Gearboxes are miniature motor accessories that are critical to a number of applications and industries, given their ability to either increase torque or reduce speed. Here we explore how worm gears and the worm-wheel drive are an ideal gearing solution for medical infusion systems, a key medical industry.

An Overview of Worm-Wheel Drive Gearing

While each type of gearing technology has its advantages and disadvantages (see Figure 1 for a broad overview of these benefits and drawbacks), in this blog we focus on the worm-wheel drive. A worm drive is a gear arrangement in which a worm, or a gear in the form of a screw, meshes with a worm wheel, which is similar in appearance to a helical gear. These two elements are also referred to as the worm screw and the worm gear.

The efficiency of the worm gear is determined by the gear quality, the lead angle, and the number of threads that are in contact with the worm wheel. A high lead angle on the worm reduces frictional loss and heat, while a low lead angle either reduces worm gear speed or increases torque. The transmission of the movement is performed at a 90° right angle, which allows the gearbox to fit in small packaging spaces as per the available device layout.

As you can see in Figure 1, when compared to other gearing technologies, the worm design delivers improved torque density and achieves a higher ratio in a single stage. These characteristics make them a popular option to use across various industrial applications, as they offer significant gear ratios in small spaces. The worm gear is also an ideal choice when large gear reductions are needed. It’s common for worm gears to have reductions of 20:1, and even up to 300:1 or greater. This means that we will get a very low-velocity ratio.

Medical Infusion Systems Benefit from Worm and Worm-Wheel Drive

One application that commonly employs worm gears and worm-wheel drives is an external infusion pump, or a medical device used to deliver fluids into a patient’s body in a controlled manner. Infusion pumps can deliver fluids in large or small amounts and may be used to deliver nutrients or medications like insulin, antibiotics, chemotherapy drugs, or pain relievers throughout the body. The worm screw and worm wheel gearbox used in infusion pumps are responsible for delivering the required amount of drug to the patient, which is controlled through an electronic controller.

As the recent trend is designing pumps in a smaller size with lower weight, space constraints and higher speed reductions become top priorities for motion solution design. Worm and worm wheel gears are commonly selected because of their 90-degree power transmission. Other reasons for their selection include:

• Easier to manufacture as compared to the bevel gear (another gearbox solution)
• Features a ratio of 10:1 to 20:1, which is accumulated in an envelope size as small as 20x20x20mm
• Noise reduction is possible due to the plastic and non-metallic material combination (worm screw material is non-metallic and worm wheel material is plastic), which is most likely found in light to moderate load situations (Note: the lubricant selection on this material combination is flexible because of the lighter load)
• Delivers high efficiency of 85% to 90%

Think a worm-wheel drive might be a great fit for your next medical infusion device? Reach out to our engineers directly to discuss!