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Roller Pinion Motion Systems Improve Medical Equipment Accuracy and Efficiency

Thu, 04/26/2012 - 10:41am
Tony Kliber
Nexen-Beds
To prevent noise that can increase patient anxiety, medical beds with roller pinion systems deliver minimal sound and vibration.

With medical technology continually advancing, manufacturers are constantly searching for motion control solutions that can operate faster, more precisely, and with less maintenance to provide higher productivity. Traditionally, the medical industry has relied on a variety of linear drive systems to provide motion control in a wide variety of equipment and applications, such as medical beds, magnetic resonance imaging (MRI) machines, and overhead gantry system imaging machines. However, due to the inherent performance limitations associated with most linear drive technologies, these systems are not ideal for all medical applications.

Linear drive systems (e.g., ball screws, rack and pinion configurations, belt drives, and linear motors) have their own performance deficiencies, including high cost, low accuracy, and backlash, and they often produce loud noise, high vibration, and time- and cost-consuming maintenance requirements, impeding productivity, efficiency, and cost-effectiveness of medical equipment.

Alternatively, roller pinion technology combines the best attributes of existing technologies while eliminating most of their limitations. Differing from a traditional rack and pinion system, a roller pinion system features a unique roller pinion and toothed rack combination. Though, similar to a pinion/rack combination, the teeth on the pinion are replaced with bearing-supported rollers, which engage a unique tooth profile to ensure high positional accuracy and the elimination of cumulative error.

How Roller Pinion Technology Works
Roller pinion systems consist of innovative bearing-supported rollers that replace spur gear teeth used in conventional rack and pinion systems to prevent sliding friction. Further, unlike other linear drive systems, a small amount of preload can be applied to the system to remove backlash without risking binding.

Nexen-Pinion
Roller pinion systems meet multiple and diverse application requirements by engaging a unique tooth profile, ensuring accuracy, zero backlash, efficiency, and low maintenance formedical equipment.

Engineered to minimize friction, roller pinion technology enables a 99% efficient rotary to linear motion conversion, greatly reducing wear and providing longer service life—even when used at extremely high speeds. The roller pinion surrounds separate teeth, simultaneously loading it in opposite directions, eliminating the need for a second pinion to counteract any system backlash. Precise machining of the tooth profile sets the rack spacing, and rollers can smoothly move forward and backward in the opposite direction. With specially-designed rollers loaded in opposition on a tangent path, these systems prevent the occurrence of backlash.

In addition to smooth motion, roller pinion systems provide accurate, repeatable positioning. Each tooth is precisely measured relative to the first, maintaining high positional accuracy and eradicating cumulative error. This results in accurate positioning of up to ±30 µm—within half the diameter of a human hair. Further, these systems are capable of speeds up to 11 meters (36.1 ft.) per second, and their low-friction design creates minimal heat and wear on components, providing high positional accuracy at high speeds.

Advantages in Medical Applications
To accommodate rising demands for high-precision equipment, medical machines must provide accuracy and efficiency with little maintenance. By utilizing advanced motion control solutions, these critical applications can meet demanding requirements and compliment today’s machine designs.

Currently, most medical equipment still utilizes ball screws or manual adjustments to modify equipment position. Ball screws work well in smaller devices, but medical equipment is continually growing in size and length. Problems with lubrication, noise, and, most importantly, length turn ball screws into an impractical option. Further, manual adjustments become unfeasible with large, heavy equipment, as workers are unable to physically manipulate equipment as quickly or precisely as a linear drive system can. With roller pinion systems being joinable, it can accommodate any system length required. They can easily be designed to complement specific medical applications requiring long or custom-sized runs of racks, allowing consistently precise movement.

With the innovative manner in which the rollers engage with the rack teeth, roller pinion systems are capable of smooth, quiet motion. While alternative technologies suffer noise caused by recirculating balls, some roller pinion systems produce less than 75 decibels at full speed. In medical applications, minimal sound and vibration is crucial, as it reduces inaccuracies in positioning and imaging during X-rays and MRIs. Additionally, reduced noise benefits patients who come into close contact with these machines and medical beds, as excess sound increases anxiety.

With its low maintenance, long life operation, roller pinion systems deliver the longevity and durability required in medical applications. The rollers are sealed and lubricated with high-performance grease, never requiring lubrication. The rack, being able to run without lubrication at lower speeds, needs lubrication as little as every six months or two million pinion revolutions in higher speed applications. Further, due to its minimal lubrication requirements, the roller pinion system has low particle emissions, making it ideal for applications that must adhere to rigid sanitation regulations.

Nexen-MRI
Roller pinion technology provides precise, repeatable linear positioning, which improves overall MRI performance and enhanced image clarity.

In the Field
With its versatile and reliable performance capabilities, roller pinion technology meets multiple and diverse medical application requirements. For example, MRI equipment requires the highest level of accuracy. Therefore, implementing roller pinion technology to provide precise, repeatable linear positioning time and again improves overall MRI performance and enhanced image clarity. Additionally, roller pinion systems streamline efficiency and productivity by enabling personnel to achieve this precision faster and easier.

Most medical environments must meet strict hygienic standards. This means that the caustic cleaners typically used to sanitize rooms and devices can corrode machine components and shorten equipment lifespans. Roller pinion systems constructed of stainless steel or carbon steel can resist these harsh chemicals. Rack teeth can be heat-treated for wear-resistance, and racks can be coated for additional protection against corrosion. Coatings can permeate the metal surface to bond with the steel, forming a durable chrome layer that prevents build-up. It is extremely durable and highly resistant to acids, alkalis, and various solvents, withstanding harsh medical environments while ensuring consistent, high-quality performance.

Conclusion
Productivity and efficiency are critical within the medical industry. Therefore, to provide quality patient care, utilizing equipment that is both precise and efficient is key. With the inclusion of a roller pinion system, medical equipment can eliminate shortcomings found in other linear drive systems to maximize accuracy and productivity.

Tony Kliber is the lead project engineer of precision automation components at the Nexen Group Inc., a leading manufacturer of precision motion control components, power transmission, and web tension control products for a wide array of industrial applications.

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