Though often regarded as a myth, it is actually a REALITY! The system automatically measures many paleomagnetic samples without any input or attention from the user. And due to the extremely low noise of the holder (a glass tube which only touches the sample on the top surface), extremely weak samples can be measured with the changer. Due to the precise control of the stepping motors which insert the samples into the magnetometer, very strong samples can be measured with the same setup!
This project began life approximately 15 years ago when Joe Kirschvink salvaged a Beckmann Instruments scintillation counter for its sample movement assembly. This tray has undergone several transformations, and the latest stage in its evolution has brought it right on track with the prophetic visions which Joe frequently shared with us.
The system consists of a tray (shown in photo above) which holds up to 100 samples and carries them around a track via a computer controlled stepping motor and gear drive mechanism. When a sample is directly above the magnetometer opening, the sample rod (glass tube just to left of vertical aluminum shaft in above photo) is lowered until the end gently contacts the sample. This is when the revolutionary vacuum pickup system comes to life!
A computer controlled "vacuum
cleaner" is turned on and the suction is routed down into the hollow sample
holder tube. A photo of the carriage assembly for this stepping-motor-controlled sample holder is shown in the
photo at left. The black flexible hose is part of the vacuum routing.
This vacuum causes the sample to be pulled upward, held against the
bottom of the sample holder rod. The sample can then be lifted, the
track moved to an open position, and the sample lowered into the magnetometer for measurement.
All samples are loaded in one direction (up or down) for their first measurements. The operator can then leave while the system runs, and when the measurementsare complete, the samples can be inverted, the procedure repeated, and the up/down measurements compared. Preliminary tests indicate negligible sample rotation during tray motion and vacuum pickup.
Bringing this system to life involved the work of many people. Joe Kirschvink was, of course, the main motivating force and generator of novel ideas, but there were others who contributed in their own ways. Vic Nenow, master of all things electrical and mechanical, built many of the electronic components, provided ideas, and built both versions of the vacuum source used in picking up the samples. An undergraduate named Gaylon Lovelace built much of the hardware used in the first stages. Graduate student John Holt then modified the main computer control system so that it would operate in a Windows environment, updated the stepping motor driver system so that it was more flexible and independent of the computer (separate micro-controller), and changed the control interface to an RS-232 based system, allowing additional control outputs and inputs. These modifications provided a much improved environment for controlling and operating the sample changer. John also supervised two undergraduate students, Hiroshi Ishii and Bryce Engelbrecht who contributed to this project. Hiroshi worked on a new operating program in VisualBasic and explored ideas for sample movement control, while Bryce machined mechanical components, primarily for the sample pickup system.
Joe put the finishing touches on the system over many months, working out bugs and coming up with more clever ways to overcome them. He also implemented the controlling software as an addition to the QuickBasic program already used for the magnetometer. VisualBasic is still in the works. Joe is now enjoying the success by making thousands of measurements per week.
Back to Caltech Paleomag Lab page.