ENGINEERING INSIGHT
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Universal joints—flexible mechanical connectors that transmit rotary motion from one shaft to another—are used in thousands of applications across a variety of fields, but some devices cannot incorporate them in their stock form. The Radius Surgical System from Tuebingen Scientific Medical (Tübingen, Germany) is one such product. Designed to fill the gap between costly surgical robotics and comparatively imprecise conventional instruments, the device consists of two hand-guided surgical manipulators linked by lengthy stainless-steel shafts to rotatable surgical attachments. The instrument uses a universal joint with a specialized hub configuration to ensure precise operation and provide a secure connection between the unit’s handle and the distal tip, which can be fitted with surgical task graspers, scissors, needle holders, and other attachments. To develop the custom universal joint, Tuebingen Scientific Medical enlisted the help of universa l joint specialist Belden Inc. (Magdeburg, Germany).
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The universal joint provides the surgical instrument with a large degree of operating freedom.
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Belden modified the standard universal joint design, fusing it with the surgical device’s internal extension component. The resulting product adheres to medical sterilization regulations and, with an outer diameter measuring 8 mm, accommodates surgical space limitations. “To satisfy Tuebingen Scientific’s requirements, we developed a design that unifies the joint with an internal extension component,” explains Belden product and sales engineer Ralf Gabriel. In addition to providing a stable connection between the instrument’s handles and its distal tip, the custom joint also delivers ergonomics, Gabriel says. “Without a custom joint, the operator would have to hold his hand in a very uncomfortable position, which would make controlling the instrument effectively impossible,” he explains. The instrument’s design enables a surgeon to comfortably use seven degrees of freedom during minimally invasive procedures.
The medical-grade stainless-steel joint adheres to sterilization regulations and can be sterilized without disassembly. Located within the handle of the instrument, the part does not touch the patient’s tissue during surgery.
Belden also offers a variety of standard universal connectors that can be modified to meet custom requirements. The company’s joints are available in various grades of stainless steel and heat-treated steel alloys. The firm’s standard-model universal joint has a 35° operational angle of deflection, but custom versions with higher angles of deflection and double-joint assemblies also can be specified. Belden is currently developing a range of miniature joints with an outside diameter of 6 mm.