WO2018001491A1

WO2018001491A1 - Heating element structure

Info

Publication number: WO2018001491A1
Application number: PCT/EP2016/065371
Authority: WO
Inventors: Francesc SALAS ROURA; Gerard GUIXE; David POU; Jaime Abel BLANCO GABELLA
Original assignee: Hewlett-Packard Development Company L.P.
Priority date: 2016-06-30
Filing date: 2016-06-30
Publication date: 2018-01-04

Abstract

Heating element structures (300) to heat surfaces of print beds (505) are disclosed. A heating element structure (300) according to an example comprises a rotary base (305, 524), to be mounted over a print bed (505) with an axis of rotation perpendicular to the printing bed. Heating elements (310, 525) are distributed on the rotary base (305, 524) to uniformly heat an effective printing area of the print bed (505).

Description

Heating element structure

BACKGROUND

[001 ] Additive manufacturing techniques may generate a three-dimensional object on a layer-by-layer basis through the solidification of a build material. In examples of such techniques, build material is supplied in a layer-wise manner and a solidification method may include heating the layers of build material to cause melting in selected regions. In other techniques, other solidification methods, such as chemical solidification methods or binding materials, may be used. In some examples, the temperature of the build material is increased prior to the melting process.

BRIEF DESCRIPTION

[002] Some non-limiting examples of the present disclosure are described in the following with reference to the appended drawings, in which:

[003] Fig. 1 schematically illustrates a heating element structure used in 3D printing systems.

[004] Fig. 2 schematically illustrates a temperature distribution chart of the print bed when heated by the heating element structure of Fig. 1 .

[005] Fig. 3 schematically illustrates a heating element structure according to an example. [006] Fig. 4 schematically illustrates a temperature distribution chart of the print bed when heated by the heating element structure of Fig. 3. [007] Fig. 5 schematically illustrates a 3D printing system according to an example.

[008] Fig. 6 schematically illustrates a controller for a heating element structure according to an example.

DETAILED DESCRIPTION

[009] In some 3D printing processes a layer of a build material in the form of a particle material, e.g. powder, is laid down on a working area of a fabrication chamber. Then a fusing agent is selectively applied where the particles are to fuse together. The work area is subsequently exposed to fusing energy. The process is then repeated until a part has been formed. During a first pass, the working area may be a print bed. Subsequently, the working area will be the layer of fused material. In some 3D printing systems a pre-heating structure is used to pre-heat the top layer of build material to a uniform temperature just below the melting point of the build material and before fusing energy is applied. A heating element structure mounted over the working area may be used for pre-heating. Some heating element structures have arrays of heating elements that are selectively controllable to provide energy in the form of heat to the working area.

[0010] Fig. 1 schematically illustrates a heating element structure proposed in 3D printing systems. The heating element structure 100 has an array of heating elements 1 10 arranged on a base. The heating lamp structure 100 may include a plurality of individual lamps, or heating elements 1 10. In the example shown in Fig. 1 , the heating element structure 100 includes ten individual heat elements 1 10. The heating element may be a heating lamp, for example halogen lamps to radiate power in the near-infrared range, or infrared Light Emit Diode (LED) lamps. However, other heat sources may be used, such as infrared bar radiators or any other radiation source or component configured to generate heat for increasing a temperature of at least a portion of the fabrication chamber. The base may form part of a top cover of a printing chamber. During operation of the 3D printing system, a layer of build material may be formed on a working area, e.g. on a print bed. Then a fusing agent may be deposited, or printed, on the layer of build material. Then the heating elements may be controllable to heat the print bed. Controlling the heating elements may comprise individual switching of the heating elements or modulating the power emanating from the heating elements. The base may include a heat sensor 150, located for example at the center of the base, to measure the temperature on the working area. The heat sensor 150, in some examples, may be a thermopile infrared (IR) sensor, capable of detecting absolute temperatures or temperature changes of a target, such as the print bed. The heat sensor 150 may include, or may be connected to, an imaging device, such as a charge-coupled device (CCD), capable of generating and/or recording a visual image representative of the detected temperature or temperature change for at least a portion of the print bed and/or build material on the print bed. In other examples, the heating element structure 100 may include multiple heat sensors 150 for measuring temperatures or detecting temperature changes of a target, which may be located among the heat elements 1 10 or elsewhere within, or remote from, the lamp assembly. The heat sensor 150 may, in some examples, register a temperature change for those portions of the print bed at which the temperature changes by a defined threshold amount, or at which the temperature changes to more than a defined threshold value. [001 1 ] The top cover may additionally comprise a controller 105, either on site or remote, and electrical parts, e.g. in the form of one or more printed circuit assemblies (PCAs), that may provide energy to the heating elements in the form of electricity. Each of the heating elements 1 10 may be connected to controller 105 via which each heating element may be controlled and receive power. In some examples, the controller may comprise a number of printed circuit assemblies (PCAs). Each PCA may be connected to a number of heating elements. In other examples, more or fewer PCAs may be used and, in some examples, the heating elements may be connected via a single PCA, or may be connected to the controller directly, without any PCAs. In some examples, the heating elements 1 10 may be connected to the controller via PCAs to reduce the risk of current peaks occurring in the heating elements. Each heating element in Fig. 1 is fixed on the base. The heating elements may be individually switched on/off or may belong to groups. In the latter case, all lamps belonging to a group may be switched on/off in unison. The controller may switch on/off each lamp or group with an intention to provide a uniform temperature on the working area.

[0012] Fig. 2 schematically illustrates a temperature distribution chart of the print bed when heated by the heating element structure of Fig. 1 . The working area is divided into zones, numbered arbitrarily as zones 1 -12. Each zone indicates an average temperature. Zones 1 -12 indicate temperatures above a pre-heating threshold. A pre-heating threshold may be a temperature below the melting point of the build material. The rest of the area (outside the zones 1 -12) indicates average temperatures below the pre-heating threshold. As may be seen from Fig. 2, the temperature may not be uniformly distributed. That is, the temperature may not be constant across the working area 200. Thus, more energy may be required to heat a certain zone, e.g. a zone closer to the periphery of the working area, to a certain temperature or some zones may not be adequately heated. Thus the effective printing area of the print bed may comprise those zones (1 -12 in Fig. 2) where heating temperature exceeds a pre-heating threshold. Otherwise, the quality of the printed product or part may be affected. In the example of Fig. 2, the effective printing area is indicated by zones 1 to 12. Within each of those zones the minimum preheating temperature may be reached using the heating element structure of Fig. 1 . However, areas outside the effective printing area may be excluded from consideration when designing a print job. Thus the effective printing area is substantially reduced compared to the available working area. Furthermore, towards the center of the working area the temperature, even if maintained below the fusing temperature, may be substantially above the minimum pre- heating temperature. This may be attributed to thermal losses around the edge of the working area. Therefore a heating element structure, to provide a minimum pre-heating temperature at a larger effective printing area, may heat the central zones (e.g. zones 6 and 7) at a higher temperature compared to the periphery (e.g. zones 1 , 2, 3, 4, 5, 8, 9, 10, 1 1 and 12). A more even distribution of heat may reduce energy consumption or allow for a wider effective printing area.

[0013] Fig. 3 schematically illustrates a heating element structure according to an example. The heating element structure 300 may be used to heat a surface of a print bed. The heating element structure 300 may comprise a rotary base 305, to be mounted over the print bed with an axis of rotation perpendicular to the print bed, heating elements 310 distributed on the rotary base to uniformly heat an effective printing area of the print bed and an infrared sensor 350 at the center. The infrared sensor 350 may be a thermopile infrared sensor. The number of heating elements may depend on the size of each individual lamp and on the size of the rotary base. Furthermore, the distribution of the lamps may be such that, when the rotary base rotates, heat from the lamps may uniformly reach a wide area of the print bed that may lie beneath the heating element structure.

[0014] As the rotary base rotates, each lamp may follow a circular path around the center of rotation. For example, heating element 310 may rotate around a circular path C. A uniform distribution of the lamps at various distances from the center of rotation may allow a uniform heating pattern on the print bed. In one example of such uniform distribution, the heating elements 310 may be arranged along a spiral path S. The spiral path S may have its center at the geometric center of the rotary base and extend outwards towards the sides of the rotary base. The spiral path S may be an arithmetic spiral (also known as an Archimedean spiral) or a logarithmic spiral. When the spiral is an arithmetic spiral the distribution of heating elements along the spiral may be in a logarithmic way. When the spiral is a logarithmic spiral the distribution of heating elements along the spiral may be in a linear way. By combining a linear spiral or distribution with a non-linear distribution or spiral, respectively, it may be possible to control the travel distance of each heating element for the same angular displacement, as a factor of the distance of the heating element from the center of the spiral. However, other distributions of heating elements are possible and may depend on the size, number, heating directionality, minimum pre-heating temperature, distance of heating element structure from the fusing area or other characteristics of the 3D printing system. By distributing the heating elements along the spiral path, the distance of each heating element from the center of rotation will increase proportionally to its position along the spiral path. Thus, the centers of the heating elements may be uniformly distributed. Arranging the heating elements along a spiral path may result in stabilization in terms of temperature uniformity. The angular movement of each heating element 310 may depend on electrical connection constraints of the heating elements 310. In the example heating element structure 300 the spiral is an arithmetic spiral and the distribution of heating elements is a logarithmic distribution. The heating elements may be distributed according to the following example equation:

[0016] In Eq. 1 , n is the index of the heating element counting from the center of the spiral and along the spiral path, P_n is the linear distance of the nth heating element on the spiral path from the center of the spiral, L is the total length of the spiral path, B the logarithmic base and N the total number of heating elements.

[0017] The heating element structure may be a rectangular of 100 cm x 100 cm. Each heating element may have a size of 10 cm x 25 cm. In the example of Fig. 3, there are ten heating elements 310 (1 -10) arranged logarithmically along the spiral path, the logarithmic base is equal to 2 and the total length of the spiral path L is equal 1 m.

[0018] Although a logarithmic function may be used, as the one discussed with the example of Fig. 3, to calculate the position and distribution of the heating elements along the spiral path, other non-lineal functions may be used with an arithmetic spiral. Alternatively, a linear distribution may be used with a logarithmic spiral. The choice of the function (non-lineal or linear) may be a factor, among others, of the spiral type, the relative size of the heating elements compared to the heating element structure, the number of heating elements, the power of the heating elements, the type of the spiral and the size of the working area.

[0019] Fig. 4 schematically illustrates a temperature distribution chart of the print bed when heated by the heating element structure of Fig. 3. As the heating element structure rotates, a wider zone of the working area may be heated above the pre-heating threshold. Furthermore, the zones that are heated above the pre-heating threshold may be more uniformly heated. Furthermore, as the heating is provided by lamps moving during pre-heating, less switch-ons/switch-offs may be performed, thus making it easier to comply with flicker regulations. More specifically, with reference to the same zones as the ones discussed with reference to Fig. 2, it may be seen that zones 6 and 7 are now more uniformly heated compared to the rest of the zones 1 , 2, 3, 4, 5, 8, 9, 10, 1 1 and 12. Furthermore, areas around the area corresponding to the effective printing area of Fig. 2 may now belong to the new effective printing area (indicated as white zones in Fig. 4). A more uniform heat distribution on the working area may imply a lower energy overall consumption (or emission) using the heating element structure 300 with the rotary base for the same effective printing area as the one in Fig. 2. It may also imply a wider effective printing area for the same energy overall consumption using the heating element structure 300 with the rotary base.

[0020] Furthermore, a better temperature uniformity between center and peripheral zones may also allow fewer lamps to be employed. When there is temperature uniformity, for the same area of interest, it may be easier to maintain the temperature uniformly just above the pre-heating threshold with less lamps because the temperature deviation from the pre-heating threshold- and thus the energy consumed may be lower.

[0021 ] As less energy may be required by a rotary heating element structure, compared to a non-rotary heating element structure, fewer lamps may be employed. Consequently, fewer lamps may require fewer power components (e.g. PCAs). An overall part reduction may thus be performed.

[0022] Fig. 5 schematically illustrates a 3D printing system according to an example. The 3D printing system 500 may comprise a print bed, or build platform, 505, a build material distributor 510, an agent depositor 515, and a rotary lamp structure 520. The print bed 505 may belong to a removable build unit that may be inserted in the 3D printing system for printing and removed when a print job is finished. The rotary lamp structure 520 may be mounted over the print bed 505. The rotary lamp structure 520 may comprise a fixed portion 522 and a rotary base 524 hosted in the fixed portion 522. The rotary base 524 may comprise heating elements 525. The heating elements may be distributed along a spiral path. The fixed portion 522 may comprise a casing 526 to host the rotary base 524, a servo-mechanism 528 attached to the casing and to the rotary base with axis 521 , and a protection glass 530. The 3D printing system may further comprise an infrared sensor 532 attached to the fixed portion 522 with axis 523 and protruding from, or flush with, the rotary base 524.

[0023] During operation, the build material depositor 510 may form a layer of build material 507 on the print bed 505. Then the agent depositor 515 may selectively deposit agent 509 on the layer of build material. The agent 509 deposited may define a fusing zone on the layer of build material 507. Based on the size and location of the fusing zone the controller of the rotary lamp structure 520 may control the switches of the heating elements of the rotary heating element structure to pre-heat the fusing zone before fusing energy is applied. The controller may control the energy of each heating element supplied to the print bed and also the rotation speed, direction and angle of the base. Therefore, based on the location and size of the fusing zone, those lamps whose arc path may pass over the fusing zone may be switched on and their power may be controlled and for the time that they pass over the fusing zone. Further to that, the rotation angle, and thus the arc length of each heating element, may be set based on the fusing zone size. Additionally, the rotary base 524 may oscillate back and forth around an axis of oscillation corresponding to a projection of an axis passing through the geometrical center of the fusing zone on the rotary base.

[0024] Fig. 6 schematically illustrates a controller for a heating element structure according to an example. Controller 600 may comprise a temperature interface 605, to receive a temperature reading from an infrared sensor of the heating element structure. Furthermore, controller 600 may comprise a power distributor 610, to provide electrical power in response to temperature readings to heating elements of the heating element structure and provide electrical power to a motor to rotate a rotary base of the heating element structure. The controller 600 may further comprise a memory 615, to store heating patterns. Each heating pattern may comprise one or more of a lamp turn-on/off sequence or power modulation pattern, a rotation direction, a rotation speed, a rotation angle. The power distributor 610 may provide electrical power according to a stored heating pattern. The controller 600 may further comprise a processor 620, coupled to the temperature interface 605, to the power distributor 610 and to the memory 615 to generate heating patterns and to provide instructions to the power distributor. These heating patterns may be generated in response to a design of the part that is to be 3D-printed or in response to temperature measurements. The generated heating patterns may be stored in memory 615 for future use. [0025] The example implementations discussed herein allow for uniform temperature distribution on an effective printing area of a working area of a 3D printing system. For a certain working area, the proposed heating element structures may allow for lower energy consumption, for reduced number of parts or for a wider effective printing area. Thus, they may improve the efficiency of a 3D printing system.

[0026] Although a number of particular implementations and examples have been disclosed herein, further variants and modifications of the disclosed devices and methods are possible. For example, not all the features disclosed herein are included in all the implementations, and implementations comprising other combinations of the features described are also possible. As such, representative examples of the present disclosure have utility over a wide range of applications, and the above discussion is not intended and should not be construed to be limiting, but is offered as an illustrative discussion of aspects of the disclosure. What has been described and illustrated herein is an example of the disclosure along with some of its variations. The terms, descriptions and figures used herein are set forth by way of illustration only and are not meant as limitations. Many variations are possible within the spirit and scope of the disclosure, which is intended to be defined by the following claims -- and their equivalents -- in which all terms are meant in their broadest reasonable sense unless otherwise indicated.

Claims

1 . A heating element structure to heat a surface of a print bed, the heating element structure comprising:

a rotary base, to be mounted over the print bed with an axis of rotation perpendicular to the print bed;

heating elements distributed on the rotary base to uniformly heat an effective printing area of the print bed;

2. The heating element structure according to claim 1 , comprising heating elements distributed along a spiral path on the rotary base.

3. The heating element structure according to claim 1 , further comprising a motor to rotate the rotary base.

4. The heating element structure according to claim 3, comprising a controller to control the motor in response to the temperature on the surface of the print bed

5. The heating element structure according to claim 4, comprising an infrared sensor to measure the heat on the print bed.

6. The heating element structure according to claim 5, wherein the infrared sensor comprises a thermopile sensor.

7. The heating element structure according to claim 5, wherein the infrared sensor is at the center of the rotary base.

8. A controller for a heating element structure, comprising:

a temperature interface, to receive a temperature reading from an infrared sensor of the heating element structure;

a power distributor, to provide electrical power in response to temperature readings:

to heating elements of the heating element structure; and to a motor to rotate a rotary base of the heating element structure.

9. The controller according to claim 8, further comprising a memory, to store heating patterns, wherein each heating pattern comprises one or more of a lamp turn-on sequence, a rotation direction and a rotation speed, and wherein the power distributor provides electrical power according to a stored heating pattern.

10. The controller according to claim 8, further comprising a processor to generate heating patterns, in response to temperature measurements, said generated heating patterns to be stored in memory for future use.

1 1 . A 3D printing system comprising:

a print bed;

a powder depositor, to deposit powder on the print bed;

an agent depositor, to deposit agent on the deposited poder; a lamp structure, mounted over the print bed to uniformly heat the print bed, the lamp structure to relatively rotate with respect to the print bed.

12. The 3D printing system according to claim 10, the lamp structure comprises a fixed portion and a rotary base hosted in the fixed portion.

13. The 3D printing system according to claim 12, wherein the rotary base comprises heating elements distributed along a spiral path.

14. The 3D printing system according to claim 12, wherein the fixed portion comprises a casing to host the rotary base, a servo-mechanism attached to the casing and to the rotary base, and a protection glass.

15. The 3D printing system according to claim 1 1 , further comprising an infrared sensor attached to the fixed portion and protruding from the rotary base.