head  5  (S 144 ). 
     Upon completing of the idle sucking operation, the cleaner unit  10  has already been set as shown in FIG. 17 by the low-speed reverse rotation of the sheet forward motor  7  performed in the aforementioned step (S 144 ). Therefore, by moving the carriage  1  to the wipe end position shown in FIG. 18, the wiping operation is performed (S 145 ). 
     The sheet forward motor  7  is rotated reversely upon completing of the cleaning operation. Since the current reverse rotation of the motor  7  succeeds the last reverse rotation, the pump unit  11  is operated without having any transmission delay caused by the intermediate transmission wheel  32 . Therefore, the pump unit  11  sucks the ink remaining in the cap  80  with a strong sucking force with the cap  80  released from the recording head  5 , and the ink in the cap  80  is thereafter discharged into the waste ink tank reliably (S 146 ). When the sheet forward motor  7  is rotated in the forward direction until the projection  32   b  of the intermediate transmission wheel  32  comes in contact with the projection  33   a  of the pump wheel  33  to thereby rotate the pump wheel  33  slightly, the cleaner unit  10  is reset, and the rollers  34  of the pump unit  11  move toward the center of the pump wheel  33  to thereby move away from the tube  35 , so that the pump unit  11  is set in the released condition (S 147 ). 
     When all the cleaning processes have been terminated, the carriage  1  is moved to the home position to be set in the condition shown in FIG.  15 . As a result, the entire circumference of the cap  80  comes into contact with the nozzle surface of the recording head  5  while receiving the compression force of all the compression springs  70 , so that the cap  80  can seal the recording head  5  reliably (S 148 ). Then, by skipping the flushing operation (S 149 ), the sheet forward motor  7  is rotated reversely to thereby mesh the retaining projection  44  of the cleaner unit  10  with the carriage stopper la as shown in FIG. 10, so that the carriage  1  is locked to thereby block unnecessary movement thereof (S 150 ). 
     It is contemplated that numerous modifications may be made to the Ink Jet Recording Apparatus of the present invention without departing from the spirit and scope of the invention as defined in the following claims.