|Plate Stack from PerkinElmer uses Kerk's B Series leadscrews to nearly eliminate noise and vibration. The leadscrews are also included in the Evolution P3, a next-generation liquid-handling machine.|
Replacing noisy ball screws with nonball-screw linear-positioning devices let engineers with PerkinElmer Life Sciences quiet several machines and reduce most of the lubrication requirements. Most ball-screw noise comes from ball-return tubes. "There is no recirculation system or ball-return tubes in nonball-screw devices," said Andrew Boyer, an engineer with Kerk Inc., Hollis, N.H., supplier of the quieter designs. "The only movement the ball-free screws have is the self-lubricated nut on the TFE-coated screw, so most noise is gone."
The PerkinElmer machines had been using a 0.625-in.-diameter design. Boyer's team replaced the noisy units with stainless-steel ScrewRails, leadscrews with a proprietary TFE coating, and modified acetal "B" Series nuts. The coating increases lubricity and typically extends normal nut life by more than 300%.
The ScrewRail has a bearing on the lower end to tighten up radial play and provide an additional guiding surface. As a bonus, the leadscrews simplify machine assembly.
-- Paul Dvorak