Sample Changer Blueprint Files
The specifications for this system are provided under an open source license based on the BSD license. Please read the license before using or modifying the files. These files were last updated on 10 January 2008.
Sample Changer System Design Overview Figure (SampleChangerSystemDesignOverview.pdf)
Parts to Order for Sample Changer System and Price Estimate (SampleChangerOrderingInfo.xls)
Compiled PDF, version 3.0 (10 January 2008): SRMSampleChangerBlueprints-3.0.pdf
Changer Base Plate Assembly
Changer Base Plate
The changer base plate is the Teflon-coated aluminum plate on which the snake chain assembly slides. First, fabricate the base plate. (You can modify the layout to see fit, but the drive belts underneath the plate will have to be adjusted to fit alternate schemes). Next, you should roughen the surface which will be bonded to the Teflon using sand paper or a shop sand-blasting tool. We recommend using a Teflon sheet that comes chemically treated on one side to stick with a special epoxy (see purchase list). Roll it smooth with a small wooden roller tool. When the epoxy hardens, trim the excess Teflon away using a razor knife, being sure to clear the holes appropriately.
Changer Cups
These systems were designed for standard paleomagnetic core samples: flat-ended right circular cylinders with a diameter close to 2.54 cm (1”), as used in most paleomagnetic laboratories. For vertical systems, every tenth cup (made from the plastic Delrin) in the snake chain is type 1 (with a hole in the bottom, allowing access to the measurement region of the 2G SRMs). For the untested horizontal design, all will be type 2 (with bottoms, including rubber O-ring). The cups are held together with brass #16 pins and connected in a continuous loop. Cogs guide the snake chain smoothly over the Teflon surface.
Nonacogs
These are two flavors of Delrin plastic gears and hardware to hold them in place. By playing around with the sample cups described above, we found that the 9-hole design was the most efficient we could produce. On each of the sample changing systems, we need to have two drive gears connected to a DC Servo motor via a brass or aluminum drive shaft to control the position of the paleomagnetic samples under the quartz-glass vacuum tube. For a 200-hole system, we need 7 unpowered idling gears arranged as shown on the base plate assembly above. (Feel free to design a bigger sample queue, if needed!)
Plexiglas Alignment Plate
On top of the base plate, where the quartz tube moves down and senses the top of each sample, it is necessary to have an alignment plate to position the tip of the quartz tube exactly over the center of the sample as it moves into position. That is done with two simple aluminum blocks that support a plexiglass plate. Note that the hole in the plate needs to be sanded slightly with 600 mesh sandpaper to allow the quartz rod to slide smoothly.
DC Servo Motor Positioning Hardware
Because the DC servo motors generate a strong magnetic anomaly, it is desirable to place them as far away from the samples being loaded on the tray as possible. In many labs, we have put layers of mu-metal shielding around the motors to knock down the residual magnetic fields. (In some labs, we have also mounted a mu-metal plate beneath the aluminum base plate as extra shielding, but that sometimes causes additional problems.). The following figures show how we solved this problem by dangling the motor below the plate and transferring torque up through a drive.
Up/Down Arm and Vacuum Valve Assembly
For the Up/Down arm, we rely on 2G Enterprises to build the sliding assembly, but have them mount the smaller DC Servo motor on it to do the sample rotation. (We do NOT use the stepping motor systems 2G have employed for many years). We plumb in a vacuum-interconnect system with a 0.75” copper pipe system, and drill several 0.25" holes in their rotating shaft assembly to connect the vacuum system to the vacuum blower motor.
Locating the Vacuum Blower Motor
The vacuum blower motor is rather noisy, so it is best to locate it in an area that humans do not inhabit frequently (like a roof or steam tunnel room), and run the vacuum tube and power cord back to the lab area. A good example of how to mount the vacuum blower is shown here from Occidental College:
DC Servo Motor Control Components
A major advance for the present system was the switch to DC Servo Motors with optical encoding (accurate to 1/8000 of a revolution), rather than the old stepper-motors used on most paleomag sampling applications. Software for controlling the motors produced by QuickSilver Controls of San Dimas, CA, were particularly easy to implement. Three motors are required: two hefty ones to move the sample dolly assembly and change the samples, and a smaller one to rotate the quartz-tube vacuum system. One limit switch is used on the system to sense when the up/down motor has reached the top of its range.
The wiring is simple. Going from the N2 (SilverNugget) controllers to the RS-232 input lines only involves 9-pin D connectors to the 48 V DC power supply.
AF and Rock Magnetism Coils
The coils for alternating fields and rock magnetic experiments are mounted in line between the bottom of the base plate and the top of the magnetometer, as shown in the overview diagram (SampleChangerSystemDesignOverview.pdf).
AF Coils
ARM Coils