When it comes to measuring and dispensing a specific volume of any liquid, pipettes are indispensable in today's laboratory environment. Depending on the size of the lab and the volume that needs to be dispensed, different types of pipettes are commonly used:
- Air displacement pipettes
- Positive displacement pipettes
- Metering pipettes
- Adjustable range pipettes
In 2020, we are starting to see air displacement micropipettes play a crucial role in the battle against COVID-19, and they are used for sample preparation for pathogen detection (e.g., real-time RT-PCR). Typically, two different designs can be used, manual or motorised air displacement pipettes.
Manual Air Displacement Pipettes vs Motorised Air Displacement Pipettes
In the example of an air displacement pipette, a piston is moved up or down inside the pipette to create negative or positive pressure on the air column. This allows the user to inhale or eject a liquid sample using a disposable pipette tip, while the column of air in the tip separates the liquid from the non-disposable parts of the pipette.
The movement of the piston can be designed to be done manually by the operator or electronically, i.e. the operator moves the piston by using a push button controlled motor.
Limitations of manual pipettes
Prolonged use of manual pipettes can cause discomfort and even injury to the operator. The force required to dispense liquids and eject the pipette tip, combined with frequent repetitive movements over several hours, can increase the joints, especially the thumb, elbow, wrist, and shoulder, at RS (I repetitive muscle strain) risk.
Manual pipettes require the thumb button to be pressed to release the liquid, whereas electronic pipettes offer better ergonomics with an electronically triggered button in this example.
Electronic Alternatives
Electronic or motorised pipettes are ergonomic alternatives to manual pipettes that effectively improve sample output and ensure precision and accuracy. Unlike traditional thumb-controlled buttons and manual volume adjustments, electric pipettes come with a digital interface to adjust volume and aspirate and discharge via an electrically powered piston.
Motor Selection for Electronic Pipettes
Because pipetting is often the first step in a multi-step process, any inaccuracies or imperfections that occur when measuring this small portion of liquid can be felt throughout the entire process, ultimately affecting overall accuracy and precision.
What is accuracy and precision?
Accuracy is achieved when a pipette dispenses the same volume multiple times. Accuracy is achieved when the pipette dispenses the target volume accurately without any error. Precision and accuracy are difficult to achieve at the same time, yet the industries that use pipettes require both precision and accuracy. In fact, it is this critically high standard that makes it possible to reproduce experimental results.
The heart of any electronic pipette is its motor, which significantly affects the precision and accuracy of the pipette, in addition to a number of other important factors such as package size, power and weight. Pipette design engineers primarily choose either stepper linear actuators or DC motors. However both stepper motors and DC motors have their own advantages and disadvantages.
DC Motors
DC motors are simple motors that rotate when DC power is applied. They do not require complicated connections to make the motor run. However, given the linear motion requirements of electronic pipettes, DC motor solutions require an additional lead screw and gearing to convert the rotary motion into linear motion and provide the required force. DC solutions also require a feedback mechanism in the form of an optical sensor or encoder to accurately control the position of the linear piston. Due to the high inertia of its rotor, some designers may also add a braking system to improve positioning accuracy.
Stepper motors
On the other hand, many engineers prefer stepper linear actuator solutions because of their ease of integration, excellent performance and low cost. Stepper linear actuators consist of permanent magnet stepper motors with a threaded rotor and an integrated filament bar to produce direct linear motion in small packages.
Post time: Jun-19-2024