摘要：
Un método para determinar un punto de ajuste para un sensor térmico (72) en un aparato para la fabricación capa por capa de un objeto tridimensional a partir de material particulado; el método comprende: (a) distribuir una capa de material particulado, proporcionando la capa una superficie de lecho de construcción (12); (b) depositar una cantidad de modificador de absorción sobre al menos una de una región de prueba (50) y un área circundante que rodea la región de prueba; (c) calentar la región de prueba (50) durante un período de tiempo con una fuente de calor (LI); (d) medir con el sensor térmico (72) un valor de temperatura TR dentro de la región de prueba (50); (e) distribuir una capa adicional de material sobre la capa de material anterior, proporcionando la nueva capa la superficie del lecho de construcción (12); - repetir los pasos (b) a (e) del ciclo de capas al menos hasta que el material particulado dentro la región de prueba (50) comienza a fundirse, en donde la etapa (b) comprende depositar una cantidad adicional de modificador de absorción sobre la región de prueba (50), en donde la cantidad adicional de modificador de absorción hace que el material particulado de la región de prueba (50) se derrita. absorber más energía de la fuente de calor (L1) que la región de prueba (50) de la capa anterior; - determinar un punto de ajuste para el sensor térmico (72) a partir de una característica del material identificada a partir de una característica en la evolución de la valor de temperatura medido TR dentro de la región de prueba (72); y aplicar el punto de ajuste determinado a mediciones posteriores del sensor térmico (72).
权利要求：
1. A method for determining a set point for a thermal sensor (72) in an apparatus for the layer-by-layer manufacture of a three-dimensional object from particulate material; the method comprising: (a) distributing a layer of particulate material, the layer providing a build bed surface (12); (b) depositing an amount of absorption modifier over at least one of a test region (50) and a surrounding area surrounding the test region; (c) heating the test region (50) over a period of time with a heat source (L1); (d) measuring with the thermal sensor (72) a temperature value TR within the test region (50); (e) distributing a further layer of material over the preceding layer of material, the new layer providing the build bed surface (12); - repeating the steps (b) to (e) of the layer cycle (100) at least until the particulate material within the test region (50) starts to melt, wherein step (b) comprises depositing a further amount of absorption modifier over the test region (50), wherein the further amount of absorption modifier causes the particulate material of the test region (50) to absorb more energy from the heat source (L1) than the test region (50) of the preceding layer; - determining a set point for the thermal sensor (72) from a characteristic of the material as identified from a characteristic in the evolution of the measured temperature value TR within the test region (72); and - applying the determined set point to subsequent measurements of the thermal sensor (72).
2. The method of any preceding claim, wherein the layer cycle (100) further comprises a step of preheating each layer to a preheat temperature value following the step (e) of distributing each layer and before the step (b) of depositing absorption modifier, wherein the preheat temperature value is lower than the melting temperature of the particulate material.
3. The method of claim 1 or claim 2, wherein each layer comprises a set of sublayers, wherein each sublayer is processed according to the same steps of distributing, preheating where present, depositing radiation absorber and heating of that layer, and wherein the measured temperature value TR of each layer is an average temperature value based on the respective temperature values TR measured within the test region (50) of one or more of the sublayers of that layer.
4. The method of any preceding claim, wherein the step of defining a test region (50) comprises defining a plurality of test areas (500) arranged over the build bed surface (12); wherein the thermal sensor (72) comprises a plurality of sensor pixels, such that step (d) comprises measuring the temperature value TR within each test area (500) with a corresponding one or more pixel of the plurality of sensor pixels, wherein the set point is determined for each of the plurality of sensor pixels based on the measured temperature value TR for each test area (500) of each layer.
5. The method of any preceding claim, wherein the step of depositing each further amount of absorption modifier comprises, compared to the preceding amount of absorption modifier, at least one of: - depositing a different amount per unit area of absorption modifier over the test region (50); and - depositing a different absorption modifier, wherein the different absorption modifier is configured to absorb a different amount of energy of the radiation of the heat source (L1) compared to that of the preceding absorption modifier; wherein at least one of the further amounts is sufficient to cause the particulate material of the test region (50) to start to melt.
6. The method of any preceding claim, wherein the absorption modifier is radiation absorber comprised within a fluid and deposited in the form of droplets using a droplet deposition head, and wherein the step of depositing each further amount of radiation absorber comprises, compared to the preceding amount of radiation absorber, depositing a larger amount of radiation absorber per unit area over the test region (50).
7. The method of any one of claims 1 to 5, wherein absorption modifier is radiation absorber provided in form of multiple fluids comprising radiation absorber deposited by respective droplet deposition heads, and wherein the step of depositing each further amount of radiation absorber comprises, compared to the preceding amount of radiation absorber, at least one of: (i) depositing each amount of radiation absorber as a multi-fluid pattern that causes the test region (50) to absorb a higher amount of energy provided by the heat source (L1) compared to a multi-fluid pattern deposited over the test region (50) of the preceding layer; (ii) depositing each further radiation absorber in the form of a pattern of a preceding fluid comprising radiation absorber and a pattern of a subsequent fluid comprising radiation absorber, wherein the two patterns are arranged to overlap by operating respective droplet deposition heads while passing them over the test region (50) of the further layer, wherein the further fluid comprising radiation absorber is capable of absorbing an intermediate amount of energy of the radiation spectrum provided by the heat source compared to the preceding and subsequent fluid comprising radiation absorber; (iii) depositing a different radiation absorber, wherein the different radiation absorber comprises a different colour capable of absorbing a larger amount of energy of the radiation spectrum provided by the heat source (L1) compared to the colour of the preceding amount of radiation absorber; and (iv) depositing a higher number of droplets of fluid per unit area over the test region (50), wherein at least one of the further amount of radiation absorber is deposited by operating the droplet deposition head while passing it over the test region (50) of the further layer more than once.
8. The method of any preceding claim, wherein the step of heating the test region (50) comprises passing the heat source (L1) across the layer while operating the heat source (L1), and wherein the period of time over which the test region (50) is heated is determined by the speed of the heat source (L1) relative to the test region (50).
9. The method of claim 2, wherein the step of preheating the test region (50) comprises operating a stationary heat source (20) provided above the build bed surface (12).
10. The method of claim 2, or of any one of claims 3 to 9 when dependent on claim 2, wherein the step of preheating each distributed layer comprises, or further comprises, passing a preheat source (L2) across the layer while operating the preheat heat source (L2) to preheat the test region (50) to the preheat temperature, and wherein the period of time over which the build bed surface (12) is preheated is determined by the speed of the preheat source (L2) relative to the build bed surface (12).
11. The method of claim 8, or of claim 10 when dependent on claim 9, wherein the steps of distributing each layer and of passing the heat source (L1) across each layer are carried out in the same direction, and where present, the step of preheating by passing the preheat source (L2) across each layer is carried out in that same direction.
12. The method of claim 11, comprising for each layer at least one of: - the power input to the heat source (L1) is substantially constant; - the power input to the preheat source (L2) is substantially the same for each layer; - the speed of passing the heat source (L1) over the build bed surface (12) is substantially constant; - the speed of passing the preheat source (L2) over the build bed surface (12) is substantially constant.
13. The method of any preceding claim, further comprising, after at least one or more of the layer cycle steps, measuring the temperature of the build bed surface (12) using the thermal sensor (72); and operating the or a stationary heat source (20) provided above the build bed surface (12) based on the measured temperature and a predefined target layer temperature between the solidification temperature and the melting temperature of the particulate material, so as to maintain the build bed surface (12) at the target temperature.
14. The method of claim 13, wherein the stationary heat source (20) is operated continuously throughout the layer cycle.
15. The method of any preceding claim, further comprising: - initiating the step of distributing each further layer after a first time interval from initiating the step of heating with the heat source (L1); - initiating the step of heating with the heat source (11) after a second time interval from initiating the step of distributing the layer; and - where present, initiating the step of preheating with the preheat heat source (L2) after a third time interval from initiating the step of distributing the layer; wherein the speed of passing the preheat source (L2), where present, and the heat source (L1) over each layer and the first, second and third time interval are constant throughout the calibration process; and wherein a subsequent object build process comprises the same layer cycle steps as the calibration process, wherein, for the build process the step (b) comprises depositing radiation absorber over an object region; and step (c) comprises heating the object region over a period of time with the heat source (L 1) so as to cause the particulate material in the object region to melt; and repeating the layer cycle for the build process until the object is complete; wherein the speed of passing the preheat source (L2), where present, and the heat source (L1) over each layer and the first, second and third time interval are the same as for the calibration process.