This technical information has been contributed by
Nook Industries

Early Collaboration is Key to Designing Linear Motion Components for Medical Applications


CLEVELAND, Ohio--Medical device designs are evolving rapidly and demanding ever higher quality standards. Many of these advanced designs are using linear motion components, which yield the best results when collaboration between designer and manufacturer begins at the early stages of the design. This is especially true when modifications to current parts or a custom design may offer the optimum solution.

Nook Industries (, based in Cleveland, Ohio, offers a wide variety of standard modular actuators and ball screws for medical applications. But as a major manufacturer of linear systems and components, Nook Industries recognizes that specifications for medical applications often exceed the capabilities of standard, cataloged products. The company is able to leverage decades of experience when modifying standard parts or creating custom designs for medical applications. Nook utilizes vigorous quality systems and a vertically integrated manufacturing model; it also implements a disciplined product realization process that reflects the Food and Drug Administration's Quality System Regulation 21 CFR-Part 280.

"We often start with the customer's performance specifications focused on the product's expected life, environmental conditions, material selection, and physical size," says Nook Industries' CEO, Christopher Nook. "We then incorporate enhancements to the product's design that address the rigors of most medical applications. This process has allowed us to sell modified standard products to the medical industry very successfully."

Priorities for Design

For finished devices intended for human use, a definition of design priorities must be incorporated, beginning with specification requirements provided by the medical device manufacturer. Design priorities that must be defined include performance (load capacity and length/range of travel requirements); efficiency (high-precision/low-precision); accuracy (lead accuracy measured in microns; tens of thousandths of inches); envelope (compact); material constraints (stainless steel, magnetism/non-magnetism, radioactive elements); and operating environment (non-direct exposure with patients or attached to the human body).

Design Reviews

Design reviews, involving comprehensive, systematic, and documented examinations of a design, are conducted at various stages. In addition to evaluating the adequacy of the design requirements, they evaluate the capability of the design to meet these requirements. Designing a ball screw isn't practical if it can't be consistently and efficiently produced. Nook employs SolidWorks® COSMOS software at this stage to provide a full range of integrated modeling and simulation options that medical product manufacturers need to design better products, faster and at lower cost.

Small Diameter Ball Screws Designed for Compact, Precision Applications

The growing worldwide shift toward smaller packaged applications typically requires lower load capacity and higher precision. Nook's Precision Screw Group has recently introduced its Small Diameter Ball Screw Assemblies (SD Ball Screw), designed for smaller-footprint applications. In addition to medical equipment, these screws are used in robots, guided missiles, unmanned vehicles, and aerospace applications.

Nook developed the small diameter ball screws as an extension to its Power-TracTM offering. Its purpose was to provide design engineers a globally accepted, metric product for compact, portable, and lightweight applications requiring high accuracy, repeatability, and durability.

The small diameter (below 10mm) ball screws are designed with a load capacity of 40-100 lbs., and high precision (lead accuracy measured in microns; tens of thousandths of inches). Designed in metric dimensions to meet universal industry performance standards, SD Ball Screw sizes are available in diameters from 6mm to 12mm.

"The Small Diameter (SD) Ball Screw's small size and customizable design offer precise, efficient movement in a compact package for medical device applications," says Christopher Nook.

Stainless Steel Modular Linear Actuators for Extreme Duty/ Hygienic Environments

To meet the high duty cycles and sterile requirements of pharmaceutical, medical, and clean room applications, Nook also offers a Stainless Steel Modular Linear Actuator Series (QLZE / QSZE / QST-KE) Positioning System. Developed by Nook's Precision Actuator Group, the Stainless Steel Modular Linear Actuator Series is reported to meet the corrosive challenges created by harsh chemical environments for the food and beverage, packaging, and petrochemical industries. The actuators are designed with a stainless steel cover band that wraps over the square aluminum profiles; the stainless steel cover helps protect the actuator when it's exposed to caustic cleaning solutions.

The standard single-carriage linear actuators offer push-pull type directional loading that can handle loads up to 1,600 lbs. of force, and maximum thrust loads up to 1,100 lbs. of force. Higher load capacities can be achieved with modified carriages configured with additional rollers or bearings added to the specification.

Nook also offers a "Four-by-One" (4 x 1) Micro-Range Ball Screw with a diameter of 4mm. The outer diameter of the cylindrical nut is 8mm, as opposed to10mm, the previous market standard. According to the company, the 4 x 1 ball screws are already being used in medical technology applications, such as removal of tissue (biopsies) for laboratory tests. They are also being used in optical devices, the company says.

Nook's 4 x 1 line includes the PowerTracTM CarryTM metric rolled ball screws and the SpeedyTM metric screws. The CarryTM high-helix ball screws are said to be wear-resistant and suitable for moving with high efficiency (rolling friction). Designed for applications that require predictable life while moving a load with high efficiency and duty cycle, the screws reportedly maintain lead accuracy that is "appropriate for most industrial applications." They are available in alloy and stainless steel, with standard diameters from 6mm to 63mm; and standard leads, from 1mm to 50mm.

This technical information has been contributed by
Nook Industries

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