Apparatus and method for dispensing powder

Abstract

Apparatus and related methods for numerically controlled powder deposition are provided. The apparatus includes a supply chamber configured to maintain a reservoir of powder in a fluidized state, and one or more dispenser elements. The supply chamber is further configured to direct the flow of fluidized powder from the reservoir to the orifice, thereby dispensing the flow of fluidized powder from the orifice.

Description

[0001] This application is a divisional application of the patent application with the application number 2019800772309, the application date of November 15, 2019, and the invention title of "Device and Method for Powder Dispensing". Background Art

[0002] Powder transportation and conveyance are commonly required in industry, and there are well-established methods for transporting powder using various sources of energy. Examples are ultrasonic sieving techniques, vibratory conveyors, and air flow fluidization techniques. These methods are typically applied on a large kilogram scale in industrial processing.

[0003] For example, in powder coating or laser printing systems (electrophotography), powder is also electrostatically deposited. This enables the deposition of powder layers of micron thickness onto various substrates by transferring powder between multiple locations using electric charges.

[0004] Powder can also be metered using an Auger screw powder delivery system.

[0005] In the pharmaceutical industry, in the manufacture of tablets and capsules, powder is also dispensed on a milligram to gram scale. There are many well-known techniques for capsule filling and tableting with high precision and high production rates.

[0006] However, dispensing powder on a microgram to milligram scale is significantly more challenging. A key industrial example is the use of inhalers, where small milligram amounts of powder are dispensed into the lungs using an air flow. However, powder metering techniques for respiratory dosing are not likely to be suitable for depositing powder onto substrates for industrial applications such as decorative and functional coatings. Summary of the Invention

[0007] The present invention arises in this context and incorporates an array of electronically controlled powder metering elements which, when operated together, include a powder printing head. The multiple metering elements enable a range of new industrial applications from decorative imaging to drug dose dispensing.

[0008] The powder printing head design of the present invention can include several key elements:

[0009] 1. Fluidized powder supply

[0010] 2. A chamber in contact with the dispensing element where the powder is fluidized under controlled energy

[0011] 3. A numerically controlled dispensing element that uses additional energy imparted by a piezoelectric actuator to meter the powder

[0012] 4. A software control system that converts an image or pattern into discrete signals to activate the piezoelectric actuator dispensing element array

[0013] The powder dispensing printhead is designed to dispense digitally defined 2D images by deposition of a patterned layer or powder.

[0014] The powder dispensing printhead is also designed to be able to precisely control the filling of a chamber with powder, such as filling a drug capsule or blister pack.

[0015] Powders are functional elements of many functional and decorative coatings. However, the direct printing of powders is technically challenging and, typically, printed powders rely on a carrier fluid to be able to transport the material to a substrate. Although laser printing (electrostatic printing) has established the principle of electrostatic deposition of micronized powders, the technique places strict requirements on powder properties, meaning that very few powders can be printed using this technique. We have solved this problem by developing a printhead for metered powder feeding on demand, which uses numerically controlled piezoelectric actuation to transport powder from a fluidized powder container to a substrate through discrete dispenser elements.

[0016] We have previously disclosed the principle of on-demand powder dispensing using single-element piezoelectric dispensers. However, due to powder "locking" and compaction in the supply system, it has not been possible to construct these systems as printheads or dispenser arrays. In addition, these single-element dispensers have not been miniaturized sufficiently to form a dense array of at least ten elements per inch. The purpose of a printhead is to deliver a two-dimensional array of deposition actuations over an extended period of time, which is suitable for manufacturing. In the present application, we disclose a novel printhead design for digital on-demand deposition of powders, which uses powder fluidization techniques to supply a plurality of piezoelectric dispenser elements for two-dimensional powder printing or dispensing.

[0017] The inventive step in the present application is to connect an energy-controlled fluidized or agitated powder supply system to a piezoelectric dispenser to produce an integrated powder printhead. It has been determined that by controlling the energy of the fluidized and / or agitated powder, which supplies a series of different piezoelectrically actuated dispenser elements, the dispenser elements can be used to meter powder doses over an extended period of time.

[0018] To date, it has not been possible to dispense powders on demand in a manner comparable to on-demand drop-on-demand inkjet printing. In the present application, we disclose a powder printhead design that utilizes the principle of digital on-demand drop-on-demand to dispense microgram quantities of powder for delivering 2D patterning, imaging, and dispensing into a 2D array of chambers. The technique can be used for industrial coatings of building materials, decorative laminates, paper and nonwoven products, food, drug dosages, and electronic and optical coatings. This method is also applied in 3D printing based on pattern-based layer-by-layer construction. Another major application is filling chambers, such as filling capsules for drug dosage forms. These and other applications of embodiments of the invention will be described in more detail in the detailed description section.

[0019] The present invention discloses a combination of a fluidized powder reservoir for controlling energy and a piezoelectrically actuated dispensing element for applying additional energy at a dispensing orifice. The present invention is based on the recognition that by controlling only the energy of the fluidized material in the reservoir, additional energy from a piezoelectric actuator can be used to meter the dose using a dispenser element in contact with a powder container.

[0020] According to the present invention, there is provided a dispenser element comprising a piezoelectric actuator and an orifice through which a fluid is dispensed, wherein the dispenser element is configured to provide sufficient resistance to powder flow to ensure that mass transport begins only when the piezoelectric actuator is energized.

[0021] For example, a powder with a static angle > 30° remains stationary in the dispenser element without the application of ultrasonic agitation.

[0022] The dispenser element can be configured to provide energy to the powder in the vicinity of the dispenser element such that powder flow occurs. The energy can be provided to the powder by high-frequency mechanical vibrations of the piezoelectric actuator. Alternatively or additionally, the vibrations can be ultrasonic. Alternatively or additionally, the energy can be provided via a direct mechanical connection between the piezoelectric actuator and the orifice. The energy delivered can be at a frequency in the range of 1 - 500 kHz, and the power delivered can be in the range of 1 to 1000 milliwatts.

[0023] The dispenser element can also include a conduit configured to transfer the mechanical vibrations of the piezoelectric actuator to the powder. The conduit can be configured as an array of holes in a tube, a slot, or a sieve.

[0024] Alternatively or additionally, the powder can be dispensed under the influence of gravity.

[0025] The orifice can be an array of holes in a plate, which array can generally be referred to as a screen. Alternatively or additionally, the orifice can be a straight-sided cylinder. The orifice can alternatively be implemented in a conical or spiral form.

[0026] The dispensing element can also include a conical tube configured to provide the fluidized powder to be dispensed to the orifice.

[0027] An array of the above-described dispensing elements can be combined to form a powder printhead.

[0028] The powder printhead can further include an energy-controlled fluidized powder supply chamber, and the powder printhead can be configured to dispense powder through the dispensing element as needed. The supply chamber can include one or more of the following components to fluidize the powder to be dispensed: a mechanical agitator; an air pump and / or an ultrasonic actuator.

[0029] The powder printhead may also include an orifice through which the powder is dispensed. The orifice may be in the range of 50 - 1000 microns; in the range of 100 - 500 microns, such as 500 microns. The size of the orifice is at least partially affected by the size of the powder to be dispensed. The average diameter of the powder of interest is in the range of 10 to 200 microns. The orifice is selected to have a diameter that is at least five times the average diameter of the particles to be dispensed.

[0030] The powder supplied to the printhead remains substantially fluidized while in the chamber of the supply dispenser element. Fluidization is maintained by continuous control using one or more of the mechanisms described above. Additionally, the pressure in the supply chamber can be controlled in the range of 1 - 6 bar.

[0031] Furthermore, according to the present invention, there is provided a method of printing using a powder printhead as described above, wherein a technique for fixing the deposited powder is carried out immediately after the printing step. The fixing technique may be selected from the group including laser heating; IR radiation heating; UV curing and consolidation by application of a fluid.

[0032] The printing step may be repeated such that multiple 2D patterned powder layers are deposited. The 2D layers may be combined to produce a 3D form.

[0033] Prior to the printing step is a step of fluidizing the powder to be printed. The fluidization step is carried out using one or more of the following mechanisms: air flow; ultrasonic energy and mechanical agitation. Description of the Drawings

[0034] The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0035] Figure 1 A side view of a printhead including an array of powder dispenser elements is shown;

[0036] Figure 2 A side view of an alternative printhead including an array of powder dispenser elements is shown;

[0037] Figure 3 A front view of an array of powder dispenser elements in a powder printhead is shown;

[0038] Figure 4 A control system used in conjunction with the printhead is shown;

[0039] Figure 5 A top view of a printing system including two printheads as shown in one or more of Figures 1 to 4 is shown; and

[0040] Figure 6 A side view of a 3D object constructed using multi-pass powder printing technology is shown.

[0041] Figure 7A Shows an example printhead device for dispensing powder onto a substrate according to the present invention;

[0042] Figure 7B Shows Figure 7A A top view of an example construction of the dispenser element of the device of;

[0043] Figure 7C Shows Figure 7B A side view of the dispenser element of;

[0044] Figure 8 Shows an alternative example construction of a device according to the present invention suitable for decoratively depositing powder;

[0045] Figure 9 Shows an alternative example construction of a device according to the present invention, the device having a dispenser element adapted to deposit a powder layer into a container. Detailed Description

[0046] Figure 1 Shows a side view of an array of powder dispenser elements 10 forming part of a printhead 100. The powder to be dispensed is added to a fluidized powder bed 22 enclosed within a chamber 24. There is a gas headspace 26 above the fluidized powder bed 22. In order to keep the powder in its fluidized form, there is a fluidizing air stream 28, which can be applied continuously or periodically as required. The gas headspace 26 is created by flowing gas through the powder to fluidize it. The size of the gas headspace 26 will depend on the application, and in some embodiments, the size of the gas headspace 26 can be minimal or even non-existent.

[0047] In other embodiments not shown separately, the air stream 28 can be replaced or augmented by a mechanical stirrer for agitating the fluidized bed and / or an ultrasonic vibration source connected to the fluidized bed, the ultrasonic vibration source being capable of transmitting vibrations to the fluidized bed 22 to maintain the uniformity of the fluidized bed 22. The advantage of a uniform bed is that it avoids the separation of particles from the fluidized powder, which can have a negative impact on the metering of the powder. A uniform bed enables control of the availability of the powder and ensures the delivery of free-flowing powder.

[0048] The dispensing element 10 includes a numerically controlled piezoelectric transducer 12 that acts as an actuator. The piezoelectric transducer 12 applies an electrical pulse 14 across the apertures 16 of a 2D array, through which the powder is dispensed. In some embodiments, an array of such piezoelectric transducers is used. The enhanced control of the powder flow provided by the uniform bed of fluidized powder enables the implementation of such a precise dispensing method without the risk of "locking" and compaction in the supply system.

[0049] Figure 2A side view of another print head 100 including an array of powder dispenser elements 10 is shown. The powder to be dispensed is added to a fluidized powder bed 22 enclosed within a chamber 24. There is a gas headspace 26 above the fluidized powder bed 22. In order to keep the powder bed 22 in its fluidized form, there is a fluidizing air stream 28, which can be applied continuously or periodically as required. In addition, an outlet 30 is provided above the gas headspace 26. The outlet 30 enables the pressure to be equalized between the chamber 24 and the remainder of the print head 100.

[0050] The dispenser element 10 includes a piezoelectric transducer 12 that serves as an actuator. The piezoelectric transducer 12 applies an electrical pulse 14 across a flow channel 18 that is provided with a tube through which, in use, the fluidized powder to be dispensed flows.

[0051] Although the outlet 30 is only shown in Figure 2 it will be apparent to those skilled in the art that the outlet 30 can also be applied to the print head shown in Figure 1 the print head shown in

[0052] Figure 3 A front view of the powder dispenser element array in the powder print head 100 is shown. There are sixteen orifices through which the powder 20 can be dispensed. Each orifice is provided with a dispenser element 10, which can be configured as a simple tube, slot, or sieve. The fluidized powder bed 22 is held above the dispenser elements 10 within a supply chamber 24. A sieve (not shown) may be present between the fluidized bed 22 and the dispenser elements 10 in order to exclude any particles that are too large to be effectively dispensed and that may compromise the integrity of the dispenser elements attempting to dispense them.

[0053] The print head 100 is positioned above a substrate 32 onto which the powder will be dispensed. The substrate 32 can be paper, fabric, or it can be a capsule into which a pharmaceutical product will be dispensed. Each dispenser element 10 is individually controllable, where the print head has an array of piezoelectric actuators and a controller that is configured to enable powder to be dispensed from a single dispenser element or multiple dispenser elements, and the controller (not shown) is configured to numerically control the actuation of the piezoelectric actuators. This enables, for example, an image to be formed on a paper substrate 32, since different dispenser elements can be configured to dispense different amounts of powder. In the case of a pharmaceutical product, the individual control elements enable a patient-specific dose to be prepared by controlling the mass of powder dispensed.

[0054] Figure 4Shows a control system for use in conjunction with a print head 100. A controller is used in conjunction with the print head 100 to control the functions of the print head 100. The print head 100 is also provided with a powder feeder 34, a screw feeder 36, and a level sensor 38. The controller controls the weight of the powder introduced into the chamber through the powder feeder 34 in order to control the density of the powder 20 within the fluidized powder bed 22, and thereby controls the amount of powder dispensed with each actuation of each dispenser element 10. The screw feeder 36 enables the dispensed powder to be replaced by fresh feed.

[0055] Figure 5 Shows a top view of a printing system including two print heads as shown in one or more of Figures 1 to 4 The two powder print heads 100 move over a substrate 32. The direction of travel is marked as A. In some embodiments, the substrate moves and the print heads remain stationary. In other embodiments, the substrate remains stationary and the print heads move relative to the substrate. The black areas represent regions where the first powder #1 has been deposited, and the shaded areas represent regions where the second powder #2 has been deposited. The white area #0 represents the portion where no powder has been deposited.

[0056] Figure 6 Shows a side view of a 3D object constructed using a multi-pass powder printing technique. This example application of the disclosed device relates to layer-by-layer digital powder bed deposition, which is useful in the additive manufacturing / 3D printing industry.

[0057] 3D printing techniques such as selective laser sintering (SLS), high-speed sintering (HSS), and selective laser melting (SLM) depend on the ability to dispense powder layers in a layer-by-layer sequence. These methods utilize patterning techniques to selectively fuse powder particles in a layer-by-layer stack to create three-dimensional shapes in polymers and metals.

[0058] The deposition of the powder layer is typically achieved by scraping or rolling the powder layer, and is limited to particles larger than 50 microns in diameter, and also requires direct contact with the powder bed.

[0059] Advantageously, the disclosed device is capable of achieving numerically controlled layer-by-layer deposition of powder using particles smaller than 50 microns in diameter, thereby enabling higher component resolution and not contacting the previous powder layer. The numerically controlled nature of the device allows the layer thickness to be quality controlled.

[0060] The layer-by-layer powder bed deposition method and device will now be described in more detail.

[0061] The initial step of the method involves applying a single short pulse, e.g., at a frequency of 50 kHz for 20 milliseconds, to the reservoir containing the powder to be dispensed, to fluidize the supply. This step is performed before dispensing each layer of powder and outside the build bed, as some powder may be dispensed during the set pulse.

[0062] Subsequently, the rectangular dispenser passes over and moves along a predefined path above the 3D printing machine build bed container while dispensing a powder layer in the manner described below for 3D printing.

[0063] The dispenser (not shown) has a length of 50 cm and includes a piezoelectric actuator assembly mounted to an active element. The active element of the dispenser deposits the powder contained therein, and the active element is actuated by the piezoelectric assembly, which includes two stainless - steel strips, each 0.6 mm thick, 23 mm deep, and spaced 10 mm apart from each other. These stainless - steel strips are overlapped by a woven steel mesh that overlaps each stainless - steel strip by 2 mm, the woven steel mesh is bonded to these stainless - steel strips with epoxy adhesive, and the woven steel mesh has a pore size suitable for the powder, e.g., 50 microns.

[0064] Each stainless - steel strip has an array of PZT disks mounted along its length, each disk having a diameter of 15 mm and a thickness of 0.15 mm, and these PZT disks are mechanically bonded to the stainless - steel strip. These PZT disks have electrodes on their uppermost surfaces and are all individually electrically connected to a drive voltage source. In some embodiments, the electrodes can also be commonly connected to the voltage source.

[0065] The active element is held in place by silicone blocks to allow free vibration. In particular, the edges of the active element are held between the silicone blocks with an overlap of, e.g., 1 mm. The dispenser device includes a hopper located above the active element, which contains the powder to be dispensed (e.g., BASF Adsint TPU 90flex TPU powder, Danthane Powder (DanQunisa Gmbh)). The walls of the hopper are perforated with a pattern of small holes, e.g., holes with a diameter of 0.2 mm in a square grid with a 10 - mm spacing. Inside the hopper walls is a volume filled with pressurized air, e.g., at 2 bar, and this volume is sealed except for the perforations in the hopper walls. The hopper contacts the active element and is adhered to the active element with epoxy adhesive. The hopper is constructed of stainless - steel with a thickness of 0.15 mm.

[0066] The powder has a D90 of approximately 10 microns. The powder is preferably a metal or metal alloy, such as grade 5 titanium. By varying the drive voltage waveform applied to the piezoelectric actuator, the powder layer can be varied digitally. This can be combined with the measured height of the layers that have been deposited so far to ensure that the desired powder layer thickness is maintained.

[0067] When the dispenser is at one end of its predetermined travel path, the powder is periodically replenished from the large hopper. The dispenser is positioned close to but not in contact with the top of the container to be filled, for example within 1 mm of the top of the container to be filled.

[0068] The build bed container of the 3D printing mechanism has a bottom plate that can be raised or lowered and starts at the top of the container. After deposition, the bottom plate of the build bed container is lowered by the height of each layer.

[0069] While in motion, the dispenser is activated and the powder is deposited into the container. The parameters of the signal driving the dispenser are such that the powder accurately fills the new space in the container.

[0070] Then a laser is used to melt the metal powder to selectively melt the powder for the final part using the selective laser sintering (SLS) method. An energy beam or printing adhesive can also be used to selectively melt some areas of the powder.

[0071] The process is repeated where the dispenser travels in the opposite direction, dispensing a layer or powder onto the substrate.

[0072] Figure 6 Four passes are shown, each pass creating a separate layer of deposited powder. These are designated as Pass 1, Pass 2, Pass 3, and Pass 4, where the area where the first powder #1 is deposited is shown in black and the area where the second powder #2 is deposited is shown with hatching. It is evident that this enables the creation of three-dimensional shapes.

[0073] Figures 7A to 7C Shown is how a dispenser device according to an embodiment of the present invention can be used in a method of laminating textiles by depositing a thermoplastic adhesive powder.

[0074] Generally, the technique involves a method where powder 20 is applied to a substrate and softened and melted to bond multiple layers of fabric together. The main example of a suitable adhesive powder is thermoplastic polyurethane (TPU).

[0075] For example, Figures 7A to 7C The printing head 100 shown in [reference] demonstrates the application of a TPU powder shape 40 onto a fabric substrate. Subsequently, the powder shape 40 is laminated by placing a second fabric layer on top and applying a hot roller to soften the TPU powder therebetween and bond the two fabric layers together. The advantage of the disclosed device is that since the piezoelectric actuator can be numerically controlled, the shape of the dispensed powder can also be digitally defined and controlled, contrary to known techniques that can only deposit full-coverage coatings.

[0076] In this example, a 30 cm wide rectangular dispenser 10 including a piezoelectric actuator drive assembly is used to dispense repetitive rectangular layers 40 of TPU powder onto a polyester fabric substrate.

[0077] The active element 44 of the dispenser deposits the powder and is actuated by the piezoelectric assembly. The active element includes two stainless steel strips 46, each having a thickness of 0.6 mm, a depth of 23 mm, and spaced 10 mm apart from each other. These stainless steel strips are bridged by a woven steel mesh 48 that overlaps each stainless steel strip by 2 mm. The woven steel mesh is bonded with an epoxy adhesive and has a pore size suitable for the powder, such as 0.5 mm.

[0078] An array of PZT disks 12 is mounted along the length of each stainless steel strip 46. Each PZT disk has a diameter of 15 mm and a thickness of 0.15 mm, and the PZT disks are mechanically bonded to the stainless steel strips. These PZT disks have electrodes on their uppermost surfaces, and the PZT disks are all individually electrically connected to a drive voltage source. In some embodiments, the electrodes can also be commonly connected to the voltage source.

[0079] The active element 44 is held in place by a silicone block to allow free vibration. The dispenser device includes a hopper 50 located above the active element 44. The hopper contains the powder to be dispensed (e.g., BASF Adsint TPU 90flex TPU powder, Danthane Powder (DanQunisa Gmbh)). The bottom of the hopper 50 is close to but does not touch the active element 44. The walls of the hopper are solid. Inside the hopper walls is a volume 26 filled with pressurized air, such as 2 bar. This volume is sealed except for a gap between the hopper 50 and the active element 44 that allows air to flow out.

[0080] Air flows through the gap and fluidizes the powder in the hopper 50, thus ensuring that the powder flows onto the active element 44. A mesh of the material passes under the dispenser and is guided by rollers, the width of which is the same as that of the dispenser and is 1 - 5 cm away from the dispenser. Adhesive powder (e.g., polyester powder with D50 = 0.3 mm and D90 = 0.4 mm) is held in the dispenser.

[0081] When the textile material passes under the dispenser, a periodic drive signal is applied to a piezoelectric actuator such as described above, such that the powder flows through the mesh of the above - mentioned material and lands on a material approximately 20 cm wide. The waveform is a 10 kHz square wave with a peak - to - peak amplitude of 50 V. The waveform is applied for 5 ms, with a 5 ms pause in between. The signal continues until the textile material of the desired length is coated with powder. The dispenser is typically open for 5 seconds and then closed for 5 seconds (covering a 30 cm band at 6 m / min). A typical shape is a 20 cm × 30 cm rectangular TPU coating.

[0082] The application of the second layer of polyester fabric can be carried out manually as follows: place the fabric on a TPU-coated substrate or a mesh to which a second material is added. For lamination, a temperature of about 100 - 120 °C and heating for 1 minute are used to laminate the two-layer structure

[0083] Figure 8 Another exemplary application of an embodiment of the present invention in applying a decorative powder coating to a paper or card substrate is shown.

[0084] Powder adhered to paper is typically used to decorate paper products such as gift cards. It has been demonstrated that the disclosed device applies decorative powder onto areas of the paper that have been pre-coated with an adhesive. In this example, the powder dispenser is mounted on an XY translation motion system and is used to deposit powder onto a shape defined by the adhesive coating or selectively deposit powder onto a substrate that is fully coated with adhesive.

[0085] A centrally symmetric circular dispenser is used, where the effective element is a stainless-steel flat ring with an inner diameter of 30 mm and a width of 25 mm. A mesh disk with a diameter of 35 mm is welded to the underside of the ring. In other respects, the effective element is structurally the same as Figures 7A to 7C shown, where actuation is controlled using a series of PZT disks mechanically connected to a stainless-steel strip.

[0086] In this example, a conical hopper 50 is used, which has an upper diameter of 50 mm and a lower diameter that matches the inner side of the element ring. The hopper is located on the mesh of the effective element and is glued in place with silicone adhesive. A screw feeder supplies the fluidized powder material to the hopper at a flow rate that matches the dispensing rate. The powder material is a decorative powder, such as glitter powder, with a D50 of approximately 200 microns. The screw feeder outlet is located above the middle of the dispenser. Typically, the bottom of the feeder outlet is flush with the top of the hopper

[0087] The PZT disks on the effective element are driven by the waveform as described for the device regarding Figures 7A to 7C The waveform is applied to individual PZT disks that are individually addressable elements. The activation pattern of the disks is numerically controlled and allows additional functions, such as gradually moving the activation around the ring to spread the material on the sieve.

[0088] In an exemplary deposition process, the dispenser moves over the substrate at a fixed height above the substrate 32, which is paper or card. The substrate is either fully or only in some areas coated with adhesive. The dispenser moves in a horizontal plane along a predetermined path that matches the adhesive pattern. The dispenser is effective for some or all of the movement, thereby depositing the powder material in a shape determined by the movement of the dispenser in the horizontal plane. Figure 9 Another exemplary application of the device according to the present invention is shown, where the device is used to fill a container with powder.

[0089] There are many powder containers for the food, consumer goods, and pharmaceutical industries. Embodiments of the present invention can accurately and numerically control the filling of containers with a powder mass with an accuracy of 5% and in the mass range of 5 mg - 50 g.

[0090] In this example, the device is used to fill containers with various types of cleaning powders for dishwashers. The deposition of multiple layers of different powders and thicknesses enables the creation of multiple functions, where each powder layer is defined by mass.

[0091] The device includes a separate array of dispensers, each dispenser containing an active element located above the container.

[0092] The active element is a single stainless - steel strip with a thickness of 0.4 mm, a width of 20 mm, and a length of 50 mm. The stainless - steel strip has an array of hexagonal holes in its center, each hole being 1 mm on its flat side and spaced 0.5 mm apart. These holes cover a circular area with a diameter of 17 mm. A 15×20 mm rectangular piece of PZT material is welded to each end of the stainless - steel strip, and the rectangular piece of PZT material is configured to actuate the stainless - steel strip when energized.

[0093] A feed tube (not shown) is used to convey the powder to the dispenser element 10. The feed tube is made of polypropylene, has an outer diameter of 16 mm, and a wall thickness of 1 mm. The feed tube is pressed against the center of the active element held by the housing. The feed tube is filled with powder (e.g., spray - dried laundry detergent) having a particle size in the range of 200 to 800 microns.

[0094] The feed tube is filled by a pneumatic powder conveying system. In an example configuration, a high - speed air stream carries the powder from a source container. Near the dispenser 10, the powder is slowed down such that it drops out of the air stream and deposits in the dispenser hopper. The powder can be slowed down by widening the channel containing the air stream to slow down the air and the powder together, or by sharply turning the air stream such that the powder impacts the channel walls and is directly slowed down (e.g., a cyclone separator).

[0095] When the dispenser 10 is aligned with the tool plate, the dispenser 10 is activated. The dispenser is driven by a waveform that is a sine wave at 12 kHz with a peak - to - peak amplitude of 300 V. This activation can last for the entire time the carriage is on the tool plate or only for a part of the time the carriage is on the tool plate. Multiple dispensers 10 can be used in series to dispense multiple powders. Each dispenser 10 can be configured to deposit different materials into the cavities of the tool plate. This allows for compositional variations, such as layers with different odors and different functions. For each dispensing, the amount of powder deposited by each carriage can be changed.

[0096] Energy - controlled fluidized powder chamber

[0097] Fluidizing powder with air as described above requires knowing the minimum fluidization velocity of the specific powder used. The minimum fluidization velocity is the velocity that the air or gas introduced for fluidization must attain. The minimum fluidization velocity of powders falling into the Geldart A classification can be calculated using the following equation:

[0098]

[0099] ● Where U mf = minimum fluidization velocity (m / s);

[0100] ● ρ P = bulk density of the powder (g / m 3 );

[0101] ● d V = volume-based average particle size (m); and

[0102] ● 420 = empirical value of particles in air (m 2 / g-s).

[0103] As long as the minimum fluidization velocity is met, a fluidized powder bed can be generated with variable energy. An air stream, vibration, piezoelectric actuator, or other mechanism is used to control the energy. The fluidized powder reservoir is in close contact with an array of dispenser elements controlled by a piezoelectric actuator. When the fluid dispenser element is "closed" or below Umf (minimum fluidization velocity), the powder cannot flow through the dispenser element because the dispenser is configured to provide a resistance that reduces the energy for the powder to pass through without additional energy from the piezoelectric actuator. When the fluid dispenser element is "open" such that the fluidized powder has a velocity higher than Umf, the powder can flow through the dispenser. Typical powders that can be used in this system are decorative pigments (such as metals), foods (such as powdered spices), and pharmaceutical formulations including active pharmaceutical ingredients mixed with lactose.

[0104] Two-stage piezoelectrically actuated powder supply system

[0105] A piezoelectrically actuated powder supply system can also be used to control the quality of the powder delivered to an array of powder dispensers. This enables the powder to be delivered to the dispenser under better controlled conditions and at a flow rate matching the main dispenser. The two-stage powder dispensing system is most preferably configured such that an array of piezoelectrically actuated sieves serves as the first stage in the powder supply mechanism, and the second stage is an array of piezoelectrically actuated sieves or orifices. An alternative for the first stage is to use a stirrer to agitate the powder to minimize agglomeration and ensure free-flowing delivery to the dispenser stage.

[0106] Piezoelectrically actuated powder dispenser array

[0107] The array of dispensers includes a plurality of orifice structures mechanically coupled to piezoelectric transducers. When driven with a typical electrical signal, such as an alternating voltage, the piezoelectric transducers deliver high-frequency (>1 kHz) vibrational energy to the system. The dispenser elements typically consist of the following structures:

[0108] 1. One or more orifices that provide resistance to powder flow

[0109] 2. A piezoelectric actuator that is used for:

[0110] a. Creating a valve that can be opened or closed

[0111] b. Overcoming the resistance to powder flow by applying vibrational energy to the powder within the dispensing element

[0112] The dispenser element can consist of structures such as:

[0113] 1. A linear tube, where the piezoelectric actuator is mechanically attached to the linear tube.

[0114] 2. A cone, where the piezoelectric actuator is attached to the outside of the cone and serves to dispense the powder within the dispensing cone

[0115] 3. A valve element, such as a flap element, that can be opened and closed by the piezoelectric actuator

[0116] 4. Structures such as an array of holes in a plane, such as a sieve. Each dispenser element is defined by a mechanical interface that uses a single or multiple piezoelectric actuators to address each unique dispenser.

[0117] a. The dispenser array can be formed from a single continuous sieve sheet, where each element is addressed by a unique piezoelectric actuator.

[0118] The dispensing process may require gravity to transfer the dispensed powder from the dispenser element to the substrate.

Claims

1. A numerically controlled powder deposition apparatus, comprising: A supply chamber, the supply chamber including a container configured to hold a reservoir of powder and impart kinetic energy to the reservoir of powder to maintain the powder in a fluidized state; An array of numerically controlled and individually controllable dispenser elements, each dispenser element including a piezoelectric actuator and an orifice configured to resist the flow of fluidized powder having energy below a first energy level; And A controller configured to digitally control the actuation of the piezoelectric actuator such that the fluidized powder is dispensed from a single dispenser element or multiple dispenser elements of the array; Wherein the supply chamber is in contact with the array of dispenser elements and configured to direct the flow of the fluidized powder from the reservoir to the orifice, the flow including a portion of the fluidized powder, and the portion of the fluidized powder having energy below the first energy level; and Wherein, upon actuation of the piezoelectric actuator by the controller, each dispenser element of the array is further configured to impart additional kinetic energy to the portion of the fluidized powder via the piezoelectric actuator such that the portion of the fluidized powder is provided with energy equal to or higher than the first energy level, whereby the portion of the fluidized powder is dispensed from the orifice.

2. The device according to claim 1, wherein, The energy is provided to the portion of the fluidized powder via a direct mechanical connection between the piezoelectric actuator and the orifice.

3. The apparatus according to claim 1, further comprising a conduit configured to transfer mechanical vibrations from the piezoelectric actuator to the flow including the portion of the fluidized powder.

4. The device according to claim 3, wherein The conduit is an array of holes in a tube, groove or sieve.

5. The device according to claim 1, wherein Deliver energy at a frequency in the range of 1 - 500 kHz.

6. The device according to claim 1, wherein The orifice is an array of holes in a plate.

7. The device according to claim 1, wherein The orifice is a straight-edged cylinder.

8. The device according to claim 1, wherein The supply chamber includes a mechanical agitator configured to apply kinetic energy to fluidize the powder.

9. The device according to claim 1, wherein, The apparatus further includes an air supply pump or a flow pump configured to apply kinetic energy to fluidize the powder.

10. The device according to claim 1, wherein, The supply chamber includes an ultrasonic actuator configured to apply kinetic energy to fluidize the powder.

11. The device according to claim 1, wherein, The diameter of the orifice is in the range of 50 - 1000 microns.

12. The apparatus according to claim 1, further comprising a software control system configured to convert an image or pattern into discrete signals to excite the piezoelectric actuators of the array of dispenser elements.

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