The newest lead screws provide many advantages for linear motion systems. According to Tom Solon, an applications engineer at Kerk Motion Products, lead screws were once believed to be a cheap substitute for ball screws, to be used in less demanding applications. The situation has changed rather dramatically with lead screws providing excellent performance and long life in demanding applications such as medical and data storage systems. The focus of this section is strictly on the nut portion of the lead screw. Special design considerations provide increased functionality with torsional and compression anti-backlash, as well as custom designs.
CUSTOM NUT DESIGNS
In addition to reducing tolerance stack-up and providing improved lead screw product life, Kerk Motion Products designs precision molded nuts to provide added functions and reduce system part count. In custom products, these application-specific nut designs can be used with small, 2 to 4 mm in diameter lead screws for precise motion or units with fast yet accurate leads of more than 75 mm/rev, diameters of 20 to 25 mm and more than 4m in length. The custom approach reduces complex assemblies to a single component and simplifies assembly and alignment. Custom nut designs can range from small applications in data storage systems to large applications in full body massage therapy systems.
COMPRESSION ANTI-BACKLASH NUT
Designed to optimize system stiffness without sacrificing life or increasing drag torque, Haydon Switch & Instrument's “C” Series Anti-Backlash Nuts or Compression Style Anti-Backlash Nuts eliminate the clearance between the threads of the nut and the threads of the lead screw. The simple nut assembly consists of front and rear nut, ring and spring. By pushing the two nuts away from each other, the compression style nut eliminates backlash. The compression spring seating against the front nut applies a force to the ring which in turn transfers the force to the rear nut. Forcing the rear nut away from the front nut removes the backlash between the two nuts. The nut design compensates for wear and eliminates lock-up problems that can occur during the transition from worn areas to unworn areas of the screw. The anti-backlash nuts target medical, food processing and industrial applications.
TORSIONAL ANTI-BACKLASH NUT
Designed to eliminate nut and lead screw clearance, Haydon Switch & Instrument's “T” Series Anti-Backlash Nuts or Torsional Style Anti-Backlash Nuts have the largest load capacity of all Haydon's anti-backlash nuts. The unit consists of two acme nut halves that fit into the internal spline of the housing and a torsion spring that hooks into both the cover and the pusher nut. The threads of the pusher nut mate with the external threads on the housing. Pushing the two nuts toward each other eliminates the backlash between the two nuts and the lead screw.
Drag torque can be adjusted to very low for light loads or very high for heavy loads. For smooth operation over the life of the assembly, a proprietary blend of self lubricating polyacetal in the nut mates with rolled 303 stainless steel screw material. The anti-backlash nuts target medical, food processing and industrial applications.