flexures

A flexure is a structural element that enables relative motion between parts primarily through elastic deformation of its material. Unlike sliding or rolling joints, a flexure provides motion without sliding contact, yielding high stiffness, low friction, and inherently repeatable positioning. Flexures are a key element of compliant mechanisms, which achieve motion through coordinated deformation of flexible members rather than discrete joints.

Common configurations include cantilever flexures, where a slender beam is fixed at one end and deflects under load to produce rotation or translation; notch or cut-out flexures that create a local compliant hinge; and multi-axis flexure systems that combine several elements to realize complex motions while preserving stiffness.

Advantages include simple construction, absence of lubrication, high positional repeatability, and smooth, backlash-free motion. They can provide micro-to-millimeter travel with nanometer-scale resolution in precision devices. Limitations include limited stroke and range, nonlinear stiffness and motion, limited load-carrying capacity, and potential stress concentration leading to fatigue. Fatigue life depends on geometry, materials, and operating range.

Materials commonly used are stainless steel, beryllium copper, spring steels, titanium, and aluminum, chosen for yield strength, endurance limit, and corrosion resistance. Manufacturing methods include precision machining, laser or waterjet cutting, wire electrical discharge machining (EDM), and, at the MEMS scale, surface micromachining and deep reactive ion etching (DRIE).

Applications are prevalent in precision positioning stages, optical mounts, metrology instruments, and micro- and nano-positioners. Flexures are favored in high-precision instruments because they provide frictionless motion, low hysteresis, and long-term stability. Design considerations emphasize stiffness, travel, natural frequency, stress distribution, and fatigue life.