Select an optimal motor for your benchtop point-of-care testing device

Brushless DC motors are a promising alternative to traditionally favored stepper and DC motors in point-of-care testing devices, and each technology offers distinct advantages for some applications.

By Dan Cisier, Portescap

In life-and-death medical situations, rapid and dependable sample testing is pivotal in ensuring fast and accurate treatments.

In the past, procedures like blood and urine sample testing traditionally required intricate equipment and highly trained technicians at specialized labs outside healthcare settings.

In order to deliver prompt and dependable outcomes, this conventional testing approach had to overcome hurdles such as sample transportation, potential congestion at testing facilities and shortages of technical experts. During the COVID-19 crisis, for example, PCR test results sometimes took several days to deliver.

Point-of-care testing (POCT) avoids many of these challenges by bringing testing capabilities directly to patients or doctors. There are two primary types of POCT devices: handheld and benchtop. Handheld devices are actuated manually or via single actuation. Although they excel at performing simple tasks, they lack the adaptability needed for complex, multi-step tests. Benchtop devices, however, are single devices specifically designed to rapidly conduct complex tests.

We’ll focus on benchtop devices, which are easy to use devices and conveniently sized to work in a doctor’s office.

Motor technology options for benchtop POCT devices

Motors perform multiple functions within benchtop POCT devices, and each has its own needs and specifications. While specific requirements may be different for each task, certain principles apply across all motion systems. Above all else, reliability is critical to ensuring consistent and maintenance-free operation throughout the device’s lifespan, thereby guaranteeing accurate test results.

A single POCT device may incorporate up to 20 motors, making factors like size, high power density and cost-effectiveness pivotal in creating a competitive unit. Beyond these general criteria, diverse tasks within the device require unique features such as high efficiency or robust holding capabilities.

Designers must consider the benefits and drawbacks of the following motor types when specifying motors for POCT devices:

• Stepper motors: In benchtop POCT devices, most of the tasks powered by miniature motors require high torque and important (unenergized) holding torque, making stepper motors an appealing motion choice. Although a stepper’s important holding torque may be seen as a disadvantage in some applications, it is beneficial for POCT devices because it drastically reduces battery use for long-term position holding and — when the number of motors in the unit are taken into account — helps maintain a competitive price point.
• Brush DC motors: The higher performance capabilities of brush DC motors makes them ideal for benchtop POCT devices. Their higher power density allows size reduction, which means a higher number of motors can be integrated into one benchtop device. For applications with a high duty cycle, brush DC motors offer high efficiency reducing power consumption and improving battery lifetime. Simple velocity control and absence of complex control electronics requirement make brush DC motors well-suited for POCT applications and help them maintain a good price point for the device.
• Brushless DC (BLDC) motors: POCT designers tend to use stepper or brush DC motors and avoid brushless DC technology due to its price and control complexity. Thanks to new developments in BLDC technology, however, this motor type is quickly evolving into a viable option for benchtop POCT devices. Brushless DC motors feature higher efficiency, higher power density and longer lifetime than either brush DC or stepper motors, thereby helping reduce size, improve battery use and device lifetimes. In addition, new developments in production and control technology are helping to significantly reduce the price of brushless motors, making them an attractive option for POCT applications.

Motor applications in benchtop POCT devices

Various benchtop POCT applications employ miniature motors. Specific examples include:

• Blister bursting: Blisters provide a controlled release of chemical reagents into the device for diagnostic purposes. Linear stepper motors are appropriate for this application because they precisely control the movement of the mechanism that punctures or opens the blister. A linear actuator stepper motor featuring a linear output and precise positioning would be particularly desirable for this process.
• Valve actuation: POCT devices are often built to accommodate disposable cartridges with many microchannels. These microchannels also require a high number of channels to control the fluid distribution. A small linear stepper motor that features linear motion, holding force and cost-efficiency would be ideal for actuating these valves.
• Liquid handling (mixing and pumping): Liquid flow within the testing device is critical and is carried out via small pumps. This task requires smooth, continuous rotation at a high speed; a a brushless DC motor or a brush DC motor could both be effective choices.
• Sample movement: POCT devices require sample insertion, placement for the test and ejection after the test. This can be automatically carried out either through linear or rotational movement with precise position control. Stepper motors are an excellent fit for sample movement.
• Door actuation and lock: Since non-qualified personnel often use POCT devices to perform sensitive, complex tasks, doors or locks are built-in to prevent tampering. High holding torque is needed for successful door actuation and locking, making stepper motors — with or without linear movement — a good fit for this task.

Different POCT applications require distinct motors

Recent advances have positioned BLDC motors as a promising alternative to traditionally favored stepper and DC motors in POCT devices, and each technology offers distinct advantages for some applications.

Stepper motors excel where demanding holding torque and precise position control are preferred, as well as for developers who prioritize cost efficiency.

For high-duty cycle and velocity applications, as well as those with size limitations, consider brush DC and BLDC motors.

Since POCT devices are used across a diverse range of applications, a motor supplier that specializes in all three technologies can help during both device development and production.

Dan Cisier is an application engineer at Portescap, with extensive experience in matching customer requirements with the ideal motion solution. He brings a customer-focused mindset to every project, working with the customer’s teams to both understand their unique needs and discover a custom solution for each application.

 

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The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of Medical Design & Outsourcing or its employees.