Position detection techniques for additive fabrication and related systems and methods
Techniques for measuring a position of a build platform in an additive fabrication device are provided. Such techniques may include detecting the onset and/or dissipation of force applied to a build platform as it moves from being in contact with, to being out of contact with, a container. In some embodiments, the techniques described herein may be applied in a stereolithographic additive fabrication device. According to some embodiments, measurement of forces applied to a build platform may be used to provide for reliable and consistent measurements of the height of the build platform relative to a container by measuring such forces at various positions of the build platform and analyzing the pattern of the forces with distance from the container.
1. An additive fabrication device configured to form layers of material on a surface of a build platform, the additive fabrication device comprising:
a container having an interior surface;
a build platform having a build surface that opposes the interior surface of the container;
one or more actuators configured to move the build platform relative to the container; and
at least one controller configured to determine a position of the build platform relative to the container by:
moving the build platform away from the container, wherein initially during said movement the build surface is in contact with the interior surface of the container and at completion of said movement the build surface is not in contact with the interior surface of the container;
measuring a force applied to the build platform during said step of moving the build platform away from the container; and
determining the position of the build platform relative to the container based at least in part on the measured force.
2. The additive fabrication device of claim 1 , wherein the at least one controller is configured to measure the force applied to the build platform during said step of moving the build platform away from the container by measuring a back electromotive force upon at least one of the one or more actuators.
3. The additive fabrication device of claim 1 , further comprising at least one force sensor configured to measure a force applied to the build platform, and wherein the at least one controller is configured to measure the force applied to the build platform during said step of moving the build platform away from the container based on a measurement output by the at least one force sensor.
4. The additive fabrication device of claim 1 , wherein the at least one controller is configured to determine the position of the build platform relative to the container at least in part by identifying a position of the build platform at which a discontinuity in the measured force occurs.
5. The additive fabrication device of claim 1 , wherein the at least one controller is configured to measure a force applied to the build platform at a plurality of different positions of the build platform during said step of moving the build platform away from the container.
6. The additive fabrication device of claim 5 , wherein the at least one controller is configured to determine the position of the build platform relative to the container at least in part by calculating a rate of change of the measured force with respect to a change in a distance of the build platform from the container.
7. The additive fabrication device of claim 1 , wherein the container is mounted on at least one compressive device.
8. The additive fabrication device of claim 1 , wherein the at least one controller is further configured to wait for a predetermined length of time between moving the build platform toward the container until the build surface is in contact with the interior surface of the container and moving the build platform away from the container until the build surface is not in contact with the interior surface of the container.
9. A method for determining a position of a build platform in an additive fabrication device, the additive fabrication device comprising a build platform having a build surface and comprising a surface opposing the build surface, the method comprising:
moving the build platform away from the opposing surface, wherein initially during said movement the build surface is in contact with the opposing surface and at completion of said movement the build surface is not in contact with the opposing surface;
measuring a force applied to the build platform during said step of moving the build platform away from the opposing surface; and
determining a position of the build platform relative to the opposing surface based at least in part on the measured force.
10. The method of claim 9 , wherein:
the additive fabrication device comprises a container comprising a liquid photopolymer,
when the build surface is in contact with the opposing surface, at least part of the build platform is immersed within the liquid photopolymer, and
wherein the measured force includes fluid forces resisting separation of the build surface and the opposing surface.
11. The method of claim 9 , wherein determining the position of the build platform comprises identifying a position of the build platform at which a discontinuity in the measured force is observed.
12. The method of claim 9 , wherein the additive fabrication device comprises one or more electrically driven actuators configured to move the build platform, and wherein measuring the force applied to the build platform comprises registering a back electromotive force upon at least one of the one or more actuators.
13. The method of claim 9 , comprising measuring a force applied to the build platform at each of a plurality of positions of the build platform during said step of moving the build platform away from the container.
14. The method of claim 13 , further comprising calculating a rate of change of the measured force with respect to a change in a distance of the build platform from the container.