Abstract:
A cleaning cart for a three-dimensional object printing system wipes an ejector head to remove debris from the ejector head. The cleaning cart includes a platform having a plurality of bearings configured to move the platform on rails of the printing system. A cleaning mechanism is movably mounted to the platform, and an actuator is mounted to the platform. The actuator is configured to move the cleaning mechanism relative to the platform to enable the cleaning mechanism to clean an ejector head that is positioned opposite the rails of the printing system.

Description:
TECHNICAL FIELD 
       [0001]    The system and method disclosed in this document relate to printers that produce three-dimensional objects and, more particularly, to cleaning mechanisms in such printers. 
       BACKGROUND 
       [0002]    Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional printing is an additive process in which one or more printheads eject successive layers of material on a substrate in different shapes. Typically, ejector heads, which are similar to printheads in document printers, include an array of ejectors that are coupled to a supply of material. Ejectors within a single ejector head can be coupled to different sources of material or each ejector head can be coupled to different sources of material to enable all of the ejectors in an ejector head to eject drops of the same material. Materials that become part of the object being produced are called build materials, while materials that are used to provide structural support for object formation, but are later removed from the object are known as support materials. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling. 
         [0003]    A prior art three-dimensional object printing system  10  is shown in  FIG. 12 . In the view depicted in that figure, a platform  14 , called a cart, includes wheels  18  ( FIG. 11 ) that ride upon track rails  22  to enable the cart to move in a process direction P between printing stations, such as the printing station  26  shown in  FIG. 12 . Printing station  26  includes four ejector heads  30  as shown in the figure, although fewer or more ejector heads can be used in a printing station. Once the cart  14  reaches the printing station  26 , the cart  14  transitions to enable bearings  34  to roll upon precision rails  38 . Precision rails  38  are cylindrical rail sections that are manufactured within tight tolerances to help ensure accurate placement and maneuvering of the cart  14  beneath the ejector heads  30 . Linear electrical motors are provided within housing  42  and are operatively connected to the wheels  18  of cart  14  to move the cart along the track rails  22  and to the bearings  34  to maneuver the cart  14  on the precision rails  38 . Once the cart  14  is beneath the printing station  26 , ejection of material occurs in synchronization with the motion of the cart. The electrical motors in housing  42  are also configured move the cart in an X-Y plane that is parallel to the ejector heads  30  as layers of material are formed in the object. Additional motors (not shown) move the printing station  26  vertically with respect to the cart  14  as layers of material accumulate to form an object. Alternatively, a mechanism can be provided to move the cart  14  vertically with respect to rails  38  as the object is formed on the top surface of the cart. Once the printing to be performed by a printing station is finished, the cart  14  is moved to another printing station for further part formation or for layer curing or other processing. 
         [0004]    An end view of the prior art system  10  is shown in  FIG. 11 . That view depicts in more detail the wheels  18  on which the cart  14  rides the track rails  22 . Bearings  34  of the cart  14  are positioned on the precision rails  38  in an arrangement that facilitates accurate positioning of the build platen on the cart  14 . Specifically, bearings  34  are positioned at a right angle to one another on one of the rails  38  to remove 4 degrees of freedom of the cart  14 , while the other bearing  34  rests on the other rail  38  to remove one more degree of freedom. A linear motor operates to move the cart  14  over an upper surface  50  of the housing  42 . The motor has a stationary motor segment within the housing  42  and a magnet  46  mounted to the underside of the cart  14 . Gravity and magnetic attraction between the stationary motor segment and the magnet  46  hold the bearings  34  in contact with the rails  38 . 
         [0005]    When carts are not present underneath the ejector heads  30 , errant drips of materials can fall from the ejector heads and produce undesired debris and contamination on the precision rails  38  and the housing  42 . Also, air-borne contaminants in the environment, such as dust or other particulate matter, can fall and collect on the rails  38  and the housing  42 . When these contaminants and debris are located at any interface between the bearings  34  and the rails  38 , the linear velocity of the cart is disrupted and the quality of the printed object is affected. Similarly, when these materials are within the gap between the top surface  50  of the housing  42  and the magnet  46 , the magnetic attraction can be affected and enable the cart to be less constrained. Additionally, the collection of material drops on top of the housing  42  can also affect the dissipation of heat from the motor and cause motion quality disturbances, impacting the performance and reliability of the motor. In order to produce three-dimensional objects with acceptable quality, the motion of the cart  14  beneath the ejector heads  30  needs to be precise. Therefore, improvements in three-dimensional printing systems that help eliminate the contamination on the precision rails and motor housing that affects the accuracy of the placement and movement of the cart would be beneficial. 
       SUMMARY 
       [0006]    An ejector head cleaning cart for a three-dimensional object printing system collects ejected materials and other debris from the ejector heads. The ejector head cleaning cart includes a platform including a plurality of bearings configured to move the platform on rails of the printing system, a cleaning mechanism movably mounted to the platform, and an actuator mounted to the platform. The actuator is configured to move the cleaning mechanism relative to the platform to enable the cleaning mechanism to clean an ejector head that is positioned opposite the rails of the printing system. 
         [0007]    A three-dimensional object printing system that incorporates improved cleaning carts includes at least one rail, an ejector head positioned opposite the at least one rail, and a cleaning cart. The cleaning cart includes a platform having a plurality of bearings configured to engage the at least one rail to move the platform on the at least one rail, a cleaning mechanism movably mounted to the platform, and an actuator mounted to the platform. The actuator is configured to move the cleaning mechanism relative to the platform to enable the cleaning mechanism to clean the ejector head of the printing system. 
         [0008]    A method of cleaning an ejector head of a three-dimensional object printing system collects ejected materials and other debris from the ejector head. The method includes moving a cleaning cart in a process direction to a first cart position at which a cleaning mechanism of the cleaning cart is located adjacent an ejector head, moving the ejector head from an initial ejector head position spaced apart from the cleaning mechanism to a first ejector head position at which the ejector head contacts the cleaning mechanism, and moving the cleaning mechanism relative to a platform of the cleaning cart from a first cleaning mechanism position to a second cleaning mechanism position such that the cleaning mechanism moves across the ejector head to remove material from the ejector head. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The foregoing aspects and other features of a cart that helps eliminate the collection of materials from the ejectors heads and other debris are explained in the following description, taken in connection with the accompanying drawings. 
           [0010]      FIG. 1  is a rear perspective view of an ejector head cleaning cart of a three-dimensional object printing system. 
           [0011]      FIG. 2  is a front perspective view of the ejector head cleaning cart of  FIG. 1 . 
           [0012]      FIG. 3  is a schematic diagram of the controller, motors, and actuator of a three-dimensional object printing system including the ejector head cleaning cart of  FIG. 1 . 
           [0013]      FIG. 4  is a side elevational view of the three-dimensional object printing system of  FIG. 3  in which the ejector head cleaning cart is positioned opposite a first ejector head. 
           [0014]      FIG. 5  is a side elevational view of the three-dimensional object printing system of  FIG. 3  in which the first ejector head is engaged with the wiper and flexure member of the ejector head cleaning cart. 
           [0015]      FIG. 6  is a side elevational view of the three-dimensional object printing system of  FIG. 3  in which the wiper of the ejector head cleaning cart is contacting the flexure member after wiping the ejector head. 
           [0016]      FIG. 7  is a side elevational view of the three-dimensional object printing system of  FIG. 3  showing the printhead retracted and spaced apart from the wiper and flexure member of the ejector head cleaning cart. 
           [0017]      FIG. 8  is a side elevational view of the three-dimensional object printing system of  FIG. 3  showing the wiper of the ejector head cleaning cart moved away from the flexure member. 
           [0018]      FIG. 9  is a side elevational view of the three-dimensional object printing system of  FIG. 3  showing the ejector head cleaning cart moved adjacent to a second ejector head. 
           [0019]      FIG. 10  is a process diagram of a method of cleaning an ejector head of a three-dimensional object printing system. 
           [0020]      FIG. 11  is a front elevational view of a prior art three-dimensional object printing system. 
           [0021]      FIG. 12  is a side perspective view of the three-dimensional object printing system of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    For a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements. 
         [0023]      FIG. 1  and  FIG. 2  illustrate an ejector head cleaning cart  100  for a three-dimensional printing system. The cleaning cart  100  includes a platform  104 , an actuator or motor  108  (also referred to herein as a cleaning cart motor), a linear slide system  112 , a wiper  116 , and a reservoir  120 . The platform  104  has six bearings  124 A- 124 F, of which four bearings  124 A- 124 D contact a first rail  128 A of the printing system, and the other two bearings  124 E and  124 F contact a second rail  128 B. The bearings  124 A- 124 F are configured to support the platform  104  on the rails  128 A,  128 B as a linear motor  132  ( FIG. 3 ) rotates the bearing  124 A-F to move the platform  104  along the rails  128 A,  128 B. 
         [0024]    The motor  108  is fixedly mounted on the platform  104  and includes a lead screw  140  extending outwardly from the motor in the direction of the wiper  116 . In the embodiment of  FIG. 1  and  FIG. 2 , the lead screw  140  extends in the process direction P, though in other embodiments the lead screw can extend from the motor in different directions. In one embodiment, the motor  108  is a stepper motor configured to rotate the lead screw  140  at specified intervals. 
         [0025]    The linear slide  112  includes a fixed support  148 , a sliding member  152 , and a threaded ring  156 . The fixed support  148  is fixedly mounted to the platform  104 . The sliding member  152  is mounted slidably on the fixed support  148  such that the sliding member  152  can move only in one linear direction. In the embodiment of  FIG. 1  and  FIG. 2 , the sliding member  152  is movable only in the process direction, though the sliding member is configured to move in different directions in other embodiments. The threaded ring  156  attached to the sliding member  152  and is threaded around the lead screw  140  such that rotation of the lead screw  140  during activation of the motor  108  moves the threaded ring  156  along the threads of the lead screw  140  in the linear direction, thereby moving the sliding member  152  in the linear direction. 
         [0026]    The wiper  116  includes a wiper mount  160 , a wiper member  164 , and a wiper blade  168 . The wiper mount  160  is fixedly attached to the sliding member  152  of the linear slide  112  such that the linear movement of the sliding member  152  relative to the platform  104  moves the wiper mount  160  in the linear direction. The wiper member  164  is mounted in the wiper mount  160  such that the wiper member  164  extends upwardly at an angle relative to vertical. In one embodiment, the wiper member  164  extends upwardly at an angle of approximately 45 degrees relative to vertical. The wiper blade  168  is attached to the edge of the wiper member  164  opposite the wiper mount  160 . The wiper blade  168  is formed of a deformable elastomeric material, for example polyurethane, to enable the wiper to deform to the shape of an ejector head when pressed against the ejector head. 
         [0027]    The reservoir  120  is fixedly mounted on the platform  104  opposite the motor  108  from the wiper  116  and includes a reservoir tray  176  and a flexure member  180 . The reservoir tray  176  defines an inner volume  184  in which collected debris are stored. The flexure member  180  has a first portion  188  extending generally vertically from a side wall of the reservoir tray  176 , and a second portion  192  extending at an angle to vertical. In one embodiment, the second portion extends at an angle of about 60 degrees relative to vertical. The uppermost edge  196  of the flexure member  180  is essentially in the same plane as the wiper blade  168 . In the embodiment of  FIG. 1  and  FIG. 2 , the plane in which the uppermost edge  196  of the flexure member  180  and the wiper blade  168  are located is parallel to a horizontal plane in which the platform  104  moves in the process direction P. 
         [0028]    The cleaning cart  100  is configured to be used in a three-dimensional object printing system  200  ( FIG. 4 - FIG. 9 ). The printing system  200  includes an ejector head unit  204  having two ejector heads  208 ,  212 . The ejector head unit  204  is operatively connected to an ejector head actuator  216 , which is configured to move the ejector head unit  204  in the vertical direction to position the ejector heads  208 ,  212  at a desired position. 
         [0029]    The printing system  200  includes a controller  220  ( FIG. 3 ) operatively connected to the motor  108  of the cleaning cart  100 , the linear motor  132 , and the ejector head actuator  216 . The controller  220  is configured to transmit electrical signals to the motor  108 , the linear motor  132 , and the ejector head actuator  216  to operate the motors  108 ,  132 , and actuator  216  and move the components operatively connected to the motors. 
         [0030]    Operation and control of the various components and functions of the printing system  200  are performed with the aid of the controller  220 . The controller  220  is implemented with a general or specialized programmable processor that executes programmed instructions. In some embodiments, the controller includes more than one general or specialized programmable processor. The instructions and data required to perform the programmed functions are stored in a memory unit associated with the controller. The processor, memory, and interface circuitry configure the controller  220  to perform the functions and processes described below. These components can be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits can be implemented with a separate processor or multiple circuits can be implemented on the same processor. Alternatively, the circuits can be implemented with discrete components or circuits provided in VLSI circuits. Also, the circuits described herein can be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits. 
         [0031]      FIG. 10  illustrates a method  300  of cleaning ejector heads in a three-dimensional object printing system. The discussion herein of the method  300  is described with reference to the printing system  200  and cleaning cart  100  discussed above and shown in  FIG. 1 - FIG. 9  for illustrative purposes. 
         [0032]    The method  300  begins with the controller  220  operating the linear motor  132  to move the cleaning cart  100  in the process direction P to a position opposite the ejector head  208  (block  304 ), as shown in  FIG. 4 . Next, the controller  220  operates the ejector head actuator  216  to move the ejector head unit  204  until the face of the ejector head  204  contacts the wiper blade  168  and the edge  196  of the flexure member  180  (block  308 ) as illustrated in  FIG. 5 . The controller  220  then operates the cleaning cart motor  108  to rotate the lead screw  140 , moving the threaded ring  156 , sliding piece  152 , and wiper  116  in the process direction P relative to the platform  104  of the cleaning cart  100  (block  312 ). The wiper blade  168  moves across the face of the ejector head  208 , wiping debris from the ejector head  168  as the wiper blade  168  moves to the position shown in  FIG. 6 . Solid debris particles wiped by the wiper blade  168  either fall from the ejector head  208  into the reservoir tray  176  or are entrained in liquid on the ejector head  208 . Liquid on the ejector head  208  is then wiped onto the flexure member  180 , where capillary action carries the liquid and entrained particles down the flexure member  180  and into the reservoir tray  176 . 
         [0033]    Once the face of the ejector head  208  has been wiped, the controller  220  operates the ejector head actuator  216  to move the ejector head unit  204  out of engagement with the wiper blade  168  and flexure chute  180  to the position shown in  FIG. 7  (block  316 ). The controller  220  operates the cleaning cart motor  108  to move the wiper  116  in a direction opposite to the process direction away from the flexure member  180  to the initial position (block  320 ) as shown in  FIG. 8 . The controller  220  determines whether additional ejector heads are to be cleaned (block  324 ). If additional ejector heads are to be cleaned, for example, ejector head  212  in  FIG. 9 , the process continues at block  304  by operating the linear motor  132  to move the cleaning cart  100  opposite the next ejector head ( FIG. 9 ). If no more ejector heads are to be cleaned, the process is complete (block  328 ). 
         [0034]    It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. 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.