Quadra 4 Operator Manual
Tomtec
172
6.0 Quadra Shuttle
The concept of the shuttle is what sets the Quadra 4 apart from its competition. The shuttle
can take plates from any of the stackers and move them to and from the pipettor. On a flat
bed pipettor, a separate device, such as a conveyor or robotic arm, is required. The six
stations of the shuttle add to its utility. One station can bring in the assay plate, while another
brings in the compound or test variable plate. One station may be used for tip washing. This
leaves three stations to handle the reagents for the assay. Using pipeline pipetting
complete assays may be completed in one pass.
The shuttle is driven by two stepper motors, one in the X-direction (left /right) and the other
in the Y-direction (front/ back). Both motors may operate simultaneously permitting a quick
diagonal move when required. The software counts steps between stations. Stepper
motors may loose steps if overloaded. This could happen if the shuttle is obstructed. This
is a nice safety feature but not good as a control element. The Quadra 4 shuttle’s stopping
position is determined by fixed position sensors at each station. They confirm that the
shuttle is where it should be.
A certain level of precision is required for the shuttle to stop on its mark. When the stage rises
the plate nest must fall precisely onto the stage locator pins. Rather than tune the shuttle
position sensors mechanically, they are tuned with software. The sensor has a wider area of
actuation than the final mark. The shuttle calibration procedure in the manual describes
tuning the final stopping mark to its exact point. The shuttle should stop so that
the stage lifts the plate nest and drops it back cleanly with little to no sideways or front/back
motion. This will center the plate nest on the stage locator pins.
7.0 Stackers
The Quadra 4 stackers are pneumatically actuated by the on board air compressor. To lift
the plate nest from the shuttle into the cassette, air pressure of approximately 20psi is
applied to the cylinder. This gives a smooth upward motion. An air pressure gauge on the
inside front panel will indicate these pressure settings. The high and low air pressure
regulators are located there also.
The escapements that release the plate from the cassette are also pneumatically driven.
The force available with pneumatics provides very reliable escapement operation. The
force of the air cylinder both opens and closes the escapement. As the stacker carries the
plate nest into the cassette, the escapement opens releasing a plate to the plate nest. As
the plate nest is lowered, the escapement closes to catch the next plate. If all microplates
had the same total height and flange height, then only one setting would be required. This
not being the case, the timing of the escapement must have some adjustment to enable
handling a wide variety of microplates.
This is accomplished with a sensor mounted on the stacker air cylinder. It tells the
escapement when to open and when to close. It is adjusted with a 3/32 inch Allen wrench
through a clearance hole. The hole is located on the side of each stackers top plate.
Turning the Allen wrench one full turn clockwise moves the sensor down 1/32 inch, two
turns equal 1/16 inch. Moving the sensor down will cause the escapement to stay open
longer. Turning the Allen wrench counter-clockwise provides the opposite effect.
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