Abstract:
An appartus detects inoperative inkjets during printing of three-dimensional objects. The apparatus includes an optical sensor that generates measurements of a height, a diameter, and a position for test dots formed on a substrate with material ejected from a printhead. These measurements are analyzed to detect inoperative inkjets to enable printhead maintenance at appropriate times to maintain the operational status of the inkjets in the printhead.

Description:
TECHNICAL FIELD 
       [0001]    The device disclosed in this document relates to printers that produce three-dimensional objects and, more particularly, to the accurate detection of inoperative inkjets 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 from a digital model of virtually any shape. Three-dimensional printing is an additive process in which one or more printheads eject successive layers of material on a substrate in different shapes. 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]    The production of a three-dimensional object with these printers can require hours or, with some objects, even days. One issue that arises in the production of three-dimensional objects with a three-dimensional printer is consistent functionality of the inkjets in the printheads that eject the drops of material that form the objects. During printing of an object, one or more inkjets can deteriorate by ejecting the material at an angle, rather than normal, to the printhead, ejecting drops that are smaller than an inkjet should eject, or by failing to eject any drop at all. An inkjet suffering from any of these operational deficiencies is known as an inoperative inkjet. If the operational status of one or more inkjets deteriorates during object printing, the quality of the printed object cannot be assessed until the printing operation is completed. Consequently, print jobs requiring many hours or multiple days can produce objects that do not conform to specifications due to inoperative inkjets in the printheads. Once such objects are detected, the printed objects are scrapped, restorative procedures are applied to the printheads to restore inkjet functionality, and the print job is repeated. An apparatus that enables detection of inoperative inkjets while printing would enable restorative procedures to be applied during object printing so a properly formed object can be produced. In this manner, product yield for the printer is improved and its printing is more efficient. The apparatus should be able to detect inoperative inkjets that eject a multitude of printing materials, such as clear, colored, translucent, phosphorescent, and waxy materials. 
       SUMMARY 
       [0004]    An apparatus that enables inoperative inkjet detection in three-dimensional printers includes a supply of substrate, an optical sensor configured to generate data corresponding to a height, a diameter, and a position of drops of material on the substrate, a transport configured to move the substrate and material on the substrate to a position opposite the optical sensor, and a controller operatively connected to the transport, the optical sensor, the controller being configured to operate the transport to move the substrate to the position opposite the optical sensor after a plurality of inkjets in a printhead has been operated to eject a predetermined number of drops of material from each inkjet in the printhead onto the substrate to form a test dot for each inkjet in the printhead on the substrate, and to identify inoperable inkjets in the printhead with reference to the data received from the optical sensor that corresponds to the height, the diameter, and the position of each test dot on the substrate. 
         [0005]    A printer that incorporates the apparatus for detecting inoperative inkjets includes a printhead configured with inkjets to eject material, a supply of substrate configured to move a substrate to a position opposite the printhead to receive drops of material ejected from inkjets in the printhead, an optical sensor configured to generate data corresponding to a height, a diameter, and a position of the drops of material on the substrate, a transport configured to move the substrate and material on the substrate to a position opposite the optical sensor, and a controller operatively connected to the transport, the optical sensor, and the printhead, the controller being configured to operate the printhead to eject a predetermined number of drops of material from each inkjet in the printhead onto the substrate while the substrate remains stationary at the position opposite the printhead to enable the predetermined number of drops of material to form a test dot for each inkjet in the printhead on the substrate, to operate the transport to move the substrate from being opposite the printhead to being opposite the optical sensor, and to identify inoperable inkjets in the printhead with reference to the data received from the optical sensor that corresponds to the height, the diameter, and the position of each test dot on the substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The foregoing aspects and other features of an apparatus or printer that detects inoperative inkjets during three-dimensional printing are explained in the following description, taken in connection with the accompanying drawings. 
           [0007]      FIG. 1  is a perspective view of a three-dimensional object printer. 
           [0008]      FIG. 2  is front view of a three-dimensional object printer having a housing that depicts a space within the housing for a module that enables inoperative inkjets in the printhead to be detected during a printing operation. 
           [0009]      FIG. 3  is a perspective view of a module for detecting inoperative inkjets that fits in the space  112  shown in  FIG. 2 . 
           [0010]      FIG. 4  is a flow diagram of a method for operating the module of  FIG. 3 . 
           [0011]      FIG. 5  is an alternative embodiment of a printer having a module for detecting inoperative inkjets during printing of a three-dimensional object. 
           [0012]      FIG. 6  is a flow diagram of a method for operating the module of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    For a general understanding of the environment for the device disclosed herein as well as the details for the device, reference is made to the drawings. In the drawings, like reference numerals designate like elements. 
         [0014]      FIG. 1  shows a configuration of components in a printer  100 , which produces a three-dimensional object or part  10 . As used in this document, the term “three-dimensional printer” refers to any device that ejects material with reference to image data of an object to form a three-dimensional object. The printer  100  includes a support material reservoir  14 , a build material reservoir  18 , a pair of inkjet printheads  22 ,  26 , a build substrate  30 , a planar support member  34 , a columnar support member  38 , an actuator  42 , and a controller  46 . Conduit  50  connects printhead  22  to support material reservoir  14  and conduit  54  connects printhead  26  to build material reservoir  18 . Both inkjet printheads are operated by the controller  46  with reference to three-dimensional image data in a memory operatively connected to the controller to eject the support and build materials supplied to each respective printhead. The build material forms the structure of the part  10  being produced, while the support structure  58  formed by the support material enables the build material to maintain its shape while the material solidifies as the part is being constructed. After the part is finished, the support structure  58  is removed by washing, blowing, or melting. 
         [0015]    The controller  46  is also operatively connected to at least one and possibly more actuators  42  to control movement of the planar support member  34 , the columnar support member  38 , and the printheads  22 ,  26  relative to one another. That is, one or more actuators can be operatively connected to structure supporting the printheads to move the printheads in a process direction and a cross-process direction with reference to the surface of the planar support member. Alternatively, one or more actuators can be operatively connected to the planar support member  34  to move the surface on which the part is being produced in the process and cross-process directions in the plane of the planar support member  34 . As used herein, the term “process direction” refers to movement along one axis in the surface of the planar support member  34  and “cross-process direction” refers to movement along an axis in the planar support member surface that is orthogonal to the process direction axis in that surface. These directions are denoted with the letters “P” and “C-P” in  FIG. 1 . The printheads  22 ,  26  and the columnar support member  38  also move in a direction that is orthogonal to the planar support member  34 . This direction is called the vertical direction in this document, is parallel to the columnar support member  38 , and is denoted with the letter “V” in  FIG. 1 . Movement in the vertical direction is achieved with one or more actuators operatively connected to the columnar member  38 , by one or more actuators operatively connected to the printheads  22 ,  26 , or by one or more actuators operatively connected to both the columnar support member  38  and the printheads  22 ,  26 . These actuators in these various configurations are operatively connected to the controller  46 , which operates the actuators to move the columnar member  38 , the printheads  22 ,  26 , or both in the vertical direction. 
         [0016]    A three-dimensional object printer with a housing is shown in  FIG. 2 . That printer  60  has a housing  64 . Within the housing  64  are six compartments that are generally cubic in shape. The housing  64  is shown in  FIG. 2  without the doors that close to conceal the compartments. Compartment  72  includes a planar support  78  on a movable platform  82 . Movable platform  82  is configured with one or more actuators and guide members (not shown) to enable the movable platform  82  to move up and down in a vertical direction. The planar support  78  is the surface on which a three-dimensional object is formed. In some embodiments, the printhead  86  has a length that is approximately equal to the length of the planar support  78  in the direction from the back wall of compartment  72  to the opening at the front of the compartment. In these embodiments, printhead  86  is mounted on support member  92  in the space between sidewalls  96  and  100  of housing  64  for linear reciprocating movement only. In other embodiments, the printhead  86  has a length that is less than the length of the planar support  78  in the direction from the back wall of compartment  72  to the opening at the front of the compartment. In these embodiments, printhead  86  is mounted on support member  92  in the space between sidewalls  96  and  100  of housing  64  for reciprocating movement in two orthogonal directions in a plane above compartment  72 . In these various embodiments, one or more actuators  104  are operatively connected to the printhead  86 . Controller  108  operates the actuators  104  to move the printhead  86  either linearly back and forth on support member  92  or to move the printhead in two orthogonal directions within a plane. By selectively operating the inkjets in the printhead  86 , vertically moving the support platform  82 , and horizontally moving the printhead  86  on the member  92 , a three-dimensional object can be formed on the planar support  78 . 
         [0017]    The area  112  outlined in dashes in  FIG. 2  identifies the placement of a module that optically senses a test pattern of material on a substrate to detect inoperative inkjets in the printer  60 . As noted above, if an inkjet fails during printing of an object by either completely or partially failing to eject material or by errantly ejecting material in a skewed direction, the object being produced is malformed. Currently, this malformation cannot be detected until production of the object is finished. By using area  112  for optically sensing inoperative inkjets, printer  60  can be configured to detect inoperative inkjets during object production as described more fully below. Some components within the module  300  can move in the horizontal direction H, depth direction D, and vertical direction V as shown in the figure. 
         [0018]    One embodiment of a module that detects inoperative inkjets during object printing is shown in the block diagram of  FIG. 3 . The module  300  is configured to fit within area  112  of printer  60 . The module  300  includes an optical sensor  304 , a substrate supply  308 , a support member  312 , one or more actuators  316 , a collection tray  320 , and a controller  324 . The optical sensor  304  is mounted for movement along guide rail  328  and the guide rail  328  is operatively connected to an actuator  316  to move the optical sensor  304  from a position over the substrate supply  308  to a position over the support member  312  and back again. The controller  324  is operatively connected to the actuators  316  to move the optical sensor  304  and guide rail as described, to displace a substrate  332  from the supply  308  to the support member  312 , and to pivot the support member  312  to drop a substrate from the support member  312  into the collection tray  320 . Alternatively, the guide rail  328  and the optical sensor  304  can be fixedly mounted to the printhead  86  so controller  108  can operate actuators  104  ( FIG. 2 ) to move the printhead  86  and the sensor  304 . As shown in the figure, printhead  86  can include an ejector head  2   a,  a curing device  2   b,  and a planarizer  2   c,  although the curing device  2   b  and planarizer  2   c  are not needed for materials that do not require curing or trimming. The substrates  332  in the substrate supply  308  are planar members made of a material that supports the build material and the support material ejected from the printhead  86 . For example, the planar substrates could be a plastic or other hard polymer substrate. The substrate supply  308  includes a lifting mechanism  336  that lifts the substrates  332  as a pushing mechanism  340  removes a single substrate from the supply and positions it onto the support member  312 . The lifting mechanism  336  can be a spring-loaded mechanism, an air spring, a mechanically actuated jack, or the like. The pushing mechanism  340  can be a solenoid or the like. The guide rail that supports the optical sensor  304  is operatively connected to one of the actuators  316  to move the guide rail  328  and the optical sensor  304  between the position over the substrate supply  308  and the position over the support member  312  in a reciprocating manner between the two positions. When the guide rail  328  and the sensor  304  are over the substrate supply  308 , the printhead  86  can be moved above a substrate  332  on the support member  312  to enable printing of a test pattern on the substrate. When the guide rail  328  and the sensor  304  are over the support member  312 , the sensor  304  is moved along the guide rail  328  to enable generation of image data of the test pattern on the substrate  332 . 
         [0019]    A method of operating a printer that produces three-dimensional objects is shown in  FIG. 4 . In the description of this method, statements that a process is performing some task or function refers to a controller or general purpose processor executing programmed instructions stored in a memory operatively connected to the controller or processor to manipulate data or to operate one or more components in the printer to perform the task or function. The controller  324  noted above can be such a controller or processor. Alternatively, the controller  324  can be implemented with more than one processor and associated circuitry and components, each of which is configured to form one or more tasks or functions described herein. 
         [0020]    At predetermined times in the printing operation, the controller  108  ( FIG. 2 ) operates an actuator  104  to move the printhead  86  into the module  300  located in the area  112  (block  404 ). In response to the controller  324  detecting the printhead in the module  300 , controller  324  operates the pushing mechanism  340  to move a substrate  332  onto the support member  312  (block  408 ). Controller  324  then generates a signal to the controller  108  to operate the inkjets in the printhead to print a test pattern on the substrate (block  412 ). In one embodiment, each inkjet in the printhead is repetitively operated to deposit material on a portion of the substrate  304  opposite the inkjet. After the test pattern is printed, controller  108  moves the printhead  86  out of the module  300  and generates a signal for controller  324 . In response to the signal from controller  108 , controller  324  operates an actuator  316  to move the guide rail  328  and the optical sensor  304  to a position opposite the test pattern on the substrate  332  (block  416 ). The optical sensor  304  is then moved along the guide rail  328  to emit a light towards the test pattern on the substrate  332 , receive the reflections from the test pattern and substrate, and generate measurements of the test pattern on the substrate  332  (block  420 ). These measurements are analyzed to identify inoperative inkjets (block  424 ) and, if inoperative inkjets are identified, a signal indicative of the defective printhead is generated for the operator of the printer (block  428 ). The operator can then take appropriate action. The process continues by controller  324  operating an actuator  316  to rotate the support member  312  about one end of the member to enable the substrate on which the test pattern was printed to drop into the collection tray  320  (block  432 ). The actuator operation is then reversed to return the support member  312  to the position for receiving the next substrate  332  (block  436 ). By operating another actuator  316 , the controller  324  returns the guide rail  328  and the optical sensor  304  to the position over the substrate supply  308  (block  436 ). 
         [0021]    In one embodiment, the optical sensor  304  is a blue laser sensor available from Keyence Corporation of America, Itasca, IL in the LJ-V7000 series of two dimensional and three-dimensional laser measurement systems. This sensor can generate measurements of the heights and the diameters of the collections of material drops on the substrate  332  as well as positional data regarding the location of the collections. These data can be used to determine whether the collections are located where they are expected to be and whether the mass of material is within a predetermined range of tolerance. Measurements that indicate an inkjet is ejecting too much or too little material or is ejecting the material with a skewed trajectory are indicative of inoperative inkjets. Alternatively, the optical sensor  304  can generate image data of the test pattern on the substrate  332  that are then analyzed to identify inoperative inkjets. 
         [0022]    In another embodiment shown in  FIG. 5 , the optical sensor module  300 ′ is formed with an endless belt substrate for the printing of the test pattern. The module  300 ′ is also configured to fit within area  112  of printer  60 . Using like numbers for like components, the module  300 ′ includes an optical sensor  304 , an endless substrate belt  310  entrained about three rollers  314 , one or more actuators  316 , a waste receptacle  322 , a controller  324 , a cleaning member  344 , and a tensioning mechanism  348 . The optical sensor  304  is mounted for movement along guide rail  328  and the guide rail  328  is operatively connected to an actuator  316  to enable the optical sensor  304  to be moved between two positions. One position for the optical sensor  304  over the endless substrate  310  enables the test pattern to be printed and the other position over the endless substrate  310  enables the optical sensor  304  to generate measurements of the test pattern on the endless substrate. The controller  324  is operatively connected to the actuators  316  to move the optical sensor  304  and guide rail as described, to drive at least one roller  314  to rotate the endless substrate  310 , and to engage the endless substrate  310  with the cleaning member  344 . The cleaning member  344  removes test pattern material from the endless substrate and lets it fall into the waste receptacle  322 . Alternatively, the guide rail  328  and the optical sensor  304  can be fixedly mounted to the printhead  86  so controller  108  can operate actuators  104  to move the printhead and the sensor  304 . The endless substrate  310  can be made of a material that supports the build material and the support material ejected from the printhead  86 . The tensioning mechanism  348  helps keep the endless substrate  310  taut so it adequately supports the mass of the build material and support material ejected onto the substrate. 
         [0023]    A method of operating a printer that includes the embodiment shown in  FIG. 5  is shown in  FIG. 6 . In the description of this method, statements that a process is performing some task or function refers to a controller or general purpose processor executing programmed instructions stored in memory operatively connected to the controller or processor to manipulate data or to operate one or more components in the printer to perform the task or function. The controller  324  noted above can be such a controller or processor. Alternatively, the controller  324  can be implemented with more than one processor and associated circuitry and components, each of which is configured to form one or more tasks or functions described herein. 
         [0024]    At predetermined times in the printing operation, the controller  108  ( FIG. 2 ) operates an actuator  104  to move the printhead  86  into the module  300  located in the area  112  (block  604 ). In response to the controller  324  detecting the printhead in the module  300 , controller  324  operates an actuator  316  to rotate a clean portion of the endless substrate  310  beneath the printhead  86  (block  608 ). Controller  324  then generates a signal to the controller  108  to operate the inkjets in the printhead to print a test pattern on the substrate (block  612 ). In one embodiment, each inkjet in the printhead is repetitively operated to deposit material on a portion of the substrate  304  opposite the inkjet. After the test pattern is printed, controller  108  moves the printhead  86  out of the module  300  and generates a signal for controller  324 . In response to the signal from controller  108 , controller  324  operates an actuator  316  to move the printed portion of the substrate  308  underneath the optical sensor  304  (block  616 ). The optical sensor  304  is then moved along the guide rail  328  to emit a light towards the test pattern on the substrate  310 , receive the reflections from the test pattern and substrate, and generate electrical signals as measurement data of the test pattern on the substrate  310  (block  620 ). These measurement data are then analyzed to identify inoperative inkjets (block  624 ) and, if inoperative inkjets are identified, a signal indicative of the defective printhead is generated for the operator of the printer (block  628 ). The operator can then take appropriate action. The process continues by the controller  324  operating an actuator  316  to rotate the endless substrate  310  and to engage the endless substrate with the cleaning member  344  (block  632 ). As the cleaning member  344  removes the material of the test pattern from the endless substrate  310 , it drops into the waste receptacle  322 . An operator occasionally removes the waste receptacle  322  from the printer and empties the accumulated material removed from the endless substrate. 
         [0025]    As noted above, the optical sensor  304  can be a blue laser sensor available from Keyence Corporation of America, Itasca, Ill. in the LJ-V7000 series of two dimensional and three-dimensional laser measurement systems. This sensor can generate measurements of the heights and the diameters of the collections of material drops on the substrate  332  as well as positional data regarding the location of the collections. These data can be used to determine whether the collections are located where they are expected and whether the mass of material is within a predetermined range of tolerance about an expected mass. Measurements that indicate an inkjet is ejecting too much or too little material or is ejecting the material with a skewed trajectory are indicative of inoperative inkjets. Alternatively, the optical sensor  304  can generate image data of the test pattern on the substrate  332  and these image data can be analyzed to identify inoperative inkjets. 
         [0026]    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 may be subsequently made by those skilled in the art that are also intended to be encompassed by the following claims.