Patent Publication Number: US-7216970-B2

Title: Mounting assembly for a print head of an ink jet printer

Description:
BACKGROUND 
   Known solid inject printers mount a single print head relative to an imaging drum. The print head deposits ink onto a print array of the imaging drum and a print media, e.g. a sheet of paper, passes over the imaging drum picking up the ink. The print head covers the entire print array of the imaging drum and the print array covers nearly the entire length of the imaging drum. Accordingly, the print head is referred to as a single nearly full width print head. 
   Periodically, the print head needs to be cleaned. The print head is mounted to a carriage that is pivoted away from the imaging drum so that the print head can be cleaned. A wiper comes down to clean the print head. 
   During printing, this known arrangement is capable of controlling the position of the print head relative to the position of the imaging drum because during the image formation phase of the print cycle the remainder of the printer is not functioning. Since during the image formation phase, the remainder of the printer is not functioning, the print heads do not experience any forces such as vibratory forces. When additional print heads are added to the printer and the printer is performing additional functions during the print cycle, the position of the print head relative to the imaging drum becomes more difficult to maintain. 
   SUMMARY 
   A mounting assembly in an ink jet printer includes a drum frame being adapted to support an associated imaging drum, a print head frame movably mounted with respect to the drum frame, at least two print heads mounted to the print head frame, a first alignment pin connected to the print head frame, and a second alignment pin connected to the print head frame. The drum frame includes first and second supports. The first support includes a first docking station and the second support includes a second docking station. The print head is movable between a printing position and a cleaning position. Both alignment pins extend from the print head frame towards the drum frame. The first alignment pin is adapted to cooperate with the first docking station when the print head frame is moved into the printing position. The second alignment pin is adapted to cooperate with the second docking station when the print head frame is moved into the printing position. 
   An ink jet printer includes a printer housing, an imaging drum, a drum frame connected to the printer housing and the imaging drum, a print head frame movably mounted in the printer housing, at least two print heads mounted to the print head frame, a first alignment pin connected to the print head frame, and a second alignment pin connected to the print head frame. The imaging drum includes first and second ends. The drum frame includes a first support connected to the first end of the imaging drum and a second support connected to the second end of the imaging drum. The first support includes a first docking station and the second support includes a second docking station. The print head is movable between a printing position and a cleaning position. Each alignment pin connects to the print head frame and extends generally towards the drum frame. The first alignment pin is adapted to be received by the first docking station when the print head frame is moved into the printing position. The second alignment pin is adapted to be received by the second docking station when the print head frame is moved into the printing position. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  is side cross-sectional view of an ink jet printer. 
       FIG. 2  is a side view of print head carriages cooperating with an imaging drum frame of the ink jet printer of  FIG. 1 . 
       FIG. 3  is a front view of an imaging drum connected to the imaging drum frame of the ink jet printer of  FIG. 1 . 
       FIGS. 4 and 5  are schematic views of a printer head carriage cooperating with the drum frame of the ink jet printer of  FIG. 1  where the drum frame is shown in a cross section taken normal to the axis of rotation of the imaging drum. 
       FIG. 6  is a front view of printer heads mounted to the printer head carriages of the ink jet printer of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   With reference to  FIG. 1 , a solid ink jet printer  10  includes a plurality of print heads  12  that transfer ink onto an imaging drum  14 . The print heads  12  and the imaging drum  14  are disposed in a printer housing  16 . Print media, which can include paper, travels around the drum  14  and picks up the ink deposited on the drum. The print heads  12  receive the ink from an ink reservoir  18  that is in fluid communication with the print heads. 
   With reference to  FIG. 2 , the imaging drum  14 , which in the depicted embodiment is cylindrical, connects to a drum frame  22  that is connected to the printer housing  16 . The imaging drum  14  rotates about an axis that will be referred to as the z-axis. To more easily describe the location and the movement of components in the ink jet printer  10 , an x-axis runs horizontally as shown in  FIG. 2  and a y-axis runs vertically as shown in  FIG. 2 . 
   With reference to  FIG. 3 , the drum frame  22  includes a first support  24  that is connected to a second support  26 . The drum frame  22  in the depicted embodiment is made from metal; however, other hard and durable materials can also be used to make the drum frame. A drum shaft  28 , or shafts, connects a first end of the imaging drum  14  to the first support  24  and a second end of the imaging drum to the second support  26 . The imaging drum  14  rotates about the shaft(s)  28  which are aligned with the z-axis. The supports  24  and  26  each include a curved surface that generally faces the print heads  12  (only a curved surface  30  is visible in  FIG. 2 ). 
   Each support for the drum frame includes a docking station that facilitates aligning the print heads  12  relative to the imaging drum  14  when the print heads are in the printing position. With reference to  FIG. 3 , the first support  24  includes a first (upper) socket  32  and a second (lower) socket  34 . The second support  26  includes a first (upper) v-shaped notch  36  and a second (lower) v-shaped notch  38 . The upper socket  32  and the upper v-shaped notch  36  are aligned with one another along a line that is parallel to the z-axis, i.e. the axis of rotation of the drum  14 . Likewise, the lower socket  34  and the lower v-shaped notch  38  are also aligned with one another along a line that is parallel to the z-axis. With reference to  FIG. 2 , the upper socket  32  and the lower socket  34  are spaced equidistant from the z-axis. Likewise, the upper v-shaped notch  36  and the lower v-shaped notch  38  are spaced equidistant from the z-axis. 
   The shape of the sockets  32  and  34  will be described with reference to  FIGS. 3 ,  4  and  5 . The sockets  32  and  34  have the same or at least substantially similar configurations.  FIGS. 4 and 5  depict the upper socket  32 , and it is understood that the lower socket  34  in the depicted embodiment has the same configuration. With reference to  FIG. 3 , the sockets  32  and  34  are conical in shape. The upper socket includes a circular mouth  42  that is wider than a base  44 , which in the depicted embodiment is pointed. A socket wall  46  is tapered from the mouth  42  towards the base  44 . In the depicted embodiment, the socket wall  46  is linear between the mouth  42  and the base  44  in a cross section taken normal to the z-axis. The lower socket  34  also includes a circular mouth  52 , a pointed base  54  and a wall  56  between the mouth and the base. In the depicted embodiment, the upper and lower sockets are aligned with one another in a line that is parallel to the y-axis; however, in other configuration the sockets need not be aligned. The base of each socket is equidistant from the z-axis. The sockets  32  and  34  can take other configurations, for example, instead of the base being pointed, the base can have a more rounded configuration. Other configurations that can perform the same function that will be described below can also be used. 
   With reference back to  FIG. 3 , the upper v-shaped notch  38  includes a mouth  52  that is wider than a base  54 . An upper tapered wall  56  extends between the mouth  52  and the base  54 , and a lower tapered wall  58  extends between the mouth  52  and the base  54 . In the depicted embodiment, when viewing the mouth  52  of the upper notch  36  from the print heads  12 , the mouth appears rectangular. The lower v-shaped notch  38  has a similar configuration to the upper v-shaped notch  36 . The lower v-shaped notch  38  includes a mouth  62 , a base  64 , an upper tapered wall  66  and a lower tapered wall  68 . The base  44  of the upper socket  32  aligns with the base  54  of the upper v-shaped notch  36  in a line that runs parallel to the z-axis. Likewise, the base  54  of the lower socket  34  aligns with the base  64  of the lower v-shaped notch  38 . 
   With reference back to  FIG. 1 , the print heads  12  connect to a print head frame  80  that is movable in relation to the imaging drum  14 . The print head frame  80  mounts on a pair of tracks  82  (only one visible in  FIG. 1 ) so that it can move linearly parallel to the x-axis away from the imaging drum  14 . Alternatively, the print head frame  80  can pivot about an axis away from the imaging drum. In either case, an actuator, such as a motor, a piston, or the like, can be used to move the print head frame  80 . After the print heads  12  have moved away a sufficient distance from the imaging drum  14 , i.e. to a cleaning position, a wiper (not shown) comes down to clean the print heads  12 . After the print heads  12  have been cleaned, the print head frame  80  moves back towards the imaging drum  14 , either by pivoting or by linear movement, back into the printing position. In the printing position, the print heads  12  align with the imaging drum  14  so that a desired image can be provided on the print media that travels through the ink jet printer  10 . 
   With reference to  FIG. 6 , a plurality of print heads  12  deliver ink to the imaging drum  14  ( FIG. 2 ). The print heads  12  can be referred to as semi-full width array print heads since each print head only delivers ink to a portion of the imaging drum  14 . The print heads in the depicted embodiment are spaced from one another along a line that is parallel to the z-axis, which is parallel to the rotational axis of the imaging drum  14 . Also, the print heads  12  can be staggered in that they can also be spaced from one another in a direction that is parallel to the y-axis and in a direction that is parallel to the x-axis (see  FIG. 2 ). In the depicted embodiment, four print heads  12  deliver ink to the imaging drum  14 ; however, a fewer or greater number of print heads can be provided. 
   The print heads  12  mount to print head carriages that attach to the print head frame  80 . With reference back to  FIG. 2 , a first (upper) print head carriage  84  connects to the print head frame  80  and carries the upper print heads  12  that are shown in  FIG. 6 . A second (lower) print head carriage  86  also connects to the print head frame  80  and carries the lower print heads  12  depicted in  FIG. 6 . If desired, only one print head carriage can be provided and the print heads can connect to this one print head carriage The upper print head carriage  84  includes a first lateral support  88  spaced from a second lateral support  92  ( FIG. 6 ). The lateral supports  88  and  92  are connected by a longitudinal support  94 . Likewise the lower print head carriage  86  includes a first lateral support  98  spaced from a second lateral support  102 . The lateral supports  98  and  102  are connected by a longitudinal support  104 . The print head carriages  84  and  86  each have the same configuration in that the lateral supports  88 ,  92 ,  98  and  102  each reside in a plane that is parallel to the x-y plane. 
   Alignment pins cooperate with the docking stations to align the print heads  12  relative to the imaging drum  14 . With reference back to  FIG. 6 , a first upper alignment pin  110  extends from the first lateral support  88  of the upper carriage  84  towards the imaging drum  14 . A second upper alignment pin  112  extends from the second lateral support  92  of the upper carriage  84  also towards the imaging drum  14 . A first lower alignment pin  114  extends from the first lateral support  98  of the lower carriage  86  and a second lower alignment pin  116  extends from the second lateral support  102  of the lower carriage  86 . The lower pins  114  and  116  both also extend towards the imaging drum  14 . The first upper alignment pin  110  cooperates with the first upper socket  32 , the second upper alignment pin  112  cooperates with the upper V-shaped notch  36 , the first lower alignment pin  114  cooperates with the lower socket  34  and the second lower alignment pin  116  cooperates with the lower v-shaped notch  38  when the print head frame  80  is moved into the printing position, such as that shown in  FIGS. 1 and 2 . 
   Cooperation between the first upper alignment pin  110  and the upper socket  32  will be described in detail, and it is understood that the other alignment pins will cooperate with the other docking stations in a similar manner, except where it is indicated to the otherwise. As the print head frame  80  ( FIG. 1 ) moves towards the drum frame  22 , the alignment pin  110  moves towards the socket  32 . The alignment pin  110  includes a convex-shaped distal end  120  that is configured to be received inside the socket  32 . The convex distal end  120  of the pin  110  has a diameter that is less than the diameter of the mouth  42  of the socket  32 . When the print head  12  is spaced from the imaging drum  14  such that the print head is not in the printing position, the print head can fall onto a stop  122  that is positioned below the print head  12 . The stop  122  is connected to at least one of the print head frame  80  and the print head carriage  84 . The stop  122  limits the movement of the print head  12  in a generally vertical direction when the print head has disengaged the drum frame  22 . The stop  122  can be positioned relative to the print head  12  so that the alignment pin  110  contacts the socket  32  inside of the mouth  42  when the print head is brought from the cleaning position back the printing position. 
   As the print head frame  80 , and thus the print head  12 , moves towards the imaging drum  14 , the alignment pin  110  first hits the wider mouth portion  42  of the socket  34 . As the print head frame  80  continues toward the drum frame  22 , the alignment pin  110  moves along the ramped sidewall  46  of the socket  34  upward and toward the base  44 . The convex shape of the distal end  120  of the pin  110  encourages this movement. With reference to  FIG. 5 , as the alignment pin  110  moves along the ramped sidewall  46  of the socket  34 , the print head  12  is lifted off of the stop  122 . A biasing member  122  that extends from a wall  124 , which can be connected to the carriage  88  and/or the print head frame  80 , biases the print head  12  towards the drum frame  24 . 
   The sockets  32  and  34  are shaped to limit movement of the first upper alignment pin  110  in five different directions: (1) movement is limited in two opposite directions that are both parallel to the rotational axis of the imaging drum  14  (e.g. the z-axis) by the distal end  120  contacting the conical side wall  46 , (2) movement is also limited in two opposite directions (e.g. vertically up and down as depicted in  FIGS. 4 and 5 ) that lie in a plane that is normal to the rotational axis of the imaging drum  14  (e.g. the x-y plane) by the distal end  120  contacting the conical side wall  46 , and (3) movement is limited in one direction (e.g. horizontally to the right as depicted in  FIGS. 4 and 5 ) that lies in the plane that is normal to the rotational axis of the imaging drum  14  (e.g. the x-y plane). 
   The upper v-shaped notch  36  is shaped to limit movement of the second upper alignment pin  112  in three different directions: (1) movement is limited in two opposite directions (e.g. vertically up and down as depicted in  FIGS. 4 and 5 ) that lie in a plane that is normal to the rotational axis of the imaging drum  14  (e.g. the x-y plane) by the upper tapered wall  56  and the lower tapered wall  58  contacting the alignment pin  112  and (2) movement is limited in one direction (e.g. horizontally to the right as depicted in  FIGS. 4 and 5 ) that lies in the plane that is normal to the rotational axis of the imaging drum  14  (e.g. the x-y plane). The alignment pin that is received in the v-shaped notch is free to move in the z-axis. This allows for manufacturing tolerances. The angle between the line running through the length of the print head, which is parallel to the z-axis, and the velocity vector of the drum  14  is controlled by the position of the docking stations located on the drum frame. 
   The gap between the print heads  12  and the drum  14  are controlled by the length of the alignment pins and the depth of the respective docking stations. The alignment pins can be threaded so that the length that the alignment pins extend from the respective print head carriage can be adjusted. The biasing force provided by the biasing member  124  on the print heads  12  retains the print heads in the respective docking stations during vibrations imparted on by the printer while it is performing other functions. 
   The mounting assembly and arrangement that has been described above has been found to limit the motion of the print heads with respect to the imaging drum in both a direction along the rotational axis of the drum and in an axis that is perpendicular to the rotational axis to provide a high-quality image on the print media. 
   It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.