Patent Publication Number: US-2021162669-A1

Title: Three-dimensional object manufacturing device and method

Description:
FIELD OF THE DISCLOSURE 
     The present application relates to a three-dimensional object manufacturing device and method using digital light processing (DLP), more specifically a three-dimensional object manufacturing device and method using digital light processing with circuitry for controlling a stage of the manufacturing device based on a torque value of a moving device for moving the stage. 
     DESCRIPTION OF THE RELATED ART 
     Various methods and devices for forming three-dimensional (“3D”) objects using printing techniques have been proposed. For example, 3D printers that use digital light processing (DLP) technology to form 3D objects are well known. With such devices, a stage is placed in a vat filled with a photopolymer and light is applied through the bottom of the vat to a cross-sectional area of the photopolymer, so as to create a layer of a desired three-dimensional object attached to the stage. The stage is then raised slightly and processing repeated until all layers of the object have been created. Such devices have benefits including fast processing speed, relatively high accuracy, and relatively little waste generated. 
     However, there is room for improvement in the effectiveness of such devices. For example, Published Patent Application JP 2015-024634A (“JP &#39;634”) discusses features to suppress falling of a three-dimensional molded object in the middle of production from a member holding the molded object, but lacks detailed discussion regarding processing accuracy and speed 
     Also, for example, U.S. Pat. No. 8,623,264 B2 (“U.S. Pat. No. &#39;264”) outlines a method and device in which a trough (vat) can be shifted horizontally, or in which multiple vats arranged on a turntable can be moved in a circle. Further, U.S. Pat. No. &#39;264 describes a method of controlling forces on a build platform (stage) during processing. However, methods outlined for measuring and controlling forces are relatively complex, leaving room for improvement in terms of a simple configuration that maintains processing effectiveness. 
     Further, for example, United States Patent Application Publication US2017/368747A1 (“US &#39;747”) discusses techniques for determining an accurate position of a build platform (stage), for example, by measuring forces, but does not discuss implications for processing speed, thus leaving room for improvement in terms of processing effectiveness. 
     SUMMARY 
     A DLP 3D printer with improved processing effectiveness that solves the above problems is desired. For this, the inventors propose a three-dimensional object manufacturing device including: 
     a vat configured to hold a photopolymer; 
     a digital light processing unit configured to apply light to at least a portion of the photopolymer in the vat so as to create a layer of a three-dimensional object; 
     a movable stage configured to be movable relative to the vat containing the photopolymer; 
     a moving device configured to move the stage; and 
     a controller configured to control a speed of the moving device based on a torque value of the moving device. 
     The inventors further propose a three-dimensional object manufacturing method including: 
     filling a vat with a photopolymer; 
     applying light using a digital light processing unit to at least a portion of the photopolymer in the vat so as to create a layer of a three-dimensional object; 
     using a moving device to move a movable stage relative to the vat containing the photopolymer; and 
     controlling a speed of the moving device based on a torque value of the moving device. 
     According to both the device and method above, the speed at which a movable stage is moved relative to a vat containing a photopolymer used to create a three-dimensional object can be controlled based on a torque value of a moving device that moves the stage. This allows for efficient and effective printing processing while preventing a workpiece from falling during printing processing. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic view of a printer, according to certain aspects of the disclosure. 
         FIG. 2  is a block diagram showing the overall configuration of a printer, according to certain aspects of the disclosure. 
         FIG. 3  is a table showing an example of work data, according to certain aspects of the disclosure. 
         FIG. 4  is a flowchart showing an example of printing processing, according to certain aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Materials, methods, and examples discussed herein are illustrative only and are not intended to be limiting. In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words “a”, “an”, and the like include a meaning of “one or more”, unless stated otherwise. The drawings are generally drawn not to scale unless specified otherwise. 
       FIG. 1  is a schematic view of printer  1 , according to certain aspects of the disclosure. Printer  1  is a device for manufacturing a 3D object, workpiece W. Printer  1  is provided with printer body  10  and controller  18 . Printer body  10  includes items such as vats  11 , digital light processing unit  12 , movable stage  14 , motor  16 , vat loader  30 , loader moving device  40 , and vacuum generator  80 . Printing processing by which printer  1  manufactures workpiece W is described in detail later. 
     Printer body  10  is housing for some of the items that configure printer  1 . Vat  11  is for holding a photopolymer (for example, P 1 , P 2 ) used for creating workpiece W. Vat  11  is a container with a bottom and side walls and an open top such that a stage can be inserted into the photopolymer loaded in vat  11  from above. Vats  11  may be provided with a lip (not shown) for support when inserted into a hole of vat loader  30  (described below). The bottom surface of vat  11  is transparent such that light from digital light processing unit  12  (described below) can reach the photopolymer in vat  11 . The configuration of vat  11  is not particular limited, so long as it can hold a photopolymer and allow light from a digital light processing unit to reach the photopolymer. In printer  1 , multiple vats  11  are provided, each holding a different photopolymer, such that workpiece W can be manufactured from multiple materials. 
     Vats  11  are loaded on vat loader  30 . Vat loader  30  is a turntable with holes for receiving vats  11  and is provided with loader moving device  40 . The holes for receiving vats  11  may be of an appropriate size such that a lip of vat  11  is supported by the edge of the hole. Vat loader  30  may also be provided with an adjustable supporting mechanism such as screws or the like to support vats of various sizes. Loader moving device  40  rotates vat loader  30  such that each of the multiple vats  11  can be moved to a stage receiving position ( 50 ) at which movable stage  14  is lowered into the vat  11  (in  FIG. 1 , the vat on the right is at stage receiving position  50 ). In printer  1 , vat loader  30  is configured as a turntable that is rotated by loader moving device  40 , but the configuration is not limited to this. The vat loader may be a rectangular plate or the like and the loader moving device may move the vats to the stage receiving position via conveyors, rollers, or the like. Alternatively, the loader moving device may exchange vats at the stage receiving position using a robot arm or the like that grips the vat using a mechanical claw. However, an advantage of using a turntable as loader moving device  40  is that this enables accurate positioning of vats  11  at the stage receiving position with a relatively simple mechanism with cheap manufacturing costs. In particular, such a configuration enables good accuracy to be maintained in the vertical direction, which is important for printing processing accuracy. Note that, accuracy levels required by such printers are often in a range of 10 to 100 microns. 
     Digital light processing unit  12  is used during printing processing to harden successive layers of the photopolymer in vat  11  to create workpiece W. Such units are well-known and a conventional digital light processing unit may be employed. For example, digital light processing unit  12  includes a light source and light adjustment mechanism (not shown), and hardens a layer of the workpiece W being created by applying light L to the photopolymer in vat  11  from below, through the transparent bottom of vat  11 . Digital light processing unit  12  receives instructions from controller  18  and adjusts the light being applied to vat  11  based on these instructions. For example, the light L may be adjusted based on information regarding the layer to be created such as shape, position, and surface area. 
     Movable stage  14  is attached to frame  90  to be movable in a vertical direction (shown by the two-headed arrow in  FIG. 1 ). Movable stage  14  is moved vertically by a moving device, for example, motor  16 . During printing processing of workpiece W, movable stage is lowered by motor  16  until a bottom surface of movable stage  14  is inside a photopolymer in vat  11 . When a layer of the photopolymer has been hardened by digital light processing unit  12 , based on instructions from controller  18 , motor  16  is driven at a given torque to raise movable stage  14 . This processing is repeated layer by layer until the entire workpiece W is complete. Details regarding printing processing are described later. 
     Movable stage  14  is also provided with multiple holes  142 . Holes  142  are open at the bottom surface of movable stage  14 . Holes  142  are connected to, for example, vacuum generator  80  such that negative pressure can be supplied to holes  142 , either collectively or individually. By applying negative pressure to holes  142 , workpiece W being created on movable stage  14  is held more securely to movable stage  14 , which prevents workpiece W from falling during printing processing. For example, this enables movable stage  14  to be raised at a faster speed, thus improving the efficiency of printing processing. Negative pressure to holes  142  may be controlled individually based on instructions from controller  18 . For example, by adjusting to which holes  142  negative pressure is applied based on a shape, position, surface area, and the like of a layer of workpiece W that contacts the bottom surface of movable stage  14 , it is possible to efficiently supply negative pressure while securely holding the workpiece W being created to movable stage  14 . The force holding workpiece W to the bottom surface of the stage is particularly important when considering the force holding the newly created layer of workpiece W to the bottom surface of the vat. This force will also vary depending on a shape, position, surface area, and the like of the current layer (the layer contacting the bottom surface of the vat). As such, both a shape, position, surface area, and the like of a layer of workpiece W that contacts the bottom surface of movable stage  14  and a shape, position, surface area, and the like of the current layer may be considered when deciding, for example, the required holding force of workpiece W and the moving speed of movable stage  14 . Details regarding varying of the moving speed of movable stage  14  are described later. 
       FIG. 2  is a block diagram showing the overall configuration of printer  1 , according to certain aspects of the disclosure. 
     As shown in  FIG. 2 , printer  1  also includes operation panel  60  (not shown in  FIG. 1 ). Operation panel  60  is used to display information to an operator and to receive inputs such as entry of job data  20  (refer to  FIG. 3 ) and instructions to start or stop printing processing. 
     Controller  18  performs overall control of printer  1 . Controller  18  may include items such as setting circuitry  182 , saving circuitry  184 , processing circuitry  186 , and memory  188 . Controller  18  may be configured from a general purpose computer or the like, including items such as a CPU, ROM, RAM, and an HDD. Memory  188  of controller  18  stores information such as job data  20  used during printing processing. Job data  20  may be entered by an operator using operation panel  60 . Details regarding job data  20  are given below. 
     Processing circuitry  186  performs processing during printing processing of printing workpiece W based on job data  20 . Saving circuitry  184  saves information generated during printing processing, such as a torque value of motor  16 . Setting circuitry  182  is used by controller  18  to set values such as separation threshold value ST and falling threshold value FT used during printing processing. Details regarding such threshold values, other information used, and printing processing are given below. 
       FIG. 3  is a table showing an example of job data  20 , according to certain aspects of the disclosure. Job data  20  is used during printing processing used to create workpiece W, and includes, for example, information regarding a workpiece type that defines the type of 3D object being created, and layer information LI. Layer information LI includes information of each layer, from LI 1  to LIx, of the workpiece type. Each LI 1  to LIx contains, for example, information representing a shape, a position, and a surface area of that layer. This information is used by digital light processing unit  12  to appropriately adjust the light applied to vat  11 . This information may also be used by controller  18  to control the supply of negative pressure to holes  142  of movable stage  14 . 
       FIG. 4  shows a flowchart of an example of printing processing. Printing processing will now be described in detail with reference to  FIG. 4 . 
     The printing processing of  FIG. 4  is performed by controller  18 . After receiving an instruction from an operator to start printing processing, in S 100 , controller  18  controls motor  16  such that movable stage is lowered into vat  11  to the start position for the next layer. 
     Next, in S 105 , controller  18  controls digital light processing unit  12  to apply light to a layer of the photopolymer in vat  11  based on layer information LI of a first layer of the 3D object being created, as defined in job data  20  (refer to  FIG. 3 ). 
     Then, in S 110 , controller  18  controls motor  16  to raise movable stage  14  at a first speed, v 1 . Note that, first speed v 1  may be determined in advanced based on, for example, the material being used as a photopolymer, and the size, shape, weight, layer surface area, and so on of the workpiece W being created. 
     Then, in S 115 , controller  18  determines whether the created layer was the first layer of the 3D object based on job data  20 . If determining “Yes” in S 115 , controller  18  proceeds to S 120 , in which, after raising movable stage  14  by a specified amount, controller  18  uses setting circuitry  182  to set separation threshold value ST based on a current torque value received from motor  16 . Note that, the torque value may be received from motor  16 , for example, based on information from an encoder of motor  16 . Controller  18  then proceeds to S 155 , wherein movable stage  14  is stopped at a predetermined upper limit. 
     If controller  18  determines “No” in S 115 , processing proceeds to S 125 . In S 125 , controller  18  determines if the current position of movable stage is greater than the predetermined upper limit. If determining “Yes” in S 125 , controller  18  stops operation of printer  1  (S 130 ), then returns to S 100 . If determining “No” in S 125 , controller  18  proceeds to S 135 . 
     In S 135 , controller  18  determines whether the current torque of motor  16  is less than the currently set separation threshold value ST. If determining “No” in S 135 , controller  18  returns to S 110 . If determining “Yes” in S 135 , controller  18  proceeds to S 140 . 
     In S 140 , controller  18  determines whether the current torque value is less than a predetermined falling threshold value, FT. Note that, falling threshold value FT may be set in advance by setting circuitry  182  of controller  18 , based on, for example, the material being used as a photopolymer, and the size, shape, weight, layer surface area, and so on of the workpiece W being created. If determining “Yes” in S 140 , controller  18  stops operation of printer  1  and issues a warning to an operator via operation panel  60  (S 145 ). If determining “No” in S 145 , controller  18  proceeds to S 150 . 
     In S 150 , controller  18  updates separation threshold value ST based on the current torque of motor  16 , then proceeds to S 155 . 
     In S 155 , controller  18  controls motor  16  to raise movable stage  14  at a second speed, v 2 , which is greater than v 1 . Note that, as with first speed v 1 , second speed v 2  may be determined in advanced based on, for example, the material being used as a photopolymer, and the size, shape, weight, layer surface area, and so on of the workpiece being created. 
     Processing then proceeds to S 160 , where movable stage  14  is stopped at the upper limit. Then, in S 165 , controller  18  determines whether the final layer of the 3D object being created is complete. If determining “No” in S 165 , controller  18  returns to S 100 . If determining “Yes” in S 165 , controller  18  ends processing. 
     As described above, with printer  1 , controller  18  is configured to control a speed of motor  16  (moving device) based on a torque value of motor  16 . Thus, by appropriately controlling the speed of motor  16 , movable table  14  is moved such that printing processing is performed efficiently and effectively, without the workpiece W being created falling from movable stage  14 . 
     Further, with printer  1 , movable stage  14  may be positioned above vat  11  and includes at least one hole  142 , hole  142  being configured to assist holding of the created workpiece W via negative pressure being supplied via the at least one hole  142 . Accordingly, the workpiece W is held more securely to movable stage  14  during printing processing, enabling faster printing processing while preventing the workpiece W being created falling from movable stage  14 . 
     Also, with printer  1 , when movable stage  14  includes multiple holes  142 , controller may be configured to control supply of the negative pressure to each of the holes  142  individually based on a workpiece type of the workpiece W, as defined in work data  20 . 
     Further, with printer  1 , further provided may be: vat loader  30  on which multiple of the vats  11  are loadable, wherein each of the vats  11  contains a different photopolymer; and loader moving device  40  for moving vat loader  30 . Movable stage  14  may be positioned above vat loader  30  and controller  18  may be configured to drive loader moving device  40  such that each of the multiple vats  11  are positioned one at a time at a position to receive the stage such that the workpiece W can be manufactured from different materials. 
     Further, printer  1  may also be provided with setting circuitry  182  configured to set separation threshold value ST that is a threshold to which to compare the torque value, and controller  18  may be configured to check whether the torque value exceeds the separation threshold value ST, and to control motor  16  to move at a first speed, v 1 , if the torque value is less than the separation threshold value ST. Accordingly, printer  1  achieves faster and more efficient printing processing. 
     Also, with printer  1 , controller  18  may be also configured to use setting circuitry  182  to set falling threshold value FT that is a threshold to which to compare the torque value, and controller  18  may be configured to perform at least one of stopping operation or issuing a warning to an operator if the torque value is equal to or greater than falling threshold value FT, and to control motor  16  to move at a second speed, v 2 , if the torque value is less than falling threshold value FT, the second speed v 2  being faster than the first speed v 1 . Accordingly, printer  1  achieves faster and more efficient printing processing. 
     With printer  1 , controller  18  may be further configured to update separation threshold value ST based on a current torque value of motor  16  that is the torque value from after comparing with falling threshold value FT. This allows printing processing of subsequent layers to be performed more appropriately. Accordingly, printer  1  achieves faster and more efficient printing processing. With printer  1 , controller  18  may also be configured to consider a surface area value of a current layer that is a layer currently being processed when setting at least one of separation threshold value ST or the falling threshold value FT. This allows separation value ST or falling threshold value to be set more appropriately, enabling faster printing processing while preventing the workpiece W being created falling from movable stage  14 . 
     Further, according to another aspect of the disclosure, printer  1  is used to perform a three-dimensional object manufacturing method including: filling a vat with a photopolymer; applying light using a digital light processing unit to at least a portion of the photopolymer in the vat so as to create a layer of a three-dimensional object; using a moving device to move a movable stage relative to the vat containing the photopolymer; and controlling a speed of the moving device based on a torque value of the moving device. This method achieves the same benefits as that of printer  1 . 
     The foregoing discussion discloses and describes exemplary embodiments of an object of the present disclosure. As will be understood by those skilled in the art, an object of the present disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the present disclosure is intended to be illustrative, but not limiting of the scope of an object of the present disclosure as well as the claims. 
     Numerous modifications and variations on the present disclosure are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced otherwise than as specifically described herein. 
     For example, although not shown in the figures, a tilting mechanism may be provided to tilt vat  11 . In this manner, the peeling forces exerted on the 3D object being created as movable stage  14  is raised may be mitigated, such that damage to the 3D object is prevented. The tilting mechanism may also be controlled based on a torque value of motor  16  (moving device). 
     REFERENCE SIGNS LIST 
       1 : printer;  10 : printer body  10 : vat;  12 : digital light processing unit;  14 : movable stage;  142 : hole;  16 : motor;  18 : controller;  182 : setting circuitry;  184 : saving circuitry;  186 : processing circuitry;  188 : memory;  20 : job data;  30 : vat loader;  40 : loader moving device;  50 : stage receiving position;  60 : operation panel;  80 : vacuum generator; L: light; P 1 , P 2 : photopolymer; T: torque; FT: falling threshold; ST: separation threshold; v 1 : first speed; v 2 : second speed; W: workpiece