Patent Application
20250187077
The proposed technology relates to the field of additive manufacturing. The proposed technology relates specifically to printing-plate lifts for metal-binder jetting.
Metal-binder jetting is a sinter-based additive manufacturing technique. A thin layer of a metal-containing powder is applied on a horizontally oriented printing plate. For example, this can be done by a powder dispenser positioned above and moving across the printing plate. The powder dispenser has an elongated slit that is transverse to the movement, and the powder is dispensed via the slit. An inkjet print head imprints an ink containing a binder in the metal layer. The powder layer is heated to dry the ink, for example by a heat lamp. The printing plate rests on a printing-plate lift that lowers the printing plate, and a new layer is applied on the existing layer. The process is repeated until the complete structure has been printed. This printed structure is commonly called a green part.
The post-printing processes may vary. One example of such a process is given here. The printing plate is placed in an oven in which the green parts are heated and cured. The cured structures are commonly called brown parts. The remaining metal powder is removed from the printing plate and the brown parts. This can be done manually or by a machine. The brown parts are placed in a low-temperature furnace in which they are subjected to a combined debinding and sintering, which completes the process and provides the final structure.
The orientation or sideways positioning of the printing plate may change when it is lowered by the printing-plate lift. This will offset the already printed layer relative to the next layer to be printed, which reduces the precision of printing. There is also a risk that the printing plate is deformed while printing, which will also result in a reduced precision. There is also a need for a high precision printing-plate lift that has a long stroke length, which enables larger structures to be printed.
It is an object of the proposed technology to improved the accuracy and precision in metal-binder jetting, in particular in the positioning and orientation of the printing plate. It is also an object to avoid deformations of the printing plate during operation. It is a further object to provide a high precision printing-plate lift with long stroke length.
The proposed technology aims at meeting the above-mentioned challenges. According to a first aspect of the proposed technology a printing-plate lift, or z-unit, for metal-binder jetting is provided. The printing-plate lift comprises: a lower support, or base support, a plate holder for supporting, or holding, a printing plate, and a plate-holder support, wherein the plate holder is attached, or fixed, to the plate-holder support. The printing-plate lift further comprises: a ball screw having a threaded shaft and a ball nut, wherein the threaded shaft is oriented vertically and rotationally supported relative to the lower support, and the ball nut is attached, or fixed, to the plate-holder support. The printing-plate lift further comprises: a drive unit having a drive shaft for delivering torque, wherein the drive shaft is positioned beside, or separated horizontally relative to, the threaded shaft of the ball screw. The printing-plate lift further comprises: a power transmission, or torque transmission, operationally connecting the drive shaft of the drive unit and the threaded shaft of the ball screw, wherein the power transmission is configured to rotate the threaded shaft at a rotation of the drive shaft.
It is understood that the lower support can be attached to, or form part of, a support for a complete printer. It is further understood that a threaded shaft is straight. That the drive shaft being positioned beside the threaded shaft means that they are not coaxial.
It is further understood that the position of the ball nut along the threaded shaft will change at a rotation of the latter. Thus, the drive unit, the power transmission, and the ball screw are configured to determine, or change, the vertical position, or elevation, of the plate-holder support relative to the lower support.
Given the same maximum elevation of the plate holder, the position of the drive shaft of the drive unit beside the threaded shaft of the ball screw allows for a longer threaded shaft as compared to the drive unit being positioned below the ball screw. This allows for larger components to be printed. It also allows for the plate holder to be elevated to a higher position, which can make the removal of the printing plate from the plate holder easier. For example, the printing plate can be raised above a table or slate positioned above the printing-plate lift.
The drive shaft of the drive unit may point, or extend, downward. It may be oriented vertically or parallel to the threaded shaft of the ball screw.
The drive unit may comprise an electric motor, or rotary actuator, operationally connected to the drive shaft. For example, the electric motor may be a rotary stepping motor or a rotary servomotor. The motor may be positioned beside the threaded shaft of the ball screw. For example, the drive shaft may be an extension of a motor shaft connected to a rotor of the motor. The drive unit may further comprise a gear train operationally connecting the motor and the drive shaft at a speed ratio, or gear ratio, that is less than one. This way, the drive shaft rotates slower than the rotor of the motor. The motor may be located above the drive shaft. Similarly, the gear train may be located above the drive shaft.
The power transmission may be configured to transfer torque from the drive shaft to the threaded shaft at a speed ratio, or gear ratio, that is lower than one. The power transmission may comprise a belt drive operationally connecting the drive shaft of the drive unit and the threaded shaft of the ball screw. The belt drive may be a two-pulley belt drive. For example, the belt drive may comprise a first pulley attached to and centered on the drive shaft, a second pulley attached to and centered on the threaded shaft, and a belt connecting the first pulley and the second pulley. The radius of the second pulley may be greater than the radius of the first pulley, thus providing a speed ratio between the input and the output that is smaller than one.
The printing-plate lift may further comprise: a first guide rod and a second guide rod, wherein the first guide rod and the second guide rod are attached, or fixed, to the lower support and oriented vertically, or parallel to the threaded shaft of the ball screw. The plate-holder support is slidably supported by the first guide rod and the second guide rod and configured to move along the first guide rod and the second guide rod. This contributes to a stable positioning of the plate holder for printing-plate lifts having a long stroke length of the plate holder support.
The guide rods may be positioned on opposite sides of the threaded shaft. The threaded shaft may be positioned at the center between the guide rods. The guide rods and the threaded shaft may be coplanar, which means that they extend in a common plane. The guide rods may have circular cross sections. These features contribute to a more stable positioning of plate-holder support and an improved precision in the printing process. The distance between the guide rods may be greater than the width of the plate holder in the direction from the first guide rod to the second guide rod. This contributes to a more stable support of the plate holder.
The printing-plate lift may further comprise: a first guide and a second guide that slidably cooperate with the first guide rod and the second guide rod. The first guide may be a first bearing and the second guide may be a second bearing, and the first bearing and the second bearing may be linear plain bearings, or linear slide bearings. The first and second guides may be configured to prevent the plate-holder support from rotating relative to the lower support, for example at a rotation of the threaded shaft of the ball screw. They may also be configured to prevent the plate-holder support from tilting relative the first and second guide rods, and in extension relative to the lower support. These features contribute to an improved accuracy and precision in the positioning of the plate-holder support, and in extension an improved precision in the positioning of the printing plate.
It is understood that the first and second guides form part of the plate-holder support. Each guide may form a through-hole with a circular cross section, and the guide rods may extend through the through hole. The guides and the guide rods may be concentric. This way, the guides and the rods jointly cooperate to prevent the plate-holder support from turning or tilting relative to the lower support.
The plate-holder support may comprise: a base part, or transverse part, extending between the first guide rod and the second guide rod, wherein the ball nut is attached, or fixed, to the base part. It may further comprise: a center part, or column, having a lower end and an upper end, wherein the lower end is attached, or fixed, to the base part at the center between the first guide rod and the second guide rod, and the plate holder is attached, or fixed, to the center part at the upper end. This means that the center part extends upward from the base part. It is understood that the base part and the center part are rigid and self-supporting structures. This allows for a printing-plate lift with a stable and longer stroke length.
The base part may form a central through-hole through which the threaded shaft of the ball screw extends. The ball nut of the ball screw may be positioned within the central through-hole.
The center part may form an enclosed space. The center part may surround, or enclose, the threaded shaft. The threaded shaft may extend into the enclosed space from below, or via the central through-hole formed by the base part. Worded differently, the threaded shaft may extend into the center part from below. The center part may be elongated and aligned with the threaded shaft. This means that its length along the threaded shaft is greater than its width transverse to the threaded shaft. The center part may define a hollow cylinder aligned with the threaded shaft. These features contribute to a longer stroke length.
The base part of the plate-holder support may be slidably supported by the first guide rod and the second guide rod and configured to move along the first guide rod and the second guide rod. The first guide and the second guide may form part of the base part. For example, they may be positioned in through-holes formed by the base part.
The printing-plate lift may further comprise: a linear encoder comprising a sensor that is fixed in position relative to the lower support and a scale that is attached, or fixed, to the center part of the plate-holder support. The sensor and the scale cooperate and are configured to determine the vertical position, or elevation, of the plate-holder support relative to the lower support, or to any component of the printing-plate lift that is fixed in position relative to the lower support.
It is understood that the scale may be aligned with the threaded shaft of the ball screw. The sensor may be an optical sensor and the scale may be a glass scale.
The plate holder is attached to the plate-holder support. Thus, the relative position of the plate holder, and in extension the relative position of a printing plate thereon, is also determined by the linear encoder.
The center part may be susceptible to thermal expansion. This is particularly the case if the powder layers are heated to dry the printed ink. The placement of the scale on the center part makes the position measurement less sensitive to the thermal expansion. The scale may be positioned closer to the upper end of the center part than to the lower end of the center part, which further reduces the sensitivity to thermal expansion of the center part. The linear encoder contributes to an improved accuracy and precision in the positioning of the printing plate.
The printing-plate lift may further comprise: an upper support, or table, wherein the first guide rod and the second guide rod are attached, or fixed, to the upper support. The upper support forms a central aperture through which the center part of the plate-holder support extends. This means that the lower end of the center part is located below the central aperture and the upper end of the center part is located above the central aperture. In extension, this means that the plate holder is located above the central aperture. It is understood that the upper support is located above the lower support. The guide rods may fix the position of the upper support relative to the lower support. The guide rods may support the upper support.
The sensor of the linear encoder may be attached, or fixed, to the upper support. It may be located at the central aperture formed by the upper support. Further, it may be located below the central aperture. The central aperture may be configured receive the scale of the linear encoder at an upward movement of the plate-holder support. Worded differently, the central aperture may be configured allow passage of the scale of the linear encoder at an upward movement of the plate-holder support.
The upper support comprises: a central guide that slidably cooperate with the center part of the plate-holder support. The central guide may be a central bearing, and the central bearing may be a linear slide bearing. The central guide may be positioned at the central aperture formed by the upper support. It may form the central aperture. The central guide may be configured to prevent the center part of the plate-holder support from tilting relative to the upper support. These features contribute to an improved accuracy in the positioning of the plate holder, and in extension the printing plate. This is particularly advantageous in the combination with a plate-holder support having a center part that extends upward from a base part and the base part being slidably supported by the first guide rod and the second guide rod, with the guide rods preventing the plate-holder support from rotating relative to the lower support, for example at a rotation of the threaded shaft of the ball screw.
The central guide may be configured receive the scale of the linear encoder at an upward movement of the plate-holder support. Worded differently, the central guide may be configured allow passage of the scale of the linear encoder at an upward movement of the plate-holder support.
The plate holder may define a planar upper surface, and the plate holder comprises: three face seals extending from the upper surface, or facing upward, for sealing to, or cooperating with, a printing plate, wherein the face seals are positioned to define, or in, an isosceles triangle having an apex corner and two side corners. The plate holder further comprises: an evacuation inlet located within each face seal. One of the face seals is positioned at the apex corner and the other two face seals are positioned at the side corners, wherein each face seal encloses a seal area, and the seal area of the face seal at the apex corner is greater than the seal area of each of the face seals at the side corners.
The evacuation inlet may be located within the seal area of the face seal. It is understood that the evacuation inlet allows for the pressure within the face seal to be reduced. This has the effect that a printing plate positioned on the plate holder is secured to the plate holder. It is understood that an isosceles triangle has a base, or base side, and two legs, or sides, and that the legs have the same lengths. An apex corner is understood as the corner that is opposite the base of an isosceles triangle. It is further understood that the legs connect at the apex corner, and that each of the legs connect to the base at a side corner.
A face seal is understood as a seal in which the sealing surfaces are normal to the axis of the seal. For example, a planar bottom surface of a printing plate may constitute a sealing surface in the radial direction with respect to the axis of the seal. Each face seal may have a symmetry axis normal to the upper surface of the plate holder. Each face seal may have at least a 180° rotational symmetry with respect to the symmetry axis. It is understood that the axis of a face seals is parallel to, or colinear with, the symmetry axis.
During use, each evacuation inlet is connected to a vacuum system that evacuates the face seal. This may deform the printing plate, as is further explained below. It is understood that the plate holder has exactly three face seals. The three face seals jointly define a contact plane for a printing plate. This reduces deformations of the printing plate, thus contributing to an improved precision in the printing. Printing plates are typically rectangular. Thus, when securing the printing plate to the plate holder by evacuating the face seals, the resulting forces acting on the printing plate will be unevenly distributed. The uneven force distribution may result in deformations of the printing plate, or even result in the printing plate coming loose. This reduces the precision of the printing, particularly if the longer sides of the rectangular printing plate are positioned parallel with the base of the triangle defined by the face seals. Thus, the above-described seal areas and positions of the face seals allow for rectangular printing plates with higher aspect ratios to be used without negatively affecting the precision.
Preferably, the isosceles triangle has exactly two sides of equal lengths. The length of the base may be longer than the length of the legs. Worded differently, the angle between the legs, or the apex angle, may be greater than 60°. For example, the length of the legs may be in the range 80-90% of the length of the base. Alternatively, the triangle defined by the three gaskets may be an equilateral triangle, which means that the lengths of the base and the legs are the same.
The geometric centers of the seal areas of the face seal may define the isosceles triangle. Worded differently, the geometric center of the seal areas of each face seal may be positioned at a corner of the isosceles triangle.
The upper surface of the plate holder may form grooves in which the face seals are fitted, or positioned.
The planar upper surface of the plate holder may be rectangular and have a first pair of parallel sides and a second pair of parallel sides, wherein the sides of the first pair are longer than the sides of the second pair, and the base of the isosceles triangle is parallel to the first pair of parallel sides. It has been found that this, in conjunction with the abovementioned seal areas, reduces the deformation of printing plates that have the same shape and are aligned with the upper surface.
Each face seal may constitute a spacer between the upper surface of the plate holder and the printing plate. This means that during use, the face seals will not compress such that the printing plate is flush with the upper surface of the plate holder. The three face seals may have equal heights relative to the upper surface. Worded differently, they may provide the same spacing between the upper surface and the plate holder.
The seal area of each of the face seals at the side corners may define a disc, or be disc shaped. For example, the face seals may be circular.
As mentioned above, the isosceles triangle may have a base, or base side, and the apex corner is opposite the base. The face seal at the apex corner may be elongated and aligned with, or parallel to, the base of the isosceles triangle. This contributes to reduce the deformation of a printing plate during use, in particular if it is rectangular and aligned with the base of the isosceles triangle. It has been found that this is particularly advantageous in combination with the face seals at the side corners being disc shaped.
The seal area of the face seal at the apex corner may be composed of two disjoint half-discs connected by a rectangle with the straight side of one of the half-discs connecting and conforming to on one side of the rectangle and the straight side of the other half-discs connecting and conforming to the opposite side of the rectangle. This means that the face seal at the apex corner is elongated. That two sides conform means that they have the same length and are mutually completing. Alternatively worded, the corners on one side of the rectangle may pairwise connect to the corners of one of the half-discs and the corners on the other side of the rectangle may pairwise connect to the corners of the other half-disc. A half-disc is understood as a disc sector of 180°. The sides of the rectangle that are disjoint from, or not connected to, the half-discs are straight. The sides of the rectangle that are disjoint from the half-discs may be parallel to the base of the isosceles triangle defined by the face seals.
The seal area of the face seal at the apex corner may be in the range 20-50%, or 30-40%, greater than the seal area of each of the face seals at the side corners. The face seals at the side corners may have the same seal area. They may define seal areas having the same geometry, for example both seal areas may be disc-shaped as mentioned above.
The plate holder may further comprise: an adjustable spacer located within each face seal, wherein each adjustable spacer defines a variable separation between the upper surface of the plate holder and the printing plate. Each adjustable spacer may be located at the geometric center of the seal area of the face seal it is located within, or at the symmetry axis of the face seal it is located within. Alternatively worded, each adjustable spacer may be located at the corners of the isosceles triangle.
Each adjustable spacer may comprise a threaded hole in the upper surface of the plate holder and a cooperating threaded screw positioned in the threaded hole. The separation between the upper surface of the plate holder and the printing plate can then be varied by turning the screw. The printing plate may be deformed by a face seal as such upon evacuation via the evacuation inlet within the face seal, typically by bulging toward the plate holder at the geometric center of the seal area of the face seal. The adjustable spacers may be employed to prevent this from happening, which contributes to an improved precision in the printing.
The plate holder may further comprise: one or more additional adjustable spacers located outside the face seal, wherein each additional adjustable spacer defines a variable separation between the upper surface of the plate holder and the printing plate. Preferably, the additional adjustable spacers are located within the isosceles triangle. Each additional adjustable spacer may comprise an additional threaded hole in the upper surface of the plate holder and a cooperating additional threaded screw positioned in the threaded hole.
According to a second aspect of the proposed technology a plate holder for supporting, or holding, a printing plate, is provided. The plate holder may have any of the features of the plate holder described above.
A more complete understanding of the abovementioned and other features and advantages of the proposed technology will be apparent from the following detailed description in conjunction with the appended drawings, wherein:
The plate-holder support 16 has a base part 52 that extends between the first guide rod 42 and the second guide rod 44 and a center part 54 with a lower end 56 attached to the base part 52 and an upper end 58 to which the plate holder 14 is attached. The base part 52 forms a central through-hole 60 and the center part 54 forms an enclosed space 62 connected to the central through-hole 60.
The ball screw 18 has a vertical and threaded shaft 20 that is connected to the lower support 12 by a bearing 110 that rotationally supports the threaded shaft 20. The threaded shaft 20 extends through the central through-hole 60 of the base part 52 into the enclosed space 62 formed by the center part 54. The ball screw also has a ball nut 22. The position of the ball nut 22 along the threaded shaft 20 can be changed by rotating the threaded shaft 20. The ball nut 22 is positioned within the central through-hole 60 and attached to the base part 52 of the plate-holder support 16. This way, the elevation of the plate-holder support 16 is determined by a rotation of the threaded shaft 20.
The drive unit 24 has a drive shaft 26 that can deliver torque. The drive shaft 26 is positioned beside the threaded shaft 20, as shown in
The power transmission 28 has a two-pulley belt drive 34 with a first pulley 36 attached to and centered on the drive shaft 26, a second pulley 38 attached to and centered on the threaded shaft 20, and a belt 40 connecting the first pulley 36 and the second pulley 38. The radius of the second pulley 38 is greater than the radius of the first pulley 36, giving a speed ratio between the input and the output that is smaller than one. This way, the power transmission 28 operationally connects the drive shaft 26 of the drive unit 24 and the threaded shaft 20 of the ball screw 18 and the power transmission 28 rotates the threaded shaft 20 at a rotation of the drive shaft 26.
As described above, the ball nut 22 is attached to the plate-holder support 16 and the elevation of the plate-holder support 16 is determined by a rotation of the threaded shaft 20. Thus, the drive unit 24, the power transmission 28, and the ball screw 18 are configured to determine the vertical position of the plate-holder support 16 relative to the lower support 12.
The first guide rod 42 and a second guide rod 44 have circular cross sections and are oriented vertically and parallel to the threaded shaft 20. The first and second guide rods 42 and 44 are attached to the lower support 12 and positioned on opposite sides of the threaded shaft 20 with the threaded shaft 20 positioned at the center between the guide rods 42 and 44 in a coplanar relationship.
The plate-holder support 16, more precisely its base part 52, is slidably supported by the first guide rod 42 and the second guide rod 44 and it can move along the first guide rod 42 and the second guide rod 44, as illustrated in
The first guide 46 and a second guide 48 are linear plain bearings and form part of the plate-holder support 16, or more precisely its base part 52. Each guide 46 and 48 form a through-hole 50 with a circular cross section, and the first guide rod 42 is concentric with and extend through the through-hole 50 of the first guide 46, and the second guide rod 44 is concentric with and extend through the through-hole 50 of the second guide 48. This way, the guides 46 and 48 and the rods 42 and 44 jointly cooperate to prevent the plate-holder support 16 from turning or tilting relative to the lower support 12.
The upper support 70 is attached to and supported by the first guide rod 42 and the second guide rod 44, thus fixing the position of the upper support 70 relative to the lower support 12. It forms a central aperture 72 through which the center part 54 of the plate-holder support 16 extends. The lower end 56 of the center part 54 is located below the central aperture 72 and the upper end 58 of the center part 54 is located above the central aperture 72, which is shown in
The upper support 70 has a central guide 74 in the form of a linear slide bearing positioned at the central aperture 72 formed by the upper support 70. The central guide 74 slidably cooperate with the center part 54 of the plate-holder support 16, thus preventing the center part 54 of the plate-holder support 16 from tilting relative to the upper support 70.
The linear encoder 64 has a sensor 66 in the form of an optical sensor attached to the upper support 70. It is located below and at the central aperture 72 formed by the upper support 70. This way, it is fixed in position relative to the lower support 12. The linear encoder 64 further has a scale 68 in the form of a glass scale that is attached to the center part 54 of the plate-holder support 16 and aligned with the threaded shaft 20 of the ball screw 18. The sensor 66 and the scale 68 cooperate to determine the vertical position, or elevation, of the plate-holder support 16 relative to the lower support 12. The linear encoder 64 can be recalibrated to determine the position of a printing plate on the plate holder 14.
Details of the plate holder 14 are shown in
Each face seal 78 encloses a seal area. The plate holder 14 has an evacuation inlet 86 located within each face seal 78 that allows for the pressure within the face seal 78 to be reduced to secure the printing plate to the plate holder 14.
The geometric centers 96 of the seal areas of the face seal 78 defines an isosceles triangle 80 indicated by dashed lines in
The rectangular planar upper surface 76 has a first pair of parallel sides 92 and a second pair of parallel sides 94, and the sides 92 of the first pair are longer than the sides 94 of the second pair. The base 88 of the isosceles triangle 80 is parallel to the first pair of parallel sides 92.
The seal area of the face seal 78 at the apex corner 82 is composed of two disjoint half-discs connected by a rectangle. The corners on one side of the rectangle pairwise connect to the corners of one of the half-discs and the corners on the other side of the rectangle pairwise connect to the corners of the other half-disc. The sides of the rectangle that are disjoint from the half-discs are parallel to the base 88 of the isosceles triangle 80. This way, the face seal 78 at the apex corner 82 is elongated and aligned with the base 88 of the isosceles triangle 80. The seal area of each of the face seal 78 at the side corners 84 defines a disc. The discs and the abovementioned half-discs have the same radius.
The plate holder 14 has an adjustable spacer 98 located at the geometric center of the seal area of each face seal 78. Each adjustable spacer 98 has a threaded hole 100 in the upper surface 76 of the plate holder 14 and a cooperating threaded screw 102 positioned in the threaded hole 100. The position of the threaded screw 102 can be adjusted by turning the threaded screw 12. This way, each spacer 98 is adjustable and defines a variable separation between the upper surface 76 of the plate holder 14 and a printing plate.
The plate holder 14 further has three additional adjustable spacers 104 located outside the face seal 78 and within the isosceles triangle 80. Each additional adjustable spacer 104 has an additional threaded hole 106 in the upper surface 76 of the plate holder 14 and a cooperating additional threaded screw 108 positioned in the threaded hole 106. As with the adjustable spacers 98, each additional adjustable spacer 104 defines a variable separation between the upper surface 76 of the plate holder 14 and a printing plate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22160564.5 | Mar 2022 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/055563 | 3/6/2023 | WO |
