Melted metal level sensor for metal drop ejecting three-dimensional (3D) object printer

Abstract

To provide a metal drop ejecting apparatus equipped with a device for determining the position of a surface level of melted metal in a receptacle of a 3D metal object printer, and a method for operating the metal drop ejecting apparatus.SOLUTION: A three-dimensional (3D) metal object manufacturing apparatus is equipped with a wire detector 190 to determine a position of a top surface of melted metal contained in a receptacle of a heated vessel 104 in the apparatus from time to time. The solid metal wire being fed into the heated vessel is retracted and the length of the retracted wire 120 is determined using a signal generated by the wire detector. The determined length of the wire is used to identify the position of the top level of the melted metal in the receptacle so the receptacle can be replenished if the level has fallen below a predetermined capacity for the receptacle.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a three-dimensional (3D) object printer that ejects molten metal droplets to form an object, and more particularly, to the measurement of the amount of molten metal available for ejection in such a printer.

Background Art

[0002] Three-dimensional printing, also known as additive manufacturing, is a process of creating a three-dimensional solid object from a digital model of virtually any shape. Many three-dimensional printing techniques use a lamination process in which a lamination device forms successive layers of a part on top of previously deposited layers. Some of these techniques use an ejection device that ejects an ultraviolet curable material such as a photopolymer or an elastomer. The printer typically operates one or more extruders to form successive layers of a plastic material that builds a three-dimensional printed object having various shapes and structures. After each layer of the three-dimensional printed object is formed, the plastic material is ultraviolet cured, solidified, and adhered to the underlying layer of the three-dimensional printed object. This additive manufacturing method is distinguishable from conventional object formation techniques that mostly rely on the removal of material from a workpiece by a subtractive process such as cutting or drilling.

[0003] Recently, several 3D object printers have been developed that form 3D objects by ejecting droplets of molten metal from one or more ejectors. These printers have a solid metal source, such as a roll of wire or pellets, which is supplied to a heated containment section in a container within the printer where the solid metal is melted, filling the containment section. The containment section is made of a non-conductive material around which electric wires are wound to form a coil. As electric current passes through the coil, it generates an electromagnetic field, which causes the meniscus of molten metal at the nozzle of the containment section to separate from the molten metal in the containment section and propel it out of the nozzle. A platform opposite the nozzle of the ejector is moved in the XY plane parallel to the plane of the platform by an actuator operated by a controller, so that the ejected metal droplets form a metal layer of the object on the platform, and another actuator, operated by the controller, changes the position of the ejector or platform in the vertical or Z direction, maintaining a constant distance between the ejector and the top layer of the formed metal object. This type of metal droplet ejector printer is also known as a magnetohydrodynamic (MHD) printer.

[0004] The molten metal in the container housing within the printer must be maintained at a level sufficient to support the metal droplet ejection operation without depleting the molten metal supply within the printer. In one metal droplet ejection printer, a blue laser is directed at the surface level of the molten metal in the housing, and a reflection sensor monitors the laser reflection by the surface level to determine the current height of the molten metal in the housing. If the sensor output indicates that the surface level has fallen to a threshold position within the housing, a wire feed actuator is activated to supply more solid metal to the housing.

[0005] The arrangement of laser and reflective sensors for molten metal pool measurement presents several problems in determining the precise surface level position within the containment. For example, the optical alignment of the laser beam and the sensor is highly sensitive to interference that can affect the sensor's ability to receive reflected light signals and maintain robust contact with them. This alignment is difficult to establish after the sensor mounting bracket is reinstalled following removal of the printer's upper block for maintenance. The laser lens can also be contaminated with condensate, which can attenuate the beam intensity. Furthermore, despite the inert gas environment such as argon within the printer, an aluminum oxide layer may form on the molten metal, leading to erroneous sensor readings. This aluminum oxide layer may also contain organic contaminants supported on the solid metal surface. This layer can be self-supporting, preventing the laser beam from reaching the true surface of the molten metal, thus resulting in erroneous sensor output. Finally, reflective sensors are expensive. A less expensive and more robust molten metal surface sensing scheme would be beneficial. [Overview of the project]

[0006] A novel method for determining the position of the surface level of molten metal within the housing of a 3D metal object printer is more robust and economical. The method includes: generating a first signal value indicating the presence of a solid metal wire using a wire detector positioned between a second end of a wire guide and a housing in a container configured to melt a solid wire received from the wire guide; generating a second signal value indicating the absence of a solid metal wire using the wire detector; and determining the position of the top surface level of the molten metal within the housing.

[0007] The new 3D metal object printer determines the position of the surface level of molten metal within the housing of the 3D metal object printer in a more robust and economical way. The new 3D metal object printer includes an extrusion head having a container having a housing within the container; a wire guide configured to receive a solid metal wire at a first end, and to direct the solid metal wire through the wire guide to a second end through which the solid metal wire passes and exits toward the housing of the container; a heater configured to heat the container to a temperature sufficient to melt the solid metal wire within the housing of the container while the container is inside the extrusion head; at least one actuator operably connected to the solid metal wire, the at least one actuator configured to move the solid metal wire bidirectionally through the wire guide; and a wire detector positioned between the second end of the wire guide and the housing in the container, the wire detector configured to generate a first signal indicating the presence of a solid metal wire at the wire detector and a second signal indicating the absence of a solid metal wire at the wire detector. [Brief explanation of the drawing]

[0008] The aforementioned aspects and other features of a method for determining the position of the surface level of molten metal within the housing of a 3D metal object printer, which is more robust and economical than those previously known, as well as a 3D metal object printer implementing the method, are described below in relation to the attached drawings.

[0009] [Figure 1] This paper presents a new 3D metal object printer that determines the position of the surface level of molten metal within the housing of the 3D metal object printer in a more robust and economical way than laser measurement methods.

[0010] [Figure 2] This is a schematic diagram of a wire supply mechanism used to supply wire to the wire guide 124 in Figure 1, and for measuring the wire drawn in from the housing of the printer container in Figure 1.

[0011] [Figure 3] This is a flowchart for the process of determining the surface level position of molten metal within the housing of a 3D metal object printer using a wire detector and metal droplet counting method.

[0012] [Figure 4] Figure 1 is a flowchart of the process for adjusting the proportionality constant K used to determine the number of ejected metal droplets counted between surface level measurements of molten metal in the casing of the printer.

[0013] [Figure 5] This is a block diagram of a 3D metal printer that uses a laser system to determine the position of the surface level of molten metal within the printer's housing. [Modes for carrying out the invention]

[0014] For a general understanding of the 3D metal object printer and the environment for its operation disclosed herein, as well as the details of the printer and its operation, refer to the drawings. In the drawings, similar reference numbers represent similar elements.

[0015] Figure 5 shows an embodiment of a previously known 3D metal object printer 100 that uses a laser beam and a reflection sensor to determine the surface level of molten metal in the printer's housing. In the printer of Figure 5, droplets of molten bulk metal are ejected from a housing of a removable container 104 having a single nozzle 108, and the droplets from the nozzle form a swath for a layer of object on the platform 112. As used herein, the term “removable container” means a hollow container having a housing configured to hold liquid or solid material, and the container as a whole is configured to be installed and removed in a 3D metal object printer. As used herein, the term “bulk metal” means conductive metal available in aggregate form, such as wires of commonly available standard sizes or pellets of macro-size ratios. A bulk metal source 116, such as a metal wire 120, is supplied to a wire guide 124 extending through an upper housing 122 within the dispensing head 140, melted in a removable container 104, and provides molten metal to be extruded from a nozzle 108 through an orifice 110 in the base plate 114 of the dispensing head 140. As used herein, the term “nozzle” means an orifice in the removable container configured for the extrusion of molten metal droplets from the housing in the removable container. As used herein, the term “dispensing head” means the housing and components of a 3D metal object printer that melts, extrudes, and adjusts the extrusion of molten metal droplets for the manufacture of metal objects. The molten metal level sensor 184 includes a laser and a reflection sensor. The reflection of the laser from the molten metal level is detected by the reflection sensor and generates a signal indicating the distance to the molten metal level. The controller receives this signal and determines the volume level of the molten metal in the removable container 104 so that it can be maintained at the upper level 118 in the housing of the removable container. The removable container 104 slides into the heater 160, the inner diameter of the heater comes into contact with the removable container, and the solid metal inside the container is heated to a temperature sufficient to melt it.As used in this document, the term “solid metal” means a metal as defined in the periodic table of elements, or an alloy formed by these metals in a solid form rather than a liquid or gaseous state. The heater is separated from the removable container, forming a volume between the heater and the removable container 104. The inert gas supply unit 128 provides a pressure-regulated source of an inert gas, such as argon, to the discharge head through the gas supply pipe 132. The gas flows through the volume between the heater and the removable container and exits through the orifice 110 in the discharge head and base plate 114 around the nozzle 108. This flow of inert gas close to the nozzle insulates the discharged droplets of molten metal from the ambient air around the base plate 114, preventing the formation of metal oxides during the flight of the discharged droplets.

[0016] The dispensing head 140 is mounted to move within a Z-axis trajectory to accommodate the vertical movement of the dispensing head relative to the platform 112. One or more actuators 144 are operably connected to the dispensing head 140 to move the dispensing head along the Z-axis and to the platform 112 to move the platform in the XY plane below the dispensing head 140. The actuators 144 are operated by a controller 148 to maintain an appropriate distance between the orifice 110 in the base plate 114 of the dispensing head 140 and the uppermost surface of an object on the platform 112.

[0017] As droplets of molten metal are ejected toward the platform 112, moving the platform 112 in the XY plane creates swaths of molten metal droplets on the object being formed. The controller 148 also operates the actuator 144 to adjust the vertical distance between the ejector head 140 and the most recently formed layer on the substrate, facilitating the formation of other structures on the object. The molten metal 3D object printer 100 is shown in Figure 3 as operating vertically, but other alternative orientations may be used. Also, the embodiment shown in Figure 3 has a platform that moves in the XY plane and the ejector head that moves along the Z axis, but other arrangements are possible. For example, the actuator 144 may be configured to move the ejector head 140 in the XY plane and along the Z axis, or it may be configured to move the platform 112 in both the XY plane and along the Z axis.

[0018] The controller 148 operates switches 152. One switch 152 may be selectively operated by the controller to provide power to the heater 160 from a power source 156, and another switch 152 may be selectively operated by the controller to provide power to the coil 164 from another power source 156 to generate an electric field for ejecting droplets from the nozzle 108. Because the heater 160 generates a large amount of heat at a high temperature, the coil 164 is located within a chamber 168 formed by one (circular) or two or more walls (linear) of the ejector head 140. As used in this document, the term “chamber” means a volume contained within one or more walls in which the heater, coil, and removable container of the 3D metal object printer are located. The removable container 104 and the heater 160 are located within this chamber. The chamber is fluidically connected to a fluid source 172 via a pump 176 and is also fluidly connected to a heat exchanger 180. As used in this document, the term “fluid source” refers to a container of liquid having properties useful for absorbing heat. The heat exchanger 180 is connected via a return to the fluid source 172. Fluid from the source 172 flows through the chamber, absorbing heat from the coil 164, and the fluid carries the absorbed heat through the exchanger 180, where the heat is removed by known means. The cooled fluid is returned to the fluid source 172 for further use in maintaining the coil temperature within a suitable operating range.

[0019] The controller 148 of the 3D metal object printer 100 requires data from an external source to control the printer for the manufacture of metal objects. Generally, a three-dimensional model or other digital data model of the object to be formed is stored in memory operably connected to the controller 148, and the controller may be able to access a remote database where the digital data model is stored via a server or the like, or a computer-readable medium where the digital data model is stored may be selectively connected to the controller 148 and become accessible. This three-dimensional model or other digital data model is processed by a slicer implemented with the controller to generate machine-ready instructions that the controller 148 executes in a known manner, thereby operating the components of the printer 100 and forming a metal object corresponding to that model. The generation of machine-ready instructions may include the creation of an intermediate model, such as when a CAD model of a device is converted to an STL data model, or to another polygonal mesh or other intermediate representation, and this intermediate model may then be processed to generate machine instructions, such as g-code, for the printer to manufacture the device. As used in this document, the term “machine-responsive instruction” means a computer language command executed by a computer, microprocessor, or controller to operate the components of a 3D metal object additive manufacturing system to form a metal object on the platform 112. The controller 148 executes the machine-responsive instruction to control the ejection of molten metal droplets from the nozzle 108, the positioning of the platform 112, and the maintenance of the distance between the orifice 110 and the uppermost layer of the object on the platform 112.

[0020] A new 3D metal object printer 100' is shown in Figure 1, using similar reference numbers for similar components and removing some components not used to determine the surface level of the molten metal in the containment. The laser 184 and reflection sensor 188 are replaced by a wire detector 190. The wire detector 190 is located at the exit of the wire guide 124. The wire detector can be an optical or inductive sensor. An optical sensor has a light source, such as an LED, on one side of the wire path from the exit of the wire guide 124 to the containment in the container 104. On the other side of this wire path is the light sensor. The light sensor generates a signal value of digital 1 or digital 0 when the wire blocks the transmission of light from the light source to the light sensor, and the opposite signal value when the wire is not between the light source and the light sensor. That is, the sensor generates a binary signal with two digital signal values ​​to indicate whether the wire is on the opposite side of the sensor. A light-transmitting sensor rated at 125°C, such as the Vishay TCPT sensor available from Vishay Intertechnology (Malvern, Pennsylvania), can be used in an empirically defined environment in one embodiment of printer 100'. The inductive sensor generates an inductive field, and when a metal wire is present in the field, the sensor generates one digital value; when the metal wire is not present in the field, the sensor generates another digital value. The wire detector 190 has a heat sink mounted on the upper housing 122 to dissipate heat from the sensor and maintain the sensor temperature within its operating range.

[0021] Determining the molten metal surface level is based on empirical observation that the wire melts within a short, repeatable distance after entering the molten metal in the containment. As a result, the length of the wire from the wire detector to the tip of the wire entering the molten metal is an indirect indicator of the molten metal surface in the containment. To determine the position of the molten metal surface, controller 148' operates one of the actuators 144 to reverse the wire feed direction, pulling the end of the wire out of the molten metal in the containment. This reversal action is stopped when the wire detector 190 generates a signal that the wire is no longer detected by the sensor. Along with the speed of the wire reversal, the length of time from the start of the wire reversal to the detection of the absence of wire is used by controller 148' to determine the current level of molten metal in the containment. The wire is then advanced in the feed direction at the same speed for an equal amount of time to place the end of the wire back into the molten metal and resume the printer's normal operation.

[0022] Figure 2 shows a mechanism 200 for supplying wire from a wire supply unit 116 through a wire guide 124 to a container 104. Mechanism 200 is one embodiment for distributing a suitable amount of wire to determine the length of wire to be drawn from the container when the position of the molten metal level is determined. A controller 148' is operably connected to an actuator, such as a stepper motor 240, to control the speed at which the wire is delivered from the supply unit 116 to the container 104. The actuator 240 drives a roller 224 and is operably connected to the controller 148' so that the controller can adjust the speed at which the actuator drives the roller 224. Another roller on the opposite side of the roller 224 is freewheeling and therefore follows the rotational speed at which the roller 224 is driven.

[0023] The slip clutch 244 is operatively connected to the drive shaft of the actuator 240 that supplies wire to the container. As used in this document, the term "slip clutch" refers to a device that applies frictional force to an object to move the object to a predetermined set point. When exceeding the range for the predetermined set point for the frictional force, the device slips and thus no longer applies frictional force to the object. The slip clutch enables the force exerted on the wire 120 by the roller 224 to remain within constraints regarding the strength of the wire, regardless of how frequently, how fast, or how long the actuator 240 is driven. This constant force can be maintained by driving the actuator 240 at a speed faster than the fastest predicted rotational speed of the drive roller 224, or by placing the encoder wheel 248 on the roller 224 and sensing the rotational speed with the sensor 252. The signal generated by the sensor 252 indicates the angular rotation of the roller 224, and the controller 148' uses this signal and the radius of the roller 224 to determine the length of the wire pulled out from the container 104 during the period from the start of the reverse until the wire detector 190 generates a signal that the wire is no longer present in the detector. That is, the mechanism 200 operates as a type of wire displacement sensor. Alternatively, a freewheeling roller opposing the driven roller 224 can have an encoder 248 attached to the freewheeling roller that generates a signal indicating its angular position, and thus the length of the metal wire supplied by the mechanism can be determined. In a further alternative design, the slip clutch 244 is omitted, and the number of steps in each direction of movement performed by the motor 240 can be recorded and used to determine the length of the linear wire movement.

[0024] To minimize disruption to the printer's operating state caused by wire feed reversal, the controller 148' is further configured with programmed instructions to implement a feedforward algorithm that continuously estimates the molten metal surface level based on the number of molten metal droplets ejected by the printer and the length of the wire supplied to the printer. Although an unknown tolerance is introduced in this estimation, this estimation method provides a simple way to determine the appropriate time to determine the molten metal surface level in the containment using the wire reversal method. The measurement frequency can be set according to the desired precision of the molten metal level control.

[0025] The controller 148' may be implemented using one or more general-purpose or dedicated programmable processors that execute programmed instructions. Instructions and data required to perform the programmed functions may be stored in memory associated with the processor or controller. The processors, their memories, and interface circuits constitute the controller to perform the operations described above and below. These components may be provided on a printed circuit card or as circuits within an application-specific integrated circuit (ASIC). Each circuit may be implemented on a separate processor, or multiple circuits may be implemented on the same processor. Alternatively, the circuits may be implemented as individual components or circuits provided within a very large-scale integrated (VLSI). Furthermore, the circuits described herein may be implemented in combination of processors, ASICs, individual components, or VLSI circuits. During the formation of the metal object, image data of the structure being manufactured is transmitted to the processor(s) of the controller

[0026] To determine the surface level of the molten metal within the storage section of the printer, a process for operating the 3D metal object printer 100’ is shown in FIG. 3. In the description of the process, the description that the process is performing some tasks or functions means that a controller or a general-purpose processor executes program instructions stored in a non-transitory computer-readable storage medium operably connected to the controller or processor to operate data or to operate one or more components within the printer to perform the tasks or functions. The above-described controller 148’ can be such a controller or processor. Alternatively, the controller can be implemented with two or more processors along with associated circuits and components, each of which is configured to form one or more of the tasks or functions described herein. Additionally, the steps of the method can be performed in any executable chronological order, regardless of the order shown in the figures or the order in which the processes are described.

[0027] Figure 3 is a flowchart of process 300 using the wire detector 190, where the controller 148 is configured to execute programmed instructions stored in non-temporary memory operably connected to the controller in order to determine the surface level of molten metal in the containment of a removable container during the object formation operation. This process begins with a determination that the surface level of the molten metal requires a check (block 304). If no measurement is required, the metal dispensing operation continues (block 308). One way to determine that the surface level should be checked is to use the total number of droplets dispensed and the amount of wire supplied to the printer. Specifically, the controller determines the amount of molten metal using the length of wire supplied to the printer since the most recent level check, minus the length of wire in the wire guide (block 312). This process also maintains a count of the number of molten metal droplets dispensed since the most recent level check and compares the volume of dispensed molten metal to the amount of molten metal to determine whether the surface level may fall below a predetermined position in the containment (block 304). If this comparison indicates that the amount of molten metal discharged since the last level check exceeds 10% of the amount of solid metal melted since the last level check, then the molten metal surface position needs to be measured more accurately. The actuator supplying the wire to the housing reverses (block 320) until metal droplet discharge is stopped (block 316) and the wire detector 190 generates a signal indicating that the wire is no longer at the sensor position (block 324). Once the reversal movement is stopped (block 328), as described above, the process determines the length of the wire removed from the container using the time to retract the wire into the wire detector and the speed of the retraction movement (block 332). If the length is longer than the distance at which the surface level would be when the volume of molten metal is less than 90% of the container volume, the process operates the actuator to move a length of wire into the container sufficient to raise the molten metal surface level to a position where approximately 95% of the container volume is filled with molten metal upon melting (block 336).Once this refilling is achieved, or if the surface level of the molten metal does not indicate that the container is less than 90% full, the metal droplet dispensing operation to form the metal object resumes until the next level check is required (block 308).

[0028] Figure 4 shows a flowchart of an alternative process 400 for performing melting level measurement during object formation. This process counts the number of molten metal droplets N discharged, corresponding to a predetermined number of multiples of the container volume, such as 10 times. This number of droplets N is formed by melting a wire length F. Due to tolerances for wire dimensions and droplet volume, it is not always possible to define the exact length F that forms N droplets. Therefore, N is related to F by a proportionality constant K. The initial value of K is determined analytically using the nominal diameter of the solid metal wire and the nominal droplet mass. The initial length F of wire that forms a predetermined number of volumes in the container can be determined using the formula N = F × K. The process in Figure 4 adjusts the constant K at each measurement of the molten metal level using the difference between the expected level and the measured level. Specifically, if the measured level is below the expected level, the constant K increases by a predetermined amount proportional to the difference between the expected and actual levels, because not enough wire has been supplied to the container. If the measured level is higher than expected, the constant K decreases by an amount proportional to the difference, because too much wire has been supplied to the container.

[0029] More specifically, process 400 begins with filling a container with molten metal and measuring the level of molten metal in the full container by withdrawing a wire from the container and measuring the length of the wire between the wire detector and the surface of the molten metal using one of the methods described above (block 404). The number of ejected metal droplets is counted until the count equals N (block 408). The level of molten metal in the container is again measured using one of the methods described above (block 412). The current measured level is compared to the previous metal level (block 416). If the current level is less than the previous level, K increases (block 420). If the current level is greater than the previous level, K decreases (block 424). If the rate of change of K decreases (block 428), K converges to an optimal value and N increases (block 432). Otherwise, the process continues with the current value of N. The value of N increases only if the change in K indicates that the value of the constant converges to a narrow range. Increasing N increases the interval between metal level measurements, reducing downtime for level measurements while increasing productivity.

[0030] It will be understood that variations or substitutions of the features and functions disclosed above and other features and functions may, preferably, be combined into many other different systems, applications, or methods. Various currently unforeseen or unexpected substitutions, modifications, variations, or improvements, which are also intended to be covered by the following claims, may subsequently be made by those skilled in the art.

Claims

1. A metal droplet ejection device, comprising: a dispenser head having a container and a receiving portion within the container, the receiving portion being in fluid communication with a nozzle of the container and located within the dispenser head, the dispenser head being configured to dispense molten metal droplets from the receiving portion through the nozzle of the container; a wire guide configured to receive a solid metal wire at a first end and configured to direct the solid metal wire through the wire guide to a second end through which the solid metal wire exits and travels toward the receiving portion of the container; a heater configured to heat the container while the container is in the dispenser head to a temperature sufficient to melt a solid metal wire within the receiving portion of the container; at least one actuator operatively connected to the solid metal wire, the at least one actuator configured to bidirectionally move the solid metal wire through the wire guide; and a wire detector positioned between the second end of the wire guide and the receptacle in the container, the wire detector configured to generate a first signal indicative of the presence of the solid metal wire at the wire detector and to generate a second signal indicative of the absence of the solid metal wire at the wire detector; and a controller operatively connected to the at least one actuator, the ejector head, and the heater, the controller comprising: operating the heater to melt the solid metal wire within the enclosure of the vessel; operating the dispenser head to dispense droplets of molten metal from the container; activating the at least one actuator to retract the solid metal wire from the housing until the wire detector generates the second signal; determining a length of the solid metal wire retracted from the housing into the wire detector using a velocity of the solid metal wire during retraction and a determined time period between initiation of retraction of the solid metal wire and the generation of the second signal by the wire detector; determining a position of a top surface of the molten metal within the vessel using the determined length of the solid metal wire drawn from the vessel into the wire detector; comparing the determined position of the top surface of the molten metal within the vessel with a position within the vessel corresponding to the vessel being filled to 90% of the vessel's volume; accumulating a count of molten metal drops dispensed by the dispenser head from the time the position of the top surface of the molten metal was determined; retracting the solid metal wire from the housing when the accumulated count of molten metal drops reaches a predetermined count N, the predetermined count N corresponding to a length F of the solid metal wire multiplied by a proportionality constant K; determining the location of the top surface of the molten metal within the enclosure after the predetermined count N is reached and the solid metal wire is withdrawn from the enclosure; and and after the predetermined count N is reached, adjusting the value of the proportionality constant K using a difference between the determined position of the top surface of the molten metal in the container when full and the identified position of the top surface of the molten metal in the container.

2. The controller: if the difference is negative, increasing the value of the proportionality constant K; and The metal drop ejection device of claim 1 , further configured to: decrease the value of the proportionality constant k if the difference is positive.

3. The controller: The metal drop ejection device of claim 2 , further configured such that N increases when the rate of change of the proportionality constant K for successive adjustments of K decreases.

4. The metal drop ejection device of claim 1 , wherein the reservoir is removable from the ejector head.

5. The metal drop ejection device of claim 1 , wherein the wire detector is an optically transmissive sensor.

6. The metal drop ejection device of claim 1 , wherein the wire detector is an inductive sensor.

7. A metal droplet ejection device, comprising: a dispenser head having a container and a receiving portion within the container; a wire guide configured to receive a solid metal wire at a first end and configured to direct the solid metal wire through the wire guide to a second end through which the solid metal wire exits and travels toward the receiving portion of the container; a heater configured to heat the container while the container is in the dispenser head to a temperature sufficient to melt a solid metal wire within the receiving portion of the container; at least one actuator operatively connected to the solid metal wire, the at least one actuator configured to bidirectionally move the solid metal wire through the wire guide; and a wire detector positioned between the second end of the wire guide and the receptacle in the container, the wire detector configured to generate a first signal indicative of the presence of the solid metal wire at the wire detector and to generate a second signal indicative of the absence of the solid metal wire at the wire detector; and a controller operatively connected to the at least one actuator, the ejector head, and the heater, the controller comprising: operating the heater to melt the solid metal wire within the enclosure of the vessel; operating the dispenser head to dispense droplets of molten metal from the container; activating the at least one actuator to retract the solid metal wire from the housing until the wire detector generates the second signal; determining a position of a top surface of the molten metal within the vessel; determining a length of the solid metal wire retracted from the containment into the wire detector to determine the position of the top surface of the molten metal in the containment, the controller using a speed of the solid metal wire while being retracted and a determined time period between initiation of retraction of the solid metal wire and the generation of the second signal by the wire detector; determining a position of a top surface of the molten metal within the vessel using the determined length of the solid metal wire drawn from the vessel into the wire detector; comparing the determined position of the top surface of the molten metal within the vessel with a position within the vessel corresponding to the vessel being filled to 90% of the vessel's volume; accumulating a count of molten metal drops dispensed by the dispenser head from the time the position of the top surface of the molten metal was determined; retracting the solid metal wire from the housing when the accumulated count of molten metal drops reaches a predetermined count N, the predetermined count N corresponding to a length F of the solid metal wire multiplied by a proportionality constant K; determining the location of the top surface of the molten metal within the enclosure after the predetermined count N is reached and the solid metal wire is withdrawn from the enclosure; and and after the predetermined count N is reached, adjusting the value of the proportionality constant K using a difference between the determined position of the top surface of the molten metal in the container when full and the identified position of the top surface of the molten metal in the container.

8. a pair of rollers, at least one of the rollers being driven by the at least one actuator; a sensor configured to generate a signal corresponding to a rotational speed of the at least one of the rollers driven by the at least one actuator; The controller:

8. The metal drop ejection device of claim 7, further configured to determine the length of the solid metal wire retracted from the housing by using the signal generated by the sensor while the solid metal wire is retracted from the housing, a radius of the at least one roller, and a determined period of time between a start of retraction of the solid metal wire and the generation of the second signal by the wire detector.

9. The controller: accumulating a count of molten metal droplets dispensed by said dispenser head; determining a quantity of solid metal wire melted within the container; and 8. The metal drop ejection device of claim 7, further configured to determine whether the top surface of the molten metal in the chamber is lower than the position corresponding to the chamber being filled to 90% of the volume of the chamber before operating the at least one actuator to retract the solid metal wire.

10. 10. The metal drop ejection device of claim 9, wherein the controller is further configured to determine the position of the top surface of the molten metal in the container by determining whether more than 10% of the amount of the solid metal wire melted in the container has been ejected.

11. The controller: if the difference is negative, increasing the value of the proportionality constant K; and The metal drop ejection device of claim 7 , further configured to: decrease the value of the proportionality constant k if the difference is positive.

12. The controller: The metal drop ejection device of claim 11 , further configured to increase N when the rate of change of the proportionality constant K for successive adjustments of K is decreasing.

13. The metal droplet ejection device of claim 7, wherein the container is removable from the ejection device head.

14. The metal droplet ejection device of claim 7, wherein the wire detector is an optically transparent sensor.

15. The metal droplet ejection device of claim 7, wherein the wire detector is an inductive sensor.

Images