M(is)aligned decomposition

So I finished coding up the 3D camera calibration routines using Singular Value Decomposition and the like, and the results were better than I expected for a first attempt, but they more or less still stink. I think the problems come from three things: nonlinear distortions, inadequate sample space, and backlash in the robot arm.

I really do think the SR-3000 has some nonlinear distortion to it. It's not extreme, but it is there. So I should learn how to account for nonlinearity and calibrate accordingly. Now don't get me wrong, the SR-3000 is a pretty nice sensor, especially considering its size, power requirements, and illumination independence. It's just not quite good enough for the precision I'm looking for. If the scan is misaligned by 0.5cm in any direction, the task is extremely difficult to do.

The inadequate sample space comes from the calibration target being mounted in a place on the arm that cannot go below about 10cm (where the highest reach of the arm is 40cm). The result appears to be that objects sitting at around 15cm are aligned perfectly, while objects below 10cm are typically off by about 1 cm. Of course, this is after playing with it for only half an hour. One solution to this may be to mount the target in/on the gripper instead of the "wrist". Another possibility would be to put a few targets on the ground plane, although that could introduce some discrepancies between my robot arm forward kinematics model and the real world. In other words, where the arm really is and where it thinks it is.

Arm backlash is probably more important than I would like it to be. The base joint basically doesn't rotate for about 2-5 degrees when you change directions. I tried to hack a software solution together, but it's not good enough. To fix that I think I'll have to modify the hobbyist servos to give noisy analog position feedback, then run it through a filter to get the actual position. Not so difficult, but it takes time. Probably a better solution would be to put digital encoders on there, but while my servo controller has analog inputs, it has no digital inputs. That means I would have to get into AVR programming. While I would love to... it all comes back to time.