Patent Publication Number: US-7708376-B2

Title: Device for cleaning an inkjet printhead

Description:
BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The invention relates to a device for cleaning an inkjet printhead, in particular in a franking and/or addressing machine. It has proven worthwhile to utilize the advantages of inkjet printing in the area of mechanical franking and/or addressing as well. In this case, the printing is carried out without contact by an inkjet printhead, see for example German patent DE 44 24 771 C1 (corresponding to U.S. Pat. No. 6,367,911) and European patent EP 0 696 509 B1 (corresponding to U.S. Pat. No. 6,390,577). However, the inkjet printing technique has the disadvantage that more ink is used for cleaning the inkjet printhead than for the printing operation. This is particularly serious in the case of individual printing. 
   A franking machine is known in which the print carriers or letters are conveyed on edge, inclined beyond the vertical for reasons of stability, with the aid of a transport belt; in this regard see German patents DE 196 05 014 C1 (corresponding to U.S. Pat. No. 5,880,747) and DE 197 57 653 C2 (corresponding to U.S. Pat. No. 6,477,511). In this case, the letter is located behind a clear-view plate on a guide plate, in which a printing window is provided and in which the inkjet printhead is disposed in a stationary manner such that its nozzle surface is disposed parallel to the guide plate. The letter is led past the printing window and the inkjet printhead and, during this, is printed on the side facing away from the viewer. 
   The problem of inkjet printhead cleaning and sealing is in this case solved by a device for cleaning the inkjet printhead, see European patent EP 0 799 135 B1, in which the inkjet printhead is fixed such that it can be pivoted alternatively from a printing position into a cleaning position and/or sealing position and back again, and the cleaning and sealing device is disposed such that it can be displaced linearly toward the inkjet printhead and away from the latter again. 
   The cleaning and sealing device contains a sealing cap matched to the inkjet printhead and having suction slots for each row of nozzles and a wiping lip that can be displaced transversely, as well as a downstream suction pump. Also provided in the sealing cap, at one end, is an extraction region having a suction opening for the wiping lip. The wiping lip is displaced by a spindle drive. 
   As an addition to this, a device for positioning an inkjet printhead and a cleaning and sealing device are known, see German patent DE 197 26 642 C1 (corresponding to U.S. Pat. No. 6,224,187), in which, for the displacement of the inkjet printhead and the cleaning and sealing device, a common gear mechanism is provided which is driven by a motor which runs in only one direction of rotation. The inkjet printhead, the cleaning and sealing device and the entire gear mechanism including motor are fixed in a common frame and in this way are combined to form a compact subassembly. This subassembly is in turn adjustably fixed to the transport device. The inkjet printhead can be pivoted by more than 90° from the printing position into the cleaning position and back again. The cleaning and sealing device is disposed underneath the inkjet printhead such that it can be displaced linearly vertically. During the cleaning operation, the cleaning and sealing device is docked on the inkjet printhead pivoted downwards. Accordingly, the procedure is also the same during spraying clear. 
   With the solutions described above, the letter transport is interrupted during the cleaning process and, accordingly, the letter throughput is reduced. In the event of spraying clear operation in the printing position during the letter transport, either the letter or the letter run—clear-view plate, transport belt—is noticeably soiled. 
   On the other hand, a franking machine having an inkjet printhead is known, see European patent EP 0 696 509 B1 (corresponding to U.S. Pat. No. 6,390,577) and U.S. Pat. No. 5,806,994, in which the letters are transported lying horizontally and the nozzle surface is disposed parallel thereto. In this machine, the nozzles that are used a little or not used during the printing are sprayed clear as long as there is no letter present in front of the printhead. For this purpose, the letter transport device is provided with appropriate cutouts and a collecting container for the ink sprayed clear is disposed underneath the same. The ink consumption is reduced in this way but the horizontal letter transport is a precondition for this. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the invention to provide a device for cleaning an inkjet printhead which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which improves the print quality, prolongs the service life of the printing device, and provides the highest possible letter throughput. 
   With the foregoing and other objects in view there is provided, in accordance with the invention, a franking and/or addressing machine. The machine contains a guide plate having a printing window, an inkjet printhead disposed in a stationary manner and is pivotable behind the guide plate in the printing window, and a transport device for guiding a print carrier along in contact and standing on one edge by the transport device. A cleaning and sealing device is disposed behind the guide plate and underneath the inkjet printhead. A first displacement device is provided for pivoting the inkjet printhead into a printing position, into various cleaning regions, and into a sealing position. A second displacement device is provided for displacing the cleaning and sealing device toward the inkjet printhead and away from the inkjet printhead. A pivotably mounted matched baffle piece is disposed underneath the inkjet printhead and is coupled to the inkjet printhead. A common ink sump is disposed underneath all of the above components. 
   In the device for cleaning an inkjet printhead in a franking and/or addressing machine, in which the letters are transported standing on one edge and the inkjet printhead is disposed in a stationary manner behind a guide plate such that it can be pivoted, and in which, in addition to the usual functions such as wiping and sealing, a spraying clear function is possible both during the letter transport and also in the rest position without the letter run being soiled. 
   In accordance with an added feature of the invention, the inkjet printhead has a nozzle surface and the guide plate is inclined beyond a vertical. The inkjet printhead is disposed such that the inkjet printhead can be pivoted appropriately by more than 85° from the printing position, in which the nozzle surface is disposed parallel to the guide plate, to an end of an outermost cleaning region and back again. Stops are provided including a first stop and a second stop defining pivot positions of the inkjet printhead. The inkjet printhead is an integral constituent part of a printing module, the printing module being inserted into a module holder. 
   In accordance with another feature of the invention, the cleaning and sealing device has a device holder with wiping lips, a spray duct, and sealing caps. All of these components are disposed in the order cited behind the guide plate. 
   In accordance with a further feature of the invention, the first displacement device includes a worm gear mechanism, an actuating motor and a rotary encoder for displacing the module holder and, consequently, also the inkjet printhead. In the printing position, the inkjet printhead is fixed by the first stop, and in an end position the inkjet print head is fixed by the second stop in the outermost cleaning region, the stops being used to calibrate the rotary encoder. The sealing position is fixed by the rotary encoder in accordance with a predefined setting wherein the nozzle surface is disposed orthogonally with respect to the wiping lips of the cleaning and sealing device. Sensors are provided for triggering various positions of the inkjet printhead, the sensors are disposed in a region of a letter run and linked to a control computer. 
   In accordance with an additional feature of the invention, the second displacement device for displacing the cleaning and sealing device has a spindle gear mechanism, an actuating motor, a guide shaft and a further sensor for defining a reference point setting. 
   In accordance with a further added feature of the invention, a holder is provided. The inkjet printhead is resiliently and kinematically coupled via the holder to the matched baffle piece, the matched baffle piece being configured as a shell. 
   In accordance with another additional feature of the invention, a wheel is fixed to the module holder holding the printing module such that the module holder can rotate. A guide edge is integrally molded on an outside of the matched baffle piece, the matched baffle piece is connected to the module holder via a tension spring. The wheel bears with a force on the guide edge and, with the guide edge, forms a slotted guide for the matched baffle piece. 
   In accordance with yet another feature of the invention, the common ink sump has a device holder being open at a front, an insert with a nonwoven and a securing clip, guided in the device holder. The device holder further has a handle for allowing easy replaceability. 
   In accordance with the invention, in a first cleaning region, for performing a spraying clear function, the inkjet printhead is pivoted so far away from the printing position that there is at least twice a distance from the print carrier but all ink drops still reach the print carrier. In a second cleaning region, for performing a spraying clear function, the inkjet printhead is pivoted so far away from the printing position that all ink drops already or still strike the matched baffle piece. In a third cleaning region, for performing a spraying clear function, the inkjet printhead is pivoted so far away from the printing position that all ink drops strike the nonwoven directly, and this also defines a position in which the spraying clear is carried out through the spray duct. In a fourth cleaning region, for performing a wiping function, the inkjet printhead is pivoted so far away from the printing position that the nozzle surface is disposed in an engagement region of the wiping lips. 
   In accordance with a further added feature of the invention, a carrier with wipers is provided for cleaning the wiping lips, the carrier is disposed in a stationary manner in an engagement region of the wiping lips. 
   In accordance with a concomitant feature of the invention, for assuming a sealing position, the inkjet printhead is docked on the cleaning and sealing device being previously positioned, and therefore on the sealing caps, coming from the fourth cleaning region, and is undocked going into the same. 
   Other features which are considered as characteristic for the invention are set forth in the appended claims. 
   Although the invention is illustrated and described herein as embodied in a device for cleaning an inkjet printhead, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
   The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front, left perspective view of a printing system in a printing position I in a franking machine having a cleaning and sealing device and a transport device according to the invention; 
       FIG. 2  is a front, left perspective view of the printing system in a sealing position VI in the franking machine having the cleaning and sealing device; 
       FIG. 3  is a rear left perspective view of the printing system in the printing position I in the franking machine having the cleaning and sealing device; 
       FIG. 4  is a diagrammatic, exploded perspective view of the insert for an ink sump; 
       FIG. 5  is a diagrammatic, left side view of the printing system in the second cleaning region III for a spraying clear function against a baffle piece; 
       FIG. 6  is a diagrammatic, left side view of the printing system in the third cleaning region for spraying clear in the spray duct; 
       FIG. 7  is a detailed, partial front view of the printing system in the printing position I; 
       FIG. 8  is a detailed, partial front view of the printing system in the first cleaning region II; and 
       FIG. 9  is a block diagram relating to the link between sensors of a transport device, a control computer and the printing system and also the cleaning and sealing device. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown schematically a franking machine having a printing system  1  and a guide plate  22  having a printing window  221 , in which two inkjet printheads  110  are disposed in a stationary manner. The guide plate  22  is a constituent part of a transport device  2  having a drive part  21  and two sensors  23 ,  24 . Sensor  23  is at a “start position” and is disposed upstream in the letter run at the start of the transport device  2  and is used to register and signal incoming letters. Sensor  24  is at “print position” and is disposed downstream in the letter run direction in front of the printing window  221  and is used to register letters located on the transport device  2  and to trigger and terminate the printing command. The two sensors  23 ,  24  and the drive part  21  are connected to a control computer  3  for the franking machine; see also  FIG. 9 . 
   The printing system  1  contains a frame  10 , two printing modules  11 , a holder  12  for the aforementioned two and an associated cleaning and sealing device; see also  FIG. 2 . Each printing module  11  contains an inkjet printhead  110  together with ink supply and control circuit board—not designated. Nozzle surfaces  111  of the inkjet printheads  110  and of the printing modules  11  are disposed parallel to the guide plate  22  but offset in relation to each other in the printing window  221  when in a printing position I—angle 0 degrees. In this way, the necessary printing gap length is achieved. Accordingly, the printing modules  11  are disposed offset in the holder  12 . 
   The holder  12  is mounted such that it can pivot about an axle  121 , which is fixed in the frame  10 . The displacement of the holder  12  is carried out by an actuating motor  124  via a worm gear mechanism  123 ; in this regard see also  FIG. 3 . A drive action is provided by the control computer  3  of the franking machine on the basis of a rotary encoder  125 ; in this regard see also  FIG. 9 . 
   Provided on the frame  10  are two stops  126 ,  127 , which limit the pivoting range of the holder  12 . The stop  126  is used to fix the printing position I, which is at the same time the first calibration position for the rotary encoder  125 ; in this regard see  FIGS. 2 ,  3  and  7 . The stop  127  is used to fix the outermost position in the cleaning region V, which is the second calibration position for the rotary encoder  125  and, in addition, a wiping position. Since the angle—85 degrees—between the two stops  126 ,  127  is predefined by the design, the rotary encoder  125  can be calibrated on this basis for the purpose of setting the various cleaning regions II, III, IV and V and also the sealing position VI; in this regard see also  FIG. 5 . Therefore, individual deviations of the rotary encoder  125  are eliminated. 
   Explanations relating to the cleaning regions follow further below. 
   According to  FIGS. 2 and 5 , both inkjet printheads  110  are resiliently and kinematically coupled to a common baffle piece  132 , which is configured in the manner of a shell. For this purpose, a wheel  122  is fixed to the holder  12  of the printing modules  11  such that it can rotate, and a guide edge  1323  is integrally molded on the outside of the baffle piece  132 , and the baffle piece  132  is connected to the holder  12  via a tension spring  1322 . As a result, the wheel  122  bears with a force on the guide edge  1323  and, with the latter, forms a slotted guide for the baffle piece  132 . 
   A cleaning and sealing device  13  has a holder  131  with wiping lips  1311 , a spray duct  1312  and sealing caps  1313 , which are disposed in the order cited behind the guide plate  22 ; see also  FIGS. 2 ,  3  and  6 . 
   For the displacement of the cleaning and sealing device  13 , a spindle gear mechanism  1314  together with guide shaft  1318  and an actuating motor  1315  and a sensor  1316  for the reference point setting are provided; in this regard see  FIGS. 2 and 3 . The sensor  1316  and the actuating motor  1315  are linked electrically to the control computer  3 ; see  FIG. 9 . 
   In order to clean the wiping lips  1311 , a carrier  1317  with wipers  13171  is provided, which is disposed in a stationary manner in the engagement region of the wiping lips  1311 ; in this regard see  FIGS. 3 and 5 . 
   An ink sump  133  is formed from an insert  1331  having a nonwoven  13311  and a securing clip  13312 . The insert  1331  is guided in the holder  131  open at the front and, for the purpose of easier replaceability, is provided with a handle  13313 ; in this regard see  FIGS. 1 to 5 . 
   While the printing position I and the sealing position VI are determined by uniquely defined positions of the inkjet printhead  110  and the cleaning and sealing device  13 , the cleaning regions II to V, as the name already states, can be adjusted smoothly continuously. The sealing position VI is fixed in accordance with a predefined setting by the rotary encoder  125  such that the nozzle surface  111  is disposed orthogonally with respect to the wiping lips  1311  of the cleaning and sealing device  13 . 
   For triggering the various positions of the inkjet printhead  110  and of the cleaning and sealing device  13 , the sensors  23 ,  24  disposed in the letter run and the sensor  1316  for the reference point setting are linked to the control computer  3 ; see  FIG. 9 . In a first cleaning region II, for the purpose of performing a spraying clear function, the inkjet printhead  110  is pivoted so far away from the printing position I that there is at least twice the distance from the letter or print carrier but all the ink drops still reach the letter. Here, use is made of the effect that, beginning from twice the envisaged printing distance, the inkjet print drops break up into correspondingly smaller satellite drops whose scattering range is so great that a detectable printing pattern is no longer provided. 
   In the second cleaning region III, for the purpose of performing a spraying clear function, the inkjet printhead  110  is pivoted so far away from the printing position I that no ink drops reached the letter any more and all the ink drops already or still strike the baffle piece  132 . 
   In the third cleaning region IV, for the purpose of spraying clear, the inkjet printhead  110  is pivoted so far away from the printing position I that all the ink drops strike the nonwoven  13311  directly. This also includes the position in which spraying clear is carried out through the spray duct  1312 . 
   As emerges from the above explanations, as distinct from the prior art, in the cleaning regions II to IV the time in which the inkjet printhead  110  is moving is also advantageously used for spraying clear, which shortens the downtimes substantially. 
   In the fourth cleaning region V, the inkjet printhead  110  is pivoted so far away from the printing position I that the nozzle surface  111  is disposed in the engagement region of the wiping lips  1311 . 
   In order to assume the sealing position VI, the inkjet printhead  110  is docked on the previously positioned cleaning and sealing device  13  and therefore on the sealing caps  1313 , coming from the fourth cleaning region V, and is undocked going into the same. 
   This application claims the priority, under 35 U.S.C.§119, of German patent application DE 10 2005 052 150.9, filed Nov. 2, 2005; the entire disclosure of the prior applications are herewith incorporated by reference.