Tray grabber calibration

Samples are moved around in the imaging base using a grabber system. The grabber is a major weakness of the system and took some reengineering to correct. The clearances for the grabber fingers are on the order of ~1 mm so they are prone to errors. Long story short, some basic misuses of the system (by LemnaTec and myself) led to some crashes that bent some of the hardware. this propogated to other not completely obvious problems that propogated into various system failures. After a lot of time and consideration I had the machine shop at WSU make new grabber fingers that are longer and wider. The benefit of having perfectly straight fingers with extra width and length has improved the reliability such that there have been no related errors in the last 6 months! We also have spares and can have more made if necessary. Previously we would bend the fingers and arms by hand to approximately get them to work again. In retrospect this was a disaster.

With the new finger design I had to recalibrate the deck positions, particularly the z. I calibrated x,y,z to be safe since I had tinkered with the settings. Calibration was done with the Teaching Tools. I will try to write up a more detailed explanation how they work later but here are some tips for calibration.

1. the most important advice I learned was never to validate a position definition by moving a tray within the deck e.g. from A1 to B1. ALWAYS move to and from the transfer station. This as a huge pain and very slow but made a huge difference. The reason is because each position as +/- 1 mm flexibility on each x,y axis. These extremely small deviations from a perfect placement in their positions will compound if you take the tray from deck position to deck position. Deck to Deck NEVER happens in operation. The movement from the transfer station to the deck is 100% of the time and needs to be perfect.
2. be very careful about moving to and from the transfer station. “Fetch/Store from Transfer Station” is usually safe. It is very picky though and the system isn’t completely failsafe. In particular, if the grabber is not in a predefined position it sometimes will make illegal moves and the grabber fingers will catch on something like the transfer station. THe transfer station has 3 or 4 defined positions that I still don’t completely understand- high, middle, low, and maybe 1 more?
3. The deltaZ at the transfer station has a maximum of 50 mm so don’t set your incoming position to >50mm above where you want to close to grab the tray.