Adjusting for Changes in Light Intensity With the Ember Printer

The light intensity (or irradiance) of the Ember printer varies from day to day for a number of reasons. Ultimately, this variation can lead to failure in the printing process. Too much light, and the printed part will stick to the window, and jam the printer. Too little and no polymer forms.

The easiest way to account for this change is to measure the light intensity of the printer, and then adjust the exposure time, so that the dose (total amount of light received) is the same from day to day. That is

Dose of light (mJ/cm2) = Light intensity (mW/cm2) x exposure time (s)

This Instructable will outline how to measure the light intensity with a G&R Labs 221 radiometer with a 420 nm probe. An ILT1400 radiometer and an SEL005 probe and an A#28762 filter would also work. However, the build arm of the printer needs to be removed beause of the size of the probe

Step 1: First We Clean

First the printer tray needs to be removed, drained, and carefully cleaned with a solvent (isopropanol preferably). Any resin left on the window will be transferred to the radiometer probe and gunk it up.

Step 2: Upload a Test File

The next step is to upload a test file to printer the irradiates a large area. One way would be too upload a large block (64 mm x40 mm x1 mm) to Emberprinter.com. Another easier is to upload the attached calibration file to the printer. This can be done by connecting to the printer via wifi or USB, and then uploading it at 192.168.1.1 or 192.168.7.2. Alternatively, one can hold down the left button on the printer fror 5 seconds, and then upload to the IP address of the printer.

Step 3: Measure

Next remove the build head (so that there is room for the probe) and start the print. For the G&R labs radiometer the range should be set to 200 and the the other switch to "MW/CM2". If your measurement is continually increasing, you are probably measuring the dose, not the irradiance.

Step 4: Adjust the Exposure Time

The final step is to adjust the exposure time so that the dose is the same as a value that worked before using the following equation.

Dose of light (mJ/cm2) = Light intensity (mW/cm2) x exposure time (s)

I have attached a chart showing thw working curve I have found to work for Autodesk Standard Clear at 25 to 50 microns. The dose required will vary resin to resin, and with layer thickness.