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issue: June 2003 APPLIANCE Magazine

Engineering Medical Appliances
Framing the Medical Appliance Industry

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ESWL Products, Inc. recently secured FDA approval of its Lithowave lithotripter, which uses Rexroth modular structural components.

Shown is the Lithowave lithotripter from ESWL Products.

Start with some steel tubing, sheet metal, and bar stock. Cut the steel. Weld it together. Machine it. De-burr it. Grind the joints. Haul it into the spray booth for priming and painting and wait 1 or 2 days for it to dry. Then, mount the hardware.

Time-consuming, cumbersome, not readily reused - welded steel is going the way of the stone tablet for a growing list of structural designs, as it is quickly being replaced by aluminum structural framing, which is no longer just for common factory structures like machine bases and workstations. Now, it is also finding its way into new applications in the medical appliance industry.

Previously, medical uses of aluminum structural framing were somewhat unusual, but more companies are developing new ways to incorporate this modular, flexible, reusable structural component. In fact, by using aluminum framing, almost any structure can be assembled without special tools or skills and in significantly less time. ESWL Products, Inc.'s (Elk Grove Village, IL, U.S.) Lithowave lithotripter, for example, is a special piece of equipment specifically designed for non-invasive treatment of kidney stones, and it is the latest design the company has developed using aluminum structural framing from Bosch Rexroth's Linear Motion and Assembly Technologies division (Buchanan, MI, U.S.).

Breaking Up

The extracorporeal shock wave lithotripsy performed on the Lithowave lithotripter is a non-surgical procedure in which shock waves are produced by the machine outside the body and focused on kidney stones inside the body. The shock waves are used to break up kidney stones into smaller pieces, thus allowing them to pass through the body's urinary system.

To generate a shock wave, the Lithowave lithotripter employs spark gap technology, which harnesses the energy released during an electrical discharge created between two electrodes submerged in water. When the reflected shock wave is positioned on the treatment area, such as the kidney stone inside the body, the repeated impact of the shock waves on the stone, at various energy levels, causes its disintegration.

The Lithowave is a third-generation extracorporeal shock wave lithotripter that offers clinicians a proven electrohydraulic spark gap energy source coupled with a fluoroscopic localization system and a multi-functional operating table. Distinct features of the patented Lithowave design include the positioning of both the treatment unit and the target localizing fluoroscopy on two frames mounted on one shaft and revolving around the same axis. This center-based design is said to offer significant advantages over traditional designs.

The system control console is the focus of control and monitoring of the system. It provides the operator with centralized means for controlling the treatment table, the lithotripsy systems, radiology, and imaging, and it is usually located in a separate control room or minimally behind an X-ray shielding partition. Positioning of the control console is said to be easy since it is completely mobile.

A touch screen interface and a fluoroscopy control panel are part of the control console. Additional controls and indicators are located on the side of the lithotripter enclosure. These switches are divided into three clusters to control main power, treatment unit positioning, and a water system.

After the stone is localized, the operator must adjust the position of the treatment unit and establish proper contact between the patient's skin and the membrane of the treatment unit. This part of the procedure is carried out using the controls located on the control panel on the side of the main enclosure. The rest of the treatment is conducted from the control console. The flexible positioning of the table and the radiology apparatus, unparalleled access to the patient, and easily accessible controls, all simplify the endourological procedures for treating kidney stones.

Medical Equipment Using Framing

The Lithowave lithotripter, utilizing aluminum structural framing in its design, recently received U.S. Food and Drug Administration (FDA) approval for marketing in the U.S. The previous design included welded steel in the internal frame, but Ken Mroz, technical sales representative for Flodyne/Hydradyne Inc., in Hanover Park, IL, U.S., a distributor of hydraulic, pneumatic, and motion control technology, is working with ESWL Products, Inc. on plans to replace the steel with 90- by 90-mm aluminum extrusions.

"By using Rexroth aluminum structural framing, we have been able to build a machine that is very physically stable, aesthetically pleasing, well received by the sales staff and the users, while also decreasing assembly time," says Christopher Nowacki, president of ESWL Products, Inc. "Obviously, there were many benefits to using this 'finished product' in the design of the Lithowave lithotripter. It was more than a structural component. The Rexroth aluminum extrusions were used for the Lithowave's control cart, as well as in the main structure of the lithotripter itself. Weight was also an issue, as the control cart is mobile and must be moved behind lead glass when operating the lithotripter. Ease of use, flexibility of design, and aesthetics were all factors in the decision."

ESWL Products, Inc. selected Rexroth aluminum structural framing because the brand offered the most aluminum profiles - 83 different high-strength, anodized aluminum profiles with dozens of different connectors and accessories - satisfying a variety of strength, ease-of-assembly, and aesthetic requirements of the Lithowave for a complete multi-functional structure.

Aluminum structural framing assists assemblers with a simple T-slot design, allowing them to simply insert a T-bolt into a T-slot and tighten. The high-strength, extruded aluminum profiles also have a natural color and anodized surface that is scratch- and corrosion-resistant, never needs painting, and is maintenance-free. ESWL Products, Inc. has used Rexroth framing in hospital bed designs as well as a number of other medical applications.

Mr. Nowacki adds: "In addition to the framing's physical characteristics and benefits, Rexroth's FMSsoft AutoCAD¨-based software reduced engineering and design time by providing product visualization and generating a bill of materials. Rexroth's FMSsoft is a suite of programs for layout, planning, and design of structures made with Rexroth aluminum structural framing. FMSsoft simplifies common tasks, improves efficiency, and reduces the time needed to design structures. With AutoCAD 2002 functionality, FMSsoft provides automatic parts list generation, integrated calculation, a 3D system library, and fast-functioning macros."

A similar control console design using welded steel would take approximately 2 days to build compared to aluminum structural framing, which can be assembled in hours. Design flexibility and the option to customize the height and width of components also factored into the decision to use the Rexroth framing. Mr. Nowacki concludes, "Rexroth framing costs less, is more versatile, and in the case of the Lithowave, does an overall better job than steel."


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