Abstract:
A printhead includes a jetting module that forms drops, a catcher, and a deflection mechanism that deflects some of the drops toward the catcher. A moveable sealing mechanism has a first position in contact with the catcher and a second position removed from the catcher that permits drops to travel past the catcher. The moveable sealing mechanism includes a first portion that is fixed to the printhead and translates the sealing mechanism relative to the catcher, and a second portion that is removably fixed to the first portion and cooperates with the catcher to form a seal when the sealing mechanism is in the first position. A removal tool for use with the printhead includes a shaft, a magnet affixed to the shaft, and a spacer affixed to the shaft. The spacer includes a valley that is aligned with the at least one magnet.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of digitally controlled liquid ejection systems, and in particular to continuous liquid ejection systems in which a liquid stream breaks into drops at least some of which are deflected. 
     BACKGROUND OF THE INVENTION 
     Inkjet printing is commonly used for printing on paper or other types of print media and is generally a non-contact application of an ink to the print media. Typically, one of two types of ink jetting mechanisms are used and are categorized by technology as either drop on demand inkjet (DOD) or continuous inkjet (CIJ). The first technology, “drop-on-demand” (DOD) inkjet printing, provides ink drops that impact upon a recording surface using a pressurization actuator, for example, a thermal, piezoelectric, or electrostatic actuator. One commonly practiced drop-on-demand technology uses thermal actuation to eject ink drops from a nozzle. A heater, located at or near the nozzle, heats the ink sufficiently to boil, forming a vapor bubble that creates enough internal pressure to eject an ink drop. This form of inkjet is commonly termed “thermal inkjet (TIJ).” 
     The second technology commonly referred to as “continuous” inkjet (CIJ) printing, uses a pressurized ink source to produce a continuous liquid jet stream of ink by forcing ink, under pressure, through a nozzle. The stream of ink is perturbed using a drop forming mechanism such that the liquid jet breaks up into drops of ink in a predictable manner. One continuous printing technology uses thermal stimulation of the liquid jet with a heater to form drops that eventually become print drops and non-print drops. Printing occurs by selectively deflecting one of the print drops and the non-print drops and catching the non-print drops. Various approaches for selectively deflecting drops have been developed including electrostatic deflection, air deflection, and thermal deflection. 
     Additionally, there are typically two types of print media used with these inkjet printing systems. The first type is commonly referred to as a continuous web while the second type is commonly referred to as a cut sheet(s). The continuous web of print media refers to a continuous strip of media, generally originating from a source roll. The continuous web of print media is moved relative to the inkjet printing system components via a web transport system, which typically include drive rollers, web guide rollers, and web tension sensors. Cut sheets refer to individual sheets of print media that are moved relative to the inkjet printing system components via rollers and drive wheels or via a conveyor belt system that is routed through the inkjet printing system. 
     For highest productivity of these inkjet printing systems, it is common for the printing systems to use print modules which include an array of printheads to span the desired print width of the print media, so that the print media can be printed in a single pass of the print media past the print module. With such arrays of printheads there is a need to be able to service the print module, by removing, servicing and replacing a printhead from the array of printheads or of removing, servicing, and replacing of a component of one of the printheads. When the printheads or printhead components are installed in the print module, there is often a need to accurately position the serviceable unit relative to other portions of the print module. In many printing systems, there are space constraints that can hinder the task of removing and reinstalling the serviceable unit. 
     There is, therefore, a need for an improved system and method for securing and locating the serviceable unit in a print module of a printing system. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a printhead includes a jetting module that forms drops, a catcher, and a deflection mechanism that deflects some of the drops toward the catcher. A moveable sealing mechanism has a first position in contact with the catcher and a second position removed from the catcher that permits drops to travel past the catcher. The moveable sealing mechanism includes a first portion that that is fixed to the printhead and translates the sealing mechanism relative to the catcher, and a second portion that is removably fixed to the first portion and cooperates with the catcher to form a seal when the sealing mechanism is in the first position. 
     According to another aspect of the invention, a removal tool for use with the printhead includes a shaft, a magnet affixed to the shaft, and a spacer affixed to the shaft. The spacer includes a valley that is aligned with the at least one magnet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
         FIG. 1  is a schematic cross sectional view of an example embodiment of a printing system made in accordance with the present invention in showing a moveable sealing mechanism is located removed from a catcher; 
         FIG. 2  is a schematic cross sectional view of the example embodiment shown in  FIG. 1  with the sealing mechanism located in contact with the catcher; 
         FIG. 3  is an exploded perspective view of an example embodiment of a sealing mechanism made in accordance with the present invention showing first and second portions of the sealing mechanism; 
         FIG. 4  is a bottom view of the sealing mechanism shown in  FIG. 3 ; 
         FIG. 5  is a perspective view of a removable (second) portion of the sealing mechanism; 
         FIG. 6  is an exploded cross sectional side view of first and second portions of the sealing mechanism shown in  FIG. 7 ; 
         FIG. 7  is a cross sectional side view of first and second portions of the sealing mechanism taken along line  7 - 7  of  FIG. 4 ; 
         FIG. 8  is a top view of the sealing mechanism shown in  FIG. 3 ; 
         FIG. 9  is a cross sectional side view of first and second portions of the sealing mechanism taken along line  9 - 9  of  FIG. 4 ; 
         FIG. 10  is a perspective view of a removal tool suitable for removing the removable (second) portion of the sealing mechanism from the first portion of the sealing mechanism; 
         FIG. 11  is a side view of the removal tool shown in  FIG. 10 ; and 
         FIGS. 12-14  are partial cross sectional sides views of the sealing mechanism and removal tool illustrating removal and installation of the removable (second) portion of the sealing mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, an apparatus in accordance with the present invention. It is to be understood that elements not specifically shown, labeled, or described can take various forms well known to those skilled in the art. In the following description and drawings, identical reference numerals have been used, where possible, to designate identical elements. It is to be understood that elements and components can be referred to in singular or plural form, as appropriate, without limiting the scope of the invention. 
     The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of ordinary skill in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention. 
     Throughout the specification, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” Additionally, directional terms such as “on”, “over”, “top”, “bottom”, “left”, “right” are used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration only and is in no way limiting. 
     As described herein, the example embodiments of the present invention can be used in printing systems, including inkjet printing systems that include a printhead or printhead components. Many applications are emerging which use inkjet printheads to emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. Such liquids include inks, both water based and solvent based, that include one or more dyes or pigments. These liquids also include various substrate coatings and treatments, various medicinal materials, and functional materials useful for forming, for example, various circuitry components or structural components. As such, as described herein, the terms “liquid” and “ink” refer to any material that is ejected by the printhead or printhead components described below. 
     Inkjet printing is commonly used for printing on paper. However, there are numerous other materials in which inkjet is appropriate. For example, vinyl sheets, plastic sheets, textiles, paperboard, and corrugated cardboard can comprise the print media. Additionally, although the term inkjet is often used to describe the printing process, the term jetting is also appropriate wherever ink or other liquids is applied in a consistent, metered fashion, particularly if the desired result is a thin layer or coating. 
       FIG. 1  shows a schematic cross section of a portion of a continuous inkjet printhead  30 . The printhead  30  includes a jetting module  48  on which a nozzle plate  49  is secured. Ink supplied under pressure to the jetting modules flows as liquid streams from the nozzles of the nozzle plate. The nozzle array extends into and out of the plane of  FIG. 1 . Conventional drop forming mechanisms (not shown) formed in the nozzle plate or secured to the jetting module cause the individual liquid streams to break up into streams of drops. In some printhead embodiments, the drop forming mechanism causes the liquid stream to break up into smaller drops and larger drops in response to input print data. An air flow across the array of drop trajectories interacts with the drops, causing the smaller drops to be deflected more than the larger drops so that the smaller drops follow a small drop trajectory and the larger drops follow a large drop trajectory. A catcher  42  is positioned to intercept one of the small drop trajectory and the large drop trajectory catching the intercepted drops while allowing the drops following the other trajectory to pass by the catcher and continue through the printhead outlet opening  44  to strike the print media. The air flow across the drop trajectories can be provided by one or both of a positive pressure air duct  72 , which blows a flow of air across the drop trajectories, and a negative pressure air duct  78 , which sucks a flow of air across the drop trajectories. A positive pressure air flow source, not shown, connected to the positive air flow duct  72  to provide a flow of blowing across the array of drop trajectories. A negative pressure source, not shown, attached to negative pressure air flow duct  78  to provide the suction to draw a flow of air across the array of drop trajectories. 
     During storage of the printhead and during maintenance operations, it has been common to seal off the outlet opening  44  with a movable sealing mechanism  112 , as shown in  FIG. 2 . With the movable sealing mechanism  112  engaged against the bottom plate  116  of the catcher  42  through the action of actuator  110 , the elastomeric portion  114  of the sealing mechanism  112  provides a seal against the against the bottom plate  116  of the catcher. It also seals against the lower wall  74  of the positive air flow duct  72 . Ink from the drop streams  57  is diverted by the sealing mechanism  112  into the liquid return channel  86  of the catcher  42 . The elastomeric portion  114  of the sealing mechanism seals against the bottom plate  116  of the catcher  42  and the lower wall  74  of the air duct  72 , the movable sealing mechanism includes a removable elastomeric portion  114 . 
     It has been found that there is a need to remove the movable sealing mechanism to service portions of the printhead. For example, it is necessary to remove the sealing mechanism  112  to enable the cleaning of lower portions of the positive air flow duct  72 , the face of the catcher  42 , the entrance region of the liquid return duct  86  of the catcher, the elastomeric portion of the sealing mechanism and the sealing edge of the catcher bottom plate  116  to remove ink residues or contaminants such as paper fibers. Removal of the sealing mechanism in the prior art system has involved removing the delicate springs (not shown) that provide the vertical force on the sealing mechanism  112  to seal against the lower wall  74  of the positive air flow duct  72 . During the removal process or the reinstallation of the sealing mechanism, these springs can be easily damaged or distorted. Over time, the elastomeric portion  114  of the movable sealing mechanism can also be damaged or wear sufficiently that the elastomer needs to be replaced. Once the servicing activity is complete, the movable sealing mechanism must be reinstalled. To ensure effective sealing against the catcher bottom plate and the lower wall of the air duct, the reinstalled sealing mechanism must be properly aligned to these other printhead components. In particular it is necessary accurately align the vertical placement of the seal and the parallelism of the seal with the bottom plate of the catcher. Unfortunately, there is often minimal clearance for both the removal and the reinstallation of the sealing mechanism. 
     To facilitate the removal and reinstallation of the seal of the movable sealing mechanism, moveable sealing mechanism  112  is made up of a first portion, commonly referred to as a non-removable portion,  120  and second portion, commonly referred to as a removable portion,  118 , as shown in  FIGS. 3 and 4 . The removable portion  118  includes a stainless steel body  122  and an elastomeric seal  124 . The elastomeric seal  124  is typically molded directly onto the stainless steel body  122 , allowing its sealing surfaces to be positioned accurately relative to registration features, commonly referred to as locating features,  126  on the stainless steel body. The non-removable portion of the sealing mechanism includes registration features, commonly referred to as locating features,  128  that engage the locating features  126  of the stainless steel body  122  of the removable portion to enable the Z position of the removable portion  118  to be consistently defined relative to the non-removable portion  120  of the sealing mechanism. A clearance gap  142  is provided between the trailing edge of the removable portion  118  and the corresponding edge of the non-removable portion  120  of the sealing mechanism, to ensure that the locating features  126  and  128  engage with each other. With this two piece construction, it is only necessary to remove the removable portion of the moveable sealing mechanism to perform the typical maintenance operations. Following the maintenance operations, the removable portion can be easily reinstalled. The locating features of the two portions of the movable sealing mechanism enable the removable portion to accurately align itself with the non-removable portion without the need for expensive tooling when it is inserted into the bottom of the non-removable portion. 
     The removable portion of the sealing mechanism is secured to the non-removable portion by means of magnets. Magnets  130  are bonded into pockets in the removable portion  118  and magnets  132  are bonded into the non-removable portions  120  of the movable sealing mechanism  112  as shown in  FIGS. 3 and 5 . The poling directions of the magnets on the two pieces are set so that the magnets  130  of the removable portion are attracted to the magnets  132  of the non-removable portion to hold the removable portion in place in the non-removable portion without the need for attachment screws or the like. The north pole of a magnet on the one part is adjacent to the south pole of the corresponding magnet of the other part, as shown in  FIG. 6 . 
     As shown in  FIGS. 6 ,  7 , and  9 , the flat upper surface  134  of the removable portion  118  contacts vertical stops  136 , also referred to as Z direction stops, on the non-removable portion  120  to define the vertical position of the removable portion  118  relative to the non-removable portion  120 ; the upper surface of the removable portion and the vertical stop of the non-removable portion being the registration features of the two portions to define a relative position of the two portions along a first axis, the Z axis. The contact of the flat upper surface of the removable portion against the vertical stops of the non-removable portion also defines the rotation of the removable portion about the X and Y axis. The magnets  130  of the removable portion are recessed into pockets  138  in the body  122  of the removable portion, such that the surface of these magnets is recessed below the surface of the surrounding steel regions. The magnets  132  of the non-removable portion are also located in pockets  140  on the non-removable portion, with the face of the magnets recessed relative the plane defined by the vertical stops  136  of the non-removable portion  120  to ensure that the vertical position of the removable portion is defined by the contact of the flat upper surface  134  of the removable portion against the vertical stops  136  of the non-removable portion rather than by contact to the magnets. The pole faces of the magnets of the removable portion are planar and parallel to the planar pole faces of the magnets on the non-removable portion. The attraction of the magnets on the removable portion  118  to the magnets of the non-removable portion  120  provides the force perpendicular to the plane of the magnet faces to hold the upper surface of the removable portion in contact with the vertical stops of the non-removable portion. 
       FIG. 8  shows a top view of the movable sealing mechanism with the magnet features of both the removable portion and non-removable portions shown. Locating features  126  at each end of the body  122  of the removable portion  118  engage the locating features  128  at each end of the non-removable portion  120 . These locating features define a relative position of the two portions along a second axis, the X axis, which is perpendicular to the Z axis. The engagement of these locating features locates the removable portion in the X direction and in rotation about the Z axis relative to the non-removable portion. The force to engage these locating features on the removable portion with the corresponding locating features on the non-removable portion is provided by the magnets  130  and  132 . As shown, the magnets  130  of the removable portion have been partially offset in the X direction, parallel to the plane of the face of the magnets, relative to the magnets  132  of the non-removable portion. The offset causes a portion of the pole face of the magnets  130  of the removable portion to not be aligned adjacent to the pole face of the magnets  132  of the non-removable portion, and a portion of the pole face of the magnets  132  of the non-removable portion to not be aligned adjacent to the pole face of the magnets  130  of the removable portion. The magnetic fields produced by the offset of the magnets produce an X direction force, parallel to the offset, and parallel to the plane of the magnetic pole faces, on the removable portion  118  to cause the locating features  126  of the removable portion to engage with the corresponding locating features  128  on the non-removable portion. In a preferred embodiment, the pole faces of both magnets in each offset magnet pair have the same size as each other. 
     The body  122  of the removable portion  118  and the non-removable  120  portion of the sealing mechanism are preferably made of a soft ferromagnetic material such as 17-4 PH stainless steel to enhance the magnetic force securing the removable portion to the non-removable portion. Alternatively, the body  120 , the removable portion  118 , or both can be made from a non-magnetic material. A soft magnetic material is a material that is easily magnetized and demagnetized. In contrast, permanent magnets are hard magnetic materials. The terms hard and soft magnetic materials don&#39;t relate to the mechanical pliability of the material. However, when a soft magnetic material is used for the bodies of the removable and non-removable ports of the movable seal, then it is necessary to provide a recessed area around the magnets of at least one of the removable portion or the non-removable portion.  FIGS. 3 ,  6 , and  9  show the face  146  of the non-removable portion  120  as recessed relative to the face of the magnet  130  in the vicinity of the magnets. Without such a recess, some of the magnetic flux from the magnets is shunted through the soft magnetic material adjacent to the magnets instead of being forced to pass directly from one magnet to the adjacent one. This significantly reduces the lateral forces produced by the offset of the magnet pairs. As an alternatively to the configuration shown in  FIGS. 3 ,  6 , and  9 , the face of the removable portion can include a recess instead of or in addition to the recess around the magnet of the non-removable portion. To prevent an edge of the removable part  118  from being attracted to and contacting the exposed sides of the magnets  132 , a ring  144  of aluminum or other non-magnetic material is placed in the recess around the sides of the magnets on the non-removable portion, to provide a non-magnetic surface around magnet. If the bodies of both the removable and non-removable portions of the movable seal are made of a non-magnetic material, then the recess regions around the magnets are not necessary. 
     In a preferred embodiment shown in  FIG. 9 , the two portions of the movable seal each have one magnet with an exposed N pole and one magnet with an exposed S pole. As the body of the non-removable portion  120  is made of a soft magnetic material, which has a high permeability, it provides a magnetic path for the magnetic flux between the unexposed north pole of the one magnet to the unexposed south pole of its other magnet. As a result, the soft magnetic material of the non-removable portion helps shield components above the movable seal, such as the air flow duct  74  ( FIG. 1 ), from the magnetic field of the magnets. By providing a magnetic path between the unexposed magnetic poles of the two magnetic, the soft magnetic material of the body also increases the magnetic attraction at the exposed faces of its two magnets. In a similar manner, body of the removable portion being made of a high permeability soft magnetic material, it provides a magnetic path for the magnetic flux between the unexposed poles of its two magnets. As a result it provides some magnetic shielding to components below the movable seal, from the magnetic field of the magnets. It also increases the magnetic attraction at the exposed faces of its two magnets. As a result, by using the magnet poling configuration shown in  FIG. 5 , the magnetic attraction of the removable portion to the non-removable portion is enhanced when compared to a magnetic poling configuration in which each of the four magnets are poled with their N poles in the same direction. While this embodiment has two magnet pairs, other embodiments can have a single magnet pair, while other embodiments can have more than two magnet pairs. 
     In this sealing mechanism application, the positioning of the removable portion in the Y direction, parallel to the nozzle array, is not critical. Therefore there is no need for alignment features on the two components to define the position of the removable portion in the Y direction. There is therefore no need to apply a biasing force in the Y direction on the removable portion. The magnets on the removable portion have no offset in the Y direction relative to the magnets on the non-removable portion of the sealing mechanism, and therefore they provide no force in the y-direction. In general it is preferred for the magnet offset to be aligned along the direction in which the vector biasing force is to be applied. 
     To enable the locating features  126  of the removable portion  118  to engage the locating features  128  of the non-removable portion  120 , the removable portion needs to be able to slide relative to the non-removable portion. It is desirable for the contacting surfaces, the vertical stops  136  of the non-removable portion  120  and the upper surface  134  of the removable portion, to be very hard (mechanically) so that the contact forces don&#39;t deform these contacting surfaces. It is also desirable for the contacting surfaces to have smooth finishes. In some embodiments, the contacting surfaces are hardened to minimize deformation and are electropolished or electrochemical deburred to produce the desired smooth finishes. 
     The elastomeric seal  124  of the sealing mechanism  112  needs to be able to moved into contact with the bottom plate  116  of the catcher  42  to close off the outlet opening  44  when the printhead is shut down, and it must retract to open the outlet opening when the printhead is ready for printing ( FIG. 1 ). At times, ink can dry at the contact point between the elastomeric seal  124  and the catcher bottom plate  116 , causing the seal to stick to the catcher bottom plate. To ensure that the retraction force applied by the actuator  110  is coupled through the non-removable portion  120  to the removable portion  118  of the eyelid mechanism  112  to retract the removable portion, the non-removable portion includes a raised barb  148 ; see  FIG. 3 . The back edge  150  of the barb  148  engages the corresponding edge  152  in an opening  154  in the removable portion to transfer the retraction force from the non-removable portion  120  to the removable portion  118 . 
     The engagement of the barb  148  of the non-removable portion with the corresponding opening  154  in the removable portion necessitates the removal of the removable portion of the sealing mechanism  112  by directly pulling the removable portion away from the non-removable portion in the z-direction. To avoid over extending the springs that hold the removable seal in place and provide the sealing force of the movable seal against the bottom surface of the air duct  74  ( FIG. 1 ), the non-removable portion is limited in downward travel by a screw, not shown, passing through the center slot  156  of the barb  148  that is anchored into another portion of the printhead  30 . This screw provides no vertical force on the moveable seal except when the movable seal is being pulled down during the process of removing the removable portion of the seal assembly. 
     To aid in guiding the removable portion into position when it is being reinstalled, the non-removable portion includes some sloped guiding surfaces which enable the removable portion to slide toward the proper position. These sloped guiding surfaces  156  include the sloped upper surfaces of the barb  148 . Contact of the removable portion with these sloped upper surfaces of the barb cause the removable portion to slide back into position. Near the locating features  128  of the non-removable portion  120 , there are additional sloped guiding surfaces  160  to slide the contacting removable portion  118  forward and into position. 
     With the minimal clearance for accessing the sealing mechanism, a removal tool  178  is desirable for removing and reinstalling the removable portion  118  of the sealing mechanism. One such removal tool  178  is shown in  FIGS. 10-13 . The tool includes three non-magnetic spacers  162 ,  164 , and  166  mounted on common shaft  180 . The three spacers are shaped as cams each with two lobes  168  spaced 90 degrees apart, with a valley  174  between the two lobes  168 . The lobes of the three spacers are aligned with the corresponding lobes of the other spacers. In a preferred embodiment, the three spacers are made of Delrin®. Partial ring shaped magnets  170  are secured to a non-magnetic core  172  on each side of the central spacer  164 . The magnets wrap around a 45 degree arc. One of the magnets  170  has its north pole on the outer surface and the other magnet has its south pole on the outer surface as shown on  FIG. 10 . The core  172  can be made of non-magnetic materials such as 304 stainless steel, aluminum, or plastics. The midpoints of the arcs of the magnets are aligned with the valley  174  between the lobes  168 . A pin  182  passing through holes in the three spacers  162 ,  164 , and  164  and the non-magnetic cores  172  maintains the alignment of the valleys  174  in the spacers and the magnets  170  attached to the non-magnetic cores  172 . In one embodiment, the two magnets  170  are secured to magnetic insert  176 , either a soft or hard magnetic material, inserted into the non-magnetic core; the magnetic material insert helps to couple the magnetic fields from the two magnets to increase the magnetic holding force of the tool to the removable portion. When the tool is positioned adjacent to the removable portion of the sealing mechanism, with the magnets of the tool facing the removable portion, the magnetic attraction of the tool to the removable portion is stronger than the magnetic attraction of the removable portion to the non-removable portion. 
     To remove the removable portion of the movable seal, the operator, holding on to the shaft of the removal tool, positions the removal tool  178  under the removable portion  118  with the magnets  170  facing the removable portion  118 , and brings the removal tool into contact with the removable portion, as shown in  FIG. 12 . With the removal tool  178  firmly secured by its magnets  170  to the removal portion of the sealing mechanism  112 , a downward force (represented using arrow  184 ) is applied to the tool. As the magnet force securing the tool to the removable portion is stronger than the magnetic force securing the removable portion of the seal assembly to the non-removable portion, the downward force on the tool causes the removable portion of the seal assembly to break loose from the non-removable portion, as indicated in  FIG. 13 . The tool with the attached removable portion can then be extracted from under the printhead. 
     To reinstall the removable portion  118 , the removal tool  178  with the attached removable portion is positioned approximately in place under printhead  30  and the removable portion is allowed to magnetically attach to the non-removable portion  120 . The guiding surfaces  158  and  160  of the non-removable portion, described earlier, help the removable portion to slide into the proper position, so the installer doesn&#39;t have to be precise in positioning the removal tool and the removable portion of the sealing mechanism relative to the non-removable portion. To separate the removal tool  178  from the removable portion  118  of the sealing mechanism, the removal tool is rotated about the axis of the shaft (represented using arrow  186 ), as shown in  FIG. 14 . This rotation rolls the contact point of the removal tool  178  with the removable portion  118  up onto one of the lobes  168  of the non-magnetic spacers to increase the spacing of the magnets of the tool away from the removable portion. This weakens the attractive force between the removal tool and the removable portion so that the removal tool can be separated from the removable portion of the sealing assembly. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
     
         
           30  printhead 
           48  jetting module 
           49  nozzle plate 
           42  catcher 
           44  outlet opening 
           57  drop streams 
           72  positive pressure air flow duct 
           74  lower wall 
           78  negative pressure air flow duct 
           86  liquid return channel 
           110  actuator 
           112  movable sealing mechanism 
           114  elastomeric portion 
           116  bottom plate 
           118  removable portion 
           120  non-removable portion 
           122  body 
           124  elastomeric seal 
           126  locating features of the removable portion 
           128  locating features of the non-removable portion 
           130  magnet of the removable portion 
           132  magnet of the non-removable portion 
           134  upper surface 
           136  vertical stop 
           138  pocket of the removable portion 
           140  pocket of the non-removable portion 
           142  clearance gap 
           144  ring 
           146  face 
           148  barb 
           150  edge 
           152  edge 
           154  opening 
           156  slot 
           158  guiding surface 
           160  guiding surface 
           162  spacer 
           164  spacer 
           166  spacer 
           168  lobe 
           170  magnet 
           172  non-magnetic core 
           174  valley 
           176  magnetic insert 
           178  removal tool 
           180  shaft 
           182  pin 
           184  downward force arrow 
           186  rotational force arrow