performance and reduce wear, leading to longer product life and lower maintenance costs. Automated, or robotic, assembly can
reduce the likelihood of errors, which can lead to cost savings in rework and scrap. Standardising components across multiple product lines can reduce inventory costs and simplify the manufacturing process. Customisation can, however, also add costs, particularly if done on one-off or low-volume production, so an ROI calculation is essential before making your decision.
Customisation may not always be optional, especially in applications subject to safety and health regulations. However, even when designers are familiar with the regulations impacting their designs, they don’t always give them the attention they deserve early enough in the process and, as a result, discover the need for unexpected customisation when they fail validation or verification. A regulation may, for example, require redesigning a brass screw due to the target territory’s banning of lead content.
Most of the lead screw customisations mentioned thus far have been at the component level, but designers can customise lead screws to their performance, compactness, cost and compliance requirements through integration at the systems level. Figure 2 shows a system integrating a lead
screw, nuts and stepper motor, supported by a round rail. Such a stepper motor assembly could improve positioning tolerances and enable greater repeatability and more precise control of either nut or screw rotation, depending on the architecture. This makes it easier to configure customised or stock components into programmed motion sequences, optimising fine incremental movement in confined spaces. It opens the door to a new realm of performance possibilities for getting more complex and precise motion control in tighter spaces.
Customising insulin pump motion control Selecting a lead screw for an insulin pump begins with a clear understanding of the patient’s needs and how those translate into a motion solution. These typically include speed and responsiveness, precise and repeatable drug dispensing, and minimal noise. Since insulin delivery must adjust according to individual needs and fluctuating blood sugar levels, pumps must be able to seamlessly modify dosages. Meeting these requirements often necessitates customisation. Infusion systems require high accuracy and
precision. While off-the-shelf components may suffice in some cases, small-scale applications almost always require customisation. For example, designers might need a shorter or longer lead screw, customised housing, or a different material or coating. Translating motion from the motor to the lead screw may require a custom-designed gearing system to align the motor resolution with the lead screw pitch, while a need for high side-load capability might call for adding ball bearings.
Figure 4: The ability to integrate a miniature lead screw, nut or actuator provides flexibility for scaled-down medical systems
Optimising laboratory automation Pipetting is a fundamental technique in medical diagnostics and analysis, playing a crucial role in tasks such as sample preparation, hematology, DNA sequencing and various biochemical assays. Traditional pipetting involves using a syringe to aspirate liquid from a location and move it to a test tube, tray or other location for exposure to various test protocols. Laboratory device designers automating pipetting systems for high-throughput clinical diagnostics and large-scale research often specify miniature motorised lead screws. As Figure 4 shows, the lead screw on the
Figure 3: Insulin pump designers must
often customise components such as lead screws to accommodate their intended patient’s need for precision and comfort. Image courtesy of Portescap
Figure 2: This illustrates how a Kollmorgen stepper motor might drive Thomson lead screws in a fluid-pumping application
Optimising load capacity in CNC equipment design A fixed infusion pump designer would not likely customise to improve load capacity because the loads they are working with are relatively small, but the designer specifying a lead screw for an industrial CNC machine might. These machines often use lead screws for precision control of a tool along various axes. Machining the screw to wider dimensions is one of the most common ways to improve load handling, especially when combined with high-strength materials such as alloy steel or stainless steel, which have better fatigue resistance and lower friction coefficients. Higher thread pitches will increase capacity as will the use of trapezoidal or acme threads, which are known for their strength and durability. Using a high-capacity nut material such as bronze or advanced polymers can also help. Advanced lubrication systems will reduce friction and wear, which can enhance the lead screw’s load capacity. Specialised lubricants are available to reduce friction in load handling. Similarly, heat treatment processes like case hardening will increase surface hardness, wear resistance and structural integrity under a load.
vertical axis raises and lowers the pipette to deliver samples to tubes in the tray, while the lead screw on the horizontal plane controls the pipette’s movement from one location on the tray to another. In a different configuration of a pipetting application, the inner workings of the motor would turn to move the lead screw backwards and forwards.
Replacing pneumatic cylinders As part of electrification initiatives designed to recapture space, gain greater control, and save time and costs, pneumatic systems, including cylinders, air hoses, valves and other elements, can be converted to a lead screw integrated with a stepper motor. These electric linear actuators could incorporate any of the customisations mentioned above to provide more flexibility, higher power output and increased energy efficiency.
The trend towards more compact, smarter, stronger, safer and personalised motion solutions is driving the need for customisation in motion control. Lead screws are indispensable in this effort, providing a simple technology for converting rotary to linear motion across a myriad of applications. The benefits of optimising the performance,
physical properties and usability of the motion solutions will accrue to the patient, lab researcher, CNC operator or any other end user, provided the process begins with a clear understanding of those needs.
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