Comparison of design approaches for low-cost sampling mechanisms in open-source chemical instrumentation

Graphical abstract


Hardware in context
Many modern chemical instruments include the use of autosamplers to introduce samples for analysis [1], including gas chromatographs (GCs), liquid chromatographs (LCs), mass spectrometers (MSs), capillary electrophoresis (CE) instruments, and flow injection analyzers (FIAs). The movement of these samplers typically relies on either a 3-axis linear motion system or a 2-axis linear motion system with a third angular rotation mechanism, both with the goal of sampling specific positions in sample trays or well plates [1]. Fraction collectors, in which the eluent from a chromatographic column or other fluidic stream is collected into separate tubes or wells over time, operate under similar principles. With the advent of 3D printing, the cost and complexity of these types of motion systems (and their associated motors) has dropped dramatically, providing an opportunity to develop open-source solutions for autosampling [2][3][4][5][6], liquid sample manipulation [3,7,8], and fraction collection [4,5]. Additional reports of 3-axis motion systems based on 3D printers that have been adapted for chemical research include mass spectrometry sampling [9,10], matrix deposition for matrix-assisted laser desorption ionization (MALDI) [11], chromatographic fraction collection [12], sample preparation and injection [13], applications in thin-layer chromatography (TLC) [14,15], and nucleic acid sample processing [16,17]. Open-source chemistry applications of angular rotation mechanisms have mainly been demonstrated through the use of sampling robotic arms thus far [18,19]. From these various reports, it is clear that the application of these approaches in chemical research are widespread and will continue to grow with the advent of open-source chemical instrumentation [20]. A key driving factor in the open-source hardware movement is a reduction in cost for laboratory tools. However, these open-source, low-cost options must still perform at acceptable levels to adequately complete desired tasks. In this report, the designs for an open-source 3-axis motion system using stepper motors similar to those adapted from 3D printers and a system using an angular rotation mechanism based on a parallel Selective Compliance Assembly Robot Arm (SCARA) mechanism [21] controlled with servomotors are both described. The systems are compared in terms of movement precision, and the 3-axis system is also demonstrated for potential use in segmented flow microfluidic workflows.

Hardware description
The 3-axis autosampler design ( Fig. 1) was ctesian plane movement system using stepper motors that is common in many commercially available 3D printers. The SCARA design (Fig. 2) relies upon angular rotation movement between multiple linker arms for x-axis and y-axis servomotor positioning, with two-position movement in the z-axis controlled by a solenoid. Both systems cost significantly less than commercial autosampler systems and are comparable in price to approaches that rely upon the modification of commercial low-cost 3D printers. With the foundation provided for each approach here, they can be further modified to accommodate additional functionality, including the many purposes described in Section 1.
The movement precision of these two design approaches has not directly been compared to date in the context of opensource chemical instrumentation. To identify which system provided finer movement control, a process adapted from ISO 9283:1998 [22] was used to determine the movement precision for each approach. As a demonstration of a specific relevant application in the field of microfluidics, the 3-axis system was applied toward the generation of segmented flow droplet streams from a 96-well plate, an approach with implications in high-throughput screening (HTS) [23][24][25][26][27][28][29].

Design files
The files listed in Table 1 are used in the construction of the 3-axis autosampler system described in Sections 5.1.1-5.1.4. The file listed in Table 2 is used to install the software for the 3-axis autosampler system, as described in Section 5.1.5. The files listed in Table 3 are used in the construction of the SCARA autosampler system described in Sections 5.2.1-5.2.3. The files listed in Table 4 are used to build the PCBs and use the control software for the SCARA autosampler system, as described in the Supporting Information and Section 6.2. Table 5 describes the materials needed to construct the 3-axis autosampler, while Tables 6 and 7 describe the materials needed to construct the SCARA autosampler. All prices are current as of December 2020. Note that some hardware pieces are listed as packs of larger quantities (e.g., 100), so the listed prices are slightly higher than the exact component cost that is needed for construction. However, this approach provides a cost based on the list price that would be used for purchase. Additional tools that will be needed for the 3-axis autosampler system include: Power mitre saw (or similar), rotary cutting tool (or similar), hex key allen wrench set, screwdriver set, standard tap & die set, and a 3D printer. For this design, an Ultimaker 3 with Ultimaker PLA filament (Ultimaker B.V., Utrecht, Netherlands) was used. Most components were printed with a 100% infill and 0.1 mm layer height using the grid pattern infill design. Larger parts ('x_carriage_frame' and 'well_plate_holder') were printed with 60% infill and 0.15 mm layer height using the same infill design.

Bill of materials
Additional tools that will be needed for the SCARA autosampler system include: Trigger clamps (6 00 ), paper towels, sandpaper, laser cutter, woodcutting saw, screwdriver set, wrench or pliers, and a soldering station, and a 3D printer. For this design, a Monoprice Mini V2 with Monoprice PLA filament (Monoprice, Inc., Brea, CA) was used to print all parts with default settings: 22% infill, 0.1 mm layer height, and a grid pattern infill design.
For both designs, the reported print settings were primarily based on default settings, so similar procedures on other 3D printers would likely be suitable to create the necessary parts.    Table 8 Movement characteristics of the two autosampler designs.    Make the frame portions from the 6 0 long piece of T-slotted framing extrusion (PN# 5537T101) by cutting 2 pieces to a length of 8.75 00 , 3 pieces to a length of 7.50 00 , and 2 pieces to a length of 6.50 00 . Cutting the T-slotted framing can be accomplished with a hacksaw or other hand tool, but this is one area where a square cut can make assembly easier. A power mitre saw is best, but if one is not accessible some vendors will make the cuts for a small fee. Make the Z-axis rails by cutting the ¼ 00 Â 8 00 long shaft (PN# 6061K101) into 2 pieces 3.65 00 long. This can be accomplished with an angle grinder or rotary tool with a metal cutting wheel. A hacksaw or similar will not work as the shafting is very hard (60 HRC).
Make the X, Y, Z-axis lead screws from the commercial parts (PN# B07QV4MRDD, PN# B07C8P1DWX). Two 9.25 00 length pieces of B07QV4MRDD are needed for the X-axis, two 8.40 00 length pieces of B07QV4MRDD are needed for the Y-axis, and two 3.40 00 length pieces of B07C8P1DWX are needed for the Z-axis. The lead screws are softer material, and therefore they may be cut with an angle grinder, rotary cutting tool, or hack saw. Reduce the four X-axis slide bushings (PN# 6687K33) to 0.160 00 thickness on one side to increase room for lead screw clearance (Fig. 3). This process can be accomplished with a file or rotary cutting tool.

Modifications to 3D-Printed parts.
1. Prepare the well plate holder by threading indicated holes into well_plate_holder.STL with an appropriate tap (see Fig. 4). 2. Prepare the X-axis carriage by threading the indicated holes into x_carriage_frame.STL with an appropriate tap (see Fig. 5).
3. Prepare the Z-axis carriage by threading the indicated holes into process_interface_carriage.STL with an appropriate tap (see Fig. 6). 4. Prepare the X, Y-axis lead screw supports (*_axis_leadscrew_support.STL)) and screw nut housings (leadscrew_nut_hous ing_*_axis.STL) by threading the indicated holes into each piece with an appropriate tap (see Fig. 7). 5. Finish the capillary holder pieces (capillary_elec_insert.STL) by filing a small groove for the capillary into one piece. While both halves have a conical feature to aid insertion, it is advisable to only file one side as shown in Fig. 8.

Sub-Assemblies for 3-Axis System
1. Press-fit the lead screw support bushings (PN# 6389K626) into the X, Y-axis lead screw supports (Fig. 9). Secure the bushings with bushing retaining button head cap screw #6-32 Â 0.25 00 . To reduce number of vendors, a 0.3125 00 bushing was specified while the lead screw is actually 0.315 00 . We enlarged bushing PN# 6389K626, but an alternate 8 mm bushing can also be purchased.  2. Bolt the X,Y-axis lead screw nuts (included with B07QV4MRDD) into their housings using four #6-32 Â 0.5 00 button head cap screws (Fig. 10). The lead screw nuts will need to have a portion of the flange removed to be congruent with the holder body. This may be done with a file or rotary tool. 3. To attach the Y-axis carriage onto well plate holder (Fig. 11), bolt four Y-axis pillow block bushings (PN# 6687K33) to the corners of the well plate holder using two #8-32 Â 0.5 00 button head cap screws each (8 total), but do not completely tighten screws to improve positioning later in construction. Attach one of the X,Y-axis lead screw nut holder from the previous step to the center of the well plate holder using two #10-32 Â 0.5 00 button head cap screws, again without completely tightening them.  4. To form the Z-axis carriage (Fig. 12), press-fit two Z-axis slide bushings (PN# 6389K627) into the bottom of the 'Process Interface Carriage' component. Bolt down the Z-axis lead screw nut (included with B07C8P1DWX) on this same side with #6-32 Â 0.5 00 button head cap screws. Turn the carriage piece over and press-fit the two remaining Z-axis slide bushings (PN# 6389K627) into place. Here, the retainer screws for the Z-axis slide bushings should not be necessary due to the retention of the press-fit.   5. To prepare the X-axis carriage that also holds the Z-axis carriage, press-fit the Z-axis lead screw support bushing (PN# 6389K626) into the top of the X-axis carriage piece and secure it with bushing retaining button head cap screw #6-32 Â 0.25 00 . Bolt the remaining X,Y-axis lead screw nut holder ( Fig. 10) to the center of the back of the X-axis carriage piece using two #10-32 Â 0.5 00 button head cap screws, again without completely tightening them. Then, connect the four X-axis pillow block bushings (PN# 6687K33) in each corner using #8-32 Â 0.5 00 button head cap screws for each outer hole and #8-32 Â 0.375 00 button head cap screws for each inner hole. The inner hole should be the reduced 0.160 00 thick portion of the bushing (Fig. 13). Again, do not completely tighten the screws due to positioning requirements later in the build. 6. Combine the X-axis and Z-axis carriage components by inserting the two Z-axis slide rails (PN# 6061K101) through both components. Secure them in place with a #8-32 Â 0.250 00 button head cap screws for each rail on the bottom of the X-axis carriage piece. The portion of the Z-axis carriage designed to extend away from the lead screw should point toward the bottom of the combined piece (Fig. 14). 7. To create the X,Y,Z-axis drive assemblies, attach the motor/lead screw couplings (PN# B073FDXHMG) to each of the three NEMA-17 axis drive motors, leaving approximately 0.325 00 of the motor shaft open below the bottom of the coupling (Fig. 15). 8. Bolt the three printed NEMA-17 mount plates (two of nema_17_xy_mount.STL and one of nema_17_z_mount.STL) using four #4-40 Â 0.375 00 button head cap screws for each plate (Fig. 16). Then, secure the lead screws to each motor using the couplings.

Frame assembly for 3-Axis system
A clean, flat work surface makes frame assembly far easier. Calipers make an excellent layout instrument as they can be set to precise lengths and used to score lines directly on the framing. Framing / Fastener type: There are two distinct types of  20 mm square framing available: 80/20 and PZRT. We have selected 80/20 here as it is generally more available, but compatible fasteners tend to be more expensive. PZRT is more difficult to acquire in small lots, but there tends to be a wider selection of lower cost fasteners. Both formats offer standard and twist-in fasteners. For the purposes of this design, the M5 screws (PN# B07C9S7V1Z) and M5 flat nuts (PN# B01HKMF2EE) are used for standard connections. Twist-in fasteners are convenient as they can be placed into a section of framing even if the end is not open (to slide the fastener in). Whichever version is selected, the most important thing is to ensure that the frame and fasteners are compatible with each other.
1. To begin assembling the base of the frame, tighten shaft supports on the left side of the 7.5 00 80/20 frame pieces, with the left edge of each support being 0.850 00 from the end of the frame piece (Fig. 17). Add in the Y-axis lead screw support on the front frame piece (without fully tightening the screws) and then place an additional shaft support on each piece (again, not fully tightened). Finally, on the back piece, slot in two additional M5 flat nuts before the frame base is completed, as they will be needed to complete the Y-axis assembly and cannot be added after the next step. 2. Use four angle brackets (PN# B076D9Z89G) to connect the two 8.75 00 pieces of 80/20 onto the two pieces prepared above, keeping the left aligned shaft supports on the left side. Attach two more angle brackets in a perpendicular position (1.180 00 from the back of the base frame) that will be used to hold the frame bridge in place (Fig. 18).  3. To assemble the frame bridge, prepare the two 6.50 00 length pieces of 80/20 extruded aluminum with angle brackets, shaft supports, and the X-axis lead screw support at the positions shown in Fig. 19. Connect the two pieces using the remaining 7.50 00 length aluminum piece as a cross-beam. Fully tighten the top shaft support and angle brackets, but do not completely tighten the other screws to enable positioning later in the build. 4. Attach the frame bridge to the base frame using the angle brackets on the top of the base frame (Fig. 20).

Axis drive Installation for 3-Axis system
1. Install the Y-axis drive by inserting the two Y-axis slide rails through the shaft supports and the bushings on the Y-axis carriage (bottom of well plate holder) as shown in Fig. 21. Start with the left side support that was fully tightened, and then slide in the right rail. Slide the Y-axis carriage to the forward-most position and tighten the remaining screws in the right front shaft support. Repeat this process with the Y-axis carriage in the rear-most position. Then, repeat the entire process for the X-axis carriage. At this point, ensure that both axis slides are moving freely with uniform resistance along each travel path. Once it is confirmed that there is no binding along the travel paths, tighten the screws in the bushings on both carriages. 2. Lean the auto-sampler onto its back side and thread the X-axis lead screw through its lead screw nut until it is fully inserted (Fig. 22). Using two M5 screws, loosely secure the X-axis NEMA-17 motor (PN# B07MP11C81) to the right of the frame using the two remaining flat nuts that were previously put in place. Rotating the lead screw by hand, move the X-axis carriage to the right-most position and fully secure the motor to the frame. Then, manually move the Yaxis carriage to the left-most position and tighten the lead screw support mounting screws. Repeat the process for the Y-axis lead screw after returning the frame to its standard, upright position (Fig. 22). During positioning, ensure that any resistance that is not electrical in nature, as stepper motors provide rotational resistance when their lead wires are shorted together.  3. Repeat a similar process for the installation of Z-axis drive by threading the Z-axis lead screw through its lead screw nut already installed in the X-axis carriage frame (Fig. 23). Then, hold the mounting plate down to the X-axis carriage with four #8-32 Â 0.5 00 button head cap screws.

Inspect the completed 3-Axis Autosampler System construction.
*Note: Simple modifications can be made with additional M5 screws and flat nuts, 3D printed mounts, and additional cuts of 80/20 extruded aluminum to mount electronic parts to the back of the frame or install a mount for a Raspberry Picompatible touchscreen interface on the front of the frame to further integrate components of the system.

Raspberry Pi connections and software installation for 3-Axis system
1. Insert two pieces of 18-gauge wire into the ends of a barrel plug splitter for eventual connection to the power supply.
Make sure the supply is not plugged in, as the exposed wires can be dangerous. Ensure that the wires are properly secured into the barrel plug splitter (included with PN# B073QTNF9F), then connect them to the screw terminal on the RAMPS board (PN# B06XZ46PDJ) as shown in Fig. 24. 2. With the power supply not plugged in, place each stepper motor driver (PN# B01FFGAKK8) into the RAMPS board (Fig. 25). These drivers often have small edges that overlap, which can be fixed by gently sanding the sides of each driver until they slide in easily. 3. Connect the RAMPS board to the Raspberry Pi 3B GPIO pins using the pin diagram shown in Fig. 26. Plug in the Raspberry Pi to an appropriate power supply so that the 5 V GPIO pin output is delivering 5 V to the RAMPS board. 4. To set the reference voltage (V ref ) for the stepper motor drivers, calculate an appropriate value based on the maximum current (I max ) for the motor using the following equation: In this design, the datasheet indicated an I max value of 1.2 A, indicating a V ref of 0.65 V. To set V ref , tune the potentiometer on the bottom of the motor driver and monitor its voltage using a multimeter. An in-depth guide on this process can be found in Ref. [31]. Once this process is complete for all three motor drivers, connect the four wires from each NEMA-17 motor to the appropriate 1A, 1B, 2A, and 2B pins for the X-, Y-, and Z-axis motor drivers on the RAMPS board (Fig. 27).  1. The first major piece of the SCARA autosampler to be constructed is the base. The three required 14 00 Â 9 00 base pieces (Base_1.dxf, Base_2.dxf, Base_3.dxf) can be laser cut from a single sheet of ¼" thick plywood (PN# 958719), as shown in Fig. 28. The dimensions do not need to be exact, though they should be at minimum 14 00 Â 9 00 . The plywood also does not need to be perfectly flat. Various plastics can also be used for a similar purpose, although some of the positioning pins and binding between the layers may need to be modified. Any warp in the board will be corrected during the gluing process. One of these sheets is to be laser cut as the very bottom layer of the base. The other two sheets are to be laser cut as the middle and top layers of the base, which are identical. After laser cutting the boards, the edges may be rough or have splinters. It may help to sand down the edges prior to continuing, though it is not necessary. 2. Place down one of the scrap board pieces (PN# 914827, similar in dimension to the three base pieces) on a flat, level surface. Place a layer of paper towel over the scrap board to avoid adhesion from glue leakage Place the bottom base piece (the one not containing an open square in the middle) on top of paper towel, with the corner containing a single hole placed at the bottom left. Cover the top surface with wood glue (PN# 107209) and spread it around with a paper towel or brush: the goal is to have a relatively thick, even layer of glue spread out over the top surface, except for the region for the cutout hole on the top two base pieces (Fig. 29). Place the two dowel pins (PN# 98381A539) at the positions shown in Fig. 29, with the bottom of the dowel pin set to be level with the bottom of the bottom base piece. 3. Place one of the two remaining boards on top of the glue layer, using the dowel pins for alignment. Press tightly down, cleaning up any glue that is squeezed out along the edges or into the well plate hole in the middle of the base. On top of this new piece, place another layer of glue, spread it out evenly, and place the final base piece board on top (again using the dowel pins for alignment). Repeat the glue cleaning procedure along the edges and in the central recess. The full assembly is shown in Fig. 30. 4. Place another paper towel on top of the base, followed by the remaining scrap piece of wood. Tighten 6-8 clamps around the stack (Fig. 31), with the scrap boards helping distribute the force and prevent indentations into the actual base. Wipe away any excess glue on the edges once the clamps are tightened. 5. Begin the glue curing process, which may take up to 24 h depending on the selected adhesive. To clean excess glue from the base once curing is complete, a razor (or similar) blade or sandpaper can be used to remove glue that has been squeezed out of the edges. A drill (#34 bit or smaller) or other cutting tool can be used to remove excess glue from the holes that did not contain the dowel pins. A completed SCARA base after curing and cleaning is shown in Fig. 32.   (Fig. 34). 3. Place two more M3 Â 20 mm screws through the holes shown on the bottom of Fig. 34 with the threads facing up. Place the back (non-wired) side of a HS422 servomotor (PN# 31422S00) in place on the existing stand, then slide the front servomotor stand onto the screws, ensuring that the wires of the servomotor are below the stand. Tighten the stand in place using M3 nuts (Fig. 35). 4. Align the combined left servomotor plate on top of the servomotor by placing the middle of the large hole over the servomotor spline and the four mounting holes on both the plate and motor/stand. Attach the plate to the motor and stand using four M4 Â 20 mm screws tightened into the threaded holes on the stand. The completed component is shown in Fig. 36. 5. The process for the attaching the right servomotor and plate is very similar, with only one small difference: M3 Â 30 mm screws are used through the base, and the servomotor stands are designed to sit on the 3D printed servomotor stand riser (Riser.STL) rather than directly onto the base (Fig. 37). The completed right servomotor module is shown in Fig. 38 and the complete base with both servomotors is shown in Fig. 39.

Linkage for SCARA system
1. For the purposes of a sampler used for the generation of segmented flow droplet streams from a well plate, costs can be decreased by limiting the Z-axis position of the sampling capillary to ''in-well" and ''above-well" positions. For the lower-cost SCARA approach, this is achieved using a solenoid coil rather than a complete stepper motor design as with the 3-Axis autosampler. The first step in construction of a component that achieves this movement is the attachment of the solenoid coil body (included in PN# 1144-1419-ND) and the end effector (EndEffector.STL). Two #4 Â 0.5"    screws are placed through the holes on the rectangular section that is orthogonal to the larger part of the plate. Align the screws with the threaded holes on the coil body, making sure that the plunger opening is facing the same direction as the top of the end effector (Fig. 40). Tighten the screws into the thread holes to attach the two pieces. 2. Attach the capillary rail (CapillaryRail.STL) and lever fulcrum (Fulcrum.STL) onto the top of the capillary plate using #4 Â 0.5 00 screws and #4 nuts in the positions shown in Fig. 41.   3. Arrange the lever attachment (LeverAtt.STL) and the main lever piece (LeverMain.STL) so that the longer holes have a gap between them. Connect the two pieces through the smaller holes using a #4 Â 0.5 00 screw and #4 nut. Then, attach the solenoid plunger to the other side of the main lever piece using a M2 Â 10 mm screw and M2 nut (Fig. 42). One hole at the center of the combined piece should remain open for connection in the next step.     4. To begin attaching the lever-plunger assembly to the capillary plate, cut the compression spring (PN# 9657 K107) to a length of approximately 0.75 00 , slide it over the plunger, and insert the pointed end of the plunger down into the solenoid coil body. Align the central lever hole with the lever pivot hole and connect with a #4 Â 0.5 00 screw. Place a drop of threadlocker (PN# 1810A27) onto the exposed threads of this screw, hand-thread the nut onto the screw, and let the     threadlocker cure for 10 min before continuing. Do not fully tighten the nut, as that will restrict the motion of the lever. Attach the capillary clamps (CapillaryClampA.STL and CapillaryClampB.STL) with #4 Â 0.75 00 screws so that they ride within the capillary rail. The capillary guide (CapillaryGuide.STL) is then attached to the bottom of the capillary plate with #4 Â 0.75 00 screws. The complete assembly is shown in Fig. 43. Attach the solenoid to a 12 V power supply and toggle the power. If the solenoid is able to fully retract the spring, then the spring length is acceptable. Otherwise, the spring should be cut further. It is recommended not to cut more than half a winding at a time. 5. To begin preparing the linkages that are connected to the capillary plate, attach the R-I (Regular, I-shaped) horns onto links A1 (LinkA1.STL) and B1 (LinkB1.STL), with the spline hole in the horn aligned with the larger hole on the link and the wings of the horn in line with the slots. Tighten two #0 Â 0.5 00 thread-forming screws through the link and into the horn so that the threads are on the same side as the horn. The screw for the inner slot can be placed in any of the holes of the horn wing. The screw for the outer slot should be placed in the hole closest to the spline. One of the horn-link connections is shown in Fig. 44. Set aside link A1 and attach links B1 and B2 (LinkB2.STL) using a 0.2 00 Â 0.5 00 Chicago screw, adding threadlocker to the threads before it is tightened. Let the connected pieces sit until the threadlocker sits. (Note: use a similar threadlocker process for all subsequent Chicago screw connections). 6. Attach the combined B1/B2 link (right sub-linkage) to the hole on the right side of the capillary plate with a 0.2 00 Â 0.5 00 Chicago screw (Fig. 45). 7. Attach links P1 (LinkP1.STL) and P2 (LinkP2.STL) to the elbow (Elbow.STL). It is important that the elbow be oriented correctly since it is not symmetric. With the longest flat edge up, the shortest flat edge should be on the right (Fig. 46). With the elbow in this orientation, link P1 should be aligned so it is concentric with the left hole of the elbow and is under the elbow, and link P2 should be aligned so it is concentric with the right hole of the elbow and is on top of the elbow. Both are attached with 0.2 00 Â 0.5 00 Chicago screws.  8. Connect links A1 and A2 (LinkA2.STL) to the remaining hole on the elbow (Fig. 47). Link A1 should be aligned under the elbow (with the horn positioned away from the elbow and pointing down) and link A2 should be aligned on top of the elbow, with all three pieces connected using a 0.2 00 Â 0.6875 00 Chicago screw. 9. Attach the completed left sub-linkage to the capillary plate as shown in Fig. 48 using 0.2 00 Â 0.5 00 Chicago screws. 10. Align the horn on the right sub-linkage (link B1) with the spline on the right servomotor and tighten with a spline screw (Fig. 49). 11. Complete the linkage assembly by aligning the horn on the left sub-linkage (link A1) with the spline on the left servomotor and tightening with a spline screw. Then, connect the remaining hole on link P1 to the remaining hole on the left servomotor plate with a 0.2 00 Â 0.5 00 Chicago screw. The completed linkage assembly is shown in Fig. 50.

Raspberry Pi connections and software Installation for SCARA autosampler
Detailed instructions for soldering the components for the power supply and control boards are included in the Supporting Information. The following steps can be performed once the boards have been completed.
1. Plug the power supply board into the control board, as shown in Fig. 52, making sure that the Raspberry Pi header and power supply header are both connected securely. Connect the 12VDC power supply (PN# Q1185-ND) to the power jack and plug it into an outlet. The three LEDs should light up when the power switch is turned on. 2. Plug the wires for the joystick and buttons into the joystick board and control board as shown in Fig. 53. 3. Solder the ends of the solenoid wire to the solenoid and then connect the solenoid to the header on the control board as shown in Fig. 54. 4. Attach the servo control board to the header on the control board as shown in Fig. 55. Connect the servo on the left of the board to Connector 0 on the control board. The right servo should be connected to Connector 1. Ensure that the signal (yellow or white) wire is facing up when connected (Fig. 55).

Operation instructions
6.1. Operation instructions for the 3-axis autosampler 1. To generate movement between a consecutive sequence of wells, click the ''Select Sequence" button (Fig. 56). The software will the record each well selected by the user. When a well is clicked, it will prompt the user to enter the length of time to remain in the well. After all wells in the sequence are selected, click the ''Select Sequence" button again to stop recording.  2. Once a sequence has been selected or loaded, click the ''Start Sequence" Button to begin the method. If no sequence is selected, nothing will happen. 3. If a wrong well is selected, or a sequence is done with use the ''Clear Sequence" button can be clicked. It is important to note that this will completely clear any sequence currently loaded. 4. If you want to save a currently selected sequence to be imported later click the ''Save Selection" button. This will pull up a prompt to select the file save location as well as the file name. 5. If you wish to load a saved sequence, click the ''Load Sequence" button. This will bring up a prompt allowing the user to select a sequence file. The selected file will be loaded and can be started with the ''Start Sequence" button. The loaded sequence can also be added to by clicking the ''Select Sequence" button, but it should be noted that any additional wells selected will be added to the end of the loaded sequence.

Operation instructions for the SCARA autosampler
The SCARA Autosampler offers several modes accessed through a command line interface (Fig. 57). Run the python program mainprogram.py. The first time the program is run it will prompt the user to perform an initial calibration. Use the x axis of the joystick to control the rotation of the right servo and the y axis for the left servo. Move the sampler head to the vial  indicated by the program and press in the joystick. The initial calibration is approximate so getting the sampler within about one centimeter is acceptable. It is recommended to rerun calibration mode after initial setup for more accurate results. After the final point, the program will create a folder in the working directory and save the calibration file. The program will then  display the main menu. The program menu lists each of the possible operating modes. Access each mode by typing the corresponding letter for each mode and pressing enter.
1. Manual Mode -''m": In manual mode, the program will ask for the row and column of the desired vial. Enter the row using the letter designator (A-H) and the column with the number (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). After pressing enter, the linkage will move to that position. The linkage will print out the x and y coordinates of the sampling head. Press the joystick down (button 1) to clear the entry and enter a new vial. 2. Auto Mode -''a": This mode will step through all of the vials on the microplate. It starts at A1 and steps through all columns before moving to the next row. It starts at column 1 for each row. 3. Sequence Mode -''s": The program will prompt for a sequence of vials to step through. The vials should be separated by commas in the format ''A1, B2, C3, etc." Press enter to start the sequence. 4. Calibrate Mode -''c": This mode calibrates the autosampler by moving to a set of points and having the user align the sampling head using the joystick. It will overwrite the existing calibration files (./calibration/cal0.csv and ./calibration/-cal1.csv) or create new files if they do not exist. The linkage will move near the first calibration point and ask the user to use the joystick. Move the sampling head directly over the vial and press the joystick (button 1) when aligned. Repeat this process for the remaining calibration points. 5. Quit -''q": Exits the program.

Precision comparison of autosampler designs
To determine the motion characteristics of each movement design, a protocol based on ISO 9283 [22] was used as a guide in developing a comparison test. For the 3-axis autosampler, each axis was tested by moving to a central ''home position", then moving a distance l (1 00 for the 3-axis system and 1.06 00 , equivalent to 3 well positions, for the SCARA system) and recording the new position with a dial caliper, and finally returning to the ''home position". Measurements for the 3-axis design were made with calipers that provide 0.0005" resolution (Mitutoyo America, Aurora, IL). This process was then repeated five more times, with accuracy calculated by:  Accuracy where ā is the mean value of the final calculated position for all trials for a given axis. The repeatability was then calculated using the following series of equations: Repeatability where a i is the deviation for an individual trial. Bi-directional movements were used for this test (a slight deviation from ISO 9283) to account for the potential of leadscrew backlash in the measurement. For the SCARA autosampler, the same process was conducted, although the Z-axis was not tested as it only moves in two positions based on the solenoid control. Measure- ments for the SCARA design were made with a dial indicator that provides 0.001 00 resolution (Fowler High Precision, Newton, MA). Results of the process are shown in Table 8.
No issues were encountered during the development and routine operation of either platform described here, although no in-depth study on total performance lifetime was conducted. Due to the modular nature of these designs, any component that fails can be changed without the need to replace the entire system.

Use of 3-Axis autosampler for generated of segmented flow droplet stream
To demonstrate the use of the 3-axis autosampler for droplet formation, two adjacent wells of a 96-well plate were milled slightly below the planar surface, filled with green and red food dye