Injection molding simplifies syringe pump

Boston, MA-- For years, syringe pumps have played an important role in the removal and infusion of small volumes of fluids in industrial applications. Designed to feed samples of varying viscosities at precisely controlled rates, they turn up everywhere. Syringe pumps control spotting in thin-layer chromatography, sample process lines, and help scientists perform air-and water-pollution research.

Pumps of traditional design require as many as 320 components, including machined metal parts and bulky wire harnesses. Engineers at ATI/Orion, Inc., a leading syringe pump maker, recently redesigned the company's Sage syringe pump line. In the process, they reduced parts count by more than 60%, and eliminated all wiring harnesses. The result of their work-a more rugged, simpler product-offers additional features and smoother motion control than previous designs.

Its syringe mounting bed is the most prominent feature of a syringe pump. By replacing sheet-metal and machined-metal parts with injection-molded components, Orion's engineers incorporate molded-in features for mounting many of the parts needed to retain syringes. For example, the motor-driven carriage that depresses the syringe plunger includes a dual gear rack, end-point-limiter retention tracks, and mounting features for a three-position syringe plunger retainer, all produced in one injection-molding operation. The case also includes a molded-in syringe holder that accommodates up to three syringes. This component's design enables it to direct fluid spills off and away from the pump.

"Simplifying the pump not only made it very easy to use," says Edward Somes, the mechanical engineering leader for the project, "but the new design resulted in a product far easier for us to manufacture, and at the same time provides many new features." Previously, users had to carefully adjust the syringe clips every time they removed or replaced a syringe. With the new molded-in clips, users can lock-in syringes with one operation. Polycarbonate gives the case a high tensile strength of 9,000 psi, rigidity (an elastic modulus of 350,000 psi), and an impact strength of 250 ft-lb/sq-inch.

Clamped in position by a plastic locking ring, a spring-loaded wireformed retainer holds the syringes in position. Users can clamp the syringe in place by turning a syringe clamping knob. This action compresses the plastic locking ring onto the retainer, securing it firmly in place. While the retainer prevents vertical motion, contact between the syringe flange and an adjustable stop mounted on the case prevents lateral motion.

A carriage that incorporates a set of gear racks driven by the motor-drive gears activates the syringe plungers. Carriage position can be set by the user, by raising the carriage off the case for repositioning by hand. According to Somes and Product Development Manager Chris McIntire, this feature provides a quick way to place the carriage in the desired starting position.

In addition, the carriage includes features for endpoint limiters that allow users to set carriage-stop positions. Users adjust the limiters manually by sliding them along the carriage to the desired position. A syringe retention clip snaps into one of three positions to accommodate different types of syringes, while allowing easy release of the syringes.

Additional details...Contact Edward Somes, ATI/Orion Research Inc., 529 Main St., Boston, MA 02129, (617) 242-3900