Recent liquid-chromatography equipment can scan and analyze samples in 15 sec versus the 60 sec needed by the previous design thanks to a compact transfer mechanism that uses modern lead screws and low-friction nuts. The X-Y arm in Acquity, the chromatography machine from Waters Corp., Milford, Mass., (waters.com), uses one 1/4-in. lead screw and two specially adapted nuts from Kerk Motion Products, Hollis, NH, (kerkmotion.com). Two Kerk spline shafts and bushings guide the Z motion. “Spline shafts are good alternatives to less-precise hex or square shafts,” says Kerk applications engineer, Bob Hawkins. Waters' original mechanism used square shafts. The assembly uses lightweight alloy steel-spline shafts mated with Kerkite composite polymer bushings. The shafts are treated with Kerk's proprietary low friction Kerkote TFE coating.

An optional sample organizer uses a 1/2-in lead screw and an antibacklash nut for Z-axis motion. This lets the machine shuttle as many as 21 sample plates back and forth to the sample manager.

“These products offer extremely long wear-life,” says Waters principal engineer Ken Plant. “This is critical because our chromatography systems must be reliable.”

“An initial design used a homemade X-Y positioner,” says Plant. “It served well in older models, but its pulleys and belts could not be squeezed into the smaller footprint we were looking for.”

After working with Waters' engineers, Kerk suggested components that would let them make a sample manager that would meet the company's size requirements and the increase the speed and performance vital to the concept. A compact footprint also lets users stack and arrange various modules easier.

“While other vendors were selling off-the-shelf items, Kerk's hardware allowed for customization and flexibility to meet customer needs. We were impressed that Kerk was willing to work with our engineers to customize their components and ensure that they would mesh into our system,” says Plant.