Patent Publication Number: US-2021187850-A1

Title: Heating element assembly

Description:
BACKGROUND 
     Additive manufacturing processes can produce three-dimensional (3D) objects by providing a layer-by-layer accumulation and solidification of build material patterned from a digital model. In some examples, layers of build material can be processed using heat to cause melting and solidification of the material in selected regions of each layer. In some examples, the solidification of build material can be accomplished in other ways, such as through the use of binding agents or chemicals. The solidification of selected regions of build material can form 2D cross-sectional layers of the 3D object being produced, or printed. In some examples, layers of build material can be preheated prior to the melting and/or solidification process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  shows an example of a 3D printing system in which an example heating element assembly may be implemented; 
         FIG. 2  shows additional details of an example print controller; 
         FIG. 3  shows additional details of an alternate example print controller; 
         FIG. 4  shows an example of a rotatable disc of an example heating element assembly; 
         FIG. 5  shows another example of a rotatable disc comprising additional pairs of thermal sensors and heating elements; 
         FIG. 6  shows an example of a rotatable disc that includes a thermal sensor on either side of a heating element; 
         FIG. 7  shows an example of multiple rotatable discs that can be rotated around different axes; 
         FIG. 8  shows an example of a Reuleaux mechanism pattern that can be used to move a rotatable disc within a square perimeter of a print bed; and, 
         FIG. 9  shows a flow diagram of an example method of heating a surface of a print bed with a heating element assembly. 
     
    
    
     Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. 
     DETAILED DESCRIPTION 
     In some 3D printing processes a layer of a build material in the form of a particle material, such as powder, is spread over a platform (e.g., a print bed) within a work area. A fusing agent can be selectively applied to the material layer where the particles are to be fused together. The work area can be exposed to a fusing energy to fuse together the areas of the material layer where the fusing agent has been applied. The process can then be repeated, one layer at a time, until a part has been formed in the work area. 
     Once the first layer of build material has been deposited over the print bed and fused, that layer becomes the platform on which a next layer of build material is deposited. Thus, each layer becomes a platform on which the next layer is formed. In some 3D printing systems a pre-heating structure is used to pre-heat each layer of build material prior to the application of fusing energy. Each layer can be pre-heated to a uniform temperature just below the melting point of the build material. 
     In some examples, a pre-heating structure can include a heating element assembly mounted over the working area with heating elements pointing down at the print bed. Some heating element assemblies have arrays of fixed or rotating heating elements that are selectively controllable to provide energy in the form of heat to the working area. Such assemblies include an IR (infrared) camera that can look down at the print bed and measure the temperature across the bed. The IR camera can be centrally located on the pre-heating structure to facilitate the gathering of temperature data across the whole print bed. Measured temperature data from the IR camera can be used to control the fixed heating elements. While such structures can help to keep layers of build material pre-heated prior to fusing, use of an IR camera can be complicated and expensive, and the level of heating across the print bed can be uneven due, for example, to the fixed placement of the heating elements. 
     Accordingly, in some examples described herein, a heating element assembly enables a more uniform temperature across the print bed in printing systems such as 3D powder-based printers. Simple thermal sensors can be used in place of the more complex and expensive IR camera, with each sensor being in direct control of an individual heating element to gather temperature data across a specific portion of the print bed. Thermal sensor/heating element pairs can be mounted at different radii on a rotatable disc to pass over regions of the print bed. Instead of measuring temperature across the whole print bed, each thermal sensor can measure the temperature of a narrow region of the print bed and can directly control an associated heating element to maintain an expected temperature within the region. In different examples, heating element assemblies can include multiple rotatable discs having thermal sensor/heating element pairs. In some examples as discussed below, heating element assemblies can employ a Reuleaux pattern motion over the print bed and a back and forth rotation to provide even heating of the print bed with a simplified control process. 
     In a particular example, a heating element assembly is to heat a surface of a print bed, and the assembly includes a rotatable disc positioned over the print bed. The assembly also includes a thermal sensor mounted to the disc at a first radius to pass over and measure the temperature of a region of the print bed as the disc rotates. The assembly also includes a heating element mounted to the disc at the first radius to pass over and heat the region of the print bed when the measured temperature is below an expected temperature. 
     In another example, a 3D printing system includes a print bed, a powder depositor to deposit powder onto the print bed, and an agent depositor to deposit agent onto the deposited powder. The system also includes a heating element assembly to rotate a thermally controlled heating element over a region of the print bed, where the thermally controlled heating element is to sense the temperature of the region and to heat the region when the sensed temperature is below an expected temperature. 
     In another example, a method of heating a surface of a print bed with a heating element assembly includes positioning a rotatable disc above the print bed and mounting a thermal sensor and a heating element to the disc. The method includes rotating the disc and measuring the temperature of a region on the print bed covered by the thermal sensor, comparing the measured temperature with an expected temperature, and causing the heating element to heat the region on the print bed when the measured temperature is below the expected temperature. 
       FIG. 1  shows an example of a 3D printing system  100  in which an example heating element assembly  102  may be implemented. The example 3D printing system  100  comprises a print bed, or build platform,  104 , a build material distributor  106 , an agent depositor  108 , and a heating element assembly  102 . The print bed  104  may be part of a removable build unit that can be inserted into the 3D printing system  100  for printing, and then removed when a print job is finished. The heating element assembly  102  can be mounted or otherwise positioned over the print bed  104 . The heating element assembly  102  comprises a fixed portion  110  and a rotatable disc  112  hosted in the fixed portion  110 . In some examples, the rotatable disc  112  can rotate at speeds on the order of one revolution per second. In some examples, the disc  112  can rotate at speeds greater than or lesser than one revolution per second. The fixed portion  110  may comprise a casing  120  to host the rotatable disc  112 , a servo-mechanism  122  attached to the casing  120  and to the rotatable disc  112  with axis  124 , and a protection glass  126 . The rotatable disc  112  comprises a thermal sensor  114  and a heating element  116  mounted to the disc  112 . In some examples, the rotatable disc  112  may additionally comprise a temperature controller  118 . In some examples, the temperature controller  118  can be integrated with the thermal sensor  114 . In some examples, the rotatable disc  112  comprises a calibrated disc  112  with associated calibration parameters  113  that can be stored on the disc  112  or in a memory on a controller such as temperature controller  118  or a printer controller  128 , as discussed in more detail herein below. 
     The example 3D printing system  100  additionally includes an example print controller  128 .  FIGS. 2 and 3  show additional details of an example print controller  128 . As shown in  FIG. 3 , in some examples a temperature controller  118  may be implemented as part of print controller  128 . Thus, in some examples the functions of the temperature controller  118  can be performed on the rotatable disc  112  as shown in  FIGS. 1 and 2 , while in other examples the functions of the temperature controller  118  can be performed off the rotatable disc  112  as shown in  FIG. 3 . 
     Referring generally to  FIGS. 1-3 , the print controller  128  can control various operations of the 3D printing system  100  to facilitate the printing of 3D objects. An example print controller  128  can include a processor (CPU)  130  and a memory  132 . The print controller  128  may additionally include other electronics (not shown) for communicating with and controlling various components of the printing system  100 . Such other electronics can include, for example, discrete electronic components and/or an ASIC (application specific integrated circuit). Memory  132  can include both volatile (i.e., RAM) and nonvolatile memory components (e.g., ROM, hard disk, optical disc, CD-ROM, magnetic tape, flash memory, etc.). The components of memory  132  comprise non-transitory, machine-readable (e.g., computer/processor-readable) media that can provide for the storage of machine-readable coded program instructions, data structures, program instruction modules, JDF (job definition format), 3MF formatted data, and other data and/or instructions executable by a processor  130  of the printing system  100 . 
     An example of executable instructions to be stored in memory  132  include instructions associated with a print module  134 , while examples of stored data can include object data  136 . In some examples, print controller  128  can receive object data  136  from a host system such as a computer. Object data  136  can represent, for example, object files defining 3D object models to be produced on the printing system  100 . Executing instructions from the build module  136 , the processor  130  can generate print data for each cross-sectional slice of a 3D object model from the object data  136 . The print data can define, for example, each cross-sectional slice of a 3D object model, the liquid agents to be applied to the build powder within each cross-sectional slice, and how fusing energy is to be applied to fuse each layer of powder build material. Thus, during operation, the processor  130  can control the build material depositor  106  to form a layer of build material  138  on the print bed  104 . The processor can also control the agent depositor  108  to selectively deposit agent  140  on the layer of build material  138  and to apply a fusing energy to fuse the layer. The processor  130  can use the print data to control printing components of the printing system  100  to process each layer of build powder until a 3D object has been formed. 
       FIG. 4  shows an example of a rotatable disc  112 . As noted above, the rotatable disc  112  comprises a thermal sensor  114  and a heating element  116  mounted to the disc  112 . In some examples, the rotatable disc  112  may additionally comprise integrated temperature controller  118 , while in some examples a temperature controller  118  may be implemented off the rotatable disc  112  as part of a print controller  128 . The thermal sensor  114  can be mounted to the disc  112  at a first radius, R, from the center axis  142  around which the disc can rotate. This enables the thermal sensor  114  to pass over and measure the temperature of a region of the print bed  104  as the disc rotates. A heating element  116  can be mounted to the disc  112  at the same first radius, R, to enable the heating element  116  to rotationally follow the thermal sensor  114 , and to pass over the same region of the print bed passed over by the thermal sensor  114 . When the temperature controller  118  is implemented on the rotatable disc  112 , electrical connections to the disc  112  may be simplified, for example, by including just a single power connection. 
     The thermal sensor  114  and heating element  116  can be coupled together by a control connection  144 . The control connection  144  enables the thermal sensor  114 , in conjunction with the temperature controller  118 , to control when the heating element  116  is turned on to provide heat to the print bed  104 . Using temperature data sensed or measured from thermal sensor  114  over a region of the print bed  104 , the temperature controller  118  can compare the measured temperature with an expected temperature  115 . An expected temperature  115  can be a pre-heating temperature that keeps the print bed  104  and material build layer  138  below a fusing temperature, but warm enough to facilitate fusing of the build layer  138  when a fusing energy is applied. The expected temperature  115  can be stored within the temperature controller  118  as an analog component of the controller  118  or in a memory  117  of the controller  118 , as shown in  FIG. 2 . In some examples, when the temperature controller  118  is implemented off the rotatable disc  112  as part of a print controller  128 , the expected temperature  115  can be stored in a memory  132  of print controller  128 , as shown in  FIG. 3 . 
     As noted above, a rotatable disc  112  can comprise a calibrated disc  112  with associated calibration parameters  113 . The calibration parameters  113  can be used by the temperature controller  118  or print controller  128  to accommodate for variations in thermal sensors  114  and heating elements  116  that might exist between different discs. Thus, each disc  112  in a heating element assembly  102  comprises a self-contained calibrated unit that can be replaced in the assembly  102  without the need for the printing system  100  to perform any additional calibration. Calibration parameters  113  can be stored in different ways both on and off the disc  112 . For example, calibration parameters  113  can be stored electronically within the controller  118 , in a memory  117  of the controller  118  ( FIG. 2 ), or off the disc in a memory  132  of the print controller  128  ( FIG. 3 ). Calibration parameters  113  can also be associated with a disc  112  in other ways, such as being printed, or stamped, or otherwise formed on the disc ( FIGS. 1, 4, 5 ) to be read by a reader such as an RFID reader. In some examples, disc usage parameters can be recorded and stored either on the disc in a memory  117  of controller  118 , or off the disc in a memory  132  of print controller  128 . Disc usage parameters can include, for example, the number of hours a heating element/lamp  116  has been in use. 
     The temperature controller  118  can compare the measured temperature with the expected temperature, and based on the comparison the controller  118  can provide control signals via the control connection  144  to the heating element  116 . The control signals can turn the heating element  116  on or off to provide an appropriate amount of heat to the measured region of the print bed  104  to maintain the region at the expected temperature. In some examples, as shown in  FIG. 3 , where the temperature controller  118  located off the rotatable disc  112  as part of the printer controller  128 , the measured temperature data from the thermal sensor  114  and the control signals can be transferred between the disc  112  and the temperature controller  118  across a connection such as a slip ring connection  145 . 
       FIG. 5  shows another example of a rotatable disc  112  that comprises additional pairs or sets of thermal sensors  114  and heating elements  116 . In general, a thermal sensor  114  paired with a heating element  116  can be referred to as a thermally controlled heating element. In the  FIG. 5  example, each thermal sensor  114  includes an integrated temperature controller  118 . As shown in  FIG. 5 , each thermally controlled heating element can be mounted on the rotatable disc  112  at a different radius (e.g., R 1 , R 2 , R 3 ) from the center axis  142  around which the disc  112  can rotate. This enables the thermal sensors  114  to pass over different regions of the print bed  104  and to measure the temperatures of the different print bed regions. Respective heating elements  116  associated with each thermal sensor  114  (i.e., coupled together by a control connection  144 ) are mounted to the disc  112  at respective radii to enable the heating elements  116  to rotationally follow their respective thermal sensors  114 , and to pass over the same print bed region passed over by their associated thermal sensor  114 . 
     In a manner similar to that discussed above with respect to  FIG. 4 , each temperature controller  118  in the  FIG. 5  example can compare the measured temperature from its associated thermal sensor  114  with an expected temperature, and based on the comparison the temperature controller  118  can provide control signals via the control connection  144  to its associated heating element  116 . The control signals can turn the heating elements  116  on or off to provide an appropriate amount of heat to the measured regions of the print bed  104  to maintain each print bed region at the expected temperature. 
     In some examples, as shown in  FIG. 6 , a rotatable disc  112  can include a thermal sensor  114  ( 114   a,    114   b ) on either side of a heating element  116 . This arrangement enables the thermal sensors and the heating element  116  to cover a region of the print bed  104  without involving complete rotations of the disc  112 . Instead, the rotatable disc  112  can rotate partially (e.g., half way around) in a first direction  146  and partially in a second direction  148 , opposite the first direction  146 . Rotation in the first direction  146  enables a first thermal sensor  114   a  to measure the temperature of a first part of a region on the print bed  104  while the heating element  116  is controlled to heat the first part of the print bed region to an expected temperature. Rotation in the second direction  148  enables a second thermal sensor  114   b  to measure the temperature of a second part of a region on the print bed  104  while the heating element  116  is controlled to heat the second part of the print bed region to an expected temperature. The style of motion enabled by this arrangement of two thermal sensors  114  can provide a simplified electrical connection to be made to the disc  112  by a loose wire bundle that twists back and forth rather than the use of slip rings that would be used for continuous rotation of the disc  112 . 
     Breaks  150  shown in the control connections  144  in  FIG. 6  are to indicate that the thermal sensor  114  associated with that control connection  144  is inactive, or not being utilized during rotation of the disc  112  in the direction shown. For example, when the disc rotates in the first direction  146 , the break in the control connection  144  associated with the thermal sensor  114   b  indicates that thermal sensor  114   b  may not be measuring the temperature of the print bed  104  at that time. The breaks  150  are not intended to indicate an actual, physical break in the control connections  144 . While one arrangement of multiple thermal sensors  114  and heating elements  116  is shown in  FIG. 6 , other arrangements are contemplated. For example, in other arrangements the single heating element  116  can be replaced with a single thermal sensor  116 , while each of the sensors  114   a / 114   b  can be replaced by two heating elements. In such an arrangement, while the disc rotates in a first direction, the single sensor can control a first heating element, and while the disc rotates in a second direction, the single sensor can control a second heating element. In yet another arrangement, a single sensor  114  and single heating element  116  can be placed on opposite sides of the disc  112 , causing their relative positions to be constant regardless of the direction of the disc rotation. 
     In some examples, as shown in  FIG. 7 , multiple rotatable discs  112  can be rotated around different axes. Each rotatable disc  112  can comprise a thermally controlled heating element comprising a thermal sensor  114  with a temperature controller  118  (not shown in  FIG. 7 ) and a heating element  116 . The thermally controlled heating elements on each disc can be positioned in the same positions on each disc in order to maintain an equal distance between the thermal sensors  114  and the heating elements  116 . In addition, the discs  112  can be rotated uniformly to maintain the distances between the thermal sensors  114  and heating elements  116 . The geared teeth on the edges of the rotatable discs  112  along with a center gear engaging each disc, as shown in  FIG. 7 , provides one example for how the discs can be rotated uniformly. Other examples can include a belt or band around the outer edges of each disc that can cause each disc to rotate uniformly when the belt is put in motion. Maintaining an equal distance between the thermal sensors  114  on the multiple discs  112  helps to ensure that temperature measurements from each thermal sensor  114  are primarily influenced by the associated heating element  116  of the respective thermally controlled heating element pair, and not by other heating elements. 
     In some examples, as shown in  FIG. 8 , a pattern of a Reuleaux mechanism can be used to move a rotatable disc within the square perimeter of the print bed  104 . In general, a Reuleaux pattern comprises a curved pattern that is based on an equilateral triangle with the curve having a mostly constant width. The oblong circular shape  152  represents a Reuleaux pattern  152  in which the thermally controlled heating elements can be rotated. As shown in  FIG. 8 , the thermally controlled heating elements include thermal sensors  114   a  and  114   b  on either side of a heating element  116 , similar to the arrangement discussed above with respect to  FIG. 6 . Thus, the thermally controlled heating elements in  FIG. 8  can rotate on a disc  112  (not specifically shown in  FIG. 8 ) in a back and forth motion as the disc  112  is moved around within (i.e., while positioned above) the square perimeter of the print bed  104 . Moving the thermally controlled heating elements according to a Reuleaux pattern in this manner, helps to provide a uniform coverage of a square print bed  104 . 
       FIG. 9  shows a flow diagram of an example method  900  of heating a surface of a print bed with a heating element assembly. The method  900  is associated with examples discussed above with regard to  FIGS. 1-8 , and details of the operations shown in method  900  can be found in the related discussion of such examples. The operations of method  900  may be embodied as programming instructions stored on a non-transitory, machine-readable (e.g., computer/processor-readable) medium, such as memory  132  shown in  FIGS. 1 and 2 . In some examples, implementing the operations of method  900  can be achieved by a processor, such as a processor  130  of  FIGS. 1 and 2 , reading and executing the programming instructions stored in a memory  132 . In some examples, implementing the operations of method  900  can be achieved using an ASIC and/or other hardware components alone or in combination with programming instructions executable by a processor  130 . 
     The method  900  may include more than one implementation, and different implementations of method  900  may not employ every operation presented in the flow diagram of  FIG. 9 . Therefore, while the operations of method  900  are presented in a particular order within the flow diagram, the order of their presentation is not intended to be a limitation as to the order in which the operations may actually be implemented, or as to whether all of the operations may be implemented. For example, one implementation of method  900  might be achieved through the performance of a number of initial operations, without performing one or more subsequent operations, while another implementation of method  900  might be achieved through the performance of all of the operations. 
     Referring now to the flow diagram of  FIG. 9 , an example method  900  of heating a surface of a print bed with a heating element assembly begins at block  902  with positioning a rotatable disc above a print bed of a printing device. The method includes mounting a thermal sensor and a heating element to the disc, as shown at block  904 . As shown at block  906 , the method includes rotating the disc and measuring the temperature of a region on the print bed covered by the thermal sensor. The measured temperature can then be compared with an expected temperature as shown at block  908 . In some examples, comparing the measure temperature with the expected temperature can include providing the measured temperature to a temperature controller integrated with the thermal sensor on the disc, providing the expected temperature to the temperature controller, and providing control signals from the temperature controller to the heating element over a control connection that couples the thermal sensor with the heating element, as shown at blocks  910 ,  912 , and  914 , respectively. As shown at block  916 , the method  900  can then include causing the heating element to heat the region on the print bed when the measured temperature is below the expected temperature.