Here's a good (real time) video of the SLA process.
The laser moves quite fast in comparison with even the fastest delta or cartesian bots. Energy levels for cure are usually around 500 to 3000 mJ/cm^2, depending on wavelength and specifics of the resin - with a spot size of 0.05 mm, that gives an area of 2x10^-5 cm^2, so a 400 mW output laser needs about 0.1 milliseconds over the area to cure (at that rate, it is 2000 mJ/cm^2 energy density).
Granted, I can turn down the laser power if I'm going with a mechanical build, or increase the spot size, but running a galvo would end up with quicker builds, and potentially higher accuracy since they have position feedback.
Speed would be controlled likely by limiting the scan rate of the galvos. Find the travel time for the X or Y mirrors to scan a full length of the build platform, slow it down so time over any specific point is ideal for curing at the current laser power level.
The other issue is beam focusing (if I was running a galvo). However, that's generally solved by a very expensive f-theta lens, or a controlled movable focus lens (fast linear actuator or piezo stack) that is hardcoded to positions based on the angle from the normal of the build platform. F-theta lenses are anywhere from about $750 to $10k, so that's probably out. Pulling a lens from a photo enlarger might work as well, they are close to flat-field focus, with a small enough deviation to be acceptable.
The laser moves quite fast in comparison with even the fastest delta or cartesian bots. Energy levels for cure are usually around 500 to 3000 mJ/cm^2, depending on wavelength and specifics of the resin - with a spot size of 0.05 mm, that gives an area of 2x10^-5 cm^2, so a 400 mW output laser needs about 0.1 milliseconds over the area to cure (at that rate, it is 2000 mJ/cm^2 energy density).
Granted, I can turn down the laser power if I'm going with a mechanical build, or increase the spot size, but running a galvo would end up with quicker builds, and potentially higher accuracy since they have position feedback.
Speed would be controlled likely by limiting the scan rate of the galvos. Find the travel time for the X or Y mirrors to scan a full length of the build platform, slow it down so time over any specific point is ideal for curing at the current laser power level.
The other issue is beam focusing (if I was running a galvo). However, that's generally solved by a very expensive f-theta lens, or a controlled movable focus lens (fast linear actuator or piezo stack) that is hardcoded to positions based on the angle from the normal of the build platform. F-theta lenses are anywhere from about $750 to $10k, so that's probably out. Pulling a lens from a photo enlarger might work as well, they are close to flat-field focus, with a small enough deviation to be acceptable.
