阅读说明：本技术 用于增材制造中的构建厚度控制的方法和设备 (Method and apparatus for build thickness control in additive manufacturing ) 是由 梅雷迪思·埃莉萨·杜伯曼 玛丽·凯瑟琳·汤普森 克里斯多佛·巴恩希尔 杨熙 于 2020-02-20 设计创作，主要内容包括：一种使用增材制造设备(10)逐层形成零件(74)的方法。增材设备(10)包括树脂支撑件(190)、台(14)、测量系统(76)和致动器(32),以改变台(14)和树脂支撑件(190)的相对位置。该方法包括：进行增材制造循环,包括：沉积未固化的树脂层(110)；将台(14)移动到目标位置；固化未固化的层(110)；和将台(14)从目标位置移开；重复增材制造循环；进行包括以下步骤的测量处理：使用测量系统(76)进行指示结构的实际位置的测量；将结构的实际位置与结构的预期位置进行比较以确定误差；以及使用误差修改目标位置。(A method of forming a part (74) layer by layer using an additive manufacturing apparatus (10). The additive device (10) comprises a resin support (190), a table (14), a measurement system (76), and an actuator (32) to change the relative position of the table (14) and the resin support (190). The method comprises the following steps: performing an additive manufacturing cycle comprising: depositing an uncured resin layer (110); moving the table (14) to a target position; curing the uncured layer (110); and moving the table (14) away from the target position; repeating the additive manufacturing cycle; performing a measurement process comprising the steps of: -making measurements indicative of the actual position of the structure using a measurement system (76); comparing the actual position of the structure to an expected position of the structure to determine an error; and modifying the target position using the error.)

1. An additive manufacturing apparatus (10), comprising:

a resin support (190) defining a build surface configured to support an uncured resin layer (110);

a table (14) configured to hold a stacked arrangement of one or more cured resin layers forming a part (74), the part (74) defining a surface positioned opposite the table (14));

a radiant energy device positioned opposite the table (14) so as to be operable to generate and project radiant energy in a predetermined pattern;

an actuator (32) configured to change a relative position of the stage (14) and the resin support (190);

a measurement system (76) configured for measuring a position of one or more structures relative to the resin support (190); and is

Wherein the structure is one of: the table (14), a surface of the uncured resin layer (77), a surface (75) of the part (74), and combinations thereof.

2. The additive manufacturing apparatus (10) of claim 1, wherein the measurement system (76) comprises a laser range finder and the structures to be measured are the surface (75) of the part (74) and the surface of the uncured resin, and the measurement system (76) is configured to generate a signal indicative of a position of the surface (75) of the part (74) relative to the surface of the uncured resin and determine movement of the table (14) based on the signal.

3. The additive manufacturing apparatus (10) according to any one of the preceding claims, wherein the uncured resin layer (110) is configured to be cured by a first range of light frequencies, and the measurement system (76) comprises an optical sensor that produces a second range of light frequencies, and the second range is different from the first range.

4. The additive manufacturing apparatus (10) according to claim 1, comprising a reference position located on the table (14).

5. A method of forming a part (74) using an additive manufacturing apparatus (10), the additive manufacturing apparatus (10) comprising a resin support (190) configured to support an uncured resin layer (110) within a build area, a table (14) configured to hold a stacked arrangement of one or more cured resin layers forming at least a portion of the part (74), a measurement system (76), and an actuator (32) configured to change the relative positions of the table (14) and the resin support (190), the method comprising the steps of:

operating the additive manufacturing apparatus (10) according to a build profile to produce a solidified build layer (79) of a part (74);

measuring a dimension of the part (74) using the measurement system (76);

determining whether the dimension contains an error;

responding to a determination of an error by modifying the build profile to include a compensation layer, wherein a thickness of the compensation layer is selected to compensate for the error.

6. The method of claim 5, further comprising the steps of:

adding the error to an accumulated error value;

determining the thickness of the compensation layer by utilizing the cumulative error value; and is

Wherein the cumulative error value is formed over a plurality of cycles.

7. The method of claim 6, further comprising the steps of:

comparing the cumulative error value to a threshold error value; and

when the cumulative error value exceeds the threshold error value, performing the step of generating the compensation layer.

8. The method of claim 5, further comprising the steps of: selecting one of the following as a compensation layer: a previously planned layer and a new layer.

9. The method of claim 5, wherein the dimension is a thickness of the solidified build layer (79).

10. The method of claim 5, wherein the dimension is a height of the part (74).

Technical Field

The present invention relates generally to additive manufacturing and, more particularly, to an apparatus and method for determining build layer thicknesses and adjusting build profiles to achieve predetermined final dimensions of a part in additive manufacturing.

Background

Additive manufacturing is a process in which materials are built up layer by layer to form a part. Each layer is made in a cycle comprising a plurality of steps. One prior art method is the tape casting (tape casting) process. In this process, the resin is deposited as a layer having the desired thickness onto a flexible, radiation transparent tape fed from a supply reel. The table or upper plate is lowered onto the resin such that the working surface defined by one of the table surface or the surface of the machined part is positioned such that the working surface just contacts the resin or compresses it between the belt and upper plate and defines the layer thickness. The radiant energy is used to cure the resin through the radiolucent band. Once the curing of the first layer is complete, the upper plate retracts upward, carrying away the cured material. The belt is then advanced to expose a new clean section in preparation for depositing additional resin in a subsequent new cycle.

Another prior art method employs a vat (vat) of liquid radiant energy curable photopolymer "resin" and a source of curing energy (e.g., a laser). Also, DLP 3D printing uses a two-dimensional image projector to build up parts one layer at a time. For each layer, the projector will flash a radiation image of a cross-section of the component on the surface of the liquid or through a transparent object defining the constrained surface of the resin. Exposure to radiation cures and consolidates the pattern in the resin and bonds it to the previously cured layer to produce a build layer. Other types of additive manufacturing processes utilize other types of radiant energy sources to consolidate a pattern in a resin.

The relative position of the working surface and the resin surface is typically defined relative to a component of the additive manufacturing apparatus having a substantially fixed position. For example, in casting molding, the relative position may be defined by the position of the support platform of the resin layer. However, the relative position of the working surface may vary due to variations in the layer thickness from which the solidified machined part is built. Further variation can be introduced by varying the thickness of the resin layer.

Thus, one problem with conventional additive manufacturing methods is that the relative positions of the working surface and the resin surface can vary from cycle to cycle.

Another problem with conventional additive manufacturing methods is that errors can accumulate, adversely affecting the final dimensions of the part.

Another problem is that the starting position of the table may not be correct.

Another problem is that the thickness of the resin layer to be cured may not be correct.

Disclosure of Invention

At least one of these problems is addressed by an additive manufacturing apparatus configured to determine the relative position of a working surface and a resin surface. More specifically, an apparatus and method are provided to measure the relative position of a work surface with respect to a resin surface and adjust the desired build layer thickness accordingly.

According to one aspect of the technology described herein, a method of producing a part layer by layer using an additive manufacturing apparatus. An additive manufacturing apparatus includes a resin support, a stage, a measurement system, and an actuator configured to change a relative position of the stage and the resin support. The method comprises the following steps: performing an additive manufacturing cycle comprising: depositing an uncured resin layer; moving the station to a target position; curing the uncured resin layer; and moving the stage away from the target position; repeating the additive manufacturing cycle; performing a measurement process, wherein the measurement process comprises the steps of: making a measurement indicating an actual position of the structure using a measurement system; comparing the actual position of the structure to an expected position of the structure to determine an error; and modifying the target position using the error.

According to one aspect of the technology described herein, an additive manufacturing apparatus includes a resin support, a stage, a radiant energy apparatus, and an actuator, and a measurement system. The resin support defines a build surface configured to support an uncured resin layer. The table is configured to hold a stacked arrangement of one or more cured resin layers that form a part defining a surface positioned opposite the table. The radiant energy apparatus is positioned relative to the table such that it is operable to generate and project radiant energy in a predetermined pattern. The actuator is configured to change the relative positions of the stage and the resin support. The measurement system is configured to measure a position of the one or more structures relative to the resin support. By way of example and not limitation, the structure is one of: a table, a surface of an uncured resin layer, a surface of a part, and combinations thereof.

According to one aspect of the technology described herein, a method of forming a part using an additive manufacturing apparatus comprising a resin support configured to support an uncured resin layer within a build area, a stage configured to hold a stacked arrangement of one or more cured resin layers forming at least a portion of the part, a measurement system, and an actuator configured to change the relative positions of the stage and the resin support, the method comprising the steps of: operating an additive manufacturing apparatus according to a build profile to produce a solidified build layer of a part; measuring the dimensions of the part using a measurement system; determining whether the size contains an error; the determination of the error is responded to by modifying the build profile to include a compensation layer, wherein a thickness of the compensation layer is selected to compensate for the error.

Drawings

The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic side view of an exemplary cast additive manufacturing apparatus including a device for measuring a position of a structure;

FIG. 2 is a schematic view of an embodiment of a portion of the cast additive manufacturing apparatus shown in FIG. 1;

FIG. 3 shows a stylized representation of initial relative positions of a stage and a platform in an additive manufacturing apparatus;

FIG. 4 illustrates a further relative position of the table and platform of FIG. 3;

FIG. 5 illustrates a further relative position of the table and platform of FIG. 3;

FIG. 6 shows a stylized representation of a failure mode;

FIG. 7 shows a stylized representation of a failure mode;

FIG. 8 shows a stylized representation of another failure mode;

FIG. 9 shows the results of two cycles of an additive manufacturing method according to the disclosed technology;

fig. 10 is a schematic view of a portion of a barrel-based additive manufacturing apparatus showing the relative positions of a working surface and a resin surface.

FIG. 11 illustrates a single layer barrel-based additive manufacturing apparatus wherein the resin layer is further defined by contact with the table; and

fig. 12 is a view of the single-layer barrel-based additive manufacturing apparatus of fig. 11, illustrating an alternative curing mechanism for use in the barrel-based additive manufacturing apparatus of fig. 10.

Detailed Description

Referring to the drawings, wherein like reference numbers refer to like elements throughout the several views, fig. 1 schematically illustrates an example of a suitable apparatus 10 for additive manufacturing with improved build layer control and thus accuracy with respect to final part thickness. The following provides a method for monitoring part geometry via part thickness with apparatus 10 while building a part, and for modifying build profiles to correct errors that may occur in the build process. As used herein, the term "build profile" refers to an instruction or set of instructions for operating the apparatus 10 to build a set of layers using additive manufacturing to collectively define a part having a predetermined final dimension.

The apparatus 10 includes a resin processing assembly 11, which is a casting device 20 according to the illustrated embodiment. The resin treatment assembly 11 includes a device 76 configured to determine the relative position of the working surface 75 and the resin surface 77. The device 76 is shown in fig. 1 with reference numeral 76A indicating one possible alternative location for the device 76.

Referring to fig. 3-8, the disclosed techniques are suitable for reducing the number and magnitude of erroneous and inaccurate build layer developments that occur using conventional additive manufacturing equipment and methods. Such apparatus and methods do not take into account the actual relative positions of critical surfaces (e.g., working surface 75 and resin surface 77). As will be described in detail below, but described here to highlight errors addressed by the disclosed techniques, the additive manufacturing apparatus includes a station 14. Referring now to FIG. 3, the table 14 defines a surface 30 on which a part 74 is formed. The part 74 defines a surface 75 on which a new layer of the part is added by transferring a cured portion of the resin layer 110 located adjacent to the surface 75 and supported by the membrane 12. Layer 110 defines resin surface 77. As shown in FIG. 4, error-free operation involves a predetermined amount of contact between surface 75 and surface 77. The predetermined amount of contact causes the solidified portion of layer 110 to transfer to form a new build-up layer 79 of part 74 and define a new surface 75. A new portion of layer 110 moves under part 74 to define a new surface 77. This configuration is shown in fig. 5.

At least two types of errors are typical when considering forming a single build layer 79. As shown in FIG. 6, layer 110 is not thick enough to allow surface 77 to contact surface 75 when table 14 and part 74 are moved to a build position that fits the existing geometry of part 74. In this case, the cured portion of layer 110 is not transferred to part 74. In a second error condition (shown in FIG. 7), layer 110 is too thick so that when table 14 and part 74 are moved to a build position that fits the existing geometry of part 74, surface 75 actually penetrates surface 77, causing the part to deform and possibly also damage the part.

There are at least three typical types of errors in considering layer-based errors that affect the formation of the entire part. In a third error case, also shown in FIG. 6, an error in the thickness of the previous layer 110 results in a series of layers 79 of the part 74, some or all of which are too thin (further examples in this regard are shown in FIG. 9 and discussed in detail below). As a result, part 74 is not as tall as intended, and surface 75 does not contact material layer 110 if the thickness of material layer 110 is as thick or thinner as intended when stage 14 is moved to a build position suitable for the intended geometry. In a fourth error case, also shown in FIG. 7, a thickness error of previously built layer 79 results in a series of layers, some or all of which are too thick. Thus, part 74 is taller than desired, such that when table 14 is moved to a build position suitable for the desired geometry, surface 75 penetrates surface 77, causing the part to deform or fail. In a fifth error case, as shown in FIG. 8, an error in the thickness of the previous build layer 79 caused the part 74 to be much higher than expected. Thus, when the table 14 is moved to the build position, the table 14 is lowered so far that it "bumps" into the layer 110, thereby damaging the part. It may also push the part 74 through the material layer 110 to contact the membrane 12 or even push through the membrane 12 to damage the machine. As shown in fig. 8, the membrane 12 contacts the feature 74 with such force that the membrane 12 separates at several locations, resulting in web damage or breakage. The disclosed technique addresses these errors by providing an apparatus and method for accurately defining the thickness of layer 110 to enable part 74 to be properly constructed.

It is to be understood that the configuration of equipment other than tape casting may be used for the apparatus 10 and the method described below may be performed. Those other configurations include different types of resin treatment equipment, such as buckets and/or plates. The method is applicable to lower viscosity resins, slurries and pastes, and higher viscosity resins and/or powders. It should be understood that other configurations of equipment may be used to implement the method. The basic components of the exemplary apparatus 10 include a material deposition device 106 and a resin processing assembly 11, which in fig. 1 is a casting apparatus 20. The casting apparatus 20 includes a support film or belt 12, and a radiant energy apparatus 18.

Referring to fig. 1, the casting apparatus 20 includes spaced apart rollers 15 with a flexible polymeric strip or foil 12 extending therebetween. A portion of the foil 12 is supported from below by a support plate 190. Suitable mechanical supports (frames, brackets, etc. -not shown) will be provided for the rollers 15 and the support plate 190. The foil 12 is an example of a "resin support".

Both the support plate 190 and the foil 12 are transparent or comprise one or more portions that are transparent. As used herein, the term "transparent" refers to a material that allows radiant energy of a selected wavelength to pass through. For example, as described below, the radiant energy used for curing may be ultraviolet light or laser light in the visible spectrum. Non-limiting examples of transparent materials include polymers, glasses, and crystalline minerals such as sapphire or quartz.

Suitable means, such as motors, actuators, feedback sensors and/or controllers of known type (not shown) will be provided to drive the rollers 15 to keep the foil 12 properly tensioned between the rollers 15 and to wind the foil 12 from one roller 15 onto the other roller 15.

The foil 12 extending between the rollers 15 defines a first "build surface" 24, which is shown as being planar, but may also be arcuate (depending on the shape of the support plate). For ease of description, the first build surface 24 may be considered to be oriented parallel to the XY plane of the apparatus 10, and the direction perpendicular to the XY plane is denoted as the Z direction (X, Y and Z are three mutually perpendicular directions).

The first build surface 24 may be configured to be "non-stick," i.e., resistant to adhesion of the cured resin. The non-stick property may be manifested by a combination of variables such as the chemistry of the foil 12, its surface finish, and/or the applied coating. In one example, a permanent or semi-permanent non-stick coating may be applied. One non-limiting example of a suitable coating is polytetrafluoroethylene ("PTFE"). In one example, all or a portion of first build surface 26 may incorporate a controlled roughness or surface texture (e.g., protrusions, dimples, grooves, ridges, etc.) having non-stick properties. In one example, the foil 22 may be made in whole or in part of an oxygen permeable material.

Means are provided for applying or depositing the resin R to the first build surface 24 in a generally uniform layer. Fig. 1 schematically illustrates a material depositor 106 configured for this purpose.

Apparatus 10 includes a stage 14, which is a structure defining a planar surface 30, planar surface 30 being capable of being oriented parallel to build surface 24 of the portion of membrane 12 located on support plate 190. Means are provided for moving stage 14 parallel to the Z direction relative to build surface 24. In fig. 1, these devices are schematically depicted as simple actuators 32 connected between the table 14 and a stationary support structure 34, it being understood that devices such as pneumatic, hydraulic, ball screw electric, linear electric, or delta drives may be used for this purpose. In addition to or instead of making the stage 14 movable, the foil 12 and/or the support plate 190 may be movable parallel to the Z-direction.

The apparatus 10 includes a radiant energy apparatus 18 configured to cure at least a portion of the layer 110. The radiant energy apparatus 18 can include any device or combination of devices operable to generate and project radiant energy on the resin R in a suitable pattern and at a suitable energy level, as well as other operating characteristics, to cure the resin R in a build process, as described in more detail below.

In one exemplary embodiment as shown in fig. 1, the radiant energy device 16 may include a "projector" 48, used generally herein to refer to any apparatus operable to generate a radiant energy patterned image having suitable energy levels and other operating characteristics to cure the resin R. As used herein, the term "patterned image" refers to the projection of radiant energy comprising an array of individual pixels. Non-limiting examples of patterned imaging devices include a DLP projector or another digital micromirror device, a 2D led array, a 2D laser array, or an optically addressed light valve. In the illustrated example, the projector 48 includes: a radiant energy source 50, such as a UV lamp; an image forming device 52 operable to receive a source beam 54 from radiant energy source 50 and generate a pattern image 59 (fig. 6-8) for projection onto the surface of resin R; and optional focusing optics 48, such as one or more lenses.

The radiant energy source 50 can comprise any device operable to generate a beam having suitable energy level and frequency characteristics to cure the resin R. In the illustrated example, the radiant energy source 50 includes a UV flash lamp.

The image forming device 52 may comprise one or more mirrors, prisms and/or lenses and is provided with suitable actuators and is arranged such that the source beam 54 from the radiant energy source 50 may be converted into a pixelated image in the X-Y plane coincident with the surface of the resin R. In the illustrated example, the image forming device 52 may be a digital micromirror device. For example, projector 48 may be a commercially available digital light processing ("DLP") projector.

Alternatively, projector 48 may incorporate additional devices (e.g., actuators, mirrors, etc.) configured to selectively move image forming device 52 or other portions of projector 48, having the effect of rasterizing or moving the position of patterned image 59 (shown in fig. 6-8) relative to build surface 24. In other words, the patterned image may be moved away from the nominal or starting position. This allows a single image forming device 52 to cover a larger build area, for example. Means for controlling (registering) or moving the patterned image from the image forming device 52 are commercially available. This type of image projection may be referred to herein as a "tiled image".

In another exemplary embodiment (as shown in fig. 12, in connection with a barrel-based resin delivery system discussed further below), the radiant energy apparatus 18 may include, among other types of radiant energy devices, a "scanned beam apparatus" 60, the "scanned beam apparatus" 60 as used herein generally referring to any device operable to generate a beam of radiant energy having suitable energy levels and other operating characteristics to cure the resin R and scan the beam over the surface of the resin R in a desired pattern. In the illustrated example, the scanning beam device 60 includes a radiant energy source 62 and a beam steering device 64.

The radiant energy source 62 may comprise any device operable to generate a beam of suitable power and other operating characteristics to cure the resin R. Non-limiting examples of suitable radiant energy sources include lasers or electron beam guns.

The beam steering device 64 may comprise one or more mirrors, prisms and/or lenses and may be provided with suitable actuators and arranged such that the beam 66 from the radiant energy source 62 may be focused to a desired spot size and steered to a desired position in a plane coincident with the surface of the resin R. The bundle 66 may be referred to herein as a "build bundle". Other types of scanning beam devices may be used. For example, scanning beam sources using a plurality of build beams are known, as are scanning beam sources in which the radiant energy source itself is movable by one or more actuators.

The device 10 may include a controller 68. The controller 68 in fig. 1 is a generalized representation of the hardware and software necessary to control the operation of the apparatus 10, the stage 14, the radiant energy device 18, the transport mechanism 20, the depositor 106, and the various actuators described above. For example, the controller 60 may be embodied in software running on one or more processors embodied in one or more devices, such as a programmable logic controller ("PLC") or a microcomputer. Such a processor may be coupled to the sensors and operating components, for example, by wired or wireless connections. The same processor or multiple processors may be used to retrieve and analyze sensor data, for statistical analysis, and for feedback control.

Optionally, the components of the apparatus 10 may be enclosed by a housing 70, which housing 70 may be used to provide a protective or inert gas atmosphere using gas ports 72. Alternatively, the pressure within the housing 70 may be maintained at a desired level greater than or less than atmospheric air. Optionally, the housing 70 may be temperature and/or humidity controlled. Alternatively, the ventilation of the housing 70 may be controlled based on factors such as time intervals, temperature, humidity, and/or chemical concentrations.

The resin R comprises a material that is curable by radiant energy and is capable of adhering or bonding the filler (if used) together in the cured state. As used herein, the term "radiation energy curable" refers to any material that solidifies in response to application of radiation energy of a particular frequency and energy level. For example, the resin R may comprise a photopolymer resin of a known type which contains a photoinitiator compound which acts to initiate the polymerization reaction, changing the resin from a liquid state to a solid state. Alternatively, the resin R may include a material containing a solvent that can be evaporated by applying radiant energy. The uncured resin R may be provided in solid (e.g., granular) or liquid form (including paste or slurry).

According to the casting embodiment shown, the viscosity of the resin R is at a higher viscosity, so that contact with a doctor blade or leveling device (e.g., table 14) is required. The composition of the resin R may be selected as desired to suit a particular application. Mixtures of different compositions may be used.

The resin R may be selected to have the ability to outgas or burn off during further processing, such as the sintering process described below.

The resin R may contain a filler. The filler may be premixed with the resin R. The filler comprises particles, which are generally defined as "a very small amount of material". The filler may comprise any material that is chemically and physically compatible with the selected resin R. The particles may be regular or irregular in shape, uniform or non-uniform in size, and may have a variable aspect ratio. For example, the particles may take the form of powders, globules or granules, or may be shaped like small rods or fibers.

The components of the filler, including its chemistry and microstructure, can be selected as desired to suit a particular application. For example, the filler may be metallic, ceramic, polymeric, and/or organic. Other examples of potential fillers include diamond, silicon, and graphite. Mixtures of different components may be used.

The filler may be "fusible," meaning that the filler is capable of being consolidated into a mass via the application of sufficient energy. For example, fusibility is a characteristic of many available powders, including but not limited to polymers, ceramics, glass, and metals.

The ratio of filler to resin R can be selected to suit a particular application. In general, any amount of filler may be used as long as the combined material is able to flow and be leveled and there is sufficient resin R to hold the filler particles together in the cured state.

An example of the operation of the device 10 will now be described in detail with reference to fig. 1 and 2. It should be understood that the part 74 is software modeled as a stack of planar layers 79 arranged along the Z-axis as a precursor to producing the part and using the apparatus 10. Each layer may be divided into a grid of pixels depending on the type of curing method used. The actual component 65 may be modeled and/or fabricated as a stack of tens or hundreds of layers. Suitable software modeling processes are known in the art.

The resin treatment assembly 11 is operated to provide new resin R in the build zone 23. After material deposition, the apparatus 10 is positioned to define selected layer increments. The layer increment is defined by some combination of the thickness of the deposited layer and the operation of the station 14. For the bucket system shown in FIG. 10, it would be the depth to which the resin is filled into the bucket.

For example, the table 14 may be positioned so that the surface 30 of the new part or the existing surface 75 of the machined part just contacts the applied resin R, as shown in fig. 11, or the table 14 may be used to compress and displace the resin R to clearly define the layer increments. Layer increments affect the speed of the additive manufacturing process and the resolution of the part 74. The slice increments may be variable, with larger slice increments used to speed processing in portions of the component 74 where high accuracy is not required, and smaller slice increments used where higher accuracy is required, at the expense of processing speed.

As described above, the apparatus 10 includes the measurement system 76. The measurement system 76 is configured to determine the location of structures within the apparatus 10. As shown, the measurement system 76 may be configured to determine the distance between structures. Such distances may be used to determine the thickness, i.e., layer increment, of new build layer 79 as described further below.

The layer increment is ultimately defined using knowledge of the relative position in the Z direction (shown as distance a in fig. 2) of the working surface 75 and the resin surface 77. It should be appreciated that determining the relative position of the working surface 75 and the resin surface 77 may be done according to a reference position such as the contact surface 191 of the support 190. Therefore, the position of the surface 191 of the support 190 in the Z direction is defined as Z ═ 0. The position of the resin surface 77 relative to the contact surface 191 is the combined thickness of the film 12 and the thickness of the resin layer 110. For purposes of the techniques disclosed herein, it may be assumed that the thickness of the film 12 and the thickness of the resin layer 110 are both constant. Therefore, the position of the resin surface 77 with respect to a reference such as the support 190 is constant. It should be appreciated that during normal operation, the position of the resin surface 77 may vary due to variations in the thickness of the layer 110. Such variations may occur in the Machine Direction (MD) along the Y-axis and in the Transverse Direction (TD) along the X-axis.

Once the resin R has been applied and the layer increments defined, the radiant energy device 18 is used to cure a two-dimensional cross-section or layer of the part 74 built as shown in FIG. 3.

In the case of the projector 48, the projector 48 projects a patterned image 59 representing a cross section of the part 74 through the foil 12 to the resin R. This process is referred to herein as "selective" curing.

Once the curing of the first layer is complete, the table 14 is separated from the foil 12, for example by raising the table 14 using the actuator 32. It should be understood that the resin R and/or cured layer need not engage, adhere, or bond with the surface of 12. Thus, as used herein, the term "separate" refers to the process of separating two elements from each other and does not necessarily imply the act of breaking a bond or separating one element from another. During the measurement process, the reference block 78 may be utilized in accordance with an aspect of the method described below.

The reference block 78 shown in fig. 1 and 2 is a set of solidified layers positioned adjacent the part 74 and, as shown, represents the thickness of the part 74 at the maximum position. In this regard, blocks 78 are formed by curing a resin having a thickness equal to the maximum thickness of each build layer 79. The block 78 may be a frame that surrounds the part 74, as shown removed when the part 74 is completed. Or reference block 78 may be one or more discrete blocks positioned around the perimeter of part 74 to be removed when part 74 is completed.

It should be appreciated that in some embodiments, building blocks 78 represent a height that is different than the thickness of part 74 at the maximum location. In this regard, the building blocks 78 may represent heights equal to a predetermined position and height within the perimeter of the boundary of the part 74. In other words, the building blocks 78 may represent heights at points along a line at predetermined X or Y coordinates for predetermined distances. Accordingly, the building blocks 78 may represent heights at predetermined XY and Z coordinates. Because the building block 78 may be configured to vary in height along the X and Y coordinates, it may represent different heights and thus different XYZ coordinate combinations. Building block 78 may be a unitary structure as shown. Alternatively, the building blocks 78 may be a plurality of structures.

The present invention may be better understood by describing its operation. In accordance with one aspect of the techniques described herein, a method of producing a part 74 layer-by-layer using an additive manufacturing apparatus 10 is provided. As described above, additive manufacturing apparatus 10 includes resin support 190, stage 14, measurement system 76, and actuator 32 configured to change the relative positions of stage 14 and resin support 190. The method comprises the following steps: performing an additive manufacturing cycle comprising the steps of: depositing an uncured resin layer 110; moving the stage 14 to a target position (e.g., a predetermined distance from the surface 191 of the resin support 190); the actual position of the table 14 is double checked by determining the actual position of the table 14 using the measurement system 76 and comparing the actual position with the target position; if the stage 14 is not within the predetermined range of the target position, repeating the step of moving the stage 14 to the target position; curing the uncured resin layer 110 after one or more movements of the stage 14; moving the stage 14 away from the target position; repeating the additive manufacturing cycle; performing a measurement process, wherein the measurement process comprises the steps of: making measurements of the actual position of the indicating structure relative to the resin support 190 using the measurement system 76; comparing the actual position of the structure to an expected position of the structure to determine an error; and uses the error to modify the target position.

Referring now to additional steps that may be performed with the above-described method, it should be understood that the step of performing the measurement process may be performed in each cycle. And therefore the step of performing the step of using the error may be performed during each cycle of performing the measurement process. As described above, each time a measurement step is performed, an error is determined by comparing the actual position of the structure with the expected position of the structure. For example, if the actual position is represented as a measure of distance, and the actual distance is compared to a desired or set point distance. The cumulative error is determined with multiple steps using the measurement system by adding the subsequent step error to the sum of all previous errors. Alternatively, the accumulated error may be determined by a single measurement of the part thickness, which will capture the total error accumulated during the part build process.

The structure to be tested can be any one or more of stage 14, the surface of uncured resin layer 77, surface 75 of part 74, the surface of film 12, surface 30 of the stage, and combinations thereof. As noted above, preferably the reference point is the resin support structure 190, and more specifically, the surface 24 of the resin support structure. It should be understood that the thickness of the membrane 12 is calculated by conventional methods. As is conventionally known, measurements taken with respect to a particular reference point (e.g., structure 190) are used to determine the relative position of the structure.

Referring now to fig. 2, the following table identifies various measurements that may be used in the above-described method, as shown in fig. 2. The indicated measurements are examples and other measurements may be utilized. It should be understood that typically these measurements will be represented as distances, however they may be represented using a coordinate system utilizing the X, Y and Z axes described above with a common predetermined origin.

Distance between two adjacent plates	Superstructure	Substructure
			A	Working surface 75	Resin surface 77
B	Surface of the table 1430	Resin surface 77
			C	Surface 30 of table 14	Surface of the membrane 12
D	Working surface 75	Surface of the membrane 12
			E	Surface 30 of table 14	Surface 24 of support structure 190
F	Working surface 75	Surface 24 of support structure 190
			G	Surface 30 of table 14	Reference block 78

It is expected that a common measurement used in the above method will be distance a. For example, the target position will be a position determined by the desired structure moving a predetermined distance a. The predetermined distance A is the distance between the surfaces 75 of the part 74, which may be defined by a reference block 78 for indicating the particular XYZ coordinates of the surfaces 75 as described above. Thus, movement of stage 14 a distance A will position surface 75 so that it is in close proximity to surface 77 of resin 110. Movement of stage 14 beyond distance a will cause surface 75 to be pushed into layer 110 to at least partially displace surface 77. As described above, in this way the desired thickness of the layer 110 can be defined immediately before curing.

Another common measurement used is the height "distance G" of the part 74 relative to the surface 30 of the table 14. The distance G may be used as described in further detail below in the description of the method for controlling the final part height.

Alternatively, the predetermined distance may not be determined point-to-point, but by an average of the actual positions or distances of a plurality of points of the surface to be measured. In this regard, the measurement system 76 is configured to determine the plane of the structure by measuring the distance at a plurality of locations on the structure. It should be appreciated that the location used to determine the average distance may vary cyclically. In this regard, the measurement system may be configured to measure the first plurality of locations after a first cycle and to measure the second plurality of locations after a second cycle, wherein the second plurality of locations is different from the first plurality of locations.

The measurement system 76 is configured to generate a signal indicative of the position or distance. The computer 68 may use the signal as part of a closed loop control loop in which the signal is feedback. The closed loop control circuit is configured to adjust the height of the table 14 relative to a desired height, as determined relative to a reference (e.g., the resin support structure 190). The desired altitude may be considered a set point in the control loop. The set point may be determined based on an adjustment distance equal to the predetermined layer thickness plus an amount equal to the accumulated error. The set point may be adjusted for each cycle to accommodate the error. Or alternatively, the set point may be adjusted after a predetermined number of cycles such that the stage is configured to move the adjusted distance after the predetermined number of cycles.

As described above, measurement system 76 may be used to determine the amount of error in the build thickness for each layer or group of layers and to store or accumulate the error. This stored value is the accumulated error that can be used to control the final part height. The accumulated error is represented as a value that is adjusted either positively or negatively with respect to each newly acquired measurement error amount. The accumulated error may be monitored and compared to a threshold accumulated error value. The threshold cumulative error value is the maximum allowable error in the height of the part 74 or the designated portion of the part 74.

When the accumulated error is equal to or greater than the threshold error value, a compensation layer is planned. The compensation layer is either an existing plan layer currently selected for modification in the build profile plan or a new layer to be added to the build profile. The compensation layer is sized so that the thickness of the part 74 is within acceptable limits based on the set point described above.

It should be appreciated that the selection of an existing planning layer for modification as a compensation layer must take into account the characteristics of the planning layer. By way of example and not limitation, the characteristics of the planning layer may be selected from the following: total planned layer thickness; the total compensation layer thickness; the geometry of the planned layer; and combinations thereof. By way of example and not limitation, relevant characteristics of the geometry of the planning layer may include: the shape, size, location of the geometries within the layers, the presence of critical and less critical dimensions of the planned geometries, and combinations thereof.

In the illustrated embodiment, a planning layer having a geometry other than a straight line cross-section with a uniform thickness is not used as the compensation layer. In other words, in the illustrated embodiment, the layer in which the microstructures are defined is not used as a compensation layer.

To produce the compensation layer, the stage 14 may be adjusted to define a final compensation layer thickness. This approach may not provide a sufficient thickness range. When the thickness of the compensation layer differs substantially from the thickness of the planned layer, the thickness of the compensation layer is determined by the thickness of the uncured resin layer at the time of deposition. In other words, it may be desirable to achieve the compensation layer thickness by increasing or decreasing the thickness of the uncured resin layer 110. It should be understood that depending on the geometry of the part 74 and the amount of accumulated error, multiple compensation layers may be used to correct the accumulated error.

The following method utilizes a compensation layer. The method comprises the following steps: operating the additive manufacturing apparatus 10 according to the build profile to produce a solidified layer of the part; a dimension, such as a predetermined thickness or distance (e.g., distance G), is measured by operating the measurement system 76 to obtain a measurement; comparing the measured value with a predetermined target set by the build profile to determine whether there is a measurement error; adding the measurement error to the accumulated error value; comparing the accumulated error value to a threshold error value; responding to the determination of the error by generating a compensation layer when the accumulated error value exceeds a threshold error value by: selecting one of the following as a compensation layer: a previously planned layer and a new layer; determining a thickness of the compensation layer by using the accumulated error value and modifying the build profile accordingly; and constructing a compensation layer.

It should be appreciated that the compensation layer may have a thickness of zero when it is determined that a previously planned layer is to be skipped. Alternatively, the compensation layer may be generated and constructed immediately after a specified number of layers or a single layer, rather than based on a comparison of the cumulative error value to a threshold error value.

Fig. 9 shows an example of a part 74 that has been subjected to two cycles according to the method described above. A set of ledger (hedger) rows 81 depicts six planning levels in the build profile. As shown, after the fifth cycle, each of the first five layers is constructed too thin. The amount of error accumulates. Therefore, the sixth layer is selected as the compensation layer. The sixth layer is produced to be thicker than originally planned. By combining the sixth and fifth thicker layers, the overall thickness of the part is matched to the intended thickness.

It should also be understood that the controller 68 may be configured to stop or pause the build part, i.e., stop or pause the "build". In this regard, a maximum correction may be defined within the controller 68 such that it may be configured to determine whether the accumulated error is too large to correct. In this case, the build may be paused to resume after further evaluation or cancellation.

A method and apparatus for additive manufacturing has been described above. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Additional aspects of the invention are provided by the following numbered clauses:

1. a method of forming a part using an additive manufacturing apparatus comprising a resin support configured to support an uncured resin layer within a build area, a table configured to hold a stacked arrangement of one or more cured resin layers forming at least part of a part, a measurement system and an actuator configured to change the relative positions of the table and the resin support, the method comprising the steps of: performing an additive manufacturing cycle comprising: depositing an uncured resin layer; moving the station to a target position; curing the uncured resin layer; and moving the stage away from the target position; repeating the additive manufacturing cycle; performing a measurement process, wherein the measurement process comprises the steps of: making a measurement indicating an actual position of the structure using a measurement system; comparing the actual position of the structure to an expected position of the structure to determine an error; and modifying the target position using the error.

2. The method according to any of the preceding clauses, wherein the step of performing a measurement process is performed every cycle.

3. The method of any of the preceding clauses, wherein the step of performing the step of using the error is performed during each cycle of performing the measurement process.

4. The method of any of the preceding clauses, wherein the total error is determined using multiple steps using a measurement system.

5. The method of any of the preceding clauses, wherein the structure is one of: a table, a surface of an uncured resin layer, a surface of a part, and combinations thereof.

6. The method of any of the preceding claims, wherein the measurement system is configured to determine the plane of the structure by measuring a set of multiple locations on the structure.

7. The method of any of the preceding claims, wherein the structure is a part.

8. The method of any of the preceding clauses, wherein the measurement system is configured to measure a first plurality of locations after a first cycle and a second plurality of locations after a second cycle, and wherein the second plurality of locations is different from the first plurality of locations.

9. The method of any preceding claim, comprising locating a reference position on a stage.

10. The method of any of the preceding claims, wherein the reference position is defined by a cured resin layer.

11. The method of any of the preceding claims, wherein the reference position is defined by the part.

12. The method according to any one of the preceding claims, wherein the apparatus is configured such that the reference position can be defined by a block built on the table in parallel with the part.

13. The method of any of the preceding claims, wherein the block is a frame positioned around the part.

14. The method of any of the preceding claims, wherein the structure is a surface of a part.

15. The method of any of the preceding claims, wherein the signal is feedback utilized by a computer to adjust the height of the stage relative to a desired height.

16. The method of any of the preceding clauses, wherein the stage is configured to move an adjustment distance equal to a predetermined layer thickness plus an amount equal to the accumulated error.

17. The method of any of the preceding claims, wherein the cured resin layer is produced in cycles and the stage is configured to move an adjusted distance after a predetermined number of cycles.

18. An additive manufacturing apparatus comprising: a resin support defining a build surface configured to support an uncured resin layer; a table configured to hold a stacked arrangement of one or more cured resin layers, the one or more cured resin layers forming a part, the part defining a surface positioned opposite the table; a radiant energy device positioned opposite the table so as to be operable to generate and project radiant energy in a predetermined pattern; an actuator configured to change relative positions of the stage and the resin support; a measurement system configured to measure a position of the one or more structures relative to the resin support; and wherein the structure is one of: a table, a surface of an uncured resin layer, a surface of a part, and combinations thereof.

19. An additive manufacturing apparatus according to any one of the preceding claims, wherein the measurement system comprises a laser range finder and the structures to be measured are a surface of the part and a surface of the uncured resin, and the measurement system is configured to generate a signal indicative of a position of the surface of the part relative to the surface of the uncured resin and to determine movement of the stage based on the signal.

20. An additive manufacturing apparatus according to any one of the preceding clauses, wherein the uncured resin layer is configured to be cured by a first range of light frequencies, and the measurement system comprises an optical sensor that produces a second range of light frequencies, and the second range is different from the first range.

21. An additive manufacturing apparatus according to any one of the preceding claims, comprising a reference position on the table.

22. A method of forming a part using an additive manufacturing apparatus comprising a resin support configured to support an uncured resin layer within a build area, a table configured to hold a stacked arrangement of one or more cured resin layers forming at least part of a part, a measurement system and an actuator configured to change the relative positions of the table and the resin support, the method comprising the steps of: operating an additive manufacturing apparatus according to a build profile to produce a solidified build layer of a part; measuring the dimensions of the part using a measurement system; determining whether the size contains an error; the determination of the error is responded to by modifying the build profile to include a compensation layer, wherein a thickness of the compensation layer is selected to compensate for the error.

23. The method of any of the preceding clauses, further comprising the steps of: adding the error to the accumulated error value; determining a thickness of the compensation layer by using the accumulated error value; and wherein the cumulative error value is formed over a plurality of cycles.

24. The method of any of the preceding clauses, further comprising the steps of: comparing the accumulated error value to a threshold error value; and performing a step of generating a compensation layer when the accumulated error value exceeds a threshold error value.

25. The method of any of the preceding clauses, further comprising the steps of: selecting one of the following as a compensation layer: a previously planned layer and a new layer.

26. The method of any of the preceding claims, wherein the dimension is a thickness of the cured build layer.

27. The method of any of the preceding claims, wherein the dimension is a height of the part.