Every square foot in a
laboratory costs money. Lab automation OEMs take this into account by designing
their equipment to handle smaller sample sizes, increasing the functionality of
each piece of equipment, and by reducing the overall footprint of their
products as much as possible. When Zinsser Analytical GmbH began developing a
new sample handler for collecting fractions (very small chemical samples
prepared for liquid chromatography), the company sought out automation design
advice to see how small things could be.
The issue Zinsser was looking
to address was a need to transfer very small quantities of liquids into 96 or
384 well microplates in a minimum amount of time. To reduce the potential for
cross contamination in this process, the platform holding the microplates would
be positioned under a non-moving liquid dispense system. This idea differs from
the more common industry practice of moving liquid handling arms over the
sample plates.
To meet optimum design
criteria for this idea, as much of the unit as possible had to be easily
accessed from above. In addition, the system needed to occupy a minimum
footprint. As for operation specifics, the equipment was also needed to process
up to 10 plates automatically. This spec required that a plate stacking system
be integrated into the design.
The answer to this new laboratory automation design came from the
flat-panel TV handling market. Engineers at
Festo,
the automation company Zinsser Analytical collaborated with on this design,
drew upon a two-axis gantry concept used in
a product Festo originally designed for the flat-panel TV handling. The
x-y gantry utilizes a single belt driven by two motors in series to control
both axes, thereby reducing both size and moving mass. The end result is a
product known as the µFRACS.
Functionally, the design concept used in the µFRACS has been around since at least
before the Etch-a-Sketch, but Festo took the single belt x-y control design and
turned it into a standard automation product.
Mounting the belt to a single
point on the stage and driving it via pulleys on the two motors results in the
same kinematics as the Etch-a-Sketch toy - when both motors move in the same
direction, the slide moves in the x axis; when they rotate against each other,
the table moves in the y direction. The design allows both motors to be
stationary, thereby simplifying wiring runs, reducing size and mass, and
lowering the total number of components needed in the system.
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By scaling the unit down to a
single extruded plate and designing the motors and controller to fit beneath
the extrusion, Festo created a full 4 x 6 inch working area in a package
slightly larger than 9 x 10 inch and only 4 inch thick. The compact design of this
"Mini H Gantry" allows supply lines for fluids, pressure or vacuum to be made
shorter. Motors in the system work in series; doubling their torque output to
achieve fast acceleration/deceleration for optimum positioning time while
maintaining a positioning accuracy of ±.004 inch.
With the H Gantry as the core
of the design, there was plenty of room for the mechanics of the stacking and
de-stacking systems using a combination of standard Festo electric and
pneumatic actuators under the table.
The design also has promise
for other areas of lab automation, as well as in other applications requiring
fast, precise x-y control in a small area. Festo has since taken this concept
and is developing a full product range of two-axis positioners with working
areas of up to 12 x 24 inch, higher precision versions, and with servo or
stepper control options.
Sam Stoney is senior project engineer, Life Sciences, at
Festo.
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