Sensor that simulates resin optical properties
A method and system for calibrating a three dimensional printing system includes a specialized sensor. The three dimensional printing system forms a three dimensional article of manufacture through a layer-by-layer process. Layers are formed by the operation of a light engine selectively curing photocure resin onto a face of the three dimensional article of manufacture. The sensor includes a photodetector overlaid by an optical element. The optical element simulates a “dense portion” of an optical path between the light engine and the face of the three dimensional article of manufacture being formed. The “dense portion” of the optical path includes a layer of photocure resin that is disposed between the light engine and the face of the three dimensional article of manufacture.
1. A calibration system for a three dimensional printing system which forms a three dimensional article of manufacture through a layer-by-layer process with layers being formed by the operation of a light engine selectively curing photocure resin onto a face of the three dimensional article of manufacture comprising:
at least one sensor including a photodetector overlaid by an optical element, the optical element simulating a dense portion of an optical path between the light engine and the face of the three dimensional article of manufacture, the dense portion of the optical path including a layer of the photocure resin, the optical element separated from the photocure resin and having optical path properties that physically simulate optical properties of the dense portion of the optical path, the optical path properties including one or more of attenuation, turbidity, and specular characteristics;
an apparatus for positioning the at least one sensor to provide coverage of a lateral build plane of the light engine; and
a controller configured to:
(a) activate the light engine to illuminate the build plane at a lateral position;
(b) receive a signal from the at least one sensor in response to received light from the light engine;
(c) repeat (a)-(b) until a set of calibration values mapping the light engine build plane is defined; and
(d) store the set of calibration values for the light engine, the calibration values compensating for a variation in the optical path as a function of the lateral position in the build plane.
2. The calibration system of claim 1 wherein light received by the at least one sensor defines a trajectory angle relative to a central axis which varies according to the lateral position, a path length of the dense portion of the optical path increases as the trajectory angle increases.
3. The calibration system of claim 2 wherein the length of the dense portion of the optical path is substantially proportional to a reciprocal of a cosine of the trajectory angle within the dense portion of the optical path.
4. The calibration system of claim 1 wherein the light engine includes an ultraviolet light source.
5. The calibration system of claim 1 wherein the portion of the optical path further includes a transparent sheet to be disposed between the light engine and the layer of photocure resin.
6. The calibration system of claim 1 wherein the optical element includes an attenuator that simulates specular characteristics of the portion of the optical path.
7. The calibration system of claim 1 wherein the optical element includes a diffuser that simulates a turbidity of the portion of the optical path.
8. The calibration system of claim 1 wherein the light engine generates an array of pixel elements.
9. The calibration system of claim 8 wherein, according to step (a), a plurality of the pixel elements are activated to provide light to the sensor.
10. The calibration system of claim 8 wherein, according to step (a), at least 100 of the pixel elements are activated to provide light to the sensor.
11. The calibration system of claim 8 wherein, according to step (a), at least 1000 of the pixel elements are activated to provide light to the sensor.