Medical Design Briefs - November 2022 - 20

Innovative Motors
cur between samples. At the end of the
manipulation, the operator ejects the
pipetting tip for disposal or reuse after
sterilization. Multi-channel pipettes
are also common, allowing lab technicians
to perform several fluid transfer
operations simultaneously, as shown in
Figure 1.
Thanks to low-cost and improved electronics,
designers can now integrate a
miniature electric motor inside a handheld
pipette. Benefits include:
* Accuracy and repeatability. An electronic
motor allows a pipette to accurately
dispense a specific volume of liquid
while ensuring repeatable results
during each subsequent manipulation.
* Cost savings. In addition to improving
accuracy and repeatability, miniature
electric motors also allow pipettes to
handle smaller volumes of liquids than
before. That means companies can reduce
the amounts of reagents they use
during analyses and save money.
* Ergonomics. Electronic pipettes require
less manual force and hand
movement, thus reducing the risk of
repetitive strain injuries. Once an electronic
pipette is set, the user simply
clicks a button to fill, empty and, in
some cases, eject the tip.
* Productivity. Thanks to built-in automation,
electronic pipettes can perform
quicker than their mechanical
counterparts and users can process
more samples.
* Flexibility. Capabilities can include a
save mode, multi dispensing, and
mixing.
Fig. 1 - An example of a multi-channel pipette.
Optimized
magnetic circuit
Special ball bearing assembly
with reduced axial play
Permanent magnet,
radically magnetized
Here is an overview of the motor technology
options for electronic pipettes.
Stepper motors. Figure 2 shows a linear
stepper motor. Also known as a digital
linear actuator (DLA), this readymade
device comes with a built-in lead
screw that interfaces directly with the pipette's
piston to provide linear movement.
Stepper motors do not require an
additional feedback sensor or encoder
for control. Instead, the stepper motor
rotates incrementally at each current
pulse, making it easier to control. The
linear travel accuracy of the motor, along
with the possibility for micro-stepping,
ensures the very high resolution that
electronic pipettes demand. This motor
can maintain a position without power,
which extends the use of the device.
DC motors. The coreless brush DC
Ultrasonic welding
Coil
Lead screw
Over-molded stator
Fig. 2 - Linear stepper motor components.
20
motor, shown in Figure 3, is highly efficient.
Unlike iron core motors, the rotor
is only comprised of a coil and a
shaft. As a result, the coreless motor has
no iron losses and achieves greater efficiency
and acceleration. Because electronic
pipettes are battery powered, the
increased efficiency allows longer periods
of use on a single charge. For pipetting
applications, the brush DC motor
requires additional components such as
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Medical Design Briefs, November 2022
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Medical Design Briefs - November 2022

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