# Patent

## Title
Stereolithography system for accurately establishing build plane

## Abstract

A three-dimensional (3D) printing system includes a vessel, a coating subsystem, a calibration block, and a controller. The vessel is configured to contain a photocurable resin having a resin upper surface. The coating subsystem includes a coater module including a coater blade, a lateral movement mechanism coupled to the coater module, a sensor mounted to the coater module, and a vertical actuator system. The calibration block has a calibration surface. The controller is configured to operate the lateral movement mechanism to position the coater blade over the calibration block, operate the vertical actuator system to lower the coater blade into engagement with the calibration surface of the calibration block, operate the sensor to measure a distance to the calibration block, and store the distance as indicative of a vertical position of a lower edge of the coater blade.

## Background
This non-provisional patent application claims priority to U.S. Provisional Application Ser. No. 63/246,536, Entitled “Stereolithography System for Accurately Establishing Build Plane” by Eric M. Innes, filed on Sep. 21, 2021, incorporated herein by reference under the benefit of U.S.C. 119(e).


FIELD OF THE INVENTION
The present disclosure concerns an apparatus and method for the digital fabrication of three-dimensional (3D) articles by a layer-by-layer selective radiative curing of a photocurable build material. More particularly, the present disclosure concerns an automated way of forming a build plane by calibrating a height and alignment of a coater blade to a upper surface of the build material.
BACKGROUND
3D printing systems are in wide use for prototyping and manufacturing articles. One type of 3D printing system utilizes a process called stereolithography. A typical stereolithography system utilizes a resin vessel, an imaging system, and a build plate within liquid photocurable resin held by the resin vessel. An article is manufactured in a layer-by-layer manner by selectively imaging and radiatively curing layers of the photocurable resin over the build plate. One challenge is to form liquid layers of the photocurable resin with an accurate and repeatable vertical dimension without difficult manual alignment procedures.



BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a schematic illustration of an embodiment of a three-dimensional (3D) printing system for manufacturing or fabricating a 3D article.
FIG. 2 is an isometric drawing that illustrates certain components of an embodiment of a three-dimensional (3D) printing system for manufacturing or fabricating a 3D article.
FIG. 3 is an isometric drawing of an embodiment of a coating subsystem in isolation.
FIG. 4 is an isometric cutaway view of an embodiment of a coater blade in isolation.
FIG. 5 is an isometric drawing of a portion of a coating subsystem.
FIG. 6 is a front view of an embodiment of a coating subsystem in isolation.
FIG. 7 is a flowchart of an embodiment of a method for vertically locating a lower edge of a coater blade.
FIG. 8 is a flowchart of an embodiment of a method of adjusting parallelism and optimal distance between a travel of a coater module and a resin upper surface.
FIG. 9 is a flowchart of an embodiment of a method performed by a controller for manufacturing a 3D article.



SUMMARY
In a first aspect of the disclosure, a three-dimensional (3D) printing system includes a vessel, a coating subsystem, a calibration block, and a controller. The vessel is configured to contain a photocurable resin having a resin upper surface. The coating subsystem includes a coater module including a coater blade, a lateral movement mechanism coupled to the coater module, a sensor mounted to the coater module, and a vertical actuator system. The calibration block has a calibration surface. The controller is configured to operate the lateral movement mechanism to position the coater blade over the calibration block, operate the vertical actuator system to lower the coater blade into engagement with the calibration surface of the calibration block, operate the sensor to measure a distance to the calibration block, and store the distance as indicative of a vertical position of a lower edge of the coater blade.
In one implementation, the 3D printing system includes a pair of linear bearings that individually extend along a Y-axis. The coater module extends along an X-axis that is orthogonal to the Y-axis. The coater module includes two end portions at opposed ends of the coater module with respect to the X-axis. The two end portions individually engage the linear bearings to support and guide the coater module along the Y-axis. The lateral movement mechanism includes motorized belt system including two belts that are individually attached to the two end portions. The vertical actuator system includes a plurality of actuators that are configured to vertically position the pair of linear bearings to control the vertical position of the coater blade as it is transported along the Y-axis. The vertical actuator system includes four vertical actuators including, for each of the linear bearings, a rear vertical actuator and a front vertical actuator that are spaced apart with respect to the Y-axis. The sensor includes two sensors that individually are positioned on one of the two end portions of the coater module. The calibration block includes two calibration blocks that individually correspond to one of the two sensors.
In another implementation, the controller is further configured to operate the lateral movement mechanism to position the coater blade over the resin upper surface, operate the sensor to obtain a sensed position of the resin upper surface, and operate the vertical actuator system to vertically position the coater blade based upon a comparison of the vertical position of the lower edge of the coater blade relative to the sensed position of the resin upper surface.
In yet another implementation, the 3D printing system includes a vertical movement mechanism coupled to a build platform and an imaging module. The controller is configured to operate the vertical movement mechanism to position an upper surface of the build platform or a 3D article at a build plane, operate the vertical actuator system to position the lower edge of the coater blade at the build plane, operate the lateral movement mechanism to translate the lower edge of the coater blade over the upper surface to form a new layer of the photocurable resin over the upper surface, operate the imaging module to selectively cure the new layer of photocurable resin, and repeat operation of the elevator mechanism, the vertical movement mechanism, the lateral movement mechanism, and the imaging module to complete fabrication of the 3D article in a layer-by-layer manner.
In a second aspect of the disclosure, a three-dimensional (3D) printing system includes a vessel, a coating subsystem, a calibration block, and a controller. The vessel is configured to contain a photocurable resin having a resin upper surface. The coating subsystem includes a coater module including a coater blade, a lateral movement mechanism coupled to the coater module, a sensor mounted to the coater module, and a vertical actuator system. The calibration block has a calibration surface. The controller is configured to operate the lateral movement mechanism to position the coater blade over the calibration block, operate the vertical actuator system to lower the coater blade into engagement with the calibration surface of the calibration block, operate the sensor to measure a distance Do to the calibration block, operate the lateral movement mechanism to position or translate the coater blade over the resin upper surface, operate the sensor to measure a distance D to the resin upper surface, and compute a distance d from a lower edge of the coater blade to the resin upper surface, d=D−D0.
In one implementation the coater blade has a major axis along an X-axis.
The lateral movement mechanism is configured to transport the coater blade along a Y-axis that is orthogonal to the X-axis. The sensor includes two sensors that are spaced apart with respect to the Y-axis. The calibration block includes two calibration blocks. Operation of the lateral movement mechanism to position the coater blade over the calibration block includes positioning each of the two sensors over one of the two calibration blocks. The distance Do is measured for each of the two sensors.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a schematic illustration of an embodiment of a three-dimensional (3D) printing system 2 for manufacturing or fabricating a 3D article 4. In describing system 2, mutually orthogonal axes X, Y, and Z will be utilized and otherwise referred to as an X-axis, a Y-axis, and a Z-axis. Axes X and Y are lateral axes that are generally horizontal. The Z-axis is a vertical axis that is generally aligned with a gravitational reference. The term “generally” implies that a direction or magnitude is not necessarily exact but is by design. Thus the term “generally horizontal” means horizontal (perpendicular to a gravitational vector) to within design and manufacturing tolerances. The term “generally aligned” means aligned to within design and manufacturing tolerances.
3D printing system 2 includes a resin vessel 6 for containing a photocurable resin 8. In the illustrated embodiment, photocurable resin 8 includes, inter alia, a monomer, a catalyst, and a filler. The catalyst allows the resin 8 to be hardened and cured with an application of radiation such as blue radiation, violet radiation, or ultraviolet radiation that would typically have a wavelength of less than about 450 nm (nanometers). Photocurable resins for stereolithography systems are known in the art.
System 2 includes a build plate 10 with an upper surface 12 upon which the 3D article 4 is formed. A build plate support structure 14 supports build plate 10. A vertical movement mechanism 16 is operable to vertically position the build plate support structure 14 and in doing so vertically position the build plate 10. In one embodiment, the vertical movement mechanism 16 includes a fixed motor coupled to a lead screw. The build plate support structure 14 includes a threaded bearing that receives the lead screw. As the motor turns the lead screw, the effect is to controllably translate the build plate support structure 14 up or down. In addition, the vertical movement mechanism 16 and the build plate support structure 14 include mutually engaging linear bearings that assure linear motion of the build plate support structure along the vertical axis Z. Various vertical and lateral movement mechanisms are known in the field of stereolithography. All typically include linear bearings for guiding motion but the movement can be based upon a lead screw, a rack and pinion system, a belt and pulley system, or well-known means of imparting motion.
System 2 includes a resin level subsystem 18 configured to maintain a resin upper surface 20 at a predetermined vertical position. In the illustrated embodiment, the resin upper surface 20 is generally coincident with a build plane 22. The resin level subsystem 18 can include a resin level sensor and a weight coupled to a pulley system. The weight is partially immersed in the resin 8 such that raising and lowering the weight alters a vertical position of the resin upper surface 20 via volumetric displacement. The resin level sensor outputs a signal indicative of a vertical position of the resin upper surface 20. The signal is analyzed and the pulley system is operated to raise and lower the weight to maintain the resin upper surface 20 to be generally coincident with the build plane 22.
An “upper surface” 24 can be defined which is either the upper surface 12 or an upper surface 24 of the 3D article 4 when it is partially formed. Before forming an additional material layer onto the 3D article 4, the upper surface 24 is positioned at a vertical position that is generally one material layer thickness below the build plane 22.
System 2 includes a coating subsystem 26. After upper surface 24 is positioned one layer thickness below build plane 22, the coating subsystem 26 is configured to pass over the upper surface and to define a new layer 28 of the resin 8 over the upper surface 24. Details of the coating subsystem 26 will be discussed infra. The new layer 28 of resin 8 has the resin upper surface 20 that is generally coincident with build plane 22.
System 2 includes an imaging subsystem 30. Imaging subsystem 30 is configured to scan an energy beam 32 over the build plane 22 to selectively cure and harden the new layer 28 of resin 8 and to form a new material layer of the 3D article 4. In an illustrative embodiment, imaging subsystem 30 includes a laser that generates a radiation beam 32 that is reflected by a scanner. The scanner scans the radiation beam 32 over the build plane 22. In an illustrative embodiment, the scanner includes two galvanometer mirrors including an X-mirror and a Y-mirror configured to scan the radiation beam along the X-axis and the Y-axis respectively over the build plane 22. Imaging subsystems are known in the field of stereolithography. Another imaging subsystem can be based upon a “light bar array” of light emitting devices that scans over the build plane 22. Yet another imaging subsystem can be based upon projection of a pixel array of radiation. All such radiation subsystems are well known in the art.
A controller 34 is coupled to the vertical movement mechanism 16, the resin level subsystem 18, the coating subsystem 26, the imaging subsystem 30, and other portions of system 2. The controller 34 includes a processor 36 (such as a CPU or central processing unit) coupled to a non-transient information storage device 38 (such as flash memory). Storage device 38 stores software instructions. Controller 34 is configured to operate the portions of system 2 as the processor 36 executes the software instructions stored on the non-transient information storage device 38. Controller 34 can includes a single unit that is associated with system 2 or it can include a plurality of control units that can be co-located with and or remotely located relative to the illustrated system 2.
FIG. 2 is an isometric drawing that illustrates certain components of an embodiment of system 2. In the illustrated embodiment from a user point of view the axes X, Y, and Z can be described. The lateral X-axis extends from left to right. The lateral Y-axis extends from front to back or from front to rear. The vertical Z-axis extends upward. The illustrated components include the resin vessel 6, build plate 10, build plate support structure 14, vertical movement mechanism 16, and resin level subsystem 18 (the weight that is raised and lowered). The vertical movement mechanism 16 includes a motor 15 coupled to a vertical lead screw for providing vertical positioning of the build plate support structure 14 and the build plate 10. Between the build plate support structure 14 and the vertical movement mechanism 16 are a pair of linear bearings (hidden in this figure) to control linearity of motion along the Z-axis. Not illustrated is the coating subsystem 26 and imaging subsystem 30.
FIG. 3 is an isometric drawing of an embodiment of a coating subsystem 26 in isolation. Coating subsystem 26 includes a wiper module 40 or coater module 40 which includes a coater blade 42 that is supported between two end portions 44 which are at opposed ends of the coater blade 42 with respect to the lateral X-axis.
FIG. 4 is an isometric cutaway view of the coater blade 42 in isolation. One end of the cutaway view illustrates an internal recess 46 that is at least partially filled with resin 8 to facilitate coating irregular upper surfaces 24 of 3D articles 4. Coater blade 42 also has a lower edge 48.
Referring back to FIG. 3, coating subsystem 26 includes a pair of linear bearings 50 at opposed ends of the coater module 40 with respect to the X-axis. The end portions 44 are in sliding engagement with and supported by the linear bearings 50. The end portions 44 slide upon the linear bearings 50 along the Y-axis.
Two belts 52 are individually supported by pulleys 54 at opposed ends of the coater module 40. The belts 52 are attached to the end portions 44 at the opposed ends of the coater module 40. A motor 56 is coupled to two of the pulleys 54. Rotation of the pulleys 54 by motor 56 causes movement of the belt and translation of the coater module 40 along the Y-axis in sliding engagement and support by the linear bearings 50. The combination of the motor 56, pulleys 54, belts 52, and other possible components can be referred to as a “lateral movement mechanism” 58 for transporting coater module 40 along the Y-axis.
A set of four vertical actuators 60 support and vertically position the linear bearings 50. The vertical actuators 60 are individually coupled between a vertical support 62 (FIG. 5) and one of the linear bearings 50. The linear bearings 50 individually are supported by a front vertical actuator 60 and a rear vertical actuator 60 which enables a height and angular tilt of each linear bearing 50 to be adjusted. In one embodiment, the vertical actuators 60 individually include a motorized lead screw that turns and thereby raises or lowers a nut that is attached to one end portion of one of the linear bearings 50. The set of four vertical actuators 60 and other associated components can be referred to as a “vertical actuator system” 61.
A set of two calibration blocks 64 are laterally disposed within a lateral range of travel of the coater module 40. The calibration blocks 64 individually have an upward facing calibration surface 66. The calibration surface 66 can have a vertical position that is approximately the same as the build plane 22 but the exact height is not critical.
FIG. 5 is an isometric drawing of a portion of the coating subsystem 26 which allows a closer view of a number of components discussed supra. The end portions 44 of the coater module individually include a distance sensor 68. Distance sensor 68 is configured to output information indicative of a distance to a surface below distance sensor 68. In the illustrated embodiment, distance sensor 68 is a laser distance sensor that operates on a triangulation principle. The sensor 68 includes a semiconductor laser and a photodiode line. The laser emits a beam that is reflected from a surface back to the photodiode line. The position of incidence upon the photodiode line is a function of the distance being sensed. Other distance sensors 68 are possible that operate on different principles such as ultrasonic sensors and are known in the art for sensing distances to surfaces.
FIG. 6 is a front view of the coating subsystem 26 in isolation. In this view, the lower edge 48 of the coater blade 42 is in contact with the calibration surfaces 66 of the calibration blocks 64.
FIGS. 7 and 8 are flowcharts that depict methods 70 and 80 for calibrating the coating subsystem 26. Controller 34 is configured to operate components of system 2 to perform methods 70 and 80.
FIG. 7 is a flowchart depicting an embodiment of a method 70 for calibrating the vertical distance sensors 68. According to 72, the coater module 40 is in a raised position. According to 74, the lateral movement mechanism 58 is operated to translate the coater module 40 along the Y-axis until ends of the coater blade 42 and the vertical sensors 68 are individually positioned over one of the calibration surfaces 66.
According to 76, the vertical actuator system 61 is operated to lower the coater module 40 until end portions of the lower edge 48 of the coater blade 42 engage and are in contact with the upper surfaces 66 of the calibration blocks 64 (as per FIG. 6). According to 78, the distance sensors 68 are operated to individually measure a vertical distance to the upper surfaces 66. This measurement is stored as a “zero position” which is a vertical height of the lower edge 48 of the coater blade. According to 79, the vertical actuator system 61 is operated to raise the coater module 40 to lift the lower edge 48 off of the calibration surfaces 66.
FIG. 8 is a flowchart depicting an embodiment of a method 80 of adjusting a parallelism and optimal distance between a travel of the coater module 40 and the resin upper surface 20 (which should be generally coincident to the build plane 22). According to 82, the coater module 40 is in a raised position. According to 74, the lateral movement mechanism 58 is operated to translate the coater module along the Y-axis until the coater blade 42 is laterally positioned at or proximate to the front vertical actuators 60 (front meaning a lower value of Y relative to rear).
According to 86, the front vertical actuators 60 are operated to lower the coater module 40 until the distance sensors 68 are at an optimal sensing range of the resin upper surface 20. The sensors 68 have a zero position at the lower edge 48 of the coater blade, the indicated distance is equal to a vertical distance from the lower edge 48 to the resin upper surface 20.
According to 88, the lateral movement mechanism 58 is operated to translate the coater module along the Y-axis until the coater blade 42 is laterally positioned at or proximate to the rear vertical actuators 60 (rear meaning a higher value of Y relative to the front). According to 90, the rear vertical actuators 60 are operated to lower the coater module 40 until the distance sensors 68 are at an optimal sensing range of the resin upper surface 20. Step 90 is essentially the same as step 86 except at an opposite end of the build plane 22 relative to the Y-axis. Steps 84-90 can be repeated to iteratively calibrate a travel parallelism and distance between the lower edge 48 and the build plane 22.
FIG. 9 is a flowchart of an embodiment of a method performed by controller 34 for manufacturing a 3D article 4. According to 102, a method 70 (FIG. 7) is performed to “zero” the distance sensors 68 to the lower edge 48 of the coater blade 42. According to 104, method 80 (FIG. 8) is performed to optimize the vertical positions of the vertical actuators 60.
According to 106, the vertical movement mechanism 16 is operated to position the upper surface (12 or 24) of the build plate at the build plane 22. According to 108, the vertical actuator system 61 is operated to position the lower edge 48 of the coater blade 42 coincident with the build plane 22. According to 110, the lateral movement mechanism 58 is operated to translate the lower edge 48 of the coater blade 42 over the build plane 22 to form a new layer 28 of the photocurable resin 8 over the upper surface (12 or 24). According to 112, the imaging subsystem 30 is operated to selectively cure and harden the new layer 28 of photocurable resin 8. As indicated, steps 106-112 are repeated until fabrication of the 3D article 4 is complete.
The specific embodiments and applications thereof described above are for illustrative purposes only and do not preclude modifications and variations encompassed by the scope of the following claims.

## Claims

1. A three-dimensional (3D) printing system comprising:
a vessel configured to contain a photocurable resin having a resin upper surface;
a coating subsystem including:
a coater module including a coater blade;
a lateral movement mechanism coupled to the coater module;
a sensor mounted to the coater module; and
a vertical actuator system;

a calibration block having a calibration surface; and
a controller configured to:
operate the lateral movement mechanism to position the coater blade over the calibration block;
operate the vertical actuator system to lower the coater blade into engagement with the calibration surface of the calibration block;
operate the sensor to measure a distance to the calibration block; and
store the distance as indicative of a vertical position of a lower edge of the coater blade.

2. The three-dimensional printing system of claim 1 further comprising a pair of linear bearings that individually extend along a Y-axis;
the coater module extends along an X-axis that is orthogonal to the Y-axis, the coater module includes two end portions at opposed ends of the coater module with respect to the X-axis, the two end portions individually engage the linear bearings to support and guide the coater module along the Y-axis.

3. The three-dimensional printing system of claim 2 wherein the lateral movement mechanism includes a motorized belt system including two belts that are individually attached to the two end portions.

4. The three-dimensional printing system of claim 2 wherein the vertical actuator system includes a plurality of actuators that are configured to vertically position the pair of linear bearings to control the vertical position of the coater blade as it is transported along the Y-axis.

5. The three-dimensional printing system of claim 2 wherein the vertical actuator system includes four vertical actuators including, for each of the linear bearings, a rear vertical actuator and a front vertical actuator that are spaced apart with respect to the Y-axis.

6. The three-dimensional printing system of claim 2 wherein the sensor includes two sensors that individually are positioned on one of the two end portions of the coater module.

7. The three-dimensional printing system of claim 6 wherein the calibration block includes two calibration blocks that individually correspond to one of the two sensors.

8. The three-dimensional printing system of claim 1 wherein the controller is further configured to:
operate the lateral movement mechanism to position the coater blade over the resin upper surface;
operate the sensor to obtain a sensed position of the resin upper surface; and
operate the vertical actuator system to vertically position the coater blade based upon a comparison of the vertical position of the lower edge of the coater blade relative to the sensed position of the resin upper surface.

9. The three-dimensional printing system of claim 1 further comprising a vertical movement mechanism coupled to a build platform and an imaging module, the controller is further configured to:
operate the vertical movement mechanism to position an upper surface of the build platform or a 3D article at a build plane;
operate the vertical actuator system to position the lower edge of the coater blade at the build plane;
operate the lateral movement mechanism to translate the lower edge of the coater blade over the upper surface to form a new layer of the photocurable resin over the upper surface;
operate the imaging module to selectively cure the new layer of photocurable resin; and
repeat operation of the elevator mechanism, the vertical movement mechanism, the lateral movement mechanism, and the imaging module to complete fabrication of the 3D article in a layer-by-layer manner.

10. A method of operating a three-dimensional (3D) printing system comprising:
providing a 3D printing system including:
a vessel configured to contain a photocurable resin having a resin upper surface;
a coating subsystem including:
a coater module including a coater blade;
a lateral movement mechanism coupled to the coater module;
a sensor mounted to the coater module;
a vertical actuator system;

a calibration block having a calibration surface;
operating the lateral movement mechanism to position the coater blade over the calibration block;
operating the vertical actuator system to lower the coater blade into engagement with the calibration surface of the calibration block;
operating the sensor to measure a distance to the calibration block; and
storing the distance as indicative of a vertical position of a lower edge of the coater blade.

11. The method of claim 10 wherein the 3D printing system includes a pair of linear bearings that extend along a Y-axis and wherein the coater module extends along an X-axis that is orthogonal to the Y-axis, the coater module includes two end portions at opposed ends of the coater module with respect to the X-axis, the two end portions individually engage the linear bearings to support and guide the coater module along the Y-axis, the lateral movement mechanism includes a two belts that are individually coupled to one of the two end portions, the two belts are coupled to motor, operating the lateral movement mechanism includes operating the motor impart motion to the two belts.

12. The method of claim 10 wherein the 3D printing system includes a pair of linear bearings that extend along a Y-axis and wherein the coater module extends along an X-axis that is orthogonal to the Y-axis, the coater module includes two end portions at opposed ends of the coater module with respect to the X-axis, the two end portions individually engage the linear bearings to support and guide the coater module along the Y-axis, the vertical actuator system includes a plurality of vertical actuators that are coupled to the linear bearings, operating the vertical actuator system includes individually actuating the plurality of vertical actuators.

13. The method of claim 10 wherein the sensor includes two sensors at opposed ends of the coater module, the calibration block includes two calibration blocks corresponding to the two sensors, operating the lateral movement mechanism to position the coater blade over the calibration block positions each of the two sensors above a corresponding one of the two calibration blocks.

14. The method of claim 10 further comprising:
operating the lateral movement mechanism to position the coater blade over the resin upper surface;
operating the sensor to obtain a sensed position of the resin upper surface; and
operating the vertical actuator system to vertically position the coater blade based upon a comparison of the vertical position of the lower edge of the coater blade relative to the sensed position of the resin upper surface.

15. The method of claim 10 wherein the 3D printing further includes a vertical movement mechanism coupled to a build platform and an imaging module, the method further includes:
operating the vertical movement mechanism to position an upper surface of the build platform or a 3D article at a build plane;
operating the vertical actuator system to position the lower edge of the coater blade at the build plane;
operating the lateral movement mechanism to translate the lower edge of the coater blade over the upper surface to form a new layer of the photocurable resin over the upper surface;
operating the imaging module to selectively cure the new layer of photocurable resin; and
repeating operation of the elevator mechanism, the vertical movement mechanism, the lateral movement mechanism, and the imaging module to complete fabrication of the 3D article in a layer-by-layer manner.

16. A three-dimensional (3D) printing system comprising:
a vessel configured to contain a photocurable resin having a resin upper surface;
a coating subsystem including:
a coater module including a coater blade;
a lateral movement mechanism coupled to the coater module;
a sensor mounted to the coater module;
a vertical actuator system;

a calibration block having a calibration surface; and
a controller configured to:
operate the lateral movement mechanism to position the coater blade over the calibration block;
operate the vertical actuator system to lower the coater blade into engagement with the calibration surface of the calibration block;
operate the sensor to measure a distance Do to the calibration block;
operate the lateral movement mechanism to position or translate the coater blade over the resin upper surface;
operate the sensor to measure a distance D to the resin upper surface; and
compute a distance d from a lower edge of the coater blade to the resin upper surface according to a formula d=D−D0.

17. The three-dimensional (3D) printing system of claim 16 wherein the coater blade has a major axis along an X-axis, the lateral movement mechanism is configured to transport the coater blade along a Y-axis that is orthogonal to the X-axis, the sensor includes two sensors that are spaced apart with respect to the Y-axis.

18. The three-dimensional (3D) printing system of claim 17 wherein the calibration block includes two calibration blocks, operation of the lateral movement mechanism to position the coater blade over the calibration block includes positioning each of the two sensors over one of the two calibration blocks, the distance Do is measured for each of the two sensors.

19. The three-dimensional (3D) printing system of claim 16 further comprising a vertical movement mechanism coupled to a build platform and an imaging module, the controller is further configured to:
operate the vertical movement mechanism to position an upper surface of the build platform or a 3D article at a build plane;
operate the vertical actuator system to position the lower edge of the coater blade at the build plane;
operate the lateral movement mechanism to translate the lower edge of the coater blade over the upper surface to form a new layer of the photocurable resin over the upper surface;
operate the imaging module to selectively cure the new layer of photocurable resin; and
repeat operation of the elevator mechanism, the vertical movement mechanism, the lateral movement mechanism, and the imaging module to complete fabrication of the 3D article in a layer-by-layer manner.