Patent Publication Number: US-2022219397-A1

Title: Object cleaning

Description:
BACKGROUND 
     There exist a multitude of kinds of three-dimensional (3D) printing techniques that allow the generation of 3D objects through selective solidification of a build material based on a 3D object model. 
     One technique forms successive layers of a powdered or granular build material on a build platform in a build chamber, and selectively applies a curable binder agent on regions of each layer that are to form part of the 3D object being generated. The curable binder agent has to be cured to form a sufficiently strong so-called ‘green part’ that may be removed from the build chamber, cleaned up, and then sintered in a sintering furnace to form the final 3D object. 
    
    
     
       BRIEF DESCRIPTION 
       Examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIG. 1A  is a simplified side view of a cleaning apparatus according to an example; 
         FIG. 1B  is a simplified isometric view of a cleaning apparatus according to an example; 
         FIG. 1C  is a simplified bottom view of a portion of a cleaning apparatus according to an example; 
         FIG. 2  is a flow diagram outline an example method of operating a cleaning apparatus; 
         FIG. 3  is a simplified side view of a cleaning apparatus according to an example; and 
         FIGS. 4A and 4B  are simplified bottom views of a portion of a cleaning apparatus according to an example. 
     
    
    
     DETAILED DESCRIPTION 
     To enable 3D printing systems to move from their currently generally low throughput object generation capabilities to high throughput object generation capabilities many of the currently manually performed processes will have to be transformed into automated processes. Cleaning of 3D printed objects is one of those processes. 
     In binder jet 3D printing, for example, successive layers of a powder, such as a metal powder, are formed on a build platform in a build chamber. A binder agent based is selectively printed on each layer based on a layer of the 3D object to be generated. The binder agent may then be cured, for example by applying heat or by applying ultraviolet light, to generate what is generally known as a green part. A green part is formed from powder particles that are bound together with the binder agent in relatively weak matrix. A green part may be sintered in a sintering furnace where binder agent is burned off, and the powder particles sinter together to form a highly dense final object. 
     Due to various issues, that may include issues such as binder agent carrier liquid leakage, when a green part is extracted from a build chamber there is often some volume of non-bound powder that adheres to the green part. Before a green part can be sintered, however, all powder adhering to the surface of the green part has to be removed otherwise it will become part of the final object after sintering. However, due to the relatively weak nature of green parts it is challenging to ensure removal of non-bound powder without damaging the green part. 
     Referring now to  FIG. 1A , there is illustrated a simplified side view of cleaning system  100  according to one example.  FIG. 1B  illustrates a corresponding simplified isometric view. The system  100  comprises a cleaning module  102  that houses an output, or cleaning, port  104  to direct a first airflow  106  generated from an airflow source  108  through a first conduit  110  to a cleaning zone  112 . The cleaning module  102  also houses an input, or extraction, port  114  to direct a second extraction airflow  116 , generated by a vacuum source  118 , from the cleaning zone  112  through a second conduit  120  to the vacuum source. 
     A bottom view of the cleaning module  102  is illustrated in  FIG. 1C . In the example shown, the cleaning module  102  is configured as and functions as an air knife having a longitudinally aligned output port  104  adjacent to a longitudinally aligned input port  114 . The length of the ports  104  and  114  span the width along the y-axis of a platform  126 , as shown in  FIG. 1B . In one example the output port  104  allows a narrow high-speed laminar air flow to be generated within the cleaning zone  112 . 
     The cleaning module  102  generates, in conjunction with the airflow source  108  and vacuum source  118 , an outward cleaning airflow into the cleaning zone  112 , and generates an inward extraction airflow from the cleaning zone  112 . The outward cleaning airflow  106  is to remove, through the action of a high speed air flow, powder particles adhered to a portion of an object within the cleaning zone and the inward extraction airflow  116  is to extract any powder particles removed by the cleaning airflow  106  from the cleaning zone  112 . The strength of the airflow  106  may be configured to adequately remove adhered powder particles from a 3D object, whilst not causing damage to the 3D object. The strength of the airflow  106  may be configured, for example, based on an expected distance between the output port  104  and a portion of a 3D object within the cleaning zone  112 , and based on the strength of the green part. The strength of the extraction airflow  116  may be configured to adequately extract powder particles removed by the airflow  106  to the vacuum source. 
     The size of the effective cleaning zone  112  may vary, for example, depending on the strength of the airflows  106  and  116 , and the nature of the ports  104  and  114 . 
     Within conduit  120  is provided a sensor  122  to determine a quantity of powder particles within the conduit  120 . In one example, a charge sensor may be provided to determine a concentration of metal powder particles within the conduit  120 . In another example, a light-based particle sensor may be provided to determine a concentration of plastic powder particles within the conduit  120 . Although not shown in  FIG. 1 , between the sensor  122  and the vacuum source  118  a filter or powder particle removal system, such as a cyclone, may be provided to remove powder particles from the extraction airflow  116  before they reach the vacuum source  118 . 
     The cleaning system  100  also comprises a platform  126  on which a 3D object, such as object  124 , may be placed for cleaning by the cleaning module  102 . Relative movement between the platform  126  and the cleaning module  102  may be imparted to allow the system to clean an object  124  positioned on the platform  126  in an automated manner. In the example shown the platform  126  is a platform that is moveable along the x-axis. In one example, the platform  126  is a moveable platform, such as a conveyor belt, a moveable platform mounted on rails, or the like. 
     A controller  128 , such as microcontroller or microprocessor, is coupled to the airflow source  108 , the vacuum source  118 , and the platform  126  to control the operation of the cleaning system  100  in accordance with cleaning system control instructions  130  stored on a machine-readable media such as a memory. The cleaning system control instructions  130  are machine-readable instructions that, when executed by the controller  128 , cause the controller  128  to control the system  100  as described herein. 
     Operation of the cleaning system  100  according to one example will now be described with additional reference to the flow diagram of  FIG. 2 . 
     A 3D object, such as a green part, is placed on the platform  126 . The object may be placed on the platform  126  by an automated system, such as a conveyor belt or a robotic arm, or by a human operator. The height of cleaning module  102  may be adjusted based on the height of the 3D object to be cleaned such that as the 3D object is moved under the cleaning module portions of the object pass through the cleaning zone  112 . 
     At block  202 , the controller  128  controls the airflow source  108  to create the output airflow  106  and controls the vacuum source  118  to create the extraction airflow  116 . 
     At block  204 , the controller  128  controls the platform  126  to move towards the cleaning module  102  at a first speed. When the first portion of the object  124  is within the cleaning zone  112  the output airflow  106  starts to dislodge and remove powder particles adhered to the first portion of the object  124 , and the extraction airflow  116  evacuates any removed powder particles towards the vacuum source  118 . The extraction of removed powder particles helps prevent those particles from abrasively damaging the green part. The sensor  122  generates a signal, such as an electrical or digital signal, in accordance with the quantity of powder particles detected in the extraction airflow  116 . In one example, the controller  128  starts the airflows  106  and  116  when the object is within the cleaning zone  112 . This may be achieved, for example, by way of a proximity sensor (not shown) located on the cleaning module  102 , or in any other suitable manner. 
     At block  206 , the controller determines the quantity of powder particles in the extraction airflow  116 , and at block  208 , the controller  128  controls movement of the platform  126  based on the quantity of powder particles detected in the extraction airflow  116 . 
     For example, when a first portion of a 3D object is moved into the cleaning zone  112  the quantity of powder particles in the extraction airflow  116  will start to increase as powder particles that can be removed by the cleaning module  102  are removed. Before the object is moved into the cleaning zone  112  the quantity of particles detected by the sensor  122  will be at or around some ambient level, such as for example at around 8 particles per cm 3  depending on the cleanliness of the air. After a short time, the quantity of powder particles in the extraction airflow  116  will start to decrease as there remains less powder to be removed from the green part. In one example, the controller  112  adjusts the movement/speed of the platform  126  to keep the determined quantity of powder particles above a predetermined minimum level. In other words, when the detected quantity of powder particles detected falls below the predetermined minimum level the controller  112  modifies the movement/speed of the platform  126 . In one example, the minimum level could be between around 8 to 16 powder particles per cm 3 . The exact predetermined minimum level may depend on whether the sensor detects particles, such as dust particles, which are not powder particles. In this way, each portion of the 3D object is not exposed to unnecessarily long exposure to the output airflow  106  which could, in some circumstances, damage the green part. Furthermore, each object may pass under the cleaning module  102  to be adequately cleaned at an optimum throughput rate. At the same time, the 3D object is cleaned in an efficient manner without any human intervention. This is particularly useful when multiple 3D objects to be cleaned are place on the platform  126 . 
     In one example, the platform  126  may be continuous conveyor belt and may have objects continually placed thereon by a suitable robotic or other mechanism. 
     In one example, depending on the determined quantity of powder in the conduit  120  the controller  128  may control the platform  126  to advance in a in a stepwise manner. For example, the controller  128  may control the platform  126  to move forward by a small distance, such as 0.5 cm, or 1 cm, or 2 cm, or 5 cm, or 10 cm, and may stop movement of the platform  126  until the determined quantity of powder in the conduit  120  falls below a predetermined level. The controller  128  may then control the platform  126  to move forward by another predetermined distance. 
     In another example, the controller  128  may control the platform  126  to advance in continuous manner, whereby the speed of the platform advance is based on the determined quantity of powder in the conduit  120 . For example, when the quantity of determined powder in the conduit  120  is relatively high, the speed of the platform may be relatively low, whereas when the quantity of determined powder in the conduit  120  is relatively low the speed of the platform may be relatively high. 
     Referring now to  FIG. 3 , there is illustrated a side view of a cleaning apparatus  300  according to an example. In this example, the cleaning module  102  is height adjustable, allowing the cleaning module to be vertically raised and lowered. In the example shown, a vertical rail  302  is provided on which the cleaning module  102  may be raised and lowered, for example using a motor or a servo. A height sensor  304  is also provided to enable the distance between the cleaning module  102  and a 3D object  124  to be determined. In the example shown, the height sensor  304  is coupled to one side of the cleaning module  102 , although in other examples a height sensor may be positioned elsewhere. In one example a laser or an ultrasonic height sensor may be used. By allowing the cleaning module  102  to be height adjustable enables 3D objects that have non-uniform geometries to be cleaned in an efficient manner, by automatically keeping each portion of a 3D object within the cleaning zone  112 . 
     In a further example, the cleaning apparatus  300  may modify the strength of the cleaning airflow  106  and/or the extraction airflow  116  without adjusting the height of the cleaning module  102  to vary the size of the cleaning zone  112  based on the distance between cleaning module  102  and a portion of the 3D object  124  being cleaned. 
     The cleaning module  102  may be configured in numerous ways. For example, as shown in  FIG. 4A , the cleaning module  102  may comprise a pair of extraction ports  114  that sandwich between them an output port  104 . In this way two extraction airflows  116  would be generated within the cleaning zone  112 . 
     In a further example, illustrated in  FIG. 4B , the cleaning module  102  may comprise an extraction port  114  that surrounds the output port  104 . 
     In a further example, the cleaning apparatus  300  may comprise a plurality of height adjustable cleaning modules  302  arranged in an in-line configuration. In this example, the controller  128  can control the height of each of the plurality of the cleaning modules  302  based on the distance between each of the plurality of cleaning modules and between a respective portion of a 3D object in proximity thereto. Such an arrangement may be useful when a 3D object to be cleaned has an irregular shape. 
     In a further example, the cleaning module  102  may be oriented at a fixed angle, such as an angle of 20 degrees, or 30 degrees, or 40 degrees, or 50 degrees, to the vertical, such that the cleaning zone  112  is oriented towards the leading portion of the 3D object as it is moved by the platform  126 . In a yet further example, the cleaning module  102  may be rotationally orientable, for example under control of the controller  128 , to adjust its orientation based on the geometry of the portion of the 3D object being cleaned. For example, the controller may use one or multiple sensors to orientate the cleaning module  102  such that the output airflow hits the portion of the 3D object in the cleaning zone within a predetermined angle of the surface normal of the object portion. In another example the controller  128  may adjust the orientation of the cleaning module  102  based, for example, on a predetermined rotational sweeping movement of the cleaning module  102 . 
     Although the examples described above describe a movable platform  126  to move 3D printed objects under the cleaning module  102 , in other examples the platform  126  could be static and the cleaning module  102  could be moveable along the x-axis relative to the platform  126 . In other examples, both the platform  126  and the cleaning module  102  could be movable along the x-axis. 
     It will be appreciated that example described herein can be realized in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are examples of machine-readable storage that are suitable for storing a program or programs that, when executed, implement examples described herein. Accordingly, some examples provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine-readable storage storing such a program. Some examples may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection. 
     All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
     Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.